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I ARY BIOLOG\

EXPERIMENTS IN EVOLUTION

Mendel found that when pure-bred green-seeded peas were
crossed with pure-bred yellow-seeded peas, the offspring were all
yellow-seeded. When these hybrid plants were crossed with one
another, the following generation produced three yellow-seeded
plants to one green-seeded plant.

Tower found that exposing the young stages of potato beetles to
extreme conditions of moisture and temperature produced in the
following generations modifications that were inherited. The results
of high temperature and low humidity are illustrated at the left of
the parent type ; the results of low temperature and high humidity
are illustrated at the right.

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ELEMENTARY BIOLOGY

AN INTRODUCTION TO
THE SCIENCE OF LIFE

BY

BENJAMIN C. GRUENBERQ :

JULIA RICHMAN HIGH SCHOOL, NEW YORK

GINN AND COMPANY

BOSTON . NEW YORK • CHICAGO • LONDON
ATLANTA • DALLAS • COLUMBUS • SAN FRANCISCO

f/r

COPYRIGHT, 1919, BY BENJAMIN C. GRUENBERG . M

ALL RIGHTS RESERVED
320.7

Cfte iStbengum 3grcg<

GINN AND COMPANY • PRO-
PRIETORS • BOSTON • U.S.A.

PREFACE

The material in this book, its arrangement, and the method of
instruction that it implies are the outcome of some seventeen years
of work and thought devoted to the teaching of science to adolescents
and to adults. They represent what seems to me at present the
kind of knowledge and the kind of attitude that are both wanted
and needed, and the kind that it is desirable, from a social point of
view, that all of our citizens should acquire sooner or later.

The point of view throughout is the fact that we have to do with
constant changes that need to be understood and that need to be
controlled. On the one hand, I have tried to eliminate the anthro-
pomorphism that seeks to answer the questions about living things in
the form of " Why ? " — implying a purposefulness in organisms that
is a hindrance rather than an aid to analysis and understanding. On
the other hand, I have sought to develop an anthropocentric interest
that should humanize the study of living things in terms of appreci-
ation and purpose. The understanding of how things work and the
solution of problems by means of such understanding are preemi-
nently human achievements ; and this view is constantly emphasized
from every angle. Man's conquest of his surroundings, through the
application of more and more knowledge, through the making of his
knowledge more and more trustworthy, furnishes a leading motif.

In the selection and arrangement of the material I have tried to
avoid the specialists' divisions into botany, zoology, etc.; to the stu-
dent these are arbitrary and seem to me to confuse rather than to
illumine. I have tried to stress the dynamic by speaking of what
plants and animals do, and how they do these things, rather than by
speaking of the various kinds of organisms that there are, and how
to know them apart. So far as possible each main division deals with
plants and animals, including man, except where the topic is specifi-
cally related to one or another group. So far as possible, each unit of
the text is related to something that has been previously learned, or
to some outside experience of the reader. I have attempted to suggest

iii

459835

iv ELEMENTARY BIOLOGY

the vastness of the living world, and the multiplicity of its interrela-
tions, without discouraging the aspiration to become acquainted with it
I have selected types of problems that best illustrate man's method of
adapting himself or his surroundings to his needs, and by means of
historical references I have sought to develop a recognition of the
interdependence of workers of all nations both in thought and in pro-
ductive labor, as well as our dependence upon the accumulations of the
past. Finally, the idea of progressive change in the organic world is
not only explicitly discussed in a special section, but is indirectly
suggested in the discussion of various processes and relations.

As to quantity, I have assumed that there must be more material
in a textbook than can be comfortably used by any class of students.
'I'his is in order to give the teacher an opportunity to select according
to individual preferences, according to local and temporary conditions,
and according to the interests of thS students ; and in order to give
individual pupils an opportunity to find things of interest that are not
" in the lesson." While the work of a class can never be completed
in any sense, it is desirable that the text give some suggestion of
scope, and that it project the imagination beyond what is actually
studied. Moreover, the more thoughtful student should have before
him, in connection with the topics discussed, supplementary matter
that will point out relations and applications in other fields of interest.

As to method, I have assumed the correlation of textbook with lab-
oratory work, with field excursions, with special topic assignments, and
with the study of m.useum material. But while constantly referring to
experiments and to objective data, the text is not interrupted with lab-
oratory directions. I have sought here not merely to keep the reading
continuous ; I have meant to indicate that there is no one best experi-
ment, no one set of facts, no one type specimen, to support a principle.
Truth may be approached by many paths, and I have tried to avoid
dogma both as to the approach and as to the conclusions. The relation
of science to human welfare is illustrated by the introduction of an
unusual amount of quantitative material, chiefly in the form of graphs.
This is on the theory that it is not sufficient to show that a scientific
principle is reasonable or helpful ; it is necessary to show that there
is a measurable difference in results when various principles are applied.
There is no better way of insinuating into the thought of our
students the real meaning of the pragmatic sanction.

PREFACE V

As to the sequence of topics, I believe that since there is no end
to the subject, one point is as good for beginning as any other. For
practical administration of instruction it is of course desirable to have
a plan of some kind, and the experienced teacher will make up a
new plan each year only to find it desirable to make changes in it
before the year is over. There is no best sequence ; the order in this
book has been followed with classes that had to be taught according
to a syllabus with a totally different arrangement, and the material
can be studied quite as satisfactorily without following the chapters
and sections in order. It has been repeatedly demonstrated that
the material is usable for beginners in the subject, and that the
text is adjustable to a variety of syllabuses ; and these are the two
important considerations from the viewpoint of course of instruction.

So far as possible, structural details are presented by means of
diagrams and pictures rather than by means of elaborate descriptions.
All the diagrams designed to clear up complex relations in space
or time have been drawn especially for this book, as well as all the
figures for which special credit has not been given. In this connec-
tion I wish to acknowledge my obligations to those who have been
good enough to lend me photographs and other illustrative material,
as well as to the artists who have so patiently collaborated in develop-
ing the drawings, — Mr. F. Schuyler Mathews, Mr. Frank M. Wheat,
Mr. Mateoto Nishimura, and Mr. Ernest Taubele.

In the course of my work I have had valuable assistance and criti-
cism from many colleagues and associates in the Commercial High
School (Brooklyn), the DeWitt Clinton High School and the Julia
Richman High School (New York), the American Museum of Natural
History, Columbia University, and other institutions. To mention any
of these would be to slight others; and while some have given me
more time and more direct aid than others, I am too keenly aware of
the influence of even passing and casual suggestion to know where
to draw the line between those who have helped me and those
who have not. I am the lens through which is focused here and
now a fragmentary and fleeting view of the biological thoughts of
a hundred men and women ; and it is this cross section of biology
that I offer to my fellow workers, with gratitude for what I have
myself received, and with the hope that it will be of help to them.

B. C. G.

CONTENTS

PART I. THE WORLD IN WHICH W^E LIVE

CHAPTER PAGE

L Introduction 3

II. What goes on in the World 7

III. Fire 11

PART II. LIFE PROCESSES OF THE ORGANISM

IV. Living Things and Non-living Things 15

V. The Living Stuff 20

VI. The Conditions of Life 25

VII. Air and Soil in Relation to Sprouting .... 29

VIII. Seeds and Seedlings 32

IX. External Forces and Plants 37

X. Absorption from the Environment 40

XL Roots of Plants 42

XII. What Food Is 50

XIII. The Origin of Food 53

XIV. The Chemical Cycle of Life ^y

XV. The Soil as the Source of our Materials ... 6$

XVI. The Leaf as Starch Factory 70

XVII. Our Dependence upon Leaves and Chlorophyl . 73

XVIII. Starch-Making and Digestion 78

XIX, Digestive System in Man 81

XX. Health and Food Standards 89

XXI. Food Requirements 94

XXII. Food and Dietaries 105

XXIII. Food Habits 114

XXIV. The Social Side of the Food Problem 122

vii

viii ELEMENTARY BIOLOGY

CHAPTER PAGE

XXV. Stimulants, Narcotics, and Poisons 131

XXVI. Alcohol and Health 133

XXVII. Alcohol and Society . 137

XXVIII. Air and Life . . ' 143

XXIX. Breathing in Man 148

XXX. Ventilation 154

XXXI. Contaminated Air 158

XXXII. First Aid and Hygiene in Relation to Breathing 169

XXXIII. Transfer of Materials in Plants 174

XXXIV. The Blood 179

XXXV. The Circulation of the Blood 185

XXXVI. Hygiene of the Circulatory System .... 190

XXXVII. The Blood as a Living Tissue 193

XXXVIII. Wastes and By-products of Organisms. . . . 201

XXXIX. Hygiene of Excretion 205

XL. Excretion and Fatigue 208

XLI. Fatigue and the Worker 213

XLII. Nerves and the Reactions of Organisms . . . 217

XLIII. Tropisms and the Beginnings of Sense . . . 224

XLIV. Eyes and Light 229

XLV. Hygiene of the Eyes 235

XLVI. Sound Sensations 238

XLVII. Responses to Gravity 241

XLVIII. Instincts 244

XLIX. Habit . 248

L. Chemical Injury to the Nervous System . . . 253

LI. Unity of Life 260

PART HI. THE CONTINUITY OF LIFE

LI I. Growth and Regeneration 265

LIII. Development 274

LIV. Conditions for Development 285

LV. New Organisms 291

CONTExVTS ix

CHAPTER PAGE

LVI. Sex 296

LVII. Flowers 300

LVI 1 1. Pollen ATioN 304

LIX. Adaptations of Flowers 310

LX. Fruit and Seed Distribution 315

LXI. Alternation of Generations 320

LXII. Reproduction in Animals 327

LXIII. Infancy and Parental Care . 331

PART IV. ORGANISMS IN THEIR EXTERNAL RELATIONS

LXIV. Obstacles to Life 337

LXV. The Conflict of Life with Life 341

LXVI. Protective Armors of Organisms 345

LXVII. Protective Pigments and Appearances .... 351

LXVIII. Protective Movements 360

LXIX. Protective Activities . 368

LXX. The Forest in Relation to Man 377

LXXI. Bacteria and Health 386

LXXII. Control and Use of Bacteria 394

LXXIIL Insects as Spreaders of Disease 398

LXXIV. Insects as Intermediate Hosts 404

LXXV. Insects and Human Wealth 412

LXXVI. Insects and Other Organisms . . . . . . . 417

LXXVII. Birds in Relation to Max 425

LXXVIII. Social Life of Organisms 430

PART V. HEREDITY AND EVOLUTION

LXXIX. Variation . 437

LXXX. Heredity 443

LXXXI. Applications of the Principles of Heredity . 450

LXXXII. Heredity and Protoplasm 457

LXXXIII. Evolution 463

LXXXIV. Applications and Theories of Evolution . . . 471

X ELEMENTARY BIOLOGY

PART VI. MAN AND OTHER ORGANISMS

CHAPTER

PAGE

LXXXV. The Classification of Organisms 475

LXXXVI. Kinds of Plants 477

LXXXVII. Kinds of Animals .32

LXXXVIII. Man and his Relatives ^oo

LXXXIX. Man's Brain ^^7

XC. Man's Conquest of Nature cqa

XCI. Science and Civilization ron

INDEX

ELEMENTARY BIOLOGY

PART I
THE WORLD IN WHICH WE LIVE

CHAPTER I
INTRODUCTION

1. A new science. At the time of the American Revolution
the name biology, which means the *' science of Hfe,'' or the
" science of hving things," had not been invented. And at
the time of the Civil War only a few men were engaged in the
study of the subject. At the present time, however, the subject
of biology has already come to be so important that everyone
should know something about it, for a variety of reasons.

2. Biology related to health. In the first place, the people
of civilized countries have come to live in larger and larger
towns and cities and in closer and closer neighborhoods, so
that it is necessary to regulate our lives in many ways that
were not necessary when most people lived on farms or in
villages. Each person may now be a source of assistance and
comfort to more people than formerly ; but he may also, quite
unintentionally, become a source of danger to many people.
When each farm was all by itself, it did not matter very
much what became of the barnyard wastes, and most of the
kitchen refuse was eaten by the pigs and chickens. In a
city the garbage may furnish materials of great practical value,
but it may also breed flies and other insects that carry germs,
if proper disposition is not made of it. The water supply of
a city is a more difficult problem than that of a rural com-
munity, and the health of the city depends very largely upon
an abundant supply of the right kind of water. We have

3

4 : -^" t L.t .^^\ ^.B^LEMENTARY BIOLOGY

found out also that there is an added danger in the greater
amount of handhng that all food materials receive in passing
from the places where they originate to the places where they
are finally used up. Again, every time a person suffering
from any one of certain diseases comes in contact with another
person, there is danger of passing the sickness on. Many of
these things were not known fifty years ago, and very many
of the regulations which have been adopted depend upon
principles derived from a study of living things.

3. Biology related to wealth. In the second place, it has
been found that many of the natural possessions or resources
of the country have been so wastefully handled in the past
that our. growing population is likely to run out of things that
are absolutely necessary for comfortable living, unless we
find some better ways of using our forests, our streams,
our soil, and so on. And we must be guided in our use
of these resources by an understanding of the principles that
can be learned only from a study of living things. The same
is true with regard to the protection of various wild animals
and plants against extermination, where these happen to be
of value to mankind directly or indirectly. And, on the other
hand, it is an understanding of biology that makes possible
the most effective fight against those plants and animals which
happen to be injurious to the living things that are useful
to us. In this connection, too, we have learned that it is
possible to get a much larger return for our labor, in the way
of raising plants and animals for human use, by applying the
principles of biology to agriculture, horticulture, poultry farm-
ing, dairying, cattle raising, and other industries, so that one
needs to understand something c^ these principles if he is to
keep in touch with what is being done by the producers of
our food and clothing and shelter materials.

4. Biology related to efficient living. In the third place, it
has been observed that much of the unhappiness and weakness
and inefficiency of human beings is caused by ignorance of

INTRODUCTION 5

those matters that have to do with the workings of the living
body. A study of hving things should give us useful ideas
about eating and drinking, about breathing and bathing, about
rest and sleep, about exercise and study, about work and play,
and so on. These things are important not only to doctors
and nurses, who have to do with sick persons, but also to
everyone who cares for health and happiness — and who of
us does not ? Moreover, a systematic study of living things
should help us to understand the behavior of the men and
women and children with whom we have dealings every day.
Much that seems to us queer or unreasonable in other people's
conduct, much that seems to us wrong, can be understood
from a biological point of view. And it is surely worth while
to avoid misunderstandings, false judgments, and ill feelings
so far as possible.

5. Biology related to enjoyment of life. Finally, the more
time we have away from our work, the more opportunity may
we have to become acquainted with the wonderful varieties of
living plants and animals that fill the world about us. And
if our minds are alert, most of us will be curious to understand
not only the habits and ways of these living things, but also
their relationships to their surroundings, to one another, and
to us. In this way we may get from our acquaintance with
nature a large share of enjoyment in life, just as we get much
from paintings and music, from natural scenery and travel,
from drama and literature, and from intercourse with other
living beings like ourselves.

As we become more civilized we shall have more oppor-
tunities to enjoy life through our understanding of the things
of nature, as well as through appreciation of the doings of
human beings.

6. All life related. We might begin our study of biology
by capturing the first plant or animal that comes within reach
and trying to find out all about it. If we did this in a thorough-
going manner, we should find out a great deal about many

6 ELEMENTARY BIOLOGY

other plants and animals, for it is an important truth of life
that no being lives by or for itself alone. The life of every
plant and of every animal is tied up closely with the lives of
many other living beings. The life of man, which is to us
so important and so interesting, is most closely bound up with
the lives of other beings, hideed^ that is just the reason why
we cannot understand human life zvithout a study of biology.
So it is possible to study this subject from the point of view
of man, and that should be the most interesting.

We could take up, one after another, the important activities
of a human being that have to do with maintaining life and
with enjoying life, and learn the relations of these activities
to one another and to the world about us. Or we could begin
by inquiring as to the causes of the various events that we
find making up our lives. One way of studying would be
just as good biology as the other. We must select, however,
the way that has been found to be most convenient and profit-
able, all things considered.

CHAPTER II
WHAT GOES ON IN THE WORLD

7. Things change. The world that we know is made up of
things that are constantly becoming different, or changi?tg.
The weather changes from hour to hour, from day to day, from
season to season. Non-living objects are constantly changing —
moving, burning, rusting, fading, crumbling. Living objects
change from day to day, from season to season ; they move
about, they fight, they build up, and they destroy — that is, they
are themselves constantly changing, and they are constantly
bringing about alterations in other objects.

8. Physical changes. In the course of these various changes
we see materials take on new for-ms, as when clay is pressed
into bricks, or when bricks are assembled into houses. We see
substances change their state^ as when solid butter melts to a
liquid, or when liquid water evaporates into a gas or freezes
into solid ice. We see solids dissolve, and we see their condi-
tions change in other ways, as when an electric current, pass-
ing through a platinum wire, makes it hot, or when an electric
current passes around a piece of iron and makes it magnetic.

In all these changes, and in many others, the material appears
to remain essentially the same stuff. These are examples of
physical changes.

9. Chemical changes. In the course of other changes, cer-
tain of the substances involved seem to disappear entirely, while
new materials make their appearance. For example, in a fire
that destroys a house or a forest, much that formerly existed
ceases to exist, and smoke and ashes appear as new substances.
In the souring of milk, or in the cooking of food, or in the

8 ELEMENTARY BIOLOGY

making of soap, certain kinds of substance disappear and new
substances seem to arise. Changes of this character are called
chemical changes.

10. Conservation of matter. Whether a change is chemical
or physical, the total amount of substance remains the same.
A pound of ice melts to a pound of water and evaporates to
a pound of steam. A quantity of fat plus lye plus water will
produce the same total of soap plus glycerin plus water. The
total of the materials involved in a fire remains the same.
Modern science has been able to demonstrate this in many
cases. But whether it can be demonstrated in all cases or not,
this principle is assumed in all scientific reasoning about what
happens in the world ; indeed, it is the very foundation of
scientific thinking.

The first law of matter is this : Matter- can neither be
destroyed nor created. Or, stated differently, the quantity of
matter remains constant.

11. Complexity of matter. If we examine a piece of granite
carefully, we see that it is clearly made up of several different
kinds of particles. In a piece of marble, however, all the par-
ticles seem to be of the same kind. Alcohol, or chloroform,
or water seems to be of the same kind of stuff all the way
through ; but it is easy to convince ourselves that milk, which
may appear to be one kind of stuff, is really made up of
several different kinds of matter.

We see that we cannot always tell from the appearance of a
body whether it is made up of one kind of stuff or of several
kinds. Thus, if we took a piece of rock candy, a piece of clean
ice, a piece of clear glass, a crystal of quartz, and a diamond,
we should find that they all look very much alike. Yet these
five substances are quite different from each other in many
ways. The chemist is able to get from the glass certain sub-
stances ; some of these are present also in quartz, and one of
them is present in the ice (water) and in the rock candy
(sugar). From the water hq can separate out two different

WHAT GOES ON IN THE WORLD 9

substances, both of which are present also in sugar. But from
the diamond he can get only one kind of stuff, no matter what
he does with it ; and that stuff, called carbon, is present also
in sugar.

12. Elements and compounds. The chemical changes that
take place when a substance is separated into simpler stuffs is
called analysis, which means a separation, or putting asunder.
The breaking up of water into oxygen and hydrogen, by means ,
of an electric current, is a kind of analysis. The chemical
change that takes place when two or more substances are com-
bined into a new substance is called a synthesis, which means
a placing together, or corn-posing. When hydrogen is burned
it combines with oxygen, and the two together form water.

The substances which the chemists have not been able to
break up into simpler kinds of matter are called elements. A
combination of two or more elements is called a compound.
Many of the elements combine with one another very readily ;
as a consequence, most of the substances with which we are
familiar are compounds. A given set of elements may form a
large number of different compounds. Thus, hydrogen, oxygen,
and carbon can form an unlimited number of compounds,
depending not only upon the pivportions in which they are
combined, but also upon the arrangement of the elements.
This we can readily understand when we think how a few
letters can make many different words, or how a given lot
of brick and mortar and wood can be combined into many
different kinds of structures.

13. Energy. All the changes that we experience seem to
be brought about by the action of some kind of force. For
example, gravitation changes the positions of the earth and
the moon and so on ; heat changes the states of matter ; light
causes chemical changes in a photographic plate or in wall
paper. It is proper to speak of the force of gravity, of heat,
of light, of electricity, of magnetism. Each of these forces
is considered a form of energy, and any one of them can be

lO ELEMENTARY BIOLOGY

changed into some other. Chemical energy and X-rays and
motion are other forms of energy.

We may think of energy as that which brings about changes
in matter, or that which does work.

14. Energy and matter. If we fix our attention upon any
happening or change, we can see that matter undergoes some
change, and that at the same time energy undergoes some
change. Moreover, we can see that whatever happens has not
only been started by some previous change, but also starts
some other changes in its turn. Thus we may get the idea
not only that energy causes changes in matter, but also that
matter causes changes in energy. One statement is just as true
as the other. We may get the further idea that every event is
a link in an endless chain of events, and that these many links
may connect up in every possible direction. .

15. Conservation of energy. One kind of energy can be
converted into other kinds of energy, but the total amount of
energy always remains the same. There is no way of getting
energy except from other energy. Energy, like matter, can
neither be created nor destroyed.

CHAPTER III
FIRE

16. Sources of energy. If we wish to make a machine work,
we must apply energy to it, from any one of several sources.
We might use the heat of the sun or the movement of the
tides, the energy of the wind or of falling water. Another
source of energy commonly employed, especially in modern
industrial cities, is the chemical energy of fuel. The burning
fuel yields heat. This is then transformed into motion or into
electricity by means of suitable machinery, and is thus used for
doing much of our necessary work. The process of burning
is so common, is so much employed as a convenient source
of energy, and is so closely related to the liberation of energy
in living bodies, that it is necessary for us to know something
more about it.

17. Burning. When something burns we may notice three
peculiar changes :

1. The fire gives off heat.

2. The fire gives off light.

3. The fuel seems to be destroyed.

From cold fuel we get heat and light — two kinds of energy.
How does this happen .''

On closer study we find that the heat and light are not
created by the fire out of nothing ; they are transformed out of
other energy which has been present in the fuel all the time.
This latent, or resting, energy is chemical energy, and repre-
sents the power to produce chemical changes in matter. As to
the disappearance of the fuel, we can find, on making suitable
experiments, that the total amount of stuff is the same after

12 ELEMENTARY BIOLOGY

the fire as it was before, although it now exists in different
forms and in different chemical combinations.

18. Air and fire. We know from experience that most
substances will not burn unless there is a supply of air. The
dependence of the fire upon the air may be due to the fact
that burning uses up air (or something in the air) just as it
uses up the combustible. Or it may be that in the course of
the burning the fuel is changed into a new substance (probably
invisible) that interferes with further burning unless it is car-
ried off in the air. We can find out by means of a simple
experiment that the fire takes from the air certain materials,
and that it also discharges into the air certain other substances.
We should also feel confident that the " new substances " are
merely rearrangements of the particles of the original fuel and
the stuff taken from the air.

19. Burning a synthesis. We have already learned that
compounds are substances consisting of two or more elements,
and that the formation of compounds is called synthesis, or
"putting together." Experiments can be made to show that
although the burning process may result in breaking 7ip com-
pounds — the compounds of the tallow, for example — it also
results in the formation of new compounds. Accordingly the
products of combustion represent more matter than is present
in the fuel. The ashes and smoke and the invisible substances
resulting from a fire together weigh as much as the original
combustible plus the amount of material taken from the air.

20. The gases in the air. The ordinary air is a mixture
of gases. Three of these are well known. In addition to the
dust and the water vapor, and some gases which are not
easily reached through our ordinary experiences and laboratory
methods, the atmosphere may be said to have approximately
this composition :

Nitrogen about 79%

Oxygen about 20%

Carbon dioxid less than -^^%

FIRE 13

Which of these three gases is it that is used up in a fire ?
Or are two of them, or are all, necessary for fire ?

Each of these gases can easily be prepared in the laboratory,
and we may try each in turn, to see how it behaves in relation
to fire. From these tests we discover the importance of oxygen
in relation to burning.

21. Oxidation. The chemist describes the facts of burning
by the statement that some substance combines with oxygen,
producing new compounds. The heat and light energy that
are set free are the equivalent of the combining force, or
chemical energy, that the fuel has in relation to oxygen — the
attraction between the two substances. The new compound that
is formed when a simple substance (an element) burns is called
an oxid. Thus, when magnesium is burned, magnesium oxid
is produced ; when sulfur is burned, sulfur oxid is produced ;
when phosphorus is burned, phosphorus oxid is produced ; and
so on. The carbon dioxid which is found in the air is a com-
pound of oxygen and carbon. Water is a compound of oxygen
and hydrogen.

When a compound, or mixture (like sugar or wood), is
burned, several oxids may be formed at the same time. When
sugar burns, the carbon of the sugar goes to form carbon
dioxid and the hydrogen of the sugar goes to form water.
The carbon and the hydrogen of the wood behave in a
similar manner when wood burns.

22. Oxidation in living things. In living bodies the energy
transformed in the various activities is derived from food.
This food is not burned directly, like the gasoline in an engine ;
it first undergoes many changes and becomes part of the living
body. And the burning, or oxidation, takes place in all the
several parts of the body instead of in one central furnace.
Another difference between the oxidation in the living body
and in our ordinary engines is this : In the living plant or
animal there is no flame. Indeed, the oxidation always takes
place in the presence of water, whereas the fires with which

14 ELEMENTARY BIOLOGY

we are most familiar cannot be kept up under water. Yet we
know that rusting of iron can go on under water, and this
rusting is really a roundabout oxidation process.

In the common animals, including ourselves, a large part of
the activities which we usually notice have to do with getting
materials that can be oxidized. And a large part of the inter-
nal activities, which we do not notice, have to do with bringing
the fuel and ox\gen together and with removing the oxids
resulting from oxidation.

The conclusion of this matter is that living beings do their
work through energy set free from fuel by oxidation, which
requires oxygen in addition to food, and that we can under-
stand the organism's need for food and air in the same way
that we understand the requirements of an engine for fuel
and draft.

PART II
LIFE PROCESSES OF THE ORGANISM

CHAPTER IV
LIVING THINGS AND NON-LIVING THINGS

23. Living bodies formed. A comparison of living and non-
living objects brings to our attention the fact that, whereas the
non-living objects of nature are, as a rule, indefinitely shaped
masses of matter, the plants and animals with which we are
acquainted generally have rather definite shapes, or forms. It
is true that crystals of various substances have definite, char-
acteristic forms, and it is true also that no two trees or no
two animals have exactly the same form. Nevertheless we
have no difficulty in distinguishing different kinds of plants
or animals by their forms, whereas, besides crystals, we do not
find many non-living (natural) objects that show distinct forms.

24. Living bodies organized. Living bodies are like machines
in being made up of several fairly distinct parts. Each of these
parts acts not usually by itself, but with the cooperation of
others and toward some result that concerns the body as a
whole. Each part of a living body that carries on some distinct
share of the total work is called an organ. The arms and legs
and wings of animals are organs of locomotion. The eyes and
feelers and ears are organs of sensation. The stomach and liver
are organs of digestion. The body of a plant or an animal is
often spoken of as an organism — something made up of organs.

Functions. The special work performed by an organ is called its
function ; and the study of functions constitutes a large part of
biology, called physiology. Thus, we may say that the function of

15

i6

ELEMENTARY BIOLOGY

the leg is locomotion ; the function of the ear, to perceive certain
disturbances of the air which we call sounds ; the function of a
root, to absorb certain materials from the earth ; and so on. In study-
ing the behavior of an organ we usually have in mind what it does in
relation to the life of the organism as a whole. For there are many
structures in living bodies that have no special functions, as the
vermiform appendix in our own bodies, or the wing of an ostrich.
Or an organ may do something that really has no significance in the
working of a living machine, as the wagging of a dog's tail or the
movement of a boy's ear.

25. Chemical composition. On comparing the chemical com-
position of living bodies with that of non-living bodies we

Oxygen 65%

Carbon
18%

Hydro-
gen

10%

Fig. I. The chemical composition of the human body

In addition to the elements named there are nitrogen (N), calcium (Ca), phosphorus (P),

potassium (K), sodium (Na), magnesium (Mg), sulfur (S), chlorin (CI), iron (Fe), and

traces of iodin, fluorin, and silicon

shall find that, of the seventy-five or eighty elements that
have been described by the chemists (see p. 9), from twelve
to fifteen are found in the bodies of very nearly all plants
and all animals.

There is nothing in this list of elements that distinguishes
living bodies. Each of these elements occurs in the soil ;
some of them occur in the Waters of the oceans and lakes ;
and a few are found in the air.

Organic and inorganic. Yet there is an important difference be-
tween living and non-living things on the chemical side. Although
the elements of the living body are the same as the elements of the

LIVING THINGS AND NON-LIVING THINGS 17

environment, they are amibined in ways that are peculiar to living
things. Certain compounds are found in nature only in the bodies of
plants and animals. Some of the more common of these are sugars,
starches, fats, albumins, certain pigments, and woody and horny sub-
stances. These substances are not themselves alive^ for we find
them also in the dead bodies of organisms.

Formerly substances that could be obtained only from organisms
were called organic and were distinguished from other substances
occurring in nature, which were called ifiorganic. The chemists have
succeeded, however, in producing large numbers of compounds that
naturally occur only in plants or animals, so that this distinction is not
used so much to-day.

Since the forms and the structures of organisms remain
about the same after death, and since probably most of the
compounds remain the same, we must find other distinctions
between living and non-living.

26. Growth. The fact of growth is universal for living
things. This does not mean that every living body is con-
stantly growing ; it means that every organism is capable of
growth at some time during its life, or that parts of the body
are capable of growth. Yet the crystals of many substances
also grow, some of them very rapidly, so that we can actu-
ally see them grow. Most of us have seen icicles grow. If
by growing we mean becoming larger, then crystals and icicles
grow just as truly as caterpillars or babies. What, then, is the
real difference between the two kinds of growth 1

When an icicle becomes larger it does so through the addi-
tion of new layers of ice-stuff (water) on the outside. The
growth of a crystal proceeds in the same way. A baby, how-
ever, does not grow in this manner, (i) The baby grows not
by the addition of baby-stuff from the outside, but by the
addition of different kinds of stuff — such as cow-stuff (milk),
or hen-stuff (eggs), or wheat-stuff (bread). (2) The growth
material is not added on the surface, but is taken in. (3) The
new material does not remain the same kind of stuff, but
undergoes chemical changes and becomes at last baby-stuff.

1 8 ELEMENTARY BIOLOGY

(4) The growth of the body goes on not merely by the exten-
sion of the surface ; it takes place in all parts at once, inside
parts as well as outside parts growing.

27. Assimilation. These differences between the two kinds
of growth may be summarized by saying that the icicle grows
by accretion, that is, by the adding of material to the outside,
whereas the baby and other living things grow by assimilation,
that is, through the conversion of foreign material into mate-
rials of the body — the "' making alike " of stuff that is different.

28. Movement. Most of the animals that we know are
capable of moving about and of moving their parts. Many
non-living objects also move, as the clouds and the waves.
But these objects do not move because of anything that takes
place inside ; we recognize that they are being pushed about
by outside forces. An examination of living plants and animals
shows us that there are movements going on inside the organ-
ism, and we can see that some of these inside movements
result in the movements outwardly visible.

29. Irritability. A very striking and interesting character-
istic of living things is their apparent sensitiveness to outward
changes, or irritability. We ourselves perceive lights and colors,
sounds, odors, tastes. The movements of the familiar animals
show that they are disturbed by much of what happens about
them, in a way that is different from the disturbance caused
to a cup when it is dropped. A dog does something when
he is hurt ; your eye does something when a sudden flash of
light is presented ; even a geranium plant changes its behavior
when placed in a sunny window. This sensitiveness of living
things is in some ways the most remarkable fact about them.

Yet we shall find that sensitiveness is not altogether con^
fined to living things. There are certain chemical compounds
that are in some ways even more sensitive than plants and
animals. Some compounds are so sensitive to mechanical dis-
turbance that they will produce a violent reaction when they
are dropped — as in the case of dynamite. This substance is

LIVING THINGS AND NON-LIVING THINGS 19

sensitive also to heat ; if a hot poker is appUed to a stick of
dynamite, the results are said to be more disastrous than the
consequences of poking a vicious dog.

30. Fitness. There is one respect, however, in which the
sensitiveness of living things differs from the sensitiveness of
non-living things. In most cases the living body responds to
a disturbance by doing something that will probably save it from
further injury. The non-living body, when sufficiently disturbed
to do anything, does something that generally results in its
further injury or destruction. Thus, when a dog's tail is pulled,
he will try to run away, or he will bark or snap at the " thing-
holding-tail." These responses are, on the whole, of a kind
that will save him from further damage. Indeed, we cannot
imagine how living beings would continue to live generation
after generation if they had the habit of doing things that
tended to injure or destroy them. In contrast to this kind of
behavior, think of what the stick of dynamite would do if
touched with a red-hot poker. There is nothing here that
looks in the least like '' trying- to-save-itself."

31. Origin. We do not know anything about the first appear-
ance of life upon the earth. But we do know that every plant
and animal now living had its origin in the body of some
other plant or animal. In general, non-living bodies do not
reproduce each other, but, so far as we know, living things can
be produced only by other, similar, living things.

32. Summary. We have seen that growth, movement, and
irritability of a certain kind may be present in non-living
bodies, but in no case have we found any non-living thing
that has all of these properties. Some have one, some another.
Living things are characterized by having all three. W^e may
say that it is the combination of these properties that distin-
guishes living bodies from the non-living and from the dead.

CHAPTER V
THE LIVING STUFF

33. Plants and animals. We have spoken of plants and
animals as *' living things " ; yet animals seem to most people
to differ from plants about as much as they do from non-living
things. Plants are just as much alive as animals are. They
are just like animals in those very points that distinguish
living things from non-living. That is to say, they are capa-
ble of growth, they are capable of movement, and they are
irritable, or sensitive to various kinds of disturbances — just as
animals are. And each organism originates from some other
organism.

Yet it is true that there are differences between plants and
animals. In the matter of growth, plants are even better
growers than animals, taking both classes as a whole. This
means that generally a ten-pound plant can grow into a twenty-
pound plant more quickly than a ten-pound animal can grow
into a twenty-pound animal. But there are great variations in
the rate of growth among animals as well as among plants.
We may also say that in general the plants use up a larger
share of their total income for growth, while animals use up
a larger proportion of their income as fuel ; that is, more of
an animal's income is oxidized, releasing energy in the form
of heat or of motion.

In the matter of sensitiveness, also, the animals seem, in
general, to be ahead of the plants, although we shall find
that there are some extremely sensitive plants and some
extremely unresponsive animals.

It is difficult to see why, in spite of all the differences,
plants and animals should still be so much alike. How is it

THE LIVING STUFF

21

that bodies organized in such very different ways come to be

so much aUke in those three points that are said to distinguish
Hving things from non-hving ?

34. Protoplasm. The answer to this
question is to be found in the fact that
in the bodies of all organisms there is
a peculiar substance (or rather a mix-
ture of substances) which seems to
have all the qualities of living bodies.
This seems to be the stuff that can
grow ; this is the stuff that moves ; this
is the stuff that is irritable. When
seen under the microscope this living
stuff seems to be a slimy, or jellylike,
substance — something like the white
of ^gg in appearance. Under a more
powerful microscope it sometimes ap-
pears to have many minute bubbles in
it, or to consist of an extremely fine
network. This stuff is called proto-
plasm, and in all essential respects

it seems to be alike in all plants as well as in all animals.
It is the

protoplasm of

a plant or of

a kitten that

grows. It is

protoplasm in

the body of

the Venus's Fig. 3. Diagram of a cell

nytrap or 01 -^hc mass of the cell content consists of the protoplasmic network,

a snake that ^^^*^^ ^^ coarser-grained nucleus. Within the protoplasm are more
solid bodies, and droplets of more liquid substances

moves when

the organism springs upon its victim. It is the protoplasm

of the geranium or of the worm that is sensitive to the light.

Fig. 2. Protoplasm moves

The arrows indicate the stream-
ing of the protoplasm within
the cells

22

ELEMENTARY BIOLOGY

Fig. 4. Various kinds of animal cells

/, flat epithelial cells, like those lining the cavity
of the abdomen in man and other animals ; z, co-
lumnar epithelial cells, like those lining the air pas-
sages, with hairlike projections of protoplasm, called

cilia; j, muscle c , unstriped, like those in the

walls of the intestine and of blood vessels; 4,
shapeless cells of naked protoplasm, like those of
Ameba or of white blood corpuscles; j, cells con-
taining fat globules, like those in adipose tissue ;
6, bone cells surrounded by hard deposits of limy
material ; 7, a nerve cell, or neuron (a, the cell
body with its branching outgrowths, or de7idritcs\
b, the longest outgrowth, the axon, ending in c, the
terminal branches)

as. Cells. It has been
known for a long time
that the body of every
plant and every animal
is made up of a large
number of tiny lumps
of protoplasm, each of
which is shut off from
its neighbors by a more
or less definite mem-
brane, or wall. A single
bit of protoplasm with its
wall is known as a cell.
This name suggested
itself to those who first
studied the structure
under the microscope,
because of its resem-
blance to the cells of a
honeycomb. When \ye
look at a living organ-
ism, we do not see
the protoplasm ; we see
the walls of thousands
of these cells. In the
larger plants and animajs
the outer layers of cells
are usually quite dead —
that is, the protoplasm
is no longer present,
only the dead wall re-
maining. This is true
of our own skin, of the
bark of trees, and of
the hide of the horse.

THE LIVING STUFF

23

With the aid of a microscope we can easily make out the
forms of many kinds of cells taken from the bodies of plants
and animals. We may
note that cells of differ-
ent kinds differ from
each other not merely
in size but in shape
as well. Some cells
have thicker walls, some
thinner walls. Some
seem to have various
kinds of solid bodies
floating about within the
covering ; others have
few or none of these.
Some have smaller and
some larger bubbles of
clearer liquid.

In some plant cells
the protoplasm can be
seen to move about.
The cells of certain
water plants are espe-
cially favorable for show-
ing this (Fig. 2).

36. Nucleus. There
is one special portion
of the protoplasm that
deserves particular no-
tice. Near the center,
or off to one side, we
can generally find a por-
tion of the protoplasm

Fig. 5. Various kinds of plant cells

/, epidermal, or skin, cells of a leaf, showing the
outer wall greatly thickened, and the cuticle ; 2, co-
lumnar cells, like those of the palisade layer of a
leaf pulp ; j, moving ciliated cells, like those of
typhoid bacilli ; 4^ swimming spores of a water
mold ; J, budding cells, like those of the yeast plant ;
6, guard cells inclosing a breathing hole, or stomate,
on the surface of a leaf; 7, a pollen tube growing
out of a pollen grain

that seems to be denser than the rest. This is called the kernel,
or 7iucleiis. Because of the transparency of the protoplasm it

24 ELEMENTARY BIOLOGY

may be difficult to distinguish the parts in many plant and
animal cells. It has been found convenient to stain masses of
cells with various kinds of pigments or dyes, to make the
structure stand out more distinctly under the microscope.
When certain dyes are used, the nucleus becomes particularly
distinct, since it absorbs these dyes more readily than do other
parts of the cell. And within the nucleus we can sometimes
see fine little rods or strands (Fig. 3).

37. Numbers of cells. The cells that you have seen under
the microscope may have suggested the question whether
a body has a definite number of cells. Most plants and
animals that you have seen probably have indefinite num-
bers, and these run into the countless millions. There are
some living things, however, that have a very definite and
limited number of cells.

One of the simplest animals is the one-celled ameba, which lives in
stagnant pools and other wet situations. Under the microscope it
appears to be an irregular lump of jellylike matter, in which various
granules and bubbles can be made out. There is a nucleus, and all
around it movements are constantly taking place. The shape of the
mass of naked protoplasm is constantly changing, resulting in sluggish
movements of the animal. The slimy mass swallows particles that
may serve as food, and it crawls away from contained particles that
are no longer of service. The animal is sensitive to physical and
chemical forces in the environment, and responds to disturbances by
contractions of the protoplasm.

38. Tissues. In the bodies of the plants and animals large
enough to be seen without a microscope, there are usually
many different kinds of cells. Masses of similar cells together
constitute what is called a tissue. Thus, in our own bodies
there are muscle tissue, bone tissue, brain tissue, gland tissue,
connective tissue, and other tissues. In the body of an ordinary
plant we may recognize bark cells, wood cells, pith cells, skin
cells, and other cells (see Figs. 4, 5).

CHAPTER VI
THE CONDITIONS OF LIFE

39. All activities dependent. We may imagine objects of all
kinds existing by themselves, but we cannot imagine them
doing anything except in relation to other things. The stars
in space influence each other in their movements, and every-
thing that human beings do depends upon the conditions
under which they live.

In order to discover the relations of the outside conditions
to the activities of a living being, particularly of a plant, we
may begin with the characteristic changes that take place in
passing from winter to spring. In the winter most of the
plants of the preceding season are dead, and those that are
not dead are, with comparatively few exceptions, either bare
of all foliage or reduced to one of several kinds of '' resting
states." There are roots and stems lying dormant under-
ground, and there are millions of seeds that look as lifeless
as pebbles — until circumstances favorable to life activity appear.

40. Sprouting of seeds. How is it that the seed sprouts in
some cases, and not in others } Seeds of many different kinds
are kept in boxes or jars for months at a stretch, or even for
years, and there is no sign that any of them has sprouted ;
yet if some of the seeds are placed in the earth, many of
them will sprout in a few days.

Just because the gardener or farmer places his seeds in the
ground, and they then sprout, we are likely to jump at the
conclusion that the soil somehow causes the seeds to begin
their active growth after their long rest. But this is not a sound
conclusion. The soil is a mixture of many kinds of stuff, some
of which may have something to do with the sprouting, and

25

26 ELEMENTARY BIOLOGY

others of which may have nothing at all to do with it. In
order to find out just what it is that causes the sprouting,
we must consider the effect of each of the various factors of
the seed's surroundings by itself.

41 . The environment. Now, in what ways do the conditions
surrounding a seed in the ground differ from the conditions in
a box or a jar ? There may be a difference as to temperature,
or as to the air, or as to the amount of water, or as to the light,
or as to some of the chemical substances present in the soil.
Experiments have been made with every one of these factors,
and we also have a great deal of experience that will help us to
answer this question in part.

Most of us know that seeds kept in jars will not sprout,
whether they are kept in the dark or exposed to light. It is
therefore safe to conclude that putting seeds in the ground
brings about their germination not on account of darkness, but
on account of some other factor. We also know that seeds
kept in a warm place and seeds kept in a cool place will both
fail to sprout, as long as they are in our jars or boxes. The
soil may be cooler than our storeroom, or it may be warmer ;
but it is not this that makes them sprout in the ground. Per-
haps the soil keeps some of the air away from the seed ; but
filling a jar with seeds and closing it up tight will not make
them sprout. So it cannot be the absence of air by itself,
nor the presence of air by itself, that causes the seeds in the
ground to germinate.

If we consider the chemical substances present in the soil,
our usual experience tells us nothing at all. Perhaps there are
certain substances there that cause the sprouting. We might
find out by trying some of them. The chemist can tell us
what there is in the soil, and he can also prepare the different
kinds of stuff in a pure condition. But if we place the seeds
in boxes containing the various ingredients of the soil, such as
sand, clay, and various salts, we shall find that none of the
seeds sprout. The failure of the seeds to sprout under these

THE CONDITIONS OF LIFE 2/

conditions may suggest that the one or many substances that
perhaps can cause sprouting would fail under the conditions of
the experiment because the dry substances cannot get into the
seeds. We should therefore try these substances in connection
with water. That, however, at once raises the question whether
water by itself has any effect on the sprouting of seeds.

42. Relation of water to sprouting. We should therefore
proceed to experiment with pure water. 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 one of the conditions necessary for starting
the germination of the seeds is the presence of a certain
amount of water.

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 water. The seeds in the first class are not injured by water; the
liquid simply prevents them from absorbing sufficient quantities of air.

43. Relation of temperature. It may be that other factors
also play a part. For example, seeds in the presence of water
may sprout at one temperature but not at another. F>om actual
experience with seeds of different species of plants wc know
that some kinds may be safely sown earlier in the spring than
others, and that some seeds will fail to sprout when it is too
cold or too warm. By means of a systematic experiment in
which groups of seeds with water are placed in a number of
different places having different temperatures, we may satisfy
ourselves that there is a limit in the range of temperature for
the sprouting of every species of seed, and that there is a
point at which the sprouting proceeds most quickly.

44. Relation of air. It may also be that the presence of
water at a favorable temperature is not enough to cause the
seeds to sprout. The air may perhaps influence the activity
of the young plant after water is absorbed. Experiments may

28 ELEMENTARY BIOLOGY

be planned to show whether, in addition to water, air also is
necessary for sprouting. In the same way we can go on and
try out the possible influence of light.

45. Summary. Since it is possible to get seeds to sprout without
any soil at all, and without any of the ingredients of the soil other than
water, it is safe to say that none of these ingredients is esse?itial to
germination. They may indeed be essential to the later growth of the
young plant ; but that is another story.

We may learn from these experiments that the sprouting of a seed
depends upon an adequate supply of water, upon a supply of air, and
upon the temperature remaining within certain limits. We may learn
that the soil, in which most seeds do actually sprout, is not itself
necessary for sprouting ; and that the light, which is really of great
importance to life, has nothing to do with sprouting.

CHAPTER VII
AIR AND SOIL IN RELATION TO SPROUTING

46. Sprouting and transformation of energy. The fact that
air is in some way necessary for sprouting suggests that the
activity of the plant is in some way similar to the process of
burning. Further experiments show closer resemblance — for
example, the fact that it is the oxygen of the air that is con-
cerned in both processes, and the fact that in both processes
the transformation of energy results in the liberation of heat.
Moreover, in both cases there is set free a quantity of an oxid
— in this case carbon dioxid, as in the case of fires using car-
bon or carbon-containing materials as the fuel. When we com-
pare these three conditions with what we find in familiar
animals, — our own bodies, for example, — we see a similarity
that suggests the possibility of all living things carrying on the
same fundamental process. And, indeed, it is proper to speak
of the young plants in the sprouting seeds as '' breathing,"
and to speak of the chemical changes going on inside the
living matter of plants and of animals as ''oxidation."

There are very many different chemical processes going on in
living things. Oxidation is only one of them. But it seems to
be nearly universal, and it seems to be the one that makes avail-
able to living matter the energy for its various other activities.

47. The soil and the young plant. We saw that seeds can
sprout without depending upon the soil. Yet we know that
the soil is essential to the growth of plants. This means that
although the young plant in the seed is for a time independent
of any soil materials, there comes a time in the course of its
development when further growth is possible only on condition
of receiving various substances from the soil.

29

30

ELEMENTARY BIOLOGY

From experiments in which the various materials that make
up soil (such as sand, clay, and the various salts) are used
separately and in combinations, we learn that it is not the
sandiness of the soil, or the color, or merely the water in it
that makes the growth of plants possible. We find that it is
something in the soil that can dissolve in ivater.

48. The salts of the soiL These soluble substances in the
soil are the salts, of which there are many different kinds.
Are all these salts related to plant growth, or only a certain
few — or perhaps only one ? These questions have been
answered by means of carefully planned and carefully conducted
experiments. In these experiments plants were grown in solu-
tions of soil minerals from which now one element and now
another was omitted.

It is found that the omission of some elements will absolutely
prevent the further growth of the plants, whereas the omission
of others will make no perceptible difference. From the results
of such experiments the following table has been constructed :

Element .

Occurrence in Plants

Special Function

Aluminum

In lower parts

No function.

Calcium

In leaves and stem

Related to the formation of plant cells ;
"makes plants hardy."

Chlorin

In lower parts

No function, so far as known, although
present universally.

Iron

In leaves and stem

Related to the formation of chlorophyl
(see p. 54).

Magnesium

In seeds and leaves

Related to the formation of seeds.

Manganese

In lower parts

No function.

Phosphorus

In seeds

Related to the activities of leaves ; takes
part in the formation of proteins (see
p. 56).

Potassium

In actively growing

Related to the formation of starch and

parts

sugar, and to the growing process.

Silicon

In stems and leaves

No special function.

Sodium

In stems and roots

No function, although present almost
universally.

Sulfur

In all growing parts

Necessary to the formation of proteins.

AIR AND SOIL IN RELATION TO SPROUTING 31

This shows not only whether a given element is found to be
necessary or not, but also in what particular way it is related
to the life of the plant.

49. The composition of plants. Another method used for
determining what there is in the soil that the plant depends
upon for its activities has been to analyze the plant to find out
of what it is composed. Such an analysis shows that certain
elements are present in the plant body, and we know that some
of these elements are present also in the soil. It is therefore
reasonable to suppose that the plant derives these elements
from the soil. It does not follow, however, that everything
taken by the plant from the soil is of use to the plant. The
most common elements found in plants are the following:

Carbon

Sulfur

Potassium

Oxygen

Phosphorus

Sodium

Hydrogen

Calcium

Iron

Nitrogen

Magnesium

Chlorin

(Compare with the composition of the human body, Fig. i,
p. 16, to see how much we are like the plants.)

Other elements may also be found in some plants, as silicon
and iodin ; but it is doubtful whether these are essential to
the life of the plant. Indeed, not all of those given in the
above list may be absolutely necessary, but most of them cer-
tainly are. Since a large part of the plant's life consists of
growing activity, the material for growth or for building up
the body must be a first condition of life.

The materials taken from the soil by the growing plant are some-
times 0.2^^6. plant food. Strictly speaking, these are not food, as we
shall see later (see p. 50); they are merely some of the materials
out of which plants manufacture their food.

CHAPTER VIII
SEEDS AND SEEDLINGS

50. The structure of seeds. On examining the outside of
any seed we can usually find a scar that was left when the seed
broke away from the little stalk by which it was fastened inside
the fruit. Very often we can also find a tiny hole through the
seed coat. This hole is called the rnicropyle. The seed may
absorb water through this hole, but it does not seem to be of
any importance in the mature seed. (See p. 302 and Fig. 134.)

The coat of the seed, which sometimes has more than one
layer, is apparently a protective covering, although in some
species of plants the protection is furnished by the fruit in
which the seed is borne. When the coat of a seed is removed,
we find the part of the seed that is really important in the life
of the plant. In fact, we may say that the seed contains a
young plant. The embryo is really a small, young plant;
and we may say that the seed is a young plant (embryo) plus
its protective covering.

51. The embryo. That the embryo is a plant can be seen
from a careful comparison with the parts of any ordinary plant.
Now, what are the parts of a plant } Ordinarily we see above
the ground only the stem and the leaves, but most of us know
that under the ground is the root. In most plants the stem
and the root are bra7ichmg organs ; in some plants the leaves
also divide or branch. All of the stem system, together with
the leaves, we sometimes call the shoot. So we may say that
the plant consists of root and shoot. But sometimes we find
flowers on a plant, or fruit. The flower is really a special kind
of shoot (see pp. 300 ff.), consisting of a very short stem with many
special kinds of leaves crowded closely together, and with

32

SEEDS AND SEEDLINGS

33

certain other special organs that have to do with the making of
seeds. One of these organs, when ripened, becomes the fruit.
Now, in the embryo of a bean or a peanut or a pumpkin
seed, it is very easy to find the parts corresponding to the root
and the parts corresponding to the shoot. The two fleshy parts
that make up the bulk of the embryo are really special kinds
of leaves. If we bend them aside carefully in the embryo of
a seed that has been soaked in water, without breaking them
off, we can see that they are attached to a short stalklike piece.
One end of this rod tapers to a point ; this end corresponds

Fig. 6. Embryos of plants

/, diagram showing relative positions of the parts of the embryo ; 2, embryo of peanut ;
3f embryo of pea ; 4, embryo of pine ; C, C, cotyledons ; E, epicotyl ; H, hypocotyl

to the root. The other end of the main stalk may be enlarged
at the tip into a tiny knob or bud ; in the bean embryo we can
make out two little leaves folded neatly over each other. This
end of the stem corresponds to the shoot.

The two fleshy leaves are called seed leaves, or cotyledons.
The part below the meeting point is called the rootlet, or the
radicle, or the hypocotyl, which means '' below the cotyledon."
The part above is called the first bud, or the plumule, or the
epicotyl, which means " above the cotyledon " (Fig. 6).

Although the cotyledons are considered to be leaves, they do
not in all plants become flat and green like the more familiar
leaves. In many cases they do not even come above the ground
during the young plant's development, as in the pea plant.

34

ELEMENTARY BIOLOGY

The function of the cotyledons seems to be confined in most
cases to the holding of reserve food^ which is drawn upon
by the baby plant until it is developed far enough to get food
for itself.

In some kinds of seeds the cotyledons are very thin ; in
such cases we usually find that there is a mass of food material
packed in all around the embryo. A mass of food thus placed
about the embryo is called the endosperm, which means
" within the seed." The grains and the castor seed are good
examples of seeds that contain endosperm (Fig. 7).

When we compare the embryo of a

grain, such as the corn, with the other

/ I J 7] / U ■ embryos that have been mentioned,

\\] l^^i/ u --^ V7 ^^ ^^^ ^^^ great difference in the

^•^ "f ^ 11 : /A Structure. The grain has but a single

cotyledon. This is rather large, though
not fleshy, and only the tip comes out
of the seed covering as the first leaf.
The base remains in contact with the
endosperm and serves as an " absorb-
ing organ," withdrawing food material
from endosperm and transferring it to
the growing plant.

There are many plants, besides the
grains, that have but one cotyledon in
the seed. This fact would not seem to be of any great importance
by itself, but it is connected with so many other characters, such
as the veins in the leaves, the structure of the stem, the structure of
the flower, and general habits of life, that we sometimes designate
one of the main divisions of seed-bearing plants as the monocotyh^
meaning the '' one-cotyls," and another as the dicotyls, or '' two-
cotyledon " plants. Among the dicotyls are included most common
weeds and cultivated plants, outside of grains.

The seeds of the plants belonging to the pine family (fir, spruce,
hemlock, etc.) have usually several cotyledons, and this family is
accordingly designated as the polycotyls in some books, this name
meaning " many cotyledons " (see Fig. 6).

Fig. 7. Seeds with endosperms

/, asparagus ; 2, poppy ; j, pine ;

^, maize, or Indian corn. (All shown

in longitudinal section)

SEEDS AND SEEDLINGS

35

52. Food in seeds. The concentrated food found in the
seeds of all plants is of interest to us in three ways : First of
all, we may infer that this food is actually used by the young
plant until such time as it is able to provide for itself. That
this is a sound inference may be tested by separating from
several seedlings the ** food reserve." Next, we can observe
that the cotyledons in such plants as the beans and peas do
actually shrivel away as the plant becomes larger ; and that the

g

Fig. 8. Young plants emerging from seeds

On the left, squash ; on the right, bean. In the squash a little outgrowth on the

hypocotyl keeps the seed coat in place while the cotyledons are carried aloft. C, C,

cotyledons ; E^ epicotyl ; //, hypocotyl ; gg^ ground line

contents of the corn grain also disappear as the seedling de-
velops. Finally, by means of chemical experiments we can see
that the changes taking place in the " food masses " of the
seedlings are of the kind we should expect to find if the
food were actually being transported to the growing portions.
(See p. 79.)

A second question that may arise is that of the origin of the food
which we find in the seeds. It is enough for the present to consider
that, as the developing seed obtained the materials for its growth from
the parent plant upon which it originated, the reserve food that we
find within the coat of the seed was probably also obtained from the

36 ELEMENTARY BIOLOGY

parent plant. How the parent plant makes its food we shall learn
in the lessons on food-making (see p. 53).

Another point of interest in regard to the food in the seed is that
of its availability for human use. This will be discussed later (see
Chapter XXII).

53. Seedlings. If we examine a few seeds that have been
planted two or three days, we may see that the hypocotyl has
emerged and is assuming the appearance of a root. At the
other end of the embryo we may see the unfolding epicotyl.
If we examine different stages of peas, squash, oats, corn, bean,
and so on, we shall be able to see a great variety of methods
by which the young plant crawls out of its covering and
establishes itself in the soil (Fig. 8).

Large seeds, containing a large amount of reserve food, are
apparently at an advantage, since they may develop more root
and more shoot before they are overtaken by the necessity of
providing themselves with food. We should therefore expect
that plants with large seeds would be, on the whole, more
successful in establishing themselves in a new territory than
plants with small seeds. We shall find, however, that the best
spreaders in the plant world are those with rather small seeds.
The speedy and secure establishment of the individual plant
is of great advantage, but even niore important is it that
seeds be well scattered. And in this respect the small-seed
plants with very numerous seeds have a decided advantage.

CHAPTER IX
EXTERNAL FORCES AND PLANTS

54. Gravity and growth. The force that acts most contin-
uously upon Hving things is doubtless gravity. Temperature
varies constantly, and the light is intermittent as well as vari-
able. We do not know much about the relation of electrical
conditions of the atmosphere to living things, and chemical
conditions we can consider only as they arise in connection
with particular kinds of substances. But gravity seems to be
constant without regard to hours or seasons. It is therefore
interesting to find how living things, and especially plants,
behave in relation to this force.

The question often occurs to people who have planted seeds,
or who have watched others do so. Does it make any differ-
ence which side of the seed falls uppermost ? We know that
the lower end of the hypocotyl becomes root, and that roots
usually live in the earth. What would happen if a seed were
placed in the ground with its hypocotyl pointing skyward ?

We can easily find out by means of experiments that permit
us to watch the development of the young plant under condi-
tions that make gravity act upon hypocotyls from different
directions. Incidentally we can discover that the shoot of a
plant is also sensitive to gravity, but that it responds in quite
the opposite way from the root. That is to say, the shoot
tends to grow away from the earth, whereas the root tends to
grow toward the earth.

55. Tropisms. To many of us this sensitiveness of the plant
will come as something unexpected, for we do not commonly
think of plants, as sensitive beings. The turnings that a plant
or an animal shows in response to the one-sided action of

37

38 ELEMENTARY BIOLOGY

some external force is called a tropism, from a Greek word mean-
ing " to turn." The response to gravity is called geotropism,
or "earth-turning." We may distinguish the behavior of the
root and the shoot by calling the former positive geotropism,.
and the turning away from the earth, negative geotropism.

56. How the plant moves. The plant has no muscles, nor
any structures that may be compared to muscles. The turning
of the root or of the stem is not the same kind of movement
as that which takes place when you turn your head or bend
your body. The curvature is brought about by a growths The
shoot or the root grows more rapidly on one side, or the growth
is stopped on one side, so that it grows in a curved line.

57. Light. That plants are sensitive to light is well known
to all who have had an opportunity to observe either house
plants or garden plants. A careful measurement of the growth
of plants left in the dark, and of similar plants exposed to
daylight, shows very definitely that withholding light from a
plant accelerates its growth. But since darkness is a purely
negative condition, it would seem that light actually restrains
the plant's growth. This is so different from what we com-
monly believe, that it is worth studying more closely.

58. Phototropism. Another response of plants to difference
of illumination is shown when we leave them exposed to a
one-sided illumination. Such an experiment will convince us
that a plant is sensitive to light just as it is to gravity.

The turning of a plant axis in accordance with the direction
of the illumination is cdiWtd phototropism. Most of our common
plants are positively phototropic in the shoot, and somewhat
negatively phototropic in the root.

59. The influence of water. The turning of leaves and
stems toward the light and the turning of roots and stems
according to the direction of the " earth's pull " are evidences
of the living organism's irritability. It has been shown that
the plant is also sensitive to various chemicals, and we can
determine for ourselves that it responds to water.

EXTERNAL FORCES AND PLANTS 39

These experiments must not be interpreted to mean that the
roots somehow know that there is more water on one side, or
that they have any way of choosing to go toward the water.
We may say merely that the plants are influenced in their
behavior by these various external conditions.

60. Fitness. In the three sets of responses studied — namely,
the responses to gravity, to light, and to water — we can see an
advantage to the plant in behaving as it does. The tendency of
the root to grow downward will, on the whole, bring the roots
of the plants into the soil, where the conditions for getting
water are more favorable than they are on the surface of the
soil. We can see that the responses of the shoot to gravity
and light are, in the long run, likely to bring the plant into
situations favorable to its further development. But it does
not follow that everything that the plant does is of advantage.

We saw that light actually interferes with the growth of the
plant, and yet, on the whole, the plant turns toward the light.
Is not this response injurious and suicidal.? But we shall find
later (p. 73) that the light is of great importance in the life
of the plant in ways connected not with growth but with the
making of food.

Many of the responses of animals — even of higher animals,
including ourselves — are just as mechanical as some of these,
simpler responses of plants. They are mechanical in the sense
that they result from the structure of the organism, and do
not involve anything in the nature of thinking or desiring or
choosing. Like the responses of the plants, most of the ani-
mal responses that we are likely to notice are of a kind that
help the organism in keeping alive — for example, by prevent-
ing injury or by helping in the obtaining of food. But among
animals, as among plants, we can find responses that seem to
be of no value whatever to the life of the organism, and some
that are even injurious under certain circumstances.

CHAPTER X
ABSORPTION FROM THE ENVIRONMENT

61. All cells absorb. The surface of a young root is made
up of cells packed so close together that even with the most
powerful microscopes we are unable to see any breaks through
which w^ater can pass. Yet it cannot be doubted that water
does pass through, and we may be sure that materials pass
through the walls of the cells.

62. Diffusion. Illuminating gas and the vapors of odorous
substances spread through the air very rapidly, by a process
called diffiisioft. Diffusion takes place also in liquids. Dif-
fusion represents a form of energy, since it is capable of
overcoming gravity, as we can see in the fact that sugar or
salt diffusing in water is actually lifted from the bottom of a
vessel and distributed to all parts. This attraction between
water and certain kinds of soluble substances helps us to
understand what happens in roots as well as in other parts of
living things.

The substance of which the root's cell walls are made up is
called cellulose. This substance cannot dissolve in water, but
it can absorb water in much the same way as glue or gelatin
does. Now water can diffuse through cellulose, although the
cellulose cannot dissolve or diffuse in water. Substances that
can dissolve in water can thus diffuse through the cell wall.

63. Diffusion through a membrane. When different sub-
stances dissolved in water are separated by a layer of cellulose
or gelatin, they may diffuse through the separating membrane.
Such diffusion is called osmosis. This process takes place in
the walls of cells, since the watery liquid on one side of such
a membrane is not the same as that on the other side. Thus

40

ABSORPTION FROM THE ENVIRONMENT 41

there is always a double current : some materials are always
passing out of a live cell and other substances are passing in.
In this way protoplasm receives from the outside its supply of
water, salts, and food. And it is by this process that materials
in the cell pass out. Gases as well as liquids diffuse through
the cell walls.

64. Osmosis in living things. The cell wall of a root cell
is seen to separate the protoplasm from the surrounding soil
water. Income through the root hair is therefore by diffusion
through the cell wall, or by osmosis. But the protoplasm
within the cell wall is not a uniform mass of substance. The
surface layer of protoplasm, the ''protoplasmic membrane,"
also offers obstacles to the free diffusion of liquids and gases
in solution, so that osmosis takes place here also. Indeed,
there are many substances that can pass through ordinary cell
walls of plants, but that cannot pass through the protoplasmic
membrane. Common sugar is an example of such a substance.

Some substances diffuse in water more easily than others.
Some of the solids with which we are acquainted do not dis-
solve at all. Of the substances that dissolve in water and can
diffuse, some will diffuse more quickly through cell walls than
others — and some may not pass through at all. Of the sub-
stances that can diffuse through cellulose, some can diffuse
through protoplasmic membranes more quickly than others —
and some cannot diffuse through such membranes at all. As
a result of these differences, cells exposed to the same material
surroundings may not be equally affected.

Not only do living things absorb materials from the outside
world by osmosis, but within the body of every plant and every
animal consisting of many cells, materials may pass from cell
to cell, or between cells and various body juices, by this process.

CHAPTER XI

ROOTS OF PLANTS

65. Structure of roots. We have already seen the general
appearance of roots, in the seedlings of the plants we used
for our earlier experiments, in the carrots, beets, and turnips

used at home, in the roots
of trees that have been pulled
up to clear the ground, etc.
The root hair is a single
cell formed by the outward
prolongation of one of the
skin cells (Fig. 9). The root
hairs are the actual absorbing
organs. Each root hair lives
but a short time, and then
shrivels up. As the tip of
the root grows on, new root
hairs are formed. The older
skin cells of the root die,
and their contents dry out.
Together with the shriveled
root hairs, these skin cells
form a protective covering
through which water does
not pass very readily. As
the plant becomes older and uses up more water, the absorbing
area of the root is increased by the formation of many side
roots and by the branching of the roots. But it is always in
the region near the growing tip of the main root and of the
many branch rootlets that absorption takes place.

42

Fig. 9. The tip of a young root
re, root cap ; h, /?, root hairs

ROOTS OF PLANTS

43

66. Wood and bark. If we examine the root of a plant
freshly removed from the ground, we shall find that there is a
soft, easily broken outer layer covering a tougher central por-
tion. This central part, running lengthwise in the root, is
called the wood or the ceittral cylinder. In a fleshy root
like a carrot or parsnip we may

distinguish the central cylinder
from the bark, or co7iex, in both
a cross section and a longitudinal
section. In very thin slices made
lengthwise through the growing
tip of a young rootlet we are
able, with the help of a micro-
scope, to see the character of the
cells (Fig. lo). The cortical, or
bark, layer can be distinguished
from the wood layer by the fact
that the cells of the former have
about the same diameter in one
direction as in another, whereas
the cells of the central cylinder
are considerably longer than they
are wide, and their long diam-
eter is parallel with the long
diameter of the root.

67. Growing layer. The layer
of cells lying between the wood
cylinder and the bark is called
the growing layer. It is only

the cells of this layer that are capable of producing new cells
by the process of cell division. The younger bark and wood
cells are capable of increasing in size, but they cannot give
rise to new cells. Growth in length is the result of the
formation of new cells by a special growing layer near the
tip of the root.

Fig. io. Diagram of root structure

e, epidermis, or skin ; c, cortex, or

bark ; g, cambium, or growing layer ;

7(', wood cylinder, consisting of fibers

and vessels ; /, pith

44 ELEMENTARY BIOLOGY

68. Vessels and fibers. In the cortex, transportation of
material probably takes place by diffusion from cell to cell.
In the central cylinder, however, we can find that liquids
are moved bodily through the long tubes or vessels that act as
the main channels in the transportation of materials taken
in by the root hairs. Through some of these tubes materials
are also brought down from the stem to the growing layer of
cells. In the central cylinder we can find that many of the cells,
instead of forming ducts, become thick-walled and stiff. These
'' fibers " give the cylinder its toughness and rigidity. Bundles
of fibers and vessels are sometimes cdW^d Jibro-vascular bundles,
the X.QrxnJibro meaning '' of fibers," and vascidar meaning " of
vessels," or tubes (Fig. lo, iv).

69. Forms of roots. The structure of roots is fairly uniform
for different kinds of plants. But roots nevertheless appear
in very many different forms, from the thin, stringy roots of
grains to the massive fleshy or woody roots of beets or trees.
These differences are found to be closely related, in many
cases, to the conditions under which the plants live. Thus,
fleshy roots are often associated with the bieiinial habit. In
such plants as beets, carrots, and parsnips the first season of
the plant's growth is spent in Ynanufacturing food and deposit-
ing it in the root. The next year comparatively little foliage
is produced, but a stalk bearing flowers (which in turn develop
into fruit, bearing seeds) uses up practically all the food that
has been left over from the previous season. In contrast with
this habit of life we find the plants that sprout, grow up into
maturity, and die, all within one season. These annual plants
have, as a rule, rather delicate, or fibrous, roots.

Trees and woody shrubs, which continue to live year after
year, develop massive shoots. Corresponding to this fact we
may note that such plants also develop elaborate, strong roots.
From this we may see that the structure of the root and its
functions are closely related to each other and to the character
of the plant. There is a connection, on the one hand, between

ROOTS OF PLANTS

45

the structure of the root and the size of the plant that it
anchors, and, on the other hand, between the size of the root
and its food-accumulating, or its absorbing, activity (Fig. ii).

70. Tap-roots. In many plants the main root continues to
grow downward into the soil as long as the plant lives and
as long as the tip of the root remains uninjured. Such a main
descending root is called a tap-root. The fleshy roots that have

A^r,

Fig. II. Forms of roots

7, tap-root of dandelion ; 2, fibrous root of buttercup ; j, bundle (or " fascicled ") root of
dahlia ; 4, fleshy root of beet

been mentioned are all tap-roots ; and a number of trees, as
certain kinds of maples, also produce tap-roots. When a tap-
root is injured or cut off, some of the side roots turn and grow
downwards, although in a few cases the tip of the , tap-root,
when not too much injured, can regrow a new tip and continue
the main line of growth.

71. Root pressure. We have found that when osmosis takes
place in a root there is likely to be an excess of movement
in one direction. We should expect more to come into the

46 ELEMENTARY BIOLOGY

root than goes out, since, on the one hand, we know that
the growth of a Uving thing depends upon an excess of income
over outgo ; and, on the other hand, we know that the soil
water is less concentrated than the juices of the root. The
stream of incoming material actually sets up a current of liquid
that is forced from the root into the upper parts of the plant.

Fig. 12. Sand dunes at Pine, Indiana

The roots of the grass Calamovilfa longifolia bind together the grains of sand, gradually
leading to the formation of larger and larger soil masses. The sand that has no plants
growing in it is blown about by the winds. (From photograph by Dr. George D. Fuller)

This can be seen in the flow of sap, as when the sugar maples
are tapped for sirup in the spring, and it can also be shown
experimentally.

72. Uses of roots. It is because of the habit of depositing
food in their roots that many plants are of especial interest to
us. Our common vegetable roots can be shown to contain a
great deal of food, such as starch, sugar, and proteins. Although
our fleshy vegetables contain from about 8o per cent to 90 per
cent of water after the skin is removed, they are still worth

ROOTS OF PLANTS

47

Fig. 13. Adventitious roots

A leaf of bryophyllum removed from the stem will
put forth adventitious roots and shoots from the
notches on the edge, thus giving rise to new plants

using for their other
contents. In addition to
the organic substances
and the useful mineral
salts that they contain,
these vegetables have a
relatively large bulk of
cellulose, which is help-
ful in stimulating the
activities of the intes-
tines (see p. 117).

Fleshy roots are used
in large quantities as
fodder for cattle. To some extent roots are also used as
sources of drugs and flavoring materials. Among the latter
the most important are the
extracts of the licorice root,
the sassafras root, and the
sarsaparilla root.

Because of the close ad-
hesion of the root hairs to
the grains of sand in the
soil, roots are very effective
agents in binding the soil,
enabling the latter to with-
stand the eroding effects of
water as well as of wind.
For this reason certain kinds
of grasses are sometimes
planted on sandy strips, to
prevent the complete re-
moval of the sand by the y,^_ ,4. Prop roots

winds. The hillocks formed ^ear the base of the trunk the corkscrew pine
by clumps of such plants (P^mia/ms) sends out prop roots in a manner
, . similarto that of the Indian corn. (From photo-
may COntmue to enlarge for graph loaned by New York Botanical Garden)

48

ELEMENTARY BIOLOGY

years, and to give protection to other kinds of plants until the
earth has become compact (Fig. 12).

Although roots do not generally put forth buds or shoots,
the roots of some shrubs and trees — as certain willows,
poplars, and hawthorns — do so, and can be used for propa-
gating the species. In some plants the roots will form new
shoots if the old shoot is completely' removed or destroyed.

On the other hand, roots
frequently arise from stems
or leaves, thus making pos-
sible the propagation of
plants by means of cuttings.
Roots that originate in this
manner are called adventi-
tioiis roots. Most of our
common house plants, and
willows and other trees, can
be propagated by keeping
twigs in water or wet sand
until roots appear, and then
transplanting them into soil.
If the leaf (or even a piece
of leaf) of a begonia or of
a bryophyllum be placed on
damp earth or sand, tiny
roots will be seen growing from various points along the edge
in the course of a few days. In these species buds will also
be produced, so that after a while we can separate small but
complete plants from the leaf, and get these to grow into
full-sized individuals (Fig. 13).

Blackberry and raspberry bushes are frequently propagated
by layering, which consists in bending the flexible stems out
and burying the tips in the ground. Adventitious roots are
formed on the covered portions, and, later, buds form new
shoots. The old connecting stem is then cut away. A similar

Fig. 15. Climbing roots

The English ivy, like many other climbing
plants, clings to its support by means of adven-
titious roots that grow out all along the stem

ROOTS OF PLANTS 49

process takes place naturally in the strawberry plant, whose
creeping stems produce new roots and new tufts of leaves, so
that in the course of a season a single plant may spread out
and cover a large area.

73. Adventitious roots. At the lower joints of the stalk of Indian
corn adventitious roots are formed very early in the life of the plant

Fig. 16. The banyan tree {Ficus bengalensis)

The adventitious roots from the horizontal branches finally attach themselves to the soil.
By means of these roots the tree is able to spread over a large area, a single tree some-
times extending over several acres of ground

(Fig. 14). Adventitious roots usually grow from the stem (though
sometimes from leaves), and are most frequently in the nature of sup-
porting or anchoring organs. The climbing organs of the English ivy
as well as of the poison ivy are adventitious roots (Fig. 15), and in
some of the tropical tree-climbing plants the roots are very fully de-
veloped as holdfast organs. The banyan tree of Asia puts forth
adventitious roots from the horizontal branches (Fig. 16).

CHAPTER XII
WHAT FOOD IS

74. The material needs of protoplasm. Several classes of
materials seem to be necessary to keep protoplasm working.
Water, for example, which we have seen to be necessary for
the sprouting of seeds as well as for the absorption of mineral
matters by the roots of a plant, is a constant and necessary
factor in the activity of live protoplasm. It is thus a necessary
part of the income of every plant and every animal. Within
the cells, too, water makes possible the movements of the
various substances, and their chemical action and reaction with
.one another. In the larger plants and animals the transfer of
materials between various parts of the organism takes place
through liquid media, — as blood, sap, bile, milk, — and these
consist very largely of water.

Certain minerals seem to be necessary parts of the income of living
things. Some of these salts, through their chemical actions, appear to
start other chemical processes, and are therefore called activators.
Other salts, or elements, appear to modify certain chemical processes
(just as the bromide used by the photographer makes the development .
proceed more slowly), and are called regulators.

We have already seen that living things generally use oxygen
in the course of their activities.

75. What food is. In addition to the water, oxygen, and
various mineral salts, every living thing uses various substances
as material out of which protoplasm is constructed by the
process of assimilation, and it uses substances that can be
oxidized within the cells and thus yield energy.

Whether everything that an organism takes in from the
outside is to be called food or not is altogether a matter of

50

WHAT FOOD IS 51

convenience. It is found less confusing to restrict the use
of the word food to such substances as can serve as building
material for protoplasm or as sources of energy through
oxidation.

76. Food organic. Using the word food in this sense, then,
we must notice first of all that food materials are found in
nature only in the bodies of living things ; that is to say, they
are organic^ to use the older term. From a chemical point of
view we may divide the foods into two main classes : those
that contain nitrogen and those that do not. The foods of
the first class are called proteins and are represented in our
familiar supplies by such substances as albumen, or white of
Qgg ; the curd or casein that is formed when milk sours ; and
the gluten, or pasty substance, in wheat flour or bread. Similar
nitrogen-containing substances are found in the cells of mus-
cles and are called myosin ; others, found in the seeds of the
plants belonging to the bean family, the Leguminosae, are
called legmnin.

Of the non-nitrogenous foods there are two main divisions,
the fats and the carbohydrates. The fats are familiar to us in ■
such substances as butter, suet, lard, tallow, olive oil, cotton-
seed oil, peanut oil, and others. The carbohydrates comprise
all the sugars and all the starches.

77. Food functions. In dividing the foods into the two
classes, nitrogenous and non-nitrogenous, we have at the same
time separated them in accordance with their true relations to
protoplasm. For the proteins are the foods that are necessary
for the building of protoplasm ; the protoplasm may be said to
consist fundamentally of protein. The fats and carbohydrates
are important in living cells as fuel, or oxidizable material.

We find accordingly that all seeds contain protein, some in larger
proportions (beans, peas, lentils, for example) and some in smaller
proportions. In addition to this, all seeds contain either fat (as the
castor bean, peanut, cotton seed, flax seed) or some carbohydrate (as
the bean, cereals, date).

52 ELEMENTARY BIOLOGY

78. Summary. We may summarize the materials required
by a living cell in this way :

1. Water. The chemical changes that distinguish living protoplasm

can take place only in the presence of water.

2. Protein. Out of this, new protoplasm is constructed, resulting

either in the growth of the cell or in the replacement of
protoplasm that may have been destroyed.

3. Fuel foods. In addition to the protein oxidized in the cell there

is usually some other material that is oxidized. Two classes
of compounds commonly furnish this fuel : namely, {a) carbo-
hydrates; (p)fats.

4. Salts. Various mineral, or inorganic, compounds are necessary

for maintaining the activities of protoplasm. These are of
many kinds, although certain of the elements contained in
these salts are used by all living protoplasm (see p. 31).

5. In the bodies of human beings and of other animals (and pos-

sibly also of certain plants) peculiar juices are produced that
have a direct influence upon the activities of cells. The
ferments contained in these juices are just coming to be
understood. It is sufficient for the present to note that they
do affect protoplasm activity, and that some of them are
necessary for certain cells.

6. Oxygen. Although this is not usually regarded as part of the

food, it is an essential part of the income of every cell. It
is the chemical union of oxygen with other substances that
sets free the energy by which the protoplasm does all of
its work.

CHAPTER XIII
THE ORIGIN OF FOOD

79. Organic foods destroyed. When proteins, fats, and car-
bohydrates become assimilated, 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. The
question may then be raised, If living matter can continue to
live only at the expense of other living matter, and if living
matter is constantly being destroyed (oxidized), how can the
total amount of protoplasm be maintained, to say nothing of
the amount of live matter being increased ?

80. The making of organic food. It is obvious that some-
where in the circle of feeding, new foods must be admitted
into the world of living things from the world of non-living
things. The answer to the question was found in the discovery
that the green parts of plants are active in the manufacture of
new organic foods.

81 . A manufacturing process. The process by which organic
materials are built up (chemically) out of inorganic materials
may be compared to a manufacturing process. In every such
process certain factors are essential. There must be (i) raw
material, (2) tools or machines for working on the material,
and (3) energy for driving the tools or machines.

In addition to these factors, we can understand that there
is (4) a main product and sometimes material left over, called
''waste," or, better, (5) the by-prod7Lct.

82. Factors in starch-making. What are the factors in the
process of starch-making }

The raw materials used by the plant are found to be water
and carbon dioxid.

S3

54

ELEMENTARY BIOLOGY

The machines or instruments directly involved are different
from the machines with which we are familiar. Instead of
having wheels or levers or other moving parts, these machines
are chemical engines, each consisting of a lump of protein
with some of the cJilorophyl that gives the familiar plants their
distinctive color. This chlorophyl is the tool, or transformer of
energy, in the food-making process (see Fig. 17, and Fig. 23,
p. 70). The chlorophyl-bearing particle is called a chloroplast.

Carbon dioxid

Light

Ener-

Sun

111111

Oxygen

• H • H
H C H •

H •
C H

Carbo-
hy-
drate

H • H • • H C
C H • H C • •

HH HH HH HH HH HH

11 1 1 11

tttttf

CH»

eg.

S Chloro-
phyl

ChloroijJ
phyl

•HC

•ijC

^.HCj

Carbo-
hy-
drate

W44-W

Water Oxygen

Fig. 17. Starch-making by chlorophyl

We may think of photosynthesis as taking place in two stages : in the first the raw
materials, water and carbon dioxid, are broken up into their constituents — carbon,
hydrogen, and oxygen ; in the second these elements are recombined into carbohy-
drates, and the surplus oxygen is set free. The energy for this chemical process is
sunlight ; the transformations are brought about through the action of chlorophyl

The energy for doing this work is the light from the sun.
Although the work cannot go on at too low a temperature, it
is the light that is used in the process, and not the Jieat.

83. Oxygen a by-product. The starch that is formed from
water and carbon dioxid by the action of sunlight through
chlorophyl contains the elements found in the raw materials
— namely, carbon, hydrogen, and oxygen. In starch, as in
most carbohydrates, hydrogen and oxygen occur in the same
proportions as they do in water. The raw materials taken in
by the plant therefore contain an excess of oxygen. This

THE ORIGIN OF FOOD 55

element is given off in a free, or uncombined, state during
the process of starch-making.

84. Sunlight and life. The process which we have called
starch-making is really a group of processes. In some green
plants starch is never found, and yet the transformation of
carbon-hydrogen-oxygen materials by the sunlight, acting through
chlorophyl, goes on in these plants. The common fact in all
these processes is that some kind of carbohydrate (usually
some kind of sugar) is produced. This process of carbohydrate
formation is called photosynthesis, from Greek words meaning
"light" (compare ///^/^-graph) and "put together." In addi-
tion to forming sugar, some plants have a way of condensing
the sugar, shortly after it is formed, into starch grains (Fig. 17).

Without going deeply into the chemistry of photosynthesis we
may note that in the making of carbohydrate the energy of the sun-
light has practically broken up a combination (COg) that is ordinarily
formed with the liberation of energy. That is to say, through the
action of light, carbon and oxygen have become separated so that
they are capable of again combining and liberating energy. Carbo-
hydrate may thus serve as a source of energy by becoming oxidized,
either in the bodies of living things or in a flame. We may thus see
that all the energy that plants or animals use as a result of the
oxidation of carbohydrates is derived from the sun's energy. There
is more than poetry in the statement that every human act is a
transformed sunbeam.

85. Origin of fats. All organic materials appear to be derived
directly or indirectly from carbohydrates. It has been found
that fats originate in the cells of animals as well as of plants,
by a modification of starches or sugars. Fats are characterized
by containing a large proportion of carbon and a small propor-
tion of oxygen. The chemical process by which carbohydrates
are changed into fats is not understood.

86. Origin of proteins. The foods of the third group, the
proteins, consist of very complex substances. They all contain
nitrogen, in addition to carbon, hydrogen, and oxygen. Some

56 ELEMENTARY BIOLOGY

also contain sulfur, and some phosphorus. From careful studies
of plants it is supposed that proteins are manufactured by certain
cells when these are supplied with carbohydrates and salts con-
taining the necessary elements. For example, nitrates contain
nitrogen, which the plant can use, phosphates contain phos-
phorus, sulfates contain sulfur, and so on. A green plant is
therefore capable of manufacturing its own food if it receives,
in addition to the water and carbon dioxid, a suitable supply
of minerals from the soil. Many plants without chlorophyl, as
certain kinds of molds, have also been shown to be capable of
manufacturing proteins when supplied with carbohydrates and
suitable minerals.

CHAPTER XIV
THE CHEMICAL CYCLE OF LIFE

87. The carbon cycle. An understanding of the behavior
of green plants in relation to food-making shows us how closely
the living things in the world depend upon each other. Let
us take the case of carbon, which is an essential constituent
of all living matter. The carbon in our bodies came from the
proteins, fats, and carbohydrates which we ate. We obtained
these either from the bodies of plants or from the bodies of
animals. In the latter case they were still derived from plants,
for the cows or pigs or chickens that we used as food got
the carbon in their bodies from the plant food which they in
turn ate.

Now^the plant gets its carbon from the carbon dioxid in the
air. (Water plants can get carbon from the carbon dioxid
dissolved in the water.) But what is the source of the carbon
dioxid ? We saw (p. 1 2) that the proportion in the air is very
small. A few warm, sunny days in August would enable the
plants of this country to use it all up, and that would be the
end of everything. But the winds are all the time stirring up
the atmosphere, so that new supplies of this important material
are brought to the plants ; and there are certain rocks — lime-
stone and marble especially — that are capable of yielding a
small quantity of this gas when they decompose. But this
amount is very small indeed when we consider what is being
used up by the plants from hour to hour. There is, however,
still another source.

We have seen (p. 29) that all living things, while using up
oxygen from the air, are at the same time throwing off carbon
dioxid. Moreover, every fire throws off quantities of carbon

57

58

ELEMENTARY BIOLOGY

dioxid. This carbon dioxid then becomes available as a source
of raw material for food in the leaves of plants. Now we must

remember that the
carbon dioxid from
fires and from ani-
mals is limited in
amount by the work
of plants, for the
only burnable mate-
rial that is available
is the organic ma-
terial manufactured
in the first instance
by the green plants.
Whichever way
we go at it, we see
that our lives are
dependent upon the
activities of the
green plants ; and
on the other hand,
the continued exist-
ence of neiv green
plants is made pos-
sible by the oxida-
tion of their organic
substances in the
bodies of animals
or in fires. There
then, a certain

Fig. i8. The carbon cycle

Fires and all kinds of living things are constantly throw-
ing carbon dioxid into the air. Green plants, represented
by the tree in the diagram, withdraw carbon dioxid from
the atmosphere and return oxygen. The material of tho
green plant is made up in part of the carbon derived
from the carbon dioxid. This material serves as foo(J for
animals and as fuel for fires. The animals oxidize^ this
material ; or they are eaten by other animals. Finally, the
carbon of larger plants and animals is oxidized by simple
organisms, such as bacteria and fungi, and is returned
to the atmosphere

IS

balance, or limited
relation, 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, there would come a time when the growth of

THE CHEMICAL CYCLE OF LIFE

59

^^rC02

CO,

nt-^

plants would be affected by the lack of carbon dioxid. Should
the amount of plant life decrease greatly, a limit to the growth
of animals would soon be reached for lack of food (Fig. i8).

88. The oxygen cycle. In the matter of oxygen we can see
a similar relation between plants and animals. The amount of
oxygen in the atmosphere is very much greater than the amount
of carbon dioxid, but it is a limited amount, and all living things
are constantly draw-
ing upon it to en-
able them to set free
the energy that they
use up in the course
of their activities.
After oxygen has
once been used in
the oxidation of or-
ganic material, it is
no longer available
for similar use. If
all green plants
should suddenly
stop their activities,
the amount of car-
bon dioxid in the
atmosphere would
steadily increase,
but the amount of

oxygen would just as rapidly diminish. A point would soon be
reached at which the maintenance of animal life would be no
longer possible. Through photosynthesis oxygen is liberated,
thus becoming again available for the breathing of animals
and plants (Fig. 19).

89. The nitrogen cycle. In the matter of nitrogen our de-
pendence upon living things of various orders is still more
marked. The plants growing in a given area take from it

C02

Fig.

CO2
[9. The oxygen cycle

Oxygen from the atmosphere is taken up by plants, by

animals, and by fires. All of these return carbon dioxid

to the atmosphere. The green plants take carbon dioxid

from the atmosphere and return oxygen

6o ELEMENTARY BIOLOGY

water and minerals. The water is replaced by the rains, but
the minerals are limited in amount. Although the movements
of water in the soil may distribute salts and make new quanti-
ties available, the exhaustion of certain minerals from soils
under cultivation is an established fact. To take the nitrates
alone, we find that the plants can manufacture proteins only
if they have a supply of nitrogen in a combined form ; that is
to say, they cannot utilize free nitrogen, such as is found in
the atmosphere, but must have nitrogen compounds.

In the course of the vital processes in the bodies of plants
and animals, proteins are broken down into simpler compounds
of nitrogen. Some of these can be used again by plants in the
making of proteins, but others disappear in the air, and so the
nitrogen is lost from the cycle of life. As a matter of national
economy, people are finding it worth while to save the manure
of the barnyard and even the sewage of cities for the combined
nitrogen that these substances 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.

Resort has been made to deposits of nitrates found in the
soil, 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 islands for hundreds of years. This guano contains
nitrogen and other elements usable for food-making by plants,
and has been imported and sold as a fertilizer. But the amount
of guano is limited and constantly diminishing. Indeed, of all
the elements, nitrogen seems to be the one that does not come
back into the life cycle by an automatic process. From the point
of view of a nation that can look ahead more years than the
length of an individual's life, this is a serious problem. The
nitrogen supply will probably last as long as you and I are likely
to live. But society expects to outlive us, and it is the business
of the statesman to look ahead for those not yet born (Fig. 20).

THE CHEMICAL CYCLE OF LIFE

6i

Nitrogen in
Atmosphere

>^Bacteria

^^ and
Fung

Fungi-^

Fig. 20. The nitrogen cycle

Nitrogen compounds are withdrawn from the soil by plants, represented by the tree in
the diagram. The nitrogen material feeds animals (as the squirrel) and also other plants
(as bacteria and fungi). Some of the waste products of life activity are returned to the
soil ; other nitrogen compounds are scattered and lost in the air. The only way by which
nitrogen from the atmosphere is regularly returned to the soil is through the action of
bacteria found on the roots of plants of the bean family, represented by a bean plant in
the diagram. Bacteria of decay bring about a return of the nitrogen in the bodies of dead

plants and animals

90. The nitrogen problem. In comparatively recent years
two solutions of the "nitrogen problem" have been presented.
One of them rests upon a better understanding of living things;
the other is an application of chemical knowledge. It has been
found that there are present in many soils tiny one-celled plants
called bacteria. They are related to the germs that are known

62

ELEMENTARY BIOLOGY

to cause certain diseases. Some of these germs, when suppHed
with carbohydrates, are capable of fixing the nitrogen of the
atmosphere by combining it into proteins and other nitrogen
compounds.

91. Nitrogen-fixing bacteria. On the roots of bean plants,
peas, clover, alfalfa, and other plants of this family there are
tiny swellings, or tubercles. Some of the nitrogen-fixing bacteria

are found in all
of these tubercles.
The bacteria can
make much more
protein than they
can use, just as
most green plants
can manufacture
much more sugars
or starches than
they can use. The
plants of the leg-
ume family con-
tain, as a result,
a much larger pro-
portion of nitroge-
nous compounds
than any other
plants (Fig. 21).

92. Rotation of crops. If we grow several crops of grain
on a farm, and find that the size of the crop tends to diminish
through lack of nitrogen, we do not have to abandon the farm,
nor do we have to import expensive nitrogen fertilizer. We
have only to plant a crop of peas or clover, and to see to it
that there is a plentiful supply of the special kinds of bacteria
that form the tubercles on the roots of our plants. It is now
possible to buy cultures of the species of bacteria that are
known to thrive best on any particular legume plant.

Fig. 21. Tubercles on the roots of red clovei

THE CHEMICAL CYCLE OF LIFE

63

->Oxyg:en-

£

-Carbon dioxid<-

1

Plants

FOOD

I

In the course of the summer the bacteria in the tubercles
will take in a large quantity of nitrogen from the air. Part
of this they will use in making proteins for immediate con-
sumption ; another part will be taken from them by the roots
of the plant upon which they grow ; and at the end of the
season there will be
present in the soil
and on the soil a
great deal more ni-
trogen in combined
form than there was
at the beginning. The
crop can be plowed
under, and the nitro-
gen compounds in
the plants will thus
be added to the soil.
After another season
of this kind of crop
there will be enough
nitrogen added to the
soil to support several
crops of grain.

This rotation of
crops has been prac-
ticed by experienced

Fungi

and

Bacteria

Soil Materials-*-

FiG. 22. The interrelations of organisms

The green plants, using water and carbon dioxid and
salts from the soil, are the source of all food and the
source of much oxygen derived from the decomposition
of carbon dioxid (during photosynthesis). The food is
used by animals and by lower plants (fungi and bacteria),
and in the end the substance of the animals is also used
by the fungi and bacteria. The carbon dioxid given off
by the animals and by the fungi and bacteria sooner or
later finds its way back to the green plants through the
air or water. The wastes given off by these organisms
also become in time raw material for the food of green
plants, through the soil

farmers for many

centuries, but it is only within the last thirty or forty years

that the significance of rotation has been understood.

For the chemical solution of the nitrogen problem we are indebted
to the Swedish chemist Svante Arrhenius, who worked out a process
for making nitrogen combine with other elements under the influence
of electric currents. This method is economical only if electricity can be
obtained at a low cost, as from waterfalls. To burn fuel for this purpose
would cost more than the value of the nitrogen compounds produced.

64 ELEMENTARY BIOLOGY

The interdependence of living things in the matter of food
manufacture has been shown from the point of view of the
oxygen cycle, of the carbon cycle, and of the nitrogen cycle.
This idea may be more clearly perceived from the diagram
on page 63 (Fig. 22).

With the outbreak of the Great War the nitrogen problem
took on a new aspect, for nitrogen compounds are as necessary
for the manufacture of explosives as they are for the manu-
facture of protoplasm, that is, the raising of crops. The
leading nations have established chemical factories for the
production of nitrogen compounds out of atmospheric nitrogen
by means of electricity obtained from waterfalls.

CHAPTER XV
THE SOIL AS THE SOURCE OF OUR MATERIALS

93. The soil. Just as the sun-light and sun-heat are the
sources of our energy, so the materials in the soil, water, and air
are the sources of our physical constitutions. We have seen
that water is necessary for all life processes, and that the
carbon dioxid in the air supplies material for the making of
carbohydrates. All the other materials found in the bodies
of plants and animals are derived from the soil.^ Those who
live in the country usually appreciate our dependence upon the
soil for our life, but most young people in the cities come to
think of the land as merely the place or surface upon which
we live. The crowding of a population may mean not simply
that people live too close together for comfort or for health ;
it may mean also a shortage of food supply due to insufficient
soil for growing crops.

As the population of a nation grows, the second kind of
crowding is likely to become serious. There was a time when
thoughtful people looked forward to such overcrowding with
a feeling that it must result in great destruction of human
life or in great suffering through general poverty. Indeed, in
past times much of the poverty and famine was due to the
inability to secure from the soil adequate supplies of food. At
the present time, however, we are rapidly learning to increase
the yield of our cultivated land out of proportion to the increase
in population.

1 This is apparently not true of the plants that float in ponds or rivers or
oceans, and of the animals that feed upon such plants. But in reality the
salts dissolved in the waters have been washed out of the rocks and soils
along which the brooks and rivers flowed on their way to the sea.

65

66 ELEMENTARY BIOLOGY

94. Exhaustion of soiL One of the dangers of the past was
the fact that after many crops of plants had been taken from
a soil, there was a lack of the mineral salts required for plant
growth. In addition to nitrogen, plants need phosphorus, pot-
ash, calcium, and iron. There is no danger of ever exhausting
the iron in a soil, for this element is used in such small
quantities that plants will have stopped growing for lack of
some of the other elements (for example, phosphorus or nitro-
gen) long before the iron supply is considerably reduced. In
many kinds of soil the same thing is true of calcium. But the
other elements are used in such large quantities (in propor-
tion to the amounts present in most soils) that they practically
limit the use of soil for crop raising. It is chiefly for this
reason that so many farms in the eastern parts of this country
have been abandoned ; the farmers found that they could not
raise, crops on the old soil.

95. Fertilizers. To make up for the withdrawal of materials
by crops, it has for ages been customary to put various sub-
stances on or into the soil. These substances are called ferti-
lizers and include limestone or gypsum, barnyard manure and
guano, crushed bones and ground phosphate rock, and many
other substances. In this country the farmers spend about
^125,000,000 annually for commercial fertilizers, besides what
they use from their own dungheaps.

The first thought in the use of fertilizers is to replace in the soil
materials that are lacking for plant growth. Some fertilizers, how-
ever, are sometimes added not so much to supply material that the
plants may use as to produce chemical changes in the soil, to make
the latter more suitable for the growth of plants. For example,
gypsum is sometimes used to supply calcium, but it may also be
used in some cases to make the phosphorus in the soil more easily
available for the plants.

96. Biology of soil. The soil is more than a mixture of
substances having physical and chemical properties. It con-
tains many different kinds of very small plants and animals

SOIL AS THE SOURCE OF OUR MATERIALS 6j

(most of them too small to be seen without a microscope)
whose activities have an important bearing upon the life of
the green plants that interest us. We have seen that some
of these microbes are useful, as in the case of the bacteria
living in the tubercles of clover and alfalfa etc. (see p. 62).
Others, however, are injurious. Some of the latter may be
destroyed by the addition of sulfur to the soil, with the result
that the size of the crop is increased. Strictly speaking, the
sulfur is not a fertilizer, although it helps to increase the yield.
Another effect of fertilizers has been shown in relation to
the fact that growing plants, like other living things, throw
off waste matters. Some of the waste matters thus thrown
into the soil are poisonous. Certain materials added to soil
containing these poisons have been found helpful, not because
they add anything usable, but because they counteract the
poisonous substances. In a similar way certain materials may
help by counteracting the poisons or acids produced by the
usual inhabitants of the soil that we do not often see.

97. Intensive cultivation. But even if, by using fertilizers
and other substances, we are able to keep the soil under culti-
vation indefinitely, the pressure of the population must appear
as soon as all the suitable farm land is settled. Modern science
has anticipated this emergency by teaching us how to get more
food out of every acre of land, through w^hat is called inten-
sive farming. This includes a thorough use of the soil through-
out the year. By forcing plants to grow more rapidly than
they would ordinarily, — by selecting rapidly maturing varieties,
by covering against cold weather, by artificial watering, by more
thorough tilling, and so on, — the cultivator is enabled to pro-
duce from two to seven crops a year on a given piece of land.
This makes possible the support of a larger population on the
same territory.

98. More soil. In addition to making the soil under culti-
vation yield more, a civilized people is able to extend its
resources in other ways. In this country, for example, nearly

68 ELEMENTARY BIOLOGY

half the land area, outside of mountain and rock, which cannot
be cultivated, consists either of swamp land or of desert land.
Soil that is too wet is just as useless for farming as soil that
is too dry. But through the cooperation of farmers and engi-
neers and workers of all kinds it has been possible to reclaim
millions of acres of swamp land and millions of acres of desert
land, and to make it all usable for raising valuable crops. By
draining the swamps and by bringing water to the arid regions,
through miles of canals and ditches and pipes, soil containing
vast amounts of food-making salts has been added to the
national wealth. There is, of course, a limit to what man
may be able to accomplish in the way of reclaiming land, — for
example, in some of the Western dry regions the bringing of
water may not be practicable if the distance is too great. But
when we consider that at the present time more than half of
the great staple food crops of the world are raised on land
that is artificially irrigated, — in China, India, Egypt, Canada,
and other countries, — we can see that the possibilities in this
direction will probably not be exhausted in many generations.
99. Soil waste. The fertility of the Nile valley seems to
be inexhaustible. This is not due to the higher concentration
of usable salts in this soil than is found elsewhere ; indeed,
if the mineral matter were too highly concentrated, the plants
could not grow, as we can see when we try to water garden
plants with sea water. The richness of this soil is due to the
fact that the river is constantly bringing down into the valley
more and more material from the rocks in the mountains
where the river has its sources. In our own country every river
that empties into the sea carries away tons of usable minerals
which thus go to waste. In connection with some of the irriga-
tion projects in the Southwest, much water is lost during the
spring, and with the water a great quantity of valuable mineral
salts. Plans are being developed for saving this water in huge
reservoirs, some of which are already completed. In this way
it will be possible not only to irrigate .larger areas but also to

SOIL AS THE SOURCE OF OUR MATERIALS 69

save from waste the soil materials out of which our food supply
can eventually be greatly increased.

So far as the soil is concerned, we need not fear that the
earth will become uninhabitable for many centuries. The
pressure of the population, even if it becomes several times as
great as it has been in China or India, can be met by the
application of science and cooperative effort to the resources
now in sight. If there is to be starvation, it will not be
because the earth and the sun and the green plants fail us.

CHAPTER XVI

Palisade layer

THE LEAF AS STARCH FACTORY

100. Leaf characters. The most common fact about a leaf
is that it is fiat and comparatively thin. Many kinds of leaves

have stalks, or pedicels, and
all leaves have veins run-
ning through the flat por-
tion, or blade. There is no
shape that is common to all
leaves. They differ as to
the character of the edge.
Some are smooth, whereas
others have wrinkled, un-
even surfaces. Some kinds
are hairy, while others are
quite bald. Even the color
of leaves is not uniform,
though there is more or
less of the green chlorophyl
present in the leaves of all
plants.

tissue

Stomate

Fig. 23. Structure of leaf
This diagram shows the tip of a leaf with a

piece removed by two cuts at right angles to
each other, as it might appear under the mi-
croscope. Note the different kinds of cells
and tissues

101. Unusual forms of
leaves. Most familiar leaves
are flat, spread-out structures.
Some plants, however, have
leaves that depart considerably
from this model. There are leaves that are nothing more than fine hairs,
as on certain cactuses, others have extensions that behave like tendrils,
and some are spines. Certain plants have leaves that are more or less
active in getting animal food.

70

THE LEAF AS STARCH FACTORY

71

102. Work of the leaf. The work of food-making in the
leaf has already been described (see p. 53), and we may now
show the relation between the structure of the leaf and the
details of this work. The cells containing the chlorophyl must
get their income from the sur-
rounding cells or from the sur-
rounding air spaces. The water
is brought up through the ves-
sels of the wood (Fig. 23), and
it passes through the cell walls
by osmosis. The carbon dioxid
is absorbed by osmosis from
the air inside the leaf, and
this air is in direct communi-
cation with the outer air by
way of the stomates. The oxy-
gen given off by the cells
passes into the air spaces and
diffuses from these to the ex-
terior by way of the stomates.

The skin cells are not di-
rectly concerned in the work
of starch-making ; their func-
tion may be described as protec-
tive. In addition to protecting
the delicate pulp cells against
mechanical injury, they are
even more useful in protecting
the plant against the loss of

water. That a great deal of water is lost by the plant through
evaporation may be inferred from what we know about the
evaporation of water from other wet surfaces (Fig. 24).

103. Transpiration. The loss of water is perhaps the most
serious danger to which most plants are exposed, since more
plants die from the results of wilting than from any other one

Fig. 24. Breathing holes of plants

7, stomates, or breathing pores, on the sur-
face of a leaf, inclosed by the " guard cells."
2, section through a leaf, showing an air
space just inside the guard cells. Stomates
are found in the epidermis of twigs as well
as on leaves. As the stem grows tougher
the breathing holes become larger and more
irregular patches connecting the spaces be-
tween the cells and the outside atmosphere.
The roughened breathing spaces on the
bark are called lenticels. j, lenticels on the
bark of birch

72 ELEMENTARY BIOLOGY

cause. And yet transpiration, as this evaporation from the
leaves is called, may be of use to the plants indirectly.

This rapid evaporation of water results in lowering the tempera-
ture of the plant. The sunlight is rapidly absorbed by the chlorophyl
bodies, but only a small portion of this energy is transformed in the
making of carbohydrates. Much of the energy is passed through
the leaf, but a great deal of it becomes converted into heat. Under
conditions that interfere with transpiration, the temperature of leaves
exposed to sunshine increases so rapidly that the protoplasm is some-
times killed — the leaves are actually scorched, although the tempera-
ture of the surrounding air may not be very high. This may be
observed in the summer time, when the sun comes out quickly after
a shower that has left a great deal of moisture in the air. The
moisture in the air prevents transpiration ; the sunshine is largely
converted into heat inside the leaves, and the protoplasm is injured
as a consequence.

104. The guard cells. While there can be no doubt that the guard
cells are extremely sensitive to changes in outward conditions, it is
by no means certain just how their movements are related to the
work of the leaf, or whether, indeed, these movements have any
practical significance in the life of the plant. The movements of
the guard cells were formerly supposed to be related to the work
of transpiration.

CHAPTER XVII
OUR DEPENDENCE UPON LEAVES AND CHLOROPHYL

105. Light and leaves. We have learned that in the
absence of Hght the chlorophyl is inactive and the process of
starch-making is suspended. Moreover, if a plant is kept in
darkness for a longer period, the chlorophyl begins to disap-
pear, and in the end the leaf will be quite white. This fact
is used in the blanching of celery. The earth is dug up about
the bases of the plants to exclude the light. When we com-
pare the outer leaves of a head of lettuce or cabbage with the
inner leaves, we see a difference as to the amount of green
pigment which illustrates the same principle.

Experiments on light in relation to photosynthesis show
that it is quite possible for plants to carry on this work
under artificial light. The light that we usually have in a
living room in the evening is hardly strong enough to affect
most house plants, but by the use of strong electric lights it
has been found possible to hasten the growth and develop-
ment of lettuce so as to get it on the market at least two
weeks earlier than could otherwise have been done. This
means that the plants were given daylight while there was
any, and were then supplied with artificial light during the
night. In this way plants can be kept working continuously,
as they apparently have no need for rest or sleep.

Experiments have been made to find out whether the dif-
ferent kinds of light that together make up white light have
any special relation to photosynthesis. It seems that the light
toward the red end of the spectrum is more effective in starch-
making than that toward the violet end. But species of plants
differ from one another in this respect.

73

74 ELEMENTARY BIOLOGY

106. Breathing and leaves. It is sometimes said that
"plants breathe in what animals breathe out, while animals
breathe in what plants breathe out." This statement is heard
so often that many people accept it as true without taking the
trouble to consider just what it means. The statement is true
only if we are careless enough to jumble up the meaning of
the word breathe. The fact is that plants and animals both
breathe in oxygen and breathe oitt carbon dioxid. This oxygen
is used in the same way in both plants and animals, and the
carbon dioxid originates in the same way. In addition to the
breathing, green plants carry on another process in which
gases are involved. In the process of starch-making, plants
use up carbon dioxid, which they take in from outside, and
they give off oxygen, which is separated out in the course of
the starch-making. Now breathing has to do with the gas
exchange concerned in oxidation and the release of energy.
The gas exchange concerned in photosynthesis is not breath-
ing. The statement that the breathing of plants differs from
the breathing of animals is therefore misleading and not true.

107. Uses of leaves. Aside from the fact that it is in the
leaves of plants that our food supplies are originally worked
up, the leaves of many plants are of use to us directly. Some
are eaten, as, for example, cabbage, lettuce, spinach, water-
cress, dandelion. The leafstalks of some plants, as the rhubarb
and celery, are also used as food, although they do not contain
very much protein, fat, or carbohydrates.

The tea and tobacco industries are founded upon peculiar
substances found in certain leaves. It is not the food value,
but the presence of an alkaloid} that makes the leaves of these
plants interesting to human beings.

The fact that in the course of its activities a plant throws
into the air large quantities of oxygen makes the plants valu-
able neighbors, especially in the cities, where oxygen is used

1 An alkaloid (that is, " like an alkali ") is an organic compound containing
nitrogen, capable of combining with acids.

DEPENDENCE UPON LEAVES AND CHLOROPHYL 75

up relatively faster, on account of the crowding of population
and on account of the many fires kept going.

The food of our domestic animals is in large part the
leaves of plants, — grass, beet tops, and the greater part of
hay, alfalfa, clover, and corn fodder ; these furnish the prin-
cipal green food of cattle and horses.

The dead leaves of plants, whether those that have dropped
in the autumn or those that reach the ground through the
death of herbs etc., form the basis of the humus of the soil.
Humus is a mass of decaying vegetable matter, with some
animal matter and soil. This forms a soil covering that is
very helpful from the point of view of retaining moisture in
the soil, and to a certain extent in returning nitrogen and
other elements to the soil.

108. Our dependence upon chlorophyl. The parts of a plant
that have no chlorophyl (for example, the root or stem of
a tree) are unable to make food substances out of inorganic
materials ; they are nourished by materials obtained from the
leaves. But animals and such plants as mushrooms, having no
chlorophyl, must get their food from the bodies of other living
things, and in the end all food comes from green plants.

The value of the food materials taken from our farms in the form
of various crops amounts to over $3,000,000,000 a year. This does
not take into account the grass eaten by horses, sheep, and cattle,
nor the vast quantities that are destroyed by insects and fungi. All
of this food results from the work of leaves. It has been estimated
that to make a pound of starch it takes a leaf area of about fifty
square yards, the leaves working through ten hours of daylight.

109. Simple food-makers. There were living things upon
the earth long before there were any leaf -bearing plants.
There must, therefore, have been some way of making food
out of simpler substances. Some of the species of plants that
are still living and that are capable of manufacturing food are
so simple that the whole body of one of them consists of but
a single cell. Some of the commoner representatives of these

76

ELEMENTARY BIOLOGY

species are the green slime (pleurococcus) that we find grow-
ing on the bark of trees, on the shingles of houses, and on
damp rocks, and the pond scum, or ''frog spit" {spirogyra),
that we find floating on the surface of ponds.

110. Green slime. The green-slime cell is a spherical cell
(Fig. 25) consisting of a mass of protoplasm with its nucleus,
a cell wall, and a quantity of chlorophyl. On the moist sur-
face of the tree it is in a position to absorb water, carbon

dioxid, and various salts that
either are washed down by the
rains from the dust that strikes
the tree or are dissolved from
the bark. Supplied with these
materials, and containing chlo-
rophyl, the plant is able to
manufacture, during the day-
time, first carbohydrates and
then proteins. The cell wall
also permits the diffusion ol
oxygen from the outside air,
and thus the plant breathes.
Oxidation takes place in the
protoplasm, releasing energy
and producing carbon dioxid.

Fig. 25. Green slime

This plant consists of a single cell. When
the cell divides into two, the daughter cells
may cling together or they may be sepa-
rated. Sometimes a cluster, or " colony,"
is formed, containing many cells ; in such
a cluster each cell is independent of the
others, since each is capable of making its
own food as well as of absorbing the raw
materials from the environment

This gas is excreted by osmosis
through the cell wall. It is possible that some of this is used,
in the daytime, in the process of photosynthesis.

The food manufactured by the cell is used almost immedi-
ately in the construction of more protoplasm, and thus the cell
grows. When a certain size is reached, the nucleus divides,
and presently there are two cells in place of one. These two
cells may remain adhering to each other or they may soon
separate. In any case they are quite independent of each other
in every way — that is to say, each cell can keep on taking in
substances from the outside, manufacturing food, growing,

DEPENDENCE UPON LEAVES AND CHLOROPHYL 77

throwing off waste oxygen from photosynthesis or waste carbon
dioxid from oxidation, without regard to what its neighbor is
doing. And each cell may also divide itself into two new cells
independently of what its neighbor is doing. It thus comes
about that we often find groups of cells in which some are
seen to have grown faster than others, or to have divided more
quickly, as is shown in the illustration.

In plants like this each cell carries on all the actwities that
together make up being alive — all the activities that in larger
and more complex plants are carried on by different special
parts or organs. But even in the most complex plants there
are some activities that are carried on by every cell. Only
certain processes are specialized.

CHAPTER XVIII
STARCH-MAKING AND DIGESTION

111. Digestion. We have learned that the simplest food
resulting from photosynthesis is probably sugar. Experiments
have shown that in many plants only sugar is formed. Most of
our common plants, however, contain starch. In our own ex-
periments we found starch in the leaves that had been exposed
to the light, and none in the leaves that had been kept in the
dark. Now, what became of the starch that must have been
present in the leaves before we began our experiments ?

The study of osmosis shows that starch, like many other
substances, cannot diffuse through a cell wall. Such substances
are called colloids (meaning '' like glue "), to distinguish them
from sugars and salts and other substances (called crystalloids)
that diffuse through membranes more or less readily. Experi-
ments show us that these colloids are changed into crystalloids
and then pass through cell walls by osmosis. The process is
called digestion and can be easily demonstrated.

In the grains and in other seeds containing starch the absorption
of water leads to the development of a substance called diastase, which
is capable of converting starch into sugar in the presence of plenty
of water. Diastase has been extracted from malted barley (that is,
barley that has been kept moist until the grains sprouted), from rice,
and from many other seeds. It can be bought in the stores. A sub-
stance that behaves in many ways like diastase is found in human
saliva and in the digestive juices of many other animals.

The change from starch to sugar makes it possible for
carbohydrates to pass through cell walls by osmosis.

112. Ferments. Substances like diastase and the active
part of the saliva are called ferments, or enzyms, and many

78

STARCH-MAKING AND DIGESTION

79

different kinds are known. They are peculiar in that they
seem to induce chemical changes in other substances, without,
hozuever, undergoing any changes themselves. As a result of
this peculiarity a comparatively large
amount of material may be made to
undergo chemical change through the
activity of a very small amount of enzym.
113. Food transportation. The cells
of the chlorophyl-bearing tissues con-
tain diastase and other ferments. In
the light, some of the sugar that is
formed passes out of the pulp cells and
is carried down in the bast, or phloem
tubes (see p. 1/6). But under favorable
conditions for food-making the sugar is
manufactured faster than it can be car-
ried away. Most of it is then converted
into starch, which is insoluble. In this
way it accumulates in the cells during
the day. When darkness sets in, a dia-
static action converts the starch into
sugar, and this is then carried down into
the stem or roots (see diagram, Fig. 26).

This explains why, leaves that are full of
starch in the late afternoon show no signs
of starch very early in the morning. As the
morning light increases in intensity, starch
is accumulated, and in the afternoon the
cells are again full. From this we can also
understand the presence of starch in potato
tubers and in other organs that do not contain

chlorophyl. The starch is formed in the cells of the tuber by the action
of a ferment upon sugar. The sugar is brought from the leaves, pass-
ing 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 wood or bark cells by osmosis, and is then converted into starch.

Fig. 26. Starch in light
and darkness

During the daytime the plant
manufactures carbohydrate in
the leaves, receiving a steady
supply of water from the soil.
In the dark the starch is
changed into sugar and there
is a stream of sap running
downward into the roots or
underground stems, where
the surplus is accumulated
as starch

8o

ELEMENTARY BIOLOGY

114. Digestion universaL The process of digestion seems
to go on in nearly all living things. In the case of the ameba,
which consists of a single unit of naked protoplasm (see p. 24),
a solid particle of food can be swallowed by the naked proto-
plasm and then digested 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. Under
suitable external conditions each cell throws out through the

Fig. 27. Digestion by bacteria

The organism a lying on a solid b^ which may serve as food, secretes an enzym, or

ferment, which passes out of the cell e and changes the material to a liquid /. This is

absorbed into the cell by osmosis, /

cell wall, by osmosis, a liquid containing a ferment capable of
digesting the solid or insoluble food material. The liquid re-
sulting from the digestion is absorbed by osmosis. This may
account for the fact that when meat or cheese rots, it becomes
fluid. The rotting in such cases is the work of the ferments
contained in the digestive juices secreted by the bacteria
(Fig. 27).

In higher animals like ourselves a similar process of diges-
tion takes place. But instead of every cell pouring out diges-
tive juices into its immediate neighborhood, only certain portions
of the body produce and throw out such juices.

CHAPTER XIX
DIGESTIVE SYSTEM IN MAN

115. The human food tube. We receive our food and drink
into our mouths. The mouth is the beginning of a long tube
inside of which all the digestion takes place. This tube is
called the food tube or the alimentary canal or the digestive
tract. This tract consists of several fairly distinct regions ;
in an adult it is about ten or eleven yards long. It manages to
keep inside the much shorter body by being coiled and twisted
in parts (see Fig. 28,7, k).

116. Mouth digestion. Since what we eat is important to us
on account of its proteins, fats, and carbohydrates, we may con-
sider the digestive processes in relation to these substances.

After the food enters the mouth, it is crushed and ground
by the teeth. During the process of chewing, however, some-
thing else happens. The taste of the food, the movement of
the jaws, and the rubbing of the food against the inside of the
mouth stimulate the action of the saliva glands (see Fig. 29)
so that a quantity of saliva is poured into the mouth and this
becomes mixed with the food. The more the food is chewed,
the smaller are the particles into which it is broken, and the
more thoroughly is the saliva mixed with the particles. As we
have already learned (p. 78), the action of the saliva upon the
starch in the food changes it into sugar. The other materials
in the food are probably not changed, except that salts and
sugars are dissolved by the water, of which the saliva contains
over 99 per cent. As the amount of ferment is very small,
the effectiveness of saliva as a digester of starch depends upon
the ferment's reaching every particle of starch, and upon its
having sufficient time to bring about the change.

81

82

ELEMENTARY BIOLOGY

The thorough mixing of
saliva with the food makes
it easier for the whole mass
to slide along into the
throat, and later into the
gullet, since the surface
of the mass is thus coated
with the slippery mucin of
the saliva.

117. Swallowing. After
the mouthful of food has
been thoroughly chewed,
it is pushed back by the
tongue and passed into
the throat chamber, or
pharynx (see Fig. 28, b)^
from which it passes di-
rectly into the gullet, or
esophagus. The swallow-
ing is not merely a falling
down of the food from the
pharynx into the stomach.
It is an active carrying
brought about by the suc-
cessive contraction of rings
of muscles that lie in a
series in the wall of the
gullet. If you watch a
horse drinking water from
a pond or from a pail set
on the ground, you can
see him swallow the water
///, and you can see, show-
ing through the skin, one wave of contraction after another
pass along the gullet, from the head to the trunk.

The digestive organs in man

«, entrance to mouth ; b, the pharynx, — a sort of
vestibule with seven passages leading out of it,
two to the nostrils, one to the mouth, one to the
gullet, one to the windpipe, and one to each ear
(the Eustachian tubes, see p. 240) ; ^, the gullet,
or esophagus ; d^ the stomach ; e^ the pylorus^
opening from the stomach to the small intestine ;
/, the liver ; g, the gall bladder ; //, duct from the
gall bladder and the liver to the small intestine ;
/, duct from the pancreas to the small intestine ;
/, small intestine ; ^, large intestine ; /, vermiform
appendix ; w, rectum ; «, the diaphragm, separat-
ing the chest cavity from the abdominal cavity;
£>, the pancreas. The arrows indicate the course
taken by food in passing from the mouth through
the alimentary canal

DIGESTIVE SYSTEM IN MAN

83

Parotid
gland

118. The stomach. Whatever fermentation has been started
by the saUva in the mouth continues in the mass of food until
this reaches the stomach. Here, however, it stops the moment
the acid, or sour, stomach juice comes in contact with the
sahva. It seems that the saUva ferment cannot act in the
presence of acid.

The stomach juice contains a special ferment known as
pepsin. Pepsin, in the presence of acid, acts upon the proteins
in the food, changing them
into soluble compounds of
similar composition, known
as peptones. Peptones dif-
fer from proteins chiefly in
this one fact, that the former
are soluble in water and are
capable of diffusing through
membranes, while the pro-
teins are generally not
capable of such diffusion.

In the stomach the swal-
lowed substances are thor-
oughly mixed with the
gastric, or stomach, juice by
the action of the muscles
in the stomach wall. The

stomach wall contains layers of muscle cells running in differ-
ent directions, as well as gland cells in which are produced the
particular substances found in the gastric juice (see Fig. 30).

As the changing of proteins to peptones goes on, the mix-
ture in the stomach becomes more and more liquid and more
and more acid. From time to time a quantity of the liquid in
the stomach is squirted out into the beginning of the intestine
by the opening of the connection (Fig. 28, ^) and the contrac-
tion of the stomach at the same time. After a while most of
the contents of the stomach has been changed to a mixture

Bhod
vessels

Sublingual

Submaxillary

Fig. 29. The salivary glands

There are three sets of glands which produce
saliva : the parotid, in the cheek, just in front
of the ears ; the submaxillary, under the angles
of the jaw ; and the sublingual, under the tongue

84

ELEMENTARY BIOLOGY

having the consistency of a rather thick pea soup, and all of
it has passed on into the intestine.

119. The intestines. There are two distinct parts, or divi-
sions, of the gut among the highest animals. The first part is
called the small intestine, and in human beings it is about
one inch in diameter and about twenty-four or twenty-five
feet long. The small intestine opens rather abruptly into the
large intestine, which is about two inches in diameter and

about five feet long (see
Fig. 28, y, k).

The wall of the intes-
tine is rather thin and
soft. You have probably
handled a piece of pig
gut or calf gut, which is
used as sausage casing.
In the living animal the
wall of the intestine is
not so hard and stiff as
we sometimes find it in
the sausage casing. This
wall is made up of
several layers of tissue.
The inner lining carries
very small glands, and
the outer layers contain
muscle cells. To this extent the wall of the intestine is like
the wall of the stomach. The muscle cells of the gut are
arranged in rings, so that when they contract they simply
reduce the diameter of the intestine at any given point. The
contraction starts at the forward end — that is, the end nearest
the stomach — and passes backward along the whole length
of the small intestine, aided by longitudinal muscles. As a
result of this wave of contraction some of the thick mixture
of food and digestive juices is moved along, a short distance

Fig. 30. Glands of the stomach

The gastric juice is poured into the stomach through

tubes, a, which are Hned by a layer of delicate cells ;

it is produced by special gland cells, b^ from materials

brought by the blood in fine vessels, c

DIGESTIVE SYSTEM IN MAN 85

at a time. This movement is called peristalsis and is very
similar to the swallowing movement of the gullet.

When a food mixture passes from the stomach, it contains
all of the fat that it contained when it first entered the mouth,
since neither the saliva ferments nor the gastric ferments have
any effect upon fats. It contains all the sugar that was there to
begin with, together with all the sugar that was formed by the
digestion of starch in the mouth. It contains whatever starch
was not digested. It contains the peptones formed by the gas-
tric digestion (in solution), and particles of proteins that were
not digested. In addition there is a quantity of water, mineral
salts, the remains of the gastric and salivary juices, and the
fibers and cell walls of the food material, which have not been
acted upon in the mouth or in the stomach. In the intestines
many changes take place in the character and composition of
this mixture.

Near the beginning of the intestine (Fig. 28, h^ i) there is a
small opening connected with two small tubes, or diccts. One
of these is connected with the largest gland in the body, the
liver \ the other is connected with another very important
gland, the pancreas (Fig. 28, 0).

120. The pancreas. The juice secreted by the pancreas
contains three important kinds of ferments :

1. A ferment that converts starch into sugar.

2. A ferment that digests proteins into simpler compounds.

Any starch that has been swallowed before the saliva has had time
to transform it into sugar, and any protein that has passed from the
stomach without being digested by the pepsin, will now be digested
by the action of the pancreatic ferments.

3. A ferment that acts upon the fats in the food, breaking
them up into glycerin and fatty acids, which latter combine
with other substances to form soaps.

The soaps and the glycerin dissolve in water and diffuse
through cell membranes.

86

ELEMENTARY BIOLOGY

The pancreatic juice thus contains all the kinds of ferments
necessary for digesting a whole meal.

121. The liver. The juice produced by the liver is called
the bile^ or gall.

I. It does not contain any ferments that seem to be impor-
tant in digestion, but it does have an influence on the absorp-
tion of the fatty acids
and soaps by the cells
of the intestine.

2. The bile seems
further to have some ef-
fect upon the activity of
the pancreatic ferments.
When the contents of
the stomach pass into the
intestine, the mixture is
acid ; the bile neutral-
izes the acid and makes
possible the activity of
the other ferments.

3- The bile is made
up chiefly of materials
that are of no further
use to the body — ma-
terials that have been
converted in the liver
and are then thrown
into the intestine, from
which they are removed frorn the body. The liver is thus
also an excretory organ.

122. The intestinal juices. The juices secreted by the glands
of the intestine contain no ferments that are of great importance in
digestion, although they do contain a great deal of sodium carbonate,
which neutralizes the acids resulting from the digestion of fats by the
pancreatic juice, and probably also other acids resulting from other

Fig. 31. The lining of the intestine

The tiny projections from the lining of the small
intestine, the villi^ give the appearance of very fine
velvet. Absorption takes place through the outer
layer of cells. Within each villus are fine blood ves-
sels and lymph spaces ; from these the absorbed food
is transferred to circulation system

DIGESTIVE SYSTEM IN MAN

87

chemical changes in the gut. There is a ferment in the intestinal
juice which converts cane sugar into simpler sugars, but this change
may also be brought about by the acids of the stomach, and possibly
also by the alkali
in the intestine.

123. Absorp-
tion. The lin-
ing of the small
intestine is like
delicate velvet.
Very small out-
growths project
into the cavity,
so that the sur-
face exposed to
contact with the
food mixture is
increased sev-
eral hundred
times. Each of
these tiny pro-
jections, called
a villus (plural,
villi), has a
rather complex
structure, as is
shown in the di-
agram(Fig.3i).

The villus seems to be a special absorbing and transforming
organ. The mixture in the intestine we now know to consist of
many crystalloids in solution, many colloids in the process of
being converted into crystalloids, and solid substances that are
not capable of changing under the conditions that exist in the gut.

The crystalloids are absorbed into the cells of the villi, so
that as the mass moves along in the intestine, more and more

Intestine
and Rectum

Fig. 32. Digestive system in fish and in bird

The main features of the digestive system are aUke in all back-
boned animals. In the birds there is a curious pouch connected
with the gullet, — the crop, — in which food may be retained in-
definitely and later either swallowed or regurgitated through the
mouth. The glandular portion of the stomach, or proventriculus,
is distinct from the grinding part, or gizzard

88 ELEMENTARY BIOLOGY

of the digested matter is withdrawn into the vilU. From the
surface cells of the villi the absorbed material is passed on, by
osmosis, to the blood vessels and to the lymph vessels. Chem-
ical changes take place in the course of the transfer, so that
the material taken into the blood is not in exactly the same
state as the material absorbed from the intestine, although, of
course, it is made up of the same elements.

By the time the dinner you have eaten has reached the end
of the small intestine, most of the proteins, fats, and carbo-
hydrates that it contained have been absorbed by the villi and
passed on into the blood and lymph. There is left in the in-
testines at this point chiefly the undigested (for the most part
indigestible) fibrous and cell-wall material of the plant or animal
tissues eaten, and the modified secretions of the various glands
that have poured into the food tube all along the way. This
mass of refuse now passes into the large intestine (Fig. 28, y^).

124. The large intestine. In the large intestine the fer-
ments of the digestive juices may still continue to act for some
time. But gradually, as the mass proceeds along the canal, it
becomes drier, through the continued absorption of material
by the lining of the intestine (there are no villi in the large
intestine), so that toward the end the only chemical changes
going on are those produced by the millions of bacteria that
are present in the intestines of all animals.

The mass of material that has accumulated toward the end
of the large intestine is of no further use to the body, and
should be removed from time to time. Birds, having no large
intestine, throw off the refuse about as fast as it passes from
the small intestine to the rectum (Fig. 32). Other animals
and infants throw off the refuse automatically. But older
children, absorbed in their games or other activities, are apt
to postpone emptying the bowels, and thus become irregular.
This neglect of the bowels often brings about serious conse-
quences, so that it is important for us to acquire regular bowel
habits while we are still young (see p. 118).

CHAPTER XX
HEALTH AND FOOD STANDARDS

125. Conditions of health. The normal, healthy digestion and
absorption of food depend upon

(i) the secretion of digestive juices by the glands ;

(2) the fermentative action of the substances in these juices ;

(3) the muscular contractions of the gullet, the stomach, and
the intestines.

We can do nothing to control these processes directly, either
to hasten them or to stop them. But indirectly we can do a
great deal to control them.

First of all, we can decide what to eat, how to eat, and
when to eat.

Then we can decide for ourselves what kind of habits we
will have with regard to the behavior of the large intestine.

And, finally, we can do a number of things that are not
directly connected with feeding, but that have important
bearings on the healthy behavior of the digestive system.

All these controls come to us from a better understanding
of the biology of nutrition and digestion.

126. What to eat. Since all living beings consist essentially
of proteins, fats, and carbohydrates, it would seem that almost
any plant or amimal stuff would be suitable for food. But we
know from experience that some of these things .are not
pleasant to the taste, or are even disagreeable, and that others
are poisonous. Some substances, while neither unpleasant nor
injurious, contain so little usable or digestible material that they
are not worth eating. In the course of ages human customs
have selected the plant and animal materials in any given
region that are most valuable for food. We are all the time

89

90 ELEMENTARY BIOLOGY

discovering useful food plants and food animals that are stran-
gers to us but familiar to people in remote parts of the earth,
and neither our instincts nor our customs tell us the best way
to use them. Even in regard to the older kinds of food we are
almost as ignorant ; for while we know that the flesh of an ox
is better for food than the hoof or the hide, and that the grain
of the wheat is better than the leaf or the root, experience has
not taught us what proportions of meat and grain and fruit are
the best for maintaining efficient health, and certainly we have
to learn that one combination of foods is best for one person,
while another combination is best for another person.

127. Dietary studies. When the study of dietaries was first
begun, it was assumed that what people actually eat is on the
average the best thing for them to eat, both as to kind and as
to quantity. Accordingly students made careful records of the
meat and bread and butter and vegetables and fruits and cheese
eaten by thousands of people. They calculated the amount of
protein, fat, and carbohydrates contained in these dietaries,
and sought thus to establish, from the averages, a standard
of what healthy people require day by day. By this method
Carl Voit in Germany and Professor W. O. Atwater in this
country concluded that a person doing a moderate amount of
work needs about four ounces of protein daily, to take the
place of the proteins oxidized in the cells of the body. But
later experiments, in which the amount of protein taken in
and the amount of nitrogenous waste given oK were carefully
measured, lead to the conclusion that an adult weighing about
one hundred and sixty pounds requires hardly fnore than two
ounces of proteins in every twenty-four hours.

Since protein is the most expensive material in our food, and at the
same time the one that is most severe upon the organs of the body,
especially the liver and kidneys, it is a matter of great importance to
know whether two ounces will suffice or whether four ounces are
necessary. We should therefore try to understand the basis upon
which these diverse standards are established.

HEALTH AND FOOD STANDARDS 91

128. Units of energy. To measure the energy expended by
the body, or to measure anything else, we must have a unit.
We measure length in inches or yards or miles. In a similar
manner we are able to measure energy by work done. But as
different forms of energy do different kinds of work, it is
necessary to find some common unit for measuring. For
example, motion can be measured by the quantity of matter
moved and the distance through which it is moved, as one
ton raised five inches, three pounds raised two feet. The unit
of measuring this kind of work may be the foot pound, or the
amount of energy it takes to raise one pound of matter one foot.

If a pint of water at room temperature (about 18° C, or about
65° F.) is placed in a pan over a burner, it will gradually be-
come warmer, until it reaches the boiling point. It takes a cer-
tain quantity of heat to change the temperature of the water
from 65° to 212° (the boiling temperature of water). For a
quart of water it would take twice as much heat to do the
required zvork. As a unit of heat energy we might use, for
example, the pint degree. The unit adopted among engineers
is the quantity of heat necessary to raise one kilogram of water
(a little more than a quart) from the temperature of 0° to the
temperature of 1° C. This unit is called a calorie.

In dealing with fuel or the conversion of fuel energy into other
forms, it is customary to record energy in terms of calories. In deal-
ing with mechanical work it is customary to record energy in terms of
foot pounds, or horse-power hours.^

1 The fuel values of proteins, fats, and carbohydrates are as follows :

Proteins . .
Carbohydrates
Fats ....

From these figures it will be seen that a given quantity of fat contains more
than twice as much latent energy as the same quantity of protein or carbohy-
drate, and that the latter two classes of compounds have the same fuel value.

92

ELEMENTARY BIOLOGY

129. Respiration calorimeter. The work of the human body
or any other animal body can be measured in terms of calories
by means of very delicate apparatus that has been developed in
recent years. In a large chamber that is completely inclosed so

Fig. 33. The respiration calorimeter

In the large chamber a man can Hve for several days or weeks under conditions that give
an accurate account of his body's income and expenditure, in the way of matter as well
as in the way of energy. A, door and window ; B, door for food etc. ; C, tank for catching
water circulating through the walls of the chamber ; D, observer's table, with devices for
measuring and regulating temperature etc. ; E, rubber bag to equalize the air pressure
within the chamber ; F, apparatus for circulation and purification of air in the chamber.
From photograph furnished by Office of Home Economics, United States Department

of Agriculture

as to prevent the escape of heat, a person may live for several
days or weeks at a time under conditions that allow us to measure
every particle of material that goes in or that comes out, as well
as the amount of heat that is given off by the body (Fig. 33).
With this apparatus exact records are made of the work a
human being does in the course of a day, measured physically

HEALTH AND FOOD STANDARDS 93

as calories or foot pounds instead of in terms of useful product,
as words written, nails driven, or yards of carpet woven.

130. Our daily needs. From experiments with the respira-
tion calorimeter it has been determined that a person weighing
about one hundred and fifty to one hundred and sixty pounds
and doing a moderate amount of physical work expends about
2800 calories a day, whereas a person engaged in a sedentary
occupation, as a clerk or bookkeeper, would not use up more
than 2400 calories. The higher of these figures is considerably
less than the standard set by Atwater, which was over 4000
calories for the moderate worker and 4500 for the hard worker.^

These experiments have been supplemented by others made by
college professors on themselves and their colleagues, on college
athletes and other students, and on soldiers. We thus learn that
most people eat too much food, and especially too much proteins.

The protein standard established by Professor Chittenden
at Yale, for adults doing various kinds of work, is just one
half that announced by Voit, namely, about two ounces in
twenty-four hours. In the experiments, students, professors,
and soldiers not only kept up their weight on this basis but
really did more and better work, and were in better health
generally, than under the larger protein allowance.

The amount of protein used up in the course of a day de-
pends not upon the amount of muscular work done but upon
the rate of growth and upon the weight of the body (not count-
ing the fat). A stonemason or miner does not need more pro-
tein than a shoemaker or stenographer of the same weight,
but he does need more fat or carbohydrates.

1 Even Voit's standard gave 3000 calories for the moderate worker and 3500
for the hard worker. A comparison of Voit's figures with Atwater's leads one
to suspect that the American workers ate more food than the German workers,
probably because food was at that time cheaper in this country, or wages rela-
tively higher. In the end we shall have to depend upon experiments to tell us
just what is the wisest thing to do in regard to eating.

CHAPTER XXI
FOOD REQUIREMENTS

131. Selection of food. When we go marketing, or when
we look over the bill of fare at a restaurant or hotel, we do
not select proteins and calories ; we select cuts of meat,
vegetables, fruits, cheese, bread, and so on. Suppose that
you had for breakfast a large banana, a glass of milk, two
slices of bread and butter, and an egg. How much protein
is there in such a breakfast, and what is the total fuel or
heat value of the food ?

We should have some means of translating the products of
the food factories and the kitchen into terms of proteins and
calories. This is furnished by tables that have been prepared
by experts working for the government, for hospitals, and for
manufacturers. We can make use of some of these results to
guide us in our own selection of food.

132. Food composition. From the table of food composition
on page 95 we can get an idea that some of the food ma-
terials which we use contain more nutrients than others, and
that some contain a larger proportion of proteins, or of fats,
or of carbohydrates. We can get these ideas more readily
from charts and diagrams. The United States Department of
Agriculture has issued a series of charts in which the compo-
sition and fuel value of a large number of articles of food are
shown m colors. A few of these are reproduced in Fig. 34.

133. Fisher's table. Professor Irving Fisher of Yale Univer-
sity has prepared a list of common articles of food, with a state-
ment of how much it takes of each kind to give approximately
one hundred calories, and the proportion of this furnished by
the protein. A portion of this table is reproduced on page 96.

94

FOOD REQUIREMENTS
COMPOSITION OF VARIOUS FOOD ARTICLES

95

Milk, whole

Buttermilk

Butter

Cheese, full cream

Eggs, edible portion

Beef, porterhouse, edible portion

Beef, dried

Bacon, smoked

Ham, lean, edible portion . . .
Lamb, leg, roast

Chicken, broiled, edible portion
Salmon, California, edible por-
tion

Brook trout

Oysters, solids

Bread, homemade

Bread, brown

Corn meal, granular

Oatmeal, boiled

Rice, boiled

Macaroni, cooked

Beans, string, cooked ....
Beans, baked, canned ....
Cabbage, edible part ....
Potato, boiled

Apple, as purchased

Banana, edible part

Figs, fresh

Figs, dried

Dates, dried, edible portion . .

Orange, whole

Watermelon, whole

Peanut, edible part

Walnut, California soft shell,

edible portion

Sugar, granulated

Per Cent

OF

Protein

3-6

3-0
i.o

25-9
14.8

20.0
30.0
9.4
25.0
195

21.5

17.8

19.0

6.2

9.0

54
9.2
2.8
2.8
3-0

0.8
6.9
1.6

2-5

0-3
1-3
1-5
4-3
2.1

0.6

0.2

25.8

16.6

Per Cent

Fats

Per Cent
OF Carbo-
hydrate

4.0

0-5
85.0

337
10.5

20.0

6.5

67.4

144
12.7

7.5
2.1
1.2

1-3
1.8
1.9
0.5
0.1
1-5

1.9

2-5

0-3
0.1

0.3
0.6

03
2.8

0.1
0.1

38.6

634

47
4.8

37

54-9
47.1

754
II-5
24.4
15.8

29.1

19.6

5.6

20.9

10.8
22.0
18.8

74.2
78.4

8.5

27

22.4

16.1

lOO.O

Per Ceni

OF

Water

87.0
91.0
1 1.0

34-2
737

60.0

54-3
18.8
60.0
67.1

74.8

63.6
77.8
87.0

33-2
43-6
12.5

84-5
72.5
78.4

95-3
68.9

91-5

75-5

63-3
75-3
79.1
18.8
154

634

37-5

9.2

2-5

96

ELEMENTARY BIOLOGY

SELECTIONS FROM DR. IRVING FISHER'S 100-CALORIE
PORTIONS TABLE

Weight

Calories

Calories

Calories

Size of Portion

OF

FROM

from

from

Portion

Protein

Fats

Carbohy-

(Ounces)

drates

Milk, whole . . .

Small glass

4.9

19

52

29

Buttermilk ....

li glasses

97

34

12

54

Butter

One pat

•45

0-5

95-5

Cheese, full cream .

i^ cubic inches

.82

25

73

2

Eggs

One large

2.1

32

68

Beef, porterhouse .

Edible part, small
steak

I -3

32

68

Beef, dried ....

Ordinary serving

1.9

67

33

Bacon, smoked . .

Small serving

•5

6

94

Ham, lean ....

Edible portion,
average serving

1-5

44

56

Lamb, leg, roast . .

Ordinary serving

1.8

40

60

Chicken, broiled

Edible portion,
large serving

3-2

79

21

Salmon, California .

Edible portion,
small serving

1-5

30

70

Brook trout . . .

2 small servings

3-6

80

20

Oysters, half shell .

I dozen

7-

49

22

29

Bread, homemade .

Thick slice

1-3

13

6

81

Bread, brown . . .

Thick slice

1-5

9

7

84

Corn meal, granular

2.5 level teaspoonfuls

.96

10

5

85

Oatmeal, boiled . .

i^ servings

5.6

18

7

75

Rice, boiled . . .

Ordinary cereal dish

31

ID

I

89

Macaroni, cooked .

Ordinary serving

3-9

M

15

71

Beans, baked, canned

Small side dish

2.7

21

18

61

Beans, string, cooked

5 servings

16.7

IS

48

37

Cabbage

Edible portion

II.O

20

8

72

Potato, boiled . . .

I large

3-6

1 1

I

88

Apple, as purchased

Two

7-3

3

7

90

Banana .....

Edible portion, i large

3-5

5

5

90

Figs, dried ....

I large

I.I

5

95

Dates, dried, edible

3 large

I.O

7

91

Orange, as purchased

I very large

94

6

3

91

Watermelon . , .

Whole

27.0

6

6

88

Peanut

Edible part, 1 3 double

.64

20

63

17

Walnut, California

soft shell ....

Edible part, about 6

•5

10

83

7

Sugar, granulated .

7 level teaspoonfuls,
3i lumps

.86

100

FOOD REQUIREMENTS

97

134. Rexford's table. Instead of considering weights or
the quantities necessary to make up one hundred calories,
Mr. Frank A. Rexford, of the Erasmus Hall High School in
Brooklyn, made up a table giving the protein and fuel values
of a portion of each of a large number of food articles, together

Fig. 34. Composition of food

The proportions of water, protein, fat, carbohydrate, and mineral matter (ash) !n a glass
of milk, an egg, two slices of bread, a pat of butter, and a banana are shown in this dia-
gram, designed after the Langworthy charts. Such diagrams enable us to tell at a glance
the relative amount of each nutrient present in our common articles of diet

with the quantity which he considers an ordinary helping. A
part of this table is given on page 98 by way of illustration.

135. The nutritive ratio. Since protein yields energy on
oxidation, as do the other nutrients, it would seem that one
could subsist on protein alone, getting Ihe double service
(building material and power) from the one nutrient. And,

98 ELEMENTARY BIOLOGY

PART OF MR. REXFORD'S ONE-PORTION FOOD TABLE

Weight of
Ordinary
Helping

(Ounces)

Ounces

OF

Protein

Ounces

of

Fats

Ounces
of Carbo-
hydrates

Milk, whole . . .
Buttermilk . . .

Butter

Cheese, full cream
Eggs, boiled (2) .

Beef, sirloin . .
Beef, chuck, lean
Beef, dried . . .

Bacon

Ham, lean . . .
Lamb, leg . . .

Chicken, broiled .
Salmon (canned) .
Brook trout . . .
Oysters ....

Bread, white, homemade
Oatmeal . . .
Macaroni, boiled
Beans, baked .

Cabbage, boiled
Potato, boiled
Apple, fresh
Banana . .

Dates . .
Figs . .
Orange
Peanut . .
Walnut, English

Sugar ....

6.0
6.0

0-5
i.o

475

2.2 ^

3-0
1.0
1.0

2.25
3-5

3-5
2.0

175
3-5

2.0

4-25
275
3-25

4.00
3.00

5-5
3-5

175
2.0

5-0
0-5
0-5

0.25

•30
.29

1.07
49

indeed, there are animals and certain plants (bacteria and
molds) that can get along very well on proteins alone ; nor is
there any reason to doubt that a human being could also live
on a pure protein diet. But, as. we shall see later, we cannot

FOOD REQUIREMENTS

99

afford to live exclusively on proteins when fats and carbohy-
drates are available ; and it is really worth while to reduce the
protein in the food to the lowest proportion of practical safety ;
that is, to find the nutritive ratio that serves our practical
purpose. From a consideration of the dietary standards of
Voit, Atwater, Chittenden, and other investigators (see p. 93)
we can see that, whichever standard is adopted, the protein
ratio falls within certain definite limits. This is clearly shown
by the comparison given in the following table :

Standard

Protein
(Ounces)

Protein
Calories

Total
Calories

Nutritive
Ratio

Voit

Atwater ....
Chittenden . . .

4
5
2

464

580
240

3000
4000
2400

1:6.5
1:7
I : 10

A protein ratio of from i r/.S to 1:9 is a good average,
although a smaller person or a person doing a large amount of
muscular work would need a lower protein ratio.

If we calculate the number of calories and the amount of
protein in our supposed breakfast, by using either the Fisher
table or the Rexford table, we shall find that the total food
represents from 620 to 750 calories, with a protein ratio of
from 1:6 to 1:7, according to the size of ^gg or banana
and the size of bread slices assumed.

136. Standard diets. To make practical use of the idea of
standard diet we have further to consider (i) the age of a
person, (2) the amount and character of his day's work, and
(3) the seasons of the year.

The age is important because (i) the digestive system of
young people may not be able to tolerate what an older person
can stand ; (2) a young person is usually smaller and so uses
up less proteins each day ; and (3) a young person is growing,
and so uses more proteins for building new tissues than an
older person does.

lOO

ELEMENTARY BIOLOGY

The food required " per man per day " being taken as one
hundred, the food requirements of children under sixteen years
of age have been given as in this table :

Age

For Boys

For Girls

Under 2 years

2 to 5 years

6 to 9 years

10 to 12 years

13 to 14 years

15 to 16 years

30
40
50
60-70
80
90

30
40
50
60
70
80

The nutritive ratio is left the same for children as it is for
adults, although we should expect children who are growing
to require relatively more protein. The balance is probably
brought about by the fact that children are relatively more
active than adults, so that they use up comparatively more
fats and carbohydrates.

The amount and character of work done by a person are
important factors in determining his food requirements. Ex-
periments made to show the quantity of energy used up by a
man under varying conditions gave the results summarized in
the following table :

Calories
Condition of the Body per Hour

At rest, sleeping 65

At rest, awake, sitting up 100

At rest, standing 117

Engaged in light muscular exercise 170

Engaged in moderately active muscular exercise . 290

Engaged in severe muscular exercise 450

Engaged in very severe muscular exercise . . . 650-675

Since people do not ordinarily sleep all the time or work all the
time, the amount of energy used up per day will depend upon one's
daily program; that is, on the distiibution of sleep and rest and
various degrees of activity. Thus, a person working in the steel mills
twelve hours a day, seven days in the week, expends more energy

FOOD REQUIREMENTS idl

than a clerk who sits at a desk eight or nine hours ; an errand boy
who really runs five or six hours a day may expend more energy than
a stout man playing golf seven or eight hours. On the basis of hours
and kinds of work done, the following calculations ^ have been made ;
these are to serve merely as a basis for comparison, and not as
absolute standards.

Character of Work Calories per Day

According to Tigerstedt

Lumberman Over 5000

Excavator, miner 4100-5000

Farm hand (in busy season) 3200-4100

Carpenter 2700-3200

Weaver 2400-2700

Shoemaker 2000-2400

According to Langworthy

Man at very hard work 6000

Farmers, mechanics, etc 3425

Business men, students 3285

Inmates of institutions (doing little or no work) . 2600

Very poor persons (usually out of work) . . . . 2100

1 More recently, experimental studies of this subject have been made on a
large scale, with the use of the respiration calorimeter, at the University of
Helsingfors in Finland. The results of these experiments, made by Becker
and Hamalainen, are given in the following table :

Calories per Day
FOR Men

Woodcutter, lumberman 5500-6000

Stonecutter, excavator, miner 4700-5200

Cabinetmaker, farm hand, painter 3500-3600

Metal worker 3400-3500

Shoemaker 3100

Bookbinder 3000

Tailor 2600-2800

Caudries per Day
for womeit

Washerwoman 2900-3700

Housemaid 2500-3200

Bookbinder 2100-2300

Seamstress (on sewing machine) 2100-2300

Seamstress (on hand work) 2000

I02 ELEMENTARY BIOLOGY

A comparison of the food requirements of men and women at
different periods of life, and according to work done, is given in the
following table, in which loo represents the requirements of a man
per day (cf . table on page i oo) :

Period of full vigor For Men For Women

Engaged in moderate work ..... loo 80

Engaged in hard work 120 100

Engaged in light work (sedentary) . . .~ 80 70

In declining vigor

In old age 90 90

In extreme old age 70-80 70-80

From the discussion and the tables given above, one should be
able to calculate the requirements of different people in the way of
proteins, fats, and carbohydrates, and to translate these requirements
into the actual food articles that make up our meals, so as to secure
a balanced diet.

One other thing needs to be considered in making up a
plan for a dietary, and that is the matter of climate and seasons.
We have learned from our reading about different races of
men that the natives of tropical countries eat very little meat,
whereas the natives of cold countries eat very little fruit but a
great deal of fat. We can understand why the Eskimos eat no
fruit : there is no fruit to be had where they live. But the in-
habitants of the tropics can get almost any kind of food they
might wish. The fact is, however, that in a cold region one
must provide for a larger supply of heat than in a hot region.
As fat yields the largest amount of energy in proportion to
weight, it is especially desirable in the diet when energy is to
be increased, rather than building material or bulk. So we
may increase our fuel foods in the winter and reduce them
in the summer.

137. Balanced diet. Many people have supposed that there
must be an ideal food, some one material that would satisfy
all the needs of the body ; if this were found, we should save

FOOD REQUIREMENTS 103

the thought and expense of arranging meals, and we should be
safe from the danger of eating the wrong kind of food. But
a glance at the table prepared by Professor Fisher (p. 96)
will show us that there are really very few substances that
have the required proportions of proteins and fuel foods to
meet our needs. A nutritive ratio lying between i : 75 and i :g
would appear on this table for any food that has between 1 1
and 13 calories due to protein for every 100 calories consumed.
It is easy to see that if you ate enough beef to supply the
protein needs of the body, and nothing else, you would have
insufficient fuel ; and if you ate enough to supply the necessary
fuel, you would take in a great excess of proteins. On the
other hand, if you tried to live on fruit, you would have to eat
the equivalent of about thirty-five pounds of apples to supply
the necessary protein ; nine pounds would supply sufficient
energy for a day for an ordinary student, but there would
then be a shortage of protein. Corn, onions, baked potatoes
(whole), almonds, and bread come very near to furnishing a
balanced diet. Potatoes and corn would have to be consumed
in large quantities to meet the day's needs ; an exclusive
onion diet would "hardly be satisfactory ; and the almond meats
would not satisfy the hungry feeling, since they would not
occupy enough space in the stomach and intestine. Taken
by itself, good bread, made of whole grains, comes the near-
est of all our food articles to furnishing a balanced diet of
approximately satisfactory bulk. Of course, "'' bread " must
be taken to include a large variety of flour preparations, such
as macaroni, Vienna rolls, shredded-wheat biscuit, and various
crackers and biscuits.

If we are not content to live on bread alone, as most of us are
not, we shall not be able to find any other one substance that
will by itself meet all the requirements of the daily diet. It is
therefore necessary to combine high-protein foods with low-
protein foods in the proportions that will furnish bulk as well
as the proper nutritive ratio, and that will at the same .time suit

I04 ELEMENTARY BIOLOGY

the taste. Since the high-protein foods are mostly of animal
origin, and the low-protein foods are mostly of vegetable origin,
a balanced ration selected to meet all three requirements men-
tioned above (bulk, protein ratio, and taste) is likely to contain
materials of both kinds. At any rate, it is only by means of a
mixed diet that we are able to maintain for a long time a satis-
factory ration. Milk for children less than a year old would
seem to be the only exception to this statement.

The importance of having the diet balanced appears among
people who are either so ignorant as to purchase food entirely
on the basis of the appetite or the temptations of the market,
or so poor as to be unable to buy any but the cheapest articles
to be obtained. The indulgence of the appetite may lead to
malnutrition through an excess of sweets, and to digestive dis-
turbances through an excess of meats (proteins). The resort to
the cheapest foods may lead to malnutrition through an excess
of starches, since; generally speaking, the starchy foods are the
cheapest, weight for weight. There are other matters, besides
the nutritive ratio, that influence the physical condition of the
body ; but this is something that cannot be safely disregarded.

CHAPTER XXII
FOOD AND DIETARIES

138. Flesh or vegetable diet. The question is frequently
raised whether animal material or plant material is better for
human food, and there are some people who would rule out all
food of animal origin, although there are probably none who
argue against the use of vegetable food. Many reasons are
given for the exclusion of animal matter from human diet.

One argument assumes that it is wrong to kill living beings
even to maintain our own lives. We know that life can con-
tinue only with a supply of proteins and fuel foods, that these
are to be found only in the bodies of living things, and that
only organisms with chlorophyl can manufacture the food them-
selves. This argument therefore implies that it is wrong for
flesh-eating animals to live at all, and that it is right to rob
plants of their food stores or to kill them for food. Some
vegetarians make the point that killing a plant is not wrong,
because plants do not have sensations and emotions \^^ those
of the higher animals. Such persons do not object to using
eggs and milk, which can be obtained without actual slaughter.

Another argument against the use of meat is based on the
structure of the human body compared to the structure of ani-
mals that are naturally flesh-eaters and animals that are naturally
fruit-eaters or grain-eaters. Our teeth are more like the teeth
of fruit-eating and nut-eating monkeys than they are like the
teeth of flesh-eating wolves or tigers. The length of the intestine
is also sometimes pointed to as an argument against flesh-eating.^

1 The table on page io6 will show us that our intestines are relatively
long, corresponding to the intestine of the non-flesh-eating animals, in which
the removal of nutrients from the food takes more time than it does in the
flesh-eating animals.

105

io6

ELEMENTARY BIOLOGY

COMPARATIVE LENGTH OF FOOD TUBE IN DIFFERENT GROUPS
OF MAMMALS

Group of Mammals

Examples

Relative Length of Alimentary
Canal

Carnivora (Flesh-eaters)

Lion, wolf

Three times length of trunk
and head

Omnivora (All-eaters)

Pig, boar

Ten times length of trunk
and head

Frugivora (Fruit-eaters)

Monkey, ape,
man

Twelve times length of trunk
and head

Herbivora (Grass-eaters)

Horse, sheep

Thirty times length of trunk
and head

This comparison proves very little, except that the relative length
of man's digestive tube is most like that of monkeys and pigs. It is
true that our food tube is three or four times as long as that of the
exclusive flesh-eaters, but it is about a third as long as that of the
exclusive vegetarians, like the cow and the camel. If the animals
nearest like man do indeed subsist upon an exclusively vegetarian
diet of fruit and vegetables, it may mean only that the monkeys have
neither the instincts nor the cleverness to provide themselves with
flesh food. The only important question to consider here is whether
in actual experience, or as a result of careful experiment, man can
thrive on a mixed diet.

There are two really serious objections to the use of meat.
The first has to do with the chemical side. In the digestion
of meat there are produced substances that may be injurious
to the cells of the body. Some people can throw off these
poisonous substances more easily than others, and hence do
not suffer from them. Many people, however, accumulate these
products until they cause real injury. Moreover, it has been
found that bacteria thrive better in the intestines of flesh-eaters
than in the intestines of non-flesh-eaters, and the products
of the activity of these bacteria may be injurious to many
people. Finally, with the use of meat we are more likely to
get an excess of protein than we are with the use of exclu-
sively vegetable food. This is a real danger, because any excess

FOOD AND DIETARIES 107

of proteins must be eliminated from the body by the action
of the Hver and the kidneys, since the body has no way of
storing up the surplus.

If we take in too much fat or carbohydrate, most of us are able to
convert some of this excess into fat, which is deposited in cells under
the skin. A small amount of this fat is not injurious, and may even be
helpful. With proteins all that is not used must be oxidized, and the
products of these changes are poisonous and so must be thrown off.

The second serious objection to the use of meat is con-
nected with the effect of the practice of killing and dressing
animals upon the minds and characters of the people who are
engaged in these occupations. Is it true, as has been claimed,
that one cannot be a butcher without being brutalized .? If it is,
have I a right to make use of meat that can be furnished me
only at the expense of brutalizing some other human being .?

It is probable, at any rate, that most of us can get along
with much less meat than we use, and that we would really
gain physiologically by reducing the meat in our diet. It is
possible that some people depend upon meat more than others ;
in such cases it is likely that they derive some stimulation from
certain substances in the meat rather than better nutrition from
the meat itself.

In favor of meat it may be said that their proteins are more
easily digested and absorbed by human beings than are most
vegetable proteins.^

139. Brain food. There has been a great deal of confusion and
superstition in regard to the use of food for the benefit of special
parts of the body. Just as people have recommended beef for muscle
and bear fat for hair, so they have recommended fish for brain and
celery for nerves. If we recognize that in the process of digestion all
carbohydrates are changed to certain comparatively simple sugars,
all fats to comparatively simple soaps and glycerin, and all proteins

1 But the whole question of the relative value of different kinds of proteins
is far from settled. Experiments are now under way that should throw light
on this subject in the course of a few years (see p. 109).

1 08 ELEMENTARY BIOLOGY

to comparatively simple nitrogenous compounds, we shall see that it
is absurd to claim a specific value for one kind of food in connection
with the building of special tissues. All the products of protein, fat,
and carbohydrate digestion are distributed without discrimination by
the blood, and from this general store all the cells absorb their supplies.

140. Minerals in the food. So far nothing has been said
about the selection of food with respect to the mineral con-
tents. The reason for this is that our ordinary food materials
contain an abundance of salts in their natural condition, and
it is comparatively rare to see a person who suffers for lack
of minerals in the diet. Before the outbreak of the European
war there was a real danger that the refinements of food
through improved methods of manufacture would result in
a real scarcity of minerals in our foods. This is illustrated
by the fact that bread made from graham (whole-wheat) flour
contains from three to five times as much mineral matter
as that made from patent white flour, in which only the
interior portions of the wheat grain are present. Not only the
lime but much of the phosphorus and other mineral substances
are lost to us by the overrefinement of food preparation. ^

The growing bones of a child or any other young mammal
can be built up only if there is an abundance of lime in the
food. Growing children, therefore, should have more lime than
adults, just as growing chicks need to be supplied with broken
oyster shells or some other form of material containing lime,
and just as laying hens need more lime than roosters, since
lime is used in the formation of eggshells. Indeed, many
farmers and poultry raisers save eggshells to feed back to
their poultry.

1 Children that suffer from lack of minerals in their food often develop the
diseased condition of the bones known as rickets. A curious disease known
in the East as beriberi, which involves an inflammation of the nerve cover-
ings, seems to be caused by a diet consisting chiefly of polished rice ; that is,
rice from which the outer coat has been removed. It is believed that the
absence of the salts of the rice (and possibly of certain organic compounds
from the outer coating) is the cause of the disease.

FOOD AND DIETARIES

109

Vitamines. Experiments with mice and guinea pigs, as well as
with human beings and other animals, have shown that the various
proteins in the materials used as food do not all behave alike in rela-
tion to maintaining body weight or in relation to growth. The chemi-
cal analysis of proteins that behave in these different ways shows
that certain groups of elements contained in some proteins are abso-
lutely necessary for growth, while other amino acids are sufficient to

Fig. 35. The importance of suitable diet

The child in these pictures was suffering from defective nutrition. In the first picture

it weighed 14 pounds 4 ounces. The second picture was taken eleven weeks later,

after expert treatment, when the child weighed 17 pounds 15 ounces. Photographs by

Dr. Henry Dwight Chapin, at the Speedwell Society

maintain weight, although they cannot be used in growth. It has also
been found that there must be present in some of the food materials
certain substances (aside from the well-known fats, carbohydrates, and
proteins) that have a direct influence upon growth. These various
unknown substances have been roughly grouped together under the
name vitamines, which suggests that they are compounds somehow
related to " life." But there are probably many very different sub-
stances which are related to life ; and they are necessary for
protoplasm activity in several different ways. Pellagra and other
diseased states are due to the use of food lacking in vitamines.

no ELEMENTARY BIOLOGY

141. Taste of food. On looking over a bill of fare the dif-
ferent persons in a party are likely to make different selections.
And in marketing for the family the mother or housekeeper
will usually order a great variety of food articles. The reason
for this is that '' tastes differ/' It is an important practical ques-
tion to consider whether people should indulge their tastes, and
especially whether children should be allowed to eat what they like.

We have been told (p. 89) that it is not wise to depend
altogether upon instinct as a guide in the selection of the
kinds and in the determination of the amounts of food eaten.
And yet we cannot ignore instinct and taste entirely. In the
first place, food that is not agreeable to the taste will be of
very slight value to a person. Experiments made originally
by the great Russian physiologist. Professor Pawlow,^ and since
repeated and extended by others, showed that the secretion
of digestive juices in higher animals depends upon the stimu-
lation of nerves connected with the tongue and throat. We
have all had the experience of the " mouth watering " when
some attractive food is smelled. Stated in other words, this
means that when certain nerves are stimulated (in the nasal
lining and in the palate), the salivary glands begin to pour
forth their special product. Now it is only when these same
and certain other nerves are sufficiently stimulated that the
stomach begins to zvater, that is, to pour forth the gastric
juices from the glands into the stomach cavity.

Gastric juice will digest proteins, in the stomach or in a
teacup, without regard to anyone's feelings. Saliva will digest
starch, in the mouth or in a tin can, without regard to
anyone's feelings. But the glands of the stomach and the
glands of the mouth will produce and secrete juices more
readily when the palate is pleasantly stimulated than when
it is not stimulated. Indeed, under certain conditions the
glands of the stomach will not secrete digestive juices at
all, although there may be a great quantity of food in the

^ Pronounced pav'lof.

FOOD AND DIETARIES ill

Stomach waiting to be digested. For these reasons health
and happiness require that our eating shall be a pleasure and
not a disagreeable necessity.

142. The appetite. We all have a natural liking for sweets.
This does not show that all sweet things are good for us,
for there are some sweet substances that are actually poisons.
But, on the other hand, a '' sweet tooth " may indicate that
there is need for more carbohydrate than one gets regularly.
If the body is in good health, the appetite can usually be
depended upon to tell us what to eat and how much, at the
dinner table. If food has been poorly prepared and the bad
taste of it concealed with sauces and spices, the appetite will
become perverted and will certainly not be a safe guide in the
selection of food.

Food may be attractive to the palate and yet be quite
unsuitable because of its indigestibility. Or food may be suit-
able for one person and not for another. A little attention to
the matter should enable every mother to find out what kinds
of food agree with her children and what kinds do not. And
a little attention should enable each one of us to find out for
himself what it is safe to eat and what it is best to let alone.
One person is always made sick by shrimp or fish but has
no difficulty with doughnuts or cheese. With another person
it is just the other way. No one can tell you whether you can
digest beans or not, and you cannot find it out from a book.
You have to find out for yourself, and then use your knowledge
for your own benefit.

143. Digestibility. Aside from individual peculiarities of the
digestive system, however, there are some foods that are more
easily digested than others. For example, milk contains the
protein, fats, carbohydrates, and salts in a very easily digested
form. Meat proteins and fats of all kinds are digested with
comparative ease. But the proteins and fats of meat are
inclosed within cell walls, the material of which is not so
easily digested. In cooking, much of this material is broken

112 ELEMENTARY BIOLOGY

down, but the manner of cooking may have an influence upon
the digestion.

144. Cooking. There are three or four primary uses of cook-
ing that can be understood from a biological point of view :

1. Cooking breaks up and softens the cell membranes, thus
liberating the proteins, fats, and carbohydrates.^

2. The chemical changes produced in meats, vegetables,
eggs, cereals, etc. by the action of heat result in the formation
of substances that are especially attractive to the sense of smell,
and thus react favorably on the secretion of digestive juices.

3. The action of heat (with or without moisture) upon starch
results in breaking up the starch grains and in making them
more easily digested.

4. Cooking has the further effect of destroying any germs
of bacteria or other microbes (see Chapter LXXI) that may be
present in the raw food, thus lessening the danger of trans-
mitting an infectious disease or a parasite (see p. 341), and
making it easier to preserve the food against decay.

Another result of cooking that has only recently received the
attention it deserves is the wastefulness involved in certain kinds of
cooking. This is a matter that is not strictly biological, although it
should be considered in connection with the subject of feeding. One
particular kind of waste, however, has biological significance. That is
the waste of mineral matters brought about by the boiling of food
and then throwing away the water which contains the valuable food
salts. Of course, with more scientific cooking these wastes will be
avoided, and our food as served to us at the table will contain the
necessary minerals, as well as the proteins, fats, and carbohydrates.

145. Food economy. Another important consideration in the
selection and preparation of food is the matter of cost. For
all practical purposes a few cents' worth of corn meal may

1 To a certain extent the materials that make up the cell walls in meats
become digested and thus contribute to the total food supply. The cellulose
that makes up the cell walls of plant tissues cannot be digested in the human
body ; but it is digested into sugars by the juices of many animals, such as
cows and other grass-eaters.

FOOD AND DIETARIES II3

satisfy one's hunger as well as a dollar dinner. It is also true
that in the selection of food for a family it is possible to bring
about a great deal of saving by comparing the food values
and the market values of the various articles, and guiding
oneself accordingly.

146. The pleasures of eating. Cattle and guinea pigs and rats can
be kept alive indefinitely on a monotonous minimum diet. When the
same thing is tried with human beings, they gradually lose those char-
acters that distinguish them from the cattle or the guinea pigs. One
of the things that drive men to drink and to drugs is the attempt to
make them live like catde. The cheapest diet is commonly recom-
mended to people who have little of the pleasures of life and little
time or training for enjoying the more refined forms of recreation.
To these people the comparatively simple pleasures of eating should
not be denied. If those who are capable of high thinking on the
basis of plain living wish to adopt the simpler diet, there can be no
objection ; these people do not depend upon the palate to help make
life more interesting.

In connection with the question of economy we must consider not
merely the money cost or the effort in the preparation of food but
the happiness and well-being that result from the preparation and use
of the food. It is in this sense that it pays to take some time in set-
ting the table, to make it attractive to the eye, to make it a pleasant
place at which to sit and eat. It is doubtless cheaper, in a money
sense, to eat standing, each member of the family helping himself to
what he wants from a general collection of pots and dishes in the
kitchen. But it pays to be human, even in the matter of eating.

CHAPTER XXIII
FOOD HABITS

147. Water with meals. Until a few years ago it was
generally considered unwise to take water with meals, because
it was assumed that diluting the digestive juices would delay
the process of digestion. Experiments have shown, however,
that the more water there is in the stomach the more easily will
the process of digestion go forward, and the more quickly will
the subsequent absorption take place. Students and soldiers
who took part in the experiment found that they could easily
take a quart of water in the course of a meal, and they were
all benefited by the practice. It is very probable that one
never drinks too much water. Still there are certain things
to guard against.

1. Water must not be allowed to take the place of saliva
in softening the food for swallowing. Therefore, water should
be taken into the mouth only when there is no food present ;
drink between courses rather than with the food.

2. The water should not be too cold. In this country the
drinking of ice water has become almost a national" vice.
Water a great deal warmer than ice water can be found quite
agreeable ; and we shall find that we can drink larger quan-
tities if it is not too cold.

148. How to eat. Anything that arouses unpleasant feelings,
as worry, anger, or anxiety, is almost sure to interfere with
the normal working of the digestive process. On the other
hand, whatever arouses pleasant feelings, whatever puts us
into good humor, helps to tone up the digestive organs. It is
therefore a wise rule that obtains in some families, not to open
letters that come just before or at mealtime ; and it is another

114

FOOD HABITS 115

good rule not to read the newspapers or to settle unpleasant
affairs before a meal. Pleasant conversation, exchange of amus-
ing experiences or anecdotes, are more helpful at mealtime
than heated discussions.

There should never be a feeling of hurry about a meal. It
is better to take two meals a day quietly and restfully than
three meals in a hurry, if time is so pressing.

Rapid eating makes it impossible for sufficient saliva to mix
with the food.

Then it makes impossible the breaking up of the food
particles, so that the gastric digestion is interfered with.

Rapid eating makes impossible the adequate stimulation of
the taste and smell nerves, necessary to bring about secretion
of gastric juices.

The time saved by eating rapidly is generally more than paid
for by later indigestion.

What has already been said about the use of water at meals
and about rapid eating will warn us to chew our food thoroughly
and to avoid washing down each mouthful with a drink.

149. When to eat. A young infant has to take food every
few hours; he takes but a little at a time, the food is liquid
and quickly digested and absorbed, and the child is soon hungry
again. Some people have relatively small stomachs, which can-
not hold much food at one time ; they may have to eat at more
frequent intervals. Others can get all they need for a day in
two meals, and many men and women have been quite healthy
and happy with but a single meal a day.

In the course of experiments made in recent years, in order
to find out the best rations for human beings, many of the
experimenters discovered that they were in better working
condition when they had only two meals a day than when they
took three meals. This improvement may have been due to
the fact that they reduced the total amount of food, or it may
be that by taking only two meals they gave their digestive
organs longer intervals of rest.

Ii6 ELEMENTARY BIOLOGY

It is impossible to lay down rules as to the number or regu-
larity of meals. This is something that each one has to settle
for himself on the basis of experience. It is probably advan-
tageous to adopt regular hours for meals, and to avoid, so far
as possible, interfering with this program either by changing
the hours or by eating between meals.

In making a program that will leave a fixed time for each
meal, we must consider the other things that are being done
during the day. It is well to avoid hard work of any kind
immediately after meals. Exertion of the muscles causes an
increase of blood-flow to those muscles and a corresponding
decrease in the blood-flow to the digestive system. As a result,
the secretion of digestive juices is reduced, and the process of
digestion is slowed down. The food remains in the stomach
a very long time, overworking the muscles of that organ, some-
times to the point of actual distress. Effects of the same kind
are produced whether the work done is in the nature of pro-
ductive labor or merely free play. Similar consequences are
found to arise from bathing too soon after a meal ; in this case
the flow of blood is to the skin, but the effect on the stomach
is the same.

150. Health habits. We have seen that we have no direct
control over the workings of the digestive system ; we must
therefore establish habits at the few points where we have
indirect control. The first point has to do with eating, and the
establishment of suitable eating habits should be our first con-
sideration. The second point at which we have control of the
digestive system is in the establishment of habits related to the
behavior of the large intestine. And, finally, there are certain
general habits of exercise and breathing and sleeping, which, on
the one hand, are largely under our control, and which, on the
other hand, have an influence on the digestive system.

We may summarize the habits that are of importance to us
in this connection ; for most of them the reasons have already
appeared in the preceding discussion.

FOOD HABITS II7

1. The selection of food

a. For nutrition and balance.

b. For digestibility.

c. For palatability.

d. Proper preparation.

e. Proportion of coarse, indigestible elements and bulk.^
/. For laxative elements.

g. For suitable quantities.

2. The avoidance of food materials that are personally undesirable,

however suitable they may be for others.

3. The avoidance of special sauces and spices as stimulants to

the appetite.

4. The observance of fairly regular hours as to eating.

5. Leisurely attitude toward the meal. This would include the tak-

ing of a few minutes of rest before eating, when tired, as well
as the avoidance of rushing off to work or to play after eating.

6. The establishment of a pleasant frame of mind for the meal, as

well as other agreeable surroundings, whenever possible.

7. Thorough mastication of the food before swallowing. This

does not mean counting the number of bites that you put
into every mouthful ; it means having the habit of chewing
until the mass in the mouth is in a nearly fluid condition, so
that it fairly " swallows itself."

8. Drinking plenty of water, — before meals, between meals, as

well as at meals, and before retiring, — but never using it
(or any other liquid) to " wash down " food in the mouth.

9. Where outdoor work with the large muscles is not a part of

the regular program, exercising (out of doors if possible) a
certain amount every day.

1 Experiments made in a European army many years ago, with a view to
finding, if possible, a concentrated ration that contained a maximum of nutri-
ent and a minimum of indigestible and nonusable substance, resulted in show-
ing that people cannot maintain their health on such a diet. The reason for
this is that the intestines can be stimulated to do their muscular work only by
the mechanical pressure of a mass of substance on the inside. When food is
refined to the point where it contains no refuse, or very little, the muscles of
the intestines cease their activities. We must therefore have a certain amount
of bulk in the food, as well as the nutrients. This bulk is supplemented by
the vegetables we eat, especially green vegetables, which contain a relatively
small proportion of nutrient and a relatively large proportion of cell walls.

Ii8 ELEMENTARY BIOLOGY

10. Deep breathing, through the nose, not a few breaths now and

then, but as a regular thing, all the time (see p. 183).

1 1 . Take plenty of sleep every night. This is better than sleeping

a little most nights, in the hope of raising the average by
sleeping later on Sundays or holidays.

12. Emptying the bowels every day, as nearly as possible at a

fixed time.

151. Constipation. The importance of this last point has
already been suggested (see p. 88), but it is worth emphasiz-
ing. The decomposition of the refuse in the large intestine
by the action of many species of bacteria gives rise to a num-
ber of poisonous substances that are absorbed into the blood
if the refuse is not thrown out with sufficient frequency. More-
over, the waste substances poured into the intestine with the
bile are also injurious to the cells of the body and should be
removed with the other undesirable matter. The absorption of
these poisons into the blood and their distribution to the cells
of the tissues bring about a real poisoning of the body. This
shows itself in a variety of ways. The most common symp-
toms of constipation — the clogging up of the bowels with
the unremoved refuse — are the following :

1. Headaches, especially the kind of headache that seems to
hammer at the temples when you bend over.

2. The " blues " — a feeling of general dissatisfaction and grouch,
when nothing that you know of has happened to give you cause for
dissatisfaction.

3. Drowsiness, although you may have had plenty of sleep within
a few hours.

4. A certain '' tired feeling " when you have hardly done enough
work to account for the tiredness.

5. Loss of appetite and indigestion.

6. A coated, or furred, tongue.

There are many headache powders on the market, and
several fortunes have been made selling people various kinds
of headache remedies. But the headache powders never cure

FOOD HABITS 1 19

people of their trouble. They generally depress the action of
the heart so that the circulation is lowered, and you do not
feel the pain caused by the disturbance of these bowel poisons.
But the poisons are still there, and if the bowels are not
emptied, more are being manufactured, whether you have
a headache or not. The thing to do is to remove the cause
of the trouble, not merely hide the damage from yourself.

In the same way you- might be cheered up by a stimulant
or by an entertainment ; but these do not remove the cause
of the trouble. In the case of acute constipation one may
obtain temporary relief by the use of a physic or an enema.
But these should never be used as regular things. Since the
chief cause of constipation is neglect of the bowels, the only
real cure is the establishing of regular habits of evacuation.
Mothers realize how important it is to get infants into regular
habits of emptying the bowels, but many of them neglect the
children when they are a little older. If regular habits are
not established in youth, they are likely never to be fixed
at all. It is certain that hundreds of thousands of people
in this country suffer from constipation, and that there is
no drug or medicine that will cure the disorder.

152. The teeth and their care. One of the commonest
causes of indigestion is found in decayed teeth. A number
of years ago an examination of thousands of school children
showed that in nearly every case of backwardness there was
also some physical defect, as of the eyes, ears, or teeth. The
surprising thing was that bad condition of the teeth was found
in children who were behind in their school work more often
than poor eyesight or poor hearing. When we consider the
relation of the teeth to digestion, and of digestion to health
and vigor, we can well understand why this should be so.
People with poor teeth simply get into the habit of swal-
lowing the food without chewing it, and then blame their
stomachs or the cook for their miserable feeling or for the
poor work they do.

120

ELEMENTARY BIOLOGY

The structure of a human tooth is shown in Fig. 36. The
enamel is a hard protective casing. Trouble with the teeth
most frequently begins with the breaking of this enamel. The
enamel can be cracked by grinding it against some hard sub-
stance, as when you try to crack a nut with your teeth ; or it
may be cracked by sudden changes of temperature. Drinking
very cold water or very hot drinks is likely to be one of the
ways of cracking the enamel. Picking the teeth with a needle

or some other hard body is also
likely to scratch the enamel
and thus to open the way for
further damage.

In the food that we put into
our months there are many bac-
teria, of many kinds. In par-
ticles of food that cling to the
teeth these bacteria begin their
digestive activities, and some
of the substances thus pro-
duced act upon the enamel,
dissolving away this protec-
tive cover. Particles of food
in the larger cracks, or fluids
in the smaller scratches and
cracks, permit the action of
the bacteria to continue, and
gradually a cavity in the tooth becomes larger and deeper,
until it reaches the pulp, and the nerve becomes exposed.
A thorough cleaning of the teeth thus becomes necessary
at frequent intervals. The most reasonable time to clean the
teeth is immediately after each meal. If you get the habit
of doing this, it will postpone the rotting of the teeth a good
many years. Unfortunately our business and industry are so
arranged that most grown-ups cannot manage to look after
their teeth after each meal. The best one time a day for

Fig. 36. Structure of mammalian teeth

A^ human grinding tooth, showing central
pulp cavity (a), containing nerves and blood
vessels and surrounded by dentme (d). The
crown is covered with enamel (c), and the
root with cement {d). B, gnawing tooth of
rabbit, which grows from below as fast as it
wears away at the tip. The chisel edge is
kept sharp by the dentine wearing away
faster than the facing of hard enamel

FOOD HABITS 121

brushing the teeth is just before retiring, that the bacteria
may not continue their destructive activities during sleep.

The best cleaning material for the teeth — as for the skin
or for clothes — is a good white soap. If you buy a dollar's
worth of tooth paste or powder, you get several cents' worth
of soap, together with some cheap perfume and a little powder
added to scrub. The perfume does not" help to keep the
teeth clean ; and it has been questioned whether the powder
does not do more harm than good. If we begin with the
younger children, we shall find that they can quickly learn
to use plain soap on the toothbrush and do not need the
fancy-smelling pink addition to make tooth-brushing an
agreeable habit.

In brushing the teeth, the motion of the brush should be
circular, so as to reach all the spaces between the teeth. If
you brush crossways, the depressions along the edges of the
teeth will not be reached at all. It is well, also, in setting out
to fix a toothbrush habit, to remember that the back teeth and
the inner faces of the teeth need to be considered as well as
the fronts ofj^the front teeth.

Unfortunately, the use of soap or other alkaline substances
causes the salivary glands to secrete mucin — the substance that
makes the saliva glary or sticky. Now this mucin furnishes a
sticky covering for the teeth, in which the bacteria can remain
and do their destructive work. Experiments have shown that
the use of some weak acid (as citric acid from lemons, or acetic
acid from vinegar) stops the secretion of mucin and makes
the mouth a cleaner place, so far as the welfare of the teeth
is concerned. It is therefore recommended that dilute vinegar
be used for cleaning the teeth, at least in the last cleaning
before going to bed. If the vinegar is used after soap, the
latter must first be thoroughly rinsed out with plain water.

Some people need to use on their teeth an antiseptic or
bacteria-killing mouth wash. Such a mouth wash, however,
is to be used in addition to brushing, and not as a substitute.

CHAPTER XXIV
THE SOCIAL SIDE OF THE FOOD PROBLEM

153. Food and water in modern times. When every family
lived in a house by itself, at some distance from its neighbors,
the water from the well or from the spring back of the barn
may have been good enough to use, and there was usually
enough of it. But when people came to live in cities, close
together, it became impossible to get enough for all needs in
the immediate vicinity. Nor was the water they could get good
enough, for the refuse of many people and households con-
taminated the water at its very source. It therefore became
necessary for a supply of water to be brought from a distance.

When most of the people lived in the country or in small
towns, it was possible for nearly everybody to know how plants
and animals were raised for the market. When Jiousekeepers
made their own preserves for the winter, they knew what the
jars contained.

But as manufacturing industry developed, people came to
live more and more in cities ; that is, away from the source
of the food supplies. Gradually we have reached the point
where a very large part of our food comes to us in sealed
packages, made we know not where, nor of what materials.
You cannot tell by the taste or by the looks of a lot of food
taken from a can whether it is nutritious or not ; nor can you
tell whether it contains any harmful preservative or coloring
matter ; nor can you tell whether it contains any adulterant.

154. Public regulation. In the case of food, as in the case
of water, it soon became necessary for the people of a city or
state, acting together through their public officials, to regulate
the wares that the buyer was offered. In the case of water even

THE SOCIAL SIDE OF THE FOOD PROBLEM 123

earlier than in the case of food, definite regulations were
adopted, requiring chemical and bacterial tests to be made for
the protection of the public. In other words, just as soon as
the public realized that the individual could not protect him-
self, it undertook to protect itself through a public agency.

155. Commerce and food supplies. In addition to changing
conditions of manufacture and living, another fact made it
necessary for the public to protect the purchaser of foods.
Growing commerce has brought to us food products of foreign
lands, in regard to which we have no standards and no judg-
ment. As individuals, we know nothing of the nutritive value
or the possible dangers of these imported materials. This makes
it very easy for dealers and manufacturers to mix cheaper
materials with those that already enjoyed a wide market, or to
substitute cheaper materials for more expensive ones. Spices
and coffee were thus among the first things to be adulterated.

Glucose, which is much cheaper than sugar, can be mixed
with jellies, preserves, candies, and other food products con-
taining sugar, thus increasing the bulk and at the same time
reducing the cost of a given quantity of finished product.

When it was found that a pretty good imitation of butter
could be made out of beef fat, at a cost much lower than the
cost of butter, people substituted oleomargarine for butter in
cooking and baking foods to sell, thus increasing their profits.
And in a similar way cottonseed oil was substituted for, or
mixed with, olive oil.

In all these cases no harm was done to the bodies of the people
who ate the substitutes or admixtures. Starch and glucose and oleo-
margarine and cottonseed oil are perfectly harmless and very useful
carbohydrates and fats. The harm done was of a commercial kind.
People do not like to pay sugar or honey prices for glucose, or butter
prices for oleo, or milk prices for water. And the merchant who is
selling pure products does not like to compete with adulterated or
substituted products ; it puts him at a disadvantage in the market
and may drive him out altogether.

124 ELEMENTARY BIOLOGY

The first regulations adopted by governments for the control of
the manufacture and sale of food products had to do with commer-
cial frauds — the selling of adulterated or misbranded foods. These
regulations mean, in effect, that when a person offers to sell you sugar,
you should not be obliged to carry your own chemical equipment to
the market, and test the wares against substitutions or adulterations.

As the scientists' knowledge about the relation of food to
bodily health and efficiency increased, and as our civilization
separated people more and more from the sources of their
everyday needs, it became necessary for the public, through
its official agents, to extend the protection of the buyer still
farther. It is not sufficient that we get full measure. It is
not sufficient that we get goods correctly labeled. We must
be assured that what is offered us is suitable for our purposes,
and that it is harmless.

If the chemists or other scientists can discover cheap substitutes
for the familiar fats and carbohydrates and proteins, they are doing
mankind a service ; they are reducing the cost of living. But we do
not care to have the dishonest manufacturer or dealer get all the
benefit of these discoveries, while the rest of us go on working as
hard as ever, and getting as little out of life as before.

156. Food dangers. In more recent years a new set of prob-
lems has arisen in connection with the protection of the public
food supply. This has to do with the sale of food that may be
decomposed and thus unfit for food, or with the sale of food
that has been made dangerous by contamination with disease-
breeding bacteria. The former is illustrated in the canning and
packing industries ; the latter in the commerce in fresh milk,
meat, fish, eggs, vegetables, and so forth.

In the canning and packing of meats, fruits, vegetables, fish,
and so on, food that is not strictly fresh has often been put
into the containers, with its odor concealed by the use of spices
or other flavoring substances. Decomposed food is a real
source of danger, for it contains, in addition to the proteins.

THE SOCIAL SIDE OF THE FOOD PROBLEM 125

fats, and carbohydrates for which we buy the food, poisons
produced by the rotting, or decay. Regulations concerning the
sale of prepared foods in which such material is present have
been adopted by the governments of nearly all the states ;
and the shipment of such preparations from one state to
another is prohibited by federal laws. Many cities also have
local regulations that enable the officials to seize and destroy
any such unsuitable food which they may find, in addition
to penalizing the dealers or manufacturers by means of fines
or imprisonment.

157. Use of preservatives. The use of preservatives in
canned or prepared foods, such as benzoate of soda, has been
under discussion for a long time, and many careful experi-
ments have been made to discover the possible injury that such
materials may cause. It was found in one set of experiments
that although benzoate of soda is injurious if taken in large
quantities, one would have to eat a peck or more of catsup
containing this preservative before he took in enough to hurt
him. The objection, however, to the use of these preservatives
is not that these substances are in themselves harmful. The
objection is that their use makes possible the admixture of
slightly decomposed vegetables into the manufactured product.
Without the use of the preservatives the manufacturer would
be compelled to use only clean, fresh material. At the present
time our federal laws protect us in this matter only to the ex-
tent of requiring the manufacturer to state on the outside of the
package what amount, if any, of preservative is present. But
the buyer has to take the chance of seeing this warning on the
package, and of knowing its full meaning when he does see it.

In the case of milk, preservatives are not to be tolerated,
since the only kinds that can be used without the buyer's
detecting them are apt to be injurious in themselves.

158. Food protection. The second class of dangers referred
to above, that of infection by disease germs, is a purely local
problem, since it has to do with the food brought to the

126 ELEMENTARY BIOLOGY

consumer day by day. Many cities have adopted regulations
requiring dealers to protect their wares against exposure to
dust, insects, or other sources of infection. They have regu-
lations as to refrigeration of meats and fresh fish. And most
elaborate regulations have been adopted in regard to milk.
Since milk is the most easily spoiled of all our foods, and
since it is at the same time so indispensable for many people,
especially children and infants and sick people, it is one that
calls for strict protection against contamination and against
adulteration. On page 127 are given the milk standards and
the milk rules of many progressive cities. You will see that
there is a biological reason for every rule in the list.

159. The public educates itself. A part of the public's
danger lies in its ignorance. New facts and new problems
are appearing every day. While the public tries to educate all
of its children through the public schools, it is impossible to
teach in the schools all that the children will need to know,
and it is certainly impossible to tell in advance what they will
need to know of the discoveries that are still to be made.
Every progressive community — whether it be a city, a state,
or a nation — seeks to advance important knowledge and to
spread it among its members as quickly as possible. The
state and local departments of health, the experiment stations,
and the schools are therefore all at work increasing the
protection of the public by means of bulletins, lectures,
announcements to the newspapers, and posters.

In extreme cases the government will adopt prohibitive legislation ;
that is, laws that prohibit the sale of articles known to be injurious.
We can no longer say, " I have a right to eat or drink what I like."
Of course it is no one's business but my own if I prefer ice cream to
apple dumpling ; and it hardly seems fair for the government to tell
me that I may not eat ice cream, when I feel like it and am able to
pay for it But in the case of certain drugs and drinks, the question
is rather one of protecting people against their own ignorance or
against vicious habits and customs (see p. 257, on drug laws, etc.).

MILK STANDARDS

I. Chemical Standards

a. Milk must not contain more than 88.5 per cent of water.

b. Milk must contain not less than 1 1.5 per cent of milk solids.

c. Milk must contain not less than 3 per cent of fats.

d. Milk must not be drawn from cow within fifteen days before

nor within five days after calving.

e. Milk must not be diluted with water or other liquid, or be

otherwise adulterated with foreign substance.

II. Bacteriological Standards

a. All cows must be in good physical condition and tested at

least once a year with tuberculin, tagged, and registered
with the authorities within three days.

b. Dairy conditions and methods must be scored and the score

registered or certified.

c. The milk must be tested and certified from time to time.

Grade A Milk {Raw): Must not contain more than 100,000 bac-
teria to the cubic centimeter, and must come from dairies that
score at least 75 per cent.

Grade A Milk [Pasteurized) : . Must not contain more than 200,000
bacteria per cubic centimeter before pasteurization, nor more
than 30,000 between pasteurization and delivery to consumer,
and must come from dairies that score at least 70 per cent.

Grade B Milk {Raw): Must not contain more than 300,000 bac-
teria per cubic centimeter, and must come from dairies that score
at least 60 per cent.

Grade B Milk {Pasteurized) : Must not contain more than i ,000,000
bacteria per cubic centimeter before pasteurization, nor more than
100,000 on delivery to consumer, and must come from dairies
that score at least 55 per cent.

These standards, with slight variations, have been adopted by

boa?-ds of health and by dairy associations in the 7nost progressive

cities all over the country.

128 ELEMENTARY BIOLOGY

A further step in the public use of special knowledge is
illustrated by laws specifying that workers in stores and fac-
tories must be allowed at least an hour for lunch every day.
Such a law means that the agents of the public have recog-
nized the importance, for the health of the people, of an
opportunity to eat the midday meal without haste. A further
regulation requires the provision, in factories and large estab-
lishments, of suitable special rooms in which the workers may
eat their meals in surroundings that are more pleasant than
the sight of the machines or piles of goods. Another regula-
tion requires the provision of suitable washing facilities, to
enable the workers to come to their food with clean hands.
Ordinarily these arrangements are not of great importance to
the manufacturer or employer ; if his workers get sick he can
always get others. But the health of the people is important to
themselves, and thus to the state. Yet it has been found that
whenever the conditions for eating lunch have been greatly
improved in any factory or store, there was an immediate
improvement in the character of the work, so that what many
employers did reluctantly under compulsion from the state has
turned out to be profitable to them. However, such regulations
are made in recognition of the importance of human life and
health, and not in consideration of making greater profits.

As the public comes to know more and more about the
relation between proper feeding and right living, it will no
doubt extend its community activity in food matters farther
and farther. For some time to come the food question to
receive most discussion is that of the school lunch. It has
been found that thousands of children in the larger cities
come to school improperly or insufficiently nourished. The
argument is made that the money spent in the effort to edu-
cate such children is all wasted, and that in order to save all
this money it is necessary to put the children into condition
to profit from the efforts of the teachers. This means that
the school should supervise, or even provide the means for,

THE SOCIAL SIDE OF THE FOOD PROBLEM 129

the feeding of children, at least so far as successful school
work depends upon proper feeding.

160. National food resources. With the growth of popula-
tion every nation comes to a point at which it must look
ahead to insure supplies of food for the coming generation —
or suffer in time from famine or national decay. It is for this
reason that our national government devotes so much attention
to the question of food resources. Scientists are constantly
engaged in solving problems connected with (i) the produc-
tion of more food on a given area, (2) utilizing materials to
better and better advantage, (3) finding new sources for food,
and (4) preventing food from being wasted.

Advances in chemical and biological knowledge have en-
abled us to find new methods for preserving food for long
periods. This makes possible a cheapening of food supplies in
two ways : ( i ) It is possible to send food a long distance, from
regions in which it is very abundant to cities and countries
where food is not so easily raised. (2) It enables us to keep the
bulk of large crops for a longer period. The condensation or
drying of milk, for example, makes the use of milk possible
in places where cows cannot be kept, and makes the surplus of
the summer's milk available in the winter. As a Frenchman
once said, '' The box of dried milk is a cow in the cupboard."

A good example of cheapening food by the application of
chemical knowledge has already been referred to (p. 123) in
connection with the extension of the use of cottonseed oil. A
later advance consists in treating this oil with hydrogen under
the influence of electricity, thereby producing, at less than half
the cost of butter, a fine solid fat which has the same food
value as butter, except that it has no flavor. This fat has the
advantage over butter that it does not easily turn rancid.

Another direction in which government agencies work to
improve or increase our food resources is illustrated by the
production of new varieties of plants and animals having
special desirable characteristics — as cows with large milk-yield,

i36 ELEMENTARY BIOLOGY

or better wheat, or more corn to the acre, as described in the
chapter on plant and animal breeding (Chapter LXXXI).

The entrance of the United States into the Great War has
made us all aware of the importance of (i) more definite knowl-
edge of national food resources and (2) more systematic control
of production, distribution, and utilization of food supplies.

Arrangements were made to record every prospective bushel
of grain or potatoes, of every head of cattle, of every catch of
fish. Bulletins and proclamations were issued broadcast, in-
structing all people how to get the most out of the food mate-
rials that they had, how to save every usable scrap of organic
matter, how to make every square yard of cultivated ground
yield more, how to preserve the food that could not be used up
immediately. Canning and drying demonstrations, as well as
cooking and gardening demonstrations, were made in all parts
of the country, and for the first time in history a whole nation
was brought together to face the food problem as a single family.

In connection with this great national need, the problem of
food distribution has come to the front as never before. We
now see that it is not sufficient merely to provide warehouses
and transportation for the year's production. It is necessary
also to see that every child and every adult finds it possible
to obtain an adequate supply of nourishment. It is more im-
portant to the nation that every living unit be kept in good
living condition than that a few individuals make large profits
out of speculation in the needs of the rest of us. For these
reasons we may expect the regulations inaugurated under the
stress of war to be continued in time of peace, to the point
where our knowledge and our skill insure the people of the
nation the material foundations for their well-being ; namely,
their " daily bread." In England it has already become a com-
mon saying that '' all must have bread before any have cake."

CHAPTER XXV
STIMULANTS, NARCOTICS, AND POISONS

161. ** Getting used.'* There are many kinds of fish that
live in salt water only, and there are many kinds that live in
fresh water only. There are some species, however, that can
be made to live in either salt or fresh water. Still, if we took
one of these fish out of the ocean and placed it in fresh water,
it would soon die. Or if we took a live one from fresh water
and put it into salt water, it would soon die. But if we slowly
increased the amount of salt in the fresh water, we could gradu-
ally bring the water to the composition of the ocean, and the
fish would remain alive. In the same way we could gradually
add fresh water to a tank of sea water, until there was a very
small proportion of salt in the mixture, then transfer our fish
to fresh water, and it would remain alive.

In a case of this kind we say that the animal " gets used "
to living in the new conditions. This illustrates a pretty gen-
eral fact about protoplasm, or about living things. It is possible
for living things to get used to new conditions of temperature,
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 sur-
roundings whatever ; we know that is not true. We know that
birds cannot get used to living in water, or that fish cannot get
used to living in the air ; we know that plants and animals cannot
get used to living without proteins or without salts. We under-
stand simply that we can change our conditions of living to a
certain degree or in certain directions, and still remain alive.

Arsenic is a violent poison for all kinds of protoplasm.
It is used for killing animals as well as plants, as in fighting
many kinds of insects and many kinds of fungi. A very small

131

132 ELEMENTARY BIOLOGY

amount of it will kill a person or a rabbit. ^ In experiments
this substance was given to rabbits in very small quantities, —
a fraction of the quantity that it would take to kill. After a
few days the animals were given a little more. The dose was
gradually increased until the animals had become so accus-
tomed to the substance that they could stand several times the
ordinary fatal dose. The arsenic acts upon the protoplasm of
the nerves or muscles in such a way as to put the animal in
a state of to7ms — that is, the way one feels when one is ''all
on edge," ready to jump or scream on the slightest provoca-
tion. The rabbits treated with arsenic thus became extremely
sensitive to the slightest disturbance ; they would jump on
hearing the faintest sound, or on seeing the slightest move-
ment, or the passing of a shadow. But the most curious result
was that after animals had been treated with the poison in this
way for a considerable time, it zvas impossible for them to live
without it. If the drug was omitted from their daily rations,
they quickly died.

162. Action of drugs. It seems that when any substance out
of the ordinary gets into the protoplasm, it may behave in one
of three ways. Either it remains without any effect on the
protoplasm, or it combines chemically with one or more of the
substances in the cell. In the latter case the partial removal
of the protoplasm material either depresses the action of the
living substance or makes it go faster.

163. Stimulants and narcotics. Anything that changes the
condition of the protein, or removes fat, or hastens oxidation
— or stops oxidation — must modify the action of the living
protoplasm. A substance that makes protoplasm work harder
or faster is called a stimulant. One that slows or depresses
the activity of protoplasm is called a narcotic. Both stimulants
and narcotics are therefore poisons^ since the final effect of
either may be to stop the action of protoplasm permanently.

\ 1 Strangely enough, a child can stand more arsenic than an adult.

CHAPTER XXVI
ALCOHOL AND HEALTH

164. An old acquaintance. One of the oldest stimulants
known to man is alcohol. This is a compound of carbon,
hydrogen, and oxygen (C^HgOH) commonly produced by the
action of the yeast plant (see pp. 291-292) on sugars.

The ancients found that when juices of fruit, or malted grain
(see p. 78) in water, were allowed to stand for some time,
they developed new flavors and tastes, and that some of them
also acquired the peculiar property of making the drinker feel
very much elated. In time the making of alcoholic drinks
developed into special trades, and in modern times into vast
industries. It is only during the past forty odd years that we
have come to understand just what happens in these ferment-
ing liquids, largely on the basis of the chemical and biological
investigations started by Louis Pasteur.

165. Is alcohol injurious ? It is still more recently that we
have come to understand what it is that happens when alcohol
or alcoholic liquors are taken into the body of an animal.

The custom of drinking these beverages is so old, and the number
of people who are directly or indirectly interested in keeping up their
manufacture and sale is so large,^ that it is naturally difficult to spread

1 In this country alone there were over two million people dependent for
their living upon the manufacture and sale and distribution of various kinds
of alcoholic beverages when we entered the Great War. This included people
who were engaged in the raising of barley and rye and corn and other plant
materials that are used in the manufacture, chemists and engineers, makers of
machinery, workers in the building trades, carpenters and cabinetmakers,
machinists and mechanics of many kinds, who were engaged in the making
and repairing of vehicles used in connection with the business, drivers and
teamsters, bottle makers, and so on. Almost every line of trade had a portion
of its workers dependent upon the liquor industry.

133

134

ELEMENTARY BIOLOGY

24 years

more

At 20
years

16 years
more

B

36K

years

more

13«^ years

more

At 30
years

llj^ years
more

At 40 ^
years

■

Fig. 37. Alcohol and expectation of life

At every age the abstainers (white) have the chance of longer
additional life than the moderate drinkers (shaded)

a true understanding of the known facts. On the other hand, there
are large numbers of people who have seen certain evil effects of the
drink habits, and these are so bitter in their attacks on the use of
alcohol that they give the impression of being "cranks," so that many

reasonable people
refuse to take
them seriously.

Another diffi-
culty about judg-
ing the good or
harm of alcoholic
drinks from ordi-
nary observation
is the fact that
people differ so
much in their
sensitiveness and
in their resistance. We may see hundreds of people who have grown
old, with the drink habit acquired many years before. You cannot
show that these people have been hurt by the drink. On the other
hand, a young person with great promise of future achievement
is ruined in a short while by becoming addicted to drink.

Is alcohol poison
or not ? If it is, un-
der v^hat conditions
or in what amounts
is it a poison ? Is
it helpful to some
kinds of people ?
We cannot answer
these questions ofihRnd, from our ordinary every-day experience.
We must therefore do two things :

1 . We must bring together the experience of thousands and
thousands of people ;

2. We must make special experiments.

The experiences of large numbers of people have been
made available in recent years by the study of the records of

15-20 years

20-30 years

Over 30 years

cn

cm

3.1:1 4.0:1

Fig. 38. Alcohol and the chances of death

The chances of dying at any given time are from 1.8 to

4 times as great for drinkers (shaded) as for non-drinkers

(white)

ALCOHOL AND HEALTH

135

Non-drinkers

Fig. 39.

insurance companies that have kept a note of the drink
habits of their poHcyholders for many years past. These
records show that there is a measurable difference between
those who use alcohol and those who do not, with respect
to at least two things : Those who never use alcohol have (i)
a measurably greater chance to survive infectious diseases
and (2) a measurably greater average length of life.

Hospital records have shown again and again that non-users
of alcohol have a measurable advantage over users in at least
two respects :

1 . They have a better chance
to survive infectious diseases

(Fig. 39) ; and

2. They have a better chance
to recover from the effects of
surgical operations.

Railway experience has shown
that non-users of alcohol are
measurably better than drinkers
in the avoidance of accidents.
This naturally is of great concern to the public at large.

166. Alcohol and digestion. It has been found that small
quantities of alcohol stimulate the secretion of gastric juice.
But the presence of alcohol restrains the fermenting action of
the pepsin. The advantages of alcohol with meals in stimulat-
ing the flow of digestive juices is therefore offset by the effect
on the digestive process proper. ^ In larger quantities alcohol
tends to dry up the mucus cells of the lining of the digestive
tube and to make the glands less sensitive ; this may lead to
dyspepsia and other forms of indigestion.

^ Experiments have shown that in the use of various liquors the alcohol
is not the only constituent that may have an effect upon the stomach and
the other organs. Wines and whiskies especially contain a large number
of oils and vegetable extractives that give color and flavor to the drink ;
some of these have been shown to have a decided effect on the workings
of the body.

Alcohol and infectious
diseases

In the cholera epidemic in Glasgow

(184 7-1849) the hospital records showed

that a larger proportion died among

drinkers than among abstainers

136 ELEMENTARY BIOLOGY

167. Alcohol and work. Experiments made with lower
animals, and with muscles taken from the bodies of animals,
showed that in small quantities alcohol has a slight stimulating
effect. But when the use of alcohol is continued, muscular
activity is actually reduced. The results of these experiments,
made on dogs and on students and soldiers, are in agreement
with the observations of army officers in Germany, in this
country, and in South Africa (British army), which agreed in
the conclusion that while a small quantity of alcoholic drink at
first stimulated the soldiers to brisker marching, the effect
wore off in about three miles (less than an hour) and that they
were then less able to continue the march than the soldiers
who had not taken alcohol. Where dogs were used in the
experiments, the total amount of muscular activity of the
alcoholic dogs was considerably less than that of the non-
alcoholic ones. The total work and the endurance are therefore
reduced by the use of alcohol. One point worth noting here
is that although the first effect is to make the action more
vigorous, the after effect more than coimterbalances the gain.
This will be referred to again later.

CHAPTER XXVII
ALCOHOL AND SOCIETY

168. Why do people drink? Many find it hard to understand
why it is that alcohol drinking continues in spite of all that has
been done to discourage the practice. Investigations show that
most of those who have the drink habit began to drink rather
early in life (Fig. 40). The reasons for beginning at all are
various, but a few stand out prominently.

1. There is the example of parents and associates. If all
the people at home and all who come to visit take a little nip
with every meal, the children will come to consider this the
proper and natural thing to do. They learn just as readily to
shovel food into the mouth with the knife, or to sip the soup
quietly. So far as the young people are concerned, there is
nothing necessarily wrong or right about any of the things
they see going on at home day after day.

2. Then, some people begin by taking alcohol-containing
drinks as a "medicine" and get the habit. In most of such
cases the victims are not aware either of the presence of the
alcohol in the medicine or of the danger of the drink. They
take the medicine because a friend who " had the same
trouble" recommends it, or because it has been advertised to
cure all the imaginable diseases. But when they get used to
it, they feel that they cannot get along without it ; and indeed
they do suffer without it.

3. Many people take to drink for the deliberate purpose of
" drowning their sorrows." It is certain that as alcohol has the
effect of weakening the attention, so it will help a person
forget what has been on his mind for some time ; and if one
has had worries or sorrow on his mind, we can understand

m

138

ELEMENTARY BIOLOGY

how he might be tempted to take something that would make
him stop caring, if only for a little while.

4. Many other persons are driven to resort to stimulants
because of the unsatisfactory condition of their nutrition.
Food that is badly cooked or otherwise improperly prepared,
malnutrition, indigestion, and so on alter a person's appetite so
that he is glad to try almost anything that his acquaintances
recommend, and alcoholic drink is more commonly recom-
mended by our well-meaning but ignorant friends than any
other one thin^, as a remedy for all sorts of ailments.

Before 6 Q4

]71

After 30 1 [s

Fig. 40. When the drink habit is formed

Dr. Alexander Lambert found the ages at which 258 alco-

hoUc patients in Bellevue Hospital, New York, acquired

the drink habit

5 . Many people
resort to drink in
order to take away
the sense of tired-
ness after a hard
day's work ; it
'' spruces " them
up a bit, and the
sensations which
result are gratify-
ing for the time
being.
6. By far the largest single cause of beginning the drink
habit is found in man's natural sociability. Up to a certain
stage of development every person has a strong impulse to do
as he sees others doing. This is not simply blind imitation,
but a genuine sympathy with one's fellows, and a desire to
share in their activities and feelings. A young fellow may
drink because it seems to him to be a manly thing to do,
since he sees so many men and older boys doing it. Or he
may desire to be '' in with " people. No one likes to be con-
sidered '' out of it." And many a young fellow who has been
taught the dangers of drink has not the self-reliance and the
backbone to say No ! when the other fellows urge him on
or even jeer at him for being a " sissy." The exaltation of

ALCOHOL AND SOCIETY

139

spirits that many attribute to the drink, when they have been
drinking in company, is probably due in reahty to the stimula-
tion that comes from doing things together with the others,
just the excitement of sociability. But since most young men
have not discovered a way of getting this excitement except by
drinking together, and since this excitement is certainly pleasant
— why, they go and drink (Fig. 41).

7. In addition to these mental and physiological facts that
lead people to drink we must mention also the economic fact
that there are hundreds of thousands of people who find it to
their interest to encourage others to drink. By means of allur-
ing advertisements, by means of suggestions, by means of

Sociability

12S«

Dull

Misery

Medic-
inal
Prepa-
rations

i

si

21^
Other Causes

Fig. 41. Why people begin to drink

This diagram shows the result of an inquiry among a large number of people addicted

to drink

attractive drinking places, they lead people on until these get
the habit ; after that they do not need to be encouraged. It is
the />rofit that so many make out of the liquor business that
makes them lead the others on.

169. Fighting the drink evil. The important things, in deal-
ing with a large problem like the drink question, are those
that go back to the causes.

Alcohol habits resulting from the use of medicines are being
prevented in several ways. Many of the patent medicines so
widely advertised in the past were not only worthless for the
curing of the diseases they were bought for, but they were found
in very many cases to be worse than useless, for they contained
alcohol, or other habit-forming substances — that is, substances
the use of which created a desire for more. People are learn-
ing the dangers of these " medicines," and the better classes

I40 ELEMENTARY BIOLOGY

of newspapers and magazines no longer advertise them.
Physicians too are warning their patients against the use of
these dangerous preparations, and, when prescribing medicines,
they are more careful to consider the danger of the formation
of alcohol or other drug habits.

People who look to liquor as a means of ''drowning their
sorrows " can be helped only by teaching them a better way of
meeting the difficulties of life. Liquor does not remove trouble,
and most people are intelligent enough to see that. We must
do what we can to diminish the causes of suffering and worry ;
but there will always remain some that cannot be prevented.

Better cooking, better food selection, better habits of eating,
knowledge of and interest in the laws of health, and the oppor-
tunity to acquire health habits, better conditions of work, more
leisure, and training for a sensible use of that leisure — these
are the things that will take the place of alcoholic drink.
Or, rather, they will remove much of the temptation and
occasion to acquire the drink habit.

The tremendous amount of drinking that is caused by man's
sociability is to be remedied not by trying to make men less
sociable but by teaching people how to be sociable in a more
profitable way, and by giving them opportunities to meet and
enjoy each other's company outside the saloon or the drinking
club. Recreation centers maintained in the public schools,
clubrooms in churches and settlements, reading rooms, gym-
nasiums, athletic fields, and similar places furnish the best
antidote to the saloon.

Finally, all the preaching against drinking will have to meet
the clever urgings of those who are interested in selling liquors.
So long as men can find a profit in selling alcohol, men will
be induced to buy it. The only way to stop this traffic, as
traffic, is to take the profit out of it. This has been done
by way of experiment in Sweden and Norway ; and wherever
the selling of liquor has been separated from the profit, the
amount of drinking has been very quickly diminished.

ALCOHOL AND SOCIETY 141

170. The social attitude toward alcohoL Where in former
years it was considered very elegant to have wines and other
Hquors at dinners and banquets, more and more people are
learning that we can be quite as elegant without trying to see
how much we can drink before showing the effects. In former
years it was considered almost indispensable to have liquors in
which to drink the health of kings and presidents and brides
and so on. Nowadays, when more and more people are coming
to know that these drinks add to the unhealth of the drinkers
(whatever the effects may be upon the person toasted), we are
becoming content to abandon the custom of drinking a health
with alcohol.

171. The economic side. The movement against alcohol is
still more marked in industry. Many railroad companies have
gradually made it impossible for drinkers to get employment
with them. At first they prohibited the drinking of alcoholic
liquors by employees ivhile on ditty. Then they made it a
cause of instant dismissal for an employee to be found dnink
at a.iy time. Then they made it a cause for dismissal for an
employee lo go into a drinking place with his uniform on. Now
they refuse to take on ivorkers who drink at all. The same
is true of large manufacturers, who have found that even
moderate drinkers are less reliable, on the average, than
total abstainers. And the insurance companies are coming
either to reject the applications of people who drink or to
charge them a higher rate on their insurance.

These social and economic forces are doing more to dis-
courage drinking customs than was accomplished in all the
years of preaching against the evils of drink. The reason
for this we can see when we consider why people take to
drink, in the first place, and why they do not stop when they
have been told of the evils.

The experience of Russia in the Great War will do much
toward eliminating the drink evil from modern life. Shortly
after the outbreak of the war the manufacture and sale of

142 ELEMENTARY BIOLOGY

whisky was stopped by the Russian government, on the
recommendation of the mihtary authorities, because the drink
was found to interfere with the efficiency of the soldiers.
Since the government there had a monopoly of the industry,
it was a comparatively simple matter to bring about the change.
In spite of the many years of custom and habit, the sudden
withdrawal of alcohol brought about quick adjustments in the
form of better workmanship and happier living, even during
the progress of the war. Restrictions were placed upon the
manufacture and consumption of alcohol in the other warring
countries. In this country the chief problem seemed to center
at first about the wisdom of permitting so much grain and
other food materials to be converted into alcoholic beverages
while we were confronted with a shortage of essential food-
stuffs. Later it became necessary to prohibit the manufacture
of alcoholic drinks both to save the material and men for more
urgent work and to protect military and civil workers from
the effects of alcohol.

The war experience no doubt had an important influence
upon the decision of American legislatures to adopt the pro-
hibition amendment to the Constitution.

CHAPTER XXVIII
AIR AND LIFE

172. Energesis. The activity of protoplasm is made possible
by a chemical process that sets free heat, or light, or motion,
or some other form of energy. In this process oxygen is
usually concerned, and it may be called energesis^ or '' energy
making."

173. Life without air. In the yeast and in certain other
simple plants there are ferments that bring about the break-
ing down of carbohydrates into simpler compounds, as alcohol
and carbon dioxid, in the absence of oxygen. Such organisms
are called anaerobic ; that is, '' living without air." The carbon
dioxid given off by anaerobes, although not the direct result of
oxidation, is still a by-product of energesis.^

The German physiologist Pfi tiger placed a live frog in a
vacuum and found that the animal continued to give off carbon
dioxid. This showed that the carbon dioxid given off by a
living organism is not directly related to the oxygen taken in.
And this has been shown over and over again by means of
careful experiments, in which the gas exchange was accurately
measured.

174. Oxygen in energesis. But if the oxygen does not
combine with the carbon and hydrogen of the protoplasm
compounds, what has it to do with the chemical processes
in a living cell ? It seems that the chemical changes can
take place only in the presence of water, and that under the

1 We can perhaps form a picture of anaerobic energesis by comparing the
chemical process to what happens when a pile of blocks is caused to break
down by the removal of one or two of the supporting blocks. As the structure
falls down into simpler combinations, a great deal of energy may be set free.

143

144

ELEMENTARY BIOLOGY

influence of certain ferments the fats or carbohydrates in the
protoplasm break up, forming simpler compounds. But these
processes can continue only to a certain point unless new

oxygen is constantly supplied.

175. Breathing. Strictly speaking,
breathing is a process of gas ex-
change,— the taking in of oxygen
and the giving off of carbon dioxid.
Breathing, or respiration, makes oxi-
dation, or energesis, possible ; but
they are not the same. In the low-
est plants and animals, which get
their oxygen directly from the sur-
rounding air or water by osmosis,
and give off their carbon dioxid
directly to the surrounding medium,
respiration and oxidation are indeed
closely connected in space and in
time. But in higher, more complex
plants and animals there is sometimes
a considerable separation between the
two processes, as we shall see.

176. Cell respiration. In an or-
ganism made up of very many cells
the cells that are farthest from the
surface must necessarily get their
oxygen supply in some indirect way.
In the interior of a leaf we have
seen that there is a constant circu-
lation of air among the cells, the

spaces between the cells being connected with the outside air
by way of the stomates (p. 71). In the young twigs the
epidermis also carries stomates that connect with the intercel-
lular spaces below the surface. In the older twigs, however,
in which the bark formation has gone on for some time, the

Fig. 42. Cell respiration

In one of the higher animals
each cell receives oxygen, as well
as food, by diffusion from the
surrounding fluids, which in turn
communicate with the blood
stream. Each cell throws out into
the blood stream carbon dioxid,
urea, and other products of pro-
toplasm activity by diffusion
through the membrane

AIR AND LIFE

145

Fig. 43. Breathing tubes in
insects

s, the spiracles in the side of the

body, opening into the tracheae

^, which branch repeatedly and

bring air to all the tissues

live cells beneath the bark get their
oxygen supply by way of the /enti-
ce Is (see Fig. 24), which open to the
exterior and connect with passages
that carry air to the cambium,, or
growing layer. Since the cells of
the plant use comparatively small
amounts of oxygen, they can get
enough from the air that diffuses
slowly through these openings and
passages. The carbon dioxid given
off by cells diffuses to the exterior
along the same paths (Fig. 42).
In insects, which use relatively large
amounts of oxygen, the cells in the interior of the body get
their supplies from very delicate tubes that branch into all parts
and connect with the outside through little openings arranged
along the sides (see Fig. 43). The movements of the body,
by compressing
and releasing
these tubes, aid
in the circula-
tion. In some
insects, as the
common locust,
there are rhyth-
mic movements
that alternately
empty and fill
the air pipes,
thus accelerat-
ing the diffusion
of oxygen and
the removal of
carbon dioxid.

Fig. 44. How the clam breathes

The water inside the shell is kept in constant circulation by
the vibration of cilia which cover the whole surface of the
body and the lining of the mantle m. The current of water
(indicated by the arrows) flows forward toward the foot /, up
past the mouth, and backward over and between the gills ^.
In the gills an exchange of gases takes place between the blood
and the flowing water

146 ELEMENTARY BIOLOGY

In all the animals that have blood, excepting only the insects,
the respiration of the interior cells is related to the blood.
That is, the cells get their oxygen from the blood, and they dis-
charge their carbon dioxid to the blood (see Chapter XXXIV).

177. Respiration and blood. In all such animals we there-
fore apply the word 7'espiration to the process by which the
air is brought from the outside to the blood and the carbon
dioxid is thrown out. The simplest kind of blood respiration

Fig. 45. How the lobster breathes

The featherlike gills of these crustaceans are protected by an extension of shell which

incloses them almost completely. By the action of appendages connected with the

mouth organs a constant current of water is made to pass over the gills through the

space under the shield, moving from the back edge forward

is found in such animals as the earthworm. In this the respi-
ration 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 (Fig. 44). In the lobster, crab, crayfish,
and related animals there are special structures in which there
is a great deal of surface in a comparatively small space,
crowded together in a particular region of the body (Fig. 45).
When we come to animals with backbones, we find that
the breathing organs are connected with the food pipe, so that
all of them can, and many of them do, breathe through the

AIR AND LIFE

H7

mouth. In the fishes the water carrying oxygen in solution
is taken into the mouth; but when it gets into the throat,
instead of being swallowed into the gullet it is forced out
through a series of openings in the sides of the pharynx and
passes over the gills. The gills are fine, feathery structures

Fig. 46. How the haddock breathes

In the fishes the gills are arranged on arches along both sides of the pharynx. Water
is taken through the mouth and passes over the gills and out again, as indicated by

the arrows

containing many delicate blood vessels. As the water passes
over the gills the oxygen in solution diffuses into the blood
from the surrounding water (see Fig. 46). In the bony fishes
the gill-slits and the gills are covered over by a special plate-
like shield.

In the amphibians the adults breathe the air into the
mouth and swallow it into the lungs, and all the higher
vertebrates breathe by means of lungs.

CHAPTER XXIX

BREATHING IN MAN

178. The lungs. Our

lungs are two soft, rather
complex bags that are sus-
pended in the thorax, or
chest cavity, and are con-
nected with the pharynx
(Fig. 28, b) by means of
a tube called the trachea.
This windpipe branches
again and again, and ends
in thousands of tiny cham-
bers lined with a layer of
thin-walled cells in contact
with very fine blood vessels.
The gas exchange between
the outside air and the blood
takes place through the lin-
ing of these small air cham-
bers, which constitute the
working surface of the lungs.
The act of breathing is thus
a process of ventilating or
changing the gas contents
of the inside of these cham-
bers (see Fig. 47).
179. The process of breathing. The lungs, consisting as they
do of air passages and air chambers, and having no muscular
tissue in their structure, are incapable of carrying on any

148

Fig. 47. The human lungs

The arrows show the course of air from the
outside, m, mouth ; «, nostrils ; /, pharynx ;
/, larynx ; jf, trachea ; b, bronchi. The right
lung is shown cut open ; the bronchi branch
again and again, the last tubules ending in
delicate expansions. «, the air cells, or sacs ;
epi^ the epiglottis, which closes over the air
pipe when food passes from the pharynx to
the esophagus e

BREATHING IN MAN

149

movements. The ventilation of the lungs
is brought about by the action of muscles
in organs outside the lungs. There are
two sets of organs that are concerned in
these movements : the ribs, with their
connected muscles, and the diaphragm
(see Fig. 48).

When the muscles of the ribs and of
the diaphragm relax, the chest cavity
shrinks, and this forces the lungs to
collapse, driving the air out. By the
alternate expansion and contraction of
the chest, inspiration and expiration, the
two movements of air in respiration, are
brought about.

The external respiration of the body
consists of (i) the muscular movements
of the ribs and the diaphragm ; (2) the
air movements into and out of the lungs ;
and (3) the osmotic movements of gases
into and out of the blood, through the
lining of the air cells.

The i7itemal respiration of the body
cells consists of the gas exchange be-
tween the cells and the blood or lymph.
Internal and external respiration are re-
lated to the vital process of energesis.

180. Control of breathing. When you
wish to do so, you may hold your breath
for a minute or two ; you may breathe
faster or slower; you may breathe with

Fig. 48. The movements
of breathing in man

When the muscular parti-
tion (called the diaphragm)
between the chest cavity
and the abdominal cavity
is pulled down, the chest
cavity is enlarged. When
the ribs are raised, the chest
cavity is also enlarged. The
rib muscles and the dia-
phragm normally work in
unison, alternately expand-
ing and contracting the
chest cavity. The shaded
portion of the diagram
shows the expanded con-
dition — ribs raised and
diaphragm lowered

your diaphragm, holding your chest wall
nearly rigid, or you may breathe with your chest, keeping the
abdomen almost immovable. Nevertheless the process of
breathing, as it is carried on hour by hour and day by day,

ISO

ELEMENTARY BIOLOGY

is an unconscious and an involuntary process. The way you
breathe is entirely a matter of habit and surroundings.

181. Nose-breathing and mouth-breathing. Normal breath-
ing carries the air — out as well as in — through the nose, not
the mouth. We should acquire the habit of breathing through

the nose rather than
through the mouth, for
the following reasons :

1 . The lining of the
nose secretes a layer of
mucus, in which fine
particles of dust are
caught before getting
to the windpipe.

2. Coarser particles
are filtered out by the
hairs that line the front
nostrils.

3. The long, narrow
nose passages warm
the incoming air before
it reaches the more deli-
cate lining of the air
pipes of the lungs.

This habit should be
formed early in life ;
most people are incap-
able of getting new
habits or breaking old habits after they grow to maturity.
Watch yourself, and when you catch yourself breathing through
the mouth, make up your mind to stop the trick, and have
your closest friend or relations help you by reminding you
when you forget yourself.

Breathing through the mouth is objectionable on two other
grounds besides the hygienic ones :

Fig. 49. Expression of face associated with
adenoids

The open mouth, the sleepy eyes, the strain about

the nose, are results of defective breathing due to

obstructions in the rear air passages of the nose.

(From a photograph by Jessie Tarbox Deals)

BREATHING IN MAN

151

1 . It looks hideous to other people ; no one likes the
appearance of a mouth-breather (see Fig. 49).

2. It sounds bad at night. That is, the mouth-breather is
likely to become a snorer. Snoring is the sound produced by
the vibration of the soft palate when a current of air strikes
it on the way out through the mouth. You don't snore when
you are awake ; but when you are asleep the muscles of the
mouth and palate relax, and the air sets the palate in motion.

182. Obstructions in nasal
passages. When children are
seen to breathe through their
mouths, and difficulty is found
in making them breathe through
their noses, they should be ex-
amined by a physician, as it is
likely that there is some ob-
struction in the nasal passages.
The most common obstruction
is an outgrowth of the lining
in the back part of the nostrils ;
such growths are called ade-
7ioid growths, and when present
should be removed (see Fig.
50). Their presence is a handi-
cap to the child, since it inter-
feres with proper breathing

and, sometimes, with the circulation of the blood in the head.
It is true that if they are not cut out, they are likely in time
to disappear, being gradually absorbed. But by the time they
are absorbed, the harm will have been done, for the growth and
mental development of the child will have become permanently
retarded by just so much.

183. Deep breathing. A second factor in breathing is that
of depth. In ordinary breathing a man at rest takes into his
lungs and throws out again with each breath about 30 cubic

Fig. 50. Adenoid growths

In the passage between the nostrils and
the pharynx (/) shapeless masses of tissue
{a) sometimes grow out, obstructing the
movement of air from the nose and lead-
ing to mouth-breathing. /, the larynx, or
voice box

152 ELEMENTARY BIOLOGY

inches of air. If he takes a very deep breath, his lungs
receive about 130 cubic inches. By forcing out of the lungs
as much air as possible and then taking a deep breath, he can
take in about 230 cubic inches. When the lungs have been
emptied as completely as possible by a forced expiration, they
still contain some 100 cubic inches of air. The lungs do not
work to full capacity in regular breathing ; that is, they are
never perfectly empty, and they are rarely perfectly full.

The 30 cubic inches of ordinary tidal air will partially fill
some of the air sacs of the lungs. The 100 cubic inches of
additional air will fill more of the air sacs and distend them
more. But some of the air sacs farthest away from the main
air pipes will be filled only by forced breathing. This is true
especially of the air sacs in the extreme upper corners of the
lungs. These air sacs are never reached in the breathing of
some people, and it is in these very corners that tuberculosis
of the lungs most frequently begins.

For the sake of the health of the lungs it is desirable that
they be thoroughly ventilated at least three or four times a day.
Vigorous exercise of the large muscles of the legs, shoulders,
or abdomen will automatically increase the depth of the breath-
ing, so that the athlete or the shovel-man will ventilate his
lungs without needing to think about the matter. But the book-
keeper or the seamstress does need to think of the matter.
A person whose occupation does not regularly compel deep
breathing should acquire the habit of ventilating the lungs by
means of ten to fifteen very deep breaths, taken three or four
times a day, outdoors if possible, but at least at the open
window. A very good habit that does not cut into one's time
is to take a dozen very deep breaths on first going out in the
morning, and again at noon and in the evening, or in fact
whenever one passes from a house to the outdoor air.

184. Posture and clothing. You cannot give the fresh air
a chance to reach all the corners of your lungs unless the
shoulders are back far enough to let the chest expand freely.

BREATHING IN MAN 153

The stooped position is not only bad for the spirits — for you
cannot feel brave and strong with your head bowed down and
the shoulders curved forward — but it is also bad for the health
in general and for the health of the lungs in particular.

Clothing that cramps the ribs or the waist is a direct
restraint on proper breathing. Tight corsets and belts do not
cause one to suffocate ; but they do prevent one from breath-
ing deeply, with the use of the diaphragm as well as all the
rib muscles.

The effect of lacing upon the liver, stomach, and intestines can be
understood on a little reflection by anyone who understands the
functions of these organs.

CHAPTER XXX

VENTILATION

Ordinary Air

Expired Air

Oxygen 20.0^

Carbon dioxid 0.03^

Oxygen 16.i%
Carbon dioxid i.lfr

185. Air requirements. The blood in the lungs absorbs
from the air about 5 per cent of the oxygen taken in with
each breath. 1 In the course of an hour an ordinary man will
give off about 1000 cubic inches of carbon dioxid when at
rest; with moderate work, about 1600 cubic inches; and with

hard work, about 3000 cubic inches.
This means that in order to
keep up the working power a
person must be supplied with
enough fresh air to keep up the
oxygen requirement and to carry
off the carbon dioxid excreted.
Of course the air in a given room
does not all have to be changed
for every breath. It is safe to use air in which the amount
of carbon dioxid has been increased from 4 parts in 10,000
(what it is in ordinary pure air) to 6 parts in 10,000, or even
much more.

A great many studies have been made, to find out the amount
of fresh air that should be supplied for each person in a room,
for the purpose of establishing standards for ventilation of
schools, factories, theaters, and so on. Some of the results
of the experiments showed that a person needs at least
3600 cubic feet of air per hour. Others called for three times
that much. It has been supposed that the change of air was

Nitrogen 78.09^ Nitrogen 78.09^

Fig. 51. Effect of breathing on
the air

The ratio of oxygen to carbon dioxid
is changed from 700.1 to 4.1

1 A comparison of expired air with ordinary air shows that the amounts of
oxygen and carbon dioxid are changed, whereas the nitrogen and other parts
remain constant (Fig. 51).

154

VENTILATION 155

necessary in order to keep up the proportion of oxygen and
to keep down the proportion of carbon dioxid,

186. Ventilation problems. More recent experiments show
that under ordinary conditions the air contains neither a breath
poison nor a dangerous proportion of carbon dioxid, even when
the ventilation is decidedly bad. Nor is there danger that the
percentage of oxygen will fall below a safe limit. It seems that
the chief problems in ventilation are (i) to keep the air at a
suitable temperature, (2) to regulate the moisture and dust in
the air, and (3) to prevent the air from stagnating.

187. Skin temperature. The body radiates heat and trans-
pires moisture all the time. Up to a certain temperature we
may remain comfortable by increasing perspiration and trans-
piration ; that is, evaporation of water from the surface of the
body keeps the temperature of the skin down. An excess of
moisture in the air stops evaporation, and we become uncom-
fortably hot. Or if the temperature becomes too high, evapora-
tion cannot go on fast enough to leave us comfortable. But this
discomfort that the skin feels when it is hot and damp is of the
same kind, only greater in degree, in the case of the lungs.
A hot, stuffy room interferes with the breathing because it inter-
feres with the radiation of heat and the transpiration of zvater
inside the lungs. The oppression felt in a poorly ventilated
room has apparently nothing to do with the amount of carbon
dioxid or with the lack of oxygen. Bad odors are offensive
and may interfere with one's breathing on that account.^

The drowsy effects of a badly ventilated room are due to the con-
gestion of the skin capillaries and the corresponding depletion of the
blood vessels that supply the brain and the muscles, quite as much as
to the influence upon the breathing.

1 In the famous Black Hole of Calcutta, in which so many people lost their
lives, the victims were supposed to have died of lack of oxygen. It seems
probable that in such cases death really results from " heat-stroke," due to the
excessive humidity (from the perspiration and the lung transpiration of the
people) and the high temperature (from the heat radiated by the bodies and
not carried off).

156 ELEMENTARY BIOLOGY

The new understanding of the effects of heat and dampness
on the body's comfort and efficiency, and of the relative unim-
portance of the percentages of oxygen and carbon dioxid in
the air, has not eHminated the problem of ventilation, however.
On the contrary, it has made the problem more difficult, for
the engineers had about solved the problem of how to supply
a given quantity of new air to a room every hour. Now we
have to consider the temperature and the moisture, and at the
same time remove the disagreeable and sometimes distressing
odors that are accumulated in a room full of people at work.

In many states the laws prescribe a minimum air space for
each worker, amounting in most cases to four hundred cubic
feet, exclusive of machinery or furniture. In a space of this
size it is possible to change the air fast enough to remove the
heat and the moisture given off by the body and the organic
substances given off by the lungs without causing a draft.

188. Temperature of air. The prevailing temperature in a
living room, schoolroom, or workshop should be kept as nearly
as possible at 65° F. When the temperature approaches 70°
it begins to be too uncomfortable and to affect the efficiency
of one's work.i

Where the character of the work requires that a lower tem-
perature be maintained, as in packing houses and in some
chemical works, the body should be provided with warmer
clothing, and the humidity of the atmosphere may be higher.
In mines, bakeries, tunnels, foundries, rolling .mills, or other
places where the temperature is necessarily high, workers
should wear very light clothing, or even be stripped to the

1 According to the studies of engineers, rooms should be warmer or cooler,
according to the activities of those who occupy them. This idea is illustrated
by the following table :

Rooms for Active Occupations

Rooms for Resting or for
Sedentary Occupations
Shop for vigorous work, 50°- 59° F. Sleeping room, 54°-59°F.

Gymnasium, 60° F. Lecture hall, 6i°-64° F.

Shop and room for moderate Living room, office, school, 68° F.

work, 6i°-66° F. Bathroom, 68°-72° F.

VENTILATION

157

waist ; the humidity must be kept low and the air must be in
constant circulation, to facilitate the removal of moisture.

189. Circulation of air. Natural ventilation will often suffice
in dwellings that have large rooms and windows, with not
too many occupants. But when many
people have to be in a room, as in
schools and workshops (especially in the
winter, when artificial heating is neces-
sary), there is likely to be a need of
special attention to ventilation. So long
as the weather permits it, ventilation
should be by means of windows, open
top and bottom for the freest possible
circulation of air. A window board may
be placed under the lower sash, as shown
in Fig. 52, to prevent a direct draft ; this
will allow circulation of air between the
sashes and at the top.

With closer occupation of rooms,
forced ventilation becomes necessary.
Several systems have been tried, in
thousands of buildings. In some the
air is pumped into the rooms ; in others
the air is drawn off.

Fig. 52. Window venti-
lation in cold weather

Experts are not agreed as to which is
better, and it is probable that neither is
altogether superior to the other. Which-
ever system is used, it can be combined
with a plan to filter the dust from the air
that comes into the rooms, with a device for adding suitable quantities
of moisture, and with the heating plant for regulating the temperature.

A board placed edgewise
under the lower sash pre-
vents drafts. The upper
sash is pulled down a few
inches, permitting fresh air
to come in between the
panes and permitting warm
expired air to pass out, as
shown by the arrows

In artificially heated houses there is often the danger of having
the air too dry. In steam-heated rooms the moisture may be
maintained by having a dish of water on each radiator.

CHAPTER XXXI
CONTAMINATED AIR

190. Gases and fumes. In many industries poisonous gases
and fumes are produced ; these either corrode the deHcate
Hnings of the lungs or are absorbed and injure the whole
system. Most acid fumes act in the former way. Alcohols
used in varnishes, phosphorus fumes, lead fumes, and others
poison the body. It is for these reasons that the manufacture
of white phosphorus matches has been entirely prohibited in
this country, and that the use of wood alcohol in varnishes and
shellacs has been prohibited in some states and cities.

Where the work produces fumes or gases, these must be re-
moved by flues connected with exhaust fans. No person should
work regularly in any establishment that permits annoying or
dangerous fumes to enter the air breathed in the shop.

Carbon niofioxid, present in the suffocating coal gas produced when
the drafts in a coal stove are closed down, is an actual poison when
it gets into the lungs, being absorbed by the blood.

191. Dust. There are dozens of occupations in which the
worker is constantly exposed to dust of various kinds. Dust is
injurious in several ways.

1. It may form a crust over part of the lung lining, thus
reducing the actual breathing surface and at the same time
weakening the resistance of the cells to disease microbes.

Examples are coal dust and the fluff from fibers used in spinning
and weaving.

2. Dust consisting of hard, sharp particles may scratch the
delicate cells lining the air sacs, exposing them to the invasion
of disease microbes.

158

CONTAMINATED AIR

159

Examples are metal and stone dust and fine sand, produced in in-
dustries in which metals are ground and polished, in which sand-blasts
are used, and in which chipping of metal or stone is carried on.

3. Dust may carry with it disease germs of various kinds. .

Street and house dusts are the most common source of this kind
of danger.

A list of the most common occupations in which the danger
from dust is an important factor is given below. It is possible
in most of the industries to reduce the dust danger almost to
the zero point.

SOME COMMON OCCUPATIONS IN WHICH DUST IS A SERIOUS
MENACE TO THE WORKERS

Mining

Crushing of metals and minerals

Sifting of metals

Molding and core-making

Grinding and polishing

Brass-working

Tool-making

File-cutting

Marble-cutting

Stone-working

Glass-working

Cement-working

Pottery and earthenware industries

Plastering and paper-hanging

Diamond-cutting

Engraving

Jewelry-making

Grain-handling

Flour industry

Starch-refining

Baking and confectionery work

Tobacco-working

Cotton textile industry

Flax and linen industries

Woolen and worsted manufacture

Silk industry

Spinning

Weaving

Hosiery and knitting industries

Lace-making

Hat-making

Hemp and cordage industries

Jute and jute-goods industries

Shoddy manufacture

Rag-picking and rag-working

Wood-turning and wood-carving

Cabinet-making

Upholstery and mattress-making

Brush-making

Paper-making

Printing industry

Lithographing

Street-cleaning

In the grinding of paints and of metals it is possible in many cases
to use a wet process, in which water or oil is used to hold down the
dust particles resulting from the grinding.

i6o ELEMENTARY BIOLOGY

In polishing furniture powdered puniice stone and oil can be used
instead of sandpaper.

In some dusty processes it has been possible to inclose the
machinery and the material in such a way as to prevent the escape
of dust into the air breathed by the workers, as, for example, in flour
mills, in certain operations that have to do with the crushing of
ores and minerals, and in the polishing of small metal objects.

Fig. 53. Dust and safety hood

In polishing metal goods this hood protects the worker from dust and, in case the wheel
bursts, from flying particles. (From photograph by New Jersey Department of Labor)

But where these methods are not possible, it is necessary to
use a special form of ventilation that draws the dust away from
the point at which it is generated. Special hoods connected
with exhaust pipes are thus placed over grinding wheels, over
rotary saw-blades, over polishing w^heels, and so on (Fig. 53).

Even with all the precautions mentioned, there will be dust
in many workrooms. In such cases the individual worker
should carry an air-filter over his mouth and nose. This

CONTAMINATED AIR

i6i

respirator consists of a canvas cup carrying a wet sponge or
cloth (see Fig. 54) through which the breathed air must pass,
leaving the dust behind. The gas masks worn by our soldiers
in France and by firemen serve a similar purpose.

Dust is constantly being produced in the home, on the
street, in the school, etc. This dust settles on the floor, on the

Fig. 54. Respirator

In many industrial processes it is impracticable to remove the dust by mechanical

means. The respirator is worn by the worker to filter the dust out of the air which he

breathes. The sectional view shows the valve, v, and the sponge, s, through which the

air is filtered. (From photograph lent by the American Museum of Safety)

furniture, and on the books and utensils. Careless housekeepers
or janitors sometimes try to produce the appearance of clean-
liness by removing the dust in the quickest way, that is, by
throwing it into the air, where it cannot be so easily noticed.
From the point of view of people's health, this is a foolish
way of keeping clean. Within the last few years feather dusters
have gone quite out of fashion, and in some places their

1 62

ELEMENTARY BIOLOGY

use in school buildings and other public places is forbidden.
From the point of view of cleanliness, as well as from the
point of view of health, wet sweeping with damp or oiled
sawdust or pieces of wet newspaper and the wiping off of
dust with a damp or oiled cloth are more satisfactory than
the old-fashioned methods of dry sweeping and dusting.

1 |iSH|j

11 1

Itlllil #

H'

'-y

Fig. 55- Dusting for looks and dusting for health

The feather duster throws the dust into the air, where it cannot be seen, but where it

can do more harm than on top of the bookcase or picture-frame. The damp or oiled

cloth removes the dust not only from the furniture but from the way of doing harm

192. Smoke. A very common source of air contamination,
especially in manufacturing cities, is the smoke from furnaces
of all kinds and from railway locomotives. Experiments have
shown that the smoke interferes with the growth of plants,
and it is certain that smoke affects the health of human
beings. Progressive cities now prohibit the pollution of air
by smoke.

193. Tobacco smoke. Whether we mind it or not, tobacco
smoke spoils the air for us and is a real injury. Apart from
possible injury to the smoker, those who do not smoke deserve

CONTAMINATED AIR 163

some consideration. Speaking for these, David Starr Jordan
said, " We ask for a free passage through the world, with
pure air all the way!'

194. Nicotine. The tobacco of commerce is made of the leaf and
stalks of the tobacco plant {Nicotiana tabacum, a member of the
potato family). The tissues of this plant contain a violent poison
known as nicotine. Nicotine is a poison, either when taken internally,
that is, into the food pipe, or when injected into the body through
the skin. The people who are interested in tobacco, however, do not
'' take " it that way ; they either smoke it, chew it, or snuff it. The
practical question is. What is the effect of nicotine when administered
in these ways t

195. Is smoking injurious? With very few exceptions the
first smoke nauseates the stomach, irritates the lining of the
windpipes and lungs, and irritates the eyes. Most people can,
with a few trials, get used to tobacco, so that further indul-
gence does not produce these acute effects. Finally, after one
has become used to it, tobacco has a soothing effect on the
nerves, so much so that the habitual user seriously misses his
supply if it is withheld for any length of time.

The effects of tobacco-using on people vary according to
their sensitiveness to nicotine, their general health, and the
kind of work they do. Although cases may be found in which
no apparent harm has been produced by the use of tobacco, a
study of the effects of smoking on large numbers of people
has shown definite results, as (i) impairment of digestion,
(2) chronic irritation of the linings of the nose, larynx, wind-
pipes, and lungs, (3) effects on nerves and disturbance of
heart action, (4) retardation of growth, and (5) sometimes a
disturbance of the eyes.

These effects of smoking need not all appear in one smoker ;
and it is quite possible that these effects are not all due to the
nicotine, of which only a small portion enters the system at
the worst. The smoke contains some of the products of

1 64 ELEMENTARY BIOLOGY

incomplete oxidation, and it is likely that much of the irrita-
tion as well as of the stimulation is due to these rather than
to the nicotine.^

196. Effect on the heart. The evidence on hand may be taken
to show that the habitual smoking of tobacco can lead to an
irregularity of heart action. This may not be dangerous in
itself, but probably makes the heart less reliable in an emer-
gency. This is one of the reasons why athletic coaches do not
permit those who are in training to use tobacco in any form
and in any amount ; when it comes to a critical test, the non-
smoker is more likely to come up to the requirements of the
athletic field.

197. Effect on the nerves. The smoker feels a soothing
effect from his smoking, but after a while this effect wears off
and he needs another smoke to soothe him again. As time
goes on, the interval between smokes is shortened or the
strength of the tobacco, or the size of the cigar, is increased.
We may compare this to what happens in the case of the
alcohol user.

Aside from the effect upon the feelings, the nicotine in
many cases produces a certain imsteadiness in the action of the
nerves. This may show itself in dimmed vision or eyestrain, in
lessened precision of hand work, in weakened attention to the
day's work, or in an increased tendency to absent-mindedness
or day dreaming.

198. Effect on growth. The most marked effects of smok-
ing are produced on grozving boys.

In a large high school in Illinois an investigation was made
for the purpose of finding out whether smoking made any

1 A special objection to cigarette smoking is said fo be the fact that the
slow burning of the paper results in the formation of a substance, called aav-
lein by the chemists, which is highly poisonous. The effects of this are sup-
posed to be cumulative ; that is, " piling up." The carbon monoxid formed
by the slow oxidation of tobacco and paper is also a source of injury, as this
gas, when inhaled, is absorbed by the red corpuscles.

CONTAMINATED AIR

165

real difference to the abilities and development of the boys.
Records were obtained for two hundred and one boys.

Of course it is not to be supposed that the grade-difference
between smokers and non-smokers is due entirely to the fact
of smoking. It is probable that the more scholarly boys do
not take to smoking, so that if those who smoked had never
done so, their marks would probably not be as high as the
highest marks, on the average. Nevertheless the advantages
seem to lean in favor of the non-smokers.

0 5 10 15 20 25 30 35 40 45 50 55 GO

70 75 80 85 90 95 1005^

Fig. 56. Smoking and school standing

The school grades of two hundred and one Illinois high-school boys. The numbers
in parentheses give the number of boys in the group. The forty-five who left school
during the year were habitual smokers. Twenty-four of the boys had learned to smoke
but had given up the practice. The average grade of the ten highest smokers was
78.9 per cent. The average of the ten highest in the school was 90.9 per cent ; none

of these smoked

The physical effects of tobacco on growing men has been
shown from the records of several colleges.

At Yale the physical measurements of entering students
have been taken for many years back. Physical examinations
of students in college were made from time to time. At one
time the givzvth of the students, as indicated by a comparison
of the earlier and later measurements, was studied according
to the tobacco habits. The records were divided into three
groups, representing (i) students who never smoked, (2) those
who smoked irregularly, and (3) those who had been smoking
for a year or more before the second measurements were

1 66 ELEMENTARY BIOLOGY

taken. In every one of the measures of growth the non-
smokers were ahead of the smokers, and the regular smokers
were behind the irregular smokers or beginners.

It is not at all likely that the smaller, lighter, weaker boys
were the ones to take to smoking in larger proportions. The
differences shown by these records must be, at least in large
part, due to the effects of smoking. When the records of
physical growth for the different groups were placed along-
side the records of scholarship, another striking fact was
brought out. This is shown in Fig. 58.

' Weight ^^^^^^^S^.6i«' wJi^ht Im^^^^^^^^^^^^^^^^^^^^^^^Io.^

H Jijht iy:^^i^;^\^^--x^\^^\^;^\»^.^,^>^in'.o^ Height b^^^^^^^^^^^^^^^^^^^^^^^ gloit

Chest I ~-| Chest | — |

Measure ^\?^^\^-^\^,^^V.>V.^\^y.^t^:?-,^ 22.0^ Measure^^^^^^J^^^^j^^;^^^:^^!^^ 26.7;^

Lung I I Lung i 1

Capacity^SMiS^ -^^^ Capacity^ 77:0^

Fig. 57. Relation of smoking to physical growth

The first column shows the average advantage of non-smokers (indicated by white space)

over occasional smokers (indicated by shaded space). The second column shows the

average advantage of non-smokers over regular smokers. These measurements are from

the physical-training department of Yale University

Similar records kept at Amherst College and at Columbia showed
similar differences between smokers and non-smokers.

In some of the investigations the ages of the students in each class
were also compared. It appears that in any given graduating class
the smokers are on the average older than the non-smokers. This prob-
ably indicates the extent to which smoking — possibly in association
with other unhygienic habits — retards a young person in his progress.

Whatever differences of opinion there may be as to the
harmfulness of smoking for adults, there is no difference
of opinion as to its effect on the young. For this reason
the government of Japan some years ago prohibited the sale
of tobacco in any form to minors, and some of our states have
done the same. The United States Military Academy and
the United States Naval Academy forbid the use of tobacco

CONTAMINATED AIR 167

by the students. Many railway companies and other large
employers refuse to take on young men who smoke. In Min-
neapolis one hundred of the leading business men agreed
not to give employment to young men who smoked.

Many officers in the army and navy and probably most of the
railway officials and large employers and business men smoke.
Yet they realize that they can get better service from young
men who do not smoke. It is not a matter of sentiment or
prejudice with them ; it is strictly a matter of business.

199. Economic and so- , , 1—

I 9o Noii-sniokers R^

cial problems. Aside
from the injury that to-
bacco-smoking does to I 10 Non-smokers t>^y^k^i^^-:^()^m^^^^^^"^^^^^^^^^
growing young people, Fig. 58. Smoking and scholarship
tne economic Siae 01 showing the proportion of smokers (shaded space)
the Question is Simplv ^^^ ^^ non-smokers (white space) among the stu-
, , . , dents of highest rank (first bar) and among students
whether, tor the same of ordinary rank (second bar) at Yale University

expenditure of human

effort as is required to raise, ^ cure, handle, manufacture, and
distribute the tobacco and various smokers' appliances, people
could get more fun out of life. Certainly those who enjoy
smoking, numbering into the hundreds of millions, feel that
they are getting their money's worth in this form of enjoy-
ment, and it is impossible to say to them that those of us who
do not smoke are having more pleasure or satisfaction.

The social and aesthetic sides of the question can be seen
more definitely.

1. The smoke of tobacco is distinctly offensive to the non-
smoker. To be sure, we can get used to that, we can learn to
stand it, but in and of itself it is a nuisance.

2. The perspiration of the smoker frequently becomes
modified so that it is distinctly objectionable.

1 Over a million acres of good land are worked in this country every year
for raising tobacco. Over two hundred and twenty-five thousand persons are
engaged in the manufacture and sale of tobacco products, besides the farmers
and the makers of pipes, boxes, labels, and so on.

l68 ELEMENTARY BIOLOGY

3. The breath of the smoker, too, is frequently offensive.

4. The discoloration of the teeth does not add to one's
attractiveness, nor does the discoloration of the fingers of
cigarette smokers.

Perhaps no smoker makes himself offensive on all of these
scores ; but, taken together, these objections to the practice
are just as real and just as serious as questions of cost or
even of health.

There is a real fire risk involved by the wide practice of smoking ;
this can be measured by insurance experts, and can be controlled and
reduced by police and educational measures.

CHAPTER XXXII
FIRST AID AND HYGIENE IN RELATION TO BREATHING

200. Air needed continuously. We can go without eating
for days or even for weeks. Water has to be taken into
the body more frequently. But we cannot go without breath-
ing for more than two or three minutes or, at most, four or
five minutes.

201. Suffocation and drowning. When, for any reason, the
gas exchange in the hning of the air chambers in the lungs
is stopped for several minutes, suffocation takes place, and
death may result. Suffocation may be due to the replacement
of air by some other gas, or it may be due to the exclusion
of air.i The replacement of the air in the lungs by water
is called drozvning.

Suffocation and drowning are commonly fatal, but in very
many cases life may be saved by prompt and persistent action.
It is necessary (i) to empty the lungs of the water or foreign
gas and (2) to reestablish the breathing movements.

When a person has been drowned, the first thing to do is to
place the body, face down, in a position that will cause the water
to pour out of the lungs. A child may be lifted up by the feet.

Breathing movements should be begun at once. In the
Schaefer method of artificial respiration the victim is laid face
down, with the arms stretched forward beyond the head ; the
head is turned to one side and supported on a cloth, to leave the
nostrils and mouth unobstructed. The operator kneels, strad-
dling the subject's thighs and facing his head, and with the

^ Breathing may also be stopped by a severe electric shock, which acts on
a group of nerves "that control the breathing movements. The treatment
should be the same, whatever the cause of the suffocation.

169

170

ELEMENTARY BIOLOGY

thumbs over the small of the back and fingers over the lowest
ribs, alternately compresses and releases the chest by swinging
forward and back, at the rate of from twelve to fifteen times a
minute. The movements should be kept up until natural breath-
ing begins, but should not be given up in less than an hour.

m

^;^^'

^S^teii-

1.^

■ ^^fel

W^

19

3

P^j^^^^^H

«i

M^^

^"^^^yMj^^Jl

yfl ■ -"If ]

m^^^^

g':'""

^^^^^^^F^ 1

Fig. 59. Sylvester method of artificial respiration, — expanding the chest

After drawing out the tongue and placing the patient on the back with a block or roll

under the shoulders, to keep the chest raised and the head thrown back, kneel behind

the head and grasp the arms just below the elbows. Draw the arms slowly backward

over the head, and hold them there about one second

While these movements are being carried out, the victim's
tongue should be pulled out and kept out, to prevent it from
slipping back into the throat and obstructing the windpipe.

The Sylvester method of artificial respiration is shown in
Figs. 59 and 60.

In case of asphyxiation, or suffocation by gases or by electric
shock, the same procedure should be followed, except that it is not
then necessary to take special steps for emptying the lungs of water.

FIRST AID IN RELATION TO BREATHING

71

Under the supervision of the United States Bureau of
Mines squads of miners are instructed in the resuscitation^
of people who become asphyxiated by gases or by electric
shock. This bureau conducted a series of experiments to
determine which of the mechanical resuscitating devices was

Fig. 60. Sylvester method of artificial respiration, — contracting the chest

After the arms have been held above the head about one second, push the elbows slowly for-
ward and downward until they are in the position shown. Press the elbows firmly against
the chest and hold them there about one second, to drive all the air out of the lungs.
(Photographs and instructions, Figs. 59 and 60, from United States Bureau of Mines)

best for various purposes. It was found that more reliance
could be placed on quick action by men who understood how
to establish respiration than on most of the machines, and
it is always safer to begin work by hand than to wait for the
best machine. One of the devices is illustrated in Fig. 6i.

202. Summary on breathing and ventilation. Since we carry
on our breathing without needing to think about it, most
people have given very little attention to the subject of air and

172

ELEMENTARY BIOLOGY

breathing. It is only in comparatively recent times, therefore,
that we have come to realize what a close connection there
is between our breathing habits and breathing conditions, on

IvMiucing- valve

Face !

Head cap
Check v:i!\

Supply tube

Fig. 61. Oxygen inhalator

This apparatus for the resuscitation of persons overcome by suffocating fumes or gases
was developed by the United States Bureau of Mines. It is used with the Schaefer
method of artificial respiration, and supplies oxygen for about thirty-five minutes, which
is usually sufficient to restore normal breathing. (Photograph by United States Bureau

of Mines)

the one hand, and our health, happiness, and efficiency, on the
other. The most important things that have been discovered
by the new attention to these details are the following :

I. Outdoor air is better than indoor air in every way.

a. It is better for playing, even in the cold and rain ; suitable
clothing will make up for these.

HYGIENE IN RELATION TO BREATHING 173

b. It is better for work, since a person can accomplish more

in a given time when breathing outdoor air than when
breathing indoor air.

c. It is better for health, even to sleep out of doors.

2. Nose-breathing is in every way better than mouth-breathing.

a. Where mouth-breathing is due to adenoids, these growths

should be removed.

b. Where mouth-breathing is due to bad habits, these habits

should be corrected.

3. Deep breathing is better than shallow breathing.

a. Where shallow breathing is due to improper clothing, the

clothing should be changed.

b. Where shallow breathing is due to habit, correct habits

should be acquired through exercise, outdoor games,
work, etc.

4. Dust is a source of danger to the health of the body and to

the lungs in particular.

a. Mechanical dust, soot, and smoke (including tobacco smoke)

coat the lining of the air sacs and reduce the breathing
surface.

b. Hard dust may scratch the lining of the air sacs and thus

increase exposure to infection.

c. Dust carrying microbes is a direct source of danger.

d. Chemical dust and fumes may poison the blood.

5. A person suffocated or drowned is not to be given up for dead

before every possible effort to resuscitate him has been made
in vain.

6. Ventilation is necessary not only to keep down the proportion

of CO2 and to keep up the proportion of oxygen in the air,
but also to (a) regulate the moisture, {p) regulate the tem-
perature, (<r) keep the air moving, (d) remove disagreeable
odors, {e) remove gases and fumes, (/") remove dust.

7. Alcohol, by congesting the capillaries, decreases the breathing

efficiency of the lining of the air sacs.

CHAPTER XXXIII
TRANSFER OF MATERIALS IN PLANTS

203. Exchange of materials in living cells. One-celled plants
and animals that move about in the water constantly come into
a new environment, from which they get supplies of water, oxy-
gen, minerals, and food
(or food-making materi-
als). In larger animals
and plants the life of
the cells, or at least
of the innermost ones,
can be maintained only
by means of an internal
transportation system.
This brings to the cells
their supplies of food,
water, oxygen, etc., and
carries from them, to be
removed to the exterior,
their waste products.

204. The conducting
systems of a plant. In
all those plants that have a body which is made up definitely
of root, stem, and leaf the diffusion of water and of dissolved
substances between parts of the body is supplemented by the
transportation of material in mass. We have seen that water
and salts absorbed by the root-hairs diffuse through the cells
of the root cortex and then move bodily through special
vessels (see p. 44). These sap-carrying vessels are of sev-
eral kinds — some long, some short, some consisting of single

174

Fig. 62. Vessels in a plant

Section of squash stem, showing phloem vessels,
/V/, which conduct food down from the leaves, and
two kinds of wood vessels, IV, which conduct water
and salts up from the roots. The two kinds of
wood vessels are those with spiral thickenings in
the walls and those with pitted walls

TRANSFER OF MATERIALS IN PLANTS

175

Medullary

cells, some consisting of series of cells from which the end
walls have disappeared, leaving long, continuous channels.
Some of these vessels are illustrated in Figs. 10 and 62.

The sap-carrying ves-
sels of the root are
continuous with similar
tubes found in the stem.
The tubes are found
arranged side by side in
bundles rather than in
single strands (Fig. 62).
The bundles of vessels
and fibers, in many
plants, are easily sepa-
rated from surrounding
cells, or pulled out. In
celery these bundles
make up the ''strings,"
and when you pull up a
leaf of the plantain, you
can see the so-called
nerves that stick out of
the broken end of the
leafstalk, which are also
fibrovascular bundles.

In woody plants the
fibrovascular strands are

Cam hi mil

Fig. 63. Structure of a woody stem

Diagrammatic view of piece of two-year-old black-
berry stem, showing the central /if/i, surrounded by
the 7vood of the first and second years, the dark, and
the epidermis E, The wood is made up of wood
fibers, Wf^ and vessels, Pd, representing a pitted
duct. Between the wood and the bark is the grow-
ing, or cambium, layer, and this is connected with
deeper layers by means of the Medjdlary rays, Mr.
Under the skin are some green cells, Gc, and running
through the bark cells C are bast fibers, Bf, as well
as bast vessels, which are not shown

compacted into solid

cylinders ; these make up the successive layers of wood (F'ig.63).

The fibrovascular bundles branch and divide so that they
reach into all the twigs and leaves. In the leaf they branch
again and constitute the so-called veins, or nerves, of the
leaf blade (Fig. 64).

The food sap does not pass through the same tubes as
the water and salts from the roots. The manufactured food

176

ELEMENTARY BIOLOGY

probably goes from the leaves by way of another set of vessels
called phloem, or bast. These vessels are generally larger in
diameter than the wood vessels (xylem) and are characterized
by having pores in the end walls. These end walls, with their
perforations, are sometimes called sieve plates (Fig. 65). The

toughened fibers associated with
the bast vessels make up the

bast fibers. ,

•

In the leaves the bast and the xylem
vessels are closely compacted in the
veins. In wood we have masses of
xylem vessels and fibers. Bast fibers
are commonly used in the form of
linen, hemp, and jute fibers. In woody
plants the bast is located in the bark.

205. The ascent of sap in trees.

Investigators have long been puzzled
by this. problem, and we are not yet
sure that we understand it. How-
ever, it is certain that the water
does rise, and that it goes through
the xylem vessels.
From certain common observations
and from the results of experiments we may reasonably infer
that sap descends. We know that organic food is formed in
the leaves, and that it is accumulated in the roots and in
underground stems of many plants. There must therefore
be a current of material passing downward from the leaves.

A tree that is girdled, that is, one that has a ring of bark
removed, will continue to live for the rest of the season. This
shows that the removal of the bark does not interfere with the
ascent of water and salts from the roots to the leaves. The
following spring, h()wever, when the opening of the buds with
the rapid expansion of leaves and twigs depends upon the food
accumulated during the previous season, the tree will be found

Fig. 64. Veins of a leaf

Leaf of apple of Sodom {Solanitm
aculeatissimiitn) ^ of the potato fam-
ily, showing network of veins

206. The descent of sap.

TRANSFER OF MATERIALS IN PLANTS

177

dead. Although water and salts may still be able to reach the
upper parts of the plant (since the channels that served during
the previous season are still open), the food that should have
been accumulated during the previous summer is lacking.

y

ii.ij

':■ ■':;.;

! 1 i

Sieve

plate ,

vessel

Fig. 65. Bark fibers and vessel

y1, a section cut lengthwise, and B,
one cut crosswise, showing bast fibers,
sieve-plate vessel, and the so-called
companion cells found next to the
sieve-plate cells

Fig. 66. Ascent and descent of sap

The arrows in the diagram are to show
that materials absorbed by the roots travel
upward through vessels located in the
wood part of the stem, and that ma-
terials resulting from the food-making
processes in the leaves travel downward
through vessels located in the bark.
When a complete ring of bark is removed
from a tree, the plant may live on to the
end of the summer ; but the buds will not
open the following spring, since they de-
pend upon food accumulated in the roots

207. Circulation of sap. In

plants there is no circulation
of materials such as we find in
the higher classes of animals.
There is, it is true, a move-
ment of liquid from the root

to the leaves, and from the leaves to the roots ; but the matter
conducted along the two sets of vessels is not the same either
in amount or in kind.

The water that moves from the roots to the leaves is
several times as great in quantity as the liquid that moves

178 ELEMENTARY BIOLOGY

from the leaves to the roots, since by far the largest portion
of it is transpired and never comes back.

The ascending current is for the most part inorganic in its
composition ; the descending current is in large part organic.

The two currents are nowhere continuous. They are prac-
tically independent of each other, except, of course, that the
life of the plant can continue normally only when both cur-
rents are maintained ; yet one may go on for a considerable
time without the other being in action.

CHAPTER XXXIV
THE BLOOD

208. 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 commonly called blood,
although not all kinds of blood are alike. In the clams the
blood contains a bluish substance, called hemocyanifi, which
easily combines with oxygen, and thus carries oxygen obtained
from the surrounding water by diffusion into the capillaries of
the skin and gills. In the earthworm there is a reddish sub-
stance, called hemoglobin, dissolved in the blood, which be-
haves in much the same way as the hemocyanin of the clams.

The blood of back-boned animals has a rather complex
structure, and is associated with an elaborate system of vessels
and a pumping organ called the heart.

209. Composition of human blood. When examined with
the microscope, human blood is seen to consist of a colorless
liquid, called the plasma, and a number of small bodies float-
ing in it. The more numerous particles are the so-called red
corptLscles. These are very small ^ and have the shape of a
disc or coin, with rounded edges and compressed towards the
middle (Fig. G'j). In addition to the red corpuscles, there are
also white, or colorless, corpuscles, some barely larger than the
red ones, others many times as large.

The fluid portion of the blood, the plasma, consists chiefly
of water. In this are dissolved various salts, organic substances
derived from the digested food, some oxygen, some carbon
dioxid, certain ferments, and other organic substances derived

1 On the average, about of an inch in diameter.

3200

179

i8o

ELEMENTARY BIOLOGY

^

from various organs and tissues of the body. It is not to be
supposed that any given drop of blood will contain all of these
substances, or all of them in the same proportions, for, as we
shall see, the composition of the blood is constantly under-
going changes in the smallest blood vessels, through the
walls of which new substances are coming in and others are
passing out.

210. The lymph. The blood, consisting of plasma and cor-
puscles, fills a set of tubes from which there are no openings ;
the system is therefore called a closed blood system, to distin-
guish it from the blood
system of clams and
certain other animals,
in which many of the
blood tubes have open
ends connecting with
various spaces in the
body. Outside of the
blood vessels in the hu-
man body, filling defi-
nite tracts as well as
spaces between tissue masses and cells, is a colorless liquid,
called lymph. It is from the lymph that the cells obtain their
food supplies, water, salts, ferments, and oxygen ; and it is to
the lymph that they discharge their carbon dioxid, urea, and
other wastes. The communication between the lymph and the
blood is by osmosis through the walls of the smallest blood
vessels (Fig. 68), and through definite connections between
lymph tubes and certain large blood vessels.

The lymph, like the plasma, consists chiefly of water, and
carries practically the same kinds of substances in solution.
In addition, the lymph has floating in it many white corpus-
cles, so that it may be compared to blood lacking the red
corpuscles. The lymph has been compared to the ocean, in
which life probably originated, and from which so many

Fig. 67. Human blood corpuscles

a, fresh leucocytes (white corpuscles) in resting and

in moving stage (note granulations and nuclei) ; b, red

corpuscles in flat and in side view

THE BLOOD

l8l

Co,

Water

Sugar etc.
BLOOD

Protein etc.

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.

211. Clotting of blood. When some blood is removed from
the blood vessels, whether it is taken out of the body or not,
it usually becomes clotted, or thickened. This clotting is
brought about by the coagulation, or solidifying, of a certain
protein in the blood known as fibrinogen, which means
" fibrin-maker." The ferment that causes the coagulation
becomes active when the lining of a blood vessel is injured ;
or it may be that the

ferment is formed . l y m I' h

only at such times.
At the mouth of a

small cut this clot oxygen Protein etc. Salts

soon stops the bleed-
ing, and furnishes
a protective covering
until the wound is
healed.

212. Serum. If
blood is allowed to
clot in a glass vessel, we can see the mass of fibers detach
themselves from the walls of the vessel, after the threads have
shrunk awhile, and the clot floats at last in a clear liquid that
is almost colorless or slightly yellowish. This clear liquid is
called a serum and is practically the same as the blood
plasma, but lacking the fibrinogen. Whatever is characteristic
or distinctive of the plasma of an individual or of a species
will be found in the serum.

213. The white corpuscles. On closer study the white cor-
puscles are seen to be cells. In many ways they are like the
ameba (see p. 24). They consist of naked protoplasm, have
no definite shape, are capable of free movement, are sensitive
to chemical and other changes in their surroundings, and are

Fig. 68.

LYMPH

What goes through the wall of a capillary

From the blood within the capillary, water, salts, food,
and oxygen pass out by osmosis ; from the surrounding
lymph, carbon dioxid, urea, and water pass into the blood.
White corpuscles work their way through the wall of the
capillary, between the cells

1 82 ELEMENTARY BIOLOGY

capable of eating small particles by swallowing them into the
protoplasm of which they consist, just like the ameba and other
one-celled animals.

These ameba-like corpuscles are found in the blood not only
of mammals but of all animals that have blood ; and they are
very much alike in all, so far as general appearance and be-
havior are concerned. Their function has come to be under-
stood only in modern times, chiefly through the works of the
Russian biologist Elie Metchnikoff, the late director of the
Pasteur Institute in Paris.

To help us understand the functions of these cells it is
well to recall that whereas the one cell of the ameba carries
on all the functions of a living body, the various cells of a
many-celled animal like a butterfly or a baby are differentiated
in regard to function as well as in regard to structure. Now,
the white corpuscles are in many ways the least differentiated
cells in the body. They are the ones that have the general
qualities of protoplasm in the greatest degree ; they have not
become specialists in any one line. They can move, like
muscle cells, but not so quickly or so vigorously. They are irri-
table, like nerve cells, but in a slighter degree. They are
chemical laboratories, like gland cells, but do not produce
specialized juices. They are digesting cells, and so on.

With this view of the white corpuscles as undifferentiated,
wandering cells we may try to understand just what they do
in the body.

1 . As eating-cells (called by Metchnikoff phagocytes, which
means *' eating-cells ") they are capable of engulfing foreign
particles with which they may come in contact. In this manner
they may eat and digest dead particles resulting from the break-
ing down of tissue cells, and live cells introduced from without
— that is, bacteria that may get into the body in various ways.

2. As sensitive or irritable cells they may respond to a
chemical stimulation by producing substances that neutralize
or counteract foreign chemicals, as various kinds of poisons.

THE BLOOD 1 83

3. As moving cells they wander about from the lymph to
the blood, or vice versa, and even into the intestines, carrying
with them dead matter to be eliminated, or crowding in large
numbers and producing some special substances that counteract
a local chemical disturbance.

Because of this peculiar behavior we have come to think
of these corpuscles as perhaps the most important agents in
keeping the body in health, at least in relation to certain
special diseases.

White corpuscles probably originate by the division of ameboid
cells in the bone-marrow and in particular portions of the lymphatic
system, enlarged lymph spaces containing crowds of the white
corpuscles.

214. The red corpuscles. The blood of vertebrate animals
contains red corpuscles in addition to the white ones. In all
except the mammals the red corpuscle has a nucleus in the
center, which makes the disc somewhat thicker in the middle,
and its shape is elliptical rather than circular.^ The largest
red corpuscles are found in the amphibia ; and even with the
lower power of the microscope we may easily see the elliptical
discs in the flowing blood of a frog's web or a tadpole's tail.

The distinctive thing about the red corpuscle is the fact that
it contains a substance known as hemoglobin, which readily
combines with oxygen or with carbon dioxid, according to the
chemical conditions to which it is exposed. The red corpuscle
thus acts as a gas-carrier in the blood.

Recent experiments made in this country show that there is a
special ferment in back-boned animals which causes the hemoglobin
to combine with oxygen in the lungs (or gills), and that there is
another ferment which causes the oxygen-hemoglobin combination to
break up in all parts of the body.

^ Among the mammals, the camel is exceptional in having elliptical blood
corpuscles. Among the fishes, the perch and a few others have circular
corpuscles.

1 84 ELEMENTARY BIOLOGY

The red corpuscles, like the white ones, are really unattached cells.
They originate by successive cell divisions of special cells found in
the marrow of bones. At first they have a nucleus; but this soon
disappears. Lacking a nucleus, these cells cannot remain alive very
long. It has been found that the older corpuscles disintegrate, and
their hemoglobin is taken up by the liver and converted into bile.^

1 In its chemical composition hemoglobin is somewhat like the chlorophyl
of plants. To form either of these pigments, protoplasm must have iron.
Iron given as a medicine or tonic is administered to assist in the formation of
hemoglobin and red corpuscles. A deficiency in the red corpuscles results in
the general weakness and paleness that are characteristic of the condition of
the body known as anemia.

CHAPTER XXXV
•
THE CIRCULATION OF THE BLOOD

215. The vessels. In all backboned animals the blood is
entirely inclosed within a set of tubes, so that everything enters
or leaves the blood only by passing through the walls of these
tubes (see p. i8o).

The tubes or vessels reach all parts of the body, so that if we could
somehow remove all of a person except the blood vessels, we should
have a pretty good imitation of the whole body.

There is a special muscular enlargement of the blood vessels
known as the heart. Through the contractions of this organ
the fluid is kept in constant and continuous motion — not in
a back-and-forth motion, as the ancients believed.

The vessels in which the blood flows from the heart are
called arteries ; those in which the blood returns to the heart
are called vei^ts.

The main arteries and veins run in parallel courses and
branch and subdivide until the smallest tubes are too small to
be seen without a microscope. The smallest branches of the
arteries connect with the smallest branches of the veins, so
that the blood that has been moving into smaller and smaller
vessels presently begins to flow into larger and larger ones
These smallest tubes, connecting the arteries with the veins'
are called capillaries. '

The walls of the capillaries are so thin that diffusion is constantly
takmg place through them ; and the white corpuscles work their way
through them, passing between the cells (Fig 68). All the changes
in the composition of the blood take place while the blood is in caoil-
laries m various parts of the body.

i8s

1 86

ELEMENTARY BIOLOGY

216. The heart. In birds and mammals the heart is a double
muscular organ, the right and left halves being quite distinct
from each other, in the sense that blood cannot pass directly
from one side to the other. Each half of the heart consists
of an upper receiving chamber and a lower pumping chamber.
The left heart is somewhat larger and stronger than the right
heart. Its ventricle, or pumping chamber, closes up, or contracts,

at fairly regular intervals,
forcing the contained blood
into the largest artery of
the body (the aorta), by
the branches of which it is
carried on to the various
organs and tissues.

The auricle, or receiv-
ing chamber, of the left
heart is connected with
a large vein that brings
blood gathered from the
capillaries of the lungs.

The receiving chamber
opens directly into the left
ventricle, by means of an
opening which is guarded
by a set of flaps that pre-
vent the blood from flowing
back when the pumping
chamber contracts. Another set of valves prevents the blood in
the aorta from flowing back into the ventricle when the latter
expands again. The left heart thus pumps blood received from
the capillaries of the lungs to arteries all over the body.

The right heart receives blood from two large veins con-
nected with its auricle, or receiving chamber (Fig. 69), and
passes it into the ventricle, or pumping chamber. The auricle
and ventricle on the right side are also connected with each

Fig. 69. Diagram of the human heart

aa, receiving chambers, or auricles ; bb^ pumping
chambers, or ventricles ; cc^ main veins, bringing
blood to the heart ; dd^ main arteries, carrying
blood away from the heart; ff^ valves, prevent-
ing back-flow from arteries to ventricles; be-
tween a and b^ valves preventing back-flow from
ventricles to auricles

THE CIRCULATION OF THE BLOOD

187

other, like the corresponding chambers on the left side, and

there is a valve preventing the back-flow of blood from the

ventricle to the auricle. The

right ventricle pumps blood into

a large artery that carries blood

toward the capillaries of the

lungs {pulmonary artery).

217. The double circulation.
The blood stream may be
traced from any point back
again to the start only by pass-
ing through the two sides of
the heart and through the pul-
monary, or lung, circulation and
the general body, or systemic,
circulation. Thus, beginning,
for example, in the capillaries
of the hand, the blood flows
into the veins and is gathered
into larger and larger vessels,
reaching the right auricle ; from
this it goes to the right ven-
tricle, and when the latter con-
tracts, it is forced into the
pulmonary artery, which di-
vides into smaller and smaller
branches, the smallest being
the capillaries that lie under
the lining of the air sacs of the
lungs. As the blood flows on,
it is gathered into larger veins
that unite to form the pulmo-
nary vein, which empties into the left auricle. From the left
auricle the blood goes to the left ventricle, and from this it
is pumped into the aorta. An artery branching from the main

Fig. 70.

The double circulation of
the blood

The arrows indicate the direction of blood
flow. The shaded portion represents blood
lacking in oxygen. From the right heart
(shaded) the blood passes to the lungs,
from which it returns to the receiving
chamber of the left heart with its carbon
dioxid replaced by oxygen. From the
pumping chamber of the left heart the
blood passes to all parts of the system,
or body, and returns to the receiving
chamber of the right heart with its oxygen
replaced by carbon dioxid

1 88 ELEMENTARY BIOLOGY

artery carries blood into the arm, and as the arteries divide,
becoming smaller and smaller, we at last reach the capillaries
in the hand, from which we started (Fig. 70).

The double circulation makes it possible for the carbon dioxid
in the body to be completely exchanged for oxygen in a com-
paratively short time. In the human body all of the blood
passes through the heart (and therefore through the capillaries
of the lungs) once in from twenty-three to thirty seconds.

The exchange of gases in the air sacs of the lungs has
already been described (see p. 148).

218. Changes in the blood. When in the capillaries of the
various tissues of the body, the blood absorbs from the surround-
ing lymph (by osmosis) carbon dioxid, urea, and other sub-
stances that are present in relatively large proportions (that is,
compared to their concentration in the blood plasma) ; and it
loses by the same process food materials, salts, oxygen, and
ferments that are relatively more abundant in the blood than
in the surrounding liquids.

In certain parts of the body additional changes take place
in the composition of the blood. In the intestines, for example,
much of the digested food is absorbed into the blood. In the
kidneys much of the urea, salts, and other waste substances
are taken from the blood.

219. Ferments in the blood. In the capillaries of certain organs
the blood receives, in addition to the usual waste products, various
special ferments, or chemical substances. For example, from the
thyroid gland, which is a Y-shaped, spongy body lying in front of the
larynx, the blood absorbs a substance that has an important influence
on the development and working of the brain.

From the pancreas the blood absorbs a substance that has an
important influence on the oxidation of carbohydrates in the cells.

From little capsules that lie just above the kidneys the blood
absorbs a ferment that influences the muscles of the blood vessels,
and also has some effect on the nervous system. The amount of this
secretion is increased whenever strong feelings are aroused, such as
fear or anger. An increase in the amount in the blood acts upon

THE CIRCULATION OF THE BLOOD 189

the liver, increasing the output of glycogen into the blood, and it
interferes with the secretions and contractions of the stomach. The
adrenin, as this substance is called, also hastens the clotting of blood.

In young mammals there is a soft organ lying in the front part of
the chest, the thymus, the ferments from which have an important
influence on the growth of the animal. Another ferment that affects
the growth is absorbed by the blood from a little body lying at the
base of the brain.

These various ferments are sometimes called internal secretions,
because they are absorbed from inside the organ, instead of coming
out of the gland through special ducts, as is the case with ordinary
glands.

CHAPTER XXXVI
HYGIENE OF THE CIRCULATORY SYSTEM

220. Care of the heart. Every contraction of the ventricles
(the two ventricles work together) sends a wave of pressure
through the blood in the arteries. The muscular and elastic
walls of the arteries '' give " somewhat to this pressure, and
this is the pidse which can be felt in any artery near the sur-
face of the body, as at the wrist, on the temples, or immedi-
ately in front of the ear. From the character of the pulse tlie
physician can often tell a great deal about the workings of
the heart and about the condition of the blood vessels. The
pulse may be regular or irregular ; it may be strong or weak.

A strong heartbeat would ordinarily increase the pressure
of the blood inside the arteries ; but if the arteries are flabby,
the additional work of the heart may fail to distribute the
blood properly to all parts of the body. Cold feet and hands
are an indication of inadequate circulation, but the cause of this
condition may be in the heart or it may be in the blood vessels.

In examining a person the careful physician, athletic direc-
tor, or insurance examiner will always listen to the beating of
the heart and examine the pulse and test the blood pressure.
From the sounds of the heart he can tell whether there is a
defect in any of the valves. A leaky heart has to do a great
deal more pumping to keep the body supplied than a sound
heart, since a portion of every stroke is wasted in pumping
blood that goes back into the auricles.

A weak heart usually shows itself in breathlessness. If you
cannot climb stairs, or take a brisk walk, or play a lively
game, without getting out of breath, the trouble is more likely
with your heart than with your lungs. In training for athletics

190

HYGIENE OF THE CIRCULATORY SYSTEM 191

one of the most important things is to acquire "wind"; that
is, the abihty to continue severe exertions without losing
breath. This is in fact a training, of the heart, as well as
a training in correct breathing habits. Under suitable direc-
tions one can strengthen his heart considerably by means of
graded exercises in walking, running, climbing, etc. Indeed,

Fig. 71. Treating a cut

When the pressure of the thumb is not sufficient to compress the blood vessels and
stop the flow, a tourniquet may be used, made by tying a handkerchief about the limb
and twisting it tight by means of a stick slipped under the handkerchief. Of course,
the tourniquet or the bandage applied in this way is to be considered an emergency
measure, and steps should be taken to have the wound attended to by a physician

one of the dangers of the athletic enthusiasm is that a student
will overdevelop his heart. But occasional severe strain upon
the heart is not the same as training it for hard work, and a
person with a weak heart should not be engaged in work that
strains this organ severely.

221. Cuts and wounds. Small wounds will usually stop
bleeding in a short time because of the clotting of the blood
(p. 181). In view of our modern knowledge about the wide

192 ELEMENTARY BIOLOGY

distribution of many kinds of bacteria, however, it is wise to
look after even small cuts and scratches.

The festering of sores and cuts, which was formerly looked
upon as a normal and necessary condition of healing, we now
know to be the result of the action of various kinds of
microbes, some of which, at least, produce serious blood
poisons (see p. 195). To prevent the festering of a sore, and
to prevent the invasion of the body by more injurious micro-
organisms, it is well to treat every cut with an antiseptic, or
sterilizing, solution, such as a solution of carbolic acid or
bichlorid of mercury, or with tincture of iodin or alcohol.
The cut should then be covered with clean cotton or gauze,
to prevent the entry of microbes later.

With larger wounds it is sometimes necessary to use
special means to stop the bleeding. When the flow of blood is
too strong, the adhesion of the clot to the sides of the wound
may be prevented. When the flow is from an artery (which
may usually be recognized by the pulsation), the limb should
be tied above the cut ; that is, on the side tozvard the heart.
When the flow is from a vein, the attempt to stop the flow
should be made on the side away from the heart.

222. Nose bleeding. In very many cases nose bleeding may
be stopped by snuffing cold water. The old-fashioned remedy
of dropping a key down the person's back rested on the fact
that the chill causes the capillaries to contract. A piece of ice
applied for a few moments to the back of the neck will be
more likely to have the desired effect. Where bleeding con-
tinues after such a simple treatment, it is probable that some
small artery has been broken, or that the person's blood is
incapable of clotting. An astringent is then advisable. Powdered
alum, tannin, or ferric chlorid may be applied on a tuft of cotton.
These substances cause the fine blood vessels to contract and
thus stop the bleeding. In extreme cases a physician will use
adrenin, an extract of the capsules lying above the kidneys
(see p. 189).

CHAPTER XXXVII
THE BLOOD AS A LIVING TISSUE

The white corpuscles respond to the stimulation of foreign
substances in several distinct ways. Some of these are signifi-
cant in fighting diseases ; others have been used in different
ways ; still others we can neither understand nor utilize in
any practical way.

223. Precipitins. When the white of an egg is taken into
the stomach of a backboned animal, it may be digested and
eventually absorbed into the blood or lymph, and from this to
the cells, where it acts as a food. But if some white of egg is
injected into the blood (of a rabbit,- for example), it will have a
curious effect upon that blood. After a few such injections
the blood contains a substance that is not present in normal
rabbit blood. This new substance, which cannot be detected
by chemical methods, can be shown to be present if a drop or
two of the serum (see p. i8i) of the treated rabbit is mixed
with a drop of water containing some white of egg. Imme-
diately there will be a visible precipitate. The substance that
is present in this serum, causing the precipitation of the egg
albumen, is called a precipitin, or precipitating substance.

The formation of the precipitin by living cells is not at all under-
stood. An important fact about the precipitin is that it is always
specific. That is to say, a precipitin formed in an animal under the
influence of white of ^gg will precipitate only white of egg, but will
have no effect on other proteins ; a precipitin produced under the
influence of a protein taken from a goat will precipitate only this
goat protein ; and so on.

The fact of precipitin formation has been put into practical use
in several ways.

193

194 ELEMENTARY BIOLOGY

I. The proteins of different species of animals may be very much
alike, so far as the tests of the chemical laboratory show, but the
living protoplasm can detect specific differences. Because of the
formation of precipitins it becomes possible to determine whether a
given drop of blood, for example, is of human origin or from some
other animal. This is often important in legal trials.

1890 1 110 Deaths for every 100.000 of population || 38.0^ of cases]

1895 I 106 In this year antitoxin was introduced | I 18. 8 1

1900 1 62 I niiil

1905

36 1

1910

37 1

1911

1

1912

22 1

1913

1

1914

1

1915

24 1

1916

18 1

1917

21 1

Fig. 72. Reduction in deaths from diphtheria in New York City (Manhattan

and Bronx)

The numbers and rectangles on the left show the number of deaths out of every hun-
dred thousand of the population. The numbers on the right show how many fatalities
there were for every hundred cases of the disease. Note the rapid falling off in both the
proportion and the number of deaths after the year 1895, when antitoxin was first used

2. In the examination of food products that contain materials from
various sources, it is impossible to determine, by the usual chemical
methods, from what organisms the materials were obtained. By means
of the precipitin tests, however, it is possible to find out whether a
given sausage, for example, contains pork or beef or horse meat.

3. Experiments now under way in laboratories and hospitals make
it appear probable that this principle will have wide application in the
diagnosis of disease.

224. Antitoxins. In the bodies of various plants and animals
are found proteins that act in a peculiar way upon the blood
of higher animals. They act as poisons that stimulate the
living cells, and especially the white blood cells, to produce

THE BEOOD AS A LIVING TISSUE

195

First
Day

0
Deaths

Second
Day

43
Deaths

Third
Day

112
Deaths

Fourth
Day

159
Deaths

Fifth
Day

or later

Deaths

specific neutralizing or counteracting substances. This class of
poisons is now known by the name toxifts (from a Greek v*^ord
meaning " poison ") and is illustrated by the venom of the
rattlesnake and of some other snakes, by a certain protein
found in the seeds of the castor-oil plant, and by one found
in the bark of the black locust. The substance produced by
the live cells under the influence of a toxin is called an anti-
toxin, and it is always specific ; that is, it will neutralize the
poison under whose stimulation it was produced, but no other.

The best-known toxins
are those produced by cer-
tain bacteria, especially
those that cause lockjaw
and diphtheria. When
a quantity of toxin, not
enough to kill, is injected
into the blood of an ani-
mal (for example, a horse),
the cells begin to throw
off antitoxin. They will
produce more than enough
antitoxin to neutralize the
poison received. After

the poison has all been destroyed, there will be a quantity of
antitoxin in the blood. If now a larger quantity of the poison
is introduced, some of it will be at once neutralized by the free
antitoxin ; and if the animal is in good health, an additional
quantity of antitoxin will be produced. In this way it is pos-
sible to increase the amount of antitoxin in the blood until
there is several hundred times as much as would be necessary
to neutralize very many fatal doses of the poison.

In preparing antitoxin for diphtheria this is practically the method
followed. In two or three months the blood of the horse contains a
large amount of antitoxin. Blood is drawn from a vein in the neck
and is allowed to clot. The serum now contains all the antitoxin.

Fig. 73. Danger in delay

Each rectangle represents one thousand children
suffering from diphtheria. Antitoxin was admin-
istered to all the children on the days indicated.
The number of deaths in a group increases with
each day's delay in the use of antitoxin

196 ELEMENTARY BIOLOGY

The use of the antitoxin is coming to be quite general in
the treatment of diphtheria, and in the prevention of diphtheria
in the case of people who have been exposed to infection. The
efficacy of the treatment depends upon its being introduced
early enough to neutralize the poison given off by the bacteria
before these have gained any headway in the body of the
patient.^

Antitoxin serums have been prepared for tetanus (lockjaw),
for snake bite, for scorpion sting, and for castor-bean poisoning.

225. Agglutinins. In the case of typhoid fever it was found that
if a few drops of the serum from a patient are mixed with a few drops
of liquid containing typhoid bacteria, the bacteria are all clumped
together in masses, instead of floating about separately. This illus-
trates the formation in the blood of a substance that acts upon bacteria
by aggliitmating them, or sticking them together. Such substances
are called agglutinins, and, like precipitins and antitoxins, they are
specific. Although the agglutinins do not kill the bacteria, they
probably interfere in some way with their action (see Fig. 74).^

226. Cytolysins. When the blood of a human being or
other backboned animal is examined under the microscope,
the red corpuscles and the various white corpuscles are seen to
float or move about apparently unaffected by one another.
But if some blood of a different species of animal is injected
into the veins of a rabbit or mouse, the foreign red corpuscles

1 The gain that has come through the discovery of the principle of anti-
toxin formation, and through its appHcation, can be measured in terms of
reduced loss of life. This may be measured in two ways :

1. Out of all the population, what is the reduction in the proportion of those
that died of diphtheria ?

2. Out of all the people who get the disease, what is the reduction in the
proportion of those that die ?

Both of these sets of facts are given in the diagrams on pages 194 and 195.

That it is always safest to use antitoxin as early in the history of a case as
possible is shown by facts like those given in the diagram (Fig. 73) based on
hospital records.

2 After a mass of typhoid bacteria has been agglutinated by a serum it is
still possible to get the same bacteria to multiply in a suitable medium.

THE BLOOD AS A LIVING TISSUE

197

are presently destroyed, being dissolved by a specific substance
that is capable of dissolving these foreign cells. This cell-
dissolving substance is not constaittly preseiit in the blood, but
is formed after the foreign cells are introduced. These cytoly-
sins, or ''cell dissolvers," are formed not only in response to
the foreign red corpuscles ; they may be
formed in the presence of other kinds
of cells, as of different tissues or of
various bacteria ; and they are always
specific. Thus, the serum of a rabbit
that has been treated with human blood
will dissolve the red corpuscles of human
blood when the two are mixed in a glass,
but not the corpuscles of any other ani-
mal. The serum of a person whose blood
has been treated with dead typhoid bac-
teria will dissolve typhoid bacteria when
the two are mixed in a glass, but not
other species of bacteria.

These facts are utilized practically in
vaccination against typhoid fever, and no
doubt other diseases will be found sus-
ceptible to the treatment. A measured
quantity of dead typhoid germs is injected
into the body. The specific cytolysin is

formed by the action of the live cells. Later, when live
typhoid germs get into the body, they are dissolved by the
cytolysin already present.

Recently a specific cytolysin active against the cells that cause
cerebrospinal meningitis has been produced experimentally in monkeys
by Dr. Simon Flexner of New York, and the serum of these animals
may be successfully used in treating the disease in human beings.

\

Fig. 74. Agglutination
of typhoid bacilli

n, bacilli swimming about
separately; b, the same
clumped together, or ag-
glutinated. The Widal test
for typhoid fever consists
in mixing a few drops of
serum from the suspected
person with a quantity of
typhoid bacteria under the
microscope. If agglutina-
tion takes place, the person
is known to be infected
with typhoid germs

The cytolysis test may also be used like the precipitin test
in the differentiation of blood stains etc. (see p. 194).

198 ELEMENTARY BIOLOGY

227. Opsonins. Although the white corpuscles (or rather
certain kinds of them, for there are really several kinds of
colorless corpuscles in our blood) will " eat " foreign particles,
including many kinds of bacteria, they will do this only under
certain chemical conditions. A substance which thus makes the
bacteria ''attractive" to the corpuscles is called an opsoftin^
which comes from a Greek word meaning " to prepare a meal."
The activity of the cell-eating corpuscles depends upon the
presence of a suitable quantity of the right kind of opsonin.
The production of opsonins may be stimulated by the introduc-
tion of* small quantities of dead or living bacteria of various
kinds.

228. Vaccines and vaccination. We have seen that the
blood meets the invasion of foreign bodies or foreign substances
in several different ways, all of them depending upon the vital
properties of the cells of the body, and especially of the white
corpuscles. In recent years various methods for increasing the
resistance of the body to specific diseases have been developed
by using in some cases one of the blood's reactions, in other
cases another. All of these are roughly classed as vaccination.

In some kinds of vaccination cytolysins are produced ; in
other kinds, opsonins or antitoxins.

229. Immunity and susceptibility. Individuals differ so
greatly that some are much more sensitive or much less sensitive
to certain substances than others. Now we find that sometimes,
or in some people, the blood is extremely sensitive to foreign
substances of a particular kind. It is a matter of common observa-
tion that some people catch colds more easily than others ; some
more frequently have boils or pimples ; some are more suscep-
tible to typhoid or to diphtheria.

Not only do individuals differ one from another ; there are
also racial differences. Thus, the dark-skinned races are less
susceptible to malaria and to hookworm than the white races ;
on the other hand, the white races are less susceptible to
tuberculosis and measles than the dark races.

THE BLOOD AS A LIVING TISSUE 199

More than this, there are important specific differences.
Just as hens are quite indifferent to the action of morphin,
and as rabbits are insensitive to atropin, human beings are
quite immune to diseases that are serious or even fatal to
birds or cattle. Such immunity is called natural immunity ^
and is inherited. In many cases it probably depends upon the
chemical peculiarity of the blood or the body juices ; in others
it depends upon the quick response of the live cells to the
poisons and other products of the bacteria. But such natural
immunity is not absolute ; that is to say, it may be weakened
or destroyed by various conditions.

We may see from these considerations how important it is
to guard the natural immunity of the body against the destruc-
tive effects of undue exposure to extremes of temperature, to
excessive fatigue (or insufficient rest ^nd sleep) or overwork,
and to prolonged hunger or thirst (or improper nutrition). We
can also understand the importance of suitable conditions and
habits of ventilation and of exercise in maintaining the resist-
ance of the body, and the danger of using drugs, alcohol, or
other substances that interfere with the action of the blood as
a living tissue.

Not only the conditions that commonly affect the energy
and resistance of the protoplasm, but disease itself may affect
the resistance of the body. After pneumonia, for example,
one is more liable to catch other diseases than he is ordinarily,
and he is more liable to catch pneumonia after typhoid or
measles than he is ordinarily. One cannot afford to be sick
even a little ; that opens the way for more serious trouble.

230. Acquired immunity. It is a well-known fact that one
who recovers from certain diseases is practically immune ; as
the common saying goes, "You can't have measles twice."
This is true of mumps, whooping cough, scarlet fever, typhoid
fever, and smallpox. This acquired immunity is no doubt
due to the substances produced in the blood in the course of
the disease. In the case of diphtheria and of some other

200 , ELEMENTARY BIOLOGY

diseases, the antitoxin that is formed gradually disappears, so
that after some time it is possible for the recovered patient to
have the disease again.

Immunity may also be acquired, as we have seen (pp. 196,
197), by artificial means. A passive immunity, lasting a com-
paratively short time, is acquired by the administration of an
antitoxin. This is called passive because the blood does
nothing to combat the disease ; it is simply protected by the
substance added to it. An active immunity may be acquired
by the use of a vaccine, which stimulates the live cells to
produce the substances that cause the immunity.

231. Disease and heredity. We know that certain diseases
have a way of "running in families." That is, a given family
may show many members that have suffered from the same
disease, as tuberculosis. It was commonly believed until recent
times that tuberculosis and other diseases are inherited, in the
same sense as the color of the eyes or the shape of the thumb
is inherited. We know that this is not true. Where tuberculosis
runs in a family, two facts are to be distinguished :

1. Where one member of a family has the disease, the
other members are more likely to be exposed to infection
than they would be ordinarily, and so the disease spreads in
that family.

2. Where a person has tuberculosis (or any other disease),
the indications are that this person has not a natural immunity
to the disease ; in other words, that he is susceptible to it,
or has a " disposition " towards it. Now it is this natural sus-
ceptibility (or immunity) that is inherited, and not the disease.
No matter how much susceptibility one had to a given disease,
he would not contract the disease unless he was exposed to
the infection by the specific microbes that cause that disease.

CHAPTER XXXVIII
WASTES AND BY-PRODUCTS OF ORGANISMS

232. The origin of wastes. Every chemical process results
in the formation of substances that did not exist before. In
the chemical processes that take place in the cells of a liv-
ing organism, substances are produced that are directly related
to the protoplasm's being ''alive." Other substances, which
are of no direct use to the living body or to the living process,
are produced incidentally. The latter are called wastes, and may
be compared to the sawdust of a mill, or to the smoke that goes
up the chimney, or to the ashes that drop through the grate.

233. Removal of wastes from cells. In our study of pho-
tosynthesis (p. 54) we found that one of the wastes or
by-products is oxygen, which diffuses out of the chlorophyl-
containing cells through the cell walls. In our study of ener-
gesis (p. 143) we found that carbon dioxid, water, urea, and
other substances may be produced. These also diffuse out
of the cell.

In plants water and carbon dioxid are usually eliminated in
the form of vapor. The carbon dioxid given off by the cells
of the roots usually remains in solution, forming so-called
carbonic acid (see Fig. 42, p. 144).

Plants often dispose of their waste substances in a way that
seems to be beneficial to them ; and the same is true of animals
(see p. 203).

234. Accumulation of wastes in plants. The waste sub-
stances produced by plants (outside of water and carbon dioxid)
are generally not eliminated from the body. They are usually
combined into insoluble or non-diffusible compounds, and in
this condition they are accumulated in dead cells in parts

202

ELEMENTARY BIOLOGY

of the plant where they do not interfere with the vital activities.
There are many classes of such waste compounds.

I. Among the most common waste substances found in
plants are various pigme^its. These are familiar to us in the
autumnal colorings of leaves, in the bright colors of many
flowers and fruits, and in the pigments of woods and roots.
The red of the radish, of the rose, and of the maple leaf,
the yellow of the buttercup, of the
pumpkin, and of the carrot, and the
blue of the pansy and of the huckle-
berry, all are examples of the waste
products that are deposited in out-of-
the-way cells (Fig. 75).

2. The attractive ^^^^rj- of many flow-
ers, preserved for us in perfumes and
essences, and the flavors of the many
spices are due to essential oils de-
posited in out-of-the-way cells of plants.
They are found in the flower, the leaf,
the fruit, the bark, the wood, and even
in the root.

3 . Tan7ti7is are chemical compounds
related to tannic acid which have the
property of forming hard, insoluble
compounds with proteins. They are
commonly found in the bark of trees, but

may also occur in other parts of the plant — often in unripe fruits.

4. The acids that we find in fruits especially, although they
are present in other plant organs, are derived from substances
diffused out of live cells. Alkaloids (see p. 74) and other
poisonous substances found in plants, and the gums and resins,
are also waste products.

5 . The excess of mineral matter absorbed f 1:0m the soil is
separated out of the live cells by being deposited in cell walls
or by being precipitated as insoluble compounds in certain of

Fig. 75. Pigment bodies in
plant cells

Most of the pigments found in
the cells of plants are probably
in the nature of waste products.
Some pigments occur in solu-
tion ; others are found attached
to protein particles, forming
definite colored granules

WASTES AND BY-PRODUCTS OF ORGANISMS 20^

the cells. Sand (silica) is thus found in the scouring rushes
and other plants ; and crystals of oxalate of lime are found in
hundreds of plants — for example, in the root of the jack-in-
the-pulpit and in other sharp-tasting plant parts (Fig. J^).

All these waste substances are useless to protoplasm, and
many of them are even injurious. But, separated as they are
from the living parts of the organism, they may nevertheless
be of some value to the plant as a
whole, or to the species, in some
special relation. Thus, the pigments
and odors of flowers may be of use in
relation to insect visits (see pp. 316-
314); or essential oils and tannins
may be of value in protecting plants
from animals and from bacteria or
fungi.

235. Excretion in animals. The
one-celled animals excrete their wastes
just as they excrete carbon dioxid. In
the higher animals, those that have
blood and lymph, the wastes are dif-
fused into these conducting fluids, and
are then eliminated from the body
through special organs, for the most
part.i

236. The kidneys. In the human
body, which in this respect is typical

of the backboned animals, the kidneys are the special excretory
organs. Water and carbon dioxid are, as we have already

Fig. 76. Crystals found in
plant cells

/, in seed of castOr-oil plant;
2, in bark of a tree ; j, in bulb
of squill. Crystals in plant cells
often represent an accumulation,
or a locking up, of superfluous
mineral matter

1 To a comparatively slight extent the waste products of animals, like the
waste products of plants, are accumulated in some of the cells. Thus, many
of the pigments found in animals are no doubt to be considered as in the
nature of 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
or the sea lily, and the coral framework of the coral polyp, no doubt fall into the
same class.

204

ELEMENTARY BIOLOGY

learned (see p. 148), excreted from the
lungs ; small amounts of urea, and pos-
sibly other organic wastes, also leave
the body through these organs. Some
water, salt, and urea, with traces of other
organic wastes, leave the body by way
of the sweat glands, and some reach the
intestines and are then thrown out. But
most of the waste is eliminated by way
of the kidneys.

The kidneys, of which there are two,
may be considered as glands whose function
is the separation from the blood of certain
specific substances (as urea, salt, etc.) and
water (Fig. 78).

237. The sweat glands. The sweat is
excreted by special glands which consist
of delicate twisted tubules surrounded by
a network of capillaries (Fig. J"]). Waste
material, with water and salt, is con-
stantly passing from the capillaries into
the tubules, and through these out upon
the surface of the skin. Ordinarily the
water part of the perspiration 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 solid
deposit is left on the outside of the skin, instead of in the
mouths of the tubules.

Fig. 77. A sweat gland

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 (capillaries)
from which water, urea, and
salts are withdrawn into the
gland tube

CHAPTER XXXIX
HYGIENE OF EXCRETION

238. Hygiene of the kidneys. The kidneys work continu-
ously. Their work can be facilitated by drinking plenty of
water every day, and by emptying the bladder with sufficient
frequency to prevent discomfort. Aside from maintaining the
general health of the body, there is nothing else that we can
do for the kidneys ; and, indeed, nothing else needs to be done.

Where a generation ago workers quenched their thirst with
beer and other prepared drinks, now employers and managers of
factories and shops are finding it worth while to provide an
abundance of clean, cool, and palatable drinking water. In some
states the law requires that suitable drinking water be supplied
in all workrooms. In a similar way the provision of suitable
toilet rooms, from being a casual accommodation or conven-
ience, is coming to be recognized as a real necessity not only
by the opinion of the experts but by the framers of laws. The
more progressive cities are also taking steps to provide suitable
drinking water for all on the streets and in public places, as
well as comfort stations for all who have to be abroad.

An understanding of the intimate relation between the wastes of
the tissues and the secretions of the kidneys has made possible the
development of special methods of diagnosis through the chemical
and microscopic examination of the urine. The sugar and the albumin
and the uric acid that the expert discovers in the urine are to be con-
sidered as indications of the general condition of the body, or of certain
organs, and not necessarily of the condition of the kidneys.

The effect of alcohol upon the kidneys is related to the
fact that it causes a congestion of capillaries. When the
capillaries of the kidneys are congested, the excretion of wastes

205

206

ELEMENTARY BIOLOGY

is to that extent impeded, and the whole body suffers in conse-
quence of the retention of urea and other poisonous by-products

of protoplasmic activity.

239. Hygiene of the skin.
The skin is more than an ex-
creting organ ; indeed, the
excretory work of the skin
may be considered rather in-
cidental. Other functions of
the skin are as follows :

1. Protection of the body

(a) against mechanical injury,

[b) against drying up, and {c)
against excessive radiation of
heat.

2. Regulation of the body
temperature.

3. Perception of sensations
of touch, heat, etc.

But it is the secretions of
the fat glands and the perspi-
ration (see Fig. yy) that give
rise to the need for special
attention to the skin.

The accumulation of wastes
left behind when the perspira-
tion evaporates and the catching of dust in the oil secreted by
the oil glands, and in the pores through which the oil is secreted,
call for periodic bathing. The best way to remove the accu-
mulated wastes and dirt is by means of hot water and soap,
with the help of a brush. But hot baths have a debilitating
effect, forcing the blood into the capillaries of the skin and thus
away from the muscles, brain, and internal organs. A warm bath
once or twice a week should be enough for ordinary cleanHness
if these supplement a daily cold bath.

Fig. 78. Kidneys and bladder

a, the main artery, and b, the main vein, in
the abdominal cavity, giving off branches
to the kidneys, cc ; d, funnel-shaped cavity
in which the waste fluid is gathered by the
gland action of the kidney ; ee, tubes lead-
ing from the kidney to the bladder, /. The
left kidney is represented as cut through
lengthwise

HYGIENE OF EXCRETION 207

For those who can stand it a daily cold bath is refreshing
and at the same time an excellent training for the skin in
adjusting itself to changes in temperature. The cold bath
should never be taken when the body is exposed to cold,
however. The best time is immediately upon rising, or
immediately after physical work or exercise that has produced
copious sweating. But since there are many people who
cannot tolerate the cold bath, because of the after-effects of
the shock, it is not to be generally recommended. Each one
must find out for himself whether he can benefit from it. All
of us can stand a splash of cold water after a warm bath or,
in the morning, over the chest and back ; and probably most
of us can gradually learn to stand the cold bath, either by
systematically lowering the temperature of the water used,
day by day, or by increasing the surface to which cold water
is applied with a sponge. In any case the cold bath should
be followed by a brisk rub with a rough towel.

It is hardly necessary to remind anyone that bathing will not main-
tain cleanliness if the underclothing is not changed with sufficient
frequency.

240. Exercise. The value of exercise for the muscles, for
the heart, for the breathing, for the digestion, and for the
work of the bowels has already been mentioned. The value
of exercise for the skin and the excretion generally are worth
noting. The slow, continuous perspiration, of which we are
not aware, leaves deposits of wastes in the tubules of the
sweat glands. More rapid perspiration washes these wastes
out. Exercise that results in sweating cleans out the pores.
In so far as exercise accelerates the flow of the blood, it
contributes also to the more rapid removal of wastes through
the kidneys.

CHAPTER XL
EXCRETION AND FATIGUE

241. Getting tired. When you ''chin" yourself on a bar
four, five, 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 .?

A modern explanation is that the waste substances begin
to accumulate in the cells as soon as the work commences ;
the wastes are formed faster than they can be carried away,
and the result is a poisoning of the protoplasm of the working
cells. Experiments have enabled us to discover the importance
of these wastes.

242. Fatigue poisons. If a muscle taken from the leg of a
frog is made to work (by being stimulated with an electric
current) until it is too tired to do any more, it may be restored
to working power by the simple process of washing it in salt
water. The salt water certainly does not supply fuel to the
muscle ; on the contrary, it would seem rather to take some-
thing away. Moreover, if the salt water that has been used
to wash the tired muscle is now injected into a fresh muscle,
one that has not been working, the latter immediately becomes
too tired to work. This would show that some unknown sub-
stance has been taken away from the tired muscle to make
it fresh, and that this same substance has been added to
the fresh muscle to make it tired. This substance has been
called fatigue poison.

208

EXCRETION AND FATIGUE 209

The presence of fatigue poisons has been shown repeatedly by
experiments similar to the above. For example, a dog has been
kept running until he is very much fatigued ; some of this dog's
blood is then introduced into the veins of a dog that has been
kept quiet the whole day. Immediately the resting dog shows all
the signs of being a tired dog.

243. 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 hard book

.inmi.miu/riiiiiiiim.ilirMiliUMiMM.ii/.Mim.irili.ii.miiiir.itii limillllllllllllllllllllllllllllllllfllllllllllllllllllllflllllll

a b

Fig. 79. General fatigue as measured by the ergograph

The ergograph records the frequency and the strength of a pull exerted by a finger, the
resf of the hand being held firmly in place. These two records were made by a medical
student on the same day : a, before beginning his day's work at college ; i>, at the end of
the day's work. The height of the vertical lines shows the difference in energy, or strength,
of each pull. The difference between the bases shows relative time of application

and begin to doze over it, I am not too tired to play a game
of tennis or even to read an interesting novel. But beyond
a certain point fatigue affects the whole body ; getting tired
from study unfits one for muscular work or play. This is shown
by certain kinds of experiments that were first carried out
in Italy.

Records made on the ergograph by any person will show great
variations, according to the condition of the body. A record made
early in the morning will differ from one made at the end of the day ;
a record made after taking a nap in the afternoon will differ from
one made at the close of a game of chess (see Fig. 79). Although

2IO

ELEMENTARY BIOLOGY

the people who made these tests did not use the middle finger in their
work, this finger showed different degrees of fatigue in accordance with
either the physical or the mental work done before the test was made.

We have learned from these and similar experiments that ex-
hausting physical work tires the brain and the sense organs ; and
we have learned that severe mental work tires the whole body.

HtiiiiimiuiniiiiliiiiiiHiiiiiiiiiiiiiiiiiiiiiiiiiiimiiiliiiiimiiili
a

H tll'illlliiUlliill llilWllinillMnilllMillilllliUlMiillilii1iniilllliiiniiilll)lllllHlMillihliinMliiHiMmininniilllliiiiitm!ui>iKWW4^

h

Fig. 8o. The pace and fatigue

These two ergograph records were made by the same student on the same day. a was
made by pulHng as rapidly as possible, and shows rapid accumulation of fatigue ; b was
made by a slow, steady pull every two seconds, and although the time was twice as
long as in a, and the work performed about four times as much, there is no appreciable
evidence of fatigue

It is not to be concluded, however, that hard work is to be
avoided. On the contrary, hard work is useful physiologically,
as well as morally and economically. But we must use this
knowledge to help organize our work in a more effective way.

EXCRETION AND FATIGUE 211

244. Rate of work. When we come to think of it, we
shall recall that getting tired is not altogether a matter of what
kind of work we are doing ; it is partly a matter of how fast
we are doing it. *' It is the pace that kills" (see Fig. 80).
Physiologically this means that at a certain rate or speed
fatigue poisons are formed faster than they can be removed
by the blood, and from the blood by the kidneys, etc., and
that when the work is done at a certain slower speed, the blood
can remove the wastes just as fast as they are formed. When
you walk very fast, you may feel tired before you have gone
a mile, although you are not out of breath ; if you walk slowly
enough (but not too slowly), you may walk ten miles without
showing any signs of fatigue.

We may therefore conclude that work can be kept up best
if we take the right pace. Work that is speeded may give
larger returns in a given time — but only for a short time. If
the high speed is maintained, the worker will have to stop
sooner or the quality of the work will fall off. This principle
has its everyday applications in athletics, in play, in housework,
in school work, and in industry.

245. Fatigue and efficiency. When Frederick W. Taylor,
the founder of scientific management, wanted to increase the
output of useful work on the part of some unskilled workers,
he did not urge them to work faster. Instead, he carefully
experimented to find out how fast the necessary movements
could be performed without accumulating fatigue poisons
during the hours of work. He actually made the men move
more slowly than they had been accustomed to. And in
shoveling dirt and carrying pig iron he more than doubled the
day's work without increasing the day's fatigue. This principle
is so well recognized among the leaders in scientific manage-
ment of works that the efforts of the experts are directed to
devising plans that will prevent fatigue on the part of the
workers. These plans usually contain two sets of factors, one
mechanical and the other biological.

212 ELEMENTARY BIOLOGY

The mechanical problem is to find out the fewest movements
that are necessary for performing the work. The biological
problem is (i) to arrange the material and the machinery
and tools in such relations to the body of the worker as to
put the least strain on the muscles, the attention, the sense
organs, etc., and (2) to establish a pace that will result in
a maximum of output with a minimum of fatigue.

In other words, the efficiency of the day's work will depend
not only on the nutrition and respiration and training of the
worker but also to a very large extent upon the prompt
elimination of wastes from the working cells.

CHAPTER XLI
FATIGUE AND THE WORKER

246. The hours of work. No matter how slowly one works,
it is impossible for him to keep on working indefinitely without
rest. How many hours a day should a person work ? How
many hours a day may one work and play and still maintain
his health ? There was a time when mill workers had to be at
their tasks sixteen and eighteen and even more hours a day.
They lived, but they died young. The shortening of the work-
day has certainly played a large share in the lengthening of
the work life.

With an excessive length of working day the body never has
time to catch up with the elimination of wastes. Fatigue ac-
cumulates from day to day, and sooner or later the machine is
clogged beyond further use. It is, then, a question whether
it is more economical to work long hours for a few years or
to work short hours for a longer period. From the point of
view of making the other person produce profits for me, it has
often seemed best to work him for all he is worth, and then,
when he is used up, to get someone else. But from the point of
view of the worker and from the point of view of society this
is certainly poor economy. Especially true is this when it
comes to considering the work of children (see Fig. 8i).

The injurious effects of long working days upon the worker
is coming to be realized by the workers and by society at large.
This realization shows itself in two ways :

1. The workers are constantly demanding a shorter and
shorter workday.

2. Legislation is constantly readjusting the legal workday
on a shorter and shorter basis.

213

214

ELEMENTARY BIOLOGY

B<py8

This official demand for shorter hours rests chiefly on two
considerations :

. I. The human stock must be preserved from the evil effects
of overwork, and the ordinary methods of bargaining about
hours and wages cannot be relied upon to secure what is

^ , fair for the workers.

2. In certain occu-
pations the fatigue of
the worker is a direct
menace to the public.
This is especially
true in such occupa-
tions as railroading of
all kinds, elevator-
operating, work on
boats and ferries, and
the work of drivers
and chauffeurs, tele-
graph and telephone
operators, etc.

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Three- Room
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Two- Room
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One- Room
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Fig. 8i. Environment and physique

Dr. Leslie Mackenzie had the weights and heights
taken of all the school children (73,848) of Glasgow.
The diagram shows the average weights of boys
(solid lines) and of girls (broken lines), divided
according to the kinds of homes the children lived
in. All the studies made show that poor food, disease,
overwork, poor housing, and other conditions in the
environment produce measurable deteriorations in
the physique of growing children

In planning our own
programs we should
keep in mind the rela-
tive amount of effort
and the relative amount
of fatigue connected with
each kind of occupation.
We cannot get the best results from our work if we have fatigued
ourselves with play in the morning; nor can we enjoy our play if
we have worked too hard during the day.

247. Work and rest. It is important to find out what kinds
of work are most fatiguing, and what arrangements of work
and rest, or what alternations of work, will make possible the
greatest amount of effective activity, with the least strain on the
human body. Short rest periods during the day, the alternation

FATIGUE AND THE WORKER 215

of physical and mental work, the distribution of work that requires
little or no active attention, are devices for achieving these ends.

In many offices and factories it is coming to be customary to in-
troduce a " pause " of from five to fifteen minutes in the middle of
the afternoon. During the pause no work is permitted, and it is found
that the total output is increased rather than diminished in this way.

In schools similar ideas are being put into practice. We take a few
minutes of physical exercise between study or recitation periods, to
stimulate the flow of blood and to fill our lungs.

In spite of all the precautions that we know should be taken,
many people, and even many children, suffer from chronic
fatigue. This condition shows itself in restlessness and irrita-
bility, in lack of appetite, in languor and lack of concentration,
in sleeplessness or disturbed sleep, in loss of weight, and in a
certain drawn expression on the face. When fatigue poisons
have got a little ahead of the excretory system, the best
thing to do is to take as complete a rest as possible.

248. Fatigue and health. Fatigue poisons affect the gland
cells as well as the nerve and muscle cells ; hence the frequent
indigestion from meals eaten when the body is fatigued.
F'atigue poisons also affect the white corpuscles, and the
chemical activity of the cells generally, so that, when fatigued,
a person is more liable to catch colds, as well as other
infectious diseases.

We may well conclude that it does not pay to become
chronically fatigued, although there is nothing better than
getting ''good and tired " every day, and then getting over it
again by the next morning. This means that sufficient sleep
is one of the prime necessities of healthful and efificient and
happy living. People whose day's tasks are too long are most
likely to get their fun in time taken from sleep.

It is during sleep that the working and growing cells can
make up for the losses of the day's work ; it is also during
sleep that the excretion can catch up with the day's accumu-
lation of wastes.

2i6 ELEMENTARY BIOLOGY

249. Standardizing work conditions. At the outbreak of the
Great War the sudden need for a rapid increase in the produc-
tion of all sorts of supplies and munitions led the managers of
industry to increase the number of hours of work and to ''speed
up " the workers in factories. They also arranged to continue
work on Sundays and holidays. This was especially true in
England. After some months of this intensive activity it was
found that the high rate of production could not be maintained,
and that there was a great deal of ill health and of physical
breakdown among the workers. A commission was appointed to
inquire into the health of munition workers. Among the impor-
tant discoveries made by this commission were the following :

1. The increase in the number of hours of work was bad
both for the health of the workers and for the effectiveness of
their work.

2. The continuous work, day after day, without weekly rest
days, was bad for the health of the workers as well as for the
standards of production.

As a result of this and of similar investigations many fac-
tories in Europe and in this country have established new
methods of determining the speed at which work shall be done.
They have divided the day's work into short shifts, or ''tricks,"
which permit fatigue products to be eliminated, instead of
forcing them to be accumulated in the bodies of the workers.
As a consequence, production has been increased, accidents
have been reduced, and the health of the workers has been
greatly improved.

CHAPTER XLII
NERVES AND THE REACTIONS OF ORGANISMS

250. What we cannot help doing. No child can keep his
face composed and look unconcerned when he is properly
tickled. He bursts out laughing, or he draws away the tickled
part, or he does both. And when he does any of these things,
he cannot help it. When something suddenly approaches your
eyes, you wink, and you cannot help it.

251. Reflexes. Movements of the kind mentioned, which take
place without any intention or desire on the part of the agent,
in direct response to some disturbance or stimulation, are called
reflexes. Some reflexes are useful, as winking, or sneezing, or
coughing, or withdrawing the hand when '' it hurts."

Reflexes need not result in movements. The " funny-bone " reflex
carries with it a definite sensation. Indeed, that is about all that we
are aware of when the funny bone is struck. This suggests that there
are some reflexes that are not altogether confined to movements. We
have already come across reflexes that do not involve movements at
all. The increased flow of gastric juice in response to the stimulation
of pleasant food, and the watering of the mouth on the mere sight of
pleasant food, are examples of reflexes that let themselves out in
glandular activity.

252. Using an animaPs reflex. If you ever catch a fish with
a hook and line, you depend upon a reflex for your success.
The fish responds to the vision of certain kinds of objects by
snapping at them with his mouth. You simply have to make
sure that you have the right kind of bait, and that it is properly
fastened to the hook, and that it is dropped into the water at
a suitable depth. Your ''luck" depends upon the fish seeing
the bait, and the reflex does the rest.

217

2l8

ELEMENTARY BIOLOGY

253. Reflexes and tropisms. Reflex actions of animals differ
from the tropisms which we studied in the young plants, both
in the greater speed with which they are executed and in the
kind of structure which brings them about. The reflexes all
depend upon certain connections of nerves^ muscles^ and special
perceiving organs, such as the eyes, ears, tongue, etc. To
understand the mechanism of the reflex we must therefore
know something about these three kinds of organs.

254. The muscle.
We all know in a gen-
eral way that the muscle
is the ''thing that
makes us move." We
also know the appear-
ance of a muscle from
having handled and
eaten the flesh of
animals.

When thousands of
millions of such cells
contract at the same
time, we can see that
the whole mass will be
considerably shortened. An ordinary muscle of the body, such
as draws up the forearm or one of the fingers, is essentially a
bundle of several masses of muscle cells, together with connec-
tive tissue, blood vessels, and nerve connections (Fig. 82).

255. Kinds of muscle. The muscles that are most familiar
to us are the skeletal muscles (those attached to bones of the
skeleton) of such animals as we use for food — chicken, lamb,
ox, etc. We have already learned that there are other mus-
cles, however, such as the muscles of the heart (p. 186) and
of the diaphragm (p. 149). The muscles connected with the
skin manifest themselves to us in the facial expressions of
those we see about us, in the movement of the ears (of which

Fig. 82. Contraction of a muscle

The movement of an organ, as the forearm, is
brought about by the contraction of a muscle. The
mass of muscle cells becomes shorter and thicker, the
parts to which its ends are attached being brought
closer together

NERVES AND THE REACTIONS OF ORGANISMS 219

Ventral

many of us are still capable), in the twitching of a horse's
skin when it is annoyed by flies, and in winking. And, finally,
we may recall the muscles of the esophagus, the stomach, the
intestines, and the
blood vessels.

Some muscles
are called volun-
tary and some in-
voluntary ^ but all
muscles contract
in response to a
stimulus received
from a nerve cell.

256. Nerves
and nerve cells.
The nerves that
are found run-
ning to all organs
of the body are
compounded of
many nerve fibers.
Many such fibers,
bound together
by connective tis-
sue and associ-
ated with blood
vessels and lym-
phatics, constitute
a nerve. For our

present purpose we are not so much concerned with the
nerves as we are with the nerve cells which compose them.

The nerve cell consists of (i) the cell body and (2) certain
processes, or outgrowths {fibers) ; together these make up a unit
of the nervous system. Such a unit is called a neuron, and may
be compared to a muscle cell as a unit of a muscle, or to a

Fig. 83. Diagram of the spinal cord

A, left half of cross section, showing impulses entering the
dorsal root and outgoing impulses passing out by the ventral
root. B^ the neurons connected with the gray matter of the
cord give off branches passing up and down the cord and
transmitting ner\'ous disturbances by way of the collaterals.
In the gray matter of the cord, branches of afferent neurons
carry impulses up and down and pass them on, by way of the
collaterals, to efferent neurons and to the brain

220

ELEMENTARY BIOLOGY

Fig. 84. Reflex arc

Stimulation of the re-
ceiving end a of an
afferent nerve A leads
to a discharge of energy
to all parts of the
neuron, including the
fine terminals, or den-
drites, d. The discharge
passes over to con-
nected nerves, as the
efferent nerve E, by way
of the interlacing den-
drites, ox synapse, s. The
discharge in E leads
to the stimulation of the
organ with which it is
connected, as a muscle
M. The disturbance
passes from a to the
spinal cord, where it is
reflected by one of the
side branches, or collat-
erals, c, of A, through
the synapse s into E,
leading to a movement
by the contraction of M

gland cell as a unit of a
gland. It always acts as
a unit (see 7 in Fig. 4).

The cell bodies are found
chiefly in the cortex, or rind,
of the brain, in the core of
the spinal cord, and in special
groups (called ganglia) in
various parts of the body.
Occasionally single cells are
also found.

The processes are of two
kinds :

1 . The long, slender fiber
extending, with other fibers,
through the nerves, is called
the axon.

2. Shorter processes, of
which there may be several,
usually branching irregularly,
''like the branches of a tree,"
are called dendrites (from a
Greek word meaning ' ' tree " ) .

In some neurons a stimula-
tion, or disturbance, is received
by the delicate branching ends
of the axon and transmitted to
the cell body. In other neu-
rons the disturbance is received
by the delicate endings of
the dendrites and transmitted
to the cell body and on through
the axon.

The axon may be very short,
as in the neurons of parts of

Fig. 85. Affer-
ent and efferent
nerves

Disturbance of a
sense organ S, con-
nected with an affer-
ent nerve A-^, may
set up nervous dis-
charges in several
connected nerves.
There maybe a mus-
cular reflex through
the efferent nerve
E^, connected with
a muscle; there may
be a gland reflex
through the efferent
nerve E^, connected
with a gland ; and
there may be a sen-
sation, or feeling,
through the disturb-
ance of a brain cell
B, by a discharge
through a con-
nected neuron A,^

NERVES AND THE REACTIONS OF ORGANISMS 221

the brain, or as in some neurons in the gray
part of the spinal cord ; or the axon may-
be very long, like those in the neurons
extending from the lower part of the
spinal cord to the ends of the toes or
through the length of the arm.

257. Kinds of neurons. The follow-
ing different types of neurons may be
recognized.

1 . Those that bring impulses toward
the cord or brain, — the afferent, or
sensory, neurons.

2. Those that carry impulses from
the cord or brain, — the efferent neu-
rons that may stimulate a muscle or
a gland.

3. Those that connect afferent and
efferent neurons, which we may call
associative neurons.

4. Neurons in the brain, many of
which are not directly related to
reflexes but are related to knowing
and feeling and the voluntary control
of muscles.

258. Nerve connections in a simple
reflex. Suppose that your finger
touches something hot. The nerve
endings in the skin are disturbed,
and the disturbance of the proto-
plasm is transmitted to the rest of
the neuron in a fraction of a second.
The fiber of the affected cell sends
off a number of branches in the

spinal cord (Fig. 83), and the dendrites at the ends of these
collaterals form fine networks with dendrites of other neurons.

Fig. 86. Behavior limited by
nerve connections

The diagram shows the nerve
connections of a simple mus-
cular reflex, with collateral con-
nections to the brain. Such
connections make possible auto-
matic reflexes as well as volun-
tary movements. If the afferent
nerve is cut, as at a-^^ only volun-
tary movement is possible, and
there is no sensation. If the
efferent nerve is cut, as at ^j,
neither reflex nor voluntary
movement is possible, but sen-
sation remains. If the spinal
cord is cut high up, as at a^^ e^,
neither sensation nor voluntary
movement is possible, but the
reflexes are not affected

222 ELEMENTARY BIOLOGY

These interlacing dendrites allow the nerve action to pass over
from one cell (neuron) to another (Fig. 84). It is possible that
in this region the protoplasm of one neuron is in touch with
the protoplasm of the next one, so that a disturbance passes
from one cell to the next just as it might pass from one part
of a single cell to another part.

The disturbed spinal-cord cell sets up nerve action in an
efferent muscle nerve, with the result that the arm or hand is
drawn back. At the same time, it sets up nerve action in a
fiber leading to a brain cell, with the result that you become
aware of the pain. But the movement has taken place before
you realize what has happened. The nerve disturbance from
the finger to the spinal cord along an afferent fiber is reflected
out through an efferent fiber, which stimulates the muscle to
action (Fig. 85). _. , '

259. Afferent and efferent neurons. If a certain part of the
sciatic nerve (which is the main nerve trunk running down
the leg) were cut, destroying the afferent fibers {a^^ Fig. 86),
one might walk on carpet tacks or hot iron and not know it
(unless he happened to be watching his feet), and accordingly
one would not jump to escape the damage. Under these cir-
cumstances a person would still be able to move his legs or to
jump if he wanted to. On the other hand, if another portion
of this nerve were cut, — the portion carrying efferent fibers
(^j, Fig. 86), — 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 hard he tried. And they certainly would
not move of themselves, for the reflex arc would be broken in
the part connecting the spinal cord with the muscles.

260. Reflexes without consciousness. If the brain of a frog
is removed or injured, or if the spinal cord is cut near the
brain {a^, e^, Fig. 86), the animal will still be able to perform a
large number of reflex actions similar to the one described.
Thus, a frog with its brain destroyed will scratch with its leg
at a spot on the skin that has a drop of acid placed upon it.

NERVES AND THE REACTIONS OF ORGANISMS 223

The sense impression produced by a touch on the skin travels
along the axon of an afferent nerve. This disturbance is
shunted off, or reflected, through a synapse into one or more
efferent neurons to the corresponding muscles and results in
a movement more or less suitable for the occasion. But this
shunting takes place in the spinal cord or in the lower
parts of the brain that do not involve feeling or consciousness
or willing. No matter how useful or purposeful such actions
appear to be, we must understand that reflexes do not represent
the animal's desires or intentions. In many animals, including
man, these reflexes may be called forth during sleep or during
unconsciousness produced by ether or chloroform. Under such
circumstances it is certain that the movements are not intended,
not '' dorie on purpose."

CHAPTER XLIII

TROPISMS AND THE BEGINNINGS OF SENSE

261. Tropisms. In the absence of neurons in the simplest
animals we cannot speak of their reflexes. Most of the reac-
tions that have been studied are classed
as tropisms. Tropisms have been ex-
plained as resulting from the unequal
contraction of the protoplasm on oppo-
site sides of the body, under the influence
of unequal, or one-sided, stimulation.

262. The general reaction of lower
animals. Many organisms are not sym-
metrical, and many, like the Paramecium,
or slipper animalcule, make progress in
a given direction by moving spirally
around the line that represents this
direction (see Fig. 87). In response to
any disturbance or change in condition,
such animals always make the same
movement (see Fig. 88).

As a result of this ''general reaction"
to all kinds of stimuli, the animal man-
ages to escape many dangers, and to
get into situations that are frequently
advantageous (see Fig. 89).

263. Chemical sense in lowest organ-
isms. The simplest animals, like the
roots of many plants, are sensitive to

many kinds of chemical disturbance. We cannot suppose that
an ameba, for example, has the feeling of sour or sweet, or

224

Fig. 87. Movement in
Paramecium

In the Paramecium, as in
many other free-swimming
protozoa (one-celled animals) ,
the organism moves forward
by spinning about its own
axis and at the same time
swinging in a spiral path

TROPISMS AND THE BEGINNINGS OF SENSE 225

that the Paramecium has an idea of nice or nasty. But it is
very plain that the protozoa are repulsed by the presence of
sand grains and attracted by the presence of various kinds
of bacteria. They will swallow the bacteria and pass the sand
grains by. There is no doubt, however, that the difference
between their reaction toward
food and their reaction toward
inert matter or toward injurious
matter is due to a certain relation
between the chemical constitution
of the protoplasm and the chemi-
cal constitution of the outside
substances. We should hardly
be any more justified in saying
that the ameba likes meat juice
than we should be in saying that
water dislikes oil. In one case,
as in the other, the reactions de-
pend upon certain relations be-
tween the chemical compositions
of the two reacting substances.
Water does not choose to dissolve
sugar and to leave sand undis-
solved ; neither can we be sure
that a protozoan chooses its food,
notwithstanding the fact that it
does take some kinds and reject
other kinds of objects or materials.
It is only when we come to the higher animals that we may
begin to speak of choice in this sense ; and even among the
highest animals most of the selecting and rejecting depends
entirely upon reflexes and instincts rather than upon thought
or feeling ; that is, they depend upon the structure of the
organism and upon the composition of certain organs rather
than upon a conscious purpose or discriminating taste.

General reaction

In many one-celled animals every stimu-
lation brings about the same response.
In the Paramecium the animal, when it
runs into an obstacle, whether physical
or chemical (O), immediately reverses
its movements, backing off a little way,
turning to one side, as shown by the
arrows, and starting off along a new path

226

ELEMENTARY BIOLOGY

In the simple organisms the response, like the irritation, concerns
the whole cell; that is, the whole organism. We cannot separate
the part of the animal's structure that is irritable in the sense in

which a neuron is irritable, from the part
that is irritable in the sense in which a
muscle fiber is irritable. Nor can we
separate the perceiving part from the
contracting part, although of course we
may readily believe that in the complex
mixture that we C2i\\ protoplasm there are
some contractile arrangements of mate-
rials and some irritable combinations.

In the Vorticella (Fig. 90) and other
one-celled animals it is indeed possible to
distinguish a strand of highly contractile
substance.

In the Hydra (Fig. 91) we can see
the beginning of separation between
irritable region and contractile region.

Fig. 89. " Trial and error " in
lowest animals

When a simple animal, like Para-
mecium, runs into a region un-
favorable to its existence, the
stimulus causes a reversal of its
movements, with a change of di-
rection. On moving forward in the
new path, 2, it may again meet the
same obstacle. The same reaction
is repeated. After a number of
trials the animal is likely to find a
clear path. This behavior gives the
appearance of trying again after
each failure until success is attained

264. Organs of touch. In our-
selves, as well as in the other higher
animals, the sense of touch is de-
pendent upon the presence of special
nerve endings in the skin, and their
connection, direct or indirect, with
other neurons (see Fig. 92).

In some parts of the body the touch
organs are much closer together than
they are in others ; for example, they
are set very close together in the skin
of the tips of the fingers, and compara-
tively far apart on the back of the hand.
It seems that we perceive hot through the stimulation of certain end
organs in the skin, and cold through the stimulation of certain others.

265. Organs of taste. On the upper surface of the tongue,
on the palate, and in other parts of the lining of the mouth

TROPISMS AND THE BEGINNINGS OF SENSE 227

and of the pharynx there are Httle projections called papillcE,
which contain the nerve endings of the neurons connected
with the cells that feel taste. The wry face that one makes
on tasting something disagreeable is a reflex in which the
afferent nerves of taste and the mus-
cular nerves controlling the muscles
of the lips, tongue, and cheeks form
the arc.

There are also associated in this kind
of reflex other neurons that stimulate
the salivary glands. Your mouth waters
on tasting something sour, but this
watering is not related to the digestive
process. It may not be unreasonable to
consider this excessive watering as useful
in the sense that it helps to dilute the
acid, or to neutralize it (since normal
saliva is alkaline), or to wash it away.

The nerves are capable of perceiving
four distinct tastes : sweet, sour, bitter,
and salty. When we perceive the vari-
ous flavors in substances that we place
in our mouths, we are really getting
stimuli that act upon the nerve endings
in the nose. We can readily convince
ourselves of this by trying to distinguish,
without the use of sight or smell, the taste
of various substances having distinct
flavors. A blindfolded person, holding
his nose to prevent currents of air pass-
ing through it, cannot distinguish ground coffee, for example, from
sawdust, or vanilla flavor from raspberry. When we speak of the
" taste" of good food, we generally mean the odor.

266. Organ of smell. The nerve endings in the lining of
the nose, and of the air passages extending back from the
nose into the pharynx, are of two kinds : some are sensitive to
touch ; others are sensitive to odors. This sense of smell is a

Fig. 90. Vorticella

This one-celled animal lives in
water, attached by its stalk to a
rock or twig. When disturbed
the animal contracts suddenly.
Running through the stalk is a
strand of highly contractile sub-
stance, shown in the figure by the
dark area

228

ELEMENTARY BIOLOGY

specialized chemical sense,
and is more highly devel-
oped in some of the lower
animals than it is in man.
The sneeze reflex

IS

0000@0(10S

Fig. 91. Simple tissues in a simple animal

The Hydra is among the simplest of many-celled
animals, consisting of a hollow bag whose wall is
made up of two layers of cells. There is apparent
a division of labor between the inner layer of
digesting cells and the outer layer of protecting
cells. In a section of the wall we may see that
the outer cells, «, have elongations, b, at their
bases, which are highly contractile, and that in-
terspersed among these cells are smaller ones, t,
which are highly sensitive and extended into
delicate threads and expansions, d, which may
be considered to correspond to nerves

Started either by a strong
odor stimulation or by a
touch stimulation in some
of the nerve endings of
the nostrils. Watering of
the mouth in response to
certain odors illustrates
reflexes that are dis-
charged to glands rather
than to muscles. The feel-
ing of nausea and the act
of vomiting are reflexes
that may be started by stimulation of the odor end-organs.
267. Stimulation and sensation. In the case of touch, taste,
smell, and other senses, the application of energy or of contact
to the nerve endings (or end
organs) sets up a disturbance
in the protoplasm of the neu-
ron. This disturbance is not in
itself a sensation. The disturb-
ance is carried along through
the neuron and is passed on
through one or more other neu-
rons until it finally sets up a
disturbance of one or more cells
of the brain. It is here that the
stimulus is at last translated
into a feeling, or sensation.

Fig. 92. The touch organs of the skin

We perceive touch or heat or cold according
to the end organ that is stimulated. These
end organs, af, lie beneath the epidermis, a,
and contain endings of nerve fibers, e ; b, the
dermis, or true skin ; c, blood vessels

CHAPTER XLIV

EYES AND LIGHT

To us the eye is a seeing organ — that is, a means of
distinguishing objects, forms, colors, shades, and lights at a
distance. It is therefore hard for us to realize, first, how animals
can get about with-
out such useful or-
gans, and, second,
how it is possible to
be sensitive to light
and shade without
eyes. Yet many ani-
mals are very sensi-
tive to light without
having any eyes, and
many animals get
along very well with-
out distinguishing

between light and darkness. We have already learned that
plants are sensitive to light (p. 38), and that the ameba will
respond to sudden changes of illumination (p. 24). From
these facts we may infer that protoplasm itself is more or less
sensitive to light — that light is a kind of energy that may
change the processes that go on in protoplasm.

268. Primitive light perception. In the ameba every part
of the body is equally sensitive to light. This is true of the
protozoa generally, and also of the simplest plants. There are
some one-celled plants, however, in which there is a special
region that is particularly sensitive to light. One of the most
common of these is the Euglena (see Fig. 93).

229

Fig. 93. Euglena

This one-celled organism is capable of moving about by-
means of the swimming lash, like many animals ; it has
chlorophyl, like many plants. Near the base of the lash
is a reddish speck which is sensitive to light. Although
it is often called an eyespot, it is no more like an eye
than a grain of powder is like a cannon

230

ELEMENTARY BIOLOGY

269. Light tropisms. There are many simple animals that
are ordinarily phototropic in the positive sense, and there are
many that are negatively phototropic. In some cases, as in the
Euglena, the tropism can be reversed \ that is, made to be the
opposite of what it was. An agitation of the water, an electric
shock, a change in the temperature, may reverse the sense

of the phototropisms. This would
show that the response depends up-
on the condition of the protoplasm.

270. MoUusks and light. Com-
paratively few of the mollusca
(oysters, clams, scallops, etc.) have
special light organs. Most of the
common bivalves have a region
about the edge of the mantle that
is sensitive to light. In the scal-
lops there are definite eyespots at
the edge of the mantle. In the
snails, the squids, and the octopus
there are definite eyes, those of the
octopus resembling the eye of the
backboned animals in many ways.

271. General sensitiveness. The
earthworm has no eyes, but the

whole skin, and especially that near the front end of the body,
is sensitive to light. The worms will crawl away from the
source of light unless the illumination is very low. Thus they
keep out of sight during the day, and crawl to the openings of
their burrows at night.

272. Compound eyes. Insects and other arthropoda com-
monly have compound eyes^ and many of them have also sim-
ple eyes (Fig. 96). There are many nerve-cell endings in
each of the eyes, and as the lens projects a tiny image upon
these endings, there is formed a patchwork of varying lights
and shadows, some of the cells being highly illuminated, others

Fig. 94. Eyespots in starfish

The eyespot at the end of each ray is
connected with the nervous system
of the animal and is more sensitive
to Hght than the rest of the body
surface. In this group of animals
(Echinodermata, or spiny-skinned)
there is a central nervous system,
so that there are true reflexes

EYES AND LIGHT

231

not at all. In this
way some tiny pic-
ture of a portion of
the outside world is
formed inside of each
of the many eyes, and
thus a mosaic of im-
pressions is produced
on nerve cells of the
animal's brain.

The images pro-
duced in the parts of
the compound eye of
an insect or a lobster
are probably not very
distinct; but as the
animal gets many
simultaneous views
from somewhat dif-
ferent angles (a com-
pound eye may have
from twenty to sever-
al thousand separate
facets), the organ is
excellently adapted to
detecting slight move-
ments. In insects the
eyes are immovable,
but most of them are
able to see the move-
ments of an object or
of a light from prac-
tically all directions,
though not at a very
great distance.

Fig. 95. Light-perceiving organs among the
mollusks

In the scallop, A, and in other bivalves, there is a row of
eyespots along the edge of the mantle. In the snails, B,
there is a more developed eye, frequently on the end
of a stalk. The octopus, C, has a pair of eyes similar in
many respects to the eyes of backboned animals

232

ELEMENTARY BIOLOGY

273. The human eye. We may think of our eye as a small
camera with sensitive nerve endings in the place where the

film or plate would be (see Fig. 97).
The space between the lens and
the retina is filled with a trans-
parent, jellylike mass, and in front
of the lens the space under the
protective coat contains a watery
fluid. Finally, the eye is moved
about in its setting by muscles
attached to the bony framework,
and is further protected by the
movable lids.

274. Other vertebrate eyes. While
our eye is in general very much like
the eyes of other backboned animals,
there are important differences, cor-
responding to the habits and the habi-
tats 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 fishes (except the
sharks) lack eyelids. Snakes have
their eyelids 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
pair of eyelids (Fig. 98).

A B

Fig. 96. Compound eye

In the Arthropoda, or jointed-legged
animals, there are compound eyes as
well as simple ones. A^ head of a
locust, showing the compound eye
with its many facets, each repre-
senting the exposed surface of an
ommatidium, or single eye. B^ an om-
matidium, seen in section cut length-
wise, a, corneal lens ; b^ lens-growing
cells ; c, cone ; d^ iris cells ; ^, retinal
cells, receiving light impressions ;
/, retinal pigment ; g^ perforated sup-
porting membrane

Although
found

IS

275. The seeing eye.

sensitiveness to light

among all branches of the plant

world and among all branches of the animal world, there are

only three main groups of animal that can actually see. These

are the highest mollusca, the arthropoda, and the vertebrates.

234

ELEMENTARY BIOLOGY

By seeing we mean not simply discriminating between light
and dark, but being capable of distinguishing forms and
colors, as well as light and shade, at some distance.

. ; ' 276. The range

of sensitiveness.
Some insects, as
ants, have shown
that they are sensi-
tive to other vibra-
tions that make no
impression at all up-
on our retina. We
can understand this
both from our ex-
perience with other
senses and from ex-
periments. Thus, we
know that a blood-
hound will perceive
odors that you and
I would pass by
without notice, and
that even most dogs
would not be able
to recognize. We
know that ordinary
dogs will recognize
persons by the odor,
but that very few human beings are capable of doing so. Again, by
means of experiments we have found out that some people can dis-
tinguish shades of red or of blue that others cannot recognize at all.
We can therefore understand that some nerve end-organs will be sen-
sitive to certain colors (rates of vibration) that leave others indifferent.
Moreover, some animals are sensitive to light of such low intensity
as others would not respond to at all, just as individuals vary as to
the quantity of light stimulation necessary to make an impression.

^^>\\\^^"'

c

Fig. 98. The third eyelid

The little fold of tissue extending from the inner comer of
the eye corresponds to the third eyelid, or nictitating mem-
brane^ in birds and certain reptiles and amphibians. The
nictitating membrane can be drawn over the eye so as to
cover it completely. «, eye of ape ; b^ eye of owl ; c^ human
eye ; ^j, the semilunar fold, eyeball removed

CHAPTER XLV
HYGIENE OF THE EYES

277. Eyestrain. No two eyes are ever exactly alike, and
while the lens of the ordinary eye may be fairly satisfactory for
ordinary purposes, we find that very many eye lenses are not
adapted to doing work at close range and with small objects.
Now in modern times our work comes to be more and more of
the kind that requires the seeing of small objects, or distinguish-
ing small markings, at short range. The strain on the muscles
that adjust the eyes for far and near vision {focusing) often
leads to headaches and irritability, or nervousness, without the
person who suffers being aware of the source of his annoyance.
An examination of the eyes by means of special instruments easily
discloses any defect of the lens, and this can be corrected by
the use of glass lenses.

A special defect often found in our eye lenses is that due to lack
of symmetry, or astigmatism. As the excessive bulging or lack of
curvature is usually along one line, it interferes with clear vision,
especially where one has to look at views in which lines are impor-
tant elements. Astigmatism also causes headaches and other
inconveniences due to eyestrain, since one unconsciously tries to
bring the view into clear vision, thus straining the muscles of the eye.

Another kind of strain results from the uneven musculature of the
eyes, causing the axis of one eye to turn inward or outward. Squint,
or strabismus^ in children can be remedied by a simple surgical opera-
tion, which evens up the tension of the muscles that move the eyeball.
In some cases special wedge-shaped or prismatic lenses are sufficient.

278. Outside sources of strain. As the eye has to do with
perceiving light stimulations, the character and intensity of the
illumination are important in their effects upon the eye and

23s

236 ELEMENTARY BIOLOGY

upon the general health. As light acts in the eye by bringing
about chemical changes in certain cells of the retina (the
"rods and cones"), prolonged exposure to light will carry
these changes so far that it is no longer possible to see.
Even before this extreme condition is reached, the cells will
show signs of fatigue, which may be accompanied by pain,
or at least by discomfort. This is what happens when the
eyes are long exposed to strong light, and the only way to
counteract the fatigue is by giving the eyes a complete rest.
Staying in a dark room or bandaging the eyes for from
twenty minutes to an hour will usually give the retinal cells
time to recover.

Flickers and flashes. The iris opens or closes in accordance
with the intensity of illumination. Sudden increases in the
amount of intensity of the light reaching the retina is likely
to cause injury to the pigment cells. This is why flashes or
a flickering light will fatigue and strain the eye, and such
sources of injury should be avoided.

Glare. A glare is produced when a comparatively strong
light strikes the retina while the pupil is open, or when
a strong light strikes a portion of the retina, the rest being
in comparative darkness. This condition results in injury to
the eye, and should be avoided as much as possible.

279. Mechanical injury to the eyes. Although the eyeball,
in its bony setting, is fairly well protected against injury by
large bodies, and although the very quick eyelash reflex keeps
many small particles out, many eyes are injured every year
either by blows or by dust. In railroading, in the building
trades, and in other dusty occupations flying particles of stone,
metal, cinders, coal, brick, etc. are sources of serious danger
to the eyes of workers. Wherever possible, workers in such
occupations should wear goggles. In any case we must be care-
ful not to rub the eye when something has got under the lid,
and whoever tries to remove a particle from under the eyelid
must approach the task with perfectly clean hands.

HYGIENE OF THE EYES 237

280. Eye infection. One of the dangers in getting dust
into the eyes Hes in the ease with which the Uning of the
eyelids becomes infected by various kinds of germs. Children
suffering from trachoma or other infectious eye diseases should
be excluded from school, where they are likely to transmit the
disease to others. There is danger, too, in rubbing the eyes
with the hands or with unclean towels or handkerchiefs. On
the first appearance of an irritation, or redness, in the eyes it
is well to wash with a solution of boric acid or argyrol, which
acts as an antiseptic without being injurious to the eyes.

A considerable proportion of all blindness could be prevented by
the exercise of greater care in dealing with injuries to the eyes, as
well as by care in avoiding injuries. The largest single source of
blindness is probably ophthalmia neonatorum^ the " baby sore-eyes,"
or the sore eyes of the newborn. This is caused by the gonococcus
bacteria, and can be prevented by placing a drop of a one per cent
solution of silver nitrate in each eye immediately after the birth of the
child. In several states this treatment is now required of all
physicians and midwives attending a birth, and in the last few years
thousands of persons have been saved from this form of blindness.

CHAPTER XLVI

SOUND SENSATIONS

281. What we hear. Certain kinds of movements, or vibra-
tions, of the air, when they make an impression upon our
nerves, give us the feehng of ''Aj(," just as certain other
kinds of vibrations give us the feeling of ''yellow." The eye

with which we see is an
organ whose nerve end-
ings receive impres-
sions from vibrations in
the ether at the rate of
from 400,000,000,000
to 800,000,000,000
per second. If the vi-
bration is much more
rapid or much slower,
the eye nerves are not
affected by them. Sound is a much slower vibration of the
air or of solids. Between 8 or 10 vibrations in a second and
40,000 to 50,000 per second the human ear discovers sounds
of varying pitch. In the middle register, which includes most
of the sounds with which we are familiar, as the pitch of the
human voice, the ear can distinguish very slight differences of
pitch. It is possible for a trained ear to distinguish more than
1000 shades of pitch in one octave.

282. Perception of other vibrations. Among lower animals the
range of vibrations that can be perceived varies considerably ; some
animals are quite insensitive to sounds of what we would consider
the common range of pitch, while some insects can perceive a much
higher tone than any human being can hear at all. The earthworm,

238

Fig. 99. Lateral line in brook trout

The line running along each side from the gill cover

to the tail is made up of nerve end-organs that are

sensitive to certain kinds of vibrations in the water

SOUND SENSATIONS

239

without any special hearing organ, cannot perceive sounds. Yet the
whole skin will receive vibrations of certain frequency, and transmit
them along nerve fibers, as can be seen when an earthworm is placed
on a piano and the instrument is played. Fishes are deaf in the usual
sense of the word, but they are capable of detecting vibrations in the
water, of a kind that we should not notice at all. The fishes probably

Fig. 100. Sound-perceiving organs in insects

In the locust, A, there is a nearly circular membrane, connected with nerve endings,

on the first segment of the abdomen. In the cricket, B, a similar hearing organ is found

on one of the joints of the front leg

receive these vibration impressions through a row of little spots ex-
tending along each side of the body, under the skin. This " lateral
line " is very prominent in some fishes (see Fig. 99).

283. Hearing in fishes. It is commonly believed that fishes hear
sounds through the water, and that they will even recognize the voice
of the person who feeds them. Experiments, however, show that
some species are much more sensitive than others to different kinds
of sounds and other vibrations. Nearly all fish can probably distin-
guish vibrations through the water, especially those of low pitch. It
is doubtful whether any fish can perceive sounds made in the air, since
such sounds are very largely reflected from the surface of the water.

240

ELEMENTARY BIOLOGY

284. Sound-perceiving organs. Among the insects there are
many special sound-producing organs, as well as many sound-
perceiving organs. It is probable also that many insects are
sensitive to rates of vibration to which our own nerve endings
are indifferent (see Fig. lOO). In some insects and spiders

the sound waves are re-
ceived on fine stretched
hairs connected with
nerve fibers. In the
male mosquito and in
other insects sound
waves are received b)'
fine hairs on the an-
tennae, or feelers.

285. The human ear»
In the air-breathing ver-
tebrates the hearing or-
gan is very much like
our own, although it is
possible to arrange a
series, extending from
the amphibians to the
mammals, in which in-
creasing complications
and refinements may be
observed. Our own hear-
ing organ is pictured in
Fig. loi.
286. How the ear works. A vibration striking the ear drum
is transmitted through the chain of bones of the middle ear to
the liquid filling the labyrinth. From this liquid it is trans-
mitted to the delicate lining of the cochlea, where nerve-end-
ings are located. Here some cells are disturbed by vibrations
of one pitch, others by those of a different pitch. The nerve
fibers are connected with special cells in the brain.

Fig. ioi. The human ear

A, the outer ear, consisting of the cartilaginous pro-
jection from the side of the head and an air passage,
or vestibule v ; B, the middle ear, lying between
the ear drum, or tympattum (/), and the inner ear, C.
The inner ear is connected with the pharynx by the
Eustachian tube e (see Fig. 28). Extending from
the drum to the inner ear is a series of three tiny
bones: h, the hammer-, a, the anvil; and s, the
stirrup. The main parts of the inner ear constitute
the labyrinth : c, the semicircular canals, consisting
of three tubes placed almost exactly at right angles
to one another ; k, the cochlea, or snail shell. The
labyrinth is filled with a fluid and lined by a delicate
membrane containing nerve endings

CHAPTER XLVII

RESPONSES TO GRAVITY

287. Geotropism. We have already learned that gravity is a
constantly acting force, and that plant organs respond to the
direction of this force (see
p. 37). Animals also have
occasion to adjust them-
selves to gravity, and they
do this in a variety of
ways. Some of the simple
marine animals are posi-
tively geotropic (or down-
ward swimming) under the
influence of light ; when
light is withdrawn (as at
night), they become nega-
tively geotropic, and swarm
to the surface of the water.
This agrees with the com-
mon observation of those
who are a great deal on
the water, that certain
animals can be found
near the surface only at
night. This is also an

example of a tropism reversed by changes in the protoplasm.

288. Insects and gravity. The common house fly seems to
be indifferent to the direction of gravity ; it will crawl upon
a surface in any plane and in any direction, and will come to
rest in any possible position.

241

Fig. 102. Statolith of a snail

A hollow structure filled with a fluid and con-
taining an unattached solid that is heavier than
the fluid ; as the position of the body changes,
the solid touches on different portions of the
sensitive lining, which is connected with nerves.
In some animals the lining of the statolith bears
delicate hairs

242

ELEMENTARY BIOLOGY

Many insect larvae, when they hatch out of the eggs, crawl
upward to the tips of the twigs. Many adult insects, when they
alight on a tree, assume a position with the head pointing up-
ward ; others always rest with the head pointing downward.
In some species the position of the insect at rest is determined

by the source of light
rather than by gravity.

289. Statoliths. In

the simplest animals the
action of gravity is prob-
ably similar to that sup-
posed to take place in
plants, namely, that the
nucleus or some other
solid particle presses up-
on the protoplasm of the
cell in a different part,
according to the position
of the cell. In some ani-
mals the organ of equili-
bration^ or of perceiving
gravity, is essentially a
hollow space with a float-
ing body and sensitive
walls (see Fig. 102).
In the lobster and crayfish similar organs are located at the base of
the antennules. The movable body here consists of some grains of sand.
These organs were formerly supposed to be related to the percep-
tion of sound waves, but it is doubtful whether they function in this
manner at all.

Fig. 103. The three dimensions of space

A solid body moves in a space which we think of as
extending in all directions. Every movement can be
thought of as a combination of movements in one
or more of the three planes representing the three
dimensions of space. The semicircular canals of
backboned animals are placed almost at exact right
angles to one another

290. Balancing organs. In the vertebrates, organs of equili-
bration, or of perception of position, are found in connection
with the inner ear. The semicircular canals of the labyrinth
{c and k, Fig. loi) are capable of detecting slight movements
of the body (or of the head) in any one of the three planes of
space (see diagram, Fig. 103). In our own body it is this

RESPONSES TO GRAVITY 243

organ, connected by means of nerve chains to the skeletal
muscles, that helps us keep our balance in walking or skating,
and in recovering our position when we trip. In addition
to this, the movements of the viscera and the strain of the
muscles at the joints help to keep us aware of the body's
position and of changes in the position at all times.

Since the introduction of airships into the army and navy, it has
become necessary to give certain classes of recruits a special kind of
physical examination, for the purpose of discovering whether the
equilibration reflexes are in good working order. Unless a person
can respond quickly to changes in bodily position, he can never learn
to control a machine that moves in the three dimensions of space.

CHAPTER XLVIII
INSTINCTS

291. A chain of reflexes. When an infant of a certain age
sees a small object, there is at once started a reflex ending in
the touching of the object. When the palm of the hand comes
in contact with the object, there is started the reflex of
closing the fingers. The touch of the object against the palm
and fingers starts the reflex that carries the object to the
mouth, and at the same time it stimulates the muscles that
open the mouth. The contact of the object with the lips and
tongue may set up a reflex of closing down on the object,
or it may set up a reflex of rejection if the taste is what
we call disagreeable.

Here we see movements in a connected series, but each part
of the series is a very definite reflex, depending upon the
association of afferent neurons connected with sensory organs,
efferent neurons connected with muscles, and associative neurons
in the spinal cord or the lower part of the brain. Such a
series we may call an instinct.

292. Instincts not perfect adaptations. A frog would starve to
death with hundreds of dead worms and insects all about him, be-
cause eating movements of this animal can be started only by the
sight of a moving object. On the other hand, the frog will swallow
bits of cloth that are dangled in front of him, and that have no
food value whatever.

Again, the female fly that is about to lay her eggs is guided entirely
by odor. If a piece of paper that has been soaked in meat juice
is placed on a table, the flies will come and lay their eggs upon it,
although this is extremely wasteful of eggs, and suicidal for the
species if persisted in. Of course, in a state of nature the only things

244

INSTINCTS 245

that smell like meat or like manure are meat and manure ; and
if the eggs are deposited in such materials, the young are supplied
with food. Therefore these instincts are, on the whole, beneficial,
or at least not fatal, to the species.

293. Instincts may be modified. We should- expect that
eating instincts would be so well fixed in the organization of
an animal that nothing could change them. But although we
cannot teach a frog to eat food that is at rest, or to avoid use-
less bits of dangling bait, it is possible to modify the instincts
of other animals in various ways. The dog who will refrain
from eating when he is not hungry illustrates the modification
of reflexes by the physiological state of the body. That is,
when the animal is no longer hungry, the condition of the
blood and of the other juices is different from what it is in
a hungry dog ; and the '' hungry " nerves and muscles behave
one way. in the presence of food, whereas the sated organism
behaves in a different way. A different situation is presented
by the goose that has had her food stuffed down her throat by
hand for some time. After a while the animal is no longer
stimulated by the sight of grain etc. to open her beak and bend
her neck and take up the food. We might say that for lack of
exercise the instinct has disappeared. It is probable, however,
that only certain of the reflexes have dropped out of the chain.

294. How an organism learns. In an aquarium a pike was
once placed in the same tank with a number of smaller fish.
The pike promptly swallowed his neighbors. A glass partition
was then put in, separating the pike from the small fish. The
pike would dart at them, however, and was often stunned by
striking the glass plate. But after a while he stopped darting
at the small fish ; and when the partition was removed, the pike
would always turn aside on approaching one of the little fish.
There was now nothing to prevent his eating them — except
certain connections in his nervous system.

This ability to form associations is of great practical impor-
tance to us not only in our control of lower animals but in our

246 ELEMENTARY BIOLOGY

own lives. It is the foundation of all our learning, whether
learning to know or learning to do or learning to like. It is
also the foundation of our learning to avoid doing, or to stop
impulses to action.

295. How neurons develop. We know from experience that
the muscles grow with exercise. The size of a muscle grows
measurably in a few weeks or months, and many boys try
their muscles from time to time, to see how they are coming
on. The explanation of this growth lies probably in the fact
that the exercise (contraction) calls forth a reflex that increases
the flow of blood, and that with increased nourishment the
muscle fibers increase in size or in number during the resting
periods between exercises. Now this sort of thing does not
take place so simply when the neurons are exercised. It ap-
pears that the body does not increase the number of neurons
after birth. But the axons and the dendrites may grow out,
and this is what happens when our nervous system develops.
The outgrowths of the nerve cell have been compared to the
pseudopodia of the ameba, as they are protoplasmic extensions
beyond the general outline of the cell, and depend upon the
cell's activities. Unlike the pseudopodia, they cannot be with-
drawn ; but, like the pseudopodia, they partake of the life of
the cell. The whole cell, including the very ends of the fine
branchings, acts as a unit. As a nerve cell is exercised, by
receiving impressions, by sending out stimuli, or by discharg-
ing its energy in some other way, these extensions of its
protoplasm are formed.

296. Learning in youth. It is by means of the expanding
outgrowths of the cells that new connections are formed, and
this is the basis for the associations that modify the conduct
of an animal as it gets older. Like other cells of the body,
the neurons are less and less capable of growth with advancing
age. Any associations that are to be formed must be made
before the neurons are too old. The development of the
ability to do things or to control the organs generally is thus

INSTINCTS 247

the result of use (exercise) or disuse. It is for this reason that
habits acquired in youth are most lasting, and it is for this
reason that '' you cannot teach an old dog new tricks." Things
that '' come natural " to us early in life become difficult if they
are not practiced ; tricks that we learn in our youth are for-
gotten if not practiced. Thus we may lose instincts and out-
grow them ; or we may fix them in our ways of life, remaining
childish though old in years.

CHAPTER XLIX
HABIT

297. Habits. The old saying, '* The burnt child dreads the
fire," refers to this common observation, that acts which have
unpleasant associations come to be avoided. The positive side
of this fact is just as important — namely, that acts which re-
sult in feelings of satisfaction come to be performed more fre-
quently. This is what a boy uses when he tries to teach his
dog or colt some new trick. If the animal is rewarded every
time he does what you want him to do, he will be more and
more likely to repeat the performance. At last he gets to the
point at which it is just as easy to perform the trick as to do
what it is natural for him to do. A boy taught his dog to
fetch his cap for him every time he started for the front door.
This trick we call a habit.

Now, if you look about you at what others are doing, or if
you watch yourself for a day, you will notice that most of our
actions are made up of habits. Turning to the right on passing
someone, or taking off the hat to a lady, is a habit ; these things
do not come naturally, for many people never do them at all.
And they are not done on purpose each time, for those who
have the habit do not stop to think each time what is the
proper thing to do. Wiping the mud off the boots before enter-
ing a house may be a habit, or it may not ; it does not come
naturally ; it is not instinctive.

298. Inhibition. It is natural to throw out of the mouth
anything that one does not wish to keep in ; but one may
learn to avoid spitting — that is, one may acquire the habit of
holding back on an impulse. This process of sending out a
nerve impulse to interfere with or stop the action started by

248

HABIT 249

another impulse is called inhibition^ and it is just as important
a part of our control as skillful action is. Indeed, skill is in large
part a matter of inhibition. In the excitement of a ball game,
the impulse of any player who gets hold of the ball is to throw
it ; the clever player will put the brakes on this impulse —
inhibit it — long enough to decide just where to throw it, or
he may even decide not to throw it at all, but to carry it some-
where, or he may go through the motions of throwing it in
one direction and then quickly turn and throw it elsewhere.

299. Practice. All movements can be performed accurately
just in proportion as a person has had practice in doing and
practice in inhibiting movements. We all know this when we
urge the other fellows to come out to practice for an important
game, or when we arrange rehearsals for theatricals, or when
we practice some new steps in dancing. We do not seem to
realize it so well when we are urged to drill on our lessons or
to practice some tedious scales on a musical instrument.

300. Kinds of habit. The education of human beings, like
the training of a dog, consists very largely of the establishment
of habits — habits of doing, habits of thinking, and habits of
feeling. Learning to walk, to handle our food or tools,
to swim, or to skate — these are examples of habits of
doing. A person who could walk only by thinking of each
step would not get along very far in the course of a day, and
he would not have much time to use his brain for anything
else if he really had to get anywhere.

301. Thinking habits. When we learn to say — or, rather,
to think — "eighty-four" on being presented by the combina-
tion " 12x7," or when ''1492 " makes us think '' Columbus,"
we are acquiring habits of thinking. Thinking shows itself
when you work out the answers to various kinds of problems,
when you draw out of your stock of remembered ideas and
experiences arguments to use in a discussion or examples to
make clear an idea that you are trying to explain to someone,
or when you work out a plan for getting certain tasks done

250 ELEMENTARY BIOLOGY

early enough to let you go to a meeting you are anxious to
attend. And each one of us learns through practice to do
these various kinds of thinking, and each one of us becomes
more skillful at one kind than at others — one person has habits
that enable him to solve mathematical problems more rapidly
than you or I can solve them, another person has habits that
make him a ready debater, and so on.

302. Feeling habits. We may have the habit of feeling
envy on seeing something new in the possession of another
person, or we may have the habit of just feeling glad that
the other person has something nice. We may have the
habit of feeling contempt toward people who are different
from ourselves, — people who wear different kinds of clothes,
or who go to a different kind of church, or who speak a dif-
ferent language, — and we may have the habit of feeling friendly
toward strangers. The sight of a bird or a squirrel may make
us feel like throwing something at it ; we may have acquired
the habit of inhibiting the impulse to throw, and yet retain the
habit of feeling destructive or cruel. Our feeling habits show
themselves in the attitudes that we assume in various kinds
of situations.

The habits which people acquire become so fixed and con-
stant that we may rely upon these sets of habits under all
circumstances. This is what we mean when we speak of a
person's character. We mean that totality of habits of feeling
and thinking and doing which distinguishes him from others.

We differ very much from each other in amount of think-
ing power, in the strength of our muscles, in our endurance,
in the depth of our feelings. But we can all acquire certain
habits that will constitute the sort of character that can be
depended upon, to the extent of our abilities, in all emergencies.

303. Selecting our habits. In acquiring habits of doing, feeling,
and thinking we must notice that habits of inhibition are just as im-
portant as positive habits. We must suppress the impulse to sneer and
the feeling that goes with it; we must inhibit the rising temper or

HABIT 251

the feeling of dismay. In the same way we find thoughts coming into
our consciousness that must be put down. Castles in Spain have their
proper place in one's life, but they must not come into our minds at
times that require close attention to something else. The thought of
skating must be inhibited when the business of the hour calls for
thinking about Washington crossing the Delaware. For the action
to be unlearned there must be no indulgence and no compromise.

Society establishes schools for the purpose of drilling children in
the kinds of habits that are supposed to be useful to them immedi-
ately or at some time in the future. But in addition to what the schools
can do, each one of us has opportunities to establish thousands of
useful habits that the schools never recognize ; and each one of us
no doubt has a number of useless habits — or habits that are worse
than useless — which it would be worth while to get out of our nerv-
ous system. By resolving to inhibit the undesirable habits — whether
of thinking, feeling, or acting — we may in time suppress them ; or
we may replace them with useful habits, as when we replace a slouch-
ing gait with erect carriage. But there are two things to remember
in the matter of habit-making and habit-breaking: first, " It 's dogged
as does it," and, second, " You can't teach an old dog new tricks,"
which, translated into English, mean. Persistence wins and You have
to catch ^ent young.

304. Value of habits. One need not go far from his own immedi-
ate experience to find out how valuable habits are when they are
of the right kind, and hoW miserable they may make us when they
are of the other kind. The amount of work or play that one can
accomplish depends very largely upon the kinds of habits one has
acquired. In the simple matter of dressing ourselves, how many
movements are necessary, and how much thought and effort they
take at first ! But to-day you probably dressed yourself without think-
ing about the buttons and sleeves at all. You ought to be able to do
all of your dressing and a hundred other things that have to be done
daily — or at least very often — without giving the actions the slight-
est attention. This means not only a great saving of time in the doing
of the necessary work, it means also a saving of thought for
matters that are much more interesting. The control over our mus-
cles comes by first giving our attention to what we are doing, and
then getting the spinal-cord connections to control the actions so that
we do not have to think about them at all.

252 ELEMENTARY BIOLOGY

We make use of the fact that animals form habits in many ways
not only in the training of animals for performing tricks for our
entertainment but in the everyday work of the farm or the stable.
By regular programs in feeding and milking cows, for example, we
give them the habit of coming in from the pasture when they are
wanted, either at sunset or when we call them ; this saves the work
of going after them. Horses learn to follow fixed routes, and they
learn to come home after they have strayed away. Chickens come in
response to a familiar call, and everybody can tell a good cat or dog
story to show how convenient it is for us that they do acquire habits.

305. Remaining young. As we grow older our protoplasm loses
the power to form new extensions and new connections readily. But
some people retain the power to form new habits much longer than
others. A part of this difference seems to be due to the fact that
some people retain their youth, so to speak, by constantly giving
their attention to the learning of new ideas, and of doing things in
new ways. It may be worth while to establish the habit of changing
old habits, or of trying to get new habits as we grow older.

CHAPTER L
CHEMICAL INJURY TO THE NERVOUS SYSTEM

306. Alcohol and the senses. The most important effects
of alcohol are upon the nervous system, as indeed is the case
with all drugs, stimulants, and narcotics. In small quantities,
alcohol dulls the sensitiveness of touch and hearing as well
as of sight. Nevertheless the drinker feels alert. In one
experiment made in Germany, four experienced typesetters
were given measured quantities of alcohol in their usual drinks,
fifteen minutes before beginning work, on alternate days. All
four of them felt that they were working faster on the days
when they drank the alcohol than on the other days. But
when the number of letters set each day was counted, it was
found that, with the exception of one man, who increased his
output each day after the first, all did considerably poorer
work on the alcohol days than on the non-alcohol days.

A similar experiment was made at the University of Heidel-
berg, where a number of students were required to add columns
of figures for half an hour each day. Although they all felt
that they were working better on the alcohol days, it was found
that they had actually done better work on the non-alcohol days.

In Sweden a number of sharpshooters from the army, when
under the influence of drink, thought that they were shooting
faster — that is, more shots per minute — and felt just as sure
of their aim. But the records showed that they actually shot
much more slowly, and very much less accurately, after drink-
ing alcohol than after going without it for several days.

These experiments show not only that the effect of alcohol
upon mental work and sharpness of the senses is detrimental,
even in small quantities, but that the feelings of the worker

253

254 ELEMENTARY BIOLOGY

are by no means a fair indication of what he is actually
accomplishing.

It is well known that in larger quantities alcohol has a de-
pressing effect upon the nervous system, lowering the acuteness
of the senses, weakening the attention, deranging the judgment,
and leading to sleepiness. It is only the feeling of elation and
alertness, which comes shortly after taking the small quantity
of alcohol, that deceives the drinker ; for the after-effect of a
small quantity is of exactly the same kind as the earlier effect of
a large quantity. This is the chief danger in the use of alcohol.
Like the rabbit that has been taking arsenic, the person who
drinks alcohol produces in himself two peculiar results :

1. He must have more and more, as time goes on, to pro-
duce the same effect that a small quantity was sufficient to
produce at first.

2. He gets to the point where he feels that he cannot live
without the alcohol — ; and, indeed, there are many people who
really suffer a great deal from the lack of alcohol, no matter
how much more they suffer when they have it.

It was formerly quite a common thing for physicians to apply
alcohol in cases that required a heart stimulus for a short time, and
in other cases. But since careful measurements have shown that the
advantageous effects of the stimulant are largely offset by the re-
action, and since it has been found that much of the stimulation is
only apparent, and not real, physicians are coming to use alcohol
as a medicine less and less. And in some hospitals it is never used
internally, except where necessary for the administration of some
other drug.

307. Coffee and tea. Next to food drinks and intoxicating
drinks the most common beverages are tea and coffee. These
drinks are prepared for the aromatic flavor and for the slightly
stimulating effects produced by an alkaloid which they contain.

The leaves of tea and the seeds of coffee contain the same
alkaloid, caffein. In a pure state this is poison, even when
taken in small amounts. In the small quantities taken with

CHEMICAL INJURY TO THE NERVOUS SYSTEM 255

the usual drink, it acts as a mild stimulant, increasing the
heart action. The chief danger in coffee- or tea-drinking lies
in the fact that one may come to depend upon it as a regular
heart stimulant. In that case one comes to require ever-
increasing amounts and to feel weak and helpless without it.
There is no excuse for children's drinking coffee.

The action of caffein resembles the action of nicotin and
alcohol in that the reaction counterbalances the first gain.
The stimulation is followed by a period of depression, just
as in the case of nicotin the narcotic effect is followed by a
period of irritation or restlessness. Again, as the protoplasm
becomes more and more familiar with the alkaloid, a larger
quantity of the latter is required to produce a given amount
of stimulation. Finally, as in the case of tobacco and alcohol,
though probably not so quickly, the continued use makes one
feel that he cannot be comfortable without it.

These consequences are not observed with ordinary foods,
but they are observed with all the drugs.

Tea leaves contain, in addition to the stimulating alkaloid and
the aromatic oil that gives the flavor to the drink, a considerable
quantity of tannin. This substance combines with proteins to form
a hard, tough substance, and is thus used in the tanning of leather.
If tea leaves are allowed to stand in the water too long, the tannin
becomes dissolved. It is this that makes strong tea pucker the lips
and the inside of the mouth. Habitual drinking of strong tea will
in the same way pucker the lining of the stomach ; as the tanning pro-
ceeds, the stomach lining becomes hardened, and digestion may
thus be interfered with.

308. Habit-forming drugs. A large number of plants that
were formerly used as medicaments have been carefully studied
in recent years, and the active substances have been separated
out in a pure state. In this way we have become acquainted
with several important substances, which are very useful in
the hands of the expert but very dangerous in the hands of
the ignorant.

256 ELEMENTARY BIOLOGY

Morphin, which is the active substance in opium, is an
alkaloid that was first separated from the poppy plant about
a hundred years ago. In fact, this was the first alkaloid to
be systematically studied.

From a medical point of view morphin is the most useful of the
alkaloids, but it stands next to cocain as a habit-forming drug, and,
from the very fact of its extensive use in medicine, has ruined
thousands of times as many victims as cocain has. In small doses
it lowers the heart action, slows the breathing, deadens pain, and
induces a dreamy, quiet feeling ending in sleep. It acts on the
nerves that carry impulses from the brain, weakening the control
of the muscles. In larger doses it causes the pupils of the eyes to
contract until they are almost closed, and lowers the respiration
dangerously near the stopping point; in fact, death by morphin is
brought about by stopping the respiration. As with other drugs, there
is a reaction later, in which the effects are to some extent reversed.

It has been said that the widespread use of opium has been
the greatest obstacle to the development and progress of the
Chinese people. So degrading are the effects of the drug
that in 1907 the Chinese government finally prohibited the
raising of the- poppy and the traffic in opium ; and in 19 18
the government of Tunis did the same, going so far as to order
all wild and all cultivated poppy plants destroyed.

While morphin* has been most commonly administered by
the smoking of opium, the habit of using it may be traced to
its administration as medicine or by injection under the skin.
Many drug-store preparations contain morphin, and it has
been found that many patent medicines attained to large sales
only because they cultivated the morphin craving in the people
who were foolish enough to take them. All the pain-killers
and soothing sirups carry the danger of developing a craving
for morphin, since they depend upon the morphin for what-
ever useful effects they produce.

Nearly all the patent medicines have depended for their
commercial success upon the fact that stimulants and narcotics

CHEMICAL INJURY TO THE NERVOUS SYSTEM 257

are so-called habit-forming agents. Caffein, cocain, heroin,
codein, acetanelid, chloral hydrate, and other alkaloids and
artificial compounds have been used to make the medicines
attractive to people in search of health or suffering from pain.

Every person should be informed of the dangers that lurk
in these preparations. Every progressive government is tak-
ing steps to prevent the use of these dangerous drugs in
the exploitation of people's ignorance, and of their desire for
health, for the private gain of a few unscrupulous men. It
is only under the direction of a competent physician that
any of these substances should be used.

309. Drug regulation. Notwithstanding the danger of drugs,
it is as important for the public to have pure drugs, and even
liquors, as it is to have pure food. In recent years both the
public and the physicians have come more and more to appre-
ciate the importance of having drugs standardized. For the
sake of those who depend upon having prescriptions that
conform to the wishes of the physician, it is necessary that
the composition and strength of the various preparations be
reduced to definite standards.

The conditions that have made it necessary for the public
to undertake the regulation of water and food supplies have
also made it necessary for the public to regulate the sale of
drugs. The interest of all people in their health, combined
with the ignorance of most people in regard to the condi-
tions of health, has made it possible for unscrupulous men
to sell for millions of dollars countless bottles and boxes of
worthless liquids and powders and pills, with the promise that
they will cure or prevent all kinds of diseases.

In recent times the public has come to realize the amount of suf-
fering that the patent-medicine business represents and the amount
of injury these supposed remedies are causing. We are accordingly
extending the regulation of business to require manufacturers to state
what their products contain. This is only a step in the direction of
complete protection, for to most people the names of even dangerous

258 • ELEMENTARY BIOLOGY

drugs on the wrapper of a bottle mean nothing. A further step is
taken by those states that prohibit absolutely the sale of dangerous
drugs, except on the prescription of a licensed physician.

310. Individual variation. Experiments show that from five
to ten persons in a hundred differ so much from the rest in
their physiological and chemical constitutions that every rule
we can make must carry exceptions with it. We are not yet
able to say anything about the action of alcohol that will be
true for all men. If it is found to be injurious in general,
there will be a few in every thousand who can take large
quantities apparently without measurable harm. If we find
that a certain drug is useful for certain purposes, in a given
dose, we shall find that there are a few people in a hundred
who will get no benefit from it in any dose. Or we shall find
that what is a harmless dose for most people will be a
dangerous dose for a few. Thus, it has been found that blond,
pale-faced people are unusually sensitive to atropin.

For all practical purposes, however, the following conclusions
of the *' Committee of Five" as to the use of alcohol may serve
as a sufficient guide to all of us in our attitude toward this and
other habit-forming substances :

1. While, in small quantities, beer and wine may be, in a certain
sense, a food, they are a very imperfect and very expensive kind of
food, and are seldom used for food purposes.

2. They are not needed by young and healthy persons, and they
are dangerous in so far as they tend to create a habit.

3. In certain cases of disease and weakness they are useful in
quantities to be prescribed by a physician.

4. When taken habitually, it should be only at meals, and as a
rule only with the last meal of the day, or soon after it.

5. Alcoholic drinks are worse than useless for preventing fatigue
or the effects of cold, although they may at rare times be useful as
restoratives.

6. They are almost always a useless expense.

7. Their use in excess is the cause of much disease, suffering, and
poverty, and of many crimes.

CHEMICAL INJURY TO THE NERVOUS SYSTEM 259

311. Anesthetics. Closely related to the narcotics through
their peculiar effects upon the nervous system are the sub-
stances known as anesthetics. Chloroform and ether are the
most common of these, although nitrous oxid, or " laughing
gas," is coming into greater use.

Chloroform and ether are liquids at ordinary temperatures,
but are easily changed to vapor when exposed to the air. The
person who is to use the anesthetic breathes the vapor into
his lungs. In a short time he is overcome by sleep, in the
course of which there is complete insensibility to pain.

CHAPTER LI
UNITY OF LIFE

312. The multiplicity of living forms. When we recall the
plants and animals that are familiar to us, at least by sight or
by name, we must be impressed by the great variety of forms
in which life is to be found. There are probably over a million
different kinds of animals and over a million different species
of plants. Yet throughout all this variety we find the common
facts of life.

A survey of what being alive means, from a biological point
of view, will show us how much alike these varied beings
really are. We may compare a one-celled organism, a common
plant such as a daisy, and the human body.

313. Unity in nutrition. In the one-celled animal there is
nutrition. This involves the taking in of food, its chemical
transformation, and the ultimate assimilation of its usable parts.

In the daisy there is nutrition. This involves the absorption
of carbon dioxid by the cells of the leaves ; it involves further
the chemical transformation of the material received, and the
ultimate assimilation of some of the product.

In man there is nutrition. This involves the taking of
foreign material into the body, its chemical and physical trans-
formation, and the ultimate assimilation of a part of the intake.

But whereas, in the case of the ameba, the absorption, trans-
formation, and assimilation are all carried on by a single cell,
the corresponding operations in the daisy and in man involve
the work of millions of cells.

In the matter of nutrition the ameba acts as a unit. The
daisy, although made up of many organs and many cells, and
the human body, although made up of still more organs and

260

UNITY OF LIFE 261

still more kinds of cells, also act as units. There is some
relation between the activity of the roots and the activity of
the leaves ; there is a very definite relation between the activity
of the hand that conveys food and the activity of the mouth
that receives it ; and also between the behavior of the digestive
system and the behavior of the conducting system.

Incidentally, organisms commonly take in, besides the usable
material, material that is not usable. The elimination of this
refuse is accomplished very simply by the ameba ; the animal
simply moves away from the refuse, leaving it behind. In the
daisy the excess of mineral matter received from the soil is
usually deposited in the form of insoluble compounds in
various parts of the root or stem or leaf. In the human body
the refuse from the food material is accumulated for a period
and then discharged by the coordinated activity of special
nerves and muscles.

314. Energesis and respiration. In the one-celled animal
there is energesis, depending upon the chemical union of
oxygen with other substances, under the influence of certain
ferments. This is also true of the daisy and of the human
body.

In the daisy, respiration is necessary for every cell ; and so
it is with man. But not all the cells of these organisms can
get their oxygen directly from the outside, nor can they all
discharge their carbon dioxid direcdy to the outside. In the
daisy the root cells absorb oxygen by osmosis, the oxygen pass-
ing directly into the epidermal cells, and from these by osmosis
into the deeper layers of cell. Carbon dioxid diffuses out by
osmosis in a similar manner. The cells of the leaf and of the
stem lying under the skin absorb oxygen from the air sur-
rounding them in the intercellular spaces ; and from these
spaces there are connections to the outside atmosphere by way
of the little breathing pores, or stomates. The gases move in
and out through these open spaces and passages, controlled
entirely by the changing osmotic pressure.

262 ELEMENTARY BIOLOGY

Every cell of the human body, Hke the cell of the ameba,
gets oxygen and gives off carbon dioxid by osmosis. But the
body as a whole can keep going only on condition that oxygen
is brought to every cell.

This involves (i) a special set of organs for receiving oxygen
from the outside — the air passages of the nose and throat;
(2) a special absorbing area closely packed into a relatively
small space — the lining of the lungs ; (3) a conducting system
that distributes the oxygen and gathers up the carbon dioxid

— the blood, with the red corpuscles ; and (4) a mechanism for
alternately filling and emptying the bags containing the absorbing
surface — consisting of bones, muscles, and nerves.

These several distinct organs and tissues act as a unit ;
there is some connection, that is, between the amount of
oxygen used and the activity of the breathing system.

315. Excretion. In all the organisms that we have been
considering, energesis involves the formation of other sub-'
stances besides carbon dioxid. But as some of these substances
are injurious to protoplasm, their removal is necessary for the
continuous life of the cells. In the ameba the wastes simply
eliminate themselves by osmosis ; in the many-celled organisms,
getting waste out of one cell would simply mean passing it on
to another.

In the daisy, wastes are accumulated in flower and root and
in some stem cells, away from the live, active cells.

In the human body we find that the conducting system (the
blood and lymph) absorbs the wastes from the active cells, and
that the wastes are then removed from the body by means of
special organs (the kidneys, with their connected tubes and
bladder, and the sweat glands).

Again, there is unity in the behavior of these special organs

— their activity is related to the activity of the body as a whole,
and especially to the circulatory system.

316. Correlations within the organism. From every point of
view that we have considered, the organisms are alike in that

UNITY OF LIFE 263

they all perform the same fundamental functions. Moreover,
each organism is a unity in that the various functions are
somehow correlated, or harmonized. In the higher animals it
is the coordination and correlation of functions that most arouse
our wonder and interest. These harmonizing relations are
brought about by three special systems :

1. The blood system.

2. The gland system.

3. The nervous system.

317. All life is one. From experiments, from our own ob-
servations, and from this discussion we should now be able
to think of the unity of life in two distinct ways :

1 . All life is one, in the sense that all organisms, large and
small, plant and animal, ancient and modern, useful and indif-
ferent and harmful, all live by virtue of doing certain things —
getting food, assimilating it after more or less change, liberating
energy, eliminating waste. They do other things, too ; but
these they all do, and all in fundament ally the same ivay.

2. All life is one, in the sense that the many parts of an
organism, however they differ from one another, are alike in
their fundamental properties, and in the sense that they pro-
duce a unified series of activities. We can understand the
body, perhaps, only by understanding the parts ; but we care
nothing about the parts except as they have meaning for the
unity, for the whole.

PART III
THE CONTINUITY OF LIFE

CHAPTER LI I
GROWTH AND REGENERATION

318. How organisms grow. A living body consisting of
many cells increases in size (i) by the increase in the number
of cells through cell divisions, and (2) by the increase in the
sizes of cells through assimilation of nutrients.

There are very many animals that keep on growing indefi-
nitely, as certain fishes ; and in plant species that have an
apparently definite limit of growth some parts may keep on
growing after the plant as a whole has reached its full height.
Most of the familiar animals reach a fairly definite limit of
gro\\th, beyond which point they may continue to live for a
long time without growing any more.

319. Limits of growth. What is it that stops the growth of
an organism without killing it ?

The gro\nh of a cell depends, for one thing, upon the intake
of suitable materials. In the presence of these the rate of
income will depend upon the amount of surface exposed to the
outside. The needs of the protoplasm, however, will depend
not upon the amount of surface exposed but upon the amount
of protoplasm — that is, upon the bulk, or volume. As a cell
becomes larger and larger its volume increases with the cube
of the diameter, but the exposed surface increases only as the
square of the diameter (see Fig. 104). As a result, the cell
soon reaches a point at which the surface is no longer suffi-
cient to admit the necessary food, water, oxygen, etc., nor

265

266

ELEMENTARY BIOLOGY

sufficient to excrete the waste matters for a larger quantity of
protoplasm than the cell contains at that moment. Beyond
this point, growth is manifestly impossible, although at this
point the protoplasm may be able to maintain indefinitely the
balance of income and outgo — that is, to ''live."

We must not suppose that
the ratio of volume to super-
ficial area is the only factor
that stops the growth of cells,
or that it necessarily has any-
thing to do with it. This is
simply a possible reason why
the growth of cells cannot go
on indefinitely. There may
be other factors, chemical or
mechanical or electrical per-
haps, that play important
roles in this matter. We may
say that the growth and mul-
tiplication of cells go on as
though the ratio of volume
to area had something to do
with it.

Fig. 104.

The ratio of volume to diameter
and area

The cube a has six surfaces, each a square and
all the same size. The larger cube, b, of twice
the diameter, has eight times the volume and
four times the surface that a has. As a body in-
creases in size the surface increases in the same
proportion as the square of the diameter, whereas
the volume increases as the cube of the diameter.
A growing plant or animal may thus reach a size
at which the surface is insufficient for the ex-
change of materials necessary to maintain the
inclosed protoplasm

In a thread-shaped alga
like Spirogyra the thread
of cells may grow indefi-
nitely, because the receiv-
ing and excreting surface
of the cell is not much reduced by contact with neighboring
cells (see Fig. 105). The thread-shaped cells of many fungi
get to be several inches in length without dividing ; this sup-
ports the idea that the ratio of surface to volume has something
to do with the amount of growth possible.

320. Healing and resumption of growth. When a full-grown
man cuts his hand, the cut will heal up by the formation of
new cells in the neighborhood of the injured surface. These

GROWTH AND REGENERATION

267

cells are derived from other cells. Or, when a bone is broken,
the ends of the bone will knit by the formation of new
cells and the deposit of bone material about these new cells.
This healing of skin or bone or other tissues is widespread
among all kinds of animals and plants, and may be considered
as a growth in response to stimulation set up by injury.

Fig. 105. Growth in a thread-shaped body

A body that grows by increasing in length only, as do thread-shaped algae, like the
Spirogyra, and as do the threads of fungi, changes the ratio of its volume to its surface
very little. In the diagram a cube is represented as increasing in one direction to seven
times its original diameter. With this growth the area has increased to five times the
original surface ; and with each addition in length the discrepancy becomes less and less

Not all kinds of tissues will produce new cells of the same kind.
For example, we learned that the number of nerve cells in the body
does not seem to increase after a child is born. An injury to the
brain will heal by the formation of a scar consisting not of neurons
but of connective tissue. In the same way many kinds of wounds
leave scars of connective tissue that close the gaps and hold the parts
together but do not function in the same way as the specific kind of
cells that were destroyed by the wound. On trees we often find scars
consisting of callus, produced as the result of some mechanical injury.

268

ELEMENTARY BIOLOGY

321. Regeneration. A small piece of a begonia leaf, placed
in close contact with moist soil, puts forth tiny roots that
grow into the soil ; and a tiny bud is formed, which starts

to -grow into a shoot. In other words,
it is possible to get a whole plant
from a part of a plant. A part of
the leaf takes on a new mode of
growth, producing root cells and stem
cells where under ordinary conditions
there would have been reproduced
only more leaf cells (see Fig. 13).

If the fore part of an earthworm
is cut off, a new fore part is
formed ; or if the hind end is re-
moved, a new ''tail" may be grown
(Fig. 106). This process of regrow-
ing a lost part is called regeneration,
and is in some ways similar to the
healing of a wound, only it goes
much farther.

Regeneration takes place to a larger
or smaller extent in all kinds of ani-
mals under normal conditions of life
that lead to mutilations of various
kinds. A single ray of a starfish will
be regenerated, or even two or three
rays (see Fig. 107).

Salamanders have regenerated tails

and legs, and the triton, one of the

lizards, can regenerate the eye. In

general, however, the higher or more

specialized organs are not readily

regenerated, and the highest animals do not regenerate as

readily as do lower animals. A finger cut from your hand will

not be regenerated, although the stump may heal up. And

a b

Fig. 106. Regeneration in

earthworms

(7, worm from which the anterior
end had been cut off; b^ worm
from which the posterior end
had been cut off. The dotted
Hnes show where the cut was
made. The shaded portions rep-
resent the new growths. (After
Morgan)

GROWTH AND REGENERATION

269

we should certainly never expect to make two whole pigs by
cutting one into two parts. ^

Among lobsters, crabs, and crayfish the power of regenera-
tion is also present in a very high degree. When one of these
animals has his claw or one of
the legs caught or mutilated,
he may throw the limb off com-
pletely, the separation taking
place along a definite plane
between two of the joints. The
wound does not bleed and the
lost limb is soon replaced by
the regeneration of another
from the tissues about the scar.

322. Vegetative propagation.
A stem separated from the
root can regenerate roots, as we
have already learned (p. 48).
Fruit growers propagate new
lots of individuals, from trees
that are especially desirable, by
setting out slips, or cuttings,
of these trees and having them
" set " roots. In this way all
tree can be indefinitely extended to a large number of trees.
Indeed, we may consider all the cuttings from a single tree as
really parts of the tree growing separately. This relation has
been described as a disco?ttimioiis groivth of a single individual.

1 The growth of the hair or of the finger nails after the ends have been cut
off does not represent a case of regeneration. The hair and the nails grow
continuously, the live cells in the follicle and in the root of the nail producing
new cells which are being pushed forward by the new cells underneath. Cut-
ting hair or nails simply removes the external, dead portion of the structure.
The new teeth that a child gets after losing the first teeth do not represent
regeneration either, since the rudiments of the second teeth are present long
before the first teeth drop out. The new teeth are independent structures
that develop normally and actually push out the first teeth.

Fig. 107. Regeneration in starfish

The mutilation of starfish does not seem
to kill them, for each part may regrow
enough to complete a new individual.
The regenerated ray shown in the figure
is smaller than the rest ; but in time the
new ray would become full size, since re-
generating tissues and organs grow faster
than the uninjured parts

the good qualities of a given

270

ELEMENTARY BIOLOGY

On the stems of most plants many more buds are produced
than ordinarily develop. But an injury or a mutilation will bring
about the development of some of the resting buds. If we cut into
the stem of a tall india-rubber plant, close to one of the nodes, we
can induce the nearest bud to swell up and begin developing. In
this way we can to a certain extent regulate the form of the plant,
by determining where branching is to take place (Fig. 109).

Fig. 108. Regeneration in lizard

The glass snake and other Uzards throw or cut off a part of the body when attacked,
and later regrow the lost tail or limb. The original tail of the lizard is an extension
of the backbone ; in the regenerated tail there are no vertebrae. Experimentally lizards
have been made to regenerate two or three tails in succession. The figure shows the

Surinam Ameiva

323. Grafting. Suppose we have a vigorous apple tree that
is perfectly healthy and satisfactory in every way, except that
its fruit is too hard or too small or too sour. We have no
way of making the fruit of that tree of a better quality. But
we can use the vigorous roots of that tree, and the food-
making factories (the leaves), to supply water, salts, and food
to a twig from another tree that bears the kind of apples we
like (see Fig. no). A notch is cut in one of the branches of
the first tree, and the wedge-shaped butt of the twig from the
second tree is fitted into the notch. The joint is covered with
a special wax preparation to keep out fungi and bacteria and

GROWTH AND REGENERATION 271

to prevent evaporation and the loss of sap. In time the grow-
ing layers (cambium) of the two stems will heal together, and
the juices will move through the twig and branch as though
they had always been parts of the same tree. This procedure
is called grafting, and consists essentially of making a part
of one organism grow into continuity with another organism.

>Ht. 109. Pollarded trees

White poplars {Populus alba) pollarded to supply building poles in Chinese Turkestan.
Pollarding is the pruning or trimming of the branches of a tree so as to make more
twigs develop. (From a photograph by F. N. Meyer, of the United States Bureau of

Plant Industry)

It is possible by grafting buds or twigs to get several different
varieties of apples, for example, to grow on the branches of one tree.
As a rule, only closely related varieties of plants can be made to
graft on one another in this way.

A scion always produces leaves, flowers, and fruit of its
own kind, and not of the stock to which it is attached. This
would show that the character of the original protoplasm

2/2

ELEMENTARY BIOLOGY

determines what kind of fruit will grow from a twig, rather
than the character of the food that is supplied.

324. Grafting in animals. Grafting is possible in all classes
of animals, but in a very unequal degree. In the insects,

Fig. iio. Grafts

A bud or twig of one plant is made to grow by means of nourishment supplied by the

root or stem of another plant. The root or stem supplying the nourishment is called the

stock ; the bud or twig grafted on the stock is called the scion. The figure shows stem,

bud, and root grafts

experimental grafts have been produced with two halves from
different individuals. The most interesting grafts, from a
practical point of view, are the fairly common skin grafts.
More far-reaching are the experiments of recent years, in which

GROWTH AND REGENERATION 273

not only have pieces of skin or bone of one animal replaced
corresponding parts of another, but whole sections of arteries,
and even kidneys and other organs, have been transplanted
from one individual to another.

With the improvement in the technique of such operations it is
not unthinkable that we may be able in time to replace a person's
diseased kidney, for example, with the kidney of a dog or a sheep, if
that is found suitable, or with the kidney of another person who has
recently died or who has had to have his kidney removed for some
reason. This principle is now applied in the repairing of crushed
bones ; the injured part is neatly cut away, and the missing portion
is replaced with a suitable piece of the same size taken from the leg
of a sheep. The chief obstacle to the practical use of grafting with
human beings and other warm-blooded animals lies in the fact that
the blood, through the chemical activity of the white corpuscles,
develops substances that are antagonistic to foreign proteins (see
Chapter XXXVII).

CHAPTER LIII
DEVELOPMENT

325. Many cells from one cell. Every cell that we have
studied originated by the dividing of some preexisting cell.
We should therefore suppose that at some time in the past our

Fig. III. Development of lancelet

a, the earliest stage of the animal, consisting of a single cell ; this divides into two
cells, b ; c, the four-cell stage ; d, eight cells ; e, a hollow ball resulting from successive
cell divisions ; /, the same still further advanced ; in g one side of the sphere has begun
to cave in ; this process continues until the opposite walls meet, forming a double
walled, cup-shaped structure, h

own bodies were made up of fewer cells than they contain to-
day. Then what is the smallest number of cells of which an
individual animal may consist } We know, of course, that there
are one-celled plants and one-celled animals. But are there
one-celled oak-trees and one-celled elephants t An examination
of the facts of development shows us that every individual,
plant or animal, starts life as a single cell.

If we begin with this one-celled body, we can understand
from our earlier studies how it may become a many-celled
body (Fig. iii).

274

DEVELOPMENT 275

326. Differentiation of cells. When there are two cells
(Fig. Ill, b), they are exactly alike. When each of these
divides, the four resulting cells are exactly alike. By repeated
divisions the number of cells is rapidly increased. In some
/species the cells are all alike until a very large number are
present. In other species of animals it is possible to observe
a difference of size after only a few divisions (see Fig. 112).

Fig. 112. Early stages in the development of a frog

In the frog's egg there is a considerable amount of food matter, or yolk, in addition to
the protoplasm. This yolk material is heavier than the protoplasm, and remains at the
bottom of the mass. So long as the cell divisions are in a vertical plane, b, c, all the
cells formed may be alike ; but when walls are formed in a horizontal plane, d, the upper
cells will be smaller than the lower ones, for while all the cells may have the same
amount of protoplasm, the lower ones will have larger quantities of yolk and will thus

be larger, ej,g

At first all the cells divide at about the same rate. Later
the cells in one region divide more rapidly than those in
other regions.

We can readily understand that while a starved cell may not be
able to do as much as a well-nourished cell, a cell that contains a large
surplus of inert food material may yet not be as active as one that is
not thus handicapped. In Fig. 112 the cells on the upper surface are
not only smaller, but in a given time they will also become more
numerous, because the cell division proceeds at a more rapid rate.

With inequalities in the rate of division, and inequalities in
the sizes of the cells, the shape of the whole mass soon
departs from that of a perfect sphere (Fig. in). With the

276

ELEMENTARY BIOLOGY

formation of new cell layers and with changes in the form of
the young embryo there gradually arise new kinds of cells.
At first these are in layers, or membranes. We may say that
the embryo at one time consists of membranes and cavities.
These membranes grow out irregularly into the cavities, form-
ing folds ; they break through in places, and they unite in other

places. In this way there
appear the tissues and the
organs that make up the
young animal.

327. Stages in develop-
ment. If we make a closer
comparison of the devel-
opment of a number of
animals, some remarkable
facts appear. In the be-
ginning, we may say that
all animals are like the
protozoa — that is, each
one consists of a single
cell. Now if we take a
large number of higher
animals, like the starfish,
the snail, a primitive, fish-
like animal called the lancelet {Amphioxiis), and others, we
shall find that in the development of each there is reached a
stage consisting of a hollow sphere of cells, — the ''mulberry"
stage, or the morula, which is shown in Fig. iii,/. This
hollow ball can be very well compared to such an organism
as the volvox (Fig. 113). In the development of the frog,
birds, and many other animals this stage does not appear so
clearly, because the presence of the yolk obscures the symmetry
of the hollow sphere.

When the hollow sphere caves in and the opposite sides
meet, forming a two-layered cup (Fig. iii, g-h), this stage of

Fig. 113. Volvox

This organism consists of a hollow sphere made
up of a single layer of cells connected by strands
of protoplasm. The colony moves about in the
water by means of cilia^ or vibrating protoplasmic
threads. Each cell contains chlorophyl

o ^

2/8 ELEMENTARY BIOLOGY

the organism may be compared to animals related to the
hydra, which get to this stage of development but never get
much farther. Then the two-layered cup becomes longer,
suggesting certain kinds of worms.

When we compare the embryos of animals that are closely
related, such as several kinds of backboned animals, or several
kinds of insects, we find still more remarkable facts. Thus,
the fish, the bird, the salamander, and the rabbit are very much
alike early in their development, not only when each consists
of a single cell, but later, when it is possible to distinguish
head and trunk and limbs (see Fig. 114). In a somewhat
later stage each has developed a little farther, and it is not
difficult to distinguish the bird from the fish or the tortoise.
But at this stage we can see certain resemblances between
the bird and the reptiles. Moreover, if we compare the
embryos of several mammals (such as the rabbit, the pig, the
sheep, and man) at this stage, we shall find them strikingly
similar. As they become older they become more and more
different.

328. Recapitulation. Now if we imagine a series of ani-
mals of different degrees of complexity, beginning with the
one-celled ameba and ending with man, we shall have before
us a picture resembling in many ways the series of stages
through which each individual human being passes, from his
one-celled stage to his maturity (see Fig. 114). This paral-
lelism between the stages in individual development and in
the whole animal series was observed long ago, and is known
as Von Baer's Law of Recapitulation. Some biologists have
gone so far as to say that each individual passes through stages
representing 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 we have passed through stages that are similar to
corresponding stages in many classes of animals.

Fig. 115. Life stages of various insects

/, red-legged locust {Melanoplusfemur-rubrum); 2, squash bug (Anasa trisiis)] 3, dragon-
fly {Libelluld) ; ^, June bug {Melalontha) ; j, wasp {Sphex gryphus). a, eggs ; b^ larva (not
shown for j) (in / and 2 the larva is similar in general form to the adult ; successive stages
are attained by molting, b^ \ c, pre-adult (in 4 and 3 this is a resting stage, or pupa) ;
ii, adult. 'J"he larva of the wasp develops within the caterpillar buried by the mother wasp

28o

ELEMENTARY BIOLOGY

329. Transformation. When we compare a chick as it comes
out of the shell with the contents of the eggshell before hatch-
ing begins, we cannot conceive that the little speck on the side
of the yolk has become the chick, with its many organs and
its many kinds of cells with their many peculiar functions.
And yet all that comes out of the eggshell must have been
there at the beginning of the incubation period. We are so
familiar, however, with the fact that chicks come from eggs,

that we are content to ac-
cept the changes that go
on inside, on the supposi-
tion that, since they are
so gradual, everything is
possible.

A study of the develop-
ment of insects will give
us an idea of how sharply
limited the stages in an
individual's life may be.
When a locust or a cock-
roach comes out of the
egg, it is very much like the parent, except that it is very
small and lacks wings (Fig. 115, /(d^, b^). By a series of
moltings the animal advances not only in the matter of size
but in the development of the wings and other organs.

When the egg of a moth or of a butterfly hatches out, the
young animal that emerges is not at all like the parent ; it
looks more like a worm (Fig. 117, b, b). It has no wings;
its mouth has biting jaws that work sideways ; its coloring
is different. Indeed, if w^e did not know that it came from
the egg of a butterfly, or that it would in time become a
butterfly itself, we should never suspect, from its appearance,
that it had anything to do with butterflies. We may well
believe that during all the months of outward inaction some-
thing was going on inside the case of the pupa, just as

Fig. 116. Molting cicada

In many jointed-legged animals (Arthropoda)
the growth takes place at intervals between
molts. The hard outer skeleton breaks open
and the soft skinned animal crawls out. After a
while the shell hardens and growth stops again

6 -- c

Tussock moth {Notolophus)

b c

Hawk moth {Hyloiciis kalmiae)

be <

Yellow swallowtail, or tiger butterfly {Papilio turnus)

a b c d

Fritillary {A rgynnis)

Fig. 117. Development of Lepidoptera (moths and butterflies)

The egg, «, hatches into a wormlike larva, or caterpillar, b. The larva feeds voraciously
and grows very rapidly. On reaching full growth it curls up, secretes a hard covering,
and goes to sleep. In this resting stage, or piipa^ c, it may remain for months, giving no
outward sign of life whatever. At the end of the resting period the cover of the pupa
breaks open, and out crawls the fully formed insect, d. In some species the two sexes
have distinct forms or color patterns in the adult stage. In the tussock moth the adult
female is a sluggish, wingless animal

ELEMENTARY BIOLOGY

b d

Fish, Chinook salmon {Oncorhynchus tschawytscha)

,<2^ %k.

Batrachian, frog {Rana palustris)

d ^

Batrachian, newt {A mbly stoma ptcnctatum)

Fig. ii8. Development in some backboned animals

a, egg ; a^^ fish ready to break out of &^g ; b^ first free-swimming stage (tadpole in
batrachians) ; b^i later stage in fish, still showing yolk sac ; c, more advanced stage (in
batrachians, tadpole just before the appearance of hind legs) ; d^ later stage ; ^, adult form

during the three weeks of hatching something was going on
inside the eggshell of the chick.

The development of an individual through a series of
well-marked stages is called a metamorphosis^ which means
"trans-formation."

DEVELOPMENT

283

In the large class of Insecta the development is characterized
by more or less complete metamorphosis (see Figs. 115 and 117).

In the life history of the frog and the salamander we find a
metamorphosis that is as well marked in some ways as that of the
insects (see Fig. ti8).

A complex animal, developing from a single cell, passes
through a number of stages that are different from the
finished form, on the one
hand, and from the simple
beginning, on the other.
This is really all that
metamorphosis means
when applied to living
things in general. It is
another name for devel-
opment. But when we
use the latter term, we
have in mind the process,
whereas when we say
'' metamorphosis," our
attention is fixed on the
forms, or stages.

330. Metamorphosis in
man. The changes that
take place in a human
being from day to day are
comparatively slow, and

the form of the infant is in general very much like that of the
adult, so that we do not commonly think of the metamorphosis
of human beings. But if we compare the proportions of a
baby with the proportions of an adult, we can see that the
changes are real even in the outward form (see Fig. 119).
A man is something more than a large baby, something
different, even in this outward form. We know, of course,
that as we become older there are many changes in the internal

Fig. 119. Metamorphosis in man

A comparison of the infant and the adult shows
that after birth the legs of the baby grow more than
any other part, whereas the head grows the least.
A study of this figure will show other changes
that take place in the outward form

284

ELEMENTARY BIOLOGY

organs : some organs present in infancy disappear, others not
present make their appearance later, and others are present
at first in a rudimentary stage and gradually reach maturity.

331. Development of plants. The simpler stages in plant develop-
ment are not so familiar to us, so that we do not have the same
opportunity to observe the similarities. In our study of the embryo

of the seed, we saw
that the young plant
had all the main parts
of a plant body, al-
though the embryo did
not at all resemble the
full-grown plant. The
embryos of related
plants look much more
alike than the adult
individuals, just as the
tadpoles of the newt
and the frog look more
alike than the adults.
Thus, the embryo and
even the seedling of
the squash and of the
pumpkin are so much
alike that it would take
a very experienced person to see any differences between them,
aside from size. The different kinds of beans appear very distinct in
the full-grown plant and in the seeds, but the seedlings with the first
pair of leaves look very much alike.

If we examine the stages in the development of the embryo, before
the seed is ripe, we shall find still greater similarities in the earlier
stages, before the stem, leaf, and root of the embryo are distinguish-
able, among plants that are not so closely related as are the squash
and pumpkin, for example (see Fig. 120).

Fig. 120. Development of a plant embryo

Beginning, like an animal, as a single cell, a, the plant

passes, by a series of cell divisions, b, c, d, e, into a mass

without any definite form, and gradually assumes distinct

structure and organs, /, g

CHAPTER LIV
CONDITIONS FOR DEVELOPMENT

332. Development and life. The conditions for the develop-
ment of young plants are the same as the conditions for growth
or for being alive. Development is, in fact, one of the aspects
of being alive — just as assimilation, energesis, irritability, etc.

I

1 \ Z

Fig. 121. Influence of thyroid on development

In each series, b shows the tadpoles that had been fed on thyroid much more advanced

in development, although smaller, than the controls, a. The control animal in / was fed

on plant food, in 2 on muscle, in j on adrenal. All full size. (After Gudernatsch)

are aspects of being alive. But development goes on so
slowly in most of the familiar plants and animals that most
people do not notice it as a distinct fact until their attention
is called to it. Changes in the external conditions influence
the development of animals, just as they influence the devel-
opment of plants.

That the development is not altogether a matter of growth
has been shown over and over again. In certain experiments
conducted by Dr. J. F. Gudernatsch, of the Cornell Medical
College, tadpoles were fed on thymus glands obtained from

28s

286 ELEMENTARY BIOLOGY

calves, while others were fed on thyroid material. The former
lot of tadpoles grew to a large size, but remained tadpoles,
whereas the latter quickly passed through the stages of
development without increasing much in size (see Fig. 121).
333. Temperature and development. The temperature of
the water in which frogs' eggs are kept will influence the

Fig. 122. Color changes in plumage

The ptarmigan {Lagopus lagopus) is snow-white in winter and replaces its coat with

feathers containing more and more pigment as the seasons advance, reversing the process

in the autumn, so that the plumage matches the surroundings the whole year round

rate of development. The warmer it is, up to a certain point,
the more quickly will the tadpoles pass into the tailless stage.
Temperature may affect not only the rate of development
but other sides of the animal's make-up. Sheep taken to the
tropics lose their wool, and in New Guinea they become almost
bald. Some English dogs that had been taken to the higher
parts of the Himalayas developed a woolly coat. The hare,
like many other animals in temperate climates, has a summer
coat and a winter coat. In the Alps the animal carries its
winter coat about half the year ; in Norway, from eight to
nine months ; in Lapland, about ten months ; and in Greenland,
the whole year round.

CONDITIONS FOR DEVELOPMENT 287

The white plumage of the ptarmigan in winter (Fig. 122),
and the white winter coat of the weasel and of other animals,
have been associated in our minds with the snows. But ex-
periments have shown that the change in the pigmentation
is brought about by a lowering of the temperature. And
observation has shown that it does 7iot always coincide with
the appearance of snow.

Another effect of temperature upon development is shown by
the experiments made on insects and other animals. There

Fig. 123. Effect of temperature on development

In the butterfly Vanessa levana prorsa the two broods have distinct patterns. By keep)-
ing the eggs, larvae, and pupae of the spring brood at a low temperature, it has been
possible to make the imagos appear in the fall with exactly the same coloring as the
spring brood. This showed that the spring form differs from the summer form because
of the influence of the temperature

are many species of butterflies that produce two broods each
year. The pupa survives the winter, and the adult emerges in
the. spring. The eggs laid shortly after give rise to a genera-
tion that reaches maturity in the summer. In many of such
species the spring form is often distinctly different from the
summer form in size, pigmentation, or pattern (see Fig. 123).

Experiments have shown that the so-called local races or varieties
of insects differ from each other chiefly, if not entirely, because of the
influence of temperature.

These examples of the influence of temperature on the life
of animals illustrate the irritability of protoplasm in a way that is
somewhat different from our earlier studies, and they illustrate
a different kind of response. Instead of getting a contraction or

288 ELEMENTARY BIOLOGY

a chemical reaction, we find that the effect of the temperature
is to produce a definite kind of organic behavior on the part of
certain portions of the animal or on the part of the animal as a
whole. This behavior is of a continuous kind, not momentary.

334. Light and development. Light influences the rate of growth
and the direction of growth in plants, and it influences the formation
of pigments in animals as well as in plants. But we know very little
about the influence of light upon the development of organisms, apart
from the influence upon growth. So far as studies have been made,
most organisms develop as well in darkness as in light, although all
protoplasm is sensitive to extreme light, which is fatal to bacteria of
many kinds and to other living beings that cannot protect themselves
adequately against the light rays. It is for this reason that the higher
organisms, which have opaque, or pigmented, exteriors, generally thrive
better in well-lighted places than in total darkness. Horses and cattle
kept in dark stables are exposed to more danger from bacteria ; human
beings that are kept in dark dwellings, workrooms, or underground
cellars or mines are exposed to more danger from bacteria.

335. Food and development. The amoimt of food received
by a plant or an animal at a given time — for example, early
in youth — has a greater effect than the amount received at
another time. If a calf has been underfed, he will have a
comparatively large head, long legs, and large joints. No amount
of overfeedi7tg later in life will even np the development. The
same is true of children. Underfeeding or unsuitable feed-
ing in infancy will not only stunt the growth, but will cause a
disproportionate growth which can never be made up later.

Experiments have shown that the character of the food will
in many cases influence the development of an organism in a
more direct way. Thus, the intestines of tadpoles fed on
vegetable matter, compared with the intestines of tadpoles fed
on more concentrated food, were found to be considerably
longer. This may be a case of stimulating the growth of a
special organ by overexercising it. In general, we should
expect a full development of all the parts of an organism only

CONDITIONS FOR DEVELOPMENT 289

when a suitable food supply — suitable in quantity as well as
in quality — -is provided. Overfeeding, especially in animals,
will affect the development, as well as underfeeding, by affect-
ing the health of the digestive organs or of the excreting
organs, or by leading to a deposit of fat in one or more organs.
Certain special substances, we have already found, may have
a direct influence upon the development as well as upon the
growth and activities of the body.

336. Chemical influences. The direct influence of chemical
substances upon the growth and development of organisms is
best observed in the lower plants and animals, in which there
is no great modification of the received material before this
reaches the protoplasm. Nevertheless we have already learned
that thyroid extract can influence the development of the body
of the frog (p. 285), and it is well known that a derangement
of the thyroid gland affects the development (especially of the
central nervous system) in human beings.^

Over forty years ago a Russian observer reported that two
species of a small crustacean of the genus Artemia could be
converted one into the other by a change in the amount of
salt in the water. The form that usually lived in the less salty
water acquired some of the characters of the other form on
being placed where evaporation increased the relative amount
of salt in the water. And the second form acquired some of
the characteristic structures of the first when placed in a brine
that was gradually diluted by the addition of fresh water.
Under natural conditions that sometimes bring about a gradual
dilution of sea water by rains, or a gradual concentration of
waters by evaporation, modifications in the development of
mollusks, arthropods, and other animals have been observed.
These modifications extend to forms, colors, shells, bristles,
and other parts. «■*

By changes in the chemical condition of the medium,
experimenters have made the eggs of certain fish develop into
animals having a single eye in the middle of the head ; and

290 ELEMENTARY BIOLOGY

other " freak " forms have been produced as a result of chang-
ing the external conditions of development.

337. Internal factors. In considering the conditions under
which development takes place, we have given attention chiefly
to the evidence that exceptional conditions will interfere with
or modify what we usually consider the normal course of
development. We must be on our guard, however, in respect
to two points :

1 . Whatever the possibilities of an egg, these possibilities can
become realities only under certain definite series of external
conditions. Thus, the egg of the frog or the fish must be in water
if it is to develop ; the egg of the hen must be kept above a
certain temperature if it is to develop at all ; and so on.

2. But the external conditions are not to be thought of as
the causes of the development, for by themselves they are not
the causes. The protoplasm inside a hen's egg, with the water
and salts and food in the egg, with the air that circulates
through the shell, with the temperature — all these factors
together cause the becoming of the chick. The fundamental
and distinctive factors are in the minute, invisible parts of the
protoplasm. The external conditions make the development
possible, but the nature of the plant or animal, or rather the
organic possibilities of the organism, are already present in
the protoplasm.

External conditions are related to development in several
different ways :

1. They may supply materials essential to the activities
of the protoplasm — for example, growth.

2. They may supply conditions for the chemical action of
the parts of the protoplasm, as moisture, heat, light.

3. They may stimulate the activities of certain parts of the
developing organism or certain of the chemical processes in
the protoplasm.

4. They may retard certain of the activities or processes,
or they may prevent certain activities.

CHAPTER LV

NEW ORGANISMS

338. Reproduction. One of the common facts about life is
that the Hfe of every organism comes to an end sooner or
later. Yet the species,
or kind, may continue
to live for centuries.
This is explained, of
course, by the fact
that new individuals
are constantly being
produced. The proc-
ess by which organ-
isms give rise to new
individuals is called
reproduction.

The term reproduc-
tion carries the idea
of a special portion of
the parent organism
being separated and
developing into an in-
dividual. The simplest

case of which we know is that of a cell division among one-
celled plants or animals. When such an organism (for example,
a Paramecium, or a Pleurococcus cell, or some bacterium) divides
into two, it at the same time reproduces. The number of indi-
viduals is thus multiplied by a process of division, or cell fission.
Cell division resulting in the multiplication of individuals occurs
among nearly all one-celled plants and animals.

Fig. 124. Yeast plant

The cells of this plant multiply by pushing out buds.
Under certain conditions the protoplasm of a cell
divides into two and then four parts, which then can
remain inactive for an indefinite time. These resting
cells are called fpores

292

ELEMENTARY BIOLOGY

339. Budding cells. In some organisms new cells are pro-
duced in a different way. The yeast plant, for example, which
absorbs its food from the surrounding liquid, continues to
grow indefinitely without undergoing cell division. When a
cell has reached a certain size, it puts forth one or several

Fig. 125, Spores in fungi

A : In the black molds, reproductive cells (spores) are formed by the repeated division of
the protoplasm in an enlarging cell at the end of a thread. When mature, the inclosing
wall breaks and the spores are scattered. B : In the blue molds, spores are formed by
the successive separation of terminal portions of the branched threads. This is a type
of fungus used in ripening Camembert cheese

swellings. As all of the exposed surface of the original cell and
of the buds absorbs food and water, the protoplasm grows, and
the buds may put forth buds in turn (see Fig. 5,5, and Fig. 124).
A bud sometimes drops down ; it then continues its growth
and its budding, like a new cell.- In an organism of this kind
the buds are to be considered as new cells or as parts of the
parent cell. It is a matter of chance when the bud drops off
and begins to live independently. This is another case of what
is called discontinuous growth (see p. 269).

NEW ORGANISMS

293

340. Spores. The

cells of yeast change
their behavior when
the yeast is growing
in a solution that is
gradually evaporat-
ing, or when the
food in the solution
is gradually being
used up, or when it
is exposed to an ex-
treme change in tem-
perature. It is often
found under such un-
favorable conditions
that the yeast plant
will produce peculiar
kinds of cells (see
Fig. 124).

A special cell like
those described in the
yeast (that is, a cell
capable of continu-
ing the growth of the
plant from which it
is derived) is called
a spore. Spores are
produced by nearly
all plants and by a
number of animals.

Fig. 126. Spore capsule of moss

a, spore case with stalk, on top of leafy plant ; ^, enlarged
view of spore case, with cap removed ; c, closed surface
of capsule tip after removal of cap ; d^ capsule bursting
open and discharging spores ; c, spores, greatly magni-
fied ; /, spore beginning to germinate by sending out
a fine thread of protoplasm, a, Thiddium virginianum ;

b, c, Fimaria americana ; d, Orthotridmm schimperi;
e, Bartramia pomiformis ; f, Funaria hygrometrica

The bacteria often
produce spores by the
formation of a rather thick cell wall when the conditions for growth
are not favorable. It is the resisting power of the spores that makes
it so difficult to kill certain species of bacteria by boiling.

294

ELEMENTARY BIOLOGY

All fungi, mosses, and ferns, and even the flowering plants,
produce spores in very large quantities (see Fig. 125).

The mosses produce spores in rather larger capsules on the
ends of very delicate but stiff stalks growing out of the top of

Fig. 127. Spores of fern

rt, back of a fern leaflet, showing arrangement of sori (singular, sorus), or clusters of
spore cases ; b^ section through a sorus, showing spore cases with inclosing layer of
thin tissue ; c, single spore case, greatly enlarged ; d, same bursting open and dis-
charging spores by the sudden straightening out of a row of thick-walled cells ; ^, spores,
greatly enlarged ; /, spore germinating into a new plant

the leafy stem. Ferns produce spores in little capsules found
in groups on the undersurface of the leaves, or, in some species,
right under the edge (Figs. 126 and 127).

341. Spores in animals. A number of one-celled animals
related to the ameba produce spores in a manner that can be
compared to the process described in the yeast plant. But the
number of spores produced is usually very large, and in some
cases the spores do not have thick walls, but are rather active.
The protozoon that is the cause of malaria is related to the
ameba, and is parasitic on the red blood corpuscles. When
the mass of protoplasm has grown to its limit, it breaks up
into a large number of pieces, and these are thrown into the

NEW ORGANISMS

295

blood plasma. The chill that accompanies this disease takes
place just at the time when the spores are being discharged.

342. Swimming spores. In many of the algae, cells may
break up into a number of spores (usually four), but these
differ from the spores of the fungi in having rather thin walls

Fig. 128. Swimming spores

In many of the chlorophyl-bearing water plants that do not produce seeds (algae), swim-
ming, or swarm, spores are produced. /, Chondrioderma diffoitiic ; 2, Confen<a bombycina;
J, Botrydhan gnmulatum ; 4, Haematococais pluvialis ; j, Chlorosphaera limicola

and in being provided with cilia, by means of which they swim
about in the water, suggesting minute animals (Fig. 128).

343. Cysts. There is still another kind of cell that may
be classed with the spores. This is formed by many protozoa
when the conditions for their usual activities are in some way
unfavorable. The protoplasm shrinks into a round mass, and
a thick cell wall, or cyst, is formed. In this encysted condition
the protoplasm may rest for an indefinite time, resisting the
unfavorable conditions. The animal may thus survive winters
or droughts, or perhaps escape destruction when taken into
the food tube of a large animal.

CHAPTER LVI
SEX

344. Conjugation in Paramecium. After reaching a certain
size the Paramecium will divide into two cells, and the new cells
will again divide, and so on for hundreds of times, when the
conditions are favorable. Under ordinary conditions, however,
this successive division does not continue indefinitely. After
a number of divisions the cells usually become smaller and less
vigorous, and then the strain is likely to die out.

Yet ordinarily the species does not die out. Sometimes two
individual cells come in direct contact, side by side, and stop
swimming. The two animals then exchange nuclear matter
(see Fig. 129). This process of exchanging nuclear material
and combining the nuclear material from two different cells is
called conjugatio7t (that is, a yoking, or joining, together).

After the conjugation the Paramecium cells seem to be
changed, since now they are better able than before to carry on
their growth and cell division. How the conjugation causes the
animal to take on its new lease of life is not understood, although
there are several theories offered to explain what happens.

345. Conjugation in Spirogyra. In the Spirogyra all the
cells that make up the threads may take part in conjugation,
when the conditions are right. The protoplasm of two cells
combines into a single cell that is capable of surviving condi-
tions unfavorable to growth (see Fig. 130).

346. Zygotes. In certain ways the cell resulting from the
conjugation of two cells is different from a spore. The im-
portant difference is in the way it originated. All the cells
which we have studied heretofore originated by the splitting,
or dividing, of some preexisting cell. The spores of yeast and

296

SEX

297

of other plants are the
result of the successive
divisions of the proto-
plasm of some preexisting
cell. But the sporelike
cell of wSpirogyra origi-
nated in the union of two
preexisting cells. This
conjugation product is
called a zygospore^ which
means a spore produced
by a joining together ; it
may be called a zygote
for short.

347. Gametes. The
cells that conjugate to
produce zygotes are called
gametes, which comes
from a Greek word mean-
ing '' to marry " — that
is, to join, or unite with.
In the case of the Spiro-
gyra, it is impossible to
tell, from the appearance
of the cells, which are to
become the resting, or
receiving, gametes and
which the moving, or
supplying, gametes. No
doubt there is some
difference in the chemical
conditions between the
two strings of cells, but
what the difference is
has not been found out.

Fig. 129. Conjugation in Paramecium

There are two nuclei : a, the small imicronucleus) ;
a.ndfi,the\a.rge(macronuctezis). A : Two individuals
become attached and their micronuclei begin to
divide. B : The half nuclei divide a second time.
Of the four units resulting, three are called polar
bodies, c, and the fourth is a germ nucleus, g,
which again divides. C : The germ nuclei "are
interchanged, one of each pair passing over to
the opposite animal. Z>, completion of the inter-
change. E, same, further enlarged. F, the active
germ nucleus fuses with the stationary one. G, same,
enlarged. In the meantime the macronucleus has
broken up and disappeared. After the restoration
of the micronucleus through fusion, F", the two in-
dividuals float apart. H: The new micronucleus, d,
breaks up into two. /, each portion splits again.
/, after a third division. /C: Four of the
nuclei become new macronuclei and four remain
as the micronuclei. The rest of the protoplasm
divides and four individuals result, each with a
micronucleus and macronucleus. (From Calkins,
after Hertwig, and Maupas)

298

ELEMENTARY BIOLOGY

Among some of the fresh-water algae the swimming cells
produced are of two sizes. In such cases the smaller cell is
usually more active in the water ; the larger cell has more food
material. In the common rockweed, or bladder wrack, of our

u

f ^
C

Fig. 130. Conjugation in Spirogyra

Cells lying close together put forth processes, or projections, toward each other, a. As
these processes finally come in contact, d, the two threads with their crosspieces have
the appearance of a ladder when looked at through the microscope, c. The cell walls at
the points of contact are dissolved, probably by the action of a ferment, and there are
thus formed continuous passages between the cells of one thread and the cells of the
opposite thread, d. In the meantime, however, changes have been taking place inside
the cells. The spiral ribbon of chlorophyl seems to break down, d; the mass of proto-
plasm in each cell draws away from the cell wall ; and the protoplasm from one of the
cells of each pair moves into the connecting tube and passes completely into the opposite
cell, e. Here the two masses of protoplasm unite into one, and a thick cell wall is formed
around the new combined protoplasm, /. The cell with the thick wall, inside the old
dead cell wall, may apparently remain in a resting state indefinitely, or may begin the
next day to put out a thread of new Spirogyra, giving rise to millions of cells in the
course of a few days

seacoast, the gametes are produced in special organs found on
certain of the bladderlike expansions of the plant body. When
formed, the gametes are discharged into the water and have
nothing more to do with the parent plant (Fig. 131).

348. Fertilization. When the two gametes are so unlike as
to be distinguishable, the process of conjugation is sometimes

SEX

299

called fertilization. The essential thing about fertilization is
the uniting of two different nuclei into one. What the meaning
of this process is in the life of organisms we do not know
with certainty. We know some of the effects of the process,
and we can tell what conditions lead up to it in some cases.

6 c d

Fig. 131. Reproduction in rockweed, or bladder wrack

a, expansions of the rockweed containing the gamete organs ; b^ section of an egg-bearing
organ ; <", the large gamete, or cgg^ with large, distinct nucleus and food granules ; d^ the
small gamete, or speim^ having the shape of a pear and bearing motile cilia. Sperms
swarm around an egg until one of them unites with the egg. After the conjugation the
zygote develops into a new individual

349. Male and female. The gametes that are so unlike as
we have seen them to be in the rockweed are distinguished
by special names. The large gamete is sometimes called the
obsphere, or ^gg cell. The small one is called the spermatozoid,
or the sperm cell. We sometimes distinguish the two gametes
by calling the large one the female and the small one the male.

Most of the familiar plants and animals reproduce by means
of male and female gametes, forming zygotes. This kind of
reproduction is called sexual reproduction, in distinction from
reproduction by spores, which is called asexual ; that is, without
sex. There are many animals and very many plants that repro-
duce both sexually and asexually (see Chapter LXI).

CHAPTER LVII
FLOWERS

350. What do flowers mean? We know that roots, stems,
and leaves, with their various parts, are more or less directly
related to the securing of water, food, and air, and to the pro-
tection of the organism against possible injuries. When we
examine the flower with a view to discovering its possible uses
to the plant, we shall find very little indeed. On the contrary,
we are likely to find the flower a source of expense to the plant,
without any compensation whatever. It takes a great deal of
material and a great deal of energy to build up a flower like
that of the poppy or the lily ; and so far as we can discover
by experiment or observation, the flower does nothing that is
of use to the plant. Are we therefore to conclude that the
flower has no meaning in the life of the plant ?

351. Structure of a flower. In most common flowers, such
as wild roses or tulips, we find certain leaflike parts that are
conspicuous because of their color. This set of conspicuous
leaflike organs is commonly associated with a less prominent,
cuplike arrangement of leafy structures, connected with the
base of the flower and partly surrounding the bright leaves
(Fig. 132).

Although the floral envelope is in most plants the first to
attract people's attention, it is by no means the most important
part of the flower. In order to understand the essential organs,
we must consider them from the point of view of the function
of the flower as a whole, which is the making of seeds.

352. The essential organs. In the center of the flower is a
structure called the pistil, from its resemblance in many cases
to the shape of a pestle (see/, Fig. 132).

300 -

FLOWERS

301

Surrounding the pistil may be found a number of rather slender
stalks, with knobs, or enlargements, on the ends (see d, Fig. 132).
These structures are called stamens^
from a word meaning '' thready."

Flowers differ greatly in size and
shape, as well as in color and odor.
The various parts differ in many
ways, but the pistil and stamen are
always and everywhere the organs
that have directly to do with seed-
making ; and their work is essentially
the same in all flowers, no matter
how varied they may be in form and
arrangement.

353. The ovary. On cutting open
the ovary of a flower we find that it
is a hollow box, with a number of
compartments in some species (see
Fig- I33)j containing from one to
very many tiny rounded bodies that
are normally destined to become
seeds. These bodies are called ovules.
As time goes on, these ovules en-
large, and the ovary also becomes
larger. When the seeds are ripe,
the ovary has become the fruit. But
the changing of ovules into seeds is
not simply a matter of growth. Every
farmer and gardener knows that it is
possible to have a good lot of flowers
or blossoms with a very poor crop of
fruit, although the conditions for the
growth of the plants may be of the
best, and although there may be no
sign that there is anything diseased or out of order with the plants.

Fig. 132. Structure of a flower

The outer set of covering leaves,
«, a, is called the calyx ; the single
parts are sepals. The inner layer,
b, b, is the corolla ; its parts are the
petals. The central organ is the
pistil; the main body of the pistil,
/, is the ova7y and contains one
or many little structures {ovtcles)
capable of becoming seeds. The
tip, <?, of the pistil is the stigma ;
this is connected with the ovary
by the style c. Surrounding the
pistil are a number of stamens, d,
consisting of a stalk, h, called the
filament, and an enlarged capsule,
g, called the anther. This con-
tains a mass of cells which can
be thrown out, i ; these loosened
cells are caWtA pollen

302

ELEMENTARY BIOLOGY

The inside of the ovule is a soft mass, made up of many
compartments, or cells, containing the jellylike living matter, or
protoplasm. One of these cells, usually near the center, is much
larger than the others (see es, Fig. 134). This large cell, called
the embryo sac, grows and divides and in time becomes the
young plant, or embryo, inside the seed. The rest of the ovule
becomes the coat, or covering, of the embryo.

354. Fertilization. Before the ovule can become a seed,
certain changes must take place in the living matter of the

embryo sac. The
nucleus of the em-
bryo sac must first
unite with the
nuclear substance
of a pollen grain.
The uniting of two
nuclei is called
fertilization. The
method by which
the two nuclei are
brought together is
shown in Fig. 134.

355. Seed and fruit. After fertilization the embryo sac,
which now contains protoplasm from two parents, divides into
very many cells. It absorbs food in large quantities from the
parent upon which it is borne, and becomes a baby plant, or
embryo (see Fig. 120). The walls of the ovule, surrounding
the embryo sac, become the seed covers. The ovule with its
embryo sac thus changes into a seed. In addition to the food
used in the growth of the embryo, the parent plant supplies
other food materials that are accumulated either in a mass
surrounding the embryo, or within the tissues of the embryo
itself. This surplus food may later be drawn upon by the
young plant, after it sprouts and before it is able to maintain
itself through the work of its own leaves and roots.

Fig. 133. Sections of ovaries

Ovaries are of many sizes and shapes. They contain but a

single ovule in some species of plants, and in other species

they bear hundreds. The ovules are definitely placed in

one or more compartments of the ovary

FLOWERS

303

Fertilization also seems to in-
duce changes in other parts of
the flower. The petals drop off,
and usually the stamens also.
The ovary begins to enlarge,
and eventually it ripens into the
fruit.i In some plants the calyx
of the flower, and even the re-
ceptacle, may become fused into
the fleshy fruit.

We must be on our guard
against thinking of the plant as
an organism that looks ahead and
supplies the later needs of its off-
spring. We may say merely that
the plants behave in such a way
that the later safety and develop-
ment of their offspring are made
more probable. The baby plant is
protected by the mother, as well
as nourished, in the sense that
the early development takes place
within the ovary, and in the sense
that in many species hard or spiny
coverings are formed which prob-
ably prevent injury.

1 In most of the common plants the fruit
will not ripen — that is, the ovary will not
continue its development — unless fertili-
zation takes place. But there are many
plants in which a seedless fruit is possible.
Seedless oranges, seedless apples, seed-
less grapes, the pineapple, and the banana
are examples of fruits that develop without
the ovule being first fertilized. The plan-
tain and the breadfruit develop a more
juicy fruit when there is no fertilization.

Fig. 134. Fertilization in a flower

When a pollen grain,/, alights on the
moist surface of a stigma, s, it absorbs
water and puts forth a thread of proto-
plasm, or a pollen tube, />i, which grows
down the style into the ovary. The tip
of the pollen tube finds its way to the
inside of the ovule, 0, through a small
passageway, the micropyle, m. The
large cell in the middle of the ovule,
called the embryo sac, es, undergoes a
number of changes which result in pro-
ducing several nuclei. One of these
nuclei at the end nearest the micropyle
corresponds to an egg cell. Similar
divisions take place in the nucleus of
the pollen grain, and one of the result-
ing nuclei corresponds to a sperm cell.
The cell walls separating the pollen
tube and the embryo sac dissolve, and
the pollen nucleus unites with the egg
nucleus. The newly formed joint nu-
cleus, or fertilized egg, begins to divide.
The embryo sac develops into a new
plant, or embryo ; the ovule becomes
a seed ; the ovary becomes a fruit

CHAPTER LVIII

POLLENATION

356. Function of poUenation. We have learned that flowers
are seed-producing structures, and that seed production takes
place only after fertilization. But in seed plants (most of which

are land plants)
the parts of the
organism which
bear gametes
are so situated
that fertiliza-
tioa is possible
only after pol-
lenation ; that
is, the transfer
of pollen from
the anthers to
the stigma. In
these plants re-
production de-
pends in a
rather peculiar
way upon cer-
tain external
factors.
357. Self -poUenation. In many plants the transfer of pollen
is brought about by the growth movements of the parts of the
flower. The style, in elongating, may bring the stigma into
contact with the anthers ; a movement of the corolla may
push the stamen against the stigma ; the stalk of the flower

304 -

Fig. 135.

Dimorphic flowers of Chinese primrose
{Primula)

In these plants there are two forms of flowers (hence the term
dimorphic). In form A the anthers are high and the stigma is
low ; in form B the anthers are low and the stigma is high. The
pollen from form A is prepotent for the pistil of form B, and
vice versa. That is, long-stamen pollen must reach long-style
pistil, and short-stamen pollen must reach short-style pistil, to
produce the best or the most seeds. This necessitates cross
poUenation, or at any rate handicaps close poUenation

POLLENATION

305

Fig. 136. Polymorphic flowers of purple loosestrife
{Ly thrum)

In species having three forms of flowers the best seed-
production seems to result from the pollenation of a pistil
by pollen from a stamen of the corresponding length,
which must necessarily be from a different flower, (After
Darwin)

may bend as it grows, dumping some of the pollen from
the anthers onto the stigma. In other cases the anthers are

placed above the
stigma, so that the
pollen is brought to
the latter organ by
the action of gravity.
There are many
plants in which the
stigma regularly
pushes through the
ring of anthers and
thus becomes pol-
lenated. In other
plants this kind of
pollenation takes
place only under
special conditions, as in extreme dampness or extreme drought.

358. Close pollenation and cross pollenation. Any process
that results in the transfer of pollen from the anther of a flower
to the stigma of the same flower is called close pollenation.
This designation is used to

distinguish the process from
cross pollenatiofiy in which
pollen is carried from the
anther of one flower to the
stigma of another flower (of
the same kind, however).
There are many plants in
which close pollenation is
impossible.

359. Obstacles to close pollenation. There are three sets
of conditions in plants that interfere with close pollenation.

I . Space relations. The relative position of stamens and pistils
within the flower may make close pollenation impossible. Or the

Fig. 137. Stigma of a grass

In wind-pollenated plants the stigmas usually
expose a large surface to the wind

3o6

ELEMENTARY BIOLOGY

stamens may be in one flower and the pistils in a different
flower, either on the same plant or on a different one.

Some common monxcious plants (that is, plants having the stami-
nate and the pistillate flowers on the same individual) are birch, hazel,
chestnut, oak, walnut, hickory, squash, maize, and the cone-bearing trees.

Some common dicecious plants are poplar, willow, box elder, tape-
grass ( Vallisnerid), begonia, sassafras, and virgin's bower.

Fig. 138. Pollenation by water

The tape-grass ( Vallisnerid) is a dioecious water plant. The pistillate individual grows up
to the surface of the water, where the flowers, a, are opened, while the staminate indi-
vidual remains beneath the surface. The staminate flowers, b^ are detached from the
stalks and rise to the surface, where they float about and gather in large numbers in the
quiet stretches of water close to solid objects of various kinds. When one of these float-
ing stamen flowers comes close to the pistillate flower of the species, the anther is brought
into direct contact with the stigma, and thus pollenation is effected

2. Time relations. The stamens and pistils of some species
of plants do not ripen at the same time, close pollenation
being thus impossible in these species.

The pollen ripens before the pistil in maize, in the mallows, in
many species of the aster family, in the creeping crowfoot, and
in the sage.

The pisrils ripen ahead of the stamens in the common plantain,
in the potentilla, or cin.quefoil, and in the oriental grass known as
Job's tears.

POLLENATION

307

3. Physiological relatio7is. In some species of plants it is
found that when the pollen is placed on the stigma of the
same flower, it will either not germinate at all or it will produce,
on the whole, poorer seeds than those produced by means of pol-
len taken from another flower. This physiological difference
in favor of outside
pollen is called /r^-
potency, and was
demonstrated by
Darwin in several
species of plants.

Prepotency is com-
monly associated with
the presence of two or
three lengths of styles
and of filaments.

In the flax, cow-
slip, Chinese prim-
rose, bluet, and other
species there are two
forms (Fig. 135).

In the purple loose-
strife {Ly thrum sali-
carid) and in certain
species of Oxalis (re-
lated to our sorrel)

there are three lengths of stamens and three lengths of pistils (in
different flowers) corresponding to them (see Fig. 136).

In buckwheat, in most orchids, in certain species of day lily, and
in certain species of the bean family the pollen will not germinate at
all on the stigma of the same flower.

Fig. 139. Pollenation by birds

Saber-billed humming bird pollenating flower with trumpet-
shaped corolla. (From exhibit in American Museum of
Natural History, New York)

There are, then, many species of plants in which close
pollenation cannot take place, or in which it is not very effec-
tive if it does take place. How, then, do these plants produce
seeds, or, rather, how do they secure pollenation 1 In other
words, how is pollen carried from flower to flower }

3o8

ELEMENTARY BIOLOGY

Stigma

360. Wind poUenation. The most common moving agency
that is able to act between plant and plant is the wind. The
abundance and the dryness of the pollen produced by many of
the common trees, and the frequency with
which pollen may be found in the dust at
certain seasons of the year, would lead us
to suspect that the wind is an effec-
tive agent in this matter (see Fig. 137).
A study of conditions on farms that pro-
duce corn, wheat, oats, and other grains
shows that these plants, as well as many
others, depend entirely upon the wind for
their pollenation. Indeed, it is sometimes
necessary to take special precautions to
prevent the wind from bringing to a
group of plants an undesirable kind of
pollen from a remote field.

361 . Water pollenation. Another agent
that is effective in distributing pollen for
plants is water. This, of course, is con-
fined to plants that live in the water.

Fig. 140. Pollenation
by insects

In the lady's slipper and
in many other flowers, in-
sects alighting on the co-
rolla crawl into the interior,
guided by the form and the
markings. In many flowers
the arrangement of the
parts is such that the in-
sect must brush against the
stigma in going in, and
against the anthers in pass-
ing out. As a result the
animal carries pollen from
flower to flower. Many
species of plants, especially
among the orchids, depend
upon single species of in-
sects for their pollenation

A good example of pollen transfer by water
is furnished by the tape-grass {Vallisnerid),
which lives near the edges of ponds (see
Fig 138).

362. Bird pollenation. Next to the
wind, the most common moving agents
that go from flower to flower are flying
animals and birds and insects. Now we
know that not all birds or all insects can serve plants as
pollen carriers ; only those that regularly visit flowers can
be considered of importance in this connection. Certain
humming birds that visit flowers lap up the sugary fluid, or

POLLENATION 309

nectar (see Fig. 139), and rub off some of the pollen in one
flower, and when they visit another flower this pollen comes
off onto the stigma.

Certain tropical flowers are said to be pollenated by bats that come
to them for nectar.

363. Insect pollenation. There are hundreds of species of
plants whose flowers are pollenated by insects, chiefly bees
and wasps of the bee order, and certain moths and butterflies.
All of these insects have sucking mouths, and they all visit
flowers that contain nectar. Some of these insects also use
pollen as food. The bees, for example, carry away quantities
of pollen, which they feed to the young in the hives. In
gathering the pollen or in sucking the nectar the insects rub
off pollen on various parts of their bodies, and then transfer,
this pollen to the stigmas when they visit other flowers of the
same kind (see Fig. 140).

CHAPTER LIX
ADAPTATIONS OF FLOWERS

364. Colors and odors. In many species of plants the colors
and odors of the flowers are no doubt of value to the plants
as furnishing aids to insect visits, and thus to the process of
pollenation. It is a mistake, however, to suppose either that
all colors and odors are of value to the plants in this way or
that there is any necessary connection between the existence
of these colors in the flowers and the habits of the insects.
There are many plants that have colored corollas and that do
not depend upon insects at all. And there are other plants
that receive the visits of insects without being particularly
conspicuous.

365. Nectar. While many insects will visit plants for the
nectar, there are many plants that produce nectar in positions
that make it impossible for the visits of insects to be of any
use to the plants. Indeed, there are certain ferns and some
seed plants that produce nectar on the stems or leaves, so
that the plants get no benefit whatever from the visits of
insects to these nectaries.

366. Fitness. We are not to suppose that the plants produce these
queer shapes in their flowers, or the colors or odors, for the special
purpose of attracting insects. Nor are we to suppose that the insects
visit the flowers for the purpose of carrying pollen, or for any other
purpose. Bees will fly toward nectar or honey, houseflies will fly
toward manure or decaying fish, moths will fly toward a light, not
because they have the idea of getting something they want, but
because they are built in a certain way.

It is interesting to note in this connection that while insects cannot
distinguish objects at any great distance, — say at more than about

310

Fig. 141. Pollenation of the fig

The larva of the little wasp Blastophaga paSses the winter in the sterile pistil, /j, of the
winter fruit, a^^ of the caprifig, A. In the spring the adults appear, the wingless male
first. After fertilizing the female, the male dies. The female flies out and crawls into
the new figs which are just forming, «.2, and loses her wings in the process. This fig
carries both stamen flowers and pistil flowers, but the latter have short styles and can
bear no seeds. The insect lays her eggs in these sterile pistils, and the young complete
their development here. When the new generation of females flies out, there is a new
growth of fig buds on the caprifig, a.^^ and also on the true fig, b on B. Some of the
females find their way into the caprifig receptacles, and some into the fertile-fig recep-
tacles, carrying with them pollen from the spring receptacle of the caprifig, «2- The
pistils of the true fig have long styles, p^, which can be pollenated. The styles are so
long, however, that the insect cannot lay her eggs on the pistil. On the other hand, the
pollen brought into the receptacle of the caprifig, a;}, is entirely wasted, since the pistils
here are sterile. A new generation of insects develops in this receptacle, and the
emerging females find their way into the autumn growth of new figs, in which the
winter is spent. The true figs can thus produce fully ripened fruit only in the presence
of the caprifig and of the wasp. But the wasp can complete its life cycle with the caprifig
alone. The insects that carry pollen (from a.^ either waste this pollen and reproduce
themselves (in ag) or they poUenate pistils and die without reproducing themselves (in b)

312 ELEMENTARY BIOLOGY

two to three yards, — they will nevertheless visit only one kind of
flower in the course of a day, or even for many days running. Thus,
if a bee starts out in the morning by visiting a red clover, it will visit
only red clovers for the rest of the day, or as long as any red clovers
are to be had.

367. The interdependence between flowers and insects. In

some cases the relation between a seed plant and some insect
is so close that it affects the practice of plant raisers.

When fig trees were first introduced into California, they
produced large, juicy fruit, even without pollenation. But the
fruits thus produced are not as satisfactory for commercial
purposes as the others : they do not dry properly, and so
cannot be prepared for shipping or for preservation. To get
the normal fruit it was necessary to find the insect that
regularly brings about pollenation. This little wasp, the Blas-
tophaga, has a curious life history which is closely adapted
to the flowering habits of the fig tree. On the other hand,
thousands of fig pistils supply breeding places for wasps
without ever producing seeds (see Fig. 141). Thus the insect
and the fig tree are of great value to one another, although
it is difficult to see what advantage either species has in its
dependence upon the other. It is quite impossible for us, at
present, to imagine how this relationship came to be established
in the course of time.

There are many cases of plants that have been transferred
from one region of the earth to another, and then failed to
bear seeds because of the absence of the suitable insect.

When vanilla was transplanted from Mexico and South
America to various islands in the Indian Ocean and else-
where, the plants grew luxuriantly, but produced no fruit,
although flowers were produced in abundance. Since the
plant was raised for the ''beans" or pods, there was no profit
in the business so long as the fruit failed to develop. It was
found that the failure was due to the absence of pollenation,
which is brought about in the native regions by certain insects.

ADAPTATIONS OF FLOWERS

313

Instead of importing the insects to carry on pollenation, it was
decided to hire women and children to go from flower to flower
and pollenate by hand
(see Fig. 142).

In our regular horti-
culture it happens occa-
sionally that trees or
bushes in full blossom
fail to yield the expected
crop of fruit because of
the lack of insects to in-
sure pollenation. This is
why wise farmers and or-
chardmen so often main-
tain hives of bees in the
neighborhood of their
fields or orchards. Even
where the honey is not
worth getting, the bees
are worth having because
they insure abundant pol-
lenation at the right time.

Fig. 14:

Hand-pollenation in the vanilla
flower
368. Advantage of insect
pollenation doubtful. In a
general way the lower fam-
ilies of seed plants are
wind-pollenated, and the
higher families are insect-
pollenated. But it must not
be supposed that there is
any real advantage to plants
in depending upon insects
to carry their pollen. In

many cases we may see that there is an actual saving of pollen.
On the other hand, many species of plants, especially among the
orchids, are so dependent upon the insect visits that they are dying

In the orchids the stamens are fused with the
stigma, placing the anthers above the stigma in
such a way as to make self-pollenation absolutely im-
possible, an, anther ; /, pollen masses ; s, stigma.
A, general view of flower ; B, position of hands
and needle in artificial pollenation ; C, needle lift-
ing pollen masses ; Z), anther raised to expose
pollen masses ; E, style raised to show opening in
stigma; F, longitudinal section to show relative
positions of anther and stigma ; G, longitudinal
section after pollenation, showing pollen masses in
the stigma. All the vanilla beans in the Seychelles
Islands are grown with hand pollenation

314 ELEMENTARY BIOLOGY

out just because of the inability to produce sufficient seed to replace
the old individuals, the suitable insects not being numerous enough.
In general, the plants that are most decidedly dependent upon the
wind for their pollenation seem to be at least as successful as those that
are dependent upon insects. Thus, the grasses and the common catkin-
bearing trees and the cone-bearing trees are widely distributed over
the surface of the earth, and none of the insect-pollenated plants seem
to have any decided advantage over them.

The insects that are able to get food from highly specialized flowers,
because of their peculiar instincts or structure, may seem to have some
advantage over insects that cannot make use of those particular flowers.
Nevertheless we find it extremely difficult to understand what advan-
tage a species may derive from such extreme adaptation, since such
dependence often leads to complete extermination (as in the case of
Blastophaga in the absence of fig trees), and in any case means pay-
ing a high price for benefits received.

CHAPTER LX

FRUIT AND SEED DISTRIBUTION

369. Seed as forerunner. We have studied seeds as arising
from the ovules in flowers (pp. 300-303), and we have studied
them as consisting of
young plants with more
or less accumulated food
and a covering (pp. 32-
36). We can realize the
full meaning of seeds in
plant life when we con-
sider that during the
winter the fields are bare
and thousands of plants
have entirely perished,
leaving behind them
the seeds as the only
living remains. It is
these seeds that repre-
sent the species of all
the annuals during the
months in which active
plant life is impossible.
And it is from the seeds

that these species will be reestablished the following season
when the conditions for growth are again favorable.

From the point of view of the seed as the forerunner of
the new generation, the fruit may be considered in relation
to the protection and the dispersal of seeds, since the fruit is
the organ within which the seed ripens.

315

&w

Fig. 143. Mechanical protection of seeds

7, bitternut {Hicoria minima)^ of the walnut family ;

2, chestnut oak {Qiiercus prinus) ; j, sweet gum

{Liquidambar siyracijiua), of the witch-hazel family ;

4, table-mountain pine {Pitius pingens)

3i6

ELEMENTARY BIOLOGY

370. Protection of seed. As living things seeds are exposed
to destruction by other plants or by animals and to injury
by inorganic factors of the environment, as excessive low tem-
perature and excessive moisture or drought. We find many
fruits covered with spines ; others have hard or tough cover-
ings or shells ; still others contain bitter or acrid substances.

Fig. 144. Dehiscent fruit

Seeds are scattered by the opening of the fruit in a definite way. /, chestnut ; 2, witch
hazel; j, poppy; 4, pea; j, monkshood

Seeds that become separated from the fruit are frequently
tough-skinned or covered with some other protective layers
(see Figs. 7 and 143).

371. Escape of seeds. The seed attached to the parent
plant and surrounded by other structures is of no significance
in the life of the species. To be in a position to perform its
functions, the seed must get out and get away — and the
farther away the better, in most cases.

Many common seeds escape from the parent plant through
the splitting open of the ripe fruit along definite lines or by

FRUIT AND SEED DISTRIBUTION

317

the appearance of holes. The pods of the bean family and
of the evening-primrose family illustrate this dehiscence, and
the poppy is a good example of the formation of pores.

Fleshy fruits often drop off, carrying the seeds with them,
and the seed escapes when the fleshy part of the fruit is eaten
by some animal or rots (that is, is eaten by some plant).

Fig. 145. Seeds scattered by the wind
/, dandelion ; 2, milkweed ; j, white maple ; 4, prickly lettuce ; 3, thistle

Many fruits, however, do not permit the seeds to escape ;
the fruit and the seed are so closely united that they constitute
a structure that acts as a whole — as in the grains, the nuts,
and the nutlets of the dandelion family.

372. Seed distribution. In their dehiscence many fruits
open so suddenly that they shoot the seeds to a distance of
a yard or more. This shooting is commonly brought about
by the rapid twisting of the parts of the pod, as in the touch-
me-not and the lupine (see Fig. 144).

Most plants depend upon outside agencies to scatter their
seeds for them. The wind is active in the case of species
whose seeds are either very small (the orchids) or have

318

ELEMENTARY BIOLOGY

expansions in the form of wings or tufts of hair that furnish
a large area in contact with the air (see Fig. 145).

Seeds that have hooks, as the cocklebur and beggar-ticks,
attach themselves to the fur of passing animals and are carried
considerable distances from the parent plant (see Fig. 146).

Fig. 146. Seeds scattered by passing animals

/, beggar-ticks, or bur marigold {Bidensf rondos a) ; 2, burdock {Lappula echinata) ; j, small-
flowered agrimony {Agrimonia patvi/lora); 4, carrot {Dauciis carota); s, enchanter's night-
shade {Circaea luteiiana) ; 6, cocklebur {Xanthium canadensis) ; 7, bur grass {Ccnchrus
tribuloides) ; 5, spike rush {Eleocharis ovata)

Seeds that are inclosed in edible fruits are often distributed
by being eaten by animals and then discharged from the intes-
tines without having suffered any injury. Cherries, black-
berries, and other small fruits are commonly distributed by
blackbirds, robins, thrushes, and other bipds (see Fig. 147).
From the point of view of the species, there are three
factors in seed dispersal that are of fundamental importance :
(i) the number of seeds that are scattered ; (2) the distance to
which they are carried ; and (3) the final lodgment in a place
favorable to germination and later growth and development.

FRUIT AND SEED DISTRIBUTION

319

It is obvious that the more seeds there are scattered, the
better are the chances that enough of them will find suitable
lodgment to replace the individuals that die each year. On
the other hand, to produce excessive seeds would be wasteful,
and might under
some circumstances
neutralize the ad-
vantage of num-
bers. Thus the
orchids, producing
relatively many
seeds, lose many ;
only a very small
proportion of them
ever develop into
new plants. On the
whole, the plants
that depend upon
the wind to scatter
their seeds seem
to maintain them-
selves and to invade

new regions more successfully than those that depend upon
other agencies for scattering the new plants.

Many plants have their seeds distributed by currents of
water, — streams of various sizes, or ocean currents, or wind
currents acting on the water. Seed plants that grow in swamps
or ponds are commonly dependent upon water currents for
the dispersal of their seeds. But it seems that many seeds
are also spoiled by the water. The coconut, for example,
which is often cited as a plant that invades ocean islands by
being carried over the sea, is really killed by the salt water.

9<»

Fig. 147. Seeds scattered by birds

Birds eat the fruit and discharge the indigestible seeds.
/, thistle ; 2, mistletoe; s, bird cherry; 4, red-osier dogwood

CHAPTER LXI
ALTERNATION OF GENERATIONS

373. Life history of a moss. In the moss plants, the individuals that
we ordinarily have in mind when we speak of moss bear at the end of
a leafy stem a group of sexual organs. Some individuals carry egg-
producing organs ; others bear sperm-produCing organs (see Fig. 1 48).

Fig. 148. Reproduction in moss

a, a leafy moss plant {Hypnum molluscum) ; b, section cut lengthwise through tip of one
of the branches, showing position of archegonia^ or egg-bearing organs ; c^ single arche-
gonium, more highly magnified, showing single large egg cell ; d, enlarged view of
antheridium, or sperm-bearing organ, of Polytrichwn formosum^ discharging sperm cells ;
e^ greatly magnified view of sperm cells ; /, tip of leafy plant from the archegonium of
which a spore plant has grown, showing stalk and spore capsule
320

ALTERNATION OF GENERATIONS

32

When the moss is covered over with water, it is possible for the male
gametes to swim about, and some of them find their way into the
archegonium. Here one of the sperm cells fuses with the egg cell,
and the fertilized egg cell begins to develop into a new moss plant
immediately — that is, while still within the body of the parent.

Fig. 149. Alternation of generations in the life history of the moss

G, the gametophyte, or gamete-bearing plant ; /, the female gamete organ ; m, the male
gamete organ ; e, the fertilized egg resulting from the fusion of egg and sperm ; S, the
sporophyte, or spore-bearing plant ; s, spores. The spore always develops into a gameto-
phyte ; the gametes (egg) always give rise to a sporophyte. G and .S represent alternate
generations that reproduce in different ways, — the first sexually, by means of gametes,
the second asexually, by means of spores

But the new plant is very different from the parent plants. It has
no leaflike organs or anything to correspond to leaves. It consists
mainly of stalk, and at its base it is buried in the tissues of the parent
plant, from which it gets most of its nourishment. It is therefore
parasitic upon the parent to a large extent. At the end of the stalk
a capsule is formed, and when this is ripe, a great many spores are

322

FXEMENTARY BIOLOGY

thrown out of the opened top. When one of these spores alights
upon a moist spot, it absorbs water, and the protoplasm breaks out
on one side ; it then proceeds to develop into the next generation.

Here again we must notice that the new plant developed from the
spore is not at all like the parent plant ; that is, the plant which

produced the spores.
At first there is a
very delicate, green,
branching thread, re-
sembling some of the
green algae found in
water. In a short
time a clump of cells,
or a bud, appears at
some point along this
branching thread, and
from this develops
the leafy stalk that
we recognize as moss,
and some colorless,
hairlike threads that
look very much like
root hairs.

The leafy moss
plant, bearing gamete
organs at the top,
is called a gatneto-
phyte, which means
a gamete plant. The
leafless plant, con-
sisting of stalk and
capsule, together with the attachment to the parent, is called the
sporophyte ; that is, spore plant. By following the history of a
number of generations of moss we may see that there is a regular
alternation of gametophyte and sporophyte. This is illustrated in
the diagram (Fig. 149).

374. Life history of a fern. In the ferns the spores are produced
on the underside of the leaves (see Fig. 127, p. 294). The spore gives
rise to a little plate of chlorophyl-bearing cells, sometimes no larger

h « c

, Fig. 150. Reproduction in fern

The gamete-bearing plant, «, of the fern, called aprothallns,
is a flat plate of cells, with hairlike roots on the undersur-
face. Flask-shaped organs, /;, each bearing a single egg
cell, are embedded on the undersurface, near the notch,
with the mouth pointing downward and backward. Near
the small end of the prothallus, on the undersurface, are
the organs, c, bearing the male gametes. These are dis-
charged into the water, and swim about freely, finding their
way into the egg organ, where fertilization takes place

ALTERNATION OF GENERATIONS

323

than the nail of your little finger, called 'a pi'othallus (see Fig. 150).
Prothalli are often found growing on flowerpots in greenhouses.

The prothallus corresponds to the gametophyte of the moss, while
the plant which is familiar to us as the fern is a sporophyte. The

Fig. 151. Alternation of generations in the life history of the fern

G, the gametophyte, or gamete-bearing plant ; /, the female gamete organ ; w, the male
gamete organ ; c^ the fertilized egg. 5, the sporophyte, or spore-bearing plant ; j-, the
spores discharged by the spore-bearing organ. The spore develops into a gametophyte ;
the gametes (egg) always give rise to a sporophyte. The alternate generations repro-
duce in different ways, — one by means of gametes, or sexually, the other by means of
spores, or asexually

spore always gives rise to a prothallus, which bears gametes. When
fertilization has taken place, the zygote formed develops not into
another prothallus but into a sporophyte. The diagram in Fig. 151
shows us the alternation of generations in this group of plants.

324 ELEMENTARY BIOLOGY

In some plants related to the ferns the two kinds of gametes are
borne on two different individuals ; that is, each individual gameto-
phyte is either male or female. In such species each spore therefore
gives rise either to a male plant or to a female plant, as is the case
with the moss. It is impossible in such cases to find any difference
between the spores that give rise to male plants and the spores that
develop into female plants.

375. Heterospory. But there are other plants related to the ferns
in which two different kinds of spores are produced, — a large spore
and a small spore. In such species the large spore always develops

Gm Gm

Fig. 152. Heterospory

Plants producing spores of two sizes, Is and ss, give rise to two distinct forms of sexual,
or gamete-bearing, individuals, female and male, G/ and Gm. The gametes, /and m,
unite to form the zygote, 2, which develops into the spore-bearing plant, 6'. There is
an alternation between the sexual (gametophyte) and the asexual (sporophyte) generation ;
and there is a differentiation between male and female gametophytes, and, finally, a differ-
entiation between two types of spores. The next step would be to have two kinds of
sporophytes, S, one bearing large spores and the other bearing small spores ; and,
indeed, there are plants in which this condition is found

into a female gametophyte, while the small spore always develops into
a male gametophyte. There are thus two kinds of spores as well as
two kinds of gametes (see Fig. 152).

376. Alternation of generations in seed plants. The pollen grain
corresponds to a small spore ; that is, one that gives rise to a male
gametophyte. The embryo sac is really a large spore, one that can
give rise to a female gametophyte. In seed plants the small spore is
scattered, as in ferns and mosses ; but the large spore remains in the
spore case — the ovule. The male gametophyte is a very much sim-
pler organism than we have found in mosses or ferns ; it is, in fact,
the simple pollen tube. It is incapable of nourishing itself, but lives
in part on the nourishment stored up in the pollen grain and in part
on material absorbed from the stigma. The only distinct organ that
it has is the divided nucleus that acts as a gamete.

ALTERNATION OF GENERATIONS

325

The female gametophyte is still further simplified, for it never gets
out of the spore wall. It is nourished altogether by the parent plant,
and its activities are confined to the dividing up of the nucleus, finally
separating the portion of nucleus that is to act as the female gamete.

Fig. 1 53. Alternation of generations in seed-bearing plants

Gw, the male gametophyte, or pollen tube ; w, the male gamete, a nucleus at end of pollen
tube ; G/, the female gametophyte, or embryo sac ; /, the female gamete, a nucleus in the
embryo sac ; ^, the fertilized egg, or embryo sac ; Si, young sporophyte, the embryo in
the seed ; ^2) the mature sporophyte, a flower-bearing plant ; s^, the large spore, giving
rise to the female gametophyte, or the embryo sac. S2, the small spores, or pollen grains,
giving rise to the male gametophyte. The spores always give rise to gametophytes, and
the gametes (producing a fertilized egg) always give rise to sporophytes. Sporophytes
alternate with gametophytes, generation after generation

Our common seed plants are accordingly seen to be sporophytes^ or
spore-bearing plants. The alternation of generations of these plants
is illustrated by the diagram in Fig. 153.

326

ELEMENTARY BIOLOGY

377. Alternation of generations among animals. Among
some of the animals related to the sea anemone and hydra
there is found a fairly regular alternation between generations
that reproduce sexually — that is, by means of gametes — and
generations that reproduce asexually. Good examples of this
alternation are furnished by jellyfish found in the ocean off

Fig. 154. The jellyfish aurelia

The mature medusa, a, reproduces sexually, the gametes being thrown into the water,
where fertilization takes place. The egg develops into an individual having the general
form of a hydra, ^, and attaches itself to a rock. The animal elongates and breaks up
into a number of individuals by means of constrictions, so that it comes to resemble a
pile of bowls. Each individual, when separated, turns over and swims away, changing"

into a medusa, a

our coasts (see Figs. 154 and 155). The complete life history
includes both kinds of individuals, male and female, and two
kinds of generations, sexual and asexual.

Alternation of generations is also found in many parasitic animals,
especially parasites that inhabit two or more different hosts at differ-
ent stages in their development. Thus, the malarial parasite repro-
duces in the blood of human beings by sporulation ; that is, by the
formation of a large number of spores. But in the body of the mos-
quito there are produced tiny protoplasmic structures that unite in
pairs ; that is, they conjugate. There is thus present a sexual method
of reproduction and an asexual method, and these alternate regu-
larly so long as the organism has the opportunity to pass from one
host (man) to the other (mosquito) and back again (see pp. 403-407
and Fig. 209).

CHAPTER LXII
REPRODUCTION IN ANIMALS

378. Aquatic invertebrates. Among the invertebrate ani-
mals — that is, those having no backbone — hving in the
water, such as sponges, corals, starfish, clams, and crayfish,
fertilization usually takes place outside the body of the parent.
In the cases of many, however, the developing egg cell may be
protected by some portion of the mother's body, as when the
young hatch in the mantle cavity of the clam.

379. Reproduction in fishes. Among the fishes, the female
gametes are usually deposited in quiet places at the bottom of
the sea, near shore, or in quiet pools of rivers. Then the male
fish swims over the eggs, dropping out a quantity of fluid con-
taining the sperm cells. These swim about in the water, fer-
tilization taking place in much the same way as in the rock-
weed (see p. 299). The fluid containing the sperms is called
mill, or semen. A sperm cell of a fish is illustrated in Fig. 156,^.
As soon as the nucleus of the egg has fused with the nucleus
of the male gamete, the combined nucleus begins to divide, and
thus the development of a new fish is started.

The female gamete of the fish contains a small amount of
food material in addition to the protoplasm. While the devel-
opment is under way the young fish lives on this accumulated
food. In some species of fish the adults swim about in the
neighborhood of the developing fry and protect them against
possible destruction by other fish. In most species, however,
the sperm and eggs are thrown out by the adult males and.
females, and then left to themselves. Thus exposed, thousands
of eggs are destroyed before they have a chance to develop
into fish. Of course, thousands are also destroyed in the case

327

328

ELEMENTARY BIOLOGY

of those species that protect their young ; but it is not probable
that in these species so large a proportion are lost.

380. Water essential to gametes. As we have seen, sexual
reproduction is possible only on condition that two gametes of
opposite sex combine. In addition to producing the gametes,
the bringing of them together is another problem of life.

Moreover, the sperm and
egg cells (gametes) are
unlike spore cells in that
they are quite incapable of
resisting drought ; drying
kills them very quickly.
It is therefore another
condition of reproduction
that the gametes be pro-
tected against drying up.
Among the animals and
plants that live in the
water, or where water may
remain in contact with
their reproductive organs,
this is simple enough.
But in organisms that
live on land, or in the
air, the older methods
of bringing, the gametes
together will no longer serve. We have seen how this con-
dition is met in the case of the flowering plants. Among
land animals there are special organs and modes of behavior
that make fertilization possible.

381. Reproduction among batrachians. The frogs, which
live on land and breathe air in their adult state, go to the
edges of ponds and puddles at the breeding season. After the
gametes are thrown into the water, fertilization takes place, and
the adult frogs pay no further attention to them.

Fig.

55. Hydromedusa [Bougainvillea
ramosa)

rt, enlarged view of portion of colony, showing
feeding individuals and reproduction individuals.
New individuals are here produced asexually, by
budding, b, the medusa stage, which originates as
a bud on the hydra colony and reproduces by means
of gametes thrown into the water

REPRODUCTION IN ANIMALS

329

In some species of toads the fertilized eggs are placed in
the mouth of the parent, where they are kept until the tadpoles
are large enough to swim away. Among the batrachians, —
which include newts and salamanders, as well as frogs and
toads, — there are very many cases of parental care of the devel-
oping young, ranging all the way from abandonment directly

Fig. 1 56. Sperm cells of animals
7, pig ; 2, bird ; j, salamander ; 4, ray ; j, threadworm {Ascaris) ; 6, lobster

after the discharge of the gametes to guarding within the
body of the mother until the young are fully formed and able
to shift for themselves.

382. Reproduction in the insects. Among the insects, which
of all animals are most distinctly adapted to living in the air,
the spermatozoa of the male are passed directly into the body
of the female through a special duct. The semen is discharged
into a receptacle, from which the spermatozoa pass, a few at a
time, into another space, wherein the female gametes (the eggs)
are fertilized. It is possible for a queen bee to retain a quantity

330 ELEMENTARY BIOLOGY

of living sperms for two or three years, or even much longer,
and to force these out of the receptacle from time to time as
she produces new eggs. Even the insects that normally lay
their eggs in the water — as the mosquitoes — have fertilization
take place within the body of the mother.

383. Reproduction in vertebrates. Among all the backboned
animals, above the amphibians, fertilization takes place within
the body of the mother. The eggs begin to develop immedi-
ately after fertilization and are retained within the parent's
body for a longer or a shorter period. Here they are not only
protected against possible injury by enemies, but they are
nourished and supplied with moisture and, in some cases,
kept warm.

The degree to which the new organism is dependent upon
the parent during the early stages in its development varies
considerably. Among the reptiles — *for example, some tor-
toises and alligators — the developing egg becomes enveloped in
a mass of food material on its way out of the mother's body
and is then supplied with a horny shell. The egg is then
deposited in the sand, where it hatches under the heat of the
sun. In certain lizards, however, the eggs hatch within the
body of the mother, and the young leave her body fully formed.

Among the birds the fertilized egg becomes covered with a
large quantity of food material (yolk and egg albumen), and the
whole mass becomes surrounded by a limy shell. Nearly all
birds protect their eggs, and they also supply the heat necessary
for the hatching of the young.

Among the mammals the development of the egg takes place
entirely within the body of the parent. The new organism is
cared for not only until it leaves the body of the parent but
for a comparatively long period after it is born. The length of
this period varies almost directly with the level of the family
of animals in the scale of development.

CHAPTER LXIII
INFANCY AND PARENTAL CARE

384. Infancy in lower plants. Among the one-celled plants
or animals each cell resulting from a cell division begins to
shift for itself immediately, as soon as it comes into existence
as a distinct cell. The simplest organisms of any series are
detached from their parents and shift for themselves early in
life. As we go up the scale we find that more and more do
the parents provide for the offspring in the way of food or
protection or both.

Among the seaweeds, like bladder wrack and many other
species, the gametes are thrown into the water, where thousands
are destroyed for every pair that fertilize and establish a new
individual.

In the mosses and ferns the female gametes are retained
within the body of the parent plant until after fertilization, and
until the new plant has been well started. In the mosses
the new plant gets nearly all of its nourishment from the
parent plant.

385. Infancy in seed plants. When we come to the highest
plants, the adaptation of structure and behavior to the apparent
advantage of the species is still greater. The spores are pro-
duced in comparatively small numbers and the gametes in still
smaller numbers. The fertilized egg is completely protected by
rather elaborate structures, and the young plant develops within
the body of the parent until it is fairly well along — in most
species until the root, stem, and leaves are quite distinguishable.
In addition to the nourishment and protection, the parent also
supplies a quantity of food that is available after the baby plant
is separated from the parent. And in most species we find a

33^

332 ELEMENTARY BIOLOGY

still further contribution of each generation to the next in the
form of special structures or organs that assist the young plant
in getting to some distance from the parent (see pp. 315-319).

386. Advantage of longer infancy to the species. In all
these various directions the organisms expend energy in ways
that enable the offspring to get a better start in life than would
be possible if the spore or the gamete (or zygote) were dis-
charged by the parent immediately upon being formed. On com-
paring the various groups of plants with respect to the amount
of nourishment or protection that parents supply to the young,
or with respect to any other services rendered by the parents to
the young, we shall see that with the ascent of plant life from
the lowest to the highest there is an increase of the dependence
of the offspring upon the parent. And with the increase of
service rendered by parents to offspring there is at the same
time an increased advantage to the species.

An advance in the scale of life seems to impose additional
burdens upon the organisms. But these are more than com-
pensated by the additional advantages. As has already been
pointed out, the production of flowers and fruits and seeds is
a source of great expense in material and energy to the organ-
ism. Yet in any species of plants that produces well-stored
seeds, well-protected seeds, and seeds well adapted to wide
dispersal every individual gets the full benefit of this addi-
tional expenditure of energy at the very beginning of his career.
We might even say that, apart from all other considerations, a
plant comes to be able to do all of its life's work just in pro-
portion as its parent has guarded its youth and has given it a
good start. In doing things for posterity a plant is thus merely
repaying to the species what was done for it in the past.

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 mean merely to point out
that certain kinds of doings may actually contribute to the prosperity

INFANCY AND PARENTAL CARE 333

of the species, whereas other kinds of doings would probably lead to
the extinction of the species. Some plants behaved in a certain way
in past ages, and their progeny to-day 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.

Fig. 157. The four-spined stickleback [Apeltes quadracus)

The adult fish swims about and through the nest, guarding the eggs while they
are hatching

387. Infancy among animals. When we study the pro-
longation of infancy among animals, we find that the advan-
tages of a protected and cherished youth are even more marked
there than they are among plants.

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

334

ELEMENTARY BIOLOGY

animals we find that much more is supplied for the young.
The lobster and crayfish mothers carry the eggs about on their
abdominal legs, or swimmerets, and even the young em-
bryos until they are able to care for themselves. Among the
insects there are some that abandon their eggs as soon as
laid, whereas others provide shelter and food for the young.

WMost fish leave their
eggs in the water with-
out further attention.
There are a few fishes,
like the stickleback, that
prepare a rather rough
protection, or nest, for
the eggs (Fig. 157).

Some toads carry their
eggs about in the mouth
until they are hatched.
Among the reptiles
and birds the egg begins
its development inside
the parent's body, and
receives a large amount
of food and a protective
covering. Most reptiles and some birds leave their eggs to be
hatched by the heat of the sun, or at ordinary temperatures.
Most of the common birds, however, build more or less elabo-
rate nests and care for the fledglings and for the eggs, besides
supplying heat for the hatching. The feeding of the young
birds by the parents is a very interesting operation to observe,
and it shows a very complex development of instincts.

388. Infancy among mammals. When we come to the
mammals, the dependence of the young upon the parents is
carried even farther. Not only does the egg develop inside
the body of the mother until it has acquired the general form
characteristic of the species, but it is nourished by the parent

Fig. 158. Wallaby and young

The babies are not only protected and kept warm in

the marsu/ium, or pouch, but are also nourished by

a milky secretion produced by glands in the lining

of the pouch

INFANCY AND PARENTAL CARE

335

for a long time after birth. Among the marsupials^ or pouch
animals, like the kangaroo and the opossum (see Fig. 158), the
young are placed in an abdominal pouch immediately after
birth. In all the other mamrhals the young suckle from the
milk glands of the mother. As we go from the lower mam-
mals to the higher, we find that the infancy of the individual
becomes proportionately greater or longer.

This is true even if we compare different races of mankind.
Among the primitive savages children are allowed to run about
without anyone to watch them as soon as they can walk ; in a
civilized community we sometimes keep close watch over chil-
dren, even at their play, for several years. It is easy to see
the advantages of a long youth from the point of view of more
and more complex civilization. There are physiological dif-
ferences also connected with the relative length of infancy.
This is shown, for example, by the length of time it takes the
individual to reach maturity.

The table below shows the duration of the growing period
for a number of animals, including man.

GROWING PERIOD OF VARIOUS MAMMALS

Animal

Length of Adolescence

Length of Life

Dormouse

Guinea pig

Lop rabbit

Cat

3 months

7 months
8-9 months
1-2 years

15 months

18 months

2 years

2 years

4i years

5 years

5 years

6 years

8 years
20-25 years
30-35 years

4-5 years

6-7 years

8 years

12-15 years

12 years

13-14 years

18 years

15-20 years

30 years

30 years

30 years

30-40 years

40 years

75 years

100-120 years

Goat

Fox

English cattle

Large dogs

Horse

Hog

Hippopotamus

Lion

Camel

Man

Elephant

PART IV

ORGANISMS IN THEIR EXTERNAL
RELATIONS

CHAPTER LXIV
OBSTACLES TO LIFE

369. Life and the environment. To live means to do. Pro-
toplasm tends to be active. But the activities of protoplasm de-
pend not alone on its own structure or composition ; they depend
in part, as we have learned, upon external conditions as well as
upon the opportunity to obtain various materials from without.
While many of the external conditions are favorable to the ac-
tivities of live matter, others are just as decidedly unfavorable.

390. Temperature and life. Observations on various plants
and animals show that the activities of life are dependent upon
temperature.

Warm-blooded animals can endure a wide range of tempera-
ture, but the protoplasm of such animals can really endure a
rather narrow range only. When such protoplasm is exposed
to a temperature several degrees below the normal, or several
degrees above, it ceases its activities and may even be killed.
On the other hand, the cells of the so-called cold-blooded
animals can actually endure extremes of temperature. Many
animals can be frozen and then thawed out again without
being appreciably injured.

In careful experiments fish have been frozen in blocks of ice to
a temperature of 5° F. (27 degrees below the freezing point), kept
this way for some time, and then slowly thawed out without being

337

338 ELEMENTARY BIOLOGY

killed. When cooled a few degrees lower, the fish were killed. Frogs
have been frozen to a temperature of — 28° C. (18.4° F.) without
being killed. Some of the animals without backbones regularly survive
even colder temperatures. Many insects that survive the winter in the
adult stage have to be frozen and then thawed out again, although
many of them no doubt escape freezing by burrowing into the ground.

In our experience with winter weather many of us have no
doubt frozen an ear or a finger. That did not kill us, but it
may have killed some of the cells in the affected part. When
frozen cells are thawed out rapidly, they are liable to burst
and thus be killed, but with a slow thawing the life of the
cells may be saved. That is why a frost-bitten ear is rubbed
with snow, to prevent it from warming too rapidly.

At the other end of the temperature scale some of the
simplest animals (ameba) have been found to survive a tem-
perature'of 122° F. when slowly heated. But most of them
died at that temperature. This does not mean that the animals
were unaffected in the gradually heated water until they were
killed. Long before this temperature is reached — at about the
temperature of our blood — they ceased active motion.

391. Water and life. We have learned that water is an
intimate part of the cell contents, and we can realize that life
is impossible without it. Yet the amount of water available for
plants and animals is constantly changing (except in the oceans
and larger lakes and rivers), so that at one time there is drought,
— at least relatively speaking, — whereas at other times there
is an injurious excess of moisture. Ponds and brooks dry up ;
and, so far as the availability of water is concerned, the same
condition arises when the water freezes. The soil dries, or it
freezes, and the water supply is thus cut off from the countless
plants that inhabit the earth. We know that a dry spring or
summer may mean a famine, and that some parts of the earth's
surface are quite uninhabitable because of the scarcity of water.

392. Light and life. We have learned that light is essential to
the manufacture of organic food, that it is the ultimate source of

OBSTACLES TO LIFE 339

all the energy which living beings constantly use. The amount
of living matter that can maintain itself on a given territory
depends largely upon the amount of light available. The tropics,
in addition to being warmer, also receive more sunlight and are
therefore more closely occupied by living beings than the frigid
zones. There is an almost continuous gradation in the density
of population ^ between the equator and the poles.

On the other hand, extreme intensity of light is itself a
serious obstacle to the normal processes of living protoplasm.
Light interferes with the growing process (p. 38) and may be
destructive to protoplasm. We see again, then, that a form of
energy that is essential to life may be a source of danger to it.

393. Salts and life. The various mineral salts found in the
ocean, in other bodies of water, and in the soil are ordinarily
absorbed by living beings through the process of osmosis, and
many of the salts take active parts in the processes that go
on in living protoplasm. Many of them are apparently indif-
ferent in their action, being neither helpful nor injurious ; a
few are injurious; and of those that are essential, some are
injurious in large quantities. On the other hand, a scarcity of
particular elements, or of compounds containing these ele-
ments, will absolutely prevent the growth and development of
living things. The kind of life that is possible in each of two
regions that are substantially alike as to temperature, moisture,
and light will in many cases be determined by the chemical
condition of the substratum.

394. Excess of air. The air, which is necessary to practically all
living beings either directly, as an immediate source of oxygen, or
indirectly, as a more remote source of oxygen (for plants and animals
living in the water) and as a source of carbon dioxid, never seems to
be injurious when in excess. Indeed, we do not know of any situa-
tion where the air is in excess. If we consider high atmospheric pres-
sure in deep holes in the earth as such situations, we may not be sure

1 Population refers here, of course, to all plants and animals and not
merely to human beings. The statement is not strictly true for human beings.

340

ELEMENTARY BIOLOGY

that it is the excess of air that interferes with life there ; no light is
available in such places. If we consider artificial conditions produced
by the digging of mines or the use of caissons under water, it is
indeed true that these conditions interfere with normal life processes ;
but they do this not because there is too much air, but because the

Fig. 159. The wind as an obstacle to life

The wind, often helpful to life and growth, is sometimes a hindrance. In the picture the
wind, besides making the tree grow one-sided, and bending over the top branches, has
blown the earth away from the roots. (Photograph lent by New York Botanical Garden)

human beings that go into these places are not adjusted to the high
pressure} Nor is there any place on earth where there is naturally a
scarcity of air, except on the very highest mountain tops ; but in
these situations other conditions are sufficiently unfavorable to life,
so that we do not usually think of the absence of plants and animals
in these places as due to the lack of oxygen.

1 The distressing disease known as " the bends," which affects many of
those who have to work in the high-pressure atmosphere of the caissons, is
very easily avoided by taking sufficient time to enter the working chamber
and sufficient time to come out. The disease is not caused by the high pres-
sure ; it is caused by the sudden change from high pressure to the normal
pressure of the surface atmosphere.

CHAPTER LXV
THE CONFLICT OF LIFE WITH LIFE

395. The predatory relations. Many of the animals, and
most of the plants, that are incapable of manufacturing their
own organic food get their food from the bodies of other plants
or animals that are already dead. But there are very many
animals, and a few plants, that kill their prey.

The gentle cow and the soft-eyed deer browse on the
herbage, and we never think of them as beasts of prey ; yet
from the point of view of the grasses and shrubs that furnish
them their food these animals are truly predatory. That is to
say, they are direct destroyers of living things. To maintain
themselves upon this earth, certain living things must somehow
protect themselves against predatory enemies, and this is just
as true of plants as it is of animals.

396. The parasitic relation. There are many plants and
animals that get their food supplies from the living bodies
of other organisms. That is to say, they eat from the living
victim, sometimes thereby killing, but not always and not
necessarily. Plants and animals that get their food in this
way are called parasites.

The most common parasites are found among the lowest
plants and animals ; but nearly every class of living things has
its parasitic representatives. Some two dozen of the common
diseases of man, and many diseases of our domestic animals,
are known to be caused by the activities of parasitic bacteria
in the bodies of the victims. Protozoa as parasites are known
to cause malaria and the sleeping sickness of Africa. Most
of our common plant diseases are caused by fungi or bac-
teria. The hookworm is a serious parasite on man ; and the

341

342 ELEMENTARY BIOLOGY

tapeworm, although perhaps not so serious, is probably more
common. Among insects are many related to the wasp and
the bee that lay their eggs in the bodies of caterpillars ; when
the young hatch out, they begin to feed on the caterpillar (see
5, Fig. 115). Among the backboned animals, certain fishes
will attach themselves to the bodies of other fishes and suck
the blood from their victims.

Most vertebrates get their food either by killing plants or
other animals or by taking dead matter (that is, plant or ani-
mal remains) of one kind or another ; in other words, there
are very few vertebrate parasites.

The idea of parasitism extends beyond the means of getting food.
The European cuckoo will lay her eggs in the nests of strange birds,
thus getting from other organisms at least two direct benefits — the
work of building a shelter for the young and the work of keeping
the eggs warm during incubation; there is also the feeding of the
young through the work of the strange foster mother. This is a
case of getting services from another organism, without giving any-
thing in return. It is in this sense that we use the word parasitism
in connection with higher animals, and especially in connection with
human affairs.

From the viewpoint of the unwilling hosts to the unbidden
guestS) parasitism is an obstacle to life ; and every species of
living things is exposed to a number of such parasitic enemies.
To be able to protect itself against parasites is one of the
conditions necessary for maintaining life.

397. The competitive relation. If all the offspring of any
plant or animal should reach maturity and reproduce the usual
number of young, and if this were continued for several gen-
erations, the earth would not be able to hold the resulting
population. 1

1 A conger eel is said to Xz.y 1 5,000,000 eggs in a year. If each of these
eggs hatched and reached maturity, and if each of these individuals repro-
duced at the same rate as the parents, the ocean would soon be crowded with
conger eels. The same thing is true of all animals.

THE CONFLICT OF LIFE WITH LIFE 343

It is evident that survival is impossible for all that are born.
Many are killed by the unfavorable conditions of life, many
are killed by mechanical injuries of various kinds, many are
killed by predatory enemies, and many are killed by parasites.
Finally, there are left those who remain to live out their lives.
But those do not all reach the full length of years. There are
still too many of them to live comfortably in the world. Many
of these are now destroyed in their competitive struggle with
one another.

This idea of competition, borrowed from the forms of business
operations that prevailed during the nineteenth century, applies to living
things, for the most part, only in a figurative sense. There are really
very few animals, and no plants, that are engaged in a direct conflict
for the materials necessary to their well-being or to their survival.
There are, however, situations in which more individuals are born than
can possibly reach full development, and in the course of time we
find that some have endured, while others have perished.

In a shaded wood, for example, the young seedlings grow
at different rates. Some grow fast enough to bring their tops
into the sunlight before others do ; they have the advantage
of more light. They now grow faster, not only because they
are more favorably situated, but because the growth of their
'' competitors " is retarded by lack of light. It is absurd to
suppose that these plants are struggling, in the sense in
which two wrestlers or two racers are struggling with each
other. No one does anything that is directly related to injur-
ing the other or to helping itself as against the other. The
result that one survives and the other perishes depends upon
certain external and certain internal conditions of the plants,
and not upon anything in the slightest degree resembling
effort, or offense or defense.

It is only when we come to the highest animals — especially
birds and mammals — that there is a real competitive struggle
that involves direct danger to the participants. A number of
wolves, for example, may fight over a carcass. In any farmyard

344 ELEMENTARY BIOLOGY

you may see chickens peck at each other when they are feed-
ing ; they peck at anything that gets in their way. More
conspicuous are the competitions among the highest classes of
animals for their mates. Male seals and walruses will fight for
the possession of the females ; male stags and other mammals
will do the same. In such struggles the individuals are actually
exposed to injurious attacks, and the survival of the individual
depends upon his superior means of protecting himself. Some
birds also fight each other in this competitive way.

We may conclude by recalling that every living thing is
exposed to a number of obstacles or direct dangers to well-
being ; that some of these arise from excess or shortage of
certain materials in the environment, and that others arise from
the various co-inhabitants of the world. To live, one must be
able to overcome these obstacles and to escape these dangers.

CHAPTER LXVI
PROTECTIVE ARMORS OF ORGANISMS

398. Walls and shields. The simple cell wall that we find
in the one-celled plants, and the cell membrane found in many
one-celled animals, may be considered to serve as protection
against mechanical injury to the protoplasm. At the same time
they permit the osmotic transfer of income and excretion.

Fig. i6o. The horseshoe crab

This animal is protected by an external skeleton, or armor, of chitin secreted by
the skin cells

In plants and animals made up of many cells we generally
find that the external layer of cells is either modified into
a protective layer or supplemented by various protective struc-
tures. The outer cell walls of skin cells in plant structures
are usually thicker than the inner walls and much thicker
than the walls of inside cells. The skin cells of leaves usually
have a secretion of a fatlike substance on the outer surface
(see /, Fig. 5), called aitin, which prevents evaporation from
within as well as water-logging from without. It adds also
to the protection against mechanical injury.

345

346

ELEMENTARY BIOLOGY

In many plants the outer surface of the leaf or fruit has,
in addition to the cutin, a layer of waxy material. This is
the bloom that we see on plums and other plant surfaces.

In many animals the cells forming the surface layer of
the body are small and thick-walled, and many kinds of
secretions add to the protective value. The horseshoe crab
(Fig. 1 60) produces his armor by secreting a substance that

hardens like a varnish in the
water. This is very similar to
the substance that makes up
the exo-skeleton (outside skele-
ton) of insects, the chitin (pro-
nounced ki'tin), which is also
formed by the secretion of the
skin cells.

In lobsters, crabs, crayfish,
and their relatives (the Cntsta-
cea) the chitin secretion is com-
bined with a comparatively large
amount of carbonate of lime.
This it is that gives the exo-
skeleton of these animals their

FiG; 161. Sea urchin

Animals of this branch deposit large

quantities of lime in their skin, and

produce knobs and spines that form a

protective armor

crusty quality. Clams, oysters, and snails have extremely soft
skins. (The name of this whole group of animals, Mollusca,
refers to the general softness of these organisms.) They receive,
however, a great deal of mechanical protection from their shells,
which consist of deposits of lime formed by the secretions of a
special fold of tissue called the mantle (see Fig. 44).

On the clapi and on the snail the lines indicate the successive
deposits of lime. The inner surface of the shell is often very beauti-
ful and iridescent because of the very fine lines that break up the
surface. This mother-of-pearl is used extensively for ornamental
purposes, — for buttons, knife-handles, etc., -■ — and the shells of many
mollusks are used for their hardness and durability in the making of
buttons and similar objects, without regard to their beauty.

PROTECTIVE ARMORS

347

.^

In the starfish and sea urchins and their relatives (Echino-
dermatay meaning " spiny-skinned ") the skin secretes a great
deal of lime, which is deposited in the form of definite rows
of plates, and in projecting spines (see Fig. i6i). We may
well imagine that no fish
would care to eat a mouth-
ful of such spiny creatures
as the sea urchin, or to bite
and swallow the harsh rays
of a starfish.

In the trunks of our
common trees there is a
growing layer that con-
stantly produces new layers
of wood and new layers of
bark (see Fig. 63). The
bark cells produced on the
outside of this cambium
layer soon die, and the
walls become corky. As
new layers are produced
underneath, the old layers
are moved farther and
farther from the center
of the plant. On the out-
side the dead cells, ex-
posed to the weather and

to mechanical injury from moving animals and other objects,
rub off or chip off. The mass of bark is thus a constantly
renewed protective layer.

Similar in some ways to the bark of a tree is the hide
or skin of a mammal. Our own skin, for example, is made
up of dead cells on the outside. These are constantly rub-
bing off, but are as constantly replaced by new cells from
beneath. The growing layer (see b, Fig. 92) gives rise to

Fig. 162. Hairs of plants

a, branching hair on leaf of tobacco plant ; b, hair
on leaf of thorn apple ; c, glandular hair on leaf-
stalk of Chinese primrose ; d, marginal tooth on
sedge leaf ; e, glandular hair on flower of hop ;
/, leaf of apple of Sodom ; g, stinging nettle,
with tip, greatly enlarged

348

ELEMENTARY BIOLOGY

new cells ; these die as they are moved toward the surface
by the newer cells beneath, becoming a layer of dead scales.
The skin protects the animals not only against mechanical
injury but also against the loss of water and against the
absorption of water, for the skin is practically waterproof, being

Fig. 163. Mullein in meadow

These plants are closely covered with fine, branching hairs, giving the leaf a flannelly

texture. We can well imagine that a cow would not care to eat anything that felt like

flannel in the mouth, and so we can understand that the hairy growth may actually

protect the plants against grazing animals. (From photograph by Dr. H. A. Kelly)

more or less oily (see p. 206). It also protects, to a certain
degree, against too rapid changes of temperature. In this
function many skins are supplemented by layers of fat on
the inside and by hairs or fur on the outside.

399. Hairs and other outgrowths. On the leaves and stems
of plants the cells of the epidermis enlarge at right angles to
the surface. This mode of growth results in the formation of
hairs (see Figs. 162, 163).

PROTECTIVE ARMORS

349

It seems likely that in many plants the hairs are really related to
the moisture. The absence of moisture, or, rather, a shortage of

Cortex

Shaft

edulla

Horny
5^ layer
'^^Wermis

Jebaceout
'""gland

hi

, 4

Papilla with
blood vessels

Fig. 164. Hair of mammals

I, human hair follicle, showing mode of growth (the dead shaft is pushed forward by

the new growth about the papilla) ; 2, hair of horse ; j, hair of mouse ; 4, hair of marmot.

a, base of hair ; d, tip ; c, more highly magnified portion of shaft

moisture, is known to bring about the production of hairs in species
of plants that ordinarily do not produce hairs when water is abundant.

Hairs are also likely
to protect many plants
against extremely high
or low temperature.

The hairs familiar to
us in common animals
and on our own skin
are much more complex
in structure than are
plant hairs (Fig. 164).

The feather of the
bird may be considered
as a highly complex
hair. In the manner of
of mammals very much,

^Sheath

Branches
of shaft
forming
barbules

Horny
layer

Growing
region

Pulp

Fig. 165. Feather structure

The feather of a bird is a skin structure that

grows in substantially the same way as a hair or

a finger nail

growth the feather resembles the hair
but in its structure it is of course very

350

ELEMENTARY BIOLOGY

different, and each feather has a determinate growth ; that is,
there is a definite limit to the size and form which a single
feather can attain (Fig. 165).

The bristles of hogs and the quills of hedgehogs and porcu-
pines are giant hairs. Hairs, quills, bristles, and feathers may

Box turtle

The exoskeleton consists partly of skin plates and partly of bony expansion. This animal

is protected not only by the withdrawal of head and limbs but by the further closing of

the hinged breastplate, shown on the right

be considered as special kinds of skin growths and may be
compared to the scales of the common fishes and of reptiles,
and to the plates found in the skin of sturgeon and the gar
pike. The shield of the turtle or tortoise is in part a skin
structure and in part produced by the skeleton (Fig. 166). The
amphibians (frogs, newts, etc.) are the only backboned animals
that never produce outgrowths on the skin, although some of
the toads have irregular thickenings in the adult stage.

CHAPTER LXVII

PROTECTIVE PIGMENTS AND APPEARANCES

400. Pigments and light. Animals that Hve at great depths
of the sea, and those that hve in caves, — situations in which
there is httle or no exposure to hght, — do not generally show
much pigment in the skin.
This fact may be interpreted
in two ways :

1. Where there is no dan-
ger of being injured by light,
the species will be able to main-
tain itself without acquiring
the pigment-forming habit.

2. Where there is no light
stimulation, pigment will not
be formed.

In the human race the dark
pigment of the skin is un-
doubtedly a protection against
the light, as shown by the
relative sensitiveness of light-
skinned races and dark-
skinned races to the influence of the tropical sun. It is also
shown by the behavior of the skin of a person who has been
tanned and the behavior of the skin of the same person before
the tan has formed. A person who does not get tanned is likely
to be sunburned with every exposure to strong sunlight. On the
other hand, in a person who is dark-skinned, or who has be-
come tanned, the pigment acts as a screen, cutting off the rays
that are injurious to the protoplasm.

351

Fig. 167. Katydids

Microcentrum reiinert'is (above) ; Cyrtophyl-
lus concavus (below). These insects match
the color of the foliage upon which they
feed ; in some species the resemblance to a
green leaf is even more striking than in the
two shown here

352

ELEMENTARY BIOLOGY

In certain experiments with flatfish that are ordinarily pig-
mented on the upper surface and white on the lower surface,
the light was supplied from below by means of mirrors, with
the result that the fish developed pigments on the lower sur-
face and remained white above.
From these experiments and
from our own experience with
getting tanned, we may feel con-
fident that at least in many cases
the formation of the pigment is
due to the stimulation of the
light. But we know also that
there are many other pigments
that are formed without refer-
ence to the light, whether they
have any protective value or not.
401. Invisibility. In relation
to enemies that can see, one of
the most obvious means of protec-
tion is something to make one in-
visible. The jellyfish (Figs. 1 54, <2',
and 155, b) is so nearly transpar-
ent that it is practically invisible
in the water.

But transparency is not the
only means by which an object
may be made invisible. The see-
ing of objects depends upon the
contrasts in lights and shadows ;
an object that is colored like the background becomes by
that fact invisible. This type of invisibility is so common
in nature that some men claim to be able to tell the kind of
surroundings an animal naturally occupies from the character
of its surface colorings. The green katydid among the green
leaves is a common example of so-called protective coloration

Fig. 168. The underwing moth
{Caiocala)

When they are at rest, the moths of
this genus resemble the bark of trees,
so that they are no doubt often over-
looked by their enemies

PROTECTIVE PIGMENTS AND APPEARANCES 353

(Fig. 167). The tree toad and the partridge become lost to the
eye, as well as the sand flea and the underwing moth (Fig. 168).
It is familiar to all of us
that desert animals are
frequently tawny in their
color, whereas arctic ani-
mals are frequently white.

There can be no doubt
that in relation to certain
enemies the resemblance
between an animal's color
and the background color
is often a real protection.
At the same time, there
is danger of exaggerat-
ing the importance of
this resemblance to the
organisms, and there is a
corresponding danger of
trying to prove too much
from this resemblance.
Thus, the whiteness of
arctic animals is appar-
ently due in many cases
not to the whiteness of
the surroundings but to
the low temperature.

The color of an animal
is often due to the char-
acter of the wastes pro-
duced by the chemical
changes going on in the
protoplasm. The character of the waste, in turn, will depend
upon the nature of the food. A change in diet will therefore in
many cases result in a change of color. This is showij in the

Fig. 169. The walking stick

This animal has startled many a person by walking
away from a hand stretched out to grasp a leaf or
twig. The insect is related to the locust and katy-
did, but it has no wings. Its body and legs are
very long in proportion to thickness, and the en-
largements at the joints and the irregularity of
outline increase the resemblance to bare twigs.
Moreover, the color of the animal changes with
the seasons, from a bright green in the spring
to a deep brown in the fall, thus matching its
surroundings very closely

354

ELEMENTARY BIOLOGY

brightening of the color of canaries by a regulation of the diet,
and by a change in the color of many insects with the change

of diet. On the other hand, if a color
is to protect, it can do so only in rela-
tion to an eye that fails to discriminate.
But if the enemy finds his prey by
means of smell or some other sense,
the color cannot be a protection.

People have frequently made the mis-
take, also, of supposing that other animals
see exactly as we do. What looks alike
to us may be readily distinguished by
other animals; and the opposite is also
true. Thus, the white spots at the rear
end of a deer, or the white stripes on
a badger, make these animals conspicu-
ous in our sight; but from the point of
view to be obtained by eyes that are
close to the ground these white spots merge with the light of the
sky, and the outlines of the animal are as completely lost as are
those of the zebra or the tiger among the stems of the underbrush.^

Fig. 170. Walking-leaf insect

This insect, related to the locust

and the katydid, resembles the

foliage upon which it crawls

Fig. 171. Tree hoppers {Membracis binotata)

These small insects resemble miniature quail quite as closely as other animals " mimic "
their models. Yet there is no conceivable advantage to the insect in this resemblance

«

402. Protective resemblances. In some animals the mottlings
and striping are often very close imitations of particular kinds
of backgrounds,- and this resemblance is further heightened in
many animals by peculiar forms (see Figs. 168, 170).

1 The art of " camouflage " as developed during the Great War rested
largely on the observations of naturalists on protective coloration.

PROTECTIVE PIGMENTS AND APPEARANCES 355

What is perhaps the most remarkable resemblance between an
animal and a part of its surroundings is furnished by the East India
butterfly Kallima (Fig. 172). The undersurface of the wings, exposed
when this butterfly is at rest, resembles a brow^n leaf with a distinct
midrib and veins passing from this
to the edges. Near one end is a dark
spot close to a nearly transparent area,
resembling very much the kind of spot
often produced by the action of some
fungus. The details are very sharply
defined and almost uniform. If one
of us should see a flying kallima come
to rest on a twig, he should perhaps
have some difficulty in distinguishing
the insect among the leaves ; it is pos-
sible also that the lizards and birds
that feed upon this species are some-
times baffled in their pursuit of prey.
Yet it is doubtful (i) whether the ad-
vantage of this resemblance has had
anything to do with its gradual appear-
ance as a character of this species, and
(2) whether, indeed, it is an advantage
(see Fig. 171).

Fig.

72. The Indian leaf butter-
fly {Kallima)

Many arguments concerning the evo-
lution of animal life have been based
on the striking resemblance between
the wings of this insect when at rest
and brown leaves. It has been said
that the animal looks like a leaf only
when it comes to rest with the head
up ; but observers who have seen the
animal in its native surroundings tell
us that it always comes to rest head
dawn^ on guard against lizards. In
this position it is sufficiently con-
spicuous to be recognized even by
untrained human eyes

403. Warning colors. We saw

that some of the wastes produced
in living bodies are poisonous (see
p. 203), and we can understand that
the presence of these poisons in the
body of a plant or an animal would
make such a body undesirable as

food for another animal. Distasteful (bitter, sour, acrid, foul-
smelling) substances may thus serve to protect organisms
against possible enemies. Poisonous and distasteful substances
in an animal body are often associated with conspicuous colors,
which have been called warning colors by some naturalists.
The idea is that the bright color warns enemies against eating

356

ELEMENTARY BIOLOGY

the animal. But this involves some way of educating the
enemies as to the meaning of the warning. It is true that
many animals instinctively avoid certain kinds of plants and cer-
tain kinds of animals, and that some of the avoided species are

really injurious. It is also true
that animals are. often poisoned
by eating unsuitable organisms,
and that animals often eat organ-
isms that are distasteful or that
make them sick.

A young chick, fresh from the
egg, soon begins pecking about
for food. A chick finds a worm
or a caterpillar and at once eats
it. Most of the material thus
taken is sufficiently palatable. But
presently the chick finds a hornet
or a woolly-bear caterpillar. This
mouthful is somewhat too much
for the chick ; it makes a profound
impression on the young animal.
The hornet may be killed, or the
caterpillar may be killed, but the
chick is impressed. She will never
eat that kind of food again. The
dead hornet or caterpillar has
taught the chick a lesson, but can-
not get the benefit of the lesson.
Other hornets, however, or other
woolly bears, are safe, so far as
that particular chicken is concerned.
The individual sampk is thus sacrificed for the benefit of the species.
When we consider that every individual has to have his own lesson,
we should think this a rather expensive mode of protection, but we
may take the idea for what it is worth. One thing is certain, many
conspicuous species lack the bitter juice, while others have the bitter
juice, and yet lack a conspicuous appearance ; and one species seems
to hold its own about as well as another.

Fig. 173. Mimicry among butterflies

The viceroy, i>, belongs to a different
genus of butterflies from the monarch,
or milkweed butterfly, a ; yet the resem-
blance at first glance is so striking that
most people will be unable to point out
any difference between the two except in
size. A close study will show us, however,
a number of differences in the pattern

PROTECTIVE PIGMENTS AND APPEARANCES 357

404. Mimicry. Growing out of our
knowledge concerning the relations of
the characters of animals to their safety
and danger, a very interesting idea was
developed by some naturalists during
the last century. This is the idea of

Fig. 174. The mimicry of the African swallowtail butterfly {Papilio

dardanus celled)

/, the male. The female, a^ occurs in three distinct forms. Each of these forms pre-
sents striking resemblances to butterflies of other genera. Thus, the form cettea, 2 «,
resembles Amauris echcria, 2 b, which in turn resembles Pseudacraea tarqidnia, 2 c.
The form lippocoon^ 3 a, resembles Amauris niavius^ 3 b, which in turn resembles Euralia
walbergi, 3 c. The form trophoftius, 4 a, resembles Danais chrysippus, 4 b, which in turn
resembles Dindema misippus, 4 c. The argument that these resemblances bring about
advantages may be sound, but too little is as yet known as to what brings about the
patterns of the insects supposed to represent the original model

protective mimicry. A common example of this near home
is the resemblance between the milkvveed butterfly and the
viceroy (see Y\g. 173).

358

ELEMENTARY BIOLOGY

The explanation that is sometimes given of this resemblance is as
follows: The milkweed butterfly has a bitter or disagreeable taste,
and therefore birds commonly avoid eating the insect. The viceroy
belongs to a family that is commonly eaten by the birds, being suffi-
ciently attractive to them. The resemblance between the viceroy and

the monarch protects
the former from the at-
tacks of the birds. Of
course it is not sup-
posed by anyone that
the viceroy butterflies
have purposely mim-
icked the monarch. It
is only supposed that
the resemblance, how-
ever it may have come
about, is of advantage
to the insects. We do
not understand how
these resemblances, or
others like them (see
Figs. 174, 175), have
come about. Some of
the theories offered to explain them are discussed in Chapter LXXXIV.
We are in. doubt not only as to how such protective mimicry may
have arisen ; we are also in doubt as to whether mimicry is in all
cases protective.

Professor Punnett, an English biologist, made a special study of
this subject in Ceylon, where examples of mimicry are unusually
abundant. He found, in regard to certain cases, that the model and
its supposed mimic never occupied precisely the same area ; at most,
the two areas overlap more or less. In the second place, the com-
mon birds, against which the mimicry is supposed to be protective,
do not molest either the model or the mimic; but the lizards eat
the mimic as well as the other members of the family, which are
supposed to be defenseless. The only other serious enemy of these
butterflies was a certain large fly that pierces the thorax of the
insect and sucks the juices. But this fly, like the lizard, attacks the
mimic and his defenseless cousins without discrimination. In other

S 4

¥iG. 175. Supposed cases of mimicry

/, Bombus pennsylv aniens^ a bumblebee, mimicked by 2,
Laphria thoracica\ j, Vespa maculata, a wasp, mimicked
by 4, Spilomyia fuscia. In these cases the models and
the mimics belong to entirely different orders of insects,
— the former are hymenoptera, or bee order ; the latter
are diptera, or fly order

PROTECTIVE PIGMENTS AND APPEARANCES 359.

words, the resemblance to the model does not protect. Moreover,
in a part of the island where monkeys are supposed to be the chief
enemies of the butterflies, the most abundant forms are those that
are supposed to be defenseless forms, whereas the mimics are scarce.

Sfcfc__l

*" jHH^HJi^^BHit^' ^'

W^^m^M

1

^^^BS^agMjdLLi^ci >{

.* .' -^Jiy-' . ^^P^

sss^^^

Fig. 176. Desert plants

Cholla cactus on the western deserts. The thickened leaves and short stems, or the

entire absence of leaves, may be considered as a more or less direct adaptation to the

high temperature and the dry soil, which together make up the danger of excessive loss

of water. (From photograph by the United States Reclamation Service)

405. Reduction of surface. Some organisms may derive a
kind of protection from a reduction of surface. This is espe-
cially common among plants that are exposed to the danger
of drought. In desert plants we observe a comparatively small
surface in proportion to their bulk (Fig. 176).

CHAPTER LXVIII
PROTECTIVE MOVEMENTS

406. Contractions. Contraction under stimulation is a com-
mon thing among living beings. When the ameba is disturbed

Fig. 177. Contraction of sea anemone

When disturbed, the surface of this animal becomes greatly reduced by repeated
contractions, until it resembles a wart on a rock

in any one of several ways, it immediately contracts. The
effect of this contraction may be protective in several ways :

Fig. 178. The pill bug

When suddenly disturbed, this animal curls up, thus reducing its exposed surface and
concealing its most delicate and sensitive parts

1 . It reduces the total amount of surface exposed to danger.

2. It hardens (condenses) the exposed surface.

3. It withdraws the animal from the point of attack.

360

PROTECTIVE MOVEMENTS 361

Here are three results of this simple reaction that may
presumably be of use to the animal under various conditions.

The sea anemone shows a remarkable amount of contrac-
tion when disturbed. In fact, all the animals of this branch
(coelenterates) are extremely contractile (see Fig. 177).

Fig. 179. Sensitive plant {.Mimosa pudica)

a, leaves in normal position ; b^ leaves reduced after disturbance. It is not necessary
for us to assume that this movement is of any real value to the plant. It is true that in
the new position the leaf exposes less surface and sheds the water better. But hundreds
of plants with similar leaves have no difficulty in shedding rain without being so sensitive.
Many plants (clover, oxalis, and others) drop their leaves in the dark in a few minutes. It
is possible that in the clover and others the drooping of the leaf is the direct result of
reduced transpiration. But that does not give the plant any advantage It is very likely
that the sensitive plant is simply more sensitive than any of its relatives (the bean family),
many of which are sensitive in the same way but not in the same degree

In clams and oysters, contraction of special muscles results
in closing the shell. In snails, contractions withdraw the body
into the shell. The turtle withdraws head and legs into his
"shields," and the box turtle closes the shell up even more
completely.

We do not usually think of plants as moving, either to get
food or to escape danger. Some plants, however, can do a
great deal of moving in connection with the capture of insects

362 ELEMENTARY BIOLOGY

and other animals. Several other plants are capable of moving
their leaves when disturbed, as the sensitive plant (Fig. 179).

407. Color changes. To be able to elude the vision of the
enemy must be of real advantage to any animal. It is therefore
reasonable to assume that the color changes of the chameleon

Fig. ,180. The true chameleon

African monitor {Varanus niloiicus). (From photograph by American Museum of
Natural History)

must be of protective value to him, and that they are brought
about by the color of the surroundings. The true chameleon,
a native of Africa (Fig. 180), and the American chameleon
(Fig. 181), or green lizard, quickly change their color through a
wide range of shades, from bright green to rather dull brown.
These changes are brought about by the contraction or expan-
sion of various parts of the skin, containing different pigments.

Careful experiments show that the color changes are produced
by a response to temperature changes or by the intensity of the
illumination rather than by the color of the background.

PROTECTIVE MOVEMENTS

363

In many situations, however, these color changes may be protective,
even though they are not necessarily protective adaptations in all cases.

408. Concealment. Another way in which an animal becomes invis-
ible to its enemies is illustrated by the cuttlefish, which ejects a dark
fluid into the water when it is pursued. This " ink-bag " trick clouds
the water and thus enables the animal to escape from its pursuer.

Fig. 181. The American chameleon

The green lizard (Ano/is carolmensis) . (From photograph by American Museum of
Natural History)

The instinct for finding shelter is very marked in many animals of
nearly all classes. In many worms we may observe a strong tendency
to crawl into cracks or angles. There are certain worms that are so
persistent in this trait that if two of them are placed in opposite
ends of a glass tube, they will approach each other and keep on
driving forwards until they have worn their heads off. The contact
of the body against the hard walls stimulates them to move forward,
and they don't know enough to stop when they have gone far enough.

A more remarkable home-finding instinct is that shown by
the hermit crab, which makes itself at home in the discarded
shells of snails. As the animal grows larger it abandons one
shell and finds another (Fig. 182). With this instinct we may
compare that of the higher animals that dwell in caves or
other ready-made openings that they find.

364 ELEMENTARY BIOLOGY

409. Flight. Beginning with the ameba, that withdraws its
'' false feet " from a point of disturbance, and reaching to man
himself, all animals that are not confined or attached protect
themselves by some form of flight or escape. With this fact is
associated a wonderful series of organs of locomotion, from the
false feet and cilia of the protozoa, the water feet of the starfish,
the flapping shell movements of the scallop, the wriggling of

Fig. 182. The hermit crab

These crabs make themselves at home in the cast-off shells of whelks and snails. (From
photograph by New York Zoological Society)

worms, and the legs and wings of insects, up to the various
kinds of legs and wings and fins of the backboned animals.

It is impossible to say that organs of locomotion are pri-
marily related to protection or that they are primarily related
to food-getting. At the very lowest levels of life, among the
protozoa, we find the same structures and activities serving
organisms in both relations. Thus, the Paramecium, moving
about by means of cilia, also gets food particles into the inte-
rior of the protoplasm by means of cilia. And farther up we
find feeding organs and locomotive organs differentiated from
the same structures (see Fig. 183).

PROTECTIVE MOVEMENTS

365

Even among the mammals we find the primates (monkeys,
apes, man) using their front Umbs in food-getting quite as
much as in locomotion,
or even more.

410. Migration. A
very interesting prob-
lem in connection with
the protective move-
ments of animals is that
of migration. The mi-
grations of the common
birds are more or less
familiar to all of us.
Those of us who live in
the northern latitudes
are likely to look upon
bird migration as '' go-
ing south in the winter
to get away from the
cold," or as ** going
south to get food." If
we live in the south we
may well ask why the
birds ever go north ;
and we can think of
no advantage to their
migration except that
of finding a breeding
place for the young in
a region free from the
usual enemies or other
obstacles (see Fig. 184).

©

c>^^^

Fig. 183. The appendages of the lobster

In the Crustacea all the appendages are built on the
same plan, but each segment of the body (repre-
sented by Roman numerals) has a distinctive organ,
/and //are sensory; ///-F combine sensory func-
tions with food-getting; VI-VIII are chiefly food-
getters, but are also related to breathing ; IX is the
nipper ; X and XI are both grasping and locomotor
organs ; XII and XIII are walking legs. The ab-
dominal appendages XIV-XVIII are called swim-
merets and probably assist in slow swimming. XIV
and XFare also related to reproduction in the male,
and in the female all the swimmerets carry the hatch-
ing eggs and larvae. XIX and XX spread out into a
flat tail-paddle, used in swimming backward suddenly

It is possible that some species migrate originally with relation to
food and weather, and that other species migrate primarily in relation
to possible enemies. Whatever the advantage to the species, it is

^
^

•^ ^ -Q

4,*

-■I

'J

PROTECTIVE MOVEMENTS

367

curious that year after year the birds will follow the same routes,
even coming out of their way many miles to go with the flock. It is
probable that the older birds lead the migrations, and that the paths
are kept by force of imitation. The young follow, and the older ones

Fig. 185. Migrating fish

Humpbacked salmon jumping low falls, Litnick Stream, Alaska, on way to breeding
grounds. (From photograph by United States Bureau of Fisheries)

continue to do as they have always done. As a result, customs are
established that persist even when they cease to be of greatest
advantage or economy.

Migrations of fishes have also been recorded, and these
seem to be related chiefly to finding safe breeding places.
Some, like the eel, will go out into the ocean to breed ; others,
like the salmon, will spend most of their time in the ocean and
will come up into the rivers to breed (see Fig. 185).

CHAPTER LXIX

PROTECTIVE ACTIVITIES

411. Home-making. When the earthworm burrows into
the ground, it thus escapes the birds and other enemies ; but
the burrowing is essentially a process of food-getting, for the

animal feeds by
swallowing dirt as
it digs along, and
absorbing from it
organic material
left by decaying
plant and animal
matter. In the
same way, the
larvae of various
insects and many
adult beetles es-
cape their ene-
mies by boring
into trees.

In the simplest
of animals, where
all the activities
of life center in
the protoplasm of
a single cell, the
movements related to protection or escape from injury are hardly
to be distinguished from the activities related to the getting of
food. The simple life will cover all of its necessities by a few
acts. But with higher animals it is often difficult to draw a

368

Fig. 186.

The piddock

This moUusk grinds its way into the rock, growing larger as it
digs deeper, so that in the end it is completely imprisoned

PROTECTIVE ACTIVITIES

369

sharp line be-
tween the proc-
esses that are
related primarily
to the getting of
food and those
that are related
to protection. In
the intestines of
a child a tape-
worm absorbs its
food from the
host and it is at
the same time
protected from
all possible ene-
mies. It would
be absurd to say
that the parasite
makes its home
and its living in
the intestines of
a vertebrate ''be-
cause " that is a
safe place, al-
though it may be
true this habitat
is indeed safe
enough. In the
same way, we
must be on our

guard against explaining the activities and peculiarities of ani-
mals as though they resulted from some purpose that the animals
had in mind. We may be sure only that, to continue to live, an
organism must be sufficiently adapted to its surroundings.

Fig. 187. Nest of the paper wasp, or black hornet

The queen wasp survives the winter alone. In the spring she
builds a small nest of wood pulp, or wasp paper, and lays a
few eggs in it. While these are hatching she fetches various
grubs and caterpillars, which serve as food for the young. On
becoming mature the workers proceed to enlarge the nest and
to bring supplies of food. The queen continues to lay eggs
throughout the summer, and most of these develop into workers,
though some of the eggs hatch into perfect males and some
into perfect females. After fertilization the males and the
workers die, leaving the queens to live through the winter and
to start new colonies in the spring

370

ELEMENTARY BIOLOGY

Fig. 1 88. Finding a home for the young

Nest of a bluebird in natural hollow of a tree
(From photograph by L. W. Brownell)

With many animals the
boring or burrowing is re-
lated altogether to protec-
tion, as with animals that
bore into rocks (Fig. i86).
From our own point of
view the safety obtained
by an animal boring into
a rock would seem to be
purchased at the price of
liberty. But we may be
sure that from the pid-
dock's point of view this
trick of boring into the
rock causes no ill feeling.
There is safety, and there
is the possibility of getting
food as well, for the long
siphon projects into the

Fig. 189. Prairie dogs

These animals dig burrows underground and live in large colonies,
photograph by Elwin R. Sanborn)

(From

PROTECTIVE ACTIVITIES

371

ocean and a constant current of
water brings oxygen and food, and
carries off wastes and reproductive
cells (see Fig. 44).

When we come to the highest
animals (the insects) of the branch
arthropods and the highest animals
of the backboned branch (birds and
mammals), we find very complex
activities related to the making of
homes. The solitary wasp goes no
farther than burying a few insects
that later serve as food for the
young. The social wasps and hor-
nets, like the related bees and ants,
build very elaborate homes out of
*' paper" (which they make from
wood pulp and other materials) and
out of wax and earth (see Fig. 187).

Nest-building among the birds
involves complex instincts, and pos-
sibly in some cases a degree of real
intelligence. From the crude whisps
of the grouse, or the simple mud
heap of the flamingo, to the deli-
cate and skillful work of the tailor
bird, we find a long series of nests
of many degrees of complexity in
structure. But with the exception

Fig. 190. Nettling cell of
jellyfish

This specialized skin cell, A, con-
tains a fine coiled thread suspended
in a capsule of acid fluid. W^hen the
surface is disturbed at the trigger,
t, the coil suddenly straightens out,
shooting the sharp needle into the
surrounding space, and at the same
time the acid fluid from the cell
passes through the hair. The sting-
ing sensation is probably produced
by this fluid. B, the discharged cell

of homes made in hollows, like that

of the woodpecker, whatever shelter nests may furnish serves

almost exclusively for the protection of the young (Fig. 188).

Indeed, we may say that the making of shelter among the

higher animals is closely related to the protection of the young.

372

ELEMENTARY BIOLOGY

or of a group, rather than to the protection of the individuaL
This is seen in the constructions of such animals as the

Fig 191. Praying mantis

This animal lies in wait for its prey with the front legs raised in a manner suggesting

the attitude of prayer. It catches small insects with its strong front legs. Large species

living in the tropics have been known to kill small birds

beaver or the prairie dog (Fig. 189), in the hutch of the rabbit,
in the diggings of the mole, and in the nest of the mouse.

.T.y*^r^^ . J^5J.lv^^?^^Vi^'i■-•■•

Fig. 192. The ant lion

a, adult ; b, larva ; b^, larva covered with dirt ; c, incased pupa ; d, pit in sand. The larva

buries itself in loose sand at the bottom of a small pit. Ants and other small crawling

insects tumble into the pit and are seized by the strong jaws of the ferocious " lion "

412. Fighting. Nothing would seem to be more helpless
and less offensive than the soft-bodied jellyfish ; the very name

PROTECTIVE ACTIVITIES

373

suggests something even milder than a clam. But if you have
ever picked up a live jellyfish, you may have thought that a

million needles had been
shot into your hand. The
skin of the jellyfish con-
tains a large number of
special cells in which
there are fine hollow
threads that shoot out
when the animal is dis-
turbed (see Fig. 190).
These '' nettling cells "
are found in many spe-
cies of coelenterates, such
as the hydra, sea anem-
one, coral polyps, and
sea walnuts.

But some animals,

like the ray, do give

their enemies a real

electric shock when they are disturbed, and this is no doubt

of value in protecting them. The animal that has been

shocked quickly lets go and learns to let other shockers alone.

Fig. 193. Fighting ants

Three forms of the Central American ant Chelio-

myrmex nortoni : a, soldier ; i>, medium worker ;

c, small worker

Fig. 194. The sting of the bee

In this order of animals the weapon is the egg-laying organ. When the bee stings some-
one, the point is likely to remain in the flesh ; and as the animal flies away, some of its
internal organs are mutilated and the insect soon dies. The value of this weapon is not
so much for the protection of the individual as for that of the colony or species. The
individual is sacrificed to protect the group or to educate the enemies of the species

Another way in which the organism can make itself disa-
greeable to an enemy, without really producing serious injury,

374

ELEMENTARY BIOLOGY

is illustrated by the skunk. This animal, as everyone knows, is
capable of ejecting a foul-smelling liquid from a gland at the
rear of the body when it is greatly agitated.

Real fighting appears among animals that have mouths and
appendages that are capable of grasping. These organs are at
;/ the same time food-

getting organs. Lob-
sters and crabs are
very pugnacious ani-
mals, or at least that
is the impression they
make upon the ob-
server. Most of the
mollusca (clams, oys-
ters, scallops, etc.) de-
pend on their armors
for defense against
possible aggressors ;
some of them, how-
ever, as the octopus,
are very good fighters
(Fig. 95).

Among the insects
many are predatory,
using their append-
ages (Fig. 191) or
their mouths (Fig. 192) in catching prey. But very few use
these organs in fighting their enemies. The colonial insects,
especially the ants, furnish the best examples of this mode of
protection (Fig. 193). The bees, wasps, and hornets fight
when they are disturbed or when the colony is disturbed,
but in fighting they use the sting (see Fig. 194), which has
nothing to do with food-getting or with locomotion.

The horns of mammals are associated with the instinct to
defend or fight, and are quite independent of the organs or

Fig. 195. The fall of a leaf

A, leaf dropping off; s, self-healing scar remaining on
twig ; B, microscopic view of section through base of
leafstalk; a, angle between base of stalk and twig. In
plants that regularly drop their leaves in the autumn
there is formed a special layer of cells in the stalk of
each leaf, and sometimes of each leaflet of a compound
leaf. These cells, s /, are thin-walled 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

PROTECTIVE ACTIVITIES

375

instincts that have to do with the getting of food. Thus, while
the ferocity of the tiger or the dog finds expression through
organs that are related to food-getting, the strictly vegetarian
rhinoceros or mountain sheep will fight fiercely and coura-
geously with horns or hoofs. The branching horns of the
deer or elk seem never
to be used aggressively
except against mem-
bers of their own spe-
cies, as when two males
are in combat.

413. Shedding of
leaves. The dropping
of leaves in the autumn,
while it does not in-
volve movements like
those of muscles, may
properly be considered
a protective act.

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. As the au-
tumn advances and the
water in the soil becomes

Fig. 196. Insect galls

It is probable that by the formation of such galls
many plants are really protected against serious in-
jury, although many of the galls may simply represent
the behavior of protoplasm when injured in a certain
way, rather than a useful way of behaving. It is in-
teresting to note that the galls are always specific.
Thus, both of these galls are on the same species —
the white oak {Quercus alba) — but are produced by
different species of insects: /, by Biorhiza forticomis ;
2, by Halcaspis globulus

scarcer, transpiration is

interfered with. Evaporation from the leaves, however, continues so
long as there is water in the cells. If the loss of water cannot be
compensated by the absorption of the roots, the live cells of the plant
must suffer injury. The leaf cells are the first to be affected. The
loss of the leaves prevents the complete drying up of the plant, and
it also prevents the freezing of live cells (see Fig. 195). The relation
of water to the fall of the leaf has been determined experimentally.

376 ELEMENTARY BIOLOGY

414. Insect galls. The response of plants to special mechani-
cal and chemical disturbances is illustrated by the formation of
the so-called insect galls ^ some of which are shown in Fig. 196.
Many insects sting plants and suck juices from them for food.
The common mosquito is an example, and the plant lice are
sometimes parasitic to a degree that is very harmful. But
many insects sting plants with their egg-laying organs and
deposit the eggs in the tissues of the plant. Associated with
the process of egg-laying there is often a secretion of some
juice from the insect's body. The mechanical or chemical
injury thus produced is probably very slight ; but the young
that hatch from the eggs deposited in the tissues of the plant
begin to feed, and the injury that they do is likely to be of a
more serious nature. We find that many plants begin to grow
rapidly about a point at which insects have laid eggs, forming
casings of various shapes and structures about the mass of
eggs, and eventually about the young insects. Within these
galls the insect larvae find a limited amount of food, and they
are cut off from the rest of the plant.

CHAPTER LXX
THE FOREST IN RELATION TO MAN

415. Forest products. Man depends in many ways upon
masses of trees growing together as forests. It is from the
trees that we get one of the most useful of materials — wood.
This is utilized in hundreds of ways, from the making of tooth-
picks and tool handles to the timbering of mines or the making
of stock for newspapers. All human habitations have some wood
in their composition, and probably most people live in houses
built almost entirely of wood. Every home has furniture made
at least in part of wood ; and in every industry, and in every
office, furniture and appliances made of wood are used.

In the railroad business millions of dollars are spent every year
for the ties upon which the rails are laid. Similar amounts are spent
upon telegraph poles and fence posts, although these are coming to
be replaced by reenforced concrete and other materials. In shipping
goods of all kinds from place to place millions of feet of lumber are
used up, in the form of packing cases and boxes and trunks.

In addition to the wood obtained from the trees these plants
furnish us with charcoal, turpentine, pitch, wood alcohol, and various
gums and resins. From tropical trees we obtain rubber and quinin.
To some extent the dye logwood is holding its own against the ani-
lin blacks, and since the outbreak of the Great War dyewoods have
taken on a renewed importance, because of the changes in the chemical
industries. Bark is taken from certain trees, especially the hemlock,
to be used, for the tannin it contains, in the tanning of leather.

The use of wood as fuel is coming to be restricted more and more,
as we find it more profitable to burn coal, gas, oil, etc., and to use the
wood for other purposes. But every forest and every wood lot produces
annually large quantities of wood that cannot be used in the making
of paper or of other useful things, and this may well be burned.

377

378

ELEMENTARY BIOLOGY

416. The forest and the air. Another use of the forest is
found in the fact that through photosynthesis fresh suppUes of
oxygen are thrown into the air, replacing the carbon dioxid.
In addition to this, the transpiration may be considered a-

help in that it keeps down
the temperature of the
plants and so of the sur-
rounding air. The shade
value of trees is highly
appreciated in the sum-
mer time even by city
dwellers, and the effect of
trees in breaking the wind
is appreciated in the winter
time, especially by those
living in the country.

417. The forest and
water. The most impor-
tant relation of the forest
to man, aside from the
direct utility of the forest
products, is in its effects
upon water. When we
compare the action of rain
water and snow on a hill-
side covered with trees
with the action upon a
similar hillside devoid of
vegetation, we can realize the practical importance of the forest
in relation to our water supply. On the bare hillside the water
soaks down into the soil almost as fast as it falls, or it runs
off, carrying particles of earth along in its course. On the
covered hillside the force of the falling raindrops is broken
by the leaves of the trees, from which the water slides down
to the ground along the twigs and larger stems. The rain

)vered Bare

Covered Bare Covered Bare

April 2-9

April 14-17 April 22-24

Fig. 197.

The relation of the forest to

water flow

In experiments made by government agents a
comparison of a covered area with one devoid
of trees showed (i) that in a given period the
covered area accumulated more snow than the
bare area (this is shown by the relative heights
of the two columns in each pair), and (2) that
in a given period the bare area lost more water
than the covered area (this is shown by the rela-
tive heights of the shaded portions in each pair)

THE FOREST IN RELATION TO MAN 379

that strikes the mulch ^ soaks through slowly ; then, in the en-
tangled soil beneath, it steadily works down to form the under-
ground streams and the springs. Snow in the forest melts
slowly and is gradually absorbed in the spongy bed beneath ;
from this the water slowly escapes into the springs and under-
ground currents. Snow upon the bare ground runs off as fast
as it melts.

Actual proof of the difference was furnished a few years ago by
an extensive experiment conducted by the United States Geological
Survey in the White Mountains. Two similar areas were selected,
each covering about five square miles. One of the regions had been
entirely cut down and burned over; the other retained the virgin
forest (Fig. 197).

The practical bearing of these facts is not hard to under-
stand. Every year, as the snows on the hills begin to melt,
the water rushes down the hillsides in the deforested regions,
causing the streams to overflow their banks and the torrents
to tear down and destroy everything in their path. The
annual damage done by floods in this country is estimated
to be equal to one hundred million dollars. This does not
include the destruction of human life that is often involved
in the floods.

Streams depending upon deforested areas for their water will
be too full in the spring and will run too low in the summer.
Water used for agricultural purposes must be had in abun-
dance throughout the summer, and the destruction of forests
in one region has often resulted in the ruin of agriculture
and the migration of peoples in a distant valley. Navigation
on the larger streams is influenced by the forest in two ways :
the steady fiow of water is maintained by a proper condition
of the forest, and the filling up of the stream by soil is at the
same time prevented.

1 The mulch forms a soft, absorbent carpet, consisting largely of decaying
leaves and other organic matter.

380

ELEMENTARY BIOLOGY

418. Water power. As our industrial civilization depends
more and more upon the use of machinery, we are pressed
to find sources of energy for driving the machines. The con-
sumption of coal has increased so rapidly that the exhaustion

Fig. 198. An eroded slope in western North Carolina

On slopes from which the vegetation has been removed the rains and melting snows

produce destructive effects of great practical importance. (From photograph by United

States Bureau of Forestry)

of the earth's supply is threatened. Water power seems to
be the only source of energy that is constantly renewing itself
at a sufficiently rapid rate. But to maintain the service of
waterfalls we must be sure of the steadiness of the water
supply, and this in turn depends upon the forest.^

1 When we burn coal as fuel we are of course again dependent upon the
forest (though not the forest of our own times), since all coal consists of the
modified remains of ancient vegetations.

THE FOREST IN RELATION TO MAN

381

419. Soil and forests. The relation of the forest to the
soil is also of great practical importance. Every year the
streams and rivers carry down to the sea a quantity of earth
estimated to be worth over a billion dollars. This is not only
a direct loss of agri-
cultural resource ; it
also interferes with the
navigation of streams
and with the condi-
tions of harbors. Mil-
lions of dollars are
spent every year dredg-
ing harbors in this
country, to remove the
soil deposited by the
streams coming from
deforested regions.
And, finally, the mil-
lions of dollars spent
in reclaiming desert
land would all be
wasted but for sup-
plies of water drawn
from regions covered
with forest.

420. Forest control.
Because of our de-
pendence upon the

products of the forest, as well as upon the water and the soil
that are so much influenced by the living trees, the proper con-
trol of the forest becomes a matter of national concern. We
cannot depend upon the private owners of forests to handle
these in such a way as to secure to the general population the
full benefits and protection that are necessary. Ordinarily the
owner of a forest cares, only for what he can get out of it,

Fig. 199. A good stand of trees, Lake Placid,
New York

Forest areas in good condition not only furnish in-
valuable materials, but protect the soil and insure a
steady supply of water. (From photograph by United
States Bureau of Forestry)

382 ELEMENTARY BIOLOGY

and he cannot be expected to take into account effects a
hundred miles away or fifty years away.

The Forest Service of the United States Department of
Agriculture has made many careful, scientific studies of forest
conditions and 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, the
importance of avoiding certain injuries to the forests, and,
second, the methods of increasing their value.

For many years, toward the end of the nineteenth century, the
people of this country were using up trees about three times as fast as
they could grow. This meant that before very long we should have
destroyed all the usable trees and been practically without a suitable
wood supply. A scientific study of the growth of trees in the forest
showed that it is possible to get all the wood we really need without
destroying our forest, if only certain principles are followed (Fig. 200).

It is to be noted that the ordinary virgin forest is practically at a
standstill so far as growth is concerned. While new growth is con-
stantly taking place, this is only enough to offset the death and
destruction among o\^^ trees.

421. Increasing forest area. To meet the growing need for more
wood, it is possible to extend the forest area of the country. Areas
that have been cut and burned over may be reforested, and this
process is under way in many parts of the country. There is a great
deal of worn-out agricultural land and sand-dune land that would be
well suited to forests ; in many cases all that is needed is to prote(^
the young growth against fires. Another method of extending the
growth area is by fuller stocking of existing forest lands. Thus, some
trees are found growing so close together that they never become
thick enough to be of great value for timber ; but in other forests the
trees are so far apart that valuable space is allowed to go to waste.
By selecting trees suitable for a given region, and starting the young
plants rather close together, and then thinning out carefully, the
amount of timber grown on a given area can be greatly increased.

422. Increasing wood yield. Another method for increasing the
wood supply is by the selection of varieties that will give a maximum
of growth in each forest area. It is likely that not more than seventy

THE FOREST IN RELATION TO MAN

383

of the 500 native species 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 advan-
tage. We could replace the red spruce in New England by the
Norway spruce, just as many areas of France denuded by the Great

kAA^AjO-LA-LJJk

LAAM

Fig. 200. Cutting trees to preserve forests

The preservation of the forest does not mean simply to avoid cutting timber. By cut-
ting trees in zones at intervals of a number of years, and by thinning out the trees
where they are too crowded, it is possible to make a given area yield continuous crops
of wood. The zone a was cut first, then zone d, and so on. By the time the last strip
has been cut, the trees on the first strip are well along, and thus a succession of cuttings
may be continued indefinitely

War, and other European regions, are being restocked with Douglas
fir imported from this country. We shall no doubt find foreign trees
better suited to our purposes in many localities than the native trees.
In the course of a number of years the rapid varieties will yield much
more timber than the others. But rapid growth is not of itself a de-
ciding factor, for it is necessary to consider the toughness of wood
and other qualities. The whitewood, or tulip tree, grows much faster
than the oak, but it can never be used as a substitute for the oak.

423. Improving wood quality. Another improvement is being
brought about by the selection of varieties for quality. Without

384

ELEMENTARY BIOLOGY

increasing the actual amount of growth, it is plain that the value of the
growth can be increased if the trees do not have curved or twisted
trunks or branches. By selecting straight-growing varieties and by
concentrating the growth in the best trees (by thinning out the least
desirable ones) it is possible to increase the yield of a forest area.

Fig. 201. United States forest reserves

The economy of national control of forests, as well as the protection of public interests
thereby, has been strikingly demonstrated since our entry upon the Great War

424. Avoiding wood waste. In the national forests the lum-
bermen are given a practical demonstration of the value of
scientific cutting, seeding, reforesting, etc., and also of the
economical handling of growth. Damage to trees often results
from careless lumbering. The tree that is being cut down is
sometimes damaged, and it is sometimes allowed to injure trees
that are left standing. When wood was cheap, a great deal
from each tree was left to rot on the ground. Now everything
that can possibly be used is saved, and the remaining brush-
wood is carefully burned, instead of being left under the trees
as a constant fire risk.

THE FOREST IN RELATION TO MAN 385

425. Advantages of public control. The extent of the national
forests is shown in the map on page 384. In these forests are
conserved and protected the water suppUes for more than a
thousand cities and towns, for over twelve hundred irrigation
projects, and for over three hundred water-power plants. In
these forests nearly ten million head of sheep, horses, and
cattle graze every year, and in them nearly half a million people
find recreation. The forest service sells timber to private users
and gives away firewood to settlers in agricultural lands included
within the forest areas.

426. Forest dangers. The forest is exposed to four serious
dangers :

1. The person who cuts recklessly and destroys for imme-
diate profit what ought to last practically forever. This enemy
can be regulated either by enforcing very strict rules as to the
uses of private forests or by making it impossible for individuals
or corporations to profit at all through the exploitation of forests.

2. Fire. Since this is probably always of artificial origin, it
can be controlled through suitable regulation or supervision.
In the national forests there are well-organized fire patrols.
They have succeeded in preventing many fires and in keep-
ing the total fire damage in the national forest down to a small
fraction of what it is in privately owned forests. 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.

3. Various species of insects.

4. Various species of fungi. These classes of organisms
(insects and fungi) destroy every year trees and timber worth
millions of dollars, and there is no one way to fight them all.

427. Other forest relations. The forest is related to human
affairs as the home of many animals and of many plants other
than the trees. It is in the forest that valuable game and fur
animals find their food and shelter, and the destruction of the
forest means the extermination of many of these animals.

CHAPTER LXXI
BACTERIA AND HEALTH

428. Bacteria and specific diseases. Before germs can cause
disease it is necessary that they enter the body of the host.
Ordinarily they cannot get through the skin. The infection^ or
entrance into the body, therefore, takes place through either
(i) a cut in the skin or (2) one of the regular openings to the
interior of the body, as the mouth or the nose.^

Fortunately for us, most bacteria do 7iot cause disease. We
may therefore carry about with us, in our mouths and air pas-
sages and food tubes, millions of bacteria without being made ill.

After the middle of the last century the improvements in the
microscope and the development of experimental methods made
possible the discovery that certain diseases are caused by mi-
crobes, and that they can be caused i7t no other way. Since the
time of Pasteur, the French chemist who first demonstrated this
idea, many physicians and biologists have succeeded in finding
the particular species of bacteria connected with some of the
most important human diseases, such as tuberculosis, diphtheria,
pneumonia, typhoid fever, tetanus (lockjaw), cerebrospinal men-
ingitis, and others. The methods developed in the course of
these studies have been successfully used in the treatment and
prevention of several other diseases, although the specific or-
ganisms that cause these are not known in all cases. F'or, in
addition to discovering that a given species of bacteria is the
specific cause of a disease (for example, the typhoid bacillus in
the case of typhoid fever), we have found (i) that the bacteria

1 In some cases the bacteria may act upon tissues without penetrating into
the interior of the host, as the diphtheria germ, which lives on the mucous
surface of the throat.

386

BACTERIA AND HEALTH

387

leave the host in special ways ; (2) that they are commonly
transferred to other hosts in special ways ; and (3) that they
then enter the bodies of the new hosts in special ways.

TRANSMISSION OF COMMUNICABLE DISEASES

Disease

How Germs Come

OUT

How Germs are
Carried

How Germs Enter

Chicken pox . .

Mouth and nose

Air

Nose and mouth

Diphtheria . . .

spray
Mouth and nose

Air, objects ex-

Nose and mouth

spray; saliva

posed to spray
or saliva

German measles .

Mouth and nose

Air

Nose and mouth

Measles ....

spray
Mouth and nose

Air

Nose and mouth

Mumps ....

spray
Mouth and nose

Air, objects ex-

Nose and mouth

spray; saliva

posed to spray
or saliva

Scarlet fever . .

Mouth and nose

Air, objects ex-

Nose and mouth

spray; saliva

posed to spray
or saliva

Septic sore throat

Mouth and nose

Air, objects ex-

Nose and mouth

■

spray; saliva

posed to spray
or saliva

Smallpox ....

Mouth and nose

Air

Nose and mouth

Tetanus (lockjaw)
Trachoma , . .
Tuberculosis . .

spray
Contact
Contact
Mouth and nose

Hands or objects
Hands, towels, etc.
Hands, objects,

Breaks in skin
Contact with eyes
Nose and mouth.

Typhoid fever . .

spray
Mouth, excretions,

etc.
Hands, various ob-

food
Food

intestinal waste,

jects, flies

Whooping cough .

and occasionally
through skin
Mouth and nose
spray

Air

Nose and mouth

429. Infection. The table above tells how the germs of
a number of common diseases are thrown off, how they are
carried about> and how they enter the bodies of the new hosts.

388 ELEMENTARY BIOLOGY

In all essentials the methods of infection and transmission
of disease are the same for the domestic animals as they
are for man. When we consider that disease is preventable
just in proportion as we understand the causes and the
modes of infection, we may well believe with certain special-
ists that the study of bacteriology is among the most im-
portant contributions of the nineteenth century to the welfare
of the human race. In Fig. 202 are given the annual losses
due to various diseases, and an indication of the extent to
which these may be prevented.

430. Protection against infection. The chief means of pre-
venting infection consists of preventing the contamination of
our food by bacteria. This means that pains must be taken as
to the exposure of fresh food to dust, to the mouth-spray of
people or other animals, and to contact with unclean hands
or with containers of all kinds. Many cities now require that
all food exposed for sale, such as meat, pastry, confectionery,
and the like, be covered against dust as well as against the
visits of insects ; but fruit and vegetables are still commonly
exposed, at least to dust. In the case of fresh fruits or vege-
tables the peel is usually a sufficient protection against bacteria.
But the peel of many vegetables contains very desirable food
material, which should not be thrown away. Fruits and vege-
tables that are cooked are generally safe, since the cooking itself
kills the bacteria (see p. 112). But lettuce, celery, and other
vegetables that are eaten without cooking have frequently been
the means of infecting people with disease, since bacteria in the
soil may cling to the plants, and some of the disease-causing
bacteria may get into the soil of gardens. Such plants should
be thoroughly washed before being used as food.

431. Care of food. The fact that food rots so readily when
left to itself shows that it contains the materials necessary to
maintain the life of bacteria. We should therefore keep it
under conditions that are not favorable to the growth of these
organisms. We have the practical choice between keeping our

99 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17

— 1 1 1 1 ! 1 1 1 I J ! 1 L ! ! ! ! I I

Fig. 202. Mortality rates for various diseases

In the early part of the period the fluctuations are irregular; in the latter part the
infectious diseases show a steady decline. There is a steady decrease in the general
death rate, and a steady increase in the death rate from cancer. The figures on the left
indicate the number of deaths per io,ooo of population in New York City; the figures
at the bottom are for the years. The general death rate and the cancer line are drawn
on a different scale from the other lines

390 ELEMENTARY BIOLOGY

food very hot or very cold. We are not usually ready to cook
our food immediately ; meats and vegetables have to be kept
for longer or shorter periods before cooking as well as after
cooking. We therefore turn to the low temperature as an aid
in preserving food against the destructive action of bacteria.
Refrigeration has been the means of preventing great loss
through the decomposition of food, since at low temperatures
bacteria cannot multiply. We must be careful, however, not to
assume that well-preserved food from the refrigerator is neces-
sarily free from injurious microbes, since any organisms that
may have been present before the food was placed in the
refrigerator are still there and are still capable of growing and
multiplying when the suitable temperature is reached. It is
also necessary to keep refrigerators perfectly clean and free
from neglected food particles that may retain bacteria. This
principle applies, of course, to all cupboards, pantries, lunch
boxes, or other places in which food is kept temporarily or
permanently.

Milk, soups, jellies, fruit juices, preserves, and similar food
preparations containing a great deal of water are exceptionally
favorable to the growth and multiplication of bacteria. They
are therefore especially subject to the decaying action of bac-
teria, and require special care in their handling and storing.
In making preserves of fruits or vegetables the chief precau-
tions are concerned with the destruction of the bacteria already
present in the materials used, and with the prevention of the
entrance of other bacteria. The first end is attained by
cooking the materials until the heat kills the germs. The
second is attained by placing the cooked material in perfectly
clean vessels that can be covered so as to exclude absolutely
all bacteria.

432. Milk regulation. The regulations prepared by the
health authorities of cities and states for those who have to
handle milk take into consideration the importance of milk
for human beings, especially for children, and the ease with

BACTERIA AND HEALTH 39I

which milk becomes contaminated. The conditions under
which the cows Hve make it almost impossible to prevent
the hairs and skin of the animal from becoming the bearers
of bacteria of many kinds. While the milk in the udder of
the cow may be quite free of any contamination, by the time
the milk has been poured from the pail to the can it is sure
to have many bacteria floating in it. The high temperature
makes the multiplication of the organisms proceed very rapidly.
By the time the milk is ready for delivery in the city, it con-
tains a large number of bacteria in every drop.

On page 127 are given the rules for the care of milk in-
tended for city markets. There is a biological reason for every
rule given, and this should be clear to every student of the sub-
ject. It has been found practically impossible to obtain milk
in large quantities without excessive numbers of bacteria. For
this reason the practice of pasteurization has come into more
and more general use. This consists of raising the temperature
of the milk to about I40°-I55°F., and keeping it there for
from ten to twenty minutes. Pasteurization does not, of course,
remove the bacteria ; it only kills them.

433. Water supply. Next to milk, the water supply is
perhaps the source of greatest danger to the community.
In towns and cities that still depend upon separate wells or
springs for water the amount of sickness and the proportion
of deaths is likely to be much higher than in such places as
have a central water supply. To be sure, if the central water
supply becomes contaminated, more people are likely to be
injured in a short time. But it is easier to control the sani-
tary condition of one large reservoir than that of hundreds of
wells. The bacilli of typhoid fever will remain alive in water
for two or three weeks, and are the most frequent disease
germs transmitted by water. But other diseases may also be
transmitted in this way. The diagram in Fig. 203 shows the
reduction in disease and death that was brought about by
improving the water supply in the state of New York.

392

ELEMENTARY BIOLOGY

When we consider that the contamination of wells, rivers, and lakes
with the germs of disease can be brought about only by discharges
from diseased persons (or at least of persons carrying the germs), we
see how closely connected are the problems of sewage and health.

20

- -f M J

1 1

:/i ^fL

* 1 i

i \ 1 M V ^

-VI 1

'-■ i 1 1

U 1 j j

1 1917 1|\
I 5-8^ 1 ^

"l 1 1 1 1 1 1 I 1 1 1 1 1 1 1 1 1 11

i !

1 !
1 !

1 1 1 1 1 1 1 1 1 1 1

1885

1895

1900

1905

1910

1015

Fig. 203. Typhoid and water supply

For twenty years the deaths from typhoid fever fluctuated between 18 and 31 per 100,000

of the population. Since 1907, when the state authorities (New York) took charge of water

regulation, the death rate from this disease has steadily declined

Wherever there is a sewage system, the law should require that every
house be properly connected with the sewer. There is unmistakable
evidence that the general health is better among people who use
modern water closets than among those who do not. It is also
certain that the latter are too frequently sources of danger to others
in that the contaminations work their way through the ground into
the water supplies upon which others are dependent. Thus again we

BACTERIA AND HEALTH 393

see the interdependence of people, living it may be at considerable
distances from each other or in different states.

Because there is not yet any adequate control over the habits of
those who dwell in the country, in the matter of disposing of house
soil, garbage, etc., it is important for those who dwell in cities that
their water supply be properly guarded, if not at the source, then
through suitable filtration or sterilization. All these activities, and
many others, suggest how human life is constantly influenced and
modified by the activities of these minute yet significant organisms.

1905 1906 1907 1908 1909 1910 1911

Hiliiliriliiii^

1912 1913 1914 1915 1916 1917

^ Fig. 204. The reduction of infant mortality in New York City

This diagram shows, month by month, for a period of thirteen years, the proportion of
infants (under one year old) who died to the infants born. There is a variation from
month to month, with a very striking increase in the number of deaths during the
summer months. When the records showed this big jump in 1905, physicians and
nurses and sanitary experts at once took steps to discover the causes and to devise
preventive measures. Year by year we can see a steady improvement. So much effort
has been made to protect the children for the bad month of July, that in recent years
this month has showed off rather better than the others, and August and September
have become the bad months. With increased knowledge, and especially with wider
application of the knowledge we already have, the high points on these black spots will
be cut down, and the general level of the spots will be considerably lowered. This is but
another way of showing that applied biology saves hundreds of thousands of lives

CHAPTER LXXII
CONTROL AND USE OF BACTERIA

434. Health and the public. As fast as we realize that our
health depends upon the control of outside conditions, we
extend public regulation to many matters that were formerly
considered purely private and individual. A bare list of the
points in regard to which public and official action has been
taken will indicate how widespread are the influences of bac-
teria, and how far progressive communities have gone in the
attempt to control public health.

Not every town has adopted regulations in regard to each of the
matters mentioned in the lists below, but on each point several towns
and cities (or states) have adopted definite regulations calculated to
protect the public health.

In regard to food in general, the methods used in preparing,
handling, and exposing for sale have been regulated. In addi-
tion there are special regulations regarding the following :

1 . Bakeries : conditions of work, ventilation, lighting, clean-
liness, etc. ; the wrapping of each loaf of bread before removal
from the factory.

2. Slaughterhouses.

3. Ice cream.

4. Soft drinks : conditions of sale, cleaning of glasses.

5 . Restaurants : condition of kitchens, cleaning of dishes, etc.

6. Drinking cups in public places.

7. Milk, butter, and other dairy products.

8. Public water supply.

9. Compulsory vaccination of school children.

10. Marriage of persons suffering from certain diseases.

394

CONTROL AND USE OF BACTERIA 395

All of these matters are related to health because they have to
do with special kinds of disease microbes.

For the purpose of enabling the public to measure from
time to time the progress (or the reverse) in matters of
health, population, etc. many states and cities require the
registration of all births as well as of all deaths, and the
notification of the health authorities in every case of conta-
gious or infectious disease. By means of records thus obtained
the public is helped in protecting itself. Many diseases are
subjected to quarantine and placarding. There are provisions
for supplying vaccines, serums, etc. through public laboratories,
and for supervising the manufacture and sale of such prepara-
tions for profit. There are laboratories for making accurate
examinations of blood and other specimens obtained from
patients for the purpose of diagnosis. Provision is made for
disinfection of discharges from the bodies of sick people ; vac-
cination where needed ; inspection of schools and factories to
determine sanitary conditions ; exclusion of sick persons from
schools etc. In some places there are visiting nurses, ambu-
lance service, and hospital service, all helping to keep down
the amount and the intensity of sickness.

The activities of various classes of workers are regulated in
the interests of public health. Licenses are required of physi-
cians, dentists, druggists, nurses, and midwives. Rules are pro-
vided to guard against the transmission of bacteria in barber
shops and through manicurists and masseurs.

The keeping of animals within city limits — dogs and cats,
as well as horses, cows, and poultry — is regulated for the
purpose of preventing the multiplication and spread of bacteria.
In many cities dogs have to be muzzled ; this device must
eventually eliminate all rabies from towns, since this disease is
transmitted by the bites of dogs. The burial or other disposal
of dead animals is also regulated.

Lodging houses, tenements, and workshops must provide suit-
able conditions of light, ventilation, and plumbing. Plumbing

396 ELEMENTARY BIOLOGY

and drainage are subject to regulation, as well as the disposal of
garbage, household and industrial refuse, ashes, etc. In many
towns the scattering of ashes or other dust and the pollution
of the air with smoke are treated as public nuisances.

The prohibition of spitting in public places has come to be
a matter of course in all wide-awake communities, and the same
is true of the use of public towels. The public is also coming
to insist that street cars, boats, and other public conveyances be
kept thoroughly clean and sanitary. In many towns the public
is making provision for baths that are either entirely free for
all to use or open for a nominal fee.

435. Uses of bacteria. We have studied the changes that
bacteria produce in dead organic matter, making the elements
of the latter again available for the living plants, and so for
animals. We have also noted the importance of certain bac-
teria in making the atmospheric nitrogen available for our
growing crops.

There is still another way in which bacteria make dead
organic matter in the soil and in waters available as food. The
bacteria themselves, feeding upon the dead remains, are in
turn eaten by various protozoa and other minute animals.
These are then eaten by larger animals, and so on until we
get to forms that are large enough to serve as food for man,
as shrimps, clams, fish, etc.

436. Bacteria in industry. The decay caused by various bac-
teria is utilized directly in the preparation of sponges for
commerce. The sponges are allowed to lie in tanks of water
until the dead cells are completely destroyed by bacteria. They
are then washed clean, leaving the horny skeletons with which
we are familiar. A similar process, involving the activity of
different kinds of bacteria, is employed in the '' retting " (really
" rotting ") of the soft portions of flax and hemp stalks, to
facilitate the separation of the fibers.

The action of bacteria enzymes is used in the making of
vinegar out of cider, wine, or other liquids containing alcohol.

CONTROL AND USE OF BACTERIA 397

In these liquids the oxidation of alcohol is due to the action
of bacteria. In the making of sauerkraut and other kinds of
pickles, as well as in the curing of silage, bacterial fermenta-
tion is used. In the work of the dairy, from the souring of the
milk and cream to the curing of cheese, bacteria are used at
several points. Cheeses of the Cheddar type and various
cream cheeses, as well as butter, depend for their flavors upon
the particular species of bacteria present during the souring.

It is very likely that bacteria play a part in the curing of tobacco
and in the making of hay, although the problems connected with
these processes have not been thoroughly worked out as yet. In the
preparation of indigo dye from the extracts of certain plants of the
bean family, it is likely that an oxidizing ferment from certain bacteria
performs an essential part of the work. In the preparation of hides
for tanning, certain of the changes are brought about by bacterial
ferments.

In the disposal of sewage in large cities, a process of converting
the decaying mass of organic matter into harmless or less offensive
forms through the action of bacteria has come into extensive use.
The sewage is collected in large tanks. After the fermentation the
" sludge " may be used as a fertilizer.

CHAPTER LXXIII
INSECTS AS SPREADERS OF DISEASE

437. Insects eat. About one half of the different kinds of
animals known to man belong in the class insects. This class
of animals is spread over most of the earth's surface, and
many of the species live in water (although all are air breathers).
In every main division of the class are to be found species that
are closely related to human welfare in one way or another.

Most insects are known to us chiefly as eaters \ and they
eat either materials that are of use to us, or they prey upon
plants or animals that are of use to us.

Like other animals, man is exposed to the attack of insects
in search of food. Many species of fleas and lice, of bedbug
and horsefly, of midges, black flies, and mosquitoes, have
made themselves obnoxious to man by sucking his blood, by
causing more or less serious irritations of the skin, and, as
we have discovered only in recent times, by infecting him
with microbes capable of causing more serious injury.

438. Insects move about. As carriers of disease, insects are
related to us in two different ways. The first is illustrated by
the common house fly, which has been shown to carry various
bacteria, protozoa, and the eggs of parasitic worms on its legs
and proboscis, and to leave these germs where they have a
good chance of entering the body of some human being.

Experiments have shown that the number and kinds of bacteria
clinging to the feet of flies depend altogether upon the kinds of places
in which the flies live. Flies caught in dirty streets showed more than
those caught in clean streets ; those caught in a pigsty showed more
than those caught in the open, and flies caught while feeding in a
swill barrel showed many millions of bacteria.

398

INSECTS AS SPREADERS OF DISEASE

399

The habits of the fly are such that we cannot afford to be
associated with this animal in any way whatever. The female
lays her eggs in horse manure ; but where there is no horse

1 8 15 22 29
JUNE

6 13 20 27
JULY

10 17 24 31 7
AUGUST

5 12 19 2
OCTOBER

Fig. 205. Flies and intestinal diseases

In New York City a careful study was made (1907-1908) to find the relation between the
prevalence of flies and the amount of tyjjhoid fever. The height of the dotted line cor-
responds to the number of flies caught in traps, week by week, from the beginning of
June to the end of October. The solid line corresponds to the number of people who
died from intestinal diseases during the same period in the same districts of the city.
Typhoid is most frequent where and when flies are most abundant, and there is a direct
connection between the insects and the distribution of the disease

manure, she will use cow, sheep, pig, or chicken manure, or
decaying fruit, fish, meat, or vegetables, — ordinary garbage, for
example, — or any mass of decaying organic matter. The adult
fly will visit, for feeding, not only such materials as have been
mentioned, but all kinds of perfectly good food that may be

400

ELEMENTARY BIOLOGY

exposed in groceries, meat shops, kitchens, restaurants, dining
rooms, or picnic grounds. FUes will visit open wounds or sores
on the bodies of animals, and they will visit the excrements of
man and other animals. We may thus see what excellent
opportunities this animal has not only to collect a varied
assortment of bacteria but also to distribute them widely.

wr#

Fig. 206. A breeding place for house flies

The community that saves itself money or trouble by permitting back yards of this kind
usually pays for its economy and indifference with disease and death. With the econo-
mies of motor cars and traction engines must be reckoned the reduction in typhoid
fever and other fly-borne diseases

From a report made by an army commission as to the causes of
epidemic fevers in the army camps during the Spanish-American War,
we learn 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 understand why it
was that more soldiers were killed by intestinal diseases than by
Spanish bullets.

Fig. 207. Food exposed to the visits of flies

Fig. 208. Food protected from flies

Many food dealers have gone to the expense of installing equipment to Protect their

customers from the danger of contaminated food. Whether the dealer can afford to do

this or not, the public cannot afford to leave its food exposed

402 ELEMENTARY BIOLOGY

439. Fighting flies. Just as soon as we realize the relations
of the house fly to mankind, we are likely to be seized with a
hatred for the whole tribe of flies ; and perhaps we may be
tempted to '' swat " every fly that we see. But if we all swatted
flies, and did only that, the fly pest would hardly receive a
serious check ; for flies breed faster than you and I can kill
them, and there is nothing to prevent the flies raised in the
stable down the street from coming into our yard.

We have to attack the insects before they are old enough
to fly about ; that is, we must prevent their breeding by either
removing or destroying, screening thoroughly, or poisoning, all
materials that may serve as food for the maggots.

The struggle between man and the fly is not a single-
handed one, — that of a particular person against a particular
fly. It is a struggle of one "species against another, and
we must carry on our end of the fight through community
or group action. Better than swatting the fly is the com-
plete elimination of the insect from all places inhabited by
human beings.

Many towns have undertaken to exterminate the fly. It has
been found that the most effective method is to provide for the
systematic removal of garbage and stable manure at least once
a week,i and to keep streets, back yards, markets, and kitchens
perfectly clean.

On the farm or in a village, stable manure can be profitably
spread out upon the ground, in field or garden, every day or
two. The manure spread out will dry quickly and be inca-
pable of breeding flies. Exposure to sunlight will kill eggs
and maggots. In larger towns and cities there should be no
difficulty in organizing the work of removing manure and
garbage frequently at a comparatively low cost, since the
manure is worth gathering for fertilizer and the garbage
has a definite commercial value. Where the amount of gar-
bage or manure accumulated is so small that its removal is

. 1 The life history of the fly covers a period of ten days.

INSECTS AS SPREADERS OF DISEASE 403

relatively expensive, arrangements should be made to screen it
so that no flies can reach it ; bul screening is very expensive
and seldom entirely satisfactory.

Lime, crude oil, copper sulfate, formaldehyde, and other poison-
ous substances have been used in the treatment of garbage and
manure to prevent the breeding of flies. But such treatment is in
general undesirable, because it makes the manure and garbage worth-
less for use as fertilizer, since it prevents also the fermentative action
of bacteria, which is necessary to make available the elements of the
organic compounds for plant growth. Borax and hellebore can be
used so as not to injure the manure.

Until a community succeeds in eliminating the flies, it is
well for every household to protect its own food supply by suit-
able screening of the house and by special care in regard to
the exposure of food. Every purchaser of food can help by sys-
tematically refusing to patronize dealers whose premises harbor
flies. And we can all help by keeping our own premises clean
and free from these insects.

CHAPTER LXXIV
INSECTS AS INTERMEDIATE HOSTS

440. Malaria. Of all the diseases from which man suffers,
malaria is said to be the most widespread, occurring all around
the earth as far north and as far south of the equator as mos-
quitoes may be found. ^ The disease is caused by any one of
three or four species of protozoa related to the ameba and
known as the plasmoditmi of malaria. The animal feeds upon
the red corpuscles of the blood of its host, and then spondates
(see p. 294). The spores enter new corpuscles, and the process
is repeated indefinitely, greatly weakening the victim and some-
times ending fatally.

The parasites were seen in the blood of patients by the French
scientist Alphonse Laveran, working in Algeria. He succeeded in in-
fecting subjects with the blood of sick people, but he could not find
out how the infection takes place naturally. It took twenty years
more of careful research and experimentation to establish the fact that
the mosquitoes of the genus Anopheles are the agents of infection.

Two English physicians, Sir Patrick Manson and Dr. Ronald Ross,
helped in the establishment of this important fact by tracing the
behavior of the parasite in the bodies of mosquitoes. Finally, in
1900, an elaborate experiment was conducted by scientists cooperat-
ing in England and Italy. In this experiment a number of volunteers
lived in the Roman Campagna, a region that had long been notorious
for being full of malaria. But the volunteers lived in houses that were
carefully screened against the entrance of mosquitoes. They were
also careful not to go out in the evening (when the Anopheles is about)

1 It has been estimated that in the United States the money cost of malaria
has been as much as one hundred milHon dollars a year. This takes the form
of time lost from work, the cost of drugs, nursing, and medical service, the
unavailability of much fertile land, and so on. In India this disease kills over a
milUon human beings a year, besides causing untold misery to millions of others.

404

INSECTS AS INTERMEDIATE HOSTS

405

without wearing veils and gloves. Thus they lived through the most
dangerous part of the year, from early in July until late in October,
and not one became sick, although many of their neighbors became

Fig. 209. The malaria parasite

The parasite attacks the red blood corpuscle of a human being, «, and when it has
destroyed the corpuscle, </, it breaks up into a large number of spores^ e, which may enter
other corpuscles and start a new cycle. When blood containing the malaria organism,/,
gets into the stomach of a mosquito {Atiopheles) ^ the protoplasm undergoes various
changes, g^ //, resulting in two sexual forms, /,/, which conjugate and produce a fertilized
^ZZi ^- This works its way into the wall of the insect's stomach, /, and breaks up into a
large number of tiny bodies, m^ which finally lodge in the insect's salivary glands, n.
When the insect again stings a person, some of these bodies, 0, get into the victim's
blood and find their way into the red corpuscles, a^ and the cycle begins again, /, stomach
of infected mosquito, showing swellings produced by the parasite

infected with malaria during the summer. At the same time some
mosquitoes were caught and allowed to suck blood from persons suf-
fering from the disease. These mosquitoes were placed in little cages
and shipped to England. Here two young men — one of them the

4o6

ELEMENTARY BIOLOGY

son of Dr. Manson — who had never suffered from the disease, and
who lived in a region where there were no cases of malaria, allowed
themselves to be stung by the suspected mosquitoes. In the course

of a few days both developed

Eggs

«

Lamm

the characteristic symptoms
of the disease. This experi-
ment showed that the night
air and the vapors from the
swamps of the Campagna
were harmless, and that the
sting of a mosquito that had
once bitten a person with
malaria was dangerous. Mos-
quitoes raised from the eggs
and allowed to sting a per-
son do not cause the dis-
ease to appear. Drinking the
water in which the mosqui-
toes developed does not cause
the disease to appear. These
conclusions were later con-
firmed by further experi-
ments, so that to-day there
can be no doubt as to the
relation between the mos-
quito and the transmission
of the disease (see Fig. 209).
The most common species
of mosquito found in various
parts of this country belong
to the genus Culex. This is a
nuisance, but, so far as known,
does not transmit any disease
to human beings (Fig. 210).
441. Yellow fever. This disease is found only in tropical or semi-
tropical regions, although there have been epidemics of yellow fever
as far north as Philadelphia, New York, and Boston. It has been in
the past a much more fatal disease than malaria, and turns out to be
carried by certain species of mosquito. While the parasite that causes

Fupce

Adults

Culex

Fig. 210. Mosquito life histories

The mosquitoes of the genus Anopheles, which
transmit malarial parasites, differ from the com-
mon Ctilex in every stage. We can readily dis-
tinguish the adults of the two genera by the fact
that when at rest the Culex holds its body parallel
to the resting surface, whereas in Anopheles the
hind end of the body is farther from the resting
surface than the head

INSECTS AS INTERMEDIATE HOSTS

407

this disease is not yet known, it is certain that, like malaria, it requires
two hosts for completing its life cycle. At the close of the Spanish-
American War a commission of American physicians undertook to
find out whether the mosquito was really the intermediary in the
transmission of the disease, as had been suspected by many students
of the subject. The commission consisted of Dr. Walter Reed,-

Fig. 211. Camp Lazear

In this building was conducted that part of the yellow-fever experiments which proved
that the disease is not transmitted by infected clothing etc. The cabin consisted of a
room, 14 by 20 feet, with two small windows facing south, closed with wire screens.
Heavy wooden shutters excluded the sunlight. Entrance was through a small vestibule
on the same side as the windows, protected by a wooden door and a screen door and
separated from the main room by a screen door, to make perfectly certain that no
mosquitoes could get in. This house was kept closed during the daytime and had a
temperature of from 92° to 95° F. It was occupied for twenty nights by three American
volunteers, and the test was repeated twice

Dr. James Carroll, and Dr. Jesse W. Lazear, and they were assisted by
a Cuban, Aristide Agramonte, who had recovered from the disease and
was therefore immune. A camp was established in which two cottages
were erected. In one of these the ventilation was intentionally very
poor. In the other there was a mosquito-tight screen separating the
two halves, and the ventilation was very good. Both cottages were
well screened to prevent the entrance or escape of mosquitoes. In
the first cottage three volunteers received cases of clothing and bed-
ding from men who were suffering from yellow fever, or who had

4o8 ELEMENTARY BIOLOGY

died with the disease. They shook out these contaminated articles and
slept in the soiled garments and in the soiled bedclothes for twenty
days. None became infected. This experiment was repeated two
times more, with no results that would indicate the slightest con-
nection between the vomits and excretions of the patients and the
infection of new cases.

In the other building a volunteer allowed himself to be stung by
a mosquito that had drawn blood from a patient some two weeks
earlier. The bedding and other utensils were thoroughly sterilized,
and the volunteer had been in quarantine for two weeks, to make
sure that he was not infected when he came into the building. On
the fourth day he developed the symptoms of the disease. Other
volunteers, on the other side of the screen, were not affected.. Ten
or more individuals contracted yellow fever as a result of stings from
mosquitoes that had previously bitten sick persons, and not one of
those who stayed on the other side of the screen. In the course of
the experiments Dr. Carroll and Dr. Lazear also became sick, the
latter dying as a result (Fig. 211).

442. Fighting mosquitoes. With a realization of the impor-
tance of the mosquito in the transmission of these serious dis-
eases arose the question of how to combat the pests. Of
course each one of us can keep on killing mosquitoes on sight
and feel that he is doing his duty. But the mosquitoes do not
recognize city limits or state lines, and gayly fly from one
man's land to another's. So far the only effective campaign
against mosquitoes has been waged on a comprehensive scale
by a whole community at a time. It seems that the best way to
prevent malaria and yellow fever is by means of ditches to drain
off marshy land,* by means of cartloads of dirt to fill in low-
lying spots, by means of oil on such puddles as cannot be filled
or drained, and by means of lids or screens to cover up such
cisterns, tanks, or buckets as have to be kept with water stand-
ing in them, while all old cans and broken crockery and other
possible containers for water are scrupulously placed where the
female mosquitoes cannot reach them. For the life history of
the mosquito requires quiet water for the laying of the eggs and

INSECTS AS INTERMEDIATE HOSTS

409

the growth of the larva and the pupa.
Without such breeding places, one
year would see the end of all mos-
quitoes in all civilized communities.
In larger bodies of water, where fish
may be kept, these will usually de-
stroy the larvae and thus prevent
the multiplication of mosquitoes ;
but in the shallow margins, where
the fishes cannot reach them, the
mosquitoes have things their own
way. Here it is necessary to keep
the borders of the ponds clear of
weeds, sedges, etc.

The practical effect of extermi-
nating the mosquito is shown by the
decrease of malaria (or yellow fever).
Fig. 212 shows the results for the
island of Cuba. A similar record
stands to the credit of our national
government in connection with the
work of digging the Panama Canal.
The region through which the canal
runs was a veritable plague spot.
During the various attempts of the
French engineers to construct the
canal, disease made the completion
of the work practically impossible.
When the United States took over
the enterprise, the first step was
the establishment of sanitary con-
ditions ; and the largest part of

the problem was the extermination of the mosquito through
draining and filling in, and the inspection of inhabited regions
to prevent the maintenance of breeding places for the insects.

1870 1880 1890 1895 1897 1899 1901
1896 1898 1900

Fig. 212. The reduction of
yellow fever in Cuba

The mortality from this disease had
always been very high, but much
worse in some years than in others.
The year 1896 was unusually bad,
and 1897 not much better. Imme-
diately after the American army of
occupation began to clean up in
Havana, in 1898, the sanitary condi-
tions showed marked improvement.
By eliminating the breeding places
of mosquitoes, yellow fever has been
completely banished from the island

4IO ELEMENTARY BIOLOGY

443. Other disease-bearing insects. Fleas have been implicated in
a very serious combination injurious to man. The bubonic plague,
which has in past times been the most dreaded of diseases, especially
in Asia, was found (in 1894) to be caused by a specific bacillus. But
the mode of infection was not known until quite recently. The Chinese
had observed, centuries ago, that there was some connection between
the dying of rats in large numbers and the appearance of the plague.
Modern scientists set to work to find out whether the rat plague was
in any way related to the human plague, and they found that the same
bacillus is the cause of both. Then it was found out that the plague
spreads from rat to rat not by contact of the animals but through fleas
that suck the blood of sick rats and later bite others, thus transferring
the infection. Further observation showed that the plague is primarily
a disease of rats, and gets into human beings when the fleas abandon
dead rats and infect men and women. The plague has spread from
the Orient, and cases have appeared at several ports in the United
States within a few years. The methods developed for dealing with
this danger are directed not toward killing the bacteria but toward
killing the rats and fleas. A ship coming from an affected port is
thoroughly fumigated to kill the fleas and rats, special devices are
attached to ropes and chains to keep rats from getting ashore (or
aboard, for that matter), and a search is made for hiding places in
which rats may be concealed. Li California it was found that the
ground squirrels have become infected with the plague bacillus, and
systematic patrols are established to catch rats and ground squirrels,
which are regularly examined for possible infection.

Since the United States joined the Great War, many important
medical problems have been solved by our investigators. One of
these had to do with the transmission of trench fever, a disease that
caused a great deal of suffering and incapacity, although it was
seldom fatal. Volunteers from the ambulance and field-hospital units
allowed the blood of patients to be injected into their veins. The
development of the disease in the men so treated showed that the
sickness is due to a germ (too small to be seen with the microscopes)
present in the blood. Other volunteers allowed themselves to be
bitten by lice taken from the bodies of sick men, and many of these
developed the disease, while others, bitten by lice from healthy men,
remained unaffected while living under exactly the same conditions.
This showed that the germs are carried over by means of the louse-

INSECTS AS INTERMEDIATE HOSTS 411

Measures were then taken to exterminate the " cooties," as the lice
were called by the soldiers. The service that these sixty-six volun-
teers rendered in this experiment was quite as important as anything
else they could do, even from a military point of view, for it estab-
lished facts that made it possible to save the equivalent of thousands
of soldiers for the fighting line.

444. Intermediate hosts. It is not uncommon to find among para-
sites the dependence upon two hosts for a complete life cycle. This
is found among plant parasites as well as among animal parasites ;
and when there is any doubt about the life history of any such organ-
ism, the investigators at once suspect the existence of an alternate
host. Through the discovery of the complete life history of many
parasites it has been possible to eliminate diseases by the attack upon
the intermediate host. For example, in the case of a certain variety
of " wheat rust " the alternate host was found to be the barberry
plant. By cutting down the barberry plants the farmers saved many
a crop of wheat from destruction by the fungus. In the case of cer-
tain kinds of tapeworm it was found that the intermediate host is the
pig. Here safety lies not in killing off all the pigs, but in cooking the
flesh of the animal so thoroughly that the resting stage of the worm
cannot reach the inside of the human digestive system alive.

CHAPTER LXXV
INSECTS AND HUMAN WEALTH

445. Insects as food. In certain parts of Africa and Asia, as
well as in South America, Mexico, and Central America, the
natives are said to use various species of locust and caterpillar

Fig. 213, The clothes moth [Tmea pellionella)

It is the larva of this animal that eats woolen and fur material. The eggs are laid on the

material and hatch out when the temperature is sufficiently warm. It is for this reason

that we rarely find the animals in the winter, and it is for this reason that furs and woolen

rugs etc. are placed in cold storage during the summer months

as food. Ants and termites, cicadas, the grubs of beetles, and
the eggs of v^ater beetles are also consumed. The Chinese
sometimes eat the pupa of the silk moth, after the silk has been
removed from the cocoon. In so-called civilized countries the

412

INSECTS AND HUMAN WEALTH

413

only insect that supplies food to man is the honeybee, whose
honey has been used by man for many centuries.

446. Insect products. The wax obtained from bees is of
great practical value, but it is coming to be replaced more
and more by paraffin, which is obtained from petroleum.

Another insect product of
growing importance, and one
for which no satisfactory sub-
stitute has yet been found,
is lac. The lac is used as a
dressing for wood and other
materials, as shellac, as a stif-
fening for felt in the making
of hats, as an insulating var-
nish in electrical work, in the
making of lithographer's ink
and of sealing wax, and in
increasing quantities in the
manufacture of phonograph
records.

The cochineal, another
member of the scale-insect
family, furnishes a beautiful
red dye, v/hich was formerly
used in large quantities. This
source of supply is of de-
clining economic importance
because of the rapid development of the anilin-dye industry.

The whole silk industry rests upon the fiber obtained from
the cocoon covering of the silk moth. Although the chemists
have devised ingenious processes for making artificial silk out
of cotton and out of wood, we shall probably continue to
cultivate the silk moth for a long time to come.

Many of the beetles may be considered as useful, since
they destroy large amounts of dead animal remains, as do

Fig. 214. Destruction wrought by ants

Part of a post completely ruined by the
excavations of carpenter ants. There are
several species of Camponotus and of other
genera which are known to bore into wood.
(From photograph by New York Botanical
Garden)

414

ELEMENTARY BIOLOGY

also some of the ants. In this way they may be looked upon
as scavengers. And a few insects, in the course of their
predacious activities, devour forms that happen to be injuri-
ous to us. This is illustrated by some of the beetles like the
lady bug, which eat plant lice and thus keep them in check.

We make direct use of very
few insects. Many species are
nevertheless of indirect value
to us as important links in that
chain of life extending from
decomposing organic matter at
one end to the larger useful
animals at the other. It is cer-
tain also that very many species
of insects are essential to the
propagation of various species
of plants, since they are the
sole agents in the distribution
of pollen (see pp. 309 ff.).

447. Destructive insects. In
this country alone insects of va-
rious kinds destroy every year
materials and goods estimated
to be worth more than two
hundred million dollars. This includes stored food, clothing,
furniture, carpets and hangings, and furs.

. The clothes moth is one of the most familiar of these destruc-
tive insects, for it is found nearly everywhere that human beings
are (Fig. 213). Thorough airing and exposure to sunlight for
a few hours will be likely to kill any of the eggs. Naphthalin
moth balls do not kill the animals, but repel them and thus
prevent destruction. Infested material should be treated with
gasoline and then thoroughly aired before being used.

The cockroaches, of which there are several species, will
eat almost any organic matter, but are seldom destructive to

Fig. 215. Meal-worm

Adult and larva of the miller beetle
{Tcncbj'to molitor)

INSECTS AND HUMAN WEALTH

415

valuable materials. Yet their presence in a house is an indica-
tion that there are crumbs and other scraps of food about, and
it is perhaps as well for the cockroaches to eat these as for

a b c

Fig. 216. The flour moth {Ephestia kuehniella)
a, larva ; b, pupa ; c, adult

some more objectionable animals to do so. On the other hand,
they may become a serious menace, in the course of their
wanderings, since they may carry disease germs to the food.

6 c d

Fig. 217. The buffalo moth

This insect {Antkrenus scrophulariae) is a beetle, but is commonly called a moth because

it injures furs and rugs in a manner resembling that of the clothes moth. «, larva;

b^ pupa in larval skin ; c^ pupa ; d^ adult

Ants have been very destructive not only to food materials
but also to furniture, clothing, wooden utensils, and even to
wooden houses (Fig. 214). The Argentine ant was introduced
into this country in the early nineties at New Orleans, and
has been more destructive in southern parts of the country
than any of our native species.

41 6 ELEMENTARY BIOLOGY

Ants and cockroaches are always a nuisance about a house
and can be exterminated, once they get in, only through care-
ful attention to their nests, cracks in the walls, etc., and to the
availability of material that will attract them. Corrosive sub-
limate is used to poison them, solutions being sprinkled into
the cracks. The cockroaches can be driven out by systemati-
cally sprinkling borax about the kitchen.

Weevils, small beetles with beaks, are very destructive to
stored grains, beans and peas, etc. There are many different
species, and they are all destructive. Infested granaries and
warehouses need to be thoroughly fumigated with carbon
bisulphid, which kills the eggs and the larvae as well as the
adults (see Fig. 219, ^).

Flour is often spoiled by other beetles, as the meal-worm
(the larva of a black beetle, Tenebrio (Fig. 215)), and by a
species of moth, Ephestia kiiehniella (Fig. 216).

Another destructive beetle is the so-called buffalo moth,
shown in Fig. 217. The larva of this carpet beetle is very
destructive to rugs and other woolen material.

CHAPTER LXXVI

INSECTS AND OTHER ORGANISMS

448. Insects and useful plants. From the time when men
first began to cultivate plants for their own use, insects of one
kind or another have caused parts of each year's work to be
wasted. There are
early records of the
destruction caused
by locusts, and this
name has come to
be applied to many
varieties of insects
that move in hordes.
One of the plagues
of Egypt was a
swarm of locusts,
insects which are
referred to in the
Bible repeatedly.

The first effort
in this country to
aid agriculture by
means of an official
investigation of in-
sect ravages was
made in the seven-
ties, when an outbreak of this pest did damage over an area
of about two million square miles west of the Mississippi River.
Since then the federal government and the various states have
kept up systematic work through experiment stations or special

417

Fig. 21

The potato beetle {Leptinotarsa
decemlineata)

There are two or three broods a year. The full-grown
larva crawls into the ground, where pupation takes place.
The winter is passed underground in the adult stage. The
tachina fly, shown in the center, is one of the most impor-
tant enemies of the potato beetle. The fly lays eggs in the
larva of the beetle, and the maggots destroy their host

4i8

ELEMENTARY BIOLOGY

agents and commissions, designed to counteract the injuries
done by insects to valuable plants. It is estimated that the
damage done to our crops by the activities of insects amounts
to from six hundred million to seven hundred million dollars
every year. To this must be added the injury to forests and
forest products, and the injury to animals.

The locusts and many other species of insects will eat almost
every kind of plant ; but many insects confine their attentions

Fig. 219. Cotton-hoW weevil {Ani^onomtis ^andis)

This animal feeds only upon the cotton plant and could probably be completely exter-
minated if the planting of cotton were suspended for a year or two. This was the advice
of the government experts to the growers of Texas about twenty years ago ; but it was
unheeded, with the result that millions of dollars' worth of cotton have been destroyed
each year since. Rotation of crops was finally forced upon many of the farmers, with
beneficial results, a, larva ; d, larva in mature boll ; c, pupa ; d, pupa in boll ; e, adult

to one or a limited number of food plants. The damage done
by such insects is accordingly confined to special kinds of crops.

The Colorado potato beetle is perhaps the best known of the
special-crop insects (Fig. 218). It is kept in check by the use
of poisonous sprays or powders applied to the growing plants.

The cotton-boll weevil has spread over a large part of our
cotton area in recent years and has ruined many a crop
(Fig. 219). This animal is very susceptible to extremes of
temperature and has many natural enemies. Planting early-
ripening varieties in wide rows, and then burning the stalks
and rubbish after the harvest, will do much to keep the pest
under control.

INSECTS AND OTHER ORGANISMS

419

The gypsy moth has been known as a pest for nearly two
hundred years. The larvae feed upon the foliage of many kinds
of forest and orchard
trees, ruining the plants
completely (see Figs. 220,
221).

The codling moth is
familiar to everyone who
has found a wormy apple.
This insect is present
wherever apple trees are
grown, and in some re-
gions it destroys from 40
to 7 5 per cent of the crop
(see Fig. 222).

The Hessian fly is so
called because it was sup-
posed to have come to
this country with the Hes-
sian soldiers during the
Revolutionary War. It
has spread to all parts of
the world, probably at-
tached in the pupal stage
to wheat straw used as
packing for merchandise
or as bedding for horses

Fig. 220.

The gypsy moth [Poyihetria
dispar)

This animal was introduced into this countr\' about
1869, in the course of some experiments made to
find a substitute for the silk moth, and in twenty
years it became so great a nuisance that the legis-
lature of Massachusetts made an appropriation for
the study of methods to be used in checking the
insect. In ten years over a million dollars was
spent in the fight, but further work was stopped
by some of the legislators whose regions had not
been affected. The insects then multiplied to such
an alarming extent that in 1906 about a quarter of
a million dollars was again spent in the fight,
a, male adult ; /;, female ; ^, larva ; d^ pupa

The Sa7i Jose scale
has been very destructive to fruit trees, attacking the leaves
and twigs as well as the fruit of many cultivated species.* It
was introduced from China on some nursery stock and was

and cattle. It has caused
great damage to wheat,
and it sometimes attacks
barley and rye.

420

ELEMENTARY BIOLOGY

first noticed at San Jose, California. In twenty years it had
spread to all parts of the United States and also into Canada.

Aside from the
insects mentioned
there are hundreds
of others that at-
tack all our garden
and field crops and
orchard and forest
trees. It is hardly
possible to find a
plant that has not
one or more serious
insect enemies.
449. Insects and
useful animals. It
has been said that
every plant and
every animal has its
parasites and its
preying enemies.
And it is probably
safe to add that
every organism of
any size has its
enemies among the
insects.

The mammals
and birds which are
most familiar to us are annoyed by various flies, lice, gnats,
and fleas, which sting and suck blood. There are a number
of parasitic diseases of animals other than man that are trans-
mitted .by insects either directly or indirectly, the insects acting
as intermediate hosts. In addition to these sources of injury
there are some insects that attack larger animals more viciously.

Fig. 221. Gypsy and brown-tail moths (191 7)

The region between the dotted line and the ocean is in-
fested with both species. The brown-tail has also invaded
the region shown by the shaded surface

INSECTS AND OTHER ORGANISMS

421

The botflies are representative of a large group of insects
that are often injurious to horses and cattle (see Fig. 223).

Fig. 222. The codling moth {Carpocapsa pomonella)

a, where the egg is laid on the apple ; d, larva, the " worm " of the apple ; c, cocoon ;
d, pupa ; e, adults

The ox warble lays its eggs on the cow. It is not certain
whether the larvae work their way through the skin or from the

Fig. 223. The horse botfly {Gastrophilus eqiii)

The egg, a, is laid on the hair of the horse and is swallowed, together with the larva, i5,
in the saliva. In the stomach the larvae attach themselves, often causing serious irri-
tations and incapacitating the animal for work. The larvae escape from the host with
the excrement, and then pupate in the ground. <r, pupa ; d^ adult

alimentary canal. They finally lodge under the skin and thus
ruin millions of dollars' worth of hides, besides making the
animals sick and reducing their milk and beef values.

422

ELEMENTARY BIOLOGY

450. Fighting insects. One of the first suggestions that
insects could be controlled by encouraging other insects was
made about a hundred years ago by two English entomologists,
who declared that an increase in the number of ladybirds in
greenhouses and fields would clean out the aphids, or plant
lice, and insure the hops against destruction (see Fig. 224).

In this country various species of native ladybirds serve as effec-
tive checks upon plant lice of many kinds. It has been possible to
control the destructive Hessian fly by means of the parasite Polygnotus.

Fig. 224. The calosoma beetle (Calosoma sycophanta)

This beautiful green animal was used by a French scientist in a campaign against the
gypsy moth in 1840. In recent years this method of fighting undesirable insects by
encouraging the spread of an enemy insect has been rapidly extended, especially in the
United States, which leads the world in applied entomology. «, adult ; b^ larva feeding
on pupa of gypsy moth ; c^ adult feeding on larva (caterpillar) of gypsy moth

Shipments of such parasitic insects from one part of the
country to another are frequently made to meet outbreaks of
injurious insects. A further step was taken when specialists
were sent abroad by the government to look for natural
enemies of injurious insects in the regions from which these
insects originally came.

The United States probably suffers more from injurious insects
than any other country, because there have come here with the mi-
grations of peoples a large number of foreign insects, without their
natural enemies. This country has also done more than any other in
the scientific and practical study of insects and of methods of control.

INSECTS AND OTHER ORGANISMS 423

Ladybird beetles have been imported from China to keep down
the San Jose scale. Calosoma beetles and several parasitic, wasplike
insects have been imported to fight the gypsy moth and the brown-
tail moth. This kind of work is growing very rapidly. There are now
several stations in this country where insects are cultivated on a large
scale, to be sent where needed in controlling injurious insects.

Sprnyifig of orchard trees, shade trees, and crop plants with various
kinds of poisonous mixtures is one of the common means used by
farmers in controlling the damage resulting from insect depredations.

The rotation of crops is used for the purpose of starving out one
generation of injurious insects. This can be used against insects that
confine themselves to special kinds of food plants.

In recent years it has been found that insects are subject to fatal
diseases caused by species of fungi. Cultures of such fungi have
accordingly been used to fight insects. A number of the insects are
caught alive and infected with the parasitic fungus, and then set free
again. The escaped insects infect their fellows, and millions are thus
killed off. This method has been successfully employed against locusts
in South Africa and in Yucatan.

The other natural enemies of insects are toads, frogs, snakes, and,
most important of all, nearly all kinds of birds. A given amount of
money spent in protecting and encouraging the native birds of a
region is likely to produce more beneficial results than any other
method of fighting insects.

451. The balance of nature^ The number of individuals in
a species fluctuates from year to year, partly on account of
climatic conditions, as when an early frost destroys plants
before the seeds are ripened, or when the frost kills off certain
enemies. But much of the fluctuation is due directly to the
variation in other species. A good year for ladybirds will mean
a poor year for scale lice ; but the following year the shortage
in scale lice will reduce the number of ladybirds. The living
beings arc related to each other in hundreds of ways,, so that the
elimination or unusual increase in one species is likely to affect
the well-being or even the existence of another. Every species
has its friends in the living world, as well as its enemies, and
when man undertakes to change the face of the earth with

424 ELEMENTARY BIOLOGY

respect to any species, he must proceed cautiously and on the
basis of a thorough knowledge of all the relations of the species
concerned, and not merely on the basis of a superficial answer
to the question. Is that species useful or harmful to me ? It
is practically impossible to reduce the numbers of one species
without producing far-reaching effects upon other species. It is
not a matter of interfering with nature's plans, as some sup-
pose. It is a matter of disturbing a certain balance that it has
taken a long time to establish, with possibilities of unknown
consequences.

When rabbits were introduced into Australia, they multiplied so
rapidly that before many years they became a real pest, and the
government offered bounties for their extermination. Here was a
region admirably fitted for the life of these animals, and until man
interfered there had been no such animals there. The same kind of
thing happened with the introduction of the water cress into New
Zealand, and with the introduction of the English sparrow into the
United States. Probably these organisms throve better in the new
surroundings because they did not here meet their old enemies.
These facts should help us to realize how closely dependent upon
one another the various species of plants and animals are.

CHAPTER LXXVII
BIRDS m RELATION TO MAN

452. The food of birds. As in the case of most animals,
birds are important to us chiefly because of the food they eat.
But unUke most insects, the feeding of birds usually turns out
to be of advantage to mankind. Observation has convicted
many birds of eating fruit in the orchards, and the sharp-
shinned hawk has been caught carrying off hens from the
barnyard. But the systematic study of the contents of birds*
stomachs has shown that most of the food of practically all
the common wild birds consists of insects, the seeds of various
undesirable weeds, and field mice, shrews, mice, and other un-
desirable animals. In other words, with a very few exceptions,
the common birds are worth more alive than dead. The value
of most wild birds as destroyers of insects, vermin, and weeds
is vastly greater than their value as sources of feathers, as
food, or as objects of sport.

453. Destruction of birds. Many birds are destroyed wantonly
by ignorant boys and men, others are killed to supply feathers,
and still others are exterminated in the destruction of eggs and
nests out of idle curiosity or in the interests of untrained col-
lecting. In rural and suburban districts the domestic cat is a
serious menace to the native birds, and does damage that is far
from compensated for by the mice or rats killed by the cats.

During their migrations many birds are killed by flying
against telephone and telegraph wires, and against plate-glass
windows. Along the shores, migrating birds frequently hover
about the lighthouses at night until they are exhausted. The
extension of cities, the clearing of forests, and the improvement
of farms are all tending to exterminate various species of birds.

425

426 ELEMENTARY BIOLOGY

The destruction of dead limbs and dead trees in forests and
wood lots will mean the disappearance of the downy and the
red-headed woodpeckers, but it is worth while to keep the
wood-lot clear.

The spraying of orchard trees with poisons intended to
destroy caterpillars has led to the death of thousands of birds
that eat the poisoned insects. It is probable that in the long
run it would be more economical to encourage the birds to
nest in our orchards and let them keep the insects in check,

454. Protection and encouragement of birds. Many of the
destructive agencies that affect birds are directly under our
control. When once we are convinced that it is worth while to
do so, it is possible to place electric wires underground, as is
now being done in the cities, for example. The Royal Society
for the Protection of Birds, of England, has had gratings
placed upon a number of lighthouses on the coast, to serve
as bird-rests. Here the migrating birds rest until morning
and then continue their flight. Thousands of birds are thus
saved from destruction ; and when we realize the value of the
birds, we shall no doubt plan to build all of our lighthouses
with some consideration for the safety of these animals.

Men and boys will have to be educated to enjoy life without
destroying useful animals, and to find sport in opera glasses
or the camera ; and girls will have to be educated to be happy
without birds' plumage, or to be content with the dyed feathers
of domestic fowl.

Those who have tried it seem to get as much fun out of
building nest boxes and shelters for birds as others can get
out of shooting or trapping them. And the birds that have
been encouraged to make their homes in our immediate neigh-
borhood 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 bird nests, we
may do ' a great deal to protect them against starvation after
heavy snowfalls. At such times there is practically no food

BIRDS IN RELATION TO MAN

427

available in the fields or woods. The scattering of grain or
bread crumbs will enable many birds to survive until the ground
is clear and they are again able to find food for themselves.

Cooper's hawk {Accipiter coopert)

Bronzed grackle {Qjiiscnbis quisaila)

Blue jay {Cyanocitta cristata) Yellow-bellied sapsucker {Sphyrapicus varins)

Fig. 225. Some undesirable bird neighbors

Cooper's hawk preys upon poultry and insectivorous birds. The blue jay and the

bronzed grackle destroy the eggs of other birds, and the grackle also eats a great deal

of grain. The yellow-bellied sapsucker injures standing trees

The cat and all its wild relatives are so destructive to birds
that it is doubtful whether we should not all be better off
with the domestic cat completely eliminated from our lives.
There are some good things to be said in favor of the cat ;
but the other things more than offset them. The red squirrel

428

ELEMENTARY BIOLOGY

often destroys the eggs and sometimes even the young of
birds, and does nothing to compensate for this damage.
These animals should therefore be killed, to give the birds a

Cedar waxwing (A mpelis cedrornm)

Crow {Corvits americanus)

Red-headed woodpecker {Melanerpes
erythrocephahis)

Great blue heron, or crane
{Ardea herodias)

Fig. 226. A bird rogues' gallery

The cedar waxwing destroys fruit and disperses weed seeds. The crow destroys grain,

fruit, useful insects, and the eggs of useful birds. The red-headed woodpecker destroys

cultivated fruit. The blue heron eats fish and frogs

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 considered serious enemies.

BIRDS IN RELATION TO MAN 429

455. Undesirable birds. It is impossible to class every spe-
cies of bird as altogether useful or altogether injurious. A bird
may be very useful in one region and injurious in another.
The red-tailed hawk feeds on field mice in one region and dis-
covers 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 black-
bird ate so much grain in Nebraska a number of years ago that
the farmers just 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.

456. Direct economic value of birds. The poultry and eggs pro-
duced in this country and sold for food every year are valued at over
five hundred million dollars. To this must be added game birds used
as food, the value of which it is practically impossible to estimate,
and importations of bird products. Imported feathers and downs
come to about eight million dollars a year.

The most valuable organic fertilizer consists of guano, which is
the refuse of millions of birds, accumulated through many years upon
various islands off the coast of South America (see p. 66).

The satisfaction yielded to the observer by the song and chatter
and by the appearance of birds would seem to be enough to pay for
the maintenance of many of these interesting animals; but we can
have these returns without paying for bird feed, and get in addition
the very considerable contribution that they make to the suppression
of undesirable insects, rodents, and weeds.

CHAPTER LXXVIII
SOCIAL LIFE OF ORGANISMS

457. Self-sufficient individuals. Among the lowest forms of
plants and animals each individual is quite independent of its
neighbors, as we may see in the case of the ameba, the Para-
mecium, the green slime, the various bacteria, and so on.

Fig. 227. Diagram of sponge structure

A sponge is a colony of cells arranged about hollow spaces, a^ which are connected with
the surrounding water by means of hollow channels, b^ carrying currents inward, and by
means of other channels, c, carrying currents outward through larger tubes, or " sewers," d.
The currents are produced by the constant vibration of cilia projecting into the spaces,
and they bring to the cells fresh supplies of food and oxygen, and carry away waste

Among many of the algae the cells generally remain attached
to form long filaments, but there is apparently no physiological
connection, and a break in the filament does not affect the
activities of the severed portions.

Among the more complex algae, such as the bladder wracks,
detached portions may continue to grow, since each portion de-
pends upon materials absorbed from its immediate surroundings

430

SOCIAL LIFE OF ORGANISMS 43 1

for its sustenance. But among these higher algae the growth
of the mass of cells assumes a rather definite form, and certain
of the groups of cells become specialized as anchorage organs,
others become specialized as reproductive organs, and so on ;
and it takes all of these together to make up a complete life^

Fig. 228. Colony of Hydractinia

In this colonial animal (related to the jellyfish and to corals), as in many others, there
are distinct kinds of individuals, called hydranths. a, vegetative, or food-getting,
hydranths, which take in and digest food for the whole colony ; b^ vegetative hydranths
in various stages of contraction : c, protective, or fighting, hydranths, which bear large
numbers of nettling cells ; </, reproductive hydranths, male and female, which throw off
sperm cells and egg cells respectively ; e, buds, or undeveloped hydranths. (Photograph
from model in American Museum of Natural History)

If we consider the whole plant as an individual, we see that
it is quite possible for a single plant to continue its life without
relation to any others of the species. In general this is true
of all the plants, from the lowest to the highest.

458. Differentiated cells. When we pass from the one-celled
animals to the sponges (Fig. 227), we find that while the life

432

ELEMENTARY BIOLOGY

of each cell is practically independent of that of its neighbor,
there is some differentiation as to cell structure, and there is a
great deal of common activity.

459. Differentiated individuals. Among the Coelenterata
(to which branch belong the hydra, jellyfish, sea anemones,
and corals) we find species in which the individuals are quite
independent, others in which there are colonies of similar

individuals, and still
others in which the
individuals are differ-
entiated in structure
as well as in func-
tion (Fig. 228). The
'' Portuguese man-of-
war" consists of sever-
al kinds of individuals,
— nutritive, locomo-
tive, and reproductive.
460. Colonial ani-
mals. Above these
simple colonial ani-
mals we find forms in which the interdependence within the
specifes is chiefly confined to reproduction and the care of
the young (see pp. 331 ff.), but toward the upper end of each
of two very important branches — the Arthropoda and the
Vertebrata — there appears a form of colonial life which is very
significant to us, from a practical point of view as well as from
a theoretical one.

In an ant colony there may be one or several queens or
female ants, thousands of workers, and many soldiers. After
the colony is started, the queen may lay eggs continually. The
workers extend the nest and keep the structures in repair.
They also go forth to forage for food, look after the eggs,
larvae, and pupae, and clean out all foreign matter that cannot
be used (Fig. 229). In some species the soldiers are quite

Fig. 229. Ant individuals

In this ant {PotteTa pemtsylvanicd)^ as in so many

others, the worker, r?, is easily distinguished from the

female, ^, and the male, c. (After Wheeler)

SOCIAL LIFE OF ORGANISMS 433

distinct from the workers, and engage in fights with other ants
that may invade or approach the entrance of the nest, whether
of the same species or of a foreign species (see Fig. 193). In
some species of ants the workers are of two distinct sizes and
show marked differences in behavior as well as in structure.

Fig. 230. Honey-pot ants

In this species of ants, found in California, some of the individuals become reservoirs
for honey gathered by the forage workers. These living honey-pots cling to the roof of
a chamber by their feet, and receive into their crops the food gathered by the workers.
From time to time one of the nurse ants comes to the honey-pot and receives into her
crop a quantity of the stored fluid, which she then transfers to the larvae

In a hive of honeybees the individuals are engaged in
several different occupations. Some are building comb, others
hang up by their feet and secrete wax plates or scales,
others pack pollen into cells, some are feeding the young,
and so on. You could probably distinguish the queen bee
from the others by her size, but all the workers would look
alike to you. Or you might notice that the nurses were more
fuzzy than the foragers. This does not mean that there are
two distinct kinds of workers. Apparently the workers behave

434 ELEMENTARY BIOLOGY

differently at different ages ; thus, when first out of tfie pupal
stage the young bee is a nurse. She does not leave the hive
to forage for a week or more, and she is more fuzzy now than
those in the foraging stage, because she has not had the time
and the trials to break or rub off her hairs.

The high degree to which the division of labor is carried among
the social insects, and the complexity of their various activities, have
led to a great deal of speculation as to how the animals are directed
in their cooperations. Do the insects remember and plan and fit their
actions to purposes in the same sense as human beings do ? There
is a great deal of evidence to show that what has been called recog-
nition by a bee or ant of others from the same colony is nothing at
all like our recognition of those with whom we are familiar. It is
more like what happens when a blind person smells a rose that
arouses agreeable feelings in him. And so with many other peculiari-
ties of these animals, it is possible to understand much of what they
do without assuming intelligence.

461. Coordination. In the division of labor there is involved
a great deal of coordination. That is, so long as it is impos-
sible for each individual to carry on a complete life, it is neces-
sary that there be some way of exchanging materials or services.
This situation has frequently been compared to the physio-
logical division of labor that we find in our own bodies and
in other many-celled organisms. We have seen that there is
a great deal of coordination through the blood system, through
the lymph, and through the nervous system. In a colony of
disconnected individuals the coordination must be brought
about by what the animals do to each other directly, or by
means of the materials with which they all deal. But it is not
necessary to assume that there is a conscious cooperation that
involves common aims and intercommunication.

There can be conscious cooperation only where there is also
a certain degree of general intelligence. In every case there is
a great deal of interdependence, so that the individual separated
from the group becomes almost helpless.

SOCIAL LIFE OF ORGANISMS 435

Among many species of birds and mammals there is a degree of
social life that extends somewhat beyond mere gregariousness. The
Russian explorer Peter Kropotkin has brought together in his very
interesting book, " Mutual Aid a Factor in Elvolution," hundreds
of examples of animals that hunt in groups, or post sentinels to
guard against danger, or fight off attacks of enemies through con-
certed action, or in other ways show mutual interrelations within
the species.

462. Interdependence. Every one of us is dependent upon
others of the same species in hundreds of ways. As members
of the community we are dependent upon each other for vari-
ous kinds of personal and specialized services. We depend
upon community action for our safety from various plants and
animals, as well as from antisocial individuals who would
prey upon the rest, and from inanimate dangers, such as
fire and flood and storm. We depend upon each other as
members of the state or nation in the exchange of materials
that are found in some regions but not in others, and upon
this is founded all of our commerce. As members of the
state or nation we depend upon joint action for the regu-
lation of those things that affect the very conditions of exist-
ence, — as the resources of the soil and the waters, the safety
of highways and waterways, the protection of food sup-
plies, the prevention of infection of man or domesticated
plants and animals, and so on. As members of the human
race we are dependent upon those of other countries, not
only for materials that are restricted in their distribution,
but even more for ideas arising out of different experiences.
Modern science, upon which rests so much of our present-
day advance in general welfare, is altogether an international
product. Every discovery and every invention rests upon hun-
dreds of other discoveries and inventions made by men and
women of many nations and of several generations. What
we call civilization is an accumulation of the most valuable
thoughts of all peoples.

23

108

167

106

33

8

mm.

9
mm.

10

mm.

11
m,m.

12

mm.

13

mm.

14

m,m.

15 16

mm. mm.

Fig. 231. Variation in size of similar units

On measuring the length of each of several hundred beans taken at random from a
large lot, it was found that the largest was about twice as long as the smallest. The
number of seeds of each size is shown by the relative height of the corresponding
column above the horizontal line. Studies of this kind, repeated by many workers
on many kinds of material, show not only that individuals vary, but that they vary

in a certain way

PART V
HEREDITY AND EVOLUTION

CHAPTER LXXIX

VARIATION

463. No two alike. In some
respects all the members of a
species are alike ; that is why
we classify them as of the
same species. But in some re-
spects every individual is unique.
If a person should get the tips
of his fingers inky and place
them on a sheet of paper, he
would make a mark that could
not be duplicated by anyone
else. Ordinarily we have no
difficulty in distinguishing from
each other human beings that
look very much alike, although
occasionally there is difficulty
in identifying a person beyond
every doubt.

All species present this fact
of variation. And variation is
found with respect to every char-
acter. There is variation in size
and in proportions (Fig. 23 1), in

437

<

^\

_,

b

/

\

1

;

(

/

— I'-

J

/

/

/

/

1

'

""-

1

I
1

\

\^

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

Fig. 232. Individual variation in the
number of repeated parts

The principal veins on each side of the
midrib on a beech leaf vary from 10 to 22.
The number most frequently found is 16.
The vertical columns correspond in height
to the frequencies with which the various
numbers of veins occur. Broken line a, a
tree in which the number of veins varied
from 13 to 17, leaves with 15 veins being
most frequent. Dotted line If, another
tree, in which the veins varied from 15 to
20, 18 veins being most frequent. Each
tree has its individuality, and each leaf
has its individuality

Fig. 233. Variation in physiological
characteristics

438 ELEMENTARY BIOLOGY

coloring and in shading, in the numbers of duplicated parts
(Fig. 232), and in physiological properties (Fig. 233). Examples
of all these kinds of variation are easily found. Examples of
physiological variation are the yield of milk, the proportions
of sugar or of some other component (Fig. 234), the amount
of sleep people need, relative immunity to infection, and so on.

464. Causes of vari-
"^^^^^^^^^^^^^^ZIL. ation. We know that

when a cow is under-
^^ nourished, she will not

yield as much milk as
■Z^^ZZI^^Z^^^^ZI^ZIZZ^Z— she does when she is

ZZI properly fed and cared

for. This accounts for

much of the difference
,, , ,. . .u w . c n between one farmer's

Each line represents the relative amount of milk

given by i6 cows in one month. The poorest yield COWS and his neighbor's

(represented by the shortest line) averaged 20 pounds ^ q^ ^^ ^

a day ; the best cow averaged 30 pounds a day. Not

only did one cow differ from another, but for each hand, in a givcn herd

cow the yield varied from day to day. In like man- . r n r u • i

ner, the percentage of fat in the milk varied from ^f COWS, all of whlch

cow to cow ; and for every cow, from day to day haVC rCCCived the SamC

care and feeding from
the Lime they were born, there will still be great variations in
the ability to produce milk. In the first case we say that the
yield of the cow has been modified by the treatment she has
received. In the second case we say that the cows are of
different breeds, or strains.

All around us we see examples of modifications resulting
from differences in the conditions of development. Differ-
ences of feeding affect plants as well as animals. In any
season we may see fields of stunted, backward crops and
fields of luxuriant growths. In every city we may see well-fed,
vigorous, and alert men and women, as well as shriveled,
miserable, and timid men and women. It is important to know
whether, and how far, these differences can be controlled.

VARIATION

439

It is quite impossible to say offhand, in any given case,
how much is due to variation in breed and how much is
due to modifications produced by surroundings. But every
farmer knows that, in addi-
tion to controlHng the con-
ditions under which his
plants and animals develop,
he must also be careful to
select the right kinds of
seed or stock. The best
of care will not make an
ordinary white bean develop
into a plant bearing lima
beans, nor will extra feed-
ing make a scrub cow give
the kind of milk that may
be obtained from a good
Jersey cow.

465. Improvement by
selection. All domestic
animals and plants have
been carefully watched for
centuries for the purpose
of selecting the most de-
sirable individuals as the
parents of the succeeding
crops or generations. The
best heads of wheat were

I — \^

12 12.5 13 13.5 14 14.5 15 15.5 16 16.5 17 17.5 18 18.6 19

Fig. 234. Variation in physiological
properties

Forty thousand sugar beets, tested individually,
showed from 12 per cent to 19 per cent of
sugar. Beets containing 15.5 per cent of sugar
were the most frequent, but there were almost
as many beets with 15 per cent or with
16 per cent. As the percentage of sugar de-
parts more from the typical 15.5 per cent, the
number of individuals with a given sugar content
diminishes, so that the extremely poor and the
extremely rich beets are also fewest

number

selected for seeding the

following year ; the best beans and the best potatoes have
been set aside as the progenitors of the crops to come. And
the same principle has been applied in the raising of ani-
mals. The best milk cows were selected to be the mothers
of the calves, the swiftest mares were the mothers of the colts,
and so on.

440

ELEMENTARY BIOLOGY

Careful observers familiar with farm life and practice have
noted that cultivated races of plants and animals tend to
deteriorate markedly in a very few generations unless the
selections are made every year. The explanation for this was
unknown, but the fact was clear, and its application was found
in steadily selecting the best or most desirable individuals or

Fig. 235. Improved varieties of domestic birds

seeds for further propagation. For one thing was certain : it
was possible to improve the stocks to a considerable degree
by constant selection (see Figs. 235, 236).

466. Mixed types. In the diagrams used to illustrate the
measurement of variations (Figs. 231-234) we see that for
every series there is one measurement that represents the
condition of a comparatively large number of individuals.
This appears in the diagram as the peak of the curve. In
many groups of individuals careful measurements will show
two such peaks. For example, the Dutch botanist Hugo de
Vries counted the number of ray-florets in a species of daisy
{Chrysanthemtim segetum) and plotted the results of his count-
ing, which are given graphically in Fig. 237.

Fig. 236. Improved varieties of domestic animals

The contrast between the modern high-bred Jersey and the ancient banting, or between

the high-bred Russian wolfhound and an ordinary yellow dog, is typical of the changes

brought about in the course of many generations by the steady work of selecting the most

desirable kinds of individuals to be the parents of the following generations

442

ELEMENTARY BIOLOGY

This diagram led to the suspicion that what had been known
under a single name was in reality a mixture of two different

plants. In order to try out this
idea, de Vries selected seeds from
heads having thirteen ray-flowers,
and planted them separately. The
rays on the flowers of the new
plants derived from these seeds
were counted, and the distribution
of the variations found to cluster
more closely around thirteen rays,
as shown by the dotted line in
the figure. This would show that
the wild daisies represented prob-
ably two distinct races, or strains,
that looked enough alike to be
considered as a single species.

Another illustration is furnished
by some beans studied by a Danish
scientist, Dr. Wilhelm Johannsen.
From the appearance of the beans,
and from the appearance of the
curve showing the distribution of
their variations, no person would
suspect that they were not all of
one kind. But when Dr. Johannsen
planted single seeds of different
sizes, and kept the plants carefully
guarded against possible cross-
pollenation, he obtained groups of
seeds that clustered around the
respective parent seeds in size.
This process was continued for several generations, until
the experimenter succeeded in separating nineteen pure lines
of plants that remained distinct in following generations.

s'g 10 1112 13 14 15 16 17 1 18' 19 20 21 22'

Fig. 237. Two-peaked curve of
variation

The' height of the line above the base
corresponds to the number of daisy
heads (Chrysanthemum segetum) hav-
ing the number of ray-florets indi-
cated at the bottom. The solid line
shows that there were many heads
with "13 florets, and very many with
21, and that the intermediate num-
bers were represented by fewer indi-
viduals, as were also the numbers
above 21 and the numbers below 13.
The broken line shows the distribu-
tion of the following year's crop,
grown from seeds out of 13-ray heads.
Note the greatly increased proportion
of 13-ray heads

CHAPTER LXXX
HEREDITY

467. The problem of heredity. How is it that the characters
of the parents are transmitted so regularly to the offspring ?
How is it that, in spite of the close resemblances between par-
ents and offspring, these are never exactly alike in every point ?
These questions have to do with the problem of heredity.

468. Analysis of the problem. Certain facts, or laws, of
heredity were first discovered in part by an Austrian monk
named Gregor Mendel (i 822-1 884). Mendel had long puzzled
about the great variations among his garden peas. There were
tall plants and short ones, plants with white flowers and plants
with colored flowers. In some plants the seeds were yellow, in
others they were green ; some seeds were smooth, others were
wrinkled. All in all, he studied seven different pairs of con-
trasting characters in regard to which pea plants differ. He
noticed further that a given plant might have any combination
of single members of these pairs. A hairy plant might be tall
or it might be short, it might have yellow seeds or it might
have green seeds, it might have full pods or shrunken pods,
and so on.

469. MendePs experiments. Fixing his attention on a single
character at a time, instead of trying to think of the variety as
a whole, Mendel crossed garden pea plants that were different.
Thus, he crossed green-seeded plants with yellow-seeded ones,
tall ones with short ones, hairy ones with smooth ones, and so
on for all the pairs of differences.

When green-seeded plants were crossed with yellow-seeded
plants, the seeds in the next generation were all yellow
(see Frontispiece).

443

444 ELEMENTARY BIOLOGY

Most people have the impression that where individuals with
differing characters are mated, the offspring will show characters
somewhere between the characters of the parents. The reason
for this common belief lies in the fact that in our everyday
experience we notice that children resemble both parents ; but
most of us have not taken the trouble to notice further that
this resemblance to both parents does not consist o^ having
every character halfway between the corresponding characters
of the parents, but in having some characters just like those of
the another and other charactei^s just like those of the father.

470. The Law of Dominance. Mendel found that this com-
plete resemblance of the offspring to one of the parents (in
regard to a particular character) was quite the rule with each
of the other pairs of characters. Thus, the offspring of a tall-
and-short cross were all tall. The offspring of a smooth-and-
wrinkled-seeded cross were all smooth, and so on. This fact
Mendel called the Law of Dominance. His idea was that
where two characters of a pair meet in an individual, one of
them dominates over the other. Of a pair of characters, that
one which did not show in the offspring is called the reces-
sive. It is not destroyed, as we shall see. Of course, he could
not tell which of the two characters in a pair would reappear
in the offspring before trying them out. In the tables on page

445 are given the dominants and their alternatives for a num-
ber of characters selected from among plants and animals.

471. The Law of Segregation. The yellow seeds of the
hybrid ^ pea plant cannot be distinguished from the pure yellow
seeds of one parent. With plants grown from the hybrid yellow
seeds Mendel brought about three classes of cross-pollenation.

1 The word hybrid was formerly applied to the offspring of two parents of
different species or races, as, for example, the mule, or a mulatto, or the off-
spring of a Caucasian and an Indian. It is now used quite generally among
biologists, horticulturists, animal breeders, etc. to mean the offspring of two
parents that differ with respect to any particular character. For example, a
seedsman might speak of a hybrid tomato, meaning a plant resulting from
a cross between two varieties of tomatoes, and so on.

HEREDITY

44S

HEREDITY IN PLANTS

Name of Plant

Dominant Charactek

Recessive Character

Wheat

Wheat

Barley |

Wheat/

Maize

Maize

Garden pea

Garden pea

Garden pea

Tomato

Cotton

Stock -]

Sweet pea r ■ - • ■

Jimson weed J

Sunflower

Nettle

Late ripening
Susceptibility to rust

Beardless

Round, starchy kernel
Yellow grain
Yellow seed
Tallness
Smooth seed
Two-celled fruit
Colored lint

Colored flower

Branched stem
Saw-edge leaves

Early ripening
Immunity to rust

Bearded

Wrinkled, sugary kernel

White grain

Green seed

Dwarf

Wrinkled seed

Many-celled fruit

White lint

White flower

Unbranched stem
Smooth-margin leaves

HEREDITY IN ANIMALS

Name of Animal

Dominant Character

Recessive Character

Cattle

Horse

Silkworm

Rabbits ^
Guinea pig/

Mice

Mice ■]

Rabbits V

Guinea pig J

Leghorn poultry ....

Salamander

Canary

Poultry

Poultry

Land snail

Pomace flies

Hornlessness
Trotting
Yellow cocoon

Short fur

Normal movements

Pigmented coat

White plumage
Dark color
Crested head
Rose comb
Short rump
Plain shell
Red eyes

Horns
Pacing
White cocoon

Angora fur
Waltzing habit
White coat

Pigmented plumage
Light color
Plain head
Single comb
Long tail
Banded shell
White eyes

446

ELEMENTARY BIOLOGY

Fi D

Fi R

3D: IR

Fig. 238. Mendel's Law of Segregation

When two individuals with a pair of alternative
characters are mated, the offspring will all have
the character of one of the parents ; this char-
acter is called the dominant one, and the alterna-
tive character is called the recessive. The hybrid
offspring of such a mating is represented in the
diagram by F-^. Offspring of this kind resemble
the dominant parent D, but experiments show
that there is a real difference. If such a hybrid
is mated with one of the pure dominant type, /,
the next generation will all be dominant. If
such a hybrid is mated with an individual of
the recessive type, 2, the offspring will consist
of dominants and recessives, in about equal num-
bers. If two such hybrids are mated, 3, the
offspring will show both dominants and reces-
sives, in the proportion of three to one. This
reappearance of recessives in the offspring of
hybrids that seem to be dominants is called
segregation, or splitting up

1. He crossed hybrids
with plants of the yellow-
seeded parent variety.

2. He crossed hybrids
with plants of the green-
seeded parent variety.

3. He crossed hybrids
with hybrids.

The results of these
crosses are indicated in
Fig. 238.

This fact of splitting
up into the two ancestral
types has been found to
be quite general among
all plants and animals that
have been tested, and it is
called the Law of Segre-
gation. The idea is that
the hybrid plant, no mat-
ter how much it may re-
semble one of the parents
(with respect to one or
more particular charac-
ters), does not constitute
a pure kind of organism,
inasmuch as it cannot
reproduce itself in off-
spring all having the
same character.

The plants resulting from
the mating of hybrids (that is,
the segregated yellow-seeded
and green-seeded individ-
uals) were experimented with

HEREDITY

447

B

ai

az

as

(^-

e-

e^-

further, and this remarkable discovery
was made : the green-seeded individuals,
whether mated with one another or
with green-seeded individuals of the
original stock, always produced green-
seeded offspring. In other words, al-
though they had hybrid parents with
yellow seeds, they themselves were
pure in the sense that they reproduced
or transmitted the green-seeded char-
acter to their offspring in exactly the
same way as their pure green-seeded
ancestors. This principle has been
found to hold true in all cases where
experiments with plants and animals
showing alternative pairs of characters
have been carried far enough. An in-
dividual of hybrid parentage having a
recessive character is called an extracted
recessive^ or the character in question
may be spoken of as the extracted re-
cessive. It is just as pure with respect
to that character as an organism
can be.

On the other hand, the yellow-
seeded offspring of the yellow-seeded
hybrids turned out to be of two
kinds: (i) those that produced only
yellow seeds in subsequent generations,
pure like the yellow-seeded ancestor;
(2) those that behaved like their hybrid

and both showing the dominant
character, are mated, they may give rise to three kinds of offspring. The germ cells
given off by A are of two kinds, a^ and a^ having the factor for dominance, while a-^
and a^ are lacking in this factor. In the same way, the germ cells given off by B are
of two kinds. Now there are four possible combinations of two kinds of eggs with two
kinds of sperms: (i) a recessive t^gg combines with a recessive sperm; (2) a recessive
egg combines with a dominant sperm ; (3) a dominant ^gg combines with a recessive
sperm ; (4) a dominant egg combines with a dominant sperm. The result is that half
the offspring are again hybrid and the other half pure, and the pure are likely to be
dominants and recessives in equal numbers. Note that the hybrids resemble the
dominant grandparent, giving the appearance of one recessive to three dominants

04©--

©6,

^©6,

■e*^

Fig. 239. The Law of
Segregation

A hybrid individual produces germ
cells of two kinds with respect to
the character in question, — one
bearing the elements needed to
bring about the development of the
dominant character, and the other
kind lacking this element. If two
individuals, A and B^ both hybrid

448

ELEMENTARY BIOLOGY

■

B

...p.

parents, that is, split up again into dominant-appearing and recessive-
appearing individuals in the proportion of three to one. The two
classes are produced in the ratio of one pure dominant to two mixed
or hybrid, although the two classes may have the same appearance.

The simplest explanations for these
mathematical relations between the char-
acters is to be seen from the diagram
in F'ig. 239.

472. Law of Unit Characters. In the
meantime we must not overlook the fact
that every organism is made up of many
characters. After finding out that his
peas behaved according to the law of
dominance and according to the law of
segregation with respect to several of the
pairs of characters, Mendel went farther
and studied the results of his crossings
to find out the behavior of combinations
of characters. For example, suppose
that two plants used in an experiment
differed with respect to height as well as
with respect to seed color, what would
be the results .? Experiments showed
that the tall, green-seeded parent trans-
mitted the tallness as a dominant and
the greenness as a recessive. In other
v^ords, if a tall green was crossed with a short yellow, the
next generation appeared to be all tall yellow, resembling
one parent altogether in one character, and the other parent
altogether in the other character (see Fig. 240).

The conclusion from this experiment, and many others like
it, is that each pair of dominant-recessive characters behaves
according to the two laws described above, without regard to
what other characters may be present. This general fact has
been found to hold for many species of plants and animals

Fig. 240. Inheritance of
two or more characters

The offspring of two parents,
A and B, resembles both par-
ents, but it does not, as a rule,
stand midway between the
parents with respect to the
several characters. Instead,
the offspring will be like one
parent in some characters and
like the other parent in other
characters

HEREDITY

449

that have been used
in experiments, and
it is known as the
Law of Unit Char-
acters {^^^ Fig. 241).

This principle will
help us to understand
how there can be
such great diversity
among the individ-
uals of any given
species of plants or
animals, or even
among the brothers
and sisters of any
family. The greater
the number of char-
acters, the greater is
the possible number
of combinations ; and
the smaller is the
chance of any given
combination occur-
ring again.

These three laws
of heredity — domi-
nance, segregation,
and 7mit character —
are known as the
Mendelian laws, or
principles, because
they were first dis-
covered by Gregor Mendel. They have been found sufficiently
reliable to serve as a basis for practical work of great impor-
tance in connection with the breeding of plants and animals.

Fig. 241. The law of unit characters illustrated
by guinea pigs

Pigmentation in these animals is dominant over albi-
nism. Short hair is dominant over long hair. Rough
coat is dominant over smooth coat. When two pure
individuals like those shown are mated, the offspring
will be short-haired, dark, and rough-coated. On mating
the hybrids together in sufficient numbers, the segrega-
tion will result in producing every combination of these
three sets of characters : dark-short-rough ; dark-short-
smooth ; dark long-rough ; dark-long-smooth ; white-
short-rough ; white-short-smooth ; white-long-rough ;
white-long-smooth. The proportions will be such that
for each pair of contrasted ckaj-acters there will be one
recessive to every three dominants. (From photographs
lent by Professor W. E. Castle)

CHAPTER LXXXI
APPLICATIONS OF THE PRINCIPLES OF HEREDITY

473. Applied Mendelism. In the region about Pullman,
Washington, which is one of the best wheat-growing countries
in the world, 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 one variety that was at all satisfactory,
and that had serious faults. This variety was known as the
*' Little Club " and had the advantage over others that the
straw was strong enough to withstand the summer storms and
that the head remained closed after the grain was ripened,
thus preventing loss before harvesting. The one great draw-
back of the Little Club wheat was the fact that when planted
in the fall, it would sometimes be frozen during the severe
winters (once in about every three or four years) ; and although
the farmers could get a better crop by planting in the fall, they
could not afford to lose every third or fourth planting. The prob-
lem was, therefore, to combine the good stem and head qualities
of the Little Club with the frost-resisting qualities of some
other variety. Mr. W. J. Spillman, of the United States Depart-
ment of Agriculture, at that time agriculturist of the experiment
station at Pullman, began a series of experiments in crossing,
or hybridizing, the Little Club wheat with other varieties.

He found that whichever plant (variety) was used as the
pollen parent, the next generation always showed the same
kinds of combinations of qualities. This is in accordance with
what we have learned as Mendel's Law of Dominance.

He also found that in the offspring of the hybrids every
possible combination of characters shown by the grandparents
occurred. This is in accordance with the Law of Segregation.

450

APPLICATIONS OF PRINCIPLES OF HEREDITY 451

By selecting individuals in this third generation and grow-
ing from them, and by keeping records of their behavior, he
succeeded in establishing strains that transmitted the desired
combination of characters. This is in accordance with the
Law of Unit Characters (see p. 448).

In this way it was possible to combine in one variety of
wheat the strong stem, the closed head, and the winter-resisting
qualities needed for successful wheat farming in this region.
By similar methods it has been possible to combine three or
more characters desired in a plant or an animal from as many
different varieties of ancestors.

474. Breeding for immunity. The chief problem of those
who have to do with plants and animals is to get organisms
that combine desirable qualities and show none of the unde-
sirable qualities. Thus, there is the American brand of cattle,
raised for beef on the large prairie ranches ; this has good
beef qualities and is very easily handled in large herds. But,
unfortunately, most of our cattle are very susceptible to the
destructive Texas fever, which has caused the loss of milHons
of dollars' worth of cattle. It had been observed that the
so-called Brahmin cattle of India were immune to the Texas
fever. On mating an immune animal 'of this breed with one
of the susceptible varieties, it is found that the immunity is
dominant. A number of years ago a herd of the Brahmin
cattle was imported into this country for the purpose of cross-
ing with our native cattle, in order to establish a variety that
would have the beef qualities of the American cattle and
would at the same time be immune to the Texas fever. This
undertaking seems to produce successful results.^

^ In the meantime it has been found out that the Texas fever is transmitted
by a Httle animal known as the tick, which sucks the blood from the diseased
cattle. By suitable quarantine it has been possible to restrict the Texas fever;
and by applying to the bodies of the cattle something that will either kill the
ticks or prevent their biting the cattle, it may be possible to eradicate this costly
disease. But if we could replace our present herds of cattle with a type that is
quite immune, the added cost would no doubt be made up in a very short time.

452' ELEMENTARY BIOLOGY

Immunity to disease is not always dominant. In the case of
wheat, immunity to the rust is recessive. It is nevertheless
possible to establish strains of wheat that combine immunity
with other desirable qualities, since, as we have seen, it is only
necessary to breed the hybrids into the next generation in
order to get a complete segregation of the various characters
in all possible combinations, and then select in a third genera-
tion the offspring that have the desired character in a pure
dominant or pure recessive condition.

475. Breeding for special points. Those who have to handle
cows or sheep often find the presence of horns in these animals
a nuisance. Many farmers therefore take steps to prevent the
development of the horns by destroying the '' button " in the
young animal by means of alkali or other chemicals. Occasion-
ally, however, animals have appeared that failed to develop
horns at all. When such a naturally hornless animal is mated
with one that has horns, the offspring is found to be without
horns. In other words, the polled, or hornless, condition is
dominant. It is therefore possible to establish breeds of cattle
that never produce horns, and this has actually been accom-
plished by breeders.

In raising sheep certain kinds of fleece are found to be
more profitable than others. In order to combine the merino
wool with hornlessness, for example, it would be necessary
to find out by means of breeding experiments which characters
were dominant and which recessive, and then establish in three
generations new breeds possessing the desired characters.

476. Practical breeding. The failure of their hybrids to breed
true has been the despair of agriculturists and breeders in the
past. Only those who were patient enough to try out large
numbers and be content with a small percentage of successes,
or only those who, like Luther Burbank, were keen enough to
detect the rare individuals that would breed true, were suc-
cessful. With the discoveries of the biologists, it is possible
for every intelligent fancier of plants or animals to produce

APPLICATIONS OF PRINCIPLES OF HEREDITY 453

new varieties of organisms without limit, having almost any
combinations of useful or fancy characters that he may desire.
This does not mean that new characters are produced by
these methods. When Burbank produced a "white black-
berry " he did not get a plant with a new character, in the^

Fig. 242. Spineless cactus [Oputitia)

This variety was established by Luther Burbank through experimentation. It grows in

arid soil that is otherwise useless, and promises to become a valuable fodder for horses

and cattle. (From photograph lent by Mr. Burbank)

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 was
able to select for segregation and for ultimate fixation the indi-
viduals that combined pure lack of pigment with some of the
other desirable qualities. Another new creation of Burbank's
is the spineless cactus (see Fig. 242).

Many of the new varieties of plants are hybrids that are incapable
of breeding true. These plants are propagated by means of cuttings or

454

ELEMENTARY BIOLOGY

grafts, or by means of bulbs or tubers. The Burbank potato, for ex-
ample, which is the best potato grown in this country, is propagated
by means of the tuber. Seedless varieties of grapes, apples, oranges,
plums, and so on would be propagated by grafts or cuttings ; and
hybrids of various kinds of fruits, although they may have seeds,

~ I ^ both affected disorder

\5

!

Fig. 243. Heredity of human traits

(Squares represent males ; circles represent females.) /, pedigree of a family showing
artistic (dark upper portion), literary (right section), and musical (left section) ability;
2, family with digestive troubles ; j, family with heart disorders ; 4, family with feeble-
mindedness (/, died in infancy; ?, uncertain mental condition). (/, 2, and j, after
Davenport ; 4, after Goddard)

would be propagated in the same way. From what we know of the
fact of segregation, we can understand how unreliable the seeds of
most common fruits are likely to be, when we consider that most
seeds are probably hybrids.

477. Heredity in man. So far as reliable facts are available,
heredity seems to follow the same course among human beings
as among other organisms.

Human beings take a comparatively long time to mature,
so that in order to get complete records for many generations

APPLICATIONS OF PRINCIPLES OF HEREDITY 455

it would be necessary to go back' several centuries ; and such
records were not kept in so remote a period. With annual
plants and many animals it is possible to get a generation each
year, and with some organisms several generations in a year.

The number of offspring in human matings is comparatively^
small, so that it is never possible to get even an approxi-
mation of all the character combinations in any one family.
Experiments are, of course, out of the question.

Finally, what we call the human race is really a mixture of
many distinct types or combinations of characters, and these
are so thoroughly mixed up that we never find a pure race
of human beings at the present time.

Nevertheless, by comparing such family records as are avail-
able with the behavior of various characters in the pedigrees
of plants and animals, it has been possible to show that
many human characters follow the same hereditary principles
of dominance, segregation, and recombination.

The diagrams in Fig. 243 show the course of certain
characters in several carefully studied cases.

The following table gives a list of human characters that
are known to be dominant or recessive :

HEREDITY IN MAN

Dominant Character

Recessivb Character

Curly hair

Straight hair

Dark hair

Light; red

Beaded hair

Even hair

Brown eyes

Blue eyes

Normal pigmentation

Albinism

Hapsburg lip

Normal lip

Normal muscular tone

Low muscular tone

Nervous temperament

Phlegmatic temperament

Fused fingers or toes

Normal digits

Supernumerary digits

Normal number

Broad fingers (lacking one joint)

Normal length

Limb dwarfing

Normal proportion

Normal growth

General dwarfing

456 ELEMENTARY BIOLOGY

The application of our knowledge of heredity to human affairs will
probably be along the line of showing us what types of marriages are
likely to produce offspring that are undesirable in one way or another.
We already know that certain abnormalities of physical structure or
of mentality are transmitted in a definite way, and we are therefore
warranted in counseling men and women who belong to families that
show these characters not to marry others of similar stock. In the
course of time we shall no doubt develop certain standards of fit-
ness for marriage which will be enforced largely by the same kind
of public opinion and tradition as now distinguishes the customs of
different peoples.

CHAPTER LXXXII
HEREDITY AND PROTOPLASM

478. What is inherited? It is common to speak of the
inheritance of characters as though something passed on from
parents to offspring. But a moment's thought will show that
nothing is transmitted in the ordinary literal sense.

What is really meant by saying that a plant or animal has
inherited certain characters from his parents is that there
is somet/mzg in the fertilized egg that makes possible the
development of those characters, and zvhatever is in the egg
must have come from the gametes, and so, presumably, from,
the parents.

479. Nuclear division. A study of cells shows that the
nucleus contains a tangle of substance which behaves in a very
definite way before cell division takes place. This substance is
called chromatin because it readily absorbs various anilin dyes
and thus appears highly colored, in contrast to other portions
of the cell, when looked at under the microscope after treat-
ment with the dyes (Fig. 244). Just before the cell divides,
the chromatin breaks up into separate bits of chromatin called
chromosomes, which means ''color-bodies." Each chromosome
splits lengthwise into two pieces, and one of these pieces
goes into one of the two new cells (see Fig. 244). In this way
each cell as it divides distributes one half of its chromosomes
to each of the two daughter cells. Thus it comes about that
each cell has exactly the same number of chromosomes as the
other cells in the body.

480. Formation of germ cells and zygotes. This process of
nuclear division goes on as the developing organism continues
to grow by the production of new cells. In the formation of

457-

458

ELEMENTARY BIOLOGY

germ cells, however, the chromosomes divide in a different
way. In a cell that is to form an egg cell half of the chromo-
somes separate out ; the remaining chromosomes then split

4 5 6 7

Fig. 244. The nucleus in cell division

/, Diagram of a cell with the chromatin in a tangle, or network ; before cell division the
chromatin assumes the form of a continuous thread. The thread breaks up into a
definite number of pieces, or chromosomes^ 2 ; the number of these is constant for any
given species of plant or animal. The chromosomes arrange themselves in a central
ring, J ; the membrane inclosing the nucleus disappears ; fine threads appear to connect
the chromosomes with tiny bodies at opposite ends of the cell. Each chromosome
splits in two lengthwise, 4. The members of each pair move from each other to opposite
ends,5. The half-chromosomes form two new tangles, 6, and gradually lose their definition.
The new masses of chromatin become the nuclei of two new cells, 7

lengthwise (see Fig. 245). As a result of these two divisions,
which usually follow each other in rapid succession, ^ the egg
cell contains one fourth of the chromatin present in the cell
from which it was formed, and only one half of the usual
number of chromosomes. The division which separates the

1 It is believed that in some cases the splitting of the chromosomes takes
place before the separation into the reduced numbers.

HEREDITY AND PROTOPLASM

459

chromosomes into two groups is called the rediictio7t divisiofi^
since it reduces the number of chromosomes.

In the formation of sperm cells also a reduction division
occurs. But instead of producing polar bodies the sperm
mother cell forms four sperm cells.

The polar bodies formed by the maturing of the ^gg cell
die and disappear.

When a sperm cell unites with an ^gg cell in fertilization,
the resulting zygote contains the full number of chromosomes,

Fig. 245. The formation of an egg cell

The chromatin material of the nucleus network, /, arranges itself into a definite number
of chromosomes, 2, which divide up into two equal groups, j. Half of the chromosomes
are pushed out of the cell, 4, and form the first polar body,/. The chromosomes of the
polar body, as well as the chromosomes remaining in the mother cell, split lengthwise,
and half of each chromosome is pushed out, j. The first polar body thus becomes two
bodies, /^ and ^2, and the mother cell puts out a third polar body, /3, retaining half the
original number of chromosomes. This cell is now the egg cell

half derived from the male parent and half from the female
parent. From all the evidence that is now available it would
seem that the chromosomes are the features of the germ cell
which bear whatever it is that determines the development of
the characters that distinguish the individual from others of the
same species, and at the same time those characters that
identify it with others of the same species.

481. The germ plasm and acquired characters. According
to August Weismann (i 834-1914) each organism is what it
is because it developed from a certain ^erm plasm. When
this organism produces new germ cells, it merely transmits

460

ELEMENTARY BIOLOGY

to these cells some of the germ plasm from which it had itself
developed. In other words, the eggs produce the organism,
not the organism the eggs (see Fig. 246).

According to this notion it would be impossible for the ex-
perience of an individual to influence the germ cells in such a
way as to make the offspring show the effects. For example,
the result of exercise or of mutilations or of sickness should
not appear in the following generation. As a matter of fact
we have no evidence whatever that modifications produced in

Fig. 246. The idea of the germ plasm

When a fertilized egg, g, develops into a new individual, b, part of the protoplasm
becomes the body, or soma, and part remains germ, within the body, where it is nurtured.
The germ is not a product of the body in any sense. Each body, b-^, b^, b^, is a branch,
or development, of the germ, but the stream of germ material is continuous. The
nature of the germ determines the kind of individuals or persons that will develop ; the
body does not influence the germ

an individual in the course of his lifetime are ever reproduced
in the offspring, although you will find many people who firmly
believe that such modifications are actually transmitted.

482. Sports. The appearance from time to time of an un-
usual kind of individual that the breeders and horticulturists
call a sport would suggest that germ plasm may undergo
important changes. There appeared on a farm in Massachu-
setts, in 1 79 1 , a queer sheep with a long body and very short,
crooked legs. This *' ancon " ram was kept for many years,
and had many offspring with normal sheep. All the hybrids
showed the same curious character. This ''turnspit" type of

rubrl- lamarcki- sdnlxtr

gigas albida ohTonga. nervis ana nanella lata lans

4th Generation f
1895-1896 i

3d Generation
1890-1891

2d Generation
1888-1889

Ist Generation
1886-1887

15 .176 8 14,000 60 73 1

In ii

Fig. 247. Mutation in evening primrose
Hugo de Vries gathered the seeds from a number of evening primroses

(CEnothera lamarckiand) which he found growing in a vacant lot. These plants are
natives of North America, and probably escaped from some Dutch garden. From seeds
thus obtained about 15,000 ordinary lamarckiana plants were grown, and in addition five
peculiar dwarfed individuals {nanella) and five with broad leaves {lata). These two sets
were different from the parents as well as from any other known varieties of CEnothera.
Later these new forms appeared again in very small numbers from very large sowings of
lamarckiana seeds (third and fourth generations). In the third sowing (1890) another
new form appeared, having reddish veins [mbriftervis). In the same manner new types
have appeared in each succeeding generation, and some of these types appeared anew
several times. By means of careful breeding it was possible to preserve the new quali-
ties, and to recombine them with one another and with the contrasting characters of the
parent type according to the Mendelian principles

462 ELEMENTARY BIOLOGY

animal is sometimes found among dogs. Peacock fanciers
sometimes find a single bird with plain black plumage. Several
times whole flocks of such birds have been established from a
single freak mated with the normal type.

483. Mutations. In more recent years special attention has
been given to these sports by many biologists, and the Dutch
botanist Hugo de Vries has developed a theory to account for
the origin of new kinds of plants and animals, based on the
fact that such freak individuals are often able to establish dis-
tinct lines of descendants. De Vries has himself cultivated many
lines of new plants that originated in this sudden manner from
various wild and cultivated species. Such suddenly arising de-
partures from the ancestral type are called mutations^ and the
individuals bearing these characters for the first time are called
mutants. De Vries's mutation theory does not attempt to ex-
plain how it is that such plants or animals originate ; it only
tries to show how such mutations may lead to the establishment
of new races of organisms (see Fig. 247).

484. Origin of new characters. There are a number of
experiments that throw some light on the origin of mutations.
One of the best known is that by W. L. Tower, an American
biologist, who subjected the eggs and larvae of potato beetles
to various unusual conditions of temperature, moisture, and
nutrition. The individuals that developed under these extreme
conditions showed no evidence of having been mistreated. But
some of the offspring of these beetles departed in a marked way
from the usual appearance of their ancestors. In the Frontis-
piece are shown some of the new types of beetles that appeared
in Tower's experiments. It is supposed that the conditions
to which the developing beetles were subjected had no direct
effect upon the bodies of the animals, but did have an effect
on the chromosomes of the cells that later became the germ
cells. On mating some of these new types with the normal
ones, it was found that there really were new characters, for
it was then possible to establish lines that would breed true.

CHAPTER LXXXIII _

EVOLUTION

485. All things change. We understand that we live in
a world of change, that in fact all of our experience, all of our
life, has to do with these changes. All theoretical studies are
concerned with changes ; and all practical studies — agriculture
and medicine, engineering and statesmanship — are concerned
with three sets of problems. These are

1 . How ca7i we cause desirable changes to take place ?

2. Hozv can we prevent undesirable changes from taking
place f

3. Hotv can zve best meet the 7inavoidable changes?

486. Cyclic changes. Many of the changes that go on about
us are of a cyclic nature ; that is, they keep on repeating them-
selves. For example, the day gives way to night, but the night
gives way to day again, and so on indefinitely.

Our seasons illustrate cyclic changes. To a mosquito (an
individual adult) weather may mean a continuous, progressive
change from warm to cold, resulting in death and ending
everything.

The seasonal changes show us not only cyclic variations in
temperature, moisture, etc. but cyclic changes in the organic
world. Eggs hatch, individuals develop to maturity, reproduce
themselves, and die. But the following year we see a repetition
of the same life histories, and so on, generation after genera-
tion. With some species of animals the cycle extends over
many years, but the point is that, however far-reaching the indi-
vidual development may be, it does not go on forever ; it comes
to a close and is replaced by others that go through exactly the
same kinds of stages. In other words, life forms or life stages

463

464 ELEMENTARY BIOLOGY

repeat themselves, generation after generation, in the same
sense as seasonal conditions of weather repeat themselves.

487. Progressive changes. While much of the happening
in the universe is of a cyclic nature, there may nevertheless
be, for the world as a whole, a certain continuity of change
that has been called evolution. We need not feel called upon
to prove that all changes are altogether cyclic, or that all
changes are altogether evolutionary. It is quite reasonable and
consistent to recognize that both kinds of changes do actually
take place.

488. Fossil evidences of evolution. How can we tell whether
the plants and animals of past times were different from those
of to-day }

The most direct evidence is furnished by the fossilized
remains of ancient plants and animals. Some two hundred
years ago people became interested in hard coal as a fuel ;
and in the digging of the coal, and in the digging into the
earth alongside of the coal seams, they came across structures
that in many ways suggested plant forms. Later they also found
stony structures that very decidedly suggested animal forms.
A study of these structures naturally led to an attempt to
classify them and to compare them with existing plants and
animals. These classifications lead to finding many resem-
blances between the organisms of the past and the organisms
of the present, but they also brought out marked differences.
Moreover, by arranging the series of fossils according to their
relative ages (which can be judged by their relative positions
in the layers of rocks) it was found possible in many cases to
show that the forms which were intermediate in age were also
intermediate in structure between the most ancient and the
most recent (Fig. 248). One of the best examples of this is
presented by the horse and his probable ancestors (see Fig. 249).

Similar series of fossils have been worked out for the
elephant in Africa, for various fishes in England and else-
where, and for many lines of birds and reptiles in all parts of

System
f Pliocene

Winged

reptiles
Crinoid
Gryphaea

Crocodile
Bivalves
Lamp shells
Insects
Amphibia
Tree ferns

Ganoid fish

Trilobites

Sponge
spicules

Graptolites

Pre-
Archaic Cambrian

Fig. 248. Geology and evolution

In the oldest rocks no remains of plant or animal life are to be found. In each succeed-
ing age of the earth more and more highly developed plant and animal forms lived, as
shown by the remains of the organisms preserved in the rocks

466

ELEMENTARY BIOLOGY

the world. In Germany there has been found a remarkably
complete series showing successively different types of snails
leading down to the present-day forms. Without regard to the
question as to how it comes about that descendants do differ
from their ancestors, there can be but one reasonable explana-
tion of the facts, — namely, that there has been modification
of plants and animals in the course of their descent.

Protorohippus
Eocene

Mesohippus
Oligocene

Protohippus
Miocene

Equus
Modem

Fig. 249. Evolution of the horse

Our ideas of the probable ancestors of modem animals are based on fossil remains.
These represent real organisms that lived thousands and thousands of years ago. In
the diagram the oldest type does not resemble the familiar horse very strikingly, but
with each succeeding age we find animals having a closer resemblance to the horse of
to-day. (After Osbom)

489. Evidence of evolution from structures of organisms.

We have observed over and over again that individual plants
and animals differ from each other, and that at the same time
they resemble each other in groups. The members of a group
that are sufficiently alike to be recognized by the casual observer
we speak of as being of the '' same kind." Thus, while no two
oak trees are exactly alike, they are all sufficiently alike to be
recognized as of the same kind. Now we expect, from our
observations, that all the oak trees, however different they
may be from each other, will give rise to new plants that will
also be enough like the parents to be classed as oaks. And
for the same reasons we take it for granted that all the oaks
of to-day are related, in the same sense in which we speak
of our cousins and second cousins as related. That is to say,

EVOLUTION 467

we believe that they are descended from common ancestors.
An attempt to classify existing plants and animals leads to an
arrangement in which similar plants (or animals) are grouped
together into species, or kinds, and these species are grouped
together into large assemblages, and these into still larger, and
so on, on the basis of resemblances. Now, since we assume
relationship or common ancestors in proportion to similarities
of structure,^ the classification suggests that if we go back far
enough, we shall find that all birds are related (that is,
descended from the same ancestors), and that if we go back
still farther, we may find that birds and reptiles are all
descended from common ancestors ; or, if we go back still
farther, we may find that all backboned animals are descended
from the same ancestors.

We can find no reasonable explanation for this ''branching-
tree arrangement " of the different kinds of living beings,
except the supposition that they have descended from common
ancestors and have become modified in the course of time.

490. Evidence from development. In our study of develop-
ment (p. 277) we saw that in the course of each individual's
lifetime he passes through a series of more or less distinct
stages ; and the farther back we go to the one-celled stage, the
more and more are these stages like the corresponding stages
of other species of organisms. Moreover, it has been pointed
out that the similarities found between different species in the
various early stages of development are in a measure parallel
to the similarities of the adults or the groups. For example,
the larvae of different kinds of mosquitoes are more alike than
are 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. And in the life history of a mammal there are

1 Most of our classification is necessarily based upon structure. A com-
parative study of the structure of organisms — the branch of science known
as morphology — shows us similarities in detail of structure that are even
more remarkable than the superficial resemblances that are obvious to the
casual observer.

468

ELEMENTARY BIOLOGY

suggestions of structures found in the life history of birds and
of fishes. Now the only explanation of these facts that appears
at all reasonable is that there is a common (or similar) develop-
ment just to the extent that organisms are related through
descent from common ancestors.

491. Vestigial structures. Another line of evidence is found
in the presence, among plants and animals, of certain organs that

Fig. 250. Vestigial structures

The vermiform appendix, a, in some mammals is reduced to an insignificant trifle, as
in man, /; whereas in other mammals, as in some of the rat family, 2, it is capable of
holding a considerable amount of food in the process of digestion. The horse walks
on his third toe, j, the others being entirely absent or represented in part by the
reduced " splints," b

are quite useless from the point of view of adaptation, but v;hich
are nevertheless persistent through whole groups. 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 dis-
tinct signs of fingers, or claws, among the wing bones.^ Other
examples can be readily understood if we suppose that all plants
and all animals are related through having had common ances-
tors ; but they cannot be understood on any other supposition.

1 The vermiform appendix (see /, Fig. 28) in man is the Hngering reminder
of an organ that developed and functioned in other backboned animals, but
that has no practical meaning in the life of man to-day — except to make
trouble sometimes.

EVOLUTION 469

492. Geographic evidence. We expect every group of organisms
to expand 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 popu-
lation. Yet when we examine the distribution of species over the^
surface of the earth, certain curious facts appear.

In the first place, we find regions in every way similar, so far as
climate, soil, etc. are concerned, 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 ; but when Europeans first came there, they found
plants and animals that are not found living naturally in other parts
of the world. The same kinds of facts are found in abundance on
comparing many regions with one another.

In the second place, we find regions that are very different occupied
by forms of plants and animals that are sufficiently similar to be con-
sidered as of the same families. Thus, goats and sheep, obviously
related to each other genetically, are found in the tropical zones as well
as in the temperate, and well up to the arctic and antarctic circles,
living in many varied kinds of surroundings.^

Darwin pointed out that where we have similar regions occupied
by different flora and fauna, these regions are always separated
from each other by impassable barriers, as oceans, mountain ranges,
deserts, etc. On the other hand, where we find similar plants and
animals inhabiting regions that are markedly different in their climate,
soil, etc., these regions are connected directly or show evidence of
having been connected in the past. For example, the plants and
animals found in oceanic islands are frequently quite distinct from
those found elsewhere, but they are also as a rule closely related to
the inhabitants of the nearest mainland. Facts of this kind can easily
be explained by the assumption that all the organisms are derived
from ancient forms, with modifications, and they cannot be easily
explained in any other way.

493. Summary. The evidences for organic evolution or for
the descent of plants and animals from common ancestors, with
divergence from ancient types, are (i) palaeontological, the

1 Of course we are now speaking of the natural range of various wild
species.

470 ELEMENTARY BIOLOGY

evidence of fossil remains; (2) systematic and morphological,
the evidence from the structure of plants and animals ; (3) em-
bryological, the evidence from development ; (4) anatomical,
the evidence from rudimentary, or vestigial, organs; (5) regional,
the evidence from geographic distribution.

The important thing to note is that all the facts in these
several groups of facts can be harmonized by the idea of evo-
lution and by no other explanation.

There are many attempts to explain how evolution is brought
about, and these may be called theories of evolution ; but as to
the fact of evolution biologists are in substantial agreement.

CHAPTER LXXXIV
APPLICATIONS AND THEORIES OF EVOLUTION

494. Direct evidence of evolution. Within the memory of
men and women now Hving there have appeared new varieties
of potatoes, apples, plums, oranges, sheep, horses, rabbits,
poultry, cats, dogs, walnut trees, wheat, and so on. And the
new varieties of plants and animals are, at least in many
instances, just as truly new species as any that occur in nature.
It is true that very often these new species have arisen under
artificial conditions ; but it is also true that there is nothing
in these conditions that may not occur in nature, except the
protection of the new forms from early extermination. We
have, then, not only indirect evidence that evolution has taken
place, but direct evidence that plants and animals can behave in
agreement with the assumption that evolution did take place.

In recent times — within a century and a half — there have
been many attempts to formulate a theory to explain how
evolution takes place. These theories may be grouped accord-
ing to their family resemblances, but there are only three or
four types of theories that are at present worth considering.

495. Lamarckian theory. The French zoologist Lamarck
(1744- 1 8 29) laid emphasis on the fact that the development
of many organs is influenced by their activity, and on the
fact that many organisms (particularly animals) adjust them-
selves to their surroundings in the course of their lives. He
came to the conclusion 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."

471

472 ELEMENTARY BIOLOGY

With our present knowledge of physiology and heredity,
most of Lamarck's theory is seen to be unsound. Notwith-
standing all the evidence to the contrary, however, many people
still believe that evolution (and human progress) takes place
through the accumulation of the results of experience in the
course of generations.

496. Selection theory. The theory of natural selection is
associated with the name of Charles Darwin (i 809-1 882),
but it was also formulated independently by Alfred Russel
Wallace (1823-19 13) and Herbert Spencer (i 820-1903).
This theory is that animal and plant species evolve through
the selective action of the environment, which kills off those
individuals in each generation that are least adapted to the
conditions of life, — a process . resulting in the "survival of
the fittest."

The theory rests on the fact of variation (see pp. 437 ff.)
and of overpopulation — that is, the fact that more individuals
(eggs, seeds, spores, etc.) are born than can possibly reach
maturity and reproduce themselves. It assumes that individual
differences may be inherited, whereas the evidence shows that
only certain kinds of differences are transmitted to offspring.
The theory assumes that the agencies which kill off so large
a proportion of each generation are selective, that is, really
act upon important individual differences, whereas we know
that at every stage of development plants and animals are
killed off by agencies and forces and accidents that make no
discrimination whatever between the fit and the unfit.

Many studies and experiments in recent years have thrown
doubts upon the theory of natural selection. It does not
account for the origin of new characters, and we know that
there is a limit to the improvement that may be brought about
by artificial selection. There is at least this much truth in the
doctrine, however : plants and animals that are unsuited to the
conditions about them, for whatever causes, are not likely to
leave similar progeny. Fitness is a requisite for all life.

APPLICATIONS AND THEORIES OF EVOLUTION 473

497. Mutation theory. Charles Darwin had collected many
examples of sports that occurred in various crops or herds,
but he supposed these to be so exceptional that he did not
consider them seriously as the material upon which selection
operates in the formation of new species. But Hugo de Vries-
has emphasized just this class of facts. We saw (p. 462) that
he had made direct observations as to the appearance of muta-
tions among plants kept in his gardens and greenhouses, and
we saw also that mutations are capable of transmitting their
peculiarities to their offspring.

The mutation theory of evolution declares that selection can
establish new species only if there first appear individuals with
heritable qualities that are distinctive . It is not claimed that
the mutants have advantages over their parental type, although
they may have ; it is sufficient for the theory if the new types
are capable of living a7id of establishing themselves. This
theory of evolution, and all the other newer theories, are
closely connected with the study of heredity and are supported
by the results of experiments.

498. Applications. It should certainly make a practical dif-
ference to us which of the many theories of evolution is proved
to be true. Suppose we were convinced — as many people are
— that the gains and losses of the individual organism affect
the constitution of the offspring. Would that not make a dif-
ference in our handling of our crops and our domestic animals }
Would it not make a difference in the way we conduct human
affairs } We might then believe that the son of a criminal must
be a criminal, or that the son of a judge must be righteous.
We might make our laws much more rigorous for the chil-
dren of evildoers, and much more lenient for the offspring
of good citizens.

Or, suppose we were certain — as many people are — that
the selection theory is true. Then we should follow the recom-
mendations of those who tell us not to build hospitals for the
sick, but to let them die — or survive. This recommendation is

474 ELEMENTARY BIOLOGY

made on the supposition that by letting disease kill whom it
will, we shall at last have a population that is immune to all
diseases. The same people would do nothing to mitigate what
they call ''the struggle for existence," for they believe that
this struggle is necessary to bring out the best qualities of
the race and to prevent the multiplication of the unfit.

With the discoveries of recent years regarding the facts of
heredity, our whole view of evolution has undergone important
changes. For one thing, '' struggle for existence " no longer
suggests the fierce competition between individuals of a species
that it formerly suggested. In the second place, the survival
of the fittest can be seen to add nothing new to the composi-
tion of a line of plants or animals. In the third place, the
characters that distinguish one race or variety from another
need have absolutely nothing to do with being better fitted
to live. And, finally, we may think of the progressive changes
in species as resulting from the successive modification of the
germ plasm, with the elimination of those resulting forms that
are not livable.

We have seen that the application of modern knowledge
about the evolution of organisms has increased our wealth
incalculably by establishing varieties of plants and animals
that are more resistant to disease or to other unfavorable con-
ditions and by establishing varieties that bear more abundantly
of those materials for which we care, — for example, more wool
in the case of the sheep, more sugar in the case of the sugar
beet, and so on. In similar ways the solution of the problems
of evolution must continue to contribute to human welfare
on the economic side, and probably also on the social and
moral side.

PART VI

MAN AND OTHER ORGANISMS

CHAPTER LXXXV
THE CLASSIFICATION OF ORGANISMS

499. Scientific classification. Apart from the fact that many
people derive satisfaction from collecting and sorting various
classes of objects, classification is of value because it facilitates
the v^ork of reference. Just as the classification of the books
in the library makes it possible to find a particular book, or a
particular kind of book with the least effort, so classifying
plants and animals furnishes a convenient scheme for placing
each specimen where it belongs.

In recent times the study of classification has acquired new mean-
ing because of the light it throws on problems of evolution and
because of its aid to the study of heredity.

Every scheme for sorting things must provide a way of bring-
ing together plants or animals that are truly related to each
other, and it must at the same time avoid bringing together,
because of superficial resemblances, plants and animals that
are not related.

500. The basis of classification. If we should sort our books
according to size or color of binding, we should often bring two
books on Mexican history together ; but we should be just as likely
to bring together a book on Mexican history and one on astronomy,
and we should be sure to separate books that really belong together.
In the sorting of plants and animals it is necessary to find a basis
that will secure the desired results.

475

4/6 ELEMENTARY BIOLOGY

The structure of organisms furnishes the basis for modern
classifications, but the word structure has a wide significance.
According to outward appearance we might place certain small
snakes with certain large worms ; but a study of the internal
structure at once separates them very widely. Again, the
appearance of certain caterpillars is much like that of certain
worms, but a study of the structure at various stages — that
is, the development — at once separates these two groups.
Modern classification of organisms accordingly considers all
that can be known about the living things, and not merely
their appearance or their uses.

CHAPTER LXXXVI
KINDS OF PLANTS

501. Higher and lower plants. We often speak of a given
kind of plant or animal as being higher or lower than another
kind. What we usually have in mind in making this distinction
is the fact that some organisms are simpler and others more
complex in structure. A dandelion is higher than the taller
willow, and the willow is higher than the pine, for the same
reason that we consider all three of these plants higher than
a fern or a seaweed.

Complexity of structure has to do with the number of dif-
ferent parts or organs. Physiologically this corresponds to a
greater division of labor. We may compare three plants to
see the general differences as to structure and specialization
of functions.

On the vegetative side the Spirogyra cell may be considered
a complete individual. It is capable of getting from the sur-
rounding water all that it needs to keep it alive, at any portion
of the surface. In a moss plant we may already see a division
into rootlike part, stemlike part, and leaflike part. The photo-
synthesis is carried on in one part of the plant ; the "absorption
of water and salts is carried on in another part. The stem is a
connecting organ that holds up the leaves and also transports
(or, rather, transmits) materials between the two other organs.
In the bean plant we see a more complex root, with several
kinds of cells (tissues), a more complex stem and a more com-
plex leaf, both having several kinds of cells. The protective
layers of cells are different from the supporting (mechanical)
tissues ; these in turn are different from the conductive tissues
and from the photosynthetic tissues.

Ml

478 ELEMENTARY BIOLOGY

On the reproductive side we may see a similar advance in
complexity from the lowest to the highest of these three plants.
In the Spirogyra every cell may act as a gamete, after behaving
for some time as a vegetative cell. In the moss certain speciaj
cells are borne, in special organs, in a special region of the
vegetative plant. And the two gametes (male and female) are
borne on two different individuals. In the bean the gametes
are still more highly specialized, each being produced in a
very simple plant that is parasitic upon the parent. But these
two simple plants grow from very highly specialized structures
(embryo sac and pollen grain) that are in turn borne on very
highly specialized organs (pistils and stamens) which together
form a structure (the flower) that is almost completely devoid
of any vegetative behavior. In the flower we have an organ
that is specialized for producing bodies which have to do ex-
clusively with reproduction and the protection and distribution
of the next generation.

502. The basis of classification. While it is possible to say
in a general way that a given plant is higher than another, it is
quite impossible to place all the known plants in a series from
the lowest to the highest. This would be as absurd as trying to
arrange all people in a series from the '' worst " to the ''best."
We find that there are several main divisions, some of which
we should place higher and some lower. But we find in each
division so many degrees of complexity that there is consider-
able overlapping when it comes to arranging all the plants.

The first separation that we can make is one between plants
that bear seeds and those that do not. The seed plants can be
further divided into those that have closed carpels (pistils), like
all the flowering plants, and those that have open or exposed
ovules, like the cone-bearing plants.

Among the non-seed-bearing plants there is a large group
in which the egg cell is borne in a special organ, the arche-
gonium (see pp. 320-321); this includes the ferns and their
allies, the mosses and the liverworts.

Fig. 251. Genealogical tree of plant life

This diagram is intended to suggest the common origin of all plant forms, with the
constant progressive departure from ancestral types, now in one direction and now in
another, like the branching of a tree. Lower and higher mean nearer to or farther from
the original types. The closer together two forms are on a given branch, the more
closely related they are considered (cf. Fig. 252)

48o ELEMENTARY BIOLOGY

Below the archegonium plants are all those that lack special-
ized vegetative organs. Here are included all the seaweeds, the
bacteria, and the fungi.

503. The main groups of plants. The chief groups of plants
are indicated in the following outline :

Division I — Thallophytes. Plants showing little or no differentiation
into stem and leaf.

A. Schizophytes (" splitting plants "). Each cell splits into two ; no other

reproduction.

1. CyanophycccC. Splitting plants with chlorophyl, — the blue algae.

{Examples. Oscillatoria, Rivularia, Nostoc.)

2. Schizomycetes. Splitting plants without chlorophyl. This group

includes all the bacteria.

The distinction between having chlorophyl and not having chlorophyl sep-
arates all the thallophytes into two main groups, the algae and the fungi.

B. Algae. The chlorophyl-bearing thallophytes.

1. The green algae. Usually yellowish green. {Examples. Pleu-

rococcus, desmids, Spirogyra, Vaucheria, stonewort, sea
lettuce.)

2. The brown algae. {Examples. Bladder wrack, Laminaria, Sar-

gassum, diatoms, sea palm.)

3. The red algae. Mostly marine ; reddish to purple. {Examples.

Nemalion, Polysiphonia, Batrachospermum.)

C. Fungi. Thallophytes without chlorophyl.

1 . Phycomycetes. Alga-like fungi. {Exatnples. Water molds [often

parasitic on fishes], phytophthora [the cause of the potato rot],
grape mildew and other parasitic forms, black mold.)

2. Ascomycetes. Fungi bearing spores in sacs. {Examples. Yeast,

cup fungi, the edible morel, the mildews, black knot.)

3. Basidiomycetes. Fungi bearing spores on outside of structure

called basidium. {Examples. Rusts, smuts, mushrooms, pore
fungi, shelf fungus, puffballs.)

D. Lichens. These curious structures are compound growths of fungi

• and algae. The hyphae in these partnerships generally belong
to ascomycetes ; the algal partner is a green alga related to
pleurococcus or one of the blue-green algae. {Examples. Rein-
deer moss, Iceland moss, Spanish moss. The common names
introduce the word moss, although these plants are in no way
related to the mosses.)

KINDS OF PLANTS 48 1

Division II — Bryophytes. Mosses and their allies. Archegonia but no
vascular system.

A. Liverworts.

B. Mosses.

Division III — Pteridophytes. Ferns and their allies. Archegonia and
vascular system ; no seeds. {^Examples. Club mosses, quillworts,
scouring rushes (or horsetails), adder's-tongue, maidenhair.)

Division IV — Spermatophytes. Seed-bearing plants.

A. Gymnosperms. Naked-seed plants. {Examples. Sago palm, ginkgo,

yews, larches, pines, cypress, sequoia.)

B. Angiosperms. Inclosed-seed plants.

1. Monocotyledons. {Exa7npies. Cat-tail, water plantain, grasses,

grains and sedges, palms, Indian turnip, rushes, spiderwort,
lilies, bananas, orchids.)

2. Dicotyledons.

a. Archichlamydeae. Flowers having no corolla or one of distinct

petals. (Examples. Catkin-bearing trees (willows, wal-
nuts, oaks, beeches), smartweed, pink family, buttercup
family, water lilies, rose family, bean family, parsley
family.)

b. Sympetalae. Flowers having corollas in which the petals are

united. {Examples. Heath family, primrose family,
gentian family, mint family, morning-glory family,
plantain family, madders, honeysuckles, composites, —
daisy, aster, sunflower, goldenrod, etc.)

CHAPTER LXXXVII
KINDS OF ANIMALS

504. The classification of animals. Distinctions between
higher and lower among animals are based on the same con-
siderations as those among plants, — namely, complexity of
structure and specialization of functions. The most striking
division among animals is that between the vertebrates (animals
having a backbone) and the invertebrates. The latter group
is made up of many diverse types that have little in common
except the fact that they are animals.

505. The main groups of animals. The chief groups of
animals are indicated in the following outline :

Division I — Protozoa. The simplest animals ; body of one cell. {Ex-
amples. Ameba, Paramecium, Vorticella, Plasmodium of malaria.)

Division II — Porifera ("pore-bearing " animals). This includes all the
sponges.

Division III — Ccelenterata. Radially symmetrical animals having a
single cavity in the body ; all aquatic, mostly marine.
Class I — Hydrozoa. {Examples. Fresh-water hydra, certain small

jellyfish.)
Class 2 — Actinozoa. {Examples. Sea anemones, most corals.)
Class 3 — Scyphozoa. {Examples. Most of larger jellyfish.)

Division IV — Flatworms (Platyhelminthes). {Examples. Tapeworm,
liver fluke, planarians.)

Division V — Roundworms (Nemathelminthes). {Examples. Hookworm,
trichina, thorn-headed worm.) Many of these animals are dangerous
parasites on man or on domestic animals.

Division VI — Wheelworms (Trochelminthes). The Rotifera, or wheel
animalcules. Mostly microscopic.

482

Fig. 252. Genealogical tree of animal life

This diagram is intended to suggest the common origin of all animal forms, with the

constant progressive departure from ancestral types, now in one direction and now in

another, like the branching of a tree. Of course only the main branches are shown.

There are probably over a million species of animals living to-day (cf. Fig. 251)

484 ELEMENTARY BIOLOGY

Division VII — Echinodermata (" spiny -skinned " animals). Radially
symmetrical, all marine.
Class I — Asteroidea. Starfish,
Class 2 — Ophiuroidea. Brittle stars.
Class 3 — Echinoidea, Sea urchins.
Class 4 — Holothuroidea. Sea cucumbers.
Class 5 — Crinoidea. Sea lilies.

Division VIII — Annelida ("ringed" animals). Wormlike animals with
segmented bodies. The two most important classes are represented
by earthworms, sandworms, etc. and by the leeches.

Division IX — Arthropoda ("jointed-legged"). The body segmented;
exoskeleton.

Class I — Myriapoda ('' thousand-legged "). [Examples. Myriapods,
centipede.)

Class 2 — Crustacea (" crusty " shells). Head and thorax fused ; water-
breathers; antennae. {Examples. Lobster, crayfish, crab, shrimp,
barnacle, sow bug.)

Class 3 — Arachnida (spider family). Four pairs of legs ; air-breathers ;
no antennae. {Examples. Scorpions, spiders, daddy longlegs, taran-
tula, mites, ticks.)

Class 4 — Insecta. Segmented bodies ; distinct head, thorax, and abdo-
men ; antennae, compound eyes ; three pairs of legs ; one or two
pairs of wings (a few forms, wingless) ; air-breathers. A list of the
chief orders of this important class is given on page 487).

Division X. — Mollusca ("soft" animals). Unsegmented animals, most
of them bearing shells.
Class I — Gastropods (" belly-footed "). Having shells of a single piece.

{Examples. Snails, slugs, periwinkle, whelk.)
Class 2 — Pelecypoda (" hatchet-footed "). Bivalve (having shells of

two valves). {Examples. Oysters, clams, piddock, scallop, mussel,

shipworm.)
Class 3 — Cephalopoda (" head-footed "), The foot partly surrounds the

head and has a number of arms, or tentacles. {Examples. Octopus,

cuttlefish, squid, nautilus.)

Division XI — Cordata. Animals having a notocord, or internal axial
basis for a skeleton. It is from this structure that the vertebral
column develops. There are a number of small animals which never
develop a true backbone, but which nevertheless have a structure
that suggests the beginning of such a column. These are included

KINDS OF ANIMALS 485

among the cordata, although they are not strictly vertebrate. {Ex-

atnpies. Acorn worm, lancelet, sea squirt.) The five important

classes of vertebrates are

Class I — Pisces (fishes). The stone hag and the lamprey are sometimes

called fishes, though they are distinct in having a round mouth (no

jaws) and no fins or scales. They never develop bones, the skeleton

remaining cartilaginous. There are four orders of true fishes :

1. Cartilaginous fishes. Gill slits not covered; "skin teeth." {Ex-

amples. Skates, torpedoes, sharks.)

2. Armored fishes {Ganoidei). Large, bony scales in the skin, espe-

cially about the head. In former times this order was very
numerous. {Examples. Sturgeon and gar pike.)

3. Bony fishes {Teleostei). {Examples. Salmon, herring, perch, cod,

flounder, etc.)

4. Mud fishes {Dipnoi). Fishes with lunglike structures. Only three

living representatives, all in the southern hemisphere.

Class 2 — Batrachians (amphibia). Breathe by means of gills in early
stages, and later develop lungs. Bony skeleton with two pairs of
appendages ; no exoskeleton. {Examples. Frog, toad, newt, sala-
mander, mud puppy, hellbender.)

Class 3 — Reptilia. Wholly air-breathers ; plates or scales in the skin.
Four orders are usually recognized :

1. Chelonia. {Exa7itples. Turtles and tortoises.)

2. Serpents. {Examples. Snakes, adders, cobras.)

3. Lacertilia. {Exa7nples. Lizards, chameleons, horned toad, Gila

monster.)

4. Crocodilia. {Examples. Alligators, crocodiles.)

Class 4 — Aves (birds). Warm-blooded ; exoskeleton of feathers ; front
limbs wings ; tendency for the bones to fuse ; air spaces in bones ;
no diaphragm ; eggs with limy shells. Living species of birds may
be divided conveniently into the running birds (ostriches, the casso-
wary, and the emu) and the flying birds. The latter include two
groups of orders, — the water birds and the land birds. Some of
the important orders are
r. Anseres. {Exatnpies. Swans, ducks, geese.)

2. Longipennes. {Exainples. Gulls, petrels, terns.)

3. Pygopodes. {Exajnpies. Loons, grebes, auks.)

4. Heron order. {Examples. Storks, ibis, bittern.)

5. Plover order. {Examples. Snipe, curlew, rail, sandpiper.)

6. Gallinae. {Examples. Hen, turkey, guinea fowl, peacock, pheas-

ant, partridge, ptarmigan.)

7. Columbas. {Examples. Pigeons, doves.)

486 ELEMENTARY BIOLOGY

8. Passeres. Perching birds ; includes about one half of our native birds.

{Examples. Sparrows and finches, swallows, robins, thrushes,
crows, etc.)

9. Raptores. Predatory birds. {Examples. Eagle, hawk, owl.)

10. Pici. {Examples. Woodpeckers, sapsuckers.)

1 1 . Cuckoo family (including kingfishers).

1 2. Whip-poor-will order (including humming birds).

Class 5 — Mammalia (mammals). Warm-blooded ; hairy exoskeleton ;
diaphragm ; suckle young.
.1. Monotremata. Egg-laying mammals. {Examples. Duckbill, spiny
anteater.) (With the exception of these two, all mammals
develop the young within the body of the mother.)

2. Marsupials. Carry their immature young in a special abdominal

pouch. {Examples. Kangaroos, wombats, opossums.)
The rest of the mammals are divided into the following orders :

3. Edentata (" toothless " mammals). {Exatnpies. Sloths, armadillos,

hairy anteaters.)

4. Cetaceans. {Examples. Whales, dolphins, porpoises.)

5. Sirenia. {Examples. Sea cow, manatee, dugong.)

6. Ungulata (" hoofed " animals).

a. Odd-toe. {Examples. Horses, zebras, rhinoceros.)

b. Even-toe. {Exa?nples. Ox, sheep, antelope, camel, giraffe, deer,

pig, hippopotamus.)

c. Proboscidea (elephants).

7. Rodentia (" gnawers "). The largest order. {Examples. Rabbits

and hares, squirrels, chipmunks, porcupine, gopher, muskrat,
rats, mice.)

8. Insectivora (" insect-eaters "). {Exatnpies. Moles, shrews, hedge-

hog.)

9. Chiroptera (" hand-wings "). {Examples. Bats, vampire.)

10. Carnivora (" flesh-eaters "). {Examples. Cat family, dog family,

bears, weasel, seal, walrus, otter, mink, skunk, badger,
raccoon, etc.)

11. Primates ("the first," or leading, order of animals, including

man). The families contained in this order are given in the
list on page 488.

506. The orders of insects. The insects constitute the most
numerous class of animals. The many species show adapta-
tions to all sorts of conditions, and from a human point of
view furnish us many friends as well as many enemies.

KINDS OF ANIMALS 487

1. Aptera (" without wings "). The most primitive insects now living.

[Examples. Silverfish and springtail.)

2. Orthoptera ('' straight-winged "). Wings lying parallel with body

or folding lengthwise ; incomplete metamorphosis ; biting
mouth. {Exa7nples. Locusts, crickets, walking sticks, katy-
dids, cockroaches, mantis.)

3. Neuroptera (" netted-veined wings "). A large group broken up into

several orders by entomologists; complete metamorphosis;
biting mouth. {Examples. Mayflies, dragonflies, termites.)

4. Hemiptera ('* half-wings "). Basal part of wings often thickened

and without distinct veining ; incomplete metamorphosis ; suck-
ing mouths. All true bugs. {Examples. Squash-bug, bed-bug,
water-bug, plant lice, scales, lice, cicada.)

5. Coleoptera ('' sheath-wings "). The front wing a hard protective

cover ; complete metamorphosis ; mostly with biting mouth.
{Examples. Beetles, weevils, fireflies, ladybird, June-bug.)

6. Lepidoptera (" scale-wings "). Rigid membranous wings covered with

minute scales ; complete metamorphosis ; sucking proboscis.
{Examples. All moths and butterflies.)

7. Diptera (" two-wings "). Hind wings reduced to tiny knobs, or

" balancers " ; complete metamorphosis ; sucking or piercing
mouth. {Exa?nples. Mosquitoes, gnats, midges, house flies,
stable flies, botflies, warbles, fruit flies.

8. Siphonaptera (" tube-wingless "). Sucking mouth, wings reduced ;

complete metamorphosis ; parasitic on birds and mammals.
{Examples. Fleas of all kinds.)

9. Hymenoptera (" membrane wings "). Complete metamorphosis ;

biting or sucking mouth. {Examples. Wasps, hornets, bees,
ichneumons, ants.)

507. The families of primates. The order Primates is no
doubt of great importance in the world, since it includes the
human species. From a zoological point of view, however, it
cannot be considered the highest group of animals, since in
many respects the skeleton, the muscles, and the teeth of
man and the apes are not so highly specialized as are the
corresponding organs of such animals as the whales or the
elephants, for example. Nevertheless, the remarkable develop-
ment of the nervous system among the primates entitles them
to a distinctive place in the animal world.

488 ELEMENTARY BIOLOGY

This order consists of the following families :

1. Lemuroidea. Small, squirrel-like 'animals living in trees and bushes.

The lemurs are found in Madagascar, the marmosets in South
America.

2. Cebidae. The New World monkeys. Nearly all have long, grasping

tails and flat noses. Smaller than the Old World monkeys.
{Examples. Howling monkey, spider monkey, capuchin.)

3. Cercopithecidae. The Old World monkeys. Tail not grasping, or

short ; nostrils pointing downward. Distinct, opposable thumb.
{Examples. Baboons, mandrill, macacus, Indian ape.)

4. Simiidae. The anthropoid (manlike) apes. No distinct tail ; arms

longer than legs. [Exa?nples. Gibbons, orang-utans, chimpan-
zees, and gorillas.)

5. Hominidae. The human race.

508. Varieties of the human race. The so-called races of
mankind have from earliest times puzzled the thoughtful. On
the one hand, the most diverse of peoples are still so much
alike as to leave no doubt as to their being human beings. On
the other hand, the variations in skin color, in hair characters,
in eyes, in shape of head, in form of eyelids, in stature, and in
other physical characters are so great as to exceed by far the
ranges of " individual variation " found in most other species.
In mental characters also, in the rate of development, and in
chemical characters (as shown, for example, by distinctive odors
of perspiration and by specific immunities to diseases) the races
differ in many striking ways. Nevertheless, by every test that
zoologists apply, all belong to the same species.

Attempts to classify the species Homo sapiens range from
three main groups proposed by Linnaeus (White, Yellow, Black)
to as many as fourteen or sixteen offered by other students. The
most common division recognizes five main races, as follows :

I. The Caucasian^ or white-skinned, or European, races and tribes :
hair from pale yellow to black ; eyes from blue to brown ; wide varia-
tion in stature and in form of features. This is to-day, and has been
throughout historic times, the most aggressive and masterful branch
of the human family.

KINDS OF ANIMALS 489

2. The Mongolian, or yellow-skinned, or Asiatic, races and tribes :
hair black and straight ; eyes dark, with characteristic eyelids ; gener-
ally shorter than the Caucasians ; rather high cheek bones and broad
skull. The Chinese and Japanese are the chief representatives. Of
very ancient civilization, that seems to have stagnated for a long time ;-
probably likely to play a larger share in world affairs in the future.

3. The Americafi, or red-skinned, races and tribes : in many
respects the North American Indians resemble the Mongolians. The
Eskimos and certain Siberian tribes show remarkable resemblances
to both groups. Partly because of the treatment to which they were
subjected, and partly because of their racial characteristics, these
people are of diminishing importance in the world.

4 and 5. The Negroid, or black-skinned, races and tribes : hair
black and woolly, or frizzled ; eyes dark ; nose broad. The African,
or Ethiopian, blacks differ in many ways from the Melanesian and
Australian blacks. Indeed, but for the color of the skin they should
be put into as distinct groups as the Chinese and the Irish, for
example. Huxley, who lumps the red-skinned and the yellow-skinned
peoples into one race, nevertheless makes two races of the Australian
and Melanesian blacks, on the one hand, and the African blacks, on
the other.

CHAPTER LXXXVIII

MAN AND HIS RELATIVES

509. Man as organism. Any definition that we can make
of living things must apply to man. We have seen that growth
and development, irritability and contractility, in general char-
acteristic of the behavior of protoplasm, are also found to be

Fig. 253. Limbs of primates
Hind and fore limbs (legs and arms) of man, gorilla, and lemur

essentially the same in human beings. Like other living things
man depends upon food and water and oxygen and minerals for
his material existence and activities. Like them he is helped
as well as hindered by the things about him, — by the living
things and by the non-living things. Like them he must at
every point adjust himself to his environment or be overcome
by it. Like them he reproduces his kind,

490

MAN AND HIS RELATIVES

491

510. Man a primate. In trying to place man in the world
of animal life we must follow the same methods as would be
used if we should find some animal that no one had ever seen
before. We have no difficulty in recognizing a newly discovered

Fig. 254. Comparison of primate skeletons

A comparison of the skeletons of the lemur, the gorilla, and man show many similarities
in details as well as in general plan of structure

animal, as, let us say, an insect, even when we see it for the
first time. We may be able to tell even in what order of in-
sects it naturally belongs. According to our familiarity with the
group, we may be able to tell the family or even the genus.

In the same way we may at once place man among the
backboned animals, and, without any hesitation, in the class of

492

ELEMENTARY BIOLOGY

vertebrates known as mammals, because, like the mammals in
general, the human species suckles its young and has a hairy
outgrowth on the skin. And, of the ten or a dozen orders into
which the class Mammalia is usually divided (see p. 486), the
highest, or primates, seems best to agree with what we know
of our own structure.

In the matter of the limbs, all primates have the thigh quite
free from the body, and the hand and foot have five distinct
digits, with the first one (inner) usually opposable, thus con-
stituting a grasping organ. The soles of the feet (or hands)

Fig. 255. Skulls of primates

Compare the size of the face and jaw with the size of the brain box. Note the appear-
ance in man of a distinct chin and a nose bridge. /, lemur ; 2. gibbon ; j, man

come down flat on the ground. The lemurs are obviously less
like man than are the monkeys, and these less than the apes.
511. Man and other primates. The important differences
between man and his nearest living relatives are found in the
erect walk, the differentiated appendages, a distinct chin, de-
cidedly larger brain, and articulate speech. Animals other than
man are able to get up on their hind legs for longer or shorter
periods, but none of them ever acquire the definite, erect walk
that all human beings develop (Figs. 253, 254).

It has been pointed out that acquiring the habit of walking alto-
gether on their hind legs gave the ancestors of the human race an
opportunity to free their arms and hands for other activities, and that
therefore it became possible to develop these organs to higher skill.
We must be on our guard against assuming that the evolution of man
(or of any other species) proceeded by the hereditary transmission
from generation to generation of the effects of practice or experience.

Fig. 256. Ancestors of man represented by remains of skulls

/, Pithecanthropus erectus, the " erect ape-man " of Java ; 2, the Neanderthal man ; 3, the
negroid man of Laussel ; 4, Nebraska glacial man. These four types represent succes-
sive advances in the evolution of the human races, although we must not think of them
as a straight series of our ancestors. Compare the size of the brain at different stages
of development: Pithecanthropus, 850 cc; Piltdown, 1300 cc. ; Neanderthal, t 600 cc;
modem man, 1500-1800CC.

494

ELEMENTARY BIOLOGY

The larger brain, carrying with it possibilities of learning,
imitating, and planning, is perhaps the most important advance
made over the simian ancestors (see Fig. 255).

Fig. 256 is a diagram which shows the distinctive traits
of several ancient specimens supposed to represent different
stages in the evolution of the human species. Fig. 258 repre-
sents restorations of some of
these primitive forms ; from
these we can get an idea of
how some of the intermediate
ancestors probably looked.

Fig. 257. Fossil remains of man

The pieces of skull, jawbone, and tooth
found in England at Piltdown in 191 1 rep-
resent a lower type of human being than
any that had been previously discovered

512. Evolution and man. Fifty
years ago much of the discussion
among thinking people centered
around the question of the validity
of the evolution theory as applied
to man. There were many who
were prepared to believe that
evolution has taken place among
plants and lower animals, but
who hesitated to accept the same
explanation for the appearance of man upon earth. One of the
strongest objections urged against the theory was the fact that it had
been impossible to produce a complete record of a graded series con-
necting man of to-day with his supposed non-human or prehuman
ancestors. This argument of the " missing link " carried a great deal
of weight with people who did not appreciate how unlikely it would
be for complete series of specimens to be preserved through geologic
times. Of the millions of human beings and other vertebrates that
die in a given region during a century, how many skeletons are likely
to remain sufficiently intact to be recognized from ten thousand to
fifty thousand years later.? From a scientific point of view it would
be sufficient if the scattered pieces found at widely different levels
(geological ages) do actually fit in with a supposed series.

The few bones found in Java by Professor Dubois in 1894 fit
into such a series in a very satisfactory way. The type of animal
to which these bones belong was named Pithecanthropus erectus, and

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496 ELEMENTARY BIOLOGY

probably represents a " missing link." This animal had among his
contemporaries a form of elephant, rhinoceros, Indian hippopotamus,
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 that region.
This form is in many ways intermediate between the apes and more
recent man, but we must not expect it to be an average between
the two extremes. It is more like Homo in some ways and more
like the apes in others ; and in some respects it is between, as in the
character of some of the teeth.

A more recent discovery of ancient remains in Sussex (England)
seems to point to a more closely related ancestor. The skull is larger
than that of Pithecanthropus, and the teeth are more like those of
modern man (Fig. 257).

Large numbers of specimens have been found in various parts of
France, Germany, and Belgium 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, and the type is frequently referred
to as the Neanderthal race. Although these had much larger skulls
than the Piltdown (Sussex), — larger even than is found among races
living to-day, — the characters of the jaws and teeth, the low and
retreating forehead, the prominent ridges over the eyes, and other
features indicate a lower stage of development. This group has been
named Homo primigenius, or Hoino neanderthalensis .

CHAPTER LXXXIX
MAN'S BRAIN

513. Hand and brain. The hand of man and the brain of
man are the organs that make all the important differences

Pigeon

Dog

Monkey Man

Fig. 259. Brains of vertebrates

Note the relative size of the cerebellum in the bird and mammals. In the mammals

note the great increase of cerebrum and the increasing amount of convolution, or

wrinkling, of the brain surface. The greater brain area in the higher animals corresponds

to greater numbers of association neurons, and thus to greater intelligence

between him and the other animals. And the doings possible
for the hand depend finally upon the powers of the brain. It
is this organ, therefore, that may properly be considered man's
supreme possession.

497

498 ELEMENTARY BIOLOGY

514. Structure of the brain. In all vertebrate animals the
front end of the central nervous system is enlarged into a mass
of neurons, connective tissue, and blood vessels constituting the
brain (see Fig. 259). In man the brain is not only a larger
part of the whole body than it is in any other animal, but it is
absolutely the largest brain, excepting only that of some of the
larger elephants.

The cortex, or '' bark," of the cerebrum consists of nerve
cells. In mammals this gray layer is very much wrinkled, so
that there is relatively more surface than in lower vertebrates. It
seems that the extent of the convolution is related to the num-
bers of cells and to the complexity of their connections. The
white part of the brain consists of connecting fibers, or axons.

On the ventral surface of the brain are many connecting
nerves, containing efferent and afferent fibers (see pp. 220-223).
The hind-brain and the mid-brain have to do with reflexes and
automatic movements of various kinds. In the cerebrum, nerve
action is connected with consciousness and voluntary movements.

The activities of the heart, the digestive system, the breathing
apparatus, etc. may go on indefinitely without being influenced
in any way by what happens in the cerebrum, and without pro-
ducing any effect upon the cerebrum (except to keep it sup-
plied with blood). Many of our activities and movements are
unrelated to the cerebrum ; but every thought, every conscious
desire, and every deliberate or purposeful action depends upon
impulses starting from the gray matter in the brain or leading
to the gray matter.

Experimental studies upon various mammals, and the experiences
with the diseased or injured brains of human beings, have established
the fact that each portion of the cerebral cortex is concerned with
specific feelings, ideas, or movements. In the diagram in Fig. 260
are indicated some of the localizations of brain function that have
been determined in these studies.

The special study of the activities of the cerebrum, as they show
themselves in thinking, feeling, willing, is Q.d^Q.di psychology.

MAN'S BRAIN

499

515. Tools and weapons. The natives of Madagascar say
that if a spear is thrown 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 gorillas

Fig. 260. Localization of functions in the cerebrum

By studying human beings anji other animals in which the brain had been injured, and
by making experiments, it has been ascertained that certain regions of the brain cortex
are related to receiving sensations from specific regions of the body, while other regions
initiate movements of specific muscles. Most of the sensory and motor nerves pass
through the spinal cord, SC. The thinking is carried on by the so-called association
areas, A-i and A-2. The frontal association area has to do with abstract thinking, self-
control, concentration, and making decisions. The hind association area has to do with
knowing and understanding concrete facts and relations

will fight with a stick used as a club. But probably no gorilla
or monkey ever carried a club or a stone about with him for
use in possible emergencies, and that is something that man
has done. Even among the earliest remains of human activity
there are indications that man chipped stones to fit his hand, to
be used as weapons or perhaps for breaking shellfish (Fig. 261).

500

ELEMENTARY BIOLOGY

516. Building. Of course other animals have built shelters,
and many species of birds build much neater nests than the
apes do, and much neater, probably, than primitive man built in
the tree tops. But man has finally succeeded in building shelters

Fig. 261. Relics of man in the Stone Age

I, hatchet; 2, hammer-head ; j, ax ; 4, j, arrowheads ; 6, fishhooks. (/, 2, and 4, after
Tyler ; 3, j, and 6, original)

SO far beyond anything that other animals have made, that it
seems ridiculous to compare them. The point is, that although
the bees and the birds may build very good shelters, they build
the same, generation after generation, controlled in their actions
by comparatively fixed impulses or instincts ; whereas man has
no natural skill or plan for doing these things, yet can learn ^

MAN'S BRAIN 501

because of the constitution of his brain, to make infinitely more
complex structures.

517. Fire. What the use of fire has meant to man is hard
for most of us to realize, because we have always had the bene-
fits of fire, and grow up accepting it as a matter of course. It
made possible his wandering from the tropics ; it made possible
his descent from the trees to dwell in caves or even 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 it
was probably helpful in early times in many other ways.

It is not to be wondered that people of all races and in all times
have not only seen in fire a great benefactor, but have been impelled
to worship the mystery of it as well. Even in our own times the
symbolism associated with fire still persists in festivals and religious
ceremonials.

518. Speech. Many animals are capable of making several
distinct sounds that actually serve as means of warning or
other communication between members of the species. The
hen, for example, can utter some twenty distinct sounds, and
each one has a different meaning. Other animals have been
observed to communicate with each other by means of calls
or cries. But in human speech there is more than a set of
significant ejaculations. Human language comes to be built up
into words, each of which consists of definite successions of
sound (which we represent by means of vowels and conso-
nants), and these words are combined into sentences capable
of expressing all kinds of ideas. Of course one may say that
our language is more complex because our thoughts are more
complex, and that is true enough. But human speech differs
from the crowing and growling and snarling of other animals
in what may be called its structural possibilities as well as in
its actual complexity, — it is capable of constant readjustment
to the needs of the thinking animal in a way that the expres-
sions of other animals are not. For example, if you have a

502 ELEMENTARY BIOLOGY

new idea, you are quite capable of giving expression to it
so that another person can understand you, by means of the
language you have acquired. It is not necessary to devise new
kinds of noises, and it is not often necessary to make up
new words.

But the use of all these things — tools, fire, speech, etc. — is
but the external indication of the fact that man has a superior
brain. This we can see when we compare, in a general way,
man's adjustment to his surroundings with that of other animals.

519. Man's handicaps. It does not take a very close exami-
nation to show us that as a living machine 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
it comes to fighting, his nails and claws are very poor rivals for
those of cats, let us say, and his teeth, which he does indeed
sometimes use, are not nearly as formidable as are those of
many other animals of his own size. His muscular develop-
ment, too, is rather inferior, when it comes to wrestling with
a non-human enemy ; and when it comes to running away, he
would be easily overtaken by very many of the inhabitants of
the forest.

Man has a very good eye, compared to other animals, and a
pretty good ear, — though not one of the best, so far as dis-
covering faint sounds is concerned ; but his smelling ability is
of very low rank. These three senses, which are so valuable
to animals in helping them discover their enemies or their prey
at a distance, are of great value to man also ; but on the whole
he has no advantage in competition with the other inhabitants
of the forest.

In spite of these various shortcomings man has contrived to
hold his own, and some branches of the species have become
virtually masters of their environment through the use of the
brain. Man has made up for his thin skin by borrowing the
skins of other animals and by devising substitutes for skins

MAN'S BRAIN 503

(fabrics) out of other material. He has strengthened his arm
by means of sticks and stones, and has lengthened his legs —
that is, increased his speed — by means of iron and brass. He
has extended the reach of his eyesight millions of miles beyond
the surface of the earth, and has seen into the world of the
little, — a thing no other backboned animal has ever done. He
can hear the footsteps of a fly (although he does not need it
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 insufficiency by using his thinking organ to
guide his hand.

CHAPTER XC
MAN'S CONQUEST OF NATURE

520. Learning from experience. We have seen that one of
the peculiarities of the human organism that gives it advan-
tages over others is the fact that it can learn from experience.
There are, indeed, other animals that also learn from experi-
ence. Experiments made with turtles, cats, crabs, earthworms,
starfish, even Paramecium, and many other animals show that
to a certain extent these organisms can profit from experience.

521. Learning from others. When human beings gather into
groups, each one learns not only from his own experience but
from the experiences of others. Experiments made with many
different animals showed that the monkeys were the only ones
that made any attempt to imitate what others were doing ; and
they were the only ones, therefore, who could possibly learn
from the experiences of others.

Among human beings there is the possibility of learning
from others, not only through imitation but also through direct
instruction. And in the fact that human beings orgajtize for
various activities (as hunting, fishing, fighting, migrating, etc.),
and cooperate, there is a further possibility of learning, — one
that other animals do not have in anything like the same degree.

522. Preserving experience. If a wasp should learn a new
trick for catching caterpillars, and use it successfully in gather-
ing 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, we have an
extreme example of the possibility of carrying on the results
of experience from generation to generation. Although it is
impossible to transmit through heredity the modifications that

504

MAN'S CONQUEST OF NATURE 505

occur in the individual organism, it is possible for man to
transmit what he has learned, through tradition or ceremonial.
Savages who know how to make fire teach their young to go
through the ceremony of making fire ; this is too importantj_
too sacred a thing, to tell a youngster offhand. In the history
of primitive peoples we find over and over again that every
good idea that they get — and many a foolish one too — is care-
fully preserved by being organized into a sacred ceremonial that
must be performed just so on special days. In this way these
people preserve whatever wisdom they manage to gather up, as
.well as a great deal of what seems to us to be foolish superstition.

523. Knowledge and control. Wherever men have known
the relations of forces and materials, wherever they have under-
stood the behavior of plants and animals, they have been able
to control nature. And wherever they have controlled they
have felt secure and confident, at peace with themselves and
with their gods. But wherever they have failed to control, they
have been aware of their own weakness ; there we find people
modest and humble to the last degree ; there we find them
cringing and fearful and superstitious.

This is well illustrated by the differing attitudes of men
toward their industries, on the one hand, and toward their crops
and their health, on the other. Men and women who know
their trades — that is, who understand the materials and the
forces with which they work — are confident about the outcome
of their undertakings. They knozv that handling tools in a cer-
tain way will produce certain results, and they have no fear, no
hesitation, in their undertakings. But when it comes to raising
crops or looking after animals, there is no such certainty.
These things depend upon the weather — and who can control
that .? So we find people making mystic signs and muttering
magic words to appease the spirits of the wind and the rain,
or we find them offering sacrifices — yes, even human sacrifices
— to gain the favor of the spirit that controls bugs or mildews.
And even then they are not sure of the results, but worry

5o6 ELEMENTARY BIOLOGY

along in doubt and dread until the crop is ripe. And when the
crop is in, they rejoice as those coming to the end of a danger-
ous journey, and again they have their ceremonials and magic.

We may observe similar attitudes toward problems of health.
Before people know what causes plague or malaria or tuberculosis,
before they know what kills their sheep and their potatoes, they are
just as fearful, just as superstitious, as they were during the Dark
Ages. In those times when witches were burned for bringing on
plague by uttering wicked words, or when foreigners were tortured
for poisoning wells by making wicked signs, no one knew and
everyone feared and suspected.

524. The measure of controL We have seen that the use
of tested knowledge to solve human problems may bring about
measiLrable results ; that is, we can measure what difference it
makes whether we use the scientific method or some other
method. Thus, we can measure how much work it takes to pro-
duce a given quantity of potatoes with the use of suitable fertilizer
and how much it takes to produce the same without fertilizQf,
and so find the advantage of one method over the other.

The following table shows the number of hours of human labor
required to produce by machinery, under conditions that prevailed at
the close of the last century, given amounts of various commodities
which it took a thousand hours of hand labor to produce under the
conditions that prevailed at the close of the Civil War. At the pres-
ent time every process has been improved so much, especially under
the pressure of the Great War, that the figures in the last column
may be reduced by one half or more in most cases.

COST IN HUMAN HOURS OF PRODUCING BY MACHINERY
THE EQUIVALENT OF 1000 HOURS OF HAND WORK

Units of Value Hours Units of Value Hours

Barley, 470 bu 42.4 Books (binding), 2190 vols. 263.4

Corn, 220 bu 151. 3 Shoes, 45 pr 135.0

Oats, 606 bu 107.5 Newspapers, 1,750,000 pages 4.8

Potatoes, 2000 bu. . . . 345.3 Envelopes, 230,000 . . . 72.6

Wheat, 310 bu 46.0 Granite (dressing), 6150 sq. ft. 77.9

MAN'S CONQUEST OF NATURE 507

A study of the average length of Ufe in various countries
during the nineteenth century showed that in several countries
the average length of life was increased (through the applica-
tion of the results of scientific study) by as much as from five
to twenty-nine years. In India, where alone the people refused
to adopt the modern methods, there was no improvement
whatever. The table below shows the death rates (number of
deaths per thousand of the population in the course of the
year) for several different countries. The extremely high death
rate of India, compared to that of other countries, or the fact
that the average length of life in India is only about twenty-four
years, compared to from forty to fifty years in the other coun-
tries, shows a measurable difference ; and all the evidence that
we have indicates that a large part of the difference lies in the
different attitudes of the people toward life. There are differences
in the theories that people have about the causes of sickness.

DEATH RATES IN VARIOUS COUNTRIES

Denmark (1906) 13.5

Sweden (1906) 14.4

England and Wales (1906) 15.4

United States (registration area, 1907) 16.5

Germany (1905) 19.8

France (1906) 19.9

Italy (1906) 20.8

Japan (1905) 21.9

India (males, 1 901) 42.3

The diagram on page 389 shows the steady improvement
of health conditions in New York City as measured by the
declining death rate for a period of years. Such measurements
are constantly being made and are a fair indication of the
effectiveness of our ways of doing things. The study of
such measurements will tell us just how far it pays to knozv.

525. The social nature of science. What we call knowledge
(or, in its organized forms, science) is never the result of an

5o8 ELEMENTARY BIOLOGY

individual's isolated efforts. It is always the product of human
intercourse. Not only does its production involve the inter-
change of thought and experience of many people ; it involves
also the presevoation of thoughts and experiences for genera-
tions. Each one adds a little to what has gone before ; if he
did not know what had been learned before him, he would
have to start at the beginning, and so each one could get no
farther than a child's experience.

Unless we think about the matter for some time, we are not likely
to realize how far-reaching is our dependence upon others for the
thousands of ideas — useful or entertaining — that we absorb from
our surrounding civilization, through books, through customs, through
instruction, through social intercourse and various institutions, such
as the church, clubs, games, election campaigns, and so on. We get
our ideas not only from our immediate neighbors but from all
corners of the earth, — not only from our contemporaries but from
the remotest antiquity.

Again, our applications are largely social. We have seen
this to be the case in hygienic matters. It is impossible for
me to save myself from tuberculosis infection by minding my
own business or by refraining from spitting etc. My safety
depends in large part upon what other people do. The same
principle holds in the matter of fighting any plant or animal
pest, whether it is merely a nuisance or a menace to our eco-
nomic welfare. The same thing holds in utilizing most of the
great discoveries or inventions, such as the telephone or the
wireless, the steam engine or the electric light.

The development of inventions depends not only upon the accumu-
lated knowledge of the past but also on the possibility for joint use.
It is only after years of experience with electric-lighting plants, for
example, that we may at last contrive to establish a small plant for
serving an isolated farmhouse ; at first the development is possible
only where people live together in communities and exchange their
services readily.

CHAPTER XCI
SCIENCE AND CIVILIZATION

526. Casual and purposeful science. Much of the science of
the past has been a casual or even accidental product. People
just happened to discover this or that. But in modern times —
within the last three centuries, and especially during the past
fifty years — science is being systematically studied for the
purpose of solving special problems. Instead of depending
upon an occasional man who is both interested in scientific
study and free to devote himself to the study without needing
to earn a living, we are coming more and more to provide
the opportunity for those who show special aptitudes in that
direction. Every large university is in a position to pay a few
hundred dollars a year to several students who are willing to
devote themselves to special investigations, and who have shown
that they have the ability to do work that is worth while.
Scholarships for such investigations are provided by the direc-
tors of industries who wish to have special problems pertaining
to their materials or processes investigated ; or wealthy people
endow such scholarships as a means of contributing to the
general betterment of society.

527. Organization of research. As we come to realize the
value of such investigations to the whole nation or to the
race, we depend less and less upon the casual endowment of
research by people who have money to spare, and depend more
and more upon public effort in this direction. Thus, every
state in the Union has one or more agricultural experiment
stations, in which investigations are being carried on with a
view to finding out the behavior of different kinds of soil in
relation to crops, the most favorable conditions for the growth

509

5IO ELEMENTARY BIOLOGY

of various crops, the best methods for eradicating weeds or
exterminating certain insects, how to get the best results from
feeding cattle or hens, the best kinds of plants or animals to
raise for various purposes, and so on.

The United States Department of Agriculture is not only
cooperating with the various state agencies, but is directing
special investigations of a kind that may be too costly for a
single station to undertake, or on problems that concern the
people of more than a single state.

In every large city the department of health has a number
of men and women whose business it is to make special inves-
tigations on special phases of the local health problems. They
study the water supply, the milk supply, the markets, the
sewerage system, the disposal of garbage ; they examine speci-
mens for the more accurate diagnosis of disease, and they con-
duct experiments with a view to increasing the accuracy of
diagnosis or to shortening the time of diagnosis, for in some
diseases a few hours may be of great significance. They ex-
periment for the purpose of improving materials and methods
in the preparation of vaccines and serums, and they investigate
the relative efficiency of different methods of fighting flies or
of ventilating factories or schoolhouses.

The departments of health in the various states are also
doing more and more systematic work in extending our knowl-
edge of the conditions that make for health. The United
States government contributes to the solution of these problems
through the work of the Public Health Service, which not only
has the supervision of the marine hospitals, but conducts im-
portant investigations on special diseases ^ and on methods for
preventing epidemics.

1 Important investigations were conducted by the United States govern-
ment scientists, leading to the discovery of the hookworm disease and
to the development of methods for curing it among the victims, as well
as for preventing it in the future. They made important studies on the
relation of rats and fleas to the plague, on the relation of pellagra to the
diet, and on other health problems.

SCIENCE AND CIVILIZATION 511

In addition to the work done by the departments of the
city, state, and national governments, ^ a great deal of scientific
investigation is carried on in a number of institutes devoted
especially to scientific research. The Rockefeller Institute for
Medical Research, the Wistar Institute of Anatomy, the Phipps
Institute, the Carnegie Institute, and many others in this coun-
try are carrying on scientific investigations in various fields, for
the benefit of the public.

It is well understood that science cannot be developed either
by those who shut themselves up from the rest of the world
or by those who seek to make some private gain through
exploiting nature's secrets. Sooner or later the search for the
world's truth must come in contact with human knowledge on
the one side, and with human welfare on the other. If man is
to continue to be master of his environment, it will be first of
all because he has learned to organize his machinery iox finding
otct^ and because he has learned to make general application of
what he finds out.

1 It is impossible to list all the public agencies that are regularly engaged
in scientific research, even in this country alone. Some of the important ones
besides those mentioned in the text are

The United States Fisheries Commission The United States National Museum

The United States Bureau of Standards The United States Census Bureau

The United States Coast and Geodetic The National Observatory

Survey The United States Bureau of Mines

The United States Bureau of Ethnology The United States Weather Bureau

Under the jurisdiction of the Department of Agriculture, investigations are
carried on in several different fields by special staffs of scientists. Some of
the bureaus, or divisions, are

The Forest Service The Bureau of Plant Industry

The Biological Survey The Bureau of Animal Industry

The Bureau of Entomology The Office of Experiment Stations

The Bureau of Chemistry The Bureau of Soils

In many cities there have been established, in connection with the education
departments, staff's of scientists to investigate various problems arising in the
work of education, psychological clinics, and other arrangements for finding
out what it is important to know. In a number of cities investigations are
being made for the purpose of determining the best way to prevent fires, —
of discovering the sources of fire dangers and how best to meet them.

512 ELEMENTARY BIOLOGY

528. Man's place in the world. We have studied the con-
ditions of life and have seen that in every essential respect
man is like other living things. We have glanced at man's
nature and have seen that in many important respects man is
decidedly different from other living things. We do not know
when or where or how man first came to use fire or weapons
or tools ; we do not know when he took to ornamenting his
body with paint and beads and feathers and nose-rings ; we do
not know how he acquired the art of weaving or the art of
pottery or how he came to sow seeds or to domesticate animals.
We do know that he has been doing these things for hundreds
of thousands of years, and that during the past four or five
thousand years he has been developing what we like to call
civilization. We know that the life of man — that is, civilized
man, the man who has the benefit of all the experience of the
race — does differ from the life of beasts and from the life of
the savage in many important ways.

From the condition in which all activities were concerned
with obtaining the means of livelihood, we have passed to the
condition in which only a relatively small part of our waking
time is needed for this purpose. From a state of uncertainty
and fear about the workings of nature, — animate nature and
inanimate nature, — we have passed to a very satisfactory
knowledge of many of these workings, and to confidence in
our methods for finding out more just as rapidly as we apply
ourselves to the investigation. From a condition of fear and
suspicion toward everything strange, — strange people as well
as strange plants and animals, — we have passed to a condition
of interest and toleration. We have developed art that may be
of value to others, but that interests us in the first place for
itself ; that is, we have found things to do other than those
absolutely necessary to keep us going. In the same way we
have become interested in problems the solution of which may
be helpful, but which interest us without regard to their pos-
sible use ; in other words, we have found things to think

SCIENCE AND CIVILIZATION 513

about that are not directly concerned with getting our food
and dodging our enemies.

Because civilized man has accumulated, in the course of his
development, so many kinds of interests, one of his real needs,
one that distinguishes him from other animals, is the need
for leisure. It is not enough to have food and clothing and
shelter ; the dray horse has that. Man wants time to use in
his own way. He wants to play games, he wants to talk things
over with people of like minds, and he wants to argue with
people of unlike minds. He wants to produce music, or he
wants to listen to music. He wants to let himself out in
making something of his own design, or at least he wants
to look at the pictures and sculptures and handicraft of other
people's make. He wants time to think matters over undis-
turbed, when he is not exhausted, and he wants a change of
air and of scene. He would like to see how other people live,
and he would like to make new acquaintances. Perhaps he
wants to cultivate a garden or keep rabbits. There are thousands
of things that men want to do, and the doing of which gives
them at least as much satisfaction as any of the activities that
are directly related to keeping alive. Indeed, these other things
are on the whole far more interesting.

No matter how much we like our food, no matter how
much we value the comfort of a warm fireside on a stormy
night, or the comfort of a good waterproof when out in the
rain, it is these other things that really matter most to-day —
these things without which life would still be possible, it is
true, but without which our lives would not be very different
from the lives of beasts. It is these things that man can do,
over and above making his living and keeping his body in
working condition, that distinguish him from all other animals.
And it is in proportion as these other things play a larger and
larger part in our lives, and in proportion as food and clothing
and shelter play a smaller and smaller part, that we may consider
ourselves humanized.

514 ELEMENTARY BIOLOGY

So far as the race as a whole is concerned, we have already solved
the urgent problems of producing the necessities of life. Without
extending our science beyond what we know to-day, we are in a
position to produce in abundance, and with a very small outlay of
human effort, all our food material and all the material needed for
our clothing and our dwellings, and for building cities and railroads
etc. The Great War has demonstrated our wonderful power and
resourcefulness in these respects. On the other hand, it has also
made clear our shortcomings. We need to know much more in order
to carry on the affairs of community life more effectively (the urgent
problems are problems of education, of crime and delinquency, and
of political adjustment of individuals and races), and, above all, in
order to distribute leisure so that each may live as human a life
as possible.

INDEX

Absorption, 40, 87, 1 14, 1 18, 477 ; in
nutrition, 260

Acclimating, 131, 257

Accretion, 18

Acetanelid, 257

Acids, 202

Activators, 50

Adaptability, 19, 39

Adaptation, 19, 55, 56; of flowers,
310; and instincts, 244; and pur-
pose, 369

Adenoids, 150 ff.

Adjustment, 131

Adrenin, 189

Adulteration of food, 123, 124

Adventitious roots, 47, 48, 49

Afferent nerves, 219, 221, 222, 498

After-effect, 136

Agglutinins, 196

Agramonte, Aristide, 407

Agriculture, and bacteria, 396 ; biol-
ogy and, 4, 67 ; and birds, 429 ; and
food supply, 75; and forests, 379;
and heredity, 450 ff. ; and insects,
417 ff . ; and science, 506

Air, circulation of, i 57 ; composition
of, 12; excess of, 339 ; and fire, 1 2 ;
and forests, 378 ; humidity of, 157 ;
and life, 172-173; pollution of, 158,
396; and protoplasm, 143; tem-
perature standards of, 156

Air cells of lungs, 148

Air requirements of man, 154

Albumen, 51

Alcohol, 133 ; and Committee of Five,
258; and digestion, 135; and fer-
mentation, 135; fighting the evil
of, 139; and infectious disease,
135; and longevity, 134; prohibi-
tion of use of, 142 ; reasons for be-
ginning to drink, 137 ; and recrea-
tion, 140; and the senses, 253; and
society, 137, 141 ; and vinegar, 396;
and work, 136

Algag, 295, 298, 480

Alimentary canal, 81 ff.

Alkaloid, 74, 202, 203, 257 ; in tea and

coffee, 254
All life from life, 19
Alternation of generations, 320 ff.
Ameba, 24, 80, 96, 229, 260, 294, 338,

363

American races, 489

Amino-acids, 109

Amoeba, see Ameba

Amphibians, 350, 485

Anaerobes, 143

Analysis, 9

Ancestors of man, 493 ff.

Ancon ram, 460

Anesthetics, 259
■ Angiosperms, 481

Animals, alternation of generations
in, 326; classification of, 482 ; cold-
blooded, 337; colonial, 431, 432;
compared with plants, 20 ; genea-
logical tree, 483 ; heredity in, 444 ;
infancy among, 333 ; reproduction
in, 327 ; regulations concerning
domestic, 395; useful, and insects,
420

Annelids, 484

Annual plants, 44

Anopheles, 404, 406

Ant lion, 372

Antheridium, 320

Antiseptic, 192

Antiseptic mouth wash, 121

Antiseptic solution, 192

Antitoxin, 193 ff. ; for diphtheria, 195

Ants, colony of, 432 ; destruction
wrought by, 413 ; destructive, 415 ;
extermination of, 416; honey-pot,

433

Aorta, 185

Appendix, vermiform, 82, 468

Appetite, 104, 1 1 1 ; loss of, 1 18 ; stimu-
lation of, 117, 138

Arachnids, 484

Arc, reflex, 220

Archegonium, 320, 478

Armors, protective, of organisms, 345

5^5

5i6

ELEMENTARY BIOLOGY

Arrhenius, Svante, and the nitrogen

problem, 63
Arsenic, becoming accustomed to,

132; insecticide and fungicide, 131
Artemia, 289

Artery, 185; pulmonary, 187
Arthropods, 280, 289, 432, 484
Arts, development of, 512
Ascent of sap, 176
Asexual reproduction, 299
Asphyxiation, 170
Assimilation, 18, 50, 260, 265, 285
Associative neurons, 221, 499
Astigmatism, 235
Astringent, 192
Atwater, W. O., food doctrines of, 90,

93' 99
Auricle, 185
Aves, 485
Axon, 220, 498

Bacteria, 61 ; in carbon cycle, 58 ;
control and use of, 394 ff. ; and
decay, 112, 118; destroyed by cook-
ing, 112; digestion in, 80 ; and
disease, 386; in food, 112, 120; in
industry 396 ; in life cycle, 63 ; and
nitrogen, 62, 67, 396 ; and soil, 396 ;
on teeth, 120; and wounds, 192

Bacteriology, 388

Balance of nature, 423

Balancing organs, 242

Bark, in roots, 43, 60 ; fibers and ves-
sels in, 176

Bast, 79, 176

Baths, after meals, 116; hot and cold,
206, 207 ; public, 396

Batrachians, 485 ; reproduction
among, 328

Becker and Hamalainen, nutritive
tables of, loi

Bee, 329 ; and orchard, 313 ; sting of,

373

Beetle, calosoma, 422 ; ladybird, 423 ;
potato, 418, 462

Behavior, as problem of biology, 5 ;
mechanical aspects of, 39, 217, 224

Bends, 340

Beriberi, 108

Biennial plants, 44

Bile, 86, 118, 184, 216

Biology, 3 ; and cost of living, 1 29 ;
and efficient living, 4 ; and enjoy-
ment of life, 512-513; and food
supply, 130; and health, 3, 507;

public protection, 126; applied to
saving of life, 393, 507 ; of the soil,
66 ; use of, 474 ; and wealth, 4, 506

Birds, 485 ; destruction of, 425 ; diges-
tive system of, 87 ; economic value
of, 425, 429; eggs of, 330; food of,
425; and insects, 426; migration
of, 366, 426; nests of, 371; protec-
tion of, 426; undesirable, 429;
young of, 334

Black Hole of Calcutta, 155

Black hornet, 369

Blackbird, red-winged, 429

Bladder, 206, 262

Bladder wrack, 298

Blanching of plants, 73

Blastophaga, 312

Bleeding, 192

Blood, 179; changes in, 188; circu-
lation of, 185 ; clotting of, 181 ; co-
ordination through, 434 ; ferments
in, 188; a living tissue, 193 ff.; and
respiration, 146; a transportation
system, 262

Blood pressure, 190

Blood system, 264

Blue jay, 427

Bluebird, nest of, 370

Blues, 118

Bobolink, 429

Bowels, see Intestines

Brain, structure of, 498

Brain food, 107

Brain functions, localization of, 498

Brains of vertebrates, 497

Breathing, 144, 148, 149, 172-173;
control of, 149; and digestion, 116,
118; habits of, 151 ff. ; nose and
mouth, 150; in plants, 74 {see also
Oxidation) ; summary of hygiene
of, 172-173

Breathlessness, 190

Breeding, for immunity to disease,
450; for special points, 452

Breeds, of plants and animals, 438 ;
variation in, 439

Bristles, 350

Bronchus, 148

Bronzed grackle, 427

Bryophytes, 481

Bubonic plague, 410

Buds, first, of seedHng, 33 ; resting, 270

Buffalo moth, 415, 417

Burbank, Luther, 452, 453

Burbank potato, 454

INDEX

517

Burrowing, 368, 370
Butter, flavor of, 397
Butterflies, development of, 281
By-products of organisms, 201

Cactus, desert vegetation, 359 ; spine-
less, 453

Caffein in coffee and tea, 254

Calcutta, Black Hole of, 155

Calorie, 91 ; measure of daily require-
ments, 93, 100

Calorimeter, respiration, 92

Calosoma beetle, 422

Calyx, 303

Cambium, 145, 271, 347; in roots,

43

Camouflage, 354

Capillaries, 181, 185, 187, 188

Carbohydrates, 51, 52, 54, 55, 90, 93,
97 {see a /so Food) ; digestion of, 81,
85, 87, 112

Carbon cycle, 57, 58

Carbon dioxid, 57, 71, 143 ff. ; in food-
making, 53, 54

Carbon monoxid, 158, 164

Carroll, Dr. James, 407, 408

Casein, 51

Castle, W. E. 449

Caucasian race, 488

Cedar waxwing, 428

Cells, 21 ; absorption by, 40; animal,.
22 ; budding, 292 ; colonies of, 420 ;
differentiated, 431 ; differentiation
of, in development, 275; division
of, 76, 265, 274, 275, 291, 457, 458 ;
egg, 299 ; exchange of material in
living, 1 74 ; fission (j-^^ Cells, division
of) ; germ, 447 ; independent, 76,
430 ; nerve, 219, 267 ; nettling, 375 ;
oosphere, 458; origin of, 274, 457,
459; plant, 23 ; respiration in, 144 ;
sperm, 299, 459; structure of, 21 ;
in tissues, 477 ; walls of, 57, 345

Cellulose, 40 ; digestion of, 112

Central cylinder, 43

Cerebellum, 497

Cerebrum, 497, 498 ; localization of
functions in, 499

Ceremony, 505

Chameleon, 362

Chances of death, 134, 507

Change, chemical, 7; cyclic, 463;
physical, 7 ; universality of, 7, 463

Chapin, Dr. Henry Dwight, 109

Cheese, curd of, 51 ; curing of, 397

Chemical changes, 7 ; in pigments of

animals, 353 ; in soil, 66
Chemical composition, of air, 23 ; of
carbohydrates, 54 ; of fats, 55 ; of
food, 51; of human body, 16;
of plants, 21; of proteins, 55; of
soil, 30 _

Chemical cycle of life, 57
Chemical engine (chlorophyl), 54
Chemical fixation of nitrogen, 63
Chemical influence upon develop-
ment, 289
Chemical injury to nervous system,

253

Chemical sense in lowest organisms,
24, 224

Chewing of food, 81, 115, 117, 1 19

Chitin, 346

Chloral hydrate, 257

Chlorophyl, 54, 73, 75, 184

Chloroplast, 54

Chromatin, 457, 458

Chromosomes, 457, 458

Cilia, 295

Circulation, of air, 157; of blood,
185 ff. ; closed and open, 185; de-
pressed, 118; double, 187; and
exercise, 116; in plants, 174 ff.

Circulatory system, 262 ; hygiene of,
190

Civilization, 435, 51 2 ; and infancy, 335

Clam, breathing of, 145

Classification, basis of, 475 ff. ; of
animals, 482; of organisms, 475;
of plants, 478 ; uses of, 475

Cleanliness and health, 128

Climbing plants, 48, 49

Clothing and health, 152

Clotting of blood, 181

Coagulation of blood, 181

Coal and forests, 380

Coal seams and fossils, 464

Cocain, 256

Cochineal, 413

Cockroaches, 414; extermination of,
416

Codein, 257

Codling moth, 419, 421

Coelenterata, 432

Coelenterates, 373, 482

Coffee, 254

Cold-blooded animals, 337

Collaterals, 219

Colloids, 78

Colonial animals, 431, 432

518

ELEMENTARY BIOLOGY

Colors, changes in, 362 ; warning,

355 (see also Pigments)
Committee of Five on alcohol, 258
Communicable diseases, transmission

of, 387
Community, 435; life of, 514
Competition, 343, 344, 474
Competitive relation, 342
Compound, chemical, 9
Concealment, 363
Conducting system of plant, 174
Conjugation, in Paramecium, 296,

297 ; in Spirogyra, 296
Connective tissue, 267
Consciousness, 498
Conservation, of energy, 10; of food

supplies, 112, 129-130; of forest,

382 ; of manure, 60 ; of matter, 8 ;

of resources, 4 ; of sewage, 60 ; of

soil, 68, 380, 381
Constipation, 88, 118
Contraction, 24, 218, 360
Control, by means of knowledge, 505 ;

of breathing, 149; of movements,

217 ; measure of, 506
Cooking, 112, 431 ; waste involved,

112
Cooperation, 434, 510
Cooper's hawk, 427
Coordination, 434
Cordata, 484
Corpuscles, 179; red, 183, 184, 262,

294; white, 181, 182, 193 ff., 273
Correlation of functions, 262
Cortex, of brain, 220, 498 ; of root, 43
Cotyledon, 33
Crab, hermit, 363, 364 ; horseshoe,

345
Crop of bird, 87
Crops, rotation of, 62, 423
Crow, 428
Crustacea, 346, 484
Crustacean, 289
Crystalloid, 78
Cuckoo, 342
Culex, 406

Cup, public drinking, 394
Cutin, 345

Cuts, treatment of, 191
Cuttings for propagation, 48, 269
Cuttlefish, 363
Cyclic changes, 463
Cyst, 295
Cytolysins, 196
Cytolysis test, 197

Dairy and bacteria, 397

Darwin, Charles, 273, 469, 472

Death rates, in various countries,
507 ; from various diseases, 389 ;
of infants, reduction of, 393 ;
diphtheria, 194, 195; malaria, 409 ;
typhoid fever, 299, 392 ; yellow
fever, 409

Decay of food, 80, 124

Dehiscent fruit, 316, 317

Dendrites, 220

Descent of sap, 176

Desert land, reclamation of, 68

Desert plants, 359

Development, 274, 476; and classi-
fication, 476; and metamorphosis,
283; conditions for, 285-289; of
plants, 284 ; stages in, 276

De Vries, see Vries, Hugo de

Diaphragm, 82, 149, 150, 153

Diastase, 78

Dicotyledons, 34, 481

Diet, and age, 102 ; and appetite,
III; balanced, 102; and climate,
102; standard, 99; studies of, 89,
90, 510; and work, 100-102

Dietaries, 90

Differentiation, 182, 477 ; of cells,

275' 431

Diffusion, 40, 76, 78, 83, 85, 144, 147,
174, 179. See also Absorption

Digestion, 78, 80, no, 111-112; and
alcohol, 135; in bacteria, 80; con-
trol of, 89, 116; exercise and, 116;
in gut, 84-86 ; hygiene of, 88 ; in
human body, 81 ; in mouth, 81 ;
organs of, 82, 83, 87 ; in stomach, 83

Dimorphic flowers, 304

Dioecious plants, 306

Diphtheria, 386 ; antitoxin of, 195

Disease, control of, 395, 398 ; and
heredity, 200 ; microbes as cause
of, 200; and parasites, 341

Diseases, alcohol and infectious, 135 ;
of animals, 420; and insects, 410;
mortality rates {see Death rates) ;
specific, and bacteria, 386; trans-
mission of communicable, 387

Division of labor, 262, 434, 477

Dogs, licensing of, 395

Dominance, law of, 444, 445, 450, 455

Dominant characters, 445 ; in man,

455 .
Drowning, 169
Drowsiness, 118, 155

INDEX

519

Drugs, action on protoplasm, 132;
habit-forming, 132, 137, 139, 255;
regulations concerning, 257

Dubois, Professor Eugene, 494

Dust, and breathing, 155; in indus-
try, 159-161 ; and occupations, 158;
as source of infection, 126, 158,
173, 192

Dusting, 162

Ear, 240 ; in man, 502

Earthworm, regeneration in, 268 ;
respiration in, 146

Eating, habits of, 89, 114 ff. ; and
mental states, 114; and muscular
work, 116; pleasures of, 113

Echinodermata, 347, 484

Economics, and alcohol, 133, 139,
253 ff. ; of bacteria, 388, 394 ff. ;
and biology, 4, 439 ff., 449, 450 ff. ;
of birds, 425 ff. ; of fatigue, 211,
213 ff.; of food, 122 ff., 128, 388;
of forests, 377 ff. ; of heredity, 449,
450 ff. ; of insects, 31 1-313, 398 ff.,
404 ff., 413 ff., 417 ff.; of photo-
synthesis, 74, 75; of roots, 46 ff. ;
of science, 124, 129, 474, 505-506,
512 ff.; of soil, 65 ff., 380, 381;
of stems, 176, 202, 377, 453; of
tobacco, 167 ff.

Efferent nerves, 219, 221, 222, 498

Efficiency, biology and, 4 ; fatigue
and, 211, 216; habits and, 251;
health and, 124, 128, 172 ; smoking
and, 166; temperature and, 156;
ventilation and, 156

Egg, of birds, 330 ; of fishes, 327 ; of
frog, 275; of insects, 279, 281 ; of
mammals, 330 ; origin of, 457 ff. ;
of plants, 299, 304, 320 ff.

Egg cell, 299

Electric shock, 170, 373

Elements, chemical, 9

Elimination of refuse, 88, 1 18-1 19, 261

Embryo, development of, 35, 274 ff. ;
in seed, 32, 276

Embryo sac, 302, 324, 478

Endosperm, 39

Energesis, 143, 149, 285; and excre-
tion, 262 ; oxygen in, 143 ; and res-
piration, 261

Energy, 7; chemical, 7, n; conser-
vation of, 10 ; daily consumption
by body, 93, 100 ; sources of, 11;
transformation of, 13,70; units of, 91

Environment, 26 ; and development,
285 ff. ; and health, 214; life and,
337 ; man's mastery of, 502 ff.

Enzyme, 78, 79, 396, 397. See also
Ferments

Epicotyl, 33, 358 -^ _

Epidemics, prevention of, 122, 125 ff,,
163 ff., 387 ff., 394 ff., 399 ff., 404 ff.

Epidermis, 23, 43, 70, 345, 348

Erosion, 380

Esophagus, 82

Etiolation (blanching), 73

Euglena, 229

Eustachian tubes, 82, 240

Evolution, 463, 471 ; appHcations of,
473 ff. ; evidence of, 464 ff.; of horse,
466; theories of, 471 ff. ; and man,

494
Exchange, in cells, 144, 174; of gas,

73-74
Excretion, 76, 201, 262; in animals,

203 ; and fatigue, 208 ; hygiene of,
•205
Exercise, 116, 118; and breathing,

152; and digestion, 141 ; and the

skin, 207
Exo-skeleton, 346
Experience, learning from, 504
Experiment, problems solved by, 28,

37' 73' 93' "O' iM, "S' "7' 121,
125, 129, 130, 132, 133, 134, 135,
143' 154' 155' 156' 162, 166, 171,
175, 176, 182, 183, 189, 193, 208,
209 ff., 222, 239, 245, 268, 270, 272,
285, 290, 352, 362, 378, 379, 386,
398, 404, 407, 410, 442, 446, 448,

452' 455. 462, 473' 498' 499' 504' 510
Experiment stations, agricultural, 417
Expiration, 149
Extracted recessive, 449
Eyelids, 232
Eyes, and light, 229 ; compound, 230;

human, 232, 502 ; hygiene of, 235 ;

infection of, 237

Factory regulations for health, 128,
156, 158, 162

Fall of leaf, 374

Fat, 51, 52; digestion of, 85-86;
origin of, 55

Fatigue, 208 ; and efficiency, 210 ; ex-
cretion and, 208 ; and eyestrain,
236; and health, 215; and rest,
215; and work, 210, 213, 215-216

Fatigue poisons, 208

520

ELEMENTARY BIOLOGY

Feather, growth of, 349, 350

Female, see Sex

Fermentation, 133

Ferments, 52, 78-79, 80, 85 ; in blood,
188

Fern, 322-323; infancy in, 331;
spores of, 294

Fertilization, 299, 302, 303, 323, 327,
328, 459

Fertilizers for soil, 66, 429

Festering of wound, 192

Fever, see Diseases, Typhoid fever.
Yellow fever

Fibers, plant, 44, 79, 176; nerve, 219,
498

Fibrinogen, 181

Fibro vascular bundles, 44, 70, 175

Fighting, among ants, 373 ; against
flies, 402; against insects, 422;
against mosquitoes, 408 ; among
organisms, 372, 374

Fire, and air, 12; forest, 385; as
source of energy, 11 ; use of, 501

First aid, in asphyxiation or drown-
ing, 169; in bleeding, 191-192 ; for
eye, 236

Fish, 485; breathing in, 147; devel-
opment of, 252 ; digestive system
of, 87 ; hatching of, 333 ; infancy
and care of young, 334 ; migration
of, 367 ; reproduction in, 327

Fisher, Professor Irving, food tables,
94, 96, 103

Fission, see Cell, division of

Fitness of organisms, 19, 39, 310 ff.
See also Adaptation

Flatworms, 482

Fleas and plague, 510

Fleshy fruits, 317

Flicker of light and eyestrain, 236

Flies, breeding places, 400 ; elimina-
tion of, 402 ; house, and food, 399,
400 ; relation to intestinal disease,

399

Floods and forests, 379

Floral envelope, 300

Flour moth, 415, 416

Flowering plants, 294, 481
\ Flowers, 300, 478; adaptations of,
310 ff . ; dimorphic, 304; fertiliza-
tion in, 303; and insects, 310 ff. ;
polymorphic, 305

Fly, Hessian, 419

Food, 31, 50, 51 ; adulteration of, 123 ;
of birds, 425 ; care of, 388 ; choice

of, 89, 98 ; composition of, 94, 95,
96,98; conservation of, 129; con-
tamination of, 124, 125; daily needs,
93, 100; decomposition of, 125;
and development, 288 ; digestibil-
ity of, III; distribution of, 130;
economics of, 112, 122-123, ^29,
130 ; and flies, 401 ; fuel, 52 ; func-
tions of, 51 ; ideal, 102-103 > insects
as, 412; kinds of, 51 ; minerals in,
108, 112; need for bulk in, 118;
plant, 3 1 , 50 ; for plant embryos, 33 1 ;
preservation of, 124, 125; propor-
tions of, needed, 70, 102-104 \ Pro-
tection of, 124, 125-126; public
regulation of, 122, 125; relation of
light to making of, 39, 53 ff. ; in
seeds, 35, 46; summary of, 102, 1 16;
taste of, no; translocation of, 79
Food habits, 89, 114 ff.
Food-getting organs, 364, 375
Fruit, 303; dehiscent, 316; fleshy,
317; and seed, 302; seedless, 303
Fuel values, 91
Plumes and the lungs, 158
Function, biological idea of, 15-16
Fungi, 294, 341, 480; dangerous to
forest, 385 ; used in fighting insects,
423

Gall, 86. See also Bile

Galls, insect, 374-375

Gametes, 297, 324, 332, 478 ; water
essential to, 328

Gametophyte, 322, 323, 324

Garbage, 3, 396, 399, 402

Gas exchange, 73-74, 144, 145; in
blood, 188 ; in leaves, 74

Gases, injurious, 158

Gastric juice, 83-84, no

Genealogical tree, of animal life, 483 ;
of plant life, 479

Generations, alternation of, 320 ff.

Geology and evolution, 464-466

Geotropism, 37, 38, 241

Germ carriers, 152

Germ cells, 447 ; origin of, 456, 463

Germ plasm, 459

Germination, 36

Gills in respiration, 146, 147, 183

Gizzard of fjird, 87

Glands, 263; ductless, 188; of intes-
tines, 84, 86, 102 ; milk, 335; saliva,
81, 83; stimulation of, no; of
stomach, 83, 84

INDEX

521

Glare, 236

Glucose as adulterant, 123

Gluten, 51

Glycogen, 189

Gonococcus bacteria, 237

Grackle, bronzed, 427

Grafting, 270, 271, 272

Grains, 34, 78, 217

Gravity, responses to, 38, 241

Great blue heron, 428

Green slime, 92

Growing period of various animals,

335

Growth, 17; as cause of movement,
38 ; discontinuous, 269, 292 ; limits
of, 265 ; and regeneration, 265 ; in
roots, 43; and smoking, 165; in
stems, 347

Guano, 60, 66, 429

Guard cells, 71, 72

Gudernatsch, Dr. J. F., 285

Gullet, 82, 87

Gut, 84, 101-104. ^^^ ^^^^ Intestine

Gymnosperms, 481

Gypsy moth, 419, 422

Habit, 248 ff. ; formation of, 150 ; for-
mation of, by protoplasm, 131

Habit-forming drugs, 255-257

Habits, eating, 89, 114; feeling, 250;
health, 114- 119; kinds of, 249;
selection of, 250; thinking, 249;
tobacco, 163 fT.; value of, 251

Habituation, 131, 163

Haddock, breathing of, 147

Haemocyanin, see Hemocyanin

Haemoglobin, see Hemoglobin

Hairs, of mammals, 349, 350 ; of
plants, 347, 348 ; root, 42

Happiness, biology and, 4

Headache, 1 18

Headache powders, 118

Health, alcohol and, 133 ; and bacte-
ria, 386; and biology, i ; fatigue and,
215; food and, 89 ; habits for con-
trol of, 1 14-1 19; public, ID, 394, 510

Healing, 266

Hearing, 238 ; in fishes, 239

Heart, 185, 186; beat of, 190; care
of, 190 ; effect of smoking upon,
164; leaky, 190; training of, 191

Heat, 9, II, 27, 54, 72, 143, 155, 156,
1 57, 206, 348, 359, 363 {see also Tem-
perature) ; and living matter, 337-
338, 391 {see also Frontispiece) ;

measurement of, 9 1 (.tv^^/jt? Calorie);
from organism, 92

Hemocyanin, 179

Hemoglobin, 179, 183, 184

Heredity, 443 ; in animals, 444 ; appli-
cations of, 450 ; and disease, 200 ;
in man, 454, 455 ; of modificationsr
461, 492, 504 {see also Frontispiece) ;
in plants, 444 ; and protoplasm,
457 ; and theory of evolution, 473,
492 {see also Frontispiece)

Hermit crab, 363, 364

Heroin, 257

Heron, great blue, 428

Hessian fly, 419

Ileterospory, 324

Home-finding instinct, 363

Home-making, 368, 371

Homo, 488, 495, 496

Homology, 365

Honey, 313, 413, 433

Honey-pot ant, 433

Hookworm, 341, 510

Horns, 315

Horse, evolution of, 466

Horse botfly, 421

Horse power, 91

Horsefly, 398 ff.

Human race, 455, 488, 501

Humanization, 513

Humus, 75

Huxley, Thomas H., 489

Hybrid, 445

Hybridizing, 450

Hydrotropism in plants, 38-39

Hypocotyl, 33

Illumination, 362. See also Light
Imitation, 494, 499 ; learning by, 504
Immunity to disease, 198, 452; ac-
quired and natural, 199; active and
passive, 200; breeding for, 451
Indigestion, 115, 118, 135, 138
Individual differences, iio-iii, 198,
234, 258 {see also Variation) ; in
digestion of food, 106; in size of
stomachy 115; in susceptibility to
alcohol, 134 ; in susceptibility to
tobacco, 163
Individuality, 437

Tndustrial dangers, 169, 171, 214, 236
Industrial hygiene, 128
Industrial poisons, 158 ff.
Industry, biology and, 4
Infancy and parental care, 331 ff.

522

ELEMENTARY BIOLOGY

Infant mortality, reduction of, 393

Infection, 386, 387 ; eye, 237 ; of food,
152; protection against, 388

Inhibition, 248

Ink bag in cuttlefish, 363

Inorganic, 16-17, 178

Insecta, 283, 484

Insects, and birds, 426 ; damage done
by, 418 ; fighting against, 422 ff. ; as
food, 412 ; galls produced by, 374-
375 ; as germ carriers, 126, 398, 410,
420; injurious, 414 ff. ; intelligence
in, 434 ; as intermediate hosts, 404 ;
life stages of, 279, 281, 282-283 ;
orders of, 486 ; predatory, 374 ;
relation to flowers, 309 ff ., 312;
reproduction in, 329 ; respiration
in, 145; sense organs of, 239, 240,
241; social, 433-435; and useful
animals, 420 ; and useful plants,
417; and wealth, 412; and young,

332
Inspiration (breathing), 149
Instincts, 244, 500 ; home-finding,

363 ; modification of, 245 ; relating

to young, 334 ; for selection of food,

90, no
Intelligence, 434, 502, 504 ff.
Interdependence, between organisms,

5, 63, 64, 424, 434, 508 ; of flowers

and insects, 310 ff. ; of people, 393,

435' 504, 507. 508, 509 ff.
Intermediate hosts, 404, 411
Internal factors in development, 290
Internal secretions, 188-189
Intestines, 82, 83, 84, 86-88, 188;

evacuation of, 88, 117, 118-119;

length of, 106; of various animals

compared, 105-106
Invertebrates, 327, 482
Invisibility, protection by, 352
Involuntary muscles, 219
Irritability, 18, 24, 158, 182, 220, 226,

287

Jellyfish, 372, 373
Johannsen, Dr. Wilhelm, 442

Kallima butterfly, 355

Kangaroo, 335

Katydid, 351, 354

Kidneys, 203, 262 ; effect of alcohol

on, 203 ; hygiene of, 205
Knowledge and control, 505
Kropotkin, Peter, 435

Lac, insect, 413

Ladybug (ladybird) beetle, 414, 422

Lamarckian theory, 471-472

Lancelet, development of, 274, 276

Language, human, 501

Langworthy on daily food consump-
tion, lOI

Lateral line, 238, 239

Laveran, Alphonse, 404

Layering, 48

Lazear, Dr. Jesse W., 407, 408

Leaf, 70-72, 300 ; and elimination of
refuse, 261 ; fall of a, 374, 375; gas
exchange in, 144; and light, 73;
uses of, 74

Legume family, 62

Legumin, 51

Leisure, 513, 514

Lenticels, 71, 145

Lice, 410

Lichens, 480

Life, without air, 1 43 ; and the
environment, 336 ; length of, 507 ;
origin of, 19; salts and, 338; and
temperature, 337 ; unity of, 260

Light, eyes and, 229 ; in food-making,
39' 54' 73 ^- 5 influence on growth
of plant, 38, 39 ; and life, t,^S ; and
pigmentation, 352, 362 ; and tan,

352

Light tropisms, 230

Linnaeus, 488

Liver, 85, 86

Liverworts, 481

Living bodies, characteristics of, 15

Living forms, multiplicity of, 260

Lizard, green, 363 ; regeneration in,
270

Lobster, appendages of, 365 ; breath-
ing in, 146 ; feeding of young, 332

Localizations, of brain functions, 498 ;
of functions in cerebrum, 499

Locomotion, 364

Locusts, 417

Lungs, 147, 148 ff., 183; capacity of,
1 51-152; hygiene of, 151 ff.

Lymph, 180, 262 ; coordination
through, 434

Machine, 14, 17 ; and organisms, 17, 20
Malaria, 294, 404, 506
Malaria parasite, 326, 341, 405
Male and female, 299
Malt, 78, 133
Mammalia, 486

INDEX

523

Mammals, 492 ; egg of, 330 ; grow-
ing period of, 335 ; hairs of, 349 ;
infancy among, 334

Man, ancestors of, 493 ; evolution
and, 494 ff. ; handicaps of, 502 ;
mastery of environment by, 502-
504 ; as organism, 490, 502 ; and
other primates, 491, 492; place in
the world, 490 ff., 512; primitive,
500 ; relation to other organisms, 6 ;
relics of, in Stone Age, 500 ; senses
of, 502

Manson, Sir Patrick, 404, 406

Mantle of mollusks, 346

Manure, 60, 66 ; and flies, 399, 402

Marriages, productive of undesirable
offspring, 456 ; regulation of, 394

Marsupials, 335, 486

Matter, composition of, 9 ; conserva-
tion of, 8 ; kinds of, 9 ; states of, 7

Meals, number and frequency, 1 1 5-1 1 6

Meal-worm, 414, 416

Meat in diet, 105-107

Medicine (see Drugs) ; as source of
alcohol habit, 137, 139

Mendel, Gregor, 443, 446, 448, 449,
461 ; law of segregation, 446. See
also PVontispiece

Mental state and digestion, 114

Metamorphosis, 283

Metchnikoff, filie, 182

Microbes, 67 {see also Bacteria) ; de-
stroyed by cooking, 112

Micropyle, 32, 303

Migration, 365; of birds, 366, 425,
426 ; of fish, 367

Milk, care of, 391 ; food value of, 97,
104; preservatives in, 125; regu-
lations in regard to, 126, 390

Milk standards, 127

Milt, 327

Mimicry, 356, 357, 358

Minerals, in food, 52, 108, 112, 202;
in manufacture of proteins, 56; in
plants, 30 ; in soil, needed by organ-
isms, 66

Missing link, 494, 496

Mixed types, 440

Modifications, by surroundings, 439 ;
transmission of, 461, 492, 504
{see also Frontispiece)

Moisture, and hair formation, 349 ;
and ventilation, 155, 173

Mold, reproduction in green, 292

Mollusca, 346, 374, 484

Mollusks, 289
Molting in cicada, 280
Mongolian races, 489
Monocotyledons (monocotyls), 34, 481
Monoecious, plants, 306

Morphin, 199, 256 _

Mortality, reduction of infant, in New

York City, 393
Mortality rates, in various countries,

507 ; for various diseases, 389
Morula, 276
Mosquito, extermination of, 409 ;

fighting against, 408, 409 ; life his-
ories of, 406
Moss, alternation of generations, 321 ;-

antheridium of, 320; archegonia of,

320; infancy in, 331; life history

of a, 320 ; spore formation, 293
Moth, brown-tail, 420; buffalo, 415,

416; clothes, 412, 414; codling,

419, 421; flour, 415, 416; gypsy,

419, 420, 422 ; silk, 413
Mouth, digestion in, 81-82; watering

of, no, 217, 227
Mouth-breathing, 150, 151, 173
Movements, in organisms, 18, 24, 217,

223 {see also Muscles) ; in plants,

361 ; voluntary, 498
Mucin, 82, 121
Mulch, 379
Muscles, 218, 228; kinds (voluntary

and involuntary), 218, 219; reflexes

dependent upon, 218
Mutants, 462
Mutation, 461, 462, 473
Mutilation, 269
Myosin, 51

Narcotic, 131, 132

National forests, 385

Natural selection, 472, 473-474

Nature, man's conquest of, 504

Navigation and forests, 379, 381

Neanderthal man, 493, 495, 496

Nectar, 309, 310

Negroid races, 489

Nerves, 218 ff., 267,497 ; development
of, 246 ; effects of smoking on, 1 64 ;
kinds of, 221, 222; and the reac-
tions of organisms, 217 ff. ; and re-
flexes, 218

Nervous system, 487 ; chemical influ-
ences, 289 ; chemical injury to, 253 ;
coordination through, 434 ; correla-
tion with other systems, 263

524

ELEMENTARY BIOLOGY

Nest of bluebird, 370

Nests, 334, 371

Nettle, 347

Nettling cells, 373

Neurons, see Nerves

Newt, development of, 282

Nicotine, 163

Nictitating membrane, 234

Nitrates, 60

Nitrogen, and bacteria, 62 ; utilization

of atmosphere, 63 ; and war, 64
Nitrogen cycle, 59, 60, 61
Nitrogen problem, 61
Nitrogenous wastes, 90
Nose as sense organ, 227
Nosebleed, 192
Nose-breathing, 150
Nucleus, cell, 23, 296 ff ., 303 ; division

of, 457. 458, 459
Nutrition, 260
Nutritive ratio, 97, 100, 103
Nuts, 317

Occupational dangers, 158, 235-236
Occupations, and air, 156; and diet,

10 1 ; and dust, 158-162 ; regulation

of, 122-124, 213 ff., 216, 395
Odors, 202

Qisophagus, see Esophagus
Oleomargarine as butter substitute,

123
Ommatidium, 232
One-celled animals, 24
One-celled plants, 75-77
Oosphere, 299, 458
Ophthalmia neonatorum, 237
Opossum, 335
Opsonins, 198
Orchids, 308, 312-313
Organic, 16, 51, 53, 176
Organism, 15, 16, 24; how it learns,

245; origin, 19, 291 ff.
Organs, 15; origin of, 276
Osmosis, 40-41, 76, 78, 79, 80, 144 ff.,

149, 174 ff., 180-18 1, 188, 201 ff.,

260
Ovary, 301, 302, 303
Overpopulation, 472
Ovules, 301, 324
Oxid, 13
Oxidation, 13, 59; in organisms, 13, 29,

• 5I' 52, 55, 57, 58, 59' 132, 143 ff-' 261
Oxygen, 12, 52; in energesis, 143,

144; in photosynthesis, 54
Oxygen cycle, 59

Palate, no

Palisade cells, 23, 70

Pancreas, 82, 85, 86, 188

Paper wasp, 369

Parallelism in development, 277, 278,
467

Paramecium, 224 ff. ; conjugation in,
296

Parasites, 410; alternation of genera-
tions in, 326; in food, 112

Parasitic diseases of animals, 420

Parasitic relations, 341 ff.

Parasitism, 342

Parent, dependence of offspring on,
332

Pasteur, Louis, 133, 386

Pasteurization, 391

Patent medicines, 256, 257

Pawlow, Professor I. P., experiments
on digestion, no

Pedicel, 70

Pellagra, 109; relation to diet, 510

Pepsin, 83

Peptones, 83

Peristalsis, 85

Perspiration, 204

Petals, 303

Pfliiger, Eduard F, W., experiments
on breathing, 143

Phagocytes, 182

Pharynx, 82

Phloem, 79, 174, 176

Photosynthesis, 53-56, 59, 73, 378, 477

Phototropism, 38, 230

Physic, 119

Physical changes, 7

Physiological variation, 438, 439

Physiology, 15

Pickling and bacteria, 397

Piddock, 368, 370

Pigments, 202, 203, 287 ; and food,
354; and light, 288, 351, 352; and
temperature, 353; protective, 351

Piltdown skull, 494

Pisces, 485

Pistil, 300, 478

Pith, in root, 43 ; in stem, 175

Pithecanthropus erectus, 493, 495, 496

Plague, 506, 510

Plants, chemical composition of, 31 ;
classification of, 478; compared
with animals, 19; conducting sys-
tem of, 174 ff. ; desert, 359 ; genea-
logical tree of plant life, 479 ; hairs
of, 347 ; heredity in, 444 ; infancy

INDEX

525

in lower, 330; kinds of, 477, 480;
movements in, 37-38; seed-bearing,
478 ; sensitive, 361 ; useful, and in-
sects, 417

Plasma, 182

Plasmodium of malaria, 404

Play, 513

Plumage, color changes in, 286

Plumbing, regulation of, 395

Poisons, 118, 131 ff., 194-195, 253 ff.,
355; fatigue, 208; in soil, 67

Polar bodies, 459

Pollarded trees, 271

Pollen grain, 324, 478

Pollen tube, 303, 324

Pollenation, by birds, 306, 307 ; close
and cross, 305 ; cross, 442 ; of fig,
311; function of, 304; by hand,
313; by insects, 309, 311 ; obstacles
to close, 305 ; self, 304 ; by water,
308 ; by wind, 308

Pollution, of air, 396; of water, 122,
392

Polycotyls, 34

Polymorphic flowers, 305-307

Population, and climate, 339; pres-
sure of, 342, 472

Porifera, 482

Posture and breathing, 152

Potato, Burbank, 454

Practice and learning, 249

Prairie dogs, 370

Praying mantis, 372

Precipitin, 193

Precipitin test, 197

Predatory insects, 374

Predatory relations, 341

Prepotency, 307

Preservatives in food, 125, 126

Pressure, atmospheric, 340

Primates, 486 ; families of, 487 ; limbs
of, 490 ; and man, 491-492; skele-
tons of, 491 ; skulls of, 492

Primitive man, see Man

Production, cost of, 506; of necessi-
ties, 514

Prohibition of alcohol, 142

Propagation, by roots, 48 ; vegetative,
269 {see also Regeneration)

Protection, of birds, 426; against in-
fection, 388; of young, 371

Protective activities, 368

Protective appearances, 351

Protective armors, 345

Protective coloration, 352

Protective invisibility, 352

Protective mimicry, 357

Protective movements, 360

Protective resemblance, 354

Protein, 51, 52; daily need, 90, 93;
danger of excess of, 90, 104, 107 ;
digestibility of various kinds, iii7
digestion of, 35, 83 ; nutritive ratio,
97 ; origin of, 55, 60 ; specific
effects of, 107, 108, 109

Prothallus, 322, 323

Protoplasm, 21, 24, 80, 131, 132, 181,
224, 228, 229, 265, 275, 287, 291,
295, 298, 302, 303, 337, 490 ; hered-
ity and, 457 ; light destructive to,
38,339; movements of, 21 ; needs
of, 50

Protozoa, 295, 341, 404, 482

Protozoon, 294

Proventriculus of bird, 87

Psychology, 498

Ptarmigan, 286

Pteridophytes, 481

Pulmonary artery, 187

Pulse, 190

Punnett, Professor R. C, 358

Pure lines, 442

Pure races, 447, 455

Purpose, 222-223, 225, 310, 332, 358,

369^ 433-434, 498, 509
Pylorus, 82

Quarantine, 395
Quills, 350

Rabbits accustomed to poison, 132

Rabies, 395

Rats and bubonic plague, 410, 510

Ray (fish), 373

Reaction of organism, general, 224 ;
and nerves, 217

Recapitulation in development, 278

Recessive character, 444 ff., 450 ff. ;
in man, 455

Reclamation, 68

Recombination of characters, 455

Rectum, 82

Red-headed woodpecker, 428

Reduction division, 459

Reed, Dr. Walter, 407

Reflex, 217 ff., 498; as adaptation,
244; chains, 244; without conscious-
ness, 222 ; nerve connections in,
221 ; using an animal's, 217

Refrigeration, 390

526

ELEMENTARY BIOLOGY

Regeneration, 268 ; in earthworm,
268 ; of the eye, 268 ; and growth,
265 ; in Hzard, 270 ; in plants, 47,
269-270 ; in starfish, 269

Registration of vital statistics, 395

Regulators, 50

Reproduction, 291 ; in animals, 327 ;
asexual and sexual, 299, 328; among
batrachians, 328; in fern, 322; in
fishes, 327 ; in insects, 329 ; in ver-
tebrates, 330

Reptiles, egg of, 330

Reptilia, 485

Research, organization of, 509; scien-
tific, 511

Resemblances, protective, 354

Respiration, 144; artificial, 170-171 ;
blood and, 146; calorimeter, 92-
and energesis, 261

Respirator, 161

Rest and work, 214

Resuscitation, 170 ff.

Reversal of physiological effects, 136

Rexford food tables, 97, 98

Rickets (rachitis), 108

Rockweed, 298

Roots, 32, 42, 300, 477 ; adventitious,
47, 49; as binding agents, 46, 47;
climbing, 48, 49 ; and elimination
of refuse, 261 ; forms of, 44, 45 ;
prop, 47, 49 ; structure of, 42, 43 ;
tap-, 4 5 ; tubercles, 62 ; uses of, 46-49

Root hairs, 42, 44

Root pressure, 45

Ross, Sir Ronald, 404

Rotation of crops, 62-63, 423

Rotting of flax, 396

Roundworm, 482

Salamander, regeneration in, 268

Saliva, 78, 81, 82

Salivary glands, 83

Salts, and life, 339 ; relation to pro-
teins, 556; relation to protoplasm,
52, 339 ; in soil, 30, 66

Sand dunes, 46

San Jose scale, 419

Sap in plants, 46, 176 ff.

Sapsucker, yellow-bellied, 427

Scale, San Jose, 419

Scales of fishes and reptiles, 350

Scholarship and smoking, 165

School lunches, 128

Science, and agriculture, 67 ; and cost
of living, 124, 129, 506 ; and natural

resources, 69 ; origin of, 509 ; and
research, 511 ; social nature of, 507

Scion, 271

Screening against flies, 403

Seedless fruit, 303, 454

Seedling, 35, 36

Seeds, 32, 315; and alternation of
generations, 324, 325 ; distribution
of, 317 ff. ; embryo in, 33; escape
of, 3x6; food reserve of, 34, 35,
301-302; and fruit, 301, 302, 315;
origin of, 301, 303; protection of,
315, 316; size of, 36, 319

Segregation, law of, 445, 446, 447, 449,

45O' 455

Selection, improvement through, 439,
440, 441 ff. ; natural, 472

Self-pollenation, 304

Semen, 327, 329

Sensation, sound, 238 ; and stimula-
tion, 228

Sensitive plant, 361

Serum, 181

Sewage, 60 ; and bacteria, 397

Sex, 296 ff., 320 ff., 331 ff. See also
Reproduction

Shedding of leaves, 375

Shellac, 413

Shelter, making of, 371

Shelter, primitive, of man, 500

Shoot (plant axis), 32

Sickness, control of, 194 ff., 395,

507
Sieve plates, 176
Skeletons of primates, 491
Skin, 345, 347, 351 ; hygiene of, 206;

temperature regulation by, 155
Skulls of primates, 292
Skunk, 374
Sleep, 118, 215
Sleeping sickness, 341
Smell, organs of, 227 ; sense of, in

man, 502
Smoke, and health, 162; and plants,

162 ; tobacco, 162
Smoking, and school standing, 165;

effects of, 163, 164 ff.
Snoring, 151
Sociability, in animals, 432 ff. ; in man,

138, 435' 504-505
Society, and air, I58ff. ; alcohol and,
137; and birds, 425 ff.; and evolu-
tion, 473-474; and food, 122 ff. ; and
the forest, 378 ff. ; and health,
388 ff., 394 ff., 399 ff. ; and insects,

INDEX

527

399 ff., 408 ff., 417 ff. ; and mosqui-
toes, 408 ff. ; and science, 507 ff. ;
and the soil, 65 ff.

Soil, 30; and bacteria, 396; biology
of, 66 ; chemical changes in, 66
conservation of, 68, 380 ; erosion
47, 380 ; exhaustion of, 66 ; and for
ests, 380-381 ; increase of, 67-68
intensive cultivation of, 67 ; relation
to sprouting, 29 ; as source of organic
bodies, 65

Sound, sensation of, 238

Spencer, Herbert, 472

Sperm cell, 299, 327, 459

Spermatophytes, 481

Spermatozoa, 299, 329

Spillman, Dr. W. J., 450

Spineless cactus, 453

Spiracles, 145

Spirogyra, 76, 266; conjugation in, 296

Sponges, 430, 431 ; and bacteria, 396

Spores, 291, 293, 296, 321, 324, 331,
332 ; in animals, 294 ; of fern, 294 ;
of moss, 293 ; swimming, 295

Sporophyte, 322, 323, 325

Sport (mutation), 460, 462, 473

Sporulation, 326, 404

Spraying, 423

Sprouting of seeds, 25 ff., 29

Stamens, 478

Standardizing work conditions, 216

Starch, 51 ; digestion of, 94, loo-ioi ;
energy in, 75 ; origin of, 54

Statistics, vital, 395

Statolith, 241, 242

Stem, 32, 174 ff., 269 ff., 300, 477

Stickleback, 332

Stigma, 301, 303, 304 ff., 311, 313

Stimulants, 119, 131 ff., 253 ff, {see
also Alcohol)

Stimulation, of glands, no, 112, 116,
217; of intestines, 119; from meat,
106; of muscles, 217; and sensa-
tion, 228

Sting of bee, 373

Stomach, 82, 83 ; glands of, 84

Stomate, 70, 71, 88, 144, 261

Stone Age, 500

Struggle, competitive, 343 ; for exis-
tence, 474

Suffocation, 169

Sugar [see Carbohydrates)

Sun, relation of, to life, 55, 75

Superstition, 505

Suprarenals, 188

Surface, of cell in relation to growth,
265 ; reduction of, as protection, 359
Surinam Ameiva, 270
Survival of the fittest, 472, 474
Susceptibility, 198. See also Immunity
Swallowing, 82, 100

Tannin, 202, 255

Tanning by light, 352

Tapeworm, 342, 369, 411

Tap-roots, 45

Taste, organs of, 226; in selection of
food, I lo-i 1 1

Tea, 74, 254

Teeth, 81, 105, ii9ff., 502

Temperature, and breathing, 1 56 ; and
development, 286; and life, 337
{see also Heat) ; color changes re-
lated to, 353, 362 ; regulation of, in
body, 187; relation of, to sprouting,
27

Test, cytolysin, 197 ; precipitin, 197

Texas fever, 451

Thallophytes, 480

Thymus, 189, 285

Thyroid, 188, 289 ; influence on devel-
opment, 285

Tick, 451

Tigerstedt on daily food require-
ments, lOI

Timber supply, 382, 383

Tired feeling, 118

Tissues, 24, 267, 276, 477

Toads, 329 ; and young, 334

Tobacco and bacteria, 347

Tobacco industry, 74, 167

Tobacco smoke, 162 ff.

Tonus, 132

Tools and weapons, 499

Touch, organs of, 226, 228

Tourniquet, 191

Towels, public, 395

Tower, Professor W. L., 462. See also
Frontispiece

Trachea in man, 148

Tracheae in insects, 145

Transformation (metamorphosis), 280

Transmission, of communicable dis-
eases, 317; of modifications, 460

Transparency, 352

Transpiration, 71, 72, 178

Transportation, within organism, 44,
79, 174 ff., 179 ff-' 185 ff.

Tree hoppers, 354

Trees, products of, 377. See also Forest

528

ELEMENTARY BIOLOGY

Trench fever, 410

Trimorphic flowers, 305

Trimorphic insects, 357

Tropism, 37, 38, 230 ; and reflexes,

218 ; and senses, 224 ff.
Tubercles, bacteria in, 67 ; nitrogen, 62
Tuberculosis, 152, 386, 389, 506, 508
Turnspit animals, 460
Type, mixed, 440
Typhoid fever, 391 ; and flies, 399 ;

and water, 392

Underfeeding, 288

Underwing moth, 352

Unit characters, law of, 448, 449, 451

Urea, 144, 201, 204

Urine in diagnosis, 205

Vaccination, compulsory, 394 ; against

typhoid fever, 197 ; and vaccines,

198
Vaccines, see Vaccination
Valves of heart, 186, 190
Vanessa butterfly, 287
Vanilla, 312
Variation, 258, 437, 472 ; causes of,

438 ; physiological, 438, 439 ; in

size of similar units, 436
Vegetarianism, 105
Veins, 185 ; of leaves, 34, 70, 175, 176
Ventilation, 154 fl^. ; and efficiency of

work, 185; and moisture, 189; of

lungs, 148, 152 ; regulation of, 395 ;

summary on, 173
Ventricles, 185, 186, 187
Vermiform appendix, 82, 468
Vertebrata, 432
Vertebrates, 482, 492 ; brains of, 497 ;

reproduction in, 330
Vessels, blood, 185 ; in plants, 44,

174, 176
Vestigial structures, 468
Vibrations, perception of, 238
Villus, 86, 87
Vinegar and bacteria, 397
Vitamines, 109
Voit, Carl, food doctrines of, 90, 93,

99
Volume of cell in relation to growth,

265
Voluntary muscles, 219
Volvox, 276

Von Baer's Law of Recapitulation, 278
Vries, Hugo de, 440, 442, 461, 462,

473

Walking-leaf insect, 354

Walking-stick insect, 353

Wallaby and young, 334

Wallace, Alfred Russel, 472

War, the Great, 64, 108, 130, 133, 142,

216, 243, 354, 383,410, 514
Warm-blooded animals, 337
Wastes of organisms, 201 ff. See also

Excretion
Water, essential to gametes, 328 ; in

food-making, 53 ff. ; in growth of

plant, 38; and life, 50, 52, 338;

with meals, 114, 117; related to

sprouting, 27
Water power and forest, 380
Water supply, 122, 123, 391; and

forest, 378 ; and typhoid fever,

392
Wax, 413

Waxwing, cedar, 428
Wealth, biology related to, 4. See also

Economics
Weapons and tools, 499
Weevils, 416; cotton-boll, 418
Weismann, August, 459
Wheat, breeding of, 450 ; immunity

to rust in, 451 ; rust of, 411
Wheelworms, 482

Whiteness of fur related to tem-
perature, 353
Wood, conservation of, 384 ; in roots,

43, 44; in stems, 174, 175; supply

of, 382, 383 ; uses of, 377
Woodpecker, red-headed, 428
Work, alcohol and, 136; hours of,

213; rate of, 211; relation of, to

food requirements, loo-ioi ; and

rest, 214
Work conditions, regulation of, 394,

395; standardizing, 216
Wounds, treatment of, 191

Xylem, 176

Yeast, 23, 133, 291-292

Yellow fever, 406 ; reduction of, in

Cuba, 409
Yellow-bellied sapsucker, 427
Young, protection of, 371. See also

Development and Infancy
Youth, 335

Zygospore, 297

Zygote, 296, 297, 332, 459 ; origin of,
457

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