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HUNTER # NEW ESSENTIALS OF
BIOLOGY

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NEW
ESSENTIALS OF BIOLOGY

PRESENTED IN PROBLEMS

BY
GEORGE WILLIAM HUNTER. PH.D.

PROFESSOR OF BIOLOGY, KNOX COLLEGE, GALESBURG, ILLINOIS

FORMERLY HEAD OF DEPARTMENT OF BIOLOGY

DeWITT CLINTON HIGH SCHOOL, NEW YORK

AMERICAN BOOK COMPANY

NEW YORK CINCINNATI CHICAGO BOSTON ATLANTA

COPYKIQHT, 1911, BY

GEORGE WILLIAM HUNTER.

Copyright, 1923, 1928, by

AMERICAN BOOK COMPANY.

All Rights Reserved.

HUNTER, NEW ESSENTIALS OF BIOLOQT.
W.P. 22

li L37

MADE TN U. S. A.

THE PLA.N AND PURPOSE OF THIS BOOK

The plan of this book recognizes first-year biology as a science
founded upon certain imderlytng and basic principles. These
principles underhe not only biology, but also organized society.
The culmination of such an elementary course is avowedly the
understanding of man, and the principles which hold together
such a course should be chiefly physiological. The functions of
all living things, plants or animals, movement, irritabihty, nu-
trition, respiration, excretion, and reproduction; the interrelation
of plants and animals and their economic relations, all these as
they relate to man should enter into a course in elementary biology.

But to make plain these physiological processes, difficult even
for an advanced student of biology to comprehend, the simplest
method of demonstration is necessary. Plant physiology, be-
cause of the ease with which simple demonstrations can be made,
is more profitable ground for beginners than is the physiology
of animals. The foods which animals use are manufactured and
used by green plants; the action of the digestive enzymes, the
principle of osmosis, and the subject of reproduction can better
be first handled from the botanical aspect. The topics just
mentioned introduced from the standpoint of the botanist gain
much by repetition from the zoological angle. The principles of
physiology, after being appHed in experiment to plants and
animals, emerge in final clarity when appHed at the last to
man, — the most complex of all hving things.

One sufficient reason for the placing of a course in biology in
the first year of the secondary course lies in the fact that at
this time the child is receptive to the message of apphed biology.
Private and public hygiene, the message of protective medicine
and sanitation, the story of pure milk and of pure water and
what they mean to a community; all these things can most
logically be presented in a course that makes man the center.
The allied topics of conservation of plant and animal life, the

V

vi PLAN AND PURPOSE OF THIS BOOK

destruction of haniifiil plants and animals, the relation of insects
and other animals to the spread of disease, and the work of civic
and government departments in the development of nature's
gifts and in the preservation of national health should be treated
in their relation to man.

Moreover, the data given should be treated from the biological
standpoint, not that of botany, zoolog}^, or human physiology.
Ideally, we might take up general principles and draw from the
great storehouses of plant, animal, and human biology" to il-
lustrate each principle before going on to the next. Practically,
however, such a plan does not seem to be workable, partly be-
cause of the difficult}^ of collecting enough material to make such
demonstrations possible. It is impracticable with immature stu-
dents, because they cannot grasp the many-sidedness of the
apphcation at once. This will come only after repetition of the
principle, each time from a shghth' different point of ^dew.

It frequenth' happens that the related study of plants and ani-
mals may be taken up to advantage. Insects and flowers, both
plentiful in the faU, ma}' weU be studied together for the relation
of life habits and adaptations in the insect to cross-pollination
of flowere. Apphed biolog}', in its relation to plants or to ani-
mals, must of com'se be 'treated from all sides. The fungi and
the bacteria in their relations to man are conspicuous examples.

Teachers often spend too much time in teaching unessentials
taken from an immense field, and do not spend enough time in
emphasizing from constanth" varied points of attack the fimda-
merital truths on which the science of biology is built. The pages
which follow are an attempt to drive home by repetition, and
from many points of view, some of the important principles of
physiological biologj^

The plan of the book includes the sohdng of a number of
problems in biolog}', each of which is more or less deteimined
by the one immediately preceding it. So far as possible, the
problems have a human interest. Abstractions are not part of
the thought of a first-year pupil. Concrete problems, related
when possible to the daily life of the pupil, have been used.
The problems are stated in the form of laboratory exercises or
suggestions, the material for which is in the hands of the pupil

PLAN AND PURPOSE OF THIS BOOK vii

or is worked out as a demonstration before the class. In all
cases the laboratory types or physiological experiments demon-
strate some important principle of biology.

The laboratory exercise immediately precedes the textbook
discussion, the latter being used to clear up any false inferences
the pupil may have made from the specimen in hand and to fix
the object of the problem in the mind of the pupil. Too often
has a laboratory exercise meant nothing to a pupil but ''busy
work." A plainly outlined and organized plan of attack, a few
references to the text or tc previous work performed, and a
definite problem wiU result in better and more definite laboratory
work. For use with this book manuals for the solution of
laboratory problems have been prepared by my coworker, Mr.
R. W. Sharpe, and by myseK. The latter manual, ''Laboratory
Problems in Civic Biology," gives an excellent point of attack
through the interests of the student and gives a varied selection
of problems for the teacher.

Two styles of type have been used in the text. The larger
type contains material which is believed to be of first impor-
tance, the smaller type the less important topics. There are
always some students whose grasp of subject matter or whose
maturity places them above the average student. It is expected
that the material in smaU type wiU be used to advantage with
such students. Thus the material in small print will, to an
extent, take the place of outside assigned reading and will, as
well, give problem and project suggestions to those students
whose interests are keenly biological.

The manuscript in its entirety was read by Professor H. E.
Walter of Brown University, and by Miss A. P. Hazen, Head of
the Department of Biology in the Eastern District High School;
to them I owe sincere thanks for many helpful criticisms and
suggestions. Acknowledgments are also due to H. G. Barber,
E. A. Bedford, John E. McCarthy, and R. W. Sharpe of the
DeWitt CKnton High School, and to Mr. C. W. Beebe, Curator
of Birds, New York Zoological Park, for their careful reading
and criticism of parts or all of the proof.

Thanks are due, also, to Professor E. B. Wilson, Mr. William
C. Barbour, Dr, John A. Sampson, W. C. Stevens and C. W.

viii PLAN AND PURPOSE OF THIS BOOK

Beebe, Alvin Davison, and Dr. Frank Overton; to the United
States Department of Agriculture; the New York Aquarium;
the Charity Organization Society; the Folmer and Schwing
Company, Rochester, N. Y.; and the American Museum of
Natural History, for permission to copy and use certain photo-
graphs and cuts which have been found useful in teaching.
R. W. Coryell and J. W. Tietz, two of my former pupils, made
several of the photographs of experiments. Many of the line
drawings in this revision are the work of Frank M. Wheat,
whose scientific and artistic conceptions have added much to
the value of the book.

At the end of each chapter is a list of books which have
proved their use either as reference reading for students or as
aids to the teacher. Most of the books mentioned are within
the means of the small school. Two sets are expensive: one,
The Natural History of Plants, by Kerner, translated by Oliver,
published by Henry Holt and Company, in two volumes; the
other, Plant Geography upon a Physiological Basis, by Schimper,
published by the Clarendon Press; but both works are invaluable
for reference.

For a general introduction to physiological biology, the follow-
ing are most useful and inspiring books: Parker, Lessons in
Elementary Biology, The Macmillan Company; Sedgwick and Wil-
son, General ^Biology, Henry Holt and Company; Shull, Principles
of Animal Biology, McGraw-Hill Company.

Three books stand out from the pedagogical standpoint as by
far the most helpful of their kind on the market. No teacher of
botany or zoology can afford to be without them. They are:
Lloyd and Bigelow, The Teaching of Biology, Longmans, Green,
and Company; C. F. Hodge, Nature Study and Life, Ginn and
Company; and Twiss, Principles of Science Teaching, The Mac-
millan Company. The last-named book gives the modern peda-
gogical interpretation of the introductory sciences. Other books
of value from the teacher's standpoint are: Ganong, The Teach-
ing Botanist, The Macmillan Company; L. H. Bailey, The Nat-
ure Study Idea, Doubleday, Page and Company; and McMurry's
How to Study, Houghton Mifflin Company.

CONTENTS

CHAPTER PAGE

I. Some Reasons for the Study of Biology 1

II. The Environment of Living Things 5

III. The Functions and Composition of Living Things . . 16

IV. Flowers and their Work 23

V. Fruits and their Uses 40

VI. Seeds and Seedlings 54

VII. Roots and their Work . 70

VIII. The Structure and Work of the Stem 84

IX. Leaves and their Work .' 98

X. Our Forests; their Uses and the Necessity for their

Protection 116

XI. The Various Forms of Plants and how they Reproduce

Themselves 126

XII. How Plants are modified by their Surroundings . . 136

XIII. How Plants benefit and harm Mankind 146

XIV. The Relations of Plants to Animals 166

XV. The Protozoa 172

XVI. Simple Metazoa — Division of Labor 181

XVII. The Worms, a Study of Relations to Environment . 194

XVIII. The Crayfish. A Study of Adaptations 204

XIX. The Insects ' . 216

XX. General Considerations from the Study op Insects . 234

XXI. The Mollusks 253

XXII. The Vertebrate Animals 261

Fishes 262

Amphibia. The Frog 272

is

X CONTENTS

CHAPTER PAGE

Reptiles 281

BiRR« 286

Mammals 303

XXIII. Man, A Mammal 3x1

XXIV. Foods and Dietaries 322

XXV. Digestion and Absorption 343

XXVI. The Blood and its Circulation 358

XXVII. Respiration and Excretion 374

XXVIII. The Nervous System and Organs of Sense 390

XXIX. Good Health and How to Keep It 404

XXX. Health and Disease. A Chapter on Civic Biology . 415

Glossary 427

Index 441

NEW ESSENTIALS OF BIOLOGY

I. SOME REASONS FOR THE STUDY OF BIOLOGY

What is Biology? — Biology is the study of living beings, both
plant and animal. Inasmuch as man is an animal, the study of
biology includes the study of man in his relation to the plants
and the animals which surround him. Most important of all
is that branch of biology which treats of the mechanism we call
the human body, — of its parts and their uses, and its repair.
This subject we call human physiology.

Why study Biology? — Although biology is a very modern
science, it has found its way into most high schools; and an
increasingly large number of boys and girls are engaged in
its study. The question might well be asked by any of these
students, Why do I take up the study of biology? Of what
practical value is it to me? Aside from the discipline it gives
me, is there anything that I can get from it which will help me
in my future life as a boy or girl with only a high school
education?

Human Physiology. — The answer to this question is plain.
If the study of biology will give us a better understanding of
our own bodies and their care, then it certainly is of use to us.
That phase of biology known as physiology deals with the uses
of the parts of a plant or animal; human physiology deals with
the uses, and hygiene (hi'ji-en) with the care, of the parts of the
human animal. Much sickness may be prevented by living ac-
cording to the laws which hygiene teaches. It is estimated
that 400,000 out of the 1,600,000 deaths that occur yearly
in this country could be averted if only every one lived in a
hygienic (hi-ji-en'ik) manner. In its application to the life of
each of us, as a member of a family, as a member of the school
we attend, and as a future citizen, a knowledge of hygiene is
of the greatest importance.

1

REASONS FOR THE STUDY OF BIOLOGY

Relations of Plants to Animals. — But there are other reasons
why an educated person should know something about biology.
We do not always reahze that if it were not for the green
plants, there would be no animals on the earth. Green plants
furnish animals with their food. Even the meat-eating animals
feed in the long run upon those that feed upon plants. How

the plants manufacture
this food and the relation
they have to animals will
be discussed in later
chapters. Plants furnish
man with the greater part
of his food in the form of
grains and cereals, fruits
and nuts, edible roots
and leaves; they provide
his domesticated animals
with food; they give him
timber for his bouses and
wood and coal for his
fires; they provide him
with pulp wood, from
which he makes his paper,
and oak galls, from which
he obtains ink. Much of
man's clothing and the
thread with which it is
sewed come from fiber-
producing plants. Most
medicines, beverages.

Banana plants. Each plant bears one bunch flavoring extracts, and

^"^ P^^°*' spices are plant products,
while plants are made use
of in hundreds of ways in the useful arts and trades, producing
varnishes, dyestuffs, rubber, and other products.

Bacteria in their Relation to Man. — In still another way, cer-
tain tiny plants vitally affect mankind. These plants, so small
that miUions can exist in a single drop of fluid, are called bacte^ria

of bananas and is then cut down,
grow up from the root.

BACTERIA, ANIMALS 3

or germs. Existing almost everywhere about us, — in water,
soil, food, and the air, — they play a tremendous part in shap-
ing the destiny of man on the earth. They help him in that
they act as scavengers, causing things to decay; they give flavor
to cheese and butter; they assist the tanner, and are invaluable
to the farmer; but they hkewise cause decay of our meat and
fish, and our vegetables and fruits; they sour our milk, and
spoil om* canned goods. More than this, they cause diseases,
among others tuberculo'sis, a disease so harmful as to be called
the " white plague." Fully one half of the deaths each year are
caused by these plants. So important are bacteria that a
subdivision of biology, called hacterioV ogy , has been named after
them, and hundreds of scientists are devoting their Uves to the
study of germs and their control. The greatest of all bacteri-
ologists, Louis Pasteur (pas-tur')/ once said, " It is within the
power of man to cause all parasitic diseases [diseases caused
mostly by bacteria] to disappear from the world." His prophecy
is gradually being fulfilled, and it may be the lot of some boys
or girls who read this book to do their share in helping to bring
about this condition of affairs.

Harmful Relation of Animals to Man. — Animals play an im-
portant part in the world in causing and carrying disease. Ani-
mals that cause disease are usually tiny, and live upon other
animals as parasites; that is, they get their living from their
hosts on which they feed. Among the diseases caused by para-
sitic animals are malaria, yellow fever, sleeping sickness, and
hookworm disease. Animals also carry disease, especially the
flies and mosquitoes ; rats and other animals are well known
also as spreaders of disease. From a money standpoint, insects
do much harm. It is estimated that in this country alone in 1922
they were responsible for over $2,000,000,000 worth of damage to
crops, stored foods, and forest products.

The Uses of Animals to Man. — We aU know the uses man
has made of .domesticated animals for food and as beasts of
burden. But many other uses are found for animal products,
and materials made from animals. Wool, furs, leather, hides,
and feathers are examples. The arts make use of ivory, tortoise

1 The diacritic marks are those used in the Webster school dictionaries.

REASONS FOR THE STUDY OF BIOLOGY

shell, coral, and mother of pearl; from animals also come
certain perfumes and oils, glue, lard, and butter; animals produce
honey, wax, milk, eggs, silk, and various other commodities.

The silkworm: 1, eggs; 2, larva or silkworm; 3, cocoon spun by the larva; 4, the
adult moth, which comes from the cocoon and lays the eggs from which new
larvae are hatched. The cocoons are made of silk threads, which can be unwound.

The Conservation of our Natural Resources. — Still another
reason why we should study biology is that we may work in-
telligently for the conser-
vation of our natural
resources, especially our
forests. The forest, aside
from its beauty and its
health-giving properties,
holds water in the earth.
It keeps the water from
drying out of the earth on
hot days and from running
off on rainy days. Thus
a more even supply of
water is given to our rivers,
and freshets are prevented.
Countries that have been
deforested, such as parts of
China, Italy, and France,
are now subject to floods,
and are in many places

Raising silkworms in Japan. The silkworms
are fed on mulberry leaves and must be care-
fully tended.

barren. On the forests depend our supply of timber and to a
large extent OTir future water power.

Plants and Animals mutually Helpful. — The study of biology
also shows us the interrelation existing between plants and ani-

RELATIONS OF PLANTS AND ANIMALS 5

mals on the earth. Most plants and animals stand in an atti-
tude of mutual helpfulness: plants providing food and shelter
for animals; animals giving off waste materials useful to plants
in the making of food. We learn also that plants and animals
need the same conditions in their surroundings in order to live;
water, air, food, a favorable temperature, and usually light.
We learn that the life processes of both plants and animals
are essentially the same, and that the living matter of a tree
is as much alive as is the living matter in a fish, a dog, or a
man.

Biology in its Relation to Society. — Finally, the study of
biology should be part of the education of every boy and girl,
because society itself is founded upon the principles which biol-
ogy teaches. Plants and animals are living things, each taking
what it can from its surroundings; they enter into competi-
tion with one another, and those which are the best fitted for life
outstrip the others. Health and strength of body and mind are
factors in man which tell in winning. The strong may hand
down to their offspring the characteristics which make them the
winners.

Man has made use of this message of nature, and has devel-
oped improved breeds of horses, cattle, and other domestic ani-
mals. Plant breeders have hkewise selected plants and seeds
with great care and thus have stocked the earth with hardier
and more fruitful domesticated plants. Man^s dominion over
the living things of the earth is tremendous. It is due to the
understanding of the principles which underlie the science of
biology.

Problem Questions. — 1. WHiy should biology be studied by
all girls and boys of high school age?

2. Of what use to the average citizen is a knowledge of
biology?

HUNT. NEW E8. — 2

II. THE ENVIRONMENT OF LIVING THINGS

Environment. — Living plants and animals are surrounded by
various substances and forces. Air, light, water, the presence
or absence of food, changing conditions of temperature, even such
a force as electricity, may influence the growth or behavior of any
living thing. Plants and animals take some outside substances
into their bodies and are externally influenced by others. The total
of all the surrounding forces which act upon living things helps
to form their envi'ronment. We shall later see that the environ-
ment may cause great changes to take place in the structure or
habits of a plant or animal. It is the purpose of this chapter
to try to explain something of how plants and animals are influ-
enced by the factors of their environment.

In order to understand better what a living plant or animal
takes from its environment, we must find out something about
the air, water, and the soil, for it is with these factors that the
plant and the animal are in immediate contact.

Problem. How to learn the 'part played hy the common elements
in the environment of living things, (Laboratory Manual,^ Prob. I;
Laboratory Problems,^ Probs. 37, 38, 39, 40.)

(a) Nitrogen.

(6) Oxygen and oxidation.

(c) Hydrogen.

(d) Carbon and carbon dioxide.

The Composition of the Air. — If we invert a large bell jar over
a deep tray containing water, having previously placed a float
holding a bit of burning phosphorus (fos'for-us) upon the surface
of the water, we find that, as the phosphorus burns, the water

1 Sharpe, A Laboratory Manual for the Solution of Problems in Biology, Ameri-
can Book Company.

'Hunter, Laboratory Problems m Civic Biology, American Book Company.

6

CHEMICAL ELEMENTS

Experiment to show the amount of
oxygen in the air. A before, and B
after the phosphorus p is lighted.

slowly rises in the jar. After a little the fire goes out. The
water now displaces a volume equal to about one fifth of the
space occupied by the air in the jar. When the water reaches
this height, it goes no higher, and, no matter how many times
or how . parefully the experiment is repeated, the phosphorus

always stops burning when
the water displaces one fifth
of the air in the jar.

Evidently, the burning of
the phosphorus uses up some
gas within the jar which
supports the flame, and the
gas which remains in the
jar, occupying about four
fifths of the space, does not
have the power to maintain
the flame. The former gas is
oxygen (ox'i-jen); nearly all
the latter is ni'trogen. These two gases form the principal
constituents of the air in nearly the proportion seen in the ex-
periment. The white gas formed by the combination of the
oxygen with the phosphorus is absorbed by the water in the
tray.

Chemical Elements. — All the materials of this universe, both
living and lifeless, are classified by chemists as either chemical
elements or chemical compounds. A chemical element is a substance
which chemists have not been able to break up or decompose into
simpler substances. Examples of elements are oxygen, making up
about 20 per cent of the atmosphere; nitrogen, composing nearly
all the remainder of pure air; carbon, an element that enters into
the composition of all organic matter; and over seventy others
of more or less importance to us in the study of biology.

Nitrogen. — The physical properties (those which we determine
through our senses) of nitrogen are its lack of color, taste, and odor.
Its chief chemical characteristics are its inability to support com-
bustion and its slight tendency to combine with other substances.
We shall later find that nitrogen is one of the most important
chemical elements found in living matter. In spite of this, animals

8

THE ENVIRONMENT OF LIVING THINGS

and most plants are absolutely unable to take any nitrogen from

the air, no matter how much they may need it.
The other principal element in the air, oxj^gen, is taken out bj"

plants and animals. We shall be able to see how, after studying

the properties of oxygen.

Preparation of Oxygen. Elements and Compounds. — Oxygen

may be prepared by heating half a teaspoonful of chlorate of

potash with a Uttle less than its bulk of black oxide of man-
ganese in a test tube
over a flame. The chlo-
rate of potash and oxide
of manganese are made
up of chemical elements
which have united to form
chemical compounds. A
combination of two or
more elements according

The mixture of chemicals in the test tube M ^^ certain laWS is called a
is decomposed by heat and gives off the gas CX)mpOUnd. In the mix-

wX!" ^' ""^'"^ ^ '""'^''''"^ ^"^ displacing ^^^ ^f ^^^ compounds

named above heat will
free the oxygen, as is proved by a glowing match end bursting
into flame when held over the mouth of the test tube, or by
testing the gas collected in a bottle as shown in the Figure.
We have decomposed the two chemical compounds and in the
process we have released the element oxygen. This is an
example of a chemical change.

Properties of Oxygen. — Oxygen, when carefuU}^ prepared, is
found to be colorless, odorless, and tasteless. Combined with
other substances, it forms a very large part by weight of water
rocks, minerals, and the bodies of plants and animals.

Oxygen has the very important propert}^ of uniting with
many other substances. The chemical union of oxygen with
another substance is called oxidation. Rapid oxidation produces
a flame or light. Oxidation, either rapid or slow, may take
place wherever oxygen is present. This fact has a far-reaching
significance in the imderstanding of the most important problems
of biology.

OXIDATION 9

Oxidation in a Match. — The simple process of striking a sulphur match
gives us an illustration of this process of oxidation. The head of the
match is formed of a combination of phosphorus, sulphur, and some other
materials. Phosphorus is a chemical element distinguished by its extreme
infiammabiUty; that is, it unites with oxygen at a comparatively low tem-
perature, producing a flame. Sulphur is another chemical element that
combines somewhat easily with oxygen but at a much higher temperature.
The rest of the match head is made up of red lead, niter, or some other sub-
stance that will release oxygen, and some glue or gum to bind the materials
together. The heat caused by the friction of the match head against the
striking surface is enough to cause the phosphorus to ignite; this in turn
ignites the sulphur; and finally the wood of the match, composed largely
of the element carbon, is lighted and oxidized. If we could take out the
different chemical elements of which the match is formed and oxidize them
separately, we should find that the amount of heat needed to start the oxi-
dation of the substances would vary greatly.

Slow Oxidation. — Oxidation may take place slowly, as seen
in the rusting of an iron nail. If the rust and nail are weighed,
the total weight will be more than the original nail. Do you see
why ? Rust is iron oxide, and is formed by the union of iron and
oxygen. Slow oxidation of chemical compounds is constantly
taking place in nature and is a part of the process of decay and of
breaking down of complex materials into simpler forms.

Heat given off as Result of Oxidation, — One of the most im-
portant effects of oxidation lies in the fact that, when anjrthing is
oxidized, heat is produced. This heat may be of the greatest use.
Coal, in being oxidized, gives off heat; this heat boils the water in
the tubes of a boiler; steam is generated, wheels of an engine
are turned, and work is performed. The energy released by the
burning of coal may be transformed into any kind of work power.
Energy is the ability to perform ivork. We shall find later that the
oxidation of certain materials in the bodies of plants or animals
releases energy. The heat of the human body is maintained by
constant slow oxidation of food materials within the body.

The Composition of Water. — If an electric current is passed
through water by means of the apparatus shown in the Figure
on the next page, the water separates into two gases, one of which
occupies twice as much space as the other in the tubes. If we
test the gas present in smaller quantity, we find it to be oxygen.
The other gas, colorless, tasteless, and odorless hke the oxygen,

10 THE ENVIRONMENT OF LIVING THINGS

differs from it by igniting with a slight explosion when a burning
match or spUnter is introduced in it. As it burns, drops of water

are formed, showing
that it is passing back
to its original condi-
tion, that is, it is unit-
ing with oxygen to
form water. This gas
is hydrogen (hi'dro-
jen). Hydrogen has a
great chemical affinity
or liking for other ele-

Apparatus for separating water into hydrogen ^lents, hence it is USU-
H and oxygen O: c, copper wire; p, platinum wire

soldered to the copper, with insulation so that no ally found m nature
copper is exposed in this tube A few drops of combined with Other
sulphuric acid should be added to the water, to . .

facilitate the action of the electric current. elements, aS with_ Oxy-

gen in water.
The Composition of the Soil. — The covering of the earth was
probably very different in former ages from what it is now. Its
molten plastic mass after cooling formed rock. This rock, by the
work of the wind, frost, heat, water, and plants, has in part been
broken into small bits. This is inorganic soil, as sea sand and
gravel, formed usually of several elements found in rocks, such
as caFcium, sodimn, magne'sium, siFicon, potas'sium, and iron,
all combined with oxygen.

A visit to the woods or to a well-kept garden shows us that there
is another kind of soil than the inorganic soil just mentioned. This
is the rich, dark soil containing hu'mus. Humus is made up largely
of dead organic matter, the decayed remains of plants and ani-
mals. If we could test the chemical elements to be found in
humus, we should find nitrogen, hydrogen, oxygen, and also
carbon, an important element found in all organic matter.

Carbon. — Carbon is found in many conditions in nature. It
is found in the bodies of plants and animals, and in coal (fossil
plants), and it exists in a nearly pure state in the diamond. The
presence of carbon can usually be detected by partly burning or
charring a substance; the carbon, if present, remains as a black
substance without taste or odor. Carbon may be collected by

OXIDATION OF CARBON

11

allowing a candle flame to burn in contact with the under side
of a sheet of glass. The black deposit is almost pure carbon.

Oxidation of Carbon and its Result. — If we burn a candle in
a closed jar containing air, the flame soon begins to flicker, and
then goes out. If the cover of the jar is carefully removed, and
a burning match lowered into the jar, the match will at once go
out, showing the presence of a gas heavier than air which will not
support a flame. Nitrogen of course is present, but we shall make a
test for another gas, — a test to which nitrogen will not respond.
If we pour into the jar a few spoonfuls of limewater,^ a colorless
liquid, and shake it up with the gas in the jar, the lime water turns
milky in color. This is a test for a compound known as carbon
dioxide, which was evidently formed by the union of the carbon
of the candle with the oxygen of the air in the jar.

All organic or living substances, when oxidized, form carbon
dioxide besides giving off water vapor. That oxidation of car-
bon takes place within our own bodies may easily be
proved by exhaling through a clean glass tube into some
limewater ; and that water vapor is given off, by breath-
ing against a clean, dry glass. The heat of the human
body (98.6° F.) is the result of
oxidation taking place within the
body. The heat given off from
oxidation of wood or coal in a
stove is determined by the supply
of oxygen we allow to pass to the
burning material. If we open the
draft, allowing more oxygen to
get to the fire, we increase the heat by more rapid oxidation;
if we shut off the oxygen supply, we decrease the amount of
oxidation.

Problem. Are mineral matter and water present in living things f
{Laboratory Manual, Prob. II; Laboratory Problems, Probs.
30, 31.)^

1 Limewater can be made by shaking up a piece of quicklime the size of your
fist in about two quarts of water. Filter or strain the limewater into bottles,
and it is ready for use.

2 See notes on page 6.

Oxygen Jn the air

32

3

Diagram of combustion or rapid
oxidation in a stove.

12 THE ENVIRONMENT OF LIVING THINGS

(a) Mineral matter,
(h) Water.

Mineral Matter in Living Things. — If a piece of wood is burned
in a very hot fire, the carbon in it will all be consumed, and
eventually nothing will be left except a grayish ash. This ash is
seen after a wood fire in the fireplace, or after a bonfire of dry
leaves. It consists of mineral matter which the plant has taken
up from the soil dissolved in water, and which has been stored in
the wood or leaves. All living things contain small quantities
of mineral substances.

Water in Living Things. — Water forms an important part of
the substance of plants and animals. This is easily seen by
weighing a number of green leaves, placing them in a hot oven for
a few moments, and then reweighing. The same experiment made
with a soft-bodied animal, as the oyster, would show the presence
of even more water than in leaves. Some jellyfish are over 90
per cent water. About 65 per cent of the human body is
water.

Gases Present. — Some gases are found in a free state in the
bodies of plants or animals. Oxygen is of course present wherever
oxidation is taking place, as is carbon dioxide. Other gases may
be present in minute quantities.

Problem. What foods do living organisms need? (Laboratory
Manual, Prob. Ill; Laboratory Problems, Probs. 26, 27, 28, 29.)

Composition of Living Matter. — The living part of a plant or
animal is made up of the elements carbon, hydrogen, oxygen, and
nitrogen, with a very minute amount of several other elements,
which collectively we may call mineral matter. The living part
of a plant corresponds closely in chemical composition to the living
part of an animal. The starch found in grains or roots of plants
has nearly the same chemical formula as the animal starch found
in the liver of man; the oils of nuts or fruits are of a composition
closely allied to the fat in the body of an animal. These and other
building materials of a plant or animal may be placed in the three
following groups of substances: carbohydrates (car-bo-hi'drats),
materials containing a certain proportion of carbon, hydrogen,
and oxygen; fats and oils, which contain chiefly hydrogen and

FOODS 13

carbon with less oxygen; and nitrogenous (ni-troj'e-nus) sub-
stances, or proteins (pro^te-inz), which contain nitrogen in ad-
dition to the above-mentioned elements. The above three kinds
of organic materials also form a large part of the foods of all
animals and plants.

Foods. — What is a food ? We know that if we eat a suitable
amount of proper foods at regular times, we shall be able to go on
doing a certain amount of work, both manual and mental. We
know, too, that day by day, if our general health is good, we may
be adding weight to our bodies, and that added weight comes as
the result of taking food into the body. A similar statement may
be made with reference to plants and foods. If food is supplied
in proper quantity and proportion, plants will live and grow; if
the food supply is cut off, or even greatl}^ reduced, they will
suffer and may die. From this, the definition which follows is
evident. Food is any material ivhich repairs or builds up the body
of a plant or animal, or, when oxidized in the body, furnishes it
with energy.

Nutrients. — Organic food substances are called nu'trients ;
they may be classed into a number of groups, each of which
may be detected by means of a chemical test. Such groups of
nutrients are carbohydrates, fats and oils, and proteins.

Carbohydrates. — Starch and sugar are common examples of
this group of substances. The former we find in our cereals, bread,
cake, and most of our vegetables. Several kinds of sugar are
commonly used as food; for example, cane sugar, beet sugar, and
glucose or grape sugar. Glucose, found as the natural sugar of
grapes, honey, and fruits, is manufactured commercially^ by pour-
ing sulphuric acid over starch. It is used as an adulterant for
many kinds of foods, especially in sirups, honey, and candy.

Test for Starch. — If we shake up a piece of laundry starch in
water, in a test tube, and then add to the mixture two or three
drops of iodine solution,^ we find that the particles of starch in
the test tube turn purple or deep blue. It has been discovered
by experiment that starch, and no 'other known substance, will be

^ Iodine solution is made by simply adding a few crystals of the element iodine
to 95 per cent alcohol; or, better, take by weight 1 gram of iodine crystals, f
gram of iodide of potassium, and dilute to a dark brown color in weak alcohol
(35 per centi or distUled water.

14 THE ENVIRONMENT OF LIVING THINGS

+n=

KJ

Test for~ starch.

turned purple or dark blue by iodine. Therefore, this has come

to be used as a test for the presence of starch.

Test for Grape Sugar. — Place in a test tube the substance

to be tested and heat it in a Uttle
water so as to dissolve the sugar.
Add to the fluid twice its bulk of
Fehling's solution ^ which has been
previously prepared. The mixture
should now have a blue color, in
the test tube. When heated, if gi-ape
sugar is present in considerable quan-
tity, the contents of the tube will
turn first a greenish, then a yellow,
and finally a brick-red color. Smaller
amounts will show less decided red.

No other substance than grape sugar will give this reaction.
Fats and Oils. — Fats and oils form

an important part of 'the composition

of plants and animals. Examples of

food in the form of fat are butter and

cream, the oils from nuts, olives, and

other fruits, and fat from animals.
Test for Fats and Oils. — The

characteristic " grease spot " is an

easy way of determining if a sub-
stance has fat or oil in it. If the

substance is a fluid, pour a little of

it on white paper; or if it is a solid,

rub it a few times on the paper.

Then hold the paper to the light. A

translucent spot indicates the pres-
ence of fat or oil. A more scientific

test is to mash the substance to be tested, place it in an evapo-

^ To make Fehling's solution (so-called after its discoverer), add to 35 grams of
copper sulphate (blue vitriol) 500 c.c. of water. Put aside until it is completely
dissolved. Call this solution No. 1.

To 160 grams of caustic soda and 173 grams of Rochelle salt add 500 c.c. of
water. Call this solution No. 2.

For use mix equal parts of solutions 1 and 2.

Test for grape sugar.

FOODS

15

kJ

rating dish, and then pour ether over it. If fat is present the
ether will dissolve it and upon evaporation of the ether the fat
will remain in the dish.

Proteins. — Nitrogenous foods, or proteins, contain the element
nitrogen in addition to carbon, hj^drogen, and oxygen of the car-
bohydrates and fats and oils. They include some of the most
complex substances known to the chemist, and, as we shall see,
have a chemical composition very near to that of living matter.
Proteins cJccur in many different substances. White of egg, lean
meat, beans, and peas are examples of substances composed largely
of proteins.

Tests for Proteins. — Place in a test tube the substance to be
tested ; for example, a bit of hard-boiled egg. Pour over it a little

strong (80 per cent) nitric acid. Note

the color that appears — a lemon
yellow. If the egg is washed in water
and a little ammonium hj^lrate added,
the color changes to a deep orange.
This shows that a protein is present.

If the substance is in a liquid state,
the presence of protein may some-
times be proved by heating, for when
it coagulates or thickens, as does the
white of an egg when boiled, protein
in the form of an alhu'men is present.

Another characteristic protein test
easily made at home is burning the
substance thought to contain it. If
the odor of burning feathers or leather Test for protein.

is given off, then protein forms part of its composition.

Proteins occur in several different forms, but the preceding tests
will cover the cases most commonly met.

Inorganic Foods. — Water and various salts, some of which,
as lime, may be found in drinking water, form important parts in
the diet of plants and animals. Later we shall see that green
plants, although they use precisely the same foods (carbohydrates,
oils, and proteins) as we do, take into their bodies the chemical
elements from which these are formed. From these raw food

NITRIC
ACID

+

AMMONIUM
HYDRATE

16 THE ENVIRONMENT OF LIVING THINGS

materials, organic foods are manufactured in the body of the
plant.

Summary. — This chapter has shown us that the factors of the
environment for both plants and animals are the same. Both use
the chemical elements in air, water, and food in building their
bodies or in releasing energy through oxidation of food materials.
Both plants and animals are affected by the forces of nature
which form part of their natural environment. It will be the work
of future chapters to explain how.

Problem Questions. — 1. What is the physical environment
of a living thing?

2. ^ATiat is an element? a compound? How is a compound
formed ?

3. Distinguish between rapid and slow oxidation. For what
purposes is food used by plants and animals?

4. What are nutrients? Explain.

5. What is the general pm-pose of this chapter?

Problem and Project References

Averj^ and Sinnott, First Lessons in Physical Science. American Book Company.

Broadhurst, Home and Coynynunity Hygiene, Chapter III. J. B. Lippincott Co.

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Martin, Human Body (Advanced Course), Revised, Chapter XXX. Henry Holt
and Company.

Sedgwick and Wilson, General Biology, Chapters II, III. Henry Holt and Com-
pany.

Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American
Book Company.

III. THE FUNCTIONS AND COMPOSITION OF
LIVING THINGS

Problem. An introduction to the nature and work of living
organisms. (Laboratory Manual, Proh. IV; Laboratory Prob-
lems, Probs. 1, 17, 18.)

(a) A living plant.

(6) A living insect.

A Living Plant and a Living Animal Compared. — A walk into
the fields or a vacant lot on a day in tbe early fall will give
us first-hand acquaintance with many
common plants which, because of their
ability to grow under unfavorable con-
ditions, are called weeds. Such plants —
the dandelion, butter and eggs, the shep-
herd's purse — are particularly well fitted
by nature to produce many of their kind
and by this means drive out other plants
which do not multiply so fast. On these
and other plants we find feeding several
kinds of animals, chiefly insects.

If we attempt to compare, for exam-
ple, a grasshopper with the plant on which
it feeds, we see several points of likeness
and difference at once. Both plant and
insect are made up of parts, each of which,
as the stem of the plant or the leg of the
insect, appears to be distinct, but which
is a part of the whole living plant or animal. Each part of the
living plant or animal which has a separate work to do is called
an organ. Plants and animals are spoken of as or^ganisms be-
cause they are made of organs.

Functions of the Parts of a Plant. — We are all familiar with
the parts of a plant, — the root, stem, leaves, flowers, and fruit

17

A weed. Notice that
the soil is barren, yet the
weed flourishes. Photo-
graph by W. A. Barbour.

18 FUNCTIONS OF LIVING THINGS

But we may not know so much about their uses to the plant.
Each of these structures differs from every other part, and each
has a separate work or function to perform for the plant. The
root holds the plant firmly in the ground and takes in water and
mineral matter from the soil; the stem holds the leaves up to the
light and acts as a pathway for fluids between the root and leaves;
the leaves, under certain conditions, manufacture food for the plant
and breathe; the flowers form the fruits; the fruits hold the seeds,
which in turn hold young plants which are capable of reproducing
adult plants of the same kind.

The Functions of an Animal. — If we examine the grass-
hopper more carefully, we find that it has a head, a jointed
body composed of a middle and a hind part, three pairs of
jointed legs, and two pairs of wings. Obviously, the wings and
legs are used for locomotion; a careful watching of the hind
part of the animal shows us that breathing movements are tak-
ing place; a bit of grass placed before it may be eaten, the tiny
black jaws biting little pieces out of the grass. If disturbed, the
insect hops away, and if we try to get it, it jumps or flies away,
evidently seeing us before we can grasp it. Hundreds of little
grasshoppers indicate that the grasshopper can reproduce its
own kind, but in other respects the animal seems quite unlike
the plant. The animal moves, breathes, feeds, and has sensa-
tion, while apparently the plant does none of these. It will be
the purpose of later chapters to prove that the functions of
plants and animals are in many respects similar and that both
plants and animals breathe, feed, and reproduce.

Organs. — If we look carefully at the organ of a plant called
a leaf, we find that the materials of which it is composed do not
appear to be everywhere the same. The leaf is much thinner
and more delicate in some parts than in others. Holding the
flat, expanded blade away from the branch is a little stalk, the
pet'iole, which extends into the blade of the leaf. Here it splits
up into a network of tiny veins which evidently form a frame-
work for the flat blade somewhat as the sticks of a kite hold the
paper in place. If we examine under the compound microscope
a thin section cut across the leaf, we shall find that the veins as
well as the other parts are made up of many tiny boxlike units.

ORGANS AND TISSUES

19

These smallest units of building material of the plant or animal
disclosed by the compound microscope are called cells. All the
organs of a plant or animal are built
of these minute structures, which are
of various sizes and shapes.

Tissues. — The cells which form
certain parts of the veins, the flat
blade, or other portions of the plant,
are often found in groups or collec-
tions, in which the cells are more or
less alike in size and shape. A col-
lection of similar cells is called a
tissue. Examples of tissues are the
cells covering the outside of the
human body, the muscle cells, which
collectively allow of movement, bony
tissues which form the framework to
which the muscles are attached, and
many others.

Adaptations of Structure to Func-
tion. — If I look at my hand as I
write, I notice that the fingers of my
right hand grasp the pen firmly; that because of the several
joints in the fingers, the wrist, and forearm, free movement can
be given to the hand when the muscles attached to the bones
move it. The hand is capable of a great number of complicated
and delicate movements, most of them associated with the work
of grasping objects. Because of the peculiar fitness in the
structure of the hand for this work, we say that it is adapted
to this function, that is, grasping objects. Each organ of the
plant is fitted or adapted in some way to do certain kinds of
work. It is the object of the chapters following to point out
how the parts of a plant or animal are adapted to their various
functions.

Section through a leaf, greatly
magnified : E, cells of upper epi-
dermis; P, palisade layer; V,
vein; M, cells with air spaces,
A, between them; L, cells of
lower epidermis; S, stoma or
mouth-like opening; g, guard
cell.

Problem. To discover the structure and properties of living
matter. {Laboratory Manual, Proh. V; Laboratory Problems,
Prob. 19.)

20

COMPOSITION OF LIVING THINGS

Cells. — Living things, when viewed under a compound mi-
croscope, are found to be made up of tiny units of structure, or
cells, each separated from its neighbors by a very delicate
membrane or a wall. The inside of the cell is composed of gray-
ish semifluid matter which seems to contain innumerable granules

of various sizes and shapes. This sub-
stance is known as protoplasm (pro'td-
plazm), and usually contains a struc-
ture known as the nucleus (nti'kle-us).
Within the nucleus are tiny bits of
matter which, when the cell is stained
with logwood or other dyes, take up
the stain more readily than the sur-
rounding material and hence are called
chromosomes (kro'm6-somz), which
means " color-bearing bodies. '^ A dis-
tinction is usually made between the
protoplasm within the nucleus and that
within the rest of the cell body, the
latter being called cytoplasm (si't6-
plazm). A cell may be defined as a
unit of structure in all living things, a
tiny mass of living matter usually con-
taining a nucleus.
The cell is surrounded by a very delicate living structure
called the cell membrane. Outside this membrane a wall is
formed by the activity of the protoplasm in the cell. These
cell walls, in plants, are of ceVlulose or wood.

How Cells form Others. — A cell grows to a certain size and
then splits into two new cells. In this process, which is of very
great importance in the growth of both plants and animals, the
chromosomes divide first. Each chromosome splits lengthwise
and the parts go in equal numbers to each of two nuclei
formed from the old nucleus. The chromosomes are believ-ed to
be the bearers of the qualities which can be handed down from
plant to plant and from animal to animal; in other words, the
inheritable qualities which make the offspring like its parents.
Lastly, a cell wall is developed dividing the cytoplasm, and two

A typical cell, composed of
protoplasm. The cell may be of
almost any shape. M, cell wall
or cell membrane; N, nucleus;
n, nucleolus; V, vacuole; F,
food or other substance.

CELLS

21

new cells are formed. This process is known as cell division.
It is the usual method of growth found ^ in the tissues of
plants and animals.

Cells of Various Sizes and Shapes. — Plant cells and animal
cells are of very diverse shapes and sizes. There are cells so
large that they can
easily be seen with the
unaided eye; for ex-
ample, the root hairs of
plants and eggs of some
animals. On the other
hand, cells may be so
minute that, as in the
case of the plant cells
named bacteria, a mil-
lion could be placed ^ . ...

. , . , . , Stages in the division of one cell to form two

Wltnin tniS letter O. cells. Note the separation of the chromosomes in
The forms of cells may ^^® nucleus. Which part of the cell divides first?

be extremely varied in different tissues; they may assume the
form of cubes, columns, spheres, flat plates, or may be extremely
irregular in shape. One kind of tissue cell has a body so small
as to be quite invisible to the naked eye, although it has a pro-
longation several feet in length. Such are some of the cells of
the nervous system of man and other large animals, as the ox,
elephant, and whale.

Varying Sizes of Living Things. — Plant cells and animal
cells may live alone or they may form collections of cells. Some
plants are so simple in structure as to be formed of only one
kind of cells. Usually living organisms are composed of several
groups of different kinds of cells. The size of the cells does not
seem to bear any relation to the size of the organism, but larger
organisms are made up of more cells. The human body, for ex-
ample, is composed of untold millions of cells, while some simple
plant or animal m-ay be composed of a very few cells or even
a single cell.

Relation to Organic and Inorganic Matter. — The cells of
which we have been speaking are examples of organic matter.
They live and grow and in doing so make use of the inorganic

22 COMPOSITION OF LIVING THINGS

matter covering the earth, as air, water, and soil. Plants and ani*
mals make their homes in earth, air, or water; they take in the
oxygen of the atmosphere; they take in water; but in the main
the food of animals consists of organic matter. Green plants,
on the other hand, manufacture most of their food out of the
inorganic matter contained in the soil, air, and water, and then
change this food into the hving matter of their own bodies.
This organic matter in turn may become food for animals.

Chemical Composition of Protoplasm. — Living matter, when
analyzed by chemists in the laboratory, seems to have a very
complex chemical composition. It is somewhat like a protein in
that it always contains the element nitrogen. It also contains
the elements carbon, hydrogen, oxygen, and a little sulphur.
Calcimn, iron, silicon, sodium, potassium, phosphorus, and other
mineral matters are usually found in very minute quantities in
its composition. We believe that the matter out of which plants
and animals are formed, although a very complex building ma-
terial and almost impossible of correct analysis, is composed of
the above-named elements. What is of far more importance to
us is the fact that it is distinguished by certain properties which
it possesses and which inorganic matter does not possess.

Properties of Protoplasm. — The properties of protoplasm are
as follows : — •

(1) It is irritable: it responds to influences or stimuli which
come to it from outside its own substance. Both plants and
animals are sensitive to touch or stimulation by light, heat, or
electricity. Green plants turn toward the source of light.
Some animals are attracted, and others are repelled by light.

(2) Protoplasm has the power to move and to contract. Mus-
cular movement is a familiar instance of this power. Plants
move their leaves and other organs.

(3) Protoplasm can take in, digest, and make food over into its
own substance. This process is known as nutrition. As a result
of this process the organism grows.

(4) Protoplasm, be it in the body of .a plant or of an animal,
uses oxygen. It breathes. Thus substances taken into the body
may be oxidized, and release energy for movement and the other
activities of plants and animals.

PROTOPLASM 23

(5) Protoplasm has the power to rid itself of waste materials,
especially those which might be harmful to it. A tree sheds its
leaves, and as a result gets rid of the accumulation of mineral
matter in the leaves. Plants and animals alike pass off the car-
bon dioxide which results from the very processes of living, the
oxidation of parts of their own bodies. Animals eliminate
wastes containing nitrogen through the skin and the kidneys.

(6) Protoplasm can reproduce, that is, form other matter like
itself. New plants are constantly appearing to take the places of
those that die. The supply of living things upon the earth is
not decreasing; reproduction is constantly taking place.

(7) Protoplasm has, as we shall see later, certain other physical
properties which help explain certain functions of plants and
animals.

Summary. — To sum up, we find that living protoplasm has
the properties of sensibility, motion, growth, and reproduction
both in its simplest state as a one-celled plant or animal and when
it enters into the composition of a highly complex organism
such as a tree, a dog, or a man. The cells in these organisms
have the same general structure in plants as in animals (with
the exception of certain minor differences that we shall see
later). Protoplasm is composed of the same chemical elements
that are found in the air, water, soil, and in organic foods. How
protoplasm is made from non-living matter is a wonderful story,
a part of which we shall hear later.

Problem Questions. — 1. Why are living things called or-
ganisms ?

2. Explain the terms function, adaptation, organ, tissue.

3. Describe from the diagrams a cell and show how it divides.

4. What is the chemical composition of protoplasm?

5. Discuss the properties of protoplasm.

Problem and Project References

Atkinson> First Studies of Plant Life, Chapter XI. Ginn and Company.

Conn, Biology, Chapters I, II. Silver, Burdett and Company.

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Sedgwick and Wilson, General Biology. Henry Holt and Company.

Shull, Principles of Animal Biology, Chapter III. McGraw-Hill Company^

Sharpe, A Laboratory Manual. American Book Company.

Stevens. Plant Anatomy, Chapter I. P. Blakiston's Sons and Company.

IV. FLOWERS AND THEIR WORK

Problem. The structure and work of the parts of a flower,
{Laboratory Manual^ Proh. VI; Laboratory Problems, Probs.

12, 21, 22.)

Structure of a Simple Flower. — You have all seen in winter
a branch of a tree bearing buds. It would not be difficult to

imagine that some of the buds are
to form branches while others
form flowers. Such is really the
case. A flower is a shortened
branch made for the purpose of
producing seeds for the plant.
Our problem will be to learn
something of the structure and
uses of the parts of a very simple
flower. The expanded portion of
the flower stalk, which holds the
parts of the flower, is called the
receptacle.

The Floral Envelope, — The
small green leaflike parts cover-
ing the unopened flower are called
se'pals. All together they make
the calyx (ka'lix). The sepals
come out in a circle or whorl on
the flower stalk. The more
brightly colored structures are
the pefals. They form the
corol'la. The corolla is of im-
portance, as we shall see later, in
making the flower conspicuous.
The Essential Organs, — A flower, however, could live with-
out sepals or petals and still produce seeds, the work for which it

24

A typical flower, cut lengthwise
to show all parts. Compare with the
picture of a flower on page 31. R,
receptacle; S, sepal; P, petal; St,
stamen; Pi, pistil. The stamen con-
sists of a stalklike filament / and a
boxlike anther a, which holds the
pollen. The pistil is made up of an
enlarged ovary o, a stalk or style st,
and a terminal stigma s.

STRUCTURE OF A FLOWER

25

exists. The essential organs of the flower are within the so-called

floral envelope. They consist of the stamens (sta'menz) and jpistily

the latter being in the center of the flower. The stamens have

knobbed ends and are arranged in a circle around the pistil.

The stalk of the stamen is called the fiVament

and the knobbed end is the an'ther, which is

in reality a hollow box which produces a large

number of little grains called pol'len. It is

necessary for the reproduction of new plants

that the pollen grains get out of the anther.

Each pistil is composed of a rather stout base

called the o'vary, containing the o'vules which

later may form the seeds, a stalklike structure

called the style, and the stigma, which is the

upper end of the style, and in some cases is

broadened. The surface of the stigma usually

secretes a sweet fluid in which grains of pollen

from flowers of the same kind can grow.

Pollen. — Pollen grains of various flowers,
as seen under the microscope, differ greatly
in form and appearance. Some are relatively
large, some small, some rough, others smooth,
some spherical, and others angular. They all
agree, however, in having a thick wall, with a
thin membrane under it, the whole inclosing
a mass of protoplasm. At an early stage the
pollen grain contains but a single cell. Later,
however, we can distinguish two nuclei in the protoplasm.

Growth of Pollen Grains. — Under certain conditions a pollen
grain will germinate; that is, burst open and grow a threadlike
projection called the pollen tube; see Figure. . Two nuclei enter
this tube. One of them, the tube nucleus, disappears after a
time. The second, germinative nucleus, divides to form two
sperm nuclei.

Fertilization of the Flower. — If we cut the pistil of a large
flower (as a lily) lengthwise, we notice that the style appears to
be composed of rather spongy material in the interior; the
ovary is hollow and is seen to contain a number of rounded

Pollen grains, in
section; oTie is ger-
minating. T, tube
nucleus ; *b', sperm
nuclei.

HUNT. KEW ES. 3

26

FLOWERS AND THEIR WORK

Pg—

structures which appear to grow out from the wall of the ovary.
These are the ovules. The ovules, under certain conditions, be-
come seeds. An explanation of these conditions may be had if
we examine, under the microscope, a very thin section of a pis-
til on which pollen has begun to germinate. The central part
of the style is found to be either hollow or composed of a soft
tissue through which the pollen tube can easily grow. Upon

germination, the pol-
len tube grows down-
ward through the
spongy center of the
style, follows the path
of least resistance to
the space within the
ovary, and there en-
ters an ovule. It is
believed that some
chemical influence at-
tracts the pollen tube.
The sperm cell pen-
etrates an ovule by
making its way
through the hole made
by the pollen tube,
called the micropyle
(mi'cr6-pil), and then
grows toward a clear
bit of protoplasm
known as the em'hryo
sac. The embryo sac
is an ovoid space,
microscopic in size,
filled with semifluid
protoplasm containing several nuclei. (See Figure.) One of the
nuclei, with the protoplasm immediately surrounding it, is called the
egg cell. It is this cell that the sperm cell of the pollen tube grows
toward; ultimately the sperm cell reaches the egg cell and unites
with it. The union of the nucleus of the sperm cell with the nucleus

A flower cut lengthwise to illustrate fertiliza-
tion: pg, germinating pollen grain which forms a
pollen tube pt and grows down through the spongy
style and through the micropyle m into the em-
bryo sac within the ovary o. The sperm nucleus
s is about to unite with an egg nucleus e to form
a fertilized egg.

CROSS-POLLINATION 27

of the egg cell in the ovary is known as fertilization. The single
cell formed by the union of the sperm cell and the egg cell is
now called a fertilized egg.

When the two cells unite to form a fertilized egg, this egg,
by constant divisions of the cells, forms an embryo or baby
plant. This is contained in the seed and, as we know, will de-
velop into an adult plant if given proper environmental con-
ditions.

Problem. A study of cross-pollination and some means of
bringing it about. (Laboratory Manual, Prob. VII; Laboratory
Problems, Probs. 13, 14, 15.)

(a) Adaptations in the flower.

(b) Adaptations in an insect agent.

(c) Other agents.

History of the Discoveries regarding Pollination of Flowers.

— Although the ancient Greek and Roman naturalists had some
vague ideas on the subject of fertilization, it was not until the
latter part of the eighteenth century that it was demonstrated
that pollen is necessary for the growth of the embryo within
a seed. In the latter part of the eighteenth century a book ap-
peared in which a German named Conrad Sprengel worked out
the facts that the structure of certain flowers seemed to be
adapted to the visits of insects. Certain facilities were offered
to an insect in the way of easy foothold, sweet odor, and es-
pecially food in the shape of pollen and nectar, the latter a
sweet-tasting substance manufactured by certain parts of the
flower known as the nectar glands. Sprengel further discov-
ered the fact that pollen could be and is carried by the insect
visitors from the anthers of the flower to its stigma. It was
not until the middle of the nineteenth century, however, that
an Englishman, Charles Darwin, worked out the true relation
of insects to flowers by his investigations upon the cross-pollina-
tion of flowers. By pollination we mean the transfer of pollen
from an anther to the stigma of a flower. Self-pollination is the
transfer of pollen from the anther to the stigma of the same flower;
cross-pollination is the transfer of pollen from the anthers of one
fl,ower to the stigma of another flower of the same hind. Many

28

FLOWERS AND THEIR WORK

species of flowers are self-pollinated and do not do as well in
seed production if cross-pollinated, but Charles Darwin found
that some flowers which vs^ere self-poflinated did not produce as
many seeds, and that the plants which grew from their seeds
were smafler and weaker than plants from seeds produced by
cross-polhnated flowers of the same kind. He also found that
plants grown from cross-polKnated seeds tended to vary more
than those grown from self -pollinated seed. This has an im-
portant bearing, as we shall
see later, in the production
of new varieties of plants.
Microscopic examination of
the stigma at the time of
pollination also shov/s that
the pollen from another
flower germinates more quick-
ly than the pollen which has
fallen from the anthers of the
same flower. This latter fact
in most cases renders it
unlikely for a flower to pro-
duce seeds by its own pollen.
Darwin worked for many
years on the pollination of
many insect- visited flowers,
and discovered in almost
every case that showy, sweet-
scented, or otherwise attrac-
tive flowers were adapted or
fitted to be cross-polHnated
by insects. He also found that, in the case of flowers that
were inconspicuous in appearance, often a compensation ap-
peared in the odor which rendered them attractive to certain
insects. The so-called carrion flowers, pollinated by flies, are
examples, their odor being like that of decayed flesh. Other
flowers, which open at night, are white and provided with a
powerful scent so as to attract night-flying moths and other
insects. Flowers adapted to be cross-pollinated by insects are

A wild orchid, a flower of the type
from which Charles Darwin worked out
his theory of cross-pollination by insects.

CROSS-POLLINATION

29

frequently irregular in shape. Thus butter and eggs is a flower
which is well fitted for cross-pollination by insects.

Suggestions for Field Work. — At this point, at least one field trip
should be introduced for the purpose of studying under natural conditions
the cross-polhnation of flowers by insects. Directions for a field trip will
be found in Hunter's Laboratory Problems in Civic Biology, pages 39-43.

Insects as Pollinating Agents. — No one who sees a hive of
bees with their wonderful communal life can fail to realize that
these insects play a great part in the life of the flowers near the

The bee is adapted for carrying pollen. How? A, dorsal view of bee; B, front
view of head; m, mouth parts; C, a leg, showing the pollen basket p. Note the
feathery hairs on the upper joints of the leg.

hive. A famous observer named Sir John Lubbock tested bees
and wasps to see how many trips they made daily from the hive
to the flowers, and found that the wasp went out on 116 visits
during a working day of 16 hours, while the bee made almost
as many visits, and worked only a little less time than the wasp
worked. It is evident that in the course of so many trips to
the fields a bee must light on and cross-pollinate many hundreds
of flowers.

Study of a Bee. — The body of a bee (and of all other insects)
is divided into three parts. Attached to the middle part (the

30 FLOWERS AND THEIR WORK

tho'rax) are three pairs of jointed legs and two pairs of tiny-
wings. By the legs and the jointed body Ave are able to dis-
tinguish insects from other animals. If we look closely at the
bee, we find the body and legs more or less covered with tiny
hairs; especially are these hairs found on the legs. When a plant
or animal structure is fitted to do a certain kind of work, we say it
is adapted to do that work. The joints in the leg of the bee adapt
it for complicated movements; the arrangement of stiff hairs along
the edge of a concavity in one of the joints of the leg forms
a structure well fitted to hold pollen. In this basket pollen is col-
lected by the bee and taken to the hive to be used as food. But
while gathering pollen for itseK, the bee catches pollen on the hair
and other projections on its body and legs and carries it from
flower to flower. Thus cross-pollination may be effected.

Pollination not intended by the Bee. — The cross-pollination
of flowers is not planned by the bee; it is simply an incident in
the course of the food gathering. The bee visits a large number
of flowers of the same species during th^ course of a single trip
from the hive, and it is then that cross-pollination takes place.

Suggestions for Field Work. — In any locality where flowers are abun-
dant, try to answer the following questions: Plow many bees visit the lo-
caUty in ten minutes? How many other insects alight on the flowers? Do
bees visit flowers of the same kind in succession, or fly from one flower on
a given plant to another on a plant of a different kind? If the bee alights
on a flower cluster, does it visit more than one flower in the same cluster?
How does a bee alight? Exactly what does the bee do when it alights? Try
to decide whether color or odor has the most effect in attracting bees to
flowers. Sir John Lubbcck tried an experiment which it would pay a num-
ber of careful pupils to repeat. He placed a few drops of honey on glass
slips and placed them over papers of various colors. In this way he found
that the honeybee, for example, could evidently distinguish different colors.
Bees seemed to prefer blue to any other color. Flowers of a yellow or flesh
color were preferred by flies. It would be of considerable interest for some
student to work out this problem with our native bees and with other
insects. Test the keenness of sight in insects by placing a white object (a
white golf ball will do) in the grass and see how many insects will alight
on it. Try to work out some method by which you can decide whether a
given insect is attracted to a flower by odor alone.

The Sight of the Bumblebee. — The large eyes located on the
sides of a bee's head are made up of a large number of little units,

CROSS-POLLINATION

31

each of which is considered
to be a very simple eye. The
large eyes are therefore called
the compound eyes. All insects
are provided with compound
eyes, with simple eyes, or, in
most cases, with both. The
simple eyes of the bee may
be found by a careful ob-
server between and above
the compound eyes.

One would suppose that
with so many eyes the sight
of insects would be extremely
keen, but such does not seem
to be the case. Insects can,
as we have already learned,
distinguish differences in color
at some distance; they can

Front view of the head of a fly. The
compound eyes are at the sides. Photo-
graph from American Museum of
Natural History, New York.

see moving objects, but they do not seem to be able to make
out form well. To make up for this, they appear to have an

extremely well-developed sense
of smell. Insects can distin-
guish at a great distance odors
which to the human nose are
imperceptible. Night-flying in-
sects, especially, find the flow-
ers by the odor rather than by
color.

Nectar and Nectar Glands. —
The bee is attracted to a flower
fcr food. This food may consist
of pollen or nec'tar. Nectar is
a sugary solution that is formed
in the flower by little collec-
tions of cells called the nectar
A my: p petal; .-S stamen (anther); glands. The nectar glands are

bEP, sepal; St, pistil (stigma). No- ^ ^

tice the nectar guides ou the petals. USUally SO placed that tO reach

32

FLOWERS AND THEIR WORK

them the insect must first brush the stamens and pistil of the
flower. Frequently the location of the nectaries (nectar glands'!
is made conspicuous by brightly colored markings on the corolla
of the flower. The row of dots in the tiger lily is an example.

Mouth Parts of the Bee. — The mouth of the bee is adapted to
take in the foods we have mentioned, and is used in this way, for
the same purposes that a man would use the hands and fingers.
The honeybee laps or sucks nectar from flowers, it chews the pollen,
and it uses part of the mouth as a trowel in making the honey-
comb. A glance at the Figure, page 29, shows us that the mouth
parts of the bee are complex. The parts consist of a pair of

very small jaws or mandibles,
certain other structures, max-
il'lcBj part of the lower lip
called the labial palps, and
a long tongue-like structure
called the lig'ula. The uses
of the mouth parts may be
made out by watching a bee
on a well-opened flower.

Other Flower Visitors. —
Other insects besides the bee
are pollen carriers for flowers.
Among the most useful are
moths and butterflies. Both
of these insects feed only on
nectar, which they suck
through a long tubelike pro-
boscis (pro-bos'is). The heads
and bodies of these insects
are more or less thickly cov-
ered with hairs, and the wings
are thatched with tiny hairlike scales. Ah these structures are
of some use to the flower because the}^ collect and carry pollen;
but the palp, a fluffy structure projecting from each side of the
head of a butterfly, collects a large amount of pollen, which
is deposited upon the stigmas of other flowers when the butterfly
pushes its head down into the flower tube after nectar.

Long-billed humming birds: above, one
at rest; below, one gathering nectar.
Photograph from American Museum of
Natural History.

CROSS-POLLINATION

33

Flies and a few other insects are agents in cross-pollination.
Humming birds (picture, p. 32) are also active agents in some
flowers. Snails are said in rare instances to carry pollen. Man
and the domesticated animals pollinate a few flowers by brush-
ing past them through the fields.

Butter and Eggs. — From July to October butter and eggs, a
very abundant weed, may be found especially along roadsides and
in sunny fields. It bears a tall and conspicuous flower cluster
known as a spike, the yellow and orange flowers being arranged
so that they come out directly from the main flower stalk^

The corolla projects into a spur on the lower side; an upper
two-parted lip shuts down upon a lower three-parted lip. The
four stamens are in pairs, two long and two short.

Certain parts of the corolla which are more brightly colored than
the rest of the flower, serve as a guide to insects. This flower is
visited most frequently by bumble-
bees, which are guided by the orange
lip to alight just where they can push
their way into the flower. The bee,
seeking the nectar secreted in the spur,
brushes its head and shoulders against
the anthers. On visiting another flower
of the cluster, it would be an easy
matter accidentally to transfer this
pollen to the stigma of that flower. In
this way cross-pollination is effected.

Insects may also cause self-pollina-
tion by rubbing against the upper pair
of stamens, thus depositing some pol-
len on the stigma as they back out of
the flower.

Cross-pollination of a Head (Clover). — In a head, which is
a closely massed cluster of little flowers, as the clover, cross-
pollination is usually effected by bumblebees which rapidly work
from one flower to another in the same group, inserting their
tongues deep into the flower cups.

Cross-pollination of a Composite Head. — The composite head is
made clear by a daisy, aster, or sunflower. This head has an

Cross-pollination of butter
and eggs by a bumblebee: A,
anther; S, stigma; N, nectar
spur.

34

FLOWERS AND THEIR WORK

outer circle of green parts which look like sepals, but in reality-
are a whorl of leaflike parts. Taken together these form an

Composite head. Photograph of gail-
lardia by Albert E. Butler, from Ameri-
can Museum of Natural Historic New
York.

Section of daisy; a composite
head. R, ray flower; D, disk flow-
er; /, involucre; s, stigma; a, an-
thers; 0, ovary.

involucre (in'vo-lu-ker). In-
side the involucre is a whorl
of brightl}^ colored, irregular
flowers called the ray flowers.
Thej^ appear to act, in some
instances at least, as an at-
traction to insects by show-
ing a definite color (see the common dogwood). The flowers
occupying the center of the cluster are the disk flowers. Pollen

is carried easily from one flower to
another even by an insect which crawls.

Adaptations to prevent Self-pollination.
— In some flowers, as is shown by the
primulas of our hothouses, the stamens
and pistils are each of two different
lengths in different flowers. Short styles
and long or high-placed filaments are
found in one flower, and long styles with
short or low-placed filaments in another.
Pollination is most likely to be effected
b}^ some of the pollen from a low-placed
anther reaching the stigma of a short-
styled flower, or by the pollen from a
high anther being placed upon a long-
Flowers which have this pe-

Section of dandelion,
showing two flowers: h,
colored leaflike bract sur-
rounding the flower; st,
stigma; s, style; a,
anthers; o, ovary. What gtyjed pistil
makes the dandelion head

conspicuous i

culiar condition are said to be dimorphic

CROSS-POLLINATION

35

Stamens (light) and pistils (dark), and course
of cross-pollination in loosestrife, a trimorphic
flower.

(Greek = of two forms). There are, as in the case of the
loosestrife, trimorphic flowers, having pistils and stamens of
three lengths.

In many kinds of
flowers we find that
the stamens ripen be-
fore the pistils, or just
the opposite may hap-
pen. Such a condition
effectually prevents
self-pollination. This
condition is called di-
chogamy (dl-c6g'a-mi).

Other examples.
Many other examples
of adaptations to secure cross-pollination by means of the visits
of insects might be given. The mountain laurel, which makes
our hillsides so beautiful in late spring, shows a remarkable
adaptation in having the stamens caught in little pockets of
the corolla. The weight of the visiting insect on the corolla
releases the anther of the stamen from the pocket in which it
rests, the anther opens, and the body of the visitor
is dusted with pollen.

Still another example of cross-pollination is
found in the yucca, a desert-loving semitropical
lily. In this flower the stigma is above the anther,
and the pollen is sticky and could not be trans-
ferred except by insect aid. A little moth, called
the pro'nuba, gathers pollen from an anther, flies
away with this load to another flower, there deposits
eggs in the ovary of the pistil, and then rubs its
load of pollen over the stigma of the flower. The
young hatch out and feed on some of the young
nating pistil of seeds which have been fertilized by the pollen placed
yucca. on the stigma by the mother, and then bore out of

the seed pod and escape to the ground, 'leaving the plant to
develop the remaining seeds without further molestation.
The pollination of the fig shows another wonderful example

36 FLOWERS AND THEIR WORK

of adaptation The fig" is not a fruit but a cluster of fruits,
growing inside the inturned ends of a fleshy flower stalk. There
may be three kinds of flowers in the clusters, some bearing
stamens only, some with pistils only with long styles, and others
with' short styles. Some fig flower clusters have long-styled
pis'tillate flowers only, others contain both short-styled and
stam'inate flowers, the latter above the pistillate flowers. All
of these flowers are visited by a Httle wasp. When it visits the
short-styled and staminate fig it lays its eggs in the ovary, which
it can easily reach with its egg-depositing organ (the ovipositor).
The females which hatch work their way out and in doing so
inrush against the staminate flowers, thus coUecting poUen on
their bodies. They then seek other figs in order to lay their
eggs. If a wasp reaches another short-styled flower cluster the
eggs are laid and development takes place as before. But if it
flies to a long-styled cluster it cannot reach the ovary to deposit
its eggs. In both cases, however, the wasp has carried poUen to
the stigma and pollination takes place with the subsequent
development of seeds. The figs we eat are the ones developed
from the long-styled pistillate flowers.

Pollination by the Wind. — Not aU flowers are dependent
upon insects for cross-pollination. Many of the earliest spring
flowers appear almost before the insects do. In many trees,
such as the oak, poplar, and maple, the flowers open before
the leaves come out. Such flowers are dependent upon the
wind to carry the pollen from the stamens of one flower to the
pistil of another.

Among the adaptations that a wind-poUinated flower shows
are: (1) The development of very many pollen grains to each
ovule. In one of the insect-pollinated flowers, that of the night-
blooming cereus, the ratio of pollen grains to ovules is about
eight to one. In flowers which are to be pollinated by the wind,
a large number of the poUen grains never reach their destina-
tion and are wasted. Therefore in these plants several thou-
sands, perhaps hundreds of thousands, of pollen grains will be
developed to every ovule produced. Such are the pines. In
May and early June the ground under pine trees is often yellow
with pollen, and the air is filled with the pollen dust for miles

CROSS-POLLINATION

37

from the trees. The same is true, also, with many of the
grasses, including corn or maize.

(2) The anthers are usually held high and exposed to the
wind when ripe. The common plantain and timothy grass are
excellent examples.

Cross-pollination of com by the wind.

(3) The pistil of the flower is pecuHarly fitted to retain the
pollen by having feathery projections along the sides which
increase the surface of the stigma. This can be seen in
grasses. In the Indian corn the stigma is the so-called silk
which protrudes beyond the covering of modified leaves which
form the husk of the ear of corn. All our grains, wheat, rye,
oats, and others, have the typical feathery pistil of the wild
grasses from which they have been developed.

(4) The corolla is often entirely lacking. It would only be
in the way in flowers that are dependent upon the wind to carry
pollen.

Imperfect Flowers. — Some flowers, the wind-poUinated ones
in particular, are imperfect; that is, they lack either stamens or
pistils. In such flowers, cross-pollination must of necessity be
depended upon. If only stam'inate flowers (those which con-
tain only stamens) are developed on one plant, and only

38

FLOWERS AND THEIR WORK

pis'tillate flowers (those which bear only pistils) on another,
we call the species dioecious (di-e'shus). A common example

is the willow.

a-

Other species have staminate
and pistillate flowers on the
same plant. In this case they
are said to be monoecious (m(5-
ne'shus). The oak, hickory,
beech, birch, walnut, and
chestnut are familiar examples.

Protection of Pollen. — Pol-
len, in order to be carried
effectively by the wind, insects,
or other agencies, must be dry.
In some flow^ers the irregular

Pistillate flower P, and staminate flow- form of the COrolla protects the
er S, of the willow; h, bract; o, ovary; ^^ ^ -, <-,,i

St, style; s, stigma; /, filament; a, anther. PoUen from dampneSS. Other

flowers close up at night, as
the morning-glory and four-o'clock. Still others, as the bell-
flower, droop during a shower or at night.

Pollen is also protected from insect visitors as ants, plant
lice, or other small crawling insects which would carry off pollen
but give the flower no return by cross-pollinating it, by hairs
which are developed upon the filaments or on the corolla.
Sometimes a ring of sticky material is found making a barrier
around the stalk underneath the flower. Many other adapta-
tions of this sort might be mentioned.

Artificial Cross-pollination and its Practical Benefits to Man.
— Artificial cross-pollination is practiced by plant breeders and
can easily be tried in the laboratory or at home. First the
anthers must be carefully removed from the bud of the flower
so as to eliminate all possibility of self-pollination. The flower
must then be covered so as to prevent access of pollen from
without; when the pistil is sufficiently developed, pollen from
another flower, having the characteristics desired, is placed on the
stigma and the flower again covered to prevent any other pollen
reaching the flower. The seeds from this flower when planted
may give rise to plants with some characteristics of each of

CROSS-POLLINATION 39

the plants from which the pollen and egg cell came. Naturally
the two plants cross-pollinated must be of the same or of closely
allied species. If they are of different species or varieties, the
new plants produced are called hy'hrids. It is this kind of work
that made Luther Bur bank famous. An excellent project report
might be made on his work by reading Harwood's New Creations
in Plant Life.

Summary. — In summarizing this chapter we find (1) that
seeds are produced as a result of the fertilization of the egg cell
by the sperm cell in the ovary of a flower; (2) this is brought
about by pollination; (3) pollination may be self (within the
flower) or cross (from the anthers of one flower to the stigma
of another flower, usually of the same species) ; (4) that insects
as well as other agents may bring this about; and (5) that there
are many adaptations within flowers to prevent self-pollination,
the chief of which are:

The stamens and pistils may be found in separate flowers, either
on the same or on different plants.

The stamens may produce pollen before the pistil of the same
flower is ready to receive it, or vice versa.

The stamens and pistils may be so placed with reference to each
other that pollination can be brought about only by outside assistance.

Problem Questions. — 1. What is the use of a flower?

2. What is fertilization ? How is it accomplished in a flower ?

3. Mention some adaptation in insects to help bring about
cross pollination in flowers.

4. Discuss three types of adaptations to insure cross-pollina-
tion in flowers.

5. What are some practical benefits from cross-pollination?

Problem and Project References

Atkinson, First Studies of Plant Life, Chapters XXV-XXVI. Ginn and Com-
pany.
Dana, Plants and their Children, pages 187—255. American Book Company.
Darwin, Orchids Fertilized by Insects. D. Appleton and Company.
Hunter, Laboratory Problems in Civic Biology. American Book Company.
Lubbock, Flowers, Fruits and Leaves, Part I. The Macmillan Company.
Lubbock, British Wild Flowers. The Macmillan Company.
Milller, The Fertilization of Flowers. The Macmillan Company.
Sharpe, A Laboratory Manual. American Book Company.

V. FRUITS AND THEIR USES

Problem. A study of fruits to discover —

(a) Their uses to a plant.

(b) How they are scattered.

(c) Their protection from animals and other enemies.
(Laboratory Manual, Prob. VIII; Laboratory Problems, Probs.

23, 21^)

A Typical Fruit, — the Pea or Bean Pod. — If a withered
flower of any one of the pea or bean family is examined care-
fully it will be found that the pistil of the flower continues to
grow after the rest of the flower withers. If we examine the
pistil from such a flower we find that it is the ovary that has
enlarged. The space within the ovary has become almost filled

sti...

sty...])

A, B, C, stages in the formation of fruit of pea; Z>, E, F, corresponding stages
in apple fruit; c, calyx; p, petals; st, stamens; sti, stigma; sty, style; ov, ovary;
/, funiculus; fr, valve of pod; s, seed.

with a number of ovoid bodies, attached along one edge of the
inner wall. These we recognize as the young seeds.

The pod of a bean, pea, or locust illustrates well the growth
from the flower. The flower stalk, the ovary, and the remains
of the style, the stigma, and the calyx, can be found on most

40

A TYPICAL FRUIT

41

unopened pods. If the pod is opened, the seeds will be found
fastened to the ovary wall each by a little stalk called the
funic'ulus. That part of the ovary wall which bears the seeds
is the jplacen'ta. The walls of the pod are called valves.

The pod, which is in reality a ripened ovary with other parts
of the flower attached to it, is considered a fruit. By defini-
tion, a fruit is a ripened ovary together with any parts of the flower
that may he attached to it. The chief use of the fruit is to hold
and to protect the seeds; it may ultimately distribute them
where they can reproduce young plants.

Formation of Seeds. — Each seed has been formed as a direct
result of the fertilization of the egg cell (contained in the embryo
sac of the ovule) by a sperm cell of the pollen tube.

Young pine trees near the parent tree. Photograph from U. S. Department of

Agriculture.

Seed Dispersal.^ — If you will go out any fall afternoon into
the fields, a city park, or even a vacant lot, you can hardly

^At this point a field trip may well be taken with a view to finding out how
the common fall weeds scatter their seeds. Fruits and seeds obtained upon this
trip will make a basis for laboratory work on the adaptations of seed and fruit for
dispersal.

HUNT. NEW ES. — 4

42

FRUITS AND THEIR USES

escape seeing how seeds are scattered by the parent plants and
trees. Several hundred little seedling trees may be counted often
under the shade of a single maple or oak tree. But nearly all
these young trees are doomed to die, because of the overshading
and crowding. Plants, like animals, are dependent upon their
surroundings for food and air. They need light even more than
animals need it, because the soil directly under the shade of the
old tree gives only raw food material to the plants, and they
must have sunlight in order to make food. This overcrowding is
seen in the garden where young beets or lettuce plants are grow-
ing. The gardener assists nature by thinning out the young plants
so that they may not be handicapped in their battle for life in the
garden by an insufficient supply of air, light, and food.

It is evidently of considerable advantage to a plant to be able
to place its progeny at a considerable distance from itself, in
order that the young plants may be provided with sufficient
space to get nourishment and foothold. This is the result
which plants have to accomplish. Some accomplish the result

more completely than others,
and thus are the more suc-
cessful ones in the battle of
Hfe.

Adaptations for Seed Dis-
persal;- Fleshy Fruits with
Hard Seeds. — Plants are
fitted to scatter their seeds
by having the special means
either in the fruit or in the
seed. Various agents, as the
wind, water, or squirrels,
birds, and other animals,
make it possible for the seeds to be taken away from the
plant.

Fleshy fruits, that is, such fruits as contain considerable water
when ripe, are eaten by animals and the seeds passed off un-
digested. Most wild fleshy fruits have small, hard, indigestible
seeds. Birds are responsible for much seed planting of berries
and other small fruit. Bears and other berry-eatmg animals aid

The blackberry, a fruit having small seeds
scattered by birds.

SEED DISPERSAL

43

in this as well. Some seeds have especial adaptations in the
way of spines or projections. Insects make use of these projec-
tions in order to carry them away. Ants plant seeds which
they have carried to their nests for a food supply. Nuts are
planted by squirrels and blue jays.

Suggestions for Field Work. — Examine the fruit of huckleberry, black-
berry, wild strawberry, wild cherry, black haw, wild grape, tomato, currant.
Report how many of the above have seeds with hard coatings. Notice
that in most, if not in all, edible fruits, the fruit remains green, sour, and
inedible until the seeds are ripe. In the state of nature, how might this
be of use to a plant?

Hooks and Spines. — Some fruits which are dry and have a

hard external covering when ripe possess hooks or spines which

enable the whole fruit to be carried away from

the parent plant by animals or other moving

objects. Cattle are responsible for the spread

of some of our worst weeds in this way. The

burdock and clotbur are familiar examples.

In both the mass of little hooks is all that

remains of an involucre. Thus the whole fruit

cluster may be carried about and seeds scat-
tered. In many of the Composites, as
in the cockleburs and beggar's-ticks, the
fruits are provided with strong curved
projections which bear many smaller
hooklike barbs.

Pappus. — Probably the most impor-
tant adaptations for dispersal of seeds
are those by which the fruit is fitted for
dispersal by the wind. That much-
loved and much-hated weed, the dande-
lion, is an example of a plant in which
the whole fruit is carried by the wind.
The parachute, or pappus, is an out-
growth of the ovary wall. Many other
fruits, notably that of the Canada thistle,

are provided with the pappus as a means of getting away. In

the milkweed the seeds have developed a silky outgrowth which

Cocklebur. Notice
the curved hooks.

Dispersal of dandelion
fruits.

44

FRUITS AND THEIR USES

may carry them for miles. In New York city the air some-
times contains the down from these seeds, brought from far
over the meadows of New Jersey by the prevaihng westerly
wind.

Dehiscent Fruits and how they Scatter Seeds. — One of the
many methods of scattering seeds is seen in dry fruits. These
simply split to allow the escape of the seeds. Examples of
common fruits that split open, called dehiscent (de-his'ent) fruits,
are seen in the fol'lide of the milkweed, a fruit which splits along
the edge of one valve, the pod or leg'ume of the pea and the bean,

Dehiscent fruits: A, green pea pod, with valves twisting and expelling the seeds;
B, milkweed follicle; C, Jimson vv^eed capsule.

and the capsule of Jimson weed and the evening primrose. The
wild geranium, a five-loculed capsule, splits along the edge of
each locule, snaps back, and throws the seed for some distance.
Jewelweed and witch-hazel fruits burst open in a somewhat
similar manner.

Winged Seeds. — The seeds of the pine, held underneath the
scales of the cone, are prolonged into wings, which aid in their
dispersal. The seeds of many of our trees are thus scattered.
Can you name five trees that have winged seeds?

Other Methods. — Sometimes whole plants are carried by
the high winds of the fall. The tumbleweed, as it dries, assumes

SEED DISPERSAL

45

a somewhat spherical shape; the main stalk breaks off, and the
plant may then be blown along the ground, scattering seeds as
it goes, until it is ultimately stopped by a fence or bush. A
single plant of Russian
thistle may thus scatter
over two hundred thou-
sand seeds.

Seeds or fruits (for
example, the coconut)
may fall into the water
and be carried thou-
sands of miles to their
new resting place, the
fibrous husk providing a
boat in which the seed
is carried.

Other seeds collect
the mud along the

in

banks of ponds and
streams. Birds which
come there to feed
carry away many seeds
in the mud attached to
their feet. The great English naturalist, Charles Darwin, raised
eighty-two plants from seeds thus carried by a bird. It is prob-
able that most of the vegeta-
tion on the newly formed
coral islands of the Pacific
Ocean has come from seeds
brought to them by birds and
by water.

Indehiscent Fruits. — Dry
fruits which do not split open to allow of the escape of their
seeds are known as in' dehiscent fruits. Such are nuts, one-seeded
fruits with usually hard outer covering, the so-called key fruits of
the maple or ash, and many others. Corn, wheat, oats, etc., are
indehiscent fruits. A grain is simply a one-seeded fruit in which
the wall of the ovary has grown so close to that of the seed that

Various methods of seed dispersal: A,
clematis fruit; B, clot bur; C, beggar's-tick; D,
squirting cucumber ejecting seeds after absorb-
ing water until the pressure is sufficient to push
out the stopperlike stem; E, wild geranium
discharging seeds.

The acorn, a nut in which the involucre
partly covers the fruit.

46

FRUITS AND THEIR USES

they cannot be separated. Some indehiscent fruits are light and
carried by the wind; others may be scattered by animals.

Large Numbers of Seeds. — Plants which do not have especial
means for scattering their seeds may make up for this by pro-
ducing a large number of seeds. The Jimson
weed is a familiar example of such a plant.
Each capsule of Jimson weed contains from
four hundred to six hundred seeds, depend-
ing upon its size. If ail of these seeds de-
veloped, the whole earth would soon be cov-
ered with Jimson weed, to the exclusion of
aU other forms of plant life. That this is
not the case is due to the fact that only
those seeds which are advantageously placed
can develop; the others will, for various
reasons (lack of moisture to start the young
seed on its way, poor soil, lack of air or sun-
light, overcrowding), fail to germinate.

The Struggle for Existence. — Those
plants which provide best for their young
are usually the most successful in
life's race. Plants which combine
with the ability to scatter many
seeds over a wide territory the ad-
ditional characteristics of rapid
growth, resistance to dangers of ex-
treme cold or heat and to attacks of
parasitic enemies, inedibility, and
peculiar adaptations to cross-pollination or self-pollination, are
usually called weeds. They flomish in the sterile soil of the
roadside and in the fertile soil of the garden. By means of rapid
growth they kill other plants of slower growth by usurping their
territory. Slow-growing plants are thus actually exterminated.
Many of our common weeds have been introduced from other
countries and have, through their numerous adaptations, driven
out other plants which stood in their way. Such is the Rus-
sian thistle. First introduced from Russia in 1873, it spread so
rapidly that in twenty years it bad appeared as a common

Grain; spikes of rip-
ened flowers.

Key fruit of maple.

ECONOMIC VALUE OF FRUITS 47

weed over an area of some twenty-fiye thousand square miles.
It is now one of the greatest pests in our Northwest.

Problem. To learn something about the economic value of some
fruits. {Laboratory Manual, Prob. IX; Laboratory Problems,
Prob. 85.)

Economic Value of Grains. — Our grains are the cultivated
progeny of wild grasses. Domestication of plants and animals
marks epochs in the advance of civilization. The man of the
stone age hunted wild beasts for food, and lived like one of them
in a cave or wherever he happened to be; he was a nomad, a
wanderer, with no fixed home. He may have discovered that
wild roots or grains were good to eat; perhaps he stored some
away for future use. Then came the idea of growing things at
home instead of digging or gathering the wild fruits from the
forest and plain. The tribes which first cultivated the soil made
a great step in advance, for they had as a result a fixed place
for habitation. The cultivation of grains or cereals gave them
a store of food which could be used at times when other food was
scarce. The word '^ cereal " (derived from Ceres, the Roman
goddess of agriculture) suggests the importance of this crop to
Roman civilization. From earliest times the growing of grain
and the progress of civilization have gone hand in hand. As
nations have advanced in power, their dependence upon the
cereal crops has been greater and greater.

'* Indian corn," says John Fiske, in The Discovery of America,
" has played a most important part in the discovery of the New
World. It could be planted without clearing or plowing the
soil. There was no need of threshing or winnowing. Sown in
tilled land, it yields more than twice as much food per acre as
any other kind of grain. This was of incalculable advantage to
the English settlers in New England, who would have found it
much harder to gain a secure foothold upon the soil if they had
had to begin by preparing it for wheat or rye."

To-day, in spite of the great wealth which comes from our
mineral resources, live stock, and manufactured products, the
surest index of our country's prosperity is the size of the wheat
and corn crop.

48

FRUITS AND THEIR USES

Corn. — More than three bilhon bushels of corn were raised
in the United States in the year 1920. This figure is so enor-
mous that it has but httle meaning to us. In the past half
century our corn crop has increased over 350 per cent. Illinois
and Iowa are the greatest corn-producing states in this coun-
try, each having a yearly record of over four hundred million
bushels.

Indian corn is put to many uses. It is a valuable food. It
has a large proportion of starch, from w^hich glucose and al-

Corn-producing regions in the United States.

cohol are made. It contains some oil, which is used for food,
as a lubricant, and for making soap. The leaves and stalk are
an excellent fodder; they can be made into paper and packing
material. Mattresses can be stuffed with the husks. The pith
is used as a protective belt placed below the water line of
our huge battleships. Corncobs are used for fuel, one hundred
bushels having the fuel value of a ton of coal.

Wheat. — Wheat is the crop of next greatest importance in
this country. Nearly eight hundred millions of bushels were
raised here in 1920, representing a value of nearly $1,000,-
000,000. Seventy-two per cent of all the wheat raised comeg

ECONOMIC VALUE OF FRUITS

49

from the North Central States and California. Much of the
wheat crop is exported, nearly half of the exports going to
Great Britain. Wheat is used chiefly after being manufactured
into flour. The germ, or young wheat plant, is sifted out
during this process and made into breakfast foods. Flour-

Wheat-producing regions.

making forms the chief industry of Minneapolis, Minnesota,
and of several other large and wealthy cities in this country.

Other Grains. — Of the other grains or cereals raised in this
country, oats are the most important crop, over one and one
half billion bushels having been produced in 1920. Illinois, Wis-
consin, Minnesota, and Iowa together produce over 50 per cent
of the total yield. Oats are distinctly a northern crop, over
95 per cent being grown north of the parallel of 36°. Barley is
a staple of some of the northern countries of Europe and Asia.
Although a hardy cereal, almost three fourths of the total pro-
duction in the United States comes from California, Minnesota,
Wisconsin, Iowa; the production of these states may be roughly
estimated as 200,000,000 bushels.

Rye is the most important cereal crop of northern Europe,

50

FRUITS AND THEIR USES

Russia, Germany, and Poland producing over 50 per cent of the
world's supply. It makes the principal food for probably one
third the people of Europe, being made into '' black bread."
It is of relatively less importance as a crop now in the United
States than in former years, only 70,000,000 bushels being pro-
duced in 1920.

Perhaps one of the most important grain crops for the world,
although relatively unimportant in the United States, is rice.
Its fruit, after threshing, screening, and milling, forms the prin-
cipal food of one third of the human race. Moreover, its stems
furnish straw, its husks make a bran used as food for cattle,
and the grain, when distilled, is rich in alcohol.

Nearly related to the grains are grasses. The United
States has a forage crop (exclusive of corn stalks) of over 100,-
000,000 tons, valued at nearly $1,000,000,000. The best hay in
the eastern part of the country comes from dried timothy grass
and clover, the stems and leaves as well as the fruits forming
the so-called hay. In some parts of the West a kind of clover
called alfalfa is much grown, as it is adapted to the semi-arid
conditions of that part of the country.

Cotton-producing regions.

ECONOMIC VALUE OF FRUITS

51

Cotton. — Among our fruits cotton is probably that of the
most importance to the outside world. The United States pro-
duces over thi'ee fourths of the world's cotton supply, and a
large proportion of the crop is exported. Nearly 12,000,000
bales were raised in 1920.

The cotton plant is essentially a warmth-loving plant. Its
commercial importance is gained because the seeds of the fruit
have long filaments attached to them. Bunches of these fila-
ments, after treatment, are easily twisted into threads from
which are manufactured cotton cloth, muslin, calico, and cam-
bric. In addition to the fiber,
cottonseed oil, a substitute
for olive oil, is made from the
seeds, and the refuse makes an
excellent fodder for cattle.

Cotton Boll Weevil. — The
cotton crop of the United
States has been threatened
rather recently with destruc-
tion by a beetle called the
cotton boll weevil. This in-
sect, introduced from Mexico
in 1894, has now spread over
almost the entire cotton-
raising area of the South. It
bores into the young pod of
the cotton and develops there,
stunting the growth of the
fruit to such an extent that seeds may not be produced. The
loss in Texas alone has been estimated at over $10,000,000 a
year. This weevil, because of the protection offered by the
cotton boll, is very difficult to exterminate. The weevils are
destroyed by birds, the infected bolls and stalks are burned,
millions are killed each winter by cold, they are the prey of
other insects; but at the present time they are one of the
greatest pests the South knows. The best method of fighting
them seems to be planting the cotton early so that it will ripen
before the boll weevil matures.

Chamber for fumigating imported
bales of cotton at Boston, Massachu-
setts, to guard against the entry of the
pink boll worm, another great pest.

52

FRUITS AND THEIR USES

Garden Fruits. — Green fruits and vegetables have come to
play an important part in the dietary of man. People in this
country are beginning to find that more vegetables and less meat
are better than the meat diet so often used.

Some of the niost important fleshy fruits — squashes, cucum-
bers, pumpkins, and melons — are examples of the pepo (pe'po)
type of fruit; tomatoes and peppers are tj^pes of berries in
botanical language, for a berry is any soft or juicy fruit con-

Various tj^pes of fruits: A, berry (pepper); B, pepo (cucumber); C, drupe
or stone fruit (cherry); D, pome (pear); E, aggregate fruit made up of drupelets
(raspberry).

taining small seeds. The so-called berries — strawberries, rasp-
berries, and blackberries — of our gardens bring in an annual in-
come of $25,000,000 to our fruit raisers. Beans and peas are
important as foods because of their relatively large amount of
protein. Canning green corn, peas, beans, and tomatoes has
become an important business.

Orchard and Other Fruits. — In the United States over
175,000,000 bushels of apples are grown every year. Pears,
plums, apricots, peaches, and nectarines also are raised in large
orchards, especially in California. Nuts form one of our im-
portant articles of food, largely because of the great amount of
protein contained in them.

The grape crop of the world is commercially valuable, because
of the raisins and wine produced. Lemons, oranges, and grape-

ECONOMIC VALUE OF FRUITS 53

truit are of commercial value ' in this country as well as in other
parts of the world. Figs, ohves, and dates are staple foods in
the Mediterranean countries and are sources of wealth to the
people there, as are coconuts, bananas, and many other fruits
in tropical countries.

Beverages and Condiments. — The coffee and cocoa *^ beans,"
both products of tropical regions, form the basis of two very im-
portant beverages of civilized man. Coffee is a stimulant, while
cocoa and chocolate rank high in food value. Black and red
pepper, mustard, allspice, nutmegs, cloves, and vanilla are all
products of various fruits or seeds of tropical plants.

Summary. — This chapter has shown us that fruits hold seeds,
that the destiny of the plant depends largely upon the adapta-
tions which the plant has for scattering its seeds. Hence we
find varied devices in fruits and seeds for getting the seeds placed
as far as possible from the parent plant.

To man seeds and fruits have a commercial and economic
value. Man's life on the earth may be said to depend largely
upon his control over the cereal crops.

Problem Questions. — 1. What are the parts of a typical fruit?

2. Classify the adaptations in fruits for scattering seeds.

3. Classify devices in seeds for scattering.

4. Name five pairs of seeds and fruits which have the same
method of dispersal.

5. Explain why three different weeds are so plentiful.

6. Make a classification of fruits, giving characteristics of
each group.

7. Discuss the economic importance of five different crops in
the United States.

Problem and Project References

Beal, Seed Dispersal. Ginn and Company.

Brigham and McFarlane, Essentials of Geography. American Book Company.

Dana, Plants and their Children, pages 27-49. American Book Company.

Duncan, Home Vegetables and Home Fruits. Charles Scribner's Sons.

Fisher, Resources and Industries of the United States. Ginn and Company.

Hodge, Nature Study and Life, Chapters X, XI. Ginn and Company.

Hunter, Laboratory Problems in Civic Biology. American Book Company^

Moore and Halligan, Plant Production, Chapter XII. American Book Company.

Sharpe, A Laboratory Manual. American Book Company.

U. S. Dept. of Agriculture, Farmers Bulletins 78, 154, 218, 225, 255, 334, 408, 818.

VI. SEEDS AND SEEDLINGS

Problem. A study of seeds in their relation to the new plant.
{Laboratory Manual, Prob. X; Laboratory Problems, Probs.
42 to 50.)

(a) The relation of the young plant to its food supply.

(6) How the young plant makes use of its food supply.

Relation of Flower to Fruit. — We have already found in our
study of the fruit that the bean pod is a direct outgrowth from
the flower. It is, in fact, the ovary of the flower, with the part
immediately surrounding it, which has grown larger to make a
fruit.

Use of Fruit. — The fruit holds and protects the seeds until
the time comes when they are able to germinate and produce

new plants like the original plant
from which they grew. Then, as
we have seen, it may help to scat-
ter them far and wide.

The Bean Seed. — We have
already been able to identify in
the pod of the bean the style,
stigma, and ovary of the flower.
The opened pod discloses the
seeds lying along one edge of the
pod, each attached by a little
stalk to the inner wall of the
ovary. If we pull a single bean
from its attachment, we find
that the stalk leaves a scar on the coat of the bean; this scar
is called the hilum (hi'lum). The tiny hole near the hilum is
the micropyle. Turn back to the Figure (p. 26) showing the fertiU-
zation of an ovule. Find there the little hole through which the
pollen tube reached the embryo sac. This hole or micropyle
remains and is found in the seed. The thick outer coat, or

54

spyle-

Vil

ura

plixmul

Wpocoty!

B

A bean seed: A, entire; B, after
removing the testa or outer coat
and one cotyledon.

FOOD IN THE BEAN SEED 55

testa, is easily removed from a soaked bean; the delicate inner
coat may escape notice. The part of the bean remaining seems
to consist of two parts, which are called the colyledoiis (kot-i-
le'dunz); but if you separate them very carefully, you find the)
following structures between them. The rodlike part is called
hypocotyl (hi-po-kot'il, meaning under the cotyledons). This will
later form the root and part of the stem of the young bean
plant. The first true leaves, very tiny structures, are folded
together between the cotyledons and are known as the plu'mule
or epicofyl (meaning above the cotyledons). The parts of the
seed within the seed coats all together form the embryo or young
plant. A bean seed contains, then, a tiny plant tucked away
between the cotyledons and protected by a tough coat.

Food in the Cotyledons. — The problem now before us is to
find out how the embryo of the bean is adapted to grow into
an adult plant. Up to this stage of its existence it has had the
advantage of food and protection from the parent plant. Now
it must begin the battle of life alone. We shall find in all our
work with plants and animals that the problem of food supply
is always the most important problem to be solved by the grow-
ing organism. Let us see if this embryo is able to get a start
in life (similar to that which many animals get in the egg) from
food provided for it within its own body.

Starch in the Bean. — If we mash up a little piece of a bean
cotyledon which has been previously soaked in water, and test
for starch with iodine solution, the character-
istic blue-black color appears, showing the
presence of starch (p. 14). If a httle of the
stained material is mounted in water on a
glass slide under the compound microscope,
we find that the starch is contained in little
ovoid bodies called starch grains. The starch
grains and other food products are made use cells ^S a^T^an:^ cw,

of by the growing plant. cell wall; sg, starch

Starches and sugars make up the great ^^^^"'
class of nutrients known as carbohydrates. Of these we shall
learn more when we take up the study of foods. (The teacher
may here refer to the chapter on Foods.)

56

SEEDS AND SEEDLINGS

Protein in the Bean. — Another nutrient present in the bean
cotyledon is 'protein, as may be proved by a test with nitric acid
and ammonium hydrate as directed on page 15.

The cotyledon contains not less than 23
per cent of protein, 57 per cent of carbohy-
drates, and about 2 per cent of fats.

Beans and Peas as Food for Man. — The
young plant within a pea or bean seed is
well supplied with nourishment which it
uses during its germinating, or until it is
able to take care of itself. In this respect
it is somewhat like a young animal within
the egg, a bird or fish, for example. So
much food is stored in leg'umes (as beans
and peas are named) that man has come to
consider them a very valuable and cheap
source of food.

Corn. — The ear of corn is not a single
fruit, but a large number of fruits in a
cluster, like a bunch of bananas, for ex-
ample. The husk of an ear of corn is sim-
ply a covering of leaflike parts which has
grown over the young fruits for their better
protection. The corncob is the much thick-
ened flower stalk on which the flowers were
clustered. The so-called silk of corn is
nothing more than a long style and stigma.
The corn grain itself was also part of the
flower — the same part that formed the pod
of the bean with its contained seeds. The
corn grain is a complete fruit and not
merely a seed.

Structure of a Grain of Corn. — Exami-
nation of a well-soaked grain of corn discloses a difference in
the two flat sides of the grain. A light-colored area found on
one surface marks the position of the embryo; the rest of the
grain contains the food supply. The scar marking the former
attachment of the silk is found near the outer edge of the grain.

Longitudinal section
of young ear of corn: O,
the fruits; *S, the stig-
mas; SH, sheathlike
leaves; ST, the flower
stalk or peduncle.
(After Sargent.)

FOOD SUPPLY OF CORN

57

A grain cut lengthwise perpendicular to the flat side and then
dipped in weak iodine shows two distinct parts, an area con-
taining considerable starch, the en'dosperm, and the embryo or
young plant. Careful inspection shows the hypocotyl and plu-
mule appearing as two points (the latter pointing up toward the
free end of the grain) and a part surrounding them, the single
cotyledon (see Figure). Here again we have an example of a
fitting for future needs, for in this fruit the one seed has
at hand all the food material necessary for rapid growth,
although the food is stored outside the embryo.

Endosperm the Food Supply of Corn. — We do not find that
the one cotyledon of the corn grain serves the same pxKpose
to the young plant as do the two
cotyledons of the bean. Although
we find a little starch in the corn
cotyledon, still it is evident from
our tests that the endosperm is the
chief source of food supply. The
study of a thin section of the corn
grain under the compound micro-
scope shows us that the starch
grains in the outer part of the en-
dosperm are large and regular in
size, while those near the edge of
the cotyledon are much smaller and irregular, having large holes
in them. We know that the germinating grain has a much
sweeter taste than that which is not growing. This is noticed
in sprouting barley or malt. We shall find later that, in order
to make use of starchy food, a plant or animal must in some
manner change it over into sugar. This change is necessary
because starch cannot be absorbed by the young plant, while
sugar can be.

Starch changed to Grape Sugar in the Corn. — That starch
is changed to grape sugar in the germinating corn grain can
easily be shown in the following way. Cut lengthwise through
the embryos of half a dozen grains of corn, place them in a test
tube with some Fehling's solution, and heat to the boiling point.
As no reaction occurs, no grape sugar is present in ungerminated

HxTNT. New Es. — 6

Grain of com, in section and
side view: E, endosperm; C,
cotyledon; P, plumule; H, hy-
pocotyl.

58

SEEDS AND SEEDLINGS

corn. Treat in the same way a half dozen grains of corn which
have germinated, and they will give a brick red color showing
the presence of sugar along the edge of the cotyledon and between
it and the endosperm.

Digestion. — This change of starch to grape sugar in the corn
is a process of digestion. Test a bit of unsweetened cracker
(which we know contains starch) with Fehling's solution to
show that no grape sugar is present. Chew some of the cracker
a short time and notice that it will begin to taste sweet. Test
the chewed cracker with Fehling's solution, and grape sugar will
be found. Here again a process of digestion has taken place.
Both in the corn and in the mouth, the change from starch to grape
sugar is brought about by the action of peculiar substances known

as digestive ferments, or enzymes
(en'zimz), and the result is that sub-
stances which before digestion would
not dissolve in water are now soluble.
The Action of Diastase on Starch.
— The enzyme found in the coty-
ledon of the corn, which changes
starch to grape sugar, is called
di'astase. It may be separated from
the cotyledon and used in the form
of a powder.

To a little starch in half a cup of
water we add a very little (1 gram)
diastase and put the vessel contain-
ing the mixture in a warm place,
where the temperature will remain
nearly constant at about 98° Fahren-
heit. On testing part of the con-
tents at the end of half an hour,
we find that some of the starch has
been changed to grape sugar. The
next morning we find that the starch
has been almost completely changed. Starch and warm water,
under similar conditions will not react to the test for grape
sugar.

The use of the endosperm to
corn: A, seedlino; with endo-
sperm removed ; B, normal seed-
ling; C, seedling with starch st
in place of endosperm.

COTYLEDONS

59

Suggested Experiment. — Germinating corn grains, if deprived of their
endosperm, soon die. But if the endosperm is removed and a Uttle corn-
starch paste is stuck to the embryo in place of the endosperm, the develop-
ment will be but little affected (see Figure, p. 58). Evidently the enzyme
formed in the cotyledon has the power to digest the starch paste, and the
cotyledon transfers the digested food to the growing parts of the embryo.

A hardwood forest showing representative
dicotyledonous trees.

A pine seedling.
Note the number of
cotyledons.

Other Foods in Corn Grain. — Other foods are present in the
corn grain. A test for protein shows a considerable amount
of this food. Oil also is found, and a small amount of mineral
matter.

Monocotyledons, Dicotyledons, and Polycotyledons. — Plants
that bear seeds having but a single cotyledon are called mono-
cotyle'dons. Although we find many monocotyledonous plants in
this part of the world, the group is characteristic of the tropics.
Sugar cane and many of the large trees, such as the date palm,
palmetto, and banana, are examples. Among the common mono-

60 SEEDS AND SEEDLINGS

cotyledons of the north temperate zone are corn, lily, grass, and
asparagus.

DicotyWdons, or plants having two cotyledons in the seed, are
those with which we come in contact most frequently in daily
Hfe. Many of our garden vegetables, peas, beans, squashes, melons,
etc., all of our great hardwood forest trees, beech, oak, birch,
chestnut, and hickory, used for the ^Hrim" of houses, all of our
fruit trees, pears, apples, peaches, and plums, and, in fact, a very
large proportion of all plants Uving in the north temperate zone,
are dicotyledons.

A third type of plant, with several cotyledons, is the group
called the poly cotyle' dons, represented by the pines and their
kin. Such plants furnish most of the lumber and shingles used
in the construction of frame houses. The soft woods (as the
pines, hemlocks, spruces, and other '' evergreens ") are also of
much value in the manufacture of paper. The wood-pulp in-
dustry has grown to such proportions as to be a menace to our
softwood forests.

Problem. A study of the factors necessary for awakening
{germinating) the embryo within the seed. {Laboratory Manual^
Prob. XI; Laboratory Problems, Probs. 33 to 37,)

(a) The part played by moisture,

(6) The function of temperature,

(c) The use of oxygen,

(d) The use of food.

In making a series of experiments it is important to keep the
conditions uniform, varying only the one we are testing.

External Factors which determine the Growth of Seeds. —
We know that a dry seed, after lying dormant and apparently
dead for months and sometimes for years, will, when the proper
stimuli are apphed to it, wake up and show signs of Hfe. Some-
thing from outside the seed must evidently start the growth of
the little embryo within the seed coats. There are several
factors which are absolutely necessary for germination, as this
beginning of growth is called.

Water a Factor. — We can prove that the bean seed will
take up a considerable amount of water and that it swells
during the process. Fill a flowerpot almost to the top with dry

GERMINATION

61

beans, cover them securely as shown in the following illustration,
and place the flowerpot in water overnight. The force exerted
by the swelling seeds is sufficient to break the flowerpot. A
dry seed will not germinate.
The exact amount of water
which is most favorable for
the germination of a seed can
be determined only by careful
experiment. An oversupply
of water will prevent growth
of seeds almost as effectually
as no water at aU. In gen-
eral the amount most favor-
able for germination is a
moderate supply.

Moderate Temperature is
Best. — Another factor influ-
encing the germination of seeds is that of temperature. The
temperature at which different varieties of seeds germinate varies
greatly. As a general rule, increase in temperature is favorable

The expansive force of germinating
seeds. The flowerpot to the left was
filled with dry beans, a block of wood
wired on, and the whole apparatus placed
in a pail of water overnight. The result
is shown at the right.

Effect of water upon the growth of trees. The trees were all planted at the same
time in soil that is sandy and uniform. They are irrigated by a small stream rim-
ning from left to right. Most of the water soaks in before reaching the last trees.

62

SEEDS AND SEEDLINGS

up to a certain point, beyond which it is injurious to the young

plant, and seeds exposed to a moderate temperature do better

in the long run than those in the heat.

Light has a certain marked effect on young seedlings, which

will be considered when we take up the growth of the stem in

more detail.

Some Part of the Air a Factor. — It is an easy matter to

prove that peas or beans will not germinate without a supply

of air. Equal numbers of
soaked peas, placed in two
flasks, one tightly stoppered,
the other having no stopper,
with identical conditions of
hght, temperature, and mois-
ture, show that the seeds in
both flasks start to germinate,
but that those in the closed
flask soon^stop growing while
the others continue to grow
almost as well as similar seeds

Experiment to show that some part of placed in an Open dish.

^^T'^^'^T^^fZ^. Why did not the seeds in

A test of the air in B shows an excess of the closed flask germinate?
carbon dioxide; how do you account for ^^ ^^^^ ^^^^ ^^^^ ^^ ^.^j^^g^
this?

the energy contained in a piece
of coal it must be burned or oxidized. This requires a constant
supply of fresh air containing oxygen. The seed, in order to
release from its food supply the energy necessary for growth,
requires oxygen, so that the oxidation of food may take place.
Hence a constant supply of fresh air is an important factor in ger-
mination. It is necessary that air should penetrate between the
grains of soil around a seed.

Food oxidized in the Germinating Seed. — But can it be
proved that food substances are burned up during the germi-
nation of the seeds? The hmewater test shows the presence of
carbon dioxide in the closed flask. The carbon in the foodstuffs
of the pea united with the oxygen of the air, forming carbon
dioxide. Growth stopped as soon as the oxygen was exhausted.

GERMINATION

63

The presence of carbon dioxide in the flask is an indication that
a very important process which we associate with animals rather
than plants, that of respiration, is taking plaee.

Internal Factors Necessary for Germination. — We have seen
that stored food is found in the seed and is used by the embryo
in getting a start in Hfe. But to grow it is also necessary that
the embryo be aUve and that aU parts be present. We speak of
the vitahty of a seed, meaning its abihty to germinate. No mat-
ter how favorable the external conditions may be, no growth will
take place unless the embryo is ahve.

Problem. What becomes of the parts of the embryo during growth
into a young plant ? (Laboratory Manual, Prob. XII ; Laboratory
Problems, Prob. 25.)

Germination. — If you plant a number of soaked kidney beans
in damp soil or sawdust and at the end of each day remove

A series of early stages in the germination of a kidney bean. A,
hypocotyl just appearing; B, hypocotyl curving downward; C,
hypocotyl arched, pulling out the cotyledons; D, hypocotyl lifting
cotyledons up, first true leaves appearing; E, cotyledons being used
up, first true leaves expanded, h, hypocotyl; c, cotyledon; p,
plumule.

one, you will be able to obtain a complete record of the
growth of the kidney bean. The first signs of germination are
the breaking of the testa and the pushing outward of the

64

SEEDS AND SEEDLINGS

hypocotyl to form the first root. A little later the hypocotyl "be-
gins to curve downward. An older stage shows the hypocotyl
forming an arch and dragging the bulky cotyledons upward. The
hypocotyl, as soon as it is released from the ground, straightens

out, and the cotyledons are
raised and opened. From
between the cotyledons the
budhke plumule or epicotyl
grows upward, forming the
true leaves and all of the
stem above the cotyledons.
As growth continues, we no-
tice that the cotyledons be-
F come smaller and smaller,
imtil eventually, their food
contents having been ab-
sorbed into the young plant,
they dry up and fall off.
The young plant is now able

Experiment to show the function of the to Care for itself. All the

cotyledonsofthepea:a,plantwithbothcoty- gf^^g^g passed throuoh bv the
ledons, b, with one removed, c, with both re- . , .

moved. A at end of one week; Bat end of yOUng plant, from the time the

three weeks. ^^^^ begins to sprout Until u

can take care of itself by m^ans of its roots and leaveSj are known
OS the stages of germination.

In the pea, hkewise, growth is at first made largely at the
expense of the cotyledons, which never rise above ground.
Removal of the cotyledons from a few germinating peas, and
exposure of these peas to the same conditions as an equal num-
ber that are normal, show that the loss of the cotyledons retards
growth and may result in the death of the seedlings.

Seeds with Endosperm. — In the seeds of the pea and bean
we have found that the embryo takes up all the space within
the seed coats. There are some dicotyledonous plants that have
food stored outside of the embryo. Such a plant is the castor
bean. A section cut vertically through the castor bean discloses
a white oily mass directly under the seed coats. This mass is
called the endosperm. If it is tested with iodine, it will be found

USES OF SEEDS TO THE PLANT

65

to contain starch; oil is also present in considerable quantity.
Within the endosperm lies the embryo, a thin, whitish structm*e.
The Uses of Seeds to the Plant. — Not only does a seed serve
to continue a species of plant in a certain locality, but it serves
to give the plant a foothold in new places. Moving to a new
home may be accompHshed, as we shall see later, to a limited
degree by cuttings, grafting, and in other ways, but the usual
way is by the production and dispersal of seeds. Seeds blown
by the wind, carried by animals, or distributed by a hundred

AiTangement of embryo in its relation to fhe endosperm:
A, asparagus; B, pine; C, castor bean; D, morning glory; E,
peanut, c, cotyledons ; e, endosperm; A, hypocotyl; p, plumule;
t, testa.

devices, work their way to pastures new, there to establish
outposts of their kind.

Inunense numbers of seeds are produced by a single plant.
This is of great economic unportance. A single pea plant may
produce twenty pods, each containing from six to eight seeds.
This would mean the possibiHty of nearly twenty-five thousand
plants being produced from the original parent by the end of
the second season and the rapid ^production of a source of food
for mankind. A plant of Indian corn may yield over fifteen
hundred grains of corn. On the other hand, many weeds pro-
duce seed in still greater numbers. A single capsule of Jimson
weed has been found to hold over six hundred seeds. One milk-
weed may set free over two thousand seeds. The thistle is even
more prolific.

Some seeds, especially those of weeds, are able to withstand
great extremes of heat and cold and still to retain their ability

66

SEEDS AND SEEDLINGS

Milkweed fruit, showing method of seed
dispersal.

to germinate. Some have been known to retain their vitahty
for over fifty years. In plants, the seeds of which show unusual

hardiness, it is found
that the food supply is
often so placed as to
protect the delicate
parts of the embryo
from injury. The food
is in a form not easily
dissolved by water or
broken up by the action
of frost, so that it is
kept in a hard state
until a time when it is
softened by the process
of digestion during the
growth of the plant. It
can be seen that plants
bearing seeds having some of the above characteristics have a
great advantage over plants bearing seeds that are poorly
protected.

Problem. To study some methods of plant breeding. (Labora-
tory Manual, Prob. XIII; Laboratory Problems, Probs. 155
to 158.)

Plant Breeding: Variation of Plants. — Examination of a row
of plants in a garden, of a hundred dandelion plants, or careful
measurements made on the pupils in a classroom, would show
us that no two plants and no two boys or girls have exactly
the same measurements or characteristics. Each plant and
animal tends to vary somewhat from its parent. This universal
tendency among plants and animals is called the law of
variation.

But a plant or animal hands down to its offspring the charac-
teristics which it possesses, usually with only slight variations.
Each one of us resembles our parents or our grandparents more
closely than other persons, and far more closely than individuals
of another race or species. Each plant produced from seed will

PLANT BREEDING

67

be in most respects like the plant which produced the seed. This
is the law of hered'ity.

These two laws, of variation and of heredity, the basis on which
Charles Darwin explained liis theory of evolution, are made use
of by plant and animal breeders. Since plants tend to vary and
since such variations may be continued in their offspring, plant
breeders have helped nature by artificially selecting and prop-
agating the plants showing the characteristics wanted. In this
way most of the varieties of our domesticated plants and
animals have been developed.

Selective Planting. — By selective "planting we mean choosing
the best plants and planting the seed from these plants with a view
to improving the yield.
In doing this we select
not necessarily the
best fruits or grains,
but the seeds from
the best plants. A
wheat plant should be
selected not from its
yield alone, but from
its abihty to stand
disease and unfavor-
able conditions. By
careful seed selection,
some western farmers have increased their wheat production
by 25 per cent. This, if kept up all over the United States,
would mean over $250,000,000 a year in the pockets of the
farmers.

Boys and girls who have gardens of their own can easily try
experiments in selection with almost any garden vegetable.
Corn is one of the best plants to experiment with. Gather for
planting only the fullest ears and those with the largest kernels.
You must also select from the plants those that produce the
most ears. Plant these carefully selected corn grains in a plot
by themselves in the garden, and compare their yield with that
of the nonselected corn. The above picture shows what can be
done by selection. Plants thus produced may become, by gradual

a b

Improvement of corn by selection: a, improved
type; b, original type from which it was developed.

68 SEEDS AND SEEDLINGS

changes through many generations, new varieties of the original
species from which they sprang.

Hybridizing and Other Methods. — We have already seen
that pollen may be carried from one flower to another of the
same species, and produce seeds. If pollen from one plant be
placed on the pistil of another of an allied species or variety,
fer'tihzation may take place and new plants be eventually pro-
duced from the seeds. Such plants are called hy'brids.

Hybrids are extremely variable and often are apparently much
unhke either parent plant. Such are some of the results of
Luther Burbank's work with the hybrid plums, the Department
of Agriculture experunents in the crossing of oranges and lemons,
and the formation of thousands of new varieties of garden plants
of various kinds — beans, peas, tomatoes, and the hke. By far
the greatest possibihties for the farmer or fruit grower seem to
come from hybridizing.

Another method of obtaining new varieties of plants is that
discovered by a Dutchman named Hugo de Vries. He found
that a great variation might arise suddenly (instead of by
gradual changes), thus producing a new variety which would at
once breed true. Such a variation is called inutation, and the
plant showing the new character is called a mutant. This law is
of great value to breeders, as new plants or animals considerably
unhke their parents may thus be formed and perpetuated. In
1862 a Mr. Fultz, of Pennsylvania, found three heads of beard-
less or bald wheat while passing through a large field of bearded
wheat. He saved them, sowed them by themselves, and pro-
duced a quantity of wheat now^ loiown favorably all over the
world as the Fultz wheat. The seedless orange is another
example of a mutant.

Still more important is the discovery made by the monk Gregor
Mendel. By experimenting with peas he found the laws under
which certain characteristics are passed on to the descendants.
Some of these unit characters, such as color of the pea, the shape
of the pods, and smoothness of coat, always appear in certain
proportions in the offspring, and some characters tend to dis-
appear rather than others, when peas having different characters
are cross bred. These facts have been so carefully worked out

PLANT BREEDING 69

that we know just what will happen if we cross breed certain
plants having definite characteristics. It is to be expected that
by a more extensive study of ''Mendel's laws" plant breeders
will be able to produce desired characters and to predict exactly
what will happen as a result of cross breeding.

Summary. — We have found that within the seed a baby plant
or embryo exists. Either packed around the embryo (as endo-
sperm) or as a part of it (the cotyledons) is the food supply.
When external conditions of temperature, moisture, and supply
of oxygen are favorable, the embryo is awakened to activity and
passes through the stages of germination.

We have seen also how the two factors of heredity and varia-
tion have produced new varieties of plants in the hands of
scientific breeders.

Problem Questions. — 1. What are the chief differences be-
tween the bean and corn? Are they both seeds?

2. What is digestion? How is it brought about? Why is
it necessary?

3. How are the forms of plants determined by their seeds?

4. What are the factors which influence germination? How
do they do this?

5. What becomes of each part of a kidney bean after germi-
nation ?

6. What are the uses of seeds to a plant? to man?

7. Discuss three factors in plant breeding. j

Problem and Project References

Atkinson, First Studies of Plant Life, Chapters I, II, III, XXV. Ginn and Com-
pany.
Bailey, Plant Breeding. The Macmillan Company.

Dana, Plants and their Children, pages 50-98. American Book Company.
De CandoUe, Origin of Cultivated Plants. D. Appleton and Company.
Downing, The Third and Fourth Generation. University of Chicago Press.
Harwood, New Creations in Plant Life. The Macmillan Company.
Hunter, Laboratory Problems in Civic Biology. American Book Company.
Hunter and Whitman, Civic Science in the Community. American Book Company.
Moore and Halligan, Plant Production. American Book Company.
Sharpe, A Laboratory Manual. American Book Company.
Stevens, Plant Anatomy, Chapter XII. P. Blakiston's Sons and Company.
U. S. Department of Agriculture, Various Year Books if available will give much
good project material. Look over list of Farmers Bulletins for topics.

VII. ROOTS AND THEIR WORK

Problem. A study of roots, to find out —

(a) Factors influencing direction of growth.

(b) Their structure.

(c) How they absorb soil water.

(Laboratory Manual, Prob. XIV: Laboratory Problems, Probs
51 to 57.)

The development of a bean seedling shows us that the root
invariably grows firstc One of the most important functions of the

root to a plant is that of a hold-
fast, an anchor to fasten it in
the place where it is to develop.
In this chapter we shall find
several other uses of the root to
the plant: the taking in of
water, with the mineral and
organic matter dissolved therein,
the storage of food, climbing, etc.
But all functions other than the
one first stated arise after the
young plant has begun to de-
velop.

Root System. — If you dig up
a young bean seedling and care-
fully wash the roots, you will see
that a long root is developed
as a continuation of the hypocotyl. This root is called the
primary root. Roots growing from the primary are called sec-
ondary, and the roots growing from the latter are tertiary roots.
The smallest branchings are called rootlets. Collectively all the
roots and rootlets make up a root system.

Downward Growth of Root. Influence of Gravity. — Many
of the roots examined take a more or less downward direction.

70

^

r/ il '^

A root system, showing primary
and secondary roots.

DIRECTION OF GROWTH

71

We are all familiar with the fact that the force called gravity
influences life upon this earth to a great degree. Does gravity
act on the growing root? This question may be answered by a
simple experiment.

Plant mustard or radish seeds in a pocket garden, ^ stand it with
the glass face vertical, and allow the seed to germinate until the
root has grown to a length of about half an inch. Then, keeping
the glass face vertical, turn the pocket garden so that the roots
will be horizontal, and allow it to
remain for one day undisturbed. The
tips of the roots now will be found to
have turned in response to the change
in position, and to point downward.
This experiment seems to indicate
that the roots are influenced to grow
downward by the force called gravity.

The response of the plant (or any
living thing) to gravity is called geot-
ropism (je-ot'ro-pizm). Roots are
stimulated to grow downward; hence
they are said to be positively geotropic
(je-6-tr6p'ik).

Experiments to determine Influ-
ence of Moisture on a Growing
Root. — The roots in the pocket
garden grow downward when all
parts of the blotting paper are equally wet. That moisture has
an influence on the growing root is easily proved.

Plant bird seed or the seed of mustard or radish in the under-
side of a^ sponge, which must be kept wet, and may be sus-
pended by a string under a bell jar in the schoolroom window.

1 The Pocket Garden. — A very convenient form of pocket germinator may be
made in a few minutes in the following manner: Obtain two cleaned four by five
negatives (window glass will do); place one flat on the table and on it place
half a dozen pieces of colored blotting paper cut to a size a little smaller than
the glass. Now cut four thin strips of wood so as to fit on the glass just out-
side of the paper. Next moisten the blotter, place on it some well-soaked radish
or mustard seeds or grains of barley, and cover it with the other glass. The whole
box thus made should be bound together with bicycle tape. Seeds will germinat©
in this box, and with care may live for two weeks or more.

Radish roots in a pocket gar-
den that was turned four times
in the direction of the arrow.

72

ROOTS AND THEIR WORK

Note whether the roots, when they reach the bottom of the
sponge, continue to grow downward, or if the moisture in the
sponge is sufficient to counterbalance the force of gravity and
pull the roots to one side or upward.

Another experiment is the folloT\dng: Divide the interior of a shallow
wooden box into two parts by a partition with an opening in it. Fill the
box with sawdust. Plant peas and beans in the sawdust on one side of the
partition, and water them very slightly, but keep the other side of the box
well soaked. After two weeks, take up some of the seedlings and note the
position of the roots.

Water a Factor determining the Course taken by Roots. —

WoieVj as well as the force of gravity, has much to do with the direc-
tion taken by roots. Water is found
below the surface of the ground,
but sometimes at a great depth.
In order to obtain a supply of
water, the roots of plants frequently
spread out very great distances.
Most trees, and all grasses, have a
greater area of surface exposed by
the roots than by the branches. The
mesquite bush, a low-growing tree
of the American and Mexican
deserts, often sends roots down-
ward for a distance of forty feet
after water. The roots of alfalfa, a
clover-hke plant used for hay in the
western states, frequently penetrate the soil after water for a dis-
tance of ten to twenty feet below the surface of the ground.

Structure of a Taproot. — To understand the structure of the
root, it wiU be easiest for us to examine a large, fleshy one. so
that we may get a httle first-hand evidence as to its internal
structure. A taproot is an enlarged primary root which stores
food — such as a carrot or parsnip. It shows the chief parts in
its composition clearly. If you cut open such a root and make
a cross section of it, you find two distinct areas — an outer
portion, the cortex, and an inner part, the wood. If you cut
another root in lengthwise section, these structures show still

Dandelion root. Notice its length.

STRUCTURE

73

Origin of^^
iecondBiyflootsltf

Cortex

-Epidermis
-Wood

,Xonducting
tubes

"Epidermis

-Cortex
--f¥ood

mare plainly and an additional fact is seen; namely, that all the
secondary roots leaving the main or primary root have a core of
wood which bores its way out

through the cortex wherever the 'Wlif— Leaves

rootlets are given off. The tubes
which conduct the Hquids up in a
parsnip may be located by cuttmg _

off the tip of the root and placing ^^^1^^
the cut end in red ink for twenty-
four hours. Sections of the parsnip
will show the red ink in the wood
and that it is most abundant in
the outer region of the wood just
within the cortex.

Fine Structure of a Root. — If
we could now examine a much
smaller and more dehcate root in Conducting^
thin longitudinal section under the ^^^^^''

compound microscope, we should Lengthwise and cross sections of a

ftnd the entire root to be made up taproot.

of cells, the walls of which are rather thin.^ Over the lower

end of the root, where the growing
tip is located, is found a collection
of cells, most of which are dead,
loosely arranged so as to form a root
cap. This is evidently an adapta-
tion which protects the young and
actively growing cells just under
the root cap, and as it is pointed, it
assists in burrowing a hole through
the earth. In the body of the root
the wood can easily be distinguished
from the surroimding cortex. The
cells of the former have somewhat
thicker walls. A series of tubehke

structures may be found within the wood. These are made of cells

^ Cross sections and longitudinal sections of tradescaaatia roots are excellent for
demonstration of these structures.
ixuNT. New Es. — 6.

t-coprEX

■ ■EPIDERMIS

•GROWINGPOINT
l-'ROOTCAP

Lengthwise section of end of a grow-
ing root, much enlarged.

74

ROOTS AND THEIR WORK

which have grown together end to end, the long axis of the cells
running the length of the main root. In their development these

cells have lost their small ends, and
now form continuous hollow tubes with
rather strong walls. Other cells, which
have developed greatly thickened walls,
give mechanical support to the tubehke
cells. Collections of such tubes, some oj
which conduct fluids wp and others con-
duct fluids down, and supporting woody
cells together make up what are known as
flhrovas' cular bundles.

Root Hairs. ■ — Careful examination
of the root of one of the seedlings of
mustard, radish, or barley grown in
the pocket garden shows a covering of
very minute fuzzy structures which are
at most an eighth or a sixth of an
inch in length. They vary in length
according to their position on the
root, the longest root hairs being found near the point marked
U. H. in the Figure, where they are most numerous also. These
structures, called root
hairs, are outgrowths of
the outer layer of the
root (the epider'mis) , and
are of very great impor-
tance to the living plant.
Structure of a Root
Hair. — A single root hair
examined under a com-
pound microscope will be
found to be a long,
threadhke structure, al-
most colorless in appearance. The cell wall, which is very flexible
and thin, is made up of ceVlulose, a substance somewhat like wood
in chemical composition, through which fluids may easily pass.
If we had a very high power of the microscope focused upon

Young embryo of corn,
showing root hairs {R. H.)
and growing stem (P.).

Diagram of a root hair: CM, cell mem-
brane; CS, cell sap; CW, cell wall; P, cy-
toplasm; N, nucleus; S, soil particles.

HOW THE ROOT ABSORBS WATER

75

this cellulose wall, we should be able to find under it another
structure, far more delicate than the cell wall. This is called
the cell membrane. CHnging close beneath the cell membrane is
the cytoplasm of the cell. The remaining space within the root
hair is more or less filled with a fiuid called cell sap. Forming a
part of the Hving protoplasm of the root hair, sometimes in the
hairhke prolongation and sometimes in that part of the cell
which is in the epidermis of the root, is a nucleus. The cyto-
plasm, nucleus, and cell membrane are ahve; all the rest of the
root hair is dead material, formed by the activity of the hving
substance of the cell. The root hair is part of a living plant cell
with a wall so dehcate that water and mineral substances from
the soil can pass through it into the interior of the root.

How the Root absorbs Water. — The process by which the
root hair takes up soil water can better be understood if we
make an artificial root hair large enough to be easily seen. This
can be done in the following way: Pour some soft celloidin into
a tube vial; carefully revolve the vial so that an even film of
celloidin dries on the inside. Remove the film,
fill with white of egg, and tie over the end of
a rubber cork, through which a glass tube is
inserted. When placed in water, the celloidin
film gives a very accurate picture of the root
hair at work. After a short time the liquid
begins to rise in the tube, water having passed
through the film of celloidin.

Osmosis. — We have all noticed how a drop
of red ink will spread through a glass of clear
water. This is due to the process called diffu^
sion. When two fluids of different density
are separated by a membrane, diffusion will
take place through it. This kind of diffusion
is called osmo'sis. By osmosis two gases or
liquids of different density when separated by a
membrane tend to pass through the membrane
and mingle with each other; but the greater flow is always toward
the fluid of greater density. The method by which the root hairs
take up soil water is osmosis.

An artificial root
hair, showing osmo-
sis taking place.

76 ROOTS AXD THEIR WORK

Passage of Soil Water in the Root. — We have just seen that
in an exchange of fluids by osmosis the greater flow is toward
the denser fluid. Thus it is that the root haii'S take in more fluid
from the soil than they give to it. The cell sap, which partly
fills the interior of the root hair, is a fluid of greater density
than the water in the soil outside. When the root hairs become
filled with water, the density of the cell sap is lessened, and the
cells of the epidermis are thus in a position to pass along their
supply of water to the cells next to them and nearer to the cen-
ter of the root. These cells, in tm'n, become less dense than
their inside neighbors, and so the transfer of water goes on by
osmosis from cell to cell until the water at last reaches the inner
wood. Here it is passed over to the tubes in the woodj" bundles
and started up the stem. The pressm-e created bj^ this process
of osmosis is sufficient to send water up the stem to a distance,
in some plants, of twenty-five to thu't}^ feet. Cases are on record
of water having been raised in the bii'ch a distance of eighty-five
feet.

Physiological Importance of Osmosis. — It is not an exag-
geration to say that osmosis is a process of ^dtal importance
not onh^ to a plant, but to an animal as well. Foods are
digested or changed into a soluble form in an animal so that they
may pass through the walls of the food tube by osmosis and
become part of the blood. Without the process of osmosis we
should be unable to use much of the food we eat.

Capillarity. — The force known as capillarity (kap-i-lar'i-ti)
also accounts for the rise of water in plants and helps it to pass
through soil. If a nmnber of smaU tubes of different bore be
placed end down in a dish of water the water will be found to
rise highest in the tube of smallest diameter, and least in the
largest tube. This is brought about by the adhesion of the mole-
cules of water to the glass. This force acts in the conducting
tubes of plants as well as between the soil particles outside, and
is a verj" probable factor in the transportation of water.

Problem. A study of some of the relations between roots and
the soil. {Laboratory Manual, Proh. XV, Laboratory Problems,
Probs. 58 to 63.)

SOIL

77

(a) Origin of soil.
(h) Kinds of soil,

(c) Water-retaining ability of soil,

(d) Fertility of soils.

(e) The relation between root hairs and soil,
(/) Root tubercles and crop rotation.

Composition of Soil. — If we examine a mass of ordinary loam
carefully, we find that it is composed of numerous particles of
varying size and weight.
Between these particles,
if the soil is not caked
and hard packed, we can
find tiny spaces. In well-
tilled soil these spaces are
frequently formed and
enlarged. They allow air
and water to penetrate
the soil. If we examine
soil under the micro-
scope, we find consider-
able water cHnging to
the soil particles and forming a delicate film around each parti-
cle. In this manner most of the water is held in the soil.

Scientists who have made the composition of the earth a
study, tell us that once upon a time at least a part of the earth
was molten. Later, it cooled into soHd rock. Soil making
began when the ice and frost, alternating with heat, chipped
off pieces of rock. These pieces in time became broken into
fragments by action of ice, glaciers, running water, and the
atmosphere. This process is called weathering. The action of
the air is largely a process of oxidation. A glance at almost any
crumbhng stones will convince you of this, because of the yellow
oxide of iron (rust) disclosed. By slow weathering the earth
became covered with a coating of inorganic soil. Later, genera-
tion after generation of tiny plants and animals which Hved in
the soil died, and their remains formed the first organic mate-
rials of the soil. As time went on, living things of larger si^e
paid their contribution to the organic soil.

Inorganic soil is being formed by weathering.

78

ROOTS AND THEIR WORK

You are all familiar with the difference between the so-called
rich soil and poor soil. The dark or rich soil simply contains
more material from dead plants and animals, and forms the
portion called humus.

Humus contains Organic Matter; Suggestions for Experiments. — It

is an easy matter to prove that black soil contains organic matter, for if
equal weights of carefully dried humus and of soil from a sandy road are

heated red-hot for some
time and then reweighed,
the humus will be found
to have lost considerably
in weight, and the sandy
soil to have lost very
Uttle. The material left
after heating is inorganic,
the organic matter hav-
ing been burned out and
most of the products of
combustion having been
dissipated in the air.

Organic soil holds
water much more readily
than inorganic soil, as a
glance at the Figure on
page 79 shows. If we
fin the vessels with equal
weights (say 100 grams
each) of gravel, sand,
barren soil, rich loam,
and leaf mold, and 25
grams of dry, pulverized
leaves, then pour equal
amounts of water (100
CO.) on each and measure all that runs through, the water that has been
retained will represent the water supply that plants could draw on from
such soils.

The Root Hairs take more than Water out of the Soil. — If

a root containing a fringe of root hairs is washed carefully, it
will be found to have httle particles of soil still clinging to it.
Examined under the microscope, these particles of soil seem to
be cemented to the sticky surface of the root hair. The soil
contains, besides a number of chemical compounds of various

This picture shows how the forests help to cover
the inorganic soil with an organic coating.

SOIL

79

mineral substances, — lime, potash, iron, silica, and many
others, — a considerable amount of organic material. Acids of
various kinds are present in the soil, — such as nitric acid, which
comes from the dead bodies of plants and animals as they decay
and oxidize, — and carbonic acid, formed by the union of the
carbon dioxide from the roots and the water in the soil. These
acids so act upon certain of the mineral substances that they
become dissolved in the water which is afterward absorbed by
the root hairs.

The proportion of each of these mineral materials is very
small compared with the water in which they are found. A very
great amount of water
must be taken up by the
roots in order that the
plant may get the needed
amount of mineral mat-
ter with which to build
its protoplasm.

Plants will not grow
well without certain of
these mineral substances.
This can be proved by
the growth of seedlings in
a so-called nutrient solution. Such a solution contains all the
mineral matter that a plant uses for food; but if certain ingre-
dients are left out the plants placed in the solution will not
live.

Relation of Bacteria to Free Nitrogen. — Plants and animals
need the element nitrogen in order to make protoplasm within
their own bodies. It has been known since the time of the
Romans that the growth of clover, peas, beans, and other
legumes in soil causes the ground to become more favorable for
the growth of other plants. The reason for this has been dis-
covered in late years. On the roots of the plants mentioned are
found Httle swellings or nodules; and in each noduje exist
millions of tiny organisms called bacteria, which take out nitrogen
from the atmosphere and fix it so that it can be used by the
plant; that is, they form nitrates (soluble compounds containing

Experiment to illustrate the kind of soil
which best retains water: A, gravel; B, sand;
C, barren soil; D, rich soil; E, leaf mold;
F, dry leaves.

80

ROOTS AND THEIR WORK

nitrogen) which are useful to plants. Only these bacteria, of all
living things, have the power to take the free nitrogen from the
air and make it over into a form that can be absorbed by the
roots. As all the compounds of nitrogen are
used over and over again, first by plants,
then as food for animals, eventually return-
ing to the soil again, it is evident that any
7iew supply of usable nitrogen must come by
means of these nitrogen-fixing bacteria.

Rotation of Crops. — The facts mentioned
above are made use of by intelligent farmers
who wish to make as much as possible from a
given area of ground in a given time. Such
plants as are hosts for the nitrogen-fixing
bacteria are planted early in the season.
Later these plants are plowed in and a
second crop is planted. The latter grows
quickly and luxm'iantly because of the
nitrates left in the soil by the bacteria which
lived with the first crop. For this reason,
clover is often grown on land in which it is
proposed to plant corn later, the nitrates left
in the soil thus giving nourishment to the
Tubercles on the roots ^^^^ plants. This alternation is known

of soy bean. ^ <=> i.

as rotation of crops. The annual yield of
the average farm may be greatly increased by this means.

Soil Exhaustion may be Prevented. — Besides the rotation of
crops, other methods are used by the farmer to prevent the
exhaustion of raw food material from the soil. One method
known as fallowing is to ailow the soil to remain idle until bac-
teria and oxidation have renewed the chemical materials used
by the plants. This is an expensive method, if land is dear.
The more common method of enriching soil is b}'' means of
fertilizers, or material rich in plant food. Manure is most fre-
quently used, but many artificial fertilizers, most of which con-
tain nitrogen, are used, because they can be more easily trans-
ported and sold. Such are ground bone, guano (bird manure),
nitrate of potash, and many others. Most fertilizers contain,

USES OF ROOTS

81

in addition to nitrogen, other important raw food materials for
plants, especially potash and phosphoric acid.

Roots help the Plant to Breathe. — Although we shall find
that leaves are the chief breathing organs of a plant, yet roots
absorb much oxygen from the soil or the water into which they
reach. The rows of dead trees around a pond that has been

Various forms of roots: ^, taproot (dandelion); B, fleshy root
(beet); C, fibrous root (crowfoot); D, fascicled root (dahlia);
E, adventitious roots (English ivy, on a wall).

raised by damming indicates that one cause of the death of
these trees was lack of oxygen. They were actually drowned.

The so-called " cypress knees," projections of the roots from
cypress trees, are adaptations to obtain oxygen.

Food Storage in Roots and its Economic Importance. — The
use the plant makes of the food stored in the root may be
understood if we take up the hfe history of the parsnip. Such
a plant is called a hien'nial because it produces no seed until
the second year of its existence, after which it dies. Its growth
the first summer forms the root we use as food. The food

82 ROOTS AND THEIR WORK

stored in its root enables it to get an early start in the spring,
so as to be better able to produce seeds when the time comes.
Such plants live only under rather cool climatic conditions.
Examples of other roots which store food are carrot, radish,
3^am, and sweet potato. This food storage in roots is of much
practical value to mankind. ]\Iany of our most common garden
vegetables, as those mentioned above and the beet, turnip,
oyster plant, and others, are of value because of the food stored
in roots. The sugar beet has, in Europe especially, become the
basis of a great industry", producing in normal times over 40 %
of the world's sugar suppl3\ The products from other roots are
used for medicine, as, for example, licorice, rhubarb, mandrake,
ginger, and asafet'ida.

Modified Roots. — Although roots are primarily anchoring and
absorbing organs they may, as we have seen, be used for food
storage as well. Usualty roots grow as a continuation of the
hypocotyl of the seedling, but they may appear in unusual
places on the stem or even from the leaves. Such roots are
called adventitious. The clinging roots developed from the stem
of English ivy, the stem roots of quick grass and the prop roots
of Indian corn are examples.

Other unusual tj'pes of roots are the air roots of the tropical
forests. Here plants called epiphytes or air plants live on tree
trunks and obtain moisture from the nearl}^ saturated air. Still
other plants, like the mistletoe, actually strike their roots into
the tissues of other plants and take their nourislmaent from
them. Such plants are called parasites because they take
their nourishment directly from other living organisms.

Summary. — We have found from a study of this chapter
that roots are very sensitive to the force of gravity and that
they have become modified for many purposes, as climbing,
props, or food storage. The principal uses of the root to the
plant are:

(1) They serve to hold the plant firmly in the ground.

(2) They serve to store food.

(3) They absorb mineral matter and water and transmit them
to the rest of the plant.

(4) They help as breathing organs.

USES OF ROOTS 83

Problem Questions. — 1. What is geotropism? How does it
act on roots?

2. What other factors influence the growth of roots?

3. What are root hairs and what is their function?

4. Explain osmosis.

5. How are roots able to take out mineral matter from the
soil?

6. What are nitrogen-fixing bacteria? How do they do their
work?

7. What proof have we that roots breathe?

8. Name some forms of modified roots and show their uses
to the plant.

Problem and Project References

Andrews. Botany All the Year Round, Chapter II. American Book Company.

Atkinson, First Studies in Plant Life, Chapters IX, XI, XII, Ginn and Com-
pany.

Coulter, Barnes, and Cowles, Textbook of Botany, Vol. I. pp. 302-322. American
Book Company.

Goff and Mayne, First Principles of Agriculture. American Book Company.

Goodale, Physiological Botany. American Book Company.

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Ilunter and Whitman, Civic Science in the Home. American Book Company.

Moore, The Physiology of Man and Other Animals. Henry Holt and Company

Sharpe, A Laboratory Manual. American Book Company.

itevena. P^nnt Anatomy, Chapter VI. P. Blakiston's Sons and Company,

VIII. THE STRUCTURE AND WORK OF THE STEM

Problem, To learn some-
thing of the structure and work
of stems. {Laboratory Manual,
Prob. XVII; Laboratory Prob-
lems, Probs. 75 to 78.)

(a) External structure of a
dicotyledonous stem (optional).

(b) Internal structure of a
dicotyledonous stem.

(c) Circulation in stems.

(d) Condition of food passing
through the stem.

A bud is said to be '' the
promise of a branch." Any

A larch, an excurrent tree (at right), and an
elm, a deliquescent tree (at left). Photo-
graphed by W. C. Barbour.

twig in winter shows
not only the terminal
bud, from which next
season's continuation of
the branch will come,
but it also shows lateral
buds placed just above
the leaf scars which
mark where last year's

leaves were attached. The position of the most active buds
determines the form of the future tree. If the terminal buds

84

DICOTYLEDONOUS STEM

85

grow more rapidly than those on the sides, we have a straight,
tall, excurrent tree with one main trmik. Such are Lombardy
poplars, pines, and cedars. If on the other hand the lateral
buds grow faster than the terminal, we have a lower, spread-
ing form of tree, as the ehn or oak. Such a tree is called
deliquescent (del-i-kwes'ent) in its method of growth.

The External Structure of a Dicotyledonous Stem. — A horse-
chestnut twig in its winter condition shows the structure
and position of the buds very
plainly. When the twig grew
last year the scales which cov-
ered the outside of the terminal
bud dropped off, and the young
shoot developed from the opened
bud. The scales w^hich dropped
off left marks forming a little
ring upon the bark of the twig.
These rings, collect ivel}' named
the hud scars, enable one to tell
the age of the branch.

Just below the lateral buds
are marks, known as leaf scars,
that show the points at which
leaves were attached. A careful
inspection of the leaf scars
reveals certain tiny dotlike traces
arranged more or less in the
form of a horseshoe. These
traces mark the continuations of
the same fibrovascular bundles
which pass from the root up
through the stem and out into
the leaves, where we see them as the veins which act as the
support of the soft green tissues of the leaf. The most impor-
tant y^e to the plant of the fibrovascular bundles is the conduction
of fluids from the roots to the leaves and from the leaves to the
stem and root.

Lenticels and their Uses. — The tiny scars, which look like

Horse-chestnut twig: th, terminal
bud ; a, lateral bud ; Is, leaf scar ;
Z, lenticel; /, flower scar; g, bud scar.
How many years old is this twig?
How can you tell?

86 THE STRUCTURE AND WORK OF THE STEM

ca-

little cracks in the bark, are very important organs, especially
during the winter season, for they are the breathing holes of

the tree. A tree is alive in win-
ter, although it is much less
active than in the warm
weather. But all the year round
oxygen is taken in and carbon
dioxide given off through the
lenticels (len'ti-selz), as the
breathing holes in the trunk
and branches of a tree are
called.

A Dicotyledonous Stem in
Cross Section. — If we cut a

Cross section of a three-year-old box CrOSS SectioU through a yOUng

elder: ob, outer bark; ib, inner bark; horse-chestnut Stem, we find it

ca, cambium layer; w, three rings of gj^^^g ^^lYee distinct regions,

wood; w, medullary ray; p, pith. . . , ,

ihe center is occupied by the
spongy, soft pith; surrounding this is found the rather tough
wood, while the outermost area is called cortex or bark. More
careful study of the bark reveals ihe presence of three layers —
an outer layer, a middle
green layer, and an inner
fibrous layer. This inner
layer is made up largely
of tough fiberlike cells
known as bast fibers. The
most important parts of
this inner bark, so far as
the plant is concerned, are
sieve tubes, made by join-
ing, end to end, long cells
having perforated ends. f^^^^P^
Through these tubes, pass- '^^^^^^^K^^MSM
ing from cell to cell through ''***'

the sieveUke ends, food Quarter section of oak. Comparing thi.

with the precedmg picture, point out the
materials move downward bark, the eambium layer, the rings of
from the upper part of wood, and the medullary rays.

DICOTYLEDONOUS STEM

87

the plant, where they are manufactured, to the stem and
roots.

In the wood will be noticed (see Figures opposite) many lines
radiating outward from the pith toward the cortex. These are
the so-called med'ullary rays, thin plates of pith which separate
the wood into a number of wedge-shaped masses. These masses
of wood are composed of many elongated cells, which, placed
end to end, form thousands of little tubes connecting the leaves
with the roots. In addition to these are many thick-walled
cells, which give strength to the mass of wood. In sections of
wood which have taken several years to grow, we find so-called
annual rings. The distance between one ring and the next (see first
Figure on page 86) usually represents the amount of growth in one
year. Growth takes place from an actively dividing layer of
cells, known as the cam'hium layer ^ which is located between the
wood and the bark; it forms wood cells from its inner surface
and bark from its outer surface. Thus new wood is formed as
a distinct ring around the old wood.-

Experiment to show that the skin of the potato (a stem; retards evaporation.

Use of the Outer Bark. — The outer bark of a tree is pro-
tective. The cells are dead, the heavy woody skeletons serving
to keep out cold, as well as to prevent the evaporation of

88 THE STRUCTURE AXD WORK OF THE STE^I

liquids from within. ]\Iost trees are provided with a layer of
corky cells. This layer in the cork oak is thick enough to be of
commercial importance. The function of the cork}^ layer in pre-
venting evaporation is easity demonstrated by the potato, which
is a true stem, though found underground. If two potatoes of
equal weight are balanced on the scales, the skin having been
peeled from one, the peeled potato will be found to lose weight
rapidh*. This is due to loss of water, which is held in -by the
skin of the unpeeled potato. (Figure on page 87.)

Passage of Fluids up and down the Stem. — If any young
growing shoot (young seedling of corn or pea, or the older stem

of gai'den balsam, touch-me-not, or
sunflower) or an apple twig is placed
in red ink (eosin), left in the sun
for a few hom'S, and then examined,
the red ink will be found to have
passed up the stem in the woody
tubes immediately under the inner
bark. These wood}^ tubes make up
the inner portion of the fibro-vascu-
lar bundles called the wood or
xylem (zl'lem).

If willow twigs are placed in water,
roots soon begin to develop from
that part of the stem which is un-
der water. If now the stem is
girdled b}^ removing the bark in a
ring just above where the roots are
growing, the part of the stem below
the girdled area wiU eventually die,
and new roots will appear above it. The food material neces-
sary for the outgrowth of roots evident^ comes from above; in
fact it moves in a downward direction just outside the wood in
the layer of bark which contains the bast fibers and sieve tubes.
These sieve tubes make up the outer portion of the fibrovascu-
lar bundles which is called phloem (flo'em). Food substances are
also conducted to a much less extent in the wood itself, and
food passes from the inner bark to the center of the tree by

Apple twigs split to show
the course of colored water
(the dark lines Just inside the
bark) up the stem.

CIRCULATION IN STEMS

89

way of the pith plates or medullary rays. It is found that
much starch is stored in this part of the tree trunk. The ex-
periment with the willow explains why it is that trees die when
girdled so as to cut the sieve tubes of the inner bark. The food
supply is cut off from the protoplasm of the cells in the part
of the tree below the cut area. Many of the canoe birches of
our Adirondack forest are thus killed, girdled by thoughtless
visitors.

In What Form does Food pass through the Stem? — We have
already seen that materials in solution (those substances which
will dissolve in water) will pass
from cell to cell by the process of
osmosis. This is easily shown
in the following experiment (see
Figure). Two thistle tubes are
partly filled, one with starch and
water, the other with sugar and
water, and a piece of parchment
paper is tied over the lower end
of each. The lower ends of both
tubes are placed in a glass dish
under water. After twenty-four
hours, the water in the dish is
tested for starch, and then for
sugar. We find that only the

sugar, which has been dissolved by Experiment showing the non-osmo-
,, . J, 1 ;i sis of starch and water (tube A), and

the water, can pass through the ^^^^^-^ ^^ ,^g^^ ^^^^^-^^ ^^^be B).
membrane.

Digestion. — As we shall see later, the food for a plant is
manufactured in the leaves or in the stems, etc., wherever green
coloring matter is found. Much of this food is in the form of
starch. But starch, being insoluble, cannot be. passed from cell
to cell in a plant. It must be changed to a soluble form. This
process of digestion seemingly may take place in all living parts
of the plant, although most of it is done in the leaves. In the
bodies of all animals, including man, starchy foods are changed
in a similar manner, but by different digestive ferments^ into
a soluble form, grape sugar.

Hunt. New Es. — 7

90 THE STRUCTURE AND WORK OF THE STEM

The food material may be passed in a soluble form until it
comes to a place where food storage is to take place, then it
can be transformed to an insoluble form (starch, for example);
later, when needed by the plant in growth, it may again be
transformed and sent in a soluble form through the stem to
the place where it will be used.

Building of Proteins. — Another very important food sub-
stance stored in the stem is protein. Of the building of protein,
little is known. We know it is an extremely complex chemical
substance which is made in plants from compounds containing
nitrogen, as the nitrates and compounds of ammonia received
through the roots from the organic matter contained in the soil,
and combined with sugar or starches in the body of the plant.
Some forms of protein substance are soluble and others in-
soluble in water. White of egg, for example, is very slightly

soluble, but can be rendered insoluble
by heating it until it coagulates. In-
soluble proteins are digested within the
plant; how and where is but shghtly
understood. Soluble proteins pass down
the sieve tubes in the bast and then
may be stored in the bast, or they may
pass into the root, fruit, or seeds of a
plant, and be stored there.

What forces Water up the Stem. —
We have seen that the process of osmosis
is responsible for taking in soil water,
and that the great extent of the absorb-
ing surface exposed by the root hairs
Diagram to show the areas makes possible the absorption of a large
ma plant through which raw ^mount of Water. Frequently this is

food materials pass up the

stem (wavy line in diagram) Hiore than the Weight of the plant every

and food materials pass dowm twenty -four hourS.

(even line in diagram). Experiments have been made which

(After Stevens.) . .

show that this water is in some way
forced up the tiny tubes of the stem. During the spring season, in
young and rapidly growing trees, water has been proved to rise to
a height of nearly ninety feet.

MONOCOTYLEDONOUS STEM

91

Root pressure is the force with which soil water passes from
the roots into the stem. This flow of water is the result of
osmosis in the root hairs and later in the cells of the root.
But root pressure alone cannot account for the rise of sap
(water containing materials taken out of the soil) to a height
of several hundred feet, as in the stems of the big trees of
California. Other factors that are believed to be at work are the
cohesion of particles in tiny columns of water, and osmosis between
living cells that lie along the course of the woody bundles of long
narrow dead cells that form the
ducts. But no complete and
adequate explanation has been n
found for the rise of sap to great \
heights. ' J^ \

A very great factor, however,
is one which will be more fully
explained when we study the
work of the leaf. Leaves pass
off an immense quantity of
water by evaporation, and this /:.
process seems to result in a kind
of suction on the tiny columns of
water in the stem. In the fall,
after the leaves have gone, much
less water is taken in by roots,

showing that an intimate rela- A broken cornstalk, with cross sec-
tion exists between the leaves tion (at left) : iV,node; R,r, rind; P,
J ,1 , p, pith; FV, fv, fibro vascular bundle.

and the root.

Structure of a Monocotyledonous Stem. — A piece of corn-
stalk examined carefully in cross and longitudinal section shows
us that the main bulk of the stalk is made up of pith, through
which are scattered numerous stringy, tough structures called
fibrovascular bundles. The latter are the woody bundles of tubes
which in this stem pass through the pith and run into the
leaves, where (in young specimens) they may be followed as
veins. The outside of the corn stem is formed of large num-
bers of fibrovascular bundles, which, closely packed together,
form a hard, tough outer rind. Thus the woody material on

92 THE STRUCTURE AND WORK OF THE STEM

the outside gives mechanical support to an otherwise spongy
stem.

Structure of a Fibrovascular Bundle in a Monocotyledonous
Stem. — A cross section of a fibrovascular bundle under the
microscope shows a collection of supporting cells and ducts

without any cambium layer. Woody
cells with thick walls serve to support
the bundles of tubes. Some, called
sieve tubes, are developed to carry
food downward from the leaves,
while others (see Figure) carry
water and air upward. The bundles
elongate rapidly, but are limited
in their growth outward by the hard-
walled, woody cells (the xylem). An
old stem of a monocotyledon con-
tains more bundles than does a
Cross section of monocoty- young stem, the bundles growing

out as veins into the leaves.

Comparison in the Growth of a
Dicotyledonous and a Monocoty-
ledonous Stem. — In the dicoty-
ledonous stem the woody bundles
appear in a ring. They are open and grow in both directions,
inward and outward, from that part of the bundle called the
cambium. This layer in older stems soon becomes a complete
ring around the tree. On the outside of the cambium layer is
found the phloem, or portion containing the sieve tubes which
bear elaborated food toward the roots. On the inside is found
the xylem or woody tubes that carry water and air upward.

In the monocotyledonous stem the bundles are scattered, lack
the cambium, and increase in number as the stem grows older.
They contain sieve tubes on the inside and water and air bear-
ing tubes in their outer part.

Food Storage. — Many monocotyledonous trees which live for
long periods of time store food in large quantities in the trunk.
The sago palm is an example. The sugar cane is a monocot-
yledonous stem of great commercial value because of the sugar

ledonous fibrovascular bundle,
much magnified: ph, sieve tubes
in which food passes down; d,
woody portion or bundle ducts
which carry air and water up-
ward; p, pith cell.

BUDDING AND GRAFTING

93

contained in its sap. Over 70 pounds of sugar on the average

is used annually by each person in the United States. Most of

the cane sugar grown in this country comes from Louisiana and

Texas, although these

states do not begin to

supply the needs of this

country.

Various types of stems
form some of the most
important sources of
man's food supply. Our
common potato, celery,
onions, rhubarb, aspar-
agus, and Jerusalem
artichoke are well-known
examples. The sago palm
is the chief support of
many of the natives of
Africa. An adult tree
will furnish 700 pounds
of sago meal, 2i pounds
being enough to support
a man one day. Maple
sugar is a well-known
commodity which is ob-
tained by boiling the sap
of the sugar maple un-
til it crystallizes. Over
16,000 tons of maple
sugar is obtained every
spring, Vermont producing about 40 per cent of the total
output.

Budding. — We have said a bud is a promise of a branch; it
may be more, the promise of a new tree. If the owner of an
apple or peach tree wishes to vary the quality of fruit borne
by the tree, he may in the early fall cut a T-shaped incision
in the bark and then insert a bud surrounded with a little bark
from the tree of the same species bearing the desired fruit. The

Palm, tapped at the top for its sweet sap,
from which a drink is made in tropical

countries.

94 THE STRUCTURE AND WORK OF THE STEM

bud is bound in place and left over the winter. When a shoot
from the embedded bud grows out the following spring, it is
found to have all the characteristics of the tree from which it
was taken. This process is known as budding.

Budding (CBD) and grafting {FG): C, shield-shaped bud from desired variety;
B, T-shaped incision, ready to receive the bud; D, bud inserted and bound in
place. F, two grafts from desired variety in place in split end of trunk; G, same
after application of grafting wax to hold them in place.

Grafting. — Of much the same nature is grafting. Here, how-
ever, a small portion of the stem of the closely allied tree is
fastened into the trunk of the growing tree in such a manner
that the two cut cambium layers will coincide. This will allow
the passage of food into the grafted part and insure the ultimate
growth of the twig. Grafting and budding are of considerable
economic value to the fruit grower, as they enable him to pro-
duce at will trees bearing choice varieties of fruit. ^

In both of the above processes, the secret of successful growth
lies in the fact that the cambium surface of the bud or the graft
comes in contact with the cambium of the tree to which it is
applied, thus putting it in direct communication with a supply
of food from the tree which is already established.

Modified Stems. — We have already seen that the factors of
the environment, light, heat, gravity, moisture, air currents and
other factors, act upon the living substance of plants, causing
them to react in various ways. The changes which take place
usually fit the plant to succeed better in its battle for life.

1 For full directions for budding and grafting, see Goff and Mayne, First Prin-
ciples of Agriculture, Chap. XIX, or Hodge, Nature Study and Life, pages 169-179.

MODIFIED STEMS

95

The potato tuber is a stem;
note the branches GB growing from
the "eyes" at one end. Ate is an-
other "eye."

Thus various modifications of stems have been brought about.

Some stems, like the sago palm and potato, become storehouses

of food. The potato tuber is

simply a much thickened stor-
age stem, as one may easily

prove by examination of the

so-called '' eyes '' of a sprouting

potato. The tiny projection

growing within the eye is a

bud, which may give rise to a

branch later. Food and water

are stored within the tuber.

Some stems have come to

exist underground because of

the protection thus afforded.

The pest called couch grass or quick grass
has such a stem. Bulbs, like the onion
or lily, are examples of stems which have
become shortened and covered with thick-
ened leaves, filled with food. Still other stems,
like that of the dandelion, have become
reduced in length, which prevents them from
being broken off by grazing animals. Climb-
ing stems, as a result of the stimulation of
the sun, twist around a support in a given
direction, some revolving with and some
against the course of the sun.

We also find stems and leaves modified to
become holdfasts for the plant. Such are
the tendrils found in climbing plants.
Thorns, a protection from animals, may be
modified parts of leaves or of stems, de-
pending upon where they come out on the

Cross and longitudi- stem. (See pictures on the following page.)

nal section of onion. f, k i. • iiji.j

Summary. — A stem is a developed bud,
the form of the plant depending upon the placing of the actively
growing buds in the young plant. Dicotyledonous and monocot-
yledonous stems differ in structure, as sunmiarized on page 92.

96 THE STRUCTURE AND WORK OF THE STEM

St-eins are seen to act as organs to hold the leaves in a favor-
able position so as to secure sunlight. They store food for the
plant and they act as organs to carry soil water and gases from
the roots to the leaves and to carry elaborated food from the
leaves to other parts of the plant.

Problem Questions. — 1. Name all the adaptations found in
scHKie bud. Give the specific purpose of each adaptation.

Catbrier; the tendrils T

are modified stipules (parts
of leaves); Th, thorn.

A honey locust; the thorns in this case
are modified branches (page 95) .

2. How do Stems help in breathing?

3. Compare a dicotyledonous and a monocotyledonous stem
(o) in method of growth;

(h) in microscopic cross section.

4. How may insoluble food be made use of by a plant?
Explain.

THE STRUCTURE AND WORK OF THE STEM 97

5. Compare budding and grafting as methods of propagation.

6. Discuss modifications in stems.

7. Name ten products obtained from stems.

Problem and Pboject References

Andrews, Botany all the Year Round, Chapters VI, VII. American Book Com-
pany.

Apgar, Trees of the Northern United States, Chapters II, V, VI. American Book
Company.

Atkinson, First Studies of Plant Life, Chapters IV, V, VI, VIII, XXI. Ginn
and Company.

Blakeslee and Jarvis, New England Trees in Winter, Bui. 69. Storrs Agricultural
Experiment Station, Storrs, Conn.

Dana, Plants and their Children, pp. 99-129. American Book Company.

Hodge, Nature Study and Life, Chapters IX, X, XI. Ginn and Company,

Hunter, Laboratory Problems in Civic Biology. American Book Company.

MacDougal, The Nature and Work of Plants. The Macmillan Company.

Sharpe, A Laboratory Manual. American Book Company.

Stevens, Plant Anatomy, Chapter X. P. Blakiston's Sons and Companyo

U. S. Dept. of Agriculture Yearbooks, 1894 to date.

Ward, The Oak. D. Appleton and Company.

IX. LEAVES AND THEIR WORK

Problem, A study of leaves in relation to their environment,
to show —

(a) Reactions of stems arid leaves to light.

(b) Structure.

(c) Important functions.

(1) Food-making and its by-product.

(2) Evaporation of excess water.

(3) The leaf as a mill (optional).

(4) Absorption and respiration.

(d) Means of protection {optional).

(e) Some leaf modifications {optional).
(/) Importance to man.

{Laboratory Manual, Prob. XVIII; Laboratory Problems,
Probs. 65 to 74.)

Differences between Roots and Stems. — A comparison of the
young root and the developing stem of a bean seedKng shows that

several marked differences
exist: (1) the color of the
stem is greenish, while
the roots are gray or
whitish; (2) the stem has
leaves and branches leav-
ing it in a more or less
regular manner, while
the smaller roots are ex-
tremely irregular in their
positions on larger roots;
(3) the stem grows up-
ward, while the general
direction taken by the
roots is downward.
Effect of Light on Plants. — In young plants which have been
grown in total darkness, no green color is found in either sterna

98

A pocket garden which has been kept in
complete darkness for several weeks. Notice
the bleached condition of stems and leaves.

EFFECT OF LIGHT

99

or leaves, the latter often being reduced to mere scales. The
stems are long and more or less reclining. We can explain this
strange condition of the seedhng grown in the dark only by
assuming that light has
some effect on the pro-
toplasm of the seedling
and induces the growth
of the green part of the
plant. Numerous in-
stances could be given
in which plants grown
in sunlight are healthier
and better developed
than those in the shady
parts of a garden or
field. On the other hand,

The growth of young stems and leaves of oxalis
toward the light.

some plants

Tall straight stems of the hemlock; the trees reach
up toward the source of light.

thrive in the shade.
Such plants are the
mosses and ferns.
Still other plants,
minute organisms,
some of them invisible
to the eye, do not
thrive in the light,
and may be killed by
its influence. Exam-
ples of such are found
among the molds,
mildews, and bacteria.
Such plants, however,
are not green. As a
matter of fact, the
stem of a green plant
which has but little
green coloring matter
develops more rapidly
under conditions
where it receives no
light.

100

LEAVES AND THEIR WORK

Heliotropism. — We saw that the stems of the plants kept in
the darkness do not always hold themselves erect, as is the case
of most stems in the light. If seedlings have been growing on a
window sill, or where the light comes in from one side, you have
doubtless noticed that the stem and leaves of the seedlings in-
cline in the direction from which the light comes. The tendency
of young stems and leaves to grow toward sunlight is called positive
heliot'ropism.

The experiment pictured on this page shows this effect of
light very plainly. A hole was cut in one end of a cigar box and

Two stages in an experiment to show that green plants grow toward the light.

barriers were erected in the interior of the box so that the
seedling growing in the sawdust received its light by an indirect
course. The young seedling in this case responded to the in-
fluence of light and grew out finally through the hole in the box
into the open air. This growth of the stem to the light is of
very great importance to a growing plant, because, as we shall
see later, food making depends largely on the amount of sunlight
the leaves receive.

Effect of Light. — We have already found that seedlings grown
in total darkness are almost yellow-white in color, that the
leaves are but slightly developed, and that the stem has de-
veloped far more than the leaves. We have also seen that a

ARRANGEMENT OF LEAVES

101

green plant will grow toward the source of light, even against
great odds. It is a matter of common knowledge that green
leaves turn toward the light. Place growing pea seedlings,
oxalis, or any other plants of rapid growth near a window which
receives full sunlight. Within a short time the leaves are found-
to be in positions to receive the most sunlight possible.

Arrangement of Leaves. — A study of trees in a park, or in the
woods, shows that the trunks of trees which are close together

A lily, showing long, narrow
leaves.

A dandelion, showing a whorled arrange-
ment of long, irregular leaves.

are usually tall and straight and that the leaves come out
in clusters near the top of the tree. The leaves lower down
are often smaller and less numerous than those near the
top. Careful observation of plants growing outdoors shows us
that in almost every case the leaves are so disposed as to get
the most sunlight. The ivy climbing up the wall, the morning-
glory, the dandelion, and the burdock all show different arrange-
ments of leaves, each presenting a large surface to the light.
Leaves are usually definitely arranged, and fitted in between
others so as to present their upper surface to the sun. Such
an arrangement is known as a leaf mosaic. Good examples of
such mosaics, or leaf patterns, are seen in trees having leaves
which come up alternately, first on one side of a branch, then
on the other. Here the leaves turn, by the twisting of their

102

LEAVES AND THEIR WORK

stalks, so that they all present theu* upper surface to the
sun. In the case of the dandelion, a rosette or whorled cluster
of leaves is found. In the horse-chestnut, where the leaves come
out opposite each other, the older leaves have longer stems
than the young ones. In the mullein the entii'e plant forms a
cone; the old leaves near the bottom
have long stalks, and the little ones
near the apex come out close to the

Palmately-veined leaf of
the maple.

The skeleton of a pinnately
veined leaf: MR, midrib; P, the
leafstalk or petiole; V, the veins.

main stalk. In every case each leaf receives a large amount of
light. Other modifications of these forms may easily be found
on a field trip.

The Sun a Source of Energy. — We all know the sun is a
source of energy, for do we not feel its heat and is not heat a
form of energy ? Solar engines have not thus far come into any
great use, because fuel is cheaper. Actual experiments have
shown that the sun gives to the earth vast amounts of energ}^
When the sun is in the zenith, energj^ equivalent to one hundred
horse power is received by a plot of land twenty-five by one
hundred feet, or the size of a city lot. Plants receive and use
much of this energy by means of their leaves.

STRUCTURE OF A LEAF

103

Pinnately-compound leaf of rose, show-
ing stipules St.

The Structure of a Leaf. — Let us now examine with some
detail the structure of a simple leaf of a dicotyledonous plant.

A green leaf shows usually (1) a flat, broad blade which may
take almost any conceivable shape; (2) a stem or petiole (pet'i-ol),
which spreads out into veins
in the blade (the veins usually
present a netted appearance
in the leaf of a dicotyledon,
but run more or less parallel
to one another in the blade
of a monocotyledonous leaf);
(3) stipules, a pair of out-
growths from the petiole at
its base. In many leaves the
stipules fall off early. Some
leaves are compound, that is,
each of the little leaflike parts
is in reality a section of the leaf blade which is so deeply indented
that it is cut away to the midrib or central vein, as in the rose

leaf. A pair of stipules found at
the base sho"ws that such a leaf
is compound. The cut just above
shows this condition in the. rose
plant. What other plants commonly
seen have compound leaves?

The Cell Structure of a Leaf. —
The lower surface of most leaves, as
seen under the microscope, shows
large numbers of tiny oval openings
called sto'mata (singular stoma) . Two
cells, usually kidney-shaped, are
found, one on each side of the stoma.
These are the guard cells. By changes
in the shape of these cells the open-
ing of the stoma is made larger or smaller. Larger cells (irregular
in dicotyledons) form the epidermis, or outer covering of the
leaf. Study of the leaf in cross section shows that the stomata
open directly into air chambers between the loosely arranged

Surface view of epidermis of
lower surface of a leaf highly
magnified; e, ordinary epidermal
cell; g, guard cell. — Tschirch.

104

LEAVES AND THEIR WORK

cells composing the lower part of the leaf. The upper surface
of leaves sometimes contains stomata, but more often is without
them. The under surface of an oak leaf of ordinary size con-
tains about 2,000,000. Un-
der the upper epidermis is
a layer of green cells closely
packed together, called col-
lectively the palisade layer.
These cells are more or less
columnar in shape. Under
them are several rows of
rather loosely placed cells
containing the air spaces
above mentioned. These
are called collectively the
spongy parenchyma (pa-
reng'ki-ma) . If we happen
to have a section cut through
a vein, we find it composed

LOWEIf
£PW£M/S

CUADD CELL

•STOMA

Section of a leaf highly magnified. The
cells containing chlorophyll bodies are in the
palisade layer and the spongy parenchyma.

of a number of tubes made up of, and strengthened by, thick-
walled cells, the fihrovascular bundles. The veins are evidently a
continuation of the tubes of the stem out into the blade of the leaf.
Starch made by a Green Leaf. — If we examine the palisade
layer of the leaf, we find cells which are almost cylindrical in
form. In the protoplasm of these cells are found a number of
small green-colored bodies, which are known as chloroplasts
(klo'rS-plasts) or chlorophyl (klo'r6-fil) bodies. If the leaf is
placed in wood alcohol, we find that the bodies still remain, but
that the color is extracted, going into the alcohol and giving to
it a beautiful green color. The chloroplasts are simply part of
the protoplasm of the cell colored green. If the plant is kept
in the sun, the chloroplasts retain their green color, but in the
dark this color is gradually lost. These bodies are of the greatest
importance directly to plants and indirectly to animals. The
chloroplasts, by means of the energy received from the sun, manu-
facture starch out of certain raw materials. These raw materials
are soil water, which is passed up through the bundles of tubes
into the veins of the leaf from the roots, and carbon dioxide,

STARCH MAKING

105

which is taken in through the stomata or pores which dot the

under surface of the leaf.

Light and Air Necessary for Starch Making. — Pin strips of

black cloth, such as alpaca, over some of the leaves of a growing

geranium in such a way that

only a part of each leaf is in

the dark; and place the plant

in a sunny window for two

or three days. Then remove

some of the partly covered

leaves after a day of bright

sunhght, and after extract-
ing the chlorophyl with wood

alcohol (because the chloro-
phyl covers up the contents

of the cells) test for starch.

We find that starch is present

only in those portions of the

leaves which were exposed to

sunlight. From this experi-
ment we infer that the sun has

something to do with starch

making in a leaf. The necessity of air also for starch making

may easily be proved: on a plant placed
in the sunlight cover a leaf with vaseKne;
after several days it will be found to con-
tain no starch, while leaves unvaselined
contain starch.

Air is necessary for the process of starch
making in a leaf, not only because carbon
dioxide gas is absorbed (there are from
three to four parts in ten thousand pres-
ent in the atmosphere), but also because
the protoplasm of the leaf is ahve and
must have oxygen. These gases are
taken in through the stomata of the leaf

from the surrounding air.

Comparison of Starch Making and Milling. — The manufac-

HuNT. New Es. — 8

A hydrangea plant, upon the leaves of
which strips of black cloth {A) have been
pinned in order to exclude sunlight.

Starchless area in leaf,
caused by excluding sun-
light by means of a strip
of black cloth.

106

LEAVES AND THEIR WORK

ture of starch by a green leaf is not easily understood. The
process has been compared to the milling of grain; in which
case the mill is the green part of the leaf. The sun furnishes
the motive power, the chloroplasts constitute the machinery,
and soil water and carbon dioxide are the raw materials taken

into the mill. The man-
ufactured product is
starch, and a certain by-
product (corresponding to
the waste in a mill) is
also given out. This by-
product is oxygen. To
understand the process
more fully, we must re-
fer to a small portion of
the leaf. Here we find
that the green palisade
cells perform most of the
work. The carbon diox-
ide is taken in through
the stomata and reaches
the green cells by way of

Diagram to illustrate the formation of starch. ,■, • , t, ,

the mtercellular spaces
and by diffusion from cell to cell. Water reaches the green cells
through the conducting tubes in the veins. It then passes into
the cells by osmosis, and there becomes part of the cell sap.
The light of the sun easily penetrates to the cells of the palisade
layer, giving the energy needed to make the food. This whole
process is a very delicate one, and takes place only when exter-
nal conditions are favorable. For example, too much heat or
too httle heat stops starch making; the presence of stored food
in the leaf has a similar effect on the process. This building up
of starch out of carbon dioxide and water and the release of oxygen
by chloroplasts in the presence of sunlight is called photosynthesis.
Chemical Action in Starch Making. — In the process of starch
making, water (H2O) and carbon dioxide (CO2) are combined in
such a way as to make starch, expressed by the chemical formula
CeHioOs. It is probable that the first product formed in the

STARCH MAKING

107

leaf is carbonic acid, which assists in making formaldehyde,
from which sugar and finally starch is formed. AU of these
changes are brought about by the action of enzymes which are
present in the cells of the leaf and help make food manufacture
possible. The starch thus formed is either stored in the leaf or
changed by digestion to some soluble form Uke grape sugar,
which can be carried to other parts of the plant, passing from

soil water

Diagram (after Stevens) to illustrate the processes of breath-
ing, food making, and transpiration which may take place in
the cells of a green leaf in the sunlight.

cell to cell by osmosis. The oxygen is passed out through the
stomata of the leaf.

Protein Making and its Relation to the Making of Living
Matter. — Protein material is a food which is necessary for the
growth of protoplasm, and is present in the leaf, the stem, and
the root. Proteins can apparently be manufactured in any
plant cell, the presence of light not being a necessary factor.
The element nitrogen is taken up by the roots as a nitrate
(nitrogen in combination with lime or potash) in the soil water,
and in making protein it unites with the carbon, hydrogen, and
oxygen found in starch and sugar. Proteins are probably not
made directly into protoplasm in the leaf, but are stored by the
ceils and used when needed, either to form new cells at a growing

108

LEAVES AND THEIR WORK

point, or to repair waste. While plants and animals obtain their
food in different ways, they probably make it into living sub-
stance {assimilate it) in exactly the same manner.

Foods serve exactly the same purposes in plants and in
animals; they either build living matter or they are burned
(oxidized) to furnish energy (work power). If you doubt that
a plant exerts energy, note how the roots of a tree bore their

An example of how a tree may exert energy. This rock has been
split by the growing tree. Photograph from the American Museum of
Natural History.

way through the hardest soil, and how stems or roots of trees
often split open solid rocks, as illustrated in the Figure.

Rapidity of Starch Making. — Leaves which have been in
darkness show starch to be present shortly after being exposed
to light, Squash leaves make three fourths of an ounce of starch
for each square yard of surface. A corn plant sends 10 to 15
grams of reserve material into the ears in a single day. This
fact explains how the rapid growth seen in grain fields or a
fruit orchard may occur and is of economic importance. Not
only do plants make their own food but they store it away, and
it becomes food for animals as well. It is fortunate that the
food is stored in such a stable form in grain or other fruits
that it may be sent to all parts of the world without spoiUng.
Ajiimals, herbivorous and flesh-eating, even man himself, all are

OXYGEN GIVEN OFF BY GREEN PLANTS 109

dependent upon the starch-making processes of the green plant
for the ultimate source of their food.

Oxygen given off by Green Plants. — It is possible to prove that
oxygen is given off by green plants in sunlight. The common
green frog scum seen in shallow ponds is often so full of bubbles
that it is buoyed up by them at the water's surface. If some
of this plant or other green water weed
is placed in a large battery jar or fruit
jar in a sunny window, bubbles of gas
will be seen to arise from it, the amount
increasing as the water is warmed by the
sun's rays.

If a glass funnel is placed upside down
so as to cover the plants, and then a test
tube full of water inverted over the
mouth of the funnel, enough gas may be
collected to test for oxygen.^

That oxygen is given off as a by-
product when starch is made by green
plants is a fact of far-reaching impor-
tance. Parks in a city are true '' breath-
ing spaces." The green covering of the
earth is giving to animals an element that
they must have, while the animals in
their turn are supplying to the plants
carbon dioxide, a compound used in food
making. Thus a relation of mutual help-
fulness exists between plants and animals.

Evaporation of Excess Water. — In order to secure the neces-
sary amount of mineral matter for the manufacture of foods,
an enormous amount of water is taken up by the roots and
passed to the leaves, where the minerals which were in solution
in the soil water are deposited and the excess water is evapo-
rated through the stomata. The process of giving off water in

Experiment to show that
oxygen is given off by green
plants in the sunlight.

1 Water contains air in solution, including some carbon dioxide, but the amount
of this gas in a jar of ordinary water may be too small. Immediate success with
this experiment will be obtained if the water has been previously charged with
carbon dioxide.

110

LEAVES AND THEIR WORK

the form of vapor is known as transpiration. That moisture is
passed out through the blade of the leaf is shown by the dia-
^am below, di'ops of water having gathered on the inside of

the bell jar. A small grass plant on a
summer's day evaporates more than its
own weight in water. This would make
nearly haK a ton of water distributed to
the air dm'ing twentj^-four hom's b}- a
grass plot twenty-five b}^ one hundred
feet, the size of the average city lot.

From which. Surface of the Leaf is Water
Lost? Experiment. — In order to find out
whether water is passed out from any par-
ticular part of the leaf or not, we maj"" remove
two leaves of the same size and weight from
some large-leaved plant — a mullein was used
for the illustrations on the opposite page — and
cover the upper surface of one leaf and the lower
surface of the other with vaseline. The petioles
of both should be covered with wax or vaseline,
and the two leaves exactly balanced on the pans
of a balance which has pre\'iously been placed
in a warm and sunny spot. Within an hour the
leaf u-hich has the upper surface covered with
vaseline will show a loss of weight. Microscopic
examination of the epidermis of a mullein leaf
shows us that the lower surface of the leaf is
Experiment to show provided with stomata. It is through these

transpiration. The top of ^ j^ ^j^^. water is passed out from the

the flower pot is covered ^. r ^-i ^ e

^■+v uu n^-u -4- tissues of the leaf.

with rubber. The moisture

comes from the leaves. Regulation of Transpiration. — The

stomata of leaves close at night, the guard cells apparently being
sensitive to Hght, and prevent the transpiration of much water.
There is little loss of water on humid daj's, because of the large
amount of water in the atmosphere. VHien the plant has water
and the atmosphere is dry, the stomata open and give off water
vapor. But the exact means by which regulation of evaporation
through the stomata takes place is not well understood.
The Effect of Transpiration on Water within the Stem. — It

RESPIRATION

111

has already been noted that root pressure alone will not account
for the rise of water to the tops of very tall trees. Experiments
indicate that evaporation of water through the stomata exerts a

Experiment to show through which surface of a leaf water vapor passes off.

pull upon the tiny column of water held together by cohesion
within the stem of the tree, thus causing the rise of water to
the leaves on the upper branches.

Respiration by Leaves. — All living things require oxygen. It
is by means of the oxidation of food materials within the plant's

rmis

Section through stomata: in A the stoma is open; in B the stoma is closed;
s, stoma; g, g, guard cells.

body that the energy used in growth and movement is released.
A plant takes in oxygen largely through the stomata of the
leaves, to a less extent through the lenticels in the stem, and
through the roots. Thus rapidly growing tissues receive the

112

LEAVES AND THEIR WORK

ox3^gen necessary for them to perform their work. The products
of oxidation in the form of carbon dioxide are also passed off
through the same organs. It can be shown by experiment
that a plant uses up oxygen in the darkness; in the light the
amount of oxygen given off as a by-product in the process of
starch making is, of coui'se, much greater than the amount used
by the plant.

Economic Uses of Leaves. — The practical us3 of green
plants to man is very great. They give off oxygen in the sun-
light and use carbon dioxide, which
is given off by animals in respiration.
We should remember, as taxpayers,
that money spent on city parks is
money weU invested, bringing as it
does a source of ox^^gen supply where
it is most needed.

Another very important use of
leaves to man is seen in the fact that
after falhng to the ground, they help
to form a rich covering of humus,
which acts as a coat to hold in moist-
ure. The forests are our greatest
source of water supply. The cutting
away of the forest always means a
depletion of the reserve water stored
in soil, with consequent floods and
droughts in alternation.

Leaves are used directly by man
for food. Examples are cabbage,
lettuce, kale, and broccoh. These
foods, properly combined with fleshy
foods, are of great importance in
giving a balance to diet. In a wider sense, all animals depend
upon leaves fc^r their food supply, either directly or indirectly.
Foods obtained from roots, stems, seeds, and fruits were manu-
factured in the leaves and transported within the plant to their
places of storage. Even meat-eating animals are in the long
run dependent upon plants, for they feed upon plant eaters.

A cactus, sho"«nng the leaves
modified into spines.

MODIFIED LEAVES

113

Modified Leaves. — Leaves, as well as stems, may be modified
for the protection of the plant. In some cacti, for example, in
order to prevent too rapid evaporation of water, the leaves have
been changed into spines. In other plants, as the mullein,
the leaves are covered with protective hairs. In still others the
leaves may be reduced or lost entirely, as in the asparagus. We
have already noted that some leaves have become modified for
climbing purposes.

Leaves as Insect Traps. — The most curious adaptations of
leaves are seen, however, in those plants whose leaves have been

Leaves modified to serve as insect traps: A, pitcher plant; B, sundew; C,

Venus's flytrap.

modified to catch and feed upon insects. It sometimes happens
that the environment of a plant will not supply the nitrogen
necessary for growth. Certain species of plants, therefore, by
means of either bladder-like leaves, as in the bladderwort and
pitcher plant, or actual traps, as are seen in the sundew and
Venus's flytrap, catch and actually use the bodies of the insects
as food. The accompanying illustrations show how this is
done.

Summary. — This chapter shows us (1) that light plays an
important part in not only attracting stems and leaves but also
in helping to make food; (2) that the structure of a leaf fits
it to be a starch making as well as a breathing organ; it also

114 LEAVES AND THEIR WORK

makes protein, gives off oxygen as a by-product of starch
making, and gives off water by transpiration; (3) that starch
making requires light, carbon dioxide, water, and chlorophyll in
addition to the delicate mechanism of the leaf; (4) that various
modifications of leaves serve for protection, storage of water,
climbing, and catching of insects for food, the last curious modifi-
cation being brought about by lack of available nitrogen in the
environment.

Problem Questions. — 1. What is heliotropism? Give ex-
amples.

2. Prove all energy comes from the sun.

3. Describe the microscopic structure of a leaf.

4. Describe the process of photosynthesis.

5. What other functions has the green leaf of a growing
plant?

6. Sum up the economic uses of green plants to the world.

7. Describe five adaptive modifications of green leaves.

Peoblem ajo) Project References

Andrews, Botany All the Year Round, pp. 46-62. American Book Company.

Coulter, Barnes and Cowles, A Textbook of Botany, Vol. I, Part II, and Vol. Vi.
American Book Company.

Dana, Plants and their Children, pp. 135-185. American Book Company.

Densmore, General Botany, Chapter VI. Ginn and Company.

Gager, Fundamentals of Botany, Part II. P. Blakiston's Sons and Company.

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Lubbock, Flowers, Fruits and Leaves, last part. The Macmillan Company.

MacDougal, Practical Textbook of Plant Physiology, Longmans, Green, and Com-
pany.

Sharpe, A Laboratory Manual. American Book Company.

Stevens, Plant Anatom.y, Chapter IX. P. Blakiston's Sons and Company.

Ward, The Oak, D. Appleton and Company.

X. OUR FORESTS; THEIR USES AND THE
NECESSITY FOR THEIR PROTECTION

Problem. To determine some uses of stems (optional). {Labo-
ratory Manual, Prob. XIX; Laboratory Problems, Probs. 80-84.)

(a) Special products from stems.

(b) Some woods and their value.

(c) Field work in forestry.

The Economic Value of Trees. Protection and Regulation
of Water Supply. — Trees form a protective covering for the
earth's surface. They pre-
vent soil from being
washed away, and they
hold moisture in the
ground. Without trees
many of our rivers might
go dry in summer, while
in the rainy season sud-
den floods would result.
The devastation of im-
mense areas in China and
considerable damage by
floods in parts of Switzer-

Working to prevent erosion after the removal
of the forest in the French Alps.

land, France, and in Pennsylvania, have resulted where the
forest covering has been removed. No one who has tramped
through our Appalachian forests can escape noticing the dif-
ferences in the condition of streams which flow through areas
covered with forest and those from around which trees have
been cut. The latter streams often dry up entirely in hot
weather, while the forest-shaded stream has a never failing
supply of crystal water.

Several cities on the Atlantic coast, such as Savannah, Wil-
mington, and Philadelphia, owe their importance to their po-
lls

116

OUR FORESTS

Erosion at SajTe, Pa., by the Chemung River.
Photographed by W. C. Barbour.

sition on navigable rivers supplied with water largely by the
Appalachian forests. Should these forests be destroyed, it is
not impossible that the frequent freshets which would follow
would so fill the rivers with silt and debris that the ship

channels in them, al-
ready costing the
government millions
of dollars a j-ear to
keep di'edged, would
become too shallow
for ships. If this
should occur, these
cities would soon lose
theii' importance.

The story of how
this veiy thing hap-
pened to the old
Greek city of Posei-
donia is graphically told in the following lines:

" It was such a strange, tremendous storj-, that of the Greek Poseidonia,
later the Roman Psestum. Long ago those adventuring mariners from
Greece had seized the fertile plain which at that time was covered with
forests of great oak and watered by two clear and shining rivers. They
drove the Italian natives back into the distant hills, for the white man's
burden even then included the taking of all the desuable things that were
being wasted b}' incompetent natives, and they brought over colonists —
whom the philosophers and moralists at home maligned, no doubt, in the
same pleasant fashion of our own day. And the colonists cut down the
oaks, and plowed the land, and bmlt cities, and made harbors, and finally
dusted their busj^ hands and busy souls of the grime of labor and wrought
splendid temples in honor of the benign gods who had given them the
possessions of the Italians and filled them with power and fatness.

" Every once in so often the natives looked lustfull}' down from the
hills upon this fatness, made an armed snatch at it, were driven back with
bloody contumeh', and the heaping of riches upon riches went on. And
more and more the oaks were cut down — mark that! for the stories of
nations are so inextricably bound up with the stories of trees — untU aU
the plain was cleared and tiUed; and then the foothills were denuded, and
the wave of destruction crept up the mountain sides, and they, too, were
left naked to the sim and the rains.

" At first these rains, sweeping down torrentially, unhindered by the

ECONOMIC VALUE OF TREES 117

lost forests, only enriched the plain with the long-hoarded sweetness of
the trees; but by and by the living rivers grew heavy and thick, vomiting
mud into the ever shallowing harbors, and the land soured with the un-
drained stagnant water. Commerce turned more and more to deeper
ports, and mosquitoes began to breed in the brackish soil that was making
fast between the city and the sea.

" Who of all those powerful landowners and rich merchants could ever
have dreamed that little buzzing insects could sting a great city to death?
But they did. Fevers grew more and more prevalent. The malaria-
haunted population went more and more languidly about their business.
The natives, hardy and vigorous in the hills, were but feebly repulsed.
Carthage demanded tribute, and Rome took it, and changed the city's
name from Poseidonia to Psestum. After Rome grew weak, Saracen
corsairs came in by sea and grasped the slackly defended riches, and the
little winged poisoners of the night struck again and again, until grass
grew in the streets, and the wharves crumbled where they stood. Finally,
the wretched remnant of a great people wandered away into the more
wholesome hills, the marshes rotted in the heat and grew up in coarse
reeds where corn and vine had flourished, and the city melted back into
the wasted earth." — Elizabeth Bisland and Anne Hoyt, Seekers in Sicily.
John Lane Company.

Prevention of Erosion by Covering of Organic Soil. — Streams
unprotected by forests may dig out soil and carry it far from
its original source. Examples of what streams have done may
be seen in the deltas formed at the mouths of great rivers. The
forest prevents this by holding back the water and letting it out
gradually. This it does by covering the inorganic soil with
humus or decayed organic material which, like a big sponge over
the forest floor, holds water through long periods of drought.
The roots of the trees, too, help hold the soil in place and pre-
vent erosion. The gradual evaporation of water through the
stomata of the leaves cools the atmosphere, and this tends to
precipitate the moisture in the air. Eventually the dead bodies
of the trees themselves are added to the organic covering, and
new trees take their place.

Other Uses of the Forest. — In some localities forests are used
as windbreaks and to protect mountain towns against ava-
lanches. In winter they moderate the cold, and in summer re-
duce the heat and lessen the danger from storms. The nesting
of birds in woods protects many plants valuable to man which
otherwise might be destroyed by insects.

118

OUR FORESTS

Forests have great commercial importance as well. Even in
this day of coal, wood is still by far the most-used fuel. It ia
useful in building. It outlasts iron under water, in addition
to being strong and light. It is cheap and, with care of the
forests, inexhaustible, while our mineral wealth will some day
be used up. Hard woods are chiefly used in house building and
furniture manufacture; many soft woods, reduced to pulp, are
made into paper. Distilled wood gives alcohol. Partially
burned wood is charcoal. Vinegar and other acids are ob"

FOREST REGIONS

The forest regions of the United States.

tained from trees, as are tar, creosote, resin, turpentine, and
other useful oils. The making of maple sirup and sugar forms a
profitable industry in several states.

The Forest Regions of the United States. — The combined
area of all the forests in the United States, exclusive of Alaska,
is about 550,000,000 acres. This seemingly immense area is
rapidly decreasing in acreage and in quality, thanks to the de-
mands of an increasing population, a woeful ignorance on the
part of the owners of the land, and wastefulness on the part of
cutters and users alike.

A glance at the map shows the distribution of our principal

USES OF WOOD

119

forests. At the present time they occupy about 35 per cent of
the total area of the country. But lumbering is still one of our
greatest industries and so heedless are we for the future that at
the present time we are cutting our forests three times as fast
as they are being renewed by natural growth. Moreover the
waste in production is enormous, it being estimated that over 65
per cent of a tree is wasted before it is used by man. Washington

Transporting logs from the forest to the mill, Washington.

ranks first of all the states in the production of lumber. Here
the great Douglas fir, one of the '^ evergreens," forms the chief
source of supply. In the Southern states, especially Louisiana
and Mississippi, yellow pine and cypress are the trees most
lumbered.

Uses of Wood. — In our forests much of the soft wood (the
cone-bearing trees, spruce, balsam, hemlock, and pine), and pop-
lars, aspens, basswood, with some other species, are made into
paper. The daily newspaper and cheap books are responsible
for inroads on our forests which cannot well be repaired. It is
not necessary to take the largest trees to make paper pulp;
hence many young trees of not more than six inches in diameter
are sacrificed. Of the hundreds of species of trees in our forests.

120

OUR FORESTS

the conifers are probabh' most sought after for lumber. Pine,
especially, is probably used more extensively than any other
wood. It is used for all hea^y construction work, frames of
houses, bridges, masts, spars, and timber of ships, floors, rail-
way ties, and many other purposes. Cedar is used for shingles,
cabinetwork, lead pencils, etc.; hemlock and spruce for heavy
timbers and, as we have seen, for paper pulp. Another use for
our lumber, especialh' odds and ends of all kinds, is in the pack-
ing-box industr3\ It is estimated that nearly 50 per cent of all
the lumber cut finds its way ultimatel}' into the construction
of boxes. Hemlock bark is used for tanning.

The hard woods, ash, basswood, beech, birch, cherry, chest-
nut, ehn, maple, oak, and walnut, are used largely for the
"trim" of om' houses, for manufactm'e of furniture, wagon or
car work, and endless other pm'poses.

Structure of Wood. — Quite a difference in color and struc-
ture is often seen between the heartwood, composed of the dead
walls of cells occupying the central part of the tree trunk, and
the sapwood, the H^-ing part of the stem. In trees which are
cut down for use as lumber and in the manufacture of various
kinds of fm'niture, the markings and differences in color are not
always easy to understand.

Methods of Cutting Timber. — A glance at the diagram of

the sections of timber shows us
that a tree may be cut radially
through the middle of the trunk
or tangentially to the middle
portion. Most lumber is cut
tangentiaUy. Hence the annual
rings appear in a more or less
irregular arrangement, causing
^. , . ^ . ^ grain in the wood, and the elHp-

Diagrams of sections of timber: a, .
cross section; b, radial; c, tangential, tical markings SCCU m many
(From Pinchot, U. S. Dept. of Agr.) gc^^ool desks.

Knots. — Knots, as can be seen from the diagram on the
following page, are branches which at one time started in theu'
outward gro\^i:h and were for some reason killed. Later, the tree,
continuing in its outward gro-wth, surrounded them and covered

DESTRUCTION OF THE FOREST

121

them up. A dead limb should be pruned before such growth
occurs. The markings in bird's-eye maple are caused by
adventitious buds which have not developed,
and have been overgrown with the wood
of the tree.

Destruction of the Forest. By Waste in
Cutting. — Man is responsible for the de-
struction of one of this nation's most valu-
able assets. This is primarily due to wrong
and wasteful lumbering. Hundreds of thou-
sands of dollars' worth of lumber is left to
rot annually because the lumbermen do not
cut the trees close enough to the ground, or
because through careless felling of trees many other smaller
trees are injured. There is great waste in the mills. In fact,

Section of tree trunk
showing knot.

A forest in the Far West totally destroyed by fire and by wasteful lumbering.

man wastes lumber in every step from the forest to the making
of the finished product.

By Fire. — It is estimated that at the present time five
sixths of our original timber has been cut or burned. During

HTJNT. NEW ES.

122

OUR FORESTS

the past five years an area greater than that covered by the
New England states has been destro^^ed by fire. Indirectly,
man is responsible for fire, one of the greatest enemies of the
forest. INIost of the great forest fires of recent years, the losses
from which total in the hundreds of millions, have been due
either to railroads or to carelessness in setting fires in the woods.
It is estimated that in forest lands traversed by railroads from

25 per cent to 90 per cent of
the fires are caused by coal-
burning locomotives. For this
reason laws have been made
in New York state requiring
locomotives passing through
the Adirondack forest pre-
serve to burn oil instead of
coal. This has resulted in a
considerable reduction in the
number of fires. In addition
to the loss in timber, the
fires often burn out the or-
ganic matter in the soil (the
"duff") forming the forest
floor, thus preventing the
growth of other trees there
for many years to come. In
New York and other states
fires are prevented by an or-
ganized corps of fire ward-
ens, whose duty it is to watch
the forest and fight forest fires.
Other Enemies. — Other enemies of the forest are numerous
fungous plants of which we shall learn more later, insect para-
sites, which bore into the wood or destroy the leaves, and graz-
ing animals, particularly sheep. Wind and snow also annually
kill many trees.

Forestry. — The American forests have long been our pride.
In Germany, especially, the importance of the forest has long
been recognized, and the German forester or caretaker of the

Woodpeckers and other birds protect
the forest by eating destructive insects.
Photograph from American Museum of
Natural History.

FORESTRY

123

>

forests is well known. In some parts of central Europe, the
value of the forests was seen as early as the year 1300 A.D.,
and many towns consequently bought up the surrounding
forests. The city of Zurich has owned forests in its vicinity for
at least 600 years. In this country only recently has the im-
portance of preserving and caring for our forests been noted by
our government. Now, however, we have a Forest Service in
the U. S. Department of Agriculture; and this and numerous
state and university schools of forestry
are rapidly teaching the people of this
country the best methods for the pres-
ervation of our forests. The Federal
Government has set aside a number of
tracts of mountain forest in some of the
Western states, making a total area of
over 167,000,000 acres. New York has
established for the same purpose the
Adirondack Park, with nearly 1,500,000
acres of timber land; Pennsylvania has
a park of 700,000 acres, and many other
states have followed their example.

Methods for Keeping and Protecting
the Forests. — Forests should be kept
thinned. Too many trees are as bad as
too few. They struggle with one another
for foothold and light, which only a few
can enjoy. The cutting of a forest should
be considered as a harvest. The oldest
trees are the '^ ripe grain," the younger
trees being left to grow to maturity.

Several methods of renewing the forest are in use in this
country. (1) Trees may be cut down and young ones allowed
to sprout from the stumps. This is called coppice growth.
This growth is well seen in parts of New Jersey. (2) Areas or
strips may be cut out so that seeds from neighboring trees are
carried there to start new growth. (3) Forests may be artifi-
cially planted. Two seedlings planted for every tree cut is a
rule followed in Europe. The greatest dangers are from fire

We must protect our
city trees. A tree badly
wounded by "cribbing"
of horses.

124

OUR FORESTS

and from careless cutting, and these dangers may be kept ir
check by the efficient work of our national and state foresters.

A City's Need of Trees. — All over the United States the
city governments are beginning to realize what European cities

have long known, that trees
are of great value to a city.
Many cities are spending
money not only to plant trees,
but for proper protection to
those already growing. Thou-
sands of city trees are annually
killed by horses which " crib"
upon them (Figure, p. 123).
This may be prevented by
proper protection of the trunk.
The Forester and his Work.
— A new and attractive pro-
fession has opened in recent
years for young men who are
fond of the great out-of-doors.
Forest rangers are state or
national officials whose duty it
is to protect the forests. They
watch for and fight fires, patrol
sections of forest to prevent

Forest ranger on steel lookout tower, illegal Cutting, regulate Cattle

watching for forest fires. This tower grazing in forest reserves, and

is connected with others by telephone. . i i i

Photograph from Pennsylvania Depart- m general Watch OVer OUr

ment of Forestry. great national asset, the forests.

Foresters are appointed by private interests also to take
practical charge of the care and growth of the forests.

Chicago has appointed a city forester, who has given the fol-
lowing excellent reasons why trees should be planted in the
city:

(1) Trees are beautiful in form and color, inspiring a constant appreci-
ation of nature.

(2) Trees enhance the beauty of architecture.

(3) Trees create sentiment, love of country, state, city, and home.

SUMMARY 125

(4) Trees have an educational influence upon citizens of all ages, es-
pecially children.

(5) Trees encourage outdoor life.

(6) Trees purify the air.

(7) Trees cool the air in summer and radiate warmth in winter.

(8) Trees improve climate and conserve soU and moisture.

(9) Trees furnish resting places and shelter for birds.

(10) Trees increase the value of real estate.

(11) Trees protect the pavement from the heat of the sun.

(12) Trees counteract adverse conditions of city life.

Let us all try to make Arbor Day what it should be, a day
for planting and caring for trees; for thus we may help to pre-
serve this most important heritage of our nation.

Summary. — Forests are of much importance because they
(1) regulate our water supplies, (2) prevent erosion, (3) change
climate, (4) are of great commercial importance. The enemies
of the forest are wind and other natural forces, fire, and man's
carelessness in cutting, and his unwillingness to look forward
into the future. The cure will come through conservation, tree
planting, and the work of the foresters.

Problem Questions. — 1. Describe ten uses of the forest.

2. How might cities depend upon the forest?

3. Describe five methods of forest destruction.

4e How can you help to prevent forest destruction?

Problem and Project References

A-pgar, Trees of the Northern United States. American Book Company.

Fernow, Care of Trees. Henry Holt and Company.

Green, Principles of American Forestry. Wiley.

Hodge, Nature Study and Life, pp. 365-391. Ginn and Company.

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Murrill, Shade Trees, Bui. 205, Cornell University Agricultural Experiment
Station.

Pinchot, A Primer of Forestry, Division of Forestry, U. S. Department of Agri-
culture.

Roth, A First Book of Forestry. Ginn and Company.

Sharpe, A Laboratory Manual. American Book Company.

Ward, Timber and Some of its Uses. The Macmillan Company.

XI. THE VARIOUS FORUMS OF PLANTS AND HOV^
THEY REPRODUCE THEIMSELVES

Problem, How to know some forms of plant life. (Optional.)
{Laboratory Manical, Prob. XX; Laboratory Problems, Probs. 11 4,

-^ (a) An alga, (c) A moss.

(5) A fungus. {d) A fern.

Adaptation to Environment. — Plants, as well as animals, are

greatl}' affected b}' what immediately suiToimds them, — their

enviromnent. We have shown
in om' experiments that a
variation in the envii'onnient
(conditions of temperatm'e,
moistm'e, light, etc.) is capable
of changing or modif3^ing
the struct m-e of plants very
greatly. The changes which
a plant or animal has under-
gone, that fit it for conditions

in which it lives, are called adaptations to environment.

The first plants probably lived in the water. ^Most of the plants

wliich are simplest in struc-
ture still hve m the water.

In such plants we can

distinguish no root, stem,

or leaf. This simplest fonii

of plant bod}' is called a

thallus. It maj' consist of

a single cell or of man}'

cells; it maj^ be of various

shapes; but a thallus never

has the organs belonging to

higher plants.

It seems likely that, as

more land appeared on the . , , , . ^ , ,. . , ,

A red seaweed, showing a imely divided

.earths smiace, plants be- thallus body.

126

A red seaweed, an example of a thallus
bodv.

ALG^

127

came adapted to changed conditions of life on dry land. With
this change in environment came a need of taking in water,
of storing it, and of conducting it to various parts of the organ-
ism. Thus we may imagine how plants came to have roots,
stems, and leaves, adapted to their environment on dry land. We
find in nature that those plants and animals which are best adapted

Rockweed, a brown alga, showing the distribution on rocks below high-water mark.

or fitted to Kve under certain conditions are the ones which
survive and drive other competitors out from their immediate
neighborhood. Nature selected those which were best fitted to
live on dry land, and they have eventually covered the earth
with their progeny. Gradually the forms of life grew more and
more complex until at last very complicated organisms such as
the flowering plants developed. Between the flowering plant
and the simplest of all plants are several great plant groups
which show steps in complexity of structure between the most
lowly and the most highly specialized plants. The simplest of
all these forms are the algae (arje).

Algae. — The algae are a diverse collection of plants, con-

128 FORMS AND REPRODUCTION OF PLANTS

taining forms of many ^hapes and sizes. The body of an
alga is a thallus; it may be platelike, circular, ribbon-formed,
threadlike, filamentous, or even composed of a single cell. A
large number of the algae inhabit the water. In color they vary
from green through the shades of blue-green to yellow, brown,
and red. The latter colors are best seen in the seaweeds, all
of which, however, contain chlorophyll.

Green Algae. — The plants known as the green algoe are of
great interest to us because of their distribution in fresh water,

and also because of their
economic importance as a sup-
ply of oxygen for fish and other
animals in the waters of our
inland lakes and rivers. Our
attention is called to them in
an unpleasant way at times,
when, after multiplying very
rapidl}^ during the hot summer,
they die suddenly in the early
fall and leave their remains in
our water supply. Much of the
unpleasant taste and odor of
drinking water comes from this
cause.
The city of New York has recently had an unpleasant
experience with a tiny alga called synu'ra. This little plant,
although harmless, gives an oily, disagreeable taste to water.
One part of the water supply in which synura was present in
large numbers had to be cut off from the main supply and
treated before it was fit for use. Such
experiences are not uncommon and are
usually prevented by treating with
copper sulphate in dilution.

Pleurococcus. — Many other forms _., '^ ^ "^ .1

'^ , Pleurococcus. A, single cell;

of algae are common. One of the sim- b, colony of four cells formed

plest is pleurococcus (pl(X)-r6-k6k'us). f'-om the ondnal cell .4 .

This little plant consists of a single tiny cell, which by division
may give rise to two or even more cells which cling together

Synura.

PLEUROCOCCUS, DIATOMS, POND SCUM 12P

[n a mass. The green color on tree trunks, stone houses, etc,
is often due to millions of these little plants.

Diatoms. — These plants are found in vast numbers living on
the mud or stones at the bottom of small streams. The plant
body is inclosed in a cell wall composed largely of silica. Many
of the diatoms are free-swinuning. They compose a large per-
centage of the living organisms found near the ocean's surface.

Pond Scum (Spirogyra). — This alga is well known to every
boy or girl who has observed a small pond or sluggish stream.
It grows as a slimy mass of green threads or filaments. Under
the low power of the microscope, the body of a thread of pond

Spirogyra: n, nucleus; s, chloropliyll bands.

scum is seen to be made up of elongated cylindrical cells, each
of which contains a spirally wound band of chlorophyll bodies.
Careful study shows the presence of a nucleus held in the
body of the cell by strands of protoplasm, the remainder of
the space within the cell being a large vacuole filled with
cell sap.

Pond scum may grow by simple division of the cells in a fila-
ment. This method of asexual reproduction is the way growth
takes place in the cells of the root, stem, or leaf of a flowering
plant, but another method of reproduction is also seen in pond
scum. The cells of two adjoining filaments may push out tubes
which meet, thus connecting the cells with each other. Mean-
time the protoplasm of the cells thus joined condenses into two
tiny spheres; the bands of chlorophyll are broken down, and
ultimately the contents of one of the cells passes through the
connecting tube and mingles with the cell of the neighboring fila-
ment. The result of this process of fusion is a thick-walled rest-
ing cell which is called a zygospore (zI'g5-spor). The cell thus
formed can withstand considerable extremes of heat and cold,
and may be dried to such an extent that it is found in dust

130 FORMS AND REPRODUCTION OF PLANTS

or floating in the air. Under favorable conditions, this spore
will germinate and produce a long filament by asexual repro-
duction.

Conjugation. — The process by which two cells of equal size unite
to form a single cell is called conjugation. It is believed to be a
sexual process which corresponds in a way to
fertilization in the higher plants.

Fungi. — The simplest plants, of which we

have just seen examples, are called thallophytes

(tharS-fits). Of these there are two groups, the

olgw or plants containing chlorophyll, and the

fungi (fun'ji), or those which do not contain

chlorophyll. As a direct result of the lack of

chlorophyll in the cells, the fungi are unable to

make their own food. They must obtain food

from other plants or animals. So7ne take up

their abode upon living plants or animals, in which

case they are called parasites', others obtain their

food from dead organic matter and are called

sapropJujtes (sap'r6-fits). The above facts make

Conjugation of the group of the fungi of immense economic

importance to man. We shall consider several

of these plants in their dii'ect relation to the

human race.

Mosses. — These are mostly shade-loving and m.oisture-

loving plants. They form velvety carpets in many of our

forests, but they often show their preference for moist localities

by covering the wooded shores of lakes and swamps.

Pigeon-wheat Moss. — One of the mosses frequently seen and
easily recognized is the so-called pigeon-wheat moss. The re-
semblance of a large number of these plants to a mimic field
of grain has given the name pigeon- wheat to this form.

Forms of Moss Plants. — Thi'ee kinds of moss plants appear
to be present: leafy plants, others bearing a stalk and capsule,
and still others which terminate at the end in a little rosette
of leaves, inclosing what appears to be a tiny flower.

Leafy Moss Plant. — A leafy moss plant has rhizoids (ri'zoidz)
or hair-like roots, an upright stem, and green leaves. In the

Spirogyra; zs, zygo
spore; /, fusion in
progress.

REPRODUCTION OF MOSSES

131

plants which have a stalk and capsule, the stalk grows directly
from the end of the leafy plant.

Sporophyie. — The capsule is the spore-producing part {spo-
ran'gium) of the moss plant. The stalk and capsule together
form the sporophyte (spo'r6-fit) or
spore-producing generation of the
moss.

Gametophyte. — The spore germi-
nates into a threadlike structure,
called a protone'ma. The proto-
nema soon develops rhizoids; tiny
buds appear which in time form the
adult moss plants. These plants may
grow only leaves, or they may de-
velop into plants that bear at the
summit a little rosette of leaves
within which lie a number of tiny
organs holding sperm cells. Other
moss plants not so tall as the sperm-
producing plants bear at the sum-
mit of the stem a tuft of leaves
which hide a number of small flask-
shaped structures, each of which
contains a single egg cell. These two
kinds of plants form the sexual gen-
eration of the moss. This stage of
the plant is called the gametophyte
(ga-me't6-fit) because it produces the
gametes or sexual cells, — eggs and
sperms. After a sperm cell has been
transferred (usually by means of a drop of dew) to the egg cell,
a fusion of the two cells takes place. This is the process of
fertilization. The fertilization of the egg cell results in the
growth of that part of the plant which forms and bears the
asexual spores, the stalk and capsule, or sporophyte. These
spores give rise in turn to a leafy moss plant which bears or-
gans producing eggs and sperms. This process of reproduction
by two alternating stages is known as alternation of generations.

Two moss plants, showing the
gametophyte G and the sporo-
phyte S.

132 FOR]\IS AND REPRODUCTION OF PLANTS

The Ferns and their Allies. — This group of plants is of
much more importance in tropical countries, where many more
forms are found than here. They are cliiefl}^ interesting to us
in our elementar}^ study because the}^, like the mosses, show
alternation of generations in their life history.

Life History of a Fern. — The common fern of om' woods
begins life as a spore. This germinates into a tiny heart-
shaped body called a
prothaVlus which con-
tains sex organs hold-
ing sperm and egg cells.
These cells after ferti-
lization produce leafy
structures (fronds)
which bear the asexual
spores. These spores
when ripe germinate in
the ground and the life
cycle begins over again,
a sexual generation al-
tei'nating with an asex-
ual generation.

It may be said that
the ferns as a group
have formed a large
part of the enormous
deposits of coal (almost
pm-e carbon) from which
we now derive the

Alternation of generations in the fern: The
fronds F produce groups of spore cases s called
sori. Each sorus is sometimes covered by an in-
dusium i. A sorus is made up of sporangia sp, and
each sporangium forms spores m. A spore may
gei-minate under favorable conditions to form a
tiny prothalkis P. Tliis in turn forms two kinds
of organs, antheridia An, bearing sperms, and
archegonia Ar, bearing egg cells e. As a result of
the union of an egg and a sperm cell E, the adult gj^erev tO run OUr mftnv
fern plant is formed. . *^

engines.
Sexual Reproduction in Flowering Plants. — Flowering plants
reproduce their kind by the formation of seeds. As we know,
the flower produces in the ovary structures which are called
ovules. In the interior of the ovule is found a clear proto-
plasmic area which is called the embryo sac._ In this area is a
cell (the egg cell) which is destined to form the future plant.
In the pollen grain is found another cell, the sperm. This cell,

SYSTEMATIC BOTANY 133

after the germination of the pollen grain on the stigma of the
flower, passes through the pollen tube, enters the ovule, and
unites with the egg cell. The fertilized egg grows into the young
plant within the seed, known as the embryo (see pages 25-27).
This method of reproduction, called sexual reproduction, is
found in the spermafophytes, that is, all seed-producing plants.

Botanists have shown that in the spermatophytes there exists
an alternation of generations as in the mosses and ferns. The
pollen grain is believed to be a spore, which develops into the
male gametophyte (the pollen tube), while the embryo sac is
another spore, within which is found the female gametophyte
Most of the life of the flowering plant is thus passed evidently
in the asexual or sporophyte stage. All plants — and all animals
as well — form the cells which compose their bodies by either
sexual or asexual growth, and the stage of asexual growth is
usually separated from the period of sexual growth.

Systematic Botany. — The plant world is divided into many
tribes or groups. Not only are plants placed in large groups
each having a few very conspicuous characteristics in common,
but smaller groupings have been made, each containing only
a few plants having many characteristics in common. If we
plant a number of peas so that they wiU all germinate under
the same conditions of soil, temperature, and sunlight, the seed-
lings that develop will differ one from another in a slight degree.
But in a general way they will have many characteristics in
common, as the shape of the leaves, the possession of tendrils,
and the form of the flower and fruit. The smallest group of
plants or animals having certain characteristics in common that
make them different from all other plants or animals is called a
species. Individuals of a species differ slightly; for no two
individuals are exactly alike.

A number of species are combined in a larger group called
a genus (je'nus). For example, many kinds of peas — the garden
peas, the wild beach peas, the sweet peas, and many others —
are all grouped in one genus because they have certain structural
characteristics in common.

Plant and animal genera are brought together in still larger
groups, the classification based on general likenesses in struc-

134 FORMS AND REPRODUCTION OF PLANTS

ture. Such groups are called, as they become successively larger,
Family, Order, and Class. Thus the plant and animal kingdoms
are grouped into divisions, the smallest of which contains indi-
viduals very much alike; and the largest of which contains very
many groups of individuals, each group having some charac-
teristics in common. This is called a system of classification.

CYMNOSPERMS ANQI05PERMS

VERTEBRATA

SPERMATOPHYTES
I
PTERIDOPHYTES

BRY0PHYTE5 /

\y FUNQI

ALO/E

BACTERIA

THALL0PHYTE5

MOLLUSCA

INSECTA cpumCEA

ECHINODERMATA

PRIMITIVE OROANISMS

Tree of life. There is little difference between the lowest forms of plant and ani-
mal life, but much difference between the highest plants (Angiosperms) and the
highest animals ( Vertebrata) .

Classification of the Plant Kingdom. — The entire plant king-
dom has been grouped as follows by botanists:

Angiosperms (an'ji-6-spermzj, true flow-
ering plants.
Gymnosperms (jim'n6-spermz), the pines
and their allies.

2. Pteridophytes (ter'i-d6-f Its) . The fern plants and their allies.

3. Bry'ophytes. Moss plants and their allies.

i ^^9^f simple plants containing chlorophyll.

4. ThaUophytes, | ^^^^^^ ^^^^^^ p^^^^^ without chlorophyll.

The extent of the plant kingdom can only be estimated, be-
cause each year new species are added to the lists. There are

1. Sperrnatophytes. \

CLASSIFICATION OF PLANTS 135

about 110,000 species of flowering plants and nearly as many
flowerless plants. The latter consist of over 3500 species of
fernlike plants, some 16,500 species of mosses, over 5600 lichens
(li'kenz) — plants consisting of a partnership between algae and
fungi, — • approximately 55,000 species of fungi, and about 16,000
species of algse. Some botanists regard bacteria as fungi, while
others make them a separate branch of thallophytes, as indicated
in the diagram on page 134.

Summary. — We have seen in this chapter that the diverse
forms of plants on the earth may be grouped into four great
divisions, the Thallophytes or very simple plants having a
thallus body, the Bryophytes or mosses, Pteridophytes or ferns,
and Spermatophytes or seed-producing plants.

The environment has doubtless played a very important
part in producing the various forms of plants, for botanists
believe that many millions of years ago the earth was covered
with a very much simpler vegetation than it is at present.
Plants have been forced to adapt themselves to new conditions
in order to live and varying conditions of environment have
resulted in developing the different kinds of plants now existing.

Problem Questions. — 1. How do changes in environment
cause changes in plant structure?

2. Why are the algae believed to be the first plants to in-
habit the earth?

3. How are algse of use to man?

4. How can you distinguish a fungus? a moss? a fern?

5. What is meant by alternation of generations?

6. What is a species?

7. What is meant by a system of classification?

Problem and Project References

Andrews, Botany All the Year Round, Chapter X. American Book Company.

Conn, Bacteria, Yeasts and Molds of the Home. Ginn and Company.

Coulter, Barnes and Cowles, A Textbook of Botany, Vol. I. American Book

Company.
Densmore, General Botany. Ginn and Company.
Grout, Mosses with a Hand Lens. A. .J. Grout, New York City.
Hunter, Laboratory Problems in Civic Biology. American Book Company.
Parsons, How to Know the Ferns. Charles Scribner's Sons.
Sedgwick and Wilson, General Biology. Henry Holt and Company.
Underwood, Our Native Ferns and their Allies. Henry Holt and Company.

XII. HOW PLANTS ARE MODIFIED BY THEIR

SURROUNDINGS

Problem, To discover how plants are modified by their suT'
roundings. {Optional.) {Laboratory Manual, Prob. XXI.)

(a) Hydrophytic society. (c) Mesophytic society,

{b) Xerophytic society. {d) Plant societies.

{e) Plant zonation.

The Way in which Plants are modified by their Surround-
ings.— As we have found in our experiments, young plants

' are delicate organisms,
which are affected pro-
foundly by the action of
forces outside themselves.
The same is true to a
certain extent of older
plants. The presence or
absence of moisture starts
or prevents growth in
seeds or young plants;
absence of light changes
the form and color of
green plants; and favor-
able temperature, which
varies for different plants,
influences the growth.
Pea seedlings may grow

Pond lilies, plants with floating leaves,
graph by W. C. Barbour.

Photo-

for a time in sawdust, but we know that they will be much
healthier and will live longer if placed in soil under natural
conditions. We are forced to the conclusion that differences in
the forms and habits of plants are caused by the action of their
surroundings upon them. The plants which have become in
various ways fitted to live under certain conditions are said to
be adapted to such conditions. Such plants as are best fitted to

136

WATER SUPPLY

137

live under the conditions in which they are placed are the ones
which will survive.

Water Supply. ^- Water supply
is one of the important factors in
causing changes in structure of
plants. Plants which live entirely
in the water often have slender
parts with finely divided leaves.
Their roots are apt to be short and
stout. The interior of such a plant
is made up of spongy tissues which
allow the air dissolved in the water
in which they live to reach all
parts of the plant. If the plant
has floating leaves, as in the pond
lily, the stomata are all in the
upper side of the leaf.

Hydrophytes. — When a plant lives in water or in soil satu-
rated with water, the conditions of its environment are said to be
hydrophyfic, and such plant is said to be a hydrophyte (hf dr6-fit).

Xerophytes. — If we examine plants growing in dry or desert

A water plant, showing the hiiely
divided leaflike parts.

A xerophyxic condition. Cacti and other plants in a desert.
Photograph from American Museum of Natural History.

HUNT. NEW ES. — 10

138 PLAXTS MODIFIED BY THEIR SURROUXDIXGS

conditions, as cactus, sagebrush, aloe, etc., we find that the leaf
sui'face is invariabh^ reduced, sometimes forming spines as in the
cactus. The stem may be thickened so as to store water; a cover-
ing of hahs or some other material ma}^ be present and lessen
the loss of moisture by evaporation. The conditions of extreme
drjmess under which such plants live are called xerophytic (ze-r6-
fit'ik), and such plants are known as xerophytes (ze'r6-fits). Ex^
amples of xeroph>i:es are the cacti, yuccas, centmy plants, etc.
Halophytes. — If the water or saturated soil in which the
plant lives contains salts, such as sea salt or the alkali salts of

A mesophytic coiidition. A valley in central New York.

some of our Western lakes, the conditions are said to be halo-
phyt'ic, and a plant living under such conditions is known
as a hal'ophyte. Haloph3i:es show mam^ characteristics which
xeroph}i;es show.

Mesophytes. — ^lost plants in the Temperate Zone occupy a
place midway between the xerophytes on one hand and hj^di'o-
phytes on the other. They are plants which require a moderate
amount of water in the soil and air surrounding them. Such
are most of our forest and fruit trees, and most of our gar-

COLD REGIONS

139

den vegetables. Conditions of moderate moisture are called
mesophytic; the plants living under such conditions are known
as mesophytes (mes'6-fits).

Other Factors. — It is a matter of common knowledge that
plants in different regions of the earth differ greatly from one
another in shape, size, and general appearance. If we study
the causes for these changes, it becomes evident that the water
supply is one of the most important factors, whether in the

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The effect of wind upon trees in an exposed location. Photograph by W. C. Barbour.

tropics or arctic regions. But in addition to water supply, the
factors of temperature, light, soil, wind, etc., all play impor-
tant parts in determining the form and structure of a plant.

Cold Regions. — : Here plants, which in lowland regions of
greater warmth and moisture have a tall form and luxuriant
foliage, are stunted and dwarfed; their leaves are small and
tend to gather in rosettes, or are otherwise closely placed for
warmth and protection. As we climb a mountain we find that
the average size of plants decreases as we approach the line of

140 PLANTS MODIFIED BY THEIR SURROUNDINGS

perpetual snow. The largest trees occur at the base of the
mountain; the same species of trees near the summit appear
as mere shrubs. Continued cold and high winds are evidently
the factors which influence the slow growth and the small size
and shape of plants near the mountain tX)ps. Cold, little light
during the short days of the long winter, and a slight amount
of moistm-e all act upon the vegetation of the arctic region,

Polar limit of trees, northern Russia. All these trees are full grown, and most of
_ them are almost one hundred years old.

and tend to produce very slow growth and dwdrfed and stunted
forms.

Vegetation of the Tropics. — A rank and luxuriant growth is
found in tropical countries with a uniformly high temperature
and large rainfall. In general it may be estimated that the
rainfall in such countries is at least twice as great as that of
New York state, and in many cases three to four times as
great. An abundant water supply, together with an average
temperature of over 80° Fahrenheit, causes extremely rapid
growth. One of the bamboo family,, the growth of which was
measured daily, was found to increase in length on the average
nearly three inches in the daytime and over five inches during
each night. The moisture present in the atmosphere allows the

VEGETATION OF THE TROPICS

HI

Cv^/^*^5^^ ; \ Region of Lichens.

''^^^cf:^'i^-•- c r^'^^iNv Region of Grasses.

^ ^-^^"^ **^^^^2:^"1^-^ Shrubby Region.
LS|fV«ESM?'WiiV^'^" °^ Cinchona trees.

/^oi ^^ p/" 953.^^^"^^*°^ ordinary large trees

Plant regions in a tropical mountain. Explain the diagram.

growth of many air plants {ep^iphytes), which take the mois-
ture directly from the air by means of aerial roots.

The absence of cold weather in tropical countries allows trees
to mature without a thick coating of bark or corky material,

Conditions in a moist, semitropical forest. The so-called "Florida moss" is a
flowering plant. Notice the resurrection ferns on the tree trunk.

142 PLANTS MODIFIED BY THEIR SURROUNDINGS

and so they have a green and fresh appearance. Monocotyledo-
nous plants prevail. Ferns of all varieties, especially the largest
tree ferns, are abundant.

Plant Life in the Temperate Zones. — In the state of New
York, conditions are those of a typical temperate flora. Ex-
tremes of cold and heat are found, the temperature ranging
from 30° below zero Fahrenheit in the winter to 100° or over

Plant societies near a pond. Notice that the plant groups are arranged in zones
with reference to the water supply, the true mesophytes being in the background.

in the summero Conditions of moisture show an average rain-
fall of from 24 inches to 52 inches.

In the eastern part of the United States the rainfall is suffi-
cient to supply very extensive forests, which aid in keeping the
water in the soil. In the Middle West the rainfall is less, the
prairies are covered with grasses and other plants which have
become adapted to withstand dryness. In the desert region of
the Southwest we find true xerophytes, cacti, yuccas, and others,
plants which are adapted to withstand almost total absence of
moisture for long periods. In the Temperate Zone as elsewhere
the water supply is the primary factor which determines the
form of plant growth.

PLANT FORMATIONS AND SOCIETIES 143

Plant Formations and Societies. — All of the factors referred
to act upon the plants we find living together in a forest, a
sunny meadow, along a roadside, or at the edge of a pond.
Any one familiar with the country knows instinctively that we
find certain plants, and those plants only, living together under
certain conditions.

Plants ' associated under similar conditions, as those of a
forest, meadow, or swamp, are said to make up a formation,

A rock society. Photograph by W. C. Barbour.

and a plant formation is brought about by the conditions of the
immediate surroundings, the habitat of its members. If we in-
vestigate a plant formation, we find it to be made up of certain
dominant species of plants; that here and there definite com-
munities exist, made up of groups of the same kind of plants.
We can see that each one of these plant groups in the society
evidently came originally from a single individual which flour-
ished under the peculiar conditions of soil, water, light, etc.,
that were found in this spot. These single plants have evi-
dently given rise to the members in each little family group,
and thus have populated the locality.

So we find among plants communal conditions similar to
those of some animals. The many individuals of the com-

144 PLANTS MODIFIED BY THEIR SURROUNDINGS

munity live under similar conditions; they need the same sub-
stances from the air, the water, the soil. They all need the
light; they use the same food. Therefore there must be com-
petition among them, especially between those near to each
other. The plants which are strongest and best fitted to get
what they need from their sm-roundings, live; the weaker ones
are crowded out and die.

But their lives are not all competition. The dead plants and
animals give nitrogenous material to the living ones, from which

the latter make living
matter; some bacteria
provide certain of the
green plants with nitro-
gen; many of the green
plants make food for
other plants lacking chlo-
rophyll, while some algse
and fungi actually Jive
together in such a way
as to be of mutual benefit
to each other. The larger
plants may shelter the
smaller ones, protecting
them from wind and storm, while the trees provide humus
which holds the moisture in the ground, giving it off slowly to
other plants. Animals scatter and plant seeds far and wide,
and man may even start entire colonies in new^ localities.

How Plants invade New Areas. — New areas are tenanted
by plants in a similar manner. After the burning over of a
forest, we find a new generation of plants springing up, often
quite unlike the former occupants of the soil. First come the
fireweed and other light-loving weeds, brought by means of
their wind-blown seeds. With these are found patches of
berries, the seeds of which w^re brought by birds or other ani-
mals. A little later, quick-growing trees having seeds easily car-
ried for some distance by the wind, like the aspen, or seeds often
distributed by birds, as the wild cherry, invade the territory.
Eventually we may have the area retenanted by the same

A community of trilliums. Photograph by
W. C. Barbour.

HOW PLANTS INVADE NEW AREAS

145

kind of inhabitants as formerly, especially if the destruction of
the original forest was not complete.

In like manner, on the upper mountain meadows or by the
sand dunes of the seashore, wherever plants place their out-
posts, the advance is made from some thickly inhabited area,
and this advance is always aided or hindered by agencies

A plant outpost. The struggle here is keen. The advancing
sand has killed the trees in the foreground.

outside of the plant — ■ the wind, the soil, water, or animals.
Thus the seeds obtain a foothold in new territory, and
new lands are captured, held, and lost again by the plant
communities.

Summary. — Plants are so modified by the factors of their
environment that they may take various forms and have many
kinds of devices to enable them to cope with the unfavorable
factors in their environment. Water plays a most important
part in modifying their form and structure. Plants are grouped
according to water supply, into xerophytic or drought-loving
plants, hydrophytic or water-loving plants, and mesophytic
plants or those which need a moderate supply of moisture.
Different species of plants are usually found in definite associa-
tions or groups. This grouping is brought about by the need
of similar environmental conditions by different kinds of
plants.

Problem Questions. — 1. Why do plants vary in different
localities?

146 PLANTS MODIFIED BY THEIR SURROUNDINGS

2. What are the chief structural differences between hydro-
phytes, xeroph3i^es, and mesophj^tes?

3. TMiat are the characteristics of tropical plants? of those
from cold regions?

4. How might a new outpost of plant life be established?

Problem and Project References

Andrews, Bof/iny All the Year Round. American Book Company.

Clements, Plant Physiology and Ecology. Henry Holt and Company.

Coulter, Plant Relations. D. Appleton and Company.

Coulter, Barnes and Cowles, A Textbook of Botany, Vol. II. American Book

Company.
Hunter, Laboratory Problems in Civic Biology. American Book Company.
Kerner, Natural History of Plants. Henry Holt and Company.
Schimper, Plant Geography. Clarendon Press.

XIII. HOW PLANTS BENEFIT AND HARM

MANKIND

Problem, To determine how fungi help or harm mankind.
(Laboratory Manual, Prob. XXII; Laboratory Problems, Probs.
87 to 94.)

(a) Yeast.

(b) Mold.

(c) Other fungi.

The Economic Value of Plants. — Besides the other relations
existing between plants and animals, there is a relation between
man and plants measurable in dollars and cents. Plants are of
direct value or harm to man. We call this an economic relation.
We have seen how they supply him with his cereals and flour,
his fruits and garden vegetables, his nuts and spices, his bever-
ages and the sugar to sweeten them, his medicines and his dye-
stuffs. They supply the material out of which many of his
clothes are made, the thread with which they are sewed to-
gether, the paper which covers the package in which they are
delivered, and the string with which the package is tied. The
various uses of the forest have been mentioned before; the
need of trees to protect the earth, their usefulness in regulating
the water supply, and their direct economic importance for
lumber and firewood. Many of us forget, too, that much of
the energy released on this earth to man as heat, light, or mo-
tive power comes from the dead and compressed bodies of
plants which thousands of years ago lived on the earth and now
form coal. Plants are thus seen to be of immense direct eco-
nomic importance to mankind.

The Harm Plants Do. — Unfortunately, plants do not all
benefit mankind. We have seen the harm done by weeds,
which scatter their numerous seeds far and wide or by other
devices gain a foothold and preempt the territory which useful
plants might occupy were they able to cope with their better-

147

148 HOW PLANTS BENEFIT AND HARM MANKIND

equipped adversaries. Plants with poisonous seeds and fruits
are undoubtedly responsible for the death of many animals and
of man as well.

But the plants by far the most harmful to mankind are the
fungi. Damage to the amount of hundreds of millions of dol-
lars a year may be laid directly to them. More than that, if
we include the tiny organisms called bacteria they are respon-
sible for over one half of the total human deaths, because of
their parasitic habits.

Yeast. — Although as a group the fungi are harmful to man
in the economic sense, nevertheless there are some fungi that
stand in a decidedly helpful relationship to the human race.
Chief of these are the yeast plants. Yeasts are found to exist
in a wild state in very many parts of the world. They aTe
found on the skins of apples, grapes, and other fruits, and they
may exist in a dry state almost anywhere in the air around us.
In a cultivated state we find them as the agents which cause
the rising of bread, and the fermentation in beer and other
alcoholic fluids.

Yeast Plants. — ■ The common compressed yeast cake contains
millions of these tiny plants. In its simplest form a yeast plant

is a single cell. If you shake
up a bit of a compressed yeast
cake in a mixture of molasses
and water and then examine
a drop of the milky fluid after
it has stood over night, it will
be seen to contain vast num-
bers of yeast plants. The
plants are tiny ovoid cells

from

1

2500

to

of

an

1 0,000

Budding yeast plants stained to show j^ch in diameter. The pro-
nucleus, highly magnified. .

toplasm IS granular and con-
tains no chlorophyll. The cells grow by means of budding, the
parent cell forming one or more daughter cells somewhat smaller
than the original cell and attached to it (see Figure). Some-
times yeast cells form spores, although we rarely see them in
the laboratory.

FUNGI 149

Conditions Favorable to Growth of Yeast. — Under certain
conditions yeast, when added to dough, will cause it to rise.
We know also that yeast has something to do with the process
of fermentation. The following home experiment will throw
some light on these points:

Label three pint fruit jars A, B, and C. Add one fourth of a compressed
yeast cake to two cups of water containing two tablespoonfuls of molasses.
Stir the mixture well, divide it into three equal parts, and pour one part
into each jar. Place covers on the jars. Put jar A in the ice box on the
ice, and jar B over the kitchen stove or near a radiator; heat jar C by
immersing it in a dish of boiUng water, and place it next to B. After
forty-eight hours, look to see if any bubbles have made their appearance in
any of the jars. If the experiment has been successful only jar B will show
bubbles. After bubbles have begun to appear at the surface, the fluid in
jar B will be found to have a sour taste and will smell unpleasantly. The
gas which rises to the surface, if collected and tested, will be found to be
carbon dioxide. The contents of jar B are said to have fermented. Evi-
dently, the growth of yeast will take place under conditions of moderate
warmth and moisture and in the presence of food.

Fermentation a Chemical Process. — In the growth of yeast
cells the sugar of the solution in which they live is broken
up by an enzyme into carbon dioxide and alcohol. This may
be expressed by the following chemical formula: C6II12O6 =
2(C2H60) + 2(C02). This means that the sugar acted upon
by the enzyme in the yeast cell, is made into alcohol and car-
bon dioxide. This process is called fermentation.

When bread dough is expected to " raise "it is put in a warm
place so that the yeast plants in the dough will grow rap-
idly. They feed upon starch, which they digest into grape
sugar. Fermentation results from the rapid growth, causing
the bubbles of carbon dioxide in the dough. When the bread is
baked the spaces which were filled with carbon dioxide remain
while the alcohol is evaporated in the baking.

The Yeast Plant a Saprophyte. — Since yeast grows upon
dead organic material it is a saprophyte. Saprophytic plants
are frequently seen in our homes and some do much damage.
Bread mold is an example.

Mold. — This is one of our most common fungi. It grows
upon bread, cake, and other organic substances under certain
conditions of temperature and moisture.

150 HOW PLANTS BENEFIT AND HARM MANKIND

We are all familiar with the tangled mass of tiny whitish
threads which are sometimes found growing over damp bread.
The mass of threads is called collectively the mycelium
(mi-se'li-mn), each thread being called a hypha (hi'fa).
Many of the hyphse are prolonged into tiny, upright
threads, bearing a little ball at the top. With the low power
microscope each of these structures is seen to contain many

Stages in reproduction of mold: A, vegetative form, showing the rootlike
rhizoids r, the mycelium m, and the spore-bearing bodies s, in three stages of growth;
B to E, stages in conjugation, resulting in the formation of a zygospore z.

tiny bodies called spores. These spores have been formed
by the division of the protoplasm within the ball or sporan-
gium into many separate bodies or asexual spores. These
spdres, if grown under favorable conditions, will produce more
mycelia, which in turn bear sporangia. The mold, however,
like spirogyra, can produce zygospores under certain conditions.
These are probably sexual spores and are evidently of use to
continue the life of the plant during unfavorable conditions.
Physiology of the Growth of Mold. — Mold, in order to grow
rapidly, evidently needs oxygen, moisture, and a favorable tern-

FUNGI

151

perature. The mold sends down into the bread rootHke proc-
esses. These branching hyphse pass out through their walls
digestive enzymes, which change the starches and proteins of
the bread to soluble substances which are taken in through the
walls of the hyphse by osmosis. Thus a mold digests its food
outside of the body and then absorbs it. These foods are then
used to supply energy and to make protoplasm. This seems to
be the usual method by which saprophytes secure the ma-
terials on which they live.

Other Saprophytic Fungi : Mushrooms. — Some of the best
known of the fungi are the mushrooms or '^ toadstools " as they
are often called. What we
see is the temporary spore-
bearing part, the mycehum
being below ground. The
mushrooms live upon decay-
ing plant or animal material,
which they digest and absorb
by means of their rootlike
hyphse. Care and good judg-
ment are needed in distin-
guishing the harmful from
the edible mushrooms, al-
though it is not hard to learn
some of the edible fungi of a
locality. Why not make this
a project to work out? Ex-
cellent books of reference
on this subject are Marshall's
The Mushroom Book, Double-
day, Page and Company, and
Atkinson's Mushrooms, Henry Holt and Company.

The Shelf Fungus. — This is a near relative of ' the mush-
room. The " bracket " found growing on dead tree trunks is
the spore case, while the mycelium is within the tissue of the
tree. Remove the bark from a tree infected with a bracket
fungus, and you will find the silvery threads of the mycelium
sending their greedy hyphae to all parts of the wood adjacent

Mushiooms; the ^'oinitj.er specimen, at
the right, shows some of the mycelium.
Photographsd by Overton.

152 HOW PLANTS BENEFIT AND HARM MANKIND

to the spot first attacked by the fungus. This fungus begins
its Hfe by the lodgment of a spore in some part of the tree
which has become diseased or broken. Once estabhshed on its
host, it spreads rapidly. Each year many fine trees, sound
except for a slight bruise or other injury, are infected and
eventually killed. In cities thousands of trees become infected
where horses have been hitched carelessly so that they could
gnaw or crib on the tree, thus exposing a fresh surface on
which spores may obtain lodgment and grow (see page 123).
There is no remedy except to burn the infected trees, so as to
destroy the spores.

Suggestions for Field Work. — A field trip to a park or grove near home
may show the great destruction of timber by this means. Count the num-
ber of perfect trees in a given area. Compare it with the number of trees
attacked by the fungus. Does the fungus appear to be transmitted from
one tree to another near at hand? In how many instances can you dis-
cover the point where the fungus first attacked the tree? How do the
spores leave the sporecase? How do they germinate on the tree attacked?

Parasitic Fungi. — Of even more importance are the fungi
that attack a living host, true parasites. The most important
of such plants from an economic standpoint are the rusts,
smuts, and mildews which prey upon grain, corn, and other cul-
tivated plants. Some fungi are also parasitic upon fruit and
shade trees. The chestnut canker, a fungus introduced from
abroad on chestnuts planted near the city of New York in
1904, had during ten years destroyed practically every chest-
nut tree within a radius of 150 miles. At the present time the
disease is spreading rapidly and may eventually destroy all of
the native chestnuts in the United States unless di'astic meth-
ods of combating the pest are used. Hundreds of millions of
dollars' damage has already been done and more will follow.
The pine tree blister rust introduced from Europe about 1909
threatens the existence of nearly $500,000,000 of timber.

Wheat Rust. — Wheat rust is probabl}^ the most destructive
parasitic fungus. For hundreds of years this rust has been
the most dreaded of plant diseases, because it destroys the one
harvest upon which the civilized world is most dependent. For
a long time past the appearance of rust has been associated with

FUNGI 153

the presence of barberry bushes in the neighborhood of the
wheat fields. Although laws were enacted in 1760 in New Eng-
land to provide for the destruction of barberry bushes near
infected wheat fields, nothing was actually known of the rela-
tion existing between the rust and the barberry until compara-
tively recent years. It has now been proved beyond doubt that
the wheat rust passes part of its life as a parasite on the barberry
and from it gets to the wheat plant, where it undergoes a com-
plicated life history. The wheat leaf, its nourishment and liv-
ing matter used as food by the parasite, soon dies, and no grain
is produced. Some wheat rusts appear to have other intermediate
hosts than the barberry, so that the problem of fighting this plant
enemy has been much more difficult than if all the facts about it
were known.

Sac Fungi. — Another group of fungi that are of considerable
economic importance is made up of the sac fungi. Some of these
fungi are called mildews. Some of the most easily obtained
specimens come from the lilac, rose, or willow. These fungi
do not penetrate the host plant to any depth, but cover the
leaves of the host with the whitish threads of the mycelium.
Hence they may be killed by means of applications of some
fungus-killing fluid, as Bordeaux mixture. They obtain their
food from the outer layer of cells in the leaf of the host. Among
the useful plants preyed upon by this group of fungi are the
plum, cherry, and peach trees. The diseases known as black
knot and peach curl are thus caused.

Problem, A study of bacteria in order to determine —

(a) Their conditions of growth.

(b) Some of their relations to man.

(c) Methods of fighting harmful bacteria.

(Laboratory Manual, Prob. XXIII; Laboratory Problems,
Probs. 95 to 103.)

Bacteria. — The bacteria are found in the earth, the water,
and the air: '' anywhere but not everywhere,'' as one writer
has put it. They swarm in stale milk, in impure water, in the
living bodies of plants and animals, and in any decaying
material. These tiny plants, ^' man's invisible friends and foes,"

HUNT. NEW ES. — 11

154 HOW PLANTS BENEFIT AND HARM MANKIND

are of such importance to mankind that thousands of scientists
devote their whole Hves to the study of bacteriology.

How Bacteria were Discovered. — As early as 1683 the
Dutchman Leeuwenhoek is believed to have seen bacteria with
his newly invented microscope. But it was not until 1865
that Louis Pasteur, the famous Frenchman, discovered the rela-
tion between bacteria and disease. Pasteur had shortly before
this proved that bacteria caused fermentation and that when
floating germs got into nutrient fluids such fluids would " go
bad '' and would decay. Pasteur laid the foundation for the

study of disease germs and his name should
be remembered, not alone for his discovery
of a cure for hydrophobia but because he
was the first man to attempt to manufacture
antitoxin serums and vaccines to fight the
poisons produced by disease. Robert Koch is
another man who helped to make bacteri-
ology an important science. We remember
him in particular as the discoverer of the
germ causing tuberculosis.

Size and Form. — Bacteria are the most
minute organisms known. A bacterium of
average size is about -g-^^ of an inch in
length, and perhaps ^^ oqq of an inch in
diameter. Some species are much larger,
others smaller. A common spherical form
is .^ L» of an inch in diameter. It will

Bacteria, highly mag-
nified: a, the germ of
typhoid fever, stained
to show the cilia, little
threads of living matter
by means of which lo-
comotion is accom-
plished; b, a spiral
form with flagella, tiny ^^ 50,000

threads longer than mean more to US, perhaps, if we realize that

cilia ; c, a rod-shaped
form, in a chaia ; d, a
spherical form.

1000 bacteria of average size might be placed
on the dot of this letter i. Three well-
defined forms of bacteria are recognized : a spherical form called
a coc'cus; a rod-shaped bacterium, the bacillus (ba-sil'us); and a
spiral form, the spiriVlum. Some bacteria are capable of move-
ment when living in a fluid. Such movement seems to be
caused by tiny threads of protoplasm called cilia or flagella, which
project from the body and vibrate rapidly. Bacteria reproduce
with almost incredible rapidity. A single bacterium, by simple
fission or splitting, will in twelve hours give rise to almost

BACTERIA

155

17,000,000 offspring if each divides only once every half hour.
It has been estimated that if a bacterium could go on multi-
plying unchecked for five days, it would fill all the oceans of
the earth to a depth of one mile. But of course nothing of the
kind ever happens because of the many unfavorable conditions
which exist. Under unfavorable conditions bacteria die or at
least stop dividing and form spores, in which state they remain
until conditions of temperature and moisture are such that
growth may begin again.

Method of Study. — In order to get a group of bacteria of a
given kind to study, it becomes necessary first to catch them.
This is easily done by expos-
ing to the air a shallow dish —
known as a Petri (pet're)
dish — containing a culture
medium on which bacteria
will grow. The medium is
made by cooking beef broth
and either gelatine or agar-
agar together for a few mo-
ments. The culture medium
is poured into a sterilized
Petri dish while it is still hot
and the cover is placed over
it quickly so that the con-
tents of the dish will remain
sterile or free from all life
until the cover is removed. If after a short exposure to the air
of the schoolroom the dish is covered and put away in a warm
place for a day or two, little spots will appear on the surface
of the culture medium.

Pure Culture. — The spots are colonies composed of millions
of bacteria. If now we wish to study one given form, it becomes
necessary to isolate it from the others in the dish. This is done
by the following process: a platinum needle is first passed
through a flame to sterilize it; that is, to kill all Hving things
that may be on the needle point. Then the needle, which cools
very quickly, is dipped in a colony containing the kind of bac-

A Petri dish culture of bacteria; the
colonies of bacteria are little spots of
various sizes and colors.

loG HOW PLANTS BENEFIT AND HARM .MANKIND

teria we wish to study. This mass of bacteria is qiiickh'
transferred to another steriUzed Petri dish containing cultui'e
mediumj and covered to prevent any other forms of bacteria
from entering. The dish is then placed in a warm oven for a
night in order to get a good gi'owth of bacteria. Wlien we have
succeeded in isolating a certain kind of bacteria in a given dish.
that is, when colonies of only one kind are present, we have a
pure culture.

Conditions Favorable and Unfavorable for Growth of Bacteria.
— Temperature. Like most h^ing things, bacteria grow most
rapidly in a favorable temperature, "^liile this is usually about
body temperature or 98.6° Fahrenheit, it is sometimes lower.
We may saj^ that at this favorable temperature bacteria have
the most rapid growth. Conversely, cold retards their growth,
as does extreme heat. Freezing will stop their growth alto-
gether, although it does not kill the more hardy fonns. Heating
to 150~ to 160" Fahrenheit will, if continued for at least thirty
minutes, destroj' bacteria with the exception of those in the
spore stage. These may resist boihng for some time. In order
to make absolutely sure that all spores are killed, the bacteri-
ologist raises the material which contains them to boihng for
a second or even a thu'd time, with a period of several hours
intervening in each case. This is known as discontmuous
sterilization.

Moisture. Bacteria requu'e considerable moistm^e in order to
grow, although they may be found in an inactive state in drj-
locahties. Household foods, therefore, if in a diy condition,
will not be spoiled bj^ bacteria, a fact worth remembering.

Light. We find that if a Petri dish containing growing bac-
teria is exposed to a strong light the growth will be retarded
or stopped completely. Simlight kills many kinds of bacteria.
This fact has been made use of in the fight against various
disease-producing bacteria, especially those which produce tu-
berculosis. A sickroom should therefore be flooded with sun-
light whenever possible, and should be provided with fm'niture
and hangings that can easily be cleaned and aii-ed.

Air. Although bacteria need oxygen in order to live, as do
all living things, some kinds thrive in the absence of air, ob-

BACTERIA

157

taining the oxygen necessary for oxidation by breaking down
the substances on which they feed, thus releasing oxygen.
Such bacteria are called anaerobic (an-a-er-6b'ik). Most of the
bacteria found in daily life live in the air and are called aerobic.

Bacteria cause Decay. — Bacteria affect mankind in many
ways, either directly or indirectly. First of all, they cause
decay. All organic matter, in whatever form, is sooner or later
decomposed by the action of untold millions of bacteria which
live upon organic matter in water and soil. These bacteria,
therefore, are useful because they feed upon the dead bodies
of plants or animals, which otherwise would soon cover the
surface of the earth to the
exclusion of everything else.
Bacteria may thus be con-
sidered scavengers. Without
bacteria and a few of the
fungi, life on the earth would
be impossible, for green plants
would be unable to get the
raw materials in forms that
they could use in making
food and new living matter.
In this respect bacteria are
of the greatest service to
mankind.

When bacteria grow in suffi-
cient numbers upon foods,
meat, fish, or vegetables, they
spoil them, and may form
poisonous substances called
ptomaines (to'-ma-inz) by
their action on protein. As
the result of eating food con-
taining these ptomaine poisons, one may become violently ill.
Fish and meats that have been kept for some time in cold
storage are very easily spoiled, and should be avoided. Canned
goods that have " worked," that is, those in which yeasts or
bacteria have caused fermentation and decay, are unfit for food.

Tubercles or nodules (little lumps) on
the roots of soy bean, containing nitrogen-
fixing bacteria.

158 HOW PLANTS BEXEFIT AXD HAR:\1 MANKIND

Nitrogen-fixing Bacteria. — Certain bacteria, in the process of
decay, ^' change over " nitrogen in organic material in the soil
so that it can be used by plants in the form of a compound of
nitrogen. But the bacteria living in tubercles on the roots of

clover, beans, peas, etc.,
have the power of ''fixing"
the free nitrogen in the au'
found between pai'ticles of
soil so that it may be ab-
sorbed as a nitrate bj^ the
root hah. This fact is made
use of bj^ farmers who rotate
'^ theh crops, gi'owing first a
crop of clover or alfalfa,
which produce the bacteria,
then plowing these up and

A pasteurizing apparatus.

planting another crop, as wheat or corn, on the same area. The
latter plants, making use of the nitrogen compounds there, pro-
duce a larger crop than when
grown in ground containing
less nitrogenous material.

Other Processes caused
by Bacteria. — Bacteria may
incidentally, as a result of the
process of decay, aid in the
process of feiTaentation. In
making vinegar the yeasts first
make alcohol (see page 149).
which the bacteria later
change to acetic acid. In
milk there are many kinds of
bacteria, some of which act
upon the milk sugar, changing
it to an acid, and thus caus-
ing the milk to sour. The
lactic acid bacteria grow very
rapidly in a warm temperature; hence milk which is kept iced
does not sour readily. Pasteurized milk (that is, milk that has

Microscopic appearance of ordinary
milk, showing fat globules and bacteria.
The cluster of bacteria on the right side
are germs that form lactic acid. Tubercu-
losis germs are sometimes found in milk.

BACTERIA

159

been heated to a temperature of about 145° Fahrenheit for
20 or 30 minutes) remains sweet for some time also if kept in a
cool place. Why ? The same lactic acid bacteria may be useful
when they sour the milk for the cheese-maker. Certain other
bacteria give flavors to cheese and butter, while still others are
used by the tanner in the preparation of leather. The '' ret-
ting '' of flax, or the rotting away of the non-usable tissues of
the flax stem, is due to the action of bacteria. Sponges are pre-
pared for the market by bacteria which decompose the sponge
tissues, leaving the skeleton behind. Bacteria are, after all,
often very useful. But in spite of the good they do, their
harmfulness is manifest, for they cause diseases, many of which
are " catching " or infectious.

Bacteria cause Disease. — Certain bacteria cause disease by
living as parasites in the human body. Millions upon millions of
bacteria exist in the
human body at all
times — in the mouth,
on the teeth, and es-
pecially in the lower
part of the food tube.
Some in the food tube
are believed to be use-
ful, others harmless;
still others cause decay
of the teeth, while a few
kinds, if present on the
roots of the teeth, may
cause disease.

It is known that
bacteria, like all other
living things, feed and
give off organic wastes.
These wastes, called toxins, are often poisons to the hosts on
which the bacteria live, and it is usually the production of a
toxin that causes the symptoms of disease. Some bacteria,
however, break down tissues and plug up the small blood
vessels, thus causing symptoms of disease.

A single cell scraped from the roof of the mouth
and highly magnified. The little dots are living
bacteria, most of them comparatively harmless.

160 HOW PLANTS BENEFIT AND HARM MANKIND

Diseases caused by Bacteria. — It is estimated that bacteria
cause annually over 50 per cent of the deaths of the human
race. As we shall see later, a very large proportion of these
diseases might be prevented if people were educated sufficiently
to take the proper precautions to prevent their spread. These
precautions might save the lives of some 3,000,000 people
yearly in Europe and America. Tuberculo'sis, typhoid fever,
diphtheria (dif-the'ri-a), pneumonia (nu-mo'ni-a), biood poison-
ing, syphilis (sif'i-lis), and a score of other ^' germ " diseases
ought not to exist. A good deal of the present misery of this
world might be prevented and this earth made cleaner and bet-
ter by the cooperation of the young people now growing up to
be our future home-makers.

How Germs get into the Body. — Germs of contagious diseases
enter the body either by way of the mouth, nose, or other
body openings or through a break in the skin. They leave the
body of an infected person with the excretions, especially those
from the nose, mouth, and intestine. They may be carried by
means of air, food, or water, and are usually acquired from the
diseased person either by personal contact, by handUng articles
used by the sick, or by using foods which have been infected.
Most germ diseases start with running at the nose, cough or
sore throat, shght fever or headache. If children and grown-ups
who have these symptoms could be kept away from other peo-
ple, many an outbreak of contagious disease would be avoided.

Tuberculosis. — The one disease responsible for the greatest
number of deaths — about one tenth of the total on the
globe — is tuberculosis. But this disease is slowly but surely
being overcome. It is believed that within perhaps fifty j^ears
with the application of the knowledge that every high-school
boy and girl now has and with the additional aid of good laws
and of sanitary living, it will be almost extinct.

Tuberculosis is caused by the growth of bacteria, called
tubercle bacilli, within the lungs or other tissues of the human
body. In the lungs they form little tubers full of germs, which
close up the delicate air passages. In other tissues tliey may
give rise to hip-joint disease, scrofuki, lui)us, and other diseases,
depending on the part of the body attacked. Many beUeve

BACTEUIA

161

that tuberculosis may be contracted by eating meat or drinking
milk from tubercular cattle. It is most often communicated
from a consumptive (tuberculous) to a well person by kissing,
or by using the same cup, plate, towels, or by spraying the germs
from the mouth of the consumptive out into the nose or mouth
of another person by coughing, sneezing, or even talking close to
his face. Although there are always some tuberculosis germs in
the air of an ordinary city street, and although we may take
some of these germs into our bodies at any time, yet the bac-
teria seem able to gain a foothold only under certain conditions.
It is only when the tissues are in a worn-out condition, when
we are " run down,'' as we say, that the parasite may obtain
a foothold in the lungs. Even if the disease gets a foothold,

How sewage containing typhoid bacteria may get into drink-
ing water: c, cesspool.

it is quite possible to cure it if it is taken in time. The germ
of tuberculosis is killed by exposure to bright sunlight and
fresh air. Thus the course of the disease may be arrested, and
a permanent cure brought about, by a life in the open air, the
patient sleeping out of doors, taking plenty of nourishing food
and very little exercise. (See also Chapter XXX.)

Typhoid Fever. — One of the most common germ diseases in
this country and Europe used to be typhoid fever. This is a dis-
ease which is conveyed by flies and by water and food, especially
milk, oysters, and uncooked vegetables. Typhoid fever germs
live in the intestine, where they multiply verv rapidly and are

162 HOW PLANTS BENEFIT AND HARM MANKIND

passed off from the body with the excreta from the food tube.
If these germs get into the water supply of a town, an epidemic
of typhoid will result. Among the epidemics caused by the
use of water containing typhoid germs have been those in
Butler, Pa., where 1364 persons were made ill; Ithaca, N.Y.,
with 1350 cases; and Watertown, N.Y., where over 5000
cases occurred. Fortunately most water supplies of cities
are now made safe by filtration and chlorina'tion. (See
Chapter XXX.) Another source of infection is milk. Fre-
quently epidemics have occurred which were confined to
users of milk from a certain dairy. Upon investigation it was
found that a case of typhoid had occurred on the farm where
the milk came from, that the germs had washed into the well,
and that this water was used to wash the milk cans. Once in
the milk, the bacteria multiplied rapidly, so that the milkman
gave out cultures of typhoid in his milk bottles. Pasteurisation
and proper inspection of our milk supply are necessary if we are
to prevent epidemics of typhoid under the present conditions.
The only sure way to keep from having the disease is to be
vaccinated against typhoid. (See Chapter XXX.)

Tetanus. — The bacterium causing tet'anus, or blood poisoning,
is another toxin-forming germ. It lives in the earth and enters
the body through cuts or bruises. It seems to thrive best in
less oxygen than is found in the air. It is therefore important
not to close up with court-plaster wounds in which such germs
may have found lodgment.

Other Diseases. — Many other diseases have been traced to
bacteria. Diphtheria is one of the best known. As it is a throat
disease, it may easily be conveyed from one person to another
by kissing, putting into the mouth objects which have come in
contact with the mouth of a patient having diphtheria, or by
food into which the germs have found their way. Septic sore
throat is another disease which is easily spread through milk
supplies, as is scarlet fever. The venereal diseases, gonorrhoea
and syphilis, probably cause more misery than any other germ
diseases. They cause hundreds of thousands of children to be
born crippled, blind, or otherwise handicapped for life and are
responsible for the deaths of many young mothers. Grippe,

BACTERIA 163

pneumonia, whooping cough, and colds are believed to be
caused by bacteria. But other diseases, as malaria, yellow fever,
sleeping sickness, and probably smallpox, scarlet fever, and
measles, are due to the attack of one-celled animal parasites. Of
these we shall learn later in the chapter on Protozoa.

Methods of fighting Germ Diseases. — As we have seen, dis-
eases produced by bacteria may be caused by the bacteria being
transferred from one person directly to another, or the disease
germs may gain an entrance into the body with food, water, or
air, or by taking them into the blood through a wound or a
body opening.

It is evident that as individuals we may each do something
to prevent the spread of germ diseases, particularly in our homes.
We may keep our bodies, especially our hands and faces, clean.
Green soap and hot water are as good cleansing agents as we
can get. Sweeping and dusting may be done with damp cloths
so as not to raise a dust; water, when from a suspicious supply,
should be sterilized, — that is, boiled to kill any germs contained
in it, — and milk should be pasteurized.

Uses of Antiseptics. — About the year 1867, an Edinburgh
surgeon. Lister, decided that germs floating in the air entered
wounds and caused blood poisoning among his hospital patients.
So he began washing their wounds with weak carbolic acid and
covering them with gauze wet with carbohc acid. In a short
time he proved to the world the value of antisep'tics or materials
that prevent bacteria from growing. We have largely given up
carboHc acid to-day and use iodine for cuts or bruises. For sore
throat argyrol (15 per cent) is best; for inflamed eyes a saturated
solution of boracic acid is good; while an excellent mouth wash
is salt and warm water (about a half-teaspoonful of salt to a
cup of water).

Summary. — The knowledge gained from the study of this
chapter should be of much practical value to every boy and girl.
We have seen that green plants not only have a decided eco-
nomic value in producing foods, medicines, dyestuffs, clothes,
paper, lumber, and fuel, but they also regulate our water
supplies, moderate our climate, and use that greatest source of
energy, the sun, for man's good.

164 HOW PLANTS BENEFIT AND HARM MANKIND

The plants without chlorophyll may be harmful, or harmless
or valuable. Some, like the yeasts, are of definite use in the
process of fermentation antl bread making; others, the molds,
have a slight value but do more harm than good in spoiling
food. The third great group, the bacteria, are man's greatest
friends as well as his most deadly foes. Without them decay
would not take place — try to unagine life on the earth with
no way to get rid of dead matter. They also give flavor to
cheese and milk, and to other foods; they are useful in the
tanner's trade as well as in many other kinds of work where
decomposition plays a part. And the fertility of the soil depends
upon certain kinds of bacteria, especially those which " fix "
free nitrogen from the air.

On the other side of the scale we can pile up a great weight
against the bacteria. Probably nearly 75 per cent of all people
on the earth die of diseases caused by bacteria and other parasites
which could have been prevented. The great mortality among
young children is due largely to bacteria causing diarrhea, the
tuberculosis germ is responsible for over one tenth of all the
deaths on the earth, while pneumonia, influenza, typhoid, ve-
nereal diseases, and many others either kill or weaken people
so that many die before reaching the threescore years and ten
allotted to them. This chapter and the ones which treat of
health and our civic obligations (XXIX and XXX) are among
the most important in the book for us.

Problem Questions. — 1. What are some of the uses of green
plants not mentioned in this chapter?

2. VThy do the farmers need bacteria? ^lention all the waj^s
in which they are useful.

3. In what ways do farmers need to guard against bacteria?

4. In what trades are yeasts useful? Harmful?

5. In what trades are molds useful?

6. Do bacteria do more harm or good? Give reasons for
both sides of your argument.

7. "WTiat specific diseases have you been able to find caused
by bacteria?

8. WTiat methods would you use to prevent " taking " an
infectious disease?

BACTERIA • 165

9. What are the best methods of controlling the growth of
bacteria ?

Problem and Project References

Broadhurst, Home and Community Hygiene. J. B. Lippincott Company.

Conn, Bacteria, Yeasts, and Molds of the Hom.e. Ginn and Company.

Conn, Story of Germ Life. D. Appleton and Company.

Davison, The Human Body and Health. American Book Company.

Frankland, Bacteria in Daily Life. Longmans, Green, and Company.

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Hunter and Whitman, Civic Science. American Book Company.

Locy, Main Currents of Zoology. Henry Holt and Company.

McCarthy, Health and Efficiency. Henry Holt and Company.

Prudden, The Story of the Bacteria. G. B. Putnam's Sons.

Ritchie, A Primer of Sanitation. The World Book Company.

Sedgwick, Principles of Sanitary Science and Public Health. The Macmillan

Company.
Sharpe, A Laboratory Manual. American Book Company,

XIV. THE RELATIONS OF PLANTS TO ANIMALS

Problem, To discover the general biological relations existing
between plants and animals. {Laboratory Manual, Prob. XXIV;
Laboratory Problems, Probs. 108 to 111,)

(a) A balanced aquarium,

(6) Relations between green plants and animals*

(c) The nitrogen cycle,

(d) A hay infusion.

Study of a Balanced Aquarium. — Perhaps the best way for
us to understand the interrelation betvv^een plants and animals
is to study an aquarium in which plants and animals live and
in which a balance has been established between the plant life
on one side and animal life on the other. Aquaria containing
green pond weeds, either floating or rooted, a few snails, some
tiny animals known as water fleas, and a fish or two will, if kept
near a Hght window, show this relation. (See Frontispiece.)

We have seen that green plants under favorable conditions
of sunlight, heat, moisture, and with a supply of raw food
materials, give off oxygen as a by-product while manufacturing
food in the green cells. We know the necessary raw materials
for starch manufacture are carbon dioxide and water, while
nitrogenous material is necessary for the making of proteins
within the plant. In previous experiments we have proved that
carbon dioxide is given off by any living thing when oxidation
occurs in the body. The crawling snails and the swimming fish
give off carbon dioxide, which is dissolved in the water; the
plants themselves, night and day, oxidize food within their
bodies, and so must pass off some carbon dioxide. The green
plants in the sunlight use up the carbon dioxide obtained from
the various sources and, with absorbed water, manufacture
starch. While this process is going on, oxygen is given off to
the water of the aquarium, and this is used by the animals.

But the plants are continually growing larger. The soaUs aud

166

RELATIONS BETWEEN PLANTS AND ANIMALS 167

fish, too, eat parts of the plants. Thus the plant life gives food
to part of the animal life within the aquarium. The animals
give off certain nitrogenous wastes which are used in the manu-
facture of protein within the plant. The animals eat the plants
and give off organic waste, which the plants use as food and
make into living matter. When the plants give off as much
oxygen as the animals use and the animals give off as much
carbon dioxide as the plants use, the aquarium is balanced.

Relations between Green Plants and Animals. — What goes
on in the aquarium is an example of the relation existing between

Carbon dioxide
(CO2)

Water
VHgO)

Carbon dioxide
n (CO2)

Simple Salts

Water
'CHaO)

(NH3)

Plants

with chlorophyll

buildup complex

organic substances

They store up

energy from the sun

in the process

and

Animals
and plants without
/ chlorophyll

I . (which tear down complex! Ammonia

organic >

'food of \ organic substances ] (NHg)

and set free energy

in the process iii

form of heat

/ t ^

Energy from sum

/ \ \

Energy set free

as heat.

The relations between green plants and animals

all green plants and all animals. Everywhere in the world green
plants are making food which becomes, sooner or later, the food
of animals. Man may not feed upon the leaves of plants, but
he eats fruits and seeds in one form or another. Even if he
does not feed directly upon plants, he eats the flesh of herbivo-
rous animals, which in turn feed directly upon plants. And so
it is the world over; the plants are the food-makers and supply
the animals. Green plants also give a very considerable amount
of oxygen to the atmosphere every day, which the animals may
make use of.

The Nitrogen Cycle. — The animals in their turn supply
much of the carbon dioxide that the plant uses in starch-
Dlaking. They also supply most of the nitrogenous matter used

168 THE RELATIONS' OF PLANTS TO ANIMALS

.^e^*^

etc

Animal Life

ng Bacteria^,

Soil)

Nitrites
"^ Nitric Bacteria

The nitrogen cycle.

by the plants, whether from the decay of dead bodies or the
excretions of the Hving. Bacteria which hve upon the roots of
certain plants, are the only organisms that can take nitrogen
from the air. Thus, in spite of all the nitrogen of the at-
mosphere, plants and
animals are limited in
the amount available.
And the available supply
is used over and over
again, perhaps in nitrog-

Bacteria/ ^^t^'*' enous food by an animal,

V^^ ^f'^^k^ then it may be given off

as organic waste, get into
the soil, and be taken up
by a plant through the
roots. Eventually the nitrogen forms part of the food supply
in the body of the plant, and then may become part of its
living matter. When the plant dies, the nitrogen is returned
to the soil. Thus the
usable nitrogen is
kept in circulation.

Symbiosis. — Plants
and animals are seen
in a general way to
be of mutual advan-
tage to each other.
Some plants, called
lichens, show this
mutual partnership in
the following interest-
ing way. A lichen is
composed of two
kinds of plants, one
of which at least may

live alone, but the two plants have formed a partnership for life,
and have divided the duties of such life between them. In most
lichens the alga, a green plant, forms starch and nourishes the
fungus. The fungus, in turn, produces spores, by means of which

A lichen (Physcia stellaris). Photographed by
W. C. Barbour.

A HAY INFUSION 169

new lichens are started in life; moreover, the Hchen is usually
protected by the fungus, which is stronger in structure than the
green part of the combination. This process of living together for
mutual advantage is called sijmhio'sis. Some animals also combine
with plants; for example, the tiny animal known as the hydra
with certain of the one-celled algse,
and, if we accept the term in a
wide sense, all green plants and
animals live in this relation of

, . 1 J 1 A • 1 Stages in the formation of

mutual give and take. ^ Annnals the lichen thaiius, showing the
also frequently live in this relation relation of the threadlike

, ^ J.^ j.T„ x* I, I,* u fungus to the green cells of

to each other, as the tmy crab which ^^^ ^^^^^ ^^^/r Bornet.)
lives within the shell of the oyster;

and the sea anemones which are carried around on the backs of
some hermit crabs, aiding the crab in protecting it from its
enemies, and being carried about by the' crab to places where
food is plentiful.

A Hay Infusion. — Still another example of the close relation
between plants and animals may be seen in the study of a hay
infusion. If we place a wisp of hay or straw in a small glass
jar nearly full of water, and leave it for a few days in a warm
room, certain changes are seen to take place in the contents of
the jar; the water after a little while gets cloudy and darker
in color, and a scum appears on the surface. If some of this
scum is examined under the compound microscope, it will be
found to consist almost entirely of bacteria. These bacteria
evidently aid in the decay which (as the unpleasant odor from
the jar testifies) is iaking place. As we have learned, bacteria
flourish wherever the food supply is abundant. The water
within the jar has come to contain much of the food material
which was once within the leaves of the grass, — organic nutri-
ents, starch, sugar, and proteins, formed in the leaf by the
action of the sun on the chlorophyll of the leaf, and now released
into the water by the breaking down of the walls of the cells.
The bacteria themselves release this food from the hay by
causing it to decay. After a few days small one-celled animals
appear which multiply with wonderful rapidity. Hay is dried
grass, upon which the wind may have scattered some of these

HUNT. NEW ES. — 12

170 THE RELATIONS OF PLANTS TO ANIMALS

little organisms in the dust from a dried-up pool. Existing in
a dormant state on the hay, they are awakened by the water
to active Ufe. In the water, too, there may have been some
living cells, plant and animal.

At first the multiplication of the tiny animals within the hay
infusion is extremely rapid; there is food in abundance and near
at hand. After a few days more, however, several kinds of

Life in a late stage of a hay infusion. B, bacteria, swimming
or forming masses of food upon which the one-celled animals,
the paiamecia, are feeding; G, gullet; F.V., food vacuole;
C.V., contractile vacuole; P, pleurococcus; P.D., pleurococcus
dividing. Highly magnified.

one-celled animals may appear, some of which prey upon others.
Consequently a struggle for life begins, which becomes more
and more intense as the food from the hay is used up. Eventu-
ally the end comes for all the animals unless some green plants
obtain a foothold within the jar. If such a thing happens,
food will be manufactured within their bodies, a new food
supply arises for the animals within the jar, and a balance of
life results.

THE RELATIONS OF PLANTS TO ANIMALS 171

Summary. — This chapter shows us that there exists a give
and take relationship between green plants and animals which is
illustrated by the condition known as symbiosis.

Problem question. — 1. How does the balanced aquarium illus-
trate symbiosis?

2. Explain the nitrogen cycle, the carbon cycle, the oxygen
cycle.

3. What kind of a relationship does life within a hay infusion
represent?

Problem and Project References

Eggerling and Ehrenberg, The Fresh Water Aquarium and its Inhabitants. Henry

Holt and Company.
Furneaux, Life in Ponds and Streams. Longmans, Green and Company.
Hunter, Laboratory Problems in Civic Biology. American Book Company.
Parker, Lessons in Elementary Biology. The Macmillan Company.
Sedgwick and Wilson, General Biology. Henry Holt and Company.
Sharpe, A Laboratory Manual. American Book Company.

XV. THE PROTOZOA

Problem, The study oj a one-celled animal. (Laboratory
Ma7iual, Problem X XV; Laboratory Problems, Probs, 112, 113.)

(a) In its relation to its surroundings.

(b) As a cell. (Optional.)

(c) In its relations to man,

A Simple Plant Cell. — We have seen that perhaps the
simplest plant would be exemplified by one of the tiny bacteria
we have just read about. A typical one-celled plant, however,
would contain green coloring matter or chlorophyll, and would
have the power to manufacture its own food under conditions
giving it a moderate temperature, a supply of water, oxygen,
carbon dioxide, and sunlight. Such a simple plant is the pleu-
rococcus, the " green slime " seen on the shady side of trees,
stones, or city houses. This plant would meet our definition
of a cell, as it is a minute mass of protoplasm inclosed in a
cell membrane and containing a nucleus. It is surrounded by a
walP of a woody material which covers the delicate membrane
formed by the activity of the protoplasm within the cell. It
also contains green granules called chloroplasts. Of their part in
the manufacture of organic food we have already learned. Such
is a simple plant cell. Let us now examine a simple animal cell
in order to compare it with that of a plant.

The Paramecium. — The one-celled animal most frequently
found in hay infusions is the Paramecium (par-a-me'shi-um), or
slipper animalcule (so-called because of its shape).

This cell is elongated, oval, or elliptical in outline, but some-
what flattened. Seen under the low power of the microscope,
it appears to be extremely active, rushing about now rapidly,
now more slowly, but seemingly always taking a definite course.

^ This shows one practical reason why plant food often contains more indi-
gestible matter thaq aniw^'l food of same bulk.

172

PARAMECIUM

173

The rounded end of the body (the anterior end) usually goes
first. If it pushes its way between dense substances in the
water, the cell body is seen to change its shape as it squeezes
through.

The cell body is almost transparent, and consists of semifluid
protoplasm which has a granular, grayish appearance under the
microscope. This protoplasm appears to be
bounded by a very delicate membrane (the
cu'ticle) through which project numerous
delicate threads of protoplasm called cilia CV^
(sil'i-a). (These are seen with difficulty
under the microscope.)

The locomotion of the Paramecium is
caused by the movement of these cilia,
which lash the water like a multitude of
tiny oars. The current of water caused by
the cilia carries tiny particles of food into a
funnel-like opening, the gullet, on one side of
the cell. Once within the cell body, the V-
particles of food materials are gathered into
little balls within the almost transparent
protoplasm. Each mass of food seems to
be inclosed within a little area containing
fluid, called a vacuole (vak'u-ol). Other
vacuoles appear to be clear; these are spaces ^^' contractile vacuole;
in which food has been digested. One or mouth; G, gullet- M,
two larger vacuoles may be found; these are macronucieus;Mi,micro-

- „ ^ - . nucleus; V, vacuole.

the contractile vacuoles; their purpose seems
to be to pass off waste material from the cell body. This is
done by the pulsation of the vacuole, which ultimately bursts, pass-
ing fluid waste to the outside. Solid wastes are passed out of
the cell in somewhat the same manner. The nucleus of the cell
is not easily visible in living specimens. In a cell that has been
stained it has been found to be a double structure, consisting of
one large and one small portion, called respectively the macro-
nucleus and the micronucleus.

Response to Stimuli. — In the Paramecium, as in the one-
celled plants, the protoplasm composing the cell can do certain

Paramecium: C, cilia;

174

THE PROTOZOA

things. Protoplasm responds, in both plants and animals, to
certain agencies acting upon it, coming from without; these
agencies we call stimuli. Such stimuli may be light, differences
of temperatm^e, presence of food, electricity, or other factors in
its surroundings. Plant and animal cells may react differently
to the same stimuli. In general, how^ever, we know that pro-
toplasm is irritable to some of these factors. To severe stimuli,
protoplasm usually responds by contracting, another power which
it possesses. We know, too, that plant and animal cells take in
food and change the food to protoplasm, that is, that they as-
similate food; and that they may waste away and repair them-
selves. Finally, we know that new plant and animal cells are
reproduced from the original bit of protoplasm, a single cell.

Reproduction of Paramecium. — Sometimes a Paramecium
may be found in the act of dividing by the process known as

fission^ to form two new cells, each of which

contains half of the original cell. In this

process the nucleus first elongates and breaks

into two, and the halves go

to opposite ends of the cell.

The cell elongates, a second

gullet appears, and ulti-
M mately the cell -breaks into

two parts, each haff pro- avl

vided with a nucleus and a

gullet (see diagram). This Paramecium, high-

_ Paramecmmdivid- -^ ^ method of aSCXUal re- ly magnified; two
mg by fission High- ^eUs just before con-

ly magnified. M, production. jugation. M, mouth;

ZTucieZ^%Tc' Frequently another stage MW micronucieus;

cronucieus, mi^., i ,. i t_ il/AC.,macionucleus;

tmcronucleus. (After 01 reproduction may be Ob- ^y contractile vac-

Sedg^ick and WU- ^^j^^^^ ^his is Called con- uole'.' (After Sedgwick

^^•> • s' J I, ^ andWHson.)

jugation, and somewhat re-
sembles conjugation in the simple plants. Two cells of
equal size attach themselves together as shown in the Figm-e.
Complicated changes take place in the nuclei of the two cells
thus united, which results in an exchange of parts of the mate-
rial forming the nuclei of each celL After a short period
of rest the two cells separate. The stage of conjugation we

MAC.
MIC.

IM!C.
MAC.

AMCEBA 175

believe in the plants to be a sexual stage. There seems every
reason to believe that it is a like stage in the life history of the
Paramecium.

Amoeba.^ — In order to understand more fully the life of a
simple bit of protoplasm, let us take up the study of the
amoe'ba, a type of the simplest form of life known, either plant
or animal. Unlike the plant and animal cells we have examined,
the amoeba has no fixed form. r;-,.^
Viewed under the compound P'^gjj'j^^^
microscope, it has the appear- )^^^§fSl^

ance of an irregular mass of "wKKi-

granular protoplasm. Its form

is constantly changing as it

moves about. This is due to ^— %I^^SIf ^•■:0:: -.- ■:"-^

the pushing out of tiny pro- ^,||p:;^;{i^^o- :S:.;:S^-;:'; '-J-'-v'-'^lgP'^

jections of the protoplasm of Ecj:^^^^^^^^-^^^
the cell, called pseudopodia ^BM

(su-do-po'di-a; false feet). ^"^i^Pl^^P^-""*^
The outer layer of protoplasm '-^$A^_JS^^0^""^
is not so granular as the inner • i^iyt^^"'-'^

part; this outer layer is called

ec'toplasm, the inside being An amoeba in search ot food. P pseu-

^ /7 7 T 1 clopodium; F, food vacuole ; £;c, ectoplasm;

called en doplasm. In the En, endoplasm; C, contractile vacuole;

central part of the cell is the ^' nucleus.

nucleus. Several theories have been advanced to account for
locomotion. The most likely one seems to be that the pseudo-
podia are elastic and when stretched out fasten themselves.
The rest of the body then flows into the extended end. Some
writers think the amoeba progresses by a kind of rolling motion.
The pseudopodia are pushed out in the direction in which the
animal is to go, the rest of the body following.

Although but a single cell, still the amoeba appears to be aware
of the existence of food when it is near at hand. Food may
be taken into the body at any point, the semifluid protoplasm

1 Amoeb£B may be obtained from the hay infusion, from the dead leaves in
the bottom of small pools, from the same source in fresh-water aquaria, from
the roots of duckweed or other small water plants, or from green algae growing
in quiet localities. No sure method of obtaining them can be given.

176

THE PROTOZOA

/ 2

4

. Mi

/f - V

simply roiling over and engulfing the food material. Within the
body, as in the Paramecium, the food is inclosed within a fluid
space or vacuole. The protoplasm has the power to take out
such material as it can use to form new protoplasm or to give
energy. It will then rid itself of any material that it cannot
use. Thus it has the power of selective absorption, sl property
found in the protoplasm of plants previously studied. Circu-
lation of food material is accomplished by the constant streaming

of the protoplasm within the
cell. The cell absorbs oxygen
from the air in the water by
osmosis through its delicate
membrane, giving out carbon
dioxide in return. Thus res-
piration takes place through
every part of the covering of
the cell. Waste products
other than carbon dioxide
formed from the life activi-
ties which take place within
the cell are passed out by
means of the contractile vac-
uole.

The amoeba, like other one-
celled organisms, reproduces
by the process of fission. A
single cell divides by splitting
into two, each of which re-
sembles the parent cell, except
that it is of smaller size.
When these new cells become
the size of the parent amoeba, they each divide. This is a kind
of asexual reproduction. When conditions unfavorable for life
come, the amoeba, like some one-celled plants, encysts itself
within a membranous wall. In this condition it becomes dried
and is blown through the air. Upon return to a favorable
environment, the cover disappears and life begins again, as be-
fore. In this respect the amoeba resembles the spore of a plant.

6

Amoeba, highly magnified, showing the
changes which talce place during division.
The dark body in each Figure is the
nucleus; the transparent circle, the con-
tractile vacuole; the outer, clear portion
of the body, the ectoplasm; the graniilar
portion, the endoplasm; the granular
masses, food vacuoles.

AMCEBA

177

From the study of the amoebalike organisms which are known to cause
malaria, and by comparison with the amoebae which live in ponds and swamps,
it seems likely that every amoeba has a complicated life history during
which it passes through a sexual stage of existence.

The Cell as a Unit. — - In the daily life of a one-celled animal
we find the single cell performing all the vital activities which
we shall later find that the many-celled animal is able to perform.
In the amoeba no definite parts of the cell appear to be set off
to perform certain functions; but any
part of the cell can take in food, can
absorb oxygen, can change the food
into protoplasm and excrete the waste
material. The single cell is, in fact,
an organism able to carry on the
business of living as effectually as a
very complex animal.

Complex One-celled Animals. — In the

Paramecium we fiijd a single cell but certain
parts of the cell have certain definite func-
tions: the cilia are used for locomotion; a
definite part of the cell takes in food, while
another definite spot passes out the waste.
In another one-celled animal called vorti-
cel'la, part of the cell has become very much
elongated and is contractile, forming a stalk
by which the Uttle animal is fastened to a
water plant or other object. The stalk may
be said to act like a muscle fiber, as its sole
function seems to be movement; the cilia
are located at one end of the cell and serve
to create a current of water which brings
food particles to the mouth. Here we have
several parts of the cell each doing a differ-
ent kind of work. This is known as physi-
ological division of labor.

Habitat of Protozoa. — Protozo'a, or one-celled animals, are
found in shallow water almost everywhere, seemingly never at
any great depth. They appear to be attracted to the surface
by light and the supply of oxygen. Every fresh-water lake
swarms with them; the ocean contains countless myriads of
many different forms.

MOUTH OPMNim

XCILIA

: --'^m^^ — ^

CUTICLE ■

1

i

STALK OR
PEDICLE

i-.....;. :...

CONTRACTILE

* BASAL
ATTACHMENT

i

■■■■■■'«■<■.;.... . ■ ■■ ■ ■■■■-»'«*v*.

Vorticella, highly magnified.
Photograph from American
Museum of Natural History.

178

THE PROTOZOA

Use as Food. — Protozoa are so numerous in lakes, rivers, and
the ocean as to form the food for many animals higher in the
scale of life. Almost all fish that do not take the hook and that
travel in schools, or companies, migrating from one place to
another, live partly on such food. Alany feed on slightly larger
animals, which in tm-n eat the Protozoa. Such fish have on
each side of the mouth attached to the gills a series of small
structures looking like tiny rakes. These are called the gill
rakers, and aid in collecting tiny organisms from the water as
it passes over the gills.

Relation of Protozoa to Disease. — The study of the life his-
tory and habits of the Protozoa has resulted in the finding of

many parasitic forms,
-f ^ ^ and the consequent ex-
"^ ' planation of some kinds
of disease. One parasitic
protozoan like the amoeba
causes the disease known
as malaria. Part of its
life is passed within the
body of a mosquito, — the
anopheles (a-nof'e-lez),
— into the stomach of
which it passes when
the mosquito sucks
blood from a person
having malaria. Within
the body of the mosquito
a complicated part of
the life history takes
place, which results in a
stage of the parasite
establishing itself within
the glands which secrete
the saliva of the mos-

(3 "^^*'^^*~ ^''^ ®^/

Life history of tiie malarial parasite. The
mosquito injects crescent-shaped bodies A into
the blood of man. Spores develop in the blood
corpuscles, and many, as at H, may enter other
corpuscles, while some (P) may be drawn into the
body of a mosquito, where the parasite passes
through sexual stages. Follow the course shown
by the arrows from A back to A, and from H back
toH.

quito. When the mosquito pierces its human prey the next
time, some of the parasites are introduced with the saliva
into the victim's blood. These parasites enter the red corpuscles

RELATION OF PROTOZOA TO DISEASE 179

of the blood, increase in size, and then form spores. The rapid
process of spore formation results in the bursting of the blood
corpuscles, and the parasites enter the fluid portion of the blood.
The chill and fever are probably caused by the destruction of the
corpuscles and release of poison into the blood. The parasites
again enter the blood corpuscles and in forty-eight or seventy-two
hours repeat the process thus described. Yellow fever is un-
doubtedly conveyed by another species of mosquito, and is due
to the presence of a protozoan similar to that of malaria in the
blood. That these diseases may be stamped out by the exter-
mination of the mosquitoes, which may be accomplished by
the use of oil to prevent their breeding in swamps, by draining
the swamps, or by the introduction of fish which eat the mos-
quito larvse, has been proved from our experience along the
Panama Canal, in the Philippines, in Cuba, and in New Orleans.

Many other diseases of man are probably caused by parasitic
protozoans. Dysentery appears to be caused by the presence
of an amoebalike animal in the digestive tract. Smallpox,
rabies, and possibly other diseases may be caused by the action
of these little animals.

Another group of protozoan parasites are called trypanosomes
(trip'a-no-somz). One of this family lives in the blood of native
African zebras and antelopes; seemingly it does them no harm.
But if one of these parasites is transferred by the dreaded tsetse
(tset'se) fly to one of the domesticated horses or cattle of the
colonists in Central or Southern Africa, death of the animal
results.

Another fly carries a specimen of trypanosome to the natives
of Central Africa, which causes ^' the dreaded and incurable
sleeping sickness." This disease has carried off more than fifty
thousand natives in a year, and many Europeans have suc-
cumbed to it. Its ravages are now largely confined to an area
near the large Central African lakes and the upper Nile, for
the fly which carries the disease fives near water, seldom going
more than 150 feet from the banks of streams or lakes. The
British government is now trying to control the disease in
Uganda by moving all the villages at least two miles from the
lakes and rivers. Why? In this country many fatal diseases

180

THE PROTOZOA

of cattle, as '' tick," or Texas fever, are probably caused by
protozoans.

Skeleton Building. — Some of the Protozoa build elaborate skeletons.
These may be formed either in or outside of the body, and are often of

great beauty when seen under the mi-
croscope (see Figure). Much of the chalk
in various parts of the world is made
of the skeletons of these tiny creatures.

A Simple Classification of Protozoa

The following are the principal classes
of Protozoa, examples of which we have
seen or read about: —
Class I. Rh'.zip' oda (Greek — root-
footed). Having no fixed form;
with pseudopodia. Either naked
as Amoeba or building lim^' {For-
aminif'era) or glasslike skeletons
(Radiola'ria) .
Class II. Infusoria (infusions). Usually
active ciliated Protozoa. Examples,
Paramecium, Vorticella.
Class III. Sporozo'a (spore animals). Usually parasitic and nonactive.
Example, the parasite that causes malaria (Plf,smodium malaria').

Summary. — This study has shown us that a single-celled
animal has all the vital functions of a more complex one. It
feeds, digests, and assimilates its food, breathes, excretes waste,
and reproduces. It is sensitive to outside stimuli and responds
by movement. It is in other words a living organism.

Problem Questions. — 1. Describe the life cycle of a Para-
mecium.

2. Compare two stages of reproduction in Paramecium.

3. What relation do the Protozoa bear to malaria? Explain.

Skeleton of a radiolarian. Highly
magnified. From model at Amer-
can Museum of Natural Historj\

Problem and Project References

Calkins, Biology. Henry Holt and Company.

Calkins, The Protozoa. Lemoke.

Hegner, Introduction to Zoology. The Macmillan Company.

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Sedgwick and Wilson, General Biology. Henry Holt and Company.

Sharps, A Laboratory Manual. American Book Company.

XVI. SIMPLE METAZOA — DIVISION OF LABOR

Problem, An introductory study of many-celled animals to
learn something about —

(a) Their development.

(b) The structure of a sponge.

(c) The hydra,

(d) The development of tissues and organs,

(e) The common functions of all animals,

(Laboratory Manual, Prob. XXVI; Laboratory Problems,
Probs. 116, 117.)

Reproduction in Plants. — Although there are very many
plants and animals so small and so simple as to be composed
of but a single cell, by far the greater part of the animal and
plant world is made up of individuals which are collections of
cells living together.

In a simple plant like the pond scum, a string or filament of
cells is formed by a single cell dividing crosswise, each of the
two cells thus formed giving rise to two more, and so on, until
eventually a long thread of cells results. Such growth of cells
is asexual.

In some instances, however, a single cell is formed by' the
union of two cells, one from each of the adjoining filaments of
the plant. Around this cell eventually a hard coat is formed,
and the spore, as it is called, is thus protected from unfa-
vorable changes in the surroundings. Later, when conditions
become favorable for its germination, the spore may form a
new filament of pond scum.

In the seed plants, too, we found within the seed a little
plant, an embryo, which, under favorable conditions, may give
rise, through the rapid multiplication of the cells forming it, to
a new plant. The embryo first arises from two cells, one of
which, called a sperm, comes from a pollen grain, while the
other, the egg, is found within the embryo sac of the ovary.

181

182 sumple metazoa — division of labor

Reproduction in Animals. — Similarly, in the reproduction of
many-celled animals the new individual is formed by the union
of a sperm and an egg cell. A common bath sponge, an earth-
worm, a fish, and a dog, — each and all of them begin life in
precisely the same way. Animals which are thus composed of
many cells are known as the Metazo'a, as distinguished from the
Protozoa, which are made of but a single cell.

Sexual Development of a Simple Animal. — In a man3'-celled
animal the life history begins with a single cell, the fertilized
egg. This c^ll, as we remember, has been formed b}^ the union
of two other cells, a tiny (usuall}^ motile) cell, the sperm, and
a large cell, the egg. After the egg is fertilized by a sperm cell,
it splits into two, then into four, then into eight, then into six-
teen cells, and so on; as the number of cells increases, a hol-
low baU of cells called the bias' tula is formed; later this ball

O

Stages in the segmentation of an egg, showing the formation of the gastrula.

sinks in on one side, and a double-walled cup of cells, called
a gas'trula, results. Practicalh^ all animals pass through the
above stages in their development from the egg, although these
stages are often not easy to see because of the presence of food
material (yolk) in the egg. In the development of the sponge
the gastrula, which swdms by means of cilia, soon settles down, a
skeleton is formed, other changes take place, and the sponge begins
life as an animal attached to some support in the water. The
early stages of life, when an animal is unlike the adult, are known
as larval stages; the animal at this time being called a larva.

The young sponge consists of three layei-s of cells: those of
the outside, developed from the outer layer of the gastrula, are
called ec'toderm; the inner laj^er, developed from the inner
layer of the gastrula, the en'doderm; and the middle, almost
structureless layer, the mes'oderm. In higher animals the
mesoderm gives rise to muscles and parts of other internal
structures.

THE SPONGE

183

A horny fiber sponge; IP, the incurrent
pores; O, osculum. Notice that this sponge
is made up of apparently several individuals.
One fourth natural size.

The Structure of a Sponge. — The simplest kind of sponge
has the form of an urn, attached at the lower end. A com-
mon sponge living in Long Island Sound is a tiny urn-shaped
animal less than an inch
in length. It has a
skeleton made up of very
tiny spicules of lime, of
different shapes. Cut
lengthwise, such an
animal is seen to be
hollow, its body wall
pierced with many tiny
pores or holes. The
bath sponge, the skeleton
of which is made up of
fibers of horn, or a
variety known as the
finger sponge, shows the

pores even better than the smaller limy sponge. In a bath sponge,
however, we probably have a colony of sponges living together.

Each sponge has a large number of
pores opening into a central cavity,
which in turn opens by a large hole,
called the os'culum, to the surround-
ing water.

A microscopic examination shows
the pores of the sponge to be Uned
on the inside with cells each having a
collar of living matter surrounding a
single long cilium called a flagellum
(fla-jerum). The flagella, lashing in
one direction, set up a current of
water toward the large inner cavity.
This current bears food particles,
tiny plants and animals, which are
seized and digested by the collared cells, these cells probably
passing the food on to the other cells of the body. The jelly-
like middle layer of the body is composed of cells which secrete

Longitudinal section of a
simple sponge: O, osculum,
P, P, incurrent pore; /,
flagella.

184 SIMPLE METAZOA — DIVISION OF LABOR

Castrula

Tentdcle —
Stinging Cell-
young Sperm-
Producing Organ.

Digestive Caviiy ^

Mature egg-
Blast ul a- -

Mature Sperm-
Reducing Organ

~ Mouth
^ Tentacle

Young egg

y. Basal disk

Longitudiual section of a hydra, magnified.

lime to form the spicules and the reproductive cells, eggs, and
sperms.

The Hydra. — Another very simple animal, which unlike most
sponges Uves in fresh water, ^ is called the hydra. This little
creature is shaped like a hollow cyhnder with a cu'cle of arms

or ten'tades at the free end.
It is found attached to dead
leaves, sticks, stones, or water
weeds in most fresh-water
ponds. When disturbed, the
hydra contracts into a tiny
whitish ball a little larger than
the head of a pin. Expanded,
it may stretch its tentacles in
search of food almost an inch
from their point of attach-
ment. The tentacles are pro-
vided with batteries of minute
darts of stinging cells, by means of which prey is caught and
killed. The outer layer of the animal serves for protection as
well as movement and sensation, certain cells being fitted for
each of those different pm-poses.

Food Taking. — The tentacles then reach out Hke arms, grasp
the food, bend over ^dth it, and pull it toward the mouth. Cer-
tain cells lining the hollow digestive ca\aty pour out a fluid
which digests the food. Other cells with long cilia circulate the
food, while still other cells hning the cavity put out pseudo-
podia, which grasp and ingest the food particles. The tentacles
are hollow, and the digestive cavity extends into them. The
outer layer of the animal does not digest the food, but receives
some of it already digested from the inner layer. This food
passes from cell to cell, as in plants, by osmosis. The oxj^gen
necessary to oxidize the food is passed through the body wall,
seemingly at any point, for there are no special organs for
respiration.

Reproduction. — The hydra reproduces itself either by budding
asexually or by means of eggs and sperms, sexually. The bud ap*

* A few Bponges, for example, spongUla, live in fresh water.

DIVISION OF LABOR 185

pears on the body as a little knob, sometimes more than one
coming out on the hydra at the same time. At first the bud is
part of the parent animal, the body cavity extending into it.
After a short time (usually a few days) the young hydra sepa-
rates from the old one and begins life alone. This is asexual
reproduction.

The hydra also reproduces by eggs and sperms. These sperms
are collected in little groups which usually appear near the free
end of the animal, the egg cells developing near the base of the
same hydra. Both eggs and sperms grow from the outer layer
of the animal. The sperms, when ripe, are set free in the water;
one of them unites with an egg, which is usually still attached
to the body of the hydra, and development begins which results
in the growth of a new hydra in a new locality.

The stages passed through in development resemble closely
those described on page 182, and it would not be hard to
imagine the gastrula stage, turned upside down with a circle of
tentacles at the open end. Our gastrula would then be a hydra.

Division of Labor. — If we compare the amoeba and the Para-
mecium, we find the latter a more complex organism than the
former. An amqpba may take in food through any part of the
body; the Paramecium has a definite gullet. The amoeba may
use any part of the body for locomotion; the Paramecium has
definite parts of the cell, the ciHa, fitted for this work. Since
the structure of the Paramecium is more complex, we say that
it is a '^ higher " animal. In the vorticella, a still more complex
organism, part of the cell has grown out like a stalk, has become
contractile, and acts and looks like muscle.

As we look higher in the scale of life, we invariably find that
certain parts of a plant or an animal are set apart to do certain
work, and only that work. Just as in a community of people,
there are some men who do rough manual work, others who are
skilled workmen, some who are shopkeepers, and still others
who are professional men, so amoiig plants and animals, where-
ever collections of cells live together to form an organism, there
is division of labor, some cells being fitted to do one kind of
work, while others are fitted to do work of another sort.

AS we have seen in plants, this results in a large number of

FTINT. NEW US. — 13

186 SIMPLE METAZOA — DIVISION OF LABOR

collections of cells in the body, the cells in each collection being
alike in structure and in performing the same function. Such
a collection of cells we call a tissue. (See Chapter III.)

Frequently several tissues have certain functions to perform
in conjunction with one another. The arm of the human body
performs movement. To do this, several tissues, as muscles,
nerves, and bones, must act together. A collection of tissues
which work together to perform one function is called an organ.

In the sponge, division of labor occurs between the cells of
a simple animal, some cells lining the incurrent pores creating
a current of water, and feeding upon the minute organisms
which come within reach, other cells building the skeleton of
the sponge, still others producing eggs or sperms. Division of
labor of a more complicated sort is seen in the hydra. Here
the cells which do the same kind of work are collected into
tissues, each tissue being a collection of cells, all of which are
more or less alike and do the same kind of work. But in higher
animals which are more complicated in structure and in which
the tissues are found working together to form organs, division
of labor is still more developed. In the human arm, an organ
fitted for certain movements, think of the number of tissues
and the complicated actions which are possible. The most
extreme division of labor is seen in the organism which has the
most complex actions to perform and whose organs are fitted
for such work.

In our daily life in a town or city we see division of labor
between individuals. Such division of labor may occur among
other animals, as, for example, bees or ants. But it is seen
at its highest in a great city or in a large business or industry.
In the stockyards of Chicago, division of labor has resulted in
certain men performing but a single movement during their
entire day's work, but this movement repeated so many times
in a day has resulted in wonderful accuracy and increased speed.
Thus division of labor attains its end.

Tissues in the Human Body. — Every animal body above the
protozoan is composed of a certain number of tissues. The cells
making up these tissues have certain well-defined characteris-
tics. In very simple animals the cells are all very much alike

TISSUES IN THE HUMAN BODY

187

but in more complex animals the cells are more and more unlike
as their work becomes more and more different. Let us see
what these cells may be, what their structure is, and, in a general
way, what function each has in the human body.

Muscle Cells. — A large part of our body is made up of
muscle. Muscle cells are elongated in shape, and have great
contractile power. Their work is that of causing movement,
and this is usually done by means of attachment to a skeleton
inside the body. In man they may be of two kinds, voluntary
(under control of the will) and involuntary.

Epithelial Cells cover the outside of a body or line the inside
of the cavities in the body. The shape of these cells varie?

Diagrams of sections of cells, greatly magnified, e, flat cell (epithelium)
from mouth; c, columnar epithelium from food tube; 6, bone-forming cell;
I, liver cell; m, muscle cell; /, fat cell; n, nerve cell.

from flat plates to little cubes or columns depending upon their
position in the body. Some bear cilia, an adaptation. Can
you think of their purpose?

Connective Tissue Cells form the framework between tissues
in the body. They are characterized by possessing numerous
long processes. Around them is found to a greater or less
degree a structureless material, called intercellular substance.
This stands in the same relation to the cells as does mortar to
the bricks in a wall.

Several other types of cells might be mentioned, as blood
cells, cartilage cells, bone cells, and nerve cells. A glance at the
Figure shows their great variety of shapes and sizes.

188 SIMPLE METAZOA — DIVISION OF LABOR

Functions Common to All Animals. — The same general func-
tions performed by a single cell are performed by a many-celled
animal. But in the Metazoa the various functions of the single
cell are taken up by the organs. In a complex organism, like
man, the organs and the functions they perform may be briefly
given as follows : — '-

(1) The organs of food taking. Food may be taken in by
individual cells, as those lining the pores of the sponge, or definite
parts of a food tube may be set apart for this purpose, as the
mouth and parts which place food in the mouth.

(2) The organs of digestion: the food tube and collections of
cells which form the glands connected with it. The enzymes in
the fluids secreted by the latter change the foods from a solid
form (usually insoluble) to that of a liquid. Such liquid may
then pass by osmosis through the walls of the food tube into
the blood.

(3) The organs of circulation: the tubes through which the
blood, bearing its foods and oxygen, reaches che tissues of the
body. In simple forms of Metazoa, as the sponge and hydra,
no such organs are needed, the fluid food passing from cell to
cell by osmosis.

(4) The organs of respiration: the organs in which the blood
receives oxygen and gives up carbon dioxide. The outer layer
of the body serves this purpose in very simple animals; gills
or lungs are developed in more complex animals.

(5) The organs of excretion: such as the kidneys and skin,
which pass off nitrogenous and other waste matters from the
body.

(6) The organs of locomotion: muscles and their attachments
and connections; namely, tendons, ligaments, and bones.

(7) The organs of nervous control: the central nervous system,
which has control of coordinated movement. This consists of
scattered cells in low forms of life; such cells are collected into
groups and connected with each other in higher animals.

(8) The sense organs: collections of cells having to do with
sight, hearing, smell, taste, and touch.

(9) The orgaRS of reproduction: the sperm and egg forming
glands.

SPONGES, CCELENTERATES

189

Almost all animals have the functions mentioned above. In
most, the various organs mentioned are more or less developed,
although in the simpler forms of animal life some of the organs
mentioned above are either very poorly developed or entirely
lacking.

Forms of Simple Metazoans. Sponges ^

Sponges (Porifera) may be placed, according to the kind of skeleton
they possess, in the following groups: —

(1) The limy sponges, in which the skeleton
is composed of spicules of carbonate of lime.
Grantia is an example.

(2) The glassy sponges. Here the skeleton
is made of silica or glass. Some of the rarest
and most beautiful of all sponges belong in
this class. The Venus's flower basket is an
example.

(3) The horny fiber sponges. These, the
sponges of commerce, have the skeleton com-
posed of tough fibers of material somewhat
like that of cow's horn. This fiber is elastic
and has the power to absorb water. In a liv-
ing state, the horny fiber sponge is a dark-
colored fleshy mass, usually found attached to
rocks. The warm waters of the Mediterranean
Sea and the West Indies furnish most of our
sponges. The sponges are pulled up from their
resting places on the bottom, by means of long-
handled rakes operated by men in boats, or they
are secured by divers. They are then spread out on the shore in the sun,
where bacteria cause the tissues to decay; then after treatment consisting
of beating, bleaching, and trimming, the bath sponge is ready for the
market.

Coelenterates

The hydra and its salt- water allies, the jellyfish, hydroids, and corals,
belong to a group of animals known as the Ccelentera'ta. The word " coe-
lenterate" (coelom = body cavity, enter on = food tube) explains the struc-

^ The matter in small type in this and other parts of the book is intended
largely as reference and outside reading or project reference reading. There
are always some members of a class who have interests more keenly biological
than others. It is thought that these pages may be particularly usefizl for such
students. These pages will also be useful when they describe material that
can be found locally and used in the laboratory.

Venus's flower basket; a
sponge with a glassy skel-
eton.

190 SIMPLE METAZOA — DIVISION OF LABOR

ture of the group. They are animals in which the real body cavity is lack-
ing, the animal in its simplest form being little more than a bag.

Medusa. — Among the most interesting of all the coelenterates inhabit-
ing salt water are the jellyfishes or medusae. These animals vary greatly

in size from a tiny umbrella-
shaped form little larger than
the head of a pin to huge jelly-
fishes several feet in diameter.

Tentdcle
food tube

Mouth

V-Tentdde

Medusa or jellyfish. Photograph
from American Museum of Natural
History.

A hydroid colony of six polyps:
/, feeding polyp; r, reproductive
polyp; m, a medusa; y, young
polyp.

Development. — Many species of medusse pass through another stage of
life. As medusae they reproduce by eggs and sperms, that is, sexually.
The egg of the medusa segments, forming ultimately a ball of cells (the
hlastula) which swims around by means of cilia. Ultimately the little ani-
mal settles down on one end and becomes fixed to a rock, seaweed, ot
pile. The free end becomes indented in the same manner as a hollow
rubber ball may be pushed in on one side. This indented side becomes a
mouth, tentacles develop around the orifice, and we have an animal that
looks very much like the hydra. This animal, now known as a hydroid
polyp, buds rapidly and soon forms a colony of little polyps, each of which
is connected with its neighbor by a hollow food tube. The hydroid polyp
differs from its fresh-water cousin, the hydra, by usually possessing a
tough covering which is not alive.

CCELENTERATES

191

Alternation of Generations in Coelenterates. — The lives of a hydroid
poiyp and a medusa are seen thus to be intimately connected. A
hydroid colony produces new polyps by budding. This is an asexual
method of reproduction. There come from this hydroid colony, how-
ever, Httle buds which give rise to free-swimming medusae. These
medusae produce eggs and sperms. Their reproduction is sexual, as was
the reproduction by means of eggs and sperms from the prothallus of
the fern. So we have in animals, as well as in plants, an alternation of
generations.

Sea Anemone. — Those who have visited our New England coast are
famihar with another coelenterate called the sea anemone (a-nSm'6-ne).
This animal gets its name because,
when expanded, it looks Hke a
beautiful flower of a golden yellow
or red color. The body of the
sea anemone is like the hydra, a
colunm attached at one end. The
free end is proidded with a mouth
surrounded with a great many
tentacles. These, when ex-
panded, look like the petals of a
flower. The sea anemone is a
very voracious animal, for by
means of the batteries of stinging
cells in its tentacles it is able to
catch and devour fishes and other
animals almost as large as itself.
When disturbed, or irritated, the
animal contracts into a sHmy ball which is difficult to dislodge from its
attachment.

Although the sea anemone is like a large hydra in appearance, its in-
terior is different. The hollow digestive cavity contains a number of par-
titions more or less complete, which run from the outer wall toward the
middle of the cavity. These partitions, known as mes'enteries, are found
in pairs. Part of the cavity, as in the hydra, is given up to digesting the
food. Food is killed by means of stinging cells found in the long thread-
Uke tentacles.

Coral. — If a piece of madrepor'ic coral is examined with a hand lens, a
number of httle depressions will be seen in the limy surface, each of which
has tiny partitions within it. These cupHke depressions were once occupied
by the coral animals of polyps, each in its own cup. The mesenteries of the
coral polyp are paired and hollow on the under surface. The partitions
seen in the coral cups lie between the pairs of mesenteries, and are formed
bj'^ them when the animal is alive. Sea water has a considerable amount
of hme in its composition. This lime (calcium carbonate) is taken from
the water by certain of the cells of the coral polyp and deposited around

Sea anemone. About one half natural
size. The right-hand specimen is ex-
panded. Note the mouth surrounded by
the tentacles. The left-hand specimen is
contracted. From model at the American
Museum of Natural History.

192 SIMPLE METAZOA — DIVISION OF LABOR

the base of the animal and between the mesenteries, thus giving the
appearance just seen in the cups of the coral branch.

Asexual Reproduction. — These polyps reproduce by budding, and
when alive cover the whole coral branch with a continuous Hving mass of
polyps, each connected with its neighbor. In this way great masses of
coral are formed. Coral, in a Hving state, is aUve only on the surface,
the polyps building outward on the skeleton formed by their predecessors.

Economic Importance of Corals. — Only one (astrangia) of a great
many different species of coral hves as far north as New York. In tropical
waters they are very abundant. Coral building has had and still has an
immense influence on the formation of islands, and even parts of conti-
nents in tropical seas. Not only are many of the West Indian islands

•M».

1

f.

w^^u

^ps

1

^^

1

^^

%^^?^^ W^

^^m^k

^^^^m

^:^^^

mmm

WW

A branching madreporic coral.

A single coral cup,
showing the walls of lime
built by the mesenteries.
From a photograph
loaned by the American
Museum of Natural His-
tory.

composed largely of coral, but also Florida and many islands of the
southern Pacific are almost entirely of coral formation.

Coral Reefs. — The coral polyps can live only in clear sea water of
moderate depth. Fresh water, bearing mud or other impurities, kills
them immediately. Hence coral reefs are never found near the mouths
of large fresh-water rivers. Polyps are frequently found building reefs
close to the shore. In such cases these reefs are called fringing reefs.
The so-called barrier reefs are found at greater distance (sometimes forty
to fifty miles) from the sliore. An example is the Great Barrier Reef of
Australia. The typical coral island is called an atoU. It has a circular
form inclosing a part of the sea which may or may not be in communica-
tion with the ocean outside the atoll. The atoll was perhaps at one time
a reef outside a small island. This island disappeared, probably by the
sinking of the land. The polyps, whi(;h could live in water up to about
one hundred and fifty feet, continued to build the reef until it rose to
the surface of the ocean. As the polyps could not exist for long above low-
waterline, the animals died and their skeletons became disintegrated by

SIMPLE METOZOA 193

the action of waves and air. Later birds brought a few seeds there, per-
haps a coconut was washed ashore; thus plant life became established in
the atoll, and a new outpost to support human life was established.

A Simple Classification of Ccelenterates

Class I. Hydrozo'a. A simple body cavity containing no mesenteries, usually
alternation of generations. Examples: Hydra, hydroids.

Class II. Scyphozoa (sl-fo-zo'a). Example: large jellyfishes.

Class III. Actinozo'a, Mesenteries present in body cavity. Examples:
sea anemones and corals.

Class IV. Ctenophora (te-nQf'o-ra).

Summary. — All animals develop from egg cells, which, after
fertilization, go through a series of divisions. A hollow ball of
cells (the blastula) is formed, and then a cup-shaped mass (the
gastrula). Some animals such as the hydra stop their develop-
ment at this stage; others reach a more complex adult stage.

The animals in the group coelenterata have certain character-
istics in common. One is the possession of stinging cells. Can
you find any other characteristics which they all have?

Physiological division of labor has been shown to be the per-
formance of different kinds of work by different collections of
cells in an organism. This is shown in a simple way in the hydra.

Problem Questions. — 1. Compare reproduction in a simple
plant and in a simple animal.

2. Describe the early stages of development in an animal.

3. Describe the structure of a simple sponge.

4. Compare the structure of a hydra and of a jellyfish.

5. Explain alternation of generations. Where have you found
it before?

6. Discuss the economic importance of three animals men-
tioned in this chapter.

Problem and Project References

Calkins, Biology. Henry Holt and Company.

Hegner, Introduction to Zoology. The Macmillan Company.

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Miner, A Guide to the Sponge Alcove. Guide Leaflet, No. 23. American Museum

of Natural History, New York.
Parker, Lessons in Elementary Biology. The Macmillan Company.
Sedgwick and WUson, General Biology. Henry Holt and Company.
Shull, Principles of Animal Biology. McGraw-Hill Book Company,
Sharpe, A Laboratory Manual. American Book Company.

XVII. THE WORMS, A STUDY OF RELATIONS
TO ENVIRONMENT

Problem. To discover the relation of the earthworm to its sur-
roundings. (Laboratory Manual, Prob. XXVII; Laboratory
Problems, Prob. 118.)

Effect of Surroundings on Plants. — Animals as well as plants
are influenced ver}^ greatly by their surroundings or environ-
ment. We have seen how green plants behave toward the
various factors of their environment; how heat and moisture
start germination in a seed; how the roots grow toward water;
how gravity influences the root and the stem, pulling the root
downward and stimulating the stem to grow upward; how the
stem grows toward the source of Hght; and how the leaves put
their flat siu-faces so as to ^et as much hght as possible; . and
how oxygen is necessary for life to go on.

It is quite possible to show that the factors of environment
act upon animals as well as plants, although it is much harder
to explain why an animal does a certain thing at a certain time.

How One-celled Animals respond to Stimuli. — We have seen
that the single-celled animals respond to certain stimuh in their
surroundings. The presence of food attracts them; when they
run into an object, they respond immediately by backing away,
thus showing that they have a sense of touch. If part of a
glass slide containing paramecia is heated slightly, the ani-
mals will respond to the increase in heat bj^ moving toward
the cooler end. Other experiments also might be quoted to
show that the living matter of a simple animal is sensitive to
its surroundings.

The Earthworm in its Relation to its Surroundings. — The
earthworm, familiar to most bo3^s as bait, shows us in many
ways liow a many-celled animal responds to stimuli. Careful
observation of the body of a living earthworm reveals that
its long tapering body is made up of a large number of ringr.

194

THE EARTHWORM 195

OP segments. The number of these segments will be found to
vary in worms of different lengths, the loJiger earthworms having
more segments.

If the two ends of the earthworm be touched hghtly with a small
stick or straw, one end wiU be found to respond much more
readily to touch than the other end. The more sensitive end
is the front or anterior end; the other end is the posterior end.
Jar the dish in which the earthworm is crawling; it will inune-
diately respond by contracting its body.

Living earthworms tend to coUect along the sides of a dish

An eaT-tliworm crawling over a smooth surface.

or in the corners. This seems to be due to an instinct which
leads theni to inhabit holes in the ground.

An earthworm placed half in and half out of the darkened area
in a box soon responds by crawling into the darkened part and
remaining there. It has no eyes visible. A careful study of the
worm with the microscope, however, has revealed the fact that
scattered through the skin, particularly^ of the anterior seg-
ments, are many little structures which enable the animal to
distinguish not only between light and darkness, and between
light of low and high intensity, but also the direction from which
it comes. An earthworm has no ears or special organs of feel-
ing. We know, however, that it responds to vibrations of low
intensity, and the sense of touch is well developed in all parts
of its body.

It also responds to the presence of food, as can be proved if
bits of lettuce or cabbage leaf are left overnight in a dish of
e^rth where earthworms axe kept.

196

WORMS

ty

Locomotion of an Earthworm. — If we measure an earthworm
when it is extended and compare with the same worm con-
tracted, we note a difference in length. This is accounted for
when we understand the method of locomotion. Under the
skin are two sets of muscles, an outer set which passes in a
circular direction around the body, and an inner set which runs
the length of the body. The body is lengthened by the con-
traction of the circular muscles. How might the body be
shortened?

The under surface of the earthworm is provided with four double

rows of tiny bristles called
8e!t(B, on all the segments
except the first three and the
last. Each seta has att,« ?hed
to it small muscles, which
tUxQ it so it may point
in the direction opposite to
that in which the worm is
moving. If you watch a
specimen carefully, you will
see that locomotion is ac-
complished by the thrusting
forward of the anterior end, followed by a wave of muscular
contraction passing down the body, thus shortening the body by
drawing up the posterior end. The setae at the anterior end serve
as anchors which prevent the body from slipping backward as the
posterior end is drawn up.

How the Earthworm digs Holes. — A feeding earthworm will
show the prosto'mium, an extension of the upper lip which is used
as an organ of sensation. The earthworm is not provided with
hard jaws or teeth. Yet it literally eats its way through the
hardest soil. Behind the mouth opening is a part of the food
tube called the phar^ynx. This is very muscular so that it can
be extended and withdrawn by the earthworm. When applied to
the surface of the soil, which is first moistened by the earthworm,
it acts as a suction pump and draws particles of the soil into the
food tube. In order to take organic matter out of the ground as
food, the earthworms pass the earth through the body. The earth

Diagram to show how Tnovement of a
seta is accomplished; M, muscles; S,
seta; W, body wall. (After Sedgwick
and Wilson.)

THE EARTHWORM

197

is mixed with fluids poured out from glands in the food tube,
which digest the food, and the soil is passed out of the body and

-^ Upper Up
-Br din
-Pharynx

Aortic arch
^ Mlet

deposited on the surface of
the ground, in the form of
little piles of moist earth.
These are familiar sights on
all lawns; they are called
worm casts. Charles Darwin
calculated that fifty-three
thousand worms may be found
in an acre of ground, that ten
tons of soil might pass through
their bodies in a single year
and thus be brought to the
surface, and that they plow
more soil than all the farmers
put together.

Comparison between Hydra and

Earthworm. — The digestive tract of

the earthworm is an almost straight

tube inside of another tube. The

latter is divided by partitions which

mark the boundary of each segment.

The outer cavity is known as the body cavity. In the hydra no body cavity

exists, there being only a digestive cavity. In the animals higher than the

Qcelenterates the digestive tract and body cavity are distinct. Food is

digested within the food tube,
is passed through the walls of
this tube into the body cavity,
and is carried by the blood to
various parts of the body.
The earthworm has no gills or
lungs, the thin skin acting as
an organ of respiration. But
the earthworm is unable to take
in oxygen unless the mem-
branehke skin is kept moist.

-Crop
-Gizzard

"Stomach - Intestine
-Bloodvessel

Fore part of an earthworm opened on
the dorsal side to show the body cavity
and food tube within it.

Diagrammatic cross section of the body of a
coelenterate, and that of a worm.

Development. — The earthworm has both male and female
sex cells present in its body and hence is said to be hermaphro-
dific (from Hermes and Aphrgdito)' In order to have the eggs

198 WORMS

fertilized when they are laid a mutual exchange of sperm cells
takes place between two worms, the sperms being placed in
four little sacs on the ventral side of each worm. Later the
swollen area called the girdle (about one third the distance from
the anterior end) forms a httle sac in which the eggs of the worm
are laid. As this sac passes toward the anterior end of the
earthworm it receives from the body openings the sperms which
were received from the other earthworm and a nutritive fluid
in which the eggs Hve. The fertihzed eggs are then left to
hatch. The sacs or capsules may be found in manure heaps,
or under stones, in May or June; they are small yellowish or
brown bags ab'^ut the diameter of a worm.

Regeneration. — If a one-celled animal be cut into two
pieces, each piece, if it contains part of the nucleus, can grow
into a whole cell. The hydra, some hydroids, jellyfish, and flat-
worms, if injured, may grow again parts that are lost. This
power is known as regeneration. Earthworms possess to a large
degree the power of replacing parts lost through accident or
other means. The anterior end may form a new posterior end,
while the posterior end must be cut anterior to the girdle to
form a new anterior end. This difference seems to be due in
part to the greater complexity of the organs in the anterior end.

Other Segmented Worms. — The sandworm, living on tidal
flats along our eastern coast, is a common sight to those who
live in that region. The leech or bloodsucker is a form known
to every small boy who has bathed in a fresh-water pond.
Discomfort, but no danger, attends the bite of this worm.

Problem. To determine some harmful animal associations,
{Laboratory Manual, Prob. XXVIII.)

Some "Worms which harm Man. — Some worms are unseg-
mented; such are the flatworms and roundworms. A common
leaflike form of flatworm may be found clinging to stones in
our fresh-water ponds or brooks. Most flatworms are, however,
parasites on other animals; that is, they obtain food and
shelter from some other living creature, but give it no benefits
in return. Parasitism is one-sided, the host giving everything,
the parasite receiving everything. Consequently, the parasite

WORMS WHICH HARM MAN 199

frequently becomes fastened to its host during adult life and
often is reduced to a mere bag through which the fluid food
prepared by its host is absorbed. Such animals as have lost
power to move about freely, to digest food, or to perform some
other function as a result of their
comfortable surroundings, are said to
have degenerated.

Sometimes a complicated life history
has arisen from parasitic habits.
Such is seen in the hfe history of the
liver fluke, a flatworm which kills a flatworm iYungm au-

sheep, and in the tapeworm. rantiaca), much magnified.

, From model in the American

Cestodes or Tapeworms. — ihese Museum of Natural History.

parasites infest man and many other

vertebrate animals. The tapeworm (Tcrnia solium) passes
through two stages in its life history, the first within a pig,
the second within the intestine of man. The eggs of this worm
are 'taken in with the pig's food. The young worm develops
within the intestine of the pig, but soon makes its way into
the muscles. When man eats pork containing tapeworms, if the
pork has not been sufficiently cooked, he may become a host
for the tapeworm. Another common tapeworm parasitic on
man lives part of its life as an embryo within the muscles
of cattle. The adult worm consists of a round headlike part
provided with hooks, by means of which it fastens itself to
the walls of the intestine. This head now buds off a series
of segmentlike structures, which are practically bags full of
eggs. These structures, called progloftids, break off from time
to time, thus allowing the eggs to escape. A proglottid
has no separate digestive system, but the whole body surface
is bathed in digested food, which it absorbs and thus the para-
site is enabled to grow rapidly.

Roundworms. — Still other wormlike creatures called round-
worms are of importance to man. Some, as the vinegar eel
found in vinegar, or the pinworms parasitic in the lower intes-
tine, particularly of children, do little or no harm. The pork
worm or trichina (tri-ki'na), however, is a parasite which may
cause serious injury. It passes through the first part of its

200

WORMS

existence as a parasite in a pig or other vertebrate (as a cat,
rat, or rabbit), where it encysts itself in the muscles of its hosts.
If the meat is oaten in an uncooked condition, the cyst is dis-
solved olT by the action of the
digestive fluids, and the living
trichina becomes free in the
intestine. Here it bores its
way through the intestinal
walls and enters the muscles,
causing inflammation. This
results in a painful and often
fatal disease known as trich-
ino'sis.

The Hookworm. — The ac-
count of the discovery by
Dr. C. W. Stiles of the
Bureau of Animal Industry,
that the shiftlessness of the
"poor whites" of the South
is due partly to a parasite
called the hookworm, another
roundworm, reads like a
fairy tale.
Effect of hookworm infection. The The people, largely farmers,

young man at the left 17 yearsold, weighs bcCOmC infected with a
156 pounds. His older brother beside

him, 18 years of age, badly infected with larval Stage of the hookworm,

hookworm, weighs only 74 pounds. which dcVClopS in m O i S t

earth. It enters the body usually through a break in the
skin of the feet, for children and adults alike, in certain local-
ities where the disease is common, go barefoot to a consider-
able extent.

A complicated journey from the skin to the intestine now
follows. The larvse pass through the veins to the heart, and from
there to the lungs. They then bore into the air passages and
eventually reach the intestine by way of the windpipe. One
result of the injury to the lungs is that many thus infected are
subject to tuberculosis. The adult hookworms, once in the food
tube, fasten themselves to the walls, which they puncture, and

THE HOOKWORM 201

feed upon the blood of their host. The loss of blood from this
cause is not sufficient to account for the bloodlessness of the
[)erson infected, but a poison poured into the wound by the hook-
worm prevents the blood from coagulating rapidly; hence a
considerable amount of blood escapes from the wound after the
hookworm has finished its meal and gone to another part of
the intestine.

The cure of the disease is very easy: th3Tiiol, which weakens
the hold of the hookworm, followed by Epsom salts. For
years the entire South undoubtedly has been retarded in its
development by this parasite. Hundreds of millions of dol-
lars have been wasted, and, what is more vital, thousands of
lives have been needlessly sacrificed.

" The hookworm is not a bit spectacular: it doesn't get itself discussed
in legislative halls or furiously debated in political campaigns. Modest
and unassuming, it does not aspire to such dignity. It is satisfied simply
with (1) lowering the working efficiency and the pleasure of hving in some-
thing like two hundred thousand persons in Georgia and all other Southern
states in proportion; with (2) amassing a death rate higher than tuber-
culosis, pneumonia, or typhoid fever; with (3) stubbornly and quite effec-
tually retarding the agricultural and industrial development of the section^
with (4) nullifying the benefit of thousands of dollars spent upon educa-
tion; with (5) costing the South, in the course of a few decades, several
hundred millions of dollars. More serious and closer at hand than the
tariff; more costly, threatening, and tangible than the Negro problem;
making the menace of the boll weevil laughable in comparison — it is pre-
eminently the problem of the South." — Atlanta Constitution.

The work of the Rockefeller Foundation in the tropics has
proved that the hookworm is found in most hot and moist cli-
mates and that consequently natives of such countries are often
attacked by it. It is thought that 75 per cent of the natives
of Southern China, 60 to 80 per cent of 300,000,000 natives
of India and over 90 per cent of the laboring classes of Dutch
Guiana and Colombia are infected with it, while over 2,000,000
pectpie in this country are its victims. If we were to estimate the
economic loss due to hookworm the world over, it would run into
hundreds of millions of dollars annually.

Other Parasitic Worms. — Somie roundworm parasites live in
Hunt. New Ee. — 14

202 WORMS

the skin, and others live in the intestines of the horse. Still
others are parasitic in fish and in insects, one of the common-
est being the hair snake, often seen in country brooks.

A Simple Classification of Worms
A. Segmented Worms (Annula'ta)

Class I. C/itefoporfa (k^-t6p'o-da; bristle-footed). Segmented worms having

setae.
Subclass I. Polychceta (p6l-i-ke'ta; many bristles). Having parapodia,

and usually head and gills. Example: sandworm.
Subclass II. Oligochoe'ta (6l-i-go-ke'ta; few bristles). No parapodia,

head, or gills. Example: earthworm.
Class II. Discophora (dls-k6f'6-ra; bearing suckers). No bristles, two

sucking disks present. Example: leech.

B. Flatworms

Body flattened in dorso-ventral direction
Class I. Turbella'ria. Small, aquatic, mostly not parasitic. Example:

planarian worm.
Class II. Tremato'da. Usually parasitic worms which have complicated

life history. Example: liver fluke of sheep.
Class III. Cesto'da. Internal parasites having two hosts. Example;

tapewonn.

C. Roundworms

Threadlike worms, mostly parasitic. Examples : vinegar eel, trichina,
and hookworm.

Summary. — The earthworm is a simple type of a segmented
worm. One of its most important differences from the hydra
lies in its possession of a body cavity as well as a digestive
cavity.

Parasitic worms such as the tapeworm, trichina, and hook-
worm play an important economic part in the life of today.
Thanks to the work of the Rockefeller Foundation and other
agencies, hookworm disease is fast being reduced in all civilized
parts of the earth.

Problem Questions. — 1. How is the earthworm of economic
importance ?

WORMS 203

2. Describe the internal structure of the earthworm and tell
the use of each part named.

3. Discuss the life history of some parasitic worm and show
how its harmfulness may be combated.

Peoblem and Project References

Darwin, Formation of Vegetable Mould. D. Appleton and Company.

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Hunter and Whitman, Civic Science. American Book Company.

Reports of the Rockefeller Foundation.

Ritchie, A Primer of Sanitation. World Book Company.

Sedgwick and Wilson, General Biology. Henry Holt and Company.

Sharpe, A Laboratory Manual. American Book Company.

XVIII. THE CRAYFISH. A STUDY OF ADAPTATIONS

Problem. A study of the meaning of the term of adaptation as
shown in the crayfish. (Laboratory Manual, Prob. XXIX;
Laboratory Problems, Prob. 118.)

(a) Protection.

(b) Locomotion.

(c) Feeding.

(d) Breathing.

Adaptations. — Plants and animals are in a continual struggle
to hold the places they have obtained upon the earth. Con-
tinually we see garden plants driven out or killed by the com-
peting weeds, simply because the weeds are better fitted or
adapted to live under the conditions which exist in the garden,
especially if it is uncultivated. An adaptation in a plant or
animal is some change in structure, habit, or ability which is of
advantage to the organism in its battle for life. We have
seen many examples of adaptations in plants, — adaptations in
flowers for securing cross-pollination, in fruits for seed-scatter-
ing, in young plants for protection, in roots for securing water;
the list is endless.

In animals, likewise, the successful competitors are the ones
with adaptations to fit them for living in the particular environ-
ment or surroundings in which nature has put them. Examples
are often seen where animals, like sheep or goats, which have
a woolly covering, when introduced by man into a warmer
country, die because the outer coat is too warm. An adaptation
for withstanding cold becomes harmful to the animal in a
warmer country.

One adaptation which we have already noticed in animals is
always protective. This is the resemblance of the animal to the
surroundings in which it lives. Other adaptations aid the ani-
mal in obtaining aucj digesting food, in protecting itself or its

m

A STUDY OF ADAPTATIONS

205

young from attacks by enemies, and in battling successfully with
the dangers around it.

The Crayfish. Adaptations for Protection. — Animals which
illustrate adaptations for hfe in the water are the fresh-water
crayfish and the salt-water lobster, both members of a large
group of animals known as crusta'ceans. The body of one of
these animals is seen to be encased more or less completely in
a hard covering, which is jointed in the posterior region. This
exoskeleton (outside skeleton) is composed largely of Hme, as
may be proved by testing with acid. The exoskeleton fits over
the anterior part of the animal, forming an un jointed car' apace,

Crayfish: A., antennae; E., stalked eye; C.P., cephalotho^ax; Ab., abdomen;
C.F., caudal fin; M., mouth; Ch., chelipeds. From photograph.

or armor. This armor is clearly protective and is therefore an
adaptation. If the crayfish is watched in a balanced aquarium,
the colors are seen to blend remarkably with the stones and
water weeds of the bottom. The animal is protectively col-
ored. The under side of the animal is less well protected than
the upper, and the joints of the abdo'men, or posterior region,
extend completely around the body. The animal is segmented,
the abdomen showing the segments plainly.

Locomotion. — Those of us who have caught crayfish in fresh-
water streams or lakes know that it takes skill and quickness.
They dart backwards through the water with great rapidity,
or they move forward by crawling on the bottom. Examina-
tion of a crayfish shows us five pairs of walking legs attached
to the under side of the cephalotho'rax (head + thorax), the

20G

THE CRAYFISH

anterior part of the body. These legs are jointed, and the first
tliree pairs bear pinchers. Tlie hirge pinchcr claws or chelipeds
(ke'li-pedz) arc used for food-catching as well as for locomo-
tion. Try to find out exactly what then- use is in a Hving
specimen.

Under the abdom6n, one pair on each segment except the last,
are found jointed appendages, made up of three parts, a base

and two branches. These
are called swimmer ets,
though they are not used
for swimming. Now look
at the broad pair of
swimmerets which, to-
gether with the last
segment of the abdomen,
form a finlike apparatus,
XhQ caudal fin. Crayfish
swim very rapidly by
means of a sudden jerk-
ing of the caudal fin in
a backward direction.
The abdomen is pro-
vided with powerful
muscles which are at-
tached to the exo-
skeleton. It is by these
muscles that the rapid
swimming is accom-
plished.
How the Crayfish gets in Touch with its Surroundings. —
Several other appendages besides those used for locomotion are
found. Two pairs of " feelers," the longer pair called the
anten'nce, the shorter the anten'nules (httle antennae), protrude
from the front of the body. The longer feelers appear to be
used as organs of touch and smell. The smaller antennules
hold at their bases little sacs called balancing organs.

Just above the antennules, projecting on stalks, are the eyes.
These eyes are made up of many small structures called om-

Female lobster, showing eggs attached to
the swimmerets. From photograph loaned^ by
the American Museum of Natural History.

A STUDY OF ADAPTATIONS

207

matid'ia, each one of which is a very simple eye. A collection of
ommatidia is known as a compound eye. Such an eye probably
does not have very distinct vision. A crayfish, however, easily
distinguishes moving objects and prefers darkness to Hght, as
may be proved by experiment.

Feeding. — Living food is obtained with the aid of the cheli-
peds and shoved toward the mouth. It is pushed on by three
pairs of small appendages called foot jaws or maxil'lipeds, and

Appenda^ges of the crayfish: 1, antennule; 2, antenna; 3, mandible;
4, first maxilla; 5, second maxilla; 6, first maxilliped; 7, second maxilliped;
8, third maxiUiped; 9, cheliped; 10, 11, 12, i 5, walking legs; 14^, modified
swimmeret in male; 15, modified swimmeret in male; 16, 17, 18, swimmerets
which carry the eggs in female; 19, uropod, the side part of the caudal fin.

to a slight degree by two still smaller paired maxiVlce just
under the maxillipeds. Ultimately the food reaches the hard
jaws and, after being ground between them, is passed down to
the stomach.

Experiment to demonstrate Breathing. — The mouth parts of a crayfish
resting in the aquarium are observed to be constantly in motion, despite
the fact that no food is present. If a crayfish is taken out of the water
and held with the ventral surface uppermost, a little carmine (mixed in
water) may be dropped on the lower surface and allowed to run down under
the carapace. If the animal is now held in water in the same position,
the carmine will reappear from both sides of the mouth, seemingly pro-

208

THE CRAYFISH

pelled forward by something which causes it to emerge in little puffs. K
we remove the maxillipeds and maxillae from a dead specimen, we find a
groove leading back from each side of the mouth to a ca\'ity of consider-
able size on each side of the body under the carapace. This is the gill
•chamber. It contains the gills, the organs which absorb the oxygen dissolved
in the water. The second maxillae are prolonged into the groove to serve
as bailers or scoops. By rapid action of these organs a current of water is
maintained which passes over the gills.

The Gills. — The gills are outside of the body, although pro-
jected by the carapace. If the carapace is partly removed on

Crayfish with the left half of the body structures removed: a, intestine;
6, ventral artery; c, brain; e, heart; et, gastric teeth; i, oviduct; I, diges-
tive gland; m, muscles; n, green gland (kidney); o, ovary; p, pjdoric
stomach; r, nerve cords; s, cardiac stomach; st, mouth; u, telson, or
last segment of the abdomen, forming the middle part of the caudal fin;
w, openings of veins into the pericardial sinus. Natural size. (Davison,
Zoology.)

one side, they will be found looking somewhat like white
feathers. The blood of the crayfish passes by a series of veins
into the long axis of the gill,' where the blood vessels divide
into very minute tubes, the waUs of which are extremely deli-
cate. Oxygen, dissolved in the water, passes into the blood by
osmosis, during which process the blood loses some carbon
dioxide. The gills are kept from drying by being placed in a
nearly closed chamber, which has a row of tiny hairs bordering
the lower edge of the carapace. Thus crayfish may live for
long pei-iods away from water.

Circulation. — The circulation of blood in the crayfish takes place In
a system of thin-walled, flabby vessels which are open in places, allowing
the blood to come in direct contact with the tissues to which it flows.
The heai't lies on the dorsal side of the bodv, inclosed in a delicate bag,

A STUDY OF ADAPTATIONS 209

toto which all the blood in the body eventually finds its way during its
circulation.

Digestion. — Food which has not been ground up previously into pieces
smaU enough for the purpose of digestion is still further masticated by
means of three strong projections or teeth, one placed on the mid-line and
two on the side walls of the stomach. The exoskeleton of the crayfish
extends into the stomach, thus forming the gastric mill just described.

The stomach is divided into anterior and posterior parts separated
from each other by a constriction. The posterior part is lined with tiny
projections from the walls which make it act as a strainer for the food
passing through. Thus the larger particles of food are kept in the an-
terior end of the stomach. Opening into the posterior end of the stomach
are two large digestive glands whose juices further prepare the food for
absorption through the walls of the intestine. Once in the blood, the fluid
food is circulated through the body to the tissues which need it.

Nervous System. — The internal nervous system of a crayfish con-
sists of a series of collections of nerve cells called ganglia (gS-ng'gll-a) con-
nected by means of a double line of nerves. Posterior to the gullet, this
chain of ganglia is found on the ventral side of the body, near the body
wall. At the anterior end it encircles the gullet and forms a brain in the
head region, from several ganglia which have grown together. From each
of these ganglia, nerves pass off to the sense organs and into the muscles
of the body. These nerve fibers are of two sorts, those bearing messages
from the outside of the body to the central nervous system (these messages
result in sensations), and those which take outgoing messages from the
central nervous system (motor impulses), which result in muscular move-
ments.

Development. — The sexes in the crayfish are distinct. The eggs are
fertilized by the sperm cells as they pass to the outside of the body of the
female. The eggs, which are provided with a considerable supply of food
material called yolk, are glued fast to the swimmerets of the mother, and
there develop in safety. The young, when they first hatch, remain
clinging to the swimmerets for several weeks.

Excretion of Wastes. — On the basal joint of the antennae are found two
projections, in ihe center of which are tiny holes. These are the open-
ings of the green glands, organs which eliminate the nitrogenous waste from
the blood, the function of the human kidneys.

a

North American Lobster. — In structure the lobster is almost
the counterpart of its smaller cousin, the crayfish. Its geographi-
cal range is a strip of ocean bottom along our coast, estimated
to vary from thirty to fifty miles in width. This strip extends
from Labrador on the north to Delaware on the south. The
lobster is highly sensitive to changes in temperature. It mi-

210

THE CRAYFISH, ETC.

grates from deep to shallow water, or vice versa, according to
changes in the temperature of the water, which in winter is
relatively warmer in deep water and cooler in shallows. Sudden
changes in the temperature of the water of a given locality may
cause them to disappear from that place. The food supply

which is more abundant near the shore
also aids in determining the habitat
of the lobster. Lobsters do not appear
to migrate north and south along the
coast. While little is known about
their habits on the ocean bottom, it
is thought that they construct burrows
somewhat like the crayfish, in which
they pass part of the time. As they
are the color of the bottom and as
they pass much of their time among
the weed-covered rocks, they are able
to catch much living food, even active
fishes falling prey to their formida-
ble pinchers. They move around
freely at night, usually remaining
quiet during the day, especially when
in shallow water. They eat some
dead food and thus are scavengers;
the same is true of the crayfish.

Development. — The female lobsters
begin to lay eggs when about seven
inches in length. I^obsters of this
size lay nearly five thousand eggs; this number is increased to
about ten thousand by lobsters of moderate size (ten inches in
length); by exceptionally large specimens as many as one
hundred thousand eggs are sometimes laid. The eggs are laid
every alternate year, usually during the months of July and
August. Eggs laid in these months, as shown by observations
made along the coast of Massachusetts, hatch the following
May or June. The eggs are provided with a large supply of
yolk (food), the development of the young animal taking place
at the expense of this food material. After the young escape

North American lobster.
This specimen, preserved at
the U. S. Fish Commission at
Woods Hole, was of unusual
size and weighed over twenty
pounds. Notice the chelipeds.

THE LOBSTER 211

from the eggs, they are almost transparent and little like the
adult in form. During this period of their lives the mortality
is very great, as they are the prey of many fish and other free-
swimming animals. It is estimated that barely one in five
thousand survives this period of peril. At this time they grow
rapidly, and in consequence are obliged to shed their exoskeleton

Metamorphosis of a lobster: 1, 2, 3, larval stages; 4, very young lobster in its

adult form.

(molt) frequently. During the first six weeks of life, when they
swim freely at the surface of the water, they molt five or six
times. ^

Molting. — During the first year of its life the lobster molts
from fourteen to seventeen times. During this period it attains
a length of from two to three inches. Molting is accomplished
in the following manner: The carapace is raised up from the
posterior end and the body is then withdrawn through the open-
ing between it and the abdomen. The most wonderful part
of the process is the withdrawal of the flesh of the large claws
through the very small openings which connect the limbs with
the body. The blood is first withdrawn from the appendage;
this leaves the flesh in a flabby, shrunken condition so that
the muscles can be drawn through without injury. The lobster
also molts the lining of the digestive tract as far as the posterior
portion of the stomach. Immediately after molting the lobster
is in a helpless condition, and is more or less at the mercy of
its enemies until the new shell, v/hich is secreted by the skin,
has grown.

1 Recent economic investigations upon the care of young lobsters show that
animals protected during the first few months of free existence have a far bet-
ter chance of becoming adults than those left to grow up without protection-
Later in life they sink to the bottom, where, because of their protectively
colored shell and the habit of hiding under rocks and in burrows, they are
comparatively safe from the attack of enemies.

212

THE CRAYFISH, ETC.

The edible blue crab. From photograph
loaned by the American Museum of Natural
History.

Economic Importance. — The lobster is highly esteemed as
food, and is rapidly disappearing fvom our coasts as the result

of overfishing. Between
twenty million and thirty
million a year are taken
on the North Atlantic
coast. Laws have been
enacted in New York
and other states against
overfishing. Egg-carry-
ing lobsters must be re-
turned to the w^ater; aU
smaller than six to ten
and one half inches in
length (the law varies in different states) must be put back;
other restrictions are placed upon the taking of the animals, in
hope of saving the race from extinction. Some states now hatch
and care for the young for a period of time; the United States
Bureau of Fisheries is also doing
much good work, in hope of
restocking to some extent the
now almost depleted waters.

Shrimps. — Several other common
crustaceans are near relatives of the
crayfish. Among them are the
shrimps and prawns, thin-shelled, ac-
tive crustaceans common along our
eastern coast. In spite of the fact
tnat they form a large part of the
food supply of many marine animals, Hermit crab, about twice natural

especially fishes, they do not appear size. From photograph loaned by
to be decreasing in numbers. Be-
sides this value as a food for fishes,
they are also used by man, the shrimp fisheries in this country aggregating
over $1,000,000 yearly.

The Blue Crab. — Another edible crustacean of considerable economic
importance is the blue crab. Crabs are found inhabiting muddy bot-
toms; in such localities they are caught in great numbers in nets or traps
baited with decaying meat. They are, indeed, among our most valuable
sea scavengers, although they are also hunters of living prey. The ante-

the American Museum of Natural
History.

CRABS

213

The fiddler crab. From photograph
loaned by the American Museum of
Natural History.

They

rior part of the body of the crab is short and broad, being flattened dorso-

ventrally. The abdomen is much reduced in size. Usually it is carried close to

the under surface of the cephalo-

thorax. In the female the eggs are

carried under the ventral surface of

the abdomen, fastened to the rudi-
mentary swimmerets in the position

which is usual for other crustaceans.

The young crabs differ considerably

from the adult in form and method

of life. They undergo a complete

metamor'phosis or change of form

during development. Immediately

after molting, crabs are greatly desired by man as an article of food

are then known as " shedders," or soft-shelled crabs.
Other Crabs. — Other crabs found along the New York coast are the

prettily colored lady crabs,
often seen running along our
sandy beaches at low tide;
the fiddler crabs, interesting
because of their burrows and
gregarious habits; and per-
haps most interesting of all,
the hermit crabs. The hermit
crabs use the shells of snails
as homes. The abdomen is
soft, and unprotected by a
limy exoskeleton, and has
adapted itself to its condi-
tions by curhng around in
the spiral snail shell, so that
it has become asymmetrical.
These tiny crabs are great
fighters and wage frequent
duels with each other for
possession of the more desira-
ble shells. They exchange
their borrowed shells for

Giant spider crab from Japan. From pho-
tograph loaned by the American Museum of
Natural History.

larger ones as growth forces them from their first homes.

The habits of these animals, and those of the fiddler crabs, might be
studied with profit by some careful boy or girl who spends a summer at
the seashore and has the time and inclination to devote to the work. Of
especial interest would be a study of the food and feeding habits of the
fiddler crabs.

A deep-water crab often seen along Long Island Sound is the spider
crab, or " sea spider," as it is incorrectly called by fishermen. This ani-

214 THE CRAYFISH

mal, with its long spider-like legs, is neither an active runner nor swimmer;
it is, howev^er, colored Hke the dark mud and stones over which it crawls;
thus it is enabled to approach its prey without being noticed. The re-
semblance to the bottom is further heightened by the rough body covering,
which gives a hold to which seaweeds and sometimes such animals as barna-
cles, hydroids, or sea anemones fasten themselves.

A spider crab from the Sea of Japan is said to be the largest crustacean
in the world, some specimens measuring eighteen feet from tip to tip of the
first pair of legs.

Symbiosis. — Certain of the spider crabs, as well as some of
the larger deep-water hermit crabs, have come to live in a rela-
tion of mutual helpfulness with hydroids, sponges, and sea
anemones. These animals attach themselves to the shell of the
crab and are carried around by it, thus receiving a constant
change of location and a supply of food. What they do for
the crab in return is not so evident, although one large Chinese
hermit crab regularly plants a sea anemone on its big claw; when
forced to retreat into its shell, the entrance is thus effectually
blocked by the anemone. The living of animals in a mutually
helpful relation has been referred to as symbiosis. Of this we
have abeady had some examples in plants as well as among
animals. (See page 169.)

Habitat. — Most crustaceans are adapted to live in the water;
a few forms, however, are found living on land. Such are the
wood lice, the pill bugs, which have the habit of rolling up into
a ball to escape attack of enemies, the beach fleas, and others.
The coconut crab of the tropics climbs trees in search of food,
returning to the water at intervals to moisten the gills.

Characteristics of Crayfish and its Allies. — Our study shows
us that animals belonging to the same group have several well-
marked characteristics in common. The most important char-
acteristic of the crusta'cea, the group to which the crayfish
belongs, are the presence of a segmented limy exoskeleton, gills,
jointed appendages, usually a pair to each segment of the body
(except the last), stalked compound eyes, and the fact that they
pass through a metamorphosis or change of form before they
reach the adult state.

Summary. — The crayfish has been used in this chapter to
give us some idea of its numerous adaptations. These have

A STUDY OF ADAPTATIONS 215

to do with its method of locomotion, feeding, breathing, in fact
all of its activities. Acts which tend to the preservation of the
race may be adaptive as well as structures which have this
purpose o

Problem Questions. — 1. Explain what is meant by the term
adaptation.

2. Name and describe adaptations in the crayfish for protec-
tion, feeding, breathing, locomotion, digestion.

3. Is molting an adaptation? Explain.

4. Discuss the life history of the lobster.

5. Discuss the economic importance of the Crustacea,

Problem and Project References

Davison, Practical Zoology, pages 133-141. American Book Company.

Herrick, The American Lobster. U. S. Fish Commission Report^ 1895.

Huxley, The Crayfish. D. Appleton and Company.

Jordan and Kellogg, Evolution and Animal Life. Chapter VIII. D. Appleton
and Company.

Mead, Reports on Lobster Industry. Rhode Island Inland Fisheries Commission.

Parker and Haswell, Zoology, Chapters on Crustaceans. The Macmillan Com-
pany.

Snarpe, A Laboratory Manual. American Book Company.

XIX. THE INSECTS

Problem, A study of some animal likenesses and differences
in order to understand an elementary classification oj insects.
(Laboratory Manual, Prob. XXX; Laboratory Problems, Probs.
8, 9, 10, 11,)

(a) Grasshopper — a straight-winged insect,

(b) Butterfly or moth — a scale-winged insect,

(c) The typhoid fly — a two-winged insect.

(d) A beetle — a sheath-winged insect.

(e) A bug — a half -winged insect.

(f) The dragon fly — a nerve-winged insect,

(g) The bee — a membrane-ivinged insect.
Qi) Summary of differences between orders.
(i) Making a logical definition.

Insects the Winners in Life's Race. — We are all familiar
with common examples of insect life. Bees and butterflies we
have already studied in connection with their work in the cross-
pollination of flowers. Mosquitoes and flies all too often come
to our notice as pests; the common household insects sometimes
annoy us, while we often hear of and see in a small way the harm
done by insects in the field and garden. Insects are a successful
group. They outnumber all the other species of animals on the
face of the earth. They hold their own in the air, in the water,
and on the land. Fitted in many ways to lead a successful life,
they have become winners in life's race.

We have already, from our study of a bee, formed some idea
of what an insect is. But it would be unfair to expect to know
all insects from our slight knowledge of one form. Our object
in the study of this chapter will be to get some first-hand
knowledge of some common insects so that we may classify
them and distinguish one from another. This great group,
containing more than half of the known representatives of
animal life on the earth, is made up of a number of groups

216

THE GRASSHOPPER

217

called orders. The insects contained in these orders have certain
characteristics of structure and life history in common, yet each
order differs somewhat from the other orders. The characteristics
which all the groups possess in common give us a working
definition of an insect.

The Red-legged Grasshopper. — One of the most conunon in-
sects in the United States is the red-legged grasshopper. Its

Poster/or m'n^ Anterior wing head Compound eye

Abdomen
Spirede oms^ Segment 'f abdomen,

^ -Antenna
-/-Posiiion of ocellus

\'(:v [Protfiom

AMmthordx \\ Labium
msthorax\ ^^emurofi^Jleg ymurofHeg
Spiracle onhesothorax
FemurofS-leg

- -Labrum
■Palpus

Parts of the body of a male grasshopper.

segmented body is divided into an anterior part, the head; a,
middle portion, the tho'rax; and a posterior portion, the abdomen.
The animal is nearly the color of the grass on which it lives.
The tough exoskeleton covering the body is composed of chitin
(kftin), a substance somewhat like that which forms the horns
of a cow.

The Thorax. — The thorax is formed of three segments, the
most anterior of which is known as the protho'rax, the middle
one as the mesothorax, and the
posterior part as the metathorax.
Each segment bears a pair of jointed
legs, and the posterior two segments
bear wings also.

The Legs. — The legs, six in num-
ber, are fitted for active hfe in
the fields. A careful study of the insect shows the hind
leg to be fitted for jumping, not only in structure but also
in position. It is long, jointed, and attached to powerful mus-
cles which enable the grasshopper to spring forward quickly to

New Es. — 15

remur

TrochankrA

Hind leg of a grasshopper.

218

THE INSECTS

Cross section through the body of an in-
sect: a, food tube; h, heart; n, nerve cord;
/, spiracle, opening of trachea.

a great distance when the size of its small body is considered.

An examination of the foot or tarsus shows a number of tiny

hooks and pads, by means of which the insect can cling to the

swaying grass stalks. Study the other legs and see if you can

find similar adaptive struc-
tures.

The Wings. — The mem-
brane-like wings, when
spread out, show differences
in structure. The outer
pair, stronger and narrower
than the inner pair, serve
to protect the latter. The
inner wings, when not in
use, fold up like a fan.
The Abdomen. — The

segmented abdomen does not bear appendages, but at the

posterior end of the abdomen of the female are found paired

movable pieces which together form the egg layer or ovipos'itor.

The male grasshopper has a

rounded abdomen. Mdncf/bfc

Breathing Organs. — Ob- \

servation of the abdomen of

a living grasshopper shows

frequent movements of the

abdomen. On each side of

the abdomen in eight of the

segments (in the red-legged

grasshopper) are found tiny

openings called spir'acles.

These spiracles open into

little tubes called tracheoe

(tra'ke-e). The tracheae

divide and subdivide like the

branches of a tree, so that all parts of the body cavity are reached

by their fine endings. Air is drawn in by the expansion of the

abdomen and forced out when it contracts. The blood of an

insect does not circulate through a system of closed blood tubes

Max/7/ary
Pa/pus

Lab/alPd/pu5.

Lab/i/m

Mouth parts of a grasshopper.

THE GRASSHOPPER 219

as in man, but instead it more or less completely fills that part
of the body cavity which is not occupied by other organs. By
means of the tracheae, air is brought in contact with the blood,
which takes in oxygen and gives off carbon dioxide.

Muscular Activity. — Insects have the most powerful muscles
of any animals of their size. Relatively, an enormous amount
of energy is released during the jumping or flying of a grass-
hopper. The tracheae pass directly into the muscles and other
tissues so that a supply of oxygen is at hand for the oxidation
of tissues and the release of energy.

Food-taking. — The grasshopper is provided with two pairs
of jaws, a forklike ventral-lying pair, the maxillce, and a pair of
hard toothed jaws for cutting, called the man'dihles. These
parts are covered when not in use by two flaps, the upper and
lower lips. The leaf upon which the grasshopper feeds is held
in place in the mouth by means of the little jaws, or maxillae,
while it is cut into small pieces by the mandibles.

Blood-making. — Just behind the mouth is a large crop into
which empty the contents of the salivary glands. It is this fluid
mixed with digested food that we call the ''grasshopper's
molasses.'' After the food is digested by the action of the saliva
and other juices, it passes in a fluid state through the walls of
the intestine, where it becomes part of the blood. As blood it
is passed on to tissues, such as muscle, to make new material to
be used in repairing that \7hich is used up during the flight of
the insect or to be oxidized to release energy.

Eyes. — Examination of the compound eye with a lens shows
the whole surface to be composed of tiny hexagonal spaces called
facets (f assets). Each facet marks the surface of a unit {om-
matid'ium) of the compound eye. The separate units of the
compound eye probably each give a separate impression of light
and color. Thus a compound eye is most favorable for per-
ceiving the movement of objects. The grasshopper has three
simple eyes also on the front of the head. The simple eyes
probably are able only to perceive light and darkness.

Other Sense Organs. — The segmented feelers, or antennce,
have to do with the sense of touch and smell. The eardrum, or
tym'panum, of the grasshopper is found under the wing on the

220

THE INSECTS

stages in the life history of the grasshopper.
Note the absence of wings in 1 and 2. The
adult female 4 is laying eggs in holes she has
made in the ground.

first segment of the abdomen. Covering the body and on the
appendages, are found hairs (sensory hairs) which appear to
make the insect sensitive to touch. Thus the armor-covered

animal is in touch with
its surroundings.

Nervous System. —
The nerve chain, as in
the crayfish, is on the
ventral side of the body.
It passes around the
gullet near the head to
the dorsal side, where a
collection of ganglia
forms the brain. Nerves
leave the central system
as outgoing fibers which
bear motor impulses.
Other nerve fibers pass
inward, and produce sensations. These are called sensory fibers.
Life History. — The female grasshopper lays her eggs in a
hole which she has dug in the ground with her ovipositor.
From twenty to thirty fertilized eggs are laid in the fall; these
hatch out in the spring as tiny wingless grasshoppers. The
young molt in order to grow larger, each grasshopper under-
going about five molts before reaching the adult state. Since
no great change in form occurs, the metamorphosis is said to
be incomplete. In the fall most of the adults die, only a few
surviving the winter.

Economic Importance. — Grasshoppers or locusts have done
great harm since the days of the Pharaohs at least. They eat
the young leaves of grass, corn, wheat, and other crops, destroy-
ing promising fields of grain and sometimes leaving desolate
and barren wastes behind them. Birds and parasites are their
natural enemies. Plowing the fields after the eggs are laid
helps to destroy them.

Relatives of the Locust. — Among the near relatives are the
brown or black crickets, cockroaches and "waterbugs," the
katydid, praying mantis, and many others. All of these in-

THE BUTTERFLY

221

on a

sects have the hind wings^ when present, folded up lengthwise
against the body when at rest mouth parts fitted for biting,
and an incomplete metamorphosis. They are placed in an
order called Orthop'tera because the
posterior wings are folded straight
against the sides of the body when at
rest (orthos, straight, pteron, wing).

The Butterfly. — The body of the
butterfly, as that of the grasshopper,
is composed of three regions. The
legs of the butterfly are relatively
smaller and weaker than those of

the grasshopper, while the wings are Scales and scale sockets

relatively larger in the first-named butterfly's wing,

insect. Under the microscope the

wing is seen to be covered with thousands of Httle colored
scales^ each of which fits into a socket in the membranous
wing. These scales cause the name Lepidop'tera (lepis. scale,
pteron, wing) to be given to this order of insects. The long pro-
boscis, a sucking tube through which the insect sucks nectar

from the flowers, is another characteristic
by which the Lepidoptera may be known.
Life History of the Cabbage Butterfly. — •
Although a frequent visitor of our gardens,
the cabbage butterfly is perhaps less famil-
iar than the earlier stage in which it ap-
pears as a long green worm which eats the
cabbage leaves.
Egg. — The eggs are laid in the early
. , „ , , , spring on the leaves of young cabbage

A butterfly's head: , , n^, n i n i

A, antenna; E, com- plants. They are small, pale yeUow, and
pound eye; L.P. labial dehcately marked with fine hues. You

palpus;- Pr., proboscis. . i i r ^^ j. n t .-i

have to look careiully to find them.
Larva, — In about a week the egg hatches and a tiny green
worm or larva crawls out. It has a long segmented body, three
pairs of small true legs on the first three segments of the body,
and five pairs of prolegs or caterpillar legs farther back, which
are of great assistance in holding on to a leaf. The mouth is

222

THE INSECTS

provided with toothed mandibles for cutting the leaves. The
larva eats ravenously and grows rapidly.

Pupa. — After two weeks of active life, the pupa, a resting
stage, is formed. The larva fastens itself to a cabbage leaf,
fence rail, or some other convenient object, and molts. As the
skin slips off, the pupa — in this case called a chrysalis (kris'a-lis)
— appears. It is a smaU oval object, usually green, but some-
times varying a Httle to
harmonize with its sur-
roundings. This stage re-
mains for two weeks in
summer and longer in cold
weather. It then cracks
open down the back and
the butterfly comes out.

Adult. — The butterfly
has two pairs of large,
strong, white or pale yel-
low wings with two or three
black spots on them. The
legs are short and weak,
the antennae are slender
and knobbed, and the suck-
ing proboscis is coiled Hke
a tiny watch spring on the
ventral side of the head.
A Complete Metamorphosis is shown by this insect, which
during its development passes through four distinct stages —
the egg, larva, pupa, and adult.

Economic Importance and Control. — The harm is done by the
larva, which riddles the cabbage leaves by means of its sharp,
pointed mandibles. Spray the plants with a solution of arsenate
of lead or Paris green as soon as the larvae are seen.

The Moth. — The big electric-light moth, cecropia, is an insect familiar
to most of us. In general it resembles a butterfly in structure. Several
differences, however, occur. The body is much stouter than that of a
butterfly. The wings and body appear to have a thicker coating of hairs
and scales, and the antennae are feathery. The position of the wings

Life history of the cabbage butterfly: A
adult; B, two views of egg, much magnified;
C, larva; D, chrysalis.

THE MOTH

223

when at rest forms another easy way of distinguishing the one insect
from the other; the butterfly's wings are then held vertical, while a moth's
are spread out horizontally or are folded over the body.

Development. The Egg. — The eggs, cream-colored and as large as a
pinhead, are deposited in small
clusters on the under side of
leaves of the food plant.

The LarvcE are at first tiny
black caterpillars, which later
change to a bluish green color
with projections of blue, yellow,
and red along the dorsal side.

The Pupal Stage. — Unlike
the butterfly, the moth passes
the quiescent stage in a case
which the larva has spun,
called a cocoon. The cocoon of
the cecropia may be found in
the fall on willows or alders.

If the cocoon is cut open
lengthwise (see Figure), the
dormant insect or pupa will be
found together with the cast-
off skin of the caterpillar
which spun the case.

Silkworms. — The American
silkworm is another well-
known moth. The cocoons,
made in part out of the leaves

Life history of the cecropia moth. Above,
the adult; the larva (caterpillar) in center;
the pupal case to right, below; the same cut
open at left, below. From photograph loaned
by the American Museum of Natural History.

of the elm, oak, or maple, fall to the ground when the leaves drop, and hence
are not so easily found as those of the cecropia. This moth is a near relative
of the Chinese silkworm, and its silk might be used with success were it not
for the high rate of labor in this country. The Chinese silkworm (p. 4) is
raised with ease in southern California. China, Japan, Italy, and France,
because of cheap labor, are still the most successful silk-raising countries.

Differences Between Moths and Butterflies
Butterfly Moth

Antennae threadlike, usually

knobbed at tip.
Fly in daytime.
Wings held vertically when at

rest.
Pupa naked.

Antennae feathery or threadlike,

never knobbed.
Usually fly at night.
Wings held horizontally or folded

over the body when at rest.
Pupa usually covered by a cocoon.

224

THE INSECTS

Complete metamorphosis of the house fly
the four stages in its life history.

Moths and butterflies are both characterized by having a sucking pro-
boscis, membranous wings covered with scales, and by imdergoing a com-
plete metamorphosis or change of form. By these characteristics we know
them to be members of the order Lepidoptera.

Diptera. The Typhoid
Fly. — This name was given
to the common house fly
by L. O. Howard, the Chief
of the Bureau of Ento-
mology, United States
Department of Agriculture;

we shall see later with what reason. The body of the fly, as

of other insects, has three divisions. The membranous wings

appear to be two in number, a second pair being reduced to

tiny knobbed hairs called balancers. The function of the

balancers is apparently that

of equiUbrium.
Head. • — The head is

freely movable, and the

compound eyes are ex-
tremely large. Seemingly

the fly has fairly acute

vision. Home experiments

can be easily made which

prove its keenness of scent

and taste. It is well

equipped to care for itself

in its artificial environment

in the house.
Mouth Parts. — The

C/aiv from tip of foot

MAQNiriED 1500 DIAMETERS

\Typhoid Bacilli

Lowe,

Joints of

Foot

MAGNIFIED
150 DIAMETERS

^^^^^ i(

Foot of a house fly, highly magnified

mouth parts of the fly are prolonged to form a proboscis, which
is tonguelike, the animal obtaining its food by lapping and suck-
ing. It is the rubbing of this file-like organ over the surface of
the skin that causes the painful bite of the horsefly.

Foot. — If possible, we should examine the foot of a fly under
the compound microscope. The foot shows a wonderful adapta-
tion for clinging to smooth surfaces. Two or three pads, each
of which bears tubelike hairs that secrete a sticky fluid, are found

THE TYPHOID FLY

225

on its under surface. It is by this means that the fly is able to
walk upside down. Hooks are also present which doubtless aid
in locomotion in this position.

Development. — The development of the typhoid fly is
extremely rapid. A female
may lay from one hundred
to two hundred eggs. These
are usually deposited in filth
or manure. Dung heaps
about stables, ash heaps,
garbage cans, and fermenting
vegetable refuse form the best
breeding places for flies. In
warm weather, within a day
after the eggs are laid, the
young maggots, as the larvae
are called, hatch. After about
one week of active feeding,
these wormHke maggots be-
come quiet and go into the
pupal stage, whence under favorable conditions they emerge
within less than another week as adult flies. The adults breed
at once, and in a short summer there may be over ten genera-

Showing how flies may spread disease by
means of contaminating food.

When flies are plentiful, there is a considerable increase in
the number of cases of illness among babies.

tions of flies. This accounts for the great number. Fortunately
few flies survive the winter.

The Typhoid Fly a Pest. — The common fly is recognized as a
pest the world over. Flies have long been known to spoil food
through their filthy habits, but it is more recently that the very

226 THE INSECTS

serious charge of spreading diseases, caused by bacteria, has been
laid at their door. The foot of the fly, covered with hair and
a sticky fluid, is adapted to carry a great many bacteria. In a
recent experiment it was found that a single fly might carry
anywhere from 500 to 6,600,000 bacteria, the average number
being over 1,200,000. Not all of these are harmful, but they
might easily include those of typhoid fever, tuberculosis, sum-
mer complaint, and possibly other diseases. The rapid increase
of flies during the summer months has a definite relation to
the increase in the number of cases of summer complaint and
probably also of typhoid. It has been estimated that the loss
caused from typhoid is in a single year $350,000,000 in the
United States alone. A large part of this loss is indirectly due
to the typhoid fly.

Control. — • All windows should be screened during the summer
months and food kept away from flies. FHes should be caught
in traps or on sticky fly paper. In order to destroy breeding
places, all manure and refuse should be removed at least once
a week.

Other Diptera. — Other examples of the Dip^tera group are
the mosquitoes, of which more wiU be said hereafter; the
Hessian fly, the larvae of which feed on young wheat; the botfly,
which in a larval state is a parasite in horses; the dreaded
tsetse fly of South Africa, which causes disease in horses and
cattle by means of the transference of a parasitic protozoan,
much like that which causes malaria in man; and many others.

Among the few flies useful to man may be mentioned the
tachina flies, the larvae of which feed on the cutworm, the army
worm, and various other kinds of injurious caterpillars.

Characteristics of Diptera. — Members of this group have only
one pair of wings; the mouth parts are fitted for sucking, rasping,
or piercing, and they pass through a complete metamorphosis.

Coleop'tera: Beetles. — Beetles are the most widely distributed and
among the most numerous of all insects. There are over one hundred
thousand living species.

Any beetle will show the following characteristics: (1) The body is
usually heavy and broad. Its exoskeleton is hard and tough, this chitinous
body covering being better developed in the beetles than in any other of

BEETLES, BUGS

227

the insects. (2) The three pairs of legs are stout and rather short.

(3) The outer wings are hard and fit over the under wings Uke a shield.

(4) The mouth parts, provided with an upper and lower hp, are fitted for
biting. They consist of very heavy curved pincher-shaped mandibles, which
are provided with palps.

The Life History of a Beetle. — The June beetle (May beetle) and po-
tato beetle are excellent examples. May beetles lay their eggs in the
ground, where they hatch into
cream-colored grubs. A grub
differs from the maggot or larva
of the fly in possessing three pairs
of legs. These grubs hve in bur-
rows in the ground, where they
feed on the roots of grass and
garden plants. The larval form
remains underground from two
to three years, the latter part
of this time as an inactive
pupa. During the latter stage
it lies dormant in an ovoid area
excavated by it. Eventually the
wings (which are budlike in the
pupa) grow larger, and the adult
beetle emerges fitted for its Hfe
in the open air.

Order Hemip'tera: Bugs. —
The cicada, or, as it is incorrectly
called, the locust, is a famihar
insect to all. Its droning song,
one of the accompaniments of
a hot day, is produced by a
drumlike organ which can be
found just behind the last pair of
legs. The sound is caused by a
rapid vibration of the tightly

stretched drumhead. The body is heavy and bulky. The wings, four in
number, are relatively small, but the powerful muscles give them very rapid
movement. The anterior wings are larger than the posterior. The legs
are not large or strong, the movement when crawling being sluggish. One
of the characteristics of the cicada, and of all other bugs, is that the mouth
parts are prolonged into a beak with which the animal first makes a hole
and then sucks up the juices of the plants on which it lives.

Life History. — The seventeen-year cicada laj^s her eggs in twigs of
trees, and in doing this causes the death of the twig. The young leave
the tree immediately after hatching, burrow underground, and pass from

•■^'v-.""" '

:;ffili*iiil

■■-■•-■•••••■%>,;,

The potato beetle: eggs, larvae, pupa,
and adults.

228

THE INSECTS

thirteen to seventeen years there, depending upon the species of cicada.
They live by sucking the juices from roots. During this stage thej' some-
what resemble the grub of the beetle (June bug) in habits and appearance.
When they are about to molt into an adult, they climb above ground,
cling to the bark of trees, and then crawl out of the skin as adults.

Cicada with wings spread, showing abdo-
men Ab, head H, thorax Th: also ventral
view, showing beak B, and eye E. Below is
seen a pupal case with split down the back.

Aphids. — The aphids are among the most interesting of the bugs.
They are familiar to all as tinj^ green Hce seen swarming on the stems and
leaves of the rose and other cultivated plants. They suck the juices from
stem and leaf. Plant lice have a remarkable hfe history. Early in the
year eggs develop into wingless females, which produce U\'ing young, all
females. These in turn reproduce in a similar manner, until the plant on
which they Hve becomes overcrowded and the food supply runs short.
Then a generation of winged aphids is produced. These fly awaj^ to other
plants, and reproduction goes on as before until the approach of cold
weather, when males and females appear. Fertilized eggs are then pro-
duced which give rise to 3'oung the following season.

The aphids exude from the surface of the body a sweet fluid called
honeydew. This is given off in such abundance that it is estimated if
an aphid were the size of a cow, it would give two thousand quarts a day.
This honeydew is greatlj^ esteemed by other insects, especially the ants.
For the purpose of obtaining it, some ants care for the aphids, even pro-
viding food and shelter for them. In return the aphid, stimulated b}' a
stroking movement of the antenna of the ant, gives up the honeydew to
its protector. (See Figure, page 241.)

Neurop'tera. — The dragon fly receives its name because it preys on
insects. It eats, when an adult, mosquitoes and other insects which it
captures while on the wing. Its four large lacelike wings give it power of
very rapid flight, while its long narrow body is admirably adapted for the
same purpose. The large compound eyes placed at the sides of the head
give keen sight. It possesses powerful jaws (almost covered by the upper
and lower lips).

NEUROPTERA, HYMENOPTERA 229

The long, thin abdomen does not contain a sting, contrary to the belief
of most children. These insects deposit their eggs in the water, and the
fact that they may be often seen with the end of the abdomen curved
down under the surface of the water in the act of depositing the eggs has
given rise to the behef that they were then engaged in stinging something.
The egg hatches into a form of larva called a nymph, which in the dragon
fly is characterized by a greatly developed lower Up. When the animal is
a;t rest, the lower hp covers the large biting jaws, which can be extended
so as to grasp and hold its prey.
The nymphs of the dragon fly
take oxygen out of the water by
• means of gill-Hke structures
placed in the posterior part of
the food tube. They may Uve
as larvae from one summer to as
long as two years in the water.
They then crawl out on a stick,
molt by sphtting the skin down
the back, and come out as adults.

A nearly related form is the Dragon fly: notice the long abdomen
damsel fly. This may be distin- and large compound eyes,

gmshed from the dragon fly by

the fact that when at rest the wings are carried close to the abdomen,
while in the dragon fly they are held in a horizontal position.

May Flies. — Another near relative of the dragon fly is the May fly.
These insects in the adult stage have lost the power to take food. Most
of their life is passed in the larval stage in the water. The adults some-
times Ave only a few hours, just long enough to mate and deposit their
eggs.

Hymenop'tera. — We have already learned something of the structure
of the bee, an example of this order. Other relatives are the wasps, ich-
neumons (wasp-like insects with long ovipositors), and the ants. The
structural characteristics of this group are two pairs of membranous wings,
and mouth parts fitted for biting and lapping. They all undergo a com-
plete metamorphosis, the young being helpless wingless creatures somewhat
like the maggots of the fly. Of this group we shall learn more later.

Characteristics of Insects. — The orders of insects mentioned
above are only a few examples of this very large group. In all of
the above forms we have seen certain likenesses and certain
differences in structure, but all of the above have had three
body divisions, three pairs of legs, and have possessed in the
adult stage air tubes called trachese. These are the principal
characteristics by which we may identify the insects.

230

SPIDERS AND MYRIAPODS

Spiders and Myriapods. — Spiders, millepedes, and centipedes are not true
insects, although they are nearly alUed to them.

The body of a spider, like that of the higher crustaceans, has onl}- two
di^dsionsJ cephalo thorax and abdomen; four pairs of walking legs mark
another difference from insects. Wings are alwaj^s lacking. Spiders usually
have four pairs of simple ej'es and breathe by means of lunglike sacs in

the abdomen, the openings of which
can sometimes be seen just behind
the most posterior pair of legs.
Another organ possessed by the
spider, which insects do not have
(except in a larval form), is kno"WTi
as the spinneret. This is a set of
glands which secrete in a liquid
form the silk which the spider
spins. On exposure to air, tliis
fluid hardens and forms a very
tough building material which com-
bines lightness with strength.

Uses and Form of the Web. —
The web-making instinct of spiders
forms an interesting study. Our
common spiders may be grouped
according to the kind of web they
spin. The web in some cases is
used as a home; m others it
forms a snare or trap. Occasionally
the web is used for ballooning,
spiders having been noticed cling-
ing to their webs miles out at
sea. The webs seen most fre-
quently are the so-called cobwebs. These usually serve as a snare rather
than a home, some species remaining away from the web most of the time.
Other webs are funnel-shaped, still others are of geometrical exactness, while
one form of .spider makes its home underground, lines the hole with silk,
and makers a trapdoor which can be closed after the spider has retreated to

its lair.

Myriapods. — We are all famihar with the harmless and common
thousand legs found under stones and logs. It is a representative of the
group of animals known as the millepedes. These animals have the body
diN-ided into two regions, head and trunk, and have two pairs of legs for
each body segment. The centipedes, on the other hand, have only one
pair of legs to each segment. Both are representatives «^f the cla,?s Myri-
ap'odo. None of the forms in the eastern part of the United States are
poisonouK.

Tarantula, a spider, about one third
actual size. The palpi and the four pairs
of legs are attached to the cephalothorax;
the spinnerets are at the end of the
abdomen, below. Photograph from
American Museum of Natural Histor3\

INSECTS AXD CRUSTACEANS C0:MPARED 231

Insects and Crustaceans Compared. — Both crustaceans and
insects belong to a large group of animals which agree in that
they have jointed appendages and bodies, and that they pos-
sess an exoskeleton. This group or phylum is known as the
Arthrop'oda. Spiders and myriapods are also included in this
group.

Insects differ structurally from crustaceans in ha^dng three
regions in the body instead of two. The number of legs (three
pairs) is definite in the insects; in the crustaceans the number

A poisonous centipede frora Texas. Half natural size,
photograph by Davison.

Fiom

sometimes varies, but is always more than three pairs. The-
exoskeleton, composed wholly of chitin in the insects, is usually
strengthened with lime in the crustaceans. Both groups have
compound eyes, but those of the Crustacea are stalked and
movable. The other sense organs do not differ greatly. The
most marked differences are physiological. The crustaceans
take in oxygen from the water by means of gills, while the
insects are air breathers, using for this purpose air tubes called
trachece.

Both insects and crustaceans, because of their exoskeleton,
must molt in order to increase in bulk.

Classification of Arthropoda

Phylum Arthropoda

Class, Crusta'cea. Arthropods with Km}' and chitinous exoskeleton, rarely
more than 20 body segments, usually breathing by gills, and having
two pairs of antennae.

232 THE INSECTS

Subclass I. Entomos'traca. Crustacea with a variable number of seg-
ments, chiefly small forms with simple appendages. Some degenerate
or parasitic. Examples: barnacles, water flea (Daphnia), and co'pepod
{Cy' clops) .

Subclass II. Malacos'traca. Usually large Crustacea having nineteen
pairs of appendages. Examples: American lobster {Hom'arus ameri*
ca'nus), crab {Cancer), and shrimp {Palcemon'etes).
Class, Hexap'oda or Insecta (insects). Arthropoda having chitinous exo-
skeleton, breathing by air tubes (trachece), and having three distinct
body regions.

Order, Ap'tera (without wings). Several wingless forms. Example:
springtails.

Order, Orthoptera (straight wings). Example: Rocky Mountain locust.

Order, Lepidoptera (scale wings). Examples: cabbage butterfly, cecropia
moth.

Order, Diptera (two wings). Examples: fly, mosquito.

Order, Hemiptera (half wing). Examples: all true bugs, plant lice, and
cicada.

Order, Neuroptera (nerve wings). Examples: May fly, dragon fly.

Order, Coleoptera (shield wings). Example: beetles.

Order, Hymenoptera (membrane wings). Examples: bees, wasps, ants.
Class, Arachnida (a-rS,k'nI-da) . Arthropoda with head and thorax fused.
Six pairs of appendages. No antennae. Breathing by lung sacs (spi-
ders) or tracheae. Examples: spiders and scorpions.
Class, Myriapoda. Arthropoda having long bodies with many segments;
one or two pairs of appendages to each segment. Breathing by means
of tracheae. Example: centipede.

An exercise for field work with a simple key for identification of orders
will be found in Sharpe's Laboratory Manual, Prob. XXX.

Summary. — This chapter has attempted to have you build
up your own definition of what an insect is by comparing a
number of orders to see what characteristics they have in
common. You have found them to have a segmented body,
with three divisions, head, thorax, and abdomen, three pairs
of jointed legs, a chitinous body covering, compound and
usually simple eyes, breathing through air tubes (tracheae), and
undergoing a metamorphosis.

Problem Questions. — 1. Give ten good reasons why insects
are so numerous.

2. Give briefly the characteristics of the Orthoptera, Lepi-
doptera, Diptera, Hymenoptera.

CLASSIFICATION OF ARTHROPODA 233

3. How do insects and crustaceans differ?

4. Make a table classifying the Arthropoda.

»

Problem and Project References

Cockerell, Zoology. World Book Company.

Comstock, Insect Life. D. Appleion and Company.

Comstock, An Introduction to Entomology. Comstock Publishing Company

Hegner, College Zoology. The Macmillan Company.

Hodge, Nature Study and Life. Ginn and Company.

Howard, The Insect Book. Doubleday, Page and Company.

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Kellogg, American Insects. Henry Holt and Company.

Needham, Outdoor Studies. American Book Company.

Sharps, Laboratory Manual. American Book Company.

XX. GENERAL CONSIDERATIONS FROM THE
STUDY OF INSECTS

Problem, To determine how insects have become winners in

lifers race by means of —

(a) Protective resemblance,

(b) Aggressive resemblance,

(c) Mimicry.
(Laboratory Manual, Prob.

Probs. U, 15.)

id) Communal life,
(e) Symbiosis.
(/) Parasitism.
XXXI; Laboratory Problems^

Insects are by far the most numerous of all animals. It is
estimated that there are more species of insects than of all other

kinds of animals upon the globe. Why
should insects have developed in so
much greater numbers than other
animals ? We cannot explain this, but
some light is thrown on the problem
when we consider some of the ways in
which insects have become winners in
life's race.

Protective Resemblance. — When
we remember that the chief enemies
of insects are birds and other animals
which use them as food, we can see
that the insect's power of rapid flight
must have been of considerable im-
portance in escaping from enemies.
But other means of protection are
seen when we examine insects in their
native haunts. We have noted that
various animals, such as the earth-
worm and crayfish, escape observation
because they have the color of their
234

Three walking sticks on a
twig, showing protective re-
semblance.

RESEMBLANCE

235

surroundings. Insects give many interesting examples of pro-
tective coloration or protective resemblance. The grasshopper
is colored like the grass on which it lives. The katydid, with its
green body and wings, can scarcely be distinguished from the
leaves on which it rests. The walking stick, which resembles the
twigs on which it is found, and the walking-leaf insect of the
tropics, are other examples.

One example frequently described is the dead-leaf butterfly of
India. This insect at rest resembles a dead leaf attached to a limb;
in flight it is conspicuous, because of its
vivid colors. The underwing moth is
another example of a wonderful simu-
lation of the background of bark on
which the animal rests in the daytime.
At night the brightly colored under-
wings perhaps give a signal to others
of the same species. The beautiful
luna moth, in color a delicate green,
rests by day among the leaves of the
hickory. When frightened, measur-
ing worms stand out stiff upon the
branches on which they crawl, thus
simulating lateral twigs. Hundreds
of other examples might be given.

This likeness of an animal to its
immediate surroundings has already
been noted as protective resemblance.

Aggressive Resemblance. — Some-
times animals which resemble their
surroundings are thus better able to
catch their prey; they show aggresive
resemblance. The polar bear is a

notable example. The mantis has strongly built fore legs,
with which it seizes and holds insects on which it preys. It
has the color of its immediate surroundings, and is thus enabled
to seize its prey before the latter is aware of its presence.
Many other examples could be given.

Warning Coloration and Protective Mimicry, — Some insects are

Underwing moth: above, in
flight; below, at rest on bark.

236 INSECTS — GENERAL CONSIDERATIONS

extremely unpleasant, either to smell or to taste, while others are
pro^dded with means of defense such as poison hairs or stings.
Those animals which are harmful and brightly colored or marked
as if to warn animals to keep off or to take the consequences,
show warning coloration. Examples of insects which show warn-
ing by color may be seen in many examples of beetles, espe-
cially the spotted ladybirds, potato beetles, and the hke.

Wasps show 3^ellow bands, while
many forms of caterpillars are
conspicuous^ marked or colored.
Some insects, especially cater-
pillars, wliich are harmless, are
brightly colored and protrude
horns, or pretend to sting when
threatened with attack. These
animals evidently mimic animals
which really are protected by a
sting or by poison, although this
is not voluntary on the part of
the insect. When a harmless
insect resembles a harmful insect
we call it mimicry.

One of the best-known exam-
ples of insect mimicry is seen in
the imitation of the monarch
butterfly by the viceroy. The
monarch butterfly {Anosia plexippus) is an example of a race
which has received protection from enemies in the struggle for
hfe, because of its nauseous taste, and, perhaps, because its
caterpillar feeds on plants of no commercial value. Another
butterfly, less favored by nature, resembles the monarch in out-
ward appearance. This is the viceroy. It seems probable that
in the early history of this edible species some of them escaped
from the birds because they resembled in both color and form the
species of inedible monarchs. So for generation after generation
the ones which were most like the inedible species lived and
produced new offspring, the others becoming the food of birds.
Ultimately a species of butterflies was formed that owed its

Monarch and ^'ice^oy butterflies:
the viceroy (below) shows protective
mimicry.

OTHER MEANS OF PROTECTION

237

existence to the fact that it resembled another more favored
species. This is one of the ways in which nature selects the
animals which exist upon the earth. Many other examples of
mimicry may be found among
insects. Some harmless flies
imitate bees, which sting, as
shown in the figure.

Other means of Protection. —
The chief insect enemies are
the birds, and from these
the most effective protection
seems to be hairs on the body.
Few birds eat hairy cater-
pillars of any species; fortu-
nately, however, the hairy
larvae of the gypsy moth, a
serious pest, are eaten by no
less than thirty-one species
of birds. The odors or ill
flavors of insects seem to
be generally protective, but
stinging insects do not appear
to be protected from all birds, flycatchers and swallows habitu-
ally feeding on the bees and wasps. There is a growing
tendency among zoologists to place less emphasis on these
adaptations as a means of preserving species.

Communal Life among Insects. — Insects are of special in-
terest to man because among certain species a system of social
life has arisen comparable to that which exists among men. In
connection with this communal life, nature has worked out a
division of labor which is very remarkable. This can be seen
in tracing out the lives of several of the insects which live in
communities.

Solitary Wasps. — Some bees and wasps lead a solitary existence.
The solitary and digger wasps do not live in communities. Each female
constructs a burrow in which she lays eggs and rears her young. The
young are fed upon spiders and insects previously caught and then stung
into insensibility. The nest is closed up after food is supplied, and the

Supposed cases of mimicry: 1, a bum-
blebee, mimicked by 2, a kind of fly; 3,
a wasp, mimicked by 4, another kind of
fly. The bumblebee and wasp are of the
order Hymenoptera; the mimics, of the
order Diptera.

238

INSECTS — GENERAL CONSIDERATIONS

young later gnaw their way out. In the life history of such an insect there
is no communal life.

Bumblebee. — In the life history of the big bumblebee we see the be-
ginning of the community instinct. Some of the female bees (known as
queens) survive the winter and lay their eggs the following spring in
a mass of pollen, which they have previously gathered and placed in a
hole in the ground. The young hatch as larvae, then pupate, and finally

become workers, or imperfect
females in which the egg-laying
apparatus, or ovipositor, is
modified to be used as a sting.
The workers bring lq pollen to
the queen, in which she lays
more eggs. Several broods of
workers are thus hatched during
a summer. In the early fall a
brood of males or drones, and
egg-laying females or queens,
are produced instead of workers.
By means of these egg-producing
females the brood is started the
following year.

The Honeybee. — The
most wonderful communal
life has been developed
among the honeybees.^

The honeybee in a wild
state makes its home in a
hollow tree; hence the term
'^ bee tree . " In the hive the
colony usually consists of a
A, worker; B, queen; queen, or egg-laying female,

The honeybee
C, male (drone),
hind leg, as seen from the
behind: 4, femur; 1, 5, tibia; 2, 7, meta
tarsus; 3, 8, foot; 6, wax shears.

Above is shown aj^orker^ ^ ^^^ hundred drones, or

males, and several thou-
sand imperfect females, or

* Their daily life may be easily watched in the schoolroom, by means of one
of the many good and cheap observation hives now made to be placed in a
window frame. Directions for making a small observation hive for school work
can be found in Hodge, Nature Study and Life, Chapter XIV. Bulletin No. 1,
U.S. Department of Agriculture, entitled The Honey Bee, by Frank Benton, is
valuable for the amateur beekeeper. Farmers' Bulletin 447 on Bees, by E. F.
Phillips, is also most useful.

COMMUNAL LIFE

239

workers. The colonies vary greatly in numbers, in a wild state
there being fewer in the colony. The division of labor is well
seen in a hive in which the bees have been hving for some
weeks. The queen does nothing except lay eggs, sometimes lay-
ing three thousand eggs a day and keeping this up, during the
warm weather, for several years. She may lay a million eggs
during her hfe. She does not, as is popularly beheved, rule the
hive, but is on the contrary a captive most of her life. Most
of the eggs are fertilized by the sperm cells of a male; the un-
fertilized eggs develop into
males or drones. After a
short existence in the hive
the drones are usually driven
out by the workers. The
fertilized eggs may develop
into workers, but if the
young larva is fed with a
certain kind of food, it will
develop into a young queen.
The cells of the comb are
built by the workers out of
wax secreted from the under
surface of their bodies. The
wax is cut off in thin plates
by means of the wax shears
between the two last joints
of the hind legs. These cells
are used by the queen to
place her eggs in, one to each

cell, and the young are hatched after three days, to begin life as
footless white grubs. For a few days they are fed on partly
digested food called bee jelly, regurgitated from the stomach
of the workers. Later they receive pollen and honey to eat.
A Httle of this mixture, known as bee bread, is put into the
cells, and the lids covered with wax by the working bees, and
the young larvae allowed to pupate. After about two weeks of
quiescence in the pupal state, the adult worker breaks out of the
cell and takes her place in the hive, first caring for the young

Hornets' nest, open to show the cells
of the comb. Photograph by Overton.

240 INSECTS — GENERAL CONSIDERATIONS

as a nurse, later making excursions to the open air after food
as an adult worker.

If a new queen is to be produced, several of the cell walls are
broken down by the workers, making a large ovoid ceU in which
one egg is left. The young bee in this cell is fed during
its whole larval life upon bee jelly, and grows into a queen of
much larger size than an ordinary worker. When a young queen
appears, great excitement pervades the community; the bees
appear to take sides; some remain with the young queen in
the hive, while others follow the old queen out into the world.
This is called swarming. They usually settle around the queen,
often hanging to the limb of a tree. While the bees are swarm-
ing, certain of the workers, acting as scouts, determine on a site
for their new home; and, if undisturbed, the bees soon go there
and construct their new hive. This instinct is of vital impor-
tance to the bees, as it provides them with a means of forming
a new colony. A swarm of domesticated bees may be quickly
hived in new quarters.

We have already seen (pages 31 and 32) that the honey-
bee gathers nectar; this is swallowed and kept in the crop until
after the return to the hive, where it is regurgitated into cells
of the comb. It is now thinner than what we call honey.
To thicken it, the bees swarm over the open cells, moving their
wings very rapidly, thus evaporating some of the water in the
honey. A hive of bees has been known to make over thirty-
one pounds of honey in a single day, although the average
record is very much less than this.

Ants. -^ Ants are the most truly communal of all the insects. Their life
history and habits are not so well known as those of the bee, but what is
known shows even more wonderful specialization. The inhabitants of a
nest may consist of wingless workers, which in some cases may be of two
kinds, and winged males and females.

Ant larvse are called grubs. They are absolutely helpless and are taken
care of by nurses. The pupae may often be seen as they are taken out in
the mouths of the nurse ants for sun and air. They are wrongly called
ants' eggs in this stage.

The nest of a colony consists of underground galleries with enlarged store-
rooms, nurseries, etc. The ants are especially fond of honeydew secreted
by the aphids, or plant lice. Some species of ants provide elaborate stables

SYMBIOSIS

241

for the aphids, commonly called ants' cows, supplying them with food and
shelter and taking the honeydew as their reward. This they obtain by
licking it from the bodies of the aphids. A Western form of ant, found in
New Mexico and Arizona, rears a scale
insect on the roots of the cactus for the
same purpose.

It is probable that some species of
ants are among the most warlike of
any insects. In the case of the robber
ants, which live entirely by war and
pillage, the workers have become
modified in structure, and can no
longer work, but only fight. Some
species go further and make slaves of
the ants preyed upon. These slaves
do all the work for their captors,
even to making additions to their nest
and acting as nurses to their young.

The entire communal life of the
ants seems to be based upon the per-
ception of odor. If an ant be put into
a colony to which it does not belong,
although one of the same species, it
will be set upon and either driven out
or killed. Ants never really lose their community odor; those absent for
a long time, on returning, will be easily distinguished by their odor, and
eagerly welcomed by the members of the nest. The communication of ants
as seen when they stop each other, away from the nest, is evidently a
process of smelling, for they caress each other with the antennae, the organs
with which odors are perceived.

Ants and their "cows
(aphids).

Symbiosis. — ^We have already seen that plants and animals
frequently live in a state of partnership or relation of mutual
help. Such a state is known as a symbiotic relation. The keep-
ing of the aphids by the ants which use them as /' cows '' is an
example of this relation among two species of insects. The ants
provide protection and sometimes food; the aphids give up the
honeydew of which the ants are so fond.

But a wider symbiotic relation exists directly between the
flowering plants and the insects. We all know the very great
service done the plants by the pollination of the flowers by the
insects, and we know that the return is the supply of pollen and
nectar as food for the insects.

242

INSECTS — GENERAL CONSIDERATIONS

Parasitism. — One of the near relatives of the bee called the
ichneumon (ik-nti'mon) fly does man indirectly considerable

good because of its habit of

laying its eggs and leaving its
young to develop in the bodies
of caterpillars which are harm-
ful to vegetation. As this is
death for the caterpillar, it
is safe to say that by the
above means the ichneumons
save millions of dollars yearly
to this country.

Unfortunately, not all insect
parasites do good. Animals
of all kinds, but especially
birds, are infested with lice
and fleas. The ticks are well
known for the harm they do,
while the larvae of the botflies
which live in the bodies of

various mammals, as the horse and sheep and cattle^ are

insect parasites which do much harm.

Problem. Some relations of insects to man. (Laboratory Manual,
Prob. XXXII; Laboratory Problems, Probs. 123 to ISl.)

(a) With reference to disease.

(b) With reference to destruction of property,

(c) With reference to benefit to man.

Ichneumon fly (Thalessa) boring in
an ash tree to deposit its eggs in the
burrow of a horntail larva, a wood
borer. From photograph, natural size-
by Davison.

The Relation of Insects to Mankind. — We already have seen
this relation is twofold, harmful and beneficial. The harmful
relation may affect man directly, as when human disease is
carried by insects, or it may be indirect, as in the case of damage
to crops, trees, stored food, or clothing. The first relation is
naturally of more importance, as malaria, an extremely prevalent
disease in some parts of the world, is carried by mosquitoes,
and typhoid and other intestinal diseases are often distributed
by flies.

DISEASE CARRIERS

243

<^.

<^^

<^^>

The Malarial Mosquito. — Fortunately for mankind, not all
mosquitoes harbor the small one-celled parasite (a protozoan)
which causes malaria. The harmless mosquito {culex) may be
usually distinguished from the mosquito (anopheles) which carries
malaria by the position of the body and legs when at rest. (See
Figure.) Culex lays eggs in tiny masses shaped like rafts
of one hundred or more eggs
in standing water; thus the
eggs are distinguished from
those of anopheles, which
are not in rafts. In a short
time enough mosquitoes to
stock a neighborhood may
develop in rain barrels,
gutters, or old cans. The
larvae are known as wig-
glers. They appear to
hang on the surface of the
water, head down in order to
breathe through a tube at the
posterior end of the body, the
end of which projects a short
distance above the water. In
this stage they may be easily
recognized by their peculiar
movement when on their way
to the surface to breathe. The
fact that both larvae and pupae
take air from the surface of the water makes it possible to kill
the mosquitoes during these stages by pouring oil on the surface
of the water where they breed. The introduction of minnows,
goldfish, or other small fish which feed upon the larvae in
the water where the mosquitoes breed will do much in freeing
a neighborhood from this pest. Draining swamps or low
lands which hold water after a rain is another method of
extermination.

Since the beginning of historical times, malaria has been
prevalent in regions infested by mosquitoes. The ancient city

Life history of two mosquitoes — at
the left, culex; at the right, anopheles.
Note the four steps of each — eggs,
larva, pupa, adult.

244 INSECTS — GENERAL CONSIDERATIONS

of Rome was so greatl}^ troubled by periodic outbreaks of mala-
rial fever that a goddess of fever was worshiped in order
to lessen the severity of what the inhabitants believed to be
a di^'ine visitation. As recently' as 1900 two doctors hved in
the most malarious district in the swampy area near Rome,
drank the water and hved the same life as did the natives;
only taking the precaution to screen themselves from the
anopheles mosquito. The}' remained free from malaria. A
little later came the proof that malaria was carried by anoph-
eles. Living mosquitoes which had bitten malarial patients
were shipped to England, and there two Enghsh doctors
allowed these mosquitoes to bite them. Thej^ came down
with malaria. These experiments and others have shown the
world how to combat malaria successfully.

Yellow Fever and Mosquitoes. — Another disease which has
been proved to be carried by mosquitoes is j^ellow fever. In the
yesLT 1878 there were 125,000 cases and 12,000 deaths in the
United States, mostlj^ in Alabama, Louisiana, and Mississippi.
Dm'ing the French occupation of the Panama Canal zone the
work was at a standstill part of the time because of the ravages
of yeUow fever.

But to-da}' this is changed, and thanks to the experiments per-
formed in Cuba in 1900 by the commission headed bj^ Major
Walter Reed, yellow fever is under almost complete control, both
here and wherever the mosquito (aedes, formerly called stegomyia)
which carries yellow fever exists. During the series of experi-
ments two doctors. Dr. James Carroll and Dr. Jesse W. Lazear,
allowed themselves to be bitten by aedes mosquitoes which had
previously bitten j^eUow fever patients. Both had j^ellow fever
and Dr. Lazear died. Later others were similar 1}^ experimented
upon with the result that we now know conclusively that
yellow fever is transmitted only by means of a mosquito.
Hence it has been possible, by draining, oiling, and screening,
to make Panama a safer place to hve in than many parts of
the United States.

Other Diseases due to Insects. — The bubonic plague, the
dreaded scourge of the East, is brought to man by fleas. The
sleeping sickness of Africa has already been mentioned (page

ECOXO:\IIC LOSSES 245

179) as carried by the tsetse fly. Several other diseases of man
and of many other animals, especially cattle, are carried by flies.
The Texas fever of cattle is carried by a cattle tick, an animal
closely allied to the insects.

Economic Loss from Insects. — The money value of crops,
forest trees, stored foods, and other materials destroyed annually
by insects is beyond behef. It is estimated that they get one
tenth of the country's crops, at the lowest estimate a matter of
some S300;000,000 yearly.

" A recent estimate by experts put the yearly loss from forest insect
depredations at not less than $100,000,000. The common schools of the
countrj^ cost in 1902 the sum of §235,000,000, and all higher institutions
of learning, cost less than 850,000,000, making the total cost of education
in the United States considerably less than the farmers lost from insect
ravages." — Slingerland.

Jb. 1874-1876 the damage to crops by the Rocky Mountain
locust has been estimated at $200,000,000. The total value of
all fann and forest crops, excluding animal products, in New
York, is perhaps $150,000,000, and the one tenth that the insects
get is worth S15,000,000. It may seem incredible that it costs
such a sum to feed Xew York's injurious insects every year, but
it is an average of $66 for each of the 227,000 farms in the state;
and there are few farms where the crops are not lessened more
than this amount by insects.

Insects which damage Garden and Other Crops. — The grass-
hoppers have been mentioned as among the most destructive
of these. The larvae of various butterflies and moths do con-
siderable haiTQ, especially the "cabbage worm," the various
caterpillars of the hawk moths which feed on grape and tomato
vines, the cutwoiTQ, a feeder on the roots of all kinds of garden
tinck, the corn worm, a pest on corn, cotton, tomatoes, peas,
and beans. The last damages the cotton crop to the amount
of several millions of dollars annuaUy.

Among the beetles which are found in gardens is the potato
beetle, which destroys the leaves of the potato plant. This
beetle formerly hved in Colorado upon a wild plant of the same
family as the potato, and came east upon the introduction of the

246 INSECTS — GENERAL CONSIDERATIONS

potato into Colorado, evidently preferring cultivated forms to
wild forms of this family. The asparagus and cucumber beetles
are also often in evidence.

The one beetle doing by far the greatest harm in this country is
the cotton-boll weevil. Imported from Mexico, since 1892 it has
spread over most of the cotton-growing states. The beetle lays
its eggs in the young cotton fruit or boll, the larvae feeding upon
the substance within the boll. It is estimated that if unchecked
this pest would destroy yearly one half of the cotton crop, a
matter of over $300,000,000. Fortunately, the experts of the
United States Department of Agriculture are at work on the

Four destructive insects: from left to right, the cotton boll weevil, the
potato beetle, the squash bug, and the celery caterpillar.

problem, and, while they have not found any way of exter-
minating the beetle as yet, it has been shown that, by planting
more hardy varieties of cotton, the crop matures earlier and
ripens before the weevils have increased in sufficient numbers to
destroy the crop (see page 51).

The bugs are among our destructive insects. The most fa-
miliar examples of our garden pests are the squash bug; the
chinch bug, which yearly does damage estimated at $20,000,000,
by sucking the juice from the leaves of grain; and the plant lice,
or aphids. Some aphids are extremely destructive to vegetation.
One, the grape Phylloxe'ra, yearly destroys immense numbers of
plants in the vineyards of France, Germany, and California.

The Hessian fly, the larvae of which live on the wheat plant,
was introduced accidentally by the Hessians in their straw

DESTRUCTIVE INSECTS

247

bedding during the Revolution, and has become one of our most
serious insect pests.

Insects which harm Fruit and Forest Trees. — Great damage
is done annually by the larvai of moths. Massachusetts has
already spent over $5,000,000
in trying to exterminate the
accidentally imported gypsy
moth. The codHng moth,
which bores int(3 apples and
pears, is estimated to ruin
yearly $3,000,000 worth of
fruit in New York alone,
which is only one of the
important apple regions of the
United States. The codKng
moth flits over the fruit
blossoms and lays an egg here
and there — one in a blossom.
The young hatch in a day or
two and eat their way into
the ovary, where they feed
and grow with the fruit.
The fruit ripens early and
often falls to the ground
before the perfect fruit is
ripe. The larva crawls out
and up the tree and pupates
in the bark.

Among these pests, the
most important to the dweller
in a large city is the tussock
moth, which destroys the
leaves of the shade trees. The
caterpillar may be recognized
easily by its long hairs of yellow, brown, and black, and a tuft of
red on its head. The cocoon is made of a combination of hairs
and silk on the bark of a tree, or on a twig. The female has no
wings and cannot crawl far. She lays her eggs, therefore, on

Tussock moth: 1, adult male; 2, adult
female, which has no wings; 3, larva;
4, pupae; 5, female laying eggs.

248 INSECTS — GENERAL CONSIDERATIONS

the outside of the cocoon and dies a few hours later. The
eggs remain over winter. By collecting and burning the egg
masses in the fall, we may save many shade trees the following
year.

Other enemies of the shade trees are the fall webworm, the
forest caterpillar, and the tent caterpillar; the last spins a tent
which serves as a shelter in wet weather.

The larv2e of some moths damage the trees by boring into the
wood of the tree on which they live. Such are the peach, apple,

and other fruit-tree borers
common in our orchards.
Some species of beetles pro-
duce boring larvae which eat
their way into trees and then
feed upon the sap of the tree.
Many trees in our Adiron-
dack Forest Reserve annu-
ally succumb to these pests
because the beetle girdles
the tree, cutting through
the tubes in the cambium
region. Most fallen logs
will repay a search for the larvae which bore between the bark
and wood.

Among the insects most destructive to trees are the scale insects
and the plant lice, or aphids. The San Jose scale, a native of
China, was introduced into the fruit groves of California about
1870 and has spread all over the country. It lives upon numer-
ous plants, and is one of the worst pests this country has seen.
It is interesting to know that a ladybird beetle, which has also
been imported, is the most effective agent in keeping this pest
in check.

Insects of the House or Storehouse. — The weevils are the
greatest pests, frequently ruining tons of stored corn, wheat, and
other cereals. Roaches feed on almost any kind of breadstuffs as
well as on clothing. The carpet beetle is a recognized foe of the
housekeeper, the larvae feeding upon all sorts of woolen material.
The larvae of the clothes moth do an inamense amount of damage

San Jose scale, and a twig covered
with the scales.

BENEFICIAL INSECTS 249

to stored clothing especially. Fleas, lice, and especially bedbugs
are among man's personal foes.^

Beneficial Insects. — Fortunately for mankind, many insects
are found which are of use because they either prey upon
injurious insects or become parasites upon them, eventually
destroying them. The ichneumon flies are examples already
mentioned. They undoubtedly do much in keeping down the
number of destructive caterpillars.

Several beetles are of value to man. Most important of these
is the natural enemy of the orange-tree scale, the lady bug, or
ladybird beetle. In New York state it may often be found
feeding upon the plant lice. The caloso'ma beetle preys upon
the gypsy moth. The carrion beetles and many water beetles act
as scavengers. The sexton beetles bury dead carcasses of animals.
Ants in tropical countries are particularly useful as scavengers.

Insects, besides pollinating flowers, often do a service by
eating harmful weeds which are thus kept in check. We have
noted that insects spin silk, thus forming clothing, that in many
cases they are preyed upon, and support an enormous multitude
of birds, fish, and other animals with food.

How the Damage done by Insects is Controlled. — The com-
bating of insects by the farmer is controlled and directed by two
bodies of men, both of which have the same end in view. These
are the Bureau of Entomology of the United States Department
of Agriculture and the various state experiment stations.

The Bureau of Entomology works in harmony with the other
divisions of the Department of Agriculture, giving the time of its
experts to the problems of controlling insects which, for good or
ill, influence man's welfare in this country. Such problems as
the destruction of the malarial mosquito and the control of the
typhoid fly; the destruction of harmful insects by the intro-
duction of their natural enemies, plant or animal; the perfecting
of the honeybee (see Hodge, Nature Study and Life, page 240),
and the introduction of new species of insects to pollinate flowers
not native to this country (see the fig wasp, page 36) , are a few
of those to which these men devote their time.

1 Directions for the treatment of these pests may be found in pamphlets
issued by the U.S. Department of Agriculture.

HUNT. NEW ES. 17

250 INSECTS — GENERAL CONSIDERATIONS

All the states and territories have, since 1888, established
state experiment stations, which work in cooperation with the
government in the war upon injurious insects. These stations
are often connected with colleges, so that young men who are
interested in this kind of natural science may have opportunity
to learn and to help. Bulletins are published by the various state
stations and by the Department of Agriculture, most of which
may be obtained free. The most interesting are the Farmers'
Bulletins, issued by the Department of Agriculture, and the
pamphlets issued by Cornell University in New York state.

TABLE SHOWING A FEW INSECTS OF ECONOMIC IMPORTANCE
AND MEANS FOR THEIR CONTROL OR EXTERMINATION

1. Beneficial Insects

Silk Moth. — Larva spins a cocoon from which silk is made.

Honeybee. — Adult produces honey and pollinates flowers.

Bumblebee. — Adult pollinates red clover and fruit trees.

Ichneumon Fly. — Female lays eggs in the bodies of harmful larvae (as the

grapevine caterpillar and the tree borers). The developing parasites

feed on the hosts and kiU them.
Dragon Fly. — Adult feeds on mosquitoes.
Ladybird Beetle. — Adult feeds on scale insects and aphids.
Gall Insect. — The developing larvse cause galls from which ink is made.

2. Household Pests

House Fly. — Adult carries typhoid, tuberculosis, and summer complaint
and other intestinal diseases. To exterminate, it is necessary to prevent
breeding and kill overwintering flies.

Mosquito. — Adult carries malaria and yellow fever. May be exterminated
by destroying the breeding places. See page 243.

Body louse. — Adxxlt carries typhus. Insects may be killed by sterilizing
infected clothing and by bathing patients in an antiseptic solution.

Flea on Rats. — Adult carries bubonic plague. Kill the rats.

Clothes Moth. — Larvae eat clothing: wool, fur, etc. They may be controlled
by shaking or brushing the clothing, and exposing it to the sun. The use
of camphor or naphthaline with clothing which is packed away deters
the moth from laying its eggs there.

Buffalo Carpet-Beetle. — Larva eats carpets. Spray benzine in the cracks in
the floor and on the carpet.

Cockroach. — Adults are scavengers and are numerous around sinks and
where food is kept. They may be exterminated with poison bait. Clean-
liness is necessary.

CONTROL OF INSECTS 251

3. Garden and Fruit Tree Pests

Potato Beetle. — Larva eats leaves of the potato plant. Spray infected

plants with arsenate of lead or Paris green.
Cabbage Butterfly. — Larva eats leaves of cabbages and may be destroyed by

a spray of arsenate of lead or Paris green.
Hawk Moths. — Larva feeds on leaves of grape and tomato vines. Spray.
Rose Beetles. — Adults feed on leaves and blossoms of the rose. Spray with

a soap solution.
Codling Moth. — Larva injures apples and pears. Spray with arsenate of

lead at the time petals faU.
San Jose Scale. — Adults suck juices from the leaves and young twigs of

fruit trees. Killed by ladybird beetles and fumigation.
Aphids. — Adult females suck juice from leaves and young twigs. Spray

with nicotine sulphate.
Boll-worm or Corn Worm. — Larva Uves in the ears of corn.
European Corn Borer. — Feeds on stalks, roots, and ears of corn plant. Con-
trolled by burning cornstalks in the faU.

4. Forest and Shade Tree Pests

Tussock Moth. — Larva eats leaves of shade and fruit trees. Destroy egg

masses and spray in early spring.
Gypsy Moth. — Damage and extermination the same as for tussock moth.
Forest Tent Caterpillar. — Larva eats leaves of shade and fruit trees. Destroy

nests and spray.

Summary. — We find first that because of numerous adap-
tations found in protective resemblance, mimicry, communal life,
and symbiotic relationships that insects are the dominant forms
on the earth to-day.

Secondly, because they are so numerous and carry certain
diseases insects are of much economic importance. Not only do
they take toll of one tenth or more of the world's plant food
supply but they are responsible for all yellow fever and malaria
as well as most of our typhoid, dysentery, and bubonic plague.

Problem Questions. — 1. Explain protective and aggressive
resemblance.

2. What is warning coloration?

3. What is mimicry?

4. Describe the communal life of the honeybee.

5. What is symbiosis? Explain.

252 INSECTS — GENERAL CONSIDERATIONS

6. Explain how mosquitoes do harm. How may they be
controlled ?

7. Discuss the methods for prevention of yellow fever.

8. Make a balance sheet giving harm and good caused by
insects.

Problem and Project References

Cragin, Our Insect Friends and Foes. G. P. Putnams Son3.

Crary, Textbook of Field Zoology: Insects and their Near Relatives and Birds.

P. Blakiston's Sons and Company.
Division of Entomology, Bulletins 1, 4, 5, 12, 16, 19, 23, 33, 34, 35, 36, 47, 48,

61. U.S. Dept. of Agriculture.
Doane, Insects and Disease. Henry Holt and Company.
Folsom, Entomology; with Reference to its Biological and Economic Aspects.

P. Blakiston's Sons and Company.
Howard, Mosquitoes and Their Control. University of Minnesota, Agricultural

Experiment Station.
Hunter, Laboratory Problems in Civic Biology (Insect Bibliography). American

Book Company.
Hunter and Whitman. Civic Science. American Book Company,
Lubbock, Bees, Ants and Wasps. D. Appleton and Company.
Sharpe, Laboratory Manual. American Book Company.

XXL THE MOLLUSKS

Problem, A study of mollusks and their enemies with refer"
ence to their economic importance. (Laboratory Manual.
Prob. XXXIII; Laboratory Problems, Prob. 119.)

To some high school pupils a clam or oyster on the " half
shell" is a familiar object. The soft "body" of the animal
Ijang between the two protecting "valves" of the shell gives the
name to this group (Latin mollis — soft). Most mollusks have
a shell composed mostly of hme, either bivalve (two-valved),
as the oyster, clam, mussel, and scallop, or univalve (with one
valve), as the snail. Usually the univalve shell is spiral in form.
Among nature's most beautiful objects are the spiral shells of
some marine forms. Other mollusks, for example the garden
slug, have no shell whatever, and one highly speciaUzed form,
the squid, has an internal shell.

The limy shell, when present, is formed from the outer surface
and edge of a delicate body covering called the mantle. The
mantle may be found in the opened oyster or clam sticking
close to the inside of the valve of the shell in which the body
rests. Between the mantle and the body of the clam or oyster
is a space, the mantle cavity, in which hang the platelike striated
gills. By means of cilia on the inner surface of the mantle and
on the gills a constant current of water is maintained through
the mantle cavity, bearing oxygen to the gills and carbon
dioxide away from them. This current of water passes, in most
mollusks, into and out from the mantle cavity through the
si'yhons; the muscular tubes forming the ''neck" of the ''soft
clam" are examples of such organs.

The food of clams or oysters consists of tiny organisms which
are carried in the current of water to the mouth of the animal,
this water current being maintained in part by the action of
cilia on the palps or Hplike flaps surrounding the mouth. A
single muscular foot enables the clam to move about slowly,

253

254

THE :mollusks

Shell of fresh-water elaru. the left half polished
to show the prismatic layer from which buttons
are made.

The shallow water of bays where clams and oysters live,
literalh' swarms with microscopic organisms which find the con-
ditions for growth ideal. The tiny plants living there get food
from the organic wastes brought down by the rivers. The
carbon dioxide from the thousands of species of fish, mollusks,

crustaceans, worms, and
other forms of animal Hfe
gives them another
source of raw food
material. The sunlight
penetrating through the
shallow waters supplies
the energy for making
the food. Thus condi-
tions are ideal for rapid
multiplication; hence
the water becomes alive with the lower forms of plant life,
among which are always found bacteria, both harmless and
harmful. In feeding upon these plants, mollusks take in many
bacteria; man feeds on the mollusks, and, if he eats them raw,
may eat living bacteria as well. If the germs of typhoid fever
are present, disease may result.
As a matter of fact, epidemics
of typhoid fever have been
traced to such sources.

Some Common Mollusks. —
The fresh-water clam, a com-
mon resident in the shallow
water of inland ponds and
rivers, has been sought in the
making of pearl buttons.
This industry is so important

that it has depleted the number of adult clams in our Middle
West : and the states affected and the United States government
have undertaken the study of the life habits of these animals
with a \new to restocking the rivei's. The development of the
fresh-water clam or mussel is complicated. The egg develops
into a free-s^'imming larval form which fastens to the gill of a

Ciam sh

;1 after the removal of disks
for making buttons.

CLAMS AND OYSTERS

255

fish and there lives as a parasite until almost mature. Then it
drops off into the sand of the river or lake where it spends the
rest of its Ufe.

The Oyster. — Oysters are never found in muddy water, for
they would be quickly smothered by the sediment. They cling
to stones or shells or other objects which project a little above
the bottom. Here food is abundant and oxygen is obtained from
the air in the water
surrounding them.
Hence oyster raisers
throw oyster shells
into the water to
make places of at-
tachment for the
young oysters.

In some parts of
Europe and of this
country where
oysters are raised
artificially, stakes or
brush are sunk in
shallow water so
that the young
oysters, after the
f r ee-s wimming
stage, may find some
object to which they

can fasten and escape the danger of smothering on the bottom.
After the oysters are a year or two old, they are taken up and
planted in deeper water as seed oysters. At the age of three
and four years they are ready for the market.

The oyster industry is very profitable, amounting to over
$15,000,000 a year during the last decade. Hundreds of boats
and thousands of men are engaged in dredging for oysters.
Three of the most important of our oyster grounds are Long
Island Sound, Narragansett Bay, and Chesapeake Bay.

Sometimes oysters are artificially ''fattened" by placing them
near the mouths of fresh-water streams. These streams ofte^

Round clam (Venus merceneria) : AAM, anterior
adductor muscle; ARM, anterior retractor muscle;
PAM, posterior adductor muscle; PRM, posterior
retractor muscle; F, foot; C, cloacal chamber;
IS, in current siphon; FS., excurrent siphon; EO,
heart; G, gills; M, mantle; DGL, digestive glands;
S, stomach; I, intestine; P, palp; R, posterior end
of digestive tract.

25t> THE MOLLUSKS

contain sewage. As this is a menace to health, it is evident that
state and city supervision ought to be exercised not only to
forbid the sale of shellfish which come from contaminated
locaHties, but also to prevent the planting of oysters or other
mollusks in the neighborhood of the openings of sewers or
polluted rivers. '

Clams. — Other bivalve mollusks used for food are clams and
scallops. Two species of the former are known to New Yorkers,
one as the "round," the other as the ''long" or ''soft-shelled"
clam. The round clam was called "quahog" by the Indians,
who used the blue area of its shell as wampum, or money. Both
species are prized for food. The clam industries of the eastern
coast aggregate over $1,000,000 a year.

Scallop. — The scallop, another moUuscan dehcacy, forms an impor-
tant fishery. Only the single adductor muscle is eaten, whereas in the
clam and oyster aU the soft parts of the body are used as food.

Pearls and Pearl Formation. — Pearls are prized the world over. It
is a well-known fact that even in this country pearls of some value are
found occasionally within the shells of such common bivalves as the fresh-
water mussle and the oyster. Most of the finest pearls, however, come from
the waters around Ceylon. If a pearl is cut open and examined carefully,
it is found to be a deposit of the mother-of-pearl layer of the shell around
some central structure. It has been believed that any foreign substance,
as a grain of sand, might irritate the mantle at a given point, thus stimu-
lating it to secrete around the substance. It now seems likely that most
perfect pearls are due to the growth within the mantle of the clam or

oyster of certain parasites, which

^^^^^f/esoffTe/jrec/CS ^^^ stages in the development of

^' •^ the fluke worm. The irritation

thus set up in the tissue causes

mother-of-pearl to be deposited

'Tentacle, around the source of irritation,

mouth^^ olfactory nerve wi*^ ^^^ subsequent formation of
endfngs a pearl.

A common snail. Gastropods. — Snails, whelks,

slugs, and the like are called ga&'-
*/ropods (stomach-footed) because the foot occupies so much space that most
of the organs of the body, including the stomach, are covered by it. Most
gastropods are partly covered by a more or less spirally formed shell which
has but one valve, in which the body is twisted spirally. In the garden
slug, the mantle does not secrete an external shell, and the naked body
is symmetrical.

HABITAT

257

Gastropods of various species do considerable damage, some in the
garden, where they feed upon young plants, and others in the sea, where
they bore into the shells of other Uving moUusks in
order to get out the soft part of the body which
they use as food.

Cephalopods. — Another class of moUusks are
those known as cephalopods (s6f'a-l6-p5dz). The
name means head-footed. As the Figure shows, the
mouth is surrounded with a circle of tentacles. The
sheU is internal or lacking. The so-called pen of the
cuttlefish is aU that remains of the shell in that
form. A cuttlefish is strangely modified for the life
it leads. It moves rapidly through the water by
squirting water from the siphon. It can seize its
prey with the suckers on its long tentacles and tear
it in pieces by means of its horny, parrothke beak.
It is protected from its enemies and enabled to
catch its prey because of its abiHty to change color
quickly. In this way the animal simulates its
surroundings. The cuttlefish has, near the siphon,
an ink bag which contains the black sepia. A few
drops of this ink squirted into the water may
effectually hide the animal from its enemy.

To this group of animals belong also the octopus,
or devilfish, a cephalopod known to have tentacles
over thirty feet in length; the paper nautilus;
and the pearly nautilus, the latter made famous by our poet Holmes.

The squid. One fourth
natural size.

Habitat of the MoUusks. — MoUusks are found in almost all
parts of the earth and sea. They are more abundant in temper-
ate localities than elsewhere, but live also in tropical and polar
countries. They are found in all depths of water, but by far
the greatest number of species live in shallow water near the
shore. The cephalopods stay near the surface of the ocean,
where they prey upon small fish. The food supply evidently
determines to a large extent where they live. Some moUusks
are scavengers; others feed on living plants.

We have found in the forms of moUusks studied that almost
all of them live in the water. There is one large group which
forms a general exception to this, certain of the snails and slugs
called puVmonates. But even these animals are found in damp
localities, and during a drought they become inactive and remain
within their shells. The European snail imported to this country

258

THE MOLLUSKS

as a table delicacy exists for months by plugging up the aperture
of its shell with a mass of sluny material which later hardens,
thus protecting the soft body within.

Economic Importance. — In general the moUusks are of
much economic importance. The bivalves especially form an
important source of our food supply. Many of the mollusks
also make up an important part of the food supply of bottom-
feeding fishes. On the other hand, some mollusks, as nat'ica,

bore into the shells of
other mollusks and eat
the animals inside. Some
boring mollusks, for ex-
ample the shipworm, do
much damage to wharves,
-VAhere they make their
homes in the piles. Still
otliers bore holes in soft
rock and live there.

The shells of mollusks
are used to a large extent
in manufactures and in
the arts, and they are
still used as money in
some parts of the world.
Sepia comes from the
cuttlefish.

Ventral or under surface of the starfish.
The dark circle in the middle is the mouth,
from which radiate the five ambulacra!
grooves, each filled with four rows of tube
feet. Photograph half natural size, by
Davison.

The Starfish. — By far the

mo'st important enemy of the
oyster and other salt-water
mollusks is the starfish. The
common starfish, as the name indicates, is shaped like a five-pointed star.
A skeleton of lime which is made up of thousands of tiny plates gives
shape to the body and arms. Slow movement is effected by means of
tiny suckers, called tube feet. Breathing takes place through the skin.
The mouth is on the under surface of the animal, and, when feeding,
the stomach is protruded and wrapped around its prey. The body of the
starfish, as well as that of the sea urchin and others of this group, is spiny;
hence the name Echinoderm (^-ki'n5-d0irm), which means spiny-skinned, is
given to the group.
Food of the Starfish. — Starfish are enormously destructive o f young

THE STARFISH 259

clams and oysters, as the following evidence, collected by Professor A. D.
Mead of Brown University, shows. A single starfish was confined in an
aquarium with fifty-six young clams. The largest clam was about the
length of one arm of the starfish, the smallest about ten millimeters in
length. In six days every clam in the aquarium was devoured.

In order to capture and kill mollusks, the starfish wrap themselves around
the valves of the shell and actually pull them apart by means of their tube
feet, some of which are attached to one valve and some to the other of their
victim. Once the soft part of the mollusk is exposed, the stomach envelops
it and covers it with the secretions of digestive glands, and it is rapidly
digested and changed to a fluid.

Hundreds of thousands of dollars' damage is done annually to the
oysters in Connecticut alone by the ravages of starfish. During the sum-
mer months the oyster boats are to be found at work raking the beds for
starfish, which are collected and thrown ashore by the thousands

Classification op Mollusks (Mollusca)

Class I. Pelecyp'oda {Lamellibranchia'ta) . Soft-bodied unsegmented ani-
mals showing bilateral symmetry. Bivalve shell, platelike gills. Ex-
amples: clam, scallop, oyster, and fresh-water mussel.

Class II. Gastrop'oda. Soft bodies asymmetrical; univalve shell or shell
absent. Some forms breathe by gills, others by lunglike sacs. Ex-
amples: pond snail, land snail, and slug.

Class III. Cephalop'oda. Bilaterally symmetrical mollusks with mouth
surrounded by tentacles. Shell may be external (nautilus), internal
(squid), or altogether lacking (octopus). Examples: squid, octopus.

Summary. — ^ Mollusks are characterized by a soft body, a man-
tle which secretes the shell when present, and a muscular foot.
Some are of economic importance as food, as the clam, scallop,
and oyster.

Problem Questions. - 1. How do mollusks move?

2. How do mollusks breathe?

3. On what kind of food do mollusks feed?

4. How are pearls formed?

5. How do starfish eat? Explain fully.

Problem and Project RBFERBNcrBS

Brooks, The Oyster. Johns Hopkins Press.

Bulletin, U.S. Fish Commission, 1899.

Kellogg, The Shellfish Industries. Henry Holt and Company.

Parker, Lessons in Elementary Biology. The Macmillan Compjacy.

Sharpe, Tjoboratory Manual. American Book Company.

XXII. THE VERTEBRATE ANIMALS

Increasing Complexity of Structure and of Habits in Plants
and Animals. — In our study of biology so far we have at-
tempted to get some notion of the various factors which act upon
and interact with living things. We have learned something about
the various physiological processes of plants and animals, and
have found them to be in many respects identical. We have
examined a number of forms of plants and have found all
grades of complexity, from the one-celled plant, bacterium or
pleurococcus, to the complicated flowering plants of considerable
size and with many organs. So in animal life the forms we
have studied, from the Protozoa upward, there is constant
change, and the change is toward greater complexity of struc-
ture and of function. A worm is simpler in structure than an
insect, and shows by its sluggish actions that it is not so high
in the scale of life as its more lively neighbor.

/n/erfebrate

Vertebrate

t/e&rt----

Stfeteton-

tnfest/neA'

Jystemi

SAeteto/i
-Afese/jter/'
-tC/ctneys

-tntest/ne

tlten^ous-.-^St^..^ m. ^ \^ (^-—:^—/feart

System

Cross section through an invertebrate animal and a vertebrate animal.

We are already awake to the fact that we are better equipped
in the battle for life than our more lowly neighbors, for we
are thinking creatures, and can change our surroundings at
will, while the lower forms of animals are largely controlled
by stimuli which come from without; temperature, moisture,

260

FISHES — ADAPTATIONS

261

light, the presence or absence of food, — all these result in
movement and other reactions.

Our next study will be of a group of animals called ver'te-
brates, because they have a bony vertebral column, made up of
pieces of bone joined one to another, forming a flexible yet
strong support for the muscles and protecting the delicate cen-
tral nervous system. This kind of an endoskeleton, or inside
skeleton, is possessed by fishes, frogs, turtles, snakes, birds, and
mammals, such as the dog, the cat, and man. We begin with the
study of some types of various kinds of vertebrates, with a view
to the better understanding of man.

Fishes

Problem, To determine how a Ush is fitted for the life it leads,
(Laboratory Manual, Prob, XXXIV; Laboratory Problems,
Probs. 133 to 139.)

The Body. — One of our common fresh-water fishes is the
perch. The body of the perch, hke that of many other fishes,

ftnsL cLorsal yliv^

lateral line
nostril

CocucLol Jir

operculum . „ .-
' -pectoral nvL

^pelvic fin.

Side view of a fish (a perch). There are two pectoral and
two pelvic fins, one on each side.

runs insensibly into the head, the neck being absent. The long,
narrow body, pointed at the anterior end, with its smooth sur-
face, makes the fish admirably adapted for swimming. Certain
cells in the skin which secrete mucus or slime, and the position
of the scales, overlapping in a backward direction, are other
adaptations which aid the fish in passing through the water.

262 THE VERTEBRATE ANIMALS

The color of many fishes, oHve above and gray or bright silver
below, is protective. Can you see how?

The Appendages and their Uses. — The appendages of the
fish consist of paired and unpaired fins. The paired fins are
four in number, and are believed to correspond in position and
structure with the paired limbs of a man. In the Figure
(p. 261) locate the paired pectoral and pelvic fins. Compare a
living fish with the Figure, and find the dorsal, anal, and caudal
fins. How many unpaired fins are there? The study of a fin
shows that it is composed of a thin membrane which is held in
shape and stiffened by long slender rods of bone or cartilage
called fin rays. The fin is light and strong, and, as powerful
muscles are attached to it, can push against the water with
sufficient force to move the body forward. Note that the dor-
sal fin has spinelike rays, while the fin rays of the caudal fins
are flexible. Do you find any fins in which both kinds of rays
occur?

The flattened, muscular body of the fish, tapering toward the
caudal fin, is moved from side to side with an undulating mo-
tion which results in the forward movement of the fish. This
movement is almost identical with that of an oar in sculling a
boat. Turning movements are brought about by use of the
lateral fins in much the same way as a boat is turned. We
notice that the dorsal and anal fins are evidently useful as
balancing and steering organs.

The Senses. — The position of the eyes at the sides of the
head is an evident advantage to the fish. Why? The eye is
globular in shape. As such an eye has been found to be very
near-sighted, it is Hkely that a fish is unable to perceive objects
at any great distance from it. The eyes are unprotected by
eyeHds, but their tough outer covering and their position at the
sides of the head afford some protection.

Feeding experiments show that a fish becomes aware of the
presence of food by smelling it as v/ell as by seeing it. The
nostrils of a fish are organs for smelUng. They are little pits,
which differ from our nostrils in that they are not connected
with the mouth cavity. In the catfish, the harhels, or horns,
receive sensations of smell and taste. The sense of smell in a

FISHES 263

fish is not quite the same as ours, for it perceives only substances
that are dissolved in the water in which it lives. The senses of
taste and touch appear to be less developed than the other
senses.

Along each side of most fishes is a line of tiny pits, provided
with sense organs and connected with the central nervous sys-
tem. This area, called the lateral line, is beheved to be sensitive
to mechanical stimuli of certain sorts. The ''ear" of the fish
is under the skin and serves partly as a balancing organ.

The tongue in most fishes is wanting or very slightly de-
veloped.

Breathing. — A fish, when swimming quietly and when at rest,
seems to be biting even if no food is present. It will be found
that a current of water enters when the mouth is opened and
is pushed back by the closing of the mouth and out through
slits located on each side back of the head. Investigation shows
us that under the broad, flat plate, or oper'culum, covering these
slits on each side, lie several long, feathery, red structures, the
gills. By the movements of the mouth a current of fresh water
is made to pass over the gills.

Gills. — In most fishes we find five pairs of gills. The founda-
tion of the gill, or the gill arch, is composed of several pieces of
bone which are hinged in such a way as to give great flexibility.
Covering the bony framework, and extending from it, are numer-
ous dehcate filaments of flesh, covered with a very delicate
membrane or skin. In each of these filaments are two blood
vessels; in one blood flows downward and in the other, upward.
While in the gill filament the blood is separated by a thin mem-
brane from the oxygen dissolved in the water bathing the gills.
An exchange of gases through the walls of the gill filaments
results in a loss of carbon dioxide and a gain of oxygen by the
blood.

Gill Rakers. — If we open wide the mouth of any large fish
and look inward, we find that the mouth cavity leads to a
funnel-like opening, the gullet. On each side of the gullet we
can see the gill arches holding the red filament. These delicate
structures are guarded on the inner side by a series of sharp-
pointed structures, the gill rakers. In some fishes in which the

264 THE VERTEBRATE ANIMALS

teeth are not well developed, there is a greater development of
the gill rakers, in which case they are used to strain out food
or small organisms from the water which passes over the gills.
(See Figure, p. 266.)

Digestive System. — The gullet leads directly into a baglike stomach.
There are no salivary glands in the fishes. There is, however, a large
liver, which appears to be used as a digestive gland. The liver contains a
good deal of oil and therefore is • in some fishes, as the cod, of considerable
economic importance. Many fishes have outgrowths like a series of pockets
from the intestine. These structures, called the pylor'ic cceca (se'ka), are
believed to secrete a digestive fluid. The intestine ends at the vent, or

Smblddder

Bdrbels

&//i/3*^~* Small intestine

Anatomy of a fish (a carp).

anus, which is usually located on the ventral side of the fish, immediately in
front of the anal fin.

Swim Bladder. — An organ of unusual significance, called the swim
bladder, occupies the region just dorsal to the food tube. In young fishes
of many species this is connected by a tube with the anterior end of the
digestive tract. In some forms this tube persists throughout life, but in
other fishes it becomes closed, and makes a thin, fibrous cord. The size
of the swim bladder can be changed through the contraction or expansion
of its walls. The fish uses it to make changes in the space it occupies,
so that the water displaced will equal its own weight. Thus the weight
of the fish is supported, no matter at what depth it wishes to remain.

Circulation of the Blood. — In the vertebrate animals the blood circulates
around the body, through a more or less closed system of tubes. In fishes
the heart is a muscular organ, with two connecting chambers: a thin-walled
au'ricle, or receiving chamber, and a thick-walled muscular ventricle from
which the blood is forced out. The blood is pumped from the heart to the
gills, wjiere it loses carbon dioxide and receives oxygen; it then passes on to

FISHES 265

other parts of the body, until it reaches very tiny tubes called cap'illaries.
From the capillaries the blood returns, in veins of gradually increasing
diameter, to the heart again. During its course around the body some of
the blood passes through the kidneys and is there relieved of its nitrogenous
waste. (See Chapter XXVII.)

Circulation of blood in the fish is rather slow. The temperature of the
blood is nearly that of the water in which the fish lives.

Nervous System. — As in aU other vertebrate animals, the central
nervous system of the fish consists of the brain and spinal cord, which are
covered by cartilage or bone for protection. The brain has nerves leading
to the organs of sight, taste, and smell, to the ear, and to such parts of
the body as possess the sense of touch. Nerve cells located near the outside
of the body send messages to the brain, where they are received as sensa-
tions. Cells of the central nervous system, in turn, send out messages which
result in the movement of muscles.

Skeleton. — In the vertebrates, of which the bony fish is an example,
the skeleton is under the skin, and is hence called an endoskeleton. It
consists of a skuU, the vertebral column, the ribs, and other spiny bones
to which the unpaired fins are attached. The paired fins are attached to
the spinal column by two collections of bones, known respectively as the
pectoral and pelvic girdles. The bones serve in the fish for the attachment
of powerful muscles, by means of which locomotion is accomplished. In
most fishes the exoskeleton, too, is well developed, modifications appearing
from scales to complete armor.

Problem. To determine some of the relations of fishes to their
food supply. {Laboratory Manual, Prob. XXXV; Laboratory
Problems, Prob. 139.)

Food of Fishes. — We have already seen that in a large
balanced aquarium the plants furnish food for the tiny
animals and a few of the larger ones, — for example, snails.
The smaller animals are eaten by larger ones until the largest
of all is fed. The nitrogen balance is maintained through
the wastes of the animals and their death and decay.

The ocean is a great balanced aquarium in which the upper
layer of water is crowded with all kinds of little organisms, both
plant and animal. Although microscopic in size or barely
visible to the eye, like the tiny crustaceans, they serve as food
for big fishes. The menhaden ^ (bony, bunker, mossbunker of

^ It has been discovered by Professor Mead of Brown University that the in-
crease in starfish along certain parts of the New England coast was in part due
to overfishing of menhaden, which at certain times in the year feed almost en-
tirely on the young starfish.

HUNT. NEW. EB. 18

266

THE VERTEBRATE ANIMALS

Oillarch Cillrakers
QUI filament

CHI arch
dill filament

Comparative size of mouth in bluefish (large
mouth) and shad (small mouth and large gill
rakers) .

our coast), the shad, and others, depend upon these minute
organisms for food. Such fishes have small mouths and very
large gill rakers which strain the water as it passes over the

-, gills and hold back the

B'^^f'^f" ^^ -^ food particles. Other

fishes are bottom feeders,
as the blackfish and the
sea bass, living almost
entirely upon moUusks
and crustaceans. Still
others are hunters, feed-
ing upon smaller species
of fish or even upon
their weaker brothers.
Such are the bluefish,
and the squeteague or weakfish. Such a fish must go after its
prey and seize it with its mouth, as it has no grasping organs
except its teeth. Consequently we find a large mouth in which
the teeth are sharp, pointed, numerous, and adapted for holding
living prey. The gill rakers are small or lacking.

What is true of salt-water fish is equally true of those in-
habiting our fresh-water streams and lakes. It is one of the
greatest problems of our Bureau of Fisheries to discover this
relation of various fishes to their food supplies so as to aid in
the conservation and balance of life in our lakes, rivers, and
seas.

The Egg-laying Habits of the Bony Fishes. — The eggs of
most bony fishes are laid in great numbers. The number varies
from a few thousand in the trout to many hundreds of thou-
sands in the shad and several millions in the cod. The time of
spawning is usually spring or early summer. After the eggs
are laid the male usually deposits milt, consisting of millions of
sperm cells, in the water just over the eggs. The sperm cells
move rapidly through the water, find the egg cells, and fertili-
zation follows. Some fishes, as sticklebacks, sunfish, toadfish,
etc., make nests, but usually the eggs are left to develop by
themselves, sometimes attached to some submerged object, but
more frequently free in the water, Some eggs which have a

FISHES

267

tiny oil drop, are buoyed up to the surface, where the heat of
the sun aids development. Both eggs and developing fish are
exposed to many dangers, and are eaten, not only by birds,
fish of other species, and other water inhabitants, but also by
their own relatives and even parents. Consequently a very
small percentage of eggs ever reach maturity.

Life History of the Yellow Perch. — This common fish has
been caught by almost every boy who reads these fines. It
frequents inland ponds and streams in the northeastern part

Life history of a fish: 1, 2, developing eggs; 3, 4, young with yolk sac;
5. 6, 7, later stages after the yolk sac is absorbed.

of the United States. Large numbers of them roam about
in schools so that if one locates a school he may be fairly sure
of a good catch.

Perch lay their eggs in masses or strings, often several hundreds
or even thousands being found in a single mass. The time of egg
laying is in March or April. After fertilization the eggs segment,
forming a mass of cells, which gradually assume the form of a
tiny fish with a yolk sac, containing food, on its ventral surface.
Eventually the yolk is absorbed by the young fish and a few
weeks from the time of hatching we find it able to take care of
itself. ^

Life History of the Chinook Salmon. — The Chinook salmon
of the Pacific coast is the salmon used in the western canning

268

THE VERTEBRATE ANIMALS

Salmon leaping a fall on the way to
their spawning beds.

industry. It is a fine, big fish, of about four or five years, when
it reaches maturity, leaves the Pacific, and enters the Columbia
or one of the other big rivers of the western slope to journey
to the cool mountain streams, where it spawns. During this

journey of from one thou-
sand to two thousand miles,
it does not eat, swims against
a strong current, and leaps
high falls. The salmon start
in early spring. Large num-
bers of them pass up the
rivers together and reach the
spawning beds in late sum-
mer in a very exhausted
condition. Here the fish re-
main until the temperature
of the water falls to about
54° Fahrenheit. Shallow
nests are made in the gravel by. the male. The eggs and
milt are then deposited, and the old fish die, leaving the eggs
to be hatched out thirty or forty days later by the heat of
the sun's rays. The young salmon pass down stream to the
ocean, where they live until mature, when they return to the
rivers to lay their eggs.

Migration of Fishes. — Some fishes change their habitat at
different times during the year, moving in vast schools north-
ward in summer and southward in the winter. In a general
way such migrations follow the coast lines. Examples of the
migratory fish are the cod, menhaden, herring, and bluefish.
The migrations are due to temperature changes, to the seeking
after food, and to the spawning instinct. T'he salmon, shad,
sturgeon, and smelt pass up rivers from the ocean to lay their
eggs. Some fish migrate to shallower water in the summer and
to deeper water in the winter; here the reason for the migration
is doubtless the change in temperature. The instinct of salmon
and other species to go into shallow rivers to deposit their eggs
has been made use of by man. At the time of the spawning
migration the salmon are taken in vast numbers,

FISHES

269

Economic Importance. — Fish are of great importance as food.
The herring fisheries have always been a source of wealth to
the inhabitants of northern Europe. The banks and shallows
of the coast of Newfoundland abound in cod. The cod fisheries
of the United States net over $20,000,000 a year, the salmon
fisheries over $16,000,000, the shad at least $1,500,000, the smelt
fishery nearly $150,000. The total annual value of the fisheries
of the United States is over $50,000,000.

The bones of fish are ground and made into fertilizers. Soap
is made from the oil of fish. Cod liver oil is used as a medi-
cine. Glue is made from the skin, fins, etc.

Problem. To learn something of the artificial propagation of
fishes. {Laboratory Manual, Proh. XXXVI.)

The Work of National and State Governments in protecting
and propagating Food Fishes. — But the profits from the
fisheries are steadily decreasing because of the yearly destruc-
tion of untold millions of eggs which might develop into adult
fish.

Fortunately, the United States government through the
Bureau of Fisheries, and various states by wise protective laws
and by artificial propagation of fishes, are beginning to turn
the tide. Certain days of the week the salmon are allowed to
pass up the Columbia unmolested. Closed breeding seasons

S70

THE VERTEBRATE ANIMALS

protect our trout, bass, and other game fish. The catching of cer-
tain fish under a stated size is prohibited also. Many fish hatch-
eries, both national and state, are engaged in artificially fertilizing
millions of eggs of various species and protecting the young fry
until they can be placed in ponds or streams at a size when
they can take care of themselves. For artificial fertihzation the
ripe eggs of a female are squeezed out into a pan of water; in

Work of a fish hatchery: fertilization of eggs. Two men with dipnets are lifting
male and female whitefish from crates into the tub at the right. The spawntaker
presses out the eggs and the milt into a pan, which is passed on to the man at the
left. After washing and hardening, the eggs are removed to the hatchery.

a similar manner the milt or sperm cells are obtained, and
poured over the eggs. The fertilized eggs are carefully pro-
tected, and, after hatching, the young fry are kept in ideal con-
ditions until later they are shipped, sometimes thousands of
miles, to their new home.

It is feared in many cases that assistance comes too late, for at
the present rate of destruction some of our most desirable
food fishes will soon be extinct. The sturgeon, the eggs of
which are used in the manufacture of the delicacy known as
caviare, is an example of a fish that is almost extinct in this

FISHES

271

part of the world. The shad is found in fewer numbers each
year, and in fewer rivers as well. The salmon will undoubtedly
soon meet the fate of other fishes which are taken at the
spawning season, unless conservation of a radical sort takes
place.

Classification of Fishes

Subclass I. Elasmobran' chii. Fishes having a skeleton formed of carti-
lage which has not become hardened with lime; gills communicating
with the surface of the body by separate openings instead of having
an operculum. Examples: sharks, rays, skates.

Sand shark, an elasmobranch. Note the slits leading from
the gills. From photograph loaned by the American Museum
of Natural History,

Subclass II. Ganoi'dei. Fishes having bodies protected by a series of
platelike scales of considerable strength. Example: gar pike.

Sturgeon, a ganoid.

Subclass III. Teleos'tei. Fishes having a bony skeleton; gills pro-
tected by an operculum. These tel'eosts comprise 95 per cent of all
living fishes.

Subclass IV. Dip'noi. A very small group of fishes that use the swim
bladder as a lung. They are thus in some respects like amphibians.
They live in tropical Africa, South America, and Australia, where
rivers and lakes go dry for part of the year.

Summary. — Fish are animals adapted to an aquatic life by
having a smooth, more or less cigar-shaped body, with modi-

272 THE VEK.TEBRATE ANIMALS

fied flattened appendages called fins and a powerful caudal fin
which serves with the muscles of the body as an organ of lo-
comotion. Gills absorb oxygen which is dissolved in the water
and give off carbon dioxide. Fishes usually lay large numbers
of eggs, and many of the young die before reaching maturity.
The egg-laying habits often take fish, as the salmon, thousands
of miles up rivers to lay their eggs. Fishes are of great
economic importance as food and need protection from govern,
ment and individuals alike.

Problem Questions.' — 1. What adaptations enable a fish to
swim? to escape its enemies? to catch its prey?

2. Discuss the egg-lajdng habits of some specific fishes. How
do you account for the differences in habits?

3. Classify the fishes.

Problem and Project References

Davison, Practical Zoology, pages 185-199. American Book Companj'.
Herrick, Textbook in General Zoology, Chap. XIX. American Book Company,
Hunter, Laboratory Problems in Civic Biology. American Book Company.
Jordan, Fishes. Henry Holt and Company.
Jordan and Evermann, American Food and Game Fishes. Doubleday, Page, and

Company.
Jordan, Kellogg, and Heath, Animal Studies, XIV. D. Appleton and Company.
Sharpe, A Laboratory Manual. American Book Company.

Amphibia. The Frog

Problem. To discover some adaptations in a living frog.
(Laboratory Manual, Prob. XXXVII; Laboratory Problems^
Probs. 140 to 145.)

Adaptations for Life. — The most common frog in the eastern
part of the United States is the leopard frog. It is recognized
by its greenish brown body with dark spots, each spot being
outlined in a lighter colored background. In spite of the ap-
parent lack of harmony with its surroundings, its color, on
the contrary, appears to give almost perfect protection. In
some species of frogs the color of the skin changes with the
surroundings of the frog, another means of protection.

Adaptations for life in the water are numerous. The ovoid

THE FROG

273

- , - -^»!^r. - ."^^w-T^^i^wrai^M^* *3"'nwiBr? j~,m

^^^'iL^

'"'OiiTiMili^jfli „''*

\..l

^^^1

t ^

4;'

^

X

-^'■■j^m

■*;

" ■"**^* 9

' .4^1

body, the head merging into the trunk, the slimy covering
(for the frog is provided, Hke the fish, with mucus cells in the
skin), and the powerful legs with webbed feet, are all evidences
of the life which the frog leads.

Locomotion. — You will notice that the appendages have the
same general position on the body and same number of parts
as do your own (upper
arm, forearm, and hand;
thigh, shank, and foot, the
latter much longer rela-
tively than your own).
Note that while the hand
has four fingers, the foot
has five long toes, con-
nected by a web to push
against the water when
swimming. As the frog
lives on both land and
water its powerful, long
legs are adapted for jump-
ing as well as for swimming. When at rest, these legs are doubled
up close to the body ready to give a quick spring forward. As
they are very long and attached to powerful muscles, the frog
moves rapidly. The short arms are used to balance the body
when at rest.

Sense Organs. — The frog is well provided with sense organs.
The eyes are large, globular, and placed at the sides of the head.
When the frog goes under water a delicate fold, called the
nictitating membrane (or third eyelid), is drawn over each eye.
Frogs probably see moving objects best at a few feet from
them. Their vision is much keener than that of the fish.
The external ear (tym'panum) is located just behind the eye on
the side of the head. Frogs hear sounds and distinguish vari-
ous calls of their own kind, as is proved by the fact that they
recognize the warning notes of their mates when any one is
approaching. The inner ear has to do with balancing the body
as it does in fishes and other vertebrates. Touch is a well-
developed sense. Frogs respond to changes in temperature

The leopard frog.

274

THE VERTEBRATE ANIMALS

under water, and go into a dormant state for the winter when
the temiperature of the air becomes colder than that of the water.

Taste and smell are probably not strong sensations in a frog
or toad.

Food Getting. — The frog's mouth is large and the sticky
tongue is long and flexible. It is attached to the front of the
floor of the mouth and is thrown out with great rapidity to secure

How a frog catches a fly.

living prey. Experience has taught these animals that mov-
ing things, insects, worms, and the like, make good food. These
they swallow whole, the tiny teeth being used to hold the
food.

Breathing. — The frog takes air into its mouth by lowering
the floor of the mouth and pulling in air through the two nos-
tril holes. Then the little flaps over the holes are closed, the
floor of the mouth is raised, and the frog swallows this air,
thus forcing it down into the baglike lungs. When the nos-
tril flaps are lifted the air is forced out by the pressure of the
body wall and the elasticity of the lungs. The lungs contain air
spaces, the walls of which are filled with blood vessels. Some of
the oxygen from the air passes through the walls into the
blood, while some of the carbon dioxide of the blood in turn is
passed into the air in the lung sacs. The skin also is provided
with many tiny blood vessels which absorb oxygen and give off
carbon dioxide. In winter, while the frogs are dormant at the
bottom of the ponds, the skin is the only organ of respiration.

The Food Tube and its Glands. — The mouth leads hke a
funnel into a short tube, the gullet. On the lower floor of the
mouth can be seen the slitlike glottis or opening into the trachea.
The gullet widens almost at once into a long stomach, which
in turn leads into a narrow, much coiled intestine. This widens

THE FROG

275

abruptly into the cloa'ca (Latin, sewer) into which open the kid-
neys, urinary bladder, and reproductive organs {ovaries or sper-
maries). Several glands, the function of which is to produce
digestive fluids, open into the food tube. These digestive fluids
by means of the ferments
or enzymes contained in
them, change insoluble
food materials into a
soluble form so that they
may be absorbed through
the walls of the food tube
and become part of the
blood. The glands (hav-
ing the same names and
uses as those in man) are
the salivary glands, which
pour their juices into the
mouth, the gastric glands
in the walls of the stomach,
and the liver and pancreas,
which open into the in-
testine. (See Digestion,
chapter XXV.)

Circulation. — The frog has
thick-walled muscalar ^^entricle

deart—i-^'

SmdII Intestine -

Spleen-- ^"^
Large Intestine

Mngs
stiver
Z-Oall Bladder

^.Stomach
L_ Pancreas

fi^JJrindr/ Bladder

Internal organs of a froR.

a well-developed heart, composed of a
and two thin-walled auricles. The heart
pumps the blood through a system of closed tubes to all parts of the body.
Blood enters the right auricle from all parts of the body; it then con-
tains considerable carbon dioxide; the blood entering the left auricle comes
from the lungs, hence it contains a considerable amount of oxygen. Blood
leaves the heart through the ventricle, which thus pumps blood contain-
ing much and little oxygen. Before the blood from the tissues and from
the lungs has time to mix, however, it leaves the ventricle and, by a delicate
adjustment in the vessels leaving the heart, most of the blood containing
much oxygen is passed to all the various organs of the body, while the blood
deficient in oxygen, but containing a large amount of carbon dioxide, is
pumped to the lungs.

In the cells of the body wherever work is done the process of burning
or oxidation must take place, for by such means only is the energy nec-
essary to do the work released. Food in the blood is taken to the muscle
cells or other cells of the body and there oxidized. The products of the
burning, chiefly carbon dioxide, and any other organic wastes given off from

276 THE VERTEBRATE ANIMALS

the tissues must be eliminated from the body. As we loiow, the carbon
dioxide passes off through the kmgs and to some extent through the skin
of the frog, while the nitrogenous wastes, poisons which must be taken
from the blood, are eliminated from it in the kidneys.

Problem, To learn about the development of a frog, {Labora-
tory Manual, ^ Prob. XXXVI; Laboratory Problems, Probs.
146 to 148.)

(a) Conditions favorable for development.

(6) Metamorphosis.

(c) Development of a toad (optional).

Field and Home Work. — During the first warm days in March or
April, look for gelatinous masses of frogs' eggs attached to sticks or water
weeds in shallow ponds. Collect some and keep in a shallow dish in a
window at home until they hatch. Make experiments to learn whether
temperature affects the development of the eggs in any way. Place eggs
in dishes of water in a warm room, in a cold room, and in the ice
box. Make observations for several weeks as to the rate of development
of each lot of eggs. Also try placing a large number of eggs in one dish,
thus cutting down the supply of available oxygen, and in another dish
near by, under the same conditions of light and heat, place a few eggs
with plenty of water. Do both batches of eggs develop with the same
rapidity? In all these experiments be sure to use eggs, from the same
egg mass, so as to make sure that all are of the same age.

Development. — The eggs of the leopard frog are laid in
shallow water in the early spring. Masses of several hundred,
which may be found attached to twigs or other supports under
water, are deposited at a single laying. Immediately before leav-
ing the body of the female they receive a coating of jellylike
material, which swells up after the eggs are laid. Thus they are
protected from the attacks of fishes or other animals which might
use them as food. The upper side of the egg is dark, the light-
colored side being weighted down with a supply of yolk (food).
The fertilized egg soon segments (divides and subdivides into
many cells), and in a few days, if the weather is warm, it has
grown into an oblong body which shows the form of a tadpole.
Shortly after, the tadpole wriggles out of the jellylike case and
begins life outside the egg. At first it remains attached to
some water weed by means of a suckerlike projection; later
a mouth is formed at this point, and the tadpole begins to

THE FROG

277

feed upon algae and other tiny water plants. At this time,
about two weeks after the eggs were laid, gills are present on
the outside of the body. Soon after, the external gills are re-
placed by gills which grow out under a fold of the skin which

Development of the frog: 1, 2, 3, eggs; 4, newly hatched tadpoles;
5, tadpole with external gills; 6 to 11, later stages; 12, frog.

forms an operculum somewhat as in the fish. Water reaches
the gills through the mouth and passes out through a hole on
the left side of the body. As the tadpole grows larger, legs
appear. The hind legs grow out first. The tail is used as an
organ for locomotion until the hind legs are ready.

278

THE VERTEBRATE ANIMALS

Shortly after the legs appear, the gills are absorbed, and
luDgs take their place. At this time the young animal may
De seen coming to the surface of the water for air. Changes
in the diet of the animal also occur; the long, coiled intestine
is transformed into a much shorter one. The animal, now in-
sectivorous in its diet, becomes provided with tiny teeth and a
mobile tongue, instead of the horny jaws used in scraping
off algae. After the tail has been completely absorbed and
thf legs have become full grown, there is no further structural
change, and the metamorphosis is complete.

In the leopard frog the change from the egg to adult is com-
pleted in one summer. In the green frog and bullfrog the
metamorphosis is not completed until the beginning of the

second summer. The
large tadpoles of such
forms bury themselves
in the soft mud of the
pond bottom during
the winter.

The Common
Toad. — One of the
nearest allies of the
frog is the common
toad. The eggs, like
those of the frog, are
deposited in fresh-
water ponds. The egg-
laying season of the
toad is later than that of the frog. The eggs are laid in strings,
and as many as eleven thousand eggs have been laid by a single
toad. ^

Toad tadpoles may be distinguished from those of the frogs, as
they are darker in color, and have a more slender tail and a
relatively larger body. The metamorphosis occupies only about
two months in the vicinity of New York, but varies gre^,tly
with the temperature. During the warm weather the tail is
absorbed with wonderful rapidity, and the change from a tad-
pole with no legs to a small toad living on land^ is often

The common toad.

AMPHIBIANS 279

accomplished in a few hours. This has given rise to the absurd
story that it rains toads, because during the night thousands
of young toads have changed their habitat from the water to
the land.

The toad is of great economic importance to man because
of its diet. No less than eighty-three species of insects, mostly
injurious, have been proved to enter into its dietary. A toad
has been observed to snap up one hundred and twenty-eight
flies in half an hour. At a low estimate it could easily destroy one
hundred insects a day for several months, and do an immense
service to the garden during the summer. It has been esti-
mated by Kirkland that a single toad may, on account of the
cutworms that it kills, be worth $19.88 a season, if the damage
done by each cutworm be estimated at only one cent. Toads
also feed upon slugs and other garden pests.

Other Amphibians. — The tree frogs (called tree toads) are familiar
to us in the early spring as the " peepers" of the swamps. They are among
the earhest of the frogs to lay their eggs. During adult life they spend
most of their time on the trunks of trees, where they receive immunity
from attack because of their color markings. The feet of the tree toad are
modified for climbing by having little disks on the ends of the toes, by
means of which it is able to cling to vertical surfaces.

Newt. From photograph loaned by the American Musexim of Natural History.

Another common amphib'ian is the newt, a salamander. This smooth-
skinned, four-limbed animal, often incorrectly called a lizard, passes its
larval life in the water, where it breathes by means of external gills. Later
it loses its gills, becomes provided with lungs, and comes out on land.
Its coat, which was greenish in the water, changes to a bright orange
color. In this condition we sometimes find newts crawhng on wood
roads after a rain. After over two years' Ufe on land, it again returns
to the water, becomes green with red spots (as seen in the Figure), and

280

THE VERTEBRATE ANIMALS

Spotted salamander. From photograph loaned by
the American Museum of Natural History.

is able to reproduce its kind. Some salamanders never have lungs, but

breathe through the moist skin.

Still other amphibians are the nuid pup})ios, sirens or mud eels, and the

axolotl. All of the amphibians differ from tlie reptiles in having a smootli

skin with no scales, and
in passing the early
stage of their existence
in the water.

Characteristics of
Amphibia. — The
frog belongs to the
class of vertebrates
known as Amphibia.
As the name indi-
cates (ainphi, both,
and hia, life), mem-
bers of this group pass more or less of their life in the water,
although in the adult state they are provided with lungs and can
live on land. In the earlier stages of their development they
take oxygen into the blood by means of gills. At all times, but
especially during the winter, the skin serves as a breathing
organ. The skin is soft and unprotected by bony plates or
scales. The heart has three chambers: two auricles and one
ventricle. Amphibians undergo metamorphosis during develop-
ment.

Order I. Urode'la. Amphibia having usuallj^ poorty developed appen-
dages. Tail persistent through life. Examples: mud puppy, newt,
salamander.

Order II. Anu'ra. Tnilless Amphibia. Hind legs well developed. Exam-
ples: toad and frog.

Summary. — The frog is one of the most common of our
amphibians and shows the characteristics of this group: (1) it
passes part of its life in the water as a tadpole and part either in
or out of the water in the adult state, (2) the skin is soft and
provided with slime glands, (3) the animal breathes as an adult
by means of lungs and skin but in the young stage by means of
gills, (4) it passes through a metamorphosis characteristic of the
group.

REPTILES 281

The group are of some economic importance in the destruc-
tion of harmful insects (toad) and as food (frog).

Problem Questions. — 1. How does a frog breatlie? catch
food? jump? swim?

2. Explain the steps in the metamorphosis of a frog and the
adaptations of each step.

3. How do the toads show amphibian characteristics?

Problem and Project References

Ditmars, The Bairachians of New York. Guide Leaflet 19, American Museum

of Natural History.
Dickerson, The Frog Book. Doubleday, Page, and Company.
Herri ck, Textbook in General Zoology, Chap. XX. American Book Company.
Hodge, Nature Study and Life, Chaps. XVI, XVII. Ginn and Company.
Holmes, The Biology of the Frog. The Macmillan Company.
Hunter, Laboratory Problems in Civic Biology. American Book Company.
Morgan, The Development of the Frog's Egg. The Macmillan Company.
Nature Study Leaflets, Cornell Nature Study, Bulletins XVI, XVII.

Reptiles

Reptiles differ from amphibians in that they always breathe
by means of lungs.

Turtles' Adaptations for Life. — The turtles form a large and
interesting group, including both sea and land animals, the latter
called tortoises. The body is flattened, and is covered on the
dorsal and ventral sides by a bony frame-
work. This covering is composed of plates
cemented to the true bone underneath, the
whole forming one big horny cover. This
shell, an adaptation for protection, is re-
markable in the box tortoise, where a hinge
on the ventral side allows the animal to
retreat within the shell, the head and legs

being completely covered. Western painted turtle.

Adaptations for Food Getting. — The
long neck and powerful, horny jaws are factors in procuring
food. Turtles have no teeth. Prey is seized and held by the
jaws, the claws of the front legs being used to tear the food.

Tiutles are very strong for their size. The stout legs carry the

HUNT. NBW B8. — 19

282

THE VERTEBRATE ANIMALS

Box tortoise. From photograph loaned by
the American Museum of Natural History.

animal slowly on land, and in the water, being slightly webbed,
they are of service in swimming. In some water turtles the
front limbs are modified into ilippers for swinuning. The strong
claws are used for cUgging, especially at the egg-laying season,
for some turtles dig holes in sandy beaches in which the eggs
are deposited^

Some Different Turtles. — Turtles are mostly aquatic in habit. Among
the exceptions are the box tortoise already mentioned and the giant tortoise

of the Galapagos Islands.
Many of the salt-water tur-
tles are of large size, the
leatherback and the green
turtle often weighing six
hundred to seven hundred
pounds each. The flesh of
the green turtle and es-
pecially the diamond-back
terrapin, an animal found
in the salt marshes along
our southeastern coast, is
highly esteemed as food.
Unfortunately for the preser-
vation of the species, these animals are usually taken during the breeding
season when they go to sandy beaches to lay their eggs.

Lizards. — Lizards may be recognized by their long body with
four legs of nearly equal size. The body is covered with scales.
The animal never lives
in water, it is active in
habit, and it does not
undergo a metamor-
phosis. Lizards are
generally harmless crea-
tures, the Gila monster
of New Mexico and
Arizona, a poisonous
variety, being one ex-
ception. Lizards are of
economic importance to
man, because they eat insects and include the injurious ones in
their dietary, The iguana of Central America and South

The Gila jnonster. Photopjraph one tenth
natural size, by Davison.

REPTILES

283

America, growing to a length of three feet or more, has the dis-
tinction of being one of the few edible lizards.

Snakes. — Probably the most disliked and feared of all ani-
mals are the snakes. This feeling, however, is rarely deserved,
for, on the whole, our common snakes are beneficial to man.
The black snake and the milk snake feed largely on injmious
rodents (rats, mice,
etc.), the pretty
green snake eats
injurious insects,
and the little De-
Kays snake feeds
partially on slugs.
If it were not that
the rattlesnake and
the copperhead are
venomous, they also

could be said to be useful, for they live on English sparrows^ rats>
mice, moles, and rabbits.

Snakes are ahnost the only vertebrates without appendages.
Although the limbs are absent, the pelvic and pectoral girdles
are developed. The very long backbone is made up of a large
number of vertebrae, as many as four hundred being found in
the boa constrictor. Ribs are attached to all the vertebrae in
the region of the body cavity.

Locomotion. — Locomotion is performed by pulling and push-
ing the body along the ground, a leverage being obtained by
means of the broad, flat scales, or scutes, with which the ventral
side of the body is covered. Snakes may move without twist-
ing the body. This is accomplished by a regular drawing for-
ward of the scutes and then pushing them backward rather
violently.

A garter snake, one of our commonest harmless
reptiles.

Feeding Habits. — The bones of the jaw are very loosely joined to-
gether. Thus the mouth of the snake is capable of wide distention. Id
holds its prey by means of incurved teeth, two of which (in the poisonous
snakes) are hollow or grooved, and serve as a duct for the passage of
poison. The poison glands are at the base of the curved fangs in the
upper jaw. The tongue is very iQng ^n4 cleit at the end. It is an organ

284

THE VERTEBRATE ANIMALS

of touch and taste, and is not, as many people believe, u^ed as a sting.

The food is swallowed whole, and pushed down by rhythmic contractions

of the muscles surrounding the gullet. Snakes usually refuse other than

living prey.

Adaptations. — Snakes are not extremely proHfic animals, but hold their

o^Ti with other forms of
life, because of their
numerous adaptations for
protection, their noiseless
movement, protective color,
and, in some cases, by their
odor and poison.

Poisonous Snakes, — Not
aU snakes can be said to be
harmless. The bite of the
rattlesnake of our own
country, although dangerous,
seldom kills. The dreaded
cobra of India has a record
of over two hundred and
fifty thousand persons killed

in thirty-five years. The Indian government yearly pays out large sums for

the extermination of venomous snakes, over two hundred thousand of

which have been kiUed during a single year.

Alligators and Crocodiles. — Crocodiles are mostly confined to Asia

and Africa, while alligators are natives of North and South America.

Skull of boa coustrictor, two thirds natural
size. Note the in-pointing teeth. Photograph
by Davison.

Young alligator. One fifth natural size.

The chief structural difference between them is that the teeth in alligators
are set in long sockets, while those of the crocodiles are not. Both of
these Hzardlike animals have broad, vertically flattened tails adapted
to swimming. The eyes and tip of the snout, the latter holding the nos-
tril holes, protrude from the head, so that the animal may float motion-

REPTILES 285

less near the surface of the water with only eyes and nostrils visible. The
nostrils are closed by a valve when the animal is under water. These rep-
tiles feed on fishes, but often attack large animals, as horses, cows, and
even man. They seek their prey chiefly at night, and spend the day bask-
ing in the sun. The crocodiles of the Ganges River in India levy a yearly
tribute of many hundred hves from the natives.

Classification of Reptiles

Order I. Chelo'nia (turtles). Flattened reptiles with body inclosed in
bony case. No teeth or sternum (breastbone). Two pairs of limbs.
Examples: snapping turtle, box tortoise.

Order II. Lacertil'ia (Kzards). Body covered with scales, usually having
two pairs of limbs. Examples : fence lizard, horned toad.

Order III. Ophid'ia (snakes). Body elongated, covered with scales. No
hmbs present. Examples: garter snake, rattlesnake.

Order IV. Crocodil'ia. Fresh-water reptiles with elongated body and
bony scales on skin. Two pairs of limbs. Examples alligator, croco-
dile.

Summary. — Turtles, lizards, and snakes belong tc the class of
v^ertebrates known as ReiptU'ia. Such animals are characterized
by having scales developed from the skin, which in the turtle
have become bony and are connected with the internal skeleton,
forming a shell. Reptiles always breathe by means of lungs,
differing in this respect from the amphibians. They show their
distant relationship to birds in that their large eggs are incased
in a leathery, limy shell.

In general reptiles are useful either as food (turtles) or as
destroyers of harmful animals. Most snakes are useful, although
the poisonous snakes and crocodiles still take a yearly toll of
deaths in some parts of the world.

Problem and Project References

Davison, Practical Zoology, pages 211-226. American Book Company.
Ditmars, The Reptiles of New York. Guide Leaflet 20, American Museum of

Natural History.
Ditmars, The Reptile Book. Doubleday, Page, and Company.
Jordan, Kellogg, and Heath, Animal Studies, Chap. XVI. D. Appleton and

Company.
Riverside Natural History. Houghton, Mifflin, and Company.

286

THE VERTEBRATE ANIMALS

Birds

Problem. To study some adaptations in birds. (Laboratory
Manual, Prob. XXXIX; Laboratory Problems: Prob. 118.)

Adaptations for Life. — Birds are distinguished from all other
animals by their covering of feathers and by the peculiar modifi-
cation of the fore Hmb into a wing for flight. Hollow bones,
feathers, and air spaces inside of the bod}'- cavity make them
light for staying up in the air. The body is boat-shaped and
pointed at the anterior end. The tail acts as a rudder. Tlie

LOWER MANDIBLE

TAIL COVERTS

CO/fffTJ

tfJNDTOE

y^^^TOES

Diagram of a bird.

bill is horny and adapted for securing food. The legs show great
variations for running, perching, swimming, and scratching.

Field Work. — Bird activities may best be studied out of doors. A city
park offers more or less opportunity for such study, for several of our
nat?ve birds make the parks their home. If not these, then the English
sparrow can be studied as it is found everywhere in the East. The best
time for making observations is early in the morning, especially in the
spring season.

Adaptation of the Wing. — The wing is a modified arm, with
the fingers very much reduced. It consists of a few long bones

BIRDS

287

and a few small muscles, covered with skin. To the posterior
edge of the wing are fastened long quill feathers which overlap
and make a broad, stiff surface for pressing against the air. The
wing is jointed and moves up and down in flight. Powerful
breast muscles are attached to the
wing bones and give great strength
in movement. The wings fold against
the side of the body when at rest.
Watch a bird in flight. The rate of
movement of the wing differs greatly
in different birds. The wing of a bird
is slightly concave on the lower sur-
face when outstretched. Thus on
the downward stroke of the wing
more resistance is offered to the air.
Birds with long, thin wings, as the
hawks and gulls, move their wings in
flight with much less rapidity than
those with short, wide wings, as the
grouse or quail. The latter birds
start with much less apparent effort
than the birds with longer wings;
they are, however, less capable of
sustained flight.

Feathers. — Few people reahze
that the body of a bird is not
completely covered with feathers.
Featherless areas can be found on the
body of any common bird, although
tiny '^pin feathers'' are found on
such areas as well as on other parts
of the body. Soft down feathers
on the body make a covering for warmth. Larger feathers give
the rounded contour to the body. In the wings we find quill
feathers; these are adapted for service in flight by having long
hollow shafts, from which lateral interlocking branches are given
off, the whole making a light structure and offering consider-
able resistance to the air. Feathers are developed from the

Feathers of a meadow lark.
Which of the above are used
for flight? How do you know?
From photograph loaned by
the American Museum of
Natural History.

288

THE VERTEBRATE ANIMALS

outer layer of the skin, and are formed in almost exactly the
same manner as are the scales of a fish or a Uzard. The first
feathers developed on the body are evidently for protection
against cold and wet, but later in life they serve other uses
as well. The feathers of most male birds are brightly colored.
This seems to make them attractive to the females of the
species; thus the male may win its mate.

Adaptations of the Legs. — The ankle of a bird is long and
reptile-like and is covered, hke the foot, with scales. The most
extraordinary adaptations are found in the feet of various birds

Adaptation in feet of birds: 1, swift (clinging); 2, ouzel (perching); 3, wood-
pecker (climbing); 4, pheasant (scratching); 5, hawk (seizing prey); 6, ostrich
(limning) ; 7, duck (swimming) ; 8, grebe (diving) ; 9, avocet (wading) ; 10, stork
(wading). In each case can you make out the way in which the bird's foot i&
adapted to do its work?

some for perching, others for swimming, others for wading, etc.
We are able, by looking at the feet of a bird, to decide almost
certainly its habitat, method of life, and perhaps its food.

In the perching birds we find three toes in front and one behind,
the hind toe playing an important part in clinging to the perch.
In swallows, rapid and untiring flyers, the feet are small. In
the case of the parrots, where the foot is used for holding food,
climbing, and cUnging, we find the four-clawed toes arranged

BIRDS

289

Cervical Vertebr9

Pelvic Qirdle
Tall

FingerBones

Sterrim

two in front and two behind. Hawks and eagles are provided with
strong curved talons with which the prey is seized and killed.

Adaptation for semiaquatic life is seen in plovers, herons, or
storks, where long legs and
long toes enable the birds
to seek their food in soft
mud among reeds or lily
pads, or along sand flats.
True aquatic birds, on the
other hand, are provided
with webbed toes. The
foot of the common barn- ^°"^^^^"^
yard duck, for example, is
much like that of the alli-
gator. In the ostrich and
cassowary the wings are
small and not used for
flight; the legs are long and
powerful and fitted for
rapid running.

Perching. — The method
of perching is an interest-
ing one. The three toes
in front ciurve around the
perch, often meeting the
posterior toe, which is curved also. The tendons of the leg
and foot are self locking, and such birds are held in place as
perfectly when asleep as when awake. A part of the ear, known
as the semicircular canals, has to do with the function of bal-
ancing. In the flamingoes and other birds, which do not perch,
balancing appears to be automatic; thus the bird is able to
maintain an upright position even when asleep.

Tail. — The tail is sometimes used in balancing; its chief
function, however, appears to be that of a rudder during flight.
Most birds have under the skin of the tail a large oil gland,
whence comes the supply of oil that is used in waterproofing
the feathers when they preen themselves.

The Skeleton. — The skeleton combines lightness, flexibility,

Fusedbones
ofankle

2ndTo
JrdToe -

4thToe-^

Skeleton of a fowl.

290

THE VERTEBRATE ANIMAI^S

and strength. Many bones are hollow or have large spongy
cavities. The bones of the head and neck show many and
varied adaptations to the life the bird leads. The vertebrae
which form the framework of the neck are strong and flexible.
They vary in shape and in number. The swan, seeking its
food under water, has a neck containing twenty-three long
vertebrae; the English sparrow, in a different environment,
has only fourteen short ones. Some bones, notably the breast-
bone, are greatly developed in flying birds for the attachment
of the muscles used in flight.

Adaptations in the bills of birds. Could we tell anything about the food of a
bird from its bill? Do these birds get their food in the same manner? 1, shoe-
bill; 2, hawk; 3, bunting; 4, thrush; 5, flamingo; 6, spoonbill; 7, pelican; 8, duck;
9, pigeon; 10, toucan; 11, bird of pai'adise; 12, swift; 13, skimmer; 14, stork.

Bill. — The form of the bill shows adaptation to a wonderful
degree, varying greatly according to the habits of the bird. A
duck has a flat bill for pushing through the mud and straining
out the food; a bird of prey has a curved or hooked beak for
tearing; the woodpecker has a sharp, straight bill for piercing
the bark of tref^s in search of the insect larvae underneath.

Birds do not have teeth. The edge of the bill may appear
to be toothed, as in some fish-eating ducks; however, the projec-
tions are not true teeth. Frequently the tongue has sharp.

BIRDS 291

toothlike edges which serve the same purpose as the recurved
teeth of the frog or snake.

Adaptations for Active Life. — The rate of respiration, of
heartbeat, and the body temperature are all higher in the bird
than in man.

These are among the greatest adaptations to the active life
led by a bird. Man breathes sixteen or eighteen times a minute.
Birds breathe from twenty to sixty times a minute. The lungs
of a bird are not large. Its bronchial tubes are continued
through the lungs into hollow spaces filled with air, which are
found between the organs of the body. Only the lungs, how-
ever, are used for breathing. Because of the increased ac-
tivity of a bird, there comes a necessity for a greater supply
of oxygen, an increased blood supply to carry the material
to be oxidized in the release of energy, and a means of rapid
excretion of the wastes resulting from the process of oxidation.
A bird may be compared to a high-pressure steam engine; in
order to release the energy which it uses in flight, a large
quantity of fuel which will oxidize quickly must be used. Birds
are large eaters, and the digestive tract is fitted to digest the
food quickly. As soon as the food is absorbed by the blood, it
may be sent rapidly to the places where it is needed, by means
of the strong four-chambered heart and large blood vessels.

The high temperature of the bird is a direct result of this
rapid oxidation; furthermore, the feathers and the oily skin
form an insulation which does not readily permit the escape
of heat. This insulating cover is of much use to the bird in its
flights at high altitudes, where the temperature is often very
low.

The Nervous System and the Senses. — The central nervous system
is well developed. A large forebrain is present, which, according to a series
of elaborate experiments with pigeons, is found to have to do with the
conscious life of the bird. The cerebellum takes care of the acts which are
purely mechanical.

Sight is probably the best developed of the senses of a bird. The keen-
ness of vision of a hawk is proverbial. It has been noticed that in a bird
which hunts its prey at night, the eyes look toward the front of the face.
In a bird which is hunted, as in the dove, the eyes are placed at the sides
of the head. In the case of the woodcock, which feeds at night in the

292

THE VERTEBRATE ANIMALS

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marshes, and which is in constant danger from attacks by owls, the eyes
have come to he far back on the top of the head. Hearing is also well
developed in most birds, as may be demonstrated with any canary.

The sense of smell does not appear to be well developed in any bird, and
is especially deficient in seed-eating birds.

Nesting Habits. — Among the most interesting of all instincts
shown by birds are those of nest building. Some invertebrates,

as spiders and ants, pro-
tect the eggs when laid.
In the vertebrate group
some fishes (as the sun-
fish and stickleback)
make nests for holding
the eggs. But most fishes,
and indeed nearly all
other vertebrates lower
than the birds, leave the
eggs to be hatched by the
heat of the sun. Birds

Nest of a phcebe under a barn floor. • i, x xt_ • J.^ i.

mcubate their eggs, that
is, hatch them, by the heat of their bodies. Hence a nest,
in which to rest, is needed. The ostrich is an exception;
it makes no nest, but lays its eggs on the ground ; then the male
and the female take turns
in sitting on them. Such
birds as are immune from
the attacks of enemies be-
cause of their isolation or
their protective coloration
(as the puffins, gulls, and
terns), build a rough nest
among the rocks or on the
beach. The eggs, espe-
cially those of the tern, are
marked and colored so as
to be almost indistinguish-
able from the rocks or sand on which they rest. Other birds have
made their nest a home and a place of refuge as well as a place

Common tern and young, showing nest-
ing and feeding habits. From group at the
American Museum of Natural History.

BIRDS

293

,»tmi^^mmmm

to hatch the eggs. Such are the nest of the woodpecker in a
hollow tree and the hanging nest of the oriole. Some nests
which might be easily seen because of their location are often
rendered inconspicuous by the builders; for example, the lichen-
covered nest of the humming birds.

Care of the Young. — After the eggs have been hatched, the
young in most cases are quite
dependent upon the parents
for food. Most young birds
are prodigious eaters; as a
result they grow very rap-
idly. It has been estimated
that a young robin eats two
or three times its own
weight in worms every day.
Many other young birds,
especially kingbirds, are
rapacious insect eaters. In
the case of the pigeons and

some other birds, food is Nest ol the chimney swift.

swallowed by the mother, partially digested in the crop, and
then regurgitated into the mouths of the young nestlings.

Problem. How birds are of economic importance. (Lahora"
tory Manual, Proh. XL; Laboratory Problems, Probs. 121, 122.)

Geographical Distribution and Migrations. — Most of us are
aware that some birds remain in a given region during the
whole year, while other birds appear with the approach of
spring, and depart southward with the warm weather in the
fall of the year. Such birds we call migrants, while those that
remain in one place the year round are called residents.

In Europe, where the problem of bird migration has been
studied carefully, migrations appear to take place along well-
defined paths. These paths usually follow the coast very ex-
actly, although in places they may take the line of coast
that existed in former geological times. In this country the
Mississippi valley, a former arm of the sea, forms one line of
migration, while the north Atlantic seacoast forms another route.

294

THE VERTEBRATE ANIMALS

It has been shown that the southern movement of migratory
birds in the fall of the year is not due entirely to the advent of
cold weather, but i^ largely a matter of adjustment to food
supply. A migrant almost always depends upon insects, fruits,
and grains for the whole or a large part of its food. Most
winter residents, as the crow, are omnivorous in diet. Others,
as the English sparrow, may be seed eaters, but under stress
change their diet to almost anything in the line of food; still
others, as the woodpeckers, although insect-eating birds, man-
age to find the desired food tucked away under the bark of
trees. Many insect-eating birds, however, because their food
is found on green plants, appear to be forced southward by
the cold weather.

Food of Birds. — Birds are of tremendous economic impor-
tance to our country and a very great help to agriculture because

a large part of their diet includes
insects harmful to vegetation,
and the seeds of weeds, enemies
also of the farmer. Birds hke
the crow and robin feed at times
upon fruit and grain and at other
times upon insects. So grateful
were the early settlers in Utah to
the seagulls for dehvering them
from a plague of ''crickets" (per-
haps locusts), that they erected
a beautiful monument to the
seagulls. A plague of insects
threatened to destroy the crops
and the people were in despair,
when along came crowds of sea-
gulls that ate the pests and
saved the crops.

Not all birds are seed or
insect feeders. Some, as the
cormorants, ospreys, and terns, are active fishers. Near large
cities gulls act as scavengers, destroying much floating garbage
that otherwise might be washed ashore to become a menace to

Food of some common birds.

BIRDS 295

health. Sea birds also live upon shellfish and crustaceans (as
small crabs, shrimps, etc.); some even eat lower organisms.
The kea parrot, once a fruit eater, now takes its meal from the
muscles forming the backs of living sheep. Birds of pre}^ (owls
and hawks) eat smaller birds and mammals, including many
rodents; for example, field mice, rats, and other pests.

Common Birds. — The following pages will help one to recog-
nize a few of our common birds which are of decided economic
value or harm. The size, color markings, food, and familiar
habits of some of our common birds will be given, with a brief
statement of the reason why they are man's friends or enemies.
• Robin. — A bird known to all of us makes an excellent type
for comparison with other less known birds. The robin is 9 to
10 inches long. The male is dark gray above tinged with olive,
brown on the wings, and black on the head and tail; the throat
is light gray with black spots, and the breast is red. The fe-
male is similar but darker in color. The robins live near houses
and in orchards and make their nests of grass and mud, in trees
or on buildings. The robin is a true thrush, whose pleasing
song dehghts us in early Spring. Its economic position is often
discussed as it eats much fruit early in the season. Ordinarily
its diet consists of about 40 per cent
insects, most of which, as ground
beetles, caterpillars, plant Hce, and
cutworms, are harmful. It eats earth-
worms, also, which are useful to the
farmer.

Bluebird. — One of our earliest mi-
grants. Its cheery note and blue coat
are easily recognized. It is Gf to 7
inches in length. The male is bright Biuebi-d.

blue above, and chestnut iinderneath. The female is duller in
color. It nests in holes in trees or posts and in bird houses.
Its food consists largely of grasshoppers with a few beetles,
spiders, and caterpillars.

Song sparrow. — Another of our earliest visitors. The male
is about 6i inches long, brown above, head reddish-brown
mottled with blackish streaks. A streak of gray runs through

296

THE VERTEBRATE ANIMALS

the center of the crown, and there is a characteristic black line
through the eye and two on the throat. The breast is spotted
on a white ground. Its nest is usually on the ground or in a
bush. It is a friendly bird and is often seen near houses, though
it prefers moist areas farther away from man. It eats some
insects, but like most of the native sparrows it feeds mainly
upon weed se^ds.

Chickadee. — A smaller bird, about 5J inches in length. It
is often an all-year-round resident. The crown of the head
and throat are black, the cheeks white, the back gray, and
the belly often a dirty white. It feeds upon spiders, plant
lice, and other insects, and in the winter time devours large
quantities of eggs laid by these pests, one bird eating more
than 430 eggs in a single day. It is certainly one of man's
best bird friends.

House Wren. — This little migrant nests around our homes,
is a great songster and a decided asset to us, because of its
varied diet of cutworms, spiders, weevils. May flies, etc. It has
been estimated to catch 600 insects a day. It is a friendly little
bird whose worst enemies are English sparrows and cats. A
proper nesting box with a small entrance is one of its best
means of protection. The house wren is not quite 5 inches long.
The upper part is brown, the lower grayish brown and white.
The wings, flanks, and tail are slightly barred. It can be recog-
nized easily by its small size,
coloring, incessant singing or
chattering, and by the fact
that its tail is frequently held
erect when at rest.

American Goldfinch. — This
bright yellow songster is one
of our most attractive birds.
It is often called the wild
canary. It is a little over 5 inches long. The male has a
bright yellow body with a black cap and black markings on
tail and wings-. The female is a deep brown. The goldfinch
eats seeds of weeds, preferring those of the dandelion and thistle,
two of our greatest weed pests.

American goldfinch.

COMMON BIRDS

297

I

Yellow Warbler. — A bird often confused with the goldfinch
is the yellow warbler. Like all warblers, this is a small bird;
it is about 5 inches in length. Its color is yellow, flecked
with olive or brown (note it has no black on the head as does
the goldfinch). It nests near houses in low trees or bushes.
It is of much economic importance because of its preference for
the browntail and gypsy moth caterpillars, and other enemies
of the forest trees. We are spending millions of dollars every
year to fight these imported pests, and the goldfinch may help
turn the scale against them if it is protected and encouraged to
nest near our homes. What can you do to help?

Phoebe. — Another tireless hunter of insect pests is the phoebe.
This bird is a flycatcher, seizing insects on the wing. It builds
a nest of mud — often under old bridges, around barns, or some-
times under a barn floor (p. 292). Its food consists of browntail
and gypsy moths, cankerworms, beetles, and flies. The phoebe is
about 7 inches long, dusky olive-brown above, yellowish white
underneath, wings and tail dusky. The head is slightly crested,
bill and feet are black. It is one of our early visitors.

Barn Swallow. — Another bird with nesting habits similar to
those of the phoebe is the barn swallow, which makes a nest
plastered to the rafters of a
barn or outbuilding. While
most birds decrease in num-
ber with the cutting of
forests and the building of
cities, the barn swallow has
increased because it feeds on
insects which live on crops
in cleared fields. It eats
moths of cutworms, codling
moths, and leaf cutters, with
many others of the farmer's
insect enemies. This swallow
is between 6 and 7 inches in length. It is dark blue above, with
forehead, throat, and upper breast chestnut; the lower breast
and belly buff. The tail is deeply forked, showing white mark-
ings when spread.

HUNT. NEW E8. — 20o

Barn swallows.

298

THE VERTEBRATE ANIMALS

Catbird. — Another bird which nests near houses and prefers
the company of man is the catbird. From early May to late
October its various calls and songs are the delight of all bird
lovers, for it is a great mimic and somewhat of a tease. The cat-
bird, although it eats much fruit, is largely an insect feeder and
gives its young 95 per cent insect food. It is an enemy to
caterpillars, especially the cutworm. It is about 9 inches in
length, and of a dark grayish color, with the top of ^ head and
the tail blackish.

Downy Woodpecker. — The woodpeckers are famiUar to most
boys and girls because of their conspicuous color and their
peculiar habits. The downy woodpecker is 6J inches long,
black and white barred, with a small patch of scarlet at the
top of the head. It runs quickly up and down the trunks of
trees, tapping the wood to locate insect holes. The bill is
strong, sharp at the end, and is used as a chisel in boring
into wood. The tongue is spearlike, 1 to 1§ inches long, and is
used to pull out the larvae which it seeks. Its chief food is larvae

of maple, birch, apple and other
borers. Woolly aphids, caterpillars,
and crysalids are also its prey.
A woodpecker has been observed
to work over 180 trees in 2 J hours'
time. In some cases a downy
woodpecker is found which lives
up to its name of sapsucker, but
the good done b3^ these little birds
far outweighs the harm done by
them.

Flicker. — This bird is not a
typical woodpecker although it has
similar habits. It is a large bird
12 inches long. The male is brown
above and golden yellow below,
with black markings, and a scarlet
crescent across the neck. It has a white rump which is con-
spicuous in flight and makes an easily recognized mark. The
flicker is generally useful, feeding upon plant lice, ants (which

Flicker.

COMMON BIRDS

299

make up about 45 per cent of its food), grasshoppers, caterpillars,
and weed seeds. Like the woodpecker, it nests in hollow trees.

Baltimore Oriole. — This bright-colored and attractive bird
is about 7J inches long. The male has the upper back and
throat black with the outer tail feathers, breast, and under parts
orange. The female is not so brilHantly colored, having a yellow
instead of orange color. The hanging nests of the oriole, often
woven with bits of string and other materials, are a common
sight in elm trees near our homes. These birds prefer inhab-
ited areas and, because of their protected nests, are on the in-
crease in spite of cats and the English sparrow. They feed
largely upon the cankerworm, tussock, browntail, and forest
tent caterpillars.

Screech Owl. — This is a small owl and one of the most useful,
as it feeds upon field mice and other small
destructive rodents as well as upon some
moths, caterpillars, and beetles. It is about
as large as a quail, or 9i inches in length.
" Its general coloring is gray on the under
parts and reddish brown above. The eye
is yellow. It usually nests in hollow trees.

Crow. — Our common crow, a glossy black
bird from 16 to 17J inches long, is one of the
few birds that may do more harm than good.
In the early spring the crow is useful and
eats insect larvae, such as cutworms and
May beetle larvae, and field mice, but
later it does much harm in the newly
planted corn fields. The crow is accused
of stealing young chickens, ducks, and turkeys, and the eggs
and young of many useful birds.

English Sparrow. — The English sparrow is an example of a
bird introduced for the purpose of insect destruction, that has
done great harm because of its relation to our native birds.
Introduced at Brooklyn in 1850 for the purpose of exterminat-
ing the cankerworm, it soon abandoned an insect diet to a large
Extent in favor of one of grain and has driven out many of
our native insect feeders. Investigations by the Department of

Screech owl.

300 THE VERTEBRATE ANIMALS

Agriculture show that in the country these birds and their j^oung
feed to a large extent upon grain, thus showing them to be injuri-
ous to agriculture. Dirty and very prolific, the}^ long since worked

their way from the East as far as the
Pacific coast. In this area the blue-
bird, song sparrow, and yellowbird
have all been forced to give way,
as well as many larger birds of great
economic value and beauty. The Eng-
lish sparrow has become a national
pest, and should be exterminated
in order to save our native birds.
^^^^'^^^^ It is feared in some quarters that the

English starling, which has recently
Cooper's hawk. been introduced into this country,

may in time prove a pest as formidable as the English sparrow.
Birds Harmful to Man. — Wliile there are a few birds that do
both harm and good Hke the crow and the robin, there are
others that are bad and we can find little or no good to say
about them. The English sparrow is the greatest bird pest, for
reasons given above. The cowbird never builds a nest nor cares
for her young. She lays her eggs in the nests of smaller birds,
where later the young cowbirds cause the death of the rightful
inhabitants of the nest. Cooper's hawk, the sharp-shinned hawk,
and the great horned owl kill smaller, beneficial birds. The
beautiful belted kingfisher sits in a tree beside the rivers and
fishes, eating aquatic insects, mice, frogs, and grasshoppers also.
Fortunately there are very few birds to put on the black Ust.
Extermination of our Native Birds. — ^Yithin recent times has
been witnessed the almost total extermination of some species
of our native birds. The American passenger pigeon, once very
abundant in the Middle West, is now practically extinct. To-
day not a single specimen of this pigeon can be found, because
they were slaughtered by the hundreds of thousands during the
breeding season. The wholesale killing of the snowj^ egret to
furnish ornaments for ladies' headwear is another example of
the impro\'idence of our feUow countrymen. The EngHsh spar-
row and wholesale killing of birds for plumage, eggs, and food,

COMMON BIRDS 301

and often for mere sport, caused the decrease of our birds to 46
per cent in thirty states and territories within fifteen years.
Laws made by state and national governments have done much
to protect the birds and check their rapid decrease. Places of
refuge or sanctuaries where birds are undisturbed during the
nesting season have saved the lives of many hundreds. Societies
and clubs have aroused interest all over the country and now
many boys and girls as well as older people are watching, feed-
ing, and protecting birds in every possible way. The effect of
killing native birds is now seen in Italy and Japan, where insect
pests are increasing. We should aU do our part in preventing
the loss of our native birds here, not only because of their
beauty and their song, but also because of their very great
economic importance.

Relationship of Birds and Reptiles. — The birds afford an
interesting example of how the history of past ages of the earth
has given a clue to the structural relation which birds bear to
other animals. Several years ago, two fossil skeletons were
found in Europe of a birdlike creature which had not only wings
and feathers, but also teeth and a lizardlike tail. From these
fossil remains and certain structures (as scales) and habits (as
the egg-laying habits), naturahsts have concluded that birds
and reptiles in distant times were nearly related and that our
existing birds probably developed from a reptile-like ancestor
many ages ago.

Classification of Birds

Division I. Rati'toe. Running birds without keeled breastbone. Exam-
ples: ostrich, cassowary.
Division II. Carina' tee. Birds with keeled breastbone.

Order i. Pas' seres. Perching birds; three toes in front, one behind.

One half of all species of birds are included in this order. Examples:

sparrow, thrush, swallow.
Order ii. Galli'nce. Strong legs; feet adapted to perching. Bealj

stout. Examples: jungle fowl, grouse, quail, domestic fowl.
Order hi. Rapto'res. Birds of prey with hooked beak and strong claws.

Examples: eagle, hawk, owl.
Order iv. Grallato'res. Waders. Long neck, beak, and legs. Shore and

water-loving birds. Examples: snipe, crane, heron.
Order v. Natato'res. Divers and swimmers. Legs short, toes webbed.

Examples: gull, duck, albatross.

302 THE VERTEBRATE ANIMALS

Order vi. Colum'bce. Like Gallinae, but with weaker legs. Examples:
dove, pigeon.

Order vii. Pica'riae. Woodpeckers. Two toes point forward, two back-
ward, an adaptation for climbiQg. Long, strong bill. Examples:
Downy and hairy woodpeckers.

Summary. — Birds are feathered vertebrates with the anterior
appendages fitted for flying. Adaptations for food getting are
numerous and well shown in the different types of beaks
and claws.

Our native birds are of great economic importance because of
their feeding habits, as follows: (1) They eat insects which
destroy crops, injure trees, and are pests in many ways; ex-
amples, the house wren, phoebe, and downy woodpecker. (2)
They eat seeds of weeds, which if allowed to grow would give
.the farmer much trouble; examples, sparrows, goldfinch, and
pigeon. (3) They kill harmful rodents, as field mice and moles;
example, screech owl. (4) They act as scavengers; example, the
herring gull.

Only a few birds are harmful, as indicated below: (1) They
eat grain and fruit; examples, the crow and the robin. (2)
They catch fish; example, the kingfisher. (3) They dig deep
holes in trees and allow the sap to run out;, example, the sap-
sucker. (4) They drive out and harm useful birds; examples,
the English sparrow and some hawks.

As the benefit received from birds is tremendous and the harm
is very slight, we should do all that we can to protect and
encourage these feathered neighbors.

Problem Questions. — 1. What are the characteristics of a bird?

2. Name some bird adaptations for food getting, for nest
making, and for protection.

3.' Discuss the food habits of ten useful birds found in your
locality.

4. Name five birds that are of doubtful economic importance
and give the reasons for your answer.

5. Classify each of the above-named birds according to the
simple classification at the end of the section on birds.

6. Explain how the food of birds determines their migrations.

7. Why are birds considered related to reptiles?

MAMMALS 303

Problem and Peoject References

Apgar, Birds of the United States. American Book Company,

Beebe, The Bird. Henry Holt and Company.

Blanchan, Bird Neighbors. Doubleday, Page, and Company.

Chapman, Bird Life. D. Appleton and Company.

Forbush, Useful Birds and their Protection. Mass. State Board of Agriculture.

Hornaday, Our Vanishing Wild Life. New York Zoological Society.

Hunter, Laboratory Problems in Civic Biology (for bibliography). American
Book Company.

Hunter and Whitman, Civic Science. American Book Company.

Ward and T> &axbovn. Birds in their Relation to Man. J. B, Lippincott Company.

Bulletins of U. S. Dept. of Agriculture, Div. of Biological Survey, Farmers' Bul-
letins 54, 383, 506, and other Nature Study Leaflets XXII, XXIII, XXIV,
XXV, Cornell Nature Study Bulletins, Publications of the Audubon
Society.

Mammals

Mammals. — Dogs and cats, sheep and pigs, horses and cows,
many other animals covered with hair, and man himself, have
struct'.iral characteristics which cause them to be classed as mam-
mals. Mammals, like some other vertebrates, have lungs and
warm blood. UnHke all other vertebrates, however, they have a
hairy covering and bear young developed to a form similar to
their own,^ which they nurse with milk secreted by glands known
as the mam'mary glands; hence the term " mammals." Mammals
are considered the highest of vertebrate animals, not only be-
cause of their complicated structure, but because of their
mental development.

Adaptations in Mammalia. — Of the thirty-five hundred spe-
cies of mammals, most inhabit continents; a few species are
found only on islands; and some, as the whale, inhabit the ocean.
They vary in size from the whale and the elephant to the tiny
shrew mice and moles. Adaptations abound; the seal and whale
have the limbs modified into flippers, the sloth and squirrel have
limbs peculiarly adapted to climbing, while the bats have the
fore limbs modeled for flight.

Carnivora. — As the word '^carniv'ora" denotes, carnivorous
mammals are to a large extent flesh eaters. In a wild state
they hunt their prey, which is caught and torn with the aid of
well-developed claws and long, sharp teeth. These teeth, so

^With the exception of the monotremes.

304

THE VERTEBRATE ANIMALS

well developed in the dog, are known as canine teefch or dog
teeth. All flesh-eating mammals are wandering hunters in a
state of nature; many, as the bear and lion, have homes or dens
to which they retreat. Some (for example, bears and raccoons)

live part of the time upon berries
and fruit. Seals, sea Hons,
whales, and walruses are adapted
to a life in the water; and their
hind limbs are almost useless on
land. Some of the fur bearers,
as the otter and mink, lead a
partially aquatic life. Others in
this great group prefer regions of
comparative dryness, as the inhabitants of the South African
belt. A few, like the raccoon, live most of their time in the
trees. Many have adaptations for food getting and escape
from enemies; the seasonal change in color of the weasel is an
example of an adaptation which serves both of the above pur-
poses. This is only one of hundreds that might be mentioned.

SkuU of dog.

California sea lion. Photographed in the Philadelphia
Zoological Gardens by Davison^

Economic Importance. — The Carnivora as a group are of
much economic importance as the source of most of our fur.
The fur seal fisheries alone amount to many millions of dollars
annually. Otters, skunks, sables, weasels, and minks are of con-
siderable importance as fur producers. Our domestic cats are

MAMMALS

305

such factors in the extermination of our native birds that their
place as house pets is seriously questioned by some people.
Homeless cats are great hunters of birds and a general nuisance
and should not be allowed to exist. In India, tigers, and in
Africa, lions, are man-eating in certain locahties, and in our
own country wolves, pumas, and wild cats do some damage.

Rodents. — Mammals known as rodents have the teeth so
modified that on both upper and lower jaws two prominent incisor
teeth can be used for
gnawing. These teeth
keep their chisel-like
edges because the
back part of the teeth
is softer and wears
away more rapidly.
The canine or dog
teeth are lacking. We
are all familiar with
the destructive gnaw-
ing quahties of one of
the commonest of aU
rodents, the rat. The
common brown rat

Skull of a porcupine, a rodent. Notice the large
overlapping incisor teeth. Compare them with
the teeth of a dog (see page 304).

is an example of a manmial which has followed in man's foot-
steps all over the world, doing him harm. Starting from

China, it spread to Europe,
and in 1775 it had obtained a
lodgment in this country. In
seventy-five years it reached the
Pacific coast, and is now fairly
common all over the United
States, being one of the most pro-
lific of all mammals. Tt is esti-
mated that the rat causes a
property loss of at least $200,-
000,000 annually. A determined
effort is being made to exterminate this pest because of its
connection with bubonic plague.

Beaver. Copyright, 1900,
Radcliffe Dugmore.

by A.

306

THE VERTEBRATE ANIMALS

Although most rodents may be considered as pests (as the

rat and mouse) others are of use to man. Some of them

furnish food, as the rabbits, hares, and squirrels. Rabbits,

although rapid breeders,
are kept in check in most
parts of this country by
their natural enemies,
birds of prey and flesh-
eating mammals. But in
Australia, where they
were introduced by man,
they have become so
numerous that the Gov-
ernment gives a bounty
for their destruction.
Thousands of sheep are
starved to death each
year because rabbits eat
their pasturage. The fur
of the beaver, one of the

largest of this order, is of considerable Value, as are the coats

of several other rodents. The fur of the rabbit is used in the

manufacture of felt hats.

The quills of the porcu-
pines (greatly developed

and stiffened hairs) have

a slight commercial

value.

Ungulates: Hoofed

Mammals. — This group

includes most of the

domesticated animals, as

the horse, cow, sheep,

and pig. Many of this

group of animals came

under the subjugating influence of man and now they form an

important part of the world's wealth.

The order of ungulates is a very large one. It is characterized

Virginia deer. From photograph loaned by
the American Museum of Natural History.

The bison.

MAMMALS

307

by the fact that the nails have grown down and become thickened
as hoofs. In some cases only two (the third and fourth) toes are
largely developed. Such animals have a cleft hoof, as the ox,
deer, sheep, and pigs. They are the even-toed ungulates. The
deer family contains the largest number of species and indi-
viduals among our native forms, and in fact the world over.
Among them are the common Virginia deer of the Eastern
states, the white-tailed deer of our Adirondack forests. The
bison, or buffalo, is nearly related to the deer and wild cattle.
Formerly bisons existed in enormous numbers on our Western
plains. They were often hunted by whites and Indians for the
hides and tongues only, and thousands of carcasses were left
to rot after a hunt. They are now almost extinct.

Evolution of the horse. The illustration is a scientist's sketch of the earliest
horse, which became extinct many ages ago. It was about the size of a fox; the
bones of its head and fore foot are shown at the left. The bones of the present
horse's head and fore foot are shown at the right. Between are those of animals
intermediate in the line of descent.

Geologic History of the Horse. — In some ungulates the
middle toe of the foot has become largely developed, with the
result that the animal stands on it. Among such animals are
the zebra and the horse.

308 THE VERTEBRATE ANIMALS

We have, from time to time, made reference to the fact that
certain forms of Hfe, now ahnost extinct, flourished on the earth
in former geologic periods. It is interesting to note that America
was the original home of the horse, although at the time of the
earHest explorers the horse was unknown here. The wild horse of
the Western plains descended from horses introduced by the
Spaniards. Long ages ago, the remote ancestors of the horse were
probably little animals the size of a fox, with five-toed feet.
The earliest horse we have knowledge of had faur toes on the fore
and three toes on the hind feet. Thousands of years later there
existed a larger horse, the size of a sheep, with three toes on each
foot. By gradual changes, caused by the tendency of animals
to vary, there was eventually produced our present horse,
an animal with legs adapted for rapid locomotion, with
feet particularly fitted for life in open fields, and with teeth
which serve well to seize and grind herbage.

Domestication of Animals; Breeding by Selection. — The
prehistoric horse for some reason disappeared in this country,
but continued to exist in Europe, and man, emerging from his
early savage condition, began to make use of the animal. We
know the horse was domesticated in early Biblical times, and
that it became one of man's most valued servants. In more
recent times, superior horses have been developed by selective
breeding.

To do this, the horses that have varied and show the char-
acteristics desired by the breeder are selected and bred together.
The young from these animals are likely to be like their par-
ents and may be even more likely to show the characteristics
the breeder desires. If this process is repeated for several
generations, it will be seen that man, by artificial selection,
may have considerably modified the type of horse with which
he started. In this manner the various types of horses familiar
to us as draft horses, coaches and hackneys, and the trotters
have been established and improved. In a similar manner the
various breeds of cattle, sheep, swine, and other domestic
animals have been obtained.

It is needless to say that man has caused a tremendous
change in animals by domesticating them and by selective

MAMMALS

309

breeding. When we realize the very great amount of money
invested in domesticated animals; and that there are over
50,000,000 each of sheep, cattle, and swine and over 20,000,000
horses owned in this country, we may see how important a
part domestic animals play in our lives.

Orders of Mammals. — The lowest are the monotr ernes, animals which
lay eggs hke the birds, although they are provided with hairy covering
Uke other mammals. Such are the AustraUan spiny anteater and the
duck mole.

All other mammals give birth
to young which are developed to
a form similar to their own.
The kangaroos and opossums,
however, are provided with a
pouch on the ventral side of the
body in which the very im-
mature, blind, and helpless young
are nourished until they are able
to care for themselves. These
pouched animals are called
marsu'pials.

The other mammals, in which
the young are born able to care for themselves, and have the form of
the adult, may briefly be classified as follows:

Order I. Edenta'ta. Toothless or with very simple teeth. Examples:
anteater, sloth, armadillo.

Order II. Ceta'cea. Adapted to marine life; teeth (of whales) sometimes
platelike. Examples: whale, porpoise.

Order III. Sire'nia. Fishlike; pectoral limbs paddle-like; pelvis absent,
no vertical dorsal fin. Examples: manatee, dugong.

Order IV. Roden'tia. Incisor teeth chisel-shaped, usually two above and
two below. Examples: beaver, rat, porcupine, rabbit, squirrel.

Order V. Ungula'ta. Hoofs; teeth adapted for grinding. Examples: (a)
odd-toed: horse, rhinoceros, tapir; (6) even-toed: ox, pig, sheep,
deer.

Order VI. Insectiv'ora. Small, insect-eating, furry or spiny covered;
long snout. Examples: mole, shrew, hedgehog.

Order VII. Carniv'ora. Long canine teeth, sharp and long claws. Exam-
ples : dog, cat, bear, seal, and sea Hon.

Order VIII. Chiroptera (ki-rop'te-ra) . Fore Hmbs adapted to flight,
teeth pointed. Example: bat.

Order IX. Primates (pri-ma'tez). Erect or nearly so, fore appendage pro-
vided with hand. Examples: monkey, ape, man.

Virginia opossum. Photograph, one eighth
natural size, by N. F. Davis.

310 THE VERTEBfL^TE AXIMALS

Summary. — The mammals are vertebrates with hair, warm
blood, fom'-chambered heart, and mammary glands. Economi-
cally they are of much importance as they fm-nish us with food,
beasts of bm-den, clothing, etc. Some are of distinct haiTQ, the
rat being perhaps the gi*eatest offender.

Problem Questions. — 1. Why are mammals considered the
highest animals?

2. How would you distinguish a rodent? A carnivorous
mammal? An ungulate?

3. Name the local mammals found in vom' com m unit v that
are of value; of harm.

Problem and Peoject Refzrexces

Hodge, Xature Study and Life, Chapter III. Ginn and Company.

Ingersoll, Wild Xeighbors. The ]Macmillan Company.

Matthew, The Ecolution of the Horse. Guide Leaflet Xo. 9. American Museurc

of Natural History.
Stone and Cram, American Animals. Doubleday, Page, and Company.
Wright, Four-footed Americans. The Macmillan Company-.

XXIII. MAN, A MAMMAL

Problem, To compare man as a vertebrate with the frog as to —
(a) Body covering,
(6) Muscles.

(c) Adaptations in the skeleton.

(d) Nervous system.

(Laboratory Manual, Prob. XLI; Laboratory Problems, Probs.
163 to 169.)

Man's Place in Nature. — -Although we know that man is
separated mentally by a wide gap from all other animals, in om-
study of physiology we must ask where we are to place him
structurally. If we attempt to classify man, we see at once he
must be placed with the vertebrate animals because of his pos-
session of a vertebral column. Evidently, too, he is a mam-
mal, because the young are nourished by milk secreted by the
mother and because his body has at least a partial covering of
hair. Among the different orders of manmials man most closely
resembles anatomically the one to which the monkeys and apes
belong, called primates.

Although anatomically there is a greater difference between
the lowest type of monkey and the highest type of ape than
there is between the highest type of ape and the lowest savage,
yet there is an immense mental gap between the ape and man.

Evolution of Man. — Undoubtedly there once lived upon the
earth races of men who were much lower in their mental organi-
zation than the present inhabitants. If we follow the early
history of man upon the earth, we find that at first he must have
been little better than one of the lower animals. He was a
nomad, wandering from place to place, living upon whatever
animals he could kill with his hands and whatever edible plants
he found. Gradually he learned to use weapons, with which to
kill his prey, first using rough stone implements for this purpose.

311

312 MAN, A MAMMAL

As man became more civilized, implements of bronze and of
iron were used. About this time the subjugation and domesti-
cation of animals began to take place. Man then began to
cultivate the fields, and to have a fixed place of abode other than
a cave. The beginnings of civilization were long ago, but even
to-day the earth is not entirely civilized.

The Races af Man. — At the present time there exist upon
the earth five races or varieties of man, each very different
from the others in instincts, social customs, and, to an extent, in
structure. These are the Ethiopian or negro type, originating
in Africa; the Malay or brown race, from the islands of the
Pacific; the American Indian; the Mongohan or yellow race,
including the natives of China and Japan, and the Eskimos;
and, finally, the Caucasians, represented by the civilized white
inhabitants of Europe and America.

The Human Body a Machine. — In all animals, and the
human animal is no exception, the body has been Hkened to a
machine in that it turns over the latent or potential energy
stored up in food into kinetic energy (mechanical work and
heat), which is manifested when work is performed. One great
difference exists between an engine and the human body. The
engine uses fuel unlike the substance out of which it is made.
The human body, on the other hand, uses for fuel the same
substances as those out of which it is formed; it may, indeed,
use part of its own substance for food. The human organism
must do more than purely mechanical work; it must be so
delicately adjusted to its surroundings that it will react in a
ready manner to stimuli from without; it must be able to
utilize its fuel (food) in the most economical manner; it must
be fitted with machinery for transforming the energy received
from food into various kinds of work; it must properly provide
the machine with oxygen so that the fuel will be oxidized, and
it must carry away the products of oxidation, as well as other
waste materials which might harm the effectiveness of the
machine. Most important of all, the human machine must
be able to repair itself.

In order to understand better this complicated machine, the
human body, let us examine the structure of its parts and thus

THE HUMAN BODY

313

get a better idea of the interrelation of these parts and of their
functions.

Structure of the Skin. — In man, the outer covering, or skin,
is composed of two layers: the epidermis and the dermis. The
outer part of the epidermis is made largely of flattened dead
cells. It is this layer that peels off after sunburn, or that sep-
arates from the inner part of the epidermis when a water blister
is formed. The inner cells of the epidermis are provided with
more or less pigment or coloring matter. It is to the varying

Sweat-Ihui

Bomy layer
Pigment layer

Xaetile Organs'
Nerve —
Stood Teasels --^

Svoeat Gland
Fat

EpidermU

>Demia

Subcutarteous layer of ^
'connective tissue arid jOt

Diagram of a section of the skin. (Highly magnified.)

quantity of this pigment that the light or dark complexion is
due. The inmost part of the epidermis is made up of small
cells which are constantly dividing to form new cells to take
the place of those in the outer layer which are lost.

The dermis, or inner layer of the skin, is largely composed of
connective tissue filled with a network of blood vessels and
nerves. This layer contains the sweat glands, some of the most
important glands in the body, and the tactile cor'puscles, which
^re connected with the nervous system, and cause this part of
the skin to be sensitive to touch.

Nails and Hair. — Nails are a development from the horny
layer of the epidermis. A hair is also an outgrowth of the horny

HUNT. XBW ES. 21

314

MAN, A MAMMAL

layer, although it is formed in a deep pit or depression in the
dermis; this pit is called the hair follicle.

The Glands of the Skin. — Scattered through the dermis, and
usually connected with the hair follicles, are tiny oil-secreting
glands, the sebaceous (se-ba'shus) glands, which keep the hair
and surface of the skin soft. The other glands in the dermis,
known as sweat glands, are to be found in profusion, over
2,500,000 being present in the skin of a normal man. These
glands excrete certain wastes from the blood in the water they
pass off. Thus the skin not only protects the body, but also
serves as an excretory organ. Its most important function, how-
ever, is the regulation of the heat of the body. How it does
this, we shall learn later. (See Chapter XXVII.)

Connective Tissue. — The layer immediately beneath the der-
mis is known as the suhcuta'neous layer. It is an important
storage place for fat. Underneath this layer we find a mass

of flesh or muscle. Intermixed with this is
a considerable amount of fat. The fat,
muscle, — in fact, all the tissues in the
body, — are held together by fibrous threads
called connective tissue.

Muscles and Movement. — We are all
aware that motion in any of the higher
animals is caused by the action of the
muscles, which contract to cause movement.
In man and the other vertebrate animals,
the muscles are almost always fastened to
bones, which, acting as levers, give wide
range of motion.

Arrangement of Voluntary Muscles in
the Human Body. — Muscles are usually
placed in pairs; one, called the extensor y
muscle; sm, a flexor serves to straighten the joint; the other,
^^^^ ^' the flexor, bends the joint. Locate, by feel-

ing the muscles when expanded and when contracted, the
extensors and flexors in your own arm. This paired arrange-
ment of muscles is of obvious importance, a flexor muscle
balancing the action of an extensor on the other side of the

sm

Frog's hind leg: tr,
triceps, an extensor

THE HUMAN BODY

313

joint. The end of the muscle that
has the wider movement in a
contraction is called the inser-
tion; the part that moves least
is the origin.

Microscopic Structtire of Volun-
tary Muscle. — With a sharp pair of
scissors cut through a muscle at right
angles to the long axis; examina-
tion will show that it is composed of
a number of bundles of fibers. These
fibers are held together by a sheath
of connective tissue. Each of these
bundles may be separated into
smaller ones. If we continue this so
as to separate the smallest possible
bits that can be seen with the naked
eye, and then examine such a tiny
portion under the compound micro-
scope, it will present somewhat the
appearance shown in the Figure. The
muscle is seen to be made up of a
number of tiny threads which lie side
by side, held together by the sheath.
Muscles, then, are bundles of long
fibers. In man, muscles which are under the control of the will have a
striated appearance, while those which are involuntary are unstriated.
Both kinds are supplied with nerves, which control them (see Figures).

Muscle Tissue and its Uses.'
— Muscles form a large part of
the body, in man nearly half
of his entire weight. Nearly
every muscle in the human body
is attached to a bone either at
one or at both ends. Move-
ment is performed by means of
the muscles, leverage being ob-
tained by their attachment to
the bones. In the human body
^, , ,. , ,. ^ . , there are over five hundred mus-

1 he delicate endings of nerves m vol- . „

untary muscle. (Highly magnified.) . .cles, varying from one Smaller

A bit of voluntary muscle fiber,
showing the cross striations as seen
under the microscope. (Highly mag-
nified.)

316

MAN, A MAMMAL

than a pinhead to a band almost two feet in length. Every
movement of the body, be it merely a change of expression or
change in the pitch of the voice, directly results from contrac-
tion of a muscle. Muscles also give form to the body, and are
useful in protecting the delicate organs and large blood vessels
within them.

Muscles and the Skeleton. — Muscles would be of little use
to animals if they were not attached to hard parts of the body
which serve as levers. In many invertebrate animals (for ex-
ample, crustaceans, insects, and mollusks), the muscles are
attached to the exoskeleton. In man they are attached to the
endoskeleton.

In the hind leg of a frog, if we cut through the muscles of the thigh
to the bone, we may make out exactly how and where the muscles of
the thigh are attached to the bone. Moving the leg in as many different
directions as possible, we notice that it may be flexed or bent; that it
may be extended to its original position; that it may be moved to and
from the midline of the body; that, with the knee held stiff, the whole
limb may be made to describe the arc of a circle.^

The same movements are possible in the leg of a man. This move-
ment between bones is obtained by means of joints. If, in the frog, we
carefully separate the muscles of the thigh to the bone,
we find that they are attached to the bone by white,
glistening tendons. Careful examination shows that the
bones themselves are held together by very tough white
bands or cords; these are the ligaments. We find, too,
that one end of the large thigh bone fits into a socket
in the hip bone or pelvic arch. It is thus easy to see
how such free movement is obtained in the leg.

Levers in the Body. — It is evident that movement
of a joint is caused by muscles which act in cooperation
with the bones to which they are attached; the latter
thus form true levers. A lever is a structure by Vhich
either greater work -power or greater range of motion is
obtained. In this apparatus, the lever works against a
fixed point, the fulcrum, in order to raise a certain
weight. A seesaw is a lever; here the fulcrum is in
the middle, the weight is at one end, and the power to
lift the weight is applied at the other end. There are three classes of
levers, named according to the position of the fulcrum.

1 At this point, if possible, demonstration with a human skeleton should be
made.

Hinge joint,
showing muscle
(a) and its ten-
don (6).

THE HUMAN BODY

317

In the first class, the fulcrum lies between the weight and the force or
power; the seesaw is an example of this. The best example in the human
body of a lever of the first class is seen when the head is raised. Here the
fulcrum is the vertebra known as the atlas; the power is the muscles of
the neck attached to the back of the skull and to the spine; the weight is

Levers of the first Class

ful

crum

force

weight

F W

"^^

Levers of the second Class
fulcrum

weight

F W

force

Levers of the third Class

fulcrum

weight

force

P^

Three classes of levers: the first case shows pushing with the toe; the second, rising
on the toe; the third, lifting with the toe.

the front part of the head. When one keeps the head erect, this lever is
used; the nodding head when one is napping shows its action.

A lever of the second class has the fulcrum at one end, and the weight
between it and the pqwer; when we rise on our toes, we use this kind of
lever.

In a lever of the third class, the fulcrum is at one end, with the power
between it and the weight. This is the kind of lever seen most frequently
in the human body. The flexing (drawing up) of the lower leg or the fore-
arm is an example of the use of this kind of lever. In such a lever, a wide
range of movement is obtained.

General Structure and Uses of the Skeleton. — Evidently
bones form a framework to which muscles are attached; thus
they are used as levers for purposes of movement. Second,
they give protection to delicate organs; they form a case around

31S

MAN, A MAMMAL

the brain and spinal cord; as ribs they protect the organs in

the body cavity. Third, they give rigidity and form to the

body.

The skeleton of vertebrate animals consists of two distinct

regions: a ver'tehral column or backbone which, with the skull,

forms the axial skeleton;
and the parts attached to
this main axis, the appen-
dic'ular skeleton (the ap-
pendages). All skeletons
of vertebrates have the
same general regions, the
size and shape of the bones
in these regions differing
somewhat in each kind of
% animal.

Skeleton of a dog, a typical mammal. ' In the axial skeleton the

vertebral column is made up of a number of bones of irregular
shape, which fit more or less closely into each other. This
can be seen easily in the frog. These bones are called vertehroe.
They possess long processes to some of which the muscles of the
back are attached. Certain of the vertebrae bear ribs (arched,
flat bones), the special function of which is to protect the organs
of the upper body cavity.

Adaptations in the Vertebral Column. — The vertebral column
in a child is made of thirty-three separate pieces of bone; sev-
eral of them grow together in
the region of the pelvis and
there are twenty-six in the
adult. Each vertebra presents
the general form of a body or
centrum of bone and a bony
arch with seven projections;
in this arch runs the spinal
cord. The vertebra directly
beneath the head is modified so as to permit the skull to rest
in it; this articulates freely with the second vertebra, thus
permitting the nodding and turning movements of the head.

Vertebra, showing attachment of ribs:
C, centnmi; R, ribs;<SP, spinous process.

THE HUMAN BODY

319

Besides these individual adaptations, the vertebral column, as a

whole, is peculiarly adapted to protect the brain from jar; this

is seen in the double bend of

the vertebral colimm and the

pads of cartilage between the

individual vertebrae. The

whole column of vertebrae

joined one above another

supports the weight of the

body. The largest vertebrae

at the base of the column

are joined to the huge pelvic

bones to support the body

above. That part of the

vertebral column of man

which bears the ribs is known

as the thoracic (th6-ras'ik)

region. The ribs, twelve pairs

in number, are long, curved

bones which combine lightness

with strength; joined by

elastic cartilage to the ster'

num in front and to the

vertebrae behind, they form a

wonderful protection to the

organs in the thoracic cavity,

and yet allow free movement

in breathing.

The Appendages. — The
parts of the skeleton to which
the bones of the anterior and
posterior appendages are
attached are respectively
known as the pectoral girdle
(from which hangs the arm)

Skeleton of man: CR, cranium; CL,
clavicle; ST, sternum; H, humerus; VC,
vertebral column; P, pelvic girdle; i2,
radius; U, ulna; C, carpals; M, meta-
carpals; Ph, phalanges; F, femur; T, tibia;
Fi,Ghvla.; Tar, tarsals; MT, metatarsals.

and the pelvic girdle (which joins the leg bones to the axial
skeleton).
The bones of the appendages attached to the pelvic girdle

320

MAN, A MAMMAL

are adapted peculiarly to locomotion and support; for this
purpose the bones are long and strong, hinged by very flexi-
ble joints. In the hand the joints are especially free to
allow for grasping. In the leg, where weight must be sup-
ported as well as carried, the bones are bound more firmly

to the axial skeleton.
The bones of the foot
are so arranged that a
springy arch is formed
which aids greatly in
locomotion.

The Human Skull. — The

skull shows wonderful adap-
tations for protection; it is
compactly built, and its
arched roof gives strength.
The eye and inner ear are
protected in sockets of bone.
The lower jaw works upon a
hinge, and furnishes attach-
ment for strong muscles which
move the jaw.

• The skull: F., frontal bone; P., parietal
bone; T., temporal bone; SP., sphenoid bone;
O., occipital bone; U.J., superior maxillary
(upper jaw) bone; L.J.^ inferior maxillary
(lower jaw) bone.

Other Organs. — We have seen that a body cavity has de-
veloped in all animals which are more complex than the bag-
like hydra, and that a food tube has come to lie within this
space. In all such animals the structures which have to do
with digestion and absorption of food, most of those which have
to do with the circulation of food and of the blood, and organs
which give oxygen to the blood, as well as the organs of excre-
tion and of reproduction, lie within the body cavity. These
organs we shall discuss in detail later.

Nerves. — Nerves are found in practically all parts of 'the
body, ending in the skin, in muscle, in the heart, lungs, and other
organs, where they receive stimuli and control movements.
The most important part of the nervous system in vertebrate
animals lies within the cavity formed by bones making up
the skull and the vertebral column. This central nervous
system, consisting of the spinal column and the hrain, is a
characteristic of the vertebrates.

THE HUMAN BODY 321

General Functions of the Nervous System. — We have seen
that, in the simplest animals, one cell performs the functions
necessary to its existence. In the more complex animals, where
groups of cells form tissues, each having a different function,
a nervous system is developed. The functions of the human
nervous system are: (1) to ^provide man with sensation, by means
of which he becomes acquainted with the world about him; (2) to
connect organs in different parts of the body so that they act as a
united and harmonious whole; (3) to provide for the acts which
we call voluntary. Cooperation in word and deed is the end
attained. We are all familiar with examples of the cooperation
of organs. You see food; the thought comes that it is good to
eat; you reach out, take it, raise it to your mouth; the jaws
move in response to your will; the food is chewed and swal-
lowed; while digestion and absorption of the food are taking
place, the nervous system is still in control. The nervous
system regulates the pumping of blood to all parts of the body,
respiration, secretion of glands, and, indeed, every bodily func-
tion. Man is the highest of all animals because of the extreme
development of the nervous system. Man is the thinking
animal, and as such is master of the earth.

Summary. — Man is a mammal. He is also anatomically a
complicated machine. This chapter has pointed out numerous
adaptations in the skeleton and muscles of the body. It has
also pointed out that coordination is brought about by means of
the nervous system. •

Problem Questions. — 1. Why is man a mammal?

2. Mention ten adaptations in the human skeleton.

3. How is movement brought about in the body?

4. What are the functions of the different parts of the nervous
system of man?

Problem ajstd Project References

Burton-Opitz, Physiology. W. B. Saunders Company.

Clodd, Primer of Evolution. Longmans, Green, and Company.

Eddy, General Physiology. American Book Company.

Hough and Sedgwick, The Human Mechanism. The Macmillan Company.

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Ritchie, Human Physiology. World Book Company.

Sharpe, A Laboratory Manual. American Book Company.

XXIV. FOODS AND DIETARIES

Problem. A study of food values and diets to determine —

SULPHUR ao3lU^oo% ^^^ ^^^^ ^^^^^^ ^^^ ^^^^'

'PHQSPH0RU51
CALCIUM

nttrogenP^

NfTROGEH
3.13X65.

HYDROGEN
I3.65\bs.

,.2iG\ts. )}% I ' (b) Nutritive values as compared with
o.z7?Th»X% cost.

(c) The family dietary,

(d) Food values.
(Laboratory Manual, Prob. XLII;

Laboratory Problems, Probs, 170 to 178.)

CARBON,

OXYGEN

^- i08.l5lb;5. '

^

Why we need Food. — We have
already defined food as anything that
forms material for the growth or repair
of the body of a plant or animal, or that
furnishes energy for it. The milHons
of cells of which the body is composed
must be given material which will
form more living matter or material
which can be oxidized to release en-
ergy when muscle cells move, or gland
cells secrete, or brain cells think.
Food, then, not only furnishes our body
with material to grow, but also gives
us the energy we expend in the acts
of walking, running, breathing, and
even in thinking.
Nutrients. — Certain nutrient materials form the basis of food
for both plants and animals. The organic nutrients have been
found to be proteins (such as lean meat, eggs, the gluten of
bread), carbohydrates (starches, sugars, gums, etc.), fats and oils
(both animal and vegetable), and vitamins. The inorganic
nutrients are mineral matter and water. The parts of the human
body, be they muscle, blood, nerve, bone, or gristle, are built
up from the nutrients in our food.

322

The chief chemical elements
of which the human body is
composed, with percentage of
each. The weight also is
given, for a body weighing
150 pounds.

NUTRIENTS 323

Proteins. — Proteins, in some manner unknown to us, are
manufactured in the bodies of green plants. They contain the
element nitrogen, and hence are called nitrogenous foods.
Nitrogen, necessary for the growth of the body, can be used
only when combined with other elements in the form of a com-
pound. Man forms the protoplasm of his body (that is, the
muscles, tendons, nervous system, blood corpuscles, the living
parts of the bone and the skin, etc.) from nitrogenous food.
Different proteins contain different amounts of available build-
ing material, hence some are more useful to the body than
others. Proteins may also be used as fuel in the body. Some
nitrogenous food man obtains by eating the flesh of animals, and
some he obtains directly from plants (for example, peas and beans).

Fats and Oils. — Fats and oils, both animal and vegetable,
are the materials from which the body derives part of its
energy. The chemical formula of a fat shows that while it has
considerable carbon and hydrogen in its molecule, there is very
httle oxygen present; hence the great capacity of this sub-
stance for uniting with oxygen. A pound of butter releases
over twice as much energy to the body as does a pound of
sugar or a pound of steak. Human fatty tissue is formed in
part from fat in the food eaten, but carbohydrate or even protein
food may be changed into fat and may be stored in the body as
a reserve supply of fuel.

Carbohydrates. — The carbohydrates, like the fats, contain
carbon, hydrogen, and oxygen. Here, however, the oxygen
and hydrogen are united in the molecule in the same pro-
portion as are hydrogen and oxygen in water. Carbohydrates
are essentially energy-producing foods.

Vitamins. — Vitamins are not very well known but they have
been proved to be necessary for Hfe. They may be destroyed
easily by heat in some foods, as milk, and endure a great deal
of heat in others, as potatoes and tomatoes. Four or more vita-
mins have been identified : A, found in milk, butter, eggs, and
some vegetables, as spinach, carrots, and sweet potatoes ; B,
found in the outer layers of cereals, in most vegetables and fruits,
yeast, and milk ; C, found in some fruits and vegetables ; and D,
found in milk and certain green vegetables. The action of the

324

FOOD AND DIETARIES

^
5

^

/8'^DAY^

/H

^/ /8"'DAY

f

Days

The importance of vitamins. Two
groups of rats were fed ample rations
of protein, carbohydrate, fat, and mineral
salts, similar to those in milk. In addi-
tion a minute quantity of milk, contain-
ing the vitamin missing from the regular
rations, was given to group A only for
the first seventeen days, and to group
B only thereafter. What was the effect
upon growth, as shown by the average
weight?

fluids, and a sufficient

third vitamin, C, is partly
destroyed hy heat, so preserv-
ing and canning foods render
such foods less valuable as
givers of vitamins.

Just what service the vita-
mins do is unknown, but we
do know" that if om' diet does
not contain all of them, growth
will not take place and illness
or even death may follow.
Scm-vy, beriberi, and probably
rickets are due to the absence
of certain \dtamins.

Inorganic Foods. — Water
forms a large part of almost
every food substance. The
human body, by weight, is
about 65 per cent water.
Water forms a large part of
the blood and the digestive
quantity is essential to health.

Foods rich in ^atamins : "A" is contained in milk, butter, and eggs; "B," in
vegetables, oranges, whole- wheat bread, and milk ; " C," in oranges and fresh vege-
tables ; and " D," in milk and green vegetables.

When we drink water, we take with it some of the inorganic
salts used by the body in making bone and in the formation

NUTRIENTS

825

BREAD, (WATER)
" , (MILK)

" , wHQu wHEiT mm
" , " " otm-

BARLEY (WHOLE)

CORN, YELLOW

OATS

RYE, CRACKED

WHEAT, KERNEL
" , BRAN

LIVER

KIDNEY

BRAINS

HEART

FISH, FAT

•' , ROE

MILK, FRESH, (UIIFUTEIIRIZED)
" , CONDENSED
" , EVAPORATED

" , DRIED, mm- ■

" , SKIMMED •■

BUTTERMILK

CREAM

BUTTER

CHEESE

EGGS •

ALMONDS

COCONUT

HICKORY NUTS

PEANUTS

WALNUTS

"A"

+

+
++

■I-

+

+

+
++

+
++
++

+

+

+

4
+++
+++
+++
+++

+

+
+*+
+++
++
+++

+

+

+
*

+

++
++
++
++
++
++
+++
+++
+ +
++
++

+

■♦■

++
++
++
++
++

+
++
++

++
+
++?
++
++
++
+4-

"C"

+

+
9

++V

+v
?

+v
+v

4V
+V

+
+
+
+

+
++

+

TOMATO m 08 mm ■ •

BEANS, KIDNEY

" , NAVY

" , STRING

BEETS

CABBAGE, RAW

, CANNED
" , COOKED bhiefu
CARROT, RAW

" , COOKED
CAULIFLOWER
DANDELION GREENS
LETTUCE (GARDEN)
ONIONS

PARSNIP

PEAS, FRESH

POTATO (BOILED)

SWEET POTATO

RUTABAGA

SPINACH, FRESH

CANNED •

SQUASH

TURNIPS

APPLES

BANANAS

GRAPE JUICE

GRAPEFRUIT

LEMON JUICE

ORANGE JUICE
PINEAPPLE (UW Ofl CtNNED)
RASPBERRIES (UW OR CtNNEtl)
F'EACHES m OR CANKED) -

'A"

++

+
+
++

++

*

++
++
++

+

++
++

?

++

•f
++

+++
+++
++

+
?

7

+
++

++

'B-

+++

+++

+++

++

+

*
++

+

+

++
++
++
++
++
++
++

+
++
+++

+

?
++
++

+

+
+♦
++
+♦
++

*

+

"C"

+++

*

+

+
■f+4-
++

+

+
+V

7

+
+++
++

7
+++
++

7
+++
+++

4-i-i-

7

***

++

+

+

++

+++

+++

+++

+++

++

■contains the Vitamin
good source of the Vitamin
excellent source of the Vitamin
mm. ■ -no appreciable amount of the Vitamin

?• • doubt as to presence or relative
amount

*■ ■ evidence lacking or insufficient
V- • variable

Vitamins in foods. From the American Medical Association.

of protoplasm. Sodium chloride (table salt), an important part
of the blood, is taken as a flavoring upon our meats and vege-
tables. Phosphate of lime and potash are important factors in
the formation of bone.

Phosphorus is a necessary element for making protoplasm.
Milk, eggs, meat, whole wheat, and dried peas and beans con-
tain small amounts of it. Iron also is an extremely impor-
tant mineral, as it is used in the building of red blood cells.
Meats, eggs, peas, beans, spinach, and prunes are foods contain-
ing some iron.

326 FOOD AND DIETARIES

Some salts, compounds of calcium, magnesium, potassium,
and phosphorus, have been recently found to aid the body
in many of its most important functions. The beating of the
heart, the contraction of muscles, and action of the nerves
appear to be due to the presence of minute quantities of these
salts in the body.

Uses of Nutrients. — The following table sums up the uses
of nutrients to man:

All serve as fud

and yield energy in

► form of heat and

muscular strength.

Protein Forms tissue (muscles,

White (albumen) of eggs, curd tendon, and prob-
(casein) of milk, lean meat, ably fat),
gluten of wheat, etc.

Fats Form fatty tissue.

Fat of meat, butter, olive oil,
oils of corn and wheat, etc.

Carbohydrates Transformed into fat.

Sugar, starch, etc.

Vitamins • • • • Accessory substances of unknown com-
position that seem to be regulating and
growth promotiug. They are essential
to life.

Mineral matters (ash) .... Aid in forming bone.
Phosphates of lime, potash, assist in digestion, etc.
soda, etc.

Fuel Values of Nutrients. — In planning for the diet best
fitted for our daily requirements the food used for energy in
the body is stated in heat units called caVories. A calorie
(large calorie) is the amount of heat required to raise the temperature
of one kilogram of water one degree Centigrade. This is about
equivalent to raising one pound of water four degrees Fahrenheit.
The fuel value of different foods may be computed accurately by
burning a given portion (say one pound) in the apparatus known
as a calorim'eter.

The Best Diet. — Inasmuch as all 'living substance contains
nitrogen, it is evident that protein food must form a part of
the dietary; but protein alone will not support life. If more
protein is eaten than the body requires, immediately the liver
and kidneys have to work overtime to get rid of the excess of
protein which forms poisonous wastes.

THE BEST DIET 327

It has been found that a man who does muscular work requires
a Uttle less than one quarter of a pound of protein, the same
amount of fat, and about one pound of carbohydrate to provide
for the growth, waste, and repair of the body and the energy
used up in one day. Put in another way, Atwater's standard
for a man at light exercise is food enough to yield 2816 calories;
of these, 410 calories are from protein, 930 calories from fat,
and 1476 calories from carbohydrate. That is, for every 100
calories furnished by the food, 14 are from protein, 32 from
fat, and 54 from carbohydrate. In actual amount, the day's
ration as advocated by Atwater would contain about 100 grams
or 3.7 ounces protein, 100 grams or 3.7 ounces fat, and 360 grams
or 13 ounces carbohydrate. Professor Chittenden of Yale Univer-
sity, another food expert, thinks we need proteins, fats, and carbo-
hydrates in about the proportion of 1 to 3 to 6, thus differing
from Atwater in giving less protein in proportion. Chittenden's
standard for the same man is food to yield a total of 2360
calories, of which protein furnishes 236 calories, fat 708 calo-
ries, and carbohydrates 1416 calories. For every 100 calories fur-
nished by the food, 10 are from protein, 30 from fat, 60 from
carbohydrate. In actual amount the Chittenden diet would
contain 2.16 ounces protein, 2.83 ounces fat, and 13 ounces
carbohydrate.^ A German named Voit gives as ideal 25 proteins,
20 fat, 55 carbohydrate, out of every 100 calories; this is nearer
our actual daily ration. In addition, an ounce of salt and
nearly one hundred ounces of water containing the necessary
mineral salts, are used in a day.

In addition to this the diet must include foods containing
vitamins. By means of the table on the following page (from
Atwater ^), which shows the composition of some food mate-
rials, the nutritive and fuel value of the foods may be seen
at a glance. The amount of refuse contained in foods (such
as the bones of meat or fish, the exoskeleton of crustaceans
and moUusks, the woody coverings of plant cells) is also
shown in this table.

iPage 18, Bui. 6, Cornell Reading Course.

2 W. O. Atwater, Principles of Nutrition and Nutritive Value of Food, U.S.
Department of Agriculture.

328

FOOO AND DIETARIES

DIGESTIBLE NUTRIENTR

INDIGESTIBLE
NUTRIENTS

MUSCLE
MAKING

FATS CARBO- MINERAL
HYDRATE^ MATTERS

NON NUTRIENTS
WATER RKFtTRE

-~ FUEL VALUF
CALORIES

FUEL INGREDIENTS

NUTRIENTS. ETC.
PER CENT.

10

20

30

40

50

60

70

80

90

\oo

FUEL VALUE OF
1 LB. (calories) ,

400 800 1,200 2.000 2,200 2,400 2,800 3,200 3,600 4,000

'M Ife

B^

Milk,
■nnskiiruned

Butter

.mm&.M^;^;r. r Ife.-^-^"

White bread

IWgW

Oat meal

Com meal

Rice

^^

Beans

t

Potatoes

Sugar

Table of food values. Determine the percentage of water in codfish, loin of
beef, milk, potatoes. Percentage of refuse in leg of mutton, codfish, eggs, and
potatoes. What is the refuse in each case? Find three foods containing a high
percentage of protein; of fat; of carbohydrate. Find some food in which the
proportions of protein, fat, and carbohydrate are combined in the right proportions.

THE BEST DIET

829

Vat
sugar
%^protein
minerals

water

A Mixed Diet Best. — Knowing the proportion of the different
food substances required by a man and the ones containing the
vitamins, it will be an easy matter to determine from this
table the best foods for use in a mixed diet. Meats contain
so much nitrogen that they should be eaten with other foods. In
milk, the proportion of proteins, carbohydrates, and fats is
nearly right to make protoplasm; a consider-
able amount of mineral matter and at least
two of the vitamins being also present. For
these reasons, milk is extensively used as a
food for children. Why? Some vegetables
(for example, peas and beans) contain the
nitrogenous material needed for protoplasm
formation in considerable proportions, but in
a less digestible form than is found in some
other foods. A purely vegetable diet contains
much waste material, such as the cellulose
forming the walls of the plant cells, which is
indigestible. The Japanese army ration used
to consist almost entirely of rice. A recent
report by their surgeon-general intimates that the diminutive
stature of the Japanese may, in some part at least, have been
due to this diet. A mixed diet should contain all the nutri-
ents in a digestible form and not too much hard indigestible
material.

The Relation of Work to Diet. — It has been shown experi-
mentally that a man doing hard muscular work needs more
food than one doing light work. The mere exercise gives the
individual a hearty appetite; he eats more because he needs
more of all kinds of food than if he were doing light work. Es-
pecially is it true that the person of sedentary habits who gets
little exercise should be careful not to overeat and to eat food
that will digest easily. Protein food should also be reduced.
Rich and hearty foods may be left for the man who is doing hard
manual labor out of doors, who has a good digestion doubtless,
and needs the energy for extra work

The Relation of Environment to Diet. — We are all aware of
the fact that the body seems to crave heartier food in winter

HUNT- NEW &tf. — ^22

The composition
of a bottle of milk.
Why is milk consid-
ered a good food?

330

FOOD AND DIETARIES

Table showing the cost of various foods. Using this table, make up an economi-
cal dietary for one day, three meals, for a man doing moderate work. Give reasons
for the amount of food used and for your choice of foods. Make up another
dietary in the same manner, using expensive foods. What is the difference in your
bill for the day?

THE BEST DIET

331

than in summer. The temperature of the body is maintained
at 98 J ° in winter as in summer, although much more heat is
lost from the body in the cold weather. Hence in winter the
heat-producing foods should be increased to provide for a greater
supply of fuel and of energy because we exercise more in cold
weather. We may use carbohydrates for this purpose, as they
are economical and are digested more easily than fats. The
inhabitants of cold countries get their heat-releasing foods
largely from fats, because less plant food is produced there.
In tropical countries and in hot weather little protein should
be eaten and a considerable amount of fresh fruit should be used.
Food Economy. — The American people are far less economical
in their purchase of food than most other nations. Nearly one
half of the total income of the
average workingman is spent on
food. He spends a large amount
on food, partly because he wastes
money in purchasing expensive and
unnecessary foods. A comparison of
the daily diets of persons in vari-
ous occupations in this and other
countries shows that as a rule we
eat more than is requhed to sup- ^hree portions of food, each con-

ply the necessary amount for fuel taining the same amount of nourish -

and on repair, and that our work- ^^^ '

ingmen eat more than those' of other countries. Another waste
of money by the American is in the false notion that a large
proportion of the daily dietary should be meat. Many people
think that the most expensive cuts of meat are the most
nutritious. The falsity of this idea may be seen by a careful
study of the table on page 330, compiled by Atwater, which
shows the relative amount of various foods purchasable for 25
cents.

Daily Fuel Needs of the Body. — It has been pointed out
that the daily diet should differ widely according to age, occu-
pation, time of year, etc. A boy requires slightly more than a
girl. The following table shows the daily fuel needs for several
ages and occupations: —

332 FOOD AND DIETARIES

Daily Calorie Needs (Approximately)
Obs.

1. For child under 2 years 000 Calories

2. For child 2-5 years 1200 Calories

3. For child 6-9 years o 1500 Calories

4. For child 10-12 years 1800 Calories

5. For child 12-14 (woman, hght work also) 2100 Calories

6. For boy (12-14), girl (15-16), man sedentary .... 2400 Calories

7. For boy (15^16) (man, Hght muscular work) .... 2700 Calories

8. For man, moderately active muscular work 3000 Calories

9. For farmer (busy season) ......... 3200 to 4000 Calories

10. For ditchers, excavators, etc 4000 to 5000 Calories

11. For lumbermen, etc 5000 and more Calories

Normal Heat Output. — We know that different amounts of
energy are released by the body at different times and under
different conditions. The following table gives the result of
some experiments made to determine the hourly and daily
expenditure of energy of the average normal grown person when
asleep and awake, at work or at rest.

Average Normal Output of Heat from the Body

Conditions op Musctjlab Acttivitt

Man at rest, sleeping .

Man at rest, awake, sitting up

Man at Ught muscular exercise

Man at moderately active muscular exercise

Man at severe muscular exercise

Man at very severe muscular exercise . .

Average
Calories
PER Hour

65 Calories
100 Calories
170 Calories
290 Calories
450 Calories
600 Calories

It is very simple to use such a table in calculating the number
of calories which are spent in twenty-four hours under different
bodily conditions. For example, suppose the case of a clerk or
school-teacher leading a relatively inactive life, who

sleeps for 9 hours X 65 Calories = 585

works at desk 9 hours X 100 Calories = 900

reads, writes, or studies 4 hours X 100 Calories = 400

walks or does light exercise 2 hours ... X 170 Calories = 340

222d

FOOD WASTE IN THE KITCHEN 333

This comes out, as we see, very close to example 6 of the
table ^ on page 332.

How we may find whether we are eating a Properly Balanced
Diet. — We already know approximately our daily calorie
needs and about the proportion of protein, fat, and carbohydrate
required. Dr. Irving Fisher of Yale University has worked out
a very easy method of determining whether one is Hving on a
proper diet or not. He has made up a number of tables, parts
of which are shown on page 334,^ in which he has designated
portions of food, each portion furnishing 100 calories of energy.
The tables show the proportion of protein, fat, and carbohydrate
in each food, so that it is a simple matter by using such tables
to estimate the proportions of the various nutrients in our
dietary. We may rely with safety upon a diet based upon
either Atwater's, Chittenden's, or Voit's standard. From the
tables on page 334 make out a simple dietary for yourself, first
estimating your own needs in calories and then picking out 100
calorie portions of food which will give you the proper propor-
tions of protein, fat, and carbohydrate.

Food Waste in the Kitchen. — Much loss occurs in the im-
proper cooking of foods. Meats especially, when overdone, lose
much of their flavor and are far less easily digested than when
they are cooked properly. The chief reasons for cooking meats
are that the muscle fibers may be loosened and softened, in
which condition they are digested more easily, and that the
bacteria and other parasites in the meat may be killed by the
heat. The common method of frying makes foods difficult to
digest. A good way to prepare meat, either for stew or soup,
is to place the meat, cut in small pieces, in cold water, and
allow it to simmer for several hours. Rapid boiUng toughens
the muscle fibers just as the white of egg becomes solid when
heated. BoiHng and roasting are excellent methods of cooking
meat. In order to prevent the loss of the nutrients in roasting,
it is well to baste the meat frequently; thus a crust is formed
on the outer surface of the meat, which prevents the escape
of the juices from the inside.

^ The above tables and those which follow have been taken from the excellent
pamphlet of the Cornell Reading Course, No. 6, Human Nutrition*

334

FOOD AND DIETARIES

Tables of Food Values, Units and Weights

Wrich T

OF 100

Calories

C'aLoRIES 1'11RNI«HED By

Name of Food

Portion containing
100 Calories

Tiut.

Pat,

Carbo.

1. Vegetable

Ounces

Crackers

2 crackers

.9

10

20

70

Wheat Dread

Thick slice

L3

9

7

84

Corn meal

Cereal dish

.90

10

5

85

(Jatmeal

U" servings

5.G

18

7

75

Beans (baked)

Side dish

2.66

21

18

61

Rice

Cereal dish

3.1

10

1

89

Sugar

3 teaspoonfuls

.86

—

—

100

Potatoes (boiled)

1 large size

3.62

11

1

88

Cabbage

4 servings

11

20

8

72

Tomatoes

4 average servings

15.2

21

7

72

Lettuce

5 average servings

18

25

14

61

2. Animal

Beef (sirloin)

Small steak

1 +

31

69

—

Brisket

Ordinary serving

1.30

42

58

—

Mutton (leg)

Large serving

1.2

35

65

—

Pork (loin)

Small serving

.97

18

82

—

Ham

Ordinary serving

1.1

28

72

—

Veal (leg)

Large serving

2.4

73

27

—

Chicken

Large serving

3.2

79

21

—

Codfish

2 servings

4.9

95

5

—

Oysters

1 dozen

6.8

49

22

29

Lobster

2 servings

4.1

78

20

2

Eggs

1 large egg

2.1

32

68

—

3. Dairy products

Whole milk

Small glass

4.9

19

52

29

Buttermilk

1^ glasses

9.7

34

12

54

Butter

Small pat

0.44

0.5

99.5

—

Cheese (Amer.)

1| cubic inches

.77

25

73

2

4. Fruits, nuts, etc.

Bananas

1 large

3.5

5

5

90

Oranges

1 large

9.4

6

3

91

Watermelon

1 whole

27.0

6

6

88

Apples

2

7.3

3

7

90

Peanuts

13

.62

20

63

17

Chocolate

I square

.56

8

72

20

ADULTERATIONS IN FOODS 335

Vegetables are cooked in order that the cells containing starch
grains may be burst open. This allows the starch to be more
easily reached by the digestive fluids. Inasmuch as water
may dissolve out nutrients from vegetable tissues, it is best to
boil them rapidly in a small amount of water. This gives less
time for the solvent action to take place. Vegetables should be
cooked with the outer skin left on when it is possible.

Problem. To determine some forms of food adidterations.
{Laboratory Manual, Proh. XLIII; Laboratory Problems, Prob.
179.)

Adulterations in Foods. — The addition of some cheaper or
non-nutritious substance to a food, with the view to cheating
the purchaser, or the replacing of some of the nutritive sub-
stances with something less nutritious, is known as adulter-
ation. One of the commonest adulterations is the substitution
of grape sugar (glucose) for cane sugar. Most cheap candy is
adulterated thus. Flour and other cereal foods are sometimes
adulterated with some cheap substitutes, as bran or sawdust.
Coffee, cocoa, and spices have been in the past subject to great
adulteration; cottonseed oil is often substituted for olive oil;
oleomargarine has been too frequently sold for butter; while
honey, sirups of various kinds, cider and vinegar, have all
been found to be either artificially made from cheaper substi-
tutes or to contain such substitutes. Sausage may have a cheap
cereal substituted for meat in it.

Probably the food which suffers most from adulteration is
milk, as water can be added without the average person being
the wiser. By means of an inexpensive instrument known as
a lactom'eter, this cheat may easily be detected. In most cities,
the milk supply is carefully safeguarded, because of the danger
of spreading typhoid fever from impure milk. Milk was formerly
often treatei with preservatives which kill the bacteria in it
and prevent the milk from souring rapidly. Such preservatives,
as formaldehyde, are harmful to health.

Pure Food Law. — • Thanks to tlie National Pure Food Law
passed by Congress in 1906, and to the activity of various city
and state boards of health, the opportunity to pass adulterated

336 FOOD AND DIETARIEST

foods on the public is now greatly lessened. This law, which
does not work so well in the case of drugs and patent medicines,
has prevented adulteration of many articles by setting up
standards of purity for food products and by requiring proper
labels on all goods put up in packages, such as canned goods,
jams, jellies, etc. Thus we may at least know when we buy
adulterated or artificially colored foods. The law also requires
the inspection of all animal products shipped from one state
to another.

Impure Water. — Great danger comes from drinking impure
water. This subject has already been discussed under Bacteria,
where it was seen that the spread of typhoid fever in particular
is due to a contaminated water supply. As citizens we must
aid all legislation that will safeguard the water used by our
towns and cities. Boiling water for ten minutes or longer will
render it safe from all germs.

Stimulants. — We have learned that food is anything that
supplies building material or releases energy in the body; but
some materials used by man, presumably as food, do not come
under this head. Such are tea and coffee. When taken in
moderate quantities, they produce a temporary increase in the
vital activities of the person taking them, but they neither build
tissue nor release energy and hence are stimulants, not foods. Tea
and coffee when used in moderation often appear to be harm-
less to adults, but they are sometimes stimulating and a few
people cannot use either without ill effects, even in small quan-
tity. It is the habit formed by relying upon the stimulation
given by tea or coffee that makes them a danger to man. In
large amounts, they are undoubtedly injurious because of a
stimulant called caffeine (kaf'e-in) in coffee and the'ine in tea.
Cocoa and chocolate, although both contain a stimulant like
caffeine, are in addition good foods, having from 12 per cent
to 21 per cent of protein, from 29 per cent to 48 per cent fat,
and over 30 per cent carbohydrate in their composition.

Is Alcohol a Food? — The question of the use of alcohol has
been of late years a matter of absorbing interest and importance
among physiologists. A few years ago Dr. At water performed
a series of very careful experiments by means of the respiration

ALCOHOL 337

calorimeter, to ascertain whether alcohol is of use to the body-
as food or not. ^ In these experiments the subjects were given,
instead of their daily allotment of carbohydrates and fats,
enough alcohol to supply the same amount of energy that these
foods would have given. The amount was calculated to be
about two and one half ounces per day, about as much as
would be contained in a bottle of light wine.^ This alcohol was
administered in small doses six times during the day. Professor
Atwater's results may be summed up briefly as follows : —

1. The alcohol administered was almost all oxidized in the
body.

2. The potential energy in the alcohol was transformed into
heat or muscular work.

3. The body did about as well with the rations including
alcohol as it did without it.

The committee of fifty eminent men appointed to report on
the physiological aspects of the drink problem reported that a
large number of scientific men stated that they were in the habit
of taking alcoholic liquor in small quantities, and many reported
that they did not feel harm thereby. A number of scientists
seem to agree that when taken in small quantities alcohol may
be a kind of food, although a very poor kind.

On the other hand, we know that although alcohol may tech-
nically be considered as a food, it is very unsatisfactory and,
as the following statements show, it has a harmful effect on
the nervous system which foods do not have.

Alcohol a Poison. — A commonly accepted definition of a poison
is that it is any substance which, when taken into the body, tends
to cause the death or serious detriment to the health of the organism.
That alcohol may do this is well known by scientists. A
study of the causes of death in the vital statistics of state or
city shows a surprisingly large number of deaths from alcoholism,

^ Alcohol is made up of carbon, oxygen, and hydrogen. It is very easily
oxidized, but it cannot, as is shown by the chemical formula, be of uss to the
body in tissue building, because of its lack of nitrogen.

^ Alcoholic beverages contain the following proportions of alcohol : beer,
from 2 to 5 per cent; wine, from 8 to 20 per cent; liquors, from 30 to 70 per
cent. Patent medicises frequently contain as high as 45 per cent alcohol.
(See page 340.)

338 FOOD AND DIETARIES

in spite of the Eighteenth Amendment. And now that home-
made substitutes for the more carefully manufactured alcoholic
drinks are consumed b}" hundreds of thousands of lawbreakers,
the chances of alcoholic poisoning are very great.

Taken in small quantities alcohol acts as a quick stimulant.
In large quantities it is a narcotic and paralyzes the nervous
system.

But a more serious charge against alcohol is that it acts as
a habit-forming drug. People who '^ get the craving " unfor-
tunately cannot break away easily from the overwhelming
desire to drink. This habit results all too often in degradation
and death.

Dr. Kellogg, of the Battle Creek Sanitarium, points out that
strychnine, quinine, and many other drugs are oxidized in the
body, but sureh^ cannot be called foods. The following reasons
for not considering alcohol a food are taken from his writings : —

"1. A habitual user of alcohol has an intense craving for his accus-
tomed dram. Without it he is entirely unfitted for business. One never
experiences such an insane craving for bread, potatoes, or any other par-
ticular article of food.

" 2. By contmuous use the body acquires a tolerance for alcohol.
That is, the amount which may be imbibed and the amount required to
produce the characteristic ejBPects first experienced graduall}" increase
until veny great quantities are sometimes required to satisfy the craving
which its habitual use often produces. This is never the case with true
foods. . . . Alcohol behaves in this regard just as does opium or any other
drug. It has no resemblance to a food.

"3. When alcohol is withdra\\'n from a person who has been accus-
tomed to its dail}^ use, most distressing effects are experienced. . . . \Yho
ever saw a man's hand trembling or his nervous system unstrung because
he couLl not get a potato or a piece of cornbread for breakfast ? In this
respect, also, alcohol behaves like opium, cocaine, or any other enslav-
ing chug.

'' 4. Alcohol lessens the appreciation and the value of brain and nerve
activity, while food reenforces nervous and mental energy.

" 5. Alcohol as a protoplasmic poison lessens muscular power, whereas
food increases energy and endurance.

"6. Alcohol lessens the power to endure cold. This is true (o such a
marked degree that ils use by persons accoinpaiiyiiig Arctic expeditions
is absolutely j^roliibited. ImxxI, on the other lisiud, increases ability to
endure cold. The temperature after taking food is raised. After taking
alcohol, the temperature, as shown by the thermometer, is lowered.

TOBACCO

339

" 7. Alcohol cannot be stored in the body for future use, whereas all
food substances can be so stored.

" 8. Food burns slowly in the body, as it is required to satisfy the
body's needs. Alcohol is readily oxidized and eliminated, the same as
any other oxidizable drug."

The Use of Tobacco. — A well-known authority defines a nar-
cotic as a substance
'' wkich directly in-
duces sleep, blunts the
senses, and, in large
amounts, produces
complete insensibil-
ity." Tobacco, opium,
chloral, and cocaine
are examples of nar-
cotics. Tobacco owes
its narcotic influence
to a strong poison
known as nicotine,
the use of which in
killing insect parasites
on plants is well
known. In experi-
ments with jellyfish
and other lowly organized animals, the author has found as
small a quantity as one part of nicotine to one hundred thousand
parts of sea water to be sufficient to affect profoundly an animal
placed within it. The illustration here given shows its effect
upon a fish. Nicotine in a pure form is so powerful a poison
that two or three drops would be sufficient to cause the death
of a man by its action on the nervous system, especially the
nerves controlling the beating of the heart.

The action of tobacco is well known among boys training for
athletic contests. The heart is affected and boys become '' short-
winded " as a result. The brain becomes stupefied and incapa-
ble of doing its best work. It has been demonstrated that
tobacco has an important effect also on muscular development,
as shown by the stunted appearance of the young smoker.

Experiment (by Davison) to show how tobacco
affects the nervous system. The nicotine caught
in the water by passing through it the smoke from
six cigarettes, was sufficient to kill the fish in the jar.

340

FOOD AND DIETARIES

The West Point and Annapolis academies forbid the use of
tobacco, and college coaches insist that men training for the
teams shall not use it. Investigations made on college students
show that groups of smokers matched against non-smokers were
found to do poorer work in their studies, to graduate at a later
date, and to grow more slowly. The use of tobacco is asso-
ciated with lack of application and of ambition. The college
cigarette fiend is usually the college loafer.

There is very complete agreement among teachers of boys
below college age that the use of tobacco is very harmful and
should at least be left alone until the boy is full grown.

Problem, — A study of some medical frauds. (Laboratory
Manual, Prob. XLIV; Laboratory Problems, Probs. 180-183.)

Use and Abuse of Drugs. — The American people are ad-
dicted to the use of drugs and, especially, patent medicines. A

The amounts of alcohol in some liquors and in some patent medicines.
A, beer, 5%; B, elaret, 8%; C, champagne, 9%; D, whiskey, 50%; E, well-known sarsapa-
rilla, 18%; F, G, /f, much-advertised nerve tonics, 14%, 18%, 12%; 7, another much-adver-
tised earsaparilla, 18%; J, a well-known tonic, 14%; K, L, bitters, 20%, 25% alcohol.

glance at the street car advertisements shows this. Most of
the medicines advertised contain alcohol in greater quantity
than beer or wine, and many of them have opium, morphine,
or cocaine in their composition. These drugs, in addition to
being harmful, affect the person using them in such a manner
that he soon feels the need for the drug. Thus the drug habit
is formed, — a condition which has wrecked thousands of lives.

USE AND ABUSE OF DRUGS 841

The American Medical Association, by means of its publi-
cations, is doing a great work in showing the public some of
the frauds which are practiced by the patent medicine interests.
It is shown, for example, that most cough medicines (or, as they
used to be known, consumption cures) contain heroin or other
habit-forming drugs, or else alcohol enough to act as a " bracer '^
and thus delude the poor victim into thinking he is better. A
great number of the bitters or sarsaparillas contain enough
alcohol to make them sought after in these days of prohibi-
tion. Some patent medicines, especially those with trade names,
are simply fakes and the buyer pays $1.00 or more for materials
that could be purchased in the drug store for a few cents.

A good rule to observe with reference to patent medicines
is not to use any unless ordered to do so by a rehable physi-
cian. It is time that the thinking American pubKc should wake
to the fact that it is not only being cheated but also harmed
physically by the patent medicines of which it is so fond.

Summary. — Certain nutrients, organic or inorganic, form the
basis of aD. foods. The organic nutrients are carbohydrates,
fats or oils, proteins, and vitamins. The first two groups con-
tain the elements C, H, O — protein contains N also. Examples
of proteins are meats and eggs; of carbohydrates, cereals and
most vegetables; of fat, butter. There are also mineral salts
and mysterious substances known as vitamins which make up
an essential part of a dietary.

It has been determined that a mixed diet is necessary to sup-
port Hfe; besides a proportion of the organic nutrients, it must
contain inorganic salts as weU.

Problem Questions. — 1. What is a food?

2. What is a calorie? How is it determined?

3. What is a balanced diet? Give examples.

4. Why are certain vegetables included in a balanced diet ?

5. What are cheap foods? Expensive foods? Give examples.

6. What are the daily calorie needs and how are they
determined ?

7. Give some standards for a well-balanced diet.

8. What is a 100 calorie portion? Illustrate.

9. Describe the Pure Food Act of 1906.

342 FOOD AND DIETARIES

10. What is an adulterant? Is adulterated food always
harmful ?

11. Is alcohol a food? Is it a poison?

12. Why are patent medicines harmful?

Problem and Project References

Allen, Civics and Health. Ginn and Company.

Broadhurst, Home and Community Hygiene. J. B. Lippincott Company.
Bulletin 13, American School of Home Economics, Chicago.
Cornell University Reading Course, Bulletins 6 and 7, Human Nutrition,
Davison, The Human Body and Health. American Book Company
Fisher and Fisk, How to Live. Funk and Wagnalls.
Harrow, Vitamines. E. P. Button and Company.

Hunter, Laboratory Problems in Civic Biology. American Book Company.
Hunter and Whitman, Civic Science. American Book Company.
Lusk, Science of Nutrition. W. B. Saunders Company.
Nostrums j,nd Quackery. American Medical Association.
Rose, Feeding the Family. The Macmillan Company-
The Great American Fraud. American Medical Association.
Sharpe, A Laboratory Manual. American Book Company.
Stiles, Human Physiology. W. B. Saunders Company.

U.S. Dept. of Agriculture, Farmers' Bulletins No. 23, 34, 42, 85, 93, 121. 132.
142, 182, 249, 295, 298, 881, 903, and others (see list of titles).

XXV. DIGESTION AND ABSORPTION

Mouth

Tongue

ThroatL

Purpose of Digestion. — We have learned that the starch and
protein food of plants is formed in the leaves. A plant, how-
ever, is unable to make use of the food in this condition. Be-
fore it can be transported from one part of the plant body to
another, it is changed into
a soluble form. Much the
same condition exists in an-
imals. In order that food
may be of use to man, it
must be changed into a sol-
uble form that will allow
its passage through the walls
of the alimentary canal, or
food tube. Digestion consists
in the changing of foods from
an insoluble to a soluble form,
so that they may pass through
the walls of the alimentary
canal and become part of the
blood.

Gullet

Liver-

Oall

Bladder-

BileDuct

Pancrea^

Large

Intestine

Small
Intestine-

Appendlx^
Rectum

Problem, — &tudy of the
digestive system of a frog in
order better to understand that
of man. (Laboratory Manual,
Prob. XLV; Laboratory
Problems, Probs. 184 to 186.)

Alimentary Canal. — In
all vertebrate animals, including man, food is normally taken
in the mouth and passed through a food tube during the process
of digestion. This tube is composed of different portions, named,

343

Organs of Digestion.

344

DIGESTION AND ABSORPTION

respectively, as we pass from the mouth, posteriorly, the gullet,
stomach, and small and large intestine.

Glands. — In addition to the alimentary canal proper, we
find a number of digestive glands, varying in size and position

connected with the canal
As we have already
learned, a gland is a col-
lection of cells which
takes up materials from
the blood and pours them
out as a secretion. They
are like the nectar glands
of a flower.

Certain substances
called enzymes, formed by
glands, cause the digestion
of food. The enz^mies are
made in the cells of the
glands and poured out
with the fluid secretion
into the food tube, where
they act upon insoluble
foods and change them
to a soluble form.

Structure. — The walls
of the food tube are mus-
cular and composed of long fibers which run lengthwise and
small circular fibers passing Kke rings around the tube. The
contraction of these muscles is very important in regulating the
movement of the food. The entire inner surface of the food
tube is covered with a soft lining of mu'cous membrane. This
is always moist because certain cells, called mucus cells, empty
their contents into the food tube, thus lubricating its inner
surface. Where a large number of secreting cells are collected
together, the surface of the food tube becomes indented to form
a pitlike gland. Often such depressions are deep and branched,
thus giving a greater secreting surface, as is seen in the Figure.
The ceUs of the gland are always supplied with blood vessels and

Diagram of a gland: i, the common tube
which carries off the secretions formed in the
cells Uning the cavity c; a, arteries carrying
blood to the cells; v, veins taking blood
away from the cells.

THE DIGESTIVE SYSTEM

345

nerves, for the secretions of the glands are under the control of
the nervous system. Think of a sour pickle and note what
happens.

Attached to the digestive tract of man are found the salivary
glands in the walls of the mouth, gastric glands in the walls of
the stomach; the liver and the pan'creas, two large glands which
empty into the small intestine just below the stomach, and
intestinal glands in the walls of the intestine.

It will be the purpose of this chapter to follow the various
food substances as they pass through the food tube in order
to find how and where the changes take place in the various
nutrients which prepare them to become part of the blood.

Mouth Cavity in Man. — In our study of a frog we found
that the mouth cavity has two unpaired tubes and four ar-
ranged in pairs leading
from it. These are (a)
the gullet or food tube,
(b) the windpipe (in the
frog opening through the
glottis), (c) the paired
nostril holes (posterior
nacres), (d) the paired
Eustachian (ti-sta'-ki-an)
tubes, leading to the ear.
All of these openings are
found in man.

The roof of the mouth
is formed in front by a
plate of bone called the
hard palate, and in back by a softer continuation called
the soft palate, which separate the nose cavity from that of the
mouth. That part of the space back of the soft palate is called
the phar'ynx, or throat cavity, from which pass out the gullet and
the windpipe. The lower part of the mouth cavity is occupied
by a muscular tongue. Examination of its surface with a looking-
glass shows it to be almost covered in places by tiny projections
called papiVlce. These papillae contain organs known as taste buds,
the sensory endings through which we determine the taste of sub-

0UKT. NEW E8. 23

Mouth cavity of man.

346

DIGESTION AND ABSORPTION

stances. The tongue is used in moving food about in the
mouth, in starting it on its way to the gullet, and plays an
important part, as we know, in speaking.

The Teeth. — The thirty-two teeth of man are divided, ac-
cording to their functions, into four groups. In the center of

each jaw in front are found
four teeth with chisel-like
edges; these are the inci'sors,
or cutting teeth. On each end
of these groups is found a
single tooth, four in all, with

-rX 3 2^ rather sharp points; they are
i J i, l\yQ canines; look for them in
a cat or dog. Two teeth on
each side, back of these, eight
in all, are called premolars.
Lastty, beyond the premolars
are the flat-top inolars, or grind-
The teeth on the right side of both i^g teeth, of which there are

jaws: 1, 2, incisors; 3, canines; 4, 5, pre- gix in each jaw. Food is CaUght
molars; 6, 7, 8, flat-top molars. , . . -, • j •

between irregular projections
on the surface of the molars and crushed to a pulpy mass.

Care of the Teeth. — Form the habit earl}^ in hfe of brush-
ing the teeth upon getting up in the morning and just before
going to bed at night. A ver-
tical movement of the brush C^otr^-
should be used between the /\/gc/c
teeth so as to dislodge bits of
food caught there. The gums b^q*.,
should be brushed as well so
as to help the circulation of the

blood there. A weak acid tooth Longitudinal section of a tooth (a

wash, made of equal parts of flat-top molar).

vinegar and water, is helpful, as is a powder containing ground

pumice. Can you see the use of each of these?

Internal Structure of a Tooth. — If a tooth is cut lengthwise, it is found
to be hollow; this cavity, called the pulp cavity, corresponds to the cavity
containing marrow in bones. In life it contains living material — the blood

■Enamel

Dentine

Root canal or
nerve chamber

THE DIGESTIVE SYSTEM

347

vessels, nerves, and cells which build up the bony part of the tooth. The
bulk of the hard part of the tooth consists of a limy material called den-
tine (den'tin). Outside of this is a very hard substance called enamel;
this substance, the hardest in all the body, is thickest on the exposed
surface or crown of the tooth. Each tooth is held in its place in the
jawbone by a thin layer of bony substance called cement. :

Problem. — How foods are chemically prepared for absorp-
tion into the blood. (Laboratory Manual, Prob. XLVI; Labo-
ratory Problems, Probs. 187 to 193.)

(a) In the mouth.

(6) In the stomach.

(c) In the small intestine.

Salivary Glands. — We are all familiar with the substance
called saliva which acts as a lubricant in the mouth. Saliva is
manufactured in the cells of three pairs of glandS which empty
into the mouth, and which are called, according to their posi-
tion, the parot'id (under the ear),
the submaxillary (under the jaw-
bone), and the sublin'gvxil (under
the tongue).

Digestion of Starch. — If we
collect some saliva in a test tube,
add to it a little starch paste,
place the tube containing the
mixture for twenty minutes in
tepid water, and then test with
Fehling's solution, we shall find
grape sugar present. Careful tests
of the starch paste and of the
saliva made separately will usu-
ally show no grape sugar in either. Experiment showing non-osmosis

If another test be made for of starch and water in tube A and

grape =ugar, aftw starch paste, osmosis of sugar solution in tube B.
saliva, and a few drops of any weak acid have been mixed for
twenty minutes, the starch will be found not to have changed.
The digestion of starch to grape sugar is caused by the presence
in the saliva of an enzyme, or digestive ferment. You remem-
ber that starch in the growing corn grain was changed to grap^

348 DIGESTION AND ABSORPTION

sugar by an enzyme called diastase. Here the same action is
caused by an enzyme called ptyalin (tfa-lin). This ferment, as we
can prove, acts only in a slightly alkaline or neutral medium at
about the temperature of the body.

How Food is Swallowed. — After food has been chewed and
mixed with saUva, it is rolled into little balls and pushed by the
tongue into such position that the muscles of the throat cavity
may seize it and force it downward. Food, in order to reach
the gullet from, the mouth cavity, must pass over the glottis, the
opening into the windpipe or trachea. When food is in the course
of being swallowed, the upper part of this tube forms a trap-
door, called the epiglot'tis, over the opening. When this trap-
door is not closed, and food '' goes down the wrong way," we
choke, and the food is expelled by coughing.

The Gullet, or Esophagus. — In man this part of the food
tube is much longer proportionately than in the frog. Like the

rest of the food tube it is
lined by soft and moist
mucous membrane. The
wall is made up of two

Peristaltic waves in the gullet of man: h, bo- sets of muscles, — the in-
ius or little baU of food. • i • j

side ones runnmg around
the tube; the outer band of muscle taking a longitudinal course.
After food leaves the mouth cavity, it gets beyond our direct
control, and the muscles of the gullet, stimulated to activity by
the presence of food in the tube, push the food down to the
stomach by a series of penstaVtic contractions. The gullet passes
directly through a muscular partition, the diaphragm (di'a-
fram), which is lacking in the frog. The diaphragm sepa-
rates the heart and lungs from the other organs of the body
cavity.

Stomach. — The stomach is a pear-shaped organ capable of
holding about three pints. The end opposite to the gullet,
which empties into the small intestine, is provided with a
ring of muscle forming a valve called the pylo'rus.

Gastric Glands. — The inner wall of the stomach has long folds
which run lengthwise. Between the folds are tiny pits, or the
openings of the gastric glands which lie imbedded in the wall of

DIGESTION

349

isophagus-

PancreaticDuct

stomach and beginning of small intestine.

the stomach. The gastric' glands are little tubes, the lining of
which secretes the gastric juice, sl fluid which is poured into the
stomach to assist in the
digestion of food. This
fluid is largely water. It
is slightly acid in its chem-
ical reaction, containing
about 0.2 per cent free
hydrochloric acid. It also Bile Duct ^^
contains a very important
enzyme called pepsin, and
another less important one /«/-^5f;«^J
called rennin.

Action of Gastric Juice.
— If protein is treated
with artificial gastric juice
at the temperature of the

body, it will be found to become swollen and then gradually
to change to a substance which is soluble in water. Most

protein substances are insoluble
and contain amino-acids which
are separated by digestion. These
amino-acids are used in building
up the cells of the body and even-
tually become protoplasm.

One enzyme of gastric juice,
called rennin, curdles or coagu-
lates a protein found in milk;
after the milk is curdled, the pepsin
is able to act upon it. " Junket "
tablets, which contain rennin, are
used in the kitchen to cause this
change.

The hydrochloric acid found in
the gastric juice acts upon lime
and some other salts taken into the stomach with food,
dissolving them so that they may pass into the blood and even-
tually form the mineral part of bone or of other tissue.

Section through wall of the stom-
ach, much magnified: A, gastric
glands; B, muscular fibers.

350 DIGESTION AND ABSORPTION

Hormones and their Work. — The modern study of physiology
is fascinating because we are just beginning to find causes for
some of the conipUcated actions that go on in the body. Many
of the happenings, sucii as the secretion of gastric juice at a time
when it will do the most good (when food is in the stomach),
seems to be brought about by a substance formed in some of the
cells lining the walls of the stomach. This substance is one of a
group of mysterious regulative agents called hormones (hor'monz).
They are formed in groups of gland cells (the ductless glands)
or in cells scattered throughout other organs, as in the walls of
the stomach and intestine and in the pancreas and liver. The
secretions, however, reach the blood stream and are carried to
various parts of the body. The regulative action of different hor-
mones is undoubtedly the factor which causes growth of various
parts of the body and promotes the smooth running of a series of
events which take place, for example, in digestion. Here one
organ after another takes up the work of digesting its part of the
meal, the initiative to do this work at the right moment being
brought about by different hormones, which, at just the right
moment, call the gland cells to do their work.

Movements of the Stomach. — The stomach walls are mus-
cular and as soon as food reaches the stomach the action of
these muscles begins and keeps the food in constant motion.
Thus the food is gradually mixed with gastric juice and some
digestion takes place. These movements are of much use
in softening and breaking up the food and when it finally
leaves the stomach it is in a semi-fluid condition with few
large lumps of undigested matter. When food is thoroughly
acidulated by means of the gastric hydrochloric acid, the ring
of muscle around the pyloric end of the stomach relaxes and
little gushes of food are allowed to pass into the small intestine.
As soon as this acid substance strikes the walls of the small in-
testine a hormone made there is at once released into the blood,
and the liver and the pancreas are made to pour out their
digestive fluid.

The Pancreas. — The pancreas, a diffuse gland opening into
the small intestine just below the pylorus, is one of the most
important digestive glands of the body

DIGESTION

351

Starch added to artificial pancreatic fluid and kept at blood
heat is soon changed to sugar. Proteins, under the same con-
ditions, are separated into amino-acids. Fats, which so far have
been unchanged except to be melted by the heat of the body,
are changed by the action of the pancreas into a form which
can pass through the walls of the intestine. These changes are
brought about by means of three enzymes: amylop'sin, which
acts upon starches, trypsirij
which acts upon proteins, and
lip'ase or steap'sin, which acts
upon fats. Pancreatic fluid
also contains a milk-curdling
enzjnue. If we test pancreatic
fluid we find it strongly alka-
line in its reaction. If two
test tubes, one containing
olive oil and water, the other
olive oil, water, and a weak
solution of caustic soda, an
alkali, be shaken violently
and then allowed to stand,
the oil and water will quickly
separate, while the oil, caustic
soda, and water will remain
for some time in a milky
emulsion. Pancreatic fluid
similarly emulsifies fats and changes them into soft soaps and
fatty acids in which form they may be absorbed.

Liver. — The liver is the largest gland in the body. It is of
a deep red color. In man it hangs just below the diaphragm,
a little to the right side of the body. It is divided into three
lobes, between two of which is the gall bladder, a thin-walled
sac which holds the bile, a secretion of the liver. Bile is a
strongly alkaline fluid of golden brown color which becomes
green on exposure to the air. It reaches the intestine through
a common opening with the pancreatic fluid. Almost one quart
of bile is passed daily into the intestine.

Functions of Bile. — The same hormone which causes

Milk, a form of emulsion, as seen under
the microscope. The tat globules appear
in groups. In the circle one group is
highly magnified.

352 DIGESTION AND ABSORPTION

the secretion of pancreatic fluid also causes the flow of bile.
The most important function of bile seems to be assisting the
pancreatic juice to digest and absorb fats. If two funnels,,
each containing filter paper, one moistened with bile, and
the other dry, be filled with oil, the oil will be found to pass
through the moistened filter paper with much greater ease
than thi'ough the dry one. Bile is shghtly antiseptic and thus
may help prevent fermentation within the intestine b}^ keeping
down the growth of bacteria.

Formation of Glycogen. — Perhaps the most important func-
tion of the Uver is the formation of a material called gly'cogen,
or animal starch. A large amount of blood received by the liver
comes directly from the walls of the stomach and intestine,
so that the Uver normally contains about one fifth of all the
blood in the bod3^ This blood is very rich in food materials,
and from it the cells of the fiver take out materials necessar}^ to
form glycogen, which is then stored in the Hver. When food
which can be oxidized quickly is needed, the gh'cogen is
changed to sugar and carried off by the blood to the tissues
which require it, and there used for this purpose. Gl3T0gen is
also stored in the muscles, where it is oxidized to release energy
when the muscles are exercised.

Small Intestine. — The process of digestion is carried on not
only in the mouth and stomach, but also in the small intestine.
This organ is described on the following page, in connection
with absorption. In the waUs of the small intestine are numerous
small intestinal glands which pour their secretions into the tube
and assist the pancreatic fluid in digesting starch, protein, and
oils.

Problem. — A study to determine where and how digested foods
pass into the blood. (Laboratory Manual, Prob. XLVII; Labo-
ratory Problems, Probs. 194 to 197.)

The Absorption of Digested Food into the Blood. — The ob-
ject of digestion is to change foods from an insoluble to a
soluble form. This has been seen in the study of the action of
the various digestive fluids in the body, each of which aids in
dissolving solid foods, and, in case of the bile, actually assist-

ABSORPTION OF FOODS

353

ing them to pass through the walls of the intestine. A small
amount of digested food is absorbed by the blood in the walls
of the stomach. Most of the absorption, however, takes place
through the walls of the small intestine.

Structure of the Small Intestine. — The small intestine in man
is a slender tube nearly twenty feet in length and about one
inch in diameter. Its walls contain muscles which, by a series
of slow waves of contraction, force the material within gradually
toward the posterior end. The
peristaltic movements of the mus-
cles of the coats are of very great
importance in the process of ab-
sorption, and these movements
are caused to a great extent (as is
the secretion of the various glands
of the digestive system) by the
mechanical stimulus of the food
within the food tube. As one
function of the small intestine is
absorption, we must look for
adaptations which increase the
absorbing surface of the tube.

This is gained in part by the diagram of a bit of the wall of
inner surface of the tube being the small intestine, greatly magni-
,1 • X X r 1 J fied. a, mouths of . intestinal

thrown mto transverse folds ^^^^^^. ^^ ^^^ ^^^ lengthwise to
which not only retard the rapid- show blood vessels and lacteal
ity with which food passes down bmnchTs^'to'oth^r !Sih!'\\ kTtes??

the intestine, but also give more nal glands; m, artery; V, vein;
1 1 • r; T) 4. r I, t, muscular coats of intestine

absorbmg suriace. But tar more ^^^

important for absorption are

millions of little projections called villi (singular, villus), which

cover the inner surface of the small intestine.

The Villi. — So numerous are these projections that the whole
surface presents a velvety appearance. The villi form the chief
organs of absorption in the intestine, several thousand being
distributed over every square inch of surface. By means of
the folds and the villi the small intestine is estimated to have
an absorbing surface equal to twice that of the surface of the

354

DIGESTION AND ABSORPTION

arm

body. The internal structure of a villus is best seen in a longi-
tudinal section. The outer wall is made up of a thin layer of
cells which absorb the digested food from within the intestine.
Underneath these cells Hes a network of very tiny blood ves-
sels, while inside of these, occupying the core of the villus, are
found spaces which, because of their white appearance after
the absorption of fats, have been called lac'teals.

Absorption of Foods. — Food substances in solution pass by
osmosis into the cells Hning the villi. These cells are alive, and

therefore have the power of selecting
certain substances and rejecting others.
Once within the villi, the sugars and
digested proteins pass through tiny blood
vessels into larger vessels comprising the
portal circulation. These pass to the
liver, where, as we have seen, sugar is
taken from the blood and stored as
glycogen. From fche liver, the food in
the blood is carried to the heart, from
there is pumped to the lungs, returns
to the heart, and is pumped to the
tissues of the body. A large amount
of water and some salts also are ab-
sorbed through the walls of the stomach
and intestine. The fats in the form
of soaps and fatty acids pass into the
cells Uning the walls of the villi but
are immediately changed back to fats,
Diagram to show how the in which form they are found in the

nutrients reach the blood. ^^^^^^^ ^^^^^^ ^.^j^-^^ ^^^ ^.jlj^ ^Sits

eventually reach the blood by way of the thoracic duct without
passing through the liver.

Large Intestine. — The large intestine has somewhat the
same structure as the small intestine, except that the diameter
is greater and it has no villi. Considerable absorption, how-
ever, takes place through its walls as the mass of food and
refuse material is slowly pushed along by the muscular walls.

In this portion of the intestine live millions of bacteria.

HYGIENIC HABITS OF EATING 355

some of which manufacture poisonous substances from the
foods on which they Hve. These substances are easily ab-
sorbed through the walls of the large intestine, and passing
into the blood, cause headaches or sometimes serious trouble.
Hence it follows that the lower bowel should be emptied of
this matter at least once a day. Constipation is one of the
serious evils the American people have to deal with, and it is
largely brought about by the artificial life which they lead, with
its lack of sufficient exercise, fresh air, and sleep.

Vermiform Appendix. — At the point where the small in-
testine widens to form the large intestine, a baglike pouch is
formed. From one side of this pouch is given off a small
tube about four inches long, closed at the lower end. This
tube, the function of which in man is unknown, is called the
vermiform appendix. It has come to have unpleasant noto-
riety in late years, as the seat of serious inflammation. It
often becomes necessary to remove the appendix in order to
prevent this inflammation from spreading to the surrounding
tissues.

Hygienic Habits of Eating; the Causes and Prevention of
Dyspepsia. — From the contents of the foregoing chapter it
is evident that the object of the process of digestion is to break
up solid food so that it may be absorbed to form part of the
blood. Any habits we may form of thoroughly chewing our
food will aid in this process. Much of the distress known as
dyspepsia is due to eating too rapidly with consequent lack of
proper mastication of food. The message of Horace Fletcher in
bringing before us the need of proper mastication of food and
the attendant evils of overeating is one which we cannot afford
to ignore. It is a good rule to go away from the table feeling
hungry. Eating too much overtaxes the digestive organs and
prevents their working to the best advantage. Still another
cause of dyspepsia is eating when in a fatigued condition. It
is always a good plan to rest a short time before eating, es-
pecially after any hard manual work. Eating between meals
is also condemned by physicians because it calls the blood to
the digestive organs at a time when it should be in other parts
of the body.

356 DIGESTION AND ABSORPTION

Effect of Alcohol on Digestion. — It is a well-known fact
that alcohol extracts water from tissues with which it is in con-
tact. This fact works much harm to the interior surface of
the food tube, especially the walls of the stomach, which in
the case of a hard drinker are likely to become irritated and
much toughened. In small amounts alcohol stimulates the se-
cretion of the salivary and gastric glands, and thus seems to
aid in digestion. It is doubtful, however, whether this aid is
real.

Experiments on dogs performed by Chittenden show that
alcohol retards digestion. He fed dogs on meat with water and
then on meat with very dilute alcohol. The meat with alcohol
took on the average about 25 minutes longer to digest.

Summary. — The organs of digestion form a tube, the walls
of which are lined with digestive glands. Muscles are also
found in the walls of the food tube; they cause an almost
constant churning movement in the stomac/ , and are also re-
sponsible for the movements known as peristalsis in the small
intestine.

Digestion is a process which causes insoluble food to pass
through a series of changes so that it becomes simpler in struc-
ture and will pass through the walls of the food tube. Diges-
tion is brought about by the action of various enzymes, each
of which acts upon a given substance.

Absorption takes place largely in the small intestine, where
many fingerlike projections called villi take up the various food
substances and pass them into the blood. Fats are not taken
directly into the blood but are first passed through tubes called
the ladeals. Eventually they reach the blood througli the
thoracic duct.

Problem Questions. — 1. How is digestion brought about?

2. What is an enzyme? How is it made? Name some
enzymes and give their functions.

3. Discuss the teeth as to function, structure, and care.

4. What is the function of the tongue in digestion? of the
salivary glands?

5. What are the functions of the stomach? How are they
accomplished?

DIGESTION 357

6. What are hormones and what do they do?

7. Why is the pancreas considered the most important di-
gestive gland?

8. What is glycogen and where is it made?

9. How and where is food absorbed?

10. What effect does alcohol have on digestion?

Problem and Peoject References

Burton-Opitz, A Textbook of Physiology. W. B. Saunders Company.

Howell, Human Physiology.

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Hunter and Whitman, Civic Science. American Book Company.

Martin, Human Body. Henry Holt and Company.

Starling, Principles of Human Physiology. Lea and Febiger.

Sharpe, A Laboratory Manual. American Book Company,

Stiles, Nutritional Physiology. W. B. Saunders Company.

XXVI. THE BLOOD AND ITS CIRCULATION

Problem. To study the composition of the blood. (Labora-
tory Maniml, Prob. XLVIII; Laboratory Problems, Probs.
198 to 200.)

Functions of the Blood. — The chief function of the digestive
tract is to change insoluble foods to such form that they can be
absorbed through the walls of the food tube and become part of
the blood. The blood in turn carries these foods in solution to
the cells of the body and removes waste materials from them.
It supplies tissues with oxygen and removes carbon dioxide.
Heat produced by the oxidation of foods is carried by the blood
from the internal organs to the surface of the body, where it is
given off. Thus the blood regulates the temperature in dif-
ferent parts of the body.

In addition to these important uses the blood carries two kinds
of substances of vital importance to the body, the hormones or
regulative substances already spoken of, and the various anti-
bodies or disease-resisting substances manufactured by the
blood, as the agglu'tinins, precip'itins and hcemoly'sins.

If we examine under the microscope a drop of blood taken
from the frog or man, we find it made up of a fluid called
plasma and two kinds of bodies, the so-called red corpuscles
and colorless corpuscles, floating in this plasma.

Composition of Plasma. — The plasma of human blood (when
chemically examined) is found to be about 90 per cent water.
It contains also amino-acids, some sugar, fat, and mineral
material. It is, then, the medium which holds the fluid
food that has been absorbed from within the intestine. When
the blood returns from the tissues where the food is oxi-
dized, the plasma brings back with it to the lungs most of
the carbon dioxide liberated when oxidation took place. Blood
returning from the tissues of the body has from 45 to 50 c.c

§58

COMPOSITION OF THE BLOOD

359

of carbon dioxide to every 100 c.c. (See Chapter XXVII.)
Fibrin' ogen and some waste products to be spoken of later,
are also found in the plasma. It also contains the hormones
and the antibodies.

Suggested Experiment : Clotting of Blood. — If fresh beef blood is al-
lowed to stand over night, it will be found to have separated into two parts,
a dark red, almost solid clot and a thin, straw-colored liquid called serum.
Serum is made up of about 90 per cent water, 8 to 9 per cent protein, and
from 1 to 2 per cent sugars, fats, and mineral matter. In these respects it
very closely resembles the fluid food that is absorbed from the intestines.

If another jar of fresh beef blood is poured into a pan and briskly
whipped with a bundle of little rods (or with an egg beater), a stringy
substance will be found to stick to the rods. This, if washed carefully, is
seen to be almost colorless. Tested with nitric acid and amimonia, it is
found to contain a protein substance called fibrin.

Blood plasma, then, is made up of serum, a colorless fluid,
and fibrinogen, or the fibrin in a fluid state. Under abnormal
conditions, such as removal from the blood vessels, a compH-
cated series of changes is started which ends with the formation
of the tiny threads of fibrin in the blood, and the subsequent
formation of a clot. A clot is simply a mass of fibrin threads
with a large number of corpuscles tangled within. The clotting
of blood is of great physiological importance, as it checks the
flow of blood; otherwise we might bleed to death from the
smallest wound.

In blood within the circulatory system of the body, the fibrin
is in the fluid form called fibrinogen.
An enzyme, acting upon this fibrin-
ogen under certain conditions, causes
it to change to an insoluble form,
the fibrin of the clot.

The Red Blood Corpuscle; its
Structure and Functions. — The red
corpuscle in the blood of the frog is
a true cell of disk-like form. The
red corpuscle of man, however, lacks
a nucleus. Its form is that of a biconcave disk. So small and
so numerous are these corpuscles that over five million are found
in a drop of normal blood.

Human blood, highly magnified.

360

THE BLOOD AND ITS CIRCULATION

The color, which is found to be a dirty yellow when separate
corpuscles are viewed under the microscope, is due to a protein
material called hmrnoglo'bin. Haemoglobin contains a large
amount of iron. It has the power of uniting very readily with
oxygen whenever that gas is abundant, and of giving it up
to the surrounding media when oxygen is present in smaller
amounts than in the corpuscle. This carrying of oxygen is the
most important function of the red corpuscle, although the red
corpuscle removes part of the carbon dioxide also from the
tissues on its return to the lungs. The taking up of oxygen is
accompanied by a change in color of the mass of corpuscles
from a dull red to a bright scarlet. The red corpuscles arise
as small cells in the red marrow of the living bones but soon

lose their nuclei and are
passed into the blood
stream. After they are
worn out it is believed
»T7 that they are destroyed in
the spleen and liver.

The Colorless Corpuscle;
Structure and Functions.
— A colorless corpuscle is

Colorless corpuscles v in the tissues outside ^ ^^^^ irregular in Outline,
the blood vessels. A, small artery; C, capil- the shape of which is COn-
laries; V, small vein. Highly magnified. j. j.i x^ • rpiu

stantly changmg. these
corpuscles are somewhat larger than the red corpuscles, but less
numerous, there being about one colorless corpuscle to every
seven hundred red ones. The colorless corpuscles have the power
of movement, and can work their way between the cells in the
walls of the blood vessels and wander into the tissues outside.
There appear to be several varieties of colorless corpuscles; some
are made in the lymph glands and others in the red marrow
of bone. Their ultimate fate is uncertain, except in the case
described in the next paragraph.

A Russian zoologist, Metschnikoff, after studying a number
of simple animals, such as medusse and sponges, found that in
such animals some of the cells lining the inside of the food
cavity take up or ingulf minute bits of food just as amoebae do.

COMPOSITION OF THE BLOOD

361

Later, this food is changed into the protoplasm of the cell.
Metschnikoff beheved that the colorless corpuscles of, the blood
have somewhat the same function, and he later proved this to
be true. Like the cells in the simple animals, the colorless
corpuscles feed by ingulfing their prey. This fact has a
very important bearing on the relation of colorless corpuscles
to certain diseases caused by bacteria within the body. If,
for example, a cut becomes infected by bacteria, inflammation
may set in. Colorless corpuscles at once surround the spot
and attack the bacteria. It has been
found, however, that bacteria are not
"' eaten " until they" are first bathed
with a chemical substance known as an
op'sonin. The presence of these op-
sonins in the blood makes the bacte-
ria attractive. If the bacteria are few
in number, they are quickly destroyed
by the colorless corpuscles, which are
known as phag'ocytes. If bacteria are
present in great quantities, they may
prevail and kill the phagoc3^tes by
poisoning them. The dead bodies of
the phagocytes thus killed are found
in the pus which accumulates in in-
fected wounds. In case of a possible
infection we must come to the aid of A colorless corpuscle A ingulf-
the colorless corpuscles by washing the ^^^ germs .

wound with some suitable antiseptic, as hydrogen peroxide.
The Disease-resisting Mechanism of the Blood. — It is
common knowledge that some of us ^' take " catching or in-
fectious diseases more easily than others. Some fortunate
people are immune to certain diseases or do not take them at
all. Such immunity is brought about by the blood when a cer-
tain substance is present in it and attacks and destroys bacteria
by chemical action or by the work of the colorless corpuscles.
This is an extremely complicated process which is probably
caused by different substances which act specifically upon differ-
ent kinds of bacteria. Just as each disease is caused by a

HUNT. NEW ES. — 24

362 THE BLOOD AND ITS CIRCULATION

specific kind of germ, producing a specific kind of poison, so
the blood appears to produce specific antibodies to fight these
specific germs.

The Amount of Blood and its Distribution. — Blood forms,
by weight, about one thirteenth of the human bod}-. Its dis-
tribution varies somewhat according to the position assumed by
the bod}^ and the amount of undigested food in the stomach
and intestines. Normally, about one half of the blood of the
body is found in or near the organs l3'ing in the body cavity,
about one fourth in the muscles, and the rest in the heart, lungs,
large arteries, and veins.

Blood Temperature. — The temperatm'e of blood in the human
body is normall}^ about 98.5° Fahrenheit, although the temper-
ature drops almost two degrees after we have gone to sleep at
night. It is highest about 5 p.m. and lowest about 4 a.m. In
fevers, the temperature of the bod}^ sometimes rises to 107° or
higher; but unless this temperature is soon reduced, death fol-
lows. Any considerable drop in temperature below the normal
also would mean death. Body heat, as we know, results from
the oxidation of food; the constant circulation of blood keeps
the temperature nearly uniform in all parts of the body. The
bod}^ temperature may be from two to three degrees higher im-
mediately after violent exercise. Wh}-?

Cold-blooded Animals. — In animals which are called cold-
blooded, the blood has no fixed temperature, but varies with the
temperature of the medium in which the animals live. Frogs,
in the summer, may sit for hours in water with a temperature
of almost 100°. In winter, they often endure freezing so that
the blood and hnnph within the spaces under the loose skin are
frozen into ice crystals. Such frogs, if thawed out carefully,
will live. This change in bod}^ temperature is evidently an
adaptation to the mode of life.

Circulation of the Blood in Man. — The blood is the carrying
agent of the body, and conveys materials from one part of the
human organism to another. This it does by means of the
organs of circulation — the heart and the blood vessels. The
blood vessels include arteries which carry blood away from the
heaxt, veins which bring blood back to the heart, and capillaries

THE HEART

363

which connect the arteries with the veins. The organs of circu-
lation thus form a system of connected tubes through which
the blood flows in a continuous stream.

The Heart; Position, Size, Protection. — The heart is a
cone-shaped muscular organ about the size of the fist. It is
located immediately above the diaphragm, and hes so that the
muscular apex which points down-
ward, moves while beating against the
fifth and sixth ribs, just a little to the
left of the midhne of the body. This
fact gives rise to the notion that the
heart is on the left side of the body.
The heart is surrounded by a loose
membranous bag called the pericar-
dium, the inner lining of which secretes
a fluid which surrounds the heart.
When, for any reason, the pericardial
fluid is not secreted, inflammation
arises in that region. Do you know

why? Diagram showing the front

T 2. 10X X £ ja. -rr ± ^3,lf of the heart cut away:

Internal Structure of the Heart.— ^^ ^orta; l, pulmonary ar-

If we should cut open the heart of a terfes; la, left auricle; Iv, left

mammal down the midhne, we could open?' n.' Wcus^d'Tr'^ mHml
divide it into a right and a left side, valve closed; p and r, puimo-
and show that each side has no internal ^^'rigirventrideTt! Tvet^

connection with the other. Each side cavae. Arrows show direction
J /. ,1 . n -I ,. ..1 of circulation.

IS made up oi a tmn-wailed portion with

a rather large internal cavity, the auricle, and a smaller chamber
with heavy muscular walls, called the ventricle. The auricles
occupy the base of the cone-shaped heart; the ventricles, the
apex. Communication between auricles and ventricles is regu-
lated by little flaps of muscle called valves. The auricles receive
blood from the veins and pass it on to the ventricles. The
ventricles pump the blood into the arteries. From the left ven-
tricle out through the aor'ta blood passes to all parts of the
body. From the right ventricle the puVmonary arteries carry
blood to the lungs. The openings to the arteries are guarded
by three haK-moon-shaped flaps, which open so as to allow

364

THE BLOOD AND ITS CIRCULATION

blood to pass away from the ventricle, and close to prevent
itG going back when the muscles relax.

The Heart in Action. — The heart is constructed on the same
plan as a force pump, the valves preventing the rehux of
blood into the auricles after it is forced out of the ventricles.
Blood enters the auricles from the veins because the muscles
of that part of the heart relax; this allows the space within
the auricles to fill. Almost immediately the muscles of the

ventricles relax, thus
allowing blood to pass
into the chambers
within the ventricles.
Then, after a short
pause, during which
time the muscles of the
heart are resting, a
wave of muscular con-
traction begins in the
auricles and ends in
the ventricles, with a
sudden strong contrac-
tion which forces the
blood out into the ar-
teries. Blood is kept
from flowing b a c k-
wards by the valves,
and is thus forced to pass into the arteries upon the contrac-
tion of ventricle walls.

The Course of the Blood in the Body. — Although the two
sides of the heart are separate and distinct from each other,
yet every drop of blood that passes through the right heart soon
passes also through the left heart. There are two distinct
systems of circulation in the body. The 'pulmonary circulation
takes the blood through the right auricle and right ventricle,
to the lungs, and passes it back to the left auricle. This is
a relatively short circulation, in which the blood receives oxy-
gen in the lungs and gives up its carbon dioxide. The greater
circulation is known a3 the system'i^ circulation; in this system

The heart is a force pump; prove it from these
diaorrams.

CIRCULATION OF THE BLOOD

365

the blood leaves the left ventricle through the great dorsal
aorta. A large part of the blood passes directly to the muscles;
some of it goes to the nervous system, kidneys, skin, and other
organs of the body. It gives up food and oxygen, and receives
the waste products of oxidation while passing through the capil-
laries, and then returns to the right auricle through two large
vessels known as the verm cavce.

It requires from twenty to Capimrm

thirty seconds only for the
blood to make the complete
circulation from the ventricle
back again to the starting
point. This means that the
entire volume of blood in the
human body passes three or
four thousand times a day
through the various organs of
the body.

Portal Circulation. — Some of the
blood, on its return to the heart,
passes by an indirect path to the
walls of the food tube, absorbs food,
and goes to the liver. Here the veins
which carry the blood (called the
portal veins) break up into capil-
laries around the cells of the liver.
We have already learned that tlie
Uver is a great storehouse of animal
sugar called glycogen. This glycogen
is a food that may be easily oxidized
to release energy, and is stored for
that purpose. The sugar that be-
comes glycogen is carried to the liver
directly from the walls of the stom-
ach and intestine, where it has been
absorbed from the food there con-
tained. From the liver, blood passes
directly to the right auricle. The portal circulation consists of three veins
which carry blood from the stomach and intestine to the liver, and is the
only part of the circulation where the blood passes through two sets of
capillaries, before going to the heart — one set in the walls of the stomach
and intestine, and the other in the liver.

Capillaries

Diagram of the circulation of blood in a
mammal.

366

THE BLOOD AND ITS CIRCULATION

Capillary circulation in the web of a
frog's foot, as seen under the com-
pound microscope.

Problem. — A study of the circulation of the blood. (Labora-
tory Manual, Prob. XLIX; Laboratory Problems, Probs. 201
to 206.)

Circulation in the Web of a Frog*s Foot. — If the web of
the foot of a hve frog or the tail of a tadpole is examined under

the compound microscope, a
network of blood vessels will be
seen. In some of these the cor-
puscles are moving rapidly and
in spurts; these are arteries.
The arteries lead into a network
of smaller vessels or capillaries
hardly greater in diameter than
the width of a single corpuscle.
The capillaries unite into larger
veins in which the blood moves
regularl}^ This illustrates the
condition in any tissue of man
where the arteries break up into capillaries which unite to form
veins.

Structure of the Arteries. — A distinct difference in structure
exists between the arteries and the veins in the human bod}^
The arteries, because of the greater strain received from the
blood which is pumped from the heart, have thicker muscu-
lar walls, and in addition are very elastic.

Cause of the Pulse. — The pulse, which can easily be detected by press-
ing the large artery in the wrist or the small one in front of and above the
external ear, is caused by the gushing of blood through the arteries after
each pulsation of the heart. As the large arteries pass away from the
heart, and divide, the diameter of each artery becomes smaller. At the very
end of their course, these arteries are so small as to be almost microscopic
in size and are very niunerous. There are so many that if they were
placed together, side by side, their united diameter would be much greater
than the diameter of the large artery (aorta) which passes blood from the
left side of the heart. This fact is of very great importance, for the force
of the blood as it gushes through the arteries becomes very much less when
it reaches the smaller vessels. This gushing movement is quite lost when
the capillaries are reached, first, because there is so much more space for
the blood to fill, and secondly, because there is considerable friction caused
by the very tiny diameter of the capillaries.

CIRCULATION OF THE BLOOD

367

Capillaries. — The capillaries form a network of minute
tubes everywhere in the body, but especially near the surface
and in the lungs. It is through their walls that the food and
oxygen pass to the tissues, and carbon dioxide is given up to
the plasma. They form the connection between arteries and
veins that completes the system of circulation of blood in the body.

Function and Structure of the Veins. — If the arteries are
supply pipes which convey fluid food to the tissues, then the

Artery

Valves in a
vein. Notice
the thin walls
of the vein.

Cells of lining^
membrdne

Muscle and -
elastic tissue

Cells of lining
membrane

Muscle and
elastic tissue

Cross section of artery and vein.

veins may be likened to drain pipes which carry away waste
material from the tissues. Very numerous in the extrem-
ities and in the muscles and among other tissues of the
body, they, like the branches of a tree, become larger as they
unite with each othe;:* on their way back to the heart.

If the wall of a vein is carefully examined, it will be found to
be neither so thick nor so tough as an artery wall. When
empty, a vein collapses; the wall of an artery holds its shape.
If you hold your hand down for a little time and then examine

368 THE BLOOD AND ITS CIRCULATION

it, you win find that the veins, which are relatively much nearer
the surface than are the arteries, appear to be very much
knotted. This appearance is due to the presence of tiny valves
within the veins. These valves open in the direction of the
blood cm-rent, but would close if the direction of the blood
flow should be reversed (as in case a deep cut severed a vein).
As the pressure of blood is much less in the veins than in the
arteries, the valves aid in keeping the flow of blood in the veins
toward the heart. The higher pressure in the arteries and the
suction in the veins (caused by the enlargement of the chest
cavity in breathing) are the chief factors which cause a steady
flow of blood through the veins in the body.

Problem. To study some changes in the composition of the
blood. (Laboratory Manital, Prob. L; Laboratory Problems ^
Prob. 197.)

The Ductless Glands and their Secretions. — One of the

greatest discoveries of modern physiology is that many groups
of gland cells give off to the blood internal secretions that play
extremely important parts in the Hfe of man. Such glands are
the suprare'nal bodies located just above the kidneys, the thy'-
roid and parathy'roid glands in the neck, certain cells of the
reproductive organs, and probably various other glands such
as the pancreas and hver. An example of the lack of some
internal secretions is seen in cre'tinism, a kind of idiocy.
Here it is found that the disease is caused by a lack of
internal secretions from the thjroid gland. If extracts of
sheep's thyroid are fed to children who show cretinism they
soon recover their normal condition. The suprarenal glands
throw into the blood substances which act as an emergency
hormone and stimulate the body to increased activity when
this is necessary. An abnormal condition of the suprare-
nals brings about a disease known as Addison's disease. The
gland cells of the reproductive organs give the characteristics
to the body which mark the differences in voice, average
height and weight, etc., between boys and girls. Our knowledge
of the work of the ductless glands is just beginning and future
study will doubtless answer many interesting questions.

CHANGES IN COMPOSITION OF BLOOD 369

Function of Lymph. — Different tissues and organs of the.
body are traversed by a network of tubes which carry the
blood. Inside these tubes is the blood, consisting of a fluid
plasma, the colorless corpuscles, and the red corpuscles. Out-
side the blood tubes, in spaces between the cells which form
tissues, is found another fluid, which is in chemical composi-
tion very much Uke plasma of the blood. This is the lymph.
It is, in fact, fluid food in which some colorless amoeboid cor-
puscles are found. Blood gives up its food material to the
lymph by passing it through the walls of the capillaries. The
lymph surrounds the tissue cells and suppHes them with food.

Some of the colorless

VESSEL- /j

CORPUSCLES K

corpuscles from the blood
make their way out be-
tween the cells forming
the walls of the capilla-
ries, and enter the lymph.
Lymph, then, is practically
blood plasma plus some
colorless corpuscles. It acts
as the medium of exchange

between the blood proper Diagram showing the exchange between blood

and the cells in the tissues ^^^ *^^ ^^^^^ °^ *^^ ^°^y-

of the body. The food supply thus brought enables the ceUs of
the body to grow, the fluid food being changed to the proto-
plasm of the cells. By means of the oxygen passed over by
the lymph, oxidation may take place within the cells. Lymph
not only gives food to the cells of the body, but also takes away
carbon dioxide and other waste materials, which are ultimately
passed out of the body by means of the lungs, skin, and kidneys.

Lymph Vessels. — The lymph is collected from the various tissues of
the body by means of a number of very thin-walled tubes, which are at
first very tiny, but after repeated connection with other tubes ultimately
unite to form large ducts. These lymph ducts are provided, like the veins,
with valves. The pressure of the blood within the blood vessels forces
continually more plasma into the lymph; thus a slow current is maintained
from the lymph spaces toward the veins. On its course the lymph passes
through many collections of gland cells, the lymph glands. In these glands
impurities appear to be removed and some of the colorless corpuscles made.

370

THE BLOOD AND ITS CIRCULATION

The lymph ultimately passes into a large tube, the thorac'ic duct, which
flows upward near the ventral side of the spinal column, and empties into
the large subclavian vein in the left side of the neck. Another smaller

lymph duct enters the right sub-
clavian vein.

The Lacteals. — We have abeady
found that part of the digested food
(chiefly carbohydrates, amino-acids,
salts, and water) is absorbed directly
into the blood through the walls of
the vilU and carried to the liver. Fat,
however, is passed into the spaces in
the central part of the villi, and
from there into other spaces between
the tissues, known as the lacteals.
The lacteals form the most direct
course for the fats to reach the blood.
The lacteals and l3Tnph vessels have
in part the same course. It will be
thus seen that lymph at different
parts of its course would have a very
different composition.

The Nervous Control of the Heart
and Blood Vessels. — Although the
muscles of the heart contract and
relax without our being able to stop
them or force them to go faster, yet in cases of sudden fright, or after a
sudden blow, the heart may stop beating for a short interval. This shows
that the heart is under the control of the nervous sj^stem. Two sets of
nerve fibers, both of which are connected with the central nervous system,
pass to the heart. One set of fibers accelerates, the other slows or inhibits,
the heartbeat. The arteries and veins are also under the control of the
sympathetic nervous system. This allows a change in the diameter of
the blood vessels. Thus, blushing is due to a sudden rush of blood to
the surface of the body, caused by an expansion of the blood vessels in
that region. The blood vessels of the body are always full of blood. This
results from an automatic regulation of the diameter of the blood vessels by
a part of the nervous system called the vasomo'tor nerves. These nerves
act upon the muscles in the walls of the blood vessels. In this way, each
vessel adapts itself to the amount of blood in it at a given time. After
a hearty meal, a large supply of blood is needed in the walls of the stom-
ach and intestines; therefore, the arteries going to this region are dilated
so as to receive an extra supply. When the brain performs hard work,
blood is supplied in the same manner to that region. Hence, one should
oot study or do mental work immediately after a hearty meal, for blood

The lymph vessels: the dark spots are
lymph glands; lac, lacteals; re, thoracic
duct.

CHANGES IN COMPOSITION OF BLOOD 371

will be drawn to the brain, leaving the digestive tract with an insufficient
supply. Indigestion may follow 'as a result.

Effect of Exercise on the Circulation. — It is a fact familiar
to all that the heart beats more violently and more quickly
when we are doing hard work than when we are resting. Count
your own pulse when sitting
quietly, and then again after
some brisk exercise in the
gymnasium. Exercise in
moderation is of undoubted
value, because it sends more
blood to those parts of the
body where increased oxida-
tion is taking place as the
result of the exercise. The
best forms of exercise are those
which give work to as many
muscles as possible — walking,
out-of-door sports, any exer-
cise that is not violent. Exer-
cise should not be attempted
immediately after eating, as
this causes a withdrawal of

blood from the digestive glands ^ Stopping flow of blood frojn an artery
, „ ,, ,, . ., by applying a tight bandage (hgature)

and from the walls Ot the between the cut and the heart.

food tube to the muscles of

the body. Neither should exercise be continued after one is
tired, as poisons are then formed in the muscles, which cause
fatigue. Remember that hard v/ork given to the heart by
extreme exercise may injure it, causing possible trouble with
the valves.

Treatment of Cuts and Bruises. — Blood which oozes slowly
from a cut will usually be checked by the natural means of the
formation of a clot. A cut or bruise should, however, be washed
in a weak solution of carbolic acid or some other antiseptic
and kept covered with clean gauze in order to prevent bacteria
from obtaining a foothold on the exposed flesh. If blood, issuing
from a wound, is bright red in color and gushes in distinct pulsa-

372

THE BLOOD AND ITS CIRCULATION

tions, an artery has been severed. To prevent the flow of blood,
a tight bandage must be bound on between the cut and the heart.
A handkerchief tied with a knot placed over the artery may stop
bleeding if the cut is on one of the limbs. If this does not
serve, then insert a stick in the handkerchief and twist it so
as to make the pressure around the limb still greater. Thus
we may close the artery until the doctor arrives and he may
sew up the injured blood vessel. If a vein is cut the blood flows
out in a steady stream. When the loss of blood is great it may
be checked by a tight bandage on the side of the cut, away from
the heart.

The Effect of Alcohol upon the Blood. — It has recently
been discovered that alcohol has an extremely injurious effect

A comparison of the chances of illness and death in drinkers and non-drinkers.
For each age shown, the light shaded area represents the probability of sickness
and death for drinkers, as compared with the dark area marked 100 for non-
drinkers. For example, if among non-drinkers aged 15 to 24 years 100 out of 8,200
are sick, then the diagram indicates that among drinkers of the same age probably
180 out of 8,200 would be sick.

upon the colorless corpuscles of the blood, lowering their
ability to fight disease germs to a marked degree. This is
clearly shown in a comparison of deaths from certain infectious dis-
eases of drinkers and of abstainers, the percentage of mortality
being much greater in the former.

CHANGES IN COMPOSITION OF BLOOD 373

The Effect of Alcohol on the Circulation. — Alcoholic drinks
affect the very delicate adjustment of the nervous centers con-
trolHng the blood vessels and heart. Even very dilute alcohol
relaxes the muscles of the tiny blood vessels, consequently
more blood is allowed to enter them, and, as the small vessels
are usually near the surface of the body, the habitual redness
seen in the face of hard drinkers is the ultimate result. The
walls of the arteries become hardened and lose their elasticity
when alcohol is in the system.

Summary. — Blood is really liquid food containing two types
of cells, red and colorless corpuscles. The former are oxygen
carriers, the latter protect the body from disease.

Blood is kept in circulation within arteries, capillaries, and
veins, by a double force piunp called the heart. The fluid
part of the blood with its load of food and gases, gets through
the walls of the smallest blood vessels and bathes the individual
cells of the body so that they may take up this food and
oxygen passed in to them. They in turn give up wastes and
carbon dioxide to the Ijrmph, as this fluid is called.

Problem Questions. — 1. Is the blood a tissue? Why?

2. What is the function of the red corpuscles? of colorless
corpuscles ?

3. What is the composition of plasma? How do you account
for this?

4. How does lymph dijffer from pla&ma?

5. Prove that the heart is a force pimip.

6. Compare the short and long circulations in the body.

7. How do cells get food and get rid of wastes ? How . do
they "breathe"?

Problem and Project References

Hunter, Laboratory Problems in Civic Biology. American Book Company.
Hunter and Whitman, Civic Science. American Book Company.
Martin, Human Body (for hormones). Henry Holt and Company,
Peabody, Studies in Physiology. The Macmillan Company.
Sharpe, A Laboratory Manual. American Book Company.
Stiles, Nutritional Physiology. W. B. Saunders Company,

XXVII. RESPIRATION AND EXCRETION

Problem. A study of the organs and the process of respiration
to determine —

(a) Organs of respiration in frog.

(b) Mechanics of respiration.

(c) Process of respiration m the lungs,

{Laboratory Manual, Prob. LI; Laboratory Problems, Probs.
207 to 213.)

Necessity for Respiration. — We have seen that plants and
animals need oxygen in order that the life processes may go on.

Food is oxidized to release
energy, just as coal is
burned to give heat to
run an engine. As a draft
of air is required to make
fire under the boiler, so,
in the human body, oxy-
gen must be given so
that foods in the tissues
may be oxidized to release
energy used in growth.
This oxidation takes place
in the cells of the body,

Air passages in the human lungs: a, larynx; be they part 01 a mUSCle,
6, trachea (or windpipe) ; c, c^, bronchi; e, bron- q Poland Or the brain,
chial tubes; /, cluster of air cells. ^ttt i ti 7 i''

The red blood corpuscles
in their circulation to all parts of the body are the agents which
convey oxygen to those places in the body where it will be used.
Respiration is taking in oxygen and giving off carbon dioxide by
the cells.

The Organs of Respiration in Man. — We have alluded to
the fact that the lungs are the organs which give oxygen to
the blood and take from it carbon dioxide. The course of air

374

ORGANS AND MECHANICS OF RESPIRATION 375

passing from the outside to the lungs in man is much the same
as that in the frog. Air passes through the nostrils, the pharynx,
the glottis, and into the windpipe. This cartilaginous tube, the
top of which may easily be felt as the Adam's apple of the throat,
divides into two bronchi (brong'ki) , each of which goes to a lung.
The bronchi within the lungs break up into a great number of
smaller bronchial tubes, which divide somewhat like the small
branches of a tree, and end in air sacs. This branching in-
creases the surface of the air
tubes within the lungs.
There are several adapta-

Bronchial
Tube

Pulmonary

Artery

Pu/monary

tions which should be noted
at this point. The folds in
the inside of the nose passage
warm and moisten the air
somewhat before it enters the
bronchi. The hairs in the
nose passage act as a strainer
which keeps most of the dust
and germs out from the lungs.
Then the bronchial tubes, in-
deed all the air passages, are
lined with cilia, which are
constantly in motion, beating
with a quick stroke toward
the mouth. Hence, if any for-
eign material should get into
the windpipe or bronchial tubes, it would be pushed upward by
the action of the cilia. It is by means of cilia that phlegm is
raised into the throat. Such action is of great importance, as
it prevents the air passages from filling with foreign matter.
The bronchial tubes end in very minute air sacs — little
pouches having elastic walls — into which air is taken when
we inspire or take a deep breath. In the walls of the air sacs
are numerous capillaries. It is through the very thin walls of the
air sacs that an interchange of gases takes place which results in
the blood giving up carbon dioxide and taking up oxygen.
The Pleura. — The lungs are covered with a thin elastic

Diagram to show what the blood gains
and loses in one of the air sacs of the
lungs.

376

RESPIRATION AND EXCRETION

membrane, the pleura, which forms a bag in which the lungs
are hung. Between the walls of the bag and the lungs is a

space filled with lymph.
mribj^^^-^. By this means the lungs
are prevented from rub-
bing against the walls of
the chest.

Breathing. — In every
full breath there are two
distinct movements, in-
spiration (taking air in)
and expiration (forcing
air out). In man an in-
spiration is produced by
the contraction of the
muscles between the ribs

^fiiaphragm

Diagram showing portion of diaphragm and
ribs in (a) expiration; (6) inspiration.

together with the contraction of the diaphragm, the muscular
wall forming the floor of the
chest cavity; this results in
pulling down the diaphragm
and pulling upward and out-
ward the ribs, thus making
the space within the chest
cavity larger. The lungs,
which lie within this cavity,
are filled by the air rushing
into the larger space thus
made. An expiration is simpler
than an inspiration, for it re-
quires no muscular effort; the
muscles relax, the breastbone
and ribs sink into place, while
the diaphragm returns to its
original position and the air is
pushed out.

Experiment to Illustrate the Me-
chanics of Breathing. — A piece of apparatus which illustrates to a degree
the mechanics of breathing may be made as follows: Attach a string to the

Apparatus to show the mechanics of
breathing.

ORGANS AND MECHANICS OF RESPIRATION 377

middle of a piece of sheet rubber. Tie the rubber over the large end of a
bell jar. Pass a glass Y tube through a rubber stopper. Fasten two small
toy balloons to the branches of the tube. Close the small end of the jar
with the stopper. Adjust the tube so that the balloons shall hang free in
the jar. If now the rubber sheet is pulled down by means of the string, the
air pressure in the jar is reduced and the toy balloons within expand, owing
to the air pressure down the tube. When the rubber is allowed to go back
to its former position, the balloons collapse.

Rate of Breathing and Amount of Air Breathed. — During

quiet breathing, the rate of inspiration is from
fifteen to eighteen times per minute; this rate
depends largely on the amount of phj'-sical
work performed. About 30 cubic inches of
air are taken in and expelled during the
ordinary quiet respiration. The air so
breathed is called tidal air. In a '' long
breath/' we take in about 100 cubic inches
in addition to the tidal air. This is called
complemental air. By means of a forced ex-
piration, it is possible to expel from 75 to
100 cubic inches more than tidal air; this
air is called reserve air. What remains in the
lungs, amounting to about 100 cubic inches,
is called the residual air. The value of deep
breathing is seen by a glance at the diagram.
When we take a full breath we ventilate the

WOCOJN,

TIDAL AIR
30CU.IN.

wmm

RESIDUAL

AIR
100 CU.IN.

230
CUM

Amounts and pro-
portions of comple-

lung sacs which otherwise would not be mental, tidal, re-

] jxu 1 J.11 rj-T- serve, and residual

used, and thus we clear the lungs of the ^ir in the breathing
reserve air with its accompanying load of of an average adult

1 T • 1 ' man.

carbon dioxide.

Respiration under Nervous Control. — The muscular movements which
cause an inspiration are partly under the control of the will, but the
movement is not wholly under our control. The nerve centers which govern
inspiration are part of the sj^mpathetic nervous system. Anything of an
irritating nature in the trachea or larynx will cause a sudden expiration or
cough. When a boy runs, the quickened respiration is due to the fact
that oxygen is used up rapidly and a larger quantity of carbon dioxide is
formed. This stimulates the nervous center which has control of respiration
to greater activity, and quickened inspiration follows.

HUNT. NEW ES. — 25

378 RESPIRATION AND EXCRETION

Problem. A study to determine the products of respiration.
(Laboratory Manual, Prob. LI I.)

Changes in Air in the Lungs. — Air is much warmer after
leaving the lungs than before it enters them. Breathe on the
bulb of a thermometer to prove this. Expired air contains a
considerable amount of moisture, as may be proved by breath-
ing on a cold pohshed surface. This it has taken up in the air
sacs of the lungs. The presence of carbon dioxide in expired air
may be detected easily by the limewater test. Air such as we
breathe out of doors contains, by volume : —

Oxygen 20.96

Carbon dioxide 04

Nitrogen (and other gases) , 79

Air expired from the limgs contains : —

Oxygen 16.02

Carbon dioxide 4.38

Water vapor .60

Nitrogen (and other gases) 79

In other words, there is a loss of between four and five per
cent oxygen, and nearly a corresponding gain in carbon dioxide,
in expired air. There are also some other organic substances
expeUed. The volume of carbon dioxide given off is always a
little less than the volimae of oxygen taken in. This seems to
show that some oxygen unites with some of the chemical ele-
ments in the body.

Changes in the Blood within the Lungs. — Blood, when leav-
ing the lungs, is much brighter red than when entering them.
The change in color is due to an absorption of oxygen by the
hcemoglobin of the red corpuscle. The changes taking place in
the blood are obviously the reverse of those that take place in
the air in the limgs. Blood in the capillaries within the lungs
gains from four to five per cent of oxygen which the air loses. At
the some time blood loses the four per cent of carbon dioxide which
the air gains. The blood, while in the lungs, gives off water
vapor also, amounting to nearly one half a pint of water
daily.

VENTILATION

379

o\

' ^^v{^?! villi

Problem. A study of ventilation. (Laboratory Manual, Prob.
LIII; Laboratory Problems, Probs. 214 to 218.)

Need of Ventilation. — Air in a living room or a schoolroom con
tains, besides dust and bacteria, carbon dioxide and other wastes
given off from the human body. About 0.6 of a cubic foot
of CO2 is given off from the body
every hour. In addition to this a
large amount of moisture is given
to the atmosphere of a crowded
room and heat is dissipated from our
bodies. We all know the discomfort
felt in a crowded room with win-
dows and doors closed. In order
that the air bearing this heat,
humidity, and carbon dioxide be
removed and fresh air substituted
it is necessary for us to ventilate
our buildings.

How We Ventilate. — In our
homes, ventilation is usually ac-
complished by opening windows. A
glance at the diagram shows three
methods of ventilation. Which is
the most adequate, and why? Too
often people think they ventilate by
opening a window either at the top
or bottom only. This changes the
air in only a very small part of the for air. Which is the best method

1 « T 1 of ventilation? Explain.

room, h ortunately for us the cracks

under and around doors, windows, and baseboards, and fire-
places give us much natural ventilation. (See the diagram.)
Two thousand to three thousand cubic feet of air per hour is
usually considered the average need of fresh air for each person.
In schoolhouses or other public buildings, where many are in one
room for a considerable period of time, it becomes necessary to
have artificial methods of ventilation. This is usually accom-
plished by means of pumping warm air through ducts into a

Three ways of ventilating a
room: i, inlet for air; o, outlet

380

RESPIRATION AND EXCRETION

room and sucking the stale air out through similar ducts. In
some instances the air is passed through a filter or is washed
to remove impurities. Often it passes in near the floor, some-
times from above. Describe the system used in your school
and see if you can understand the science underlying its
plan.

Sweeping and Dusting. — It is very easy to demonstrate the
amount of dust in the air by looking at a beam of light in a
darkened room. We have already proved that spores of mold

and yeast exist in the air.
That bacteria are also
present may be proved
by exposing a sterilized
gelatin plate to the aii
in a schoolroom for a few
moments.^

Many of the bacteria
present in the air are
active in causing diseases
of the throat and lungs,
such as diphtheria, mem-
branous croup, tubercu-
losis, colds, bronchitis
(inflammation of the
bronchial tubes), and
pneumonia (inflamma-

Plate culture exposed for five minutes in a
school hall where pupils were passing to recita-
tions. Each spot is a colony of bacteria or mold.

tion of the tiny air sacs of the lungs).

Dust, with its load of bacteria, will settle on any horizontal
surface in a room not used for three or four hours. When a
vacuum cleaner is not available dusting and sweeping should
always be done with cloth and broom which are damp, other-
wise the bacteria are simply stirred up, sent into the air, and
allowed to settle down on the furniture and floor again. The
proper watering of streets before they are swept is also an im-
portant factor in preserving health.

^ Expose two sterilized dishes containing culture media ; one in a room being
swept with a damp broom, and the other in a room which is being swept in
the usual manner. Note the formation of colonies of bacteria in each dish.
In which dish does the greater number of colonies form? Why?

VENTILATION 381

Ventilation of Sleeping Rooms. — Sleeping in close rooms is
the cause of much illness. Beds should be placed so that a
constant supply of fresh air is obtained without a direct draft.
This may often be managed with the use of screens. Bedroom
windows should be thrown open in the morning to allow free
entrance of the sun and air, bedclothes should be washed fre-
quently, and sheets and pillow covers often changed. Bedroom
furniture should be simple, and but little drapery allowed in
the room.

Hygienic Habits of Breathing. — Every one should form the
habit of inspiring slowly and deeply and to the full capacity of
the lungs upon going into the open air. A slow expiration
should follow, forcing out as much air as possible. Breathe
through the nose, thus warming the inspired air before it
enters the lungs and chills the blood. Repeat this exercise
several times every day. You will thus prevent certain of the
air sacs which are not often used from becoming hardened and
permanently closed.

The Relation of Tight Clothing to Correct Breathing. — It
is impossible to breathe correctly unless the clothing is loose
over the chest and abdomen. Tight corsets and tight belts pre-
vent the walls of the chest and the abdomen from pushing out-
ward and interfere with the drawing of air into the lungs. They
may also result in permanent distortion of parts of the skeleton
directly under the pressure. Other organs of the body cavity,
as the stomach and intestines, may be forced downward, out of
place, and in consequence they do not perform their work
properly. r

Relation of Exercise to Deep Breathing. — We have already
seen that exercise results in the need of greater food supply,
and hence a more rapid pumping of blood from the heart.
With this comes need of more oxygen to allow oxidation which
supplies the greater energy used. Hence deeper breathing dur-
ing time of exercise is a prime necessity in order to increase the
absorbing surface of the lungs.

Suffocation and -Artificial Respiration. — Suffocation results
from the shutting off of the supply of oxygen from the lungs. It
may be brought about by an obstruction in the windpipe, by a

382

RESPIRATION AND EXCRETION

lack of oxygen in the air, by inhaling some other gas in quantity,
or b}^ drowning. A severe electric shock may paralyze the ner-
vous centers which control respiration, thus causing a kind of
suffocation. In the above cases, death often may be prevented
by prompt recourse to artificial respiration. To accomplish this,
lay the person face down, with the forehead resting on one

arm. This position will
bring the tongue forward
and allow the water to es-
cape from the lungs if it is
a case of drowning. Now
get astride of the patient,
with one hand on each side
of the body, place the
fingers on the ribs and
press down and in. Relax
the pressure so as to allow
air to get into the lungs.
Repeat this about fifteen
times a minute and con-
tinue if necessary for three
or four hours.

Common Diseases of the
Nose and Throat. — Catarrh is^ a disease to which people with
sensitive mucous membrane of the nose and throat are subject.
It is indicated by the constant secretion of mucus from this
membrane. Frequent spraying of the nose and throat with
some mild antiseptic solution is found useful. Chronic catarrh
should be attended to by a physician. Often we find children
breathing entirely through the mouth because the air passages in
the nose are closed. When this goes on for some time the nose
and throat should be examined by a physician for enlarged tonsils
and adenoids, or growths of soft masses of tissue which fill up
the nose cavity, thus causing mouth breathing. Many a child,
backward at school, thin and irritable, has been changed to a
healthy, normal, bright pupil by the removal of adenoids.
Sometimes the tonsils at the back of the mouth cavity become
diseased as well as enlarged, and are the cause of colds and tliroat

Schaefer method of artificial respiration.

ORGANS OF EXCRETION

383

troubles as well as the beginning of tuberculosis. Infected
tonsils sometimes cause acute rheumatism and heart trouble.

Cell Respiration. — It has been found, in the case of very
simple animals, such as the amoeba, that when oxidation takes
place in a cell, work results

from this oxidation. The oxy-
gen taken into the lungs is not
used there, but is carried by
the blood to such parts of the
body as need oxygen to oxidize
food materials in the cells.
The quantity of oxygen used
by the body is nearly depend-
ent on the amount of work
performed. From twenty to

l/mphrube 0- •-

The respiration of a cell.

twenty-five ounces of oxygen is taken in and used by the body
every day. Oxygen is constantly taken from the blood by tissues
in a state of rest and is used up when the body is at work.

While work is being done certain wastes are formed in the cell.
Carbon dioxide is released when carbon is burned; and when
proteins are burned, a waste product containing nitrogen is
formed. These wastes must be passed off from the cells, as they
are poisons. Here again the blood and lymph, common carriers,
take the waste materials to places where they may be excreted
or passed out of the body.

Organs of Excretion. — ■ All the life processes which take place
in a living thing result ultimately, in addition to giving off car-
bon dioxide, in the formation of organic wastes which contain
nitrogen. In animals one of these wastes is called u'rea. In
man, the lungs, skin, and kidneys perform the function of
eliminating wastes and are called the organs of excretion.

The Human Kidney. — The human kidney is about four inches
long, two and one half inches wide, and one inch thick. Its
color is dark red. If the structure of the medulla and cortex
of the kidney (Figure, p. 384) is examined under the compound
microscope, you will find these regions to be composed of a vast
number of tiny branched and twisted tubules. The outer end of
each of these tubules opens into the 'pelvis, the space within the

384

RESPIRATION AND EXCRETION

kidney; the inner end forms a tiny closed sac in the cortex.
In each sac, the outer wall of the tube has grown inward and
carried with it a very tiny artery which breaks up into a mass

of capillaries. These capil-

Cortex

Medulla

■Pyrdmids

Pelvis
Ureter

Lengthwise section of kidney.

laries, in turn, unite to form a
small vein as they leave the
little sac. Each of these sacs
with its wall netted with blood
vessels is called a glomer'ulus.
Wastes given off by the

'A~D lA t- ^^^^^ i^ the Kidney. — In the
ll ^ glomerulus the blood loses by

osmosis, through the very thin
walls of the capillaries, first, a
considerable amount of water
(amounting to nearly three
pints daily); second, a nitrog-

enous waste material known as urea; third, salts and other
waste organic substances, uric acid among them.

These waste products, together with the water containing them, are
known as urine. The total amount of
nitrogenous waste leaving the body each
day is about twenty grams; this is nearly
all accounted for in the urea passed off by
the kidney. The urine is passed through
the ureter (u-re'ter) to the urinary bladder;
from this reservoir it is passed out of the
body, through a tube called the ure'thra.
After the blood has gone through the
glomeruh of the kidneys it is purer than
in any other place in the body, because,
before going there, it lost a large part of

its carbon dioxide in the lungs, and in the ra, small renal artery; GL, capil-
kidneys it lost much of its nitrogenous laries in the glomerulus; RVy
waste. So dependent is the body upon small renal vein ; C tubule lead-
., , . c -. • J. • 1 xu X iiig to the pelvis of the kidney,

the excretion of its poisonous material that,

in cases where the kidneys do not do their work properly, death may ensue
within a few hours.

A glomerulus, much magnified:

Structure and Use of Sweat Glands. — If you examine the
surface of your skin with a lens, you will notice the surface is

ORGANS OF EXCRETION 385

thrown into little ridges (see diagram, page 313). Between the
ridges may be found a large nimiber of very tiny pits; these are
the pores or openings of the sweat-secreting glands. From each
opening a little tube penetrates deep within the dermis; there,
coiling around upon itseK several times, it forms the sweat
gland. Close around this coiled tube are found many capillaries.
From the blood in these capillaries, cells lining the wall of the
gland take water, and with it a little carbon dioxide, urea, and
some salts (common salt among others). This forms the excre-
tion known as sweat. The combined secretions from these glands
amount normally to a little over a pint during twenty-four hours.
At all times, a small amount of sweat is given off, which is
evaporated or is absorbed by the underwear; as this passes off
unnoticed it is called insensible perspiration. In hot weather or
after hard manual labor the amount of perspiration is greatly
increased.

Relation of Body Heat to Work Performed. — The body
temperature of a person engaged in manual labor will be found
to be but Httle higher than the temperature of the same person
at rest. When a man works, he releases energy by oxidizing
food material or tissue in the body and heat is released. Mus-
cles, nearly one half the weight of the body, release about five
sixths of their energy as heat. At aU times they are giving up
some heat. How is it that the body temperature is not much
higher when work is being done than when at rest?

Regulation of Heat of the Body. — The temperature of the
body is largety regulated by means of the activity of the sweat
glands. The blood carries much of the heat, liberated in the
various parts of the body by the oxidation of food, to the sur-
face of the body, where it is lost in the evaporation of sweat.
In hot weather the blood vessels of the skin are dilated; in cold
weather they are made smaller by the action of the nervous
system. The blood loses water in the skin, and as the water
evaporates, we are cooled off. The object of increased perspira-
tion, then, is to remove heat from the body. With a large amount of
blood present in the skin, perspiration is increased; with a
small amount, it is diminished. Hence, we have in the skin a
regulator of body temperature under automatic control.

386 RESPIRATION AND EXCRETION

Sweat Glands under Nervous Control. — The sweat glands, like the
other glands of the body, are under the control of the sympathetic nervous
system. Frequently the nerves dilate the blood vessels of the skin, thus
helping the sweat glands to secrete, by giving them more blood.

" Thus regulation is carried out by the nervous system determining, on
the one hand, the loss by governing the supply of blood to the skin and the
action of the sweat glands; and on the other, the production by dimin-
ishing or increasing the oxidation of the tissues." — Foster and Shore,
Physiology.

Comparison with Cold-blooded Animals. — We have seen that the body
temperature of a frog remains nearly the same as that of the surrounding
medium. Fishes, aU amphibious animals, and reptiles are alike in this re-
spect. This change in the body temperature is due to the absence of regu-
lation by the nervous system. A sort of regulation is exerted, however, by
outside forces, for the cold in winter causes the cold-blooded animals to
become inactive. Warm weather, on the other hand, stimulates them to
greater activity and to increased oxidation. This is naturally followed by
an increase in body temperature.

Problem. A final study of changes in the composition of blood
in various parts of the body. (Laboratory Manual, Prob. LIV;
Laboratory Problems, Prob. 219.)

Summary of Changes in Blood within the Body. — We have al-
ready seen that red corpuscles in the lungs lose part of their load
of carbon dioxide that they have taken from the tissues, replac-
ing it with oxygen. This is accompanied by a change of color
from a deep crimson (in blood which is poor in oxygen) to that of
bright scarlet (in richly oxygenated blood). More changes take
place in other parts of the body. In the walls of the food tube,
especially in the small intestine, the blood receives its load of
fluid food. In various parts of the body it receives enzymes
and hormones. In the muscles and other working tissues the
blood gives up food and oxygen, receiving carbon dioxide and
organic waste in return. In the liver, the blood gives up its
sugar, and the worn-out red corpuscles which break down are
removed (as they are in the spleen) from the circulation. In
glands, it gives up materials used by the gland cells in their
manufacture of secretions. In the kidneys, it loses water and
nitrogenous wastes (urea). In the skin, it also loses some waste
materials, salts, and water.

Hygiene of the Skin. — The skin as an organ of excretion is

COLDS AND FEVERS 387

of importance. It is of even greater importance as a regulator
of body temperature. The mouths of the sweat glands must
not be allowed to become clogged with dirt. The skin of the
entire body should, if possible, be bathed daily. For those who
can stand it, a cold shower or sponge bath in the morning is
best. Soap should be used daily on parts exposed to dirt.
Exercise in the open air is important to all who desire a good
complexion.

Cuts and Burns. — In case the skin is broken the entrance
and growth of bacteria may be prevented by applying iodine
or by washing the wound with weak antiseptic solutions, such
as 3 per cent carbolic acid, 3 per cent lysol (li'sol), peroxide of
hydrogen (full strength), or a xV per cent solution of hichlo'ride
of mercury. These solutions should be applied immediately.
In the case of a burn apply a mixture of equal parts of linseed
oil and lime water, or if this is not at hand cover the injured
part with a paste of baking soda and water. In the case of a
bad burn or deep cut call a doctor at once.

Colds and Fevers. — The regulation of blood passing through
the blood vessels is under control of the nervous system. If
this mechanism is interfered with in any way, the sweat glands
may not do their work, perspiration may be stopped, and the
heat from oxidation held within the body. The body tempera-
ture goes up, and a fever results.

If the blood vessels in the skin are suddenly cooled they
contract and send the blood elsewhere. If the chiUing of the
blood is too great or lasts for too long a time, a congestion or
cold foUows. Colds are, in reality, a congestion of membranes
lining certain parts of the body, as the nose, throat, windpipe,
or lungs, and a growth of bacteria which were present in the
mouth or throat. Some colds are contagious and gain entrance
to the body when the resistance is low.

When suffering from a cold, it is therefore important not to chill
the skin, as a full blood supply should be kept in it and away
from the seat of congestion. For this reason hot baths (which
call the blood to the skin), the avoiding of drafts (which chill the
skin), and warm clothing are useful factors in the care of colds.

One of the greatest deceptions played upon the drinker by

388

RESPIRATION AND EXCRETION

alcohol is that it helps to make him warmer when he is cold.
But this is far from the case. As a matter of fact he feels
warmer for a little while because the alcohol paralyzes the nerves
which control the amount of blood going to the skin and the
skin becomes flushed and gorged with blood. But as we have

seen under such conditions heat
is lost from the blood through
the skin. In a short time
therefore the drinker has lost
more heat than the abstainer
and numerous cases are on
record where drinkers have
suffered or lost their lives from
exposure while abstainers un-
der the same conditions have
survived.
Alcohol and tobacco have

^W5b.?-=^^So^oO^^J'^S^ bad effect upon respiration and

the cells Hning the respiratory
organs. Statistics show with-
out a doubt that the use of
alcohol together with bad con-
ditions of living has had a
very serious effect in raising
the death rate from tubercu-

At blood vessels in skin normal; B, when ]osis of the lunes
congested. a i i i i i*

Alcohol also has a serious
effect upon the kidneys. It is well known to alcoholic drinkers
that even beer and light wine are prohibited to the man who
has kidney trouble. Moreover, much of the fatty degeneration
of the kidneys, and Bright's disease may be attributed directly
to the overuse of alcohol.

Summary. — Respiration really takes place in the cells of the
body where work is done. The structures which provide for
this are the lungs and blood vessels, which allow the air taken
in to come in contact with the blood through the delicate linings
of the lung sacs.

B

RESPIRATION AND EXCRETION 389

Since oxidation takes place in cells the products of burning
must be removed as well as other organic wastes. This is
done eventually by the lungs, skin, and kidneys.

Problem Questions. — 1. How are the lungs adapted to their
work?

2. Explain the mechanics of breathing.

3. What are the products of respiration?

4. What is ventilation? Why is it necessary?

5. What is cell respiration? Explain fully.

6. How does the kidney do its work?

7. How does the skin excrpte wastes? j

8. What is a congestion and how is it caused?

Problem and Project References

Eddy, General Physiologij. American Book Company.

Fisher and Fisk, How to Live. Funk and Wagnalls Company.

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Hunter and Whitman, Civic Science. American Book Company.

Martin, The Human Body. Henry Holt and Company.

Sharps, A Laboratory Manual. American Book Company.

■Cell Body
"Nucleus

XXVIII. THE NERVOUS SYSTEM AND ORGANS

OF SENSE

Problem. A study of the nervous system, reactions to stimuli,
and habit formation. (Laboratory Manual, Prob. L V ; Laboratory
Problems, Probs. 220 to 233.)

Divisions of the Nervous System. — In a complicated machine
like the human body there must be some means of obtaining

cooperative action of
the different organs to-
ward definite ends. In'
the vertebrate animals,
such as man, this is
brought about by two
divisions of the nervous
system. One includes
the brain, spinal cord,
and cranial and spinal
nerves, which together
make up the cerebro-
spinal nervous system.
The other division is
called the autonom'ic or
sympathetic nervous sys-

The central cerebro-spinal tem. The activities of Diagram of a neuron
nervous system. ^^^ ^^^^ ^^^ Controlled or nerve unit.

from nerve centers by means of fibers which extend to all parts
of the body, and end in muscles. The brain and spinal cord are
examples of such centers, since they are largely made up of
nerve cells. Small collections of nerve cells, called ganglia, are
found in other parts of the body. These nerve centers are con-
nected, to a greater or less degree, with the surface of the body
by the nerves which serve as pathways between the end organs

890

Axis Cylinder

Ner/eEnds

BRAIN AND NERVES 391

of touch, sight, taste, etc., and the centers in the brain or spinal
cord. Thus sensation is obtained.

Nerve Cells and Fibers. — A nerve cell, like other cells in the
body, is a mass of protoplasm containing a nucleus, but, un-
like them, it is usually rather irregular in shape, and possesses
many delicate, branched protoplasmic projections. One of these,
the axis cylinder, is much longer than the others and forms the
pathway over which nervous impulses travel to and from the
nerve centers. A nerve cell is ■ a center of activity and sends
impulses over this thin strand of protoplasm (the axis cylinder
process) prolonged into a nerve fiber many hundreds of thou-
sands of times the length of the cell. A nerve is a bundle of
nerve fibers.

The Brain of Man. — In man, as in the frog, the central
nervous system consists of a rrocop/iu ^— >--^^^^^^^
brain and spinal cord inclosed J ^iii^XZ^^^S^-V^C^^^)^'^
in a bony case with the nerves f^^}v/r^Th \-\^^^^~^\^
leaving it. From the brain, >{~^vJ_^^"V^V^-^^
twelve pairs of nerves are u/ ^^^T/^^'^^x^o^'^^y^
given off; thirty-one pairs leave f\>0^^^^i>tA.^^
the spinal cord. The brain V,^^^^r3_^**'^%sj2:^
has three divisions. The cere- Cf^ff^^^^^C"} ^OA/S
brum (ser'e-brum) makes up ^^v\l/(/Jfim
the largest part. In this re- ^^^^^O™.-.-™^^^^^
spect it differs from the cere- Cf/i^BaiUM mlp^
brum of the frog and other ^^

vertebrates. It is divided into ^^^ ^^^i^- ^*^ p^^^ separated to show

7.7 each clearly.

two lobes, the hemispheres,

which are connected with each other by a broad band of nerve
fibers. The outer layer of the cerebrum, which is thrown into
folds or convolutions, is gray in color, and made up of nerve
cells and supporting material. The inner part, which is white,
is composed largely of fibers passing to other parts of the
brain and down into the spinal cord. Under the cerebrum lies
the Kttle brain, or cereheVlum. The two sides of the cere-
bellum are connected by a band of nerve fibers which run
around into the lower hind-brain or meduVla, This band of
fibers is called the pons.

392 NERVOUS SYSTEM AND ORGANS OF SENSE

Sensory and Motor Nerve Fibers. — Nerves which are con-
nected with the central nervous system may be made up of
fibers bearing messages from sense organs in the skin or elsewhere
to the central nervous system, the sensory fibers, or of other
fibers which carry impulses from the central nervous system to
the outside, the motor fibers. Some nerves are made up of both
kinds of fibers, in which case they are called mixed nerves.

The Autonomic Nervous System. — The autonomic (or sympathetic)
nervous system consists of a series of ganglia connected with each other
and with the central nervous system through some of the spinal and
cranial nerves, especially the tenth cranial. The autonomic system, both
in the frog and in man, controls the muscles of the digestive tract and blood
vessels, the secretions of gland cells, and the heart.

Functions of the Parts of the Central Nervous System of the Frog. —
From careful study of Hving frogs, birds, and some mammals we have
learned much of what we know of the functions of the parts of the central
nervous system in man.

It has been found that if the entire brain of a frog is destroyed or
separated from the spinal cord, " the frog will continue to hve but with a
very peculiarly modified activity." It does not appear to breathe, nor does
it swallow. It will not move or croak, but if acid is placed upon the skin
so as to irritate it, the legs make movements to push away and to clean off
the irritating substance. The spinal cord is thus shown to be a center for
defensive movements. If the cerebrum is separated from the rest of the
nervous system, the frog seems to act a Uttle differently from the normal
animal. It jumps when touched, and swims when placed in water. It will

croak when stroked, or swallow if food be placed in
its mouth. But it manifests neither hunger nor fear,
and is in every sense a machine which will per-
form certain actions after certain stimulations. Its
movements are automatic. If we watch the move-
ments of a frog which has the brain uninjured in
any way, we find that the frog acts spontaneously.
It tries to escape when caught. It feels hungry
and seeks food. It is capable of voluntary action.
It acts like a normal individual.

Regions of the head

Functions of the Cerebrum. — In gen-
and action of the different eral, the functions of the different parts of
parts of the bram. ^j^^ brain in man agree with those we have

already observed in the frog. The cerebrum has to do with con-
scious activity. It presides over what we call our thoughts, our
win, and our sensations. Each part of the area of the outer layer

REFLEX ACTIONS

393

Diagram of the path of a simple nervous reflex action.

of the cerebrum is given over to some one function, as speech,
hearing, sight, touch, movements of body parts. The con-
scious movement of the smallest part of the body has its defi-
nite locahzed center in the cerebrum. Our knowledge on this
subject is derived from experiments performed on monkeys, and
from observations made on persons who had lost the power of
movement of certain parts .of the body, and were found,
after death, to have
had diseases local-
ized in certain
parts of the cere-
brum.

Reflex Actions;
their Meaning. —
If through disease
or for other reasons
the cerebrum does
not function, no
will power is ex-
erted, nor are intelligent acts performed. All acts performed
in such a state are known as reflex actions. An example of a
reflex may be obtained by crossing the legs and hitting the knee
a sharp blow. The leg, below the knee, will fly up as a result
of reflex stimulation. The involuntary brushing of a fly from
the face and the attempt to move away from the source of an-
noyance when tickled with a feather, are other examples. In
a reflex act, a person does not think before acting. The nervous
impulse comes from the outside to cells that are not in the cere-
brum. The message is short-circuited back to the surface by
motor nerves, without ever having reached the thinking centers.
The nerve cells which take charge of such acts are located in
the cerebellum or spinal cord.

Automatic Acts. — Some acts, however, are learned by con-
scious thought, as writing, walking, running, or swimming.
Later in life, however, these activities become automatic and
are controlled by the cerebellum, medulla, and spinal ganglia.
Thus the thinking portion of the brain is relieved of part of its
work.

HUNT. NEW ES. — 26

394 NERVOUS SYSTEM AND ORGANS OF SENSE

Habit Formation. — The training of the different areas in the
cerebrum to do their work efficiently is the object of education.
When we learned to write, we exerted conscious effort in order to
make the letters. Now the act of forming the letters is done
without thought. By training, the act has become automatic.
In the beginning, a process may take much thought and many
trials before it is accomplished successfully. After a little prac-
tice, the same process becomes almost automatic and a habit is
formed. Habits are really acquired reflex actions. They are the
result of nature's method of training. The conscious part of
the brain has trained the cerebellum or spinal cord to do certain
things that, at first, were taken charge of by the cerebrum.

Importance of forming Right Habits. — Among the habits
to be acquired early are the habits of studying properly, of con-
centrating the mind, of self-control, and above all, of content-
ment. Get the most out of the world about you. Remember
that the immediate effect of the study of some subjects in school
may not be great, but the cultivation of correct methods of
thinking may be of the greatest importance later in life.

" The hell to be endured hereafter, of which theology tells, is no worse
than the hell we make for ourselves in this world by habitually fashioning
our characters in the wrong way. Could the young but reaUze how soon
they will become mere walking bundles of habits, they would give more
heed to their conduct while in the plastic state. We are spinning our own
fates, good or evil, and never to be undone. Every smallest stroke of
virtue or of vice leaves its never-so-Uttle scar. The drunken Rip Van Winkle,
in Jefferson's play, excuses himself for every fresh derehction by saying,
' I won't count this time! ' Well ! he may not count it, and a kind Heaven
may not count it; but it is being counted none the less. Down among his
nerve cells and fibers the molecules are counting it, registering and storing
it up to be used against him when the next temptation comes. Nothing
we ever do is, in strict scientific Hteralness, wiped out. Of course this
has its good side as well as its bad one. As we become permanent drunkards
by so many separate drinks, so we become saints in the moral, and au-
thorities in the practical and scientific, spheres by so many separate acts
and hours of work. Let no youth have any anxiety about the upshot of
his education, whatever the line of it may be. If he keep faithfully busy
each hour of the working day, he may safely leave the final result to itself.
He can with perfect certainty count on waking up some fine morning,
to find himself one of the competent ones of his generation, in whatever
pursuit he may have singled out." — James, Psychology.

TOUCH

395

Necessity of Food, Fresh Air, and Rest. — The nerve cells,
like, all other cells in the body, are continually wasting away and
being rebuilt. Oxidation of food material is more rapid when
we do mental work. The cells of the brain, like muscle cells, are
not only capable of fatigue, but show this in changes of form and
of contents. Food brought to them in the blood, plenty of fresh
air, especially when engaged in active brain work, and rest at
proper times, are essential in keeping the nervous system in
condition. One of the best methods of resting the brain cells is
a change of occupation. Tennis, golf, baseball, and other out-
door sports combine muscular exercise with brain activity of a
different sort from that of business or school work, thus exer-
cising other brain cells.

Necessity of Sleep. — Sleep is an essential factor in the health
of the brain, especially for growing children. Most brain cells
attain their growth early in Hfe. Changes occur, however, until
some time after the school age. Ten hours of sleep should be
allowed for a child, and at least eight hours for an adult. It
is during sleep that the brain cells have opportunity to rest and
store food and energy for their working period.

The Senses

Touch. — In animals hav-
ing a hard outside covering,
such as certain worms, insects,
and crustaceans, minute hairs,
which are sensitive to touch,
are found growing out from
the body covering. At the
base of these hairs are found
nerve cells which send nerve
fibers inward to the central
nervous system.

Organs of Touch. — In
man, special nerve endings
called the tactile corpuscles, which give the sense of touch, are
located in the skin. The number of tactile corpuscles present

Nerves in the skin: a, nerve fiber; b,
tactile papillae, containing a tactile cor-
puscle; c, papillae containing blood ves-
sels. (After Benda.)

396 NERVOUS SYSTEM AND ORGANS OF SENSE

in a given area of the skin determines the accuracy and ease
with which objects may be recognized by touch.

Experiment: Touch. — K you test the different parts of the body, as
the back of the hand, the neck, the skin of the arm, of the back, or the
tip of the tongue, with a pair of open dividers, a vast difference in the ac-
ciu-acy with which the two points may be distinguished is noticed. On the
tip of the tongue, the two points need be separated by only -^-^ of an inch
to be distinguished. In the small of the back, a distance of two inches may
be reached before the dividers feel like two points.

Temperature, Pressure, Pain. — The sensations of temperature, pressure,
and pain are determined by different end organs in the skin. Two kinds
of nerve endings exist in the skin, which give distinct sensations of heat
and cold. These areas can be located by careful experimentation. There
are also areas of nerve endings which are sensitive to pressure, and still
others, most numerous of all, sensitive to pain.

Taste Organs. — The surface of the tongue is folded into a number of little
projections known as papillae. In the folds between these papillae on the top
and back part of the tongue, are located the organs of taste, called taste bvds.

How we Taste. — Four kinds of substances may be distin-
guished by the sense of taste. These are sweet, sour, bitter, and

salt. Certain taste cells located
near the back of the tongue are
stimulated only by a bitter taste.
Sweet substances are perceived by
cells near the tip of the tongue,
sour substances along the sides, and
salt about equally all over the
surface. A substance must be
dissolved in order to be tasted. Taste and smell are often
confused and many things which we believe we taste are in
reality perceived by the sense of smell. Such
are spicy sauces and flavors of meats and
vegetables. That we do not taste certain
foods is proved easily by holding the nose and
chewing several different substances, such as
an apple, an onion, and a raw potato.

Smell. — The sense of smell is located in
the membrane lining the upper part of the
nose. Here are found a large number of rod-shaped cells which
are connected with the forebrain by means of the olfactory

Section of circumvallate papilla:
E, epidermis; T, taste buds; N,
nerve fibers.

TASTB CELLS

SUPP0RTIN9
CELLS

Isolated taste bud.

TASTE, SMELL, HEARING 397

nerve. In order to perceive odors, it is necessary to have them
diffused in the air; hence we sniff so as to draw in more air over
the olfactory cells.

Outer Ear. — The organ of hearing is the ear. In the fish,
frog, and reptile, the outer ear, so prominent in man, is entirely
lacking. The outer ear

consists of a funnel-like /^,:, Jfe^/br^.^^r^^f"^^^

organ composed largely

of cartilage which is of

use in collecting sound

waves' and the auditory l\ '^^^^>a^B^^r^^ g?%-lL^r<?rA^^

canal, which is closed at

the inner end by a tightly %^7 ''^^^^"&^

stretched membrane, the f/^^/^cr^ ' ■ m hr ~^^ ' -

tympan'ic membrane. We >?/7////

have seen the tympanic

membrane of the frog on ^^^^^^^ ""^ ^^"^^^ ^^^•

the outer surface of the head. The function of the tympanic

membrane is to receive sound waves, or vibrations in the air,

which are transmitted, by means of a complicated apparatus

found in the middle ear, to the inner ear.

Middle Ear. — The middle ear in man is a cavity inclosed by
the temporal bone of the skull and separated from the outer
ear by the tympanic membrane. A little tube called the Eusta-
chian tube connects the middle ear with the mouth cavity. By
allowing air to enter from the mouth, the air pressure is equal-
ized on the tympanic membrane. For this reason, we open the
mouth at the time of a heavy concussion and thus prevent the
rupture of the delicate tympanic membrane. Placed directly
against the tympanic membrane and connecting it with another
membrane which separates the middle from the inner ear, is a
chain of three tiny bones, the smallest bones of the body.
The outermost is called the hammer; the next the incus, or
anvil; the third the stirrup. All three bones are so called
from their resemblances in shape to the objects for which they
are named. These bones are held in place by very small mus-
cles which are delicately adjusted so as to tighten or relax the
membranes guarding the middle and inner ear.

398 NERVOUS SYSTEM AND ORGANS OF SENSE

The Inner Ear. — The inner ear is one of the most compli-
cated, as well as one of the most delicate, organs of the body.
Deep within the temporal l)one there are found two parts, one
of which is called, collectively, the sctnicircular canals, the other
the cochlea (kokle-a), or organ of hearing.

It has been discovered by experimenting with fish, in which
the semicircular canal region forms the chief part of the ear,
that this region has to do with the equilibrium or balancing
of the body. We gain knowledge of our position and our
movements in space in part by means of the semicircular
canals.

That part of the ear which receives sound waves is known as
the cochlea, or snail shell, because of its shape. This very com-
plicated organ is lined with sensory cells provided with cilia,
and its cavity is filled with a fluid. It is believed that some-
what as a stone thrown into water causes ripples to emanate
from the spot where it strikes, so sound waves are transmitted
by means of the fluid filling the cavity to the sensory cells of
the cochlea and thence to the brain by means of the auditory
nerve.

The Eye. — The eye, or organ of vision, is an almost spherical
body which fits into a socket of bone, the orbit. A stalklike

structure, the o-ptic nerve, con-
nects the eye with the brain.
Free movement is obtained by
means of six little muscles which
are attached to the outer coat
of the eyeball, and to the bony
socket around the eye.

The wall of the eyeball is made
up of three coats. An outer
tough white coat, of connective
tissue, is called the sclerot'ic
coat; this coat is lacking in the
exposed part of the eyeball, but may be seen by lifting the eye-
lid. Where the eye bulges out a little in front, the outer coat
is replaced by a transparent tough layer called the cor'nea. A
second coat, the choroid (ko'roid), is supplied with blood vessels

CillaryHusck

Section of human eye.

SIGHT 399

and cells which contain pigments. The i'ris is the part of this
coat which we see through the cornea as the colored part of the
eye. In the center of the iris is a small circular hole, called
the pupil. The iris is under the control of muscles, and may be
adjusted to varying amounts of light, the hole becoming larger
in dim light, and smaller in bright light. The inmost layer of
the eye is called the ret'ina. This is, perhaps, the most delicate
layer in the entire body. Despite the fact that the retina is
less than gV of an inch in thickness, there are several layers of
cells in its composition. The optic nerve enters the eye from
behind and spreads out over the surface of the ret-
ina. Its finest fibers are ultimately connected with
numerous elongated cells which are stimulated by
light. The retina is dark purple in color, this color
being due to a layer of cells next to the choroid
coat and accounts for the black appearance of the
pupil of the eye, when we look through it into
the darkened space within the eyeball. The retina
acts as the sensitized plate in the camera, for on it
are received the impressions which are transformed Diagram show-
and sent to the brain and result in sensations of i^s i^ow the lens

changes its form.

sight. The eye, like the camera, has a lens. This
lens is formed of transparent, elastic material. It is directly
behind the iris, and is attached to the choroid coat by
means of delicate Hgaments. In front of the lens is a small
cavity filled with a watery fluid, the a'queous humor, while
behind it is the main cavity of the eye, filled with a trans-
parent, ahnost jellylike, vifreous humor. The elasticity of the
lens permits a change of form and, in consequence, a change of
focus upon the retina. By means of this change in form, or
accommodation, we are able to see both near and distant objects
clearly.

Defects in the Eye. — In some eyes, the lens is in focus for
near objects, but is not easily focused upon distant objects;
such an eye is said to be nearsighted. Other eyes which do not
focus clearly on objects near at hand are said to be farsighted.
Still another eye defect is astig'matism, which causes images of
fines in a certain direction to be indistinct, while images of lines

400 NERVOUS SYSTEM AND ORGANS OF SENSE

transverse to the former are distinct. Many nervous troubles,
especially headaches, may be due to eye strain.

Experiment ; How we See. — Suppose an object be held in front of the
eye; rays of light pass from every part of the object and are brought to
a focus on the retina by means of the transparent lens. You can form an
image in the same manner by using a reading glass, a box with a hole in
one end, and a piece of white paper. Notice that the image is inverted.
The same is true of the image on the retina. When an image is thrown

Diagram to show how an image is formed in the eye: a, object; b, lens;

c, image upon retina.

on the sensory layer, the rods and cones of the retina are stimulated and
the image is transmitted to the forebrain. We must remember that the
optic nerve crosses under the brain so that images formed in the right eye
are received by the left half of the forebrain, and vice versa.

Care of the Eyes. — Remember that a delicate organ like the
eye is easily irritated and fatigued. Do not rub the eye, for
it is easy to introduce germs by means of dirty fingers. If
any foreign matter like dust gets in the eye, pull the upper lid
down by means of the eyelashes. If the body is not removed
by the flow of tears that follows, roll the upper eyelid back over
a pencil or other small rounded object and remove the foreign
body with a piece of clean, soft cloth. Boracic acid dissolved
in warm water makes the best eye wash.

Fatigue of the eye may be brought about in a number of ways
in which the tiny muscles of the eye are overtaxed and exhausted.
Where a bright light falls on white paper and makes a reflection
the eye becomes tired from trying to shut out some of the light-

EFFECTS OF ALCOHOL 401

Too much or too little light is bad, as is reading in a flickering
light, as on the cars. Especially must we watch a farsighted eye
for eye strain, as its vision seems perfect but there is a constant
strain on the part of the muscles of acconmaodation which soon
results in headache.

Effects of Alcohol. — We have abeady spoken of alcohol hav-
ing a paralyzing effect upon the nervous system. This seems
to be shown in a number of different ways.

Professor Hodge of Clark University describes many of his own experi-
ments showing the effect of alcohol on animals. He trained four selected
puppies to recover a ball thrown across a gymnasium. To two of the dogs
he gave food mixed with dietetic doses of alcohol, while the others were
fed normally. The ball was thrown 100 feet as rapidly as recovered. This
was repeated 100 times each day for fourteen successive days. Out of
1400 times the dogs to which alcohol had been given brought back the ball
only 478 times, while the others secured it 922 times. This seems to indi-
cate that the puppies given alcohol in their diet did not react as quickly
to the stimulus of the thrown ball as the others did. They were sluggish,
both mentally and physically.

Dr. Parkes experimented with two gangs of men, selected to be as
nearly similar as possible, in mowing. He found that with one gang ab-
staining from alcohoHc drinks and the other not, the abstaining gang
could accomphsh more. On transposing the gangs the same results were
repeatedly obtained. Similar results were obtained by Professor Aschaffen-
burg of Heidelberg University, who found experimentally that men " were
able to do 15 per cent less work after taking alcohol."

The Effect of Alcohol upon Intellectual Ability. — It has been thought
that alcohol in smaU quantities quickened the mental action, but a long
series of experiments shows conclusively that this is untrue. KraepeUn
shows that alcohol lengthens the time taken to perform complex mental work.

The Drink Habit. — One of the harmful effects of alcohol
upon those who use it is the formation of the alcohohc
habit. The first effect of drinking alcoholic Hquors is that
of exhilaration. After this feeling is gone, for it is a tempo-
rary state, the subject feels depressed and less able to work
than before he took the drink. To overcome this feeUng, he
takes another drink. The result is that before long he finds a
habit formed from which he cannot escape. With body and
mind weakened, he attempts to break off the habit. But
meanwhile his will, too, has suffered from overindulgence. He
has become a victim of the drink habit!

402 NERVOUS SYSTEM AND ORGANS OF SENSE

Self-indulgence, whether in gratification of such a simple de-
sire as for candy or the more harmful indulgence in tobacco or
alcoholic beverages, is dangerous — not only in its immediate
effects on the tissues and organs, but in its more far-reaching
effects on habit formation.

The Moral, Social, and Economic Effect of Alcoholic Poison-
ing. • — In the struggle for existence, it is evident that the man
whose intellect is the quickest and keenest, whose judgment is
most sound, is the one who is most likely to succeed. The

paralyzing effect of alcohol
upon the nerve centers
must place the drinker at
a disadvantage. In a hun-
dred ways, the drinker
sooner or later feels the
handicap that the habit of
drink has imposed upon
him. Who knows the num-
ber of railway accidents
that have been due to the
uncertain eye of some en-
gineer who mistook his
signal?

In business and in the
professions, the story is the
same. The abstainer wins
over the drinking man.

Not alone in activities o)
life, hut in the length of life,
has the abstainer the ad-
vantage. Figures presented by life insurance companies show
that the nondrinkers have a considerably greater chance of long
life than do drinking men. So decided are the results shown by
those figures that several companies have lower premiums for
nondrinkers than for the drinkers who insure with them.

It is the economic argument that largely won the fight for
prohibition that resulted in the Eighteenth Amendment. Think-
ing people all over the United States began to realize the

Proportion of crime due to alcohol in various
countries.

ALCOHOLIC POISONING 403

harm that the abuse of Hquor wrought on the nation. Follow-
ing the enforcement of the prohibition law, we find example
after example of better economic conditions. Money which
formerly went for drink is now used for better food and niore
of it, for useful and helpful articles in the home, for the purchase
of homes and for investment and saving.

Summary. — It would be impossible to sum up in a few
words the contents of this chapter. We have seen that the
nervous system through its sense organs (as the eye, ear, and
organs of pressure, touch, heat, cold, and taste) informs us con-
cerning our environment. The central nervous system directs
and coordinates action through the sensory and motor nerves
and the brain. There is also an autonomic system which takes
care of the body functions not under our control.

Problem Questions. — 1. What is the work of the central
nervous system? of the autonomic nervous system? How
have these facts been proved?

2. What are the functions of the cerebrum? the cerebellum?
the spinal cord?

3. What is a neuron?

4. What is a reflex? Explain fully.

5. How are habits formed?

6. What are sensations? What are sense organs?

7. How do we taste? hear? see?

8. What are some eye defects and how may they be cor-
rected?

9. What are the chief reasons against the use of alcohol from
the standpoint of the nervous system?

Peoblem and Project References

Davison, The Human Body and Health. American Book Company'.

Gulick, Control of Body and Mind. Ginn and Company.

Hough and Sedgwick, The Human Mechanism. Ginn and Company.

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Martin, The Human Body. Henry Holt and Company.

Ritchie, Human Physiology. World Book Company.

Sharpe, A Laboratory Manual. American Book Company.

Starling, Human Physiology. Lea and Febiger.

XXIX. GOOD HEALTH AND HOW TO. KEEP IT

Problem. A study of personal hygierie. (Laboratory Manual,
Proh. LVI; Laboratory Problems, Probs. 234 to ^49.)

Health and Disease. — In previous chapters we have con-
sidered the body as a machine more deHcate in its organiza-
tion than the best-built mechanism made by man. In a state
of health this human machine is in good condition; disease
is a condition in which some part of the body is out of order,
thus interfering with the smooth running of the mechanism.

Personal Hygiene. — It is the purpose of the study of hygiene
to show us how to live so as to keep the body in a healthy
state. Hygiene not only prescribes certain laws for the care of the
various parts of the body, — the skin, the teeth, the food tube
and the sense organs, — but it also shows us how to avoid dis-
ease. The foundation of health later in life is laid down at
the time we are in school; for that reason, if for no other, a
knowledge of the laws of hygienic living is necessary for all
school children. Unlike some of the lower animals, we can
change or modify our immediate surroundings so as to make
them better and more hygienic places to live in. Hygienic
conditions in homes and around them should be improved as we
learn more about the value of a sanitary environment. It is the
purpose of this chapter to show how we may do our share to
cooperate with those in charge of the public health in our towns
and cities.

Some Methods of Prevention of Disease. — The proverb,
" An ounce of prevention is worth a pound of cure," has much
truth in it. Disease is largely preventable. Fresh air, the
needed amount of sleep, moderate exercise, and pure food
and water are essentials in hygienic living and in escape from
disease.

Pure Air Needed. — What do we mean by fresh air, and why
do we need it? We have already seen that oxidation takes

404

PURE AIR

405

place within the body, and that air receives the carbon dioxide
which is given off as a product of respiration. In addition to
the carbon dioxide, water vapor and heat are given off as well as a
very small amount of organic material of a poisonous nature.
It is the presence of this material that gives rise to the odor
noticeable in a close room. But other organic material is
found in air. Dust from the street contains bacteria of many
kinds, some of which may be disease-producing. Thus may be
spread bacteria from the respiratory tracts of people who have

■j

1

E^^^"^

M

^1

^m

^^^^^

m|

^m^^^^g^

^^^liS

In

j|||||iB^^^ ^

^

1

■HhHII^^.-..

. ^

„

^m

A. B.

Two cultures. A was exposed to the air of a dirty street in the crowded part of
Manhattan. B was exposed to the air of a well-cleaned and watered street in
the uptown residence portion. Which culture has the more colonies of bacteria?
How do you account for this?

colds, pneumonia, diphtheria, or tuberculosis. Much of the dust
is dried excreta of animals. Soft-coal smoke does its share to
add to the impurities of the air, while sewer gas and illuminat-
ing gas are frequently found in sufficient quantities to poison
people. Pure air is, as can be seen, almost an impossibility in
a great city.

How to get Fresh Air. — As we know, green plants give off
in the sunlight considerably more oxygen than they use, and
they take in carbon dioxide. The air in the country is naturally
purer than in the city, as smoke and bacteria are not so preva-
lent there, and the numerous plants give off oxygen. In the
city the night air is purer than day air, because the fac-
tories have stopped work, the dust has settled, and fewer

406 GOOD HEALTH AND HOW TO KEEP IT

people are on the streets. The old myth that " night air " is
injurious has long since been given up, and thousands of people
of delicate health, especially those who have weak throats or
lungs, are regaining health by sleeping out of doors or with the
windows wide open. It is essential in sleeping out of doors
or in a room with a low temperature that the body be kept
warm and the head be protected from strong drafts by a night-
cap or hood. Proper ventilation at all times is one of the
greatest factors in good health.

Change of Air. — Persons in poor health, especially those hav-
ing tuberculosis, are often cured by a change of air. This is
not always due so much to the composition of the air as to
change of occupation, rest, and good food. Mountain air is
dry, and relatively free from dust and bacteria, and often helps
a person having tuberculosis. Air at the seaside is beneficial
for some forms of disease, especially hay fever and bone tuber-
culosis. Many sanitariums
have been established for
this latter disease near the
ocean, and thousands of lives
are being saved in this way.
The Relation of Pure
Food and Pure Water to
Health. — Thanks to the
care of state and city govern-
ments there is little need
nowadays for the health of
any individual to suffer from
impure food or water. But
that people do become sick
and die from such causes
every day is well known, as
is shown by the many cases of typhoid fever, summer com-
plaint, and ptomaine poisoning of various sorts. Our milk may
have been watered or sent in cans washed with water containing
typhoid germs, we may eat oysters bred in contaminated lo-
calities, we may. have received and eaten fruits or vegetables
sprinkled with water containing the germs. Our laws, however

Tracks of germs left by a fly crawling on
* sterilized media in a dish. *

EXERCISE AND SLEEP 407

good, cannot cope with human carelessness. Not only should
we as individuals demand from the source of supply pure
food and water, but we should do our share at home to keep
them pure. Flies and other insects shpuld be prevented from
reaching food. Vegetables and fruits must not be eaten in
an unripe or half-rotten condition, nor should the latter be
canned or preserved. All raw fruits and vegetables should
be either peeled or washed before eating. In general, foods
may be made safe to eat by cooking long enough to kill the
germs. Milk to be rendered absolutely safe should be pas-
teurized (so called after Louis Pasteur, the originator of the
process), that is, heated to 160° Fahrenheit for 20 minutes.
Ptomaine poisoning is often caused by bacteria in canned
material which were not killed in the cooking and which act upon
the proteins causing them to form poisons or ptomaines. Such
foods are dangerous, for cooking does not destroy the poison.
Meats which have been hung so long as to have an odor,
and cold storage meats that appear to be decayed, should be
avoided.

Relation of Proper Exercise and Sufficient Sleep to Health. —
We are all aware that exercise in moderation has a beneficial
effect upon the human organism. The pale face, drooping
shoulders, and narrow chest of the boy or girl who takes no
regular exercise are too well known. Exercise, besides giving
work to the muscles, increases the activity of the heart and lungs,
causing deeper breathing; it liberates heat and carbon dioxide
from the tissues where the work is taking place, thus increasing
the respiration of the tissues themselves, and aids mechanically
in the removal of wastes from tissues. It is well known that
exercise, when taken some little time after eating, has a very
beneficial effect upon digestion. Exercise and games, especially
if a change of occupation, are of immense importance to the
nervous system as a means of rest. The increasing number of
playgrounds in this country is due to this acknowledged need
of exercise for growing children.

Proper exercise should be moderate and varied. Walking in
itself is a valuable means of exercising certain muscles, and so is
bicycling, but neither is ideal as the only form to be used. Vary

408 GOOD HEALTH AND HOW TO KEEP IT

your exercise so as to bring different muscles into play, take
exercise that will allow free breathing out of doors if possible,
and the natural fatigue which follows will lead to the rest and
sleep that every normal body requires.

Sleep is one way in which all cells in the body and particularly
those of the nervous system get their rest. The nervous system,
by far the most delicate and hardest worked set of tissues in the
body, needs rest more than do other tissues, for its work direct-
ing the body ends only with sleep or unconsciousness. The
afternoon nap, snatched by the brain worker, gives him re-
newed energy for his evening's work. It is not hard applica-
tion to a task that wearies the brain; it is continuous work
without rest.

Effect of Alcohol on the Ability to Resist Disease. — Among
certain classes of people the behef exists that alcohol in the
form of wine, beer, brandy, or some other drink, or in patent
medicines, rhalt tonics, and the like, is of great importance in
building up the body so as to resist disease or in curing it after
disease has attacked it. Nothing is farther from the truth.
In experiments on over three hundred animals, including dogs,
rabbits, guinea pigs, fowls, and pigeons, Laitenen of the Uni-
versity of Helsingfors and Professor Frankel of Halle found
that alcohol without exception made these animals more sus-
ceptible to disease than were the controls.

Use of Alcohol in the Treatment of Disease. — In the Lon-
don Temperance Hospital alcohol was prescribed seventy-five
times in thirty-three years. The death rate in this hospital
has been lower than that of most general hospitals. One of the
most serious misconceptions is that alcohol helps people who
have tuberculosis to fight that disease successfully. Nothing
is farther from the truth.

In a paper read at the International Congress of Tubercu-
losis, in New York, 1906, Dr. Crothers reported that alcohol
as a remedy or a preventive medicine in the treatment of
tuberculosis is a most dangerous drug, and that all prepara-
tions of sirups containing spirits increase, rather than diminish,
the disease.

Professor Guttstadt of Berlin publishes statistics showing;

EFFECTS OF ALCOHOL

409

that in Prussia of every 1000 deaths of men over twenty-five
years, 161 are from tuberculosis. Of every 1000 deaths among
bartenders, 556 are from tuberculosis; among brewery em-
ployees, 345; school-teachers, 143; physicians, 113; clergy, 76.
The fifty-fifth annual report of the British Registrar General
gives the average death rate of England as 13 per thousand, but
among brewers it is 41 per thousand, only four occupations
showing a higher rate.

Experience of Insurance Companies. — The United Kingdom
Temperance and General Provident Institution of London in-
sures in two departments, a general section and one for total ab-
stainers- During the 60 years from 1841 to 1901 there were
31,776 whole-life policies in the general or nonabstaining sec-
tion. These passed through 446,943 years of Hfe, and there were
8947 deaths. In the abstaining section there were 29,094 whole-
life policies, passing through 398,010 years of life, with 5124
deaths. If the death rate in the abstaining section had equaled
that in the general section, there would have been 6959 deaths
instead of 5124. In other words, the mortality averaged 36
per cent higher in the nonabstaining section than in the
abstaining section.

JL

2P

JL

,^ 53,044
liveto/OYrs.

Of 100,000
Non drinkers

aged20yrs,

OfmOOO I 42,/09

40

JSL.

60

7.0

SO

90

46.956
die earlier

57,981
die earlier

10 20 30 40 SO 60 TO

Effect of drinking upon probability of long life.

80

90

100

100

In an article published in a book by Horsley and Sturge,
Dr. Arthur Newsholme shows that of 100,000 total abstainers
starting at the age of 20 years, 53,044 reach 70 years, while
46,956 die before 70 years; but of 100,000 moderate drinkers
starting at 20, 42,109 reach 70 years, while 57,891 die before
70 years.

In the Scottish Temperance Life Assurance Society, in the

HUNT. NEW E8. — 97

410 GOOD HEALTH AND HOW TO KEEP IT

twenty years ending 1897, the deaths amounted to 69 per cent
of the expected mortaHty in the general section, while in the
total abstainers' section they amounted to only 47 per cent of
the expected number. The number of deaths in the general
section of the Sceptre of Life Association, England, was 80.34
per cent of the expectation in the fifteen years ending 1898,
but in the total abstainers' section it was only 56.37 per cent
of the expected mortaUty.

In considering the statistics of the insurance companies, it is
well to remember that those insured in the general sections were
picked men as well as those in the total abstainers' sections.

In discussing the experience of fraternal societies, Dr. News-
holme gives the following statistics from the report of the Pub-
lic Actuary of South AustraHa: —

Average Mor- Average

TAiiiTY Per Sickness in

Cent Weeks

Abstainers' Societies 0.689 1.248

Nonabstainers' Societies 1.381 2.317

Mortality Per Average Weeks op

Cent op Sick Sickness per Each

Members Member Sick

Abstainers' Societies 3.557 6.45

Nonabstainers' Societies 6.532 10.91

Attention should be called to the fact that the nonabstain-
ers' societies have many members who are total abstainers,
but, unlike the abstainers' societies, they do not refuse to ad-
mit nonabstainers. The number of weeks of sickness in the
table refers to the average number of weeks for which the
members call upon the sick fund of the society. All of these
facts quoted prove that from the standpoint of health as well
as economically alcohol is a menace.

Rules of Hygiene. — The following are rules of individual
hygiene as summarized by Professor Irving Fisher, of Yale.

Air

Keep out of doors as much as possible.

Breathe through the nose, not through the mouth.

When indoors, have the air as fresh as possible —

(a) By having aired the room before occupancy.

(6) By having it continuously ventilated while occupied.

RULES OF HYGIENE 411

Not only purity, but coolness, dryness, and motion of the air, if not very
extreme, are advantageous. Air in heated houses in winter is usually too
dry, and may be humidified with advantage.

Clothing should be sufficient to keep one warm. The minimum that will
secure this result is the best. The more porous your clothes, the more
the skin is educated to perform its functions with increasingly less need
for protection. Take an air bath as often and as long as possible.

Water

Take a daily water bath, not only for cleanliness, but for skin gym-
nastics. A cold bath is better for this purpose than a hot bath. A short
hot followed by a short cold bath is still better. In fatigue, a very hot
bath lasting only half a minute is good.

A neutral bath, beginning at 97° or 98°, dropping not more than 5°,
and continued 15 minutes or more, is an excellent means of resting the
nerves.

Be sure that the water you drink is free from dangerous germs and
impurities. ' " Soft " water is better than " hard " water. Ice water
should be avoided unless sipped and warmed in the mouth. Ice may
contain spores of germs even when germs themselves are killed by cold.

Cool water drinking, including especially a glass half an hour before
breakfast and on retiring, is a remedy for constipation.

Food

Teeth should be brushed thoroughly several times a day, and floss silk
used between the teeth. Persistence in keeping the mouth clean is good
not only for the teeth, but for the stomach.

Masticate all food up to the point of involuntary swallowing, with the
attention on the taste, not on the mastication. Food should simply be
chewed and relished, with no thought of swallowing. There should be
no more effort to prevent than to force swallowing. It will be found that
if you attend only to the a^eeable task of extracting the flavors of your
food, nature will take care of the swallowing, and this will become, Hke
breathing, involuntary. The more you rely on instinct, the more normal,
stronger, and surer the instinct becomes. The instinct by which most
people eat is perverted through the " hurry habit " and the use of abnor-
mal foods. Thorough mastication takes time, and therefore one must
not feel hurried at meals if the best results are to be secured.

Sip Uquids, except water, and mix with sahva as though they were
soUds.

The stopping point for eating should be at the earliest moment when
one is really satisfied.

The frequency of meals and time to take them should be so adjusted
that no meal is taken before a previous meal is weU out of the way, in

412 GOOD HEALTH AND HOW TO KEEP IT

order that the stomach may have had time to rest and prepare new juices.
Normal appetite is a good guide in this respect. One's best sleep is on an
empty stomach. Food puts one to sleep by diverting blood from the head,
but disturbs sleep later. Water, however, or even fruit may be taken
before retiring without injury.

An exclusive diet is usually unsafe. Even foods which are not ideally
the best are probably needed when no better are available, or when the
appetite especially calls for them.

The following is a very tentative list of foods in the order of excellence
for general purposes, subject, of course, to their palatability at the time
eaten: fruits, nuts, grains (including bread), butter, buttermilk, salt in
small quantities, cream, milk, potatoes, and other vegetables (if fiber is
rejected), eggs, custards, digested cheeses (such as cottage cheese, cream
cheese, pineapple cheese, Swiss cheese, Cheddar cheese, etc.), curds, whey,
vegetables (if fiber is swallowed), sugar, chocolate, and cocoa, putrefactive
cheeses (such as Limberger, Rochefort, etc.), fish, shellfish, game, poultry,
meats, liver, sweetbreads, meat soups, beef tea, bouillon, meat extracts,
tea and coffee, condiments (other than salt), and alcohol. None of these
should be absolutely excluded, unless it be the last half dozen, which, with
tobacco, are best dispensed with for reasons of health. Instead of exclud-
ing specific food, it is safer to follow appetite, merely giving the benefit of
the doubt between two foods, equally palatable, to the one higher in the
list. In general, hard and dry foods are preferable to soft and wet foods.
Use some raw foods — nuts, fruits, salads, milk, or other — daily.

The amount of protein required is much less than ordinarily consumed.
Through thorough mastication the amount of protein is automatically re-
duced to its proper level.

The sudden or artificial reduction in protein to the ideal standard is
apt to produce temporarily a " sour stomach," unless fats be used abun-
dantly.

To balance each meal is of the utmost importance. When one can trust
the appetite, it is an almost infallible method of balancing, but some
knowledge of foods will help. The aim, however, should always be —
and this cannot be too often repeated — to educate the appetite to the
point of deciding all these questions automatically. •

Exercise and Rest

The hygienic life should have a proper balance between rest and exer-
cise of various kinds, physical and mental. Generally every muscle in the
body should be exercised daily.

Muscular exercise should hold the attention, and call into play will
power. Exercise should be enjoyed as play, not endured as work.

The most beneficial exercises are those which stimulate the action of
the heart and lungs, such as rapid walking, running, hill climbing, and
swimming.

RULES OF HYGIENE 413

The exercise of the abdominal muscles is the most important in order to
give tone to those miLscles and thus aid tlie portal circulation. For the
same reason erect posture, not only in standing, but in sitting, is im-
portant. Support the hollow of the back by a cushion or otherwise.

Exercise should always be hmited by fatigue, which brings with it
fatigue poisons. This is nature's signal when to rest. If one's use of diet
and air is proper, the fatigue point will be much farther off than other-
wise.

One should learn to relax when not in activity. The habit produces
rest, even between exertions very close together, and enables one to con-
tinue to repeat those exertions for a much longer time than otherwise.
The habit of lying down when tired is a good one.

The same principles apply to mental rest. Avoid worry, anger, fear,
excitement, hate, jealousy, grief, and all depressing or abnormal mental
states. This is to be done not so much by repressing these feelings as by
dropping or ignoring them — that is, by diverting and controlling the atten-
tion. The secret of mental hygiene Hes in the direction of attention.
One's mental attitude, from a hygienic standpoint, ought to be optimistic
and serene, and this attitude should be striven for not only in order to pro-
duce health, but as an end in itself, for which, in fact, even health is prop-
erly sought. In addition, the individual should, of course, avoid infection,
poisons, and other dangers.

Occasional physical examination by a competent medical examiner is ad-
visable. In case of illness, competent medical treatment should be sought.

Finally, the duty of the individual does not end with personal hygiene.
He should take part in the movements to secure better pubHc hygiene
in city, state, and nation. He has a selfish as well as an altruistic motive
for doing this. His air, water, and food depend on health legislation and
administration.

All the foregoing rules are important. The results which
may be obtained by following them depend largely on the
thoroughness with which they are followed. This is true es-
pecially of fresh air and mastication. If all the rules are
followed and followed thoroughly, including the one most com-
monly neglected, — namely, keeping within the fatigue limit,
— the average man may reasonably expect to add greatly to his
length of life, his activity per day, his satisfactions, and his
usefulness. The laws of " humaniculture " can be depended
upon as much as those of agriculture, horticulture, or stock
raising.

Summary. — The human machine, In order to do its most
efficient work, must be properly cared for. This chapter has

414 GOOD HEALTH AND HOW TO KEEP IT

given us some suggestions. Pure air and plenty of it, sun-
light, pure food and water, a dietary selected from the best of
foods given on page 412, rest and recreation as well as work
and a careful following out of Dr. Fisher's laws of health will go
far toward making each one of us healthy and happy.

Problem Questions. — 1. What has fresh air to do with
health?

2. How can we get fresh air best in large cities?

3. What is pure water? How can we be sure it is pure?

4. What is pure milk and how can it be obtained?

5. What is the relation of exercise to health?

6. What is the relation of alcohol to health as proved by
statistics?

7. Make up a balanced diet for yourself for one week. Why
choose the foods you have taken?

8. What is fatigue? How does it cause trouble to a young
person ?

Problem and Project References

Bergey, Principles of Hygiene. W. B. Saunders Company.

Broadhurst, Home and Community Hygiene. J. B. Lippincott Company.

Chapin, Health First. The Century Company.

Fisher and Fisk, How to Live. Funk and Wagnalls Company.

Hazen, Clean Water and How to Get It. Wiley.

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Hunter and Whitman, Civic Science. American Book Company.

Lee, Health and Disease. Little, Brown and Company.

Pyle, Personal Hygiene. W. B. Saunders Company.

Sherman, Chemistry of Food and Nutrition. The Macmillan Company,

Sharpe, A Laboratory Manual. American Book Company.

XXX. HEALTH AND DISEASE. A CHAPTER ON

CIVIC BIOLOGY

Problem. How the civic authorities protect us from disease.

Public Sanitation and Hygiene. — To-day, as never before,
people are beginning to realize their part in the campaign against
disease. Not only is the teaching of hygiene required in our
schools but much practical health work is being done by the
boys and girls in the schools. High school boys and girls have
organized anti-fly and anti-mosquito campaigns which have
resulted in the stamping out of diseases carried by flies and of
malaria in some communities. High school boys and girls have
organized sanitary and service squads which have resulted in
better sanitary conditions in schools and school grounds. High
school boys and girls have taken the inspiration for healthy
living from their biology laboratories to their homes and have
planted in them the seeds of practical hygiene and sanitation.
This chapter may help other boys and girls to do their part in
making conditions better in their communities.

The Work of the Department of Street Cleaning. — In any
city one menace to the health of its citizens exists in the refuse
and garbage. The city streets, when dirty, contain countless
millions of germs which have come from decaying material, or
from people ill with contagious diseases. In large cities a depart-
ment of street cleaning not only cares for the removal of dust
from the streets, but also has the removal of garbage, ashes, and
other waste as a part of its work. The practice of putting
open cans containing ashes and garbage into the street for
removal is an indirect means of spreading disease, for flies breed
and germs thrive in them. The street-cleaning department
should be aided by every citizen; rules for the separation of
garbage, papers, and ashes should be kept. Garbage and ash
cans should be covered. The practice of upsetting ash or garbage

415

116

HEALTH AND DISEASE

cans is one which no young citizen should allow in his neigh-
borhood, for sanitary reasons. The best results in street-clean-
ing in summer are obtained by washing or flushing the streets,
for thus the dirt containing germs is prevented from getting
into the air. The garbage is removed in carts, and part of it
is burned in huge furnaces. The animal and plant refuse is
cooked in great tanks; from this material the fats are ex-

A style of truck for collecting rubbish (on top) and garbage or ashes (below).

tracted, and the solid matter is sold for fertilizer. Ashes are
used for filhng marsh land. Thus the removal of waste matter
may pay for itself in a large city.

The Necessity of a Pure Milk and Water Supply. — The city
of New York has spent hundreds of milHons of dollars to
bring a supply of pure water to her citizens. Other cities are
doing the same. The world has awakened to the necessity of a
pure water supply, largely because of the number of epidemics
of typhoid which have been caused by contaminated water.
Typhoid fever germs live in the food tube, hence the excreta of
a typlioid patient contain large numbers of germs wliich often
pass from the sewers into the drinking water. Many cities take

MILK AND WATER SUPPLY

417

their water supply directly
from rivers, sometimes not
far below another large
town. Such cities are in
danger of having their wa-
ter supply polluted. Some
cities on very large lakes
take their supply of water
from the lakes into which
their sewage flows. In cities
which drain their sewage
into rivers and lakes, the
question of maintaining
sanitary conditions is a
large one, and many cities
now have means of dispos-
ing of their sewage so that
it is harmless to their
neighbors. Filtering pol-
luted water by passing it
through settling basins and
sand filters removes about
98 per cent of the germs.
The results of drinking un-
filtered and filtered water
in certain large cities are
shown graphically in the
diagram. In addition to
filtering, some cities add
chlorine to their water in
very minute quantities but
enough to kill all harmful
germs. Thus water from
impure sources is made fit
to drink.

In the country typhoid
may be spread by the germs
getting into a well or spring

Growth of bacteria in a drop of im-
pure water allowed to run down a steril
ized culture in a dish.

Cases of typhoid per 100,000 inhabitants
before filtering water supply (solid) and after
(shaded) in A, Watertowii, N. Y.; B, Albany,
N. Y.; C, Lawrence, Mass.; D, Cincinnati, O.
What is the effect of filtering the water supply?

418

HEALTH AND DISEASE

from which the supply of water comes. This may be avoided
by having privies and cesspools some distance from the well or
spring and so placed that they drain away from it. Wells should
have a cemented cap around the top so as to keep out surface
water. The deeper water is less dangerous, as germs rarely Hve
long more than five feet below ground.

Serious outbreaks of typhoid have been traced to contam-
inated milk supplies. A case of typhoid exists on a farm; the
sewage gets into the well from which water is used for the
washing of milk cans. Typhoid germs thrive in the milk. Thus

^?AJ9M A

\

•

•••• ••••

•• ••••

•

•• • •••

► -

*

• ••••••

• • •• •

•• ••••

•

• •••••

•••

•

•••

• •••

• •

•
•

•

• •••• •

■ •• ••••••

A L^J I 1

♦—*•

J^AftM B

• • • •• • •

How typhoid may spread. Each square represents a city block,
and each black dot represents a case of typhoid in houses sup-
plied with milk from Farms A and B. There is a case of typhoid
at Farm A. The cans from B are washed at A and returned to B.

the milkman spreads disease. The diagram on this page illus-
trates a recent epidemic, which was traced to a farm on which
was a person having typhoid.

Railroads are often responsible for spreading typhoid. It is
said that an outbreak of typhoid in Scranton, Pa., was due to
the fact that the excreta from a typhoid patient traveling in a
sleeping car were washed by rain into a reservoir near which
the train was passing. Railroads are thus seen to be great open
sewers. A sanitary car toilet should be provided so that filth
and disease will not be scattered over the country.

BOARDS OF HEALTH 419

Work of a Board of Health. — Although it is absolutely
necessary for each individual to obey the laws of health if he
or she wishes to keep from disease, it has also become neces-
sary, especially in large cities, to have general supervision over
the health of people Hving in a community. This is done by
means of a department or board of health which cares for pub-
He health. A Hst of regulations and laws known as the Sani-
tary Code is given out to the citizens. These regulations concern
the care of buildings and plumbing, the cleanliness of street cars
and other public vehicles, the protection and supervision of foods
sold, the inspection of our suppHes of milk and water, and, par-
ticularly, the control of contagious diseases.

How the Board of Health fights Typhoid and Other Dis-
eases. — Pure water is the first essential in preventing epi-
demics of typhoid. Health board ofl&cials are constantly test-
ing the water supply, and if any harmful bacteria appear
the water is chlorinated and a warning is sent out to boil the
water. Boiling water for 10 minutes kills harmful germs.

The milk supply is also subject to rigid inspection. Milk
brought into a city is tested, not only for the amount of cream
present to prevent dilution with water, but also for the pres-
ence of germs. The cleanliness of the cans, wagons, etc., is
also watched. The cows are also tested to see if they have
tuberculosis, for infected cows might spread the disease to
human beings.

During the summer months many babies die from diarrhoea.
This disease is spread almost entirely through impure milk,
which often becomes infected by flies carrying the germs to it.
Spread of diseases through milk can be prevented by careful
pasteurization (heating to 160° F. for 20 minutes). In many
large cities pasteurized milk is sold at a reasonable price to
poor people, and thus much disease is prevented.

How the Board of Health fights Tuberculosis. — Tubercu-
losis, which a few years ago killed fully one seventh of the
people who died from disease in this country, now kills less
than one tenth. This decrease has been largely brought about
because of the treatment of the disease. Since it has been
proved that tuberculosis if treated early enough is curable, by

420

HEALTH AXD DISEASE

quiet Kving, good food, and 29?€7?/?/ of fresh air and light, we
find that numerous sanatoria have come into existence which
are supported by private or pubhc means. At these sanatoria
the patients live out of doors, and sleep in the open ah^, while
they have plenty of nourishing food and httle exercise. By
tenement-house laws which require proper air shafts and win-
dow ventilation in dweUings, by laws against spitting in pub-
He places, and in many other ways, the boards of health
in our towns and cities are waging war on tuberculosis.

Tuberculosis Camp, Raybrook Sanatorium, New York. Patients live in the open
air the year round, with open tents for shelter.

Diseases Carried by Food. — Disease germs of various sorts,
typhoid, tuberculosis, scarlet fever, diphtheria, and many others
ma}' be transferred through the agency of food. Fruits and
vegetables maj^ be carriers of disease, especially if they are sold
from exposed stalls or carts and handled b}' the passers-b3^ All
vegetables, fruits, or raw foods should be carefully washed
before using. Spoiled or overripe fruit, as well as meat which
is decayed, is swarming with bacteria and should not be used.
The board of health has super\'ision over the sale of fruit;

BOARDS OF HEALTH 421

meats, fish, etc., and frequently in large cities food unfit for
sale is condemned and destroyed.

Infectious Diseases; Quarantine and Disinfection. — One

of the important means for preventing the spread of diseases
caused by bacteria or protozoa is by quarantine, or isolation of
the person who has the disease. No one save the doctor and
nurse should enter the room of the person quarantined. After
the disease has run its course, the clothing, bedding, etc., in the
sickroom should be disinfected by boiling in soapy water. The
patient should be washed carefully, including the mouth, face
and hair, and should be dressed in sterile clothes before being
allowed to see people again. The room should be thoroughly
cleaned and the woodwork washed with hot soapy water. In this
way disease germs are destroyed and the danger of contagion is
prevented.

Immunity. — To prevent germ diseases we must kill many of the
germs by attacking them directly with poisons (the poisons thus
used are called germicides or disinfectants), and we must keep
in such condition that we do not take disease when we come in
contact with the germs that cause it. This insusceptibility or
immunity may be either natural or acquired. Natural immunity
seems to be in the constitution of a person, and may be inherited.
It is racial, some races being more and others less susceptible
to certain diseases. Natural immunity may be reduced by ex-
posure to unfavorable conditions of temperature, by lack of proper
food, by unsanitary living or working conditions and, in particu-
lar, by fatigue. This shows the importance of careful living on
the part of each one of us. Immunity for some diseases may be
acquired by means of antitoxin, as in diphtheria. This treatment,
as the name denotes, is a method of neutralizing the poison
(toxin) caused by the bacteria in the system. It was discovered
by a German, Von Behring, that the serum of the blood of an
animal immune to diphtheria is capable of neutrahzing the poison
produced by the diphtheria-causing bacteria in people. Horses
develop large quantities of antitoxin when given the diphtheria
toxin or poison. The serum (or liquid part) of the blood of these
horses is then used to inoculate the patient suffering from or
exposed to diphtheria, and thus the disease is checked or prevented

422

HEALTH AND DISEASE

IJUrriber qf Deathspw- loo
cases o''jDij*ttK.eria, -wKeru
flntito%ii\ 14 used, oiv Sj^Crf^t-*

•^Lstloy No DecftKs

Antitoxin must be
used in the early stages
of diphtheria to be of
value.

altogether. This is known as artificial immunity. By the toxin-
antitoxin treatment, immunity to diphtheria can be given to those

who have not been exposed to the disease.
The Schick test determines at any time
whether a child is already immune : a very
small amount of diphtheria toxin is placed
under the skin of the arm, and the spot will
turn red if the child is not immune.

Vaccination. — Smallpox was once the
most feared disease in this country ; 95 per
cent of the people suffered from it. As late
as 1898, over 50,000 persons a year in Russia
lost their lives from this disease. It is a
contagious disease, probably not caused by bacteria, but by an
animal germ. Smallpox has been brought under absolute con-
trol by vaccination with the substance (called virus) which causes
cowpox in a cow. Cowpox is like a mild form of smallpox, and
the introduction of this virus gives a person complete immunity
to smallpox for several years after vaccination. This immunity
is caused by the formation of a germicidal substance in the blood,
due to the introduction of the vaccine containing the weakened
virus. Vaccination was first tried by the English physician
Jenner, who noted that dairymaids who had had cowpox did not
take smallpox.

Vaccination for typhoid and paratyphoid is now practiced
almost universally. Since the World War it has
been proved that man can be kept free from
these diseases, which in our Spanish-American
War killed many times more soldiers than did
Spanish bullets. This type of vaccination con-
sists in introducing into the body the dead germs
which cause typhoid. These germs have their
toxins still in their dead bodies and immediately
cause the blood to manufacture antibodies to
fight the poisons thus introduced.

After three inoculations, each containing from
500,000,000 to 1,000,000,000 or more dead germs, the body
obtains enough of the resistant antibodies to become immune

■Wo ATitJtow. Antitoirir-'

-U5€<3L OA^ used.-or>->

•iOOcoot*-' J^ coSc*

Jr

J^ealK»

Typhoid anti-
toxin has greatly
reduced the death
rate from typhoid.

PUBLIC CONTROL OF DISEASE 423

fco typhoid. Similar treatment is also used for boils, colds, and
influenza.

Immunity which is gained by the blood being stimulated
to form antibodies which fight the bacteria or their poisons is
known as active immunity. Examples of such immunity are seen
in the treatment of smallpox or typhoid.

Public Control of Disease. — Not only do we have city health
departments but state- and nation-wide agencies are at work also.
State departments of health are active in twenty-six states. The
Federal PubHc Health Service now exercises interstate control of
communicable diseases — malaria, meningitis, hookworm, and the
like. In addition to this the Rockefeller Institute is inves-
tigating the harm hookworm is doing all over the world. It
has been found that 75 per cent of the inhabitants of Southern
China, from 60 to 80 per cent of the 300,000,000 inhabitants
of India, and practically all of the laborers of some South Ameri-
can tropical regions are infested with hookworms. Since this
tiny organism not only reduces the working ability of a per-
son, but also makes him much more liable to other diseases,
especially tuberculosis, it can be seen that if the disease ia
stamped out the world will be much better off. This is not
a difficult task if all cooperate, for the hookworms can be forced
out of the body by means of thymol and Epsom salts.

Many other diseases, such as tuberculosis, bubonic plague,
typhoid, and smallpox, will eventually be practically wiped out
of existence by medical knowledge, and helpful cooperation of
rich and poor ahke.

Summary. — Examples of what private and public control
of diseases may do are seen when we consider the specific case
of the disease known as smallpox. In the eighteenth century
5,000,000 people are said to have died from it; one hundred
years ago it was exceedingly common in all large cities in this
country. To-day an epidemic of smallpox is impossible, thanks
to the discovery of vaccination and prompt action by the
health departments. Tuberculosis at the present time kills
more people annually than any other disease, and yet it is be-
lieved that by sanitary Hving we shall stamp out the disease
within fifty years if we go on at the present rate. Public

424

HEALTH AND DISEASE

400

300

200

100

^^—

hygiene is largely responsible for the lessening of deaths from
typhoid fever and other diseases whi(;li aie transmitted through
the milk and water supplies. It is estimated that pure milk,

pure water, and pure
air supplied to all would
lengthen the average hu-
man life in the United
States eight years. In
this country and in parts
of Europe where sanita-
tion and hygiene are
practiced, the life of
human beings is gradu-
ally being lengthened.
In India, on the other
1850 I860 1870 1880 1890 1900 1914 mo hand, where little hy-

The curve showing a decreasing death rate giene IS knOWn Or prac-
from tuberculosis. Why do fewer people die ^{qq^ among the maSSeS
from the disease than formerly? 1,11 ,i <•

of people, the length 01
life is not being increased. Theodore Roosevelt said in one of
his last messages to Congress : —

" There are about 3,000,000 people seriously ill in the United States, of
whom 500,000 are consumptives. More than half of this illness is prevent-
able. If we count the value of each life lost at only $1700 and reckon the
average earning lost by iUness at $700 a year for grown men, we find that
the econonu'c gain from mitigation of preventable disease in the United
States would exceed $1,500,000,000 a year. This gain can be had through
medical investigation and practice, school and factory hygiene, restriction
of labor by women and children, the education of the people in both pub-
lic and private hygiene, and through improving the efficiency of our health
service, municipal, state, and national."

Problem Questions. — 1. What is the value of public health
agencies in a conmiunit}^?

2. How does water affect health? Milk? Foods?

3. How may typhoid be spread? tuberculosis?

4. What is immunity? How may it be obtained for ty-
phoid? smallpox? diphtheria?

5. What pubhc agencies control disease?

HEALTH AND DISEASE

425

6. What is the hookworm disease and how may it be fought ?
(See pages 200-201.)

Problem and Peoject References

Allen, Civics and Health. Ginn and Company.

Broadhurst, Home and Community Hygiene. J. B. Lippincott Company.

Davison, The Human Body and Health. American Book Company.

Gulick, The Efficient Life. Doubleday, Page and Company.

Gulick, Town and City. Ginn and Company.

Hough and Sedgwick, The Human Mechanism. Ginn and Company.

Hunter, Laboratory Problems in Civic Biology. American Book Company.

Lee, Health and Disease. Little, Brown and Company.

Richman and Wallach, Good Citizenship. American Book Company.

Ritchie, Primer of Sanitation. World Book Company.

Sharpe, A Laboratory Manual. American Book Company.

Wood, Sanitation Practically Applied. Wiley.

Zinsser, Infection and Resistance. The Macmillan Company.

Part of the supply of pure water for the city of New York; the CrotOQ

Dam and Spillway.

HUNT. NEW E8. — 28

GLOSSARY OF SCIENTIFIC TERMS

(Generic and specific names are not included)

Abdo'men (Lat. abdomen, belly) : the third region of the body of an in-
sect; the region of the body below the chest in man.
Absorp'tion (Lat. ahsorbere, to swallow down): the process of taking up

food or other substances by chemical or molecular action from the

digestive tract or elsewhere.
Adapta'tion (Lat. adaptare, to fit): fitness for surroundings; fitness to do

a certain kind of work; changes which a plant or animal has undergone

that fit it for the conditions in which it fives,
Ad'enoids: fleshy growths in the back of the nose cavity which clog the

air passages.
Adul'terant: a substance put in another to cheapen it; usually reducing

its strength or otherwise injuring it.
Aero'bic organisms: bacteria or other organisms which require free oxygen

as opposed to anaerobic organisms (bacteria and some parasitic worms)

which do not require free oxygen.
Arcohol: a narcotic poison.
Al'ga (pi. Algae) : a low form of plant containing chlorophyll. Its body is

usually a thallus.
Altema'tion of generations: the alternating of a sexual ^dth an asexual

phase in the fife-history of a plant or animal.
Anten'na (pi. Antennae) (Lat. antenna, a sailyard) : a jointed feeler on

the head of an insect or crustacean.
Anten'nules : smaU antennse, or feelers.
Ante'rior (Lat. anterior, former): nearer the head end (Zo5l.); facing

outward from the axis (Bot.).
An'ther (Gr. aniheros, flowery) : the part of the stamen which develops and

contains pollen.
An'tibodies: substances found in the blood which fight against bacteria

or prevent them from harming the body.
Antisep'tic (Gr. anti, against; sepsis, putrefaction): a substance which

prevents the growth of harmful microorganisms.
A'nus (Lat.) the posterior opening of the food tube.
Aor'ta (Gr. aorte, from aeirein, to lift): the large artery leaving the left

ventricle of the heart.
Append' age: a jointed organ attached to the side of the body.

427

428 GLOSSARY

Ar'tery (Lat. arieria, windpipe, artery): a tube which conveys blood

from the heart.
Asep'tic (Gr. a, not; sepHkos, putrid): free from pus-forming bacteria or

other harmful organisms.
Asex'ual: having no sex.
Assimila'tion (Lat. assimilare, to make like): the conversion of digested

food into living matter.
Astig'matism (Gr. a, without; s%ma, spot): a defect of the eye, caused by

an irregularity in the curvature of the lens. It results in indistinctness

of vision.
Au'ricles (Lat. auricula, httle ear) : chambers which receive blood when it

enters the heart.
Autonom'ic nervous system (Gr. autos, self; nemos, province): a part of

the nervous system not under control of the will; the sympathetic

nervous system.

B

Bacil'lus: a rod-shaped bacterium.

Bacte'ria (Gr. bakterion, a little staff): microscopic one-celled plants, some

of which cause specific diseases.
Bacteriology: a study of bacteria.
Bile: a fluid secreted by the liver.
Biorogy (Gr. bios, life; logos, discourse): the study of matter in a living

state, the study of plants and animals.
Blade: the flat portion of a leaf.
Blas'tula (Gr. blastos, a bud): a stage in the segmentation of an egg in

which the cells form a hollow ball with a wall one layer thick.
Bud: an undeveloped branch.

Cal'orie (Large calorie) (Lat. calere, to be warm) : a heat unit, namely, the

amount of heat required to raise the temperature of one kilogram of

water one degree Centigrade.
Calorim'eter : a machine for measuring heat units.
Cam'bium: the growing layer of a stem.
Cap'illaries (Lat. capillus, a hair): minute tubes which connect arteries

with veins.
Capillar'ity: a phenomenon shown by liquids rising in fine tubes.
Car'apace (Sp. carapacho, a covering): a shell-hke covering on the dorsal

side of some animals, as crustaceans.
Carbohydrate (Lat. carbo, coal; Gr. hydor, water): a class of nutrients

composed of carbon, oxygen, and hydrogen, having the oxygen and

hydrogen in the same proportion as water.
Car'bon (Lat. carbo, coal): an element found in all organic compounds.
Carbon dioxide: a gas, a product of the oxidation of carbon.

GLOSSARY 429

Cell: the structural and physiological unit in plant and animal bodies. A

small mass of protoplasm inclosed in a cell membrane and usually

containing a nucleus.
Cell membrane: the deUcate Uving covering of a cell.
Cell sap; water, with materials in solution, found in the vacuoles of plant

cells.
Cellulose: a dead substance found in the cell walls of plants.
Cen'tnim (Lat. centrum, center): the stout body of a vertebra.
Cephalotho'rax (Gr. kephale, head; thorax, chest): body region in crus-
taceans formed by the fusion of head and thorax.
Cerebel'ltmi (Lat., diminutive of cerebrum) : part of the brain between the

cerebrum and the medulla oblongata.
Cer'ebnim (Lat. cerebrum, the brain): the anterior part of the brain.
Chel'ipeds (Gr. chele, claw): pincher claws of arthropods.
Chemical element: a substance which has never been broken down into

simpler substances.
Chi'tin (Gr. chiton, a tmiic): a hard substance present in the exoskeleton

of insects.
Chlo'rophyll (Gr. chloros, grass green; phyllon, a leaf): the green coloring

matter of plants.
Chlo'roplasts: small bodies of protoplasm which contain chlorophyll.
Cho'roid: the middle coat of the eye.
Chro'mosome (Gr. chroma, color; soma, body): a deeply staining body in

the nucleus of a cell, supposed to carry the determiners of hereditary

qualities.
Chrys'alis (Gr. chrysos, gold) : the uncovered pupal stage of butterflies.
Cil'ium (Lat. cilium, an eyehd with hairs growing on it): a tiny hairhke

thread of protoplasm extending from a cell.
Cloa'ca (Lat. cloaca, sewer): the common cavity into which the digestive,

urinary, and reproductive systems open in some kinds of vertebrates.
Coc'cus (Gr. kokkus, berry): a ball-shaped bacterium.
Cocoon': The egg-case of spiders; a silky covering around a pupa.
Cce'lom (Gr. koilos, hollow): the true body cavity, through which the

digestive tract passes.
Compound eye: an eye made up of many simple eyes or ommatidia.

Arthropods have compound eyes.
Conjuga'tion (Lat. cum, together with; jugare, to yoke): the temporary

union of two sex cells of equal size, with a fusion of nuclei and inter-
change of nuclear material.
Connective tissue : collections of cells which support and connect other tissues.
Contrac'tile vac'uole: a small vesicle, found in the cytoplasm of many

protozoa, which appears and disappears with regularity. It is beHeved

to be an organ of excretion.
Cor'puscles (Lat. corpusculum, a Uttle body): the red and colorless cells

in the blood.

430 GLOSSARY

Cor'tex: a fleshy portion of the root, outside the central cylinder.

Cotyle'don (Gr. kotyledon, socket): the seed leaves. Plants may be
grouped as monocotyledons, having one seed leaf; dicotyledons, having
two seed leaves; and polycotyledons, having many seed leaves.

Cul'ture: a growth of bacteria or other microorganisms in prepared nu-
trient media.

Cy'toplasm (Gr. kytos, a vessel; plasma, anything formed): the living
substance of the cell outside of the nucleus and inside the cell mem-
brane.

D

Dehis'cent fruits (Lat. de, from; hiscere, to open): fruits that spUt open to

discharge their seeds.
Deliques'cent tree (Lat. deliquescere, to melt, dissolve) : a spreading tree, as

the elm.
Der'mis (Gr. derma, skm): the layer of skin below the epidermis.
Di'aphragm (Gr. diaph ^nmxi, a partition wall): the muscular partition

between the thorax and the abdomen.
Di'astase: an enzyme formed in plants which changes starch to grape

sugar.
Dichog'amy (Gr. dicha, in two; gamos, marriage): a condition in which

the stamens ripen before the pistil or vice versa, thus preventing

self-pollination.
Dicotyle'don: a plant that bears seeds having two cotyledons.
Diges'tion (Lat. digestio, the dissolving of food): the process of preparing

food for absorption.
Dimor'phic (Gr. di^, twice; morphea form): flowers which have two forms,

one having long pistils and short stamens, the other short pistils and

long stamens.
Disinfect'ant: something which kills bacteria.

Dor'sal (Lat. dorsum, the back): of or pertaining to the back or top side.
Ductless glands: glands which have no communication with an outer

surface, and which manufacture hormones.

E

Ec'toderm (Gr. eclos, outside; derma, skin;: the outer layer of a many-
celled animal.

Em'bryo (Gr. emhryon, a young one) : the early stage of a developing plant
or animal.

Em'bryo sac: the structure within the ovule which holds the egg cell.

Emursion (Lat. emulgere, to milk out): a mixture of liquids which do not
dissolve, the particles of one floating as small globules in the other.

En'dodenn (Gr. endon, within; derma, skin): the inner layer of cells in
an embryo, giving rise to the digestive tract, etc.

En'doskeleton (Gr. endon, within; skeletos, hard): a skeleton inside the
body as opposed to the outer or exoskeleton.

GLOSSARY 431

En'dosperm (Gr. endon, within) : food stored in the seed outside the embryo.
En'ergy (Gr. energos, at work); work power; ability to perform work.
Envi'ronment (Fr. environ, about) : the surroundings of an organism.
Eu^zyme (Gr. en, in; zyme, leaven) : a substance which brings about a

chemical action, assisting in digestion.
Epider'mis (Gr. epi, upon; derma, skin): an outer layer of cells; the

outside skin.
Ep'iphytes {epi, upon; Gr. phyton, plant) : air plants and tropical plants that

obtain moisture from the atmosphere.
Ero'sion (Lat. erodere, to gnaw off) : the wearing away of rocks through

the agency of water, wind, glaciers, and other agencies.
Essen'tial organs: the stamens and pistils, parts of a flower which have

to do with the production of seeds.
Eusta'chian tube: the canal connecting the tympanic cavity with the

pharynx, named for its discoverer, Eustachio, an Italian physician.
Excur'rent tree (Lat. ex, out; currere, to run): a tall slender tree with

one main trunk, as the cedar.
Exoskereton: an outside skeleton.

Fatigue' (Lat. fatigare, to weary) : the effect produced by long stimulation

on the cells of an organism.
Fats: a class of nutrients composed of much carbon and hydrogen with a

little oxygen.
Fermenta'tion (Lat. fermenium, ferment): the chemical transformation of

organic substances through the agency of enzymes or ferments, or

through the agency of bacteria.
Fertiliza'tion (Lat. fertilis, fruitful) : the union of an egg cell and a sperm

cell.
Fibrovas'cular bundles: collections of tubular cells, supported by woody

cells, which conduct fluids in plants.
Fin: a fold of skin, with skeletal supports, used for swimming.
Fis'sion (Lat. fissum, cleft) : division of a cell into two parts.
Flagel'lum (Lat. fiagellum, whip) : a vibratory threadlike projection of

certain cells.
Food: a substance that forms the material for the growth or repair of the

body of a plant or an animal or that furnishes energy for it.
Fruit: a ripened ovary together with any parts of the flower adhering to it.
Func'tion (Lat. functio, performance): the normal action of an organ or

organs.

G

Game'tophyte (Gr. gamete, wife): the phase in the life history of a thallus

plant that produces the sex organs,
Gan'glion (pi. Ganglia ) (Gr. ganglion, little tumor) : a mass of nervous

matter containing nerve cells which give rise to fibers.

432 GLOSSARY

Gas'tric glands (Gr. gaster, stomach): digestive glands found in the walls
of the stomach,

Gas'trula (Gr. gaster, stomach): a cuphke structure formed by the in-
vagination or turning in of the blastula.

Geot'ropism (Gr, ge, earth; tropein, to turn) : response to gravity.

Germina'tion : the beginning of growth in a seed or pollen grain.

Gill rakers : small spinehke structures attached to gill arches which prevent
escape of food.

Gills: breathing organs for use in water.

Gland (Lat. glans, an acorn): an organ which secretes material to be used
in or excreted from the body.

Gly'cogen (Gr. glykus, sweet; -gen, producing): animal starch, found in
the liver.

Guard cells: epidermal cells, found on each side of a stoma.

Guriet (Lat. gula, gullet): a muscular canal extending from the mouth
cavity to the stomach.

H

Haemoglo'bin (Gr. haima, blood; globos, sphere): red coloring matter of

the blood.
Hair follicle (Lat. folliculus, a Httle bag): a little pit in the skin from

which a hair grows.
Harophjrte (Gr. hals, salt) : a plant which grows best in salty soils.
Heliot'ropism (Gr. helios, sun; tropein, to turn) : response to light.
Hered'ity (Lat. heres, heir) : transmission of quahties from parent to child.
Hermaphroditic (Gr. hermaphroditos, combining both sexes): an organism

having both male and female sex organs,
Hi'lum: a scar on the testa left where the seed was attached to the pod.
Hor'mones (Gr. hormaein, to excite) : substances from the organs of the

body which effect a chemical coordination.
Hu'mus (Lat. humus, ground): vegetable mold, a black or dark colored

substance formed by the decay of organic substances in the soil.
Hy'brid (Lat. hyhrida, mongrel): the offspring of parents of two different

species or varieties.
Hy'drophyte (Gr. hydor, water): a water-loving plant.
Hy'giene (Gr. hygeia, health): a study of the preservation of health.
Hypocot'yl (Gr. hypo, under): the part of the developing embryo which

forms the root and the lower part of the stem.

Immu'nity (Lat. immunis, free from duty): the successful resistance of an

organism to infections from microorganisms.
Imperfect flowers: flowers having only one kind of essential organs, either

stamens or pistils.
tntes'tine (Lat. intestinus, internal) : the food tube in vertebrates from the

GLOSSARY 433

pyloric end of the stomach to the anus. It is divided into the small

and the large intestine.
InVolucre (Lat. involucrum, a wrapper): a whorl of leafiike bracts around

the base of a flower cluster.
I'ris (Gr. iris, rainbow): the colored portion of the eye, having the pupil

in the center.

K

Kad'neys: glands which secrete urine.

Elinet'ic (Gr. hinein, to move): energy employed in producing motion.

Lac'teals (Lat. lacteus, milky): lymphatic vessels which carry fats and

other substances from the intestine to the thoracic duct.
Lar'va (Lat. larva, a ghost) : an embryo which becomes self-sustaining but

which does not have the characteristics of the adult.
La'tent (Lat. latere, to lie hid) : lying dormant but capable of development.
Leg'umes (Lat. legere, to gather): plants which bear seeds in pods — peas,

beans, and the like; also the seeds of such plants.
Len'ticel: a breathing hole in the bark.
Lig'ament (Lat. Ugare, to bind): a band of connective tissue binding one

bone to another.
Liv'er: a digestive gland which secretes bUe.
Lymph (Lat. lympha, water): plasma and colorless corpuscles outside of

the blood vessels.

M

Macronu'cleus (Gr. makros, large): the large nucleus, as opposed to

the micronucleus, or small nucleus.
Mam'mary glands (Lat. mamma, breast): milk-secreting glands found in

mammals.
Man'dible (Lat. mandere, to chew) : in insects, a hard cutting jaw.
Man'tle (Lat. mantellum, a cloak) : the soft outer fold of skin in moUusks

which secretes the outer shell.
Maxil'la (Lat. maxilla, a jaw) : an appendage near the mouth of arthropods,

modified in insects to form an organ for getting food.
Maxil'liped (Lat. mxixilla, jaw; pes, foot): an appendage next posterior

to the maxilla in arthropods. Foot jaw.
Medul'la oblonga'ta (Lat. medulla, pith): the most posterior part of the

brain.
Med'ullary rays (Lat. medulla, pith) : thin plates of pith which separate the

wood of dicotyledonous stems into wedge-shaped masses.
Mes'oderm (Gr. mesos, middle; derma, skin): the middle layer of cells

in a young animal embryo.
Mes'ophjrte (Gr. mesos, middle): a plant preferring moderate conditions

of moisture.

434 GLOSSARY

Metamor'phosis (Gr. meta, after; rnorphe, form): change of form undergone

from egg to adult, as in insects.
Metazo'a (Gr. meta, after; zoon, animal): animals having many cells in

the body.
Mic'ropyle (Gr. micropyle, a Httle gate): the hole where the pollen tube

enters the embryo sac.
Mid 'rib: central vein of a leaf.
Mi'grant: an animal which moves from one place to another and back

regularly at stated seasons of the year. Many birds migrate to warmer

regions for the winter.
Mim'icry (Gr. mimikos, imitative): the imitation in form or color of a

harmful insect by a harmless one which is protected thereby.
Monocotyle'don: a plant that bears seeds having but one cotyledon.
Mo'tor (Lat. movers, to move): connected with movement.
Mu'cous membrane (Lat. mucus, slime; membrana, skin): a delicate moist

membrane lining all body passages which have an external opening.
Mus'cle (Lat. musculus, muscle): a contractile tissue capable of bringing

about movement.
Muta'tion: a heritable modification arising from internal causes in an

organism.
Mycelium: the threadlike body of a mold, the individual threads being

called hyphae.

N

Narcotic (Gr. narkotikos, making dumb): a substance which blunts the

senses and in large quantities causes insensibility.
Nec'tar (Gr. nectar, drink of the gods): a sweet fluid secreted by certain

groups of cells known as nectar glands in a flower. From this substance

bees make honey.
Nic'titating membrane (Lat. nictare, to wink): the third eyelid, a delicate

membrane covering the eye in birds and frogs.
Ki'trogen (Lat. nitrum, natron; -gen, producing): a gaseous element,

found in many organic compounds and forming almost four fifths

of the atmosphere.
Nu'cleus (Lat. nucleus, a kernel): the center of activity in the cell.

Ommatid'ium (Gr. omm/i, eye): one of the elements of a compound eye.
Oper'culum (Lat. operculum, a Hd): a lid or flap in fishes, covering the

gills.
Op'sonin (Gr. opsonein, to cater for) : a substance in the blood which helps

colorless corpuscles destroy bacteria.
Or'ganism (Gr. organon, an instrument): a body which is made up of

organs or parts, each of which has a special function; any animal or

plant.

GLOSSARY 435

Osmo'sis: diffusion of dissolved substances through a semi-permeable
membrane, the greater flow being toward the denser medium.

O'vary (Lat. ovum, egg) : the base of a pistil, containing the ovules.

Ovipos'itor (Lat. ovum, egg; ponere, to place): a specialized structure
for depositing eggs, foimd in insects.

Oxida'tion: the chemical union of oxygen with some other substance.

Ox'ygen (Gr. oxvs, acid; -gen, producing): a gaseous element found in
the air and in many compounds.

Pal'ate (Lat. palatum): the roof of the mouth. The hard palate is sup-
ported by bone; the soft palate is a fold of mucous membrane lying
posterior to the hard palate.

Pal'pus or palp (Lat. palpare, to touch) : in arthropods, an appendage at-
tached to a mouth part; usually an organ of touch or taste.

Pan'creas (Gr. pan, all; kreas, flesh): a digestive gland which secretes
pancreatic juice.

Pap'pus: a downy or flufty outgrowth from the ovary wall.

Par'asite: an organism which secures its hving directly from another
hving organism without giving anything in return.

Pas'teurize (from Pasteur the scientist, p. 3) : to heat milk to about 160°
Fahrenheit for about 20 minutes for the purpose of killing bacteria in it.

Pec'toral girdle (Lat. pectoralis, pertaining to the breast): bones which
support the anterior pair of appendages in vertebrates.

Pel'vic girdle (Lat. pelvis, a basin): the bony arch to which the posterior
pair of appendages are attached in vertebrates.

Pet'al: one of the leaflike parts of the corolla.

Pet'iole (Lat. petiolu^, sl Httle foot): the stalk of a leaf.

Phag'ocjrte (Gr. phagein, to eat; kytos, cell): a colorless corpuscle which
destroys bacteria.

Phar'ynx (Gr. pharynx, gullet) : an irregular cavity at the back of the mouth.

Phlo'em (Gr. phloos, bark): the outer part of a fibro vascular bundle con-
taining the sieve tubes.

Photosyn'thesis (Gr. phos, hght; synthesis, a putting together): the proc-
ess of making starch out of carbon dioxide and water by the aid of
sunlight, as done by a green cell.

Physiolog''ical division of labor: performance of different kinds of work
by different parts of an organism.

Physiorogy (Gr. physis, nature; logos, discourse): study of the fimctions
of plants and animals.

Pis'til: a structure in the flower containing the ovary, in which the seeds
are formed.

Pith: the soft, spongy center of a dicotyledonous stem.

Plas'ma (Gr. plasma, anything formed or molded): the colorless fluid
part of blood.

436 GLOSSARY

Pleu'ra (Gr. pleura, the side) : the membrane which covers the lungs and

lines the cavity containing them.
Plu'mule: the part of the embryo above the cotyledons which develops

into the stem and leaves.
Pol'len grain: a structure in flowers which contains the sperm cell or

male gamete.
Pollina'tion: the transfer of pollen from the anther to the stigma. Self-
pollination is transfer between parts in the same flower ; cros^-pollination

is transfer between different flowers, or, some say, between flowers on

different plants.
Polycotyle'don: a plant that bears seeds having several cotyledons.
Poryp (Lat. -poly-pus, a polyp): a simple actinozoan, as a sea anemone or

a single coral individual.
Poste'rior (Lat^. posterior, later): behind, last, or tail end of an animal.
Pri'mates: the highest order of mammals, including the monkeys, the apes,

and man.
Probos'cis (Gr. pro, before; boskein, to feed) : a slender sucking tube found

in insects.
Proglot'tids (Gr. pro, forward; glotta, tongue) : reproductive body segments

of a tapeworm.
Pro 'leg: an unjointed abdominal appendage of insect larvae.
Prosto'mium: a projecting part of upper hp of the earthworm.
Protec'tive resemblance: the hkeness of hvdng organisms in color or form

to their immediate surroundings, thus securing protection from attack

of enemies.
Pro'teins (Gr. protos, first): nitrogenous compounds found in the bodies

of plants and animals; a class of nutrients composed of nitrogen, car-
bon, hydrogen, and oxygen, together with other elements in some cases.
Pro'toplasm (Gr. protos, first; Lat. plasma, a thing formed): the hving

substance of plants and animals.
Protozo'a (Gr. protos, first; zoo7i, animal): one-celled animals.
Pseudopo'dium (Gr. pseudes, false; pov^, foot): a projection of protoplasm

used for locomotion in protozoa.
Pto'maine (Gr. ptoma, a corpse): poisonous alkaloidal material probably

the result of decomposition of organic matter.
Pu'pa (Lat. pupa, puppet): the quiescent stage in insect development

preceding the adult.
Pylo'rus (Gr. pyloros, gatekeeper): the opening of the stomach into the

intestine.

Q

Quar'antine (Fr. quarante, forty): isolation of the sick to prevent spread
of infectious disease.

R

Ray flowers: modified flowers at the outer edge of a flower cluster such
as a composite head.

GLOSSARY 437

Regenera'tion (Lat. re, again; generare, to beget): the growing again of

a part of an animal which has been lost.
Respira'tion (Lat. re, again; spirare, to breathe): taking in of oxygen and

giving out of carbon dioxide by Kving cells.
Ret'ina (Lat. rete, a net): the coat of the eye in which the optic nerve

fibers terminate.

Sali'va (Lat. saliva, spittle): the secretion of the salivary glands.
Sap'rophyte (Gr. sapros, rotten; phyton, plant): an organism which derives

its nourishment from dead organic matter, as a mold or mushroom.
Sclerot'ic coat (Gr. skleros, hard): the outer coat of the eye.
Scute (Lat. scutum, a shield): an external scale, as in the snake.
Seed: a structure formed in a fruit as a result of the fertilization of the

egg cell.
Seg'ment (Lat. segmentum, a piece cut off): one of a number of serial

divisions of an animal's body or of an organ.
Sen'sory (Lat. sensu^, feehng): having direct connection with any part of

the seat of sensation.
Se'pal: a leaflike part of the calyx or outer circle of parts in a flower.
Se'tae (Lat. seta, a bristle): bristles, used for locomotion in earthworms

and other animals.
Sex'ual (Lat. sexus, sex): pertaining to or having sex.
Si'phon (Gr. siphon, a tube) : a "tube through which water may pass into

and out from the mantle cavity of a mollusk.
Spe'cies: the smallest group of organisms having characteristics in common

that make them different from all other organisms.
Sperm cell: the male sex cell or gamete.

Spi'nal cord: a cord of nervous tissue lying in the vertebral column.
Spir'acles (Lat. spiraculum, breathing hole): breathing holes in insects.
Spirillmn (Lat. spira, coil): a spiral form of bacteria.
Spongy paren'chyma (Gr. para, beside; en, in; chein, to pour): a layer

of loosely placed cells forming a tissue in the leaf.
Sporan'gium (Gr. sporos, a seed; aggeion, a vessel) : a sac containing spores.
Spore: a reproductive cell capable of growing into a mature organism.
Spo'rophyte: spore-bearing part of a plant.
Sta'men: an organ of the flower in which pollen is formed.
Ster'ilize (Lat. sterilis, barren): to destroy bacteria and other organisms,

usually by heating.
Stig'ma (Gr. stigma, the prick of a pointed instrument) : the part of a pistil

which receives the pollen grains.
Stim'ulant (Lat. stimulus, a goad): a substance which causes temporary

activity of nerve or muscle.
Stim'ulus (Lat. stimulare, to incite): an agent which causes an organism

or some part of it to react when affected by it.

438 GLOSSARY

Stip'ule (Lat. stipida, stem): a leaflike outgrowth at the base of the

petiole.
Sto'ma (pi. Sto'mata) (Gr. stoina, a mouth): a breathing hole in a leaf.
Stom'ach (Gr. stomachos, throat): a sac-like part of the food tube between

gullet and intestine.
Sweat glands: excretory glands in the skin.

Swim'merets: paired appendages on the abdomen of crustaceans.
Symbio'sis (Gr. symbio>iis, a living together): a condition in which two

organisms of different kinds hve together in a mutually beneficial

partnership.

Tac'tile corpuscle (Lat. fati'gcrc, to touch): sense organ of touch.

Tar'sus (Gr. tarsos, sole of foot): the ankle-bones, also the last region of

the leg of an insect.
Taste bud: end organ of taste found on the tongue.

Teeth: limy structures in the mouth of man and other animals, consist-
ing of incisors or cutting teeth; canines, tearing teeth; and molars

and premolars, crushing and grinding teeth,
Ten'don (Lat. tendere, to stretch): a band of connective tissue attaching

muscle to muscle or muscle to bone.
Ten'tacle (Lat. tentacidum, a feeler): a flexible organ at the anterior end of

an animal used for feehng, grasping, etc.
Tes'ta: the thick outer coat of a seed.
Thal'lophytes (Gr. thallos, young shoot; phjjton, plant): plants having a

thallus or ribbonhke bodj'.
Thorac'ic: pertaining to the chest region.
Thorax (Gr. thorax, the chest): the part of the body between the head

and the abdomen.
Tissue (Fr. fissu, a web): a collection of cells all more or less alike and

ha\'ing the same fimction.
Tra'chea (Lat. trachia, -u-indpipe) : the windpipe; also a respirator}' tube

of insects.
Transpira'tion (Lat. traths, through; spirare, to breathe): the gi\'ing off

of water vapor from plants.
Trichi'na: pork worm, a parasitic roundworm causing the condition called

trichinosis.
Trimor'phic (Gr. tri, three; morphe, form) : flowers ha\'ing three lengths

of stamens and pistil; for example, the loosestrife.
Tryp'anosomes (Gr. trypanon, an auger): protozoa which cause diseases

such as sleeping sickness.
Tym'panum (Gr. tympanon, a drum): the eardrum.

U

U'rea (Lat. urina, urine): a nitrogenous waste excreted in the urine.

GLOSSARY 439

Vaccina'tion: inoculation with a vaccine, containing living or dead bac-
teria, to protect the body from disease.
Vac'uole (Lat. vacuus, empty): a space in protoplasm containing air,

water, sap, or food material.
Varia'tion: in biology, the occurrence of differences between individuals

of the same species.
Vein: a tube which conveys blood to the heart.
Ven'tral (Lat. venter, belly) : the opposite of dorsal.

Ventila'tion (Lat. ventilare, to air) : changing of air in a room or building.
Ven'tricle (Lat. ventriculus, a httle beUy): a muscular chamber of the

heart, which forces the blood out.
Ver'miform appendix (Lat. vermis, worm): a narrow tube about four

inches long, closed at the outer end, near the beginning of the large

intestine of man.
Ver'tebrse (Lat. vertere, to turn): bones of the vertebral column.
Ver'tebrate: an animal ha\dng a backbone.
Vil'lus (Lat. villus, shaggy hair): a minute projection, an absorbing organ

of the small intestine.
Vi'rus: an unknown agent causing disease, as opposed to bacteria or

protozoa which are known causes of specific diseases.
Vi'tamin (Lat. vitay life) : unknown substances in food apparently necessary

to support life.
Vcruntary (Lat. voluntas, will): subject to the will (used with reference

to muscles), as opposed to involuntary.

X

Xe'rophyte (Gt. xeros, dry): a plant which lives under conditions of

extreme dryness.
Xy'lem (Gr. xylon, wood): the inner woody part of a fibrovascular bundle

which conducts water up the stem

INDEX

(Illustrations are indicated by page numerals in bold-faced type.)

Accommodation of eye, 399.
Acts, automatic, 393.
Adaptation, 19, 30, 204. ^
Adaptations, for pollination, 35, 36;

for respiration, 375;

for seed dispersal, 42, 43, 44, 45,
46;

in birds, 286, 288, 290, 291;

in frogs, 272;

in mammalia, 303;

in snakes, 284;

in turtles, 281;

in vertebral column, 318;

to environment, 126, 234.
Adenoids, effects of, 382.
Agglutinins, 358.
Aggressive resemblance, 235.
Air, amount of, in breathing, 377;

changed in lungs, 378;

composition of, 6, 7;

factor in germination, 62;

fresh, how to get, 405;

in hygiene, 410;

necessity of, 395;

value of change of, 406.
Alcohol, and ability to do work, 401 ;

and disease, 408;

and longevity, 409;

a poison, 337;

as a food, 336, 338;

effect on blood, 372;

effect on body heat, 387;

effect on circulation, 373;

effect on digestion, 356;

effect on intellectual ability, 401;

effect on respiration, 388;

in patent medicines, 340;

in treatment of disease, 408;

paralyzes nervous system, 401.
llcoholic poisoning, economic, moral
and social effects of, 402.

HUNT. NSW £8. — 29

Algae, 127.

AUmentary canal, 343.
Alligator, 284.

Alternation of generations, in coelen-
terates, 191;

in fern, 132;

in mosses, 131;

in spermatophytes, 133.
Amino-acids, 349, 351.
Amoeba, parts of, 175;

reproduction of, 176.
Amphibia, 272;

characteristics of, 280;

classification of, 280.
Angiosperms, 134.
Animals, cold-blooded, 362;

domestication of, 308;

relation of, to man, 3;

vertebrate, 260.
Annulata, classification of, 202.
Antennae, 206.
Antennules, 206.
Anther, 25.
Antiseptics, 163.
Antitoxin, 421, 422.
Ants, 240;

and their "cows," 241.
Anvil, 397.
Aphids, 228;

and ants, 241.
Appendages of skeleton, 319.
Aptera, 232.

Aqueous humor, 398, 399.
Arachnida, 232.
Arteries, 362;

structure of, 366, 367.
Arthropoda, classified, 231.
Asexual reproduction, amceba, 17^

coelenterates, 191, 192;

in fern, 132;

in hydra, 184;

441

442

INDEX

Asexual reproduction, in mold, 150;

in moss, 131;

in Paramecium, 174;

in spirogyra, 129.
Astigmatism, 399.
Atoll, 192.
Auricle, 363.

Bacillus, 154.
Bacteria, 153;

and fermentation, 158;

carried by fly, 225, 406;

cause decay, 157;

cause disease, 159;

conditions for growth, 156;

discovery of, 154;

from human mouth, 158;

in impure water, 417;

in milk, 159;

LQ school room, 380;

in streets, 405;

method of study, 155;

nitrogen-fixing, 167, 158;

size and form, 154;

their relation to man, 2.
Bacteriology, defined, 3.
Balanced aquarium, 166.
Balancing in birds, 289.
Banana plants, 2.
Bark, use of, 87.
Barley, production of, 49.
Bean, 54.

Beans, as food, 56.
Beaver, 305.
Bees, 30, 32, 238.
Beetle, characteristics of, 226.
Berry, 42, 52.
Beverages, 53.
Bile, functions of, 351.
Bile duct, 343.
Biology, 1;

civic, 415;

its relation to society, 5;

reasons for study of, 1.
Birds, body of, 286;

care of young, 293;

classification of, 301;

distribution of, 293;

economic importance of, 294;

extermination of, 300;

Birds, feathers of, 287;

feet of, 288;

harmful to man, 300;

migrations of, 293;

nesting habits of, 292, 293;

perching in, 289;

wings of, 286.
Bison, 306.
Bladder, urinary, 384.
Blastula, 182.
Blood, amount of, 362;

and its circulation, 358;

changes in, in body, 386:

changes in, in lungs, 375, 378;

clotting of, 359;

course of, 364, 365;

disease-resisting mechanism of.
361;

distribution of, 362;

effec^: of alcohol on, 372 ;

exchs.nge in, 369;

function of, 358;

tempei'ature of, 362;
. vessels, congestion in, 388;

wastes of, to kidney, 384.
Bluebird, 295.
Body, daily fuel needs of, 331 ;

normal heat output of, 332.
Bodv heat, affected bv alcohol,

387;

in cold-blooded animals, 386;

regulation of, 385.
Box elder, section of, 86.
Brain, functions of parts, 392;

of man, 391.
Bread mold, 150.
Breathing, and tight clothing, 381:

hygienic habits of, 381;

mechanics of, 376;

movements in, 376:

rate of, 377.
Bronchi, 374.

Bruises, treatment of, 371.
Bryophjiies, 134.
Budding, 93, 94.
Bugs, 227, 228.
Bumblebee, 30, 238.
Burbank, Luther, 68.
Burns, treatment of, 387.
Butter and eggs, 33.

INDEX

443

Butterfly, 221; compared with moth,
222, 223;
head of, 221.

Caffeine, 336.

Calorie, defined, 326.

Calyx, 24.

Cambium layer, use of, 87, 94.

Canal, semicircular, 397, 398.

Capillaries, 362.

Capillarity, 76.

Capillary circulation in frog's foot,

366.
Carapace, 205.
Carbohydrates, 13, 323.
Carbon, properties of, 10.
Carbon dioxide, test for, 11.
Carnivora, 303.
Catarrh, 382.
Catbird, 298.
Cell, 20;

as a unit, 177.
Cell membrane, 20, 74, 75.
Cell sap, 74, 75.
CeU wall, 74.
Cells, 187.

in tissues of man, 187;

nerve, 391;

sizes and shapes of, 21.
Centipedes, 231.
Centrum, 318.
Cephalopods, 257, 259.
Cephalothorax, 205.
Cerebellum, 391.
Cerebrum, 391;

functions of, 392.
Cestodes, 199.
Chelipeds, 205, 206.
Chemical element and compound, 7.
Chickadee, 296.
Chitin, 217.
Chlorophyll bands, 129;

bodies in leaf, 104.
Chromosomes, 20.
ChrysaUs, 222, 223.
Cicada, 227, 228.
Ciha, 154, 173.
Circulation, effect of alcohol on, 372;

effect of exercise on, 371;

in a mammal, 365;

Circulation, in capillaries, 366, 367;

in crayfish, 208;

in fishes, 264;

in frog, 275, 366;

in kidney, 384;

in man, 362;

organs of, 188;

portal, 354, 365;

pulmonary, 364, 365;

systemic, 364, 365.
Clam, fresh-water, shell of, 254;

round, parts of, 255.
Class, defined, 134.
Coccus, 154.
Cochlea, 397, 398.
Coelenterates, 189, 190, 191, 192*

compared with worms, 197.
Colds, care of, 387;

cause of, 387.
Coleoptera, 226, 232.
Combustion, 11.
Composite head, parts of, 34,
Condiments, 53.
Conjugation, 130, 150;

in mold, 150;

in Paramecium, 174.
Coral, 191;

madreporic, 192.
Coral reefs, 192.
Corn, ear of, 56;

grain of, 56, 57;

production of, 48;

uses of, 48.
Corn grain, foods in, 57, 59.
Cornea, 398.
Corolla, 24.

Corpuscle, colorless, functions of
361;

structure of, 359, 360.
Corpuscle, red, function of, 359;

structure of, 359.
Corpuscles, tactile, 313, 39&
Cortex, 73;

in stem, 86.
Cotton, fumigation of, 51;

production of, 50, 51;

uses of, 51.
Cotton boll weevil, 51, 246.
Cotyledons, food in, 55;

functions of, 64;

Ui

INDEX

Cotyledons, in bean, 54, 55;

of corn, 57.
Crab, blue, 212;

fiddler, 213;

giant spider, 213;

hermit, 212.
Crayfish, adaptation for protection,
205;

and aUies, characteristic of, 214;

appendages, 207;

external structure, 205;

internal structure, 208;

locomotion of. 205;

senses of, 206.
Cretinism, 368.
Crocodiles, 284.
Crops, rotation of, 80.
Cross-pollination, defined, 27.
Crow, 299.
Crustaceans, 205;

habitat of, 214.
Culture, pure, 155.
Cuts, treatment of, 371, 387.
Cytoplasm, 20.

DandeUon, 72.

Decay by bacteria, 157.

Deer, Virginia, 306.

Dehquescent tree, 84.

Dermis, 313.

Development of bee, 238, 239;

of crayfish, 209;

of fly, 225;

of frog, 276, 277, 278;

of lobster, 210, 211;

of moth, 223.
Diaphragm, 348;

in respiration, 376.
Diastase, action of, on starch, 58.
Diatoms, 129.
Dichogamy, 35.
Dicotyledons, 59, 60
Diet, best, 326.
Diffusion, 75.
Digestion, 343;

and absorption, 343;

effect of alcohol on, 356;

in corn grain, 58;

in crayfish, 209;

in fishes, 264;

Digestion, in plants, 89;

of starch, 347;

organs of, 188, 343;

purpose of, 343.
Digestive tract in frog, 274, 275
Dipnoi, 271.
Diptera, 224, 226, 232.
Disease, prevention of, 404.

pubHc control of, 423.
Diseases, carried by food, 420;

caused by bacteria, 159, 162;

due to insects, 243, 244;

infectious, 421;

of nose and throat, 382.
Disinfection, 421.
Division of labor, 181;

in honeybee, 239;

in hydra, 186;

in vorticella, 177.
Dragon fly, 228, 229,
Drone, 238.

Drugs, use and abuse of, 340.
Drupe, 52.
Dusting, 380. •

Dyspepsia, causes and prevention
of, 355.

Ear, human, 397.

Earthworm, development of, 197;

locomotion of, 196 ;

relation to surroundings, 194.
Eating, hygienic habits of, 355.
Economic importance^ of alcoholic
poisoning, 402;

of birds, 294;

of carnivora, 304;

of corals, 192;

of earthworms, 197;

of ferns, 132;

of fish, 269;

of food in roots, 81 ;

of insects, 225, 243, 244, 245, 246,
247, 248, 249;

of leaves, 112;

of lobster, 212;

of moUusks, 255, 256, 258j

of parasitic worms, 203^

of plants, 146;

of snakes, 283;

of starfish, 258;

INDEX

445

Economic importance, of toads,
279;

of trees, 115, 117.
Ectoderm, defined, 182.
Egg, development of, 182.
Egg cell, 26, 182, 266, 276.
Egg-laying habits of fishes, 266.
Elasmobranch, 271.
Embryo sac, 26, 132.
Endoderm, defined, 182.
Endoskeleton, 261, 265.
Endosperm, use of, 57, 68, 64, 65;
Energy, defined, 9.
Entomostraca, 232.
Environment, 6.

Enzyme, action upon fibrinogen,
359;

in saliva, 347.
Enzymes, 58, 344;

in gastric juice, 349.
Epicotyl, 54, 55.
Epidermis, 313.
Epiglottis, 345.
Erosion, by streams, 115, 116;

prevented by organic covering,
117.
Esophagus, 343, 345, 348.
Eustachian tube, 345, 397.
Excretion, in crayfish, 209;

organs of, 188;

organs of, in man, 383, 384.
Excurrent tree, 84.
Exercise, and health, 407;

in hygiene, 412.
Exoskeleton, 205.
Expiration, 376.
Eye, care of, 400;

coats of, 398;

defects in, 399;

human, 398;

image formed inj 400:

of crayfish, 206;

of insect, 219.

Facets, 219.
Fallowing, 80.
Family, defined, 134.
Fatigue, 371.
Fats, 14, 323;
test for, 14.

Fermentation, chemistry of, 149.
Fern, life history of, 132.
Fertilization, 26, 27, 131.
Fevers, cause of, 387.
Fibrin, 359.
Fibrinogen, 359.
Fibrovascular bundles, 74;

of a monocotyledon, 92 ;

use of, 85.
Filament, 25.

Fish hatchery, work of, 270»
Fishes, appendages of, 2613

body of, 261;

classification of, 271;

migration of, 268;

protection of, 269.
Fission, 174.
Flagella, 183.
Flatworm, 199.
Fhcker, 298.
Flower, defined, 24;

dimorphic, 34;

fertilization of, 25;

pistillate, 38;

relation to fruit, 54;

staminate, 38;

structure of, 24;

trimorphic, 35.
Flowers, work of, 24.
Fly, foot of, 224;

head of, 31;

typhoid, 224, 225,
Food, 13;

and dietaries, 322;

and disease, 420;

and health, 406;

economy, 331;

in hygiene, 411;

laws, 335;

necessity of, 395;

storage in stem, 92;

swallowing of, 348;

vacuoles, 173;

waste in kitchen, 333, 334;

why we need, 322,
Food taking, in birds, 294;

m clams, 253;

in crayfish, 207;

in earthworm, 196, 197;

in fishes, 265;

446

INDEX

Food taking, in frogs, 274;

in grasshopper, 219;

in hydra, 184;

in snakes, 283;

in starfish, 259;

in turtles, 281;

organs of, 188.
Foods, absorbed into the blood, 352,
354;

adulterations in, 335;

costs of various, 330;

inorganic, 15, 324;

organic, 13;

values of, 328.
Forest destruction, 121, 122. •
Forest regions in United States, 118.
Forester, and his work, 124.
Forestry, 122.
Forests, protection of, 123;

their uses and protection, 115.
Frog, leopard, 272, 273 ;

study of, 272-

tree, 279.
Fronds, 132.
Fruit, defined, 41;

stages in formation of, 40.
Fruits, and their uses, 40;

dehiscent, 44;

economic value of, 47;

garden, 52;

indehiscent, 45;

orchard, 52.
Functions, of parts of an animal, 18,
188;

of parts of a plant, 17.
Funiculus, 41.
Fungi, 130;

parasitic, 152, 153;

saprophytic, 148, 149, 151,

GaU bladder, 343, 351.
Gametoph^-te, in moss, 131, 132.
GangUa, 390.
Ganoid, 271.
Gastric juice, 349.
Gastric miU, 209.
Gastropods, 256, 259.
Gastmla, 182. ,

Genus, defined, 133.
Geotropism, 71.

Germination^ factors in, 60; of

bean, 63.
Gila monster, 282.
Gill rakers, 263;

in shad and bluefish, compared,
266.
Gills, fish's, structure of, 263.
Girdle, pectoral, in man, 319;

pehdc, in man, 319.
Glands, defined, 344;

ductless, secretions of, 368;

gastric, 348, 349;

intestinal, 352;

l5Tnph, 369, 370;

salivar\', 347;

structure of, 344;

sweat, 384.
Glomerulus, 384.
Glycogen, formation of, 352=
Goldfinch, American, 296,
Grafting, 94.
Grain, 45, 46.
Grape sugar, test for, 14.
Grasses, production of, 50.
Grasshopper, red-legged, 217=
Guard cell-, 103.
GuUet, 343, 345, 348.
Gymnosperms, 134.

Habit, alcohohc, 401.

Habits, formation of, 394.

Hsemoglobin, 360.

Haemolysins, 358.

Hair, development of, 313.

Halophytes, 138.

Hammer, 397.

Ha}' infusion, life in, 170.

Health, and disease, 404;

department of, 419;

department of, work of, 419;

good, and how to keep it, 404.
Hearing, organ of, 397.
Heart, a force pump, 364;

in action, 364;

ners'ous control of, 370;

position of, 363;

protection of, 363;

structure of, 363;

valves in, 363.
Heliotropism, 99, 100.

INDEX

447

Hemiptera, 227, 232.

Heredity, 67.

Hilum, 54.

Honeybee, 238.

Hookworm, 200.

Hormones, work of, 350.

Hornets' nest, 239.

Horse, geologic history of, 307.

Hmnan body a machine, 312.

Humus, 10, 78.

Hybridizing, 68.

Hybrids, 39, 68.

Hydra, 184.

Hydrophytes, 137.

Hygiene, Fisher's rules of, 410;

personal, 404;

pubUc, 415.
Hymenoptera, 229, 232.
Hypha, 150.
Hypocotyl, 54, 55.

Ichneumon fly, 242.

Immunity, 421.

Inorganic soil, relation to organic, 78.

Insects, 216;

and crustaceans compared, 231;

beneficial, 249, 250;

characteristics of, 229;

communal life, 237;

control of damage by, 249, 250,
251;

disease-carrying, 243, 244, 245;

divisions of, 232;

muscular activity of, 219;

noxious, 245, 246, 247, 248, 250,
251;

relation to mankind, 242;

«ense of smell, 31;

sight of, 31;

winners in life's race, 216.
Inspiration, 376.
Intestine, large, 343, 354;

small, 343, 352;

small, stracture of, 353.
Invertebrate, cross section of, 260.

Joint, hinge, 316.

Key fruit, 46.

Kidney, human, 383, 384.
Knots, cause of, 120, 121.

Lacteals, 354, 370.

Larva, 222, 223.

Larval stages, defined, 182.

Lateral Hne, function of, 263.

Leaf, cell structure of, 103, 104;

respiration in. 111;

structure of, 102, 103.
Leaves and their work, 98;

arrangement of, 101;

as insect traps, 113;

modified, 112, 113.
Legs, of grasshopper, 217.
Lens of eye, 399.
Lenticels, use of, 85.
Lepidoptera, 232.
Levers, classes of, 317;

in body, 316.
Lichens, 168.
Life history, of aphid, 228;

of beetle, 227;

of butterfly, 221, 222;

of cecropia, 223;

of Chinook salmon, 267;

of cicada, 227, 228;

of fly, 224, 225;

of frog, 276, 277, 278;

of grasshopper, 220;

of honeybee, 239;

of lobster, 211;

of mosquito, 243;

of yellow perch, 267.
Light, effect of, upon plants, 98, 99,

100.
Lily, leaves of, 101.
Liver, 343, 351.

Living matter, composition of, 12.
Living things, environment of, 6;

functions and composition of, 17.
Lizards, 282.

Lobster, North American, 209, 210.
Locomotion, in crayfish, 205;

in frogs, 273:

in snakes, 283;

of earthworm, 196;

organs of, 188.
Locust, relatives of, 220.
Lumber, transportation of, 119, 121.

448

INDEX

Lymph, defined, 369;

function of, 369.
Lymph vessels, 369, 370.

Macronucleus, 173, 174.
Malacostraca, 232.
Malaria and the mosquito, 178, 243.
Mammal, circulation in, 365;

man a, 311.
Mammals, 303;

classification of, 309;

hoofed, 306.
Man, brain of, 391;

circulation in, 362;

evolution of, 311;

mouth cavity of, 346;

place of, in nature, 311;

races of, 312;

stomach of, 343, 349.
Mandible, 218, 219.
Mantle cavity, 253.
Marsupials, 309.
Maxilla, 218, 219.
MaxilUpeds, 207.
May flies, 229.
Medulla, 391.
Medusa, 190.

Membrane, tympanic, 397.
Mendel, Gregor, 68.
Mesoderm, 182.
Mesophytes, 138.
Metazoa, 181.
Micronucleus, 173, 174.
Micropyle, 26; of bean, 54;
Mildews, 153.
Milk, an emulsion, 351;

and typhoid, 418;

bacteria in, 159;

necessity of pure, 416, 418.
Milkweed, dispersal in, 66.
Mimicry in insects, 236, 237.
Mineral matter, in living things, 12.
Molars, 346.
Mold, 149, 150.
Mollusks, 253;

classification of, 259;

habitat of, 257;

some common, 254, 255, 256, 257.
Molting, 211.
Monarch butterfly, 236.

Monocotyledons, 59.

Monotremes, 309.

Mosquito, and malaria, 178, 243;

and yellow fever, 244;

kinds of, 243;

malarial, 178, 243.
Mosses, 130, 131.
Moth, compared with butterfly,

222, 223.
Mouth, 343;

of grasshopper, 218.
Mouth cavity, of man, 345.
Mucus, 344.

Muscle tissue, use of, 315.
Muscles, and skeleton, 316;

arrangement of voluntary, 314;

extensor, 314;

flexor, 314;

nerve endings in, 315;

of frog's leg, 314;

structure of voluntary, 315.
Mushrooms, 151.
Mutant, 68.
Mutation, 68.
^Mycelium, 150.
Myriapods, 230, 232.

Nails, development of, 313.

Narcotic, defined, 339.

Natural resources, conservation of, 4.

Nectar, defined, 31.

Nectar glands, 31.

Nectar guides, 31.

Nerve, optic, 398;

parts of, 390.
Nerve cells, 391.
Nerve fibers, 391.
Nerves, mixed, 392;

motor, 392;

sensory, 392;

vasomotor, 370.
Nervous control, of blood vessels,
370;

of heart, 370;

of respiration, 377;

of sweat glands, 386;

organs of, 188.
Nervous system, and sense organs,
390;

autonomic, 392;

INDEX

449

Vervous system, cerebrospinal, 390;

divisions of, 390;

functions of, 321;

in birds, 291;

in fishes, 265;

in man, 321;

of crayfish, 209;

of frog, 392;

of insects, 220.
Neuroptera, 228, 232.
Newt, 279.
Nicotine, 339.
Nictitating membrane, 273.
Nitrogen, in plant growth, 79, 80;

properties of, 7.
Nitrogen cycle, 167, 168.
Nitrogen-fixing bacteria, 157, 158.
Nucleolus, 20.
Nucleus, 20;

in amoeba, 175.
Nutrients, 13, 322;

fuel values of, 326;

in beans, 56;

uses of, 326.
Nymph, 229.

Oak, section of, 86.
Oats, production of, 49.
Oils, 14, 323;

test for, 14,
Ommatidia, 207.
One-celled animals, 177.
Operculum in fishes, 263.
Opossum, Virginia, 309.
Opsonin, 361.
Orbit, 398.
Orchid, wild, 28,
Organ, defined, 17, 134, 186.
Organic and inorganic 'matter, 21.
Organism, defined, 17.
Organs of a plant, 18.
Oriole, Baltimore, 299.
Qrthoptera, 232.
Osculum, 183.
Osmosis, 75;

importance of, 76;

of sugar, 89, 347.
Ovary, 25.
Ovipositor, 218.
Ovule, deyelopment of, into seed, 27-

Owl, screech, 299.
Oxidation, defined, 8;

heat the result of, 9;

in germination, 62;

in human body, 11;

of carbon, 11;

rapid, 11;

slow, 9.
Oxygen, evolved in starch making,
109;

in air, 7;

preparation of, 8;

properties of, 8.
Oyster, 255.

Palate, hard, 345;

soft, 345.
Pancreas, position of, 343, 350.
Pancreatic juice, function of, 351.
Papillge, 345.
Pappus, 43.
Paramecium, 172, 173;

reproduction of, 174;

response to stimuli in, 173.
Parasites, 130.
Parasitism, in insects, 242.
Pasteurizing, 158.
Patent medicines, alcohol in, 340.
Pearl formation, 256.
Peas, as food, 56.
"Peepers," 279.
People, 52.
Pepsm, 349.
Pericardium, 363.
Perspiration, insensible, 385.
Petal, 24.
Phagocytes, 361.
Pharynx, 345.
Phloem defined, 88.
Phcebe, 297.
Photosynthesis, 106.
Physiology, defined, 1;

human, 1.
Pigeon-wheat moss, 130, 131
Pistil, 251.
Placenta, 41.

Plant and animal compared, 17
Plant body, simplest, 126.
Plant breeding, 66.
Plant invasions, 144.

450

INDEX

Plant life, in temperate zones, 142;

forms of, 126;

in tropics, 140;

upon mountains, 141.
Plant modification, cold a factor in,
140;

water a factor in, 137, 138;

wind a factor in, 139.
Plant outpost, a, 145.
Plant societies, 142, 143.
Plants, adaptation to environment,
144;

beneficial and harmful, 146;

classification of, 134;

harm done by, 146;

modified by surroundings, 136,
137;

relations to animals, 2, 4, 166,
167.
Plasma of blood, 358.
Pleura, 375.
Pleurococcus, 128, 172.
Plumule, 54, 55.
Pocket garden, 71.
Pollen carriers, 32, 33.
PoUen, growth of, 25;

protection of, 38.
Pollination, 27;

artificial, 38;

by humming bird, 32 ;

by insects, 29;

by wind, 36, 37;

history of, 27.
Polycotyledons, 59, 60.
Polyps, coral, 192;

hydroid, 190.
Pome, 52.
Pond lilies, 136.
Pond scum, 129.
Pons, 391.

Potato beetle, 227, 246.
Potato tuber, 95.
Precipitins, 358.
Premolars, 346.
Proboscis, 32.

Proglottids of tapeworm, 199.
Pronuba, 35.

Protective resemblance, 234, 235.
Protein, in bean, 56.
Protein making in plant, 107.

Proteins, 15, 323;

building of, 90;

test for, 15.
Prothallus, 132.
Protonema, 131.
Protoplasm, composition of, 22;

properties of, 22.
Protozoa, 172;

classification of, 180;

habitat of, 177;

relation to disease, 178;

use as food, 178.
Pseudopodia, 175.
Pteridophytes, 134.
Ptomaines, 157.
Ptyalin, 348.
Pulmonates, 257.
Pulse, cause of, 366.
Pupa, 222, 223.
Pupil, 398, 399.
Pylorus, 348.

Quarantine, 421.
Queen, 238.

Radiolarian, 180.

Ray flower, 34.

Rectum, 343.

Reflex action, examples of, 393;

meaning of, 393;

nervous, 393.
Regeneration, defined, 198.
Relation, of birds and reptiles, 301;

of body heat to work, 385;

of breathing to exercise, 381;

of environment to diet, 329;

of flies to disease, 225;

of Protozoa to disease, 178;

of work to diet, 329.
Rennin, 349.
Reptiles, study of, 281;

classification of, 285.
Reproduction, in animals, 182;

in plants, 181;

organs of, 188.
Respiration, 374;

adaptation for, 375;

artificial, 381, 382;

effect of alcohol on, 388;

effect of tobacco on, 388;

INDEX

451

Respiration, excretion^ 374;

in a cell, 383;

in birds, 291;

in crayfish, 207;

in fishes, 263;

in frog, 274;

in insects, 218;

necessity for, 374;

nervous control of, 377;

organs of, in man, 374.
Rest, necessity of, 395, 412.
Retina, 398, 399.
Rhizoids, 130, 150.
Ribs, attachment of, 318;

in respiration, 376.
Rice, production of, 50.
Robin, 295.
Rodents, 305.
Root, absorption in, 75;

effect of moisture on, 71, 72;

food storage in, 81;

influence of gravity upon, 70;

passage of soil water in, 76;

tip of, 73.
Root hair, structure of, 74.
Root hairs, 74.
Root pressure, 91.
Root system, 70.
Roots, and their work, 70;

different from stems, 98;

modified, 81, 82.
Roundworm, 199.
Rye, production of, 50.

Salamander, spotted, 280.
Saliva, function of, 347.
Salmon leaping a fall, 268.
San Jose scale, 248.
Sand shark, 271.
Sanitation, public, 415.
Saprophytes, 130.
Sea anemone, 191.
Sea lion, 304.
Seaweeds, 126.
Seed dispersal, 41, 42, 66.
Seedling, defined, 64.
Seeds, and seedlings, 54;

formation of, 41;

uses of, 65;

winged, 44.

Selective absorption, 176.
Selective breeding, 308.
Selective planting, 67.
Self-pollination, defined, 27.
Sense organs, 188, 219, 273;

in birds, 291;

in fishes, 262;

in man, 395.
Sepal, 24.

Serum of blood, 359.
Sexual development of simple ani-
mal, 182.
Sexual reproduction, in animals,
174, 177, 184, 190, 191, 266, 276;

in plants, 130, 131, 132.
Shelf fungus, 151.
Ship worm, damage by, 258.
Shrimps, 212.
Silkworm, 4, 223.
Skeleton, and muscles, 316;

appendicular, 318;

axial, 318;

of birds, 289;

of dog, 318;

of fishes, 265;

of man, 319;

structure of, 317;

uses of, 317.
Skeleton building in Protozoa, 180.
Skin, hygiene of, 386;

structure of, 313.
Skull, of boa constrictor, 284;

of dog, 304;

of man, 320;

of porcupine, 305.
Sleep, and health, 407;

necessity of, 395.
Smell, organs of, 396.
Snail, 256.
Snake, garter, 283.
Snakes, poisonous, 284;

value of, 283.
Soil, composition of, 10, 77;

organic matter in, 78;

water in, 77, 79;

weathering of, 77.
Soil exhaustion, prevention of, 80.
Sparrow, English, 299;

song, 295.
SpecieS; defined, 133.

452

INDEX

Spermatophytes, defined, 133, 134.

Sperm cell, 25, 182.

Spiders, 230.

Spinnerets of spiders, 230.

Spiracles, 218.

Spirillum, 154,

Spirogyra, 129.

Sponge, structure of, 183.

Sponges, 189.

Sporangium, 150.

Spores, 150.

Sporophyte, in moss, 131.

Squash bug, 246.

Squid, 257.

Stamens, 25.

Starch, in bean, 55;

non-osmosis of, 89, 347;

test for, 13, 14;

to grape sugar, 57.
Starch grains, 55.

Starch making, and milling, com-
pared, 106;

by green plants, 104;

chemistry of, 106, 107;

light and air in, 105;

rapidity of, 108.
Starfish, 258.
Stem, dicotyledonous, 85, 86,;

dicotyledonous and monocoty-
ledonous, compared, 92;

modified, 94, 95;

monocotyledonous, 91;

movement of fluid in, 88, 90;

structure and work of, 84.
Stems, 95, 96.
Sternum, 319.
Stigma, 25.
Stimulants, 336.
Stimuli, response to, in Paramecium,

173.
Stirrup, 397.
Stomach, movements of, 350;

of man, 343, 348, 349.
Stomata, 104, 111.
Street cleaning, 415, 416.
Struggle for existence, 46.
Sturgeon, 271.
Style, 25.
Suffocation, 381.
Sugar, osmosis of, 89, 347.

Sun, a source of energy, 102. •
Sunlight, in starch making, 105.
Swallow, barn, 297.
Swarming, 240.
Sweat, 385.
Sweat glands, 313;

nervous control of, 386;

structure of, 384;

use of, 384.
Sweeping, 380.
Swim bladder, 264.
Swimmerets, 206. ,
Symbiosis, 168;

between plants and insects, 241;

in crabs, 214;

inhchens, 168, 169;
Synura, 128.
Systematic botany, 133.

Tail of birds, function of, 289.

Tapeworms, 199.

Taproot, 72; 73.

Tarantula, 230.

Taste, organs of, 396.

Taste buds, 345, 396.

Teeth, canine, 304, 346;

care of, 346;

incisors, 346;

kinds of, in man, 346.
Teleosts, 271.
Temperature, feeling of, 396;

in germination, 61.
Tentacles, 184.
Testa, 54.
Tetanus, 162.
Thallophytes, 134.
Thallus, 126.
Theine, 336.
Thoracic duct, 370.
Thoracic region, 319.
Thorax, 217.
Throat, 343.
Timber, cutting of, 120.
Tissue, 19, 186, 314.
I'issues, of human body, 186.
Toad, common, 278.
Tobacco, effect on nervous system,
339;

effect on respiration, 388;

use of, 339.

INDEX

453

Tongue, 343, 345.
Tonsil, 345.
Tooth, section of, 346.
Tortoise, box, 282.
Touch, experiment in, 396;

organs of, 395.
Toxin, 159.
Tracheae, 218, 345.
Transpiration, in plants, 110, 111.
Tree, wounded by "cribbing," 123,

124.
Trees, city's need for, 124.
TrilUums, 144.
Trypanosomes, 179.
Tuberculosis. 160;

death rate from, 424 ;

fighting, 419, 420.
Turtle, 281.

Tussock moth, larva of, 247.
Typhoid fever, 161;

due to milk supply, 418;

due to water supply, 417 ;

fighting, 419.

Undent' ing moth, 235.
Ungulates, 306.
Urea, 384.
Ureter, 384.
Urethra, 384.
Uropod, 207.

Vaccination, 422.

Vacuole, contractile, 173, 174, 175,
176;

food, 173, 175, 176.
Valves, 41.
Veins, 362;

function of, 367;

structure of, 367.
Ventilation, methods of, 379;

need of, 379;

of sleeping rooms, 381.
Ventricle, 363.
Venus's flower basket, 189.
Venus's flytrap, 113.
Vermiform appendix, 343, 355.
Vertebra, 318.

Vertebral column, 318, 319.
Vertebrates, compared with inver-
tebrates, 260.
Vicerov butterfly, 236.
Vilh, 353.

Vitamins, 323, 324, 325.
Vitreous humor, 398, 399.
VorticeUa, 177.

Walking sticks, 234.
Warbler, yellow, 297.
Warning coloration, 236.
Wasp, solitary, 237.
Water, and health, 406;

and typhoid, 417;

composition of 9, 10;

factor in germination, 60, 61;

in hygiene, 411;

in hving things, 12;

necessity of pure, 416, 417.
Water supplj^, factor in modification,
137;

regulated by forests, 115, 116.
Weathering, 77.

Web, spider's, uses and forms, 230.
Weed, 17, 46.
Wheat, production of, 49;

uses of, 49.
Wheat rust, 152.
Wings, of grasshopper, 218.
Wood, structure of, 120;

uses of, 119.
Woodpecker, downy, 298.
Worker, 238.
Worms, classification of, 202;

harmful, 198:

study of adaptation-s, 194.
Wren, house, 296.

Xerophytes, 137.
Xylem, defined, 88.

Yeast, 148, 149.
YeUow fever, 244.

Zvgospore, formation of, 129, 130,
150.

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