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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

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

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-

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.

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

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.

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

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,

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

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

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

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.

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

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,

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.

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

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

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

!""■

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

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,

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

.-•..- -.-.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,

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.

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?

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

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

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

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.

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.

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.

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

f^.

> CLASS

mm:

Monocotyledons

Dicotyledons

SUB-
CUSS

Peppers Willows Oaks Mallows (20-30 orders) Heaths
Ifr::^^ vTV ^ ^"Y-^ _ Rosales

> 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

SUB-
FAMILY

> GENUS

> SPECIES

THE MAIN SUBDIVISIONS OF THE PLANT WORLD

Chordata Arthropods Mollusca Echinoderms (10-12 phyla)

PHYLUM <

CUSS <

SUB-
CUSS

ORDER <

FAMILY

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)

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.

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

- (.P<jU'^*'^<t*rt:

EXPLORATtONS AND PROJECTS

1 To find a basis for classifying leaves, collect enough leaves of about 25
different plants to supply one of each kind for each pair of workers. Examine the
leaves to find details of form, coloring, margins and arrangements that suggest
resemblances and differences. Select what seems to be the most obvious character
that will serve to divide all the leaves into two groups. Record the names of all
the species placed in each group by this first dichotomy, or "forking", and also the
basis for the separation.

Within each group of leaves, select a second prominent characteristic, and divide
each pile into two more piles according to the new criterion. (It is sometimes possible
on this second sorting to use the same criterion in dividing both piles.) Record the
basis for separation used and list the species in each of the four groups.

Continue subdividing until the leaves left in each pile appear to have enough
in common to be considered as of the same family or "kind".

Check on the adequacy of the criteria and on the consistency of the work by
noting whether all the oak leaves, for example, did get into the same pile, and
all the clover leaves into another single pile; and by noting whether leaves of
different kinds came into the same group.

From the records of this procedure, it is possible to construct a "key" with
which one could quickly identify any of the leaves included.

2 Select a spot where a variety of living plants can be found and picked.
Work in squads or committees, each with definite plants to find and to identify cor-
rectly— algae, fungi, lichens, mosses, liverworts, ferns, horsetails, club mosses, coni-
fers, monocots and dicots. After each committee has verified or checked its collection,
spend the remaining time hunting additional specimens of special interest.

3 Collect from a brook or pond numerous living animals by pulling a dip
net through the clusters of aquatic plants growing there. Bring these living speci-
mens to your laboratory in vessels of water. Place them in shallow glass dishes
for easy observation. Find, sketch and name as many different kinds of animals as
you can. Group them according to outstanding characteristics that you recognize.

QUESTIONS

1 What is the use of naming the various forms of living things?

2 What is the use of classifying the various forms of living things?

3 What must a scheme of sorting do if it is to be of practical value?

4 What are some of the common bases used in grouping plants or animals
for specific purposes?

5 What bases are used for grouping plants or animals in the most widely
accepted scientific scheme of classification ?

6 What is meant by a species?

7 What names are used to designate successive subdivisions, or branches, in
the classification of plants and of animals?

8 Why is it not sufficient to use common names for different kinds of plants
and animals?

CHAPTER 3 • HOW DOES MAN DIFFER

FROM OTHER LIVING THINGS?

1 What is the same in other animals as in ourselves?

2 How can we compare the human body with plants?

3 Are the insides of other animals like our own ?

4 Which animals are least like human beings?

5 Have any animals exactly the same number of bones as we

have ?

6 Do drugs act on other animals as they do on us?

7 Are there any sicknesses that are the same for animals and for

people ?

8 Can animals reason ?

9 Have any animals as much brain as human beings?

10 Some animals have keener hearing or keener smell than we
have: are any of our senses keener than those of other
animals ?

What a piece of work is a man!

how noble in reason! how infinite in faculties!

in form and moving how express and admirable!

in action how like an angel! in apprehension how like a god!

the beauty of the world! the paragon of animalsl— Hamlet, Act II, Scene ii

Each person is one of many billions of natural objects that make up our
world. Each one is in a sense unique: there is no exact duplicate of him
anywhere. Yet, different as one person is from the next, there is the class
"human beings". Certain qualities and characteristics we all have together,
and among all the many classes of objects man stands out distinct.

To ask how man differs from other living things is to recognize that
man in many ways resembles other living things. Is man then like a fish,
or like a flower? What is it that all living things, including man, do?
Which living things are most like man ? What is unique about mankind ?

What Living Things Are Most Like Man?

Basis for Comparison' Our notions of "life" come to us from what we
ourselves do and experience. It is therefore most helpful, in order to get
our bearings, to compare ourselves with those forms of life that resemble
us most — the vertebrates, i.e., animals that have a backbone.

iSee No. 1, p. 59.
45

Like the bodies of other vertebrates, the human body has a brain-box
at the front end of the backbone. Comparing our arms and legs with the
hmbs of four-footed animals shows a remarkable correspondence in detail,
bone for bone^ (see illustration, p. 48). The resemblances extend to the
bones of a bird's wing or the flipper of a whale (see illustration, p. 49).
Muscles, blood vessels, brains and nerves, kidneys, reproductive organs,
sense organs, and digestive organs of all vertebrates have much in common;
and the human systems of organs fit the same general pattern.

Man and Other Mammals' The five classes of vertebrates are repre-
sented by a perch, a frog, a turtle, a turkey, and a squirrel. When we say
that "man is a mammal", we mean that man has all the qualities which
mammals have i7i common. That is not the same as saying that man has
the qualities of all the mammals, which is, of course, not true. Man has
qualities that no other mammal has; every mammal has qualities that no
human being has. Man cannot climb trees like monkeys or squirrels, nor
live on grass like sheep and cows, nor cut through trees with his teeth like
the beaver. But man is able to do what all these and other mammals also
do — in common. He sees with the same kind of eyes, pumps blood with
the same kind of heart, breathes with the same kind of lungs.

All the mammals are alike in having milk-glands, which furnish food
to the suckling infant. They are all "warm-blooded". The newborn indi-
vidual has the same general form as the adult. The skin is more or less
covered with hairs, at least during part of life. In all these ways man is also
a mammal, although he differs from all the other mammals.

Various mammals can get up on their hind legs for longer or shorter
periods. But none of them regularly walk erect, as human beings normally
do. It has been suggested that by walking altogether on their hind legs,
the ancestors of the human race freed their arms and hands for other
activities, and were therefore enabled to develop these organs to higher
skills. It is true, at any rate, that, if we judge from fossil remains, ancient
man was an erect animal, whereas the front legs are used in moving about
on the ground by all the other modern primates (the "first" order of mam-
mals, which includes the apes and monkeys as well as man).

How Does Man Differ from Other Primates?

Hands and Feet The differences between man's front limbs and hind
limbs are related to the erect walk. The front and hind limbs are distinct

^We must not be disturbed by so much attention to dry bones, nor attach to the bones
any strange virtues. Scientists use bones in many of their comparative studies only because
these structures can be more easily preserved and more accurately measured and compared
than other parts.

-See No. 2, p. 60.

Aiiiericaii Museum of Heallli

'THE TRANSPARENT MAN"

How man differs from other animals in reason, in imagination, in apprehension, in
action, we should never discover by comparing organs and tissues and cells. But if
we compare man's life with that of other animals, we may perhaps understand and
appreciate man's resemblance to gods and angels

American >Iuseuni 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.

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

Neanderthal man

^"^^^

Cro-Magnon man

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.

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

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

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

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,

.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

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,

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 (<?) means of passing on experience from generation
to generation. Compare your suggestions with those of others and summarize the
observations in one or more general statements.

4 To study communication in various animals, examine reliable reports or
personal observations of specific instances of communication among domestic or
wild animals of any kind, or between members of two different species. Discuss
the following critically: How can we establish the fact that there has been com-
munication? How do the modes of communication resemble those used by human
beings? How do they differ? How can we explain what happens in such cases?

QUESTIONS

1 In what respects does man resemble other living things? In what respects
does he differ from them?

2 How do the various living processes of the human body compare with
those of other animals? of plants?

3 How do the basic structures of man compare with those of the other
vertebrates ?

4 In what sense are the structures of living organisms adaptive?

5 In what respects is man inferior to other animals? In what respects
superior?

6 How does man differ from other primates in structure? in capacities?

7 What are the outstanding advantages that man has in comparison with
the other primates?

8 What is meant by the statement that man is able to deal with abstract

ideas?

9 What is meant by saying that man is a "creator"?

10 How can we be sure that man is the only animal that makes his dreams
come true?

CHAPTER 4 . HOW DO INDIVIDUALS DIFFER?

1 What brings about differences among people?

2 In what respects are all individuals exactly alike?

3 What characteristics of a person are important to his friends,

fellow workers, neighbors?

4 What characteristics of a human being are important to himself?

5 Why are there different kinds of people in different parts of the

world ?

6 Are the distinctive characteristics of persons inherited by their

children ?

7 Has the human race improved within historic times?

8 Does a large head mean greater intelligence?

Humpty Dumpty, you may recall, was not sure that he would recognize
Alice if he should meet her again since, like other people, she had an eye
on each side of the nose, mouth across face under nose, hair on top of head,
and so on. In some ways all of us are alike. In some ways all the members
of a species or "kind" are quite alike. That is what we mean when we call
cows "cow" and all pine trees "pine tree". Among thousands of distinct
objects we take some to be of "the same sort"; that is, we emphasize simi-
larities and disregard differences.

Individuals of a species differ from each other. Perhaps you have mis-
taken one person for another: the two were so much alike. But then you
discovered your mistake. If all were exactly alike, however, you never could
have discovered your mistake, nor would it have mattered. If you feel
like making a gift to a friend, it does matter that you get it to the right
person.

Each of us wants to be enough like others to be recognized as "belong-
ing", as being "regular". But each of us wants also to be known for him-
self, for what is distinctive, and not be mixed up with a dozen or a hundred
others, or even one other. Each knows himself to be unique. Of what does
this uniqueness consist?

In What Ways Do People Differ?

Physical Differences^ The people whom you know differ from one
another in almost every way that you can observe — height, girth, coloring,
the relative sizes of the various features of the face, the relative length of
arms and legs and trunk. You distinguish your acquaintances not alone by
their general appearance, but also by their voices — which means that the

^See Nos. 1 and 2, p. 74,

vocal cords are of varying proportions, and that tlie insides of their mouths
vary in shape.

One hundred boys in a large high school all had their birthdays in the
same month of the same year. The tallest boy was twelve or thirteen inches
taller than the shortest. The heaviest weighed nearly twice as much as the
lightest. These boys differed from one another in at least two characters —
height and weight. Two of the boys might have been exactly the same in
one respect, and quite different in the other.

If boys or girls, arranged in a row according to height, should all sit
down on benches of the same height, some would then appear out of place.
That is, people of the same height need not have trunks of the same length
or legs of the same length.

Our acquaintances differ in the shapes of their eyes and in the colors of
their eyes, which range from pale gray to almost black. Their hair ranges
in color from pale yellow to black. Some have hair of various shades of red
to brown that do not quite fit into this series from lightest to darkest. Some

LONG AND SHORT; THICK AND THIN

There is great variation in the shapes of people having the same height, and greal
variation in the heights of people having the same weight

72 —
68 —
64 —
60 -t

15 20

23
1

30 35 40

50 55 60 65 70 75 80 85 90 95 100

VARIATION IN STATURE

When 100 boys of the same age stood in a row in the order of height, the tops of
their heads formed a line like this row of dots. The middle part of the line was nearly
horizontal; that is, there were several boys of almost exactly the same height

have fine, silky hair; the hair of others is coarse. The hair of some is
straight; that of others is wavy, curly or kinky. Rarely do we find two indi-
viduals with exactly "the same kind" of nose or mouth or ears or chin or
cheeks or lips.

Chemical Differences Skin-colors distinguish the large groups we call
"races" — Caucasian, Mongolian, Negro, redskin, and so on. Color differ-
ences usually indicate chemical differences. There are, in fact, several dis-
tinct pigments in the human skin, hair and iris, and in corresponding parts
of other animals. And these pigments are present in varying proportions.
Even within any one "race" there are wide variations in the colorings, as
well as in the intensity of pigmentation.

A person who has had the measles is usually unable to get that disease
again: he is said to be immune. This change does not show in one's appear-
ance, but is due apparently to some chemical alteration in the blood or in
other juices of the body. People differ also in their original immunity, or
resistance to disease. Thus, when two individuals are exposed to typhoid
fever, one may remain unaffected while the other gets sick. On the other
hand, one who is immune to typhoid may succumb to tuberculosis. Such
facts indicate chemical differences among people.

Each of us knows some individual who suffers from asthma or hay

VARIATION IN FACIAL FEATURES

Whether we consider the form of any feature, such as the nose, mouth or chin, or
the color of hair or eyes, or any other trait, we find endless variations in countless
details

I'ress Association

RECOGNIZING A PERSON BY HIS ODOR

Here we make practical use of the fact that each individual differs from others chemi-
cally. We recognize persons by their appearance or by their voices or even by the
"style" of their art or workmanship, but it takes a dog to smell a particular indi-
vidual's "blood"

fever. Other members of the same family are immune. Why is it that "one
man's meat is another man's poison"? In general, individuals appear to
differ chemically as well as physically.

Organic Differences Two boys who appear to be equally well de-

Brewster Aeronautical Corporation

PHYSICAL CHARACTERISTICS AND SPECIAL PERFORMANCE

From among many different kinds of persons, we pick those having special qualities
for carrying out special tasks. Sometimes we consider tallness or weight. Sometimes
agility is more important, or endurance, or dexterity, or a quick eye

veloped physically set out on a hike, but after an hour one of them has to
stop for a rest. Perhaps the two can do about the same amount of work
in the course of a day, but one of them has to take his task in short units.
Again, of two girls of the same height, one is decidedly slender; yet she

appears to have more endurance. We are familiar with differences in
muscular capacity, as well as in ability to acquire various skills: one does
better in basketball or hockey; another does better in tennis or in marks-
manship.

In most of our work, games, sports and hobbies, we are constantly
aware of differences among people. We select members for our teams, try-
ing to get the best players, or the potentially best players. Then we assign
each one to the particular task for which he is best fitted. Whatever quali-
ties we consider of value, however, we seldom think of them as chemical
and physical peculiarities in the materials and organs of people.

What Is Normal?

The One and the Many Twenty thousand people attend a great ball
game. The players are carefully picked and trained. But nobody cares
who the spectators are — except each one himself. For certain purposes, we
are all alike. We are so many million mouths to feed, or so many custom-
ers, or so many passengers carried so many miles. Particular persons appear
to be overlooked. In most cases, when something happens to one of these,
nobody cares whether it happens to this one or to another — except the par-
ticular person himself and his immediate relatives and friends. For himself
each one is somebody in particular. Each one feels himself to be unique:
he wants to be himself and he can admit no substitute.

There seems to be a contradiction between wanting to be like every-
body else and wanting to be different. If we were all actually alike in every
respect, problems of personality would never arise. What you consider your
self probably comes into being only as you discover that you are separate
from and different from other persons. Yet you do not want to be so dif-
ferent as to be classed in-human, or even as super-human.

In everyday life we accept variation in a hundred details, and we make
use of the differences — in selecting our friends, our public officers or our
favorite artists and authors. But how much variation can we accept in
others? or in ourselves? How do we measure degrees of variation? What
could we use as a standard?

The Average and the Normal We ordinarily judge other people by
ourselves — by how far they agree with us in appearance, in behavior, in
speech, in ideas. Yet hardly anybody is so pleased with himself as to sug-
gest that he should be considered the standard. We commonly speak of
the "average" as if that were a clearly understood standard. Almost anyone
is "average" in most respects. Yet we would hardly take any individual at
random as the standard by which to judge the rest of us.

We look for a standard by comparing large numbers of individuals. A

Margaret Bourke-White

INTERCHANGEABLE UNITS

However different these men and women appear, any one will do as a "medical stu-
dent at the University of Tiflis" in Transcaucasia

common way of setting up norms (from a Latin word, norma, meaning
"a rule") is by getting the "average" of a large number of measurements or
counts. This number is obtained by adding all the measurements and then
dividing the sum by the number of individuals measured. The average is
a useful basis for comparison: you can say, for example, that Marion is taller
or shorter than the average.

The average, however, is not necessarily an absolute standard. We see
this when we consider characteristics that we can count. Thus, if we took
the average number of eyes in a population, we should find it to be about
1.995; yet the normal number of eyes is 2.0.

When we are first impressed with the fact of "variation" we are likely
to assume that it is haphazard, that each individual may be "different" in
almost any way at all. But about a hundred years ago (1845) a Belgian
mathematician, after measuring and recording the dimensions of thousands
of people, came to the conclusion that there is a certain regularity, or order-
liness, in these variations. Lambert Adolphe Quetelet (1796-1874) showed
that variation in stature, for example, could be represented by means of a
simple mathematical formula (see illustration on page 69). This idea is
pictured also in the diagram about the line of boys of the same height (see
page 63).

Normal Variation' No matter what we measure about human beings,
we find the same regularity. And we observe the same regularity if we
measure any characters of plants and animals — number of stamens in roses,
for example, yield of milk in cows, and so on. Every group of living things
consists of individuals that differ from each other: each one is "irregular"
or unique in his own way: Yet there is a regularity in their variations.

United States Department of Agriculture

AVERAGES ARE NOT ALWAYS MEANINGFUL

It is true that the average weight of the pigs in this picture is 41.6 pounds. But that
tells us nothing that is characteristic of the group or of any individual. The "average"
figure gives no hint of the fact that the 350-pound mother weighs about 14 times
as much as all the little pigs together — each weighing about 3 pounds

iSee No. 3, p. 75.
68

shells

15 rays 16 rays 17 rays 18 rays 19 rays

American Museum of Natural History

Number per 1000
150

150

145
men

110

100

90
men

90
80
70
60

57-
men

50
40

34 _

men

16 20

men

,10

ill!

■

R I

■

"IIS

ill

I i » i « <

: s I s

IS IS

7 "

men

il ill I

:f1 1 In

60 62 64 66 68 70 72
Height in inches

100

men

9
men

men

THE NORMAL DISTRIBUTION OF VARIATIONS

In any large sample of natural objects the variations fall into a regular pattern.
More than half the men in our army are within two inches of the "average height".
Only about a tenth are three inches taller than the average, and about the same
number are three inches shorter. The number in each stature-group declines as we
assemble groups of taller and taller or shorter and shorter men. If we arrange scal-
lops according to the number of ridges, or rays, or if we arrange earthworms accord-
ing to the number of rings, we find similar "curves of distribution"

This fact of regularity furnishes a basis for a new kind of norm. It is
not enough to say that one is thicker or thinner than the "average". We
want to know how much thicker or thinner, or in what part of the range
of variation a particular individual stands, or how near to one or the other
extreme.

Human beings probably differ from one another in more ways than the
individuals of any other species. At the same time, each of us is sensitive
about being "different". Many of us feel a constant struggle between the
desire to be distinctive, to stand out on our own, and the fear of being dif-
ferent. This is because our population is itself a mixture of many races and
groups that are but slowly learning to live with strangers. The most uni-
form objects of the same kind are the products of modern machinery — like

Simon M. Schwartz

AVERAGES AND DIFFERENCES

The eight Jones boys stood in a row for a family photograph in 1898, and again in
the some order in 1940. The average height or weight means nothing for the boys
in the first picture. Although no two are exactly alike on the second exposure, not
one is very far from the average

screws or milk bottles. We have to accept the fact that for human beings
variation is itself normal.

When Are Individual Differences important?

The Individual and His Individuality Human beings are not satisfied
to exist merely as separate individuals, like the separate ants in an anthill.
Each of us wants to be recognized as a distinct person, with his own name,
and never mistaken for anybody else. Each of us wants a chance to live
as a unique person, to be his own self. It is no doubt true that one's dis-
tinctiveness comes out of the particular combination of his many traits. It
is true that we sometimes wish that we had a little more of this or a little
less of that. But in the end we feel that the selfness is the important thing.

We get definite information about every detail by comparing, weighing
and measuring. But since we most frequently use numbers in trade and
finance, many of us come to think that more or le'is of anything must also
mean better or worse, or of greater or less worth. We are influenced also
by the fact that in many of our everyday activities and relationships quan-
tity is of great importance — running faster, for example, or lifting a greater
weight. Yet the distinctive quality is probably the "whole self". The varia-
tions in detail have to be accepted — both in ourselves and in others — as
perfectly "normal", or typical, for the species. Variation is not a technical
term with some mysterious meaning, but a direct description of a general
fact that we can observe all around us.

Equality and Individuality In our kind of democracy we hear a great
deal about "equality". This term suggests something that we feel is im-
portant. Yet it often confuses us, for we know that actually we are un-
equal: we differ in regard to every trait that we take the trouble to measure.
On the other hand, being different does not necessarily make one "better"
or "worse!'. The best mathematician may be poor in languages. The best
orator may be afraid of the dark. The great musician may be color-blind.
The great financier may be a poor companion at home or among friends.

We consider each human being important for himself, not for any
special talent or virtue he may have. We consider it necessary that each
person have the opportunity to live the kind of life that is most satisfying
to himself. This means, of course, that all others must have equal oppor-
tunity. It is in this sense, then, that we are all equal. However much we
differ physically and intellectually, we are equal as members of the family
or of the nation ; we are equal as persons or as members of a religious group.

If we were all actually equal in every way, the question of equal oppor-
tunity or of democracy would have no meaning at all. Equality of oppor-
tunity, in the sense required by democracy, is important precisely because

we are not identical in our needs. And it means not that we all have a
chance to do exactly the same things in the same way, but that we have
equal chances to be different — for one person to be a vegetarian, if he likes,
and for another to eat meat.

Since human beings normally live with others, each one must make some
concession to those others in various ways. We have to observe the rules
of the road and the traffic signals. We have to hold back at mealtime, even
if hungry, out of consideration for the group. We have to accept "regi-
mentation" as to the exact time for catching trains or boats or for listening
to a radio broadcast. This is the price we have to pay for the satisfactions
we get from living with other individualities.

In every kind of civilization the individual is tolerated if he conforms
to the rule. Making the most of himself depends upon the kind of civiliza-
tion in which he lives, on what kinds of freedom and what kinds of "equal-
ity" there are. We value democracy because it is a kind of relationship in
which the individual can speak up to suggest changes in customs and in
laws or in architecture and education. Such freedom is "equal" for all: it
rests on the regard we feel for one another rather than on the privileges of
power or standing. For the "right" to speak up and criticize and suggest
improvements obliges each one to consider what the others have to say.

In such a civilization, invention and initiative by countless individuals
constantly adjust what we have to what we want or need. It is not neces-
sary to wait for a great genius or a dictator or a "revolution" to make a
fresh start after conditions have become intolerable. Those who consider
individuality important must ask about their civilization. What are the
rules? Who makes the rules .^^ How can they be revised? What are they
supposed to accomplish? How many of us thrive under these rules, how
many of us suffer?

Is There Individuality among Other Living Things? •

No Two Alike Each of us knows scores of persons apart, even if we
do not know all by name. A shepherd looking after 150 or 200 sheep is
usually able to know each one, and he can tell immediately that some
particular one is missing. His charges may behave like sheep, but each has
about him something distinctive.

Among several peas taken out of the same pod, we can easily find differ-
ences in shape or in the coloring or in the wrinkles of the skin. If we weigh
or measure each pea in a pint of peas, we find differences. If we arrange
them according to size, we find nearly half close to the average size, very
few of the largest, very few of the smallest, and the rest distributed regu-
larly on both sides of the middle measure (see illustration, p. 69).

Plain arch

Tented arch

Loop

Plain whorl Central pocket loop

FINGERPRINTS AS DISTINCTIVE AS FACES

Double loop

Federal Bureau of Investigation
Accidental

Details so small as ordinarily to escape notice show such variations that they serve
as a most dependable means of identifying particular individuals — whether they are
criminals wanted by the police or kidnaped businessmen wanted by their families

Two fish may be of exactly the same size, or two leaves on a tree of the
same length, just as a hundred girls may all weigh exactly ninety-nine
pounds. Yet each is unique. For however much alike they may be in two
or three or ten characteristics, they still differ in vastly more details. We are
able to distinguish one from the others, in spite of many resemblances.

The fine skin ridges on the tips of our thumbs and fingers are so distinct
that they are generally used for reliable identification of individuals (see
illustration above). We do not, of course, recognize our friends by these
unique marks, nor do we take any special pride in our own unique patterns.
That is to say, being unique is not necessarily a source either of satisfaction
or of chagrin: in many respects it just doesn't matter.

Every living thing is thus a unique combination of particular characters
or qualities. Among human beings, however, the individual is conscious of
himself as a person. We consider the uniqueness of the human individual
important, whereas we do not consider the uniqueness to be important to
the individual oyster or fly, for example. The unique combination might
be— and actually is— altered without affecting what we value in personality
or individuality.

In Brief

Each individual differs from other members of his group in physical
characteristics, in chemical make-up, and in many organic capacities.

Each person builds up his own picture of what is normal, or standard,
with respect to the numerous details of life.

A common way of finding norms for groups is to determine the average
for each of several sets of measurements.

The individuality of any living thing lies in its unique combination of
many varying factors.

Although each individual is unique, several unique things resemble each
other sufficiently to let us deal with them as of the "same" species or kind.

Each person apparently wishes to be like others of his group, yet distinct
enough to be recognized as an individual.

Standardized ways of doing things under different circumstances repre-
sent the price we pay for the satisfactions and benefits we derive from liv-
ing with others.

EXPLORATIONS AND PROJECTS

1 To find the variations among the individuals of a group, note the ways in
which the various members of the class differ from one another. List the kinds of
variations found. Do the same for the individuals in a litter of mammals, or a
brood of chicks, or the leaves from a given tree, or some other group of "the
same kind".

2 To find the extent to which the members of a group vary in stature:
Line members up in order of height and note (a) the region in which there

are the greatest numbers having almost the same height; {h) the relative numbers
of very tall, of very short, and of medium height.

To find the middle height, or median height, of the group, count from either
end, to locate the middle person. The height of this person (or the average height
of the two at the middle, if the group happens to be even-numbered) is the
■median. This measurement is also called the 50-percentile, as half the group are
taller and half are shorter. By counting individuals either way from the median,
pick out the persons whose heights may be considered 25-percentile and the
75-percentile. Those taller than the 75-percentile are considered in the upper
quartile, and those shorter than the 25-percentile are considered in the lower quar-
tile, so far as height is concerned. Compare the median with the calculated
average for the group.

To find the range of variation, determine the difference between the shortest
and tallest members, or the total variation in height of the class. Find how the
range of the lower half compares with that of the upper half. Find how the
range of each of the four quarters compares with that of the others.

3 To make a graphic representation on the blackboard of the "frequency
distribution" of the statures for the members of a group, enter a bar or stroke for
each individual corresponding to his height-class. Plot along the horizontal base
line spaces about 3 inches wide, say, for each inch of height (60-61, 61-62, etc.).
For each person having each specified height, mark off an inch space above the
base line.

In each column the spaces marked off correspond to numbers of individuals.
The diagram shows that there are more of one stature than of another. It enables
us to determine at a glance (a) what statures are most frequent or least frequent;
(b) the median height; (c) the proportion of individuals having nearly median
height; (d) the extreme range of statures in the group; (e) what the distribution
is among the four quarters.

QUESTIONS

1 In what ways do individuals of your acquaintance resemble one another .f'
differ from one another?

2 How can we measure the differences or resemblances among individuals.''

3 In what ways are differences important to us personally.'^

4 How do we get our ideas as to what is normal for people.?

5 Wherein does the individuality of a particular person consist .f"

6 What are the sources of the differences among individuals .f*

7 In what kinds of society have the individuals who differ widely from the
norm greatest opportunity to use these differences to the full? In what kinds of
society have such individuals least opportunity?

8 In what ways is it an advantage to a group to have people differ from
one another? a disadvantage?

9 What evidence would be necessary to prove that some other race is su-
perior to our own?

10 What evidence would you consider sufficient to prove that our race is
superior to some other?

UNIT ONE — REVIEW • WHAT IS LIFE?

Since plants and animals come so close to our lives in a variety of ways, it
is necessary for us to know^ the different kinds apart, especially to know
which are beneficial and which are destructive. We have to understand
how they act and how we can turn them to our purposes. But children and
primitive people everywhere always interpret what plants and animals do
— as they interpret other natural happenings — as if the objects were influ-
enced by human likes and dislikes, or as if the objects were caused to act
by outside beings like ourselves. They attribute to plants and animals — and
nonliving things — the kinds of feelings which we human beings experience,
such as fear, hunger, affection, anger, jealousy. Healdi and sickness, har-
vest and blight, sunrise and thunder, drought and flood, they explain as the
work of spirits. These invisible fairies and imps push and pull things about;
they get into and out of natural objects. They act just as we do, and for
the same kinds of reasons.

Now it is natural and reasonable for us not only to interpret whatever
goes on in relation to our own interests, but also to judge events according
to ourselves. For we have no way of judging — at least at first — except by our
own doings and feelings. But while that kind of explaining is easy, and for
a time satisfactory, it leaves us in doubt; it leaves us worried and anxious.
This is because those spirits cannot be relied upon; they are capricious. If
all goes well, it is comfortable to feel that the friendly spirits are in control.
But if things go wrong — as they often do — we are not sure how we can
manage the unfriendly spirits. Men have long been searching for under-
standings and interpretations of life that would enable us to make things
happen our way with greater certainty.

People have improved their understanding by enlarging their horizons.
The more plants and animals we are able to observe and compare, the
broader is our outlook. Comparing many kinds from different regions en-
ables us to sort them more satisfactorily and to communicate with one an-
other about them on a world-wide scale. Such comparing reveals what
plants and animals have in common with us, but also what distinguishes
them from us. We learn that living things, including ourselves, have much
in common with nonliving things; and that enables us to examine our
problems with less emotion and with clearer vision. We try to find out
what actually makes one cow yield more milk than another without blam-
ing the difference upon the beliefs of the owners or upon the day of the
week on which the cow or owners were born.

We discover many objects that are very different from us and yet cer-
tainly "living". We discover in all living things a slimy protoplasm that

uses food and grows and that responds to external changes in adaptive ways.
We discover that plants and animals undergo regular changes, sometimes
reproduce themselves, and unless in the meantime destroyed, complete a
pattern of activities, or die. The combination of characteristics which dis-
tinguishes the living from the nonliving joins us human beings to the grass
of the field and the birds and the beasts and the very fleas that infest the
world. But beyond all that he shares with animals and plants, man has a
hand and a mind with which he can reconstruct his world and make his
dreams come true.

Finally, we think of ourselves as unique individuals, recognizing that
being "different" is inseparable from being "alive". And so we come to
accept ourselves and all others as equal — but different — members of that
unique human species, just people, able to share in the great adventure of
raising ourselves more and more above the beast.

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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?

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

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.

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.

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

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— 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.

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.

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<seen in
wilted plants. By means of appropriate solutions and indicators we can demonstrate
the passing of dissolved food materials and gases into and out of such "cells"

all. Cell walls and similar substances are therefore called "semipermeable".
Osmosis appears to be selective. As a result of the difference in the be-
havior of dissolved substances, osmosis will be greater in one direction than
in the opposite; and cells exposed to the same material surroundings may
not be affected in the same way.

We can imitate the passage of materials into and out of cells by making
model cells of small widemouthed glass bottles, each closed with a bladder
membrane (see illustration above). By using appropriate solutions and indi-
cators, we can demonstrate the movement of dissolved food materials and
dissolved gases into and out of these "model cells".

Osmosis and Turgor^ When a cell has absorbed water so that the mem-
brane is stretched, the cell is said to be turgid — that is, swollen. Turgid cells
in the tissue of a plant or animal make the structure stiff, whereas wilted
tissues are flabby — just as an empty meal sack is limp, whereas a full sack
will stand on its own bottom. Similarly, turgid tissues crack through easily,
as we see in the brittleness of celery or in the crispness of a juicy sausage. We

If we nearly split off a thin layer
of a crisp rhubarb stalk and then
place it back, it no longer reaches
the full length. The shrinkage is
due to the loss of water. The
epidermal tissues are normally
turgid, but when water evapo-
rates from the cut surfaces each
cell collapses somewhat

TURGIDITY AS SUPPORT

^See No. 8, p. 95.
88

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OSMOSIS AND TURGIDITY

The gardener finds it easier to cut weeds with his hoe in the early morning, when
the plants are turgid and brittle. Farmers plan to use the rotary hoe on young grow-
ing corn after the plants have wilted slightly, as otherwise the fingers of the hoe
would break the plants

place the ends of celery stalks and of other leafy and root vegetables in cold
water, and store them in a cool place, to keep them from wilting — that is,
to retain their crispness.

The turgidity of plant tissue holds stems and leaves up, even where there
is little mechanical or fibrous tissue present. This is especially noticeable in
the spring, when rather tender tissues push through the ground in their
rapid growth. At the same time, these turgid stalks are easily broken, as
every farmer and gardener knows (see illustration above).

How Do Living Things Adjusf Themselves to Changes in Water Supply?

Adjustments The dryness or wetness of the environment varies in the
course of the day, from day to day, from season to season, and from place
to place. Marine organisms living along the shore experience alternate dry-
ness and wetness with each change in the tide. Only plants and animals
that live continually in deep water escape the seasonal variation in their
environment. Land plants and animals that are exposed to drying condi-
tions have, as a rule, coverings that prevent the rapid loss of water. Our own
skin separates the marine-like interiors from dry and variable conditions
outside.

Section of the skin
of a lizard

QLx^J^UijOc^"

Section of the skin
of a salamander

MEMBRANES AND SCALES

The moist outer covering of a salamander is a living membrane which loses water
readily. The dry scaly covering of a lizard is really dead tissue which is relatively
impervious to water. We can see how quickly a frog loses water by balancing one
on a scale in a warm, dry room for only a few minutes

BLOWOUT IN INDIANA DUNES

Most living things find the extreme heat and dryness of a blowout in the dunes in-
tolerable. In brilliant sunshine the sand catches and reflects the light until a person
walking through the blowout feels as if he were in a reflector oven. Dune grasses
and some other species eventually get a foothold even in this desiccated environment

Stem '^ Separation Stalk
tissue layer tissue

THE FALL OF A LEAF

Plants that regularly drop their leaves in the autumn form a special layer of cells in
the stalk of each leaf, and sometimes of each leaflet of a compound leaf. These
cork cells are thin-wailed and turgid. Their contents break down into a mucilaginous
mass, which dries up. A slight movement is now sufficient to break the fibrovascular
bundle at this point, and as the leaf is removed the exposed surface becomes a
self-healing scar

Organisms withstand heat and dryness very unequally. Man, for in-
stance, dries out rather quickly in the hot, dry desert, although the evapora-
tion from the skin and lungs lowers the body temperature and protects the
protoplasm against becoming too hot. But the lost water has to be replaced,
or the protoplasm will suffer other injury. During the Second World War
many men who were saved from torpedoed ships, or from planes forced
down on the ocean, later died for want of water. This was an urgent prob-
lem, and several lines of research were followed to solve it. Before any
practicable means had been worked out for making sea water fit to drink,
Gifford Pinchot (1865- ) sought for fresh water in the life of the sea.
Pinchot, who started the conservation movement, showed by experiments
that the juice squeezed from the flesh of salt-water fish could serve men as
drink in place of fresh water, as the raw flesh may serve as food. As a
result of these experiments, airplane rafts and steamship lifeboats were
equipped with fishing tackle and instructions for living on what the ocean
yields.

i. Expanded Contracted „ , , .

CONTRACTION IN THE SEA ANEMONE

When disturbed, the animal greatly reduces its surface by repeatedly contracting
until it resembles a wart on a rock

Seasonal Change As the autumn advances, the soil becomes drier as
well as cooler. Fewer root hairs are now formed. The movement of water
out of the leaves is reduced. Evaporation continues, however, so long as
there is water in the cells. If the roots do not absorb enough to compensate
for the loss of water, the live cells of the plant must suffer injury. The leaf
cells are the first to be affected. The shedding of leaves seems to be related
to the water factor, as well as to the temperature factor, which we usually
associate with the change of seasons. This has been determined experi-
mentally. The loss of the leaves prevents the complete drying up of the
plant, and it also prevents the freezing of live cells (see illustration, p. 91).
We may properly think of the fall of leaves as adaptive.

Life in a Tide Pool Organisms living along the seashore withstand
drying when exposed to air and beating by waves when submerged. The
seaweeds are tough and gelatinous, and often ribbonlike, offering little re-
sistance to the water currents. Sea anemones, although consisting largely of
water, have a firm outer membrane. Many of the animals secrete hard
shells. These protect the soft bodies against the rushing water, enemies and
drying. The mussels and barnacles close their shells while the tide is out.
Clams draw in their siphons, sea anemones draw in their waving tentacles,
snails close their horny trap doors, tube worms cover their burrows, and
crabs move with the water or remain in pools left by the receding tide. All
these water animals of this most exciting of environments lie low until the
next tide surrounds them with water, permitting them to resume their
search for food (see illustration, p. 579).

In Brief

Water, air, and a suitable temperature are essential conditions for the
germination of seeds. *

The chemical changes that are continuously going on in living proto-
plasm can take place only when it is in a fluid state.

The energy of protoplasm is derived from the oxidation of food mate-
rials within living cells.

Using oxygen and liberating heat are characteristic of nearly all living
things.

Living cells continually exchange materials with the fluid medium
which surrounds them, by osmosis, or the diffusion of fluid substances
through a membrane.

In larger organisms dissolved substances reach the living cells through
the medium of water.

Water filling the cells and tissues of plants stretches the outer mem-
branes and furnishes mechanical support.

Organisms exposed to drying conditions often have protective coverings
which prevent desiccation.

The shedding of leaves may be considered an adjustment to seasonal
variation in water supply.

Living things show many adaptations to the extreme variations in the
moisture, light and heat of their environment.

EXPLORATIONS AND PROJECTS

1 To find whether carbon dioxide is discharged when ordinary fuel burns,
collect gases, given off by the flame of a lighted match or a candle, by holding over
the flame an inverted clean and dry widemouthed bottle. Test the contents of the
bottle for carbon dioxide and also the air in a similar bottle that has not been held
over a flame/ Compare the reactions in the two cases and draw conclusions.

Incidentally, this procedure has also furnished information on the liberation
of water during oxidation; for, starting with a dry vessel, we could see moisture
condensed inside the bottle held above the flame. This can be checked by holding
a similar bottle over a match or candle, not lighted, under the same conditions.

2 To see in what ways the oxidation of ordinary food substances is like that
of common fuel, heat some sugar, starch, bread, butter, olive oil, lard, or other
food material in an evaporating dish until it bursts into flame; remove the burner.
In each case, ascertain whether water and carbon dioxide are discharged. In what

^A common test for carbon dioxide is a solution of slaked lime, "limewater", which turns
milky when carbon dioxide comes in contact with it. In this experiment pour a little lime-
water into the jar and shake up to mix with the air.

Ink

solution

Inverted jar
for light gas

Porous cup in
position (a)

Porous cup in
position (b)

Erect jar for

I heavy gas

ways IS oxidation of food substances like the oxidation of ordinary fuel? In what
ways is oxidation of food substances different from oxidation of orduiary fuel?

3 To show that slow oxidation liberates heat, place a tablespoon of dry potas-
sium permanganate on a folded paper towel in a shallow pan above sand or
asbestos. To a crater in the top of the permanganate add a teaspoon of glycerm.
Cover with another folded paper towel (to prevent too rapid loss of heat). Rest pan
on asbestos pad. Leave undisturbed until there is no doubt as to whether (a) heat
is given oflf, or (b) oxidation is taking place. Record results and conclusion.

4 To find whether germinating seeds give out carbon dioxide, place about
two tablespoons of soaked seeds in a sealed flask. Let stand overnight in a warm
place. On the following day replace the solid stopper with a two-hole stopper
carrying a thistle tube and a bent glass tube leading to a test tube containing Hme-
water. Pass the gas from the flask through limewater by pouring water into the
thistle tube. Bubble the air from a similar flask containing dry seeds through
another test tube of Hmewater. Compare results and note conclusions.

5 * To find out whether the air we exhale contains more carbon dioxide than
the air we inhale (that in the room), inhale and exhale through two separate
bottles of limewater several times. Compare results and note conclusions.

6 To demonstrate the diffusion of gases, set up an apparatus as in the dia-
gram. Fill an inverted quart jar with a light gas, such as hydrogen or illuminat-
ing gas, and place it over the porous cup in the position (a). Similarly, fill an up-
right jar with carbon dioxide and place it around the porous cup as shown in
position (b). Compare what happens in the ink-solution indicator as you test
different gases, and account for the results.

7 To demonstrate osmosis: Temporarily seal the small end of a thistle tube
and fill the bulb with granulated sugar. Pour as much ink or colored water as pos-
sible on the sugar in the bulb. Tie a moist bladder or sausage-casing membrane
firmly in place over the large end with about twenty turns of thread. Invert the
thistle tube, attach a long glass tube to the open end with a piece of rubber tubing,
and place bulb in a jar of water.

Hollow out the thick end of a large carrot (use apple-corer if convenient) and
partially fill the space with sugar and ink; seal a glass tube in the open end of the
carrot with a one-hole rubber stopper. Keep top of carrot dry during this sealing
process. The outside may be reinforced by wrapping with friction tape; the top
may be sealed with candle wax or paraffin. Submerge the carrot in a jar of water.

Record results in both cases and account for them.

8 To show how water can furnish mechanical support by filling the cells
and tissue and stretching the outer membranes:

Prepare two widemouthed bottles to represent cells, as shown in illustration
on page 88; fill one with a concentrated salt or sugar solution and the other with
pure water; tie an "osmotic" membrane securely over the top of each; submerge
the one containing the sugar or salt in a pan of water and the other in a pan of
water containing salt or sugar solution. Compare the behavior of the two mem-
branes and show wherein one of the model cells represents the condition found in
the cells of wilted celery, the other in fresh celery.

Cut fresh rhubarb stalks squarely at one end; then peel down a narrow strip
nearly the full length from the cut end; place the peeled portion back along the
cut surface and note that the two no longer match. Split dandelion stems length-
wise; note how they curl. Place some of the split stems in fresh water and others
in salt water. Record results in each case and explain how they came about.

Cut four thin slices each of carrot, turnip and potato. Place one slice of each in
fresh water, one in a salt solution, one in a saturated sugar solution, and one in air.
The following day note the differences among the slices and account for them.

, Water one pot of rapidly growing seedlings (corn, oats, or wheat) with a
saturated salt solution and another with tap water. After a few days compare the
behavior of the plants in the two pots and account for the differences.

QUESTIONS

1 What conditions are essential for the germination of seeds?

2 In what respects are the chemical processes which go on inside a living
organism like those which take place outside .f' In what respects are they different.''

3 How is the energy of protoplasm derived?

4 What kinds of energy are released by protoplasm?

5 In what respects is osmosis like the passing of water through a sieve? In
what respects is it different?

6 What relation is there between temperature and the rate of diffusion?

7 What conditions will produce turgidity in living tissues?

8 In what ways do living things adjust themselves to changes in water sup-
ply? What conditions produce the most severe changes in water supply?

CHAPTER 6 • WHAT IS THE RELATION OF FOOD TO LIFE?

1 Must all living things have food ?

2 Do all animals have mouths?

3 How do plants get food?

4 How is it that some animals eat animals and others eat plants ?

5 Do any plants eat animals?

6 Is the food of one organism suitable for other organisms ?

7 Can we change the nature of an animal by feeding it different

foods ?

8 What do hibernating animals use for food?

9 Do all people have to use the same foods ?

10 What do different kinds of food do for a living thing ?

We know that we must have food to keep alive, but the connection be-
tween feeding and keeping alive is not always clear. We assume that all
other organisms must also have food, although we do not recall ever seemg
a plant feed. Many of us think that feeding is the same as eating. Yet the
plants, and many species of animals too, have no mouths; and they must
somehow take food. Is the water that a plant soaks up through its roots
food for the plant ? Or is the fertilizer which we place in the ground ?

Since it is the protoplasm in any organism that is alive, it may help to
think of food in its relation to the peculiarities and activities of protoplasm.
What has being alive to do with food ? What has food to do with being
alive ?

How Does Food Act in Living Protoplasm?

Chemical Needs From a dozen to twenty or more different chemical
elements are present in the tissues of various species of plants and animals
(see illustration opposite). Most of these elements are found in practically
all species. But that does not necessarily mean that they are all involved in
living. Nor does it mean that we or other species could live on a supply of
these elements. For protoplasm is an active process in which various mate-
rials are involved, not merely a collection of those materials. Indeed, if it
were possible to arrange such a collection of "elements" anywhere, no
plant or animal could live in it. We know that food is the source of these
elements in living bodies. But we have to ask how the various foods are
related to the doings of protoplasm.

Protoplasm-Builders We may think of protoplasm as consisting basi-
cally of nitrogen-containing compounds called proteins, suspended in water,
along with various salts and other substances, some of them dissolved m the
water. The growth of protoplasm depends essentially on a supply of pro-

COMPOSITION OF HUMAN BODY

Chemically, the human body (like all other living things, for that matter) consists
largely of oxygen, carbon, hydrogen and nitrogen. The proportions of the other
elements vary somewhat with the kind of plant or animal, but there are always sev-
eral, and certain of these have always been found indispensable whenever we have
taken the trouble to experiment with them

teins, of which there are many different kinds. They all have this in com-
mon, however, that they consist of the elements carbon, hydrogen, oxygen,
nitrogen and, in addition, either sulfur or phosphorus. Chemists have
shown that proteins consist of combinations of simpler nitrogenous com-
pounds called amino-acids. Different proteins have different combinations
of amino-acids.

Proteins are thus present in almost every part of every animal or plant.
That is not to say that all animal and plant materials are suitable as food.
In many cases the proportion of protein is very low. In other cases addi-
tional substances present render the materials unsuitable for food, or at least
for human food. It means only that protein is necessary for the making of
more protoplasm.

In our common foods the proteins are represented by albumen, or white-
of-egg; casein, the curd formed when milk sours; and gluten, the pasty
substance in wheat flour or bread. Similar nitrogen-containing substances
are present in the muscle (flesh) cells of many animals. All seeds contain
some proteins, some kinds in rather large proportions — as peas, beans, pea-
nuts, lentils and others of the bean family.

Protoplasm Action' In active protoplasm, as we have seen, the energy
comes from the oxidation of "fuel". Protein itself oxidizes in living cells,
and yields energy. In the process it is of course destroyed, breaking up into
simpler nitrogen compounds, water and carbon dioxide. Other fuels, which

iSee No. 1, p. 111.
97

are formed in practically all protoplasm, are represented by two classes of
familiar compounds— fats and carbohydrates. We all know such fats as
butter, suet, lard, olive oil, peanut oil, and others. The carbohydrates in-
clude 'all the sugars and starches. When fats and carbohydrates oxidize,
water and carbon dioxide result.

Proteins, fats and carbohydrates together are called "organic nutrients''
because they occur in nature only in the bodies of living things, or or-
ganisms. Animals obtain their organic food from other animals or from
plants. Green plants are able, as we shall see, to build up carbohydrates
from water and carbon dioxide. They are able also to build up proteins out
of these carbohydrates when they have supplies of nitrogen, sulfur and
phosphorus salts. Both plants and animals are able to build fats out of
carbohydrates— fats and carbohydrates consisting of carbon, hydrogen and
oxygen in various proportions.

Inorganic needs Plants accordingly must receive supplies of various
mineral substances, for these furnish elements used in building proteins.
We have not been considering these materials as "foods" chiefly because
most people, most of the time, are unaware of taking them into the body.
We get practically all we need in our fruits and meat and vegetables and
milk. The one great exception is common salt, which has to be added to
much of our food. But even so, people do not think of salt as "food",
perhaps because it is seldom that one eats salt by itself.

At any rate, these minerals are quite as essential to maintaining proto-
plasm as are protein and the other "organic" substances. Salts and water
do not yield energy, but they make possible that complex of chemical
changes in protoplasm which we call metabolism. Some compounds ap-
parendy act indirectly, influencing special chemical processes, just as the
bromides used by the photographer slow the development of the negative.

Animals and plants naturally absorb the various elements from their
surroundings, according to the composition of the sea water or of the par-
ticular soil. Calcium is more abundant in some regions, iodine is almost
entirely lacking in others, and so on. Such variations must influence what
the organisms take in, and may influence the way in which the protoplasm
actually grows and acts.

The Soil and the Life It Sustains Studies made in Florida show that
variations in the character of the soil are reflected in the plants growing on
it, and that these in turn influence the cattle that feed upon them and the
human beings who depend upon the plants and animals. Plants grown
in some soils contain two to three times as much iron as plants of the same
species grown in a different soil. Cattle that range where the salt licks are
inadequate show defective bone formation and other nutritional defects.
The children in such areas also have defective bone formation and have low

Bean

Pea

Fish

Cow Sheep

Olive

Goose

Peanut Bra2al nut

Pig

Carbohydrates ^,

Sugar ceme Sugar beet

SOURCES OF BASIC NUTRIENTS

Other grains

No natural food can be classed as strictly protein, carbohydrate, or fat. Nearly
every animal and nearly every plant yields some of each nutrient, but seldom in
proportions suitable for our needs. By using plants and animals of various kinds, we
can get what we need most conveniently or most economically

hemoglobin content. Rats fed on milk from the cows in such regions show
nutritional deficiencies and die in large proportions unless minerals are
added to their diet.

It is possible that some of the elements or compounds which we find in
various plant and animal bodies are residues of material taken in but no
longer used by the protoplasm; that is, they are waste products. In some
species, for example, the roots or the underground stems contain crystals of
a calcium compound, calcium oxalate, which we can recognize by the acrid
taste, as in jack-in-the-pulpit. These crystals may represent wastes resulting
from metabolism or leftovers from processes in which the plant has more
calcium than the living protoplasm can use (see illustration, p. 215).

From actual experience and special experiments, we know that some of
the elements found in protoplasm are indispensable — sodium, potassium,
calcium, phosphorus, magnesium, iron and chlorine, for example. Where
farming goes on year after year, some of the minerals from the soil are
carried off with each crop. In time the soil can no longer maintain the
plants. In this country, farming has in the past consisted largely of work-
ing fields until they could yield no more, and then moving on. For this
reason many of the abandoned farms are quite worthless.

Special Elements Some dozen elements take part in the growth and
activity of most kinds of protoplasm. In addition, many species use certain
minerals in special ways. The bones and teeth of vertebrates, for example,
are typically hard and rigid. We find that they contain very large propor-
tions of calcium phosphate, which consists of calcium, phosphorus and
oxygen. Again, the shells of moUusks consist of almost pure calcium car-

Larynx

Parathyroid

glands behind

thyroid

Trachea-

Thyroid
gland

The food and water which the
organism takes in contain a very
small proportion of iodine. The
product of the thyroid gland,
however, the thyroxin, contains
65 per cent of iodine by weight.
Apparently this gland absorbs
all the iodine that the body
receives and concentrates it in
the thyroxin, which is essential
to "the normal growth and devel-
opment of the organism. Unless
there is sufficient iodine in the
diet, the thyroid cannot make
enough thyroxin. The parathy-
roid glands influence calcium
concentration in the body fluids

IODINE AND THE THYROID
100

Ratio per 1000 examined
0.25.1.00
1.01-3.99

^M 4.00 -10.00
^H 10.01 - 27.00

GOITER DISTRIBUTION IN THE UNITED STATES

In the First World War, drafted men from the Great Lakes region and from the Pa-
cific Northwest had more goiters per thousand than other groups. The soils in these
goiter areas contain relatively little iodine, which the body uses in making thyroxin,
the thyroid hormone. It is as if the gland enlarged to keep up production from a
diet deficient in iodine

bonate. The exoskeletons of crustaceans (lobsters, crabs, and so on) also
contain large quantities of calcium carbonate.

Iodine, which exists in relatively large amounts in sea water, has been
found to be essential in the life of land mammals and birds and other
classes of animals. We should not have suspected that from the very small
amounts actually present in our tissues — about forty parts per million.
Iodine appears to be an essential constituent of thyroxin, which is secreted by
the thyroid gland, located in front of the neck (see illustration opposite).
In some mountainous regions, and in upland areas having moderate or high
rainfall, the iodine has been leached out of the soil. The plants seem to
thrive about as well here as elsewhere. But the animals that feed on these
plants indicate the lack of iodine in their development and in their activities
(see page 311).

Iron is another element present In relatively small amounts yet absolutely
necessary in the metabolism of many species. In animals having red blood,

101

WHERE SELENIUM POISONING

In certain portions of the
North Central great plains,
plants absorb enough sele-
nium from the soil to injure
animals that feed upon them.
The poisoning may result in
a slow disease known as
"blind staggers"or as"alkali
disease", or it may be quickly
fatal. As a result of the
selenium, the joints of the
leg-bones become badly
eroded. The hoofs develop
abnormalities or drop off.
Locomotion is impaired. The
effect of the selenium per-
sists, for the animals do not
usually recover even if re-
moved from such a region
and fed a good ration

OCCURS

iron is an essential constituent of the hemoglobin (see page 205). Copper
compounds are generally poisonous to most kinds of protoplasm; yet for
some species copper is necessary in small amounts. Copper is an essential
element in the bluish oxygen-carrier hemocyanin of the king crab and the
lobster.

In some of the Western states the soil contains the element selenium.
This element is present also in plants growing in such soil, although it does
not appear to affect them in any way. But animals that feed upon such plants
are often seriously poisoned (see illustration opposite). In other regions
variation in the amount of fluorine in the soil may be important to us.

The element fluorine, which is very widely but unevenly distributed,
seems to play a role in the assimilation of calcium and phosphorus, and so
affects the formation of the teeth. A study of 7000 girls and boys of high-
school age in various middle and southwestern states brought out the fact
that there was much more tooth decay, or caries^ in communities whose water
supplies were free of fluorine than in communities using water with 0.5 or
more parts fluorine per million parts water. Thus, the population of a certain
part of Texas, Deaf Smith County, was found to have an exceptionally low
number of decayed teeth ; and this relative freedom from dental caries is asso-
ciated with more than usual amounts of fluorine in the local waters.

In other regions unusual amounts of fluorine in the soil and soil waters
apparently bring about the development of "mottled teeth" among the
children living there. Nobody wants blotchy teeth, but nobody wants caries

102

A cow showing the character-
istic symptoms of so-called
"alkali disease", which killed
many army horses eighty
years ago. The cause of this
disease has been traced only
in recent times to the eating
of grain or other plant stuff
grown on land containing
an excess of selenium. The
selenium poisoning results in
a poor coat, bald tail, and
elongated and split hoofs

Uni I Dept. of Agriculture

AN EXAMPLE OF SELENIUM POISONING

either. Recent experiments have suggested that by keeping the fluorine in-
take at a certain level it may be possible to prevent caries, which is one of the
most common "disabilities" in our population; but this amount of fluorine
is not enough to cause mottling of the enamel.

Experiments have shown that boron, gallium, manganese, aluminum,
and other elements play a role in the growth or activity of some organisms,
although they are present in minute quantities. It is possible, however, that
the various species could thrive in most cases just as well — if in a some-
what different manner — without all these rare elements.

What Are Vitamins?

How the Sailor Became a Limy During the centuries before the Chris-
tian era, when slavery was common, outbreaks of "epidemic" diseases were
not rare. Some of these "visitations of the gods" spread to all portions of
the population. Others, however, seemed to be restricted to the poor masses.
Hippocrates (430-370 b.c), often called "the father of medicine", described
one such disease; and from his descriptions we can recognize "scurvy" as
the cause of the great distress.

This disease appeared among the crusaders and on the long sea voyages
that preceded and followed the discovery of America. Jacques Cartier, the
French explorer who discovered the St. Lawrence River, lost 25 of his men
in the winter of 1536 through scurvy, and many others were sick. An Indian
told him that a water extract of the leaves of a certain evergreen tree was
drunk by his people as a good medicine for that trouble. They cut down a
tree and boiled the leaves; and his men recovered.

Scurvy appeared among the crowded emigrants from old countries seek-
ing a home and fresh opportunities in the new. By the seventeenth century

103

Europeans were learning through travel and trade that scurvy was due to
the lack of something which soldiers and sailors and long-trail wanderers
were unable to get. By about 1750 the Dutch, interested in the East Indies
trade, and the British, with their expanding navy, had discovered that fresh
fruit and fruit juices helped to keep their sailors well. But on long naval
voyages scurvy continued to injure large numbers of the forces.

The famous Captain John Cook, in his voyage around the world, man-
aged to keep his crew in very good condition for over three years through
the use of lime-juice. For this achievement he received a medal from the
Royal Admiralty in 1776. Within twenty years the use of lime-juice or
lemon-juice became obligatory in all the ships of the British navy, with
satisfactory results in preventing scurvy. That's how the British sailor
became a limy.

For over a hundred years nobody knew just what the connection is be-
tween scurvy and lime-juice. Is it the citric acid.? Is it the oil of lemon ."^
Is it the mineral salts ? Is it some of the other organic materials ?

How Vitamins Were Discovered^ Ancient Chinese records describe a
disease common among poor folks who managed somehow to exist on the
very edge of starvation. This is the "beriberi" of the Far East.

Beriberi prevailed in one situation or another in China and Japan until
recent times. After Pasteur established his ''germ theory", beriberi was sus-
pected of being an infectious disease. But as Oriental physicians learned to
use European methods, they made sure experimentally that this is noi
the case.

BERIBERI, OR POLYNEURITIS, IN PIGEONS

Growing pigeons fed only white, or "polished", rice and water lose appetite and
weight. After a short period of time they lose control of their bodies and at times
draw back their necks in typical polyneuritic fits. Such animals can be quickly re-
stored to health by feeding them vitamin Bi or brown rice

^See Nos. 2, 3 and 4, p. 112.

104

NORMAL GROWTH CURVE FOR RATS

4 5

7 8

10 11 12 13 14 15 16 17 18 19 20 21 22
Age in weeks

GROWTH AS AN INDEX OF NUTRITION^

Deficiencies in food quickly influence the rate of growth in young animals, which we
therefore use for making experiments in nutrition. Rots are most sensitive to deficiencies
in diet during the first twelve weeks of life, when they grow most rapidly. The curve
shows the average week-by-week growth of large numbers of male(o-") and female {$)
rats kept on a suitable diet

About a third of the Japanese soldiers were on the sick list every year,
suffering from this disease. Takaki, a naval surgeon, investigated the con-
ditions in the early eighties and decided that there was nothing wrong with
the climate or with the sanitary conditions. He suspected the diet. He sent
two warships on a long journey. One had the usual rations, in which white,
or "polished", rice was the chief ingredient. The other carried less rice, but
more barley, meat, vegetables and condensed milk. On the first ship about
two thirds of the men suffered from beriberi, and several died of it. On the
second ship only a few sailors became sick, and they were all sailors who
would not change to the newfangled diet. The Japanese government im-
mediately ordered the new diet for all its soldiers and sailors. The men's

^Adapted from Teaching Nutrition to Boys and Girls by Mary S. Rose, The Macmillan
Company. After "The Influence of Food upon Longevity" by Sherman and Campbell, Pro-
ceedings of the National Academy of Science, Vol. 14.

105

Individuals taken from stock of healthy animals

Supplied with "pure nutrients" lacking vitamin C

lost 142 grams in five weeks

Continued on "normal" diet

gained 150 grams in five weeks

Individuals taken from cages of scurvy animals

Supplied with "protective" food

gained 75 grams in six weeks

Continued on "deficient" diet

lost 103 grams, died in six weeks

SCURVY IN GUINEA-PIGS RELATED TO DIET

When guinea-pigs or humans or monkeys are supplied diets deficient in vitamin C,
they develop swollen joints. Their gums become tender and bleed easily. Hemor-
rhages occur readily, for the v/alls of the capillaries deteriorate. The flesh becomes
sore and blackened when bruised. (The two animals representing each experiment
were litter mates)

health improved immediately and decidedly. Yet neither Takaki nor any-
one else knew just what the connection was between the new diet and the
prevention of beriberi. The diet specialists thought it was the additional
protein in proportion to the carbohydrates.

Toward the end of the century, however, a Dutch physician in Java,
Christian Eijkman (1858-1930), attacked beriberi experimentally. He fed
pigeons and chickens on "polished" rice — that is, rice from which the hulls
had been rubbed off. The birds developed the symptoms of the nerve in-
flammations typical of beriberi. Did anything in the white rice injure the
birds? Eijkman fed the sick birds rice "polishings", or the removed bran,
and restored them to health. The condition was apparently due to the lac\

106

of something — a something removed during the poHshing. What that some-
thing is Eijkman did not know. But he showed that to keep an animal in
health something is necessary besides proteins and fats and carbohydrates.

For ten or fifteen years following, Dr. Frederick Gowland Hopkins
(1861- ) of Cambridge University was feeding rats on a diet of the
several substances that make up cow's milk. He used pure casein, pure
butterfat, pure lactose (milk sugar), and the purified minerals present in
milk. He tried to account for everything. While the rats fed on cow's milk
thrived, those fed on the combination of purified nutrients appeared mis-
erable and deficient. Hopkins added a few drops of "real milk" each day
to their synthetic diet and made these sickly rats well again. A "balanced
diet" containing the usual organic nutrients and the necessary minerals is
obviously not sufficient. Something must be present in the cow's milk that
is not present in die artificial combination of fats, proteins, and minerals.
What was this "accessory factor", as Hopkins called it ?

Later, a Polish scientist, Casimir Funk (1884- ), having made similar
observations in the laboratory, suggested for this "unknown something" the
name vitamine — vital because it is essential to life; and amine because he
assumed it to be one of a class of compounds characteristic of the structure
of proteins, namely, amines or amino acids (see page 99). This name
(spelled now without the e) has continued in use, although the substances
are not amines at all, and although it applies to a growing series of substances.

The experimental work has continued, and has become greatly ex-
panded. The typical procedure is illustrated by the study of scurvy in
guinea-pigs^ (see illustration opposite). Later research attempted to answer
the questions How much of a given vitamin is necessary for a pound of
live animal } and What is a vitamin, anyhow ?

What Do Vitamins Do?

Indirect Action We know that vitamins are organic compounds
which are essential in the diet of at least the higher animals. Unlike pro-
teins and mineral salts, they cannot be considered as building materials.
Unlike the other organic foods — fats, carbohydrates and proteins — they can-
not be considered sources of energy. Yet without vitamins normal metab-
olism cannot take place.

Without increasing protoplasm or supplying energy, vitamins do influ-
ence metabolic processes. In this respect they are like the hormones pro-
duced within the body (see pages 302-304). Like the hormones, the
vitamins produce effects highly disproportionate to the amount present.

^The guinea-pig is not a pig at all, but a rodent — more like a rabbit. Nor is it from
Guinea, being a native of South America. Its proper name is cavy.

107

They seem to "regulate" or balance some of the protoplasmic activities, as
certain minerals do.

Each vitamin was first known by its effects on metabolism, and not at
all by its chemical nature. Investigators labeled the "unknown something"
present in milk, but not present in a diet of pure nutrients, "A". The
"unknown something" lacking in polished rice and resulting in beriberi
and polyneuritis wheti it wasn't there, was called B. That which was lack-
ing in food that brought scurvy was named C. As new discoveries were
made, additional letters were used to designate the unknown factors. Some-
times different investigators used the same letter to designate different sub-
stances. Even today our letter designations are somewhat confusing.

Naming the Vitamins Early in the study, the vitamins were separated
into two groups, those soluble in fats and those soluble in water. Feeding
experiments yielded at first contradictory results because, as was later found
out, the different fat-soluble substances are unevenly distributed in various
foods. Accordingly the results were due in some cases to a deficiency of one
factor, and in some to a deficiency of another. In 1922 the fat-soluble ex-
tract, then called A, was clearly separated into two distinct factors, now
called vitamins A and D. Similarly, in the water-soluble extract then called
Bj a dozen or more factors have been identified by their metabolic effects.

In America the first two factors isolated from the original B extract
were called vitamins B and G. In England these same factors were known
as Bi and B2. Later, vitamin G or B2 was found to include two or more
factors. Sometimes the name was applied to riboflavin, a substance found
in plants, sometimes to a product formed within the animal body by a
union of riboflavin with another unknown substance. Some of the bodily
disorders originally attributed to the lac\ of vitamin G (for example, the
disease pellagra) were found to result from a lack of niacin.

As more vitamins came to be recognized without reference to the orig-
inal fat-soluble extract or water-soluble extract, they were designated by
additional letters in the alphabet. Thus, vitamin E was discovered during
studies on the ripening of eggs in rats, and vitamin K was discovered in the
study of the clotting of the blood. As we have come to know the chemical
make-up of the various vitamins, we have substituted chemical names for
the former letter designations. Thus vitamin B becomes thiamin, vitamin C
ascorbic acid, and so on (see table, pp. 132-133).

Differentiating the Vitamins Most of the vitamins were discovered in
connection with diseases that developed in their absence. We have accord-
ingly come to think of them as anti this and anti that. In fact, we have
anti-names for most of them, as well as the alphabet names. It would be
more helpful, however, to think of the positive values of vitamins in nor-
mal metabolism than of the effects of their absence. This is especially im-

108

portant because in America people suffer much more from the "hidden
hungers" of moderate deficiencies than from the so-called "deficiency dis-
eases" (see table, pp. 132-133).

From a chemical point of view, little can be said about vitamins as a
group, for each has distinct and specific characteristics and effects. Dis-
covering a new fact about one vitamin gives no reason for presuming that
it will be true of any of the others or of vitamins in general. But we are
likely to group the vitamins when thinking of nutrition, since they were dis-
covered in a relatively short time through feeding experiments with animals.

In the early attempts to measure the quantity of a given vitamin neces-
sary for health, experimental animals were fed on carefully prepared diets.
The first standard unit was developed by Dr. Henry C. Sherman
(1875- ) of Columbia University, as "the smallest amount of vitamin C
sufficient to keep a guinea-pig of definite age and weight free from scurvy
for from 70 to 90 days".

As research continued, several vitamins were identified as specific chem-
ical compounds. So it becomes possible to make direct chemical tests in
place of the long tests with living animals. Thus, Albert Szent-Gyorgyi
(1893- ), the Hungarian scientist, now living in the United States, in 1932
identified vitamin C as a definite chemical substance, ascorbic acid. The
following year some Swiss chemists produced this acid synthetically. It was
then possible to ascertain the amount of vitamin C, or ascorbic acid, in a food
by measuring the bleaching effect on a dye. Sherman's "unit" is accordingly
recognized as being equivalent to about 0.75 milligram of ascorbic acid.
During the Second World War, Russian scientists demonstrated what the
Canadian Indians knew four hundred years earlier, by a different name.
They showed that the leaves of pines and other evergreen trees contain small
quantities of vitamin C, which they were able to extract economically for
the use of armies and civilian populations that could not easily get citrus
fruits or tomatoes (see page 103).

The Sources of Vitamins For generations, cod-liver oil was used in
European countries to help children through the dark days of winter,
nobody knowing just what made this rather unpleasant stuff so valuable
until vitamins A and D were discovered in our own time. During the
Second World War it became impossible to get supplies of this oil, but
almost immediately a new industry developed off the eastern shores of
Florida — that of catching sharks for the oil in their livers. Incidentally,
every bit of the animal is used in one way or another, from the hide, made
into tough leather, to the last scrap of flesh used for dog food, poultry food
and fertilizer.

Vitamins seem to have their beginnings in plants. Vitamins present in
animal tissues are derived from plants or from substances formed in plants.

109

Most herbivorous animals and some carnivorous animals, like man, are able
to produce vitamin A from carotin. Other carnivorous animals — cats, for
example, and carnivorous fish — lack what it takes to transform carotin
into vitamin A.

In both plants and animals vitamin D results from the action of sunlight
on ergosterol, a fatty substance. Ergosterol, however, originates, so far as
we know, only in plants. Many mammals (though not man, the monkey,
or the guinea-pig) are able to synthesize ascorbic acid.

The cow can thrive without taking vitamin B in her food. Apparently,
certain species of bacteria that live in the rumen, or paunch, of the animal's
complex "stomach" are able to make thiamin out of other materials. Ex-
periments have been carried on to see whether it is possible to domesticate
such bacteria in the human intestine and so make it unnecessary for us to
get thiamin with our food.

Our knowledge of the functions of the vitamins in the animal body is
dependable, so far as it goes. However, not all the vitamins have been
clearly identified as definite chemical compounds. Until we are sure that
all the substances that are known by a particular name really are the same
substance, we cannot be sure that the effects observed in organisms are
always due to the vitamin (or whatever other class of materials) to which
we have attributed them.

Until recent years the various vitamins have not been available in large
quantities. However, improved methods of isolating or producing them
are being developed. With adequate supplies of pure materials, and with
improved techniques for dealing with them, we may hope to solve many
of the outstanding nutritional problems. At the same time, having large
quantities of certain vitamins enables us to remedy deficiencies in diet
among masses of our population.

With all these gains, there is real danger. For we are all naturally Im-
pressed by the dramatic achievements of "vitamin cures". People may too
easily get the idea that we can prevent or cure all sorts of ills by feeding
ourselves assorted vitamins by the spoonful or in capsules. The indiscrimi-
nate use of vitamin concentrates for self-medication may introduce other
privations or deficiencies, as well as positive injuries. We are not yet cer-
tain what effects various vitamins may produce if used in excessive quan-
tities. Moreover, people can generally use their food money to better
advantage by going to natural foods for the vitamins they need. We cannot
afford to pay caviar prices for cabbage leaves.

During the Second World War the British Ministry of Health con-
ducted two series of experiments to find out whether vitamin concentrates
were of any help to school children or to workers. Over a period of from
two to nine months, hundreds of children and of workers were supplied

vitamin tablets in addition to the regular rationed diets, and equal numbers
had only the regular diets. Height, weight, and sickness records showed
no difference whatever between the two groups. A suitable diet needs no
supplement; a diet that is not suitable should be replaced with one that is.

In Brief

Body-building, energy-yielding, and regulative nutrients are essential to
all living protoplasm.

Proteins, the nitrogen-containing nutrients, serve both as protoplasm-
building and as energy-yielding material.

Fats and carbohydrates supply energy only.

Certain chemical elements are indispensable to protoplasm; if soils or
food lack any of these, the growth of living organisms is limited.

Several minerals are essential to the growth activities of many kinds of
protoplasm; some minerals are used in the formation of special tissues,
such as bones or shells.

Some of the mineral substances found in cells are probably waste prod-
ucts; others may be injurious substances separated out of the protoplasm.

Normal development of living organisms depends upon the presence in
the diet of minute traces of certain "regulative" substances.

Vitamins have been associated with extremely abnormal symptoms de-
veloped by organisms entirely deprived of them, and have received anti-
names. Moderate deficiency is more common, and has been widely
remedied by supplying adequate amounts of the various vitamins.

The ultimate sources of vitamins are plants.

Present knowledge indicates that with a little care adequate amounts of
all the vitamins can be obtained in natural foods, so that we do not gen-
erally have to depend upon the drugstore for these substances.

As we come to know the specific composition of vitamins, we can use
chemical tests for their presence in foods instead of tests on experimental
animals.

EXPLORATIONS AND PROJECTS

1 To find the effect of a diet deficient in energy, feed two rats three to four
weeks of age all they will eat of the complete diet given in footnote 2, p. 112, and
feed two other rats just j as much of the same diet in proportion to their weight.
About 0.12 gram per gram of rat per day should hold their weight nearly constant.
At the end of four or five weeks, give the low-energy animals all the food they
will eat and see whether they catch up with the control animals. Record and
graph daily weights; interpret results.

Ill

2 To find the effects produced when pigeons are fed diets lacking thiamin
(vitamin B), feed one young pigeon brown rice and water and another white rice
and water — that is, a diet lacking thiamin. Keep a daily record and graph of the
food consumed and of the weight of each pigeon. Should the growth curve of the
pigeon on white rice drop sharply, give close attention to the animal, as poly-
neuritis and death will result if the animal is kept on this diet too long. The
pigeon may be saved, even after polyneuritis develops, if it is promptly given
thiamin. What effect does a lack of thiamin have upon the appetite? What
abnormal effects does a lack of thiamin produce?

3 To find the effect of a diet deficient in ascorbic acid feed one of two guinea-
pigs, weighing approximately 300 g each, a complete diet and the other a diet
lacking ascorbic acid.^

Keep a record of weights and make a graph showing the growth curve of each
animal. Compare results in weight and appearance and note conclusions.

4 To find the effects of vitamin A and thiamin deficiencies, keep three pairs
of rats on diets having vitamin differences. Keep one pair of rats, from three to
four weeks old, on a complete diet; one pair on a similar diet lacking vitamin A;
and the third pair on a similar diet lacking thiamin. All the conditions for the
three pairs should be exactly the same, except for the variations in the diet.^
Weigh weekly for six weeks and plot the growth curve of the rats on each diet.
Compare results and note conclusions.

^This diet consists of a mixture of rolled oats and bran, equal parts by volume, 50 g;
skim-milk powder (heat for 4 hr at 110° C), 30 g; butter, 10 g; and table salt, 1 g. For the
normal, or control, diet use the same combinadon but add 10 g or more of spinach or other
greens, or 1 mg of pure ascorbic acid (vitamin C) daily. Prepared rabbit foods on the market
are complete in every essential but ascorbic acid, and may be substituted for the mixture
given above in performing this experiment.

^Formulas for rat diet:

DIET 1 COMPLETE

DIET II LACKING THIAMIN

DIET III LACKING A

Meat residue or casein, 18 g

Cornstarch, 48 g

Hydrogenated fat, 8 g

Cod-liver oil, 2 g

Salt mixture, 4 g

Yeast, dried baker's, 20 g

same, but vitamin-free, 18 g

same

same, but autoclaved, 20 g

same, but vitamin-free, 18 g

same

10 g

none

same

Note that hydrogenation of oils results in solid fats. Hydrogenated cottonseed oil is
commonly used as shortening in place of lard and other solid fats.

A good salt mixture to use contains in each 100 g: 5g NaCl, 16 g MgSO^ 7 H.O, 10 g
NaH.PO^Hp, 28 g K.HPO^, 38 g calcium lactate, 3 g iron lactate.

Note that the thiamin-deficient diet (Diet II) is the same as the complete diet except
that the protein is vitamin-free and the yeast is autoclaved (that is, heated at 110° C for
4 hr) to destroy the thiamin.

Note that the vitamin-A-deficient diet (Diet III) is the same as the complete diet except
that the protein is vitamjn-free and the cod-liver oil (source of vitamin A) is omitted.

112

QUESTIONS

1 What are the different functions that foods perform in the body?

2 What functions do all nutrients have in common?

3 What substances are sometimes deficient in a diet which furnishes plenty
of energy-yielding material?

4 What elements, sometimes lacking in soils, so modify the food content of
plants as to limit the growth of animals which feed upon them?

5 What are the special functions in animal bodies of such minerals as
iodine, calcium, phosphorus and iron?

6 What known vitamins are essential to the normal development of or-
ganisms?

7 What are the sources of all vitamins?

.8 How can each of us be sure that he gets an adequate supply of the various
regulative substances which he needs?

9 Why do so many of the vitamins have anti-names?

10 What are some of the specific dangers that we now face in our use of the
various vitamins?

113

CHAPTER 7 • WHAT KINDS OF STUFF SERVE AS HUMAN FOOD?

1 Can we trust our instincts or feelings in deciding what to eat

and how much to eat?

2 Can we Hve on vegetable diets only or on meat only?

3 Will eating meat make us strong?

4 Does sugar yield quick energy?

5 Are "sweets" harmful?

6 Do restaurants and hotels serve balanced meals?

7 What foods are fattening?

8 How did our grandparents get along without knowledge of

vitamins ?

9 Are irradiated foods better than others?

We should expect that in half a million years or more the human race
might have learned all there was to know about what to eat and how to
eat it. Most people, however, do not know, either from instinct or from
daily experience, the best way to manage their personal food problem.
Everywhere children suffer from defective nutrition, and grown folks from
disturbances of digestion. Starvation and overfeeding exist side by side.
In the course of ages we have found that some parts of animals and plants
(muscle, grain) are better than others (hide, wood). Customs have se-
lected the plant and animal materials that are most valuable as food — in
any given region. We are constantly discovering useful food plants and
food animals. But experience has not taught us the best proportions or
combinations of meat and grain and fruit for bodily comfort and efficiency.

What Are the Food Needs of the Body?

Energy to Keep Going Like all chemical processes, metabolism results
both in breaking down some compounds and in building up other com-
pounds. Metabolism leads in part to the formation of new protoplasm and
tissues, and in part to the breaking down of proteins and other complex
substances.

The rate at which the chemical transformation or metabolism goes on
varies from one kind of tissue to another. It varies also with the activity of
the body from time to time. In a person running to a fire, the chemical
activity is high. During sleep or rest the metabolism is at its lowest level,
and is pretty constant. This low, constant level represents the basic need
for energy.

The amount of food one needs for growth varies in the course of his
lifetime. During the first year of life the baby grows very rapidly (see illus-

114

Year
of life

1st

5th

7th

9th

11th

13th

16th

17th

19th

— — ■— i. 1 ■*■'■ ' ■

■HI^^^Hl

■1

' ' ' ' — 1

warn Bo

rls

Pounds gained 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

AVERAGE ANNUAL GAINS IN WEIGHT

Men and women attain adult size during the first eighteen years of their life. The
gain is exceptionally rapid during the first year and again during adolescence.
Twelve-year-old and thirteen-year-old girls are larger than boys of the same age,
for they grow faster during the twelfth year. The boys, however, overtake them dur-
ing the fifteenth year and get progressively farther ahead during the fifteenth to the
eighteenth year. (The weights represent gains in weight)

tration, p. 115). The baby's parents have already attained their full growth.
The amount of food that a person needs to make up for the heat radiated
from the surface of the body varies w^ith the size and also w^ith the shape
of the body (see illustration opposite). The smaller a child, the more surface
he has in proportion to his body weight, and hence he loses relatively more
heat. By actual measurement, a one-year-old child needs approximately
twice as much energy per pound of body-weight as does an adult.

Energy needs are indirectly related to sex. Girls and women have a
thicker layer of fatty tissue beneath the skin than boys and men. This fat
prevents rapid radiation of heat from the body. It is interesting to recall
that most long-distance swimming records are held by women rather than
by men. Exposure also affects the body's loss of heat. The body loses heat
faster in a cold, dry, windy climate than in a warm, moist climate. Cloth-
ing and shelter are, of course, factors in the loss of heat.

Circulation of the blood, breathing, and other processes are continually
going on when the body is at rest. "Warm-blooded" animals maintain a
constant temperature. The heat continually radiating from the surface is
constantly being replaced. Muscular movements are continually taking
place in the digestive organs, and energy is used in various other ways
within the body. From 40 to 50 per cent of the body is made up of mus-
cular tissue. The bulk of this tissue is attached to the skeleton and is used
in standing as well as in locomotion and other voluntary actions. At all
times, even when these muscles are relaxed, energy is used in keeping them
somewhat on the stretch.

Above the Base Line The amount of energy that the body uses, even
while it is "doing nothing", is constantly influenced by two sets of factors.
Digesting food involves a measurable amount of energy. Thus the body
uses about 6 per cent more energy soon after a meal, when the digestive
organs are most active, than just before a meal, when digestion is practi-
cally at a standstill.

When you are sitting and reading, or when you are standing quietly,
your body uses about one-and-a-third times as much energy as it does
while sleeping. Walking at a moderate pace uses about two-and-a-half
times as much; running uses about seven times and stair-climbing about
fifteen times as much.

Unit of Energy To measure the energy expended by the living body,
we use a unit developed by engineers. This is the Calorie (Cal), and, like the
more familiar foot-pound (ft-lb) used in measuring work, it is composed
of two factors. We measure work as if it always consisted of some quantity
of matter (pounds) moving a certain distance (feet). In a similar way we
measure heat as a quantity of matter, for example, 1 kilogram (kg) of water,
being heated a certain "distance" (1 degree on the centigrade scale).

116

Surface/ volume = "^/-^

SURFACE DEPENDS UPON SIZE AND SHAPE

A 1-inch cube exposes 6 square inches of surface. Eight such cubes combined into
a single large cube expose 24 square inches of surface; when arranged in a tall
column, 34 square inches; and when scattered separately, 48 square inches. Similarly,
a tall person weighing 160 pounds exposes more surface than a stocky person of
the same weight, but decidedly less than eight babies weighing 20 pounds each

For very delicate work, a smaller unit is used, sometimes called the
"small calorie" and spelled by the engineers with a small c; this is the
gram-degree calorie, and is of course only one thousandth of a Calorie.
We measure fuel or energy value of foods in the "large Calories"; but in
ordinary reports and tables people do not generally make a point of spell-
ing Calorie always with a capital.

Measuring the Body's Work^ For finding out how much energy an
organism actually transforms in a given time, the respiration calorimeter
was developed about the beginning of the century. Later types of calorim-
eter are all based on the general fact, established by experiment, that the
amount of energy set free by an organism is in direct proportion to the
amount of carbon it oxidizes. Accordingly, if we knew the exact amount of
carbon dioxide that a person breathed out in one day, for example, we
should be able to calculate the total amount of work he had done. But the
calorimeter measures this "work" as a physical fact — that is, as calories or
as foot-pounds — not as useful products, words written, nails driven, or
buttons sewed.

The calorimeter has been of tremendous help in solving many problems
of nutrition, as well as problems of metabolism, under various exceptional
conditions, including illness. For example, it has been indispensable in de-
veloping high-altitude and stratosphere flying, in which the fliers are sup-
plied with oxygen in measured quantities. As the calorimeter becomes more
widely used in hospitals, in mining, and in industry, simpler types are de-
veloped, and simpler procedures too. Thus, we can determine the amount
of heat a person generates by measuring the amount of oxygen he consumes
— for under controlled conditions the body liberates 0.004825 Calorie for
each cubic centimeter of pure oxygen (see illustration opposite).

Basal Metabolism It is extremely difficult to measure a person's con-
stant, or basic, metabolism during sleep. Investigators and medical men
have therefore agreed upon an arbitrary measure which is called basal
metabolism. This is the rate of energy expenditure by a person who is
awake, lying still and relaxed, and who has not eaten any food during the
preceding twelve hours. It is customary to take these tests early in the
morning before the patient has had any breakfast. This is the nearest ap-
proximation to basic metabolism that can be obtained with any device
other than the respiration calorimeter, of which there are but a few in the
country.

Standards for Boys and Girls" The basal metabolism measurement has
been made with calorimeters on thousands of boys and girls. For com-
parison, the results are calculated to show the daily need "per pound of
body weight" (sec table, p. 121). Since these figures represent averages,
iSee No. 1, p. 135. -See No. 2, p. 135.

118

Calories

150
Calories

800

Calories

ENERGY EXPENDITURE UNDER VARIOUS CONDITIONS

Experiments have shown that a 110-pound boy or girl uses 50 Calories per hour
under "basal" conditions. When sitting or walking, one uses much more energy.
When one is engaged in strenuous activity, such as running, swimming, or climbing
stairs, he spends energy from eight to sixteen times as fast as when he is asleep

Metal

Ytube

%" diam

Soda lime to
[absorb carbon dioxide

Rubber stopper

■Wire screen to keep air passage clear of soda lime i

Bureau of Publications, Teachers College, Columbus University

HOMEMADE RESPIRATION CALORIMETER

Energy expenditure of the subject while sitting is measured by the oxygen he con-
sumes in a given time. The calorimeter is first filled with oxygen from the cylinder.
The subject then starts breathing from the calorimeter. The quantity of gas in the
calorimeter is adjusted with the pump so that the rubber cap just touches the gauge
wire each time the subject exhales. The number of pumpfuls of air put in to
make up for the oxygen used by the subject is recorded. One member of the crew
keeps time

they do not exactly fit any particular individual. However, they do in-
dicate pretty closely one's basal needs. Thus a girl of 14 who weighs
90 lb and who is lying still and "doing nothing" would have to take in
fuel food equivalent to (90 X 17) = 1530 Calories per day just to keep
alive. Everything she does above that calls for additional energy — addi-
tional food.

120

6 8 10

Years of age

AVERAGE DAILY ENERGY EXPENDITURE AT DIFFERENT AGES^

The high expenditure of energy per pound of body weight during the first year is
due to the relatively large body surface and to very rapid growth. The increased
energy expenditure between twelve and fifteen years of age is due to accelerated
growth at this time

Average Basal Energy Metabolism of Boys and Girls in Terms of Body Weight-

AGE IN YEARS

CALORIES PER POUND PER DAY

AGE IN YEARS

CALORIES PER

'OUND PER DAY

Boys

Girls

Boys

Girls

Energy Cost of Activities' By the use of the respiration calorimeter
the energy cost of several different activities has been worked out. These
figures tell us how many additional Calories an individual spends per

^After Foundations of Nutrition by Mary Swartz Rose. By permission of The Macmillan
Company, publishers.

-Adapted from Mary Swartz Rose, Foundations of Nutrition, 1938, p. 90. By permission
of The Macmillan Company, publishers.

"See No. 3, p. 136.

121

pound of weight per hour of activity, above basal metabolism. A few of
these are given in the accompanying table.

Energy Cost of Activities^

ACTIVITY

CALORIES PER POUND
PER HOUR

ACTIVITY

CALORIES PER POUND
PER HOUR

Bicycling (racing)

Bicycling (moderate speed) .

Carpentry, heavy

Cello-playing

Dancing, fox trot

Dancing, waltz ......

Dishwashing

Dressing and undressing. . .

Eating

Fencing

Ironing (5-pound iron) . . .

Playing ping-pong

Runnm*'

3.4
1.1
1.0
0.6
1.7
1.4
0.5
0.3
0.2
3.3
0.5
2.0
3.3

Sawing wood

Sewing, hand

Sitting quietly

Standing relaxed

Swimming (2 miles per hour)
Typewriting rapidly . . .

Violin-playing

Walking (3 miles per hour) .
Walking rapidly (4 miles per

hour)

Writing

Energy saved during sleep .

2.6
0.2
0.2
0.2
3.6
0.5
0.3
0.9

1.5

0.2

0.05

Daily Energy Needs of Boys and Girls Boys and girls of a given age
differ in size, and they differ in amount of activity. It is nevertheless help-
ful to know the average requirements for large numbers, as given in the
table below. If a boy is both active and large for his age, his daily food
needs will be near the upper limit. If a girl is active but small, her
energy requirements w411 be about midway between the extremes given
for her age.

Average Number of Calories Needed Daily-

CALORIES

PER DAY

AGE IN YEARS

CALORIES PER DAY

Boys

Girls

Boys

Girls

900-1200

800-1200

2100-2700

1900-2600

1100-1300

1000-1250

2100-2800

2000-2800

1100-1400

1050-1350

2300-3000

2100-3000

1200-1500

1150-1450

2500-3500

2300-3400

1300-1600

1200-1500

2600-3800

2400-3000

1500-1900

1450-1800

2700-4000

2400-2800

1600-2100

1500-1900

2700-4000

2250-2800

1700-2300
1900-2500

1600-2200
1800^2500

2800-4000

2250-2800

^N. Eldred Bingham, Teaching Nutrition in Biology Classes. A Lincoln School Research
Study, Bureau of Publications, Teachers College, Columbia University, 1939, p. 50. Adapted
from Mary Swartz Rose, Foundations of Nutrition, 1938, pp. 606-607. By permission of The
Macmillan Company, publishers.

2Henry C. Sherman and Caroline S. Lanford, Essentials of Nutrition, 1943, p. 84. By
permission of The Macmillan Company, publishers.

122

Energy Needs of Different Workers We should expect that a person
working in the steel mills expends more energy than a clerk who sits at a
desk making out payrolls. The energy needs for various kinds of work are
given in the table below, which combines the results of many studies. Men
and women of above-average weight require more than indicated ; similarly,
men and women of light weight need less.

Energy Needs and Kinds of Work^

DAILY CALORIE ALLOWANCES

KINO OF WORK

For Men of Average Weight
(154 lb) Ages 20 59

For Women of Average Weight
(132 1b) Ages 20-59

Very active work — rapid heavy lifting or pulling with
exDosure to weather

4500
3000

2700
2400

3000

Moderately active work — standing or walking with mod-
erately heavy loads

Light work — seated with considerable arm or leg move-
ment, or standing and walking with little lifting or
strain

2500
2300

Sedentarv work — seated, involving little arm or leg move-
ment

2100

Building Stuff Like all other living animals, the human organism
needs proteins and minerals out of which protoplasm develops new tissues
(see pages 96-97). The body makes use of a wide variety of proteins, al-
though some are more completely used than others. Proteins differ in the
proportions of the amino-acids they contain (see page 97). The combination
of amino-acids found in the protoplasm of any species differs somewhat
from that found in other living things. Those proteins which are most like
human protoplasm are most usable in the growth of new body tissues.

The mineral needs of the body are also essentially the same as those of
other animals. It is significant that a newly born child is relatively poor in
calcium and rich in iron. Furthermore, the skeleton, composed largely of
calcium and phosphorus (see page 100), gets most of its growth during the
first eighteen years of life. Nearly one third of the phosphorus found in
the body is in the muscles and other soft tissues, which also develop rapidly
during the first years of life. Thus growing children require relatively more
calcium and phosphorus than adults. Although the iron in the body is but a
small quantity, its function in respiration does not permit a shortage (see
page 101). Some diets are inadequate in this respect.

^Hazel K. Stiebeling and E. F. Phipard, Diets of Families of Employed Wage Earners
and Clerical Workers in Cities, United States Department of Agriculture Circular No. 507,
1939.

123

Studies of American diets indicate that, with the exception of iodine (see
pages 100-101), the foods usually eaten contain adequate supplies of the re-
maining salts essential to our protoplasm.

Chemical Regulators We have seen that various inorganic substances
play an important role in the building and in the activities of protoplasm.
In addition, how^ever, mineral salts appear to be important because their
relative cojjcentration in the cells and body fluids affects osmosis and the
distribution of material (see page 87). The rhythmic contraction and re-
laxation of heart muscle depends upon certain proportions of calcium,
sodium and potassium in the body fluids (see page 99). When the supply
of calcium is too low, body muscles become tense and rigid; some convul-
sions are caused in this way. Other salts affect the oxidation of food in the
cells. When the concentrations or proportions of these salts fluctuate too
much, the metabolism is disturbed.

How Can We Plan a Diet to Suit Our Body Needs?

More than Day by Day We usually know immediately whether our
food pleases us or when our hunger has stopped. If something goes wrong
with the digestion, we soon discover it. But we may continue a very long
time on a diet that is seriously lacking in essentials, without realizing it. For
this reason it is important that everybody acquire food preferences and food
practices guided by reliable knowledge of daily needs. Such knowledge
rests upon studies of what people do actually eat and upon experiments
with the diet and its effects on college students, soldiers and other people,
and on various animals.

In discussing metabolism and life needs so far, we have said very little
about food: we have considered only such abstractions as Calories, proteins
or vitamins. When we sit down to a meal we see none of these things; we
are confronted instead with various breadstuffs, fruits, vegetables, meats,
and the like. We know that some of the foods which we use contain more
of the essentials than others (see illustrations, pp. 126 and 127). How can
we translate the products of the food factories and the kitchen into proteins
and Calories and vitamins ? The information which we need for such trans-
lating has been furnished by research workers in government laboratories,
in hospitals, in universities, and in other institutions. It is available to us in
convenient tables that have been prepared by various experts.

Food Groups^ We group or classify the common foods according to
what they furnish in our diet.

^See Nos. 4 and 5, p. 136.
124

1. BreadstufTs and other grain products are economical sources of energy
and proteins and vitamins, but lack proportionate amounts of mineral.

2. Starches and sugars (carbohydrates) are concentrated sources of
energy but furnish nothing else to the diet.

3. Fats are even richer fuels, yielding approximately two-and-one-fourth
times as much energy as the same quantity of carbohydrates or proteins/
Some fats, especially yellow fats, contain vitamins A and D.

4. Meats, including fish and poultry, are rich in proteins and energy,
but, in general, are deficient in minerals and vitamins.

5. Fruits and vegetables vary greatly in their protein and energy values,
but are excellent sources of mineral elements anci vitamins.

6. Milk forms the most nearly perfect human food we know. Milk and
milk products furnish high-quality proteins, much like those found in the
human body. Milk contains all the essential mineral elements and all the
essential vitamins. It can be considered the most valuable of all foods for
making up for any deficiencies in the diet.

7. Eggs are high in nutritive value, are rich sources of high-quality pro-
teins, of phosphorus, and of vitamins A, B, D, and G.

Enriched Flour For many years the grinding of wheat into flour has
included the removal of the bran and parts of the germ, or embryo, of the
grain. The bran is removed because people seem to prefer the pure white
flour, and the germ is removed because that makes it possible to keep the
flour from spoiling as it is shipped to all parts of the world or stored in-
definitely. But as a result of such superior grinding the flour lacks certain
components that are essential for the nutrition of those for whom flour
bread is a large part of the diet. In 1942 the Food and Drug Administration
ordered that all white flour used for baking bread be "enriched" with various
vitamins and minerals.

Within a year after this order went into effect, a large New York hospital
reported that beriberi and pellagra cases in its wards had declined by more
than half. The legality of the order had been challenged, but the Supreme
Court of the United States upheld the Administration in its authority to
make the requirements in the interests of public health. Since October 1,
1943, the millers rather than the bakers must make the addition of vitamins

^The energy value of nutrients within the body is as follows:

CALORIES PER GRAM

Proteins 4

Carbohydrates 4

Fats 9

A given quantity of fat furnishes more than twice as much energy as the same quantity of
proteins or carbohydrates.

125

SHAEKS OF
1 tablespoonful butter

paI|Pro|Ca[trotij A j B

mm % cup milk 2^

MB^ log ^-^ 1-5 0 9Piil

:CalJFjo Ca Iron ABC

UtRIEMTS

1 tablespoonful lard
0 0 0 0 0 0

CaliProlCaSrod A

34 cup oatmeal
1.8 V, -7..^ 2.3

lITllo

S^Ca^rool a"

0.4

C G

1 serving
round steak

COMPARING FOODS

For one who needs 2500 calories a day, twenty-five shares of any of the foods
shown on these two pages would supply fuel for a day's work. We should not be
satisfied with a diet of lettuce only, or even of oranges or steak. If one tried to live
on eggs alone, the excess of protein would put extra work on the liver and kidneys,

IN 100-CALORIE PORTIONS OF FOODS

2 tablespoonfuls sugar
i 0 0 0 0 0 0

iy2 tablespooniuls maple
^ 0 ^2Tff2^3l 0 %^^0

FOR BUILDING DIETS

and the extra vitamins A and G would not make up for the lack of vitamin C. All
kinds of food are "good" for us, but no kind of food is suitable as an exclusive diet.
Even milk, which comes nearest to a balanced food for human beings, would have
to be supplemented with a few shares of iron and vitamin C

and minerals to all white flour. Now all white flour must have not more
than 15 per cent moisture, and each pound should contain

NOT LESS THAN NOT MORE THAN

2.0 milligrams Vitamin Bi (thiamin chloride) 2.5 miUigrams

1.2 milhgrams Riboflavin (vitamin G) 1.5 milhgrams

16.0 milligrams Nicotinic acid (niacin) 20.0 milligrams

13.0 milligrams Iron (Fe) 16.5 milligrams

The addition of vitamin D and calcium is optional ; the maximum of calcium
allowed is 625 milligrams per pound.

Schemes and Rules We can plan a diet by selecting items from each
of these groups of foods. Thus Sherman gives two simple rules for select-
ing Calories, proteins, and the like in terms of food classes:

1. Let at least half the needed food calories be taken in the form of the
"protective" foods — milk and its products, fruits, vegetables and eggs.

2. Whatever breadstuffs and other cereal or grain products are eaten,
let at least half be in the "whole grain" or "dark" or "unskinned" forms.

Sherman also recommends two arbitrary rules to follow in purchasing
food. "Whatever the level of expenditure, it seems wise that (1) at least
as much should be spent for milk (including cream and cheese if used) as
for meats, poultry and fish; and (2) at least as much should be spent for
fruit and vegetables as for meats, poultry, and fish."

A simple way to use the results of some of the findings in nutrition re-
search is to select food articles in wide variety from each of the seven classes
listed above. This plan is likely to supply the needed minerals as well as
the necessary vitamins, and it is likely also to satisfy the palate.

Share Technique A very useful scheme for the easy planning of
balanced diets, the so-called "share" technique, was worked out by the late
Mary Swartz Rose. Rose defined a share as that quantity of any food essen-
tial which supplies one thirtieth of the daily requirement of an adult using
3000 Calories per day. Accordingly, one share of energy is equivalent to 100
Calories, one share of protein to 2.33 grams, and so on. The share values of
the different food essentials and the recommended daily allowances of each
shown in the table on page 130 differ but little from the original recom-
mendations of Rose.

Not all the known dietary factors are included in the table on page 130.
For example, one cannot plan his shares of vitamin D, since some of this
factor is obtained in one's food while some of it is built up by the body;
the quantity synthesized depends upon the amount of sunshine one gets. Ac-
cording to present knowledge, if one gets enough "shares" of energy, pro-
tein, calcium, iron, vitamin A, thiamin, ascorbic acid and riboflavin from

128

COMPARING FOOD VALUES

A large glass of sweetened and flavored water — a "soft drink" — can yield more
"food energy" than almost any helping of good food you might choose in a restau-
rant. But it furnishes nothing at all of other food values, whereas each of the ordi-
nary foods with which the soft drink is compared supplies essential proteins, min-
erals and vitamins. We can measure human energy in calories, but the body can
release energy only if it is supplied with the other nutrients in suitable amounts

Share Values and Daily Requirements of Different Food Nutrients^

KIND OF NUTRIENT

QUANTITY OF NUTRIENT IN
ONE SHARE

TOTAL DAILY REQUIREMENT OF MODERATELY ACTIVE
MAN OF AVERAGE SIZE (154 LBj

In Shares

In Other Units

Energy

Protein

Calcium

Iron

100 Cal

2.33 g
27 mg

0.4 mg
167 international units
0.06 mg

2.5 mg

0.09 mg
0.6 mg

30
30
30
30
30

30
30

3000 Cal

70 g
0.8 g
12 mg
5000 international units

1.8 mg
(600 international units)

75 mg
(1500 international units)
(1500 U. S. P. units)
2.7 mg
18 mg

V^itamin A

Thiamin (vitamin B) . .

Ascorbic acid (vitamin C)

Riboflavin (vitamin G) .
Niacin^

^These values are based on the Recommended Daily Allowances for Specific Nutrients sug-
gested by the Committee on Foods and Nutrition of the National Research Council in May, 1941.

-The fact that there have been too few analyses of the niacin content of food makes it
impracticable to calculate "shares" of niacin.

natural foods, he will also get sufficient supplies of phosphorus, niacin and
all the other essential nutrients.

Requirements in Shares No single food furnishes a balanced diet.
That is, nothing we eat has exactly the proportions of fuel, protein, calcium,
and so on that are listed for one "share". If we analyze various foods and
calculate what they actually contain in proportion to 100 Calories of energy,
we find that most of the other essentials are present either in much larger
or much smaller ratios than 1.0. We can see this at a glance in the table on
the opposite page. All the food we eat yields energy — except water, minerals
and vitamins. Conversely, various essentials are obtained with most of the
energy foods, unless one is restricted to pure sugars and fats. But to get an
adequate diet it is necessary to take a variety of foods.

By comparing various foods, we discover that some yield one essential
in relatively large proportions, whereas others are rather restricted in their
offerings. It is easy to make a great ado about a particular dish or prepara-
tion being exceptionally rich in a particular vitamin or in "quick energy",
and to overlook everything else it lacks (see illustration, p. 129).

For most people a variety of foods selected in share units according to
the total energy requirements will supply all needs. Growing children need
a greater number of "shares" of protein, calcium, iron, vitamin A, and
ascorbic acid in proportion to their "shares" of energy than do adults. Also
special circumstances (such as the need for a reducing diet) or special con-
ditions (such as pregnancy and lactation) require that the relative number

130

Nutritive Values of Foods in Shares^

FOOD

Cereals

White bread (see p. 125j.
Whole-wheat bread . . .
Rolled oats, cooked . . .
Shredded wheat . . . .

Mill^ and Cheese

American cheese ....

Cottage cheese

Whole milk, pasteurized .

Fruits and Vegetables

Apples

Bananas

Lima beans, fresh, steamed
Carrots, fresh, steamed

Lettuce

Oranges

Peas, fresh, steamed . . .
Potatoes, white ....
Raisins, seedless ....
Spinach, chopped, steamed
Tomatoes, fresh ....

Fats

Butter

Oleomargarine with vita-
min \ added

Lard

Salad oil, corn, cottonseed,
olive

Sugars

Brown sugar . .
Granulated sugar
Loaf sugar . . .
Maple sirup . .

Meats and Eggs

Beef, round . , .

Eggs

Fish, mackerel . .
Liver, fried . . .
Pork chop, broiled

MEASURE

2 slices
Ig slices
I cup
1 bi.scuit

Ig-in. cube
5 tbsp
I cup

1 large

1 medium
icup

I§ cups

2 large heads.
1 large

I cup
1 medium
2i tbsp
2| cups

3 medium

1 tbsp

1 tbsp
1 tbsp

1 tbsp

3 tbsp
2 tbsp

4 pieces
\h tbsp

avg servmg

1 large
avg serving
avg serving

2 chop

CAL-
ORIES

PRO-
TEIN

CAL-
CIUM

IRON

VITA-
MIN A

THIA-
MIN (B)

ASCORBIC
ACID(C)

1.(1

\.u

0.4

1.0

1.7

0.8

2.8

1.9

—

1.0

l.S

0.7

^.0

—

1.^

—

I.O

1.4

0.4

3.1

—

1.4

—

1.0

2.8

7.4

0.8

4.1

0.2

1.0

8.2

2.8

0.2

0.1

—

1.0

1.1

6.7

0.9

1.7

1.5

0.9

1.0

0.2

0.5

1.4

0.6

1.1

4.0

1.0

0.6

0.3

1.6

1.7

1.3

3.2

1.0

2.6

0.9

4.9

2.4

2.0

4.8

1.0

3.8

3.4

40.8

i.l

2.7

1.0

3.0

12.0

16.0

13.0

8.0

32.0

1.0

0.7

2.0

1.5

2.6

3.6

42.0

1.0

2.8

0.9

4.9

6.6

7.9

3.9

1.0

1.1

0.5

2.8

0.3

1.0

0.3

0.7

2.5

0.1

0.8

—

1.0

3.5

26.5

500.0

5.5

28.0

1.0

2.3

1.7

5.3

24.7

7.7

44.0

1.0

—

0.1

3.3

—

1.0

0.1

0.2

3.3

—

1.0
1.0

1.0

0.9

1.8

1.0
1.0
1.0

—

2.1

2.7

—

1.0

5.7

0.3

4.7

0.1

1.7

1.0

3.9

1.6

4.9

6.1

1.8

—

1.0

5.8

0.3

1.6

0.8

1.1

—

1.0

6.8

0.3

23.6

35.0

3.9

2.4

1.0

3.4

0.2

3.0

—

3.4

—

RIBO-
FLAVIN
(G)

0.4
0.4
0.3

1.3
3.0

?>.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

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

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

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

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

Ascorbic acid is synthe-

Is easily destroyed

Is not stored in

Tomatoes and citrus

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

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

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

C17H20N4O6

yeast

Niacin

Niacin (nicotinic acid)

Is relatively sta-

Is stored to a

Liver, lean meat, fish,

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

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.

III

VII

VIII

Name of

Duration

No. of

Cubic

Calories

Bodv-

Calorics

Subject

of Test in

Pumptuls

Centi-

Used

Weight

Used

Minutes

of Oxy-

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- \

synthesis 3^

Carbon
dioxide

air

K't

»y

Bodie

Carbon

and
oxygen

<:>'.

,ee5

soil

.^1^

,^^

Bodies

Excretion

^Q'j

:'o.<f

^j^

Herbivores

.;s.j

A-

Omnivores

*^.,

Food

Carnivores

THE CARBON-OXYGEN CYCLE

The material of green plants consists in part of carbon derived from the carbon diox-
ide of the air. This carbon is passed on to animals as food, or returned to the air
by respiration or by burning. Animals either pass on the carbon to other animals
which eat them, or return it to the air by respiration. Some of the carbon is locked
temporarily in the soil as excretions or as dead bodies. Through decay, the action
of bacteria and fungi, this carbon is returned to the air as carbon dioxide

water, through the soil and other organisms. And while the atmosphere
is nearly four-fifths uncombined, or "free", nitrogen, green plants cannot
utilize it.

As a matter of public economy, people have found it worth while to save
the manure of barnyards and even the sewage of cities for the nitrogen com-
pounds that these contain. But in spite of all our saving, vast quantities of
nitrogen are washed out to sea or thrown into the air beyond the reach of
our common plants.

It has been possible to use nitrates, which are found as mineral deposits
in certain places, especially in Germany and Chile. But the quantity of these
nitrates is limited, and they are relatively expensive. On certain islands off
the coast of South America there are extensive deposits of guano, or bird
refuse, left there by countless birds that have built their nests upon these

150

Legumes

THE NITROGEN CYCLE

Most plants take nitrogen from the soil, as soluble nitrates. Most animals receive
nitrogen from plants or from other animals, as proteins in their food. Nitrogen in
the bodies of plants and animals passes on to other living things as food or in the
process of decay — which means the feeding of bacteria or fungi. Or it passes into
the soil or the air as a result of death and decay. All living things eventually depend
upon nitrogen-fixing bacteria, which return to the soil atmospheric nitrogen combined
into forms that other living things can use

islands for hundreds of years. This guano contains nitrogen and other ele-
ments usable by plants in food-making, and it has been imported for use as a
fertilizer. But the amount of guano is limited and constantly diminishing.

The nitrogen supply will probably last as long as the present inhabit-
ants of the earth are likely to live. But society expects to outlive its indi-
vidual members and must look ahead through its statesmen for those not yet
born (see illustration above). Two solutions of the "nitrogen problem"
have developed in comparatively recent years. One comes from a better
understanding of living things; the other is an application of chemical
knowledge.

Rotation of Crops If we grow several crops of grain on a farm, the
yield tends to diminish in time because the nitrogen gives out. But we do
not have to abandon the farm, nor need we import expensive nitrogen ferti-

151

Hugh Spencer

The swellings are inhabited by a vast
number of tiny one-celled organisms that
feed upon carbohydrates produced by
the alfalfa plant. These guests absorb
nitrogen from the air and combine it
with material taken from the host, pro-
ducing proteins. The alfalfa plant makes
use of the excess protein. Nitrogen-
fixing soil bacteria form similar tubercles
on the roots of peas, beans, clover and
other plants of this family. The bacteria
produce much more protein than they
can use, just as most green plants pro-
duce much more sugar or starch than
they can use. As a result of this part-
nership the plants of the legume family
contain much larger proportions of
nitrogenous compounds than those of
any other family. And a crop of such
plants leaves more nitrogen in the soil
than there was at the start

BACTERIAL SWELLINGS ON ROOTS OF ALFALFA

lizer. We have only to plant a crop of peas or alfalfa, and to make sure of
the special kinds of bacteria that form the tubercles on the roots of these
plants. It is now possible to buy cultures of the species of bacteria that are
known to thrive best on any particular legume species.

In the course of the summer the bacteria in the tubercles will "fix" a
large quantity of nitrogen from the air. Part of this they will make into
proteins and consume in growth. Another part will be taken from them
by the plants upon which they grow. And at the end of the season there
will be present in the soil and above the soil (in the green plants) a great
deal more nitrogen in combined form than there was at the beginning.
The clover or alfalfa can be plowed under, and the nitrogen compounds
in the plants thus added to the soil. After another season of this kind of
crop enough nitrogen will be restored to the soil to support several crops
of grain. This rotation of crops has been practiced by experienced farmers
for many centuries, but it is only within the last fifty or sixty years that
the significance of rotation has been understood.

Industrial Fixation of Nitrogen For the chemical solution of the
nitrogen problem we are indebted to a Swedish scientist, Svante Ar-
rhenius (1859-1927). Arrhenius worked out a process for making nitro-
gen combine with other elements under the action of electric currents.
A process for combining nitrogen from the air with hydrogen, forming
ammonia, was worked out by the German chemist Fritz Haber (1868-

152

I'niteii States Forest Sen ice

VIRGIN FOREST

Under natural conditions where the soil is covered with forest or grass, the topsoil
builds up slowly from the weathering of rock material and the accumulation of or-
ganic debris. Forest litter, organic matter in the soil, and roots absorb the rains and
prevent water from washing away the soil

Soil Conservation Service (Ia-154)

DOWNHILL PLOWING INVITES EROSION

We have removed the native cover of trees, shrubs, vines and grass. We have pul-
verized the soil and exposed it to the elements year after year, as in row-crop or
clean-culture farming. With this treatment, the rich soil is v/ashed from the upper
portions of slopes, burying the crops at the bottom

1936), and developed on an enormous scale in Germany. During the
First World War the shortage of nitrogen compounds threatened to set
a limit to further fighting, especially in the central nations. The nitrogen
supply was important for military activities as well as for raising crops
and for industry, since all explosives are based on nitrogen compounds.
Haber's invention solved the nitrogen problem for the Germans, and en-
abled them to hold out for many months longer than would otherwise
have been possible,

Haber died in Switzerland, an exile from his native land. In the
meantime, the leading nations of the earth have been using his process,
with various improvements, for converting atmospheric nitrogen into
ammonia, nitric acid, and other essential compounds. These are widely
used in fertilizers, in industry, and in explosives. In this way these na-

154

w. '^

*^^* I&

K.iuliiiiiiui Fabry

POWER MACHINERY AND CULTIVATION

The use of power machinery has enabled us to plow and cultivate much more acre-
age than formerly. In this picture one man with a tractor cultivator is seen doing
work as fast as six men can do it with horse-drawn cultivators

tions are becoming independent of natural supplies of nitrogen com-
pounds, which most of them would otherwise have to import. But by
the end of the first year of its participation in the Second World War, it had
become necessary for the authorities in the United States to restrict the use
of nitrogen fertilizers for all nonessential crops, lawns, and flower gardens.
Out of the Earth Those who live in the country usually understand
how our lives depend upon the soil, but city dwellers come to think of
the land as merely the surface, or place, upon which we live. We have
seen that water is necessary for all life processes, and that the carbon
dioxide of the air supplies material for the making of carbohydrates. All
the other substances present in the bodies of plants and animals come out
of the soil. Just as sunlight and sun-heat are the sources of our energies,
so earth, water and air are the sources of our bodies. The crowding of a
population may reduce food supplies through a shortage of soil materials.

155

A few generations ago thoughtful people looked forward to over-
crowding in the fear that it would lead to great destruction of human
life, or at least to great suffering. Indeed, the poverty and hunger of
past times were largely due to man's inability to obtain from the soil
adequate supplies of food. At the present time, however, our special
knowledge and processes are so advanced that we are able to produce food
and other essentials and many conveniences far in excess of the quantities
needed for general comfort. We are, in fact, producing more foods of
various kinds than we are able to distribute through existing systems of
exchange — that is, through our business and financial machinery. This
does not mean that everyone has all the food he needs. Even before the
Second World War, not only was a very considerable part of our popula-
tion misnourished, but a substantial part was actually undernourished.

Saving the Soil Increasing agricultural efficiency and activity does
not assure abundance for everybody. Over large parts of the country we
have made every cultivated acre yield three or four times as much food
as had been usual in past generations. At the same time, we have removed
from many areas tremendous quantities of minerals, so that the fertility of
the soil is gone. And in addition, our ways of working the soil have ruined
millions of acres by removing that portion of the earth's crust which is usable
for crop production.

Under natural conditions, where the soil is covered with forest or grass,
the topsoil builds up slowly from the weathering of rock material and the
accumulation of organic debris (see illustration, p. 153). Even though some
erosion takes place, the building-up processes more than make up for the
loss. But we have removed the native cover of trees, shrubs, vines and grass.
We have pulverized the soil and exposed it to the elements year after year,
as in row-crop, or clean-culture, farming. As a result, soil has been removed
from the top much faster than it is built up from below. Water and wind
have carried the loose topsoil from the exposed hillsides and gullies into
valleys and streams. After the topsoil has gone from the hills, the poor
subsoil washes away, too, and in many cases covers the rich soil previously
deposited in the valleys.

In Brief

Carbohydrates originate in green plants through the action of sunlight
upon water and carbon dioxide in the presence of chlorophyl; oxygen is a
by-product of this photosynthesis.

All other organic materials are derived from carbohydrates.

Both plant cells and animal cells synthesize fats from starches and sugars.

When supplied with carbohydrates and suitable mineral salts, non-green

156

plants, as well as those having chlorophyl, synthesize proteins, which con-
tain nitrogen and other elements in addition to the carbon, hydrogen and
oxygen derived from carbohydrates.

Single-celled green plants carry on all the activities that together make up
being alive; all other cells of plants and animals depend upon chlorophyl-
bearing cells for food.

Water and dissolved minerals absorbed by root hairs pass into the central
cylinder by diffusion; from here they move bodily to other parts of the plant
through special vessels; food is returned to the roots through other vessels.

The stem of a plant is an organ of support and of transportation. Water-
conducting and food-conducting tubes of plant stems, as well as much of the
supporting tissue, are arranged in bundles.

In monocot stems the fibrovascular bundles are scattered in the pith; in
dicot stems they are arranged symmetrically.

The upward flow of water through the plant is due to osmosis in the
roots and between cells, and to transpiration.

Animal life depends upon the activities of green plants; but the con-
tinued existence of green plants depends upon the oxidation of the organic
substances which in nature goes on chiefly in the bodies of animals.

Various forms of living things are interrelated through the continuous
interchange of materials described as the carbon cycle, the oxygen cycle,
and the nitrogen cycle.

EXPLORATIONS AND PROJECTS

1 To demonstrate the iodine test for starch, add a few drops of iodine^ to
each of several test tubes prepared as follows: water only; water with cornstarch;
water with piece of potato; water with white flour. Use small quantities of
material and heat each tube to boiling. Note the blue-black color in the test tube
containing starch. All kinds of starches produce a similar reaction with iodine;
but chemists have found no other common substance that does so. We therefore
take a blue-black color resulting from the addition of iodine to a substance to
indicate the presence of starch.

2 To show the relation of light to starch-making in leaves, expose one of
two healthy potted plants to sunlight and keep the other in the dark. At the end
of the day, remove leaves from each plant and boil them about a minute to soften
the tissues and to fix the starch. Then place in alcohol to remove the chlorophyl.
When convenient, test the leaves for starch with an iodine solution. Compare
results and formulate conclusions.

3 To show the relation of chlorophyl to starch-making, use a plant with
variegated leaves, which have chlorophyl in some parts but not in others. After

^Tincture of iodine may be used, or a solution of 0.3 g of iodine crystals and 0.3 g of
potassium iodide in 100 cc of water,

157

a day in sunshine, remove leaves and test for starch, as in No. 2 above. Describe
results. What do they show.?

4 To demonstrate the liberation of oxygen during photosynthesis, place two
healthy potted plants under separate open-topped bell jars. Place a Hghted candle
in each bell jar and seal. After the candles are extinguished, allow the jars to cool
for about 10 minutes; then carefully Hft the stopper of each and insert a glowing
splint. After making sure that there is no longer sufficient oxygen within the bell
jars to keep a flame burning, place one jar in the dark and the other jar in the
light. After several hours of sunshine, test the air in both jars for oxygen. Com-
pare results and note conclusions,

5 To demonstrate the relation of light to stoma movements, place one of
two similar potted plants in the dark and one in a sunny location. To the under
surfaces of a few leaves on each, apply benzine with a small paintbrush. If the
stomata are open, the benzine quickly penetrates to the inside, giving a transparent
appearance. If the stomata are closed, it takes longer for the benzine to penetrate.
Compare and note conclusions.

6 To observe the closing of stomata through the microscope, peel the lower
epidermis from a leaf of a plant that has been exposed to direct sunlight for some
time. Place in water on a microscope slide. Apply a drop of concentrated sugar
solution to one edge of the cover-glass while watching a stoma through the micro-
scope; draw the sugar over the epidermis, by applying a bit of filter paper to the
opposite edge of the cover-glass. The sugar solution removes water from the
guard cells by osmosis. How do the guard cells react.? How would you explain
what happens?

7 To show that osmotic pressure in the roots pushes liquid up, replace the
shoot of a plant with a glass tube. Cut the stem off a healthy potted plant about
an inch above the soil line; fasten a long glass tube to the stump by means of
rubber tubing. Tie the rubber tubing securely on the stem with a string. Stick a
similar glass tube in the soil. Keep the soil well watered. Compare results after
one or two days and account for the differences.

QUESTIONS

1 What are the sources of all organic materials?

2 In the process of photosynthesis, what are the raw materials, what is the
source of energy, what by-products are given off, and what "machinery" is
essential ?

3 What materials can both plant and animal cells synthesize from carbo-
hydrates ?

4 What elements are present in protein substances?

5 From the standpoint of food synthesis, what functions do the stems of
plants serve?

6 How does girdling kill a tree?

7 How are various forms of living things interrelated through the carbon
cycle? through the oxygen cycle? through the nitrogen cycle?

8 In what respect is the soil a natural resource?

158

UNIT TWO — REVIEW • UNDER WHAT CONDITIONS CAN WE LIVE?

We all feel that "life" is the central and the important thing in the world.
We often speak of "life" as if it were.a peculiar something or being which
happens to dwell in certain natural objects, but which might as well exist
elsewhere, or not at all. Yet what we know of "life" is what we can observe
and understand about the activities of living plants and animals. These
plants and animals, in turn, continue to be alive — to "have life" — only under
rather special circumstances.

There are many kinds of substances in the world — some ninety elements
and numberless compounds. Certain of these are present in all living things.
A few are present occasionally, in a few species; and some are never found
in living things, or may even be injurious. But in every case life goes on
only on condition that these few elements are available — or rather certain
of their compounds.

Living forms are found in all zones of the earth, in the waters and on
the mountains, and in the deserts too. But everywhere water is an essential
material condition of life. At the same time, water may be a source of
injury. It is not merely that some of us might drown if completely sub-
merged, but for various plants and animals an excess of water means a
diluting of the intake, or a bloating of the tissues.

These materials contribute both to the bodies of living things and to the
processes that characterize plants and animals. These constant chemical
changes are in a sense both the processes of living and the conditions of
living. These chemical processes continue under a wide range of physical
circumstances. Each species, however, can live only within relatively re-
stricted ranges. Thus living things exist close to the freezing point of water
at one extreme and near the boiling point at the other. It is only the very
simplest types of organisms that endure such extremes of temperature —
different species at each extreme. But many of the back-boned animals are
adapted to a wide temperature range by special protective coverings and by
complex mechanisms that keep the inside of the body at a nearly uniform
temperature.

Light influences protoplasm in various ways — even injuriously, when of
extreme intensity. And yet it is upon sunlight that the whole world of
plants and animals ultimately depends for its nourishment. For this form
of energy makes possible the construction of carbohydrates out of water and
carbon dioxide. And plants and animals utilize these compounds, first as
sources of energy for their own activities, and second as bases for the pro-
teins out of which new protoplasm is constantly being made.

The million or more different species, and the countless individuals in
each species, all depend upon essentially the same basic conditions. All

159

organisms depend upon the same reservoir of water and soil and air. Yet
the various Hfe forms depend upon one another. Animals and plants lack-
ing chlorophyl depend upon green plants for their food. But the continuous
action of green plants depends in tu];n upon those other forms, which, by
oxidizing their food, restore carbon dioxide to the air and the waters. These
basic materials are in constant circulation, passing from the nonliving sur-
roundings into plants and on into the bodies of animals. The vast total of
"life" appears to be possible precisely because there are so many different
kinds. Each species is completely surrounded by other "life" which con-
tributes— and also takes away. There is a constant destruction, but there is
also a constant restoring or balancing.

Millions of us satisfy our need for foods of various kinds, draw water
(hot and cold) from convenient faucets, and buy our clothes according to
means and taste without ever finding out that we are drawing upon the
earth. The soil as the source of our material existence and well-being is
actually managed by a diminishing fraction of the population. Fewer
farmers and fishermen and hunters and foresters supply a larger population
than lived here a generation ago. It takes fewer acres, as well as fewer men,
to grow the crops and animals we consume. It is nevertheless of first im-
portance that the entire soil be conserved, that the nation's entire water sys-
tem be protected and developed, that all our forests and streams be main-
tained at a constant productive level. For, however far we may get from
the land, our life is inseparably tied to the soil.

160

UNIT THREE

How Do Living Things Keep Alive?

1 How can living things without mouths get what they need?

2 How can the same food produce such different results in a calf and a

baby?

3 What happens to food after it is swallowed?

4 How is it that our stomachs digest tripe but do not digest themselves?

5 What makes sawdust food for termites but not for horses?

6 What is it that makes one breathe faster at some times than at others?

7 What keeps the heart beating when other muscles get tired and quit?

8 Why are some animals warm-blooded and others cold-blooded?

9 How con animals tell what is injurious to them and what Is useful?

The conditions for living are fundamentally the same for all species, and
they are essentially the same for plants as for animals. We are impressed
by the great variety of living forms that keep going, and under such wonder-
fully diverse conditions. The whale and the jellyfish live in the same ocean.
The eagle and the lichen make their homes on the same bare rock.

How does any particular organism actually keep alive? How can two
or more totally different species keep alive in the same surroundings ? How
can a similar animal manage in what appears to be quite a different set-
ting? We know that every living cell depends upon a supply of food and
oxygen. How, then, do the cells in the innermost parts of a person's body,
or at the tips of the limbs, get the needed supplies?

Not only do these many different kinds of plants and animals keep alive,
but many withstand the most extreme physical conditions. Their ways ap-
pear in each case to fit the special conditions, as well as the seasonal changes
of their habitation. They are fitted to using a wide variety of foods. They
are able also to adjust themselves to scarcity as well as to abundance.

Living protoplasm produces more and more of itself out of food that
is quite unlike it. But out of the same kind of food an ox makes beef, a
sheep mutton, a horse horseflesh, and a grasshopper something entirely dif-
ferent. We call it "assimilation" in every case, but what happens between
the arrival of food in an animal and its becoming beef or mutton or human
flesh?

As life goes on, wastes are produced. The simplest organisms move
along, leaving their wastes behind them, just as primitive people move away
when their camp sites become too littered and offensive. How do larger
plants and animals dispose of the wastes their bodies produce? Do these

161

wastes threaten to obstruct life as they accumulate in the earth or in the

water? . u u

When we recover from some diseases, we become immune to them, but
other diseases one may have again. Plants and animals recover from in-
juries. What changes take place in the body when it is sick? How does
vaccination work? Why can we immunize against certain diseases, but not

against others?

We may understand some of the similarities among plants and animals
which we include under the broad idea of "life". But many questions are
raised by the variety of living forms, and especially by the complexity of
our own bodies and of other familiar species. How do such totally different
things as a man and a clam, a bird and a mushroom, all manage to carry
on essentially the same processes ?

162

CHAPTER 9 • HOW DO LIVING THINGS

GET AND MANAGE THEIR FOOD?

1 What happens to food after it is eaten?

2 How does the food which we place in the mouth and swallow

get to the other organs of the body?

3 How is it that grass is suitable for the buffalo, flesh for the tiger,

and wood for the termite?

4 Could meat-eating animals thrive if they were fed exclusively

on vegetable matter? Or could cattle live on meat?

5 How do growing plants get at the food stored in seeds, roots, or

underground stems?

6 How can some animals eat their meal and chew it later?

7 What connection is there between body build and feeding

habits ?

8 How are the activities of animals related to food-getting?

9 Why are some kinds of food more easily digested than others?

Some animals eat but a limited number of things. Others, like man,
feed on a great variety. Species that feed on meat alone differ in structure
and in behavior from those that feed on grass alone, for example. The
talons and beak of a hawk, the rough, grasping tongue of the ox, the pierc-
ing mouth of a mosquito, and the biting mandibles of the grasshopper all
seem to be especially related to getting particular kinds of food. In fact, the
whole nature of an animal seems closely connected with his eating habits.
Do the digestive systems of different animals vary, as the food-getting
habits do?

How Do Plants Manage the Food They Make?

Digestion^ The sugars which are first produced during photosynthesis
are in many plants later changed into starches. Most of our common plants,
however, produce starch in their leaves. Now starches are colloids — that is,
they are like glue and cannot diffuse through cell walls — whereas sugars are
crystalloids, or like crystals, and can diffuse through a membrane. Experi-
ments show that in both animals and plants starches are changed into sugars.

When grains and other starch-bearing seeds germinate, the starch slowly
changes into sugar. We can wash out of such sprouting seeds a substance
called diastase. And we can show that in the presence of water, diastase
converts starch into sugar. This process is called digestion.

iSee Nos. 1, 2 and 3, pp. 182-183.
163

Diastase can be extracted from "malted" barley (that is, barley kept moist
until the grains sprout), from rice, and from many other seeds. Malt is pro-
duced in quantities from sprouting seeds, and is used in making beer. A
substance similar to diastase is found in human saliva and in the digestive
juices of many other animals. The digestion of starch into sugar makes it
possible for carbohydrates to pass through cell walls by osmosis.

Enzymes Substances like diastase and the active part of the saliva are
called ferments, or enzymes. Many different kinds are known. Like vita-
mins and hormones, enzymes induce chemical changes in other suhstanc-es
out of proportion to their amounts. These substances resemble what the
chemists call a "catalyst" — something that seems to induce or accelerate
chemical changes in other materials while remaining apparently un-
changed itself.

Food Transportation Sugar formed in leaves during daylight diffuses
out of the pulp cells and moves down through the bast or phloem tubes.
When sugar is produced faster than it can be carried away, the excess is
converted into insoluble starch. Starch thus accumulates in the leaf during
the day. When darkness sets in, diastase converts starch into sugar, and this
is then carried down into the stem or roots (see illustration opposite). That
accounts for the fact that green leaves are full of starch in the late after-
noon, but have no starch at all before dawn.

In the cells of potato tubers and of other organs that do not contain
chlorophyl, starch is formed from sugar by the action of an enzyme. This
process is just the reverse of digestion. The dissolved sugar in the leaves
passes at first from cell to cell by osmosis, then in the sap by way of the bast
tubes. In the root or tuber the sugar passes from the vessels to the pulp cells
by osmosis, and is then converted into starch.

Digestion Universal The process of digestion seems to go on in nearly
all living things. The ameba, which consists of a mass of naked protoplasm,
swallows a solid particle into itself at any point and then digests the "food"
inside the cell. Among the bacteria, which are the smallest living things
known, each individual is a single cell consisting of protoplasm and cell
wall. These tiny plants can get food only in a liquid state; yet many of
them live on solid food that is not soluble in water. When meat or cheese
rots, it becomes fluid. The rotting in such cases is the work of the digestive
ferments secreted by the bacteria (see illustration, p. 166). When certain
bacteria get established in the nose, for example, or in the throat or the
appendix, the digestive action of their enzymes destroys living tissue, pro-
ducing inflammation and soreness.

In higher animals like ourselves, a similar process of digestion takes place.
But not every cell pours out digestive juices into its immediate neighbor-
hood: only certain portions of the body produce and secrete such enzymes.

164

CARBOHYDRATES BY NIGHT AND BY DAY

In daylight, photosynthesis normally produces sugar faster than it can diffuse out
of the cells and move into growing tissues or into underground ports. Surplus sugar
in the leaves, and the sugar brought from the leaves into underground structures,
become converted into starch. In the dark the starch that has accumulated in the
leaves becomes transformed into sugar, which is carried into tubers or other under-
ground "storage" structures

How Is Food Digested in Man?

The Human Food Tube^ The mouth is the beginning of a long tube
inside of which all the digestion takes place. This tube is called the ali-
mentary canal, or food tube. It consists of several fairly distinct regions. It
is ten or eleven yards long and is coiled or twisted in parts (see illustra-
tion, p. 167).

In the mouth, food is crushed and ground by the teeth. The taste of the
food, the movement of the jaws, and the rubbing of the food against the
inside of the mouth stimulate the saliva glands. As a result, a quantity of
saliva flows into the mouth and becomes mixed with the food. An enzyme

1 See No. 4, p. 183.
165

in the saliva changes the starch into sugar. Over 99 per cent of saUva is
water, and this water dissolves salts and sugars.

The amount of enzyme is very small. The digesting of the starch de-
pends upon (1) the ferment's reaching every particle of starch and (2) suf-
ficient time for the ferment to act. Mixing saliva thoroughly with the food
coats the mass with the slippery mucus of the saliva. That makes it easier
for the mass to slide along into the throat and down the gullet.

After the mouthful of food has been thoroughly chewed, it is pushed
back by the tongue and passed into the throat chamber, or pharynx. From
the pharynx it passes directly into the gullet, or esophagus (see illustration
opposite). Muscular rings in the wall of the gullet contract in series and so
push the food toward the stomach. If you watch a giraffe or a horse drink-
ing water from a pond or from a pail on the ground, you can see him
swallow up-yoM can see one wave of contraction after another pass along
the gullet, from the head to the trunk.

The Stomach' When nerve-endings in the mouth or nose are stimu-
lated, glands in the stomach wall are aroused. These secrete stomach juice,
or gastric juice. The fermentation started by the saliva continues until the
mass of food gets into the stomach. Here the action is stopped by the acid
stomach juice. The swallowed food is thoroughly mixed with the gastric
juice by the churning action of the stomach muscles.

The gastric digestion breaks proteins into compounds that dissolve in
water and diffuse through membranes. As digestion proceeds, the mixture
in the stomach becomes more and more liquid and more and more acid.
From time to time a quantity of the liquid passes into the intestine. Most

DIGESTION BY BACTERIA

In the presence of "food" and under suitable conditions of moisture and tempera-
ture, each cell discharges through the eel! wall, by osmosis, one or more enzymes,
or ferments. The enzymes digest the food material, changing proteins, for example,
into simpler compounds that are soluble in water. The resulting fluid .s then ab-
sorbed through the cell wall into the protoplasm, and is then assimilated

iSee Nos. 5 and 6, p. 183.
166

Sublingual
Submaxillary

Parotid gland

Esophagus

Liver

Opening of

ducts from

liver and

pancreas

Gall bladder

Opening to

large

intestine

Appendix

Stomach

Pancreas

Large
intestine

Small
intestine

Rectum

THE DIGESTIVE SYSTEM IN MAN

of the contents of the stomach become in time changed to the consistency
of a rather thick pea soup, and all pass on into the intestine.

The Bowles, or Intestines' Among the vertebrates the gut has two dis-
tinct divisions. The first is called the small intest'uie, and in adult human
beings it is about one inch in diameter and about twenty-four or twenty-five
feet long. It opens rather abruptly into the large intestine, which is about

iSee No. 7, p. 183.
167

two inches in diameter and about five feet long (see illustration, p. 167),
Pig gut and calf gut are used as sausage casing.

The wall of the intestine is thin and soft. The lining carries very small
glands, and the outer layer contains muscle cells. The muscles run around
the tube in rings, as in the esophagus, so that, as they contract, the diameter
of the intestine is reduced. Waves of contraction start at the forward end
(nearest the stomach) and pass backward along the whole length of the
small intestine. The contractions move some of the contained mixture along,
a short distance at a time. This movement is called peristalsis and is similar
to the swallowing movement of the gullet. In vomiting, the peristaltic
action of the food tube is reversed.

On leaving the stomach the food mixture contains in solution all the
sugar that was there to begin with, all the sugar that was formed by the
digestive action of the saliva; it contains the peptones resulting from the
gastric digestion, and various mineral salts. This mixture contains what-
ever starch was not digested; any undigested proteins; and all the fats,
which are affected by neither the saliva ferments nor by the gastric enzymes.
In addition, there is a quantity of water, the acid remains of the juices, and
the fibers and cell walls of the food material.

The fats and the remaining starches and proteins are digested in the
intestine.

Intestinal Digestion^ Near the beginning of the intestine two small
ducts or tubes empty at a common opening. One of them leads from the
largest gland in the body, the liver; the other from the pancreas (see illus-
tration, p. 167).

The juice secreted by the pancreas contains three important enzymes:
(1) an enzyme that converts starch into sugar; (2) an enzyme that digests
proteins into simpler compounds; (3) an enzyme that breaks up fats into
glycerin and fatty acids.

The pancreatic juice thus contains ferments that digest all classes of or-
ganic nutrients. The fatty acids that result from the splitting combine with
other substances into "soaps". Soaps and glycerin dissolve in water and
are absorbed by cells lining the Intestine. Farther along, where the intestinal
fluid is acid, this kind of digestion is impossible.

The liver produces bile, or gall, which contains no digestive enzymes.
But the bile neutralizes the acid of the gastric juice and so furthers the work
of the pancreatic enzymes, which are active only in an alkaline solution.
The bile also influences the diffusion of soaps and fatty acids into the cells
of the intestine.

The bile consists largely of materials that are of no further use in the
body; the liver is thus also an excretory organ.

^See No. 8, p. 184.
168

Tubule of
gland ▲

Drop of

secretion

I (B i o ) o ' < . mnitlini

Tubule of glan

Ghnd - cell secretion

Lymph

■='^=^_^ Capillary

^Food material

Blood vessels

HOW A GLAND SECRETES

a.f:

Materials are transformed in a gland by chemical action in the epithelial, or lining,
cells. The raw materials are derived from the blood stream or the lymph. The
specific substance formed by the gland is diffused out of the epithelial cells into the
tube or pit which they surround. The secreted substance is discharged from the gland
through a duct, or little tube. The excretions of the specific secreting cells are re-
moved by osmosis into the lymph or blood, as in the case of other body cells

Glands and Juices We have seen that the carbohydrates, fats and pro-
teins are split into simpler compounds by specific ferments in the juices
secreted by glandular organs. But there are many sugars and many fats and
many proteins. Among the enzymes secreted by glands in the walls of the
small intestine, some convert sucrose and other complex sugars into simpler
ones. A certain enzyme will split one sugar, but will have no effect what-
ever on another sugar. Proteins, when digested, break first into proteoses,
then into peptones, then into numerous peptids, until finally only many
kinds of amino-acids are left. At each stage in the cleavage of a protein into
the fifteen or more amino-acids, a special enzyme operates.

There are many kinds of glands besides those which produce digestive
juices. For example, the tears come from special glands, as do sweat, milk,
the mucus. The shell of an oyster may be considered as a precipitated lime
secreted by skin cells acting very much like glands. The kidneys are really
large glands which remove wastes from the blood, making them into urine,
and then discharge the urine through special ducts (see page 218). Still

169

other "glands", as we shall see later (Chap. 16), are characterized by having

no ducts.

Absorption of Digested Food Tiny projections into the cavity of the
small intestine increase the absorbing surface of the lining several hundred
times (see illustration opposite). These projections are called villi (singular,
mllus), from a Latin word meaning "shaggy hair" which gives us also
velvet. The villi act both as absorbing and as transforming organs. That is,
the materials they absorb become chemically changed before being passed
on into the lymph, the colorless fluid which surrounds all the living cells in
the body. They thus behave like glands, only, so to say, in reverse. For
glands normally absorb materials from the lymph, transform them chemi-
cally, and then pass out new substances.

Gland cells in
surface layer

Simple tubular

Simple alveolar

:m II \:\^^^J

Complex tubular

Complex alveolar

TYPES OF GLANDS

Glands consist essentially of secreting cells arranged in a layer, which tends to fold
into depressions, or pockets. A gland may thus consist of one or a few cells secret-
ing on the surface, or it may consist of a simple tube, more or less enlarged toward
the bottom into an "alveolus", or pit. in some glands the tubes branch and subdi-
vide extensively, so that a great deal of secreting surface supplies one opening or
tube. The liver, the largest gland in the body, is a compound tubular gland. Alveolar
glands may also branch and become complex— the pancreas, for example

170

The velvety appearance of
the inner surface of the small
Intestine is due to the multi-
tudes of projecting villi. The
layer of cells covering these
villi absorbs digested food
from the food tube. The di-
gested food, after some chem-
mical changes, diffuses out
into special lymph tubes, the
lacteals, and finally gets into
the blood. The action of the
villi may be compared to that
of glands; but whereas the
movement of materials is from
the blood stream to the spe-
cial secretions in the case of
the glands, it is from the food
supply to special blood sub-
stances in the case of/the villi

Villus -

Network of

blood

vessels

Lacteal, or
lymph
vessel

Intestinal
gland

THE LINING OF THE INTESTINE

The mixture in the intestine now consists of (1) many crystalloids in solu-
tion, (2) many colloids in the process of being converted into crystalloids,
and (3) solid substances that are not changed under conditions that exist in
the gut.

When the dinner that you have eaten reaches the end of the small in-
testine, most of its carbohydrates, proteins and fats have been absorbed by
the villi and passed into the lymph and blood. There are left in the intestines
chiefly (1) the undigested (mostly indigestible) fibrous and cell-v^all parts
of the plant or animal tissues eaten, and (2) the chemically changed mate-
rial from the various glands that have poured their products into the food
tube along the way. This mass of refuse now passes into the large intestine
(see illustration, p. 167).

The Large Intestine In the large intestine the enzymes of the digestive
juices may continue to act for some time. The lining of the intestine con-
tinues to absorb fluids, although there are no villi in the large intestine.
Finally, the only chemical changes going on are those produced by the mil-
lions of bacteria that are present.

The mass of material that accumulates toward the end of the large in-
testine is of no further use to the body. To this refuse are added dead cells
from the lining of the intestine and waste materials absorbetl from the
surrounding fluids and cells. The refuse, or feces, is normally removed from
time to time. Birds, having no large intestines, throw off the refuse about

171

Products of Glands with Ducts

FUNCTIONS

GLANDS

PRODUCTS

Digestive

SaUvary

Gastric

Pancreas

Liver

Intestinal

Saliva

Gastric juice
Pancreatic juice
Bile
Intestinal juice

Lubricant

Mucous
Serous
Lachrymal
Sebaceous
Wax glands in

ear canal

Mucus

Serous fluids

Tears

Oil

Wax of the ear

Cooling

Sweat glands
Mucous glands

of respiratory tract

Perspiration
Mucus

Food

Mammary
Villi

Milk

Fats and proteins from absorbed foods

Excretory

Kidneys
Sweat glands
Liver

Urine

Perspiration

Bile

as fast as it passes from the small intestine to the rectum. Other animals and
human infants automatically throw off the refuse from time to time.

What Do Other Kinds of Animals Do with Food?

Kinds of Feeders The digestive system in the human body disposes
of the proteins, carbohydrates, and fats from a great variety of sources-
plants and animals of many different kinds. Animals are of course re-
stricted in their diet by what happens to be present in their immediate sur-
roundings. But many species are limited also by their natural equipment
for making the food available. The cow eating grass, for example, dis-
regards the flies which are gobbled up by the frog not far away. The crow
eats worms and grubs and the seeds of many plants. The squirrel in the
same region concentrates on nuts. Some animals kill others and devour
them without special preparation. Snakes and owls swallow their prey
whole, digest what is usable out of the mass, and eventually reject the bones,
hide and hair. Related to the many ways of getting food, to the kind of
food obtained, and to the conditions of food-getting, are the distinctive di-
gestive systems of various species of animals.

Chewing at Leisure Several of the even-toed ungulates, or hoofed
animals, such as cows, sheep, goats, antelopes, deer, giraffes and camels,
browse until they have filled their first stomach, the rumen, with unchewed
roughage composed of grass and other vegetation. They then lie down in

172

Pancreas Gizzard Esophagus
Kidney 1 .„^,..-....«-^\" i ismmmsim

Cloaca
Large intestine

Proventric-
ulus

Gall bladder

Intestine ^i^..
Bird

Liver

Intestine "" ^ Stomach

Fish

r /^Gallbladder

Stomach

Esophagus
Mouth

Lobster

Digestive gland

DIGESTIVE SYSTEMS OF BIRD, FISH AND LOBSTER

In all chordates and arthropods (elongated, bilaterally symmetrical animals) the
food tube extends the length of the body from the mouth to the anus, and has vari-
ous glands opening into it. In birds the gullet has a curious pouch, the crop, in which
food may be retained indefinitely and later either swallowed into the stomach or
regurgitated through the mouth. The glandular portion of the stomach, the proven-
triculus, is distinct from the grinding portion, or gizzard. In the lobster the stomach
is in the head

First stomach
(rumen)

Connection
of gullet

Fourth

stomach

(abomasum)

Connection
of intestine

Gullet

Second stomach
(reticulum)

Third stomach
(omasum)

THE STOMACHS OF A CUD-CHEWING ANIMAL

The cow swallows food into the first stomach without chewing it. The contents of the
stomach are returned to the mouth in small quantities when the animal is lying quietly,
and thoroughly chewed. The mixture of saliva and ground food is then swallowed
into the second and third pouches of the stomach, where salivary digestion continues.
In the fourth stomach gastric digestion of protein goes on

some comfortable spot, regurgitate a wad at a time and grind it to bits
When the cud is thoroughly macerated, it is swallowed mto the second
stomach, and on it goes through the remainder of the food tube. Bacteria
in the food tube decompose the cellulose of the plant tissues, exposmg the
cell contents of the swallowed material to the digestive juices.

Off the Main Line In many animals, the horse, rabbit and rat, for
example, food in the digestive tube is held up for a considerable time in a
blind gut. This side branch of the large intestine is located at the junction
of the small and large intestines, and is called the caecum, from a Latin
word meaning "blind". Chickens and doves have two caeca. Bacteria in
the caecum digest the cellulose of plant tissues, as they do in the first
stomach of ruminating animals. At the end of the caecum, in most mam-
mals, is an extension or appendix. In some species this is "wormlike' and
hence is called the "vermiform" appendix (see illustration opposite). In
many the blind gut is small and has a poor blood supply. An infection of
the appendix, a condition known as "appendicitis", is often serious.

174

Food-Getting and Food-Using Digesting food is but a special detail
of the total activity of a living organism, and it is related to the whole man-
ner of living. The main divisions of the food tube are much alike in all
classes of vertebrates, and even in other classes; but many differences in
detail are seen to be related to the kinds of food eaten, to modes of locomo-
tion, to the sense organs, to the whole scheme of habits. Thus, most preda-
tory, or preying, animals have a short food tube; this appears to be related
to the relatively high protein content of the food.

All predatory animals, whether tiger beetle or shark, falcon or rattler,
squid or lion, have powerful offensive weapons. Tigers, lynxes, leopards,
and other cats have supple bodies, sharp claws, pointed teeth, and a stealthy

THE VERMIFORM APPENDIX

The blind sac is relatively smaller in some orders of mammals than in others. It is
least active in digestion among the primates. In the human species, it is actually
larger in the fetus than in the adult

175

Molars

Incisors

Horse

Cow

Molars J^^rs

Giraffe

Molars

Elephant

THE TEETH OF HERBIVOROUS ANIMALS

The sharp incisors cut or tear the leafy material. The broad grinding surfaces of the
molars macerate or shred the food

yet ferocious behavior effective in capturing and killing prey. The weapons
of wolves and other members of the dog family are similar, but their hunt-
ing habits are different.

Among the birds there is a great range in size, from the humming-bird,
which weighs less than an ounce, to the ostrich, which may attain a weight
of over 200 pounds. There is a corresponding range in foods, from the
nectar of flowers and insects caught on the wing to nuts and fruits, frogs,
rabbits, sheep, and even larger animals (when dead), as in the case of the
buzzards. And there are corresponding types of beaks and also of feet.

The great French anatomist Georges Cuvier (1769-1832) found the vari-
ous organs of the birds which he studied so closely related to the ways of
life that he was able to tell a great deal about the habits of an unknown
species from examining merely one of the bones (see illustration, p. 178).

Birds, like ruminants, cannot stop to chew, but gulp their food. Many
also store the swallowed mass temporarily, in a pouched enlargement of the
food tube called the crop (see illustration, p. 173). Birds swallow small
stones into a muscular grinding organ called the gizzard. Food passes
quickly through the relatively short digestive tract of birds,

176

Seal

Walrus

TEETH OF FLESH-EATERS

The large canine, or "dog", teeth act as weapons in fighting or grasping. The short
incisors cut tough tissues, and the heavy molars break and crush bones

Takers and Sharers Nearly every species of plant and animal acts as
an unwilling "host" to one or more life forms that live at its expense. Com-
mon examples of parasites, as such uninvited guests are called, are the leech,
the sheep tick, the liver-fluke and the bedbug. Many diseases result from
the destructive action of parasites, such as the malaria plasmodium, the
Treponema pallidum, or syphilis parasite, the hookworm, and the bacteria
of many common diseases.

An interesting partnership between two species is seen in the symbiosis
or "living together", of a species of termite and certain protozoa that live
within its digestive tract (see illustration, p. 179). The termite lives in dead
wood, in the forest or in buildings, mining through it by chewing the wood
into small bits, which it swallows. Within the digestive tract live the pro-
tozoa which produce enzymes that change the cellulose into soluble sugars.

Periodic Feast and Famine All animals convert some of their surplus
food into fat. This is stored within the body and is used in times of emer-
gency or of food shortage. Some species, the bear and the woodchuck, for
example, feed and fatten during the summer months and spend the cold
months in a deep sleep, called hibernation, or "wintering". At this time
they live on the food stored during the summer feasting.

Another illustration of getting food while the getting is good is seen in
the distinct stages characteristic of many species of insects (see illustration,

177

Great blue heron

Duck

Kingfisher

Hawk

Quail

Mu.<)k Sftncer-

FOOD-GETTING ORGANS

A beak is a beak, but the bill of a hawk is different from that of a heron. The dis-
tinctive beaks of various species of birds, like their feet and legs, are related to
distinct modes of life — which include, of course, the character of food available and
especially the ways of getting food

Holomastigotes
elongatum .

Winged male and
female (alates)

Trichonympha
agilis /jj^.

Spirotrichonympha
flagellata v , >^

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

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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 .

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

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

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

:.,.,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

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,lllllllllllll

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 lllMllillllliillllMIIIIIIIIIIIIMIIIlllllMllillinllll:-'!

THE PACE THAT TIRES

,1 hlullllllllllNIII IlllllllllllllJllllllHIHIlllllllllllHIIllllllllllllllllI IIIMIIIIIIIIIIIIIIIIIIII 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

]

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<Ked under skin

growing in a broth /^tokili bacteria separate toxin of healthy horse

Doses repeated daily - increasing amounts for several weeks

Blood drained
^*>^ ^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

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: 49,000,0<X}

Number of smallpox cases in the eight -year period

2,462

11,551

52,680

Average number of cases per year

308

1,444

6,57S

Average numb|FM"caMs...aaPaall±„Bgi.fiailhim.^^

7.1

3S.2

SMALLPOX AND VACCINATION IN THE UNITED STATES (1933-1940)

In three groups of states divided according to their vaccination laws, average annual
smallpox cases per million inhabitants varied from 7.1 to 134.2. In at least eight of
the stjtes in the "Liberty" group conditions were worse in recent years than they
were twenty years earlier. And in recent years the United States had more cases of
smallpox than any other country except India

237

" Deaffis per
100 cases

25 30

U^Hk'

■^1

■■'*"™"

'"1

mt.

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. ; J.

1893

'•■ f

1894

1895

Antitc

>xm 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

-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,

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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<f-adjustment.
But from its very nature, too, the several processes of living are related to
a central unity. It is in this wholeness, or unity, of the many different
processes that life is distinctive. Does life make the parts work together?
Or does the working together of the parts bring about life?

250

CHAPTER 14 • HOW DO LIVING THINGS ADJUST THEMSELVES?

1 Are there any conditions in which Hving things are perfectly

adapted ?

2 Do all Hving things make mistakes?

3 How do living things fit themselves to new conditions?

4 Do all living things learn from experience?

5 Do plants learn in the same way as animals do?

6 Do other animals learn in the same way as human beings do?

7 Does the adaptation of a living thing carry over to later genera-

tions ?

8 Can human nature be changed?

9 Can the nature of other species be changed?

Living means doing, acting. We cannot think of life existing as a pebble
on the beach exists, or as a gold brick in a vault. Life is a system of proc-
esses. It is related, in one direction, to meeting outside conditions; but it is
related, in another direction, to keeping itself going. Life persists through
the changes that it brings about.

And yet, only to a certain point. The environment in which, and in rela-
tion to which, a particular plant or animal lives is itself a changing system.
The light changes. The temperature changes. Water vapor and other sub-
stances vary in amount. Other living things, also in action, interfere, injure,
destroy, although still others furnish food. Plants and animals become
diseased. They are poisoned, starved, suffocated. They make mistakes.

How do living things meet new situations? How do they change
through experience?

How Do Plants Respond to Changes?

Response to Short Season A crop of wheat in the extreme north, as
in Canada or Alaska, will ripen in, say, about ninety days after the sowing.
In a more temperate climate the same strain will take four months or more
to ripen. The adjustment of the plant to the shorter season is very impres-
sive. How can the plant tell that the frost is going to come earlier in
Manitoba than in Oklahoma? Perhaps this adjustment is easier to under-
stand if we attend to the actual facts.

In any given species, such as a particular strain of wheat, developing
from the seed to the ripe grain requires a certain amount of nourishment.
But this in turn depends upon a certain amount of sunshine. From our
knowledge of the earth and its movements, we can understand that one
hundred days in the short season of a northern region have, on the average,

251

Plants ripen more rapidly in
some regions than in others.
These two chrysanthemums
were grown under identical
conditions except that the
one on the right was shaded
with black cloth from 4.30 P.M.
every afternoon, beginning
the first of August. The
shaded plant was in full
bloom by September 5, be-
having like plants .growing
where the days are relatively
short in late summer. The
other was then just begin-
ning to form buds

p. W. Zimmerman and A. E. Hitchcock, from Boyce Thompson Institute

DO PLANTS KNOW THE CALENDAR?

more daylight hours than the same calendar days in a southern region. In
the northern latitude, accordingly, plants need fewer days to receive enough
light to complete their growth than they would in a southern region. We
may say, then, that if conditions are otherwise suitable, ripening will take
place after a certain amount of exposure to sunlight.

Another seasonal adjustment that is related to light is seen in the forma-
tion of tubers by the artichoke or in the late blooming of the aster. The
plant does not ''know" what is going to happen later in the season. But as
the nights become longer in late summer, more carbohydrate material moves
into underground parts and accumulates as starch (see illustration opposite).
By shading an aster plant part of each day we can hasten the blooming.

Illumination and Leaf Growth The leaves near the top of a tall tree
(which are constantly exposed to light) are generally smaller and greener
than those in the lower and shaded portions. This is a definite response to
differences in light. If we examine cross sections of the leaves with a micro-
scope, we find that there is much more chlorophyl in the smaller leaves.
Although the leaf can make more food in the light than in the shade, it
apparently grows more rapidly in the shade. In accordance with this fact,
the tree seems to fill out its leaf surface to the best advantage (see illustra-
tion, p. 254).

Changing Illumination All who have had a chance to observe either
house plants or garden plants have been impressed by the fact that the
leaves face the light, and that stems bend toward the light. If we turn the
plants in the window halfway around, we shall find on the following day
that the leaves have actually turned to face the light again. If we keep a

252

1'. w X.iiiiMiciMiaii ;iiiil A. K. Ilitcliiixk, from Boyce Tlidiniisun Institute

RUSHING THE SEASON

The artichoke normally starts to form tubers late in the summer, when the nights be-
come longer. By shading the entire plant, or the tips of the stems, from the sun in
the latter part of the day, from the middle of July, we can get it to form tubers several
weeks earlier than its unshaded neighbors

FOLIAGE AS A LIGHT BARRIER

This maple presents a mosaic of nearly continuous leaf surface exposed to the sun.
Inside its canopy of leaves, very little skylight filters through between leaves; and
we see that very little leaf surface is shaded from the light by other leaves

young plant in a dark closet, we shall find after a few days that the tip has
been growing toward faint light coming through the keyhole. What
makes leaves face the light? Do they somehow "know" that light is neces-
sary for photosynthesis and so turn to it ? Do they like the light ?

Water Changes Since roots absorb water (and mineral substances)
from the soil, the work they can do will depend upon moisture conditions.
Now we know that if there is relatively little water in the soil, roots will go
down deeper, into the moister layers of earth. From experiments we can
see that roots will change the direction of their growth according to the
side on which there is the greater humidity.

Up and Down No matter which way seeds fall upon the ground, if
they sprout at all the stem grows upward and the root downward. If an
ordinary plant is placed in a horizontal position, the tip of the stem will
bend upward, and the root will bend downward. What makes the root
grow downward and the stem grow upward? These questions have been
fairly well answered by experiments conducted on many plants, in various
countries, over a long time.

254

1^'

< %

IS THE PLANT A RUBBERNECK?

Like other species of plants, the sunflower turns its head toward the sun. The leaves
also move, facing east in the morning, south at noon, and west late in the afternoon.
In no plants, however, can we find anything to correspond to the muscles by means
of which we turn our heads to face now in one direction, now in another

Fitness The tendency of the root to grow downward will, on the
whole, bring the roots of plants into the soil, where the conditions for get-
ting water are more favorable. The responses of the shoot to gravity and
light are likely, in the long run, to bring the plant into situations favorable
to its further development. But it does not follow that everything a plant
does is to its advantage. Nor is it clear just how the plant brings about
these adaptive movements.

How Do Plants Bring About Their Adaptive Movements?

Light and Growth' We know very well that growth depends upon
food. We have also learned (see page 138) that green plants make their
food in daylight. Yet we can easily establish the fact that seedlings and
other plant structures grow more rapidly in the dark than in the light. It
is not so easy to show how darkness, which is a negative condition, or an

iSee No. 1, p. 270.
255

Boston Sewer Dirision

POPLAR ROOTS REMOVED FROM A SEWER

Roots of willows, poplars and other plants have been known to grow hundreds of
feet in the direction of relatively abundant moisture in the soil. Some cities prohibit
the planting of poplar trees along the streets because they tend to fill the sewers
with their roots

absence of something, can make the stem grow faster. Or is it possible that
the light actually restrains the plant's growth ? In any case, the unequal
growth of the two opposite sides of the stem would explain the turning of
a plant toward the light.

Tropisms^ The bending of a plant in response to the action of some
external force has been called a tropism, from a Greek word meaning "to
turn".' The turning of a plant axis (or any other living organ or organism)
in response to illumination is called photo-tropism — that is, "light-turning".
Similarly, we apply the name hydro-tropism to the response of a plant or
plant part to water. The stem and the root are said to show geo-tropism, or
earth-turning, under the one-sided influence of gravity. A plant sometimes

^See No. 2, p. 270.

"The root of this word is the same as that of the word tropic used in geography. The
Tropic of Cancer and the Tropic of Capricorn were the astronomers' time points in the
calendar when the sun turned back in its apparent north-and-south migrations in the seasonal
cycle. The tropics are the regions between these two turning-points; that is, they are the lati-
tudes in which the sun is directly overhead at some time between one turning and the next.

256

responds in the direction from which the stimulus or disturbing factor
comes to it, and sometimes in the opposite direction. We distinguish tro-
pisms accordingly. The turning of leaves and stems toward the light we call
positive tropisms, whereas the bending of the stem away from the direction
of gravity we call a negative tropism.

These are convenient terms, but we must not let them mean "for" or
"against" in the sense in which we speak of our own likes and dislikes or
our attitudes in a debate. Nor must we suppose that these terms in any way
explain what happens. They are convenient for summing up the facts that
nearly everybody can observe for himself. We are still in the dark as to
how these delicate and adaptive changes are brought about, even when we
call them changes in growth.

Growth Substances' In 1927 Frits Warmolt Went (1903- ), a
young Dutchman who came to the California Institute of Technology, suc-
ceeded in answering partially the question, What besides food or tempera-
ture affects the rate of a plant's growth ? He cut off the tips of young oat

If we keep some sprouting potatoes
or seeds in the dark and others in
the light, we find that those in the
dark grow faster. Farmers remove
seed-potatoes from dark cellars
and spread them out in a lighted
shed to prevent the growth of long
sprouts

L. P. Flory, from Boyce Thnmpson Institute

Plant loves light and bends toward

it. Light attracts plant. Shaded

side grows faster, bending stem

toward light.

Do these statements all mean the

same thing?

Do they equally describe what we

can see?

Which most agree with the facts?

I.. I'. Flory, from Hoyre Tlionipsoii Institute

LIGHT AND GROWTH

^See No. 3, p. 271.
257

seedlings and found that the remaining portion quickly stopped growing.
If, however, he replaced the tips immediately, the growth was not greatly
retarded. Does something in the tip move into the growing region and
there stimulate growth .f* To answer this question, he removed some tips
and placed them on a small piece of agar (a substance similar to gelatin)
for a short while, hoping thus to soak out the supposed something. Then
he touched this agar to the original cut stumps of the oat shoots. The
effect was the same as that of replacing the cut tips, whereas ordinary agar
blocks did not stimulate growth (see illustration opposite). Apparently some
substance passed from the tip into the agar, and then from the agar into the
cut stumps. Apparently growth occurs only when this unknown substance
is present. Because this substance stimulates growth in the plant, it was
called auxin, from a Greek word meaning "to grow". Because it influences
metabolism as do certain animal secretions, we call it « plant hormone (see
pages 303-304).

But what is the connection between an auxin and a plant growing faster
in the dark? It was known that if the tips are cut from young seedlings,
the stalks do not respond to light. Is more auxin present on the shady side
of growing stems than on the lighted side } Does light in some way destroy
or repel this substance?

One investigator separated the lighted halves and the shaded halves of
hundreds of growing stems into two piles. From the shaded halves he ex-
tracted more growth-stimulating substance than from the lighted halves.
Apparently an auxin makes the shaded side grow faster. But why is there
more of this substance on the shaded side?

This question we cannot yet answer. We may feel certain, however, that
a plant responds as it does to light because of chemical changes going on
within. The plant is obviously as unaware of these changes as you are of
the increased quantity of oxygen in your blood after it has traveled through
the capillaries in the lungs.

Geotropism and Auxins In order to find out whether a hormone con-
trols geotropism as well as phototropism, scientists placed growing stems in
a horizontal position. They found that the cells on the lower side contained
more auxin than those on the upper side. If a growth substance makes the
lower side of a horizontal stem grow faster, then the tip will bend upward.
But we do not understand why the auxin moves toward the lower surface.

Chemists have produced several compounds that behave in many ways
like the natural auxin. One of these, indole-acetic acid, counteracts the natu-
ral auxin (see illustration, p. 261). From such experiments it is reasonable to
conclude that the growth and the form of the plant, as well as some of its
tropisms, are determined by chemical substances having particular arrange-
ments of atoms in their molecules.

258

}

When seedlings have
the tips removed.

If the removed tips A
are
immediately
replaced,

they

stop

growing

the seedlings
continue
to grow

If there is a water-soluble
growth substance in the tip,
it will be absorbed by agar

^s$a

i,|o

When plain agar and

treated agar blocks

are placed on beheaded

seedlings,

Grox^rth substances absorbed
by agar will be reabsorbed
by the beheaded seedlings

■-^-•■■Bir^^

only the seedlings

with treated agar blocks

continue to grow

,,, --.^ '■' ' ja^jfcf -Iff 1 1

ifi

ip^inpl

■B^.^nmipp^

Will plain agar affect

the growth of

beheaded plants?

GROWTH SUBSTANCE

How can we tell that there are special growth substances? Experiments show that

a substance formed in the tip of the shoot stimulates the growth of the plant

p. W. Zimmerman and A. E. Hitchcock, from Boyce Thompson Institute

NEGATIVE GEOTROPISM IN PLANTS

Stems of most plants tend to grow upward, unless forced or disturbed by some
outside agency. Is the tomato's turning away from the earth connected with the
formation and distribution of growth substances? If it is possible to remove auxins
from the tips of oat seedlings, is it possible to remove auxins — if any — from the
lower or upper halves of the horizontal tomato stem?

Further experiments showed that this "artificial auxin" counteracts plant
auxin in the normal negative geotropism of stems (see illustration opposite).
From these experiments we may conclude that auxin and indole-acetic acid
have essentially the same effects in stimulating growth-responses to light
and to gravity. Chemists have found certain similarities between the chemi-
cal make-up of natural plant auxin and that of several synthetic compounds
which all have the same effects on plant growth.

Do Animals Respond to Stimuli Automatically?

Animal Tropisms^ Fruit flies and common houseflies turn toward the
light. Earthworms turn away from strong light, but toward a very weak
light. Such turnings usually involve the whole organism rather than merely
a single organ or portion. On summer evenings we can see swarms of in-
sects, usually several different species, around any street lamp or other
exposed light. Insects in large numbers often get stuck in the radiators of
motorcars driving through the country at night. Lighthouse-keepers report
that hundreds of birds dash themselves against the windows and get killed,
especially during the migration periods.

These tropisms of animals are unlike the growth-movements of plants,
for they are brought about by the contractions of special portions — the

iSee No. 4, p. 271.
260

Tomato plants laid on their sides, with the light coming from the right.

turn their tips upward, and also toward the light

If now the lighted side in the erect plant and the upper sides in the horizontal plants are treated
with indole-acetic acid.

the plants bend away from the light and also turn downward

p. W. Zimmerman and A. E. Hitchcock, contributions from Boyce Thompson Institute

RESPONSE OF PLANTS TO LIGHT, GRAVITY AND GROWTH SUBSTANCES

Is the tomato plant's turning toward the light and away from the earth deter-
mined by auxins, or growth substances? Is it possible to remove auxins — ^ if any
— from the plant? Both extracted auxins and synthetic compounds reverse the
plant's responses to light and gravity. Can we change the behavior of animals by
chemical means?

muscles — in all but the simplest animals. But they resemble the plant tro-
pisms in that they take place automatically, or mechanically. That is, they
are in no way voluntary, or controlled by a "will". From the fact that the
moth flies to its own destruction we may at least argue that there is no
intention in the act. Although the animal has a very good set of compound
eyes and a comparatively complex nervous system, it seems to have no
choice.

Responses to Gravity Whatever "gravity" is, it acts upon animals and
plants, as well as upon stones and planets. Some animals adjust themselves
to the action of gravity in a variety of ways that are tropic, but not all. The
housefly, for example, seems to be indifferent to the direction of gravity; it
will crawl upon a surface in any plane and in any direction, and it will
come to rest in any possible position. Yet, if you place a fly on its back, it
will right itself, as would a backboned animal or a starfish.

Many adult insects, when they alight on a tree, assume a position with
the head pointing upward; other kinds always rest with the head pointing
downward. In still other species, the source of light determines the position,
rather than gravity. In some species the young larva crawls toward the tip
of the twig. This movement is adaptive since it brings the young insect to
its food. But in some species the animal moves toward the light, whereas in
others it moves up, as we can tell by experimenting.

Some of the simple marine animals appear to be influenced by both light
and gravity. Certain species of minute crustaceans swim near the surface
only at night; under the influence of light they become negatively geotropic
— that is, they swim down from the surface. Experienced fishermen have
learned that many species of fish are to be found at varying depths accord-
ing to the time of day: in a given lake, however, at a given hour, hundreds
of fish of the same kind will be found at about the same level. There is
probably a combination of influences at work — temperature, as well as light
and gravity. And many of the variations in an animal's reactions appear to
result from changes in the chemical or physical state. The larvae moving
toward the tip of the twig show a reversed tropism after they have eaten.

Reflex Action When you are tickled, you draw away the touched
part. When something approaches your eye, you wink. A slight touch in-
side the nose leads to a sneeze. A solid particle on the lining of the windpipe
makes you cough. When you place a solid in a baby's palm the hand closes
down. Such reactions to particular stimulations have always been known.
In the members of any species of animal they are remarkably uniform. And
in any individual they are remarkably constant.

A famous French philosopher and mathematician, Rene Descartes (1596-
1650), suggested for this type of action in animals the name reflex. It is as
if a force entering the body at some point — the skin or the eye, for example

262

GEOTROPISM IN LARVAE OF TENT CATERPILLAR

Before
eating

After
eating

When larvae first hatch out of the eggs, they After their first feeding excursion, the larvae

move up — toward the tips of the twigs, where move down — away from the tips — to a crotch,

leaf buds are opening. But if the twig is bent where they spin a "tent". But if the twig is bent

over, they still move up — away from their pro- over, the larvae still move down — toward the tips

spective food of the bore twigs

DO THE LARVAE KNOW WHAT THEY ARE DOING?

The young larvae normally move toward the young leaves when they are hungry
and away from the leaf buds when they have filled up on food. But apparently they
move up or down under different Internal conditions, even at the risk of going hungry

— were "reflected" into a muscle. The nature of the force and the actual
connection between the stimulus and the response were not worked out for
nearly two hundred years. The idea was a helpful one, however, and the
term reflex remains in use.

And we make use of the fact too. For if you ever catch a fish with hook
and line, your success depends upon a reflex. The fish responds to the sight
of certain kinds of objects by snapping at them with its mouth. If the con-
ditions are suitable, if you have the right kind of bait, if it is properly fastened
to the hook, and if you drop it into the water at a suitable depth, your "luck"
depends upon the presence of the fish and his seeing the bait. The reflex
does the rest. This appears to be a mechanical act, like a tropism. We cannot

263

assume that the fish means to get caught, any more than the moth intends
to get singed in a flame. Neidier can avoid acting as it does.

Human Automata Winking, sneezing, coughing, swallowing and
other familiar reflexes take place in the human organism in direct response
to some stimulus. They are acts that take place without being intended or
desired. They take place in practically the same way in all members of the
species, and, generally speaking, they cannot be prevented. Human beings,
like other living things, sometimes act like mechanisms.

A different type of automatic response that is at the same time adaptive^
or helpful in keeping the organism going, we have already considered in
connection with homeostasis (see page 194), When you increase your mus-
cular work for any purpose — moving furniture about, climbing stairs — your
heart begins to speed up, your breathing changes, your kidneys begin to
work faster. Some of these alterations are more like plant responses, result-
ing from chemical and physical interactions. Speeding up the respiration
rate, however, is a reflex: this is set up by a chemical stimulation (in-
creased concentration of carbon dioxide in the blood) upon a certain nerve
center.

Our reflexes do not always show themselves in movements. When the
"funny bone" is struck, for example, we become aware of a tingling sensa-
tion in the palm of the hand. This is apparently due to the reflex con-
traction of small skin muscles, which in turn stimulate sensory nerves.
"Watering of the mouth" is a gland reflex to an odor stimulus.

Reflexes and Tropisms Reflex action differs from the tropic move-
ments of plants in being usually much more rapid, and in resulting from a
different kind of structure, or mechanism. Reflexes depend upon nerve cells
and nerve connections, and the movements themselves involve muscles —
two kinds of cells that we do not find in plants.

To say that a reflex act is like the movement of a bell clapper when the
right button is pushed may seem to belittle human conduct; nevertheless the
statement appears to be true. However, we must not read it to mean that
human action is "nothing but mechanical", for each reflex is but a fraction
of human behavior, and there is much more that cannot be described or
"explained" as mechanical.

Instincts When a baby is touched on the cheek near the mouth, he
turns his head to bring his mouth toward the point of contact. When an
object touches his lips, the baby usually opens his mouth and grasps the
object. When something gets into the mouth, the touch stimulus sets up
the sucking movements. When something touches the back of the throat,
the stimulus starts the swallowing reflex. Here is a chain of reflexes which
together bring about adaptive action. We can show that each step is a reflex
by setting it off independently of the others.

264

! ( hace

UNLEARNED CONDUCT IN YOUNG ANIMALS

Young chicks, pecking at food or walking about, perform these acts about as well
the first time as later. Baby chicks or ducks follow the mother about, and that seems
a useful, or adaptive, "instinct". Apparently they would follow many other moving
objects of about the same size

Many of the so-called instincts in animals are either simple reflexes or
combinations of reflexes. It is characteristic of many of the adaptive and
useful activities that they are not learned. Young chicks, for example, peck-
ing at food or walking about, perform the acts about as well the first time
as later. Moreover, all the members of the species normally act in the same
way. Apparently instincts depend upon special sets of structures that are
characteristic of the species. Yet we know that animals do change their
instincts.

How Do Organisms Change through Experience?

Changing Instincts A pike was placed in an aquarium with a num-
ber of smaller fish. The pike swallowed his neighbors. A glass partition
was then put in, separating the pike from the smaller animals. The pike
would dart at them, however, and was often stunned by striking the glass
plate. But in time he stopped darting after the small fish. Later the parti-
tion was removed. Yet the pike always turned aside when he approached
one of the little fellows. Nothing now prevented his eating them except his
past experience. That is to say, his natural behavior had become modified.

The bruised pike shuns small fry; a burnt child dreads the fire. Acts
which have unpleasant accompaniments come to be avoided. Certain natural
impulses become repressed. On the other hand, acts associated with feelings
of satisfaction come to be performed more readily. This is the principle that
you would use if you tried to teach a dog or a colt a new trick. If you re-
ward the animal with praise or a piece of sugar every time it does what you
want it to do, it will be more likely to repeat the performance. At last the
acquired trick takes the place of the animal's earlier spontaneous behavior.

A baby crying for food will at first keep on crying until something ac-
tually touches his mouth. In a few days he stops crying as soon as he hears
his mother's voice. Some will say that the child "recognizes" his mother's
voice, or that he "knows" that she is about to feed him. But from observa-
tions and experiments with the young of many animals, including babies,
we say rather that the sound has become associated with the feeding. And
this association of two experiences has modified the natural response. A new
stimulus — in this case, a particular sound — now acts as a substitute for the
original stimulus to stop the crying or to start the sucking. This new mode
of responding, the new trick of behavior, is sometimes called a habit. This
familiar word habit is commonly used in a broad (and not always a very
exact) sense. But from experiments with many animals, including human
beings, we have learned a great deal about how conduct is modified.

Conditioning The most famous and extensive of these experiments,
mostly with dogs, were directed by the Russian physiologist Ivan Petrovich
Pavlov (1849-1936). They started from the well-known fact that a dog's

266

mouth "waters" when meat is offered him. But the mouth does not always
water: a dog that has just finished a good meal, for example, behaves dif-
ferently. The chemical condition of the body's juices seems to make a
difference. At any rate, Pavlov arranged a tube inside the dog's cheek to
collect the secreted saliva; and then he took the amount of saliva delivered
to indicate, or measure, the dog's response to a particular stimulus. Since it
was found that the dog's response — saliva secretion — varied with the condi-
tion of the animal's nutrition, the experimenters then used dogs in a
"hungry" state.

Now in one series of experiments some special stimulus was combined
with the feeding. For example, just before the meat was presented, a bell
would be sounded, or a light would be flashed, or the dog's name would be
called. After a number of such experiences — more with some dogs than
with others — the animal's mouth would water as soon as the stimulus acted,
before he saw or smelled the meat. Later, dogs were taught to discriminate
between different lights or colors or sounds. For example, the note G on a
piano or tuning-fork was sounded every time the animal was fed. At other
times, a different note — say G sharp — was sounded, but unaccompanied by
food. After a period of training the dog would secrete saliva when he heard
G, but not when he heard G sharp. In these cases a new stimulus — the note
G, or a flash of light, or a particular color — acted as a substitute stimulus
for setting up saliva-secretion.

We can see some resemblance between the modified behavior of animals
and the tricks which dogs and horses and other animals "learn". But Pavlov

Pavlov started his famous researches that
developed the Idea of "conditioned reflex"
with experiments on secretions of the di-
gestive system. Such secretions are some-
times started by stimuli that are not directly
related to food. Your mouth waters when
you see food through a window, or even
when you read about food. How does
that happen? Do other animals secrete
juices without relation to immediate food
conditions? Pavlov tried to measure the
reflexes by measuring the amount of saliva
secreted by a dog under different condi-
tions. His work started with a dog that
had been wounded in the stomach, and
has had a great influence in furthering
research, and in interpreting human be-
havior, as well as animal behavior

IVAN PETROVICH PAVLOV (1849-1936)
267

and his associates were careful to avoid the idea that such changes corre-
spond to what happens when one of us "learns" any kind of lesson. Indeed,
Pavlov is said to have penalized any workers in his laboratories who used
the word learn in connection with these experiments.

Such conditionings were carried out in very complex combinations. For
example, the dog's food would be placed at a certain point in the room, and
the dog in time came directly to that location. Then a special stimulus pre-
ceded his admission to the room, until that signal came to mean for the dog
"come and get it". A different stimulus preceded an electric shock, which
made the animal turn and run away. These two "signals" thus became asso-
ciated with coming and going. But they were also substituted for the stimulus
"see meat", so that seeing meat no longer made the dog's mouth water.
Now the conditioned dog had to come or go when he saw meat, but he had
to wait until he saw which signal was up (see illustration, p. 671).

The natural responses of many birds and mammals and other animals
have been conditioned experimentally. Even an earthworm can be condi-
tioned to turn always in a certain direction for food.

By feeding and milking cows on a regular program we get them to
come in from pasture at sunset or when we call them. This saves the work
of going after them. Horses come to follow fixed routes, and they come
home after they have strayed away. Chickens come in response to a familiar
call. We train animals to perform tricks for our entertainment.

Learning and Feeling The experiments show us that conditioning is
not merely a matter of repeating and repeating: it involves the satisfactions
or pains that are associated with experience. Indeed, this has always been
generally recognized and used in the training of animals. Nearly everybody
recognizes this principle to some extent; we encourage one kind of conduct
with rewards, and we discourage other actions by means of punishment.

All this works well enough in laboratory experiments or in training
animals. But it presents some difficulties when we are dealing with human
beings. Most of us are intelligent enough to discover that we can obtain
certain rewards for doing what others demand of us. One hates to practice
scales, for example; but he can stand the annoyance for half an hour in
exchange for candy or a visit to the movies. But unless the "practice" yields
other satisfactions, he seems to make no headway. Or one may learn how
to dodge penalties provided for disapproved behavior, instead of learning to
abhor such behavior.

The education of human beings, like the training of a dog, begins with
the changing of natural or impulsive behavior. But human learning, skill
and character go much farther and involve much more than training or con-
ditioning. The great differences between man and other species seem to be
related to the complex brain and nervous system that distinguish our species.

268

Training and Education A human infant's behavior is constantly
being modified by his day-by-day experiences. His impulses and his desires
become modified, as well as his ways of carrying out his impulses, his ways
of satisfying his desires. But we attend chiefly to what the child does, rather
than to what he feels or needs. So we drill children and adults into standard
ways of acting in many routine situations, in many types of skills. We try
to establish good manners or correct form to cover almost every hour of the
day. All these habits and learnings may be useful, but only in repeated
situations and relationships.

No scheme of fixed habits can fit a human individual for an entire life,
unless he is to remain an infant or a slave, directed entirely by others. Since
each person is himself altering the world for those around him, all of us have
constantly to meet new situations, new problems, new relationships with
others. In civilized, democratic living, each of us must of course do well what-
ever he has to do. We must acquire special skills, master a thousand tricks.
But we must also be prepared at any moment to do something we have never
done before, to take initiative, to make decisions — to break routines.

For these reasons, habits must be subordinated to sound attitudes and
judgment. In human affairs it is more important for the individual to care,
to feel responsible, to be concerned — to care about traffic safety, for example,
and not merely fear being caught by the traffic police. It is more important
for one to be true to himself, to what he considers of greatest worth, than
to be clever in avoiding detection. In educating for human living training
is necessary; but more and more is it necessary to develop the feelings in
relation to what is desirable or worthy — to develop sound attitudes toward
people and things.

Adjustments Living things adjust themselves to their surroundings
in many different ways. Apparently they can tolerate considerable variation
in the conditions that surround them — more or less moisture, light, mineral
salts, higher or lower temperature. But always there is a point beyond which
too much or too little is fatal. The protoplasm adjusts itself by slowing its
action or hastening it, or by changing the rate of some processes more than
that of others. Among more complex animals the nervous system plays an
important role in bringing about particular movements, in retarding or
accelerating processes.

In general, however, life carries on by interacting with the environment.
It receives stimuli and it reacts. It receives materials, and it returns other
materials. It distributes materials among its own parts; it distributes stimuli
and reactions among its own parts. These interchanges of materials and
energies are balanced within the organism. And they are balanced as be-
tween the organism and the outside world. But the balance is never quite
perfect.

269

In Brief

The behavior of plants and animals appears to us as the fitting of or-
ganisms to the conditions under which they live; of course those organisms
which fail to fit the conditions soon cease to exist.

Some of the adjustments which living things make to their environment
are fixed in their structure and development.

Other adjustments appear to be the result of experience or of exposure to
new conditions.

Plants show turning, or tropic, responses to gravity, water and light;
these appear to result from specific alterations in rates of growth.

The bending of a plant toward the light is due to unequal growth, the
more rapid growth taking place on the darker side. The differential growth
appears to result from the action of light, which decreases the amount of
auxin, or growth-stimulating substance.

The more we study the remarkable adjustments of living organisms to
their environment, the more of these adjustments do we find to be auto-
matic: the organisms cannot help responding as they do.

Each particular kind of protoplasm thrives best in a particular set of con-
ditions; yet each is capable of adjusting itself to conditions that are some-
what different in one detail or another.

The behavior of many species of animals in response to stimuli can be
conditioned or modified into new forms and patterns.

Education consists in part of forming appropriate patterns of action or
avoidance. Habits are useful in doing things that have to be done in the
same way over and over again.

Practice is effective in establishing habits when it is associated with strong
feelings.

To meet new situations habits have to be subordinated to sound attitudes
and intelligence.

EXPLORATIONS AND PROJECTS

1 To observe the effect of light on movement within a cell, place a leaf from
the tip of a rapidly growing elodea on a slide and examine under the microscope
(use high power). Increase the intensity of illumination on the leaf by adjusting
the mirror so as to direct sunlight on it. Note effect on the streaming of the
protoplasm inside the cell.

2 To study the growth movements, or tropisms, of plants:

To find the relation of light to the direction of growth, place a pot of rapidly
growing seedlings under one-sided illumination; allow it to remain undisturbed
for several days. Note the position of stems and leaves at the start, and again
later.

270

To find the cfifect of light upon the growth rate in plants, place one of two
pots of growing seedlings or of sprouting potatoes in a light room and the other
in a dark closet. Keep all the conditions except the intensity of light the same.
Compare growth after a few days. Record difTerences and account for the results.

To find the relation of gravity to the direction of growth of roots and shoots,
place several soaked seeds on moist blotting paper between two large panes of
glass so that they may be observed. Fasten the panes in vertical position with
bottom edges resting in a tray of water. With a wax pencil mark the positions of
the roots and of the shoots when they appear. Then turn the arrangement one
fourth of the way around and allow to stand in tray for two days more. Mark
the position of each shoot and each root daily. Turn the arrangement one fourth
of the way around further and again mark positions of roots and shoots. How do
the roots and shoots respond to the shifts in position?

3 To find the effect of growth-modifying substances on the growth-response
of plants to light, place several vigorous potted plants of the same kind in a
window and apply the material to all but one of them, on the side of the stem
exposed to the light.^ After a week or so, compare the plants for any difference
in growth.

4 To study the responses of organisms to stimuli, observe the behavior of
paramecia through the microscope, while changing the physical and chemical
conditions surrounding them.'

To find the response of paramecia to changes in temperature, bring into con-
tact with the slide on which the animals are mounted a clean slide that has been
heated by moving it back and forth above a low flame, and watch the animals as
they are slowly warmed. Cool the slide by placing an ice cube on one end of it.
How do changes in temperature afFect the behavior of the animals .f"

To find the response of paramecia to acid, place a drop from a test tube of
water through which carbon dioxide has been bubbled (from the lungs or from
a generator) near the drop in which the paramecia are swarming. Draw the two
drops together with a pin and note the changes in the behavior of the animals.
Describe the response. How can this response be related to the animal's method of
getting food?

To find the response of paramecia to electricity, place about 50 cc of the culture
in a shallow dish, and at opposite sides of the dish insert two carbon rods that are
attached by wires to the two terminals of a 6-volt battery. Describe the reaction of
paramecia to the electric current. Do they migrate equally toward both poles, or
away from both poles, or toward one pole and away from the other?

^Use indole-acetic acid or naphthalene-acetic acid as growth substances. Prepare mixtures
in following proportions: (1) 10 mg growth substance to 1 g lanolin; (2) 2.5 mg to 1 g;
(3) 0.6 mg to 1 g; (4) 0.15 mg to 1 g. Dip a glass rod into each preparation in turn and
touch it to side of stem of one plant.

-Prepare a hay infusion by tying a double handful of hay in a cheesecloth bag and sus-
pending it in a gallon jar of water. After this has rotted for one week, add some water
collected among vegetation along the edge of a pond. In about two weeks the top of the hay
infusion should be teeming with paramecia.

27\

QUESTIONS

1 In what sense are the adjustments of Hving things to their environment
fixed in their structure or in their development?

2 To what stimuU do plants commonly respond?

3 How do plants respond to different stimuli?

4 What makes plants grow faster in some regions than in others?

5 In what respects are the mechanical responses of plants adaptive?

6 In what respects are the tropisms of animals like those of plants ? different
from those of plants?

7 What factors determine whether plants and animals that have been shifted
from their natural environment will adjust themselves to the new surroundings?

8 How do various kinds of living things repair injured tissues?

9 How can the native instincts in organisms be modified into new forms of
behavior ?

10 In what respects are habit formation and education alike? In what
respects different? Which receives the more emphasis in the training of animals
to do stunts? in the guidance of human beings?

11 In what respects is the behavior of men Hke that of other animals? In
what respects different?

272

CHAPTER 15 • WHAT DO THE NERVES DO?

1 Are there any animals that have no nerves?

2 How can some animals get along without special sense organs ?

3 Do animals feel pain as we do?

4 Are there any activities in the body that we cannot control?

5 What is the use of pain?

6 What is the "funny bone"?

7 Would there be any harm in killing the nerves in the teeth ?

8 Are people with larger heads smarter than those with smaller

heads ?

9 Is it true that if one of the senses is injured, the others become

more keen to make up for it?
10 How can we tell whether other animals perceive the work!
through the senses just as we do?

Among the lowest organisms, different stimuli may produce similar
effects. Thus an ameba contracts when touched, when suddenly illumi-
nated, when stimulated by some chemical substance or by a charge of elec-
tricity. In our own bodies the division of labor is so great that there are
several highly specialized organs — the eye, the ear, the tongue, and so on.
Each of these is sensitive to only a limited class of stimuli. Moreover, the
various organs respond in special ways. Sometimes there is a rather violent
reaction through sudden movement. Or a stimulus may bring about a
chemical change, as in the formation of an antitoxin or ih the increased
secretion from a gland.

The most striking feature in the structure of higher animals is perhaps
the presence of the nerves. These specialize in receiving disturbances and
in transmitting them. How do the nerve cells really differ from other kinds
of cells? How do they influence the action of other kinds of cells? How
do they make the parts of the body work together?

What Kinds of Cells Are Nerves?

Special Functions and Special Cells In the ameba and other one-celled
species each cell carries on all the life functions — feeding and assimilating,
breathing and oxidation, moving, excreting, sensing, reproducing (see il-
lustration, p. 23). But the cells in larger plants and animals impress us
not with their similarities but rather with their differences — as between the
bone cell and the gland cell or between the skin cell and the muscle cell.

In each special tissue we find an exaggeration of some special function
that is common to all protoplasm. Thus chemical processes of various kinds

273

Protective

muscular,

cells

Muscular cell

Bud

gestive
ceU

i Endoderm-^

Sensitive
cell

Digestive
cell

Ectoderm

Endoderm

& General Biological Supply House, Inc.

SPECIALIZATION IN HYDRA

In each of the two layers of cells that make up the hollow bag and tentacles of
Hydra, there are sensitive "nerve" cells and also especially contractile "muscular"
cells. In the outer layer there are also "protective" stinging cells, which dart out fine
hollow needles and on acrid fluid when disturbed. Some inner-layer cells secrete
digestive fluids

go on in all protoplasm, but in gland cells there is mass production of par-
ticular kinds of compounds. All protoplasm contracts more or less, but
muscle cells contract more energetically and more extensively than most
other protoplasm. All protoplasm is irritable, or sensitive to disturbances,
but nerve cells are especially sensitive.

There are, of course, no special tissues or special kinds of cells in the
protozoa. But where the cells, as they are formed by the division of the
mother-cell, cling together instead of drifting apart, division of labor takes
place. Thus, in the poriferans and in the coelenterates (see Appendix A),
we can see two or more different kinds of cells.

The simplest organism having distinct nerve cells is the hydra (see il-
lustration above). When one of these is disturbed, it does not contract, as
does the ameba, but it transmits the disturbance, or stimulus, to all parts of
itself and on to other cells. It specializes in sensitiveness and in transmit-
ting. Its many branches touch many different cells; its structure suggests a
reaching out in all directions. When delicate nerve-endings at the surface

274

Cell body

Receptor

Effector

are disturbed, muscular cells contract. As we watch the
hydra in the water, we can see the stimulation lead to
movements of the tentacles and of the whole body, al-
though we can see neither the nerve cells nor the
motor cells.

Nerve Cells In man, as in all vertebrates, and in
other species of complex animals, the nerve cells, or
neurons, are clearly distinct from other kinds of cells.
A neuron may be compared to a muscle cell as a unit
of muscle, or to a gland cell as a unit of gland. More-
over, there are several kinds of nerve cells (see illustra-
tion in margins) : (1) Neurons that receive impressions
from the outside (for example, through the skin, the
eye, etc.) we may call receptors, or receivers of stimuli.
Since they transmit impulses toward the brain or spinal
cord, these sensory neurons, or receptors, are also called
^/-ferent, that is, bearing toward. (2) Neurons that
arouse muscles or glands into action are called effectors
— effect-producing. Since effectors bear impulses away
from the cord or brain, they are also called ^/-ferent
neurons. (3) Neurons that connect afferent and efferent
neurons are called associative neurons, or simply con-
nectors.

The whitish strands commonly called nerves reach
to all parts of the body, and some of them are large
enough for us to see without a microscope. Nerves con-
sist of many fibers bound together by connective tissue
and associated with blood-vessels and lymphatics. The
cell bodies are grouped in the brain, in the core of the

TYPES OF NEURONS

A typical nerve cell has a nucleus and
an extension, or axon, that ends in fine
treelike branching, or dendrites. The
endings are in close contact with
dendrites of other cells, or with sensory structures, or with muscles or glands

275

Sense
organ

Muscle

Impulse
from here

■>^.

Sensation
, received
here

Impulse

received here

(receptors)

Action

produced here

(effectors)

FUNCTIONS OF NERVE CELLS

A living body senses outside events at the ends of "receiving" nerves, or receptors.
Nerve impulses are transmitted by nerves toward central organs. The living body
also produces "effects" upon the outside world, through special organs, such as
muscles of the hands, called effectors

spinal cord, and in special clumps called ganglia. These masses of cell
bodies make up the "gray matter" of the nervous system; the strands of
fibers make up the "white matter".

There are also special neurons in the gray portions of the brain that are
related to knowing, feeling, imagining, and the voluntary control of muscles
(see illustration above).

The protoplasm of one nerve cell and the protoplasm of the next are
connected through the branching ends of the axons and the dendrites. If
the endings of a sensory, or afferent, neuron are stimulated, the disturbance
passes through the cell body and the axon to the terminals, which are in
contact with the dendrite of an associative cell. From this cell the impulse
is transmitted to the dendrites of an efferent cell and on through the axon
of this one to the terminals in some effector — for example, a muscle or a
gland (see illustration, p. 275),

The Main Nerve Axis^ Among the vertebrate animals, as among other
bilaterally symmetrical animals, such as insects and segmented worms, a

^See Nos. 1 and 2, p. 298.
276

Sensory end -organs of retina

r*r

End plate of nerve in muscle fiber
Nerve endings

in gland

Motor

Sensory

NERVE CONNECTIONS

Associative

Nerve cells are connected with sensory receptive organs (such as eyes or ears),
with muscles or glands, and with other nerve cells. The end branchings of a nerve
cell form intimate connections with the branchings of another nerve cell or with other
tissue cells. Nerve impulses pass through a nerve cell in one direction only, although
on electric current can be made to pass through a nerve cell in either direction

main nerve runs the length of the body. This has side branches which con-
nect with the skin and special sense organs and also with muscles (see illus-
tration above). These connections have been definitely traced in many kinds
of animals, including man. Moreover, experiments show clearly that the
parts of the structure behave in complete agreement with the idea of a
"reflex" (see page 262). There is a definite nerve connection between the
point of stimulation and the acting muscle. This path consists of at least two
parts: (1) an afferent or incoming neuron, the sensory portion; and (2) an
efferent or outgoing neuron, die motor portion. Most reflexes involve one or
more intermediary associative neurons. The entire path makes up the reflex
arc (see illustration, p. 282).

In all animals with a central nervous system the axis contains fibers that
run, so to say, forward and backward, connecting ganglia in the various
segments. Through these nerve connections stimuli acting upon receptors
in one part of the body can produce effects in other segments, both in front
of and behind the stimulated region.

277

"SPl^

Effector
branch -

SympathJetic
ganglia

Receptor
branch

,•1

THE MAIN NERVE AXIS IN VERTEBRATES

Among bilaterally symmetrical animals there is a main nerve axis with side branches
which lead to the skin and special sensory structures, and to muscles. Many stimuli
and many reactions of the organism may be completed within a narrow sector of
the body; but the cord carries vast numbers of connecting nerve fibers which relate
all parts of the body to all the other parts

These neurons connecting different "levels" of the nervous system help
us to understand some of the more complex movements that appear to be
just as automatic as simple reflexes involving only the parts of a segment.
Let us suppose that one smells a strange odor. If it produces any impression
at all, one is likely to turn toward it — or away from it. In any case, the
muscles used may include those of the neck and shoulders and even those
of the trunk and legs.

The Brain In all vertebrate animals the front end of the central nerv-
ous system is enlarged into a mass of neurons, connective tissue and blood
vessels, together constituting the brain (see illustration, p. 281). The average
weight of the brain of adult males in western Europe is about 1400 grams;
and of that of the females, about 100 grams less. Many human brains weigh
from 1500 to 1800 grams. With two exceptions, man's is the largest brain
among the inhabitants of the world. The true whale has a brain of 6700
grams; and the brain of the Indian elephant attains over 5400 grams. In
relation to the size of the body, however, man's brain is much greater than

278

/Dorsal root

IN AND OUT NERVE PATHS

If the dorsal root of an intervertebral nerve is cut or broken, stimulating the end away
from the spinal cord produces no effects; but stimulating the end connected with the
cord arouses the same sensations as stimulating the corresponding sensory endings.
That is, this branch transmits impulses only toward the brain. If the ventral branch
of the nerve is cut or broken, stimulating the end near the cord produces no results;
but stimulating the portion away from the cord arouses muscular contractions or
glandular secretions, or both. That is, this branch transmits impulses only outward
from the center

that of any of these animals. Thus the ratio of brain-weight to body-weight
is 1:40-42 in man; 1:500 in the elephant; and 1:12,000 in the humpbacked
whale. On the other hand, some of the smallest mammals have relatively
larger brains: the ratio of brain- weight to body-weight is 1:22-26 in some of
the marmosets and some fancy breeds of mice, and even more in some of the
spider monkeys — about 1:17-20 (see table, p. 297).

The cortex, or "rind", of the cerebrum consists of nerve cells. In mam-
mals this gray layer is very much wrinkled, so that there is relatively more
surface than in lower vertebrates. The primates have more complex brains
than other mammals. The cortex of the primates has five distinct layers of
cells, as against three in other mammals. This fact is apparently related to
the greater capacity of primates to learn ; and in the case of man this means
also the capacity to imagine, to form and to remember abstract ideas, to

279

Dorsal (afferent)

White matter

Gray matter

Ventral (efferent)

Branching
nerve
roots

A cross section of the spinal
cord shows a rather distinct
gray pattern, somewhat like
a butterfly in outline, within a
whitish moss. The white part
of the cord consists largely of
axons, which transmit nervous
impulses up and down — to-
ward the brain and toward
other segments of the body.
The gray matter consists
largely of cell bodies that act
as switching centers, receiv-
ing impulses from afferent
nerves and shunting them oflF
into efferent nerves as re-
flexes or transmitting impulses
from efferent as well as from
afferent nerves, up and down
the axis. Ganglia usually con-
sist of cell bodies; the nerve
strands consist of axons and
supporting tissues

THE NERVE CONNECTIONS OF THE SPINAL CORD

plan, to think. Although man has neither the largest brain by absolute
weight nor the largest in relation to the size of his body, his brain is probably
the most efficient for bringing about changes in the world and for making
adjustments to changes.

We have seen that an awareness is associated with some of the reflex
actions. We interpret this fact by supposing that the receptor and the effec-
tor neurons of the reflex arc are connected also with the brain, by way of
the spinal cord (see illustration, p. 282). Impulses to the cerebrum have to
do with consciousness. Impulses from the cerebrum control voluntary ac-
tion, but the cerebrum cannot control the reflexes, of which we are in most
cases not aware.

Certain portions of the cerebral cortex appear to be connected with specific
sensations or movements. The charting of these connections is based upon
experimental studies with various mammals, and upon experiences with the
diseased or injured brains of human beings (see illustration, p. 283). The
matter is not so simple, however, as the diagram suggests, for the function
of each region seems to be influenced by all the others. Every conscious
desire, as well as every deliberate or purposeful action, seems to depend upon
impulses starting from the gray matter in the brain or upon stimuli leading
to the gray matter.

280

Dog

Monkey

Pigeon

Man

THE BRAINS OF VERTEBRATES

In birds the cerebellum is relatively larger than in mammals. In mammals there is an
increase in the amount of convolution, or wrinkling, of the brain cortex — the "bark"
of the cerebrum. The extent of the wrinkling is connected with the number of cells
and the complexity of their connections

Living without a Brain^ You have no doubt heard of someone run-
ning around Hke a hen with her head chopped off. A bird or frog can
survive for days without using its brain. If the base of a frog's brain is cut
through, the animal will still move a hind leg so as to brush away anything
that touches the skin on that side. Many experiments show that animals can
carry out rather complex movements involving many parts of the body
when practically all the brain has been removed.

We explain such brainless activities by the fact that nerve paths to the
effectors may be stimulated by processes outside the brain. These brainless
animals still lack something of being fully "alive". They never start any-
thing on their own initiative, not even taking food when it is placed right
before them. They will swallow food placed in the mouth, digest food, and
carry on other so-called "vital" functions. They will move away when
pushed, but will not dodge a threat.

Such a brainless animal is indeed not strictly dead, but its living is largely

iSee No. 3, p. 299.
281

From I
brain t

To
brain

Sensory cell
body

Receptor

Association
nerves

Afferent

nerve

path

Effector
(muscle)

Efferent
nerve path

THE BURNT HAND DRAWS BACK

When nerve endings in the skin are disturbed, an impulse travels up the afferent,
or sensory, nerve cell. The disturbance is discharged to an efferent, or motor, nerve
cell. Some is discharged also to an associated cell and transmitted to the brain.
The stimulus in the motor nerve cell arouses contraction of muscle. The path from
the receptor to the spinal cord to the effector is called a reflex arc

vegetative. A person without a brain, or with one not working, is also
largely vegetative, even if he sometimes uses his striped muscles vigorously.

The Brain and Reflexes^ It is not diflftcult to show that animals —
whether those with brains or those without — depend upon reflexes, or upon
the reflex arcs in the nervous system. Let us suppose that a certain part of
the sciatic nerve (the main nerve trunk running down the leg) were broken,
destroying the continuity of the a^erefit fibers (see illustration, p. 284). One
might then walk on carpet tacks or hot iron and not know it unless he
happened to be watching his feet. Accordingly, one would not jump to
avoid injury. Under these circumstances a person would still be able to
move his legs or to jump if he wanted to. On the other hand, if the por-
tion carrying e§erent fibers were cut, one would remain just as sensitive as
ever to carpet tacks or hot iron or tickling; but he could not move his legs,
no matter how much he wanted to. And they certainly would not move
of themselves, for the part of the reflex arc connecting the spinal cord with
the muscles would be broken.

A large part of human activity may thus be seen to be mechanical, or

^See Nos. 4 and 5, p. 299.
282

Cortex

of left

cerebrum

an CO association

./. ,/ Ig^ A^ :§ axea

l3 Fmger^ co

Speech A ^"^^ Speech t\
OHacto.y.r^ %^ ^ V

Froatal
associ-
ation
area

w
O

Medulla
oblongata

LOCALIZATION OF FUNCTIONS IN THE CEREBRUM

Certain regions of the brain cortex seem to be related to receiving sensation from
specific regions of the body, while other regions of the brain initiate movements of
particular muscles. "Thinking" appears to be carried on by the association areas:
the hind area has to do with knowing and understanding concrete facts and rela-
tions; the frontal area has to do with abstract thinking, self-control, concentration,
and making decisions

Motor

impulse

from

here

Sensation
received
here

Vif

automatic, as is much of the activity of
other species. But while reflexes are in-
separable from human conduct, they are
not the distinctive characteristic of our
behavior. For each reflex is a segment, or
fraction, which we are able to study by
itself. What we learn from these frag-
ments does not necessarily tell us that
the organism always acts as a whole. Or
that the activity of the organism is always
in relation to a complex situation, not
merely a simple response to a single
stimulus.

There are mechanical elements in hu-
man action, but life is more than the sum
of these elements. Beyond these reflexes,
there are high degrees of intelligence,
high skills in adjustment, high levels of
imagination, initiative and ingenuity. It
is these that distinguish the animal with
the modern brain from all other species.

Efierent
nerve —

\fferent
-nerve

How Do Nerves Receive Different
Kinds of Stimuli?

General Sensitiveness and Special Sen-
sitiveness^ The naked protoplasm of
various small plants and of the ameba
and other protozoa seems to be equally
sensitive to many different kinds of
stimuli or disturbances. The protoplasm
reacts to mechanical pressure or direct

Stimulus here

BEHAVIOR LIMITED BY NERVE CONNECTIONS

If the afferent nerve of the arm or leg is cut,
one might move the limb freely, but could not
feel any stimuli that it might receive from the
outside. He could walk so long as the efFerent
nerves were intact. If the efferent nerve were
cut, he could feel pain or tickling in his hands
or feet, but could not move a limb
^See Nos. 6, 7, and 8, pp. 299 and 300.
284

touch, to electrical disturbance, and to chemical action. Changes in tempera-
ture and light also stimulate protoplasm. In the more complex types of
animals, however, most of the protoplasm is inside the body and protected
against contact with happenings outside. Such animals receive stimuli
through special organs, just as they act upon their environments through
special effectors — hands and feet, for example, or jaws and teeth.

Thousands of nerve endings in our skin are sensitive to slight pressure or
contact (see illustration, p. 217). The touch receptors are more closely
crowded in the tips of the fingers and on the tongue than in other regions.
There are also special end-organs sensitive to heat and others sensitive to
cold. The stimulation is carried along through one or more neurons until
it finally sets up a disturbance in one or more cells of the brain cortex. Here
the stimulus is at last translated into a feeling, or sensation. We say that the
finger is hot, but it is in the brain that we feel the stimulus. The elevator
operator looks at the indicator and says, "Somebody rang on the tenth floor".
A button was pushed on the tenth floor, but he heard the bell wherever he
happened to be at the time, and he "knew" that the signal came from the
tenth floor because the indicator said "10" to him.

Inside the organism, mechanical pressures or contacts may also act as
stimuli — the pressure of food in the intestine, for example, or the presence
of urine in the bladder. Some of these touch or pressure stimuli start re-
flexes; others bring impulses to the cortex and make us aware of the con-
dition or the position of the body.

If you lie quietly with your eyes closed, you are still able to tell the posi-
tion of your body and of your limbs, because of nerve-endings which are
stimulated at the points in contact with the supporting surface. The vary-
ing tensions of the muscles attached to the bones of the skeleton give you a
feel of the relative position of the trunk and limbs. As you turn about,
changing strains of the floating viscera and variations in pressure on parts
that are not rigid contribute to the same feeling of position in space, or of
movement. In the inner ear is a special organ that seems to be directly re-
lated to the sensation of position-of-the-body and to sensations of spinning
and turning, which sometimes lead to dizziness (see illustration, p. 286).

Our balancing organs are highly specialized contact receptors, which,
however, we do not ordinarily appreciate as we do our other sense organs. In
the swollen region near the end of each ear canal sensitive hairs project into
the liquid. When the head starts moving or turning, the liquid lags behind
somewhat, bending the hairs in the opposite direction. One "senses" the
changed position at this point. As the fluid's movement catches up with that
of the canal, the hairs become erect (see illustration, p. 287).

In many crustaceans and molluscs there is a balancing organ, or statocyst,
which consists essentially of a hollow space with sensitive walls that con-

285

Semicircular
canals

Cochlea

B,F

BALANCING ORGAN IN MAN

In vertebrates the balancing organ consists essentially of three hollow rings lined
with sensitive nerve endings. These three rings correspond to the three planes of
the space in which we move about. We do not ordinarily "feel" the balance, but in
skating, dancing, flying, tightrope walking, in all physical activities that involve rapid
changes in the body's position, the co-ordination of movements depends largely
on these canals

tains some floating grains of sand (see illustration, p. 288). An experimenter
removed the sand from several crayfish and replaced it v^^ith iron particles.
This did not affect the movements of the crayfish; but w^hen he brought
a magnet near one of these animals, it behaved as if the side tow^ard
the magnet were down. This experiment shows that the statocyst works
through the displacement of the solid particles in the course of the animal's
movements. It also shows the automatic character of some of the animal's
adjustments.

Hearing When we hear the low roar of the airplane engine becoming
steadily louder, it does not occur to us that we are touched by anything. We
think of the sound as coming from a great distance, as we think of the air-
plane itself going a great distance. Yet we may reasonably think of our
hearing organs as highly specialized touch receptors. For according to the
studies of physicists, sensations of sound correspond to vibrations in the air
— actual air movements striking upon our eardrums much as waves of the

286

p r

Ampulla

Section of ampulla in motion

HOW OUR BALANCING ORGAN WORKS

In the rapid movement of a plane, every turn, bank, climb, or dive involves the
centrifugal effects upon the semicircular canals. As a result, the pilot is frequently
confused and unable to judge his position or direction except by means of special
instruments. In steady movement the hairs and the fluid in the canals move together
and there is no sensation. In a quick start or turn or stop, the fluid in the canals
holds back or runs ahead and so bends the sensitive hairs

sea strike against a floating buoy, setting it in motion. In other air-breathing
vertebrates the hearing organ is very much like our ow^n (see illustration,
p. 289). The stretched membrane, or drum, is the receiving area for sound
vibrations in many diflerent types of animals. In some insects and spiders,
however, the sound waves are received by fine, stretched hairs connected
with nerve fibers or by fine hairs standing out on the antennae.

Animals differ very much as to the range of sound vibrations they can
perceive. Some animals are quite insensitive to sounds that nearly all hu-
man beings can hear, while some insects can perceive a much higher pitch
than any human being. The human ear discovers sounds of various pitch
when the vibrations of the air are at least 16 to 20 per second but not more
than 25,000 to 40,000 per second. In the middle register, which includes the
range of the human voice and most familiar sounds, we can distinguish
very slight differences in pitch. A trained ear can distinguish more than
1000 shades of pitch in one octave.

Chemical Sensitiveness Protozoa are attracted by the presence of vari-
ous kinds of bacteria, but they are repelled by various chemical substances.

287

They will swallow the bacteria and pass sand grains by. Our white cor-
puscles react to various kinds of bacteria much as the ameba reacts to
chemical stimuli (see page 188). In the retina of the eye light brings about
chemical changes, just as it does in chlorophyl or in a photographic film.
But in the retina, the chemical action sets up nerve stimulations.

The tip of the tongue is more sensitive to touch than are the tips of the
fingers. Yet we think of the tongue not as a touching organ, but as a tast-
ing one — that is, an organ sensitive to chemical stimulations. Touch and
taste are related, however, since chemical action takes place only when two
substances come in contact. Another related sense is that by which we dis-
tinguish odors. In both tasting and smelling, stimulation depends upon the
presence of particular substances in direct contact with the nerve-endings.
These materials dissolve in water and diffuse directly into the sensitive
cells.

The special receptors of taste are very small projections on the upper
surface of the tongue and in other parts of the mouth lining and of the
pharynx. These contain nerve endings connected with the brain cells,
through which we are made aware of taste. Our taste system can distin-
guish four classes of tastes: sweet, sour, salt, and bitter.

The lining of the nose is sensitive to touch, as well as to odor. The
sneeze reflex is started by either a strong odor stimulation or by a touch on
some of the nerve endings in the nostrils. The sense of odor, in which the
chemical stimulant touches the surfaces in a volatile state, is much more
acute in many insects and lower mammals than it is in man.

The little "stone" in the cavity of
the statocyst rolls about freely as
the body changes its position.
As it moves about in this way, it
comes in contact with delicate
hairs that line the cavity, now
touching one group, now another.
These hairs are outgrowths of
sensitive 'cells which connect with
nerve cells. These nerve cells in
turn are connected with muscles,
forming reflex arcs. As different
parts of the lining are stimu-
lated, different skeletal muscles
are made to contract. In this
way the animal retains or recov-
ers its position in relation to the
horizontal

BALANCING ORGAN IN A SNAIL
288

Semicircular
canals

Nerve to
brain

Cochlea

Eustachian
tube

■^

Passage from
outer air

THE HUMAN EAR

Stirrup

A sound vibration of the air strikes the tympanum, or drum, and is transmitted through
a chain of tiny bones to the liquid filling the "labyrinth". Disturbances of the liquid
stimulate delicate nerve endings in the cochlea, and the nervous impulses ore trans-
mitted to special regions of the brain

We can see the relationship between these two chemical senses and to
an organism's adjustments in various ways. Thus both pleasant food odors
and food tastes arouse the salivary reflexes. A blindfolded person, holding
his nose to prevent currents of air from passing through it, cannot distin-
guish ground coffee, for example, from sawdust, or vanilla flavor from
raspberry. When we speak of the taste of good food, we usually mean the
odor. Feelings of nausea and the act of vomiting may be started by dis-
agreeable odors.

Sensitiveness to Light We value seeing perhaps more than our other
senses because it puts us "in touch" with more of the world — with much
of the world that we are, in fact, unable to touch directly. We are able,
however, to understand that seeing depends upon chemical changes in the
sensitive structures — in the pigments that characterize all light-sensitive or-
gans. The source of the light, the objects that reflect the light by which we
see, may be very far away. The action on the nerve-endings, however, is
very close by, just as close as in the case of odor and taste or as in the case
of an actual push!

289

All branches of the plant world and all branches of the animal world
are sensitive to light. But only three main groups of animals can actually
see. These are the highest mollusks, the arthropods, and the vertebrates.

By seeing we mean not simply discriminating between light and dark,
but distinguishing forms at some distance. The starfish, for example, has
light-sensitive spots at the ends of the rays, but these are not true eyes (see
illustration, p. 230). Comparatively few of the mollusks have special light
organs. In most of the bivalves the edge of the mantle is vaguely sensitive
to light. The scallops have "eyespots" at the edge of the mantle, but in the
snails, the squids, and the octopuses there are definite eyes. The eye of the
octopus resembles that of the backboned animals in many ways.

Vertebrate Eyes Among all backboned animals the eyes are very
much alike (see illustration opposite). Important differences correspond to
the habits and the habitats of the different groups. Animals living in the
water, for example, have a different kind of lens. Animals that prowl about
at night have a different kind of pupil. The eye is moved about in its set-
ting by muscles attached to the bony framework, and is further protected
by the movable lids and watery secretions.

The fishes (except the sharks) lack eyelids. The eyelids of snakes are
permanently closed, but transparent. Among the birds and in many reptiles
there is a single eyelid that passes over the eyeball from the inner corner,
under the outer pair of eyelids.

Compound Eyes Insects and other arthropods commonly have com-
pound eyes, and many of them have also simple eyes. In each of the eyes
there are many nerve-cell endings. The lens projects upon these sensitive
points a tiny patchwork of varying lights and shadows. Thus each of the
many eyes forms some tiny picture of a portion of the outside world.

A compound eye of an insect or lobster may have from twenty to several
thousand separate facets. The impressions produced in the units of a com-
pound eye are probably not very distinct. But as the animal gets a mosaic
of many simultaneous views from somewhat different angles, it is disturbed
by very slight movements. Most insects are able to detect movements in
practically all directions, though not at a very great distance.

The Senses and Adjustment^ Most of the organs through which we
receive stimuli from the outer world depend upon direct contact between
the body and some object. Reaction to such stimuli is ordinarily immediate
— of a reflex character. If an animal is to profit from its ability to sense
such stimuli, it must respond promptly. And if the stimulus comes from
possible food, the reaction must take place before the food has time to
get away.

The three senses that enable an organism to receive stimuli from objects

^See No. 9, p. 300.
290

Pigment
layer

Retina

y Focusing
muscles that make the lens

-T/^/is brought about by

v^" //

more convex
for near vision

Iris and pupil
Diaphragm

more flat
for distant vision

Life

THE VERTEBRATE EYE

The eye, like the camera, has a lens at one end and a sensitive surface at the
other end. In front of the lens a diaphragm regulates the amount of light admitted.
In the eye the sensitive surface (retina) is backed by a layer of pigment and con-
nected with the optic nerve

at some distance — sight, hearing, and smell — give opportunity to discover
food or enemies while there is still a little time before action is imperative.
Accordingly, these senses act in many situations without bringing about an
immediate reaction. Now, as we have already observed, a stimulus may
lead to an immediate reflex, but the reflex seldom exists by itself. On the
one hand, the stimulus may start impulses that are transmitted to higher
levels of the nervous system, as well as to the usual effectors. On the other

291

hand, a stimulus seldom acts upon the body apart from all other stimuli, so
that the normal reaction to one stimulus may interfere with the normal re-
action to one or more other stimuli. A dog about to seize a piece of meat
which he spies might be stopped in his tracks by a simultaneous loud
sound.

The impressions which an organism receives through various stimuli
that do not immediately set up the normal reflex seem to register somehow
in the brain cells. In this way some of the experiences influence the animal's
later activities. It is in some such way that we are capable of learnifig
from experience; the delayed or obstructed reaction gives the organism an
opportunity to react in one of several ways, and the way ''selected" seems
to depend upon previous experience. It is probably in the delayed reaction
that the organism makes a beginning at control — control of its own actions,
and so in the end control of its environment.

How Do the Nerves Make the Other Organs Work?

Nerve Impulse If an efferent nerve that is connected with a gland is
detached and applied to a muscle, it can act in its new position to stimulate
the muscle. This kind of transposition has been repeatedly carried out in
experiments. The results show that the nerve in such cases acts merely as
a transmitter of energy or of a stimulus. The nerve apparently has no in-
fluence upon the character of the response. An electrical disturbance ap-
plied to a motor nerve brings about contraction of the muscle. A me-
chanical stimulus, such as that in the statocyst of a lobster (see page 285),
brings about movements corresponding to the position of the mova-
ble sand grains — that is, to the particular nerve endings that are being
stimulated.

How does disturbance at one end of a neuron bring about a change at
the further end, sometimes many inches away ? The transmission is accom-
panied by chemical and electrical changes. Perhaps it is a chemical dis-
turbance which passes from point to point through the length of the neuron.
Or the transmission may be a simple electrical impulse, such as passes
through a wire. But apparently it is neither of these. Nor is it like the
transmission of a shove through a billiard cue. Nerve transmission seems
to be peculiar to protoplasm. And changes in the protoplasm itself take
place in the process.

Voluntary and Involuntary Muscles In the simplest animals the whole
protoplasm takes part in receiving a stimulus and in reacting to it. In our
bodies, movements are brought about by the contraction of muscles, which
make up the "flesh" in all larger animals (see illustration, p. 296). Through
the striated skeletal muscles the animal moves about, grasps, gets and chews

292

Ainciiran Museum iif Natural History

HOW WE AND THE HEN SEE THE SAME WORLD

The hen's eye is not only nearer the ground than ours, but the curvature of its lens
is different. Her retina probably differs from ours in its sensitiveness to colors. And
certainly what she sees in this some world means one thing to her and something
else to us

food, moves the eyes and ears, and makes sounds with the lungs and larynx.
These muscles are called voluntary, being under more or less direct control
of the central nervous system — the brain and spinal cord; or they contract
in response to stimuli received by the sense organs. The heart muscles, how^-
ever, are striped, but are not controlled voluntarily.

The smooth muscles relate the parts of the body to one another. Their
contractions w^ork the stomach wall, move the food along in the diges-
tive tube, and control the diameters of the blood vessels. These involun-
tary muscles make up a system that works constantly, even while we are
asleep. Life may go on indefinitely if most of the skeletal muscles are
paralyzed, but if the smooth muscles are paralyzed, death comes quickly.

Infantile paralysis is a communicable disease, apparently caused by a
virus. It is often fatal, but where victims recover they are usually crippled
for life. No cure has been found for this disease. However, Elizabeth
Kenny, an Australian nurse, found a way to prevent the paralysis in those
who recover. In 1910 she had four sick children on her hands in a village
far from hospitals and physicians, and she set to work with them, doing the
best she could. The children recovered and she saved them all from becom-
ing crippled. She had noticed that in the acute and most painful stage of the
disease the skeletal muscles are in a state of continuous contraction or spasm.
She helped the children to relax these muscles by means of hot applications.
Then she helped the blood circulation move through the muscles by mas-
saging them and by moving the limbs. Later she got the children to try to
move the parts themselves, until they gradually acquired control over their
muscles. Her method has been recognized by physicians to be sound and
practical; and she has been training hundreds of nurses and technicians to
use the method for preventing those who are attacked by the disease from
remaining crippled.

Our Double Nervous System Corresponding to the two sets of mus-
cles, we have two sets of nerves: (1) The spinal cord and the brain, with
their connections with the receptors and effectors, regulate the adjustment
of the organism to its surroundings. (2) The autonomic, or self-regulating,
system connects the internal organs with one another (see illustration,
p. 295). It has no central organ. It consists of a double series of ganglia,
or nerve-cell clusters, located in front of the spinal column (see illustration,
p. 278).

We have already seen that as the activities of the brain and of the mus-
cles vary, there is an automatic regulation of the heart, of breathing, of the
blood-vessels, and of various glands. Some of these adjustments seem to
result directly from an alteration of the processes in a remote part by chemi-
cal substances in the blood. When you increase muscular activity, for ex-
ample, oxidation in the tissues is increased, and more carbon dioxide is

294

I - Upper division <

Spinal cord
Ganglion —

Esophagus

II - Middle

division, or
sympathetic
system <

Adrenal gland
Kidney

III - Lower

division s

■Tear gland

Parotid gland ^

Submaxillary
gland

■ Sublingual
gland

Salivary
glands

/^f

Trachea

Lung

Heart

Diaphragm

Nerve from

upper division
to stomach

— Nerve from
sympathetic system
to stomach

Stomach

Liver

Large intestine

Small intestine

Bladder

THE AUTONOMIC NERVOUS SYSTEM

A double chain of ganglia in front of the vertebral column connects the vegetative,
or co-ordinating, system into a well-knit whole. These ganglia are connected not
only with each other, but also with the circulatory, digestive, excretory, and repro-
ductive organs, the glands, and the spinal nerves as well. Thus the unconscious and
involuntary processes are tied up with the conscious and voluntary ones

es) .-"^

/ Voluntary
/ muscle
cells

Involuntary-
muscle cells

VOLUNTARY AND INVOLUNTARY MUSCLES

Muscles attached to the bones and skin consist of cells that appear to be striped
when seen with a microscope. They are connected with the brain or the spinal cord
and are subject to voluntary control. Muscles of the blood vessels and the viscera
are not striped; they are all involuntary muscles

discharged into the blood. Now the chemical condition of the blood di-
rectly stimulates the vagus nerve, which in turn acts upon the heart and
the breathing. The adjustment of the pulse rate and breathing rate to chang-
ing conditions of the blood is thus almost immediate.

Because of its many connections with all the organs of the body, the
autonomic nervous system ties all the parts together so that they act as a
whole through the reflexes. The autonomic system includes in its control,
however, much more than involuntary muscles. Some of the endocrine
secretions (see page 313) act upon the autonomic nervous system; this in
turn acts upon some of the endocrine glands.

296

Size of Brain (Brain-weight in Grams)

Various primates

Gorilla 600

Chimpanzee 365-400

Gibbon 95-130

Earlier forms of man

Pithecanthropus 900

Piltdown man 1300

Neanderthal 1400

Cro-Magnon 1550

Modern man 1400-2000

Various groups of peoples 950-1500

"One hundred eminent scholars", average weight 1478

In Brief

In all the higher animals specialized organs and tissues carry on in an
exaggerated degree some special function that is common to all protoplasm.

Specialized structures are co-ordinated by the activities of sensitive cells
called neurons, elaborated in vertebrates into the central brain-spine system,
which connects with all parts of the body.

In all the members of a species the same reflexes occur in practically the
same way. A refiex arc is the nerve path consisting of afferent and efferent
neurons, with associative neurons.

Neurons of the central nervous system, that is, those related to knowing,
feeling, and voluntary control, are classified according to their functions into
(1) afferent nerves, which conduct impulses inward or toward the central
portions; (2) efferent nerves, which bear impulses only outward, usually to
muscles or to glands; (3) associated neurons, which act as intermediary, or
bridging, paths.

Nerve-endings throughout the body, as well as on the surface, act as
receptors for stimuli. Even a simple stimulus frequently sets going a whole
group of reactions.

Many of the so-called "instincts" observed in animals are either reflexes
or chains of reflexes. Most of the chains of responses which organisms make
appear to be well suited to the situation from which they receive the
stimulus.

Through specialized sense organs animals are sensitive to several varie-
ties of stimuli. Species vary in the range of sensitiveness to different stimuli.

Movements in our bodies are brought about by the action of muscles:
striated muscles are subject to voluntary control, smooth muscles are not.

297

The spinal cord and the brain, connected with the receptors and ef-
fectors, regulate the adjustment of an organism to its environment; the
autonomic, or self-regulating system, ties all the parts together so that they
act as a whole through the many reflexes.

The size and complexity of the brain are related to the ability of an
organism to learn, to form associations between past experience and future
conduct.

Certain portions of the cerebral cortex are supposed to be involved in
specific sensations or movements.

Man lives under the greatest variety of conditions, probably because he
is the most flexible in adjusting his natural responses and the most tenacious
in accumulating experiences.

EXPLORATIONS AND PROJECTS

1 To study reflex responses in a vertebrate, stimulate a frog gently in various
ways and note what responses the animal consistently makes to particular stimuli.

To find what responses the frog makes to touch, tickle the nostril, touch the
eye, scratch the back gently, and stroke the back with thumb and forefinger.
Enumerate as many simple and consistent responses as may be observed for each
stimulus.

To find the responses of the frog to chemical stimuli, use weak ammonia:
a matchstick moistened in ammonia. Bring it near the nostril; also touch it to
the frog's back. Repeat each test several times to be sure that the movements are
not random or accidental. (Wash the frog under running water after each appli-
cation.)

To find the responses of the frog to electrical stimulation, use a two-point
electrical terminal connected with a 6-volt battery^ and touch the frog in several
places. Note the consistent responses.

Compare the frog's responses to contact, to chemical stimulation, and to
electrical stimulation.

2 To observe reflexes in human beings:

To observe the knee jerk, have subject sit erect with the legs crossed, so that
the upper leg hangs limp from the knee; tap sharply just below the kneecap and
observe the movement that results. Note whether this movement can be con-
trolled.

To observe the wink responses, have someone make a sudden motion toward
the subject, as if to strike the eye, and note reaction. To what extent can this
reaction be controlled?

To observe the iris reflex, work in pairs: have the subject face the source of

^Fasten the ends of two wires to the end of a glass rod by means of adhesive or friction
tape so that they project about a quarter of an inch and are held about a quarter of an inch
apart.

298

light, with observer facing subject. Shade one eye with the hand for a minute,
then quickly remove it while observing any changes in the iris. To what extent
can iris movements be controlled by the subject?

To observe the automatic focusing, or fixation, response, have subject and
observer face each other. Subject holds a pencil vertically at arm's length and
fixes his eyes upon it while slowly bringing it toward his face until it is too close
to be comfortable. How do the subject's eyes behave? What is there to show
whether this is a native or a learned reaction?

3 To find whether the brain takes part in the reflexes of an animal, use a
pithed frog and repeat the stimulations in No. 1 above. ^

4 To observe chains of reflexes, or "habits", watch individuals performing
familiar and repeated acts to see how closely the succession of movements is
duplicated at different times.

Observe such sequences as using table utensils, cutting food, handling napkin,
and so on; dressing and undressing — the order and manner in which the various
garments are taken off and put on, and how they are laid down; and smoking —
the sequence of acts that a habitual smoker follows.

Have several classmates remove their coats and lay them on their seats; then
have each put his coat on again. Repeat this operation two or three times, and
note, first, the different ways in which individuals may be doing what is "the
same thing", and then the consistency with which each one follows his own
pattern.

5 To determine reaction time, we may use a series of repeated acts, since it
is difficult to measure the fraction of a second involved in most reactions. With
one individual keeping time, have the other members of the group form a circle,
each member facing the back of the person in front of him; the stimulus is a
slap on the back, and the response is a slapping of the back of the person next in
front. All will be alert to transmit the stimulus as quickly as possible, but will
not anticipate by watching. Repeat the series several times; average the time
around and average the time per individual.

6 To see whether vision is involved in ordinary body equilibrium, compare
ability to stand still on one leg, without swaying, with eyes open and then with
eyes closed.

7 To find variations in the skin's sensitiveness to touch, explore different
parts of the skin for discrimination between two points touched. Work in pairs,
using a two-point contact needle. Explore the back of the hand, the palm of the
hand, the tip of the index finger, the forearm, the back of the neck; the experi-
menter touches the skin either with one point or with both points at exactly the
same time. (Do not press too hard, as a sensation of pain is different from that
of touch.) The subject, not seeing the contact, reports whether he feels one point
or two. Test each region a sufficient number of times to determine the smallest
distance between points which the subject can detect. Use spreads of 20 mm,
10 mm, 5 mm, 3 mm, and 1 mm.

What are the smallest intervals that could be distinguished in each area?

^See footnote 4, p. 183.
299

8 To show that sensitiveness to temperature may be influenced by temporary
conditions, place both hands in a basin of lukewarm water, after one hand has
been for a time in very hot water, while the other has been kept in cold water.
Describe the sensations in each hand and explain the difference between them.

9 To observe your own progress in learning, time yourself on successive
efforts to perform a given task — as writing the alphabet backwards — until further
progress is no longer possible. Plot a graph to show the relation of the number
of trials to the reduction in time of performance.

QUESTIONS

1 How is an organism equipped to receive significant stimuU, external and
internal?

2 To what kinds of stimuli do the specialized sense organs of higher
animals respond?

3 What kinds of organs act as effectors?

4 What is a reflex arc?

5 What is meant by a chain of reactions?

6 What is known about the nature of the impulse transmitted by different
nerve cells?

7 Of what does the central brain-spine system consist?

8 How are the voluntary movements of our bodies brought about?

9 In what respects is the autonomic nervous system like the brain-spine
system? In what respects different?

10 How are the activities of the specialized organs and tissues of higher
animals co-ordinated?

11 How do modern living conditions bring special dangers to our sense
organs ?

300

CHAPTER 16 • HOW DO GLANDS WORK?

1 Do glands influence our abilities?

2 Do glands influence personality?

3 How can a slight change in one part of an organism bring

about adaptive responses in other parts?

4 How do gland substances reach other parts of the body?

5 What good does it do living things to feel fear?

6 Are all people naturally or instinctively afraid of the same

things ?

7 Can we learn to overcome fear or to control anger?

8 Can people act against their instincts?

9 Why do we learn more easily at some times than at others?
10 Can human nature be changed?

When Abraham Lincoln was President of the United States, the country
was torn by civil strife. The entire population was constantly agitated by
strong feelings — bitterness and hatred, anxious waitings and eager hopes,
high elations and shattering disappointment. The President himself, with
all his patience, was subject to moods of depression. It was easy to give
good reasons why one should be angry at one time and joyous at another.
But nobody suspected that "glands" had anything to do with people's
feelings.

In the following forty years much was learned from the study of patients
in hospitals and clinics, from experiments, and from the comparison of men
and women living in different regions under different circumstances. We
had already learned enough to suspect that some of President Theodore
Roosevelt's characteristics were related to glands, and he was often de-
scribed as "hyperthyroid".

How can glands influence people's feelings or their behavior? What
are glands anyhow? What do they do? How do they produce effects in
other parts of the body?

What Are Glands?

The Humors Hippocrates, the most famous Greek physician, ad-
vanced the idea that the health of the body depends upon a balance of four
master fluids or "humors" within the body. Blood is one of these, the red
one; and the others were white, black, and yellow. For centuries this sup-
position guided the doctors in treating their patients. And it still shows itself
in our daily language, for we speak of a person's being in ill humor, or
being phlegmatic or melancholic — that is having too much white humor or

301

too much black humor, or bile. Physicians who accepted this interpretation
treated their patients chiefly by trying to increase or diminish the amount of
one or the other of these humors, so as to restore the balance.

Chemical Foundations Today we know that the chemical processes
in living protoplasm are accelerated or retarded in various ways. The heart-
beat, for example, is accelerated by a slight increase of carbon dioxide in the
blood (see page 196).

The relation between the behavior of an organ and the chemical condi-
tions is illustrated in certain experiments by the American biologist Jacques
Loeb (1859-1924). When Loeb placed strips of a turtle's heart in dishes of
salt solution resembling the lymph of the animal, they continued to con-
tract and expand regularly. When he added small quantities of various salts
to the different dishes, some of the strips beat faster, some slower. These
strips of heart continued to beat for weeks after the rest of the animal had
been cut up, some of it destroyed, and all of it "dead".

Chemical Factories Metabolism itself results in various kinds of sub-
stances, such as carbon dioxide and water, urea and lactic acid, and other
waste products. In addition to these oxidation products, every kind of cell
produces various special substances. Do not some of these substances in-
fluence the metabolism of other cells ? Indeed, we have already discovered
that very many of the natural "poisons" and "drugs" are themselves a result
of plant and animal metabolism.

Glands We have seen that in the digestion of food several special
fluids take part — the saliva, the gastric juice, the bile, the pancreatic solu-
tion (see page 169). Any organ that produces a specific substance is called
a gland.

The glands are richly supplied with blood vessels. They commonly dis-
charge their special products on surfaces lining small cavities or tubes (see
illustration, p. 170). The specific product of most glands is secreted or dis-
charged through a special duct or tubule.

In the middle of the last century a famous French physiologist, Claude
Bernard (1813-1878), discovered that the carbohydrate reserves in the liver
get directly into the blood-stream circulating through that organ. That is to
say, a substance can get out of an organ without passing through a special
duct. It was already known that waste substances are carried off by the
blood. But Bernard was impressed by the fact that special and usable prod-
ucts get directly into the blood-stream from the cells in which they are located
or formed. That was the beginning of the idea of ductless glands, as we
now think of these structures.

Ductless Glands What makes the pancreatic juice come into the in-
testine when food from the stomach arrives there? What makes bile come
from the gall bladder into the intestine just when the food is ready for it

302

Pancreatic

juice

(2) Veins from
intestine carry substance
from lining cells--"

Modified blood,
brought by arteries
stimulates pancreas
^,, to secrete

vpy After meal dog's blood
^ contains something that

stimulates
pancreas of
an unfed
dog

Pancreas

Food getting

into beginning

of intestine

stimulates

lining cells

HOW A CHEMICAL MESSENGER WAS DISCOVERED

When some blood from a dog that has just been feeding is injected into the veins
of a dog that has been without food for several hours, the pancreas of the hungry
dog begins to secrete digestive juices. Otherwise the pancreas becomes active only
when food enters the intestine from the stomach

and not at other times? Toward the end of the nineteenth century, two
British scientists, experimenting on dogs, found a surprising answer to these
questions. They could find no nerve connections to account for what hap-
pens. Instead they found that when food arrives in the intestine, some cells
in the wall of the intestine start producing a special substance, which is not,
however, discharged into the food cavity. This special substance is ab-
sorbed by the blood and carried off in the blood-stream.

When blood containing this substance reaches the pancreas or the liver,
it starts the gland secreting its special product. How can we tell that it is
this something in the blood that sets ofl the gall bladder and the pancreas?
If we take some blood from a dog shortly after food has passed from the
stomach to the intestine, and inject it into the veins of a dog whose stomach
is empty, both pancreatic juice and bile will in a few moments appear in
the intestine of the second dog. William Maddock Baylies (1860-1924) and
Ernest Henry Starling (1866-1927), the experimenters, called this unknown
substance secretin, and described it as a hormone, from a Greek word mean-

303

ing to arouse or stir up. Later an American physiologist showed that secretin
consists of at least two different substances, one of them acting on the
pancreas, the other on the gall bladder.

What Ductless Glands Are There?

Modern Humors No scientific physician today takes the four humors
seriously. For one thing, the number is much too small. Instead of going
back to Hippocrates, we now watch a growing list of hormones, specific
chemical substances that influence metabolism. The fluids produced by the
ductless glands are also called internal secretions, or endocrines. Each of
these hormones is distinct chemically, and it is distinct in the effects which
it produces in the body; but all have certain features in common: (1) they
change the rate of metabolism in various cells or tissues; (2) they originate
in specific tissues; (3) they are rapidly distributed by means of the blood;
(4) they produce effects, although present in amazingly small quantities.

Hormones do not supply fuel; yet they may determine the rate at which
energy is released, or whether oxidation takes place at all. Hormones do
not supply building material for protoplasm, but they may influence the
rate of assimilation, the growth of cells, and the growth of tissue. Some of
them arouse chemical actions but others may repress or retard them. An
extremely small quantity of a particular hormone may at any moment
determine the issue between life and death.

The Endocrine System^ At present at least eight or nine distinct struc-
tures have been sufficiently studied to be classed as hormone-producers. Be-
sides the ductless glands shown in the diagram on the opposite page, the re-
productive organs, or gonads (ovaries and testes), also produce hormones in
addition to the reproductive cells (see page 379). Scattered throughout the
body are small groups of cells that behave like some of the endocrine tissues.
Although every one of the endocrines is distinct, each may reinforce or
counteract one or several of the others. Taken together, therefore, they
behave like a unified system; and as each hormone influences the various
organs and tissues and processes in a distinct way, the endocrines play an
important role in unifying the several parts of the entire organism.

One interesting feature of the endocrines is their great similarity in all
mammals and probably in all vertebrates. This has made it easier to carry on
research by trying out our problems and hypotheses on various smaller ani-
mals, and also to make use of new discoveries. If a human being is deficient
in the pancreatic hormone, for example, the shortage can be made up by
using extracts from the pancreas of a sheep or an ox or a pig.

iSee No. 1, p. 320.
304

f^v

Parathyroids

Thymus

Adrenals

Pineal body

Pituitary, or
hypophysis

Thyroid, or

"shieldlike"

gland

Pancreas

LOCATION OF ENDOCRINE GLANDS IN THE HUMAN BODY

The glands of internal secretion produce substances that are distributed by the
blood and produce effects in remote parts of the body. Their names tell us nothing
about their functions. The name "hypophysis" means merely "under-body", from its
position under the brain. Adrenals are next-to-kidneys, while para-thyroids are
beside-thyroids. The names "thyroid" and "pineal" refer merely to shapes. The
pineal gland was supposed by Descartes to be the "seat of the soul"

About a dozen hormones have been recognized. About half of these
have been obtained in a pure crystaUine form of a definite chemical com-
position. A few have been reproduced synthetically. Several of the en-
docrine organs produce more than one kind of hormone. The thyroid, like
the paired parathyroid, however, produces one particular kind of hormone
and nothing else, although each hormone may produce more than one kind
of effect.

305

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Chemical Activators The endocrine glands are stimulated to secrete
by nerve impulses, primarily by those from the autonomic nervous system.
They are also influenced by chemical changes in the blood and by hormones
from other glands. The hormones, the specific products of the endocrine
glands, have been called "chemical messengers". In their rapid distribution
they act like nerve impulses, which arouse action at points remote from a
stimulus: something happens here and sets offs some action there.

Since the blood keeps the fluids of the body constantly stirred up, these
chemical messengers take part in all that happens in the body. They pro-
duce effects in all parts of the body, and events in the various organs con-
stantly influence the kinds and amounts of hormones secreted. Like the
nervous system, the endocrine system keeps all the parts in constant com-
munication. We consider the endocrine system as "older", or more primi-
tive, than the nervous system; for among simpler organisms that have no
nervous structures, the protoplasm is sensitive to chemical stimulation, and
it also responds to stimuli with chemical changes. Moreover, the hormones
operate in higher vertebrates, like ourselves, for example, without producing
sensations and without seeming to stir the "newer" parts of the nervous
system to consciousness.

What Do Hormones Do?

Temporary Service The pineal gland and the thymus (chest sweet-
bread at the butcher's) seem in all mammals to be active only during the
early period of life. That is, the structures normally shrink away before
sexual maturity is reached. The relation of the pineal structure to life proc-
esses is still very uncertain; but when the organ is injured, the results suggest
a specific hormone which influences sexual development.

Hormones and Growth Some hormones accelerate growth, either of
the whole organism or of special parts. When the thymus, for example, is
injured or removed, as through disease, the organism is stunted. When it is
overactive, the body grows very rapidly. In certain experiments J. F. Guder-
natsch, of the Cornell medical school, fed some tadpoles on thymus glands
obtained from calves, and others on thyroid material. The first lot of tad-
poles grew to a large size, but remained tadpoles. The second lot, however,
quickly passed through the stages of development without increasing much
in size (see illustration opposite).

In human beings the thymus reaches its greatest relative size during the
second year. Where, for any reason, the thymus persists past puberty, the
person remains childish in many ways; that is, he fails to mature physically,
intellectually and emotionally.

One of the several hormones found in the front lobe of the pituitary also

308

influences growth (see illustration, p. 310). If the pituitary becomes over-
active after the long bones have reached their normal full growth, the

Thyroid I Thyroid ^1 Thyroid

Plant-fed Muscle-fed Adrenal-fed

control control control

After Gudernatsch

INFLUENCE OF THYROID ON DEVELOPMENT

In three series of experiments, young tadpoles fed on thyroid tissue developed toward
adult stage so rapidly that they hardly had time to grow. These are full size

bones of the face, jaw, hands and feet may now continue to grow. Such
disproportionate enlargements of the face, the nose, the lips and the hands
are often very distressing.

Hormones and Development As an organism increases in size, it
normally changes also in proportions. Everybody recognizes that the body
of a mature person is in many ways different from that of a very large
baby (see illustration, p. 347). In bodies like our own the maturing appears
to be related to the rate of metabolism. But the rate of metabolism is in
turn very much influenced by the hormones, especially by thyroxin, the
thyroid hormone (see illustration above).

Where the thyroid is deficient at birth or in early infancy, the child
remains sluggish, sometimes to the point of being idiotic. This is not the
same as being born with a defective brain. It means that although all the
parts of the organism are present, they are not operating effectively. Chil-
dren in this condition, called cretins, have appeared in some regions in much
larger proportions than in others. In fact, it was long generally believed that
the population of certain parts of Switzerland and of other mountainous
regions were degenerate because there were so many cretins among them.
It was assumed that this condition was inherited and represented a defec-
tive stock.

In recent times, however, we have learned to distinguish idiocy, due to
defective brain development, from cretinism, due to a thyroid deficiency.
Moreover, we have learned to cure and prevent cretinism (see illustration,
p. 311). The hormone produced in the thyroid has been chemically identi-
fied and is today produced synthetically. It is distinguished from most other
organic compounds by the presence of iodine. Where the soil — and the food

309

DWARFS AND GIANTS FROM CHEMICAL ACTION

An excess of the hormone produced by the anterior lobe of the pituitary seems to
cause the excessive growth of giants, while a deficiency retards growth so that one
may reach his full development while still no larger than a child

COMPENSATING FOR THYROID DEFICIENCY^

Thyroid deficiency sometimes retards a child's development, both mentally and physi-
cally. A "mongoloid" cretin treated with thyroxin showed steady improvement. Many
such cases are being restored to normal life

raised on the soil — lacks iodine, the thyroid cannot develop adequately, and
human beings and other mammals suffer accordingly. In this country sev-
eral regions are lacking in iodine sufficiently to bring about a condition
known as simple goiter in a large proportion of young people, especially
girls (see map, p. 101). This is a slight sw^elling of the thyroid, which has
been cured. It ordinarily disappears, however, in a few years. At present,
however, this type of goiter is being completely prevented in entire popula-
tions by adding small quantities of iodine to the common table salt.

Hormones and the Rate of Metabolism" In addition to influencing de-
velopment during early stages, thyroxin influences the rate of metabolism at
all stages. An excess of thyroxin leads to an overdriving of all the body's ac-
tivities. This means increased oxidation ; and if food is not supplied in suitable
proportion, the organism oxidizes its reserves and loses weight. The speeding
up of metabolism results also in higher body temperature and in general nerv-
ous excitement. There may be drying of the hair and excessive perspiration.
Sometimes the eyeballs protrude while the lids are held wide open. Such
cases are frequently helped by the removal of a portion of the thyroid.

Since excessive thyroid activity increases the oxidation of fats and carbo-
hydrates in the body, some people have used thyroid extract for reducing
body weight. But this is a dangerous practice and should in no case be
followed except under the direction of a physician.

^From Lectures on Endocrinology, by Walter Timme, published bv Paul B. Hocbcr, Inc.
-See Nos. 2 and 3, p. 320.

311

In time of extreme excitement or emergency, an
increase of thyroxin in the blood makes possible
an exceptional output of energy. When thyroxin
is continuously present in excess, the alarmed
look and high tension indicate a disproportionate
discharge of energy, with the danger of ex-
haustion

EXOPHTHALMIC GOITER^

A significant clue to the ductless glands, and especially to the thyroid,
was furnished by observations made in England on middle-aged women
suffering from myxedema. In this condition of disturbed metabolism pa-
tients have cold hands and feet, a bloated appearance, thickened lips and
tongue, coarsened skin, a dull feeling, and loss of memory. It had been
observed that in such patients the thyroid had shrunk or deteriorated. In
1891 a British physician treated one such case with the dried thyroid of
sheep. He restored his patient and kept her alive and in normal health for
twenty-eight years, until she died at the age of seventy-four.

Hormones and the Release of Energy In the cylinders of a gas-engine
the energy-releasing explosion of the fuel-oxygen mixture is set of? by a
spark. In the protoplasm of a mammal's body the oxidation of sugar or
other fuel depends upon the hormone insulin. This hormone was extracted
from the pancreas by two Canadian scientists, Frederick Grant Banting
(1891-1941) and Charles H. Best (1899- ). The men were following up
a thirty-year-old clue from Strassburg. There a physician in the hospital
noticed that flies were clustering in one pen of dogs being kept for medical
experiments, but not in the neighboring pen. Since the pancreas had been
removed from some of the dogs, Dr. Naunyn immediately suspected that
the treated dogs were suffering from diabetes, — a condition in which there
is an excess of sugar in the blood and urine. Through further experiments it
was established that this disease is due to defective action of the pancreas —
not of the liver, from which the reserve glucose gets into the blood.

^From The Endocrine Glands, by Max Goldzieher, published by D. Appleton-Century Com-
pany, Inc.

312

Insulin is not a cure for diabetes, for a deficient pancreas remains a
deficient pancreas. Insulin obtained from the pancreas glands of cattle can
be used to make up for the body's deficiency. By attending to his diet and
adding insulin regularly to the blood-stream, a person suffering from dia-
betes may continue to live with a deficient pancreas and carry on his normal
activities for many years. People often ask. Why should not the insulin or
pancreas tissue be taken in with the food ? The answer is that the digestive
fluids, including those of the pancreas itself, destroy insulin.

Hormones and Emergencies In our day-by-day activities the exertions
and energy output of the body are constantly changing. Changes in the
secretion of insulin and thyroxin accompany changes in the rate of metab-
olism, the rate of breathing, and the pulse rate. Through these variations
the organism adjusts itself minute by minute. An emergency, however,
places exceptional strains upon the body. A situation may threaten one's
safety or arouse one's rage.

When the organism is under great stress the adrenals come into action,
stimulated by a nerve impulse from the autonomic system. The medulla, or
core of the adrenal capsule, discharges into the blood the hormone epineph-
rine sometimes called also adrenin. Like thyroxin, epinephrin accelerates
the general metabolism of the body, but it does not act equally on all parts.
We have no sensation in the adrenal, and we cannot "feel" the epinephrin
in the blood. But the changes produced by epinephrin are obviously adap-
tive. When the hormone is in the blood, it increases the fuel and hastens
the blood-fiow to the muscles; it raises the tension of the muscles, widening
the nostrils and deepening the breath, setting the eyes and all the senses on
the alert. A person who shows some of these characteristics under normal
conditions probably has an excess of epinephrin in his blood (see illustra-
tion, p. 314). In many cases such a person is likely to make trouble for others,
or for himself.

Adrenin decreases the blood supply to the digestive system, but makes
more blood available to the muscles. It seems to reduce fatigue even while
energy output increases. When the amount of this hormone is increased by
great excitement or sudden fright, the skin turns white, the eyes open wide,
the heartbeat is accelerated, and blood pressure rises. The organism is all
set for fighting or for running away. If it sustains its effort under high ten-
sion, epinephrin continues to come into the blood. The effect is to raise the
entire level of energy output to what athletes sometimes call "second wind".

After the emergency is over, the metabolism in the various organs and
tissues returns to the usual rates. From our own experience we know that
after any great excitement we are actually weaker than at ordinary times.
In fact, we nearly always feel a decided letdown after any excitement.

The cortex, or rind, of the adrenal produces another hormone, called

313

High blood pressure, high pulse rate, bulging
eyes, and emotional tension ore characteristic of
certain conditions which the individual "feels"
and which are often associated with excessive
thyroid secretion. Experimental treatment showed
that in this case the condition was due to an
excess of adrenin

ACTION OF EPINEPHRIN'

cortin. Cortin seems to have some relation to the water-and-salt balance of
the blood and to the body's resistance to infection. Like insulin, cortin in-
creases the oxidation of glucose. Cortin seems also to influence the develop-
ment of the reproductive organs, probably by interacting with the hormones
of the pituitary gland.

The Master Gland The most complex of the endocrine organs is the
pituitary, which has been called the "master gland" because the several dis-
tinct hormones which it produces affect various organs and various proc-
esses in important ways. The hormones of the pituitary interact with the
other endocrine organs. As a result, they have the effect of maintaining a
balance among the various processes of the organism. But, because they
interact, a serious disturbance of one endocrine may cause a serious disunity
in the growth, development, or activity of the whole organism. As we have
already seen, one of the pituitary hormones affects the rate of growth (see
pages 308-309).

Glands of the Reproductive Organs The ovaries and the testes of
backboned animals produce respectively the eggs and the sperm (see pages
379-381). Among the cells that form sperms or eggs, but apparently not
directly connected with them, are other cells that produce special hormones.
We might compare these hormone-producing cells of the gonads with the
islands of the pancreas. The so-called sex hormones appear to be especially
related to the "secondary sexual characters" — that is, the features that dis-
tinguish male individuals from female individuals. They include the distri-
bution of hairs, pigmentation, horns, the voice, the development of the milk

^From Lectures on Endocrinology, by Walter Timme, published by Paul B. Hoeber, Inc.

314

glands, and other features that distinguish the two sexes among birds and
mammals. These are called secondary characters because they are not pri-
marily related to the reproductive function (see pages 391-393).

One of the pituitary growth hormones stimulates the development of the
gonads. When these reach a certain stage, they discharge into the blood
their own specific sex hormones. One of these in turn acts upon a portion
of the pituitary gland so as to stop its further secretion of growth hormones.
As a consequence, the general growth of the body is likely to stop about the
time when reproductive organs mature. If their maturing is delayed, gen-
eral growth may continue further.

What Have the Hormones to Do with the Feelings?

Hormones as Unifiers During an emergency the appearance and the
behavior of a person (or of any other animal) change decidedly. The in-
ternal organs also change their action. Such situations arouse distinct feel-
ings. You feel a tingling in the skin, or you feel a difficulty in breathing.
You feel your heart thumping or perhaps some of the arteries in the head
throbbing. In addition to such feelings, however, there are others which we
cannot so clearly locate in any one part of the body. When you are fright-
ened, for example, you are frightened all over. When you are angry, you
are angry all over. When you are glad, you are glad all over, not merely in
the eye that sees the pleasing object or reads the happy news. Whatever
happens, you are normally all set, to take it — or to fight it, or to run away.

Organic Sources of Emotions In general, emotions accompany the
organic processes that have to do with keeping alive or with preserving the
species. In the case of nutrition, for example, we may become so hungry
that we are driven to get food through special effort. We cannot keep quiet,
and we get no rest or satisfaction until food is obtained. If the hunger
makes us do somediing, we speak of the emotion as a motive, or drive. In
fact, the word emotioji means that which moves one to action. There may
be great discomfort or dissatisfaction, a desire for something, and finally a
deep satisfaction when the desire is fulfilled. We say in such cases that the
emotion is one of relief from a previous strain.

Joy and Sorrow Agreeable emotions are associated with the healthy
workings of internal organs, with the satisfying of desires, and with activi-
ties that lead toward such satisfying. Merely hearing sounds or swinging
the arms, or merely shouting or walking may yield such satisfactions. Dis-
agreeable emotions are usually aroused by internal strains or by any inter-
fere?ice with desire or activity. If the urine is retained too long in the
bladder, if somebody blocks your path, if your wishes are denied you, un-
pleasant feelings are aroused. Even holding a baby's head firmly, without

315

Child Study Laboratory, Vassar College

HAVING FUN

For the young child all experience, oil
action, all sensation, may yield satisfac-
tion and pleasure. It is only later that
his play or fun takes on the form of
games, or of activities that have a pur-
pose. It is fun to be alive and to feel the
touch of the world as it strikes us — not
too hard, of course — and as we Impress
ourselves upon it

LET GO!

Anything that interferes with our free
movements arouses anger. Learning to
control our anger may mean learning to
sense the difference between important
situations and those that do not matter.
But it may also mean letting others dic-
tate our way of living, always hating
them for it, but afraid always to show our
resentment

producing any pain whatever, is enough to make him very angry. Free,
spontaneous, satisfying activity, and healthy, vigorous, smooth working of
the internal organs — such are the bases for the joy of living. Restraint, co-
ercion, frustration in action, or flabby, inharmonious, or perhaps even pain-
ful working of the organs — such are the bases of sorrow, distress, and disgust
with life.

Many people belittle our moods or emotions as being "only states of
mind". But these states of mind are the very substance of what we value
in life, as they are the drives that make our lives go on.

We must not expect a particular emotion for each natural act or impulse.
Moreover, our natural responses become conditioned. We acquire particular
tastes and aversions through our experiences. We respond one way to per-

316

sons we like and differently to those we dislike. We respond in a particular
way to our school or national flag; others respond in a similar way to other
stimuli — that is, to their schools or flags.

Organic Aspects of the Emotions' When a person is angry, he some-
times acts violently. We say, "the blood rushes to the head" — and it does.
He "sees red" — but not clearly. Instead of thinking clearly about what he
needs to do or how to do it, he is apt to act wildly.

When anger is aroused, one may be "white with rage". A rapid increase
of epinephrin in the blood makes the fine capillaries of the surface circula-
tion contract. But it also raises the blood pressure and presently one can be
red with rage. The rapidly diffused adrenin increases the flow of blood to the
skeletal muscles, which become tense, ready to act promptly and powerfully;
but it has an opposite effect upon the circulation of the digestive tract. Even a
young child can discover that when strong feelings are aroused, he does not
feel like eating; and it is not wise to urge food at such times. As the
stomach and the intestines stop all glandular and muscular work, one may
suffer acute indigestion. Under a strong emotion one may "feel sick at the
stomach".

These changes in the circulation of the blood and in blood pressure are
not ordinarily apparent to the observer. But we know from experiments
that they are as truly parts of the emotions as the feelings themselves, as the
facial expressions, and as the changes in behavior.

In the case of fear, we may find many departures from the normal be-
sides those of the facial expression. On the other hand, it is possible for one
to be "consumed by jealousy" or by curiosity without showing it outwardly,
at least without showing it in a way that most of us would recognize.

Whatever happens to the emotions influences the whole body, probably
through the chemical effects of substances from the ductless glands. The
experiences and activities of the whole body in turn modify the ductless
glands and the emotions, probably through the reflexes of the autonomic
nervous system. It is said that when one is frightened and starts to run, the
movements and the whole attitude of the body will tend to strengthen the
fear feelings. If, on the other hand, one faces the object of fear and begins
to act against it, those feelings soon evaporate. This is so true that we can
see every day the relation between a person's posture and his habitual dis-
position. The sergeant may be able to force the recruits to stand up like
soldiers, but unless they somehow learn to feel like soldiers, they will slump
into some other way of standing as soon as the discipline is withdrawn.

Kinds of Learning A person cannot help becoming hungry when he
has been short of food for a long time. The nature of the organism compels
a certain emotion under certain conditions. But the manner of satisfying

iSee No. 4, p. 320.
317

An angry person does not see
very clearly; he cannot calculate
his movements and place each
stroke where it will do the most
good. He may act with ail his
energy — but he acts wildly. The
calm person acts deliberately,
intelligently. He knows exactly
what he wants to do, and how
to do it. But his action usually
lacks drive. It takes training and
self-control to enable one to
punch with all his might and yet
make every stroke count

TRAINED ACTION

our hunger is largely within our control. Hungry people have fought one
another for food; that is one way. Hungry people have gone out to hunt
game, or they have organized work that would bring them food; that is
another way. Even at the table you can see hunger driving some people
into one kind of behavior and others into a different kind. The different
behaviors of hungry people show that we can acquire not only different
kinds of action ''habits", but also different kinds of emotions or feelings
about things and activities, about ourselves and about other people.

These feelings which incline us to act one way rather than another, or
which make us favor some kinds of dealings or relationships and turn away
from others, we call attitudes. These attitudes, like tastes, are no doubt due
in part to natural individual peculiarities. To a certain degree, however,
they can be learned or acquired through our experiences. These attitudes
are quite as much a part of our behavior as the natural and unconscious
responses of our internal organs or our reflexes or chemical adjustments, and
as much so as the things we do intentionally. In fact, our whole manner of
living represents a scheme in which emotions, thoughts and actions are all
parts of a unity. One who shows what we call breeding, or good manners,
at table has a different set of feelings from one who shows bad manners.
Both may be equally hungry. Differences in behaving represent differences
in ways of feeling and thinking, not merely differences in "habits".

If a baby is accustomed to feel the joy of satisfied hunger immediately
after hearing a certain sound, he will soon come to have that joyous feeling
on hearing the sound. If people discover that controlled anger brings more
satisfaction than uncontrolled anger, they will in time find a way to control
anger.

The habits that we acquire all involve feeling, as well as thinking and

318

doing. The nerves, reaching all parts of the body, are sensitive to changes
and in turn bring about changes. Again, the blood, reaching all parts of the
body, is altered chemically by slight changes in any set of organs, and so
brings about important changes in the activity of protoplasm in all parts
of the body. In this way emotions influence our thinking, our actions, and
the behavior of the internal organs. On the other hand, both our thinking
and the action of the skeletal muscles can modify our emotions.

In Brief

Since the time of Hippocrates, people have associated temperament and
illness with the fluids, or "humors", of the body.

In the higher animals the rate at which the chemical processes in the
living protoplasm go on is influenced by the amounts or proportions of
certain specific substances in the body fluids.

The ductless glands are special organs that produce and discharge spe-
cific substances directly into the blood. Distinct from one another, they are
closely related in a system of interactions.

Everything that modifies the normal action of any of the internal organs
at once brings about an increase or decrease in the secretion of one or more
of the ductless glands.

The internal secretions of the various ductless glands, called hormones or
endocrines, are rapidly distributed by the blood and act in amazingly small
quantities to stimulate action in various organs, including other ductless
glands.

The endocrines of all the mammals are very similar, so that it is possible
to use animal extracts in making up human deficiencies.

Some of the endocrine glands act throughout life, others for only a rela-
tively short period; some produce but a single known hormone, others pro-
duce several hormones; some of the hormones secreted have but a single
known effect, others have multiple effects.

Hormones modify the basic protoplasmic activities: some affect growth
and development, some sensitiveness to external conditions, some the use
of energy in movement or other activities.

In higher animals, emotions seem to accompany the processes that have
to do with preserving the organism or the species.

Whatever happens to the emotions influences the whole body, probably
through the chemical effects of the substances from the ductless glands; the
experiences and activities of the whole body in turn modify the ductless
glands and the emotions.

319

EXPLORATIONS AND PROJECTS

1 To find the location of the various endocrine glands, dissect a thoroughly
anesthetized laboratory animal, identify from charts and examine the form, struc-
ture and texture of as many of the glands as possible.

2 To demonstrate the effect of thyroid extract, feed animals on diets that
differ only in its presence. Place a male and a female rat, from three to four weeks
old, in each of two cages; feed both pairs the same diet.^ To the rats in one cage
feed, in addition, half of a one-tenth-grain tablet of thyroid extract each day. The
half tablet must be olaced in the mouth of each rat to make sure that it is taken in.
Keep record of weight; make a graph of daily growth. Compare the behavior, as
well as the growth, of the rats in the two cages. In what ways does the thyroxin
seem to afl^ect the personality.'^ Compare results of this experiment with known
cases of hyperthyroid persons.

3 To find the effect of thyroid extract on the development of tadpoles, feed
two sets the same diet, but supply one set with thyroid extract. Place the tadpoles
from the same batch in two aquariums. Feed both sets on flour, but add to the
flour for one set a crushed tablet of thyroid extract. Continue watching for several
weeks. Describe the differences observed between the two sets of tadpoles.

4 To demonstrate the relation of emotions to muscular activity, to facial ex-
pression, and to posture, observe your classmates under various situations that
involve distinct emotions or attitudes. What facial movements are involved in
"registering" anger, anxiety, fear, affection, cruelty, or eagerness?

Have an individual with his back to the class assume postures intended to
express distinct emotions, and see how generally the intent can be recognized.

Attempt to combine posture and gestures of one mood with an imaginary
situation that would put one in a contrasting mood. For example, try to loo}{
friendly and helpful while imagining yourself in a situation that would make you
feel resentful or full of hate — or vice versa. Or try to look as if you were having
a hilarious time while imagining yourself at the funeral of a person you love and
respect — or the reverse. In each case, note the movements or combination of
movements that appear especially appropriate, or especially inappropriate, for the
mood or emotion under consideration.

QUESTIONS

1 What factors influence the rates at which the various chemical processes
take place in higher animals?

2 In what respects are the hormones Hke vitamins? like enzymes? unhke
either vitamins or enzymes?

3 How are the internal secretions distributed throughout the body ?

4 Which of the specific hormones affect growth? Which affect energy
liberation? Which affect the rate of metabolism?

^The complete diets suggested on page 112 are suitable. A half-and-half mixture of rolled
oats and whole-wheat flour, with milk to drink, is very satisfactory. Certain prepared dog
biscuits are good.

320

5 In what respects are the various endocrines independent of one another?
In what respects are they interrelated?

6 Which ductless glands operate only temporarily? Which permanently?
Which operate under special circumstances?

7 How does the endocrine system operate when the body is in an emer-
gency ?

8 How are the various ductless glands co-ordinated in their activity?

9 How are the ductless glands affected by the emotions?

10 How are the emotions affected by the internal secretions?

11 In what ways are the endocrine systems and the hormone? of various
mammals alike?

12 To what extent does the endocrine system regulate and co-ordinate the
organs and tissues of the body independently of the nervous system?

13 In what ways are the nervous system and the endocrine system related?

14 In contrast to the natural expressions of the emotions, how does a good
actor bring about the "registering" of various emotions?

321

CHAPTER 17 • WHAT MAKES THE ORGANISM A UNITY?

1 Can a part of an animal continue to live away from the rest ?

2 How much can an animal have removed from its body and still

remain alive?

3 Can any animal grow into an entirely new individual from

one portion, as many plants can?

4 Are there any plants that die if certain organs are removed?

5 Can one live without a stomach?

6 Can any of the organs be spared?

7 If a tooth is removed, will another grow to take its place?

8 Can any destroyed organs be regrown?

9 If a kidney is removed, does the remaining one do double work

or grow to double size?
10 When an animal dies, do all the parts die at the same time?

Living things occur in nature as wholes, and they behave as wholes. We
find many thousands of distinct kinds of plants and of animals; but unless
something has gone wrong, there is in each case a whole fish or bird or
worm. We do not find, in nature, legs or eyes or clamshells, except as these
parts have been removed from whole organisms. When a part has been
removed, it no longer acts as it did when it was still with the other parts.
But while the parts are together, they behave in relation to one another
and in relation to the whole in a very distinct way, so long as there is life.
What makes the parts of a living thing all work together as they do ? Why
cannot the parts behave in the same way when they are separated?

Why Cannot Separate Parts of Living Things Continue to Live?

Anatomizing Life has been so hard to understand that we have felt
obliged to take plants and animals to pieces in order to study the organs or
parts. For four hundred years the study of medicine has rested on the
anatomy — that is, the "cutting-apart" — of the human body. We have di-
vided the various organs into their tissues and cells. These we have taken
apart chemically, to find out of what substances they consist. We have
carried our anatomizing so far that we often overlook the life which we
started out to find.

Living Fragments Although living organisms in nature occur only as
wholes and act as wholes, it is possible for fragments to continue alive. We
all know that it is possible to remove a portion of a tree or of a worm with-
out killing it. And we know that the portion removed may become a whole
organism. If, however, the fragment does not regenerate, it dies.

322

Li'iiirle Laljuiatorics. Jin-.

THE CULTURE OF IMMORTAL CHICKEN TISSUE IN THE LABORATORY

In 1912 Dr. Alexis Carrel of the Rockefeller Institute removed tiny pieces of heart
muscle from a chicken embryo still inside the egg shell, at about the ninth or tenth
day of hatching. He placed these fragments in a nutritive medium, kept at a suitable
temperature and supplied with air. Every two days the growing piece doubled in
size; it was divided, and a part placed in a fresh medium. This has been going on
for all those years. Most of the new growth has, of course, been thrown away; if
all had been allowed to grow, there would not have been room enough for that
chicken heart in all the world

It has been possible in the laboratory to keep a part of an animal "alive"
without regeneration. There are the fragments of a turtle's heart which
Loeb kept beating away for weeks (see page 302). Even more striking are
the experiments of Alexis Carrel (1873- ), who started cultures of
chicken tissue that have been kept going for over thirty years (see illustra-
tion above). We may consider these tissues as "alive", for they grow and
produce more cells like themselves. But they are hardly living chicken.
They can do nothing that is typical of the life of a chicken. The growing
lump is not a whole, although it continues to carry out life-activity in part.

With the assistance of Colonel Charles A. Lindbergh, Carrel later de-
veloped a more complex apparatus which supplies a rather large piece of
tissue, or even an entire organ, with food and air, maintains a suitable tem-
perature, and removes the products of metabolism. If we had a whole set of
such organs, even all the organs of any particular animal, we still should not
have a living animal — a chicken or a dog.

These "cultured" cells or organs are unable to supply themselves with
food, air, or water. They cannot keep themselves warm. They cannot pro-
tect themselves. They cannot develop, but merely continue to grow only as
material is supplied them by the laboratory attendants.

To be sure, there are species of living things that depend in a similar
way upon others. There are, for example, parasites living in the bodies of
larger organisms, where they find the materials and conditions essential for

323

their living (see page 177). Such parasites, however, do act as whole or-
ganisms; they grow to maturity and reproduce themselves, even if they do
not rush around for supplies.

To understand the human body or the body of any other living thing,
we have to study the parts. But when we analyze and anatomize, we find
that all the chemical elements in living bodies are present also in nonliving
things, although there they never form the same compounds. We find too
(see pages 19-20) that whatever goes on in a living thing may go on
also in nonliving things, although the various processes are never carried
on together in any nonliving thing. The parts of living beings may all be
the same as the parts of nonliving things; but the combination of parts in a
living thing is always unique, and it always acts as a whole. However
thoroughly we come to know the details, the details themselves have no
meaning except in terms of the whole animal or plant.

What Brings About the Wholeness in a Living Thing?

Wholes before Parts Before we can buy a steak, some apples, or a
fur coat, somebody has to raise entire cattle or apple trees, or a hunter has
to get a whole fox or rabbit. Our earliest experiences are with entire plants
and animals, entire human beings. In time we come to give attention to the
separate parts that we can use or to the parts that become injured and so
destroy the unity or effectiveness or well-being of the whole. And in time
we come to wonder how such diverse parts as we see in any common animal
or plant can keep working together.

The microscope enables us to get more detailed information about the
parts of plants and animals. Most helpful has been the study of one-celled
organisms, in which the wholeness does not seem so hard to understand.
The parts here are all so close together, so directly connected, that we can
hardly see how any part of an ameba, for example, could be disturbed with-
out affecting all the rest. In the larger and more complex organisms the
connections are not so obvious. How does seeing an object at a distance
make all the muscles change their tensions or movements, or make the hair
stand on end, or change the rate of breathing ? How does an odor bring a
happy expression to the face, or how does another odor "turn the stomach" ?

If we find it easy to see how the one-celled organism acts as a whole, it
may be helpful to remember that every larger organism was once a one-
celled being. The wholeness of a horse or a fish has grown up with it from
the beginning. However large an organism may get to be, however many
different kinds of organs or tissues It comes to have, it continues to be one.

Unifying Processes' Ordinarily, we raise questions about the whole-
ness of an organism only when parts of the body fail to work harmoniously

iSee No. 1, p. 337.
324

together. We see mutilated animals, as well as plants, carry on instead of
being killed by the injuries they have received. Sometimes in ourselves
joints stiffen, vision dims, muscles are less prompt or less effective than we
should like. The more complex an organism is, the more likely is some
part to get out of step. But what is it that maintains the harmony when
nothing is out of order ?

We have seen that homeostasis, or the constancy of the blood, is main-
tained by continuous and delicate adjustments to slight changes in the tem-
perature and chemical condition of the blood. The tropic movements of
plants also result from chemical responses to changes in temperature, illumi-
nation, pressure, and so on. Among simple animals too, many of the tropic
movements seem to come from chemical responses to stimuli, whether these
are originally electrical or mechanical, whether they are changes in light or
in temperature. In the most complex organisms, the warm-blooded birds
and mammals, the blood acts as a unifying medium, for it rapidly distributes
the chemical "messengers", or hormones, which the endocrine glands release
under various circumstances. These hormones stimulate various parts of
the body or retard their action in various ways. On the whole, however, the
net effect is to bring the behavior of the entire system into harmony. That
is, the endocrines harmonize the parts of the body in relation to one an-
other, while the body as a whole acts — in most cases — with relation to
existing conditions.

In addition to the chemical processes which have the effect of unifying
the parts of the body, the nervous system does the same thing. In one-celled
animals it is possible to locate surface spots that are exceptionally sensitive
to stimuli, and also strands of protoplasm through which stimuli appear to
be transmitted. We may think of the sense organs and the nerves of many-
celled animals as elaborations of such areas. The sensitive spot comes to be
one of several special sense organs. The sensitive strand appears as a nerve
cell. There are simple nerve paths in animals connecting receptor directly
with effector. There are reflex arcs, and chains or groupings of reflex arcs.
In the backboned animals the central nervous system, with the brain and
the autonomic nerves, ties together the sensory and muscle systems with the
visceral and endocrine systems. We may say that as the one-celled animal
behaves as a unity because it is all one, a many-celled bird or mammal be-
haves as a unity because it is in all its parts firmly bound together by
chemical and nervous strands; it is hardly possible to touch a point without
affecting all parts, directly or indirectly.

Instead of asking how the parts of a plant or animal do work together,
it might be more helpful to think of the organism as a distinct kind of
unity; or we might ask how this unity comes to have so many distinct kinds
of parts, or even why the parts sometimes fail to work together.

325

Why Do Organisms Sometimes Fail to Maintain Unity?

Health and Sickness Perhaps no organism long remains perfectly
adapted to the conditions around it, capable at all times of meeting every
situation suitably. Perhaps no organism is immediately killed when some
one part fails to act just right. Among human beings, as among other
species, there are defective individuals. Some are born with imperfect or-
gans, and all acquire various disabilities as they go along. We can imagine
"perfection", but we need neither expect to find it nor give up because it
does not appear in our lives. We may be sure, at any rate, that various forms
of general or partial incapacity, various forms of sickness and deficiency,
have troubled human beings from earliest times.

In nearly every language the most common greetings refer to health.
"How are you?" We do not stop to answer each time, or we should not get
on with our business. "Hail!" is apparently a shortening of "Be hail" (or
"hale") — that is, Be whole, or be well. "Farewell!" is a parting wish for
one's welfare, including health. The Latin ave and vale have similar mean-
ings. The very word salute, from the Latin solus, means "health".

As a rule, we think of illness as a condition in which something in the
body — that is, some part — goes wrong, and we often speak of illness or ail-
ing in relation to some part, such as the stomach, the liver, or the knee. We
seldom think of the whole organism as being sick. The trouble consists in
a disturbance of the wholeness. In the course of ages many different ideas
or theories have been used to explain such interferences with harmonious
workings of the organism. Such theories are always important, since they
guide us in restoring sick persons to health, or wholeness.

Evil Spirits One of the earliest ideas for explaining sickness is that of
"evil spirits". Today we consider such explanations "superstitious" because
they rest on suppositions which do not agree with known facts. Without
such facts, however, most superstitions are quite as logical as our own wiser
notions. We know, for example, that a scratch or a bite may cause pain. A
cut may disable a hand; a sprain may disable a whole limb. We can see a
stick strike and cause injury. It is reasonable to explain inner aches and
pains as if they were caused by unseen sticks and stones in unseen hands —
by spirits, in short. And naturally they must be evil spirits, imps or devils,
for they cause evil.

To this day millions of people can understand their Inner troubles only
by assuming that evil spirits somehow get in and cause mischief. To be sure,
we cannot "prove" that evil spirits cause troubles, for spirits are naturally
beyond the reach of our senses. We know only the effects they produce. On
the other hand, we can never prove that evil spirits do not cause sickness,
for we cannot prove a negative. If we assume that evil spirits, or devils,

326

In the Louvre in Paris there is a statue

from ancient Chaldeo representing

the demon of the Southwest Wind.

The inscription directs that it be hung

in a window or doorway
to ward off illness and evil influences

After Lenormant

SPIRITS CAUSE ILLNESS

cause illness by getting into the victim's body, what is more reasonable than
to try to drive them out of the body?

Driving Out Spirits Through the ages there have been many systems
for driving out these unwelcome visitors by making it as uncomfortable for
them as possible. Loud and hideous sounds, nasty odors produced by burn-
ing various substances, very bitter and nauseous mixtures — to be taken in-
ternally by the patient, of course. Sometimes a medicine man utters magic
words to frighten devils. Or he writes them on bits of bark or shell, which
he applies to the body of the patient. These magic words probably work
just as effectively as the loud sounds and the disagreeable odors and drugs.
At any rate, that was the basic philosophy of sickness and cure through
many centuries. It is still the basic philosophy among many tribes in many
parts of the world. It persists essentially unchanged among many of our
present-day fellow citizens. We have astrologers and quacks and spirit heal-
ers in nearly every community. This spirit theory has the merit of appealing
to common sense. It has the disadvantage that we are unable to compare
the results of spirit activity with the workings of different kinds of cures.
We have no way of checking up on the workings of this philosophy.

Sickness and Sin A child early learns that he is made to suffer if he
displeases his elders, or if he fails to do as he is told. From this experience

327

Tenskwatawa, the Indian prophet, healed
the sick and kept evil spirits away from
his people with his medicine fire and his
sacred beans. We can imagine common
objects having qualities besides those we
discover through our senses. A gift from
a beloved person, for example, or a
trophy may do to us what a duplicate
bought in the market could not do. But
are these magical qualities in the objects
or in the persons who feel and imagine
and believe? And do people really be-
lieve in such magic? We have only to
ask ourselves why it is that one flag, one
statue, one building, arouses in us a par-
ticular set of feelings — but not in other
people. Or why another flag or picture
or house arouses in us quite different
feelings. Does something come into us
out of those stones or does something stir
within?

I ouitmith Annual Report of the Bureau of Kilinnlugy

MAGIC PARAPHERNALIA

it is but a sliort step to the idea that suffering or pain results from offending
some unseen power or spirit. If you eat forbidden fruit, you will suffer. If
you violate a taboo — for example, if you drink from a sacred spring or cross
an imaginary line that you should not cross — you will be made to suffer.
This idea is like the invading-spirit theory of sickness, except that it attempts
to explain why the spirit or spirits should choose a particular victim. Sick-
ness is thus considered the wages of sin.

The theory appears reasonable — if we grant the assumptions. According
to this view, a sick person needs first to find out what sin he has committed
and then to make his peace with the tormenting gods or spirits. Millions of
people with all kinds of backgrounds and with many different kinds of
religious views look at sickness in very much this way, even where an ill-
ness clearly follows a physical injury or a fall.

We find, however, that eating forbidden food and performing forbidden
acts bring evil results among some parts of the human race, but not among
others. We find also that some sicknesses, like rain, strike good people and
wicked people without discrimination. Of course we can save our theory
by saying that "good people" who are smitten only seem to be good — that
they are really being punished for their secret sins. Obviously that kind of
argument does not get us very far. Like the spirit theory of sickness, it does
not let itself be checked.

328

Truth in Falsehood Strange as these and other old notions appear to
us today, it is not fair to laugh at them. For one thing, what people with
queer notions think seems to them just as reasonable as our thoughts do to
us. For anodier thing, we have ourselves at some time held views sincerely
and very earnestly only to abandon them later. But most important is the
possibility that there is at least a small grain of truth in queer notions. For
example, one could say that the notion that evil spirits cause disease is true
if we only substitute microbes for spirits, although these "spirits" cannot be
driven out by beating drums, or burning incense, or eating bitter herbs.
Again, though we reject the "humors" of the ancients, we know that the
hormones have important bearings upon health; but we do not remedy an
imbalance of these juices by the methods employed by the ancients.

"COME TO THE EGG. COME, LITTLE PAINS, INTO THE EGG," SAID TRINI^

There are witch-doctors and magic healers in nearly every community. The magic
ideas have the advantage of appealing to "common sense", so that the patient hcs
confidence in the healer. Certainly these ideas cannot be disproved. They have the
disadvantage that they cannot be tested in a scientific way nor made to serve people
generally

'From The Forgotten Village, by John Steinbeck, © 1941, by permission of The Viking
Press, Inc., New York.

329

In one conception of illness, evil spirits correspond to ideas or thoughts
rather than to devils. Thus many people believe that the body may be dis-
ordered by "evil thoughts", eidier those of the victim himself or those of
some wicked enemy. This kind of belief is hard to deal with, since we can-
not experiment with it. It would be very hard to prove, for example, that
my toothache was not caused by somebody's throwing toothache-thoughts
at me while I was asleep — and equally hard to prove that it was. Neverthe-
less the health of the body and the health of the mind are closely connected.

How Does the Mind Affect Health?

Physical Basis of Mental Disturbances Most of us cannot keep our
minds on our work when we have any kind of pain, whether it is a slight
bruise or a jumping toothache. When the liver is out of order, it is almost
impossible to maintain a cheerful mood; we have the blues, or we are
grouchy or irritable. Under the influence of alcohol or other drugs, men
have committed acts of folly and of violence. When one is exhausted from
hunger or fatigue, not only does the mind work poorly, but there may be
even uncontrolled images or wild thinking. The chemical condition of the
blood affects not only the rate of breathing and the digestive processes, but
also the brain and mental processes. People have become insane and ir-
responsible from the poisoning of the blood by physical disease or by altera-
tions in the relative quantities of the hormones. We must recognize that
the mind is influenced by the physical conditions of the body.

Effects of Ideas on Organic Processes But the opposite may be just as
true. One who is very much excited by good news or bad news is likely to
suffer from indigestion. A person who worries is likely to become run-
down physically. A cheerful frame of mind keeps up the action of the
blood. A hopeful disposition helps a sick person become well more rapidly.
In some mental disturbances or insanities die bowels fail to carry on their
work, or the breathing becomes impaired. The physical condition of the
body can influence one's dreams; but dreams or the reading of stories may
affect the condition of the body so as to make one shake with laughter or
shiver with cold. Instead of saying that all disorders are due to physical
causes or that all are due to mental causes, we may find it more helpful to
think of the body as a living organism, a unity, or whole, in which every
happening may influence every part.

Mental Health and Mental Healing If we think of the organism as a
unity, we shall find it easier to understand "health" as very largely a style,
or mode, of life, and the state of mind as an important phase of that style,
or "habit". This does not mean, of course, that all illness can be prevented
by proper training, or that health can be assured by merely getting certain

330

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ideas into our minds. It means only that the entire organism keeps whole
or well — or not. If anything goes wrong, it is important to find out what
causes the trouble. But no one medicine or one trick can cure all disorders,
just as there can be no one answer to all questions. We must guard against
the idea that somebody has found a universal remedy, whether it is a kind
of drug or a kind of exercise or a kind of lucky stone or a kind of happy
thought.

How the Mind Unifies the Organism^ At any given moment the dif-
ferent processes of the body are unified by the chief activity. If you are
playing a game, such as basketball or tennis, the heart and the lungs and the
perspiration glands and the liver and the kidneys are adjusting their ac-
tivities to the body's purposes. The whole organism is on the alert. Your
senses and your muscles are all set, in readiness for whatever your adver-
saries and partners may do, for whatever move the ball may make. You
may become quite excited in the game, and everybody knows that excite-
ment may work in opposite ways. If you are not warmed up or excited
enough, if you do not care enough, you will not see enough of what goes
on to guide your movements; you will not hit hard enough. You will not
be quick enough with your responses. On the other hand, if you are too
excited, if you begin to think about the score or possible failure, if you
begin to wonder whether certain eyes are watching you, you may spoil the
game by playing too wildly. In any case, the body works as a whole just
so far as it is controlled by a single purpose or desire, and in proportion to
the strength of the purpose (see illustration, p. 331).

Concentration, orderliness and perseverance make for unity and strength.
On the other hand, mind-wandering and day-dreaming, indecision and
worry, suspicion and jealousy, concealment and shyness, indicate a lack of
unity or wholeness. At the same time, they interfere with the satisfactory
co-operation of all the powers of the body in achieving a goal. A strong
will may mean holding firmly and with clear vision to a definite purpose.

Attitudes The word attitude commonly refers to the "point of view",
or position, that one takes in relation to the environment. This is illustrated
by the close connection we expect between the physical posture and the
state of mind in such cases as fear, defiance, curiosity and shame. Indeed,
you can hardly pronounce these words and think of their meanings with-
out having different muscles actually pull toward getting your face and
arms and legs and back into positions corresponding with these various
feelings. We have seen that the emotions are closely connected with all the
important functions and processes of the body (see pages 308-318).

Some emotions — hunger, fear, love, anger, curiosity — sometimes drive us
to do things that we should otherwise not do at all. Our impulses to action

iSee No. 2, p. 337.
332

■"1

Kaislen Stapelfeldt

ATTITUDES

The muscles of the face contract or relax, altering the expression in ways that cor-
respond to every change in the emotions. But muscles in all parts of the body also
respond to the feelings, even to our thought about such feelings as fear, anger,
aversion, shame. Even if you cannot tell what a person is thinking from the expression
on his face, you can often know what he "has on his mind" from the physical posture,
which is closely related to the "mental attitude"

are modified by experience so that emotions become associated with certain
actions. We then refrain from doing what we otherwise feel impelled to
do. For example, fear, shame, and the desire to please certain people prevent
us from doing certain things and teach us to regard them as wrong or
improper. Or the same emotions push us to do things that would other-
wise be too difficult.

Our emotions may be aroused by a great variety of situations, and they
may in turn bring about a great variety of changes in the body. Anger, for
example, may be aroused by an unfriendly act or by striking an obstruction
or by seeing a bully abuse a child or by thinkjng about the abuse of power
by high officials. This feeling of anger may, in turn, bring about various
changes in the expression of one's face and the clenching of one's fists, in-
volving skeletal, or striped muscles. It may cause a sudden flow of blood to
the head and increased heartbeat, involving involuntary muscles. It may

333

stop the flow of gastric juice, make the breath come stronger, and bring
about other changes in various organs.

The manner in which we allow various happenings to stir our feelings,
and the manner in which we allow our feelings to find their way out in
action, both depend largely upon experience. They are "learned" rather
than "natural". These feelings we have of liking or disliking, of being for
or against anything, are our attitudes.

What Is Mind? We intend many of the things we do; that is, we can
give a reason for doing them. Thus we drink because we are thirsty; we
do other things because they help us carry on our lives. But many of the
things which the bird or the ant does also help it carry on life. We are
therefore disposed to say that the animal does things on purpose just as we
do, or that the unity of the organism is due to the "mind" in one case as
in the other.

It would be quite impossible to prove that this interpretation of the facts
is not a true one. For all we know, it is the "mind" of the insect or of the
bird or of the morning-glory that makes it behave as it does. But if it is a
mind, it is a different kind of mind from ours. For, as we have seen (see
pages 255-264), a great deal of the behavior in plants and animals at all
stages of development is automatic; it comes from the structures or from
the chemical compounds in the organs, rather than from any intention or
purpose.

When we speak of our own minds or of doing things with design, or
purpose, we do not include all our actions, not even all the useful ones. In
the course of the individual's development, for example, the thymus gland
gradually degenerates. However useful this change may be, none of us
would maintain that the gland degenerates as the result of any design on
our part. As the body does more work, and as the tissue cells give off more
carbon dioxide, the heart comes to beat harder. Yet it is doubtful whether
anybody ever intended to have his heart work harder. Certainly no one
ever planned to grow himself a heart in the first place, useful as that organ
happens to be.

What we do intentionally or willingly, whether wise or foolish, can
hardly come from the same "mind" as that which guides the growth of the
body and its unconscious internal and external adjustments to what is hap-
pening. On the other hand, we really know only such mind as our own,
and that mind does play an important role in our own adjustments. But
we recognize degrees of mind in other species, even if we can also see a great
deal of adaptive response that is mechanical or automatic.

334

Are There Internal Causes of Illness?

Irregularities in Development It seems logical to distinguish from the
external sources of harm possible internal sources. But these are not so easy
to recognize or to classify. Wc have learned a great deal about spontaneous
disturbances in metabolism, but that idea is a hard notion to deal with scien-
tificallv- For to say "spontaneous" is really to say that we do not \now how
such disturbances arise. The endocrine system may be thrown out of bal-
ance, for example, by faulty nutrition, as by a deficiency of iodine or of
calcium. Generally speaking, however, most cases of hormone imbalance do
not seem to arise in that manner.

Individual differences in development not only bring about obvious
changes in the proportions of the various organs, they bring about also ob-
scure changes in the workings of different organs. Thus, as one grows
older, a change in the shape of the eye lens may make one more and more
farsighted. A change in body weight may put an increasing burden upon
the heart. Other changes may alter the quantities of various hormones pro-
duced; for example, diabetes may appear "normally" in some individuals
past a certain age as a part of the developmental changes.

Disturbed metabolism shows itself in growths that have no adaptive value
to the organism (as certain kinds of tumors) or that may be destructive (as
in the case of cancer). Some of these abnormal growths are no doubt due
to local irritation or to some chemical disturbance from the outside. We are
unable, however, to find a universal formula for these diseases or for diseases
in general.

Ways of Living The mode of life influences the internal adjustments
and may bring about an organic imbalance even if no specific cause can be
found for illness.

Many of the inner processes are affected by our "habits" — exercise, work,
rest, recreation, posture — and states of mind. That is to say, fatigue and
circulation, breathing and excretion, anxieties and worries, excessive eager-
ness or fear, exaggerated emotional activity, are so closely associated with
endocrine disturbances that it is often difficult to say which is the cause and
which the effect. Much dyspepsia or heart disease, for example, may mean
not any specific defect in stomach or heart structure, but faulty workings of
organs in response to high-pressure living or to constant anxiety. Thus
physicians distinguish between organic and junctional disorders. They em-
phasize the idea that aches and pains and difficulties indicate a disturbance
of the organism's unity, or wholeness, but not necessarily the cause of the
disturbance. This is a practical distinction in medical treatment, for it
means that we are to remove the sources or causes of a patient's disunity
rather than merely get rid of the symptoms.

335

In Brief

A living being acts as a unit, or whole, not as a mere collection of parts.

Specialized cells or tissues may be grown in the laboratory; in a culture
they are able to grow and multiply, but they are not able to supply them-
selves with food, air, or water. They can continue to live only so long as
their needs are met by laboratory attendants.

We cannot understand the parts of a human body, or of the body of any
other living thing, except in terms of the whole living organism, in which
every happening may influence every part.

In the larger plants and animals, the complete unity of an organism is
observable in its every action, at every stage in its development.

As diiTerentiation of parts occurs in the development of an animal, dif-
ferent cells act in somewhat different ways; yet the whole mass of cells
behaves as one organism.

Some of the functions or activities of specialized cells are more general
than others; thus an organism can continue to live if certain parts are
destroyed, but not if other parts are destroyed.

The more elaborate and specialized an organism is, the more of its body
consists of specialized accessory organs and tissues, and the more of it con-
sists of nonliving structures.

Throughout the ages there have arisen various beliefs and explanations
for sickness which later generations ridiculed as foolish. But we are unable
to prove or disprove these beliefs, as each involves, to some extent, reliance
on supernatural beings or forces, with which we cannot experiment.

Illness results when the unity of an organism and the effectiveness of its
adjustments are thrown out of balance by any of a variety of events.

The chemical condition of the body fluids influences mental processes,
as well as others.

Various habits of feeling and thinking and acting influence the internal
adjustments of the body and may bring about an organic imbalance.

The body works as a whole so far as it is controlled by a single purpose
or desire.

We distinguish as work of the "mind" that control which is purposive,
or conscious, or voluntary, in contrast to. that unconscious control which
automatically adjusts the body both to internal and to external changes.

336

EXPLORATIONS AND PROJECTS

1 Take a field trip to observe bird behavior. In a region in which birds
abound, locate some species feeding. Note its activities to see its relations to the
character of the food. Or observe parent birds feeding their young. In what ways
are the various activities of the birds tied together?

2 To observe the wholeness of response in a young child, have someone
volunteer to bring a baby brother or sister for the rest to watch. Take every pre-
caution to protect the child against the possibility of frightening. Everything in
the situation is new. Normal behavior cannot be observed unless each one in the
group is extremely co-operative. Note any evidence that the child responds to
various stimuli — the people in the room, the strange surroundings, the known
brother or sister, or to such things as light, sound, heat, contact, odor. Touch
lightly the sole of the child's foot, the palm of the hand, the cheek near the mouth,
or touch the child under the chin. Note whether any stimulus seems to hold the
child's attention, whether he follows a moving object or a sound, whether he
responds to an approaching object. Observe every movement; note any associated
responses in other parts of the body. How does the child explore the new envi-
ronment ?

In what sense may the activities of the child be considered as simple responses
to stimulation? In what sense may the activities be considered as expressions of a
single being, or a unity?

QUESTIONS

1 In what respects does a one-celled organism act as a whole?

2 In what respects is the unity of a mature complex organism like that of a
single-celled organism? In what respects is it unlike that of a single-celled
organism ?

3 In what sense does the presence of specialized organs indicate the complete
unity of a living organism?

4 How do various injuries or diseases affect the unity of the organism?

5 In what ways can physical conditions influence mental processes?

6 In what ways can mental processes influence physical processes?

7 What, if any, physical processes in the body have no influence whatever
upon the mind?

8 What, if any, mental processes have no connection whatever with physical
changes? How can you tell?

9 What connections are there between health and emotions?

10 What kinds of physical habits keep one well ? What kinds of mental habits
keep one well ? What kinds of emotional habits keep one well ?

11 How is it possible to be happy without complete health? How is it pos-
sible to be of great use to others without complete health?

337

UNIT FOUR — REVIEW • HOW DO THE PARTS

OF AN ORGANISM WORK TOGETHER?

Students of biology are in somewhat the same predicament as boys who
take clocks or cameras apart and are scolded for being "destructive". Our
defense, which is reasonable enough, is that we want to find out how a
thing works. But then we are challenged (1) to put the parts together
again, which is not always very difficult, and (2) to make the machine
work again, which is often impossible.

Biologists have sorted out over a million distinct kinds of plants, a mil-
lion distinct kinds of animals. They have anatomized or analyzed animals
and plants into many kinds of organs and tissues. They have analyzed
organisms chemically into many kinds of compounds, and they have listed
the elements found in all organisms, as well as elements and compounds
found only in certain special kinds. When we try to put the pieces together
again, we are baffled.

Biologists have analyzed the conditions under which various plants and
animals live — light, temperature, water, chemical substances, and so on; and
they have studied the changes in living things which result from alterations
in these conditions. We can take a plant or a bird away from its natural
surroundings and study it in the laboratory, but we cannot keep anything
alive apart from the environment. Organism and environment are insep-
arable, except in our thought about them.

We can measure pulse rates, blood pressures, oxygen exchanges and
nerve impulses. Yet none of these things exists — as a living process — when
separated from the others. We know a great deal about muscles. But
muscles have meaning in "life" only in relation to other muscles, in con-
nection with nerves, in exact timing with blood flow or heart action or with
chemical changes in remoter parts of the body. However much we find out
about each part, we can recognize life only as a unified interaction of many
processes, involving all the parts. In the ameba and other one-celled or-
ganisms we say that the protoplasm is alive. The single cell carries on all
the life functions — feeding and assimilation, breathing and oxidation, move-
ment, excretion, sensation, reproduction. A lobster or a fish performs va-
rious necessary functions through various organs. This fact of having special
organs related to special functions has been called the physiological division
of labor.

In higher animals division of labor appears gradually during develop-
ment. This means that digestion goes on in a living thing before it has
any digesting organs; breathing goes on before it has any gills or lungs;
excretion goes on before it has any kidneys. This idea may be easier to
grasp if we recall that in the evolution of society clothes were made long

338

before there were any tailors, food was prepared before there were any
cooks, and so on. We summarize this idea by saying that "function precedes
structure." Protoplasm is able, then, to grow the special organs, as well as
to perform the various functions.

In spite of the many kinds of organs that we find in the human body
and other complex species, the orgajusm always acts as a whole. The various
functions, however different they may appear, are all junctions of proto-
plasm. It is this unity of the organism that makes life both significant and
interesting; the more complex the organism, the more varied its parts, the
more wonderful is the total life in variety and interest.

Of course the human body does not come from joining together millions
of cells that were once distinct. Like other organisms, it develops from a
single cell that divides into two cells, each of which again divides, and so
on until millions are formed. The many different kinds of cells and the
many different organs appear gradually by a process of differentiation, and
the different tissues and organs gradually take on specializations in their
functions. The organism has been a unity from the first. It is only because
we have taken the body apart in our studies that we must ask ourselves how
the parts are kept working together. It may be more helpful to ask. How
comes a bit of protoplasm to take on such complex forms and grow itself
into so many specialized organs ?

The various organs or systems do work together because they are, so to
say, continuous with one another. They make up, essentially, a unit of
protoplasm, confronting the world in all directions as one, in spite of the
many specialized parts. All cells are connected through the blood, which
distributes nutrients and oxygen and which removes the products of metab-
olism. All the body cells are sensitive to the slightest changes in the
chemical state of the blood, and they all bring about changes in the blood.
Operating through the blood are the hormones, which are sensitive not
alone to the chemical state of the blood, but to more specialized stimulations
by way of the nerves. In turn they act upon the entire protoplasm — counter-
acting, compensating, reinforcing.

Finally, the irritability of protoplasm manifests itself, in the more com-
plex animals, by the formation of the nervous system. This reaches all parts
of the body; and it is sensitive to changes inside, as well as to the changes
and disturbances in the environment. The nerves are connected not merely
with the muscles and the organs of special sensation (eye, ear, tongue, and
so on), but also with the blood-vessels and with the ductless glands. Be-
cause of their extreme sensitiveness and their quick response, they constitute
a very striking system of co-ordination, or unification, in the body.

In the behavior of every plant and every animal we are impressed by the
fitness of the actions and of the chemical processes. Plant and animal action

339

often suggests what we would ourselves do under similar circumstances, so
that the behavior appears purposeful. We know that we are able to select
lines of conduct that do not come spontaneously. By so choosing, we obtain
from the world many advantages that we should not otherwise have; or we
escape many dangers or inconveniences to which we should otherwise be
exposed. We have a certain control both over the workings of our bodies
and over our environment. Or, rather, we have a certain control over our
environment by means of the control which we have over our own actions.
This control of our own activities comes by way of the most elaborate part
of the nervous system, the brain. Nevertheless we cannot say that plants
and simple animals act with design, or purpose, no matter how useful the
processes are.

For one thing, we can reproduce the parts of many of these processes by
means of physical and chemical mechanisms. For another thing, purpose
means nothing unless we assume the presence of a mind like our own,
which can thinly of the future \ and from what we know of these organisms
we cannot asume that they have such a mind. Indeed, most of our own acts
can be shown to be without purpose, even where they are of value to the
organism. It therefore makes no sense to attribute purpose to organisms of
whose "minds" we know nothing. What they do, like most of what we do,
comes from being the kinds of organisms they are; they cannot help it.
The wonder still remains: "How come.''"

34Q

UNIT FIVE

How Do Living Things Originate?

1 How do difFerent kinds of plants and animals live through the winter?

2 Does a seed or egg contain a miniature of the parent?

3 How does a worm change into a butterfly?

4 How do animals without eggs reproduce themselves?

5 How does the egg change into a complete animal?

6 What is the difFerence between growing and developing?

7 What becomes of all the seeds in nature that do not grow into plants?

8 Is there sex in all kinds of animals?

9 Why are the young of some species helpless at birth, whereas those

of other species are not?

Everybody knows that chickens hatch from eggs and that kittens come
from mother cats. Everybody knows that weeds, garden truck, and farm
crops come from seeds. Such famiHar facts receive very Uttle thought from
most of us. From earhest times, however, people commonly believed that
plants and animals whose seeds or eggs were not generally known arose
spontaneously, that is, of themselves. The sun acting on mud might produce
frogs, for example; a piece of meat or cheese allowed to rot soon swarms
with wormlike maggots.

From the time of Aristotle down to less than a hundred years ago, well-
informed and intelligent men still assumed that fleas and mosquitoes and
many other living things arose spontaneously from decaying matter. They
accounted in this way for worms found in the intestines of man and other
vertebrates, and even for rats and mice. In the sixteen-hundreds an Italian
scholar and physician, Francesco Redi (about 1626-1697), attacked the prob-
lem by the method with which his countryman Galileo Galilei had startled
the world; that is, he used the method of experiment. Instead of arguing,
he said "Let's try it."

Redi placed fresh meat in several jars. He left some of the jars open.
He covered others with thin cloth, and still others with parchment. In all
the jars the meat began to decay. In the open jars the meat became wormy,
but not in the covered jars. On the other hand, the cloth covers had on them
the eggs of flies. Redi established the fact that maggots come from the eggs
of flies. Yet he continued to believe that other forms of life do develop
spontaneously. Two hundred years later a French chemist, Louis Pasteur
(1822-1895), and an English physicist, John Tyndall (1820-1893), showed
by experiments that even the rotting of materials is due to the action of

341

"microbes", that is, small living things; and that the microscopic organisms
which bring about decay arise in each case from others like themselves.

Every single plant and every animal about which we have positive in-
formation has come from another organism of the same kind. Yet that all
life comes from life is one of those big ideas which we can never prove in
an absolute sense. Our knowledge is limited to what we have been able to
observe. In our general statements we reach out to other objects and events
of the same kjnd. In thus reaching out, we rely upon two important
assumptions: (1) We assume that things "of the same kind" are the same
in origin, structure, qualities, behavior, and so on. (2) We assume diat wt
can recognize things "of the same kind" when we come across them, with-
out always stopping to ask in exactly what ways and to exactly what extent
they are really "the same".

Among so many different kinds of living things, it is conceivable that
they originated in different ways. Moreover, in our constant efforts to find
general rules or general ideas, we cannot help wondering what connections
there are between the various processes or events and the beginnings of new
individuals. What connection is there between modes of reproduction and
the conditions under which different species live? Are the methods the
same among plants as among animals? among land forms and water
forms ? Is there any connection between the length of life and the methods
of reproduction ? And why is it that some species produce very many tggs
or seeds, or many new individuals, whereas other species produce only one
or a very few offspring at one time ?

Questions about the origin of new individuals may come in many cases
from idle curiosity. Yet answers often have important practical bearings.
It is important for us to produce large numbers of some kinds of plants and
animals, and it is important for us also to check the multiplication of otbe:s.

342

CHAPTER 18 • GROWTH AND DEVELOPMENT

1 What makes a plant or animal stop growing?

2 Is there anything besides feeding that makes the members of a

species differ in size or development?

3 Is there any advantage in being larger or smaller than the

average r

4 Can anything be done to quicken growth or to slow it ?

5 Does every part of the body need exercise in order to develop?

6 Why do people grow faster at some times than at others r

7 Why do some parts of the body grow faster than others?

8 Do any new organs develop after one is born ?

9 Can a part that has stopped growing be made to start growing

again ?
10 Do people become more alike or less alike as they grow older?

Most of the people you know have grown in the last year or two. Nearly
everybody, but not quite all. For in addition to the universal fact that living
beings grow is a second general fact, namely, that they stop growing. More-
over, the parts of a plant or animal grow at different rates, so that shapes,
forms or proportions change.

In some species of plants, like the famous redwood trees of California,
the individual may keep on growing for centuries. Some animals keep on
growing as long as they remain alive, as certain fish. But in most of the
familiar species the individuals reach a fairly definite Hmit of growth. They
may then continue to live for a time, but without becoming larger. On
the other hand, even after the body reaches full size, some parts may con-
tinue to grow, as do our hair and nails or the fruits on many shrubs and
herbs.

Why does not the increase in size of living things continue through life ?
What determines the different rates of growth among different species or
among the different parts of one plant or animal ? How can the growth
of living things be controlled ?

How Do Plants and Animals Increase in Size?

The Steps in Growth When the conditions are suitable, an organism
grows by two distinct processes:

Cells enlarge as they form new protoplasm by assimilating food. This
is true of one-celled organisms, as well as of many-celled organisms. A cell
may indeed increase in size by absorbing a quantity of water, just as a piece
of leather or wood swells when it absorbs water. But bv growth we usually
mean the making of more protoplasm.

343

In addition to producing new protoplasm, a growing organism produces
new cells through cell-division (see illustration below). Cell-division in-
creases the number of cells. Each new cell is, of course, smaller than the
mother-cell. In one-celled as well as in many-celled organisms, cell-division
increases the number of cells; assimilation increases the quantity of proto-
plasm. And in every case living is continuous', the new protoplasm formed
is like the old protoplasm, and the new cells are like the old cells.

Sizes of Cells We have seen that as a body grows larger, the volume
increases more rapidly than the surface (see illustration, p. 117). In time,
therefore, the ratio of surface to volume may be too small to allow for the
absorption of surplus for new protoplasm. At that point, of course, there
can be no further growth (see illustration opposite).

Conditions of Growth The most prominent single condition for the
growth of protoplasm is a supply of food, more specifically, protein. It does
not follow that a surplus of food will ensure greater growth. A Shetland
pony, for example, cannot grow to the size of a draft horse by merely in-
creasing its food intake. An excess of food may make a mouse grow to be

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GROWTH BY CELL DIVISION AND ASSIMILATION IN ONION ROOT

Cell division increases the number of cells; the stained nuclei are close together.
Each new cell is, of course, smaller than the mother cell was; but it grows larger by
assimilating food, so that the entire structure increases in size

344

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LIMITATION ON GROWTH

A cube twice as large as another has 8 times as much material in it, but only 4
times as much surface. But it would be difficult to make sure that any particular cell
actually stopped growing because its volume had become too large in proportion to
its surface. This purely mathematical idea is supported, however, by the fact that
thread-shaped cells or series of cells, like those of certain algae and fungi, appear
to grow indefinitely in length. In the growth of such structures the volume increases
very little faster than the surface

larger than some of its hungry companions, but it will not make a mouse
grow to the size of a rat. Conversely, insufficiency of food, though it may
not kill the organism, may stunt its growth.

Size, like any other characteristic of a living thing, is influenced by the
surrounding conditions. The pine tree, for example, attains its size and
shape influenced in part by soil and weather; that is, it grows better in some
locations or in some climates than in others, growing faster when it is
warmer. The squirrel in the tree's branches is also influenced in its growth
by the food it can get, by weather conditions, and perhaps by enemies. In
each case, however, the organism reaches a size that is fairly characteristic
of the species; that is, how fast an organism grows and how long it con-
tinues to grow are determined in part by the kjnd of protoplastn of which it
consists (see illustrations, pp. 346 and 561).

Moreover, as a baby or any other living thing grows, it is constantly
changing in shape, as well as in size. That means, of course, that some parts
are growing faster than others, or that some parts slow up or even stop
growing, while other parts keep right on. In the body of any particular
individual, each cell stops growing when it reaches a certain size; and the
cells of a particular part will stop dividing when the structure or organ
reaches a certain size (see illustration, p. 347). As a consequence, our own
bodies, for example, contain many different kinds of cells, of many dif-
ferent sizes, and in various proportions.

345

United Status iJuieuu of Aniiudl Industry

OBSTACLES TO LIVING

Two herds of cattle of the same age and the same breed were supplied with abun-
dant food. One, however, was infested with ticks, which interfered with the nutrition
and health and growth of the animals

How Do Different Kinds of Cells Arise?

Variations in Protoplasm^ The individual has grown from a single
cell. This has given rise to more and more protoplasm. It has divided into
more and more cells. There come to be many different parts, many different
tissues, each having distinct qualities (see illustration, p. 348). Hovv^ can the
growing body be constantly changing and still remain the same individual ?

One way of answering the question is to say that there is really no im-
portant change between the egg and the later stages; there only seems to be.
That is, the chicken has always been in the egg, only too small for us to
recognize. If we open a swollen bud in the spring, we can see the tiny
leaves, which merely enlarge and unfold as they absorb water: nothing
changes. The oak tree is already present in the acorn, and growing up is
merely an expanding, an unfolding. In most seeds we can actually see the
distinct parts of an entire plant — root, shoot, and leaf.

Preformation This idea that the organism exists — in miniature — in
the egg and merely unfolds as it grows is a very old one and appeals to many
people as quite reasonable. Through many centuries people thought that
pre-formation was the correct explanation — that everything that the indi-

iSee No. 1, p. 364.

346

■^,

BERNaap -
FQiEOMAN

--^

1 >

i m

iii

METAMORPHOSIS IN MAN

Before birth the head grows proportionately more than any other part. After birth
the legs grow most and the head least. Many other changes in proportion take
place in all parts of the body

vidual becomes is already formed in advance, but too small for us to see.
When Leeuwenhoek and others introduced the microscope, many rushed to
examine the earliest stages of various plants and animals. Some of these
searchers found what they were looking for. They could see the outlines of
a fish or a frog by looking through the microscope at the egg of a fish or
a frog. Others could see the outlines of an animal by looking through the
microscope at the sperm.

With what they had thought out in advance and what they thought they
could see through the microscope, many actually drew pictures of tiny ani-
mals, and even of a tiny human form— a "homunculus", or minute human
being, preformed and destined in good time to develop into a person. How-
ever reasonable this idea of preformation may seem, it raises special difficul-
ties. It suggests, for example, that in the "homunculus" there are already
present the germ cells, or "seeds", each with its own preformed individual;
and that these tinier individuals in turn have inside themselves the seeds for
the next generation, each with its still tinier individual, and so on to the end
of time. And if that is really the case, then we should have to assume that that
condition existed from the very beginning — so that, as some writer put it,

347

Ferfilizedl egg cell

> y^ Epithelial

cells of pancreas

(filiated tracie^

Cardlage cells

THE DIFFERENTIATION OF CELLS

In the earliest stages of an individual's development all the cells are very much
alike. When there are several hundred cells, it is possible to make out layers of
distinct kinds of cells. Later we can recognize different tissues, or masses of similar
cells, such as skin, muscle, bone. After the distinct tissues are established, a dividing
cell produces new cells like itself

the whole of the human race must have been present in Mother Eve! How-
ever, better microscopes and more thorough study have convinced most peo-
ple that 'preformation" does not agree with all the known facts.

Transformation Another way of answering the paradox about chang-
ing and remaining the same is to recognize that the trouble may really be
with the words and not with the facts. A living thing is constantly chang-
ing, physically and chemically; and yet it remains the "same" individual.
The only way it can continue to be the same individual is through constantly
changmg. The real question is. Just exactly what changes take place be-
tween being an tgg and being a hen? We still have to get the facts in each
particular case. Just how does an tgg become transformed into a hen ?

From Egg to Hen' Aristode was probably the first person to try to
answer the question How does an egg become a hen? by experimenting in-
stead of arguing. If we place a number of tggs under a hen (or in an
incubator kept at 103° F), we expect the same number of chicks to come
out of the cracked shells in about three weeks. We might follow Aristotle's
plan, removing the eggs one at a time and examining the contents. In a
fresh egg, even before the hatching begins, we are able to see a whitish
speck floating on top of the yolk— the "germ spot". Day by day this speck
becomes larger. In half a day, the speck is longish. Even without a micro-
scope we can see the beginning of structure; there is a darker line down the
middle (see illustration, p. 350). We are able to see more than Aristotle
saw, for he had no microscope. We can see in the changing chick within
the tgg what is perhaps more easily seen in the corresponding parts of
simpler animals.

The Origin of Tissues' Eggs of frogs and of various fishes are easily
kept in dishes of water at ordinary room temperature. Patient watching of
these tggs reveals progress from the one-celled stage through several more
or less distinct many-celled stages (see illustration, p. 351). What we see in
the simpler backboned animals or in insects is similar to what we find in
mammals and in other classes of animals.

In some species differences in size among the cells appear after only a
few divisions. In the early stages of a frog's development the cells in the
upper portion of the cell mass are much smaller than those in die lower
portion, and more numerous.

Inequalities in the rate of division and inequalities in the growth of the
cells soon change the shape of the whole mass. Gradually new kinds of cells
appear in the young embryo. At first these are in layers, or membranes.
The embryos of many different species consist, at one stage, of mem-
branes with spaces, or cavities, among them. The membranes grow out
irregularly into the cavities, forming folds. They break through in some
iSee No. 2, p. 364, 2See Nos. 3 and 4, p. 365.

349

places, and they become joined in other places. In this way the three orig-
inal layers — outer, inner and middle — give rise to the several kinds of tissues
that make up the organs of the animal.

When a locust or a cockroach comes out of an egg, it is very much like
the parent, except that it is very small and lacks wings (see illustration,
p. 352). By a series of moltings the animal not only becomes larger but puts
on wings and other organs. When the tgg of a moth or of a butterfly

23 hours

30 hours

72 hours

96 hours

kill Supply House, Inc.

FOUR STAGES IN THE DEVELOPMENT OF CHICKS

While Aristotle followed the scientific method to answer the question of how an egg
becomes a chick, it was impossible until comparatively modern times to see in great
detail just what happens during the development

350

Top view after
First division second division

-■^

Two -layer cup

Caving in

Section of

hollow sphere

EARLY STAGES IN THE DEVELOPMENT OF A FROG

The yolk material is heavier than the protoplasm and remains at the bottom of the
mass. When a cell division takes place in a horizontal plane, the upper cells are
smaller and more active, and the lower ones, with more inert food material, larger and
less active. At one time the frog is a hollow sphere; at another, a two-layer cup

hatches out, the young animal looks more like a worm than like the parent.
It has no wings, as has the adult. Its biting jaws work sideways. It differs
from the adult so much that we should never suspect its connection with
butterflies if we did not observe its origin or its later development. In the
life history of frogs and salamanders there are also distinct stages, in some
ways as well marked as those of the insects (see illustration, p. 355). The
development of an individual through a series of well-marked stages is
called a metamorphosis, which means "trans-formation".

Diflerentiation' There is another way of looking at the process of
development. As the mass grows and as it undergoes changes in form, the
cells become more and more unlike the original cell from which their
growdi started. They also become more and more unlike one another. The
skin and muscle cells become distinguishable from the bone and nerve cells.
The cells of the stomach glands become different from those of the saliva
glands. Cells come to differ from one another in size, in shape, in coloring,
in texture, and in their chemical peculiarities. There is a progressive dif-
jerentiation. Growth, differentiation, metamorphosis, are various aspects of
the same general fact of development, which is characteristic of all livina
things.

^See Nos. 5 and 6, p. 365.
351

Eggs

Young
larva

Eggs

Young

Grasshopper {Melanoplus)

Pupa Adult

June bug (Melolontha)

Egg on
paoralyzed
caterpillar

Larva

Pupa

Wasp iSphex)

METAMORPHOSIS IN INSECTS

In some orders of insects, the young hatching out of the eggs resemble the adults of
the species, although they lack wings. Since they have an external skeleton, they can
grow only while this is still soft. After feeding awhile a young insect molts, or casts off
its hard shell, and then grows rapidly until a new exoskeleton hardens

Egg mass

Ne . , '..^y

Pupa Adult

Gypsy moth iPorthetria)

Larva

Eggs

Pupa

Adult

Larva

Hawk moth iPhlegethontius)

. /

Eggs

Larva Pupa

Tiger swallowtail iPapilio)

Adult

Eggs

Larva

Pupa
Fritillary (Argynnis)

Adult

METAMORPHOSIS IN INSECTS

In some orders of insects the young resemble "worms", or grubs, rather than their
parents. In later stages the individual differs in structure and in behavior from both
the adult and the young, wormlike stage. Where the several stages are quite dis-
tinct, the development is called a "metamorphosis", which means a transformation

Through What Stages Do Different Kinds of Organisms Pass?

Similarities in Development At the very start, every animal is like a
protozoon; it exists as a single cell. In a large number of more complex
animals, like the starfish, the snail, the lancelet, there is a stage m the
development that consists of a hollow sphere of cells. In the development
of the frog, birds, and many other animals this hollow-sphere stage is not
so clear, being obscured by the yolk. The hollow sphere caves in and the
opposite sides meet, forming a two layered cup. This stage of the organism
may be compared to such animals as the hydra, which never gets much
farther than being a two-layered cup (see illustration, p. 274). Then the
two-layered cup becomes longer, suggesting certain kinds of worms.

The embryos of animals that are closely related, such as several kinds of
backboned animals or several kinds of insects, show still more remarkable
resemblances. Thus the fish, the bird, the salamander and the rabbit con-
tinue very much alike when it is aheady possible to distinguish head and
trunk and limbs (see illustration, p. 459). In a somewhat later stage it is
not difficult to distinguish the bird from the fish or the tortoise. But at this
stage there are still certain resemblances between the birds and the reptiles.
Moreover, the embryos of several mammals (rabbit, pig, sheep and man,
for example) are at this stage strikingly similar. As they become older,
they become more and more different.

Metamorphosis in Man^ In general form, the human infant resembles
the adult. We therefore do not commonly think of metamorphosis in
human beings. But if we compare the proportions of a baby with the pro-
portions of an adult, we can see that the changes are real. But a man is
something more than a large baby, something different in every detail (see

illustration, p. 347).

We know, of course, that as we become older many changes take place
in the proportions of the various external organs, particularly of the head
and face. Changes take place also in all the internal organs, in the relative
sizes of the heart and lungs and liver and stomach. Some organs that are
present in infancy may disappear. Others not present at one stage make their
first appearance later on. Some structures which appear at first to be form-
less knobs or buds gradually acquire definite shapes, with distinct parts, as
the body reaches maturity.

Like other animals, the individual human being develops from a single
and comparatively simple cell to a very complex being made up of many dif-
ferent organs. The organs, as we know, consist of many different tissues,
each consisting of coundess cells of distinct kinds (see page 348). Through a
series of cell divisions that double the number of cells at short intervals, the

iSee No. 7, p. 365.
354

Chinook salmon (Oncorhynchus)

Leopard frog {Rana palusihs)

Spotted salamander
{Ambystoma maculatum)

METAMORPHOSIS IN VERTEBRATES

Among the vertebrates only amphibians seem to have the distinct stages making up
a "metamorphosis". Among birds and mammals the transformations during the in-
dividual's development are much more complex, but they take place within the egg
or within the body of the mother, so that the individual has already attained the
general form distinctive of the species when he first appears as "free-living"

single cell becomes in a few days a spherical mass of many more or less

similar cells.

In three weeks the mass of cells has become elongated, but hardly recog-
nizable as any particular "kind" of animal, although it has distinct vertebrate
characteristics. There are many kinds of cells. The surface, or "skin", cells
differ from the internal cells. Certain layers come to be more like "muscle",
and others come to be definitely digestive structures. It is possible to see
little knobs of cells that correspond in position and form to prospective
"bone" masses. Other lumps of cells suggest the beginnings of nerve tissue.

By the end of the fourth week there can be no doubt that the young
embryo is a mammal, and not a fish or a bird. At five weeks, little buds in-
dicate the positions of arms and legs. Later the tips of these buds begin to
divide into the rudiments of fingers and toes. While the head end of the
embryo has in the meantime been growing faster than other parts, we could
hardly recognize the features as being especially "human" until about a

month later. .

Now the eyes and ears and nose and chin become steadily more distinct
—and more distinctly human. By the time the baby is born, it is already a
particular person.- In every family those who see the young infant usually
remark upon its resemblance to one or another of its various relatives. One
observer sees the mother's eyes or the father's mouth. Somebody else recog-
nizes an aunt's chin or a grandparent's forehead. In other words, that in-
distinguishable cell or lump of cells has come to be not only a human being
but a unique human being, a distinct combination of organs and features
and tissues and chemical characteristics that is different from any other living
combination. And at the same time, not only does this human being con-
sist of the "same" kinds of organs and tissues and processes as other human
beings and other mammals, but it has passed through the "same" distmct
stages of development as other backboned organisms (see illustration,

P-459). .^ 1 r u

Recapitulation The foundations for the scientific study of embry-
ology were laid by Karl Ernst von Baer (1792-1876), who was born of Ger-
man parents in Estonia, but was educated in Germany, where he did most
of his work, spending the latter part of his life in Russia. Von Baer was the
first to work out the development of the hen's egg layer by layer, so to say.
He was also the first to see the original egg cell in a mammal, in 1827,
twelve years before the form.ulation of the cell theory.

In comparing all the embryos that he could study, von Baer was im-
pressed by the corresponding stages of development among different species.
This uniformity has been called von Baer's "biogenetic law"-a general
description of what we can observe in the development of many kinds of
eggs into adult animals. Half a century later some biologists expanded this

356

idea into the theory that each individual recapitulates in his development
the history of his race. The stages are supposed to represent all the types of
his ancestors. In a general way this is true only as a restatement of von
Baer's law. But, strictly speaking, it is not true, for example, that you once
passed through a hydra stage or a fish stage. All we can say is that each of
us has passed through stages which resemble corresponding stages in many
classes of animals (see illustration, p. 459).

What Brings About Differentiations during Development?

Conditions for Development External conditions influence the de-
velopment of organisms, just as they influence growth or metabolism in
general. Thus plants growing in northern regions, with long days and
short nights, during the summer, mature more rapidly than those grown
from the same stock in regions having shorter days (see pp. 251-252). The
submerged leaves of certain plants are quite unlike those growing above
the surface of the water (see illustration, p. 203).

Temperature influences development in many ways, sometimes very
strikingly. The eggs of frogs will develop into tadpoles very much more
rapidly in warm water than in cold. Jacques Loeb showed that by chang-
ing the temperature it is possible to modify the rate of development and the
life-duration of animals. Fruit flies, for example, live about eight weeks,
from the Qgg to the end of adult life, at ordinary room temperature. At
the temperature of a warm summer day (about 86° F), all their life proc-
esses are so speeded up that development is completed in three weeks. By
lowering the temperature to 50° F we can retard all the life processes of the
insect and stretch its life to nearly six months.

Temperature influences various aspects of metabolism and various tissues
in different ways. Some species of butterflies and moths produce two broods
a year, surviving the winter in the pupal stage. The spring form is often
strikingly different from the late summer form in size and pigmentation.
Experiments indicate that so-called local races or varieties of insects differ
from one another chiefly, if not entirely, because of temperature.

Chemical Influences We can most easily observe the influence of
chemical substances upon growth and development in the lower forms.
But more complex forms also show modifications. Mollusks, crustaceans,
and other animals have apparently become modified under natural condi-
tions in which sea water is sometimes diluted by rains or concentrated by
evaporation (see illustration, p. 359). Professor Charles R. Stockard (1879-
1939), of the Cornell medical school, brought about amazing changes in
development of the minnow Fundulus by changing the chemical composi
tion of the sea water (see illustration, p. 360).

357

Gaura
parviflora

Sunshine

Solidago
(goldenrod)

Mountain

Atitr Uiuc'iil/er^. Ihv blori/ ol Evolution Aftci Clements

INFLUENCE OF ENVIRONMENT UPON PLANTS

Effects of excessive sunshine are shown in the first pair of plants. Effects of low tem-
perature and excessive loss of water are shown in the second pair.

We have come to take chemical influences for granted in all proto-
plasmic activities, both as foods and as poisons. We have also come to think
of the vitamins and hormones as chemical modifiers of protoplasm. But
growth is not the same as development, and the two processes are not
necessarily influenced in the same way by any particular chemical.

Inner Factors Temperature, light, moisture, chemicals, oxygen, and
the like influence metabolism in many species. But what is it that brings
about differentiation in the first place ? One way of thinking about what
happens during the progressive change from a single cell (or a few similar
cells) to the many millions of differentiated cells is to follow cell-divisions

step by step.

When two daughter cells are formed, they are apparently just alike. But
if they remain clinging together, each has a surface flattened against the
other. These cells are no longer round, the same in all directions. After a
second division, the four cells press against one another at different relative
parts. After a division takes place in a horizontal plane, the food supply
is different for the upper cells from what it is for the lower ones. Each
cell comes to be influenced in a different way by pressure, food supply,

358

exposure, and so on. We may, then, suppose that its metaboHsm is modified
in a distinct way. It may produce distinct substances or different proportions
of by-products. Respiration goes on more rapidly in some cells than in
others. The by-products of each cell will in turn influence neighboring cells
somewhat differently. Differentiation, having once started, continues in all
directions.

Twins and Quintuplets In a sense, differentiation begins with the very
first cell division. The single cell has in it all the "makings" of a complete
and complex individual which it in time becomes and which contains
perhaps trillions of cells. But so has each of the two daughter cells into
which the egg divides. This we know from the fact of twins. Experi-
mentally, the two cells in the two-celled stage of a frog or fish or sea urchin
or some other species can be separated. Each cell then rounds up and starts
to divide again. Under suitable conditions, each develops into a complete
individual — the two as much alike as true twins are known to be. In other
words, a single egg has the makings of a complete individual; and half the
egg also has the makings of a complete individual. If the two halves re-
main together, however, each produces only half an individual! Something
must make the two-together different from the two-separated.

More water
(or less salt)

Artemia
aiietina

From Gnicnhers. T/ic stori) uf Eroluliun. After Abonyi

RELATION OF SALT TO DEVELOPMENT OF THE BRINE SHRIMP

The brine shrimp, Artemia arietina, lives in brackish water. A Russian experimenter,
Schmankewitsch, diluted the water slowly, and in other cases let the water evaporate
so that the salts became more concentrated. The forms that appeared in the course
of a few generations had been recognized previously as different "species". Other
experimenters have repeated this process, which seems to be "reversible".

359

After the cells of the first pair have undergone the next division, so that
there are now two groups of two cells each, we may again separate the
daughter cells. Each of these four can produce a complete individual, so
that perfect quadruplets result. In fact, the armadillo ordinarily gives birth
to four babies that appear to have been derived from the same egg. With
some species the cells of the third segmentation may be made to develop,
yielding eight identical individuals. There is reason to believe that all the
Dionne quintuplets came from the same egg (see illustration opposite).

From what we know, it is reasonable to assume (1) that at some stage
in the growth of a mass of cells internal changes arise, and (2) that these,
in turn, influence the development of other parts. It has been shown, in
fact, that specific substances, or organizers, in various parts of the embryo
influence the development of other parts in such a way that all the parts
are kept related, or co-ordinated. There is evidence that relative positions
in the embryo also influence the development of tissues and organs. How-
ever, this may mean the same thing, namely, that particular substances,
produced in particular regions, influence the behavior of neighboring or
remoter cells in the course of development.

How Can We Tell that There Are Specific Organizers
or Growth Substances?

Position Is Everything — Almost In many games, in military opera-
tions, and in other human relations a great deal depends upon position. The
position of cells in an embryo seems also to be important.

f'~^

After Stockard

CHEMICAL MODIFICATION OF DEVELOPMENT

360

Ordinary minnow eggs develop
into familiar minnows, with one
eye on each side of the head.
Practically ail do so in ordinary
sea water, which contains many
different substances. By system-
atically changing the relative
amounts of magnesium and cal-
cium in the sea water, experi-
menters were able to make various
types of freak minnows hatch out
of the same batch of eggs. In one
very striking form that hatched in
water containing a high propor-
tion of magnesium the two eyes
started to develop on the right
and left sides but steadily moved
together and fused in the middle

Fertilized

egg cell

First
segmentation

(Possible twins)

Second segmentation

(Possible {
quadruplets)

/ Third ^
segmentation

Yvonne

Annette

Ceciie

Emilie

Marie

Kin^ FcMliiirs S,\iiclir;ile. Inc.

FIVE GIRLS FROM ONE FERTILIZED EGG

Each cell resulting from the first two or three cell divisions of a developing embryo
would seem capable of becoming a complete individual. The most reasonable inter-
pretation of the resemblances and differences among the "Quints" is that after the
second cell division, three of the four cells developed into Yvonne and Annette and
Ceciie, while the fourth cell divided again, developing Emilie and Marie

Each of the cells resulting from the first three or four segmentations of
the egg is capable of developing into a complete individual. In some species
the capacity to form individuals is present in later cell-generations. By the
time the embryo has reached the two-layer stage (see page 351), each part
is fairly well set for its "destination". The end which is to become head is
already determined. The parts that are to form skin and nerves are already
distinct from the parts that are to form the food tube. Cells removed from
the outer layer, or ectoderm, can keep on growing in a suitable fluid. But
they will grow only ectoderm cells. Similarly, endoderm cells removed

361

from an embryo will grow only endoderm cells. Each part seems to carry
on according to its position.

But position is not absolute. It is always in relation to something else. In
the embryos of salamanders and frogs and other mammals we soon recog-
nize parts that are to become brain, parts that are to become eyes or legs.
Is the character of every tissue or organ already fixed at this stage ? In one
series of experiments a bit of tissue that would ordinarily have become eye
was transplanted to the abdomen of an embryo, and a piece of leg tissue was
transplanted to where wing should have developed (see illustration below).
The eye-prospect became an eye, and the leg-prospect became a leg. Here
the cells developed what we might suppose to have been their "natural"
qualities, those belonging to the position from which they were taken.

A Master Organizer In the gastrula, or cup, stage, the ectoderm and
the endoderm run together at the edge (see illustration, p. 351). The upper
edge of the opening, called the "dorsal lip", seems to be a special center of
protoplasmic activity. If a bit of this tissue is grafted on any part of an
embryo, it starts to develop a new embryo. It apparently influences all the
surrounding cells so that, as they grow and multiply, the mass shapes itself
in relation to these dorsal-lip cells. Chemical study of these cells has located
in them special "organizer" substances.

BERN ARC

Transplanted
eye

After Viktur Jlaiiiburger

GROWING ORGANS OUT OF PLACE

When the eye-bud in a chick embryo was grafted on the side of the abdomen, it de-
veloped into a complete eye, although the nerve connections were not established.
The transplanted portion developed according to characteristics normal to its tissues

362

Eyebcdl formed from
outgrowth of
embryonic
brain

from skin cells

Inside of eye ■

formed from

mesoderm ^^'

INTERACTION OF DEVELOPING STRUCTURES

The eyeball and retina develop as an outgrowth of the brain in the young embryo,
whereas the lens develops as an ingrowth of the skin. If the eye-bud of an embryo is
removed at an early stage and implanted under the skin on any other part of the
body, the skin cells will develop a lens, where it cannot possibly be of use

Even young tissues act in specific ways. It is therefore possible that there
are several or many organizer substances. In any case, the evidence shows
that the parts of the embryo probably act on one another during develop-
ment through chemical substances.

In some very clever grafting experiments Hans Spemann (1869-1941), a
distinguished German biologist, used embryos of two different kinds of
salamander. Spemann removed bits of shjn from the abdomen of a sala-
mander embryo and grafted it on the brain of one of the other type. In this
position the skin cells developed brain, but they retained the character of
their own species. Let us suppose that these developments were determined
by the presence of organizer substances. We should then say that the or-
ganizer in the brain region changed skin cells into brain tissue, while the
organizer in the skin cells determined the appearance or perhaps the pig-
mentation of the new (brain) cells formed.

More striking are experiments in which organs are made to develop in
strange locations. In many vertebrates the eye is formed as an outgrowth of
the brain, at a very early stage. The lens, however, is formed by an in-
growth of the skin, above the eyecup — but it takes something in the eye-
bud to make skin cells form a lens (see illustration above). Again, the
external eardrum of the frog, which is easily examined, is formed by the
regular skin cells above a ring of cartilage. If this cartilage is removed in
the embryonic stage and grafted under the skin on the back or side of the
frog, the local skin will become thin and form the peculiar eardrum tissue.

Thousands of experiments have been carried out on embryos of many
species. The results agree with the notion that particular substances are

363

formed in the embryo, and that they influence the growth and differentia-
tion of tissues and organs. At later stages, as we all know, further develop-
ment is influenced by exercise, food, sleep, disease, and other factors. But
in the early stages, when definite organs are already recognizable, some of
these, by producing hormones, influence further development.

In Brief

There has never been a clear demonstration of "spontaneous" genera-
tion; all plant and animal individuals are assumed to have originated from
previous life.

Every organism starts life as a single cell.

The single cell from which the complex individual develops has in it
all the potentialities of the individual, but probably has not structures cor-
responding to all parts of the adult.

In each species the development proceeds through fairly consistent stages,
which are sometimes very distinct.

Groups of species are remarkably similar in the early stages of develop-
ment, although quite distinct later.

In some respects each individual recapitulates, in his own development,
the history of the race.

The rate of growth and the longevity of a cell vary with the specific
nature of the protoplasm of which it is composed.

The parts of a developing embryo influence one another, probably
through the formation of specific chemical substances.

EXPLORATIONS AND PROJECTS

1 To find out how fast plants grow, and what parts grow most rapidly, mark
growing plants at equal intervals and watch for alterations of levels. Plant seeds
of sunflower, beans, corn or tomatoes and grow to maturity. Place India-ink
marks on stems from time to time as stems elongate. When seedlings are only
two or three inches tall, make marks i inch apart; later use 1-inch intervals. Sum-
marize results to answer the questions raised. Record growth-differences as indi-
cated by changes in the relative positions of ink spots. Measure the height of the
plant periodically and plot its growth.

2 To investigate the development of the chick embryo, incubate fertile eggs,
and open one or more day by day to observe the changing embryos.^ Since the

^Place eggs under a sitting hen, or else in an incubator at 103° F. Eggs should be turned
each day. The incubation period is 21 days. A convenient way to plan for the study of
chick embryos is to place one or more fresh fertilized eggs in the incubator each day for 21
successive days, dating each egg, and then to open all eggs at once for study. To open eggs,
insert fine-pointed scissors through the shell and membrane and cut out a circular portion.

364

embryo always floats on top of the yolk, it may be readily observed with a hand
lens (or in later stages without such lens) by lifting ofT a piece of the shell.

Watch for the first appearance of circulatory and nervous systems, and for
limbs. Note the distinguishable parts that become structures of the embryo or of
later stages; note what functions other parts of the egg serve. Make a summary
record of the development, with the help of drawings or photographs.

3 To study the growth and development of houseflies, grow cultures under
observation in the laboratory.^ Note (a) what conditions favor the growth and
development of the species studied; (b) the number of offspring; (c) the character
and amount of parental care; (cI) the habits of the species that make them particu-
larly dangerous as carriers of disease or otherwise; (e) what methods suggest
themselves for their eradication.

4 To make a study of the early development and metamorphosis of frogs,
toads or salamanders," watch the animals through the stages, in an aquarium.
Make careful notes and appropriate drawings showing the different stages in the
development.

5 To find out how the snail develops, keep an egg-mass from an aquarium
in a small jar, where development can be traced in detail. (Snails require no
attention whatever if they are supplied with aquarium water containing a little
vegetation.) Examine the egg-mass regularly with a good hand lens or with a
microscope. Follow the development of the embryos. Describe the embryonic
development.

6 To study the life history of a fish, observe the early and mature stages in a
fish hatchery. Find out how the eggs and sperms are obtained and used in the
artificial fertilization of fish; how the young are reared, and how they are trans-
ferred to streams and lakes. Describe the early development.

7 To find out whether human proportions change between infancy and
adulthood, obtain several measurements of distance from foot to hip, hip to
shoulder, and shoulder to top of head, and plot the average measurements for each
dimension and for each age. Compare the separate curves as to slopes, which
indicate the relative rates of growth. Note which measurement changes the least
from infancy to maturity, and which the most. Find out whether there is any
period in development when growth takes place at an increased rate in all the
measurements. Summarize conclusions and interpretations.

^To raise a generation of houseflies, place a pair of adult flies in a screened jar or cage
half filled with manure, or expose the jar for a day or two where there are flies. Use sufficient
manure to keep the mass moist, though not wet.

-Collect eggs early in the spring from shallow pools along the borders of a pond or
stream. Supply green algae as food, and change the water frequently.

365

QUESTIONS

1 How does growth in many-celled organisms resemble that in one-celled
organisms? How do the two kinds of growth differ?

2 How do the results of cell-division in a one-celled organism differ from
the results of cell-division in a many-celled organism?

3 How does the one-celled stage of a bean plant become a many-celled bean
plant ?

4 What changes besides increase in size take place in an organism passing
from the one-celled stage to maturity?

5 In what parts of the human body does growth take place? In what parts
of a tree's body?

6 In the one-celled stage various species are not unlike. What brings about
the vast differences among different kinds of adult organisms?

7 What theories account for the successive steps in the development and
differentiation of an embryo?

366

CHAPTER 19 • REPRODUCTION OF LIFE

1 Does every animal start life as a single cell?

2 How does the beginning of a new animal resemble the beginning

of a new plant?

3 Is there sex in plants, as well as in animals?

4 How do different kinds of animals reproduce themselves?

5 Does any animal species reproduce in more than one way?

6 Do all species of plants produce seeds?

7 How do seedless plants multiply themselves?

8 In what ways are eggs and seeds alike?

9 In what ways are eggs and seeds different?

The life of every indi\idual, plant as well as animal, comes to an end —
after only a few minutes or after many centuries. The rolling seasons bring
increase and abundance, followed by drought and killing frost. Whether
through privation or illness, through \iolence or mischance, or through the
natural internal changes, everyone must die. Dying is part of being alive.

The life of the individual continues, for longer or for shorter, as the dying
protoplasm is constantly replaced within each cell. But while each individual
life comes to an end, life goes on. The species or race may continue to live
for thousands and thousands of years. How are dying individuals replaced?
How does life go on from season to season, from generation to generation?
How does a species reproduce itself?

How Is Reproduction Related to Growth?

From the End to the Beginning^ Li\ing plant and animal cells often
end their existence by dividing into two. When we break a rod of wood or
glass into two pieces, we double the number of rods, but we do not increase
the amount of wood or glass. Nor do we destroy any glass or wood. We
destroy merely the integrity or identity of the original rod.

In much the same way, a one-celled plant or animal ends its existence by
dividing into two. It neither increases nor decreases the amount of proto-
plasm. It distributes its living matter between two new cells, which come
into being through this process. The mother-cell at the same time destroys
its identity; it ceases to exist. We might say that a pleurococcus cell or an
ameba is born an orphan.

Individual cells are constantly being devoured by other organisms, or
killed in other ways. W'hen a cell divides, there is a multiplication of cells.
We may think of this as a kind of reproduction in one-celled species or as a

iSee Nos. 1 and 2, pp. 394-395.
367

Resting stage, Chromatixi in tangled Spireme divided Chromosomes form

chromatin in network thread, the spireme into chromosomes ring in middle

Each chromosome
splits lengthwise

New chromosomes New chromosomes Chromatin in network

move apart form two tangles of two new tangles

NUCLEAR CHANGES DURING CELL DIVISION

The spireme separates into a definite number of chromosomes. Each chromosome
splits lengthwise; each half becomes part of the nucleus of one daughter cell. The
chromatin becomes exactly divided. The daughter cells have exactly the same num-
ber of chromosomes as the parent cell

Stage in the growth of many-celled species. But the protoplasm of a one-
celled plant or animal seems to be able to grow and then divide, without
end. Of course no single cell continues to live forever, but the protoplasm
— as distinct from the individual — appears to be immortal!

Nuclear Division^ The sameness of the protoplasm, through all the
successive cell-divisions, appears to be related to the behavior of the cell
nucleus (see illustration above). We are impressed by the precise division
of the chromatin material. It is possible that other parts of the nucleus, and
the cytoplasm, also divide in the same precise manner. But of that we cannot
be sure, since the substances are for the most part indistinguishable with our
present methods of study.

In multicellular plants and animals cell-division is an essential feature of
development, as well as of growth, for at certain stages it results in new kinds

iSee No. 3, p. 395.
368

Scion

Fitted
and tied

Stock

Whip graft

Waxed

Side graft

Scions

Inserted
and tied

Bud graft

Stock Scions inserted Waxed

Cleft graft

TYPES OF PLANT GRAFTS

For successful grafting, the cambium tissues of the bud or scion must be placed in
contact with the cambium of the slock, to allow nourishment to pass from one to the
other. Speed is essential to avoid drying of the delicate cut tissues. Grafting is
carried out in the winter or early spring, while all buds are dormant. Budding is done
in the late summer or early autumn — the bud not opening until the following spring

of cells and tissues. Under special condidons, cell-division brings about the
healing of wounds, breaks or injuries (see page 228). And through regenera-
tion cell-di\ision may give rise to new indniduals; a fraction of a worm or a
starfish, for example, may become a new indi\'idual.

Regeneration and Reproduction^ Fruit growers propagate new lots of
individuals by setting out slips, or cuttings, from especially desirable plants,
and having them take root. Even where culti\ated plants bear seeds, it is
sometimes more practicable to use this vegetative propagation than to depend
upon seeds. The strawberry and other common plants normally split them-
selves into multitudes of individuals through vegetative propagation (see
illustration, p. 372). A long shoot of forsythia or of wisteria may droop to the
ground and take root; later the connection with the parent plant dies away.
The horticulturist regularly makes use of this process, as in "layering" rasp-
berries: he brings a stem over and fastens it in contact with the ground
until it establishes itself by means of roots (see illustration, p. 373).

For all practical purposes, new individuals do arise from cell-division in
budding, regeneration, and other growth processes. But we commonly dis-
tinguish between growth, which means an increase in the quantity of Hving
matter, and reproduction, which means the bringing of new individuals into
being. Moreover, we usually think of reproduction as an event or process
that separates one generation from the next.

How Is Reproduction Different from Growth?

Spores and Cysts" If the conditions for growth become unfavorable,
some species of protozoa form a thick cell-wall inside of which the protoplasm
may remain indefinitely inactive. In this incased state, or cyst, the animal
may resist drought or frost, or even the digestive juices of some stomach into
which it may get. The cyst is thus a resting stage in which animals can survive
adverse conditions.

Among the simplest plants unfavorable conditions lead to the formation
of a somewhat similar resting stage. Yeast cells, for example, divide the
protoplasm into four parts, each of which puts out a thickened wall (see illus-
tration opposite). Such a special cell is called a spore, and is able to resume
growth when conditions are again favorable. Spores are produced in nearly
all species of plants and in some animals. They are also usually formed in
large numbers and are very resistant to unfavorable conditions. In the spore
stage some kinds of bacteria cannot be killed by boiling water.

One class of protozoa, the Sporozoa (see Appendix A), consists of parasitic
forms which reproduce by means of spores. These special cells result from

iSee No. 4, p. 395. -See No. 5, p. 395.

370

spore formation

Coo

THE YEAST PLANT

The cells of this plant push out buds, which drop off at various stages, and continue
to grow and bud so long as food and other conditions are favorable. Under certain
conditions the protoplasm of a cell divides into two and then four parts, each of which
may remain inactive for an indefinite time. Such resting cells are called spores

successive cell-divisions of the growing protoplasm, and they can dry up and
withstand conditions unsuited to growth for a long time. The malaria para-
site belongs to this class. The plasmodium, or ameba-like stage, of this species
is parasitic in red blood corpuscles. When it has grown as far as possible in a
corpuscle, the protoplasm divides into a large number of spores, which are
discharged into the blood plasma (see illustration, p. 622).

Spores are so small, and they are produced in such tremendous quantities,
that they become widely scattered in the air. We can hardly find a sample
of dust that does not contain spores of several different species, including, of
course, bacteria. This accounts for the difficulty of keeping organic matter
from spoiling at ordinary temperatures in the presence of moisture. The
molds and mildews and yeasts and bacteria that spoil bread and other food,
cloth, leather, paper, damp hay, wood, and so on get started from such spores.

In mosses we can see tiny puffs of spores come out of the graceful little
capsules at the tips of stiff bristles (see illustration, p. 412). On the backs of
fern fronds we can see the dark "fruiting bodies", which are masses of spore
capsules (see illustration, p. 387). The yellowish pollen which ardent fiower-
smellers get on their noses consists of tiny spores. And it is such flower spores,
scattered by the wind, that have brought certain species of plants into dis-
repute with many people because they are responsible for hay fever and asthma.

W^e may think of these most widely scattered dust particles, produced in
inconceivably great numbers, as the resting stages in which species keep their
hold on life during the lean seasons. We may think of them as special means
for spreading out in space and so improving the chance of finding a favorable

371

Orchard grass

Gladiolus conn

VEGETATIVE PROPAGATION

Plants naturally increase in numbers through vegetative propagation. New indi-
viduals develop from a portion of the parent plant, before or after that^becomes
detached

Geranium plant

Cuttings in water

Phlox plant

Phlox plant divided

Vine layering

Rooted stem

New plants

ARTIFICIAL PROPAGATION OF PLANTS

By propagating vegetatively we can get innumerable plants from a single choice
specimen. We can thus reproduce in quantity a variety of flower or fruit that 'suits
our fancy or our needs, which we could not get so surely or so quickly in any other way

jConjugation
tube

Zygote

Vegetative ceil

Beginning of conjugation tube .i ..-^-^ ,

Hugh Spencer

CONJUGATION IN SPIROGYRA

In threads of Spirogyra lying close together, the cells put forth projections, which grow
toward their opposites. The projections dissolve at the point of contact, and the
protoplasm of one cell moves entirely into the opposite cell. The fused protoplasm
becomes a single spore with a thick wall

location for resuming life's activities. Or we may think of them as the "germs"
which initiate new plants and animals to replace the life that has come to an end.

Cell Fusion Like the cells of growing tissues, spores result from a divid-
ing up of existing protoplasm. We think of spores as highly specialized rep7V'
ductwe cells, for they "do" nothing unless there is a chance to start growing a
fresh line of protoplasm; and when a spore does start a new individual, it at
once goes out of existence itself. Now, in addition to extending life by growth
or by spores, most plant and animal species reproduce by a method that is in
a sense the reverse of cell-division. Under certain conditions two distinct cells
unite, or fuse, into one cell. This new cell that results from such a joining is
then the first cell of a new growth.

In the common pond scum spirogyra, the individual cells all look alike;
and they are almost independent of one another, although they cHng together
in long threads. Each cell has chlorophyl and manufactures its ov/n organic
food. In the course of a few sunny days in the spring, a pond may become
covered over with millions of the green threads. In darkness and at low tem-
perature, as the threads become entangled in the water, two cells lying op-
posite each other may put forth budlike outgrowths which meet end to end.
The cell-walls at the point of contact dissolve, and the protoplasm from one

374

, Sporangia

Formation*^
of zygote

O O' _

Germinating
spores ^

igj/

Kyphae /

Penicillium

[ V

SPORES IN COMMON MOLDS

Absorbing

hyphae

Spores are generally formed by the repeated division of protoplasm. In the black
mold, spores are formed in an enlarging cell at the tip of a vertical thread; this re-
sults in a capsule, which breaks and lets the spores scatter. In the blue mold, spores
are separated off from the terminal branches of threads. In the black mold two
threads sometimes meet, so that the protoplasm combines into a sporelike cell called
a zygospore

of the cells passes over into the opposite cell; the two masses of protoplasm
unite and form a new kind of cell (see illustration opposite).

Like a spore, this new cell (which forms a thick, dark cell-wall) is able to
start a new growth after waiting indefinitely through unfavorable conditions.
But it is unHke a spore in its origin, for it arises from the conjugation, or unit-
ing, of two pre-existing cells. The cells that take part in the conjugation are
called gametes, from a Greek word meaning "to marry"^ — that is, to join, or
unite. The cell that results from the conjugation is called a zygospore — that
is, a spore formed by a yoking, or joining together. It is sometimes called a
zygote for short.

The common molds are widely distributed by the millions of spores which
they produce by the successive division of the protoplasm. In addition,
zygotes are produced in black mold by the fusion of protoplasm from two
different hyphae (see illustration above). There are distinct strains in the
species, and conjugation can take place only if threads of two different strains
come together. There are no doubt chemical differences between the two
strains of mold, but what the differences are has not yet been found out.

375

A speim

ceU

An egg cell

Sperm entering egg All ckromosomes distinct

Nuclei fuse;

chromosomes mixed

at random

Cliromosomes
form tangle

Chromosomes
distinct,each
splitting lengthwise

Chromosome
halves separate

THE CHROMOSOMES IN FERTILIZATION

The essential fact about fertilization, in both plants and animals, is the uniting of
chromosomes from two cells into one nucleus. Although the male and female gametes
are quite different in most common species, the chromosomes supplied to the zygote
by the two parents are almost identical

In most ancient ci\'ilizations people believed that "fruitfulness", or the
producing of offspring, in many plants, as well as in most animals, depends
upon two parents, male and female. They recognized and accepted the fact
that the members of most species exist in two forms, male and female. "Male
and female created he them." The oldest myths and legends make a point of
sex differences. But the exact connection between sex and reproduction could
not be known until the microscope had been invented and improved.

It was as recently as 1875 that a German physician and embryologist,
Oskar Hertwig (1849-1922), was able to show that the essential fact in fertiliz-
ing, or "making fruitful", is a uniting of two di^erent cell nuclei into one (see
illustration above).

While the two gametes are indistinguishable in some species, the combining
cells in most plant and animal forms differ from one another in many ways. And
in most species of animals the two kinds of germ cells, or gametes, are borne by
the two different kinds of individuals, male and female. The female gamete is
the egg, and the male gamete the sperm (see illustration, p. 388). The union
of a sperm with an egg, or fertilization, takes place in all sexual reproduction.

376

How Does Sexual Reproduction Take Place in Vertebrates?

Vertebrate Reproduction' In backboned animals the reproductive or
germ cells are borne in special organs called gonads, and they are usually pro-
duced in two different individuals. The gonads are generally paired organs
located in the hind part of the abdomen. The eggs, or ova, are formed in the
ovary diVid are discharged into the general body cavity. They then pass through
a long twisted egg-tube, or ow-duct, eventually reaching the exterior.

The sperms are produced in spermaries, or testes, and are discharged to the
exterior by way of special ducts (see illustration, p. 379). In fishes that we
commonly use as food we can often find the ovaries with their masses of eggs,
or "roe", in the female specimens, and the corresponding spermaries, or
"milt", in male specimens. In the other classes of backboned animals (rep-
tiles, amphibians, birds, mammals), the essential organs are the same. The
distinctive variations are related to the manner in which the eggs and sperms

Mature plant

Section of conceptacle
with egg organs and sperm organs

Egg surroxinded by sperms

REPRODUCTION IN ROCKWEED, OR BLADDER WRACK

The eggs and sperms of the bladder wrack are discharged into the water. Numerous
sperms swarm around a single egg until one sperm unites with it. The result of the
union is a fertilized egg, or zygote

^See No. 6, p. 395.

377

are brought together and to the protection and nourishment of the new
individual.

Aquatic Vertebrates^ Among the fishes the female usually deposits the
eggs in quiet places at the bottom of the sea, near shore, or in quiet pools
of rivers. Then the male swims over the eggs, dropping a quantity of the
seminal fluid which contains sperms (see illustration, p. 380). The countless
sperm cells swarm about the heavier egg cells. One of the many sperm cells
swimming around a particular egg forces itself through the covering membrane,
and the fusion of the two cells takes place. As soon as the nucleus of the male
gamete and the nucleus of the female gamete have united, the combined
nucleus begins to divide, and so the development of a new fish is started.

Whether or not the sperm cells are attracted to the eggs by specific chemi-
cal tropisms, two conditions favor fertilization: (1) both gametes are dis-
charged into the water in the same region and at about the same time; (2) the
proportion of sperm cells to egg cells is enormous.

The ^gg cell of the fish contains a quantity of food material in addition to
the living protoplasm. The young fish developing out of the fertilized egg
lives on this accumulated food. In some species of fish one or both parents
swim about in the neighborhood of the developing fry and protect them against
destruction by their natural enemies.

Reproduction among Amphibians- In the common frog the male and
the female are not ordinarily distinguishable. During the breeding season,
however, the ovary becomes very much enlarged as the eggs are being formed,
so that the female is rather swollen. In the spring the adult frogs come out
of their winter sleep and move to the ponds. Near the edge of the pond a
male gets on the back of a female and clasps her firmly with the front legs.
During this copulation, or joining, the eggs emerge from the female, enclosed
in a mass of gelatinous slime; at the same time the male discharges the seminal
fluid over the emerging eggs. Fertilization thus takes place in the water.
The parent frogs swim off and pay no further attention to the fertilized tggs
or to one another. In some species of amphibians, however, there is a great
deal of parental care (see page 421).

Among all the vertebrate animals above the amphibians the &ggs are ferti-
lized while they are still inside the mother's body. But internal fertilization
takes place also among several groups of amphibians and even among fish.
The little guppy, a tropical fish often cultivated in home aquariums, is an ex-
ample of a viviparous species; that is, one in which the female brings forth
"living" young, in distinction from oviparous species, which are "egg-bearing".
Now most water animals discharge their eggs into the water, where they are
fertilized by the swimming sperms. The oviparous reptiles and birds, as well

iSee No. 7, p. 395.
2See No. 8, p. 396.

378

Oviduct

Testis

Efferent
duct

Ureter

and
sperm

duct

Seminal
vesicle

Reproductive system
of female frog

Reproductive system
of male frog

REPRODUCTIVE ORGANS OF THE FROG

Eggs discharged by the ovaries into the
body cavity get into the funnel-lil<e open-
ing of coiled egg tube. Eggs become
covered with gelatinous substance se-
creted by lining cells of the oviduct. Past
the thin-walled enlargement of the ovi-
duct, called the uterus, eggs leave body
by way of the cloaca

The sperms are formed by cells lining the
fine tubules that make up the spermary,
or testis. The sperm cells float in the
spermatic fluid, or semen. The semen is
gathered into a duct that joins the urine-
conducting tube from the kidney (the
ureter), and is then discharged from the
body by way of the cloaca

as insects, deposit eggs that hatch outside the mother's body, after they are
fertilized inside the body.

Reproduction in Mammals^ In mammals, including man and the other
primates, the paired ovaries and testes develop from early budding of the
endoderm into what later becomes the body cavity. As in all vertebrates, the
gonads originate early in the embryo's development in close association with the
kidne)'s. But the ovaries and the testes are complex organs: in addition to
their gamete-producing functions, they produce special hormones, or endo-
crines (see page 314). In the males of nearly all mammals the testes change
their positions in the abdominal cavity, gradually descending into a pouch,
or bag, which extends outside the body wall. This is called the scrotum.

The ovaries consist of masses of cells that produce eggs only near the sur-
face. The core of the ovary contains cells that produce the specific "female

iSee No. 9, p. 396.
379

United Staler Fish and Wildlife Service

ARTIFICIAL INSEMINATION OF FISH AT A RAINBOW-TROUT HATCHERY

By stroking a mature female fish, the fish-breeder forces ripe eggs into a pan of
water. Then he "strips" the seminal fluid into the water from a male fish

hormone", which is absorbed into the blood and carried to all parts of the body.
As each egg ripens, it detaches itself from the ovary and floats in the fluid of
the body cavity.

During copulation, the seminal fluid is discharged into the vagina, which
connects with the lower end of the womb, or uterus (see illustration, p. 383).
The sperm cells swim in the mucus secretion lining the womb, and into the
oviducts. An egg cell descending the Fallopian tube may be fertilized at any
point where the tgg and sperm meet. The fertilized egg starts segmentation
immediately after the fusion of the two nuclei.

The developing embryo attaches itself to the lining of the uterus by means
of outgrowths, or "villi", through which food material is absorbed from
the lymph of the mother (see page 423). At a certain stage in its de-

380

velopment, the new individual is pushed out of the mother's body by con-
tractions of the uterus. The cord breaks off close to the abdomen; the scar
formed is called the navel. Later the placenta and the cord are also forced out;
this is the so-called "afterbirth".

How Do Invertebrates Reproduce?

Reproduction among Insects There seems to be a direct relation be-
tween the modes of reproduction in different classes of plants and animals and
the conditions under which the various species live. In the life of each in-
dividual organism the earliest stages of the egg's development are passed in
water. Only in the more complex forms are the latest stages passed on land
or in the air. But whereas spores appear, in general, to be adapted to endure
and sur\'i\'e drought, sperm and Qgg cells are quickly killed when away from
moisture. Some of the distinctive characteristics of land and air species may
be regarded as adaptations to the fertilization of tgg cells while they are still
in the body of the mother.

Among insects, which of all classes of animals are most definitely adapted to
life in the air, the sperm cells of the male, suspended in a fluid, are passed
directly into a receptacle in the body of the female through a special duct, or
tube. From this receptacle the sperm cells pass, a few at a time, into another
space, in which the eggs are fertilized. A queen bee can retain a quantity of
li\'ing sperms for two or three years, or even much longer. She forces sperms
out of the receptacle from time to time as she produces new eggs.

Even in insects that normally lay their eggs in the water, such as mosquitoes,
fertilization takes place within the body of the mother. There is a wide
range, however, between species that leave the eggs as soon as they are laid
and those others (like the wasps, bees, and ants) that build elaborate nests for
the eggs and young, store away food, and actually nurse or protect the young.

Aquatic Invertebrates Among invertebrate animals li\^ing in the water,
such as sponges, corals, starfish, clams, and some crustaceans, eggs and sperms
are discharged into the water. The eggs contain relatively large amounts of
food material and sink to the bottom. The swimming sperm cells swarm
about the eggs. Fertilization takes place when one sperm penetrates the
protoplasm of an egg.

When the nuclei of the germ cells have united, the fertilized egg cell forms
a denser membrane. Other sperms cannot then enter. In some species of w^ater
animals, segmentation, or cell-division, starts immediately; in others there
are varying intervals. In most species the fertilized ^ggs, like the gametes,
are abandoned by the parents. In some invertebrates, however, the eggs re-
ceive a degree of mechanical protection. In lobsters and crayfish, for example,
the eggs are fastened to the abdominal legs of the mother by a sticky substance,

381

Kidney -

Ureter-

Vas deferens

Testis

FRIEDIv;aN

-Kidney

Ureter

■Vcis deferens

-Testis

Urethra

AAALE REPRODUCTIVE ORGANS IN MAMMALS

The sperm cells originate in the linings of fine twisted tubules that make up the mass
of each spermary (testis). The seminal fluid accumulates in small reservoirs, the seminal
vesicles. The tubes run together into common ducts leading into the urethra, which
also carries urine from the bladder

until the young are able to swim. Among the clams the eggs are discharged
into the mantle cavity, where they are fertilized by sperms swimming in the
water that circulates there (see illustration, p. 209).

Reproducdon in Coelenterates^ In the hydra and its relatives the indi-
vidual polyps attach themseKes at the base of the stalk. In some forms they
remain permanently attached, in others only temporarily. In most species
the stalk puts out buds, which become new polyps. In this way a colony of
countless branches is formed, each one ending in a polyp — as in coral colonies.

Among some of the species related to the hydra and the sea anemones there
is a regular alternation between a generation that reproduces sexuall} — that
is, by means of conjugating gametes — and a generation that reproduces by
budding, or without sex (see illustration, p. 384).

Two Kinds of Generations" Since many species of plants and animals
reproduce vegetatively, or by means of spores, as well as sexually, we may
wonder whether the individuals that reproduce in these two different ways

iSee No. 10, p. 396.

-SeeNos. 11 and 12, p. 396.

382

Oviduct

(Fallopian

tube)

Kidney

Ureter

Oviduct

(Fallopian

tube)

Urethra

BEhNAPD
FRIEDMAN

FEMALE REPRODUCTIVE ORGANS IN MAMMALS

The egg discharged into the body cavity, enters the Fallopian tube, carried along by
movements of cilia on the lining cells. The egg meets the sperms and .s fertilized
inside the egg tube. The oviduct ends in the muscular uterus, within which the new
individual develops

differ from each other as do male and female, for example. Indeed, this
condition is quite general. It would be strictly true to say that many species
are not merely dimorphic, or existing in two forms, sexually, but have three

or even more "forms". t u f

We saw that the Sporozoa reproduce by means of spores. In the case ot
the malarial parasite, for example, the spores are discharged into the plasma
of the host's blood. If now a mosquito draws some of such infected blood, the
stage of the parasite inside the mosquito reproduces sexually; the protoplasm
divides up into tiny structures which unite in pairs. The sexual and the asexual
state alternate so long as the parasite can get into a mosquito, then into a
warm-blooded host, into a mosquito again, and so on (see page 622).

Is There Alternation of Generations in Plants?

The Life History of the Moss In the common species of mosses, the
familiar green plants with small leaflets are male and female plants. In addi-
tion, there is a generation that reproduces by means of spores. Among the

383

Hydra

TWO KINDS OF GENERATIONS

The hydra and its relatives reproduce by budding and also by means of gametes,
which are discharged into the water. In the common salt-water jellyfish Obelia, there
is a sexual generation, called the "medusa", which is quite distinct from the vegeta-
tive generation

leafy scales at the tips of some individuals flask-shaped structures develop.
These produce a single egg cell each, and are called archegonia. In other in-
dividuals the corresponding structures produce large numbers of swimming
sperm cells; these club-shaped organs are called antheridia. When the moss is
covered with water, usually in the spring, the antheridia burst open, and sperm
cells swim into the archegonia, where one fuses with each egg. The fertilized
egg immediately begins to develop into a new individual, but this new plant
is quite different in structure and appearance from either the male or the female
parent. It consists of a bare stalk which forms a capsule at the tip — the spore
capsule. Its base digs into the top of the mother-plant, from which it derives
most of its nourishment (see illustration, p. 412).

When a moss spore alights on a suitable place, it absorbs water and puts
out a thin thread of protoplasm. This develops chlorophyl and looks like
one of the simpler algae. Later a clump of cells forms a sort of bud from which
the vertical leafy stem grows into either a male or a female moss plant. In

384

such species the spore-bearing generation gives rise — through the spores —
to a sexual generation. The sexual generation reproduces — by means of the
gametes — and gives rise to a spore-bearing generation. There is thus a regular
alternation between spore-bearing and gamete-bearing generations. These
two generations are called sporophyte and gametophyte respectively — that is,
spore plant and gamete plant.

Among the common ferns there is a similar alternation of generations. The
familiar stage, with green fronds and usually a distinct underground stem,
is the sporophyte (see illustration, p. 387). The spores, produced in tiny
capsules on the under surface, are widely scattered by the wind. When a
spore germinates, it gives rise to a flat somewhat heart-shaped plate of green
cells, known as a prothallium — that is, a /^rothallus or a thallus that precedes
(in this case, the fern plant). Unlike the moss, the gametophyte stage is not
dimorphic; the prothallium bears both archegonia ^w^antheridia. The sperm
cells swim in water. The zygote develops into the familiar fern sporophyte.

In What Ways Are Males and Females Different?

The Two Kinds of Gametes In the simplest of plants and animals,
such as Spirogyra and Paramecium, we cannot distinguish the vegetative, or
growing, stage of a cell from the reproductive stage — except at, or just before,
the time of conjugation. Nor can we distinguish the passive, or receiving,
gamete from the active, or supplying, gamete except in their behavior at this
time: one moves and the other remains in place. As we pass on to more com-
plex forms, the difference becomes more pronounced.

The swimming sperm cells of the bladderwrack and of other large algae,
as well as of most animals, are decidedly active. They often have very dis-
tinct swimming cilia, or flagella, as well as shapes that suggest movement
through water. In fact, when cells of this type were discovered by micro-
scopists, from the time of Leeuwenhoek down past the middle of the nine-
teenth century, they were described as "new species" of "animalcules".

We can easily observe size, shape, food content, movement. Underlymg
these differences between the male and female gametes, we must assume others
that are related to differences in their behavior. As sperm cells swarm about
restlessly, they seem to turn definitely toward any tgg of the same species
that may be in the vicinity. We know that the eggs of certain plants influence
the sperms through some chemical peculiar to the species. But when one of
the active male gametes penetrates the egg membrane, something happens
instantly; for all the others immediately swim away as if they had suddenly
lost interest in the ^gg. But at the moment that the sperm enters, the egg
actually forms a membrane through which no more sperms can enter. In any
case, the fertilized egg does differ from the female gamete chemically.

385

In one respect male and female gametes are alike. Both have the same num
ber of chromosomes, and this number is half that found in the tissue cells of
the same species (see illustration, p. 388). Now the chromosomes are evi-
dently related to the qualities or characteristics developed by the new in-
dividual. It is probably true, as Hertwig surmised about seventy years ago,
that the mother-cell and the father-cell contribute in equal measure to the
constitution of the offspring (see page 374).

From Water to Land As we compare different classes of plants or differ-
ent classes of animals, from the simplest to the more and more complex, we
find the male and female gametes increasingly different. Moreover, the or-
gans that bear the two kinds of gametes, and various accessory organs and
structures, also become more and more differentiated.

When the egg and sperm unite during fertilization, their chromosomes
combine, so that the zygote has the number "normal" for the species, called
the diploid or double number. In distinction from this, we speak of the gametes
having the haploid number (from a Greek word meaning "single").

In the mosses, for example, the male plant and the female plant look very
much alike, except for the archegonia, or egg-organs, and the antheridia, or
sperm organs, formed at the tip of the leafy gametophytes. After fertiliza-
tion, which takes place inside the archegonium, the new individual grows out
from the tip of the mother-plant, upon which it depends for nourishment.
This new individual, as we saw, is a sporophyte, and it has the diploid, or
double, number of chromosomes in its cells.

Among the ferns (which attained the size of great trees in former times)
and among the seed-bearing plants, the familiar and conspicuous generation
is the sporophyte, or spore- bearing, stage. In such types fertilization still
takes place in water, although the plants seem to be high and dry above the
soil. In most species of ferns the sexual generation, or prothallium, is rather
inconspicuous (see page 387). In fact, Linnaeus classed all seedless plants as
"cryptogamous" — that is, having hidden, or secret, marriage. That means
merely that in his time we did not know how conjugation, or fertilization,
takes place in the nonflowering plants, and we had only some guesses in regard
to the seed plants. Although we consider the ferns farther advanced than the
mosses, we find that both the egg-organs and the sperm-organs are borne on
the same individual. As we come to the more complex fio\^'ering plants, how-
ever, maleness and femaleness become more sharply differentiated. Yet the
gametophyte, or sexual, generation is so far reduced — especially in contrast
with the sporophyte — that we have found the actual structures and processes
only in modern times.

Among some of the lower orders of animals there are many species in which
each individual bears both eggs and sperms. Such animals are sometimes
spoken of as hermaphrodite, after a mythical Greek character having both

386

Hugii Spencer

LIFE CYCLE OF A FERN

The fern plant that we commonly notice is a sporophyte. It produces spores which
develop into gametophytes. The fertilized egg always gives rise to a sporophyte.
The alternate generations reproduce in different ways — one by means of gametes,
or sexually, the other by means of spores, or asexually

male and female traits (from Hermes and Aphrodite). In common earthworms,
for example, each individual bears both ovaries and spermaries. But no in-
dividual fertilizes its eggs with its own sperms. There is an exchange of seminal
fluid between two individuals, and the eggs of each are fertilized by sperms
received from the other.

The common oyster of the northern Atlantic coast is interesting in this
connection, since each individual is both male and female — but not at any one
time. A female oyster will produce a large number of eggs, which are dis-
charged into the water, where they are fertilized by sperms from other in-
dividuals. After a time, the ovaries become inactive and spermaries develop.
Each individual periodically reverses its sex.

Primary Sex Characters In countless varieties of plants and animals
reproduction consists only in the fusing of two unspecialized cells into a
zygote. Biologists have therefore come to apply the terms male and female
primarily to the gametes and to the special organs that produce these special-
ized reproductive cells. A male individual is thus one that bears sperms; a
female, one that bears eggs.

Maleness and femaleness were generally taken for granted in familiar ani-
mals, but in ancient times it was commonly believed that there could be no
sex in plants. Farmers and gardeners and fruit-raisers, however, knew from
very ancient times that it is the flower of the common plants that produces
the fruit and seed. They knew also that merely bearing flowers and having

MALE AND FEMALE GERM CELLS

The female gamete is usually spherical and inert, or passive, containing a great deal
of nutrient material in proportion to its living protoplasm. The diameter of the human
egg is about four times the length of the sperm, which means that it is many thousand
times as large in volume. Sperm cells are typically ciliated or flagellated, and they
swim rapidly in all directions

388

/ .

^i^

Chromatin network
in germ mother cell

Chromatin in
thickened spireme

Chromosomes Chromosomes at equator

in pairs

Chromosome
pairs separate

Chromosomes migrate
toward poles

Chromosomes form
two new groups

Two new nuclei

THE FORMATION OF GERM CELLS

In the formation of gametes in plants and animals, the chromosomes of each pair be-
come separated during one cell division. As a result, each germ cell finally has only
half the number of chromosomes present in the body cells of the species

good healthy growth would not be sufficient to ensure seed. And they knew
that flowers would fail to produce seed unless some of the powdery or sticky
pollen, or flower-dust, gets onto a special part of the flower, the stigma (see
illustration, p. 399). Yet Aristotle and other great thinkers rejected the idea
that there could be "sex" in plants.

It was difficult to think of sex in plants, first for the reason that we com-
monly associate maleness and femaleness with two distinct kinds of individuals
in most familiar animals. In addition, the familiar seed-bearing plants do not
directly bear eggs or sperms. Although the experience of the race had es-
tablished the fact that pollen somehow makes flowers capable of bearing
seeds, it was necessary to wait for the microscope before anybody could know
just what the connection is. So it came about that it was only about two
hundred and fifty years ago that anybody did know just what the pollen has
to do with the "setting" of seed. This was first worked out by a German
botanist and physician, Rudolph Jacob Camerarius (1665-1721), who reported
his discoveries in letters he wrote in 1694.

If we assume that the union of two cells is the essential fact about sex, it is
interesting to note that some of the characteristics of the male and female
gametes appear to be repeated and enlarged, or even exaggerated, in the entire
organism. Maleness shows itself as movement, restlessness, a seeming drive to
go places. We may recognize femaleness in a certain inertness, or remaining

389

TlK' Metiupulitdn Mu.iuiii ^i Alt

THE RITUAL OF FERTILIZING THE DATE

The ancient Assyrians knew that the date palm never bears fruit unless the flower-
dust of the "male" plant reaches the stigmas of the "female" plant. The king started
the work of transferring pollen in a religious ceremony, which was recorded in stone
tablets or monuments. Date-growers in California use essentially the same method
systematically, but without ceremony. (Stone tablet from the palace of Ashur-nasir-pal
II, king of Assyria, 885-860 B.C.)

Amerkmi Museum of Natural Uistory

SEXUAL DIMORPHISM IN INSECTS

The cabbage butterfly, the female having two spots on the front wing, in addition to
the dark tip

in place, in the absorbing of excess food which is normally passed on to the
next generation. And there is almost uniformly a marked difference in size
between the male structures — or even individuals — and the female, the female
being generally the larger. Looked at from this point of view, maleness and
femaleness seem to extend to many traits of plants and animals that are not
directly connected with reproduction.

Secondary Sexual Characters We may see that in both plants and
animals there are many characteristics which have nothing directly to do
either with getting food and growing or with splitting off special reproductive
cells — whether spores or gametes. In connection with producing and dis-
charging eggs and sperms, some of these supplementary structures and proc-
esses seem to get far away from the essentials. We speak of such organs and
activities as secondary sexual characters. The differentiations between male
and female individuals are most striking and elaborate in flying animals —
birds and insects. We can understand these as being in a way related to the
fact that the gametes have to be brought together in a fluid medium. But

Aiiicrican Museum of Natural Uistory

SEXUAL DIMORPHISM IN CRUSTACEANS

Female and male of the fiddler crab, Uca brevifrons

391

lerican Museum or Natural Historj

SECONDARY SEXUAL CHARACTERS AMONG BIRDS
The drab female and gay male, African ostrich

some of these secondary sexual characters are found even among the water-
inhabiting fishes and some of the crustaceans and other invertebrates, as well
as in all classes of vertebrates (see illustrations, p. 391).

Here we see again a certain resemblance between maleness or femaleness
in the individual and the special characteristics of the gametes. There is the
roving disposition of the male, for example, as against the passivity of the
female, or the contrasting aggressiveness and receptivity of the two sexes.
These differences are associated in more complex animals with differences in
nerves and muscles, in sense-organs and the effectors.

Among birds, we are impressed by the extravagant plumage of the peacock,
in contrast with the plain garb of the peahen. In the bird of paradise and in
the domestic fowl, the flashy dress and ornaments of the male are accompanied
by show-off behavior and song. The spurs are related to a fighting temper.
Among mammals, the males seem to go in for beards and ferocious-looking
manes, for horns and large teeth. In many species there is a great difference
in size between the sexes, the male being generally larger and more belligerent
(see illustrations above and opposite).

The floral displays of seed -bearing plants and the specialized spore-
distributing and spore-catching adjustments are so varied that they have
occupied the Ufelong study of many devoted scientists and nature-lovers.
When the facts about seed-bearing plants are described, as they often are, by

392

Ai.,(iiijii ..hi. luiii i)f Naluicil ll.biury

SEXUAL DIMORPHISM IN MAMMALS
Wapiti deer in Northern Colorado

poets rather than by scientists, we are made to see at once the resemblance
between maleness or femaleness in plants and the corresponding characteris-
tics of animals. And this in spite of the great differences between plant be-
havior and animal behavior, and in spite of the great differences in the matter
oi feeling, which is immeasurably more intense in the highest vertebrates than
we can conceive it to be in other species of organisms. The flowering plants
deserve at least a chapter for a survey (see Chapter 20).

In Brief

Unicellular plants and animals reproduce themselves by cell-division;
their protoplasm is potentially immortal.

Cell-division is an essential feature of development, as well as of growth.

In multicellular organisms cell-division results in growth, in the healing of
injuries, or in the regeneration of lost parts, and in the reproduction of new
individuals.

Many species produce specialized cells, or spores, from which new individ-
uals develop; these spores are capable of resisting unfavorable conditions
almost indefinitely.

Many species produce specialized reproductive cells, gametes, which
unite in pairs into zygotes; these, in turn, develop into new individuals.

393

The union of two gametes, a sperm and an egg, is the essential fact of sex-
ual reproduction. It is called fertilization.

In the vertebrates, eggs, discharged into the body cavity by the ovary,
pass through an oviduct before reaching the exterior; sperms, developed ii?
the testes, also pass through a special duct to the exterior.

The distinctive variations in reproductive organs are related to the manner
in which eggs and sperms are brought together and to the way the fertilized
egg cell is nourished.

In the more complex species the gonads — the ovary of the female and the
testes of the male — are both hormone-producing as well as gamete-producing
organs.

Among mammals the embryo develops within the uterus until it attains a
form distinctive of the species.

Many species of plants and animals produce vegetatively, as well as sexually.

Some species of plants and animals reproduce alternately by vegetative
and sexual processes.

Among insects, as among reptiles, birds and mammals, fertilization takes
place within the body of the mother.

At all levels of animal life the male gamete, or sperm, is motile; the female
gamete, or egg cell, is passive and richly supplied with food.

The number of chromosomes present in gametes is half that present in
body cells.

Most familiar plants, as well as animals, reproduce by forming male and
female gametes, that is, sexually.

Among lower forms of animal life there are hermaphroditic species, that is,
forms in which the individual bears both male and female gametes.

Parallel to the differences between the gametes, males are characteristically
restless, roving, searching, aggressive; the females are passive, receptive,
eventually directing their resources to the nourishment of offspring.

Characteristic differences between males and females which have no direct
connection with reproduction are spoken of as secondary sex characteristics.

EXPLORATIONS AND PROJECTS

1 To study reproduction in the ameba, examine several specimens mounted
under a cover-glass, with both low and high magnifications; watch for cell-
division. Sketch different stages in the division. Try to distinguish the nuclei
within. Describe the way the ameba reproduces.

394

2 To study reproduction in the paramecium, prepare slides having numerous
individuals on them. Search for individuals that are dividing; follow one in the
process of fission under low magnification until the process is complete. Note the
length of time it takes. Compare the new individuals as to the oral groove and
other structural characters that may distinguish them. Describe the type of repro

duction in the paramecium.

3 To find out how mitosis, or cell-division, takes place, examine models or
charts showing the several phases in mitosis. To see the various stages of division,
study with the aid of a compound microscope prepared slides of sections ot an
onion root-tip, in which cells reproduce rapidly. Draw and describe the essential

facts in mitosis. • i u

4 To demonstrate regeneration in plants, propagate plants vegetatively by
means of cuttings, tubers, bulbs, corms, rhizomes, runners, budding and grafting.
Make cuttings from healthy plants with a sharp knife and place in moist-sand
flats After roots have formed, transfer new plants to good soil. Transplant tubers,
bulbs, corms, parts of rhizomes, or buds from runners directly into good soil.
Compare these modes of producing new individuals with the regeneration of new
individuals from fragments of flatworms. Compare the new plants produced by
these vegetative means with the original plant from which the organs were

removed. .

5 To find out how mold reproduces, grow a rich colony and examine parts
with the microscope.^ Examine threads and sporangia with low power and with
high power. Place spores on a sterile agar plate, or in a 1 per cent sugar-solution
on a slide, or in some other suitable medium, to find out whether they are capable
of producing new mold plants. (Keep in a warm, moist place for a few days.)
Watch for new threadlike growths emerging from single spores. Describe this

method of reproduction. • . , r

6 To study the egg-laying organs of a hen, dissect out the single left ovary
and oviduct and examine carefully. Describe the essential structures. Where does
fertilization probably take place? Describe the reproductive process in poultry.

7 To see viviparous reproduction in fish, grow guppies under observation in
the laboratory. (The larger fish is the female. When her body becomes swollen,
watch for the very small young to be born. Remove the young immediately to

iFor cuttings use willow, forsythia, privet, geranium, coleus or begonias. For tubers use
potatoes, cinnamon vines or Jerusalem artichokes. For bulbs use tulip, omon hyacinth or
my. For corms use gladiolus, spring beauties or trilliums. For rhizomes use bluegrass, ins,
rhubarb or yarrow. For runners use strawberry or cinquefoil. ., , . ,

Farmers' Bulletin No. 1567, Budding and Grajttng, gives detailed information on pro-
cedures. Different varieties of apple can be grafted onto one tree. Apple, pear and quince can
be grafted onto one another; peach and plum may also be grafted on each other. The cam-
bium layer of the cutting, called the saon, must come in contact with the cambium layer of
the stock to which it is being grafted. In doing cleft grafting apply dormant scions to stock
before the buds begin to swell. Seal cuts with grafting wax.

^To grow mold, expose a slice of bread to the air for ten minutes for some mold spores
to fall on it. Keep in a warm place on moist paper on a plate, covered with a )ar or tumbler.
In a few days black dots (the "fruit-dots", or sporangia) will be seen scattered in the white
fuzzy growth.

395

another aquarium, as the mother fish may soon eat the young.) Compare this
method of reproduction in fish with that observed in most other fishes. Note the
probable mode of fertiUzation in these viviparous fish,

8 To study the reproductive organs of frogs, dissect freshly killed male and
female frogs; locate, examine and describe the spermaries, sperm ducts, ovaries and
oviducts. Note the large size of the ovaries and oviducts. Count the eggs in a
portion of the ovary and estimate the total number in one female frog. From the
study of the internal organs describe reproduction in frogs.

9 To find out how the fetus of a mammal develops within the uterus of the
female, dissect a pregnant guinea-pig, rat or rabbit late in the gestation period.
Note the stretched and enlarged uterus. Find the sac within which each fetus is
located. Note how the placentas are embedded in the uterine wall. Describe
mammalian reproduction.

10 To investigate the reproduction of the hydra, examine living specimens
ander low magnification,^ identify buds in various stages and find individuals
with developed sex organs. Describe the methods by which hydras reproduce.

11 To discover the reproductive organs of moss plants, use living male moss
plants which are distinguished by a cup-shaped tip, female moss plants, and female
moss plants with sporophytes attached. Place the tip of a male plant in a drop of
water on a slide, and with a stirring motion of a dissecting needle tease out the
antheridia (club-shaped organs bearing sperms). Remove the scales from the tip
of a female plant and then dissect out the archegonia on a slide with a needle.
Examine the base of a sporophyte and its attachment to the tip of the female, or
mother, plant. Examine spores from the capsule at the end of a stalk. Crush a
sport capsule over the surface of a dish of diluted Knop's solution' and set aside
for the growth of new individuals. Describe and illustrate methods of reproduc-
tion in mosses.

12 To study reproduction in ferns, grow prothallia from fern spores and
observe microscopically from eight to ten weeks later.^

While prothallia are developing, examine under surfaces of leaves for the sori,
or clusters of sporangia. Crush sporangia on a sHde and examine them and dis-
charged spores with microscope.

Look for antheridia and archegonia on under surfaces of fern prothallia (arche-
gonia just behind the notch; antheridia farther back). Mount prothallium on slide
and look for sperms swimming in the water.

^Hydras can frequently be found on the sides of aquariums set up months earlier with
plants, snails, insects, and pond water collected locally. Cultures of living hydras can be pro-
cured from biological supply houses.

^Knop's solution consists of 1 g each of potassium nitrate, magnesium sulfate, and potas-
sium phosphate, and 3 g of calcium nitrate dissolved in 1 liter of distilled water. Dilute to
■^ strength to grow protonemata of moss.

^Collect mature leaves of polypody, shield, or Christmas fern, with sporangia; dry in
dustproof boxes for a few days. Fill a thoroughly cleaned 3-inch or 4-inch flowerpot with
sphagnum moss or wet toweling; invert in a wet tray and dust fern spores on it; cover outfit
with inverted battery jar. Place culture in a cool place under moderate light. Water with
diluted Knop's solution. Germination should occur in a few days, and prothallia should
mature in from eight to ten weeks.

396

Describe the two methods of reproduction in ferns. Note ways in which they
are aUke and ways in which they are different. Note conditions under which
each takes place. Compare reproductive stages and structures of the fern with
those of the moss.

QUESTIONS

1 In what different ways do unicellular plants and animals reproduce?

2 How does reproduction in one-celled plants and animals differ from that
in many-celled ones.f*

3 In what ways do familiar plants reproduce vegetatively ?

4 Why do we prefer to multiply many domestic varieties of plants by vege-
tative methods.?

5 What different kinds of specialized reproductive cells are formed in
plants ?

6 How do gametes act in reproduction.'' How do male and female gametes
differ from each other.?

7 What are the relative advantages of the mammalian method of reproduc-
tion ? the disadvantages ?

8 In what main groups of animals are male and female individuals distinct
from one another.?

9 In what groups of organisms are individuals male and female.?

10 In what groups of animals does the sex vary periodically or with external
conditions .?

11 What are the stages in the alternation of generations in moss plants? in
fern plants?

12 In what respects is reproduction in ferns more advanced than in mosses?

13 In what groups of animals does fertilization take place within the body
of the female.?

14 What are the relative advantages of fertiHzation within the body of the
female ?

15 How does the number of chromosomes in the gametes compare with the
number in the tissue cells.?

16 What in addition to the gametes do the gonads of the more complex
species produce? How do the gonads influence development.?

17 What are the secondary sex characteristics of familiar birds and mammals?

397

CHAPTER 20 • REPRODUCTION IN FLOWERING PLANTS

1 Can flowering plants reproduce in any other way than by seeds?

2 Can any plants produce seeds without flowers?

3 How does pollen act in a flower?

4 Are the eggs of all flowering plants fertilized inside the flower?

5 Is there anything in animals to correspond to seeds?

6 Is there anything in plants to correspond to the egg of a bird?

7 Do any animals depend upon other species in reproduction, as

flowering plants depend upon insects?

8 Is there anything in animals to correspond to pollen?

By far the most varied in the number of species, and certainly the most
complex, are the flowering, or seed-bearing, plants. Some of them live but a
few weeks of summer weather; others grow to be hundreds of years old. And
they have spread all over the habitable earth. These plants are typically sta-
tionary, firmly rooted in the soil, in contrast to land animals, which move
about freely. Yet they manage to bring about sexual reproduction between
individuals far apart, and to spread their offspring out in all directions ahead
of the free-moving animals. They manage to capture various natural move-
ments that go on about them, both animate and inanimate, just as they have
captured the energy of sunlight through their chlorophyl.

In their formation of gametes, and especially in the mechanism by which
two gametes are brought together, the flowering plants present an amazing
and fascinating variety of forms and structures.

In What Ways Are All Flowers Alike?

The General Idea of a Flower^ Almost anything on a green plant that
is not green catches the attention. There are many leaves and other growths
that arrest the eye; but a flower is a highly speciaUzed structure. Flowers
range in size from an eighth of an inch or less across to perhaps a yard or more.
They dirfer also in shape and relative numbers of parts, as well as in colors.
And they difl"er in their arrangement — in relation to the leaves and in relation
to one another on the stems of a plant (see illustrations, pp. 12 and 31).

The essential organs in all flowers are those that have to do with producing
seeds. The seeds originate from tiny structures called ovules, or "little eggs",
which are borne in special organs at the center of the flower, called carpels —
from a Greek name for fruit, J^arpos.

The single carpel of a flower, or the structure formed by the carpels fused
together, is sometimes called a pistil, from the fancied resemblance to the

iSeeNo. I, p. 414.
398

]n some species each flower has a single carpel. In other species each flower has several carpels,
as in as in

^..

>--

Plum

Milkweed

Bean

Buttercup

Apple

■~.:s^!^

Stiawberry

The two or more carpels in a flower may be quite Each carpel may contain a single ovule, or seed,
distinct, as in the columbine and strawberry, or they as in
may be more or less fused, as in

Tomato

Melon

Lily

Each carpel

may

bear several

ovules,

as in

Cheny

Sunflower

Hazel

Or each carpel may bear very many ovules, as in

y "^fes

Apple

Pea

Larkspur

\^^. f f

Cotton

Poppy

Pumpkin .

apothecary's pestle (see illustration below). The enlarged portion, which
encloses the space that bears the ovule or ovules, is called the ovary — the
same name as that given to the egg-bearing organ in animals. Where the
pistil consists of several carpels, the ovary is often divided into as many com-
partments. The tip of the pistil is called the stigma, meaning "spot", and
it plays an important role in the reproduction of the plant.

Stigma— rO"^

Style- 1 Y

Ovary

(^y-^ Stigma
^ Style

Ovary -

Willow

Squash

'Ovary'
Maize Hollyhock

399

Seeds are borne in the ovary. The stigma may be close to the ovary or
separated from it by a longer or shorter stalk, the style. The stigma may
be simply a rough or sticky surface, or it may be a lobed, hairy, or sticky
expansion.

Anthers

Sweet pea

Willow

Anthers

Apple

Squash

Surrounding the pistil, in most common flowers, are a few to very many
slender stalks with enlarged ends, called the stamens, from a Latin word mean-
ing "thread". In some species, however, the stamens and pistils are in dif-
ferent flowers, or even on different individual plants. The enlargement at

Common ragweed
{Ambrosia elatior)

Ironweed
(Vernonla arbuscula)

Willow
iSalix fragilis)

.. J .. Hercules' club

-y^ 7^ (Aralia spinosa)

Sunflower
{Helianthus annuus)

Pumpkin
(Cucurhita pepo)

Goldenrod
iSolidago
speciosa)

Sagebrush
iAiteniiisia tiidenlata)

Chicory
iCichorium Iniybus)

Stokes' aster
iSlokesia laevis)

Beech
(Betula popuhlolia)

Russian thistle
iSalsola pestiver)

POLLEN GRAINS!

^ After Pollen Grains, by R. P. Wodehouse, copyright McGraw-Hill Book Company.

400

the end of the stamen is the pollen box, or anther, from a Greek word for
flower. The anthers bear sticky or powdery pollen grains, which correspond
to the spores of simpler plants.

The pollen grains resemble the spores of various kinds of simpler plants,
such as mosses and ferns (see illustration, p. 387). And Hke such spores they
normally give rise to a structure that corresponds to a gmnetophyte, as in mosses
and ferns (see page 385). But this is a very small plant that can be seen only
with a microscope, and so is easily overlooked. Moreover, this gametophyte,
which produces only a sperm cell and is therefore considered a male, carries on
its activities for the most part within a flower; and its short life ends in
fertilization.

The ovule contains a large cell which we take to correspond to a spore that
gives rise to a jemale gametophyte. This completes its entire life as a parasite
within the ovule. For these reasons the pistil is sometimes spoken of as the
female organ of the flower.

Where the corolla is a cup or tube, we can usually Where the petals are distinct, their number is usu-
make out a definite number of points or lobes, ally definite for a particular class — three or four
which we take to represent so many petals, as in or five, or a multiple of the number — as in

Morning glory

Potato

Sunflower

Trillium

Mustard

Buttercup

In "double" or other cultivated plants, like dahlias. Outside the corolla a group of greenish, leaflike
the number of petals may be very great, as in parts form a cup or calyx, as in

Peony

Buttercup

Apple

In some families of plants the calyx is hardly dis- And in many species of trees and grasses the en-
tinguishable from the corolla, as in velope is inconspicuous or entirely absent, as in

Star grass

Tulip Dogtooth violet Willow

... ___i__ .. ■!■ ... ■ ■ . t. .

401

Oak

Orchard grass

Accessory Organs of Flowers Surrounding the stamens and pistils in
all the familiar flowers is a ring of colored or white leaflike structures that make
up the corolla, or "crown", of the flower. The separate parts are called petals.

The Ovule as a Female Organ As the ovule develops, two layers of
tissue grow around the large cell on the inside and finally enclose it, leaving a
small opening at the end. In the meantime, the nucleus of the central cell
undergoes two divisions, the second division leaving the number of chromo-
somes reduced by half (see page 385). One of the nuclei enlarges and crowds
the three others to one end, where they eventually die. The enlarged cell
with its haploid nucleus is called the eynbryo sac.

We saw that the reduction in the number of chromosomes is characteristic
of the formation of sexual reproductive cells. The embryo sac, however,
despite its haploid nucleus, is not a germ cell: it corresponds to a spore. Now
the embryo sac nucleus divides, and the new nuclei divide further several
times. The haploid nuclei resulting rearrange themselves, but no cell walls
are formed. One of these nuclei becomes the female gamete and moves
toward the end of the embryo sac near the opening in the ovule. Other nuclei
later take part in the complex processes that accompany fertilization and the
early stages of development. They seem to be related to the nourishment of
the fertilized egg and the young embryo.

Two layers of tissue grow around large cell inside ovule

while nucleus of central cell divides twice

Spore mother
cell dividing

Second division
(reducing)

Mature ovule

Spore

Micropyle

THE OVULE AS A FEMALE ORGAN

402

Reduction division
in spore mother cell

Division of two
haploid nuclei

Formation of four
haploid cells

Four liberated
pollen grains

THE ORIGIN OF POLLEN GRAINS

In the pollen mother-cell the nucleus undergoes two divisions without the formation of
cell-walls. In one of the divisions the chromosomes are reduced to half the normal
number. Around each of the four nuclei a thickened cell-wall is formed. This more
or less rounded cell becomes separated from the others and is a pollen grain

What the earUer gardeners and biologists did not know, and could not know
until certain microscopic studies had been made, is that in "fertilization" a
haploid nucleus from a pollen grain gets into the embryo sac and fuses with
the particular haploid nucleus which we have called the "egg", or female
gamete.

The Anther as the Male Organ With the help of a microscope we can
distinguish inside an anther the cells that are to produce pollen grains (see
illustration above). These pollen mother-cells contain dense, granular pro-
toplasm. In each mother-cell the nucleus divides, and each new nucleus di-
vides again, but no cell-walls are formed. In either the first or the second
division, varying with the species, the number of chromosomes becomes
reduced to the haploid number (see page 386). The four haploid nuclei be-
come separated, and a thickened wall is formed around each, with its
cytoplasm.

In the formation of these "male spores" the mother-cell gives rise to four
spores. In the formation of the embryo-sac nuclei, the original mother-cell
gives rise to only one female nucleus, the other three disappearing. However,
the protoplasmic material is not destroyed, but becomes organized around the
single female nucleus.

We see, then, that in flowering plants the male and female gametophytes
are reduced to single cells. Yet inside these cells very complex activities take
place, leading to the formation of a single gamete in each case — the male and
the female.

403

Two sperm nuclei

Growth nucleus'

Hugh Spencer

POLLEN TUBE

Under suitable conditions, pollen grains sprout like spores, the protoplasm growing
out into a long thread. The haploid nucleus in the pollen divides into two. One of
the nuclei seems to direct the growth of the tube. The other divides again: these
final nuclei are the true sperm, or male, cells

How Does Fertilization Take Place in a Flower?

The Meeting of Gametes^ In most common plants stamens and pistils
are borne in the same flower. Fertilization is nevertheless brought about in
a very roundabout way. The embryo sac remains inside the ovule, as the ovule
remains inside the ovary. All the traveling is done by the pollen.

When the pollen grain alights upon the stigma of a pistil, it absorbs some
of the fluid on the latter. Then a very thin thread of protoplasm grows out
of the pollen grain — the "pollen tube". It is comparatively easy to get pollen
grains of many different kinds to sprout their pollen tubes in a drop of sweet-
ened water, on a microscope slide, and to observe some of the changes that
take place (see illustration above).

The pollen tube normally grows through the style of the pistil into the hol-
low of the ovary. Then it grows through a small hole in the ovule that reaches
toward the embryo sac (see illustration opposite). Pollen tubes appear to be
chemotropic. When the tip comes in contact with the embryo sac, the cell-
wall melts away, and the two sexual nuclei combine. This is the essential fact
of fertilization. The zygote, having the double, or diploid, number of chromo-
somes, is the first cell of a new individual. It corresponds to the fertilized egg
of a fern or moss — or, for that matter, of an animal.

The New Individual^ After fertilization, the mass in the embryo sac
absorbs food from the parent plant and grows into an embryo (see illustration
opposite). The surrounding walls of the ovule become the seed coats. The
ovule, with its embryo sac, thus changes into a seed. In addition to the

iSee No. 2, p. 414. 2 See No. 3, p. 415.

404

Micropyle

Ovule

Pollen tube

Pollen grain

Embryo sac

Stigma

FERTILIZATION IN A FLOWER

A thread of protoplasm grows from the pollen grain on the stigma, penetrates through
the style and through a little opening in the wall of the ovule. When the tip of the
pollen tube reaches the embryo sac, a nucleus of the embryo sac and a nucleus of
the pollen tube unite. This is the essential fact in fertilization

food used by the embryo as it grows to the stage of a ripe seed, other
food materials are accumulated in the ripening seed. These reserves are
either in the embryo tissues or immediately surrounding the embryo — ^in
the so-called endosperm. After the seed sprouts, and before the young plant
is ready to supply itself, the new individual lives on this accumulated reserve
or surplus.

FertiHzation brings about changes in other parts of the flower. The petals
drop off or shrivel away, and usually the stamens also. The ovary begins to
enlarge and at last ripens into the central or the main body of the fruit. In

THE EMBRYO OF A FLOWERING PLANT

The fertilized egg cell passes by a series of cell divisions into a mass that gradually
takes on a definite form. In most species it becomes possible to distinguish the root,
the stem, and the first leaf or leaves

405

some plants the calyx of the flower, and even the enlarged end of the stalk,
the receptacle, may become fused into the fleshy fruit.

In most of the common plants the fruit will not ripen (that is, the ovary
will not continue its development) unless fertilization takes place. But many
plants ripen a seedless fruit; we have varieties of seedless oranges, seedless
grapes and seedless apples. The pineapple and the banana are examples of
fruits that develop without the ovule's being first fertilized. The plantain
and the breadfruit develop a more juicy fruit when the ovary is not fertilized.
In more recent times it has been found that ovaries of tomatoes and other
plants can be stimulated to grow into fruit by means of chemicals related to
the auxins (see page 258).

How Does Pollen Get to the Stigma?

Self-pollenationi In many plants the pollen is carried from the stamen
to the stigma by the growth movements of the parts of the flower. The style,
as it gets longer, may bring the stigma in contact with the anther. Or the
corolla, as it grows and opens, pushes the stamen against the stigma. In some
species the stalk of the flower may bend over as it grows, and so dumps some
pollen from the anther onto the stigma. In some flowers the anther stands
above the stigma, and the pollen is carried over by the action of gravity. Thus
there are many kinds of plants in which the flower may be said to pollenate
itself. This process is called self-pollenation and takes place in such varied
flowers as

Round-leaved
mallow

Sweet pea.

Tomato

Knotweed

Wheat

Obstacles to Self-pollenation There are many plants, however, in which
self-pollenation is quite impossible. In some species the stamens and the
stigmas do not ripen at the same time; self-pollenation is then impossible.
The pollen ripens before the stigma in maize, in the mallows, in many
species of the aster family, in the creeping crowfoot, and in the sage. The
stigmas ripen ahead of the stamens in the common plantain, in the poten-
tilla, or cinquefoil, and in the Oriental grass known as Job's- tears.

^See No. 4 p. 415.
406

In some species stamens and pistils are so placed In many plants the stamens and pistils are borne on
that the pollen cannot get to the stigma, as in different flowers, as in pumpkin end in

In some species of plants the staminate flowers are In some species the flowers are in two or three
borne on one individual and the pistillate flowers forms, with the anthers in one matching the relative
on another, as in position of the stigmas in another, and pollen acts

only on stigmas of corresponding height, as in

Purple loosestiife

Primrose

In some species of plants, if the pollen gets to the stigma of the same flower,
it will not lead to fertilization. The pollen will in some cases result in poorer
seeds than those produced by means of pollen taken from another flower. But
in buckwheat, in most orchids, in certain species of day Hly, and in some
members of the bean family the pollen will not even put out a tube if placed
on the stigma of the same flower.

Cross-poUenation Plants that cannot pollenate themselves depend upon
outside moving bodies to transfer the pollen for them. The most common
moving agency is the wind. That the wind is an effecti\'e agent in pollenation
is seen in the amount of pollen present in the dust at certain seasons of the year
(see illustration, p. 408). Corn, wheat, oats, grasses generally, many of the
common trees, as well as many other plants, depend entirely upon the wind
for their pollenation. Another effective agent in distributing pollen for plants
is moving water. This is illustrated by the tape-grass, or eel-grass {Vallisneria),
which lives near the edges of ponds. The pistillate individuals of the eel-
grass grow up to the surface of the water, where the flowers open. The
staminate individuals remain below; the closed flowers become detached

407

Rutherford Piatt

Single Flower of Elm, Magnified

THE DISTRIBUTION OF POLLEN BY WIND

Staminate Catkin of Birch

The rather dry pollen of our common trees is shed from the stamens in vast quantities
and scattered widely by the wind

and float to the surface in large numbers. Here they open, and as they
come in touch with the exposed stigmas, the pollen is transferred directly.

Next to the wind, the most common moving agents that pollenate flowers
are flying animals, like species of birds and insects that regularly visit flowers.
Certain tropical flowers are said to be pollenated by bats that come to them
for nectar.

In thousands of species of plants the flowers are pollenated by insects,
chiefly varieties of bees and wasps and certain moths and butterflies. All these
insects have sucking mouths, and they all visit flowers that contain nectar.
Some of these insects also use pollen as food. In gathering the pollen or in
sucking nectar the insects rub off pollen on various parts of their bodies; and
when they visit other flowers of the same kind, they then transfer the pollen
to the stigmas (see illustration, p. 410). Many species of flowering plants,
especially among the orchids, depend so completely upon particular insects
that they produce barely enough seeds to maintain themselves.

Flowers as Secondary Sexual Structures We saw that among many
species of animals males and females difl"er from each other strikingly in details
that are only remotely or not at all related to the formation of gametes or to
their conjugation. The flowers that are often so highly specialized in the struc-

408

ture, coloration, and odor of their envelopes may also be considered secondary
sexual characters. They are certainly related to reproduction, and especially
to bringing pollen near the embryo sac. Yet they cannot be considered spe-
cifically male or female, since in most flowers both functions are carried on.

Like some of the display features in animals, floral colors, shapes, odors,
nectaries, may be said to "attract". But they attract chiefly insects rather
than pollen. On the other hand, the sticky or fuzzy stigma of many flowers
is well adapted to catching and holding any pollen that does come by, whether
brought by insects or by the wind.

Another interesting fact about the flowers is their presence only in sporo-
phytes — that is, plant generations that bear asexually produced spores. The
envelopes of flowers and the other accessory structures are nevertheless re-
lated to sexual reproduction, like the secondary sexual characteristics of ani-
mals. And we may consider such structures, in both plants and animals, as
elaborations of extras, or "luxuries", which are possible only when a species
has become so eflicient that it can draw upon a great deal of reserve or surplus
food.

How Do Plants Scatter Their Seed?

Seeds and the Species' During the winter the trees and shrubs are bare.
But millions of other plants perish entirely. Of thousands of species, nothing
remains alive except the hard and inert seeds. It is through their seeds that
these species will renew themselves when conditions again make growth possible.

In the Ufe cycle of a seed-bearing plant, the fruit is the organ within which
the seed originates and ripens. We may consider the great variety of fruit
forms as related to the protection of seed against possible enemies and dangers
— including the danger of remaining right at home. Seeds that are enclosed
in edible fruits are often distributed by animals that eat the fruit and then
discharge from their intestines the uninjured seeds, as in many berries, vibur-
num, and cherrv.

Many fruits open so suddenly, usually by a twisting of the parts of the pod,
that they shoot the seeds to a distance of a yard or more, as in squirting
cucumber, lupins, and monkshood.

Most plants depend upon outside agencies to scatter their seeds for them,
as they do for the distribution of pollen. Seeds that are very small, or that
have expanded winglike surfaces or tufts of hairs, are scattered by the wind,
as in milkweed, clematis, thistle, cottonwood, elm, maple, and linden.

Such fruits or seeds cannot be said to fly, like airplanes or birds — or even to
glide, for they are carried without goal by the winds of chance.

Some fruits have hooks which catch in the fur of passing animals and are

^See No. 5, p. 415.
409

Inez Mct'oinhs, based on photograph by Kutherford Platl

INTERDEPENDENCE OF INSECT AND FLOWER

The bumblebee and the lobelia seem to fit one another in size and in the arrangement
of parts, and to serve one another in their behavior. The insect, going about its
business in one flower after another, leaves on each stigma some of the pollen that
has clung to its hairy body

carried considerable distances, as in cocklebur, sandbur, tick trefoil, cosmos,
and Spanish nettle.

From Generation to Generation When we think of the lowest plants
and animals, we cannot make a sharp distinction between parents and offspring.
In the simplest organisms, as we have seen, a whole life span is included be-
tween one cell-division and the next. During this lifetime there is very little
change in structure: the youngest resemble the oldest in almost everything
but size (see illustration, p. 10). The "mother" cell goes out of existence
at the moment the "daughter" cells come into being: parents and offspring
cannot exist at the same time.

Among the larger seaweeds the expanding vegetative plants bear special
reproductive organs on some of their branches, and discharge tremendous
numbers of eggs and sperms into the water. For every pair of gametes that
conjugate, thousands are destroyed. For every zygote that starts a new in-
di\idual, thousands are destroyed. The mosses and ferns retain the female
gamete within the body of the parent until it is fertilized.

In many species of mosses each green gametophyte ripens but a single egg,
and then it nourishes the nearly parasitic sporophyte to maturity. But then
one sporophyte discharges thousands of spores (see page 387). The ferns seem
about to have soK'ed the problem of li\'ing on dry land. The sporoph)'te has
come to be the prominent generation, with expanded green foliage, with
stems having definite conducting vessels and mechanical structures, and with
fairly good roots. The gametophytes, as we have seen, are flat little plates of
cells (see illustration, page 387). These plants depend upon a wet season only
for the short period during which the sperms swim out and reach the egg
cells. The fertilized egg starts out well nourished within the body of the
gametophyte. The expansive sporophyte contributes to the species a vast
number of spores, with the chance that the wind will carry a few to spots
favorable to starting new gametophytes (see illustration, p. 412).

Infancy in Seed Plants^ Among the most complex plants, structures and
behavior seem to be still further adapted to the advantage of the species.
Spores are produced in relatively small numbers. The gametophytes are
trivial, one-celled structures that remain dependent upon the parent sporo-
phyte. It is through the structures of the sporophyte that pollen spores are
enabled to reach a spot suitable for germination. And the parent sporophyte
also furnishes the structures through which the pollen tube (male gameto-
phyte) reaches the female gametophyte.

The fertilized egg remains within the wall of the gametophyte, but since
this is within the ovule, it is nourished not by the "parent" but by the "grand-
parent"— the sporophyte. And the food which the seed accumulates is also
supplied by the grandparent. The fertilized egg is nourished until the new

iSee No. 6, p. 415.
411

ALTERNATION OF GENERATIONS IN PLANTS

Green moss plants are gametophytes, while ferns and seed plants are sporophytes.
Seed plants surpass ferns and ferns surpass mosses in their ability to manufacture
food, to protect the young, and to adapt themselves to a wide range of living conditions

sporophyte individual is pretty well advanced — in most species until the
leaves, roots, and stem are definitely formed. And it is through the materials
and activities of the grandparent that the seed is protected and finally sent off
into the world on its own.

Parenthood in Seed Plants^ Seed plants have come to be tremendously
effective organisms as absorbers of material and of sun energy. Each individual
expends a considerable part of this accumulated material and energy in ways
that do not help it at all. The making of fiowers and seeds, for example, do not
contribute to the well-being or safety of the plant.

And advance in the scale of life seems to impose additional burdens upon
the organisms. But these are more than compensated by the additional ad-
vantages. In a species that produces well-stored seeds, well-protected seeds,
and seeds well adapted to wide dispersal every individual gets the full benefit of
this additional expenditure of energy at the very beginning of its career. We might
even say that a plant is able to do its life's work effectively just in proportion
as it gets a good start. In doing things for posterity a plant is thus merely
returning to the species what it received from its immediate ancestors.

Of course we are not to suppose that the plants do this or that because they
have any feeling of gratitude, or ability to foresee future needs. In speaking
of the advantages or disadvantages of various types of behavior on the part of
plants, we merely note that certain kinds of doings may actually contribute
to the prosperity of the species, whereas other kinds of doings might lead to
the extinction of the species. Some plants behaved in a certain way in past
ages, and their progeny today occupy the surface of the earth. Other plants
behaved quite otherwise, and we know of them only by the traces they have
left in the ancient rocks of the hills.

In Brief

The essential organs in all flowers, pistils, and stamens are those that have
to do with producing seeds.

The pistil, or female organ, consists of a stigma, a style, and an ovary,
which bears the ovules.

The stamens produce pollen, spores that give rise to male gametophytes,
within the anthers.

Within the ovule a single large cell, the embryo sac, gives rise to the female
gametophyte, the egg-producing organ.

The egg nucleus, generated within the embryo sac, and the sperm nuclei,
generated within the pollen grains, each have but half the number of chro-
mosomes found in the parent tissue cells.

^See No. 7, p. 415.
413

The sperm nuclei are carried \o the egg nucleus within the pollen tube of
the male gametophyte as it grows into the pistil.

Fertilization occurs when the two sexual nuclei combine.

After fertilization the mass of the embryo sac absorbs food and grows into
an embryo; the surrounding walls of the ovule become the seed coats.

Fertilization also brings about the ripening of the ovary into a fruit; in
some plants the calyx and even the receptacle become fused into the fleshy
fruit.

In some species the flowers are usually or always self-pollenated; in others
they are cross-pollenated.

Many flowering plants depend upon external agencies, such as wind or
flying insects, to bring about pollenation.

The coloration, specialized structures and odors of flowers may be consid-
ered as secondary sex characteristics, since they are but remotely connected
with the formation of the gametes.

Thousands of species would not survive the winter but for the hard, inert
seeds through which they renew themselves when conditions again make
growth possible.

Seeds are scattered in a variety of ways.

The offspring of flowering plants have the advantages of a good food supply
and a wide dispersal in the well-protected seeds produced by the parent.

EXPLORATIONS AND PROJECTS

1 To find out how reproduction takes place in flowers, examine some com-
plete, regular, perfect flower, such as a wild rose, sedum, tulip, evening primrose,
geranium, forsythia, apple, lily, or gladiolus. Identify the stamens and the pistil,
and compare these with stamens and pistils of other species. Open the ovary to
locate the ovules; note their attachments and their arrangement in the one or
several carpels. Identify the outer accessory parts, sepals and petals, the parts
respectively of the calyx and the corolla. Identify the various structures in as many
different species as time permits.

2 To find out how pollen carries the sperm to the ovule, germinate pollen
grains and examine under the microscope.^ Note the tubes projecting from some
of the grains. Look for distinguishable structures — the sperm nuclei — within the
protoplasm. Apply a little iodine or other stain to the side of the cover slip, to
make the sperm nuclei more easily visible. Make longitudinal sections of some
pistils to locate pollen tubes within. Relate the growth of the pollen tube to bring-
ing the sperm from the stigma to the ovule within the ovary.

^To germinate pollen grains, rub them from stamens into a drop of a 3 per cent sugar
solution on a microscope slide. Cover with a cover glass and set aside at room temperature
in a moist chamber or germinating dish for twenty-four hours.

414

3 To find out what development takes place in the early formation of a seed,
compare the ovaries of some pea blossoms, some partially developed pods, and
some mature pods of peas. Identify the ovules in the ovary of the blossom; com-
pare them with the ovules in a later stage and with the ripe seeds. Find evidences
that not all the ovules in the pea pods were fertilized. Describe the development
that takes place after fertilization.

4 To discover structures that favor or hinder self-pollenation or that favor
cross-poUenation by wind or by insects, examine as many diflerent varieties of
flowers as are to be had and note:

u. Position of stamens with relation to floral envelope (whether exposed to the
wind or shielded; whether corolla permits the pollen to be dusted off on any casual
contacts, or is arranged so as to permit insects to enter only along special paths).

b. Position of the anthers in relation to the stigma (whether above or on a
lower level, whether on same or on separate flowers).

c. Relative time of ripening of stigma and pollen (whether at the same time
on a given flower, or whether at different times on the same flower).

d. The character and amount of pollen produced.

e. Shape and position of pistil with reference to contact with visiting insects or
with wind-blown pollen.

/. Presence or absence of distinct colors, odor or sweet nectar.

List the structures that favor self-pollenation; those that hinder it; those that
favor insect pollenation; those that favor wind pollenation. List the flowers
showing each of these adaptive structures.

5 To discover how seeds travel, collect as many kinds of seeds as are available
in an open meadow or vacant lot in the fall of the year. Note the various struc-
tures that relate seeds to moving air, animals, or other agencies. Look for seeds or
fruits with hooks or spines; with a pappus, a hairy parachutelike arrangement;
with wings. Look for fruits or pods which, as they ripen and dry, mechanically
throw the seeds; for fruits encased in fleshy pulp. Note any other ways in which
seeds travel. Classify the various kinds of seeds according to the manner or agency
of dispersal.

6 To find the relation of the parts of the seed to the parts of the young
plant, soak seeds of several varieties overnight (use Lima beans, peas, and corn
grains). Remove coat from soaked seeds and carefully lay apart structures found.
Make drawings to show structures and their attachments to one another. Identify
the following: the hilum, the scar of attachment of the seed inside the fruit; the
micropylc, the tiny hole through which the pollen-tube passed into the ovule; the
embryo, or young plant, usually the entire contents of the seed coat; the cotyle-
dons, or seed leaves, the large fleshy structures in such seeds as beans, peas, etc.;
the hypocotyl, the little "tail" to which both cotyledons are attached; and the
epicotyl, or plumule, usually lying between the cotyledons and attached to both.
Compare the parts of embryo in different species.

7 To see how varying amounts of nutrition affect the growth of seedlings,
place a quantity of soaked bean seeds and corn grains in a germinating dish, be-
tween layers of wet blotting paper; cover and set in a warm place. When the seeds

415

have germinated, remove from several of the corn seedlings varying fractions of
the endosperm, up to half or more, leaving some uncut; and remove from several
of the bean seedlings varying fractions of the cotyledon, up to half or more, leav-
ing some undisturbed. Return to the germinating dish; cover and leave for several
days longer. Compare the amount of growth in the various seedlings, with rela-
tion to the amount of endosperm or cotyledon removed. Tabulate the results and
note conclusions.

QUESTIONS

1 What are the essential organs of a flower .f*

2 How do the sperm nuclei within the pollen get from the stigma to the
ovule?

3 In what different ways is pollen transferred from the anthers to the stigma
in flowering plants?

4 What are the advantages of self-pollenation ? of cross-pollenation? What
structures in different plants favor self-pollenation? favor cross-pollenation?

5 In what respects is reproduction in flowering plants more advanced than
that in ferns?

6 How do spores differ from seeds? In what ways are they alike?

7 In what ways are seeds and fertilized eggs alike? different?

8 What are the advantages to a species of producing a relatively large
number of eggs or seeds? the disadvantages?

9 To what risks or dangers are eggs and the young of plants or animals
exposed ?

10 In what sense can plants be said to care for their young?

416

CHAPTER 21 • INFANCY AND PARENTHOOD

1 Why is a cat more helpless at birth than a calf?

2 How does an animal benefit by looking after its young?

3 Why do not all animals take care of their young?

4 Against what do the young of plants and animals have to be pro-

tected?

5 Why do some species produce such tremendous numbers of eggs

or seeds?

6 Can anything be done to hasten or to slow up the d£velopment of

a plant or an animal?

7 Can a kitten's development be hurried by forcing its eyes open?

8 What makes a hen want to sit on the eggs at one time, but not at

another?

Each plant and each animal typically starts life as a single cell. When a
one-celled plant or animal reproduces itself, it gives up absolutely everything —
its own individual existence — to the offspring. Young and old are much aUke;
the new individual at once starts out on its own.

In more complex organisms the initial cell is usually a spore or a zygote;
and the initial stage is in every way different from the adult. Among the
many-celled species the individual that reproduces normally holds on to life,
but the new individual is helpless and dependent.

In what ways are the more complex species better off than the simpler ones?
Why do we call them higher? In what ways are the simplest organisms less
capable of surviving?

Why Do We Consider Some Forms of Life Higher than Others?

Lines of Differentiation Even among the lower classes of many-celled
plants and animals, speciaHzation of function is already beginning. And there
is a corresponding specialization of structures or of organs. In the hydra, for
example, the outer and the inner cell layers behave differently in relation to
external stimuU and in relation to food; the middle layer gives rise to
reproductive cells (see illustration, p. 274). The cells grow and divide, as
in one-celled animals, according to the food supply and other conditions.
But the whole individual continues over a much longer period. The longer
span of life means more development, more ways of getting about, more ways
of getting food — and more dangers to run into, too.

The earliest division of labor in the history of life is probably that between
food-getting and food-using, as in the hydra. We might even go farther back
and think of the entire plant world and the entire animal world as distinct

417

lines of differentiation. One line departs from a more primitive life by special-
izing in vegetative activities; the other specializes in using up food (see
frontispiece.)

Complex systems of organs make possible a greater variety of life outside
the water. We have seen how ferns and seed plants managed to free themselves
from dependence upon constant wetness (see page 386). Each land animal in
effect carries about in its body a section of the primitive ocean, so that it is
able to tolerate a great deal of variation in external moisture. Birds and
mammals maintain a fairly uniform temperature and a fairly uniform rate of
metabolism on the inside, in spite of the great changes in outside temperature.
In these respects the "higher" animals are free from the constant changes in
temperature and moisture, which constantly suspend or stop metabolism in
simpler organisms.

Food-getting, protecting, body-building, and other processes are ap-
parently carried on more efficiently in organisms having specialized organs
and tissues. It is true that in the common plants and animals a considerable
part of the body consists of nonliving materials, such as wood and bark or bone
and shell. Nevertheless such an organism can grow a much greater total
of living matter from a single cell in a season, or in the course of years, than
can a simple organism that is nearly all protoplasm — like an ameba, for
example.

"Division of labor", or specialization of functions, operates in an organism
about as it does in human society. Through becoming specialized, each unit
carries out its particular processes more efficiently, although it neglects others.
It can produce a surplus of its specialized product or services. It can continue
to live, however, only in co-operation with other specialized units. The ex-
changes and co-ordinations of the many different organs use up materials and
energies. This is like the fact that modern industrial and commercial life uses
up more work and materials than older ways in hundreds of tasks that are
not directly "productive" — transporting, communicating, recording, account-
ing, managing, and so on. But these additional needs are more than made up
for by the increased effectiveness of the total.

Thus a blood system consists only in part of living protoplasm; a bone
system carries on very little "growth" after it has reached full size. Yet the
blood makes possible a much higher degree of effective brain and muscle and
gland work in all parts of the body than the various cells could carry on as
independent units. The bones make possible the building up of masses of
protoplasm that could not otherwise hold together. The greater the degree
of specialization, the greater the amount and also the intensity of living.

Vegetative and Reproductive A one-celled organism absorbs and assimi-
lates food, and grows: that is vegetation. Past a certain point the cell does
not grow further, but divides into two cells. While we might call this act

418

American Museum of Natural History

SPECIALIZATION IN VOLVOX

The cells arranged in a single layer as a hollow sphere are connected with one
another by strands of protoplasm. Each cell, with its chlorophyl and vibrating cilia,
carries on all the life functions except reproduction. Certain cells within the hollow
sphere become segregated: these specialize in reproducing new colonies

reproduction, exactly the same process in a many-celled plant or animal results
merely in growing larger, becoming more. When a many-celled organism
produces spores or gametes that we can distinguish from the parent, we can
distinguish reproduction from vegetation. Certain cells now arise that cannot
continue to grow and divide except as an individual distinct from the parent
tissues. Reproduction has become differentiated from vegetation.

This differentiation of reproduction from vegetation, or of offspring from
parent, means that reproduction can become more than replacement. The life
of the parent organism, past the point of reproduction, is in a sense a net gain.

419

It means that more life is going on than merely keeping alive and being re-
placed. As in differentiation of structures and functions in vegetative life,
the specialization seems to yield more than it costs.

In What Ways Do Animals Care for Their Young?

Infancy among Animals^ Among most of the lower animals the mother
lays large numbers of eggs — in the water, on leaves, in the soil — and abandons
them. But toward the upper end of many series of animals we find that the
parents supply much more for the young. The lobster and crayfish mothers
carry the eggs about on their abdominal legs, or swimmerets, and they carry
even the young embryos until they are able to care for themselves (see illustra-
tion below). Among the insects some species abandon their eggs as soon as
they are laid, whereas others supply shelter and food for the young.

In some species of toads the father places the fertilized eggs in his mouth
and keeps them in his croaking pouches until the tadpoles are large enough to
swim away. Several species of newts and salamanders guard the developing
young within the body of the mother until the young are fully formed and able
to shift for themselves.

^See Nos. 1 and 2, p. 432.

*~»((K-J- ''■««?»»«;51pSW™f^-S(^»

United Slates Fish and^Wildlife Service

A "BERRIED" LOBSTER

420

In some species of toads the fertilized
eggs ore carried about on the back of
the female until the tadpoles are able
to swim away. In other species the
male tangles the gelatinous string of
fertilized eggs around his body and
hind legs and carries the offspring
about until the tadpoles swim away.
The male of still other species of toads
carries the hatching eggs about in
his mouth

^ '

^g^^

..JfKmmM

j^r^

\ {

"f:-^

^^«BB

i ■ .,.„...

American Museum of Natural History

MOTHERING AMONG TOADS

Among the reptiles and birds the fertilized egg begins to develop inside
the parent's body; and before the young embryo is removed, it is surrounded
by a mass of food material (the yolk and the white) and a protective shell.

New York Zoological Society

BREEDING HABITS OF SIAMESE FIGHTING FISH

After building a bubble nest for the eggs, the male Siamese fish twists his body
around the body of the female, fertilizing the eggs as she discharges them. As the
eggs drop, both the male and the female take them in their mouths and place them
in the nest. The male then drives the female from the nest and guards the eggs until
they hatch

421

New York Zoological Society

A VIVIPAROUS SNAKE

In the garter snake and in some other species, the fertilized eggs remain within the
body of the mother until the young are developed to the adult form

Most reptiles and some birds leave the eggs, which are hatched by the heat
of the sun or at ordinary temperatures. Most of the common birds, however,
build more or less elaborate nests and keep the eggs warm during hatching.
And most birds care for the fledglings, as well as the eggs. In many species the
young learn their "song" from the parents or other older birds. Domesticated
canaries are sometimes trained as songbirds, or at least protected against un-
desirable noises, since they are very imitative. The feeding of young birds
by the parents is a very interesting operation to watch, as it shows the de-
velopment of rather complex instincts.

Infancy among Mammals We consider the mammals the highest class
of vertebrates — and indeed of all living things. In this class the dependence
of the young upon their parents is carried to the greatest extreme. In the
entire class the female develops special milk glands — hence the name, from
mammae, the breasts or teats. Related to the presence of the milk gland is the
infant's equipment of nerve-and-muscle sucking mechanism, and his complete
dependence upon the milk supply for his nourishment.

In the marsupials the egg hatches within the uterus of the mother, as in
the "true mammals", but the fetus leaves at a rather early stage — in the

422

Growing Period of Various Mammals

ANIMAL

GESTATION PERIOD

MATURING TIME

LIFE SPAN

Mouse

Rat

20-30 days
21 days
30-32 days
9 weeks
8-9 weeks
16 weeks
9 weeks
60-62 days
21-22 weeks
4 months

9 months
8 months

10 months
13 months

11 months
20 months
6 months
270-280 days

6-7 weeks
8-9 weeks
6-9 months

7 months
1-2 years
6 years

10 months-2 years

18 months

1-1^ years

5 years

2 years

5 years

4^ years

8 years
2-4 years
30-35 years
2 years
20-25 years

6 years
3 years
8 years

7 years
12-23 years
30-40 years
15-30 years
13-14 years
12-15 years
30 years

30 years
30 years
40 years
40 years
30-60 years
1 00 years
18 years
75 years +

Rabbit

Guinea pig

Cat

Lion

Dog

Sheep

Pig

Cattle

Deer

Camel

Horse

Monkey {Macacus) . .

largest species, the kangaroos, when only about two inches long. The mother
places the newborn young in the brood-pouch, where they are kept protected
and warm and where they feed on milk from the glands of the mother.

As we go from the lower orders of mammals to the primates, we find that
the young are protected and nourished for a longer period preceding birth.
And the young depend upon their parents for longer and longer periods after
birth also. The table above compares several species of mammals, including
man, in regard to the period of gestation within the mother, the time to sexual
maturity, and the total length of life.

The Embryo in Mammals Among all except the pouched and the egg-
laying mammals (see Appendix A), the embryo remains within the uterus of
the mother until it attains a body form resembling in a general way that of the
adults of the species. While still a tiny spherical mass, suggesting a golfball
with a fluid interior, the fetus attaches itself to the lining of the uterus (see
illustration, p. 383). Outgrowths from the surface cells dig into the lining
by a sort of digestive process, with the result that the fetus comes to be sur-
rounded by lymph from the mother's capillaries. Nourished through the
extensions into the tissues of the uterus, the inner cells of the fetus grow
and divide rapidly, and the mass takes on a definite form — which is steadily
changing (see pages 354-356).

The outer layer, with its extensions, also enlarges and acts as a special
nutritional organ until the embryo completes its development. This special
organ is called the placenta and has multitudes of villi, or outgrowths,
which contain blood vessels. These villi are somewhat like the villi of the

423

.s. A. Grimes, from National Audubon Society

MOTHER BROWN THRASHER FEEDING HER FAMILY

Among most species of birds the new individual depends upon the parents for the
heat that is essential for the development of the embryo; and the newly hatched birds
depend entirely upon the parents for food and protection during the first few weeks

intestines (see page 171); but whereas the villi of the digestive system
extend freely into the food cavity, those of the placenta are embedded
among blood vessels of the uterus. The blood stream of the embryo is sup-
plied with nourishment from the blood stream of the parent, but the two
streams never mingle: they are separated by the two distinct sets of capil-
laries and by lymph spaces.

The embryo is thus in every sense a "parasite", living within the larger
organism. Diffusion is constantly taking place between the blood vessels of
the uterus and the blood vessels of the placenta, which are parts of the
embryo's circulatory system. In this diffusion there is an exchange of dis-
solved food and of dissolved urea and other waste substances resulting from
the metabolism of the embryo. There is also an exchange of dissolved oxygen
and carbon dioxide. The embryo thus depends upon the mother not alone
for its digested food supply, but for its respiration and excretion too — as
well as for mechanical protection and a constant temperature.

The capillaries of the placenta are connected with the blood system of
the embryo by way of arteries and veins running through a flexible "umbilical

424

cord". At birth the placenta detaches itself from the lining of the uterus,
and then the umbilical cord is torn and broken off close to the infant's
abdomen, leaving the familiar scar, or navel.

Behavior of Parents Among the mammals, and to a less degree among
the birds, the long dependence of the young upon their parents is associated
with corresponding behavior of parents and offspring. The hen clucks a danger
signal and the chicks rush to cover under her wings: she enfolds them and
threatens to fight anybody who comes near. The cow licks her calf with her
tongue, and the calf seems to like it. If you try to take the eggs from an eagle's
nest, or to touch the young, you run the risk of a dangerous attack by the
adults. The ferocity of the mothers of the cat family is notorious. And with
most species of birds and mammals, the young behave in relation to the
adults in a manner that impresses us with its fitness, its adaptability to the
needs of the organisms or of the species.

On the whole, the most dependent of infants do normally get off on their
own at last; and then they seem to have a fuller equipment of life tricks and
reserves than those which get on their feet more promptly after birth. There
are great variations as to the length of time that the offspring depend upon

MOTHER LOOKING AFTER HER YOUNG^

The raccoon feeds and protects her young ones until they ore about a year old
1 From Lool^ at Life, by Lynwood Chace. By permission of Alfred A. Knopf, Inc.

425

Kuiopean

KOALA BEAR TOTING HER YOUNG

At eight months of age this young marsupial is no longer carried in the pouch on the
mother's abdomen, and it is able to eat a little of everything that the adults eat.
But the mother still carries the baby around and protects it

the parents among different peoples, and even among different sections of
the same population, as the rural and urban in America.

Infancy in Man^ The length of immaturity and dependency differs
among various races of mankind, and among different types of culture. Chil-
dren among primitive people run about with little direction or supervision
almost as soon as they can walk. In a modern industrial community they are

^See No. 3, p. 432.
426

sometimes closely watched even at their play, until they are well on in years.
These differences in customs are to a degree conventional and more or less
arbitrary. Some of the differences are probably adaptations to extreme con-
ditions of climate, for example, or of crowding. Or they may be related to
natural resources, for when food is abundant young and old are likely to be
carefree and easygoing. It is possible, too, that among races, as among varieties
in some other species of animals, there are inherited or constitutional differ-
ences, as well as those connected with the modes of living.

One of the important differences between human beings and other animals
is the ease with which humans learn, or change their "instincts". Living for a
long time in one place or with other people produces an effect. One becomes
"attached", as we say; one's feelings become involved. And this applies to
parents and young both. We learn to like, we learn to love deeply — ^just as we
learn to dislike unpleasant associations, things and places and people that
hurt or annoy us. Children imitate their elders and they learn many tricks
about getting along, about what to eat and what to avoid. They learn how to
do various things, how to manage various situations.

By the time they are running about and getting acquainted with other
children, our youngsters already have a substantial amount of lore to guide
them, to protect them. If the shelter of older people continues, they may
presumably accumulate more skills, more useful knowledge, more under-
standing of how to deal with various problems and situations. It is for these
reasons that so much effort has been made to increase and to improve school-
ing. The idea has always been to give young people the greatest possible
amount of preparation before they are exposed to the difficulties and dangers
of adult Hfe. And, generally speaking, communities or cultures that have made
the greatest provision for their young have also managed to get fuller and
longer lives for their members.

Are All Plant and Animal Activities Necessary for Living?

Necessities and Extras We depend for our subsistence upon plants and
animals, and eventually upon photosynthesis and nutritive processes. We
are, of course, interested also in the reproduction of plants and animals, and
for two distinct reasons. We want an abundance of the useful plants and ani-
mals, and that means regulating their reproduction. And we also depend more
and more upon grains, fruits, and seeds of plants, rather than on leaves, roots,
and tubers; and we are using greater quantities of eggs and dairy products, as
against the flesh of animals. But people seem to be more fascinated by some
of the "secondary" structures and activities associated with reproduction and
with the preservation of the various species. One does not need to be a scien-
tist or a practical farmer or a technician to be interested in flowers or in the
songs and plumage of birds or in the playing of a cat with her kittens.

427

Is there among other species a similar interest in experiences or activities
that are not essential to life? We do not know how the secondary sexual
characters originated, nor how important they are in maintaining life. But
human beings cannot avoid speculating and wondering and experimenting.
And perhaps we cannot help trying to use the ideas we get to support our
older beliefs or preferences. For example, many secondary characters are
clearly related to sexual reproduction in species that live far from the
original home of life in the ocean. But it does not follow that all secondary
differences between males and females contribute to this result or are other-
wise useful to the species. We know that in many species of moths the two
sexes have different wing patterns and colorings, which have nothing to do
with mating. These insects fly and mate only at night, anyhow, and their
movements are apparently directed by odor. One experimenter glued wings
of males on female bodies and vice versa, and discovered that the male finds
the female just as well.

It is easy for us to "explain" what other living things do as if plants and
animals had feelings and tastes and purposes and enjoyments like our own.
Indeed, we sometimes give them credit for being more able and more clever
than we are ourselves. Perhaps the honeysuckle grew itself flowers in order
to attract insects so as to get them to carry pollen and so help it produce
seeds. Perhaps the male elk grew himself large horns in order to impress the
female of the species or in order to overcome rival males. Perhaps the nightin-
gale grew himself a song box, and the goat grew himself whiskers, in order to
attract the female. Perhaps. But would any of us claim that we grew our-
selves our own attractive or effective colorings, our hands and teeth and other
features, in order to ... ? We really don't know.

Life is possible without the secondary sexual characters, as it is, indeed,
possible without sexual reproduction. Fine feathers and showy flowers are of
themselves without apparent "uses" in the economy of the individual organ-
ism. They consume energy and material, and they seem to contribute noth-
ing toward keeping the individual alive.

In the course of time, however, modes of life seem to have become
more complex and to have involved more complex modes of reproduction.
All the elaborations in plants and animals, whether related to vegetation or to
reproduction, seem to have arisen only when there was a surplus of food and
energy. When a few algal or protozoan cells cling together after cell-division,
instead of drifting apart, there is already the possibility of some surplus. Where
several cells have teamed up, they can increase their total product through
division of labor; and their joint action makes it possible to produce "extras"
— which may or may not become "useful".

We know that in the long run tools and machinery more than pay for
themselves in human organization. But we cannot design, not to say con-

428

struct, such devices until we have on hand a reserve of food, housing, clothing,
materials, and other necessities upon which people can live while they are
producing these extras. In the same way, the extra and often extravagant
developments in plants and animals become possible only where the race or
species is already able to maintain itself and still produce surpluses for "orna-
ment" or "display".

In its exuberance, life sometimes runs off into extravagant, bizarre, and
even wasteful forms. But that is no more astonishing or mysterious than the
more precise and economical adjustments of structures and functions about
which mankind has always marveled. And the uses to which exuberant hu-
man beings put their surpluses of time and energy and materials are often
quite as extravagant or bizarre.

The Human Side From a human point of view, life is, of course, pos-
sible without song or fairy-tales or play-acting or adventures or frills, just as it
is possible without schools or motion pictures or airplanes. Among the most
primitive of humans however, there is a disposition to ornament or decorate,
to sing and to dance, and to tell fish stories. The amount of such "play"
in the lives of people depends largely on how much free time and energy and
materials are available after food and other necessities have been assured.

The distinctive things we remember about the past, or that we find in-
teresting in strange peoples, are their art, music, dance, oratory, fiction,
drama, poetry, architecture, decorations. The rise and fall of civilizations have
been inseparable from the cultures of peoples, from the skill with which they
have kept themselves well and supplied with the essentials, from the uses that
they have made of their surpluses. In human life it is the play of fancy and the
creation of beautiful accessories to life that matter — the dreams and religions
and sciences and philosophies. And in particular individuals it is these things
that really mean most to us.

These distinctly human expressions of life trace back to savagery. Savages
were able to make slow accumulations of surpluses, as well as of past experience,
by continuing to live together in groups or as families. We cannot say that
primitive men and women decided to look after helpless infants, or to cling
together after the mating season, because they saw some advantage in doing so.
It is more reasonable to assume that the earliest associations of males and females
or of parents and young were unconscious or "instinctive". They appear to
be so with other species. Man is a social animal: human beings apparently
preferred companionship to solitude before anybody thought about it.

The association of individuals of all ages in a co-operative group results in
developing affections and mutual regard and consideration. However family
or social life first started, we may reasonably suppose that it continued among
human beings and expanded because it yields practical advantages and in-
creasing satisfactions — because it adds to the life of persons. In his individual

429

development a person ordinarily acquires attachments to those close by, and
as he grows up he attaches himself to more groups. And he comes normally to
feel himself a member of an ever larger group. He depends upon others and
comes to help others in ways that create more satisfaction for all than would
be possible if each tried to live alone.

The Family and Civilization All the records we have of human living
show that, whatever the form ot society, people always lived in families. The
individual is born into the family, he is shaped by the family, and he nor-
mally expresses himself as an independent adult through the family. All
social life, then, rests upon the family, which first of all nurtures and protects
the infant. The amount of care given to the child determines the degree of
social development. And this is also an index of social development. That is,
the more advanced a civilization is, the more it uses its resources for the
benefit of children and youth. And the more effectively any civilization
serves its children and youth, the better off is the entire community likely
to be.

It is a sound principle for any civilization to protect and free its youth,
but there is no simple rule for applying this principle. It is a mistake, for
example, to assume that postponing the problems and responsibilities of life
will itself ensure advantages for the protected individuals. Boys and girls
who have all their needs supplied and who are as "free" as babies from any
obligations are likely to grow up into rather helpless and useless persons whom
nobody likes but themselves.

For over a hundred years in this country thoughtful people have recognized
that protecting the health and development of children hnngs general benefits.
Schooling and legal protection are of public concern, not merely privileges
for those who can afford them. Training and educating children result in the
well-being and happiness of the whole community. But it does not follow
that every individual will gain from every additional year of schooling, or will
be better off as an adult, or a better member of the family or the community,
because of more schooling. For schooling, past a certain point, like food or
medicine or clothing, has to be suited to the particular individual. And it has
to be suited to the kind of culture in which he is to live.

To be effective and cumulative, the gains of civilization have to reach
down to the infant long before the child can take part in schools or clinics or
radio concerts. Most of our devices for better living act upon the individual
through the family. Health services attempt to reach the child before he is
born, through maternity clinics and through the education of parents. The
nutrition of children before school age has come to be a matter of public con-
cern, especially in time of war. Every child brings with him to school or
kindergarten, out of his home, a multitude of conditionings and attitudes
that influence the way he adjusts himself to social living. Some children

430

overcome the handicaps of homes that are lacking in material and cultural
resources with great difficulty; and some never do.

A single measure of the social and the organic advantages of providing
children with more care and services may be seen in varying birth rates.
Among the vertebrates that do the least for their offspring, each female pro-
duces and distributes thousands, even hundreds of thousands, of eggs, and so
contributes to keeping the species alive — that is, she so replaces the adults.
Among the mammals and birds each female produces a few or only one or two
young at a time, and so the species maintains itself.

Among human beings a mother bears from a \'ery few to twenty or more in
the course of her life. But in some types of social life it takes a dozen or more
children per family to keep the population constant, whereas in other types
an axerage of about three per family can maintain the population. Where the
young are well cared for, adults find many interesting things to do besides
bear many children — and bury most of them. Or, from another point of
view, where there are only a few young, the adults can furnish them the best
of care and preparation and still have more time for themselves to spend in
useful and interesting ways; at the same time each developing individual can
have more resources and better preparation for using the adult years in pro-
ductive and satisfying ways.

In Brief

Accompanying the ascent of plant and anim.al life from the lowest to the
highest forms, there is an increase in the dependence of the offspring upon
the parent.

In more complex species the individual remains relatively longer dependent
upon the previous generation, and is in turn better equipped in development,
and often in reserves of food, to li\'e in a more complex en\'ironment.

Among the mammals and to a less degree among the birds, the long de-
pendence of the young upon their parents is associated with a corresponding
behavior of parents and offspring.

In the higher forms of life the species generally maintain themselves with
relatively fewer offspring.

In advancing civilizations, as in advancing forms of life, the extent to
which each generation provides services and reserves for the offspring is re-
lated to the level of development.

All social life rests upon the family, which first of all nurtures and protects
the infant.

To be effective and cumulative, the gains of civilization have to result in
improved conditions for the young.

431

EXPLORATIONS AND PROJECTS

1 To discover to what extent guppies care for their young, raise some under
observation. Compare the activities of the parents in relation to the young with
the conditions that you would furnish to ensure survival of the young. Compare
the parenthood of guppies with that of domestic animals with which you are
familiar.

2 To study the behavior of birds in rearing and caring for their young, locate
a pair of birds that are building their nest (in the spring). Watch activities of the
birds from day to day; note when the first egg appears; note when the female
starts sitting on the eggs; note what the male does. Record date when first egg
hatches and, if possible without disturbing the family, take a picture of the young.
Continue daily observations until the young have left the nest. Keep definite
records, with pictures if possible, to show successive stages in the development of
the young birds. Note factors in the behavior of the parents that seem related to
(a) self-protection; (b) welfare of offspring; (c) other possible "values". Note
factors in behavior of young that seem related to (a) their dependence, or helpless-
ness; (b) their progressive adjustment, or independence.

3 To survey the variety of practices among human beings in relation to
infancy, find out what is available regarding parent-child relationships among
different peoples. Note what most primitive people do with or for their young.
Contrast types of education, guidance, and regulation of children in a primitive
tribe with corresponding services of our time. Compare the kinds of parental care
given by various sections of our own population in guarding the health of their
children; in helping their children prepare for their vocations or professions.
Relate differences to probable causes.

QUESTIONS

1 In what different ways do animals care for their young?

2 What are the advantages to a species of having the offspring become self-
sustaining at the earliest possible mpment.'* the disadvantages?

3 In what respects is human infancy like that of other animals? In what
ways different?

4 What are the advantages of the early parental care provided by birds and
mammals? the disadvantages?

5 How is the duration of infancy in man related to the civiHzations he has
developed ? i

432

UNIT FIVE — REVIEW • HOW DO LIVING THINGS ORIGINATE?

Everybody has known for centuries that chickens come from hen's eggs
and that great oaks from little acorns grow. But not everybody knows that
living things come only from other Uving things more or less like them. And
until comparatively recent times, hardly anybody could be sure of this. For
there are endless tales of maggots coming out of decaying meat, of horsehairs
turning into worms, and of mud becoming converted into eels or frogs. In-
deed, many sober-minded persons had reported seeing such things happen
under their very eyes.

Still more difficult has it been to reach clear notions as to just what goes
on in the egg to convert it into a chicken; or as to what happens to make the
acorn be what it is, with its wonderful capacity to grow at all, or to grow into
an oak and nothing else. It has seemed reasonable to ask, Is there a preformed
miniature hen inside the egg? Or does formless matter become changed into
the organized bird? But we have learned enough to see that the answer is
neither one nor the other. There is indeed no miniature hen. But neither
is the living part of the egg formless. It is a highly complex and highly special-
ized bit of matter that becomes a particular hen, of a particular breed, through
an orderly series of changes. And every individual plant and animal passes
through an orderly series of changes in much the same way. The transforma-
tion of a microscopic germ into an individual involves growth — increase in
the amount of protoplasm. And it involves development, a process of becom-
ing progressively different.

We accept the familiar fact that wounds and bruises heal. But we are im-
pressed when we see missing organs replaced, even to the extent of making
"new individuals" out of fragments of old individuals. These various kinds
of happenings, however, are essentially of the same order. We may think of
regeneration of common plants and of a few animals as a special aspect of
growth: new cells are formed by cell-division. Vegetative propagation or
reproduction is an extension of the fact of growth and repair of tissue. More
highly specialized is the formation, among most common plants and some
animals, of buds or outgrowths which can develop into independent indi-
viduals.

In general, the making of new Individuals Is closely related to the fact
that no living beings can continue to live forever. We may think of repro-
duction as the continuing of life processes from individual to individual or
from generation to generation. Plants and animals almost universally produce
special structures or stages that keep "alive" under conditions that do not
permit normal metabolism. Spores, seeds, pupae, cysts, protected eggs,
survive drought or cold or heat in what is essentially suspended, or extremely
reduced, metaboHsm. Whatever goes on inside such structures is more or less

433

independent of external conditions. They are, so to say, means for bridging
a special interval of time. And sometimes they also span space, as in the case
of migratory spores or the seeds of many species.

As we survey life forms from the smallest and simplest to the familiar
and complex animals most like ourselves, we see a progressive increase in the
amount of differentiation that takes place during the individual's develop-
ment. That is, there come to be more kinds of cells, more kinds of organs and
tissues. This differentiation includes the appearance of specialized repro-
ductive structures and processes. These culminate in sexual, as distinguished
from vegetative or asexual, reproduction. In this process, among plants as
among animals, two germ cells or units of protoplasm unite into one, which
becomes the beginning of a new individual.

In the simplest forms of sexual reproduction, almost any cell may act as a
gamete. But there is a progressive differentiation of gametes into male and
female. The two gametes differ in the simplest forms chiefly in size. But in
later forms they show other distinctive characters, such as relative motility
and relative amount of accumulated food material. There appear highly
specialized gamete-bearing structures, with various adaptations to the distri-
bution of gametes and to the bringing together of sperm cells and tgg cells.

Along with speciaHzation of gametes there is a progressive development
of secondary sexual characters. These involve, among the more complex
members of the various plant and animal phyla, modes of behavior that dis-
tinguish the male and the female of the species. And there is further develop-
ment of specialized structures and modes of behavior that have to do with the
protection of zygotes and their distribution.

In the higher vertebrates, organs and processes related to perpetuating the
species develop side by side with organs and processes that increasingly free
the organisms from external conditions and dangers. And from a human point
of view, there is a tremendous increase of free activity that brings satisfac-
tions over and above merely keeping alive. There is in particular the excep-
tionally long period of childhood, in which relative freedom and security make
it possible to develop talents and interests of great personal and community
significance.

434

UNIT SIX

How Did Life Begin?

1 How did life begin?

2 Did all kinds of living things begin at the same time?

3 Is there life anywhere else in the universe besides on our earth?

4 How con we tell about the kinds of life that there were in very early

times?

5 Has the earth always been populated with the same kinds of plants

and animals?

6 Can living things come into being today from non-living materials?

7 Why are there not the same kinds of plants and animals in different

parts of the world that have the same climate?

8 What kinds of characteristics are inherited? What kinds are not?

9 How can we tell that distinct kinds of plants or of animals are related?
10 How do we create new kinds of plants or animals?

From what we know it is reasonable to believe that all things living today
are the direct descendants of similar plants and animals — that they came from
parents. And we may assume that these ancestors also came from parents,
and so on back for generations and for centuries. But this process of living and
reproducing similar offspring could not have been going on forever. For
there is good reason to believe that at some time in the past the conditions
on the surface of the earth were not suitable for any of the existing plants and
animals. There must, then, have been a time when there were no plants or
animals at all. What were the ancestors of present-day species? How did
life start in the first place?

We expect different species of plants and animals to inhabit different
climates. But the tropical animals of Africa are different from the tropical
animals of America. And the inhabitants of the southern Temperate Zones
are different from those of the northern Temperate Zones. Did the ancestors
of these different groups come into existence separately? That may well have
been, for all we can tell. We are puzzled still further by another fact: al-
though these widely distributed species are different, they have in common
very much that is apparently unrelated to their conditions and modes of living;
and yet they seem to develop along the same basic pattern.

We assume from our daily observations that every living thing reproduces
its own kind — that figs come from fig trees and kittens from cats. Human
children generally resemble their parents more than other members of the
species. Brothers and sisters resemble each other more than they do their
cousins. But then, even the offspring of the same parents are not exactly

435

alike. In fact, we can find differences even between twins. Dees this varia-
tion continue, for any species, in any particular direction? Is there steady
improvement or steady deterioration? Does any species, in the course of time,
show more and more or less and less of any particular trait? If the actual
forms of life come to difler as time goes on, the process must be very slow. For
we do not observe such changes in a lifetime, nor have we any records of sev-
eral thousand years of human history to answer these questions with assurance.

Certain evidences, however, leave no doubt that there formerly ex-
isted species which no longer exist: these are the fossils. And there is reason
to believe that at various periods in the past the plant and animal species of
today did not exist at all. What is the connection between the species of the
present and the utterly different species of the past? Or did each species come
into being independently of the others?

We cannot help wondering, for example, how life came into being or
how it came to be what it is. More practical questions concern the sources
of human qualities, the possible relation between an individual's character-
istics and the characteristics and conduct of his parents. How can we preserve
useful plants and animals against deterioration? How can we improve the
qualities of domestic plants and animals?

Where did mankind come from? In what way is man related to the rest
of life? What is man's destiny? How can we get dependable answers to
these questions? What practical difference would the answers to such ques-
tions make?

436

CHAPTER 22 • OPINIONS ON THE BEGINNINGS OF LIFE

1 If all life comes from life, where did the first come from?

2 Was there only one form of life at the beginnmg, or were there

many different species?

3 Did life start in all parts of the world or in one region and then

migrate to other places?

4 If life could start by itself at one time, why can it not start at

another time, or in various places?

5 If life had a beginning, then is it not likely to come to an end?

6 If life originated from nonliving matter, would it not be possible

to create life artificially?

7 Has life originated on other planets or in other parts of the uni-

verse?

8 Are there any things that stand between Hving and not-living?

9 Could life have come to the earth from some other planet?

Every primitive people has its own explanation of the source of life and of
the nature of life. The god on the sun brought life down to the earth. The
daughter of the ocean came up with life. A great bird came from over the
sea, with the eggs and seeds of all the different species. It was the sunlight
acting on the mud. It was an invisible spirit, "a breath", that entered the
clay and made it live.

The notion of "breathing life" into lifeless matter is very old. Man's
early conflicts with other living things— larger animals, lions or bears — im-
pressed him with the greater amount of "life" which they had. Heavy
breathing is the very sign of a powerful and dangerous enemy. The last
breath of a dying person is often a heavy expiration. And when the breath
goes, life ends.

The creation myths of primitive peoples were all very much alike, except
for the names of the gods and the symbols employed. How do they differ
from our modern answers? In what way are modern answers better? How,
indeed, can we know what happened so far in the past?

How Can We Know about Life In the Past?

Before We Were Born^ What happened before our time or outside our
experience we have to learn from others, usually. If we trust those who tell
us, we believe. If strangers or people we dislike tell us, we generally do not
believe. As we grow older, however, we may find that our authorities often
know only what others told them. Or that, like ourselves and other human

^See No. 1, p. 449
437

beings, they are sometimes mistaken. Then we want evidence that is more
reliable than goodwill or sincerity. What kind of evidence do we want?
What kind is possible?

We can know about the past, and especially about events that occurred
before any human being could report or record them, only by interpreting
significant facts. But the only facts we have are about present conditions in
the world and about processes now going on. What can present facts tell us
about the past?

The facts themselves tell us nothing. They take on meaning only as we
ourselves make up our minds as to how things come to happen. If we make
certain assumptions about the workings of the world, the facts tell us one
thing; if we make other assumptions, the same facts tell us something quite
different. We know, for example, that the farther we dig into the earth, the
hotter it gets. One person concludes that when the earth was made, the core
was made hot and the crust cold. Another, from the same "facts", declares
that something is happening inside the earth to generate heat. A third might
say, "The earth must have been very hot at one time, and it hasn't completely
cooled yet". Or take the fact that brooks and rivers wear away soil and rocks,
which later settle to the bottoms of lakes and ponds and oceans; or the fact
that rocks are found in layers of different thicknesses, and at various angles.
One person says, "When the earth was made, parts of it were laid in hori-
zontal layers and other parts were made with layers slanting at various angles".
Another person might say, "In the course of time sediment became hardened
into rock; some layers took much longer to form than others; the character
of the sediment varied from time to time; something must have pushed the
horizontal layers out of place".

Choice of Assumptions We all make assumptions about the nature of
the world, about why things happen as they do. But we do not all make the
same assumptions. In these imagined cases one observer seems to assume that
"the world was made" once and for all and has remained as it is from the be-
ginning. Another seems to assume that what we see today is the present state
in a long process, that what is has come naturally out of what was. We are
apparently free to assume, or "believe", whatever we wish. But the choice
we make is not entirely a matter of taste or of religion. For our assumptions
turn out to be of great practical importance.

In all practical studies — agriculture and engineering, medicine and states-
manship, business and housekeeping — three sets of problems have to be solved:
(1) How can we cause desirable changes to taJ^e place? (2) How can we prevent
undesirable changes from talking place? (3) How can we best meet unavoidable
changes?

To solve such problems, however, we must first settle the "theoretical"
question How do things wor)(? What are we to assume about the world? We

438

can shrug our shoulders and say, "Anything might happen; there is no way
of knowing". But it appears to be more profitable in every way to assume
that all happenings are related, that there is a connection between what
happens today and what happened yesterday, that the materials and forces
operate consistently and not erratically. We do better by depending upon
the consistencies which we can observe — that is, upon experience. That helps
us to interpret the past, as well as to plan the future.

Everybody does probably assume that there is an order and consistency in
the happenings of the world. If one really believed that "anything can hap-
pen" without regard to what had happened before, he would be living in a
world that had no certainties in it whate\'er, in which you could not be sure
that food would ever reach your mouth or that it would do inside you today
what it did yesterday. The difficulty comes when we ask questions about
things that are not familiar; and when thinking becomes difficult, some of
us give up. At any rate, we do assume that in the past things happened as
they do now; water dissolved some substances but not others; gravity and
light and chemical processes acted then as they do now; gold has always been
heavier than iron and it has always been more resistant to acids. It is these
observed consistencies that give us a clue to what the world was like, probably,
thousands and millions of years ago — if we assume that consistency itself is
permanent.

Has Life Always Existed? Year after year we may see fish hatch from
eggs, and oaks grow from acorns. Without examining every single fish or every
single oak, we say, "Life comes from life". Probably everyone has asked,
more or less seriously, "Which came first, the hen or the egg?'' Many reason-
able answers may be thinkable. We are unable, however, to test such answers
in a scientific way. We cannot get back to the beginnings and observe what
happened. Records of the past are incomplete. One of the easiest ways to
dispose of the hen-and-egg question is to say that there is no problem. If we
assume, for example, that the different kinds of plants and animals have always
existed, we make it unnecessary to decide which came first, or whether there
was ever a time when living things did not exist.

There is something to be said for that view. When we look about us, we
are impressed with the constant repetition of particular events. Night follows
day, the seasons roll on year after year, the planets swing around the sun,
again and again and again. Birth, growth, death, and decay follow over and
over and over. When we look more closely at the materials of the world, we
see constant transformations in endless cycles. Every speck of water moves
from the clouds to the earth, from the earth to the oceans, from the oceans
to the air, and again into the clouds, endlessly. A particle of carbon goes from
the air into the solid structure of a plant, from wood to the fire. Or it goes
from a bit of starch in a potato into the blood of an animal, into some brain

439

FOR EVER AND EVER

From our limited experience we conclude that eggs and hens alternated for many,
many years before we arrived, and that they will continue to alternate long after wc
are gone. Looking forward we see world without end; looking backward we see
world without beginning. That illustrates about all we mean by always, and about
all we know of natural law

perhaps, and there burns up and eventually returns to the atmosphere, having
furnished energy for the happy thought of a poet. All our knowledge, all our
certainties, come in fact from our experience with repetitions. What happens
the same way again and again and again gives us our feeling of constancy,
order, permanence. Things are and they continue to be the same — yesterday,
today, and forever. We cannot imagine a time when things were really
different, except in detail. With respect to plants and animals specifically, like
produces like. We see no exceptions, and we conclude that it must always
have been so.

Yet, from a study of the earth's crust and from a study of what is hap-
pening to stars and planets, we know that there must have been a time during
the formation of the earth when the temperature was too high for life. The
water was probably in the form of vapor, so that the earth was also too dry to
support life. No food was available. Sometime later — many many thou-
sands of years — living things were present. The scientist wonders what hap-
pened during that interval, for it was then that "life" began upon this earth.

Life from Afar One theory supposes that the first living germs came
floating through space from other planets, and found upon the earth a favor-
able habitation. Life germs took hold, and in time took on the many forms of
plants and of animals. We can imagine spores small enough to be carried
through space, pushed by beams of light — some of them falling at last upon the
earth and establishing themselves as living protoplasm. This theory has to
meet many difficulties. These are: the intense cold in the empty space be-
yond the earth, the absence of moisture, the extremely long t'me that it would
take anything to come from the nearest system beyond our sun, and perhaps
the destructive effects of the ultraviolet light.

To assume that life came from some other galaxy or solar system is merely

440

to push the problem back a few million years. This theory tells us nothing
about how living matter could have arisen in the first place. It accepts the
appearance of life as of one date rather than another. A further difficulty with
this theory is that it tells us nothing about particular forms of life. It merely
offers a "germ" or "spore", which in due course came to be this species and
that species and another species.

We cannot harmonize what we know of the earth and its past and what we
know of other bodies in space with the idea that life has "always" existed,
nor with the idea that it came in some form from another world.

How Can We Know about the Beginnings of Life?

Two Distinct Questions We know that a particular robin or radish
came from a particular egg or seed. When we ask how life started, we raise
two distinct questions.

Sometimes our question means, What is the origin of particular species —
horses, for example, or oaks? This question is a scientific one, for it has to do
with facts: When did bees first appear, or seed plants? We can compare similar
plants and animals from different regions. We can compare similar forms
that lived at different times in the past. From the facts so gathered, we can
infer a coherent, even if incomplete, story of events, just as the historian or
the detective pieces together bits of evidence into a consistent, although in-
complete, story of "what must have happened". We may thus reasonably
attempt a scientific answer to the question "How did different species arise?"

Sometimes, however, our question as to the origin of life refers to that
peculiar something about all plants and animals which somehow distinguishes
living things from all others. This is a question about which we can speculate
or argue, but not one about which we can readily make experiments or observe
conclusive facts. The very question presupposes that life exists apart from
living objects or apart from matter and energy. The question is in some
ways like the question What becomes of the reflection in the mirror when the
lights go out? or What becomes of your lap when you stand up?

Vitalism All that we know about life is what we know about living plants
and animals. We know that animals and plants assimilate food and grow, that
they respond to external disturbances by movements and by chemical changes,
that they reproduce themselves. We sum up what we know about millions
of plants and animals by saying — for convenience only — life increases in
amount, life responds to changes, life reproduces itself.

We can study more closely the activities of particular living things. We
can then break some of the facts down into simpler and more familiar facts.
We can see that solution, osmosis, oxidation, evaporation, diffusion, and other
physical and chemical processes go on in organisms. We are confident, from

441

E!r?:?fi!i;

JUDGING THE AGE OF THE ROCKS

We can see rivers cutting gullies through layer after layer of soil and rock. We as-
sume that rivers produced gorges and canyons in the same way through the ages.
We can see lakes, and even the seashore, filling up with silt. We assume that the
upper layers of mud and rock are more recent than the deeper layers

After Neumayr

LATER SPECIES DIFFER FROM THEIR PREDECESSORS

Thousands of pond-snail shells dug out of mountains in Slavonic, at different levels,
were arranged in order from the oldest to the most recent. They showed increasing
departure from the oldest type; and the most recent resembled most closely the
forms still living in the mountain lakes

our Studies, that the total energy output of an organism balances exactly the
total energy income. Similarly, we find that the total material growth and
output of a Hving thing balances exactly the material income. From a purely
physical or chemical point of view, "vitality" is neither a particular kind of
matter nor a particular kind of energy. Yet we are sure that a living organism
is different from the same organism dead.

While we are thus unable, in a strictly scientific sense, to locate or manipu-
late any vital principle, many nevertheless choose to "believe" that there is
such a something. For it is often convenient to explain what happens as if
such a principle were actually at work. In the past scientists spoke of caloric
or of phlogiston to explain various happenings or appearances associated with
fire and heat, just as in earlier times "spirits" explained sickness, thunder, and
other mysterious happenings. This is not to say that a vital principle does
not exist. It is to say only that when we do choose to believe in something of
this nature, we owe it to ourselves to recognize that we are dealing with a
supposition, or hypothesis, not a fact.

Did Life Originate from the Not-Living?

The Scientist's Dilemma^ Scientists reject the sun myths and ocean
myths of ancient times. They treat modern tales of the "spontaneous" trans-
formation of rubbish and dirty water into worms or mice as examples of false
inference or of faulty observation. Nor will most scientists admit that life
has "always" existed on the earth or that it came into being through a "mir-
acle". That is, we cannot admit that there has ever been any violation of
those orderly relationships between substances and forces which we call the
"laws of nature". Nevertheless, scientists are obliged to assume that life
originated from nonliving matter. Life did and still does so originate.

Life out of Nonliving Through photosynthesis lifeless water and carbon
dioxide become starch and sugar. Through the oxidation of sugar chemical

iSee Nos. 2 and 3, p. 449.
443

,* ■^.'

SPECIES LIVING TODAY DIFFER FROM THOSE OF THE PAST

Just as there are many kinds of bears or bananas living today, the fossils show us
that there were in the past many kinds of plant and animals which strongly resembled
present-day species, yet differed from them in many ways

energy becomes muscular action. It is true tiiat lifeless matter is transformed
into starch and into muscular action only by existing organisms. But in the
course of a century chemists have been converting such lifeless matter into
more and more complex carbon compounds and nitrogen compounds of kinds
that have not been found in nature except as' parts of plants and animals (see
page 99). Lately chemists have made synthetically compounds related to
proteins and have even duplicated compounds of the vitamin and hormone

type.

In recent times chemists have shown that under certain conditions of tem-
perature and light and dilution, some of the simpler "organic" molecules
arise "spontaneously". These conditions set up in the laboratory are prob-
ably like those that existed ages ago before there were any organisms, when the
oceans were warmer and less salty than at present. These facts make it seem
reasonable to suppose that there first appeared various molecules of sugars and
proteins and fats — substances that are basic in protoplasm. Such compounds
by themselves are not, of course, Hving. Yet combinations of such compounds
behave in ways that suggest "life".

These findings of biochemists support the hypothesis that compounds,
becoming more and more complex, lead in time to mixtures and combinations
that approach the living. We cannot say that life arises spontaneously at a
particular time. But it is reasonable to think that over a long period life
evolved out of forms of matter which had not existed in earlier stages of the
earth's history.

Between Living and Nonliving On the basis of his "germ theory" of
communicable, or infectious, diseases, Pasteur managed the dramatic cure of
Httle Joseph Meister, bitten by a mad dog. He was unable, however, to find
the "germ" of rabies, and concluded that it was too small to be seen with any
microscope. Later it was found that this virulent or poisonous something
would pass through the pores of a clay or porcelain filter, which are too small
to let the smallest visible particles pass through. By the end of the century a
number of "filterable viruses" were known to cause infectious diseases. In

444

Wendell M. Stanley and Journal ul ttiuluyicul Vhemiatry

BETWEEN LIVING AND NOT-LIVING

Seen through an electron microscope (right), tobacco-mosaic virus suggests "microbes".
Yet it seems to have definite chemical composition, since it crystallizes like a non-
living salt (left), although, like living protoplasm, it is able to assimilate foreign matter

this group of diseases are hoof-and- mouth disease of cattle, yellow fever, small-
pox, measles, mumps, influenza, encephalitis, infantile paralysis, and the so-
called mosaic diseases of tobacco and other plants.

Like living bacteria, a virus may increase in quantity by feeding at the
expense of other substances — in the case of the mosaic diseases, the materials
of a living plant or animal body. A virus thus grows and reproduces itself,
becoming more and more. In some respects, however, a virus behaves like a
large molecule of protein. It has no discoverable structure, such as the simplest
of plants and animals have. A virus seems thus to be a distinct chemical sub-
stance which may form crystals, and may conceivably arise without the
previous action of life. And yet such a substance shares some of the charac-
teristics of living matter.

In 1918, the Canadian Felix d'Herelle (1873- ), a bacteriologist,
started an investigation on just what happens to overcome the living bac-
teria when a person recovers from dysentery. D'Herelle separated out a
substance that destroys and actually dissolves the bacteria. He called this
something bacteriophage — that is, "bacteria-eater". Unlike the antibodies
formed in an organism reacting to bacterial infections (see pp. 232-234),
bacteriophage can increase in quantity outside the body of the host.
D'Herelle, and later others, fed masses of bacteria to bacteriophage in glass
dishes and so increased the quantity of the substance.

445

Later it was found (I) that there must be several kinds or strains of bac-
teriophage, each one specific for a particular species of bacteria, and (2) that
bacteriophage will not attack dead bacteria. It is not yet certain whether
bacteriophage could increase apart from living bacteria which it eventually
destroys, just as living organisms can grow in an artificial broth. From chemi-
cal studies, however, it appears that a bacteriophage resembles a virus; that
is, it is a "substance" rather than an "organism", although it behaves in some
respects like a "hving" something.

Many chemical compounds that have been produced synthetically re-
semble in their behavior complex protein molecules in living things. We can-
not call. these substances living. But we can at least imagine that under certain
conditions combinations of such unstable molecules bring about a new system,
which interacts with other substances as does a virus or a bacteriophage. That
is, each makes more like itself out of substances that are different; it assimilates.
But we are still far from creating life in a test tube. Indeed, the more we find
out about these complex molecules, the less hopeful we are of duplicating any
of nature's Hving beings artificially.

Like the theory that life comes from another planet or another solar sys-
tem, the theory of spontaneous generation is concerned with the origin of
life in general. It has nothing to say about the beginnings of particular plants
and animals. It assumes that whatever makes it possible for living matter to
arise from nonliving matter makes it possible also for new forms to develop
further with changing conditions. The theory of spontaneous generation thus
has a variety of meanings. It depends upon the way we formulate our ques-
tion and upon what we assume about the nature of the world or about what
makes things happen.

Our Limited Knowledge If a plant or an animal should some day arise
"spontaneously" out of "nonliving" material, we should be quite unable to
know about it. Even if a "worm" should crawl out of a lump of mud under
our very eyes, we could not tell whether it had developed from an egg or from
a grain of sand. All we can say is that, under strictly controlled experimental
conditions, nobody has yet seen any evidence of "spontaneous generation".
That is, we cannot "prove"''' that spontaneous generation is impossible. We can
say only that we have experienced no clear case of it. We are therefore unable
to say in advance what may or may not appear from further studies and
experiments.

Did Various Plants and Animals Arise at the Same Time?

Special Creation What happened between the early period when there
was no life on the earth and the later period in which there was life? Some-
thing extraordinary must have happened, that is, something that is not fa-

446

miliar to us. We cannot really I^now. Accordingly, some persons frankly
ascribe the beginning of life upon the earth to a "miracle", a direct act of
"creation". In different stages of civilization, among different types of people,
this miracle was described in different ways. Sometimes these descriptions
involve religious ideas and sentiments. Sometimes they are straightforward
attempts to explain the world as a natural process. It is interesting to compare
these different explanations, although they tell us less about how the world
and life originated than they do about how the human mind thinks.

For certain purposes it is convenient to suppose that all species were
created at about the same time, and that each species has remained from the
beginning exactly as we now find it. For "like produces like". This was, in
fact, the assumption of Carl Linnaeus, the great Swedish naturalist (see page
34). This point of view leaves many questions unanswered, but it is not in
itself impossible. Indeed, it is the most common view among the populations
of Europe and America.

In one form the direct-creation theory supposes that every detail which
we can observe was made just as it is to fit into some general scheme. In an-
other form the theory declares merely that the universe was so created that
in due course it brought about life of various forms, and in time man himself.
According to this view, which was held by Saint Augustine, Christian scholar
of the fifth century, the creation did not finish making the world and its in-
habitants; it merely started things off on a long course of constant change.
Everything that has happened from the beginning has followed naturally
and automatically from the way the world was made to go.

Many Creations A still different conception of the creation miracle was
proposed by Georges Cuvier, the great French naturalist (see page 176).
According to this view, the many different forms of life that have inhabited
the earth at various times were separately created. Each new species was
unrelated to any that had existed before. In the course of time, too, some of
the species died out. All the great changes in the history of the world which
we infer from a study of the crust of the earth, Cuvier explained as the results
of special violent events, or cataclysms — inundations, volcanic eruptions,
earthquakes, and the like.

Cuvier and Saint Augustine seem to have been better informed than Lin-
naeus concerning the great changes in the earth's inhabitants that evidently
took place through the course of ages. They agreed with Linnaeus, however,
that the parade of living things was started by an act of creation. Cuvier did
not agree with Saint Augustine on one important point. Whereas Saint
Augustine thought that the creation set going a process in the course of which
new species eventually arose, Cuvier thought that new species were being
created from time to time, following earlier forms but not descended from
them (see table on page 448).

447

Classic Views on Creation and Evolution

SAINT AUGUSTINE

GEORGES CUVIER

CARL LINNAEUS

Agreed that life arose as a special creation

Species of plants and animals inhabiting the earth have
changed through the ages

Creation included the proc-
esses by which new species
arose from previous forms

Each species was created

anew from time to time,

without relation to previous

forms

Species have remained in

time exactly as they were

created

All these theories, whether or not they involve miracles, resemble scientific
hypotheses in assuming or supposing some agency or process that could reason-
ably account for the facts to be explained. But these views differ from scien-
tific conceptions in one important respect: they rest on assumptions that
cannot be checked or tested by further facts. The scientist tries to shape his
theories in ways which will permit them to be checked by further observa-
tions or experiments. Obviously we cannot make any experiments regarding
what happened millions of years ago. But the scientist can do one of two things.
Either he can say frankly that he does not know or that he cannot imagine.
Or he can think out "explanations" or suppositions that not only are "reason-
able" but that enable us to experiment with materials and processes and events
that are at hand now.

In Brief

To talk about the "origin of life" implies that life exists apart from matter
and energy.

It is impossible, in a strictly scientific sense, to locate or manipulate any
"vital principle".

What we know of the earth and its past and what we know of bodies in
space can be harmonized neither with the idea that life has always existed on
the earth, nor with the idea that it came in some form from another world.

In the laboratory, complex compounds have been made which approach
the make-up of various substances that occur naturally only in protoplasm.

Filterable viruses and bacteriophage behave in some ways like living beings,
yet appear to be chemical compounds rather than organisms.

Many distinct yet plausible explanations of the origin or creation of the
world and of life have been developed by peoples in all parts of the world and
in all stages of civilization.

Some of the creation theories assume beings or forces about which we can
have no positive knowledge.

448

Science is not primarily concerned with disproving beliefs which have
served to explain the phenomena of life.

Explanations offered by scientists must be not only plausible, but, in addi-
tion, susceptible of being checked against all the facts of observation or ex-
periment.

EXPLORATIONS AND PROJECTS

1 To find out what explanations different peoples have given concerning the
origin of life, read portions of Bulfinch's Age of Fable or of Frazer's Golden
Bough. The bibles of different religions or races will suggest other theories of how
life began. Have your librarian suggest other sources, such as books on mythology
and on the teachings of some of the great philosophers and religious leaders.

2 To see whether we can get micro-organisms to arise spontaneously in dead
organic matter, expose some sterilized bouillon where nothing can get to it from
the air, and some under ordinary atmospheric conditions. Compare after a few
days or a week. Describe changes that indicate the presence of living matter in
either or both of the flasks.

3 To determine whether maggots (fly larvae) develop spontaneously, expose
meat where flies cannot get at it, but where the air can. Place some meat in the
bottom of each of three jars; leave one open; cover one with fine gauze and the
third with parchment. Keep near an open window or where flies abound. After
a week or so, examine each jar carefully; compare results and explain any dif-
ferences.

QUESTIONS

1 How do we derive our information about life?

2 In what respects are questions about life essentially different from our
questions about particular living things?

3 What evidence is there that life has always existed ? that it has not always
existed ?

4 What evidence is there to show that life has always remained the same?
that it has changed?

5 What explanations have been proposed of the origin of life? What kind
of evidence have we to support or refute these explanations? What chance is
there of proving with certainty the truth or falsity of any of these various ex-
planations?

6 In what respects are certain laboratory compounds of organic material like
protoplasm? In what respects are they different?

7 What kinds of answers are possible for questions about the origin of any
particular individual or species? for questions about the origin of life as distinct
from nonliving matter? How do answers to the first question help us in an-
swering the second?

449

CHAPTER 23 • HISTORY OF LIFE ON EARTH

1 How many different kinds of species are there?

2 Has the number of species always remained the same?

3 How can we tell how long there has been life on the earth?

4 Were there ever forms of plants and animals that no longer live?

5 How can we tell that some of today's species came into being

later than others?

6 What could make a species of plants or animals die out?

7 How can we tell that fossils were produced by living things?

8 How can we tell that some fossils belong to an earlier period than

others?

9 How can plants or animals of different kinds be related?

10 How can a plant or animal be descended from a different species?

Inside a "time capsule" objects might remain "unchanged" for centuries.
A living plant or animal, however, could not remain exactly the same for very
long. For an organism is essentially a system of constant changes; it can
continue to be itself only by changing from moment to moment. An or-
ganism grows, develops, matures, reproduces, and finally dies. In the world
of life there are (1) cyclic, or repetitive, changes, as in breathing, the circula-
tion of the blood, or the succession of new but similar individuals from genera-
tion to generation as each species reproduces itself, and (2) developmental, or
progressive, changes, through which a living thing becomes different from
hour to hour or from year to year.

Much of what happens in the world is of cyclic nature — day and night,
ebb and flow of tides, the seasons, erosion and sedimentation. There is also
a historical process, a certain continuity of change for the world as a whole.
The earth itself has undergone changes through the centuries. How can we
tell that the forms of life have also changed? Is evolution still going on?
How can we tell?

How Can We Tell What Kinds of Organisms Lived in the Past?

Digging into the Past^ Digging into the earth for all sorts of purposes,
men have come across various unexpected finds. They have found buried
treasures, ruins of cities, wrecks of automobiles, bones of human beings and of
other animals. Among the finds which have interested people for centuries
are fossils — from a Latin word meaning "to dig". These fossils are the most
direct evidence we have about the inhabitants of the earth in ancient times.

There have been theories to explain the existence of fossils and their pecul-

^See No. 1, p. 470.
450

GEOLOGIC
ERAS PERIODS

I Receat

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S ,<o g I Pliocene

§ ■S ^ ; Miocene

^^ H 3 ; Oligocene

O i Eocene

i Paleocene

" Cretaceous

MILLIONS' FIRST APPEAR-

OF years! ance of new

AGO i TYPES OF UFE

Ccmamchean
Jurassic

Triassic
Permian

O Petmsylvanian^

Modern man
Primitive main
Man-like apes

60 Primates

Placental mamnjals

135 i

DOMINANT LIFE FORMS

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450

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Fishes

Fish-hke
vertebrates

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NEW LIVING TYPES IN SUCCESSIVE DEPOSITS OF THE EARTH'S CRUST

iar forms. Fossils were merely freak resemblances to plants or animals. Na-
ture could make rocks of any shape, like crystals, or like a leaf, or a queer bird,
or an old shoe — why not? Perhaps nature had tried out various forms before
deciding on the kinds to be produced in quantity; fossils were the experi-
mental models that had been rejected. Leonardo da Vinci (1452-1519), the
great artist and engineer of the time of Columbus, took them to be the remains
of ancient life.

The great objection to da Vinci's view was that many mountain fossils
obviously resembled sea animals. How could sea-shells and the bones of ocean
fish get up into the mountains? Da Vinci's view is today supported by
vast numbers of facts. And today we know that in the course of millions of
years the surface of the earth in any region may have been alternately under
the floor of the ocean and high up in the mountain levels.

Students of fossil structures naturally tried to classify them and to com-
pare them with existing plants and animals. Many resemblances were found
between the organisms of the past and the organisms of the present, but also
marked differences. Assuming that the relative ages of fossils correspond to
their relative positions in the layers of rocks, we find that forms that are
intermediate between the most ancient and the most recent are also inter-
mediate in structure (see illustration, p. 443). One of the best examples is
seen in the horse and his probable ancestors (see illustration opposite). Similar
series of fossils have been worked out for the elephant in Africa, for various
fishes in England and elsewhere, and for many lines of birds and reptiles in all
parts of the world. A remarkably complete series was found in Germany,
showing successively different types of snails, leading down to the forms
existing today.

Pickled Fossils Since the time of Cuvier, who founded the science of
comparative morphology, scientists have been "reconstructing" ancient life
forms from fossil fragments. In many cases there are only fragments of skele-
tons, sometimes only fragments of bones. Reconstructions are necessarily
based on inference, since there is no way of "proving" the guesses as to how
these ancient plants and animals really looked. But early in this century
John C. Merriam (1869- ), an American paleontologist, found a remarkable
collection of complete skeletons of animals that must have lived from fifty to a
hundred thousand years ago. Near the present site of Los Angeles an old
"tar hole" at Rancho La Brea was being worked for asphalt. Almost daily the
workers observed that chickens, squirrels, and various other birds and small
mammals would get entrapped in this brea, or tar. And as these animals
struggled to escape, they attracted larger predatory mammals, which in turn
would also be swallowed up in the asphalt.

The workers, digging deeper and deeper, would bring out, with the asphalt,
remains of old trees (which made very good firewood) and thousands upon

452

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Pleistocene''

Pliocene

Blanco

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Pliohippus

Miocene

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John D9m««9m,
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Jurassic
Triassic

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foot foot teeii

After Mattlii'us, American Museum of Natural History

ANCESTORS OF THE HORSE IN AMERICA

The oldest of the fossils do not resemble the corresponding parts of the modern horse
very strikingly, but with each succeeding age the skulls, the bones of the feet> and
the teeth resemble those of the horse more and more closely

thousands of various kinds of bones. They recognized some of these bones as
coming from famiUar animals, such as were currently being swallowed up in
the tar. From lower depths, however, there came bones which nobody could
recognize. At last, when it was no longer profitable to work the bed, scientists
got their chance. They brought up probably several million bones, which
they began to clean and put together.

A remarkable thing about these unmistakable bones was that they repre-
sented forms of life which no human being had ever seen on this continent.
There were gigantic members of the cat family, lions and saber- toothed tigers,
large bears, mastodons, elephants, camels, extinct types of horses, wolves, and
bisons. Any doubt that fossils were really the remains of animals and plants
that at one time lived upon the earth is definitely cleared up by the bones
from Rancho La Brea. If the facts are unmistakable, however, there is still
room for argument about their interpretation.

453

These and many other varieties of snail
fossils are distributed through the rocks
in Slavonic as if they were descended
from common ancestors. Forms (b) and
(d), for example, resemble (a) more than
one another; (c) is more like (b) than
any of the others; (e) is more like (d);
and soon. Fossils resemble most closely
those in the nearest layers above or
below. If we should find these forms
scattered over widely separated areas,
experts would undoubtedly consider
them as distinct species. Only one
reasonable explanation has been sug-
gested for the distribution of these shells
in the various layers and in the regions
of the entire area, and that is that
descendants have come in time to differ
more and more from their ancestors

After Neumayr

DIVERGENCE RELATED TO TIME

Refrigerated Fossils Paleontologists and morphologists had reported
the ancient existence of mammoths, animals supposed to resemble the ele-
phants of India, but having shaggy wool and very long, slender and curled
tusks. But nobody had ever seen such an animal. There were indeed pictures
of such animals on the walls of caves in France, made presumably by pre-
historic man (see illustrations, page 57). Scientists inferred the former
existence of this type of animal from fossils picked up from time to time in
various parts of northern Europe and northern Asia. They inferred a great
deal about the size, the form, the mode of life of this animal. For many cen-
turies the natives in parts of Siberia had made quite a business of digging up
bits of the tusks and selling them to the Chinese, who made carved ivory orna-
ments of them. But nobody had ever seen a mammoth. There had been no
"history" or tradition to tell us of such animals.

u Early in this century Russian explorers in northeast Siberia found buried
under many feet of ice a complete mammoth. This animal had apparently
fallen into a crack in the ice, had been covered by snow, and had been frozen
solid. So well preserved was this animal that the blood in the veins and arteries
could be thawed out. The contents of the stomach could be identified as made
up of grasses and other plants of the region. And when the flesh was thawed
out, it was eaten by the dogs. Since then, some two dozen more such per-
fectly preserved mammoths have been found in the frozen swamps.

Interpreting Fossil Facts^ Some strange petrified bones that had been
dug up from under the streets of Paris were brought to Georges Cuvier. At

iSee No. 2, p. 470.
454

once he declared the bones to be those of an elephant. It was not the kind of
elephant, from Africa or from India, that one sees at a menagerie, but a kind of
elephant nevertheless. But there are no elephants in the region of Paris!
That is true, Cuvier admitted; but at one time there must have been. And
none of their descendants are living today. Cuvier beheved that the earth had
several times been cleared of its living inhabitants, and repopulated by a new
set especially created — that the elephants of today resemble certain elephant-
like animals of the past, but that they are in no way related. Others find it
easier to imagine that the life of today has descended from the life of the past.

How Can Different Species Be Related?

Resemblances and Relationships The historical idea of plant and animal
species is that the members of a species are all descended from the same an-
cestors. But in describing a species we have assumed relationship, or common

^i'

Carnegie Institution of Washington

BONES FROM THE CALIFORNIA TAR PIT

Among the bones removed from the tar pit at La Brea were many belonging to animals
that are not known to be living anywhere today — saber-toothed tigers, mastodons,
species of camels, extinct horses and various birds and small mammals

455

Painting by Charles B. Knight, from American Museum of Natural History

HAIRY MAMMOTH

Scientists could not "prove" their guesses about the characteristics of this animal, or
even about its existence some 100,000 years ago, but for the rare chance that some
of these giants had "been caught in the swamps and had been preserved in the frozen
state — and were then dug up by men who had the wit to piece the story together

ancestry, on the basis of resemblance (see page 36). That is, we see and
handle only individuals, but if several are enough alike for us to consider them
of the "same kind" or species, we call them by a common name and ta\e for
granted a common ancestry.

Now, according to the older idea of Linnaeus and others, each animal
species and plant species is distinct from all the others, and came into existence
independently. It "exists" in the same sense as a particular individual exists.
But arranging plants and animals according to degrees of resemblance leads to
a grouping of species into genera, of genera into families, of families into orders,
and so on into larger and larger assemblages (see page 38).

The characteristic "branching- tree arrangement" of all the kinds of living
things recalls the arrangement of individuals in a "family tree", where the
relationships are known. This similarity naturally suggests that different
classes and orders and genera of plants and animals are related to each other as
are members of a species, namely, in the sense of having descended from com-
mon ancestors (see frontispiece). Indeed, Linnaeus, in the first edition of his
great work, treated the "genus" as if it represented the original ancestor and
the species as mere variations on the theme.

456

The differences between the species in one genus are often trivial as against
the resemblances between two genera. Species must be "related" in the same
sense as cousins are related. The only question is, How far back in the family
tree can we find "common ancestors"? Our classifications suggest that if we
go back far enough, we may find that ducks and geese are related; or that all
birds are related; or that all fishes are related — that is, descended from the
same ancestors. If we go back still farther, we may find that all backboned
animals are descended from the same ancestors.

There is no reason in advance against assuming that each species has been
separately created, or has otherwise arisen independently of all others, as have
artificial objects. If that were true, however, we might reasonably expect to
find, among the million or more distinguishable forms, at least an occasional
species that stood out by itself. It would be like a special commemoration
stamp, or some freak "gadget", which differs in its design from all its con-
temporaries. However, we find no such unique cases among organic species.
Even when we classify the extinct forms, we find that they fit logically into
the same general branching arrangement of living forms.

Measures of Resemblance If we compare various insects, for example,
we shall find that most of the functions are carried on by corresponding organs
in the different animals. Thus the locomotive organs in bees, butterflies, and
grasshoppers are the legs and wings; and in every case the relative position

A LIVING ARGUMENT ABOUT FOSSILS

In 1939, off the coast of Africa, a living, breathing, scrapping Coelocanth was brought
up from the depths in a fishing net. He did not live very long, but long enough to
indicate that certain fossils found in old rocks correspond closely to an armored
fish that did actually live, although considered as long extinct

457

of each organ and the general plan of structure are the same. If we examine
the mouths, we shall again find many basic similarities, in spite of the great
differences.

The questions raised by these facts may be clearer if we compare the in-
sects in general, let us say, with backboned animals. We call the walking or-
gans of insects and those of frogs or mammals "legs". But these legs are not all
built on the same plan, although they have numerous resemblances. More-
over, the flying organs of butterflies and those of birds are quite difl^erent in
their plans and in the arrangement of muscles (see illustration, p. 18). This
comparative study, which shows us the similarities and differences in every
detail of the structure of organisms, is known as morphology. The resemblances
thus disclosed are even more remarkable than the superficial ones obvious to
the casual observer.

Homology Among animals that are built on substantially the same plan,
the corresponding parts are said to be homologous. Thus the thorax of one
insect is homologous with the thorax of another insect. Or the fiver and
teeth and hair of a dog are homologous with those of a bear.

Most striking, perhaps, are the homologies so evident in the skeletons of
the vertebrates. In each, the axis consists of a series of similar-shaped hoUow
bones, through which the spinal cord extends. At the front end is a bony
cranium which completely incases the brain. The ribs are similar in shape and
attachment. If we limit our comparisons to the mammals, we find an amazing
similarity in the number and arrangement of the bones in the fore limbs and
hind limbs, and in their attachment to the spinal axis. At the base of the
spine is a ring of bony structure, called the pelvic girdle, to which the hind
limbs are attached. The fore limbs are connected by a similar set of bones,
spoken of as the pectoral girdle (see illustration, p. 49). It is difficult to ac-
count for these homologous structures unless we assume that the organisms
have a common ancestry.

Analogy Structures of different type, or belonging to different types
of organisms, but carrying on similar functions, are said to be analogous.
Thus the jaws of a grasshopper may be considered analogous to the jaws of a
cow. They are not homologous.

When we compare plants with animals, we often find similar functions car-
ried on by organs that are so different that it is not easy to decide at once
which organs are "analogous" in the two forms. Many plants, for example,
have no special breathing organs that are strictly analogous to our nostrils or
to the spiracles of insects, for they may absorb oxygen from the air at any part
of their surface, as do most "worms". And as for homology, most people
never discover any at all between plants and animals.

Resemblances in Development We have seen that in the course of a
lifetime each individual passes through a series of more or less distinct stages

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(see page 347). And we have seen that the farther back we go toward the
one-celled stage, the more and more do these stages resemble corresponding
stages of other species. Thus in the life history of a mammal there are struc-
tures that suggest stages in the life history of birds and of fishes (see illustration,
p. 459). The larvae of different kinds of mosquitoes are more alike than the
larvae of mosquitoes and beetles; the larvae of insects in general are more
alike than the larvae of insects and crabs, and so on (see page 355). Now the
most reasonable explanation of such facts is the supposition that there is a
common (or similar) development just to the extent that organisms are "re-
lated" through having descended from common ancestors.

Useless Structures Relationship is further inferred from the fact that
in plants and in animals certain organs persist through whole groups, although
they are quite useless from the point of view of adaptation. For example, the
whale develops legs that are never used, and the same is true of certain snakes.
The skeleton of many a bird shows distinct signs of fingers, or claws, among
the wing bones. The vermiform appendix (see illustration, p. 175) in man has
been interpreted as the lingering remains of an organ that developed and took
part in digestion in other backboned animals. It has no practical meaning in
the life of man today — except to make trouble sometimes. We can under-
stand such examples readily if we suppose that all plants and all animals are
related through having had common ancestors. No other theory that agrees
with all the facts has been suggested to explain such "vestigial" structures.

Geographic Distribution We expect every group of organisms to ex-
pand its range just as far as conditions permit. And we rather expect a given
kind of situation to maintain one kind of population and a different kind of
situation to maintain a different kind of population. Yet when we examine
the distribution of species over the surface of the earth, certain curious facts
appear.

Regions in every way similar, as to climate, soil, and so on, are inhabited
by totally different plants and animals. Thus the climate of Australia is
not very different from that of most of Europe and large parts of Africa,
Asia, North America and South America, yet Europeans who first came
to AustraUa found plants and animals that are not found in these other parts
of the world. Many such puzzling differences are found in comparing the
flora and fauna (plant and animal populations) of regions that are geograph-
ically similar.

On the other hand, regions that are very different in climate, soil, and so
on, are occupied by plants and animals that are so much alike that we class
them in the same families. Thus goats and sheep, obviously related to each
other genetically, occur naturally in the Tropical Zones, as well as in the
Temperate Zones, and well up into the Arctic and Antarctic circles, Uving in
many kinds of surroundings.

460

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Alier (Jruenljera. 'J'lie iiluii/ ut Evulution

AN INFANT'S RESEMBLANCE TO ITS ANCESTORS

The almost shapeless Sacculina (C) growing as a parasite on the abdomen of the crab
(D) has nothing in its structure or behavior to suggest a relationship to its host. Yet
in its early development (A, B) it seems destined to become an unmistakable crus-
tacean. Without a study of its life history we should never have guessed that host
and parasite are of the same class of animals

Darwin pointed out that similar regions which are occupied by different
flora and fauna are always separated from each other by impassable barriers,
such as oceans, mountain ranges, and deserts. On the other hand, when
regions which differ markedly in climate, soil, and so on are inhabited by
similar plants and animals, they are either directly connected at present or
show evidence of having been so connected in the past. For example, the
plants and animals found on oceanic islands are frequently quite distinct from

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SIMILAR INHABITANTS OF DIVERSE CLIMATES

If each region is inhabited by plant and animal types especially designed for it, we
want to know why variations of the same type — dog, for example — occur as timber
wolf in the cold regions of North America and as wild dogs in the temperate regions
of Africa

those found elsewhere, but they are, as a rule, most closely "related" to the
inhabitants of the nearest mainland (with which such islands were apparently
connected in the past). Facts of this kind can be explained if we assume that
ail organisms are derived from ancient forms, with modifications. But they
cannot be easily explained in any other way.

463

How Can We Explain Changes in the Earth's Population?

Facts and Explanations According to the records preserved in the
rocks, in coal mines, in tar pits, and elsewhere, there can be no doubt that the
species of animals and plants which inhabited the earth in the past were suc-
ceeded through the ages by different species. This is as truly a matter oi fact
as the statement that the men, women and children in a given town have
changed in the past ten years, even if the total number remains the same.
But while people of ordinary intelligence can grasp and accept the facts, it
has been difficult to find an explanation that would satisfy everybody.

We saw that Georges Cuvier, who helped to establish the historical fact
that life forms have changed through the ages, thought of the succession of
species as discontinuous (see page 447). That is, he believed that as existing
forms were destroyed in one or another cataclysm, other species were created
to take their places.

A different type of explanation was offered by an older contemporary of
Cuvier's, the French zoologist and philosopher Jean Baptiste Lamarck (1744-
1829). According to Lamarck's view, life has been continuous from the begin-
ning, regardless of how living things came to be in the first place. Descendants
differ from their ancestors; and when the deviation has reached a certain
degree, there is a new species.

These two types of explanation account for the same facts. Both can be
supported by good arguments and by further facts. On the whole, however,
the theory that there has been modification with co72tinuity of descent fits in
with more kinds of known facts and calls for fewer special assumptions. This
theory does not, of course, answer the question How did living beings originate
in the first place? Nor does it, of itself, tell us just how modifications have
taken place. But it does lend itself better to further experimental exploration
than the theory of a new special creation for each species.

Haifa century later, when explorers and investigators had brought together
vast numbers of observations about plants and animals in all parts of the
world, the question was again brought into violent controversy by the Eng-
lish naturalist Charles Darwin (1809-1882). Darwin, Lamarck and Cuvier all
agreed that the living species of today are different from their predecessors
of ancient times. But according to Cuvier, the predecessors were not the
ancestors, whereas Lamarck and Darwin emphasized that "like begets like",
and thought therefore that the succession of forms was continuous. That is,
they declared the present species to be descendants of earlier ones, with modi-
fications. Yet Darwin and Lamarck did not agree as to how the modifications
had come about.

Lamarck's Explanation Lamarck based his explanations on two familiar
sets of facts: (1) As everybody knowS; the development of an organism is in-

464

fluenced by its activities or its experiences; muscles grow more if they are
used more. (2) Organisms, and especially animals, adjust themselves to their
surroundings in the course of their lives — for example, a mature animal is
better fitted to supply its needs or protect itself than it was in its younger
stages; a child exposed to sunshine will come to have a darkened skin.

From his reflections, Lamarck concluded that "all that has been acquired,
begun, or changed in the structure of an individual in the course of its life is
preserved in reproduction and transmitted to the new individuals which spring
from that which has experienced the change."

This view, widely held, appears quite reasonable. It "explains" the long
neck of the giraffe, for example. By stretching to reach the leaves on trees,
the ancestors of this species pulled their heads higher and higher above the
ground, the argument runs. In any particular generation the stretching may
have been very slight, but this little gain was inherited by the offspring. They,
in turn, added a little to their height in the same manner. And this process,
continuing generation after generation, resulted in the long-necked animal we
know today.

This theory can also explain the webbed feet of water birds. A young bird
thrown into the water would naturally spread its toes as far as possible to ex-
pose the maximum surface for paddling. As the animal continued to stretch
its toes apart, the skin between them would gradually spread, resulting after
many generations in the webbed foot of the duck or goose.

Lamarck's views appeal to many as common sense. "It stands to reason"
that the gains which are made in the course of a generation should benefit the
following generation. The analogy from society is impressive. Those who are
industrious and thrifty and accumulate more than their neighbors naturally
"pass on" more to their children; the latter inherit more. A good home
gives children a good start. And they in turn, when they grow up, provide
better homes for their children. Communities that have good schools, for
example, progress more rapidly than those without schools or with poor
schools. Well-nourished plants produce larger seeds, and larger seeds grow
into better plants, which in turn produce larger seeds. It all "stands to rea-
son." But what are the facts?

Objections to Lamarck's Explanation We may grant that his experi-
ence and activities modify the individual in the course of his development, or
that the new species appear to be as well adapted to their surroundings as
their ancestors probably were. Lamarck's argument is nevertheless far from
conclusive, for in it is concealed an assumption which may turn out to be
unwarranted. Are the effects of experience or activities actually transmitted to
the offspring? Is bUndness resulting from injury to an eye reproduced in one's
children? Is the effect of a broken leg or of practice on a piano inherited? The
sons of blacksmiths may have better muscles than the sons of bookkeepers,

465

on the average. But is that because they have inherited the effects of their
father's activities? Or is it, perhaps, because they have inherited the kind of
constitution that easily develops large muscles? Are "acquired characters"
transmitted? That is not a matter of opinion, but something to be established
through repeated observations.

Darwin's Explanation^ The theory of the modification of species in the
course of descent that is associated with the name of Darwin was also for-
mulated independently by Alfred Russel Wallace (1823-1913) and by Herbert
Spencer (1820-1903). This theory, like that of Lamarck, is intended to ex-
plain (1) how new life forms or species appear in the course of ages and (2) how
plants and animals come to be so well adapted to their surroundings.

Darwin's theory rests on two main sets of facts: (1) the fact of variation,
that no two individuals are exactly alike; (2) the fact that more individuals
(eggs, seeds, spores, and so on) are born than can reach maturity and reproduce
themselves. The facts are clear and generally recognized. There is a great
deal of variation among individuals. In nature every species does produce
new eggs or seeds entirely out of proportion to the number of individuals that
could find standing room, to say nothing of food. The resulting "pressure of
population" leads to what has been called the struggle for existence.

Now every individual dies in the end. For each individual it is a matter of
chance whether he does sooner or later. The net result, according to Darwin,
is that the destruction of so many plants and animals leaves those to survive
and reproduce that are best adapted. In other words, the outcome of the
"struggle" is a survival of the fittest.

Natural Selection Darwin compared this natural process to the artificial
selection carried on by the plant or animal breeder. He frankly used the ex-
pression natural selection as a figure of speech, as a quick way to describe just
what our common sense would lead us to expect. Darwin did not intend to
say that "nature picks out what she wants to preserve", or that "nature
favors" one group at the expense of another. He attempted merely to ex-
plain how the adaptations of species come about, by emphasizing the general
fact, which is easily observed, that members of a family differ from one an-
other in ways that fit some of them to the special conditions of living better
than others.

Objections to the Selection Theory "Struggle for existence" is a fair
description of the activities of plants and animals. And much of the outcome
is "selective" in the sense that individual differences often mean advantage or
disadvantage. Darwin's theory is nevertheless not a satisfactory explanation
of how new species have arisen in the course of descent.

Along with the unquestionable facts, this theory makes use of two sets of
assumptions. First, it assumes that the differences among individuals are all

iSee No. 3, p. 470.
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inherited. At least, Darwin did not distinguish clearly between those char-
acteristics that are inherited and those that are not. As in the case of Lamarck's
assumption, this is not a matter of opinion; and the facts in the case were not
known in Darwin's time.

The second assumption is that the destruction of living things is in most
cases selective. That is, that individuals generally die because of some heritable
disadvantage, as compared with those who survive in the same circumstances.
There are about every plant and animal multitudes of details that distinguish
it from closely related species but that can have no conceivable bearing upon
survival. Moreover, vast numbers of individuals are destroyed indiscrimi-
nately by floods, fires, general drought, and so on, with only a few survivors
remaining, largely through chance.

Darwin's theory may explain the extinction of some strains and the sur-
vival of others; but it has no suggestion as to how new characters arose in the
first place. If we grant that variations in degree of fitness influence the sur-
vival of types, we have remaining the question of origin: How do new char-
acteristics originate? Darwin was aware of this difficulty, as appears in his
book The Origin of Species:

Several writers have misapprehended or objected to the term Natural Selection.
Some have even imagined that natural selection induces variability, whereas it
implies only the preservation of such variations as arise and are beneficial to the
being under its conditions of life. No one objects to agriculturists speaking of the
potent effects of man's selection; and in this case the individual differences given
by nature, which man for some object selects, must of necessity first occur. Others
have objected that the term selection implies conscious choice in the animals which
become modified; and it has even been urged that, as plants have no volition,
natural selection is not applicable to them! In the literal sense of the word, no
doubt, natural selection is a false term; but who ever objected to chemists speak-
ing of the elective affinities of the various elements? — and yet an acid cannot
strictly be said to elect the base with which it in preference combines. It has been
said that I speak of natural selection as an active power or Deity; but who objects
to an author speaking of the attraction of gravity as ruling the movements of the
planets? Every one knows what is meant and is implied by such metaphorical
expressions; and they are almost necessary for brevity. So again it is difficult to
avoid personifying the word Nature; but I mean by Nature, only the aggregate
action and product of many natural laws, and by laws the sequence of events as
ascertained by us. With a Httle familiarity such superficial objections will be
forgotten. 1

The difficulty that all these explanations have in common seems to come
from trying to reconcile two unquestionable facts: (1) Like produces like,
and (2) Species inhabiting the earth today are dirferent from the species that
lived in the past.

^The italics are ours, not Darwin's.
468

Before we can decide whether today's plants and animals are descendants
of ancient species, we must first answer the question Is it possible for any
plants or animals to have o^spring that are sufficiently different to maf^e up a
new species?

It was many years after the death of Darwin before students of heredity
had accumulated enough knowledge to answer this question helpfully.

In Brief

Fossils furnish our most direct evidence about early forms of life.

The fossil record includes entire organisms, skeletons, shells, petrifactions,
casts and molds.

Similarities in the structure and life histories of living organisms suggest
relatedness; the greater the similarities, the less remote we assume the com-
mon ancestry to have been.

Corresponding parts of different organisms built on substantially the same
plan are said to be homologous. The presence of homologous parts is taken to
indicate relatedness.

Unlike parts of different organisms which carry on similar functions are
said to be analogous.

Similarities found between the early stages of development in different
species are taken to indicate relatedness.

The presence of certain useless structures within living things is difficult
to explain unless we assume that all plants and animals are related through
common ancestry.

The uniqueness of life in isolated regions, as contrasted with similarities of
life in adjoining regions, can be most satisfactorily explained by assuming that
existing species are derived from ancient forms.

The accumulating evidence that plant and animal species populating the
earth have changed in time brought two different types of answers: (1) Special
creation must have taken place again and again, or new species arose spon-
taneously again and again. (2) Life has been continuous, but species have
become different from their ancestors.

The origin of species cannot be known directly. Either we depend for the
answer upon acceptable authority, or we build up the most reasonable hypothe-
sis from actual facts.

Both the theory of natural selection and the theory of transmission of
acquired traits are intended to explain (1) the procession of changing plants
and animals and (2) the fact that each species is so remarkably well adapted to
live in its own special surroundings.

469

There is no conclusive evidence that modifications arising in an individ-
ual's Ufetime are transmitted to the offspring.

The theory that species originated through natural selection rests on the
facts (1) more individuals are produced in each species than can possibly ma-
ture and reproduce, and (2) individuals in a species vary among themselves.
The theory rests upon the suppositions (1) in the "struggle for existence"
which ensues from the pressure of population only the "fittest" survive, and
(2) the survivors transmit their advantageous characteristics to their offspring.

The theory of natural selection (1) overlooks destructive conditions that
are in no sense "selective", (2) disregards the apparent modifications that are
not adaptive, and (3) fails to distinguish clearly between variations that are
inherited and those that are not.

EXPLORATIONS AND PROJECTS

1 To make a collection of fossils, visit exposed beds of sedimentary rock;
split open pieces of limestone or shale, or concretions found in coal or shale
deposits, in search of imprints or remains of living things which may be con-
sidered as fossils. Identify and label specimens, recording place where found, date,
kind of rock in which found, name of fossil, and the geological era or period in
which it probably was formed.

2 To become acquainted with life forms characteristic of Paleozoic, Mesozoic,
and Cenozoic times, visit a natural-history museum and study the types of life
dominant in each era.

3 To estimate the reproductive possibilities in a single plant, collect the seed-
stalk and count the number of seeds. Select a plant which easily becomes a weed
pest, such as dock or ragweed, or a plant commonly raised for food, such as corn
or wheat or radish. Estimate how many plants could be produced in three or
four seasons if each seed grew and each successive plant produced the same
number of seeds.

QUESTIONS

1 Why do not all observers of the same facts come to the same conclusions?

2 What assumptions do you prefer to make as a basis for interpreting the
past history of the world.'' Why do you select these assumptions rather than
others ?

3 What are fossils? Where do we find them? In what different ways are
they preserved?

4 If we accept fossils as representing past life upon the earth, what do the
actual fossils and their distribution suggest about the history of life on the earth?
What changes do they suggest in the earth itself?

5 What likenesses and differences do we find among the various mammals ?
among all vertebrates?

470

6 How do the similarities found among the vertebrates in the early stages
compare with those found in adult stages?

7 What theories can explain the presence of useless structures within the
bodies of living things? Which explanations agree best with established facts and
most widely accepted assumptions?

8 How can we account for the fact that forms living today are different
from their predecessors?

9 How did Lamarck explain the origin of new species? What support is
there for his explanation ? What are its limitations ?

10 How did Darwin explain the origin of new species? Upon what observ-
able facts was his explanation based? What support is there for his explanation?
What are its limitations?

471

CHAPTER 24 • THE FACTS OF HEREDITY

1 What makes living things resemble their parents?

2 Why are not all the offspring of the same parents alike?

3 Why do individuals of the same species differ from each other?

4 Is inheritance due to something in the blood?

5 Does one parent have more influence on inheritance than the

other?

6 How are new breeds of plants or animals produced?

7 Are the effects of experience, training or injury passed on to the

new generation?

8 How can we tell whether a certain trait is due to outside in-

fluence or to something that is inborn?

9 Are mental qualities inherited, as well as physical?
10 Can anything be done to counteract heredity?

We are so familiar with resemblances between parents and offspring that
they somehow seem "natural". But differences are also natural. They are
often obscured by the fact that in common species each individual has two
parents. For the individual, resembling both parents, seems to us somehow
"between" the two. Yet there are always characteristics that we cannot
trace to either parent or to other ancestors. Moreover, in the course of an
individual's growth he is being modified continuously by the surroundings —
nutrition, temperature, light, chemical factors, and so on. In human beings,
as well as in other species, experience and training, injury and disease —
various conditiojiings — all produce effects. Habits and skills, attitudes and
sentiments, likes and dislikes, become changed. Even under uniform condi-
tions there appear to be differences.

What causes these differences? For that matter, what causes the resem-
blances? What happens when varieties are crossed? Are mental qualities
inherited in the same way as physical characters?

How Can We Trace Inheritance through Successive Generations?

Race Experience People everywhere seem to believe that "heredity
always runs in families" (see illustration opposite). Many ancient peoples had
strict rules regulating marriage. Some forbade the marriage of cousins and of
even more remote relatives. Some had no such restrictions. In some societies
brother-sister marriages were accepted as proper, although these are looked
upon with abhorrence by most peoples today. The reasons for the various
rules rest on what people assumed or believed about heredity or about "race".

Breeders of race horses train the animals for swiftness, and then try to

472

Four

• • • • • • ■ •

Uncles and aunts

Cousins

grandparents VZX o ?

Father

Mother

Brothers

Sister

Uncles and aunts

Ernest

Cousins

WHAT RUNS IN FAMILIES?

Ernest has blue eyes, although both his parents and his sister and his brothers have
dark eyes — like his cousins and his uncles and his aunts. Some say he gets his blue
eyes from his grandmother Brown, but others say he gets them from his grandfather
Green. How can we tell?

improve the stock by breeding from the swiftest. And the modern race
horse is indeed a great improvement upon the progenitor of only a few decades
back. Do- the training and racing of horses influence the performance of
their offspring? Or does the performance reveal the possibilities of the
stock? Or how is the stock improved?

What people have believed about the connection between parent qualities
and offspring qualities has influenced their treatment of pregnant mothers.
There has been a widespread belief, for example, that if a pregnant female
experienced a violent shock or a violent pleasurable emotion, the unborn child
would somehow show the effects. Birthmarks, deformities, and even special
talents were often ascribed to such experience. Many animal-breeders tried
to influence the coloring or markings of their calves or lambs by exposing the
mothers to appropriate scenery. Similarly, many human mothers today hope
to ensure beautiful features for their unborn babies by gazing on the pictures
of beautiful women or men.

People generally think of "heredity" as a strange, mysterious force, which
may or may not strike, like lightning or good luck or a pestilence. It is only
in modern times that systematic research has attempted to solve the larger
problems of heredity. For example, how can we measure degrees of resem-
blance among individuals? Houj far can selection be carried? Can a stable,

473

or constant, species be established with no variation among individuals? Can
standard surroundings be established to prevent variation? What connection
is there between the characteristics of individuals and the structure of eggs
and sperms?

Analyzing the Problem The first systematic experiments in heredity
of which we have any record were those of Gregor Mendel (1822-1884), an
Austrian monk. Mendel had long puzzled over the great amount of variation
among his garden peas. There were tall plants and short ones, plants with
white flowers and plants with colored flowers, with yellow seeds and with green
seeds, with smooth seeds and with wrinkled seeds. He noticed further that a
given plant might have any combination of the single members of these pairs.
Thus a hairy plant might be tall, or it might be short; a tall plant might have
white flowers or pink flowers; it might have yellow seeds or green seeds; and
so on. All in all, Mendel studied seven different pairs of contrasting charac-
teristics in the pea plants (see table, below).

Mendel's Experiments with Garden Peas^

CONTRASTING CHARACTERS IN

THE TWO PARENTS

CHARACTER IN OFFSPRING

1. Seed coat

Smooth X wrinkled

All smooth

2. Cotyledon color

Yellow X green

All yellow

3. Height of stem 6-7 ft or 1-2 ft

Tall X dwarf

All tall

4. Pods — inflated or sunken between seeds

Hard X soft

All hard

5. Unripe pod, color

Yellow X green

All green

6. Position of flower

Axial X terminal

All axial

7. Seed-coat color

White X colored (gray or brown)

All colored

In one plot Mendel placed pollen from a tall plant upon the stigma of a
short, and vice versa. In another he crossed smooth-seeded and wrinkled-
seeded plants, in both directions. In this way Mendel made reciprocal crosses
with hundreds of pairs of plants having contrasting characters.

Mendel's First Discovery- When Mendel crossed green-seed and yellow-
seed plants, the resulting seeds developed into plants yielding only yellow
seeds. When he crossed tall and dwarf plants, the offspring were all tall.
With each of his seven pairs of characters, Mendel found that the offspring
resembled one of the parents completely. Thus the offspring of colored -flower
and white-flower strains all had colored flowers. If these results are sur-
prising, it is because most of us have failed to notice that the resemblance
of children to their parents consists not only in having characters lying

^Breeders long tried, without success, to find out how a hybrid "variety" acts in heredity.
Mendel crossed plants that differed from each other in a particular character — tallness, for example,
or color. In thousands of crossings between individuals with contrasting characters, he found that
all the hybrids in each series were alike, whether the quality in question had been carried by the
male parent or the female parent "See Nos. 1 and 2, p. 503.

474

Mendel anticipated by thirty-five years the
practical establishment of the art of breed-
ing new species of plants and animals,
kinds that had never existed in nature. It
is commonly assumed that an organism
transmits its distinctiveness entirely, or else
not at all. This means that a Jersey cow,
for example, transmits to her offspring all
her "jerseyness" or that a cherry transmits
all its "burbankness" — or none. Mendel
analyzed the "character" of a strain into its
many separate qualities. His basic scien-
tific and practical contribution was the
working out experimentally of a method
for ascertaining the essential facts as to
just what is inherited — just what particular
characteristics appear in successive gen-
erations, what ones fail to appear, what
ones reappear later

GREGOR MENDEL (1822-1884)

Historical Pictures Service

between the corresponding characters of the parents, but partly in having
some characters just Uke those of the mother and other characters just like
those of the father (see illustration, p. 476).

The results which Mendel obtained he generalized as the law oi dominance.
His idea was that where the two "factors" causing the contrasting characters
meet in an individual, one of them dominates over, or masks, the other one,
which Mendel called the recessive. The recessive is not destroyed, as we shall
see. Of course it is impossible to tell in advance which of two characters in a
contrasting pair will be dominant and which will be recessive. The cross has
to be tried out (see the tables on pages 480 and 481).

The Law of Segregation^ The yellow seeds of a hybrid plant are not
distinguishable from the yellow seeds of the pure yellow-seeded parent — just
as you cannot tell whether a brown-eyed person has two brown-eyed parents
or only one. With plants grown from hybrid yellow seeds, Mendel carried
out three classes of cross-pollenation (see illustration, p. 477): (1) He crossed
hybrids with plants of the parent (pure) yellow-seeded variety. (2) He
crossed hybrids with plants of the parent (pure) green-seeded variety. (3) He
crossed yellow-seeded hybrids with yellow-seeded hybrids.

From these experiments, which have now been made with hundreds of
species of plants and animals, it is seen that the hybrid does not reproduce itself
in offspring having uniform characteristics. Some of the offspring resemble the
grandmother's type, and some the grandfather's type. This general fact of
"splitting" is called the law oi segregation. It agrees with the past experience

iSee No. 3, p. 503.
475

Parent 2

Offspring

MENDEL'S FIRST SURPRISE

From our common experience we expect offspring to resemble both parents. When
Mendel crossed a pure breed of tall plant with a pure breed of dwarf, ail the offspring
were tall. When he crossed a pure smooth-seed variety with a wrinkled-seed variety,
all the offspring had smooth seeds. The hybrid of hard-pod and soft-pod varieties
all had hard pods. The results were the same whichever parent had the special trait

of breeders, who consistently failed to establish new varieties even where they
constantly mated hybrids with similar hybrids.

Inbreeding of the hybrids yields two kinds of offspring: (1) those with
the dominant character and (2) those with the recessive character (see illustra-
tion opposite). That is, the two original qualities — green and yellow seeds, for
example — reappear. The progeny of the hybrids break up into two types,
resembling the two ancestral types. These two types of offspring segregate
in the proportion of three dominants to one recessive (3 :1). Inbreeding in
the next generation leads to further segregation — a fact which had always
confused hybridizers in the past. But here a new fact appears: all the reces-
sive green plants in the second hybrid generation breed true, and also some of
the dominant yellow.

Purifying the Mixture The recessives (greens) breed true in every
succeeding generation. This is in spite of the fact that they were derived from
yellow (hybrid) parents. Such "extracted" recessives are considered "pure,"
for they always breed true.

A76

In each generation, then, the descendants of hybrids will behave in three
possible ways with respect to a particular characteristic: (1) the recessives will
remain pure, or capable of reproducing the recessive trait; (2) one out of
every three dominants will turn out to be a pure dominant; (3) two out of
the three seemingly dominant plants will behave like hybrids and split up
again when they reproduce.

Combinations of Characters^ We know that every organism consists of
not one, but many characters. Mendel also experimented on the results of cross-
ing peas with different combinations of characters. Two plants, for example,
differ not only as to the color of the seed but also as to tallncss. What happens
when they are crossed? Mendel crossed tall green-seeded plants with short
yellow-seeded ones. All the next generation were dominant for size (tall),
and dominant for seed-color (yellow). The hybrids resembled one parent
altogether in one character, and the other parent entirely in the other charac-
ter (see illustration, p. 478). In the following generation the offspring of such
hybrids appeared in four types: tall-yellow, short-yellow, tall-green, short-
green. That is, there was "segregation" for each pair of characters.

Experiments of this kind have since been repeated by the thousand. From
them we conclude that each pair of alternative characters behaves according
to the first two laws {dominance and segregatio?2), regardless of the other char-
acters present. This general fact is called the law of independent assortment,
or the law of unit "characters" (see illustration, p. 479).

This principle of independent characters may help us understand how

When hybrids of two pure strains (which are all dominant in appearance) are mated —

with pure dominants, like their

parents, all the ofFspring are

dominant, as we should expect

Hybrid Dominant

All dominant

with pure recessives, like their
parents, half the progeny is
dominant and half recessive

with similar hybrids, the offspring

resemble dominant and recessive

grandparents in the ratio 3 : 1

■ijWilWBM

mim-

Hybrid Recessive Hybrid Hybrid

^ r

Two
dominant

Two
recessive

Three One

dominant recessive

HYBRIDS IN THE SECOND GENERATION

iSee No. 4. p. 503.
477

tY |l

'"^

' " ' iVi/ # € W, iV S.':/ %Ky iv W

.{^

INHERITANCE OF TWO OR MORE CHARACTERS

Mendel crossed a strain that had one character dominant with one that had a differ-
ent character dominant — say, a tall green-seeded plant with a dwarf yellow-seeded
one. All the offspring had both dominant characters. When the hybrids, Fi, were
mated, segregation of the dominant and recessive characters in the ratio of 3 : 1 took
place in the following generation, F2, independently for each pair of contrasting
characters

there can be such great diversity among individuals of any given species, or
even among the brothers and sisters of any family. The greater the number
of characters, the greater is the possible number of combinations, and the
smaller is the chance that any given combination will occur again.

These three laws of heredity — dominance, segregation, and independent
assortment — are known as Mendelian laws, or principles, because they were
first discovered by Gregor Mendel.

The Rediscovery of Mendel Gregor Mendel read a paper on the re-
sults of his experiments in 1865, and the following year published the paper
in the journal of the local scientific society. There it remained in dead storage
to the end of the century. For there is no indication that any of the scientists

478

or practical breeders discovered this work or noted its significance. Others
were also carrying on experiments, however. By the end of the century three
botanists, working independently and each one experimenting with different
material, were arriving at the same conclusions Mendel had reached. They
discovered Mendel's old report and called attention to it. These three bot-
anists were the Hollander Hugo de Vries, the Austrian Erich Tschermack, and
the German Karl Correns.

While these investigations were going on, an American breeder was making
the same discoveries in an effort to develop a wheat especially suitable for
growing in the Northwest. In the region about Pullman, Washington, the
farmers had for years tried out many varieties of wheat in order to decide
which was the most profitable to grow. They found only the Little Club
variety at all satisfactory. The straw was strong enough to withstand the
summer storms, and the head remained closed after the grain was ripe, thus
preventing loss before harvesting. But when Little Club was planted in the

BERNAUD
I- Ri CD MAN

,- .^

i.^'

White-long-
smooth (1)

Black-long-
smooth <3)

White - long - rough [3]

Black-short-smooth [9]

' \

,^'

White- short-
rough (9)

White-short-
smooth (3)

INDEPENDENT ASSORTMENT OF CHARACTERS

Black-short-
rough (27)

Black- long -
rough (9)

AfHT exi)erimeius by W, K. Castle

In guinea-pigs pigmentation is dominant, as are shortness of hair and roughness of
coat. When two pure-bred individuals like Pi and P2 are mated, all the hybrids will
be dark, short-haired, and rough-coated, like Fi. If such hybrids are now mated in
sufficient numbers, the next generation will yield every possible combination of the
three sets of characters, including the "pure" grandparent types, in the proportions
indicated by the numbers in brackets. And for each pair of characters there will be
three dominants to one recessive

479

Heredity in Plants

NAME or PLANT

DOMINANT CHARACTER

R:CESS1VE CHARACTER

Wheat

Late ripening
Susceptibility to rust
Beardless

Early ripening
Immunity to rust
Bearded

Barley

Beardless

Bearded

Maize

Round, starchy kernel
Yellow grain
Purple grain

Wrinkled, sugary kernel
White grain
Yellow grain

Garden pea

Seeds free in pods
Green foliage

Seeds clinging
White-spotted foliage

Garden bean

Yellow seed
Tallness
Round pod
Blunt leaf tip

Green seed
Dwarf

Flattened pod
Sharp leaf tip

Tomato

Two-celled fruit

Many-celled fruit

Plum

Red, purple, black fruit
Purple flower

Yellow fruit
White flower

Potato

Purple in tuber
Shallow "eyes" in tuber

White in tuber
Deep "eyes" in tuber

Cotton

Colored lint

White lint

Stock
Sweet pea
Jimson weed

Colored flower
Colored flower
Colored flower

White flower
White flower
White flower

Sunflower

Branched stem

Unbranched stem

Nettle

Saw-edge leaves

Smooth-margin leaves

fall, it would be frozen during severe winters — once every three or four years.
Although the farmers could get better crops by planting in the fall, they
could not afford to lose every third or fourth planting. The problem was,
therefore, to combine the good stem and head qualities of Little Club with
the frost-resisting quaUties of some other variety.

W. J. Spillman (1869-1931), agriculturist of the experiment station at
Pullman, began a series of experiments in crossing, or hybridizing, the Little
Club wheat with other varieties. Whichever variety he used as the pollen
parent, the same group of characters appeared in the next generation. This
agrees with what we have learned as Mendel's law of dominance, although
Mendel's work and his special terms were not known to breeders or biolo-
gists (see page 475). Spillman found also that among the offspring of hybrids,
every possible combination of the grandparents' characters occurred. This
agrees with Mendel's principle of segregation.

480

Heredity in Animals

NAME OF ANIMAL

DOMINANT CHARACTER

RECESSIVE CHARACTER

Cattle

Hornlessness

Horns

Horse

Trotting

Pacing

Guinea-pig

Colored coat

Albino

Black or brown coat

Yellow

Self-colored

White-spotted

ATOUti fur

Nonagouti fur

Short fur

Angora fur

Rosetted coat

Smooth coat

Rabbits

Colored coat

Albino

Agouti fur

Nonagouti fur

Short fur

Angora fur

Mice

Pigmented coat

White coat

Normal movements

Waltzing habit

Dogs

High head carriage

Low head carriage

Trail barking

Trail silently

Narrow chest

Broad chest

Narrow head

Broad head

Long head (in greyhound)

Short head

Short hair (in some breeds)

Long hair

Short foot (in German

Shepherd)

Long foot

Black or liver color

Red

Poultry

Rose comb

Single comb

Short rump

Long tail

White plumage

Pigmented plumage

Extra toes

Normal toes

Feathered shanks

Bare shanks

Crested head

Uncrested head

Brown eggs

White eggs

Broodiness

Nonbroodiness

Salamander

Dark color

Light color

Canary

Crested head

Plain head

Silkworm

Yellow cocoon

White cocoon

Land snail

Plain shell

Banded shell

Pomace flies

Red eyes

White eyes

By growing from the seed of selected individuals in this third generation
and by keeping careful and complete records of the results, Spillman suc-
ceeded in combining in one variety of wheat three important characteristics
— the strong stem, the closed head, and the frost-resisting qualities. Using
similar methods, breeders combined three or more characters desired in a
plant from as many different varieties of ancestors.

481

Rules and Exceptions The rediscovery of Mendel's studies and the
simultaneous discovery of his principles by several independent investigators
aroused widespread interest. Hundreds of students immediately set to work
to check on the amazing new "laws" of heredity. Supporting facts were found
through experiments on maize, mice, hens, rabbits, silkworms, wheat, various
flowering plants, and many other species of animals and plants.

Earlier experience, as well as many experiments since Mendel's time,
show that with some pairs of characters there is not complete dominance. In
the case of the blue Andalusian fowl, for example, or of the four-o'clock flower
there appears to be what Galton called "blended" inheritance. But from
further experiments we now understand that these seemingly blended hybrids
behave exactly as do Mendel's hybrid dominants, except that the dominant
factor does not completely hide the recessive one.

William T. Bateson (1861-1926), a British surgeon and investigator,
had stressed the desirability of studying heredity by experimenting with
distinct traits that did not merge or blend gradually into others. He quickly
recognized the importance of the Mendelian principles and urged further
research. He carried on experiments himself, and on the whole his results
agreed with Mendel's findings. But Bateson (who, by the way, invented the
name genetics for "the science of heredity and variation") discovered some
curious exceptions to the principle of independent transmission of traits. For
example, purple sweet peas having long pollen grains were crossed with red-
flowered varieties having round pollen grains. In the second hybrid generation
the segregation did not yield the four possible combinations in the propor-
tion 9:3:3:1 (see illustration, p. 478). Instead the long-pollen and purple
came out together, and the round-pollen and red came out together. In other
experiments the large petal, or "standard", of the pea-flower appeared to
remain associated with color; it always droops in white flowers and is erect
in purple ones. That is, there is some connection, or "coupling", between
these two characteristics: they are not transmitted independently.

Other exceptions appeared in the offspring of two different strains of white-
flowered sweet peas. The hybrids have colored flowers, and their progeny in
turn segregate into six different color combinations, in addition to some pure
whites. Here, again, the proportions did not fit the expectation according to
the Mendelian formula. Many scientists began to feel that they had to take a
stand for MendeHsm or else against Mendelism.

Multiple Factors Although Mendel's work remained so long forgotten,
his selection of material was very fortunate since it enabled him to develop
his three "laws" in about eight years, with the least amount of confusion.
With other material he might have been completely baffled. The mating of
red wheat with white wheat, for example, yields a grain of an intermediate
color. In the following generation there is a breaking up into a long series of

482

shades, including the original types. The latter breed true, but the inter-
mediates continue to split up. After breeders had learned to count the num-
ber of individuals of each type that appeared in the progeny of hybrids, it
was easy to figure out that the color of wheat grain is inherited through the
combined effects of two or more "independent factors". This is in contrast to
the "single determiner" which Mendel assumed to account for each of the
seven pairs of contrasting characters in his garden peas.

Perhaps we can get the idea of "multiple factors" from a more familiar
experience, that of variation in stature. In a group of men with an average
stature of (yl inches, some of the individuals are, let us say, only 63 inches tall
and others, say, lli inches tall. Variation in stature is "fluctuating" or con-
tinuous. We do not think of a special character "seventy-three-inchness" or
"sixty-four-inchness", but we do assume that "tallness" or "shortness" is
related to the heredity of the individual^ — that is, to something transmitted
from the parents. But the tallness, whatever it may be in a particular individ-
ual, is a composite made up of the x inches of the head, let us say, plus thejy
inches of the trunk plus the z inches of the legs.

Charles B. Davenport (1866-1944), for many years director of the
Laboratory for Experimental Evolution of the Carnegie Institution of
Washington, suggested that stature is probably inherited as four (or more)
independent "factors" (see illustration, p. 484). That is, any segment of
"tallness" might be inherited independently of the others, according to the
Mendelian formula. Moreover, "long" might be dominant over "short" in
one segment and recessive in another. Some such supposition would help
to explain the familiar fact that children are sometimes shorter than both
parents, sometimes taller than both parents.

It would also explain why the sons of a thousand tall fathers are taller (on
the average) than their contemporaries in general, but not as tall as their own
fathers, on the average — an illustration of Galton's "law of regression".

The hundreds of experiments that agreed with Mendel's formulas, as well
as those that failed to match these formulas, made people wonder more and
more, Jus; \ow are the characteristics of plants and animals transmitted.''

What Is the Connection between Heredity and Reproduction?

What Is Inherited? It is common to speak of the inheritance of charac-
ters as though something passed from parents to offspring. But a moment's
thought will show that nothing is transmitted in the ordinary literal sense.

What we really mean by saying that a plant or animal has inherited certain
characters from his parents is that there is something in the fertilized egg that
brings about the development of those characters. But whatever is in the egg
must have come from the gametes, and so, presumably, from the parents.

483

Human stature
100-

80
70
60
50
40
30
20
10
0

MULTIPLE FACTORS IN INHERITANCE

A person's stature is represented, on a percentage scale, as the sum of four seg-
ments, the length of each being determined by independently inherited factors. The
average proportions of ^the Jour segments are shown at A. The extremes for the
head-neck segment are shown'at B, those for the trunk at C, and so on. One does
not inherit six-footed ness, or even tallness or shortness, as a simple trait. One
inherits several independent factors which, acting together, result in a man's being
5 feet 6 inches or 6 feet 1 inch. (Based on data from C. B. Davenport)

When Mendel made his experiments, little was known about the nucleus
of cells, and nothing about the behavior of chromosomes during cell-division.
To explain his findings, however, Mendel made certain suppositions, or guesses,
about what probably goes on as eggs and sperms are being formed. And his
suppositions turned out to agree in some ways remarkably well with the facts
(see illustration opposite).

Nuclear Division We have already seen that when germ cells (eggs and
sperms) are being formed, the number of chromosomes becomes reduced to
half the number present in each body cell. When a sperm cell unites with an
egg cell in fertilization, the resulting zygote contains the full number of
chromosomes. Half of these came from the male parent and half from the
female parent (see illustration, p. 376). If we suppose that the chromosomes
bear Mendel's assumed "determiner", the behavior of the chromosomes fits
in astonishingly with the facts found by Mendel and other experimenters.
This was pointed out by an American biologist, W. S. Sutton. The facts of

484

Pure

dominant

parent

Pure

recessive

parent

Mendel supposed that a certain factor, or element, in the gamete brings about the dominant
character; In its absence, the recessive appears

A pure dominant produces
gametes with the factor

(5) (a)

A pure recessive produces
gametes lacking the factor

These two kinds of gametes can combine in two ways:

Dominant egg X recessive sperm vj/ B

Recessive egg X dominant sperm \}—y J

' All hybrid individuals have the factor and resemble the dominant parent

But hybrids produce two types of gametes — with factor and without

(S) (i) @ (S

/ / / /

Gametes produced by hybrids can combine in four different wayn

(1) Dominant egg X dominant sperm v y /

(2) Dominant egg X recessive sperm \~/ /^

(3) Recessive egg X dominant sperm \J— |/ j*

(4) Recessive egg X recessive sperm vtJ/ j''^

From these combinations three kinds of individuals can result:
One lacks the factor and appears to be recessive (4)
Three contain the factor and appear dominant (1) (2) (3)
But two of these are like their hybrid parents (2) and (3)
and one is a pure, or breeds true, like the dominant grandparent

HOW MENDEL EXPLAINED SEGREGATION: THE PRESENCE-AND-ABSENCE THEORY

/ ^

SS *

Individuals of pure breed can produce only one com-
bination of chromosomes in their gametes

If they are not crossed, their gametes can result only
in pure individuals, having the same combinations of
recessive and dominant traits as the parents

When gametes from two strains combine, the zygote
receives chromosomes of different kinds

Pure gametes can combine in two different ways:

Parent type A eggs X B sperms
Parent type B eggs X A sperms

The zygotes have the same chromosome combination
in either case, and in all the hybrid progeny each trait
is dominant in appearance

@@@© @@@0

When hybrid individuals form germ cells, the pa-
rental chromosomes of each pair become separated in
the reduction division

Four types of eggs and four types of sperms make
sixteen different zygotes possible

rms->'

Ts
TS

ts
TS

TS
Ts

Ts
Ts

ts
Ts

ts
ts

ts
tS

TS
ts

Ts
ts

ts
ts

The segregation agrees perfectly with the results of
Mendel's experiments:

12 tall : 4 not-tall

12 smooth : 4 not- smooth

In appearance, they are

9 TS : 3 Ts : 3 ts : 1 ts

CHROMOSOME BEHAVIOR AND INHERITANCE

In this type of succession, how many individuals resembling a grandparent can
transmit both the latter's distinctive traits?

POSSIBLE COMBINATIONS OF CHROMOSOMES

When a zygote is formed, the paternal chromosomes combine with the corresponding
maternal chromosomes. When reduction division takes place as gametes are formed,
the chromosomes become separated at random. Where there are four pairs of
chromosomes, 16 combinations are possible — 2", n being the haploid number

reduction division and fertilization agree with the simple formulas based on
Mendel's experiments. But the theory that the chromosomes are the deter-
miners raises new problems (see illustration opposite).

Are Chromosomes Determiners? If each inherited character, or trait,
were determined by a particular chromosome, the number of chromosomes in
the germ cells would strictly limit variation among individuals. The tremen-
dous variation among human beings, for example, would have to be explained
by the combination and recombination of twenty-four pairs of chromosomes.
Theoretically the number of combinations possible in any species is V", x
being the number of pairs of chromosomes. In a species which had, let us say,
only three pairs of chromosomes, the number of combinations possible would
be 2^, or 8. In tobacco or in human beings, with twenty-four pairs of chromo-
somes, the largest possible number of combinations would be 16,770,216.
And this number would include thousands of cases in which two individuals
were identical except for one or a few details.

We are forced to assume that each chromosome must bear several, or even
many, determiners. Indeed, there is so much evidence on this point that for
many years students have been speaking not of determiners in the chromo-

487

somes, but of genes, a term first used by Johannsen. If now we suppose that
each chromosome contains several genes, then independent assortment could
take place only between characteristics whose genes were in separate chromo-
somes. That is, two genes or determiners in the same chromosome would
always pass from generation to generation together — just as, in fact, the
"hnked characters" are found to do (see page 482).

Chromosome Numbers in Various

Species of Plants and Animals

Potato {Solanu?n tuberosum) : 48

Fruitfly {Drosophila) :

Various other species: 24, 36, 60, 72

Housefly:

Blackberries and raspberries (Rubus):

Grasshopper:

various species: 14, 28, 42, 56, 70, 84

Rat:

Other varieties: 35, 49

Swine:

Plums: 16, 32, 48

Man:

Citrus fruit, varieties: 9, 18

Cattle:

Chromosomes and Linkage^ The discovery of linkage as an apparent
exception to Mendel's rule of independent assortment of unit characters
turned out to be a severe test or "proof" of the theory. As experiments were
extended, more and more cases of linkage were discovered: not all inherited
traits sort out independently. Moreover, these linkages included large numbers
of characters, rather than two or three, which at first seemed to be exceptions
to Mendel's principle.

The most telling facts came from experiments with fruit flies of the species
Drosophila melanogaster (see illustration opposite). Hundreds of trained work-
ers have studied wild forms of this species (see page 491). With the study of
linkages it became possible to locate the various determiners, or genes, on each
chromosome. One of the earliest Unkages studied in the fruit fly was the
case of an artificial combination containing two distinct recessive characteris-
tics— a very much reduced wing and a black coloration of the body (see illus-
tration, p. 490).

Other examples were of linkage of this reduced wing with a certain eye-
color; another eye-color is usually associated with an ebony body; a vermilion
eye is linked with a curious notch on the wing; and so on. The linkages occur
in three groups of many characters and a fourth group including only a few
characters. These facts strengthen the suspicion (1) that each determiner
occurs normally in a particular chromosome, and (2) that the gene is a real
something, since the larger chromosomes apparently carry more determiners
than the small ones.

But how can we locate a particular gene in a particular chromosome?

Sex-Linked Characters"- The clue to identifying the chromosomes came
from the discovery that in many species the chromosome picture was not

iSee No. 5, p. 504. -See No. 6, p. 505.

488

After MoFRan

ADULTS AND CHROMOSOMES OF THE MALE AND FEMALE FRUIT-FLY, DROSOPHILA
MELANOGASTER

This species has been more thoroughly studied than any other animal, with the pos-
sible exception of man himself. Thousands of inheritance experiments have been
made on the ordinary traits of the wild forms of the species, and hundreds of muta-
tions have been traced through dozens of generations

the same in males as in females. Although we speak of all the chromosomes
as paired in body cells, in one of these pairs the two members are not quite
matched. In some species these two unmatched chromosomes differ merely
in size (see illustration, p. 491). In some species the smaller one may be so far
reduced as to be quite absent, or at least invisible. In other species there is a
difference in shape (see illustration above). Associated with this inequality
is the fact that in some species the sex of the individual is determined by the
constitution of the sperm, whereas in other species it is determined by the
chromosome character of the tgg (see illustration, p. 492).

Now it is well known that among human beings a form of color-blindness
in which a person cannot distinguish red and green is seldom found in females.
If we suppose that this characteristic results from the presence of a special
gene in the sex chromosomes, we can explain the actual distribution of color-
blindness. Color-blindness "skips a generation" in inheritance, being trans-
mitted not from fathers to sons, but from grandfathers to grandsons, and only
through the daughters (see illustration, p. 493). This is a familiar sex-Hnked
character.

In studies on the fruit fly about two hundred characters have been found
to be sex-linked. The genes which determine these characters have been
assumed to be in the sex chromosomes, the so-called X-Y pair, shown in the
illustration above as a short, straight chromosome and one sharply bent.
Then there are two larger linkage groups which have been assigned to genes in
the two larger chromosomes. There is a much smaller group of linked char-
acters which have been assigned to the smallest chromosomes.

489

LINKAGE OF TWO CHARACTERS IN THE FRUIT-FLY

After Morgan

Blackness and short wings in a male mutant are recessive to normal coloration and
normal wing. In the second hybrid generation these two characters do not become
segregated, but always come out together; as we should expect, "independent
assortment" takes place. It is inferred that the determiners lie close together in the
same chromosome

5 7\ 9, 11 13 15 17 19 21 23 X

\\ \\

4' 6 8' 10' 12 14 16 18 20 22 Y

I'aililrl'

CHROMOSOMES IN MAN

The 24 pairs of chromosomes are shown in order of size. The members of each pair
ore indistinguishable, except that the smallest, marked X and Y, differ in size in the
male. During reduction division, when sperm cells are being formed, the X goes to
one sperm and the Y to another. All eggs, however, have the X chromosome. Struc-
tural variations which the microscope may reveal among chromosomes of different
individuals cannot be related to personal or racial traits

Chromosome Maps We have seen that it was through the idea of
linkage that Morgan and his fellow workers came to place certain genes to-
gether in particular chromosomes — that is, from fcllowing up exceptiotis to
Mendel's law of independent assortment. Since a chromosome is generally
an elongated structure, it seems reasonable to suppose that the genes are
probably arranged along the length of the chromosome. Now the question
naturally arose. Is there any way of locating particular genes more exactly
along any particular chromosome?

This problem was solved by studying the exceptions to the idea of linkage.
Characters are coupled; but linkage is not 100 per cent consistent. Certain
pairs or groups of linked characters become separated in succeeding genera-
tions more frequently than others. If we suppose that the genes are arranged
in a series, we should expect that those which are close together in a chromo-
some would seldom become separated, whereas those at opposite ends of a
chromosome might become separated more frequently. But what happens in
the chromosomes to produce such a break in the chain (see illustration,
p. 494).?

The observed fact that parts of chromosomes sometimes break off and
cross over to the other member of the pair seems to run parallel with the
experimental fact that characters which are usually coupled together in suc-

491

i I . / ^

^! X Y ' Composition of parents i W Z ! y Z Z

o! ; 9'K-^..y ^1

(X CX') iX| |Yl Gametes produced (W) fZ) iZl [Z

X X ) ^1 X Y I OHspring f W Z j ^; Z Z

TWO TYPES OF SEX DETERMINATION

In many species of mammals, insects and plants, all eggs have an X-chromosome, but
half the sperm cells have an X-chromosome and half a Y-chromosome. Fertilization
by an X-bearing sperm results in a female. In many birds and butterflies the eggs
are of two kinds — one with a Z and one with a W chromosome. The combining of
two Z-chromosomes results in a male

ceeding generations sometimes become separated. Assuming that there is a
real connection between these two sets of facts, Morgan and his associates
developed their famous chromosome "map" oi Drosophila. In this map hun-
dreds of spots on the chromosomes are assigned to the various genes that are
supposed to determine particular characteristics. Relative positions of genes
are based on the relative consistency with which two or more traits remain
linked in successive hybrid generations. Fragmentary chromosome maps on
the same plan have been made for various species of plants and animals,
including man.

Multiple Factors — Multiple Action After being for centuries the source
of endless confusion, superstition, and fruitless speculation, the problems of
"heredity" began to clear up almost suddenly when scientists attacked them
experimentally around the turn of the century.

We have learned to think oi genes as particular objects — perhaps particular
kinds of molecules — because this idea has helped us analyze (1) the behavior
of the chromosomes during cell-division, during the formation of eggs and
sperms, and during fertilization, and (2) the distribution of characteristics in
particular species of plants and of animals.

We now know pretty definitely that the inheritance of characteristics and
the chromosome behavior are closely related. But we have learned also that
no one gene does actually bring about a particular characteristic. On the con-
trary, all the findings point to the probability that (1) each gene, or "deter-
miner", produces a multitude of effects and not merely the one which happens
to catch our attention as a basis for experimenting; and (2) each "character"

492

Color-blind
male

Zygotes

Color-blind
female

COLOR BLINDNESS LINKED TO MALENESS IN MAN

To understand why color blindness is generally found only in males, we assume that
it is determined by a recessive factor in the X-chromosome. If the affected X com-
bines with a normal X, the recessive character does not show. A female would be
color-blind only with two affected X-chromosomes — that is, if she were the daughter
of a color-blind man and of a normal woman whose father or grandfather was also
color-blind

results from the interacting of many elements or factors from several genes
being present together, often in separate chromosomes. An interesting ex-
ample of these ideas is seen in the commercial production of "Silver Fox"
furs (see illustration, p. 495).

Two distinct mutations have occurred among the foxes, both producing
a black, or silver, fur; and both breed true. The Standard Black, as it is
called, originated in Eastern Canada; the Alaskan Black, in Alaska. Both

493

During conjugation of germ
cells, the two members of
each pair of chromosomes be-
come intimately intertwined.
When they separate again,
portions of the two chromo-
somes seem to have become
interchanged. The occasional
failure of linkage would seem
to be due to the occasional
interchange of chromosome
segments between the pater-
nal and maternal chromo-
somes of a particular pair

CROSSING OVER

are black, as the photograph shows; yet they are distinct in appearance —
and distinct in their hereditary or breeding behavior. When these two
types are mated, there appears only the "Blended Crossfox" type. When
these hybrids are mated, their offspring divide into nine easily recognized
types, which are shown in the picture. That is, the hybrids are hetero-
zygous with respect to some of the genes, or factors, that determine the
coat characteristics. This is, of course, what we should expect on a simple
Mendelian interpretation. But further study shows that the situation is
not simple. Among the offspring of these hybrids 25 per cent, on an
average, are of the parental hybrid type, the crossfox; but there are also
four other "hybrid types" — 12^ per cent of each. And finally, there are
four types that are "pure" — two like the black grandparents, as we might
expect, and two quite different. These two are the so-called "double black",
which is quite new, and the "red" fox — the original wild type.

An analysis of these experiments indicates that there are probably two
pairs of genes that account for the facts. The types shown in the four
corners of the illustration all breed true; that is, each of the genes in ques-
tion occurs in a homozygous state — altogether dominant or altogether
recessive. This is represented by the symbols AABB, AAbb, aaBB, and
aabb. We can check this idea by working out (1) the result of inbreeding
any of the hybrids; and (2) the result of mating any two of the hybrid
types, using the Punnett squares.^

Each character of the organism, each part, perhaps even each gene in the
chromatin of a cell, influences the whole body. And each part or process is
influenced by all the others. The organism continues as a unity.

Our method of study makes it necessary to analyze. We analyze the or-

^See No. Ab, p. 504.
494

it J

Red

AABb

Smoky
red

Standard
black

*«

Alaskan
red

AaBb

Blended
cross iox

Sub-standard
black

Alaskan
black

Sub-Alaskan
black

Double
black

! , _ . _

Inilcd Stall's Fish and Wildlife Service

MULTIPLE FACTORS IN THE TRANSMISSION OF COAT COLOR AMONG FOXES

ganism into the many structures we can distinguish and finally into its par-
ticular characteristics, or variations. We analyze the chromosome-action,
trying to find the smallest possible units, in the hope of explaining very com-
plex processes. But however far we may carry our analysis, the problem of
heredity remains the problem of life itself: (1) a living organism builds itself
out of foreign materials; (2) it passes through a cycle of change which ends
in its death; but (3) it perpetuates its own distinct qualities in the living
processes of other objects — the immediate offspring or later descendants.

What Are the Practical Applications of Genetics?

Need for Better Types of Organisms Fanciers, commercial breeders,
and seedsmen are constantly looking for interesting novelties, both among
their own growths and the world over. Occasionally there appears a ''sport",
or an exceptional individual, with valuable characteristics (see page 509).
Furthermore, breeders of plants and animals have not been content with find-
ing desirable individuals or strains by chance, but have attempted to bring
about variations of a kind that are both useful and permanent. But it is only
since the beginning of the present century that we have known the biological
principles for combining systematically in a race or variety a number of
desirable qualities, and avoiding undesirable ones.

Among the most serious of the "undesirable" qualities in domestic plants
and animals is susceptibility to disease. The late blight of the potato causes
an annual loss of about nine million bushels. In the poultry industry the loss
of pullets runs from thirty to forty per cent. It is not possible, as we have seen,
to transmit all the characters that appear in a hybrid or even in a combination
that results from segregation. It is necessary that those factors or "genes''' in
the two parental gametes which determine a desired character shall be either
both dominant or both recessive. If only one of the germ cells is dominant, a
particular individual may have the quality in which we are interested, but its
offspring will be of two kinds (see illustration, p. 486).

Breeding for Immunity Certain American breeds of good beef cattle
that could be handled in great herds on large prairie ranches were susceptible
to the destructive Texas fever. The "Brahman" cattle of India were immune
to Texas fever. On mating these immune animals with a susceptible variety
the immunity appears as dominant. Brahman cattle were accordingly im-
ported for crossing with our native cattle. A new variety was established;
this combined the beef quaUties of the American cattle with the immunity of
the Hindu type. In this case, breeding for immunity ceased to be important
when we learned to prevent the disease (see page 617). But in other cases this
principle has been of great value.

In the case of wheat, immunity to "rust" is recessive. It has nevertheless

496

been possible to establish strains of wheat that combine immunity to rust
with other desirable qualities. For, as we have seen, it is necessary to breed
a sufficient number of hybrids only into the next generation in order to get a
complete segregation of the various dominant and recessive characters, in all
their possible combinations. In a third generation we can begin to select off-
spring with the desired characteristics in a pure dominant or pure recessive con-
dition. Experiments are under way to develop wheat varieties that can resist
more severe winters. Crosses between wheat and rye promise to yield valuable
results. Some of the many varieties that appear after the hybrids are inbred
have valuable wheat quaUties combined with the rye's resistance to cold.

Practical Breeding The failure of their hybrids to breed true was the
despair of plant and animal breeders in past centuries. Only a few, like Luther
Burbank, were successful. Burbank was patient enough to try out vast num-
bers of hybrids. And he was keen enough to detect the rare individuals that
would probably breed true with regard to the desirable combinations of quali-
ties. With our present knowledge of heredity it becomes possible to produce
almost any combination of useful or fancy characteristics that we may desire.
This does not mean that new characters are produced by these methods. When
Burbank produced a "white blackberry" he did not get a plant with a new
character, in the biological sense. He combined a plant having pale-yellow
berries, of no value as fruit, with one having large, black berries — the Lawton
blackberry. From the hybrids he obtained segregating offspring. And from
the segregated lines he was able to fix the strain that lacked pigment and had
other desirable qualities in a "pure" state — that is, had only recessive genes
or only dominant ones from both parents.

Every year experiment stations and private gardens of seed-producers,
nurserymen, and horticulturists offer us "new" flowers, fruits and vegetables.
Many of these new varieties are hybrids which cannot breed true. Such plants
are propagated by means of cuttings or grafts or by means of bulbs or tubers.
The Burbank potato, for example, which originated as a seedling and has been
one of the best-known potatoes in this country, has to be propagated by means
of the tuber. Seedless varieties of grapes, apples, oranges, and so on, would, of
course, be propagated by grafts or cuttings. But all cultivated fruits are
propagated vegetatively even when they have seeds. Since they are hybrid,
their seedlings would "split up" the combination of qualities that is of value.

Novel combinations in annual plants, which have to be grown from seeds
every year, present special difficulties. But the breeders are offering more
and more varieties of hybrid seeds for field and garden. These seeds will grow
into plants having the desired combinations of characters. But the seeds of
these plants will "throw back" into the numerous ancestral types; that is,
they will segregate.

If one wants to continue growing plants with the same qualities, he has to

497

buy new seeds every year. Hybrid corn is offered that has been built up of
more "elementary" types of corn, which in turn were obtained by systematic
/^-breeding. These plants are small and poor in many ways. But the hybrids
are vigorous and combine the desired features of several strains. If you plant
seeds /or purple petunias, you will get a handsome growth; but if you plant
the seeds from purple petunias, you will get half a dozen or more varieties,
but very rarely a purple flower.

The production of giant blueberries illustrates the range and complexity of
problems involved in the creation of new plants. These blueberries are self-
sterile. It is therefore necessary to grow them along with another variety to
supply the pollen. The plants do not easily form roots on cuttings; this
difficulty is met through the use of growth-stimulating substances (see page
257). But we do get the giant blueberries.

Through modern methods of crossing and testing, those interested in
special types of plants are constantly producing new varieties with distinct
characteristics — early ripening, long fiber, particular colors and flavors, re-
sistance to heat or drought, resistance to various diseases, and so on.

Problems of Animal Breeding In every species of domestic animal
there are many more or less distinct varieties. In fact, two artificial breeds
of dogs or horses, for example, may differ more, outwardly, than two distinct
species in nature. The breeder's first problem is to find the variety or breed
that is of greatest value or most suitable for his particular purposes. The next
problem is to get the desirable qualities to repeat themselves generation after
generation. Those who have to handle cows or sheep, for example, often find
the horns in these animals a nuisance. Many farmers therefore prevent the
development of the horns by destroying the "button" in the young animal
by means of alkali or other chemicals. Occasionally, however, there appears
an animal without horns; the Polled Angus was a "sport" of this kind.
Polled, or hornless, individuals have appeared also among Jersey and Hereford
stocks. If a polled individual is mated with one that has horns, all the off-
spring will lack horns. That is, the polled condition is dominant. A purebred
hornless bull may thus become the father of whole herds of hornless cattle.
But if hybrid polled animals are mated, the following generation will show
segregation in the way already described for the yellow-green color contrast
in peas and for other plant characters (see illustrations, pp. 476 and 477).

In sheep-raising certain kinds of fleece are found to be more profitable than
others. In order to combine merino wool with hornlessness it would be
necessary to find out by means of breeding experiments which characters are
dominant and which recessive. In three generations we could then establish
new breeds having the desired combination.

In actual practice the matter is, of course, not quite so simple. Some of
the characteristics in which we are interested may depend upon the presence

498

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of two or more genes. There is also the fact of linkage, which holds together
through the generations two or more characters, of which one may suit us
while the others are quite undesirable. In mammals, for example, genes for
coat-colors and genes for ear-defects are curiously linked and so place a limit
on carrying out what we intend in animal-breeding. Nevertheless breeders
systematically apply the principles of genetics to produce new varieties of
animals, that is, combinations of qualities that have never appeared before.
The Orpington fowl is an artificial breed of this kind, and new breeds are con-
stantly being brought out. And as in the case of plants, breeders supply young
hybrid poultry having desired characteristics, but not capable of passing on
these qualities.

Heredity in Man^ So far as reliable facts are available, heredity seems
to follow the same course among human beings as among other organisms
(see table below).

Human beings take a comparatively long time to mature. To get com-
plete records for many generations it would be necessary to go back several

Heredity in Man

DOMINANT CHARACTER

Curly hair

Dark hair

Beaded hair

Hairlessness, associated with lack of teeth

White forelock

Brown eyes

Normal sight

Hereditary cataract

Normal hearing

Normal ear

Normal pigmentation

Hapsburg lip

Normal muscular tone

Nervous temperament

Fused fingers or toes

Supernumerary digits

Broad fingers (lacking one joint)

Fused joints of digits

Double- j ointedness

Normal growth

Limb dwarfing

Immunity to poison ivy

SEX-LINKED CHARACTERS

Normal blood
Normal hair
Normal vision

RECESSIVE CHARACTER

Straight hair

Light; red

Even hair

Normal condition

Normal, even coloring

Blue eyes

Night blindness

Normal eye

Deaf-mutism

Otosclerosis

Albinism

Normal lip

Low muscular tone

Phlegmatic temperament

Normal digits

Normal number

Normal length

Normal joints

Normal condition

General dwarfing

Normal proportion

Susceptibility to poison ivy

Hemophilia

Baldness

Color-blindness

^See No. 7, p. 505.
500

BREEDING FOR UTILITY AND FOR SPORT

Animal-breeders are constantly producing new varieties by combining in "homo-
zygous" individuals the qualities considered of value. They start with individuals
having desired characteristics and produce hybrids. In subsequent generations the
desired qualities are recombined, the undesirable ones eliminated

centuries; and such records were not being kept so long ago. The number of
offspring in human ma tings is comparatively small. We can therefore never
get even a hint of all the possible character-combinations in any one family.
Since human mating normally involves so many elements of taste, sentiment,
affection, and other feelings and values, experiments are out of the question
among free people. Finally, what we call the human race is really a mixture
of many distinct types or combinations of characters, and these are so thor-
oughly mixed up that we cannot find a "pure" race of human beings at the
present time. It has nevertheless been possible to compare the facts obtained
from family records with the behavior of various characteristics in the pedi-
grees of plants and animals. Such studies show that many human characters
reappear in families according to the hereditary principles of dominance,
segregation, recombination, and linkage.

We shall probably apply our knowledge of heredity to human affairs along
the line of showing what types of marriage are likely to produce offspring with
one or another undesirable trait. We already know that certain abnormalities
of physical structure or mentality are transmitted in a definite way. We
therefore counsel men and women in whose families certain undesirable reces-
sive characteristics appear not to marry others of similar stock. In the course
of time we shall no doubt develop certain standards of fitness for marriage
which will be enforced largely by the same kind of public opinion and tradi-
tion as now distinguish the customs of different peoples.

In Brief

Of the many characteristics, or traits, present in any organism, certain ones
are transmitted, or inherited, independently of certain others.

With regard to a pair of alternative traits, a hybrid may resemble one
parent completely, presenting the dominant character, and not show in its
appearance or behavior the possibility of transmitting the alternative recessive
quality.

Individuals that are pure-recessive for a given character breed true, as do
individuals that are pure-dominant; but hybrids cannot transmit the dominant
character to all their offspring. Matings of hybrids result in segregation, or a
breaking up of the combinations of characters derived from different ancestors.

To say that a plant or animal has inherited certain characters from the
parents means that there is something in the zygote, or fertilized tgg, which
makes possible the development of those traits, and that whatever is in the
zygote must have come from the gametes and so, presumably, from the parents.

The recurrence and disappearance of certain peculiar traits in successive
generations agrees with the behavior of the chromosomes in plants and ani-
mals during the formation of gametes, during fertilization, and during develop-

502

ment. It has been helpful, accordingly, to assume that each inheritable trait
depends upon something in one of the chromosomes.

Specific determiners, or genes, are apparently arranged in each chromosome
in a series, like beads on a string. The genes, or determiners, in each chromo-
some tend to remain associated, or linked, although they may be transmitted
independently.

Although the inheritance of characteristics and the behavior of the chromo-
somes are remarkably parallel, it is probable that each "character" depends
upon the interaction of several genes, and that each determiner produces
several effects in addition to the one we happen to observe.

The chief problem in dealing with plants and animals, from the breeders'
point of view, is to get organisms that can transmit combinations of desirable
qualities. Breeders and experimenters have succeeded in producing strains
that maintain such combinations, quite distinct from any "natural" species.

EXPLORATIONS AND PROJECTS

1 To study the inheritance of certain traits in rats, cross a hooded rat with an
albino; then mate the hybrid generations among themselves. Tabulate the results
for the two successive generations. Compare the distinctive traits in parental, first-
hybrid, and second-hybrid generations. Interpret results.

2 To study the inheritance of traits in guinea-pigs, cross male and female pigs
having contrasting characters, such as rough coats versus smooth coats, long hair
versus short hair, solid color versus spotted appearance, agouti versus nonagouti, or
black versus albinism.^ Tabulate results and note conclusions as to which traits
are dominant and which recessive.

3 To demonstrate the 1 :2 :1 ratio by chance combination, work in pairs and
flip two coins 100 times. Record the heads and tails for each double throw. The
theoretical ratios are both heads, 25 times; 1 head, 1 tail, 50 times; both tails, 25
times. Compare results with the theoretical expectations. Combine the results of
several sets of trials; compare the total with the theoretical expectations. Note un-
usual deviations from "expected" results.

4 To work out interpretations and probabilities in hereditary phenomena, make
diagrams and calculations in various concrete or imaginary situations, such as the
following:

a. Pure smooth peas are crossed with pure wrinkled peas. Note (1) the appear-
ance of the hybrid generation; (2) the genetic make-up of hybrids. (Use capital S
to represent dominant smoothness and small s to represent recessive wrinkledness.)
Show (1) the probable appearances in the following generation if the hybrid in-
dividuals are mated; (2) the genetic make-up of the various types; and (3) the
ratios of the different phenotypes and the ratios of the different genotypes.

^The gestation period in guinea-pigs is 65 days. The pigs can be fed on the complete diet as
given on page 112, or upon commercial rabbit chows supplemented by green foods and milk. If
green grass or clover is available, it may well constitute the bulk of the diet.

503

b. Pure smooth green peas are crossed with pure wrinkled yellow peas. What
will be the appearance of the hybrid generation? the genetic make-up? (Let
capital Y and S represent the dominant yellowness and smoothness respectively,
and small y and s represent the recessive greenness and wrinkledness.) Note (1) the
appearance of offspring; (2) the kinds of gametes that the hybrid generation will
bear. Work out the results of crossing these gametes, using the "checkerboard" or
Punnett squares.

c. Pure dominant strains of tall smooth yellow peas are crossed with short
wrinkled green peas. Use the Punnett-squares method to find (1) the appearance
of the hybrid generation; (2) the genetic make-up of the hybrid; (3) the possible
gamete types produced by these hybrids; (4) the different phenotypes produced;
(5) the ratios among the body types in the offspring; and (6) which types will breed
true in later generations, and which will break up again.

d. A child of brown-eyed parents has blue eyes. Show by the use of genetic
symbols and a diagram the probable composition of immediate ancestry.

e. Henry and Susan both have normal hearing. One of Henry's grandparents
was a deaf-mute; among Susan's near relatives two first cousins are deaf-mutes.
Show by diagram and genetic symbols the possibility that, should Henry and Susan
marry, some of their children might be deaf-mutes.

/. What would be the expected offspring of a mating of a long-haired guinea-pig
with a short-haired guinea-pig one of whose parents was long-haired?

g. A rough-coated black guinea-pig whose mother was smooth-white is mated
with a smooth-white animal. Work out the kinds of offspring and the ratios of the
various kinds.

h. A girl of normal vision whose father was color-bHnd marries a color-blind man.
Work out the probabilities as to color-blindness among their sons and daughters.

5 To study the inheritance of traits in fruit flies, cross the wild type with pure
cultures showing characters readily distinguishable without a microscope. Such
characters as ebony body and vestigial wings illustrate Mendelian inheritance; white
eyes and yellow body illustrate sex-linked inheritance.

In mating, it is essential to use only virgin females. Since adults in a given culture
mate within a few hours after emerging from the pupa, use only cultures in which
there are no adults over an hour old. To cross, select one male and one virgin female,
from etherized cultures.^ Place pair in a prepared bottle containing suitable food.^
After eight to ten days remove these parents so that there is no chance for them to

^For etherizing, use a bottle the same size as the culture bottles (widemouthed, 8 oz, or half-
pint milk bottle); attach a wad of cotton to a cork with a wire. Moisten cotton with ether. Trans-
fer flies from culture to bottle; close and etherize one minute. Dump insects on a piece of clean
paper and sort with a camel's-hair brush. The females have a slightly wider abdomen than the males
and also small lines across the tip of the abdomen; the males, which are smaller, have a black-tipped
abdomen. To prevent the growth of mold, use the commercial preparation "Moldex".

^To make a growing medium, add 100 g of corn meal, f cup of molasses, and 15 g of agar to
750 g of boiling water, while stirring. Cook about 10 minutes. Pour into sterilized bottles, about
5 in. in each; then insert in each a strip of paper toweling, on which the larvae may crawl to pupate.
With a clean medicine-dropper add to each bottle one drop of water in which a bit of yeast cake has
been dissolved.

504

mate with the emerging hybrid flies. ^ For the second generation, simply transfer
several hybrid male and female flies to new bottles. Again remove the adults after
they have laid their eggs.

6 To study the inheritance of traits in poultry, incubate hybrid eggs of known
parentage and brood the chicks in the classroom or at home. (The inheritance of the
barred factor in the sex-chromosome can be demonstrated by crossing a Rhode
Island Red rooster and a Barred Rock hen.) Describe appearance of cockerels and
pullets. Account for the results you obtained.

7 To trace the probable inheritance of human traits, collect evidence as to the
occurrence of various traits in the members of a family. Distinguish those character-
istics which seem certainly to be inherited as dominant or as recessive. Note any
evidence that a trait may be inherited but remain undeveloped under special condi-
tions. Note any evidence as to whether a child inherits more traits from the parent
of the same sex than from the parent of the opposite sex.

QUESTIONS

1 How has hybridizing been used to Improve our plants and animals.'' What
are its advantages.? its Hmitations?

2 What is it that actually continues from one generation to the next, in sexual
reproduction.^'

3 How can the changes in the chromosomes be related to the simple Mendelian
laws of dominance, segregation, and independent assortment.''

4 In what sense are the facts of linkage, imperfect dominance, and multiple
factors exceptions to the Mendelian laws.i^

5 How does a further study of these seeming exceptions strengthen the hypoth-
esis that the bearers of heredity are in the chromosomes?

6 How is it that individuals sometimes lack qualities which are present in one
or both of the parents?

7 How can an individual sometimes manifest qualities which neither of the
parents has?

8 How do the common fruits and vegetables in use today differ from those of a
generation ago? How did the changes come about?

9 What are the necessary steps in establishing a new breed of plants or animals?

10 What advantages has the plant-breeder over the animal-breeder?

11 How does our present knowledge of heredity agree with the idea that off-
spring inherit the effects of experience, exercise, injury, sickness, and other modifica-
tions?

12 In what way can the experience or condition of a pregnant female influence
the offspring?

^ Ordinarily it takes about two weeks for the fruit fly to complete its life cycle, though in an
incubator at from 75° F to 80° F it takes from 10 to 12 days.

505

CHAPTER 25 • HOW SPECIES HAVE ARISEN

1 What causes new species to arise?

2 How do new species come to fit their surroundings?

3 Are modern plants and animals superior to ancient forms?

4 How can we tell whether any kind of plant or animal is really a

new species?

5 What kinds of variations are inherited?

6 Why are some variations more fit than others?

7 Does the human race consist of one or of several species?

8 How can we tell whether man has resulted from evolution?

9 What is meant by a "missing Hnk"?
10 Is evolution taking place today?

All life is one. Every plant is like all other plants, every animal is like
every other — in the basic capacities. That is, each grows, develops, responds
adaptively to what goes on around it, reproduces.

Yet every individual is unique. Indeed, the individual is all that we can
know directly — the individual, and many other individuals more or less Hke it.
From our experience with many unique individuals we may feel that we know
whole classes of similar individuals. We speak with confidence of the cat or
dog family, of the class "fishes", of the order "beetles", or of all mankind.

Since individuals resemble their parents and other ancestors, they form
groups that remain fairly constant through many generations. But individ-
uals also differ from their parents, as well as from each other. The actual
constitution of a species or of a genus is constantly changing, just as the exact
chemical make-up of an individual is constantly changing. But does this
process bring about the formation of new species? And how, in spite of such
changes, do living things continue to be adjusted to their surroundings?

How Can New Species Arise Out of Old Ones?

New Species or New Individuals There can be no doubt that species
of plants and animals became extinct throughout ancient times, and that new
species came into being from time to time. How can a new species arise
ready-made, with a complete set of individuals at all stages of development,
like the inhabitants of a beehive? But it is no easier to imagine a species
starting out as a pair of adults, or as a number of eggs, which would first have
to develop into adults and then reproduce themselves. Cuvier cut across all
such difficulties by saying simply that when the time came, new species were
created, and they repopulated the world. And the new species, he was sure,
had no connection whatever with their predecessors, although they had been
created along similar lines.

506

If we assume, with Darwin and Lamarck, that life has been continuous,
then we have to answer the question How did different forms come to be?
We know that individuals differ from their parents, but will their offspring
differ still more from the grandparents? And will individuals in such a line
of descent ever differ enough from their ancestors to be a new species?

The Germ Plasm The basic question is, of course, What connection is
there between an organism and the germ cells which it bears? or What con-
nection is there between a fertilized egg and the individual into which it
develops? These questions could not be effectively considered until after the
essential facts of fertilization had become known. According to the German
zoologist, August Weismann (1834-1914), each organism is what it is because
it developed from a certain germ plasm (see illustration, p. 508).

It was Weismann's notion that the experience of an individual cannot in-
fluence the germ cells so as to make the offspring show the effects. The result
of exercise or of mutilations or of sickness, for example, should not appear in
the following generation. There is, in fact, no evidence whatever that modi-
fications produced in the course of an individual's lifetime ever appear in the
offspring, although many people firmly believe that such modifications are
actually passed on.

In human beings and in other mammals, illness, alcoholism, or chemical
injury to the parent may bring about some effects in the offspring. But such
effects are not generally of the same kind in the child as in the parent. It is
easier to explain what happens in such cases as an injury that interferes with
the development of the fetus.

It is, of course, impossible to prove a negative — that acquired characteris-
tics are not inherited (see page 342). The most that we can say about La-
marck's assumption is that no one has yet shown unmistakably that acquired
traits have been transmitted. But we have learned from countless experi-
ments since the time of Weismann that the chromosomes appear to be con-
stant and that the "genes" appear to be unchanged by the experience of the
body.

What Kinds of Differences Are Inherited? When Weismann made
the distinction between germ plasm and soma, or body plasm, he anticipated
important later discoveries about the behavior of cell chromosomes (see
pages 368 and 386). We can now say with assurance that those qualities
which are determined by the germ substance or genes are inherited, whereas
the effects of experience or of external forces — which do not affect the germ
— are not inherited.

We recognize, of course, that parents never actually hand over to their off-
spring particular features. Mother still has her curly hair; father still has his
round chin. Parents transmit a ctns^m germinal constitution. In order to de-
cide in any case how a particular organism came to be just as it is at the mo-

507

Fertilized

egg

Germ plasm

Body 1

perm plasnt

Body 2

iGerm plasm

Body 3

Germ

plasm

After Wcismaiin

THE IDEA OF GERM PLASM

We commonly think of germ cells as produced by the organisms which bear them.
We may also think of the fertilized egg as dividing into cells that become a body
and others that continue as germ plasm, which later gives rise to new individuals —
and more germ plasm. The stream of germ material persists indefinitely, carried
through successive generations in the bodies — which it produces

ment, it is not enough to compare two individuals or two groups of individuals.
The problem really involves four sets of questions. We can see this if we
generalize it to cover all essentials.

1. How do organisms of uniform genetic constitution develop in en-
vironment A}

2. How do organisms of uniform genetic constitution develop in en-
vironment B}

3. What is the effect of a particular environment upon the development
of organisms having constitution C?

4. What is the effect of the same environment upon the development of
organisms having constitution D}

These are practical questions for all who have to raise plants or animals, as
well as for breeders. Some varieties or strains of plants and some kinds of
animals — including human beings — can thrive in one setting but not in an-
other. We invite failure if we plan to raise bananas in Kansas or to run a fox
farm in Florida. But we have to be discriminating even if we plan to raise
wheat or corn in Kansas and oranges in Florida.

The physician and the nurse, the politician and the teacher (as well as the
poultryman or the rancher), have to know that you cannot treat all individ-
uals alike if the individuals are to develop to their full capacities. The old
saying that you cannot make a silk purse out of a sow's ear still holds true.
We must recognize that individuals of one constitution will make aviators,

508

but individuals of a different constitution will do better as composers or
inventors.

The individual differences that correspond to "constitution" are due to
inherited genes. A particular constitution or talent may never be trans-
mitted as a whole, since it results from the interaction of many genes — some
dominant and some recessive. Individuals will thus continue to differ from
their parents, but they will not deviate in a consistent direction because
of similar experience, as Lamarck thought. Nor will they deviate in a
consistent direction because of selection, as Darwin thought. The species re-
mains constant, just as the level of the sea remains constant, or the composi-
tion of the blood, on the average — that is, through constant fluctuations.

If Species Are Constant, How Can New Forms Arise?

Sports From time to time animal-breeders and horticulturists report
the appearance of an individual that is in some respect strikingly different
from his ancestors. Such an individual is a "sport" and it is often a deformed
plant or animal which cannot live very long. Or it may be strong enough to
survive, a freak like those exhibited in the side show of a circus. In many
cases, however, a sport has some valuable or interesting qualities that the
breeders seek to preserve.

There appeared on a farm in Massachusetts, in 1791, a queer sheep with
a long body and very short, crooked legs. This freak, ancon sheep was not
particularly handsome. When it had grown up the owner considered the odd
shape of value. It kept the animal from jumping fences. By using this sport
as one of the parents for a new flock he obtained in the course of years an in-
creasing number of these short-legged sheep (see illustration below). The
original ancon breed was kept going about a hundred years. More recently

There are no known descendants
of the original ancon ram that
suddenly appeared on a Massa-
chusetts farm in 1791. More val-
uable sheep sports have since
appeared and have become es-
tablished, but the ancon remains
of interest as a classic example
of a breed's becoming estab-
lished through the selection of a
recessive character that started
as a freak or sport. The ancon
mutation in the picture appeared
on a farm in Norway, in 1919

I hi i^tian Wriedt

A CLASSIC TYPE OF MUTATION
509

the same type of sport has again appeared in this country and in Sweden, This
"turnspit" type of animal is sometimes found among dogs, the Dachshund
being a common example.

At other times there have appeared sheep with unusually long wool, and
these were saved as a basis for further breeding. Peacock fanciers sometimes
find a single bird with plain black plumage. Several times whole flocks of
such birds have been established from a smgle freak mated with the normal
type. These sports, or jumps, occur also in plants, A wild dewberry without
thorns was the basis for Luther Burbank's thornless blackberry. A grain stalk
may appear without the sharp bristles, or awns, among the grains, A seedless
plum or a seedless orange grows unexpectedly upon a tree that had previously
borne only respectable fruit with seeds.

Mutations^ Darwin knew of such sports, but looked upon them as
freaks rather than as significant features in the formation of species. In more
recent years biologists have been giving special attention to sports. From the
fact that such freak individuals sometimes establish distinct lines of descend-
ants, the Dutch botanist Hugo de Vries developed a theory to account for
the origin of new species. De Vries himself cultivated many lines of new
plants which originated in this sudden or discontinuous manner from evening
primroses and from other species, both wild and cultivated (see illustration
opposite). Such suddenly arising departures from the parental type de Vries
called mutations. The individuals bearing the new characters for the first
time are called mutants — from a Latin word meaning "to change".

In most cases, the observed mutants do not deviate greatly from their
parents. The changes are usually confined to one or a few details, such as
shape or coloration or size or the number of like parts. Nor are most of the
mutations observed of any great importance, either as natural advantage to
the organism or as useful in practical cultivation.

The mutation theory does not attempt to explain how it is that plants and
animals do depart from the parent types. It declares merely that new types
become established only if individuals appear with distinctive qualities which
they, in turn, transmit to their offspring. It does not assume that mutants
have any superiority or advantage over the parental type, although some may
have. It is sufficient for the theory if new types of individuals are capable of
living and of establishing themselves through their progeny. This theory, like
the theory of Lamarck and the theory of Darwin (see pages 464 and 466),
depends upon the facts of heredity.

We know definitely that such jumps occur. We do not know what brings
about such freak behavior during the reproduction of plants and animals. We
know merely that such a jump away from the ancestral line is, in effect, the
beginning of a new species.

^See page 522.
510

gigas

albida oblonga rubri- lamarck- nanella lata scintLl-
nervis iana lans

176

3d generation
1890 - 1891

2d generation
1888 - 1889

1st generation
1886 -- 1887

4th generation
1895 - 1896

10,000

15,000

8 14,000 60

U Parental type

MUTATIONS IN THE EVENING PRIMROSE

From 1886 on, Hugo de Vries planted seeds from the common evening primrose.
Among thousands of new plants grown each year he found from one to several
individuals that departed in some definite way from the parental type. He gathered
and planted the seeds of these deviates, and in the course of time had a number of
distinct strains. From these experiences he developed the mutation theory to explain
how new species originate

Mutations under Glass Practical breeders and horticulturists bring
into the market every year beautiful new colorings among flowers and new
varieties of prize- winning animals. But most of these novelties do not con-
tinue long. They are replaced by other novelties. Sometimes this is a matter
of fashion and interest. At other times, however, the breeders are unable to
maintain a consistent variety for several generations. This has been the case
especially when novelties have arisen as the result of mating two different lines.
These hybrids are said to break up in succeeding generations, or to throw back
to the ancestral characteristics. The tremendous improvement in our under-
standing of heredity since the beginning of the century has made it possible
to follow closely plants and animals under controlled conditions.

Among the most intensively studied animals were the famous fruit flies of
Professor Thomas H. Morgan (1866- ), of Columbia University and later
of the California Institute of Technology. The fruit flies are of no known
value in practical affairs. They were used only for convenience, for they can
be kept in large numbers in a comparatively small space. They have distinct
characteristics, which make it easy to study them with reference to particular
traits. And they reproduce at short intervals so that some twenty-five gen-
erations a year can be studied without too great cost or effort.

Under these controlled conditions, Morgan and his associates were able to
observe in almost every generation from one to several mutations. Some of
the departures from the ancestral pattern reappeared in subsequent genera-
tions. In considering the rise and reproduction of these various fruit flies, no
question is raised as to the adaptive value of the new qualities. In many cases,
indeed, the freak was unable to reach maturity or to reproduce itself. Nor for
the moment was any question raised as to what feature in the general environ-
ment, in the food, or in the strain itself brought about such mutations. It was
necessary merely to make sure that the freak arose in a "pure line" — that is,
was not itself the result of crossing, or "hybridizing" — and that the new
characters reappeared in the offspring.

Similar observations have been made with many kinds of plants, as well
as with other animals, in all parts of the world. Literally thousands of muta-
tions have been described, and they have furnished a valuable basis for the
interpretation of the problems of inheritance.

Mutations in the Making Speculation as to the cause of a mutation led
to experiments with the various factors of the environment. The effects of
temperature, chemical conditions, dryness, changes in the food, have all been
tried. In 1928 H. J. Muller (1901- ), then of the University of Texas
and since working in research laboratories in different parts of the world,
showed that under certain conditions X rays produced marked effects upon the
germ substance of mature fruit flies. Treating cultures of insects with X rays
increased the proportion of mutations in the following generation. This

512

After Morgan

MUTATIONS OF THE FRUIT-FLY

In the course of systematic observation and experimenting, Morgan and his associates
found hundreds of individual fruitflies that arose as distinct types year after year.
They differed from their parents in a single character, sometimes in several characters
— eye color, wing shape, body color or shape, and many other details

showed at least that without modifying the parent, something may happen
to the germ cells in a way that alters the characteristics of the offspring. It
did not enable us to produce particular mutations at will, nor did it tell us
exactly how the X rays exert their influence. Among these mutants, as among
those which appeared "naturally" in the laboratories of other investigators,
were some with white eyes, some with smaller wings, and many other freaks.
Many of these were entirely new in the sense that they had not been found
by other experimenters or observed to occur "naturally".

In recent years startling results have been produced by treating plants
with the drug colchicine, obtained from a plant of the crocus family. The first
effect observed is a great increase in the size of parts treated, often associated
with coarse tissues or rank growth. The giant character is inherited. Closer
study indicates that the colchicine acts upon cells at the time the nucleus
divides, by keeping newly formed chromosomes from separating into two
sets. The result is a doubling of the chromosomes, and a modifying of the
growth and other characteristics. A "harvest spray" containing colchicine
has been used to keep apples of Mcintosh and other varieties from dropping
off the stem too soon while ripening. This spray improves the quality as
well as the yield, from the orchardist's point of view.

We have every reason to think that new forms are constantly arising, more

513

rapidly in some regions or among some species than in others. None of the
physical or chemical features in the conditions of living is known to give rise
to mutations. Some of the mutations certainly are incapable of perpetuating
themselves. From the facts that we do know, however, it seems reasonable
to assume that (1) mutations have taken place among living things throughout
the centuries; (2) some of the existing species arose, through mutation, from
ancestors having somewhat different characteristics.

Does the Idea of Evolution Apply to Human Beings?

Kinds of Resemblances On the basis of structure and form, human
beings are most like the apes and monkeys. For the zoologist Homo sapiens
represents one family of the order Anthropoidea. The other famiUes of this
order are represented by the marmosets, the New World monkeys, the Old
World monkeys, and the simians, or apes (see p. 53 and Appendix). We have
seen that in hundreds of details the homologies of structure show remarkable
similarities between man and the other mammals, but more specifically the
other anthropoids. The teeth, for example, vary among the primate families,
but the numbers and kinds of teeth are the same in men and the apes.

In the course of its development the human embryo passes through stages
which are impressively like those of other vertebrates, of other mammals, and
especially, again, of the other primates (see illustration, p. 459). During this
development the embryo puts on details of structure that recall details in
other species, but that have no relation to the human mode of life (see pages
174 and 460). We might conceive all these resemblances to be merely coin-
cidences, and without any bearing upon man's history or ancestry.

Chemical Resemblances Some of the similarities between man and
the other primates, however, appear more significant. The human race, as a
whole, is immune to certain species of microbes that cause disease in other
species, but the apes are susceptible to about the same diseases as men are.
That is, there is a chemical similarity between man and the other primates,
as well as a physical, or structural, similarity. The parasitic protozoon that
causes the disease syphilis affects other primates, but with a virulence that is
almost in direct proportion to their structural resemblance to man: the resem-
blance is strongest in apes, weaker in monkeys.

We have seen that bringing foreign substances into the blood of an animal
leads to the formation of specific antibodies (see page 233). White-of-egg, for
example, would result in one kind of antibody, and the protein of a fish would
result in a different kind. This general fact was at first put to practical use in
deciding whether blood-stains had been made by human blood or by the
blood of some other animal.

If small quantities of human blood are repeatedly injected into a rabbit

514

over a period of time, the rabbit's body will form specific antibodies that will
produce a cloudiness if mixed with human blood. The antibody is said to
"precipitate" the specific human protein, but the rabbit's serum will not
react in this way with the blood of a hen or a sheep. But it will precipitate —
somewhat — if mixed with monkey blood. And it will precipitate more if mixed
with ape blood (see page 240).

These and similar experiments carried on over many years show that the
structural resemblances between animals which we class as "related" have their
parallel in chemical resemblances. The blood of man is more like that of an
ape than it is like the blood of a monkey, and it is more like the blood of a
monkey than it is like that of a lemur.

In structure, in the common functions, in development, in chemical pecu-
liarities, and in genetic behavior man is like other organisms. And the degree
of resemblance, as well as the degrees of difference, warrants us in thinking that
man is subject to the same forces or influences as have brought about trans-
formations in other species.

Evolution and Man At the close of the last century thinking people
were discussing the evolution theory as applied to man. Many who were
willing to assume that evolution had taken place among plants and lower
animals hesitated to accept the same explanation for the appearance of man
upon earth. One of the strongest arguments urged against the theory was the
fact that it had been impossible to produce a complete record of a graded
series connecting men of today with his supposed nonhuman or prehuman
ancestors.

This argument of the "missing link" carried a great deal of weight. For
most people do not appreciate how unHkely it would be for a complete series
of specimens to be preserved through the far-reaching changes which the
earth itself has undergone. Of the millions of human beings and other verte-
brates that die in a given region during a century, how many skeletons are
Ukely to remain sufficiently intact to be recognized from ten to fifty thou-
sand years later? From a scientific point of view, it would be sufficient if the
scattered pieces found at widely different levels (geological ages) did actually
fit in with a supposed series.

The few bones found in Java in the early eighteen-nineties by the Dutch
army surgeon Eugene Dubois (1858-1940) fit into such a series in a very
satisfactory way. The type of animal to which these bones belong was named
Pithecanthropus erectus, and probably represents a "missing link." This animal
had among his contemporaries a form of elephant, rhinoceros, Indian hip-
popotamus, tapir, hyena, a deer, and an animal somewhere between a tiger
and a lion. The climate and vegetation were similar in many ways to those
we now find in southern India and the islands of the region.

A later discovery of ancient remains in Sussex (England) seems to point

515

to a more closely related ancestor. The skull is larger than that of Pithecan-
thropus, and the teeth are more like those of modern man (see illustrations,
pp. 51 and 52).

In various parts of France, Germany and Belgium large numbers of speci-
mens have been found that belong apparently to the same races of primitive
men. The first of these was found in a cave in the Neanderthal in Germany,
in 1856. The type is frequently referred to as the Neanderthal race. These
men had much larger skulls than the Piltdown man of Sussex — larger even
than the skull of races living today. However, the jaws and teeth, the low and
retreating forehead, the prominent ridges over the eyes, and other features
indicate an earlier stage of development. This group has been named Homo
primigenius, or Ho?no neanderthalensis. More recently, teeth and fragments of
skull dug up in eastern China have led anthropologists to construct what is
probably an earlier member of the human family, the Pekin man.

Human Races From a biological point of view, all human beings be-
long to the same species, in spite of the great variations among the distinguish-
able "races". There is complete fertility among all varieties and stocks, and
the hybrids, or progeny of any crossings, are normally fertile.

Classifying the races of man becomes more difficult rather than easier as
our knowledge increases. A few centuries ago European travelers could report
that they had seen strange peoples of various colors, and several races were
accordingly listed in the geography books. Today, however, every attempt
to classify human races breaks down completely because "types" overlap so
much and there are such extensive mixtures of hereditary traits. The first
difficulty, of course, is to find a basis for classification. The color of the skin
is the most obvious difference. We may start out confidently to speak of the
white, or Caucasian, race, the black, or Negroid, race, and the yellow, or Mon-
golian, race. But we are immediately reminded of the dark-skinned inhabit-
ants of India and southwestern Asia, who are just as truly Caucasians as are
the "Nordics" of England or the state of Georgia.

Shall we consider the straightness or curliness of the hair? The Negroes of
Africa and the Melanesian islands typically have woolly hair. But so have
many fair-skinned and yellow-haired and blue-eyed families of nearly every
European country, as well as of our own country. Shall we be guided by the
shape of the head? The Nordics, the Mediterraneans and the Hindus have
narrow heads. But so have all the main divisions of mankind. At the same
time, broad heads are typical of the Alpine whites, the Mongolians, and the
small Negroid tribes. Is tallness or shortness a suitable basis for separating
races? Among the taller strains in the human population are certain Negro
tribes, the Polynesians, the North American Indians, and the north Euro-
peans. That is to say, whites. Negroids, and Mongolians come in tall, medium,
and short strains.

516

Black

Brown

Hriiwii liriiilur.s; II. L. Shapiro; American Museum of Natural History
Yellow Red

SORTING PEOPLE BY COLOR

Differences in skin color are obvious enough — except where shades or colors blend.
We cannot find any color group in which the members are so much alike in most of
the other characters as to be considered "of the same kind". Nor do those who
differ in color differ consistently in most of the other characters, so as to be con-
sidered "a different kind"

The medical students of the Caucasian University at Tiflis (shown in the
illustration on page 67) are probably all of "Caucasian" stock. To what
extent are they essentially alike as to stature, or pigmentation, or the char-
acter of the hair, or the shape of the head^ — or any other trait? For that
matter, what physical characteristics have these students in common that
are not found also among yellow, black, red, or brown people ?

As with other species, inbreeding for many generations is likely to estab-
lish a fairly uniform type of human beings in any given locality. There are
indeed many villages or tribes in which nearly the entire population has some
distinguishing physical characteristics, just as a particular region may show a
distinct dialect or idiom. In the course of centuries not only have the main
"races" been formed, but also subraces and specialized stocks. The North
American Indians, for example, are unquestionably descendants of ancient
Mongolians who came either across the land bridge from Siberia to Alaska, or
perhaps by boat. After many centuries they had spread southward into South
America and had also moved eastward toward the Atlantic coast and the is-
lands off Florida. When the Europeans first came to America, they found
relics of very old civilizations in Peru and Mexico. They also found scattered
over the continent other "Indians" who differed from the Mexican and South
American Indians both in physical features and in their modes of life. And to
this day another branch made up of the Eskimos is obviously different phys-
ically and in its mode of life.

Among the North American Indians there are several distinct branches
which apparently became separated from the main stem many generations
ago. While we have no pure race, there are many such isolated stocks that

517

are fairly consistent. This means probably that generations of inbreeding
have separated out a population which has several distinctive characters in a
homozygous state, that is, either pure dominant or pure recessive.

Human Hybrids From the earliest times of which we have any record,
tribes everywhere seem to have had rules intended to keep the population
"pure". That is, peoples tried to guard against "contamination" by foreign
blood. Every tribe, every village, was the very center of its own universe,
and each cherished legends regarding its origin through a special act of the
gods. All strangers were likely to be enemies. In the course of time, tribes
have become amalgamated into larger units. Hostility toward outsiders and
loyalty to insiders gradually consolidated neighboring groups into larger
federations and nations. The many tribal myths which made each fairly dis-
tinct group feel itself to be God's chosen people had to be expanded to fit the
nation. Today, however, neither the facts of history nor the facts of biology
can justify us in identifying race with nation.

Human types have apparently always crossed wherever two or more tribes
came close together, whether through war or commerce. In modern times,
with the amount of travel tremendously increasing through larger and swifter
cars, boats and airplanes, there has been more and more intercrossing of stocks.
As a result, there are more kinds of "hybrids" and also subsequent segregation
and distribution of distinctive physical traits. In a mixed crowd in every
large city you can see faces that you recognize as coming from faraway
regions. And you can see many individuals whom it is quite impossible to
assign to any particular nation or even "race". Eyes and noses and lips and
chins and head shapes and cheek bones have been brought together from
all parts of the world in new combinations (see illustration opposite).

Many of the distinct traits that we see in human beings must result from a
multiplicity of factors or genes, since there is a great deal of "blending". We
may observe almost perfectly continuous gradings in the various characters,
such as stature, coloring of skin, hair and eye, proportions of the head,
and shapes of the various features. Today we must search in out-of-the-way
places for examples of "pure" strains, and explorations by airplane will no
doubt continue to reveal isolated groups of human beings — like the
village of "white Indians" found in Central America before the Second
World War.

As in other species, hybridizing among human beings shows no effects that
are uniformly advantageous or disadvantageous. In many cases, indeed, the
offspring of mixed marriages do "combine the best features of both" parental
stocks. Those who have feared the possible ill effects of racial mixture seem
to have been influenced by group pride or feelings of superiority rather than
by any actual knowledge of the outcome of crossing. All kinds of crossings
seem to produce harmonious combinations.

518

American Museum of Natural History

WHERE DO THESE COME FROM?

Here are several American citizens who acknowledge their European ancestry.
Which can we definitely recognize as "Nordic", which as Spanish, or Russian, or
Scandinavian, or Scotch, or French, or Italian? How can we recognize them?

Human Types and Cultures The process which has been going on in
our American "melting pot" has been going on also along the world's high-
ways. In Paris, Capetown, or Singapore one can easily recognize an "Ameri-
can". But a sample of such wandering Americans would show almost as great
a variation in stature, complexion, coloring, hair, and other physical features
as samples taken at random from various nations or "races". What makes
them all recognizable as Americans? Apparently it is not so much distinct
physical characteristics as something in their manner and bearing. It is these
subtler elements of behavior that distinguish modern groups. And the an-
thropologists have found it much more satisfactory to consider prehistoric
and early historic mankind from this same point of view, distinguishing cul-
tures rather than separate races.

Over large areas and for long periods there has been great consistency in
types of pottery, basketry, housebuilding, tools and weapons, as well as in
types of language, religion, customs, ceremonials and beliefs. That is, peoples
have remained distinct in what they maJ^e and do. There has been no corre-
sponding agreement in physical characteristics. On the one hand, distinct
physical types may share in a particular culture. Many different kinds of
human "organisms" may act in much the same way, think in the same way,

519

have similar attitudes toward the various things that appear important in life.
On the other hand, people of the same physical type may carry on totally
different modes of life in different parts of the world, or in different ages. They
not only speak different languages, but may have quite different ideas about
the world and different ideals about values and goals. At the same time, a
study of living races shows very little consistent variation in the internal or-
gans or even in the bones, corresponding to recognizable types. There is no
evidence whatever that the human organism has changed in any essential
detail in the past ten thousand years.

The chief objection to mixed marriages Is the social one. Where a com-
munity disapproves of mixed marriages, the children are likely to be at a dis-
advantage. They may be excluded from recreational, economic and cultural
opportunities, or be otherwise socially handicapped. There is also the more
immediate difficulty in many cases of disharmony between the parents. For
with different training and background, they may not agree as to the right
way to do any one of the thousand little things that make up our daily living
with others. Such disadvantage, however, is obviously unrelated to questions
of race or organic constitution. We may see disasters in families of well-
meaning men and women who have not learned how to meet differences in
points of view, in temperament, in mannerisms, and in the routine manage-
ment of affairs. These difficulties arise even where the mates are of the same
stock, the same religion, the same political views, but come from different
kinds of homes. They arise with the two or three generations of the same
family, living in the same house!

Race Superiority The American melting pot has brought Into being a
population that combines cultural resources from all over the world. Regard-
less of the motives which sent people from the homes of their ancestors into
this new world (and some were forced to come here unwillingly), each has
brought with him something of human value. But this mixing of peoples has
also raised many new problems. Those who have been occupying a particular
portion of the earth for any length of time can hardly help feeling that new-
comers are intruders. If these newcomers please us, we are glad to have them
stay; but if they annoy us, we may tell them to go back where they came from.

It is easy to forget that we and our ancestors have been here but a short
time, perhaps a few generations at the most. And there were others here
before us who resented our coming. From this point of view, there is no
question of right. Primitive people fought it out, and the stronger drove the
weaker away or destroyed them. From a broader point of view, however, the
human race in its life through the centuries has been made up of many kinds
of peoples in constant migration and in constant conflict.

It is largely a matter of chance that you and your family live In one state
rather than another, or on this continent rather than another. Nevertheless

520

we cling'^to our own — that is, the familiar. And we fear those whom we do
not understand. Being intelligent and more or less civilized, we have to make
up good reasons for our dislikes and our antagonisms. We do, therefore,
exactly what very primitive people do: we assert that we are the people, and
that all others are at best not quite so good. We may base our claim to su-
periority on almost anything that we have in larger measure than others. It
does not matter whether it is tallness or large teeth or big muscles or narrow
skulls. Whatever distinguishes us is naturally superior. When we see others
claim superiority, their action appears to be childish.

In our own times and in our own country, as well as in many European
countries, we have attempted to be more "scientific". We have tried to
*'prove" by tests and measurements and lists of characteristics that our people
are superior. And, properly, we have laid emphasis upon those qualities that
distinguish human beings from other species — intelligence, imagination, crea-
tive ability in the arts, skills of various kinds. Unfortunately, however, we
have neither adequate scales for measuring these qualities nor satisfactory
methods of distinguishing native, or inherited, abilities from the effects of
culture and tradition. How could you tell, for example, that an Eskimo or a
native of New Zealand had a natural aptitude for music or mathematics or
mechanics or art appreciation? It would not help us to compare the present
accomplishment of a hundred Eskimos of, let us say, twenty years of age with
a hundred twenty-year-old Californians or Swedes.

Illiterate Mexicans learn to operate automobiles and to keep them in re-
pair. Ignorant Russian peasants learn to make and to operate huge agricul-
tural tractors and military tanks. Peruvian Indians learn to play European
musical instruments and to compose symphonies in the classical form. De-
scendants of slaves in our own states become distinguished poets, musicians,
scientists and mathematicians.

By the way, the four men shown in the illustration on page 519 all claimed to
be Irish. A still greater variety could have been selected from among the "Irish"
examined by one local draft board during the First World War; and these "types"
could be duplicated by Scandinavian Lutherans, Italian Catholics, Scotch Presby-
terians, or Russian Jews who came before the same draft board.

In Brief

Some species of organisms have become extinct; new ones have replaced
them.

Occasionally individuals that depart decidedly from their ancestral pat-
terns transmit their distinctive quaUties to their offspring.

The mutation theory of evolution supposes that natural selection, acting
upon sports, or mutations, results in new species. '

521

By applying the theory of mutation and the techniques of breeding, new
"artificial" species of plants and animals have been established experimentally.

On the basis of structure and form, on the basis of chemical and functional
characteristics, and on the basis of stages in development, human beings are
most like monkeys and apes.

The blood of man is more Hke that of an ape than it is like that of a monkey,
and it resembles that of a monkey more than that of a lemur.

From a biological point of \'ie\v, all human beings are of the same species,
notwithstanding the great variations among distinct "races".

As with other species, inbreeding of human beings for many generations
appears to establish a fairly uniform type in a given localit)'.

As in other species, hybridizing among human strains shows no effects that
are consistently advantageous or disadvantageous.

EXPLORATIONS AND PROJECTS

To find out about the origin and development of new varieties of vegetable, fruit
and crop plants or the recent developments in livestock, investigate among seeds-
men, horticulturists, poultrymen, dairymen, breeders of livestock, fanciers, or others
who have direct contact with the practical work of improving or multiplying live
plants or animals. Report on origins of new types that breed true — whether chance
discovery or deliberate creation; methods used, special value or interest, and so on.

If direct information is not accessible, use catalogues, reports of associations, the
1936 and 1937 yearbooks of the United States Department of Agriculture, or other
sources. Summarize material to show how principles of heredity have been applied
in the development of new species.

QUESTIONS

1 What is the relation of an organism to the germ cells It bears?

2 How did de Vries explain the origin of new species.? Upon what facts did he
base his explanation? What is there to support his explanation? What are its
limitations?

3 What does an individual get from its environment.? from its ancestry by in-
heritance?

4 How do you account for the origin of new species?

5 What evidence Is there of man's relatedness to other organisms? To which
other groups is man most closely related?

6 In what respects do we consider the origin of the human race like that of
other species?

7 What evidence Is there that certain races are superior to other races? Why is
the evidence Inconclusive? What are the social and political Implications of the Issue?

8 How might the universal use of airplanes and modern science Influence our
ideas of race superiority?

522

UNIT SIX — REVIEW • HOW DID LIFE BEGIN?

Something happened. There were no witnesses whom we can question
now. No dependable records were made. Is it possible to find out what hap-
pened .f* Can we solve a crime mystery without witnesses or "clues" or records?

Looking into the remote past, we ask questions about beginnings: How
did the earth begin .-^ How did life begin? But the answers must be largely
speculative. There is no direct evidence. But we cannot help wondering,
How could it have been? We cannot help guessing. But we must not pretend
to l^now — just how the world began, for example, or how life first appeared.
Certainly we do not know merely because we have learned what the ancient
Assyrians or Egyptians believed. How could those ancients really know?

As in attacking a murder mystery, we can undertake to solve these com-
plex and difficult problems in two quite distinct ways. We can solve the
mystery according to the way we feel about the persons or objects involved.
We can say, for example, "It must have been the butler, for I do not like his
eyes or his hair," or "It couldn't have been the duchess, for she came from our
town." In much the same spirit, we can explain night and day, for example,
by our need for darkness to sleep in. Or we can say that life could not have
evolved, because we do not like to be compared to lobsters or lions.

The other general method starts out by asking. What are the facts? Of
course we cannot get the facts 2ihou\. just what happened. If we could, there
would be no mystery to solve. But there are facts, and we have to get all the
facts that bear upon our problem — without prejudice. We might consider,
for example, that there are some very nice people with hair or eyes like the
butler's, or that even in our town there have been some people who really
were not very nice. Or we might consider that day and night are sufficiently
explained by observing the movements of the sun around the earth.

As to the origin of life, we have to consider facts about the history of the
earth — not what is told by people who remember what they were told — but
facts. We must have facts about the contours of the earth's surfaces and about
the constant distribution of earth material and waters. We must have facts
about the structure of the earth's crust, about the chemistry of the oceans
and of soils, about the varieties of life-forms and their distribution. These
facts by themselves tell us only what we can see now. To form any sensible
ideas as to what happened millions of years ago — and even to "believe" that
there have been millions of years rather than a few hundred or a few thousand
— we have to go a step farther. We have to make up our minds about what
we shall assume about happenings in general. Do things just happen? Is
there any order in the universe that we can discover? Is there any connection
between what happened yesterday and what will happen tomorrow? If we
assume that anything can happen, that there is no sense, no understandable

523

connection between events, then facts are of no consequence. And for that
matter, the question itself has Uttle meaning. But if we assume that there are
relationships among events, and that we can unravel them, then we can begin
to use the facts to solve the great mystery^ — at least in part.

Assuming thajt there is order in the universe, we attempt to interpret the
past by what we can see in the present. What is the connection between plants
and animals living today and those that lived last year, a hundred years ago, a
thousand years ago, or before people made records? From the bones in grave-
yards, from the shells in abandoned camp sites of primitive people, from the
carvings on ancient temples and paintings in ancient caves, from bones dug
out here and there the world over, we make up our answers. There must have
been elephants where Paris now stands. And there must have been horses and
camels in America long before there were any white men — or any Indians
either. The predecessors of those elephants and of those horses must have been
different. Were those different animals also the ancestors of the ones we see
today? And did water animals once dwell where now we see the Alps?

Such guesses are logical. But are they plausible? To answer that we seek
other facts. How do mountains originate? How are layers of shale and lime-
stone actually formed? How are mountains worn away? What makes the
sea salt? How long does it take a river to remove a million tons of earth from
the middle of a continent? How fast does sediment build up the ocean bottom?

The most important facts about the origin of life-forms have been dis-
covered since the beginning of the century, although there were good guesses
and preliminary scouting and experimenting before. Species do actually arise
from ancestors that were different. It is not necessary to "believe" that the an-
cestors of present-day life might have been different. It is almost impossible
to believe otherwise if one faces the facts — unless one dislikes the messenger's
voice. The facts of heredity, the facts of classification, the facts of develop-
ment, the facts dug out of the earth's crust and ocean-beds build up an
unassailable case for the descent of species from earlier forms, with modifica-
tion. Incidentally, these facts enable us to produce "artificial" species.

We can do little more than speculate as to the origin of the first living
beings. But today speculating on such problems is considered futile unless it
suggests theories that we can test experimentally. We are far from making
life or from knowing how it came to be. We cannot even define life except as
a process, a changing — not as a thing. There is a vast difference between
"living matter" and chemical compounds as we know them in the laboratory.
Viruses, ferments, vague and almost formless bits suggesting minute bacteria,
seem in some ways to fall between the two. Life is certainly not something
by itself. It is a process of change inside organisms and also outside them, in
the surrounding world — which includes other organisms as well. It is a way
stuff behaves, under certain conditions, when it gets started.

524

UNIT SEVEN

Why Cannof Plants and Animals Live Forever?

1 Are all plants and animals useful to man?

2 Can a plant or animal be injurious to us in one way and useful in

another way?

3 Does an animal's instincts always make it behave in a way that is good

for getting what it needs or for escaping danger or enemies?

4 Do most plants and animals die a natural death?

5 Is it possible for plants and animals to live without injury to other

living things?

6 Could a given region support more life if all animals ate only plants?

7 What causes some pest or some disease to increase rapidly at certain

times?

8 What makes epidemics usually stop abruptly?

9 Why has man been called the most destructive of living species?

10 What happens in a region when native plants or animals are driven
out of it or exterminated?

We can figure out a complete balance of chemical and physical forces in
organisms, like the balance of income and output of an engine. We feel never-
theless that "life" yields something over and above the chemical and physical
transformations of matter. As conscious beings, thinking of our pleasures and
satisfactions, of our plans and purposes, we wonder sometimes, "Why cannot
this go on forever?" Even in moments of suffering and sorrow or of disap-
pointment, we hope and reach out for better days. We cling to life and we
want more. Life is good. Why must it end? From what we observe in other
species, we assume that there is in all organisms a constant urge to keep on.
Presumably life is "worth living" wherever it is possible. But to the extent
that we are aware of life satisfactions, and especially of life possibilities, we are
puzzled and disturbed by the limitations. We recognize, of course, that in
nature nothing endures "forever". Natural objects are combinations of other
objects or bits. And these combinations are constantly being broken; the
parts are constantly being rearranged; the balance is constantly being upset.
Wherever anything is going on, any action whatever, all objects change; the
very mountains and the planets change. And to live means above all to do, to
rearrange.

Life in general goes on, then. But individual plants and animals come and
go — some more quickly across the stage, some more slowly. And at any given
moment, in any particular spot, life goes on at all only as some individual
succumbs and yields its body to others as food or as raw material. And even-

525

tually each returns the very molecules and atoms of its constitution to the air
and the waters, and to the earth, from which its substance came.

It is impossible for every new individual to live out the full cycle typical
of his species. A single pair of frogs may produce thousands of eggs in a given
season. From a single pair of houseflies starting out in the spring would come
enough progeny by the end of the season — // all lived and grew and repro-
duced— to fill a space as large as a city block to a height of six or seven stories.
Essentially there is the same disproportion between the new admissions and
life opportunity for every species — even the slowest growing and the least
fertile.

There is not only a limited amount of space. We may imagine that as
species become more differentiated, many will fill in unoccupied spaces and
so increase the total amount of living matter in the world. There is, however,
a definite limit to the total amount of carbon, hydrdgen, sulfur, nitrogen,
phosphorus, and so on. And only a limited fraction of these essential ele-
ments can be embodied in living organisms at any time. For plants and ani-
mals are "alive" only while the material is actually shifting from the non-
living world into the living, from organism to organism, from the organism
outward.

All species are, in fact, closely interrelated through their living processes.
Not only do they come into conflict for limited space, light, water, air, the
earth elements; but no species could thrive if the others died out, for the
various forms of life depend upon one another. Living means dealing with
the inanimate world, but it also means dealing with other organisms, directly
or indirectly. There is but Httle chance to continue indefinitely the life of
individuals; more abundant life seems to be a matter of adjusting the inter-
dependent and the conflicting elements for a balanced total. This balance
among all living things is itself a constant rise and fall, a constant coming and
going, a constant give and take. Like the waves of the sea, which endlessly
take on similar shapes and yet are never for two moments the same, life is a
continuous balancing and adjusting rather than a crystallized and finished
fact.

526

CHAPTER 26 • THE LIMITATIONS OF LIFE

1 What things must organisms ha\e to hve?

2 Do all living organisms ha\e to have the same thmgs?

3 Why do organisms get old?

4 Why do some species live so much longer than others? Why do

some individuals of the same species live so much longer than
others?

5 Is it conceivable that man may sometime be able to live forever?

6 What environmental factors limit life?

7 Why can some animals live only in the tropics, while others live

only in the arctic?

8 Do desert plants grow better if kept dry?

9 How do organisms spread from place to place?

10 Why is it that we do not find two species of large cats living in
the same region?

Living things act as if they were driven from within to keep on living.
The drive for food, with its thousands of marvelous adjustments, often in-
volves violence or stealth. But these are matched by the violence and stealth
through which organisms protect themselves against the food-seekers. Both
food-getting and resistance to food-getting — by others — are essential parts
of that self-preservation which has been called "nature's first law".

This drive to live encounters continuous changes in conditions — night and
day, hot and cold, changing moisture and minerals and air. It also pushes off
the inevitable end of individual life. The drive to live involves reproduction
and replacement. And life moves through space, pushing outward in all
directions, from every established individual plant, from every group of
animals.

What factors or native qualities favor particular species? What are the
factors which limit the increase and spread of a species? Why is the total life
in a place greater at one time than at another? What part has man played in
modifying the distribution of life on the earth?

Is Death a Natural Process?

Life Is Self-limiting In all plants and animals metabolism depends
upon certain external conditions. The intensity of light, for example, in-
fluences the rate of photosynthesis or the rate of growth. At one temperature
metabolism in a particular kind of organism proceeds at the highest rate; at
another temperature it ceases altogether. But even if each special condition
were at some point most favorable to absorption, assimilation, oxidation,

527

contraction, excretion, and so on, metabolism could not remain constant; It
cannot just "keep on".

For being alive means something more than the sum of all these processes
which we observe in organisms. Each detail of action depends not only upon
the outside conditions; it depends upon all the other processes. And the re-
lationships among these processes are always changing. Assimilation, for exam-
ple, depends upon absorption. The rate of oxidation depends upon the tem-
perature as well as upon supplies of oxygen and of fuel. Metabolism depends
further upon the removal of wastes, but this in turn depends upon the relative
concentration of substances inside the cell and outside it. No process goes on
by itself.

Even in so simple an organism as a bacterium, the processes cannot con-
tinue uniformly, although the food supply, the water, and the temperature
may "remain the same" for a long period. For, as the cell grows in size, the
surface through which it absorbs and excretes enlarges more slowly than the
mass of protoplasm (see illustration, p. 345). The supply of food therefore
steadily diminishes for each unit of protoplasm, and excretion becomes slower
and slower. Sooner or later, then, every cell must stop growing. This is not
the only feature about living cells that sets a limit to indefinite growth, but it
suggests how a process may limit itself.

Under conditions favorable to growth, a particular kind of cell — -a bac-
terium, for example — divides into two when it reaches a certain size. The
mother cell goes out of existence. It has not died, for the protoplasm of which
it consisted continues alive and active; but it no longer exists.

Life Is a Pattern The external factors upon which living things depend
are not always uniform. But even where they are fairly constant (as deep in
the ocean or inside a warm-blooded host) each individual, each cell, has its
definite pattern of growth. In each species the individual grows and develops,
from stage to stage, in a relatively fixed or consistent pattern. Every stage of
life leads automatically to the next. And in most species this succession leads
to a "natural death". If we measure the intensity of metabolism by cell
division or by growth, we find a general slowing down. As the zygote starts
to grow, it doubles its weight several times in the first few days. A human
baby doubles its weight in the first six months after birth. Each year it
adds a smaller fraction of its weight, until growth becomes at last negligible.

One cannot, by taking thought, add to his stature. Neither can one turn
back his developing, nor skip a stage, nor dally indefinitely along a pleasant
stretch. It is no wonder that men, reflecting upon life, have been impressed
with the idea of "fate" — which compels everything to happen in its appointed
time, everything to happen in its preordained spot in the great procession.

What Causes Death? In spite of this picture of an irresistible and ir-
reversible march of events, life is anything but uniform. Individuals differ in

528

the pattern of development. Among human beings, for example, we differ
as to the time when the first teeth appear, or the last teeth. We differ as to
the age at which we begin to walk or to talk, as to the time at which we ma-
ture, and as to how long we remain at each stage. And especially do we differ
as to how long we postpone the end of individual existence. In addition to
having such inherited differences, the individual's pattern of development
is frequently altered and blocked. Yet it has been difficult to find out what
brings about "natural death". One reason is that very few human beings die
a "natural death". There have been many theories regarding the chemical
and physical changes which lead to death, where no injuries have taken place.

August Weismann, already mentioned as the author of the "germ plasm"
idea (see page 507), pointed out that the protozoa (and one-celled plants too)
are potejjtially immortal. In this way he emphasized the idea that under suit-
able conditions a line of such simple protoplasm can remain alive indefinitely
through successive cell-divisions. There is no natural death in these species,
as we have seen.

In the more complex many-celled species the germ plasm may continue
indefinitely, so long as reproduction takes place. The individual body, or
soma, however, which we conceive to be an offshoot of the germ plasm, may
have a limited duration, except where there is vegetative propagation (see
illustration, p. 508).

According to this view, life became "mortal" when it acquired a many-
celled body, in which germ cells are differentiated from soma, or body, cells.
But we must not confuse the idea that "protoplasm continues to live" with
the idea that a particular "individual" or person continues to live. Even in
the case of the ameba or paramecium the life of the individual has a definite
limit.

What Are the Advantages of Specialization?

Division of Labor We can see the advantages of "physiological" divi-
sion of labor from our experience with social or economic division of labor. In
fact, we are so familiar with specialized organs carrying on specialized functions
that we find it in some ways more difficult to understand a "simple" system,
like a bacterium, than a complex one, like a human body.

Imagine the life of, say, a dozen scattered human beings roaming over
several square miles, each one living by himself. Compare these with a group
or family of the same number living together. In the simplest of human
societies, where there is only a family group, division of labor is already pres-
ent. The men hunt while the women look after the children and prepare food
and shelter. Members too old to take part in the strains and dangers of hunt-
ing keep weapons in repair or make new ones. Children too young to do more
difficult work can fetch and carry for the older members, saving the time of

529

G.ill.iway

ADVANTAGES OF SPECIALIZATION

Ten persons can do ten times as much as one person on an average. If we break
the task into ten jobs for a crew of ten workers, they can easily double their average
output. If we break each job down so that it takes the work of, say, 30 or 40 persons
to complete the task, the crew will multiply its average output still further. What are
the sources of the additional production?

the latter. Such co-operation, or teamwork, enables the group to use to best
advantage the efforts of the more able, for these can avoid the light or simple
tasks, which children can do just as well. And it enables the less capable to
make fuller use of their skills and energies than they could if they lived by
themselves.

The net result of such co-ordination of specialized functions is not only a
larger total amount of living effort, but surpluses of food and time that increase
the total satisfactions. Organic specialization, like social specialization, makes
possible a more efficient use of materials and energies, and it makes living pos-
sible under new conditions. As we have seen, almost everything that dis-
tinguishes one level of plant or animal life from the levels below is an adjust-
ment to new conditions of living (see page 386). Specialization has added
to the total of life.

530

Galloway

DISADVANTAGES OF SPECIALIZATION

The grower who specializes in cotton finds himself out of work until the market catches
up with the cotton in stores and warehouses and factories. In the meantime, he cannot
eat his cotton

Advantages of Specialization^ In our society such surplus production
enables some people to give all their time to making music, or painting pic-
tures, or dreaming up poetry and plays and amusements for the rest of us. It
enables more and more men and women to follow their hobbies, and in many
cases to make careers of their hobbies — as in the arts or scientific research or
play-acting or professional athletics or doing stunts of all kinds. That is to
say, specialization has made possible more specialization. We do not all have
to dig and saw wood and fetch water, because our potatoes and fuel and water
can be supplied by relatively few but highly expert specialists. As a result,
all of us have more time to play, and some of us can enrich the playing of all.

Disadvantages of Specialization In the individual organism, as in
social life, excessive specialization may bring its disadvantages. When an earth-
worm is cut in half, the less specialized segments near the middle produce new
growth and replace the differentiated head and tail. Among vertebrates serious
injury to the more highly specialized organs, such as the heart, the liver,

iSee No. 1, p. 538.
531

the kidneys, or the brain, destroys the life of the whole. Animals in general
have carried extreme specialization much farther than plants; but in many
plants the more specialized structures, such as flowers, cannot be regenerated.

Excessive specialization has the further disadvantage that it requires more
complete co-ordination, as in the endocrine and nervous systems of human
beings, for example. In society "each minding his own business" makes no
sense. There is no point in turning valves, pulling switches, pushing buttons,
grinding tools, mixing paint or dough, firing ovens, or pumping water except as
each special task is related to a common plan. Water comes out of the faucet
not merely because you turn the spigot, but because thousands of men and women
whom you will never see have been for years doing their thousands of sep-
arate jobs, all planned to place water under pressure behind your valve.

In the organism, chewing food concerns more than the face. Pumping
blood and secreting bile are not carried on "for their own sakes". Nor is it the
eye that "enjoys" the scenery. In such complex organisms as man extreme
specialization carries the risk of upsetting the balance, or unity, of the organ-
ism through a relatively slight injury to a very small part. This is probably
one reason why "functional disorders" and "queerness" are more prevalent
among human beings than among other forms of life.

Balanced Functions^ A person who weighs 118 pounds is heavier after
each meal, and loses weight before the next one. In a complex organism like a
mammal there is constant alternation of piling up and using up. That is true
for life in general and for human populations. We accumulate great stores of
food and fibers and other products of plant and animal life during the summer,
and then use up the reserve during the winter. The balance is not a state of
rest, like the sides of a scale that are perfectly level. It is a moving and fluctuat-
ing condition in which a swinging in one direction balances that in the op-
posite, it is a process, it takes time. There must be Oi^^r-production to balance
the periods when consumption exceeds production; the problem is that of
maintaining the balance.

In a primitive economy human beings depend upon their own skills to get
them what they need directly from nature. They are thus largely at the
mercy of the weather and other changing conditions which influence the
abundance of plant and animal life. In our economy of highly specialized
functions not only do we store seasonal surpluses for long periods, but we trans-
port food and other materials from regions in which they are plentiful to re-
gions in which they do not occur at all. On the other hand, our economy
has been characterized by ups and downs that appear unrelated to the actual
abundance of needed food or clothing or building material. During so-called
business depressions of the past people spoke of "overproduction" as if a sur-
plus of materials could explain widespread hunger and privation,

iSee No. 2, p. 538.
532

From a biological point of view, it is of course meaningless to speak of over-
production so long as any portion of the population continues to be in want.
There might be at worst an unbalanced production, so that efforts which
should have gone into the making of shoes, for example, went into a surplus
of fiddlesticks. Whatever the details in such a crisis, a living system appears
to be thrown out of joint not because of any failure in the environment or in
the specialized functions, but because each member minded his own business
without regard to the relative amounts of his products that were needed. We
can see this if we compare the situation to that of a self-contained family that
produces what it needs with little regard to what others do, or fail to do.
Normally, satisfactory living was obstructed by shortages rather than by sur-
pluses. The important point for society as for the organism is balanced pro-
duction, distribution and use.

It is not only the loss or injury of a specialized organ that may handicap
the whole organism, but also the overgrowth or excessive development of
some part. Such overgrowth or overfunction threatens the wholeness, or the
balance, of the body, particularly when it affects the nervous or the gland
system. In plants and animals too there may be faulty co-ordination, or un-
balanced functions, interfering with continued growth or development.

If there is an overgrowth of some tissue, an enlarged thyroid, for example,
or a tumor, the surgeon may remove the surplus and restore the balance of
the organism's functions. We cannot so easily cut out superfluous farmers or
brokers or harness-makers. The distress which comes from disturbances in
the proportions of various functional or occupational groups suggests the dis-
advantages of overspecialization in society. But in time of war or of great
natural disaster, brokers and harness-makers can take on other functions.

What Are the Physical Limitations on Total Life?

Limitations in the Environment^ As we have seen, the adults of almost
any species would produce enough offspring to fill the earth or the ocean in a
relatively short time // all the eggs or seeds reached maturity, and if all in-
dividuals reproduced at the average rate. From the very nature of life, how-
ever, there are in every case too many requirements that cannot be met.
Few individuals in any species actually go through the entire cycle of growth
and development. What determines which ones are destroyed along the road,
and which ones will actually reach the end of the journey? Of a thousand
persons born at about the same time, the number living diminishes gradually
until none remain after about 100 years.

The exceptional survival record of our population is possible, of course,
only because we have been able to obtain abundant food and to avoid various

iSee No. 3, p. 538.
533

illnesses — able, that is, to restrict the lives of other species. For we know
that growing and developing and reproducing are possible for some indi-
viduals only on condition that other living things are destroyed; here too
life is self-limiting. Now the destruction is going on all the time, just as the
production of new protoplasm — and new individuals — is going on all the time.
Making of new is limited by destroying of old. Just as the growing body
carries on by oxidizing parts of its own protoplasm, life in general continues
as individuals die and are replaced by others.

The Life-and-Death Cycle Since there must be a limit to the various
kinds of elements, and since plants and animals make use of the materials in
the earth and the air and the waters, will not these materials at last become
exhausted? And would not that mean the end of all life?

The plants and animals in a restricted area, such as a farm, might live for
several years without the need for replacing what they removed from the soil.
But as the products of a farm are normally carried off to be used elsewhere,
the soil must in time be deprived of certain elements essential to further life.
But what happens in a balanced aquarium, in which the carbon dioxide ex-
haled by the animals is converted by the green plants into food used by the
animals, and in which the animals are supplied with oxygen?

In addition to the balance of carbon and oxygen, the living organisms in
this restricted area must have a supply of the materials that become permanent
parts of the protoplasm — nitrogen and certain salts. The nitrogen also cir-
culates through the organisms, the soil, and the water, as we have seen (see
pages 151, 152). But some of the inorganic material remains largely within the
living bodies until they die.

When we consider life in general, maintaining a succession of living things
appears to depend upon the circulation of materials. There is no danger
that all life will come to an end merely because the materials may become ex-
hausted. The same materials enter into a constant succession of new living
things. The chain is endless because it includes the remains of plants and ani-
mals that have died. The materials, instead of being "locked up" in bodies,
whether living or dead, pass on into other cells, other plants and animals.
Each particle in the course of years becomes part of many different organ-
isms, of many different kinds (see illustrations, pp. 151 and 153).

How Can Man Regulate Population for His Purposes?

Distribution of Life^ In the world as a whole there are about 2000 mil-
lion human beings. If we should spread out evenly over the land surface, we
should be about 33 to each square mile. That would give us plenty of elbow-
room. But a very large fraction of us would soon die. For millions of those

iSee No. 4, p. 538.
534

square miles are barren mountains, jungles, and swamps, and vast stretches of
desert that can support very little life of any kind and no human life at all.

As we know, the density of human life varies from one region to another.
But most of us would be astonished to learn how great the variation actually
is. For Australia the population a\crages a little over 2 to the square mile;
in Alaska it is 1 to 10 square miles; in Japan it is over 400 to one square mile.
In both China and India there is so much desert and mountain area that the
ratio of people to /o/rt/area is very misleading — something o\er 100 per square
mile for China and about 180 per square mile for India. Similarly, the average
distribution ior Egypt is about the same as that for the United States — under
40 per square mile. But if we consider the regions actually occupied, the
density of Egypt's population rises to over 1000 per square mile.

Europe is the most densely populated continent, and Belgium the most
densely populated country in Europe, having 635 to the square mile, as against
482 for Great Britain. If we consider England and Wales separately, however,
the density is about 650. This comparison suggests many questions about the
distribution of human life in general and about the concentration of life in
particular regions.

The earliest concentrations of human population were along the shores and
rivers, then in fertile regions that supplied game as well as fish, and eventually
on soil suitable for grazing cattle and for raising crops. Cities became possible
only when division of labor had gone far enough. For it takes trade and traffic
to bring together from over a \\'ide area the needed food and raw materials
that city dwellers cannot produce themselves. The large industrial centers,
which in modern times have become the most highly crowded areas, could not
support life abundantly except through extensive intercourse with other
communities.

Distribution Automatic If we all tried to live at the seashore, the total
amount of human life would be but a fraction of what it actually is. Through
thousands of years the human population of the earth probably increased very
slowlv. For aside from all other considerations, there is a limit to the number
of persons who can find a livelihood on the seashore or in any other specialized
environment. It became possible for the race to increase in numbers only as
it came to live in a great variety of environments. In modern times a rapid in-
crease in human population had to wait until we knew enough biology to con-
trol (1) many species of plants and animals that yield food and other useful
materials, and (2) those other species that interfere with our health and
other interests.

The distribution, or spread, of a species away from a center is influenced
by the pressure of population and by the conditions in the new regions. But
the limiting factors always include other species, as well as the physical cop
ditions.

535

^jj^JMCwe^Wm" 2

\ I

WHAT KEEPS A SPECIES FROM SPREADING

The distribution of a species away from a center is influenced by the pressure of
population and by the physical conditions in surrounding regions. But the limiting
factors always include other species — possible food, possible enemies — as well
as soil and climate

Hindrances to Human Life^ Human population can increase only
where the soil and the climate are suitable for those species that we depend
upon for food and for other materials. But suitable soil and climate are not
enough to make a region secure for human habitation. Other animals and
plants may have established themselves ahead of us, and they may succeed in
keeping us out. Breaking new territory has often meant fighting wild animals
and driving out inhabitants already there. When early settlers cleared forests
to make their homes and farms, they removed not only trees, but a vast amount
of animal life — birds, mammals large and small, insects of many species. And
they created conditions in which many species of plants could no longer keep
going.

The expansion of human population would seem to be a simple problem of
replacing the native population with cultivated plants and domestic animals.
When this process was repeated over and over again, and more and more
rapidly, other things began to happen. Sometimes the attempts to cultivate
crops in a new region succeed from the first: the soil and the climate happen
to be right. Sometimes a species succeeds even better than it did in the old
home from which the settlers came, for the insect pests or the parasitic fungi
of the old home were not brought along. In other cases, however, the best

iSee No. 5, p. 538.
536

knowledge and skill fail to make such efforts go. There are new enemies never
encountered before. In their attempts to penetrate tropical regions, Euro-
peans have been for several centuries obstructed by the new kinds of diseases
and pests. Where many different plant and animal species have become es-
tablished, man's arrival often interferes with conditions seriously. We some-
times destroy what we should like to preserve, or else increase forms that we
find objectionable.

We have already seen that many of our cultivated plants depend for com-
pleting their life cycles upon the co-operation of certain insects (see page 408).
Other cultivated plants are destroyed by other insects. To preserve and mul-
tiply our plant and animal populations, we have to look after many other
species — encourage some and destroy others. To ensure a human population,
it is not enough to establish physical and chemical conditions that favor cul-
tivated plants and animals. We need further to guard against bacteria, pro-
tozoa and worms that cause disease, and against mosquitoes, fleas, flies, various
rodents and other carriers of infection.

To make the earth support more human beings, it becomes necessary to
control the distribution and the density of hundreds of other species — some
of them directly useful, of course, but others important in various indirect
ways. Some affect the health of humans and of our cultivated organisms.
Some supply food for our cattle and other domestic animals. Some affect the
physical conditions in ways that are important. No man can live by himself
alone; but it seems that no other species can live by itself alone.

In Brief

Life is self-limiting and in every cell there is an orderly succession of stages
from beginning to end.

Among simple organisms a line of protoplasm can remain alive indefinitely,
whereas in the more complex, many-celled body it cannot.

As in social organization, organic specialization makes it possible to use
available materials and energies more efficiently and to carry on life under
new conditions.

Increased specialization involves a more complete and more delicate co-
ordination, which is accompanied by a lessened capacity of the parts to re-
generate and to adjust themselves.

Growing and developing and reproducing arc possible for some individuals
only on condition that other living things are destroyed.

A species increases in numbers as favorable conditions arise, or as it moves
into favorable environments; man goes further and increases in numbers as
he finds ways of adjusting a great variety of environments to his needs.

537

Materials released from organisms, living and dead, pass on into others,
each particle in the course of years having been part of many organisms.

Where a balance has been established through the interaction of many
different plant and animal species, intruding man often disturbs existing rela-
tionships by destroying what he would like to preserve or by increasing forms
that he considers objectionable.

EXPLORATIONS AND PROJECTS

1 To investigate certain advantages and disadvantages of specialization, com-
pare the relative effectiveness with which different species of plants and animals
carry on particular functions. For example, we might compare earthworms with
caterpillars and with adult insects as to the speed and effectiveness of locomotion,
the manner of food-getting, and recovery or regeneration after injury. Compare
structures and living habits of various parasites of birds and mammals and of the
dodder, a common parasite of clover. Relate the characteristic stages and special-
ized structures to the mode of life. Show wherein specialization is an advantage; a
disadvantage.

2 To investigate the physical conditions involved in certain plant associations,
visit a neighboring woodland and compare the growth on different slopes, on differ-
ent soils, and under different moisture conditions. Note the relative heights of the
trees, the kinds of trees growing, the density of the shade, the number of species, the
luxuriance of the growth, the dominant forms, the presence of simple pioneer plants,
and any differences in the kinds of animal life found in the various plant associations.
Summarize the results of observations by relating the various physical conditions to
the kinds of plant associations found.

3 To find the relation of crowding upon growth, plant seeds of a rapidly growing
plant very close together in one pot, and widely separated in a second pot. Maintain
optimal growth conditions in both pots for several weeks and compare results.
Account for differences in terms of physical conditions that limit development.

4 To investigate the problems associated with a shifting population, find out
how the population of the United States is distributed and how this population has
shifted during the past seventy or eighty years; relate these shifts to conditions
that brought them about and to their effects upon economic resources and develop-
ments.^ Construct a large map showing present centers of population; list the chief
areas in which population is centered; indicate on the map or on the lists or on both
the chief contributions to human life in each area.

5 Report on population shifts resulting from the development of a new
industry, from the discovery of mineral resources, from changes in the soil or in
the water supply, from the emergency needs of the Second World War, or from
the introduction of better means of transportation, as railroads, highways, or air
fields.

^Refer for information to the National Resources Committee report The Problems of a Changing
Population, May, 1938, or to an atlas or to a geography.

538

QUESTIONS

1 In what different ways is the total amount of Hfe at any given time or place
limited by the physical environment?

2 What conditions bring about an increase in the numbers of any species of
plant or animal, including man? a decrease in numbers?

3 In what ways are the numbers of individuals of one species in a given region
limited by other species?

4 How can we show that the activity of one pari of the body depends upon that
of another? or that it may interfere with the full activity of another part?

5 \\'hat advantages come to a living thing through the division of labor among
organs and tissues? What disadvantages?

6 What are the conditions for a high degree of division of labor among human
beings? among different nations?

7 What usually happens to a natural community when man arrives on the
scene ?

8 To what extent can man control the numbers of other living things in any
given region? the numbers of his own racei^

9 How are post-war conditions likely to influence the distribution of popu-
lations?

539

CHAPTER 27 • THE CONFLICTS OF LIFE

1 Do any plants fight in the way that animals fight?

2 Do any species ever die out in nature?

3 How can we tell whether animals which are new to us are useful,

or harmful?

4 How do animals know their enemies instinctively?

5 If species result from adaptation to particular conditions, how

can they live in strange surroundings?

6 Do animals ever kill for any reason except to get food or to pro-

tect themselves?

7 Do animals ever kill others of their own species?

8 Is it possible to avoid competition?

9 Are the survivors in a conflict always superior?

10 Would there really be room for all the persons who are born?

Life is always interfering with things, always rearranging things. It will
not let things remain as they have always been. That is why people have
thought of life as a kind of "force". It is like rushing water, changing the face
of the earth. It is like a storm, stirring everything up. It is Hke raging fire,
destroying what it touches. Yes, life is like all these "forces". But it differs
from them all, too.

It is more helpful to think of life as unique, in a class by itself — not as a
something, not even as a force. Life is what living things — all organisms — do
in common. It is a persistent enlarging and extending of itself in all directions,
a grasping of the outer world, a converting of the outer world to itself.

But the world seems unwilling to be taken in that way. Everything is
always interfering with life. This life process constantly meets resistance.
Especially is there resistance and interference from parts of the world that
are really playing the same game — that is, other living things. There is re-
sistance, and sometimes a fighting back. Life is a struggle, not a flowing along,
not a one-sided action. It is interaction, a give and take with the entire en-
vironment, including other life.

How Can We Say that Plants Struggle?

Passive Struggles^ We have learned to think of the activities of com-
mon plants as rather quiet processes of osmosis, diffusion of gases, chemical
change, as in photosynthesis, or very slow — and "cold" — oxidation. What is
there here to suggest a struggle? If water is abundant in the soil, the roots
will absorb it rather quickly — as an old rag might. But if the atmosphere is

iSeeNo. 1, p. 557.
540

saturated, so that water docs not quickly evaporate from the surfaces, ab-
sorption from the soil may be stopped.

If soil minerals are present in certain proportions, or concentrations, the
plant absorbs accordingly. But if there is too little, then the plant absorbs
and discharges more gallons of water for every grain of salt. Or if there is too
much salt, the flow through the root cells is outward instead of inward. Plants
living in salt marshes are in many ways like desert plants, absorbing water
against great resistance, or drying up!

With changes in temperature, most plants continue their metabolic activi-
ties more rapidly or more slowly. But sudden or extreme changes stop metabo-
lism. And temperature affects also evaporation, or transpiration. Changes in
illumination also alter the metabolism, especially photosynthesis, ^nd the
rates of growth of the various parts. /

Such variations in conditions influence plants, but they do not, as a rule,
bring out any striking reactions. Plants seem obliged to take what happens
as it comes, since they are not able to run away, or dodge, or hit back. Here,
then, the "struggle" is between a particular organism and changes in the
surroundings. The particular organism, which seems to us rather passive,
does not really remain as it is very long. A plant does move, if less slowly
than most animals. It responds to stimulation or to changing conditions by
moving — ^so slowly in most cases that we have to take special pains to see
what happens.

Plants Are Sensitive and Active^ The simplest evidence that plants are
more or less sensitive we may see in the destruction that results from some
external change. A plant may be poisoned or overheated or chilled. If the
changes are not too severe, however, the plant behaves in ways that, on the
whole, protect it from injury. Tropisms (see page 256) on the whole prevent
injury, or they increase the likelihood of getting needed supplies. Some
plants can capture animal food, in the form of small insects (see illustration,
p. 542). Some reduce the exposed surfaces when disturbed by too much sun-
shine, as the eucalyptus tree. Some close down in the dark, as the clo\'er or
sorrel. And very many drop their leaves in the autumn, apparently in re-
sponse to a shortage of water.

Generally speaking, however, plants respond to external changes very
mildly compared with familiar animals. The success of the indi\idual plant
in living through a season of changes seems to depend very largely upon the
structures and qualities that it develops from the time it starts out as a sprout-
ing seed. Continuing to live depends upon the kind of skin and bark or
spines that it grows, or upon the kind of conducting and mechanical tissues it
develops, or upon the delicacy and efficiency of its food-making equipment
and its food-storing mechanism. And the success of the species depends upon

iSee No. 2, p. 558.
541

Kutherford Piatt

THE CARNIVOROUS PLANT VENUS'S FLYTRAP, DIONAEA MUSCIPULA

The trap at the tip of the leaf consists of two parts that come together like the halves
of an open book when an insect touches against one of the three trigger hairs on
the inner surface of each flap. The sections come together rather quickly; curved
bristles around the edge prevent the escape of the insect

producing so many seeds that some at least are likely to alight where they can
establish themselves, and that one or two at least are likely to reach maturity.

How Plants Compete^ Struggle commonly suggests our own experience
of competition and conflict with other members of our species. But most life
activities are not conflicts or rivalries in that sense. Nevertheless plants do
"compete". Thousands of plants get started in a garden or field, for example,
where only a few can find water and salts — and space — to grow up.

Seeds can get started even while they almost touch one another. For the
time being there is room for all, water for all, air for all. And each has its own
food reserves to last for a few to many days. But in a few days many of them
have germinated. Almost hour by hour others put out their first sprouts —
usually the hypocotyl or root-tip. Now they begin to crowd. For after
having absorbed enough water to start the sprouting, each is several times
as large as it was in the dry state. The crowding raises some away from the
soil. And when these lose their touch with mother earth, the tip of the sprout

^See Nos. 3 and 4, p. 558.
542

dries; and that's that. Those more favorably situated begin to dig in. Some
act faster than others. The faster ones get the water and send their shoots up
before the slower ones get a firm grip on the soil. And as the earlier ones
keep on growing and absorbing, the lead becomes greater and greater. The
struggle for limited quantities of minerals is similar. And the parts that are
aboveground, which soon turn green, have to grow fast enough to catch the
sunshine before they are outgrown and shaded by other indn'iduals.

We have already seen that where many different species are present in an
area, their specializations usually make possible a larger total population than
a single species could maintain. Because species differ in height, in spread of
leaves, in depth of roots, in rate of absorption, and so on, several different
species fill the area more nearly completely. Nevertheless even different
species may compete for the things that they all need, especially water, min-
erals, and a place in the sun. The competition among the plants is, at any
rate, real, even if the struggle does not involve violence.

Pure Chance Each individual seed or plant has a very narrow range of
action, and no ability to make decisions or choices. Accordingly, mere chance
plays a large role in the lives of plants. The inherited capacities of this tiny
sleeping baby plant inside a seed have no relation to where it will alight —
whether upon a dry surface or on a moist one, on a bit of fertile soil or on a
barren spot. If it never gets to first base, there can be no reproach. Nobody
can say that it lacks any of the virtues which are proper to members of its
species. It simply had no chance at all. Seeds that get a start and send their
roots down may be stopped by a flock of birds or insects, which destroy every
scrap of organic matter big enough to grab. These animals destroy the "good"
individuals along with the "bad" ones^ — as would a flood or a fire or a complete
drought. We can see why it is that of the thousands and thousands of in-
dividual seeds which a mature plant produces, only a very few will in turn
reach maturity and reproduce themselves.

How great the role mere chance can play is suggested by comparing the
survival rates among human beings. Out of a thousand babies born, some
will die almost immediately because of defective organs or functions — breath-
ing, digestion, circulation, temperature adjustment, or whatever. In the
course of the first year others will die for various reasons — failure of the organ-
ism at some point to meet the conditions of nutrition or excretion or infection
or changing temperature. But the number of such failures is probably small.
For among different peoples, or among different sections of the same popula-
tion, the infant death rate varies from about 30 to about 300 per thousand
(see illustration, p. 545).

This great variation has been used to argue that some stocks are "inferior"
to others. But if we accept this, we must account for the further fact that
in the course of time the rates decline more for the "inferior" stocks than for

543

the "superior" ones. Perfectly helpless babies of any "race" will survive the
first year only under the suitable care of elders. That is, the survival rate
depends more upon the care and protection that babies receive than upon
individual variation in the capacity to carry on as organisms — ^after the early
difficulties are overcome. A poor home will destroy the promising and the
worthless in about the same proportions.

The struggle of plants is against enemies, against competitors, against
changing physical and chemical conditions. All but a very few individuals
are likely to be destroyed in the course of a season, without regard to the
particular qualities which might be of advantage in the "struggle for existence".

What Is Meant by the Struggle for Existence?

One in a Thousand Some species can keep alive only if each adult
(or pair of adults) bears many thousands of new individuals — eggs or seeds.
The early stages are subject to frost and drought. And since they contain
concentrated food material, they are exposed also to hungry plants and ani-
mals of many kinds. A little later the young are still exposed to changing
conditions of moisture, temperature, light — and hungry hordes of other
enemies.

From one spot to another on the surface, in the soil, in a pond or in the
ocean, the physical conditions vary. Here it is colder, and there warmer.
Here the concentration of carbon dioxide is high; there it is low. Here there
is an excess of one kind of salt, and a shortage of another; but there the con-
ditions are just the reverse. These variations mean that one organism can live
here, but not there; that this one can live here, but not another.

Other features also vary. At some points the moisture varies tremen-
dously from season to season, perhaps even from day to day or hour to hour.
At another point the nights are very cold and the days very hot. At tide level
this spot is well covered with sea water for hours at a stretch, but later it is
almost dry and exposed to the glaring sunlight. A living plant or animal may
get a start at some point, but be constantly threatened not alone by "enemies",
but by the fluctuations in physical conditions. The urge of each organism to
get food and to meet the various threats and dangers results in a complex
process which has been called the "struggle for existence".

Among human beings the "struggle for existence" is in part a struggle of
intelligence and understanding rather than one of swift movements or tough
skin or powerful muscles. For the bulk of the human race, infants seem to
survive in larger or in smaller proportions according to the kinds of families or
civilizations they are born into (see charts on opposite page and on page 547).

This struggle includes many processes that are in themselves rather mild
or even passive — like the growing of a shell by the clam, or the growing of a

544

SenBany (1937 letrii:*
Englemd and Wales

Scotland
France
tJnitedi States
Switzerland
Ketheriands
Spam
"IFoxtugar [

Deaths under

1 yt per 1000

live bklhs

For period from 1926 to 1930

Japan

Germaay
'Ingland aad

Scotland
^franco

United StateB

Switzerland

Netherlands

Spain

Poitugal

For period from 1931 to 1935

Japan

Germany

England aad Wales
ScoUaad
France
United States
Switzerland
Netherlands ^
_^paixi_

For period from 1936 to 1940

Japan
Germany^
England and Wales
■ Gotland
France
United States

Switzerland- ^

Nt uerlanda

Spain

THE RELATIVE FITNESS OF DIFFERENT PEOPLES AS MEASURED BY INFANT
DEATH RATES

long taproot by the radish, or the dropping of leaves in the autumn. The
struggle is a continuous activity at every stage of life. It is an overcoming of
obstacles and resistances which arise from the changing environment and from
the activities of other living things. It goes on even where there are no
enemies or rivals, and even where the needed food, water, air and minerals
are abundant. Life is itself aggressive, and all its processes are attacks upon the
outer world — or resistance to attacks from that outer world.

The Meaning of Fitness From the fact that more individuals are born
than can possibly survive comes the pressure of population. Only a small
fraction of those born will live long enough to reproduce themselves. But
which one will die at this stage, or the next? Which ones will complete the
cycle? The elimination which goes on in the struggle has been called the "sur-
vival of the fittest". This expression is quite misleading, for it suggests some
absolute quality, a general superiority that is important in itself. But as we
have seen (p. 467), the intention of Darwin and of others was to describe some-
thing more directly related to a specific situation. Thus the fittest rabbit
when rabbits are being chased by dogs or foxes is the swiftest rabbit. But
when a severe frost attacks the tribe, the fittest rabbit is the one with the best
fur, or the one that has stored up the most fat under the skin during the pre-
vious summer and autumn. There is no absolute standard for plants and
animals. Fit7iess is a relationship between the organism and all the features of its
surroimdifigs that may influence it, including possible enemies, possible food,
possible competitors.

We must not read into the story our own likes and dislikes. The wolf and
the vulture may be just 2isfit as the sheep and the chicken. The thistle and
the ragweed are just asfltas the fig-tree and the rose. But no plant species and
no animal species can altogether fit in where some other one is now living.
The "fitness" of a form, or its adaptation to its surroundings, is of a special
kind that it has taken hundreds of thousands of years to attain. When the
conditions in any region change radically, the character of the entire vegeta-
tion and of the animal life must also change.

What All Species Need All protoplasm depends eventually upon
water and air, upon the same few chemical elements, and upon the same
classes of chemical compounds. Yet the countless forms of plant and animal
life find congenial surroundings in nearly all parts of the world, whereas each
species is closely restricted to a rather narrow range of temperature and
moisture. We have all been impressed by the striking differences between
tropical forms and related arctic forms, or between water animals and related
land animals (see illustration, p. 548 ).

We are accustomed to expect polar bears in Greenland rather than in the
Everglades. In Florida we should expect to find alligators. The Canada lynx
is distributed throughout a large part of Canada and in some of the northern

546

Deaths under 1 yr
peflOOO live births 30

Maoris in New Zealand
Argentina
Mexico

110 120130 140

160 170 180190-

'210 220

"l^onwhites in U.S.A.
"Europeans ia , Now Zoa
Maoris in New Zealand (no

Argentina

Mexico

Whites in U.S.A.

Noawhites in iTS. A
Europeans la ] Nt a

For period from 1926 to 1930

India (BritisE piovmces)

British Ceylon

Palestine (Moslems^
Palestine (Jews)

period from 1931 to 1935

mit^s in U.^.A.^
Nonwhites in U.S.A.

Europeans in^ New Ze.
Maoris in New Zealand
Argentina _
Mexico

Jndia (British provinces)
_British Ceylon
Palestine (Moslems)
Palestine 0ews)

Whiteslnag.A;;

Nornvhitee in U^S.A.
Europeans inl New .'.
Maonsjn New Zealand
Argentina

J'or period from 1936 to 1940

ilexicp^

Jtndia_(British provjccos)
British Ceylon
Palestine (Moslems)

Palestine tfews)

myes jn ujrAZJ'X^

r-Monwhites inU.S.A.
Europeans J in New
Maoris in New Zealand

^Argentina

Mexico

iaTBritisn provinces)

British Ceylon
Palestine (Mosler
jPalestine 2e W8l„

THE RELATION OF TRADITIONS AND CUSTOMS TO THE BABY'S CHANCES
FOR LIFE

American Museum of Natural Hismry

DIVERGENCE OF RELATED FORMS

Comparing the otter and the skunk, both classed in the "marten family", we cannot
see how the supposed ancestor became "modified" into either species. But we are
impressed by the fact that species which are so much alike in their fundamental
structures do fit such widely different surroundings

parts of the United States, while the koalas and the kangaroos are limited to
the continent of Australia. Some species of plants and animals are quite cos-
mopolitan, ranging over large sections of the earth's surface. Most species,
however, are restricted to small areas. Certain giant tortoises and other
distinct forms are found only on the Galapagos Islands.

548

American Museum of Natural History

CONVERGENCE OF DIVERSE FORMS

Marsupials living almost exclusively in Australia and near-by islands resemble in
outward appearance various placental mammals living in other parts of the world.
How came the koala and the bear to be so much alike? One series of species appears
to be as well adapted as the other

A different kind of restriction is illustrated by the fact that clover and
alfalfa can grow only where there is an abundance of lime in the soil, whereas
blueberries and cranberries, which belong to the heath family, thrive on acid
soil. Most seed plants depend upon nitrogen compounds in the soil. Members
of the bean family, however, can get along on soils deficient in nitrogen; but

549

that is because they live in partnership with bacteria that are able to combine,
or "fix", nitrogen from the air into compounds that the larger partners can
use (see page 152).

Jack Sprat Principle You recall that Jack Sprat could eat no fat,
whereas his wife could eat no lean. These two people did not let differences
in taste cause ill-feeling and bickering. Instead, according to legend, they
managed amicably and sensibly to make the most of their undoubtedly
limited resources. They licked the platter clean, and we may assume that
both continued to be well nourished. At any rate, we can observe this prin-
ciple of specialization at work when we consider the wide variety of condi-
tions under which different species of plants and animals thrive. The most
obvious specialization is, of course, between water-dwelling species and land-
dwelling species. There are many species of plants and animals, however, that
live on the margin between land and water — marsh plants and animals, tide-
water forms, and so on. Thus ferns, mosses, skunk cabbages, and certain fungi
thrive along woodland streams, but are seldom found growing in open fields.
Muskrats, cattails, sedges and red-winged blackbirds are associated in marshes
or swamps. The amphibians are typical in-between forms, the very life cycle
of the frog being adapted to alternation of wetness and dryness. However,
Hving in air and Hving in water involve such great differences in structure
and in behavior that most species live in either one medium or the other.

Adaptation to Change The emergence of many species may be looked
upon as an adaptation — in the course of time — to new situations into which
living beings are forced by the pressure of population. We have seen that
many specialized types of plants and animals do in effect fill in gaps among
other species. We may see this more clearly if we consider what happens when
a decisive change takes place in climate, for example, or in a river when
industrial wastes are discharged into it.

Let us imagine a relatively dry region occupied by plants of many species
and a corresponding population of animals. The speciaUzed types fit the physi-
cal surroundings — the soil and its chemical contents, the moisture, the tem-
perature, the sunshine. And they fit one another — taller plants and low
growths, the insects and the worms, the bacteria and the birds, all make up a
fairly constant mixture season after season. But now, if this region should
become flooded, a large proportion of both plant and animal inhabitants would
be destroyed. Only those that were not too highly speciaUzed would survive,
mostly simple plants and animals that can endure a great range of dryness or
moisture. Those that are too finicky or else too rigid would be killed off. A
marked change in physical conditions always destroys some species.

On the other hand, as the water destroys thousands of individuals of many
species, it also favors certain other species^ — less specialized water-dwellers or
forms that thrive in wet situations. Life is destroyed; but life goes on.

550

How Do the Conflicts of Animals Differ from Those of Plants?

Intensification of Life' Since all living things carry on essentially the
same fundamental processes, animals are, so to say, just like plants — only
more so. But that is not quite true, nor all the truth. For plants in general are
much more effective food-makers and food -assimila tors. A pound of plant
protoplasm can become two pounds more quickly than can a pound of animal
protoplasm, adequate supplies being assumed, of course, in both cases. And
plants can take a great deal more punishment without gi^■ing up. But perhaps
that is only another way of saying that by means of growth they can more
easily make up the injuries they sustain.

This suggests, however, more far-reaching differences. If most animals
cannot take so much abuse, they do not have to take it — for they are motile
and can get away or hit back. Or they can sense danger at a distance and dis-
appear before trouble reaches them. Most animals are able to carry on — to
struggle — in ways that plants generally cannot match.

The rate of metabolism in animals is generally higher. That means that for
each unit of protoplasm they use up more food in a given time. But since
animals are not food-makers, they spend relatively more time and energy in
foraging. These facts suggest differences in the intensity of living, although
many animals are fixed in their positions like plants, and others are very slug-
gish in their movements.

Sensitiveness Animals seem generally much more sensitive than plants,
although a passing cloud will change the rate of photosynthesis and of res-
piration in a plant. If we survey the various types, from the simplest to
the more complex, we see more and more specialized sense organs. From the
eyespot of the euglena we go to the complex eyes of \ertebrates and the
cephalopod mollusk — the octopus, for example. From sensiti\'eness to me-
chanical disturbance in the ameba and sensitive hairs in the coelenterates
(hydra, sea-anemones) we go to the antennae of insects and crustaceans and
the ears of vertebrates. From the chemical sense of the paramecium we go
to the fine sense of smell in many mammals. Animals seem to extend their
contacts with the world, to enlarge the range of the environment to which
they relate themselves — and fit themselves. Thus an animal can discover
enemies or food at a distance, and act accordingly.

In the case of human beings the sense organs and their connections have
made the task of obtaining food and escaping enemies both more complex and
easier. The sense organs are "receptors", or receivers of impressions, signals,
information, and so on (see page 275). They make the tasks of life easier, for
they enable the organism to draw upon greater resources. But they make life
more complex too. For they compel the organism to take note of a greater

iSee No. 5, p. 558.
551

variety of objects and happenings, some of which might perhaps be just as
well ignored.

Discovering the outside world and the practical meanings to us of the
various objects — possible utilities, possible dangers — is important in the strug-
gle for existence. But by itself that is not sufficient. Whatever our senses tell
us, it is necessary to get action, to produce some effect. Animals have always
impressed us with their motility. Not only do they move themselves from
place to place, they move other things about. They grasp, they bite, they
scratch and claw, they tear apart. Or they fetch and carry, build nests and
dams and hives. Some species of ants tend captive plant-lice. Others culti-
vate fungus plantations. Many animals gather more food than they can eat,
and store or hide some of the surplus. They hide themselves away, sometimes
for months at a stretch, in natural hollows or in burrows of their own making.
Even such going to sleep is a kind of action, for it produces the effect of run-
ning away from cold weather and bare pickings, like the more spectacular
migrations of birds. All these activities are phases of the urge to live; they are
aspects of a struggle, which consists of all living activities.

Struggle Patterns We find it difficult to describe the struggle of com-
plex organisms, except in terms of our own activities. We say that the bird
(the early one, of course) catches the worm, that the fawn dashes away from
the hounds, that the worm swallows earth. We see "struggle" in a pattern of
reaching out and grasping for food or other "needs", and of running away,
of dodging or escaping, of thrust and parry.

One June, along the inner shore of Cape Cod, a dark spot was seen in the
water, a little way off shore, a spot about as large as two or three acres. The
dark area was drifting in closer to shore. The darkening of the water was due
to millions of tiny mackerel, each some three inches long. These mackerel
were milling and churning about as if vainly trying to evade some pursuing
enemy. And sure enough, literally thousands of small squid, each about six
inches long, were chasing back and forth among the fishes. A squid would
dart forward, reverse, grasp two or three of these tiny mackerel in its ten-
tacles, and proceed to devour them.

When we think of "struggle" we usually think also of its outcomes, and
especially of whether it is successful. Here was a struggle between the fish and
the squid, or between "hunger" and "self-preservation". But was the struggle
successful? The squid had plenty of food for some time to come, but they were
reducing the number of mackerel. In the absence of squid or of other enemies,
the mackerel might conceivably so increase in numbers that most of them
would die for want of food. In the absence of mackerel, however, the squid
would be devouring other fish, or small crustaceans perhaps. And in any case,
most of the squids themselves are sure to be eaten by other animals.

Here, then, is a struggle that never ends^ — or hardly ever. And it is always

552

successful — or almost always. That is to say, whichever species succumbs at
any moment, it enables others to continue, and so the struggle continues.

A struggle like the one between Uttle fish and larger enemies ends when a still
larger animal, like a whale, suddenly swallows several barrelfuls of ocean, with
all the hundreds of squirming struggling life. That struggle ends — but the
vanquished participants enable the whale to continue a while longer, A storm
washes out the life of plants and animals in an acre. The struggle of a few
moments ago ends. But those destroyed plants and animals now become the
raw materials for other living things. Life goes on, nou in these forms, now
in those others. And so the struggle, which is one way of describing life ac-
tivities, also continues.

How Does the Human Struggle for Life Differ from That

of Other Species?

Man and Other Animals Under certain circumstances, or for certain
purposes, man is the same as other animals. But nearly always he is different
too. Like animals, we need food to still our hunger. Yet we can learn to
postpone eating — for a time — without letting the hunger distress us too much.
At the table human beings do not have to claw each other, or even elbow each
other, to make sure that each gets enough. We can wait at least long enough
to have things passed our way. This fact alone makes a great difference not
alone in the manner of eating, but in the whole manner of life. For it means
that we can guide conduct by imagining the future, as well as by remembering
the past. Man can plan; he can struggle for food between meals, when he is
not hungry. Where other animals are driven by the feeling of hunger, man
acts to avoid hunger. He can shape his conduct through ideas or knowledge.

Fighting Drives We can make almost any animal fighting mad by
striking it, or by stopping it as it is chasing possible prey, or by taking its
food away from it. In general, man fights under very much the same circum-
stances as other animals. When there is not enough food (or other things they
want), men will fight other animals, and they will fight one another. When
men are blocked in their efforts, they will fight those who obstruct them.

Animals can be aroused to fight by a threat or a gesture — as if you were
about to strike. But man alone can be aroused to fighting by words in a news-
paper or on a banner. When the jocular shepherd boy shouts "Wolf! Wolf!"
in a certain tone of voice, other shepherds come rushing along as if there were
really wolves to fight. Or when another humorist shouts 'Tire! Fire!" he
can drive perfectly sensible people into a panic. We can be deceived into
fighting imaginary enemies, and by imaginary fears. We can also be deceived
into submitting to abuses, into remaining quiet while we are being robbed.

We can imagine so much more than we can experience that we sometimes

553

become the victims of our very excellence. For we can imagine what has
nothing to do with the facts of the world — that is, we can be mistaken, we can
deceive ourselves. Human beings use cleverness and deceit not only in fight-
ing their natural enemies, but also in fighting each other. In fact, many con-
sider the conflict of man with man as the best means of advancing mankind,
as well as the most satisfactory expression of individual human life.

Man as Social Organism Man has overcome his organic handicaps
largely through his disposition to form groups, to co-operate, or act jointly,
with others. Community action may be observed at every level of life, and is
in fact the central advantage in all higher organisms. Men li\e m communi-
ties and identify themselves with their families and their neighborhoods and
their towns and tribes and nations. They can therefore be aroused to fight
and to sacrifice for "their own", for the interests of the larger group, which is
truly their own deeper or larger self.

Through his inventiveness and imagination man can change the methods
of his fighting, as he can completely change the goals of his struggles. When
man discovers that he can get all he wants of those things that animals fight
for, he turns his efforts to fight for what he considers greater values, or more
worthy objectives. Men will fight for honor or for the glory of some group or
institution. They will fight for ideas, for liberty, for security, for their heroes
and leaders.

Struggle and Competition By the middle of the last century the old
patterns of agricultural life and production through handicrafts were begin-
ning to change rapidly. Industrial developments and the means of transpor-
tation and communication had already reached a very high stage. Machinery
was coming to be more economical than slave labor.

Where families had been living largely through their own labors on their
own land, some families thrived better than others because of differences in skill
and intelligence. Now the organization of industry and commerce was intensi-
fying the competition among individuals, among groups of individuals, among
different regions, and even among different nations. Migrations from country
to country and from farms to cities brought together peoples with many
different kinds of backgrounds and abilities. And a large proportion of the
transplanted organisms did not "fit" their new surroundings and conditions.

When we look back over what has happened in about a century and a half,
it seems natural that people should have been influenced by these rapid and
extensive transformations in their ways of living. The atmosphere was full of
"struggle" and "competition" and "success". This was, of course, very dis-
tressing to those who had been brought up in more peaceful surroundings and
friendly relationships. It was becoming necessary to justify competition as
"right", since it not only brought great suffering to many, but was actively
opposed as unsound socially and morally.

554

when fierce competition was the prevailing pattern in human affairs, it is
not so strange that several scientists simultaneously came to the same inter-
pretation of what happens to plant and animal species through the ages. As
we have seen, Charles Darwin and Alfred Russel Wallace independently hit
upon the idea of "survival of the fittest in the struggle for existence" as an
explanation of how new species arose (see page 466).

We may well believe that neither Darwin nor Wallace had the slightest
intention of connecting his scientific ideas with business or politics. For
years at a stretch Wallace was away in the tropics exploring, fir from public
discussions. And although Darwin lived in England most of the time after
his early voyages, his life too was far removed from political and economic
questions. It is therefore interesting to see not only that their thoughts con-
verged in this way, but also that many immediately seized these ideas to get
the support of science for their way of carrying on affairs.

The doctrine that "nature selects" the "fittest" by forcing all living beings
to "struggle for existence" against great odds appeared to justify intensive
competition as a means of ensuring "justice" and "progress". Competition
results in justice because it enables the "fittest" to get ahead of the others.
It makes for "progress" because it forces the less able out.

Men Must Fight As we have seen, dividing tasks up more and more
makes it possible — and necessary — for more and more individuals to attend
to problems that are not life-and-death issues (see page 530). Human life
could go on if nobody ever crossed the ocean or made stainless steel or ever
broke another speed record. At the same time fewer men have to struggle
with wolves or bears or fight snakes and tigers.

The struggle has taken on new forms and calls for new skills. But it also
calls for primitive qualities of courage, of hitting hard, of fortitude and en-
durance, of shrewdness and wile. We are not much concerned with old fight-
ing skills and tricks, but we still value the qualities of warriors and heroes; we
still go out for risk and adventure. We are concerned with carrying out more
quickly and more eflficiently a great variety of acts that are utterly meaning-
less in themselves, but that are related to the lives of vast multitudes. Thus
men spend hours boring holes in the earth or in various kinds of stuff, in load-
ing parcels into cars, in transferring fluid from one tank to another, in piling
up stones, in sharpening tools, in polishing doorknobs, or in mixing mortar or
dyes or insect sprays.

These various specialized tasks are not interesting in themselves and are
likely to become rather dull. They are not always obviously related to human
welfare. Nevertheless we come to realize how completely each of us depends
upon what all the others are doing — or fail to do. We come to appreciate the
necessity for teamwork, for fitting our own activities into a common program
of action.

In more recent times, communication has been rapidly extended and
speeded up. Processes based upon scientific research have become extremely
specialized and refined. We have become aware of our dependence upon a
larger and larger group. In an epidemic, for example, the individual who
relies only on himself is completely helpless in spite of his intelligence or good
intentions or bank account or special talents or other powers and fighting qual-
ities. His salvation depends upon various specialists in all parts of the world,
working night and day to protect — not him personally, nor themselves, but
the entire community or region. When there is a flood or a plane crash or a
hurricane, the damage done is usually unrelated to the virtues or the physical
strength of the men and women and children who get thrown around. But
from such disasters we often learn how future damage may be avoided or re-
duced. And dealing with the immediate disaster and guarding against future
repetitions create fighting jobs. But these jobs are only for people who can
see danger or the "enemy" in natural processes, and who can see the goal of
striving in broad human needs. Fighting spirit and fighting quaUties are con-
stantly needed. But the struggle need not always be on the level of a hungry
fox or of two dogs tearing at the same scrap of meat.

The Moral Equivalent of War Men will fight. But will they fight
like pigs over the contents of the feeding trough, spoiling more than they use?
or like other beasts, over the scraps in the garbage cans.? Will they fight like
bandits or marauders, preying upon strangers? or like gangsters, holding up
anybody who may come along? or like racketeers dressed up like civilized
people, pretending to render a service — quacks looking like doctors, shysters
disguised as counselors, embezzlers offering to help widows and orphans with
their financial problems? Will they fight in organized armies, trying to ensure
their own survival at the expense of inhabitants of other regions? Or, even-
tually, will men fight as human beings, using their talents and skills and in-
genuities and sciences to overcome the many obstacles to decent living? Will
they attack the common need for abundant supplies of the earth's yield?
Will they fight to overcome pests and pestilences, to prevent and cure human
ills, to clear jungles and swamps, to restore the soil, to build highways, span
rivers, tunnel mountains?

Human beings are engaged in the same struggle for existence as are mice and
mildews and mosquitoes. They have a larger world to conquer, and more
delicate, as well as more powerful, weapons to fight with. The goals they set
themselves depend upon the ideas they have of their own natures and needs,
and upon their notions about the world they seek to conquer. The courage
and energy and spirit with which they conduct their fight depend upon their
appreciation of dangers and needs. Men content to fight for bread alone will
hardly get more out of life. If men imagine a world of general health and
general well-being, they may never be able quite to realize their dreams. But

556

they will, at any rate, use different methods. These methods of mutual aid
and of striving for common ends are also ways of fighting. They involve what
William James (1842-1910), the great American psychologist, called "the
moral equivalent of war".

In Brief

The processes in a living plant or animal include attacks upon the outer
world and resistance to attacks from that outer world, which together make
up the "struggle for existence".

To live at all an individual plant or animal must be adapted, or fit, to get
the essentials and to avoid destruction in the specific conditions of its environs.

The competitive aspects of plant and animal life come from the pressure of
population upon the means of subsistence.

Most individual plants and animals are probably eliminated by chance
rather than by specific failures or deficiencies.

"Self-preservation" is the persistence of an organism's working unity
under changing conclitions and under attacks from outside.

Man, like other species of animals, is a fighter, being aggressive in the pur-
suit of his goals and aroused when balked.

Man's modes of fighting are influenced not alone by the opposition he
meets, but by the multitudes of special weapons and skills accumulated in his
culture and by his being a member of a co-ordinated social group.

The goals which human beings set themselves are influenced by their un-
derstandings of their own nature and needs and of the nature of the world,
and by their feelings as to what is of value — whether food or shelter or home
and security or honor and liberty.

Men have joined together to use their skills and talents and imagination to
build for the future, to avoid hunger, to increase security, and to overcome
obstacles to decent living.

Perhaps men will eventually use all their resources jointly for attaining
common benefits, rather than for getting special group advantages at the
expense of others.

EXPLORATIONS AND PROJECTS

1 To investigate the "struggles" of plants, make a survey of the number of dif-
ferent species present within a limited area. Select a wild spot twenty-five feet in
diameter having as wide a variety of conditions and vegetation as possible. Using
general and common names rather than exact scientific ones, list all the organisms
found living within the area. Which kinds of plants are dominant? Which of their

557

distinctive qualities fit them to grow in the region where you find them? In what
respects are the dominant forms com.peting with other species? with individuals of
the same species? What animal forms gain their living directly or indirectly from
the vegetation studied? Summarize your findings.

2 To study the characteristics which qualify a plant as a "weed", collect several
weeds from cultivated fields and find out in what ways they seem particularly
adapted to grow and reproduce. What is there about the roots, stems, leaves, fruits
or seeds that particularly fit these plants to compete successfully with crop plants?

3 To see whether weed seeds or seeds of cultivated plants sprout faster, mix
several varieties of weed seeds with garden-flower seeds and grow in a box under
optimal conditions. Chart the individual germination and early growth of the
various seeds and plants day by day to show variations in rates. Summarize and
interpret your findings.

4 To find out how plants escape being eaten, study as many different plants as
you can to see what special characteristics about them are Hkely to repel animals.
List the plants and describe or picture the protective adaptations of each.

5 To study the various adaptive structures, list a number of animals under
observation, and opposite each name state the structures and other characteristics
that enable the animal (a) to get food and {b) to escape enemies. Summarize your
findings.

QUESTIONS

1 What various activities are carried on by animals in their "struggle for
existence"?

2 In what sense do plants "struggle"?

3 In what ways does the "struggle for existence" among animals resemble
that among plants? In what ways do the two differ?

4 What is the connection between fitness and environment?

5 To what extent are the factors which determine whether or not an organ-
ism will live and reproduce selective} To what extent mere chance?

6 How do radical changes in the physical conditions of a region bring about
changes in the vegetation and animal fife?

7 What are the advantages that come to man from his social mode of life?
What are the disadvantages?

8 What other species show a high degree of social organization? In what re-
spects is the social life of these organisms like man's? In what ways is it different?

9 How does the struggle for existence among men resemble that among other
animals? In what ways does it differ?

10 Upon what assumptions do men base their goals, or aims? To what extent
can better understandings improve or redirect the goals of men?

11 How can we direct the "struggles" of men away from getting special ad-
vantages at the expense of others to striving to attain the greatest benefits for all?

558

CHAPTER 28 • THE INTERDEPENDENCE OF LIFE

1 Why cannot any species of plant or animal live entirely alone?

2 Can the individuals of a species live by themselves?

3 Are parasites of any use?

4 Are weeds of any use?

5 Can a plant or animal be useful to some species and injurious to

others?

6 Does the number ot individuals in a species remain about the same

year after year?

7 Could we make all land surfaces bear only useful plants?

8 Is the division of labor among different species the same as the

division of labor among the members of a beehi\'e?

9 Could we get rid of all injurious plants and animals?

Many a poet has sung about an island on which he might be alone, or sighed
for the wings of a dove on which to fly to the solitude of some vast wilderness.
And many a hermit has actually gone off, expecting to find comfort and peace,
as well as abundance and elbowroom, flir from other men.

It is easy to understand \\'hy one should want to escape from hardships and
annoyances that he cannot oxercome or thrust out of his life. But if one had
the whole world to himself, he w^ould not get very far. Each of the multitude
of species can continue generation after generation only because many of the
other species also continue to live. Through the ages life has come to be a
complex of many species acting upon each other in ways that are often mu-
tually destructive, but such a complex seems to make possible the greatest
total amount of living matter — in a particular region or in general.

Cannot any species live entirely alone? What happens to the others if any
species dies out? What happens to repopulate a region in which all life
has been destroyed?

Could Any Organism Live by Itself?

Life and Light All organic matter seems to derive from carbohydrates,
which, so far as we know% arise only from the action of light on chlorophyl.
We should therefore expect the first forms of life in any region or in the world
to have been green plants. Certainly no animal of the kinds living today, and
no plant lacking chlorophyl, could live before other plants or animals had
left some of their substance that might be used as food.

We do not know that the earliest forms of life were "green plants". It is
conceivable that such compounds as viruses and enzymes developed into some
kinds of "living" forms before chlorophyl- bearing species appeared (see page

559

444). If there were only green plants in the world, all the carbon dioxide would
at last be used up. Any plant that died would permanently retain its carbon
compounds and so keep carbon out of circulation, since under such conditions
nothing would decay.

The Food Cycle^ Under the sod, where it is too dark for green plants
to make new carbohydrates, we find hundreds of species of bacteria, fungi,
larvae of various insects, snails, moles, ant colonies, many kinds of "worms"
and perhaps snakes. Some of these organisms live on the roots of plants that
hold their crowns or leaves above the ground. The larger or the more active
of the animals move out of their burrows and gather food abo\'e the ground.
The ants, for example, forage on leaves, on various bits of dead organic matter,
and on plant lice. Sometimes a swarm of ants will attack a living caterpillar
or other insect that is not too active.

Earthworms live on dead leaves and other plant parts, and on dead organic
particles in the soil. A worm swallows masses of earth and digests the organic
contents in the food tract. Snakes come out for their prey, as do ants. Through
the processes of decay, bacteria and fungi release the proteins, fats and car-
bohydrates locked up in dead plants and animals. As a result, these organic
compounds break down into carbon dioxide, water, urea, ammonia salts, and
other nitrogenous compounds.

Many of the inhabitants of the soil are parasitic on others. And all plants
and animals discharge into the soil some of the products of metabolism, or
wastes. As a result, carbon, nitrogen, sulfur, and other materials return to the
air and water and soil, and become again and again incorporated in living
bodies, taking part for longer or shorter periods in "being alive" (see illus-
trations, pp. 150, 151).

Each organism that is not a food-maker gets food from others, and in turn
supplies food to others. Plants and animals thus stand in a sort of continuous
food "chain". This is not exactly a friendly give-and-take, since it seems to
run in one direction only. Beginning with the simplest chlorophyl- bearing
plants, the species in a food chain become generally larger and larger.

There is, however, a limit to this chain. This does not mean that the largest
trees or the largest animals are free of all enemies. It means merely that there
are other ways of getting food besides that of destroying smaller neighbors.
As practically everybody knows, small fleas "have smaller still to bite 'em;
And so proceed ad infinitum^ Parasites are also links in the iood chain. In
this series the plants and animals become smaller and smaller, although, as
with the main food chain, there are exceptions at many points. It does not
follow, for example, that flesh-eating "cats" are larger than those vegetarian
deer upon which they prey. A lion can successfully attack a giraffe.

Flesh-eating animals that travel in packs or work in gangs often have ad-

^See Nos. 1, 2, and 3, p. 576.
560

Lawrence H. Kobblns

A FOOD CHAIN

Beginning with the simplest chlorophyl-bearing plants, each organism eats, and in
turn is eaten. Animals generally get their food from those that are smaller. Each
takes what he can and gives only what he must

vantages over larger animals. Wolves will attack a herd of cattle or deer.
The driver ants, which always travel in vast regiments, will attack large
animals — lizards, snakes, and even cattle. If the latter cannot escape the
swarm by running away, the countless ants will sting it to death and carry
off the flesh bit by bit. Not all flesh-eaters, however, are compact and ener-
getic fighters. The whale, for example, takes into its mouth a fraction of the
ocean, filters out most of the water, and finally swallows some hundred pounds
of small fry.

As we should expect, a species that serves as food must be more numerous
than another which feeds upon it. It is estimated, for example, that one Hon
may kill as many as forty or fifty zebras in the course of a year. Since many
zebras must die every year without waiting for lions to kill them, the ratio of
zebras to lions must be much greater if zebras are to survive — or, for that
matter, if the lions are to survive. For if lions destroy too much of their food
supply, it will go hard with them the following season. To be sure, lions can
feed on other animals besides zebras; but the principle is still the same.

The food chain is in a sense endless. Or rather, it goes round and round, as
we saw in considering food cycles. A single shrub may have on it millions of
plant lice. These plant lice furnish food for thousands of insects and spiders.

56\

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j<:>j ■ ""^ ' .tJixf, -.

CLOVER CROP DEPENDS ON SPINSTERS

The red clover prospers if there are plenty of bumblebees (which are able, however,
to thrive on other plants). But bumblebees are destroyed by field mice, which are
kept in check by cats. If certain kind ladies did not harbor the cats, the mice might
become too numerous and destroy the bumblebees, and we should then not be in
clover

These in turn are devoured by a dozen or a score of small birds. But these
birds can barely supply a single pair of hawks or a domestic cat. The hawks
or cats do not, of course, finish the cycle, even if they have no serious enemies
to contend with. For if there are no enemies large enough to destroy them,
the parasitic chain gets in its work sooner or later. Exceptional prosperity
leads to high density of population — which invites an epidemic. An epi-
demic in turn exhausts itself, or it is destroyed by another epidemic.

Natural Groupings of Organisms We can separate a plant or an animal
from others of the same or of other species. But we cannot keep it alive in
isolation indefinitely. The organism depends upon other species in its natural
setting — on some directly as food, on others indirectly as food for its prey or
host. The cat seems not to care much about clover; but she can feed on
field mice only because the clover and the bumblebee have an arrangement
of their own.

When you see a field aglow with fireweed or black-eyed Susan, you may
be sure it was the winds of pure chance that brought the seeds. Yet the
insects which now fly around those flowers were directed by something more
definite. And whatever becomes of the next crop of seeds, these insects will

562

have had a share in bringing them into existence. We notice in any region
chiefly the plants, both because they stay put and because they are usually
present in masses of individuals of the same kind. The animals manage for
the most part to remain out of sight. The many species of plants and animals
of any region, however, make up a coherent whole.

The different species depend upon one another not alone in the food chains
— or, rather, food cycles. They depend upon each other also for "shelter".
Thus birds and mammals hide in the trees, or smaller plants live in the shade
of larger ones. And they depend upon each other for "services" — as in the
case of insects transporting pollen or of mammals transporting seeds. We may
regard some of the activities as in the nature of "protection" — as when ants
keep the plant lice in check on a shrub. Such a grouping of many different
species that depend upon each other in these different ways is sometimes
called a "natural community".

What Determines the Composition of Natural Communities?

Life on the March In every plant and animal species population con-
stantly presses in all directions. From wherever there is an established popu-
lation, to wherever it can find a place to take hold, life is on the move. What
enables species to move forward? What obstructs this movement.f^

The climate, the contours of the earth, large bodies of water, may restrict
some plants and animals pretty closely. On the other hand, winds carry
seeds and spores over all kinds of obstacles, and the rivers distribute living
forms. Ocean forms become widely distributed, being restricted chiefly by
climatic conditions. The birds often fly over obstacles that block other species,
and they often carry seeds and spores far from their place of origin.

On the relatively low mountains in the eastern United States, for example,
one finds species of plants and animals that are typical of the Canadian zone of
life. Plants on the barren tops of these mountains are typical of the arctic
region and of the higher Alps, the so-called Arctic Alpine life zone. It is quite
a thrill to recognize one of these Alpine species after an exhilarating climb to
the summit. Lichens and mosses grow on barren rocks and in protected cre\ -
ices above the timber line, under climatic conditions which no higher forms of
life can long endure.

There is much evidence to show that the distribution of plants and animals
today is in some ways unlike that of the distant past. Thus we find in the
arctic coal deposits which must have been produced ages ago, although the
conditions there today are impossible for plants that can form coal. How did
coal deposits get into the arctic regions? Was the coal formed farther south
and then somehow shifted into the arctic? Or were conditions in these parts
of the world favorable to plant life in past ages?

563

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RELATED INDIVIDUALS IN SCATTERED REGIONS

This "southern white cedar" (Chamaecyparis thyoides), growing in Connecticut, is
really a kind of cypress and grows on the margins of swamps. But swamps are in-
frequent to the north of central New Jersey, while the plant is found on their margins
as far as Maine. How can we account for the distribution of this species in such
widely separated areas?

The prickly-pear cactus, which is common only in desert regions, is found
also in a few isolated barren localities in the highlands of New York and north-
ern New Jersey. How is it that we find these plants so far removed from their
normal range .^ One suggested explanation assumes that after the retreat of
the last glacier, warm, arid conditions prevailed throughout most of the
northeastern United States, so that plants requiring more moisture died out;
only desert plants survived, and they spread all the way from New Mexico to
New York. With changing conditions other plants have replaced the cacti
over most of the area. Another situation which is similarly explained is the
presence of the southern white cedar on the margins of fresh-water swamps in
lower New York State; this is a species that normally ranges southward from
the Carolinas.

Barriers to Migration Species living on a highland, or on a continent
widely separated from other continents by oceans, have little chance to visit
other lands. The living forms or types found in such isolated places are often
unique. For example, British explorers found no placental mammals in Aus-
tralia in the decades after it was discovered by Captain Cook. This was not a

564

Organ-pipe cactus in a desert habitot — southern Dune grass on a wind-swept seashore — Cape
Arizona Hatteras

United States Department uf the liitericir; Glacier National I'ark

Epiphytes in cypress trees in a swamp habitat — Bear gross at the summit of the Rockies — Glacier
Everglades, Florida Notional Park

TYPES OF NATURAL COMMUNITIES

If placed in one of the other environments shown, any of these distinctive plants
would be crowded out by the native species, or it would be destroyed by the in-
organic conditions

question of "fitness", for when rabbits were later introduced, they multiplied
rapidly among the native marsupials, and actually became a pest.

The most effective barriers or obstacles to migration may turn out to be a
relatively small feature of the soil or the population. Acres of seemingly good
earth may remain sterile for want of a chemical element which plants use in
very small quantities at most, such as magnesium. On the other hand, early
settlers may obstruct migration, either by pre-empting all the available space
or by being actively antagonistic. Human wanderers have frequently been
stopped by micro-organisms producing tropical diseases rather than by wild
beasts or by previous settlers.

Types of Community To most of us a forest is the most familiar natural
community. The inhabitants of a desert make up quite as distinct a com-
munity, but most of us would have to be shown, since we commonly think of a
desert as having no life at all. A swamp has its characteristic plants and ani-
mals, as has a scrub or a sand-dune.

The inhabitants of the ocean differ from those of fresh-water lakes, but
there are many types of communities in the former and also in the latter.
Tidewater plants and animals differ in many ways from those that occupy the
bottom offshore, as well as from those that live at or near the surface. And
deep-sea forms differ from both (see illustration opposite). Brook life and pond
life differ from each other, and they differ also from the forms living in larger
streams and in large lakes. Among the most important life communities in
this country are the grasslands — of two types, the semiarid plains and the
moister prairies — which have played a great role in the development of our
food resources (see illustrations, pp. 89, 569, 643, 646).

How Are Communities Formed?

The First Settlers To a barren spot containing no organisms whatever,
the winds would ordinarily bring thousands of seeds and spores representing
dozens of species. Which species could take hold would depend upon the
amount of moisture, the temperature, the sunlight, and the chemical condi-
tion of the soil. To establish themselves in such a barren situation, plants
must be able to endure the winds, glaring sunlight, extreme fluctuations in
temperature and in moisture, and extreme combinations of soil chemicals.
Most of the plants with which we are familiar could not endure so much pull-
ing and pushing. Early settlers have to be tough.

The pleuroccus cell might hold on to the rough surface of a rock. If there
is enough moisture in the air, it may grow and multiply. But then, it cannot
stand sunlight. The gemmule of a lichen might do better, since the fungus
partner can absorb enough moisture from the atmosphere to supply both it-
self and the algal partner (see Appendix A). The excretions of the lichen grad-
ually dissolve some of the rock's surface and so contribute to the making of soil,

566

Iclmann

OCEAN DEPTH AND OCEAN SURFACE

Ocean animals living near the surface depend for food upon green plants and
a chain of larger and larger animals. In the depths, where chlorophyl action is
impossible, larger animals feed upon smaller ones, down to worms and protozoa,
all finally depending upon the decomposition going on at the bottom

/To establish themselves in a barren region tough seed-plants must be able
to push their roots down rather quickly. They usually have harsh skin, often
prickly surfaces or hairy coatings, and can endure extreme changes in moisture
and in temperature. Such "pioneers" are able to make a living in rather un-
promising conditions. Through this very growth, however, these pioneers
change the surroundings. The roots break up the soil and make the latter fit
for more tender plants. The dead leaves falling to the ground make a blanket
that retains moisture: now the earth does not dry so quickly after a rain. Or-
ganic matter slowly accumulates and gets into the soil. In the shade of pio-
neers the seeds of more tender plants can get started. In time these early set-
tlers change the soil, and the climate close to the ground. They have made an
environment suitable for other species of plants. They have provided also a
setting for insects, worms, and bacteria and other nongreen species.

The first animals to arrive in such a situation may find little to attract
them or to hold them. In time, however, food becomes available for more
kinds of plant-eating species. The remains of dead plants and animals supply
conditions suitable for scavenger animals like certain kinds of worms and in-
sects, and for decay organisms — bacteria, yeasts, fungi. Roaming birds and
other animals act as carriers — whether they remain or pass on. They bring
new kinds of seeds, as well as worms, protozoa, and insect species small enough
to take the ride, whether inside or outside the bodies of the larger forms.

Changing Population The pioneer seed-plants are not merely tough in
relation to the physical and chemical conditions. They must also be self-
sufficient for pollenation. Or they must at least be able to get along with wind
and gravity, and not depend upon insects or birds. After insects arrive, there
may be a chance for the more sophisticated species of plants that do depend
upon insects. In much the same way, seeds of legumes (plants of the bean
family) may get started; but unless the right kinds of soil-bacteria are also
present, they will not be able to establish themselves (see pages 149, 151).

The composition of a living population is thus constantly changing. Some
species become relatively more numerous. There are constantly new arrivals.
Some of the new settlers expand rapidly. Some of the early settlers gradually
disappear: they are crowded out, or they die out. In some cases, plants and
animals take on new patterns of living. A plant whose ancestors lived on moist
soil has now leaf habits and root habits that enable it to live in the drier region.
Or an insect whose ancestors lived for generations on a particular species of
plant takes to a different diet. But most species apparently make no experi-
ments unless driven by "hunger".

The Climax Community^ Plants of diflferent species are constantly
competing for the limited amounts of water and of minerals in the soil. Some
compete for sunshine, although others thrive in the shade of their taller

iSee No. 4, p. 576.
568

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The characteristic plants of a region are determined, in a sense, by the nature of
the soil, the water supply, the climate. The animals in turn are determined by the
characteristic plants. But in time the plants depend upon the animal population as
much as the animals depend upon the plants

neighbors. Changes through the seasons and the years affect not only the com-
position of the population, but also the composition of the soils. And there is
also some effect upon the climate. For example, the conditions of moisture,
light, temperature, and air movement close to the ground in a forest are quite
different from the corresponding features on a prairie; and they are made
different as the plant-and-animal community develops.

Of two species living side by side, one may grow faster and shoot up into
the air. But the other may mature more quickly and shoot a thousand seeds
into the air before the first one has started to flower. The quick grower may
fill an acre in the second year; the other, however, may spread over six acres.
These differences are, of course, not the only ones. Nor do they tell us which
species will in the end survive.

Through the interactions of plants and animals, of organisms and the soil
and the immediate atmosphere, the composition of a population gradually
reaches an optimum for the region. There is a balance between the chloro-
phyl organisms and the others. There is a balance between plant-eaters and
flesh-eaters, between insects and birds feeding on insects, between plants that
supply nectar to insects and insects that pollenate the flowers, between the
number of nuts and the number of squirrels.

When this state is reached, it may continue indefinitely. It is called a
climax of life development, since it represents the fullest continuous yield of
Hfe for the region. And because particular types of plants are characteristic
in such situations, various formations are usually designated by the names of
"dominant" plant species — for example, a pine forest, a tamarack swamp, a
scrub-oak mountaintop, a maple-birch community, and so on (see illustrations,
pp. 204 and 564).

Moving Equilibrium In a stabilized, or cHmax, formation all the vari-
ous species are mutually adjusted in equilibrium. And the whole living popu-
lation is in equiUbrium with the physical conditions. Soil, cUmate, plants and
animals make up together a complete whole. All the parts are related to each
other in such a way that the "whole" remains pretty much the same, although
changes are going on in every part all the time.

When the climax has been reached, each species reproduces itself at a rate
that keep.s its numbers about the same year after year. Many species that
were conspicuous early in the development have disappeared, and new ones
seldom make their appearance. Moreover, the kinds of organisms that thrived
at one stage of the development cannot thrive in a later stage. Weeds are
usually tougher plants than our cultivated varieties, and they are always
pushing out into unoccupied spaces. But they are generally not so efficient
where the soil and the other inhabitants have become adapted to a more ad-
vanced stage.

Because the larger plants are always the most conspicuous features of such

570

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DIVERSE APPEARANCE IN RELATED SPECIES

Anybody can recognize all these animals as chipmunks. It is not so easy to tell how
their differences came about. Are they the "same species", developing different
sizes or colorations on account of the conditions under which they live? Are the dif-
ferences in any sense of "value" — the dark ones being better protected, for ex-
ample, In one region and the light ones in another? Are some larger because food
is more abundant — or smaller because some particular detail in their surroundings
prevents full development? Are they, indeed, the "same species"?

stable life communities, we often overlook the close interdependence among
all the species. We are especially likely to overlook the smaller plants and
animals in the soil or in dark corners — just as we often overlook the obscure
parts of a human population when we travel about, and judge a community
or a civilization by some conspicuous features.

It is of course reasonable for us to cut trees for our use or to capture animals
for their furs or to catch fish for food. Like other things, we have to get from
nature what we need. And timber, food, fur, are the values that we see in
these various life communities. It should be clear, however, that in a stable
life community, in nature as well as in a human civilization, no individual and
no species can live by itself — nor, very long, for itself. Each can live only as
a member of the larger group, and this group continues only as its essential
members maintain a due balance of numbers and of activities.

Is Man a Member of a Natural Community?

Man an Interloper Man is apparently a late arrival among the many
species of living things, in a world already old. We can hardly suppose that
he had a place all ready and waiting for him. Like other species, he must have
had quite a struggle to make a place for himself. But where?

Today man is more widely spread over the face of the earth than any other
species, except the simplest water-dwelling animals. We must except also the
parasites that man has taken with him, and some of the domesticated animals,
especially the dog. Man today finds himself at home in the tropical jungle
and amid the arctic snows, in fertile river valleys and on relatively dry pla-
teaus, along the seashore and in the mountains, in forests and on the open
plains.

Always, however, man could migrate only into regions that had already
established an equilibrium of plants and animals. For only there was there
a sufficient variety and sufficient number of living beings to supply him suffi-
cient food and sufficient materials for shelter against the weather and against
dangerous animals.

Man the Wanderer The spread of the human species to nearly all cor-
ners of the earth took many thousands of years. It is only in recent centuries
that the human population seems to have increased rapidly. And only in
modern times has it been possible to observe closely the processes by which
man extends his sway over the earth. The earliest settlers from Europe in
North America found small encampments of Indians occupying but sparsely
a vast forest on very good land. As these new arrivals from Europe all came
from crowded regions, everybody eagerly reached out for as many acres as
possible. Very often they seized many more acres than they could ever use.
One result was that after the first colonies had become fairly well established

572

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Although man uses more difFerent species of
plants and animals than any other living form,
he manages to make himself at home where few
other species can remain alive, and to make
himself a home out of almost any material that
comes to hand — the snow in Greenland, skins
and sticks in Saskatchewan, the sun-dried cloy
in Arizona

AincriciiU Museum uf .Naluial liisluii

MAN THE WANDERER

along the Atlantic coast, the pioneers moved on into the wilderness and
spread out. Each farm or settlement then became pretty much a self-sustaining
unit, usually some miles from the nearest neighbors.

These human pioneers had to do everything themselves, under difficult
conditions. Men, women and children, like plant pioneers in the wilderness,
had to be "tough". They had to fight not only the soil and the weather and
wild animals, but also the Indians whom they were displacing and other mi-
grant pioneers, other colonials.

From old settlements and farms waves of pioneers kept pushing out, gen-
erally westward. Basically, the onward drive comes from the simple fact
that agricultural populations always outgrow their lands. But today, as in-
creasingly for a hundred years, surplus farm population is not seeking new
lands so much as new opportunities in towns and cities. Farmers have been
coming to town in ever greater numbers. The farms have been supplying not
only their plant and animal products to feed city dwellers, but also the boys
and girls to become city dwellers to swell the urban population.

Human Communities We have seen that plant "pioneers" are tough.
In the formation of a natural community the composition of the population
changes through the arrival of new species. These can live in the new sur-
roundings which their predecessors created. And, on the whole, they can put
the material resources and conditions to better use than their predecessors did.

In the wilderness, men, women and children, like plant pioneers, have to
be tough. They have to fight the soil and the wild animals and the weather
—and sometimes other human beings. As human communities develop, the
population consists continuously of members of the same species. New modes
of life are developed, differing from those suited to pioneer conditions. The
community offers new opportunities, but it also makes new demands. Divi-
sion of labor and specialization increase efficiency, but they increase mutual
dependence and demand more co-operation and mutual consideration.

As in the natural community, a growing human community makes it pos-
sible for more tender types to flourish. The skilled craftsman need not be
able to do all the different things a pioneer has to do. He is of value in the
larger group because he does his own job so well — and there are enough people
to use all he can produce. On the other hand, as the number and variety of
these tender specialists increase, it becomes "tougher" for the tough pioneer
type. He is relatively inefficient in every job he is capable of doing. Skilled
miners and skilled farmers become "unskilled laborers" when they look for
city jobs. Even if such a pioneer is still tough, the tender engineers and me-
chanics soon find ways of doing without his heavy muscle, just as they have
learned to do without his mule or ox.

There are other hardships for the pioneer. He was able to meet pioneer
difficulties through his self-reliance, his physical strength and endurance, his

574

resistance — his toughness. In the city, however, he has to observe a hundred
restrictions and interferences. There are traffic regulations; he cannot come
and go as he pleases. He has to step aside or adjust his pace to that of others.
He cannot spit whenever or wherever he feels like spitting. He is constantly
reminded that he may be makmg a nuisance of himself. There are demands
upon his manners, his dress, his speech. These all "cramp his style". And yet
he cannot get tough with these tender people. They have even specialized
here: toughness is handled by the police.

Social Integration The human community, like the natural community,
becomes progressively more integrated, or unified. The increasing variety of
activities become more and more closely co-ordinated. And they become
more and more closely related to the outside. The rural and the urban, for
example, become more closely knit. Manufacturing, or processing, becomes
more closely related to production of raw materials and to the machinery of
marketing or distributing. Transportation and communication services mul-
tiply^out of all proportion to the growth of population.

All these changes mean closer interdependence. Each individual must be
more sensitive to the moods and needs of others, must be more tolerant of
others, more ready to give, as well as to take. And interdependence extends
to an ever larger area as interchange of goods and services covers eventually
the whole earth; and civilized man becomes at last a citizen of the world com-
munity. The ruggedness of the individual who minds his own business and
disregards everybody seems to be out of place.

Man and Other Communities^ When an equilibrium is reached, whether
in a natural community or in a human community, it may be disturbed by a
variety of happenings. By a radical change in climate, for example, as has
happened repeatedly in the past, or by a volcanic eruption, an earthquake, a
flood, the diversion of a river, a hurricane. But again and again a natural
community of plants and animals has been seriously disturbed by the intru-
sion of one restless, roving, ruthless species — man. Man makes his own com-
munity and tries to subordinate the rest of life to his purposes. And some-
times he destroys the very beings upon which his further existence depends.

In Brief

Decay, which is itself a living process, breaks up the organic compounds in
the bodies of larger plants and animals and makes the elementary substances
again and again available as raw materials for living bodies.

Plants and animals are related in continuous food series, or "chains".

There is a numerical relationship between the members of one species and
those of other species in the same food chain.

iSee No. 5, p. 577.
575

Deserts, prairies, mountain ranges, tundras, forests, oceans, rivers, and the
like each obstruct the migration of certain species, and at the same time fur-
ther the distribution of others.

In any area the composition of the population changes through the arrival
of new species which happen to fit the conditions brought about by their
predecessors and which make, on the whole, better use of the existing situation.

Through the interactions of plants and animals with each other and with
the soil, water and atmosphere, the composition of a population gradually
reaches a point which represents the optimum, or climax, for a region.

The many different interdependent species in a region make up what Is
called a natural community.

As man subordinates other forms of life to his purposes, he sometimes
destroys the very species upon which he depends for his further existence.

As in the natural community, a growing human community makes it pos-
sible for new types to flourish; the pioneer becomes relatively inefficient in
every job he is capable of doing and so is replaced by interdependent special-
ists of many and diverse kinds.

EXPLORATIONS AND PROJECTS

1 To study the way in which earthworms mix and aerate the soil, place between
two vertical panes of glass an inch apart a layer of rich loam and above it a layer of
coarse sand. Introduce earthworms and observe for several days. (Keep soil rela-
tively moist, though not wet.) Describe what happens to soil and sand and explain
how this is related to the growth of plants.

2 To investigate food chains, start with any species of animal that is convenient
and find out (a) upon what species it feeds and (b) what species feed upon it. Extend
the chain in both directions. That is, after each species in list a, enumerate in order
the species that supply it food, tracing as far back as possible; and similarly, after each
species in list ^, enumerate in order the species that use // as food, again tracing each
line as far as possible. The food chains and food cycles of such organisms as a lady-
bird beetle, an earthworm, a swallow, a crustacean, or a zebra would be interesting
to investigate. Represent your findings diagrammatically.

3 To work out the food chains in a restricted habitat, find what organisms dwell
in it, and so far as possible determine what eats what. In such a habitat as a decayed
log one can study various relationships among fungi, sow bugs, millepedes, spiders,
caterpillars, ants, aphids, termites, protozoa, bacteria, seedlings, birds, centipedes,
snails, slugs, etc. Record and interpret your findings.

4 To become familiar with various habitats, visit a varied stretch of countryside,
identifying different habitats, along with the dominant forms of life found in each.
Some interesting kmds of habitats to study are a moist woodland gorge, a pine wood,
a deciduous forest, a cypress swamp, a floating sphagnum-moss bog, a riverbank, a
seashore, a sand-dune, a second-growth brush, a meadow, a barnyard, a mountaintop.

576

Record your findings. Draw conclusions concerning the specific conditions which
favor the growth of plants in the distinct habitats which you visit.

5 To contrast the topsoil in a forest and in a run-dovn cultivated field, select
two locations similar in all other respects, and examine the soils. With a spade dig a
hole through the topsoils in each case. Determine how they compare in depth, in
proportion of organic material to sand and clay, in water-absorbing and water-
holding capacity, in amount of decay that is taking place, in compactness, in resist-
ance to erosion, and in other features. Record your findings. Relate what you have
found with reference to the effect of forests upon fertility and upon floods.

QUESTIONS

1 What kinds of living things can be entirely independent of other organisms.?

2 Why cannot all hving things be entirely independent of others.''

3 Why are there more parasites among microbes than there are among the
larger plants and animals.?

4 Why is it important to distinguish between symptoms and causes of diseases.?
Why is it important to know the symptoms and the causes of diseases.?

5 How can the abundance of a particular species of plant or animal (reindeer,
oranges, whales, cotton, sugar cane, sheep, cattle) influence the whole mode of life
of a community?

6 How may certain physical features act as barriers to the spread of some
species, and at the same time aid in the distribution of others.?

7 In what ways are conditions in a pioneer community like those in a climax
community.? In what ways diff^erent.?

8 What factors bring about the normal shift within a community toward the
climax grouping of organisms.?

9 What are some of the advantages of carrying the division of labor still
farther among individuals.? among nations? What are the disadvantages.?

10 Is a person with a special talent better off in a large community or in a small
one.? Why.? How about a person with a special handicap?

11 In what respects are human communities Hke those found in nature.? In
what respects different.?

577

CHAPTER 29 • THE BALANCE OF LIFE

1 If living things are in balance, how can the population of any

species increase?

2 Why are there more insects or fish in some years than in others?

3 How can a species thrive as well in a strange region as it does in

its natural or original home?

4 Does introducing a new species into a region always cause harm

to others?

5 Does any harm result from exterminating any species?

6 How have some species been exterminated?

7 Can species change their feeding or other habits to fit a new set

of conditions?

8 Are there any regions that once had much Ufe but now have

little — or vice versa?

9 Does increasing the amount of life in one region have to reduce

the amount in another?
10 Does growth of human population mean that other species are
reduced in numbers?

We keep a young child away from complicated machinery because there is
danger he might get hurt poking among the moving parts which he does not
understand. Another reason is he might injure the machinery, or start some-
thing that might lead to even greater disaster. When we poke about in this
complicated world of plants and animals, we are not always aware that we may
be starting trouble. Shooting blackbirds for fun may mean merely shooting
blackbirds. But it may mean advancing the price of bread in far-away cities
next autumn. For while each hunter may kill only a few birds, the sport may
turn the scales between locusts and wheat. Neither the hunter nor the house-
keeper buying bread far away may know what birds here have to do with the
price of bread there.

Living for generations in a particular locality, people learn pretty well
what plants and animals they can afford to encourage or to destroy. As we
move rapidly into strange regions, the task of maintaining a balance of
Hfe becomes increasingly difficult. This is not so much because the problem
becomes more complex, for we can construct and operate very complex
machinery: we can learn which lever or button to press for desired results.
But when man interferes with natural processes, he cannot always be sure
what he is setting loose or what he is bringing on. And yet we have to in-
terfere. Living means interfering with nature. Is it possible to upset the
balance without bringing about undesirable results? How can we tell how far
it is safe to go?

578

AiiiciiLai) Mustura of \aluijl History

ADJUSTMENT TO EXTREME CONDITIONS

Inhabitants of this tide pool or of the ocean shore must be tough to stand the beating
waves and the rushing tides. Twice daily they are exposed to the drying air and
then submerged again. The surrounding conditions ore of many kinds, but the or-
ganisms survive the variations, which are fairly regular, or periodic, and limited
in degree

How Is the Balance of Nature Upset?

Life Is Always Upsetting When a plant-animal community has reached
a fairly stable "climax", it contains the greatest amount of living matter that
the particular region can sustain. This situation is similar to that in a balanced
aquarium with green plants or in a "ripe" hay infusion. Such a condition of
balance is like the resting position of a pendulum or of a scale-beam — it is
easily upset, by a comparatively slight disturbance.

The balance of nature, however, is not a state of rest. It is more like the
continuous swinging of the pendulum back and forth, within certain limits.
We might perhaps better speak of the hahndng. For the condition in a for-
est, for example, or in a tide-pool is one of continuous change (see illustration
above). And it is also one of continuous <fx-change. Materials move from
the air and soil into green plants, from plants to animals, and eventually back
to soil and air.

The relative numbers of the different species may remain essentially the
same indefinitely, though they do, of course, fluctuate from day to day and

579

from season to season. Plants grow but are constantly destroyed by other
plants and by animals. Baby suiifish increase in size, while the insect larvae
on which they feed diminish in numbers. They themselves diminish in num-
bers, while a perch grows at their expense.

At the end of a good growing season insects and worms and birds and ro-
dents, as well as plants, will be more numerous than after a poor growing
season. That in turn will mean a prosperous year for hawks and foxes and other
carnivorous animals. Later on various fungi, worms, beetles and bacteria will
be exceptionally numerous. A species expands to the limit of exceptional
abundance only to furnish a stroke of luck for those who depend upon it.
There is no endless up and up; life is a succession of ups and downs. Even
in the steady growth of an old tree we can find indications that its "fortune"
has fluctuated with changes in the amount of sunshine (see illustration
opposite). These records are so consistent that it has been possible to ascertain
the dates of timbers in ancient structures through them. And it has been
suggested that human affairs might be profitably studied in terms of the
changing abundance of plant and animal life in the past.

Food and Elbowroom Experiments with flour-beetles and other in-
sects show that in a given area the number of individuals never increases past
a certain point regardless of the amount of food. A colony of bacteria in a
food medium will grow only so far and then stop, long before exhausting the
food. Apparently there is a point beyond which more and more food does not
mean more and more growth — for a particular individual or for a colony of
individuals or for a species.

In a given field a thousand seeds of corn or of tomato will start more plants
than five hundred seeds. But five hundred may produce a greater number of
mature individuals and a greater yield. For spacing and air are quite as es-
sential as root-hold. With human beings food is a first condition for growing
and multiplying, and elbowroom is a close second. And yet the race appears
to have multiplied more rapidly where the density of population is already
highest. In slums of industrial cities and in parts of India, for example, the
birth rate is higher than in other parts of the community. Yet in many such
places the death rate exceeds the birth rate. People continue to live there
only because new individuals and families are constantly being pushed in from
outside. Such crowding of one species offers very favorable opportunities for
other parasitic or predatory species.

Epidemics People in past ages looked upon epidemics of disease or of
pests exactly as many of us today look upon an unexpected hurricane or earth-
quake. They just happen. In the quaint language of insurance company
lawyers, they are described as "acts of God" — without necessarily implying
either any theory as to how things come to happen or any theory of religion.

Today we do have definite theories about how epidemics come about, and

580

Began growing
550 A. D.

~ Goths expelled from Italy

60(321 Pope Gregory

800—

Time of Mohammed

900 Norsemen to England

William tke Conqueror (1066)

HOQ-—

5 Rrst Crusade

1200— Magna Carta (1215)

1300—

1400—

1500 —
1600—

Mariner's compass

Columbus discovers America

Lanang^rf Mayflower (1620)

-^^13feClarauOT"Ci inue|Mil'iuence

Pagteur

• Cut in 1891

This giant tree was 1341 years
of age at date of cutting

Diameter 16^2 ft (inside bark)

Circumference — 52 ft (approx.)
Height 250 ft (approx.)

American Museum of Natural History

LIGHT AND LIFE

Variations in the rings of a tree's wood evidently correspond to yearly variations in
conditions favorable to growth. But these variations appear to be periodic; and the
rhythm corresponds in a remarkable degree to the rhythm of sunshine intensity,
which in turn is related to the sunspot cycle of about eleven years

we are so much better prepared to deal with them. If the scale-lice, for exam-
ple, cover the twigs of a tree in a thick layer, the ladybird beetles will de\our
them voraciously, and then multiply very rapidly. The happy and prosperous
plant lice are all but wiped out. Their very prosperity has invited an epidemic
of their enemies. An epidemic may in fact be considered as a very prosperous
opportunity for some plant or animal that unexpectedly gets into a crowd of
its potential hosts or victims.

581

To the parasitic and predatory organisms the situation is an exceptional
period of prosperity and expansion. For the victims, however, it is an epi-
demic, a visitation of misfortune. On the other hand, a period of prosperity
and expansion is Hkely to be followed by a period of privation, as, for example,
with the ladybirds who have all but exterminated the scale insects in a region.
Moreover, long before most of the prosperous and abundant Httle beetles have
a chance to suffer from famine, they will have furnished a feast for various
birds and their babies.

An epidemic usually comes to an end abruptly because the successful
species has destroyed its own food supply. In the case of insect or fungus pests,
an epidemic — that is, an unusual crowding — invites another species to take
advantage of the unusual abundance of food. In the long run the victor be-
comes the spoils.

How Has Man Disturbed the Balance of Nature?

Man's Intrusion^ Long before the dawn of history man had domesti-
cated the dog and species of ox, sheep and goats. He was able to maintain a
steady food supply. The family was enabled to enlarge, and to stay in one
place for a relatively long period. Herdsmen did, of course, have to move
when rains failed or when their cattle ate up all the grass in the neighbor-
hood. But the nomads were more orderly in their rovings than hunters.
Living generally became better organized.

From being a hunter to being a herdsman man took a step forward. From
being a herdsman to settling down as a soil- tiller, he took another step for-
ward. The gains may be measured by the fact that population grew. The
domesticated plants and animals multiplied in numbers. But man's success
threatened to upset the natural balance. Increasing the population of men
and of domesticated species furnished their enemies and parasites exceptional
opportunities. Flies and liver-flukes increased rapidly. Man has invited to
his farms all kinds of vermin, insects, fungi and worms that had previously
Uved on the sparse vegetation or animals of the natural life-community.

These changes in man's mode of life meant more intensive hunting of birds
and game and fish. They meant changing the composition of the streams into
which he threw his refuse. In proportion as man has thrived and grown in
numbers, he has made increasing demands upon the earth and has exerted
increasing pressure upon other species. Concentrating population — human,
vegetable, animal — brought about the destruction of some species and the
increase of others.

Mining Wood Man could find an opportunity to live only in a region
at or near the climax of its development (see page 568). The forest has been

iSee Nos. 1 and 2, p. 598.
582

Lte fiom L' S U A ; Soil t( nsun^i mn .^criice

TWO WAYS OF LUMBERING

In irresponsible lumbering as much wood was allowed to rot and to burn as was
actually removed for practical use as timber. In scientific lumbering, selected trees
are cut clean, close to the ground; branches are trimmed and the underbrush is
cleared away. More timber is used, and all of it is replaced by new growth

most favorable for man, as for other mammals. And man's use of the forest
well illustrates the effects of his interference with the balance of nature. The
settlers cleared land as rapidly as possible to make room for farms and homes.
Much of the wood they used to construct shelters, barns, fences, bridges.
Year by year, however, as the population grew and extended westward, for-
ests became the source of valuable material which needed merely to be cut and
shipped. They were treated like mines that would last forever.

In the first hundred years after the formation of the Union, timber was so
recklessly cut that millions of acres of forests which had taken centuries to
grow were destroyed. Since a virgin forest is a well-balanced living com-
munity, its growth is at a standstill. New growth is just enough to offset the
death and destruction among old trees. When man invades the forest, not
only does he remove wood faster than the new growth can replace it, but he
destroys also the shelter and food upon which birds and mammals normally
depend. As a result, the weeds, insects, and other small animals upon which
these birds and mammals feed begin to multiply at a rapid rate, so that the
entire community is thrown out of balance.

Man and Birds Like most animals, birds are important to us chiefly
because of the food they eat. But unHke insects, for example, birds in their
feeding are usually of advantage to mankind. Many birds have been con-
victed of eating fruit in the orchards. And it is true that the sharp-shinned
hawk has been caught carrying off young chickens from the barnyard. Never-
theless, with a very few exceptions, the common birds are worth more to us
alive (as destroyers of insects, vermin and weeds) than dead (as sources of
feathers or food) or as objects of sport.

We cannot class each species of bird as altogether useful or altogether in-
jurious. The red- tailed hawk feeds on field-mice in one region and discovers
that chickens are good to eat in another. The bobolink is a serious menace to
the rice fields in the South, but is a valuable insect destroyer in the North.
The red-winged blackbird ate so much grain in Nebraska one year that the
farmers took up arms and killed the bird off. The following year, however, the
absence of the blackbirds enabled the locusts to multiply so rapidly that many
of the grain crops were ruined.

In Pennsylvania, in the 1880's, the state legislature voted a bounty for
killing hawks and owls, which were supposed to be killing chickens. In less
than two years nearly $100,000 was paid in bounties. Biologists who studied
the situation in detail found that the predatory birds might have killed chick-
ens worth a few thousand dollars. But they found further that the mice which
birds did not kill damaged the crops to the extent of $4,000,000. The law was
repealed.

Destruction of Birds Many birds are destroyed wantonly by ignorant
boys and men. Some are killed to supply feathers. Still others are exter-

584

>{~-Csff"Wt

I iiUtil Males l-Dic-bl hi-nice

BEFORE AND AFTER MINING LUMBER

Hillsides stripped of native forest cover soon become denuded of soil. Afterward the
barren, unproductive soil may be deposited on fertile valley lands during floods,
destroying their productivity as well

minated when their eggs and nests are destroyed out of idle curiosity or in the
interests of untrained collecting. In rural and suburban districts domestic
cats have probably done far more damage to the native birds than they paid
for by killing mice or rats. It is an open question whether we should not be
better off in most cases without the cat.

During their migrations many birds are killed by flying against telephone
and telegraph wires and against plate-glass windows. Along the shores, mi-
grating birds frequently hover about the lighthouses at night until they are
exhausted. The clearing of forests, the extension of cities, and the improve-
ment of farms all lead to the extermination of various species of birds. De-
stroying dead limbs and dead trees in forests and woodlots may drive out the
downy woodpecker and the redheaded woodpecker. But it is worth while to
keep the woodlot clear.

There is no evidence that poison sprayed on trees to destroy caterpillars
ever injures birds. Even if this did sometimes happen, however, we should
have to continue spraying, for as we cultivate more plants, the insects that
feed upon them multiply too rapidly for the birds to keep in check.

Protection of Birds Many of the destructive agencies that affect birds
are directly under our control. Gratings placed on certain lighthouses off the
coast of England enabled countless thousands of migrating birds to rest in their
flight, instead of dashing themselves to destruction against the lights. As elec-
tric, telephone and telegraph wires come generally to be placed underground,
as they are now in the cities, birds come to have a chance to fight it out
with their natural enemies and the natural obstacles to their survival.

Men and boys will have to learn to find sport in opera glasses or the cam-
era, as women and girls are learning to be happy without bird's plumage or to
be content with the dyed feathers of domestic fowl. It is possible to get as
much fun out of building nest boxes and shelters for birds as out of shooting
or trapping them. Birds encouraged to make their homes in our immediate
neighborhood will continue to furnish us with interesting sights and sounds
long after dead birds would have been forgotten. In addition to providing
suitable boxes for birds' nests, we may scatter grain or bread crumbs after
heavy snowfalls and so enable many birds to survive until the ground is clear
and they are again able to find food for themselves.

The red squirrel often destroys eggs and sometimes even young birds, but
does nothing to compensate for this damage. These animals should therefore
be killed, to give the birds a better chance. The weasel, the skunk, the fox,
the raccoon, and other mammals sometimes kill birds or eat their eggs; but
as they do not feed exclusively or largely upon birds, they are not to be con-
sidered serious enemies.

Migration When food is scarce in any region, it is "natural" as well as
intelligent for man to move away. Plants that propagate vegetatively may

586

K^y-f

•New lurk Uotamciil Garden

MIGRATING FROM A CENTER

This "fairy ring" of mushrooms (Lepiota) on a ranch in Colorado suggests how a
vegetation or population, fixed to the earth, moves outward as it exhausts the food
available

often be seen moving away from a center in all directions, and in ever- widening
circles (see illustration, above). Man, along with other species, has pushed out
into new regions not only to find more food, but to escape enemies. Indeed,
many of us today move from one place to another for our health. The partic-
ular climate, the presence of particular plants or animals, may make our present
location unsuitable — for some of us. Again and again people have moved in
hordes from regions considered unwholesome and regions invaded by pests.

But in moving away the individual or horde becomes an interloper. Every
new arrival disturbs the existing "balance" and threatens to drive some of the
plants and animals away or to destroy them. Men moving in large numbers
are like a swarm of locusts moving across the land and destroying every scrap
of vegetation. In a comparatively short time European man has driven from
their former habitations the Indians who had lived in North and South
America for centuries. He has reduced to a small fraction of their former
numbers many species of wild mammals, birds and fishes. He has destroyed
the trees on millions of acres, practically all the grasslands, and the fish in
hundreds of miles of stream.

To offset the destruction, man has made millions of acres bear vastly greater
quantities of particular kinds of vegetation than would have been possible
under natural conditions. The corn, the potato, the tomato, the tobacco, the
peanut, the strawberry, had inhabited this continent long before the white
man came. But never had any of these species thrived so luxuriantly and so

587

FORMER INHABITANTS

Beavers, foxes, bears, minks, antelopes, moose and^ elk_are very rare today.Wiid
turkeys, passenger pigeons, and heath hens are gone, with the buffaloes of the
plains. Such bison herds as the one pictured above are protected in national parks

abundantly as they have done under man's care and cultivation. These plants,
as well as other species imported from various countries, have taken the place
of dozens of species that might otherwise have thrived on this area under
"natural" conditions.

Transportation Man, moving with his household effects and his cattle
and his seeds for future planting, carries with him all the vermin, all the de-
structive parasites of his household and his associates. Europeans traveling to
the islands of the Indian and Pacific oceans brought with them infectious
diseases that turned out to be very destructive to the natives. The whites, in
turn, succumbed in large numbers to tropical diseases. Negroes brought as
slaves to America in the eighteenth and nineteenth centuries carried with
them an internal parasite, the hookworm, which they seemed able to tolerate
without serious discomfort or privation (see page 615), Later, however, when
this hookworm became established in the soil of our Southern states, the
parasites infested large sections of the white population, with disastrous effects.
Conversely, measles and other diseases long familiar to the white population
attacked the Negroes with exceptional severity.

From these examples we see that a parasite moving into a new region may
find a host that is incapable of defending itself, and the parasite thrives. Or a
species enters a new region and becomes the prey of parasites against which it
has no defense. Or an invading species may be particularly destructive be-
cause it finds suitable food but does not run into its old enemies.

588

'X iMWiiiiiiii iwmlwtifttiiwiliiiwiiiw!

'J^ I'

. >..'l--

iioil Cunservalion Service

CROPS NURTURED BY MAN

Man makes wheat grow where formerly buffalo grass thrived; but only by constant
care and management. Wheat never grew so luxuriantly by itself; yet how quickly
would it be replaced by other grasses should man cease his nurture!

We saw that rabbits, introduced into Australia, became a pest (see page
564). They interfered not only with the native wild animals but with agri-
culture and sheep- raising. Bounties were paid to encourage the destruction
of the rabbits. The water-cress was similarly introduced into New Zealand,
and in a comparatively short time it choked all the rivers. Elodea and the
muskrat were brought to England and multiplied much more rapidly than
they had done in their older habitats. The English sparrow was brought to this
country to destroy the tent caterpillar, which was injuring shade and orchard
trees. The sparrows took to living in the cities too, feeding largely on the un-
digested seeds in the droppings of horses. By the end of the century they
had become a nuisance. They were not helping to fight the insects, and they
were interfering with other birds. They have been gradually disappearing
from our cities, however — but not because we have done anything to dis-
courage them. We replaced our horses with automobiles, which yield no by-
product that sparrows can use.

Mining versus Cropping Man was intelligent enough to devise weap-
ons and tools which enabled him to kill and destroy out of all proportion to
his actual needs. Using his excess power, he changed the balance among living
species in the areas he occupied. In his hurry to get a quick profit from the
forest while the getting was good man not only destroyed the forest, but
exterminated game and fur animals and birds. He brought about far-reaching
changes in the soil and water relations of areas stretching across the states.

589

By "mining" the living resources of the earth instead of husbanding and
cultivating them, we have produced ugly, desolate holes. We have replaced
luxuriant and balanced life-communities with scavenger and decay organisms.
The results of his handiwork force man to move on. Only as such results
accumulate have we gradually come to recognize the danger of some day
pushing ourselves off the earth. To keep ourselves going, we must keep the
earth continuously fertile and fruitful.

How Can We Meet Our Needs without Destroying the Sources?

The Conservation Idea^ Those who enjoy hunting and fishing, or who
sell what they kill or catch, find it very difficult to see why anyone should
want to interfere with their sport or business. After all, hunting and fishing
are very ancient vocations and very ancient modes of enjoying life. There
were hunters before there were farmers and long before there were foresters
and game wardens. Present-day hunters and fishers feel close to nature and
close to "natural law". But modern man, having learned to write and to
figure, is able to look ahead more than a lifetime and backward more than a
generation. He is able to calculate the danger of trying to Hve like a hunter
and fisherman in a world of growing populations, automatic machines, air-
plane transportation and radio communication. It is impossible for the earth
to maintain its present population (to say nothing of the future) on the sim-
pler basis (see pages 534-535).

Forest ControP Before the beginning of the present century it became
evident that we were destroying forests faster than they could grow. There
was a movement for conserving the forests, for introducing more economical
methods of using the natural but limited resources, and for developing meth-
ods to replace with new growth what was removed each year. This movement
met with much opposition. Those who agitated for conservation were easily
discredited as cranks. Every effort to protect the public's interest in the for-
ests as a national resource was denounced as interfering with private business.

Theodore Roosevelt, during his Presidency (1901-1909) supported Gif-
ford Pinchot in his attempt to educate the public, as well as forest-owners and
forest-operators, to a more scientific — and in the long run a more productive —
policy. Research and practical development since then have made more and
more people recognize that the forest is something more than a lot of trees
that happen to be on somebody's acres for him to use as he sees fit.

We all depend upon the products and the inhabitants of the forest, as well
as upon the water and soil that are influenced by the living trees. Control of
the forest, therefore, becomes a matter of national concern. In the past, pri-

iSee Nos. 3 and 4, p. 598. «Sce No. 5, p. 598.

590

vate owners of forest land cared only for what they could get out of it.
We could not expect them to feel much concern about effects a hundred
miles or fifty years away. We therefore could not depend upon them to
handle forests so as to assure the general population full benefits and neces-
sary protection.

The Forest Service The Forest Service of the United States Depart-
ment of Agriculture, which was established in 1875, has made many careful
scientific studies of forest conditions in different parts of the country. It has
thus been able to give sound advice on the care and management of forests
and wood-lots from every point of view. From these investigations we learn,
first, how to protect forests against certain injuries and, second, how to increase
their value. We now know that it is possible to get all the wood we really need
without destroying our forests, if only we follow certain principles.

Over one hundred million acres of land have been left barren by "timber
mining" and fires. The reforesting of such areas is continuously under way in
many parts of the country. A great deal of worn-out land and sand-dune land
is well suited to forests. In many cases it is necessary only to protect the young
growth from fires. Another method of extending the area of growth is to
stock existing forest lands more fully.

Increasing Yield and Quality It is likely that not more than from
seventy to one hundred of the nearly one thousand native species of trees in
this country are worth growing, from the economic point of view. The red
cedar grows very slowly; the white pine or the red oak could be grown in
the same soil to great advantage. We could replace the red spruce in New
England with the Norway spruce, just as many areas of France denuded by
the First World War, as well as other European regions, have been restocked
with Douglas fir imported from this country. In some localities we may per-
haps find foreign trees better suited to our purposes than the native trees. In
the course of a number of years the rapid-growing varieties will yield much
more timber than the others. But rapid growth is not of itself a deciding fac-
tor, for it is necessary to consider the toughness of wood and other qualities.
The whitewood, or tulip tree, for example, grows much faster than the oak,
but it can never be used as a substitute for the oak.

Without increasing the amount of growth, the value of timber can be in-
creased through efforts to keep the trunks and branches straight. By thinning
out the crooked or twisted trees, it is possible to concentrate the growth in
the best trees and so to increase the yield of a forest area.

Avoiding Wood Waste In the national forests lumbermen are given
practical demonstrations of scientific cutting, seeding, reforesting, etc., and
also of the economical handling of growth. In careless lumbering, a tree ij:
sometimes damaged while being cut down, and trees left standing are some-
times injured. At the forest-products laboratories and the forest experiment

591

United States Forest Service

FOREST AREAS IN COLONIAL TIMES AND TODAY

It is estimated that in 1620 the forest area was more than 800 million acres. By the
beginning of the present century we had less than 500 million acres. This has
gradually been increased to over 600 million, nearly a third under public administra-
tion or control. And increasingly our forests are being operated for continuous yield

Stations investigations are constantly being made to find the best methods of
utiUzing wood and other forest products for various purposes, as well as of
getting optimum yield.

Forest Dangers The person who cuts recklessly and destroys for im-
mediate profit what ought to last practically fore\^er menaces our forests.
This enemy can be regulated either by enforcing strict rules as to the private
management of forests or by making it impossible for individuals or corpora-
tions to profit from the exploitation of forests.

592

Fires, most of which are of artificial origin, annually destroy much of our
forests. In the unprotected areas the damage, measured in acres burned, is
proportionately sixteen times as great as in the protected areas. Well-organized
fire patrols in the national forests have succeeded in preventing many fires
and in keeping the total fire damage down to a small fraction of what it is in
the privately owned forests. The chief damage done by forest fires is to young
growths; this prevents restocking. The rules for fire prevention in forests are
posted on trees, and every person who has occasion to go into the woods should
heed these regulations.

Important but less serious dangers to forests are various species of insects
and various species of fungi. Every year these organisms destroy trees and
timber worth millions of dollars, and there is no one way to fight them all.

Hand-to-Hand Fighting One way of dealing with pests is to go after
them directly when they show themselves. We slap every mosquito that
alights on our skins. We swat flies or pull a tomato worm from the vine. We
pull up weeds. Somehow weeds, flies and other pests seem to multiply faster
than we can pull them up or kill them. We look for wholesale methods. We
set traps to catch the enemy in large numbers: traps for rats and mice, for
Japanese beetles, for houseflies. These can work while we sleep or are other-
wise engaged. We place poison where we think it will do most good — for
mildews and for insects and other species.

Barriers Where the enemy is known, we are often able to put up bar-
riers against his depredations. We may fence in our cattle against wolves or
quarantine them against infection, just as we screen our houses against flies
and mosquitoes. But keeping the enemy out is not always practicable, es-
pecially when we do not know the enemy well enough. For after all, how does
the liver-fluke get into the sheep? How do cattle "catch" Texas fever.?
How does the worm get into the apple? A large part of the research work of
the United States Department of Agriculture since the time of Lincoln has
had to do with learning the life histories of insects and other parasitic or
predatory animals and plants. These studies reveal to us not only the weakest
Jink in an organism's life cycle, but also the weakest links in the food chains
of which the species may be a part.

According to such studies we find that when we cannot shut all the pos-
sible gates against an enemy, we can sometimes stop him in his tracks. By
destroying the barberry bushes in the regions that grow wheat, we make it
impossible for the wheat-rust fungus to complete its life cycle. In the case of
the liver-fluke, we find the key in ponds that harbor certain snails: no snails
in the pond, no liver-fluke in the sheep (see page 615). The alternate host of
the white-pine blister is the wild currant or the gooseberry. The most familiar
example of breaking the life-chain to control a pest is perhaps the case of the
mosquito. By draining swamps, covering rain-barrels, oiling ditches, we

593

After Bureau of Entomologj and Plant Quaiantine, U.S.D.A.

A DOUBLE-FACED ENEMY

The destructive black stem rust of wheat spreads rapidly through the summer by
means of spores, in two or three successive generations. The two-celled spores that
survive the winter cannot infect wheat. In the spring these spores produce short
hyphae, which bear multitudes of rather tender spores, which are also indifferent
to wheat

eliminate mosquitoes, which depend upon wetness for their early stages —
egg, larva and pupa. And in doing so, as we all probably know, we interfere
with the continuity of the malaria parasite or of the yellow-fever virus (see
table, p. 620).

Fighting Fire with Fire Biologists have found that a most effective
way of fighting an epidemic is with a counter-epidemic. Thus, since a trouble-
some species is probably kept in check in its native habitat by its natural
enemies, we can restore a disturbed balance by finding the natural enemy of
our pest.

It has been possible to control the destructive Hessian fly by means of the
parasitic insect Polygnotus. The gypsy moth has been a constant source of
destruction to various cultivated crops since about 1870; it seems to be
coming under control with the introduction of the calosoma beetle from France
(see illustration, p. 596). One of the first suggestions that insects could be

594

Bureau of Entomology and Plant Quarantine, U.S.D.A.

AN INNOCENT-LOOKING HIDEOUT

The new spring spores of wheat rust attack the young leaves of the barberry. By
destroying the barberry, we are able to control the black stem rust of wheat, for the
rust dies out during the winter months. The species has no way to keep going unless
both its hosts are present in the same area

controlled by encouraging other insects was made in the early part of the last
century by two English entomologists. They declared that the aphids, or
plant Hce, which did great damage to hops, could be cleaned out of the green-
houses and fields by increasing the number of ladybirds (see page 581).

Since 1916 the Japanese beetle has been spreading destruction to more
than two hundred and fifty varieties of crop, garden, and orchard plants in
twenty-two states (see page 655). After years of search in Japan and Korea
agents of the United States Department of Agriculture found two natural
enemies of this pest that promise to help check its injurious career. One of
these is a genus of antlike winged insects. The female burrows in the ground,
where the beetle larva destroys the roots of plants. She stings a larva and
paralyzes it, and then lays an egg in it. As the young parasite hatches out of
the egg, it feeds upon the larva and destroys it. The other promising natural
enemy of the beetle is a spore-bearing bacillus that produces a fatal disease in
the larva. The bacteria multiply in the blood of the insect and turn it into a

595

gs;;y:i:-y>!-?>-'>>-:^:™::<-:

Larvae (dorsal view)

Eggs

'i; 1J

Larvae fventral view)

Adult beetle feeding on
gypsy moth larvae

ENGAGED TO FIGHT OTHER INSECTS

Pupae

Gypsy moth pupae
destroyed by beetle larvae

Bureau of Entomology and Plant Quarantine, U.S.D.A.

This beautiful green calosoma beetle (Calosoma sycophanta) was used by a French
scientist in 1840, in a campaign against the gypsy moth (Porthetria dispar). In recent
years this method of combating undesirable insects by encouraging the spread of
their natural enemies has been rapidly developed

milky fluid. Dead larvae, the skin containing now millions of spores, are dried
and ground to dust, and mixed with an inert powder. The mixture is dis-
tributed on the soil of an infested area, and the larvae become infected.

Other insects have been successfully combated with parasitic bacteria and
fungi. In South America and in Yucatan this method has been used against
locusts. Quantities of the insects are caught alive, infected with the parasitic
fungus, and then set free again. The escaped animals transmit the infection
to their fellows, and millions are killed off. One epidemic is made to over-
come another, until a balance is restored.

Man the Disturber Man has been extending his domination over the
earth at an ever-increasing pace. He has succeeded not by growing stronger
muscles, longer teeth or sharper claws, but through his scheming, planning,
devising, manipulating. He began by handling sticks and stones that he could
pick up. These enabled him to exert power and to produce effects at a dis-

596

tance. He has gone on to rearranging the very face of the earth, to rerouting
its rivers, to altering the character of its plant and animal life. He distributes
species and changes the relative numbers of various species, all to serve his
needs and his desires. But in extending his domination, man sets up processes
the remote results of which he cannot possibly anticipate. Who could have
foreseen that placing a paper factory at one point along a river would ruin
the life in the river or the water supplies of cities far away? Who could have
guessed that making fine wheat and cotton grow in rich crops in place of the
scrubgrass would end by destroying the soil itself?

When we undertake to change the numbers of any species, it is not enough
to know that a particular species is useful or harmful. We ha\'e to proceed
cautiously, and seek as thorough a knowledge as possible of all the relation-
ships in which each species is involved. Nor is it a simple matter, as many
assume, of "interfering with nature's plans". Nature's "plans" include man
and Ufe, and Ufe is always interfering. It is a matter of altering certain slowly
movmg processes of mutual adjustment, certain balancings, so that we can fit
ourselves into them while advancing our own welfare.

In Brief

Within a balanced community of living things, the essential ratios and re-
lationships of the different species remain fairly constant.

Each wave of abundance for any species lasts only until the organisms have
expanded to the limit of the resources.

Within any living community there is a point beyond which more food
does not mean more growth, for other factors limit the results.

An epidemic may be considered as an exceptionally favorable opportunity
for some plant or animal that finds itself among a crowd of its potential hosts
or victims.

In proportion as man has thrived and grown in population, he has made
increasing demands upon the earth and has exerted increasing pressure upon
other species.

By making many plants and animals of the same kind live close together,
man has brought on a constant succession of epidemics.

With every migration, the new individual becomes an interloper; every
new arrival competes with plants and animals in an existing balance and threat-
ens to drive some away or to destroy them.

A parasite moving into a new region may find a host that is incapable of
defending itself, or it may become the prey of a species against which it has
no defense.

597

Invading species may become particularly destructive if they find an
abundance of suitable food and no natural enemies.

By destroying forests, man exterminated much of the wild life and brought
far-reaching changes in the soil and water relations of areas stretching across
states.

Increasingly, our forest areas are being operated for continuous yield.

By concentrating our forest growth in the best trees it is possible to in-
crease the yield of a given area.

The four most serious dangers to the forests are ruthless cutting for profit,
fires, various insects, and various fungi.

The extension of cities, the clearing of forests and the improvement of
farms, all result in exterminating various species of birds.

Our attempts to utilize natural resources more thoroughly for our own
advantage often disturb balances and bring about epidemics.

In general, the most effective way to fight an epidemic is with a counter-
epidemic, that is, a restoring of the biologic balance by encouraging the
natural enemies of the pest.

EXPLORATIONS AND PROJECTS

1 To see how man upsets the balance of nature, screen either or both of the
United States documentary films entitled The Plow That Brol^e the Plains and The
River. Relate the scenes shown in the films to conditions in the nearest region in
which man's activities are making rapid inroads on natural resources.

2 Report on changes that have taken place in your own community or state, in
comparatively recent times, in the prevalence of {a) wild life, {b) forest land, {c) cul-
tivated crops, {d) weeds, or {e) domestic animals. Account for the reduction in
numbers of certain forms and the appearance and spread of new forms. Which
changes have produced results favorable to human beings? unfavorable? What
species should be further reduced, or what ones should be protected? Be sure you
have considered all factors in making your recommendations.

3 To find out what can be done to conserve natural and human resources after
balance has been upset, investigate the work of the Tennessee Valley Authority in
its program of conservation, flood control and power development.

4 To find out what methods of farming are least wasteful of our nation's soil,
investigate some of the better farming practices employed in scientific farming.
These methods include general farming, feeding of crops to livestock, careful tech-
niques in the handling of manure, rotation of crops, the use of cover crops, legume
crops, green-manure crops, commercial fertilizers, Ume, drainage, and methods of
tillage which lessen erosion. Report your findings.

5 To investigate the succession of plant forms which take over an area after
the climax forest cover has been removed, visit areas that have been cut over re-

598

cently, a decade ago, and a generation ago. Compare the dominant forms of plant
life in each with that found in virgin timberland. Work out the succession of plants
which develop in your region when forests are cut or destroyed.

QUESTIONS

1 Why does a plant or animal sometimes thrive better when carried to a
strange region."^

2 How can insects that are not harmful in one region do great damage in
another region?

3 How can insects that are harmless at one time become injurious at another
time.?

4 What conditions allow one pest or one disease to increase with extreme ra-
pidity at times?

5 What are some of the dangers of interfering with the natural balance of life?
What are some of the consequences of man's interference with it?

6 What are the chances that man's fight against insects will someday be
finished? Why?

7 What can be done to make possible a larger population without undue
crowding?

8 What animals or plants would it be desirable to exterminate from your
region? Why?

9 How could the extermination of any plant or animal species bring about
undesirable consequences?

10 What is the most effective way to fight any epidemic?

11 What dangers threaten our forest areas?

12 What do you consider the most valuable organic resource of the country?
To what extent are we husbanding this resource?

599

UNIT SEVEN — REVIEW • WHY CANNOT PLANTS

AND ANIMALS LIVE FOREVER?

With our own strong desire to live, it is natural for us to seek ways of
lengthening individual life, as well as of enriching it. And with the use of
modern knowledge we have indeed stretched the average duration of human
lives in this country by more than ten years since the early part of the present
century. It is likely that we shall succeed in reducing the death-rates at the
younger ages still further. But under the most favorable conditions there is
still a limit to the length of individual life, and we need not search for physical
immortality. Is, then, the life of the individual self- limiting?

The more we study the activities and the processes of plants and animals,
the clearer it becomes that it could not be otherwise. Although cells of dif-
ferent tissues or of different species vary greatly in size, each cell reaches a
limit of growth. This limit seems necessary because the interchange of ma-
terials between the protoplasm and its environment is limited to the ratio of
the surface of the cell to the mass.

There is a further limit in the fact that as the individual grows, the parts
become more and more specialized. Now living depends upon a close co-
ordination of all the parts. But handicaps or incapacities increase as minor
injuries accumulate in specialized structures which cannot regenerate or be
repaired. Finally, growing older involves accumulating wastes; lime, silica,
and other inert matter are deposited and so reduce the metabolic activities
in proportion to the total protoplasm.

A different set of conditions limits both individual and total life. In the
whole world there is only so much carbon, only so much phosphorus, only so
much nitrogen — a limited amount of each of the elements essential to living
protoplasm. These materials are so distributed that only a fraction of the
total present is available for living things — in the waters and in the soils near
the surface of the earth. And even then they are present in proportions that
permit only a fraction of the accessible materials to be used by plants and
animals. There is, in fact, a surplus of one or another of these elements almost
anywhere, but that does not make up for those that happen to be deficient.
Now, li all the available materials essential to living things should at any time,
and in a particular region, become embodied in living plants and animals,
there would be the largest possible amount of protoplasm — and of "life".
But then, that condition could last for but a moment; for all the organisms
would immediately proceed to starve, or they would begin to destroy one
another. In either case, that "maximum" amount of life could not continue.

Living depends upon a continuous flow of materials. Each individual is a
center of interchange of materials: this is a basic relationship between an
organism and its environment. Some species are related to one another

600

through their mutual dependence upon this constant stream. Individual plants
and animals take from it, but each one also yields to it — at first perhaps only
wastes but eventually up to the very last atom of its physical being. The life
of a region becomes slowly richer in total life and richer in forms as new
species move into it or perhaps evolve in it. These changing inhabitants are
capable of operating more efficiently, in the special circumstances, than their
predecessors. The total population attains at last an optimum — the climax of
plant and animal increase in a balanced system of mutual interdependence.

In the course of slowly building up a climax population, life and death in-
teract. Chlorophyl-bearing plants and some of the simplest species that build
up more complex compounds might live indefinitely in the absence of animal
species. The animal species, however, could not live in the absence of the
former. And by destroying plants and oxidizing organic materials, animals
restore to the surroundings raw materials that make possible new plants.
There is thus a mutual exchange, a constant give-and-take. Much of this is a
quiet, even invisible process — diffusion of gases, diffusion of dissolved sub-
stances in water, breathing, absorbing, excreting. But much of it involves
activities that are fairly described by the term struggle — the capture of prey,
the pursuit, the flight, the direct combat. Every phase of this struggle is, of
course, destructive of living individuals; but it is also the condition for pro-
longing the lives — of other individuals.

During this struggle of living beings with one another, as well as with the
nonliving environment, the total amount of life may steadily increase — up
to the time that a cHmax is reached. Then the actual amount and the actual
composition of the plant and animal population continue to change from
moment to moment, from season to season, from year to year; but there is a
balance. The life destroyed is quickly replaced by new growths or new births,
and the new life destroys its own equivalent.

One feature of life that is at once a source of destruction, and also a means
for filling in every possible gap, is the fact that each species not only repro-
duces, but multiplies. As a result, there is a constant push outward from every
single plant, from every group of animals. We might imagine a slower rate of
reproduction, a replacement rate, which might permit every individual to
live out his own cycle, according to the species. But that would overlook the
fact that at each stage every animal species is food for others. The species
breeding most slowly could attain an optimum of survivals only as it managed
to get food without itself being eaten.

The pressure of population is constantly disturbing the balance in any life-
community. When human beings come into a situation that they find favor-
able, they are disposed to work it intensively. As a result, they often destroy
its capacity to maintain human life further. Migration has been part of man's
history from the beginning. The conditions of mutual aid, division of labor,

601

cc-operation, have increased the efficiency of human living in any given
situation. But they have not necessarily ensured an adjustment of Hfe to the
balance of nature, so as to make the conditions continuously suitable for man.
It is indeed only in recent times that we have been aware of the underlying
balance of the plant and animal forms on which our own existence depends.
We can enlarge our population, we can lengthen individual life — but only to
a point.

Life has endured for millions of years. But each individual has his little
day, and is gone. He gives way to others — to others of many different species
or to others of the same species — as he himself has been able to live only as
others have given way before him.

602

UNIT EIGHT

What Are the Uses of Biology?

1 In what ways are biologists any better off than other people?

2 In what kinds of business or profession is biology necessary?

3 How important are the kinds of work that rest on biology?

4 What occupations make use of biological knowledge incidentally oj

indirectly?

5 What is the use of biology outside of any occupation?

6 How can the ordinary citizen make use of biology?

7 How did people get along before there was any biology?

8 In what ways has biology improved conditions of human life?

9 In what ways has biology made us healthier?
10 In what ways has biology made us happier?

Man shares with other organisms the basic needs — food and air. Air is
free, usually, but food one has to get. The helpless human infant survives
day by day only because others nourish him and shield him. Gradually,
however, the child learns to handle food, eventually to select. And in prim-
itive societies the child also helps gather and prepare food as soon as he can
toddle about and discriminate among different leaves, berries, seeds, and so on.

Biology is "learned" in this simple way from the earliest years without
lessons, without having a name even. It consists of knowing many plants
apart and many animals too: these things you may eat; these you may not
eat. Knowing where to find good berries or roots, how to catch fish. Know-
ing that these things you may eat as you gather them, but these you may eat
only after they have been treated — cooked, mashed, ground, cured, mixed
with other things.

When thirsty, one drinks water. If the appearance or the taste of the
water does not please you, you need not drink it. If you are very thirsty, how-
ever, you may swallow even unpleasant water. Some peoples cook their
water or make teas or some other brews. That was in many cases a good rule,
for those who boiled their drinking-water were better off than the others.
It was good "biology" even when people did not know the right reason for it.

Compared with those of other mammals, man's activities are most dis-
tinctive in his use of tools and in the making of things. Handling things more
skillfully and intelligently than other species, he is able to wander over a
wider range. He can create shelters out of whatever materials may be at
hand — skins of animals, grass, bark, leaves, sticks, stones, snow.

Traditionally men have thought of their material needs as food and shelter
— housing and clothing. But even the most primitive peoples need more.

603

They need tools and weapons, as means for getting the primary essentials.
And nearly all seem to get satisfaction from gathering odds and ends of things
with which they decorate their bodies or their garments and their dwellings.
Even weapons and tools are often ornamented.

Ornaments are often symbols of what people deeply treasure. A savage,
for example, keeps the tusks or horns of animals he has killed. These are
trophies, or proof of his prowess. Some of the North American Indians kept
the scalps of enemies they had slain. These things had no trade-in value for
food or clothing. They were symbols of worthiness, signs to all the world
that this individual amounts to something. They were thus sources of satis-
faction and self-assurance. Migrating tribes could not carry with them such
trophies. But another feather is no burden, or a notch cut in the handle of the
club, or a bead on a string, or another tassel of bright-colored wool. These
tokens have value over and above material necessities. They correspond to
certain goals that we moderns strive for — titles, medals, ribbons, badges.

Other objectives for which people struggled had religious or magical vir-
tues. Eating the heart of a lion was not only nutritious; it gave one courage.
Certain plant and animal parts might cure or prevent sickness, but they had
religious or magical virtues in addition. People would go to great pains to get
a toad by moonlight or to cHmb the high mountains for the lucky edelweiss.

It is true that human beings, like other organisms, can continue to live with-
out these ornaments, without these symbolical and magical objects. But as
human beings we cannot be happy and comfortable without them. For these
objects mean the difference between being nobody and being somebody.
They are the outward and visible signs of inner worth. They are necessary
for gaining the respect of others, and sometimes for gaining power over them.
They are needed to ensure courage and self-confidence and peace of mind.
And so they are necessary for health and comfort.

Man reaches out beyond food and clothing and shelter. A better under-
standing of the forms and activities and characteristics of plants and animals
enables people to get more easily what they need. It helps them avoid with
greater certainty what may injure or annoy them. Keeping well and avoiding
illnesses also depend upon a better knowledge of living things.

We started out by saying that everybody has to know some biology. In
all parts of the world people have their local ways of selecting and preparing
food, of raising crops, of catching fish or kilUng game, of preventing pests, of
keeping well. They live — well or ill — by what they actually do. In addition,
however, they have various and conflicting notions to explain how plants and
animals work, or reasons for their rules and practices. And these ideas and
reasons often conflict with what we today know — or beHeve.

How does finding out more about living things increase our powers.'' Or
our material resources .f* Or make us any healthier or happier .f*

604

CHAPTER 30 • BIOLOGY AND HEALTH

Public health is purchasable; within certain limitations, a community can determine its own
death rate. — Hermann Biggs, health officer. New York City, 1911

1 What is the best way of keeping well?

2 Why must there be sickness?

3 Can anything in the food or water or air make us sick?

4 Can the lack of anything in the food, water or air make people

sick?

5 Can things get into the body in other ways than through the

mouth or nose, and make people sick?

6 How can we be sure that the "evil eye" or malicious wishing

does not cause disease?

7 Can all diseases be prevented?

8 How can we tell that new ideas about sickness are better than

old ones?

9 What disease can be cured by purely mental methods of healing?
10 Why must there be so many specialists?

People have always wondered what made them sick. This is no idle curi-
osity. The correct answer may solve an important practical problem, namely:
How can sickness be cured when it strikes? Men have dared to think even
more boldly: How can we prevent sickness from striking?

Early ideas about disease were very much confused. It is easy enough to
make guesses about the causes of a particular disorder or of disease in general.
But there are always more false guesses than right ones; and in the past there
was no way of checking them, to find which was right. How can we tell that
the newer ideas and practices about keeping people well are more dependable
than earlier ones? Why do doctors change their theories about disease? Why
do not doctors always agree about what to do?

How Important Is Sickness?

How We Measure Sickness^ Ordinarily we become interested in health
only when we are in pain or disabled, or when we see others suffering. On an
average, six millions of the population of the United States are suffering each
day from disabling sickness. Some of us do not lose a day through sickness for
years at a stretch. Others are aiUng a large part of the time. The average
time out from work or from school — or from play — is about ten days a year.

Health-department reports usually deal with communicable diseases only.
Another way of measuring the health of populations is to compare their aver-
age length of life or their death rates (the number of deaths in one year for

iSeeNo. 1, p. 638.
605

every 1000 of the population). In 1940 the death rate of twenty-seven large
American cities v/ith a total population of over twenty-seven million was
11.4. In one city the rate was as low as 8.3, while a rate as high as 15.3 was
the worst record. The relative magnitudes of the three rates are shown
graphically by these three lines:

11.4

8.3

15.3

A closer measure of a people's health is the number of babies who die
before their first birthday for every thousand born. In the same twenty-
seven cities the rate varied from a low of 29 to 30 to a high of over 64; and
the rate for the total was 38. Ten years earlier the cities with the best records
had an infant death rate of 50.0, while the worst of the records stood at about
90. There has thus been a consistent decline in the infant death rates, but
this decline apparently corresponds to improvements in the care and nutri-
tion of children, and in the care of mothers before childbirth.

Aside from these relatively exact measures of illness, we know that there
is a tremendous amount of ailing that never gets into the records. Millions
keep right on working with such minor troubles as "common colds", sore
joints, stiff backs, or just a miserable feeling. And these ailments vary in
amount and in frequency not only among the individuals who suffer, but
among whole sections or classes of the population.

What Makes These Diflferences? Among our own acquaintances some
are more "healthy" than others, more vigorous, take punishment more easily,
spring back, or recover, quickly when struck in any way. Others are easily
upset, lose much time ailing, never quite come up to par in anything. In-
dividuals differ in organic vigor and capacity. There are also differences
among families. And for that matter, illness strikes unannounced even among
people who have excellent health records. Nobody knows who is going to be
struck next. But what about differences between one city and another, be-
tween one region of the country and another.? Why is it that year after year
the health record of some cities or counties is consistently better than the
average — or consistently worse?

Some of the differences among communities, as to death rates, are due to
the composition of the population. In some of the Western states, for example,
with a large proportion of adult males and relatively few women and children,
the death rate is low. In some communities special health risks are associated
with local industries. In general, rural life is considered more wholesome than
urban life, although health conditions have been improving more rapidly in
cities than in rural areas.

Some of the health differences may be due to the different stocks present

606

HEALTH DIFFERENCES AMONG CITIES

The infant death rate is steadily declining in all cities, as well as in the country as a
whole. When we compare the four cities making the poorest showing in any one
year with the four cities making the best showing, we are struck by the large number
of deaths that could probably be prevented

in our population. This is, however, not a matter of "race" but of modes of
living, of understanding how to meet conditions, how to make adjustments.
People who find themselves in a strange region are always at a disadvantage.
This is true of explorers and adventurers and of families migrating of necessity
or in the hope of improving their lives. Whole populations are pushed
around by floods and famines, as well as by wars; and being a stranger in a
strange land is always hard and always involves health. Minority and alien
groups are generally at a disadvantage and pretty helpless, even in the demo-
cratic countries. If we compare the minority races with the white, in various
cities, in various parts of the country, we see a preponderance of sickness
among the underprivileged.

Minority groups are, in general, more poorly housed, more poorly fed,
more poorly clothed. They are likely to be overworked. And they are likely
to be underprivileged with respect to schooling and other opportunities to
find out better ways of living. They are likely to be anxious and worried.

Poverty and Sickness We can see that economic conditions bear upon
health whenever we compare living conditions, on the one hand, with sick-

607

p«iooopop«u«on 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 IS X6 17 18

New York

Philadelphia

Baltimore

St. Xouis

Washington, D. C.

New Orleans

Cincinnati

Newark

Kansas City, Mo.

Louisville

Atlanta

THE RELATION OF HEALTH TO POSITION IN THE COMMUNITY

The preponderance of sickness among the underprivileged shows itself in excessive
death rates among the colored population. In ten cities having 10 per cent or more
of Negro population, the general death rate among colored persons is consistently
higher than among white persons

ness rates and death rates on the other. Endless investigations have shown
that death rates are considerably higher among the poor than among the
comfortable; infant death rates are higher among the poor; tuberculosis ill-
ness rates and death rates are higher among the poor; the frequency and
severity of illness have been uniformly higher among relief and marginal-
income families than among others.

Poverty is associated with sickness because being poor means being unable
to get adequate food. It means unsuitable housing — crowded, too cold or too
hot, poorly lighted and poorly ventilated, too damp or too dry, lacking in
sanitary facilities, and hard to keep clean. Poverty usually means overwork,
both at home and on the job. Poverty usually means anxiety, worry, and an
excess of irritation.

Sickness and Ignorance Although the poor suffer more from various
diseases than the well-to-do, there is among the families of the well-to-do a
great deal of preventable illness due to ignorance. Men and women with
many years of schooling are not expected to manage an airplane or a poultry
farm on the basis of the history they studied; neither can they keep well
with their history or languages.

All of us, rich as well as poor, could get better value for what we spend on
food, for example, if we knew more. Malnutrition is partly a matter of in-

608

Per 100,000 population o 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190

I I I I 1—1 — t— I — I — t-l I I I I -f-^^^-^^z^E

1 230 240 250 260

UNEQUAL USE OF SCIENTIFIC KNOWLEDGE IN COMBATING TUBERCULOSIS

Variations in the death rates from preventable diseases are related to position in the
community. The death rate from tuberculosis among colored populations, for example,
Is from two to seven times as great as among the whites in eleven large cities that
have more than 10 per cent of Negroes in their populations

sufficient food, but it is also a matter of faulty choice of food. Wise choice
calls for knowledge and understanding, which do not necessarily come with
money. It is probably significant that the states which have been spending
most to improve their schools have consistently had good health records,
whereas those which have been spending least for schools have the highest
death rates. "Health" and "education" and "wealth" are not independent
facts. Poor people, for example, who suffer most from sickness, are also de-
prived of their share in modern knowledge and understanding.

It is true that for the individual and for the family it is practically impos-
sible to make use of new scientific knowledge as it comes along. But a com-
munity that is well informed will get its officials or its professional leaders to
produce results that seem miraculous to those who do not understand what is
happening. Over a period of years before the Second World War the health
department of Detroit carried on a special campaign to locate every case of
tuberculosis and to provide the necessary care and treatment. When the war
came, with its great strain upon workers, its exceptional crowding, and its
deterioration of living conditions, the health administration continued its
efforts to drive the tuberculosis rate down and was successful, whereas in
other war-industry centers the rate turned upward.

609

INFANT SURVIVAL AND SOCIAL STATUS IN THE UNITED STATES

The infant death rates shown In solid black are for white babies. Averages for en-
tire population are shown by tops of gray bands, from about 100 in 1915 to less
than 50 in 1940. The highest rates are for nonwhites. We might interpret the dif-
ferences as organic or inherited differences but for the fact that, as social and
economic conditions improved, the Infant death rates went down more rapidly for
the nonwhites than for the whites

FAMILY
INCOME

NUMBER OF ILLNESSES OF
ONE WEEK OR LONGER PER 1000 PERSONS

On relief

Under $1000

$1000 to $2000

$2000 or over

Entire population

^£^ ^^^ ^E:^ ^E:2:j ^^=:3j ^:i^ ^a^ ^e:^ ^^i2j ^^^ ^=2( ^

]^^ ^E-l ^=^ \^^'^ ^^^ ^^ ^^ ^gUS) ^
^^S:^ ^^^ ^^==1 ^::^ ^E:2| ^Z2j ^^ ^
^^=:^ ^^ ^==^ ^E:^ ^E:^ ^^ ^^ ^

N^^i h^^ \'^^~^ \^'^~^ [^'■'^s^ [^g=-^ [^>g=^ h^-j h

Each ["^^^^^ =r 20 illnesses

Average for
entire population

THE POOR GET SICK MORE OFTEN

It has always been known that being poor increases the chances of being sick. But
how poor must people be to be sicker than the average? Does a high enough income
insure against all illness? And are not people sometimes poor because they are too
sick to produce and earn?

Ways of Living^ If we compare peoples in different periods or in dif-
ferent parts of the world, we find certain connections between modes of life
and states of health or well-being. Epidemic diseases are, of course, associated
with crowding. Famine is associated with depending too closely upon "na-
ture"— living from hand to mouth, making no provision for possible drought or
for other interferences with crops or game. We are no better able than the an-
cients to control the weather, but we do know a little farther in advance when
changes in weather are likely to take place, and we can plan farther ahead.

Within our large and mixed population, families and groups differ greatly
in their ways of managing their homes and persons, in their ways of eating and
dressing, in their ways of working, resting, playing. These variations bring

FAMILY
INCOME

DAYS OF DISABIUTY PER PERSON PER YEAR

On relief

$1000

$2000

©©©©©©©d

$3000

©©©©©©©

$4000
$5000

THE POOR REMAIN SICK LONGER

Not only is sickness more frequent among the poor, but the average loss of time for
each illness is also greater among them. If it were merely a matter of luck whether
sickness strikes one person rather than another, there should not be this great differ-
ence in time needed to recover

iSee No. 2, p. 638.

611

about diflferences in health or sickness. Some parts of our population keep
well because they manage according to our best knowledge and make use of
expert knowledge and skills when there is need. Others are kept well by
being looked after by competent persons — as inmates of certain institutions.
But other parts of the population just drift along, and these consistently fur-
nish an excessive share of the ailing and the sick and the premature deaths.

How Do Other Organisms Influence Our Health?

Invaders^ The germ theory of disease, with which we commonly asso-
ciate the name of Louis Pasteur (see page 444), is really several hundred years
old. During the Middle Ages most physicians and scientists suspected that
plagues were due to "germs" carried from sick persons. But it was impossible
to prove the existence of these objects, because they are so small. The very
name malaria reveals the common understanding of the sources or causes of
disease. Everybody knew that it was the "bad air" — especially bad night air
— that brought on the fever and ague. People continued to speak of what
passed between one person and another as "vapors" or "miasmas" — and to
think of them as "spirits".

Pasteur, who was not a physician, but a chemist, had discovered minute
objects as always present in the fermentation of wine and milk, and present in
sick silkworms. But he had not succeeded in proving beyond doubt that a
particular species of microbe was an essential factor in a particular disease.

The first actual proof, or test, of Pasteur's germ theory was made by a Ger-
man physician, Robert Koch (1843-1910), working with an epidemic disease
of cattle — spleen fever, or anthrax. This proof consists of three distinct steps:

1. Finding the specific bacteria or other suspected parasites always present
in every organism showing the symptoms of the disease;

2. Isolating and multiplying the specific parasite in a pure growth outside
the body of the host, usually in a sterilized preparation of special food;

3. Inducing the same disease in a healthy organism by inoculating it with
material from the pure culture.

Bacteria of one kind or another will grow wherever there is organic mat-
ter, moisture, and a temperature not too low or too high. They are destroyed
by sunshine, by various chemicals, by X rays, and by the temperature of
boiling water. Many species endure prolonged boiling. The metabolism of
bacteria will be suspended when the temperature gets too low, but as a rule
microbes cannot be destroyed by freezing

Some diseases are caused by plant parasites more complex than bacteria.
The skin disease known as ringworm is due to a moldlike fungus (see page 375)
and has nothing to do with worms. The irritation and damage are annoying

iSee No. 3, p. 638.
612

Staphylococci

y .--"^^

y /'

Streptococci

Pneumococci

Typhoid bacilli

Anthrax bacilli

-s.--

Glanders bacilli

Spirillum undula
(Showing Hagella)

TYPES OF BACTERIA

Cholera spirilla

Spirillum rubrum

United States Army Medical Museum

Bacteria are divided into three main groups according to the general shape of the
cell: round-cell, or coccus, type, in which the cells cling together either in chains or
in clumps; rod-shape, or bacillus, type; and spiral, or spirillum, type. Some bacilli
and some spirilla move by means of cilia. Each group includes pathogenic, or disease-
producing, bacteria

and unpleasant, but not serious. Treatment should be left to a physician, and
persons who are infected should use care to prevent the spread of the parasite.
The condition known as "athlete's foot" is also due to a fungal parasite. The
treatment and prevention of the disease, and of others not caused by bacteria,
are possible because of knowledge derived from studies started by the germ
theory.

Virus Disease By saving from rabies a little boy who had been bitten
by a mad dog, Pasteur convinced the world of the soundness of his germ
theory of disease (see page 444) . This brilliant achievement aroused tremen-
dous public interest and led to the establishment of the Pasteur Institute in
Paris, and later of similar institutes for research into the problem of disease,
in all parts of the world. But to this day nobody has yet seen the germ of
rabies, or hydrophobia.

We have seen that in rabies, smallpox, and several other diseases the specific
cause of the disorder is a filterable virus (see pages 444-445). A virus is more
like a protein than like an organism, although it multiplies like a parasite at
the expense of the host. Virus diseases destroy plants, as well as animals;
and they arouse in the host reactions similar to those produced by injurious
bacteria. Infection by virus is also similar to that by bacteria. For these
reasons virus diseases are treated very much like bacterial diseases.

Animal Microbes Many protozoa are parasitic. Malaria, dysentery,
syphilis, African sleeping-sickness, tick-fever in cattle, and other diseases in
man and the lower animals are caused by different species of protozoa.

Many species of flatworms and roundworms live as parasites in the bodies
of higher animals. They are important to us because they injure either human
beings or domestic animals.

A very striking fact in the life history of some of these animals is that dis-
tinct stages in the life cycle are passed in different hosts (see illustration
opposite). The same fact has been observed in many parasitic plants, as the
wheat rust, one variety of which spends part of the cycle on the wheat and
part on the barberry plant (see page 594).

This fact of multiple hosts led to a great deal of confusion when scientists
first attempted to make a complete study of these parasite species. In the
end it turned out to be of great help in our struggle to overcome them, since
the more links there are in a chain, the better are our chances of finding one
that we can break.

Parasite Worms The name tapeworm is applied to several species of
flatworms of the genus Taenia (see illustration opposite). It has a comparatively
simple structure, consisting of hardly more than a series of flat sacs containing
excretory tubes and reproductive organs, with a holdfast, or anchoring organ,
at the end (or rather the beginning) of the series. Three or four species of
tapeworms inhabit the human intestine.

614

Hookworm

ALTERNATE HOSTS OF PARASITIC WORMS

The complex life history of the parasitic liver fluke was the first one understood to
include alternation of hosts and of distinct generations. Tapeworm is transmitted to
the human host by infested meat that has not been cooked enough to kill the worms
in the resting stage. Hookworm can be prevented by suitable sanitation, wearing
shoes and avoiding contact with the soil

The secondary stage of the tapeworm is sometimes injurious to the other
host also, forming what is called a bladder-worm. Sometimes the human or-
ganism serves as the secondary host. In that case the bladder-worm may
cause serious destruction of some tissue or organ.

Parasites of the roundworm group embed themselves in the muscles of a
mammal. One of these, Trichinella, usually alternates between man and pig,
producing trichinosis in human beings, and the condition known as "measly
pork" in the meat industry.

Tapeworm, trichinella and hundreds of other parasitic species find their
sustenance and their way of life in the food eaten by mammals and other
larger animals — the food and its migrations through the bodies of these
animals. We can control many of these parasites (1) by individual or family
care in the selecting and cooking of meat, and (2) by public regulation and
inspection of the raising of food animals and the preparation and marketing
of meat products.

The Hookworm Early in this century investigations conducted under
the'dircction of Dr. Charles W. Stiles (1867-1941), of the United States Public
Health Service, disclosed the fact that the "poor whites" of our Southern
states were suffering from an intestinal parasite, the hookworm. This round-
worm depleted their energies, emotional and intellectual, as well as physical
(see illustration, p. 615). The announcement of this discovery was at first
ridiculed; nobody would take the "laziness germ" seriously. Self-righteous
people said, "Laziness is laziness, and that's all there is to it," or they said,
"There's no use blaming sickness or worms for being lazy." Yet the fact
remains that with the removal of the parasite these white folks appear to be
equal to the best stocks in the country.

In some districts almost every inhabitant was infected when the investiga-
tions were made. The remedy and the prevention are comparatively simple.
The parasite can be driven from the host by the use of thymol and epsom salts.
Where sanitary privies and modern toilets are installed, the parasites are un-
able to multiply in the surface soil and come under complete control. But
in the South, where nearly a third of our population Uves and where intes-
tinal parasites are most prevalent, 15 per cent of the farm homes had no
toilet facilities of any kind in 1940.

Ticks and Mites The itch often causes extreme irritation, but its chief
danger is the great temptation to scratch, for that may lead to infection by
some more dangerous parasite. The little animal that causes the itch is a
mite, a nearly invisible relative of the spiders. Preventing the itch is largely a
matter of personal cleanliness. Another skin parasite related to spiders is the
tic\, which is about an eighth of an inch long. This bloodsucker may produce
a painful bite, but its greatest danger is as a possible carrier of disease germs
(see illustration opposite).

616

Seed

ticks

THE TICK

Young
adult female

Engorged
adult female

Female
laying eggs

Bureau of Entomology and Plant Quarantine. I .s.U.A.

The tick is known to transmit Rocky AAountain fever, or spotted fever, among human
beings. Another species transmits the Texas cattle-fever, which was formerly a very
expensive scourge in this country. (The ovipositor, on the abdomen, points forward
behind the mouth, so that the discharged eggs spread all around the female's head)

How Do People Become Infected?

Communicable Diseases Following the methods and the principles
developed by Koch, investigators have identified the specific parasites causing
some of the most important human diseases, such as tuberculosis, diphtheria,
syphilis, typhoid fever, tetanus, pneumonia, malaria, gonorrhea, Asiatic chol-
era, bubonic plague and hookworm. These diseases are important because
they have again and again killed from a tenth to nearly half the population in
great plagues or epidemics. And without flaring up into plagues they have
been the greatest causes of deaths, year in and year out, in many regions.

Common observation and countless experiments with plants and animals
leave us certain that the communicable diseases are caused by parasites or
viruses. And that they are communicated by the entrance of something mate-
rial into the body — either through one of the regular openings to the interior,
as the mouth, nose, or urethra, or else through a cut or break in the skin.

Wounds and Germs For ages common experience had recognized the
general fact that wounds fester. Nobody knew why; nor why some festering,
or pus-making, ended in healing, whereas other festering was fatal. That is
the way wounds act. Whether the skin is broken by a gunshot, a jagged rock,
or a surgeon's knife, the two possibilities are present. In hospitals it had been
observed that however skillful a surgeon might be, his patients often died as
a result of the festering, or "blood-poisoning" as it was called. There was
also an excessive number of maternal deaths associated with fever and blood-
poisoning. And nobody knew why, nor what to do about it.

617

In Boston, Oliver Wendell Holmes (the father of the late Supreme Court
Justice Holmes) had suspected from his hospital experience that this septicemia,
or "rotting of blood", was due to something brought into the patient through
breaks in tissues. In Vienna and in other cities observant physicians and sur-
geons had come to the same conclusion. After Pasteur and Koch had made
their demonstrations, an English surgeon, working in Edinburgh, Joseph
Lister (1827-1912), hit upon the idea of keeping "germs" out of wounds.
He fitted his surgery up with suspended sheets that he soaked with carbolic
acid. He cleaned the wounds of his patients with this germ-killing solution.
And he promptly reduced the casualties following surgical operations.

Since then many fl«//-septics have been used for destroying bacteria in
wounds of all kinds, and especially in surgery. The problem has always been
to find something powerful enough to kill all the kinds of germs, but not
likely to injure the host or the tissues. With the rapid development of syn-
thetic chemistry, the "sulfa" drugs have come in recent years to be widely
used with most amazing results (see page 242). They have been especially
valuable on the battlefield and in surgical situations complicated by fester-
ing. Many persons suffering from inflammation of the appendix come to the
surgeon after the appendix has burst. Then millions of bacteria of several
kinds are thrown into the body cavity, spreading the inflammation to the
tender tissues, frequently with fatal results. It has been found that pouring
dry sulfanilamide powder on the affected area soon destroys the germs and
gives the patient a chance to recover. Several hospitals have reported series
of from two to three hundred such cases without a death.

The Chain of Infection^ It is not difficult to analyze the problem of
protecting a population against communicable diseases. In addition to what-
ever physicians and nurses can do for the patient attacked by a parasite, it is
necessary merely to attack the enemy at one of three points: (1) where para-
sites leave the host; (2) where parasites travel to another host; (3) where
parasites enter a new host.

In actual practice, however, the task is not so simple. We need first to
know, in the case of each disease, something of the nature of the parasite or
virus. Then we have to know in exact detail just at what points and in what
manner it gets out of the patient, and just how it is carried from one host to
the next, and just how it enters the body. We cannot count upon complete
isolation either to render the present patient harmless or all possible victims
secure.

The problem is complicated still further by the fact that several serious
diseases are transmitted by common insects. The common housefly, for exam-
ple, was found to be the chief vector, or conveyor, of typhoid-fever germs, and
later also of other intestinal parasites. A commission on the causes of epidemic

*See Nos. 4 and 5, p. 639.
618

fevers in the army camps during the Spanish- American War reported that
"flies swarmed over infected fecal matter in the pits and fed upon the food
prepared for the soldiers in the mess tents. In some instances where lime had
recently been sprinkled over the contents of the pits, flies with their feet
whitened with lime were seen walking over the food." We can readily under-
stand why it was that more soldiers were killed by intestinal diseases than by
Spanish bullets.

The fly lays her eggs in manure, or in decaying meat or fish or other gar-
bage. She visits also exposed food of all kinds, open wounds on animals, and
the excrements of man and other animals. This insect is thus in an excellent
position to collect and distribute a varied assortment of bacteria.

The many species of mosquitoes, which together cover nearly the whole
of the habitable earth, have probably always been a nuisance. But now we
know that several species are also the sole carriers of various serious diseases,
especially malaria and yellow-fever. Moreover, the mosquito is an inter-
mediate host of the parasite involved, and not merely a mechanical conveyor,
like the fly.

Fleas appear to be links in a chain that invoK'es man and one of the most
dreaded of diseases, the bubonic plague. The specific bacillus that causes this
disease was discovered in 1894, but the mode of infection remained unknown
until after th^ First World War. The Chinese had long ago noticed that there
was some connection between the dying of rats in large numbers and the
appearance of the plague. Now scientists know that the disease in men and
the plague in rats is caused by the same bacillus, that indeed the parasite is
primarily one that lives in the rat. But it is transmitted from rat to rat by
fleas, which sometimes get away from dead rats and infect men and women.
Here, then, the flea is a simple vector, but rats and other rodents act as breed-
ing centers, or reservoirs, of the .parasites.

How Are Disease-Carriers Exterminated?

Fighting the Housefly As the horse is gradually removed from our
daily lives, opportunities for flies to breed and multiply are reduced. There
are still too many about, however, and they are still a menace to health. The
individual family cannot protect itself so long as flies are free to breed in
neighbors' yards, free to fly through the air, and free to alight on food.

Whether through a public-health agency or through the intelligent co-
operation of all citizens, the fly has to be treated as a community problem.
It is necessary to screen or cover all garbage and manure, all stables, and all
body discharges that are not immediately removed by suitable sewers or
sanitary privies. It is necessary to screen or cover all food, whether for private
use or for sale. Every purchaser of food can help the community, as well as

619

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himself, by avoiding dealers whose premises harbor filth and the flies it breeds
or attracts. And we can all help by keeping our own premises clean and free
from flies.

Mosquitoes and Malaria Of all the diseases from which man has suf-
fered, malaria is said to be the most widespread. It occurs all around the earth
and as far north and as far south of the equator as mosquitoes breed. Wher-
ever malaria is present, it shortens life, it keeps people from their work, it
reduces human capacity to work and to enjoy Hfe, it demands costly drugs,
nursing, and medical services, and it throws millions of fertile acres out of use.

In India malaria kills over a million human beings a year, besides causing
untold misery to millions of others. A French scientist, Alphonse Laveran
(1845-1922), working in Algeria, was able to infect volunteers with the blood
of malaria patients, but he could not find out how infection takes place
naturally. The disease is caused by any one of three or four species of protozoa
related to the ameba and known as the plasmodium of malaria. The animal
feeds upon the red corpuscles of the blood of its host and then spondates, that
is, breaks up into a large number of tiny bits of protoplasm called spores. The
spores enter new^ corpuscles, and the process is repeated indefinitely, greatly
weakening the victim and sometimes killing him (see illustration, p. 622),

In 1900 scientists in England and Italy co-operated in an elaborate experi-
ment to find the connection between malaria and mosquitoes. A number of
volunteers lived in the badly malarious Roman Campagna through the most
dangerous part of the year, from early in July until late in October. But they
lived in houses that were carefully screened against mosquitoes, and when they
went out in the evening (when Anopheles is about), they always w^ore veils
and gloves. Not one became sicJ{, although many of their neighbors became in-
jected with malaria during the summer.

At the same time, some mosquitoes were caught and allowed to suck blood
from malaria patients. These mosquitoes were shipped to England in little
cages, and stung two young men who had never suffered from the disease and
who lived in a region where there had been no cases of malaria. In the course
of a few days both developed the characteristic symptoms of the disease.

This experiment showed that (1) the night air and the vapors from the
swamps of the Campagna are harmless and (2) the sting of a mosquito that had
once bitten a malaria patient is dangerous. Mosquitoes raised from the eggs
and allowed to bite a person do not transmit the disease. Nor does drinking
water in which the mosquitoes develop. Today nobody who knows the facts
can have any doubt as to the relation between the mosquito and the trans-
mission of malaria (see illustration, p. 623).

Mosquitoes and Yellow Fever In the past yellow fever has been much
more fatal than malaria. It occurs only in tropical or semitropical regions,
although there have been epidemics of yellow fever as far north as Philadel-

621

MAN

MOSQUITO

•■=L-r-''i'!r^C^ii:

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Corpuscle |

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Mere spores

from salivary

glands

Corpuscle

THE MALARIA PARASITE

Inside the body of the mosquito the parasite undergoes many changes, which include
the formation of sexual stages and a conjugation. The zygotes find their way into
the walls of the stomach; and after repeated subdivision of the protoplasm, tiny
spores in swellings formed in the salivary glands are discharged when the insect
stings again

phia, New York, and Boston. It had long been suspected by many students
of the problem that this disease is transmitted by mosquitoes. At the close of
the Spanish-American War a commission of American physicians definitely
proved the charge against Stegomyia fasciata, now called Aides. The com-

622

Culex
mosquito

<s.

Eggs

Larvae

Pupae

Adults

Anopheles
mosquito

KINDS OF MOSQUITOES

The most common mosquito in this country is the Culex, which does not transmit
malaria. Malaria is transmitted only by the Anopheles. The two genera are quite
distinct at every stage in the life history

mission consisted of Dr. Walter Reed, Dr. James Carroll, and Dr. Jesse W.
Lazear. They were assisted by a Cuban, Aristide Agramonte, who had re-
covered from the disease and was therefore immune.

Two well-screened cottages were used. In one of the two cottages the
ventilation was intentionally very poor. In the other, having very good ven-
tilation, a mosquito -tight screen separated the two halves. In the first cot-
tage three volunteers received clothing and bedding from men who were
suffering from yellow fever or uho had died with the disease. Not one be-
came infected.

In the other building eleven volunteers on one side of the screen allowed
themselves to be stung by mosquitoes that had drawn blood from yellow-
fever patients two weeks earlier: in four days they all came down with the
disease. Volunteers on the other side of the screen — breathing "the same
air" and living in much the same way, but not stung by mosquitoes — re-
mained well. In the course of the experiments Dr. Carroll and Dr. Lazear
were also stung and became sick, the latter dying as a result. It has since
been found that yellow fever is caused by a virus.

The mosquito lays her eggs in quiet water. Here the larva and pupa grow
and develop. The best means of preventing malaria and yellow fever are
therefore (1) ditches to drain off marshy land, (2) cartloads of dirt to fill in
low-lying spots, (3) oil on such puddles as cannot be filled or drained, and
(4) lids or screens to cover cisterns, tanks or buckets in which water must be
kept standing. In addition, it is necessary to make sure that there are no old

623

I W — ( rl '■4»-Vv^:^4;

'^\Ar''

.OKUL

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^^ niii). '.oHi

United States Public Health Service

DECLINE OF MALARIAL AREAS

The systematic elimination of breeding places has re-
moved the mosquito from many areas, and at the same
time malaria has declined, in some cases to absolute
zero

624

cans and other possible
containers for water
where the female mos-
quito can reach them.
Without such breeding-
places one year would
see the end of all mos-
quitoes in all co-opera-
tive communities. In
larger bodies of water
where there are fish,
these will usually de-
stroy the larvae. In the
shallow margins, how-
ever, where the fish can-
not reach them, the
mosquitoes have things
their own way. It is
necessary to keep the
borders of ponds clear
of weeds, sedges, etc.

The practical effect of
exterminating the mos-
quito is shown by the
decrease of malaria and
yellow fever (see maps).
For decades French engi-
neers had made repeated
attempts to construct
the Panama Canal. Each
time the "fever" made
it impossible to continue
the work. When the
United States took over
the enterprise, the first
step was to establish san-
itary conditions. And
the largest part of the
problem was to extermi-
nate mosquitoes by elim-
inating their breeding-
places.

When the Second World War moved into the tropics, it suddenly raised
serious health problems for the armies of countries that had considered them-
selves quite finished with malaria and yellow fever and other tropical diseases.
When the Japanese captured the Dutch East Indies, the supply of quinin was
cut off from the United Nations. It was out of the question to drain swamps
and fill in marshes in the Philippines: Corregidor and Bataan submitted to
malaria quite as much as to the bombs and machine guns of the enemy. Since
then, however, chemists and physiologists have developed a substitute for
quinin, starting with a German product, "atrabine", which we are able to make
in our own laboratories. Atrabine is not as effective as quinin in curing
malaria, but has been helpful as a preventive, especially when combined with
quinin. In the meantime a very satisfactory vaccine to meet the yellow-
fever menace has been developed through researches of scientists supported
by the Rockefeller Foundation.

Rats, Plagues and Fleas The plague has spread from the Orient, and
at various times cases have appeared at several ports in the United States.
In dealing with this danger, efforts are directed toward killing rats and fleas
rather than toward killing bacteria. A ship coming from an affected port is
thoroughly fumigated to kill the fleas and rats (see illustration, p. 628). A
search is made for hiding-places in which rats may be concealed. In California
the ground-squirrels had become infected with the plague bacillus early in this
century. Systematic patrols had to be established to catch rats and ground-
squirrels, which are regularly examined for possible infection. To protect
human life it is necessary either to exterminate some of our neighbors or to see
that they keep well. We can hardly undertake to protect the rats and other
rodents from plague; we can protect ourselves only by exterminating the rats.

Lice and Ticks Trench fever is seldom fatal, but it caused a great deal
of suffering and incapacity among soldiers during the First World War, Volun-
teers from the ambulance and field-hospital units allowed themselves to be
infected with the blood of patients. Other volunteers, who allowed them-
selves to be bitten by Hce taken from the bodies of patients, developed the
disease. Still others, however, living under exactly the same conditions, but
bitten by lice from healthy men, remained unaffected. These experiments
showed that the infection is carried by the louse. By "delousing" all the
men, including officers, the disease was brought under control.

In the past there were frequent epidemics of typhus and of related diseases
among crowded people or where it was difficult to keep clean. In these epi-
demics the mortality was often very high — from 20 to nearly 50 per cent.
All these diseases are now known to be caused by similar microbes, which are
parasitic upon rats and other small mammals, as well as upon man. And they
are transmitted by insects — chiefly the body louse.

Several diseases resemble typhus in their outward symptoms. The group

625

includes ship-fever, jail-fever, camp-fever and Rocky Mountain spotted
fever. The Rocky Mountain fever is transmitted by a tick (see page 616).
Since the flea is comparatively rare in the United States, ship-fever, jail-fever
and camp-fever have not become epidemic here.

Are All Diseases Caused by Parasites?

The Fight against Specific Diseases We have succeeded remarkably
well in preventi?7g communicable diseases. We have not exterminated all
specific or communicable diseases, of course, and probably never shall. But
we have completely exterminated some of them in some areas (see illustra-
tion opposite).

In the early part of the century, rates for various communicable diseases
fluctuated irregularly. Later there was a steady decline in the incidence of
many of these diseases, and especially in the mortality which they caused.
In the chart on the opposite page, the figures on the left of each graph in-
dicate the number of deaths per year in the case of each disease, for 100,000
persons. For the general death rate, however, the figures are per thousand
of population.

It is always a particular person who is well — or sick. Yet most individuals,
whether as patients or as potential victims of infection, have done very little
to reduce or eliminate communicable diseases. We go about our affairs pro-
tected by experts and specialists of whose existence most of us do not even
know. Increasingly, however, each of us must co-operate if the optimum re-
sults are to be attained. We notify health officers of the existence of com-
municable diseases. We remain at home when we suspect an infectious dis-
ease. We avoid acts that may endanger others, such as spitting, disposing
carelessly of refuse, smoke, vapors, dust, and so on. We have to accept in-
spection of our premises or persons, vaccination and other immunizations, and
quarantine regulations. We do many things that we would not do sponta-
neously or would not do wilhngly if left to ourselves. We avoid doing what we
should otherwise want to do. To get the benefits of science we have to accept
numerous regulations, restraints of our "personal liberties".

Nonspecific Diseases The revolutionary results of the germ theory
made it reasonable to suspect parasites in every disease. We have learned,
however, that the metabolism may be disturbed by a variety of "causes"
other than infections. Specific deficiencies — or excesses — in diet may modify
growth or development, and so result in distinct diseases. Simple goiter, for
example, has been traced to a shortage of iodine. A faulty balance of calcium
and phosphorus seems to influence unfavorably the development of bones and
teeth. An excess of selenium in the soil brings about a sick condition in cattle,
and probably in human beings too by way of the plants they eat. Pellagra,

626

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DIPHTHERIA

DECLINE OF COMMUNICABLE DISEASES

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KEEPING RATS FROM GEHING ASHORE — OR ABOARD

Ships plying between ports in which there are infected rats and other ports receive
special attention from health officers. Metal shields are used to prevent rats infected
with the plague from getting off the boats, or from getting aboard in plague areas.
In addition, of course, pains are taken to destroy rats on ships, and to prevent their
breeding

scurvy, beriberi, rickets, and other diseases are due to the lack of specific vita-
mins in the diet.

Modern industry and modern city living have brought into our environ-
ment physical and chemical changes that often disturb us. Various dusts and
fumes affect the breathing organs, or introduce into the body substances that
modify the metabolism. The materials handled by workers affect the skin,
the nerve-endings, and perhaps deeper tissues and organs. Lighting condi-
tions, unusual or loud sounds, affect the inner co-ordination of processes, even
when we are not aware of them. Eyestrain has been found to result in nervous
tension which in turn influences the digestive process and possibly other proc-
esses by way of the autonomic nervous system and the endocrines.

General fatigue has long been recognized to be an outcome of excessive exer-

628

tions and anxieties. Indeed, many of the so-called "functional" disorders, in
which the physicians can find no structural or chemical defects in any organs,
appear to result from strains and anxieties arising out of working and living
conditions, rather than from physical or chemical features of the environment.
Certain forms of "heart disease" appear to come from disturbed emotional
states rather than from chemical or physical injuries of the organ.

The rising rate of certain noninfectious diseases may be in part explained
by the lengthening of the average span of life. That is, as the proportion of
older men and women in the population becomes greater, the disorders pecu-
liar to old age will naturally increase. The greatest gains from preventing
disease have come in the lower age-groups. Each child starts out today with a
very much better chance of getting past his tenth, twentieth, or fortieth birth-
day because he is not so likely to succumb to diphtheria, smallpox, typhoid or
malaria. But his chances are so much greater of eventually incurring deteri-
orations of the kidneys, the nervous system, the heart or the arteries.

We cannot blame the parasites for all our troubles. Many of our diseases
result from our faulty management of our daily lives. There have been great
improvements in general health as a result of better diet, better housing, bet-
ter working and living conditions, better use of our resources for enjoying
life. We could prevent much illness, however, if we used our present knowl-
edge more generally. And there is still a great deal to find out.

How Can People Get the Benefit of Scientific Knowledge about

Keeping Well?

Joint Services^ People moving from village to city, or from one region
to another, have always had to learn new ways of living. But today the in-
dividual is helpless among the many specialists with their various knowledges
and skills. He must learn both to depend upon others instead of trying to do
everything by himself, and to serve others instead of trying to do everything
jor himself. To protect the individual and to ensure him what he must have,
it became necessary for neighbors to co-operate in ever larger groups. Even-
tually, co-operation extends to the whole civilized world, particularly where
health is involved.

A community health program starts out to be protective and preventive.
More and more, however, it comes to include positive services. In a sparse
community, for example, it may be necessary to regulate the location and
treatment of cesspools and the disposal of refuse, in order to prevent the con-
tamination of wells or of the soil. But in cities it becomes necessary to estab-
lish joint water supplies and elaborate systems for the disposal of household
wastes, garbage, and so on. At one stage of development it is enough if public

»See Nos. 6 and 7, p. 639.
629

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THE LENGTHENING SPAN OF LIFE

Each child born in a civilized community today starts out with a much better chance
of getting past his tenth, twentieth or fortieth year than had his parents or grand-
parents and their contemporaries. He is not so likely to succumb to diphtheria, small-
pox, typhoid, malaria, scarlet fever, or other communicable disease. He has an even
chance of attaining seventy years

officials inform physicians and private citizens about improved or standard
tests, serums, and other special materials and procedures for curing or pre-
venting disease. Later it is found to be more effective and more economical
to supply materials, tests, immunizations, inspections, and other services
directly through a central agency.

Water Supply and Sewage Disposal As population becomes more
dense, surface wells become less adequate, and they are in increasing danger of
pollution. Deep wells are, as a rule, quite satisfactory for small towns, but
cannot supply large cities. Cities usually depend upon lakes, streams and
reservoirs that collect the runoff from a vast watershed. The entire water-
shed, as well as the reservoir, must be protected against pollution by excreta
and industrial wastes. Suspended matter and harmful germs are removed by
means of storage, chemical treatment, settling basins, filtration, or some com-
bination of these methods, depending upon the circumstances. Bacteria in
the water are destroyed by very small amounts of chlorine.

630

INCREASE IN ORGANIC DISEASES

As communicable diseases come under control, more men and women survive to ad-
vanced ages. More deaths, therefore, result from various diseases of old age —
cancer, heart disease, kidney disease and others

The privy and the home-sewage-disposal plant found on individual farms
or in outlying portions of towns frequently become dangers to health. The
cesspool lets the raw sewage drain quickly into the ground water, where it
sometimes pollutes wells and springs in the vicinity. The septic tank is much
safer than the cesspool, for in it any harmful microbes are destroyed by anaero-
bic bacteria.

In towns and cities elaborate sewer systems are Installed to remove wastes
from the individual homes. Some cities allow the sewage to flow into a stream
or lake without any treatment. This is cheap, but it makes the stream unfit
for bathing and swimming and fishing; and it may create a distinct nuisance.
Furthermore, the bacteria which live on the decaying refuse may use so much

631

of the oxygen dissolved in the stream that fish and other desirable forms of
life can no longer survive. Such disposal of sewage may endanger the health
of cities located downstream.

To avoid these disadvantages sewage is managed by several different meth-
ods. These include sand filters and chemical treatment for precipitating sus-
pended matter. Other satisfactory systems depend upon the action of aerobic
or anaerobic organisms.

As population becomes more concentrated, it is found to be more satis-
factory from the point of view of health to have central municipal agencies
remove and dispose of ashes, rubbish and garbage. And in the long run com-
munity agencies are the most economical.

Food Protection A large part of our food comes to us in sealed packages.
We do not know where or of what the food is made. Expanding commerce
brings us food products from foreign lands. As individuals, we cannot tell
from the appearances or the taste whether the preparations contain harmful
preservatives or coloring matter or adulterants, or whether, they lack any of
the essentials. It has become necessary to protect buyers of food and other
products through public regulations and official agencies.

As we learn more about the relation of food to health and efficiency, and
as we become more and more separated from the sources of supply, the public
must protect the buyer still further. We must be assured (1) that what is
offered is suitable for our purposes and (2) that it is harmless.

Because food travels greater distances from its source, and is kept for
longer periods, nearly all the states regulate the sale of prepared meats, fruits,
vegetables, fish, that may become spoiled or contaminated. Shipping spoiled
food from one state to another is prohibited by federal laws. In many cities
special ordinances authorize officials to seize and destroy any unsuitable food
that they may find, and to penalize dealers or manufacturers who offer such
food for sale.

It has been practically impossible to obtain milk in large quantities without
excessive numbers of bacteria. The practice of pasteurization has therefore
come into general use. This consists of keeping the milk at a temperature of
145° F for twenty minutes.

Food in Wartime In Great Britain during the first three years of the
Second World War, the general health of the population appeared to improve.
And this in spite of the great strains brought on by the bombings and other
conditions, and in spite of the rationing of food. The improvement is in part
explained by the fact that a considerable fraction of the food used was raised
on the island instead of being imported. This made certain that only needed
food was produced, while imports were carefully planned. And the rationing
ensured everybody a suitable diet within the limits of what was available.

In every factory employing two hundred and fifty or more workers, com-

632

munal meals were served. That meant better marketing, better preparing and
cooking, and a more economical use of food. At all schools lunches were
served; that made certain at least one substantial meal of good quality for
every school child. Younger children and mothers received relatively richer
meals, with prior rights to limited supplies of milk. Similar methods were
developed in the United States, in Canada, and in other countries, demonstrat-
ing the value of applying scientific methods to our common but complex
problems.

Government and Microbes A bare list of the governmental agencies
and activities related to health will give us an idea of how far we depend upon
our environment and upon one another. Many diseases are subjected to
quarantine and placarding. Public laboratories provide vaccines, serums, and
other special preparations, and supervise the manufacture and sale of such
products for profit. Official laboratories examine specimens of blood and of
other fluids or tissues obtained from patients for diagnosis. We inspect dwell-
ings, schools, factories, camps, theaters, and other places where people live or
assemble, to make sure that conditions are sanitary. We exclude sick people
from schools, and if we knew how we would exclude them also from places of
work and of amusement. We disinfect discharges from the bodies of sick peo-
ple and disinfect premises that have become infected. We inspect slaughter-
houses and regulate the cleaning of vessels in public eating places. We regu-
late drinking-cups in public places and the wrapping of bread before it leaves
the bakery.

In some cities, visiting nurses, ambulance service and public hospitals help
to keep down the amount of sickness and to reduce the suffering. States
license physicians, dentists, druggists, nurses and midwives, as well as barbers,
manicurists and masseurs, to maintain suitable standards of health; and they
license plumbers, electricians and automobile drivers to ensure greater safety.

Prohibitions and Regulations Conditions that made it necessary for the
public to regulate its water and food supplies made it necessary to regulate the
sale of drugs also. All people are interested in their health, but most people
are ignorant in regard to the conditions of health. The vast drug industry
has made available to millions of people convenient packages of standard
remedies, chemicals and household supplies related to health and cleanliness.
But this business has also frightened and deceived the public into buying
remedies for "symptoms" which we might better disregard or else bring to
the attention of reliable physicians. Men and women have been induced to
drug themselves with worthless and even harmful "remedies" while neglecting
their actual needs.

Gradually the public is coming to realize that it has a right to know what
it is buying and what merits there may be in the strange products. Moreover,
it is coming to feel strongly that people's health is more important than any

633

Bad Conditions

Division of Industrial JlTg.enc, New York State Department of Labor
Good Conditions

RELATION OF WORKING CONDITIONS TO HEALTH

Wherever lead dusts or fumes are produced, effective exhausts and perfect cleanli-
ness are necessary to prevent lead poisoning. As industrial managers spend more
effort and more money trying to prevent injuries and accidents among workers, as
they improve conditions for the health of workers and their families, they save more
and more in the cost of production. It is actually cheaper to keep workers well than
to pretend that health is a purely private matter

private business. Some states prohibit absolutely the sale of dangerous drugs
except on the prescription of a licensed physician. In general, we are becoming
suspicious of any business that thrives on "secrets" or on the ignorance of other
people.

Working Conditions The men and women whose work makes living
conditions better for all of us are themselves often exposed to bad working
conditions. Some occupations are strikingly dangerous, involving serious acci-
dents. Among these are marine service, quarrying and mining, iron and steel
manufacture, and work under high air pressure. Other occupations are dan-
gerous to health, although they are not classified as hazardous or as involving
great risk of accident. The dangers in such occupations arise from the special
materials used or from the conditions under which the work is carried on. In
the making of chinaware and pottery, for example, there may be danger of
lead poisoning.

In some manufacturing establishments, dangers may lie in badly ventilated
workrooms. As soon as we recognize that the objectionable conditioris are not
necessary, we must take steps to find remedies. And as science has helped to
improve conditions of living and to increase production, it can be made to
improve conditions of working. Air-conditioning, for example, is being more

634

and more widely installed for reasons of comfort and health. Yet the art was
first developed because variations in moisture and temperature sometimes
interfered with speed or quality of production in textile mills and in printing.

In many industries it is impossible to prevent the formation of dirt of
various kinds, which may be injurious to the physical health of the workers.
In some industries the processes themseK'es call for a higher or a lower tem-
perature than is best for human beings. In many industries poisonous gases
and fumes are produced. Most acid fumes may "eat away" the delicate linings
of the lungs. Alcohol fumes and the fumes of other solvents used in varnishes,
phosphorus fumes, lead fumes, and other fumes are absorbed and so poison
the body.

In certain occupations the worker is constantly exposed to injurious dust.
(1) Coal dust and the flufl from the fibers used in spinning and weaving may
crust or cover part of the lung lining. This reduces actual breathing surfaces
and lowers the resistance of the cells to disease microbes. (2) Hard, sharp par-
ticles of metal or stone and fine sand, or silica, may scratch the delicate linings
of the air sacs and expose them to the entrance of disease microbes. Such dust
is produced where metals or stones are ground, polished or chipped, and where
sandblasts are used. (3) Street and house dusts may carry disease germs of
various kinds.

Intelligent managers long ago discovered that it was profitable from a
strictly business point of view to maintain working conditions that protected
the health of the workers and that made the surroundings pleasant and agree-
able. Most workers, however, were neither fortunate enough to select in-
telligent managers nor able, otherwise, to insist upon suitable conditions.
They were obliged, therefore, either to organize like other professional or
business groups and to use their joint influence to better the situation, or else
to wait patiently until the community was sufficiently sensitive and sufficiently
responsible to regulate working conditions through public agencies.

In the course of years we have gradually developed public standards, and
set up machinery for enforcing standards in industrial and commercial estab-
lishments. These standards cover a wide range, ensuring a subsistence wage,
sanitary washrooms, suitable drinking-water, suitable places for meals, and the
removal of dusts, fumes and gases from the atmosphere. They include also pre-
vention of disturbing noises, provision of safety appliances, regulation of hours
of work, and prohibition of certain kinds of work to women and children.

We know enough biology to raise the physical and mental well-being of the
entire population to a much higher level than that which the top quarter now
enjoys. We know also that from an economic point of view good health pays;
that is, it brings returns beyond anything that it may cost in money. But we
do not yet know how to organize our practical affairs so as to make full use of
our science for all the people.

635

Some Occupational Hazards

DUSTS

Kinds of Iniuiy

Sources

Industries Affected

Scratching or piercing lung
epithehum

Silica
Glass

Mining, rock drilling, stonecutting,

foundry work, bnckmaking, grinding,

glassmaking, glassworking and

Steel

grinding

Machinery operations, steelworking

and grinding

Crusting or covering lung lin-
mg: interference with breath-
ing; reduction of resistance to

Asbestos dust
Talc
Wood

Insulation work, roofing, painting,

packing, flooring
Milling, furniture-making, fixtures.

invading germs or viruses

Plant fiber
Paper

Rubber

luggage, autos, sporting goods, cabi-
nets, caskets, or milling, woodworking
of all kinds
Textile industries

Conveying infective agents

Grain
Leather
Feather

Fur

IMETALS

Certain metals that arc
volatile are absorbed and

Lead

Pottery and earthenware, printing,
soldering, storage battery

produce various organic disturb-

Zinc

Mining, smelter, gaKanizing,

ances or poisoning

fabricating

Chromium 1
Silver J

Plating, working

Copper 1
Mercury

Mining, refining, working

FUMES AND VAPORS

Poison in various ways

Carbon monoxide

Foundries, hat industry, use of gas-
heated appliances

Carbon tetrachloride

Solvent in many industries, clean-
ing works

Acetone

Benzol

Paints

Lacquers

Spray painting

RADIUM

Superficial and more serious
"burns"

Radium emanations

Laboratory workers, hospital aids,
luminous-dial manufacture

636

Some Occupational Hazards (Continued)

SKIN IRRITANTS

Kinds of Injury

Sources

Industries Affected

Dry or chafe the skin in

Dyes

Dye works

various ways: producing sores or

Solvents

Chemical works

tender areas; sometimes specific

Oils

Electrical works

or systematic reactions .

Paint-remo\ers

Rubber works

Expose to infections; affect

Chlorinated

Textile industry

blood vessels; affect nerves or

compounds

Fur industry

nerve endings

Degreasing materials

Airplane industry

PHYSICAL STRAINS

Back injuries

Lifting or carrying ex-

Various industries, construction

Hernia

cessive weights

work, transportation

Foot injuries

Standing too long on

Store work, patrolling

Varicose veins

feet; walking exces-
sively or in awkward
positions

EXPLOSIONS AND OTHER ACCIDENTS

Physical injuries to various

Explosions of boilers

Marine work, transportation

parts of body from blows, being

or engines

thrown violently; from burns.

Static electricity ig-

Flour mills, aniline works, gasoline

cuts, electric shocks, etc.

niting mixtures of air

and organic dusts or

vapors

industries

Moving parts of ma-

Heavy industries, construction

chinery, spars, pro-

work, mining

pellers, etc.

Falling objects, rock.

Power plants

dirt

Fire hazard

In Brief

With every improvement in economic conditions, there is a consistent
lowering of sickness and mortality rates. Among underprivileged groups both
sickness rates and death rates are relatively high.

To make use of new knowledge and to fit into changing conditions, in-
dividuals and members of families need constantly to re-educate themselves
and to change their practices.

The spread of communicable diseases can be prevented by attacking the
parasites at the point where they leave the host, in the course of transit to a
second host, or at points of entry into the body.

By exterminating flies and mosquitoes, it has been possible to reduce radi-
cally or even to eliminate typhoid fever, malaria, yellow fever, and other diseases.

637

Rat fleas, body lice and wood ticks are known carriers of serious diseases;
we can fight these diseases most effectively by fighting the carriers and rats or
other secondary hosts.

As the average span of life is lengthened by improved nutrition and the
prevention of communicable diseases, there is an increase of "old age" diseases,
resulting from deterioration of tissues or organs. Studies of these conditions
point to better ways of managing our lives.

There is a limit to the use of scientific knowledge by the individual or by
the family; co-operation with others is increasingly necessary both to prevent
the spread of communicable diseases and to ensure adequate water supplies,
disposal of sewage and wastes, and other essential services.

Increasingly we depend upon joint supervision, regulation, and direct
services by public agencies to protect and promote the health of the com-
munity and of its members.

Our actual health conditions, because of fixed habits, customs, and ideas or
**beliefs", lag behind those that scientific knowledge might make possible.

EXPLORATIONS AND PROJECTS

1 To find out the chief causes of ill health, investigate mortality and morbidity
tables from the departments of health of your city or state, from the United States
Public Health Service, and from the statistical reports of various insurance com-
panies. Information can be obtained on the number of cases of infectious diseases
and on the chief causes of death at different age levels. Supplement these data with a
study of the severity, nature and control of each of the more frequent causes of ill
health or death.

2 To find how medical care is provided, read and discuss various publications of
the United States Public Health Service and of the American Medical Association,
and also various Public Affairs Pamphlets. Organize material and arrange to discuss
how the public can best assure itself of needed health and medical services.

3 To determine the relative number of bacteria in various waters, collect in
sterilized bottles samples of water from near-by lakes, streams, swimming pools,
wells, cisterns, and city-supply taps. Bring samples to the laboratory immediately
and place in a refrigerator. Dilute 1 cc of each sample in 99 cc of sterile water..
Shake each dilution thoroughly; then pour 1 cc of the dilution into a sterile Petri
dish and add sterile liquid nutrient agar.^ It is well to make duplicate cultures of
each sample. Allow cultures to harden and then place upside down in a warm part of
the room. Examine in 48 hours. By counting the colonies, determine the number of
bacteria present in each sample of water.

^To prepare desiccated nutrient agar for use, dissolve 25 g of the powder in 1 1 of boiling
water. Place some of the nutrient agar in each Petri dish and sterilize the Petri dishes by keeping
them in a steam bath for 30 min or in a pressure cooker at 15-pounds pressure for 20 min.

638

4 To find out whether water is contaminated with sewage bacteria, inoculate
fermentation-tubes of brilliant green-bile medium^ with 1 cc of each of several
samples of water. Try samples from wells, springs, swimming pools, rivers and the
hke. Incubate the cultures at 37.5° C. Examine in 24 hours to see whether fermen-
tation has produced gas in any of the cultures. The presence of gas indicates the
presence of Bacillus coll.- Summarize results to show which of the waters are and
which are not safe to drink, or to swim in,

5 To determine the relative number of bacteria present in various places, expose
sterile agar plates and find out how many bacteria grow from each inoculation. Ex-
pose dishes to the air in the classroom, in the street, in the home; test clean silver-
ware and dishes; expose plates to doorknobs, drinking fountains, pencils, coins,
fingers (both before and after careful washing with soap). Inoculate other plates by
kissing, by sneezing, with scrapings from under the fingernails, with combs, with
used handkerchiefs, with dishwater, with footprints of a housefly, etc. Incubate cul-
tures and examine after 24 hours. Tabulate and summarize your results, to tell in
what kinds of places bacteria are abundant. Relate your findings to the spread of
disease.

6 To study the sanitation of your community, take trips to the water-
purification plant, the incinerator, and the sewage-disposal plant. Find out how each
operates. If such plants are not accessible for study, investigate the water supply of
various homes or farms, as well as methods used in disposing of refuse and sewage.
Report your findings.

7 To find out about the work of your local health department, arrange to visit
its bureaus or divisions of statistics, foods and drugs, and preventable diseases; the
laboratories, and various cfinics, especially those deaUng with child health, tuber-
culosis and venereal diseases. Plan a panel discussion in which you share your
findings.

QUESTIONS

1 In what ways can we prevent the spread of communicable diseases.?

2 Why are not doctors and nurses, who are so much in contact with sick
people, more often sick than others.?

3 What is the advantage of having physicians report certain diseases to the
state or city health officer.? What is the disadvantage.?

4 How can one preserve his own health without depending upon others.?

^Brilliant green-bile medium can be purchased in dry form from laboratory supply houses. This
medium contains three ingredients which differentiate Bacillus coli from other forms of bacteria,
namely, anihne dye, which is poisonous to other bacteria, but not to B. coli in the dilution used;
bile, which kills most bacteria, but which does not inhibit the growth of B. coli; and lactose sugar,
which is fermented readily by B. coli but not by most other bacteria. The formation of gas in
this medium within a period of 24 hours is quite conclusive evidence of the presence of B. coli.
If gas does not form within 24 hours, but does form to a limited extent later, the test is considered
negative, as soil bacteria of a certain group also grow to a limited extent in this medium.

^Bacillus coli normally grows within the intestines of warm-blooded animals. The presence of
B. coli in a sample of water indicates contamination with fecal matter, which may or may not be
human excreta. If human excreta are draining into the water, there is, of course, danger that in-
testinal parasites which cause typhoid fever may also be present.

639

5 How does travel to new regions bring dangers to health?

6 What is there to show that flies are dangerous neighbors?

7 What can the individual do for his protection if the community continues
to tolerate flies?

8 What is the evidence that mosquitoes endanger health?

9 At what point in the life history of the mosquito is it most easily extermi-
nated?

10 How can mankind use knowledge of the life histories and habits of other
species?

11 What is the connection between a people's habits and customs and its like-
lihood of becoming infested with hookworm? with trichina?

12 How can the home water supply be protected in the country?

13 How can house waste, garbage, and other refuse be kept from injuring
health?

14 What methods of milk inspection are used in your community? of dairy in-
spection? of testing milk as to quality? of testing milk as to bacteria?

15 In what ways do the newspapers in your community promote better health?
obstruct improvement in health?

16 What changes in your conduct or habits have resulted from anything you
have learned about health? from the services of school-health inspection? from
anything done by your physician?

17 Why is it necessary to have Federal health service in addition to what the
different states and cities are doing?

18 What diseases have been of diminishing importance in your community
during the past ten years? What brought about the change?

19 What diseases have been causing more injury in your community during the
past ten years? What brought about the change?

640

CHAPTER 31 • BIOLOGY AND WEALTH

1 Do all things exist for the use of man ?

2 What do people need besides food, clothing and shelter?

3 Are people better off today than they were in the past?

4 Are people better off under our kind of civilization than they are

in simpler cultures?

5 How can we make better use of our resources?

6 If there is overpopulation for other species, can there not also be

for man?

7 Can we produce enough to supply everybody's needs?

8 Can our country support a larger population?

9 Should we not be better off if our population were smaller?

10 Should we be better off if we tried to live on what we have with-

out importing or exporting?

11 Is there not a necessary limit to the earth's human population?

Under simple conditions of living people accumulate very few material
things. It takes about all the time there is to get the bare necessities and to
fight enemies of one kind or another. The only surplus is Hkely to consist of
weapons, simple tools, and trophies of the chase or of war.

With increasing division of labor and with the growth of agriculture, in-
dustry and commerce, more and more is produced. It becomes possible to
construct more permanent buildings and bridges, ships and roads. People
can store up large accumulations of food, cloth, fuel, tools, raw materials,
ornaments. These usable objects and materials constitute a people's wealth —
the physical basis of their welfare.

In considering the wealth of a people we sometimes include all the natural
resources, such as fertile soils, rninerals, forests, waterfalls, wild life of land
and water, and so on. All these things can be converted into usable wealth by
means of people's skill and science. How much of our material welfare depends
upon Uving things? How far does our control of material wealth depend upon
our understanding of life — our biology?

How Has Science Changed Our Management of the Earth?

Undermining Ourselves^ Ages ago men learned that the land upon
which they dwelt is the very source of their Hvelihood, and not merely stand-
ing room. By becoming farmers men found ways to obtain food with more
certainty and from a smaller area. But the more effectively they raised and
removed crops, the more quickly did they exhaust the soil, sometimes literally

iSeeNo. 1, p. 656.
641

forcing themselves off the face of the earth. By mishandling the soil and itr
living cover man has, in fact, made vast stretches of the earth's surface worth-
less. And every year, in various parts of the world, millions of acres are being
ruined.

The good earth of our Great Plains, stretching from Montana and the
Dakotas to the middle of Texas, had for centuries yielded only grass to feed
the bison, and so maintained a sparse and scattered Indian population. Farm-
ers moving westward after the Civil War hoped that their hard work on this
land would furnish abundance for their families. The flat lands would be
easy to work. In the course of some sixty years large-crop farming developed
rapidly. There were good years and poor years, of course. But as years went
by, the earth came to yield less and less to man's efforts. By 1938 millions of
acres had become so changed that they could no longer support the population
that had been depending upon them (see illustration opposite).

The Great Plains land and farms, as well as millions of acres in other parts
of the country, were destroyed in part by man's interfering with the natural
relationships between living things and the underlying soil and waters. They
were destroyed in part by a working of the soil which we have called mining —
carrying off as fast as possible whatever is of value. We could, of course, re-
place the essential food-making minerals of the soil with materials brought
from other regions. But we had also replaced the perennial grasses, which
had in the past bound together the particles of the soil, with cultivated an-
nuals. And in this way we exposed the surface of the earth to the destructive
action of wind and water (see illustration, p. 644).

Fifteen million acres can no longer be plowed. On most of the range lands
production has declined from 25 to 50 per cent in some places and by as much
as 75 per cent in other parts. Moreover, these acres can be of value in the future
only if we change radically our ways of treating and using them. It is not
exacdy a case of killing the goose that laid the golden eggs, for the acres are
still there. That is, the goose is not quite dead. But if she is left to herself,
she will not revive fast enough to be of help to us for at least a generation

or two.

The Soil's Fertility From ancient times people traditionally saved
household and farm wastes for manuring their fields (see page 150). It was
only in the first half of the last century that the foundations of soil chemistry
were laid by the researches of a Frenchman, Nicholas de Saussure (1767-1845);
a German, Justus von Liebig (1803-1873); and an Englishman, John Lawes
(1814-1900). From their work we learned to restore to the soil the essential
chemical and physical conditions.

Working the soil physically to get the best results also had to be learned, at
first through trial and error, and later through systematic research and ex-
perimenting. Throwing seeds on the ground would yield something. Scratch-

642

^Sk.-. ■ '•■■■-

p*te>^ J|(»r-!

jim*^

-i^^i^WBt ■^-tv /2E#^f4vm»6fiS8ffie!3^:<s:Si.«^!uASi.*.

FARMS BLOWN OFF THE EARTH

Without waiting for the great storms, farmers are constantly letting the sources of our
living be blown and washed away. The wind blows the creative soil from a farm, and
it is gone forever; but the shower of dust continues to destroy whatever it covers

Run-off in per cent of total precipitation

Land use

Soil loss in tons per acre per year

16.2

14.5

Hative grass
(protected)

Native grass
(clippsd)

Kafix

Wheat

Wheal
(on erodedi soil)

s " io is qM

Ceibysi%dasfto8W.5?8.siop.,,,,...g

20 10

annual precipitation 20.36 ttidies

g-ye8i]»riQd 1^4935

Runoff in per cent of total precipitation

Land use

Soil loss in tons i3er acre per year

28.64

Cotton il% slope)

Cotfcoa

FaUow (tiUed)

Fallow (cot tilled)

Btam ^ 1-75

Milo

10.89

14.07

'30 20 10

Average annual precipitation 20.91 inches

S-yeaf i»riod 1^6-1933

5 10 15 20

Abilene day toam,2% slope (except plot 1)

USING THE LAND AND LOSING THE SOIL AND WATER

The rains ancJ snows run off the land more or less rapidly and thoroughly, according
to the way the soil is used and treated. Modern methods of extracting from the
earth its precious yield, as quickly as possible, and more than the inhabitants can use,
sometimes destroy the very earth upon which we depend

ing the old growth away with a stick before scattering the seeds would yield
more. Man learned to scratch deeper. He hitched an ox or a camel to a
heavier stick. Later he used horses. He put a steel edge on his plow. Finally,
all merely mechanical work of man and beast is transferred to machinery.

By using more and more machinery in cultivating, weeding, watering,
harvesting, and so on, a small crew of skilled operators is able to work twenty
or thirty times as much land as they could with horses and their own labor
(see illustration, p. 646). Through such intensification of effort, combined
with other improvements in practice largely based on biological knowledge,
men were able to increase the output per worker and also the yield per acre
up to several hundred per cent. But in this progress they failed to note
that there is a point beyond which bigger and bigger does not necessarily
mean better and better. For by using more powerful machinery for work-
ing the soil, they came to plow deeper and deeper and so defeated their own
purposes. Turning the soil over too completely covered the stubble and

644

roots of the previous crop and exposed the new soil to wind and water.
This deep soil, brought to the surface, lacks the product of organic change
going on near the surface, and it also fails to hold together mechanically.
Such deep plowing has probably contributed to the ruin of the soil in many
parts of the flat farm country.

From better ways of working the soil we learned also how to conserve the
soil, and eventually to keep it from becoming exhausted. Millions of farms
have been allowed to deteriorate so that they can hardly be reclaimed. At the
same time, we can see other farms continuing to yield year after year, in
spite of more intensive working.

Earth and Water We depend upon rain for the growth of plants; yet
every year the rain washes tons of earth into streams and rivers. The quantity
of earth carried down to the sea every year is estimated to be worth over a
billion dollars. Not only is this a direct loss of agricultural resources, but it
also interferes with the navigation of streams and chokes the harbors. We
have to spend millions of dollars every year to dredge rivers and harbors to
remove this soil. As we saw, it is the mining of timber that has been largely
responsible for disturbing the water balance and for injuring the soil, by
destroying the absorbent forest floor (see pages 589 ff,). Conversely, reclaiming
desert lands depends upon supplies of water from regions that are continually
covered with forest.

The Forest and Water^ Every year, as the snows on the hills begin to
melt, the water rushes down the hillsides in the deforested regions. The
streams overflow their banks, and the torrents tear down and destroy every-
thing in their path. The annual damage done by floods in this country is
estimated to be equal to one hundred million dollars. This takes no account
of the destruction of human life that often accompanies the floods.

For agricultural purposes, water must be had in abundance throughout the
summer. The destruction of forests in one region has often resulted in the
ruin of agriculture and in the migration of people in a distant valley. Streams
that depend upon deforested areas for their water will be too full in the spring
and will run too low in the summer. The forest influences navigation on the
larger streams in two ways: (1) it maintains a steady flow of water, and (2) it
prevents the filling up of a stream with soil.

Water Power As our industries expand, we are pressed to find sources
of energy for driving our machines. The consumption of coal has increased
so rapidly that the earth's supply threatens to be exhausted. Oil, which is
also limited in quantity, seems to be more valuable for use in cars, trucks, air-
planes and boats. Water power seems to be the only source of energy that is
constantly renewing itself. But to maintain the service of waterfalls, we must
be sure that the water supply will be steady. And this in turn depends upon

iSee No. 2, p. 656.
645

6 *:r^^ ..^V'«<>-X;'i*'**''*

Soil Conservation Service

BETTER WAYS OF SCRATCHING THE EARTH

The improvements in agriculture since the abolition of slavery have exceeded all the
improvements made in over two thousand years before. Fifty years after Thomas
Jefferson proposed a metal plow and the common school, we were still using wooden
plows generally and were just thinking of starting common schools for all

the forest.^ Soil and water can be a permanent source of wealth for human
beings, but only if they are worked in ways that preserve their usefulness.

What Are the Limits to Man's Production of Wealth?

Basic Needs- When we compare diflerent nations or different periods
in history, we find that people have the same basic needs always and every-
where. They must have food, and they must protect themselves against
various kinds of dangers. Many different kinds of materials serve as food in
different parts of the world. And with modern means of transportation and
preservation, many diflerent kinds of food can be had by people in modern
cities and towns. Shelters vary, according to chmate and according to ma-
terials available. In some regions people wear very little clothing of any kind,
aside from ornaments. In other regions they expose very little of their skins
out of doors.

Supplies of food material, fibers, timber, furs, drug plants, and oth?r
usable plant and animal products have been made available in ever-larger
quantities through our new ways of working. These new technologies depend
upon using scientific methods of solving problems. They have made it pos-
sible for mankind to increase rapidly in numbers and to spread over the face
of the earth. Regions that were in the past uninhabitable have been made
into comfortable and healthy communities. We can assure our entire popula-
tion of whatever it needs of organic materials with a smaller fraction of work-
ers engaged in agriculture and animal husbandry (see illustration, p. 648).

Human beings are unique among all living species in the many wavs in
which they make use of materials for other purposes than "keeping ali\-e".
Paper, for example, is a necessity in every industry, business, go\'ernment,
sport. We use it not only for books and journals, or for correspondence and
records and accounting, but also for lining our rooms, insulating our walls
and roofs, wrapping our groceries and other purchases, and for making money
and washtubs and carwheels. We similarly use plant and animal fibers, orig-
inally gathered or raised for clothing, in entirely new ways — cordage, burlap,
sailcloth, airplane wings, bunting and parachutes.

Human Needs These many new uses, and the "needs" which they
serve, are, of course, incidental to man's other pecuUar traits — his distinct
kind of brain and hands, for example, his sociability and language, his imagina-
tion and self-consciousness. Because of these distinctive traits human beings
have "needs" that other animals do not have. In addition to being hungry
like other species, man can be anxious about the uncertainty of the next meal.
Human beings need to feel secure. Accordingly, they often pile up much more

^Since all coal consists of the modified remains of ancient vegetation, burning coal as fuel still
means drawing upon the forest, though not the forest of our own times.
2 See Nos. 3, 4, 5 and 6, p. 656.

647

CHANGING PROPORTIONS OF THE ECONOMIC ELEMENTS OF THE POPULATION

When the Constitution of the United States was adopted, 19 persons were engaged
in agriculture for each person in other kinds of work. It took that much of our total
labor power to keep the population supplied with food and organic raw materials
for clothing and shelter. At the beginning of the Second World War 19 persons en-
gaged in agriculture could maintain 80 in other kinds of work. What brought about
these changes? What further changes are likely?

than they can use. Where trade and commerce are established, men try to
accumulate "wealth", or else money which can be exchanged for usable things.

Because of their social disposition human beings need to feel that they
belong in a particular set, or have a place in the community. To meet this
need they sometimes wear special garments or ornaments to tell the world to
what set they belong or how important they are — the old school tie, for exam-
ple, or a sorority pin. We put up badges and signs to assure ourselves that we
rate. More important than signs and labels (which after all may be false, or
merely "put on"), we need to make genuine impressions upon one another
and upon the materials around us. Above all, each individual needs to feel
his own power over things or over others in order to feel secure and important.

Men make things they need or things they want to have or use — houses,
furniture, pies, roads, garments, tools, vehicles. But they make also dolls
and masks, pictures and drums, model airplanes, and many, many more fancy

648

,/'^ik"-<^

High-breed hen

EGG PRODUCTION IN

Scrub hen
U.S.A.

Average egg production
per hen -- 1900

Average egg production
per hen -- 1942

Average egg production
of 10 superior hens

Average egg production
of 10 sets of daughters

of these hens
(10 flocks of 232 hens)

00000 000

00000 00000 d

Each 0=10 eggs

00000 00000 00000 00000 00000 Od

Average per flock

00000 00000 00000 00000 oooo

00000 00000 00000 00000 00000 OOG

IMPROVEMENT IN^EGG PRODUCTION IN THREE SETS OF EXPERIMENTS
Australia ] England

Eggs
per hen

(average)

1903

171
173

i935

199
200

1?22
186

Connecticut, U.S.A.

1930

192

1915

1933

159
169
157

235
217
220

MAKING HENS PAY FOR THEIR KEEP

Getting 100 eggs a-year for each hen, or getting over 200 eggs weighing at least
2 ounces each, depends not so much upon the amount of muscular work one does as
upon the intelligence used in supplying suitable food and living quarters, in protecting
against enemies and parasites and in selecting the stock

lamp shades and foot stools than we ever have a chance to use. In making
such things that are not "necessary" the individual does two things: He asserts
himself as a person; he impresses himself upon the material world, beyond his
hunger or thirst or need for shelter. This is the artist or artisan in man. And

649

he assures himself of his power by assuring others of his cleverness or v\'orth.
He needs to feel that he counts.

These creations embody man's imagination and ingenuity. That is why we
are always interested not only in what we ourselves make, but in what others
make. We admire the handiwork of the ancients and of faraway peoples, quite
aside from any question of its beauty or usefulness. We like to gaze at collec-
tions of human product in museums and galleries and market-places. We like
window-shopping. Man is a maker. Ha\ing to do and to make is quite as
much a need as ha\'ing to eat or to keep warm.

Human Power Because of this restless drive to assure himself and his
fellows that he is quite all right, man is constantly using up more and more of
the materials around him. He is also accumulating surpluses that are never of
any use — except to show that somebody was smart enough to accumulate
larger heaps than others. Modern science and technology — which developed
more rapidly in the mechanical arts and in chemistry than they did in the
biological fields — have enabled us to make more and more things. That means
also to use up still more and more materials. These heaps of things are the
outward sign of our power over nature, and they furnish us much satisfaction.

The tremendous productivity of modern industry should yield a sense of
security; for we are now able to produce all we need — nobody need ever suffer
want. We are able to produce an abundance through only a fraction of our
traditional effort; more and more men and women can therefore be free to
enjoy leisure time. More and more men and women may be free to follow
special interests — music, art, science, exploration, whatever the heart desires
(see page 648). Truly science has given us great abundance and vast powers.

In spite of our increased productivity, which has been tremendously ex-
panded during the Second World War, people continue to be overworked.
Large sections in every country continue to be ill fed, ill clothed, ill housed.
People remain anxious about what they have, and fear want. They are in-
secure and fear their neighbors as possible thieves.

The Sources of New Powers We have seen that these powers come
from increasing division of labor, which enables us to use the great variety of
talents in human beings to the utmost (see page 529). These subdivisions re-
move more and more of us, as "consumers*', from the plans and processes of
production, while they remove the individual workers farther and farther from
the finished product (see page 530). Millions of men and women have learned
to control vast accumulations of energy, or to direct the movements of large
numbers of persons, by performing rather simple operations. A child can shift
a traffic signal and make hundreds of cars come to a stop. A fool can pull a
false alarm and throw hundreds into a panic. A man makes some marks on a
piece of paper, and hundreds of famiUes in another state lose their chance to
make a living.

650

AVERAGE YIELD OF ALL HERDS IN U. S. A. FOR FORTY YEAR PERIOD
Milk - 4000 lb per year | Butterfat - 170 lb per year

AVERAGE YIELD OF DAIRY COWS AT BEGINNING OF CENTURY

I 7500 lb milk per year | 322 lb butterfat, the record yield in 1903

TODAY'S RECORDS FOR JERSEY COWS SHOW

A "POOR" JERSEY YIELDS

yil,0001b , mi)k^xymi__
I 530 lb butterfat per year

AN "EXCELLENT' JERSEY YIELDS

.^_ ^ 14,837 lb milk per yeajc

I 750 lb butterfat per year

SELECTIVE BREEDING IMPOVES BUTTERFAT YIELD

12 selected cows
11 daughters

^^^^^^^lljpther daughters

MORE MILK FOR LESS WORK

Average butterfat yield

American Jersey Cattle C'liih

One of the most effective ways of saving labor in producing the nation's necessary
food is that of improving the breeds of plants and animals

The powers which such individuals exercise are real and effective. But we
too often forget that these powers do not properly belong to the individuals
who push buttons or make the special marks on paper. These powers have been
brought together by hundreds of persons, from widely separated areas, and
stored in the comparatively small machines which particular individuals
operate. No scientist or engineer could, by himself, either make or use such
powerful devices — a telephone system, for example, or a printing press, or a
textile mill. Nor could any individual — by himself — use such powers. The
press is useful only because hundreds of persons are interested in reading the
same book or paper. The telephone is useful only if thousands of people,
scattered over a large territory, are interested in communicating with each
other. If you had a whole factory to work or play with — by yourself — it
would not add much to your control over your environment.

Any person standing at a switch and making one train go along one track
and the next along another track may get the notion that he is doing it all
himself. Many individuals do in actual Hfe control power in much that way.
And they grow into the conceit that it is theirs to do with as they like. But
it is our power. It will continue to grow, and it will continue to serve man-
kind, only as we are satisfied to use it for common purposes, rather than for
the benefit of the individual who happens to be standing at the switch, or at
the traffic signal.

Human power has grown by increasing numberless special skills and special
devices which are of use to those who have them only because others need them.
A doctor cannot make a living by using his medical knowledge on his own body
or on his family. A cotton-grower cannot Hve on cotton, nor the tanner on
his product. The power which comes from division of labor and exchange of
services is socially created power — that is, power created by people living to-
gether. And the power can benefit human beings only as it is put to work
through co-ordinated and co-operative effort; only socially is it usable.

Interdependence The advancement of science has been accompanied
by a rapid growth of cities in population and wealth. These changes have
been so striking that many of us have assumed that by sending everybody
into the city we can assure abundance for everybody. The appearance, how-
ever, is misleading. In a city like New York or Chicago several thousand
persons can indeed live on a square mile of land, but only because our division
of labor and our highly perfected means of transportation and communication
enable us to bring them the organic materials essential for life.

Under the best agricultural practices it would take thousands of acres and
thousands of rural workers and transportation workers to supply food to even
a small city. In a state like Connecticut or in a country like England the popu-
lation can continue to live only so long as vast quantities of fresh and preserved
foods continue to be brought in from distant points. The people living in

652

United States Bureau of Plant Industry

INCREASING YIELD WITH LESS EFFORT

For the same amount of work in the fields, it is possible to raise cotton that will ripen
in time to escape damage by the boll weevil, which at one time destroyed 30 per cent
of the crop in a year; to raise a variety that resists the wilt, a disease which for-
merly destroyed entire crops; and to produce a fiber superior to the best available
forty years ago

England could, if necessary, raise on their land sufficient food to maintain
themselves. They could do so, however, only by replacing a large part of their
idle lands or deer-parks with farms and by releasing industrial workers for
farm work.

Man's competitors for the produce of the earth are too numerous and
too elusive to be fought by any person singlehanded. Our greatest successes
have come from joint efforts through a strategy based on knowing more
about the enemy than he can possibly understand about us.

Limitations of Self-sufficiency Our use of science for increasing pro-
duction has gone hand in hand with more extensive commerce within every
country and more extensive international trade. Each region cao develop
intensively whatever special resource it has — iron in one place, sulfur in an-
other, timber somewhere else, or fish — and send it off to other parts of the

653

world, in exchange for a great variety of useful materials and objects such as
it never could produce itself. Portions of the earth which could not otherwise
yield its inhabitants a livelihood have thus been made serviceable. A tre-
mendous amount of navigation and railroading and trucking has grown up.
There has also, however, grown up a very complex scheme of relationships
in which every civilized country depends for its continuous well-being upon
other parts of the world. Under such conditions, hardly any nation can be
self-sufficient.

The colonial system of modern times has been developing for several centu-
ries as a means of assuring certain European countries adequate supplies of raw
materials from backward countries. This arrangement led repeatedly to wars
for more territory or for territory that could furnish particular kinds of ma-
terials, and it produced a system of competing and conflicting empires. People
living in those backward countries, and people living in countries that were
without colonies, found it hard to understand why the more powerful nations
could not mind their own business. But in a country at war today everybody
realizes how dependent we are upon other countries for a multitude of supplies
that we cannot produce ourselves.

Between the First World War and the Second World War, statesmen every-
where played with the idea of making their own countries self-sufficient — just
in case. The British Commonwealth of Nations established trade agreements
that would assure the entire group practically all kinds of materials needed for
modern Uving, but no single nation in the group could be self-sufficient. The
forty-eight states of the continental part of the United States have a great
range of mineral, plant and animal resources, but no one state can be self-
sufficient, nor can the entire Union. The Russian Union of Soviet Socialist
Republics covers an even greater variety of soils and climates and minerals
and living forms, and was aiming at self-sufficiency before the Second World
War. The Germans had lost their colonial empire and were attempting to
develop their chemical industries so as to produce substitutes for the rubber
and oil and fats that they were unable to obtain.

Whatever the benefits of modern civilization, they would almost of neces-
sity be lost by any people that persisted in being self-sufficient — in living by
itself. On the contrary, it is getting to be impossible to maintain a scientific
civilization in any part of the world without extending the benefits to all
people everywhere.

In Brief

Men use more materials and objects to supply food, clothing and shelter
than for all other needs combined.

The materials used in connection with the care of the body in health as in
disease are derived largely from plants and animals.

654

Averade

annual loss

EGG

LIFE STAGES OF INSECT
LARVA PUPA ADULT

Damage to

cotton crop - ya*«««-">

$118,000,000 '^ *"^

Methods of "1
checking

Early-ripening

varieties of plants

to beat life cycle

of weevil

Bum stalks

COTTON BOLL WEEVIL

-rrr

Damage to
com crop -

$17,000,000

;-^^

If!

Destruction of

infested stalks

below ground

Late fall plowing

of stubble

Ensilage for

stalks

EUROPEAN CORN BORER

Damage to

potato crop -

$16,500,000

Poison sprays
and powders

(Effective against
both larvae
and adults)

COLORADO POTATO BEETLE

Damage to
grain crops -

$13,000,000

Planting alter
fly-free period

Burning stubble

Crop rotation

HESSLAN FLY

Damage to
cotton crop -

$3,000,000

1<.

Poison sprays
and powders

(Contact sprays
most effective)

COTTON APHID

Damage to

orchards,

truck crops,

trees, etc.

$2,700,000

Poison sprays
and powders

Capture in traps

(effective for

adults only)

JAPANESE BEETLE

Damage to
bean crops -

$1,275,000

Poison sprays
and powders

(Effective against
both larvae
and adults)

MEXICAN BEAN BEETLE

OBSTACLES TO HUMAN WELFARE

Streams depending upon deforested areas for their water are too full in
the spring and run too low in the summer; the destruction of forests in one
region has often resulted in the ruin of agriculture and the displacement of
peoples in a distant valley.

Soil washed away by water is not only a direct loss of agricultural resources;
it also interferes with the navigation of streams and with conditions of harbors.

With the abundance made possible by science, further growth and enrich-
ment of populations seem to be limited by our clinging to attitudes which
belong to simpler modes of Uving — attitudes of mutual suspicion and conflict
among men and among tribes.

EXPLORATIONS AND PROJECTS

1 To learn of the extent to which erosion is being and can be controlled, read
and report findings obtained from various government publications. ^

2 To find the extent to which our forest resources have been and are being ex-
ploited, investigate the changing forest areas within the United States. Find out
what proportion of our original forests still remains; whether forest areas are being
depleted at the present time; and what is being done to conserve and to replace
forests.

3 To find out how staple crops are produced, investigate the growing, storage
and marketing of such crops as corn, wheat, oats, cotton, tobacco, clover, alfalfa,
potatoes, apples, oranges, grapefruit, and the various vegetable crops. Prepare a
written report on your findings.

4 To find out how various meat, dairy and poultry products are produced, in-
vestigate the feeding, breeding, care and marketing of beef cattle, dairy cattle, hogs,
sheep, chickens, and the like. Prepare a written report of your findings. •

5 To learn how to can fruits, vegetables and meats, try packing some as de-
scribed in Farmers' Bulletin No. 1762, entitled Home Canning of Fruits, Vegetables,
and Meats, or in other available descriptions of the process. Describe the essential
steps in the canning of foods.

6 To learn about the new uses of agricultural products in industry, investigate
the many commercial uses of various products manufactured from soybeans, from
cotton seeds, from corn, from peanuts, from milk, and from other agricultural
products.

QUESTIONS

1 What are the outstanding needs for which man uses other living things and
their products?

2 What kinds of plant or animal products are most useful in meeting the
primary needs of man ?

iReport of the Mississippi Valley Committee of the Public Works Administration, pp. 61-68,
119-126. United States Department of Agriculture Miscellaneous Publication No. 321, entitled
To Hold This Soil. United States Department of Agriculture Yearbook, 1937, entitled Soils and
Men,

656

3 For what other purpose does man use plants and animals?

4 How does a feeling of security or insecurity with regard to these primary
needs influence health and effective Hving?

5 How can forest conditions in one region influence the interests of people in
another region?

6 How do any particular forests influence conditions in your region?

7 What damage results from forest fires besides the destruction of trees?

8 What lands in your region would be available for forest without loss to farm-
ing? When is it better to use land for trees than for agriculture?

9 What biological ideas have helped to enrich our people?

10 What are the advantages of living in a self-sufficient nation? What are the
disadvantages?

11 What does international trade contribute to a people besides making im-
ports available?

657

CHAPTER 32 • BIOLOGY AND THE PURSUIT OF HAPPINESS

1 Do all living things feel pain and pleasure?

2 Can other animals besides human beings feel happy or unhappy ?

3 Whv do some people seem to be more consistently cheerful, or

more consistently unhappy, than others ?

4 What conditions are likely to increase human happiness*

5 Does happiness depend upon circumstances or upon one's nature?

6 Can people be happy if they are not in good health'

7 Are children happier than adults'

8 How does being civilized make people happier than sa\ages are?

9 Whv is it said that more knowledge means more sorrow-

10 If wealth does not ensure happiness, wh\- do people try so hard
to get it?

A babv gets what he needs when he needs it. He is protected from harm.
His comfort is looked after. Nothing worries him. He need not exert himself.
Could anvone be happier.' From this point of view, the pillow on which the
babv lies mav be still happier. It has no needs. Hardly anything can hurt it.
It can experience no discomfort. It can neither exert itself nor worry. Many
of us feel at times that we should like to change places with a baby. Hardly
anvone would want to change places with a pillow.

The most complex animals are the most sensiti\e to stimuli. They are ac-
cordinglv able to feel the most pain — but also the most pleasure. Man, \\ ith
his exceptional intelligence, finds ways to reduce sickness and pain, to lengthen
life. He has managed to increase the margin of free time and energy, to use as he
Hkes. He can enjoy Life, not merely make a living. He can carry on activities
that are distinctly human. He finds satisfactions that are distinctly human.

But is man today better off than his ancestors were? Are people in scien-
tific countries anv happier than those in backward countries?

Just What Is Happiness?

Pain and Pleasure^ The most "real" of all experiences are the feelings
of pleasure or of pain which accompany our sensations and our activities.
These feelings influence all our actions. Ever\'body wants to avoid pain and
to get pleasure, more and more pleasure. Yet "pleasure'' is not the same as
happiness. Indeed, the mother of a new baby insists she is very happy while
her phvsical pains are quite severe. A player who has been hurt in a game says
that he is happy o\-er the outcome. But the immediate practical goals in the
pursuit of happiness are largely to satisfy desires and to avoid or reduce pain.

^See No. 1, p. 673.
658

Pain and Privation Man has succeeded pretty well in assuring himself
of the basic necessities, through his fight against natural forces and enemies.
Actual hunger has been reduced, even if many are still undernourished. We
no longer accept starvation as a regular part of Ufe, as people in many parts
of the world did in the past, and still do in some. Probably fewer people to-
day suffer from extreme cold or exposure, from bad housing and inadequate
clothing. Yet here, again, our population is far from adequately supplied
with the necessities for modest but safe living.

We have also reduced the suffering due to many preventable diseases and
to infections that sometimes follow bruises, cuts, the stings and bites of animals,
childbearing, surgical operations.

From ancient times people have been seeking ways of overcoming physical
pain. Opium, which is prepared from the latex of the seed-capsule of the
Oriental poppy, has been used to produce drowsiness and stupor. For many
centuries people have used alcohol to "cheer" them up and to "drown their
sorrows". Other drugs and devices have been used in efforts to reduce suffer-
ing. Generally speaking, however, physical pain has, until comparatively
recently, been accepted as in the nature of things, as part of man's lot. Only
since 1800 have people begun to consider seriously the idea that physical pain
could be attacked systematically, like any other human problem. In that year
Humphry Davy (1778-1829) suggested that pain might be deadened by the
use of nitrous oxide, or "laughing gas" — which had been discovered in 1776
by Joseph Priestley (1733-1804). In about forty years nitrous oxide and later
ether came into use for destroying pain during the pulling of teeth. Gradually
it became customary to prevent pain in all surgical operations by using
anesthesia, a name suggested by Dr. Oliver Wendell Holmes and meaning
"lack of sensation".

Joseph Y. Simpson (1811-1870), a Scottish surgeon, first used chloroform
to avoid pains in childbirth. Many groups opposed this on "religious" grounds.
They did not argue that chloroform might be injurious, but were convinced
that "God intended" woman to bear children in pain. When Queen Victoria
gave birth to a child with the help of chloroform, the opposition began to
die down.

After the middle of the century it was discovered that cocain destroys sen-
sitivity to pain in the tissues into which it has been injected. Later it came
into use as a local anesthetic. As a result of modern chemical and physiological
studies, we now have various preparations that ease or completely overcome
physical pain, and that without destroying consciousness. We have perhaps
all read about the surgeon whose leg was crushed in an accident and who,
after receiving the suitable "anesthesia", directed the amputation and con-
versed with the other surgeons. The drug blocks some of the afferent nerves
but leaves certain efferent paths and the higher brain centers unaffected.

659

Positive Needs Reducing pain and privation or preventing sickness
and physical suffering is but part of our problem. We want positive satisfac-
tions and pleasures. As human beings, however, we want more. "Life is more
than meat." We want to do a thousand things that are not necessary to us as
organisms, but that are necessary for our comfort and satisfaction — and our
happiness — as human beings. To be happy man must have a chance to go after
what he wants, whether he ever attains it or not. Perhaps that is what is meant
by the right to the "pursuit of happiness" — rather than the right to happiness.

Values^ We cannot compare satisfactions felt by different persons, nor
measure degrees of satisfaction that we ourselves feel. Yet we are constantly
making choices or decisions in the effort to increase our pleasures. With ex-
perience, we learn that some of life's offerings are not worth much to us. But
we will go out of our way to see a particular game or exhibit, to hear a particu-
lar composition or performer, to take part in a particular meeting or athletic
event. Our strivings are for values, and each one has to learn what is of
most worth to him. We learn also to consider what is of greatest worth in the
long run.

How Do Our Needs Differ from Those of Other Species?

Obstacles to Satisfaction Whatever interferes with our efforts to satisfy
our wants is itself a cause of dissatisfaction or unhappiness. Being blocked or
frustrated arouses anger or sulking or sour temper or resentment. One may
come to dislike particular persons or situations that he associates with the
obstacle. These unhappy feelings seem to come in addition to the chemical
or physical results of any privations or injuries.

Again, almost any obstacle may act as a challenge. We climb a mountain
just for the fun of getting to the top. We jump over a fence instead of going
through the gate. We devise obstacle races: clearing a hurdle seems to be
more important than merely getting to the other side. Men fight not only
for what they must have. They are especially aroused to fighting whatever
stands in the way of their purpose.

Increasing the Range of Needs Human beings remember and imagine
more than other species. They are exceptional hunters and prowlers. They
pry into hidden corners. They poke their fingers into hornets' nests or their
feet into the mud. We say that they are curious. They thus get into new
situations with which they are unable to cope. They taste what never had
been eaten by human beings before. They pick things to pieces. As human
beings, we seem unable to let well enough alone. Prying, exploring, experi-
menting, analyzing, often lead to missteps, mistakes, or tragic blunders. But
it is only by yielding to this curiosity and experiencing mistakes that man
makes progress.

^See Nos. 2 and 3, pp. 673 and 674.
660

(iendieau

ADVENTURING AND EXPLORING

Why does anybody bother to reach the south pole or the top'of a high mountain?
What's there besides snow when the goal is reached? Why hunt for tigers or poison-
ous snakes, or experiment with deadly bacteria?

In general, then, we are disposed to wonder, to explore, to inquire, al-
though we are also commonly held back by fear. In time some learn to ex-
plore cautiously, knowing dangers. Men have extended their explorations in
all directions on the surface of the earth, and into the waters and into the air.
We have wondered about the remotest reaches in space and in time, about the
very constitution of the universe and of matter. We have wondered how the
things we see came into being. What makes things happen as they do? What
will happen in the future?

Substitute Values Our imagination not only creates new needs, but
furnishes types of satisfaction that are probably different from those of other
species. We cannot all go out to explore the bottom of the sea, for example, or
the south pole. We may, however, share — in imagination — some of the ex-
citement and satisfaction of hunting big game, of discovering new regions or
new kinds of human beings. We read about such adventures, or look at pic-
tures made by others, or hear someone describe his experiences. We are able
to throw ourselves, in imagination, into new scenes, new situations. We
share the excitement of the players in a game that we are watching, or of a
boxing or wrestling match. We "put ourselves in the place" of other persons.
And to the extent that we do so we get the corresponding feelings.

We are able to enjoy vicariously — through substitution — the satisfactions
and excitements and adventures of other people, to get the benefits of make-
believe. But we can also feel the anxieties that go with the dangers. We can
almost feel the pain of a blow in watching a fight. As we watch a game, are we
going to feel more satisfaction or more disappointment? That depends in
part at least on the side with which we have identified ourselves.

Aesthetic Values^ In every experience our tastes seem to be rich sources
of satisfaction. To enjoy music, works of art, natural objects and scenery,
particular types of plays or fiction, the watching of particular games, the
company of particular persons, is to add to the fullness of life. What we like
means more to us than other things.

The tastes of each person depend in part upon the actual sensitivity of the
receptor organs (see pages 284ff.). One person can discriminate shades of color
or degrees of illumination much more delicately than another. One can hear
several distinct tones between one note on the piano and the next, whereas
another cannot tell the difference between B and B flat. For some individ-
uals food is food; enjoying food more means for them merely eating more
food. Others, however, are aware of delicate flavors and combinations that
are in themselves sources of genuine enjoyment quite aside from the need to
appease hunger.

For most of us, differences in taste are largely acquired, within the limita-
tions of the sensory system, our imagination and our intelligence. For example,

^See Nos. 4 and 5, p. 674.
662

Roberts; Keystone

VICARIOUS ENJOYMENT OF PRIMITIVE IMPULSES

Why is it so important to these players what happens to that ball? Why is it so im-
portant to the thousands of onlookers? Why is it so important to the hundreds of
thousands who listen to the broadcast account, or who read the newspaper reports?

we all like a scene that recalls pleasant hours of childhood, or persons we have
liked since childhood, or songs that we Uked in childhood. In many cases we
develop preferences under the influence of people for whom we have high
regard. If our hero, at a certain stage in our development, liked artichokes,
we learned to like artichokes and to feel superior to those who do not. Or if a
person we greatly admired disliked a particular poet or composer, we found it
difficult to enjoy that poet or composer.

People of influence in a community or in a school often impose their own
likes and dislikes upon others, often indeed without meaning to. Those of us
who have no decided preferences are likely to borrow preferences that seem
to be approved or in good repute. It is largely for this reason that it is pos-
sible to bring about rapid changes in fashions without much regard to what
persons of sensitivity and fine discrimination consider in good taste.

Finally, many become accustomed to particular styles in clothing, architec-
ture, table manners, patterns of meals, social customs, and so on, to the point
where everything that is different seems to be ugly, wrong, or in poor taste.

663

WE ALL LOVE BEAUTY

Why do some creations appeal to larger numbers than others do? Why do some
continue to be liked for many years, whereas others soon lose their interest?

In general, likings and dislikings, no matter how they have been acquired,
play a large role in the pleasures of life on every level of human interest.

Anticipation We may concede that a hungry dog or horse "enjoys"
his food. We can even find evidence that the agreeable feelings which an ani-
mal may associate with the gratifying of hunger are to a degree anticipated:
the dog, for example, moves toward his food with alacrity, he behaves as if he
were looking forward to a good time. Human beings, at any rate, derive
positive satisfaction from the activities which more or less directly lead to the
gratifying of desires or the carrying out of purposes.

Every important project involves many disagreeable or even painful de-
tails. An animal engaged in a fight will often stick it out against severe strain

664

and probable si ifering. But man alone seems able to plan and persist against
difficulties over a long stretch of time. The work of the farmer, for example,
continues over many months in anticipation of the harvest.

Anticipation is not all stimulating, however. A mother preparing a meal
for the family may be troubled by anxieties instead of enjoying in advance
the satisfaction of feeding the hungry ones. She is troubled by uncertainty
as to the next day's meals, and can therefore enjoy neither the meal itself nor
the preparations for it. Some might say that looking ahead does not help the
mother, since it leads her to worry. But she was able to plan and prepare this
meal only by looking ahead.

How Does Social Living Influence Happiness?

Learning Restraints We all want to be free to do as we like. Yet the
infant would soon perish if he were left to do as he liked. And later we replace
what we feel like doing with liking to do something else.

We all learn rather early that some restraints upon our impulses are neces-
sary from the nature of things. The child learns, for example, that he prefers
not to touch a flame, or to pull the cat's tail, or to grab a knife. But the regu-
lations that other people prescribe for us often seem arbitrary and unreason-
able. These Donts and Thou-shalt-nots — prohibitions and denials — make a
child unhappy. Why may I not do as I like? Why may I not eat those apples
or that candy? Why may I not stay up longer? Why may I not say what I
think about that old Mrs. Sourpuss? Why must I wait for Jimmy?

It is not satisfactory to be told by a larger and stronger person, "Because
I said so!" For all one knows to the contrary, the parent or the teacher or the
lawmakers might have said just the opposite. Indeed, as we grow older, we
discover that other teachers, other people's parents, other lawmakers, have
said just the opposite. It does seem arbitrary. Yet we also learn gradually
that at least some of the forbidden acts often bring their natural pains and
penalties. In some things, the older people seem to know better. In other
cases, forbidden acts deprive us of the friendliness and approval of those we
like, or they deprive us of those upon whom we depend for favors or for our
comfort. And in still other cases, we feel that we can afford tol^rake a chance:
perhaps we shall not get caught this time; or perhaps it will not hurt so much;
or perhaps the fun is worth the suffering or penalty. That is, we learn rather
early in life to weigh values — our present desires against later consequences.

Becoming Human The infant not only depends upon others from the
first for his health and survival; as he grows older he depends increasingly
upon others for a multitude of satisfactions and services. He depends upon
others for praise and approval, for consolation and encouragement, for under-
standing and affection.

665

An infant might indeed be kept by himself in good health for many years,
but then grow up into an animal that is human in hardly more than form.
Only in the group does one find the stimulation and guidance which convert
him from a little animal into a person. It takes experience with others to learn.
language, the arts of handling food or common tools, our particular ways of
living. Becoming human means becoming a member of a group, with all the
satisfactions and helps — and all the interferences too. That is, it involves
getting certain benefits — taking; but it means also making adjusrinents,
making allowance, making concessions — giving.

Discovering Ourselves The infant discovers himself partly in what he
learns to do with the objects around him. It is fun merely to handle things,
move things around, piling up and knocking over, tearing paper or breaking
sticks, throwing, scribbling, kneading dough or clay. Gradually the piles he
builds up or the markings he makes come to have meaning; they suggest
familiar objects; that is a house, that is a tree. The child discovers that he
can make — he is a creator! That is tremendously gratifying. The child may
never become an artist, a builder, a designer, an architect, a statesman. For
the time being, however, the act of creating satisfies his pride, his self-esteem.
Now he feels I do! I mallei

Satisfactions of such an order are important throughout life. Many men
and women who have all they want of physical materials, housing, amuse-
ments, medical and other special services, yet remain always unsatisfied be-
cause they cannot impress themselves directly upon the material world. That
is why there is so much interest and value in all kinds of handicraft hobbies and
old-fashioned household activities. Through cooking and knitting, through
whittling and cabinetmaking, through gardening or furniture-repairing, one
may create something to show for his effort. This is especially needed, ap-
parently, by those whose daily work consists of details that become absorbed
in products which they never see themselves. One makes a particular series
of buttonholes, but never a completed garment. One keeps the working-time
in a lumber-yard, but never sees what the lumber is built into.

The individual discovers himself further through the effects which he learns
to make upon others. I can scribble something and call it a tree, or a poem,
or a poem about a tree. But unless others recognize it about as I intend it, I
cannot be quite sure that my work is good, that it has value. For I must have
the understanding and approval of others. The friendly encouragement of
my parents (who like me and who may be biased) is not enough. I need
further the judgment of many others, who appraise my work — and me — at a
true worth.

The individual, then, has to express himself by what he does to persons, as
well as by what he can do to things. He has to impress others, as well as assert
himself. He must draw to himself the regard of others.

666

We discover the peculiarities of the
world around us by trial and error.
As we push and pull at things, some
objects resist our efforts and others
yield. From what happens or fails to
happen as we handle things or as we
try to make them serve us, we get
most of our practical knowledge about
matter — hard and soft, heavy and
light, tough and tender. And in just
the same way we discover our own
possibilities and limitations — what we
can do with things, how to manage dif-
ferent kinds, how far we can go, and
points beyond which we are helpless

Child Study Laboratory, Vassar College

LEARNING BY DOING

Social Sensitivity The developing person wants the approval and re-
gard of those for whom he cares. In childhood this means members of the
family, playmates, the neighbors.

The fact that we do care for others and want others to care for us influences
our purposes and desires. For we wish to please those whom we like, to help
them, to protect them against hurts of all kinds. Accordingly, as human
beings, we determine for one another what we consider important, what we
strive for, what we value. One does not ask himself whether he should be
devoted or loyal to those he likes, or whether he should sacrifice immediate
pleasures or control his impulses. We feel loyalty and devotion toward those
with whom we identify ourselves. And these feelings determine our actions.
What one does "for others" he really does for himself or for that group of which
he feels himself a part.

In a group of those who thus give and take, further satisfactions come from
sharing. We want our friends to know of our achievements, our successes;
and we are pleased by the achievements and successes of our friends. In this
way pleasures are increased. On the other hand, when we share our disappoint-
ments or our sorrows, they become easier to bear. It is en-tro^/r-aging — that
is, heart-tmng — to feel that others are with you, that they care for you, that
they will back you up. In any case, there is the need to feel that one belongs.
This is quite as important for one's health and happiness as adequate food or
shelter.

Individuals in the family, among friends, or in a club normally feel mutual
regard and consideration. The members of such a group do not ask themselves
whether they are going to get as much as they give. Each one who truly be-
longs not only is confident that he will get all that is due him but is eager to
do everything he can for the others or for the group. The best-integrated

667

social unit among all kinds of peoples is probably the family. The members
of this group are usually bound together by affection. The stronger members
protect and help the weaker. Each one exerts himself according to his special
abiUties or talents. And each one receives according to his special needs. The
"equality" within the family does not consist of giving young and old equal
quantities of milk or meat, or giving everybody shoes of the same size. It
consists of assuring each an equal chance to get what he needs or what is best
for him — within the limits of the common resources — and of assuring each an
equal chance to assert himself as a distinct person.

Human Possibilities Each one of us discovers some things that he can
do with satisfaction. But each discovers that there are more things which
he cannot hope to master. Is he going to get his satisfactions out of what is
possible, or will he draw his misery out of what is beyond him? If one is too
easily satisfied, he will get relatively little out of his life; he will fail to get
the regard of others and of himself in proportion to his capacity to do and to
enjoy. On the other hand, if he attempts the impossible, if he is too am-
bitious, he not only will be disappointed, but will make himself ridiculous.

It is not easy to find our way in the swirling currents and countercurrents
to which our own strokes or flounderings contribute. Human life need not
be the kind of struggle that goes on in the jungle, but it is still a struggle, and
probably always will be. The struggle now, however, is not for each one to
dig from the earth and to grasp for himself the bare necessities. Cold and
hunger can be met much more simply. The struggle is between one's own
feelings and desires — ^as a person, as one among others — and the demands and
pressures put upon him by others.

We have seen that a frustrated infant becomes angry. The individual who
is constantly frustrated becomes permanently angry, resentful, full of hatred.
And he turns these feelings aggressively against others — against weaker per-
sons, against those he envies or those he holds responsible for his difficulties,
against institutions, against all society. A child who fails to make a satisfactory
impression upon others feels humiliated. He is tempted to withdraw from
others; he wants to be let alone. But at the first chance he may try to make
up for his troubles by bullying or attacking weaker children.

Individuals may make a satisfactory adjustment within a small group but
find it impossible to fit into a larger community. A club may be merely a
group of congenial persons who have something in common and like to be
together for carrying on some special activity. There are many social clubs
or hobby clubs. On the other hand, the members of such a group may have
little to share with the larger community. They may become a "gang". The
individuals in such a group have to get the approval and applause of their
fellows. But sometimes they do so in ways that are quite objectionable to
the rest of the community.

668

IL L^' fe.^

-^iranL

Equality of opportunity
The same kinds and sizes of shoes for all

Equality of responsibility
The same load and the same task for everybody

First come, first served; no favorites
First one down gets all the cream

Each according to his needs

NOTIONS OF DEMOCRACY IN THE FAMILY

We use various slogans to justify our conduct or to explain why we consider some
acts right and others wrong. But these slogans often hide inconsiderate or undemo-
cratic acts. Our rules are perhaps not as important as our attitudes

Some individuals fail to mature into independence and self-assurance. An
adult who has no suitable ways of getting what he wants among others some-
times continues to use baby tricks. There are men and women, for example,
who break into fits of anger or tantrums, who pound the table and shout, or
go into hysterics. They have learned no other ways of meeting problems, or
of adjusting themselves to other persons.

In modern times we have learned that we can control events increasingly
as we come to know more about the nature of the world around us. We can
prevent certain diseases altogether. We can reduce many kinds of accidents
substantially. We can lengthen life. But our controls over pestilence and
plague and food -shortage and physical pain come only from the pooling of
experience and knowledge and our practical programs.

In the same way we can reduce our individual anxieties and uncertainties
only by pooling our risks and our resources. We are unable to predict when or
where death or misfortune will strike. But we can estimate rather closely
how many deaths or accidents there will be in a given population for a year
or more in advance, or how many days of sickness there will be, or what the
chances are that a hailstorm will destroy a crop. Through our insurance sys-
tems, whether commercial, co-operative, or public, we divide the burden of
disaster. Insurance cannot prevent calamity or death. It can only give the
individual that comfortable feeling that he has the backing of the entire
group: whatever happens, the immediate needs will receive consideration.
The individual feels that he shares, that the odds are not against him.

Inner Conflicts Did you ever see a child hold up the traffic at a party
because all the cookies or candies on a plate were equally attractive, so that he
could not decide which one to take? Each of us frequently meets a situation
in which action is blocked because we wish to turn to the right and to the
left at the same time. In extreme cases, a person with such divided purposes
becomes unable to carry on the ordinary affairs of life. The condition appears
to be not so much inherited or constitutional as acquired; or perhaps it is a
relic of a childish state that one has not outgrown. At any rate, similar states
have been cultivated in animals experimentally.

The classic experiments were made in Pavlov's laboratory (see page 267).
A dog was "conditioned" to come toward a certain spot in the laboratory
when a circular disk was illuminated, by the consistent offering of food. He
was also conditioned to move in the opposite direction whenever an elliptical
disk was lit up, by the consistent application of an electric shock. After the
dog had thoroughly mastered these signals, the experimenter changed the
shape of the ellipse slightly every few days, making it a little shorter and a
little wider. The dog continued to go through his performances several times
a day, never making a mistake. One day, however, when he came into the
laboratory, he suddenly went mad: he jumped about, but made no headway

670

^"•CE^-.^

' '^-Si

PAVLOV'S ARTIFICIAL NEUROSIS

Pavlov conditioned a dog to come whenever a certain signal appeared and to run
away whenever another signal was presented. Then the elliptical go-away signal
was gradually shortened and fattened. When the dog could not distinguish the two
signals, he acted like a person who does not know whether he is coming or going

in any direction, turning rapidlv now one way now another; he yelled and
whined, and gave every indication of being very unhappy indeed. What had
happened to change this well- trained dog into a raving "neurotic"?

Many people get into this state because they do not learn early enough that
throughout life we simply miL<:t make decisions. The child must learn that he
cannot have everything, that he cannot eat his cake and have it, too. A mul-
titude of choices does not mean that we can eat several meals at once or wear
four hats at once just because we can afford them. Human life is the richest
life, but we should not be embarrassed bv our riches.

Through experience a child can learn that he likes vanilla better than
strawberry, or the other way round. It certainly is not always easy to make
decisions, but we have to learn the relative worth to us of the many possibili-
ties. No set rules will assure happiness. Sometimes we hesitate because we
have to choose between something of value now and a future value. Many
try to live by the rule "Eat, drink, and be merry, for tomorrow we die." It
must seem silly to take chances with a future, which is necessarily uncertain,

671

and to postpone the enjoyment of life. A considerable fraction of those who
act on this rule will survive the gay carnival to suffer privations and head-
aches or worse. Many outlive by many years their very capacity to enjoy
anything at all.

We cannot follow our childish impulses, for they do not fit our needs and
circumstances of later years. Besides, our impulses have been conditioned by
experience, our thought, our sensitiveness, our affections; and there are always
conflicts among them. On the other hand, we should not go mad when we
are confronted by a dilemma. Unlike Pavlov's dog, human beings can learn
to stop and consider, to weigh \'alues.

Sometimes we have to weigh immediate desires against remote conse-
quences— consequences to others as well as to ourselves. A child constantly
asks, "Why must I?" or "Why mayn't I?" He does not understand possible
consequences. But an older, responsible person has to make decisions that
consider far-off consequences in many different directions. Eventually, ma-
ture men and women seem to adopt a style of life that does take account of
consequences as a matter of course.

Whether a person who knows more and considers more and is sensitive to
more is "happier" than one who does from moment to moment as he likes it is
impossible to answer. We can say only that as people do become more sensi-
tive and more understanding and more considerate, they seem also to get
more out of life. Human beings are social and do not normally choose to live
as "individualists" in isolation. Living in the group, we cannot carry on,
however, the kind of conduct that suits the protected and irresponsible in-
fant, or the kind that a hermit might work out for himself. It comes down to
a question of what kind of group one lives in, and how satisfyingly he adjusts
himself to the social world of which he is a part. How does one live in the
family, among his friends, in his economic life, in the club, in the church, in
the community, in his whole civilization?

In Brief

The feelings which accompany our sensations and our activities are the
most "real" and immediate of all experiences.

Avoiding pain and privation and gratifying the natural impulses are the
beginnings of contentment and happiness.

In addition to the basic needs we share with other animals, we need the
chance to act freely, to play, to make, to create by handling materials.

Human beings are disposed to explore, to wonder, to inquire, although
they are also held back by fear; men must have the chance to go after what
they want, whether they ever attain it or not.

672

The refining of our discriminations and appreciations seems to increase
our satisfactions in every type of human experience; yet the capacity to enjoy
goes with the capacity to suffer. •

Feehngs of insecurity and anxiety interfere with activities and situations
that might otherwise be very satisfying.

Through our imagination we are able to feel the satisfactions and anxieties
of other people, as well as those of fantasy.

If one's goals are too easily attained, he will get relatively little out of life;
if one attempts the impossible, he not only may be disappointed, but may
make himself ridiculous.

Our strivings are for values and each of us has to learn what is of most
worth to him: we sacrifice immediate satisfactions for greater ones more
remote; we do many things that are in themselves uninteresting or even un-
pleasant, because we consider them necessary for achieving the major satis-
factions.

, Man is a social organism: he lives in groups and gets pleasures and satis-
factions from others, as well as obstructions and irritations.

What one does "for others" he really does for himself, or for that larger
self of which he feels himself a part.

We learn to consider what is in the long run of greatest worth, including
the welfare of others involved in the consequences of our acts.

EXPLORATIONS AND PROJECTS

1 To see how far the physical state of an organism influences responsiveness to
stimulation,

a. Compare the responses of hungry animals and well-fed animals to food or to
other objects. (A single animal might be studied before and after a meal.)

b. Compare the behavior of a hungry and a well-fed animal (dog or cat) when
invited to play, or when teased.

If there is an opportunity to visit a menagerie at different times, compare the be-
havior of caged animals in response to stimulations of various kinds before and after
they are fed. Summarize observations in general statements. Supplement your own
observations with examples from history, biography, and fiction, to show how human
conduct appears to be modified by extremes of thirst or hunger.

2 To find out what there is in common among a variety of substitute interests,
have each member of a group list what he finds most satisfying or interesting in some
particular type of passive recreation, such as the movies, sport news, comic strips,
poetry, and visiting an art gallery. (It is, of course, not sufficient to record merely
that one "Ukes" or "enjoys" reading a book or seeing the movies; each should stop
and ask himself just what it is that he likes or enjoys or finds satisfying in a particular

673

type of experience.) Find as many common items as possible among the different
sets of "enjoyments". How do these satisfactions differ from similar satisfactions
derived from active participation in sports, in adventure, in work, etc. ? In what ways
may we account for the resemblances between actual experience and substitute ex-
perience? How may we account for resemblances among the satisfactions furnished
by various types of substitute experience?

3 To see how far variations in taste may be traced to their sources, have each
member of a group list three "best liked" and three "most disliked" foods, plants,
colors, animals, types of person, or other class of experience. Have each one try to
account for a strong like or a strong dislike by telling either {a) how he came to have
strong feeling in the case, or {b) why he considers the item desirable or undesirable,
pleasing or displeasing. How far are we able to account for our preferences? To
what extent are our preferences determined by good "reasons"? To what extent do
our tastes seem to be influenced by the customs or usages of those among whom we
have grown up?

4 To show how far human activities yield satisfactions unrelated to practical
"needs", have members of a group list games or hobbies in which they are individ-
ually interested and analyze them to find out just what features appear to furnish
pleasant feelings. What is common to many different games or hobbies? What
appears to appeal to some individuals but not to others? What hobbies or games
have been developed into careers or means of HveHhood? What hobbies have de-
veloped results in the form of knowledge or devices that are socially valuable?
Gather examples of hobbies that depend upon interest in living objects — collecting,
classifying, comparing structure, dissecting, displaying, social statistics, painting,
modeUng, etc. Gather examples of hobbies that depend upon interest in living
processes — migration, combat, food-getting, training animals, experimentation,
breeding plants and animals, landscaping, social work, nursing, law, education. Red
Cross or relief work, fishing, city-planning, etc.

5 To estimate the importance that is increasingly attached to recreation find
out {a) what your own community has been doing over a period of years through the
department of parks, through the schools, and through other pubUc and private
agencies to provide facilities for recreation; {b) what your state agencies have been
doing; and {c) what is being done by the United States Department of the Interior
through the national parks (obtain the Department of the Interior publication Parl{
and Recreation Structures, which describes the various facilities available and offers
suggestions for constructing similar appliances in local playgrounds). A committee
might profitably survey recreational needs in the community and confer with repre-
sentatives of other groups or organizations with a view to increasing or improving
faciUties.

QUESTIONS

1 How do the needs of human beings differ from those of other species?

2 In what ways is human capacity for pain and for pleasure probably different
from that of other species?

3 In what ways do individuals come to prefer some experiences to others?

674

4 In what sense is it true that human beings make more "mistakes" than
members of other species? Why is that not a handicap in the struggle for existence?

5 In what way does the fun of running or swimming differ from the fun of
running or swimming in a race, and from the fun of watching a race or watching a
motion picture of others in action?

6 What is there to show that painful or pleasurable feelings are possible with-
out the direct stimulation of sensory nerves?

7 What scientific discoveries have helped to reduce mental and physical
suffering associated with disease or injury?

8 In what ways do human satisfactions increase from our living in society?
In what ways do they suffer from this fact?

9 How is material wealth related to happiness? How is it possible to be happy
without wealth? How is it possible to have abundant wealth without being happy?

10 What are some of the obstacles to the wider use of our material and cul-
tural resources?

11 In what sense are the things people do for fun as important as "necessary"
work?

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UNIT EIGHT — REVIEW • WHAT ARE THE USES OF BIOLOGY?

Far back in the earliest stages of man's existence, human beings must have
had some sort of knowledge about life, about living things, about the human
body and its workings. These ideas about plants and animals, about pain and
hunger, about plagues and famines, together made up the "biology" of any
particular tribe or family, of any particular period or region. These ideas
guided the practices by which man lived. While other animals learn from
experience, human beings appear to be the only ones that invent words and
signs which enable them to carry experiences from one to another, as from
parents to children. Men also invent imaginary beings to help them explain
how things work. These inventions or ideas may be in the form of ghosts and
goblins or in the form of natural forces or "principles". They help in many
ways to carry on the needed work. But often they keep us from making the
best use of experiences and resources. They may actually interfere with learn-
ing from further experience.

When ancient peoples began to keep records of their cattle and crops, their
priests had already begun to write down their secret wisdom. They recorded
good and evil plants and animals, correct ways of ensuring good harvests or
increasing livestock, secrets about curing various sicknesses or about over-
coming a drought. We should probably rate most of this lore as not very
reliable, perhaps even as superstitious. At least, we cannot understand how
the color of an ox used in plowing, for example, can influence the growth and
ripening of the grain; or how the symbols painted over a barn-door can en-
sure the health of the cattle. Primitive biology often mixed religion and
morals with practical rules and prohibitions; but it served.

Modern biology, as a branch of scientific study, has made rather sharp
separations between what is and what we wish or fear. It has attempted to
analyze the actual workings of all kinds of plants and animals, both in their
outside relations and in the inner processes of organs and tissues. These studies
furnish much more dependable understandings of our own body and the
conditions essential to its healthy growth and development than we ever had
in the past. As a result, we have completely revolutionized our ideas about
keeping human beings well and supplying them with what they need.

By developing scientific methods of dealing with problems, we learned
rather suddenly to overcome some of the oldest of the obstacles to the enjoy-
ment of life. The causes of many sicknesses are definitely known. Promising
research on the causes of others is under way. Bacteria, protozoa and viruses
could not have been known in earlier periods, because they cannot be re-
vealed without our modern instruments and techniques. As invisible but
unquestionably powerful agents, they could in the past be reasonably con-
sidered as "spirits".

676

Epidemics that formerly wiped out from 15 to 50 per cent of a population
have come under control. Several communicable diseases are no longer the
leading causes of death. Not only are people generally better nourished and
better able to work and play, but the life span has been substantially length-
ened. We have not conquered death, but we have postponed the funerals
for millions of men, women and children now living, by an average of ten
years or more.

The many measurable improvements in health and the tremendous in-
crease in usable materials of plant and animal origin are due to advances in
various branches of biology. But biology does not advance by itself. Basic
reasons why all sciences developed rapidly in the past century are the great ex-
pansion in popular education, a great increase in the amount of reading, and
improved communications among workers of different nations. But these
things are not independent happenings. They are related to one another, and
they are related to the so-called industrial revolution, which made possible
the rapid development of productive technology. These industrial changes
set free more and more time that people could use for exploring, ex-
perimenting, thinking and research. The resulting gains in turn helped to
accelerate the process.

These tremendous gains have not been universal. Large sections of the
population are still undernourished, badly housed, suffering from preventable
sicknesses and deficiencies, and still living in gross ignorance and superstitions
and fear. Yet there is hardly a farmer who does not make use of modern
science. He uses chemical knowledge about fertilizers, bacteriological knowl-
edge about life within the soil, soil knowledge and water knowledge about
plowing and cultivating. He uses genetic knowledge in deciding what types
of seed to use, mycological knowledge and entomological knowledge in pro-
tecting the crops against pests. His daily work with his livestock involves a
wide range of specialist knowledge regarding each particular type of animal,
and again he uses the knowledge of the biochemist, the bacteriologist, the
geneticist, the physiologist.

It would be absurd to pretend that each farmer is an expert in all branches
of biology, as well as the other sciences. Yet his present-day performances
and his achievements would not be possible without the work of hundreds of
specialists. Indeed, if he could himself carry in his own head all the knowledge
of these many specialists, he could not possibly use that knowledge through his
own activities. That is to say, this modern farmer makes daily use of countless
discoveries from laboratories scattered throughout the world; he spreads
seeds, fertilizers, poisons and sprays assembled from all quarters of the earth;
and he works the soil with machinery brought from widely scattered factories
and made of many different metals and other materials which he could not
gather by himself in a lifetime.

677

No one person can be "scientific" by himself. The science which we use
is a social product that has involved countless workers from all over the
world for generations. Using our science depends also upon thousands of
widely scattered technical jobs that furnish multitudes of materials and prod-
ucts. These have to be distributed through commercial channels and placed
finally in the hands of the individual "scientific" farmer or "consumer".

Using scientific knowledge, devices and practices for preventing sickness
and for maintaining health involves similar complications and interrelations.
One keeps well or gets well through public and private agencies and through
professional workers — doctors, dentists, nurses, pharmacists, hygienists, bac-
teriologists, pathologists, radiologists, anesthetists, sanitarians, and other
socialized aids and assistants.

We have abolished pain and hunger and other physical suffering — in spots.
But those very qualities of human beings that have made possible all their
civilization in the past have created new demands — which are not so easily
satisfied. For man has enlarged his world and strengthened his control through
his imagination and invention and curiosity and experimentation. It is
through his language and social interactions that he has accumulated ex-
periences from all regions and all ages to use upon particular problems. But
these characteristics sensitized him also to new kinds of unhappiness.

Man seems to need symbolical, or representative, activities that assure
him of his own worth and ability — and that impress others. He must satisfy
these inner needs through work and play. If he cannot find forms of activity
that are socially acceptable, he is likely to find modes that are socially offensive
— bullying, browbeating, tricky mischief, cruelties. Various peaceful pursuits
normally furnish individuals outlets for both their physical energies and their
need to assert themselves and express themseKes. The arts and crafts, games
and specialized collecting, and numerous ma\ing interests should serve. But
some individuals seem incapable of mastering such interests sufficiently or of
finding them satisfactory. Then they find their happiness in forms that result
in exploiting or abusing others. Or perhaps society has not yet succeeded in
finding for all individuals civilized uses for their surplus time and energies.

The desire for power no doubt indicates something essential in "human
nature" — whether it appears in physical conflict, in social or economic domina-
tion over others, or in military forms. To let these forms persist is to let a few
attain their happiness at the expense of the multitudes. We need not seek
for a change in "human nature". A solution can come only through cultivat-
ing still further equally human qualities of regard for human dignity, of sym-
pathy and mutual aid, and through cultivating a better understanding of life,
its needs, its possibilities.

678

IN CONCLUSION

Man the Creator

Like beavers and blue jays, human beings can put together stones and
sticks and other odds and ends in their constructions. But human beings are
truly creative, for they are able not only to put together what they can grasp
with their hands, but also, through their thinking and imagination, to
abstract, or draw out, ideas from their experiences and then recombine them
into new ideas of things that never existed before. This we can see in the
imaginary creations of old mythologies — gorgons, flying horses, magic
carpets, evil spirits — and in the creations of artists.

Our practical work and our scientific thinking are also creative. Every-
body recognizes that the remarkable progress of modern times in the solving
of practical problems is connected with the growth of scientific knowledge.
But it is not due to knowledge alone. The results come from combining
people's purposes with the exact knowledge and big ideas of the scientists.
The inventor, or the "creator" of something new, does not make something
out of nothing. He combines elements of past experiences with ideas of a
need to be met. Edison is said to have admitted that there was nothing in
his electric lamp that had not existed before — glass bottles with air removed,
copper wires, charred fibers from a plant, and so on. It was the combina-
tion that was new, and revolutionary.

The great advances in modern times have resulted in large part from
inventing new devices and methods for carrying on the day's work or new
gadgets for our amusement. But perhaps of greater moment has been the
distribution of new understandings about the nature of the world, scientific
ways of thinking, scientific ways of solving problems. A common under-
standing of what makes things happen has made it easier to introduce new
methods of farming, for example, new methods of selecting, preserving and
preparing food or new ways of preventing sickness. But it has also enabled
more and more people to use scientific ways of solving their practical prob-
lems both at home and in industry, and it has greatly accelerated the process
of invention. It has made it easier for people to find out what is going on in
other parts of the world or what ideas and methods are being used else-
where; and it has made it easier for people to adjust themselves to new con-
ditions and new ideas.

In the very process of adjusting ourselves to new discoveries, new inter-
pretations, new practices, we are breaking down old habits, old prejudices,
old customs; and we are recombining elements of our own experience with

679

the experience of others into something new. That is creative, that makes
each day almost a new day, with new possibiUties that we could not have
anticipated.

The most striking achievements in the creative use of biological knowl-
edge are seen in the new species of plants and animals that have taken the
place of breeds formerly cultivated. These creations are made possible by
the same peculiarity of the human mind as is revealed in the other creative
arts — the trick of analyzing and synthesizing. We analyze what different
strains of cattle, cotton, beans, hens, tomatoes, dogs, strawberries, wheat and
horses can do, what qualities they have. Then we set to work to combine
useful or interesting qualities from different strains into new combinations
and so produce new types of cattle, cotton, beans and so on.

This is not quite as simple as the work of the child who makes some-
thing "new" by drawing the shape of a pear and laying on it the color of a
black cat. But essentially the creative process is the same. There is the
analyzing of the things we observe into the different components or quali-
ties. These elements are abstracted, or taken away, from the objects by our
own thinking — the shapes, colors, dimensions, roughness, conductivity, hard-
ness and so on. These qualities are "abstract", they do not exist by them-
selves; but, with our imagination and our language, we can both "think"
about them and tell others about them. In a particular situation, to meet a
particular need or mood, we make up a new combination of these "abstrac-
tions"— in our minds. To be able to produce something real with the new
combination of qualities takes more time and more than merely thinking.
But while such imagining and thinking are not sufficient, they are necessary
conditions for "creating" new plants and animals.

Another creative use of biology is seen in the transformation of a cretin
into a more nearly normal human being. This was made possible by analyz-
ing certain organic processes, structures and relationships. We check on the
"ideas" that go into explaining the facts by experimenting — by performing
certain planned acts under controlled conditions. The test of an idea is in the
answer to the question How does it work out ? Later we use our knowledge
to prevent the appearance of cretins. Similarly we have cured rickets and
then prevented rickets. Getting rid of communicable diseases over larger and
larger areas means the creating of new living conditions; but in time it may
mean creating a new population.

We are now creating such a new population. Here and there in various
civilized communities men and v/omen are growing up undisturbed by the
fears and anxieties that destroy the mental health of those who are ignorant
and superstitious. They do not fear lightning and thunder, for they do not
associate these phenomena with evil spirits or mysterious powers seeking to
destroy human beings. They do not fear an eclipse of the sun, or the witches

680

who would poison wells. They do not fear famine, pestilence or plagues, for
they rely upon the techniques which enable us to control much more effec-
tively than ever before the operation of soils and waters, fertilizers and seeds,
tractors and harvesters, as well as the means for combating insect pests and
microbes. They do not fear their neighbors, for they have learned tliat their
own welfare and their health are tied up with the health and welfare of
their neighbors, and they carry on with their neighbors a constant inter-
change of goods and services, of ideas, sports, music and art.

Such populations are new not only in their freedom from the anxieties
that cripple millions of people everywhere. They differ from the others also
in their outlook on the future. By using their science in their daily work,
they are able to assure to everyone the essentials of decent living. They there-
fore have an exceptionally broad margin of time and energy to use for
activities that only human beings can carry on — just for fun. They can play.
They can travel. They can explore. They can experiment. They can analyze
ever new areas of human experience. And they can create.

Not everybody can make music or paint pictures or write verse that others
will care about. But every healthy person can create. He can create in ways
that give him satisfaction, give him the feeling that he is a person, some-
thing more than a machine, something more than an animal. He can do
something distinctive — even if no more important than a parlor trick or a
wisecrack, something that gets friendly recognition and approval, at least
for the moment. He can make himself useful to those around him as a
person, not merely as a hand.

Science Disarranges Things Some of us have no interest in science.
Perhaps we are too busy with other things, or we protect ourselves against
all new ideas. Yet we cannot escape what science is doing to our manner
of life. The achievements of scientific research are daily brought to our
attention not only through the newspapers and magazines, but through
changes in the things we have to buy. There are new packages, but new
ways of preparing the contents too. Our food materials come from remote
corners of the earth, and we eat new preparations of what formerly had not
been used. Today cotton fiber, as well as cotton oil and filterpress residue
and other materials, serves us in totally new ways. At the beginning of this
century, cottonseed oil was not used as human food at all. Soybeans and a
dozen other crops have come to be important features of American agri-
culture in comparatively recent years. We raise fur-animals on farms instead
of waiting for trappers and hunters to bring the pelts. And new furs that
trappers never saw are being created — such as the white mink, derived from
an albino mutation.

Some of the gains of science reach the ordinary person through various
professional workers. Dentists and physicians change their methods. They

681

use new materials and new instruments. They make a diagnosis more
quickly or less annoyingly. They perform their operations more expedi-
tiously or painlessly. Nearly every trained worker, in almost every field, is
constantly saying to his public, "We don't do things that way now, we do
thus instead, for the scientists have found out that . . ." The service he
renders may be several years more modern than his diploma, even if it is
not up to the sensational statement in this morning's paper.

At the same time, we are very far from making full use of the power
which our science and technology obviously make possible. Some men and
women in every occupation continue to operate as they have always done.
What was good enough for their fathers they consider good enough for
them. They do not seem to recognize that what was good enough for their
fathers was the best to be had at the time. It is no longer good enough
when a large part of the population can do better. Besides, the same meth-
ods today are really not the same. Farming on virgin soil, for example,
allowed a succession of good-enough crops. The same procedure on ex-
hausted soil is the same only in carrying out the same motions. To continue
old procedures when the conditions have changed is like repeating magic
words and magic gestures without knowing what they mean or how they
are supposed to produce their magical effects.

Obstacles to Progress There are many obstacles to making prompt use
of new knowledge. Nearly every home, every farm, every industry or busi-
ness establishment, has on hand equipment and supplies and materials that
have been serviceable in the past. To take on a new style of living or operat-
ing would mean to make a considerable part of these assets worthless. In
our daily dealings we try to make the old car or the old furniture last as
long as possible. When we do have to install new equipment, we try to
trade in the old for whatever it will bring. In fact, we cannot afford to scrap
all the old things. From the business point of view, putting new ideas to
work nearly always means scrapping old machinery and equipment, or
getting new capital, or both.

Putting new scientific ideas to use often means designing new machinery,
organizing plans for operating it, planning changes in distribution or sell-
ing. It means training workers. Older workers often resist such training.
Many feel that if their skills were valuable in the past, they must continue
to be valuable into the future. The really good craftsman, however, like the
competent professional worker, has been continually adjusting himself as
new ideas, new tools, new materials, came along. One of the most useful
things an individual can learn is just this trick of making constant adjust-
ment to the changes in our ways of working, as well as in our ways of living.

Each step involves its own particular difficulties and obstacles, expenses
and risks. And each, of course, takes time. When the advertiser gets around

682

to telling you about the very latest, there must have been months, or even
years, of planning and changing and getting ready.

Perhaps the chief obstacle to making fuller use of scientific discoveries
and scientific ways is the attitude of the general public, which has not been
educated to understand science as something that concerns everybody. Edu-
cation has meant for most people, until recently, learning what's what and
blocking the road to everything different — which includes everything new.
The great obstacle is thus in ourselves. Most of us are willing enough to
replace our old clothing or furniture with something more fashionable. But
we are not so ready to replace old habits or old beliefs — or old feelings.
Particularly are we afraid of anything that threatens our comfort or security.
Scientific discoveries, scientific theories and new inventions come into con-
flict with our customary thinking, our established advantages or special
privileges.

The Cost of Improvement At any given moment we may be able to
figure out that a particular change would be an improvement — insulating
the roof, for example, or using some new plastic in place of wood. An elec-
tric refrigerator is an improvement on the icebox. In a particular family the
details can be worked out — and now you have your refrigerator. But what
about the iceman? How about the man who cut and stored ice from the
lakes during the winter ? How about those good icehouses remaining idle or
cracking up ? How about the man who had been trucking sawdust to the
icehouses or ice to the railway station ? Those people are all very far away,
and we do not have to think about them. Besides, we cannot be responsible
for everybody.

Every change that is brought about by our scientific advances has far-
reaching consequences — for better very often, but also for worse. The re-
frigerator and the internal-combustion engine and methods for fixing
atmospheric nitrogen were not worked out by biologists, but they all have
a direct bearing on our using biological knowledge. That is, we can apply
our knowledge of plant needs to raising crops by using the chemist and the
electrician to supply nitrogen for soil that lacks it. We can use tractors to
ease our working of the soil. Our trucks can redistribute materials that are
excessive in one area and deficient in another. Improved transportation en-
ables us to bring our soil products to cities far from the cultivated lands.
And our refrigerators enable us to keep food from spoiling for a long period.

On an average, we are making great advances. But we are becoming
more and more concerned with what happens to particular men and women
and to their children as a result of our advances. It is, of course, not the
"improvements" that make trouble, but the dislocations or disarrangements
without which we seem unable to put the improvements into effect. It has
been nobody's business what happens to the iceman, or to Chile's nitrate-

683

diggers, or to the horse-raiser, the harness-maker, the wheelwright. It has
been nobody's business if the iceman and others Hke him feel themselves
pushed out of modern life, with all its exciting improvements.

It should not be difficult for us to understand why the iceman found
natural ice superior to mechanical, or artificial, ice. Or why the harness-
maker thought that it must be bad for our insides to be shaken up by the
automobile. Or why the candlemaker and dealer in oil lamps suspected that
electric light must be bad for the eyes. If we have used these various mod-
ern devices without harm, we may suspect that persons are biased in their
judgments by their special interests.

Science Is Objective In scientific research it is necessary to guard
against the fact that we are all influenced by our interests, by our earlier
experiences and associations. We are all likely to form advance judgments,
or pre-judices. Scientists therefore try very hard, in thinking of their prob-
lems, to avoid the usual human concerns and anxieties and purposes as much
as possible. We say diat the scientist tries to describe what is, no matter
what the effect may be on people's likes or dislikes, their losses or profits.
That is what is meant by saying that "science attempts to form judgments
uninfluenced by considerations of value".

One of the unfortunate consequences of separating "value" considerations
from scientific pursuits is that many grow up with the idea that there is
some special virtue in disregarding human feelings and interests. That is
why scientists often appear "cold", or indifferent to people's sentiments.
When the scientist watches his microscopic preparations and his test tubes
and his indicators, he must not let himself or his observations be influenced
by what he would like the results to be. He must record unflinchingly just
exactly what he finds. But it is foolish to pretend that the scientist's efforts
and results are "good for their own sake".

The efforts and findings of the scientist, aside from amusing the scientist,
are good only because they may help human beings ease their difficulties,
solve their real problems, enrich their lives. To be sure, we must not expect
the scientist to tell us day by day of what use his findings are. Some dis-
coveries are not ready for us to use until many years after the discoverer is
dead. Some cannot be used until after certain other discoveries have been
made, or certain devices have been perfected. But we do have a right to ask
the scientist whether he conceives his efforts to be of human value, or of
interest to himself alone. We have a right to ask this because the scientist's
work is really paid for by all of us, and it is made possible by the accumula-
tions of learnings and ideas from the past. These inheritances from the past
belong, of course, equally to all of us; but the scientist is the person who has
had the opportunity to master a part of this heritage and is in a position to
manage it. He manages it, however, as society's custodian.

684

There is another question that is becoming more and more urgent for
us to answer in connection with science. Since science grows in a special
social medium, which furnishes the opportunities and the heritage from the
past, and since making use of science depends upon very complex organiza-
tion and wide co-operation, we shall have to answer the question Who owns
science? Is it the individual investigator making a particular discovery? Is
it the university or other laboratory in which he works ? Is it the individual
or corporation that hires the scientist, often using his results for private gain
rather dian general advantage?

Man's adjustments to life depend more and more upon his imagination
and intelligence and invention. They depend more and more upon the di-
vision of labor, co-operation on a larger and larger scale, and more socializa-
tion of effort. Science cannot continue to serve us unless we give it a chance
to serve the whole community, the entire race. For if we do not use it crea-
tively to serve all, but let it be turned aside for private or partial interests,
we shall convert the power which science yields into the most destructive
that man has yet tried to control. Any individual or any group that seeks
to control science becomes the enemy of all mankind.

685

APPENDIX A

Grouping of Plants and Animals

We separate all the forms of living things we know into "plants" and "animals"
without any effort. All except a very few of the plant species have chlorophyl, and
all but a few remain in a fixed place. All the others we call animals, although there
are many species of animals that do not roam about. Some natural objects, however,
are unmistakably "living" and yet are not so easily classed as plants or animals. We
have seen that a "virus" resembles a chemical compound rather than a complex
living structure (see page 444) ; and yet a virus increases in quantity at the expense
of suitable "food", just as growing protoplasm does.

Other living forms that lie between plants and animals are the so-called "slime
molds", or Myxomycetes, which are sometimes classified as true fungi. In the active,
or vegetative, state the organism consists of a large mass of naked protoplasm con-
taining numerous nuclei. This mass moves about in an ameboid fashion, and is nega-
tively phototropic. When exposed to drying or to light, it develops rather complex
spore- bearing structures, resembling some of the molds.

Pleuiocoocua

>*r^Protopldst escaping
\ —^S^^ injm spore

Flagellate stages

Plasmodium

Slemonitia

Sporangium ^ Stauiastnim MiciasteriM

• Xanthidium

Euglena

Euglena is an example of a group of one-celled chlorophyl-bearing organisms that
are sometimes classed with the green algae (see illustration, below). But these
species have distinct "animal" traits. In the whiplike flagellum, or swimming lash,
the organism resembles the flagellate protozoa. In its method of swallowing food,
it resembles the ameba. Yet it is useful and convenient to think of living species in
these two main divisions — plants and animals.

Most of the names used in classifying plants and animals are Latin or Latin in
form. In these outlines all Latin names have been anglicized to facilitate their
pronunciation except where the Latin form is as easy or as familiar.

The outlines are, of course, not complete. The subdivisions have been carried
only as far as students are likely to need them. Groups which are of little interest
to any except the professional taxonomist have been either treated by a special
note or omitted entirely.

The successive subdivisions in the plant-and-animal classification scheme are
shown on pages 40 and 41; the "relatedness" of the various branches is shown in
the frontispiece.

687

Gleocapsa

Osdllatoria

Nostoc

SanjgQssum Laminana Didtoim

Polysipbonia

A. MAIN GROUPS OF PLANTS

The chief groups of plants are indicated in the following outline. As one be-
comes acquainted with more plants, it becomes necessary to use a more complete
classification.

PHYLUM I THALLOPHYTES ("bud or shoot plants"). Plants showing no
differentiation into true stem and leaf; include the smallest as well as the largest
plants in the world. The thallophytes have little in common except the absence
of distinct roots, stems, and leaves. All thallophytes, except the Class schizo-
phytes, reproduce sexually, that is by the fusion of protoplasm from two sources.
The schizophytes reproduce only by the simple division of protoplasm into two
masses. The presence or absence of chlorophyl distinguishes the two divisions of
the schizophytes; and it distinguishes the other two Classes of thallophytes—
the algae and the fungi.

CLASS 1 SCHIZOPHYTES ("splitting plants"). Each cell splits into two;
"^ no other mode of reproduction.

Order 1 Cyanophyceae ("blue seaweed"). Splitting plants with
chlorophyl— the "blue-green algae". Examples, Oscillatoria, Rivu-
laria, Nostoc.

Order 2 Schizomycetes ("splitting fungus"). Splitting plants with-
out chlorophyl— the bacteria (see illustration, p. 613).

CLASS 2 ALGAE ("seaweeds"). The chlorophyl-bearing thallophytes; all
live in water or in moist places.

Order 1 Chlorophyceae ("green seaweed"). The green algae;
usually yellowish green. Examples, pleurococcus, desmids, stonewort,
sea lettuce, spirogyra (see illustration, p. 375).

Order 2 Phaeophyceae ("dusky seaweed"). The brown algae;
mostly marine. Examples, Laminaria Sargassum, giant kelp, sea palm,
bladder wrack (see illustration, p. 111).

Shelf fungus

(Po//ponis)

Water mold

TrufQe

Edible moiel

Black knot

Ergot Com smut
ton rye)

Boletus

688

Remdeer moss

Cross section ol
Uchen tballus

Section oi thallua

PoreUa

Order 3 Rhodophyceae ("rose seaweed"). The red algae; mostly
marine; attached to rocks; reddish to purple. Examples, Nemalion,
or threadweed, Polysiphonia, Batrachospermum.

CLASS 3 FUNGI ("mushrooms"). Thallophytes without chlorophyl.

Order 1 Phycomycetes ("alga fungus"). Algalike fungi; no divi-
sions in hyphae. Examples, water molds (often parasitic on fishes),
Phytophthora (the cause of potato rot), downy mildew, black or bread
mold (see illustration, p. 375).

Order 2 Ascomycetes ("bladder fungus"). Fungi bearing spores in
sacs; hyphae divided into cells. Examples, cup fungi, the edible morel,
the mildews, black knot, yeast (see illustration, p. 371).

Order 3 Basidiomycetes ("basidium fungus"). Fungi bearing spores
on outside of a steplike structure called a basidium, from basis, or
pedestal. Examples, rusts, smuts, mushrooms, pore fungi, shelf fungi,
puffballs (see illustration, p. 594).

Group 4 Lichens These curious structures are compound growths of
fungi and algae. The fungal partner is generally an ascomycete; the
algal partner is a green alga related to pleurococcus or to one of the
blue-green algae. Examples, rock tripe, reindeer moss, Iceland moss,
Spanish moss.

PHYLUM II BRYOPHYTES ("moss plants"). Mosses and their allies. This
phylum of plants shows several advances over the algae and fungi. There is a
well-marked sexual reproduction with archegonia and antheridia, as well as defi-
nite formation of spores; all have a regular alternation of sexual and asexual
generations. There is no vascular system, that is, no specialized conducting tissue
in the supporting structures.

CLASS 1 HEPATICAE ("liver"). Liverworts; body consists of flat, leaf-
like, green, forking thallus; live in moist places. Examples, Marchantia,
Riccia.

Plant

Section of leal
Peat moss

Haiicap moss

Maium

'^s^

689

MAidenhaii fern
iAdiontum)

Christmas fem

(Polysttchum)

Horsetail
{EquiMttum axveiue)

Ground pine
(X/copodi'iuD obacuma)

Ground cedar

iLycopodium
complonatum) \

Shining clubmoss
(£/copoabua lucidulum}

CLASS 2 MUSCI ("moss"). Mosses; small erect or trailing plants with a
beginning of differentiation into stalk, leaflike outgrowths, and rootlike
hairs; spores borne in capsule, at end of hairlike bristle. Examples, sphagnum,
or peat, moss, hair-cap moss, fern-leaf moss, pin-cushion moss, pigeon-wheat
moss.

PHYLUM III PTERIDOPHYTES ("fern plant"). Ferns and their allies; have
distinct leaves, stems, and roots with vascular system; archegonia and an-
theridia present in prothallus, or sexual, generation; spore-bearing asexual gen-
eration grows into trees in some species.

CLASS 1 FILICALES ("fern"). The ferns; have large pinnately veined
leaves csdled fronds; young fronds uncoil from buds and suggest "croziers";
roots and stems anchored in soil; sporangia in characteristic clusters called
sori (see illustration, p. 387). Examples, polypody fern, Christmas fern,
cinnamon fern, bracken fern, sensitive fern, tree ferns.

CLASS 2 EQUISETALES ("horse bristle"). The horsetails; erect, fluted,
jointed, green stems grow from horizontal underground stems; leaves cluster
around vertical stems, suggesting shape of horse's tail; sporangia borne in
conical structure at tip of stems. Examples, scouring rushes, horsetails.

CLASS 3 LYCOPODIALES ("wolf foot"). The club mosses. Small ever-
green plants usually found in moist woods; sporangia in club-shaped cones.
Examples, ground cedar, ground pine, shiny club moss, ground cypress,
selaginella.

PHYLUM IV SPERMATOPHYTES ("seed plants"). Seed-bearing plants;
produce true seeds which arise from fertilized eggs, and also spores. There is a
true alternation of generations, as in the mosses and ferns; but that is not so
easily observed, since the egg-and-sperm, or sexual, generation can be studied
only with the use of microscopes and difficult preparation of materials. As in the
case of the ferns, the familiar generation is the spore-bearing one. The pollen cor-
responds to spores (see illustrations, pp. 12, 31, 412, 399-408, 410).

W«li»-iobia

Century plant

Date palm

Pineapple

Peanut

Junaon weed

Foxglove

Milkweed

SoyNvin

iTtjjuuni

(ilgavil

W^atna)

lAnaaasi

(AiwJUa)

lAtfura)

Wiailalu)

iAadtpiOM)

(So/aaas)

690

CLASS 1 GYMNOSPERMS ("naked seed"). Naked-seed plants; include
all the cone-bearing trees. Examples, cycads, ginkgo, sago palm, yews, larches,
pines, cypress, spruces, cedars, sequoias.

CLASS 2 ANGIOSPERMS ("enclosed seed"). Enclosed-seed plants; most
of the familiar plants belong to this class; includes the broad-leaved trees,
shrubs, grasses, herbs, vegetables, fruits, and farm crops.

SUBCLASS 1 MONOCOTYLEDONS With one cotyledon; bundles scat-
tered throughout the stem; parallel- veined leaves; flower parts usually in 3's
or 6's. Examples, cat-tail, water plantain, grasses and grains, sedges, palms,
Indian turnip, rushes, spiderwort, lilies, bananas, orchids (see illustration,
p. 146).

SUBCLASS 2 DICOTYLEDONS With two cotyledons; woody bundles
arranged symmetrically in stem; net- veined leaves; flower parts usually in
4's or 5's (see illustration, p. 147).

Order 1 Archichlamydeae ("primitive coat, or envelope"). Petals
in flowers either quite separate or entirely lacking. Examples, catkin-
bearing trees (willows, walnuts, oaks, beeches), smartweed, pink family,
buttercup family, water lilies, rose family, parsley family, bean family.

Order 2 Svmpetalae ("joined petals"). Petals united into tube or
cup. Examples, heath family, primrose family, gentian family, mint
family, morning-glory family, plantain family, madder family, honey-
suckle family, composites (daisy, aster, sunflower, goldenrod, etc.).

B. MAIN GROUPS OF ANIMALS

The main branches of animals and the subdivisions of the more important
branches are outlined below.

PHYLUM I PROTOZOA ("first animals"). The simplest animals; body of
one cell; live for the most part in fresh or in sea water, but many species are
parasitic in plants and animals.

CLASS I SARCODINA ("flesh"). Body without definite shape; move by
means of false feet, or pseudopods (see illustrations, pp. 23 and 25).

CLASS 2 MASTIGOPHORA ("whip-bearing"). Body of definite shape
enclosed in cuticle; move by means of one or more whiplike flagella (see
illustration, p. 179).

Ameba radiosa

Actinophiys

RAdiolarUn

(Heliospbacra QctiDOta}

AieeUa

^^^V^ 1 1 \ \ \ Foranuniieran Trypanost

VorUcella

Spirosiomiuo

691

Euplectella Cbalina oaslata

Euspongia
oflicinalia

Coral
ICoralhum zubnia)

Sea walnut
(PkuiobracbtQ pileu$)

CLASS 3 INFUSORIA ("poured into"). Move and feed by vibrating hair-
line projections called cilia, which extend through the tough outer covering;
abound in hay-infusions.

CLASS 4 SPOROZOA ("spore animals"). Parasite forms; produce spores
at some stage in the life cycle; malaria fever, Texas cattle fever, and the silk-
worm disease pebrine are caused by representatives of this group (see illustra-
tions, p. 622).

PHYLUM II PORIFERA ("pore-bearing"). Consist of innumerable similar
cells supported on a porous calcareous, siliceous, or horny skeleton; mostly
marine.

PHYLUM III COELENTERATES ("hollow mtestine"). Radially symmet-
rical animals having a single cavity in the body; all aquatic, mostly marine;
many have a marked alternation of generations in their life cycle.

CLASS 1 HYDROZOA ("water animal"). Exatnples, fresh-water hydra,
certain small jellyfish (see illustrations, pp. 274 and 384).

CLASS 2 ANTHOZOA ("flower animal"). Examples, most sea-anemones,
most corals (see illustration, p. 92).

CLASS 3 SCYPHOZOA ("cup animals"). Examples, most of the larger
jellyfish.

CLASS 4 CTENOPHORE (ten'ofor, "comb-bearer"). Examples, comb
jellies and sea walnuts. The ctenophores differ from the coelenterates in
many essentials and are sometimes classed as a separate phylum.

PHYLUM IV FLATWORMS (Platyhelminthes, "flat worms"). Ribbonlike
soft-bodied animals without skeleton; many are parasitic. Examples, tapeworm,
liver fluke, planarians (see illustrations, pp. 615 and 229).

PHYLUM V ROUNDWORMS (Nemathelminthes, "thread worms"). Small
cylindrical, soft- bodied animals without skeleton, unsegmented, both parasitic
and free-living forms (see illustration, p. 615). Examples, hookworm, trichina,
ascaris, thorn-headed worm.

Anthocepbala

Ascaris

Tnchinella

Case building rotifer

{FloscuJaiia)

Glass worm

692

(Opiu'opiioJ

_ cucumber!

P' ITbyone) /j .'>

Sea uichin
^ {Arbacia)

Sea mouse
iAphrodjf)

PHYLUM VI WHEELWORMS (Trochelminthes, "wheel worms"). Minute
"worms" with front end of body cihated and hind end usually forked; the
beating cilia on the rotifers give impression of one or more revolving wheels;
abound in stagnant water.

PHYLUM VII ECHINODERMS ("spiny-skinned"). Radially symmetrical
marine animals; usually with calcareous spines in skin and with well-developed
water-tube system (see illustration, p. 230).

CLASS 1 ASTEROIDS. Starfish.

CLASS 2 OPHIUROIDS. Brittle stars.

CLASS 3 ECHINOIDS. Sea urchins.

CLASS 4 HOLOTHUROIDS. Sea cucumbers.

CLASS 5 CRINOIDS. Sea lilies.

PHYLUM VIII ANNELIDS ("ringed"). Cylindrical worms with segmented
bodies; red blood in a closed circulatory system; comparatively highly developed
nervous and sensory system. The two most important classes are represented by
earthworms and sandworms, which have bristles, or setae; and leeches, which are
without bristles and have a sucker at each end.

PHYLUM IX ARTHROPODS ("jointed legs"). Have jointed limbs, a hard
outer covering, the exoskeleton, and segmented bodies; jaws work sidewise.

CLASS 1 MYRL^PODS ("thousand legs"). The millepedes, with incon-
spicuous antennae and two pairs of legs on each segment; and the centipedes,
with conspicuous antennae and one pair of legs on each segment.

CLASS 2 CRUSTACEANS ("crusty shells"). Head and thorax fused into
a cephalothorax; five or more pairs of legs; water-breathers; antennae.
Examples, crayfish, crab, shrimp, barnacle, sow-bug, lobster (see illustrations,
pp. 173, 359, 391, 420 and 461).

CLASS 3 ARACHNIDS (spiders, "spinners"). Four pairs of legs; air-
breathers; no antennae; a cephalothorax. (The horse-shoe crab is an excep-

Sow bug

693

tion in that it is a water- breather and has six pairs of legs.) Examples, scor-
pions, spiders, daddy longlegs, tarantula, mites, ticks (see illustrations, pp. 617
and 561).

CLASS 4 INSECTS ("cut in"). Body segmented; three distinct parts —
head, thorax, and abdomen; three pairs of legs; usually two pairs of wings;
antennae; compound eyes; breathe air through numerous branching tubes
called tracheae; metamorphosis of some forms includes tgg, larva, pupa, and
adult stages (see illustrations, pp. 352, 353 and 655). This important class
comprises more than half the animal species. The chief orders are as follows:

Order 1 Diptera ("two-wings"). Hind pair of wings reduced to tiny
knobs, or balancers; complete metamorphosis; sucking or piercing
mouth. Examples, mosquitoes (see illustration, p. 623), gnats, midges,
houseflies, stable flies, botflies, warbles, fruit flies (see illustrations,
pp. 489, 490, and 513).

Order 2 Lepidoptera ("scale- wings"). Rigid membranous wings
covered with minute scales; complete metamorphosis; sucking pro-
boscis. Examples, all butterflies and moths (see illustrations, pp. 180,
263, 353, 391 and 655).

Order 3 Hymenoptera ("membrane- wings"). Complete metamor-
phosis; biting or sucking mouth. Examples, wasps, hornets, bees,
ichneumons, ants (see illustrations, pp. 352 and 410).

Order 4 Coleoptera ("sheath- wings"). The front wing a hard pro-
tective cover; complete metamorphosis; mostly with biting mouth.
Examples, beetles, weevils, fireflies, ladybird, June-bug (see illustra-
tions, pp. 352, 596 and 655).

Order 5 Heteroptera ("unlike- wings"). Front pair of wings
usually leathery at base and membranous near tip; incomplete meta-
morphosis; sucking mouths. Examples, all true bugs, squash-bug,
water- bug, bed-bug.

Order 6 Homoptera ("like- wings"). Usually have two pairs of wings
with front pair uniform in texture throughout; incomplete metamor-
phosis; sucking mouths. Examples, cicadas, plant lice, scales, hoppers,
white flies.

Order 7 Orthoptera ("straight- wings"). Wings lying parallel with
body or folding lengthwise; incomplete metamorphosis; biting
mouth. Examples, locusts, crickets, walking sticks, katydids, cock-
roaches, mantis.

694

Order 8 Odonata ("toothed"). Four elongate, net-veined wings,
almost exactly alike; incomplete metamorphosis; large biting mouth.
Examples, dragon flics, damsel flies.

Order 9 Isoptera ("equal-winged"). Four leathery wings of equal
width; incomplete metamorphosis; biting mouth; whitish lx)dy.
Example, termites (see illustration, p. 179).

Order 10 Neuroptera ("net wings"). F'our elongate wings with
cross-veins; complete metamorphosis; biting mouth. Examples, ant-
lions, aphis-lions.

Order 11 Suctoria ("sucking"). No wings; complete metamor-
phosis; sucking mouth; body flattened from side to side; hind legs
fltted for jumping. Example, fleas.

Order 12 Siphunculata ("tube"). No wings; incomplete meta-
morphosis; sucking mouth; body flattened from top to bottom.
Examples, lice, cooties.

PHYLUM X MOLLUSKS ("soft"). Unsegmented, soft-bodied animals, most
of them bearing shells. The most important classes are

CLASS 1 GASTROPODS ("belly-footed"). Having shells of a single piece.

CLASS 2 PELECYPODS ("hatchet-footed"). Bivalve, that is, shells have
two valves. Examples, oysters, piddocks, scallops, mussels, shipworms, clams
(see illustrations, pp. 32 and 209).

CLASS 3 CEPHALOPODS ("head-footed"). The foot partly surrounds
the head and has a number of arms, or tentacles. Examples, octopus, cuttle-
fish, squid, nautilus.

PHYLUM XI CHORDATES ("cord"). Animals having an internal axial basis
for a skeleton, called a notochord, from which the vertebral column develops. A
number of small animals have this structure, which suggests the beginning of
such a column, but never develop a true backbone. Examples, acorn worm,
lancelet, sea squirt. These animals are included among the chordates in subphyla
distinct from the vertebrates. All the common large animals are vertebrates.

SUBPHYLUM VERTEBRATES ("joint" or "turning"). Includes all animals
with segmented backbone. The five important classes are as follows:

CLASS 1 PISCES ("fish"). Fishes are aquatic, cold-blooded animals; they
have a two-chambered heart. The stone hag and the lamprey are sometimes
called fishes, though they are distinct in having sucking mouths, no jaws, no
side fins, and a smooth skin without scales. They never develop bones; the
skeleton is of cartilage.

Order 1 Elasmobranchs Cartilage skeleton; platelike gills; no gill
covers; no air bladder. Examples, skates, rays, sharks.

Order 2 Ganoids Armored fishes; large bony scales in skin, es-
pecially around the head; have gill covers and air bladders. Examples,
sturgeon and gar pike (see illustration, p. 457).

695

Order 3 Teleosts Bony fishes; have scales in skin; air bladder.
Examples, salmon, herring, perch, cod, flounder (see illustrations,
pp. 173, 210 and 421).

Order 4 Dipnoi ("double breathers"). Fishes with lunglike struc-
tures, as well as gills; certain species skip over mud flats when tide is
out;' others burrow, in mud and live through the hot dry season in a
mucus-lined cocoon. Found only in the Southern Hemisphere.

CLASS 2 AMPHIBIANS ("double life"). Breathe by means of gills in
early stages, familiar to us as tadpoles, and later develop lungs; have bony
skeleton with two pairs of appendages and a three-chambered heart; cold-
blooded; skin is without scales. Examples, frog, toad, newt, salamander, mud
puppy (see illustrations, pp. 211, 309, 355, 379 and 421).

CLASS 3 REPTILES ("crawl"). Wholly air-breathers; dry scaly skin;
four-chambered heart; cold-blooded; eggs large, with a membranous cover-
ing. Four orders are usually recognized :

Order 1 Chelonia Protective shell composed of bony plates covered
with horny plates; toothless jaws. Examples, turtles and tortoises.

Order 2 Serpents Reptiles without legs. Examples, snakes, adders,
cobras (see illustrations, pp. 4 and 422).

Order 3 Lacertilia Body and tail usually long and slender, with
four legs. Examples, lizards, chameleons, horned toad, Gila monster,
glass snake (see illustration, p. 230).

Order 4 Crocodilia Large, semiaquatic, four-legged animals; though
air-breathers, can remain under water for five or six hours without
drowning. Examples, alligators, crocodiles, caymans, gavials.

CLASS 4 AVES ("birds"). Warm-blooded; four-chambered heart; cover-
ing of feathers; front limbs are wings; air spaces in bones; no diaphragm;
eggs have limy shells; horny beak, no teeth.

Living species of birds can be conveniently divided into the running, or
flightless, birds (ostrich, cassowary, emu) and the Jlying birds. In this classi-
fication the more important orders of flying birds have been grouped, so far
as possible, according to their habitats, since the shapes of the limbs and beak
are so distinctly associated with the mode of life. Some of the more im-
portant orders of the flying birds are listed below, with examples of typical
families (see illustrations, pp. 30, 178, 293, 362, 392 and 649).

Order 1 Divers. Loon family, grebe family.

Order 2 Tube-nosed swimmers. Shearwater and petrel family, storm-
petrel family.

Order 3 Pelican tribe. Tropic- bird family, pelican family, gannet and
booby family, cormorant family.

Order 4 Storklike birds. Heron and bittern family, stork and wood-
ibis family, ibis and spoonbill family, flamingo family.

696

Order 5 Anseriformes ("goose-like"). Swan, goose, and duck family.

- Order 6 Cranes. Wading marsh-dwellers. Crane family, limpkin
family, rail family.

Order 7 Shore-birds tribe. Gull and tern family, plover and turnstone
family, woodcock, snipe, and sandpiper family, auk and puffin family,
skinner family.

Order 8 Falcon tribe. Diurnal birds of prey. Vulture family, kite,
hawk, and eagle family, falcon family.

Order 9 Owl tribe. Nocturnal birds of prey. Typical owl family,
barn-owl family.

Order 10 Galliformes ("hen-like"). Hen family, grouse and ptar-
migan family, partridge and quail family, pheasant family, turkey
family.

Order 11 Columbiformes ("pigeon-like"). Pigeon and dove family.

Order 12 Psittaciformes ("parrot-like"). Parrot, parakeet, and
macaw family.

Order 13 Cuculiformes ("cuckoo-like"). Cuckoo, road-runner, and
anis family.

Order 14 Caprimulgiformes ("goatsucker-like"). Goatsucker family
— nighthawks, whippoorwills, etc.

Order 15 Hummingbird tribe. Swift family, hummingbird family.

Order 16 Kingfisher tribe. Kingfisher family.

Order 17 Piciformes ("woodpecker-like"). Woodpecker family,
which includes flickers and sapsuckers.

Order 18 Passeriformes ("sparrow-hke"). Perching birds; in-
cludes most of our common birds. Lark family, swallow family, jag,
magpie and crow family, titmouse and bush-tit family, nuthatch
family, creeper family, wren family, mockingbird and thrasher family
(see illustration, p. 424), thrush and bluebird family, warbler and king-
let family, wagtail and pipit family, waxwing family, shrike family,
starling family, vireo family, wood-warbler family, weaver-finch and
sparrow family, European tree sparrow, meadowlark and blackbird
family, tanager family, grosbeak, finch and bunting family.

CLASS 5 MAMMALS ("breast"). Suckle young; hairy covering; four-
chambered heart; warm-blooded; diaphragm. Except in the orders mar-
supials and monotremes, the embryos receive nourishment from the blood
of the mother through a placenta, which becomes embedded in the uterus wall
of the mother, and the young reach an advanced stage of development before
birth (see page 423).

SUBCLASS and Order 1 Monotremes Egg-laying mammals; eggs hatch
outside the body. Examples, duckbill, spiny anteater.

697

SUBCLASS and Order 2 Marsupials Pouched mammals without placenta;
eggs develop within the body of the mother, but young are born in a very
immature state, and continue to develop within a pouch on the mother's ab-
domen, where they attach themselves to her teats. Examples, kangaroos,
wombats, opossums, koalas, Tasmanian wolves, Tasmanian devils, wallabies,
bandicoots, pouched rats, pouched mice (see illustrations, pp. 426 and 549).

SUBCLASS Placental mammals Conveniently classified according to the
hard tissues at the ends of the "fingers" and "toes."

Order 3 Edentates ("toothless"). Clawed feet. Examples, sloths,
armadillos, hairy anteaters, scaly anteaters, aardvarks.

Order 4 Chiroptera ("hand- wings"). Clawed feet. Example, bats.

Order 5 Insectivores ("insect-eating"). Clawed feet. Examples,
flying lemurs, moles, shrews, hedgehogs.

Order 6 Rodents ("gnawing"). Clawed feet. Examples, rats, mice,
hares, rabbits, pikas, squirrels, chipmunks, gophers, woodchucks,
prairie dogs, muskrats, beavers, capybaras, cavies, porcupines.

Order 7 Carnivores ("flesh-eating"). Clawed feet. Several distinct
and widely distributed families (see illustrations, pp. 463 and 548).

Dog family. Wolves, coyotes, foxes.

Hyena family.

Catfaynily. Lions, tigers, leopards, cheetahs, jaguars, ocelots,

pumas, bobcats, domestic cats.
Moitgoose faynily.

Bear family. Black bear, grizzly bear, polar bear.
Marten family. Otters, minks, weasels, ferrets, wolverines, skunks,

badgers.
Raccoon family. Coatis, kinkajous, pandas (see illustration, p. 425).
Sea- lion family. Sea lions, fur seals.
Walrus family.
Seal family. Ringed seal, harbor seal, elephant seal.

Order 8 Artiodactyls ("even-toed"). Hoofed feet.

Suborder Suina ("pigs"). Examples, hippopotamus, swine, peccaries.

Suborder Ruminants ("cud-chewers"). See illustration, p. 174.

Camel family. Camels, llamas.

Deer family. Moose, elk, caribou, antelopes, waterbucks, gazelles.
Girafe family . Giraffes, okapis.

Oxen family. Gnus, goats, sheep, cattle, musk oxen, water
buffaloes, yaks, bison (see illustrations, pp. 7, 78, 588 and 651).

Order 9 Perissodactyls ("odd-toed"). Hoofed feet. Examples,
horses, asses, zebras, tapirs, rhinoceroses.

Order 10 Proboscidians ("with proboscis"). Hoofed feet. Example,
elephants.

698

Rhesxu monkey

Order 11 Sirenia ("siren"). Aquatic mammals with flippers. Ex-
amples, sea-cow, manatee, dugong.

Order 12 Cetacea ("whale"). Aquatic mammals with flippers.

Whalebone, or baleen, whale family. Whalebone whales, right
whales, gray whales, humpback whales, rorquals.

T oothed- whale family . Sperm whales, beaked whales, killer whales,
white whales, narwhals, dolphins, porpoises.

Order 13 Primates ("first"). The leading order of animals, including
man; flat nails at ends of digits, usually five on both hands and feet;
thumb and great toe usually opposable.

Suborder Lemuroids ("lemur-like"). Small furry animals; some
digits have nails, other claws; doglike snout. Aye-aye family, tarsier
family, lemur family.

Suborder Anthropoids ("man-like"). Nails on all digits with excep-
tion of the marmosets, which resemble man in face only.

Marmoset family.

New World monkeys. Nearly all have long grasping tails and flat
noses; thumb not opposable except in capuchin monkey. Ex-
amples, howling monkeys, squirrel monkeys, spider monkeys,
capuchin monkeys, owl monkeys, titis monkeys, woolly
monkeys.

Old World monkeys. Tail not grasping; narrow nose with nostrils
pointed downward; bony external ear; thumb opposable.
Examples, baboons, mandrills, macaques.

Simians (apes). Large, no distinct tail, thumb opposable, narrow
nose, bony external ear, arms longer than legs; have an appendix.

Gibbons. Long arms and legs; smallest of apes.
Orangutans. Long arms, small flat ears.
Chimpanzees. Large ears, short stout body, intelligent.
Gorillas. Small ears, largest of apes.
Humans. The human race (see illustrations, pp. 47, 52 and 517).

Howler

699

APPENDIX B

Supplementary Readings

When using encyclopedias or other general reference books or textbooks,
it is helpful in each case to locate the parts that are of special interest by means
of the table of contents or of the index. For each unit of this text, several
special books are listed in the pages following. In addition, some of the more
general sources of interesting reading matter are suggested. Most of the
items are listed under their authors' names, which are arranged alphabetically;
the most important book for a particular reader may appear at the very end
of the list. Many of the books are not too specialized, and contain material
of interest in connection with topics in two or more units. Each book is
listed only once, however; and it is hoped that the reader will discover the
resources of each book for later use.

Each agricultural experiment station and the extension division of each
state university or college of agriculture in the several states publish useful
bulletins and pamphlets.

The United States Department of Agriculture will send lists of Farmers
Bulletins and other biological publications.

The Superintendent of Documents, Government Printing Office, Wash-
ington, D.C., issues free lists of government pamphlets on forestry, plants,
health, children, birds, wild animals, food and other subjects.

College textbooks on agricujtuje, biology, botany, hygiene, physiology,
zoology and so on make useful reference books.

Yearbooks of the Department of Agriculture and the annual reports of
the Smithsonian Institution can usually be obtained through the Congressman.

Books on natural history, exploration, geography and biography often con-
tain material that is interesting to the student of biology.

BucHSBAUM, Ralph. Animals without Backbones. University of Chicago Press, 1938.
[Splendid illustrations, mostly from photographs, with reliable and not difficult reading.]

Carlson, Anton J., and Johnson, Victor. The Machinery of the Body. University of
Chicago Press, 1941. [Well-told and well-arranged accounts of the parts of the body
and their workings.]

Darwin, Charles. Voyage of the Beagle. Macmillan, 1933. [Surprisingly interesting
look around the world by a young man who turned out to be a great scientist at heart.]

HoGBEN, Lancelot. Science for the Citizen. Knopf, 1938. [A very modern and very large,
but also very exciting book; to be taken in small doses.]

Snyder, Emily Eveleth. Biology in the Malting. McGraw-Hill, 1940. [An easy introduc-
tion to the men who made biology, how they tackled their problems — and why.]

701

Wells, H. G., Huxley, Julian S., and Wells, G. P. Science of Life. Doubleday, 1934.
[An excellent organization of interesting and informative material about all aspects of
life; best used as a reference book with the help of the index.]

UNIT ONE • WHAT IS LIFE?

Collingwood, G. H. Knowing Your Trees. American Forestry Association, 1941. [Il-
lustrated from photographs of the flowers, fruits, leaves and bark of trees, as well as
entire trees.]

Fasten, Nathan. Introduction to General Zoology. Ginn and Company, 1941. [This college
textbook can serve as a stimulating survey of the forms and problems of animal life.]

Hegner, Robert. Parade of the Animal Kingdom. Macmillan, 1935. [Good pictures and
interesting natural-history accounts by a distinguished biologist.]

Jaques, H. E. How to Know the Insects. Published by the author. Mount Pleasant, Iowa.
[Convenient key to common orders and famihes, with practical help for collecting and
mounting.]

Peterson, Roger Tory. A Junior Bool^ of Birds. Houghton, 1941. [A good introduction
to the more common forms.]

Pool, Raymond }. Basic Course in Botany. Ginn and Company, 1940. [While intended
for college students, this book contains interesting information about plants, especially
as they take part in the transformation of matter upon the earth.]

RoMER, Alfred S. Man and the Vertebrates. University of Chicago Press, 1939. [Helpful
survey of backboned animals; good illustrations.]

UNIT TWO • UNDER WHAT CONDITIONS CAN WE LIVE?

Dahlgren, B. E. The Story of Food Plants. Field Museum, Chicago, 1940. [A good sur-
vey of the plants that man has used in various parts of the world to advance his own life.]

Furnas, C. C, and Furnas, S. M. Man, Bread and Destiny. Reynal & Hitchcock, 1937.
[How man's efforts to feed himself have changed the face of the earth.]

Lamb, Ruth de Forest. American Chamber of Horrors : the Truth about Food and Drugs.
Farrar & Rinehart, 1936. [Some useful information about food and drugs as biological
problems, and especially as problems created by the social nature of the human species.]

Peattie, Donald Culross. The Flowering Earth. Putnam, 1939. [A fascinating account
of chlorophyl in making the world a charming possibility for life.]

Taylor, Clara Mae. Food Values in Shares and Weights. Macmillan, 1942. [A useful
combination of the latest scientific information about nutrition, with a practical scheme
for working out dietaries.]

Food and Life. United States Department of Agriculture Yearbook for 1939.

UNIT THREE • HOW DO LIVING THINGS KEEP ALIVE?

Cannon, Walter B. The Wisdom of the Body. Norton, 1940. [How the parts of the body

influence one another in maintaining a united front in relation to the changes of the

surrounding world.]
de Kruif, Paul. The Fight for Life. Harcourt, 1938. [.\ very lively account of men's

efforts to find remedies for their bodily ills.]
Gerard, Ralph W. The Body Functions. Wiley, 1941. [Very readable and informative

on what the title promises; written for grownups but quite usable by younger people.]
Needham, James G. About Ourselves. Cattell Press, 1941. [The kind of being man is,

both as an organism and as a social and emotional and intelligent being.]

702

Silverman, Milton. Magic in a Bottle. Macmillan, 1941. [About the medicines people
use, what we know about them, and also some of the things we do not know.]

Williams, Jesse Fiering, and .Oberteuffer, Delbert. Health in tlie World of \Vorl{.
McGraw-Hill, 1942. [.\11 except a very few of us work or expect to; this book tells
us about how our health affects our work and also about how our work affects our health
— and what we can do about it.]

UNIT FOUR . HOW DO THE PARTS OF AN ORGANISM WORK TOGETHER?

Allee, W. C. The Social Life of Animals. Norton, 1938. [How the individuals of various
species behave in relation to one another.]

Edman, Irwin. Arts and the Man. Norton, 1939. [The connection between our senses,
our enjoyments, and our creations.]

(Gregory, Jennie. The ABC of the Endocrines. Williams & Wilkins, 1935. [A picture-
book introduction to the glands of internal secretion.]

Menninger, Karl A. The Human Mind. Knopf, 1937. [A very absorbing introduction
to the nature and workings of our minds and our emotions.]

Sure, B. The Little Things in Life. .•Xppleton-Century, 1937. [Hormones, vitamins,
enzymes, etc., and how they influence metabolism and behavior.]

Teale, Edwin Way. Grassroot Jungles. Dodd, Mead, 1937. [Insect life and special adap-
tations; beautiful illustrations.]

UNIT FIVE • HOW DO LIVING THINGS ORIGINATE?

Gerard, Ralph W. Unresting Cells. Harper, 1940. [Includes technical material on the

living that goes on in cells, but reads easily and draws you on.]
Keliher, Alice V. Life and Growth. Appleton-Century, 1941. [Answers clearly the

most common questions about the beginnings, development and adjustments of the in-
dividual human being.]
Knott, James E. Vegetable Gardening. Lea, 1941. [A practical guide to the running of a

garden, applying important principles regarding the development and reproduction of

plants. ]
Levine, Milton I., and Seligman, Jean H. The Wonder of Life. Simon and Schuster,

1941. {.\ simple introduction to the facts of reproduction and early development.]
QuiNN, Vernon. Seeds — Their Place in Life and Legend. Stokes, 1936. [Interesting in-
I formation on the practical aspects of plant seeds in human affairs.]
Strain, Frances Bruce. Being Born. Appleton-Century, 1937. [An elementary account

of reproduction and development.]

UNIT SIX • HOW DID UFE BEGIN?

Benedict, Ruth, and Weltfish, Gene. The Races of Manl^ind. Public Affairs Pamphlets,
1943. [A simple and rapid survey of the problem of races, especially of races living
together.]

Klineberg, Otto. Race Differences. Harper, 1935. [Interesting results of experimental
comparisons of races, without prejudice; helps us to clear up what is and what is not
important.]

Lucas, F. A. Animals of the Past and The Hall of Dinosaurs. American Museum of Natural
History. [Two interesting and well-illustrated museum manuals, containing a great deal of
interesting information on both the facts and the interpretation of life forms of the past.]

703

ScHEiNFELD, Amram. You and Heredity. Stokes, 1938. [An amusingly wrkten and illus-
trat«i account of heredity among human beings, full of varied and reliable information-
a special section on the inheritance of musical talent.]

Whitney, David D. Family Treasures. Cattell Press, 1942. [Fully illustrated records of
the inheritance of various physical features of human beings.]

United States Department of Agriculture Yearbooks: 1936, Better Plants and Animab I-
1937, Better Plants and Animals, II. Government Printing Office. [Splendid reference
books on both the practical and the theoretical aspects of improving domesticated breeds
oi plants and animals.]

UNIT SEVEN . WHY CANNOT PLANTS AND ANIMALS LIVE FOREVER?

CoLCORD, Joanna C. Your Community, Its Provisions for Health, Education, Safety and
Welfare Russell S^ge. Foundation, 1941. [A good outline to suggest what to look for
in deciding upon the practical steps citizens have to take to further the life and welfare
of the community.]

Eberson, Frederick. The Microbe s Challenge. Cattell Press, 1941. [Makes clear every-
body s concern with the interrelations between the various microbes and the human race ]

Fitzpatrick, Frederick L. The Control of Organisms. Bureau of Publications, Teachers
College, Columbia University, 1940. [An interesting survey of man's methods for en-
couraging or suppressing various species of plants and animals that bear upon our lives ]

Root, Amos J. The ABC and XYZ of Bee Culture. Root, 1935. [A very good practical
manual on all phases of raising bees and making them produce honey for us.]

Sears, Paul B. Life and Environment. Bureau of Publications, Teachers College Colum-
bia University, 1939. [An interesting and eye-opening account of the interactions be-
tween plant and animal communities.]

Zinsser, Hans. Rats, Lice and History. Little, Brown, 1935. [A delightful and enter-
taining book about things in general, but particularly about typhus fever and the rela-
tion of trivial animals to the course of history.]

UNIT EIGHT . V/HAT ARE THE USES OF BIOLOGY?

Bell, Howard N. Youth Tell Their Story. American Council on Education, 1938.
Based on interviews with young people; clears up the connections between the prob-
lems each one has to face and the changing customs of the entire population.]

Butler, Ovid. American Conservation in Picture and Story. American Forestry Associa-
tion, 1935. [Easy reading; shows how far-reaching the influences of any industry or
business can be.]

de Kruif, Paul. Health Is Wealth. Harcourt, 1940. [Snappy account of the relation
between our general welfare and the controllable factors that influence our health ]

Furnas, C. C. The Next Hundred Years. Reynal & Hitchcock, 1936. [A survey of what
science has done to change our lives, with an attempt to look ahead to further changes
in our welfare and our ways of living.]

Huxley, Julian S. Science and Social Needs. Harper, 1935. [Based on radio interviews
with British scientists and others; easy reading and full of suggestions about the chang-
ing world.]

United States Department of Agriculture Yearbooks: 1940, Farmers in a Changing World;
1938, Soils and Men. [Excellent surveys of the relationship between man and the soil, and
of the great changes brought about in our lives by the growth of science, seen especially
from the point of view of the farming population but full of significance for all of us.]

704

INDEX

Key : fate, pref ace, care, am, in f^nt, arm, ask, so id, eve, e vent, end, re cent, ev er, ice, ill,
old, 6 bey, orb, 6dd, con nect, food, foot, use, u nite, urn, up, cir cms

Abdomen (ab do'men), of mammals, 14; of

insects, 15
Absorption, by root, 142 ; of digested food,

170f.
Accretion (akre'sh/m), 19
Acquired characters, 465 f.
Activities, energy needs for, 121 ff.
Adaptation, 20, 550 ; in plants, 255 ff.
Adenoid (ad'e noid), 205
Adjustments, 89 ff., 269
Adrenals (ad re'nalz), 305, 307
Adrenin (ad ren'in), 307, 313
Aeration (a er a'shfm) of soil, 83
Aesthetic values, 662 f.
Afferent nerve, 277, 282, 284
Agglutination test, 241
Agglutinin (a gloo'ti nin) , 242
Air, and seeds, 81 ; and life, 83 ; composition

of, 84 ; and energy, 84 ; as rav^' material, 85
Air bladder, 173
Air-tubes, 207
Albumen, 97
Albumin, 220

Alfalfa, tubercles of, 152, 203
Algae (al'je), frontispiece, 25, 688 f.
Alimentary canal, 165
"AlkaH disease", 102, 103
Alkaloids, 216, 231
AUergy (al'er ji), 242
Alligators, 211

Alternation of generations, 383 ff.
Aluminum, 103
Alveolar glands, 170
Alveoli (al ve'6 h), 205
Ameba (cme'bc), 10, 23, 24, 25; digestion

in, 164; functions in, 273
Amino-acids, in protein, 97, 123 ; as product

of digestion, 169
Amphibians, 38, 696 ; red corpuscles in, 189;

breathing of, 210 ; metamorphosis in, 355 ;

reproduction of, 378
Ampulla (am piil'a), 287
Anaerobic (an a er ob'ik) organisms, 209

Analogy, 458

Anaphylaxis (an a fi lak'sis), 243

Anatomy, 322

Ancon ram, 509

Anemia, 197

Anemone (a nem'6 ne), sea, 92

Anesthesia (an es the'zhic), 659

Anesthetic, local, 659

Anger, 316 f.

Angiosperms (an'ji 6 spunnz), frontispiece,
691

Animals, activities of, 17 ; cells of, 25 ; clas-
sification of, 41, 691 ff. ; predatory, 175;
excretion in, 216 ; removal of wastes from,
216 ff. ; heredity in, 481 ; breeding of, 498

Annelids (an'e lidz), frontispiece, 693

Anopheles (a nof'e lez), 621

Antennae (an ten'e), 14

Anther, 401, 403

Antheridia, 384, 385

Anthrax, 612

Anthropoids, 699

Antibodies, 236

Antineuritic vitamin, 133

Antirachitic (an ti ra kit'ik) vitamin, 133

Antiscorbutic (an ti skor bu'tik) vitamin,
133

Antiseptics, 618

Antisterility factor, 133

Antitoxin, 233 f., 236, 238, 239

Aorta (a or'tc), 190, 191

Apes, 699 ; and man, 53 ; characteristics of,
54

Aphids (a'fidz), 595

Appendages, of vertebrates, 48

Appendix, 167, 174, 175

Arachnid (a rak'nid), 693

Arc, reflex, 277

Arch, of fingerprint, 73

Archegonia, 384, 385

Arctic Alpine zone, 563

Areas of brain, 283

Argon (ar'gon), 84

705

Arrhenius, Svante (1859-1927), 152

Arsenic, 232

Arteries, 189

Arthropods (ar'thro podz), frontispiece, 693 ;

food tube of, 173 ; blood of, 207
Artichoke, 253
Ascorbic acid, 108, 109, 132
Assimilation, 19, 83 ; by cells, 343
Associative neurons, 275
Asthma, 242, 371
Athlete's foot, 614
Atmosphere, composition of, 83, 84
Atropin (at'ro pin), 231
Attitudes, 318, 332 f.
Augustine, 447
Auricle (6'ri k'l), 190, 191
Autonomic (6 to nom'ik) nervous system,

294 fif.
Auxins (ok'sinz), 258 ff.
Aves (a'vez), frontispieces, 696 f.
Aviation and circulation, 196, 207
Axis, nerve, 276 ff.
Axon (ak'son), 25, 275 f.

Bacillus colt, 639

Backbone, 46

Bacteria, 24, 25, 36, 688 ; on alfalfa roots,

152; and digestion, 164; coccus group of,

242 ; spores of, 371 ; as cause of disease,

612 ; type of, 613
Bacteriophage (bak ter'i o faj), 445
Baer, Karl E. von (1792-1876), 356
Balance of nature, 579 ff. ; disturbance of,

582 fif.
Balancing organs, 285, 286, 287
Banting, Frederick G. (1891-1941), 312
Barberry, 595
Barnacle (bar'no k'l), 92
Barriers, 461
Basal metabolism, 118 fif.
Basidium, 689
Bast, 144, 147

Bateson, William T. (1861-1926), 482
Batrachia {ha tra'kic), frontispiece
Bats, 698
Beaks, 178
Bear, 177
Bedbug, 177

Beetle, calosoma, 594, 596
Begonia, regeneration in, 231
Behring, Emil von (1854-1917), 237, 240

"Bends", 207

Beriberi (ber'i ber'i), 104 ff., 125
Bernard, Claude (1813-1878), 302
Best, Charles H. (1899- ), 312
Biennials, 180
Bilateral symmetry, 13, 14
Bile, 168, 189; and vitamin K, 132
Binomial nomenclature, 36
Biogenetic law, 356
Biology, 4 ; kinds of, 6 f.
Birds, differences between, 30 ; digestive
system of, 173; size of, 176; beaks of,
178; migration of, 179, 181; breathing
of, 21 1 ; tropisms of, 260 ; pollination by,
408; development of, 421; destruction
of, 584 ; protection of, 586 ; classification
of, 696 f.
Bison, 7, 588
Bladder, 219
Blended inheritance, 482
"Blind staggers", 102, 103
Blood, clotting of, 108 ; corpuscles of, 186 fif. ;
circulation of, 189 ff. ; changes in, 192 ff. ;
types of, 197 ; of arthropods, 207 ; reac-
tions of serum of, 240 ff.
Blood banks, 197
Blood count, 188
"Blood-poisoning", 617
Blood vessels, in insect, 16; human, 189
"Blue baby", 192
Blueberries, 498

Body, plan of mammal, 13, 48 ; plan of in-
sect, 14; surface of, 117
Boll weevil, 653, 655
Bones, cells of, 25, 348 ; of vertebrates, 48,

100 ; defective formation of, 98
Boron, 103

Botulism (bot'uliz'm), 237
Boys, gain in weight by, 115 ; basal metabo-
lism of, 118 ff.
Brahman cattle, 7 ; in breeding, 496
Brain, human, 50, 51 ; of vertebrates, 278 ff. ;
and reflexes, 282 ; areas of, 283 ; size of,
297 ; ceUs of, 348
Bran, 125

Bread, requirements for, 125
Breathing, in man, 204 ff. ; in vertebrates,

209 ff. ; rate of, 296
Breathing tubes, in insects, 16
Breeding, for immunity, 496 ; practical,
497 £.; problems of 498 ff.

706

Bronchial tubes, 204, 205

Bryophyllum, regeneration in, 231

Bryophytes (bri'6 fits), frontispiece, 689 f.

Bubonic plague, 619, 625

Budding, 369

Butler salts, 196

Bulbs, 395

Burbank, Luther (1849-1926), 497

Burning of food materials, 83

Butterfly, 350

Cabbage, epidermal cells of, 87

Caecum (se'kr<m), 174

Calcium, 97, 98, 123 ; and parathyroids,
100; and heart action, 124; in flour, 128

Callus, 229

Calorie, 116

Calorimeter, respiration, 118, 120

Calosoma (kal 6 so'mc) beetle, 594, 596

Cambium (kam'bi um), 146, 147; in grafts,
369

Camerarius, Rudolf J. (1665-1721), 389

Canadian zone, 563

Cancer, 230

Canines, 177

CapiUaries, 189, 190

Carbohydrates, 98, 125 ; energy value of, 125

Carbon, in protein, 97

Carbon cycle, 148 ff.

Carbon dioxide, in air, 84 ; as raw material,
85, 138 ; test for, 93 ; and heartbeat, 302

Caries (ka'ri ez), 102

Carnivores (kar'ni vorz), 150, 151, 698;
teeth of, 177

Carnivorous plant, 542

Carotin (kar'6 tin), 110, 132

Carpels, 398, 399

Carriers, disease, 245

Cartier, Jacques (1491-1557), 103

Cartilage cells, 348

Casein (ka'se in), 97

Catkin, 408

Cattle, selenium poisoning of, 102, 103 ; and
ticks, 346

Caucasian, 63

Cells, 20 ff. ; division of, 10, 368 ; variety of,
24, 25 ; multiplication of, 24 f. ; diffusion
between, 85 ff. ; epidermal, 87 ; gas ex-
change of, 201 f . ; nerve, 273 ff. ; growth
of, 343 ff. ; differentiation of, 348 ; fusion
of, 374 ff.

Cellulose (sel'u los), 84, 86

Centipedes, 693

Central cyhnder of root, 143, 144

Cerebellum (ser e heViim), 281, 283

Cerebrum (ser'e br«m), 279 ff. ; functions of,
283

Cesspool, 631

Characters, in heredity, 475 ; combinations
of, 477 f. ; sex-linked, 488

Chemical influences on development, 357 f.,
360

Chicken, tissue of heart of, 323 ; develop-
ment of, 350

Chimpanzees, 699 ; brain of, 297

Chin, human, 50, 52

Chlorophyl (klo'rofil), 138, 141

Chloroplasts (klo'ro plasts), 27, 215

Chordates, food tube of, 173, 695

Chromatin, 368, 389

Chromosomes, 368, 376, 389 ; and inherit-
ance, 486 ff. ; and linkage, 488 ; numbers
of, 488 ; in man, 491 ; maps of, 491

Cities, biological problems of, 6 ; health
differences among, 600

Civilization, 72, 430

Clams, 92, 209, 695

Classes of plants and animals, 38, 688 ff.

Classification, 29 ff. ; basis of, 34 ff. ; of
plants and animals, 687 ff.

CHmate, influence of, 460, 462, 463

Cloaca, 173

Clotting of blood, 108, 133, 187

Club mosses, 690

Cocain, 659

Coccus (kok'ws) group of bacteria, 242

Cochlea (kok'lec), 286

Cockroach, 350

Cod-liver oU, 109

Coelenterate (se len'ter at), frontispiece,
692 ; reproduction in, 382

Coelocanth (se'16 kanth), 457

Colchicine (kol'chisen), 513

Colloids, 163

Colonies, coral, 382

Color blindness, 493

Communicable diseases, 617; combating,
620, 626 ff.

Communities, natural, 563 ff. ; formation of,
566 ff. ; climax, 568, 570

Competition and struggle, 554 f.

Composite (kom poz'it), 31

707

Compound eye, 14, 15, 290
Compound leaves, 43
Concentration and osmosis, 124
Conditioning, 266 ff., 316, 670 ff.

Conflicts, 670 ff.

Conjugation, 374, 375

Connectors, 275

Conservation, of forests, 590 ff. ; of soil, 156,
645

Convolutions of brain, 281

Convulsions, 124

Copper, in hemocyanin, 102

Copperhead, 4

Corals, 692

Cork ceUs, 91, 147

Corms, 372, 395

Corn, 12 ; stem of, 146; hybrid, 498, 499

Corn borer, European, 655

CoroUa, 401, 402

Corpuscles, red, 186, 189; white, 188

Correns, Karl (1864-1933), 479

Cortex, of root, 143, 144; of cerebrum,
279 ff., 283 ; of adrenals, 307

Cortin, 307, 314

Cotton aphid, 655

Cotyledon (kot i le'dzm), 145, 415

Cow, stomachs of, 174; teeth of, 176; milk
production by, 651

Cowpox, 235

Crab, 92, 391

Creation, special, 446 f .

Cretinism (kre'tm iz'm), 306, 309, 311

Crocodiles, 211, 696

Cro-magnon (kro ma nyon') man, 52, 57 ;
brain of, 297

Crop, in bird, 173, 176

Crops, rotation of, 151 f.; damage to, by
insects, 655

Crossing over, 494

Cross-poUination, 407 f.

Crustaceans, 101, 693 ; balancing organ of,
285 ; modification of, 357 ; sexual dimor-
phism in, 391

Crystalloids, 163

Cud-chewing animal, 174

Cultivation, of plants, 83, 155

Cultures, 429, 519 f.

Cuttings, 370, 373

Cuvier, Georges (1769-1832), 176, 447

Cypress, 204
Cysts (sists), 370 f.
Cytolysins (si tol'i sinz), 242
Cytoplasm, 368

Dandelion, 12

Darwin, Charles (1809-1882), 461, 464^
466 £f.

Davenport, Charles B. (1866-1944), 483

Davy, Humphry (1778-1829), 659

Death, 20, 527 ff. ; rates of, 605 f.

Deficiencies, nutritional, 100, 104 ff. ; of
ductless glands, 306 f .

Deficiency diseases, 104 ff., 133

Deforestation, 645

Democracy, 71

Dendrites (den'drlts), 25, 275 f.

Dermis (dur'mis), 217

Descartes, Rene (1596-1650), 262

Descent, 35 ; continuity of, 464

Development, influence of thyroid on, 309 -,
irregularities in, 335; of chicks, 350; of
frog, 351 ; similarities in, 354; conditions
for, 357 ff. ; changes in, 450 ; of verte-
brates, 459

Diabetes, 195, 307, 312 f.

Diaphragm, 205, 206

Diastase (di'a stas), 163 f.

Dicots (dl'kots), frontispiece, 145, 147, 691

Diet, minerals in, 123; planning a, 124 ff.;
shares of nutrients in, 126 f.

Differentiation, 61 ff., 351, 357 ff. ; lines of,
417 f.

Diffusion, 85 ff.

Digestion, 163 f . ; in man, 165 ff. ; intestinal,
168

Dimorphism (dl mor'fiz'm), sexual, 391

Diphtheria, 233 f., 235, 239, 240; carriers
of, 245

Diploid (dip'Ioid), number, 386

Diseases, specific tests of, 242 ; communi-
cable, 617 ; organic, 631

Distribution, geographic, 460 ff.

Division, of cells, 25, 344 ; nuclear, 368 ; of
labor, 529 ff.

Dobson fly, 209

Dog, teeth of, 177 ; conditioning of, 266 ff. ;
brain of, 281 ; pancreas of, 303

Dominant characters, 475 ; in plants, 480 ;
in animals, 481 ; in man, 500

Dorsal root, 279

708

Drives, fighting, 553

Ductless glands, 302 ff. ; functions of, 306 f.

Dunes, 19, 90

Dust storm, 643

Dusts, as occupational hazard, 636

Dwarfism, 306, 310

Ear, human, 289

Eardrum, 15

Earthworm, 208; tropisms of, 260; repro-
duction in, 388

Echinoderms (e ki'no durmz), frontispiece,
693

Ectoderm, 362

Edentates, 698

Education, 269, 430

Effectors, 275

Efferent nerve, 277, 282, 284

Efficiency and fatigue, 223

Egg, 125; fertilized, 348, 376; segmenta-
tion of, 361

Eijkman, Christian (1850-1930), 106

Electron microscope, 445

Elements, necessary chemical, 97 fl.

Elephant, 176, 698; brain of, 278

Elliptical leaves, 43

Embryo (em 'brio), of grain, 125; of ani-
mals, 349, 354 ; in flowering plant, 405 ;
in mammals, 423 f.

Embryo sac, 402

Emotion, organic sources of, 315 ff.

Encephalitis (en sef a ll'tis), 445

Endocrines (en'do krlnz), 296, 304 flf.

Endoderm, 362

Endosperm, 405

Energy, of protoplasm, 83 ; air and, 84 ;
forms of, 85; required, 114 f.; unit of,
116 ; expenditure of, 118 flf. ; needs of, by
workers, 123; value of, from nutrients,
125; radiant, 138; hormones and release
of, 312 f.

Enriched flour, 125

Entire leaves, 43

Environment, moisture in, 89; desiccated,
90; adjustments to, 269; and growth,
345 ; influence of, 357 f. ; limitations in,
533

Enzymes (en'zlmz), 164, 169

Epicotyl, 415

Epidemics, 580 f .

Epidermis (ep i dur'mis), 87, 141 , 144, 147, 21 7

Epiglottis, 205

Epinephrin (ep i nef'rin), 196, 307, 313,
314

Epiphysis (e pif'i sis), 306

Epithelial cells, 25, 348

Eras, geologic, 451

Ergograph, 223, 224, 225

Ergosterol (er gos'ter ol), 110, 132

Erosion, 154

Esophagus, human, 166, 167; of bird, 173;
of lobster, 173

Essential oils, 216

Euglena (u gle'na), 687

Evening primrose, mutations in, 511

Evolution, 514 ff. ; classical views on, 448

Excretion, in animals, 216

Exopthalmic (ek sof thal'mik) goiter, 306,
312

Exoskeletons, 101

Eyes, of mammals, 14; of insect, 14 f . ; in-
vertebrate, 290 ; vertebrate, 290, 291 ; in
embyro, 363

Facial features 13, 63

"Fairy ring", 587

Fallopian tube, 380

Family, 38, 430, 668

Family tree, of plants and animals, frontis-
piece

Fat glands, 217

Fat-soluble vitamins, 132

Fatigue, 222 ff.

Fats, 98, 125 ; energy value of, 125 ; test for,
183

Fauna (fo'nfl), of prairie, 78; of swamp, 78

Fear, 317

Feces (fe'sez), 171

Feelers, 14

Fehling solution, 183

Ferments, 164

Ferns, 385, 690 ; life cycle of, 387, 412

Fertilization, 376, 403 ; in flower, 404 ff.

Fertilizer, excess of, 87

Fetus (fe't«s), appendix of, 175

Fibrin (fl'brin), 187

Fibrovascular bundles, 91, 141, 144

Filaments, 400

Fingerprints, 73

Fish, 32, 695 f. ; digestive system of, 173;
breathing of, 210; heart of, 210

Fitness, 20 ; meaning of , 546

709

Fixation of nitrogen, 152 f.

Flagellates (flaj'^lats), 179

FlageUum (MjeVtim), 687, 691

Flatworms, 692 ; regeneration in, 229

Fleas and disease, 619, 625

Flies and disease, 619

Flora, swamp, 78 ; of prairie, 78

Flour, enriched, 125

Flowering plants, reproduction in, 398 ff. ;

life cycle of, 412
Flowers, 11, 12, 31; structure of, 398 ff. ;
fertilization in, 404 ff. ; as secondary
sexual structures, 408 f. ; interdependence
of insect and, 410
Fluorine (floo'orin), 102
Flying and circulation, 196
Food cycle, 560 f.

Food and Drug Administration, 125
Food tube of insect, 16
Foods, oxidation of, 83 ; and living proto-
plasm, 96 ff. ; need for, 1 14 ff. ; groups of,
124 f.; lOO-calorie portions of, 126 f.;
transportation of, 164; absorption of,
170 f.; protection of, 632; in wartime,
632
Forest Service, 591
Forests, virgin, 153 ; conservation of, 590 ff. ;

and water, 645
Fossils, 52, 450 ff.; "pickled", 452 f.; of

horse, 453 ; "refrigerated", 454
Foxes, inheritance in, 493 ff.
Frog, 38, 210, 211; development of, 351;
metamorphosis in, 355; reproductive
organs of, 379
Fronds, 371, 385
Fruit, 11, 12, 125

Fruit flies, 357 ; chromosomes in, 489 ; mu-
tations of, 512 f.
Fumes as occupational hazard, 636
Functional disorders, 629
Functions, 16, 18; balanced, 532 f.
Fungi (fun'jl), frontispiece, 689 ; disease due

to, 612
Funk, Casimir (1884- ), 107
Fusion of cells, 374 ff.

Gall bladder, 167, 303 ; in bird, 173
Gallinae (ga li'ne), 30
Gallium (gal'i iim), 103
Gametes (gam'Sts), 375 ; two kinds of, 385 f. ;
formation of, 389 ; of flower, 404

Gametophyte, 385

Ganglia (gang'glio), 276, 278, 279

Gas gangrene, 237

Gastric juice, 166 .

Gastrula (gas'troo Id), 362

Genes (jenz), 488, 491

Genetics (jenet'iks), 482; applications of,

496 ff.
Genus (je'nws), 37, 38
Geographic distribution, 460 ff.
Geotropism, in plants, 258, 260 ; in animals,

262
Germ, 125, 377, 507 f.
Germination, 82

Gestation (jes ta'shwn) period, 423
Gibbon, 699 ; brain of, 297
Gigantism, 306, 310
Gills, 208

Giraffe, 5; teeth of, 176
Girdling trees, 147

Girls, gain in weight by, 115; bai-al metabo-
lism of, 118 ff.
Gizzard, 173, 176
Glands, 172, 302 ; digestive, 167, 169; types

of, 170 ; fat, 217 ; ductless, 302 ff.
Glass snake, 229

Glomerule (glom'er ool), 218, 221
Glucose, oxidation of, 84
Gluten (gloo't^n), 97
Glycogen (gll'ko jen), 221
Gnu (noo), 7

Goiter (goi'ter), 306; distribution of, 101 '
Gonads, 305, 307, 314 f., 377
GoriUa, 51,699; brain of, 297
Government and health, 633
Grafting of organs, 362
Grafts, types of plant, 369
Grasses, of prairie, 78; of dunes, 90; of

Great Plains, 642
Grasshopper, 14 f., 352
Great Plains, 642
"Green-slime", 25

Growth, of animals, 17; of plants, 17; of
organisms, 19; food for, 114f. ; sub-
stances determining, 230, 257 ff. ; light
and, 255 f. ; steps in, 343 f. ; conditions
of, 344 f. ; limitation on, 345 ; reproduc-
tion and, 367 ff. ; period of, of mammals,
423
Grubs, 353
Guano (gwa'no), 150

710

Guard ceUs, 24, 141, 143

Guinea pigs, 107; scurvy in, 106; pigmen-
tation in, 479

GuUet, 166

Gums, 216

Gymnosperms (jim'no spurmz), frontispiece,
691

Gypsy moth, 353, 594, 596

Haber, Fritz (1868-1936), 153 f.

Habits, 318

Hair, color of, 63 ; follicle of, 217

Hales, Stephen (1677-1761), 146

Hand, human, 50

Haploid (hap'loid) number, 386, 403

Happiness, 658 ff.

Harvey, WiUiam (1578-1657), 185

Hatchery, 380

Hatching of insects, 352

Hay fever, 371

Hazards, occupational, 636 f.

Head, of mammals, 14; of insects, 14

HeaUng, 228 ff.

Health, and sickness, 326 ; and mind, 330 flf. ;

differences in, among cities, 607 ; and

social status, 607 ff.
Hearing, 286 f.
Heart, 189 ff. ; muscular action of, 124 ; and

carbon dioxide, 302
Heat, radiation of, from body, 116
Heidelberg man, 52
Height, variation in, 69, 70
Hehum (he'll iim), 84
Hemocyanin (he mo si'c nin), 102, 207
Hemoglobin (he mo glo'bin), 189, 205 f. ; de-
fective content of, 100 ; iron in, 102
Hens, egg production by, 649
Hepaticae (he pat'i se), 689
Herbivores (hur'bi vorz), 150, 151 ; teeth of,

176
Heredity, 472 ff . ; in plants, 480 ; in animals,

481 ; and reproduction, 483 ff. ; in man,

500
HereUe, Felix d' (1873- ), 445
Hermaphrodite (her maf'ro dit), 386
Hertwig, Oskar (1849-1922), 376
Hessian fly, 594, 655
Hibernation (hi ber na'shim), 177
Hilum (hl'lum), 415
Hippocrates (430-370 B.C.), 103, 301
Homeostasis, 193

Homologies, 458 ; invertebrate, 49

"Homunculus", 347

Hoof-and-mouth disease, 445

Hooke, Robert (1635-1703), 21, 22

Hookworm, 177, 244, 615, 616

Hopkins, Frederick G. (1861- ), 107

Hormones (hor'monz), 303 ff. ; plant, 258
ductless glands and, 306 f . ; and release
of energy, 312 f. ; and emergencies, 313
as unifiers, 315 ; and emotions, 315 ff.

Horse, appendix of, 175; teeth of, 176
fossils of, 453

Host of parasite, 177

Human body, 13 f. ; composition of, 97

Humming-bird, 176

Humors, 301, 304

Hunger, 195

Hybrid corn, 498, 499

Hybrids (hi'bridz), 474, 475 ff. ; human, 518

Hydra (hi'dra), specialization in, 274, 382,
384

Hydrogen, in protein, 97

Hydrophobia, 614

Hyphae (hi'fe), 375, 689

Hypocotyl (hi p6 kot'il), 415

Hypophysis (hi pof'i sis), 305, 306

Ignorance and sickness, 608 f .

Illness, causes of, 335

Illumination and growth, 252 ff.

Imagining, 57

Imitation by animals, 56

Immunity, 63, 234 ff. ; in plants, 244;

natural, 244 ; breeding for, 496
Inbreeding, 476
Incisors, 176
Individuals, differences between, 61 ff.,

71 ff. ; uniqueness of, 66; and equalitv,

71 f.
Indole-acetic acid, 258
Industries, hazards in, 637 f.
Infancy, among animals, 420 ff. ; in man,

354, 426 f.
Infant death rates, 545, 547, 606, 610
Infantile paralysis, 294, 445
Infection, chain of, 618
Influenza, 445
Infusoria, 692
Inheritance, 472 ff. ; and chromosomes.

486 ff. ; of differences, 507 f .
Inoculation, 235

711

Insectivores, 698

Insects, 14 f., 16, 694 f. ; air-tubes of,

207 f . ; water-breathing, 209 ; tropisms

of, 260 ; reproduction of, 381 ; sexual

dimorphism in, 391 ; pollination by, 408 ;

and disease, 618 ff. ; damage to crops by,

655
Insulin, 307, 312 f.
Interdependence, 652 f.
Instincts, 264 ff.
Internal secretions, 304 ff .
Intestine, 167 ff. ; lining of, 171 ; large, 171 ;

in bird, 173 ; in fish, 173 ; in lobster, 173
Invertebrates, reproduction of, 381 ff. ;

aquatic, 381
Iodine (I'o din), 98; and thyroid, 100, 101
Iris, color of, 63
Iron, 98, 123 ; in hemoglobin, 102 ; in flour,

128
IrritabiHty, 19 f.
Irritants, skin, 637
Isles of Langerhans, 307

James, WiUiam (1842-1910), 527

Japanese beetle, 595, 655

Java ape man, 51

Jaws, 16

Jellyfish, 32, 692

Jenner, Edward (1749-1823), 235, 236

June bug, 352

Kangaroo, appendix of, 175

Kelp, 688

Kenny, Elizabeth, 294

Kidney, of bird, 173; function of, 195,

218 ff.; human, 218
Koala (ko a'lc) bear, 426
Koch, Robert (1843-1910), 612
Kripton (krip'ton), 84

Labor, division of, 529 ff.

La Brea, 452, 455

Lacteal (lak'te(il), 171

Lactic acid, 222

Lamarck, Jean B. (1744-1829), 464 f., 467

Lanceolate (lan'se 6 lat) leaves, 43

Land types of North America, 569

Larvae (lar've), 179, 180, 263

Larynx, 100

Latex tubes, 215

"Laughing gas", 659

Laveran, Alphonse (1845-1922), 621

Lawes, John (1814-1900), 642

Layering, 370, 373

Lead, poisoning by, 231

Leaf, 11, 12; cells of, 24; variety in char-
acters of, 43 ; fall of, 91 ; photosynthesis
in, 138 ff.; transpiration in, 140; structure
of, 141 ; fibrovascular bundles in, 144,
145 ; in air and water, 203 ; illumination
and growth of, 252

Learning, 268 f . ; by doing, 667

Leech, 177

Leeuwenhoek, Anton van (1632-1723), 21,
22

Legumes (leg'umz), 31, 151

Lemurs (le'm»rz), 55, 699

Lens of eye, 15

Lenticels (len'ti selz), 143, 202

Lice and disease, 625

Lichens, 689

Liebig, Justus von (1803-1873), eA2

Life, 9 ff. ; preservation of, 20 ; origin of,
20 ; characteristics of, 20 ; and water, 78 ;
in the past, 437 f., 439 f . ; in space, 440 ;
beginnings of, 441 ff. ; from nonliving,
443 ff. ; and death, 527 ff. ; distribution
of, 534 ff. ; and light, 559

Life expectancy, 630

Life span of mammals, 423

Light, function of, 138 ff. ; and growth,
255 f. ; sensitiveness to, 289 f. ; and life,
559

Lime-juice for scurvy, 104

Linear leaves, 43

Linkage, and chromosomes, 488 ; in fruit
fly, 490

Linnaeus, Carl (1707-1778), 34, 36, 447

Lion, teeth of, 177

Lister, Joseph (1827-1912), 618

Liver, human, 167, 168; in bird, 173; in
fish, 173; and blood corpuscles, 189;
cells of, 348

Liver-fluke, 177, 615

Liverworts, 689

Lizard, skin of, 90 ; regeneration, 230

Lobed leaves, 43

Lobster, digestive system of, 173 ; regenera-
tion in, 229 ; infancy of, 420

Lockjaw, 233, 237

Locomotion, means of, 49

Locust, 350

712

Loeb, Jacques (1859-1924), 302

Loeffler, Friedrich (1852-1915), 240

Logwood tree, 7

Longhorn, 7

Loop of fingerprint, 73

Lumbering, 582 ff.

Lungs, 204 ff., 216

Lymph (limf), 170, 186 f.

Lymph vessel, 171

Magic, 328, 329

Malaria, 6, 177, 244, 371 ; and mosquitoes,
621 f., 624

Malpighi, Marcello (1628-1694), 21, 190

Mammals, frontispiece, 14, 46; body plan
of, 13 ; body pattern of, 48 ; breathing of,
211 ; endocrines in, 304 ; reproduction in,
379 f. ; reproductive organs in, 382, 383 ;
infancy among, 422 f. ; embryo in, 423 f. ;
growing periods of, 423 ; classification of,
697 ff.

Mammoth, 57, 456

Man, limbs of, 46, 49; "transparent", 47;
hand of, 50; brain of, 50, 51, 281, 297;
chin of, 50, 52 ; and ape, 53 ; uniqueness
of, 53 ff. ; characteristics of, 54 ; supe-
riority of, 56 ff. ; appendix of, 175 ; meta-
morphosis in, 347, 354, 356 ; infancy in,
426 f. ; chromosomes in, 491 ; heredity
in, 500 ; evolution and, 515 ; and struggle
for existence, 553 ff. ; as social organism,
554 ; as migrant, 572 ff. ; and balance of
nature, 582 ff. ; and birds, 584 ; produc-
tion of wealth by, 647 ff.

Manganese, 103

Maple, 37

Margins of leaves, 43

Marrow of bones, 1 89

Marsupials (mar su'pi 5lz) , 422, 549, 698

Marten, 548

IMass production, 224

Mayfly, 209

Measles, 244, 445

Meats, 125

INIedulla of adrenals, 307

Medulla oblongata (me dul'o 6b 'long ga'tfl),
283

Medusa (me du'so), 384

ISIembranes, 85, 86, 90 ; of embr\'o, 349

Mendel, Gregor (1822-1884), 474 ff.

Mental disturbances, 330

Mercury, poisoning by, 231
Merriam, John C. (1869- ), 452
Metabolism, 98, 114; and vitamins, 107;
, basal, 1 18 ff. ; hormones and rate of, 31 1 f.
Metals as occupational hazard, 636
Metamorphosis (met a mor'fo sis), in man,

345, 347, 351, 354, 356; in vertebrates,

345, 355 ; in insects, 352 f.
Metchnikoff (1845-1916), 188
Mexican bean beetle, 655
Microbes, 342 ; animal, 614
Micropyle, 415
Microscopes, early, 21
Migration, of birds, 179, 181 ; barriers to,

564 f . ; of man, 586 f .

Mildews, 371, 689

Milk, 125 ; production of, 651

Millepedes, 693

Milt, 377

Mind and health, 330 ff.

Minerals, needs of, 123 ; absorption of, by

plant, 142
Minnow, 357, 360
Mites, 616

Mitosis (mi to'sis), 395
Molars, 176

Molds, 689; water, 24; spores of, 371, 375
Mollusks (mol'zfeks), frontispiece, 695;

shells of, 100 ; balancing organ of, 285 ;

modification of, 357
Mongolian, 63

Monkeys, 55, 699 ; brain of, 281
Monocots, frontispiece, 145, 691
Monotremes, 697
Moose, 78

"Moral equivalent of war", 556
Morgan, Thomas H. (1866- ), 512
Morphin (mor'fin), 231
Morphology (morfol'ojT), 458
Mosquitoes, and disease, 619 ; and malaria,

621 ; and yellow fever, 621 ff.
Mosses, 371, 689 f. ; life history of, 383 f.,

412
Moth, 350; codling, 180; gypsy, 353;

hawk, 353
Motor nerves, 277
Mottled teeth, 102
Moultings, 350
Mouth, of mammals, 14; of insect, 15;

human, 50
Movement, of animals, 17 ; of plants, 17

713

MuUer, H. J. (1901- ), 512

Multiple factors, 482 f. ; in inheritance,
492 ff.

Mumps, 235, 445

Muscles, 292, 294, 296 ; and calcium con-
centration, 124

Mushrooms, 689; "fairy ring" of, 587

Musk-ox, 7

Mussels, 92

Mutations, 489, 490, 509, 510 ff.

Myriapods, 693

Myxedema (mik se de'mo), 306, 312

Naming, 29 ff. ; binomial, 36

Natural selection, 466

Nature, balance of, 579 ff.

Neanderthal (na an'der tal) man, 51, 52;
brain of, 297

Needs, human, 647 ff., 660

Negro, 63

Neon (ne'on), 84

Nerves, 275 ff., 277, 282, 284; in insects,
16; endings of, 217 ; impulse of, 292

Net-veined leaves, 43

Neuron (nu'ron), 25, 275

Neurosis, artificial, 670 ff.

New Stone Age, 55

Niacin, 108, 128, 132

Nicotinic acid, 128, 132

Night bUndness, 133

Nitrates, 150

Nitrogen, in air, 84 ; in protein, 97 ; fixation
of, 152 f.

Nitrogen cycle, 149 ff.

Nitrous oxide, 659

Non-communicable diseases, 628 ff.

Normal distribution, 68 f.

Normality, 66 ff.

Norms, 66 ff.

Nose, lining of, 288

Nucleus, of cell, 10, 24; of neuron, 275;
changes in, 368

Nutrients, organic, 98 ; sources of, 99 ; de-
ficiencies of, 100; energ>- value of, 125

Nutritive values in shares, 131

Nymph (nimf), 179

Occupational diseases, 634

Odors, 288 ; individual differences in, 64

Old Stone Age, 55

Ommatidium, 15

Omnivores (om'nivorz), 150

Opium, 659

Orangutan (6 rang'oo tan), 699 ; appendix
of, 175

Orbicular leaves, 43

Orchids, 408

Orders, 39, 688 ff.

Organisms, 18 ; difference of, from nonliving
things, 19 f.; anaerobic, 209; of the
past, 450 ff. ; grouping of, 562 f.

Organs, 18,354; comparison of, 18; graft-
ing of, 362

Osborn, Henry Fairfield (1857-1935), 53

Osmosis (osmo'sis), 86; in roots, 87, 143;
in living things, 87 f . ; and turgor, 88 ; and
concentration, 124 ; in leaf, 139 ; in blood
vessels, 187; in lungs, 192

Ostrich, 176

Otter, 548

Ova, 377

Ovary, 305, 307, 314, 377 ; in flowers, 398 ff.

Ovate leaves, 43

Oviducts, 380

Oviparous species, 378

Ovules, 398, 399, 402

Oxidation of food materials, 83

Oxygen, in air, 84; in protein, 97; from
photosynthesis, 138

Oxygen cycle, 149 f.

Oxyhemoglobin, 205 f.

Oyster, 388, 695

Pain, 658 f.

Pahsade cells, 24, 139, 141

Palmate leaves, 43

Pancreas, human, 167, 168; of bird, 173;

as ductless gland, 303, 305, 307 ; cells of,

348
Parallel-veined leaves, 43
Parasites, 177, 370, 614
Parathyroid (par a thi'roid) glands, 100, 305,

306
Parents, behavior of, 425
Pasteur, Louis (1822-1895), 341
Pavlov, Ivan P. (1849-1936), 266 ff., 670 ff.
Peas, Mendel's experiments with, 474 ff.
Pellagra (p^la'grc), 108, 125, 133
Penicillin, 240
Peptids, 169
Peptones, 168, 169
Perennials, 180

714

Periods, geologic, 451

Peristalsis (per i stal'sis), 168, 219

Perspiration, 217

Peruvian bark, 6

Petals, 401, 402

Petioles, 140

Phagocytes (fag'oslts), 188

Pharynx (far'ingks), 166, 205

Phloem (flo'em), 144, 145, 147

Phosphorus, 123 ; in protein, 97 ; poisoning
by, 231

Photosynthesis, 138 flf.

Phototropism, 256

Phyla (fi'lc), 38, 688 flf.

Ph^'lloquinone, 132

Physical differences, 61 f.

Pigeon, beriberi in, 104; brain of, 281

Pigmentation in guinea pigs, 479

Pigments, 63, 216

Piltdown man, 51, 52 ; brain of, 297

Pinchot, Gifford (1865- ), 91

Pineal body, 305, 307, 308

Pinnate leaves, 43

Pisces (pis'ez), frontispiece, 698 f.

Pistil, 398

Pith, 146, 147

Pithecanthropus (pith'e kan thro'pws) erec-
tus, 51, 515 ; brain of, 297

Pituitary (pi tu'i tar i), 305, 306, 308, 310,
314

Placenta (plo sen' to), 380, 423, 697

Planarians, 228, 692

Plants, parts of, 11 f.; activities of, 17;
cells of, 24 ; classification of, 40, 688 ff. ;
cultivation of young, 83 ; wastes from,
215, 216; storage in, 215; adaptive
movements of, 255 ff. ; alternation of
generations in, 383 ff., 412 ; reproduction
in flowering, 398 f. ; poUination of, 406 ff. ;
scattering seeds by, 409 ff. ; heredity in,
480 ; breeding of, 496 ff. ; struggle of,
540 ff.

Plasma, 186; reserves of, 197

Plasmodium, 371

Plasmolysis (plaz mol'i sis), 87

Platelets, 186, 187

Plover, golden, 179

Plowing, downhill, 154

Plumule, 415

Pneumonia, 242, 243

Poisons, 230 ff.

Polled cattle, 498

PoUen, 14, 400, 401, 403, 404, 406 ff.

Pollination, 406 ff.

Polyneuritis (pol i nu ri'tis), 104 ff.

Polyps, 382, 384

Poppy, 12

Population, economic elements of, 648

Porifera, frontispiece, 692

Portal vein, 191

Potassium, 100; and heart action, 124

Potato beetle, Colorado, 655

Poverty and sickness, 607 ff.

Prairie, flora and fauna of, 78

Precipitin (pre sip'i tin), 241

Predatory animals, 175

Preformation theory, 346 f.

Priestley, Joseph (1733-1804), 659

Primates (prima'tez), frontispiece, 46, 699;
brains of, 51, 279, 297

Proliferation, 228

Propagation, vegetative, 362, 372 ; artificial,
373

Proteins, 96 f. ; body use of, 123 ; energy
value of, 125 ; test for, 183

Proteoses, 169

Protoplasm (pro'to plaz'm), 22 ff. ; funda-
mental nature of, 25 f . ; streaming of, 26 ;
water in, 80 ff. ; food and, 96 ff. ; builders
of, 96 f. ; protein in, 97 ; action of, 97 f. ;
metabolism, 114; effect of foreign sub-
stances upon, 232 ff. ; variations in, 346

Protozoa (pro to zo'o), frontispiece, 274, 370,
691 f . ; parasitic, 614

Pseudop)odia (su do po'di a), 24

Pteridophytes (ter'i do fits), frontispiece, 690

Pulmonary artery, 191

Pulse rate, 296

Pupa (pu'po), 180

Purkinje, Evangelista (1787-1869), 22

Pus, 188

Quadruplets, 360
Quick-grass, 12
Quinin (kwi'nin), 231
Quintuplets, 360, 361

Rabbits, 589

Rabies (ra'biez), 614

Races, 63, 516 f.; and susceptibility, 244;

superiority in, 520 f .
Radiant energ>', 138

715

Radium, poisoning by, 231 ; as occupational

hazard, 636
Range of variation, 74
Raptores (rap to'rez), 30
Rats, growth of, 105 ; formulas for diet for,
112; appendix of, 175; and bubonic
plague, 625, 628
Recapitulation theory, 356
Receptacle, 406
Receptors, 275 ; touch, 285
Recessive characters, 475 ; in plants, 480 ;

in animals, 481 ; in man, 500
Rectum, 167

Redi, Francesco (1626-1697), 341
Reduction division, 402, 403
Reflexes, 262 ff., 277 ; brain and, 282
Regeneration, 228 ff., 370
Regulators, chemical, 124; vitamins as, 133
Reproduction, 20 ; in animals, 1 7 ; of plants,
17; and growth, 367 ff. ; vertebrate,
377 f.; of amphibians, 378; in flowering
plants, 398 fif. ; and heredity, 483 ff.
Reptiles, frontispiece, 696; breathing of,

211 ; development of, 421
Resin, 215, 216
Respiration, and photosynthesis, 142 ; in

roots, 202 f. ; external and internal, 208
Respiration calorimeter, 118, 120
Rest, metabolism during, 114; phvsiology

of, 222
Restraints, 665
Retina, cells of, in insects, 15; in embrj^o,

363
Rhizomes (ri'zomz), 395
Rhubarb, 12
Riboflavin, 108, 128, 132
Ribs, 14, 48, 206
Rice, polished, 104 ff.
Rings of tree, 581
Ringworm, 612
Rocky Mountain fever, 626
Rodents, 698
Roe, 377

Root, 11, 12 ; hairs of, 86, 87, 142, 144 ; work
of, 142 f. ; structure of, 143 ff. ; storage
in, 180; respiration in, 202 f.
Rose, Mary S. (1874-1941), 128
Rotation of crops, 151 f.
Rotting, 341
Roundwbrms, 692
Roux, fimile (1853-1933), 240

716

Rumen (roo'men), 172
Ruminants, 698
Runners, 395
Rust of wheat, 544, 595

Sacculina (sak'ti li'nc), 461

Salamander, 38, 355 ; skin of, 90; regenera-
tion in, 229

Saliva, 165

Salts in protoplasm, 98

Sap, circulation of, 146 ff.

Saussure, Nicholas de (1767-18^5), 642

Scale-lice, 581

Scales, 90

Scallops, ridges of, 69

Scar tissue, 229

Scarlet fever, 235

Schick test, 242

Schizophytes (skiz'6 fits), 688

Schleiden, Matthias (1804-1881), 22

Schwann, Theodor (1810-1832), 22

Sciatic (si at'ik) nerve, 282

Scion of grafts, 369

Scurvy, 103 ff.

Sea anemone (a nem'6 ne), 92, 382

Sea water, modification by, 357, 360

Seal, teeth of, 177

Seashore, organisms of, 92

Seasons, changes of, 89, 92; response to,

251 ff.
Seaweeds, 92, 688
Secondary sexual characters, 314; flowers

as, 408 f.
Secretin (se kre'tin), 303
Secretions, by glands, 169; internal, 304 ff.
Seedless fruit, 406
Seedling, 140, 144
Seeds, 11, 12, 400, 404 ff. ; sprouting of,

81 ff. ; scattering of, 409 ff.
Segmentation of egg, 361
Segregation, law of, 475 f. ; Mendel's ex-
planation of, 485
Selection, natural, 466
Selenium (se le'ni um) poisoning, 102, 103
Self-pollination, 406 f.
Self-sufficiency, limitations of, 653 f.
Semicircular canals, 286
Semipermeable membrane, 85
Sensitivity, 19 f., 284 ff., 551; of animals,

17; of plants, 17; chemical, 287 ff. ; to

light, 289 f.

Sensory nerves, 277

Separation layer, 91

Septic tank, 631

Septicemia (sep'ti se'me a), 618

Serum (se'rwm), 187; dried, 197; antitoxic,

237 ; reactions of, 240 ff. ; specific, 242
Sewage disposal, 630 ff.
Sex, energy needs related to, 116; determi-
nation of, 492
Sex characters, primary, 388 f. ; secondary,

391 f.
Sex-linked characters, 488 f. ; in man, 500
Shares of nutrients, 126 f., 128 ff.; require-
ments in, 130; nutritive values in, 131
Sharks, 210
Sheep tick, 177
Shellfish, 32

Sherman, Henry C. (1875- ), 109
Shoot, 11, 12
Shorthorn, 7
Shrimp, 359

Sickness, and health, 426 ; measurement of,
605 f.; poverty and, 607 f., 611; and
ignorance, 608 f .
Simians (sim'iSnz), 699
Simpson, Joseph Y. (1811-1870), 659
Siphon of clam, 92, 209
Skeleton, 48; minerals in, 123
Skin, of mammals, 14; colors of, 63, 517;
ridges on, of fingers, 73 ; of lizard, 90 ; of
salamander, 90; function of, 216 f.; sec-
tion of, 2177- irritants of, 637
Skunk, 548

Sleep, metabolism during, 114
Slime molds, frontispiece, 36, 687
Slips, 370

Smallpox, 235 f., 237, 445
Snail, 92 ; balancing organ of, 288 ; fossils

of, 454
Snakes, 4, 211,422, 696
Sneeze reflex, 288
Social organism, man as, 554
Social sensitivity, 667
Sociality, 56

Sodium, 100; and heart action, 124
Soil, and seeds, 81 ; aeration of, 83 ; evapo-
ration from, 83; character of, 98, 100;
conservation of, 156, 645 ; fertility of, 644
Soma (so'mfl), 507
Sorting, 29 ff.
Sparrow, English, 589

Specialization, 529 ff. ; in Volvox, 419
Species, 36 ff. ; origin of, 446 ff., 506 ff. ; re-
lationship of, 455 ff.
"Speedup", 224

Spemann, Hans (1869-1941), 363
Spencer, Herbert (1820-1903), 466
Sperm, 376

Spermaries, 305, 307, 377
Spermatophytes (spur'mo to fits'), 398 ff.,

412, 690 f.
Sperti, George (1900- ), 230
Spicules (spik'ulz), 195
Spiders, 693 f.

SpiUman, W. J. (1869-1931), 480
Spinal cord, 275, 278, 279, 280, 294
Spiracles (spir'a k'lz), 16
Spireme, 368
Spirogyra, 374, 688
Sporangia, 375
Spores, 370 f., 375
Sporophyte, 385
Sporozoa, 370, 692
"'Sports", 496, 509
Sprouting of seeds, 81 ff.
Squash bug, 352
Squid, 552

Stalk, 12; tissue of, 91
Stamens, 400
Starch, 98, 125; manufacture of, 140; test

for, 157 ; and sugar in plant, 165
Starfish, 32, 228, 693 ; regeneration in, 230

Starling, Ernest H. (1866-1927), 303

Statocyst (stat'6 sist), 285

Stature, variation in, 63, 69 ; inheritance of,
483, 484

Stems, 11,12; tissue of, 91; types of, 145 f. ;
circulation through, 146 ff.; dicot, 147;
storage in, 180

Stigma, 399

Stiles, Charles W. (1867-1941), 616

Stimuli, 284 ff.. 290 ff.

Stock, in grafts, 369

Stockard, Charles R. (1879-1939), 357

Stoma (sto'mc), 141, 143, 302

Stomach, human, 166; of fish, 173; of
lobster, 173 ; of cow, 174

Stone Age, 55

Storage, of vitamins, 132; of food, 180; in
plants, 215 f.

Struggle for existence, 466, 540 ff. ; mean-
ing of, 544 ; patterns of, 552 f.

717

Sugar, 98, 125, 138; and starch in plant,
165 ; test for, 183 ; in urine, 221

Sulfa drugs, 242

Sulfur in protein, 97

Sunflower, 255

Sunlight, and vitamin D, 132 ; and life,
138

Surface, of body, 117

Susceptibility, 244

Swamp plants, 204

Sweating, function of, 195, 217

Swimmerets, 420

Swordfish, 32

Symbiosis (sim bi o'sis), 177, 179

Symmetry, bilateral, 13, 14

Synapse (si naps'), 277

System, digestive, 165 flf. ; of bird, fish, and
lobster, 173; endocrine, 304 ff. ; nervous,
325 ; reproductive, of frog, 379

Systemic circuit, 192

Szent-Gyorgyi (1893- ), 109

Tadpoles, 357

Tannins, 216

Tapeworm, 614, 615, 692

Tap-roots, 204

"Tarpit", 452, 455

Taste, 288, 348

Taxonomy, 7

Teeth, of vertebrates, 100; decay of,
102; of herbivores, 176; of carnivores,
177

Temperature, for germination, 82, 83 ; regu-
lation of, in body, 196

Tentacles of anemone, 92

Termite (tur'mit), 177, 179

Testes, 314, 377

Tetanus {iet'd niis) , 233, 237

Thallophytes, 688 f.

Thiamin (thi'c min), 108, 128, 132

Thorax, of mammals, 14; of insect, 15; of
man, 204

Thrombin (throm'bin), 187

"Throwback", 497

Thymus (thl'm«s) gland, 305, 307, 308

Thyroid (thi'roid) gland, 100, 101, 305, 306,
309, 311

Thyroxin, 100, 101, 306, 309, 311

Ticks, 616 f. ; and cattle, 346; and disease,
625

Tide pool, 92, 579

Tissues, stem, 91, 147,354; stalk, 91; muscu-
lar, 116; of leaf, 141; conducting, 146;
origin of, 349 f . ; transplanting, 362

Toad, 38; infancy of, 420, 421

Tobacco, fungus disease of, 244; mosaic
diseases of, 445

Tocopherol (to kof'er 61), 132

Tomato, 6

Tongue, sensitiveness of, 288

Tonsil, 205

Tonus (to'nf^s), 232

Toothed leaves, 43

Toxicology, 232

Toxoid (tok'soid), 236 f.

Trachea (tra'kec), 100, 204

Tracheae (tra'ke e) of insect, 16

Transfusions, 197

Transpiration, 140 f., 148

Transplanting tissue, 362

Tree, rings of, 581

Trench fever, 625

Trichinella (trik'i nel'o) , 616

Tropisms (tro'plz'mz), plant, 256 ff. ; animal,
260 ff.; chemical, 378

Trypsin (trip'sin), 188

Tschermack, Erich, 479

Tubercles (tu'ber k'lz) of alfalfa, 152

Tuberculosis, 244 ; death rates from, 609

Tubers, 253, 395

Tubular glands, 170

Turgor and osmosis, 88 f .

Turtles, 211

Twins, 359

Tympanum, 15

Tyndall, John (1820-1893), 341

Typhoid, agglutination test for, 241, 242;
carriers of, 245

Typhus, 625

Underground stem, 12

Ungulates (iing'gia lats), 172

Unifying processes, 324 f.

Urea (ure'c), 202

Uric acid, 221

Urine, 195 ; composition of, 218 flf.

Uterus, 380

Vaccination, 235 f., 237
Vagus (va'gz/s) nerve, 296
Values, 660 fif.
Valves of heart, 190

718

Variation, 466 ; in stature, 63 ; normal, 68

Vegetables, 125

Vegetative propagation, vS62, 372

Veins, of body, 189

Venation of leaves, 43

Venom, 233

Ventral root, 279

Ventricle, 190, 191

Vermiform appendix, 174, 175

Vertebrates, 45, 695 ; plan of, 48 ; limbs of,
49; bones and teeth of, 100; metamor-
phosis in, 355; reproduction in, 377 f.;
aquatic, 378 ; stages of, 459

Vestigial (ves tij'i d\) structures, 460

ViUi (vil'i), 170, 171

Vinci, Leonardo da (1452-1519), 452

Virginia creeper, 12

Viruses (vi'r»s ez), frontispiece; of infantile
paralysis, 294, 444; disease from, 614

Vitalism, 441, 443

Vitamin chart, 132 f.

Vitamin A, 125, 132

Vitamin Bi, 104, 128, 132

Vitamin B2, 108

Vitamin C, 108, 132

Vitamin D, 108, 125, 132

Vitamin G, 108, 128, 132

Vitamin K, 108, 132

Vitamins (vi'tfl minz), discovery of, 104 flf.,
132 f. ; action of, 107 ff. ; naming of,
108; differentiating, 108 f.; sources of,
109 f.

Viviparous (v! vip'fl riis) species, 378, 422

Vocal cords, 62

Vol vox, 419

Vries, Hugo de (1848-1935), 479, 510

Walking, significance of, 46
WaUace, Alfred R. (1823-1913), 466
Walls, of ceUs, 24
Walrus, 5 ; teeth of, 177
Warm-blooded animals, 116
Wartime, food in, 632
Wasp, 352
Wasserman test, 242

Wastes, from cells, 214; plant, 215, 216;

from animals, 216 ff.; removal of, by

kidneys, 220, 221
Water, and life, 78; in protoplasm, 80 ff.,

98 ; adjustments to supply of, 89 ff . ;

effect of amounts of, 254 ; pollination

by, 407
Water-soluble vitamins, 132
Water supply, 630
W-chromosome, 492
Weapons, of Stone Age, 55
Weight, annual gains in, 115; and basal

metabolism, 121
Weismann, August (1834-1914), 507
Went, Frits W. (1903- ), 257
Whale, 699 ; brain of, 278
Wheat, 251 ; breeding of, 497
Wheelworms, 693
Whooping cough, 235
Whorl of fingerprint, 73
Widal's test, 241, 242
Wilting, 87, 88

Wind, pollination by, 407, 408
Wings, comparison of, 18
Wood, composition of, 84
Woodchuck, 177
Workers, energy needs of, 123
Worms, tube, 92 ; parasitic, 614 f.
Wounds, 617 f.

X rays, pictures by, 189; and mutations,

512 f.
X-chromosome, 492
Xenon, 84
Xylem (zl'lem), 144, 145, 147

Yak, 7

Y-chromosome, 492
Yeast, 24, 370, 371,689
Yellow fever, 235, 445; and mosquitoes,
621 ff.

Z-chromosome, 492
Zygospore (zl'gospSr), 375
Zygote, 375

PRINTED IN THE UNITED STATES OF AMERICA

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