BIOLOGY AND HUMAN LBF] GRUENBERG -o\ , t en G u *c75 _G to O v. "— • ji .2 = 3 c )—• ^_^ >. :-j «! -^5 5 •r b.l ^ 5 ^ ~ rj != o < = -2 a; c .b c c c c i'i en <" = i o OJ O .^ X! O u >^-i 2 o ^ 2 = o .^ c ^ c P Q. rt 5. E Q. i 0>, ^ BIOLOGY AND HUMAN LIFE ^ BY BENJAMIN C. GRUENBERG FORMERLY HEAD OF THE BIOLOGY DEPARTMENT IN THE JULIA RICHMAN HIGH SCHOOL, NEW YORK GINN AND COMPANY BOSTON • NEW YORK • CHICAGO • LONDON ATLANTA • DALLAS • COLUMBUS • SAN FRANCISCO COPYRIGHT, 1925, BY BENJAMIN C. GRUENBERG ALL RIGHTS RESERVED 225.4 GINN AND COMPANY • PRO- PRIETORS • BOSTON • U.S.A. PREFACE The report of the National Education Association committee on the "Reorganization of Science in Secondary Schools" lays down the principle of a synthetic treatment of biology. In some quarters the change appears to have gone no farther than the substitution of ''plant biology" for botany, ''animal biology" for zoology, and so on. The present book assumes that the tendency toward a unified treatment of more comprehensive principles, which rs paralleled in other departments of instruc- tion, represents the most fruitful adjustment of schooling to the rapidly growing body of scientific knowledge. It takes account further of another tendency in our current life, namely, the rapid extension of secondary-school opportuni- ties to new population groups. The high schools now receive increasing numbers of boys and girls whose interests and aspira- tions are radically different from those of earlier generations of pupils. The high school is no longer primarily or chiefly a college-preparatory institution. More and more of our students are concerned with the concrete and the practical rather than with the abstract and theoretical. Boys and girls who look for- ward to an early entrance upon occupational activities and the responsibilities of earning and spending money have as much need for the study of biology as have those who plan to go to college or the professional schools. Even among these last there are very many for whom the subject can be most interestingly and most profitably developed in terms of our everyday affairs rather than in terms of academic analysis. The division of this book into three main parts ("Getting Acquainted with Life," "Biology of Health," and "Biology of Wealth") is intended to emphasize applications of science to human affairs, and at the same time to suggest that we have to get knowledge before we can apply it. Each chapter is preceded vi BIOLOGY AND HUMAN LIFE by a few questions that are designed to represent the pupil's point of view. The questions at the ends of the chapters, to- gether with the outlines and summaries, represent rather the teacher's point of view ; they do not call for a mere reproduction of the matter in the text, but are intended to stimulate the pupil to resurvey the subject matter, to reorganize it, and to reorient it for himself. The organization of the text, the questions, and the outlines carry for the teacher implicit suggestions as to what procedure will best furnish the concrete observation, experimen- tation, demonstration, etc. needed for an understanding of the ideas treated ; and for the pupils they carry something more than explicit suggestions as to the meaning of reliable method in the solving of various problems. The reference readings are mostly from materials readily obtained from government agencies. The text has been carefully checked against Thorndike's word list for ninth-grade pupils. New words that do not have their meanings revealed by the context are defined, and the Index will serve as a pronouncing vocabulary as well as a reference to defi- nitions or explanations. Many of the illustrations are taken from the author's "Elementary Biology," some of them with slight modifications; many, however, have been made espe- cially for this book, and some are for the first time made acces- sible to high-school teachers and pupils, such as the Ancon type of sheep mutation and the arterial system of the arm as shown by the X rays. Acknowledgment for photographs and other materials is made in connection with the several illustrations, but the author wishes here to express his deep appreciation of the splendid cooperation received from the various scientists and institutions, as well as for the patient efforts of the artists who have assisted in developing many of the special drawings— Mr. F. Schuyler Mathews, Mr. Frank M. Wheat, Miss Marcelle Roigneau, and Mr. Carl A. Schwarze. B.C.G. o CONTENTS PART I. GETTING ACQUAINTED WITH LIFE CHAPTER PAGE I. What is Biology ? 3 II. What Kinds of Things are Living ? 13 III. Some Life Relationships: Butterflies and Bees . 26 IV. The Cycle of Life : Flowers 41 V. Living Matter 56 VI. Living Conditions ; the Seed 64 VII. The Sorting of Plants and Animals 72 VIII. Mother Earth 91 PART II. THE BIOLOGY OF HEALTH INTERMEZZO. WHAT EVERYBODY WANTS KEEPING THE BODY IN CONDITION IX. The Meaning of Food loi X. Where Food Comes From 107 XL How Food is Taken In 126 XII. Working over the Body's Income 131 XIII. What to Eat 139 XIV. Hygiene of Food and Feeding 152 XV. The Air ... 160 XVI. Hygiene of Respiration and Ventilation . . . 168 XVII. Distribution of Material within the Body . . 176 XVIII. Hygiene of the Blood and the Circulation . . 187 XIX. Elimination of Wastes 193 XX. The Skin and the Appendages 198 XXI. The Unity of Life 208 vii viii BIOLOGY AND HUMAN LIFE THE CONTROL OF THE BODY CHAPTER PAGE XXII. The Nervous System 216 XXIII. The Special Sense Organs 226 XXIV. Hygiene of the Sense Organs 235 XXV. Instincts and Habits 241 XXVI. The Emotions 251 XXVII. The Meaning of Health 261 XXVIII. The Human Organism and Keeping it Fit . . . 272 INTERMEZZO. MAN'S DEPENDENCE CONTROL OF THE ENVIRONMENT FOR HEALTH XXIX. How Diseases are Caused 299 XXX. Microbes and their Control 307 XXXI. Insects in Relation to Disease 317 XXXII. Worms and Other Controllable Disease Agents . 332 XXXIII. Artificial Immunity in the Control of Disease . 338 XXXIV. Community Activities related TO Health . . 351 XXXV. The Home in Relation to Health 365 XXXVI. Industrial Problems of Health 379 XXXVII. Organization of Activities for Protecting Health 398 XXXVIII. The Day's Work in Relation to Health . . . 406 PART III. THE BIOLOGY OF WEALTH INTERMEZZO. WEALTH PRODUCTION XXXIX. Plants and Animals as Sources of Useful Ma- terials 415 XL. Classes of Plants and their Economic Importance 429 XLI. Classes of Animals and their Economic Im- portance 448 CONTENTS ix CHAPTER PAGE XLII. Multiplication in Plants 466 XLIII. Multiplication in Animals 481 XLIV. Improving Qualities in Plants and Animals . . . 491 XLV. Plant Breeding 504 XLVI. Animal Breeding 5^9 CONSERVATION XLVII. The Earth for Mankind .... XLVIII. The Forest in Relation to Man XLIX. Insects in Relation to Human Wealth L. Birds in Relation to Man .... LI. People for the Earth 532 549 561 574 580 INDEX TO THE TEACHER While the organization of the text is believed to be both logical and pedagogical the teacher will find no difficulty in de- parting from it as desired ; we have long recognized that both in the development of our subject and in the assignment of les- sons it is unnecessary to go from page to page through a text- book. Moreover, since it is necessary to base the pupil's study of his textbook upon concrete observations and experiences, the use of the book must be to some extent influenced by the mate- rial available from time to time. The questions preceding the chapters offer suggestions for in- dividual and joint projects of various kinds. Although they often take the form of a challenge to the teacher, we should pro- ceed with our work on the assumption that we and our pupils are equally interested in discovering what is true and impor- tant. Where individuals can give us reliable and authoritative answers, the class, including the teacher, should be glad to re- ceive them, although each individual, including the teacher, may reserve the right to ask the informant, "How do you know ? " Often we shall find that the best knowledge we have is a more or less workable hypothesis ; often we shall find that knowledge is still to be dug out of resistant reality; and at other times we shall find that the questions are not real ques- tions at all, being based on assumptions contrary to fact. When we come to the questions at the ends of the chapters, we may treat them frankly as teacher's questions. Yet these are all offered without prejudice ; that is to say, they are offered without intent to impose any doctrine. Where we ask about the advantage of a process or a procedure, we must be ready to con- sider also the disadvantage; where we ask, in comparing, for similarities, we must consider also differences; and so on. xi Xll BIOLOGY AND HUMAN LIFE Many of the questions assume that the teacher and pupils have actually seen, handled, experimented with, tested, smelled, and taken apart or put together ; they can be answered, if at all, only as a result of field or laboratory or museum study. In other cases the replies to questions must be in the form of inferences calling for further testing or verification. There are also sug- gestions for civic studies in terms of what is actually being done tn the community— how we obtain our means of livelihood, how we manage our joint affairs, how we meet our common enemies. It is not to be expected that every pupil will obtain an accept- able answer for every question. On the other hand, many of the questions are of a type that permits endless variation in terms of local conditions or matters of current importance ; it may not be sufficient, then, if the pupils can answer only the ques- tions given. At best the questions are to be used as stimuli for thought and investigation. The outlines, or summaries, at the ends of the chapters, often in combination with the questions, are intended to assist in the organization of ideas. They should show relationships of topics to one another within the subject of the lesson, but they should also suggest relationships between these topics and others pre- viously studied, as well as others not yet touched upon. In other words, while a useful summary or outline must answer questions that arise in the course of the study, it should also raise new questions : there are no periods in these outUnes. ^ Most of the reference readings are to government publica- tions of various kinds. It would be well for each school to obtain from the Superintendent of Documents, Government Printing Office, Washington, D. C, a list of the price Hsts. From this list the various price hsts can be ordered, and from these price lists we can learn what pamphlets and books are available. Every teacher should acquaint himself with the more impor- tant types of government publications and with the methods of obtaining them for the school with the least cost or effort. In many cases documents can be obtained with the cooperation of the congressman. Besides the pamphlets in the various price TO THE TEACHER xiii lists, you should get, through your congressman, the yearbooks of the Department of Agriculture, the annual reports of the Surgeon-General of the Public Health Service, and the annual reports of the Smithsonian Institution. State agricultural ex- periment stations, state and local boards of health, state and other museums, and the larger insurance companies also issue publications of value to the students of biology. Several of the larger voluntary health organizations have in recent years come to cooperate in some of their administrative problems, and can all be reached at one address — 370 Seventh Avenue, New York. Most of the following organizations have available literature of value in the teaching of biology: the American Child Health Association ; American Heart Association ; American Social Hy- giene Association ; American Society for the Control of Cancer ; National Committee for ]\Iental Hygiene ; National Tubercu- losis Association; American Association for Medical Progress; American Committee for the Prevention of Blindness. Some of the most helpful material is to be found in current magazines and newspapers, and pupils should be encouraged to find both problems and applications in the current record of the human life about them. The classification of plants and animals appeals to individuals here and there, but we cannot afford to give it too much time as a branch of biology. Yet it is worth while to indicate briefly both the methods and principles of classification, and the prac- tical uses of careful description and naming. The material in the text, it must be clearly understood, is not something to be learned, but a convenient scheme of reference. Every plant or animal that comes to the attention of the class should be placed within its phylum, or class, or order, as conditions per- mit; but no attempt should be made to get the pupils to memorize the definitions of the various groupings. With fre- quent reference to the scheme, however, it is certain that most children will get all they need of taxonomy. There are no separate chapters on the chemical processes often presented in elementary studies as fundamental to phys- XIV BIOLOGY AND HUMAN LIFE iology. Many of the high schools offer biology after general science so that this material is frequently no longer necessary. Where the pupils have had no such instruction, however, or where it seems necessary to review, a few simple experiments on oxidation and its products, on acidity and alkalinity, and on the idea of chemical reaction as illustrated by various types (precipitation, effervescence, color change), as well as chemical tests for nutrients, for carbon dioxid, etc., may be introduced early in the course (see Part I of the author's ^'Manual of Suggestions for Teachers"). Most teachers may prefer to prepare their own instructions to pupils for carrying out experiments, field observations, and other projects, for keeping records of their observations, read- ings, etc., and for gathering data of various kinds. Where there are large classes, or many of them, it will be economical to use printed manuals for students. In any case the teacher will pre- pare his own lesson by making up his mind clearly in advance just what he expects the pupils to get out of the lesson and what methods are to be followed for reaching the goal. BIOLOGY AND HUMAN LIFE PART I. GETTING ACQUAINTED WITH LIFE * 1?-. .# jr- **4 f. s. -•' < , i CHAPTER I WHAT IS BIOLOGY? Questions. 1. What does biology mean? 2. How is biology used? 3. What makes biology interesting ? 4. How is biology studied ? 5. What is life ? 6. How do living things differ from other things ? 1. Definition. The word biology is easily defined. It means "life knowledge/' or "life teaching," from bios (life) and logos (the word, or knowledge) . But, like many other simple words, it covers a great deal of what people know, as well as much more that they do not know. Many men have spent their lives in trying to find out just what science, or real knowledge, is. Still, we need not be afraid of the subject. Every one of us may reasonably hope to get a considerable amount of reliable and usable and satisfying knowledge concerning life. 2. What is life ? Suppose you asked an expert electrician, like Edison or Marconi, "What is electricity?" He would be likely to answer very frankly, "I don't know." Yet everybody knows something about how wonderfully electricity is controlled and used. So we must say frankly we don't know just what life is, although we have gathered many wonderful and important jacts about life. These facts we are able to use in many ways. We give the name life to all that distinguishes living things from those that are not living. Some people think that life is a kind of force, or energy \ but if it is, it differs in many ways from electricity and other forms of energy. Some people think that life is a kind of substance, or fluid ; but if it is, it differs in many ways from all the other kinds and states of matter that we know. All we can say is (i) that life is present only in certain objects or bodies {plants and animals), which contain many different kinds and states of matter; and (2) that in these 3 4 BIOLOGY AND HUMAN LIFE bodies life is present only under certain conditions, which in- clude electricity, chemical energy, heat, and others. But we cannot think of life by itself. It means nothing to us except the way living things behave— what plants and animals do. 3. How biology is used. Many plants and animals have a bearing upon human life. A little reflection will show that whatever we can do about living things we can do more Fig. I. Fossil remains of plant life The plants that left these impressions in the rocks at Florissant, on the western side of Pikes Peak in Colorado, lived a million years ago or more. (From photograph furnished by the American Museum of Natural History) effectively or usefully if we have a better understanding of life. In the case of our useful plants and animals, biology can teach us how to increase their numbers, how to protect them from their enemies or disease, and also how to improve their qualities. In the case of our own bodies, biology teaches us substantially all we know about preserving health and about curing disease. It is applied biology that has made it possible, since the Civil War, to add over ten years to the average length of life of people WHAT IS BIOLOGY? 5 living in this country. A knowledge of plants and animals is a constant source of satisfaction when we come in contact with wild or domesticated forms and have a chance to observe their structures and activities "just for fun." The more we learn about life the better able we are to understand ourselves and our fellow beings, and so better able to manage ourselves in many situations. Finally, biology is coming to be used more and more in the management of our common affairs, in town Fig. 2. Fossil remains of animal life The fish that left this record in the rocks at Twin Creek, Wyoming, lived between two and three million years ago. (From photograph furnished by the American Museum of Natural History) and city and in the nation at large, in industry, and wherever people have to come together for any purpose. But the greatest value of biology, as of every other study, will be tested by its ability to make life easier to help us get more out of life. 4. What there is to study about living things. Almost from the first, little children want to know the names of the different objects that come to their attention, and about the classes to which each new acquaintance belongs. One department of biological study concerns itself chiefly with describing and comparing all sorts of plants and animals for the purpose of making complete classifications. Here the student wants to 6 BIOLOGY AND HUMAN LIFE make sure that each kind has its own name, and that a given name stands always and everywhere for the same kind. This work is not only interesting for those who like that sort of thing, but it is also of great value to other workers. It is im- portant to know, for example, when a farmer complains of some insect or mildew injuring his crop, exactly who the enemy is, and not to confuse him, from slight resemblances, with another insect or mildew that may be harmless. Hundreds of situations are constantly arising in which it is important to know to what group a particular individual belongs, or whether a given plant or animal species has ever been described and named before. So exact description, classification, and naming are well worth while. Another branch of study concerns itself with the places upon the earth where each kind of living thing is to be found, or un- der what conditions it lives. Still another study has to do with the kinds of living things that existed upon the earth in ancient times, as may be learned from the remains in the rocks (fossils) and coal beds, or perhaps preserved in the glaciers, or ice fields, of Greenland and Siberia. Many people concern themselves with the study of structure and arrangement of parts in plants or animals. Others, again, are more interested in what living things do ; and people were interested in that long before there was any systematic science of biology. In modern times more and more attention is being given to questions about how living things carry on the various processes and activities that distinguish them from non-living things. How do plants get food ? How are moths attracted by light? How does vaccination prevent disease? How do mi- grating birds find their way? How do seedless plants repro- duce? Hundreds of questions are constantly coming to mind. Many people are chiefly interested in such questions as How came there to be all the different kinds of plants or animals? What makes different kinds resemble each other, for they are not altogether different? What brought about the changes in the inhabitants of Europe or North America during the past WHAT IS BIOLOGY? 7 million years or more? What has caused ancient types of plants and animals to disappear? How did existing species originate? How came plants and animals to fit in so beauti- fully into their particular living conditions? There are always men and women, boys and girls, who like to ask practical questions about everything that happens. What difference does it make if caterpillars do have biting jaws, or if clover plants have little lumps on their roots? What can we do about it ? What should we do about it ? It is impossible for everybody to think of all these questions, much less to get the answers to all. The more we find out, the more questions arise. So, more and more, people are choosing just what particular questions or classes of questions they will specialize in. Yet every one of us can learn some of the more important questions in each department, and something about why they are important, without becoming specialists. 5. What makes biology interesting? It is impossible to say beforehand just what will interest a certain person. Some of us go in for postage stamps, while others prefer Chinese puzzles or music. A subject like biology, which covers so much of the world we live in, has in it something of interest for almost everybody. There are several million different kinds of plants and animals ; this must interest those who care about collect- ing, sorting, matching, naming. New species are being dis- covered, classified, and named every year. Hundreds of men and women are constantly hunting for new varieties. Plants and animals occur under such a great variety of conditions, and show such remarkable variety of structure and habit corre- sponding to these conditions, that they are a constant source of amazement. Many remarkable relations are found among the parts of any given plant or animal, as well as among the different plants and animals in a given region. Thus, a slight chemical change in one part of the body may bring about a violent change in the action of the heart or of the nervous system ; or the extermina- tion of an insect in one region may have a striking effect upon 8 BIOLOGY AND HUMAN LIFE the health of human beings or of some species of plant. Many of us get much satisfaction from the beauty of living things ; and while enjoying the song of a bird or the fragrance of a flower is not quite the same as studying biology, there is the possibility of increasing our satisfaction by increasing our knowledge of living things. Indeed, for many boys and girls there is more of a thrill in solving a problem about the how of living things than in almost any other kind of experience. Bi- ology may be a great adventure of exploration into a wonderful Oxygen 65% Carbon ••:'■ Hydro- gen 10% K Na Hg SCIFe [Gil WM Fig. 3. The chemical composition of the human body In addition to the elements named there are nitrogen (N), calcium (Ca), phosphorus (P), potassium (K), sodium (Na), magnesium (Mg), sulfur (S), chlorin (CI), iron (Fe), and traces of iodin, fluorin, and silicon. The same chemical elements are found in other living bodies world of which the largest part is still unknown. To many peo- ple biology is interesting because it answers practical questions about the relations of plants and animals to our business, our health, our sources of timber and furs and other useful material, our laws, and so on. 6. How biology is studied. Everybody knows some biology, even without having studied it. Whatever you know about tak- ing care of the baby, or a pet animal, or a garden, or a potted plant, whatever you know about taking care of yourself, is so much practical biology, no matter where or how you learned it. We are constantly picking up a great deal of reliable and useful information, just as we are picking up a great deal of rumor or gossip or superstition that is neither true nor useful. To get WHAT IS BIOLOGY? 9 the utmost value from what we finally carry around with us in the way of ideas about plants and animals there should be some systematic study. You might go out and gather up all the samples of plants and animals you come across, and start sorting them. Or you might use a magnifying glass and discover in every sample many things that you would otherwise never have found out. Or you might cut your samples open and find out something about their internal organs, and perhaps guess at what makes them go. Or you might sit still and watch what is going on in the ground, in the water, in the air, and make note of what you see and hear. You might take your samples into the laboratory and test them to find out what kinds of material enter into their composition, or what changes they bring about in the materials they take in. Or you might experiment with them to find out what makes them do the many queer things. All the methods of classification, observation, and experimen- tation may be used on all living things. But we do not have to do all these things for every animal and plant. Indeed, we shall find these methods very slow, even if we confine ourselves to the study of only a single kind of life form. We shall have to get a very large part of our knowledge at second hand, by be- ing told what others have found out before us, through conversa- tions, through lectures, through reading, through pictures. Yet, no matter how much we may get out of books, it is well to remember that all useful knowledge originates in the observa- tions and experiences and experiments of people like ourselves. Whether we use our naked eyes or have the assistance of micro- scopes and telescopes, whether we taste and smell bits of plants and animals or make use of chemicals, whether we merely pull a lizard's tail to see what he will do or develop long and complicated experiments, the source of all biological knowledge is in the plants and animals themselves and not in books. 7. What living things do. All living things, even plants, are constantly doing something that brings about changes in the world. Some of these activities are very rapid, or sudden, or dramatic : a hawk swoops down and carries off a fowl, or an 10 BIOLOGY AND HUMAN LIFE army of locusts travels across a state and destroys every bit of grass and foliage in its path. Some of these activities are slow or not easily observed. Thus, the coral animals, in the course of centuries, build up an island in the midst of the sea ; a grow- ing tree splits a great rock asunder with its expanding roots. Some plants and animals produce effects that do not last long or reach very far, but others produce effects that reach down through long periods of time or spread over wide regions. For Fig. 4. The shipworm, or teredo This animal does a vast amount of injury to piers and wharves by boring into timbers that are kept in salt water. The teredo is not a worm but a relative of the clam. The one in the picture was nearly 20 inches long and made a hole about ^/i inch in diameter. Hundreds of thousands of holes cut into a log in all directions will soon ruin it. (Courtesy of National Research Council) example, the teredo worm (which is not a worm at all, but a kind of clam) honeycombs the timbers of a harbor so that at last a large wharf crashes down (see Fig. 4) ; or a slowly grow- ing forest gradually changes the stream flow or even the whole weather condition of a large and remote area. Some of these changes produced by plants and animals are interesting to us because of their unusualness or their dramatic qualities. Others are of importance to us because they influ- ence our own lives for better or for worse. ]Moreover, what is WHAT IS BIOLOGY? ii going on inside of every animal and every plant may be of inter- est or importance to us in many ways. So, taking it all in all, the world of life offers many things for serious study as a life work or for interesting hobbies as pastimes, just as our own life is a constant challenge to our ingenuity and skill in solving problems and overcoming difficulties, whether we go at it like tackling a stiff job or like playing an absorbing game. WHAT IS BIOLOGY? Definition: bios, life; logos, study What is science ? What is life — a kind of energy? a kind of stuff? what plants and animals do ? How biology is used To protect useful plants To lengthen life and animals To help us understand ourselves To increase useful plants To help in the management of and animals plants and animals To improve useful plants To help in the management and animals of human beings and affairs To cure sickness To give pleasures of various To prevent sickness kinds What there is to study about things Kinds, classifications, and names The distribution of plants and animals on the globe Conditions under which different living things live The plants and animals of past times How Hfe is carried on The structure of plants and of animals How the parts of living things work The origin of different kinds of plants and animals Why ancient forms disappeared The uses of various species The injury that various species may cause What makes biology interesting That depends upon individual taste Interest in classifying and in collecting Interest in discovery of new facts 12 BIOLOGY AND HUMAN LIFE Interest in understanding relationships Interest in increasing usefulness 5. How biology is studied We pick up odds and ends of information Observation of plants and animals and their activities Comparison and classification of forms, structures, and activities Tests and experiments ; second-hand learning 6. What plants and animals do to us Produce changes in our surroundings and in us Useful changes ; harmful changes ; indifferent changes Produce materials and objects that we can use QUESTIONS 1. What ten animals do you know by name when you see them ? 2. What ten plants do you know by name when you see them ? 3. How does a living plant differ from one that has ceased to live ? 4. How does a living animal differ from one that has ceased to live ? 5. In what ways does a living plant resemble a dead one ? 6. In what ways does a living animal resemble one that has died ? 7. How does a living plant differ from an object that has never been alive ? a living animal ? 8. How does a living plant resemble a living animal ? 9. Give three examples of making use of electricity, although we do not know exactly what electricity is. 10. What else can we use without having full knowledge of it ? IL Give three examples of having better use of anything after getting a better knowledge of it, 12. Give five facts that you know about some plant or plants without ever having studied them ; about some animal or animals. 13. Name all the occupations that you know about which make use of knowledge concerning living things. Name some which do not. 14. Make a list of ten questions that have occurred to you in the past about plants and animals, whether you know the answers to them or not. CHAPTER II WHAT KINDS OF THINGS ARE LIVING? Questions. 1. Can all living things move ? 2. Can plants feel ? 3. Can insects hear ? 4. Are plants alive in the same way as animals are ? 5. Are animals alive in the same way as we are ? 6. Can plants protect themselves ? 8. Great variety among living things. At first thought living things differ so much among themselves that to many people it seems hopeless to find out what they have in common. How shall we begin to compare the eel and the elephant, the cow and the cabbage, the spruce and the sparrow? We may begin by dividing our problem up into sections, and then examine some material to solve each section separately. First we can profit- ably consider general forms and structures, then chemical char- acteristics, and finally the behavior, or doings, of living things ; for, after all, it is what plants and animals do that most con- cerns us. And we may proceed by studying a representative plant with two or more representative animals. 9. A whole plant. If we examine a geranium plant, or any other small plant that is easily handled, we find that the part which is usually below ground (the root) differs from the part above the ground (the shoot) in several ways. There is a differ- ence in color and a difference in texture ; the smallest branches or subdivisions of the root are, as a rule, more delicate than those of the shoot. The shoot also has parts which we easily distinguish (in most kinds of plants) as stem and leaves; and the leaves differ from the stem in shape, color, and texture. At certain seasons of the year the stem bears other structures besides leaves, namely flowers. In most kinds of plants the flowers last but a short time and are succeeded by fruits, inside of which there are usually seeds. 13 Corolla y- •> iM.Carpel Leaj Fig. 5. A whole plant Like most of the familiar plants, the poppy consists of an underground portion, the root, and of a portion aboveground. the shoot. The shoot is made up of stem and leaves, and on special stems or stalks there are special clusters of leaves which together make up the flower WHAT KINDS OF THINGS ARE LIVING? 15 10. A representative insect — the grasshopper {Acridium, Melanoplus, Caloptenus, or some other genus). If we examine a grasshopper, we find the general plan of structure to be that of a main body with several kinds of outgrowths. The body has three easily distinguished regions : the head, the thorax, and the abdomen. The head bears two feelers, or antennae (singular, antenna), pro- jecting forward, and the eyes oc- cupy a large part of the surface. These large eyes are called com- pound, because each consists of nu- merous complete eyes (see Fig. 6). In addition there are three tiny simple eyes on the front of the head. The mouth occupies the end of the head which is toward the ground when the animal stands in the normal position, and it consists of several distinct parts. The thorax, which is covered by the wings when the animal is at rest, is made up of three more or less distinct segments, or rings. Each of these carries one pair of jointed legs. Two of the segments carry one pair of wings each, and the anterior (forward) wings cover the posterior ones when at rest. Coming to the abdomen, we find that this too is segmented. Indeed, in the whole class of ani- mals called Insects the body is cut up, or segmented, like the body of an earthworm. On the side of each segment there is a tiny spiracle, or breathing hole (see Fig. 7). The foremost seg- Fig. 6. Compound eye In the Arthropoda, or jointed-leggea animals, there are compound eyes as well as simple ones. A, head of a locust, showing the compound eye with its many facets, each repre- senting the exposed surface of an ommatidium, or single eye. B, an ommatidium, seen in section cut lengthwise, a, corneal lens; b, lens- growing cells; c, cone; d, iris cells; e, retinal cells, receiving light im- pressions; /, retinal pigment; g, perforated supporting membrane i6 BIOLOGY AND HUMAN LIFE ment has on each side a small eardrum, or tympanum (see Fig. 8). The hindmost segment bears special structures that have to do with the throwing out of refuse {feces), and others connected with reproduction. In the female these terminal parts to- gether constitute the ovipositor, or egg-laying organ. 11. A representative mammal — man {Homo sapiens). We are so familiar with this species that we need merely to recall the main fea- tures of the outward form and struc- ture. Like the insect, this mammal has a main body, with a distinct head at the anterior end and append- ages (two pairs) attached to the trunk— one pair at the anterior end (the arms), the other pair at the posterior end (the legs). We see, further, that both animals have a definite bilateral (two-sided symmetry, the right and left halves being almost identical in form {although opposite in placing and facing). Certain kinds Fig. 7. Breathing tubes in insects s, the spiracles in the side of the body, opening into the trachese t, which branch repeatedly and bring air to all the tissues Fig. 8. The main divisions of an insect's body In the grasshopper, as in other insects, the body is made up of a rather distinct head at the front end; the main "trunk," or abdomen : and, between these, the thorax, which bears both the legs and the wings. Near the front end of the abdomen the grasshopper has a rather large eardrum of parts are common to the two animals, although these cor- responding parts (for example, mouth, ear, eye, leg) are very different in structure; and there are other differences which WHAT KINDS OF THINGS ARE LIVING? 17 appear when the two forms are compared. Yet we consider both types to be living things, and we class both as animals. 12. Organs; organisms. Now, what similarities can we find among living things in general ? If we consider merely the three examples so far discussed (a seed plant, an insect, a mammal), we find, first of all, that each has a number of distinct parts. If we examine each of these parts more closely, we find that each part is made up of several different kinds of material, arranged in a particular way. Moreover, if we looked into the interiors of the insect, the plant, and the mammal, we should find in each case some more distinct parts. Indeed, most of us already know that our own bodies have such parts as brain, stomach, liver, kidney, heart, and bladder. This brings us to a third important fact. Each of these parts is something more than a structural unit, like the many bricks which make up a wall. Each one carries on a particular kind of work or behaves in a particular way in relation to the others or in relation to the plant or animal as a whole. Accordingly we get the idea that each of these parts is an organ, or instru- ment, which performs some special service, or function, in relation to the others or in relation to the whole body. Any plant that you know is made up of organs ; any animal that you know is made up of organs. We may therefore call a plant or an animal an organism. To be sure, not all plants or all animals have exactly the same organs ; and, as we shall see, the organs of some plants and animals are not easily distin- guished. Nevertheless, the term organism is a convenient one to use, meaning a living thing. 13. Chemical characters of organisms. People have long searched the bodies of plants and animals for something that \nll distinguish organisms chemically from non-living things. jVIay there not be some substance or substances peculiar to organisms, something that makes the real difference between living and non-living? The moment we start chemical tests with living things we are likely to kill them, or at least to change them in some important 1 8 BIOLOGY AND HUMAN LIFE way. Yet we now know enough to say rather positively that the chemical elements of which human beings and other organ- isms consist are exactly the same as those found in the air, in the waters, and in the soil and rocks that make up our world (see Fig. 3). At the same time, plants and animals contain compounds, or combinations of these elements, that occur naturally only in living things. Examples of such are starches and sugars, fats and oils, proteins and amino acids, and chloro- phyl and other pigments. All such substances have accordingly been called organic, to distinguish them from water, salts and other minerals, metals, etc., which are called inorganic. Or- ganic compounds are present in all plants and animals. Within the last hundred years chemists have been able to reproduce a large number of substances that ordinarily originate only in the bodies of plants and animals ; and they have made up new compounds along similar lines, that are never found in nature. 14. Activities of animals. As we watch our grasshopper and our plant we are at once reminded of a striking difference be- tween them ; that is, the liveliness, or movement, of the animal as contrasted with the quietness of the plant. Since we are looking for similarities, we are tempted to set this point aside and search for other features ; but let us keep the facts before us without prejudice, and let us complete our record of the grasshopper's activities before making up our minds which are important for our purpose. Very well, then, the grasshopper moves. He not only moves from place to place, but he moves parts of his body in relation to one another, as the antennae and the parts about the mouth. These movements at once suggest other activities ; the mouth movements suggest eating, and the movements of the antennae suggest feeling. From our experience with food we already know that it is related to growing ; and while the grasshopper does not increase in size under our eyes, we know that he must have grown, for he was not born full size. And that suggests another thing that animals do— they reproduce. WHAT KINDS OF THINGS ARE LIVING? 19 Returning for a moment to feeling, we can easily convince ourselves that there is more to the antennae than a mere wild waving. There is about the animal something that makes it move under certain outward conditions which act upon these feelers. Moreover, there is something about the animal that makes it move under certain conditions which act upon the eyes. Without looking into the interior of the animal we can learn that it takes food and grows, that it feels or sees and moves, and that it reproduces. And so much we can say of all the animals we know. Some eat one kind of food, some another ; some grow rapidly, some slowly ; but all take in food and grow. So, too, animals differ as to how sensitive they are, as to what kinds of conditions influence them, and as to how rapidly or how vigorously they move ; but all are sensitive to changes and all do move. And all animals originate from other animals ; that is, all species of animals reproduce themselves. 15. Activities of plants. What now of our plant? Does it also move ? Is it sensitive to what goes on around it ? We know •very well that plants grow, and everybody who has ever thought of getting new plants for any purpose knows that they com- monly come from seeds, and that these seeds in turn come from other plants. Plants, then, do reproduce themselves. But if plants really do move, and if they really do respond to changes in their surroundings, most of us have not noticed these facts. Still, the very fact of taking in food, which is essential to growth, implies some movement. To be sure, plants do not reach out and grasp food, as do the grasshopper and the baby, for ex- ample ; nor does the plant eat with a mouth ; yet it does take materials into itself from the surroundings (by way of the roots and by way of the leaves), and it transports, or moves, these materials from one part to another. Most of the movements in a plant are slow and minute, so that we should need a microscope to observe them directly. But the rapid movement of the leaves in a disturbed sensitive plant, and the slower but very distinct turnings of many com- mon plants under one-sided illumination, are easily observed. 20 BIOLOGY AND HUMAN LIFE These movements show us, at the same time, that plants are really very sensitive to what is going on around them, although, compared to animals, they respond rather slowly (see Fig. 9). Thus we find that plants and animals have in common certain processes or functions— food-taking and growth, irritability (or sensitiveness) and movement, and reproduction. There are, to be sure, many differences also ; plants and animals differ very Fig. 9. Sensitive plant (Mimosa pudica) a, leaves in normal position; b, leaves folded after disturbance. It is not necessary for us to assume that this movement is of any real value to the plant. It is true that in the new position the leaf exposes less surface and sheds the water better. But hundreds of plants with similar leaves have no difficulty in shedding rain without being so sensitive. Many plants (clover, oxalis, and others) droop their leaves in the dark in a few minutes. It is possible that in the clover and others the drooping of the leaf is the direct result of reduced transpiration. But that does not give the plant any advantage. It is very likely that the sensitive plant is simply more sen- sitive than any of its relatives (the bean family), many of which are sensitive in the same way but not in the same degree much as to the materials which they take in from the out- side, for example, and as to the way in which they make use of this material; but we are now considering their common characteristics. 16. Comparison with non-living things — growth. The fact of growth is universal for living things. Yet the crystals of WHAT KINDS OF THINGS ARE LIVING? 21 many substances also grow, some of them very rapidly, so that we can actually see them grow. Most of us have seen icicles grow. If by growing we mean simply becoming larger, then crystals and icicles grow just as truly as beets or babies. What, then, is the real difference between the two kinds of growth ? When an icicle becomes larger, it does so by adding new layers of ice-stuff (water) on the outside. The growth of a crystal proceeds in the same way. A baby, however, does not grow in this manner. 1. The baby grows not by the addition of baby stuff from the outside but by the addition of different kinds of material — such as cow material (milk), or hen material (eggs), or wheat stuff (bread). 2. The growth material is not added on the surface, but is taken in. 3. The new additions do not remain the same kind of material, but undergo chemical changes and become at last baby stuff. 4. The growth of the baby goes on not merely by the exten- sion of the surface; it takes place in all parts at once, inside parts as well as outside parts growing. These differences between the two kinds of growth may be summarized by saying that the icicle grows by accretion, whereas the baby and other living things grow by assimilation. By accretion we mean the addition of material on the surface. By assimilation we mean the transformation of foreign material into the material of the body, the "making aUke" of stuff that is different. 17. Movement. Most of the animals that we know are capable of moving about and of moving their parts. Many non-living objects also move, as the clouds and the waves. But these bodies do not move because of anything that takes place inside. We recognize that they are being pushed about by outside forces. In living plants and animals there are movements going on in- side the organism. Some of these inside movements result in the movements which are outwardly visible. 2 2 BIOLOGY AND HUMAN LIFE 18. Irritability. We ourselves perceive lights and colors, sounds, odors, and tastes. The movements of the familiar animals show that they are disturbed by much of what happens about them, and these disturbances are different from the kind that is caused when a cup is dropped, for example. A dog does something when he is hurt. Your eye does something when a sudden flash of light is presented. Even a geranium plant changes its behavior when placed in a sunny window. This sensitiveness of living things is in some ways the most remark- able fact about them. Yet we shall find that sensitiveness is not altogether confined to living things. There are certain chemical compounds that are in some ways even more sensitive than plants and ani- mals. Some compounds are so sensitive to mechanical disturb- ance that they will produce a violent reaction when they are dropped, as in the case of dynamite, which is by no means the most sensitive. This material is sensitive also to heat. If a hot poker is applied to a stick of dynamite, the results are said to be more disastrous than the consequences of poking a vicious dog. 19. Fitness. There is one respect, however, in which the sen- sitiveness of living things differs from the sensitiveness of non- living things. In most cases the living body responds to a disturbance by doing something that will probably save it from further injury. The non-Hving body, when sufficiently disturbed to do anything, does something that generally results in its further injury or destruction. Thus, when a dog's tail is pulled, he will try to run away, or he will bark or snap at the "thing- holding-tail." These responses are, on the whole, of a kind that will save him from further damage. Indeed, we cannot imagine how living beings would continue to live, generation after generation, if they had the habit of doing things that tended to injure or destroy them. In contrast to this kind of behavior, think of what the stick of dynamite would do if touched with a red-hot poker. There is nothing here that looks in the least like " trying-to-save-itself ." WHAT KINDS OF THINGS ARE LIVING? 23 20. Origin. We do not know anything about the first appear- ance of life upon the earth, but we do know that every plant and animal now living had its origin in the body of some other plant or animal. In general, non-living bodies do not reproduce themselves ; they do not produce other objects, either like them- selves or different ; but, so far as we know, living bodies can be produced only by other, similar, living things. WHAT KINDS OF THINGS ARE LIVING? 1. Great diversity among living things Need for breaking up material for comparison Forms Chemical composition Structures Activities 2. The parts of a plant (seed-bearing) Root Shoot Stem Leaves Flowers Fruits (seeds) 3. The parts of an insect (grasshopper) Head Mouth Eyes Compound ; simple Antennae Thorax (segmented) Legs Wings Abdomen (segmented) Breathing organs (spiracles) Hearing organs Reproductive organs 4. The parts of the human body Head Trunk Mouth Arms Eyes Legs Nose Ears 24 BIOLOGY AND HUMAN LIFE 5. Comparison of insect with mammal Similarities Differences Bilateral symmetry Segmentation in insect, not Distinct head in mammal ^ Special organs that cor- Distinct thorax and abdo- respond in function men in insect Mouth Wings £ygs Number and location of legs £^s Differences in corresponding Breathing openings organs Legs Grasping hand in man Paired appendages 6. Organs; organisms; organic Peculiarities of plant and animal parts Structural features Functional features Related in action to one another Related in action to body as whole All plants and animals made up of organs Living things as organisms Chemical pecuHarities of organisms Organic and inorganic compounds 7. Activities of animals Activities of plants Growth Growth Food-taking Food-taking Irritability Irritability Movement Movement Reproduction Reproduction 8. Comparison of living things with non-living things Growth Movement By assimilation Irritability By accretion Fitness Origin QUESTIONS 1. In what different ways is the grasshopper able to move about? 2. What special organs does the grasshopper use in each kind of locomotion ? 3. What is there about each of these organs that fits in wdth the special kind of locomotion that it serves ? WHAT KINDS OF THINGS ARE LIVING? 25 4. Under what circumstances is each form of locomotion used ? 5. In what way does the ability to move about help the grasshopper ? 6. How might an organism be able to keep alive without any means of locomotion? 7. Of what movements is the grasshopper capable, other than those of locomotion? 8. How do these movements help in the life of the grasshopper ? 9. What is there about the organs of locomotion that fits them for the special work they do? 10. How could an animal get along without the abihty to carry on these movements ? 11. What kinds of organs can you find in the grasshopper but not in the human body ? 12. In what way are any of these organs essential to life ? 13. How are the corresponding functions carried on in your own body ? 14. How are the corresponding functions carried on by a plant ? 15. Make a table of four vertical columns headed: Functions Grasshopper Man Plant In the first column (functions) list all the distinctive activities and processes of living things. In the second column name the structures or organs of the grass- hopper that are related to the corresponding functions or processes. In the third and fourth columns carry out the same idea for man and for a plant respectively. REFERENCE READINGS Densmore, H. D. General Botany, pp. 14-19. Gager, C. S. Fundamentals of Botany, chap, ii, The Parts of a Flower- ing Plant. LuTZ, F. E. Fieldbook of Insects. FoLsoM, J. W. Entomology, with Special Reference to its Biological and Economic Aspects, chap, ii, Anatomy and Physiology; sect, i, Skele- ton (pp. 21-56), sect. 2, Integument (pp. 56-68). Farmers* Bulletin 606, Collection and Preservation of Insects and Other Material for Use in the Study of Agriculture. Hough and Sedgwick. The Human Mechanism, chap, i, The Human Mechanism. CHAPTER III SOME LIFE RELATIONSHIPS : BUTTERFLIES AND BEES Questions. 1. In what ways are different kinds of insects alike ? 2. Do all bees sting? 3. How do bees sting? 4. Can butterflies bite or sting ? 5. Can moths bite ? 6. How do moths destroy cloth or fur ? 7. Upon what do butterflies feed ? 8. In what ways are butterflies and moths useful to mankind ? 9. How are butterflies and moths injurious to man ? 21. The butterfly. The butterfly belongs to the same class of animals as does the grasshopper. The general plan of the body is the same— head, thorax, abdomen. The number of legs and of wings is the same, and the arrangement of these organs is the same. The butterfly has antennae and compound eyes, as has the grasshopper. But with all these resemblances nobody is likely to mistake one of these animals for the other. Let us examine carefully a butterfly (or moth). We find that every organ is in some way distinct from the corresponding organ of the grasshopper. On the other hand, every organ of the butterfly follows the general plan of the corresponding organ of the grasshopper. Even the mouth, which shows perhaps the greatest differences, can be seen to follow the same general plan. A comparison of the behavior of butterflies with the behavior of grasshoppers brings out still more striking differences, as well as important similarities. Suppose we answer for both animals such questions as How does it find its food ? How does it take in food ? How does it get impressions from the outside? How does it move about ? How does it breathe ? How does it reproduce ? Two facts are very likely to impress us : 1. Corresponding organs carry on corresponding functions. 2. Differences between corresponding organs are related to differences in the surroundings and habits. 26 BUTTERFLIES AND BEES 27 Thus, locomotion is brought about by means of legs and wings. Both insects breathe through spiracles arranged in a row on each side of the abdomen. Food is in both cases taken in by the mouth ; but the grasshopper has a biting or chewing mouth, whereas the butterfly has a sucking mouth.^ 22. Development of the grasshopper. If we study the whole life of these insects from the beginning to the end, we shall find some more interesting similarities as well as differences. The mother grasshopper lays her eggs in the ground, where they remain the whole winter. When the young hatch out they look like tiny grasshoppers without wings, and their heads are a Fig. 10. Red-legged locust (Melanoplus femur -rubrum) a, eggs in the ground; b^, young wingless larva; b^, larva molting; c, pre-adult; d, adult insect rather large in proportion (see Fig. 10). The animal begins eat- ing almost immediately, but for a time it does not increase in ^When making comparisons between various organisms we must be con- stantly on our guard not to read into our observations more than the facts allow. For example, it is a very easy matter to state what we observe about the mouths of the insects in this way : " The mouth of this insect has biting jaws, since it feeds upon solid food, whereas the mouth of the other is a suck- ing mouth, since it feeds upon fluids." A little thought will show us that it would be just as true to say : "The grasshopper feeds upon solids, since it has a biting mouth, and the butterfly sucks nectar from flowers, since it has a long, sucking mouth." In other words, all we really know, from our observa- tions, is that the structure of each animal somehow fits in with its activities or habits — that each animal uses its organs in its own particular way. We do not know how each kind of animal came to have the structures and habits which we find it to have, or how it came to have the ways of living that it has. There are many attempts to explain what we find, and we shall study some of these proposed explanations later. 28 BIOLOGY AND HUMAN LIFE size, for its outer covering, the exoskeleton, is of rather hard material that can neither grow nor stretch. After some days, however, this exoskeleton splits lengthwise on the dorsal side (the back, or side away from the ground), and the animal crawls out, head first (see Fig. ii). Now, with no stiff exo- skeleton to interfere, the insect grows rapidly for a short time, until a new exoskeleton is formed by the hardening of a sub- stance w^hich is secreted, or given off, by the skin. The process of casting off the exoskeleton is called molting. From time to time the insect molts again, gaining in size after each molt ; and with each molt there are other visible changes, such as the development of the wings and the altered pro- portions of the parts. After the fifth molt the animal is full grown. 23. Development of the butterfly. The mother but- terfly usually lays her eggs upon the leaves of some plant. When the young hatch out they resemble the parent so Httle that many people never discover the relation between the wormlike caterpillars and the beautiful adult moths and butterflies which are their parents, and into which caterpillars in time develop. The larva, or young butterfly in this caterpillar stage, begins at once to feed upon the leaves. The anim.al now has a biting mouth : the jaws work right and left, very much like those of grasshoppers. A young larva eats several times its own weight of leaves in the course of a day, and it grov/s very rapidly. Although the caterpillar looks more like a worm than like any familiar insect, a closer examination shows many resemblances to insects. The head is fairly distinct, and the rest of the body is segmented. The first three segments behind the head, corre- Fig. II. Molting cicada In many jointed-legged animals (Arthropoda) the growth takes place at intervals between molts. The hard outer skeleton breaks open and the soft-skinned animal crawls out. After a while the shell hardens and the growth of the animal stops again BUTTERFLIES AND BEES 29 spending to the thorax, bear small legs ; but no wings are to be seen. Unlike adult insects, the caterpillar of some species bears several pairs of legs on some of the abdominal segments. After reaching full growth as a caterpillar the animal goes into a resting stage, in which the exoskeleton becomes very hard (see c, Fig. 12). Among the moths the resting stage generally includes a silky covering, or cocoon, about the exoskeleton, as in the case of the silk-moth. This resting stage may last from a few weeks to several months, according to the species. Among many species in temperate regions it lasts over the winter. The pupa, whether in a cocoon or naked, appears to be perfectly life- less, but we know that great changes are taking place inside. When these changes are completed, the pupa breaks open, and out crawls the fully formed butterfly adult, or imago. 24. Metamorphosis. The great differences in appearance and structure between the adult butterfly and each of the other stages through which it passes in the course of its life history (egg, larva, pupa, imago) have long aroused the wonder of observers. The succession of changes from one stage to the next is called metamorphosis, which means the same as transformation, that is, a changing over from one form to another. ^letamorphosis in development is found among many kinds of insects, but not among all. The development of the grasshopper is said to show an in- complete metamorphosis, since at each stage the change is not so great as that observed among butterflies. Metamorphosis in development is found also among higher animals, such as the newt and the frog, although in these cases the stages do not correspond exactly to the four stages in the butterfly's life (see section 227). 25. The bee (Apis mellifera, honeybee; or Bombus sp., bumblebee). Insects of the order represented by the honeybee and the bumblebee differ in many ways from both the grass- hopper and the butterfly. We see again the same general plan of body, consisting of head, thorax, and abdomen ; the same number and arrangement of legs and wings ; the same type of food-getting and sensory organs. Moreover, there is a segmen- tation of the thorax and of the abdomen, and there are spiracles a Tussock moth {Notolophus) a b c Hawk moth {Hyloicus kalmiae) -O- a b c Yellow swallowtail, or tiger butterfly {Papilio iur>ms) a b ^^ c d Fritillary {Argynfiis) Fig. 12. Development of Lepidoptera (moths and butterflies) The egg, a, hatches into a wormlike larva, or caterpillar, b. The larva feeds vora- ciously and grows very rapidly. On reaching full growth it curls up, secretes a hard covering, and goes to sleep. In this resting stage, or pupa, c, it may remain for months, giving no outward sign of life whatever. At the end of the resting period the cover of the pupa breaks open, and out crawls the fully formed insect, d. In some species the two sexes have distinct forms or color patterns in the adult stage. In the tussock moth the adult female is a sluggish, wingless animal. (All about f size) BUTTERFLIES AND BEES 31 by means of which the animal breathes. But there are distinc- tions in wings and legs and mouth, as well as in other details in all parts of the body. In development the insects of this order (which includes wasps and hornets, ichneumon flies and ants) show a complete metamorphosis. 26. Division of labor. One of the most interesting facts about the bee and ant order {Hymenoptera, see page 84) is the com- paratively high development of social habits. The beehive and the ant colony have for ages represented to students a w^onderful example of the possibilities of social life. There is complete Fig- 13- The honeybee The insect develops from an egg, a, into a tiny wormlike grub, or larva, b. The larva feeds upon material in its chamber, or cell; the food is supplied by adult bees. When the larva reaches its full growth (in about five days), the cell is closed with wax; during the resting stage, or pupa period, c (which lasts about thirteen days), the insect is transformed into an adult. There are three kinds of individuals : drones, or males, d; queens, or females, e; and workers, /. The queen develops in an extra large cell, g, which projects above the surface of the comb and is supplied with spe- cial food. (The larvae are shown rather stretched out in their cells; they really lie at the bottom curled up in a ring) cooperation of large numbers of individuals, year after year, without any sign of friction or conflict within the group. There is also a marked degree of what we call division of labor, whereby each individual attends to a single part, or a very few parts, of the total work done by the colony as a whole. Among the bees cells are constantly being built of wax. Honey is being made; nectar gathered. Prepared food is being stored in the cells. After the eggs hatch out, the young larvae are looked after. At any given time the gathering of material, the storing of food, the nursing of the young, the cleaning of the hive, the building 32 BIOLOGY AND HUMAN LIFE of cells, are all carried on by different individuals; yet there seems to be no central government or directing officers. Each bee goes about her affairs just as regularly, and we might say as reliably, as does any solitary butterfly or grasshopper ; yet all work together in perfect harmony to produce results that could not be brought about by individuals working separately. In the bee colony there are three different kinds of individuals produced— males, females, and workers. In any one nest or hive there is but one female, the queen, and (during the sum- mer) a number of males, or drones. The hundreds or thousands of other bees are workers, which are really females that do not Fig. 14. The sting of the bee In this order of animals the weapon is the egg-laying organ. When the bee stings someone, the point is likely to remain in the flesh; and as the animal flies away some of its internal organs are mutilated and the insect soon dies. The value of this weapon is not so much for the protection of the individual as for that of the colony or species. The individual is sacrificed to protect the group or to educate the enemies of the species develop all their organs completely. Much of the time there are no drones, for the male dies immediately after the female is fertilized in the spring, and any other males are killed by the workers on the approach of winter. There is here, then, first of all, a division of labor between the reproducing individuals and the individuals that do all the other kinds of work that have been mentioned. But is there a particular class of workers for each particular class of activity? Among the honeybees the young adult, or imago, immediately after coming out of the pupa stage, sets to work as nurse, looking after the larvae, which have to be fed for a few days after hatching from the eggs. Later these same adults turn to other work within the hive, and after a few days more they go forth to gather pollen BUTTERFLIES AND BEES 33 and nectar from flowers. Thus the division of labor is not be- tween one kind of individual and another, but between one period of life and another — like the division of labor in some factory in which the younger workers make the parts for the manufactured product and the older workers assemble the parts. 27. Interdependence. The division of the total work of the bee- hive or the ant nest has been compared ( i ) to the similar divi- sion of labor among human beings in society and (2) to the division of functions among the organs of any plant or animal. The individual bee, for example, continues to live by carrying on many fairly distinct processes— eating, breathing, feeling, moving, and so on. We have already seen that there are special organs that carry on these special processes. The mouth is a food-taking organ ; the leg an organ of locomotion ; the eye a see- ing organ ; and so on. Now, in the case of a single organism, as in the case of a colony or society, division of labor means the dependence of one part upon all the others. The mouth can take in food only if the wings bring the insect to the flower. But that in turn depends upon the eye seeing the flower. More- over, the wings and the eye and the mouth cannot do their work unless the food taken in by way of the mouth is somehow changed into a usable form and then distributed to the muscles of the wings, the nerves of the eye, and the complex machinery of the mouth. And, finally, the parts have to work in harmony or balance, and their activities have to be timed so that they fit together effectively. There is thus a certain interdependence among the parts, as well as a correlation. This idea of interdependence applies not only to the relation among the parts of the organism or among the members of a colony or society ; we see it illustrated also in the dependence of different species upon each other. The bee, for example, de- pends upon the clover for pollen and nectar to make food and wax. The clover species, in turn, depends upon the bee to render the important service of transportation. The forma- tion of seeds in flowers remains in many species impossible un- less some insect first carries the pollen from the organ in which 34 BIOLOGY AND HUMAN LIFE it originates (the stamen) to the seed-bearing organ (the pistil) (see page 42). The bees and the butterflies represent two groups that are most generally active in this process of pollena- tion (see Chapter IV). This interdependence between insects and seed-bearing plants is in some cases so great that certain orchids are dying out because the insects necessary for pollena- tion are not sufficiently abundant to insure seeds every year. In other cases insects in- troduced in a new re- gion cannot maintain themselves because the needed food plants are not present. In our reg- ular horticulture it hap- pens occasionally that trees or bushes in full blossom fail to yield the expected crop of fruit because of the lack of insects to insure pollen- ation. This is why wise farmers and orchard- men so often maintain hives of bees : even where the honey itself is not considered worth producing, the bees are worth having because they insure abundant pollenation at the right time. 28. Homology. The division of labor among the organs of the bee is of course the same as that which we find in other in- sects, or even in entirely different classes of animals such as our own bodies ; but if we compare the insects already studied with one another, we shall find that most of the functions are carried on by corresponding organs in the different animals. Thus, the locomotive organs in bees, butterflies, and grasshoppers are the legs and wings, and in every case the position of the organ and the general plan of structure are the same. If we examine the Fig. 15. Division of labor among ants Three forms of the Central American fighting ant (C/ieliomyrmex nortoni): a, soldier; b, medium worker; c, small worker BUTTERFLIES AND BEES 35 mouths, we shall again find many basic simi- larities in spite of the great differences. Among animals that are built on substan- tially the same plan the corresponding parts are said to be homologous. Thus, the thorax of one insect is homologous with the thorax of another insect. More- over, the thorax of a butterfly is said to be homologous with the three distinct segments immediately behind the head of the caterpillar. We may also say that the three pairs of legs on one insect are homol- ogous with each other, since they originate and develop in the same way, in spite of differ- ences, as between the hind leg of the grass- hopper, for example, and the front legs. In the same way we con- sider the "balancers" of a fly homologous with the hind wings of the butterfly and the wing covers of the beetle homologous with the front wings. The idea of homology helps us to understand a certain same- ness among organs that appear to be very different in structure Fig. 1 6. Homology in the appendages of the lobster In the Crustacea all the appendages are built on the same plan, but each segment of the body (rep- resented by Roman numerals) has a distinctive organ. I and // are sensory; III-V combine sen- sory functions with food-getting; VI-VIII are chiefly food-getters, but are also related to breath- ing; IX is the nipper; X and XI are both grasp- ing and locomotor organs; XII and XIII are walking legs. The abdominal appendages XIV- XVIII are called swimmerets and probably assist in slow swimming. XIV and XV are also related to reproduction in the male, and in the female all the swimmerets carry the hatching eggs and larvse. XIX and XX spread out into a flat tail-paddle, used in swimming backward suddenly 36 BIOLOGY AND HUMAN LIFE or even in their functions. We can understand the bones of the arm, for example, much better if we compare them part for part with the bones of the leg ; or the wing of a bird, if we compare it part for part with our arm (see Figs. i6 and 130). 29. Analogy. We have seen that there are several functions which are carried on by all living things, plants as well as ani- mals—food-taking, breathing, responding to outward changes, reproducing. We have also seen that all the common plants and animals are organized ; that is, made up of organs, or mem- bers, that share in the total work and that somehow correlate their functions. We have probably known these facts from early childhood, and it is very likely that human beings noted these facts early in the history of the race, for in every language common forms of expression take such facts for granted. For example, we speak of the legs of a lobster and the legs of a horse, the wings of a bird and the wings of a butterfly, the tail of a cow and the tail of a dragon fly. The two examples given for each name are not at all homologous ; they do not correspond to each other as does the front wing of a butterfly to the hard wing of a beetle. In each pair named the two structures, or organs, resemble each other either in performing similar functions or in having a superficial similarity in position. The legs are walking organs ; the wings are flying organs ; the tails are relatively thinner parts of the animals, projecting at the posterior end. Two organs of different type, or belonging to different types of organisms but carrying on similar functions, are said to be analogous. Thus, the jaws of a grasshopper may be considered as analogous to the jaws of a cow. They are not homologous ; the}' are not developed in the same way, they are not con- structed in the same way, and they are not operated in the same way ; but in both cases the jaws are biting or chewing organs. The antennae of a lobster may perhaps be considered analogous to the whiskers of a cat, but the claws of a lobster are neither homologous nor analogous to the claws of a cat. When we compare plants with animals, we often find the same function carried on by organs that are so different that it is BUTTERFLIES AND BEES 37 not easy to decide at once which organs in one case are analo- gous to organs in the other ; and as for homology, most people never discover any at all between plants and animals. Many plants have no special breathing organs that are strictly analo- gous to our nostrils or to the spiracles of insects, for they may absorb oxygen from the air at any part of their surface. ^lost plants have no organs that are analogous to the mouth which is present in most animals, for plants do not take food as we do, but simpler materials w^hich they later work over into food. Plants have no organs that are analogous to the heart, for the circulation of material within the organism is in their case brought about by a totally different process. Even their irri- tability and their movements depend upon different structures. On the other hand, the growth of plants, like the growth of animals, is a process that is carried on by every part of the body, and not by a special organ. Indeed, we shall see presently that all the fundamental functions are really carried on by all parts of the body. The idea of division of labor, the idea of homology, and the idea of analogy all correspond to real facts ; but they do not apply to every detail of life. 30. Being alive. Whatever organism we may be thinking about, we shall always find that so long as it is alive it keeps on doing certain things, and that it remains alive only so long as it does these things, that is, so long as it (i) takes food and assimilates it, (2) transforms the assimilated material so as to get from it the energy for movement or for other processes, and (3) responds more or less suitably to changes going on around it. Our own bodies and those of the other animals that we have studied are alive because they show irritability, assimilation, and contractility ; and any other animal and any plant is alive because it is sensitive to changes, because it transforms ma- terial from outside into its own body, and because it can bring about movements or other changes that fit the conditions. Like the insects that we have studied, every plant and every animal also originates from an egg or some other structure that is analogous or homologous to an egg. 3^ BIOLOGY AND HUMAN LIFE SOME INTERRELATIONS OF LIVING THINGS AND BEES BUTTERFLIES I. The butterfly (class Insecta) Resemblance to other insects General plan of body Appendages Kinds Numbers Location Sense organs Feeding organs Breathing organs Development of grasshopper Egg stage (where eggs are deposited) First active stage (nymph) Molting Development of butterfly Eggs Larva Pupa Imago Metamorphosis In insects Kinds Stages In other animals The bee Resemblances to other insects Distinctive characters Division of labor among social honeybee) Kinds of work done Kinds of individuals Work done by each Advantages To the colony To the individual Distinctive characters of order Lepidoptera (moths and butterflies) Structural Head, thorax, abdomen Legs Wings Mouth organs Sense organs Habits and behavior of special organs Growth between moltings Other changes Adult Resemblances between larva and adult Differences between larva and adult insects (for example, the Disadvantages To the group To the individual BUTTERFLIES AND BEES 39 7. Interdependence Division of labor among organs of an animal Kinds of work ; kinds of organs ; how the parts are coordinated Interdependence among social insects Interdependence \\'ithin a human society Examples ; advantages : disadvantages ; limits Interdependence between species Example : insects and seed plants What it means to the insects What it means to the plant species Importance to man 8. Homology Corresponding parts or organs in any organism Corresponding parts or organs in different species of same type Examples of homologous organs that are very different in appear- ance or in function 9. Analogy Organs or structures of different types but having similar functions 10. Life functions of plants and animals Food-getting and assimilation Release of energy from food (movement and other changes) Irritability and adaptive response to outward changes Origin from previously existing organism (reproduction) QUESTIONS 1. What similarities are there in the structure of grasshoppers and that of bees and butterflies ? 2. What is alike in the activities and functions of grasshoppers, butter- flies, and bees? 3. How do the structures of the grasshopper and the bee differ? of the grasshopper and the butterfly ? 4. How does the structure of the butterfly differ from that of the bee ? 5. In what respects does the behavior of the grasshopper differ from that of the butterfly ? 6. How do the functions and activities of the grasshopper differ from those of the bee ? 40 BIOLOGY AND HUMAN LIFE 7. Contrast the habits of the bee with those of the butterfly. 8. What is there about the structure of these insects that protects them from possible enemies ? 9. What do these animals do to protect themselves against enemies ? 10. What are the important distinctions between the development of an animal and its growth ? IL How can we show that a human being develops as well as grows ? 12. What division of labor is there among the members of a family ? 13. What kinds of division of labor are there among the workers in an office ? a store ? a factory? 14. What determines the division of labor among the different states or natural regions of a country ? 15. How does division of labor affect the independence of any given individual ? 16. What are the advantages of division of labor within a profession? 17. In what other ways can these advantages be obtained? 18. What are the disadvantages of extreme division of labor ? 19. How can these disadvantages be overcome ? 20. In what ways do human beings depend upon other species of animals or upon plants ? 21. In what ways do other living things depend upon us ? REFERENCE READINGS Farmers^ Bulletin yoS, The Leopard Moth, a Shade-Tree Insect. Fanners^ Bulletin yoi, The Bagworm, a Shade-Tree Insect. Farmers^ Bulletin 447, Bees. United States Department of Agriculture. Bulletin 1222, Growth and Feeding of Honeybee Larvae. Maeterlinck, Maurice. The Life of the Bee (extract in C. H. Ward*s "Exploring Nature," pp. 88-95). Latter, O. H. Bees and Wasps. FoLSOM. J. W. Entomology, chap, iii, Development ; sect. 2, External Metamorphosis (pp. 126-148). CHAPTER IV THE CYCLE OF LIFE : FLOWERS Questions. 1. Do all kinds of plants produce seeds ? 2. Do all kinds of plants bear flowers ? 3. What is the use of flowers to plants ? 4. How does the odor of a flower help the plant ? 5. How does the odor of a cultivated rose help the plant ? 6. How are seeds made ? 7. Can a plant of one kind produce seeds of a different kind ? 8. Are all bright flowers visited by insects ? 9. Do insects get anything from flowers besides nectar ? 10. Does it hurt plants in any way to remove the flowers ? 31. Individual life is limited. The life of every individual, plant as v^ell as animal, comes to an end after only a few min- utes, or after many centuries ; dying is a part of being alive. Yet the species, or kind, may continue to live for thousands and thousands of years. New individuals are constantly being pro- duced. The species reproduces itself, although not every living individual can reproduce itself. The term reproduction carries the idea of a special portion being separated from the parent and developing into an individual. Among the more familiar plants, reproduction is by means of seeds. The flower is a special structure related to the making of seeds. 32. Structure of the flower. In most common flowers, such as wild roses or buttercups, we find certain leaflike parts that attract our notice because of their color. This conspicuous part of the flower is called the corolla, and is commonly surrounded by another set of leaflike parts that make up the calyx, or cup (see Fig. 17). Although this floral envelope (calyx and corolla) is in most plants the first to attract our attention, it is by no means the most important part of the flower. Many species produce seeds without having these organs. 33. The essential organs. The seeds originate from tiny struc- tures called ovules, which are borne in special organs found at 41 42 BIOLOGY AND HUMAN LIFE the center of the flower, called carpels (see Fig. i8). Sometimes there is a single carpel, as in the pea flower {4, Fig. 197) ; sometimes there are several. When there are two or more, they may be quite distinct or they may be more or less completely fused together (Fig. 18). The carpel may contain a single ovule (cherry, oak, strawberry), or a few (bean, apple), or very many (poppy, cucumber). The name pistil (from a fancied re- semblance to the pestle, with which the apothecary crushes substances in his mortar) is sometimes given to the single carpel or to the combined car- pels in a flower. The enlarged por- tion, bearing the ovule or ovules, is called the ovary (Fig. 17, /). The upper tip of the pistil is called the stigma, which means spot (Fig. 17, e). Surrounding the pistil are several slender stalks with knobs or enlarge- ments on the ends (see d, Fig. 17). These structures are called stamens, from a word meaning "thready." Flowers differ greatly in size and shape, as well as in color and odor. The various parts differ in many ways as we compare the flowers of different species ; but the pistils and stamens are always and everywhere the organs that have to do with seed-making, and their work is the same in all flowers. Because seeds are produced only by these organs, pistils and stamens are some- times spoken of as the essential organs of the flower. Fig. 17. Structure of a flower The outer set of covering leaves, a, a, is called the calyx; the single parts are sepals. The in- ner layer, b, b, is the corolla; its parts are the petals. The central organ is the pistil; the main body of the pistil, /, is the ovary and contains one or many little structures {ovules) capa- ble of becoming seeds. The tip, e, of the pistil is the stigma; this is connected with the ovary by the style c. Surrounding the pistil are a number of stamens, rf, consisting of a stalk, li, called the filament, and an enlarged capsule, g, called the anther. This contains a mass of cells which can be thrown out, i; these cells loosened from the anther are called pollen THE CYCLE OF LIFE : FLOWERS 43 34. The ovary. If you cut open the ovary in any flower, you will find that it consists of a hollow box, with several compart- ments in some species, corresponding to the carpels (see Fig. i8). This hollow box contains from one to very many of the tiny ovules, each of which may become a seed. As time goes on these ovules enlarge and the ovary also becomes larger. By the time the seeds are ripe the ovary has become the jruit. In the mean- time the corolla and the calyx, as well as the sta- mens, have fallen off or shriveled away in most cases, so that most peo- ple never discover for themselves that one has anything to do with the other. But the chang- ing of ovules into seeds is not simply a matter of growth. Every farmer and gardener knows that it is possible to have plenty of flowers or blossoms with a very poor crop of fruit, even when the conditions for growth are of the best, and even though the plants are perfectly healthy. 35. Fertilization. Farmers and orchaidists have known for many centuries that flowers will remain sterile (that is, they will fail to produce seed) unless some of the powdery pollen (/, Fig. 17) from the stamen somehow gets onto the stigma. This transfer of pollen was accordingly called fertilization, the idea being that the pollen makes the pistil jertile, or capable of bearing seed. But less than a hundred years ago the real facts about seed-making were discovered. When the pollen grain gets to the stigma, it absorbs some of the sirupy fluid on the latter. Then there begins to grow out of it a very thin thread, or tube, Fig. 18. Sections of ovaries Ovaries are of many sizes and shapes. They contain but a single ovule in some species of plants, and in other species they bear hundreds. The ovules are definitely placed in one or more compartments of the ovary. Each compartment, with its style and stigma, is sometimes called a carpel 44 BIOLOGY AND HUMAN LIFE Fig. 19. Fertilization in a flower When a pollen grain, p, alights on the moist sur- face of a stigma, s, it absorbs water and puts forth a thread of protoplasm, or a pollen tube, pt, which grows down the style into the ovary. The tip of the pollen tube finds its way to the inside of the ovule, 0, through a small passage- way, the micropyle, m. The large cell in the middle of the ovule, called the embryo sac, es, undergoes a number of changes which result in producing several nuclei. One of these nuclei at the end nearest the micropyle corresponds to an egg cell. Similar divisions take place in the nucleus of the pollen grain, and one of the re- sulting nuclei corresponds to a sperm cell. The cell walls separating the pollen tube and the em- bryo sac dissolve, and the pollen nucleus unites with the egg nucleus. The newly formed joint nucleus, or fertilized egg, begins to divide. Thus it develops into a new plant, or embryo; the ovule containing it becomes a seed; the ovary becomes a fruit which can be seen only with the microscope (see 7, Fig. 32). This pollen tube grows through the style and into the hol- low of the ovary, then through a small hole in the ovule, the micropyle, which means "small gate- way" (see in, Fig. 19). Finally it reaches the central space of the ovule, where there is a special mass of jelly like living stuff, the embryo sac (see es, Fig. 19). Here a portion of the matter in the pollen tube unites with a portion of the matter in the em- bryo sac, and from this united mass a new plant begins to develop. The uniting of the two masses of living matter is now called fertilization. This is the real act of repro- duction, for its result is in fact a new individual (see Fig. 19). 36. Seed and fruit. After fertilization takes place the mass in the em- bryo sac absorbs food in large quantities from the parent plant and becomes THE CYCLE OF LIFE : FLOWERS 45 a baby plant, or embryo. The surrounding walls of the ovule become the seed coats. The ovule, with its embryo sac, thus changes into a seed. In addition to the food used by the embryo in its development and growth the parent plant supplies other food materials. These are accumulated either immediately around the embryo or within the embryo itself. After the seed sprouts and before it is able to supply itself the young plant uses this surplus food. Fertilization brings about changes in other parts of the flower. The petals drop off, and usually the stamens also. The ovary begins to enlarge and at last ripens into the central or even the entire body of the fruit.^ In some plants the calyx of the flower, and even the enlarged end of the stalk, the receptacle, may be- come fused into the fleshy fruit. 37. Pollenation. In many plants the pollen is carried from the stamen to the stigma by the growth movements of the parts of the flower. The style, as it gets longer, may bring the stigma into contact with the anther ; or the corolla, as it grows and opens, pushes the stamen against the stigma; or the stalk of the flower may bend over as it grows, and so deposit some of the pollen from the anther on the stigma. In some flowers the anther stands above the stigma, and the pollen is carried over by the action of gravity. Thus there are many kinds of plants in which the flower may be said to pollenate itself. This process is sometimes called close-pollenation. There are many plants, however, in which close-pollenation is quite impossible. I. Space relations. The position of the stamen in relation to the pistil may make close-pollenation impossible, as in the iris, or blue flag, in the milkweed, in all the orchids, and in many other groups of plants. In some species there are two kinds of iJn most of the common plants the fruit will not ripen (that is, the ovary will not continue its development) unless fertilization takes place. But there are many plants in which a seedless fruit is possible. Seedless oranges, seed- less apples, seedless grapes, the pineapple, and the banana are examples of fruits that develop without the ovule being first fertilized. The plantain and the breadfruit develop a more juicy fruit when there is no fertilization. 46 BIOLOGY AND HUMAN LIFE flowers, some bearing only stamens and others bearing only pistils, as the corn and other grasses, birch, hazel, chestnut, oak, squash, and the cone-bearing trees. Such plants are some- times called monoecious, meaning "of one household." It is of course impossible for close-pollenation to take place in these. There are still other plants in which the stamen-bearing flowers are borne on one individual and the pistil flowers on a different one, as in poplar, wiUow, box elder, tape grass {V allisneria) (see Fig. 20), begonia, Fig. 20. Pollenation by water The tape grass {V allisneria) is a dioecious water plant. The pistillate individual grows up to the surface of the water, where the flowers, a, are opened, while the staminate individual remains beneath the surface. The staminate flowers, b, are de- tached from the stalks and rise to the surface, where they float about and gather in large numbers in the quiet stretches of water close to solid objects of various kinds. Whenever one of these floating stamen flowers comes close to the pistillate flower of the species, the anther is brought into direct contact with the stigma, and in this way pollenation is effected sassafras, and virgin's bower {Clematis). Such plants are sometimes called dicecioiis, meaning "of two households." Close-pollenation must be impossible in these plants also. 2. Time relations. In some species of plants the stamens and the stigmas do not ripen at the same time, close-pollenation being thus impossible. The pollen ripens before the stigma in maize, in the mallows, in many species of the aster family, in the creeping crowfoot, and in the sage. THE CYCLE OF LIFE: FLOWERS 47 The stigmas ripen ahead of the stamens in the common plantain, in the potentilla, or cinquefoil, and in the Oriental grass known as Job's tears. 3. Physiological relations. In some species of plants it is found that if the pollen gets from the stamen to the stigma of the same flower, the pollen will not lead to fertilization. In buckwheat, in most orchids, in certain species of day lily, and in some members of the bean family the pollen will not even put out a tube if placed on the stigma of the same flower. There are, then, many species of plants in which close-pollenation cannot take place, or in which it is not very effective if it does take place. How, then, do these plants produce seeds, or, rather, how do they secure pollenation? In other words, how is pollen carried from flower to flower? 38. Cross-pollenation. Plants that cannot pollenate them- selves simply depend upon outside moving bodies or moving forces to transfer the pollen for them. 1. Wind pollenation. The most common moving agency that acts between plant and plant is the wind. The dryness and abundance of the pollen produced by many of the common trees, and the presence of pollen in the dust at certain seasons of the year, would make us suspect that the wind must dis- tribute a great deal of pollen (see Fig. 21). 2. Water pollenation. Another agent that is effective in dis- tributing pollen for plants is water. This is of course limited to plants that live in the water (see Fig. 20). 3. Bird pollenation. Next to the wind the most common moving agents that go from flower to flower are flying animals, like birds and insects. We know that not all birds or all in- sects can serve plants as pollen carriers, but only those that do regularly visit flowers (see Fig. 22). 4. Insect pollenation. There are hundreds of species of plants whose flowers are pollenated by insects, chiefly those of the bee order and of the butterfly and moth order. All these insects have sucking mouths, and many of them visit flowers that con- 48 BIOLOGY AND HUMAN LIFE tain nectar. Some of these insects also use pollen as food. The bees, for example, feed quantities of pollen to the young in their hives. In getting pollen or nectar the insect rubs off pollen on various parts of its body. Later, when it visits another flower of the same kind, the pollen is rubbed off against the stigma (see Fig. 23). 39. Adaptations in flowers. Wherever we see a living thing we cannot help being impressed by the ''fitness" of its parts and of its activities. The organs and functions are beautifully related to one another as members of the organism, and they are beautifully re- lated to the surroundings, making life possible. Thus in the flowers we may see the wonderfully delicate structures bearing pollen and ovules. Many flowers close toward sunset and open again at dawn, expos- ing the anthers and stigmas to insects by day but pro- tecting them at night. The various colors in the corolla, the odors, the nectar, all very evidently attract insect visitors. The curious shapes match almost perfectly the sizes and shapes of particular insects. The stigma is rough, or hairy, or sticky, just right for catching pollen, and bears the fluid in which the pollen sprouts out the pollen tube. Inside the style there is a hol- low passage or a spongy structure through which the pollen tube readily works its way. The pollen tube's irritability guides it toward the ovule. In the ovule is the micropyle, through which the pollen tube finds its way to the embryo sac. And we could go on multiplying illustrations of the remarkable adaptation of part to part and of all to the conditions surrounding the plant. Of course the same may be said of the many details that make Fig. 21. Stigma of a grass In wind-pollenated plants the stigmas usu- ally expose a large surface to the wind. A study of conditions on farms that produce corn, wheat, oats, and other grains shows that these plants, as well as many others, depend entirely upon the wind for their pollenation. Indeed, it is sometimes necessary to take special precautions to prevent the wind from bringing to a group of plants an undesirable kind of pollen from a remote field THE CYCLE OF LIFE : FLOWERS 49 up the structure and activities of the various insects that visit the flowers. While it is true that in order to be alive the activi- ties of an organism must fit the surrounding conditions, it would be a mistake to suppose that every structure and every character and every activity is of value in keeping the organism alive. There are many plants that have colored corollas (some kinds of beans, for exam- ple) but that do not depend upon insect visitors at all, and there are other plants that receive insect visi- tors without being particularly showy. Again, while there are many insects that help in pollen- ation when they come for nectar, there are certain plants that yield nectar without get- ting Fig. 2 2. Pollenation by birds The saber-billed humming bird visits certain large flowers and laps up the sugary fluid, or nectar, and so rubs off some of the pollen. When it visits another flower, this pollen comes off onto the stigma. Certain tropical flowers are said to be pollenated by bats that come to them for nectar. (From an exhibit in the American Museum of Natural History, New York) any use from the visits of the in- sects. For example, nectar is sometimes formed on the stems and leaves of vari- ous plants, including ferns (which produce no seeds at all). 40. Interdependence. In some cases the dependence between insects and flowers is so great that it has an important bearing on the practice of plant raisers. A poor supply of blossoms may mean a poor honey crop and fewer bees the following season. The lack of bees to pollenate the blossoms may mean a poor fruit crop. 50 BIOLOGY AND HUMAN LIFE Stigma Fig. When plants are transferred from one part of the world to another, it sometimes happens that they fail to bear seeds be- cause the particular insect upon which they depend is absent in the new region. This was the case when vanilla culture was extended from Mexico and South America to various islands in the Indian Ocean. Here the plants grew luxuriantly and bore many flowers, but ripened no pods, or "beans" (for which the plants are raised), because the insect necessary for pollenation was not present (see Fig. 24). When fig trees were first introduced into California they produced large, juicy fruit ; but they did not dry properly and could not be prepared for shipping. To get the normal fruit it was necessary to find the insect that brings about pollena- tion. This little wasp has a curious life history which is closely tied up with the fig plant. The wasp cannot complete its life cycle except with the aid of the fig; the fig cannot complete its life cycle ex- cept with the aid of the wasp. A living thing cannot live by itself alone, or at least not completely. In gen- eral, all animals depend upon plants for their means of life, and many plants de- pend directly upon animals. But there seems to be no advantage in being so dependent upon some particular plant or animal as to be unable to live without Plants that are not so highly special- ized, depending upon the wind for pollenation, seem to be at least as well off, or at least many are quite as capable of reach- ing to all parts of the earth— for example, the grasses, the 23. Pollenation by insects In the lady's slipper and in many other flowers, insects alighting on the corolla crawl into the in- terior, guided by the form and the markings. In many flowers the arrange- ment of the parts is such that the insect must brush against the stigma in going in, and against the anthers in passing out. As a result the animal carries pollen from flower to flower. Many species of plants, especially among the orchids, depend upon single species of insects for their pollenation it (see section 27) THE CYCLE OF LIFE : FLOWERS 51 cone-bearing trees, and the catkin-bearing trees. 41. Homology and anal- ogy in the flower. If you have studied several dif- ferent kinds of flowers, you must have noticed the very great differences among petals of different species or among pistils. Indeed, you will often have some difficulty in making up your mind whether some particular structure is one of the regular parts of a flower or something totally dif- ferent. A part of the fas- cination that many peo- ple find in studying new varieties of wild flowers is that of recognizing famihar structures under strange disguises, or like that of solving puzzles. Stamens may be large or small, with long filaments or with none, standing freely or fused with one another or with the co- rolla. Similar modifica- tions are found in the other parts. Some stu- dents of plant life go even farther and point out that stamens and carpels, as well as petals and sepals, are special kinds of leaves (see Fig. 25, Fig. 24. Hand pollenation in the vanilla flower Instead of importing the needed insect to carry on pollenation, the raisers of vanilla decided to hire women and children to go from flower to flower and pollenate by hand. In the orchids the stamens are fused with the stigma, placing the anthers above the stigma in such a way as to make self-pollenation absolutely impossible. an, anther; p, pollen masses; s, stigma. A, gen- eral view of flower; B, position of hands and needle in artificial pollenation; C, needle lifting pollen masses; D, anther raised to expose pollen masses; E, style raised to show opening in stigma; F, longitudinal section to show relative positions of anther and stigma: G, longitudinal section after pollenation, showing pollen masses in the stigma. All the vanilla beans in the Sey- chelles Islands are grown with hand pollenation 52 BIOLOGY AND HUMAN LIFE Fiff. 2' Homology in the structure of a flower and 5, Fig. 197). All the various structures that we may con- sider as having the same kind of origin (in this case, outgrowths from the stem) and the same fundamental structure (in this case, a more or less flattened structure with nerves running through it) are said to be homologous (see section 28). Nearly every beginner in the study of flowers is deceived by the daisy and the dandelion, of the sunflower family, because these plants have structures that are analogous (see section 29) to those we have already studied, but not homolo- gous. In this family of plants the flowers are very small, but many of them are clus- tered in a head, so that we commonly speak of the whole head of a hundred or more flowers as a flower. Certainly a head has the general appearance of a flower, and we may consider it analogous to a flower since, like a larger corolla, it at- tracts insects, as in the daisy or the sunflower, where the small flowers around the outer edge of the head have elongated or strap-shaped corollas that are sometimes mistaken for single petals (see Fig. 184). At the base of the head are many small, leaflike structures which we may consider analogous to a calyx. This structure is called an involucre, and the single leaves are called bracts. In the Jack-in-the-pulpit and the calla lily (both of the Arum family, not lilies) many tiny flowers are arranged on a spike, and a very large bract, sometimes mistaken for a corolla, sur- rounds the whole (see Fig. 26). In the dogwood the four large white or pinkish ^'petals" are really bracts. Thus we see that in plants as well as in animals a structure carries on the func- In the water lily (as well as in the peony and some other flowers) it is possible to see that the stamen may be considered as a special kind of leaf. There is a gradual passing from sepal to petal, and as we pass toward the center of the flower some of the structures become less and less like "leaves," and more and more narrovA", until they are definitely stamens, made up of the sfalklike filament and the distinct anther THE CYCLE OF LIFE : FLOWERS 53 tion that normally belongs to a different organ, and that one organ may take on a variety of functions. 42. Conservation of wild flowers. People are coming to have more time for recreation, and it is becoming easier to get into the woods and unoccupied spaces. As a result more and more people are tempted to gather wild ilowers because of their beauty and interest. There has actually been a serious reduction in many species. ]Many of our native plants have been al- most entirely exterminated, and others are going fast in certain parts of the coun- try. The trillium, or wake-robin, of which there are several species, is almost un- known in regions where it was very plen- tiful a dozen or twenty years ago. The same is true of the dogtooth violet and of the clintonia, and of many native orchids. The dogwood is so conspicuous in the spring that hiking parties and automo- bile tourists are tempted to carry away large quantities of the blossom-bearing branches. Those of us who value beauty in nature (which includes, of course, the colors of flowers and the songs of birds), and who realize the importance of preserving it for as many as possible to enjoy, will do all we can to protect from wanton de- struction or wasteful collection the wild flowers that we still have with us. We can all get more enjoyment by leaving them in their natural surroundings. For collecting or scientific study we can usually get enough by means of photographs and notes and sketches. For the study of structure we can use either cultivated plants or weeds, the destruction of which will do the community more good than harm. Fig. 2 0. Jack-in-the- pulpit In plants of this family there are two kinds of flowers, the pistil-bearing and the stamen-bearing. Both are found growing in clusters on the same stalk, the pistil flowers near the base and the stamen flowers toward the end. A large, leaflike organ, the spathe, almost incloses the spike bear- ing the flowers 54 BIOLOGY AND HUMAN LIFE There has been developing an interest in propagating wild flowers by means of seeds planted in suitable places. Protected from careless pleasure seekers, plants can in this way be made to cover unused spots, and some of the rarer varieties may be preserved from extermination. This seems to be a good plan to follow in many parts of the country, and is worth helping. THE CYCLE OF LIFE: FLOWERS 1. Reproduction (what it means) Related to the beginning of life Related to the end of life 2. Structure of flowers The floral envelope The calyx — (sepals) ; the corolla — (petals) Essential organs Stamens Carpels — (pistil) Anther — (pollen) Ovary — (ovule) Filament Stigma Style 3. PoUenation (meaning) Close-pollenation and cross-poUenation Agencies of cross-pollenation Wind ; insects ; water ; birds 4. Origin of new plant FertiHzation Pollen tube ; embryo sac ; fusion Growth of seed Fertilized embryo sac becomes embryo Ovule becomes seed Ripening of seed Ovary becomes seed-bearer (fruit) 5. Interdependence between insects and flowers 6. Homologous parts of flowers 7. Analogies in composite and other clusters of flowers 8. Conservation of wild flowers Spare ; protect ; propagate THE CYCLE OF LIFE : FLOWERS 55 QUESTIONS 1. Supposing that everything else about organisms remained the same, what would happen if every plant and every animal suddenly be- came incapable of dying ? 2. How does a baby plant originate ? How does it get nourishment ? 3. How can plants be multiplied without the use of seeds ? 4. How is pollenation brought about in each of ten plants that you have observed ? 5. How does the living matter in the pollen grain reach the living matter in the embryo sac ? 6. What are the advantages or disadvantages of having a very long style (as in the Indian corn, for example), compared to having a very short style (as in the buttercup) ? 7. In the flowers that you have studied, what distinguishes those with more division of labor from those with less division of labor ? 8. Many common flowers have their parts in fours or fives ; others have their parts in threes. Can you find any other peculiarities of the plants in one group or the other ? 9. What are the advantages of keeping bees in the neighborhood of farms and orchards ? 10. Why do plants that are brought to a new region, with suitable soil and climate, sometimes grow very well but fail to produce fruit ? 11. In what ways is an involucre like a calyx? In what ways is it different ? What is the nature of the rays on a sunflower ? REFERENCE READINGS Bergen and Caldwell. Practical Botany, chap, vii. Flowers; chap, viii, Pollination and Fertihzation. OsTERHOUT, W. J. V. Experiments with Plants, chap, vi, The Work of Flowers. Gave, Selina. The World's Great Farm (extract in C. H. Ward's '' Ex- ploring Nature," pp. 74-75). Lubbock, John. Flowers, Fruits, and Leaves (extract in C. H. Ward's ''Exploring Nature," pp. 79-87). Weed, Clarence. Ten New England Blossoms. Any manual or field book for identifying the common plants by their flowers. CHAPTER V LIVING MATTER Questions. 1. Does life come from one particular part of the body, like the heart or the blood, or is it in all parts ? 2. Why can some parts of an organism be destroyed without killing the body, whereas it does kill the body to destroy other parts ? 3. What is the smallest portion of a plant or animal that can remain alive ? 4. What are the smallest plants or animals ? 5. Are there any living things too small to be seen ? 43. Protoplasm. A man has none of the organs that a tree has ; a tree has none of the organs that a man has. Indeed, animals differ so much from plants that it is difficult at first to see how they can be so much alike in those three qualities (growth, movement, and irritability) which distinguish living things from non-living things. The solution to this difficulty is found in the fact that the bodies of all organisms are made up of a peculiar substance (or rather a mixture of substances) which seems to have all the qualities of living bodies. This is the stuff in living things that can grow ; this is the stuff that moves ; this is the stuff that is irritable. The microscope shows this living stuff to be a slimy, or jelly- like, substance something like the white, of egg in appearance. Under a more powerful microscope it sometimes appears to have many minute bubbles in it or to consist of an extremely fine network. This stuff is called protoplasm (/>ro^o5, first; plasma, forming material), and in all essential respects it seems to be alike in all plants as well as in all animals. It is the proto- plasm of a plant or of a kitten that grows. It is protoplasm in the body of the Venus 's-fly trap or of a snake that moves when the organism springs upon its victim. It is the protoplasm of the geranium or of the worm that is sensitive to light. S6 LIVING MATTER 57 ■ \*- . •: •:•■ I*- ■ ••,■ Fig. 27. Protoplasm moves The arrows indicate the streaming of the protoplasm within the cells was suggested by the microscope to the cells 44. The body and protoplasm. Most of the plants and animals that we know do not look a bit slimy. The proto- plasm does not appear on the surface of most organisms. Even when you cut your linger or pluck a flower you do not expose protoplasm so that you can see it. Indeed, protoplasm very rarely occurs in masses large enough to be seen by the unaided eye. Yet in the course of its growth it builds up the enormous bulk of the elephant or of the massive "big trees" of California. 45. Cells. From the latter part of the seventeenth century, when the mi- croscope was first able to show such small structures, we have known that the body of every plant and every ani- mal is made up of a number of tiny compartments called cells. This name resemblance of a mass seen under the , or chambers, of a honeycomb. During Fig. 28. Diagram of a cell The mass of the cell content consists of the protoplasmic network, with the coarser- grained nucleus. Within the protoplasm are more solid bodies, and droplets of more liquid substances the past hundred years it has been found that the living con- tents of a cell is protoplasm. When we look at an organism 58 BIOLOGY AND HUMAN LIFE ■Mhs 3)- LIVING CONDITIONS; THE SEED 69 60. Food in seeds. The concentrated food found in seeds of common plants is of interest to us in three ways : First of all, we may infer that this food is actually used by the young plant until it is able to provide for itself. That this is a sound infer- ence may be tested by separating from several seedlings the "food reserve." Next we can observe that the cotyledons in such plants as the beans and peas do actually shrivel away as the plant becomes larger. The con- tents of the corn grain also dis- appear as the seedling develops. Finally, by means of chemical experiments we can see that the changes taking place in the food masses of the seedlings are of the kind that we should expect to find if the food were actually being transported to the growing portions (see section 105). 61. Seedlings. Examine a few seeds that have been planted two or three days, and you will see that the hypocotyl has emerged and is assuming the appearance of a root. At the other end of the embryo you may see the unfolding epicotyl. If we examine different stages of peas, squash, oats, corn, beans, and so on, we shall be able to see a great variety of methods by which the young plant crawls out of its covering and establishes itself in the soil (Fig. 35). Large seeds, containing a large amount of reserve food, are apparently at an advantage, since they may develop more root and more shoot before they are overtaken by the necessity of providing themselves with food. We should therefore expect that plants with large seeds would be, on the whole, more Fig. 34. Seeds with endosperms /, asparagus; 2, poppy: 3, pine; 4, maize, or Indian corn. In some kinds of seeds the cotyledons are very thin. In such cases we usu- ally find that there is a great deal of food material surrounding the embryo, whereas in seeds with fleshy cotyledons there is food packed within the cotyledon. The food packed around the seed is called endosperm, which means "within the seed." (All shown in longitudinal section) 70 BIOLOGY AND HUMAN LIFE successful in establishing themselves in a new territory than plants with small seeds. We shall find, however, that the best spreaders in the plant world are those with rather small seeds. Fig. 35. Young plants emerging from seeds On the left, squash; on the right, bean. In the squash a little outgrowth on the hypocotyl keeps the seed coat in place while the cotyledons are carried aloft. C, C, cotyledons; E, epicotyl; H, hypocotyl; gg, ground line The speedy and secure establishment of the individual plant is of great advantage, but it is even more important that seeds be well scattered, and in this respect the small-seed plants with very numerous seeds have a decided advantage. LIVING CONDITIONS; THE SEED 1. Nothing exists by itself Living things are dependent Upon non-living materials and conditions Upon one another 2. Seeds as showing dependence Dependence upon water Dependence upon temperature How demonstrated Maximum ; minimum ; optimum Amount of water needed Relation to air LIVING COXDITIOXS; THE SEED 71 3. Seed structure Covers — ]\Iicropyle ; (hilum) (Endosperm) Embryo Hypocotyl Cotyledon Epicotyl Root ; stem One ; two ; many Stem ; leaves 4. Seedlings Structure Methods of emerging Food supply from ground QUESTIONS 1. What objects move or act without relation to any other objects ? 2. How can we tell whether soil is essential to the sprouting of seeds ? 3. How can we find the conditions necessary to make seeds sprout ? 4. How do sprouting seeds show that ''enough is better than more"? 5. How does a grain (for example, the corn) differ from such a seed as the bean or squash seed ? In what ways are they alike ? 6. What structures in the seed are homologous to other structures that you have studied ? 7. What part of a bean plant is homologous to the shell of a peanut ? 8. What adaptations can you find in the structure and properties of the seeds that you have studied ? 9. How could you show that the micropyle is not essential to the life of the ripe seed ? 10. What practical use can be made of rehable knowledge regarding the conditions favorable to the sprouting of seeds ? 11. What practical use can be made of the fact that certain plants accumulate considerable quantities of food material in the cotyledons or endosperm of their seeds ? 12. Which conditions favorable to the sprouting of seeds are also fa- vorable to the life of human beings ? Which ones are not favorable ? REFERENCE READINGS Bergen and Caldwell. Practical Botany, pp. 136-144. OsTERHOUT, W. J. V. Experiments with Plants, chap, i, The Awakening of the Seed; chap, ii, Getting Established. Fanners' Bulletin 1175. Better Seed Corn. United States Department of Agriculture. Yearbook for 191 5. Reprint 679, How Seed-Testing helps the Farmer. CHAPTER VII THE SORTING OF PLANTS AND ANIMALS Questions. 1. What is the use of classifying plants and animals ? 2. Why is it not sufficient to classify plants by size — herbs, shrubs, and trees ? 3. Why is it necessary to have so many main divisions ? 4. Why do we use Latin names for plants and animals ? 5. Why are not single names sufficient ? 6. What is the easiest way of finding out the name of a new plant or animal ? 7. Who makes up the scientific names of plants and animals ? 8. Is it necessary for everybody to know the scientific names ? 9. Is it necessary for anybody to know the scientific names ? 62. Scientific classification. Many people derive satisfaction from collecting and sorting various classes of objects. Classi- fication is of value because it helps in the work of reference. Just as classification of books in the library makes it possible to find a particular book, or a particular kind of book, with the least effort, so classifying plants and animals furnishes a con- venient scheme for placing each specimen where it belongs. If we sorted our books according to size, or according to color of binding, we should often bring two books on radio together; but we should be just as likely to bring together a book on radio and one on cooking, and we should be sure to separate books that really belong to- gether. Every scheme for sorting plants and animals must provide a way of bringing together plants or animals that are truly related, and it must at the same time keep separated plants and animals that are not re- lated, even though they have superficial resemblances. The structure of organisms furnishes the basis for modern classifications, but the term structure has a wide significance. According to outward appearance we might place certain small snakes with certain large worms, but a study of the internal structure at once separates them very widely. Again, the ap- 72 THE SORTING OF PLANTS AND ANIMALS 73 pearance of certain caterpillars is much like that of certain worms ; indeed, many people call caterpillars worms ; but a study of the structure at various stages in the course of the organism's life — that is, its development— at once separates the two groups. We find that the caterpillar is the young stage of some insect (see page 30), whereas the worm never gets to be anything but an older worm. iModern classification of organ- isms accordingly considers all that can be known about living things, and not merely their appearance or their uses. In recent times the study of classification has acquired new value be- cause of the light it throws on problems of new species, and because of its aid in the study of heredity and plant and animal breeding (see Chap- ters XLV, XLVI). 63. The basis of classification. We have divided all organisms roughly into plants and animals, without trying to define either of these terms. We really ought to know more about them before we attempt any definition. Within each of these two principal divisions it is possible to say in a general way that a given species is "higher" or "lower" than another. Yet it is impossible to place all the known plants (or all the known animals) in a series from the'lowest to the highest. This would be about as sensible, or as absurd, as trying to arrange all the people in a series from the worst to the best. We find that there are several main branches (among plants as well as among animals), some of which v^^e should place higher and some lower. But we find in each branch so many degrees of complexity that there is considerable overlapping when it comes to arranging all the organisms. The diagram on page 74 (Fig. 36) will give a general idea of the relationships of the main branches of plants, and the one on page 75 (Fig. 37) will suggest the same for the animals. "ftto" In placing here the general scheme of plant classification and that of animal classification it is not intended that you should learn or memo- rize them by study. There are many terms in the descriptions of the various divisions and subdivisions which can have no meaning for the Fig. 36. Genealogical tree of plant life This diagram is intended to suggest the common origin of all plant forms, with the constant progressive departure from ancestral types, now in one direction and now in another, like the branching of a tree. Lower and higher mean nearer to or farther from the original types. The closer together two forms are on a given branch, the more closely related they are considered (cf. Fig. 37) Fig. d/' Genealogical tree of animal life This diagram is intended to suggest the common origin of all animal forms, with the constant progressive departure from ancestral types, now in one direction and now in another, like the branching of a tree. Of course only the main branches are shown. There are probably over a million species of animals living today (cf. Fig. 36) 76 BIOLOGY AND HUMAN LIFE beginning student; but from the examples given in each section you should be able to get a rough notion of where any specimen belongs. The best way to use these tables is to refer to them whenever a new plant or animal comes to your notice, in order to get an idea of the general position of the new species in the whole scheme. By us- ing the diagrams and the tables in this way you will soon become familiar with the main branches and the more important classes. As you become acquainted with more plants and animals you will probably want to use a more complete classification. Fig. 38. Euglena / This one-celled alga is capable of moving about by means of the swimming lash, like many animals; it has chlorophy], like many plants. Near the base of the lash is a reddish speck which is sensitive to light. Al- though it is often called an eyespot, it is no more like an eye than a grain of powder is like a cannon B Fig. 39. Mold fungi A : In the black molds, reproductive cells (spores) are formed by the repeated di- vision of the protoplasm in an enlarging cell at the end of a thread. When mature, the inclosing wall breaks and the spores are scattered. B : In the blue molds, spores are formed by the successive separation of terminal portions of the branched threads. This is a type of fungus used in ripening Camembert cheese THE SORTING OF PLANTS AND ANIMALS 77 64. The main groups of plants. The chief groups of plants are indicated in the following outline : BRANCH I — THALLOPHYTES. Plants showing no differentiation into true stem and leaf. •J' mi- UI4 Fig. 40. Reproduction in moss a, a leafy moss plant (Hypnum moUuscum)\ b, section cut lengthwise through tip of one of the branches, showing position of archegonia, or egg-bearing organs; c, single archegonium, more highly magnified, showing single large egg cell; d, enlarged view of antheridiiim, or sperm-bearing organ, of Polytrichiim jormosum, discharging sperm cells; e, greatly magnified view of sperm cells; /, tip of leafy plant from the archegonium of which a spore plant has grown, showing stalk and spore capsule A. ScHizoPHYTES ('' Splitting plants ")• Each cell splits into two; no other reproduction. 1. Cyanophyceae. Splitting plants with chlorophyl — the blue- green algas. (Examples. Oscillatoria, Rivularia, Nostoc.) 2. Schizomycetes. Splitting plants without chlorophyl. This group includes all the bacteria. 78 BIOLOGY AND HUMAN LIFE The distinction between having chlorophyl and not having chlorophyl separates all the thallophytes into two main groups, the algae and the fungi. B. Alce. The chlorophyl-bearing thallophytes. Fig. 41. Alternation of generations in the Hfe history of the fern G, the gametophyte, or gamete-bearing plant; /, the female gamete organ; in, the male gamete organ; e, the fertilized egg. S, the sporophyte, or spore-bearing plant; s, the spores discharged by the spore-bearing organ. The spore develops into a gametophyte; the gametes (egg) always give rise to a sporophyte. The alternate generations reproduce in different ways — one by means of gametes, or sexually, the other by means of spores, or asexually 1. The green algae. Usually yellowish green. {Examples. Pleu- rococcus, desmids, Spirogyra, Vaucheria, stonewort, sea lettuce.) 2. The brown algae. Mostly marine. {Examples. Bladder wrack, Laminaria, Sargassum, diatoms, sea palm.) THE SORTING OF PLANTS AND ANIMALS 79 3. The red algae. Mostly marine ; reddish to purple. {Examples. Nemalion, Polysiphonia, Batrachospermum.) C. Fungi. Thallophytes without chlorophyl. 1. Phycomycetes. Algalike fungi. {Examples. Water molds (often parasitic on fishes), phytophthora (the cause of the potato rot), grape mildew and other parasitic forms, black mold.) 2. Ascomycetes. Fungi bearing spores in sacs. {Examples. Yeast, cup fungi, the edible morel, the mildews, black knot.) 3. Basidiomycetes. Fungi bearing spores on outside of structure called basidium. {Examples. Rusts, smuts, mushrooms, pore fungi, shelf fungus, puffballs.) D. Lichens. These curious structures are compound growths of fungi and algae. The hyphae in these partnerships generally belong to ascomycetes ; the algal partner is a green alga related to pleurococcus or one of the blue-green algae. {Examples. Reindeer moss, Iceland moss, Spanish moss. The common names introduce the word moss, although these plants are in no way related to the mosses.) BRANCH II— BRYOPHYTES. Mosses and their allies. Archegonia but no vascular system. A. Liverworts. B. Mosses. BRANCH III— PTERIDOPHYTES. Ferns and their allies. Archegonia and vascular system; no seeds. {Examples. Club mosses, quill- worts, scouring rushes (or horsetails), adder's-tongue, maiden-hair.) BRANCH IV— SPERM ATOPHYTES. Seed-bearing plants. A. Gymnosperms. Naked-seed plants. {Examples. Sago palm, ginkgo, yews, larches, pines, cypress, sequoia.) B. Angiosperms. Inclosed-seed plants. 1. Monocotyledons. {Examples. Cat-tail, water plantain, grasses, grains and sedges, palms, Indian turnip, rushes, spiderwort, lilies, bananas, orchids.) 2. Dicotyledons. a. Archichlamydeae. Flowers having no corolla or one of dis- tinct petals. {Examples. Catkin-bearing trees (willows, walnuts, oaks, beeches), smartweed, pink family, buttercup family, water lilies, rose family, bean family, parsley family.) b. Sympetalae. Flowers having corollas in which the petals are united. {Examples. Heath family, primrose family, gentian Fig. 42. Vorticella This one-celled ani- mal lives in water, attached by its stalk to a rock or twig. When disturbed it contracts the stalk and "bell "suddenly Fig. 43. Diagram of sponge structure A sponge is a colony of cells arranged about hollow spaces, a, which are connected with the surrounding water by means of hollow channels, b, carrying currents inward, and by means of other channels, c, carrying currents outward through larger tubes, or "sewers," d. The currents are produced by the constant vibration of cilia projecting into the spaces, and they bring to the cells fresh supplies of food and oxygen, and carry away waste Fig. 44. The jellyfish Aiirelia The mature medusa, a, reproduces sexually, the gametes being thrown into the water, where fertilization takes place. The egg develops into an individual having the gen- eral form of a hydra, b, and attaches itself to a rock. The animal elongates and breaks up into a number of individuals by means of constrictions, so that it comes to resemble a pile of bowls. Each individual, when separated, turns over and swims away, changing into a medusa, a THE SORTING OF PLANTS AND ANIMALS 8i family, mint family, morning-glory family, plantain family, madders, honeysuckles, composites — daisy, aster, sunflower, goldenrod, etc.) 65. The main groups of animals. The chief groups of animals are indicated in the following outline : BRANCH I — PROTOZOA. The simplest animals ; body of one cell. {Ex- amples. Ameba, Paramecium, Vorticella, Plasmodium of malaria.) .j>i^>.^ V::V^m::^ NJ'S 11 Fig. 45. Eyespots in starfish The eyespot at the end of each ray is con- nected with the nervous system of the ani- mal and is more sensitive to light than the rest of the body surface Fig. 46. Sea urchin Animals of this branch deposit large quantities of lime in their skin, and produce knobs and spines that form a protective armor BR.\NCH II— PORIFERA (''pore-bearing" animals). This includes all the sponges. BRANCH III — CCELENTERATA. Radially symmetrical animals hav- ing a single cavity in the body : all aquatic, mostly marine. Class i — Hydrozoa. {Examples. Fresh-water hydra, certain small jellyfish.) Class 2 — Actixozoa. (Examples. Most anemones, most corals.) Class 3 — Scyphozoa. {Examples. Most of larger jellyfish.) BRANCH R' — FLATWORMS (Platyhelminthes). {Examples. Tape- worm, liver fluke, planarians.) BRANCH V— ROUNDWORMS (Nemathelminthes). {Examples. Hook- worm, trichina, thorn-headed worm.) Many of these animals are dangerous parasites on man or on domestic animals. 82 BIOLOGY AND HUMAN LIFE Fig. 47. The pill bug When suddenly disturbed, this animal curls up, thus reducing its exposed surface and concealing its most delicate and sensitive parts BRANCH VI— WHEELWORMS (Trochelminthes). The Rotifera, or wheel animalcules. Mostly microscopic. BRANCH VII— ECHINODERMATA (''spiny-skinned" animals). Ra- dially symmetrical, all marine. Class i — Asteroidea. Starfish. Class 2 — Ophiuroidea. Brittle stars. Class 3 — Echinoidea. Sea urchins. Class 4 — Holothuroidea. Sea cucumbers. Class 5 — Crinoidea. Sea lilies. BRANCH VIII— ANNELIDA (''ringed" animals). Wormlike animals with segmented bodies. The two most important classes are repre- sented by earthworms, sandworms, etc. and by the leeches. BRANCH IX— ARTHROPODA (" jointed-legged"). The body seg- mented ; exoskeleton. Class i — Myriapoda ("thousand-legged"). {Examples. Myria- pods, centipede.) Class 2 — Crustacea ("crusty" shells). Head and thorax fused; water-breathers ; antennae. {Examples. Lobster, crayfish, crab, shrimp, barnacle, sow bug.) Class 3 — Arachnida (spider family). Four pairs of legs; air- breathers ; no antennae. {Examples. Scorpions, spiders, daddy longlegs, tarantula, mites, ticks.) Class 4 — Insecta. Segmented bodies; distinct head, thorax, and abdomen ; antennae, compound eyes ; three pairs of legs ; one or two pairs of wings (a few forms wingless) ; air- breathers. The chief orders of this important class are as follows : I. Aptera ("without wings"). The most primitive insects now living. {Examples. Silverfish and springtail.) THE SORTING OF PLANTS AND ANIMALS 83 Fig. 48. The walking stick This animal has startled many a person by walking away from a hand stretched out to grasp a leaf or twig. The insect is related to the locust and katydid, but it has no wings. Its body and legs are very long in proportion to thickness, and the enlargements at the joints and the irregularity of outline increase the re- semblance to bare twigs. Moreover, the color of the animal changes with the seasons, from a bright green in the spring to a deep brown in the fall, thus matching its natural surround- ings in a most remarkable way Fig. 49, Praying mantis This animal lies in wait for its prey with the front legs raised in a manner suggesting the attitude of prayer. It catches small insects with its strong front legs. Large species living in the tropics have been known to kill small birds 2. Orthoptera ("straight-winged"). Wings lying parallel with body or folding lengthwise ; incomplete metamorphosis ; biting mouth. (Examples. Locusts, crickets, walking sticks, katydids, cockroaches, mantis.) 3. Neuroptera ("netted-veined wings"). A large group broken up into several orders by entomologists ; complete metamor- 84 BIOLOGY AND HUMAN LIFE Fig. 50. The dragon fly Libelhila 0^ egg; b , young wingless larva; b , larva molting; c, nymph, or pre-adult stage; d, adult phosis ; biting mouth. (Examples. Mayflies, dragon flies, termites.) 4. Hemiptera (''half-wings"). Basal part of wings often thick- ened and without distinct veining ; incomplete metamor- phosis ; sucking mouths. All true bugs. (Examples. Squash-bug, water-bug, plant lice, scales, Hce, cicada.) 5. Coleoptera (''sheath-wings"). The front wing a hard protec- tive cover ; complete metamorphosis ; mostly with biting mouth. (Examples. Beetles, weevils, fireflies, ladybird, June-bug.) 6. Lepidoptera ("scale-wings"). Rigid membranous wings cov- ered with minute scales ; complete metamorphosis ; suck- ing proboscis. (Examples. All moths and butterflies.) 7. Diptera ("two- wings"). Hind wings reduced to tiny knobs, or balancers ; complete metamorphosis ; sucking or piercing mouth. (Examples. Mosquitoes, gnats, midges, house flies, stable flies, botflies, warbles, fruit flies.) 8. Siphonaptera ("tube-wingless"). Sucking mouth, wings re- duced ; complete metamorphosis ; parasitic on birds and mammals. (Examples. Fleas of all kinds.) 9. Hymenoptera ("membrane wings"). Complete metamorpho- sis ; biting or sucking mouth. (Examples. Wasps, hornets, bees, ichneumons, ants.) BRANCH X— MOLLUSC A ("soft" animals). Unsegmented animals, most of them bearing shells. Class i — Gastropods ("belly-footed"). Having shells of a single piece. (Examples. Snails, slugs, periwinkle, whelk.) Fig. 51. Squash-bug (Atiasa tristis) a, eggs on leaf of plant; b, larva; c, pre-adult stage; d, adult a b Early filage FitJIij grown Fig. 52. The "June-bug" beetle {Melalontha) a, eggs; b, larva, or grub; c, pupa, resting stage; d, adult Fig. 53. The underwing moth (Catocala) When they are at rest, the moths of this genus resemble the bark of trees, so that they are no doubt often over- looked by their enemies Egg on iralyzed 'caterpillar a Mother hvrying caterpillar Fig. 54. A wasp (Sphex gryphus) a, caterpillar in which the mother wasp has laid an egg; b. mother wasp burying the stung caterpillar in the ground. The larva feeds upon the caterpillar and changes into c, pupa, or resting stage, and d, adult 86 BIOLOGY AND HUMAN LIFE Fig. 55. The snail, a belly-footed mollusk Fig. 56. The scallop Class 2 — Pelecypoda ("hatchet-footed"). Bivalve (having shells of two valves). {Examples. Oysters, clams, piddock, scallop, mussel, shipworm.) Class 3 — Cephalopoda ("head-footed"). The foot partly sur- rounds the head and has a number of arms, or tentacles. {Examples. Octopus, cuttlefish, squid, nautilus.) BRANCH XI — CORDATA. Animals having a notochord, or internal axial basis for a skeleton. It is from this structure that the vertebral column develops. There are a number of small animals which never develop a true backbone, but which nevertheless have a structure that suggests the beginning of such a column. These are Fig. 57. The octopus, a cephalopod These animals have eyes that resemble in many ways those of backboned animals THE SORTING OF PLANTS AND ANIMALS 87 included among the cordata, although they are not strictly verte- brate. {Examples. Acorn worm, lancelet, sea squirt.) The five important classes of vertebrates are as follows : Class i — Pisces (fishes). The stone hag and the lamprey are some- times called fishes, though they are distinct in having a round mouth (no jaws) and no fins or scales. They never develop bones, the skeleton remaining cartilaginous. There are four orders of true fishes : 1. Cartilaginous fishes. Gill slits not covered; ''skin teeth." {Ex- amples. Skates, torpedoes, sharks.) 2. Armored fishes {Ganoidei). Large, bony scales in the skin, es- pecially about the head. In former times this order was very numerous. {Examples. Sturgeon and gar pike.) 3. Bony fishes {Teleostei). {Examples. Salmon, herring, perch, cod, flounder, etc.) 4. Mud fishes {Dipnoi). Fishes with lunglike structures. Only three living representatives, all in the southern hemisphere. Class 2 — Batrachians (amphibia). Breathe by means of gills in early stages, famihar to us as tadpoles, and later develop lungs. Bony skeleton with two pairs of appendages ; no exoskeleton. {Examples. Frog, toad, newt, salamander, mud puppy, hellbender.) Class 3 — Reptilia. Wholly air-breathers; plates or scales in the skin. Four orders are usually recognized : 1. Chelonia. {Examples. Turtles and tortoises.) 2. Serpents. {Examples. Snakes, adders, cobras.) 3. Lacertiha. {Examples. Lizards, chameleons, horned toad, Gila monster.) 4. Crocodilia. {Examples. AlHgators, crocodiles.) Class 4 — Aves (birds). Warm-blooded; exoskeleton of feathers; front limbs wings ; tendency for the bones to fuse ; air spaces in bones ; no diaphragm ; eggs with limy shells. Living species of birds may be divided conveniently into the running birds (ostriches, the cassowary, and the emu) and the flying birds. The latter include two groups of orders — the water birds and the land birds. Some of the important orders are as follows : 1. Anseres. {Examples. Swans, ducks, geese.) 2. Longipennes. (Examples. Gulls, petrels, terns.) 3. Pygopodes. {Examples. Loons, grebes, auks.) 4. Heron order. {Examples. Storks, ibis, bittern.) c / Fig. 58. Fish, Chinook salmon {Oncorhynchus tschawytscha) a, egg; b, fish ready to break out of egg; c, more advanced stage; d, later stage, still showing yolk-sac; e, j, more advanced stages; g, adult stage Fig. 59. Batrachian, newt (Amblystoma punctatuni) a, egg; b, first free-swimming stage, tadpole; c, more advanced stage, tadpole just before the appearance of hind legs; d, later stage; e, adult form iv ^ U'^'"' ■ Fig. 60. Wallaby and young The babies are not only protected and kept warm in the marsup'mm, or pouch, but are also nourished by a milky secretion produced by glands in the lining of the pouch THE SORTING OF PLANTS AND ANIMALS 89 5. Plover order. {Examples. Snipe, curlew, rail, sandpiper.) 6. Gallinae. {Examples. Hen. turkey, guinea fowl, peacock, pheas- ant, partridge, ptarmigan.) 7. Columbae. {Examples. Pigeons, doves.) 8. Passeres. Perching birds ; includes about one half of our na- tive birds. {Examples. Sparrows and finches, swallows, robins, thrushes, crows, etc.) 9. Raptores. Predatory birds. {Examples. Eagle, hawk, owl.) 10. Pici. {Examples. Woodpeckers, sapsuckers.) 11. Cuckoo famfly (including kingfishers). 12. Whippoorwill order (including humming birds). Class 5 — Mammalia (mammals). Warm-blooded; hairy exoskele- ton ; diaphragm ; suckle young. 1. Monotremata. Egg-laying mammals. {Examples. Duckbill, spiny anteater.) (With the exception of these two. all mammals develop the young within the body of the mother.) 2. Marsupials. Carry their immature young in a special abdom- inal pouch. (Examples. Kangaroos, wombats, opossums.) The rest of the mammals are divided into the following orders : 3. Edentata (''toothless" mammals). {Examples. Sloths, arma- dillos, hairy anteaters.) 4. Cetaceans. (Examples. Whales, dolphins, porpoises.) 5. Sirenia. {Exa?nples. Sea cow, manatee, dugong.) 6. Ungulata ("hoofed" animals). a. Odd-toe. (Examples. Horses, zebras, rhinoceros.) b. Even-toe. (Examples. Ox, sheep, antelope, camel, giraffe, deer, pig, hippopotamus.) c. Proboscidea (elephants). 7. Rodentia (''gnawers"). The largest order. {Examples. Rab bits and hares, squirrels, chipmunks, porcupine, gopher^ muskrat, rats, mice.) 8. Insectivora (''insect-eaters"). {Examples. Moles, shrews, hedgehog.) 9. Chiroptera ("hand- wings"). {Examples. Bats, vampire.) 10. Carnivora ("flesh-eaters"). (Examples. Cat family, dog fam- ily, bears, weasel, seal, walrus, otter, mink, skunk, badger, raccoon, etc.) 11. Primates (''the first," or leading, order of animals, including man). This important order consists of the following families : 90 BIOLOGY AND HUMAN LIFE a. Lemuroidea. Small, squirrel-like animals living in trees and bushes. The lemurs are found in Madagascar, the mar- mosets in South America. b. Cebidae. The New World monkeys. Nearly all have long, grasping tails and flat noses. Smaller than the Old World monkeys. {Examples. Howling monkey, spider monkey, capuchin.) c. Cercopithecidae. The Old World monkeys. Tail not grasp- ing, or short ; nostrils pointing downward. Distinct, oppos- able thumb. {Examples. Baboons, mandrill, macacus.) d. Simiidae. The anthropoid (manlike) apes. No distinct tail ; arms longer than legs. {Examples. Gibbons, orang-utans, chimpanzees, and gorillas.) e. Hominidae. The human race. QUESTIONS 1. Why are there two names for each kind of plant and animal? 2. In what sense is the cat related to the tiger or lion ? 3. What is meant by saying that one species is related to another ? 4. W^hat do we need to know about a plant or an animal before we can tell in what group to place it ? 5. In what ways are the different plants in one branch alike ? 6. In what ways are the different animals in one branch alike ? 7. How can you tell to what class a particular animal belongs, even if you do not know what particular kind it is ? 8. How is it that a plant or an animal belonging in one group can be mistaken for one in another group ? 9. WTiy do people keep on changing the classifications of organisms ? REFERENCE READINGS BiGELOW. M. A. Applied Biology, chap, vii, Classification of Animals and Plants. Moon, T. J. Biology for Beginners, chap, xxi. Arthropods. CocKERELL. T. D. A. Zoology, chap, xxii, Principles of Classification. Calkins, G. Biology, pp. 162-172. Any convenient manuals for the identification and classification of com- mon plants, including trees, ferns, mosses, and fungi, and of common birds, insects, fishes, batrachians, mammals, etc. CHAPTER VIII MOTHER EARTH Questions. 1. What do we mean when we say that *'man is made of earth " ? 2. In what sense is this statement not true ? 3. What chemical elements are present in the human body but not in plants ? 4. What chemical elements are present in the human body but not in the earth ? 5. Are any elements present in the earth but not in the bodies of living things ? 6. How cail people find out what substances are present in a plant or animal? 66. Man is made of earth. What does this statement mean ? Our flesh and blood and our delicate nerves are very different from the coarse materials of the earth, although the bones are more easily likened to stones. Some people seem to picture to themselves a clay image that is somehow suddenly inspired with life, like the miracle of Galatea. Yet the statement is perfectly true, and the process is as wonderful as any miracle, although we understand many parts of it pretty well. " Man is made of earth" because every particle in his body, like every particle in the body of every other living thing, comes directly or indirectly out of the soil out of the water, out of the air— the material world in which we find ourselves. The food out of which we build up our bodies comes directly from the bodies of other ani- mals or from the bodies of plants. These other animals nearly all derive their food from plants. The plants in turn build up their bodies directly from three sources— water, air, and soil. 67. The soil and the young plant. We saw that seeds can sprout without depending upon the soil. Yet we know that the soil is essential to the growth of plants, after the reserve in the endosperm or cotyledons is all used up. We can plan experiments in which the various materials that make up soil (such as sand, clay, and the various salts) are used 91 92 BIOLOGY AND HUMAN LIFE separately and in combination. From such experiments we learn that it is not the sandiness of the soil, or the color, or merely the water in it that makes the growth of plants possible ; it is something in the soil that can dissolve in water. 68. The salts of the soil. These soluble substances in the soil are the salts, of which there are many different kinds. Are all or any of these salts related to plant growth? In carefully planned and carefully conducted experiments plants were grown in solutions of soil minerals from which now one element and now another was omitted. The omission of some elements seems to result in no perceptible difference, but the omission of others will absolutely prevent the further growth of the plants. From the results of such experiments the following table has been constructed: Element Occurrence in Plants Special Function Aluminum In lower parts No function Calcium In leaves and stem Related to the formation of plant cells ; " makes plants hardy " Chlorin In lower parts No function, so far as known, although present universally Iron In leaves and stem Related to the formation of chlorophyl (see page 108) Magnesium In seeds and leaves Related to the formation of seeds Manganese In lower parts No function Phosphorus In seeds Related to the activities of leaves ; takes part in the formation of proteins (see page 109) Potassium In actively growing Related to the formation of starch and parts sugar, and to the growing process Silicon In stems and leaves No special function Sodium In stems and roots No function, although present almost universally Sulfur In all growing parts Necessary to the formation of proteins This table shows whether or not a given elemicnt is found to be necessary for plant life. It also shows in what particular way each element is related to the life of the plant. MOTHER EARTH 93 69. The composition of organisms. Another way of finding out what there is in the soil that the plant depends upon is to make an analysis of the plant to see of what it is composed. Analysis shows that certain elements are present in the plant body; some of these elements are also present in the soil. It is therefore reasonable to suppose that the plant derives these elements from the soil. It does not follow, however, that every- thing taken by the plant from the soil is of use to the plant. The most common elements found in plants are the following : Carbon Sulfur Potassium Oxygen Phosphorus Sodium Hydrogen Calcium Iron Nitrogen Magnesium Chlorin Compare these with the composition of the human body (Fig. 3) to see how much we are like the plants. Chemical studies show that all animals have a composition differing very little from that of the human body. The materials taken from the soil by the growing plant are sometimes called plant food. Strictly speaking, these are not food, as we shall see later (see Chapter X) ; they are merely some of the materials out of which plants manufacture their food. 70. Exhaustion of soil. After many crops of plants are re- moved the soil lacks some of the mineral salts required for plant growth. There is no danger of exhausting the iron in a soil, for this element is used in such small quantities that plants will have stopped growing for lack of some of the other elements (for example, phosphorus or nitrogen) long before the iron supply is considerably reduced. In some soils the same may be true of calcium. But the other elements are used in such large quantities (in proportion to the quantities present in most soils) that they practically limit the use of soil for crop raising. To make up for the withdrawal of materials by crops it has for ages been customary to put on or into the soil various substances called fertilizers. These include limestone or gyp- sum, barnyard manure, guano, crushed bones, ground phosphate 94 BIOLOGY AND HUMAN LIFE rock, and many others. In this country the farmers spend over $300,000,000 annually for commercial fertilizers, besides what they use from their own dungheaps. The first use of fertilizers is to place in the soil the materials needed for plant growth. Certain fertilizers, however, are sometimes added not to supply material but to produce chemical changes in the soil, to make the latter more suitable for the growth of plants. For example, gypsum is commonly used to supply calcium ; but in some cases it is used to make it easier for the plant to get the phosphorus in the soil. 71. Biology of the soil. The soil contains many different kinds of very small plants and animals, most of which can be seen only with a microscope. Some of these microbes are useful, as in the case of the bacteria living in the tubercles, or little swellings on the roots, of clover and alfalfa etc. (see page 301). Others, however, are injurious. Some of the latter may be destroyed by the addition of sulfur to the soil, with the result that the size of the crop is increased. Strictly speaking, the sulfur is not a fertilizer, although it helps to increase the yield. Growing plants, like other living things, throw off waste mat- ters. Some of these wastes thrown into the soil are poisonous. Certain materials added to soil containing such poisons are helpful, not because they add anything usable but because they counteract the poisonous substances. In a similar way certain materials may help by counteracting the poisons or acids pro- duced by the usual inhabitants of the soil that we do not often see. 72. Intensive cultivation. By using fertilizers and other sub- stances we may be able to keep the soil under cultivation indefinitely ; yet as soon as all the suitable farm land is settled and cultivated there must be a crowding, or pressure, of popula- tion. Modern science teaches us how to get more food out of every acre of land through intensive farming. By forcing plants to grow more rapidly than they would ordinarily (by selecting early-maturing varieties, by covering against cold weather, by artificial watering, by more thorough tilling, and so on) the MOTHER EARTH 95 cultivator is enabled to produce from two to seven crops a year on a given piece of land. This makes possible the support of a larger population on the same territory. 73. More soil. In this country nearly half the land area (outside of mountain and rock, which cannot be cultivated) consists either of swamp or of desert. Soil that is too wet is just as useless for farming as soil that is too dry. Through the cooperation of farmers and engineers and workers of all kinds it has been possible to reclaim millions of acres of desert lands, and to make it all usable for raising valuable crops. By drain- ing the swamps and by bringing water to the arid regions, through miles of canals and ditches and pipes, soil containing vast quantities of food-making salts has been added to the national wealth. There is, of course, a limit to what man may be able to accomplish in the way of reclaiming land. In some of the Western dry regions the bringing of water may not be practicable if the distance is too great. At the present time more than half of the great staple food crops of the world are raised on artificially irrigated land (in China, India, Egypt, Canada, and other countries) ; the possibilities in this direction will probably not be exhausted for several generations. 74. Soil waste. The fertility of the Nile valley seems to be inexhaustible. This is not because the usable salts are more concentrated in this soil than they are in other soils. The rich- ness of this soil is due to the fact that the river is constantly bringing down into the valley more and more material from the rocks in the mountains where the river has its sources. In our own country every river that empties into the sea carries away tons of usable minerals, which thus go to waste. In con- nection with some of the irrigation projects in the Southwest much water is lost during the spring, and with the water a great quantity of valuable mineral salts. Plans are being devel- oped for saving this water in huge reservoirs, some of which are already completed. In this way it will be possible not only to irrigate larger areas but also to save from waste the soil mate- rials out of which our food supply can eventually be increased. 96 BIOLOGY AND HUMAN LIFE 75. The soil and population. The crowding of a population may mean not merely that people live too close together for com- fort or for health ; it may mean also a shortage of food supply due to insufficient soil for growing crops. As the population of a nation grows, the second kind of crowding is likely to become serious. There was a time when thoughtful people looked for- ward to such overcrowding with a feeling that it must result in great destruction of human life or in great suffering through general poverty. Indeed, in times past much of the poverty and famine, and even of warfare, was due to man's inability to get from the soil adequate supplies of food. At the present time, however, we are rapidly learning to increase the yield of our cultivated land out of proportion to the increase in population, chiefly through the application of biological knowledge. So far as the soil is concerned, we need not fear that the " Great Mother " will become uninhabitable for many centuries. The pressure of the population, even if it becomes several times as great as it has been in China or India, can be met by the ap- plication of science and cooperative effort to the resources now in sight. If there is to be starvation, it will not be because the earth and the sun and the green plants fail us. It will be be- cause of our own failure to make use of our knowledge in har- mony and cooperation with our fellows. MOTHER EARTH 1. Source of all living matter Earth; water; air 2. Elements taken from the soil by plants 3. Elements found in plants Elements found in the human body Carbon Magnesium Carbon Magnesium Oxygen Potassium Oxygen Potassium Hydrogen Sodium Hydrogen Sodium Nitrogen Iron Nitrogen Iron Sulfur Chlorin Sulfur Chlorin Phosphorus lodin Phosphorus lodin Calcium Calcium MOTHER EARTH 97 4. Exhaustion of the soil Elements that are not likely to be exhausted Elements that are constantly removed in considerable quantities by crop plants : nitrogen ; phosphorus ; potash ; calcium Effect on farming 5. Use of fertilizers Purposes . Kinds To replace needed materials Quantities and costs To destroy injurious organisms To alter the chemical state of the soil 6. Organisms in the soil Injurious to plants Helpful to plants 7. How soil is made to yield more By selecting more prohfic varieties By selecting early-maturing varieties By covering against cold weather By artificial watering By more thorough tilling By systematic fertilizing of soil 8. How more soil is made available By reclamation Swamp (drainage) ; desert (irrigation) Limits in reclamation 9. Waste of soil Rivers emptying into the sea (Relation to deforestation) Dissolved salt Mechanically carried silt 10. Relation of soil to population The soil The people Quantity How they use the soil Quality How they use their knowledge How they deal with each other 1, QUESTIONS What kinds of fertilizers are produced in your part of the country? 2. What kinds of fertilizers have to be imported into your region ? 3. Why do farmers have to spend a larger part of their income for fertilizers in some regions than they do in others ? 98 BIOLOGY AND HUMAN LIFE 4. If there are abandoned farms in your part of the country, find out for what reasons any were abandoned besides the exhaustion of the soil. 5. If any abandoned farms have been reclaimed, find out what methods were used. 6. Have fashions changed as to the kinds or varieties of plants raised in your part of the country ? In what ways are the newer plants more advantageous to the gardener or farmer ? 7. What portion of the area of your state is naturally tillable ? What percentage of the tillable land is being cultivated ? 8. How much reclaimed swamp or desert land is cultivated in your part of the country ? 9. Which of our regular commercial crops come largely from re- claimed lands ? 10. What are the principal sources of soil loss in your part of the country ? How can this waste be prevented ? IL How can a knowledge of plant chemistry help to reduce the cost of living ? 12. How can the cost of living be reduced by preventing the growth of weeds in cultivated areas ? 13. What is the advantage of increasing the human population of the country ? of the entire earth ? What is the disadvantage ? 14. How can the earth be made to yield more on each acre cultivated ? REFERENCE READINGS Bergen and Caldwell. Practical Botany, pp. 434-451. BuRKETT, C. W., and Others. Agriculture for Beginners, chap, i. The Soil. Waters, H. J. Essentials of the New Agriculture, chaps, xxiv-xxxi. United States Department of Agriculture (office of the Secretary). Cir- cular 38, Conservation of Soil (address by President Taft). United States Department of Agriculture. Yearbook for 191 7 : Reprint 728, Fertilizers from Industrial Wastes. Reprint 729, Sources of our Nitrogen Fertilizers. Reprint 730, Phosphate Rock, our Greatest Fertilizer Asset. Reprint 733, Conservation of Fertilizer Materials from Minor Sources. United States Department of Agriculture. Yearbook for 1920. Re- print 854, Uses of the Soil Survey. PART II. THE BIOLOGY OF HEALTH Without trying to define health at the start, we can take it for granted that it involves (i) keeping the body in condition; (2) making suitable use of the body; and (j) keeping our surroundings in condition WHAT EVERYBODY WANTS Human welfare depends upon the satisfactory use of our time in play and work. We find that very often peo- ple fail to attain satisfactory living because health is de- fective, and many people spend much of their thought and effort in chasing after health, as though that were the most important thing in the world. Very often, too, satis- factory living is impossible because people lack material things, or wealth. Accordingly, many men and women spend their thought and effort in the pursuit of wealth {which is represented to them by money), as though that were the most important thing in the world. In the end both the health-seekers and the wealth- seekers fail to find happiness, for that is a bird that cannot be caught or trapped. If everything goes right about the place, it flies in through the open window and makes itself at home ; and it stays just as long as everything does go right— and we ignore it. When we turn our attention to it, away it flies! Health is necessary; a certain amount of wealth is necessary ; but neither can be obtained by itself. Neither is possible without some measure of the other, and neither is possible except as we manage our bodies, our resources, and our relations to other people in the right way, that is, except as we work and play properly. But we cannot work or play properly if we suffer from ill health or from a lack of material things. It is neces- sary to organize our everyday activities so as to take care of the essentials without being obliged to give too much thought to our health. But to do that requires a great deal of skill and understanding. A part of the understand- ing at least we can get from biology. KEEPING THE BODY IN CONDITION CHAPTER IX THE MEANING OF FOOD Questions. 1. Why must we eat food ? 2. Must all living things have food ? 3. How do plants take in food ? 4. Have all animals mouths ? 5. Is the food of one organism suitable for other organisms ? 76. The material needs of protoplasm. We know that we must have food to keep us alive, but the connection between feeding and keeping alive is not always clear. Many people think that feeding is the same as eating; yet the plants and many animals have no mouths, and they also must feed. Since it is the protoplasm that is alive, we should think of food in re- lation to the peculiarities and activities of protoplasm. The fact of growth means the need for a material income suitable for protoplasm building. It is impossible for proto- plasm (or any other substance) to be made out of nothing. The fact of movement calls for materials that can yield energy. The nearly fluid state of active protoplasm, and the chemical changes that are constantly going on within it, call for a water income. We find also that various salts or mineral substances are a necessary part of protoplasmic constitution, although we do not know exactly how each one acts in this complex mixture. Some of the salts seem to start chemical processes among other materials that make up the protoplasm. Other salts (or ele- ments, perhaps) appear to modify certain chemical processes, just as the bromide used by the photographer slows up the development of his negative ; these are called regulators. In addition, nearly all protoplasm must have air, or rather oxygen, which the protoplasm gets from the air. lOI 102 BIOLOGY AND HUMAN LIFE 77. Nutrients. It is convenient to distinguish those incomes of an organism that serve as protoplasm-building material and those that serve as sources of energy, or fuel, as foods proper or, better, nutrients. These materials occur naturally only in the bodies of living things, and so are organic (see section 12). Protoplasm-builders all contain the element nitrogen ; they are called proteins. The proteins are represented in our com- mon food by albumen, or white of egg ; casein, or the curd formed when milk sours ; gluten, or the pasty substance in wheat flour or bread. Similar nitrogen-containing substances are found in the muscle (flesh) cells of many animals and are called myosin. Others, found in the seeds of plants belonging to the bean family (the Leguminosae) , are called legumin. The non-nitrogenous nutrients are of two main classes, fats and carbohydrates. We are familiar with such fats as butter, suet. lard, tallow, olive oil, peanut oil, and others. The car- bohydrates include all the sugars and starches. These substances serve as fuel, combining with oxygen and so yielding energy. Protoplasm may be said to consist fundamentally of proteins sus- pended in it'ater containing various salts in solution and various other or- ganic substances dissolved or floating in it. The proteins have in recent years been further broken up into simpler nitrogen-containing substances called amino acids, which combine in various ways to make up the proteins. Since protoplasm consists fundamentally of proteins, we shall expect to find protein in almost every part of every animal or plant. That does not mean that all animal or plant materials are suitable for food. In some miaterials the proportion of protein is very low; other materials contain additional substances which render them unsuitable as food, or at least as human food. All seeds contain some proteins ; some in rather large proportions (for example, beans, peas, lentils). In addition to this all seeds contain either fat (as the castor bean, peanut, cotton seed, flax seed) or some carbohydrate (as the bean, cereals, the date). 78. Vitamins. During the past dozen years or so experiments made upon mice, guinea pigs, pigeons, and human beings have shown that, in addition to the protoplasm-builders (proteins) and fuels (fats and carbohydrates), certain substances must be present in our food to insure growth. Very little is known of THE IMEANING OF FOOD 103 the chemistry of these regulators, but they have been grouped together under the name vitamins. Three groups of vitamins have been recognized. One, soluble in fats and oils, is called fat-soluble A. The other two, which dissolve in water but not in fat, are called water-soluble B and water-soluble C. It is likely that as these substances come to be better known they will receive more distinctive names based upon their composi- tion, their actions, or their sources. For the present, however, enough is known to guide us in the selection of food, especially for infants and children and for those whose growth is not proceeding satisfactorily. We know also that pellagra, beriberi, scurvy, and probably other diseases result from the use of food that lacks one or another of the vitamins. These have accord- ingly been called deficiency diseases. Unlike proteins and the fuel nutrients, vitamins do not seem to be universally present in all protoplasm. Still it may turn out that it is only a matter of quantity. Vitamin A (fat soluble) is most abundant in butter, or milk fat, in the yolks of eggs, in cod-liver oil, and in certain vegetables (see table on page 105). Water-soluble B is supplied by milk, tomatoes, lemons, spinach, carrots, cabbage, onions, parsnips, potatoes, the common grains, beans, and nuts. Yeast that has not been dried seems to con- tain a large proportion of this vitamin. The C group occurs most abundantly in cabbage, lettuce, tomatoes, lemons and oranges, and in smaller quantities in spinach, fresh peas, onions, and grapefruit. In comparing different foods with respect to vitamins two interesting facts stand out. ( i ) Excepting eggs and dairy prod- ucts, foods of animal origin have small or negligible quan- tities of the vitamins. Cod-liver oil, which is rich in vitamin A, is not commonly considered a food. (2) The cereals, which are fairly rich in vitamin B, contain these substances chiefly in the outer tissues, so that highly milled flour and polished rice are almost wholly without these essential materials. 79. Summary. From what has been said it should be clear that the material intake of the organism bears an important 104 BIOLOGY AND HUMAN LIFE relation to the protoplasm. We must therefore guard against thinking of food as related especially to the tissues or organs. There is no such thing as brain food or muscle food ; all food is protoplasm food or it is not food at all. We may summarize the material requirements of a living body in this way: 1. Water. The chemical changes that go on in living pro- toplasm can take place only in the presence of water. In the larger organisms water is also the chief medium for the transportation of materials within the body. 2 . Oxygen. Although this is not usually regarded as part of the food, it is an essential part of the income of every cell. It is the chemical union of oxygen with other substances (organic) that sets free the energy by which the protoplasm does all its work. 3. Protein. Building material for the construction of new , protoplasm or for the replacement of protoplasm that has been destroyed (oxidized) in the course of the activities of the protoplasm is supplied only by the amino acids of proteins. 4. Fuel foods. In addition to the proteins that are oxi- dized there is usually some other organic material that is oxidized. Two classes of compounds commonly furnish this fuel: namely, {a) carbohydrates and (b) fats. 5. Salts. Various mineral or inorganic compounds serve in the protoplasm as activators or regulators. 6. Vitamins. In some of the higher animals an essential part of the income consists of organic substances that influ- ence growth and nutrition. Three groups have been recog- nized, which are called for the present A (fat soluble), B (water soluble), and C (water soluble). THE MEANING OF FOOD A. Organic substances 1. Building material for protoplasm (for growth) Proteins (consisting of amino acids) 2. Energy or fuel material (for movement and other processes) Carbohydrates Fats Starches ; sugars THE :\IEAXIXG OF FOOD 105 RELATIVE AMOUNTS OF \ ITAMIXS IX DIFFERENT FOODSTUFFS The number of + signs after each item indicates the relative amount of the given kind of vitamin found in it. This information has been brought together by various workers from many sources Classes of Foodstlffs Vitamin A Lean meats Calf's brains Liver Kidney Pancreas (" belly sweetbreads ") Thymus (" chest sweetbreads ") Milk, whole . . . Milk, skimmed . . Butter Cream Cheese, full cream Eggs Bread, whole wheat Bread, white Rice, whole grain Rice, polished Oats, maize (whole grain) . . . Cereals, fine meal, bran removed Cabbage, fresh Cabbage, dried Spinach . . . Lettuce . . . Sweet potatoes Parsnips . . Carrots . . . Potatoes . . Beans, peas, lentils, dried Peas, fresh Onions Apples, pears, limes . . Lemons, oranges . . . Grapefruit Tomatoes Cod-liver oil Lard, cottonseed oil. olive oil . . Sugar, meat extracts, malt extract Yeast, fresh + + + + + + o o + + + o + + + + + -f- + + + + + + + + o + + + + + + + + + + + + + + + + + o o + o o o + + + + + + o o o Vrr.\Mix B Vitamin C + + -f- + + + + + + o + + + + o + + + + + + -r . + -!-- O + -f- ^ o + + -F + + + + -^ + -- + + + + + J- -L _L + + 4- + -4- + + + + + -h O O o + + + + o o + o 5 o o o o - + + + + + + + + + + + + + o + + + + + + + + + + + + + + + + + + + o o o o io6 BIOLOGY AXD HUMAN LIFE 3. Regulators (influencing growth and other processes) Vitamins Fat-soluble A ; water-soluble B ; water-soluble C B. Inorganic needs of protoplasm 4. Water Solvent Medium in which proteins etc. Transportation agency are suspended 5. Oxygen Combining with organic matter and so yielding energy 6. Salts Activators Building material in part Regulators (lime in bones) QUESTIONS 1. What distinction should you make between feeding and eating? 2. What income of the body does not come through the mouth ? 3. What kinds of nutrients would be used in relatively large quantities by a person who is growing rapidly ? 4. What kinds of nutrients would be used in relatively large quantities by a person who is very active ? 5. Why do we drink more w^ater in warm weather than in cold ? 6. W'hat are some of the more important sources of proteins ? of fats ? of carbohydrates ? 7. What are some of the more important sources of fat-soluble vita- min A ? of water-soluble B ? of water-soluble C ? 8. What are some of the more important sources of salts in our diet ? REFERENCE READINGS Hough and Sedgwick. The Human Mechanism, pp. 91-99. OsTERHOUT, W. J. V. Experiments with Plants, pp. 164-178. Farmers' Bulletin 800, Foods the Body Needs. Harrow, Benjamin. Vitamines, Essential Food Factors, chap, ix, Vita- mines (extract in C. H. Ward's ''Exploring Nature," pp. 186-189). United States Department of Agriculture. Bulletin 1138, Vitamin B in Edible Tissues of Ox. Sheep, and Hog. Public Health Reprint 689, Antineuritic Vitamin in Skim-Milk Powder. CHAPTER X WHERE FOOD COMES FROM Questions. 1. How do new supplies of organic material originate? 2. Could all living things make their own food if there were no others from whom they could take it ? 3. How is air necessary for food- making ? 4. Is it true that plants breathe in what animals breathe out, and that animals breathe in what plants breathe out ? 5. Can plants live without roots ? 6. Where is the stem of the beet plant ? 7. What is the smallest piece of plant that can grow into a new plant ? 80. Organic foods destroyed. When proteins, fats, and car- bohydrates become assimilated into the protoplasm of any plant or animal they are still available as food for other living beings ; but when any of this material becomes oxidized, it is thrown out of the world of living things. Now, living matter can continue to live only at the expense of other living matter, and living matter is constantly being destroyed (oxidized). How, then, can the total amount of protoplasm increase or even remain the same ? The answer to the question was found in the discovery that the green parts of plants are active in making new organic foods out of inorganic materials. 81. A manufacturing process. The making of organic sub- stances out of inorganic materials may be compared to a manu- facturing process. In every such process there must be (i) raw material, (2) tools or machines for working on the material, and (3) energy for driving the tools or machines. There is also (4) a main product and sometimes left-over material called waste or, better, (5) the by-product. 82. Factors in food-making, i. The raw materials used by the plant are found to be water and carbon dioxid. 2. The plant's machines or instruments are different from those with which we are familiar. Instead of having wheels or 107 io8 BIOLOGY AND HUMAN LIFE Palisade layer -Fibrovascular bundle Air space in ongy tissue levers or other moving parts these machines are chemical engines, each consisting of a lump of protein with some of the chlorophyl {chloros, ''green"; phyllum, "leaf") that gives familiar plants their distinctive color. Chlorophyl is the tool, or transformer of energy, in the food-making process (see Fig. 6i). 3. The energy for doing this work is the light from the sun. Although the work cannot go on at too low a temperature, it is the light that is used in the process, and not the heat. 83. Oxygen a by-product. The starch or sugar formed by the action of sunlight upon chlorophyl contains the elements present in the raw materials, namely, car- bon, hydrogen, and oxygen. In starch, hydrogen and oxygen occur in the same proportions as they do in water (H2O). The raw materials taken in by the plant contain an excess of oxygen, since the carbon dioxid (CO2) also furnishes oxygen. This element is given off in a free, or uncombined, state during the process of starch-making. 84. Sunlight and life. Some green plants never form starch ; but they produce some kind of carbohydrate (usually some kind of sugar) by the sunlight acting on chlorophyl. This process of carbohydrate formation is called photosynthesis, from Greek words meaning "light" (compare photogrdc^h.) and "put to- Fig. 61. Stomate Structure of leaf The cells containing the chlorophyl (the pal- isade cells and the spongy tissue) get their income from the surrounding cells or from the surrounding air spaces. The water is brought up through the vessels of the wood {fibrovascular bundle) and it soaks through the cell walls. The carbon dioxid is ab- sorbed from the air inside the leaf, and this air is in direct communication with the outer air by wayof the breathingholes,or stomates (from the Greek stoma, "mouth") WHERE FOOD COMES FROISI 109 gether." In addition to forming sugar some plants have a way of condensing the sugar, shortly after it is formed, into starch grains (Fig. 62). 85. Origin of fats. All organic materials appear to be derived from carbohydrates. Fats originate in the cells of animals as well as of plants, by a modification of starches or sugars. Pigs and poultry can be fattened on food that contains no real fat or oil. Fats contain a large proportion of carbon and a small proportion of oxygen, compared to carbohydrates. Carbon dioxid Light Energ-y from 5'jn Oxygen 000000 C C C C C C 00 00 00 00 00 00 O H O H O H O H C H O O C H O O C O O H O H O H O O H C C H O H C O O HH HH HH HH HH HH ♦ ^ ^ ^ A A tin II Carbo- by- drate CHHO CHHO CHHO CHHO CHHO CHHO i Cbloro- phyl Chloro-/^ pbyl V CHHO CHHO CHHO CHHO CHHO CHHO Carbo hy- drate U4- Water Oxygen Fig. 62. Starch-making by chlorophyl We may think of photosynthesis as taking place in two stages : in the first the raw materials, water and carbon dioxid, are broken up into their constituents — carbon, hydrogen, and oxygen; in the second these elements are recombined into carbohy- drates, and the surplus oxygen is set free. The energy for this chemical process is sunlight; the transformations are brought about through the action of chlorophyl 86. Origin of proteins. The proteins are very complex substances. All contain nitrogen in addition to carbon, hydrogen, and oxygen. Some also contain sulfur, and some phosphorus. From careful studies of plants it appears that proteins are manufactured by certain ceils when these are supplied with carbohydrates plus salts containing the necessary ele- ments ; for example, nitrates contain nitrogen, phosphates contain phos- phorus, sulfates contain sulfur, and so on. A green plant is therefore capable of manufacturing its own food if it receives, in addition to the water and carbon dioxid, a suitable supply of minerals from the soil. Many plants without chlorophyl, as certain kinds of molds and yeast, are capable of manufacturing proteins when supplied with carbohydrates and suitable minerals. More recently we have learned that certain bac- no BIOLOGY AND HUMAN LIFE teria, molds, and yeasts and probably wheat and other green plants are capable of making proteins by using nitrogen from the atmosphere ; this may prove to be a matter of great practical importance. 87. The leaf. The common green plants carry on photo- synthesis in special organs, the leaves. The most common fact about a leaf is that it is flat and comparatively thin/ Some leaves have stalks, or pedicels, and all have veins running through the flat portion, or blade. They differ as to the charac- ter of the edge. Some are smooth, whereas others have wrinkled, uneven surfaces. Some kinds are hairy, while others are quite bald. Even the color of leaves is not uniform, for the chloro- phyl varies in density, and in some plants the appearance is modified by other coloring matters, the hair, etc. (Fig. 63). 88. Work of the leaf. The structure of a leaf is shown in Fig. 61. The oxygen given off by the cells passes into the air spaces and diffuses from these to the exterior by way of the stomates (see Fig. 64). The skin cells are not directly con- cerned in the w'ork of starch-making. Their function may be de- scribed as protective. They protect the delicate pulp cells against mechanical injuries and the whole plant against the loss of water. 89. Transpiration. The loss of water is perhaps the most se- rious danger to which most plants are exposed, since more plants die from the results of wilting than from any other one cause. And yet transpiration, as this evaporation from the leaves is called, may be of use to plants indirectly. The rapid evaporation of water results in lowering the temperature of the plant. If conditions interfere with transpiration, the temperature of leaves exposed to sunshine increases so rapidly that the protoplasm is sometimes killed. This kind of occurrence may be observed in the sum- mer time, when the sun comes out quickly after a shower that has left a great deal of moisture in the air. The moisture in the air prevents tran- spiration ; the sunshine is largely converted into heat inside the leaves, and as a consequence the protoplasm is injured. iJn some plants leaves depart considerably from this model. Some leaves are nothing more than fine hairs, as on certain cactuses; others have exten- sions that behave like tendrils; and some are spines. Certain plants have leaves that are more or less active in capturing animal food. Fig. 63. Various forms of leaves I, black willow, showing stipules at base; 2, apple; 3, water oak; 4, hobble bush; 5, chestnut; 6, sugar maple; 7, compound leaf of honey locust; 8, white oak; g, com- pound leaf of poison ivy; 10, live-forever; //, compound leaf of Virginia creeper 112 BIOLOGY AND HUMAN LIFE 90. Light and leaves. In the absence of Hght, chlorophyl is inactive and the process of starch-making is suspended. More- over, if a plant is kept in dark- ness for a longer period, the chlorophyl begins to disap- pear, and in the end the leaf will be quite white. This fact is used in the blanching of celery. When we compare the outer leaves of a head of lettuce or cabbage with the inner leaves, we see a differ- ence in the amount of green pigment, which illustrates the same principle. Experiments on light in rela- tion to photosynthesis show that it is quite possible for plants to carry on this work under artificial light. By the use of strong elec- tric lights it has been possible to hasten the growth and develop- ment of lettuce so as to get it on the market at least two weeks earlier than could otherwise have been done. The plants were given daylight while there was any, and were then supplied with artificial light during the night. In this way plants can be kept w^orking continuously, as they apparently have no need for rest or sleep. More recently a crop of wheat was harvested in Minne- sota, having developed "from seed to seed" in continuous artificial light. 91. Uses of leaves. Leaves are the original sources of most of our food. The leaves of many plants are of use to us directly. Some are eaten, as, for example, cabbage, lettuce, spinach, water cress, dandelion. The leafstalks of rhubarb and celery are also used as food, although they do not contain very much Fig. 64. Breathing holes of plants j,stomates,or breathing pores, on the sur- face of a leaf, inclosed by the " guard cells." 2, section through a leaf, showing an air space just inside the guard cells. Stomates are found in the epidermis of twigs as well as on leaves. As the stem grows tougher the breathing holes become larger and more irregular patches con- necting the spaces between the cells and the outside atmosphere. The roughened breathing spaces on the bark ^xtlenticels. 3, lenticels on the bark of birch. (Mi- croscopic views about X 200) WHERE FOOD COMES FROM 113 protein, fat, or carbohydrate. Tea and tobacco are used because of the presence of an alkaloid^ that makes the leaves of these plants interesting to human beings. The fact that plants throw large quantities of oxygen into the air makes them valuable neighbors, especially in the cities, where oxygen is used up relatively faster on account of the crowded population and the many fires. Our domestic animals feed largely on the leaves of plants : grass, beet tops, hay, alfalfa, clover, and corn fodder furnish the principal green food of cattle and horses. The dead leaves of plants (whether they have dropped in the autumn or have reached the ground through the death of herbs etc.) form the basis of the humus of the soil. Humus is a mass of decaying vegetable matter, with some animal matter and soil. This forms a soil covering that is very helpful from the point of view of retaining moisture in the soil, and to a certain extent it also serves in returning nitrogen and other elements to the soil. 92. Simple food- makers. There was life upon the earth (and therefore some way of making food out of simpler substances) long before there were any leaf-bearing plants. In some of the simplest plants the whole body consists of but a single cell. Among the commoner examples are the green slime (see section 47 and Fig. 30) and the pond scum or "frog spit" (Spirogyra) that we find floating on the surface of ponds. In such plants each cell carries on all the activities that together make up being alive — all the activities that in larger and more complex plants are carried on by different special parts or organs. In the most complex plants some activities are carried on by every cell, but certain processes are specialized : there is division of labor among the root, the stem, and the leaf. 93. The root. This organ takes on many different forms, from the thin, stringy roots of grasses to the massive fleshy or woody roots of beets or trees (Fig. 65). But in a general way it may be considered an organ of attachment and of absorption. ^ An alkaloid (that is, something that is "like an alkaU") is an organic com- pound containing nitrogen and capable of combining with acids. 114 BIOLOGY AND HUMAN LIFE Differences in form are often related to the conditions under which the plants live. Thus, fleshy roots are often associated with the biennial (two-year) habit. In such plants as beets, carrots, and parsnips the plant's first season is spent in manufacturing food and depositing it in the root. The next year comparatively little foliage is produced, but a stalk bearing flowers uses up substantially all the food that had been accumu- lated. In contrast with this habit of Hfe we find the plants that sprout, Fig. 65. Forms of roots I, taproot of dandelion; 2, fibrous root of buttercup; 3, bundle (or fascicled) root of dahlia; 4, fleshy root of beet grow to maturity, and die, all within one season. These ammal plants develop in their short lives rather delicate or fibrous roots, as a rule. Trees and woody shrubs, which continue to live year after year, develop massive shoots. Corresponding to this fact we may note that such plants also develop elaborate, strong roots. From this we may see that the structure of the root and its functions are closely related to each other and to the character of the plant. There is a connection (i) be- tween the structure of the root and the size of the plant that it anchors, (2) between the size of a root and the length of its life, and (3) between the size of a root and its food-accumulating or its absorbing activity. In many plants the main root continues to grow downward into the soil as long as the plant lives and as long as the tip of the root remains WHERE FOOD COMES FROM 115 uninjured. Such a main descend- ing root is called a taproot. The fleshy roots that have been men- tioned are all taproots ; and a number of trees, as certain kinds of maples, also produce taproots. When a taproot is injured or cut off, some of the side roots turn and grow downward. In a few cases the tip of the taproot, when not too much injured, can grow a new tip and continue the main line of growth. The first function of a root may be said to be the absorp- tion of water and of dissolved substances. This work is car- ried on by the "root hairs" (see Fig. 66). 94. Structure of roots. To understand the structure of roots, use a carrot or parsnip root that has been standing for twenty-four hours or longer with its tip in water containing red ink. Cut slices both crosswise and length- wise, and use a magnifying glass (see Fig. 67). The fiber and vessel cells can grow, but they cannot divide. In the young root there appear layers of cells which separate the water- carrying bundles from the food-carrying bundles. These cam- bium cells are capable of producing new fiber and duct cells of the two kinds— the water-carrying, or wood, and the food- Fig. 66. The tip of a young root The root hair is a single cell formed by the outward prolongation of one of the skin cells. The root hairs are the actual ab- sorbing organs. Each root hair lives but a short time and then shrivels up. As the tip of the root grows on, new root hairs are formed. The older skin cells of the root die and their contents dry out. Together with the shriveled root hairs these skin cells form a protective covering through which water does not pass very readily. As the plant becomes older and uses up more water, the absorbing area of the root is increased by the formation of many side roots and by the branching of the roots. But it is always in the region near the growing tip of the main root and of the many branch rootlets that absorption takes place. The rootcap re protects the grow- ing point ii6 BIOLOGY AND HUMAN LIFE P Fig. 67. Diagram of root structure The skin, or outer layer, c, is called the epidermis. Under this comes the bark, c, or cortex. The central portion, running lengthwise of the root, cyl, is the central cylinder and corresponds to the wood of a stem. In either a cross section or a longitudinal section you can distinguish the central cylinder from the cortex. Some of the long cells in the central cyl- inder serve as tubes or vessels through which liquids move up into the stem. Other vessels in the central cylinder carry food materials from the leaves and stems down into the growing parts of the root. In addition to the cells which form ducts there are others with thickened walls. These fibers add to the toughness and rigidity of the cylinder. Bundles of fibers with water-conducting vessels or of fibers with food-conducting vessels are called fibrovascular bundles, fibro mean- ing ''of fibers" and vascular meaning "of vessels" or tubes, p, the pith carrying, or bast, system. Growth in length results from the formation of new cells by a special growing layer near the tip of the root. 95. Uses of roots. Many plants have the habit of de- positing food in their rocts : starch, sugar, and proteins. Although our fleshy vege- tables contain from about 80 per cent to 90 per cent of water after the skin is re- moved, they are still worth using for their organic sub- stances and the useful min- eral salts. These vegetables have a relatively large bulk of cellulose, which is helpful in stirring the intestines to action (seepage 154). Fleshy roots are used in large quantities as fodder for cattle. Some roots serve also as sources of drugs and flavor- ings, as licorice root, sassafras root, and sarsaparilla. Because root hairs adhere very closely to grains of sand in the soil, roots are very effective in binding the soil, enabling it to withstand the wearing away by water and by wind. For this reason cer- tain kinds of grasses are some- times planted on sandy strips WHERE FOOD COMES FROM 117 to prevent the complete removal of the sand by the winds. The hillocks formed by clumps of such plants may continue to en- large for years, and to give protection to other kinds of plants until the earth has become compact (Fig. 68). Roots do not generally put forth buds or shoots, but the roots of a few plants do so— certain willows, poplars, and hawthorns. X.:^L-.aQt!^ Fig. 68. Sand dunes at Pine, Indiana The roots and underground stems of the grass Calamovilfa longijolia bind together the grains of sand, and larger and larger soil masses are gradually formed. Barren sand is blown about by the winds. (From photograph by Dr. George D. Fuller) Roots of such plants can therefore be used for propagating the species. In some plants the roots will form new shoots if the old shoot is completely removed or destroyed. Roots frequently arise from stems or leaves, thus making possible the propaga- tion of plants by means of cuttings (see Fig. 69). Blackberry and raspberry bushes are frequently propagated by layering, which consists of bending the flexible stems outward and bury- ing the tips in the ground. New roots are formed on the covered portions, and, later, buds form new shoots. The old connecting ii8 BIOLOGY AND HUMAN LIFE Fig. 69. Adventitious roots If the leaf (or even a piece of leaf) of a bryophyl- lum be placed on damp earth or sand, tiny roots will form at certain points along the edge. Buds will also be produced, so that after a while we can separate small but complete plants and get these to grow into full-sized individuals. The same results can be obtained with the common house plant begonia Fig. 70. Climbing roots The English ivy, like many other climbing plants, clings to its support by means of adventitious roots that grow out all along the stem. The poison ivy also climbs by means of adventitious roots, and in some of the tropical tree-climbing plants the roots are fully developed as holdfast organs stem is then cut away. A similar process takes place naturally in the strawberry plant: its creeping stems bear a cluster of new roots at each tuft of leaves, so that in the course of a season a single plant may spread out and cover a large area. Roots that originate from stems or leaves are called adventitious roots (see Fig. 70). In the Indian corn and some other plants ad- ventitious roots serve as props (see Fig. 71). The banyan tree of Asia puts forth sup- porting adventitious roots from the hori- zontal branches. 96. The stem. Con- necting the leaf with the root is the stem, which is both an organ of support and an or- gan of transportation. The water and salts from the roots pass through one set of tubes, and the manu- factured food from the leaves through another. WHERE FOOD COMES FROM 119 The fibrovascular bundles conducting water from the roots are called xylem, or wood. Those conducting saps from the leaves are called phloem, or bast. The end walls of the bast vessels have pores in them and are called sieve plates (Fig. 72). In woody plants the xylem bundles are arranged in concentric cylinders, or tubes inside of tubes, and make up the wood. The phloem bundles are ar- ranged around the wood, in theinnerportionof the bark. Between the outer layer of wood and the inner layer of bast is the cambium, or growing layer, from which all thenewxylemandall the new phloem cells originate. The fibrovascular bun- dles branch and divide so that they reach into all the twigs and leaves. In the leaf they branch again and make up the so-called veins or nerves of the leaf blade. The sap-carrying vessels of the root are connected with similar tubes found in the stem. In many plants the bundles of vessels and libers are readily pulled out from among the surrounding pith cells. In celery these bundles make up the "strings," and in the plantain the so-called " nerves " that we see sticking out of the stalk when we pull up a leaf. 97, The circulation of sap. We do not yet understand all about the rise of sap in trees. It is certain, however, that the water taken in by the roots does rise to the leaves, and that it goes through the xylem vessels. We know also that organic food is formed in the leaves, and that it accumulates in roots Fig. 71. Prop roots Near the base of the trunk the screw pine (Paudamus) sends out prop roots in a man- ner similar to that of the Indian corn. (From photograph lent by the New York Botanical Garden) I20 BIOLOGY AND HUMAN LIFE and underground stems of many plants. There must, therefore, be a current of material passing downward. A tree that is girdled (that is, one that has a ring of bark removed) will continue to live for the rest of the season. This shows that the removal of the bark does not interfere with the ascent of water and salts from the roots to the leaves. The following spring, however, when the opening of the buds with the rapid ex- pansion of leaves and twigs depends upon food accumulated during the previous summer, the tree will be found dead. Although water and salts may still be able to reach the upper parts of the plant (since the channels that served during the previous sea- son are still open), the food that should have been accumulated during the previous summer is now lacking. By far the largest portion of the water that moves from the roots to the leaves evaporates and never comes back. The smallest plants that we or- dinarily notice thus show a great division of labor, with special organs and special tissues. 98. Our dependence upon chlorophyl. The parts of a plant that have no chlorophyl (for example, the root or the stem of a tree) are unable to make food substances out of inorganic mate- rials and are nourished by materials obtained from the leaves ; but animals and such plants as mushrooms, having no chloro- phyl, must get their food from the bodies of other living things. In the end all food comes from green plants. That is to say. through the action of Hght on chlorophyl, the carbon and the oxygen in CO^ become separated so that they are capable of again combining and liberating, or setting free, energy. A carbohydrate may thus serve as a source of energy by becoming oxidized, either in the Fig. 72. Bast fibers and vessel A, a section cut lengthwise, and B, one cut crosswise, showing bast fibers, sieve-plate vessel, Sp, and the so- called companion cells, cc, found next to the sieve-plate cells. (X 400) WHERE FOOD COMES FROM 121 bodies of living things or in a flame. Thus we may see that all the en- ergy which plants and animals use as a result of the oxidation of carbo- hydrates is derived from the sun's energy. There is more than poetry in the statement that every human act is a transformed sunbeam. WHERE FOOD COMES FROM 1. Organic matter is constantly being destroyed Through oxidation in protoplasm (Through decay) (Through fire and industrial processes) 2. Organic matter is constantly being made anew Primarily Through photosynthesis Material : water ( H._,0) ; Energy : sunlight carbon dioxid (CO^) Product; carbohydrates Instrument: chlorophyl By-product; oxygen Secondarily Through transformation of carbohydrates By plant and animal protoplasm Into fats ; into proteins Through assimilation of nutrients (proteins, fats, and carbo- hydrates) By plant and animal protoplasm Into substances peculiar to the different species of plants and animals Through (other) chemical processes of protoplasm Into substances peculiar to the activities of different species of plants and animals 3. Structure and activities of chief food-producers (seed plants) The leaf General character Origin From stem (From buds) Epicotyl Cotyledon Different forms (compare also parts of flower) Structure Epidermis - Pulp (chlorophyl-bearing cells) Stomates Palisade layers (Hairs) ; (Wax) Spongy (air-space) layers 122 BIOLOGY AND HUMAN LIFE Veins (fibrovascular bundles) Fibers (mechanical support) Vessels (conduction) Bringing water and salts to chlorophyl cells Taking away finished food The root General character Origin Primary Secondary From hypocotyl From other roots From stem 1 , T^ , r f- adventitious From leaf J Different forms Taproots Prop roots Fibrous roots Climbing roots Fascicled roots Aerial roots Structure Epidermis Root hairs Rootcap Cortex Pith and central cylinder, including fibers Vessels Conveying water and salts toward stem and leaf (xylem) Bringing finished food toward growing region (phloem) Growing regions Cambium layer ; growing point Functions Anchorage (holdfasts) (Storage of reserve food) Absorption of water and salts (Climbing) (Propagation) The stem General character Origin Primary From epicotyl Secondary From other stems From root "] From leaf l-adventitious From injured stem J WHERE FOOD COMES FROM 123 Different forms Erect Simple ; branched (various types of branching) Shortened (''stemless plants") Structure Creeping Chmbing Underground Rhizome ; tuber ; bulb Epidermis Fibrovascular structures Lenticels ; (hairs, Fibers (mechanical support) spines, etc.) Wood ; bast Cortex Vessels (conduction) Pith To leaves (wood ; xylem) From leaves (bast ; phloem) Growing areas Growing points (buds) Terminal ; lateral (at nodes) Cambium layers (in internodes) Functions Communicating between leaves and roots Raising leaves (Raising flowers and fruits) Propagation Storage of reserve food 4. Circulation of sap Ascending currents Composition Water Dissolved salts Channels Drive (Osmosis in roots) (Capillarity through vessels) (Transpiration from leaves) Root hairs through cortex of root (by osmosis) Xylem vessels of root, stem, leaf Leaf vessels to pulp cells (by osmosis) Descending currents Composition Drive Dissolved food material (Probably osmosis from leaves and gravity) Channels Leaf cells into phloem vessels Phloem vessels to growing regions of stem (cambium and buds) and of root (cambium and growing points) Phloem vessels to flowers (fruit, seed) Phloem vessels to accumulation tissues of stem and root 124 BIOLOGY AND HUMAN LIFE 5. Uses of leaves Direct As food As source of specific mate- As fodder for cattle rials in certain plants As humus and mulch Indirect Source of nearly all human food, and. in fact, of nearly all organic matter that we use, including our own bodies 6. Uses of roots As food and fodder ; specific drugs etc. ; propagation 7. Uses of stems As food (potato, sugar For drugs, gums, resins,. cane, sago, etc.) dyes, tanning material For fibers For wood and cork 8. Food-making in simple plants Essential organs (chlorophyl organs) Sources of material Water ; carbon dioxid ; (salts) How materials are obtained Q. Our dependence upon sunshine QUESTIONS 1. In what sense does Hfe depend upon the destruction of (the living being's own) protoplasm ? 2. In what sense does life depend upon destruction of other living things ? 3. How can life be destroyed without making for more life ? 4. What are the inorganic materials from which carbohydrates origi- nate ? What is the source of each ? 5. How can we show that fight is necessary for photosynthesis? 6. How can we show that carbon dioxid is essential to photosynthesis ? 7. How can we show that oxygen is given off during photosynthesis ? 8. How do mushrooms and other non-green plants get their food ? 9. What organic materials in a plant or animal are not produced by photosynthesis ? 10. What organic substances are there in your body (or in any other organism) that are not nutrients ? WHERE FOOD COMES FROM 125 11. How does a leaf get carbon dioxid to its chlorophyl cells? water? 12. What parts of a leaf are not directly concerned with food-making ? What relation have these parts to the life of the plant? 13. How is the root of a plant related to food-making ? 14. How does a root grow in length ? in thickness ? What is the source of the grow- th material ? 15. How is the stem of a plant related to food-making ? 16. How does a stem grow in length ? in thickness ? What is the source of its growth material ? 17. What use can we make of the fact that chlorophyl disappears from plant cells in darkness ? 18. What use can we make of the fact that chlorophyl transforms light into heat that may "scorch" the leaf? 19. What use can we make of the fact that plants accumulate surplus food in leaf, in stem, or in root ? 20. What use can we make of the fact that various parts of a plant may replace missing organs and form a complete plant ? 21. What use can we make of the fact that, in spreading out toward the light and air, plants develop various mechanical structures ? 22. What use can we make of the fact that in the course of their activities plants produce a variety of substances that are neither nutri- ents nor mechanical supports nor protection ? 23. How can we tell that living leaves give off water ? 24. How can we tell that matter from the soil travels through a plant along different channels from those followed by food sap? REFERENCE READINGS Bergen and Caldwell. Practical Botany, pp. 15-20. 55-71. OsTERHOUT, W. J. V. Experiments with Plants, pp. 180-203; chap, v, The Work of Stems. Densmore, H. D. General Botany, chap, vi. The Structure and Func- tions of Stems, Roots, and Leaves; pp. 11 7-1 24, 142-146. Gave, Selina. Why Plants need Water (extract in C^H Ward's ''Ex- ploring Nature," pp. 69-74). /\ f^BO/?^ CHAPTER XI HOW FOOD IS TAKEN IN Questions. 1. How does a cell distinguish between what it may take in and what may be injurious ? 2. How do roots select the soil materials that they can use ? 3. Why does not the substance in a root hair or other living cell go out into the soil or water ? 4. How can hving things with- out mouths take in food ? 99. Diffusion. Illuminating gas and the vapors of odorous substances spread through the air very rapidly, by a process called diffusion. Diffusion takes place also in liquids. Salt or sugar left in the bottom of a vessel of water is gradually dis- solved, lifted from the bottom, and distributed to all parts of the liquid, overcoming gravity. Diffusion therefore represents work, or the expenditure of energy. This attraction between water and certain kinds of substances helps us to understand what happens in roots and in other parts of living things. 100. All cells absorb. In many one-celled animals, like Ameba, the protoplasm is said to be naked, since there is no permanent cell covering or wall. In most plants and animals the protoplasm of each cell is more or less completely inclosed by a membrane of non-living material. We know that the root is capable of absorbing material from its surroundings and that the many cells inside every plant or animal, away from the surface, all absorb their water, food, and oxygen through the cell wall, yet a powerful microscope fails to show any openings through the cell walls, or even between adjoining cells. The substance which makes up the cell walls in most plants is called cellulose. This substance cannot dissolve in water, but it can absorb water in the same way as glue or gelatin. Now water can diffuse through cellulose, although the cellulose cannot dis- 126 HOW FOOD IS TAKEN IN 127 solve or diffuse. Substances that dissolve in water can thus dif- fuse through a cell wall as long as the cellulose is full of water. 101. Diffusion through a membrane. When solutions of two different substances are separated by a layer of cellulose or gel- atin, they may diffuse through the water contained in the sep- arating membrane. In this way they may diffuse through the membrane itself. Such diffusion is called osmosis. This proc- ess takes place in the walls of cells, since the watery liquids on the two sides of such a membrane are not the same. Thus there is a double current : protoplasm receives from the outside its supply of water, salts, and food, and materials in the cell pass out. Gases as well as liquids diffuse through the wet cell wall. 102. Osmosis in living things. The cell wall of a root cell separates the protoplasm from the surrounding soil water. In- come through the root hair is therefore by diffusion through the cell wall, or by osmosis. But the protoplasm within the cell wall is not a uniform mass of substance, and diffusion takes place between one part and another. Some substances dissolve in water more easily than others. Some of the common solids do not dissolve at all. Of those that can dissolve in water and diffuse, some will diffuse more quickly through cell walls than others, and some will not pass through at all. Of the substances that can diffuse through cellulose, some can diffuse through protoplasmic membranes more quickly than others, and some cannot diffuse through such membranes at all. As a result of these differences, cells exposed to the same mate- rial surroundings may not be equally affected. Living things absorb materials from the outside world by osmosis. W^ithin the body of every plant and every animal con- sisting of many cells, materials also pass from cell to cell, or between cells and various body juices, by this process. 103. Plant income. Green plants, as we know, manufacture their food out of raw material— water, carbon dioxid, and various salts. Water is readily absorbed by cellulose. Through the cell walls saturated with water, carbon dioxid from the air and salts from the soil pass by diffusion, or osmosis. Within the 128 BIOLOGY AND HUMAN LIFE plant these substances pass from cell to cell, or through special vessels or spaces. Leaves are particularly well fitted to absorb gases from the air and to pass gases into the air (see Fig. 6i and Fig. 64). Roots are generally well fitted to absorb water and dissolved salts from the soil, the surface being greatly enlarged by the outgrowth of root hairs (see Fig. 66). 104. Animal income. The sugars are the only nutrients that can dissolve in water. Starches and proteins, while capable of absorbing water, cannot dissolve. Such substances are called colloids (which means "like glue"), to distinguish them from sugars and salts, called crystalloids, which can dissolve in water and diffuse through cellulose and other membranes. Moreover, most of our food consists not of pure sugars, starches, and pro- teins, but of plant and animal tissues the nutrients of which are locked up in cells. Finally, seeds, stems, and other portions of many plants contain colloid starch, which we have considered as food for the growth of the plant. How can plant and animal cells make use of such colloids ? 105. Digestion. Experiments show that colloids can be changed into crystalloids ; and then the material can pass through cell walls by osmosis. The process of transformation is called digestion and can easily be demonstrated. In the grains and in seeds containing starch the absorption of water leads to the development of a substance called diastase. This can con- vert starch into sugar. Diastase has been extracted from malted barley (that is, barley kept moist until the grains have sprouted), from rice, and from many other seeds. It can now be bought in the stores. A sub- stance that behaves in many ways like diastase is found in human saliva (spit) and in the digestive juices of many other animals. Substances like diastase and the active part of the saliva are called ferments, or enzyms, and many different kinds are known. They are peculiar in that they seem to induce chemical changes in other substances, without, however, undergoing any changes themselves. As a result of this peculiarity a comparatively large amount of material may be made to undergo chemical change through the activity of a very small amount of enzym. HOW FOOD IS TAKEN IN 129 106. Digestion universal. Digestion seems to go on in nearly all living things. In the ameba, which consists of a single cell (see section 47), a solid particle of food can be swallowed by the naked protoplasm and then digested inside the cell. Among the bacteria, which are the smallest living things known, each indi- vidual is a single cell consisting of protoplasm and cell wall. These tiny plants can get food only in a liquid state, yet many of them live on solid food that is not soluble in water. Under suit- able external conditions each cell throws out through the cell Fig. 73. Digestion by bacteria The organism, a, lying on a solid, b, which may serve as food, secretes an enzym, or ferment, which passes out of the cell, c, and changes the material to a liquid, I. This is absorbed into the cell by osmosis, / wall, by osmosis, a liquid containing a ferment capable of di- gesting the solid, or insoluble, food material. The liquid re- sulting from the digestion is then absorbed by osmosis. This is why meat or cheese becomes fluid when it rots. The rotting in such cases is the work of the ferments contained in the diges- tive juices given off or secreted by the bacteria (Fig. 73). In higher animals like ourselves a similar process of digestion takes place; but instead of every cell's pouring out digestive juices into its immediate neighborhood, only certain portions of the body produce and throw out such juices. HOW FOOD IS TAKEN IN I. Diffusion Materials capable of diifusion Gases ; liquids ; solids in solution Conditions in which diffusion can take place Free contact of diffusible substances Certain kinds of membranes (semipermeable) 130 BIOLOGY AND HUMAN LIFE 2. Osmosis Meaning of osmosis Osmosis in living things Into cells ; out of cells ; 3. Absorption in organisms Root absorption Materials Organ Relation to life of plant within cells Absorption in one-celled organisms What is taken in How material is taken in Absorption in larger animals Digestion Character of change Importance to living things Leaf absorption Where it takes place What is absorbed Relation of absorbed material to life of plant Relation of intake to life How brought about Enzyms ; ferments QUESTIONS 1. What practical use do we sometimes make of the fact that gases diffuse readily ? 2. What would be the condition of our atmosphere if the different gases in it did not diffuse ? 3. What substances swell in water without dissolving ? 4. Why will ink spread on wet paper but not on dry ? 5. Why does the protoplasm inside a cell shrivel or shrink up when the cell is placed in salt water ? 6. Will a root or a sausage shrink or swell in salt water ? Why ? 7. Under what conditions will a cell absorb more than it gives out ? 8. Under what conditions will a cell give out more than it absorbs ? 9. How can animals make use of solid food ? How can plants ? REFERENCE READINGS Bergen and Caldwell. Practical Botany, pp. 7-9. OsTERHOUT, W. J. V. Experiments with Plants, pp. 1 21-124. Densmore, H. D. General Botany, pp. 137-142. Fabre, J. The Glowworm's Anaesthetic (extract in C. H. Ward's "Exploring Nature," pp. 101-107). CHAPTER XII WORKING OVER THE BODY'S INCOME Questions. 1. What happens to food after it is eaten? 2. How does the food which we place in the mouth and swallow get to the other organs of the body? 3. What connection is there between the stomach and the other inside organs ? 4. Why are some kinds of food more easily digested than others ? 5. What causes indigestion ? 107. The human food tube. The mouth is the beginning of a long tube inside of which all the digestion takes place. This tube is called the food tube, or alimentary canal. It consists of several fairly distinct regions. It gets to be ten or eleven yards long and is coiled or twisted in parts (see ;, k, Fig. 74). 108. Mouth digestion. After the food enters the mouth it is crushed and ground by the teeth. The taste of the food, the movement of the jaws, and the rubbing of the food against the inside of the mouth stimulate the saliva glands, that is, set them in action (see Fig. 75). As a result a quantity of saliva is poured into the mouth and becomes mixed with the food. The action of the saliva upon the starch changes it into sugar (see section 105). The other materials in the food are probably not changed, except that salts and sugars are dissolved in water, of which the saliva contains over 99 per cent. As the amount of ferment is very small, the effectiveness of saliva in digesting starch depends upon (i) the ferment's reach- ing every particle of starch, and (2) its having sufficient time to act. Mixing saliva thoroughly with the food makes it easier for the mass to slide along into the throat, and down the gullet, since the mass is thus coated with the slippery mucin of the saliva. 109. Swallowing. After the mouthful of food has been thor- oughly chewed, it is pushed back by the tongue and passed into the throat chamber, or pharynx (see b, Fig. 74), from which it 131 132 BIOLOGY AND HUMAN LIFE passes directly into the gullet, or esophagus. In the wall of the gullet is a series of muscular rings which contract one after another, carrying the food toward the stomach. If you watch a horse drink- ing water from a pond or from a pail on the ground, you can see him swallow up ; and you can see one wave of contraction after another pass along the gullet, from the head to the trunk.- 110. The stomach. The fermentation started in the mouth continues in the mass of food until it gets into the stomach. Here it is stopped when the acid, or sour, stomach juice comes in contact with the saliva. The swal- lowed food is thoroughly mixed with the gastric, or stomach, juice by the ac- tion of the muscles in the stomach wall. These muscles run in different directions ; by their con- tractions the contents be- come thoroughly churned. The wall of the stomach also contains the glands in which the digestive fluids are produced (see Fig. 76). Fig. 74. The digestive organs in man a, entrance to mouth; b, the pharynx — a sort of vestibule with seven passages leading out of it, two to the nostrils, one to the mouth, one to the gullet, one to the windpipe, and one to each ear (the Eustachian tubes, see Fig. 115); c, the gullet, or esophagus; d, the stomach; e, the pylorus, opening from the stomach to the small intestine; /, the liver; g, the gall bladder; //, duct from the gall bladder and the liver to the small intestine; i, duct from the pancreas to the small intestine; ;', small intestine; k, large in- testine; I, vermiform appendix; m, rectum; n, the diaphragm, separating the chest cavity from the abdominal cavity; 0, the pancreas. The ar- rows indicate the course taken by food WORKING OVER THE BODY'S INXOME 133 Parotid gland Blood vessels Sublingual The peptones resulting from stomach digestion differ from pro- teins chiefly in being soluble in water and capable of diffusing through membranes. As the changing of proteins into peptones goes on, the mixture in the stomach becomes more and more liquid and more and more acid. From time to time a quantity of the liquid passes into the intestine. After a while most of the contents of the stomach has been changed to a mixture having the consistency of a rather thick pea soup, and all of it has passed on into the intestine. 111. The bowels or in- testines. Among the high- est animals the gut has two distinct divisions. The first is called the small intestine, and in human beings it is about one inch in diameter and about twenty-four or twenty-five feet long. This opens rather abruptly into the large intestine, which is about two inches in diam- eter and about five feet long {seej,k, Fig. 74). You have probably handled a piece of pig gut or calf gut, which is used as sausage casing. The wall of the intestine is thin and soft. The Hning carries very small glands, and the outer layer contains muscle cells. The muscle cells are ar- ranged in rings: when they contract they simply reduce the diameter of the intestine at any given point. The contraction starts at the forward end (nearest the stomach) and passes backward along the whole length of the small intestine, aided by longitudinal muscles. As a result of these contractions some of the thick mixture of food and digestive juices is moved along, Suhnaxillary Fig. 75. The salivary glands There are three sets of glands which produce saliva : the parotid, in the cheek, just in front of the ears; the submaxillary, under the angles of the jaw; and the sublingual, under the tongue. The more the food is chewed, the smaller are the particles into which it is broken, and the more thoroughly is the saliva mLxed with these particles 134 BIOLOGY AND HUMAN LIFE a short distance at a time. This movement is called peristalsis and is similar to the swallowing movement of the gullet. In vomiting, this peristaltic action of the food tube is reversed. Neither the saliva ferments nor the gastric ferments have any effect upon fats. When a food mixture passes from the stomach, it contains all the sugar that was there to begin with, all the sugar that was formed by the di- gestive action of the saliva, and whatever starch was not digested. It contains the peptones resulting from the gas- tric digestion, and par- ticles of proteins that were not digested. In addition there is a quantity of water, min- eral salts, the remains of the gastric and sali- vary juices, and the fibers and cell walls of the food material. In the intestines further Fig. 76. Glands of the stomach The gastric juice ispoured into the stomach through tubes, a, which are lined by a layer of delicate cells; it is produced by special gland cells, b, from materials brought by the blood in fine vessels, c. The stomach juice contains, in addition to an acid, a special ferment, pepsin. In the presence of acids pepsin acts upon proteins and changes them into soluble peptones changes take place. Near the beginning of the intestine two small tubes, or ducts {h, i, Fig. 74), empty at a common opening. One of them leads from the largest gland in the body, the liver ; the other from another important gland, the pancreas (see 0, Fig. 74). 112. The pancreas. The juice secreted by the pancreas con- tains three important kinds of ferments : 1. A ferment that converts starch into sugar. 2. A ferment that digests proteins into simpler compounds. Any starch that has been swallowed before the saliva has had time to transform it into sugar, and any protein that has passed WORKING OVER THE BODY'S INXOME 135 from the stomach without being digested by the pepsin, will now be digested by the action of the pancreatic ferments. 3. A ferment that breaks up fats into glycerin and fatty acids. The latter combine with other substances to make soaps. Soaps and glycerin dissolve in water and diffuse through the cell walls. Pancreatic juice thus contains the ferments necessary for digesting all nutrients. 113. The liver. This produces bile or gall. 1. Bile contains no digestive ferments, but it does influence the absorption of the fatty acids and soaps by the cells of the intestine. 2. The bile seems to have some effect upon the activity of the pan- creatic ferments. When the contents of the stomach pass into the intestine, the mixture is acid. The bile neutral- izes the acid and makes possible the activity of the other ferments. 3. The bile is made up chiefly of materials that are of no fur- ther use to the body ; the liver is thus also an excretory organ. 114. The intestinal juices. The juices secreted by the glands of the intestine contain no ferments of great importance in digestion, but they neutralize the acids resulting from various chemical changes in the gut. One ferment in the intestinal juice converts cane sugar into simpler sugars. Fig. 77, Lining of the intestine, (x 150) The tiny projections from the lining of the small intestine, the villi, give the appearance of very fine velvet. Absorption takes place through the outer layer of cells. Within each villus are fine blood vessels and lymph spaces ; from these the ab- sorbed food is transferred to the circulation sys- tem. Chemical changes take place in the course of the transfer. As a result the material taken into the blood is not exactly the same as that absorbed from the intestine, although it is made up of the same elements 136 BIOLOGY AND HUMAN LIFE 115. Absorption. Very small outgrowths project into the cavity of the small intestine, so that the surface exposed to con- tact with the food mixture is increased several hundred times. Each of these tiny projections, called a villus (plural, villi) (see Fig, 77), acts as a special absorbing and transforming or- gan. The mixture in the intestine now consists of (i) many Esophagus Prove 11 ulti's Gizzard ■ v. - ^ I Gnll jA^- WA\ / bladder Liver Large Intestine and Rectum Fig. 78. Digestive system in fish and in bird The main features of the digestive system are alike in all backboned animals. In the birds the gullet has a curious pouch, the crop, in which food may be retained indefi- nitely and later either swallowed to the stomach or regurgitated through the mouth. The glandular portion of the stomach, or proventriculus, is distinct from the grinding part, or gizzard crystalloids in solution, (2) many colloids in the process of being converted into crystalloids, and (3) solid substances that are not capable of changing under conditions that exist in the gut. When the dinner that you have eaten reaches the end of the small intestine, most of its carbohydrates, proteins, and fats have been absorbed by the villi and passed into the blood and WORKING OVER THE BODY'S INCOME 137 lymph. There is left in the intestines chiefly ( i ) the undigested (mostly indigestible) fibrous and cell-wall parts of the plant or animal tissues eaten, and (2) the modified secretions of the various glands that have poured into the food tube along the way. This mass of refuse now passes into the large intestine {k, Fig. 74). 116. The large intestine. In the large intestine the ferments of the digestive juices may continue to act for some time. Gradually, as the mass proceeds along the canal, it becomes drier as the lining of the intestine continues to absorb fluids (there are no villi in the large intestine). Toward the end the only chemical changes going on are those produced by the mil- lions of bacteria that are present in the intestines of all animals that have intestines. The mass of material that has accumulated toward the end of the large intestine is of no further use to the body, and should be removed from time to time (see section 131). Birds, having no large intestines, throw off the refuse about as fast as it passes from the small intestine to the rectum (Fig. 78). Other animals and human infants throw off the refuse automatically. WORKING OVER THE BODY'S INCOME I. The digestive tube of man Mouth (organs related to nutrition) Teeth ; salivary glands ; (tongue) Pharynx (seven openings) Mouth (Windpipe) (Eustachian tubes, 2) (Nostrils, 2) Gullet (esophagus) Gullet Stomach Swallowing muscles Gastric glands ; muscles Small intestine Large intestine Glands ; muscles ; villi Connection with small Connection with liver and intestine gall bladder (Vermiform appendix) Connection with pancreas Rectum 138 BIOLOGY AND HUMAN LIFE 2. Digestion of nutrients in the human body Starch changed into grape sugar SaHva (ptyaHn) ; pancreatic juice (amylopsin) Protein changed into peptones and amino acids Stomach juices (pepsin; acts in acid) Pancreatic juices (trypsin ; acts in alkali) Fat changed into glycerin and fat Pancreatic juice (steapsin) Cane sugar changed into grape sugar Intestinal juice 3. Absorption Villi of small intestine Lining of large intestine Transfer to blood stream 4. Undigested refuse QUESTIONS 1. Why cannot the cells of our body make use of the food as we receive it from the kitchen ? 2. What kind of nutrient is digested by the mouth juices ? 3. Why should we chew food that is not digested by mouth juices ? 4. What use does the body make of the saliva secreted as a result of chewing gum if the saliva is thrown out ? if the saliva is swallowed ? 5. How can we show that pepsin acts upon proteins but not' upon starch or fat ? How can we show that pepsin acts in an acid solution but not in an alkaline solution ? 6. How can we show that saliva acts upon starch but not upon protein ? 7. How can we show that crystalloids will pass through the wall of the intestine but that colloids will not ? 8. Why is it important to prevent accumulation of refuse in the large intestine for a long period ? REFERENCE READINGS Bergen and Caldwell. Practical Botany, pp. 144-145. OsTERHOUT, W. J. V. Experiments with Plants, pp. 155-178. Densmore, H. D. General Botany, pp. 124-130. Hough and Sedgwick. The Human Mechanism, pp. 99-134. CHAPTER XIII WHAT TO EAT • Questions. 1. Why can we not safely trust our instincts in deciding what to eat or what not to eat ? 2. Why can we not always safely trust our feelings in deciding how much to eat ? 3. Why can we not always depend upon the customs of people in deciding how much to eat or what kinds of food are good ? 117. Why eating must be learned. We should expect that in half a million years or more the human race might have learned all there was to know about what to eat and how to eat it. Most people, however, do not know, either from instinct or from daily experience, the best way to manage their personal food problems. Everywhere children suffer from defective nu- trition and grown folks from disturbances of digestion. Starva- tion and overfeeding exist side by side. Although all living beings consist fundamentally of proteins, fats, and carbohydrates, not all plant or animal stuff is suitable for food. Some plant and animal materials are not pleasant to the taste, or are even disagreeable, and others are poisonous; and some contain too little usable or digestible substance to be worth eating. In the course of ages human customs have se- lected the plant and animal materials in any given region that are most valuable as food. W^e know that some parts of animals and plants (muscle, grain) are better than others (hide, wood) ; but experience has not taught us what proportions of meat and grain and fruit are the best for bodily comfort and efficiency, and we still have to learn that one combination is best for one person, and another combination for others. With the increase in travel, communication, and transport we are constantly dis- covering useful food plants and food animals, and neither our instincts nor our customs tell us the best way to use them. 139 140 BIOLOGY AND HUMAN LIFE 118. Food and health. All the chemical changes and activi- ties that are constantly going on in living protoplasm are called metabolism. Some of these processes are constructive, leading to the formation of new protoplasm and tissues. Other changes are destructive, resulting in the breaking down of proteins and other complex substances. The activity of the protoplasm dur- ing the rest or sleep of the body is fairly constant, and is called the basic metabolism. We can measure the metabolism or ac- tivity in an organism by measuring the amount of heat that the body gives off, since all the chemical and mechanical processes end in this form of energy. Even the cold-blooded animals and plants give off heat.^ Now the first function of food is to supply the materials used up in metabolism— proteins and fuels (fats and carbohydrates)— in proportion to the daily needs of the body. These needs vary with the basic metabolism and with the amount of external work done. Two men of the same weight have about the same food requirements so long as they both keep quiet ; but if one is more active than the other when not resting, he needs more food. It is possible to determine pretty accurately (i) how much protein is needed for a growing body, (2) how much protein and fuel food is needed for basic metabolism, and (3) how much fuel food is needed for the additional work of the body. In addition to the nutrients (see page 102) the body needs cer- tain mineral substances (chiefly calcium, phosphorus, and iron) and supplies of vitamins (see page 102). A deficiency in protein cannot be made up by an excess of fats or carbohydrates, al- though fats and carbohydrates may replace each other as fuels. Vitamins, while needed in but very small quantities, cannot be excluded from the diet without bringing about serious disturb- ances in metabolism. In the same way, a lack of calcium may bring about softening of the bones in the case of a growing child, iThe unit of energy used in measuring heat is the calorie. This is the amount of heat that is used up in raising the temperature of a kilogram of water (a little more than a quart) from 0° to 1° C. For very delicate work the "small calorie" is used; this is one thousandth of a "large calorie." WHAT TO EAT 141 or a defect in the milk of a nursing mother ; iron must be pres- ent for the formation of the red coloring matter in the blood cells (hemoglobin) : and so on. The food must contain a va- riety of substances, in certain proportions which vary with the age of the eater, his size, and the amount of work that he does. 119. Selecting our food. People know from painful expe- rience how unwise it is to depend altogether upon our feelings or "instincts" in deciding the kinds and quantities of food eaten; yet our tastes and appetites deserve respectful consideration. Taste. Most people like sweets. This does not show that all sweet things are good for us, since some are actually poisonous ; but a "sweet tooth" may show that the body needs more carbo- hydrate than it gets regularly. On the other hand, food that is not tasty interferes with the digestion. The secretion of the digestive juices depends upon a pleasurable stimulation of the nerves connected with the nose and tongue. We all know that smelling some attractive food makes the '^ mouth water." In the same way, the pleasurable stimulation of certain nerves makes the stomach water, or secrete the gastric juices. Now while saliva can digest starch in a test tube, and gastric juice can act upon meat in a tin cup, without regard to anyone's feel- ings, the glands of the stomach and of the mouth will secrete juices readily only when the taste is pleased. Appetite. A healthy body of sound habits is not likely to feel hungry except when it needs food ; nor will such a body acquire either violent desires or violent dislikes for particular kinds of food. But in order to form sound habits we must have expe- rience in recognizing just what conditions of eating and what kinds of food are best suited to us. Food may be attractive to a given person and yet be unsuitable for him because he cannot digest it. W^hoever has charge of young children should dis- cover whether each kind of food is suitable for each particular child, or whether the child is acquiring unreasonable prejudices toward particular kinds of food. Later each one of us has to continue his own education. No person or book can tell you whether shrimp or cheese will agree with you ; you have to find 142 BIOLOGY AND HUMAN LIFE out for yourself with respect to every kind of food, and then use your knowledge. You will have to find out how much you can best eat at one time, or how often you have to eat. Digestibility. Aside from individual peculiarities of the di- gestive system, some foods are more easily digested than others. For example, milk contains the proteins, fats, carbohydrates, and salts in a very easily digested form. Meat proteins and fats are in general more easily digested than vegetable proteins and fats ; but the meat proteins are inclosed in materials that may not be so easily digested. Nutritive value. We usually know immediately whether our food pleases us, or whether we have stopped our hunger ; and if something goes wrong with the digestion, we soon discover it. But we may continue a very long time on a diet that is seriously lacking in essentials without realizing it. For this reason we must see that everybody acquires tastes and habits guided by reliable knowledge of daily needs. Such knowledge rests upon studies of what people do actually eat, and upon experiments with the diet and its effects on college students, soldiers and other people, and on various animals. Some of these experiments are made with a very elaborate and very accurate apparatus called the respiration calorimeter (see Fig. 79). 120. Daily needs. From these studies and experiments it has been possible to make out tables of daily needs for men and women, boys and girls, at different ages, in different occupa- tions, at different seasons of the year. The age is important because ( i ) the digestive system of a young person may not be able to tolerate what an older person can stand ; ( 2 ) a young person is usually smaller and so uses up less proteins in the basic metabolism each day; and (3) the young person is still growing, and so uses up more proteins for building new tissues than does the older person. The occupation is important be- cause the amount of energy used up in the day's work must be supplied by the fats and carbohydrates, in addition to the nu- trients required for the basic metabolism. So in the winter we need more fuel to keep up the body temperature. WHAT TO EAT 143 121. Nutritive ratio. It would be possible for a person to subsist on a protein diet, since these nutrients are also oxidized in the cells, and yield energy; and many animals and some plants do actually get along on proteins alone. But a sur- plus of protein puts an additional burden upon our livers and Fig. 79. The respiration calorimeter In the large chamber a man can live for several days or weeks under conditions that give an accurate account of his body's income and expenditure, in the way of matter as well as in the way of energy. A, door and window; B, door for food etc.; C, tank for catching water circulating through the walls of the chamber; D, observer's table, with devices for measuring and regulating temperature etc.; E, rubber bag to equal- ize the air pressure within the chamber; F, apparatus for circulation and purification of air in the chamber. (From photograph furnished by Office of Home Economics, United States Department of Agriculture) kidneys, besides being relatively more expensive financially. It is really worth while to reduce the protein in food to the lowest proportion of practical safety. This proportion of protein in the diet is called the nutritive ratio. In countries which have relatively cheap supplies of meat there has been a tendency to consume an excess of proteins. The best studies we have point 144 BIOLOGY AND HUMAN LIFE to a daily consumption of about three ounces of protein as being safe from a health point of view, and at the same time abundant to meet the needs of metabolism and growth. 122. Age and diet. If we take the food required by a man of about 150 pounds weight, doing moderately hard work, such as a weaver or a bookbinder, as one hundred, the amounts needed by children at different ages are about as follows : Age For Boys For Girls Under 2 vears 30 40 60-70 80 90 30 40 50 60 2 to t; vears 6 to vears 10 to 12 vears i^ to 14 vears 70 So 15 to 16 years The nutritive ratio is left the same for children as it is for adults, although growing children need more proteins. The bal- ance is brought about by the fact that the children are more ac- tive than adults and use up comparatively more fuel. Indeed, some students of the problem would give boys and girls of high- school age more food than hard-working adults. This agrees with the fact that at this period many of us seem to be always eating, or at any rate always hungry. The basic metabolism is known to be greater at this period, so it is likely that we shall have to correct our figures upward. 123. Work and other conditions. Experiments made to show the quantity of energy used up by a man under varying condi- tions gave the results summarized in this table : r. T^ Calories Condition of the Body PER Hour At rest, sleeping (corresponds probably with basic metabolism) 65 At rest, awake, sitting up 100 At rest, standing 117 Engaged in light muscular exercise 170 Engaged in moderately active muscular exercise 290 Engaged in severe muscular exercise 450 Engaged in very severe muscular exercise 650-675 WHAT TO EAT 145 Since we do not sleep all the time or work all the time, the amount of energy used up per day will depend upon one's daily program. Thus, a person working in the steel mills twelve hours a day, seven days in the week, expends more energy than a clerk who sits at a desk eight hours making out pay rolls. The energy needs of various classes of workers are given in the follow- ing table, which combines the results of many different studies : Classes of Workers Calories per Day Woodcutter, lumberman 5000-6000 Stonecutter, excavator, miner 4700^5000 Farmer, cabinetmaker, painter 3500-4000 Metal worker, mechanic 3400-3500 Carpenter 2700-3400 Weaver, bookbinder, tailor, shoemaker 2500-3200 Business man, student 2400-3000 Studies made in Finland with the respiration calorimeter give the following table on the needs of women workers : Classes of Workers Calories per Day Washerwoman 2900-3700 Housemaid 2500-3200 Bookbinder 2100-2300 Seamstress (on sewing machine) 2100-2300 Seamstress (on hand work) 2000 124. Climate and seasons. We know that the natives of tropical countries eat very little meat, and that the natives of cold countries eat very little fruit but a great deal of fat. W' e can understand why the Eskimos eat no fruit ; but the inhabitants of the tropics can get almost any kind of food they wish. The fact is, however, that in a cold region it is necessary to provide for a larger supply of body heat than in a hot region. Since fat yields the greatest amount of energy for a given weight of fuel,^ ^The fuel values of proteins, fats, and carbohydrates are as follows: Calories per Gram Calories per Pound Proteins 4.1 4.1 9-3 i860 Carbohydrates Fats i860 4219 146 BIOLOGY AND HUMAN LIFE it is especially desirable in the diet when energy output is needed rather than building material or bulk. Accordingly we may increase the proportion of fuel in the winter, eating more fat, and reduce it in the summer. 125. Food composition. How can we translate the products of the food factories and the kitchen into terms of proteins and B-otdn 3.6°/. Fat 4%-\ Carbohydrate . . 4.7% Ash 0.7% Protein 14.8% Tax 10.5% Aah 1% ■Protein 1.3'/, ■MU 0.6% Fig. 80. Composition of food The proportions of water, protein, fat, carbohydrate, and mineral matter (ash) in a glass of milk, an egg, two slices of bread, a pat of butter, and a banana are shown in this diagram, designed after the Langworthy charts. Such diagrams enable us to tell at a glance the relative amount of each nutrient present in our common articles of diet calories and vitamins ? The means for such translation is fur- nished by tables that have been prepared by various experts working for the government, for hospitals and other institu- tions, and for manufacturers. We can make use of the results obtained by these experts to guide us in our own selection of food. From the diagrams in Fig. 80 we can see that some of the WHAT TO EAT 147 food material which we use contains more nutrients than others. We also know that they contain varying proportions of proteins, fats, and carbohydrates. Mr. Frank A. Rexford of Brooklyn has prepared a convenient table (see page 149) which shows the composition of an ordinary helping of various food articles, giving (i) the usual quantity, (2) the amount of protein, fat, and carbohydrate that such a helping contains, and (3) the amount of energy it yields. 126. Balanced diet. The practical thing about diet is that the food taken shall be ( i ) sufficient in amount to yield the needed energy; (2) suitable in composition to yield about three ounces of protein per day; (3) of a composition containing the needed vitamins and minerals; (4) palatable for the person who is to eat it ; (5) adapted to the digestion of the individual. Each of us must find out for himself what foods will suit our taste and the digestion. A good rule is to learn to eat all kinds of food, so as to be able to meet all circumstances. Now fuel value, the proportion of protein, and the various kinds of vita- mins and minerals depend upon the composition of what we eat. From the table on page 149 we see that broiled chicken contains about three quarters of an ounce of protein to an ordinary help- ing of about three and a half ounces. Four such portions a day would supply enough proteins, but less than 500 calories of fuel value ; and enough chicken to supply the necessary fuel would furnish a large excess of proteins. On the other hand, if you tried to live on fruit, you would have to eat the equivalent of from thirty-five to fifty pounds of apples to supply the necessary protein, although nine or ten pounds would supply the necessary fuel, in the form of sugars. Most of the animal foods have an excess of proteins, whereas most of the foods of vegetable origin have a relative shortage of proteins. In order to get a satisfactory diet that meets all the conditions, it is most convenient to mix our rations. By using food of various kinds we can get a balance combined with bulk and taste. For children under one year of age, milk alone can be made to serve. 148 BIOLOGY AND HUMAN LIFE Uninformed people are in danger of taking food entirely on the basis of their taste or the temptations of the market. They are likely to suffer from malnutrition through an excess of sweets or from digestive disturbances through an excess of pro- teins. People who are both ignorant and poor are in danger of getting their food altogether on the basis of its cost, and suffer from malnutrition through an excess of starchy food, which is usually the cheapest. 127. Food fads and notions. That the race has not yet learned what is best for it in the way of eating is shown by the wide- spread interest in new food fads, and the great variety of no- tions about food. There is frequent discussion about flesh food versus vegetable food, with all sorts of arguments that have little to do with real facts. For example, one hears that it is ^Svrong to kill living beings to maintain our own lives" or that ''we become what we eat." If we understand the basic facts of nutrition, we realize that all our food must come from "living beings," and that, with the exception of green plants, all living beings, including ourselves, must depend upon other living be- ings for their food. In his ignorance the savage may believe that eating the heart of his enemy will give him the courage of his enemy, or eating the flesh of an ox will give him the strength of an ox. But we have learned that all the food we eat, no matter what its source, must first be converted into amino acids and simple sugars before it is taken into the protoplasm of our own cells. And we have learned that these sugars and amino acids are built up into human protoplasm. A well-balanced diet, obtained by means of a variety of food articles, is likely to supply the needed minerals (see page loi), as well as the necessary vitamins (see page 102), and it is likely also to be of sufficient pleasure to the palate to insure suitable activity of the digestive glands. The best arguments in the matter of eating are based on facts, and the most reliable facts that we have at present are derived from systematic scien- tific experimentation. Everybody who takes a little trouble can get the full benefit of the results for his own practical use. I WHAT TO EAT 149 PART OF MR. REXFORDS ONE-PORTION FOOD TABLE Milk, whole . . . Buttermilk . , . Butter Cheese, full cream Eggs, boiled (2) . Beef, sirloin . . Beef, chuck, lean Beef, dried . . . Bacon Ham, lean . . . Lamb, leg . . . Chicken, broiled . Salmon (canned) . Brook trout . . . Oysters . . . . Bread, white, homemade Oatmeal . . . Macaroni, boiled Beans, baked . Cabbage, boiled Potato, boiled Apple, fresh Banana . . Dates . . . Figs . . . Orange . . Peanut . . . Walnut, English Sugar .... Weight of Ordinary Helping (Ounces) 6.0 6.0 0-5 i.o 475 2.25 1.0 1.0 2.25 3-5 3-5 2.0 1-75 3-5 2.0 4.25 2-75 3-25 4.00 3.00 5-5 3-5 1-75 2.0 5-0 0.5 0-5 0.2; Ounces OF Protein Ounces OF Fats .19 .18 •05 .26 .64 •37 •57 .26 .1 •49 •75 •44 •jj .21 .iS •13 •36 •03 .oS .02 •o; .04 .09 .04 •13 .08 24 03 43 34 50 Z^ 4 07 66 55 44 09 24 36 04 03 02 02 18 09 01 02 02 05 01 01 19 ".2 Ounces OF Carbo- hydrates Calories Furnished •30 .29 .02 1.07 •49 2.00 1.08 .06 •73 •77 •59 ^•5 .58 .12 .08 •25 123.6 61.9 112.5 122.4 227.1 137-1 172.5 49.4 188.6 203.2 194-3 1 10.5 114.1 135-9 36-4 153-1 76.5 286.2 182.0 35^2 82.8 99-6 100.8 177.6 184.4 75-0 8o.i 103.4 27.0 150 BIOLOGY AND HUMAN LIFE WHAT TO EAT 1. Why choice of food must be learned Our instincts are not related to the usefulness or the harmfulness of the many things that we can put into our mouths There is no necessary connection between the food value of natural objects and their appearance or taste There is no necessary connection between contents of natural objects and their possibly poisonous properties or their digestibility New plants and animals of food value are constantly being intro- duced from other parts of the world New discoveries are constantly being made about the relation of natural materials to the health of the human body New discoveries are being made about the influence of cooking, preserving, etc. upon the food value and effects of natural materials 2. Relation of food to health Upkeep of basic metabolism Supply of growth material Energy for day's work Vitamins and mineral activators and regulators 3. What should influence selection of food (quality) Taste ; digestibility ; nutritive value 4. Daily needs (quantity) Nutritive ratio (about 11 per cent of total calories from proteins) Age and food needs Work and food needs Climate or season and food needs 5. A balanced diet (proportion) Importance of enough proteins etc. Disadvantage of excess proteins Sources of malnutrition Insufficient food Deficiency of particular constituents Protein ; vitamin ; minerals ; energy 6. Food fads Related to ignorance, which is not aware of the facts about protoplasm and its nutrition Related to simple-mindedness, which tries to solve a very com- plex problem with a very simple rule WHAT TO EAT 151 QUESTIONS 1. Why can we not have a standard ration suitable for all the people of a country ? 2. Why can we not have a standard ration for ourselves and eat the same thing every day ? 3. How can the art of cooking help make people healthier ? happier ? 4. How can people spending plenty of money for food suffer from malnutrition ? 5. What are the advantages of a mixed diet ? disadvantages ? 6. What kinds of food are best for the brain ? for the heart ? to make the hair grow ? 7. What differences in diet should you prescribe for a minister and a blacksmith? Why? 8. What should you recommend for a person who is under weight ? over weight ? REFERENCE READINGS Farmers^ Bulletin 142, Principles of Nutrition and Nutritive Value of Foods. Farmers' Bulletin gys, Food Values ; how Foods meet Body Needs. Fanners' Bulletin 138 j, Food Values and Body Needs shown Graphically. Farmers' Bulletin 1313, Good Proportions in the Diet. Farmers' Bulletin 817, How to select Cereal Foods. Farmers' Bulletin 824, How to select Protein Foods. Farmers' Bulletin 256, Preparation of Vegetables for the Table. Farmers' Bulletin 717, Food for Young Children (from Three to Six Years). WiNCHELL, Florence E. Food Facts for Every Day. Various chapters for special reports. United States Bureau of Education. Keep-Well Series, No. 11. Mal- nutrition, Helpful Advice to Parents. Get from the Superintendent of Documents, Government Printing Office, Washington, D.C., Prist List 11, Foods and Cooking. CHAPTER XIV HYGIENE OF FOOD AND FEEDING Questions. 1. How often should a person eat? 2. What is the ideal number of meals per day ? 3. What is the advantage of cooked food over raw food ? 4. What is the harm of eating between meals ? 5. What is the objection to drinking water with meals ? 6. Why can we not eat concentrated food, like pure sugar, pure fat, and so on ? 128. When to eat. A young infant eats but a little at a time, the food is liquid and quickly digested and absorbed, and the child is soon hungry again. Some people have relatively small stomachs, which cannot hold much food ; they may have to eat at shorter intervals than others. Some people can get all they need for one day in tv^o meals, v^ithout any discomfort, and many men and women have been quite healthy and happy wath but a single meal a day. In trying to find out the best rations for human beings, some experimenters discovered that they were in better working con- dition with only two meals a day than they were with three meals. The improvement may have been owing to the reduction in the total amount of food taken, or it may have been owing to the longer rest periods given the stomach. It is impossible to lay down fixed rules as to the number and regularity of meals, to suit all people and all conditions. On the other hand, it is just as unwise to avoid all regularity and eat whenever you happen to be hungry. 129. Cooking of food. The cooking of food has several dis- tinct uses : I. Cooking breaks up and softens the cell membranes of the plant and animal tissues used as food. This liberates the fats, proteins, and carbohydrates contained in the cells. 152 HYGIENE OF FOOD AND FEEDING 153 2. The heat makes the food more "tasty," adding to the pleasure of eating and causing the digestive juices to flow more freely in the mouth and stomach. 3. The action of the heat, with or without moisture, breaks up the starch grains, making them more easily digested. 4. The heat destroys bacteria and other microbes that may be present in the raw food. This reduces the danger of trans- mitting an infectious disease (see page 356). Cooked food is also more easily preserved against decay for the same reason. Valuable mineral matters are sometimes lost when the water in which food is boiled is thrown away. Prolonged heating of food, especially in the presence of air or of alkalis, may destroy some of the vitamins. Still, all parts of value can be preserved by skillful cooking. 130. How to eat. To some people, eating is one of the chief pleasures in life. To others, eating is a duty : if not exactly dis- agreeable, it is still not altogether a pleasure. It is a mistake to let ourselves get into either class if we can help it. 1. Emotions. We want to get the most out of eating, even from an organic point of view. Anger, fear, worry, and anxiety almost always interfere with the proper secretion of digestive juices and with the operation of the muscles of the stomach and the intestine. When you are greatly excited or distressed, you are apt to say," I cannot eat now" ; and it is just as well to omit the meal until your feelings are more composed. There is less danger of starvation than there is of indigestion. On the other hand, whatever arouses pleasant feelings, whatever puts us into good humor, helps to tone up the digestive organs. It is there- fore a wise custom to avoid unpleasant affairs before a meal. Pleasant conversation and good cheer are more helpful at meal- time than heated discussions or disputes. Even if the food it- self means little to us, we can make the meal a happy event and so get the most out of it in every way. 2. Relaxation. Rapid eating makes impossible the complete stimulation of the taste and smell nerves, necessary to bring about secretion of the digestive juices. Rapid eating makes 154 BIOLOGY AND HUMAN LIFE impossible a thorough mixing of sahva with the food and the breaking up of food particles so that the gastric (stomach) juices may reach the proteins properly. The time saved by eating too rapidly is generally paid for later by indigestion. 3. Water with meals. Many people have the notion that water must not be taken with meals or with fish or with some other particular kind of food. Experiments show, however, that a person can take a quart of water at a meal without any harm- ful results but, rather, with beneficial results. Probably none of us ever drinks too much water. On the other hand, it is not well to take water or any other fluid while there is solid food in the mouth. Softening the food in this way hastens the swallow- ing and prevents a thorough mixing of saliva with the food. Water should never be a substitute for saliva to soften the food or to aid in swallowing. Then the water should not be too cold. Ice water as an introduction to a meal should especially be avoided, since chilling the stomach is a decided handicap for the work that is about to be placed upon it. 4. Humanly speaking. Cattle and guinea pigs can be kept alive indefi- nitely on a monotonous diet of ''essentials." When the same thing is tried with human beings, they gradually lose those characters that dis- tinguish them from the cattle or the guinea pigs ; one of the things that drive men to drink and to drugs is the attempt to make them live like cattle. The cheapest diet is commonly recommended to people who have little of the pleasures of life and little time or training for enjoying the more refined forms of pastime and recreation ; but the comparatively simple pleasures of eating should not be denied to these people. 131. Constipation, The digested foods are absorbed for the most part by the villi of the small intestine (see section 115). The refuse remaining by the time the mass has passed into the large intestine is now subject to the decaying activities of bac- teria, which are always present in the food tube. There are thus produced substances which are poisonous if absorbed into the blood and distributed to the living cells of the body. The poisoning of the body by waste substances absorbed from the large intestine is sometimes called autointoxication, or self- HYGIENE OF FOOD AND FEEDING 155 poisoning. The most common symptoms of constipation (the clogging of the bowels with refuse) are the following: 1. Headaches, especially the kind of headache that seems to hammer at your temples when you bend over. 2. The "blues" — a feeling of general dissatisfaction and grouch when you know of nothing to give you cause for dissatisfaction. 3. Drowsiness, in spite of plenty of sleep within a few hours. 4. A certain ''tired feeling" when you have hardly done enough work to account for the tiredness. 5. Indigestion and loss of appetite. 6. A coated or "furred" tongue. There are many headache powders on the market, but they never cure people of their trouble. They generally depress the action of the heart so that the circulation is lowered, and you do not jeel the pain caused by the disturbance of these bowel poisons. The poisons, however, are still there, and more are being produced, whether you have a headache or not. The thing to do is to remove the cause of the trouble, not merely hide the damage from yourself. In a case of acute constipation one may obtain temporary relief by the use of a physic or an enema, but these should never be used as a regular thing. Our food should have enough bulk to leave a considerable amount of undigested material in the intestine. This bulk, ob- tained chiefly from coarse vegetables, such as cabbage, lettuce, and turnips, is sometimes called roughage, from the idea that this mass of coarse cellulose sweeps out the bowels. There should also be plenty of juicy fruit, fresh or stewed, for the laxative property of the salts and other substances. Since the chief cause of constipation is neglect of the bowels, the only real cure is the establishing of regular habits of empty- ing them. Mothers often try to get infants into regular habits, but many of them neglect the children when they are a little older. If regular habits are not established early, they are likely never to be fixed at all. It is certain that hundreds of thousands of people in this country suffer from constipation, and that there is no drug or medicine that will cure the disorder. 156 BIOLOGY AND HUMAN LIFE 132. The teeth and their care. One of the commonest causes of indigestion is found in decayed teeth. People with poor teeth get into the habit of swallowing the food without chewing it. Then they blame their stomachs or the cook for their miser- able feeling or even for the poor work they do. The structure of a human tooth is shown in Fig. 8i. The enamel is a hard protec- tive casing. Trouble with the teeth very frequently begins with the breaking of this enamel. The enamel can be cracked by sudden changes of temperature, or by grind- ing it against some hard sub- stance, as when you try to crack a nut with your teeth. Picking the teeth with a needle or some other hard body is also hkely to scratch the en- amel and thus to open the way for further damage. In the food that we eat there are many bacteria, of many kinds. In particles of food that cling to the teeth these bacteria begin their digestive activities (see Fig. 73). Some of the substances thus produced act upon the enamel, dissolving away this protective cover. Gradually a cavity becomes larger and deeper until it reaches the pulp and the nerve becomes exposed.^ ^In recent years it has been found that many serious disorders in various parts of the body may result from a sick condition of the teeth. Studies on patients and experiments with animals have shown that when the root of a tooth is abscessed (infected with certain kinds of bacteria), living bacteria and the poisons which they produce can be carried by the blood to remote parts of the body and there set up local but serious disturbances such as rheumatism of the joints, inflammation of the heart, kidney disease, or ulcers of the stomach. Fig. 81. Structure of mammalian teeth A, human grinding tooth, showing central pulp cavity (a), containing nerves and blood vessels and surrounded by dentine (b). The crown is covered with enamel (c), and the root with cement (d). B, gnawing tooth of rabbit, which grows from below as fast as it wears away at the tip. The dentine wears away faster than the facing of hard enamel, thus keeping the chisel edge sharp HYGIENE OF FOOD AND FEEDING *i57 A thorough cleaning of the teeth at frequent intervals thus becomes necessary. The most reasonable time to clean the teeth is immediately after each meal. If you get the habit of doing this, it will postpone the rotting of the teeth a good many years. Unfortunately business hours are so arranged that most grown- ups cannot manage to look after their teeth after each meal. The best time for brushing the teeth, if it can be done but once a day, is just before retiring, that the bacteria may not continue their destructive activities during sleep. The best cleaning material for the teeth— as for the skin or for clothes — is a good white soap. If you buy a dollar's worth of tooth paste or powder, you get several cents' worth of soap, together with some cheap perfume and a little powder added to scrub. The perfume does not help to keep the teeth clean, and it has been questioned whether the abrasive or scrubbing powder does not do more harm than good. If we begin with the younger children, we shall find that they can quickly learn to use plain soap on the toothbrush and do not need the fancy-smelling pink addition to make toothbrushing an agreeable habit. In brushing the teeth the motion of the brush should be up and down, so as to reach all the spaces. If you brush crossways, the depressions along the edges of the teeth will not be reached at all. In setting out to fix a toothbrush habit, it is well to re- member that the back teeth and the inner faces of the teeth need to be considered as w^ell as the fronts of the front teeth. 133. Health habits. We have seen that we have no direct control over the workings of the digestive system. We must therefore establish habits at the few points where we have in- direct control. The first point has to do with eating, and the establishment of suitable eating habits should be our first con- sideration. The second point at which we have control of the digestive system is in the establishment of habits related to the behavior of the large intestine. And, finally, there are certain general habits of exercise and breathing and sleeping which, on the one hand, are largely under our control and, on the other hand, have an influence on the digestive system : 158 BIOLOGY AND HUMAN LIFE 1. The selection of food (see page 141). 2. The avoidance of food materials that are personally undesirable, however suitable they may be for others. 3. The avoidance of special sauces and spices as stimulants to the appetite. 4. The observance of fairly regular hours as to eating. 5. Leisurely attitude toward the meal. This would include the taking of a few minutes of rest before eating, when tired, as well as the avoid- ance of rushing off to work or to play after eating. 6. The establishment of a pleasant frame of mind for the meal, as well as other agreeable surroundings, whenever possible. 7. Thorough mastication of the food before swallowing. This does not mean counting the number of bites that you put into every mouth- ful ; it means having the habit of chewing until the mass in the mouth is in a nearly fluid condition, so that it fairly ''swallows itself." 8. Drinking plenty of water — before meals, between meals, as well as at meals, and before retiring — but never using it (or any other liquid) to "wash down" food in the mouth or to take the place of saliva for softening food. 9. Where outdoor work with the large muscles is not a part of the regular program, exercising (out of doors if possible) a certain amount every day. 10. Deep breathing, through the nose, not a few breaths now and then, but as a regular thing, all the time. 11. Plenty of sleep every night. This is better than sleeping a little most nights, in the hope of raising the average by sleeping later on Sun- days or holidays. 12. Emptying the bowels every day, as nearly as possible at a fixed time, QUESTIONS 1. What is the relation between pleasant feeling and the work of the digestive system ? 2. What besides digestion is influenced by our emotions ? 3. What are the advantages of jumping right into your work or play immediately after a meal ? the disadvantages ? 4. What are the advantages of softening the food with water or milk? the disadvantages? 5. What are some of the common causes of constipation ? How can they be avoided ? HYGIENE OF FOOD AND FEEDING 159 6. What are some of the symptoms of constipation ? How can they be overcome ? What is the advantage of hiding symptoms ? 7. What are some of the effects of constipation ? 8. What is the difference between curing constipation and curing the symptoms ? Which is preferable ? W^hy ? 9. What is the difference between curing constipation and preventing it ? Which is preferable ? W^hy ? How would you do it ? 10. In what different ways are the teeth related to health ? 11. How can diseased teeth cause trouble in other parts of the body? 12. What is the best way to keep the teeth whole and sound ? REFERENCE READINGS Hough and Sedgwick. The Human Mechanism, chap, xix, The Hygiene of Feeding; pp. 398-402, 404-405. WiNCHELL, Florence E. Food Facts for Every Day, chaps, vii and viii. Fanners' Bulletin 1374, Care of Food in the Home. United States Department of Agriculture. Bulletin 637, Method of Calculating Balanced Rations. United States Bureau of Education. Bulletin 37 (1921), Malnutrition and School Feeding. Public Health Reprint 895, A Study of the Treatment and Prevention of'Pellagra. Public Health Reprint 707, Importance of Good Teeth and Prevention of Decay. Public Health Reprint 622, Children's Teeth, a Community Responsi- bility. American Medical Association. Nostrums and Quackery, ''Food Tonics," p. 468; ''Headache Cures," p. 494. CHAPTER XV THE AIR Questions. 1. What has breathing to do with life? 2. How long can one go without breathing ? 3. Are all parts of the air necessary for life ? 4. Do all animals need the same amount of air ? 5. How do fishes breathe ? 6. Have whales lungs or do they breathe like fishes ? 134. Air and life. The atmosphere has approximately the composition shown by the diagram in Fig. 82. When air is shut off, we suffocate, as in drowning. Now, what is the con- nection between air and being alive ? This question has already Nitrogen 78jJ + Carbon dioxid, less than 0.1 5S Fig. 82. Composition of the air The air consists of several gases. The exact proportions of these gases are constantly changing. The most important of the gases are oxygen and carbon dioxid, but nitro- gen is the most abundant been answered in part (see section 76) by the statement that the energy of protoplasm, in all its activities, comes from the burn- ing, or oxidation, of materials derived from food. The food is not burned directly, like the gasoline in an engine ; it first under- goes many changes (digestion, assimilation) and becomes a part of the living protoplasm. Nor is the oxidation, or burn- ing, like the familiar flame : it takes place only in the presence of water, whereas the fires with which we are familiar cannot be kept up under water. The nearest thing to the oxidation in protoplasm that is familiar is the rusting, or oxidizing, of iron, 160 THE AIR i6i which also takes place in water. Protoplasm oxidation probably depends upon the action of special ferments, or enzyms (see section 105). (i) It involves (a) material that can act as fuel, and ib) oxygen. (2) It results in the formation (a) of carbon dioxid (since all the fuel contains carbon), (b) of water (oxid of hydrogen, since all the fuel contains hydrogen), and (c) of other oxids, depending upon the character of the fuel. The familiar fires give off heat and light. Oxidation in protoplasm may also re- sult in other forms of energy. Some of these are motion (as in muscles), electricity, and the peculiar processes that are confined (so far as we know) to nerve and brain cells, such as thinking, wish- ing, suffering, enjoying. 135. Cell respiration. In an engine the oxidation takes place in the fire box or the cylinder. In a living plant or animal oxidation takes place in every single cell. In plants and animals that consist of very many cells the innermost cells are too far from the surface to get their oxygen directly from the surrounding air or water in this manner. In such cases the air either diffuses through special spaces (in plants) or special tubes (in insects: see Fig. 7), or it travels in a solution (blood) that reaches all parts of the body. In every case, then, the protoplasm of the individual cell ( i ) gets Fig. 83. The human lungs The arrows show the course of air from the outside, m, mouth; «, nostrils: p. pharynx: /, laryrLx; t, trachea; b, bronchi. The right lung is shown cut open; the bronchi branch again and again, the last tubules ending in delicate expansions, a, the air cells, or sacs; epi, the epiglottis, which closes over the air pipe when food passes from the pharynx to the esophagus, e l62 BIOLOGY AND HUMAN LIFE its oxygen from its immediate neighbor- hood, and (2) discharges its carbon dioxid and other products of oxidation into its immediate surroundings. 136. Breathing in man. Breathing, or respiration, means a process of gas ex- change — taking in oxygen and giving off carbon dioxid. It makes oxidation pos- sible. In man (as, in fact, in all back- boned animals except fishes and the young of amphibians) air is taken from the outside into the lungs (soft bags sus- pended in the thorax, or chest cavity), and carbon dioxid is discharged to the exterior from the same organs (see Fig. 83). The lungs consist of air sacs (which are lined with a layer of thin- walled cells and surrounded by very fine blood vessels) and air tubes (see Fig. 83 ) . The filling of the air sacs with fresh air and the emptying of the lungs are brought about by the action of (i) mus- cles attached to the ribs and (2) a large muscular organ called the diaphragm (di'a fram). This separates the chest cavity from the abdominal cavity (Fig. 84). When the muscles of the ribs and of the diaphragm relax, the chest cavity shrinks ; this forces the air out of the lungs. By contracting the muscles of the ribs and the diaphragm we force the chest cavity to enlarge, reducing the pressure in the lungs and drawing air into them. Inspiration and expiration, the two movements of air in respiration, are thus brought about by the alternate ex- pansion and contraction of the thoracic cavity. There are sev- Fig. 84.The movements of breathing in man When the muscular parti- tion(called the diaphragm) between the chest cavity and the abdominal cavity is pulled down, the chest cavity is enlarged. When the ribs are raised, the chest cavity is also enlarged. The rib muscles and the dia- phragm normally work in unison, alternately expand- ing and contracting the chest cavity. The shaded portion of the diagram shows the expanded con- dition — ribs raised and diaphragm lowered THE AIR 163 t^^ to o o Lung cell or air sac eral steps between the outside air and the Hving cells ; these are pointed out in the diagram (Fig. 85). 137. Control of breathing. When you wish to do so, you may hold your breath for a minute or two, or modify the rate and manner of breathing in other ways. Nevertheless our everyday breathing is an unconscious and involuntary proc- ess. The way you breathe is a mat- ter of habit; the best control comes from establishing sound habits.^ We need to practice correct breathing constantly rather than take special exercises to make up for bad habits. There are three points in regard to which faulty breathing habits are very common. I. Mouth breath- ing. For several reasons we should acquire the habit of breath- ing through the nose rather than through the mouth (see Fig. 86) . a. By means of the slimy mucus secreted by the lining of the nostrils and by means of the hairs in the front part of the nos- trils the dust particles are filtered out of the air we breathe. CO, Fig. 85. External and internal respiration The external respiration of the body consists of (i) the muscular movements of the ribs and the diaphragm; (2) the air movements into and out of the lungs; and (3) the osmotic movements of the gases into and out of the blood, through the linings of the air sacs. The inter- nal respiration of the body cells consists of the exchange of gases between the cells and the blood or lymph ^The rate of breathing is controlled automatically from certain nerve centers, which are influenced by the proportion of carbon dioxid in the blood. When you run fast, or exert yourself in some other way, the gas exchange in the lungs (and so the gas exchange in the blood and in the working cells) is increased; when you lie still, the gas exchange is reduced. 164 BIOLOGY AND HUMAN LIFE b. The long, narrow nose passages warm the air before it reaches the more delicate lining of the air pipes of the lungs. c. The appearance of a mouth breather is unattractive. d. Mouth breathing leads to snoring, which is due to the vibration of the soft palate by a current of air coming from the pharynx through the nose. People do not snore while awake ; during sleep the muscles of the mouth and the palate relax, and the moving air sets up a vibration of the hind palate. A frequent cause of mouth breathing is some obstruction in the nasal passage. The most common obstruction is an outgrowth of the lin- ing in the hind nostrils, called an adenoid growth (see Fig. 87). Such a growth is a handicap to a child, since it interferes with proper breathing and sometimes with the cir- culation of blood in the head. 2. Deep breathing. Some of the air sacs Fig. 86. Expression of face associated with adenoids The open mouth, the sleepy eyes, the strain about the nose, are results of defective breathing due to obstructions in the rear air passages of the nose, (From a photograph by Jessie Tarbox Beals) of the lungs (especially those in the upper corners) can be ventilated only by forced breathing ; and it is in these very parts that tuberculosis of the lungs most frequently begins. It is desirable that all the air sacs be completely filled from time to time. Vigorous exercise of the large muscles of the arms and legs and trunk will auto- matically force deeper breathing. Those of us whose occupa- THE AIR i6s tions do not regularly compel deep breathing should make out- door games a part of our program. Outdoor playing is certainly better than special exercises in breathing, and a healthy pro- gram of play and work will give a lung capacity proportioned to our needs. 3. Posture. It is impossible for the air to reach all the cor- ners of the lungs if the shoul- ders are curved over or forward. The shoulders must be kept back to give the chest a chance to expand freely. However, good posture is not merely a matter of correct form; it is closely related to a person's spirit or attitudes (see Fig. 143 ) . It is probably true that in most cases a boy or girl w^ho stands up to the w^orld joyfully and courageously will automat- ically (i) maintain correct posture, (2) breathe correctly, and (3) use the voice correctly. In many cases, however, we get into bad habits early in life, and these have to be corrected. Moreover, in many cases the lack of joy or of courage probably results from defective posture brought about by neglect during the early years. At any rate, breathing and many of the other important bodily functions are closely related to the individ- ual's state of mind, and all have to be right together. 138. Clothing. Clothing that cramps the ribs or the waist restrains proper breathing. Tight corsets and belts do not cause one to suffocate, but they do prevent one from breathing deeply, using the diaphragm as well as the rib muscles. Tight lacing is likely also to have an injurious effect upon the liver, the stomach, and the intestines. Fig. 87. Adenoid growths In the passage between the nostrils and the pharynx, p, shapeless masses of tis- sue, a, sometimes grow out, obstructing the movement of air from the nose and leading to mouth breathing. When ade- noid growths are present they should be removed bj^ a physician. The operation is simple and safe. I is the larynx, or voice box i66 BIOLOGY AND HUMAN LIFE THE AIR 1. Composition of the atmosphere Nitrogen, 78 + % ; oxygen, 20 % ; 2. Relation of air to life Oxidation of protoplasm Yields energy Heat Motion Chemical action Electricity Light Nerve and mental energy Comparison with other oxidation 3. Respiration In one-celled organisms Income Outgo carbon dioxid, o.i — % Human breathing system Structure Lungs Connections with outside Connections with body cells Breathing habits and control Mouth breathing versus nose breathing Removal of dust etc. Temperature Disagreeable appearance Disagreeable sounds Adenoids What they are How they influence breathing 10 Products of oxidation Carbon dioxid (COg) Water Urea (Other oxids) In many-celled organisms Income Special openings Special tubes Distribution Blood and lymph (Tracheae in insects) Gathering of oxids Outgo Process of breathing Action of diaphragm Action of rib muscles Effects upon air currents Deep breathing Posture Related to breathing Related to attitude Exercise Clothing THE AIR 167 QUESTIONS 1. How can we show that air is necessary to keep a fire going? 2. How can we show that a fire gives off water and carbon dioxid ? 3. How can we show that the lungs give off water and carbon dioxid ? 4. Why should you expect a pound of insect protoplasm to use up more oxygen in an hour than a pound of earthworm protoplasm ? 5. Why is it difficult for a person to do his usual amount of work on a very high mountain ? 6. How should you expect a decrease in the atmospheric nitrogen to influence living things ? 7. How does the gas exchange in a one-celled animal (the ameba, for example) resemble the gas exchange in a one-celled plant (green slime, for example) ? How does gas exchange differ in the two organisms ? 8. How does gas exchange in a one-celled animal resemble breathing in man ? How do the two differ ? 9. How does breathing in man resemble breathing in an insect ? How do they differ ? 10. How can you show that posture is connected with a person's mental state ? What use is sometimes made of this fact ? REFERENCE READINGS Hough and Sedgwick. The Human Mechanism, chap, x, Respiration. Fisher and Fisk. How to Live, pp. 18-28. CocKERELL, T. D. A. Zoology, chap, v, Respiration. CHAPTER XVI HYGIENE OF RESPIRATION AND VENTILATION Questions. 1. Why is outdoor air better than indoor air ? 2. Why does dry air feel colder than moist air ? 3. What is the harm in breathing through the mouth ? 4. Is it bad to run until you are out of breath ? 5. Why are drafts dangerous ? 139. Ventilation and its problems. Every breath we take re- moves from the air a certain amount of oxygen and replaces it with carbon dioxid. In order to keep up the working power the body must be supplied with enough air to furnish the needed oxygen and to carry away the excreted carbon dioxid. Of course it is not necessary to change all the air in a room for every breath. It is safe to use air in which the amount of carbon dioxid has been increased from about three or four parts in 10.000 (what it is in ordinary outdoor air) to 6 parts in 10,000, or even much more (see Fig. 88). How much fresh air should be supplied for each person in a school or factory ? Re- cent experiments show that under ordinary conditions the air contains neither a "breath poison" nor a dangerous amount of carbon dioxid, even when the ventilation is decidedly bad. Nor is there danger that the proportion of oxygen will fall below a safe limit. The chief problems of ventilation are (i) to keep the air at a suitable temperature, (2) to regulate the moisture and dust in the air, and (3) to keep the air in motion. I. Temperature. The temperature of the air in a living room, schoolroom, or workshop should be kept as nearly as possible at 65° F. At this temperature the internal temperature of the body or blood remains fairly constant (at about 98^° F.) through the steady radiation of heat from the surface and through the evaporation of water. As the temperature rises we remain comfortable by increasing sweat or perspiration and 168 HYGIENE OF RESPIRATION AND VENTILATION 169 evaporating more water from the skin. At 70° it begins to be uncomfortable and to affect the efficiency of our work. 2. Moisture. The more moisture there is in the air, the slower the evaporation will be, and the more heat the body will retain. The lower the humidity, the more rapidly will water evaporate, and the more rapidly will the body lose heat. A hot, stuffy room interferes with breathing and comfort because it interferes with the radiation of heat and evaporation of water in the lungs. Ordinary air Carbon dioxid 0.03"^, Expired air Nitrogen 78.09 5« Carbon dioxid 4.1 i Fig. 88. Effect of breathing on the air The ratio of oxygen to carbon dioxid is changed from 700: i to 4: i The advantage of large spaces in workshops and other places where people are likely to be crowded together is that they make it possible for the heat and moisture given off by the body to be removed fast enough to insure comfort. The amount of oxygen or of carbon dioxid seems to have nothing to do with the diffi- culties of suitable ventilation. The drowsy effects of a badly ventilated room are due to the conges- tion, or crowding, of the skin capillaries with blood and the corresponding lack of blood in the brain and the muscles. In the Black Hole of Cal- cutta, in which so many people lost their lives, the victims were supposed to have died from lack of oxygen. It seems more likely that in such cases death really results from heat stroke, due to the excessive humidity (from the perspiration and lung transpiration of the people) and the high temperature (from the heat radiated by the bodies). 1 70 BIOLOGY AND HUMAN LIFE In artificially heated houses there is often danger of having the air too dry, since the air coming from the outside contains but a fraction of the moisture which it may hold after it be- comes warmed. Special efforts must be made to insure enough moisture. 3. Movement. The air next to the skin soon becomes saturated with moisture and nearly as warm as the body itself. If this air is allowed to remain next to the skin undisturbed, we soon become very uncomfortable. Where there are large rooms and windows, and not too many occupants in a room, the natural movement of the air will be sufficient (see Fig. 89). When many people have to be in a room, as in schools and work- shops (especially in winter, when arti- ficial heating is necessary and windows are likely to be closed), there is need of special attention to ventilation, and forced ventilation may become necessary. It is often found desirable to use an electric fan to insure movement of the air, even when there is no change in the amount or quality of the air. Many people fear drafts as though the mere movement of the air were dangerous. What is dangerous about a draft is the sudden chilling of the skin, with a resulting congestion of the blood vessels. In general, chilling the body lowers the resistance to infection (see page 339). By means of cold baths most of us can accustom the skin to react vigor- ously to rapid changes in temperature. 140. Suffocation and drowning. When the gas exchange in the air sacs of the lungs is stopped for several minutes, suffoca- tion takes place, and death may result. Suffocation may be due Fig. 89. Window ven- tilation in cold weather So long as weather per- mits, ventilation should be by means of windows, open at top and bottom for the freest possible circulation of air. In cold weather a window board placed under the lower sash pre- vents drafts and allows circulation between the sashes and the top HYGIENE OF RESPIRATION AND VENTILATION 171 to the replacement of air by some other gas, or it may be due to the exclusion of air. The replacement of the air in the lungs by water is called drowning. Breathing may also be stopped by a severe electric shock, which acts on a group of nerves that con- trol the breathing movements. Suffocation and drowning are commonly fatal, but in many cases life may be saved by prompt Fig. 90. Silvester method of artificial respiration — expanding the chest After drawing out the tongue and placing the patient on the back with a block or roll under the shoulders, to keep the chest raised and the head thrown back, kneel behind the head and grasp the arms just below the elbows. Draw the arms slowly backward over the head, and hold them there about one second and persistent action. It is necessary (i) to empty the lungs of the water or foreign gas and (2) to reestablish the breathing movements. When a person has been drowned, the first thing to do is to place the body, face down, in a position that will cause the water to flow out of the lungs. A child may be lifted by the feet. Breathing movements should be begun at once. 172 BIOLOGY AND HUMAN LIFE In the Schaefer method of artificial respiration the patient is laid face down, with the arms stretched forward beyond the head. The head is turned to one side and supported on a cloth. The operator kneels, straddling the subject's thighs and facing his head, and places the thumbs over the small of the back and the fingers over the lowest ribs. Then, by swinging forward and I Fig. 91. Silvester method of artificial respiration — contracting the chest After the arms have been held above the head about one second, push the elbows slowly forward and downward until they are in the position shown. Press the el- bows firmly against the chest and hold them there about one second, to drive all the air out' of the lungs. (Photographs and instructions, Figs. 90 and 91, from the United States Bureau of Mines) back, he alternately compresses and releases the chest at the rate of from twelve to fifteen times a minute. The movements should be kept up until natural breathing begins, but should not be given up in less than an hour. The patient's tongue should be pulled out and kept out, to prevent it from slipping back into the throat and obstructing the windpipe. HYGIENE OF RESPIRATION AND VENTILATION 173 The Silvester method of artificial respiration is shown in Figs. 90 and 91. In case of asphyxiation, or suffocation by gases or by electric shock, the same procedure should be followed, except that it is not necessary to take special steps for emptying the lungs. Under the supervision of the United States Bureau of ^Nlines squads of miners are instructed in the resuscitation, or reviving, of people who become asphyxiated by gases or by electric shock. This bureau conducted a series of experiments to de- termine which of the mechanical resuscitating devices was best, for various purposes. It was found that more reliance could be placed on quick action by men who understood how to establish respiration than on most of the machines. It is always safer to begin work by hand than to wait for the best machine. From experiments conducted on various animals we now know that our breathing is influenced by the amount of carbon dioxid in the blood. When you run for a while the muscle cells work harder and oxidize more sugar and use up more oxygen and give off more carbon dioxid. The excessive carbon dioxid in the blood acts upon certain nerves, which forces deeper breathing. That is why we breathe faster when we exert our- selves. A very useful application of these facts has recently been made. When a person is overcome by gases or fumes, air with a certain amount of pure carbon dioxid is forced into the lungs. This gas, acting in the same way as carbon dioxid that results from overexertion, forces deep breathing and so helps to restore normal breathing again. By this method firemen who had been suffocated at a fire were quickly restored so that they were able to go on with their work immediately. 141. Poisonous fumes. With the increasing use of internal- combustion engines, and especially of automobiles, there has come a serious danger of poisoning by carbon monoxid (CO). Like carbon dioxid (CO2), this gas combines with the red pig- ment of the blood corpuscles ; but, unlike carbon dioxid, it brings about chemical changes that are not reversed when oxygen is present. Every year many persons die as a result of 174 BIOLOGY AND HUMAN LIFE inhaling fumes in a closed or poorly ventilated garage, since this gas is produced when a motor is driven with insufficient air. 142. Summary on breathing and ventilation. It is only in recent times that we have found out the close connection there is between our breathing habits and conditions and our health, happiness, and efficiency. The most important details that have been discovered are the following: 1. Outdoor air is better than indoor air in every way. a. It is better for playing, even in the cold and rain ; suitable cloth- ing will make up for these. h. It is better for work, since a person can accomplish more in a given time when breathing outdoor than when breathing in- door air. c. It is better for health, even to sleep out of doors. 2. Nose breathing is in every way better than mouth breathing. a. Where mouth breathing is due to adenoids, these growths should be removed. b. Where mouth breathing is due to bad habits, these habits should be corrected. 3. Deep breathing is better than shallow breathing. a. Where shallow breathing is due to improper clothing, the cloth- ing should be changed. h. Where shallow breathing is due to habit, correct habits should be acquired through outdoor games, outdoor work, etc. 4. Ventilation is necessary not only to keep down the proportion of CO2 and to keep up the proportion of ogygen in the air, but also to (a) regulate the moisture, {b) regulate the temperature, {c) keep the air moving, {d) remove disagreeable odors, (e) re- move gases and fumes, (/) remove dust. 5. A person suffocated or drowned is not to be given up for dead be- fore every possible effort to resuscitate him has been made in vain. 6. Dust as a source of danger to the health of the body and to the lungs in particular is discussed more fully in Chapter XXXVI. a. Mechanical dust, soot, and smoke (including tobacco smoke) coat the lining of the air sacs and reduce the breathing surface. b. Hard dust may scratch the lining of the air sacs and thus in- crease exposure to infection. c. Dust carrying microbes is a direct source of danger. d. Chemical dust and fumes may poison the blood. HYGIENE OF RESPIRATION AND VENTILATION 175 QUESTIONS 1. How many cubic feet of air is there for each person in your schoolroom ? in the Hving room or dining room at home ? 2. Why is a kitchen at 70° F. Hkely to be more uncomfortable than a sitting room at the same temperature ? 3. How does stirring up the air add to the comfort ? 4. How does fanning help to keep cool ? 5. What are the disadvantages of stirring up the air ? 6. What is the difference between suffocation and drowning ? What difference should there be in the treatment ? 7. What is the difference between suffocating by carbon dioxid and suffocating by carbon monoxid ? 8. Why should the Bureau of Mines be concerned with resuscitation ? 9. What other pubhc agencies are concerned with reviving drowned or suffocated persons ? 10. What public agencies are concerned with keeping air properly ventilated in pubhc places ? REFERENCE READINGS Hough and Sedgwick. The Human Mechanism, chap, xxix, Ventilation; PP- 397-398, 402-404, 405-406. Fisher and Fisk. How to Live, pp. 7-14. Pubhc Health Reprint 753, Adenoids. Pubhc Health Reprint 854, Effects of High Temperatures and Humid- ities on Body Temperature and Pulse Rate. Supplement 2, Public Health Reports. Indoor Tropics. Pubhc Health Reprint 728, Treatment of Carbon-Monoxid Poisoning. United States Bureau of Mines. Technical Paper 82, Oxygen Mine Rescue Apparatus and Effects on Users. CHAPTER XVII DISTRIBUTION OF MATERIAL WITHIN THE BODY Questions. 1. Do all animals have blood? 2. Do all animals have hearts ? 3. Is the sap of plants the same as the blood of animals ? 4. How does blood help keep us alive ? 5. How can the blood of one person be made to work in the body of another (transfusion)? 6. Can the blood of one animal be transfused into the body of another ? 7. Why does the blood of some people clot more quickly than that of others ? 143. Transfer of materials in plants. All plants and animals except the very smallest have some way of distributing ma- terials between the surface and the inside cells, or between the different parts of the body. In most of the familiar plants one set of tubes or vessels carries water and dissolved salts from the roots, through the stems, to the leaves, and another set of vessels carries organic food from the leaves to other parts of the plant, where it is either used up in the growth of new organs or stored up, as in seeds or potato tubers. The two currents are inde- pendent of each other, consisting of different materials and be- ing without connections at any point (see section 97). 144. Blood. In most of the familiar animals the blood moves in a continuous stream. In the clams the blood contains a bluish substance, called hemocyanin, which easily combines with oxy- gen and thus carries oxygen obtained from the surrounding water by diffusion into the blood vessels of the skin and gills. In the earthworm the blood carries in solution a reddish sub- stance, hemoglobin, which behaves in the same way as hemo- cyanin. Among the backboned animals the blood has a more complex structure and flows in an elaborate system of vessels, driven by a pumping organ, the heart. Human blood consists of a colorless fluid, called plasma, and a number of small bodies, the corpuscles, floating in it (see Fig. 92). 176 MATERIAL WITHIN THE BODY 177 145. The plasma. The plasma consists chiefly of water. In it are dissolved various salts, organic substances derived from the digested food, a little oxygen and carbon dioxid, and sub- stances derived from various organs and tissues, some of them waste products. Not every drop contains all these materials, or all of them in the same proportion, for substances are constantly coming into the blood and other substances are passing out. While passing through certain organs the blood takes up, in addition to wastes, special chemical products that have pecul- (^^ ^^~^ /^'^^ (^^\ iar effects upon the organs ^o sJ'^'^S b vKvi^V and activities of the body. " ^ ^y^^^" <_>- For example, fronri the thy- pig. 92. Human blood corpuscles . Toid gland, a Y-shaped, spongy body Iving in front '\ ''"' more mmierous red corpuscles (about ^,L^ f fS 1 ' ' t ui ^ ^" diameter) in fiat and in edge view; 01 the larynx, the blood b, the less numerous white or colorless corpuscles, absorbs a substance that ^"^ leucocytes (some barely larger than the red has an important influence °"''' °^^'''' T""'' ^^"''' ^' ^^?^^ *" '''^^"" ^"^ , , , m moving stage; note granulations and nuclei upon the development and workings of the brain. From the pancreas the blood absorbs a substance that has an important influence upon the oxidation of sugars in the cells. In recent times it has been possible to prepare extracts of this substance (insulin) from the pancreas of other animals and to use it in overcoming the condition known as diabetes, in which sugars are insufficiently oxidized. From little bodies that lie next to the kidneys the blood absorbs two or more substances that influence the muscles of the blood vessels and that have some effect upon the nervous system. The amount of these materials is increased whenever strong feelings are aroused, as fear or anger ; and an increase of the amount in the blood causes the liver to put out more glycogen, which becomes available as fuel in the active organs. This seems to be the reason why a person can put out more energy when excited. The adrenin, as this substance is called, also in- terferes with the secretions and contractions of the stomach, so that di- gestion cannot go on happily during anger (see page 153), and it hastens the clotting of blood (see section 148). The products of a soft organ lying in the front part of the chest in young mammals, the thymus, are 178 BIOLOGY AND HUMAN LIFE distributed by the blood and have an important influence upon the growth of the animal. Another of these substances that affects growth is absorbed by the blood from a little body lying at the base of the brain, the pituitary. These various substances, or ferments, are sometimes called internal secretions, because they are absorbed by the blood directly from the tissues of these special organs, instead of coming out through ducts, or tubes, as is the case with the more familiar glands. These internal secre- tions are also called hormones. 146. The red corpuscles. These cells are found in all verte- brates. They contain hemoglobin, which combines chemically with either oxygen or carbon dioxid, according to which is more abundant. This makes the red corpuscle a gas carrier floating in the plasma (see Fig. 85). Red corpuscles, like the white ones, are really unattached cells. They originate by cell division of special cells in the marrow of bones. At first they have a nucleus, but this soon disappears.^ The older corpuscles go to pieces, and their hemoglobin is taken up by the liver and converted into part of the bile (see section 113). 147. The white corpuscles. We owe much of our understand- ing of the white corpuscles to the great Russian biologist, Elie Metchnikoff, who was director of the Pasteur Institute in Paris. Like Ameba (see page 59), these cells consist of naked protoplasm and have no fixed shape. Whereas the one cell of the ameba carries on all the functions of a living body, the various cells of a many-celled animal like an ant or a baby have specialized functions as well as specialized structures. Now the white corpuscles are in many ways the least specialized cells in the body. They have the general qualities of protoplasm in the greatest degree. I. As eating cells (or phagoc5rtes, which means ''eating cells," as they were called 'by Metchnikoff ) they are capable of flow- ing about or engulfing foreign particles with which they may come in contact. They may swallow and digest dead particles 1 Among vertebrates other than mammals the corpuscle retains its nucleus. MATERIAL WITHIN THE BODY 179 Water CO« resulting from the breaking down of tissue cells, as well as live cells that get into the blood from without, such as bacteria of various kinds. 2. As sensitive or irritable cells they may respond to a chemi- cal stimulation, such as the presence of various kinds of poisons, by producing substances capable of counteracting or neutral- izing foreign chemicals. 3. As moving cells they wander about from the lymph to the blood, or vice versa, and even into the intestines. In this way they carry with them dead matter to be thrown out, or they crowd together in large numbers and produce special sub- stances that counter- act a local chemical disturbance. Because of their peculiar behavior in the presence of for- eign substances and Urea L Y M P H Water Oxygen Sugar etc. BLOOD Protein etc. Salts L Y M P H Fig. 93. What goes through the wall of a capillary From the blood within the capillary, water, salts, food, and oxygen pass out by osmosis; from the sur- rounding lymph, carbon dioxid, urea, and water pass into the blood. White corpuscles work their way through the wall of the capillary, between the cells particles we have come to think of the white corpuscles as the most important agents of keeping the body in health, at least in relation to certain special diseases. White corpuscles are found in all animals that have blood, and they are very much alike in all, so far as general appearance and behavior are concerned. In our bodies the white corpuscles probably originate by the division of ameba-like cells in the bone marrow and in certain enlarged lymph spaces containing crowds of the white corpuscles. 148. Clotting of blood. When blood is removed from a blood vessel, whether it is taken out of the body or not, it usually be- comes clotted, or thickened. This clotting is brought about by the coagulation, or solidifying, of a certain protein in the plasma known as fibrinogen, which means "iibrin-maker," since the i8o BIOLOGY AND HUMAN LIFE Fig. 94. An X-ray view of arteries of the arm The arteries of a new-born baby (dead) were injected with a mixture that is opaque to the X-rays, originated by Dr. Eben C. Hill. The blood vessels reach all parts of the organ. (Courtesy of Johns Hopkins Bulletin) solidifying is in the form of fine fibers. The ferment that causes the coagula- tion becomes active when the lining of a blood vessel is injured ; possibly it is formed only at such times. At the mouth of a small cut this clot soon stops the bleeding, and it furnishes a protective covering until the wound is healed. 149. Serum. If blood is allowed to stand for a time in a glass vessel, we can see the mass of fibers detach them- selves from the walls of the vessel until the clot floats at last in a clear liquid which is al- most colorless or slightly yellowish. This clear liquid is called serum and is practically the same as blood plasma but lacking the protein fibrinogen. What- MATERIAL WITHIN THE BODY i8i ever is characteristic or distinctive of the plasma of an in- dividual or of a species will be found in the serum. 150. The lymph. The blood is confined to a set of tubes from which it cannot escape— as blood. The whole system is there- fore called a closed system. Outside the blood vessels, filling definite tracts as well as spaces between tissue masses and cells, is a colorless liquid called the lymph. It is jrom the lymph that the cells obtain their food supplies, water, salts, ferments, and oxygen ; and it is to. the lymph that they discharge their carbon dioxid, urea and other wastes, and any special substances that they may secrete. There is a definite connection between lymph spaces and certain large blood vessels. The main com- munication between the lymph and the blood is by osmosis through the smallest blood vessels (see Fig. 93). The lymph, like plasma or serum, consists chiefly of water, and carries prac- tically the same kinds of substances in solution. In addition the lymph has many white corpuscles floating in it, so that it may be considered the same as blood but lacking red corpuscles. 151. The heart and the vessels. The blood is kept moving by the rhythmic contractions of the pumping organ, the heart. Blood comes into the heart through vessels which are called veins ; blood flows out of the heart in tubes known as arteries. The arteries branch and divide again and again, reaching all parts of the body. The smallest branches, the capillaries, form a network, combining into larger and larger tubes and bringing the blood over from the arteries to the veins. Among warm-blooded animals (birds and mammals) the heart is a double organ: blood cannot pass directly from the right half to the left half. Each half of the heart consists of an upper receiving chamber and a lower pumping chamber (see Fig. 95). The left heart is somewhat larger and stronger than the right heart. Its ventricle, or pumping chamber, closes up, or con- tracts, at fairly regular intervals, forcing the contained blood into the largest artery of the body, the aorta. The branches of the aorta carry the blood on to the various organs and tissues. The auricle, or receiving chamber, of the left heart is connected l82 BIOLOGY AND HUMAN LIFE with a large vein that brings blood gathered from the capillaries of the lungs. The opening between the receiving chamber and the pumping chamber is guarded by a set of valves that prevents the blood from flowing back when the ventricle contracts. An- other set of valves prevents the blood from flowing back from the aorta into the ventricle when the latter expands again. The left heart thus pumps blood re- ceived from the capillaries of the lungs into arteries all over the body. The right heart receives blood into its auricle from two large veins, and passes it into the ventricle, or pumping chamber. The auricle and the ventricle on the right side are con- nected, as are the corre- sponding chambers on the left side, with a valve that prevents the back-flow of blood when the ventricle contracts. The right ven- tricle pumps blood into a large artery {pulmonary artery) that carries it to the capillaries of the lungs. The right heart pumps blood re- ceived from all over the body to the capillaries of the lungs. 152. The double circulation. The stream of blood makes two circuits: (i) from the heart (left) through arteries, capillaries, and veins of the body and back to the heart ; (2) from the heart (right) through arteries, capillaries, and veins of the lungs and back to the heart (see Fig. 96). The blood-stream may be traced from any point and back to the start only by passing through the two sides of the heart, through the pulmonary, or lung, circuit, and through the systemic, or body, circuit. Thus, Fig. 95. Diagram of the human heart aa, receiving chambers, or auricles; bb, pump- ing chambers, or ventricles; cc, main veins, bringing blood to the heart; dd, main arteries, carrying blood away from the heart; //, valves, preventing back-flow from arteries to ven- tricles; between a and b, valves preventing back-flow from ventricles to auricles MATERIAL WITHIN THE BODY 183 beginning, for example, in the capillaries of the hand, the blood flows into the veins and is gathered into larger and larger vessels, reaching the right au- ricle. From this it goes to the right ventricle ; and when the latter contracts, the blood is forced into the pulmonary artery. The lung arteries di- vide into smaller and smaller branches, the smallest being the capillaries that lie under the lining of the air sacs in the lungs. As the blood flows on, it is gathered into larger and larger veins that unite to form the pulmonary vein, which empties into the left auricle. From the left auricle the blood goes to the left ventricle, and from this it is pumped into the aorta. An artery branching from the main artery carries blood into the arm, and as the arteries divide, becoming smaller and smaller, we at last reach the capillaries in the hand, from which we started. This "double circulation" makes possible a rapid ex- change of carbon dioxid for oxygen. In the human body all the blood passes through the heart (and therefore through the capillaries of the lungs) once in from twenty- three to thirty seconds. The exchange of gases in the air sacs of the lungs has already been described (see Fig. 85). Fig. 96. The "double circulation" of the blood The arrows indicate the direction of blood flow. The shaded portion represents blood lacking in oxygen. From the right heart (shaded) the blood passes to the lungs, from which it returns to the receiving chamber of the left heart with its car- bon dioxid replaced by oxygen. From the pumping chamber of the left heart the blood passes to all parts of the system, or body, and returns to the receiving chamber of the right heart with its oxy- gen replaced by carbon dioxid i84 BIOLOGY AND HUMAN LIFE 153. Changes in the blood. While in the capillaries of the various tissues of the body the blood absorbs from the surround- ing lymph (by osmosis) carbon dioxid, urea, and other sub- stances that are present in relatively large proportions (that is, compared to their concentration in the blood plasma) ; and by the same process it loses food materials, salts, oxygen, and fer- ments that are relatively more abundant in the blood than in the surrounding liquids. In certain parts of the body additional changes take place in the composition of the blood. In the intestines, for example, much of the digested food is absorbed into the blood. In the kidneys much of the urea, salts, and other waste substances is taken from the blood. DISTRIBUTION OF MATERIAL WITHIN THE BODY 1. Comparison of one-celled organisms with many-celled organisms regarding relation to environment Income ; outgo 2. Comparison of plants and animals regarding means of distributing material The two kinds of sap in plants and the two kinds of vessels The blood in animals 3. Composition of mammahan blood (including human blood) Plasma Corpuscles Water White Dissolved nutrients Eating cells (phagocytes) Dissolved salts Moving cells Dissolved gases Irritable cells Ferments (hormones) Red Fibrinogen Gas carriers (hemoglobin) 4. Clotting of blood Fibrin formation Conditions of clotting How it takes place Cut or bruise of capillaries Possible uses to organism (Some diseased conditions) Remaining fluid (serum) 5. The lymph Its character Its composition Its functions MATERIAL WITHIN THE BODY 185 6. The pumps and the pipe-Hnes of the blood system Structure of the heart Vessels Chambers Out-carrying (arteries) Receiving (auricles) In-carrying (veins) Expelling (ventricles) Crossover (capillaries) Valves Between chambers on same side Between ventricles and outlets 7. The circulation Systemic Pulmonary Left ventricle Right ventricle Aorta Pulmonary arteries Systemic arteries Pulmonary capillaries Systemic capillaries Pulmonary vems Systemic veins Left auricle Right auricle 8. Loading and unloading the blood-stream At what points the blood takes on what it carries At what points the blood throws off what it carries Nutrients Oxygen Hormones Water Carbon dioxid Urea Salts QUESTIONS 1. How does the fibrovascular bundle of a plant show division of labor ? 2. How are the various functions of our blood system carried on by a one-celled plant or animal ? 3. What is the appearance of a red blood corpuscle under the micro- scope ? of a white corpuscle ? 4. How does the white corpuscle obtain its food and oxygen ? 5. In what ways is the blood plasma like serum ? In what ways is it different? 6. How does serum resemble lymph ? How do the two differ ? 7. What are the similarities between lymph and plasma ? What are the differences ? 8. What work is done by the upper chambers of the heart ? by the lower ? 1 86 BIOLOGY AND HUMAN LIFE 9. What work is done by the right chambers of the heart ? by the left? 10. What changes take place in the blood while it is passing through the capillaries of the intestines ? of the lungs ? of the muscles of the arm ? 11. How does the blood in the pulmonary veins differ from the blood in veins leading from the brain ? 12. How does the blood in the pulmonary arteries differ from the blood in the pulmonary veins ? in muscular veins ? 13. How does the blood in the arteries going to the brain differ from that in the veins leading from the brain ? 14. How is the work of the heart carried on in a tree ? REFERENCE READINGS Bergen and Caldwell. Practical Botany, pp. 78-80. OsTERHOUT, W. J. V. Experiments with Plants, pp. 224-258. BiGELOW^, M. A. Applied Biology, pp. 53-55, 482-486. Hough and Sedgw^ick. The Human Mechanism, pp. 13 5-1 51. Parker, George H. Biology and Social Problems, lecture on Hormones. Public Health Reprint 896, Importance of our Knowledge of Thyroid Physiology. CHAPTER XVIII HYGIENE OF THE BLOOD AND THE CIRCULATION Questions. 1. How can nosebleed be stopped? 2. How should bleed- ing from a wound be stopped ? 3. Why does the doctor feel the pulse ? 4. Why does the doctor listen to the heart ? 154. The health of the blood. The condition of the blood de- termines the life conditions, and so the health, of all the cells and tissues of the body. To keep the blood in suitable condi- tion we must supply it with plenty of water, with suitable food in right quantities, with necessary salts, and with oxygen ; and we must give the blood a chance to get rid of carbon dioxid and the other waste substances that it gathers from all parts of the body. This is but another way of saying that we must eat properly, breathe properly, exercise properly, rest and sleep properly, and so on. There is no special food for the blood. The blood is the medium through which the food of the body is con- veyed from the food tube (digestive tract) to the living cells. There is no special way of breathing or exercising for the sake of the blood. The body behaves as a whole, and the blood is one of the means of unifying the many different parts. At the same time it is true that the body may be injured by way of the blood, just as it may be injured by way of the mouth or the lungs. 155. Cuts and wounds. Small wounds will usually stop bleed- ing because of the clotting of the blood (see section 148). For- merly the festering of sores and cuts was looked upon as a normal and necessary condition of healing. Now we know it to result from the action of various kinds of microbes, some of which, at least, produce serious blood poisons (see page 303). To prevent the festering of a wound, and to prevent the invasion of the body by more injurious microorganisms, it is well to treat 187 i88 BIOLOGY AND HUMAN LIFE every cut with an antiseptic, or sterilizing, solution. Tincture of iodin or alcohol or carbolic acid or bichlorid of mercury may be used. The cut should then be covered with clean cotton or gauze, to prevent the entry of microbes. With large wounds it is sometimes necessary to use special means to stop the bleeding. If the flow of blood is too strong, it may prevent the clot from holding to the sides of the wound. Fig. 97. Treating a cut When the pressure of the thumb is not sufficient to compress the blood vessels and stop the flow, a tourniquet may be used, made by tying a handkerchief about the limb and twisting it tight by means of a stick slipped under the handkerchief. Of course, the tourniquet or the bandage applied in this way is to be considered an emergency measure, and steps should be taken to have the wound attended to by a physician When the flow is from an artery (which can usually be recog- nized by the pulsation), the limb should be tied above the cut, that is, on the side toward the heart. When the flow is from a vein, the attempt to stop the flow should be made on the side away from the heart (see Fig. 97). 156. Nose bleeding. In very many cases nose bleeding can be stopped by snuffing cold water. The old-fashioned remedy of HYGIENE OF BLOOD AND CIRCULATION 189 dropping a key down the person's back rested on the fact that the sudden chill causes the capillaries to contract. A piece of ice applied for a few moments to the back of the neck will be more likely to have the desired effect. Where bleeding con- tinues after such simple treatment it is probable that some small artery has been broken, or that the person's blood is in- capable of clotting. An astringent is then advisable. Powdered alum, tannin, or ferric chlorid may be applied on a tuft of cot- ton. These substances cause the fine blood vessels to contract, and thus stop the bleeding. In extreme cases a physician will use adrenin, an extract of the glands lying close to the kidneys (seepage 177). 157. Increase in heart disorders. For a number of years past the records show that there is a steady increase both in the num- ber of people who die as a result of some defect or failure of the heart and in the number of young people who suffer from some form of heart trouble. The reasons for this condition are not very clear. It is possible that one large source of heart trouble among young people is the fact that improvements in the med- ical arts have saved the lives of many boys and girls who would otherwise have been killed by various common diseases, such as scarlet fever and diphtheria. In many cases these diseases leave as an after-effect a more or less serious injury to the heart. Another source of heart trouble (besides the special dis- eases) is in the poisoning of the system by bacteria that do not cause special diseases. Decaying teeth, abscesses, and rheu- matism would come in this class. Tobacco is known to cause irregularity in the heartbeat in young people. There are also strains and overwork for many people, as well as unsuitable diet. Athletic enthusiasm in many cases leads to an over- training of the heart. As a result the heart is either too strong in proportion to the normal life of later years or leaves a need- lessly large area exposed to injury. Defects of the heart are of two types: (i) deterioration of the valves, usually resulting from some infection or disease; and (2) a deficiency in the muscle. 190 BIOLOGY AND HUMAN LIFE The veins and arteries are also subject to special disorders. Varicose veins are those in which the walls and valves have deteriorated, resulting in obstructions to the ready flow of blood toward the heart at these points. They are related to over- strain, and particularly to standing a great deal without suffi- cient exercise. Laundry workers and motormen show large numbers of cases, whereas letter carriers and others who walk about a great deal rarely suffer from this disorder. Hardening of the arteries is a more serious condition. It may be due to va- rious infectious diseases, to alcohol, to overwork, and to malnu- trition. In this condition the arteries lose their elasticity and so interfere seriously with the circulation of the blood ; and they are more easily burst by a sudden increase in blood pressure. 158. Care of the heart. Every contraction of the ventricles sends a wave of pressure through the blood in the arteries. The muscular and elastic walls of the arteries ^^give" somewhat to this pressure, and this is the pulse which can be felt in any artery near the surface of the body, as at the wrist, on the tem- ples, or directly in front of the ear. From the character of the pulse the physician can often tell a great deal about the work- ings of the heart and about the condition of the blood vessels. The pulse may be regular or irregular ; it may be strong or weak. A strong heartbeat would ordinarily increase the pressure of the blood inside the arteries ; but if the arteries are flabby, the additional work of the heart may fail to distribute the blood properly to all parts of the body. Cold feet and hands are an indication of inadequate circulation, but the cause of this condition may be in the heart or it may be in the blood vessels. In examining a person the careful physician, athletic direc- tor, or insurance examiner will always listen to the beating of the heart and examine the pulse and test the blood pressure. From the sounds of the heart he can tell whether there is a defect in any of the valves. A leaky heart has to do a great deal more pumping to keep the body supplied than a sound heart, since a portion of every stroke is wasted in pumping blood that goes back into the auricles. HYGIENE OF BLOOD AND CIRCULATION 191 A weak heart usually shows itself in breathlessness. If you cannot climb stairs, or take a brisk walk, or play a lively game, without getting out of breath, the trouble is more likely with your heart than with your lungs. In training for athletics one of the most important things is to acquire ^'wind," that is, the ability to continue severe exertions without losing breath. This is in fact a training of the heart, as well as a training in correct breathing habits. Under suitable directions one can strengthen his heart considerably by means of graded exer- cises in walking-, running, climbing, etc. Indeed, there is the possibility of overdeveloping the heart. But giving the heart occasional severe strain is not the same as training it for hard work. A person with a weak heart should not be engaged in work that strains this organ severely. HYGIENE OF THE BLOOD AND THE CIRCULATION 1. The relation of the blood to the health of the body SuppHes tissues with needed materials from outside Water ; food ; oxygen Removes wastes from living cells ; removes broken-down (dead) parts ; removes foreign particles Distributes materials produced in special parts (hormones) Counteracts foreign substances 2. The relation of different organs and organ systems to the healthy condition and effectiveness of the blood Food system Hormone system Breathing system (Nervous system) (Excretion system) 3. The pulse and sounds of the heart Cause of pulse Character of pulse under different conditions Meaning of pulse characteristics : soft ; irregular How '' leaky heart " is recognized Meaning of leaky heart 4. Treatment of bleeding Cuts and wounds Nosebleed From arteries How to stop bleeding From veins Precautions against infection 192 BIOLOGY AND HUMAN LIFE 5. Relation of exercise to blood system Exercise and appetite Exercise and circulation Exercise and breathing Exercise and heartstrain 6. Disorders of the blood system Heart defects Arterial defects Sources Lack of elasticity Infections Hardening (arteriosclerosis) Strains Venous defects Kinds Varicose veins Muscular Capillary defects Valvular Walls too thin Bleeding easily QUESTIONS 1. In what sense does the blood unify the body? 2. How can you tell whether the blood at a wound comes from the veins or from the arteries ? 3. How should you stop the bleeding from a w'ound on the face ? 4. What should you do to a wound besides stopping the bleeding? 5. Is a cut more likely to clot when a person is "fighting mad" or when a person is lying still ? Why ? 6. How does being chilly interfere with good brain work ? 7. What part does the blood play in the sick condition resulting from constipation? REFERENCE READINGS McCarthy, J. D. Health and Efficiency, pp. 125-134. Hough and Sedgwick. The Human Mechanism, pp. 152-165. Harrow, Benjamin. Glands in Health and Disease, chap, xi, The Influ- ence of the Ductless Glands on Growth and Metabolism. Williams, J. F. Healthful Living, pp. 235-251. Public Health Reprint 893. Methods of Administering lodin for Pre- vention of Goiter. Red Cross, Woodcraft, or Scout manuals for first aid. CHAPTER XIX ELIMINATION OF WASTES Questions. 1. Why does an organism produce substances that it does not need ? 2. Are excretions of protoplasm injurious to living things ? 3. Have all animals kidneys ? 4. Why does a physician sometimes ask for a specimen of the patient's urine ? 159. The origin of wastes in living things. Every chemical process results in the formation of substances that did not exist before. In metabolism (the chemical processes of protoplasm) some of the substances produced are related to keeping the pro- toplasm alive, for example, digestive ferments, and chlorophyl and other pigments. Incidentally, however, other substances are also produced, which may be of no use to the living body or to the living process. Some may even be injurious. Such sub- stances are called wastes and may be compared to the sawdust of a mill, or to the smoke that goes up the chimney, or to the coal tar of a gas factory. 160. Removal of wastes from cells. We have already seen (Chap. XV) that oxidation in protoplasm gives rise to carbon dioxid, water, urea, and other waste products. These diffuse out of the cell by osmosis. In our study of photosynthesis (sect. 83) we found that one of the wastes, or by-products, is oxygen, which diffuses out of the chlorophyl-containing cells through the cell walls. In plants water and carbon dioxid are thrown out, in the form of gas or vapor, from the parts exposed to the air. The carbon dioxid given off by the cells of the roots usually remains in solu- tion, forming so-called carbonic acid. Other wastes produced by plants are not generally eliminated from the body but are more likely to be locked up in cells, where they can do no harm to protoplasm. Among the waste substances thus accumulated 193 194 BIOLOGY AND HUMAN LIFE in plants are various kinds of pigments, insoluble crystals, tan- nins (commonly found in the bark of trees and in unripe fruit), various acids, and alkaloids, gums, and resins. The one-celled animals excrete their wastes directly into the surrounding water. In the higher animals, those that have blood and lymph, the wastes are diffused from the living cells into these conducting fluids and are then eliminated from the body through special organs. 161. The kidneys. In man and the other backboned animals the kidneys are the special excretory organs. Water and car- bon dioxid, as we have already learned (see page i6i), are ex- creted from the lungs, as well as small quantities of urea and possibly other organic substances. Some water, salts, and urea, with traces of other organic w^astes, leave the body by way of the sweat glands (Chap. XX) ; and a certain amount of waste matter gets into the intestine directly through the lining cells, in part by way of the white corpuscles (p. 179) and in part through the secretions of the liver. From the intestine these substances are removed, together with the refuse from the food, in the feces. But most of the wastes given off by the body cells are taken into the blood and filtered out by the kidneys. There are two kidneys, each about as long as the width of your hand and bean-shaped. They are located in the back of the abdominal cavity, a little lower than the stomach. The structure of the kidney is that of a gland, a mass of tiny tubules, branched and twisted, with a complex network of capillaries. The waste substances diffuse through the walls of the capillaries into the tubules, and the fluid (urine) is gathered by these tubules into a funnel-shaped hollow (see d, Fig. 98). 162. Hygiene of the kidneys. The kidneys work constantly, and their continuous operation is essential to the health of the body as a whole. The whole system would be quickly poisoned if the wastes were allowed to remain in the blood or the cells. Since the kidney removes wastes in solution, an abundance of water is a necessary part of the daily income. We can do little more toward maintaining the health of the kidneys than ELIMINATION OF WASTES 195 drink plenty of water and empty the bladder often enough to prevent discomfort, which is an indication of strain. On the other hand, we may do something indirectly through attention to our diet and our exercise and our general mode of living. An excess of proteins means an excess of urea to be filtered through the kidneys. Lack of exercise results in poor cir- culation, so that wastes re- main in the blood a long time. Bad breathing habits add to the load upon the kidneys. Alcohol causes congestion, or clogging, of the capillaries, and in the kidneys that means de- laying the removal of wastes. In short, keeping well or healthy is not the simple arithmetic of keeping a num- ber of organs in condition. Everything of importance affects the whole organism, although it may strike now at one organ and now at another. A generation ago every worker was allowed to quench his thirst in his own way, as best he could. The sale of beer and other prepared drinks concerned only the buyers and the sellers. Now, however, employers and managers of factories, shops, stores, and offices are finding it worth while to provide an abundance of clean, cool, and palatable drinking water. In some states the law requires that suitable drinking water be supplied in all work- rooms. In a similar way, the provision of suitable toilet rooms, Fig. 98. Kidneys and bladder a, the main artery, and b, the main vein, in the abdominal cavity, giving off branches to the kidneys cc; d, funnel-shaped cavity in \Yhich the waste fluid is gathered by the gland action of the kidney; ee, the tireters, tubes leading from the kidneys to the bladder /. From the bladder the urine is discharged at intervals through a tube leading to the exterior, the urethra. The left kidney is represented as cut through lengthwise 196 BIOLOGY AND HUMAN LIFE which was formerly considered a mere accommodation or con- venience, is coming to be recognized as a real necessity. The more progressive cities are also taking steps to provide suitable drinking water for all on the streets and in public places, as well as comfort stations for all who have to be abroad. Under ordinary conditions we give off a quart of water a day from the skin and lungs and about twice as much from the kidneys. In addition to the water that we take as part of our food, and drink with our meals, it is necessary to have access to water between meals ; and in warm weather or at hard work and play the amount must be further increased. 163. Excretions as health indicators. Our knowledge of the chemistry of metabolism and of the special processes that go on within the body has been increasing rapidly. It is now pos- sible to learn a great deal about the condition of the organism from an examination of the urine, the feces, and the perspira- tion and other fluids or products of the body. The amount of uric acid in the urine, the presence of carbohydrates or of albu- min, bits of cells revealed by the microscope, and so on, all in- dicate distinct facts about what is going on in various parts of the body, not alone in the kidneys; and such information is often of importance to the physician as a means of discover- ing diseased conditions that might not otherwise be suspected. When a person is examined by the physician of a life-insurance company, the urine is included because very often it contains the only sign that the organism is not in good working order. Many lives are being saved by systematically examining the urine and by guiding diet, exercise, etc. accordingly. ELIMINATION OF WASTES I. Wastes of an organism Sources Kinds Oxidation of protoplasm Carbon dioxid Other chemical processes Water Urea Other compounds (Oxygen in green plants) ELIMINATION OF WASTES 197 2. Excretion in one-celled organisms Materials How put out 3. Excretion in larger plants Through leaf ; through stem ; through root (Through locking up in inactive tissues) 4. The kidneys and bladder Structure Function Tubules and capillaries Elimination of wastes in Funnel liquid form Ureters Hygiene Bladder Water supply for body Urethra Elimination of urine 5. Importance of condition of urine as index of condition of body QUESTIONS 1. How do waste products originate in an organism ? 2. What waste products of metabolism are harmless to protoplasm ? What products are injurious ? 3. What organs in a one-celled plant are analogous to the kidneys ? 4. What are the advantages of taking all the water needed for the day at one drinking ? What are the disadvantages ? 5. Of what concern is it to the public whether stores and workshops provide suitable toilets ? REFERENCE READINGS McCarthy, J. D. Health and Efficiency, chap. xv. Hough and Sedgwick. The Human Mechanism, pp. 180-183. CHAPTER XX THE SKIN AND THE APPENDAGES Questions. 1. Why do people sweat ? 2. Why does the skin come to be tougher on some parts of the body than on others ? 3. What causes pimples ? 4. How can the complexion be kept clear ? 5. How often should one bathe ? 164. The functions of the skin. As a covering of the whole body the skin is a protective organ, shielding the delicate tissues underneath from many possible injuries. As the point of contact between the organism and the outside world it is sensitive to various changes. It is sensitive to touch (which has been called the mother sense), to heat and to cold, and also to light. Con- tact or pressure, heat, and cold affect the nerves of the skin so that we become aware of what is going on. Light, however, does not as a rule arouse consciousness ; yet we see its effect in tan and in the more painful sunburn. The skin maintains the temperature of the body (p. i68) by means of the sweat glands, through which water, salts, urea, and other organic wastes are excreted to the surface. The skin therefore serves four rather distinct functions: it is a protective, a sensory, a heat-regulating, and an excretory organ. 165. The structure of the skin and its outgrowths. The sur- face layer of the skin consists of dead cells (see Fig. 99 and Fig. 100). These horny cells are constantly rubbing off but are constantly being replaced by new cells from the live layer of dermis beneath. The skin is practically waterproof. Unless the epidermis is broken, it is also proof against the absorption of salts or poisons and against the entry of bacteria. Constant rubbing or pressure will cause the layer of dead cells to increase in thickness ; it is thus that we acquire corns and calluses. 198 THE SKIN AND THE APPENDAGES 199 Embedded in the dermis, or true skin, are several distinct kinds of structures having distinct functions. 1. Sweat glands. A sweat gland consists of a delicate tubule opening upon the surface of the skin at one end, the pore, and twisted or coiled into a clump at the other. Surrounding the coiled end is a network of very fine capillaries, from which the water and dissolved wastes diffuse into the tube (see Fig. loi). 2 . Oil glands. Groups of cells in the deeper layers of the dermis convert some of their food (obtained from the capillaries) into an oily substance. Cortcx-r,.^}''f^ Medulla Hair- muscle Horny laijcr yDermis ,Sebaceou$ gland ''I- Fig. 99. Touch organs of the skin We perceive touch or heat or cold according to the end organ which is stimulated. These end organs, d, lie beneath the epidermis, a, and contain the end- ings of the nerve fibers, e; b, the dermis, or true skin; c, blood vessels Papilla with blood vessels Fig. 100. Hair of mammals Human hair follicle, show- ing mode of growth. The dead shaft is pushed for- ward by the new growth about the papilla This oil the glands secrete on the surface of the skin all over the body, but especially at the roots of the hairs (see Fig. 100). 3. Nerve endings. The sense organs in the skin consist of delicate clumps of nerve tissues connected with nerve fibers. Some are sensitive to touch only, others to cold, and still others to warmth. It is probable that the amount of perspiration is controlled at least in part by the response of these nerve organs to changing temperature in the surroundings (see Fig. 99). 4. Hairs. Like the external portion of the skin, the part of the hair which we see consists of dead matter. The root of the 200 BIOLOGY AND HUMAN LIFE hair, the follicle, is a cylinder of living cells with a tiny papilla containing blood vessels (see Fig. loo). Connected with the base of the follicle are fine muscle fibers capable of raising the hairs, as in the case of the hedgehog's bristles, or in human beings under the in- fluence of a great fright. 5. Nails. The horny parts of the nails consist of dead cell walls formed in much the same manner as hairs. The living portion at the base of each nail forms successive layers of new cells which are pushed out, new ones taking their place. There is usually a layer of fat cells under the skin of well-nourished persons, but fat de- posits may be found in all parts of the body. Like all living tissues of the body, the dermis has blood vessels in it. 166. Appearances. It may be true that "beauty is only skin deep," but it is quite proper for us to desire good appearance. Indeed, it may be considered a duty to look as well as possible ; for we all like to see nice people, and it is only fair for us to do our share in making the population good to look upon. A clear complexion and good color depend upon proper nu- trition, vigorous circulation, plenty of oxygen, and thorough elimination of wastes. These conditions of the body are to be obtained by correct habits of eat- ing, breathing, exercise in the open, work and play, regular movements of the bowels, etc. If our com- plexion does not please us, we still want it to please others. Many of us think that we have found a short cut to a good ap- pearance by using "skin food" and massage or some other spe- cial treatment which is guaranteed to make us beautiful at least Fig. 10 1. Sweat gland The sweat gland consistsof a fine tubule opening to the surface of the skin at one end and coiled up in a knot at the other. The coiled portion is surrounded by blood vessels (capillaries) from which water, urea, and salts are withdrawn into the gland tube THE SKIN AND THE APPENDAGES 201 skin deep ; others find a short cut by applying a layer of beauty on the outside of the natural skin, in the form of paints and pow- ders ; but we ought to know that there is no way of feeding the skin except through the blood vessels. There is no way of re- moving pimples or blotches except through the blood vessels, and there is no satisfactory way of getting red cheeks except by way of the blood. All this is of course quite apart from the question of what kinds of complexions we prefer, either in our- selves or in others ; that is a matter of taste. Another aspect of appearance depends upon mental states. Drooping corners of the mouth might be concealed by an artistic make-up, but in time our habitual moods impress themselves upon our faces so that they cannot be concealed. On the other hand, it is asking too much of most people to demand cheerful- ness and joyousness and good nature when they are suffering from deficient organs, from bad health habits, or from worry about their personal affairs. The remedy in such cases, how- ever, cannot be applied to the skin. Nevertheless, both appearance and health require that some attention be given to those parts that we show the world. 167. Care of the skin. The evaporation of the water in the sweat leaves behind salts and organic substances. Dust clings to the oil on the skin and gets into the pores. The organic wastes often have a disagreeable odor. Some people think they can remedy the disagreeable odor by the use of perfumes, but perfumes neither remove dirt nor deceive anybody as to the real need. On the contrary, we are likely to be suspicious of the person who always smells like a barber shop. If we could ex- pose our skins to the air a great deal and rub ourselves off briskly with a coarse towel at intervals, most of us could no doubt get along very well without bathing ; but the condi- tions under which civilized people live make bathing necessary. A warm bath, with soap, once or twice a week, should be enough for ordinary cleanliness if there is a daily cold bath, A daily cold bath is refreshing and at the same time an excellent training for the skin in adjusting itself to changes in tempera- 202 BIOLOGY AND HUMAN LIFE ture, but it should never be taken when the body is exposed to cold air. The best time is immediately upon rising, or after vigorous work or play that has produced free sweating. Yet there are many people who cannot tolerate a cold bath because of the after-effects of the shock, and it cannot be recommended to everybody. Each one must find out for himself whether he can benefit from it. All of us can stand a splash of cold water after a warm bath, or in the morning, over the chest and back ; and probably most of us can learn to stand the cold bath, either by systematically lowering the temperature of the bath day by day or by increasing the surface to which we apply cold water with a sponge. In any case the cold bath should be followed by a brisk rub with a coarse towel. The slow, continuous perspiration, of which we are not aware, leaves deposits of wastes in the tubules of the sweat glands. INIore rapid perspiration w^ashes these wastes out. Exercise that results in sweating cleans out the pores. It also increases the circulation of blood in the skin and so helps to clear the complexion and maintain the tone of the skin muscles. One of the great advantages of athletics from a health point of view is the fact that the exercise is commonly followed by a shower bath and that it makes us take a certain satisfaction in the good condition of the body. Bathing itself, aside from making for cleanliness, has also the additional virtue that it gives us a satis- fying habit of feeling that the body is in good condition. We have a special problem to keep the scalp and the hair clean and to keep up vigorous circulation in the skin of the scalp. A shampoo of pure soap or soft soap two or three times a month, with a thorough rubbing of the scalp and vigorous brushing every day, will take care of the cleanliness. A stiff brushing that reaches to the scalp and energetic work with the finger tips will be needed to insure circulation in the scalp. General exercise that induces sweating will serve the skin on the head just as it does the skin on other parts of the body. 168. Clothing. The clothes that we wear are related to our health in two different ways. They influence the work and the THE SKIX AND THE APPENDAGES 203 condition of the skin, and so of the circulation, kidneys, and other parts of the body, and they influence our state of mind and our satisfaction with ourselves and our surroundings. The first consideration in clothes is the relation to tempera- ture and moisture. Woolen clothing, especially next to the skin, has the advantage that it prevents the rapid loss of heat from the body. On the other hand, it is oily and does not absorb moisture readily, so that perspiration is left on the skin. Cotton, linen, and silk also have advantages and disadvantages ; no material is perfectly suited to all conditions. For young and energetic people linen or cotton underwear of special weaves is best, all the year round, to take care of the perspiration. Even in the winter we spend most of our time (indoors) at a temperature of 65°-7o° F. For cooler weather we should depend upon the outer garments for protection from excessive loss of body heat. Woolen underwear gives protection with less weight ; it is therefore desirable for older people, for those who do not take vigorous exercise, and for those who are exposed for long stretches of time to cold air, whether indoors or outside. Since the underwear absorbs the perspiration, it should be aired at night and changed frequently. We should avoid tight belts, garters, hatbands, corsets, shoes, and other articles that may compress blood vessels and so inter- fere with the circulation. On the side of our mental comfort, young people are often perplexed as to whether being fashionable is worth all that it costs in the way of worry and fussing, as well as in the way of money. The fact is that one cannot afford to appear slovenly and negligent, and one cannot afford to give too much thought to the constantly changing whims of fashion-mongers and cloth- ing designers. It is quite possible to maintain a good appear- ance and the corresponding satisfaction in yourself without yielding too much to the fads of the day. 169. Sunlight. One of the effects of sunlight upon the skin is to cause the formation of pigment in the dermal cells. Many of us, however, especially extreme blonds, are incapable of produc- 204 BIOLOGY AND HUMAN LIFE ing this dark pigment. Upon exposure to extreme sunshine we are apt to be burned by the rays, which cause serious injury to the exposed protoplasm. Yet the sunshine is of value in keeping up the health of the skin by promoting brisker circula- tion and active perspiration. It probably also produces in the skin chemical changes of a helpful kind. Moreover, the sun- shine destroys many kinds of bacteria, or germs, and sun baths have been found of great value in the treatment of tuberculosis and rickets. One of the advantages of the ordinary summer vacation, with its swimming and other sports, is the increased exposure of the skin to sunshine. It is wise to expose the skin gradually and get as much tan as possible without getting sunburned. 170. The hands. The skin of the hands is always exposed to contact with dirt of various kinds, and with bacteria. We should therefore try to keep the hands as clean as possible, especially when we handle food ; and we should keep them away from the mouth or eyes, which are particularly liable to suffer from an introduction of dirt or bacteria. The chief value of our hands lies in what we can do with them as wonderful tools ; but as we cannot keep them out of sight, their appearance is a matter of some concern to us. It is worth while to keep the nails well trimmed, to press the cuticle back, to cut off hangnails ; it is worth while to disinfect cuts and scratches, and to keep the fingers out of the mouth, as well as other objects that do not belong there ; it is important to avoid biting the nails ; but it is hardly worth while to treat the hands as though they were ornaments to be exhibited. 171. The feet. While our feet are generally well concealed from the eyes of other folks, they need in some ways even more care than the hands. A very large proportion of us suffer from cramped toes and misshapen feet resulting from tight or poorly shaped shoes. Most of us suffer because our shoes do not per- mit the water of the perspiration to evaporate from the skin. Many people suffer from corns, which are thickenings of the epidermis resulting from constant pressure, and from bunions, Fig. 102. High heels The effect of high heels is to throw the leg forward and to upset the balance of the body. This results in unnecessary strains upon various muscles of the legs and trunk, and in an awkward gait Fig. 103. Flat feet Broken, or fallen, arches result in strains upon the leg and back mus- cles, often leading to headaches as well as to severe pains in the feet themselves a Fig. 104. Position of the feet An important factor both in posture and in general good feeling is the position of the feet in standing and in walking, a, correct position. ]Many people get the habit early in life of spreading their toes apart, 6, or of turning them toward each other. Both positions are bad, since they put unnecessary strains upon the leg muscles and make walking difficult 2o6 BIOLOGY AND HUMAN LIFE which are swellings at the joints resulting from pressure. Per- haps the most common and most serious foot troubles arise from high heels (see Fig. 102) and fallen arches (see Fig. 103). Broken, or fallen, arches are due to a weakening of the muscles of the foot, which may result from improper shoes or from improper habits of walking. In most cases suitable exer- cises will lead to a strengthening of the muscles and complete correction of the defect. In other cases it is necessary to use special arch supporters, but these should be obtained only with the aid of competent physicians or foot specialists. • In walking the swing of the leg should be in a plane running directly front and back, and the line of support in the foot should move in this plane also (see Fig. 104). THE SKIN AND THE APPENDAGES 1. The structure of the skin The dermis The epidermis Outgrowths : hair and nails Living parts ; non-living parts ; manner of growth Glands : sweat ; oil Nerve endings 2. The functions of the skin Protection ; excretion ; sensation ; temperature regulation 3. Care of the skin etc. Objects Methods Appearance Cleanliness Health Washing Bathing : hot ; cold Brushing hair 4. Hygiene of clothing Advantages and disadvantages of clothing Advantages and disadvantages of particular materials Tight garments, belts, garters, corsets 5. Care of the hands 6. Care of the feet Posture ; shoes ; heels ; corns THE SKIX AND THE APPENDAGES 207 QUESTIONS 1. Why is the skin on the chest more sensitive to light than the skin on the hands ? 2. Why is the back of the hand usually darker than the palm ? 3. How can we find out what parts of the skin are sensitive to cold and what parts to heat ? What parts are most sensitive to touch ? 4. Why does a surgeon wear rubber gloves when he is operating ? 5. What is the advantage of vigorous sweat ? What is the dis- advantage ? 6. What are the advantages of cold baths ? W' hat are the dis- advantages ? 7. What is the relation of heart action to the complexion ? 8. How does the healthy condition of the kidneys and bowels in- fluence the complexion ? 9. How can the complexion be treated from the inside ? 10. How does the state of mind influence a person's appearance ? REFERENCE READINGS McCarthy, J. D. Health and Efficiency, chap. viii. Hough and Sedgwick. The Human Mechanism, pp. 184-188; chap.xxiv, Hygiene of the Feet ; chap, xxv, Bathing ; chap. xxvi. Clothing. United States Bureau of Education. Keep- Well Series, No. 12. Flat Foot and Other Foot Troubles. CHAPTER XXI THE UNITY OF LIFE Questions. 1. How are different parts of the body made to work to- gether ? . 2. Do all plants and animals have nerves ? 3. How can a slight change in one part of an organism bring about suitable responses in other parts ? 4. How can organisms that are so different from each other as the different classes of plants and animals do so many things that are exactly alike ? 172. Multiplicity of life. There are probably over a million different kinds of plants and over a million different species of animals. No one person can possibly know them all ; but if we consider only those that are familiar to us, it is hard to see what there is about a potato plant and about the potato beetle to make both alive, or why man and the ameba should both be considered animals. Yet throughout this endless variety there are certain facts in common, and it is these that make up lije. In spite of the great variety of form and structure, all life is one in the sense that all organisms, large and small, plant and ani- mal, ancient and modern, all live by doing certain things. They get food, they assimilate it after more or less change, they lib- erate energy by oxidizing assimilated food, and they eliminate wastes. They do other things too, but these they all do, and in fundamentally the same way. 173. Division of labor. Another problem that we meet when we try to locate life in an organism is the great number of or- gans and processes. In which one of them is life really located? Is it in digesting food or in assimilating it ? in breathing oxygen or in oxidizing ? Is it in the brain, where we are aware of pain and pleasure, of curiosity and fear, of joy and sorrow, or is it in the muscles or flesh, where movement, activity, work, are produced? 208 THE UNITY OF LIFE 209 In the ameba and other one-celled organisms the single cell carries on all the life functions— feeding and assimilation, breathing and oxidation, movement, excretion, sensation, repro- duction. Here we can say that the protoplasm is alive. But in a many-celled plant or animal we are not impressed by the similarity of the protoplasm in all species or in all parts of one organism ; we are impressed rather by the differences between the bone cell and the gland cell and between the skin cell and the muscle cell. The ameba does with the whole body, so to speak, everything neces- sary to keep alive. A lobster or a fish does one kind of work with one or- gan and another kind of necessary work with another 000(30 o o Fig. 105. Simple tissues in a simple animal The hydra is among the simplest of many-celled animals, consisting of a hollow bag whose wall is made up of two layers of cells. There are many outgrowths around the open end. There is a division of labor between the inner layer of digesting cells and the outer layer of protecting cells. In a section of the wall we may see that the outer cells, a, have elongations, b, at their bases, which are highly contractile, and that interspersed among these cells are smaller ones, c, which are highly sensitive and extended into delicate threads and expansions, d, which may be considered to correspond to nerves. (Microphotographs lent by J. R. Bray Productions, Inc.) This fact of having special organs for special functions has been called the division of labor (see section 26). The division of labor (or the physiological division of labor, as it is sometimes called) in plants and animals began very early in the history of living things ; but it must have begun after cells began to cling to- organ 210 BIOLOGY AND HUMAN LIFE gether instead of drifting apart upon being formed by the split- ting of the mother cell. In the animals related to corals and jellyfish (Fig. 44) there is a beginning of this division in that the outer layer of cells shows more sensitiveness, while the inner layer is more active in digesting food (see Fig. 105). x^mong plants one of the earliest divisions found is that between the vegetative cells (those that have to do with the making of food) and the reproductive cells (see Fig. 106). Later divi- sions are seen in root and shoot ; and the shoot di- vides into stem and leaf. The leaf divides into pro- tective tissues and veg- etative tissues; the latter again into transportation tissues and photosynthetic tissues. In higher animals the division of labor has re- sulted in the development of many kinds of organs —locomotive, protective, food-getting, food-crush- ing, digesting, distributing, storing, waste-removing, and so on. It is interesting and helpful to remember that in every case function precedes structure ; that is, digestion (for example) went on in living things long before there were any digesting organs ; breathing went on long before there were any gills or lungs ; excretion went on before there were any kidneys ; animals moved about before there were any legs or wings or fins.^ ^This idea is true also if we apply it to the division of labor in society or in the community. Clothes were made long before there were any tailors; food was prepared before there were any cooks; and so on. Fig. 106. Volvox This organism consists of a hollow sphere made up of a single layer of cells connected bj^ strands of protoplasm. The colony moves about in the water by means of cilia, or vibrating proto- plasmic threads. Each cell contains chlorophyl. Groups of cells (represented by the dark spots) separate from the wall of the hollow sphere and produce reproducing cells THE UNITY OF LIFE 211 This means ( i ) that the capacity for these various functions is present in all protoplasm, and (2) that division of labor with the specialization of functions results from bringing together many units and giving them a chance to live together. 174. E pluribus unum. In spite of the many kinds of organs that we find in the human body and other well-developed species the organism always acts as a whole. The various func- tions, however different they may appear, are all junctions of protoplasm. We can understand the body, perhaps, only by studying all the parts, but the several parts have no meaning except in relation to the organism as a whole. It is this unity of the organism that makes life both significant and interest- ing : the more complex the organism, the more varied its parts, the more wonderful is the total life in variety and interest. Of course the human body does not come from joining to- gether millions of cells that have once been separate. Like other organisms, it develops from a single cell that divides into two, each of which again divides, and so on until millions are formed (see Fig. 107). The many different kinds of cells and the many different organs appear gradually by a process of di^er- entiation, and the different tissues and organs gradually take on specializations in their functions. The organism has been a unity from the first. It is only because we have taken the body apart in our studies that we must go a step farther and ask our- selves how the parts are kept working together. 175. How unity is maintained in higher animals. We have seen that the food-getting and digesting organs deliver the ma- terial ready for assimilation to the blood (see page 136) ; that the oxygen-getting organs deliver their oxygen to the blood (see section 136) ; and that all the cells of the body take from the blood the materials that they use, and throw back into the blood their wastes (see section 1 50) . The blood system is there- fore in touch with all the other systems and organs, and con- stantly tends to bring about a certain unity of the body, at least in a chemical or nutritional sense. The nutrition of every cell is dependent upon the condition of the blood, the oxygen 212 BIOLOGY AND HUMAN LIFE supply, and the removal of wastes— all are unified by this transportation system. In addition to the main sets of organs already mentioned there are in the body several glands, some of them paired, which throw their special fluids directly into the blood (see sec- tion 145). These ductless glands are sensitive to very slight changes in the chemical condition of the blood, and in turn the substances which they discharge into the blood produce striking effects upon the protoplasm in all parts of the body. Fig. 107. Early stages in the development of a frog The development of the frog's egg may represent for us the development in all back- boned animals. The fertilized egg, a, divides into two cells, b. Each of these divides again, c, and the process is continued. As the number of cells increases, there soon begins a differentiation; that is, instead of the cells' continuing to be alike, some become smaller, and in time distinct regions, organs, and tissues are distinguishable Through these internal secretions the strains and needs of vari- ous organs are counteracted or supplied, so that the unity of the organism is increased. Finally, the irritability of protoplasm manifests itself in more developed animals by the formation of the nervous system. This reaches all parts of the body and is sensitive to changes inside, as well as to the changes and disturbances in the environment. The nerves are connected not merely with the muscles and the organs of special sensation (eye, ear, tongue, etc.) but also with the blood vessels and with the ductless glands. Because of their extreme sensitiveness and their quick response they constitute a very striking system of coordination, or unification, in the body. THE UNITY OF LIFE 213 176. Control in higher animals. When a simple animal ad- justs itself to food particles, or escapes from an enemy, we are impressed by the fitness of its action. We are also impressed by the activities of a plant in relation to its surroundings. Never- theless we cannot say that plants and simple animals act "on purpose," no matter how useful the processes are. For one thing, we know that we can reproduce the parts of many of these processes by means of physical and chemical ap- paratus. For another thing, purpose means nothing unless we assume the presence of a mind like our own, which can have a purpose; and we cannot assume this from what we know of these organisms. Indeed, most of the acts committed by ourselves can be shown to be without purpose, even where they are of value to the organism. We therefore have no right to attribute purpose to organisms of whose minds we know nothing. What they do, like most of what we do, comes from being the kinds of organisms they are ; they cannot help it. At the same time, we know that in our own case it has been possible to select lines of conduct that do not come naturally. In so doing we obtain from the world many advantages that we should not otherwise have ; or we escape many dangers or in- conveniences to which we should otherwise be exposed. We find great variety in the manners and customs of different races, as well as great differences in modes of living even in our own home town. These suggest that we have a certain control both over the workings of our bodies and over our environment ; or, rather, we have a certain control over our environment by means of the control which we have over our own actions. This control of our own activities comes from the nervous system. THE UNITY OF LIFE I. All life is one All living things are alike In depending upon certain materials and conditions In carrying on certain processes Everything going on in an organism is related to the life of that organism 214 BIOLOGY AND HUMAN LIFE 2. Unity of life in a plant Relation of various organs to the plant's life Root processes Stem processes Leaf processes Flower and fruit processes Seed processes Processes going on in all the organs of the plant Assimilation Respiration Excretion Cell division (reproduction) Response to change 3. Unity of Hfe in an animal Relation of various organs to the life of the whole Food-getting organs Digestive organs Breathing organs Locomotive organs Excretory organs Circulatory organs Sensory organs Reproductive organs Processes going on in all the organs of the animal Assimilation Respiration Excretion Cell division (reproduction) Response to change 4. How unity of life is maintained in higher animals The blood as a unifying system The internal secretions The nervous system QUESTIONS 1. Show how different kinds of organs do the work of food-getting. 2. What is there in the butterfly that does the work of our teeth ? 3. What is there in the human body that corresponds to the spiracles of an insect ? In what sense do these correspond ? THE UNITY OF LIFE 215 4. What is there in an insect's body that corresponds to the red corpuscles of our blood ? In what sense does it correspond ? 5. How does locomotion among insects resemble that among mam- mals and plants ? How does it differ ? 6. What advantages come to a living thing through the division of labor among organs and tissues ? What disadvantages ? 7. What are the conditions for a high degree of division of labor among human beings ? among different nations ? 8. What are some of the advantages of carrying the division of labor still farther among individuals ? among nations ? What are the disadvantages ? 9. Is a person with a special talent better off in a large community or in a small one ? Why ? How about a person with a special handicap ? 10. How can organisms without breathing organs breathe ? 11. How can plants and animals digest without stomachs? 12. How can a man live after his stomach is removed by a surgeon ? 13. How can we show that the activity of one part of the body may interfere with the full activity of another part ? 14. How can we show that the activity of one part depends upon that of another ? REFERENCE READINGS Beebe. William. Jungle Peace. ''The Army Ants of Guiana" (extract in C. H. Ward's ''Exploring Nature," pp. 96-100). CocKERELL, T. D. A. Zoolog>% chap. vi, The Individual. THE CONTROL OF THE BODY CHAPTER XXII THE NERVOUS SYSTEM Questions. 1. What is the use of pain ? 2. Would there be any harm in killing the nerves in the teeth ? 3. Are there any animals that have no nerves ? 4. Do animals feel pain as we do ? 5. Are there any activities in the body that we cannot control? 6. What is the use of the funny bone? 177. Irritability. The irritability of protoplasm (see sec- tion 43) is the basis of our brain and nerves. There are mix- tures of substances (non-living) that are exploded by a beam of light. The distinctive thing about the irritability of protoplasm seems to be that instead of exploding and going to pieces when disturbed, as dynamite does, for example, protoplasm brings about a change that on the whole tends to preserve it from further injury. It may shrink away from the point of disturb- ance; it may bring about a chemical change that counteracts the disturbance ; it may rearrange itself so that the disturbance does no damage. But it cannot be said that protoplasm meets every disturbance in a suitable way, for it is possible to poison or kill protoplasm. We can only say that in general what proto- plasm does in response to what happens to it is more or less suited to help the organism or to save it from injury. 178. Specialized irritability. With the division of labor in many-celled plants and animals, there is also a specialization of irritability. In our own body, for example, certain cells or tissues respond to disturbance by a rather sudden contraction. Others show that something has happened by increasing the amount of chemical change going on in them, and secreting 216 THE NERVOUS SYSTEM 217 more of their special products, as is the case with the gland cells or with the white corpuscles. Most striking is the fact that some cells have specialized in receiving disturbances and in transmitting them — the nerve cells. A flash, a sound, a push, any occurrence to which protoplasm is sensitive is called a stimulus. The contraction, the turning aside, the scream, or whatever it is that the organism does when it is stimulated, is called the reaction or the re- sponse.^ In the highest animals, like ourselves, we recognize three dis- tinct types of reaction : 1. Muscle. A stim- ulus may set up move- ments. Some of these we can see in the limbs, the trunk, the face, and so on ; others take place in the heart, in the walls of the intestine, and so on (see Fig. 108). A sudden noise may startle one so that the whole body is visibly shaken : in another case one may keep his outward composure, yet react by a change in the heartbeat. 2. Gland. A stimulus may set up reaction in one or more glands. The odor of well-liked food starts the salivary glands ^ Note that the relation between the stimulus and the reaction is not of the same kind as that between the pushing of an object and its sliding or falling. In the latter case the object moves in direct proportion to the strength of the push that was applied to it. In a living organism the stimulus may represent a very slight amount of energ\', while the reaction may involve a very great amount of energy. A slight touch on the sole of a man's foot may bring forth a violent kick. The relation between stimulus and reaction, so far as the amount of energ:>' is concerned, can better be compared to the relation between the pressure on the trigger and the explosion of the gun. Fig. 108. Contraction of a muscle The movement of an organ, as the forearm, is brought about by the contraction of a muscle. The mass of muscle cells becomes shorter and thicker, the parts to which its ends are attached being brought closer together. The movement of the muscle is set off by a nerve, not shown 2l8 BIOLOGY AND HUMAN LIFE Fig. 109. Reflex arc Stimulation of the re- ceiving end a of an afferent nerve A leads to a discharge of en- ergy to all parts of the neuron, including the fine terminals, or dendrites, d. The dis- charge passes over to connected nerves, as the efferent nerve £, by way of the interlacing dendrites, or synapse, s: The discharge in E leads to stimulation of the organ with which it is connected, as a muscle M. Starting from a, in the spinal cord the disturbance is reflected by one of the side branches, or collat- erals, c, oi A, through the synapse 5 into E, leading to a movement by the contraction of M working. A lowering of the amount of sugar in the blood starts the liver discharging more glycogen. The sight of a ghost increases the flow of sweat from the skin glands. 3. Nerve. Sometimes a stimulus fails to bring about an immediate reaction, but pro- duces instead some change in the nerve cells of the brain. You hear a word, one of many- used in sentences — a lecture, a scolding, the rules of a game. You do nothing about it, apparently, at the time, but later you give evidence that the word had an effect : you recall the word when needed, you do what you were told to, and so on. The whole behavior of a man or an ameba could be described as a system of reactions to stimuli. We cannot always recognize the stimulus ; we cannot always discover the connection between the stimulus and the re- action ; nevertheless both the single cell of the ameba and the nervous system of man, made up of many millions of cells, can best be understood in this way. 179. Reflexes. When you are tickled, you draw away the touched part. When some- thing gets close to your eye, you wink. When the illumination is suddenly increased, the pupil of your eye contracts ; when it is di- minished, the pupil expands. When some- thing tickles the inside of your nose, you sneeze. When a solid particle touches the lining of your windpipe, you cough. When you chew tasty food, the glands of the stom- ach secrete the gastric juice. When some- thing touches the lining of the pharynx, you swallow. THE NERVOUS SYSTEM 219 Reactions of the kind mentioned are called reflexes. They take place in direct response to some stimulus, without any intention or desire, and they cannot be prevented. Some reflexes are useful to the organism ; probably none are injurious, although we sometimes wish we could control them. For example, a person takes something into his mouth and realizes just after it gets back of the tongue that it is poison ; but he cannot help swallowing it, no matter how much he may wish to. Vojniting, the reverse of swallowing, sometimes takes place against our will. Like other reflexes, it is entirely beyond our control. Reflexes do not always show themselves in movement. When the funny bone is struck, we become aware of a tingling sensation in the palm of the hand. Many reflexes work out through glands, as we have already seen. Some reflexes take place in organs of which we are never conscious unless they are disordered ; examples are movements in the digestive system, breathing, the heart- beat. They go on just as well during sleep as in our waking hours, and in many cases they go on just as well in the absence of the brain or Avhen the connection between the organs and the brain has been cut. No matter how useful such actions or reactions appear to be, reflexes do not represent the desires or intentions of the organism. We do not do these things "on pur- pose." We do them because our nerves are connected in a certain way. 180. Nerve connections. The reflex rests upon a comparatively simple connection between ( I ) a nerve cell acting as a receptor, or stimulus- receiving structure, and (2) a muscle (or ij Fig. no. Affer- ent and efferent nerves Disturbance of a sense organ S, con- nected with an af- ferent nerve A may set up dis charges in several nerves. There may be a muscle reflex through the effer- ent nerve £j, con- nected with a mus- cle; a gland reflex through the effer- ent nerve £o, that is connected with a gland: and a sen- sation, or a feeling, through a disturb- ance of a brain cell 5 by a discharge through the con- nected neuron Ac, 220 BIOLOGY AND HUMAN LIFE gland) acting as an effector, or effect- producing structure (see Fig. 109). Nerve cells, which differ from the other cells of the body in their special irritability, have distinct structural peculiarities (see 7, Fig. 31). There are (i) a cell body, which contains the nucleus, and (2) outgrowths, or libers, of two kinds— a long, slender fiber called the axon, and shorter processes that branch irregularly, like a tree, called dendrites (from a Greek word meaning ''tree"). A nerve cell is sometimes called a neuron. Neurons are found in all parts of the body, but the cell bodies are usually crowded together in special groups or regions, while the fibers are grouped into long nerves. The nerve- cell bodies are found chiefly in the gray cortex, or "bark," of the brain, in the core of the spinal cord, and in special groups, or ganglia, in various parts of the body. The single neuron connects with other neurons through a close network formed by the dendrites and the branchings of the axon. It is not cer- tain whether the protoplasm of one cell actually touches the protoplasm of the next in one of these connecting regions, but it is certain that the stim- ulation of one cell can transmit the disturbance to the next through such a connection, which is called a synapse (see s, Fig. 109). In some nerve cells a stimulation is received by the delicate branch- Fig. III. Behavior limited by nerve connections The diagram shows the nerve connections of a simple mus- cular reflex, with collateral con- nections to the brain. Such connections make possible automatic reflexes as well as voluntary movements. If the afferent nerve is cut, as at a^, only voluntary movement is possible, and there is no sen- sation. If the efferent nerve is cut, as at Cj, neither reflex nor voluntary movement is pos- sible, but sensation remains. If the spinal cord is cut high up, as at a 2, e^, neither sensa- tion nor voluntary movement is possible, but the reflexes are not affected THE NERVOUS SYSTEM 221 ing ends of the axon and transmitted to the cell body. In other neurons the stimulus is received by the dendrites and trans- mitted from these to the cell body and thence on through the axon. The connection between a neuron and an effector is by means of the branching ends of either the axon or the dendrite. Pigeon Dog Monkey Man Fig. 112. Brains of vertebrates Note the relative size of the cerebellum in the bird and mammals. In the mammals note the great increase of cerebrum and the increasing amount of convolution, or wrinkling, of the brain surface. The greater brain area in the higher animals corre- sponds to greater numbers of association neurons, and thus to greater intelligence 181. Kinds of neurons. Four types of neurons have been recognized, classified according to their behavior. 1. Neurons that transmit impulses toward the brain or spinal cord. These are called the afferent (bearing toward) or sensory neurons, because so many of them are connected with the sense organs on the surface of the body. 2. Those that carry impidses from the cord or brain — the efferent (bearing out) neurons. These may stimulate muscles or glands (see Fig. in). 3. Those that connect afferent and efferent neurons. These may be called associative neurons. 222 BIOLOGY AND HUMAN LIFE 4. Neurons in the brain. Many of these are not directly re- lated to outward reactions but are related to knowing, feeling, and the voluntary control of the muscles. Suppose a certain part of the sciatic nerve (the main nerve trunk runnino; down the leg) were cut, destroying the afferent Fig. 113. Localization of functions in the cerebrum By studying human beings and other animals in which the brain had been injured, and by making experiments, it has been ascertained that certain regions of the brain cortex are related to receiving sensations from specific regions of the body, while other regions initiate movements of specific muscles. Most of the sensory and motor nerves pass through the spinal cord, S.C. The thinking is carried on by the so-called association areas, A-i and A~2. The frontal association area has to do with ab- stract thinking, self-control, concentration, and making decisions. The hind associa- tion area has to do with knowing and understanding concrete facts and relations fibers (a^, Fig. iii)." One might then walk on carpet tacks or hot iron and not know it, unless he happened to be watching his steps. Under these circumstances a person would be able to move his legs or to jump if he wanted to, but the reflex, or automatic, jumping would be impossible because the arc would be broken. On the other hand, suppose another portion of the THE NERVOUS SYSTEM 223 Ventral Dorsal root sciatic nerve were cut— the portion carrying efferent fibers (^1, Fig. Ill)— one would remain just as sensitive as ever to hot iron or tickHng, but he could not iz.«t^nT>i^-rm.{ } ^-^ ^ — --m- move his legs, no matter how hard he tried ; and cer- tainly they would not move of them- selves, for the re- flex arc would be broken, as in the first case. 182. The brain. The brain of man has the same gen- eral structure as the brain of other backboned ani- mals (see Fig. 112).^ The brain is the front end of the main nerv- ous axis, and contains blood vessels and con- nective tissue in addition to many millions of neu- rons. The cortex of the cerebrum (see Fig. 113) consists of nerve cells, and in mammals it is very much wrinkled. The ex- tent of the wrinkhng is related to the number of cells and to the complexity of their connections. 1 Excepting the whale and the elephant, man has the largest brain ; and while the brain of man is about one fiftieth of the whole body, in the elephant it represents only one five-hundredth and in the whale but one ten-thousandth. Fig. 114. Diagram of the spinal cord A, left half of cross section, showing impulses entering the dorsal root and outgoing impulses passing out by the ven- tral root. B, the neurons connected with the gray matter of the cord give off branches passing up and down the cord and transmitting nervous disturbances by way of the col- laterals. In the gray matter of the cord, branches of af- ferent neurons carry impulses up and down and pass them on, by way of the collaterals, to efferent neurons and to the brain .224 BIOLOGY AND HUMAN LIFE Study of diseased or injured brains has established the fact that each portion of the cerebral cortex is concerned with some special feelings, ideas, or movements. In the diagram (Fig. 113) are indicated some of the localizations of brain function that have been determined in such studies. All the afferent and efferent neurons related to reflexes are also connected with the brain by way of the spinal cord (see Fig. 114). When you burn your finger you withdraw your hand, and then you feel the pain (see Fig. 1 10) . If you waited for ac- tion until you were aware that something had happened, it would in most cases be too late. The cerebrum has to do with conscious and voluntary action. It cannot control the reflexes, and in most cases it is not aware of them. Many of our activi- ties and movements are unrelated to the cerebrum ; but every thought, every conscious desire, and every deliberate or pur- poseful action depends upon impulses starting from the gray matter of the brain or leading through this gray matter. THE NERVOUS SYSTEM 1. Irritability General (all protoplasm) ; special (special organs or tissues) 2. Stimulus and response Depends upon general irritability of protoplasm Special structure for response to stimuli (reflex arc) Receptor (afferent path) Connector (association path) Effector (efferent path) Kinds of effectors Muscles ; glands ; nerves 3. Nerve structure Cell body ; axon ; dendrites ; synapse 4. The brain General structure Tissues Connections Cortex Spinal cord Association fibers Cranial nerves 5. Control Movements and processes that are automatic and uncontrolled Movements and processes that are controlled THE NERVOUS SYSTEM 225 QUESTIONS 1. How is irritability related to being alive in the case of a plant ? 2. What is there in a one-celled animal that corresponds to our nervous system? 3. What useful movements does your body perform without the con- trol of your purpose ? 4. What other useful adjustments or responses does your body make without the control of your purposes ? 5. What advantages would there be in being able to control these movements and processes ? What disadvantages ? 6. What automatic movements are performed in your body that are useless or possibly injurious ? 7. What automatic movements would it be desirable to control ? 8. What automatic movements can we learn to control ? 9. How can we tell that reflexes depend upon nerve connections ? 10. How can we tell that some nerves carry only afferent disturbances and others only efferent disturbances ? 11. Under what conditions is it of advantage to an organism to be sensitive to what is happening ? 12. Under what conditions is it disadvantageous to be sensitive ? 13. What reflexes seem to be of no use to the body ? 14. What becomes of nervous energy that is discharged by a stimulus when there is no outward movement ? How can you tell in such cases that something really happens in the body, even if it does not show on the outside ? 15. Of what value is it to the organism to be able to defer or postpone its reaction or to prevent an immediate reaction ? REFERENCE READINGS Hough and Sedgwick. The Human Mechanism, chap, vii, The Adjust- ment, or Coordination, of the Work of Organs and Cells; chap, xv, The Nervous System. Parker, G. H. Biology and Social Problems, lecture on The Nervous System. CHAPTER XXIII THE SPECIAL SENSE ORGANS Questions. 1. How can some animals get along without special sense organs ? 2. Is it true that if one of the senses is injured, the others be- come more keen to make up for it ? 3. Why is it difficult or impossible to distinguish flavors or food when one has a cold in the nose ? 4. Are all animals equally sensitive to odors ? to sounds ? 5. How can we tell whether other animals perceive the world through the senses (see, hear, smell, taste) just as we do ? 183. The nervous system and the outside world. The behav- ior of a living thing is always related to the outside world. Indeed, life has been defined as continuous adjustment to ex- ternal changes. This constant interplay between the environ- ment and internal processes can be readily observed in very simple animals and plants. In complex organisms like the human body many things happen on the inside for which ad- justment is necessary. For example, an increase of muscular activity calls for an increase of heart work, of lung work, and of kidney work. But that is another way of saying that the organ- ism acts as a whole, for increase of muscular activity has to do with the outside, or the environment : it brings about changes either in the position of the organism or in the environment itself. Many of the reflexes protect from injurious contacts or ex- posures, as the winking reflex, or the pupil reflex, or a with- drawing-from-pain reflex. Others serve to get the animal food. If you ever catch a fish with a hook and line, you depend upon a reflex for your success. You simply have to make sure that you have the right kind of bait ; your "luck" depends upon the fish's seeing the bait, and the reflex does the rest. We must not think of reflexes as perfect instruments for get- ting the necessaries or for escaping danger and enemies. From 226 THE SPECIAL SENSE ORGANS 227 the very nature of life there could be no such perfect instru- ments. Consider, for example, the fish. If the reflexes of the fish were perfect, it would always get every bit of prey for which it made a dash ; and if the reflexes of the other animals were perfect, they would always escape their enemies. This, you can see, is a contradiction or impossible condition. Never- theless we may say that most reflexes are useful to the organism. In the lowest organisms the reactions to stimuli are of few kinds, and there is very Httle distinction between the effect of one kind of stimulus and the effect of another. Thus, an ameba may contract when touched, or when suddenty illuminated, or when stimulated by some chemical or by a charge of electricity. In our own bodies the division of labor has gone so far that we have several highly specialized organs, each of which is sensitive to only a limited class of stimuli. 184. The skin. In the skin are delicate nerve endings that are sensitive to slight pressure or contact (see Fig. 99). In some parts of the body the touch organs are very close together^ as on the tips of the fingers and on the tongue. It seems that we perceive heat through the stimulation of certain end organs in the skin, and cold through certain others. The disturbance, or stimulation, is carried along through the neuron and is passed on through one or more other neurons until it finally sets up a disturbance in one or more cells of the brain cortex. Here the stimulus is at last translated into a feeling, or sensation. We say that the finger is hot, but it is in the brain that we feel the stimulus. 185. Chemical sensitiveness. The simplest animals, like the roots of many plants, are sensitive to many kinds of chemical disturbance. We cannot suppose that the ameba, for example, has the feeling of sour or sweet, or that the Paramecium has an idea of nice or nasty. Yet it is very plain that the protozoa are attracted by the presence of various kinds of bacteria, and that they are repulsed by various chemical substances. They will swallow the bacteria and pass sand grains by. We cannot say the ''ameba likes meat juice" as we cannot say "water dislikes 2 28 BIOLOGY AND HUMAN LIFE oil." In both cases the reaction depends upon some relation between the composition of one body and the composition of the other body or substance. Water does not choose to dissolve sugar and to leave sand undissolved; neither can we be sure that a simple organism chooses its food, although it does take some kinds and reject other kinds of objects or materials. It is only when we come to the higher animals that we may speak of choice, and even among the highest animals most of the selecting and rejecting depends upon reflexes and instincts rather than upon thought and feeling ; that is, it depends upon the structure of the organism and upon the composition of cer- tain organs. Even in our own bodies, there are reactions to chemical stimuli similar to those of the ameba, as in the way the white corpuscles react to the presence of various kinds of bacteria that invade the body (see page 178). In addition, we have two special chemical senses, taste and smell. 186. Organs of taste. On the upper surface of the tongue, and in other parts of the lining of the mouth and of the pharynx, there are little projections called papillce. These contain the nerve endings of the neurons connected with the brain cells that are aware of taste. The wry face that you make on tasting something disagreeable is a reflex of which the arc is formed by (i) the afferent nerves of taste and (2) the efferent nerves controlling the muscles of the lips, tongue, and cheeks. Another reflex started by taste stimuli is the watering of the mouth. A blindfolded person, holding his nose to prevent currents of air from passing through it, cannot distinguish ground coffee, for example, from sawdust, or vanilla flavor from raspberry. When we speak of the taste of good food, we usually mean the odor. Our taste system can distin- guish four classes of tastes : sweet, sour, salt, and bitter. 187. Organs of smell. Some of the nerve endings in the lin- ing of the nose, and of the air passages extending back from the nose into the pharynx, are sensitive to touch ; others are sensi- tive to odors. This specialized chemical sense is more highly developed in many of the lower animals than it is in man. THE SPECIAL SENSE ORGANS 229 The sneeze reflex is started either by a strong odor stimula- tion or by a touch stimulation in some of the nerve endings in the nostrils. Watering of the mouth in response to odors illus- trates reflexes that are discharged to glands rather than to mus- cles. The feeling of nausea and the act of vomiting are reflexes .that may be started by stimulation of the odor end organs. In both taste and smell the stimulation depends upon the pres- ence of particular sub- stances in direct contact with the delicate linings of the end organs. These materials must dissolve and apparently pass right to the nerve end- ings by osmosis. 188. Mechanical sen- sitiveness. The varying pressure of bones and other structures, pres- sure of food in the in- testine, pressure of urine inside the bladder, and other contacts and pres- sures within the body Fig. 115. The human ear A, the outer ear, consisting of the cartilaginous pro- jection from the side of the head and an air pas- sage, or vestibule, v; B, the middle car, lying between the eardrum, or tympanum, t, and the inner ear C. The inner ear is connected with the pharynx by the Eustachian tube e (see Fig. 74). Extending from the drum to the inner ear is a series of three tiny bones : h, the hammer; a, the anvil; and s, the stirrup. The main parts of the inner ear constitute the labyrinth: c, the semi- circular canals, consisting of three tubes placed almost exactly at right angles to one another; k, the cochlea, or snail shell. The labyrinth is filled with a fluid and lined with a delicate membrane containing nerve endings itself act as stimuli. Some of these touch or pressure stimuli start reflexes; others start nerve discharges that end in our being aware of conditions. Related to these, but depending upon special organs in the inner ear, is the sensation of the position of the body and the sensation of turning or spinning, which sometimes results in dizziness. These organs consist of three tiny tubes, each in the form of a half circle, arranged at right angles to one another 230 BIOLOGY AND HUMAN LIFE (see c, Fig. 115). It is apparently through this organ also that we become aware of falling or dropping, and that we manage to keep our balance when walking, running, skating, etc. Everyone who wishes to become an air pilot must take a special kind of examination for the purpose of discovering whether the balancing, or equilibration, reflexes are in good working order. Unless a person can- respond quickly to changes in bodily position he can never learn to con- trol a machine that moves in the three dimensions of space, and often without permitting the aid of sight (see Fig. 116). 189. Sight. Many animals are very sen- sitive to light without having any eyes, and many animals do not distinguish light and darkness. We know that plants and the ameba are sensitive to light. These facts mean that light is cap- able of modifying the processes that go on in protoplasm. Only in three of the main branches of the animal world is seeing possi- ble ; these are the highest mollusks, the arthropods, and the vertebrates. By seeing we mean not merely discriminating be- tween light and dark but being able to distinguish forms and colors at some distance from objects. Our own eye may be compared to a small camera with sensi- tive nerve endings in the place where the film or plate would be (see Fig. 117). The nerve endings in the retina of the eye receive impressions from vibrations in the ether at the rate of from 400,000,000,000 to 800,000,000,000 per second. If the Fig. 116. The three dimensions of space A solid body moves in a space which we think o*f as extending in all directions. Every movement can be thought of as a combination of movements in one or more of the three planes representing the three dimensions of space. The semicircular canals of backboned animals are placed almost at exact right angles to one another ivexity backed trans- moved ^ O ■£ '^ ^ - " •- j: - -= -c .S ^ >. *- *- *J •^ (U o ;f - £ ,-S C ^ S-- .-' o ^- >. - ^ >» B ^ ^ ^ ■" -sl ^ §^ je o •a ■^ .S S "" -2^ T-! ^'"2 S S y (U = r'. ifi « aj ,r; ^^a^ - o ^ T3 ~ ^ n3 ?^ «5 ct3 ::: ^ a^ ^ d :^ ^ ^ ^ = c u ;: 3 C C r? M) ^= t^ ° ^.s - o (U -^ J3 Ga B :3 j:^ t« o -rr c "^ ^" C C ^ -> M — — to o c 0^ tfi c „ o to ^ .2 c ^ — ^ rt >i c E u ^ S r. ="" c 2i o 4) - ^ tri Cw r— ^ :^ C 3 C 232 BIOLOGY AND HUMAN LIFE vibration is much more rapid or much less rapid, the nerves of the eye are not affected by them. Some insects, as ants, are sensitive to other vibrations that make no impression at all upon our retina. 190. Hearing. When the vibrations are more than from i6 to 20 per second and less than from 25,000 to 40,000 per second, the human ear discovers sounds of various pitch. In the middle register, which includes most of the sounds with which we are familiar, as the range of the human voice, the ear can distin- guish very slight differences in pitch. A trained ear can dis- tinguish more than 1000 shades of pitch in one octave. In the air-breathing vertebrates the hearing organ is very much like our own, which is pictured in Fig. 115. A vibration striking the eardrum is transmitted through the chain of bones in the middle ear to the liquid filling the labyrinth. From this liquid it is transmitted to the delicate lining of the cochlea (snail shell), in which the nerve endings are located. Here some of the nerve endings are stimulated by vibrations of one pitch, others by those of a different pitch. The nerve fibers are con- nected with special cells in the brain. Animals differ very much as to the range of sound vibrations they can perceive. Some animals are quite insensitive to sounds that nearly all human beings can hear, while some insects can perceive a much higher pitch than any human being can discover. The stretched membrane, or drum, is the receiving area for sound vibrations in many different types of animals. In some insects and spiders, however, the sound waves are received by fine stretched hairs connected with nerve fibers and by fine hairs standing out on the antennae, or feelers. 191. The senses and adjustment. Most of the organs through which we receive stimuli from the outer world depend upon having something come in direct contact with the body. Reac- tion to such stimuli is ordinarily immediate — of a reflex char- acter. If an animal is to profit from its ability to react to such stimuli, it must react promptly ; and if the stimulus comes from possible food, then reaction must take place before the food has time to get away. THE SPECIAL SENSE ORGANS 233 The three senses that enable the organism to obtain stimuli from objects at some distance from the body— sight, hearing, and smell — give opportunity to discover food or enemies while there is still a little time before action is imperative. We find, accordingly, that although there are many reflexes set up by these senses, there are also many situations in which the stim- ulus does not bring out an immediate reaction. The impres- sions obtained through these senses somehow register in the brain cells and set up activities later. It is in some such way that we are capable of learning from experience ; the delayed reaction gives an opportunity to react in one of several differ- ent ways, and the way selected depends upon previous experi- ence. It is probably in the delayed reaction that the organism makes a beginning at control— coniroX of itself and so control of its environment. THE SPECIAL SENSE ORGANS 1. Relation of nervous system to adjustment Through reflexes Through delayed reactions Through acquired (learned) reactions 2. Relation of nervous system to unification of organism In coordination of movements In coordination of systems of organs 3. Specialized sense organs Mechanical Chemical Touch Taste Gravity Smell Light Sound Seeing Hearing 4. Relation of sense organs to control of environment Near perception Distant perception Limit to perfection of reflexes QUESTIONS 1. How do reflexes enable living things to get what they need ? 2. How do reflexes enable living things to escape dangers ? 3. What would happen if every animal had perfect reflexes for getting food (catching prey) and perfect reflexes for escaping enemies ? 234 BIOLOGY AND HUMAN LIFE 4. What use can we make of our knowledge of the reflexes of other organisms ? 5. How can we make use of our knowledge about human reflexes ? 6. How can we tell whether simple organisms and root hairs choose what they absorb ? 7. How could we show that the skin is sensitive to light ? 8. How can we show that leaves and stems are sensitive to light ? 9. How could we show whether roots are sensitive to light ? 10. How can you tell whether the distinctive quality of anything recognized through the mouth is an odor or a taste ? IL Through what organs are we capable of finding out only about things that touch the body? 12. Through what organs do we find out about things at a distance ? 13. What practical use do we make of the workings of the semi- circular canals ? What practical use do we make of our knowledge of their workings ? 14. In what ways do reflexes give organisms control over their environment ? 15. In what ways do reflexes fail to give organisms control of their environment ? 16. How can we tell that there are vibrations (light or sound, for example) that produce no effect upon our sense organs ? REFERENCE READINGS Hough and Sedgwick. The Human Mechanism, pp. 242-276, 395-396. Darwin, Charles. The Formation of Vegetable Mold through the Action of Worms, chaps, i and ii. Habits of Worms. CHAPTER XXIV HYGIENE OF THE SENSE ORGANS Questions. 1. Why do so many people have to wear glasses today? 2. Why do people living in cities have greater need for glasses than those living in the country? 3. W^hy are the special sense organs in greater need of protection than other organs of the body ? 4. What concern is it of the taxpayer's if some children do have defective eyesight or hearing ? 192. Hygiene of the skin. The end organs of touch, heat, cold, and pain form an intimate part of the skin. Their health depends upon the general tone of the skin, the circulation of the blood near the surface, and the condition of the blood. What- ever keeps the body as a whole and the skin in good condition will serve for these organs also (see Chapter XX). We prob- ably cannot increase the sensitiveness of our organs by anything we do, although it is possible to dull them. The extreme sensi- tiveness in the finger tips of a blind person probably results from learning to interpret impressions received and not from an increase in the delicacy of the nerve endings, but the conges- tion of the skin capillaries from using alcohol may result in false impressions regarding the temperature of the surrounding air ; one may feel warm when the air is really cold. 193. Taste. The tongue, considered as a sense organ, needs no special attention to preserve its health. Disagreeable tastes in the mouth may arise from disturbances of digestion, or from the presence of decaying particles of food between the teeth. The sensitivity of the tongue may be impaired by excessive use of spices and condiments and by excessive smoking. 194. The nose. The chief source of disturbance to the sense of smell is a cold in the nose, which results in the accumulation of mucus in the nasal passages and so in an obstruction of the sensory surfaces. An additional danger of colds in the nasal 235 236 BIOLOGY AND HUMAN LIFE passages is that of having the affected area spread into the sinuses (the bone spaces of the skull), which are connected with the nostrils. The snuffing of a salt solution (a teaspoonful of salt to a pint of water) or the use of antiseptics, such as argyrol, is often helpful ; but it is better in all cases to get the advice of a physician than to take any chances with these organs. 195. Hygiene of the ear. The best care to give the ear is to let it alone most of the time. When the secretion of wax in the ear tube needs to be removed, the corner of a clean handker- chief, twisted stiff, will serve. If an excessive accumulation threatens to interfere with hearing, let the physician look after it. The lining of the tube is too easily scratched, and the drum is too easily broken, to allow unskilled hands to get at them. Of course nothing should be put into the tube. If an infant gets a button or a pea into it, have a skilled person remove the in- truder. The danger of ordinary children's diseases, such as measles, scarlet fever, and whooping cough, includes that of infection of the inner ear by way of the Eustachian tube, which connects the inner ear with the pharynx (see e, Fig. 115). There is the further danger that the infection will spread into the mastoid bone (the thick but spongy bone just back of the ear), and through this to the brain. Such infection is often fatal. The outer ear needs merely to be kept clean on every surface. 196. Hygiene of the eye. The eye of the higher mammals is distinctly a distance receptor, that is, an organ adapted to re- ceiving impressions or stimuli from distant objects. But most people in civilized communities use their eyes chiefly for seeing objects or small markings at close range. The strain on the muscles that adjust the lens for far and near vision (focusing) often leads to headaches and irritability or nervousness. In most cases the person who suffers does not know what ails him. This kind of strain should be avoided by frequently looking away from the work, gazing out of the window for a few mo- ments at a time, or even closing the eyes. In many cases there are imperfections in the lens of the eye or in the distance of the HYGIENE OF THE SENSE ORGANS 237 retina from the lens. These errors of refraction can be cor- rected by suitable glasses or spectacles (see Fig. 118). As age advances the lens in many persons loses its elasticity, so that Fig. 118. Eyes and spectacles A "normar' eye, one in which the curvature of the lens matches perfectly the length of the eyeball, a, is very rare. If the curvature of the lens is relatively too great the image falls in front of the retina, b; this near-sightedness can be made up by a concave lens of suitable curvature. Most eyes (of human beings) are far-sighted, so that the image of near objects falls behind the retina, c; a convex lens compensates for the flatness of the eye lens. Sometimes far-sightedness is due to extreme short- ness of the eyeball, d: a convex lens is then necessary to bring the image forward to the retina, c. The opposite defect, extreme length of eyeball, /, is compensated by a concave lens, g. Spectacles do not correct defects of the eye; they can only correct the vision by compensating or making up for certain defects. Thus they can improve vision and reduce strains. (The curvatures and proportions are exaggerated in these figures) it is necessary for those who do close work to have one pair of glasses for far vision and another for reading, sewing, and so on. The lens surface of some eyes is uneven, so that the rays com- ing in are not turned equally from all parts of the field. This 238 BIOLOGY AND HUMAN LIFE condition, which is called astigmatism, may cause severe strain and headaches, especially with those who have to discriminate views or patterns in which lines are important, as in reading. It cannot be corrected, but can be compensated by suitable spectacles that are ground with a cylindrical surface. Another kind of strain is the effect on the eyeballs of unequal muscular arrangement, which causes the axis of one eye to turn too far inward or outward. Strabismus, or squint, can be rem- edied by a simple surgical operation. In some cases the use of special wedge-shaped or prismatic glasses is sufficient. If the eyes have to be examined, it is well to go to a com- petent eye doctor, or oculist, rather than to an optician. A scientific examination of the eyes sometimes reveals serious con- ditions. The optician is trained to discover shortcomings in re- fraction, but he is not able to discover other sick conditions. The spectacles which he prescribes may be suitable for what he finds, but they cannot help the other conditions. Since the eye is particularly sensitive to light, incorrect illu- mination may affect the eye unfavorably, and through the eye the general health. Prolonged exposure of the eye to light will cause fatigue, and in extreme cases pain, discomfort, or even temporary blindness. For our daily routine we should therefore avoid work in direct sunlight, where the light can be reflected directly into the eyes. Flickering lights and sudden flashes cause injurious strains, since the iris cannot move fast enough to protect the retina from excessive exposure, and the iris reflex may become overworked. Another source of injury to the retina is glare, which is produced when a strong light strikes the retina while the pupil is open, or when a strong light strikes part of the retina while the rest is in comparative darkness. The eyeball, in its bony setting, is fairly well protected from injury by large bodies, and the very quick eyelash reflex keeps many small particles out. Nevertheless many eyes are injured every year either by blows or by dust. In railroading, in the building trades, and in other dusty occupations, cinders and flying particles of metal, stone, brick, coal, etc. are sources of HYGIENE OF THE SENSE ORGANS 239 serious danger to the eyes of workers. Wherever possible, work- ers in such occupations should wear goggles. In any case we must be careful not to rub the eye when something does get under the lid, and whoever tries to remove a particle from under the eyelid must approach the task with perfectly clean hands. One of the dangers of getting dust into the eyes lies in the ease w^ith which the Hning of the lids becomes infected by various kinds of germs. Children suffering from trachoma and other infectious eye diseases should be excluded from school, w^here they are likely to transmit the disease to others. There is dan- ger, too, in rubbing the eyes with the hands or with soiled towels or handkerchiefs. On the first appearance of an irritation or redness in the eyes it is well to wash with a solution of boric acid or argyrol ; these act as safe antiseptics. A considerable proportion of all blindness could be prevented by the exercise of greater care in dealing with injuries to the eyes, as well as by care in avoiding injuries. The largest single source of blindness is probably ophthalmia neonatorum, "baby sore-eyes," or the sore eyes of the newborn. This is caused by bacteria, and can be prevented by placing a drop of a i per cent solution of silver nitrate in each eye immediately after the birth of the child. In several states this treatment is now- required of all physicians and midwives attending a birth, and in a few years thousands of persons have been saved from permanent blindness. HYGIENE OF THE SENSE ORGANS 1. Relation to general health Nutrition ; circulation ; respiration ; excretion ; exercise 2. Special precautions Skin; taste; nose; ear; eye 3. The eye Eyestrain Errors of refraction Causes Near-sightedness Effects Far-sightedness Prevention Astigmatism Remedies (Strabismus) 240 BIOLOGY AND HUMAN LIFE Protection of eyes Mechanical injuries Infection Illumination Kinds Glare Trachoma Flicker Blindness in babies Poor lighting Prevention QUESTIONS 1. What are the chief dangers to which our special sense organs are exposed ? 2. How do modern living conditions bring special dangers to our sense organs ? 3. What are the ordinary symptoms of eyestrain ? How can you tell that they are due to eyestrain ? 4. What are some of the advantages of properly fitted eyeglasses ? the disadvantages ? 5. How can difficulty in hearing affect the health ? 6. What help can be found for people who are hard of hearing ? 7. Why should legal regulations be established regarding the lights in public places, in factories, and on automobiles ? What objections are there to such regulations ? 8. What regulations (statutes or ordinances) are there in your com- munity designed to protect people's special sense organs ? 9. What arrangements are made in your school on account of the great individual variations among eyes and ears ? REFERENCE READINGS Hough and Sedgwick. The Human Mechanism, chap, xxii. The Care of the Eyes and the Ears. Public Health Bulletin 140, Studies in Illuminations. United States Bureau of Education. Bulletin 65 (iqiq)- Defective Vision, Methods of Prevention and Correction. Supplement 8, PubHc Health Reports. Trachoma, its Nature and Pre- vention. Bureau of Standards. Technological Paper 93, Glasses for Protecting the Eyes from Injurious Radiations. CHAPTER XXV INSTINCTS AND HABITS Questions. 1. Which is more rehable, our instincts or what we learn ? 2. Can people act against their instincts ? 3. Have all races the same in- stincts ? 4. Can human nature be changed ? 5. Why do some people learn more easily than others ? 6. Why do we learn more easily at some times than at others ? 7. Why do we learn some things more easily than others ? 8. Are there ways of making learning easier ? 9. Can old habits be broken ? 197. Instinctive acts. Among the most striking and interest- ing facts to be observed in animals is the precise manner in which they perform certain acts. Think of the bird making a nest, the wasp paralyzing caterpillars, bees building wax cells, a dog following a scent. In most cases the animals perform these activities perfectly the first time they try. Indeed, in the case of insects and many other animals, there is only one try ! The wasp, for example, builds her nest, accumulates food in it, lays her eggs, and then dies, never having a chance to see her offspring, just as she never saw her parents: the animal could never have learned to do what it does. Such unlearned activities are called instinctive. They depend, like reflexes, upon the animal's being born with a set of nerve connections tying together receptors and effectors. In many cases we can analyze an instinctive act into a series of reflexes. In many cases the instinct shows itself when the animal is well along in its development, but nevertheless it rests upon structures that are inborn. 198. Instincts not perfect. To many people the word instinct suggests an act or a mode of behavior that is perfectly adapted to the needs of the animal in its environment. It is also some- times supposed to stand for a very shrewd kind of unconscious 241 242 BIOLOGY AND HUMAN LIFE intelligence which enables the animal a'lways to do what is best for it under given circumstances. That kind of "instinct" is largely a myth. A frog would starve to death with hundreds of dead worms and insects all about him, because his eating move- ments can be started only by the sight of a moving object. Or the frog will swallow a bit of cloth that is dangled in front of him, and that has no food value whatever. Again, a female fly will lay her eggs on a piece of paper that has been soaked in meat juice, al- though this is extremely wasteful of eggs. Of course, in a state of nature the only things that smell like meat or manure are meat and manure ; and if the eggs are deposited in such mate- rials, the young will be supplied with food. These instincts are, on the whole, beneficial, or at least not fatal, to the species. We have seen that it is impossible for all animals to have per- fect reflexes (see section 183). The same principle is true with respect to instinctive acts of all kinds. The relations of living things to one another is such that they cannot all get the food they need and at the same time escape being eaten by others. 199. Instincts can be modified. Eating is so fundamental to keeping alive that we should expect instinctive activities related to this process to be very well fixed in the constitution of an or- ganism. We cannot teach a frog to eat food that is at rest, or to ignore useless danghng bait ; yet eating instincts can be modified in various ways. The dog refrains from eating after he has had a good meal ; that is, when he is no longer hungry, the chemical condition of his blood and of the other juices is different from what it was, and the "hungry" nerves and muscles behave in one way in the presence of food, whereas the muscles and nerves of an organism that is not hungry behave in a different way. If a goose has its food stuffed down the throat for several days, the animal is no longer stimulated by the sight of grain etc. to open the beak and take up food. In an aquarium a pike was placed with a number of smaller fish. The pike swallowed his neighbors. A glass partition was then put in, separating the pike from the smaller animals. The pike would dart at them, however, and was often stunned by INSTINCTS AND HABITS 243 striking the glass plate. But in time he stopped darting after the small fish. Later, the partition was removed; the pike would always turn aside when he approached one of the little fellows. Nothing now prevented his eating them except his past experience. That is to say, new connections had been formed in his nervous system, modifying his natural behavior. 200. Habit. The bruised pike shuns small fry ; a burnt child dreads the fire. Acts which have unpleasant accompaniments come to be avoided; the impulse to such action becomes re- pressed. There is a positive side to this fact which is just as important : acts that are associated with feelings of satisfaction come to be performed more readily. This is the principle that you would use if you tried to teach a dog or a colt a trick. If you reward the animal with praise or a piece of sugar every time it does what you want it to do, it will be more likely to repeat the performance. At last it will reach a point where it is easier to perform the trick than to do what was formerly natural for it to do. Suppose that every time a baby cries for food the mother calls to him before feeding him. At first the child will keep on crying until something actually touches his mouth. In a few days he stops crying as soon as he hears his mother's voice. Some will say that the child recognizes his mother's voice, or that he understands that she is about to feed him ; but from similar observations and experiments with the young of many animals, including babies, we should rather say that the sound has become associated with the feeding and that the reflex has been modified by this association. A new stimulus (a particular sound) now serves as a substitute for the original stimulus to stop the crying or to start the sucking. The new mode of re- sponding, the new trick, the modified reflex, is called a habit. If you will watch yourself and others for a day, you will observe that most of our actions that are not reflexes are made up of habits. Turning to the right on passing someone is a habit. Taking off your hat on entering a house or a church, or on meeting a lady, is a habit. These things do not come natu- 244 BIOLOGY AND HUMAN LIFE rally ; many people never do them at all. And they are not done "on purpose" each time, for those who have the habit do not stop to think each time. 201. Inhibition. The pike and the burnt baby illustrate what may be called negative habit, the habit of avoiding or repressing an action. Thus, Don't spit ! signs are supposed to restrain the impulse to eject something from the mouth. The process of sending out a nerve impulse to stop an action started by an earlier impulse is called inhibition, and inhibition is just as important a part of our control as is doing. All movements can be performed skillfully or accurately just in proportion as a person has had practice in doing and inhibiting. 202. How practice makes habits. Many boys try their mus- cles from time to time, to see how they are coming on. This growth as a result of exercise probably comes from the facts (i) that the contraction of the muscles calls forth a reflex that increases the flow of blood, and (2) that with increased nourish- ment the muscle fibers increase in size or in number during the rest between exercises. The case is not so simple when the neurons are exercised. It appears that the number of neurons does not increase after birth. When the nervous system de- velops, the axons and the dendrites grow out. The outgrowths of the nerve cell have been compared to the pseudopodia of the ameba, for, like the pseudopodia, they are extensions of the protoplasm. Unlike the pseudopodia, these extensions cannot be withdrawn ; but, like the pseudopodia, they take part in the whole life of the cell. The whole cell, including the very ends of the finest branches, acts as a unit. As a nerve cell is exer- cised (by receiving impressions, by sending out stimuli, or by discharging its energy in some other way) these extensions of its protoplasm are formed : and this is the basis for the associations that modify the conduct of the animal as it gets older. The development of the ability to do things or to control the organs generally is thus the result of use (exercise) or disuse. With advancing age the neurons, like other cells, become less and less capable of growth and of forming new associations. INSTIN'CTS AND HABITS 245 Habits acquired in youth are the most lasting, and it is for this reason that ''you cannot teach an old dog new tricks." 203. Aspects of habit. It is of great practical importance to us that new nerve connections can be formed, that associations can be established, that instinctive conduct can be modified. We are thus enabled to control the lower animals and to control and enlarge our own lives. This fact is the foundation of all learning, skill, and character. The education of human beings, like the training of a dog, consists in the formation of habits- habits of doing, habits of thinking, habits of feeling. I. Action. Conduct or behavior is the outward and visible manifestation of what is important about a person: we notice first of all his habits of doing. How does he walk or handle his food, how does he work, how does he swim or skate? We usually note the answers to such questions when we make up our minds about anybody. These habits of doing seem of pri- mary importance because they determine both how well we do things and how muck we accomplish. A person who could walk only by thinking of each step would not get very far in the course of a day, and he would not have much time left to accomplish anything else after he got there. 2. Thinking. When we learn to say (or, rather, to think) "eighty-four" on seeing ''12 x 7," or when ''1492" makes us think "Columbus," we are acquiring habits of thinking. Think- ing habits show themselves when you solve problems, when you draw out of your stock of remembered ideas and experiences arguments or examples to use in a discussion, or when you plan to get certain tasks done early enough to let you go to a show. Each one of us learns through practice to do these various kinds of thinking; some of us become more skillful at one kind, some more skillful at other kinds. 3. Feeling. One may feel envy on seeing another person have something new, or he may feel glad that the other person has something nice, or he may enjoy the beautiful things without any relation whatever to ownership. We may have the habit of feeling contempt toward people who are difi'erent from our- 246 BIOLOGY AND HUMAN LIFE selves— people who wear different kinds of clothes, who attend a different church, or who speak with a different dialect or a different accent; or we may have the habit of feeling kindly toward strangers. Our feeling habits show themselves in the attitudes that we assume in various kinds of situations. Our habits become so fixed and constant that they may be relied upon under nearly all circumstances. This is what is meant by character: it is the whole combination of habits of feeling and thinking and doing which distinguishes one person from another, or a mature person from a child. We differ very much from one another in thinking power, in strength of mus- cles, in endurance, and in depth of feeling ; but all can acquire habits to make a character that can be depended upon, to the extent of our abihties, in all emergencies. 4. Physiological habits. A different class of habits is illus- trated by an experiment performed on rabbits^ome years ago. A very small quantity of arsenic, which is a violent poison for all kinds of protoplasm, will kill a person or a rabbit.^ In this experiment arsenic was given to rabbits in a fraction of the amount that would ordinarily kill them. After a few days the rabbits were given a little more. The dose was gradually in- creased until the animals had become so accustomed to the poison that they could stand several times the ordinary fatal dose. The arsenic acts upon the protoplasm of the nerves and muscles in such a way as to put the animal in a state of tonus, that is, the way one feels when one is "all on edge," ready to jump or scream on the slightest provocation. The rabbits thus treated became extremely sensitive to the least disturbance; they would jump on hearing the faintest sound or on the pass- ing of a shadow. But after the animals had been treated with the poison in this way for a considerable time, it was impossible for them to live without it. If the drug was omitted from their daily rations, they quickly died. Instead of establishing new nerve connections the arsenic feeding established a new condition of the nerves. This illus- 1 Strangely enough, a child can stand larger doses of arsenic than an adult. INSTINCTS AND HABITS 247 trates a very general fact about all protoplasm, or about living things. Living things can get used to new conditions of temper- ature, or of light, or of chemicals, or of food. This does not mean that every living thing can come to live in any kind of surroundings whatever. We know that is not true : birds can- not get used to living in the water, fish cannot get used to living in the air, plants and animals cannot get used to living without proteins or without salts ; but the conditions of living can be changed to a certain degree or in certain directions and the or- ganism may still remain alive. Many substances modify the activity of protoplasm in such a way that the protoplasm be- comes dependent upon them. These so-called habit-forming drugs are dangerous not only because of the immediate injury they bring about but also because they make the victim require increasing quantities and at last make him a slave in complete dependence upon them. 204. Importance of habit. The amount of work or play that you can accomplish depends very largely upon the habits you have acquired. In dressing yourself, how many movements are necessary, and how much thought they take at first ! But now you can dress yourself without thinking about the buttons and sleeves at all. We ought to be able to do all of our toilet, and a hundred other things that have to be done daily, or at least very often, without giving the actions the slightest attention. This means not only a great saving of time in doing necessary work ; it means also a saving of thought for matters that are much more interesting. The fact that animals form habits is made use of in many ways in training animals to perform tricks for our entertain- ment and in the everyday work of the farm or stable. By regular programs of feeding and milking cows, for example, we give them the habit of coming in from pasture when they are wanted, either at sunset or when we call them, and this saves the work of going after them; horses learn to follow fixed routes, and they learn to come hom.e after they have strayed away ; chickens come in response to a familiar call. 248 BIOLOGY AND HUMAN LIFE 205. Habit as control. The control over our muscles comes from giving attention to what we are doing and then getting connections in the spinal cord to control the actions so that we do not have to think about them at all. In acquiring habits of doing, feeling, and thinking we must recognize that habits of inhibition are just as important as positive habits. We must suppress the impulse to sneer and the feeling that goes with it. We must inhibit the rising temper or the feeling of dismay. In the same way we find thoughts coming into our minds that must be put down. Castles in Spain have their proper place in life, but they must not be a-building at times that require close at- tention to something else. The thought of skating must be in- hibited when the business of the hour calls for thinking about ''dividing by fractions" or "the election of the Senate" or the designing of a dress. Schools are established for the purpose of driUing children in the kinds of habits that grown folks believe to be useful. In addition to the habits acquired in school, each one of us gets hundreds of habits that the schools never recognize, some of them very useful, others not so useful, or even injurious. In fact, by the time a child is old enough to think about it he has gotten into so many useless habits that he has a job waiting for him, to get rid of them. Moreover, by the time we are old enough to think about it we realize that there are many things which we should have learned earlier but never did, for one rea- son or another ; and that gives us a second big job. Better still, we can replace undesirable habits with desirable ones, and that is a large part of life, after we get to be old enough to think of such things. As we become older our protoplasm loses the power to form new extenstion and new connections readily, but some people retain the power to form new habits much longer than others do. A part of the difference is no doubt due to the fact that some people have the habit of looking forward, of considering new ideas, of trying out new ways of doing things, and this is one of the most valuable habits we can get. INSTINCTS AND HABITS 249 INSTINCTS AND HABITS 1. Unlearned reactions Direct responses of protoplasm Reflexes Instincts Adaptive instincts Indifferent instincts Adaptation not perfect 2. Modification of instincts By chemical conditions . By experience — habit Relation of feeling to habit formation Pain Pleasure Negative (inhibition) and positive (action) aspects Kinds of habits Motor (muscular, action) Thinking (association nerves ; cortex) Feeling (nerves and internal secretions) (Physiological, depending upon direct reaction of protoplasm) 3. Place of instinct and habit in life Reliability of instincts in natural conditions Need for modification Value of habit for certain kinds of activities Value of retaining ability to learn Habit as a means of control Over our environment Over ourselves Habit as basis for character QUESTIONS 1. How can you distinguish instinctive actions from acquired ones ? 2. In what class of actions do people show most similarity ? most difference ? Why ? 3. How can you distinguish instinctiv^e actions from reflexes ? 4. Why is it that the sight of certain food will make one person's mouth ''water" but not another's? Why is it that certain food will make your mouth "water" at one time but not at another? 2 50 BIOLOGY AND HUMAN LIFE 5. Why is it that you sometimes accomplish more with a small amount of practice than you do at another time with a greater amount ? 6. What use can we make of our knowledge about the way different animals learn? about the way infants learn? 7. What kinds of habits have we that do not show in our conduct ? How can we tell that the habits are there if they do not show in action ? How can such habits be of any use or harm ? 8. What are the advantages of having all habits for life fixed during childhood ? the disadvantages ? 9. What besides practice is necessary for fixing habits ? 10. How does our environment or experience force certain habits upon us ? How do our habits enable us to control our experience ? 11. How can people be controlled by their habits? How can people come to control their habits ? REFERENCE READINGS Hough and Sedgwick. The Human Mechanism, pp. 284-285. Fabre, J. H. The Wonders of Instinct. Darwin, Charles. The Formation of Vegetable Mold through the Action of Worms, chaps, i and ii, The Habits of Worms. CHAPTER XXVI THE EMOTIONS Questions. 1. Are all people naturally (instinctively) afraid of the same things ? 2. What good does it do living things to feel fear ? 3. Does fear ever interfere with adjustment ? 4. How does anger help life ? 5. Do all people naturally feel anger at the same things ? 6. Can we learn to overcome fears ? 7. Can we learn to control anger ? 8. Can we make use of our fears and angers ? 206. Our double muscular system. In the simplest animals every stimulus may result in a contraction or a movement. The whole protoplasm takes part in receiving the impression and in producing the reaction. In our bodies movements are brought about by the action of muscles (see Fig. io8), of which there are two kinds, (i) Those with which we are most familiar (in the flesh of animals that we use as food) are attached to the bones of the skeleton and to the skin. The fibers of these mus- cles show characteristic cross stripes (see Fig. 119). They are sometimes called voluntary muscles, because we can cause them to contract at will. (2) Those muscles that are present in the inner organs— the stomach, the walls of the intestines, the blood vessels— are not striped (see 3, Fig. 31). They are called invol- untary muscles, because we cannot contract them at will.^ The striped, or skeletal, muscles hold the body in position : they make possible locomotion, grasping, getting and chewing food, directing our sense organs, and making sounds with our voice. The smooth muscles relate the parts of the body to one another. Through their activity food is moved, blood is trans- ported and delivered, and so on. The voluntary system usually works under more or less direct control of the central nervous 1 The muscles of the heart are striped, resembling those of the skeleton ; but they are not voluntar>% resembling those of the viscera. 2;i 2^2 BIOLOGY AND HUMAN LIFE system or of stimuli coming through the sense organs. The involuntary muscle system works constantly, as long as there is life, even while we are asleep. Even if the skeletal muscles are paralyzed, life may go on for an indefinite time. If the smooth muscles are paralyzed, then the end comes quickly. 207. Our double nervous system. Corresponding to the two sets of muscles we have two sets of nerves : (i) The spinal cord and the brain, with their connections to the recep- tors and effectors, regulate the ad- justment of the organism to its surroundings. (2) The autonomic, or self-regulating, system connects the internal organs with one another (see Fig. 120). It has no central organ: it consists of a double series of gan- glia, or nerve-cell clusters, located in front of the spinal column. Be- cause of its many nerve connections the various activities of the organism become very closely tied together and the organism acts as a whole. We have already seen that as the activities of the muscles and of the brain vary there is an automatic reg- ulation of the heart, of breathing, of the blood vessels, and of various glands. This regulation is brought about by reflexes of the autonomic system. The autonomic system includes in its control, however, much more than muscles. Certain glands are of special importance in connection with the work of the autonomic nervous system. 208. Our emotions. When stimuli from the skin or some spe- cial sense organ start a nervous discharge into neurons that Fig. 119. Fibers of muscle The flesh, or muscle, of animals is made up of fine threads, or fibers. Portions of three fibers are shown, with their peculiar cross stripes, and the fine blood vessels, or capillaries THE EMOTION'S 253 connect with the cortex of the brain, we become aware, or conscious, of peculiar feel- ings, or sensations (see Chap- ter XXIII). Some of these we recognize as hot, sweet, green, buzz, and so on. But most of the stimuli and re- actions of the autonomic sys- tem are entirely unconscious. We are not aware of a slight change in the chemical con- dition of the blood, such as an increase in the amount of carbon dioxid (see page 173). We are ordinarily not aware of the action of the liver and the kidneys, of the stom- ach and the small intestine. Sometimes, however, we do become aware of internal events, and usually in an un- pleasant way. After a person has gone without food for a long time, he may have pangs of hunger, which are con- nected with violent contrac- tions of the stomach. When the liver is out of order, one may feel grouchy, irritable, or pessimistic. The feelings that we have when disturbances of the autonomic system come to consciousness are called emo- tions. They differ from sen- Inlesline Fig. 120. The autonomic nervous system In front of each vertebra is a pair of gan- glia, gg, which are connected ( i ) with each other: (2) with the spinal nerves, S.V; and (3) with the organs of digestion, circula- tion, elimination and leproduction, and the glands. The middle portion of this system, regulating the organs in the thoracic and lumbar regions, is sometimes called Xht sym- pathetic nervous system. Through these nerves the unconscious and involuntary proc- esses are connected with the voluntary and conscious ones 2 54 BIOLOGY AND HUMAN LIFE sations in that they cannot be localized or referred to a par- ticular region of the body. We feel glad all over, or we feel angry all over, or we feel scared all over, not merely in one spot. Of course, as in the case of sensations, our being aware means probably that certain cells of the brain cortex have been stimulated. In general, emotions accompany the organic functions that have to do with keeping one alive or preserving the species. In the case of nutrition, for example, we may become so hungry that we are driven out to get food through special effort. We are unable to keep quiet and we get no rest or satisfaction until food is procured. If the hunger makes us do something, we speak df the emotion as a motive or drive. In fact, the word emotion means that which moves to action. There may be great discomfort or dissatisfaction, a desire for something, and finally a deep satisfaction when the desire is fulfilled. We say in such cases that the emotion is one of relief from a previous strain. 209. Joy and sorrow. Agreeable emotions are associated with the healthy workings of internal organs and with the satisfac- tion of desires, or the activities that seem to satisfy the desires. The mere hearing of sounds, or the mere swinging of the arms, or the mere exercise of walking of itself, may yield such satis- factions, since they are healthy activities of the organs. Dis- agreeable emotions are usually associated with internal strains or with interference encountered by any desire or activity. If the urine is retained too long in the bladder, if somebody blocks your path, if your wishes are denied you, unpleasant feelings are aroused. Even holding a baby's head firmly, with- out producing any pain whatever, is enough to make him very angry. The free, spontaneous, satisfying activity, the healthy, vigorous, smooth working of the internal organs— this is the basis for the joy of living. Restraint, coercion, frustra- tion in action, flabby, inharmonious, or perhaps even painful working of the internal organs— this is the basis of sorrow, distress, and disgust with life. Yet we must not expect a par- THE EMOTIONS 255 ticular emotion to correspond with every instinctive act. Nor must we forget that a habit may make the same demands upon the organism as an instinctive impulse does (see section 203), 210. Expression of the emotions. The changes in facial ex- pression which we connect with changes in people's moods are called the expressions of the emotions. The raising or lowering of the corners of the mouth, the pursing or curling of the lips, the lifting of the eyebrows or frowning, the bulging of the eyes or the narrowing of the eye slit are very striking and distinctive. Even a very young infant soon learns to judge the disposition of his elders by these movements of the facial muscles. It is probably true that we may be miseducated by the extravagant or exaggerated way in which some popular actors try to register various emotions. They may thus give us not only false ideals of beauty but misleading notions of human nature and of the relative importance of the various things that happen in life. 211. Organic effects of emotions. In anger the blood is driven from the skin; one is "white with anger." At the same time the pressure of the blood in the vessels is increased ; the skeletal muscles become tense ; the stomach stops all work— the secretion of gastric juice as well as its muscular work. These changes are ordinarily not apparent to the observer, but they are as truly parts of the emotion as the changes that we see in the face. When one is angry he sometimes acts violently; the blood rushes to his head, we say. Instead of thinking clearly about what he is to do or how he is to do it, he is apt to act wildly, and this peculiar conduct is also a manifestation of the emotion. In the case of fear we may find many departures from the normal besides the facial expression. On the other hand, it is possible for one to be "consumed by jealousy" or by curiosity without showing it outwardly— at least without showing it in a way that most of us would recognize. Aside from all the outward manifestations, and from the less apparent ones, important chemical changes take place in the 2 56 BIOLOGY AND HUMAN LIFE human body in connection with every emotional disturbance. Everything that modifies the normal action of any of the inter- nal organs at once brings about an increase (or decrease) in the secretion of one or more of the ductless glands (see section 145) . In anger, for example, there is a rapid increase in the output of the suprarenal capsules (which lie next to the kidneys). An injection of extract of these glands (adrenin) into the blood at once sets up changes similar to those observed in anger. The question may well be asked, then, whether anger is a state of mind or a chemical state of the blood. Is there anything in anger besides the outward manifestations? We are pretty sure of this : what happens to the emotions influences the whole body, probably through the chemical effects of the substances from the ductless glands ; and the experiences and activities of the whole body in turn modify the ductless glands and the emotions. It is said that when one is frightened and starts to run, the movements and the whole attitude of the body will tend to strengthen the fear feelings. If, on the other hand, one stands fast, clenches his fists, and takes on the posture of fearlessness, the feeling soon evaporates. This is so true that we can see every day the relation between a person's posture and his habitual disposition. The sergeant may be able to force the recruits to stand up like soldiers, but unless they get the habit of feeling like soldiers they will slump into some other way of standing as soon as the discipline is withdrawn. On the other hand, one of the best ways of getting ourselves to feel self-confidence, or generosity, or kindness is to get the habit of standing up like self-confident persons, of going through the motions or postures that belong with the feelings we wish to cultivate (see Fig. 143). 212. Emotion habits. A person cannot help becoming hungry when he has been short of food for a long time ; the nature of the organism compels a certain emotion under certain condi- tions. But the manner of satisfying our hunger is entirely within our control. Hungry people have fought one another for food ; that is one way. Hungry people have gone out to hunt THE EMOTIONS 257 game, or they have organized work that would bring them food ; that is another way. Even at the table you can see hunger driving some people into one kind of behavior and others into a different kind. These examples of the different ways in which hungry people may behave show different kinds of emotion habits as well as of action habits. In fact, our whole manner of living represents ascheme of habits in which emotions, thoughts, and actions are all parts of a unity. One who shows what we call breeding or good manners at table has a different set of feelings from one who shows bad manners. Both may be equally hungry. The difference in behavior represents differ- ence in habits— feeling and thinking habits as well as action habits. 213. The formation of habits. If a baby is accustomed to feel the joy of satisfied hunger immediately after hearing a certain sound, he will soon come to have that joyous feeling on hearing the sound. If people discover that controlled anger brings more satisfaction than uncontrolled anger, they will in time find a way to control anger. The habits that we acquire all involve feeling as well as think- ing and doing. The nerves, reaching all parts of the body, are sensitive to changes and in turn bring about changes. The blood reaches all over the body: slight changes in any set of organs alter the chemical condition of the blood ; slight changes in the chemical condition of the blood bring about important changes in the activity of protoplasm in all parts of the body. In this way emotions influence our thinking, our actions, and the behavior of the internal organs. On the other hand, both our thinking and our exercise of the skeletal muscles can modify our emotions. THE EMOTIONS I. Double system of movements in the organism Related to external adjustments Striped muscles (skeletal) Connected with nerves from brain and spinal cord Voluntar\' (direct control) 258 BIOLOGY AND HUMAN LIFE Related to internal adjustments Smooth muscles (visceral) Connected with nerves of autonomic system Involuntary (indirect control) 2. Sensations and adjustment Related to stimuli Related to sense organs Related to cortex of brain Different kinds (specific and localized) Uses to organism 3. The emotions Comparison to sensations Resemblance Appear in consciousness Differences Felt all over, not in special part Felt in connection with types of situations, not with specific objects or stimuli Cannot be readily recalled Sources Disturbances of autonomic nervous system Chemical changes in the blood Kinds (examples) Pain Hunger Fear Anger Love (Curiosity?) General qualities Joy, or pleasurable emotion From activities of sense organs From activities of doing, making, etc. From release of strain, satisfaction of desire, etc. Sorrow, or painful emotion From interference or obstruction of normal activity From overworking of normal activity From strain or discomfort in functions Effects Driving to effort or action Blocking or modifying action THE EMOTIONS 259 4. Expression of the emotions (emotion affects the whole organism, hence may show itself in any part or in all parts) Skeletal muscles Posture Gesture ^ Facial expression Internal organs Breathing Heart action Digestion Intestines Cerebrospinal system May cause wild action ^lay unify actions to a purpose 5. Training of emotions Feeling a part of every experience Feeling a part of every habit formation Feeling habits formed by training in actions connected with par- ticular feehngs Feehng habits determine our actions in new situations Feeling habits influence our thinking QUESTIONS 1. How does irritability help an organism get what it needs from its environment ? What does it need ? 2. How does irritability enable an organism to avoid or escape from dangers in its environment ? What are the dangers ? 3.1s everybody afraid of snakes? of thunder? of fire? of dark- ness ? of ghosts ? 4. How does one acquire fear of a particular object or stimulus ? 5. Do you know any animals that are afraid of objects or conditions that are harmless ? How do they show their fears ? How do they get their fears ? 6. Do you know any animals that become angry when there is no real need for anger ? How can you tell that they are angry ? 7. Under what conditions are strong feelings hkely to be of help to a living thing ? How ? 8. Under what conditions are strong feelings likely to be a hindrance to living things ? How ? 2 6o BIOLOGY AND HUMAN LIFE 9. Of what use is it to be able to recognize the feelings of other people or animals ? 10. Under what conditions is it of use to show our f eehngs to others ? 11. Under what conditions is it of use to hide our feelings from others ? ' 12. How can we hide our feelings ? 13. How can we control our feelings ? 14. How can we make use of our feelings ? 15. Is it desirable to suppress all feelings ? Is it desirable to give im- mediate expression to all feelings and impulses ? 16. In what ways should we be better off if we had no emotions what- ever? In what ways worse off? 17. What objects arouse the feelings of people in one country but not the feelings of those in another country? 18. What kinds of emotions can we experience that are not felt by the people of other countries ? REFERENCE READINGS Williams, J. F. Personal Hygiene Applied, pp. 309-319. Darwin, Charles. Expression of the Emotions in Man and Animals, chap, iv, Means of Expression in Animals; chap, vi, Special Expres- sions of Man. CHAPTER XXVII THE MEANING OF HEALTH Questions. 1. Why is it important to know how different diseases are caused ? 2. What is the best cure for disease ? 3. What kinds of disease can be caused by the "evil eye" or by malicious wishing? 4. What dis- ease can be cured by purely mental methods of healing ? 5. Which is more powerful, the mind or the body ? 6. Why do doctors prescribe drugs less than they used to ? 214. Different notions about health and disease. There have always been people who suffered from some ailment or other. Perhaps nobody is perfectly well, although some people "ail" much more than others. The first step toward curing sick people is to know just what ails them, and the first step toward preventing illness is to know what causes illness. People have thought that illness was caused by evil spirits getting into the body— perhaps imps or devils. In such cases the common-sense thing to do was to drive out the evil spirits or devils by making it uncomfortable for them in the body of the patient. So they would make loud, hideous sounds, or create a disagreeable odor by burning various materials, or perhaps give the patient something very bitter or nasty to take inside (see frontispiece). Among other people the cause of disease was thought to be in a disproportion of the various juices, or "humors," of the body. Too much or too little of one juice made a person bilious or melancholy. The way to treat a person having too much juice of one kind or another was, of course, to remove the surplus. So they used to draw off some of the blood, either by cutting a vein or by means of a leech— a wormlike animal that attaches itself to the skin and sucks blood. The physician may be spoken of as a leech in some of the books that you will read. So probably 261 2 62 BIOLOGY AND HUMAN LIFE originated the red-and-white barber's pole, for the barber did the bloodletting during a long period in European history. In another period of thought men tried to find a connection between various natural objects, like plants or animals, and the symptoms, or sights, of disease. The argument was something like this : Nature made everything to be of some use to man- kind ; the exact use does not always appear in every case, but by careful search we should find the signs that will tell us. So a plant with kidney-shaped leaves must have leaves of this shape as a sign that the plant is useful in kidney trouble. The wrinkled kernel of the walnut must have that pecuHar appearance, re- sembling the brain, with the shell corresponding to the skull, as a sign that it is useful for brain trouble, and so on. 215. Truth in falsehood. Strange as some of these notions ap- pear to us today, it is not fair for us to laugh at them. For one thing, what people with queer notions think seems to them just as reasonable as our thoughts do to us. For another thing, we often find that there is the possibiHty of at least a small grain of truth in queer notions. For example, we know today that many sicknesses depend upon the presence in the body of cer- tain tiny plants or animals called microbes (meaning small living things), of which there are many kinds (see Chap- ter XXIX). One could say today that the notion that evil spirits cause disease is a true one if we only substitute mi- crobes for spirits. On the other hand, these spirits cannot be driven out by beating drums or burning incense or eating bitter herbs. In a similar way, we know from modern investigations that there are present in the body various juices (the internal secre- tions) which have an important bearing upon health. If one is in excess, we get one kind of disorder ; if another is in excess, we get a different disorder. To be sure, these juices do not corre- spond to the "humors" of the ancients, but they are real juices, and some of them can be prepared in the laboratory and used for definite changes in the body to bring about cures. We do not, however, remove excess of these juices by bleeding. THE MEANING OF HEALTH 263 Another conception of evil spirits has appeared from time to time, in which "spirit" corresponds less to a devil or an organ- ism than to ideas or thought. Thus, many people believe that a disorder of the body may be brought about by evil thoughts, either on the part of the patient himself or on the part of some wicked enemy. This kind of belief is hard to handle, because it has to do with matters that do not lend themselves to experi- menting. It would be very hard for you to prove, for example, that my toothache was not caused by someone's throwing tooth- ache thoughts at me while I was asleep. Nevertheless the health of the body and the health of the mind are closely connected. 216. Physical basis of mental disturbances. Most of us are unable to keep our minds on our work when we have any kind of pain, whether it is a slight bruise or a jumping toothache. When the liver is out of order, it is almost impossible for most people to maintain a cheerful mood ; we have the blues, or we are grouchy or irritable. ]\Ien have committed acts of folly and of violence when under the influence of alcohol or other drugs. When one is exhausted from hunger or fatigue, not only does the mind work at lower pressure, but there may be even uncon- trolled images or wild thinking. Just as the chemical condi- tion of the blood may change the rate of breathing and influence the digestive organs, so it may influence the brain and mental processes. People have become insane and irresponsible from the poisoning of the blood by physical disease, or by alterations in the quantities or the relative quantities of the internal secre- tions. So we cannot help recognizing that the mind may be influenced by physical conditions of the body. 217. Mental effects on physical conditions. Now we have to see that the opposite may be just as true. A person who is very much excited by some good news or bad news is likely to suffer from indigestion ; a person who is worried is likely to become run down physically. A cheerful frame of mind keeps up the action of the blood ; a hopeful disposition enables a sick person to get well more rapidly. In some cases of mental disturbance or insanity the bowels fail to carry on their work or the breathing 2 64 BIOLOGY AND HUMAN LIFE becomes impaired. The physical condition of the body can in- fluence one's dreams, and certain dreams, or the reading of cer- tain stories, can produce marked effects upon the condition of the body, such as shivering with cold or shaking with laughter. Instead of saying that all disorders are due to physical causes or that all are due to mental causes, it might be more helpful for us to think of the body as a living organism, in which every happening may influence every part. 218. Mental health and mental healing. If we realize that the organism is a unity, it is easier for us to understand that health is very largely a habit, and that the state of mind is a large part of the habit. This must not be taken to mean, how- ever, that all illness could be prevented by proper training, or that health is to be obtained by merely getting certain ideas into our minds. It is necessary to keep the whole organism well ; but if something does go wrong, it is important to find out what the cause of the trouble is. No one medicine or one trick can cure all disorders, just as no one ideal food can suit everybody all the time and just as there can be no one answer to all questions. We must guard against the idea that somebody has found a universal remedy, whether it is a kind of drug, or a kind of exercise, or a kind of lucky stone, or a kind of happy thought. 219. Health as habit. We have already seen that in order to maintain Hfe and a sound working of the body it is necessary to provide certain materials and conditions, and we have seen that in regard to all the bodily needs that we have studied it is desir- able to acquire certain habits, since there are better ways of do- ing things and poorer ways. Some of these desirable habits are: 1. Habits of eating, to get the necessary materials; to get them in the right proportions to meet the needs of the body, in- cluding the need for muscular activity of the intestines and of the jaws ; to get them in the right condition to be readily used by the body, including flavor, digestibility, etc. 2. Habits of breathing, including constant demand for fresh air, suitable ventilation, etc THE MEANING OF HEALTH 265 3. Habits of elimination, including regularity of the bowels as well as of removal of urine, frequent perspiration, and gen- eral cleanliness. 4. Habits of exercise, including various kinds of work and play, to maintain circulation, breathing, elimination, etc. There are people who get the proper food, properly prepared, in suitable quantities, who chew the food properly and have good table manners, but who nevertheless bring trouble upon themselves by occasionally putting dangerous things or sub- stances into their mouths. Or one may disregard what happens to his eyes, or run into a moving automobile and lose a hand — or worse. Many conditions all around us demand constant vigi- lance if we are to avoid injuries. We might prescribe a general habit of caution, as represented by the slogan "Safety First." Being careful may be looked upon as a sort of habit, but it differs in one respect from most habits with which we are famihar. Instead of being exercised when a particular kind of stimulus reaches the senses (for example, the sight of a knife or the sound of a fire bell) carefulness is constantly at work in all sorts of situations. It is an attitude of general preparedness which many kinds of signals can change into activity. 220. Attitudes as habits. The w^ord attitude, which means about the same as posture, is commonly used when referring to the posture, or position, that the mind takes in relation to the environment. This is illustrated by the close connection that we come to expect between the physical posture and the state of mind in such cases as fear, defiance, curiosity, and shame. In- deed, you can hardly pronounce these words and think of their meaning without having different muscles of your body pull toward getting your face and arms and legs and back into posi- tions corresponding with these various feelings. As we saw in our study of the emotions (sect. 208), we have here feelings that are closely connected with all the important functions and processes of the body. Some emotions drive us to do things that we should otherwise not do at all.— such as hunger, fear, love, anger, curiosity. After some experience in infancy our 2 66 BIOLOGY AND HUMAN LIFE impulses to action are modified so that emotions become asso- ciated with certain actions and so keep us from doing what we otherwise feel impelled to do; for example, fear, shame, and the desire to please certain people will prevent us from doing things that we learn to regard as wrong or improper. Our emo- tions may be aroused by a great variety of stimuli, and they may in turn bring about a great variety of changes in the body. Anger, for example, may be aroused by an unfriendly act, or by striking an obstruction, or by seeing a bully abuse a child, or by thinking about the abuse of power by high officials. This feel- ing of anger may, in turn, bring about various changes in the expression of your face and the doubling of your fists (skeletal, or striped, muscles) ; it may cause a sudden flow of blood to the head and increased heartbeat (involuntary muscles) ; it may stop the flow of gastric juice and bring about other changes in various organs. The manner in which we allow various happenings to stir up our feelings, and the manner in which we allow our feelings to find their way out in action, both depend largely upon habits. These feeling habits, then, are our attitudes. 221. Useful attitudes to cultivate. Since the emotions are so important in controlling organic processes, it is important for us to know how we can control our emotions. We cannot move the unstriped muscles or cause the thyroid to secrete at will. The only parts of the body that we can control voluntarily are the cortex of the brain (our thoughts) and the striped muscles that move our bones and skin. It is therefore through our thoughts and our actions that we may try to control our feelings and to establish feeling habits. If a child learns early in life to "grin and bear it," he will be able later to stand pain and to avoid crying whenever he may be hurt. If you learn to "count ten" when you are provoked, to put your hands in your pockets when they feel like striking, to press your lips together tight when certain unkind words are trying to burst out, you may find that after a while anger does not make you do what you do not wish to do. There is some truth in the statement that we are THE MEANING OF HEALTH 267 afraid because we run away ; that is at least as true as saying that we run away because we are afraid. You cannot control the palpitation of your heart and the chemical condition of your blood ; you must make your effort in connection with the large muscles of running, for over these you have some control. It seems easier to form undesirable habits, but that is because most of us do not know what we want or how to get what we want. To begin with, every child is attracted to everything he sees or hears. A useful lesson to learn early is this : You cannot have everything. If you choose the blue, you must go without the pink. We waste much time making a choice, and then worry because we think we might have preferred the other. There is one secret about a quick decision which many people never learn: the harder it is to make up your mind, the less does it matter, in most cases, which you choose. If it mattered a great deal, you would either recognize the difference or would learn after a few mistakes. With some people, hesitating seems to be a habit which they carry all through life. It is childish, to chng to the desire to eat your cake and keep it too. Every choice means a rejection, a giving up, as well as an acceptance or taking ; we cannot have one without the other. This means, in the long run, learning how to make the most of what we do get day by day instead of repining over what we might have had. Sometimes the choice is not so simple as that between two kinds of amusements ; we feel strong desires to act in two ways that cannot be harmonized and that are equally pressing. It may be the desire to buy something very tempting and the desire to save for something in the future— candy now and a tennis racket later, or a bicycle now and going to college later. It may be a decision involving real sacrifice — between continuing in school and going to work to help the family, or between wearing last year's clothes to help some sick person and looking stylish to make a hit with certain persons. In such cases, too, we soon get a habit — some of us will nearly always choose immediate satisfaction, and others will nearly always choose the satisfac- tion of delaying for the greater object ; some people never 268 BIOLOGY AND HUMAN LIFE sacrifice anything, and some never miss a chance to sacrifice. Most of us try to use our judgment in every case, but in the end we are able to distinguish two main classes of habits : (i) those of people who can find good excuses for doing what they like, and (2) those of people who can find satisfaction in doing what they think is right. In both cases we choose a satis- faction. Of course, if our habits do not fit in with the condi- tions in which we have to live, we are in a bad way ; then none of our decisions bring satisfaction. We are, then, like people whose eating habits or thinking habits do not fit the require- ments of life. It is a good rule to choose what you want and go for it hard. Wanting everything means getting nothing. Wanting what is unattainable is getting nothing, for it is like the baby crying for the moon. Wanting things merely because others have them (covetousness, envy) means in the end cheating yourself, for even if you get them they do not satisfy, since they do not meet your own real needs. 222. How the mind unifies the organism. At any given mo- ment the different processes of the body are unified by the chief activity. If you are playing a game, like basket ball or tennis, the heart and the lungs and the perspiration glands and the liver and the kidneys are adjusting their activities to the body's needs. Your senses and your muscles also are "on the stretch" to see what your adversaries and partners are doing, and to be ready to act according to the movements of the ball. You may become quite excited in the game, and everybody knows that excitement may work in two opposite ways. If you are not excited, or warmed up, enough, if you do not care enough, you will not hit hard enough ; you will not see enough of what goes on to guide your movements ; you will not be quick enough with your responses. On the other hand, if you are too excited, if you begin to think about the score or about possible failure, if you begin to wonder w^hether certain eyes are watching you, you may spoil the game by playing too wildly. In any case the body works as a whole THE MEANING OF HEALTH 269 just as far as it is controlled by a single purpose or desire, and just in proportion to the strength of the purpose. Habits of concentration, orderliness, and perseverance make for unity and for strength. On the other hand, habits of mind- wandering and day-dreaming, of indecision and worry, of sus- picion and jealousy, of concealment and shyness, indicate a lack of unity or wholeness ; and at the same time they interfere with the satisfactory cooperation of all the powers of the body in fulfilHng the heart's desire. A strong will may mean the habit of holding fast to a clear picture of a definite purpose. THE MEANING OF HEALTH 1. Ideas about sickness Evil spirits get into the body The humors, or juices, are out of balance Something is lacking that can be supplied from a corresponding object in nature (doctrine of signatures) Some part or organ is overworked or strained Some part is injured Mechanicallv Chemically Some part functions below or above normal E\il thoughts cause sickness Thoughts of the patient himself Thoughts of others against the patient (Parasites destroy or poison) 2. Truth fragmentary Even false notions may have a trace of truth in them The best knowledge that we have is never complete The most useful ideas are those that lend themselves to tr\'ing out. or experimenting 3. Relations between mental and physical processes in an organism Physical conditions intluence mental processes Pain interferes with calm thinking Disordered liver prevents cheerful mood Chemicals (alcohol, drugs) modify mental operations Physiological conditions (hunger, fatigue) may prevent con- trolled conduct or thought Disease may upset the mental balance 2 70 BIOLOGY AND HUMAN LIFE Mental conditions influence physical or physiological processes Excitement affects visceral functions Digestion-; breathing; heart and blood Worry lowers resistance to disease Cheerfulness and determination raise resistance and make more energy available Mental disturbance may interfere with action of bowels and other functions Fears lower metabolism Thoughts and dreams affect conditions of body and actions The organism acts as a whole Every happening influences the whole organism Changes may show themselves chiefly as physical manifesta- tions or chiefly as mental manifestations Cures must be directed toward the causes of disturbance, not toward the manifestations There can be no one cure for all kinds of disturbance 4. Health as a habit Habits of eating (see Chapter XIV) Habits of breathing (see Chapter XVI) Habits of elimination (see Chapters XIX, XX) Habits of exercise Work and play 5. Attitudes as habit Meaning of attitude Position the mind takes in relation to the environment Acquiring of attitudes Related to the emotions Fixed in connection with conduct Control of feehngs indirectly through striped muscles, espe- cially the larger muscles of the body Attitudes as emotion habits Useful attitudes to cultivate Caution Quick decision You cannot have everything Arbitrary choices Play the game hard Immediate satisfaction versus deferred satisfaction Principle versus expediency Select your own values, not other people's ; self-confidence THE MEANIXG OF HEALTH 271 6. Mental habits as unifiers Purposes and ambitions Ideals (examples) Thoroughness Concentration ReliabiHty Orderhness Perseverance Integrity QUESTIONS 1. In what ways can physical conditions influence mental processes? 2. In what ways can mental conditions influence physical processes ? 3. What physical processes in the body have no influence whatever upon the mind ? How can we tell ? 4. What mental processes have no connection whatever with physical changes ? How can we tell ? 5. Is it possible to be happy without health ? Is it possible to be of great use without health? What is the evidence? 6. What is the advantage of patent medicines over special prescrip- tions by a physician ? W'hat are the disadvantages ? 7. How can we tell that some ideas keep people in better health than others ? 8. How is it that several persons suffering from different ailments sometimes get help from the same specialist or the same treatment ? 9. How is it that several people who have the same ailments are sometimes helped by different treatments ? 10. What kinds of physical habits help to keep one well ? What kinds of mental habits help to keep one well? What kinds of emotional habits help to keep one well? 11. What kinds of habits can prevent disease altogether? 12. How can education promote people's health ? REFERENCE READINGS Williams, J. F. Personal Hygiene Applied, chap, i. The Meaning of Health. Hough and Sedgwick. The Human Mechanism, chap, xvi, Introductory to Hygiene ; chap, xviii, Hygiene of the Nervous System. Pubhc Health Reprint 164, Mental Hygiene. CHAPTER XXVIII THE HUMAN ORGANISM AND KEEPING IT FIT Questions. 1. Of what use is it to know the structure of the body? 2. Of what use is it to know about the workings of the various parts ? 3. What is the use of studying the bodies of other organisms ? 4. What is the use of making experiments upon the bodies of various animals ? 5. How can we tell that experiments on animals have helped mankind ? 6. Is it true that men have more ribs on one side than on the other? 7. How do broken bones heal ? 8. How do some people come to have one leg shorter than the other ? 9. Are people with large muscles healthier than people with small muscles ? 10. Which is better for health, games or gymnastics ? 223. Getting under the skin. A person does not need to know anything about his stomach in order to digest food prop- erly, and some of the greatest brain workers that the world has known were totally ignorant about the nature of the brain and about its very existence ; but pain and discomfort come to most people at one time or another, and in every community there are people whose chief topic of conversation is a comparison of the ailments that they "enjoy," so that someone has wittily called these frequent health discussions "organ recitals." Is it not almost a universal custom to greet people with an inquiry as to their health, and to part from them with wishes regarding their health? Hail (really the same as hale) and farewell/ Our words salute, for greeting, and valedictory, for leave-taking, also show that the race has always had before it the problem of health, or wellness ; and yet most "organ recitals" are absurd in the ignorance that people display regarding their bodies ; and they are foolish too, because, instead of helping in any way, they only keep people in an unhealthy frame of mind. Nevertheless, it is of value for all of us today to know some- thing about the body and its workings, both ( i ) to help us keep 272 THE HUMAN ORGANISM 273 ourselves well and fit and (2) to enable us to cooperate with others in keeping the community well and fit. For many cen- turies even physicians were unable to become thor- oughly acquainted with the structure and workings of the human body, because (i) popular superstition stood in the way of dissect- ing, or cutting apart, bodies for the purpose of training physicians and surgeons ; and (2) almost complete reliance upon authority in all studies left students satisfied to learn what the masters handed down from generation to generation, instead of trying to learn facts at first hand. Today we are able to get more reliable information from books, charts, manikins, and models, and more direct knowledge from a Fig. 121. The leopard frog [Rana virescens) This common batrachian shows the general external plan of structure among vertebrates: a head with a mouth and most of the sense organs, and a trunk with two pairs of limbs. (Courtesy of .American Museum of Natural History) Fig. 12 2. Homology in hind legs of vertebrates The hind legs of all four-footed animals and the legs of birds correspond to the paired hind fins of fishes. In spite of the many differences between them we can easily find the resemblances in the legs and feet of the frog, a; the lizard, b; the bird, c; the horse, d; the rhinoceros, c: and the elephant, /. H is the heel in each case study of prepared material and from dissections of other animals. It is remarkable how much we can learn even from Fig. 123. Anterior limbs of vertebrates The limbs of the different classes of backboned animals are so distinct that most people never discover that they are all different forms of the same organ. W, the wrist : a, frog; b, partridge; c, man; d, bat; e, dolphin; /, blackfish Pituitary gland Thyroid gland Thoracic or chest cavity Heart Diaj)hragm Suprarenal gland Abdominal cavity Fig. 124. The body cavity of man In the thorax, the part above the diaphragm, are located the heart and the lungs, together with air vessels, blood vessels, and the part of the food tube connecting the mouth with the stomach. In the abdomen, the part below the diaphragm, are located the stomach, the liver (with the gall bladder), the small and large intestines, and the reproductive organs, together with blood vessels and special ducts. The digestive organs are not shown in this figure, but the kidneys, the bladder, and the connecting ureter can be seen. (Courtesy of J. R. Bray Productions, Inc.) THE HUMAN ORGANISM 275 Oall bladder Liver ^' Pancreas Jnlestine Kidney carving poultry or from studying the joints of meat and other m.aterials that come from the butcher shop. 224. General plan of vertebrates. On page 16 we started to make a comparison between the human body, representing a vertebrate, and an insect body. The frog is a convenient ani- mal for showing the general plan of vertebrates. We note the main body, or trunk, with the head at one end and with two pairs of appendages. In the more familiar groups of vertebrates (mammals, birds, amphibians, and certain rep- tiles such as lizards and tur- tles) the posterior (hind) appendages are so much alike that we generally call them by the same name — legs. To be sure, the flippers of the seal or the whale resemble the fins of fishes more than they do the limbs of land animals, and the fins of fishes do not resemble our legs or arms at all, except perhaps in their positions on the body; yet they are truly homologous organs (see Figs. 122 and 123). The head is easily recognized in all classes, although it is not always on a distinct neck. The trunk of the frog consists of a body wall inclosing a large cavity. In the mammals, including man, the body cavity is divided into two chambers by a muscular partition called the diaphragm (see Figs. 84 and 124). Inside the cavity of the Fig. 125. The viscera of the frog In the body cavity of the frog are lo- cated the principal breathing organs (the lungs) ; the principal digestive organs (stomach and intestines, liver and gall bladder, and pancreas) ; the principal excreting organs (the kidneys) ; the blood- pumping organ (the heart); and the re- productive organs (ovaries or testes). The largest blood vessels, air tubes, and con- necting ducts are also in this cavity 276 BIOLOGY AND HUMAN LIFE Trachea Lungs Liver {turned back) Gall bladder trunk are the viscera, or the organs directly connected with the main functions of nutrition (including respiration, circulation, and excretion) and reproduction (Figs. 125 and 126). In fishes, which have no lungs but breathe through the gills (see Fig. 186), the viscera of the digestive system lie fairly well forward (see Fig. 78). The dissolved oxygen, which is taken from the air by the water, is absorbed from the water by osmosis. Among all vertebrates there is, of course, a portion of the food tube con- necting the mouth and the stomach {esophagus) that passes through the thorax. Among ver- tebrates that have no diaphragm (all classes of backboned animals except mam- mals) there is no sharp distinction be- tween the thorax and the abdomen, and we find a great deal of overlapping of organs. Running through both thoracic and abdominal cavities is a double chain of nerve ganglia mak- ing up the ''sympathetic nervous system" (see page 253), which lies at the very back of the cavities, in front of the spinal column. In all except the lowest vertebrates the head carries a dis- tinct jaw and several special sense organs, the eyes and the ears being the most prominent. The larger part of the head in man consists of the brain box, or cranium. In the frog you Heart I Diaphragm Stomach Pancreas Large intestine Small mtesline Appendix vermiformis Fig. 126. The viscera of man In all air-breathing vertebrates the internal organs have essentially the same general structure and the same gen- eral arrangement 'K^^/ Fig. 127. Skulls of vertebrates Compare the size of the face and jaw with the size of the brain box. Note the ap- pearance in man of a distinct chin and a nose bridge. /, alligator, 18 inches long; 2, chicken, i^ inches; 3, lion, 11 inches; 4, lemur, 3 inches; 5, gibbon, 5 inches; 6, man, 8 inches b W Fig. 128. The third eyelid The little fold of tissue extending from the inner corner of the eye corresponds to the third eyelid, or nictitating membrane, in birds and certain reptiles and amphibians. The nictitating membrane can be drawn over the eye so as to cover it completely. a, eye of ape; b, eye of owl; c, human eye; c^, the semilunar fold, eyeball removed Shoulder, or pectoral girdle Collar bone, or clavicle Breastbone, or sternum Shoulder blade, or scapula Humerus Radius Ulna Scicrum Kneecap, or patella Fig. 129. Human skeleton The skeleton consists of bones attached to one another by tough bands of connective tissue called ligaments. At various points bones next to each other are separated by tough, elastic pads of connective tissue, as between the parts of the vertebral column; at other points two bones that move against one another are separated by special joint surfaces that are perfectly smooth and lubricated by a fluid; at other points distinct bones appear to be fused together; and in some places the bones run into a tough tissue called cartilage, which is the same as the gristle in the outer ear. All the bones, together with the cartilages and ligaments, make up the skeleton THE HUMAN ORGANISM 279 can easily see the eardrum back of the eye; there is nothing corresponding to the external ears of mammals. If you watch a living frog for a little while, you will notice something peculiar Fig. 130. Homologies in the skeletons of vertebrates In spite of the different appearance and different functions of the limbs of backboned animals the supporting structures have the same general plan. W, the wrist bones : a, man; b, lion; c, vulture; d, bat; e, whale; /, halibut Fig. 131. Homologies in the bones of the hind leg Walking, crawling, swimming, loping — all the various modes of locomotion found among backboned animals — are carried on by organs having the same fundamental structure. A, ankle bones: a, man; b, lion; c, wolf; d, duck; e, crocodile; /, seal in the way he "winks" (see Fig. 128). Fishes have no eyelids at all, and in snakes the eyelids are always closed but transparent. The nostrils in the frog correspond to ours and lead into the mouth cavity; they can be closed. In all vertebrates the breathing organs are connected with the mouth, but in none of the invertebrates. The tongue is a muscular outgrowth 28o BIOLOGY AND HUMAN LIFE a Fig. 132. Some curious but useless relics In the glass snake, a kind of lizard (Anguis jragilis), the buds of the front legs are present during an early stage of development, a, but the fully formed animal is foot- less. In the porpoise {Phocaeua communis) the buds of the hind legs (or flippers) are present during an early stage of development, b, but the fully developed animal has only front flippers Fig. 1-^ -^ 00- Human vertebrae Each of the units of the spinal column consists of a main body (with an arch on the dorsal side) and various projections. The openings in the arches make up a tube, or canal, in which the spinal cord lies from the floor of the mouth, and acquires a great variety of forms and functions in different species of backboned ani- mals : in most cases it is either a food-getting organ or one that moves food around during the process of chewing. THE HUMAN ORGANISM 281 225. The skeleton. Among vertebrates the skeleton, the mechanical framework of the body, is an internal structure. This is in contrast to the insects and other arthropods (crabs, lobsters, spiders, etc.) and to the mollusks (clams, snails), which have their skeletons on the outside of the body. The general plan of the skeleton is that of the body as a whole. There is a main axis, the backbone, or vertebral col- umn, extending back from the brain box, or skull, and there are two bony rings to which the appendages are attached— the pectoral, or shoulder, girdle, and the pelvic, or hip, girdle (see Fig. 129). Bones of animals often persist, buried in the earth, long after the other tis- sues have completely disap- peared. As a result we have remains of animals that lived millions of years ago, and that show many stages between series that are liv- ing today. Thus, there are skeleton remains, or fossils, of animals that resemble both birds and reptiles. Again, in some animals bones develop during the early stages of growth but never reach the condition of perform- ing any function. This is true of leg bones in the whale, and the legs of certain snakes, which never appear above the surface of the body (see Fig. 132). The spinal-column units, or vertebrae (singular, vertebra), are all built on very much the same plan (see Figs. 133 and 134). Among fishes and some of the reptiles there may be an indefinite number of vertebrae, but in the other classes of vertebrates there Fig. 134. The vertebrae and the nerves On each side of each vertebra, aa, passing out between the stalks of the arches, are the spinal nerves, bb. These nerves connect (i) with the muscles and viscera at correspond- ing levels, and (2) with the corresponding sympathetic ganglia, cc 282 BIOLOGY AND HUMAN LIFE Cranium Sieruiim is a tendency toward the development of a fixed number. In mammals, for example, there are always seven vertebrae in the cervical, or neck, region; the giraffe has no more than a mouse. The thoracic region has twelve vertebrae. The ribs are of varying lengths and make up a sort of cage for the delicate organs in the thoracic cavity (see Fig. 84). They are capable of considerable motion and so permit the breathing move- ments. In birds the bones tend to fuse together and the ribs are not movable. In man the first seven ribs are attached to the breast- bone, or sternum, by straps , of cartilage. The eighth, ninth, and tenth are con- nected by cartilage that is attached to the cartilage of the seventh rib. The elev- enth and twelfth ribs are not attached in front. In most mammals, rep- tiles, and fishes the spinal column is nearly straight, or somewhat arched, curving outward on the dorsal side (see Fig. 2). In early stages of human development the column also has the form of a continuous arch from the head to the coccyx; but in adults and in birds it has a more complex curvature (see Fig. 136). Pelvis Coccyx Fig. 135. The human backbone Each region has a rather definite number of vertebrae. In some of the lower vertebrates (fishes, reptiles) there is considerable varia- tion. The five vertebrae in the sacral region are fused together, and the pelvic girdle is fused to the sacrum. Four or five small verte- brae make up the coccyx. In early stages of development there may be as many as eight or nine bones in this "tail" region THE HUMAN ORGANISM 283 The skeleton of the head region shows many adaptations to the workings of the organism, as well as to external relations. Besides the bony protecting case of the brain we find sockets for the eyeballs and joints for the jaw. The teeth are not bones but special skin structures ; there are definite sockets in the jaws, however, for all the teeth. The spaces in the face bones are very intricate and are connected with both the sensory and the respiratory functions of the nose. The whole of the hearing apparatus, together with the balancing organ, is inclosed by the bone of the skull (see page 232). There are many openings in the base of the brain box, through which nerves and blood vessels pass. In a saddle-shaped depres- sion in the base of the skull, back of the eyes, lies a two-lobed organ, the pi- tuitary gland, which pro- duces important internal secretions (see Fig. 124 and page 178). 226. The structure and growth of bones. The skeleton of vertebrates differs from the exoskeletons of invertebrates in one very important respect : it is made up of living tissue. Bone cells absorb from the lymph a large proportion of mineral matter and deposit this as lime salts outside of themselves (Fig. 137). In the development of the individual from the one-celled stage there appear groups of Fig. 136. Development of the erect form In relation to the upright carriage of human beings, the backbone gradually changes its shape from infancy .on. When the erect po- sition is attained the backbone shows four distinct curves 284 BIOLOGY AND HUMAN LIFE cartilage cells at various points. Some of these cartilage cen- ters in time become bones ; the cartilage at the ends of certain bones does not become completely ossified (that is, changed into bone) until maturity is reached (see Fig. 94). Some cartilage structures never become bony. In some of the lowest fishes the entire skeleton remains permanently cartilage. The long bones have hollow shafts containing marrow. Where two bones move against each other the enlarged ends furnish in- creased surfaces. Here the bones are spongy on the inside. Thus the skeleton combines me- chanical strength with relatively light weight. Among birds the bones are rather more compact but contain larger holl.ows and are relatively lighter. Through cell division in sur- face layers, which make up the periosteum, the bone grows in thickness ; and it is also from these tissues that injuries are re- paired by the formation of new bone. Bones increase in length through cell division in special sections between the shaft and the head at each end. As age advances, these grow^ing areas become hardened and further growth is impossible. The large proportion of cartilage in the skeleton of an infant accounts for the softness and flexibility of the young organism as compared with the adult or aged. With increasing propor- tions of lime the bones become more brittle. It is accordingly important to prevent pressures and postures in childhood that may lead to distorted or misshapen organs. Primitive peoples used to press the heads of babies out of shape, and some used to squeeze the feet out of shape. Even in comparatively modern times, in Europe, children have been crippled or twisted in order to serve as bait for charity in the business of begging. Fig. 137. Growth of bone Living cells, a, deposit lime around themselves but remain connected by tiny canals with one another and with the circulation of lymph, b THE HUMAN ORGANISM 28 227. Development. The transformations observed during the de- velopment of insects (metamorphosis, see page 29) are matched by equally great changes in the development of backboned animals. For most of the familiar vertebrates this process is concealed from us be- cause it takes place within the body of the mother or, among birds and reptiles, inside the egg. In fishes and amphibians, however, the stages can be easily seen, as the development takes place in the water (see Fig. 138). Since every individual begins life as a single cell, this stage has been compared to a protozoon. This one cell, or fertilized egg, divides into two ; each of these divides again ; and so on. For a considerable part of the journey from a one-celled organism to a many-celled organism all the higher species are very much alike (see Fig. 107). When we com- pare the embryos of several kinds of backboned animals, as the fish, the a Fig. 138. Development of the frog {Rana palustris) a, eggs; b, newly hatched tadpole; c, older tadpole with gills and front legs; d, tad- pole with hind legs; e, young adult (gills and tail absorbed) and older mature frog bird, the salamander, and the rabbit, we find that they are ver>' much alike early in their development, not only when each consists of a single cell but even later, when it is possible to distinguish head and trunk and limbs (see Fig. 139). As they become older they differ from each other more and more. During the development of the human organism after birth the different parts of the body do not grow at the same rate (see Fig. 140). The bones of the skull in the newborn infant do not quite meet at the edges (Fig. 141). 228. Hygiene