Marine Biological Laboratory R.rPiv.H J^iy 17 AS44 57595 Accession No. Given By Dr. B. C. Griienberg Nev: York City Place THE FAMILY TREE OF PLANT LIFE When we try to sort living things (or any other things, for that matter), we find our arrangements branching off the main line and branching off again and again, like the twigs of a tree. Some living forms cannot be classed definitely as plants or defi- nitely as animals l)rauiii;;s hy Uoiu-rt UlaitiiiT THE FAMILY TREE OF ANIMAL LIFE The farther a type is from the base of the trunk, the more complex and the more distinctive it is, as a rule. If we suppose that each living form descended from an- other plant or animal, the arrangement suggests that in the course of time species departed from ancestral types BIOLOGY AND MAN By BENJAMIN C GRUENBERG Consultant, Social Security Board Formerly Chairman Biology Departments Commercial and Julia Richman High Schools New York City and N. ELDRED BINGHAM Horace M^ann-Lincoln School Teachers College, Colum.bia University GINN AND COMPANY 'Boston • 'M.etv Yor\ • Chicago ■ Atlanta • Dallas • Columbus • San Francisco • Toronto • J^ondon COPYRIGHT, 1944, BY GINN AND COMPANY ALL RIGHTS RESERVED 344.2 gtie gtfttngum ^refl< GINN AND COMPANY • PRO- f EIETORS • BOSTON • U.S.A. PREFACE Our secondary schools today are common schools in the sense that ele- mentary schools were common fift)' years ago. That is, they enroll somewhat over two thirds of the boys and girls of the age they are designed to serve. In the past our high schools were responsible for special services to boys and girls who were in line for careers in the professions or for leadership in their communities. Today our high schools must furnish guidance, instruction and training of value to everybody. We have tried in this book to introduce a unified science of living things, which we regard as a valuable part of our common heritage. Like the traditional three R's of our common schools, this introduction opens the way for all, expecting that each will continue as far as he wishes or needs to along particular lines. Some will wish to go further with botany or entomology, for example, or with gardening or breeding, whether as a hobby or as a profession. Some will wish to become nurses or technicians, physicians or administrators, and so will follow their "biology" in different directions. And some will find that this book will serve as a solid and ample foundation for college work. These young men and women honestly want to understand the essential facts of personal and social life and the practical implications of these facts for themselves. These students are already on the verge of being the adult workers and voters and policy-makers of their time. They will have to decide scores of issues involving human beings as organisms — organisms that want food and shelter, that want to be well and to prolong their lives, that have to live together without destroying one another. These young men and women want to know more about the human species than they can possibly get out of the specialized subjects that ignore the organic nature of man, and more than they can possibly get out of a "biology" that ignores the distinctively human characteristics of this particular species — its intellect, its imagination, its inventiveness, its emotions and sentiments, and the very sociality that makes it possible for us to have any science at all. We have accordingly tried to depict life in terms sufficiently broad to include man himself and sufficiently concrete to be within the grasp of the common mind. This has meant developing the material from points of view that are generally meaningful, the familiar functions, activities and relation- ships of living things: eating and breathing, growing and maturing, origins and developments and death, health and sickness, the helps and hindrances to life that come from the inanimate world and from other living things— and from the doings and intrusions of man. Ill Each unit and each chapter of this book starts with a number of questions that represent, in our experience, the common curiosities and wonderings of young people. These questions focus the interest and attention of the reader and give direction to the discussion. But there is no pretense that these ques- tions are about to be answered; for while they are genuine and relevant enough, they cannot always be answered in the form they take. Many imply assumptions that are at least of doubtful validity; others involve ambiguous terms. Even a question consisting of but a few familiar words may be quite unanswerable. Why is sugar sweet? Or, Why is blood red? The easiest answers to give and to "understand" and to remember are of course the oldest answers — the kind that primitive man could think up and that the race has indeed remembered to this very moment. Since we frequently are not satisfied with such answers, for we believe them to be often not only evasions of the questions but in most cases effective obstacles to further thinking, we have assumed that it is a large part of our task to clarify the very questions for which answers are sought. At the ends of the chapters are questions (sometimes the "same" questions) which we assume now have new meanings, explore new understandings; and, again, there are questions that can be answered only by interpreting meanings. Accepting the scientific way of constructing knowledge out of thought and experience, we suggest at the ends of the chapters numerous "explora- tions and projects", through which students may obtain practical experience in organizing material to guide and check their thinking. (These activities are referred to by number in footnotes at the points in the chapters where they are likely to be most helpful.) Another characteristic of the scientific method is the analysis of materials and problems into smaller and smaller bits in search of the ultimate atoms. This leads to a rapid expansion of our knowledge; but it often results in forms of thinking that disregard major problems of daily living. We hope to counteract such atomism by making it clear that life is essentially an inte- grative process, one of bringing various elements together into dynamic wholes. We consider it of special importance today to further a common understanding of the role of co-ordination wherever there is "division of labor", in social life as well as in organisms. This need seems to us quite urgent in a time when the great conflicts of the world arise from the efforts of the several self-conscious groups, associations, classes, nations and other fragments of mankind to control for private ends the social and cultural values to which all have contributed and which arise in any case only from social and cultural interactions. We have taken special pains with the illustrations and are particularly grateful to the artists, photographers and others, whose co-operation is acknowledged throughout. The drawings are by Bernard Friedman, Hag- iv Strom Company, Marcel Janinet, Herbert Paus, Hugh Spencer, and Karsten Stapelfeldt. Although many of the illustrations are more or less self- contained in that each conveys a complete idea, they, with their accompany- ing legends, are intended to be integral supports for the text. Many are, of course, convenient devices for conveying ideas of structure or of form; but most of them involve ideas of process, of relationship, of historical tlevelop- ment, or of logical development. In some cases they raise questions that cannot be answered on a purely "factual" basis. All these graphic pieces are intended to facilitate the work of the student, but for the most part they cannot be lightly skimmed over like items in a picture book: they call for close attention and reflection. We have been helped in our work by the many colleagues in the business of teaching and by the many students through whom we think we have come to understand the problems of the learner and his world. We wish to acknowl- edge especially the helpful suggestions and criticisms and detailed information and other material received from Dr. Louis I. Dublin, Chief Statistician, Metropolitan Life Insurance Company; Dr. A. H. Ebeling, Lederle Labora- tories; T. Swann Harding, United States Department of Agriculture; Dr. Charles R. Knight, American Museum of Natural History; Professor Oliver Laud, Antioch College; Algernon Lee, New York; Dr. Lloyd A. Rider and Dr. Milton Hecht, Abraham Lincoln High School, Brooklyn; and Mrs. Emily Eveleth Snyder, High School, Little Falls, New York. B. C. G. N. E. B. >c CONTENTS PAGE INTRODUCTION • You and Biology 3 UNIT ONE . What Is Life? 9 1 • What Distinguishes Living Things? 11 2 • How Can We Know the Different Kinds of Living Things? 29 3 • How Does Man Differ from Other Living Things? 45 4 • How Do Individuals Differ? 61 UNIT TWO • Under What Conditions Can We Live? 79 5 • What Have Water and Air to Do with Being Alive? 80 6 • What Is the Relation of Food to Life? 96 7 • What Kinds of Stuff Serve as Human Food? 114 8 • How Do Food Stuffs Come into Being? 137 UNIT THREE • How Do Living Things Keep Alive? 161 9 • How Do Living Things Get and Manage Their Food? 163 10 • How Does Food Reach the Different Parts of the Body? 185 11 • How Do Plants and Animals Breathe? 201 12 • How Do Living Things Get Rid of Wastes? 214 13 • How Do Organisms Resist Injury? 228 UNIT FOUR • How Do the Parts of an Organism Work Together? 249 14 How Do Living Things Adjust Themselves? 251 15 • What Do the Nerves Do? 273 16 • How Do Glands Work? 301 17 • What Makes the Organism a Unity? 322 UNIT FIVE • How Do Living Things Originate? 341 18 • Growth and Development 343 19 • Reproduction of Life 367 20 • Reproduction in Flowering Plants 398 21 • Infancy and Parenthood 417 VII J7525 PAGE UNIT SIX • How Did Life Begin? 435 22 • Opinions on the Beginnings of Life 437 23 • History of Life on Earth 450 24 • The Facts of Heredity 472 25 • How Species Have Arisen 506 UNIT SEVEN • Why Cannot Plants and Animals Live Forever? 525 26 • The Limitations of Life 527 27 • The Conflicts of Life 540 28 • The Interdependence of Life 559 29 • The Balance of Life 578 UNIT EIGHT • What Are the Uses of Biology? 603 30 • Biology and Health 605 31 • Biology and Wealth 641 32 • Biology and the Pursuit of Happiness 658 IN CONCLUSION • Man the Creator (i]9 APPENDIX A • Grouping of Plants and Animals 687 APPENDIX B • Supplementary Readings 701 INDEX 705 ••• VIII BIOLOGY AND MAN INTRODUCTION You and Biology You have to learn biology, whether you like it or not. Everybody does. And why so? Because the curriculum requires it? Or because some college entrance board says so? Not for these reasons. It is because we are the kind of people that we are. Indeed, all of us have already learned a great deal of biology — very largely without meaning to. It just cannot be helped. Life Is Everywhere As far back in time as human beings first roamed the earth, they were surrounded by many different kinds of plants and ani- mals. All around were many kinds of birds, many kinds of tur-bearing animals, both large and small, many kinds of creepy and crawly things, bugs and worms and spiders, and fleas too. In the waters were many kinds of fish and crabs and clams, as well as frogs and newts, which shifted be- tween land and water. There were trees and shrubs and herbs, with flowers and thorns and berries, and some with thick, fleshy roots. What We Need to Know Through all the ages it must have been necessary for human beings to kjiow a great deal about many of these plants and animals, and for two very good reasons. First, it was necessary to know which of these natural objects could be used for food, or for clothing, shelter, tools, and weapons. Is that good to eat? Is that kind of wood good for a bow or for a club? Second, it was necessary to know which of these different kinds of things were injurious or dangerous. Is that snake poisonous? or that berry? Is that animal one to run after, or one to run away from? It is important to know how difiFerent kinds of birds and fishes behave, or we should have no luck killing or catching them. It is necessary to know something of the habits of wild beasts if we are to act in a manner that suits our needs. If you want to raise beans, you have to know something of the condi- tions suitable to the growth of beans. If you want to get rid of poison ivy or rats, you have to know what conditions destroy these forms of life. If you care about your own well-being, you must know some things about the workings of your own body: you must know what dangers to avoid, what conditions favor health, what to do in an emergency. Human beings have, in fact, always known a great deal about plant life and about animal life. Such knowledge is, as you can see, extremely prac- tical — that is, it bears directly upon what people do. Two plants or two 3 Rattler '.'■ ;.^ , .."jCopperhead American Museum of Natuial Historj KNOWLEDGE AND ACTION To some people all snakes look alike; but it is not safe to treat them all alike. With a little biological knowledge (about snakes) one learns that it is safe to handle a black or garden snake and to treat the rattler or the copperhead in a diflFerent way birds may look enough alike to confuse the ordinary observer; and one may be fit to eat while the odier is decidedly not. It is important to distinguish. Biology The V vast knowledge about plants and animals which people must have had from earliest times was divided in small bits among die many scattered tribes. Until modern times there was not even a name for diis knowledge or study about living things. The word biology is from the Greek bios ("life") and logos ("word" or "knowledge"), and means life- knowledge, or life-science. It was first used in diis sense by a German botanist (a student of plants) named Treviranus, who in 1802 published a book with the title Biology ^ or a Philosophy of Living Nature. A American Museum of Natural History BIOLOGY STARTS AT HOME People living in the uplands of Africa know some biology of the giraffe, but little about the lobster or the walrus. Eskimos can manage animals of the arctic, but know nothing of coons or squirrels. But everybody learns some biology If the subject is so Important, why did it take so long to reach a common name for it.-^ A general science of living things became possible only after human beings began to move away from their villages and hamlets, and to see strange people, strange plants and animals. People had first to discover that the world is much larger than their own country, and that it contains many "wonders" that are perfectly familiar and commonplace to other people. The Greeks appear to have been the first people who tried in an orderly way to bring together facts about all kinds of animals and plants from all parts of the world. Collecting samples from everywhere must have been D very difficult. Luckily, the emperor Alexander ordered his governors and generals to send natural objects from all regions, to please his old teacher Aristotle. As people traveled more widely and saw more and more kinds of living things, they naturally changed their ideas about life. For one who moves about must broaden his outlook upon the world. He comes to see his fel- lows and the other inhabitants of the earth in a different way from one who lives always in the same neck of the woods or along the same stretch of shore. As time goes on, we move about and see larger regions of the world and more of its inhabitants. Wherever strangers meet, knowledge increases: we learn from each other. We thus lengthen our lists of known plants and animals and find new uses for various kinds. The Spanish missionaries brought Peruvian bark to Europe; and for over three centuries that was the only remedy we had for malaria. People formerly threw to the dogs por- tions of food animals which we now know to be worth more to us than the meat itself. A few very old men and women remember when the tomato was considered a poisonous fruit. The weeds and vermin of one region are valued and cultivated in another. Men migrating to new regions often found new pests attacking their crops or their cattle. And they often met new diseases too. As population grows, we have to make farms yield more. Growing cities create problems of water supply and ventilation, sanitation and the transporting of food, which is always in danger of spoiling. New chemicals and smokes and dusts in new industries bring new problems of protecting the health of workers. Today, when planes encircle the globe in a few days, or survey inacces- sible mountain valleys, or bring together on short notice representatives of widely scattered peoples, biology means more than ever. Plants and animals of any region come to be important to people far away. Human life every- where may profit from whatever people anywhere can get out of biology, whether it is a substitute for quinin or an antitoxin, a new sulfa drug or a new idea about managing things. And flying itself is possible for more people only as special biological problems are solved. Modern biology, or life science, is thus one of the outcomes of the great social, economic, and political changes of the past three or four centuries. And in turn biology is bringing about still further changes — many of them no doubt improvements in our ways of living. Kinds of Biology We can ask many different questions about any given subject. Among the first questions that each of us probably asked after we learned to speak are those that have to do with class, or kind. What kind of tree is that? What kind of stone is that? And the usual , . It j Shorthorn Longhom Gnu Brahman Yak Bison Musk-ox { (Europe and (South (India) (Tibet) (North (Greenland North America) Africa) America) and Canada) THE FAMILIAR AND THE STRANGE Cowlike animals found in various parts of the world are all alike in some ways. But the strangers differ from the cow and also from one another answer is a name, that is a sycamore tree; that is a ruby. Sorting and nam- ing are, of course, very important to us, especially while we are growing up and constantly coming across strange new objects. But the task is endless, for there are a million or more distinct kinds of animals and probably as many kinds of plants. There are numerous varieties of apples or wheat, hundreds of species of beetles and clams. It is impossible for anybody to "know all the kinds of living things". How many different kinds of oak trees can you distinguish, or dogs, or butterflies, or roses? Classifying and naming plants and animals occupy large numbers of men and women the world over. This branch of biology is called taxonomy, from a Greek word meaning "arrangement" or "order". Other common questions about living things have to do with the use we can make of them, or with the harm they may do. But to answer such questions about the economics of plants and animals, we must be able to distinguish the various kinds. The logwood tree, a relative of the locust tree living in semitropical regions, was formerly the chief source of black dye. But shiploads of "logwood" came to market with none of the essential pigment-producing materials: the "real" logwood and the not-quite-the- same logwood were not easily distinguishable. We commonly recognize familiar species of plants and animals by their general forms, sometimes relying upon surface patterns or coloring. But that raises special problems. For example, is a worm to be considered a small snake, or a snake a large worm? Is the whale a kind of fish? Is moss a kind of grass? The more closely we examine and compare plants and animals, the more satisfactorily can we arrange them or sort them. But then we raise new problems. For example, we notice that the arms of a man "correspond" in some way to the forelegs of a horse or a squirrel, and also to the wings of a bird; yet the wings of a bird and those of a butterfly do not correspond in the same way, although they do the same kind of work, 7 Again, we notice that the whole collection of living things in any one place is constantly changing. Has each kind always existed as we see it now? What of the kinds that formerly lived here? How did the indi- viduals originate ? Even if we begin with the practical questions of getting what we need and avoiding injury, many other questions are bound to arise. What conditions favor living or interfere with it ? How do different kinds of living things influence one another? Each of these questions may start us off on a new study or special "science of life", of which there are many. The answers we get to such questions make us act differently in connec- tion with various plants and animals, including other people. But what we do changes the conditions around us — and raises new problems. So we have to learn about living beings, including ourselves, whether we like biology or not. And everybody is doing it. For biology is that branch of science which has to do especially with life processes. This knowledge helps us to preserve and improve our own lives. UNIT ONE what Is Life? 1 How many different kinds of animals are there? 2 How many different kinds of plants are tfiere? 3 What does it mean to say that the tiger belongs to the cat family? 4 In what ways are different kinds of animals "related", or different kinds of plants? 5 How can we recognize each kind of animal or each kind of plant? 6 Can one kind of living thing be changed into another kind? 7 In what ways is man like animals? 8 Is man the most important being in the world? The proper study of mankind, said Alexander Pope, is man. Centuries before the time of Pope a wise Greek recommended "Know thyself." But one difficulty in studying ourselves is the fact that we are too close to our- selves to see clearly. And we have our prejudices too. Besides, it does seem rather conceited. For how important are we, or how important is mankind ? When Columbus started on his journey toward the setting sun, prac- tically everybody in Europe thought that the earth was the center of the uni- verse: it was put there to be the abode of man. Fifty years after Columbus returned, Galileo and other scientists stirred up a great deal of bitter feeling by suggesting that the earth moves around the sun, not the sun around the earth. This idea caused much excitement because it pushed man with his little earth away from the center of the stage. It seemed to belittle man. And people — mostly poor, frightened, helpless — could not endure that. Yet what is more important than man.? Larger animals, or taller trees, or tougher fighters ? Is a rare flower or insect or diamond more important ? How can we get outside ourselves in order to see in true perspective.? We do actually compare ourselves with one another in order to decide upon relative merits and capacities. We compare ourselves with other living things too. We may assume without apology that man stands rather high among all living beings, if only because he alone appears capable of askjtig such questions] At any rate, there is only one excuse for all our effort, all our wondering and investigating and puzzling. And that is to enable human beings to live better, to get along better, to get more satisfaction, to enjoy life more. For us, at least, man is the most important thing in the world, and life the most important happening. To investigate "life" we must begin with ourselves, for we have to start 9 from wherever we happen to be — which is with ourselves. Indeed, we can- not do otherwise. We "understand" other people as we recognize in their actions our own purposes and motives and interests. When people act in ways very different from our ways, they may amuse us or annoy us, but they also puzzle us. And we try to "understand" other living things, and even nonliving things, by assuming that they have purposes and concerns like ours. We enlarge our knowledge by moving away from our starting-point. We compare more and more kinds of living things with ourselves, but also with one another. We compare living things with those that are not alive. We try to find out what the living and the nonliving have to do with each other, how they are related. We try to find out what "life" is by studying its various forms and its ways of acting — and what it means to man, who is still at the center of our universe. By enlarging our knowledge we come slowly to useful understandings, which help us to get along better. Original |''?\cell :fe^--7(^ \-'jy^ Nucleus Nucleus elongates ^^^^^ THE LIFE OF A SIMPLE ANIMAL ^/M) Two nuclei move apart ^■^■ Two ends of cell move apart Two distinct cells result The ameba has no definite shape, but moves about, pushing its jellylike mass now in one direction, now in another. After an ameba reaches its full growth, the nu- cleus, or kernel, lengthens out and gradually divides into two parts. The rest of the animal's body also lengthens, and the two ends seem to move slowly away from each other until there are two distinct individuals. Each of these is as complete as the other, and both are the same as the original mother cell except for size 10 CHAPTER 1 • WHAT DISTINGUISHES LIVING THINGS? 1 Are tliere animals tliat do not move? 2 Can plants feel? 3 Can insects hear? 4 Are plants alive in the same way as animals are? 5 What is there the same about plants and animals? 6 Are animals alive in the same way as we are? 7 Can plants protect themselves? 8 What becomes different in a plant or an animal when it dies ? 9 Can part of a living animal be dead, like a dead branch on a tree ? 10 Are there parts of animals that are of no use? We distinguish various kinds of natural objects by their colors, shapes, sizes, and arrangement of parts. But being aliife is not like being round or soft or purple. It means doing something. Living is acting in a cer- tain way. When we speak of a "live spring" or of a "live volcano", we mean that there is action. But we do not confuse a spring or a volcano with living things. A cloud moves across the sky, and it constantly changes its shape; but it is not alive. Action is a necessary part of our idea of life; but action is not sufficient to distinguish the living from the nonliving. How do living things differ from other objects? Is it their structure? or their chemical composition ? or the particular things they do ? or the way they originate ? Are plants alive in the same way as we are ? What is there about living things that makes them alive, that keeps them alive? How Are Plants and Animals Alike? The Parts of Plants^ If we examine a geranium plant, or any other small plant that is easily handled, we find that the part below ground (the root) differs in several ways from the part above ground (the shoot). They differ in color and in texture. The smallest branches or subdivisions of the root are, as a rule, more delicate than those of the shoot. In most kinds of plants the shoot consists of distinct stem and leaves, which differ from each other in shape, color, and texture. At certain seasons of the year the stem bears other structures besides leaves, namely flowers. Most kinds of flowers last but a short time and are succeeded by fruits, inside of which there are usually seeds. And these parts, the seeds, as we already know, are the beginnings of new plants. iSee No. 1, p. 27. 11 Virginia' creeper Rhubarb Hu,(, .'jptKl A WHOLE PLANT Most familiar plants consist of an underground portion, the root, and of a portion above ground, the shoot. The shoot is made up of stem and leaves. And on some special stems, or stalks, there are special clusters of leaves which together make up a flower. In some plants the root seems exceptionally large; or the stem may be underground; or roots may appear aboveground BILATERAL, OR TWO-SIDED, SYMMETRY^ The three "faces" are of the same person. The middle is a normal full-face photo- graph. The first is made up of the right half of the face and a "mirror image" of the same. The third consists of the left half with its "mirror image" We might say of such plants, (1) their bodies consist of distinct parts, and (2) the parts undergo orderly changes in the course of the year. The Human Body Since we are most familiar with our own bodies, we naturally use the body as a standard for judging other living things, or Bear Man I 1 \ Kangaroo BODY PLAN OF MAMMALS In all these animals there is a main axis, with the head at the front end. There are two pairs of limbs — the front ones attached at the "shoulders" and the hind ones attached at the "hips" ^From Expression of Personality by Werner Wolff. By permission of Harper & Brothers. 13 as the basis of "reference". Cats, dogs, horses, cows, and other famiHar mammals (animals that suckle their young) do resemble the human body in many ways. They all have a two-sided symmetry, the right and left sides being almost mirror-images of one another (see illustration, p. 13). They all have the same body "plan" (see illustration, p. 13). On the head are three pairs of special structures — the eyes, the ears, and the nostrils — which seem to relate the animal to the outside world. The mouth or food opening is in the middle line, below the nostrils. At the posterior or hind end of the trunk are special openings that are related to removing wastes from the body, and to reproduction. The skin of mammals usually has a more or less complete hairy cover. Although the limbs of common mammals are jointed or hinged, the body covering shows no distinct breaks over die joints. The forward part of the trunk, the thorax or chest, has a firm wall made up of curved bones, the ribs. The hind part of the trunk, the abdomen, has no such enclosing framework (see illustration, p. 48). An Insect In the grasshopper, a representative insect, the general plan of structure is that of a main body with distinct regions and several kinds of outgrowths or attachments (see illustration below). The head bears two feelers, or antennae (singular, a^itenna), projecting forward. The eyes occupy a large part of the surface of the head. Since each of these consists of numerous complete eyes, it is called a compound eye (see illustration, p. 15). In addition, there are three tiny simple eyes THE BODY PLAN OF AN INSECT In the grasshopper, as in other insects, the bilateral body is made up of a rather dis- tinct head at the front end; the main "trunk", or abdomen; and, between these, the thorax, which bears both the legs and the wings. The grasshopper has a rather large eardrum near the front end of the abdomen 14 Compound eye Lens of ommatidium Perforated supporting membrane Retinal pigment Retinal cells Corneal lens Cone Iris cells Lens- growing cells INSECT EYES The head of a locust showing the compound eye with its many facets, each repre- senting the exposed surface of an ommatidium, or single eye, and an ommatidium seen in section cut lengthwise. In the arthropods, or animals with jointed legs, there are compound eyes, as well as simple ones on the front of the head. The mouth, at the lower end of the head, con- sists 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 segment carries one pair of jointed legs. Two of the segments carry one pair of wings each, and the anterior (forward) wings cover the posterior (hind) ones when at rest. The abdomen, like the thorax, is distinctly segmented. Indeed, the name of this class of animals. Insects, refers to the fact that the body is "cut in", or segmented, like the body of a caterpillar. This is easily observed in the abdomen of dragonfiies, bees, moths and beetles (see illustrations oppo- site). The foremost segment has on each side a small tympanum, or drum, which is actually an eardrum (see illustration opposite). The hindmost seg- ment bears special structures that have to do with the removal of refuse, other structures with reproduction. In the female these terminal parts to- gether constitute the egg-laying organ, or ovipositor. The bodies of insects and of mammals, like the bodies of plants, consist of many distinct parts or organs. And if we take the time to watch any ani- mals over a long period, we see that they too, like plants, undergo regular changes in form and in behavior. Comparing The moment we begin to compare carefully, we dis- cover that structures can correspond in many ways and yet not be the same, even if we call them by the same name. Thus parts may be "alike" in relative position— as the "tail" of a cat and the "tail" of a dragonfly, 15 Blood vessel Food tube Spiracles Tracheae ^Nerve BREATHING TUBES IN INSECTS Each spiracle In the side of the body opens into a trachea, which branches repeatedly and brings air to all the tissues which is really the abdomen (see illustration, p. 18), or as the "thorax" of an insect and a human thorax, which differ in both their structures and their workings. Sometimes a name is carried over on account of similarities in the func- tions or workings of parts. Thus, the insect type^ represented by a grass- hopper, and the mammal type, represented by man, both have eyes, or seeing organs; legs, or locomotor organs; and jaws, or food-chewing organs. Yet the insect's eyes, legs, and jaws differ from the corresponding organs of the mammal in many details of form and structure, and in the way they develop from the earliest stages. Again, leaves have been called the "lungs" of plants because in both leaves and lungs an exchange of gases takes place between the inside and the outside. Yet the two do not resemble each other at all in appearance, in structure, or in actual workings. Such comparisons bring out many differences among living things, as well as many resemblances. Through them we come to certain general facts that are the same in plants and animals. 16 What Do Both Plants and Animals Do? Activities of Animals' Every familiar animal moves from place to place. It also moves its parts, as in striking or biting. To us such move- ments at once suggest other activities. Mouth movements suggest eating. Eye movements suggest searching and watching. The movements of an in- sect's antennae suggest groping or "feeling", as we feel with our fingers. From our past experience we know that food is related to growing. And while neither a person nor any other animal enlarges under our eyes, we know that each must have grown, for neither was born full size. And that suggests another thing that animals do: they reproduce. There is also about each animal something that makes it move or change its movements when certain outside conditions act upon its feelers, or eyes, or ears, for example. Some of the animals we know 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 of the same kind. Activities of Plants What now of plants ? We know that plants grow. When we want new plants for any purpose, we usually look to getting them from seeds, which in turn come from other plants. That is, plants reproduce themselves. But do they also move } Is a plant sensitive to what goes on around it? Most of us have not noticed whether plants do really move or whether they respond to changes in their surroundings. Certainly plants do not reach out and grasp food, as do the kitten and the baby, for example. Nor does the plant eat with a mouth. Still the very fact of growing, which de- pends upon taking in food, implies some movement. The plant does take materials into itself from its surroundings, by way of the roots and by way of the leaves. And it does move, or transport, 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 we can easily observe a rapid movement of the leaves of a disturbed sensitive-plant. And we can observe slower, yet very distinct, turnings of many common plants toward the light (see illustration, p. 257). These movements show us that plants are sensitive to what is going on around them. ^See No. 2, p. 27. 17 Thus we find that plants and animals have in common certain processes or characteristics. They take food and they grow. They are sensitive. They move. They reproduce themselves. There are, to be sure, many differences also, but we are considering now their common characteristics. Organisms Each of the distinct parts in a plant or animal is some- thing more than a structural unit, like one of the bricks which make up a wall. Each special structure carries on a particular kind of work, it behaves in a particular way in relation to the other parts or in relation to the v/hole plant or animal. It is for this reason that each of the special parts is called an organ, or instrument. That is, each performs some special service or "function" in relation to the whole body. Most organs or parts do some- thing toward keeping the body alive. Any plant or animal that you know is made up of organs. Although living things do not all have exactly the same organs, the term organism is a useful one to mean any living being. Trunk ^ / \ DIFFERENT WAYS IN WHICH ORGANS CORRESPOND We often use the common names of the familiar parts of our own bodies for corre- sponding parts of other objects, living and nonliving. The trunk and limbs of a tree do correspond to the trunk and limbs of a human body, but only superficially Butterfly Airplane The wings of a bat, of a bird, and of a butterfly "correspond" to the wings of an airplane; but in structure, development, and workings they are quite different 18 TWO KINDS OF GROWTH Both plants and sand dunes enlarge by taking substances from the outside world. The dune grows as the winds bring it more sand, and as some of the grains stay put. The plant, however, grows by absorbing many different kinds of stuff from the air and from the soil, by transforming this material into new combinations, some of which ore finally plant stuff, and by laying down particles of plant stuff in all its parts How Do Organisms Differ from Nonliving Things? Growth All living things grow. Yet the crystals of many substances also grow, some of them very rapidly, even as we watch them. Most of us have seen icicles grow. If by growing we mean simply becoming larger, then snowdrifts and icicles grow just as truly as beets or babies. What, then, is the real difference between the two kinds of growing.^ An icicle becomes larger as new layers of ice-stuff (water) are added. The growth of a crystal proceeds in the same way. A baby, however, does not grow in this manner. The icicle grows by the piling on of ice material on the surface, or by accretion. The baby, like other living things, grows not by adding to the surface but by adding materials in all parts. Moreover, it transforms into its own substance stuff from the outside that is different: the organism assimilates, or makes stuff like itself. Irritability^ We perceive lights and colors, sounds, odors, and tastes. From the movements of familiar animals we infer that they are also in- fluenced by what happens around them. A dog does something when he is struck. Your eye does something when there is a sudden flash of light. Even a geranium plant changes its behavior when placed in a sunny window. The effects of these happenings are different from those caused by dropping a cup, for example, or by striking a stone. This irritability, or sensitiveness, of living things is in some ways the most remarkable fact about them. iSee No. 3, p. 27. 19 Yet sensitiveness is not altogether confined to living things. The chemi- cal compounds of the photographic film are in some ways even more sensi- tive than plants and animals. Some compounds are so sensitive that they will produce a violent reaction when they are dropped. It may be more disastrous to push a hot poker into a stick of dynamite than to poke a vicious dog. Unlike a living organism, however, the sensitive dynamite is destroyed by its reaction. Fitness If an animal is attacked, it usually acts in a way that will probably save it from further injury. 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". On seeing its kind of food, an animal will usually take steps to get it. Such responses tend, on the whole, to preserve life. This characteristic of plants and animals is sometimes called adaptiveness, or the capacity to fit, more or less completely, the surrounding conditions. Indeed, how could organisms continue to live, generation after generation, if they acted exactly the same under all circumstances? Origin We know nothing about the first appearance of life upon the earth. So far as our observation has gone, each plant and animal begins its existence in or on the body of some other plant or animal. In general, or- ganisms reproduce themselves, but nonliving bodies do not. Being Alive We may conclude that a living organism, a plant or an animal, is distinguished by these characteristics: It originates from another similar organism. It takes in materials from the outside and assimilates this food into its own substance. It transforms the assimilated material, getting from it the energy by which it moves and carries on other processes. It is sensitive to the conditions and changes in its surroundings. It responds to changes in ways that are adaptive — that is, more or less suited to preserving it, or keepifig it alive. It may reproduce others like itself. The adaptiveness of a plant or animal is never perfect. Most living things sufTer injury or privation, and are at last starved or destroyed. Living is a risky business. But even under most favorable conditions, the regular changes which normally take place in a living plant or animal at last come to an end. If not previously "killed", the organism eventually stops living. It dies. Dying is part of life. Nonliving objects can of course be destroyed: but they do not "die". What Is there about Plants and Animals That Keeps Them Alive? Cells' Plants and animals differ greatly in their forms and in struc- ture and activities; yet they are alike in growing, moving, being irritable, iSee No. 4, p. 27. 20 Anton van Leeuwenhoek (1632-1723) was a Dutch businessnnan with the hobby of making microscopes and looking at things nobody had ever seen before. He discov- ered tiny animals in pond-water One of Leeuwenhoek's microscopes. Through the nearly spherical lens in a copper plate tiny objects could be seen greatly magnified The Bi'tlmann Arrhive The Bettmann Archive An English contemporary of Leeuwen- hoek's, Robert Hooke (1635-1703), had the same hobby. As a scientist he made more systematic studies of bits of plants and animals In a thin slice of oak bark or cork, Hooke saw little compartments to which he gave the name cells or chambers, since they suggested the cells of a beehive or the rooms of a house. The Italian Malpighi also saw such "cells" in other plant frag- ments THE MICROSCOPE AND CELLS DIAGRAM OF A CELL Under better microscopes the living stuff looks like a very fine foam full of tiny bub- bles, or like a very fine network in which tiny particles are enmeshed. It is the pro- toplasm that is the living content of the cell, and that actually builds up the cell and being adaptive. Where is the underlying sameness? It was impossible to answer this until the microscope had been improved to a certain point. In the seventeenth century it was already possible to find hundreds of living things that are too small for the human eye to see unaided. A Dutch merchant, Anton van Leeuwenhoek (1632-1723), and an English contem- porary, Robert Hooke (1635-1703), made their own microscopes and peered at all kinds of very small objects. In a thin slice of cork Hooke saw little compartments to which he gave the name cells, or chambers, since they reminded him of the cells of a beehive — or a monastery (see illustra- tion, p. 21). Subsequently hundreds of students saw that all the plants and animals that they examined consist of "cell", although these are of many sizes and shapes. In 1839 a German botanist, Matthias Schleiden (1804-1881), and his friend Theodor Schwann (1810-1832), a zoologist, developed the idea that the "cell" is the "unit of structure" in all living things (see illustration, p. 21). They were not clear as to just what goes on in the cell. And they gave their attention mostly to the walls or membranes of the cells. But using the cell idea led to further important discoveries. Protoplasm About a hundred years ago various investigators in France, Italy, Germany, Bohemia, and no doubt elsewhere, were searching in cells for the secret of life. They began to observe a curious slimy or jelly- like substance in both plant material and animal material— something like white-of-egg in appearance. By 1840 the Bohemian scholar Johannes Evangelista Purkinje (1787-1869) suggested the name protoplasm (from protos, first, and plasm, forming-material). Other investigators hit upon 22 the idea that this protoplasm is essentially the same in all plants and ani- mals. It has, in fact, been called "the living substance", although we know that it is a very complex mixture of many different substances (see illus- tration, p. 22). We continue to speak of the cell as "the unit" of living things, even !""■ © General Biological Supply House AN EXCEPTIONALLY LARGE AMEBA, Chaos chaos The protoplasm is constantly stirring around, constantly changing its shape, moving sluggishly about. The slimy mass wraps itself around food particles, and it crawls away from particles within that are no longer usable. Without distinct regions or organs, the omeba does all it takes to keep alive 23 Bacteria witti TYPES OF PLANT CELLS though in many of the simplest plants and animals the body is not divided into distinct chambers or cells. We speak of the individuals in these forms as consisting of single cells. One of the simplest animals is the ameba, which lives in stagnant pools and looks like an irregular lump of jelly enclosing tiny granules and bub- bles. The animal responds to physical and chemical disturbances by con- tracting the protoplasm, or by drawing in its pseudopodia, or "false feet". Variety of Cells When we look at an ordinary plant or animal, we do not see the protoplasm, nor even the cells, but masses of walls of cells. In the larger plants and animals the outer layers of cells are usually dead — that is, they are walls without living protoplasm, just the kinds of cells that Hooke saw in cork. The microscope enables us to see that some cells have thicker walls or enclosing membranes than others, some hardly any (see illustrations, pp. 24-25). We can see various kinds of solid bodies floating in the protoplasm. There are also bubbles of clearer liquid. In some living cells it is possible to see the protoplasm streaming about (see illustration, p. 26). Nucleus Near the center of each living cell, or at one side, we can usually find a portion that seems more dense than the rest. This is called the ?jucleus, which means "kernel". Since protoplasm is usually transparent, it is difficult to distinguish its structure, even with the microscope. Now we know that various kinds of dyes stain some materials more readily than others. We can therefore use them to help distinguish the nucleus as well as other structures in bits of plant and animal tissue (see illustration, p. 10). Multiplication of Cells Most of the plants and animals that you have seen contain indefinite but very great numbers of cells. Some living things, 24 Flat epithelial cells ^ \ "^ >-A:< Columnar epithelial cells Unstriped muscle cells Dendrites TYPES OF ANIMAL CELLS Bone cells ~ Shapeless ameba cells Cells containing fat globules Axon Nerve cell, or neuron Terminal .--- •O"'^?^ 1 branches' however, consist of very few cells or, like the ameba, of a single cell. Bac- teria, of which everybody hears a great deal, are one-celled plants. So are many algae, for example the "green-slime", which lives on the shady side of trees or on damp shingles. But every plant or animal, whether it consists of a single protoplasm unit or of many millions of cells, starts out as a single cell. Among the one-celled organisms, a new individual originates by a comparatively simple division of a parent cell — one cell becomes two! The nucleus divides into two equal parts, and then the rest of the protoplasm divides. Thus two distinct cells result (see illustration, p. 10). In many-celled animals the body grows as cells increase in size. When a particular cell reaches its full size, it may divide into two. The nucleus splits first and then the rest of the protoplasm. A new individual usually arises from special cells which become separated from the parent body (see Chapter 19). Protoplasm Is Fundamental In the one-celled ameba, as we have seen, the single bit of protoplasm carries on all the life activities. It grows, it moves, it reproduces, and so on. Yet in the larger plants and animals, those having many kinds of cells and millions of each kind, the protoplasm of each cell carries on the same fundamental activities. However different a bone cell may be from a brain cell, or a tree cell from a dog cell, the protoplasm in all cases is irritable, it can grow, it can move, and at some stage of its life it can reproduce itself. The many different kinds of plants and animals, with their peculiar forms and organs and many kinds of activities, are a constant source of wonder. Yet they all apparently arise from protoplasm, which is always the 25 .-•..- -.-.v.- --:/.., •-.•.••.^. .. _.:• . '.•.•?r...-r •.:•;•• .-•.-'••■.' \1' PROTOPLASM MOVES In many types of cells that have been studied, we can see portions of the fluid stream- ing or circulating about, as suggested by the arrows same in some respects, but always capable of changing as circumstances change. Fundamentally the same in all organisms, it is in every particular case distinct and peculiar. That is characteristic of protoplasm, as it is char- acteristic of life. At any rate, scientists are pretty well agreed that it is this protoplasm of a plant or 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. In Brief Plants and animals take in food and grow by assimilation; nonliving objects grow only by accretion. Living plants and animals move through processes going on inside the organisms, while inorganic objects are pushed around by outside forces. Living things are irritable, or sensitive to changes in their surroundings. The responses of living things to disturbances are generally adaptive; that is, they tend to help living things to keep on living. Living things originate from others of the same kind, and may produce offspring like themselves. Living things consist of special parts, or organs, that carry on distinct services or functions, 26 Protoplasm, the living stuflf of organisms, is a very complex mixture of many different substances. It is distributed in more or less distinct and specialized units called cells. In all kinds of organisms the protoplasm of each cell grows, reproduces, moves, antl is irritable. In the larger plants and animals individual cells carry on specialized activities in addition to the fundamental ones. EXPLORATIONS AND PROJECTS 1 To survey the "whole plant", compare in several difTercnt kinds of plants the main structural parts; look for and record suggestions as to the different ways in which each part contributes to the life of the plant. 2 Study grasshoppers. Note and list the many things that this living organ- ism does but that nonliving objects do not do. Note carefully also how it does everything it does. Watch for breathing movements. 3 To find out in what ways a living frog differs from nonliving matter, tabulate observations on a living frog and corresponding characteristics and activi- ties of a nonliving object. Attend especially to indications of sensitiveness. Look for indications of breathing and for the manner of breathing; for differences in behavior in the water and in the air; for the use of feet in swimming, in jumping; for ways of getting and eating food. 4 To observe cells, tear a bit of the thin skin from an inner layer of an onion, place it on a microscope slide in a drop of water, lay a cover slip over it, and examine under the low power of the microscope. To stain the tissue, touch a drop of ink to the edge of the cover slip. By a similar procedure observe other plant cells — for example, a bit of the underskin of a leaf; some pond scum; some green-slime scraped from a piece of wet bark; some yeast cells from a crushed bit of yeast cake; small leaves from peat moss and from elodea or other water plants; the skin of a potato; or the skin of a flower petal. In most cases it will be possible to make out the cell walls, the nucleus, and greenish bodies called chloroplasts. Examine groups of cells from various animal sources. Take scrapings from the inside of your own mouth or that of a frog, or other animal. Examine a culture of Ameba proteus or of Chaos chaos. Note the forms, num- bers, and movements of the pseudopods. What seems to be going on just inside of the forward-moving tip? Look for changes in direction of movements; for the engulfing of food material. Compare the form and structure of the ameba with other cells that you have studied. 27 QUESTIONS 1 What qualities distinguish Hving from nonliving material? 2 How does a living animal differ from one that has ceased to live? 3 In what ways does a living plant resemble a dead one? 4 In what ways do plants move? 5 In what respects is the structure of a living object different from that of a nonliving object? 6 In what respects is the growth of an icicle like the growth of a living organism ? 7 How do movements of living things differ from those of nonliving objects? 8 How does the irritability of living things differ from the sensitiveness of nonliving objects? 9 How does a living plant resemble a living animal? 10 How does a living organism differ from a machine? 11 What are some of the specialized activities of cells in complex organisms? 28 CHAPTER 2 . HOW CAN WE KNOW THE DIFFERENT KINDS OF LIVING THINGS? 1 How many different kinds of animals are there in the world? 2 What is meant by saying that the dog is related to the wolf, or that the lion is related to the tiger? 3 In what sense is one species related to a different one? 4 Can the animals of different species breed together? 5 How can we tell a weed from a useful plant? 6 Why do we class some animals higher and others lower? 7 What do we need to know about a plant or animal before we can tell in what class to place it? 8 What is the easiest way of finding the name of a new or strange plant or animal? 9 Why are Latin names used for plants and animals instead of common names? 10 Who needs to know all the scientific names? The world is so full of a number of things that we should be very much confused if we could not put them — and keep them — in some kind of order. About the first question we ask regarding a new and strange object is "What is that?" As we grow older, we want to know more than the name. For the new and strange thing is in some ways like whole groups or classes of objects we have known before, although it differs from them in some ways too. In time we learn to say, that is a kjnd of deer or sheep, that is a t{ind of daisy: each novelty is one of a class which we already know. The grouping or sorting of objects is necessary for making order out of our world. The naming of objects is necessary for keeping order. The better we sort and the clearer we name, th-e better we can manage the great heap which would otherwise be chaos. How Is Sorting Started? Naming before Sorting We name common things so that we may communicate about them with one another. And naming is probably an important part of thinking about things. At first the child becomes acquainted with separate objects — this plate, mother, that bottle. He usually receives a separate name for each particular person. Later he calls many separate, but similar, objects by the same name: all chairs, all cats, all trees, all persons. We use one name for many distinct objects because they appear enough alike to let us take one for another. And for many practical purposes one 29 ALL BIRDS LOOK ALIKE, BUT— At first, all birds may look alike to you, except for differences in size or color; the swallow is as much bird as the ostrich or penguin. As you meet more and more kinds of birds, you come not only to distinguish them or to recognize them by name, but also to notice that they can be grouped into several families or orders — those with flat bills, for example, and those with pointed bills; or those that ore more or less like the familiar hen and those that resemble in many ways the hawk or the eagle kinds of flowers ^^ik^ Composites FLOWERS ARE FLOWERS, BUT— At first all flowers, or blossoms, are just flowers, except for differences In size or color. A violet Is as much flower as a "sunflower" — which is really a combination of hundreds of small "flowers". As we see more and more kinds of flowers, we not only distinguish different kinds and recognize them by name, but we notice that they con be grouped into several classes or families — those with petals arranged around a center, for example, and those that have right-and-left halves; or those that are more or less like daisies and sunflowers, and those that resemble in many ways the flower of the sweet-pea Jellyfish GENERAL NAMES AND SPECIAL NAMES Starfish To class these animals as "fish" is to say that they are alike in some way. But they are alike only in the fact that they all live in water. The first part of each compound name tells us that each of these "fish" differs in some special way from "fish" in general glass of milk, one spoon, or one tree may serve as well as another. When we need to distinguish, we usually add something to the class-name: the blue chair, or the tree-with-the-swing. We do not make up the names ourselves. We find most names already in use, and accept them without question. The name tree goes with a cer- tain class of objects; the name fish, with another class. Assembling and Separating' Sorting is a process of noting difTerences and resemblances at the same time. When we know a considerable num- ber of birds or of flowers, we cannot help seeing that the birds are not all alike, or that the flowers are not all alike. We keep together all "birds", and under the label "flower" we keep together many other kinds of objects. Now we make distinctions among members of each class. Next we keep apart those that differ enough to call for distinct names. Ordinarily we use an older class-name for the larger or general group, and then add a special name for the smaller subgroup. In this way we speak of blue-bird, black-bird, snow-bird, and so on; or we speak of apple-tree, pear- tree, or cone-tree. ^See No. 1, p. 44. 32 Flying animals Clothing animals Water animals Nuisance animals L WAYS OF SORTING Shipworm We can classify animals according to our concern with them or according to their ways of living. Either of these classifications is useful and sensible. But neither is of general value or inclusive. Some people would not consider lobsters or frogs "food" animals. The mosquito and the frog spend a part of each lifetime in the water; but one is for the rest of its life a "flying" animal, the other is in part a land animal. A sheep is both a "food" animal and a "clothing" animal; a fox is both a clothing animal and a nuisance. What is a good classification? What Is the Basis of Classification? Many Bases We could classify living things, as we classify stamps and ships, in many different ways. One of the oldest and commonest methods of sorting animals is according to the way they concern us. There are ]ood animals, ]ur animals, nuisances. Or we might classify animals according to the regions or the conditions in which they live — arctic animals and tropical animals; mountain animals and lowland animals; land animals, air animals and water animals. Each basis of sorting may be useful. But the first plan suggested would bring together sheep, chickens and salmon; or sheep, foxes and buffaloes. It would bring together mosquitoes, rats, foxes and shipworms. The second plan also has its uses, but it brings together birds, bugs and bats, which all fly; or whales, fish and oysters, which live in water; or spiders, elephants and penguins. A good classification has a place for each "kind" and it avoids counting any particular "kind" more than once. A land-water classification would have to place the frog in one group as a tadpole and in the other group as an adult. If we had a useful-harmful classification, the farmer and the fur- rier could not agree about the fox. Choosing a Basis for Classification In classifying living things today, we consider not merely their appearance or their uses to us, but all that is known about them. Separating all organisms into plants and animals is very old and appeals to common sense. We recognize that in a general way animals are more active than plants, and more sensitive to changes in the This Swedish botanist and explorer de- veloped a system for classifying plants and animals which served to bring or- der out of great confusion. Linnaeus believed that every species was sep- arately created, but saw similarities among species which he placed in the same genus. He grouped genera into orders and orders into classes. He also devised the binomial, or two-name, method of naming species in use today and made a place in his system for ev- ery known plant and animal, including man. His work stimulated the search for new species, and laid the founda- tion for the comparative study of living things CARL LINNAEUS (1707-1778) 34 RELATIONSHIP TO PRESENT REPRESENTATIVE OF FAMILY Gieat-grandparents Great-uncles and great-aunts Grandparents on father's side in 1899 Father, two auntj, ana an uncle in 1920 Marriage of my parents In 1922 fWy parents, sisters, and brother In 1940 I married W. M. in 1942 o 6 O D D and ■o 6 6 D ■o f ODOO -a RELATIONSHIP THROUGH DESCENT Simon SI. Schwartz RELATIONSHIP TO HEADS OF FAMILY. 1865 We, our eight sons, and lour daughters in 1890 Marriage of our son Charles in 1899 Our son Charles, our daughlerin-law, and four grandchildren in 1920 Marriage of grandson Orville in 1922 Grandson 0. and his wife and five great-grandchil- dren in 1940 Marriage of our great-granddaughter Lucille to W. M. in 1942 Individuals are "related" because they have some ancestors in common. All "re- lated" persons of today might trace family connections to a couple of parents some- v/here along the line away back in time (D = male; O — female) surroundings. At the same time, we know that some animals remain fixed in one spot and move very Uttle, whereas some plants are rather sensitive or move visibly (see illustration, p. 257). Animals usually depend upon other organisms for their food, whereas most of the common plants construct food out of raw materials. In addition to fairly distinct animals and fairly distinct plants, there are many living beings that we cannot so surely classify as either plants or ani- mals. The bacteria and the "slime molds" belong in this borderland. Among plants, as well as among animals, we find some species that we consider "higher" or more complex than others. Thus we think of an insect as higher than a worm or of an oak tree as higher than a palm. We can- not place all the known plants in one series and all the animals in another series, running from the simplest or "lowest" to the most complex or "high- est." That would be like trying to arrange all people in a straight series from the worst to the best, or from the smallest to the largest. We take account of degrees of complexity, as well as types of structure. Why Must There Be So Many Names? Discriminations Each human being is important enough to have his name distinct from all others. We do not have an individual name for each particular object — each chair, each strawberry or mosquito — because in most cases it is enough to use a class-name. For most people, most of the time, mosquitoes are mosquitoes, wheat is wheat. Yet it is sometimes necessary to distinguish. Some mosquitoes transmit malaria, some do not. We need a new name whenever we make an important distinction. Double Names We use double names every day in speaking of per- sons — Sam Brown or Sally White. Such names consist of the family name and the individual, or personal, name. We also use double names to distin- guish entire groups that have some resemblances, as blue-birds, black-birds, and so on. The plan of using binomial or two-name designations for all species, or kinds, of plants and animals was introduced in 1735 by the Swedish naturalist Carl Linnaeus (1707-1778). Thus he labeled man Homo sapiens (man-wise), and a certain frog Rana virescens (frog-greenish). What Is a Species? When we speak of a "family" of human beings — the Franklins or the Hills — we include the idea that the individuals are related. The Hill boys and girls have the same father and mother. The father of their cousins and their own father are brothers. They have also grandparents and other cousins with different family names. We say that these are related to the Hill children on the mother's side. But we think of all the Hills and all the millions of other human beings as of the same kjnd. 36 ^ J 1 1 l_, Sugar maple {Acer saccharum) GENUS AND SPECIES Red maple {Acer rubrum ) Striped maple {Acer pennsylvanicum) ■. After you know a maple from an elm or an oak, you may continue to give the name "maple" to trees that are in many ways distinct. When you get to know sugar-maples, for example, from red-maples, and after you find them to remain consistently like other sugar-maples and consistently different from red-maples, you attach to the general or genus name qualifying or species labels. From the time of Linnaeus scientists have systematically used double names — a general name and a special name — for every species. For example, we use the Latin "genus" name Acer to denote maple, and the Latin "species" names saccharum, rubrum, and pennsylvani- cum to designate particular kinds of maple When we say that all mankind make up one species/ Homo sapiens, we mean that all human beings alive today had the same ancestors thousands of gefieratiofis bacl{. When we say that all the greenish frogs are of the species Rana virescens, we mean that they are all descended from a common ancestor. Of course we cannot "prove" this through family records, for either frogs or men. But we have good reasons for assuming that there is this connection between members of a species. At any rate, the usual idea of a "species" is "all the individuals are enough alike to let us assume that they descended from a single pair." How Are Different Species Related? Linnaeus recognized that only by using double names could we have distinct names for each species. ^The word species has the same form in the singular and plural. 37 Wood frog Grass frog {Rana {Rana sylvatica) pipiens) Bullfrog (Rana catesbiana) Spotted salamander Common toad {Ambystoma (Bufo maculatum) amencanus) RELATED GENERA The grass frog, the wood frog, and the bullfrog are distinct species of the genus Rana, the Latin name for frog. Frogs and toads are grouped in the same family. These and other genera, together with the salamanders and other "relatives", make up the class Amphibia — animals that live both on land and in water When we ask a question like "What kind of frog . . .?" we already say that "frog" is a general name including two or more species. Such a group of species we call a genus (plural, gejiera). As in all classifying, we sort animals and plants on the basis of resem- blances and differences. And we consider them "related" according to the degrees of resemblance. Thus we speak of frogs and toads being related, as of the same family, although we do not have to decide what species was their common ancestor, or even whether they actually had any common ancestors. In fact, Linnaeus himself believed that each species had existed as we see it from the very beginning. How Are the Larger Groups Related? Kinds of Divisions The main branches of both the plant "kingdom" and the animal "kingdom" are called phyla (meaning "tribes"; singular, phylum) after Linnaeus's plan. These phyla are divided into classes} In some phyla there are but a few classes; in other phyla there are many. In some phyla the classes are rather distinct; in others there seem to be "re- lated" forms that are not so easily grouped by their characters. Accordingly, ^Note that here the word class is used in a very special sense, meaning one of the chief di- visions of a phylum, not merely any grouping whatever for which we may have a name. Note also the special use of the word family in classifying plants and animals. 38 it is sometimes convenient to have another separation between the phylum- division and the class-division. So we have two or more "sub-phyla." There may also be "sub-classes." In fact, we may make a sub-division wherever we find it convenient, or wherever the material is sufficient in amount and variety. For we need not suppose that a "class" — like bird or fish or i?isect, for example — exists and merely waits for us to recognize it. In a sense, all our sorting is artificial, although it is based on facts that we can actually observe in natural objects. The "classes" have been broken down into "orders," and these into "families." Within the families are the genera (singular, genus), each with a variable number of species. As in the case of the species themselves, each of these divisions is determined by the resemblances and differences that we can observe. There can be no rule as to how much difference it takes to set up a new species, or how many species should go into a genus. New species are constantly being described, and older groups are constantly being re- combined. A General Scheme The names we give to the main divisions and sub- divisions in our schemes of classifying organisms are arbitrary or conven- tional. It is nevertheless well to use them in the special senses of the taxonomists instead of the informal everyday sense. Thus we speak of the cat family, the dog family, the class birds, the order butterfly, the phylum chordates, and so on. Since we sort according to physical characteristics, we naturally cannot use the same basis for classifying plants and animals. Linnaeus classified plants primarily on the flowers and other structures associated with reproduction. He classified animals chiefly on the more obvious structural characteristics and on their modes of locomotion and food-getting. Among both plants and animals, however, the successive subdivisions are given the same names (see pages 40 and 41). Using Classification^ No person can ever know all the plants or all the animals. By observing and comparing different species, an individual could in a lifetime learn to know several thousands of species by name. At the same time, he could learn to recognize at a glance the class, order or family in which to place many thousands of other species that he had never seen before. This is not as difficult or mysterious as it sounds, for everyone does just that every day without much effort. Suppose you see a kind of "animal" that you have never seen before. You recognize it at once as a "kind of bird" (class). Or you might say offhand, "That is a kind of parrot" (order) or "a kind of woodpecker" (family). You might not guess that the peacock is classed as in the "same family" as the common fowl, but you would guess that the duck and the goose are "related". ^See Nos. 2 and 3, p. 44. 39 Thallophytes Bryophytes Spermatophytes > PHYLUM Gymnosperms Angiosperms x' f^. > CLASS mm: Monocotyledons Dicotyledons J > SUB- CUSS Peppers Willows Oaks Mallows (20-30 orders) Heaths Ifr::^^ vTV ^ ^"Y-^ _ Rosales J > ORDER Rose family Leguminosae Saxifrages Plane trees / ^^1 "^ ^ €^ / I >^^ ^ r Acacia subfamily Cassia subfamily Bean and pea subfamily fi^ii^ tK y<:rr ^ ^ "^ ^ Papilionaceae > FAMILY J SUB- FAMILY > GENUS > SPECIES J THE MAIN SUBDIVISIONS OF THE PLANT WORLD Chordata Arthropods Mollusca Echinoderms (10-12 phyla) PHYLUM < CUSS < SUB- CUSS ORDER < FAMILY v. J SUB- FAMILY GENUS < Cyclostomes Fish Amphibians Reptiles ^ Birds Mammals ^■o<^'n W,»^^^ * 1 ^ ^^ •^^ ^\ Monotremes ^True mammals Marsupials Insectivora Chiroptera Carnivora Rodents \ Even-hoofed Proboscidea ^Hyanidae 7 ■.:•■ Pantherinae Cheetah subfamily ^:2) V c SPECIES < F. sylvestris F. domestica THE AAAIN SUBDIVISIONS OF THE ANIMAL WORLD Nobody should try to memorize the tables showing the chief types of plants and animals (Appendix A). The best way to use these tables is to refer to them and to the "trees" (frontispiece) whenever a new species of plant or animal comes to notice. Before long one can then recognize the place which each of the more common forms has in the entire scheme. After becoming familiar with representatives of the main branches, or phyla, one can easily see the meanings of the "definitions" for most of these groups. The more common classes and families are also easily learned. Many are astonished and pleased to find that although the "scientific" names appear at first outlandish and "difficult", they are no harder to pro- nounce than are those of our common language. Nor are they hard to remember if one takes pains from the first to find out what they mean. In Brief We classify living things in various ways for different purposes. We usually group together under one name individuals or objects that are equivalent or interchangeable. The number of subdivisions we name depends upon our need to dis- tinguish, or discriminate, among similar forms. Any scheme of sorting must bring together individuals or groups of individuals according to what they have in common, and exclude those which differ, even though they show superficial resemblances. We do not usually invent names for common groups, but accept those already in use. We divide all living forms roughly into the plant "kingdom" and the animal "kingdom". Both plants and animals are classified according to a branched arrange- ment in which the larger groups are progressively subdivided into smaller groups. The classification tree branches first into phyla, then into classes, then orders, then families, then genera, and finally into species. A species includes all the individuals that are so much alike that we feel warranted in assuming that they descended from a single pair of ancestors. We consider different species related to each other according to the degree of resemblance among them. 42 fs«*:waw"9rss'?v?": _ Leaf margins Sharp-toothed Blunt-toothed Double -toothed Lobed Leaf forms Entire Elliptical Cherry\ '^\ ' Wj 3'- y. I j Sweet I y gum Dogwood \y Pinriate Palmate Axial Pinnate Palmate Parallel- veined Net- veined Compound leaves Locust Pinnate VARIETY IN LEAF CHARACTERS Virginia creeper Palmate Strawberry - (.PIuseuni of Natural History THE BODY PATTERN OF MAMMALS In all vertebrates the brain and spinal cord are entirely incased in bone; the heart and lungs are enclosed within a lattice-like arrangement of ribs. There are two pairs pf appendages Elbow- Wrist, Man Vulture Whale Halibut Man Wolf Ostrich Duck Crocodile Seal HOMOLOGIES IN FORE LIMBS AND IN HIND LIMBS OF VERTEBRATES Walking, crawling, swimming, flying — all the various modes of locomotion found among backboned animals — are carried on by organs having the same fundamen- tal structure in other mammals too — in the bat, for example, or the kangaroo. But among the primates the human hand stands out, with its distinct thumb and the possibilities for fine "handling" of objects. 49 Roberts THE HUMAN HAND The versatility of the human hand is illustrated by the delicacy and sureness with which an artist or surgeon operates, or by the variety and power of movements exe- cuted by a workman The Enlarged Brain A third characteristic of our species is the large brain, especially the forebrain (see illustration opposite). This brain is prob- ably the most distinctive feature of man's whole life and history. For with this organ is associated man's capacity to learn from the past and to push his purposes and his plans farther and farther into the future (see table, p. 54). The Chin and Mouth Distinctive of the human face is the well- defined chin (compare profiles in the illustration on page 52). We are impressed when we see a person who has either no chin or one that is exceptionally large. There is no obvious merit in this structure, although it is probably related to the workings of the jaw and the mouth. The lips as well as the teeth and the jaw show distinctive characteristics. These are related to the fact that man is the only animal that uses articulate speech. Speech^ The hen can utter some twenty distinct sounds, and each one has a different meaning. Other animals communicate with each other through calls or cries. But in human speech there is more than a set of calls and cries. Human language consists of words, each with a definite pattern of sound. And these words are combined into sentences that express all kinds of ideas. Unlike the crowing and growling and snarling of other ani- mals, human speech can be constantly adjusted to the changing and grow- ing needs of the thinking animal. If you have a new idea, you can, by means of the language you have acquired, express it so that another person can ^See Nos. 3 and 4, p. 60. 50 Modern man Neanderthal man Piltdown man — Pithecanthropus (Java ape-man) Gorilla Modem man Neanderthal man Piltdown man Java ape - man Gorilla THE BRAINS OF HUMAN TYPES AND OF OTHER PRIMATES These five types of skulls and brains suggest relationships. The larger and larger brains correspond to more and more recent types, although they do not necessarily indicate straight lines of descent Wsv Modern man ~\ V Neanderthal man ^"^^^ Cro-Magnon man y Piltdown man Heidelberg man MAN'S DISTINCTIVE CHIN Fossil remains of human bones indicate progressive changes from the earlier chin- less jaw of Heidelberg man, resembling that of the gorilla, to the less massive jaw, with its prominent chin, of modern man; and they indicate corresponding changes in the teeth understand you. You do not have to invent new kinds of noises, and it is not often necessary to make up new words. Man's Shortcomings Man is unquestionably the highest form of Hfe. As a hving machine, however, man is in many ways decidedly inferior to other animals. For example, his skin is much more tender than that of any other animal of his own size, and the hairy covering is not of much help. When he fights, his nails and claws are very poor rivals for those of cats, let us say. And his teeth are not nearly as formidable as are those of many other animals. His muscular development too is inferior when it comes to wrestling with a nonhuman enemy. When it comes to running, whether to capture a rabbit or a bird, or to escape an enemy, man would be easily out- distanced by many of the inhabitants of the forest. Seeing, hearing and smelling are very helpful to animals for discovering enemies or food at a distance, and they are also of great value to man. Compared to other animals, man has a very good eye and a pretty good ear — though not one of the best for discovering faint sounds. But man's smelling ability is of very low rank. Man and Apes A convenient summary of contrasts between the human family and tlie ape family was made by Dr. Henry Fairfield Osborn (1857-1935), the distinguished American naturalist and anthropologist. The comparisons on page 54 are based on fossil materials and other evidence of former life. They apply not so much to present-day human beings and present-day apes as to the ancient representatives of these two families. What Is Unique about Man? Man's Advantages In spite of his various shortcomings, man has contrived to hold his own. And some branches of the species have become virtually masters of their environment. His hand and brain seem to have made up for all the important deficiencies. Man has made up for his thin skin by borrowing the skins of other animals and by devising substitutes for skins (fabrics). He has strength- ened his arm by means of sticks and stones. He has lengthened his legs — that is, increased his speed — by means of iron and brass. And with other contrivances, he has soared aloft, to rival the very birds. He has pushed his eyesight millions of miles beyond the surface of the earth, and has looked into the world of the littlest things. He can hear the footsteps of a fly (although he does not need to do so either for protection or for food). And he has caught vibrations through miles of space. In every direction man has made up for his organic weaknesses by using his thinking organ to guide his hand. 53 Contrast between the Human Family and the Ape Family HUMAN CHARACTERISTICS 1 Ground-living biped; habit adapted to rapid travel and migration over open country 2 Development of the walking and running type of foot and great toe 3 Use of legs for walking and running 4 Escape from enemies by vigi- lance, flight and concealment 5 Tree-climbing by embracing main trunk with the arms and legs, after the manner of the bear 6 Shortening arms and lengthen- ing legs 7 Walking and running power of the foot increased by enlargement of the great toe 8 Use of arms and tools in offense and defense, and in the arts of life 9 Development of the tool-making thumb 10 Adaptation and design of im- plements of many kinds in wood, bone and stone 11 Design and invention directed by intelligent forebrain 12 Progressive intelligence; rapid development of forebrain APE CHARACTERISTICS 1 Tree-dwelling; four-handed; habit adapted to living chiefly in trees 2 Quadrupedal habit followed when walking on the ground 3 Use of legs in tree-climbing and limb-grasping 4 Escape from enemies by retreat through branches of trees 5 Tree-cHmbing always along branches, never by embracing the main limbs and trunk 6 Lengthening arms and shorten- ing legs 7 Grasping power of the big toe for climbing, modified when walking 8 Use of the arms for climbing; and for grasping food and enemies 9 Loss of thumb and absence of tool-making power 10 Adaptation of the foot and hind limbs to the art of tree-climbing 11 Design limited to the construc- tion of very primitive tree nests 12 Arrested development of intelli- gence and of brain 54 American Museum of Natural History TOOLS AND WEAPONS OF THE STONE AGE Relics of the Old Stone Age (1, 2 and 3) are roughly shaped. New Stone Age man had learned to chip his flints skillfully (4, 5, 6 and 7). Later he tried to smooth and even to polish his stone creations (8 and 9) Tools, Weapons and Shelter The natives of Madagascar say that if you throw a spear at a lemur, the animal will catch it and throw it back with deadly precision. Monkeys will crack nuts by pounding them against some hard object, and the gorilla will use a stick as a club in fighting. But probably no gorilla or monkey ever carried a club or a stone about with him to use in possible emergencies; and that is something that man has done. Even among the oldest remains of human activity are stones which men had chipped to serve as weapons or as tools (see illustration above). Many species of birds and of other classes of animals builci very neat nests — much neater, probably, than primitive man built in the treetops. But man has finally succeeded in building shelters so far beyond anything other animals have made that it seems ridiculous to compare them. Fire What using fire has meant to man most of us cannot realize, for we take the benefits of fire for granted from childhood. Fire enabled man to get out of the trees and live in caves or tven in the open, for with fire he could keep the beasts away. It made available to him food that he could otherwise not use. And fire was probably helpful in many other ways from early times. Fire enabled man to wander from the tropics, so that of 55 all mammals man is the most widely distributed species. The dog is a close second, but only because man has taken him along. Sociality How did human beings first come to use tools, fire and speech? These obvious advantages for human living are related to a char- acteristic of the species that does not show if we study merely the structure of the organism. This is the important fact that man always exists normally in groups. Man is a social animal. There are of course other social animals. The bees and the ants at once come to mind. Wolves hunt in packs. The wild bison and other animals of the cow family roam in herds. Even very low types of animals form colonies with a considerable division of labor among the members (see illus- tration, p. 419). Social life among human beings, however, involves more than division of labor and the fitting of each individual to some special tasks. It involves the feelings which each individual has about others — ^his liking or disliking them, his admiration or contempt. It involves further what he feels about himself in relation to others — his fears, or pride, for example, or his envy. For man needs not merely supplies of food, or material comforts; he needs also a chance to deal with others in many different ways. Man depends upon others^ and others make demands upon him. The fact that man prefers society to solitude has far-reaching consequences. Animals living by themselves would have no use for "communicating". At any rate, the ability to use tools and fire and to speak, and social living are all closely related to man's superior brain. How Is Man More than an Animal? Preserving Experience Human beings can learn from experience, as can other backboned animals, and many lower classes too. They can learn certain things more quickly than other species. And they continue to learn through a longer stretch of years. Quite outstanding, however, is man's ability to learn from the experiences of others. Experiments with many different species show that the apes and monkeys alone imitate what others are doing, although some birds imitate sounds. They seem to be the only ones, therefore, that could possibly learn from the experience of their fellows. Man, however, learns not only by imitating others, but also through direct instruction — the use of speech, If a wasp should discover a new trick for catching caterpillars, and used it successfully in gathering food for her offspring, her acquired wisdom would die with her. For the eggs which she lays do not hatch out until after she is dead. Among human beings, however, the results of experience are carried on from generation to generation, through tradition and cere- monial. Savages preserve the art of making fire by teaching their young 56 Anicriraii Jluseuni of Natural History CRO-MAGNON ARTISTS PAINTING THE WOOLLY MAMMOTH Men living perhaps twenty thousand years ago left hundreds of paintings, clay fig- ures, scratchings on walls, carvings in stone, etchings and carvings in horn. These records show that early man was able to imagine, to abstract, and to think the solemn ceremony of fire-making. In the history of primitive peoples every good idea seems to have been preserved by means of ceremonial as well as by strict rules. In time, the race has managed to gather up a great deal of wisdom — as well as a great deal of what seems to us to be foolish or superstitious. Imagining and Abstracting We can shut our eyes and call to mind a picture of something that we have once seen. We can recall particular scenes or particular pieces out of past experiences. These imagined frag- ments are not always selected. Something may "flash into the mind" un- expectedly. Perhaps something now present "reminds" us. This ability to imagine — to recall and reconstruct bits of past experience — is of tremendous importance, for our imagination enables us to use past experiences in deal- ing with new problems. We can shut our eyes and see green grass, even when there is no green grass around. We can then think of greeti apart from the idea of grass. We can think of the sweetness of a fruit apart from the idea of the fruit, or apart from the color or the shape. In imagination, we detach the "quali- ties" of things that we have experienced from the things themselves; we abstract — that is, draw away from. Our thinking consists largely of such abstracting. We analyze our experiences or take them apart in imagination, 57 .4-J! .- HUMAN CREATIONS Marvelous is each living being in the use it makes of its structures and adjustments. The eagle and the hummingbird and the horse go as high and as far and as fast as their bodies permit. Man alone of all living things has vied v/ith the gods in creat- ing out of what he finds at hand new combinations of use and beauty and power, of delicacy and grandeur. Of all animals, man alone makes his dreams come true and then combine the elements in new ways. We thus use past experiences in a way that no other Hving being can. Creativity A dog will play with a stick, or a cat with a ball of yarn. Young children pile up blocks or put together bits of glass or wood. They try now one arrangement, now another. The various kinds of play may appear very much alike. Yet in children this kind of play includes the be- ginning of what we may call creative activity. For presently we see the child's play go beyond the mere handling of things. In his imagination the child can abstract, or remove, the red of a cherry and place it on a piece of paper. One can remove (in imagination) the wings of an eagle and attach them to the shoulders of a horse or perhaps of a human being. Was it not by some such act that man eventually arose from the earth and soared into the sky? We take for granted the bridges and wings that man has created to carry him across the chasms that would stop him in his wanderings. We take for granted the artificial caves that man has made for shelter. With his imagining and abstracting man has been creating new kinds of materials that nature never made, even new kinds of plants and new kinds of ani- mals — actually 7iew species (set pages 496-501). In recent times he has been trying to change himself over to meet his idea of what is good — not merely applying cosmetics and surface ornaments, but changing the 58 inner processes of his own body. Man has been correcting and re-creating himself, improving on his own "nature". More than Beast Man must eat and sleep, like the very beasts. But it is foolish to say, "Man is only an animal", for as Shakespeare suggests, man can do more. Whoever can read these words senses that the ordinary person has in him something that shares in mankind's advances from beast- liness and savagery. The advances have indeed been slow and uneven. There have been many setbacks. And it is true that within each man lies a cruel and cunning brute. But in addition, man is able to dream beyond all that is, and to strive toward the highest that his dreams can create. No other species can do that. In Brief The human body, with its parts, resembles in its structure the bodies of other backboned animals. Man shares all the characteristics which are common to the members of the group mammals, and more strikingly those of the primates. Man differs from the other primates in his erect walk. Man's hands and arms differ more from his feet and legs than do the forelimbs and hindlimbs of other primates. Man's hand and brain are the organs that have most distinguished him from other animals. In several respects man is quite inferior to other animals. The distinctive chin and mouth of man are closely related to the fact that he is the only animal that uses articulate speech. Man always exists normally in groups; that is, man is a social animal. Man learns from experience to a much greater extent than any other animal, and he preserves and passes on his experience from generation to generation through his language and social institutions. Man's capacity to imagine, to abstract, and to create exceeds anything comparable among the other animals. EXPLORATIONS AND PROJECTS 1 To compare the structure of various mammals, visit a zoo or circus where several different mammals can be observed, or visit a museum in which skeletons of several mammals and other vertebrates can be studied. Give particular atten- tion to the general framework and limbs of the body. Identify structures which correspond to your shoulder and collarbone, upper arm, elbow, forearm, wrist, 59 hand and fingers. Also, identify the structures which correspond to your pelvic girdle, hip, thigh, knee, shin, ankle, heel, foot and toes. In what ways are the limbs of the various animals studied alike? In what ways are they consistently different.'^ In general, do the forelimbs and the hind limbs of the various animals differ more or less from each other than do our arms and legs? 2 To compare man with the other primates, visit the monkey house at a zoo and compare the faces, arms and legs of the different primates with your own. What resemblances do you find? What differences? Are the hands and feet of the different monkeys more alike, or less, than are your own hands and feet? How does the posture of the monkeys resemble your own? How does it differ from yours? 3 To explore the ways in which human beings communicate, make a list of various ways in which we human beings can communicate with one another. Group these ways under the following headings: (a) means of expressing fear, pam, joy, and other emotions; (b) means of communicating through space; (c) means of communicating through time; (d) means of passing on experience from person to person; and ( (/> (/) o o W1 D £ D) ^ •4- a C .^ o lO +- D to < 1- M- 1 O +- ^ _D D o i/i 1- C -D *C ^ (U O- *C LU ,_ 'd U- D l- — ; c Q. Q Z _^ ■o < 0) >- Q£ LU OJ > 1— ^ *4- < ■V- _o ^ c UNIT TWO Under What Conditions Can We Live? 1 Why are there more plants and animals in some places than in others? 2 Why are there living things in some places but not in others? 3 Are there parts of the earth where there are no living things at all? 4 Are there any conditions in which man cannot live? 5 What limits the spread of mankind over the earth? 6 How do plants and animals remain alive while inactive during the winter? 7 Why are seeds killed if they are allowed to become damp? 8 Why do not fish drown in water? Why can they not live in air? 9 Why can we live longer without food or water than without air? Man has spread over more of the earth's surface than any other of all the miUion or so species hving today. He has taken with him in his wanderings some of his domesticated plants and animals, and also the fleas and worms and bacteria that live on or in his body. Man has made himself at home where the tiger or the bison had been master. In every region he has turned to his use the native plants and animals. And he has destroyed many species that he could not use, or that interfered with his plans. He wipes out a forest to make room for homes and gardens and field crops. Or he pushes snakes and wildcats aside to make room for cattle and chickens and dogs. Man is not, of course, the only wanderer. Living forms everywhere push out into the surrounding regions. At the edge of a garden are weeds, and beyond the weeds are cultivated plants "escaped" from the garden. After a piece of land has been cleared, seedlings from the surrounding woods appear. The range of every animal species changes in the same way. Most of the flies that trouble us, and the vermin too, breed, of course, on the neighbors' prem- ises. The locust swarms over the land, seeking what he may devour. Life is always on the move. But in any given situation, or with any given species, life moves so far, but then meets many kinds of obstacles. The edge of the ocean stops the spread of life in both directions. The very conditions that enable some species to live make life quite impossible for others. Fishes live only in water ; the trap-door spider and the horned toad only in arid regions. Butterflies flit in the air and sunshine, but tapeworms dwell in the dark recesses of a little boy's intestines. The green-slime thrives on the bark of a tree, but the malaria plasmodium must get inside a blood-cell. Lichens live under the snows of Iceland, but Florida winters are too severe for the banana. Life is truly wonderful, since it gets along under all these different conditions. Y^/ no single kind of plant or animal can live under all these di^erent conditions. What conditions are really essential to life? 79 CHAPTER 5 • WHAT HAVE WATER AND AIR TO DO WITH BEING ALIVE? 1 Is water necessary for all living things? 2 How can there be any life in the desert? 3 Do lichens growing on rocks need water? 4 How long can we live without water? 5 How long can one go without breathing ? . 6 What has breathing to do with life ? 7 Are all parts of the air necessary for life ? 8 What makes dry seeds sprout ? 9 What happens to the living things in a pond when the water freezes solid ? 10 What happens to the life in a stream when all the water dries up? 11 How does the air we breathe out differ from the air we breathe in? On a farm, the weather seems very important. Crops grow more luxu- riantly where rains are frequent. Prolonged drought ruins them. Forest vegetation likewise depends upon rainfall (see illustration, p. 78). What makes things grow faster when water is plentiful? How does water act in plants ? The amount of water varies not only from region to region, but from season to season, in any one place. During winter there may be as little sign of life as in a desert: most plants and animals of the preceding season are dead. Of those plants that are not dead most are either bare of all foliage or reduced to some kind of resting state. Roots and stems are lying dormant — that is, sleeping — underground. Millions of seeds look as lifeless as pebbles. In general, similar facts may be observed regarding animals. The winter state is in some ways a dry state. Has water anything to do with the way seeds behave in winter, as compared to the way seeds behave in spring or summer ? What is the connection between water and being alive ? How Does Water Act in Protoplasm? Protoplasm a Chemical Machine Living machines differ from most of our artificial machines in depending directly on chemical changes going on within the protoplasm. The protoplasm itself is largely water — well over 90 per cent in many kinds of plant and animal cells. Of the various sub- stances in the protoplasm in addition to water, some are in solution, like salt that has dissolved in water. Others are suspended in water, like the solid 80 part of mucilage or like fine particles in a muddy pond. These various sub- stances are constantly undergoing chemical changes. Chemical processes inside a plant or animal, like those in a test tube or a soap kettle, can take place only in a fluid state. In living things this fluidity is maintained by the large amount of water. Unlike the test tube or kettle, however, the living cells of leaves and stems, of muscles and nerves, require a constant flow of water. For the water itself takes part in some of the chemical transformations of proto- plasm, so that it is constantly being destroyed. In other cases the activities involve a loss of water through the walls or membranes of the cell. There is in fact a constant flow of water between a living cell and its surround- ings — water coming in and water going out. Sprouting of Seeds In the spring the gardener or the farmer places his seeds in the ground, and they sprout. Since our common cultivated plants normally grow in soil, we are likely to assume that the soil somehow starts the seeds to begin their active growth after their long rest. The soil is a mixture of many kinds of stuff, some of which may have something to do with the sprouting, but not the others. Most of us know that seeds kept in jars will not sprout, whether they are kept in the dark or exposed to light. Hence it is not on account of dark- ness that seeds germinate in the ground. Seeds kept in a warm place and seeds kept in a cool place will both fail to sprout so long as they remain in our jars or boxes. It cannot be temperature alone that makes them sprout in the ground. Perhaps the soil keeps some of the air away from the seeds } But keeping air out of the jar will not make the seeds sprout. In regard to the chemical substances in the soil, our usual experience tells us nothing at all. If we place the seeds in boxes containing the various in- gredients of the soil, such as sand, clay and various salts, we shall find that not one of the seeds sprouts. This suggests that even if any of the substances might cause sprouting, none can get into the seeds in the dry state. We should therefore try these substances with water. But has water by itself any effect on the* sprouting seeds ? An experiment in which some seeds are placed with various amounts of water, while other seeds from the same lot are kept under similar conditions of air, light and temperature — but without water — will easily convince us that a certain amount of water is a necessary condition for starting the germination of the seeds. We shall find also that some kinds of seeds will fail to sprout if they are completely covered with water, although other kinds will sprout under those conditions. This suggests that water may have injured the seeds, or that they drowned because of lack of air. 81 WATER VARIATION No water 1 cc per seed 2cc per seed 5 cc per seed Daily Flooded TEMPERATURE VARIATION 29° F 2 weeks after planting 50° F 2 weeks after planting 68° F 7 days after planting 86° F 5 days after planting 110°F 2 weeks after planting Ij. p. Flory. Boyce Thompson Institute GERMINATION INFLUENCED BY MORE THAN ONE FACTOR Experiments in which equal numbers of seeds were exposed to different tempera- tures and to varying moisture showed that at a given temperature suitable for ger- mination, there may be too little water or too much water; and that with a suitable amount of water, the temperature may be too low for the seeds to sprout, or it may be too high CULTIVATION TO CONTROL GROWTH OF YOUNG PLANTS Hard rains sometimes pack the soil, limiting the air supply. Cultivation loosens and aerates the soil. It also limits the loss of water by evaporation. Cultivating beans at the time the "necks" are pulling the seed leaves above the ground may break off and kill many of the young plants It may be that other factors also play a part after all. For example, in the presence of water seeds may sprout at one temperature but not at another. From actual experience we know that we may safely sow seeds of some species earlier in the spring than others. From experiments we learn also that some seeds will fail to sprout when it is too cold or too warm. How Is Air Related to Life? Air and Life The atmosphere has approximately the composition shown by the diagram in the illustration on page 84. When air is shut off, we suffocate, as in drowning. Now what is the connection between air and being alive? The energy of protoplasm, in all its activities, comes from the burning, or oxidation^ of materials derived from food. The food is not burned directly, like the oil in a furnace. It hrst undergoes many changes through which it is finally assimilated, or made into living protoplasm. Nor is the oxidation, or burning, like the familiar flame. It takes place only in the presence of water, whereas the fires with which we are familiar cannot burn under water. 83 VHEUUM J NEON 1002*5?, ^ XENON The air consists of at least seven distinct gases. Nitro- gen and oxygen together make up about 99 per cent of the total. Although the proportions of these gases are constantly changing, the turbulence of the air mixes them so thoroughly that sam- ples taken in different places vary but little. In addition to these gases, the air contains varying portions of water and dust. So far as life is con- cerned, the most important parts of the air are oxygen, carbon dioxide, and water. Nitrogen is an essential part of all living matter, but very few organisms can get it di- rectly from the atmosphere COMPOSITION OF DRY AIR The nearest thing to the oxidation of protoplasm that is famiHar to most of us is the rusting, or oxidizing, of iron, which also takes place in water. Air and Energy^ We may compare the oxidation of food in living pro- toplasm with the burning of fuel. When we burn coal, which consists chiefly of the element carbon, oxygen of the air combines with the carbon, forming carbon dioxide and liberating heat: C + O2- carbon oxygen • CO2 (and heat) carbon dioxide Wood is composed chiefly of cellulose, an insoluble material consisting of carbon, hydrogen and oxygen, in the same proportions as they are found in a simple sugar. When wood burns, heat is liberated, and water is given off, as well as carbon dioxide. Familiar Aires give off heat and light. Oxidation in protoplasm also re- sults in heat and other forms of energy. When glucose, a kind of sugar, is oxidized in protoplasm, energy is liberated, and carbon dioxide and water pass off as waste substances: CeHisOe + 6 O2 — >" 6 CO2 + 6 H2O (and release of energy) glucose oxygen carbon dioxide water vapor In an engine the oxidation takes place in the firebox or in the cylinder. In a living plant or animal oxidation takes place in every living cell. iSee Nos. 1-5, pp. 93-94. 84 Among the forms of energy liberated by protoplasm are motion (as in muscles), heat, electricity, light, and the processes that are confined (so far as we know) to nerve and brain cells, such as thinking, wishing, suffering, enjoying. In glowworms and fireflies, as well as in certain bacteria, slow oxidation liberates much of the energy in a sugar as light. Air as Raw Material Although carbon dioxide is but a fraction of 1 per cent of the atmosphere, it is a very important factor in the life of the world. For this fraction is a considerable part of the raw material out of which the green plants make sugars and starches (see pages 137-138). And these in turn are the beginnings of all foods, for us and other animals, as well as for the plants. How Does Exchange of Materials Take Place between Living Cells and Their Surroundings? Diffusion^ If a bottle of perfume or ammonia is opened in a corner of a room, the odor will become perceptible in all parts of the room. Sugar left in the bottom of your coffee, without stirring, will in time spread throughout the liquid. Every portion of the now cold coffee will become equally sweet. The process by which a liquid or gas penetrates another liquid or gas is called diffusion, a "spreading apart". When salt or sugar gradually diffuses from the bottom of a vessel of water to all levels, "work" is going on. For material is being raised against gravity and distributed through space. It helps us to understand what hap- Sugar molecules •Semipermeable membrane separating * tvfo liquids K^' .H^/ vi^. ' *•* * ^!.o ! -%^^\ * :• % — Water molecules -Wall of containing vessel DIFFUSION THROUGH A MEMBRANE We may think of the molecules in any liquid or gas as in constant motion. Some molecules are smaller than others. In the diagram the sugar molecules are repre- sented as too large to pass through the pores of the semipermeable membrane. Since more water molecules bombard a given area on the right side of the mem- brane than on the left side, more water moves toward the left side than in the reverse direction ^See No. 6, p. 94. 85 HOW DIFFUSION TAKES PLACE If we throw balls of different sizes at a tennis net, we may expect most of the smaller balls to go through the net, and all or most of the larger ones to be stopped. In much the same way, we imagine, some of the rapidly moving molecules of dissolved substances pass through the pores of an osmotic membrane, while larger molecules move through in smaller numbers or not at all pens in roots and in other parts of living things if we think of this work as the action of the rapidly moving molecules. But there is still the problem of understanding how roots work, since they seem to be raising water against gravity, and they seem, at any rate, to be taking more out of the soil than they might be giving off. The cell walls of the root, and of practically all plant parts, consist of cellulose, a substance that does not dissolve in water, but does absorb water in the same way as glue or gelatin. Now, we must imagine that wherever there is water, substances dissolved in it will diffuse in it. When the cellulose walls of root-hair cells are saturated with water, the molecules of dissolved substances diffuse through this water. This kind of "diffusion through a membrane" is called osmosis, from a Greek word meaning "to push". We conceive osmosis to be taking place through the walls of all cells, those of animals as well as those of plants. Since the liquid or solution inside the root hair is different from the soil water surrounding the cell, we should expect that some of the substances would be diffusing into the cell, and other substances moving out of the cell. 86 The root hair absorbs water from among the soil particles by osmosis through the cell mem- brane. In the cells near the sur- face of the root, the proportion of water molecules to other mole- cules is greater than in the deeper layers of cells, as we should expect. Water in the surface layers diffuses from cell to cell, passing through several cell membranes by osmosis. Sur- rounding a live root hair there is a constant flow of liquid OSMOSIS IN ROOTS Indeed, from what we know of the chemical activities of protoplasm, we should expect materials to be passing into cells and out of cells by osmosis, all the time. That is, tliere is a double current: (1) the protoplasm of a cell receives from the outside its supply of water, salts and food; and (2) mate- rials of various kinds pass out of the cell. Gases as well as liquids diffuse through the wet cell wall. Every cell receives its income by osmosis, and it gets rid of its wastes by osmosis. Osmosis in Living Things^ Some substances dissolve in water more easily than others, and some solids do not dissolve at all. Substances in solu- tion will diffuse, but not all will diffuse through a given membrane equally fast. And through some membranes certain substances will not diffuse at i '4^%f^ L. v. I'lury, iluycu Thuinpson Institute PLASMOLYSIS IN EPIDERMAL CELLS OF RED CABBAGE When living plant or animal cells are placed in concentrated salt solution, the pro- toplasm shrinks from the walls of the cells as water diflFuses out. An excess of fer- tilizer makes a plant lose water through the roots and wilt ^See No. 7, p. 95. 87 TURGOR AND OSMOSIS IN ARTIFICIAL CELLS From the bulging of the membrane we infer that something passes through the mem- brane faster in one direction than in the other — increasing or decreasing the internal "pressure". In a living cell increased pressure results in a turgid, or swollen, condi- tion, whereas reduced "pressure" results in a flaccid, or flabby, condition,:a5.7 0.5 0.7 2.3 2.2 11.0 0.4 2.4 0.8 0.5 16.0 2.7 1.5 2.7 5.4 19.1 0.8 +Vitamin is present. —Not present in appreciable amounts. *Calcium not available. ^Adapted from Clara Mae Taylor, Food Values in Shares and Weights, 1942, pp. 8-41. By permission of The Macmillan Company, publishers. 131 Vitamin VITAMIN STABILITY STORAGE IN BODY RICH FOOD SOURCES A Derivative of carotin, Is not easily de- Is Stored to a con- Milk and milk products. the yellow color of car- stroyed at cook- siderable extent. especially butter and rots. Body forms it ing temperatures. especially in the cream, eggs, fish- liver from carotin. Is stable in acids liver oils, liver, yellow vege- C20H29OH and alkalies. Is tables, and green leafy slowly destroyed vegetables -1 on exposure to air D Is formed from ergos- Is stable to heat, Is stored in skin. Fish-liver oils, sparingly lerol, a plant fat, when acids and alkalies, brain, thymus. present in ordinary ca it is exposed to ultra- but deteriorates adrenals, liver and food. Found in egg violet light. Is formed slowly kidneys yolk, milk and butter. in human skin when Less is found in milk exposed to direct sun- light. products in winter than in summer. Small -J C27H43OH amounts are found in o meat and fish Tocopherol Tocopherol is made syn- Resists heat and Is amply stored Is widely distributed. Is (E) thetically; is also ob- oxidation, thougii in the body in all dairy products, tained from the germ decomposes when in the oil of the germ oil of wheat and other exposed to ultra- of wheat and other ■ grains. violet light grains; in eggs and C29H60O2 green vegetables. (Is < not found in fish oils) Phylloquinone Two forms occur natu- Is relatively Is stored to a Widely distributed in (K) rally, and related syn- stable; withstands hmited extent in foods. Concentrated thetic products have heat liver form is prepared from similar effect. Is lack- ing in body when there is a deficiency of bile; is synthesized by bac- teria living in intestine. C31H46O2 fish meal or alfalfa Ascorbic Acid UJ Ascorbic acid is synthe- Is easily destroyed Is not stored in Tomatoes and citrus (Q sized in pure state by heat, especially body to any ap- fruits are especially -J from glucose. Some in presence of al- preciable extent rich sources. Other mammals form this kalies. It also oxi- fruits, leafy vegetables. vitamin; man, monkey dizes readily in and germinating seeds and guinea pig do not. the air are also good sources z> Cell sOe Thiamin Is formed by certain bac- Withstands ordi- Is not stored to Germs of seeds, whole- (Bi) -J teria, fungi and yeasts. nary cooking but any extent in ani- grain cereals, nuts, to- Has been extracted in is easily destroyed mal tissues; liver matoes, spinach and o pure state from rice "pol- in presence of a has slight amount peas are good sources. ishings". little soda. Lx)st Liver and heart tissue C12H16N3CI2OS if cooking waters are fair sources are discarded Riboflavin Riboflavin has been iso- Is generally sta- Is stored in body Liver, meat and fish. (G) lated from milk, eggs, ble; withstands tissues, especially milk, eggs, green vege- yeast and other sources. heat in liver tables, tomatoes and UJ C17H20N4O6 yeast Niacin Niacin (nicotinic acid) Is relatively sta- Is stored to a Liver, lean meat, fish, t- is made synthetically ble; withstands limited amount milk, eggs, peanuts. as well as by green plants heat in lean meat and green vegetables, to- < and veast. in Hver matoes and yeast S CeHsOsN 132 Chart REGULATIVE EFFECT EFFECT OF DEFICIENCY Affects metabolism and growth; is es- sential in epithelial tissues and in vision Deficiency results m lesions in nerve tissue and in mucous linings of respiratory tract, of alimentary canal, of reproductive and excretory organs, of the eye, and in various glands within the body. Deficiency results in night blindness. Though this vitamin is not specifically anti-infective, a lack of it results in tianiaged tissue, which increases likelihood of infection Is essential in tiie absorption of calcium and phosphorus from the intestine and in their metabolism within the body Lack of this vitamin results in poor bones and teeth. Extreme deficiency results in rickets, a deformed condition of the bones. In this sense it is called antirachitic Is essential in the formation of placenta in female rats and other rodents Lack of it causes embryos to die and males to become sterile. No conclusive evidence is at hand as to the necessity of this vitamin in human reproduction. Is called antisterility factor Is essential for formation of prothrom- bin, an important coagulating con- stituent of the blood When deficient, blood will not clot. Hence called antihemor- rhagic, although hemorrhages are initiated by conditions other tlian the "absence" of phylloquinone Is essential for the normal development and maintenance of bones, teeth, capillary wails, gums and joints. Is essential in normal growth Inadequate supply results in irritability, lack of stamina, retarda- tion of growth, fragile bones, weakened capillaries, and pains in joints. Extreme deficiency results in hemorrhages in various organs, discolored areas under skin, tenderness and swelling of joints, swollen and bleeding gums, and loosening of teeth in sockets, all characteristic symptoms of scurvy. Is called anti- scorbutic Influences appetite, digestion, particu- larly motility of intestine, growth, and nervous system. Is essential in carbohydrate metabolism Slight deficiency results in loss of appetite, sluggishness of stomach and intestine, nervousness and irritability. Extreme deficiency interferes with nerves, resulting in a paralysis of the limbs, a condition called beriberi in humans and polyneuritis in other animals. Is called antineuritic Combines with phosphoric acid and pro- tein, forming respiratory enzymes. Is essential for normal health at any age Deficiency results in digestive disturbances, nervousness, weakness, unhealthy skin. Mouth lesions occur at the junction of the mucous membrane and skin around the mouth. Characteristic lesions appear in the cornea Essential in formation of respiratory enzymes. Is needed for normal health and growth, especially in skin and gastrointestinal tissues Deficiency results in a disease called pellagra, in w hich the patient has an inflamed skin, is nervously depressed, and may develop an inflamed tongue and mouth lining and a severe disorder of the digestive tract. The dermatitis usually occurs symmetri- cally on the body as on the backs of the hands, on the forearms, or on the ankles. The typical pellagrin usually suffers from a lack of riboflavin and thiamin as well as niacin 133 of "shares" of energy be proportionately less than the number of "shares" of each of the other essential nutrients. Shares in Foods' With this device of "shares" it is easy to plot an indi- vidual's total needs and to plan to meet those needs with shares of food. The table on page 131 shows the contributions of common foods to the diet in relation to their energy value. Note that in many cases a share of energy corresponds roughly to a serving we commonly take. By representing with bar graphs the shares of each of these dietary essentials, one can quickly visualize which foods are rich in energy, or mineral, or ascorbic acid, and so on (see pages 126, 127). Lettuce, spinach, and other fresh vegetables and fruits contain a high percentage of water; they therefore yield relatively little energy per pound. On the other hand, butter and other fats are extremely rich sources of energy (see footnote, p. 125). Sugar, candy, and other sweets yield much energy and little else. Milk, cheese, meat, fish, eggs, peas and beans are rich sources of proteins. The mineral content of milk, cheese, eggs, and various fruits and vegetables is high. Some foods are rich in one vitamin and poor in other vitamins. In general, milk, eggs, liver, and various fruits and vege- tables are high in vitamin content. The foods arbitrarily listed in the table, p. 131, illustrate the shares present in different kinds of foods. In Brief The basic needs of the body vary primarily with the rate of growth and with the amount of heat lost from the body surface. Above minimum, or basic, energy expenditure the activities determine the energy required by an individual from hour to hour. The energy expenditures of the body are measured in heat units, Calories, by various types of calorimeters. The basal metabolism of a person is his rate of energy expenditure when he is awake, relaxed and lying still, at least twelve hours after the last meal. Because children vary in size, in rates of growth, and in activity, their energy requirements at any given age vary widely. The total energy requirement of a day-laborer doing heavy work is ap- proximately twice that of a similar person engaged in clerical work. One can continue for a long time on a deficient diet without realizing it, but in the meantime injuries accumulate. It is therefore important to acquire tastes and practices guided by reliable knowledge of food needs. Milk and milk products, eggs, and fruits and vegetables are considered "protective" foods because of the minerals and vitamins they contain. iSee No. 6, p. 136. 134 Diets can be planned to meet daily needs by using the "share" technique. A share of any food-essential is that quantity which supplies one thirtieth of the daily needs for an adult using 3000 Calories per day. Thus a share of energy is equivalent to 100 Calories. EXPLORATIONS AND PROJECTS 1 To measure the rate at which a person spends energy, find out how much oxygen he uses in a given time. Where a basal-metabolism apparatus is not acces- sible, it is possible to construct one patterned after Benedict's Student Respiration Apparatus/ The subject (sitting or lying quietly) holds the mouthpiece in mouth while breathing through the nose. Attach oxygen tank to air inlet and fill inside of apparatus with oxygen. Remove hose from oxygen tank and connect pump." When everything is in readiness have the subject start breathing through his mouth. Place nose-clip on his nose. Count the time from the first exhalation that fails to make the rubber cap touch the stop wire. The starting time can be has- tened by adjusting the amount of air inside the apparatus with the pump, im- mediately after the subject starts breathing from it. As the test proceeds, keep the volume of gas constant within the apparatus by pumping in air to replace oxygen used by the subject. Oxygen used by the subject is measured by the quantity of air pumped in to replace the oxygen consumed. The carbon dioxide breathed out by the subject is absorbed by the soda-lime. Tests should be run from five to ten minutes. From the number of cubic centimeters of oxygen used and the duration of the test, calculate the amount of energy the subject would spend in a day if he used energy continuously at the same rate.^ Record the observations and make the calculations in table form.* (Do not write in this book.) 2 To calculate your own basal expenditure of energy per day, use the table on page 121. 'See illustration, p. 120. The material, with the exception of the rubber gas-mask valves, rubber bathing cap, and the soda-lime, can be picked up locally. This apparatus is just as satisfac- tory for classroom measurements as the more expensi\e purchased ones. (Respiradon apparatus and accessories may be obtained from Warren E. Collins, 555 Huntington A\ e., Boston, Mass.) "The pump can be calibrated by measuring the volume of vv'ater that each pumpful of air displaces from a graduated cylinder inverted over a water bath. ^Assume .004825 Calorie for each cubic centimeter of oxygen used. ^Figures for column IV are obtained by muldplving the number of pumpfuls (III) bv the volume of the pump in cubic centimeters. Figures for column VI are obtained by multi- plying cubic cendmeters per minute (column V) by 1440, the number of minutes per day. 1 n III IV V VI VII VIII IX Name of Duration No. of Cubic Cubic Cubic Calories Bodv- Calorics Subject of Test in Pumptuls Centi- Centi- Centi- Used Weight Used Minutes of Oxy- meters meters meters per Day in Pounds per Day gen Used Used during Test Used per Minute Used per Day per Pound ot Body- Weight 135 3 To show that activity increases the rate of energy expenditure, compare the person's oxygen consumption at rest and while active. Make a respiration test as described in No. 1 above. As soon as the test has been started, have subject raise and lower kilogram weights in each hand for remainder of the time. Compare rate of oxygen consumption, or expenditure of energy, when subject is exercising and when sitting still; compare additional energy expenditure of several working at different rates. 4 To determine the percentage of water in various foods, remove the water from each of several kinds of food by heating weighed quantities at 100° C for sev- eral hours and weighing what is left. From these figures calculate the percentage of water in each food. Use 100-Calorie portions of each so that you can compare the relation of water content to energy value. 5 To determine the amount of mineral matter in these same foods, burn out the organic portion of each and weigh the ash that is left. 6 To compare the contributions of different foods to the diet, make bar graphs representing the "shares" in the foods listed in the table on page 131. For comparative purposes, all the bar graphs should be made on the same scale. Use i-inch graph paper and allow three squares for each share of each nutrient. Use a distinct color or shading for each nutrient. QUESTIONS 1 What connection is there between muscle activity and breathing.^ between muscle activity and heartbeat? between muscle activity and exertion? 2 How can one overeat and at the same time be malnourished? 3 What factors influence the basic needs of the body? 4 What determines the energy required by an individual beyond the basic expenditure of energy? 5 What factors determine the wide variations in the energy requirements of children at different ages? 6 How far can we trust our feelings in deciding what and how much to eat ? 7 How is it that energy expenditure can be measured in terms of the amount of oxygen consumed? 8 In what sense are certain foods "protective" foods? 9 How can we classify foods according to what they furnish in our diet? 10 How can we use the "share" technique in planning our diet? 11 Which vitamins are water-soluble? fat-soluble? 12 Which vitamins are most stable? least stable? 13 Which vitamins are generally stored within the body? which are not so stored ? 14 What are the regulative effects of each of the vitamins? 15 What dysfunctions result from a deficiency of each of the vitamins? 16 How can one make sure that vitamin values are not lost in cooking? 136 CHAPTER 8 • HOW DO FOOD STUFFS COME INTO BEING? 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 Is it true that plants breathe in what animals breathe out, and that animals breathe in what plants breathe out? 4 Can plants live without roots? 5 Where does the carbon in foods come from? 6 Where does the nitrogen in foods come from? 7 Why is it necessary to buy nitrogenous fertilizers when there is so much nitrogen in the air? 8 Is soil important now that we can grow plants without it? 9 Why do farmers prefer valley lands to upland farms? 10 Is there danger of exhausting our soil resources? When proteins, fats, and carbohydrates become assimilated into the pro- toplasm 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 this question was found in the discovery that the green parts of plants create new organic foods out of inorganic materials. But how can green plants make new organic foods when other living things cannot do so ? Out of what do plants make these foods ? How Is Organic Material Made Anew? A Manufacturing Process^ The making of organic substances out of inorganic materials may be compared to a manufacturing process. In every such process there must be (1) raw material, (2) tools or machines that work on the material, and (3) energy to drive the tools or machines. There is of course (4) a main product, and sometimes there are (5) left- over wastes, or by-products. The simplest organic product that we can recognize in a plant is a sugar. The raw materials used by the plant in making carbohydrates, or sugars, are water and carbon dioxide. The plant's machines or instruments differ from those with which we are familiar and which consist of wheels and levers or other moving parts. iSee Nos. 1-4, pp. 157-158. 137 Light / onnnaa nouM innnrPFx Water and minerals Food (sugars, fats, proteins) Oxygen Carbon dioxide Oxygen THE LEAF AS A MANUFACTURING PLANT The plant uses chemical engines, each consisting of a lump of protein with some of the pigment that gives familiar plants their distinctive color. This substance is called chlorophyl (from the Greek chloros^ ''green", and phylloii, "leaf"). Chlorophyl is the actual transformer of energy in the food-making process (see illustration above). The energy for doing this w^ork is the light from the sun. Although the work cannot go on at too low a temperature, it is radiant energy, light, that is active, not heat. The sugar formed by the action of sunlight upon chlorophyl consists of the elements carbon, hydrogen and oxygen, which are derived from raw material, water (H-O) and carbon dioxide (COl>). Sunlight and Life In the presence of light and chlorophyl the elements of carbon dioxide and water recombine, forming sugar and liberating oxy- gen. The action may be represented thus: 6 COo + 6 H2O — > CeHisOe + 6 O2 We may read this formula thus: six molecules of carbon dioxide plus six molecules of water (under the action of sunlight) form one molecule of sugar and six molecules of oxygen (see illustration, p. 139). Energy equiva- lent to that absorbed from the sunlight is present as latent or "fuel" energy in the carbohydrate. T38 The process of carbohydrate formation by chlorophyl is called photo- synthesis, from two Greek words meaning "light" (compare ^y^o/ograph) and "a putting together". It is easy to show that in the absence of light, chlorophyl is inactive and photosynthesis is suspended. Moreover, if a plant is kept in darkness for a longer period, the chlorophyl begins to dis- appear, and in the end the leaves will turn yellow or even white. We use this fact in the blanching of celery. We also know that the outer, exposed, leaves of a head of lettuce or cabbage are much greener than the inner leaves. Experiments have shown that plants can carry on this work under artificial light. By the use of strong electric light during the night, lettuce plants have been hastened in their growth and development, and brought PHOTOSYNTHESIS IN A LEAF Palisade cells receive water from the roots by way of fine tubules, and carbon diox- ide by osmosis from the surrounding air spaces. Under the action of sunlight, the chlorophyl combines carbon, oxygen and hydrogen from water and carbon dioxide into sugar or starch molecules, and an excess of oxygen passes out of the cells by osmosis 139 to market at least two weeks earlier. Some plants can apparently be kept working continuously, as they seem to need no "rest" or "sleep". Leaves as Starch Factories Common plants carry on photosynthesis in a special organ, the leaf. The characteristic feature about leaves is the blade, or flat and comparatively thin structure. Some leaves have stalks, or petioles; and all have "veins" running through the blade. Leaves vary remarkably in size, shape and the character of the edges and of the surface (see illustration, p. 43). Some are hairy; others are quite bald. Even the color is not uniform, for the chlorophyl varies in density, and the appear- ance is influenced by other pigments, air spaces, wrinkles, hairs, and other details. And many "leaves" depart widely from our ordinary notion of what a leaf is. Some are hardly more than stiff bristles, as on certain cac- tuses. Others have sensitive extensions, or tendrils. In some species the leaves are more or less active in capturing animal food (see page 542). But starch-making proceeds in about the same way in all leaves containing chlorophyl (see illustration, p. 139). Transpiration^ Water evaporating from the leaves sets up currents that distribute throughout the plant water and salts absorbed from the soil. This loss of water, or transpiration, is at the same time a source of danger to the plant, for more plants die from wilting than from any other one cause. iSee Nos. 5 and 6, p. 158. I. p. Flory. Boyce Thompson Institute LIGHT AND CHLOROPHYL Normal seedlings grown in the light appear green from the start. Seedlings kept in the dark remain white until after they are placed in light. Albino plants never de- velop chlorophyl, and wither when the seed nutriment is exhausted 140 Palisade layer ^-''•^' ,«<^» t^r-i > ^.r ^ " r ---X"^ JTv^ ^?^4ee Fibrovascular bundle Guard cell of stoma Epidermis Air space in spongy tissue Stoma STRUCTURE OF LEAF Vessels of the fibrovascular bundles, the air spaces among the cells, and the stomata in the epidermis act as channels through which the living cells inside the leaf com- municate with lower parts of the plant and with the surrounding atmosphere Transpiration may also be of use to the plant indirectly, for the rapid evaporation of water lowers the temperature of the plant. Sometimes in the summer the sun comes out quickly after a shower. Then the moisture left in the air may prevent transpiration, and as a result the sunlight is converted into heat inside the leaf so rapidly that the protoplasm is injured. Both "breathing", or gas exchange, and transpiration appear to be regu- lated by the guard cells of the stomata (see illustration, p. 143). Our Dependence upon Chlorophyl From careful chemical studies it appears that plant cells make proteins when they receive, in addition to carbohydrates, salts containing certain elements. Nitrates, for example, contain nitrogen; phosphates contain phosphorus; sulfates contain sulfur; and so on. A green plant can therefore produce its own food if it receives, in addition to the water and carbon dioxide, a suitable supply of minerals from the soil. Many plants without chlorophyl, such as molds and yeasts, are also able to make proteins when supplied with carbohydrates and suitable minerals. And we know that our own bodies as well as those of other animals and of plants can transform starches and sugars into fats. 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 materials. They are nourished by materials obtained from the leaves. But 141 animals and such plants as mushrooms, which have no chlorophyl, must get their organic food from the bodies of other living things. Ce^i206 +60 PHOTOSYNTHESIS AND RESPIRATION When photosynthesis takes place, light energy is absorbed and stored. When sugar is oxidized, the stored energy is liberated as heat. The waste products of respiration are the raw materials of photosynthesis In the end, all food comes from green plants. It is as if the carbon and the oxygen in CO2 were pulled asunder by the action of sunlight through chlorophyl. They are then able to combine again and so liberate energy. It is thus that carbohydrates yield energy in becoming oxidized, whether in the body of a living thing or in a flame. All the energy which plants and animals get from the oxidation of carbohydrates, fats, or proteins is thus derived from the sun's energy. There is more than poetry in the statement that every human act is a transformed sunbeam. How Do Minerals Reach the Leaves? The Work of the Root^ Roots are familiar to us as plant anchors. They are also special organs through which plants absorb water and dis- solved minerals, and through which they get rid of wastes. The actual exchange of material between the plant and the soil takes place through the thin walls of the delicate root hair (see illustration, p. 144). As the plant grows larger, its absorbing area increases by the branching of the roots. But it is always in the regions near the growing tips of rootlets that root hairs are formed — and that absorption takes place. iSee No. 7, p. 158. 142 In roots of such plants as the carrot or parsnip we can distinguish an easily broken outer layer and a tougher core, or "central cylinder", running lengthwise. The two layers correspond respectively to the bark and the wood seen in the stem of a tree. With a microscope we can see that there are several different kinds of cells in the root (see illustration, p. 144). In the central cylinder the cells are much longer in proportion to their width than are those in the cortex^ or bark; and their long diameters run length- wise of the root. Such fleshy roots illustrate a third function that many roots carry on, namely, that of "storing", or accumulating, surpluses of food material. But whether roots are fleshy or stringy or woody, they generally absorb and transfer materials. Vessels and Fibers In the cortex of a root, movement of material re- sults from simple diffusion or osmosis from cell to cell. In the central cylinder, however, liquids move bodily through long tubes or vessels that act as main channels in the plant. There are, in fact, two sets of conducting tubes. Through the smaller vessels in the central cylinder food materials produced in the leaves are carried down toward the growing parts of the Hugh Speueer AIR HOLES OF PLANTS Thin-walled "guard cells" enclose each stoma and carry on photosynthesis. When they are turgid, the stomata are open; when they become flaccid, the stomata are closed. Stomata occur in the epidermis of twigs, as well as on leaves. As the stem grows tougher, the holes become larger and more irregular. The roughened spaces on the bark are lenticels 143 Cortex Epidermal cells Central cylinder Root hairs Root cap Radish seedling Hugh Spencer THE TIP OF A YOUNG ROOT Each root hair is a single cell formed by the outward prolongation of one of the skin cells. Each root hair lives but a short time and then shrivels up. New root hairs are formed as the tip of the root continues to grow. The older skin cells of the root die and dry out, making a protective cover through which little water passes root. The tubes through which water passes from the roots to the leaves are called xylem, or wood vessels; those through which organic foods pass downward from the leaves to all other parts of the plant are called phloem, or bast vessels. Associated closely with the two kinds of ducts, or tube-cells, there are other elongated cells having rather thick walls of cellulose. These are the fibers, which are usually more tough and rigid than those we find in the carrot. The bundles of fibers and vessels together make up the "fibro- vascular bundles", which are conspicuous in all our common plants above the rank of mosses and liverworts — that is, from the ferns onward (see Appendix A). The fibrovascular bundles of the root are continuous with those of die leaf, by way of the stem. They branch and subdivide as the plant grows; and in the leaves we can see the bundles reaching to all parts as "veins" (see illustration opposite). The fibers are most conspicuous in the stems of plants, which we readily recognize as mechanical supports. The wood of trees consists very largely of fibers, as do the tough parts of bark. We make extensive use not only of wood, but of the fibrovascular bundles of many plants in the form of 144 FIBROVASCULAR BUNDLES IN LEAVES The living cells in the blade of the leaf receive water and dissolved minerals and send food through an intricate system of small veins, which extend to all regions of the leaf. These small veins, or fibrovascular bundles, connect with larger veins in the leaf, the stem and the roots separate threads— for example, flax, hemp, sisal, linen, and so on. Chil- dren like to pull the "nerves" out of the leaves of plantain, and we are all familiar with the "nerves" in the celery stalk and with the strings in cornstalk. The arrangements of fibrovascular bundles in stems and leaves are so characteristic that they enable us to recognize at once members of the two mam divisions of seed-plants, namely, monocots and dicots (see Appen- dix A). In the monocots, plants having but one cotyledon in the seed, the veins run almost parallel, as in grasses, lilies and bananas. In the leaves of dicots, plants having two cotyledons in the seed, the veins run into each other, forming networks, as in the potato plant, the elm, or the geranium (see illustration above). Types of Stems In monocotyledonous plants fibrovascular bundles are scattered throughout the stem (see illustration, p. 146). They are much more numerous toward the outside. The water-conducting vessels (xylem) are toward the center of the stem, and the food-conducting cells (phloem) are toward the outside. Between the xylem and phloem tubes and sur- rounding them are the thick-walled woody fibers. 145 • Rind Pith Vascular bundles Conductive Rind Pith bundles Kislit. i? General Binlogical Supply House. Inc. CONDUCTING TISSUES IN CORN STEM The tough fibrovascular bundles of conducting cells ore surrounded by tender pith cells; these con be readily shredded away and the bundles exposed. The arrange- ment of the bundles clustered toward the outer rind is analogous to the hollow-tube construction of a bicycle frame as a supporting structure In dicotyledonous stems the fibrovascular bundles are arranged sym- metrically around the center. As in the monocots, the xylem tubes are toward the center, and the phloem tubes are toward the outside. In the dicots, however, these two sets of vessels are separated by a layer of un- differentiated, growing cells. This layer is called the cambium layer. The new cells which the cambium produces toward the center become woody fibers and xylem tubes. Cells formed on the outer side of the cambium become bast fibers and phloem tubes. As the stem grows in thickness, the cambium layer is pushed away from the center. As the bark is pushed out- ward, the outermost layers split or peel in various ways. This results in the characteristic markings of various species, such as a birch tree or an oak, for example. Circulation of Sap in Plants The rise of water to the tops of tall trees has always puzzled people. There was no systematic study of the problem before about 200 years ago, when Stephen Hales (1677-1761), an English preacher, first used mercury gauges to measure the pressure with which sap rises in plants. Hales came upon the idea of measuring the sap pressure when he tried to stop the "bleeding" of a vine. He tied a piece of bladder over the cut end, and then noticed that the bladder swelled up. He continued his experiments and showed that the root pressure, which we now recognize 146 Three - year- old linden Cork layer — Phloem ducta- ^ Cambium Xylem ducts -Wood fibers Bast fibers / Epidermis -Pith- ■^ Pith ray- Left, © General Biological Supply House, Inc. STRUCTURE OF A DICOT STEM Growth in the cambium layer produces new woody tissue on the inside and new bark tissue, or cork, on the outside of this layer. During the spring, when growth is rapid, large xylem tubes are formed. Later, growth slows down, and a definite ring of denser tissue is formed. The number of annual rings in the woody part of the stem tells us the age of a tree. Food travels down the stem from the leaves through the phloem tubes; water and dissolved mineral salts travel up from the roots through the xylem tubes. Rays of pith cells connect the cambium with the xylem tubes as due to osmosis, and transpiration were sufficient to explain the rise of sap (see illustration, p. 148), The minute diameters of the xylem vessels probably also play a part in connection with osmosis and transpiration. No vessels reach the whole length of a plant, so that the "capillary" attraction can raise water but a short distance in each cell. Other experiments have shown that water is ''pulled" through the xylem tubes as it evaporates from the cells of the leaves. This is explained by the fact that particles of water cohere, or cling together, when confined in the narrow tubes. The network of water-threads in the plant can carry a considerable amount of strain, equal to a pull to the top of the tallest trees. Fluids in plants not only rise, but, as we have seen, move also from the leaves toward the roots. We can show that this part of the circulation is by way of the phloem vessels. If the bark is removed from a tree so as to leave a complete ring or "girdle" unprotected, the tree can continue to live for the rest of the season. This shows that the water continues to rise from 147 Left L. P. f: - Porous cup Water Water Mercury Inj'.itute If we cut the stem of a living plant under cold water that has been boiled to remove the air, and then connect it with a glass tube while still under water, the vessels of the stem and leaves are in communication with the water in the tube. Now we may set the stem upright, with the lower end of the tube dipping into mercury. In this arrange- ment mercury rises in the tube as if the water were being pulled or pushed into the stem. With a porous cup full of water in place of the twig, the water and mercury behave in the same way. What becomes of the water that dis- appears out of the glass tube? How is the water actually raised? WATER RAISED BY TRANSPIRATION the soil with its dissolved salts — but not in the bark or phloem vessels. The following spring, however, the buds will not open; the tree will be dead. This is because the water now coming from the roots is without organic food. The food reserves could not come do\Mi into the roots after the tree was girdled, for it is through the phloem vessels that organic food comes from the leaves to the lower parts of the plant. Is There Danger of Exhausting the Supply of Raw Materials Used by Plants in Food Production? The Carbon Cycle If we understand how green plants make food, we can see more clearly how the living things in the world depend upon each other. The carbon in our bodies, for example, came from the proteins, fats and carbohvdrates which we ate. We obtained these either from the bodies of plants or from the bodies of animals. The cows or pigs or chickens that we used as food had in turn obtained the carbon in their bodies from the plant food which thev had eaten. Now die plant gets its carbon from the carbon dioxide in the air. But what is the source of this fraction of 1 per cent of the atmosphere.^ The plants in North America could use it all up in a few sunny August days — and that would be the end of everything. Certain rocks — limestone and marble especially — yield small quantities of this gas when thev decompose. 148 But this amount is very small indeed when we consider what is being used up by plants from hour to hour. There is, however, still another source. We have seen (see page 84) that all living things, while using oxygen from the air, are at the same time throwing off carbon dioxide. Moreover, every fire discharges quantities of carbon dioxide. This carbon dioxide in the air then becomes raw material for food in green plants. However, the amount of carbon dioxide that fires and animals can yield is limited by the quantity of plant life. For the only fuel available is the organic material which green plants manufactured in the first place. We see, then, that our lives depend upon the green plants, and that, on the other hand, the growth of green plants depends upon the oxidation of organic substances in the bodies of animals or in fires. There is, thus, a certain balance between the total quantity of plant life in the world and the total quantity of animal life. If the amount of animal life should diminish very greatly, the growth of plants would in time be slowed or stopped by the lack of carbon dioxide. Should the amount of plant life decrease greatly, the growth of animals would soon reach a limit for lack of food (see illustration, p. 150). The Oxygen Cycle Oxygen is the most abundant of the elements in the earth's crust; and the amount of oxygen in the atmosphere is very much greater than the amount of carbon dioxide. But it is a limited amount. Now all living things are constantly drawing upon this oxygen, for living includes the release of energy by the oxidation of food sub- stances. After oxygen has taken part in the oxidation of organic material, it is no longer available for similar action. Through photosynthesis, oxy- gen is liberated, and thus becomes again available for the breathing of animals and plants. If all green plants should suddenly stop their activ- ities, the amount of oxygen would as rapidly diminish. In a short time animal life would cease (see illustration, p. 150). The Nitrogen Problem In the bodies of plants and animals proteins break down into simpler compounds of nitrogen. Plants can use some of these in making new proteins, but others disappear in the air, and so nitrogen is lost from the cycle of life. But of all the common elements, nitrogen seems to be the one that does not come back into the life cycle by an auto- matic process. The dead bodies of plants and animals on the ground and in the ground contain vast quantities of nitrogen compounds, as well as of fats and carbohydrates. These bodies are devoured by smaller organisms, down to the decay action of bacteria and fungi, and the material is finally returned to the soil and the earth. Particles of nitrogen at any moment present in a living thing, as well as the particles of other elements, are thus on their way out — in a constant process of circulating through the air and 149 Oxygen in air k Respiration Green .- {f:":^' ;- plants; >■■- ^^-; ■- ■ ^ .!#*-» Fire ^ / 1 ^ Photo- Respiration | / ^ synthesis '^' N Photo- \ F^ synthesis 3^ Carbon dioxide in air K't >/ »y Bodie Carbon and oxygen m <:>'. ,ee5 ^y soil ^! .^1^ ^5 ,^^ Bodies Excretion ^Q'j :'o.^ Soldier Young nymph Eggs Young nymph SYMBIOSIS AMONG ANIMALS The flagellates which live within the digestive tract of the termites change wood into soluble carbohydrates. The termite furnishes the protozoans a comfortable shelter and keeps them supplied with small bits of wood — which the termite can break down mechanically, but cannot digest p. 180). Very many of such species take practically all the food for a life- time during the larval stage, living the rest of the time on accumulated reserves. A third type of intermittent feeding is illustrated by the golden plover. This bird summers in the arctic and then migrates to southern South Amer- ica. It travels 2400 miles in a nonstop flight, on energy from the fat stored within its body. The intermittent feeding of animals is not unlike the habits of many plants. In the common annual plants that start from seeds and end in seeds within a few months, there is a long stretch of time during which metabo- lism is at a standstill. The food for the renewal of life in the spring is the 179 reserve packed in the seeds. Such biennial plants as carrots, beets, parsnips, turnips, and many of the dock-weeds store food in large fieshy roots during the first growing season. Then, in the following spring, the food stored in the roots is used in developing a new shoot, which bears seeds before the end of the second summer. Many perennial plants — in fact, all that pass through a dormant stage during the winter — store food in the roots or stems during the growing season. And from this store they develop new buds and leaves the following spring. Asparagus, as marketed, consists of tender young shoots grown from food stored in roots and underground stems during the preceding seasons. I mud Malii Uuitaii of Ent(jini)logy and Plant Quarantine LIFE HISTORY OF THE CODLING MOTH The "worm" of the apple is the larva of the codling moth, which feeds only during the larval stage. In early summer the larva enters the open end of newly set green apples, where the tips of the sepals come together. It feeds on the apple pulp and grows larger. Early in July it emerges from the fruit and pupates on the bark. The adult comes out of the pupa and later lays eggs on the bark of twigs. These eggs hatch into larvae, which eat their way into the sides of apples. The full-grown larvae come out of the apple in late fall and form pupae in protected places under the bark, where they pass the winter. The moth thus produces two broods in one year 180 FOX SPARROW BIRD MIGRATION The winter home, the breeding range, and the migration routes of three North American birds rn Brief In plants and in animals, starches, proteins, and other nutrients are con- verted into soluble crystalloids by the action of various enzymes. Excess sugar produced in leaves is converted into starch by the action of an enzyme — a process just the reverse of digestion. At night starch is con- verted into sugar by the digestive enzyme diastase, and the sugar is trans- ported to other parts of the plant through the phloem tubes. Digestion takes places in plant cells which make or store food. Single- celled animals digest food within their bodies. Bacteria give out enzymes which digest food in the surrounding medium. Higher animals carry on digestion in specialized organs. Food entering the mouth passes successively through the pharynx, gullet, stomach, small intestine and large intestine. Food is moved along through the alimentary canal by peristalsis. Undigested portions are discharged from the body through the rectum. Digestive juices are produced in special glands and delivered by ducts into the food canal. Other products of glands with ducts are lubricants, cooling secretions, excretory substances, and food. Starch is changed to sugar by digestive enzymes present in the saliva and in the pancreatic juice. Complex sugars are changed to simple sugars by several specific enzymes present in the intestinal juice. Proteins are split into amino-acids by enzymes in the gastric, pancreatic and intestinal juices. Fats are split into fatty acids and glycerin by an enzyme secreted in the pancreatic juice. This digestion requires an alkaline medium, which is furnished by the bile. Digested food is absorbed and transformed by the Villi, specialized ab- sorbing organs that project into the cavity of the small intestine. Plants and animals accumulate surplus food in their tissues, and then use it when new supplies are scarce. EXPLORATIONS AND PROJECTS 1 To determine which food substances diffuse through osmotic membranes, place dilute starch paste, corn sirup, olive oil, and raw egg white in four wide- mouthed bottles, tie bladder membranes tightly over the tops, and suspend in jars 182 of water overnight. Test the material in both the bottles and the jars for the appropriate substances.^ 2 To find out whether digestion takes place during germination, test the coty- ledons and endosperms (ci) of several dry seeds for starch and simple sugar and (b) of similar seeds after they have sprouted. Compare and explain your findings. 3 To extract the starch-splitting enzyme diastase from germinating seeds and grains, grind a mass of seedlings in which the sprouts are about half an inch long in a mortar; just cover with water and let mass stand a half hour. Filter off clear liquid and test for diastase by trying to digest starch with it. 4 To show the digestion of starch by saliva and by diastase, mix dilute starch paste with saliva and with diastase, set it in a warm room overnight, and then test for simple sugar and for starch. Do tests on saliva, diastase and starch paste, as well as on the mixtures which have stood overnight. Account for your results. 5 To demonstrate the effect of rennin on milk, add a little rennin, dissolved in water, to a cup of fresh, lukewarm milk, and let stand for ten minutes." (Ren- nin acts on milk in the stomachs of animals as it does on the milk in the vessel.) What relation has this action to digestion? 6 To find out how proteins are digested in the human body, expose small cubes of boiled egg white to the different digestive fluids and note the effects.^ Gather some saliva in a test tube. Place protein cubes in four test tubes contain- ing respectively (a) water, (h) saliva, (c) gastric juice, and (d) pancreatic juice. Leave all together in a warm part of the room or in a laboratory incubator. The next day examine the cubes of protein to determine whether and how much they have been "eaten away". Tabulate results observed and note conclusions. 7 To study the digestive organs and their movements: To observe peristalsis, kill a suitable animal quickly, and open the abdomen to expose the large intestine.* ^For starch, test with iodine (see page 157). For simple sugars, as grape sugar or glucose, use Fehling solutions. Add about 5 cc of Fehling copper solution to the solution to be tested, and boil for a few minutes. Then add a similar amount of Fehling alkaline solution. If a slight amount of sugar is present, the color will be green; if more is present, yellow; if still more, orange; and if there is a con- siderable amount, red. For the liquid fats, observe the fluid in the botde and in the jar to see if any oily drops are present. (To test for fats in solid substances, crush them, pour on ether to dissolve any fat present, then pour ether on a piece of paper. A permanent translucent spot indicates presence of fat.) For proteins, add a few cubic centimeters of nitric acid, and heat. Nitric acid turns pro- teins to a yellow color. If sufficient sodium hydroxide is then added to make the soludon alkaline, the protein turns an orange color. -Rennin is available in various trade preparations. ^To make artificial gastric juice, dissolve dry pepsin in water and add a few drops of hydrochloric acid. To make ardficial pancreatic juice, add pancreatin to water, with a small pinch of sodium bicarbonate. ''Frogs, chickens, rats and guinea-pigs are all suitable for use in this study. It is interest- ing to use all of them, for the internal structures vary significandy. To observe peristalsis, open the animal immediately after it is anesthetized. The frog may be "pithed" by quickly de- stroying the brain with a needle or a sharp knife. 183 To view the digestive structures, open on the ventral side to expose the diges- tive organs in their normal position within the body. Note the relative arrange- ment of the liver, stomach and intestines. Also, note the fine connective tissue carrying blood vessels, which connects with the folds of the small intestine and holds them in position. Beginning at the anus, cut out the intestinal tract of each of the animals and sever connective tissues so that the intestines may be stretched out full length; compare the organs in the several animals. 8 To show the effect of pancreatic enzyme on fat, place a few drops of feebly alkaline emulsion of olive oil containing blue litmus upon a microscope slide, and add a little pancreatic juice. Under the microscope note that the tissue becomes sur- rounded by a red halo. This shows a formation of acid; it is due to the fatty acids set free from the fat by the enzymes present. 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 is it necessary to chew food that is not digested by the mouth juices? 4 How can plants, which have no stomachs, digest food? 5 How can we show that saliva acts upon starch but not upon protein? 6 In what respects are enzymes like vitamins? In what respects are they different ? 7 How do digested nutrients reach the body cells? 8 How are undigested portions of food moved along through the food tube ? 9 What glands secrete digestive juices, and what effects are produced by each juice? 10 What functions other than digestion do gland products carry on in the body? 11 In what ways are the digestive systems of various animals especially adapted to digesting distinctive kinds of foods? 12 What makes plant tissues, as a rule, harder to digest than animal tissues? 13 How is it possible for a person to live after a surgeon has removed his stomach ? 14 How are various species able to survive on an intermittent food supply? 184 CHAPTER 10 • HOW DOES FOOD REACH THE DIFFERENT PARTS OF THE BODY? 1 Is the sap of plants the same as the blood of animals ? 2 Do all animals have blood ? 3 How does the blood help to keep us alive? 4 Of what is blood composed ? 5 How does exercise speed up the heart? 6 Do all animals have organs corresponding to hearts? 7 How does blood clot ? 8 How does the blood keep the body warm? 9 What can the doctor tell from feeling the pulse ? or from listen- ing to the heart ? 10 How can the blood of one person be made to work in the body of another? 11 Can the blood of one animal be transfused into the body of another ? 12 Why must blood be "typed" before a transfusion is made? In all except the very smallest plants and animals there is some way of distributing materials among the different parts of the body. In the com- mon plants one set of tubes carries water and dissolved salts from the roots, by way of the stems, to the leaves; and another set of vessels carries organic food from the leaves to other parts of the plant. The two currents are inde- pendent of each other. They consist of different materials and are not con- nected at any point. The red fluid that spurts out when the flesh is cut has always impressed mankind as both important and mysterious. People have explained almost everything they could observe or imagine about life by pointing to the blood. It is truly a marvelous juice! The very color has itself been exciting and has been widely used as a symbol. On flags and emblems it has represented the blood that men have shed to ensure their rights and freedoms. It has also represented the blood brotherhood of all humanity. Some of the ancient Greeks held the notion that the blood moves. That the heart actually pumps blood and keeps it in circulation was first worked out by the English physician William Harvey (1578-1657). Harvey's argu- ment, from the facts then known, was perfect. There was in it, however, one missing link: how does the blood get from the arteries to the veins? Harvey could not tell. He was certain only that somehow it must. Nobody then could know either the structure of the blood or the existence of capillaries, for the microscope revealed its secrets only after Harvey died. 185 Of What Are the Body Fluids Composed? Blood In all animals above the corals and sea-anemones, and certain kinds of worms, there is present a circulating mass of liquid which is com- monly called blood, although not all kinds of blood are alike (see pages 205- 207). The blood of backboned animals has a rather complex structure, and is associated with an elaborate system of vessels and a pumping organ, called the heart. The fluid portion of the blood is a colorless liquid, called the plasma, and consists chiefly of water. In this are dissolved various salts, organic food sub- stances, some oxygen, some carbon dioxide, certain enzymes, and other or- ganic substances derived from various organs and tissues of the body. Floating in the plasma are large numbers of corpuscles — that is, "small bodies". The most easily seen are the so-called red corpuscles. About 3200 of these corpuscles placed side by side would stretch an inch. In addi- tion to the red corpuscles there are also colorless bodies of irregular shape, the white corpuscles, of several distinct sizes and other characteristics. Some- what resembling the red corpuscles in appearance are the very small color- less "platelets" (see illustrations below and opposite). The Lymph The blood, consisting of plasma and corpuscles, fills a set of tubes which have no openings through their walls. The system is therefore called a closed blood system, to distinguish it from the blood systems of clams, crustaceans, and certain other animals, in which some of the blood tubes open into various spaces among the tissues. Outside the blood vessels, filling the spaces among tissue masses and cells, is a colorless liquid called lymph. It is from the lymph that the cells obtain their food supplies, water, salts and oxygen. And it is to the lymph that they discharge ,s *W ^^0^ (O Geneial Biological Siipph House. \m HUMAN BLOOD 186 Under a microscope, human blood appears to consist of a colorless liquid with many small bodies floating in it. The more numerous particles are the disk-shaped yellowish, or "red", corpuscles, having rounded edges. Some of the white, or colorless, corpuscles, which resemble the ameba, are barely larger than the red ones, others many times as large. And there are disk- shaped platelets,much smaller than the red corpuscles Water Urea CO. Oxygen ^jSjE^yWWWB Protein etc BETWEEN THE BLOOD AND THE LYMPH From the blood within the capillary, water, salts, food and oxygen pass out by os- mosis. From the surrounding lymph, carbon dioxide, urea and water pass into the blood. White corpuscles squeeze through the walls of the capillaries, between the cells their carbon dioxide, urea, and other wastes. The lymph and the blood com- municate by osmosis through the walls of the smallest blood vessels (see illustration above), and by way of definite connections between lymph tubes and certain large blood vessels. Like plasma, lymph consists chiefly of water and carries practically the same kinds of substances in suspension and in solution, although in smaller quantities. In addition, the lymph has floating in it many white corpuscles. It thus resembles blood lacking red corpuscles. The lymph has been com- pared in its composition to the ocean, in- which life may have originated, and from which so many one-celled organisms obtain their supplies directly. The lymph is an internal ocean from which all the cells of the many-celled animal obtain their supplies. Clotting of Blood When blood gets out of the blood vessels, it usu- ally coagulates, or becomes thickened. The clotting is itself a solidifying of a certain protein in the plasma known as fibrinogeti — that is, "fibrin-maker". The process is started by any injury to the lining of a blood-vessel or by contact of the blood with a foreign substance. The platelets then break down and discharge a special enzyme. This acts upon another substance in the blood and produces the actual clotting agent, thrombin, which solidifies the fibrinogen into fibrin. If we let blood clot in a glass vessel, we can see the mass of fibers detach itself from the walls of the vessel, as the threads shrink and the clot floats at last in a clear, almost colorless or slightly yellowish liquid, called a serum. 187 The serum is practically the same as the blood plasma, lacking the fibrin- ogen. Whatever is characteristic or distinctive of the plasma of an individual or of a species v^^ill be found in the serum. The White Corpuscles There are several types of white blood cor- puscles, all of them resembling the ameba in consisting of naked protoplasm (see page 25). Some of them have no definite shape and move about freely and also eat like the ameba. All seem to be sensitive to chemical changes, and probably other changes, in their surroundings. These active corpuscles are very similar in all animals that have blood. Their function has come to be understood only in modern times, chiefly through the work of the Russian biologist Ilya Metchnikoff (1845-1916), who was director of the Pasteur Institute in Paris. It helps us to understand the functions of these cells if we recall that whereas the ameba cell carries on all the functions of a living body, the various cells of a many-celled animal, like a butterfly or a baby, are spe- cialists. 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. They can move, like muscle cells. They are irritable, like nerve cells. They are chemical laboratories, like gland cells. As eating cells, white blood corpuscles engulf foreign particles with which they may come in contact. For this reason, Metchnikofl called them phagocytes, that is, "eating cells". They eat and digest the dead particles that result from the breaking down of tissue cells. They may eat also live cells introduced from without, such as bacteria (see page 177). As moving cells, the white corpuscles 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, which is then thrown out. Or they crowd together in large numbers wherever an injury or an invasion by foreign organisms takes place. If an infection is severe, vast numbers of young phagocytes, which originate in the red bone marrow, swarm into the circulating blood. In exceptional conditions die number in the blood increases to three and four times the normal number. From the "blood count" physicians often judge the severity of an infection. Pus is formed in a wound by the conflict between the white blood cor- puscles and bacteria. Bacteria destroy some of the corpuscles. Corpuscles liberate a protein-digesting enzyme called trypsin, which digests dead bac- teria and any body cells that may be killed by the bacteria. Some of the other white corpuscles appear to take part in the healing of wounds and the repair of injured tissues. These originate in lymphatic tissues. Because of their peculiar behavior in the presence of foreign sub- stances and particles, we have come to think of the white corpuscles as important agents in keeping the body in health. 188 r- ^.^j;^ ^M ^^^^^ ^H ■F^ c";, !.. -' ■ ^:^^^S3sb CTB^^fe>B|iSi^sK3^^^S| ^^m^^p j |^9H^ rt " fflH^^^fS" --- ^ ^' ,- *■' '. -■i^v WT^^^^ ^^^^^^^■' i ,^T'-^ \"-.'- ■' ----"„. 1 Courtesy of Johns Hopkins Bulletin and Dr. Eben C. Hill BLOOD VESSELS REACH ALL PARTS OF THE BODY If we could see the arteries and veins in any living animal, with the connecting capil- laries, the entire mass would practically correspond to the entire body. An X-ray picture of a baby's arm, showing the arteries The Red Corpuscles The color of the blood is due to a yellowish pig- ment called hemoglobin. This readily combines with oxygen and gives it up again, according to the chemical conditions to which it is exposed. For this reason the red corpuscles play an important role in breathing (see page 205). Red blood cells originate by cell-division from special cells in the red marrow of bones, which occurs in the ribs, the vertebrae, and in the upper ends of the armbone and thighbone. In the embryo, red corpuscles originate in the liver and in the yellow marrow of the long bones. Each corpuscle starts out with a nucleus. But among the mammals this soon disappears. The older corpuscles in the mammals go to pieces, and their hemoglobin is taken up by the liver and converted into part of the bile (see page 168). The largest red corpuscles are found among the amphibians. Even with the low power of a microscope we may easily see the elliptical disks in the flowing blood of a frog's web or a tadpole's tail. How Is the Blood Circulated? 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, reach- iSee Nos. 1, 2 and 3, pp. 198-199. 189 Main veins Main arteries Open; Closed ^Semiiuna^ valves If icuspid valve THE HEART A DOUBLE ORGAN The two auricles receive blood at the same time from veins. Blood passes from the auricles to the ventricles, through valves that prevent flow in the opposite direction. The two ventricles discharge blood at the same time into the main arteries, through the semilunar valves, which keep blood from returning when the ventricles expand ing all parts of the body. The smallest branches, the capillaries, form a network and combine into larger and larger tubes — the veins. The capil- laries thus carry the blood over from the arteries to the veins. The capillaries were first seen by the Italian Marcello Malpighi (1628-1694), who was born in the very year that Harvey published his book on the circulation of the blood, and who solved Harvey's puzzle — How does the blood complete its circuit? Among warm-blooded animals (birds and mammals) the heart is a double organ. Each half of the heart consists of an auricle, or receiving chamber, and a ventricle, or pumping chamber (see illustration above). Blood cannot pass directly from either side to the other. The lejt heart is somewhat larger and stronger than the right heart. Its ventricle contracts at fairly regular intervals, forcing the contained blood into the largest artery of the body, the aorta. Branches of the aorta carry the blood on to the various organs and tissues of the whole body. The auricle of the left heart receives blood from a large vein into which blood gathers from the capillaries oj the lungs. A set of valves between the auricle and the ventricle keeps the blood from flowing back when the ventricle contracts. Another set of valves prevents the blood from flowing back from the aorta when the ventricle expands again. The left heart thus pumps blood received from the capillaries of the lungs into arteries reaching to all parts of the body. The auricle of the right heart receives blood from two large veins, and 190 Veins to head and arms Arteries to head and arms Aorta Circulation of liver Portal vein Circulation of digestive system Veins of legs Arteries of legs THE CIRCULATION OF THE BLOOD Blood from the capillaries of the stomach and the small intestines is carried by the portal vein and through the capillaries of the liver before it goes back to the heart. That is, the blood here goes through two sets of capillaries on the way from the left heart to the right heart passes it into the ventricle, or pumping chamber. The right ventricle pumps blood into the large pulmo7iary artery, which carries it to the capillaries of the lungs. As with the corresponding chambers on the left side, a valve pre- vents the backflow of blood when the right ventricle contracts or expands. 191 The right heart pumps blood received from all over the body to the capillaries of the lungs. The "Double Circulation" The blood-stream courses from any point and back to die start only by passing through both sides of the heart — that is, through both the pulmonary, or lung, circuit and the systemic, or body, circuit (see illustration, p. 191). This "double circulation" of all warm-blooded animals makes possible a rapid exchange of carbon dioxide 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 between the air sacs of the lungs and the capillaries is by osmosis (see page 208). Changes in Circulation In the frog and some of the reptiles there is only one ventricle, so that the heart pumps a mixture of oxygenated blood from the lungs and deoxygenated blood just returned from the other organs. There is a suggestion of this condition in the unborn baby. In the unborn human baby the blood from the pulmonary artery is short- circuited directly into the aorta, and from the right auricle into the left auricle, without passing through the lungs — which have of course not yet started to operate. At birth the opening between the pulmonary artery and the aorta ordinarily closes at once; the opening between the two auricles, widiin a few days. Occasionally, however, these passages do not close nor- mally. The baby is bluish, for some of the blood is not aerated in the lungs. A "blue baby" often survives, but only if these "short-circuits" close. Changes in the Blood While in the capillaries of the various tissues of th-e body the blood absorbs from the surrounding lymph carbon dioxide, urea, and other substances that are present in relatively large proportions. By osmosis it also loses food materials, salts, oxygen and enzymes 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 kidneys much of the urea, salts, and other waste sub- stances is removed from the blood. In addition to furnishing the cells of the body with a uniform supply of materials, the blood in its circulation tends to equalize the temperature of the body tissues, much as the circulating water in a car's radiator cools the engine. Among all living things, birds and mammals have the most deli- cately balanced internal fluid media. Lymph taken from a healthy body is an excellent medium for the growth of living cells of many kinds. Inside the body of a mammal or bird, with its "warm" interior, the conditions would seem to be ideal for the growth and activities of protoplasm. But those ideal conditions cannot re- main ideal very long. As the blood and lymph move rapidly through the 192 body, many kinds of material are constantly diffusing into and out of the stream. A cell absorbing food is moment by moment reducing the supply for itself, as well as for its neighbors. It is at the same time poisoning the lymph with its wastes and other products of its metabolism. The environ- ment must be a constant source of needed supplies, if life is to continue. But if the environment remains constant, life cannot continue. How Does the Blood Maintain Its Stability? The Steadfast Blood^ In spite of the physical and chemical changes going on in it all the time, the blood of animals, especially of warm-blooded ones, is remarkably stable. This constancy of the blood has been called homeostasis — standing or remaining the same. Homeostasis is not, how- ever, a static fact or a fixed condition. It is rather a complex process; indeed, it is a living process, remaining "the same" only because it is constantly changing. Homeostasis is attained not by preventing changes, or by insulating the blood against all happenings, inside and outside the body. It is attained by making adjustments that neutralize alterations or compensate for them. Chemical changes in the blood, for example, mean an increase in the pro- portions of some substances and a decrease in the proportions of others. Or they mean greater acidity or less, or the appearance of new substances. The blood meets such changes, in general, by removing surpluses and by re- plenishing deficits. The circulation itself is a factor in bringing about uniformity, since it stirs up and so redistributes the contents. In addition, however, the struc- ture of the blood, the nervous system, and special "glands" interact in ways that bring about compensations and adjustments from moment to moment. Excesses and Deficiencies We are familiar with many adaptive proc- esses that help to keep the blood stable. It is not always clear, however, just how the adjustments are brought about. What is the connection, for exam- ple, between sweating and getting warm ? Or between feeling hunger and running short of nutrition? How does running make one out of breath.? When the quantity of a particular substance increases in the blood, some of it diffuses into the tissue spaces by osmosis (see page 87). If the propor- tion of this substance diminishes, some of the relative excess in various tissues diffuses back into the blood. Through osmosis relative excess or shortage becomes equalized. Surpluses removed from the blood-stream may remain temporarily in the spongy network of connective tissue under the skin, and around muscle fibers. Such "temporary storage" in tissue spaces has been compared to the merchant's practice of displaying on his shelves iSee No. 4, p. 199. 193 Summary of the Principal Changes in the Bloods MATERIALS IN BLOOD Water Sugar Fat Amino-acids . . Mineral matter , FROM Vitamins Oxygen . . . Carbon dioxide Lactic acid . . Nitrogenous wastes Hormones . . . . Red corpuscles . . White corpuscles . TO Digestive tract Body cells, Where it is formed by the oxidation of food Reserve in tissues Digestive tract Surplus stored as glycogen in liver Digestive tract Surplus stored in adipose tissue Digestive tract Surplus stored in liver Digestive tract Surplus stored in tissues^ Digestive tract Surplus stored in tissues^ Lungs Body cells through oxidation of food Muscles during vigorous exercise Temporary storage as sodium lactate Body cells through wear and tear Ductless glands Cells in marrow of bones'^ Surplus stored in spleen Cells in marrow of bones^ Migration from tissues Kidneys Sweat glands Lungs Tissue cells Storage in tissues Storage as glycogen in liver Oxidation in body cells Storage in adipose tissue Oxidation m body cells Storage in liver Growth of new tissue Oxidation in body cells Growth of new tissue Storage in tissues Kidneys Sweat glands Digestive glands Use in body cells Storage in tissues Kidneys Oxidation of food in body cells Lungs Oxidation to carbon dioxide or con version to glycogen Temporary storage as sodium lactate Kidneys as sodium lactate Kidneys Use in body cells Kidneys Removal in liver Storage in spleen Removal in liver Injuries to skin as pus Migration into tissues ^Adapted from N. Eldred Bingham, Teaching Nutrition in Biology Classes, p. 18. A Lmcoln School Re- search Study, Bureau of Publications, Teachers College, Columbia University, 1939. sCalcium and phosphorus are stored as calcium phosphate in crystals formed mside the spongy tissue ot the lone bones. , . , ,. i • i • 3 Vitamins A and D are stored in the liver: xitamins B and G are stored in the liver and in muscle tissue; vitamin C is not stored in the body. "Human blood normally contains about 5,000,000 red cells per cubic milhmeter. SHuman blood normally contains 7000 white cells per cubic millimeter; their proportion is as 1 : 700 red cells. 194 and counters a fairly uniform assortment and storing part of his wares out of sight. Sometimes surplus materials accumulate in special cells or tissues, in a relatively insoluble state. When there is an abundance of calcium, for example, the excess is deposited in small spike-shaped structures, or spicules, inside the long bones. When the intake of calcium is meager, these spicules disappear, being apparently dissolved and redistributed. Fats and proteins, like calcium, are also stored by being segregated in special regions. Such segregation of "reserve" material is in some ways like the storage of reserve carbohydrates in underground parts of plants; that is, it seems to be regulated by osmosis and by the action of enzymes. Some of these en- zymes condense soluble substances into colloids or insoluble forms, and some "digest" the reserves into crystalloid forms. In more complex animals, however, the storage of reserves (as well as their later release into the cir- culation) is largely regulated by the nervous system and the "ductless glands" (see pages 302-304). The nerves and glands are set working, how- ever, by chemical changes in the blood. Overflow Another way in which the materials in the blood are kept constant is through excretion, or overflow. Waste substances that get into the blood from the active tissues are normally removed by the lungs, the kidneys, and the sweat glands (see pages 216-218). If such substances be- came too concentrated in the blood or lymph, they would be reabsorbed by the cells and there act as poisons. But an excess of sugar, salt, vitamin C, and other substances may be discharged through the kidneys. An excessive intake of water is compensated by an increased flow of urine or by increased sweating: the blood does not become perceptibly diluted. Similarly, exces- sive amounts of carbon dioxide in the blood are quickly removed by the increased ventilation of the lungs and an overflow of carbon dioxide into the lung sacs. Under normal conditions only wastes are excreted. Needed reserves may be excreted during certain diseased conditions, however. In diabetes, for example, valuable sugar overflows through the kidneys and is lost in the urine. In other conditions the calcium reserve is lost. Hunger and Intake Maintaining the stability of the blood requires not merely removing excesses, but also ensuring suitable intake. Chemical changes in the blood due to deficiencies in nutrients or in water act upon the nerves and upon ductless glands. Feelings of "hunger" or of "thirst" arise in higher organisms, and these "feelings" influence the further conduct of the organisms — specifically with respect to food or drink. Having an appetite or being thirsty does not, of course, ensure getting what the organ- ism needs. But these conditions are parts of the adaptive behavior of or- ganisms, and they are related to the constancy of the blood. 195 Faster and Slower^ Organisms are continually generating and losing heat. When the internal temperature rises in our own body, the blood vessels of the skin dilate. More warm blood flows to the body surface, and more heat is lost by radiation. If the rise in temperature continues, sweating and panting cool the body by evaporation. On the contrary, if the surface is chilled, the blood vessels of the skin become constricted. If cooling continues, a secretion from a ductless gland (the adrenal) is discharged into the blood; and this induces more rapid oxidation and so increases the heat. The so-called goose-flesh that results from chilling the skin corresponds to the "hair-raising" sometimes observed in dogs and cats and other mam- mals, and to the fluffing out of feathers in birds. This reaction increases the air insulation between die body surface and the cold environment. Vigorous muscular activity increases the oxygen consumption of cells. At the same time the pumplike movements of the limb muscles make the blood return to the heart more quickly. The heartbeat is quickened, and with an increased quantity of blood in the heart each contraction delivers more blood. As muscular activity increases, the active cells yield more lactic acid and carbonic acid. This slight increase in the acidity of the blood stim- ulates a nerve center and accelerates breathing. Chemical changes similarly stimulate the secretion of epinephrine (see page 313), which in turn brings more sugar into the blood. As activity ceases, the composition of the blood returns to normal. If there is still an excess of acid dissolved in the blood, it is temporarily neutralized by the so-called "buffer salts" — some of the sodium compounds. If the condition of the blood swings toward the alka- line side, respiration becomes slower, and alkaline, or basic, salts are ex- creted through the kidneys until neutrality is re-established. We see, then, that the blood maintains its balance both as to materials and as to processes. It draws upon reserves and eliminates or stores sur- pluses. It changes the rates of continuous processes. In almost every emer- gency changes within the body and the action of the "sympathetic" part of the nervous system maintain homeostasis, or the constancy of the in- ternal environment. Flying and Circulation There are situations in which the organism cannot adjust its blood system. When a dive-bomber plunges down rapidly and then suddenly turns his plane to fly upward, the blood in his vessels continues down toward his feet and leaves his brain depleted. That condi- tion may last only a few seconds, but that is enough for a complete "black- out" or loss of consciousness. In those circumstances being unconscious for only a short time may be disastrous. Even in ordinary flying, a rapidly moving plane making a turn banks iSee No. 5, p. 200. 196 over so much that the flier's blood goes to his feet and sometimes leaves him dazed or helpless. These situations are, to be sure, far from natural; and we shall have to find ways of meeting them artificially, instead of counting upon the heart to make all the adjustments. Transfusions Where a person has lost a great deal of blood for any reason, his life can be saved in many cases only by replacing the loss with blood from another human being. Such transfusion has come to be a stand- ard procedure in hospitals. There is one serious obstacle, however, to its general and immediate use. That is the fact that there are four "types" of blood that are incompatible. That is, corpuscles from a person having one type act in the blood of one of a different type like a foreign substance, and bring about a clotting. These inherited characteristics make it necessary in each case to find a healthy donor of the "same type", and that is not always possible on short notice. People who are able and willing to furnish a quantity of blood for such emergencies are commonly registered by large hospitals. Replacing the lost blood promptly has saved thousands of lives, for it has the immediate mechanical effect of restoring the internal pressure of the blood system; in this way it re-establishes the action of the heart. Blood Banks To be prepared for emergencies on a large scale, two devices have been developed in recent times. One is the "blood bank", or reserve of blood of each ''type" preserved at low temperatures. The other is the plasma "bank", which combines the plasma of many men and women. The plasma is prepared by removing the corpuscles from the blood mechanically. In England such plasma reserves were established early in the Second World War; the contributions of all classes and races were used indiscriminately for all conditions in which the loss of blood is involved. A further improvement, developed later in the war, is the use of dried serum. The combined serum is dried and sterilized, and measured quan- tities are sealed in vacuum bottles. In the field, the medical officer or nurse dissolves the dried serum in distilled water and injects the fluid into the veins of the injured person. The plasma and serum can be used for all "types" of individuals because they are free of corpuscles. Later still, however, Russian surgeons found that they could make good use of the red corpuscles which had been removed from blood in preparing the serum. In certain cases of anemia it was not sufficient to make up the lost blood with plasma: the red corpuscles were helpful in restoring the hemoglobin. 197 In Brief There is a dual circulation in plants : one part carries liquids up from the roots, the other part carries food down from the leaves. The blood of human beings and other vertebrates consists of a colorless fluid, the plasma, in which numerous red and white corpuscles float. The blood, circulating in a closed system of vessels, transports oxygen, carbon dioxide, food and wastes. The colorless lymph fills spaces between tissue masses and between cells. This constitutes an internal fluid medium from which the cells of the body obtain their food and oxygen and into which they discharge carbon dioxide and other wastes. When blood vessels are injured, the interaction of special substances leads to the formation of a clot; the clear liquid left by the clotting and the separation of the corpuscles is the serum. The white blood corpuscles resemble the ameba. They wander in the body fluids and engulf foreign particles or organisms that enter the body, or particles of cells that have been destroyed. The blood is propelled through the vessels by the rhythmical contraction of the heart. In warm-blooded animals there is a double circulation; the left ventricle supplies the systemic circulation, and the right ventricle supplies the pul- monary, or lung, circulation. The circulating blood distributes heat to the body extremities and equal- izes the temperature of the whole body. The stability of the body fluids, or homeostasis, is maintained by imme- diate and automatic compensatory responses to chemical deviations and to changes in concentration and temperature. EXPLORATIONS AND PROJECTS 1 To observe the beating of the heart, anesthetize a rat or guinea-pig, open the ventral side, exposing the abdominal viscera, as well as the heart, lungs, and vessels of the thorax, but without cutting any of them. Note the rhythmic pul- sation of the arteries, which carry blood from the heart. Observe a gradual filling of the auricles during the resting period. Note whether the heart begins a beat at one end or contracts all at once. Describe the heartbeat. 2 To study the structure of the heart and of the adjoining vessels, use a "haslet" (lungs with heart attached, as removed from animal) from a butcher shop. 198 Distinguish the pulmonary arteries from the pulmonary veins. Probe into the cut vessels leading into and out of the heart. Through which of these can you push a pencil.'' Compare the thickness of the walls of the veins and of the arteries. Lay open the side of the aorta by cutting with scissors. Note the structure of the semilunar valves. Cut the heart open so as to expose the four valves. Compare the thickness of the auricle walls and ventricle walls. Trace the passage of the blood, as it moves through the heart, past various openings. 3 To observe the flow of blood in living tissues, watch the web of a frog's foot through a microscope, first under the 16-millimeter objective and then under the 4-millimeter objective. Note that the blood moves rapidly in some vessels, slowly in others, and that the pulsation can be seen in some but not in others. Find places where arterioles branch to form capillaries, and places where capillaries are joined into small veins. Observe the extent to which capillaries reach all parts of the tissue. 4 To demonstrate the "buffering" action of various compounds, treat solu- tions of "buffer salts" with measured quantities of acid and of alkali, and compare with the action of plain water. Use (a) plain water as control, or basis of comparison, and make up four solu- tions as follows: In 200 cc of water dissolve (b) 1 teaspoonful of baking-soda (NaHCOs) ; (c) 1 teaspoonful of dibasic sodium phosphate (Na^-HPOi) ; (d) 1 teaspoonful of monobasic sodium phosphate (NaHoP04) ; (e) \ teaspoonful each of dibasic sodium phosphate and monobasic sodium phosphate. As an indicator use extract of red cabbage. {Boil the leaves in water to extract the red juice.) When acid, this extract has a pink color; when neutral a blue color; and when basic, a green color. Prepare five sets of three containers each, using 100-cubic-centimeter beakers or small tumblers or bottles (all of the same diameter, to make comparisons of colors easier). Place 50 cc of water in each beaker of set a; 50 cc of baking-soda solution in each of set i^; 50 cc of dibasic sodium phosphate solution in each of set c; 50 cc of monobasic sodium phosphate in each of set d', and 50 cc of the mixed dibasic and monobasic sodium phosphate in each of set e. Add 10 cc of the cabbage extract to each vessel. Compare the colors of five sets of the solutions. Note that some are slightly alkaline, some are neutral, and some slightly acid. Record the state of each. Set up one burette with a half-and-half mixture of hydrochloric acid and water, and a second beaker with a half-and-half mixture of concentrated ammonia and water. Add acid, a drop at a time, to one of the beakers having water (fli) until there is a pink color (two drops should be enough). Add sufficient base to the second water beaker {a-,) to give a barely green color (two drops ought to be enough). Add enough drops of acid to one of the vessels in each of the four other solutions {bi, T], ^1, e^) to give the same pink color shown by the acid water solution (ai) and record the amount of acid each required. Record the number of drops of base required by each of the four solutions bo, Co, do, and €■>, barely to give the green color of the basic water solution (a^). Compare the number of drops of acid and 199 of base necessary to shift the acidity or alkalinity in each of the solutions to the same degree as two drops did in the water solutions. Record the results in a table, summarize, and then explain what you understand by the "buffering" actions of these salts. 5 To find the effect of exercise on the pulse rate, determine the number of heartbeats per minute while at rest, and again after taking exercise. Compare the rate and the intensity of the pulse before and after the exercise. QUESTIONS 1 Of what does human blood consist.^ 2 In what respects is blood like lymph? In what respects do the two fluids differ? 3 How does clotting take place? 4 What do the blood and the lymph do? 5 How is the blood circulated throughout the vessels of the body? 6 How does the heart of a frog resemble that of a man? How do the two differ? 7 What is the advantage of a "double circulation"? 8 What are the principal changes that take place in the blood? 9 How is the stability of the blood and of other body fluids maintained? 10 What compensating reactions take place when muscular activity is in- creased? when an organism is exposed to extreme cold? 11 How is homeostasis maintained by an acceleration of processes that are continually taking place anyway? 12 How do "buffer salts" tend to preserve the alkalinity of the blood? 200 CHAPTER 11 • HOW DO PLANTS AND ANIMALS BREATHE? 1 Do plants breathe, as well as animals? 2 What makes a fish die when it is taken out of water? 3 What makes men drown where fish thrive? 4 How do frogs breathe without a diaphragm? 5 How do fish breathe? 6 Have whales lungs, or do they breathe like fish ? 7 How do the cells in the roots of water plants get oxygen ? 8 How do animals in deep water breathe? 9 How do clams breathe when they are buried in the sand ? The simplest plants and animals get their oxygen directly from the sur- rounding air or water and discharge their carbon dioxide directly to the surrounding medium by osmosis. Here respiration and oxidation are close together in space and in time. But in more complex plants and in animals, as in man, there is sometimes a considerable separation between the two processes. The respiration of simple organisms, and the internal respiration carried on by the cells of higher organisms, are very much alike, since the body cell lives in a liquid medium, as does the ameba in the pond. But how do the various complex plants and animals get oxygen and excrete carbon dioxide ? Do all the organisms that live in water get their oxygen directly from the water ? How do the innermost parts of large plants and animals get air ? How Do Cells Obtain Air? Gas Exchange of the Ceir Plants and animals consisting of single cells absorb gases from the surrounding air or water by osmosis. And gases are removed from such cells by osmosis, diffusing into the surrounding air or water. In large, many-celled organisms air reaches the living cells either by diffusing through special spaces, as in plants, or through special tubes, as in insects (see page 16). Or it travels in a solution (blood) that reaches all parts of the body (see page 186, and illustration, p. 202). In every case, then, the protoplasm of the individual cell (1) gets its oxygen from its immediate neighborhood, and (2) discharges its carbon dioxide and other products of oxidation into its immediate surroundings. In the interior of a leaf air constantly circulates through the air-spaces among the cells. Gas exchange between the various cells and the surround- ^See Nos. 1, 2 and 3, p. 212. 201 ing space also takes place by osmosis through the cell walls. If we think of the ingoing and outgoing gases, and disregard the chemical changes in which the gases take part, we may speak of this process as respiration, or breathing. Stomata in the epidermis, or skin, of young twigs connect with the intercellular spaces below the surface (see illustration, p. 142). In the older twigs, however, in which bark-formation has been going on for some time, the live cells beneath the bark get their oxygen supply by way of the lenticels. The comparatively small amounts of oxygen used by the plant cells diffuse slowly into them from air in these openings and passages. The carbon dioxide from the cells diffuses to the exterior along the same paths. In most plants the stomata, or breathing holes, are located on the under side of the leaf. In water-lily pads and similar floating leaves, these openings are on the upper surface, where they are exposed to the air. In some plant species, variation in leaf structure seems definitely related to respiration. Leaves exposed to air "breathe'' through stomata, whereas submerged leaves carry on gas exchange by osmosis through the general surface. Respiration in Roots The roots of most familiar plants and staple crops, with the exception of rice, absorb oxygen dissolved in the moisture on the outer surfaces, and also give out carbon dioxide by osmosis. Most roots suffocate when the water table is too high — that is, when the free INCOMES AND OUTGOES OF A LIVING CELL In the body of one of the larger or more complex animals, each cell receives oxygen, as well as food, by diffusion from the surrounding fluid. Each cell discharges into this surrounding fluid carbon dioxide, as well as urea and other products of metabo- lism — also by diffusion through the cell wall. The fluid, or lymph, communicates in turn with the blood stream 202 Ranunculus Potamogeton Sagittaxia LEAVES IN AIR AND IN WATER The deeper the leaves of the water crowfoot are submerged, the more divided up they are. For a given amount of tissue, finely divided leaves have a greater absorb- ing surface. Pondweeds and arrowheads bear broad leaves in the air and long ribbon-shaped leaves in the water water filling the soil spaces keeps the roots submerged too long. The roots of rice are fine and threadlike, exposing much surface through which an adequate supply of oxygen is obtained from the surrounding water. If the water table is near the surface as after prolonged rains in the early summer, corn roots, for example, do not penetrate very far into the soil. Then if a drought follows, the crop suffers badly, for the shallow root- system cannot reach the lower water levels, and the plant quickly dries out. On the other hand, when the early summer is exceptionally dry, the young roots grow deeper, so that a prolonged drought later in the season is not so destructive. Alfalfa will not thrive in a soil that is not well drained, for the roots "drown". Plants growing in swamps, where the level of the water is rather con- stant, have shallow root-systems ; and they breathe through the portions that extend above the water. 203 What Do Lungs and Gills Do? Breathing in Man^ The lungs are soft bags consisting of air-tubes and air-sacs, which are lined by a layer of thin-walled cells and surrounded by very fine blood vessels. They are suspended in the thorax, or chest cavity, and air comes into the air-sacs of the lungs, and also passes out, by way of the windpipe, or trachea (see illustration opposite). The trachea divides and branches again and again into the bronchial tubes. While the air-sacs are filled with air, oxygen diffuses from these spaces into the lymph and blood of the surrounding vessels, and carbon dioxide diffuses in the opposite direction (see illustration, p. 208). The lungs are filled with fresh air and emptied again by the action of (1) muscles attached to the ribs and (2) a large muscular organ called the Rutherford Piatt BREATHING ARMS OF SWAMP PLANTS In cypress trees, which are typical swamp plants, the roots breathe through the so-called "knees", which rise above the level of the water. The roots of many trees spread out, as in the tamarack, soft maple, pin oak, spruce, hemlock, and cedar, in drier soil they form deeper roots; in swamps they spread roots near the surface. Trees that form tap-roots, such as hickory and ash, are never found in swamps iSee Nos. 4, 5, and 6, pp. 212-213. 204 Adenoid Tonsil Bronchial tubes Right lung Dia- phragm Alveoh LUNGS IN MAN The main windpipe from the throat divides into main branches, the bronchi, one to each lung. The bronchi divide again and again, the smallest air tubules ending in the alveoli, or tiny sacs. The epiglottis drops over the trachea when food is being swallowed from the pharynx to the esophagus diaphragm. This separates the chest cavity from the abdominal cavity (see illustration above). Inspiration and expiration are caused by the alternate expansion and contraction of the thoracic cavity. Blood-Red We have seen that the circulating blood takes part in dis- tributing oxygen and carbon dioxide, as well as foods, wastes, and other sub- stances. And that the actual oxygen-carrier is the yellowish hemoglobin of the red corpuscles, since it combines readily with oxygen, forming oxyhemo- globin (see page 189). When oxygen is relatively scarce, it gives up oxygen. 205 Ribs Raised Lowered Diaphragm Lowered Raised Inspiration Expiration BREATHING MOVEMENTS IN MAN When the diaphragm, the muscular partition between the thorax and the abdomen, is pulled down, the chest cavity enlarges. When the ribs are raised, the chest also expands, and air comes in through the windpipe. The rib muscles and the diaphragm normally work in unison. When these muscles relax, the chest cavity contracts and forces out the air in the lungs This taking on or putting ofT of oxygen seems to depend upon the relative quantity of oxygen, and is a "reversible" reaction, as shown in this equation: Hemoglobin + oxygen T^ oxyhemoglobin When blood reaches tissues far from the oxygen supply, the reaction moves to the left. In the vicinity of the lung (or other respiratory organ) the change moves to the right. When the blood contains much oxyhemo- globin, it is bright red; M^hen little, a maroon color. A man row^ing in a race or climbing a mountain may use about one and one-fourth gallons of oxygen per minute. If he had no red blood corpuscles, it would be necessary to circulate 375 gallons of fluid each minute to supply this amount of oxygen.^ ^Actually, there is but about one and a half gallons of blood in the body. At this rate all the blood would have to rush round the body 250 times a minute, or about four times each second. Obviously, no human heart could sustain such a load. One gallon of blood with hemoglobin carries as much oxygen as 60 gallons would without it. It takes about 300 gallons of water at body temperature to dissolve one gallon of oxygen. 206 The plasma of the blood, Hke the water of the sea, carries in solution varying amounts of the atmospheric gases. Ordinarily, these seem to make no difference. When men are exposed to high atmospheric pressures, as in deep tunnel work or in deep diving, the amount of nitrogen in solution seems to increase. On returning to the surface, nitrogen bubbles out of the blood and expands in the capillaries. That results in a very painful and sometimes fatal condition known as the "bends". It is possible to prevent that by having the workers come back to normal air pressure very slowly, through so-called "decompression chambers". A similar difficulty arises in aviation when airplanes are brought rapidly from the surface to very high altitudes, where the air pressure is very low: here again the nitrogen may "boil" out as bubbles. It is customary to prepare aviators who are about to make high ascents by having them spend some hours in low-pressure chambers, where they can breathe the needed amount of oxygen and slowly eliminate some of the nitrogen dissolved in the blood. Another problem arising out of high flying is the impossibility of breath- ing in and distributing enough oxygen at the highest levels, where the air is so very "thin". Aviators are supplied with special masks, through which needed amounts of oxygen are delivered from flasks or tanks. Many persons find that merely going to the mountains, not to mention flying up into the air several miles, puts too much strain upon the heart. And those who always live in high mountains have relatively larger hearts than those who dwell at the seashore. Strange as it may seem, the real blue bloods of the animal kingdom are cold-blooded arthropods, not man. In crabs, lobsters, and the like the blood contains hemocyanin^ a pigment in which the metallic element is copper. Hemocyanin turns blue when it combines with oxygen, and is colorless in the absence of oxygen. It is not carried in special corpuscles, but dissolved in the body fluid. In all animals that have blood, cell respiration is related to the blood. That is, the cells get their oxygen from the blood, and they discharge their carbon dioxide to the blood. In all such animals we therefore apply the term respiration to the process by which the air is brought from the outside to the blood, -and by which the carbon dioxide is thrown out. Air-tubes^ Insects use relatively large amounts of oxygen. Movements of the body compress and release the delicate branching air-tubes, which reach all parts, thus aiding in the circulation of air (see illustration, p. 16). In some insects, as the common locust, rhythmic movements alternately empty and fill the air-pipes, and so accelerate the diffusion of oxygen and the removal of carbon dioxide. ^See No. 7. p. 213. 207 CeU 1 Broncm al tubes Pul ^ vein Air Pulmonary *S^ artery ^y^-'^ ^s^ ^2t^ ^ f^-^->^ J O2 Lymph Blood ■ vessel EXTERNAL AND INTERNAL RESPIRATION The external respiration consists of all the processes that bring oxygen to the sev- eral millions of cells in the body, and remove from them the carbon dioxide which they excrete. The internal respiration consists of the gas-exchange between any body cell and the surrounding lymph. The external respiration thus includes the muscular activities of pumping air into and out of the lungs; the actual movement of air into and out of the lungs; and the osmotic movements of oxygen and carbon dioxide between the air sacs and the blood, and between the blood vessels and the lymph Gills^ The simplest kind of blood respiration is found in such animals as the earthworm. In this, the respiration takes place by osmosis through the moist epidermis, or skin. In some worms there are extensions of the skin surface into little outgrowths, called gills. In clams and oysters there are special outgrowths that multiply the breathing surface in much the same way (see illustration opposite). We may think of the gills in lobsters, crabs, and other water animals as structures in which the blood is brought close to a great expansion of surface within a comparatively small space. Although insects are in general "air-breathers", some make their abode in water for at least a part of the life cycle. The diving beetle comes to the surface and takes down a supply of air under its wings. So does the water boatman. Mosquitoes, in the larval and pupal stages, live in water; they get ^See No. 8, p. 213. 208 Gills Some water insects breathe air from above the water sur- face through special open- ings into the tracheae. The hellgrammite and a fewothers breathe through leathery gills, which expose relatively large surfaces to the water A WATER-BREATHING INSECT air at the surface of the water through special breathing tubes. The "hell- grammite", the larval stage of the Mayfly and of the Dobson fly, has pro- jecting gills, through which air is absorbed from the water. Life without Air A few species generate energy without a supply of oxygen. In yeast and in certain other simple plants, ferments, or enzymes, bring about the breakdown of carbohydrates into simpler compounds, as alcohol and carbon dioxide, in the absence of oxygen. Such organisms are called anaerobic^ that is, living without air. The release of energy from com- plex chemical compounds without oxidation may be likened to the release of energy that results from the collapse of a structure when a particular small detail is disturbed. Breathing in the Vertebrates^ All the backboned animals, except the fishes and the young stages of amphibians, breathe by means of lungs. In the fishes, water with oxygen in solution is taken into the mouth. But Water inside the clam's shell is kept in constant circulation by the vibration of cilia which cover the whole surface of the body, the lining of the mantle, and the surfaces of the gills. The water also passes through tiny openings in the gills themselves. As the water passes over the gill surfaces, gas-exchange takes place between the flowing water and the blood circulat- ing Inside the gills. Water comes into the mantle cavity and is discharged again through the siphon Gills Mouth HOW THE CLAM BREATHES iSee No. 9, p. 213. 209 .«i*J^ Gills Ovary Portad vein Stomach Auricle Ventricle HOW FISH BREATHE Water taken in by the mouth passes over the gills and out again, as indicated by the arrows. The fish has one auricle and one ventricle. The heart pumps the blood gathered from the body to the gills, in which gas-exchange takes place. The oxy- genated blood is gathered into arteries: one main branch goes forward to the brain and head, the other goes backward toward the rest of the body instead of being swallowed into the gullet, the water passes out through a series of openings in the sides of the throat and over the gills (see illustra- tion above). In the sharks the gills slits are open to the exterior; in bony fish they are covered by a plate with a free edge toward the rear. The gills are fine, feathery structures containing many delicate blood vessels, and are arranged on arches, four on each side of the pharynx. As the water passes over the gills, the oxygen in solution diffuses into the blood from the sur- rounding water. Among the amphibians the adults swallow air into the lungs. The young, however, have moist skin and gills through which gases diffuse be- tween the lymph and the surrounding water. Adult frogs differ from toads in having moist skins and in being able to live under water for considerable periods of time. 210 HOW THE FROG BREATHES The frog swallows air into the lungs. Lowering the floor of the mouth enlarges the mouth cavity, and air comes into it through the nostrils. The nostrils are closed, and the floor of the mouth is raised. The air is thus forced into the pipe leading to the lungs. If the frog were forced to keep his mouth open, he would suffocate Reptiles and all the higher vertebrates breathe entirely by means of lungs. Reptiles swallow air, as do the amphibians. Birds rely solely on rib move- ments, as they have no diaphragm. All mammals breathe like man. Water- snakes and snapping turtles spend most of their time in water, but come to the surface from time to time to breathe. Alligators and crocodiles have raised nostrils, which protrude above the water when the rest of the animal is submerged. Whales, like other mammals, breathe air in lungs. In Brief Living cells always exchange gases with the liquid which immediately surrounds them. In many-celled organisms, cells remote from the surface get their oxygen supply indirectly. Roots get oxygen that is dissolved in the soil water which immediately surrounds them. Air diffuses into the leaves and bark of plants through special openings. Plants growing in swampy areas have shallow root-systems; roots suffo- cate if submerged too long or too deeply. 211 The hemoglobin of red-blooded animals carries oxygen; human blood carries 60 times as much oxygen as dissolves in an equal volume of water. The oxygen-carrying substance in animals with blue blood is hemo- cyanin. In all animals with blood, external respiration is the gas exchange be- tween the blood and the outside; internal respiration is the gas exchange between the blood and the living cells. Insects breathe by means of tracheae, or air-tubes, which open to the sur- face and reach the fluids in all parts of the body. Body movements compress and release these tubes, setting up air movements. In some animals respiration takes place by osmosis through a moist skin or through gills, which are specialized skin outgrowths within which blood circulates and around which the oxygen supply moves. Other animals breathe by means of lungs. Fresh air is brought into the lungs, and stale air is exhaled, by muscular movements. Dissolved gases pass into and out of the blood by osmosis through living membranes of the lungs and through walls of blood vessels. EXPLORATIONS AND PROJECTS 1 To find the relation of air to plants and animals living in water, place small fish from the aquarium in two vessels, one containing ordinary tap water and the other tap water which has been cooled in a closed flask after the air has been removed by boiling. Compare results and note conclusions. 2 To show that dissolved gases diffuse through a membrane, prepare two 8-ounce widemouthed bottles as model cells (see page 88), one containing plain water, and the other water through which carbon dioxide has been bubbled for about fifteen minutes. Invert the two bottles, after the membranes have been securely fastened, in two dishes containing water. On the following day add a few drops of pinJ{^ phenolphthalein solution to each vessel. If the indicator loses its color, the water has become acid from carbon dioxide dissolved in it.^ Compare results and note conclusions. 3 To find out whether oxidation is accompanied by a loss in weight, compare the dry weight of equal quantities of corn or wheat grains before and after germination. Account for the results. 4 To study the structure of the respiratory tract, obtain a haslet from the butcher. Blow air into the trachea and note the expansion of the lung tissue. Compress the trachea and bronchial tubes. What holds them so rigid? Open one side of the trachea and of the main branch of the bronchial tube within one of the lungs, to show the many little openings through which small tubes carry air to and from the larger tubes. ^Red cabbage extract (see page 199) can also be used as an indicator. 212 5 To observe the effect of exercise on the rate of breathing, record the rate of breathing before and after exercise. Use a graph to show the individual varia- tions, as well as the relation between the amount of exercise and the rate of breathing. 6 To demonstrate the effect of exercise on the excretion of carbon dioxide, compare the length of time it takes to turn a measured amount of pink phenol- phthalein colorless, by exhaling through it with a glass tube before exercising, and through a similar amount immediately after exercising. 7 Examine the sides of the abdomen and the under surface of the thorax of a large grasshopper (or other insect) for spiracles, or breathing pores. Observe in a live insect at rest the body movements which would tend to move air through these holes. Dissect the animal under water and identify the air-tubes, or tracheae, which carry air to all parts of the body. Examine some of these tubes under the microscope. 8 To study the structure of gills, dissect the mouth and the gill cover of a fish, exposing the gills. Note their position with reference to water which flows through the mouth and out under the gill covers. Examine a small portion of the gill with the microscope and note its feathery texture. 9 To study the respiration of a frog, place a frog in an aquarium or large jar of water so that it cannot rise to the surface except by swimming. Note whether the frog comes to the surface to breathe. How can it carry on respiration when beneath the surface.'* Is there anything to show that the animal is suffering for lack of air if it is kept from coming to the surface for several minutes.'* Re- move the frog from the aquarium and place it on a table. Watch movements of the throat and of the abdomen, and describe their relations to getting air into and out of the animal's lungs. Contrast the breathing of a frog with that of a mammal. QUESTIONS 1 What is the source from which living cells ultimately get oxygen, and what eventually becomes of the waste gases which living cells liberate.'* 2 Since living matter oxidizes itself, how do animals nevertheless keep on living.'* 3 What different special oxygen-carrying substances are found in different species .'* 4 In many-celled organisms, how do cells remote from the surface get their oxygen supply? 5 What conditions within the body influence the rate of respiration.? 6 How do organisms without breathing organs respire.? 7 How does the breathing of the frog resemble that of the fish ? How do the two differ.? 8 How does the breathing of a frog resemble that of a bird.? How do the two differ? 213 CHAPTER 12 • HOW DO LIVING THINGS GET RID OF WASTES? 1 How does an organism come to produce substances that it does not need? 2 Are tlie wastes produced by protoplasm poisonous? 3 Does the excreted urine in animal manure make it injurious to plants ? 4 Do plants excrete wastes? 5 What kinds of wastes are excreted ? 6 Is sweat a kind of waste? 7 Have all animals kidneys? 8 How do the kidneys make urine out of wastes in the blood ? 9 Why do physicians sometimes analyze a patient's urine? 10 What other organs besides kidneys remove wastes? Living things are continually taking in fooci and oxygen. From the oxidation of food within their living cells they derive energy. We know that whenever fuel burns, there are formed ashes and hot gases that would smother tlie flame unless they were removed. Would any of the substances formed during metabolism in living organisms interfere with further metab- olism? Are there any wastes produced besides the carbon dioxide and water removed by the lungs? How do living things dispose of any such wastes? How does the body remove waste fluids without losing essential food constituents? What Kinds of Wastes Are Produced in Living Things? The Origin of Wastes in Living Things In every chemical process substances are formed that did not exist before. Some of the substances pro- duced in the metabolism of a complex organism are related to keeping the protoplasm alive, as, for example, digestive ferments and chlorophyl. In- cidentally, however, other substances are also produced, and these may be of no use to the living body or to the living process. Some may even be injurious. Such substances are wastes, like the sawdust of a mill or the smoke that goes up the chimney or the coal-tar of a gas factory. Removal of Wastes from Cells Carbon dioxide, water, urea, and other waste products of oxidation in protoplasm diflfuse out of cells by osmosis. Oxy- gen, which is one of the wastes or by-products of photosynthesis (see page 138), also diffuses out of the chlorophyl-containing cells through the cell-walls. In plants, water and carbon dioxide are usually eliminated in the form of gas. The carbon dioxide discharged by the cells of the roots usually re- mains in solution, forming so-called carbonic acid. 214 Iff Cystolith in leaf of rubber plant iiij '■111' Resin in duct of pine Shedding of bark PLANT WASTES .<^->^ Raphides in root cell of spiderwort Glandular Chromoplasts Calcium hairs of in petal of oxalate in geranium nasturtium linden phloem Latex tubes in dandelion root Latex tubes of rubber tree m Oil gland in orange peel Fall of leaves Gum exuding from injured cherry tree Crystals and other bodies found in plant cells or in specialized ducts and spaces are often waste materials locked up out of the way of active living cells. Where such materials are accumulated in leaves and bark of long-lived plants, or even in seeds, they become removed from the plant protoplasm Storage and Stowage in Plants The masses of starch, fat and protein accumulated in the cells of many plants are normally used by the plants themselves — unless we or some other animals take them away first. But because of their obvious share in the life of the plants, we speak of them as "stored" foods. Yet the same plants and many others accumulate in their tissues quantities of insoluble materials which they never use again. These substances are in many cases injurious to living protoplasm, although hu- man beings have found ways of using them for their purposes. Such mate- 215 rials are regular by-products of metabolism which we may consider as "wastes". And they are stowed in plant cells, rather than stored, instead of being pushed out of the system, or excreted, much as useless rubbish is stowed away in the cellars and attics of many homes. Excess of mineral matter absorbed from the soil is separated out of living cells and precipitated as insoluble compounds. Thus crystals of oxalate of lime are found in hundreds of species — for example, the horse-radish, the root of jack-in-the-pulpit, and other sharp-tasting parts (see illustration, p. 215). We usually classify the most common organic wastes in relation to their possible uses to us, as below: Human Uses of Organic Plant Wastes Pigments. Direct enjoyment of color in flowers, fruits, leaves, wood, etc. Extraction of dyes for use on fabrics. Essential oils. Direct enjoyment in fruits and flowers; spices. Extraction for perfumes, seasoning foods, candy, etc. Gums and resins. Adhesives, waterproofing, protection of materials against insects and fungi, sealing joints. Tannins. Chiefly for tanning leathers; drugs. Alkaloids. Poisonous generally; used as drugs — morphin, quinin, atropin, cocain, caffein, digitalin, etc. Although these waste substances are useless to protoplasm, they may be of some value to the plant as a whole, or to the species, in some special rela- tion. Thus pigments and odors of flowers may be of use in relation to insect visits, or essential oils and tannins may be of value in protecting plants from animals and from bacteria or fungi. Excretion in Animals To a comparatively slight extent waste prod- ucts of animals are accumulated in some of the cells, like the waste products of plants. Thus some of the pigments found in animals are no doubt to be considered as wastes deposited in the cells of the skin or even in the interior of the body. Much of the lime found in the skin of such animals as the starfish and the sea lily and the coral framework of the coral polyp fall into the same class. Small quantities of lead are found in the skeletal tissues. One-celled animals excrete their wastes just as they excrete carbon di- oxide, by diffusion. In animals that have blood and lymph, wastes diffuse into these conducting fluids and for the most part are then eliminated from the body through special organs. How Are Wastes Removed from Animal Bodies? The Lungs and the Skin Water and carbon dioxide are excreted from the lungs, as well as small quantities of urea and possibly other organic sub- stances (see page 187). A certain amount of waste gets into the intestine 216 idermis Fat glands Capillaries Dermis SECTION OF THE SKIN The sweat gland consists of 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 from which water, salts, and traces of urea are withdrawn into the gland tube. Around the base of each hair ore fat glands. Sensitive nerve endings come close to the surface directly through the lining cells, in part carried by the white corpuscles (see page 188), and in part through the secretions of the liver. From the intes- tine these substances are removed, together v^^ith the refuse from the food, in the feces. Sweat is excreted by special glands which open on the surface of the skin (see illustration above). The water part of the perspiration usually evaporates as fast as it comes out of the glands, leaving a solid deposit of the wastes. When perspiration is more rapid, we can see the drops of sweat on the skin. When this dries, the solids are left on the outside of the skin, in- stead of in the mouths of the tubules. Ordinarily we perspire from 400 to 750 cubic centimeters daily. The sweat contains about 2 per cent of solids. Thus miners and other laborers who sweat excessively lose some of the essential materials of the body. They need to perspire freely to keep the body cool. But they need also to increase intake of water and salt to com- pensate for the materials lost through the sweat glands (see page 195). 217 The Kidneys^ Most of the solid waste substances from body cells are filtered out of the blood by the kidneys, which are the typical excretory organs of the backboned animals. In the human body there are two bean-shaped kidneys, each about as long as the width of the hand. They are located in the back of the ab- dominal cavity, one on each side of the spinal column, slightly lower than the stomach. The kidney is like a gland in structure (see page 169), 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 illustration opposite). How Do the Kidneys Separate Waste from the Blood? The Gland Unit The kidney separates, or filters, organic wastes from the blood by a combination of osmosis and the action of special cells. The separation starts in a tangle of capillaries called a glomerule, embedded in a "capsule" that opens into a long, thin-walled and greatly twisted, or con- voluted, tubule (see illustration, p. 221). The process is as follows: 1. Waste substances diffuse into the capsule from the blood in the capillaries of the glomerule. 2. The wastes are carried by the tubule toward the funnel-like pelvis of the kidney, into which all the tubules empty. 3. Much of the water and some of the dissolved substances are reabsorbed from the tubules by the blood in capillaries entangled with the tubule. 4. At the end of the tubule there remains the watery solution called urine. Composition of the Urine" The urine is about 96 per cent water. The dissolved substances include inorganic salts and organic substances which result from the breakdown of proteins during metabolism. Contents of the Urine INORGANIC SALTS Sodium chloride Sodium Potassium Calcium Magnesium as sulfates and phosphates ORGANIC SUBSTANCES Urea Uric acid Creatinin Coloring matter The composition and the concentration of the urine are constantly changing. The proportion of solids and water varies with the activities of ^See No. 1, 226. 2See Nos. 2, 3, and 4, p. 226. 218 Right kidney Pelvis Ureter ^ — Aorta Bladder Urethra L_ :.,.,JJ,jJJl^&^ KIDNEYS AND BLADDER Blood is carried to each kidney by a branch from the descending aorta. The small- est arteries form a network of capillaries within the cortex and the medulla of the kidney. Veins carry blood from the capillaries to the descending vena cava. Urine secreted from the capillaries of the cortex passes through collecting tubules that open into the pelvis. By peristaltic motion urine is forced through the ureter into the bladder, in which it is temporarily stored, being expelled at intervals through the urethra the organism and with the temperature. Increased sweating, for example, removes water continuously. And unless this is made up by taking in more water, the urine will be more concentrated. On the other hand, any excess of water taken in is quickly removed by the kidneys, so that the urine be- comes diluted. During strenuous exercise albumin may be temporarily present in the Ward's Natural Science Establishment, Inc. URINE-COLLECTING TUBES IN A KIDNEY If the urine tubes of a sheep's kidney are filled with latex and all the tissues are then corroded away chemically, there remains a "latex cast" of the tube system. This shows how the urine discharged from the thousands of uriniferous tubules in the cortex of the kidney is collected in the pelvis 220 Glomerulus Absorbing capillaries Urinary tubule L Bowman's capsule Convoluted tubule THE REMOVAL OF WASTES BY THE KIDNEYS Each tubule starts from on enlarged double-walled capsule. Blood from the artery flows first through the capillaries of the glomerulus, out of which waste material dif- fuses by osmosis. These fluids continue through the tubule, which is very long and very much tangled. The blood continuing past the glomerulus runs through a sec- ond set of capillaries, which are closely enmeshed with the tubules. At this stage much of the water, sugar, and salts that had diffused into the capsule becomes re- absorbed into the blood urine. And sometimes growth is so rapid during adolescence that the albumin content rises. But if albumin is constantly present in the urine, it indicates that the kidneys are in a diseased condition. The sugar content of the urine is temporarily increased by eating large quantities of sugar. Whenever the sugar content of the blood rises above 180 milligrams per cubic centimeter, sugar overflows into the urine. But when sugar continues to overflow from the body through the urine, a diseased condition is indicated. An excess of sugar in the urine is one of the symptoms of diabetes. Since the activities of the body are not carried on at an even rate, there is sometimes a draft upon reserves — the glycogen in the liver, for example. And sometimes wastes may be produced faster than they are removed by the excretory organs. In extreme cases, failure of excretion may be fatal: an accumulation of uric acid in the blood acts as poison. 221 What Connection Is There between Overwork and Excretion? Getting Tired^ When you "chin" yourself on a bar four, five, or six times, until you can do no more, this does not mean that you will never be able to chin yourself again. After resting awhile, perhaps a day or an hour, or perhaps only ten or fifteen minutes, you can chin yourself again as well as at first. What happens in the first place to make you stop? Or what happens during the rest to enable you to do the work again? As soon as work commences, waste substances begin to accumulate in the cells. The wastes are formed faster than they are carried away. The result is a "poi- soning" of the protoplasm of the working cells. When muscles are working slowly, the glucose fuel is oxidized, first into lactic acid, then into water and carbon dioxide. When muscles work very rapidly, as in running, lactic acid formed in the first stages of oxidation accumulates in the cells and is but slowly removed by the blood. Since the lactic acid results from using oxygen faster than it is supplied by the blood and lungs, it is said to represent an "oxygen debt". During rest this "oxygen debt" is quickly repaid by an increased rate of respiration and circulation (see page 193). In the meantime the lactic acid interferes with the opera- tion of the muscles and in effect "poisons" nerves and other tissues. When hard work is sustained for any considerable time, we say that the muscle is fatigued. Some of this lactic acid is distributed by the blood to other tissues of the body, and tissues which have not been active become "fatigued". Fatigue May Be General We have all been taught that "a change of work is the best kind of rest." To a certain extent this is true. When I am reading a difficult book and begin to doze over it, I am not too tired to play a game of tennis or even to read exciting fiction. But past a certain point, fatigue affects the whole body; getting tired from study unfits one for muscular work or play. Thus records made on the ergograph by any person will show great variation, according to the condition of the body. A record made early in the morning will differ from one made at the close of a game of chess (see illustration, p. 224). From these and similar experiments we have learned that exhausting physical work tires the brain and the sense organs. And we have learned that severe mental work tires the whole body. We cannot conclude, however, that hard work is to be avoided. On the contrary, hard work is useful physiologically, as well as otherwise. It stimu- lates the many metabolic processes and so helps to keep the body in good condition. We can use knowledge about fatigue to organize our work in more effective ways. By planning carefully, by adjusting the rate of work, and by arranging alternate periods of work and relaxation we can do much to reduce fatigue. iSee No. 5, p. 226. 222 Rate of Work When you walk very fast, you may feel tired before you have gone a mile. If you walk slowly enough (but not too slowly), you may walk ten miles without showing signs of fatigue. Getting tired is not altogether a question of what kind of work we are doing, nor of how much. It is partly a matter of how fast we are doing it. "It is the pace that kills" (see illustration, p. 225). Physiologically this means that (1) at a certain rate or speed, lactic acid and perhaps other fatigue substances are formed faster than they can be removed by the blood, and from the blood by the kidneys, etc.; and (2) when work is done at a certain slower speed, the blood can remove the wastes just as fast as they are formed. This principle has its everyday applications in athletics, in play, in housework, in school- work, and in industry. Fatigue and Efficiency In emergencies men and women exert them- selves to the point of exhaustion. When we manage our own time and efforts, we sometimes find it expedient to work under great pressure, expect- ing to even up the organism's account later. In managing other people's work and time, the problem and the motives are essentially different. But studies made by engineers and physiologists have shown that in the long run the greatest output of work is possible only where fatigue is system- atically avoided. It is difficult to observe the maxim "Make haste slowly" when we are eager to get as much as possible from the work of others. People can endure a spell of exceptional exertion if it seems necessary, but everybody hates to A MACHINE FOR MEASURING WORK CAPACITY AND FATIGUE The ergograph measures and records the frequency and the strength of a pull ex- erted by a finger while the rest of the hand is held firmly in place, in the record, the heights of the vertical lines indicate the relative amount of energy output for each pull on the ring. The distances between vertical lines correspond to the time intervals between pulls 223 be driven. Workers may resent the "speedup" because they fear being over- worked, but they probably resent even more having the pace set for them .lllllllllllllUll Illllllllllllklll[l .l /Mlllllll)llllllllllll,lll llllllllll MORNING RECORD liiiiiiiliiiiilliillliiiiiiiiiiniiiiihiiliiiiiiiiiiDiiiiiiiiiii / LATE-AFTERNOON RECORD These two records on the ergogroph were made by a medical student on the same day. Although he made no special exertions with his middle finger during the day's work, the record made by the pulls of this finger show a general fatigue — that is, one of the whole body — toward the end of the day by somebody who is unconcerned about their continued well-being. In trying to make the most out of mass-production methods we have generally overlooked the fact that individuals differ with regard to their working rhythms and resistance to fatigue. When a machine sets the pace for a large block of workers, some of the individuals are almost certain to be over- worked, while about the same number will be kept from working at their own best speed. The First World War compelled works managers to select workers more carefully for the various tasks. The Second World War forced them to go even farther: they must determine "average" speeds and hours of work in relation to the capacities and limitations of the particular organisms under their direction. Early in the Second World War, British factories quickly intensified their efforts to increase the production of war essentials by speeding the work and also by increasing the hours of work. In a short time it was found that accidents increased, workers collapsed, and the actual output failed to keep up with plans. In this country workers in many plants were tempted to work extra long hours to earn the additional wages. But within a few months after the United States was at war it was found necessary to restrict the number of hours a worker might keep at his job to forty-eight a week. These regulations were based on studies of the effects upon workers of 224 staying too long at the job without suitable rest periods. The regulations required also a full day of rest in seven, and vacation periods as well as adequate time allowances for lunch. Excessive work schedules were found to reduce the flow of production as well as to impair the health and effi- ciency of the workers. In Brief Among the substances produced in living things during metabolism, some are useless or even injurious to the protoplasm. Plants eliminate carbon dioxide and water, but usually accumulate other wastes in insoluble combinations in various tissues, where they do not inter- fere with vital activities. Animals deposit wastes in special tissues of the body to a slight extent. In the higher animals wastes are diffused into the blood and removed from the body by special organs, such as sweat glands and kidneys, or by the intestines. In the vertebrates, nitrogenous and other wastes are removed from the blood by the two bean-shaped kidneys. Each kidney consists of a mass of tiny tubules interwoven with a com- plex network of capillaries. The wastes diffuse from the blood into the tubules, from which they are discharged from the body as urine. The urine, which is about 96 per cent water, contains dissolved substances resulting from the breakdown of proteins during metabolism. The composition and concentration of the urine are constantly changing. 11. J lllMllillllliillllMIIIIII IIIIIIMIIIlllllMllillinllll:-'! THE PACE THAT TIRES ,1 hlullllllllllNIII IlllllllllllllJllllllHIHIlllllllllllHIIllllllllllllllllI IIIM IIIIIIIIIIIIIIIIIIII I IIIIIIIMIIUliKUmXl->-''VMlimJllll. These two ergograph records were made by the some student. The first he made by pulling as rapidly as he could and as far as he could: this shows fatigue coming on rapidly. The second was made by a slow, steady pull, taking two seconds each time. Although the action continued twice as long in the second case and the actual work performed was about four times as much, there is hardly any evidence of fatigue 225 The continued presence of albumin or of sugar in the urine indicates a diseased condition of the body. When wastes accumulate in active tissues faster than they can be ex- creted, they are diffused to other tissues and may bring about a state of general fatigue. An excess of uric acid in the blood may be fatal. Efficiency in work can be increased by setting a pace that will avoid fatigue through balancing metabolism and excretion. EXPLORATIONS AND PROJECTS 1 To study the position and structure of vertebrate excretory organs: Dissect an anesthetized frog, guinea-pig, or rat, opening it on the undersurface, and remove the viscera. On either side of the backbone will be found the two bean-shaped kidneys. The ureters, the bladder, and the urethra may be seen in their normal position. The arteries and veins leading to and from the kidneys may also be readily seen. Cut a sheep or beef kidney lengthwise through the "pelvis". Note general structure. 2 To find the specific gravity of a sample of urine, float a hydrometer in the urine placed in a tall cylinder. (Clear amber-colored fluid normally has a specific gravity of about 1.02.) 3 To determine whether urine is acid or alkaline, use litmus paper or phenolphthalein or nitrazine paper. The reaction is usually slightly acid because of the presence of acid sodium phosphate (NatioPOi). 4 To test urine for sugar, use Fehling solution (see footnote 1 on page 183). 5 To observe the effect of fatigue on muscular activity, note the change in rate and speed of work as several individuals "chin" themselves as many times as they can without stopping. 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 How are the waste substances of plants separated from the living parts of the organism? How do animal cells dispose of wastes? 4 In the higher animals, how is the waste removed from the many cells throughout the body? 5 In the higher animals, what specialized organs remove the wastes of metabolism from the body? 6 How is the structure of the kidney related to its function? 7 What factors affect the composition and the concentration of the urine? 226 8 What is indicated by the continued presence of glucose in the urine? 9 What is indicated by the continued presence of albumin in the urine? 10 What is the advantage of a vigorous sweat? the disadvantage? 11 What are the advantages of cold baths? the disadvantages? 12 Why is it important to prevent the accumulation of refuse in the large intestine for a long period? 13 What are the advantages of standardized working hours? the dis- advantages ? 227 CHAPTER 13 • HOW DO ORGANISMS RESIST INJURY? 1 How can a sick person get well ? 2 What makes an organism sick? 3 Are all kinds of diseases caused by bacteria ? 4 Are blood sicknesses inherited? 5 Does vaccinating prevent all diseases? 6 What is antitoxin? 7 Are there antitoxins for all diseases ? 8 Can any medicine be suitable for all kinds of sickness ? 9 How does one become immune to certain diseases? 10 What is the difference between a serum and a vaccine? Living things are always exposed to mechanical injuries. A fish snaps at another fish and gets away with only part of the prey, A wind blows a bough off a tree or tears off a piece of bark. A bird catches a lizard by the leg, and the lizard slinks off on his remaining three. A parasite gets inside an animal and destroys part of the tissues, or it excretes substances that are poisonous to the host. Such dangers are parts of the risks of living. If an injury is too extensive, or if too much of an organism is removed or destroyed, death is likely to result. But how much is too much? What happens when the injuries are chemical, or result from poison? How does a sick organism recover? How much punishment can an organism take and still continue to live? How Much Damage Can an Organism Endure? Healing and Regeneration^ Plants and animals of nearly all classes repair mechanical injury by growing new tissue that closes the wound. In organisms like ourselves the gap in the tissues at first fills with fluid from the surrounding cells and spaces — lymph. Then the surrounding cells multiply rapidly, forming new cells. (This rapid formation of new cells is called proliferation.) Such healing is almost universal. But it is not equally effective among all species, nor among all the tissues of a given plant or animal. At one extreme, planarians will regenerate, or regrow, complete indi- viduals from rather small fractions of worms (see illustration opposite). The earthworm can regrow the missing part if its hind end is cut off. Oystermen who formerly tried to slaughter the destructive starfish by chopping them with hoes and shovels discovered that the enemy could regenerate the parts iSeeNo. 1, p. 246. 228 /\ ] i^ REGENERATION IN FLATWORMS Experiments with flatworms show the regeneration of a complete animal from a seg- ment. If the head is removed, if the hind part is removed, if a section is cut from the middle, a complete animal will be regrown. The shaded areas represent the new growth removed. A lobster will regrow a complete new claw. Salamanders re- generate complete tails and legs. The glass snake (which is really a lizard with reduced legs) leaves his tail behind when it is grasped, but then grows himself another (see illustration, p. 230). At the other extreme are more highly specialized warm-blooded organ- isms. We can regrow skin, or bone, or connective tissue. When nerve and brain cells are injured, however, they are replaced by scar tissue. Scar tissue closes a gap, but it does not have the characteristic of nerves, nor does it do the work of the destroyed nerve cells. Plants usually heal wounds more directly: exposed cells dry up. In many cases, however, regeneration or healing may be observed. In some species, even a small piece of leaf or stem may regenerate leaves and roots and, under suitable conditions, a complete plant (see illustration, p. 231). When the bark is scraped from a tree, and the growing layer is exposed, proliferation of cells results in a mass of callus. This covers the wound but does not con- tinue to grow. 229 Regenerated stump Regenerated ray Size of original tail REGENERATION IN STARFISH AND LIZARD A starfish can regrow as many as four rays to full size, if the disk remains intact. Many lizards will regrow missing limbs or tails. In the regenerated tail of Ameiva from Dutch Guiana there are no vertebrae Growth Substances Biologists have long been puzzled by the various ways in which plants and animals respond to injury. Healing and regenera- tion are obviously adaptive: they help to preserve the Injured or mutilated Individual. But what makes the healing start? One suggestion is that the tissues stopped growing In the first place through die action of the cells upon one another. That is, each cell might still be able to grow and divide but is kept from doing so by the presence of neighboring cells. When cells are broken, however, two conditions are changed: (1) there is now more room for further growth, and (2) injured cells may throw some growth substance Into the surrounding space. These new conditions might explain the sudden proliferation of new cells into the space formed by a wound. According to experiments by George Sperti (1900- ) and associates at Cincinnati and by other investigators, Injured cells do produce substances that stimulate cell-division of living cells. From yeast cells and chicken embryo cells killed under suitable conditions, experimenters removed special substances that hasten the growth of injured tissues. Ointments prepared from such materials have been very helpful in healing severe burns and other wounds. Incidentally, these studies have fur- nished some clues to the further Investigation of the causes of cancers. Cancers are ''wild" growths In tissues that had already completed dieir nor- mal development: the Idea is that injured cells Introduce special growth substances and so bring about abnormal proliferation. Poisons The idea of poisoning must be very old In the experience of the race. Something taken into the system interferes with comfort or with life. Acids and alkalies obviously injure tissues, as on the skin. Undoubtedly 230 they act in similar ways when taken into the system. Poisoning may be of various kinds. Thus certain substances combine with proteins in ways that interfere with normal metabolism. Some substances retard, others accel- erate, metabolism. Some substances seem to attach themselves to special tissues. Among inorganic poisons the most dangerous for human beings are compounds of lead, mercury and phosphorus, which are used in certain in- dustries. Since about 1910 legislation has stopped the use of white phosphorus in the manufacture of matches because the fumes caused serious injuries in the workers. More recently, radium compounds, used for luminous watch and instrument dials, were found to disturb seriously the metabolism of those who work with such materials; and strict regulations have been adopted to prevent further injury. Some of the most useful drugs obtained from plants are poisons of the alkaloid group, such as morphin, atropin and quinin. These act in specific ways, but often produce undesirable results along with their useful results; and they are dangerous in large doses. For these reasons scientists have been trying to find substitutes that are more readily controlled, in the form of artificial synthetic compounds. The specific substances are not all useful, nor do they act equally on all living things. Hens, for example, appear to REGENERATION IN LEAF OF BRYOPHYLLUM The leaves of bryophyllum, of begonia, and of a few other genera will form complete plants if removed from the stem. In some experiments with bryophyllum leaves, a plant was regenerated at each notch when the leaf had been cut into strips from the edge to the midrib 231 be indifferent to the action of morphin, and rabbits are insensitive to the alkaloid atropin, or belladonna. Members of the same species also differ greatly among one another. Some persons are more susceptible than others to the effects of tobacco or alcohol; some more susceptible to the specific poisons of particular kinds of bacteria. How various poisons act upon the organism and how they can be counteracted are the problems of a special study — toxicology. In the last few decades we have learned a great deal about how the body reacts to foreign substances of various kinds. How Is Protoplasm Influenced by Foreign Substances? Getting Used to Changed Conditions There are many kinds of fish that live in salt water only, and there are many kinds that live in fresh water only. Some species, however, such as the salmon and eel, spend part of their lives in the ocean and part in fresh water. Still, if we took one such fish out of the ocean and placed it in fresh water, it would soon die. Or if we took one from fresh water and put it into salt water, it would soon die. But if we slowly dilute sea water, or gradually concentrate the salt in fresh water, we can keep some fish alive now in one medium and now in the other. In a case of this kind we say that the animal "gets used" to living in the new conditions. This illustrates a pretty general fact about protoplasm, or about living things. Living things can get used to new conditions of tem- perature 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. That is not true. Birds cannot get used to living in water; fish cannot get used to living in the air. Plants and animals cannot get used to living with- out proteins or without salts. But we can all change our conditions of living to a certain degree or in certain directions and still remain alive. Habit-Forming Poisons Arsenic is poison to all kinds of protoplasm. It is used in fighting many kinds of insects and many kinds of fungi. A very small amount of it will kill a person or a rabbit.^ In experiments this substance was fed to rabbits in very small quantities — a fraction of the quan- tity enough to kill. After a few days the animals were given a little more. The dose was gradually increased until the animals could stand several times the ordinary fatal dose. The arsenic acts upon the protoplasm of the nerves or muscles to put the animal in a state of tonus, or stretch — that is, the way one feels when one is "all on edge", all set to jump or scream on the least provocation. The treated rabbits thus became extremely sensitive to the slightest disturbance. They would jump on hearing the faintest sound, ■^Strangely enough, a child can tolerate more arsenic than an adult. 232 or on seeing the slightest movement or the passing of a shadow. But still more curious, after the animals had been fed the poison in this way for a considerable time, they became unable to live without it. If the drug was omitted from their daily rations, they quickly died. The rabbit's protoplasm adjusted itself to new surroundings. The proto- plasm became able to live under conditions that would normally destroy it. In experiments with bacteria similar results were obtained. Bacteria of va- rious species were placed in dishes with the usual food materials, but with the addition of a small amount of phenol or other germicide. When the colony had about used up all the food in the dish, some bacteria were trans- ferred to a similar dish containing a slightly greater concentration of the poison. This was repeated several times. In the end there was a growth of bacteria that could tolerate much more poison than would normally kill their ancestors. Persons suffering from malaria are systematically treated with quinin to keep the parasite in check. After a long and seemingly successful treatment a patient sometimes relapses. It has been suggested that in such cases the malaria parasite has become able to tolerate relatively large quantities of quinin, so that it is useless to drug the patient further. Such observations suggest that while each particular kind of protoplasm thrives best in a particular set of conditions, it is able also to adjust itself to different conditions — provided they are not too different. It is not clear just what change takes place in the protoplasm itself under such circum- stances. Antitoxin Different kinds of bacteria produce substances that act as poisons in the bodies of animals. Such protein poisons, or toxins, are found also in the venom of various snakes and in the tissues of various higher plants. When some toxin gets into living tissue, it stimulates the protoplasm to produce specific neutralizing, or counteracting, substances. The reaction of the invaded protoplasm may be compared to some of the chemical proc- esses that bring about homeostasis — the release of acid under the stimulus of alkali, and vice versa (see page 193). The reaction of protoplasm to the toxins is apparently much more complex, however. The counteracting sub- stance produced by living cells under the influence of a toxin is called an antitoxin, and it is always specific. That is, it will neutralize the poison under whose stimulation it was produced, but no other. Among the best-known toxins are those produced by the bacteria that cause lockjaw and diphtheria. When a quantity of toxin, not enough to kill, is injected into the blood of a healthy animal (a young horse, for example), the cells begin to produce and excrete antitoxin. They will pro- duce more than enough antitoxin to neutralize the poison received by the body, and the surplus antitoxin remains in the blood. This surplus can then 233 Bacilli of diphtheria SnMll quantities ,. Heated Filtered to 0^"Q> inje^ ^from large vein in horse's neck Blood Serum clots ^ containing // antitoxin Serum tested on Sterilized ed Divided into doses, or units, of antitoxin guinea pigs PREPARING DIPHTHERIA ANTITOXIN For making antitoxins, carefully selected and perfectly healthy young animals are used. The toxin is produced by millions of bacteria grown in special nutritive solu- tions. The dissolved poison is filtered from other substances in the culture, which is heated to kill the bacteria. Increasing doses of toxin are injected into the animal over two to three months. Blood is drawn from the animal from time to time; after the blood clots, the antitoxin is in the serum. After the removal of other materials the serum is tested both for its potency and for the possibility of any injurious sub- stance being in it. It is then put up in sealed units for use against diphtheria be used to cure a person infected with the corresponding disease germs. That is, the antitoxin produced in the body of a horse or a goat is used to reinforce the natural capacity of the human body to combat the poison of the invading germs (see illustration above). Are Chemical Changes in an Organism Permanent? Modified Protoplasm If the body recovers from a mechanical injury, it may afterward be exactly as it was before, for all we can tell — except perhaps for some mutilation. But when a person recovers from certain kinds of sickness, there are apparently lasting changes in the protoplasm. It 234 is a common saying that "you can't have measles twice". The changes which make one immune during mumps, whooping cough, scarlet fever, yellow fever and diphtheria are practically permanent. In former times, people in Asia and in southeastern Europe took advan- tage of the fact that recovering from smallpox usually meant a degree of immunity. They would induce the disease in a mild form by inoculating a person with pus from a patient having the disease. After recovering from the induced smallpox one was just as immune as if he had "caught" it unintentionally. Instead of taking a chance with an epidemic, one could choose to have the disease in a comparatively mild form and perhaps at a convenient time. The practice of inoculating against smallpox had long been common in the East. It was not brought to the attention of western Europe and Eng- land until about 1720, through Lady Mary Wortley Montagu, the wife of the British ambassador to Turkey. Inoculation was shown to be relatively safe, as well as effective. Many physicians began to inoculate against small- pox, but the practice met with a great deal of opposition. It was sometimes unsuccessful. Worse still, it sometimes resulted in introducing another dis- ease. In some cases an inoculated person infected somebody else, who then suffered a violent or fatal form of the disease. Inoculation was, at any rate, a strange practice, contrary to familiar customs and to "common sense". George Washington wanted all his soldiers inoculated; later, laws were passed forbidding inoculation. For nearly a hundred years controversy raged about inoculation in England, in this country, and in all parts of Europe. Then an English physician, Edward Jenner (1749-1823), was told by a dairymaid that there was no use inoculating her, for she could not have smallpox — she had once had "cowpox". To a learned physician, this was merely ignorant folklore. But to a scientific physician, it was something to look into. Jenner found that this idea was quite general among dairymen and dairywomen, and that they could cite any number of cases. Moreover, dairy people actually had less than their proportion of smallpox. Since cowpox is a very mild disease, Jenner saw advantages in using cowpox pus for inoculating — /'/ it would work. He tried it. He inoculated a boy with cowpox. After several weeks he inoculated the same boy with smallpox. This did not "take". He tried it again, with the same negative results. Later he tried the experiment on others. He concluded that a cowpox inoculation protects against a smallpox inoculation. Would it also protect against smallpox "caught" in the usual way? Vaccination^ After years of experimenting, Jenner came to the con- clusion that the cause of cowpox is related to the cause of smallpox. He iSee No. 2, p. 246. 235 © National Portrait Gallery EDWARD JENNER (1749-1823) Jenner had received irregular but good training in pharmacy and surgery, having studied under the great John Hunter; but he preferred to practice medicine in his small home town. Hearing of the common belief that those who had recovered from the "cowpox" — a mild disease common among dairy workers — could not take small- pox, he watched for a chance to test this experimentally. From his work the practice of vaccination rid the world, in time, of smallpox, except in a few out-of-the-way places called this mild disease Variola vaccinae (that is, cow-variola; vaccinae is from the Latin vacca, "cow"). Today the term vaccination is used loosely for any procedure that brings about immunity, whether or not the active "germ" or virus is introduced. The general principle involved is that foreign material stimulates the organism to produce something that counteracts //. That is, as a result of the treatment, the body actively produces the anti- bodies. This is in contrast to inducing passive immunity by adding antitoxin to the blood, as in a case of diphtheria. In typhoid-fever "vaccination", cultures of the bacteria are killed and then introduced under the skin. Active immunity against diphtheria is brought about by means of a mixture of the toxin with some antitoxin. The antitoxin protects the body against the poison, but the free toxin stimulates 236 the protoplasm to form more antitoxin. In using toxoid, lasting immunity is brought about usually with one or two injections. Permanent Values of Immunization There is no evidence that im- munity acquired in a person's lifetime is transmitted to offspring. However, a baby may be for a time immune as a result of substances developed in the mother's blood during pregnancy. Artificial immunization may not last a lifetime. Vaccinating or immunizing is nevertheless of tremendous value for those communities that have learned to use it. Before the German bacteriologist Emil von Behring (1854-1917) worked out the antitoxin principle in the early nineties, diphtheria was most dreaded by parents. For this disease in children was not only very distressing, but resulted in a very high proportion of deaths — 45 per cent or more. The widespread use of antitoxin as a cure has so reduced the fatality from diph- theria that it is no longer dreaded as a scourge. However, it was the system- atic immunization of children to prevent the disease that reduced the prevalence of diphtheria. There are now many cities that have for years been free of diphtheria. Antitoxic serums have been developed against the poisons of gas gan- grene, the tetanus or lockjaw organism, and botulism. In none of these cases has the antitoxin resulted in such striking success as in that of diphtheria. This is largely because some toxins destroy living protoplasm before the Compulsory vaccmation 13 states (including the District of Columbia) PopulaUon: 43,000,000 I^cal'option 14 states Population: 41,000,000 Do as you Vik& 22 states Population: 49,000,0xm came : into use 1896 1897 1898 1899 1900 HOW ANTITOXIN SAVED LIVES The records of a large metropolitan hospital in London showed the number of deaths in each hundred cases of diphtheria for five years before and five years after anti- toxin came into use presence of the disease can be recognized. The antitoxin is then without effect. Tetanus antitoxin is a dependable preventive, but the disease is too rare to vi^arrant routine inoculations. Doctors use it wherever a wound may have become infected with the tetanus organism. What Kinds of Anti Bodies Do Organisms Produce? Protoplasm Strikes Back We cannot measure humanity's gains from Jenner's work in preventing smallpox, or from Behring's work a century later in curing diphtheria. We can say that two very important sources of mankind's miseries have been wiped out completely in many regions, and are being pushed farther back as fast as people make use of our knowledge. 238 #^' #^ #' DECLINE OF DIPHTHERIA AS A CAUSE OF DEATH (1880-1942) The long zigzag line shows the fluctuation in deaths from diphtheria per 100,000 population in New York (Manhattan and Bronx, for which the most complete records are available). After 1895, when antitoxin came into use, there is a rapid drop, and then a steady decline for twenty-five years. With the introduction of the Schick test for susceptibility and the immunization of children against diphtheria, this disease became an almost negligible cause of death. The record for the last few years is shown in the inset, as the figures are too small to show on the large graph And we can say that the Hves of milHons and millions of children have been prolonged into adulthood. But these two discoveries illustrate an important principle of living matter. They lead on to a better understanding of life, and possibly to better ways of managing our lives. The important principle in immunization is represented by the familiar fact that if you annoy a cat she is likely to strike back. We might generalize the idea further: Living matter tends to react to changes in a way that neutralizes or counteracts disturbances in metabolism. Chemical disturb- ances call out chemical responses. A specific poison calls out a specific counter-poison — something that is chemically related to ]ust that, and not to disturbances in general, not to poisons in general. Chemical Conflict We may think of the formation of an antitoxin as a normal result of the interaction between two kinds of protoplasm. It should not seem strange that among the hundreds of species of micro- 239 Shortly after the bacillus which couses diphtheria was discovered by Friedrich Loeffler, in 1884, Emil Behring hit upon the idea that a living organism "fights back" against the attacking parasite by some chemical means. In the meantime Emile Roux, a French investigator at the Pasteur Institute in Paris, found that the bacilli of diphtheria produce a virulent poison. After long and difficult experimenting, Behring established the principle of "anti-toxin". He produced a sheep serum with which he cured guinea pigs and rabbits that were sick with diphtheria. Roux started to make gallons of antitoxin serum by using horses. In 1901 Roux and Behring together received the Nobel prize for their important contri- bution EMIL VON BEHRING (1854-1917) organisms living in the soil, a particular species will produce a substance that is injurious to some other species. This seems, indeed, to be a general fact, although few particular cases have been worked out. Some species of Pemcillium, the very common "blue" or "green" mold (see illustration, p. 375), produce a substance that is destructive of certain species of bacteria. This substance, penicillin, has been extracted and found to be a very power- ful germicide, or germ-killer. It has been found so helpful during the Sec- ond World War that many special plants have been established for producing it on a large scale. Investigators are experimenting with the idea of growing the mold Peiticillium on wound dressings and so preventing infection. The experiments so far made suggest an explanation for the fact that when infected materials are buried in the earth, they appear in time to be- come "purified". By means of experiments biologists and other scientists have found that organisms react to injurious foreign substances in many different ways. We may consider the formation of antibodies in larger or- ganisms as adaptive changes in the blood. But since we cannot detect these changes with a microscope, or even by ordinary chemical means, we look for them in the behavior of the serum — the clear fluid left after the clot is removed from blood. Blood-Serum Reactions When white-of-egg is placed in the stomach of a backboned animal, it acts as food. If it is injected directly in the blood (of a rabbit, for example), it produces a totally different effect. If, after several such injections, we mix a few drops of serum from a treated rabbit with water containing some egg albumen, a white precipitate will imme- 240 diately appear. There has been formed a new substance that does not occur in normal blood serum. This new precipitating substance, or precipitin, will precipitate only white-of-egg. If a different kind of protein is used, the precipitin formed will act on that only. That is, the precipitin is specific. We do not know how the protoplasm of an animal produces precipitin, but we can use what we do know about precipitins in several ways: (1) We can tell whether a bloodstain was produced by human blood, let us say, or by the blood of some other species. (2) We can tell, by the precipitin test, what kinds of meat there are in a sausage or hash, when all other tests fail. A. With a small syringe, blood is removed from the suspected patient cind left to clot C. Serum from the clotted blood B. In the meantime a clean growth of typhoid bacilli is made ready In this growth bacteria move about freely and singly ^i^ is mixed with a '1 -T) Vieo sterile salt solution in different proportions D. To a drop of each senim-salt mixture there is added a drop of typhoid culture If bacilli stick together even in dilute serum, the patient probably has typhoid fever; If the bacilli remain apart even in concentrated serum, he is probably not infected with typhoid WIDAL'S AGGLUTINATION TEST FOR TYPHOID 241 Another type of chemical response to foreign substances is revealed by the serum of a typhoid-fever patient (see illustration, p. 241). The new sub- stance is called an agglutinin because it clumps the bacteria together in masses. Like precipitins and antitoxins, agglutinins are specific; that is, each acts only on a particular species of bacteria. The agglutinins do not kill the bacteria, but probably interfere in some way with their action. It is certain that in their presence the phagocytes more readily attack the bacteria (see page 188). In the blood of a backboned animal, red and white corpuscles float about unaffected by one another. But if blood from a different species is injected into the veins of a rabbit or mouse, say, the foreign red corpuscles are pres- ently destroyed. After the foreign cells are introduced, the body seems to form a new substance that dissolves the invading material. Such specific cytolysins, or "cell-dissolvers", are formed in response to various kinds of cells or tissues and to various bacteria. Thus the serum of a rabbit that has been treated with human blood will dissolve human corpuscles, but not those of a goat or a monkey. Specific Tests of Disease^ The antibodies that develop after an infec- tion or after an inoculation are specific and are present in the blood. They therefore appear in the serum. We sometimes speak of such a serum as an "immune" or as a "specific" serum. Because of the specific characteristics of such altered serums, we can use them for the quick and reliable diag- nosis of certain diseases, as the Wassermann test for syphilis and the Widal lest for typhoid fever (see illustration, p. 241). Other tests tell us whether a person is susceptible to a given disease or sensitive to a particular sub- stance. The Schick test is used to show whether a person is immune or susceptible to diphtheria. Similar tests are used to discover the plant or animal substances to which sufferers from asthma or other "allergic" con- ditions are sensitive. It has been possible to distinguish in the laboratory thirty-five or more distinct types of pneumococcus bacteria that can cause pneumonia. It has been possible to prepare specific serums for a few of these types. But physi- cians are unable to recognize from the patient's symptoms which particular type of germ is present ; and testing for type takes time, and sometimes every hour counts. Before all the types could be readily distinguished, and before dependable serums were available for more than a few types, biochemists had found a more promising treatment. This is the use of the synthetic drugs of the so-called "sulfa" series. These act alike on all types of pneu- monia, as well as on gonorrhea and other diseases caused by bacteria of the coccus group (see page 613). Individuals differ in their reaction to various sulfa drugs, but research to improve these compounds is going forward iSee No. 3, p. 246. 242 Pneumonia death rates per 100,000 popul New York State, since 1920 ation, ^Pi^\ ': i ; ' - i loU , 150" \ — ' ! ; 1 j 14U-|t — 1 nri • 1 / \ ■ ion J « 1 X "> k,. / •^ . Syste distril of se majic 110- 100- 90- 80 70- 60 f N ?uupn, rum ^ s. i j ....... .^ j > N k I i J i ! i N .^^ r-^ .-^ (. \ c py -be lulfa i Pc eu3 yp, ive noikia V lidine d€ 4J.y op^d \ ailable 1 DU /in 1 \ *--, ^ •4-U 30- 20 ! i. 1 1 A^/ ^/ .y ^' .%' sy a'>/ n^/ <^ r^/ */ r^/ ^/ r^/ .r ^^ ^/ ^ &/ ^/ ^/ DECLINE OF PNEUMONIA FATALITIES The general downward trend of fatalities from pneumonia was accelerated in the thirties by the development of special serum "types", and in ^the early forties by the introduction of sulfa drugs rapidly. In the meantime, pneumonia, while still a serious disease, is coming to be a less prominent cause of death. Anaphylaxis In the early days of antitoxin the treatment usually re- sulted in almost miraculous cures. But occasionally a patient would collapse and die after the injection of the immune horse serum. This baffling re- action was found later to result not from the antitoxin but from a horse protein to which some people are sensitive. Furthermore, if horse serum is used in vaccinating against one disease, and later a horse serum is used in vaccinating against another disease, the patient is much more likely to show this violent reaction, or anaphylaxis. By using a sensitivity-test for horse serum the doctor can prevent such a reaction. Various serums and vaccines are now prepared in goats, rabbits, and some other animals, as well as in horses. 243 United States Bureau of Plant Industry NATURAL IMMUNITY IN PLANTS One variety of tobacco was grown between rows of other varieties. All the plants were sprayed with fluid containing spores of black shank, a fungus disease of to- bacco. Among plants, as among animals, individuals and strains of individuals differ from others in the degree to which they are susceptible to particular parasites or diseases Immunity and Susceptibility Individual variation includes great dif- ferences in sensitivity to particular substances. Some people catch colds more easily than others. Some more frequently have boils or pimples. There are also racial differences. Thus dark-skinned races are less suscep- tible to malaria and to hookworm than white races. On the other hand, white races are less susceptible to tuberculosis and measles than dark races. Again, human beings are quite immune to diseases that are serious or even fatal to birds or cattle (see illustration above). Such immunity is called natural immunity, and is inherited. In many cases it probably depends upon the chemical peculiarity of the blood. In others it depends upon the quick response of the living cells to poisons or to other products of bacteria. But such natural immunity is not absolute; that is to say, it may be weakened or destroyed by various conditions. The quantities of certain antibodies in human blood can be tremendously in- creased by the inoculation of suitable foreign substances. This is the basis for the various kinds of artificial immunization, which are popularly called "vaccination". 244 Carriers We may think of an infectious disease as a process, a conflict between two species. The invader attacks with a small army, which grad- ually increases in numbers as the parasite lives at the expense of the host. The beginnings are therefore mild, and for a time there is no indication that the host is being injured. When fever and other "symptoms" appear, the host has already begun to react. If antibodies are produced rapidly, the host recovers. Sometimes, however, the host recovers without completely routing the invader. The parasite adapts itself to the chemical conditions of the host, and the host tolerates the parasite: neither appears to be injured. But the germs being discharged from the body are just as virulent when they invade another host. That makes the "carrier" a possible danger to other persons. The first typhoid carrier on record in the United States was Mary Mallon, to whom seven outbreaks of typhoid fever were traced over a period of years, by 1907. Later 30 other cases were traced to her directly, making a total of 56 cases, of whom three died. She was kept under observation or in confinement for over thirty years, until her death in 1939. As many as 400 typhoid carriers have been under control at one time in New York State. Diphtheria carriers are also watched in a similar way. In such cases the "dangerous" person is perfectly innocent of all wrongdoing; yet he has to be regulated in his activities and movements for the protection of others. In Brief Most plants and many of the lower animals can regenerate parts that are injured or destroyed. Among the higher animals cut and damaged tissues are replaced with scar tissues. Injured cells apparently give out substances that stimulate the growth of new tissue. Some poisons stop metabolism; others retard or accelerate it. Living organisms react to certain drugs in ways that make the proto- plasm unable to get along without these habit-forming drugs. The living organism reacts chemically to foreign substances in ways that are generally adaptive. The chemical changes, usually in the blood, result in antibodies that counteract specific poisons or parasites, so that the body becomes temporarily or lastingly immune. Serums containing specific anti-substances are used to bring about passive immunity. Immunity to certain diseases can be acquired by recovering from them. 245 Immunity may also be induced artificially, as in vaccination, by introducing substances that stimulate the blood to actiue production of specific anti- bodies. The specific reaction of the body, particularly the blood, to foreign sub- stances makes it possible to recognize, or diagnose, specific diseases and to discover specific immunities and sensitivities by means of serums. The discovery of serum reactions in the last decade of the past century led to far-reaching changes in the treatment and prevention of communi- cable diseases, making it possible practically to exterminate some diseases. EXPLORATIONS AND PROJECTS 1 To demonstrate the extent of regeneration in flatworms (planarians), cut several well-fed worms into two, three or four pieces.^ Observe them frequently for two weeks to see the extent to which lost parts are regrown. 2 To ascertain whether members of the class are susceptible to diphtheria, arrange with the school nurse or doctor to have each one given the Schick test. What connection is there between susceptibility and age, sex, previous illnesses, general health, vaccinations in the past? 3 To find out about the diagnostic tests used in safeguarding the health of the residents of your community, visit the health department and gather informa- tion about its activities. QUESTIONS 1 How does a wound heal? 2 How do organisms regenerate lost organs? 3 In what different ways do poisons affect the body? 4 How does the action of habit-forming drugs differ from that of other drugs or poisons? 5 How do antitoxins differ from serum preparations? 6 What is immunity? In what different ways can immunity be acquired or induced ? 7 Why is it that an active immunity is much more lasting than a passive immunity ? 8 What kinds of substances are produced by the body which tend to make it immune to different foreign substances or diseases? 9 Why are the various immunizing serums prepared from several different animals? ^Keep flatworms in shallow glass dishes. Feed fresh liver every day or so. Change water a half-hour after each feeding to remove liver not eaten. 246 UNIT THREE — REVIEW • HOW DO LIVING THINGS KEEP ALIVE? We may survey the world of life from the point of view of man or from that of the ameba. In each case we are left uncertain whether the uniformi- ties or the diversities are more impressive and remarkable. Hundreds of thousands of plants and animals differ enough to be kept clearly apart by the observing. Yet they are enough alike to carry on the same basic proc- esses. Cabbages and kings both grow on proteins, fats and carbohydrates. Both depend upon water and air. Both discharge their wastes into the outer world. Both are beset by various parasites. And both, after death, become the food of a million humbler beings. The naked protoplasm of the ameba is most intimately related to its environment of changing fluid and floating particles. It swallows portions of this environment and assimilates them. Other portions (water, dissolved salts and gases) flow in and out, now faster, now slower, bringing in and taking away. This inward and outward diffusion is determined in part by the nature of the protoplasm and in part by the momentary state of the surroundings. The material condition of living is an interaction of a living unit and the rest of the world; it is a stream of events rather than a static combination of substances at a particular temperature. Living protoplasm is a constant aggression against the environment. It takes from the world a variety of materials which it makes its very own — its very being. The life of an organism consists of building itself up into more and more, and of dodging dangers. The earliest life forms were probably even simpler than the ameba, and they must have been able to transform inorganic compounds into more complex ones by absorbing free energy, as chlorophyl-bearing cells store sunshine energy in carbohydrates. Getting stuff from the surroundings may be as simple as absorbing fluid or gas by osmosis. We may consider the many thousands of plant species as elaborations of protoplasm more and more specialized in the direction of more efficient capture and storage of sunshine. The elaborations establish communication between protoplasm far from the surface and the outside world. The specializations include transportation systems and supporting systems. A large tree will make tons of wood and bark in the course of raising its leaves aloft and sending its roots afield. The living processes, however, are confined to the protoplasmic contents of living cells. Further elaborations are related to tiding-over periods not favorable to metabolism and to resisting the constant threat of destruction by other living things. Essentially, however, the plant is a system of processes and structures through which the environment is selectively taken in and transformed into more plant. It is a system of maintaining a constant stream of materials through the protoplasm. 247 Specializations among animals have developed in the direction of greater mobility and of greater sensitivity to what happens in the environment. This involves a greater consumption of materials in the release of energy, as against the mere accumulation of materials in which sun energy is latent. It involves also more rapid exchange of materials between the interior and the exterior. And, in the larger animals, it involves a remarkable combina- tion of (1) rapid transportation of materials through an "inner ocean"; (2) rapid interchange of materials between the several millions of living cells and this ocean; and (3) a high degree of stability, or homeostasis, in the internal fluids. Specializations in animals are thus related to more complex mechanisms of (1) attacking and taking in outside materials, including oxygen; (2) transforming and distributing these materials to the ultimate consum- ers in the diverse kinds of cells; (3) collecting wastes and by-products of the cells and tissues and discharging or excreting them. Incidental to these processes are means of locomotion and of defense, as well as of attack; specialized sense organs related to getting food and escaping enemies; and, again, means of resisting or surviving periods during which the ordinary life activities cannot be carried on. In the highest animals, birds and mammals, the organism supplies its liv- ing cells a well-protected and stabilized inner environment, a fluid medium at constant temperature and constant acid-alkaline balance. Materials are con- tinually diffusing into and out of the blood at varying rates. Yet the concen- trations of sugar, proteins, fats, mineral salts, oxygen, carbon dioxide, and nitrogenous wastes fluctuate within very narrow limits, regulated by nerves, muscles, and special chemical "messengers", the hormones (see page 304). The circulating blood distributes whatever heat there is throughout the body and so helps the organism to react to its environment as a whole. It is impossible to have a sick foot or liver and not have the whole body affected. Another remarkable specialization of blood is the rapid mobiliza- tion of white corpuscles at points of injury or infection. Other activities are slowed up until damage is repaired. We may describe the specialized structures and processes of plants and animals in terms of the common activities — food-getting, oxidation, excre- tion, and so on. It is necessary to keep constantly in mind, however, that the unity of the organism is not a private possession, so to speak. Each species has, indeed, its characteristic details; it has its own way of dealing with the outside world. But these characteristics are related to other living things, and not merely to the salt water of the ocean or some abstract supply of food. To keep whole and to keep going, a plant or animal must carry on certain processes inside itself; but these involve intimate adjust- ments in dealing with other organisms, both friends and enemies. 248 UNIT FOUR How Do the Parts of an Organism Work Together? 1 How can a living thing tell what materials or organisms are suitable for food? 2 How can an animal or a plant distinguish its enemies from harmless organisms? 3 How perfectly are plants and animals adapted to their various ways of living? 4 How does an animal meet an emergency? 5 How do the nerves carry messages? 6 How do plants and the animals without nerves get along? 7 Can all animals learn from experience? 8 Can plants learn from experience? 9 How do living things adjust themselves to changing conditions? 10 How are the different parts of the body made to do teamwork? Conditions surrounding life are constantly changing. We say that proto- plasm is sensitive, for it responds to changes in the environment. But the responses of protoplasm are also adaptive. They are somehow related to preventing injuries or to counteracting them, or to getting for the organism substances or conditions that help to keep it alive. When food gets into the mouth, for example, a new series of movements and chemical actions is started. If a parasite gets into the body, a special series of actions and proc- esses is started. When one runs, the body temperature rises, but the heating and the chemical changes in the blood are then counteracted or balanced. How does the organism meet the changes around it? Sooner or later, we know, most plants and animals starve or are destroyed, for their responses are not always adequate. Some part just misses, or it breaks down. Mankind is nevertheless impressed by the unity of the organism. An- cient fables try to impress us with the importance of social co-operation by comparing the community to an organism. There is the fable of the various organs that went on strike. The legs remembered that they were carrying the whole weight of the body, but had forgotten that they were being supplied all the nourishment that they could use and were being guided by the eyes and brain. Or the heart complained that it could never take time out, working night and day — forgetting that it could live at all only be- cause the mouth and the stomach and the liver were sticking to their jobs. Such fables are repeated to teach a lesson to ordinary people or to children 249 who may show signs of being dissatisfied. What indeed would happen if every person were to decide for himself when he would work or how much he would do! If each member of the community attempted to mind his own affairs, and disregarded the common welfare, of course we should all suffer. This analogy between society and an organism, incomplete as it is, helps us to appreciate one of the most interesting problems in the field of bio- logical study and thought. How does each organ fit its activity in with the activities of all other organs ? How does the activity of the whole organism, made up of the activities of the several parts, balance, moment by moment, the demands of the outside world? The eye or the ear catches a hint of something stirring. Is it possible prey? Is it a possible enemy? Is it some- thing to move toward, or something to hide from or to flee from ? Of course the animal does not go through this kind of speculation. Indeed, there is no time for that. The muscles and the nerves and the blood-stream do co- operate immediately with the senses and the underlying drive to get or to escape, as the situation may require. Otherwise one would not succeed in capturing his prey or escape his enemy most of the time. Helpful as is the comparison between the individual organism and society, we must not take our fables too literally. For one thing, no society is ever as perfectly organized as any living plant or animal. For another thing, the individuals who make up our societies, in contrast to the units of an organism, are persons — human beings like yourself, each having his own dreams and hopes and purposes and initiative. In human society, as indeed in the best adapted of organisms, there is likely to be almost always a degree of maladjustment among the parts. There is dissatisfaction, there is strife, and, sometimes, there is civil war. Co-operation is of course necessary if most persons are to get the most out of life. But it does not follow that each of us is to take what comes without complaint or protest. There are abuses. Some individuals do carry more than their share of the burden. Some individuals do gather in more than their share of benefits. Even in a living body, a heart may be overworked, or a brain may be undernourished. Sometimes surplus fat accumulates where it does no good. From its very nature, life is a process of change, of constant r