BIOLOGY FOR BEGINNERS
TRUMAN J. MOON
GIFT OF
From the collection of the
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o Prelinger
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San Francisco, California
2006
CHARLES DARWIN 1809-1882
BIOLOGY FOR
BEGINNERS
BY
TRUMAN J. MOON
MIDDLETOWN, N. Y. HIGH SCHOOL
NEW YORK
HENRY HOLT AND COMPANY
-
COPYRIGHT, I Q2 I
BY
HENRY HOLT AND COMPANY
PREFACE
THIS text is an attempt to present the fundamental facts of
elementary biology as clearly and briefly as a reasonable scientific
accuracy will allow. Three years' use in manuscript form has
dictated the topics included and the arrangement followed in order
that the book may be easily taught and readily understood.
The course emphasizes the fact that biology is a unit science,
based on the fundamental idea of evolution rather than a forced
combination of portions 0f botany, zoology and hygiene.
Emphasis has been placed upon a logical arrangement within
the chapters, so that it is easy for the pupil to study, outline,
and remember each lesson.
A larger proportion of pages is devoted to outlines, tabulations,
and diagrams than in any other similar text. This means that
the pupil has less text matter to cover, and more help to assist
him in doing it.
No laboratory work is included. Any laboratory manual can
be used with the text, however, as it covers much more than the
required ground. It is thought that a separate manual will allow
the teacher to emphasize in the laboratory, those subjects which
he considers most important.
Experience has indicated that the "vocabularies" save the
pupil much time and confusion. Particular care has been taken
to keep the vocabulary of the text as simple as possible. Careful
explanations are made where this seems advisable. The definitions
in the text are not complete, but, for the sake of clearness, are
purposely limited to those meanings which fit the use in the chapter
concerned.
In any science subject collateral reading is highly important.
To facilitate this, lists of references have been placed at the ends
of the chapters, covering such books as should be available in a
well-equipped school. This outside reading should be encouraged.
v
462251
vi ACKNOWLEDGMENT
The large number of line drawings is intended to simplify
matters of structure for the beginner who would have difficulty
in selecting the essential points of a more detailed drawing or
photograph. Since the object of illustrations in an elementary
text is to call attention to essential facts, the simple diagrammatic
outlines and complete labeling found in this book are worthy of
notice. It is hoped also that a reasonable use of line drawings
will help the pupil in his own work by affording models which
he can easily approximate.
The economic applications of biology have been given very full
treatment, especially as to their bearing on agriculture and civic
problems.
The scope of the matter presented is broad enough so that the
teacher can select what seems most important, and still be sure
of covering any requirement in any elementary biology syllabus.
On the other hand the attempt has been made not to burden the
pupil with matter required for advanced biology only.
ACKNOWLEDGMENT
IN offering this text book to the public, recognition is due to
many sources of aid and information.
The lists of references appended to the various chapters fulfill
the double purpose of indicating some of the authorities which
have been consulted and of telling the student where fuller in-
formation may be obtained.
The cuts, in so far as they are not original, are credited to the
proper sources in each case. In many cases, these are changed
in some degree, to conform to the uses of the text.
The author is especially indebted to the cheerful assistance of
his wife in the laborious task of reading and correcting the manu-
script and proof, and to his fellow teacher, Miss C. E. Reed,* for
many helpful suggestions as to content and arrangement.
If there be aught of use or value in this book let it be to the
credit of the authorities consulted and the help received; for its
many shortcomings the author alone is responsible.
T. J. MOON
CONTENTS
PAGE
CHAPTER I. INTRODUCTION 1
Definition of Biology. Reasons for study. Organic things. In-
organic things. Familiar biology.
CHAPTER II. THE LIKENESS OF LIVING THINGS 5
Processes common to organic things.
CHAPTER III. ELEMENTS, THE ALPHABET OF LIVING THINGS 9
Oxygen and oxidation. Occurrence, properties and uses of other
common elements.
CHAPTER IV. COMPOUNDS, BIOLOGY'S BUILDING MATERIALS 18
Water; Carbon dioxide; Proteids; Fats; Carbohydrates;
Method of testing.
CHAPTER V. PROTOPLASM, THE "Bios" OF BIOLOGY 25
Protoplasm, its composition and properties. Cell, Tissues, Organs,
System. Adaptation.
CHAPTER VI. THE STRUCTURE OF SEEDS 31
Parts of typical seed. Bean and Corn seeds as examples.
CHAPTER VII. GERMINATION 41
Conditions necessary. Stages hi germination. Corn and Bean.
CHAPTER VIII. ROOTS 49
Characteristics. Structure. Functions. Adaptations.
CHAPTER IX. ABSORPTION AND OSMOSIS 58
Use of water to plants. Turgescence. Osmosis, definition and
essentials for. Root hairs. Geotropism. Hydrotropism.
CHAPTER X. STEMS, THEIR FORMS AND FUNCTIONS 68
Characteristics. Functions. Kinds of branching. Forms of stems.
Buds.
CHAPTER XI. STEM STRUCTURE 75
External structure. Grafting. Internal structure, dicot. and monocot.
types.
CHAPTER XII. LEAVES AND LEAF STRUCTURE 86
Functions. General structure. Minute structure. Adaptation.
Modified forms. Fall of leaves.
vii
viii CONTENTS
PAGE
CHAPTER XIII. LEAF FUNCTIONS . . ^.^ 96
Photosynthesis. Digestion. Assimilation. Respiration. Transpi-
ration.
CHAPTER XIV. FLOWERS: POLLENATION AND FERTILIZATION 108
Structure and function of flower parts. Adaptations for pollenation
by wind and insects. Pollen; Ovule; Fertilization stages.
CHAPTER XV. FRUITS AND THEIR USES 118
Definition; Types of fruits; Functions. Dispersal. Economic
importance.
CHAPTER XVI. SPORE-BEARING PLANTS 127
Classes of plants. Representatives. Fungi as type of spore plants.
CHAPTER XVII. BACTERIA .' 133
Kinds. Method of study. Useful and harmful forms. Natural and
artificial protection. Antiseptics. Disinfectants. History.
CHAPTER XVIII. PROTOZOA 146
Relation to higher animals. Amoeba and Paramoecium as types.
Life functions compared.
CHAPTER XIX. METAZOA 154
Development. Specialization. Classification.
CHAPTER XX. WORMS 161
Representatives. Structure. Adaptations. Economic importance.
Parasitism. Earthworm. Trichina. Hookworm. Tapeworm.
CHAPTER. XXI. ARTHROPODS 172
Characteristics. Classification. Scientific classification explained.
CHAPTER XXII. CRUSTACEA, A CLASS OF ARTHROPODS 179
Characteristics. Crayfish as type. Structure and adaptations of
crayfish. Homology. Life history.
CHAPTER XXIII. INSECTS, A CLASS OF ARTHROPODS 192
Characteristics. Grasshopper as type. Structure of grasshopper.
Adaptations. Life History. Economic importance.
CHAPTER XXIV. INSECTS; BUTTERFLY, MOTH AND BEE 205
Structure and adaptations of each. Communal life and specialization
of bee. Economic importance.
CHAPTER XXV. INSECTS AND DISEASE 220
Structure and Life History of Fly and Mosquito. Relation to dis-
ease; how proven. Means of prevention and control.
CHAPTER XXVI. THE VERTEBRATES 234
Classification of animals. Development. Classification and types
of vertebrates.
CONTENTS ix
PAGE
CHAPTER XXVII. FISHES 239
Structure, external and internal. Life History. Adaptations.
Economic value.
CHAPTER XXVIII. THE FROG AND ITS RELATIVES. . .' 252
Characteristics of the amphibia. Structure of frog. Adaptations.
CHAPTER XXIX. THE AMPHIBIA; LIFE HISTORY AND HABITS 267
Metamorphosis of frog. Toad, Salamander and Frog compared.
Economic importance.
CHAPTER XXX. REPTILES 273
Representatives. Characteristics. Adaptations. False ideas.
Poisonous snakes. Treatment.
CHAPTER XXXI. BIRD STRUCTURE AND ADAPTATIONS 281
Characteristics. Adaptations for flight. Adaptations for active
life. Adaptations of beaks and feet.
CHAPTER XXXII. BIRD HABITS 294
Food. Nesting. Eggs. Migration. Economic importance.
CHAPTER XXXIII. MAMMALS 310
Characteristics. Adaptations of limbs, teeth, and body coverings.
Special adaptations of rodents, ungulates, carnivora and primates.
Man's place in the group.
CHAPTER XXXIV. THE DEVELOPMENT OF MAN 321 .
Relation to other animals. Idea of evolution. Evidences of evo-
lution.
CHAPTER XXXV. THE METHOD OF EVOLUTION 326
Antiquity of the idea. Lamarck's theory. Darwin and Natural
Selection. Summary of the theory; its conclusions.
CHAPTER XXXVI. THE DEVELOPMENT OF CIVILIZED MAN 333
Ancient records. Primitive man. Stages in development. Imple-
ments used. Results of higher mentality. Present races.
CHAPTER XXXVII. FOOD 342
Necessity. Definition. Functions of various food stuffs. Measure-
ment of values. Proportions. Balanced ration. Digestibility.
Cost. Cooking. Lipoid. Vitamines.
CHAPTER XXXVIII. NUTRITION 363
Digestive changes. Digestive organs. Mouth. Teeth. Stomach.
Intestine. Glands. Absorption. Assimilation.
CHAPTER XXXIX. RESPIRATION 382
Development of organs, in lower forms. Structure and adaptation
of nose, trachea, lungs, diaphragm. Changes in air and blood. Venti-
lation.
CHAPTER XL. CIRCULATION 392
Function. Blood, its composition and use. Heart. Arteries, Veins,
Capillaries. Lymph circulation.
x CONTENTS .
PAGE
CHAPTER XLI. EXCRETION 403
Source of waste. Organs of excretion. Kidneys, Lungs, Skin. Heat
regulation.
CHAPTER XLII. THE NERVOUS SYSTEM 408
Location and functions of cerebrum, cerebellum, medulla, . spinal
cord, sympathetic system. Regions of control for various activities.
CHAPTER XLIII. THE SENSE ORGANS 415
Irritability. Touch. Taste. Smell. Hearing, structure of ear,
care of ears. Sight, structure of eye, care of eyes.
CHAPTER XLIV. BIOLOGY ,AND HEALTH 425
Hygiene of Muscles, of Digestion, Breathing. Bathing. Care of
eyes, teeth, feet. Posture. Sleep.
CHAPTER XLV. Civic BIOLOGY 440
Food control. Sanitation. Disease prevention. Housing conditions.
Food laws. Medicines.
CHAPTER XL VI. ECONOMIC BIOLOGY OF PLANTS 446
General uses. Harmful forms. Plant uses in detail.
CHAPTER XLVII. ECONOMIC BIOLOGY OF INVERTEBRATES 467
General uses of animals. Harmful forms. Importance of each
group in detail. Harmful insects and their treatment.
CHAPTER XL VIII. ECONOMIC BIOLOGY OF VERTEBRATES 480
Fish. Amphibia. Reptiles. Birds. Mammals.
CHAPTER XLIX. BIOLOGY AND AGRICULTURE 486
Soil formation. Plant breeding and protection. Animal husbandry.
Bacteria on the farm.
CHAPTER L. ECONOMIC IMPORTANCE OF FORESTS 495
Value of forests. Enemies of forests. Protection. Timber structure.
Street trees.
CHAPTER LI. TOBACCO AND TABLE BEVERAGES . 508
Tobacco, physical and social objections to its use. Tea, Coffee,
Cocoa, and Chocolate.
CHAPTER LII. ALCOHOL IN RELATION TO BIOLOGY . . 514
Composition and kinds of alcoholic liquors. Physical effects. Not
a food. Alcohol and disease. Waste of resources.
CHAPTER LIII. SOME GENERAL BIOLOGIC PROCESSES . . 524
Osmosis in life processes. Oxidation. Circles in Nature. Evolution
of life functions.
CHAPTER LIV. HISTORICAL DEVELOPMENT OF BIOLOGY . .
Biologic development. The work of Pasteur, Roux, von Behring,
Lister, Carrell, Flexner. Darwin, Huxley, Mendel, Burbank.
INDEX.. 549
BIOLOGY FOR BEGINNERS
CHAPTER I
INTRODUCTION
The student should make sure that he understands every term used in his
Biology lessons. This book will include vocabularies like the following, but
in addition, a good dictionary should be consulted frequently and derivations
studied. As is shown in the first paragraph on this page, a great deal can
be learned about the meanings of scientific terms by looking up their deri-
vations.
Vocabulary
Domestic, tamed, as applied to animals and plants used by man.
Biology, the science of living things.
Organic, pertaining to living things.
Inorganic, things which have never been alive.
Biology is a study of living things. The dictionary tells us that
this term comes from two Greek words, " Bios " which means
" life," or " living things," and " ology," a word-ending meaning
" the science or study of." The two parts thus make a perfect
definition of biology, which is, truly, " The science of living things."
Classes of Things. All things in the world can be divided into
two classes; those which are, or have been alive, and those which
have never lived. The former are called organic substances, and
the latter inorganic.
Organic things include both plants and animals, together with
all substances derived from them. Inorganic things include the
members of the mineral kingdom such as stone, glass, or iron, as
well as water, carbon dioxide, oxygen and similar substances.
Biology is the science which deals with the study of organic things,
as its derivation shows.
Words as Tools. Since three new words have been used already
biology, organic, and inorganic it may appear that the subject
1
BIOLOGY FOR BEGINNERS
"is to : be -made -diffieuk because of many hard and strange terms.
There need be no alarm at the prospect if we will consider each
new word as a tool which will enable us to do our work better,
more accurately, and more easily.
It is simpler to say " organic substances " than to say, " sub-
stances which are or have been alive." It is also more accurate,
and furthermore we have increased our vocabulary by the addition
of this new tool.
We should think a carpenter very foolish who cut all his lumber
with a jack knife because he thought it too much trouble to learn
to use a saw. Students in their school life are workmen, and their
most important tools are words. Each subject taken up, like
different kinds of carpenter work, requires the use of a certain
number of new tools (words). These must be learned before
the student can do his work efficiently.
On the other hand a carpenter would be foolish to load up his
chest with a lot of tools which he rarely used, and so, in our study,
we have included only those new names and terms without which
we could not possibly get along. If we learn to use them, we will
not have to " cut off our board with a jack knife."
Sciences Included in Biology. . Although biology is a single and
closely united science based on the study of all things that are or
have been alive, it is so broad in scope that it includes many
special branches.
Some of these are already familiar, such as botany, which deals
with plants; zoology, which deals with animals; hygiene, which
concerns the care of the human body; physiology, which is the
science of the use or function of living organs; and many others.
Familiar Biology. To begin with, each one of us has studied
biology already by observing the things of nature about us. Is
this not true? We know some plants and trees by name. We
know how to cultivate gardens, what will help plants grow, the
names of many flowers. All of us buy and use fruits, grain, and
vegetables. We also know something about the care of animals,
and, most important of all, are anxious to learn all that we can
about the care and use of our own bodies.
INTRODUCTION 3
Reasons for the Study of Biology. Biology is a required study
in many schools, and we have a right to ask why it is considered
so important that we are obliged to study it.
In the first place there are few subjects that add so much to
ANIMAL
PLANT .
FIG. 1. Diagram to show the relation of General Biology to the biological
sciences. From Calkins.
general culture by increasing the number of things in which we.
are interested and about which we should have information.
Few people really see very much of the things about them
accurate observation is a very rare but valuable trait, and biology
will greatly increase the powers of observation.
4 BIOLOGY FOR BEGINNERS
Mere observation of facts is not enough, however, for one should
be able to draw correct conclusions from what he sees. This
ability to think and reason is one of the chief aims of the laboratory
work in biology or any other science.
Although these reasons for the study of biology are by far the
most important, others can be mentioned which may seem more
practical. Tt is the foundation of farming, gardening, and forestry
and upon its laws are based the care and breeding of all domestic
animals and plants.
In even a more personal way, biology deals with the health
and care of our own bodies hygiene. It also includes the study
of the cause and prevention of disease, the work of bacteria, and
means of maintaining healthful surroundings sanitation.
One-half of all human deaths are caused by germ diseases and
at least half of these could be prevented by proper knowledge
and practice of hygiene and sanitation. This in itself is sufficient
reason for interest in the study of biology.
SUMMARY
Biology, a study of living things.
1. Derivation: Bios, Logos.
2. Definition.
3. Classes of things.
Inorganic (meaning and examples).
Organic (meaning and examples).
Plants:
Animals.
4. Words as tools.
5. Sciences included.
6. Familiar biology.
7. Reasons for study.
Adds to culture.
Cultivates power of observation.
Teaches to think and reason.
Importance in many industries.
Relation to health.
Hygiene.
Sanitation.
CHAPTER II
THE LIKENESS OF ALL LIVING THINGS
Vocabulary
Similarity, likeness.
Assimilation, " to be made the same," that is, the process by
which food stuff is made into tissue.
Nutrition, all the processes by which food is prepared and assimi-
lated in the body.
Excretion, the passing off of waste matter from plant or animal.
Biology, then, is the study of organic, or living things, and
living things include both plants and animals. At first one would
say that plants and animals have very little similarity and that it
would be difficult to study them together, but let us see if this
is true.
Nutrition. First, both plants and animals are alive and grow
in size and that means that they both need food. A cat, for instance,
has to eat, and a geranium has to have earth, in order to live. The
cat uses organic food and the plant inorganic. The cat obtains
its food by means of its claws and teeth, while the food-getting
of the plant is done largely by the roots. They are both dependent
on food.
After they get their food, both plants and animals have to put
it into liquid form in their bodies. We call that process digestion.
Then the digested food undergoes a change by which the milk or
meat actually becomes part of the cat, while the plant foods be-
come part of the geranium. This is a very wonderful process and
is called assimilation. (Look up this word in the dictionary and
see if you can tell why it is used in this way.)
Food-getting, digestion, and assimilation together make up the
process of nutrition (getting nourishment). The animal and the
plant have this process in common.
5
6 BIOLOGY FOR BEGINNERS
Respiration. Another point in which our two examples are alike
is that they both breathe. If we keep either one in an air-tight
box it will die. The cat breathes by means of its lungs and it is
easy to see the muscular movements involved. The leaves of the
plant breathe too, although our eyes cannot detect the way in
which this is done. The process of breathing is called respiration
in both cases.
Excretion. Both cat and geranium use the food that they
assimilate to build up their bodies or to give them energy, and
both throw off from their bodies unused and changed food materials
by a process called excretion. The animal does this by means of
the lungs, skin, intestines and kidneys; the plant by means of
the leaves.
Motion. Another way in which all living things are alike is in
the power of motion. It is easy to see the cat move, but few observe
how the geranium turns its leaves to the light and its roots to the
water. Though animals usually have greater freedom of motion,
plants do not lack it altogether.
Sensation. In a general way, all plants and animals have the
power of responding to touch, heat, light, and other forces outside
of themselves. This is sensation, and may vary in its expression,
from the mere turning of leaves toward light to the delicate opera-
tion of a wonderful sense organ like the human eye.
Reproduction. Both plants and animals reproduce others like
themselves. Kittens are born and grow to be cats, and the plant
bears seeds which will produce other plants like itself. By this
wonderful provision of nature, although all organic things die,
others like them are left to take their places. The processes of
reproduction and nutrition are the two most important charac-
teristics of all living things.
Likeness of all Living (Organic) Things. The cat before the
fire and the geranium on the window sill, though apparently
different, are really alike in all of the necessary processes of life.
It is, therefore, possible and easy to study plants and animals
together. Biology is not merely botany plus zoology, but a study
of the life processes of all living things.
THE LIKENESS OF ALL LIVING THINGS 7
Difference from Inorganic Things. The points, in which all
living or organic things are alike, are also the points in which they
differ from inorganic things. A stone and a piece of iron are
familiar examples of inorganic matter. We cannot imagine a stone
taking food or growing, or a piece of iron moving or reproducing
its kind. Our study of biology is thus sharply separated from
inorganic things.
To be sure, plants can take inorganic matter and by certain
wonderful processes make it into the living plant as we have
mentioned. But it then ceases to be inorganic and becomes a
part of the plant. Plant and animal are alike in all essential ways
and they also differ in these ways from all inorganic substances.
SUMMARY
Organic things (Plant and Animal).
1. Live, grow, and move.
2. Obtain food.
3. Digest and absorb food.
4. Assimilate food as part of themselves.
5. Excrete waste.
6. Reproduce.
Inorganic things can perform none of the above processes.
Organic and Inorganic things resemble each other in the following points:
1. They are composed of similar elements.
2. They contain, use and produce similar compounds, such as carbon
dioxide, water, etc.
3. They have characteristic shapes and weights.
4. They undergo chemical changes.
5. They liberate energy.
Organic things differ from Inorganic, in the following points:
1. They have organs for various functions.
2. They are composed of cells.
3. They always contain protoplasm.
4. Their growth is from within.
5. They respond to their surroundings (irritability).
6. They follow a " life cycle."
7. They depend upon oxidation for life.
BIOLOGY FOR BEGINNERS
PROCESSES IN WHICH ORGANIC THINGS ARE ALIKE
Process
i
In plants is per-
formed by
In animals is per-
formed by
Food-getting
Roots, leaves
Teeth, claws, etc.
Digestion
Ferments in the tissues
Stomach, intestines,
glands, etc.
Absorption
All live tissues
Intestine, stomach, etc.
Assimilation
U
All live tissues
Respiration (oxidation)
Air spaces and tissues
Lungs, gills, etc., all
tissues
Excretion
Leaves
Kidneys, skin, etc.
Motion
Flowers, leaves, ten-
Legs, wings, fins, etc.
drils, etc.
Sensation
Leaves, tendrils
Nerves, sense organs
Reproduction
Seeds, slips, etc.
Eggs, live young
What evidences can you give of any of these processes, in either
plants or animals?
Since both plants and animals perform similar processes, what
might you expect about the stuff they are made of?
COLLATERAL READING
General Biology, Sedgwick and Wilson, pp. 1-19; Applied Biology,
Bigelow, pp. 10-22, 122-132; Practical Biology, Smallwood, pp. 1-10;
Essentials of Biology, Hunter, pp. 26-30; Elementary Zoology, Galloway,
pp. 36-54, 72-97; Biology, Calkins, pp. 6-15; General Zoology, Pearse,
pp. 25-36.
CHAPTER III
ELEMENTS, THE ALPHABET OF ALL LIVING THINGS
Vocabulary
Individual, separate.
Innumerable, very many.
Oxidation, the union of any thing with oxygen.
Combustion, rapid oxidation, producing light and heat.
Restrain, to hold back.
All the words of our language are made from less than thirty
letters. If we think of our big dictionaries we realize what an
enormous number of different combinations can be formed from
a few letters.
Elements and Compounds. In something the same way, all
the matter in the world is composed of about eighty individual
substances called elements. These we might think of as the letters
in a chemical alphabet which spell all the substances both
organic and inorganic that are in existence. When elements
unite, they form all the innumerable things that compose the
world around us. -These substances, formed by the union of two
or more elements, are called compounds. For example, iron is an
element. Oxygen in the air is also an element. When these two
unite, they form a compound which we call iron rust.
Organic substances utilize only about ten elements, but when
we stop to think of the thousands of kinds of plants and of animals,
and of all the different substances of which they are made, we see
that ten elements are enough to make a wide variety of compounds.
What to Learn about Them. The complete study of these
elements and their compounds is called chemistry, but for the
present we need to learn only four things about the elements
which compose organic substances: (1) their names, (2) where
9
10 BIOLOGY FOR BEGINNERS
they are found, (3) enough of their characteristics or properties
so that we can recognize them, and (4) their use to living things.
OXYGEN
Where it is Found. We already know that oxygen (O) is part
of the air, but it is also a part of water, sand, soil, rock, and many
other things. It may be hard to understand how a gas, like oxygen,
can be a part of a liquid, like water, or of a solid like wood, but
this is true. Oxygen is found in all plant and animal substance.
In fact it is the most abundant element in the world, and is itself
one-half of the solid material of the earth.
Properties. We shall see oxygen prepared in the laboratory, and
shall discover that it is a colorless, odorless, and tasteless gas. It
is heavier than air, will dissolve slightly in water, and most curious
of all, though it will not burn, it nevertheless makes other things
burn very rapidly. Iron, copper, and many other substances
which do not seem to burn at all in the air will do so in oxygen,
while sulphur and wood, which do burn in air, burn very fast in
oxygen.
Test. It is the only substance which will cause a glowing splinter
to burst into flame. This fact is utilized in testing whether a gas
is oxygen or not, and is therefore called a test for oxygen.
Oxidation. When anything unites with oxygen, the process is
called oxidation, and the compound formed by the substance and
the oxygen is called an oxide.
Oxygen may unite with substances rapidly, as when a stick
burns, or slowly, as when iron rusts. An oxide is always the product,
and there is always a more important product, namely, heat energy.
Both plants and animals use oxygen. Heat energy is necessary
for all life. All plants and animals therefore depend on oxygen
which they take into their bodies by breathing, as we have seen
in CKapter II. As the living tissues become oxidized they produce
heat and energy, leaving a residue of oxides and other material to
be thrown off as waste. The food assimilated as tissue contains
the vital energy which oxidation releases.
THE ALPHABET OF ALL LIVING THINGS
11
Live and Dead Engines. A living organism is often compared
to a steam engine. Both need a supply of food (fuel), and both
must have oxygen to unite with (oxidize) the food and set free
its energy. In both, heat is produced by this oxidation and then
changed into motion, and in both there are waste products which
have to be removed.
But an engine is only an inorganic thing. It cannot get" its
own food, it does not assimilate or grow, it does not excrete its
waste products, or reproduce. Really the only way in which it
resembles a living thing is that it depends on energy which is
released from substances by uniting with oxygen, and turns this
energy into motion.
RESEMBLANCES
A living organism
A steam engine
Requires
Food
Fuel
To unite with
Oxygen
Oxygen
By means of
Respiration
Draft
To produce
Heat and energy
Heat and energy
Leaving waste
Unused food
Ashes
Carbon dioxide (in
Carbon dioxide (in chim-
breath)
ney gas)
DIFFERENCES
A living organism .
A steam engine
Is alive
Grows in size
Repairs wear
Reproduces
Is not alive
Does not grow
Wears out
Cannot reproduce
Similarities based on oxidation, differences based on functions of the
protoplasm.
Other Uses of Oxygen. Oxygen has many other uses in nature.
It causes combustion from which we get heat and power. It also
causes rusting, oxidation, and decay. Its myriad compounds are
12 BIOLOGY FOR BEGINNERS
absolutely necessary as food and drink. But its chief importance
in biology is that, by uniting with the substance of both plant
and animal, it sets free the energy which keeps them alive. Without
oxygen, no life can exist.
NITROGEN
Where it is Found. Nitrogen (N) is another important element.
It makes up four-fifths of the air. It is found combined with several
minerals in the soil and exists in the living tissue of all organic
things.
Properties. Nitrogen resembles oxygen in being colorless, odor-
less, and tasteless, and in that it will not burn. It is less soluble
in water and lighter in weight. It is the exact opposite of oxygen
in its behavior, for it will not cause combustion, nor will it combine
readily with other elements. Its compounds decompose easily.
Uses. It is found in the active living substance of all plants
and animals and is essential to their life. Its various compounds
are our most necessary foods.
All fertilizers which we use for plants, as well as meat, milk,
eggs, and many other animal foods contain very important com-
pounds of nitrogen.
If the air were pure oxygen, fires could not be controlled and
things would oxidize too rapidly. Thus, another important use of
nitrogen is to restrain the activity of oxygen and make the at-
mosphere suitable for life.
HYDROGEN
Where it is Found. Hydrogen (H) occurs combined in water,
plant and animal tissue, wood, coal, gas, and all acids.
Properties. It resembles both nitrogen and oxygen in being
colorless, odorless, and tasteless. It does not dissolve much in
water and it will not cause things to burn, but unlike either nitrogen
or oxygen it burns readily and even explodes when mixed with air
and brought into contact with fire. It is the lightest substance
known and, because of this fact, is used to fill balloons.
THE ALPHABET OF ALL LIVING THINGS 13
Uses. Hydrogen is important to the biologist because it unites
readily with oxygen and forms water. It also combines with both
oxygen and carbon (another element) and forms a whole series of
compounds called fats, sugars, and starches. It is an essential
ingredient in all organic tissue.
CARBON
Carbon (C) is an element with which we are more familiar; coal,
charcoal, and wood are common forms. Lead-pencils do not
really contain lead at all but another form of carbon called
graphite. Strangest of all, the diamond is carbon, too, though
not a common form.
Properties. Carbon is (except in the diamond) a black solid,
not soluble in any thing. At ordinary temperature it is very
inactive. When heated, however, it unites readily with oxygen,
(that is, it burns) and forms an oxide which is called carbon dioxide
a compound very necessary to plants, as we shall see later.
Uses. Carbon's importance to biology is due to the fact that it
is a part of all organic substances, combining with hydrogen,
nitrogen, and oxygen and other elements to form all plant and
animal tissues and many of their foods.
We know that if any plant or animal substance is partly burned
a black solid is produced. This, in every case, is carbon. We also
know that if the burning is continued the carbon will disappear.
This means that it becomes oxidized into carbon dioxide, which is
an invisible gas.
Plants alone have the power to obtain their carbon from the
carbon dioxide of the air. Animals depend entirely on plant
foods for the carbon compounds which are necessary for their life.
SULPHUR
Sulphur (S) is a yellow solid element, which (like carbon) will
not dissolve in water, but can be dissolved in other chemicals.
Sulphur itself has no odor, but it readily unites with oxygen,
even at low temperatures. It also burns readily, producing in
14 BIOLOGY FOR BEGINNERS
both cases an oxide of sulphur (SO 2 ) with the familiar, suffocating
odor which we wrongly associate with sulphur itself.
Its importance in biology is due to the fact that it is a part of
the living substance of all organic things though in smaller amounts
than any of the preceding elements.
Mustard, onions, and eggs will blacken silver dishes. This is
due to the sulphur compounds which they contain; but sulphur,
in smaller quantities, is found hi all plants and animals.
PHOSPHORUS
Phosphorus (P) is a light yellow, waxy, solid element. Like
sulphur, it dissolves in several other liquids, but not in water.
It also resembles sulphur in that it unites readily with oxygen.
In fact it unites with oxygen more readily than does sulphur, for,
if exposed to air, it will take fire and burn fiercely, forming an
oxide of phosphorus. It has to be kept covered with water to
prevent it from burning and is a dangerous and poisonous element.
It seems strange that such a substance should be a necessary
ingredient of our bodies and, in fact, of all living things. To be
sure it is present in small amount but is absolutely essential,
being especially abundant in bone and nerve tissue.
You have probably heard plant fertilizers called " phosphates."
This is because they contain phosphorus compounds.
IRON
Iron is another element. We are familiar with it as a heavy,
solid metal; and we know it unites slowly with oxygen forming
iron oxide (rust). This is about the last thing we would think to
be of use in the bodies of plants or animals. However, iron is
absolutely necessary in the green coloring matter of plants and in
the red blood of animals. Later we will learn the remarkable
services which its compounds perform in these substances.
THE ALPHABET OF ALL LIVING THINGS 15
SODIUM, POTASSIUM, AND CALCIUM
Our list of elements important to organic life will end with three
similar ones sodium, potassium, and calcium. These are light,
metallic substances which burn when put in water and are there-
fore very dangerous to handle. Potassium compounds must be
in the soil if plants are to thrive, while sodium and calcium com-
pounds are necessary for the blood and skeleton of animals.
Nitrogen, sulphur, phosphorus, iron, sodium, potassium, and
calcium are all obtained from their mineral compounds in the soil;
animals use salt (a sodium compound) directly, while they get
the other elements from plant foods. Plants in turn obtain them
from the soil.
By themselves, all these elements are inorganic substances, but
in the wonderful process of assimilation, plants and animals can
combine them to form the living stuff of which their tissues are
made. On the other hand, by the processes of oxidation, death,
and decay, the complex organic compounds are broken up into
simpler forms, and return to the soil or air as inorganic compounds
or elements, to be used over again by organic things.
Here is an estimate of the composition of the human body,
which may give an idea of the comparative amounts of the different
elements in animal tissue.
16
BIOLOGY FOR BEGINNERS
A person weighing 154 pounds would be composed of;
Oxygen 97.2 pounds
Carbon 31.1 "
Hydrogen 15.2
Nitrogen 3.8 "
Calcium 3.8
Phosphorus 1.75 "
Sulphur .27 "
Chlorine .25 "
Fluorine .22 "
Potassium .18 "
Sodium .16 "
Magnesium .11 "
Iron .01 "
Oxygon 97.2
Carbon 31.1
Hydrogen
15.2
Nitro-
gen
3.8
a Iron .01
D Magnesium .11
D Sodium .16
D Potassium .18
D Fluorine .22
Chlorine .25
Phosphorui
1.75
Calcium
3.8
FIG. 2. Elements composing a human body weighing 154 pounds. (Figures
express pounds.)
COLLATERAL READING
See index of any text book in Elementary Chemistry. Applied Biology,
Bigelow, pp. 5-9; Elementary Biology, Peabody and Hunt, pp. 5-13;
Essentials of Biology, Hunter, pp. 17-25.
THE ALPHABET OF ALL LIVING THINGS
17
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CHAPTER IV
COMPOUNDS, BIOLOGY'S BUILDING MATERIALS
Vocabulary
Extinguish, to "put out" a flame.
Constitutes, composes.
Converted, changed.
Emergencies, sudden needs.
Distinguish, to show differences between.
Characteristics, properties by which a substance may be known.
We have learned the names and something about the charac-
teristics of a few of the elements. In dealing with these elements
and their compounds it is necessary to find some way to distinguish
one from another, in order that they may be properly studied.
Method of " Testing " Substances. Such means of distinguish-
ing are called " tests " and we have already referred to one in the
case of oxygen. The test consisted in the fact tha,t oxygen, and
no other substance, would cause a glowing spark to burst into flame.
Before taking up any test three things must be considered.
1. A substance known to be the one we are studying must be
tested, so that we may know the correct result, and be able to
recognize it in an unknown case.
2. The test must be true of the substance sought, and of no
other. You can readily see, that if even one other gas would kindle
the glowing splinter, then that could not be used as a test for oxygen.
3. The test must be made in the same way, every time, or else
one might suppose that the result was affected by the difference
in treatment.
INORGANIC COMPOUNDS
Carbon Dioxide. When carbon unites with oxygen, it forms a
colorless, odorless, and tasteless gas called carbon dioxide (CO 2),
which is heavier than air and will extinguish a flame.
18
BIOLOGY'S BUILDING MATERIALS 19
Carbon dioxide is like nitrogen in many ways (mention them),
but if it be mixed with lime water, it causes the clear liquid to be-
come milky, while nitrogen does not. This is the test for carbon
dioxide.
Carbon dioxide is a plant food; plants having the power to
take this gas from the air, combine it with water, and make it
into their tissues in fact it is from this source that all organic
carbon comes.
Water. When hydrogen combines with oxygen, water (H^O) is
formed as we found when studying hydrogen. This compound is
so familiar that we do not need to learn any test for its presence.
It may be well to realize, however, that water constitutes much
over half the weight of all organic matter; that it is absolutely
essential to all life; and that it is not only a food, but a means of
carrying food to the tissues of all plants and animals.
Mineral Compounds. The next compounds we shall take up
are made of the elements mentioned last in our list: sulphur,
phosphorus, iron, potassium, sodium, and calcium.
Calcium unites with sulphur and oxygen to form calcium sulphate,
and with phosphorus and oxygen to form calcium phosphate.
Sodium and potassium unite with oxygen and nitrogen to form
sodium or potassium nitrates and so on with many other com-
pounds.
Fortunately we do not have to learn to test for these separately.
When found in organic tissue, they are usually grouped together
and called " mineral matter " or " mineral salts," and the fact
that they remain as ash, when organic matter is completely burned,
is a sufficient test for these compounds at present.
Notice that all the elements except carbon and hydrogen may
exist, combined as mineral compounds, in the soil where the plants
can get them. Hydrogen is obtained from soil water and carbon
from the carbon dioxide of the air.
All the compounds mentioned so far, water, carbon dioxide,
and numerous mineral salts, are inorganic substances.
One of the most important ways in which plants differ from
animals is that they can use inorganic substances solely for food
20 BIOLOGY FOR BEGINNERS
and recombine them into organic compounds, a thing which no
animal can do. Nor can we imitate it in any laboratory experiment.
Though animals use water and some mineral salts, they depend
for their life on the organic compounds made by the plants. Flesh-
eating animals live on other animals, which in turn use plant food.
The fact that plants can use inorganic food, while animals depend
on plants for their inorganic nourishment, is one of the most im-
portant facts for us to remember.
Of course the plant forms these organic compounds for its own
growth and food, to be stored away by the plant and used when
necessary. Whenever we eat a loaf of bread or a piece of candy
we are using material the wheat plant or sugar cane had assimilated
and would have used as food for itself.
ORGANIC COMPOUNDS. NUTRIENTS
Fortunately, the very complicated compounds which the plants
provide and which both plants and animals use for food and
growth, can be grouped into three great classes called: (1) Pro-
teids, (2) Carbohydrates, (3) Fats. These are sometimes taken
all together and called organic nutrients.
Proteids. These are very numerous and are found in all living
substances; the following are some that are common and found
in large amounts.
Proteid Where found
Gluten in grains
Legumin in peas and beans
Myosin in lean meat
Albumen in the white of egg
Casein in milk and cheese
It is not necessary to learn these names but the list is put in
to show that proteids are of many kinds and, though first provided
by plants, are needed in animal tissue as well.
Test for Proteids. Proteids differ in many ways but there is
one point in which they all behave alike and which is different
BIOLOGY'S BUILDING MATERIALS 21
from any other substance hence we can use it as a test. If a
substance supposed to contain any proteid is put into nitric acid
and heated gently, it will turn bright yellow. Then if the acid be
washed off and ammonia added the proteid, if present, will become
orange color. This is the test for any proteid for no other substance
will act in the same way.
The proteids are the most useful of the nutrients for they make
up most of the active living substance of plant and animal; they
are called tissue builders on this account. Proteids are composed
of the elements carbon, hydrogen, oxygen, nitrogen, sulphur,
phosphorus, with sometimes mineral salts as well, so we see they
are very complex organic compounds.
Carbohydrates. Next to proteids in importance to all living
things come the carbohydrates. They are composed of carbon,
hydrogen, and oxygen, with always twice as much hydrogen as
oxygen, and varying amounts of carbon.
Carbohydrates are found almost entirely in plants, whose
tissues they largely compose. When animals eat them, they
either make them over into proteid tissue or else oxidize them as
fuel to produce heat and energy. Some are converted into fats
and stored as such.
Some common carbohydrates are:
The starches.
Corn starch from corn
Potato starch " potato
Flour starch " wheat
Tapioca starch " cassava root
The sugars.
Cane sugar ^ SUgarC K ane ) (saccharose)
Beet sugar sugar beet J
Grape sugar " fruits (Glucose)
Milk sugar " milk (Lactose)
Cellulose.
Complicated forms found in wood, paper, cotton, linen.
22 BIOLOGY FOR BEGINNERS
(Glycogen is an animal carbohydrate found in the liver of some
animals and called " liver starch." It seems to be stored there for
later use.)
It is a little strange to think of cotton and starch, or wood and
sugar as being so nearly related, but they consist of the same three
elements, and are produced by the plants from water and carbon
dioxide. It would be a cheap diet, if we could take water from
a reservoir and carbon dioxide from the air and make them into
flour. 'Man has to depend on plants for this wonderful process,
and can only begin where the plants leave off, using the plant-
made carbohydrates for his food.
The Test for Starches. No one test can be used for all the carbo-
hydrates, but we can test for any starch by dissolving the substance
supposed to contain it in hot water and then adding a drop of
iodine. The solution will turn blue if starch be present. No
substance other than starch will act this way under these
conditions.
The Test for Grape Sugar. There is no one test for all sugars,
but grape sugar (glucose) is very common and can be easily dis-
tinguished from our household (beet or cane) sugar by what is
known as the Fehling Test so named from the man who devised it.
Two solutions are used in the Fehling test, one colorless, and one
blue. When these are added in equal amounts to a similar amount
of the substance to be tested, and the mixture heated, a yellow-
brown solid will form if grape sugar be present. Cane or beet sugar
will not act this way.
Fats. The last class of nutrients is the fats and oils, which are
also composed of carbon, hydrogen, and oxygen. They differ
from carbohydrates in having less oxygen. Hence they oxidize
more readily and as a result their chief use is to produce energy.
Plants store fats in their seeds to supply energy for growth;
animals store fats in various places and use them for the same
purpose.
Kinds. Cotton-seed oil, olive oil, and the oils from various
nuts are examples of vegetable fats; while lard, butter, and fat
meats are familiar examples of fat from animals.
BIOLOGY'S BUILDING MATERIALS
23
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24 BIOLOGY FOR BEGINNERS
Test for Fats. To test for fats the substance should be crushed
as finely as possible and treated with ether. This will dissolve
out any fat that may be present and can then be poured off. When
the ether evaporates the fat will remain in the dish.
COLLATERAL READING
See index of any Chemistry Text for the Compounds mentioned. General
Biology, Sedgwick and Wilson, pp. 33-40; Biology, Bailey and Coleman,
Introduction; Elementary Biology, Peabody and Hunt, pp. 13-25; Chemis-
try of Plant and Animal Life, Snyder, see index; Source, Chemistry and
Use of Food Products, Bailey, pp. 1-24; Food Products, Sherman, pp. 1-23;
Botany for Schools, Atkinson, pp. 13-19.
CHAPTER V
PROTOPLASM, THE "BIOS" OF BIOLOGY
Vocabulary
Protoplasm, see text.
Fundamental, that upon which all else is built.
Essential, necessary.
Nucleus, most active part of cell protoplasm, controls growth
and reproduction usually visible as a denser spot.
Minute, very small.
Function, use or work of a special part.
Adaptation, fitness for use.
Environment, all that makes up the surroundings of any living
thing.
Primary, first in origin and importance.
Since it appears that plants and animals are composed of the
same elements and use similar compounds for food it would be
only natural that their foundation material should be the same.
This is, in fact, the case. The foundation substance is called
protoplasm, a name derived from two Greek words, protos (first)
and plasma (form or substance). It is well named, for it is the
first and most necessary substance of all organic things.
Protoplasm is alive and, in truth, the only living substance. We
do not know what life is but we do know that as long as life exists
in plants or animals, their protoplasm is active. When it ceases
to act, death is the result.
Protoplasm may be defined as the fundamental, essential, living
substance of all plants and animals. It is a jelly-like substance
composed of carbon, hydrogen, oxygen, nitrogen, sulphur, and
phosphorus; but while we can analyze it and state its composi-
tion, we cannot combine the elements to make it. There is only
one Power that can create life.
25
.26 BIOLOGY FOR BEGINNERS
Because it is alive, protoplasm has certain remarkable properties:
1. It takes in, digests, and assimilates food.
2. It oxidizes food and excretes waste.
3. It grows in size and form.
4. It has power of motion.
5. It responds to light, heat, moisture, etc.
6. It reproduces.
D/ A SIT Atf OF 4 TYPICAL CIL
FIG. 3. Animal and plant cells similar in structure but varying in form.
We observe that this list is much like the one which gave the
points in which the cat resembled the geranium. Now we can see
the reason: both depend on protoplasm for life, so, of course, their
life processes would be similar.
PROTOPLASM 27
The Cell. In most plants and animals the protoplasm is divided
into very small parts called cells. These are merely the simplest
units of protoplasm of which* the plant or animal is composed.
A living cell usually consists of a tiny mass of protoplasm surrounded
by a membrane called the cell wall. The central portion of the
protoplasm, more active than the rest, is called the nucleus. The
cell wall gives definite shape to the cell and the nucleus seems to
regulate growth and reproduction. Cells are usually very minute,
but are of innumerable shapes, varying with the special work they
may have to perform.
Some plants and animals consist of only one cell. In more
complicated animals, there are a great many different groups of
cells, each fitted for some one purpose, as, for example, the vast
number of cells that together make up a muscle and have developed
especially the power of motion.
Tissues. A group of similar cells, devoted to a single use, is
called a tissue. There are many kinds of tissues, as wood, bark,
and leaf, in plants, and bone, muscle, nerve, etc., in animals.
Organs. In all the more familiar plants and animals, various
tissues are grouped together to form a more complex part, which
has some important general use. The stem of a tree, for instance,
whose use is to support the leaves, flowers, and fruit, consists of
wood, pith, bark, and other tissues, all working together for one
purpose. The leg of a cat is made up of bone, muscle, nerve, and
other tissues, working together to make locomotion possible. Such
groups of tissues are called organs and the purpose or use of any
part is called its function.
So we can say that all living things are composed of protoplasm;
the protoplasm is usually divided into cells; the cells are grouped
into tissues, and these, in turn, into organs fitted for some particular
function or functions.
Systems. Often in the higher forms, especially among animals,
several organs are grouped together to perform related functions.
Such groups are referred to as systems, as, for example, the circu-
latory system, which includes the heart, arteries, veins, and capil-
laries. These are organs, all united in the work of circulation.
28 BIOLOGY FOR BEGINNERS
The comparison is sometimes made between a plant or animal
and a book, as follows:
The elements correspond to the letters.
Compounds correspond to words.
Cells correspond to sentences.
Tissues correspond to paragraphs.
Organs correspond to chapters.
The plant or animal corresponds to the whole book.
To illustrate this method of structure we may look at the hand.
It is made of millions of cells, as shown by the microscope, each
having its characteristic shape and the usual cell parts: protoplasm,
nucleus, and wall.
Numerous as these cells are, they can be classified into a com-
paratively few kinds. Groups of similar cells are called tissues,
and we find in the hand, muscle tissue, bone tissue, nerve tissue,
skin tissue, and some others. Each of these tissues has its special
use. The muscle is used for motion; the bone, for support; and
so on. All together they are combined into one organ', whose
general function is prehension (grasping things).
In a similar way with plants, the cell is the unit of structure,
and in a stem, for instance, there are several kinds of cells. These
are grouped into wood tissue, bark tissue, tubular tissue, and pith
tissue, each made of similar cells and each with different functions.
However, they are all grouped together to form the plant organ,
called the stem, with its general functions of support and circulation
of sap.
Relation of Structure to Use. Organic things are composed of
the same elements, combined in similar compounds, which appear
as living protoplasm, whether of animals or plants. This proto-
plasm performs very similar functions in either case, but by very
different organs. The plant gets its food by way of leaves and
roots, while an animal like the cat uses its claws, teeth, and swift-
ness. Our whole course in biology deals with the essential life
functions of plants and animals, but, in order to study these func-
PROTOPLASM 29
tions intelligently, we must first know something of the structure
of the organs concerned in their performance.
As soon as one understands structure in its relation to function
it becomes apparent that each organ is wonderfully fitted for its
particular work. This fitness of structure to function is called
adaptation, and is a very important topic in all biologic study.
Structure, function, and adaptation are the foundation stones of
our subject and will always be presented hi the order here named.
We shall study both plants and animals with 'the idea of learning
how their structure adapts them for the functions which both
have in common and shall begin with plants, because, while their
functions are similar to those characteristic of animals, their
structure is much simpler. The following functions are common
to both plants and animals:
Food getting Excretion
Digestion Motion
Absorption Sensation
Assimilation Reproduction
Respiration
We know already the names of the principal organs of a plant
the root, stem, leaves, flower, fruit, and seed and understand, in
some measure the functions performed by each. We must also
remember the varied surroundings of the plant, the kind of soil,
amount of moisture, temperature, insect enemies, and all that goes
to make up its conditions of life (environment). In our study we
shall start, as the plant starts, with the seed. Then we will follow
an account of its growth, and the development, structure, and
use of the different plant parts mentioned above.
COLLATERAL READING
General Biology, Sedgwick and Wilson, pp. 20-32; Applied Biology,
Bigelow, pp. 39-44; Elementary Biology, Peabody and Hunt, pp. 29-32;
Essentials of Biology, Hunter, pp. 31-33; Botany for Schools, Atkinson,
pp. 33-36; Botany of Crop Plants, Robbins, pp. 4-9; Fundamentals of
Botany, Gager, pp. 14-20; Plant Anatomy, Stevens, 1-10; Plant Physi-
30 BIOLOGY FOR BEGINNERS
ology, Duggar, pp. 15-32; College Botany, Atkinson, pp. 1-12; Biology,
Calkins, pp. 6-25; Encyclopedia Britannica, articles on "Physiology,"
"Protoplasm," "Protozoa."
SUMMARY
Protoplasm is the primary, essential living substance of all plants and
animals.
A cell is the simplest unit of plant or animal structure. It consists of
protoplasm, nucleus, and cell wall.
A tissue is a group of similar cells having a special function.
An organ is a group of various tissues, having a general function.
A system is a group of organs concerned in one or more related functions.
1. Protoplasm.
Derivation: Protos, Plasma.
Definition.
Composition: C, H, O, N, S, P.
Properties :
(1) Takes and assimilates food.
(2) Oxidizes and excretes waste.
(3) Growth.
(4) Motion.
(5) Response to heat, light, etc.
(6) Reproduction.
2. The cell.
Definition.
Essential parts Function
Protoplasm. Any of above properties.
Cell wall. Gives form to cell.
Nucleus. Controls growth and reproduction.
(Diagram)
3. Tissue.
Definition.
Examples.
4. Organ.
Definition.
Examples.
5. System.
Definition.
Examples.
6. Relation of Structure to Use..
Similarity of functions.
Difference of structures.
Adaptation or fitness of structure to function.
7. Order for study.
Structure, function, adaptation,
CHAPTER VI
THE STRUCTURE OF SEEDS
Vocabulary
Immature, not fully developed.
Primitive, simple or early form of an organ.
Transmit, carry (similar to transport).
Modified, changed for different use.
It is so common a fact that a seed reproduces the whole plant
that the wonder of it is often overlooked. In the seed must exist,
alive, all the beginnings for the full-grown plant, together with
nourishment to start growth and adequate protection.
The seed, then, is a plant organ which consists of three parts:
the immature plant (embryo), stored food, and protective coverings.
Seed Coats. The outer covering of most seeds is called the
testa, and is usually thick enough to protect from injury by contact,
moisture, or insects. It may also have special adaptations for
dispersal. A second inner thin coat (tegumen) is present in some
seeds.
Since the seed was once a part of the parent plant, it bears a
scar on the testa, called the hilunt, which marks this point of
previous attachment. Near this scar is usually visible a tiny
opening called the micropyle, from two Greek words meaning
" little door." This little door has two uses; it lets the pollen
enter the seed when it is fertilized (see Chapter XIV), and it lets
the young plant out when it begins its growth.
Kernel. Within these coats is the kernel or, seed proper. It
may consist wholly of the undeveloped plant (embryo); or may
have, outside the embryo, a store of nourishment called the
endosperm.
31
32
BIOLOGY FOR BEGINNERS
TYPICAL SEED
rut INTtHHKL iTRUCTUXC
Embryo. If endosperm be present, the embryo may be poorly
developed, even showing no sign of its usual parts, as in the
orchids. On the other hand, the embryo may be highly developed
and show well-defined stem and leaves, as in the bean; for since
there is no endosperm in the bean, the plantlet must seek its own
nourishment very early. The embryo, or miniature plant, consists
of three parts: the cotyledons, plumule, and hypocotyl.
Cotyledons. These are the seed leaves or the first leaves of the
plant and, though often not resembling ordinary leaves either in
appearance or use, still
play a very important
part in the early growth
of the seedling. They
may be really leaf-like
and come up when the
plant begins to grow,
forming true green leaves,
as in the squash. In this
case they are thin and
have little stored food,
because they get all they
need as soon as they rise
above the soil. On the
other hand the cotyle-
dons may be so well sup-
plied with food that they cannot act as leaves at all, merely coming
above ground, giving over their stored food to the growing seedling,
and then withering and dropping off, as is the case with most beans.
In other cases, such as the pea, the cotyledons are so greatly en-
larged .with food, that they cannot be lifted from the soil at all,
and so supply the plant from their place in the ground below.
In cases where the food is stored outside the embryo as the endo-
sperm, the cotyledon often remains in contact with it to digest and
transfer food from endosperm to embryo, as is the case in corn.
Not only do the cotyledons vary in size and use (function),
but also in number, there being only one in many plants such
FIG. 4. The internal structure of
a typical seed.
THE STRUCTURE OF SEEDS 33
as corn and other grasses, lilies, palms, etc., two in many common
plants like the bean, squash, apple, and buttercup, and many in
pines and other evergreens. So important is this difference that
all plants that bear seeds are classified as:
Monocotyledonous (having one cotyledon),
Dicotyledonous (having two cotyledons),
Polycotyledonous (having three or more cotyledons),
and can be placed in one of these three divisions, which also agree,
as well, in structure of stem, leaf, and flower.
Plumule. The plumule is that part of the embryo above the
cotyledons, from which develops the shoot proper, consisting of
stem, leaves, and flowers. It may vary much in size and develop-
ment. If much food be stored, either in cotyledons or endosperm,
the plumule may be small. On the other hand if little food be
provided, the plant must early shift for itself, and so the plumule
may have several well-formed leaves, wanting only exposure to
light to become a self supporting plant.
Hypocotyl. The primitive stem, or all that part of the embryo
below the cotyledons, is the hypocotyl. From its lower end the
root system develops. Upon its upward lengthening depends
whether the cotyledons shall emerge from the soil when germination
takes place.
Endosperm. Though the endosperm is usually present at some
stage, it is not found in all seeds when they are mature, since it
may be entirely absorbed by the growing embryo, its function of
food storage being assumed by the cotyledons. It is, however,
very important in many seeds, especially the grains. From its
store of starch we derive our bread. Food for the embryo may
be stored either in the endosperm or cotyledons. Our laboratory
tests show that this stored food consists largely of starch, to-
gether with considerable proteid, a little fat or oil, and some
mineral matter.
The seed has within itself the miniature plant', or embryo, and
all the kinds of nutrients needed for growth except water. This
34 BIOLOGY FOR BEGINNERS
the seed must get from the soil before it can grow. The growth of
a seed is a very wonderful process. Though inactive, dry, and
apparently dead the protoplasm is really alive and only awaits
favorable conditions for growth to begin.
The insoluble, stored foods must be digested by the embryo,
made soluble, united with the water which has been absorbed from
the soil, and assimilated, to form all the new kinds of tissue in
the growing seedling. It may seem strange to speak of a seed as
digesting food, but there is a substance (diastase) in the seed,
which digests its food just as truly as the fluids of our stomach
digest ours. Here, then, are digestion, absorption, and assimila-
tion going on in the seed as it begins to grow. If the food stuffs
in the seed were not stored in a dry and insoluble form, they
would dissolve and decay. It is necessary, therefore, if a seed
is to keep over winter, that its food must be both dry and
insoluble.
EXAMPLES OF SEED STRUCTURE
Each seed differs somewhat from the general description just
given; the parts of the embryo may be well or poorly developed;
the number of cotyledons may vary; and the endosperm may be
lacking altogether.
All that is necessary for a true seed is the embryo, stored food,
and protective coverings. These are often very different in
structure, to adapt them to various surroundings.
The bean is presented as an example of a dicotyledonous seed
without endosperm, while the corn is taken as a type of a mono-
cotyledonous seed in which there is a very large endosperm.
The Bean. .External Structure. This familiar seed is usually
kidney-shaped or oval in outline, several being borne in a pod,
which is the true fruit of the plant.
The testa is usually smooth and may be variously colored; on
the concave side it bears a scar (hilumj, marking where it was
attached to the pod. By means of this attachment it also received
nourishment when growing on the parent plant.
THE STRUCTURE OF SEEDS
35
Near the hilum is a tiny opening (micropyle), and toward this
there sometimes extends a ridge which shows the location of the
hypocotyl, which will emerge here on germination.
The tegumen is very thin and often cannot be separated from
the testa.
The Bean. Internal Structure. On removing the seed coats,
the kernel is seen to consist of the embryo only, the endosperm
having been completely ab-
sorbed. All the nourishment
is now stored in the cotyle-
dons which are large, not at
all leaf-like, and contain
much proteid and starch.
The hypocotyl is seen as a .
linger-like projection, fitting
into a protective pocket in
the seed coats. To it the
cotyledons are attached on
either side.
By removing one " half "
(cotyledon) of the bean, the
plumule is exposed, attached
to the hypocotyl above the
cotyledons and closely pack-
ed in between their ends. It
is fairly well developed and
can be seen to consist of two
small leaves, with well-mark- (
FIG. 5. Structure of bean, exterior;
ed veins, folded over each
with seed coats removed ; with one cotyl-
edon removed.
Other.
It will be noted that the
upper end of the hypocotyl is the one point where all three parts
of the embryo are united. When the cotyledon is removed, a scar
showing its place of attachment is left on the side of the hypocotyl.
The pea seed shows a structure similar to that of the bean
except that the cotyledons are so enormously swelled with stored
36
BIOLOGY FOR BEGINNERS
FIELD CORN KtRNEL
food that they do not come above ground as do most beans. They
remain below and never approach the appearance of leaves.
However, having so much stored food, the plumule of the pea
does not need to develop early, so is very small, and even when
growth commences, the first leaves of the plumule are mere scales,
and do not have much ability to get food. The true leaves do not
make their appearance till the food in
the cotyledons becomes scant.
Corn. External Structure. The corn
seed, as it is usually called, is really a
fruit corresponding to the bean pod,
rather than to the bean itself. One seed
completely fills the fruit, so that the
seed coats and fruit coats cannot be
distinguished.
As a result of this fact, the hilum
and micropyle are covered by the fruit
coats and what might be mistaken for
the hilum is really the point of attach-
ment of the corn fruit (grain) to the cob.
On one side of each grain can be seen a
light-colored, oval area, which marks the
location of the embryo, visible beneath
the coats. On the same side, but at the
FIG. 6. External and in- end opposite the point of attachment, is
ternal structure of corn seed, located a tiny point, the silk scar,
where the corn " silk " formerly grew.
Corn. Internal Structure. Internally the corn consists of a
large endosperm, containing much starch, proteid, and some oil,
and at one side near the point of the grain, a much smaller part,
the embryo.
This embryo has but one cotyledon, a rather irregular, oval
structure, wrapped around the plumule and hypocotyl, and lying
in close contact with the endosperm. Its function is to digest and
transmit the food stored in the endosperm to the growing seedling.
It is a real digestive organ, which secretes, ferments, and makes
Slllt S(AH
fr orATTftHnnnr,
THE STRUCTURE OF SEEDS
37
the food soluble, just as truly as does an animal's stomach or
intestine.
The hypocotyl of the corn is a small pointed organ, aimed toward
the attached end of the grain, thus leading us to suppose the
micro pyle to be in that region. It is covered with a cap which pro
tects it as it passes through the soil when the root begins to develop.
STRUCTURE or CORN EAR
FIG . 7. The corn ear is really a spike of fruits closely grown together.
The plumule is also protected by a sheath or cap, and consists
of several very small leaves rolled, not folded, into a compact
" spear " which can safely push upward through the earth.
The cob, on which the kernels are borne, is really a stem of the
spike of flowers, each of which produces one kernel. Thus the corn
ear will be seen to be a spike of fruits, closely grown together,
38 BIOLOGY FOR BEGINNERS
and not a single fruit like a bean pod. The chaff around the grains
represents some of the outer flower parts while the silk is a portion
of the central organ of the flower called the pistil, and its function
is to catch and transmit the pollen grains. This will be explained
in the chapter on fertilization. The husks are modified leaves
developed to protect the corn ear.
Bean Corn
Has hilum, testa, micropyle Hilum, etc., covered by fruit
coats
Two cotyledons One cotyledon
Large embryo Small embryo
No endosperm Large endosperm
Plumule fairly large Plumule rather small
Plumule leaves folded Plumule leaves rolled
The fruit a pod, with many The fruit a single grain, with
seeds one seed
COLLATERAL READING
Lessons in Botany, Atkinson, pp. 2-208; Natural History of Plants,
K. and O., Vol. I, p. 601; Natural History of Plants, Vol. II, p. 450;
Lessons with Plants, Bailey, pp. 132-133, 252; Plant Structures, Coulter,
pp. 183-184, 210-214; Studies on Plant Life, Atkinson, pp. 158-192;
Practical Botany, S. and H., p. 343; Plant Relations, Coulter, pp. 111-115,
138-140; Seed Babies (L), Moreley, entire; Elementary Studies in Botany,
Coulter, pp. 317-325; Plant Life and Uses, Coulter, pp. 325-353; Experi-
ments in Plants, Osterhout, pp. 1-68; Practical Biology, Small wood,
pp. 259-267; Cornell Leaflets, Bui. L, pp. 401-414.
SEED STRUCTURE
Definition of seed.
A plant orsjan whose function is to reproduce the plant, consisting of:
1. The living miniature plant (embryo).
2. Stored food.
3. Protective coverings.
Structure of seeds.
1. Coats. Function, Protection.
Testa (outer coat).
Hilum (scar on testa). Point of attachment for supply of
nourishment.
Micropyle (opening). Entrance of pollen, exit of hypocotyl.
Tegumen (inner coat).
THE STRUCTURE OF SEEDS 39
2. Kernel.
Embryo (miniature plant, always present).
(1) Cotyledons (seed leaves)
Development.
(a) Leaf-like (squash).
(b) Store food, but come up (bean).
(c) Store food below ground (pea).
(d) Digest and absorb from endosperm (corn).
Number.
(a) Monocotyledonous (one cotyledon) (corn).
(b) Dicotyledonous (two cotyledons) (bean).
(c) Polycotyledonous (several) (pine).
(2) Plumule (undeveloped shoot).
Development.
(a) Small if much stored food.
(b) Large if little stored food.
(3) Hypocotyl (part below cotyledons).
Development.
(a) Root from lower end.
(b) Raises cotyledons if it grows up.
Endosperm (stored food, may be lacking).
(a) Why not always present?
(&) Use to man.
Food in seeds.
May be stored in cotyledons or endosperm.
Why stored dry and nearly insoluble.
Need of digestion, use of diastase.
TYPES OF SEED STRUCTURE
Bean (Dicot., no endosperm). The pod is the fruit.
External structure.
Shape, colof, etc.
Testa.
Hilum, caused by attachment to pod, used to receive nourishment
from plant.
Micropyle, used for exit of hypocotyl (see ridge),
used for ingress of pollen (see fertilization).
Tegumen, thin, unimportant.
Internal structure.
Kernel.
No endosperm (what has become of it?).
Cotyledons, two, large and rather thick.
contain starch and proteid.
Hypocotyl, finger shaped. In protective pocket.
Plumule, moderately developed, two plain leaves, veins, etc.
40 BIOLOGY FOR BEGINNERS
Corn ("Kernel" is the true fruit).
External structure.
Seed coats covered by fruit coats.
Hilum and micropyle hidden.
Items to be located.
Point of attachment to cob, at narrow end.
Embryo mark on side.
Silk scar at broad end.
Internal structure.
Endosperm, large much stored starch, proteid, oil.
Embryo.
Cotyledon, one, oval, against the endosperm, used to digest and
transmit food, has ferments for digestion.
Hypocotyl, protective cap, points to attached end of seed.
Plumule, protective cap, rolled leaves, adapted for piercing soil.
Cob, the stem of flower spike.
Chaff, outer flower parts.
Kernel, the fruit.
Silk, the pistil for catching pollen.
Husks, leaves for protection.
CHAPTER VII
GERMINATION THE SEED WAKES UP
Vocabulary
Distinct, of separate kinds.
Tolerate, to bear or endure.
External, pertaining to the outside.
Dispersal, the act of scattering, as pf seeds.
Emergence, coming out of anything.
Penetration, forcing a way through
The seed is not a thing totally distinct from the parent plant,
though it is separated from it. It contains the same protoplasm
as the parent plant, with this distinction; its protoplasm is in a
condition of rest. The seed is not dead, it is asleep and waits
only for favorable conditions to wake into the activity of growth.
Function of the Seed. This resting stage is of two-fold value
it condenses the essential nature of the whole plant within small
compass, capable of easy and wide dispersal, and, most important
of all, protects the vitality of the embryo so that the seed can
withstand periods of drought, cold, heat, or other conditions
which would be fatal to the parent plant.
Both dispersal and preservation are steps toward the chief
function of the seed, which is to reproduce the plant that is at
rest within it. This resumption of active life is called germination.
Necessary Conditions for Germination. For the germination of
most seeds at least three conditions are required, in amounts
varying between wide but definite limits; these are moisture,
heat, and air.
There are a few plants whose seed will develop under water
while others retain enough of the scant dews of the desert nights
to waken the seed into growth. Usually, however, a moderate
41
42 BIOLOGY FOR BEGINNERS
water supply is essential, too much causing decay, and too little
precluding growth altogether.
As to temperature, a maple seedling will germinate on a cake
of ice and many other seeds grow in extreme cold, while a smaller
number tolerate high temperatures. The majority, however,
germinate most freely between 60 and 80 F.
Air from some source is essential to growth, for seeds, like all living
things, must breathe. Many can obtain the needed supply even
from the air dissolved in the water in which they maybe submerged.
In addition to these external conditions, the embryo must also
have a supply of stored food for immediate use while the roots
and leaves are developing. This food may be stored in the coty-
ledons, as in the bean and pea, or outside the embryo, as in the
case of the endosperm of the corn and other grains.
Stages in Germination. Germination consists of three steps,
emergence from the seed coats, penetration of the soil, and the
obtaining of first nourishment.
In getting out of the seed coats, the hypocotyl appears first,
emerging by way of the micropyle. The rest of the embryo follows
by various ingenious schemes, all apparently planned by Nature
to enable the seedling to escape uninjured from the testa, on whose
protection it has so long depended.
Penetration of the soil may be either from above or from below.
When seeds are scattered on the surface of the soil they are enabled
to gain a foothold in the earth by various contrivances so that the
roots may be sent down into the soil. In the case of buried (planted)
seed the process of penetration not only has to do with sending
down roots, but the seed must find a way out of the earth, un-
harmed by its passage. This latter problem is solved most often
by the plantlet being started from the seed in an arched position.
One end of the arched stem takes hold of the ground and sends
out roots, while the other, attached to the wide cotyledons or the
delicate plumule leaves, gently pulls these through the ground
after the growing arch has broken away to the surface. If forced
directly upward these bulky appendages would be stripped off
by soil pressure.
GERMINATION THE SEED WAKES UP
43
This arch may be caused by the weight of the cotyledons and
soil (as in the case of the bean), which hold back, the bulky end
of the plantlet until the stem is strong enough to lift it out of the
I. Z. 3.
C COTYUEDOMS
H HYFOCOTVI.
F "PLUMULE.
& L CrRouNp LINE
GERMINATION
ground, or (as in the case of the pea) by the tip of the plumule
being held tightly between cotyledons that are not lifted from
the ground at all. In the latter case the hold of the cotyledons
44 BIOLOGY FOR BEGINNERS
weakens after its store of food has been partly exhausted and the
plumule is released.
Another method of penetrating the soil is found in the corn
and in general by those plants whose first leaves are long and
slender. In these cases protection is secured by the leaves being
tightly rolled into a point and covered by a cap, so that they
pierce the soil directly, thus meeting less resistance and securing
safety.
The lifting force of germinating seeds is seldom noticed, but is
very great. Masses of earth a hundred times their weight are
lifted by our tiny garden seedlings as they come up, forcing their
way through the hardest soil.
The last and most important step in germination is the establish-
ment of the young plant in its new environment. In describing
this process it is necessary to treat of the development of each
part of the embryo by itself.
The hypocotyl first penetrates the testa. Protected by its root
cap and directed downward by gravitation, it begins at once the
production of the primary root from its lower end. From this,
in turn, the whole root system rapidly develops. The only region
of growth is just back of the tip, which, protected by the cap, is
safely pushed downward into the earth.
The cotyledons, as before explained, may rise above ground if
the hypocotyl lengthens upward, or, if not, may remain below.
In either case they act as a storage of food for the seedling.
The development of the plumule usually attracts most attention
for from it arise the leaves, stem, and, later, the flowers and fruit.
It constitutes the shoot of the plant.
The first organ to develop in germination is the root, because
the function required by the seedling is the absorption which the
root performs. We shall take up the study of this important
organ in the next chapter.
Many of the statements made in this, and the preceding chapter,
can be proven by simple experiments.
In the first place, the kind of foods stored in the seeds can be
proven by the tests described in Chapter IV.
GERMINATION THE SEED WAKES UP 45
The Necessity of Stored Foods. The necessity of this stored
food can be shown by taking a number of well-started seedlings,
removing part of the stored food (in cotyledon or endosperm) in
some of them, removing it all in others, and leaving still others
unharmed. If these seedlings are then placed so that the root can
dip into water, by suspending them on a netting over a well-filled
glass, their development can be watched.
Several seedlings must be used in each group, lest we draw
conclusions from too few instances, or perhaps be misled in case
some one seed were abnormal. The conditions of growth must
be the same in each case, lest it appear that these varying condi-
tions, and not the loss of stored food, produces the results.
After a few days it will be seen that the whole seeds grow well
and rapidly; that those with part of their food removed start
more slowly and soon cease growing; while those with all the stored
food removed scarcely start at all. This is because of the fact
that, until the seedling can develop roots and leaves, it depends
solely on this store of food whose removal is shown to have so
serious results.
The Digestion of Stored Foods in Seeds. To prove that these
food stuffs must be digested before they can be used in germinating
plants, corn seeds can be tested for starch and for grape sugar,
both before and after germination has started.
Starch is insoluble in cold water, and does not pass readily
through the absorbing membranes. Therefore it has to be digested
(changed to soluble sugars) before the plant can use it.
This digestive change is accomplished by a substance in the
seed, called diastase, which acts somewhat like the digestive
fluids in our bodies.
If the corn be tested before germination has begun, much starch
and little or no sugar will be found. If it be tested in the same ways,
after germination has proceeded for a few days, the reverse will
be discovered, as most of the stored starch will have been converted
into soluble form, sugar, by the diastase in the cotyledon.
Conditions for Germination. That sufficient heat, air, and
moisture are essential conditions for germination, can be proved
46 BIOLOGY FOR BEGINNERS
by setting up experiments in which several seeds are given
similar treatment, except that one of these factors is changed in
each.
To prove the necessity of air, place several seeds in each of two
bottles, give them moist moss to grow in, and keep in places of
similar temperature. Seal one tightly and leave the other open.
The results show that the sealed seeds, though they start growth,
cease as soon as the air in the bottle is used up, while those in the
open bottle grow naturally. In this, as in all experiments, several
seeds should be used, so as to prevent drawing a false conclusion
from incomplete evidence. Using many seeds and repeating the
same experiment increases the accuracy of the test. Emphasis
must also be placed upon giving the same conditions, with the one
exception, in every case. In the above experiment, if the seeds
are not kept in places of similar temperature and moisture, the
result of the experiment might be attributed to the differences in
these factors and not to the presence or absence of air.
In the same way, it can be proved that seeds require a definite
amount of moisture for germination. If none be supplied, or if
they be completely covered with water, most seeds will not grow
even when the air supply and temperature are properly regulated.
A similar experiment may be used to show the effect of tempera-
ture on seed growth. Arrange several seeds in each of three or
four bottles; give the same amount of moist moss to grow in, and
expose all to free air supply. The one condition to be varied is
the temperature. It will be found that those in extreme cold
usually do not start growth at all, those in very warm places usually
decay, and only those in a moderate temperature germinate
naturally.
Suppose some of these last sets of seeds had been given vary-
ing amounts of moisture as well as different temperatures, what
ob'ection could be raised to the conclusion given?
Experiments like those above in which no air or water or warmth
were supplied and in which no results occurred are sometimes
called " check " experiments. They are very important, as show-
ing that a certain result will not occur without certain conditions.
GERMINATION THE SEED WAKES UP 47
which is often as necessary as proving that it will occur with certain
others.
Heat Energy and Carbon Dioxide Set Free. It has been stated
in Chapter II that all living things breathe. This means that they
take in oxygen, which oxidizes their tissues, produces energy, and
liberates carbon dioxide as a waste product. We readily realize this
in the case of animals but with plants it needs experimental proof.
Provide two large-mouthed bottles each with some moist moss,
a vial of lime water, and a stopper through which is inserted an
accurate thermometer. In one of them put a handful of soaked
seeds and leave the other with none.
As the seeds begin to grow it will be observed that the thermom-
eter in that bottle stands higher than in the one with no seeds, also
that the lime water in the seed bottle is much more milky, which
proves the presence of more carbon dioxide. The lime water in
the seedless bottle is slightly milky due to the carbon dioxide
present in the air. Without this check experiment, nothing could
be proved, as the rise of temperature could not be compared
and the presence of the carbon dioxide could be attributed to that
known to be in the air. Moss was put in both bottles so that all
conditions should be the same ; if this had not been done, it might
have been objected that the presence of the wet moss affected
the temperature or gave off carbon dioxide.
While plants do not breathe as actively as animals, still it is
thus proved that they do breathe in the same way and for the
same purpose, namely, to liberate energy for life. The fact that
they are less active and need less energy accounts for less evidence
of their breathing.
SUMMARY
The seed, a stage of rest, not stoppage of life.
Value of this resting stage:
Dispersal 1 g toward reproduction.
Protection over winter J
Germination (resumption of active growth).
Conditions for germination:
Moisture Air supply, why necessary experimental evidence.
Heat Stored food
48 BIOLOGY FOR BEGINNERS
Stages in germination:
1. Emergence from seed coats.
Adaptations, Micropyle, Cap on hypocotyl.
2. Penetration of soil.
Adaptations.
By arching method caused by
(1) Soil pressure (bean) .
(2) Cotyledon pressure (pea).
By direct piercing.
(1) By rolled plumule with a sheath as in corn.
3. Obtaining nourishment.
(1) From stored food in cotyledons.
(2) " " " endosperm.
(3) Obtained directly by leaf-like cotyledons (squash), roots from
hypocotyl, development of plumule leaves.
NOTE. If the hypocotyl does not lengthen upward, the cotyledons
must remain below ground; if it does lengthen the cotyledons "come up."
Cotyledons may store food below ground or above; they may become
true leaves, or merely act as absorbing organs. (Give an example of each.)
Experiments to show:
1. The kind of food stuffs stored in seeds.
2. The necessity for this stored food.
3. The need of digestion before it can be used.
4. The necessity of air, moisture, and warmth for germination.
5. That growing seedlings produce heat and carbon dioxide (that is,
that they breathe).
COLLATERAL READING
Natural History of Plants, Kerner and Oliver, Vol. I, p. 599; Vol. I
(2), pp. 598-623; Vol. II (1), pp. 420-427; Lessons with Plants, Bailey,
pp. 336-341; Lessons in Botany, Atkinson, pp. 210-216; Studies in Plant
Life, Atkinson, pp. 1-6; Seeds and Seedlings, Lubbock, Vol. I, pp. 4-77;
Textbook in Botany, Gray, pp. 9-27, 305-314; The Teaching Botanist,
Ganong, pp. 161-190; The World's Farm, Gaye, pp. 277-299.
Lessons with Plants, Bailey, pp. 316-335; Plant Relations, Coulter,
pp. 138-141; Botany for Schools, Atkinson, pp. 1-25; Elementary Botany,
Atkinson, pp. 307-313; Experiments in Plants, Osterhout, pp. 69-86;
Plants and Their Children, Dana, pp. 75-98.
CHAPTER VIII
ROOTS THEIR STRUCTURE AND FUNCTION
Vocabulary
Constitute, to forri part of.
Immersed, covered by water.
Adventitious, growing at unusual places.
Retain, to hold.
Epidermis, the outer layer of plant or animal tissues.
Cortex, a spongy layer under the epidermis of roots.
Cambium, region of active growth in root or stem.
The. developing seedling consists primarily of the root and
the shoot. The latter bears the buds, leaves, flowers, and fruit,
while the root, usually hidden and unnoticed in the soil, plays an
equally important part in furnishing food and stability to the
plant.
Characteristics of Roots. The root differs from the stem in the
following points:
Root Stem
Bears no leaves or flowers. Bears leaves and flowers.
Grows irregularly. Grows by definite nodes.
Growth mostly at tip. Growth in each internode.
Tip protected by cap. Tip protected by scales.
Branching very irregular. Branching regular.
Turns toward gravity. Turns away from gravity.
Branches start internally. Branches external.
Root System. When a plant is pulled from the soil, the root
system is exposed. This may consist of one long central portion,
the primary root, from which many secondary branches grow;
or it may be a fibrous mass of small roots with no apparent primary,
49
50 BIOLOGY FOR BEGINNERS
as in most grasses. In either case the soil particles are closely
held to the root by tiny root hairs, the active agents in absorption
which are adapted to take up the thin film of water that surrounds
all soil particles.
While the form of the root system varies greatly, according to
the kind of plant, soil, and climate, yet, in general, all roots have a
very similar internal structure, as is shown by a study of sections
FIG. 8. Section of corn root, showing root hairs formed from elongated
epidermal cells. From Atkinson.
of roots in the laboratory. The tips of young roots, split length-
wise and dyed, so as to make their structure plain, should be used
for the purpose.
Internal Structure. A typical root has a single outer layer, the
epidermis, composed of thin-walled, brick-shaped cells, from which
extend innumerable outgrowths called root hairs. Beneath the
epidermis is a thicker layer of thin- walled, loosely packed, roundish
ROOTS THEIR STRUCTURE AND FUNCTION 51
cells, the cortex. This is separated by a boundary layer from the
central cylinder which occupies the remainder of the root.
In this central cylinder there are three sorts of tissues which
are also found in stems, though differently arranged. They are:
(1) wood and ducts, (2) bast, (3) cambium.
The woody tissue is composed of thick-walled, hard cells which
give strength to the root but carry little sap, and ducts, which are
long, tubular cells, used principally for the transfer of sap upwards
toward the stem.
The bast tissue consists of tough, fibrous cells, interspersed
with tubular ones. Its function is both to give toughness and to
carry sap downwards.
The cambium is the most remarkable tissue in the plant. It
consists of thin-walled, very active cells, full of living protoplasm
which have the power of rapid growth. In fact, all growth of
the plant occurs here, and if the cambium be destroyed, the plant
will die.
Since these tissues extend into the stem, where we will hear of
them again when we study stem structure, it is important that we
should remember their function in the root.
The wood and ducts are generally grouped in four areas near the
center, and alternating with them, though outside, is found the
bast. The cambium forms a more or less complete ring between
the two. This arrangement permits the soil water to reach the
ducts without mixing with the digested food brought down from
the leaves by the bast.
Around the tip of each growing root and extending up a little
way along each side is the protective root cap, composed of loose
cells easily rubbed off without allowing injury to the sensitive tip
as it pushes through the soil. The region of most active growth,
being back of this cap, is protected from injury, as would not be
the case if located at the extreme tip.
Function of Root Parts. The function of the epidermis and its
root hairs is mainly absorptive. The cortex absorbs, retains, and
transfers the soil water; the ducts and bast tubes transfer liquids
and air, while fibers in both bast and wood give toughness and
52
BIOLOGY FOR BEGINNERS
fi.r**<r 7?o r
FIG. 9. Root Structure.
Figure 1. A Fleshy Root. In this diagram can be seen the general region
of a typical root, so enlarged by food storage as to be easily visible to the
naked eye.
Note especially the ducts in the central cylinder, from which extend
secondary branch roots, penetrating the cortex, but not connecting with it.
Where they come out they make the tiny cavities characteristic of the surface
of a carrot or parsnip.
See also that the stem is mainly connected with the ducts of the central
cylinder, and not with the cortex which is mainly an outer layer of stored food.
Figure 2. Root Tip. Here is shown the general structure of a root tip
under low power magnification; these parts can be seen on any growing root
from germinating seed.
Note the protective root cap, and back of that a region without root hairs
which includes the growing point. The root hairs, if developed here, would
be torn off as growth proceeded, hence begin to grow further back from the tip.
The root hairs are infinitely numerous, and only a few are shown to indi-
cate their comparative length and thinness of wall, and how they develop
from epidermal cells.
The central cylinder and cortex can be distinguished in such a root, es-
pecially if it be left in a red ink solution till the ducts have begun absorption,
which makes the central cylinder much darker than the cortex.
Figure 3. The Root Tip in detail. This shows the extreme tip, much more
highly magnified. The separate cells show plainly, and those near the grow-
ing points are particularly full of protoplasm and have large nuclei, showing
that they are in active growth.
The loose cells of the cap have few nuclei and are largely dead cells, thrown
off as protection to the delicate tip.
The ducts begin to show as thicker rows of cells though not very tubular
at this stage.
The epidermis shows plainly as a single layer of cells packed in like bricks.
ROOTS THEIR STRUCTURE AND FUNCTION 53
strength. The most important function, however, is performed
by the cambium, which is the region of active growth, and from
which both wood and bast are produced.
Functions of Roots as a Whole. Absorption. The root, as is
evident from its structure, is primarily an absorbing organ, and
this function will be taken up at length. However, it has many
other uses and is adapted to perform very different duties in
different plants.
Fixation. A second use, common to nearly all roots, is that of
attaching the plant to the soil, and holding it in an upright position.
Storage. Frequently the root has sufficient bulk to act as a very
efficient storage place for foods. This is particularly important
for plants that retain life through long winter months.
Propagation. It may happen that enough nourishment is stored
so that the plant can send up shoots at various places or even
be divided, so reproducing the plant.
Adaptations of Root Form. From the foregoing it is evident
that roots must be profoundly varied in structure and form to
perform the different functions mentioned. And it must be re-
membered that not only function, but other factors such as climate,
soil, moisture, and exposure, which together make up the plant's
environment, affect growth. We shah 1 learn that only so far as a
plant is fitted to its environment will it thrive.
Kinds of Roots. The usual place from which roots develop is
the lower end of the hypocotyl. Such roots are called normal roots.
If they grow from other places such as the stem, leaves, or upper
part of the hypocotyl, they are called adventitious roots.
NORMAL ROOTS
Soil Roots. Of all forms of normal roots, the commonest are
the soil roots and these are of many kinds, depending upon what
functions they must perform and the character of the soil, moisture,
or climate that surrounds them. They in turn may be divided
into three general classes.
Fibrous Roots are made up of many fine slender rootlets, giving
54 BIOLOGY FOR BEGINNERS
large extent of surface for absorption. The roots of the grasses,
for instance, are so numerous that they hold the soil together,
forming a compact layer called the " turf."
Tap Roots are greatly enlarged primary roots which enable the
plant to go deep after water supply and hold firmly in the ground.
The thistle, dandelion, burdock, and many more of our worst
weeds are thus adapted to make a living under adverse
circumstances.
Fleshy Roots are adapted for storage of food stuffs and have the
main part greatly thickened, as in the carrot, turnip, and beet.
They are generally found in plants which require two seasons
to mature their seed and so need stored food to carry them over
the winter. In other cases, as the dahlia and sweet potato, the
fleshy root is used to reproduce the plant.
Aerial Roots. Some tropical orchids which live attached to
trees and never reach the earth at all develop aerial roots. They
have a very thick, spongy cortex, which absorbs water from the
moist ah* of the forests.
Aquatic Roots. These are found in a few floating plants such
as the duck- weed and water hyacinth. They are usually small,
few in number, and lacking hi root hairs. They do not need
extra surface for absorption because they are surrounded by an
abundant water supply.
ADVENTITIOUS ROOTS
Brace Roots. From the stems of corn and many other grasses,
develop brace roots, which help to support the slender stems or to
raise them again if they are bent down.
Roots for Propagation. In certain plants if the stem lies in
contact with the soil for a sufficient length of time, roots will
spring from the joints and produce new plants. The stems of
various berry bushes can thus be fastened to the earth " staked
down " and will take root in this way. The new root systems,
when sufficiently developed, can be separated from the parent
plant to make a new berry bush.
ROOTS THEIR STRUCTURE AND FUNCTION 55
Slips or cuttings from certain plants develop adventitious roots
from the stem or leaves and start new plants by this means. Many
plants, like the strawberry, send out horizontal stems called
" runners " from which adventitious roots develop and produce
other individuals.
Climbing Roots. The stems of poison ivy, trumpet creeper,
and some other vines grow climbing roots which act chiefly as
means of support. These plants have ordinary soil roots, also,
for the purpose of absorption.
Parasitic Roots. In a few plants, such as the dodder and mistle-
toe, parasitic roots develop from the stem, penetrate into the
tissue of some other plant, and absorb food from their victim,
often causing its death or serious injury. The dodder is parasitic
upon clover, golden-rod, and other plants; the mistletoe usually
grows upon the oak.
REFERENCES FOR COLLATERAL READING
Natural History of Plants, Kerner and Oliver, Vol. I, Part 1, pp. 82-99;
Part 2, pp. 749-767; Textbook of Botany, Gray, pp. 27-33; The World's
Great Farm, Gaye, pp. 124-128; Plant Relations, Coulter, pp. 89-108;
Elementary Studies in Botany, Coulter, pp. 253-270; Plant Life and its
Uses, Coulter, pp. 123-141; Experiments in Plants, Osterhout, pp. 87-162;
Plants and their Children, Dana, pp. 99-112; Outlines of Botany, Leavitt,
pp. 36-45; Botany all the Year Round, Andrews, pp. 120-142; First
Course in Biology, Bailey and Coleman, pp. 32-48; Civic Biology, Hunter,
pp. 71-83.
Characteristics of Roots:
1. No leaves, or flowers.
2. Growth back of tip, not at nodes.
3. Root cap for protection, instead of bud scales.
4. Irregular branching.
5. Turn towards gravity against light.
6. Internal structure.
Root system consists of
Primary root, or fibrous roots.
Secondary roots.
Root hairs.
56
BIOLOGY FOR BEGINNERS
INTERNAL STRUCTURE
Part
Structure
Function
1. Epidermis
Thin, brick shape
Protection
Root hairs
Thin, tubular, sensi-
Absorption
tive
2. Cortex
Loose, thin, round
Transfer
Storage
3. Central cylinder
Wood
Thick, fibrous
Support
Ducts
Thick, tubular
Transport
Bast
Thin, tubular
Transport
Cambium
Delicate, active
Growth
4. Root cap
Loose, thin cells
Protection
Region of growth.
Functions of roots :
Absorption (most roots).
Fixation in soil (most roots).
Storage (carrot, etc.).
Propagation (hop, dahlia, etc.).
Modification of Roots:
Caused by difference in
Function.
Climate.
Soil.
Moisture.
General surroundings.
Exposure.
KINDS OF ROOTS
Normal forms
Examples
Adapted for
1. Soil Roots
(a) Fibrous
(6) Tap-root
(c) Fleshy
2. Aerial
3. Aquatic
Grass
Dandelion
Carrot
Orchid
Duck-weed
Wide surface
Deep water supply
Storage
Absorption from air
Absorption from water
ADVENTITIOUS FORMS
1. Brace-roots
2. Propagation
3. Climbing roots
4. Parasitic
Corn
Strawberry
Poison-ivy
Dodder
Support
Reproduction
Support, climbing
Stealing nourishment
ROOTS THEIR STRUCTURE AND FUNCTION 57
Adaptations of Roots:
For penetration of soil:
1. Protective cap.
2. Growing point back of tip, for protection.
3. Root hairs back of tip, for protection.
4. Geotropism and hydro tropism (see next chapter).
For storage:
1. Large size.
2. Protection in soil from cold, drought, and animals.
3. Poisonous or bad tasting, to protect from animals.
For support:
1. Depth and extent of root system.
2. Toughness of wood and bast fibers.
3. Special brace roots, climbing roots, etc.
NOTE. Look up cypress "knees," and adventitious roots of banyan tree.
CHAPTER IX
ABSORPTION AND OSMOSIS
Vocabulary
Gravitation, the attraction of the earth which draws everything
downward.
Successive, one after another.
Aerial, living in the air, as applied to roots.
Hydrotropism, the response of plant parts to water.
Geotropism, the response of plant parts to gravitation.
Osmosis, the diffusion of two liquids or gases through a membrane,
the greater flow being toward the denser substance.
Turgescence, the support of plant parts, especially leaves, due to
the presence of water in the tissues.
The preceding chapter should have given us a rather definite
idea as to the structure of roots, and the names, at least, of some
of their functions.
This chapter deals with absorption, the most important function
of all, since it is one of the principal ways in which plants obtain
food materials. We shall study in detail the adaptations of the
root for this fundamental function.
Necessity of Water for Plants. All living matter depends more
or less on liquids of various sorts, and the plant, like the animal,
has its circulating fluids, bearing nourishment and removing
waste, storing food, and supplying oxygen to convert that food
into living energy.
From the delicious juices that flavor the peach and sweeten
in the heart of the sugar cane, to the bitter milk that flows in the
dandelion or lures the unwary to death in the poisonous mush-
room, all consist largely of water, absorbed from the soil by the
action of the roots.
This absorbed water is of threefold value to the plant. It
supplies a very necessary portion of the plant's food, as water
58
ABSORPTION AND OSMOSIS 59
itself and as mineral matter dissolved in that water; it acts as a
means of transfer within the plant for the various foods needed
in the different parts, much like the blood of animals; and this
absorbed water supports' many parts of the plant. This latter
statement will need some explanation.
Turgescence. When a plant is deprived of water, its leaves
droop and we say it wilts. This is due to the fact that, normally,
each cell is expanded by the water within it and so is kept in posi-
tion. If the water be withdrawn, these cells will collapse like an
empty balloon, allowing the leaves and plant to droop. If water
be supplied before the protoplasm dies, however, the leaves and
plant will resume position.
This stiffness of plants, due to presence of water, is called tur-
gescence and is very important in supporting the smaller plants
whose stems are not stiffened with wood fibers. Nearly all leaves
depend on this water pressure for their expansion.
Osmosis. The water to supply these absolutely essential needs
comes from the soil, often apparently dry, but always containing
at least a little moisture which the plant must obtain if it is to live.
This vastly important root function of absorption depends on
a physical process called osmosis which may be defined as the
mixing or diffusion of two liquids or gases of different densities,
through a non-porous membrane the greater flow being toward
the denser substance. Osmosis is one of the most important
biologic processes, and upon it depends not only absorption in
roots, but all forms of absorption in plant and animal, all digestive
processes, excretion, respiration, and assimilation. Wherever a
liquid or gas passes through any tissue, osmosis is the acting cause,
controlled sometimes by the living protoplasm that lines the cell.
The essentials for osmosis are a dense liquid, a less dense liquid,
and the osmotic membrane. In the root the wall of the root hair
or epidermal cell acts as the membrane, the cell sap as the denser,
and the soil water as the less dense liquid.
Root Hairs. It has been estimated that there may be a total
length of a mile in the roots of a corn plant, and alfalfa roots have
been found to extend twenty feet deep in dry soil.
60 BIOLOGY FOR BEGINNERS
For the purpose of absorbing as much as possible, the surface
of the active parts of all roots is covered with root hairs. These
are outgrowths of the epidermal cell walls and increase the total
absorbing surface enormously. They also enable the osmotic
membrane to actually touch the film of water, which, even in the
driest soils, clings close to the soil grains.
So important are these root hairs that their injury or loss might
mean death to the plant, hence they are never borne at the extreme
tip of the root, where its growth through the soil would strip them
off, but are found a little back from the tip and extending various
distances along the younger roots.
As the root grows, new hairs are produced near the tip, to gather
moisture from new areas; the upper ones die away; the cortex
and epidermis thicken, cease active absorption, and become
protective in use. In frequent cases, the root hairs secrete a weak
acid which helps in dissolving soil substances and in penetrating
hard earth.
The adaptations of root hairs may be summarized as follows:
1. Extent of surface. 2. Thinness of walls.
3. Protection from injury. 4. Location.
5. Close contact with soil grains. 6. Acid secretion.
Geotropism. In order that roots may always grow where they
can best absorb food materials, they show a tendency always to
grow downward, i.e., toward the earth. This might at first thought
be credited to mere weight, but it is evident that stems, though
equally heavy, cannot be made to grow down, and that roots,
though lighter than the soil, still force their way through it, and
cannot be made to grow upward, even though repeatedly started
in that direction.
This turning of roots and stems is caused by the attraction
of the earth, called gravitation, and this response that plants
make to gravitation is called geotropism positive in the case of
roots, and negative in the case of stems. Positive geotropism
plays an essential part in absorption by causing the roots to pene-
trate the soil rather than grow in any chance direction.
ABSORPTION AND OSMOSIS 61
Hydrotropism. Roots respond similarly to the presence of
water, turning toward moisture even at long distances. This
tendency, called hydrotropism, is very useful, especially if soil
water be scant. Vast numbers of fine roots are often found project-
ing into springs and streams, forcing their way into water pipes
or piercing deep into the soil, led by this force that turns them
toward the needed moisture.
Selective Absorption. Another fact connected with absorption
is, that plants, though growing side by side, take very different
matters from the same soil. This apparent impossibility is ac-
complished by the action of the protoplasm which lines the inner
walls of all active cells and has the remarkable power to select,
in a considerable degree, what substance the roots shall absorb
with the water. This selective absorption, as it is called, accounts
for the variety of food substances taken from the same soil by
different plants.
Successive Osmosis. All this arrangement for absorption would
be useless, were there not some way provided for passing on the
absorbed liquids after being taken up by the root hairs. When
the outer layer of cells has taken in soil water their contents are
diluted, and they become less dense than those next within. Their
contents tend to pass to the next inner layer, as the osmotic
current is always toward the denser liquid.
This last step removes the newly absorbed soil water from the
epidermal cells and leaves them denser again, ready to absorb
more soil water from without.
Root Pressure. This process continues inward, from cell to
cell, till the ducts are reached, when the liquids rise up through
root and stem, causing the uplift which is known as joot pressure.
This root pressure is one important cause of the circulation of
sap in plants, and is often sufficient to raise the water to heights
of one hundred feet or more. But neither this nor any other known
cause is equal to the task of lifting water as high as some of our
tallest trees, and the method by which that is done is still unknown.
This inward osmosis may be reversed by putting salt in the soil. It
dissolves in the soil water, makes it denser than the contents of
62
BIOLOGY FOR BEGINNERS
wer MOSS
the cells, which are therefore robbed of their water, since the
osmotic flow is toward the liquid of greater density. This fact is
often utilized in killing weeds and grass along the sidewalks.
Variations in Osmosis. Osmosis hi roots is affected by the
temperature and amount of moisture in the soil, being less in cold,
dry seasons. Also the presence of organic acids in bogs, or of
certain mineral matters in some soils, tends to hinder or prevent
the process. Hence it follows that in our cold season, most plants
shed their leaves, so that
C-E T8 P / 5 ^ tnev nave ^ ess sur f ace fr m
~~ which to evaporate water,
because their supply is cut
down by the cold.
In the case of both bog
and desert plants, many
schemes to retain moisture
have developed. Though
in such different surround-
ings, both classes of plants
have difficulty in absorbing
enough water, because of
the stoppage of osmosis.
Aerial roots find even
greater difficulty in obtain-
ing sufficient water, and
many wonderful devices
have been developed in
FIG. 10. Compare the position of root the way of hairs to radiate
and of stem in A and B. heat, scales to catch water,
and enormous, thickened
cortex to retain it when once it is absorbed.
EXPERIMENTS WITH ROOTS
To Prove that Roots turn toward Gravitation. If well-started
seedlings be inserted in a split cork which is then put into a test
tube of water and inverted, it will be found that the upward
PLANT INVERTE O
ROOT3 TURAHNfr DOWM
TURNING UP
(pQS -)
ABSORPTION AND OSMOSIS
63
pointing root, will soon turn downward at the tip, as will all of its
branches. This can be repeated with any kind of seeds. It would
not do to infer a general rule from one or two cases.
If a germinating box with well-grown seedlings be turned on
its side, the roots will turn down, no matter how often the experi-
ment be changed, thus proving the same thing in another way.
Our experience with
planting seeds in the
garden also is a good
experiment in the same
line; the root turns
down, no matter how
the seed is placed.
The same experi-
ments prove that stems
turn away from gravi-
tation's pull. This is
called negative geotro-
pism, and applies to
most plant parts except
roots. It is evident
that what we call
" weight " has nothing <*
to do with the direction 5 s EB os IN
of either root or stem. <*
,. XX ^>X WET
-=ST
nojs
ROOT
I
i
Cr
BY
INCLINED SIEVE
If INFLUENCED
ONLY
FIG. 11. Note different direction taken
roots, when attracted by moisture.
by
The root, though not
so heavy as the soil,
penetrates it on its way
downward, and the
stem, despite its weight, turns upward, due to this effect of gravita-
tion on all the living cells.
It might be thought that light had something to do with this
change of direction in plant parts. How could it be decided by
experiment?
To Prove that Roots Turn toward Moisture. If seeds be planted
on the bottom of a coarse sieve which is then filled with wet moss
64
BIOLOGY FOR BEGINNERS
and tilted at an angle of about 45 degrees, the direction taken by
the roots will be different from what might have been expected
from the above experiment.
.
LIQ.UIO
teas DCft
I.IOUIO
SI/CrAft
SOLUTION
__.
//v
HOOT - N
CELL WALL
SOt L.
i WATE K
FIGS. 12 and 13. Osmosis in root-hair. Laboratory experiment to
demonstrate osmosis of liquids.
The roots will start downward at first, directed by gravitation,
but when they have penetrated the sieve, they will turn toward
it again and reenter the moss in order to find moisture.
ABSORPTION AND OSMOSIS 65
This response of roots to moisture is called hydrotropism, and
will cause roots to turn toward a water supply if the surroundings
be dry, even though they turn partly away from the direct down-
ward line.
To Demonstrate Osmosis. Fill an artificial diffusion shell (such
as can be purchased from dealers in laboratory supplies) with
molasses and fasten it tightly to a long glass tube by wiring it
to a rubber stopper. Insert the shell in a jar of water. Here
are the three essentials for osmosis. The shell is the osmotic
membrane, the molasses, the dense liquid, and the water, the
less dense liquid.
The rise in the tube will be rapid and usually reaches a height
of several feet. This illustrates in a way the action of a root hair
in causing root pressure, though the root hair, because of its
protoplasmic lining, selects what will be absorbed, while the
apparatus does not.
With the same apparatus, starch or proteid or fat can be placed
in the shell, and it will be found that no osmosis goes on, and that
they cannot be found in the water outside the diffusion shell.
On the other hand, the sugar, peptone, or other soluble food stuff,
will pass through the membrane, and can be found by test in the
water outside.
Not only does plant absorption depend upon osmosis but nearly
all the life processes of plants and animals utilize this process in
some degree, as will be seen as we proceed.
COLLATERAL READING
ABSORPTION
Elementary Botany, Atkinson, pp. 22-27; Lessons in Botany, Atkinson,
pp. 36-44; Physiological Botany, Gray and Goodale, pp. 230-232; Text-
book of Botany, Bessey, pp. 175-176; The Story of Plants, Allen, pp. 53-73;
Introduction to Biology, Bigelow, pp. 41-45.
GEOTROPISM
Lessons with Plants, Bailey, p. 330; How Plants Grow, Bailey, p.
350; Plant Relations, Coulter, pp. 69, 89-91, 138-141; Textbook of Botany,
Stevens, pp. 24, 43, 61, 114; Plant Structures, Coulter, pp. 303-309; Ele-
mentary Botany, Atkinson, pp. 82-84; First Studies in Plant Life, Atkinson,
66
BIOLOGY FOR BEGINNERS
pp. 27-32; Lessons in Botany, Atkinson, p. 108; Textbook of Botany,
Bessey, pp. 194-196; Nature and Work of Plants, pp. 38-39, 74; Natural
History of Plants, Kerner and Oliver, Vol. I, Part 1, pp. 88-90; Textbook
of Botany, Strasburger, p. 254.
HYDROTROPISM
Plant Relations, Coulter, pp. 89-93; Plant Structures, Coulter, pp. 307-
309; Elementary Botany, Atkinson, p. 90; Natural History of Plants,
Kerner and Oliver, Vol. I, Part 2, p. 775; Physiological Botany, Gray,
pp. 393-394; Textbook of Botany, Strasburger, pp. 261-280; Textbook of
Botany, Stevens, p. 102.
OSMOSIS
(See references at end of Chapter LIII.)
SUMMARY
Necessity of water.
1. Food.
2. Transportation of food, mineral matter, etc.
Transportation of oxygen.
Transportation of waste.
3. Turgescence.
Meaning of term.
Where it is active.
Importance, in absence of woody support.
Osmosis.
1. Definition.
2. Processes dependent upon osmosis:
Absorption
Assimilation
Digestion
Respiration
Excretion
Essentials for osmosis
In plant
In experiment
Membrane
Dense liquid
Less dense liquid
Root hair or cell walls
Cell sap
Soil water
Diffusion shell
Sugar solution
Water in bottle .
(Diagram of root hair of experiment)
Root hairs.
Structure (see diagram). Location back of tip.
Adaptations for absorption.
ABSORPTION AND OSMOSIS 67
1. Large extent of surface.
2. Thin walls for osmosis.
3. Location for protection and large contact with soil.
4. Acid secretion to dissolve mineral matter.
Geotropism. (Contrast action of mere weight.)
Definition.
An adaptation for
Penetration of soil.
Obtaining water in soil.
Obtaining nourishment.
Positive in roots.
Negative in stems.
Hydrotropism.
Definition.
Function, reaching water supply.
Selective absorption.
Meaning of term. How controlled.
Successive osmosis.
Meaning of term. Explanation.
Root pressure.
Meaning of term. Reverse osmosis.
Experiments with roots: Geotropism; Hydrotropism.
CHAPTER X
STEMS: THEIR FORMS AND FUNCTIONS
Vocabulary
Node, the point on a stem at which a leaf is attached.
Inter-node, the space between the nodes.
Propagate, to reproduce a plant or animal.
Terminal, at the end.
Lateral, from the side.
Deliberately, intentionally.
The stem is all that portion of the plant body above the root.
It differs from the root in the following points:
1. It bears leaves, flowers and fruit.
2. The leaves and branches are borne in regular order, at points
called nodes.
3. Growth takes place in the spaces between the nodes
(internodes).
Functions. The functions of the stem are:
1. To expose leaves to light and air.
2. To support flowers for pollenation.
3. To support fruit for dispersal. .
4. To transport liquids up or downward in the plant.
5. To connect the two food-getting organs, roots and leaves.
6. To store food stuffs.
7. To propagate the plant.
Naturally there are many adaptations for these various functions
resulting in many forms of stem growth and structure, which
modify the whole appearance of the plant.
.68
STEMS, THEIR FORMS AND FUNCTIONS 69
KINDS OF BRANCHING
Due to Leaf Arrangement. (Opposite and Alternate) The
branches of the stem originate as buds, which may be at the end
of the stem (terminal), or at the nodes, just above the leaves
(lateral). Insomuch as the branches always originate in this
way, it follows that if the leaves are opposite on the stem, the
branches will be opposite also, and if the leaves are alternately
arranged, the branches will arise in the same order.
Examples of opposite arrangement are found in the ash, maple,
and horse-chestnut. The alternate type is represented by the elm,
oak, beech, and apple.
In either case the chief object of the branch arrangement is to
expose the leaves uniformly to light and air. This is accomplished
in various ways, depending upon the development of the branch
buds, which influences the shape of the plant even more than the
leaf arrangement.
Branching Due to Bud Development. Excurrent. If the termi-
nal bud keeps in advance of the lateral buds, a slender, cone-
shaped outline results, called the excurrent type, such as is shown
in the pines and spruces.
Such trees have several advantages:
1. They grow rapidly above their neighbors.
2. Their slender, flexible tops offer little resistance to storms.
3. They can grow close together and still let light down to the
lower branches.
4. Their lower branches can bend and shed snow easily.
For these reasons the excurrent type is particularly adapted to
cold northern regions, where it is most frequently found.
Deliquescent. If, on the other hand, the lateral buds equal or
exceed the terminal ones, the plant assumes a broad spreading
outline called the deliquescent type as shown by the elm, apple,
and oak. This type is very successful in competition with other
forms, because, even though it may start late, its broad top shades
and kills its neighbors. All plants which grow mixed with these
70 BIOLOGY FOR BEGINNERS
broad-shouldered and broad-leaved giants, must either get a start
before the leaves come in the spring or else must have learned to
live with very little light.
Forked Branching. Indefinite Branching. The growth of the
terminal bud may be checked by bearing flowers. If so, the branch
usually forks in a Y shape, producing round-topped plants, such as
the horse-chestnut and magnolia. In some shrubs the terminal
bud is unprotected for winter, hence is killed back and thus produces
FIQ. 14. Creeping stem of the water fern (marsilia). From Atkinson.
a very irregular type of branching, called indefinite. This is well
illustrated by the sumach.
MODIFICATION OF STEMS
As would be expected, stems are variously adapted to suit
different conditions and functions, thus giving rise to many forms.
Shortened Stems. In some plants like the dandelion, the stern
is so shortened that the leaves seem to come in a rosette, directly
from the top of the root. On this account, the term " stemless "
is sometimes applied to such cases. These low-growing plants
have many advantages, among which may be mentioned :
STEMS, THEIR FORMS AND FUNCTIONS 71
1. Escape from grazing animals.
2. Escape from crushing by being stepped on.
3. Crowding away neighbors by the wide, close leaves.
4. Water is retained near the root, by the cover of leaves above.
Creeping Stems. The creeping stem is another type, with
common examples, such as the strawberry, in which a plant,
though having a weak and slender stem, is, with great economy
of wood tissue, enabled to spread its leaves widely. By this habit
it also escapes injury from wind, cold, or storms, since it is closely
attached to the earth at frequent intervals. Besides, these
" runners," as the horizontal branches are called, furnish a valuable
means of propagation, since they send out roots at the nodes,
and grow even if separated from the parent plant.
Climbing Stems. Many stems succeed in exposing their leaves
to the light without producing much more supporting tissue than
do the creepers. These are the climbing stems which use supports
outside of their own structures to lift themselves into the light.
One means of climbing is by twining round some supporting plant,
as in case of hops and pole beans. Another similar method is by
means of tendrils, which are usually leaves reduced to the mere
skeleton of veins, as in the grape, wild cucumber, etc.
The coiling of tendrils or twining stems is a curious process,
for it frequently seems as though a plant or tendril had started
straight for a certain support and deliberately coiled about it.
This is not the case though the real process is scarcely less wonderful.
The tip of the twiner or the tendril grows unequally on different
sides, causing it to swing through the air in circles, as it grows.
Thus it has a chance to reach anything within the radius of its
swing, which is often several inches.
Having reached a support, the growing point can no longer
swing as a whole, but the tip coils about the support as it grows,
enabling it to rise as high as its sturdier neighbors. Tendrils also
coil between the support and the plant, raising the latter and hold-
ing it by a spring which will yield to wind pressure without break-
ing. This later coil usually reverses midway to avoid twisting the
tendril off.
72 BIOLOGY FOR BEGINNERS
Other methods of climbing are found in plants like the poison
ivy, which produces adventitious roots to attach itself, and in the
nasturtium, which climbs by hooking its leaf stalks around the
supports.
In any case, the climbing habit is very successful, especially in
crowded tropical forests where the shade renders necessary some
means for a slender plant to reach up into the light to display its
leaves. This the climbers do with least possible outlay of wood tissue.
Fleshy Stems. Another modification of stems which frequently
occurs is developed for the storage of food. The stem assumes a
fleshy form, allowing a large storage volume with little exposure
of surface. Such fleshy stems are usually developed underground
in order to protect their stored food from animals and cold. Like
the fleshy root, these underground stems enable the plants to get
an early start in spring and also often propagate the plant very
successfully. The simplest underground stem is the root stock
found in sweet flag and Solomon's seal. Other common forms are
the tuber of the potato, and the bulbs such as the onion, lily, tulip,
etc. It may seem hard to think of these as stems, yet if we turn
to the first paragraph of this chapter, we will find that they have
the characteristics mentioned there and are merely modified to
adapt them to special functions.
Bud Structure. A bud is really an undeveloped stem, with the
spaces between its leaves greatly shortened, and the leaves them-
selves very small and closely packed. The chief function of a bud
is to keep the growing point of the stem protected from harm
and yet ready for rapid growth at the right time. To carry out
this purpose, buds have several interesting adaptations.
In the first place, they are usually covered with small leaf-
like organs called bud-scales, which overlap as shingles do, and
protect the tender shoot from loss of water, mechanical injury,
rain, and insect attacks. Often the scales are covered with a
sticky gum, which aids it, especially as regards the control of water.
Within the bud, the tiny leaves are frequently packed in a
woolly down, which helps protect from injury, especially when
the bud is first opening, and may also prevent ill effects from
STEMS, THEIR FORMS AND FUNCTIONS 73
sudden changes of temperature. The leaves themselves are
wonderfully well packed, so as to expose little surface, and econo-
mize space; they may be folded, rolled, or coiled, but always
in the same way in the same plant.
Buds are always developed either at the end of the stem
(terminal), or just above the leaves (lateral). Their growth
consists of three stages, the opening of the scales, the lengthening
of the stem, and the expansion of the leaves. The scales fall off
during this process, leaving the bud-scale scars to mark their
former place. As most buds begin growth in the spring, these
rings of scars mark the beginning of each year's growth. The
age of the stem can thus be calculated as long as the scars show.
SUMMARY
Definition.
Characteristics of stem
Bears leaves, flowers, fruit.
Leaves and branches at nodes.
Growth between nodes.
Functions :
{of leaves for light and air.
of flowers for pollenation.
of fruits for dispersal.
Transportation of liquids between root and leaf
Storage of food.
Propagation.
Kinds of Branching:
Object of branch arrangement in general.
Branching due to leaf arrangement.
Opposite. (Ex.)
Alternate. (Ex.)
Branching due to bud development.
1. Excurrent. (Ex.)
Shape of tree. Cause.
Advantages:
Rapid growth in height.
Little storm resistance.
Can grow closely.
Shed snow readily.
2. Deliquescent. (Ex.)
Shape of tree. Cause.
Advantages, shades out its neighbors.
Few can grow together.
74 BIOLOGY FOR BEGINNERS
3. Forked. (Ex.)
4. Indefinite. (Ex.)
Modification of Stems:
1. Shortened stems. (Ex.)
Advantages, escape grazing animals, or crushing.
Crowd away neighbors.
Retain water at roots.
2. Creeping stems. (Ex.)
Advantages, widespread, little wood.
Escape injury.
Propagation.
3. Climbing stems.
Advantages, escape from shade conditions.
Expose leaves with little wood tissue.
Means of climbing:
Twining. (Ex.) Method of operation.
Tendrils. (Ex.) Method of operation.
Adventitious roots. (Ex.)
Leaf stalks. (Ex.)
4. Fleshy stems. (Ex.)
Advantages: Safe storage, early start, propagation.
Buds.
Definition.
Function.
Adaptations:
Scales.
Gum or hairs.
Woolly packing.
Leaf arrangement.
Location.
Manner of growth.
Bud scale scars.
COLLATERAL READING
Studies in Plant Life, Atkinson, pp. 33-39; Lessons with Plants, Bailey,
pp. 1-44; School and Field Botany, Gray, pp. 27-32, 69-70; Plant Rela-
tions, Coulter, pp. 53-87; Botany for Schools, Atkinson, pp. 37-60; Text-
book of Botany, Gray, pp. 45-51, 69-85; Kerner and Oliver, Vol. I, Part
2, pp. 465-482, 710-736; Plant Life and Uses, Coulter, pp. 143-198;
Experiments in Plants, Osterhout, pp. 224-285; Plants and their Children,
Dana, pp. 112-124; Applied Biology, Bigelow, pp. 163-188; Structural
Botany, Gray, pp. 50-64, 70-82; Plant Structures, Coulter, pp. 280-296;
Lessons in Botany, Atkinson, pp. 61-68; Elementary Studies in Botany,
Coulter, pp. 224-252.
CHAPTER XI
STEM STRUCTURE
Vocabulary
Lenticels, openings in the bark for passage of air and water vapor.
Radiating, extending out from the center.
Fabric, woven material such as cloth.
Perennial, living year after year.
Dicotyledonous, plants having two cotyledons. (Dicots.)
Monocotyledonous, plants having one cotyledon. (Monocots.)
EXTERNAL STRUCTURE
The external structure of all ordinary stems, though varying
greatly, has some points in common. It will be seen that there is
an outer covering, the epidermis or bark, which protects from
injury by storm and insects and prevents undue loss of water, as
a result of drought or cold.
Lenticels. Through this bark are openings (lenticels) which
permit a regulated escape of water- vapor, and also admit air.
Leaf Scars. On the bark will be found scars left by leaves of
preceding seasons, varying in location according as the leaves
were opposite or alternate, and having above them the buds for
the coming year's branches. On these scars will be found dots
marking the severed ends of the ducts, which can be traced into
the stem and found to extend to the roots. Over these scars is a
water-proof coat (abscission layer) which formed before the leaf
fell to protect the plant against the loss of so many leaves and
consequent bleeding from thousands of tiny wounds.
Flower-bud and Fruit Scars. It frequently happens that the
bearing of a flower or fruit makes a scar differing from those made
75
76
BIOLOCzY FOR BEGINNERS
by falling leaves. These are especially plain in the horse-chestnut.
A flower-bud always ends the growth of the stem that bore it, hence
further growth is by lateral buds which produce a forked type of
branching, where the flower was borne.
Bud-scale Scars. At various places on the stem are rings of
small scars caused by the bud-scales of previous years which were
shed as spring activity
commenced, thus mark-
ing the first growth of
each year. Other mark-
ings are frequently met
with, caused by injuries
from weather or insects.
These the plant has met
by thickening its bark.
INTERNAL STRUCTURE
On cutting across the
stem of , any common
tree, the general internal
structure will be shown,
in most cases, without
the use of lenses. Three
regions can be dis-
tinguished easily bark, wood, and pith. A closer inspection
reveals a fourth, between bark and wood. This is the cambium,
a thin, light-colored zone of very juicy cells, which here, as in
the root, produces all the other tissues.
Wood. The wood will be seen to be arranged in circles, " annual
rings " of alternately coarse and fine tissue, the ducts, and wood
fibers, while radiating from the pith and extending across these
rings are the pith rays that connect pith and bark.
Bark. The bark will repay a closer scrutiny with a hand
lens and will be found to consist of an outer epidermal layer,
often variously thickened and roughened by growth; next, the
-*- or * Srtrsy
FIG. 15. Stem showing lenticels and diff-
erent kinds of buds and scars.
STEM STRUCTURE
77
" green layer " (cortex), and within this the bast fibers and tubes,
which transfer liquids downward and give toughness to the bark.
FIG. 16. Diagram of maple stem show-
ing the development of wood and bark
through first and second years. At the tip
is a mass of living formative material
(shown unshaded) from the sides of which
arise protrusions that become leaves. Also
arising from the formative region, just
above the base of the very young leaves,
are protrusions which develop into forma-
tive regions like those of the main tip,
and, as growing-point, produce leaf-bearing
branches of the main stem. In the center,
around the axis, the formative material as
it grows older becomes pith (shown as
dotted) and this pith is continuous with
that of the branches. The surface becomes
changed into a skin or epidermis (coarse
shading) covering both stem and leaves.
Parts of the formative material between
the epidermis and the pith become vari-
ously hardened into "bundles of fibrous ma-
terial; around the central pith arise strands
of wood (fine shading) ; near the epidermis
arise corresponding strands of bast (shown
by black) surrounded by more or less pith-
like material which may become green or
corky, called cortex (shown dotted like the
pith); and between the rings of wood and
bark is a layer of formative material which
is continuous with the tip and is called the
cambium. From this cambium in successive
years new wood is added to that within
and new bark to that on its outer side, and
thus both wood and bark increase in thick-
ness by annual layers. But on the outside
the epidermis, and then the older bark, is
pushed off or worn away so that the total
thickness of the bark is limited. Both
wood and bark are continued into the
leaves, but not the cambium. The strands
of wood and those of the bark are so connected as to form a sort of net-
work through the meshes of which extend radially the plates of pith called
pith-rays.
From Sargent.
78 BIOLOGY FOR BEGINNERS
FUNCTIONS OF STEM TISSUES
The tissues in order from without are the epidermis, cortex,
bast fibers (hard bast), bast tubes (soft bast), cambium, wood,
ducts, pith, and pith rays from center to cortex. Each of these
layers has its definite functions, several of which have been stated.
Epidermis. The outer layer, or epidermis, is largely protective
and hi several ways. Its thickness guards against injury from wind,
weather, and attacks of insects. It does not allow loss of water,
except at the lenticels, thus preventing undue drying of the deli-
cate tissues beneath. It also keeps out the spores of parasitic fungi
that might otherwise find entrance and destroy the plant.
Cortex. Under the epidermis is the cortex, whose function is
to help prepare starch food for the plant, much as do the
leaves.
Bast Fibers. The bast fibers give toughness to the bark, some-
times helping support the stem. Man has taken advantage of
the fiber strength of hemp and flax (look up) to make fabrics.
Bast Tubes. The soft bast conveys food prepared by leaves
downward to various places where it is used or stored.
Cambium. The growth function of the cambium cannot be too
often mentioned, as from it, by a complicated process of cell divi-
sion, bark tissues on the outside and wood and ducts within are
formed.
Ducts. The ducts transfer liquids up and air down in the stem,
and add their strength to the woody portions, whose fibers are the
chief support of the stems of all larger plants. Together they make
up the bulk of the stem tissue.
Wood Fibers. Both the wood fibers and ducts are arranged in
very definite circles, called annual rings because usually each ring
marks a year's growth. These rings are caused by the cambium
which produces larger ducts and more of them in the spring when
the sap is flowing than later, when more wood fiber is produced.
In the winter, the growth practically stops, only to begin the fol-
lowing spring with a layer of large ducts again, thus marking, by
these successive rings of tissue, the seasons' changes.
STEM STRUCTURE 79
Pith. The pith may be a minute remnant of the formative tis-
sue, or a larger storage place for foods and the pith rays serve as
cross channel for liquids to follow in their circulation in the stem.
So we have one protective region, the epidermis; one digestive
region, the cortex; one formative region, the cambium; one storage
region, the pith. The ducts, soft bast, and pith rays are the chan-
nels for circulation of fluids while the wood and bast fibers are for
strength and support.
Grafting. The remarkable ability of the cambium cells to grow
and produce new tissues is utilized in grafting. Grafting consists
in bringing into close contact the cambium layer of a small active
twig with that of the tree upon which it is to grow. This may be
done by splitting the stem, and inserting the fresh-cut twig, or by
raising the bark and inserting an active budded twig beneath it,
with the cambium layers in contact. The wound is then protected
by wax and growth between the two cambium layers soon unites
the new stem with the old.
The cambium also provides for the healing of injuries and the
covering of scars where branches are cut off. New tissue forms at
the edges of the wound and gradually covers the whole area, pro-
vided that spores and bacteria do not first cause decay of the ex-
posed surface. To prevent this, cut or injured surfaces should al-
ways be tarred or painted to kill and keep out bacteria, while new
tissue is growing. If decay has begun the rotted wood must be
cleanly removed, the cavity sterilized with tar and filled with
cement. The cambium growth will now extend the tissue inward
from the edges and often cover the scar, filling and all. ,
In rare instances two limbs, or even two separate trees of the
same kind, will chafe together in the wind, till the cambium is
exposed in both. Then if undisturbed, an automatic graft may
occur and a curious condition will develop, in which the two trees
will continue to grow firmly together.
Other Kinds of Stem Structure. In the chapter on seed struc-
ture it was stated that plants whose seeds had two cotyledons
(dicotyledonous plants) had stems that differed from plants whose
seeds had one cotyledon (monocotyledonous) . The stem just
80
BIOLOGY FOR BEGINNERS
described is such a one as would be found in a dicotyledonous
plant. The monocotyledonous stem differs in so many ways that
it requires special consideration.
Corn Stems. The common
corn stalk is a good example of
the monocotyledonous type of
stem. If we cut a section across
it, we find the tissues very dif-
ferently arranged from those in
the dicotyledonous stem, just
discussed. The monocotyledon,
in place of a bark of several lay-
ers, has a rind of only one kind of
tissue thick- walled, hard cells
whose function is mainly to sup-
port the plant. The wood,
cambium, and bast tissues are
grouped in numerous "vascular
bundles" which, instead of being
in definite rings, are scattered
through the stem, the larger and
older ones toward the center and
smaller and younger ones near
the edge. The cambium in mono-
cotyledons ceases to build new
tissue, after a time. Hence the
stem does not continue to in-
crease in diameter as does the
dicotyledonous stem, but pro-
duces tall slender plants like corn,
grasses, bamboos, and palm trees.
The bulk of the stem consists of
the soft thin-walled pith, instead
of wood and ducts, so that the
FIG. 17. Diagram of palm stem
(monocot). From Sargent.
structure is almost reversed in these two types of stems although
the same tissues are present. As one result of this striking dif-
STEM STRUCTURE
81
ference we obtain many of our wood products from the dicoty-
ledonous stems, while the monocotyledonous, having little wood
and much pith for storage, provide us with foods such as hay
and grain, sugar-cane, and starch.
Do not think that the monocotyledonous stem is weak because
it has so little wood tissue the case is quite the contrary as you
may prove for yourself.
Select a tall grass stem,
such as timothy or rye.
Measure its height and its
diameter. How many
times its thickness is the
height? Suppose it were a
tree one foot in diameter
how tall would it be? Com-
pare this with the actual
height of trees. Figure
this out and you will
jttHacorvi.C.DO/1 o us Trff .
FIG. 18. Cross section of typical
monocotyledonous stem.
have more respect for the
strength of the grass stem, as well as for the " sturdy oak."
Polycotyledonous Stems. Seeds having several cotyledons
(polycotyledonous) have a woody stem with annual rings, but
differing in other ways from 'the two preceding types. We shall
not take up its structure in detail; pines, spruces and all ever-
green trees belong to this last group and their resinous wood
furnishes us with our best lumber.
Not only are their stems of great strength, but some of them
are the largest and oldest living things in the world. The Big
Trees (Sequoia) of California are the oldest, even among trees.
One of these ancient giants, the " General Sherman Tree," is nearly
four thousand years old, 279 feet high, and 36 feet in diameter.
To put it another way, it was a flourishing sapling, twenty or
thirty feet high when the Exodus of Israel and the Trojan wars
took place. It was a thousand years old at the time of Solomon
and two thousand at the birth of Christ. All our European and
American history are but events of yesterday to this patriarch of
82
BIOLOGY FOR BEGINNERS
FIG. 19. Sequoia Washingtoniana (Bureau Forestry, U. S. Dept. Agr.)
From Atkinson.
STEM STRUCTURE
83
the organic world, which now towers higher than a twenty-story
building and is still growing. Some animals, such as the elephant,
may live two hundred years, but even these, or man, with his three
Courtesy of the American Museum of Natural History.
FIG. 20. Section of one of the big trees of California, the " Mark Twain,"
16 ft. in diameter, and 1341 years old.
score years and ten, are the merest infants beside such ancient
inhabitants of the vegetable world.
This illustrates a fact which is often overlooked, that perennial
plants really have no limit of growth, as do animals, but keep on
84
BIOLOGY FOR BEGINNERS
STEM STRUCTURE
External Features
Structure
Function
Bark
Protection
Lenticels
Spongy openings
Let out water vapor
Admit air
Scars left by
1. Leaves showing
Duct scars
Cut ends of ducts
Abscission layer
Water proof cover
Prevent loss of sap
2. Bud scales
Formed in spring
Mark year's growl h
3. Flowers and fruit
Usually terminal
Cause branch to fork
Internal Features
1. Bark
Epidermis
Thin if young, corky in
Protect from insects,
older stems
fungi and weather
Retain water
Cortex
Thin walled, soft cells
Food making and di-
gestion
Bast fibers
Thick and tough
Strength
Bast tubes
Long, tubular cells
Downward transfer
2. Cambium
Very active, proto-
Growth
plasm
3. Wood region
Wood fibers
Thick walled, stiff
Support
Ducts
Thick walled, tubular
Upward transfer
4. Pith
Thin walled, weak
Storage
Pith rays
Cross transfer
Comparison of Dicot and Monocot Stems
Features of each
Dicot
Monocot
Outer layer
Bark of several tissues
Rind of one tissue
Vascular bundles
In regular rings
Scattered
Bulk of stem
Wood
Pith
Supported by
Wood region
Rind
Cambium
Permanent
Not permanent
Growth
Continuous in height
In height only
and thickness
Use
For lumber, fuel, etc.
For food stored
Usual shape
Thick
Tall, slender
Examples
Broad-leaved trees and
Grasses, lilies, palms,
common plants
sugar-cane, etc.
STEM STRUCTURE 85
increasing slowly in size for indefinite periods, while animals reach
a maximum size and grow no larger, no matter how old they become.
The reason is probably that in plants, little energy is required,
hence little food is used in oxidation and more is left for additional
growth, whereas in animals, which use more energy, a point is
reached, where the nutritive processes are just balanced by oxida-
tion and further growth ceases. As soon as the destructive proc-
esses exceed the constructive, old age enters and finally death
itself.
COLLATERAL READING
Science of Plant Life, Transeau, pp. 118-136; Botany of Crop Plants,
Robbins, pp. 33-41; Fundamentals of Botany, Gager, pp. 61-68; Plant
Anatomy, Stevens, pp. 28-60; Principles of Botany, Bergen and Davis,
pp. 57-79; Botany for Schools, Atkinson, pp. 51-60; Introduction to Botany,
Stevens, pp. 45-64; Plant Life and Plant Uses, Coulter, pp. 162-185; Plant
Structures, Coulter, pp. 232-237; Elementary Botany, Coulter, pp. 224-252;
Applied Biology, Bigelow, pp. 163-188; Elementary Biology, Peabody and
Hunt, pp. 45-52; Biology, Coleman and Bailey, pp. 59-72; Plant Relations,
Coulter, pp. 83-87.
CHAPTER XII
LEAVES AND LEAF STRUCTURE
Vocabulary
Surplus, an extra supply.
Originate, to begin.
Accumulated, collected together.
Excessive, too great.
Communicate, to connect.
Stomates, openings in leaf epidermis to admit air and let out water
vapor.
Heliotropism, the response of plant parts to light.
Chlorophyll, the green coloring matter of plants.
Transpiration, the passing off of excess water from plants.
Vascular, composed of "vessels" or tubular cells, such as the
vascular bundles of ducts in stem and leaf.
Parenchyma, thin-walled, spongy plant tissue.
Leaf Functions. The leaf is one of the most remarkable and
important parts of the plant. Within it are performed more life
functions than in any other plant or animal organ. Its chief and
unique function is the manufacture of starch out of water from the
soil and carbon dioxide from the air. Animals cannot prepare
starch from these two compounds and must therefore depend
upon plants for their supply. Not only does it prepare, but it
also digests and assimilates food, sending its surplus, by way
of the veins (duct bundles), to all living parts of the plant.
Furthermore, the leaves are constructed so as to admit air for
oxidation, and to throw off carbon dioxide (respiration). Ex-
cretion of water (transpiration) and of other wastes is another
function of these versatile organs. They also possess in some
degree the powers of motion and reproduction. Food making,
digestion, assimilation, respiration, excretion, motion, reproduction,
these are all the functions that any living thing can perform.
One entirely, and all to some extent, are performed in the leaf.
86
LEAVES AND LEAF STRUCTURE
87
GENERAL STRUCTURE OF LEAVES
A leaf usually consists of a thin flattened portion (the blade)
stiffened by a framework of veins which are really bundles of
ducts connecting with those in the stem. Usually the blade is
attached to the stem and held out into the light by a stalk (the
petiole). Its point of at-
tachment is called the
node of the stem, above
which all branch buds
originate. The veins may
form a network throughout
the leaf or may be almost
parallel (grass). There
may be one large midvein
with branches like a feather
(elm), or several veins of
equal size may spread from
the petiole like the fingers
of your hand (maple),
but whatever the arrange-
ment, their function is
to support the blade and
transfer the liquids concerned in the various leaf processes.
Leaf Forms. The outline of a leaf depends largely upon the
arrangement of its veins. If netted veined the leaves are usually
broad, notched, or lobed; while if the veins are parallel they are
usually long and slender. The forms of the leaves are almost as
various as the kinds of plants; some having regular or entire edges
(lily), others notched, lobed, or finely divided (elm, maple, carrot),
while still others are composed of separate leaflets (pea, horse
chestnut), and so are called compound.
ADAPTATIONS FOR EXPOSURE
Form. These different-shaped leaves are developed with but
one end in view the complete exposure of the leaf tissues to
FIG. 21. Structure of leaf exterior.
88
BIOLOGY FOR BEGINNERS
light and air, on both of which all the activities of the leaf
depend.
Arrangement. Not only are leaves adapted by their shape for
this exposure, but by their arrangement on the stem. Look at a
tree from above or at a house plant from the " window side " and
observe that the branches and leaf stems (petioles) have so ex-
tended and twisted them-
selves, that each leaf is
exposed and very few cast
any shade upon their
neighbors.
Heliotropism. Another
adaptation for leaf ex-
posure is their ability to
constantly turn them-
selves toward the light.
This is an every day
observation, but no one
can explain just how they
do it. The process is called
heliotropism (which means
sun turning), and is very
essential to the work of
the leaves. Roots turn from light (negative heliotropism) while
this response made by leaves toward the light is termed positive
heliotropism.
Modified Leaves. Like roots, leaves are often modified to
perform special functions: They may be reduced to mere ten-
drils for climbing (pea) or they may develop as thorns for protec-
tion (barberry). They may thicken up with stored nourishment
and even reproduce the plant (live-f or-e ver) , or most curious of
all, may develop into traps for insects (sundew and pitcher-plant) .
Fall of Leaves. Most plants of temperate climates shed their
leaves, either all at once in autumn (maples, elms) or a few at a
time the year round (pines and spruces). They do this so they
may rid themselves of waste mineral matter that has accumulated
FIG. 22. Sunflower with young head turned
to the morning sun. From Atkinson.
LEAVES AND LEAF STRUCTURE
89
and, in the case of the broad-leaved plants, this shedding also comes
because it is necessary to reduce the exposed surface so that too
much water may not be evaporated in the winter, when the roots
can supply but little. Of course one can see another reason for
plants that grow in climates where snow prevails during the winter.
The weight of snow accumulated by the leaves would tend to
break the plant down.
In the case of the pines
with their slender
needles this reason does
not apply.
The color changes of
autumn are not due to
frost entirely, but may
be caused by anything
which stops the activity
of the plant. The
beautiful yellows and
reds that make our
autumn a blaze of glory
act as a protection to the
sensitive green sub-
stance of the leaves,
which is being withdrawn and stored for use another year.
Before the leaves of a plant fall there is formed at each leaf
base a waterproof layer (abscission layer) which prevents the loss
of sap after the leaf is gone.
The enormous amount of ashes left when the leaves are burned
gives some idea of the amount of unused mineral matter which
the plant had stored there, and incidentally reminds us that plant
ashes, whether from stems or leaves, are useful food materials for
plants and ought to be put back on the soil for use another year.
MINUTE STRUCTURE OF LEAVES
The chief function of the leaf is the manufacture of food ma-
terials. To understand this, a thorough study of the minute
structure is necessary.
FIG. 23. The same plant at sundown
showing the head turned to the west. From
Atkinson.
90 BIOLOGY FOR BEGINNERS
If the blade of a leaf be cut across and studied with a micro-
scope, the following tissues may be observed. Mentioned in order
from the upper surface they are:
1. The cuticle (sometimes lacking).
2. The upper epidermis.
3. The palisade cells.
4. The spongy layer (traversed by veins).
5. The air spaces.
6. The lower epidermis (penetrated by stomates).
The Upper Epidermis. This usually consists of a single layer
of cells often very irregular, as seen from above, but brick shaped
when viewed in cross section. There are few stomates in the
upper epidermis, since they would be exposed to dust and rain.
The function of the upper epidermis is to prevent loss of water.
To aid in this, it is sometimes covered by a waxy layer, called
the cuticle, as in ivy, cabbage, and other leaves that shed water
in drops. A second function of these epidermal cells may be to
act as lenses and concentrate the sunlight upon the inner parts
of the leaf. The fact that their upper and lower surfaces are
curved like a lens, leads to this supposition.
The Palisade Layer. Next beneath the upper epidermis is the
palisade layer. It consists of long narrow cells, placed endwise,
at right angles to the surface of the leaf. Within these cells is
found the chlorophyll, which is the green coloring matter of all
plants. As you will learn later, it is very sensitive to light and
these long cells permit the chlorophyll grains to move to the upper
ends if the light be dim, or to retreat to the long side walls if the
light is too strong.
The function of the palisade layer, then, is to regulate the ex-
posure of chlorophyll to light, and to carry on starch making.
The Spongy Layer. Beneath the palisade layer is a spongy
layer which consists of thin-walled cells and air spaces, and is
penetrated in all directions by veins (duct bundles). The spongy
cells are roundish, irregular, and loosely packed, thin walled, and
full of protoplasm and chlorophyll. In them, as in the palisade
LEAVES AND LEAF STRUCTURE 91
layer, starch making and all the other leaf functions are carried
on. The passing off of water to the air spaces is part of its work.
The air spaces are usually large, irregular cavities among the
spongy cells. They open through the lower epidermis by way of
the stomates, their function being to receive water vapor from the
spongy cells and to pass it out through these openings. They
also permit oxygen and carbon dioxide to pass to all the cells of the
spongy layer. They are very important, since through them food
making, respiration, and transpiration go on. They occupy about
three-fourths of the bulk of the spongy layer. The veins or duct
bundles are scattered through the spongy layer transporting water
and food stuffs and supporting the blade of the leaf.
The Lower Epidermis. Like the upper, the lower epidermis
usually has but one layer of cells. Through it open many stomates
which regulate the passage of air and water vapor to and from the
inside of the leaf.
The Stomates. These have been referred to as openings through
the epidermis. They are minute slit-like holes, about one-twen-
tieth as wide as the thickness of this paper. On each side of the
slit is an oval guard cell which regulates the opening and closing
of the stomate. Controlled by the needs of the plant, the sto-
mates open when there is an excess of water to be passed off, and
close in a drought. They open when carbon dioxide is required
for starch making or air for breathing, and close when either process
stops, thus regulating, in a remarkable degree, the activities of the
leaf. The function of the stomates is threefold,
1. To admit carbon dioxide for starch making.
2. To regulate transpiration of water vapor.
3. To admit oxygen and liberate carbon dioxide in respiration.
However, this elaborate mechanism would be of little use were
it not for the extensive system of air spaces in the spongy tissue of
the leaf into which the stomates open, and by means of which all
parts may have access to air for starch making, respiration, and
transpiration. Their number may vary from 60,000 to 450,000
per square inch and is usually greatest on the lower surface where
they are best protected from dust and rain. Floating leaves have
92
BIOLOGY FOR BEGINNERS
all their stomates on the upper surface. In vertical leaves they
are evenly distributed.
Chlorophyll. The green coloring matter of plants is the most
important part of the leaf. Practically the whole function of the
CROSS
FIG. 24. Leaf Structure.
rest of the leaf is to expose the chlorophyll to light and provide
it with materials upon which to work. Chlorophyll is composed
of nearly all the elements we find in any plant tissue, but is espe-
cially rich in iron compounds which give it its green color. It is
LEAVES AND LEAF STRUCTURE 93
found in the form of very minute particles called chlorophyll
grains, or chloroplasts, which seem to consist of active protoplasm
combined with the green chlorophyll. This is the substance which
performs the essential function of the leaves. It is found mainly
in the palisade cells and spongy layer. The former are arranged
to regulate its exposure to light, and the latter to provide it with
carbon dioxide and water to use in starch making. We shaU devote
the next chapter to the way in which it does its work. For the
present, think of chlorophyll as occurring in the form of active,
green grains, found in all green parts of plants and very essential
to their growth.
SUMMARY
Functions :
1. Starch making.
2. Digestion and assimilation.
3. Respiration.
4. Excretion.
5. Reproduction.
General structure:
1. Blade.
2. Petiole (leaf stalk) attached at nodes.
3. Veins (duct bundles).
Functions, support and transportation.
Arrangement :
Parallel (grasses).
Netted:
Feather veined (elm).
Finger veined (maple).
4. Outline.
Irregular margin in netted veined leaves.
Regular margin in parallel veined leaves.
Adaptation for exposure to light and air:
1. Shape, so as to let light through to others.
2. Arrangement, opposite or alternate.
3. Heliotropism.
Positive in leaves and flowers.
Negative in roots.
Modified leaves, as
1. Tendrils, for climbing (pea).
2. Thorns for protection (barberry).
3. Thickened, for storage (cactus).
4. Traps, for catching insects (sun-dew).
94 BIOLOGY FOR BEGINNERS
Fall of Leaves:
1. Reasons.
Remove waste mineral salts.
Lessen exposure to storms.
Reduce surface for transpiration.
2. Cause of coloration. Function.
3. Abscission layer.
SUMMARY OF MINUTE STRUCTURE OF LEAVES
1. Upper Epidermis.
Structure: One layer, brick-shaped cells, few stomates.
Cuticle sometimes present.
Function: Prevent loss of water.
Concentrates sunlight on chlorophyll.
2. Palisade Layer.
Structure: Narrow, perpendicular cells. Contain chlorophyll.
Function: Regulate exposure of chlorophyll.
3. Spongy Layer.
(a) Spongy cells.
Structure: Thin, irregular, loose, active.
Function: Starch making and transpiration.
(6) Air spaces.
Structure : Large irregular cavities.
Function: Transpiration, air supply.
(c) Veins.
Structure: Bundles of ducts and wood fibers.
Function: Transportation and support.
4. Lower Epidermis.
Structure: Single layer of cells, many stomates.
Function: Regulation of water and air supply via stomates.
5. Stomates.
Structure: Slit-like opening and guard cells.
Function: Regulate transpiration, supply of carbon dioxide and of
oxygen.
Distribution: Lower epidermis usually very numerous.
6. Chlorophyll.
Structure: Active green grains, rich in iron compounds.
Function: Photosynthesis or starch making.
Distribution: Palisade cells and spongy layer.
COLLATERAL READING
General study: Elementary Studies in Botany, Coulter, pp. 187-223;
Plant Life and its Uses, Coulter, pp. 201-218, 234-255; Experiments in
Plants, Osterhout, pp. 163-223; Familiar Trees, Mathews, pp. 1-19;
Plants and Their Children, Dana, pp. 135-185; Plant Relations, Coulter, pp.
6-52; Botany for Schools, Atkinson, pp. 70-89; Flowers, Fruits and Leaves,
LEAVES AND LEAF STRUCTURE
95
Lubbock, pp. 97-147; Textbook of Botany, Stevens, pp. 85-98; Elementary
Botany, Atkinson, pp. 36-38; Lessons in Botany, Atkinson, pp. 56-59;
Plant Structures, Coulter, pp. 141-142; Nature and Work of Plants, pp.
80-86; The World's Great Farm, Gaye, Chap. XII.
HELIOTROPISM
How Plants Grow, Bailey, pp. 350-000; Lessons with Plants, Bailey,
pp. 330-000; Lessons in Botany, Atkinson, pp. 109-114; Elementary
Botany Atkinson, pp. 84-88; Plant Structures, Coulter, pp. 305-000;
Plant Relations, Coulter, pp. 8-13, 68-70, 138-141, 330-000; Textbook of
Botany, Strasburger, pp. 250-253; Textbook of Botany, Gray and Godale,
pp. 392-393; Textbook of Botany, Bessey, pp. 193-194; Textbook of Botany,
Stevens, pp. 120-122; Nature and Work of Plants, pp. 73-00.
STOMATA
Plant Physiology, McDougal, pp. 196-203; Plant Anatomy, Stevens,
pp. 127-133; Lessons in Botany, Atkinson, pp. 58-59; Elementary Botany,
Atkinson, pp. 42-44, 46; Plant Structures, Coulter, pp. 141-143; Plant
Relations, Coulter, pp. 38-39; Nature and Work of Plants, McDougal,
pp. 84-00.
LEAF ARRANGEMENT
Flowers, Fruits and Leaves, Lubbock, pp. 97-147; Introduction to Botany,
Stevens, pp. 81-84; Plant Relations, Coulter, pp. 6-27; Kerner" and
Oliver, Vol. I, Part 2, pp. 593-597 and 623-640; Nature and Work of
Plants, McDougal, pp. 72-75; Textbook of Botany, Strasburger, pp. 37-
40; Textbook of Botany, Bessey, pp. 149-150.
MINUTE STRUCTURE
Parts
Structure
Function
Epidermis (upper
One layer; irregular cells
Prevents loss of water
and lower)
Stomates
Slit opening and guard cells;
Regulation of excretion
open into air spaces
Admit oxygen and CO2
Palisade cells
Oblong, endwise to surface
Expose chlorophyll to
Have chlorophyll grains
light
Chlorophyll
Green, living grains in the
Make starch
protoplasm
Spongy cells
Irregular, loose
All leaf functions
Have chlorophyll grains
Air spaces
Large and irregular
Excretion
Connect with stomates
Respiration
"Veins"
Duct bundles extending from
Support
the stem
Transportation
CHAPTER XIII
LEAF FUNCTIONS
Vocabulary
Illumination, source and supply of light.
Liberated, set free.
Photosynthesis, the process of starch formation in leaves, uniting
carbon dioxide and water by means of light.
Soluble, that which can be dissolved.
Photosynthesis. The process, by which carbon dioxide from
the air and water from the soil are united by the leaves of plants
to form starch through the action of sunlight on the green coloring
matter in the leaves, is called photosynthesis (meaning combina-
tion by light).
The ability of plants to take these two non-living substances
and build up their own food from them makes the chief destinc-
tion between plants and animals, for the latter depend on plant
foods either directly or indirectly. They cannot use the raw ma-
terials as do the plants.
Chlorophyll. The essential feature of the leaf, so far as pho-
tosynthesis is concerned is the green coloring matter, chlorophyll
(leaf green). This, as described in Chapter XII, is found in the
palisade cells and spongy parenchyma, in the form of minute grains,
embedded in the protoplasm.
Chlorophyll has the very wonderful property of absorbing some
of the energy of the sun's light and by the utilization of this energy
it is able to combine carbon dioxide and water into starch. This
starch is the primary form of plant food. At the same time that
starch is made, oxygen is thrown off as a waste product. This
replaces in the atmosphere, that which is used in respiration by
animals. Therefore animals depend on photosynthesis for both
food and oxygen supply. It is evident now why so many adapta-
96
LEAF FUNCTIONS
97
tions are found for exposing leaves to light, since, without light,
starch-making cannot go on, and without starch the plant cannot
survive. The chlorophyll is placed in the long palisade cells so
that, if the light be weak, the chlorophyll bodies may move to the
upper ends of the cells and get better illumination; or if the light
is too bright, they line up along the sides and so escape the direct
rays. In the deeper tissue of the spongy parenchyma of the leaf,
Light
Courtesy of American Museum of Natural History
FIG. 25. Activities going on in the "cells" and. air spaces of a leaf.
the chlorophyll is sufficiently protected and does not need to move
in this way; here we find the cells irregular in shape.
Materials used in Photosynthesis. The water for starch mak-
ing is supplied from the soil by means of the absorption of the
roots. It rises to the leaves by way of the ducts and veins. Any
excess is disposed of through the stomata. The carbon dioxide
is supplied from the air, where oxidation, respiration, combustion,
fermentation, and decay are constantly producing it. As fast as
the plants remove it they return the oxygen. As a result the
composition of the air remains practically constant.
BIOLOGY FOR BEGINNERS
pBocesses
8t Proci.
Prd tran.fr,(duct.)
cunward trar.ifer, (bait}
upport I expour of
The Energy for Photosynthesis. The chemical energy of the
sun's light, which causes these two substances to unite, is some-
thing that we know very little about, but is, nevertheless, a very
real and a very great force. We realize that the sun gives us light
to see by, and heat is evident enough, but when we think of how
it tans our skin, bleaches our clothes, and makes our photographs,
we have some evidences
of the chemical action
of light, though none of
these can compare with
the work done by these
same rays in the leaf
laboratory, during the
making of starch in the
plant.
This word photo-
synthesis can now be
better understood, mean-
ing as it does " union by
means of light," since it
is by the chemical power
of the light rays that
the water and carbon
dioxide are united.
The leaf is sometimes
compared to a mill in
which the power is the
sunlight; the machinery
is the chlorophyll; the
raw materials are the carbon dioxide and water; the product is
starch; and the waste material is oxygen.
The Waste Product. A benefit arising from photosynthesis
almost as important as the production of starch itself, is the libera-
tion of oxygen as a by-product. We have learned that every living
tissue breathes in oxygen. The resulting oxidation produces the
energy without which we could not live.
Absorbed by root
lotlc* th connsctlon
btwtn root hair* and duett
thence to I.T ( .
FIG. 26. Diagram of Plant Processes.
LEAF FUNCTIONS 99
We have also learned that this oxidation produces carbon di-
oxide which we throw off in respiration. Now we can see that the
plants use this discarded carbon dioxide for making their food,
and return to us the oxygen which is necessary for our life.
This is a glimpse of one of the great " circles of nature."
Other Leaf Functions. Starch making, while the most im-
portant, is not the only function of leaves. In their marvelous
chemical laboratory go on the processes of digestion, proteid manu-
facture, assimilation, respiration, and excretion of water (trans-
piration) . Digestion is necessary to put the food stuff into soluble
form so that it may act in osmosis and flow through the ducts.
As to proteid manufacture, little is known, except that the carbon,
hydrogen, and oxygen of the starch are combined with nitrogen,
sulphur, and phosphorus from the soil water in a way that we
cannot understand, much less imitate, and that proteids are the
result of the process. Assimilation is active in leaves and all other
living parts of the plant, since this is the process by which the
nutrients actually become part of the living protoplasm and tissue
of the organism. Respiration (oxidation) goes on wherever liv-
ing plant tissue is directly exposed to air; while less active than
in animals the process is just as essential, since it supplies the
energy which keeps the plant alive. Much extra water is absorbed
at times by the roots, in their transfer of nitrogen compounds and
mineral salts from the soil. The useful elements are used in food
making and the surplus water is passed off by way of the spongy
layer, air spaces, and stomata. This process is called transpiration
and differs from mere evaporation, in that the loss of water is
regulated by the stomata and so corresponds to the needs of the
plant. It does not depend upon the temperature alone, as does
evaporation.
We find in the leaf the processes of food manufacture, diges-
tion, and assimilation; these are building up, or constructive,
processes and require a supply of energy from the sun or the living
protoplasm to bring them about. This food is then united with
oxygen, thereby releasing this sun-given energy. It is this energy
which keeps the plant alive and permits it to grow. This last
100
BIOLOGY FOR BEGINNERS
process is, however, a destructive one as far as food and tissue are
concerned and necessitates excretion in order* to remove the waste.
/too t r/ CAT i ON of FUNCTION
FIG. 27. Modification of Function in Plant Parts.
The circles at the left represent the usual parts of the plant, those at the
right, the forms into which they may be modified, to perform the functions
named.
The usual function is connected with its plant part by a heavy line; those
less frequent by lighter lines. Thus the roots' normal function is absorption,
but it may be modified to form tendrils, spines, leaf supports, or for storage, as
the lines show.
This diagram is intended to show the wide range of adaptation of struc-
ture to function.
SUMMARY
1. Photosynthesis.
The manufacture of starch from carbon dioxide and water.
2. Digestion.
Making the food soluble by means of plant enzymes, such as,
Diastase j acting on sugars an( j starches.
Lipase, acting on fats.
Pepto-trypsin acting on proteids.
LEAF FUNCTIONS
3. Assimilation.
C, H, O, combined with N, S, P, etc., form proteids, etc.
4. Respiration.
Tissue and food plus oxygen = energy plus CO 2 .
5. Transpiration.
Giving off large excess of water.
The Leaf as a Factory
The factory Green leaves (or other green tissue).
The work rooms The cells of palisade and spongy layers.
The machines Chlorophyll grains and protoplasm.
The power Sunlight.
Materials Carbon dioxide and soil water.
Supply department Root hairs, ducts, air spaces, stomates.
Transportation dept. Ducts, bast tubes, pith rays.
Finished products Starch, sugar, proteids, tissues.
Waste product Oxygen.
. I Manufacturing dept. daylight only.
Hours of work
{ Transport and supply depts. day and night.
Comparison of Photosynthesis and Respiration
Photosynthesis Respiration
Constructive process Destructive process
Food and tissue accumulated Food frnd tissue used up
Energy taken in from sun Energy released
Carbon dioxide taken in Carbon dioxide given off
Oxygen given off Oxygen taken in
Complex compounds formed Simple compounds formed
Produces starch, etc. Produces CO 2 and H 2 O
Goes on only by day Goes on day or night
Only in presence of chlorophyll In all parts exposed to air
EXPERIMENTS WITH LEAVES
To show that Leaves (and Stems) turn toward Light. Two
thrifty plants are provided, one is placed in a light-tight box,
-102
"-BIOLOGY FOR BEGINNERS
with an opening at one side for light to enter. The other is placed
under the same conditions of heat and moisture, but is given light
from all sides.
The plant in the box will be found to turn toward the light and
to grow rapidly in that direction. However, its stem will be weaker
FIG. 28.
Coleus leaf showing green and Similar leaf treated with iodine, the
white areas, before treatment with starch reaction only showing where
iodine. the leaf was green. From Atkinson.
and slenderer, its leaves smaller and paler than the one with
uniform lighting.
This experiment shows the response that plants make to light,
and also the effect of a limited supply of light on their growth.
Every time we see the leaves of house plants turning toward the
window, we have a similar experiment in heliotropism. The
plant kept outside the dark box was used as a check for this ex-
periment.
LEAF FUNCTIONS 103
Photosynthesis. To show that Green Plants produce Starch.
Leaves can be taken from active green plants, scalded to kill the
protoplasm and release the chlorophyll, and soaked in alcohol
to remove the green color. Then, if tested with iodine, a dark blue
color is produced, showing that starch was present. The chlo-
rophyll had to be removed so that this blue could be seen. This
proves that starch was in the leaf. To prove that it is made there, by
the action of light on the chlorophyll, requires further experiment.
To show that chlorophyll is necessary, a leaf from a green and
white-leaved geranium may be used, as above, when it will be found
that little starch is revealed in the white portions.
To show that light is necessary, parts of an active leaf are cov-
ered with corks, pinned through, on both sides. After a few days
the covered portions will not yield, the starch test, while the ex-
posed parts will still do so. Another proof of the same thing is
to keep a plant entirely in the dark, as a check experiment, and
when it has become pale, test for starch, which will be found
lacking. Of course the same kind of plant, under the same con-
ditions, except the light, should be used in this and in the experi-
ment to be compared with it.
To show that Green Plants produce Oxygen. Oxygen is the
waste product of photosynthesis; it is thrown off when starch is
made. It is easier to collect a gas over water, hence a water plant
is used for this experiment, but all green plants carry on the same
process.
The water plant is submerged in a glass jar under a glass funnel,
whose stem is covered by a small test tube, filled with water and
inverted. The apparatus is set in the sun and soon bubbles of gas
will rise in the funnel and be collected in the tube. These, when
tested, prove to be oxygen. If carbon dioxide be dissolved in the
water, the process will go on faster, as carbon dioxide is one of
the materials used in photosynthesis, and that in the jar of water
is soon exhausted.
Another similar experiment ought to be set up in the dark, so as
to prove, again, that light is the source of energy for this very
important process.
104
BIOLOGY FOR BEGINNERS
To prove that the oxygen did not come from the water, another
check could be used, in which the apparatus was the same, but no
plant was present, in which case no oxygen would be produced.
In experimental work of this kind, the check experiments show
almost as much as the ones which actually " work." Merely stat-
ing that the water plant was put under the funnel, and that oxygen
was produced, would not
prove anything. It would
be asked " How do you
know that the oxygen came
from the plant? " and
" How do you know that
light had anything to do with the
process? " both of which questions
are answered by the " checks."
Transpiration. To show that
Plants pass off Water Vapor. A
thrifty cutting is tightly sealed into
a bottle of water and placed under
a bell jar; another similar bell jar
is set alongside, containing no plant.
Water drops will soon be seen on
FIG. 29. Bubbles of gas will rise . ...
in the funnel. From Atkinson. the mslde of the J ar Wlth the P lant >
none on the other. As the bottle
was sealed, no water could escape, except such as passed through
the leaves of the plant. As the empty jar showed no water, it did
not merely condense from the air, hence must have been passed
off by the leaves. A potted plant could be used, but the pot and
earth surface would have to be wrapped in oiled paper or sheet
rubber, to prevent evaporation.
To show which surface of a leaf gives off this water vapor, two
watch glasses can be fastened, one on either side of a leaf. More
water will be found to condense on the glass fastened to the lower
surface, showing that transpiration is more active here. This is
as one would expect, since here the stomata are more numerous.
Cobalt paper, which turns pink when moist, can also be fastened
LEAF FUNCTIONS
105
to the upper and lower surfaces of a leaf, and will show the same
result.
Thus the end products of all these processes are the carbon
dioxide and water, with which the photosynthesis started. The
oxygen involved in the destructive processes is the by-product
of photosynthesis, so that all three elements, carbon, hydrogen,
and oxygen pursue a circular course.
FIG. 30.
FIG. 31.
Figure 30 shows plant with pot sealed, but giving off water vapor which
has condensed on bell jar.
Figure 31. Left-hand figure, shows plant with sealed pot, giving off water
vapor enough to turn the cobalt paper pink within fifteen minutes. The right-
hand figure is a check experiment, to show that the moisture in the air would
not cause the change in the same time. From Atkinson.
COLLATERAL READING
Plant Relations, Coulter, pp. 148-161; Botany for Schools, Atkinson,
pp. 90-116; Elementary Botany, Atkinson, pp. 53-70; First Studies in
Plant Life, Atkinson, pp. 121-125; Lessons in Botany, Atkinson, pp.
70-72; Experiments in Plants, Osterhout, pp. 191-202; Biology Text,
Hunter, pp. 132-134; Essentials of Biology, Hunter, pp. 115-132; Intro-
duction to Biology, Bigelow, pp. 55-75; Plant Life and its Uses, Coulter,
pp. 218-234; The Great World's Farm, Gaye, pp. 157-176; The Story of
the Plants, Allen, pp. 33-53; Textbook of Botany, Gray, pp. 85-110.
106
BIOLOGY FOR BEGINNERS
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LEAF FUNCTIONS
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CHAPTER XIV
FLOWERS: POLLENATION AND FERTILIZATION
Vocabulary
Pollenation, transference of pollen from anther to stigma.
Fertilization, union of sperm nucleus and ovule nucleus to form
the embryo.
Conspicuous, noticeable.
Glands, organs for secretion of any liquid, as nectar glands.
Nectar, a sweet liquid secreted by plants to attract insects. Bees
make it into honey; plants do not secrete honey.
Learn names of flower parts from the text.
If we refer to the list of life functions it will be seen that we
have dealt with all of them except reproduction. All the others
have had to do with the life of one individual plant, its food getting,
energy production, or waste removal. Now we have to do with a
function as important as all the rest, the propagation of new
individuals.
The Function of the Flower. In most of the common plants
the flower is the organ whose function is reproduction, and, while
there are other methods, we shall deal with the commonest one
first, since it is found in at least 130,000 different kinds of plants.
The final product of the flower is the seed. To produce the
seed, fertilization must take place and to cause fertilization, pol-
lenation must precede it. While these terms will be made plain
later, we can remember that the flower is provided with means
for securing pollenation, fertilization, and seed production.
Structure of the Flower. We will take for an example the ge-
ranium, either a " single " flowered house species or the common
wild geranium, which though different as to genus, is still suffi-
ciently similar for our purpose. As we look at the flower from
the rear, or stem side, we will see a row of small green, leaf-like
108
FLOWERS: POLLEN ATION AND FERTILIZATION 109
organs called the sepals. This is the calyx. Its function is to pro-
tect the flower in the bud condition and to help support the other
parts when it opens.
Inside the calyx comes the corolla consisting of a row of colored
parts called petals. These are often for the attraction of insects
as we shall see when studying
pollenation, and may also
help to protect the inner and
more essential parts.
Next inside the corolla
we will come to several
knobbed, hair-like organs.
These are the stamens. The
knobs at their tops (anthers)
are very important, as they
produce and scatter a yellow,
dust-like substance known as
pollen. They are placed on
these thread-like supports
(filaments) so that the pollen
will have a better chance to
be distributed.
In the very center of the
flower is the pistil consisting
of a sticky knob at the top
(stigma) to catch pollen, a
slender stalk (style) to support the stigma, and an enlarged portion
at .the base (ovary) which contains the undeveloped seeds (ovules)
and later develops into the fruit.
Pollenation. In order that a flower may produce seed, the pollen
must be transferred from the anther to the stigma, and usually it
must be from the anther of one flower to the stigma of another of
the same kind. This transfer of pollen from anther to stigma is
called pollenation. If, as in most cases, it is between different
flowers, it is called cross pollenation and is the process for which the
flower parts are adapted. Insects and wind are the two chief
S. $,**!.. (CM
P. ftTAi., ft
STYLt
OvAftr
OVULES
FIG. 32. The flower is provided with
means for seed production.
110 BIOLOGY FOR BEGINNERS
agents in pollenation and there is no process for which more curi-
ous adaptations have been developed. We shall deal first with
those that fit the flower for pollenation by insects.
Adaptations for Insect Pollenation. The bee and the flower are
associated in our minds, of course, but it is not so commonly realized
that one could not exist without the other, and that many other
insects, besides bees, are just as closely concerned.
The insect comes to get its food from the sugary nectar which
is secreted at the base of the petals ; in getting this, its body catches
some of the pollen from the stamens which are shaped for this
purpose. When the insect visits the next flower some pollen is sure
to be rubbed off on the pistil of that flower, and a new supply
FIG. 33. Hawk-moth posed before a jimson-weed, Datura stramonium (after
Stevens; one-half natural size).
brushed from the stamens as it crawls out. In this way pollena-
tion is accomplished.
In order that the insects may surely see each flower, they have
developed conspicuously colored corolla and attractive odors.
They often grow in clusters so as to be easily noticed and visited.
After the insect arrives, not only does it find a reward of nectar,
but often the flower is shaped to provide a convenient landing
place. Colored lines lead to the nectar glands. Stamens and
pistils hold their anthers and stigmas in just the proper position so
that pollen shall be transferred while the insect is obtaining its
sweet reward for unintended labors.
Nearly every flower has a slightly different scheme for cross
pollenation. When we find one with irregular-shaped corolla, we
FLOWERS: POLLENATION AND FERTILIZATION 111
may be almost sure that some special adaptation for insect visitors
stands behind the curious shape.
Adaptations for Wind Pollenation. Flowers which depend on
wind for their pollenation are very differently adapted. They
produce enormous quantities of pollen, but they have no nectar
or odor. Their pistil is usually large to catch the flying pollen,
and they secure access to the wind by having very small corollas
and by producing their flowers above the leaves of the plant.
FIG. 34. Salvia-flower.
A, showing position of pistil and stamens;
B, anthers of stamens in normal position;
C, anthers of stamens tipped down;
D, bee entering flower;
E, flower, natural condition.
(After Lubbock, natural size.)
Many grasses and sedges and all the evergreen trees have their
pollen distributed by the wind. In fact, near large pine forests
the yellow pollen fills the air and covers the ground at certain
seasons, forming what people call " sulphur showers."
Protection of Pollen. Since pollen is absolutely necessary to the
plant, it has to be protected from rain and from insects which
would eat it and from those which are too small or too smooth-
bodied to carry it. Protection against rain and dew is secured by
the drooping or closing of the corolla, while unwelcome insect
112 BIOLOGY FOR BEGINNERS
visitors are kept out by hairy or sticky coatings on stem and
calyx or on the inside of the corolla.
Essential Organs. Notice that the only organs absolutely needed
FIG. 35. Spartium, showing the dusting of the pollen through the opening
keels on the under side of an insect. (From Kerner and Oliver, see Kellogg.)
to produce seeds are the stamens and pistil. Hence they are called
the " essential organs." The corolla and calyx have, as their
function, the protection of these essential organs and the securing
of pollenation.
FLOWERS: POLLENATION AND FERTILIZATION 113
The pollen grain from the anther and the ovule in the ovary
are actually the most necessary factors in the process of reproduc-
tion and must now be dealt with more completely.
FIG. 36. Seed Development.
Part I. Pollenation
Fig. 1. The stamen is shown with part of the filament, and the anther open-
ing to set free the pollen. This may be transported either-by wind or insects,
to the stigma of the pistil of a similar kind of flower, shown in Fig. 2.
After arriving there, the pollen develops a long tubular cell which reaches
clear to the ovary, down the whole length of the style, even though it be as
long as a "silk" of corn.
The development of this tube, and the passage of the sperm nucleus from
the pollen, down it, are shown here, though they are really steps in fertilization.
Pollenation is really the mere transfer of the pollen.
Part II. Fertilization.
Fig. 1. The pollen tube is entering the micropyle and the sperm nucleus is
at its lower end. Note the ovule nucleus, with which it is to unite. Both one-
celled stages.
Fig. 2. The sperm nucleus has passed out of the pollen tube and is approach-
ing the ovule nucleus.
Fig. 3. The sperm and ovule nuclei have united; this is the actual fer-
tilization, from which the development of the embryo begins.
Fig. 4, 5 and 6 show stages in the early cell divisions as the embryo develops.
Fig. 7 shows the matured seed. The parts of the embryo have gone as far
as they will till germination commences. Extra stored food remains unused
outside, as endosperm.
114 BIOLOGY FOR BEGINNERS
Pollen Structure. The pollen grain is at first a single cell but
if transferred to the stigma of a flower of its own kind, it begins to
grow, forming three cells, one of which develops into a very long
tube which reaches from stigma to ovary, no matter how long
that may be. The other two cells, containing the most active
kind of protoplasm, are called the sperm or male cells, and their
union with the ovule is called fertilization and produces the
embryo in the seed.
Ovule Structure. The ovules (undeveloped seeds) are protected
inside the ovary and can be reached only by way of the pollen tube
from pollen grains on the stigma. They are much larger and more
complicated than the pollen grains. Each ovule in the ovary has
a protective covering which later becomes the testa of the seed.
Within this is the nucleus of the ovule cell which divides into eight
cells, two of which form the endosperm and one, the most im-
portant, becomes the egg or female cell. As has been said, the
pollen tube grows downward through the style till it reaches the
place where an ovule is attached to the ovary wall ; near this point
of attachment is an opening through the ovule coats, called the
micropyle, and through this the pollen tube makes its way till it
reaches the egg cell within.
Fertilization. The sperm cell then passes down the pollen tube
and unites with the protoplasm of the egg nucleus. This union of
the sperm nucleus of the pollen with the egg nucleus of the ovule
is called fertilization. The fertilized egg now has the very re-
markable power to grow, and from its one cell, to develop the
countless numbers which go to make up the embryo within the
seed and finally the whole new plant. Notice that in this wonder-
ful process each plant is reduced to a single cell, the sperm or
the egg, that they unite and again form a single cell, and that
from this develop the embryo and the whole organism.
Fertilization is essentially the same in both plant and animal so
you must try to think of all living things as having developed from
a single fertilized egg cell.
Origin of Seed Parts. Look back at Chapter VI and notice
that we have just been studying the origin of all parts mentioned
FLOWERS: POLLENATION AND FERTILIZATION 115
in the structure of the seed: the ovule walls become the testa and
tegumen; the opening for the pollen tube is the micropyle; the
fertilized egg develops into the embryo, and the endosperm nuclei
produce the endosperm.
The embryo may develop, to a great extent within the seed and
use all the endosperm, or it may develop but little and leave un-
used endosperm for the germination process. In either case it was
present at one time.
Notice that the seed stage is only a pause in the continuous
circle of growth. The parent plants produce the pollen and ovules;
these produce sperm and egg; both grow and finally unite. The
embryo is formed and grows more or less within the seed, then
merely waits and rests till it shall have conditions favorable for
continuing its growth to an adult plant, again. In this way the
life cycle is completed. The parents die but parts of their actual
protoplasm live on, forever, in the new generation.
COLLATERAL READING
POLLENATION
Cross and Self Fertilization in the Vegetable Kingdom, Darwin; The
Great World's Farm, Gaye, pp. 208-214; With the Wild Flowers, Hardinge,
pp. 47-55; Ten New England Blossoms, Weed, pp. 1-17, 90-98; Beauties
of Nature, Lubbock, pp. 117-138; The Fairy Land of Science, Buckley,
p. 212-237; Elementary Studies in Botany, Coulter, pp. 151-166; Plant
Life and Uses, Coulter, pp. 301-322; Natural History of Plants, Kerner
and Oliver, Vol. II, Part 1, pp. 129-283, 426-436, Part 2, 833-840, 862-866;
Experiments in Plants, Osterhout, pp. 286-311; Plants and their Children,
Dana, pp. 187-255; The Living Plant, Ganong, pp. 303-326; Practical
Biology, Smallwood, pp. 296-308; The Story of Plants, Allen, pp. 73-135;
Outline of Botany, Leavitt, pp. 120-127; Textbook of Botany, Bessey,
p. 421; Textbook of Botany, Strasburger, pp. 281-283; Plant Rela-
tions, Coulter, pp. 123-137; . Introduction to Botany, Stevens, pp.
166-201; Plant Structures, Coulter, p. 181; Nature and Work of
Plants, McDougal, pp. 149-153; Lessons in Botany, Atkinson, pp. 192-
193; Elementary Botany, Atkinson, pp. 351-367; Botany for Schools,
Atkinson, pp. 167-181; Elementary Biology, Peabody and Hunt, pp.
74-88; Flowers, Fruits and Leaves, Lubbock, pp. 1-44; Plant Life, Step,
pp. 35-58; Wonders of Plant Life, Herrick, pp. 149-173; Blossom Hosts
and Insect Guests, Gibson, entire; Flowers and their Friends, pp. 121-133;
231-239; Fertilization in the Vegetable Kingdom, Darwin, pp. 356-414,
116 BIOLOGY FOR BEGINNERS
FERTILIZATION
Botany for Schools, Atkinson, pp. 182-186; Elementary Biology, Peabody
and Hunt, pp. 74-88.
FLOWER STRUCTURE
Plant Structures, Coulter, pp. 218-231; Lessons with Plants, Bailey, pp.
131-150; Botany for Schools, Atkinson, pp. 140-166; Elementary Biology,
Peabody and Hunt, pp. 70-74; Plant Life and Uses, Coulter, pp. 258-300;
Applied Biology, Bigelow, pp. 196-213.
SUMMARY
Function of flower, reproduction by means of seeds.
Steps in seed production.
1. Pollenation.
2. Fertilization.
3. Growth of embryo in seed.
Flower parts. Function.
Calyx (sepals) Protection and support.
Corolla (petals) Insect attraction for pollenation.
Protection of essential organs.
Stamens,
Anther Production of pollen.
Filament Support of anther for pollenation.
Pistil,
Stigma To catch pollen: sticky, sometimes
large.
Style To support stigma so as to catch
pollen.
Ovary Contains ovules, forms fruit.
Pollenation.
Definition. Meaning of "cross-pollenation."
Means for pollenation:
Insects (clover, etc.)
Adaptations for insect pollenation.
. Nectar, Odor,
Bright color, Growth in clusters,
Landing places, Special shapes.
Wind (pine, corn, grasses, etc.)
Adaptations for wind pollenation.
Flowers high above leaves, not conspicuous.
Petals and sepals small or lacking.
Pistils large and sticky.
Abundant pollen (why?)
No nectar nor odor.
FLOWERS: POLLENATION AND FERTILIZATION 117
Pollen protection.
From rain by closing or drooping of flower.
From unwelcome insects by sticky stems or hairy flowers.
Essential organs.
What are they?
Why so called?
Fertilization.
Definition: union of sperm nucleus of pollen with egg nucleus of the ovule.
Pollen.
1. Produced by stamen (anther).
2. Structure: one-cell stage.
Three cell stage.
Pollen tube (use ?).
Sperm cells (use ?).
Ovule.
1. Produced in the ovary: undeveloped seed.
2. Structure: coverings (seed coats later).
One-cell stage.
Eight-cell stage.
Two cells from endosperm. *
One forms egg cell, proper.
Fertilization.
1. Pollen tube penetrates micropyle.
2. Sperm cell passes down pollen tube.
3. Nuclei of sperm and egg unite (fertilization proper).
4. Embryo begins to develop.
Origin of seed parts.
1. Ovule walls become seed coats.
2. Opening for pollen tube is the micropyle.'
3. Fertilized egg becomes the embryo.
4. Endosperm nuclei become the endosperm.
Endosperm may be used by developing embryo.
Endosperm may remain to be used in germination.
CHAPTER XV
FRUITS AND THEIR USES
Vocabulary
Matured, fully developed.
Infinite, endless.
Superficial, careless.
Relatively, comparatively.
While the seeds are developing, the ovary grows also, and the
final result is what we call a fruit. This does not necessarily mean
" fruit " in the sense of a fleshy edible product, but applies to
the seed-holding organ of any plant. A fruit may be denned as
the matured ovary, its contents, and all intimately connected
parts. Thus a fruit may consist of a single ovary with only one
seed, as in grains, nuts, cherries, or plums, or it may develop from
a single ovary which has several seeds, as in pansy, pea, poppy,
or apple. On the other hand there are many flowers which have
several ovaries. These combine to form compound fruits like the
strawberry or raspberry. Fruits may therefore be either dry or
fleshy, simple or compound, depending on the character and de-
velopment of the ovary which formed them.
Types of Fruits. The peach is a good example of a one-celled,
simple, fleshy fruit. In it the ovary wall develops two parts, an
outer fleshy layer and the hard inner " stone " which encloses the
seed. Such a fruit is called a stone fruit.
The apple develops from a five-celled ovary which forms the
core. Outside of this is a fleshy region, usually bounded by a faint
line which is probably the fleshy ovary wall, or may be an enlarged
receptacle. Outside of this is the bulk of the apple, which is a
greatly thickened calyx, as is indicated by the five tiny sepal tips
which persist at the blossom end. Inside these tips the dried sta-
118
FRUITS AND THEIR USES 119
mens and pistil may sometimes be found. A section through an
apple shows the outer skin, the calyx layer, the fleshy ovary wall,
the hard ovary wall and the seeds attached to the central axis,
with their points toward the stem. A fruit of this type is called
a pome and is represented by the apple, pear, quince, and
medlar.
The bean pod is a type of a many-seeded dry fruit, called a
legume. At the stem end may be found the remains of the calyx
lobes. The bulk of the pod is the ovary; the pointed tip is the style,
on which the stigma may sometimes be found in young pods, as a
tiny knob. The " string " is a vascular bundle bringing nourish-
ment to the growing ovules, which are attached along one side of
the pod. Their point of attachment is called the placenta, and the
scar left on the seed, when it is removed, is the hilum. The bean
fruit thus includes mainly the greatly enlarged ovary and its con-
tents, with the style and possibly the stigma also..
Functions of Fruits. The chief functions of fruits are to protect
the ovules and seeds from attack by insects, or fungous spores; to
prevent loss of water; and to provide for dispersal. To provide
for these purposes the ovary develops in various ways. Tufts of
hair, wings, or hooks may be produced to aid in dispersal. Tough
shells or rinds may form for protection as in nuts or lemons. De-
licious flesh may envelop the hard inner stone, tempting animals
to eat the fruit and discard the seed at a distance from the parent
tree. The peach or cherry are examples of this. In addition to
the developments of the ovary wall, the calyx may become
fleshy and envelop the ovary as in apples and pears. In other
cases the end of the stem (receptacle) enlarges and becomes
a part of the fruit, as in the case of the strawberry and
blackberry.
Seed Dispersal. That the ovary wall protects the seeds from
insect attack, drought, decay, and weather is plain enough, but
how the other function, dispersal, is accomplished may not be so
evident. The most superficial observation of any common plant,
such as the dandelion, will reveal two facts: (1) an enormous num-
ber of seeds are produced and (2) each full-grown plant requires a
120
BIOLOGY FOR BEGINNERS
FIG. 37. Fruit Structure.
Figs. 1 and 2. The Apple. These drawings are diagrammatic, but intend
to show the origin and structure of the regions in one of the more complicated
fleshy fruits.
The outer region, (A) is probably the greatly thickened calyx, as the per-
sistance of the five calyx tips at the blossom end would indicate. However
some botanists consider it to be an enlarged end of the stem called the re-
ceptacle, which has carried up the calyx lobes with its growth.
The region (B) shows in most apples by being separated from (A) by a faint
line or row of dots. This is the fleshy outer wall of the ovary. Inside of this
region is where "water cores" sometimes develop.
(C) is the real "core" of the apple, tough and leathery enclosing the seeds(D).
This core has five chambers or cells enclosing one or more seeds. Running
through the center is a tough axis to which the seeds are attached, with their
points toward the stem end.
These same parts are shown in the cross section, and the seeds are cut in
two which shows the two cotyledons in each.
In the cavity at the blossom end may sometimes be found the dried up
remains of the stigma and stamens.
The parts included in the apple are the calyx and ovary at least, and pos-
sibly others.
FRUITS AND THEIR USES 121
Figs. 3 and 4. The Bean. This is a typical dry fruit with several seeds,
which opens to scatter them.
It consists of the fully developed pistil, the bulk being the greatly enlarged
ovary, with the stigma reduced to the tapering tip, and the stigma usually
fallen off in a fully matured pod.
The "string" which we remove in preparing for food, is a duct bundle that
brought nourishment to the ovules and reached each by way of the hilum.
The point of attachment to the pod is the placenta, (P) and shows in both
drawings.
The pod is the thickened ovary wall (O), and at its base the shriveled calyx
is sometimes found.
The cross section shows a seed cut across, displaying the seed coats (C),
and the two cotyledons (Cot.).
relatively large amount of room. Evidently, then, the seeds must
be scattered if they are to survive, and usually those plants pro-
ducing most seeds or needing most room best attend to this matter
of seed dispersal. There is scarcely a more interesting chapter in
biology than this one which deals with the wonderful adaptations
by which seeds, though having no power of locomotion, still manage
to transport themselves long distances and in great numbers.
Plants use the wind, water, animals, and various mechanical
schemes to scatter their seeds. Sometimes it is the seed by itself
which is transported, sometimes the whole fruit, but the end is the
same, to get a new place where there shall be space, food, light,
and moisture for the development of the waiting embryo.
Adaptation for Wind Dispersal. Adaptations for wind dispersal
are found in the tufts of down on thistle and dandelion fruits and
milkweed seed, in the wings on the fruits of elm, ash, or maple, or
on the seeds of the catalpa or pine.
Adaptations for Dispersal by Animals. Burs and hooks, as in
burdock and " pitchforks," enable the fruits to steal rides on
animals and man, and get themselves picked or shaken off at great
distances. The delicious flesh of peach or apple, grape or berry is
merely a sort of bribe to reward some animal for carrying off the
fruit. The seeds of all such are indigestible and so are carried far
from the parent plant. It is noteworthy that unripe fruits are usu-
ally poisonous or bad tasting. Thus they are not eaten before
the seed is ready for dispersal.
122
BIOLOGY FOR BEGINNERS
Seed dispersal.
No. 1. Maple "key," one of a pair of fruits which separate as they fall.
They whirl in a horizontal plane, and so fall slowly and are blown to some dis-
tance. The heavy end works down to the ground, giving the enclosed seed a
chance to germinate.
No. 2. Pine seed. Not a fruit, like the maple, though dispersed in the
same way. Shaken out of the cone when ripe.
No. 3. The Bass-wood. A group of fruits, with a parachute which lets
them fall slowly and so reach some distance, also it will drag them some farther
after alighting, especially on a "crust" in the winter.
No. 4, Clematis and No. 5, the Dandelion, are both fruits with parachutes
made of downy hairs. The Milkweed has a similar device on its seed.
No. 6, the Bladder-nut and No. 7, a Sedge, are both provided with water-
tight life preservers, which float the seeds to distant landing places. Bladder-
nut is also light enough to blow.
No. 8. The Poppy fruit, has many tiny openings at the top of its "pepper
box" capsule. The stem is stiff and springy and the small heavy seeds whip
out in the wind, a few at a time, assuring at least some of them, favorable
conditions.
FRUITS AND THEIR USES 123
No. 9. The Pea, a type of all the family, which throws out the seeds by the
twisting of the pod, as it dries.
No. 10. The Wild Geranium, slings its seeds, as the pod splits upward.
No. 11, the Violet and No. 14, the Witch-hazel, pinch their seeds out, as the
pod dries and closes together.
No. 12, the "Pitch-fork" and No. 13, Desmodium, catch on animals, by
their hooks, and are thus scattered.
Dispersal by Water. A considerable number of plants secure
dispersal by having fruits that float, without absorbing water,
FIG. 39. Milkweed (Asdepias cornilu) dissemination of seed. From
Atkinson.
and so are carried by rivers or ocean currents to favorable places
along the shore. Sedges and coconuts are examples of this type.
Mechanical Dispersal. Some of the most curious adaptations for
seed dispersal are the mechanical devices by which seeds are thrown
from the pods for a considerable distance. The touch-me-not,
124
BIOLOGY FOR BEGINNERS
whose pod explodes when ripe; the witch hazel, which pinches
the seed between the open ovary walls till it shoots out; the tall
stalked mullein and poppy, which whip in the wind and sling their
fine heavy seeds far away are examples of this interesting type.
FIG. 40. Seed distribution of Virgin's Bower (clematis). From Atkinson.
Economic Importance of Fruits. So far as the plant is concerned,
the object of the fruit is to secure reproduction by providing the
enclosed seeds with protection and transportation. However, man
has learned to depend upon fruits for food and other uses, so
FRUITS AND THEIR USES 125
that they are the most important part of the plant for his
purposes.
To begin with, we must remember that the grains, such as wheat,
rice, and corn, are fruits and not merely seeds as we commonly
think. These furnish more food than all other plant parts, com-
bined. Then there are the fleshy fruits like the apple, orange,
grape, and peach which we use raw, cooked, and canned, and
from which many other food products are manufactured. From
the downy contents of the cotton boll we obtain that most essential
fiber, which nature intended to help in dispersing the seed.
On the other hand, the fruits of some weeds are altogether too
efficient in their methods of dispersal, and we have to fight the
spread of plants like the dandelion, hawk weed, burdock, and
thistle. Some fruits are poisonous, presumably better to protect
the seeds, and these occasionally do harm to man; among them
may be mentioned the Jimson weed, night-shade, and water hem-
lock.
COLLATERAL READING
Seed Dispersal, Beal, entire; Little Wanderers, Morley, entire; Plant
Relations, Coulter, pp. 112-122; Introduction to Botany, Stevens, pp.
207-217; Plant Structures, Coulter, pp. 210-215; The World's Great Farm,
Gaye, Chap. 17 and 18; Textbook of Botany, Strasburger, pp. 288-291;
Lessons in Botany, Atkinson, pp. 292-299; Elementary Botany, Atkinson,
pp. 368-373; Lessons with Plants, Bailey, pp. 336-341; Plants and their
Children, Dana, pp. 50-73; Botany for Schools, Atkinson, pp. 198-205;
Flowers, Fruits and Leaves, Lubbock, pp. 45-96; Natural History of Plants,
Kerner and Oliver, Vol. II, Part 2, pp. 833-878; Elementary Studies in
Botany, Coulter, pp. 167-186; Experiments in Plants, Osterhout, pp. 312-
325; With the Wild Flowers, Hardinge, pp. 202-216; The Story of the
Plants, Allen, pp. 149-161; The Living Plant, Ganong, pp. 378-402.
SUMMARY
1. Definition of Fruit
2. Types of fruits.
Stone fruit, one-celled, fleshy (peach).
Pome, many -celled, fleshy (apple).
Grain or nut, one-celled, dry (corn, pecan)
Legume, many-celled, dry (bean).
3. Functions of fruits.
Protection.
Dispersal.
126 BIOLOGY FOR BEGINNERS
4. Dispersal.
Reason for dispersal.
Means of dispersal:
1. Wind, adaptations for wind dispersal.
Tufts of down (dandelion, thistle).
Wings (maple, ash, elm).
2. Animals, adaptations for animal dispersal.
Burs (burdock).
Hooks ("pitchforks").
Edible flesh (peach).
Hard or bitter "pits" (why?)
Bad tasting when unripe (why?)
3. Water.
4. Mechanical devices.
Explosive fruits (touch-me-not).
Pinching fruits (witch hazel).
Whipping fruits (poppy, mullein).
5. Economic Importance.
Plant propagation.
Food supply (cereals and fleshy fruits).
Cotton fiber.
Harmful weed seeds.
Poisonous fruits.
CHAPTER XVI
SPORE-BEARING PLANTS
Vocabulary
Complicated, not simple in structure.
Parasite, plant or animal which obtains nourishment at the ex-
pense of another.
Scavengers, destroyers of waste matter.
The majority of plants with which we are familiar obtain food,
grow and reproduce by root, leaf, flower, and fruit, just as we
have been learning, but there are a large number of important,
but less conspicuous, forms that have no flowers, and so produce
no seeds. These flowerless plants reproduce by single cells called
spores which, by a more or less complicated process, develop into
the plant again.
Classification of Spore Plants. The simplest of these flower-
less plants are the algae, which may consist of only one cell as in
pleurococcus which forms the green coating often seen on stones,
bark, and old fences, or they may grow to large, many celled forms,
such as the sea weeds, or from the green mats of pond scum
(Spirogyra) that cover our ponds. The fungi are another large
group of spore plants which have no chlorophyll and hence have
to depend on other plants or animals for organic food. They are
parasites, and among them we find mushrooms, puff balls, moulds,
yeast, and bacteria. The next group, lichens, are really organisms
consisting of algae and fungi living together as one plant and are
familiar as the variously colored, flat, scaly forms that grow in
patches on rocks and trees. More familiar still are the mosses
forming the green carpet of the woods, and finally we come to the
largest and most complicated of the spore plants, the ferns and
their relatives, the horse-tails and ground-pines.
127
128
BIOLOGY FOR BEGINNERS
While it is not necessary to learn these names or figures, the fol-
lowing table will show you how large and varied the plant kingdom
really is and how few we know of its members.
FIG. 41. Rock lichen (Parmelia contigua). From Atkinson.
Flowering plants, spermatophytes (producing seeds) :
True flowering plants and \
Pines and their relatives / 130 ' 00
Flowerless plants (producing spores) 96,600 kinds
Thallophytes (algae and fungi) :
Algae 16,000 kinds
Fungi v 55,000 kinds
Bryophytes (mosses and their relatives) 16,500 kinds
Lichens 5,600 kinds
Ferns 3,500 kinds
SPORE-BEARING PLANTS 129
The Fungi. With the exception of the fungi, all these plants
have chlorophyll and so can make their own starch foods; but
this particular group has developed the habit of taking its food
from other plants or animals, either dead or alive, and so are called
parasites. This parasitic habit crops out occasionally in the
flowering plants, also, such as the Indian pipe and beech drops
but they, as well as all the fungi, pay a twofold penalty for their
laziness.
Results of Parasitic Habit. When a plant or animal ceases to
use an organ that organ degenerates, and the plant or animal
loses the ability to use it. So it is with the fungi; they can no
longer make their own organic food, and are totally dependent on
others for their life. They have to produce millions of spores,
since only a few can hope to survive.
Many fungi perform a useful function in nature by using dead
organic tissue for their food, thus acting as scavengers. They
also convert such useless matter into food materials which the
higher plants can use again. Fungi that feed on dead organic
tissue may be useful as scavengers, but unfortunately this dead
tissue may also be needed by man for food. The fungi that at-
tack our stored meats and vegetables cause a great deal of loss
and expense.
Because of this habit, the fungi bear a peculiar and important
relation to other plants and animals, and especially to man. There-
fore we shall deal with them as an example of the spore-producing
type of plants.
Examples of Fungi. The mushrooms are the largest fungous
forms and while some few are edible the majority are useless for
food. Many are poisonous, and the shelf -shaped mushrooms found
on trees do enormous damage to timber. Just a word of warning
at this point: a " toad stool " is merely a name that some people
attach to poisonous mushrooms. There is really no such dif-
ference. No " rule " or " sign " can be given by which you may
distinguish poisonous forms. Their food value is very slight while
the poison of the harmful forms is usually fatal. Bearing this in
mind there is but one conclusion, either learn to recognize one or
130
BIOLOGY FOR BEGINNERS
two edible kinds and use them only, or leave them all severely
alone as food.
Another class of the fungi includes the rusts and smuts which
attack grains, corn, and other grasses, doing enormous damage
to crops. Mildew is a common fungus whose chief harm is the
causing of rot in potato and similar crops, and destruction of grapes
and other fruits. Molds are also familiar forms which thrive upon
FIG. 42. Colonies of budding yeast cells (Sedgewick and Wilson)
From Calkins.
food stuffs, bread, meats, canned fruits, and even wood and paper,
if conditions are such that their spores can germinate.
Yeast plants are a still simpler class of fungi. We use them so
commonly that we hardly realize that they are plants at all. Yeast,
however, is a true one-celled plant, living on dilute sugar solutions
which it changes to alcohol. It sets free carbon dioxide gas as a
waste product. Thus yeast is used in two very different kinds of
SPORE-BEARING PLANTS 131
industry, the manufacture of alcoholic liquors, where the alcohol
is the desired product, and in the making of bread, where the car-
bon dioxide is required to make the loaf " light " by its expansion.
Yeast consists of single oval cells. It reproduces very rapidly if
kept warm and moist and supplied with sugar for food. Buds
develop on each parent cell and soon become full-sized cells which
again reproduce, the process being extremely rapid. A loaf of
bread is the product of at least two very different kinds of plants,
(1) the complicated wheat plant whose store of starch we make into
flour and (2) the simple yeast which helps to make it palatable.
We have left till the last the most important member of the
fungous group the bacteria. They are of such vast influence
both for good and harm, that the next chapter will be entirely de-
voted to them.
COLLATERAL READING
Applied Biology, Bigelow, pp. 232-297; General Biology', Sedgwick and
Wilson, pp. 184-191 (yeast); Practical Biology, Smallwood, pp. 338-375;
Elementary Biology, Peabody and Hunt, pp. 140-153; Essentials of Biology,
Hunter, pp. 170-189; The Science of Plant Life, Transeau, pp. 234-292;
Plant Life and Plant Uses, Coulter, pp. 360-410; College Botany, Atkinson,
pp. 137-291.
SUMMARY
Plants in general.
Seed plants.
Spore plants. Examples
Algae pond scums, sea weeds, etc.
Fungi mushrooms, toadstools, molds
Lichens rock and bark patches
Mosses common mosses
Ferns common ferns
Horse-tails
Ground-pines
Fungi as typical spore plants.
No chlorophyll. Consequence.
Parasitic habit:
Result to plant itself: degeneration: dependence.
Result to other living organisms:
1. Harm to hosts
2. Destruction of food
3. Value as scavengers
132 BIOLOGY FOR BEGINNERS
Examples of fungi:
Mushrooms, some edible, cf . " toadstools "
some poisonous
harmful to timber, etc.
Mildews, cause rot in potato, etc.
Molds, attack bread, meats, cheese, etc.
Yeasts, structure, oval cells
growth, by budding
conditions for growth:
moisture
warmth
food
food, sugars
products, alcohol and carbon dioxide
uses, bread and beer
CHAPTER XVII
BACTERIA
Vocabulary
Sterilized, treated so as to kill all germs, either by heat or chemicals.
Culture medium, a substance prepared for growth of bacteria.
Peptone, soluble form of proteid.
Inoculation, intentional infection with germs.
Immunity, a condition in which the body is not affected by bac-
terial attack.
Indispensable, very necessary.
Bacteria are very minute, one-celled, parasitic fungous plants.
There are many kinds but they are sometimes classified into three
groups according to their shape.
1. Coccus forms round
2. Bacillus forms oblong
3. Spirillium spiral and curved
Do not forget that certain one -celled, parasitic animal forms also
cause disease so that when we speak of the germ or microbe, it may
mean either a plant or animal parasite, but when bacteria are
mentioned, only the plant forms are included. Another point to
bear in mind is that not all bacteria are harmful nor are all infec-
tious diseases due to bacteria.
Bacteria are very small, one ten thousandth to one fifty thou-
sandth of an inch in diameter. Some are so minute that they can
neither be caught by a filter nor seen by a microscope.
Reproduction. Bacteria, since they have but one cell, absorb
food and excrete waste directly. Under favorable conditions of
food supply, temperature, and moisture, they reproduce with
enormous rapidity, so that one of these microscopic cells would,
if unchecked, produce a mass of bacteria weighing 7000 tons in
133
134
BIOLOGY FOR BEGINNERS
TYPS
TYPE .
FIG. 43. Some forms of useful and of harmful bacteria. (Greatly
enlarged.)
BACTERIA 135
three days. Fortunately this rate is never maintained because the
food supply soon becomes exhausted, or their own excreted waste
matters check their rapid growth. The tuberculosis bacterium
divides every thirty minutes; compute the possible number pro-
duced per day.
Occurence. Bacteria are found almost everywhere in air, water,
soil, food, inside plant and animal bodies whether dead or alive,
wherever they can find food and suitable living conditions. It is
fortunate that most of this host of one-celled neighbors are either
harmless or useful.
The study of bacteria is called bacteriology. It is a science in
itself. The methods used in its study are interesting.
Sterilization. In the first place all dishes and apparatus used
are sterilized ; that is, they are heated or treated with chemicals so
as to kill any bacteria that might come from the air or water.
Making the "Medium." Then a "culture medium" is made
from some jelly-like substances such as gelatin or agar, with which
beef extract or some similar food is mixed and often peptone and
soda are added to make it easier for the bacteria to get their
nourishment.
Inoculation. This culture medium is put in sterile dishes and
again sterilized several times by heat to kill any bacteria that
might be present; the dishes are plugged with sterilized cotton
which will keep other bacteria from getting in. Now we are ready
for the next step, called exposure, or inoadation of the cultures.
This is done by pouring upon the surface of the culture, a small
amount of the milk or water to be tested, or by exposure to the air
in the room where the bacteria are to be studied. Touching with
the fingers, exposure to dust, and various other means will permit
access of bacteria if any be present.
Growth of Cultures. After exposure, the dishes are again covered
and set in a warm place for a few hours. We know that the culture
was sterile, i.e., had no bacteria in it, and we know that conditions
favorable to growth are provided. As a result if any bacteria have
been brought in contact with the culture they soon multiply so
greatly that a spot or colony develops on the gelatin.
136 BIOLOGY FOR BEGINNERS
Pure Cultures. Thus the number and kind of bacteria to be
found in the substance tested can be determined. Other gelatin
can be inoculated from some one kind of colony forming a pure
culture, so that further study can be made and slides can be pre-
pared for use under the miscrocope.
When our mothers " put up " canned fruits or vegetables at
home, they go through the first part of this same process. They
boil the cans, covers, and rubbers, which sterilizes them. Then
they fill them while still hot with the fruit, which has been sterilized
by cooking; and finally seal the cans to keep any other bacteria
from getting in and causing the contents to ferment or " work."
Useful Forms of Bacteria. Do not forget that bacteria do not
always mean disease, for as a matter of fact, there are many kinds,
without which we could not live. If we pull up a clover plant,
there are usually found attached to its roots, numerous small
round bunches, called tubercles. These are the homes of millions
of bacteria which have the ability to take the free nitrogen of the
air and combine it into soil compounds which other plants can
then use. These nitrogen compounds are absolutely essential to
life. No other plant forms can manufacture them from the air.
Therefore we see how important these bacteria are in keeping up
the fertility of the soil. Nitrifying bacteria are found on the roots
of all members of the clover family, such as peas, beans, and al-
falfa. It had long been known that plowing under a crop of clover
made the soil better for the other crops, but the reason was not un-
derstood till the nitrifying bacteria were studied.
Other helpful bacteria are those which, like fungi, aid in decay
and therefore act as scavengers, removing harmful waste, and re-
turning it to the soil as plant foods. This process is utilized in
sewage disposal systems, where certain bacteria act on the city's
sewage changing it to an odorless and valuable fertilizer instead
of a dangerous and expensive waste product.
The souring of milk, the making of butter and cheese, the
" ripening " of meats, and the fermentation of vinegar, sauer
kraut, and ensilage, are some food processes in which bacteria are
indispensable. The separation of hemp and flax fiber from the
BACTERIA 137
rest of the plant and several steps in the tanning of leather, curing
tobacco, and preparing sponges, are other processes which depend
on bacteria.
Harmfu Bacteria. On the other hand, tuberculosis, which causes
one-seventh of all the deaths in the world, is due to the attack of
a bacterium. At least fifty per cent of all deaths are due to this and
other bacterial diseases, of which the following is a partial list.
tuberculosis tooth decay anthrax
erysipelas pneumonia cattle fevers
leprosy ptomaine poisoning grippe and colds
syphilis typhoid fever lockjaw (tetanus)
diphtheria eye diseases cholera
whooping cough
Often when bacteria attack nitrogenous foods, poisonous sub-
stances, called ptomaines, are produced. These sometimes cause
illness or death when such food is eaten. Some serious plant diseases
or " blights " are caused by bacteria and result in great crop losses.
Bacteria were discovered by Pasteur in his reaserches along this
line.
Defences against Bacteria. With this formidable list in view, it
is evident that we ought to know how to prevent these bacteria
from attacking our bodies and how to combat and destroy them
when they obtain a foothold in our systems.
Skin. Our first line of defence against these ever-present enemies
is our skin, and the mucous membranes which line the inside of the
body. If they are clean, whole, and healthy, few bacteria can get
inside our defences.
NATURAL RESISTANCE
If they break through this outer breastwork, the bacteria have
to face the second line of defence, which is the natural resistance of
a healthy body to any harmful invader. This second line is de-
fended by the white corpuscles in the blood, which actually de-
vour some of the disease germs, and also by antitoxins, which
overcome the poisons made by the bacteria, and which are produced
138 BIOLOGY FOR BEGINNERS
in the blood by the presence of the bacteria themselves. Thus
the attack tends to produce a defence against itself, if the body
be healthy. This natural resistance to disease is called natural
immunity, and constantly protects us from germs of whose pres-
ence we are entirely unconscious.
To provide conditions favorable to resist disease it is evident
then that general good health is essential, aided by cleanliness,
pure and abundant food, light, air, and whatever will keep each
cell of our body keyed up to repel the invader before his rapid in-
crease gives him the advantage. We know how often when the
body is " run down," diseases are contracted, which would other-
wise be fought off without our knowing that the bacteria had
attacked us. How often a " mere cold " develops into some serious
ailment, because the cold, though perhaps not regarded as serious,
lowers the resisting power of the body and then bacteria find en-
trance and overcome our physiological garrison.
Defence by Antitoxins. In case the bacteria do find lodgment
in our bodies, there is usually a period of some days between the
time of exposure and the actual illness: this period of incubation
is the time in which the bacteria are overcoming the body's first
resistance and multiplying sufficiently to gain the advantage.
Then the colonies of bacteria develop in some organ, as when
diphtheria bacteria attack the throat. The throat is not the only
portion harmed, for the bacteria also secrete a poison (toxin) which
causes more serious trouble to other organs of the body. If the
patient recovers it is because his body has been able to gradually
increase the amount of antitoxin in his system and so overcome the
poisons produced by the bacteria which are causing the disease.
White Corpuscles. The lymph glands in various parts of the
body produce white corpuscles, and if the body is in good con-
dition at the tune of disease attack, they greatly increase the num-
ber of these defenders. These corpuscles are able to actually " eat
up " the bacteria or else carry them back to the lymph glands
where they are destroyed.
Opsonins are chemical substances in the blood whose function
is not thoroughly understood, but which have to do with com-
BACTERIA 139
bating the attack of disease germs, by making them more suscep-
tible to the white corpuscles. It seems as if the opsonin in the blood
can be increased by the injection of dead germs, and this method
is sometimes used to produce immunity to certain diseases.
Acquired Immunity. In some diseases, it seems as if the fact of
having had the attack and successfully overcoming it, had provided
the body with such ability to supply that particular antitoxin
that the person seldom has the disease again, as for example in
the case of measles and whooping-cough. The body has been
trained, as it were, to oppose that kind of attack and this is called
a condition of " acquired immunity."
ARTIFICIAL PROTECTION
Vaccination. From this it follows that if one has a mild attack
of a serious disease, he may develop sufficient antitoxin strength
to oppose the dangerous form, somewhat as a sham battle pre-
pares the soldier to protect himself in the real engagement. This
fact is the basis of vaccination which is the inoculation of a well
person with a mild form of smallpox, by which he becomes able
to resist the attack of this terrible disease. (Smallpox is due to
a one-celled animal germ, not a bacterium.) In a similar way
protection is obtained against typhoid fever and hydrophobia.
Weak doses of the toxins of these diseases are administered, so
that the body gradually increases its antitoxin defences and be-
comes immune to fatal attack. Some people oppose vaccination
because when improperly performed, other germs are introduced
and serious illness follows but this is a very rare occurrence. Be-
fore vaccination was practiced 95 per cent of all people had small-
pox, thousands died and all were scarred for life. Then it was
one of the plagues of the world, whereas it is now one of the rarest
of diseases.
Antitoxins. Another method of helping our bodies to repel
germ attack is by administration of the antitoxin directly. In
vaccination the body learns to make its own, but there are cases
where a child is too weak to do this and the actual antitoxin is
140 BIOLOGY FOR BEGINNERS
used. This is especially true in treatment of diphtheria. This
antitoxin is obtained from horses, which have acquired immunity
by having been inoculated with frequent doses of the diphtheria
toxin, till their blood has an excess of antitoxin, which may then
be drawn off, prepared and injected into the system of the patient
early in the attack, thus supplying more antitoxin than the child
might be able to produce in its own cells even after days of illness,
if at all.
Another dreadful disease which is successfully treated in this
way is tetanus or lockjaw. This is a frequent result of wounds in
which dirt gains entrance, such as Fourth of July pistol injuries,
and cuts on the feet, which are apt to be infected from the soil.
It is not the fact that the nail is rusty which makes it dangerous
to step on, but that a rusty nail generally is a dirty nail, and may
infect with disease.
Germicides. Other means of destroying bacteria are by the
use of antiseptics, and disinfectants which are chemical substances
that destroy or hinder the growth of disease germs. Some valuable
antiseptics which should be used, even in small wounds, are iodine
hydrogen peroxide, alcohol, ichthyol ointment, 4 per cent solution
of carbolic acid or 10 per cent solution of potassium permanganate.
Boric acid, camphor, thymol, and even common salt are useful in
some cases.
Disinfectants are chemicals used to kill germs outside the body,
as in case of clothing, utensils, bedding, and rooms that have been
occupied by persons ill with infectious diseases. Bichloride of
mercury, a dangerous poison, is valuable for disinfecting the hands
or washing woodwork; dilute carbolic acid may be used for the
hands, clothing, or bedding. Formaldehyde solution may be simi-
larly used, though sometimes injurious to the skin; several coal
tar products such as cresol, lysol, cresoline, etc., are said to be as
efficient as carbolic acid, and less dangerous. For outdoor disin-
fection of cesspools, garbage cans, or privies, chloride of lime, or
freshly prepared milk of lime, may be used, the former being es-
pecially useful in typhoid fever. To disinfect a room following in-
fectious disease, all woodwork should be thoroughly scrubbed with
BACTERIA 141
soap and water, walls re-papered or calcimined if possible, bedding
either sterilized or burned and the room tightly closed and fumi-
gated. For this purpose formaldehyde gas is best and may be
prepared by burning a formalin candle, boiling a strong solution
of formalin, or by adding permanganate of potash crystals to the
solution in the proportion of one-half pound of crystals to each
pint of formaldehyde. While not -so efficient, and also likely to
bleach colored furniture, burning sulphur produces a gas which is
a useful disinfectant. One or the other of these substances should
always be used in rooms where an infectious disease has occurred.
Germs, both bacteria and animal forms, are mostly killed at boil-
ing temperature. Drying checks their growth and direct sunlight
destroys them rapidly. When we cook our foods, we not only make
them more digestible and attractive, but sterilize them as well.
Milk may be freed of the most dangerous bacteria by pasteuriza-
tion, which means heating to a temperature of from 140 to 150 F.
for a period of 30 minutes. After pasteurizing it must be quickly
cooled and kept closed and cool, or other germs will find entrance.
This brings us to another way in which bacteria do harm to man:
they attack his foods, causing them to sour, ferment, or decay.
Cooking and canning are two ways which have been mentioned
of preserving food from bacteria. Meats are protected by canning,
cold storage, salting, smoking, pickling, etc. ; fruits and vegetables
may be canned, dried, or pickled in vinegar and spices which are
really antiseptics. Other more active antiseptics have been used
to preserve foods, such as borax, formalin, salicylic acid and ben-
zoate of soda, but, while they kill the bacteria, they also harm the
person using the foods, and so have mostly been forbidden by law.
Development of Bacteriology. Our knowledge of the action
of bacteria dates back only about forty years, but during this time
great headway has been made in their control. Pasteur discovered
the relation of bacteria to fermentation about 1860 but it was not
until 1880 that their connection with human disease was established.
Pasteur's great work against rabies mad dog poison was
done about 1885 and now only one per cent of the victims die,
instead of practically every one, as formerly. In 1894 Von Behring
142
BIOLOGY FOR BEGINNERS
and Roux developed the antitoxin for diphtheria. In the United
States, deaths from this cause have decreased from 15 to 2 per
10,000 of population in fact 98 per cent will recover if treated
within two days. In similar ways we are learning to control ty-
phoid fever, tetanus, influenza, and pneumonia. Our knowledge
of the means of transmission of disease has led to preventive meas-
ures even more efficient in preserving human life.
Another result of modern investigation is the cheering fact that
no germ disease is hereditary. You may inherit low resistance to
germ attack, but if precautions are taken to increase this resistance
and avoid infection, you need not suffer from the disease.
Vaccination
Anti-toxin treatment
Method
Mild or dead germs intro-
Serum of blood from im-
duced into body
mune animal introduced
into body
Result
Body reacts and forms its
Anti-toxins directly sup-
own anti-toxins
plied
Duration
Immunity develops slow-
Immunity provided at
ly but persists longer
once but for only the
one case
Diseases treated
Small-pox
Diphtheria
Typhoid fever
Tetanus
Rabies
Meningitis
COMPARISON OF PASTEURIZING AND BOILING MILK
Boiling
Pasteurizing
Temperature
212 deg.
140-150 deg. (30 min.)
or
Effect on bacteria
All killed, both harmful
and useful
160-165 deg. ( 1 min.)
Most harmful ones killed
Useful ones unharmed
Effect on taste
Effect on food value
Changed
Less palatable
Much reduced
Unchanged
Unchanged, except
Less digestible
vitamines
BACTERIA
143
BACTERIAL ATTACK AND CONTROL
Point of Attack
Disease caused
Means of control
Food
via digestive
organs
Typhoid
Cholera
Dysentery
Cook foods, destroy flies
Secure pure water supplies
Pasteurize milk, keep food cold
and clean
Air
via lungs
Tuberculosis
Pneumonia
Measles, mumps
Whooping cough
Avoid dust, check "colds"
Anti-spitting laws
Quarantine laws, avoid contact
with sick
Good food, sleep, general
health
Skin
via wounds
Blood poisoning
Tetanus, syphilis
Pus infections
Cleanliness
Use of antiseptics and disin-
fectants
Protect from further bacterial
attack
Foods or skin
via insect trans-
mission
Typhoid
Malaria
Yellow fever
Destroy breeding places
Drainage
Cleanliness, screens, etc.
See Chapter 25 on " Insects and
Diseases"
COLLATERAL READING
Civic Biology, Hunter, pp. 130-157; Primer of Sanitation, Ritchie, entire;
Story of Bacteria, Prudden, entire; Dust and Its Dangers, Prudden,
entire; Drinking Water and Ice, Prudden, look over; Bacteria and Their
Products, Woodhead, pp. 24-47, 75-86; Our Secret Friends and Foes,
Frankland, look over; The Story of Germ Life, Conn, entire; Bacteria and
Daily Life, Frankland, pp. 35-119; Bacteria and Country Life, Lipman,
look over, especially Chap. 2, 5, 6, 7, 13, 17, 34, 41 to 49; Introduction to
Biology, Bigelow, pp. 256-279; Applied Biology, Bigelow, pp. 276-297,
554-560; Human Body and Health, Davidson, pp. 46-53; Principles of
Health Control, Walters, pp. 218-346; General Physiology, Eddy, pp. 493-
503; Essentials of Biology, Hunter, pp. 170-183; The Human Mechanism,
Hough and Sedgwick, pp. 463-504; Practical Biology, Smallwood, etc.,
pp. 232-258; Plants and their Uses, Sargent, pp. 492-495; The Rat Pest,
Geographic Magazine, July, 1917; Elementary Biology, Peabody and
Hunt, Part II, pp. 10-43; Scientific Features of Modern Medicine, Lee, pp.
64-79; High School Physiology, Hewes, pp. 265-275; Experiments in Plants,
Osterhout, pp. 361-408; Introduction to Botany, Stevens, pp. 256-263;
Nature Study and Life, Hodge, pp. 457-477; Practical Biology, Smallwood,
144 BIOLOGY FOR BEGINNERS
pp. 343-353; Scientific Features of Modern Medicine, Lee, pp. 86-109;
Community Hygiene, Hutchinson, pp. 233-247; Handbook of Health,
Hutchinson, pp. 286-313; Immune Sera, Bolduan and Koopman, look
through; Infection and Immunity, Sternberg, look through; General
Biology, Sedgwick and Wilson, pp. 192-201; General Science, Caldwell
and Eikenberry, pp. 79-101
SUMMARY
Definition: minute, one-celled, parasitic, fungous plants.
Kinds, coccus (round); bacillus (oblong); spirillium (spiral).
" Germ or microbe" may be either plant or animal forms.
" Bacteria" applies only to plants.
Characteristics:
Size.
Rate of reproduction (why limited).
Favorable conditions: food, moisture, warmth.
Occurrence.
Methods of Study.
1. Sterilization of apparatus (why necessary).
2. Making of "culture medium" (a sterile, moist food supply).
3. Inoculation with forms to be studied.
4. Growth of bacterial "colonies," on the medium.
5. Selection, and making of " pure cultures."
(Explain precautions taken in canning fruits.)
Useful forms of Bacteria.
1. Nitrogen fixers on clover roots (why useful).
2. Scavengers and decay producers (why useful).
3. Forms necessary in following processes:
Souring of milk, making of cheese.
Fermentation of alcohol, vinegar, etc.
Tanning leather.
Preparing hemp and flax.
Harmful forms of Bacteria.
(See list of bacterial disease in text.)
One-half all deaths, one-seventh by tuberculosis.
Those causing food decay. Plant blights.
Natural defences against bacteria, etc.
1. Skin and mucous membranes (clean, whole and healthy).
2. Natural bodily resistance, secured by
General good health.
White corpuscles (destroy germs).
Antitoxins (oppose bacterial poisons).
Opsonins.
BACTERIA 145
Stages in bacterial attack.
1. Incubation (overcoming bodily resistance).
2. Rapid growth of bacteria.
3. Secretion of toxins by bacteria.
4. Secretion of antitoxins by blood.
5. Struggle between body and bacteria.
6. Acquired immunity in some cases.
Artificial Protection.
1. Vaccination (smallpox and typhoid).
Body resists mild attack, makes own antitoxins.
2. Antitoxin treatment (diphtheria and tetanus).
Antitoxins developed in other animals (horse).
Directly administered where body is not able to make its own.
Germicides (germ killers).
Antiseptics (used mainly in contact with body):
Hydrogen peroxide Alcohol
Carbolic acid, 4%. Ichthyol
Boric acid Potassium permanganate, 10%
Camphor Thymol, salt
Disinfectants (used mainly outside the body):
Bichloride of mercury furniture, hands
Carbolic acid, 4% clothing, hands, etc.
Formaldehyde. rooms, clothing
Creosol, lysol, etc. clothing, etc., as directed
Chloride of lime, garbage, refuse, etc.
Germs also killed by
Heat, as in boiling and cooking, pasteurizing
Sunlight
Hindered by dry conditions
Pasteurizing
Heat to 140-150 degrees
Cool quickly
Exclude other bacteria
Kills most harmful bacteria, does not change milk
To Disinfect a room:
1. Clean all woodwork with soap and water
2. Refinish the walls if possible
3. Disinfect furniture and bedding (see above)
4. Fumigate with
Formaldehyde
Formaldehyde and potassium permanganate
Burning sulphur (danger of bleaching)
Development of Bacteriology.
Pasteur, 1860-1880
Von Behring, 1894, diphtheria
Roux, 1894, diphtheria
CHAPTER XVIII
PROTOZOA
Vocabulary
Protozoa, " first animals," that is, simplest in structure: one-celled.
Microscopic, minute, so small as to be seen only with microscope.
Fission, reproduction by division into two parts.
Conjugation, reproduction by union of parts of the nucleus.
Stagnant, not flowing, as applied to water.
Vacuoles, bubble-like cavities in protoplasm, used in excretion.
In the study of plants we have seen how various forms start in
a one-celled stage, the egg, and develop into very complicated
forms with separate tissues of various kinds of cells. We have
seen also that there are plants so simple that they never have
more than one cell, in which is performed all the functions neces-
sary to the plant. With animals the same conditions are found;
there are the very complex types such as birds, insects, and man
where each function has many sorts of cells (tissues) concerned in
its performance while at the other extreme, there are simple
one-celled animals, all of whose life functions are performed in their
single, microscopic ceils.
These simplest forms are called the protozoa (first animals) and
though vastly numerous and widely distributed, they are not
familiar because of their small size. Small as they are they are very
important in nature, forming food for higher animals, acting as
scavengers, causing disease in a few cases, and even forming layers
of the earth by the deposit of their countless shells, as in the case
of the chalk-making forms.
Amoeba. One of the simplest of these simple animals is the
amoeba which lives in the slime at the bottom of most streams
and ponds. Though barely visible to the naked eye, under the
146
PROTOZOA
147
microscope it is seen to consist of an irregular mass of jelly-like
protoplasm without even a cell wall, hence its body (the one cell)
constantly changes shape, with a sort of flowing motion. A nucleus
may be seen as well as tiny particles of food which are scattered
through the protoplasm, and also a bubble-like cavity (vacuole)
which expands slowly and then contracts suddenly, forcing out its
FIG. 44. Amoeba proteus in active moving condition, c.v., contractile vacuole;
f.v., food vacuole; , nucleus; />, remains of former pseudopodia. w.v., water
vacuoles. The arrows indicate the direction of protoplasmic flow. (Sedgewick
and Wilson.) From Calkins.
contents. Simple as is its structure, one learns to look with re-
spect and interest upon an animal which with so little material,
can yet perform all the functions necessary to any organism,
however complex.
The amoeba obtains food by extending lobes of its protoplasm
and actually flowing around each particle. Digestion and as-
148
BIOLOGY FOR BEGINNERS
trio* fnut*i
similation go on directly in contact with the food, and undigested
particles are merely left behind when it flows away from them or
they pass out through any part of the cell. Oxygen is taken by
contact from the water in which it is dissolved and combines
directly with the food and protoplasm producing energy, just as
in all living things. The contractile vacuole acts as an excretory
organ, getting rid of waste. Locomotion is secured by the flowing
of the protoplasm, projec-
tions being pushed out on
one side and withdrawn
on the other. Some form of
sensation must be present
because it responds to light,
food, moisture, or sudden
jars.
Reproduction occurs as
soon as growth reaches a
certain size. The nucleus
first divides in two similar
portions, then the rest of
the protoplasm gradually
separates in two masses,
each with a nucleus and capable of independent life and growth.
This simple reproduction by mere division is called fission. Repro-
duction by union of anything like the sperm and egg cells of plants
and other animals has never been observed in the amoeba, though
it seems almost necessary that there should be some such process.
There are nearly a thousand close relatives of the amoeba, some
of which attach a protective covering of tiny sand grains to their
body; others secrete. a layer of flint or lime. These shelled proto-
zoans are so abundant in the tropical seas that they tinge the water
white and their shells, falling to the bottom, make deposits of
limestone, such as the chalk cliffs of England.
Paramoecium. Another common protozoan is the paramcecium
which is also abundant in stagnant water. We cultivate it in the
laboratory by putting some dry hay or leaves in water and leaving
FIG. 45. Progressive stages of fission
of amoeba. After Schultz.
PROTOZOA
149
TIHCHOCY6T3
S CAHAL9
them in a warm place for a few days. When observed the liquid
will be found to be swarming with various kinds of protozoa, of
which many are paramcecia. Their appearance is due to the fact
that most protozoa can live
in a dried condition and so
are blown around like dust.
They become attached to
the hay or leaves and only
await moisture and warmth
to begin active life again.
This is not reproduction
but only a resting stage to
carry them over unfavora-
ble periods.
Structure. The para-
moecium has a cell wall
which gives it a definite
oval shape. There is .also
a funnel-shaped cavity on
one side which acts as a
mouth. The cell is covered
with tiny hair-like cilia by
which the paramoecium
swims rapidly and also pad-
dles food particles toward
the mouth cavity. Inside
the cell there are, of course,
the protoplasm, nucleus,
and contractile vacuoles.
The latter are two in num-
ber and situated in definite
places at the two ends of
C
penisrotif
MOUTH AHO QVLLET
FIG. 46. Diagram of structures of Para-
caildatum from an individual about
125 of an inch in length. From Calkins.
the cell.
Specialization. Now you can understand that while the para-
moecium and amceba perform similar functions, still, the para-
mcecium is much more fully adapted for them, in so much as it
150 BIOLOGY FOR BEGINNERS
has a fixed shape; cilia for locomotion and food-getting; a definite
mouth and gullet, and definite regions for excretion. This increase
in adaptation of structure to function is called specialization, or
division of labor, and is the mark of higher development in any
plant or animal.
Reproduction. In paramcecium this function is more highly
developed than in amoeba and consists of two processes, fission
and conjugation. Fission takes place, preceded, as usual, by the
division of the nucleus, and two new individuals are produced,
much as in amoeba, but in a more definite manner. This process
can go on for only about 150 times, when the vitality seems to be
reduced and conjugation takes place.
In conjugation, two paramcecia unite by joining the region near
the " mouth " cavity, and their cell wall becomes thin at the point
of union. Complicated divisions take place in the nucleus of each
and finally a stage is reached where there are two parts to each
nucleus, one of which is stationary and the other not. The two
movable nuclei now exchange places, passing through the pro-
toplasm of the cells and finally unite with the stationary nucleus of
the opposite individual. After Jthis exchange and union of nuclei
the paramcecia separate again. There has been no gain in numbers
but the vitality of the protoplasm has been increased so that re-
production by fission can go on again.
This conjugation does not make more individuals as true
reproduction does, but it enables both participants to repro-
duce by fission and is the first step toward fertilization in ani-
mals, which, as in plants, is the union of two different cells from
two individuals.
Parasitic Protozoans. Some protozoans are parasitic, attack-
ing other animals and producing serious diseases, much as do the
bacteria. They are often classified with the latter as " disease
germs " or " microbes." If we realize that these terms include
both one-celled parasitic plants (bacteria) and one-celled parasitic
animals (protozoa) then their use is correct.
Some diseases caused by protozoan parasites are in the following
list. The way in which they are transmitted will be more fully
discussed under insects (Chapter XXV).
PROTOZOA 151
malaria sleeping sickness cattle fever
smallpox dysentery trachoma
yellow fever scarlet fever bubonic plague
COMPARISON OF AMCEBA AND PARAMCECIUM
Amoeba Paramoecium
Form
Variable
Constant
Cell wall
None
Present
Locomotion
Flowing lobes
Cilia
Speed
Slow
Rapid
Food
Reproduction
Absorbed at any point
Fission
Definite region of absorption
Conjugation and fission
COLLATERAL READING
Elementary Text (Zoology), Colton, pp. 286-306; Elementary Text
(Zoology), Linville and Kelley, pp. 280-291; Elementary Text (Zoology),
Davenport, pp. 280-288; Elementary Text (Zoology), Galloway, pp. 154-162;
General Zoology, Herrick, pp. 24-35; Lessons in Zoology, Needham, pp. 9-
21; Practical Zoology, Davison, pp. 178-184; Animal Life., Jordan and
Kellogg, pp. 1-50; Animal Studies, Jordan, Kellogg & Heath, pp. 22-42;
Animals and Man, Kellogg, pp. 37-48, 118-123; Economic Zoology, Kellogg
and Doane, pp. 25-47; Fconomic Zoology, Osborne, pp. 10-35; Applied
Biology, Bigelow, pp. 300-319; Biology Text, Peabody and Hunt, pp. 164-
176; Practical Biology, Smallwood, pp. 45-62; Life and Her Children,
Buckley, pp. 14-32; Animal Life, Thompson, pp. 210-221; Life in Ponds
and Streams, Furneaux, pp. 99-113; Protozoa, Calkins, entire 1 ; Proto-
Zoology, Calkins, entire 1 ; General Biology, Sedgwick and Wilson, pp. 192-
201.
See also references on "Insects and Diseases."
1 Look through, note pictures especially.
SUMMARY
All living things start in one-celled stage.
Sperm and egg cells in higher forms.
Bacteria: one-celled plants.
Protozoa: one-celled animals.
Protozoa (first animals) :
1. Characteristics,
Minute size, numerous, widely distributed.
One-celled, simple structure.
152
BIOLOGY FOR BEGINNERS
PROTOZOA, ETC.
VOLVOX
KOT i
FIG. 47. Various types of protozoa, rotifers, and other organisms often
found in aquarium cultures. (Greatly enlarged.)
PROTOZOA
153
2. Economic importance,
Food, scavengers, soil and rock formation.
Producing certain diseases.
Amoeba (a very simple protozoan).
Where found. Appearance.
Structure.
Protoplasm, nucleus, lobes, vacuoles, food grains.
Paramcecium. (A more specialized protozoan.)
Where found. Appearance. How distributed.
Structure.
Protoplasm, nucleus, cell wall, cilia, "mouth," vacuoles, food grains.
Points of advance over amoeba:
Fixed shape (cell wall).
Cilia for locomotion and food-getting.
Definite mouth region.
Two definite places for excretion.
Reproduction both by fission and conjugation.
COMPARISON OF THE MEANS OF PERFORMING THE
Life Functions
in Amoeba
and Paramoecium
Food-getting
Digestion and assimi-
lation
By flowing lobes
By contact anywhere
By cilia
In definite regions
Oxidation
Contact with dissolved air
Same
Excretion
Locomotion
Sensation
Vacuole, variable
Lobes, variable
Responds to heat, light,
Two vacuoles, definite
Cilia, definite
Same
Reproduction
contact, moisture, etc.
Fission
Fission and conjugation
Comparison of Fission and Conjugation
Fission (increases numbers) Conjugation (increases vitality)
1. Nucleus divides.
2. Cell divides.
3. Growth to adult size.
1. Union of two individuals.
2. Complicated nuclear division.
3. Cross transfer of part of nucleus.
4. Union of portions of nuclei.
5. Separation of individuals.
CHAPTER XIX
METAZOA
Vocabulary
Metazoa, " animals further along," that is, in development and
specialization, many-celled animals.
Specialization, development of separate organs for different
functions, division of labor.
Respective, separate or individual.
Stimuli, any outside forces that affect plant or animal, such as
light, heat, contact, sound, etc.
All one-celled animals are called protozoa (first animals); all
those consisting of more than one cell are called metazoa (animals
further along), meaning that they are more complex in structure
and more specialized in function than a single-celled animal can be.
Development. No matter how complicated a plant or animal
may eventually become, it started in a one-celled stage, the fertil-
ized egg. This in turn was the product of the union of the single
sperm cell with the single ovule cell. To trace the development
from this one-celled stage to the highly complicated forms is too
difficult at present, and forms the basis for the whole science of
embryology. However, some of the steps in the process can be
briefly mentioned.
A one-celled animal (protozoan) takes in food and oxygen, and
excretes waste only by means of its. exposed surface. If the di-
ameter of a solid be doubled its surface area is squared, but its
bulk is cubed. Hence if a protozoan increased much in size, it
would reach a point where the surface was too small to provide for
the bulk, and it would die. Before this point is reached, division
takes place and growth begins again, up to limit of size set by
the ratio between surface and bulk. This is why protozoa are so
small and why they divide so frequently. The size which a cell
may reach is therefore limited by the extent of its surface.
154
METAZOA 155
The paramoecium is much more highly developed than the
amoeba but a -limit to its specialization and growth is soon found
and a stage is reached where further specialization in function or
increase in size is no longer possible. If further advance is to be
obtained, larger and more complicated forms must develop. Sup-
pose that when a protozoan divides, the cells did not separate but
remained attached, grew, and divided again and again. There
would soon be produced a mass of cells much larger than any single
one, and with abundant surface exposed for food-getting and
breathing. In such an animal the outer cells could best attend to
locomotion, sensation, and food-getting, while the inner cells
could carry on digestion and reproduction. Pandorina and other
simple metazoans represent this stage.
If a solid mass of cells continued to enlarge, the innermost ones
would be so far from contact with food and air that a limit in size
of the mass would be reached, just as with the single cell. To
meet this condition, the next higher forms consist of hollow spheres
of cells, thus giving an inner and outer surface, and permitting
much larger and more complicated forms. Volvox is a representa-
tive of this condition. It consists of thousands of cells, is large
enough to be visible to the eye, and has very highly developed
reproductive and locomotor cells.
A hollow sphere cannot increase indefinitely in size as the single
cell layer would not be strong enough, so in the next higher forms
an infolding of the wall takes place, much as a hollow rubber ball
can be squeezed into a cup-shaped form. Its walls will now be
double with a space between them, in which a third cell layer de-
velops. This three-layered stage is reached in the simplest sponges,
and from the three layers develop all the tissues of higher
forms.
It is important to remember that every plant and animal began
life as a single cell, the fertilized egg. This by repeated divisions
passed through the stages just described, developed from a mass
of unspecialized cells into higher forms with tissues and organs.
Finally it reaches its destined stopping place whether in the simple
volvox or the complicated insect, bird, or man.
156 BIOLOGY FOR BEGINNERS
Specialization. Robinson Crusoe on his desert island had to
perform all the processes needed to supply his wants. He had to
catch and prepare his food, make his clothes and shoes, build his
house and defend himself against enemies. Even though he be-
came somewhat skillful at all these duties he could never hope
to excel in any. He was, in fact, in the position of the protozoan
where all the life functions are performed by one cell. Even though
that cell be highly developed as in paramoecium or vorticella, still
its limit of advance is soon reached.
Now, if there had been ten men shipwrecked with Crusoe, it
would have been possible for one to get food, another to prepare
it, others to build houses and so on. The increase in numbers per-
mitted division of labor. This is precisely the case with such forms
as volvox and all higher types; the increase in the number of their
cells makes possible a separation of life functions, which is actually
division of labor among cells.
To return to the desert island again, if one man continued mak-
ing shoes or another did all the building, each would soon acquire
skill and perform his duty better; he would have become a special-
ist in his line. Cells also are able to perform their functions better
and better by constant use. Specialization is the term applied to
this condition in cells as well as in men.
Finally, both cells and men would acquire special fitness for
their tasks. This special fitness is called adaptation and is
the permanent result of specialization. The more perfectly a
plant or animal is adapted to its environment, the better is
its chance to survive; hence this matter of development,
division of labor, specialization, and adaptation is of the utmost
importance.
Interdependence. There is, however, another phase of this mat-
ter of specialization, which cannot be overlooked. The man who
devotes himself solely to the making of shoes, loses the ability to
do many other necessary things. Cells and tissues which become
adapted for special functions are all the more dependent upon other
specialized cells for equally important services. So it comes to
pass that the more highly specialized a plant or animal becomes
METAZOA 157
the more each part depends upon all the others, and the more dif-
ficult it is to replace or to do without a damaged tissue or organ.
A simple protozoan can be divided and each half perform all the
vital functions. Needless to say this cannot be done with higher
specialized forms like the insect or bird, in which the interdepen-
dence has developed to a considerable degree.
By increase in numbers
Division of Labor is made possible,
by which
Workmen"* " ^ Col 1st
gain. tfafn
Adaptation
for
Business
called called
SPECIALIZATION
FIG. 48. Chart showing evolution of specialization.
Forms of Metazoans. The sponges have their division of labor
confined to specialization of separate cells for various functions.
The next higher group (ccelenterates) which includes the hydra,
coral polyps, sea anemone, and jellyfish, have cells performing
similar functions grouped together in true tissues.
The next group (true worms), such as the earthworm, carry this
division of labor still farther, having special digestive, circulatory,
and excretory organs, of complicated structure, and a true nervous
system with perhaps the beginning of a brain.
Still more complicated in structure and specialized in function
are the molluscs which include clams, oysters, snails, squids, and
devil fish. These have very complicated gills for breathing, heart
and circulatory system much more developed, muscular and
158 BIOLOGY FOR BEGINNERS
nervous systems becoming very efficient. In some there are found
eyes and other sense organs.
The arthropods, which include the lobster and crab, all insects,
and spiders, constitute an enormous and highly specialized group
whose adaptations we shall study in detail. Then at the top of the
list come the vertebrates, including all backboned animals, fish,
frog, snake, bird, cat, and man whose place at the head of the class
is due, as always, to the specialization and development of the
organ with the highest function, namely the brain, with its ability
to think and reason.
All this increase in adaptation brings the animal in closer touch
with its surroundings or environment. The amoeba vaguely turns
toward food and moisture, contracts if disturbed or perhaps turns
away from strong light. As development progresses, response is
made to other outside forces (stimuli) and we have organs for
touch, taste, smell, hearing, and sight, all of which enable the
animal to adapt its life to its environment and by that means be-
come successful in the struggle for existence which goes on with
its neighbors.
COLLATERAL READING
General Zoology, Linville and Kelly, pp. 292-304; Animal Life, Jordan
and Kellogg, pp. 24-49; Animal Studies, Jordan, Kellogg and Heath,
pp. 33-42; Animal Life, Thompson, pp. 143-152; Comparative Zoology,
Kingsley, pp. 318-320; Elementary Zoology, Kellogg, pp. 57-63; Essentials
of Biology, Hunter, pp. 199-210.
SUMMARY
Protozoa (first animals), one celled.
Metazoa (animals further on), more than one celled.
1. Development.
Plant and animal begin as single cells (sperm, ovule).
Stages of progress.
One cell.
Two cells to many in mass (Pandorina).
Hollow mass of cells (Volvox).
In-folded, hollow form, three layers (Sponges).
All higher forms, tissues from these layers.
METAZOA 159
COMPARISON OF PROTOZOA AND METAZOA
Protozoa
Metazoa
One-celled
No specialization in simplest except
the nucleus
Some have a cell wall, cilia, " mouth "
but no regular systems of organs
Reproduce by fission or conjugation
Excretion by vacuoles
Minute size
No "body wall" either in embryo or
adult
Many celled
Specialized tissues and organs
Digestive, respiratory and nervous sys-
tems
Reproduce by eggs and sperms
Excretion by kidneys, or analogous or-
gans, skin, and lungs
Much larger size
Three layers in embryonic body wall
which develop as follows:
1. Ectoderm, forms outer skin and its
appendages : Nervous system
and sense organs
2. Mesoderm, forms inner skin, fat,
bone, muscle, connective tissue,
serous membranes
3. Endoderm, forms mucous mem-
branes and all organs that it
lines, gills, lungs, glands
Classes of
Metazoans
Degree of Specialization
Representative
1. Sponges
Cells adapted for food getting, di-
gestion and reproduction
Bath sponge
2. Coelenterates
Tissues for the above processes and
for locomotion
Hydra
Jelly fish
3. Worms
Organs well developed, nerves, blood
vessels, muscles
Earthworm
4. Molluscs
Sense organs, gills, heart, etc. more
complicated
Snail
Clam
5. Arthropods
Great specialization, skeleton, all
senses, very active, nervous sys-
tem and instinct
Insects
Crayfish
Spiders
6. Vertebrates
Great internal specialization, high
special senses, brain, instinct, and
reason, varied locomotion, skeleton
Fish
Frogs
Reptiles
Birds
Man
160 BIOLOGY FOR BEGINNERS
2. Specialization.
Beginning as single cell.
Increase in number of cells.
Separation of functions (division of labor).
Better performance of functions (specialization).
Development of fitness for functions (adaptation).
3. Interdependence.
1. Advance in development means advance in adaptation.
2. Advance in adaptation means closer contact with sur-
roundings.
3. Both of which mean success in the struggle for existence.
CHAPTER XX
WORMS
Vocabulary
Anterior, the end toward the head, usually the end that precedes
in locomotion.
Posterior, the end farthest from the head.
Analogous, having similar function.
Homologous, having similar structure or origin.
Setae, hair-like projections by which some worms travel.
Incalculable, impossible to estimate.
Degeneration, loss of ability to perform function, loss of structures
due to disuse.
The worms may be taken as a class of animals showing a mod-
erate degree of specialization. They include the common earth-
worm, leeches, bloodsuckers, tapeworms, horsehair worms, etc.
THE EARTHWORM
External Features. The earthworm is familiar and will do to
represent the group. Its slender body is divided into rings or seg-
ments. The larger end, near which is a light colored girdle, is the
head (anterior) end; while the vent, or opening of the intestine
marks the opposite (posterior) extremity. Projecting from each
segment are four pairs of bristles (setae) which are operated by
separate muscles and are used in locomotion. The girdle secretes
the case in which the eggs are deposited and near it are the tiny
openings of the egg and sperm ducts, since the organs of both
sexes are found in the same animal. On opening the body, the wall
is found to consist of a very thin cuticle and two thick layers of
muscle, one running lengthwise, and the other around the body.
Digestive System. Inside the body wall, the large digestive
system can easily be recognized, there being a muscular pharynx, a
161
162 BIOLOGY FOR BEGINNERS
crop, stomach, and long, straight intestine, terminating at the vent.
Circulatory System. Not so conspicuous is the circulatory
system, which consists of two large blood vessels, one above, the
other below, the digestive tract, connected by branches in each
segment. Some of these branches pulsate, acting as a heart, to
drive the blood through the system. It must be remembered that
the functions of any circulatory system are ones of transportation.
It carries food from the digestive organs to the tissues, oxygen
from the breathing organs to the tissues, and waste products from
tissues to the organs of excretion. In all animals less specialized
than the worm, the structure was so simple that these processes
were carried on directly by osmosis, but in the worm, division of
labor is more complete, the various tissues more complicated and
so, for the first time, a transportation system is developed.
Excretory and Nervous Systems. Besides the circulatory organs,
there are rather complicated sets of tubes in each segment, which
excrete waste matter. There are two sets of reproductive glands
between the pharynx and stomach. On the lower (ventral) side
of the body is a double row of light-colored threads (the nervous
system), united in each segment, and ending in a tiny knob near
the mouth, which corresponds somewhat to the brain. When
such an- animal is compared with the paramoecium, it is evident
that its functions have much better machinery for their perform-
ance.
Locomotion. The worm is adapted for locomotion by the body
muscles and setae. The muscles extend the anterior part of the
body, the setae are slanted backward and grip the soil, and the
posterior part of the body is pulled forward with a sort of wave-
like motion. By this means the worm travels on the surface or
burrows in the ground. Burrowing is assisted by the fact that the
earthworm practically eats its way, taking the soil into its digestive
tract, absorbing what organic matter it can use as food, and bring-
ing the unused earth to the surface as " worm castings." These
are often seen on lawns, tennis courts, and golf greens.
Analogous Organs. Organs in different animals which perform
similar functions are called analogous organs. The setae and
WORMS
163
retractor and protractor
muscles of the pharynx,..
cesophageal pouches-
seminal receptacles'
seminal
cerebral ganglion
pharynx
iphagus
FIG. 49. Dissection of the earthworm, Lumbricus sp. From Kellogg.
164
BIOLOGY FOR BEGINNERS
muscles of the worm are analogous to the cilia of the paramcecium,
or the flowing lobes of the amoeba. (What analogous organs in
fish, bird, and man?)
PARASITIC WORMS
TAPE WORM
HEAP
10 IN
FIG. 50. Diagram showing structure of tapeworm.
Food. The food of the earthworm consists of leaves of cabbage,
celery, and other plants, as well as some kinds of meat, together
with organic matter found in the soil. This is gathered at night,
WORMS
165
taken into the burrows and eaten, while the waste is brought to
the surface with the earth as castings.
Economic Value. This method of feeding loosens and enriches
the soil, performing about the same work as does the farmers'
plow, though to a greater extent, for the worms are found in all
parts of the world, in such numbers that they pass through their
HOST
FIG. 51. Life history of beef tapeworm. A, adult tapeworm in intestine of
man; B, proglottid full of eggs on ground; C, eggs on ground; D, six-hooked
larva (onchopore) set free and bores through tissues of cow; E, cysticercus
or bladderworm, hi cow's flesh; F, young tapeworm in man. From Pearse.
bodies an average of ten tons of soil per acre, every year, and thus
do an incalculable service to the farmer. Thus the humble earth-
worm, whose function may have seemed to be to furnish bait for
fishing, now is seen to be a very useful member of society. It
has, however, some very bad relatives, which do a great deal of
harm and therefore require special mention.
166
BIOLOGY FOR BEGINNERS
PARASITIC WORMS
In this group are included the tapeworm, trichina, hookworm,
and many others. As is often the case, they are harmful because
parasitic. A parasite, as has been said,
takes the nourishment of another creature
instead of getting its own.
Tapeworm. The tapeworm lives first
within the body of pigs or cattle, the egg
being taken in with their food. It develops
in the intestine, bores its way into the
muscles and goes into a resting stage.
If the flesh of such animals be eaten when
not thoroughly cooked the development
continues in the intestine of man, where
the worm attaches itself by hooks on its
head, lives on the digested food with which
it is surrounded and by robbing its host of
needed nourishment, produces segment after segment till a length of
thirty to fifty feet may be attained. These segments are practically
FIG. 52. Encapsuled
trichinae in trunk muscle
of pig. (Greatly magni-
fied, after Braun.) From
Kellogg and Doane.
FIG. 53. Hookworm, Necator americanus. a, Male; b, female. (Greatly
enlarged; after Wilder.) From Kellogg and Doane.
sacs of eggs which break off from time to time, allowing the eggs
to escape, dry, and scatter, where hogs or other animals may eat
them and start the circle over.
WORMS
167
Trichina. Round worms are another class of parasites, of which
the " vinegar eel " and the intestinal pin worms are comparatively
harmless forms. The pork worm (trichina) of this same class may
cause serious illness or death. These worms pass their first stage
in the pig, dog, cat, ox, or horse, where they bore into the muscles,
surround themselves with a coating (cyst), and remain alive but
inactive. If such flesh be eaten when improperly cooked the cyst
is dissolved, the worms develop,
bore through the tissues
again, and produce the painful
and often fatal disease known
as trichinosis. The tapeworm
is large; usually only one is
present and it does its chief
harm by absorbing food
needed to nourish the body.
The trichina, on the other
hand, is microscopic in size,
vastly numerous, and pro-
duces acute disease by penetra-
tion of the tissues. Careful in-
spection and thorough cooking
Fig. 54. Section through the skin
of a dog two hours after it has been
infected with the Old World hook-
worm. (Greatly enlarged; after
Wilder.) From Kellogg and Doane.
of meats are lessons to be learned
from the above life histories.
Hookworm. The hookworm is another parasite, found in the
southern states, which attacks man by way of the feet and thence
by way of the veins, lungs, and throat, penetrates to the intestine,
where it absorbs food and causes loss of blood. This lowers its
victim's strength and produces the characteristic laziness of the
" poor whites " of the South. Almost all animals, from clams and
insects to cattle and man, are subject to the attacks of parasitic
worms. The hookworm alone costs this country about twenty
million dollars ($20,000,000) per year, in loss of labor due to its
effect on health.
Note: The " horsehair snake " which you frequently find in
ponds and streams has nothing to do with a horsehair, nor is it a
168
BIOLOGY FOR BEGINNERS
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WORMS 169
snake. It is one of the round worms (related to the " vinegar
eel " which is also not an eel) and is parasitic upon beetles, grass-
hoppers, and other insects, thus doing considerable good.
COLLATERAL READING
Vegetable Mould and Earthworms, Darwin, entire; Life and Her Chil-
dren, Buckley, pp. 135-152; Economic Zoology, Osborne, pp. 67-120;
Economic Zoology, Kellogg and Doane, pp. 98-105; Elementary Text, Lin-
ville and Kelly, pp. 195-235; Practical Zoology, Davison, pp. 150-161:
Applied Biology, Bigelow, pp. 340-354; Animal Studies, Jordan, Kellogg
and Heath, pp. 59-88; Life in Ponds and Streams, Furneaux, pp. 114-126.
See also articles under "Worms," "Tapeworm," "Trichina," "Leech"
in encyclopedias.
SUMMARY
Representatives.
Earthworm, tapeworm, hairworm, vinegar eel, leech, etc. (not cater-
pillars).
anterior and posterior (define in notes),
dorsal and ventral (define in notes).
External Structure. Shape.
Segments, count them as far as girdle.
Girdle, function.
Mouth, call attention to pre-oral lobe. Vent.
Setae, adaptations.
1. Number.
2. Location on sides.
3. Attached muscles.
Functions of Setae.
1. Locomotion, 2. burrowing, 3. food-getting.
Reproductive openings on segments 9, 10 and 14, 15.
Both sexes in individual.
Internal Structure.
Body wall, two muscle layers, use of each. Cuticle.
(Lack of skeleton and consequent slow motion.)
Digestive system.
Mouth, manner of food-getting.
Muscular pharynx, function.
Crop, stomach, and intestine with special functions.
(Glands and schemes for increase of digestive area.)
Circulatory system.
Dorsal and ventral vessels.
Cross tubes in each segment, some pulsate.
170 BIOLOGY FOR BEGINNERS
Functions of any circulatory system.
Transfer of food from digestive organs to tissues.
Transfer of oxygen from lungs to tissues.
Transfer of waste from tissues to excretive organs.
Excretory organs.
Pair in each segment, well developed.
Nervous system.
Simple " brain " and ventral nerve chain.
Separate nerve branches, much higher than previous animals studied.
Locomotion:
Adaptations for,
1. Body muscles, two layers, different motions.
2. Setae with their own muscles.
3. Habit of flattening the " tail " region in burrow.
Burrowing:
Adaptations for,
1. As above.
2. Habit of swallowing earth through which it goes.
3. Evidence shown in "castings."
Food-getting :
Food, celery, lettuce, meat, etc., from surface, ta^en below; organic
matter in soil,
(manner of eating; use of pharynx and air pressure).
Economic value:
Earthworm, loosens and enriches soil, brings up fresh earth,
takes down organic matter, 10 tons per acre per year.
Reasons for development of circulatory system in higher forms.
More numerous cells.
Greater division of labor.
All tissues not in reach of food or air by mere osmosis.
Need for transportation system.
Analogous organs:
Definition.
Examples: setae, cilia, pseudopodia, all for locomotion,
similar examples from fish, bird, man, etc.
Parasitism.
Results:
Harm or death to host.
Degeneration.
Loss of organs. .
Absolute dependence.
Need for vast reproduction.
to parasite.
WORMS 171
Tapeworm.
1. Eggs eaten by pigs or cattle.
2. Egg develops in intestine.
3. Young bore into muscles, and go into resting stage.
4. Meat eaten by man (not thoroughly cooked).
5. Development continues. Causes weakness and anaemia.
6. Head attaches by hooks, absorbs food, grows by segments.
7. Segments produce many eggs, which are scattered.
Trichina (related to vinegar worms, and intestinal worms) :
1. Young 'bore into muscles and form cysts (in animals).
2. Uncooked flesh eaten and cyst dissolves (in man).
3. Young again bore into muscles producing disease, cr death.
Hookworm.
1. Enters by way of feet, veins, lungs, throat, intestine.
2. Punctures intestines, causing loss of blood and absorbs food.
3. Lowers strength, makes susceptible to other diseases.
4. Loss in labor of $20,000,000 per year in U. S.
Explain:
" Horse hair snakes."
Vinegar " eels."
" Raining down " of earthworms.
CHAPTER XXI
ARTHROPODS
Vocabulary
Segmented, made up of joints or sections.
Dorsal, the region of the back, usually, but not always, uppermost
in animals.
Ventral, the side opposite the dorsal, the region of the belly, usually
underneath.
Genus, next to the smallest general division in classification;
plural is genera.
Species, the smallest general division in classification; plural
is also species (specie means money).
The group of animals next to be studied is called the arthropods
(jointed foot) because all their leg-like appendages are divided in
joints or segments.
Characteristics. They are the largest group of living things in
the world, outnumbering all the other species of the animal king-
dom. These numerous forms all agree in the following points:
1. They have jointed appendages.
2. They have an external skeleton.
3. The body is segmented and consists of three regions,
(a) head specialized for food-getting and sensation.
(b) thorax for locomotion.
(c) abdomen not highly specialized.
4. Heart is in the back (dorsal) region.
5. Nervous system is beneath (ventral).
Classes. The arthropods are divided into three or sometimes
four classes, the fourth being rather indefinite, and including the
worm-like forms such as the centipedes and " thousand legs."
1. Crustacea, which include crayfish, lobster, crab, shrimp, and
many others.
172 '
ARTHROPODS 173
2. Accra ta, the spiders
3. Insecta, the insects.
4. Myriapods, worm-like forms.
The members of each of these classes have all the characteristics
of the arthropods, but there are additional points of resemblance
within each class. For instance, all the Crustacea have the head
and thorax united into a cephalothorax (head-thorax) which is
covered by a part of the external skeleton
called the carapace. Usually they have
five pairs of legs and breathe by gills
attached to them.
The acerata (spiders) have no carapace,
have four pairs of legs and breathe by air
sacs or tracheae. The insects' head and
thorax are separate; they have three pairs
of legs and usually wings as well, and
breathe by means of tracheae. (For
further comparison see tabulation.)
Classification. Each of these three
classes is further divided into groups called
orders, the orders into families, and the
families into still smaller groups called
genera (singular: genus) and genera into
species (singular: species also).
As we come down in the classification,
the groups have more and more points of
resemblance, but of course include fewer
individuals. Take, for instance, the com-
mon grasshopper; it belongs to the FIG. 55. A centipede,
Branch of the animal kingdom called Scol P end S P- (J; rom
Specimen.) From Kellogg,
arthropods
Class, insecta
Order, orthoptera
Family, acrididae
Genus, melanoplus
Species, femur-rubrum.
174
BIOLOGY FOR BEGINNERS
k********^^
Onycophora
.Ancestral arthropod
FIG. 56. A scheme to show how the arthropods have developed from their
ancient ancestor. The branches are not intended to represent actual relation-
ships but to indicate the lines of specialization which have been followed.
From Pearse.
We do not have to learn these apparently difficult names. What
we ought to try to understand is the method of classification, be-
cause it is used in all animal and plant groups and is so well il-
ARTHROPODS 175
lustrated by the arthropods. In the case of the grasshopper, the
species group includes just that one kind of grasshopper and no
others so they are alike in all points; the genus includes several
species with a good many points of resemblance. The family in-
cludes the members of several genera which resemble each other
but less closely than the members of the genus. The order, or-
thoptera, includes several families with members as different as
the cockroach, locust, katydid, grasshopper, and crickets, while
the class insecta includes all the different orders of insects, such as
bees, moths, flies, and beetles which of course include many in-
dividuals but resemble each other in still fewer points. As stated
before, the Insecta is one of the three classes into which the ar-
thropod branch is divided and have the characteristics of that
enormous group, in common with the acerata and Crustacea.
Value of Scientific Classification. This may seem very com-
plicated but is really very necessary, for if there were no way of
grouping the different forms, they could never be studied or un-
derstood, much less named and identified. Not only this, but
resemblance in points of structure shows actual family relationship,
those forms most alike being nearest related and those with less
points in common, more distantly connected. Classification is not
only a convenient arrangement to save labor in the study of living
things, but shows their relationship and descent, as well.
Let us classify the grasshopper fully according to this outline,
and see how much is included in merely its proper scientific
classification.
Kingdom: Animal '
Branch: Arthropoda (jointed-foot animals)
Class: Insecta (body " cut into " three regions)
Order: Orthoptera (straight-winged)
Family: Acrididae (locust family)
Genus: Melanoplus (black armored)
Species: femur-rubrum (red-legged)
From just the translation of the names used, one can obtain a
fair description of the animal concerned, and if the characteristics
176 BIOLOGY FOR BEGINNERS
of each successive group are known, a complete description is
obtained.
If a person in Africa were addressing a letter to this country, and
gave a full and exact address, it would cover as many items, as the
following comparison- shows.
Grasshopper
Letter
Kingdom: Animal
Branch: Arthropoda
Class: Insecta
Order: Orthoptera
Family Acrididae
Genus: Melanoplus
Species: Femur-rubrum
Nation : United States of America
State: Illinois
City: Chicago
Street: Madison
Number: 3561
Surname: Smith
First name: John J.
In the case of the letter as many items have been mentioned as
with the scientific classification, and for the same purpose, namely,
that both shall be absolutely definite and apply to one only. If,
in addition, we could so address our letters that the appearance
and relationship of the addressee were included, it would cor-
respond to the very remarkable system of classification used in all
biologic work.
Scientific Names. When speaking of a plant or animal the genus
and species names are usually all that are given, assuming that the
relationship to the larger groups will be known. The genus is
placed first and begins with a capital letter, the species follows,
and begins with a small letter unless it be from a proper name.
The genus name is usually a noun and the species name an adjec-
tive; the genus name precedes the species name, as is the regular
Latin order. We follow it in our lists of names in all formal records
where John J. Smith would appear as Smith, John J. Thus,
Melanoplus femur-rubrum is the scientific name of the common
grasshopper. It is a long name, even for a scientific one, and was
chosen on that account, but how much more convenient and ac-
curate than saying " the black-armored grasshopper with red legs."
Another advantage of scientific names is that they are uniform
ARTHROPODS 177
throughout the world. People of all languages use the same name
for the same plant or animal in their scientific works, and as a
result there is no confusion, nor any need for learning a new set of
names. Common local names are always uncertain, for there are
often several names for the same plant or animal. With the scien-
tific names there is but one possible, and therefore there can be
no chance for mistake.
Scientific names have these advantages:
1. They are absolutely definite.
2. They are used by people of all languages.
3. They are usually descriptive.
4. They are easier to study than separate descriptions.
5. They show relationship and descent.
COLLATERAL READING
Applied Biology, Bigelow, pp. 358-404; General Zoology, Linville and
Kelly, pp. 138-156; Animal Studies, Jordan, Kellogg and Heath, pp.
109-129; Economic Zoology, Kellogg and Doane, pp. 106-125; Economic
Crustacea, U. S. Fish Commission Report, 1889-1893; Life and her Chil-
dren, Buckley, pp. 153-177; Zoology Text, Colton, pp. 54-77; Elementary
Zoology, Kellogg, pp. 144-156; Zoology Text, Shipley and MacBride, pp.
118-135; Elementary Zoology, Galloway, pp. 232-265.
SUMMARY
Meaning of name: . Number of members.
Characteristics :
1. Jointed appendages.
2. External skeleton.
3. Three-body regions.
Head, food-getting and sense organs.
Thorax, locomotion.
Abdomen, reproduction, less specialized.
4. Dorsal heart and ventral nervous system.
Animal Kingdom divided into
1. Branches, which are divided into
2. Classes, which are divided into
3. Orders, 4. Families, 5. Genera, 6. Species.
Note:
Larger groups have fewer points in common, more individuals.
Smaller groups have more points in common, fewer individuals.
Smaller groups have all characteristics of the larger groups of which
they are a part, and certain peculiar to their own.
178
BIOLOGY FOR BEGINNERS
Classes
Characteristics
Examples
Crustacea
Head-thorax united
Lobster
Acerata
Carapace, gills
Five pair legs
No carapace, no gills
Four pair legs
Air sacs or tracheae
Crayfish
Crab, shrimp
Spiders
Horseshoe-crab
Insecta
Head and thorax separate
Three pair legs; wings
Breathe by tracheae
Beetles
Grasshoppers
Butterflies
Classification:
1. Based on likeness of structure (homology).
2. Hence shows relationship and descent.
3. Assists in study and placing of new forms.
Scientific Name:
1. Consists of genus and species names.
2. Avoids long descriptions.
3. Is universally used.
4. Makes meaning absolutely definite.
5. Shows relationship of different forms.
CHAPTER XXII
CRUSTACEA, A CLASS OF ARTHROPODS
Vocabulary
Carapace, the external protective covering of the thorax in
Crustacea.
Mandibles, jaw-like organs.
Maxillae, little jaws, aid in holding food.
Maxillipeds, jaw-feet, aid in catching, holding, and chewing food.
Literally, actually, truly.
Our study of the worms showed us a group of animals in which
tissues and organs had become somewhat specialized, circulator}-
organs developed, and adaptations formed for an inactive under-
ground or parasitic kind of life. In the Crustacea we deal with
animals such as crayfish, lobster, and crab, which are adapted for
an active, aquatic (water) life, in which division of labor among
their various organs has been carried to a higher point.
CRAYFISH
External Structure. The crayfish, which we will study as a type,
has the body covered with a dark-colored, limey, external skeleton
'(exo-skeleton) divided into two regions, the cephalo-thorax (head
thorax) being covered by the united carapace, and the abdomen
made up of seven separate movable segments. This is the first
animal we have studied which has had any skeleton at all and it
may seem strange to find it on the outside of the body while ours
is inside. However the same functions are performed in both
cases, namely to protect the organs and act as levers for the muscles.
Protection is most important in the Crustacea which really have
a suit of mail, such as the knights used to wear. Their joints are
179
180
BIOLOGY FOR BEGINNERS
made to bend by the same arrangements, only better adapted than
man's, and they cover their head and body by a shield (carapace)
far lighter and more efficient than ever warrior carried. Not
only is their exo-skeleton strong, light, and flexible, but it is colored
so as to escape notice from enemies (protective coloration). It
is also provided with sharp spines and projects downward at the
sides, thereby guarding the gills and soft under parts of the body.
In addition to its protective function, the skeleton forms a rigid
. FIG. 57. The crayfish a type of Crustacea.
series of levers, by means of which a complicated system of muscles
provides for swift motion and locomotion, essential for escape,
attack, and food-getting. The development of a skeleton has
also enabled its possessor to advance in many ways.
As stated before, the body consists of segments (20 in all) though
only the abdominal ones are movable, those of the cephalo- thorax
being fused (united) together for greater strength and protection,
while the numerous appendages provide for the needed freedom of
motion. Each of these twenty segments has a pair of appendages,
ARTHROPODS
181
antennule
opening of green (/land
maxillipeds
thorax
genital aperture
'anus
uropod
telson
FIG. 58. Ventral aspect of crayfish (Cambarus sp.) with the appendages of
one side disarticulated. From Kellogg.
182 BIOLOGY FOR BEGINNERS
most of which are adapted for different purposes (being developed
from the ordinary swimming leg) as is shown in the tabulation.
The front of the carapace extends forward into a protective beak,
the rostrum (why so called?) , on either side of which are the eyes,
set on movable stalks and each composed of many lenses.
Head Appendages. Beginning at the anterior (head) end, we
first come to the small and large feelers (antennae) at whose base
open the ear sacs and excretory organs respectively. Then come
the true jaws (mandibles) and two pairs of little jaws (maxillae)
which aid in chewing the food. To the posterior maxilla is attached
the " gill bailer," a scoop-shaped organ for paddling water over
the gills, the flow being toward the anterior. So far, the organs
named belong to the head. Notice the various functions performed.
Also observe that the jaws work from side to side and not up and
down, because they are merely leg-like appendages adapted for
chewing and so continue to have a horizontal motion as do the legs.
Thoracic Appendages. The first appendages of the thorax are
three pairs of maxillipeds (jaw feet) whose function is holding and
chewing food. To these are attached gills for respiration. Next
come the large claws, evidently for defence and food getting, then
two pairs of legs with claws at the tip and two more pairs with-
out claws. These four pairs of legs are concerned mainly with
walking, and to them and to the large claws as well, gills are at-
tached, which extend up under the carapace into the gill chamber.
Abdominal Appendages. The appendages of the abdomen are
called swimmerets and are similar on the first five segments, being
adapted for paddling forward in the water. They are also used by
the female for attachment of her eggs. The sixth swimmeret is
enormously developed into a wide fin or flipper while the ap-
pendage of the seventh segment is reduced to a mere spine and the
segment itself is flattened. The' sixth and seventh segments to-
gether form a powerful organ for backward locomotion, for they can
be whipped forward by the strong muscles of the abdomen and the
animal will shoot backward at high speed.
Adaptation. While we do not have to memorize all these append-
ages, there are two lessons that their study must teach; first how
ARTHROPODS
183
FIG. 59. The appendages from the entire right side of the body of a lobster,
arranged serially to illustrate serial homology. From Calkins.
184 BIOLOGY FOR BEGINNERS
remarkably division of labor may be carried out, and second that
we have here the modification of one kind of organ for many uses.
The tabulation will show how many and how varied are the func-
tions performed. It will also be seen that these various organs are
developed from a simple kind of appendage (the swimmeret). By
the addition and modification of segments, organs have been de-
veloped as widely different as the large claws and the antennae.
Homology. When we find organs (either in the same or different
animals) which were developed from the same part, that is, whose
origin and structure are similar, we call them homologous organs.
Thus we may say that the antennae and claws of the crayfish are
homologous to the swimmerets, or that our arm is homologous to
the foreleg of a horse, even though the functions are so different.
This word is the mate to analogous which meant similar in function.
We might say that the gills of the crayfish and the lungs of man
are analogous, because they both perform the function of respira-
tion but we cannot say they are homologous, since the gills are de-
veloped from the legs, while the lungs are outgrowths of the throat.
Internal Structure. Internally, also, there is a considerable de-
gree of specialization. The digestive system and its glands occupy
a large part of the cephalo-thorax, there being three sets of kvth
in the stomach, to complete the chewing of the food which was
begun by the jaws. A well-developed circulatory system and a
complicated heart mark an advance along this line. The e\m i tory
and reproductive organs are present and fairly developed. The
nervous system, though similar, is much more specialized than in
the worms. The senses of touch and smell, located in the antennae,
are probably acute. The eyes are on movable stalks and are com-
pound, each consisting of numerous lenses, but the sight is prob-
ably not keen. The ears are located at the base of the antennae
but neither hearing nor taste seem to be especially developed.
While these sense organs do not seem very efficient, yet enor-
mous advance can be seen when they are compared with the earth-
worm with no organs of special sense at all. The worm probably
feels only touch and vibration sensations through the body wall,
with a possibility of taste and heat or light sensations in the region
ARTHROPODS
FIG. 60. Longitudinal section of the lobster showing the arrangement of the
internal organs. From Calkins.
186 BIOLOGY FOR BEGINNERS
of the head. Since the degree in which an animal can get in touch
with its environment marks the stage of its advancement, the
Crustacea far excel the worms in development.
Locomotion. This function is provided for by the swimmerets
which carry the body slowly forward, by the tail flipper which drives
it swiftly backward, and by the four pairs of walking legs which
can travel in either direction and sideways as well. All are operated
by powerful muscles, assisted by the exo-skeleton. You can see
why the slang expression " to crayfish " means to back out of any
agreement.
Protection. The Crustacea's adaptations for protection are the
exo-skeleton with its color and spines, the powerful jaws and claws
for attack, speed for escape, fairly keen senses, and a nervous
system to guide its actions.
Respiration. Respiration in protozoa was accomplished by
contact of the cell with dissolved oxygen in the water; in the worm
by contact of the body wall with oxygen in the air; osmosis was
the method in both cases. In the Crustacea we have organs called
gills, specially developed for carrying on the exchange of oxygen
and carbon dioxide. These gills are thin walled, to allow osmosis,
feathery to expose much surface, provided with many blood vessels
to receive oxygen and to liberate carbon dioxide, and also are
arranged to insure a constant flow of fresh water over them. This
last is brought about in part by the gill bailer, attached to the
second maxilla and partly by the gills being attached to the
appendages. These move in the water, with every motion of a
leg or maxilliped. Finally, as the water passes under the carapace
from behind toward the head, this flow is aided every time the
animal swims backward. The gills are protected by the carapace,
which extends over them and forms a chamber which will
hold moisture for some time, thus keeping them alive when
removed from the water. Notice the importance of the fact that
oxygen is soluble in water; if it were not, the aquatic animals
could not exist, since it is the oxygen dissolved from the air,
and not the oxygen of the water (H^sO) itself which all water
animals use.
ARTHROPODS 187
Food-getting. The food of the Crustacea is usually animal,
either alive or dead, some even being cannibals, while others act
as useful scavengers. A few of the smaller forms are peaceful
vegetarians. Their swiftness, claws, mouth parts, color protection,
and sense of touch and smell all are adaptations for food-getting
and their large number shows how well able they are to cope with
their surroundings.
Life History. The eggs, which often number thousands, are laid
by the female, fertilized by sperms from the male as they are laid,
and attached to the swimmerets where they are carried and pro-
tected by the mother for about ten months. The young after hatch-
ing, which occurs in summer, cling to the swimmerets for some time.
When first hatched they are very small, not entirely like the adult
in structure, and they remain at the surface of the water for the
first stages. After moulting four or five times, they settle down on
the bottom among the rocks, where they live on smaller crus-
taceans. During these early stages which occupy ten to fifteen
days they are nearly defenceless and millions are destroyed by
other aquatic animals for food. After reaching the bottom they
are somewhat better protected though still destroyed in large
numbers. This high mortality is the reason for the production of
such large numbers of eggs. During their life at the bottom,
moulting occurs at longer intervals until adult size is reached at
the age of five years (in case of the lobster) after which they do not
moult oftener than once in one or two years.
Moulting. This moulting, or shedding of the exo-skeleton is a
direct result of having the hard parts outside. They cannot grow
larger except by shedding their armor, and this is a point in which
the internal skeleton of the higher animals is a very great ad-
vantage. With it, growth may be continuous. However, the exo-
skeleton provides better protection. When ready to moult, the lime
is partly absorbed from the skeleton; the carapace splits along the
back, water is withdrawn from the tissues which makes them
smaller and the animal literally humps itself out of its former
skeleton, leaving behind the lining of its stomach and its teeth.
Immediately water is absorbed and growth proceeds very rapidly.
188 BIOLOGY FOR BEGINNERS
The lime is replaced in the new and larger armor and Richard is
himself again. Usually the later moults take place in hidden
locations and with haste, as the animal is totally helpless and a
prey to all sorts of enemies when growing its new suit. It is at this
time that " soft shell crabs " are caught, which are merely the
ordinary crab in the act of moulting.
Reproduction of Lost Parts. In moulting or in battle with
enemies, it often happens that appendages are lost or injured, in
which case the limb is voluntarily shed between its second and
third segments. A double membrane prevents much loss of blood,
and a whole new appendage is developed to replace the injured
member. This accounts for the common sight of crayfish, etc.,
with one claw much smaller tha"n its mate.
This reproduction of lost parts depends upon the degree of com-
plexity of the part. The earthworm may be able to regrow the
whole posterior of its body while a starfish can develop all its or-
gans if one ray and its base be left. The hydra and corals nor-
mally reproduce by budding off new individuals and the protozoa,
simplest of all, regularly reproduce the whole animal by division
in two parts. On the other hand, higher forms, such as man, have
tissues so highly specialized that we cannot even grow a new
finger. The best we can do, is to develop scar tissue to fill a wound,
or grow new hair, nails, skin, and (once only) teeth. This is one
penalty for high specialization.
COLLATERAL READING
(Crayfish and Lobster)
N Y. State Forest, Fish and Game Report (1898), p. 290; U. S. Fish
Commission Report (1898), p. 229; Invertebrate Morphology, McMur-
rich, p. 377; Advanced Text, Claus and Sedgwick, p. 461; Invertebrate
Anatomy, Huxley, pp. 265-293; Advanced Text, Parker and Haswell
(Vol. I), pp. 498-514; Advanced Text, Packard, pp. 226-272; Animal
Forms, Jordan and Kellogg, pp. 93-104; Animal Studies, Jordan, Kel-
logg and Heath, pp. 109-120; Animal Activities, French, pp. 101-114;
Elementary Text (Zoology}, Kellogg, pp. 144-155; Elementary Text (Zo-
ology), Colton, pp. 61-86; Elementary Text (Zoology), Linville and Kelly,
pp. 125-156; Elementary Text (Zoology), Morse, pp. 130-147; Elementary
Text (Zoology), Needham, pp. 111-129; Elementary Text (Zoology), Daven-
ARTHROPODS
189
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ill
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190 BIOLOGY FOR BEGINNERS
port, pp. 120-152; Economic Zoology, Osborne, pp. 174-200; Economic
Zoology, Kellogg and Doane, pp. 106-125; Applied Biology, Bigelow, pp.
358-376; Life and Her Children, Buckley, Chap. VIII; Animal Life,
Thompson, p. 25; Seashore Life, Mayer, pp. 77-112; Life in Ponds
and Streams, Furneaux, pp. 179-200; Talks About Animals, pp. 3-45;
The Crayfish: an Introduction to Zoology, Huxley, entire; Practical
Zoology, Davison, Chap. IX.
SUMMARY
Contrast, worms, having only simpler tissues and organs, no skeleton,
inactive.
Crustacea, with high specialization, skeleton, active, aquatic.
Characteristics:
External skeleton adapted for protection.
Jointed appendages adapted for rapid motion.
High specialization adapted for division of labor.
Gills and connected organs adapted for aquatic life.
Crayfish (as type of Crustacea).
External Structure:
Exo-skeleton, for protection and to act as levers for muscles.
Protective adaptations:
Hard, limy, color, spines,
Projection over gills and abdomen.
Carapace, rostrum.
Lever adaptations:
Hollow, strong, light,
Hinge joints in all directions.
Body regions, cephalo- thorax and abdomen.
Cephalo-thorax :
Includes head and thorax, 13 segments,
United for strength, rostrum for protection.
Carapace over anterior and gills.
Head appendages:
Sense organs.
Antennules, antennae, for feeling or smell.
Eyes, ear sacs, sense hairs.
Mouth parts.
Mandibles, one pair for chewing.
Maxillae, two pair aid in holding food.
Maxillipeds, three pair, catching and chewing food.
Thoracic appendages.
Maxillipeds, three pair, holding and chewing food.
Large claws, defence and food getting.
Clawed feet, two pair, locomotion, prehension.
Unclawed feet, two pair, locomotion.
(Gills on all above appendages.)
ARTHROPODS 191
Abdominal appendages:
Swimmerets, five pair for swimming and egg attachment.
Tail fin, sixth and seventh pairs, backward motion.
Study of appendages shows
1. Modification of similar part, swimmeret, for different uses
(Homology).
2. Adaptation for different functions (specialization).
3. Division of labor among homologous parts.
Homology, likeness in structure and origin, shows relationship.
Analogy, likeness in function, not necessarily in structure.
Adaptations of Crayfish for
1. Locomotion.
Swimming forward by means of swimmerets.
Swimming backward by means of tail fin.
Walking either forward, backward, or sidewise.
2. Protection.
External skeleton, color, spines, carapace, projecting sides,
speed, claws.
3. Food-getting (what food?)
Claws, speed, mouth-parts, senses, color.
4. Respiration (cf. protozoa and worms).
Gills, adapted by being thin; for osmosis
Being well supplied with blood.
Being protected; large surface.
Water current provided by
Gill bailer.
Locomotion backward.
Leg motion in all directions.
5. Sensation.
Eyes, ears, feelers, hairs.
Life History:
1. Egg fertilized, attached to swimmeret (protection, aeration).
2. Hatch in summer, remain attached to mother.
3 Grow by moulting (reason).
4. Top swimmers when young, then on bottom.
5. Why so many eggs needed.
Moulting:
Reason (cf. internal skeleton).
Process: Absorption of lime from shell.
Carapace splits.
Water withdrawn from tissues, causing shrinkage.
Humps out of shell.
Re-absorption of water and rapid growth.
Hasty formation of new skeleton.
Lost Parts Reproduced:
What animals can reproduce lost parts?
Why not so much in higher forms? (Greater specialization.)
What tissues can man reproduce?
CHAPTER XXm
OTSECTA, A CLASS OF ARTHROPODS
Vocabulary
Trachea, a breathing tube, admitting air to the tissues. Plural:
tracheae.
Chitin, a horn-like, elastic substance found in the external skeletons
of insects and other arthropods, pronounced "kite-in."
Accessory, additional or assistant organs.
Palpus, feeler or sense organ attached to the mouth parts of in-
sects, etc. Plural: palpi.
Spiracles, external openings of the tracheae, used in breathing.
Ganglion, a mass of nerve tissue. Plural: ganglia.
The Insects include that division of the Arthropods which have
head, thorax, and abdomen separate, one pair of antennae, three
pairs of legs, usually two pairs of wings, and which breathe by
means of tubes called tracheae. This group includes more species
than all the other living animals together, there being about 300,000
kinds known already. Experts regard this as not more than one-
fifth of all in existence. Not only are there many kinds of insects,
but each kind produces myriads of individuals like the locusts and
mayflies, whose swarms darken the sky. Their struggle for ex-
istence is very severe and this results in manifold adaptations of
structure.
High Specialization. Highly specialized mouth parts for dif-
ferent kinds of food, wonderful leg and wing development for
swift locomotion, marvelous instincts and complicated internal
structure are some of the lines along which insects have developed
in order to survive among their countless competitors in the race
of life. Some are adapted for aquatic life, some take refuge by
burrowing, some live in colonies like bees and ants, others fight
their battles alone; some have become swift in running, leaping,
or flight, while, others have fallen back on parasitic laziness.
INSECTA, A CLASS OF ARTHROPODS
193
Classification. We cannot study all, or even one, species
thoroughly. However the accompanying table will show the
names and representatives of a few of the sixteen different orders,
and then we shall take up two or three types in greater detail.
Order
Orthoptera
Pseudo-neuroptera
Hemiptera
Diptera
Coleoptera
Lepidoptera
Hymenoptera
antennae
/' \
Representative
grasshopper cricket locust
dragon-flies
true bugs lice scale insects
flies mosquitoes fleas, gnats
beetles
moths butterflies
bees ants wasps
auditory organ
ocellus :
' head compound eye I
ovipositor
femur*
tibia-''
torsal segments
FIG. 61. Locust (enlarged) with external parts named. From Kellogg.
The Grasshopper. The grasshopper (which really is a locust)
will be taken as a type of all the insects. It belongs to the order
Orthoptera, which means " straight winged " and refers to the
narrow folded wings, held straight along the body.
Exoskeleton. As in all Arthropods, the skeleton is external,
but differs from the crayfish in that it contains no lime. It consists
194
BIOLOGY FOR BEGINNERS
entirely of a light, tough and horny substance called chitin which
is usually protectively colored. The head, with its sense organs
and mouth parts, the thorax with its legs and wings, and the ab-
domen, with its vent and reproductive organs, are all readily
distinguished.
Head
Sense Organs. The antennae are- the most anterior append-
ages and, as usual, are many jointed and devoted to the senses
of touch and smell. There are two kinds of eyes, three simple
ones located respectively at the base
of each antenna and on the ridge be-
tween them, and the large compound
eyes projecting from the sides of the
head and consisting of hundreds of
six-sided lenses. The shape, location,
and number of lenses in the eye seem
to adapt the insect for sight in several
directions at once, but the image
formed cannot be very sharp.
Mouth Parts. The mouth parts of
the grasshopper are fitted for biting
and chewing hard foods and consist
of labrum, mandibles, maxillae, and
labium, named in order from the
anterior. Though the mouth parts of insects are very greatly
modified to suit all kinds of food, still these four sets of organs are
always present, so we must become familiar with their names and
appearance.
The labrum is the two-lobed upper lip which fits over the strong,
toothed, horizontal jaws or mandibles. The pair of maxillae, or
accessory jaws, are next behind the mandibles. They aid in cutting
and holding food, and also have a sense organ, like a short antenna.
This is called a palpus (plural: palpi). Posterior to the maxillae
comes the labium or lower lip, a deeply two-lobed organ, also
provided with palpi, which aids in holding food between the jaws.
FIG. 62. Part of coraeal
cuticle, showing facets, of the
.compound eye of a horsefly,
Therioplectes sp. (Photomicro-
graph by Mitchell; greatly
magnified.) From Kellogg.
INSECTA, A CLASS OF ARTHROPODS
G7MSS HOPPED
195
LP
L. 1-AB.Run.
Mt. MANDIBLES.
MX M AX I Ll_ AE .
M.P. MAXILLARY -PALPI
L.P. LABIAL PAL.PI
Lab. LABlUfl.
Lob.
FIG. 63. Grasshopper.
Part I. Mouth Parts.
The upper lip or labrum is a thin scoop-shaped organ, which helps to hold
food between the jaws.
The mandibles or jaws, are very thick at the edge, sharply toothed and
operated by powerful muscles. They are dark brown in color and hard enough
to gnaw dry wood.
The maxillae or accessory jaws are very complicated organs consisting of
two sharp hook-shaped parts backed by a sort of hood. These help in hold-
ing food and perhaps in chewing it, too. Back of the hood are the palpi, whose
196 BIOLOGY FOR BEGINNERS
tips bear sense hairs, and perhaps enable the grasshopper to judge of the kind
of food he may be eating.
The "tongue" or hypopharynx in the center, fits closely in the throat and
seems to act as a sort of piston in helping to suck in the food particles.
The labium or lower lip, like the upper one, helps hold the food in place,
but is much larger and has a pair of palpi, like those on the maxillae.
Such mouth parts are typically for biting and chewing and are similar to
those found in many beetles, also.
Part II. The Leaping Leg.
The two short segments next the body are called the coxa and trochanter.
Their function is to give freedom of motion to the base of the leg and to set it
out a little from the side of the body so that it can push directly backward in
jumping.
The thick part is the femur and contains some very powerful muscles, though
the body muscles also help in jumping.
The tibia is the long thin part and is provided with backward projecting
spines which prevent back sliding and aid in cliirbing through grass.
The foot consists of several tarsal joints with flexible pads and backward
projecting spines which prevent slipping just like the spiked shoes of the human
jumper. The claws at the end aid in this and also in climbing.
The knee and ankle joints move only in one plane, but the joints next the
body can move sidewise also.
Thorax
The thorax consists of three segments, the pro-, meso- and meta-
thorax. The prothorax is a large saddle-shaped segment to which
the head is attached and bears the first pair of legs; the middle
or mesothorax bears a pair of legs and the first pair of wings; while
the last segment (metathorax) bears the leaping legs and the last
pair of wings.
Legs. Each of these six legs consists of five parts or segments,
connected by strong joints and adapted for locomotion by walking,
while the posterior pair is also enormously developed for leaping.
The feet (tarsi) are provided with spines, hooks, and pads to give
firm grip when jumping or crawling. A joint near the body almost
like a " ball and socket " permits sufficient freedom of motion.
Wings. The anterior (mesothoracic) wings are long, narrow,
and rather stiff. They protect the more delicate under wings and
act as planes in aiding flight and leaping. The posterior (meta-
thoracic) wings are thin and membranous. They are supported
INSECTA, A CLASS OF ARTHROPODS 197
by many veins and, when not in use, are folded lengthwise, like a
fan, beneath the narrower anterior wings.
Abdomen
The abdomen consists of ten movable segments, each composed
of an upper and lower part, united by a membrane which allows
it to expand and contract in the process of breathing. There
are no jointed appendages as on the head and thorax, but eight
of the segments have breathing pores (spiracles) on each side.
The segment next to the thorax bears the ears which are large
membrane-covered cavities on either side.
The extreme posterior segments in the female bear two pairs of
hard and sharp-pointed organs called ovipositors (egg placers)
whose function is to dig a hole in the ground in which the eggs are
laid. The males have no such organs but the posterior of the ab-
domen is enlarged and rounded upward.
Active Life. The activity of insects is well known but little ap-
preciated. They have the most enduring and powerful muscles
of any animal, in proportion to their size. Think of the long swift
flight of bees, often extending for miles, at enormous speed; think
of the loads carried by ants and beetles; of the hard labor done by
boring and burrowing insects, then compare their size and
weight with our own and see how fast we ought to fly or run, how
far we should jump, or how much we should carry, if we had their
muscular ability. Of course their enormous activity requires a
great deal of energy which means that they must use a large amount
of food, and this, in turn, implies a complete digestive apparatus.
The digested food requires oxygen to oxidize it and liberate its
energy and this requires a perfect system for breathing to supply
the oxygen. To control such a powerful high-speed engine, a well-
developed nervous system is also demanded.
The foregoing sounds like the " House that Jack Built " but is
an outline of just what we find to be the case, not only in insects
but in all higher forms. It is merely another instance of our order
of study, " Structure, Function, Adaptation."
198 BIOLOGY FOR BEGINNERS
Internal Structure. The internal structure is very complex, some
insects having over twice as many separate muscles as we have in
our whole body. The digestive system is well developed, there
being salivary glands, a crop, stomach, digestive glands, intestine,
ancf rectum.
Excretion is provided for by a large number of thread-like tubes
at the junction of stomach and intestine. Circulation, while not
entirely inclosed in blood vessels, is controlled by a six-chambered
heart on the dorsal (upper) side, from which the light-colored blood
is forced toward the head and around throughout the tissues, in
contact with the air tubes.
Respiration. The respiratory system is highly developed. It
consists of an extensive network of air tubes called tracheae, there
being six main tubes running lengthwise, from which branch air
sacs and smaller tracheae reach every tissue in the body.
These tracheae open by means of the spiracles, which are tiny
holes, protected from dust by hairs, found on the abdomen (8 pairs)
and on the thorax (2 pairs). By alternate expansion and contrac-
tion of the segments at the rate of sixty-five per minute air is
pumped in and out of these spiracles, and circulates through the
tracheae, where, by osmosis, the oxygen from the air and carbon
dioxide from the blood exchange places. A peculiar feature of the
insect respiration is the fact that the air goes to the blood by means
of the tracheae instead of the blood going to the air in capillaries
as in our lungs. Another curious fact is that the veins of the wings
are probably tracheae, adapted for the function of support rather
than respiration.
Nervous System. The nervous system of insects reaches a
higher degree of development than that of any invertebrate group
and a comparison of the types studied can well be made at this time.
The protozoan cell received its impressions directly, it responded
throughout, to heat, light, contact, and possibly other stimuli,
but vaguely and without the aid of any nervous tissue.
In animals like the hydra, certain groups of cells seem more
sensitive than others to external influences and also appear to
control the activities of the animal. These are the simplest ex-
INSECTA, A CLASS OF ARTHROPODS 199
amples of a nervous system and might be regarded as uncon-
nected nerve ganglia.
In the worms each segment has its nerve mass or ganglion, but
all are connected by a double nerve fiber and each sends out many
branches to various organs, which are thus controlled. Then,
too, in the worms, there is a larger ganglion in the anterior end,
above the mouth, which sends special nerves to the mouth parts
and skin. Although there are no special organs of sensation, and
the structure is very primitive, there is, nevertheless, an organ
corresponding to a brain.
In the Crustacea, the head ganglion, or brain, is located at the
base of the rostrum. It is much larger than in worms and has
branches extending to the eyes, ears, antennae, and mouth parts.
This brain is connected with ganglia along the under side of the
body but instead of having one for each segment, as in the worms,
they are combined into eleven larger and more complicated nerve
masses.
In the insects this combination of ganglia has gone farther still.
Including the brain there are two ganglia in the head, three in the
thorax, and five in the abdomen, and the brain and sense organs
are much more specialized in function.
If we could study more kinds of animals we would observe this
general tendency toward increasing the development of the head
ganglia, of combining others and reducing their number, while
increasing their ability, and the development of more efficient
sense organs and greater motion control.
As soon as the simplest animal forms developed far enough to
have one end always go forward (anterior) in locomotion, then
that end, naturally, "'ran into" contact with its environment.
So, at the anterior end the sense organs could be most useful, which
is the reason for this headward tendency in development.
In all animals the nervous system performs two general func-
tions; it receives and appreciates impressions from without (sen-
sation), and causes and controls motions from within (motor im-
pulses) . As the animals increase in complexity, the nervous system
correspondingly develops. As the complexity increased, there was
200
BIOLOGY FOR BEGINNERS
greater need of one controlling region, so that all the body's nu-
merous functions could operate in harmony and as a result the
need of a brain developed. Its location, as explained above, was
almost of necessity in the " head " or anterior end of the animal.
FIG. 64. Developing stages, after hatching, of a locust, Mdanoplus femur-
rubrum, a, just hatched, without wing-pads; 6, after first moulting; c, after
second moulting, showing beginning wing-pads; d, after third moulting; e,
after fourth moulting; /, adult with fully developed wings. (After Emerton;
younger stages enlarged; adult stage, natural size. From Kellogg.)
Life History. The eggs are fertilized internally, and are deposited
in two masses, protected by a gum-like substance, in holes which
the female digs in the earth with her ovipositor. From twenty to
thirty eggs are thus deposited in the fall, and hatch the following
spring. This illustrates a twofold advantage of egg reproduction,
for, not only is the number of individuals increased, but they pass
INSECTA, A CLASS OF ARTHROPODS 201
the winter safely in the protected egg, while most of the adults
are frozen to death. The young (nymph), though small, red,
and wingless, still resembles the adult in most respects, but as
is often the case with the young, the head is disproportionately
large. As with all arthropods, they grow by moulting, usually
five times, and at each step, develop in size and wings till they
reach full growth. The moulting, which takes about half an hour,
is followed by rapid growth and formation of a new exo-skeleton,
the former one having split along the thorax to allow the exit of
the growing insect. It emerges head first but very weak and limp,
and often does not survive the process.
Metamorphosis. In many animals the development from egg
to adult passes through more or less distinct stages instead of
being a gradual increase in size. Such a life history is called a
metamorphosis.
Among insects these stages may be several in number and the
differences between them slight, as in the grasshopper, or there may
be four definite and distinct stages, the egg, larva, pupa, and adult
as found in the butterfly, for example. The former type is called
an incomplete metamorphosis, the latter a complete metamorphosis.
Economic Importance. The members of the order to which
the grasshopper belongs (orthoptera) are with one exception, all
harmful to man. Their food is mostly cereal grains or crop
plants, which they often destroy over wide areas. Locusts and
grasshoppers have been a plague since ancient times. They are
often referred to in Scripture and the second chapter of Joel con-
tains a very vivid description of the destruction wrought by a
swarm of locusts. The only useful relative is the mantis, which
is carnivorous and eats other insects, many of which are harmful.
COLLATERAL READING
Life History of American Insects, Weed, pp. 67-81 ; Insect Book, Howard,
pp. 334-340; Insect Life, Comstock, pp. 70-233; Manual of Insects,
Comstock, pp. 104-118; Guide to Study of Insects, Packard, pp. 556-572;
Lessons' in Zoology, Needham, p. 48; Textbook of Zoology, Parker and
Haswell, Vol. I, p. 584; Textbook of Zoology, Packard, p. 308; Animal
Forms, Jordan and Kellogg, p. 117; Animal Life, Jordan and Kellogg,
202 BIOLOGY FOR BEGINNERS
p. 234; Textbook of Zoology, Linville and Kelly, pp. 11-14; Elemen-
tary Zoology, Kellogg, pp. 161-163; Injurious Insects, Treat, p. 269;
Injurious Insects, Saunders, p. 157; Introduction to Zoology, Daven-
port, pp. 1-4; Economic Zoology, Smith, pp. 11-51, 79-100; Economic
Zoology, Kellogg and Doane, pp. 14-25; Descriptive Zoology, Colton, Chap.
I-III; Practical Zoology, Davison, Chap. I-VII; Farm Bulletins, Nos.
47, 59, 70, 80, 132, 209, 211, 247, 264, 284.
SUMMARY
Characteristics of Insects:
Separate head, thorax, and abdomen.
One pair antennae, three pair legs.
Usually two pair wings.
Breathe by means of tracheae.
High degree of specialization (adaptation) because of
Severe struggle for existence, because of
Very large number of species and individuals.
Specialized for various foods:
Vegetable foods Grasshopper (biting)
Blood suckers Mosquitoes
Sap suckers Bugs and scale insects
Scavengers Flies and beetles
Nectar Bees and moths
Specialized for locomotion:
Crawling Beetles, etc.
Flying Bees, etc.
Jumping Grasshopper
Swimming Beetles and some bugs
Water surface Striders
Burrowing Ants, etc.
Specialized instincts:
(See references on Bees, Ants, Wasps, Termites).
General Structure:
1. Exo-skeleton, chitin, light, strong, and protective colored.
2. Regions:
Head for sense and food-getting organs.
Thorax for locomotion (respiration).
Abdomen for reproduction and breathing (ear).
Head:
Antennae, one pair, functions, cf. crayfish.
Eyes, simple, three, location,
compound, structure, why not on stalks?
INSECTA, A CLASS OF ARTHROPODS 203
Mouth-parts (biting).
Upper lip, Labrum, for holding food.
True jaws, Mandibles, for chewing.
Accessory jaws, Maxillae, to aid jaws (palpi).
Lower lip, Labium, to hold food (palpi).
Thorax.
Anterior thorax, Prothorax, Movable; legs attached.
Middle thorax, Mesothorax, Strong; wings and legs.
Posterior thorax, Metathorax, United to mesothorax wings and
jumping legs.
Legs,
Functions: walking, clinging, leaping.
Structure.
Adaptations:
Strength of muscles.
Length of leverage.
Free backward movement.
Spines, pads, etc.
Point of attachment.
Wings.
First pair, planes and protection, concave, stiff, straight.
Second pair, thin, folded fan- wise, propellers.
Abdomen (structure).
Adaptations for respiration, spiracles, motion of segments.
Adaptations for reproduction, ovipositors.
Adaptations for hearing, ears.
Activity requires energy.
Energy requires food to supply it.
Food requires oxygen to release its energy.
Oxygen" supply requires good breathing organs.
All this energy requires high nerve control.
Internal Structure.
Muscles, complex, strong, and very numerous.
Digestion, glands, crop, stomach, caeca, intestine, rectum.
Excretion, malpighian tubes.
Circulation, open system, dorsal, light color blood.
Respiration, spiracles, trachea, motion of abdomen.
Nervous system, high, senses well developed.
Development of nervous system :
Protozoa, direct to protoplasm, sense heat, light, contact.
Hydra, special nerve cells in groups (ganglia), motor control.
Worms, ganglia connected, beginning of brain.
Crustacea, fewer ganglia, cephalization, sense organs.
Insecta, very high brain ganglia, iew others, great motor control, instinct.
204 BIOLOGY FOR BEGINNERS
General tendency of nervous development:
1. Fewer ganglia.
2. Increasing complexity (centralizing control).
3. Location in anterior (first contact with environment).
General functions of nervous system.
1. To receive impressions from without (sensation).
2. To control and originate motion (motor impulses).
Life History:
1. Kgg, fertilized, buried in earth by ovipositors.
20-30 in two masses, in autumn.
Functions: to reproduce and to pass winter protected.
2. Nymph, like adult but small and wingless.
Growth by moults, development of wings.
Complete and incomplete metamorphosis compared.
Economic Importance.
CHAPTER XXIV
INSECTA, CONTINUED
Vocabulary
Vestiges, remnants or traces of organs.
Metamorphosis, the series of changes in the life of an animal.
Credible, believable.
Communal life, life in colonies for mutual help.
Gorged, filled with food.
Bearing in mind the fact that all insects have, in general, the
same organs as those found in the grasshopper, we shall now briefly
study how they are developed in representatives of a few other
insect orders.
LEPIDOPTERA
The butterflies and moths belong to the order lepidoptera (scale
winged) and furnish a familiar type of quite a different group of
insects.
Head. The antennae of butterflies are club shaped or knobbed
at the tip while those of moths are usually feather like. The com-
pound eyes are very large and rounded and the neck very flexible,
but it is in the mouth parts that they differ most from the or-
thoptera, these being adapted for sucking nectar from flowers.
The labrum and mandibles are reduced to mere vestiges while
the maxillae are enormously lengthened and locked together to
form the coiled proboscis or tongue which, when extended, may
equal in length all the rest of the body and is always long enough
to reach the nectar glands of the flowers they prefer. The labium
is reduced in size, two feathery palpi being all that is left of it in
most cases. Thus in this set of mouth parts, we have an example
205
206 BIOLOGY FOR BEGINNERS
of organs homologous to those of the grasshopper, but very differ-
ently adapted.
Thorax. The legs of the lepidoptera are small and weak, having
the same general structure as in all insects. Obviously the but-
terfly neither walks nor jumps. It uses its legs only for clinging to
its resting places and spends most of its time in the air. The
wings are large and covered with colored scales from which the
order gets its name. These scales help the few veins in giving
FIG. 65. Butterfly.
Fig. 1. Side view of head. Note the club shaped antennae with sense hairs
at tip. .
The enormous eyes curve out so far that vision is possible in all directions.
The small organs below the eyes are palpi from the labium, which are also
sense organs.
The partly uncoiled "tongue" is composed of the two maxillae, and has a
roughened tip for opening the nectar glands of flowers. It is called the pro-
boscis.
Fig. 2. Front view of head. Same parts shown as mentioned above except
that the proboscis has been cut through to show the two maxillae, joined edge
to edge with the tube between them for sucking nectar.
strength to the wing, and in some cases in color protection as well.
The thorax and its muscles which move the wings are not very
powerful, and the butterfly, though easily supported by its large
whig spread, is not a swift flyer.
Abdomen. The abdomen resembles that of the grasshopper,
but has fewer segments, and as in all insects is the least specialized
body region.
Life History. The eggs of most lepidoptera are deposited on
or near the plant which will be the food of the young. Some pass
INSECTA, CONTINUED
207
the winter in this stage but usually eggs are
deposited in the spring and partly develop
that same season.
The egg does not hatch into a form at all
resembling the adult, but instead, there
emerges a tiny worm-like form called the
larva, which differs entirely in structure,
having no wings, nor compound eyes, but
possessing several extra pairs of legs and
biting mouth parts. In fact, these and
other insect larvae are what we often call
" worms," which they do somewhat resem-
ble in shape. However, they are really one
step in the development of an insect, and
are vastly more complex than the true
worms. The larval stage devotes its whole
attention to eating, growing, and moulting,
and after about five changes of clothing,
it stops this gluttonous life in which it
often does a great deal of
harm, and goes into a
resting stage called the
pupa.
In butterflies, when the
last moult occurs, a pupa
case or chrysalis is formed
which protects the insect
during its long pause. The
larva often seeks a pro-
tected spot or burrows in
the earth before this
change occurs. The moth
larva, on the other hand,
spins a wonderful case of
silk, the cocoon, by which
it protects and attaches its pupa for its period of retirement.
FIG. 66. Sphinx moth, showing pro-
boscis; at left the proboscis is shown coiled
up on the under side of the head, the nor-
mal position when not in use. Large figure,
one-half natural size; small figure, natural
size. From Kellogg.
208
BIOLOGY FOR BEGINNERS
This pupa stage in which the lepidoptera usually pass the winter,
is not really a period of entire rest. Marvelous changes take place
which are not well understood,
but this at least is known, the
worm-like larva emerges totally
changed both in internal and
external structure, as the adult
butterfly or moth.
Whereas the larva's func-
tion was to eat and grow, the
adult eats only the nectar of
the flowers and its life work
is to produce or fertilize the
eggs for the next generation.
Such a life development,
consisting of distinct stages,
is called complete metamor-
phosis, as distinguished from a
life history of gradual changes
(like the grasshopper) which is
called incomplete metamor-
phosis. Complete metamor-
phosis is not confined to the
FIG. 67. Diagram of wings of
monarch butterfly, Anosia plexippus,
showing venation, c, costal vein; s.c.,
subcostal vein; r, radial vein; ca, cubital
vein; a, anal veins. In addition, most
insects have a vein lying between the
subcostal and radial veins, called the
medial vein. Natural size. From
Kellogg.
lepidoptera. The bees, beetles,
and flies all pass through
similar series of changes
which can be tabulated as
follows:
f Deposited near source of food
I Period of increase in number
f Period of eating and growth (usually harmful)
I Worm, grub, or maggot stage
f Period of quiet, internal transformation
\ Usually pass winter in this stage
( Cocoon or chrysalis
Adult Reproductive stage
Egg
Pupa
ENSECTA; CONTINUED
209
The larva of the lepidoptera is often very harmful as it feeds
on man's crops, the multitude of so-called " worms " being only
too familiar examples. The pupa stage of the silk moth furnishes
us with silk from the threads of its cocoon. The adults aid in
Courtesy of the A merican Museum of Natural History.
FIG. 68. This caterpillar of the monarch butterfly is ready for the meta-
morphosis. It hatched in late summer and grew for two weeks. It stopped
eating, chose a secure spot and spun a small thick carpet of silk. It walked over
this until the hind feet were entangled in the silk, then it hung head downward,
motionless. The skin now loosens, and after twenty-four hours splits over the
head. At this stage the caterpillar, by musuclar contraction works the skin
off upward into a small shriveled mass; then during the few seconds longer
that it still remains attached to the skin, it reaches out its slender end and with
great effort and force pushes it up into the silk carpet. The whole process has
taken but three or four minutes. Slowly the shape changes, the segments above
contracting, the form rounding out; and behold an emerald-green chrysalis
studded with golden spots! In two weeks the pattern of brown and orange
wings begins to show through, finally the chrysalis skin splits over the head,
and the butterfly crawls out.
210
BIOLOGY FOR BEGINNERS
the pollenation of flowers, by reason of their thirst for nectar and
their hairy bodies which carry the pollen.
FIG. 69. Metamorphosis, complete of monarch butterfly, Anosia plexippus.
a, egg (greatly magnified); b, caterpillar or larva;' c, chrysalis or pupa; d, adult
or imago. After Jordan and Kellogg. Natural size. (From Kellogg.)
Moths and butterflies are often confused, but can be distinguished
by the following comparison :
Butterfly
Day flier
Chrysalis for pupa
Wings vertical when at rest
Antennae knobbed
Abdomen slender
Moth
Night flier
Cocoon for pupa
Wings held horizontal
Antennae feathery
Abdomen stout
INSECTA, CONTINUED
ORDER: HYMENOPTERA
211
The hymenoptera (membrane winged), which include the bees,
ants, and wasps, represent the most highly specialized type of
insect. In structure, instinct, and manner of life they far excel
all their relatives. A complete account of the doings of some of
the higher forms makes a common fairy tale seem credible by
comparison. Huxley said that an ant's " brain " was the most
/tONr BEE.
yuva -tmucruitr.
FIG. 70. Honey Bee Mouth Parts, etc.
Figs. 1 and 2. Mouth parts. The mouth parts as a whole are fitted for
biting, cutting and lapping liquids.
The labrum is reduced to a small triangular organ, of slight importance except
as a guide for the other parts.
The mandibles (Md.), are powerful, sharp-edged jaws with which wax or
leaf material can be cut and worked.
The maxillse (Mx.), are slender, pointed organs which can also be used for
cutting and working in wax.
The labium is the most highly modified of the mouth parts (La.), and is
212 BIOLOGY FOR BEGINNERS
used for lapping up nectar from flowers. For this purpose it is long, slender
and flexible, with roughened tip to hold more liquid. The labial palpi (L.P.)
are attached at the side and are probably sense organs.
As a whole the bee mouth parts present a very high example of specializa-
tion, in which the usual six parts are developed to a condition little resembling
the typical condition in the grasshopper.
Resulting from this, the bee can do several different operations with its
mouth parts, while in most cases they would be fitted only for one, such as
biting in the case of the grasshopper, or piercing in case of the mosquito.
Fig. 3. The Wings. Attention is called to the relatively small size and
fewness of veins in the bee wings. This is evidence of high specialization here,
also, as they are perhaps the most efficient flying 'apparatus possessed by any
insect, yet are comparatively small and light.
The few veins are placed in exactly those regions where strain is greatest,
the wing muscles are powerful, and operate at a high rate of speed, which
accounts for their small size.
The posterior pair bears a series of hooks which may attach it to the anterior
pair, so that both act as one wing in flight, but fold back separately when at
rest.
wonderful piece of protoplasm in the world, and this would apply
almost equally to several other representatives.
Honey Bee. As an example of this order we shall study the
honey bee, since it is a form with which all are familiar. The body
regions are very distinct, the head being attached to the thorax
by a flexible neck and the thorax to the abdomen by a slender
waist. Each region is highly developed.
Head. The sensitive, elbowed antennae, the enormous compound
eyes and three simple eyes are easily seen, but the mouth parts
are very complicated and are really a set of tools by themselves.
The labrum is small, but the mandibles are developed into efficient
cutting and biting organs. They are used in manufacturing wax,
leaves, etc., into cells. The maxillae are complicated organs adapted
also for cutting and piercing as well as aiding in the work of the
labium. The labiuni and its palpi form a very efficient " tongue "
for lapping up the nectar upon which they live.
Thorax. The thorax is large, strong, and is provided with
powerful muscles which operate the legs and wings.
The bees are notably swift and enduring flyers and their wings,
while small, are exquisitely proportioned and operate at very hi.uli
speed, producing the familiar hum. The anterior wing is much
INSECTA, CONTINUED 213
the larger and the posterior wing may be attached to it, in flight,
by tiny hooks. Honey bees often wear out their wings by constant
use.
The three pairs of legs are each provided with special adapta-
tions. On the anterior pair is found a notch and comb through
which the antennae are drawn to clean them of pollen. The middle
pair have a spine or spur which is used in transferring pollen back
to the hind legs, which are most highly specialized of all. This
pair has one segment bordered with strong hairs to form a basket
for carrying pollen. The next segment has a series of combs for
handling it, and between the two segments is a movable notch
which is used as a shear for cutting and shaping the wax.
Abdomen. The abdomen consists of six segments, with ovipositor
or sting at the posterior end. Between each segment are glands
which secrete wax for comb making.
Life History. The life history of the honey bee is the best
example of communal life and mutual help. Each member of the
colony works for the good of all, and this unselfish habit has
resulted in great success as a whole, as well as remarkable develop-
ment for each individual. There are three forms of bees in any
colony, the queen, drones, and workers.
The Queen. The queen is almost twice as large as the worker,
with a long pointed abdomen, but with no pollen basket nor comb,
her particular function being the production of eggs to continue
the colony. She may produce as many as three thousand per day,
which is twice her own weight. The queen develops from an
ordinary egg, but the workers enlarge the wax cell in which it is
to grow and feed the grublike larva with extra portions of nourish-
ing food. This causes the development of a queen, or fertile
female, instead of a worker, which is a female without the ability
to lay eggs. After being thus fed for five days, the larva weaves
a silken cocoon, changes to a pupa, and is sealed into her large
waxen chamber by the workers. When the mature queen emerges
from her cell, she seeks out other queen larvae in the colony and
kills them, or if she finds another adult queen, they fight till one
is killed. She never uses her sting except against another queen.
214
BIOLOGY FOR BEGINNERS
After a few days she takes a wedding flight in the air, where she
mates with a drone, or male bee. Then the eggs are fertilized,
and she returns to the hive and begins her life work of laying eggs.
If the workers prevent her from destroying the other queens, she
takes part of the colony and " swarms " out to seek a home else-
where. A queen may live from three to ten years.
PC
BE
FIG. 71. Honey Bee Leg Adaptations.
Notice that in all the legs there are the same number of segments, but dif-
ferently developed. This is an excellent example of division of labor or speciali-
zation among homologous parts.
The anterior leg has, at the first tarsal joint, a notch and a movable spine
over it, so that the antennae may be drawn through and cleaned of pollen
after visits to the flowers. When you realize that the antennae are the insect's
most important sense organs, except possibly the eyes, this is seen to be an
important special function.
The middle leg is only slightly modified, but has a strong spine which is used
INSECTA, CONTINUED 215
in passing back the pollen from the other legs and depositing it in the pollen
baskets.
The posterior leg, of which both surfaces are shown, is most highly special-
ized. Along the edges of the tibia are developed strong rows of hairs which
form a pocket or basket, in which the pollen is carried.
The joint between the tibia and the first tarsal segment is shaped like a pair
of shear jaws, and is used for wax working.
The first tarsal segment is provided with rows of stiff hairs which help to
comb the pollen into the baskets, or from the opposite legs.
The rest of the tarsal segments are developed as usual, for clinging in loco-
motion, in the case of all three sets of legs.
In the bee, then, there are at least six different functions performed by the
legs, for which they are provided with special structural adaptations.
Such high development is probably the result of the habit of communal
life which permits greater. division of labor than is possible where animals live
alone or in pairs.
The Drones. The drone, while larger than the worker, is smaller
than the queen and has a thick, broad body, enormous eyes, and
very powerful wings. It is not provided with pollen baskets,
sting, or wax pockets.
His tongue is not long enough to get nectar, so he has to be fed
by the workers and his sole function is to fertilize the eggs of the
queen. However, this easy life has its troubles for with the coming
of autumn when honey runs low, the workers will no longer support
the drones, but sting them to death, and their bodies may be found
around the hives in September.
The Workers. The workers are by far the most numerous
inhabitants of the hive; they are undeveloped females, smaller
than drones with the ovipositor modified into the sting, and with
all the adaptations of legs, wings, and mouth parts, which have
been described.
With the exception of the process of reproduction, all the varied
industries and products of the hive are their business and they
perform, at different times, many different kinds of work as well
as providing the three hive products wax, honey, and propolis.
In summer they literally work themselves to death in three to
four weeks, but may live five to six months over winter.
Products of the Hive. Wax is a secretion from the abdominal
segments of workers, which comes after they have first gorged
216 BIOLOGY FOR BEGINNERS
themselves with honey, and then have suspended themselves by
the feet in a sort of curtain. As the wax is produced, it is re-
moved by other workers, chewed to make it soft, and then carried
to still others by whom it is built into comb.
This comb is a very wonderful structure, composed of six-sided
cells in two layers, so arranged as to leave no waste space, and
afford the greatest storage capacity with the use of the least
material. Not only is it used for storage of honey, and " bee
bread " (a food substance made from pollen and saliva) but also
for the rearing of young bees, the eggs being placed one in a cell
by the queen and sealed up by the workers, making what is called
" brood comb."
Honey is made from the nectar of flowers which is taken into
the crop of the bee, its cane sugar changed to the more easily
digested grape sugar, and then emptied into the comb cells, where
it is left to ripen and evaporate before being sealed up. Until the
seventeenth century, people did not know how to make sugar,
and depended upon honey entirely for this necessary food. At
present the bee products in United States are worth $22,000,000
per year.
The removal of honey by man does not harm the bees if about
thirty pounds be left for their winter use, that being sufficient to
feed the average colony of about 40,000 bees for an ordinary winter.
Propolis, or bee glue, is another important product of the hive.
It is gathered from the sticky leaf buds of some plants. Bees will
even use fresh varnish if they can get at it. It is used to make
smooth the interior of the hive, to help attach the comb, to close
up holes and cracks, and even to varnish the comb if it is left
unused for a time; it is the brown substance which may be seen
on section boxes in the stores.
Industries of the Colony. Not only do the workers prepare the
wax, honey, and propolis, as needed, but they have other duties
as well, which they also take turns in performing. Some attend
and feed the queen or drones; some act as nurses to the hungry
larvae, which they feed with partly digested food from their own
stomachs; some clean the hive of dead bees or foreign matter; some
INSECTA, CONTINUED
217
fan with their wings to ventilate the hive and, all the time, thousands
of others are bringing in the nectar, pollen, and propolis as needed
for use of the colony. Such a communal or colony life illustrates
the highest development of division of labor found among the
animals lower than man, and occurs among some ants and wasps
as well as bees, though nowhere carried to a higher point than in
the honey bee.
Larval Forms. The larval forms of many insects are so different
from the adults that they have received separate names which
sometimes confuse the relationship.
The larva of the
beetle
fly
bee '
mosquito
butterfly
moth
is called a
grub
maggot
grub
wiggler
caterpillar or " worm "
( caterpillar or " worm "
We speak of " silk worms," or " apple worms," etc., when we
really refer to larval forms of moths; " cabbage worms " and
" currant worms " are larvae of butterflies.
" Wire worms " are beetle larvae; the " moth " that eats woolens
is the larva and not the moth itself; the " carpet bug " or " buffalo
bug " is the larva of a beetle.
COLLATERAL READING
Manual for the Study of Insects, Comstock, pp. 48-76, 104-118; Insect
Life, Comstock, pp. 11-21; Guide for the Study of Insects, Packard; En-
tomology for Beginners, Packard, pp. 178-223; Insecta, Hyatt and Arms;
Elements of Zoology, Davenport, pp. 11-89; Animals and Man, Kellogg,
Chap. XV; Textbook of Zoology, Colton, pp. 1-53; Lessons in Zoology,
Needham, pp. 36-104; Practical Zoology, Davison, pp. 30-125; Compara-
tive Zoology, Kingsley, pp. 213-234; Elementary Zoology, Galloway, pp.
232-273; First Book of Zoology, Morse, pp. 49-108; General Zoology, Lin-
ville and Kelly, pp. 1-100; General Zoology, Herrick, pp. 153-195; Animal
Life, Jordan, Kellogg and Heath, pp. 149-155; Animal Studies, Jordan,
Kellogg and Heath, pp. 130-149; Elementary Biology, Peabody and
Hunt, pp. 9-61; Introduction to Biology, Bigelow, pp. 279-286; Applied
Biology, Bigelow, pp. 380-398; Nature Study and Life, Hodge, Chap.
218 BIOLOGY FOR BEGINNERS
V, X, pp. 181-294; Handbook of Nature Study, Comstock, pp. 308-451;
Life in Ponds and Streams, Furneaux, pp. 202-345; Life and Her Chil-
dren, Buckley, pp. 201-268; Insect Friends and Foes, Craigin, pp. 53-76;
Insect Life of Farm and Garden, Sanderson, see index; Insects Injurious
to Fruits, Saunders, see index; Injurious and Useful Insects, Miall, see
index; Insects and Insecticides, Weed, see index; Insects Injurious to
Vegetation, Chittenden, see index; Insect Pests of Farm and Garden,
see index; Insects Injurious to Trees, N. Y. State Report; Economic
Entomology, Smith, pp. 11-51, 79-100; Economic Zoology, Osborne, pp.
235-310; Economic Zoology, Kellogg and Doane, pp. 14-25, 125-182;
Life Histories of American Insects, Weed, see index; Insect Book,
Howard, pp. 332-346; Butterfly Book, Holland; Moth Book, Holland; How
to Know the Butterflies, Comstock; Cornell Leaflets (bound volume),
1894-1904, pp. 135-140; Cornell Leaflets, pp. 226-261; Cornell Leaflets,
pp. 529-557; Cornell Leaflets, pp. 213-223; Cornell Leaflets, 1915, pp.
153-190; Cornell Leaflets, 1916, pp. 122-152.
SUMMARY
Lepidoptera (scale winged) moths and butterflies.
1. Structure:
Head, antennae, knobbed or feather shaped.
Compound eyes.
Mouth parts (adapted for sucking nectar).
Labrum and mandibles reduced.
Maxillae form proboscis.
Labium reduced to palpi.
Thorax,
Legs small and weak.
Wings large, few veins, scaled, slow motion.
Abdomen,
Little specialized.
2. Life history (complete metamorphosis):
Egg laid on food plants.
Larva, caterpillar (eating stage), harmful.
Pupa, cocoon or chrysalis (quiet stage), silk.
Adult, moth or butterfly (reproductive stage) pollenation.
Hymenoptera (membrane winged) bees, ants, and wasps.
1. Structure:
Head, antennae, short, elbowed.
Eyes very large.
Mouth parts (adapted for biting, lapping, and sucking).
Labrum, small, triangular.
Mandibles, sharp for biting.
Maxillae, long, sharp, for cutting wax, etc.
Labium, tongue-like, for lapping nectar.
INSECTA, CONTINUED 219
Thorax, large and strong.
Wings small but powerful.
Legs, anterior with antenna cleaner,
middle with pollen spine,
posterior with pollen basket and wax shears.
Abdomen, six segments.
Ovipositor or sting.
Wax glands.
2. Life history (complete metamorphosis) communal life.
Egg, laid by queen in comb cells.
Larva, helpless grub, fed by workers.
Pupa, sealed in wax cell.
, Adult, three forms as follows:
Queen, large, fertile female, produces eggs.
Drone, thick body, large eyes, fertilizes eggs.
Workers-, smaller, sting in place of ovipositor.
3. Hive products:
Wax, secreted from abdominal segments of workers.
Honey, concentrated and partly digested nectar.
Propolis, glue made from plant gums. " Bee bread."
4. Division of labor (among workers).
Collection of nectar, pollen and gum.
Preparation of wax, honey, propolis, and bee bread.
Feeding queen, drones, and larvae.
Ventilating hives by fanning, cleaning hives.
Guarding hives from intruding insects and robber bees.
CHAPTER XXV
INSECTS AND DISEASE
FLIES AND MOSQUITOES
Vocabulary
Excrement, waste matter thrown off by animals from the intestine
or kidneys.
Cooperation, working together for a single purpose.
Invariably, always, without exception.
Contract, to " take" a disease.
Another insect order which we shall take up very briefly is the
diptera (two-winged) which includes the flies and mosquitoes.
They are studied chiefly because of their relation to the carrying
of disease germs. The diptera differ from all other insects by
having but one pair of wings, the posterior pair being replaced by
flat or knob shaped balancers. Their mouth parts are fitted for
piercing, rasping, and sucking, and their metamorphosis is complete.
The Typhoid Fly. The common house fly (typhoid fly) has very
highly developed mouth parts adapted for rasping and sucking,
large eyes, and short fleshy antennae. Its wings, though but two
in number, are well developed, and operated at high speed by the
powerful muscles of the thorax; the posterior pair are replaced by
flattened balancers. The six legs are well developed and the feet
(tarsi) are provided with claws and sticky hairs which aid in loco-
motion. Unless these hair tips are very free from dust they will
not stick well and the fly cannot walk readily on smooth surfaces,
hence the care with which it cleans its feet by constantly rubbing
them against each other and its body.
Life History. However, our principal concern is with the life
history and habits of the fly rather than with its structure, since
it is in this connection that it affects man's health.
220
INSECTS AND DISEASE
221
The eggs are deposited in
horse manure if it is to be
found, or in other similar
matter, about two hundred
being laid by each female.
They hatch in one day into
the larval form which we call
maggots, and in this stage
do some good as scavengers.
After eating and growing for
about five or six days, the
larvae pass into the pupal
condition, inside the last lar-
val skin, which thus takes
the place of a cocoon. From
this the adults emerge in
about a week. The whole
process occupies about two
weeks, begins early in spring,
American Museum of National History
FIG. 73. Eggs of the housefly.
Courtesy of the American Museum of Natural History
FIG. 72. Common house (typhoid) fly.
and continues till cold
weather. Supposing that
half the eggs produced fe-
males and these reproduce
at the same rate, calculate
the number of flies that
might be produced by one
adult which had survived the
winter, and the enormous
number of flies in existence
will be accounted for.
Danger from Flies. Flies
have always been regarded as
more or less of a nuisance, as
they crawl over our food and
our bodies, fall into milk and
other liquids, and annoy man-
222 BIOLOGY FOR BEGINNERS
kind in various ways, but their real harm has only recently
been realized.
They live in and feed upon manure and filth, then come and
crawl over our food and faces, or wash themselves in the cream
pitcher. When we realize that typhoid, cholera, and dysentery are
intestinal diseases, that the germs are carried off by the excrement
in which flies thrive, it is no wonder that they infect our food when
FIG. ?4. Larvae and pupae of housefly, Musca domestica, in manure. Natural
size. From Kellogg and Doane.
they crawl upon and share it with us. The fly is not only a filthy
but a very harmful insect and one to be avoided and destroyed.
A fly eats its own weight of food every day. Its food is largely
manure, sputum, and other filth, though it also samples our food
at table. Disease germs pass through the fly's intestine unharmed
and remain active in the familiar " fly specks " which are deposited
at intervals of five minutes. Thus the fly carries filth and disease
INSECTS AND DISEASE
223
both externally on its feet and body and internally by way of its
food and excreta.
Our common flies transmit typhoid, cholera, summer complaint,
dysentery, tuberculosis, and probably other diseases where the
germs pass from the body in any form of excrement, pus, or sputum.
The tsetse fly of Africa transmits the deadly " sleeping sickness."
Thus it is seen that flies which we formerly regarded as an un-
FIG. 75. Foot of housefly showing claws, hairs, pulvillae and the minute
clinging hairs on the pulvillae. From Kellogg and Doane.
avoidable nuisance, have been proven to be responsible for the
death of more people than all wild beasts and reptiles together,
and that actually they are more dangerous to man than the tiger,
grizzly, or rattlesnake.
Rate of Reproduction. In the face of its enormous rate of in-
crease, " swatting " of individual flies is a losing battle as the
following figures show. Supposing that reproduction was un-
checked and that all offspring survive (which fortunately is not
224 BIOLOGY FOR BEGINNERS
always the case) then one fly would produce in the different
generations of two weeks each as follows.
1st 200 (half females)
2nd (100x200) 20,000 ( " " )
3d (10,000x200) 2,000,000
4th 200,000,000
5th 20,000,000,000
6th 2,000,000,000,000
2,020,202,020,200 total in 12 weeks
or the perfectly unthinkable number of over two million millions
in half the breeding season, which would be over 20,000 flies to
be killed by each man, woman, or child in the United States -
and this the progeny of one adult female which survived the winter.
Fly Control. Fortunately there are more efficient ways of de-
stroying this dangerous pest. These are briefly tabulated below:
government bulletins fully describing all methods may be had for
the asking, and general cooperation has much reduced the pest
in many cities. The following are the most efficient methods of
control :
1. Horse manure and other filth can be removed, screened, or
chemically treated to kill the larvae.
2. Garbage and sewage can be properly covered and removed.
3. Houses can be screened.
4. Food, especially in stores, can be protected.
5. Fly traps and wholesale poisons are helpful.
The Mosquito. The mosquito is another member of the diptera
which demands mention because it, too, transmits serious diseases
to man though it acts in a different way from the fly. The germs
actually develop a part of their life history within the mosquito's
body, while the fly merely carries its dangerous burden,
mechanically.
Mouth Parts. In the mosquito, the labrum, tongue, mandibles,
and maxillae are reduced to sharp, lance-like bristles, enclosed
within the labium as a sheath, and are adapted for piercing and
sucking. In order to dilute the blood, so that they can withdraw
INSECTS AND DISEASE
225
it, they inject a little saliva, which causes the usual irritation and
swelling of a mosquito bite.
Disease Transmission. This would be bad enough, but it has
SOURCE
Nasal discharges
Open sores
DISEASE HOW ENTERS MAN
Carcasses
Sputum
Privies 1
Manure}
infantile paralysis
optha/mia
syphi/is
yaws
anthrax
faberca/osis
typ/io/d
diarrhoea
Cfio/era
tapeworm
Open jore
rood
SWAT THE:
FIRST
FLY
2S9Z0OOO
rfy lays /ZO e0QS
MAY 10. 60 Hits lay
MAYZO. 3600 Hies fay
MAY3O.ZI6OOO F/itt /ay
JUNE /O. I Zf 60000 Hie* /ay
JUA/EZO-77000O00 Flies lay 933/2.0O00O0 e<&S
"JUME 30-304665600000 f/tes /ay JS987Z00OO000 e&S
= JULY 9- 279 9 J6 0000000 r/ies /ay 3ZS9Z3ZOOOOOO00 e<?&S
JULY 1 1- 167^6/600000000 Flies lay 2O/ SSJ9&OO OOOOOOO eggS
JUL Y 2 c l-/00'r 76 <3600O0o0OOO Flies lay /1093ZJ JX.00O0006OOO e#0S
AUGUST S-60466/760000O0OOO0Flie3 lay 7'<3'>5 e: i4/l2O00OO0O0000 Sf&S
FIG. 76.
Upper. Diagram showing, the relation of flies to disease.
Lower. Cartoon from newspaper showing rate of increase of the fly.
From Pearse.
been absolutely proven that if certain species of mosquitoes bite
a person having either malaria or yellow fever, the protozoan
which causes the disease, is taken up with the blood, develops in
the mosquito's body and may be injected with the saliva into the
226
BIOLOGY FOR BEGINNERS
blood of a well person. Not only has this been shown, but by means
of experiments in which several men sacrificed their lives, it is also
proven that this is the only way in which these, and probably
other diseases, are transmitted. Men tended yellow fever patients,
slept hi their beds, wore their clothes and though exposed hi every
way, did not contract the disease as long as screened from mos-
quitoes. Others who allowed themselves to be bitten by mos-
quitoes which had previously bitten yellow fever patients, in-
variably contracted the disease, which in some cases resulted in
their death. From these sacrifices, methods of control have
FIG. 77. Mass of mosquito eggs.
developed which have saved thousands of lives in all parts of the
world.
Life History. As with the fly, a knowledge of its life history
enables man to contend with the mosquito, and these campaigns
are much more successful than those against the fly. The eggs
are laid in stagnant water; ponds, rain barrels, and even tin cans
furnish ideal breeding places. They are deposited in tiny rafts,
consisting of many eggs covered with a waterproof coating, and
when they hatch the larvae emerge downwards into the water,
and become the familiar " wigglers " seen in rain barrels. Though
living in water the mosquito larva breathes air, which it obtains
through a tube, projecting from the posterior of its abdomen.
It may often be seen with this tube at the surface and the body
INSECTS AND DISEASE
227
hanging head downwards in the water. The pupa stage is also
passed in the water and differs from most insect pupas in being
an active " wiggler " as well as the larva. It differs from this larva
in having a large head provided with two air tubes for breathing.
The adult emerges from the floating pupa skin and is easily killed
by any shower that wets its unexpanded wings, or any spray that
may be thrown upon it.
Our commonest northern mosquito (culex) probably does not
\
FIG. 78. Mosquito eggs and larvae (Theobaldin incident); two
larvae feeding on bottom, others at surface to breathe.
From Doane.
transmit disease and may be distinguished from anopheles, which
carries malaria, by the fact that the latter stands almost on its
head when at rest, while culex holds its body more nearly hori-
zontal. Fortunately, stegomyia which transmits yellow fever,
is a tropical species of mosquito and does not usually invade the
temperate regions.
Mosquito Control. This outline of the metamorphosis gives the
key to the methods of attack which consist of:
228 BIOLOGY FOR BEGINNERS
1. Drainage of swamps, covering or removal of rain barrels,
cisterns, cans, or any hollows where water may accumulate.
2. Spraying swamps and ponds with petroleum which covers
the water with a film of oil so that neither larva or pupa can
breathe, and also kills any adults which it strikes, though
this oil treatment is injurious to plants and fishes in the
water thus treated.
FIG. 79. Mosquito larvae and pupae, T. incidens, with their breath-
ing-tube at the surface of the water. From Doane.
3. Fish and dragon flies are natural enemies of mosquitoes and
should be encouraged.
4. Careful screening of houses and wearing of protective clothing
especially in infected regions is a helpful precaution.
5. Persons suffering from malaria should avoid being bitten
lest they thus infect others. Yellow fever cases are now
quarantined in screened rooms for the same reason.
INSECTS AND DISEASE 229
By such methods both malaria and yellow fever have been
stamped out in many regions formerly very dangerous. The chief
obstacle to the completion of the Panama Canal by the French
was the awful death rate due to these diseases. Now, with proper
sanitary measures, the canal zone has a lower death rate than
New York City. Because of the modern knowledge of disease
transmission and control as applied by Colonel W. C. Gorgas,
the completed canal stands as a monument to American health
science as well as to American engineering. The consequences of
heroic experiment have been far reaching in other notable plague
spots. Central America, West Indies, and the Philippines are
now healthful regions. New Orleans, formerly scourged by epi-
demics of yellow fever, is now almost free from this dreadful malady.
A Biologic Victory. One of the most brilliant chapters in the
history of the war against disease recounts the work of four Ameri-
can Army Surgeons in the conquest of yellow fever.
In 1900, Doctors Reed, Carrol, Lazear, and Agramonte were
sent to Cuba to study this disease which had always been a scourge
in the West Indian region and was now spreading among our
soldiers. They suspected a certain kind of mosquito as the carrier,
but could not test their theory on animals, as only human beings
have yellow fever. So they decided to try it on themselves, and
allowed mosquitoes, which had bitten yellow fever patients, to
bite them and infect them with the deadly germs. Carrol was the
first to be ill, but after a long and painful sickness, finally recovered.
Lazear was the next to come down with the disease and he died
Still the experiments went on, despite the terrible risk, and there
were many new volunteers. Two others were selected, a soldier,
Kissenger, and a civilian, Moran. Both insisted that they receive
no pay, as they willingly offered their lives for the benefit of
humanity. Both men recovered after severe illness, but Kissinger
was permanently disabled as the result of his heroism.
Based on the work of this gallant band of soldiers of science,
they were able to prove that the mosquito was the only carrier of
yellow fever, and to propose means for its control. An active
campaign was begun at once and in 1901 only eighteen deaths
230 BIOLOGY FOR BEGINNERS
occurred in Havana and none at all in 1902. The terrible curse
of the tropics was wiped out.
Major Reed writes " In my opinion this exhibition of moral
courage has never been surpassed in the Army of the United
States."
The history of medicine and sanitation is full of such examples
of quiet heroism, where men have offered themselves to suffering
FIG. 80. A female mosquito, T, incidens; note the thread-like
antennae. From Doane.
and death far worse than is incurred in battle and without the
excitement of war or the encouragement of popular applause.
The conquest of malaria was brought about in similar manner,
by the careful research and courageous experiment of English
and Italian doctors. As late as 1894 the Standard Dictionary of
Medicine said that malaria was caused by "an earth-born poison
generated in the soil " and, as its name signifies, was associated
with bad air especially night air.
INSECTS AND DISEASE 231
The malaria germ had been seen by a French surgeon in 1880,
but not associated with mosquitoes at all, though in 1884 an
American, A. F. A. King, had urged this as possible. In 1897
two English physicians, Manson and Ross, traced the germ of
bird malaria to the mosquito and the following year two Italians,
Grassi and Bignami, found the germ of human malaria in the body
of mosquitoes.
By experiments similar to those described for yellow fever, it
FIG. 81. A male mosquito, T. incident; note the feathery antennae.
From Doane.
was proven possible to live in health in the worst swamps of the
Roman Campagna, if protected from mosquitoes. To finally
prove their action in malaria transmission, Doctor Manson's son
and another volunteer were inoculated with malaria by mos-
quitoes brought from Italy. Both took the disease, but fortunately
were cured. It is to such work as this that science owes her victories
and to it we owe also our greater safety from disease.
232
BIOLOGY FOR BEGINNERS
SOME MEANS or DISEASE TRANSMISSION
Disease
Transmitted by
Means of prevention
Malaria
Mosquito
Drainage and oiling of swamps
Screening and isolation of patients
Yellow fever
Mosquito
As above
Typhoid fever
Flies
Destroy breeding places
Kill breeding females in spring
Screen food and waste
Tuberculosis
Flies
As above
Dysentery
Flies
Spotted fever
Ticks
Destruction of insect pest
Cattle fever
Ticks
Cleanliness
Relapsing fevers
Lice
Cleanliness, destruction of pests
Bedbugs
Sleeping sickness
Tsetse fly
Protection against fly attack
The "Plague"
Fleas on rats and
Destruction of rodent hosts
squirrels
COLLATERAL READING
Principles of Health Control, Walters, pp. 347-369; Civic Biology,
Hunter, pp. 217-231; Economic Zoology, Kellogg and Doane, pp. 349-385;
General Zoology, Linville and Kelly, pp. 284-287; Town and City, Jewett,
pp. 228-241; Primer of Sanitation, Ritchie, pp. 145-150, 103-116; Applied
Biology, Bigelow, pp. 282-286; Mosquitoes or Man, Boyce, pp. 204-210;
Protozoology, Calkins, pp. 279-285; Essentials of Biology, Hunter, pp. 258-
260; The House Fly, Howard, entire; Civic Biology, Hunter, pp. 217-226;
Lab. Problems in Civic Biology, Hunter, pp. 149-157; Sanitation Practically
Applied, Wood, pp. 420-444; Community Hygiene, Hutchinson, pp. 220-
232; Scientific Features of Modern Medicine, Lee, pp. 79-85; Rural School
Leaflet (Cornell), Vol. IX, pp. 184-186; Bulletin No. 74 Mississippi Exp.
Station, entire; Numerous other Government Bulletins.
See also references in encyclopedia or any textbook index on,
Flies
Mosquitoes
Fleas
Protozoa
Etc., etc.
Typhoid fever
Malaria
Yellow fever
Bubonic plague
INSECTS AND DISEASE 233
SUMMARY
Reason for study of diptera.
Characteristics of diptera.
One pair of wings, balancers, complete metamorphosis.
Mouth parts for rasping and sucking (fly).
Mouth parts for piercing and sucking (mosquito).
Fly.
Mouth parts for rasping and sucking, large eyes.
Thick fleshy antennae, powerful wings, sticky feet, hairy.
Life History.
Egg, laid in manure or filth, 200, hatch in one day.
Larva, maggot, scavengers, period: 5-6 days.
Pupa, passed in last larva skin, period: 7 days.
Adult, develop in two weeks all summer (compute numbers).
Harm done by flies.
Annoyance to people and animals.
Transfer filth to food.
Transfer germs externally and internally.
Typhoid, cholera, dysentery, tuberculosis, sleeping sickness.
Methods of control or prevention.
Cover manure Remove garbage Use screens
Cover foods Use traps " Swat 'em "
Mosquito.
Structure.
Mouth parts for piercing and sucking, saliva injected.
Mandibles, maxillae, labrum, and tongue inside labium.
Relation to disease.
Malaria and yellow fever. How proven.
How transmitted.
Life History.
Egg, in rafts on the water.
Larva, wigglers, breathe head downwards.
Pupa, also active, breathe head upwards.
Adult, female bites animals, male harmless.
Control and prevention.
Drainage of swamps. Spraying with oil.
Fish and dragon flies. Screening houses.
Protecting those who are sick.
Kinds.
Culex, common northern mosquito, body horizontal.
Anopheles, malaria, body almost vertical.
Stegomyia, yellow fever, tropical.
CHAPTER XXVI
INTRODUCTION TO THE VERTEBRATES
Vocabulary
Specialization, development of parts for special function.
Survival, remaining alive.
Ultimate, furthest.
Vertebrates, animals having a back bone composed of vertebrae.
While it is certain that all living things are more or less related
to each other, still they have developed along very different lines,
and to very different extents.
Among animals, the protozoa seem to have carried the specializa-
tion of the single cell about to its limit, which, while assuring their
survival, could not possibly raise them very high in the scale of
development.
The sponges have obtained the utmost possible advantage from
colonizing slightly specialized cells in unspecialized bodies; and
have attained a considerable advance over the protozoa.
The hydra and its relations reached a much higher plane by
development of tissues for special purposes and among them first
appear the three-layered body wall from which the organs in higher
animals are derived.
The worms mark a very diverse class but some of them have
well-developed systems of organs, digestive, circulatory, nervous,
etc., which had never appeared in previous forms.
Diverging from the worm type it seems as if nature had tried
out several schemes of development, carrying each to a point where
it could no longer be much improved.
The molluscs represent the ultimate advantage to be gained
from a protective shell and rather high internal development,
234
INTRODUCTION TO THE VERTEBRATES
235
coupled, in most cases, with an inactive life. This made for safety
first, but limited increase in activity and intelligence.
The arthropods, especially the insect class, tried what could be
done with an external protective skeleton, but one provided with
joints, so that activity need not be sacrificed to safety. This has
produced the winners in life's race, if numbers be the standard.
FIG. 82. Showing endo- and exo-skeletons.
The bones in a man's leg are surrounded by muscles; the
skeleton of a grasshopper's leg consists of tubes with muscles
inside. From Pearse.
But the external skeleton and the ventral nervous system imposed
obstacles to large increase in size, on the one hand, and to a highly
developed brain, on the other.
A third line of development, with the internal skeleton and the
nervous system dorsal in the body, was attempted by the group
of animals called the vertebrates. This permitted great increase
in size both of body and brain, and while giving less protection,
236 BIOLOGY FOR BEGINNERS
this very fact necessitated an active and intelligent life to oppose
or escape their enemies. The vertebrates thus have come to be
the highest in the scale of animal development and include the
following classes:
1. The Pisces (fishes).
2. The Amphibia (frogs, toads, salamanders).
3. The Reptiiia (snakes, turtles, lizards).
4. The Aves (birds).
5. The Mammals (rat, cattle, cat, man, etc.).
The vertebrates include many very different animals, but they
all agree in the following points, in which they also differ from all
the other forms studied. These other forms are sometimes all
classed together as the invertebrates.
All vertebrates have,
1. An internal skeleton of bone or cartilage.
2. A spinal column composed of vertebrae.
3. A dorsal nervous system.
4. Two body cavities: a dorsal one for the nervous system and
a ventral one for the other organs.
5. Eyes, ears, and nostrils always on the head.
6. Jaws, not modified limbs; move up and down.
7. Eyelids and separate teeth are usually present.
8. The heart is ventral and blood is red.
9. Never more than two pairs of limbs.
The human body is a true vertebrate type as we can see by
comparing its structure with the above points and we only hold our
place in the race of life by our superior brain development. There
is not one of the lower groups but has members which excel us in
other respects.
Compare our swimming with the fish, our flight with the bird,
or our speed with the deer and it will be seen that we are inferior
in many respects to the different members of the animal kingdom.
It is the development of our brain that has enabled us to retain
the lead in the race of life. Superior intelligence compensates
many times over for various physical disadvantages.
INTRODUCTION TO THE VERTEBRATES 237
Here, as everywhere in Nature, we can see increase in com-
plexity, permitting greater division of labor, and this in turn
resulting in better adaptation and more perfect performance of
function.
If we compare the protozoan to the man on the desert island,
then the sponge would represent a condition where there were
enough men (cells), so that one could do one thing and one, another.
It would be like a small village where one man could make all the
shoes, or do all the baking.
In the hydra we find groups of similar cells (tissues) performing
CROSS-SECTIONS
VCRTE-BRATI
FIG. 83. Note differences in location of similar organs of vertebrate
and invertebrate.
a single function. This would correspond to the case where the
town had grown large enough so that many shoemakers or bakers
were required and they each worked together, as in a factory.
Worms and higher forms, with their tissues grouped into organs,
would correspond to larger cities where many kinds of factories
were required to carry on the business of the still larger group of
people.
COLLATERAL READING
Applied Biology, Bigelow. pp. 417-419; Animal Studies, Jordan,
Kellogg and Heath, pp. 161-169; Economic Zoology, Kellogg and Doane,
pp. 237-240; Winners in Life's Race, Buckley, pp. 1-19; Animal Life,
Thompson, pp. 248-272; Comparative Zoology, Kingsley, pp. 127-156; Zo-
ology, Shipley and MacBride, p. 306; Elementary Zoology, Davenport,
pp. 289-297; Elementary Zoology, Galloway, pp. 274-280.
238
BIOLOGY FOR BEGINNERS
SUMMARY
Development of the branches of the Animal Kingdom.
Branch. Examples (in notes)
Protozoa
Sponges
Hydra
Worms
Molluscs
Arthropods
Vertebrates
Line of development.
Specialized single cells.
Groups of slightly specialized cells.
Larger size, colonial habit.
Three-layered body wall, tissues.
Systems of organs, sense organs.
Protection, inactive, low intelli-
gence.
Jointed exo-skeleton, active.
High developed senses and in-
stinct.
Size and brain development lim-
ited.
Internal skeleton.
No limit to size of brain.
Less protected but more intelli-
gent.
Classes of vertebrates
Pisces
Amphibia
Reptilia
Aves
Mammals
Characteristics of vertebrates
Spinal column
Internal skeleton
Dorsal nervous system.
Two body cavities
Two pairs of limbs or fewer.
Representatives
Fishes,
Frogs, toads, salamanders.
Snakes, turtles, lizards.
Birds.
Rat, cow, cat, man.
Sense organs on head.
Jaws not developed from limbs.
Eyelids, separate teeth.
Ventral heart, red blood.
CHAPTER XXVII
FISHES
Vocabulary
Aquatic, pertaining to the water.
Cartilaginous, made of cartilage, a gristle-like tissue.
Nasal, pertaining to the nose.
Operculum, the covering over the gills in fishes.
Filaments, any thread-like organs.
Prehension, the function of grasping.
Visceral, pertaining to the viscera or abdominal organs.
Pectoral, pertaining to chest or shoulders.
Pelvic, pertaining to the hips.
Fishes are aquatic vertebrates, with either a cartilaginous or
bony skeleton ; they breathe by means of gills; are usually covered
with scales; and have limbs in the form of fins.
External Structure. The body can be divided into three regions,
the head, trunk, and tail. There is no narrowing to mark the
neck, since the smoother outline is better fitted for passing through
the water. The general outline of the body is spindle shaped,
flattened more or less at the sides to aid in locomotion by displacing
the water as easily as possible.
Scales. The whole body, except the head and fins, is covered
with scales overlapping toward the rear, giving protection and at
the same time allowing great freedom of motion. They are supplied
with a slimy secretion which aids in locomotion and in escape from
enemies. In some fish, such as the trout and catfish, the scales
are minute or lacking, but in any case, the color of the skin corre-
sponds to the fish's surroundings and is therefore a protection.
Head. The head is usually pointed, protected by plates instead
of scales, and attached directly to the trunk. The lack of a neck
is no disadvantage, as the fish can turn its whole body as quickly
as most animals can turn their heads.
239
240 BIOLOGY FOR BEGINNERS
The mouth is usually at the extreme anterior since it is the only
organ for food-getting or defense, and it is provided with numerous
sharp teeth, arranged on three sets of jaw bones and slanting in-
ward so that there is little chance for a victim to escape.
FIG. 84. Fish External Features.
The Fins can be divided into those on the median line and those which are
paired. The former are probably parts of a continuous fin which, in earlier
forms, extended completely around the body, as in the eel or tadpole.
The dorsal fins can be erected and are armed with spines for protection.
Smaller spines are also found in the anal and pelvic fins.
The caudal fin is the chief propelling organ and has flexible fin-rays for its
support. All the fins in the median line aid in locomotion and steering.
The paired fins are homologous to the limbs of higher animals. The pelvic
fins aid in supporting the fish when at rest on the bottom, and both pairs help
in balancing and swimming.
The Lateral Line seems to consist of a series of gland-like sacs whose function
is thought to be to provide a depth or pressure sense.
The Nostrils have two openings each, so that water can flow through them
as the fish swims, bringing with it the particles which cause the sensation of
smell. They do not connect with the throat and have nothing to do with
breathing, as is the case of air breathers.
The Scales are arranged overlapping to the rear, to give all possible protec-
tion, and at the same time permit perfect freedom of motion, and offer no
resistance to the water. A slippery secretion aids in locomotion and escape
.'rom enemies. Often their color is of advantage in escaping observation, either
by enemies or prospective prey.
The Operculum is a strong covering which protects the very delicate gills
from injury. It has a slight motion, so as to permit the water to pass out under-
FISHES
241
neath it. The free ventral edge extends far forward under the head almost
meeting in a narrow throat region, the isthmus.
t All the above features are adaptations for aquatic life, and, together with
other internal organs, have made the typical fish unusually well suited to its
environment.
The general outline of most fish is about like the perch in having the flattened
sides and tapering posterior, which make for speed. All fish have the bulk of
their body composed of flexible muscle plates which permit powerful and free
use of the caudal fin in locomotion.
There are two nasal cavities each with two nostrils, but they are
used for smell only, since they do not connect with the throat
and cannot be used in breathing.
The eyes are large, somewhat movable, and have no lids, but
have a cornea, lens, retina, etc., somewhat similar to our own,
and are entirely different from the compound eyes of the insects.
The ears are embedded in the skull and do not show externally;
they probably function as balancing organs and are used to detect
vibration, rather than sound, as fish have no sound-making apparatus
and probably cannot " hear " in the sense that we do.
The Gills. At each side of the head is a crescent-shaped slit
which marks the rear
border of the gill cover or
operculum. These slits
almost meet on the ventral
side, leaving only a narrow
isthmus at the , throat
region, and thoroughly
exposing the gills to the
water. If we look inside
the mouth we can see that
the throat has five slits on
each side, leaving four
gill arches between them
and if the operculum be lifted the outer sides of these gills can be
seen.
Each gill consists of an arch of bone between the slits in the
throat wall, to which are attached two rows of thin- walled thread-
FIG. 85. Fish structure of gill.
242 BIOLOGY FOR BEGINNERS
like appendages called the gill filaments. These filaments are
richly provided with capillaries, so that the blood is brought in
close contact with the water over a very large surface. This
permits the exchange of oxygen (dissolved in water) and carbon
dioxide by means of osmosis. The gill arches have finger-like projec-
Courtesy oj the A merican Museum of Natural History
FIG. 86. Skeleton of European Perch, Percaflumatilis, illustrat-
ing the bony framework of the higher fishes. After Cuvier.
The whole fish is adapted for thrusting rapidly forward through the water.
The tapering head ends in a sharp prow extending from the nose to the neck.
The brain-case is braced on all sides to receive the forward thrust of the many-
jointed backbone, which is driven forward by the tail. The fins are spread upon
bony sticks or rays, which are supported by bony pieces that are embedded
in the flesh. Between the supporting pieces and the fin rays there are usually
movable joints. The ventral fins are fastened beneath the pectoral fins, an
arrangement which facilitates quick turning.
The propelling muscles and their bony supports are extended along the
sides of the backbone and outside the ribs. The ribs enclose the stomach,
intestines and other vital organs. These extract from the food the energy
which is given out in muscular exertion. The region of the gills is covered by
an elaborate system of jointed plates.
The mouth is guarded by bony jaws which are attached to the lower side
of the skull.
tions on the side toward the throat called gill rakers, which prevent
food or dirt from getting into the filaments and also keep the arches
separate to allow free circulation of water.
The water is taken in at the mouth, which is then closed, forcing
it through the gill slits over the filaments and out beneath the
operculum ; the forward motion of the fish aids in this process.
FISHES 243
Here, as in all breathing organs, we find a large extent of surface,
thin membranes, and rich blood supply, all adaptations for osmotic
exchange, together with protective devices in the form of operculum
and gill rakers, and provision for a free circulation of water.
Trunk. Extending along both sides of the body backward from
the operculum is a row of pitted scales with sense organs beneath
them, known as the lateral line, which probably aids the ears in
feeling vibrations, and functions as a pressure organ to estimate
the depth at which they swim. The fins are the most characteristic
and noticeable appendages of the trunk and consist of a double
membrane, supported by cartilaginous or spiny rays, and operated
by powerful muscles. Their shape and number vary with the kind
of fish, but there are always two pairs, the pectoral (anterior) and
pelvic (posterior) fins, which are homologous with the arms and
legs of other vertebrates. The other fins are all on the median
(middle) line of the trunk, there being sometimes two dorsal fins;
always a large tail (caudal) fin, and an anal fin just back of the
vent. In general the fins are beautifully fitted for locomotion
in the water, but they are differently used in this process, the caudal
fin being the chief propelling and steering organ. The paired
fins aid in locomotion and in balancing, and also support the body
when resting on the bottom. The other median fins aid in steering
and are often provided with sharp spines for defense as well.
The bulk of the fish's body consists of powerful muscles. The
flexible backbone is made up of very numerous vertebrae, which,
together, permit the fins to be utilized to the fullest extent and
provide a system of aquatic locomotion, second to none in the
world, aided as it is by the pointed, scale-covered, slippery
body.
Internal Structure. Digestive System. The food of most fishes
consists of other aquatic animals, though a few are vegetarians.
It is grasped by the mouth, but the teeth serve only for prehension
and not for chewing. On this account the gullet is large and short,
the stomach provided with powerful digestive fluids and usually
with finger-like outgrowths (caeca) to increase the digestive surface.
As in most carnivorous animals, the intestine is rather short,
244
BIOLOGY FOR BEGINNERS
making only two loops, and opening into it is the duct from a well-
developed liver between whose lobes the gall sac can be found.
Circulation. The fish has a heart consisting of two chambers,
an auricle and a ventricle, located just posterior to the isthmus.
So it is literally true that its " heart is in its throat." The blood
leaves the heart by a large artery that branches to each of the
gills, in whose filaments it is relieved of its carbon dioxide. Then
laden with oxygen it flows into a dorsal artery with branches to
all the muscles and in-
'"""""" *"-" ternal organs where it
exchanges this oxygen
for carbon dioxide. The
blood which flows to the
digestive organs receives
the digested food-stuffs
which they have pre-
pared, and passes
through the liver and
so back to the auricle of
the heart. Thus it hap-
pens that the heart is always pumping blood that is rich in nutrients
and carbon dioxide but poor in oxygen. The course of the blood
stream is from the ventricle of the heart, to gills, to general circu-
lation and digestive organs, to liver, and back to auricle of the
heart again, though a part passes through the kidneys each time,
where urea and other wastes are removed.
Nervous System. The central nervous system in all vertebrates
is located in the dorsal body cavity, protected by outgrowths from
the spinal column. This arrangement is entirely different from
that found in the invertebrates, where the nervous system lies
along the ventral side and is not separated from the other internal
organs.
In the case of most fishes the nervous system consists of the
spinal cord, extending the whole length of the body, protected by
arches of bone attached to each vertebra. From it many nerves
extend to the muscles and internal organs. At the anterior, the
FIG. 87. Diagram of circulation in fish.
FISHES 245
cord enlarges to form a brain, entirely different in structure from
the so-called brains of the lower forms, in that it has developed
separate regions for different functions. The fish's brain consists
of five principal parts. Beginning at the anterior, come the olfactory
lobes from which the nerves of smell extend to the nostrils. Pos-
terior to these, and considerably larger, are the two lobes of the
cerebrum, which control the voluntary muscles of the animal.
The largest parts of the brain are the two optic lobes connected
directly with the eyes and concerned, of course, with the sense of
sight. Behind them comes the cerebellum, and finally the enlarged
end of the spinal cord, the medulla, both of which have to do with
regulating muscular action and the work of the internal organs. The
medulla is also a region from which branch many important nerves.
The brain as a whole, compared with other vertebrates, is not
highly developed. The cerebrum, the center of voluntary control,
is actually smaller than the optic lobes, and the whole brain does
not fill the cranium or skull cavity, which is partly occupied by a
protective liquid. It is only when compared with the invertebrate
forms, that the real advance of the fish brain can be realized. In
them there were no special parts for separate uses, no division of
labor or specialization, and so a highly developed instinct was the
best such a brain could achieve.
In the vertebrate, the development of specialized parts of the
brain, though very primitive at first, paved the way for a cerebrum
which would exceed all the other brain regions in bulk, and control,
not only voluntary motion, but thought and reason, as well. So
when studying the simple brain of the fish, do not forget that it
contains the possibilities of great advance, and is to be the line
along which the highest vertebrate development will be attained.
Air Bladder. Another organ, simple in the fish, but which has
a great future before it, is the air bladder which is found in most
species. This consists of a thin-walled elliptical sac, located in
the dorsal part of the visceral cavity and sometimes connected
with the throat by a tube. Its function is to assist the fish in
maintaining a level in the water; by contraction of its walls the
fish can sink, and by expansion, rise without other effort.
246
BIOLOGY FOR BEGINNERS
It develops in the embryo fish as an outgrowth from the throat,
extending back and enlarging into the present form, and often
losing all connection with the outer air. It is in precisely similar
manner that the lungs of all higher forms push out from the throat,
while retaining their connection with the mouth and performing
an entirely different function. Yet they are regarded as of like
origin and structure, so the lungs are homologous to the air bladder
of fishes, but by no means analogous (or like in function).
In this connection it is interesting to note that in certain Aus-
F 6 H
FIG. 88. Embryonic development of fish.
A, unfertilized egg; gd, germinal disc; y, yolk; B, zygote formed by union
of ovum and spermatozoon; C, D, cleavage; E, young embryo showing neural
groove at left; F, showing yolk nearly overgrown by the vascular membrane
(blastoderm) growing out from embryo; G, embryo with "yolk sac"; H, young
fish, just hatched, with yolk sac not yet absorbed. From Pearse.
tralian fishes the air bladder is actually used as a lung and the gills
are poorly developed for breathing.
As the development of higher forms goes on, the simple air
bladder becomes two lobed, its walls develop ridges, and finally
many-celled chambers which enormously increase the ulterior
surface. To the walls of these delicate cells a network of capillaries
brings the blood, and devices are provided to pump air in and out.
Thus from the air bladder of the fish, the lung of a bird or man
may trace its origin.
FISHES
247
Life History. The breeding habits of fish vary so greatly that
it is difficult to make any general statements about their life history
to which there will not be many exceptions.
The eggs vary in size from over an inch in skate, to the micro-
scopic offspring of the herring. Their number may vary from five
hundred in the trout to millions in cod, sturgeon, or flounder.
The eggs are fertilized after being laid, by means of the spermatic
liquid (milt) which the male sprays over them, sometimes stirring
the eggs and milt together so that more shall be fertilized. There
is little chance that all the eggs will be fertilized, since, as in the
Stickleback Dogfish
FIG. 89. Fish nests. From Pearse.
plant, a sperm cell must reach each egg cell if it is to develop.
Hence the large number of eggs is partly to make up for the small
chance of fertilization. The eggs and young are prey to many
other fish and similar enemies, while man destroys the adults for
food, fertilizer, and fun. Out of enormous numbers of eggs, so
few survive, in some cases, that artificial fish culture has to be
utilized to prevent total destruction of certain species. In many
cases both the fertilization and the care of young are left to chance,
while in others, such as the bass, sunfish, trout, and catfish, a sort
of nest is made on the stream bottom, where the eggs are guarded
by the male, or may be covered with sand for protection.
248 BIOLOGY FOR BEGINNERS
As development proceeds the form of the embryo fish may be
seen within the egg from which it soon emerges, retaining the yolk
of the egg attached to the body, to be absorbed as nourishment
until the tiny fish can shift for itself, and grow gradually to its
normal size.
Life History of the Salmon. While no one fish can be taken as a
type of all, the life history of the Pacific salmon is as well known
as any and since it is so familiar an article of food, we shall take up
its breeding habits somewhat in detail.
The adult salmon lives in the ocean all along the northern
Pacific coasts. In spring or early summer both sexes migrate in
enormous numbers up the Columbia and other rivers often to a
distance of one thousand miles. It is during these " runs " that
the canners make their annual catches by means of barriers or
machines which scoop up the passing fish.
This migration may be for the purpose of finding greater safety,
cooler water, or better food, or it may be a relic of the time when
they may have been entirely fresh-water fish. At all events they
begin in March to make their last journey. Slowly at first and
later many miles per day they work their way against the current
to the spawning beds far from the sea.
Here, in water not warmer than 54 degrees, each female deposits
about 3500 eggs. The male spreads over them the " milt " or
spermatic fluid at large in the water. It is much like wind pollena-
tion in flowers and many eggs are not reached by the sperms,
hence do not develop.
The males are brilliantly colored at the breeding season but
both sexes soon lose their beauty and strength, partly in fighting
other fish and partly by injuries from the stones in the spawning
beds.
The eggs are deposited on fine gravel and the process extends
over several days after which the strength of the parents seems
to be exhausted and both die.
After from thirty to forty days the eggs hatch, but as usual with
fish, the yolk remains attached until all is absorbed in growth and
the fry, as they are called, can shift for themselves.
FISHES 249
Although many young salmon fall prey to other fish the majority
find their way back to the ocean where they reach adult life, and,
if they escape the canner's machines, live to repeat the self-sacrifice
of their parents.
Adaptations. The study of the fish reveals an animal, first of
all adapted for aquatic life, and nearly all features of its structure
and habits tend to this result, as the following summary will show.
SUMMARY OF ADAPTATIONS
For Locomotion in Water.
1. Shape of body, slimy secretion.
2. Scales, fins.
3. Flexible spinal column and powerful muscles.
For Life in Water (see above, also).
1. Gills for respiration.
2. Air bladder, to regulate depth.
3. Lateral line to determine pressure.
4. Structure of eye, spherical lens.
For Protection.
1. Color, dark above, light below.
2. Scales, spines, teeth.
3. Speed, to escape enemies.
For Food Getting.
1. Location and size of mouth.
2. Shape and location of teeth.
3. Wide gullet and powerful digestion.
4. Speed.
COLLATERAL READING
General description and structure: American Food and Game Fishes,
Jordan, pp. 364-367; Fishes, Chap. XXXIII, Jordan, p. 508; Fishes,
Chap. X (adaptations), Jordan, pp. 51-78; Familiar Fish, McCarthy,
Chap. 7; American Natural History, Hornaday, pp. 380-387; Life in
Ponds and Streams, Furneaux, p. 353; General Zoology, Linville and
250 BIOLOGY FOR BEGINNERS
Kelley, p. 305; Elementary Zoology, Packard, pp. 142-175; Animal
Structures, French, pp. 169-178; Winners in Life's Race, Buckley, pp.
20-42; Economic Zoology, Osborne, pp. 338-355; Elementary Lessons in
Zoology, Needham, pp. 161-378; Practical Zoology, Davidson, pp. 185-
199; Comparative Zoology, Kingsley, pp. 21-39; Elementary Zoology,
Galloway, pp. 281-295; Elements of Biology, Hunter, pp. 271-278; Ap-
plied Biology, Bigelow, pp. 419-424; Elementary Biology, Peabody and
Hunt, pp. 120-137; Forms of Animal Life, Rolleston, pp. 83-102.
Advanced works on structure: Advanced Zoology, Packard, pp. 411-460;
Textbook of Zoology, Claus and Sedgwick, pp. 120-150; Forms of Animal
Life, Rolleston, pp. 83-98; Anatomy of the Vertebrates, Huxley, pp. 59-65.
Classification and kinds of fish: American Food and Game Fish, Jordan
(key), pp. 29-34; Elements of Zoology, Davenport, pp. 298-324; Fresh
Water Aquarium, Eggeling, pp. 107-216; Pet Book, Comstock, pp. 226-245;
Handbook of Natural History, Comstock, pp. 149-180; Nature Study
Leaflets (bound), Cornell, pp. 157-166; Winners in Life's Race, Buckley,
pp. 43-69.
Economic Value and Life History: Fishes (life history), Jordan, pp. 1-24;
Fishes (as food), Jordan, pp. 129-148; Familiar Fish (propagation), Mc-
Carthy, Chap. 2; American Natural History, Hornaday, pp. 375-377;
Practical Biology, Smallwood, pp. 103-112; U. S. Fish Commission Report,
1897; Economic Zoology (good), Kellogg and Doane, Chap. 21; Elementary
Biology, Peabody and Hunt, pp. 137-150; Talks About Animals, pp. 7-35;
Animal Life, Thompson, pp. 109-110, 253-256.
SUMMARY
Characteristics: bony skeleton, gills, scales, fins.
External Structure.
Shape, spindle outline for easy swimming.
Scales, for protection and ease of motion (cf. crayfish).
Head.
Mouth and teeth for prehension and defence.
Nasal cavities for smell, not breathing.
Eyes, with lens, cornea, etc., but no lids (cf. crayfish).
Ears, internal, detect vibration or balance.
Gills.
Gill openings, two at sides of head.
Operculum, cover over gills.
Gill arches, four, bony, hook shaped, support the
Filaments, numerous, much surface, thin, capillaries.
Gill rakers, clean and spread arches.
Trunk.
Lateral line, for depth sense.
Fins, a double membrane supported by rays.
Paired, pelvic, posterior, for locomotion and balance,
pectoral, anterior, for locomotion and balance.
FISHES 251
Median, caudal, locomotion, and steering (tail),
dorsal (back) steering,
anal (vent) steering.
Body very muscular.
Internal Structure.
Digestive system.
Teeth for prehension, not chewing.
Stomach, with caeca, powerful fluids.
Intestine short and large, liver large.
Circulation.
Heart two chambered, anterior, ventral.
Blood flows to gills, to body, to heart, to gills, etc.
Nervous system.
Brain, separate parts for different functions (result),
Spinal cord, dorsal, protected by vertebrae.
Air Bladder.
Outgrowth from throat.
Function: to regulate depth.
Homologue of lung.
Life history.
Eggs small and numerous. (Why?)
Externally fertilized.
Slight parental care, many enemies.
Embryo retains yolk sac for food.
Grows gradually, not by stages. (Why?)
Life history of the salmon.
Adaptations.
See summary in text.
CHAPTER XXVHI
THE AMPHIBIA
THE FROG AND ITS RELATIVES
Vocabulary
Transition, period of change.
Vegetarian, using vegetable food.
Carnivorous, using animal food.
Constitute, to make up or compose.
Pulmonary, pertaining to the lungs.
Aerated, supplied with air.
Viscera, all the internal body organs.
Particular interest attaches to this group because of the fact
that, in their life history, we can see the steps in development
between the fishlike animals adapted solely for aquatic life and
the land animals which cannot live under water.
In this transition from water to land forms, many strange
combinations of gills and lungs, fins and legs, have occurred,
gills being found on animals with legs, and fins sometimes ac-
companied by lungs. All together this is a very good object
lesson in the development and adaptations of animal forms.
The name amphibia, meaning " having two lives," refers to
the fact, that they usually are aquatic, fishlike animals when
young, and abandon that manner of life for the land when they
become adults. This series of changes is called a metamorphosis,
just as was the life history of some insects.
Characteristics. The characteristics of the group may be
summarized as follows, though there are some exceptions:
1. They undergo a metamorphosis.
2. Eggs are directly fertilized as laid.
3. Usually they are covered by a smooth skin.
252
THE FROG AND ITS RELATIVES
253
254 BIOLOGY FOR BEGINNERS
4. Larval forms are vegetarian; adults, carnivorous.
5. The heart is three chambered, and circulation well developed.
6. The brain, especially the cerebrum, better developed than in
fish.
Among the representatives of this curious group, are several
common animals. Frogs, toads, tree-toads,' newts and salamanders
are all familiar both by sight and sound.
The Frog. The frog will be taken as a type not only because
common and convenient, but also because of the resemblance of its
structure to that of the human being.
In the work with the frog, it is particularly desirable to compare
its structure and development with that of the fish, whenever
possible, noting those points in which it is more highly developed
and the differences which its land life has made necessary in its
structure.
External Features. The frog's body is short, broad, and angular,
evidently not as well adapted for submarine locomotion as the
fish, nor has it achieved the graceful form of a highly specialized
land animal. The covering is a loose skin, colored to resemble its
surroundings, and provided with no scales nor hairs, but supplied
beneath with many blood capillaries. It is evident that the skin
is not for defense like the scaly armor of the fish but attains some-
what the same end by its protective coloration. Its thinness and
rich blood supply permit a certain amount of respiration to take
place through it. Many amphibians absorb water through the
skin instead of by drinking. Some secrete a slimy mucus which
assists in locomotion and escape from enemies. The head is broad,
flat, and attached directly to the body. The nostrils are located
near the anterior and connect directly with the mouth cavity,
thus permitting them to be used for respiration. They can be
closed by a valve-like flap when under water.
Head Structures. The Mouth. The mouth is enormous and
extends literally from ear to ear. This is a very necessary adapta-
tion for food-getting as the insects which constitute its principal
diet have to be snapped up in this veritable trap. Another strik-
ing adaptation for the same purpose is the arrangement of the
THE FROG AND ITS RELATIVES
255
tongue. This is attached at the front of the lower jaw, is very
muscular, and has two sticky fingerlike projections at its tip.
This peculiar tongue can be flipped out of the mouth so quickly
FftOG
ffjorecnrf Pos/no*
IM WAT fit
FIG. 91. Frog. External Features.
Fig. i. Mouth Structure. The mouth is shown as if opened quite flat.
There are no teeth on the lower jaw, as they would interfere with the tongue
when extended as in Fig. 2. The teeth on the roof of the mouth are just where
they will catch any insect which has been flipped into the mouth by the tips
of the tongue.
The openings into the vocal sacs enable the frog to inflate his throat and,
with these hollows as a sounding board, make such loud calls in the mating
season.
Notice that the food has to pass over the trachea to reach the gullet, so the
former is protected by a sort of lip-like valve.
The curved enlargements by the eustachian tubes are caused by the down-
ward projection of the eyeballs.
Figs. 2, 3, and 4, show stages in the operation of the frog's tongue, in catch-
ing insects.
The tip is two lobed and sticky, the mouth enormous in width, and the
256 BIOLOGY FOR BEGINNERS
speed of the tongue is so great as almost to elude the sight, so it all makes
a very efficient food getting device.
Usually the frog jumps at the same time it extends its tongue, thus increas-
ing its range very greatly.
Toads also have the same adaptation, and some salamanders are even better
provided.
Fig. 5 shows the position of rest in the water, with the prominent eyes and
anteriorly placed nostrils, just above the surface. In this position, either at
rest on the bottom, or afloat with hind legs extended, the frog is almost invisible
and thus escapes its enemies.
Note the inturned front feet, mere props and the hind legs, folded ready to
swim or leap on the instant.
that the eye cannot see the motion; the insect sticks to it and is
instantly thrown back within the capacious jaws, just where a
set of teeth on the roof of the mouth will hold and crush it. There
are no teeth on the lower jaw, as they would interfere when the
tongue was thrown out over them. Those on the upper jaw are
small, and in toads both sets are lacking entirely, as the real organ
of prehension in either case is the remarkable tongue.
As we look inside the frog's mouth the nostril openings can be
seen near the anterior of the upper jaw; the tongue folded back
occupies the floor of the lower jaw; farther back at the sides are
the openings of the eustachian tubes from the ears; and at the
extreme rear, in the middle, can be found the wide gullet and slit-
like opening of the breathing tube or trachea. The walls of the
throat are loose and can be greatly expanded with air when the
frog is calling, thus acting as resonating chambers. This gives
great volume to the sound for which all frogs are noted.
Other Organs. The eye of the frog is one of the most beautiful
in all the animal kingdom, having the black pupil surrounded by a
handsome bronze colored iris of large size. It projects conspicuously
from the top of the head, but can be withdrawn, level with the
skull. It is protected by lids and an extra covering, the nictitating
membrane, which can be raised from below and probably protects
the eye when under water.
The location of the nostrils at the very tip of the head, and the
high projection of the eyes enable the frog both to see and breathe
while the rest of the body is covered by water. When in this
THE FROG AND ITS RELATIVES 257
position it is able to avoid observation, and so escapes from large
water birds which feed upon them.
The ears are located just behind the eyes and consist, externally,
of the round tympanic membrane, which is connected with the
internal ear beneath and also with the mouth cavity, by means of
the eustachian tube.
Legs. The anterior legs are short and weak. They are provided
with four inturned toes, which help little in locomotion but serve
as supports to the body when on land. The hind legs, however,
are enormously developed and adapted in several ways for leaping
and swimming. The thigh and calf muscles are very powerful
and are so attached to the hips that they move the legs as very
efficient levers, in locomotion. Added to this is the great develop-
ment of the ankle region and toes, which together are longer than
the lower leg and add greatly to the leverage of these organs. Be-
tween the five long toes is developed a broad flexible web membrane,
which accounts for the frog's notable ability as a swimmer.
Some frogs can leap fifty times their own length or twenty times
their height, while a man, to equal this feat would have to make a
broad jump of three hundred feet or clear the bar at a height of
one hundred and twenty feet.
The legs of the frog are homologous to the paired fins of the
fish but resemble much more closely our own arms and legs. A
study of a prepared skeleton of the frog shows that the foreleg
has the same regions as our arm. The hind leg even more closely
resembles our leg, though with many differences due to being
adapted for very different functions. Still the homology is plain
as the following table shows.
258 BIOLOGY FOR BEGINNERS
COMPARISON OF APPENDAGES OF FROG AND MAN
Front leg and arm
Frog
Man
Upper arm (humerus)
Lower arm (radius and ulna)
Wrist (carpus)
Hand (metacarpus)
Fingers (phalanges)
Short and weak
Short, bones united
Very short, stiff
Turned inward
Four, short and weak
Long and muscular
Long, bones separate
Longer and flexible
Straight
Five, long and flexible
Hind leg and leg
Upper leg (femur)
Lower leg (tibia and fibula)
Ankle (tarsus)
Foot and toes (metatarsus
and phalanges)
Very long and muscular
Very long, bones united
Very greatly lengthened
Five, very long webbed
toes
Medium length, not so
muscular in propor-
tion
Medium length, bones
separate
Short
Five short toes, not
webbed
Not only are the regions and the bones similar in general structure,
but many of the muscles, blood vessels, and nerves of the limbs of
man and frog are of similar form and name. The chief difference
lies in the fact that man has developed his forelegs into organs for
prehension (grasping) and no longer uses them in locomotion.
This has resulted in his erect position and has produced many
changes in structure to adapt the arm and hand for its altered
function.
The muscles of the fish are in the form of flat plates, extending
across the body and moving it as a whole, while in the frog, the
muscle tissue is grouped into true " muscles " like our own, at-
tached to bones by tendons, and acting on them as levers, thus
marking a great advance in structure, and permitting greater
variety of motions.
The Digestive System. The digestive system of any animal
begins with the mouth, teeth, and food -getting adaptations which
we have already described in this case.
THE FROG AND ITS RELATIVES 259
A short gullet connects the large mouth cavity with the stomach
which is an oval enlargement of the digestive tube, set diagonally
in the body cavity and partly covered by the liver which is anterior
and ventral to it. Continuing from the stomach is the intestine,
of medium length, coiled, and enlarging near the vent into a short,
broad rectum and cloaca. The digestive tract is longer than that
of the fish, but the fingerlike projections (caeca) are lacking in
the stomach, the absorbing surface being increased by the coiled
intestine, instead. Connected with the food tube are the usual
digestive glands, the salivary and mucous glands in mouth and
gullet, gastric glands in the walls of the stomach, and the large
liver and smaller pancreas opening into the intestines.
Here as usual we have the essential features of any vertebrate
digestive system: a tubular canal, provided with large extent of
surface for absorption by osmosis, and a series of glands which
secrete the fluids used to get the food into soluble form for this
absorption.
Circulatory System. In so complicated an animal as the frog,
it would be expected that the circulatory system would need to be
better developed than in the fish, especially as the lungs are present
for the first time, to purify the blood. To provide for this added
burden, we find a three-chambered heart located well forward
in the body cavity, and consisting of two auricles and one muscular
ventricle. Extending from the ventricle is a large artery which
at once divides in two branches like a letter Y and each of the arms
again divides into three separate arteries on each side. The
anterior pair of these branches (the carotids) carries blood to the
head; the middle pair arch around to the back of the body cavity
and unite to form the dorsal aorta which supplies the muscles
and viscera; while the posterior (pulmonary) arteries carry the
blood to the lungs and skin for purification.
The blood supplied to the muscles returns laden with carbon
dioxide and other oxidation products, while that going to the di-
gestive tract takes up the digested foods as well. It returns by
way of the veins, in part to the liver, and, finally, all to the right
auricle of the heart. Meanwhile the blood which went to the
260 BIOLOGY FOR BEGINNERS
lungs and skin has been relieved of its carbon dioxide and re-
supplied with oxygen, and this returns by the pulmonary veins
to the left auricle of the heart. The blood from both the general
and the pulmonary circulation then enters the ventricle, but by
means of a complicated valve, that having most oxygen is sent to
the head and brain. The next best goes out into the aorta, while
that with most carbon dioxide is diverted into the pulmonary
arteries and goes to the lungs and skin.
On each complete trip, some of the blood passes through the
kidneys, so that all of the nitrogenous waste can be removed as
urine. Really the purest blood in an animal's body is that which
has just left these very important organs, even though it may
have more carbon dioxide than when leaving the lungs.
The blood which returns from the digestive tract is gathered
into a large vein (portal) and passes through the liver, where
some food substances may be stored, and certain impurities re-
moved, after which it flows back to the right auricle.
Several important differences will be noted in the frog's circula-
tory system, as compared with the fish. The frog's heart is three
chambered and is located farther back in the body; the blood
leaves the heart in two circuits, the pulmonary and the general,
while in the fish, it makes only one continuous trip. In other
words, the blood twice returns to the heart of the frog in any single
complete circulation, and only once in the fish.
Respiration. In the larval form, as a tadpole, the young frog
breathes by means of gills but the adult develops a pair of simple
lungs, opening into the throat by a trachea and glottis. These
lungs are rather cone-shaped, sac-like organs, whose inner walls
are honey-combed with delicate air cells provided with many blood
capillaries so that the conditions for osmosis are fulfilled.
The frog has no ribs or diaphragm to expand the lungs so that
air may come in, and is therefore forced to " swallow " whatever
air it gets by a sort of pumping motion of the throat which can be
observed in any living frog. Air is taken in through the nostrils,
which are then closed and the air " swallowed " by the action of
the abdominal muscles. The elasticity of the lung tissue forces
THE FROG AND ITS RELATIVES
261
the air out again. The slight throbbing of the throat is not breai .
ing; it merely pumps air in and out of the mouth. When air is
really " swallowed'" the sides of the body expand and the floor
of the mouth rises. Then the expired air is forced back into the
mouth where the constant pumping, above mentioned, gradually
P.U. FVknoMARY ARTERY
FETROOUCTIVL ON
T*. TRACHEA
FIG. 9 1 a.
replaces it with fresh air, which is then swallowed and the process
repeated.
Considerable blood is aerated by the capillaries in the skin,
which act as a sort of gill, obtaining dissolved oxygen when the
animal is under water. This is an evident adaptation for its
amphibious life.
Nervous System. The nervous system shows considerable ad-
vance over that of the fish. The cerebrum is larger compared with
the other brain parts. The brain as a whole is more specialized
262
BIOLOGY FOR BEGINNERS
and more nearly fills the cranial cavity of the skull; while the
spinal cord is shorter, thicker, and has its branches arranged
much more like those of the higher animals.
Observation of the living frog shows that all the senses are
fairly developed except possibly that of taste. Sight and hearing
ADAPTATIONS OF THE FROG
By Means of
For the purpose of
External features
Head
Limbs
Digestive organs
Circulatory organs
Respiratory organs
Protective color
Shape, and slimy secretion
Large mouth
Location and shape of
tongue and teeth
Nostrils at tip of nose
Projecting eyes
Short fore limbs
Long hind legs
Very long feet and toes
Powerful muscles
Webbed toes
Gullet and mucous glands
Stomach and gastric glands
Intestine, liver, and pan-
creas
Three chambered heart
Veins
Arteries
Capillaries
Blood
Gills in tadpole
Two lungs in adult
Lung lining cellular
Rich blood supply
Throat and body muscles
Thin vascular skin
Escape from enemies
Locomotion and escape
Catching food
Catching food
Breathing when partly sub-
merged
Vision when partly sub-
merged
Landing after leaping
Increasing leverage for
leaping
Leaping and swimming
Swimming
Swallowing
Digesting proteids
Digesting and absorbing all
food stuffs
Forcing blood through body
Bringing blood to heart
Carrying blood from heart
Distributing blood to the
tissues
Transportation of food,
oxygen, waste, CO*
Absorbing dissolved oxygen
Absorbing free oxygen
Increase of absorbing area
Carrying oxygen , etc.
Taking air into lungs
Additional breathing when
submerged
THE FROG AND ITS RELATIVES 263
are probably good, and its varied life on land and water necessarily
presents a wider range of experiences and hence some advance
in intelligence.
Excretory System. Excretion is provided for by a pair of well-
developed kidneys with a large bladder. Water, uric acid, and
other nitrogenous waste are removed by these organs, while the
lungs and skin also help dispose of waste matter, particularly
carbon dioxide and water.
Reproduction. As in the fish, the sexes are separate, and the
reproductive organs are easily found upon dissection. The ovaries
appear as masses of eggs, the size depending on the season of
year. The sperm glands of the male are small oval organs near
the kidneys. Both sets of organs have coiled ducts which eventually
connect with the posterior part of the intestine (cloaca) into
which the bladder also empties.
It may be well to remember that in the frog we find systems of
organs adapted to perform all the life functions, and that in the
higher animal forms, few new structures are developed, but rather,
these are carried to a greater complexity or perfection.
The following list illustrates this and would apply in general to
most vertebrate animals.
1. Digestive system
Mouth, tongue, teeth, throat cavity, salivary glands
Gullet and stomach, gastric glands
Intestine, small and large, rectum, and cloaca
Liver and gall sac, pancreas
2. Respiratory system
Nostrils, mouth cavity, glottis, and trachea
Lungs, air cells, and capillaries
Skin
3. Circulatory system
Heart, auricles, and ventricle
Arteries, aorta, etc.
Capillaries, and veins
Lymph vessels, and spleen
264 BIOLOGY FOR BEGINNERS
4. Excretory system
Kidneys, and their ducts (ureters), bladder
Lungs, and skin
5. Nervous system
Brain: consisting of
Olfactory lobes
Cerebrum
Optic lobes
Cerebellum
Medulla
Spinal cord and nerves
Sense organs, eye, ear, etc.
6. Supporting system
Skeleton, bone, and cartilage; ligaments
Connective tissue
7. Muscular system
Body muscles, tendons
Muscles of internal organs, heart, intestines, etc.
8. Reproductive system
Ovaries and oviducts
Spermaries and sperm ducts
COLLATERAL READING
General Structure: Economic Zoology, Kellogg and Doane, pp. 1-13;
Economic Zoology, Osborne, pp. 356-374; Biology of the Frog, Holmes,
entire; Types of Animal Life, Mivart, pp. 96-122; Forms of Animal Life,
Rolleston, pp. 74-81; Winners in Life's Race, Buckley, pp. 70-88; Rep-
tiles and Birds, Figuier, pp. 17-33; The Animal World, Vincent, p. 25;
Textbook of Biology, Peabody and Hunt, pp. 101-119; The Frog Book.
Dickerson, pp. 171-185; U. S. Fish Commission Report, 1897, pp. 251-261;
Zoology Textbook, Davenport, pp. 325-348; Familiar Life t Matthews,
pp. 1-56; Talk about Animals, pp. 151-154, 160-164; Wilderness Ways,
Long, pp. 75-87; General Zoologv, Colton, pp. 181-195; Zoology Textbook,
Linville and Kelly, pp. 327-347. '
SUMMARY
Amphibia (two lives).
Characteristics: metamorphosis direct fertilization
no scales larva vegetarian
three-celled heart adult carnivorous
fairly developed brain
THE FROG AND ITS RELATIVES 265
Representatives: Frogs, tree-frogs, salamanders, toads, newts.
Frog.
External Structure.
1. Shape, irregular, not graceful.
2. Covering, loose smooth skin, absorbs water.
Adapted for protection by color and slime.
Adapted for respiration by capillaries, thinness.
3. Head (no neck).
Nostrils anterior, connect with mouth, valve.
Mouth, large for catching insects.
Tongue, fixed in front, two tips, sticky.
Teeth, none below, small on upper jaw and roof.
Interior structure.
Nostril openings Eustachian tubes
Folded tongue, Gullet, trachea.
Eyes.
Large, projecting as protective adaptation.
Can be retracted, three lids.
Ears, flat drum on surface of head.
4. Legs. Anterior, short for support only.
Posterior, long, strong, for leaping and swimming.
Adaptations.
Powerful calf and thigh muscles.
Long levers, especially ankle and toes.
Webbed toes. Large hip bones.
Comparison with man (see text).
Legs homologous to paired fins of fish.
Legs homologous to legs and arms of man.
Legs and fins analogous (locomotion).
Legs and arms not analogous (prehension and locomotion)
5. Muscles. Spindle shaped as in higher animals.
Attached to bones with tendons.
Not in separate plates like the fish.
Internal Structure.
Digestion.
'( tongue, attachment, shape, sticky.
Food-getting adaptations -j teeth, upper jaw and roof of mouth.
I mouth, location, size.
Organs of digestion.
Gullet, short, broad (why?).
Stomach, oral, diagonal, covered by liver.
Intestine, medium length, coiled (why?), rectum.
Glands, salivary and mucous in mouth.
Gastric and mucous in stomach.
f emptying into intestine.
Pancreas J
266 BIOLOGY FOR BEGINNERS
Essentials for digestive system.
Tubular canal.
Glands for secretion.
Devices to increase surface, for osmosis absorption.
Circulation.
Heart, location,
Three chambers, two auricles, one ventricle.
Arteries, carry blood from the heart.
Carotid, from ventricle to head, oxygenated blood.
Aorta, from ventricle to body, oxygenated blood.
Pulmonary, from ventricle to lungs, de-oxygenated blood.
Veins, carry blood toward the heart.
Portal-caval, from digestive system to right auricle, de-oxygenated.
Caval, from muscles, etc., to right auricle, de-oxygenated.
Pulmonary, from lungs to left auricle, oxygenated.
Blood changes in lungs, water, carbon dioxide, out, oxygen, in.
Blood changes in kidneys, water, urea, salts, out.
Blood changes in liver, impurities, bile, out, sugar changes.
Advance over fish.
Three-chambered heart.
Two circuits of blood, pulmonary and general.
Lungs instead of gills.
Respiration.
Gills in larval stage, lungs later.
Lungs, shape, location.
Wall structure, air cells, and capillaries (why?).
Action of lungs in breathing.
Air pumped into mouth by throat and swallowed.
No diaphragm (cf. man).
Air exchange in mouth, nostrils with valves.
Use of skin, how adapted for breathing.
Nervous System.
Brain larger, specialized parts, nearly fills skull.
Spinal cord thicker, shorter, with specialized branches.
Senses better (Ex. taste). Higher intelligence (why?).
Excretion. Reproduction.
Kidneys, shape, location. Ovaries.
function. Sperm glands.
Lungs and skin. Ducts.
What excreted by each.
CHAPTER XXDC
THE AMPHIBIA, LIFE HISTORY AND HABITS
Vocabulary
Caudal, pertaining to the tail.
Cellular, composed of cells.
Obscured, hidden.
Hibernate, to remain inactive over winter.
Eject, throw out.
Vicissitudes, changes and accidents of life.
Life History. The life history of a frog is a true metamorphosis
and illustrates perfectly the development of an air-breathing land
animal from a gill-using aquatic form.
The female lays the eggs in the water, early in the spring, and
they are fertilized immediately, thus assuring more certain develop-
ment than in the case of fish. Each egg is surrounded by a jelly-
like coat which swells in the water until all are joined in a gelatinous
mass. In this, dark-colored eggs about as large as peas can be
seen, each surrounded by a transparent covering. The rate of
embryo growth depends somewhat upon temperature and food
conditions but usually the parts can be distinguished within each
egg in less than ten days. The little tadpoles themselves leave
the mass within two weeks.
At this stage they fasten themselves to stones by means of
sucking discs and live by absorbing the attached egg yolk, no
mouth being developed. There are three external gills, a narrow
fish-like body, well developed, and a caudal fin.
Next they become free swimmers. The mouth now appears,
and a very long coiled digestive tract begins work on the vegetable
scums which are their food. Gradually a fold of skin grows back-
ward over the gills, like an operculum, leaving only a small opening
267
268 BIOLOGY FOR BEGINNERS
on the left side. This has an internal connection to the right gills
so that both are supplied with water.
These latter changes may have occupied nearly two months,
and the tadpole is now a fish-like animal, with gills, lateral line,
fins, two-chambered heart, and one-circuit circulation, but soon
other changes follow, gradually adapting the aquatic animal for
land life.
A sac-like chamber develops backward from the throat like the
fish's air bladder, but soon separates into two lobes with cellular
walls which we recognize as lungs. To correspond with this, the
circulation is gradually modified; the gill arteries are changed to
carotids, pulmonaries, and aortic arches; the heart becomes three
chambered, and the circulation flows in two circuits. At this
stage the tadpole may be seen coming to the surface for air to fill
his new lungs as his gills no longer are used for breathing but are
being modified into mouth parts and other organs.
While these notable changes are occurring to the respiratory
and circulatory systems, others no less remarkable are taking
place elsewhere. The mouth widens, teeth develop, and the
intestine becomes shorter and larger to adapt it for animal diet
which the young frog now begins to use.
The external changes, which have accompanied these last
mentioned, have been more conspicuous, though less important,
and are as follows. The tail is gradually absorbed (not shed),
limbs develop at the place where it joined the body, and the body
itself changes shape. The front legs begin growth about the same
time but do not show so soon since they start beneath the operculum
in the gill chamber and are smaller even when full grown.
By this time, the tadpole is a well-developed frog which comes
on land, breathes air, eats animal food and gradually grows in size
till he reaches the full stature of an adult. These latter changes
have occupied usually another month, making a total of about
three months for an average frog metamorphosis, though growth
in size may continue much longer.
Representatives. Let us now briefly take up a few of the common
representatives of the amphibia, which includes, besides the frog,
the toads, salamanders, newts, etc.
THE AMPHIBIA, LIFE HISTORY AND HABITS 269
Toads. The common toad is a much abused and little appre-
ciated member of society: he suffers from many false accusations
and his undeniably plain looks have obscured his many virtues.
To begin with, toads do not cause warts; they do not " rain down ";
they do not " eat their tails "; and they are never " found alive
in solid rock " as some newspaper scientists would have us
believe.
On the other hand, the toad is a very useful and interesting
animal and makes a good pet. They destroy enormous numbers
of harmful insects, though we seldom see them in action as they
hunt at night, when their prey is abundant and their enemies,
the snakes, are asleep. So valuable is their service in insect de-
struction that in Europe toads are regularly for sale to gardeners
and others, to be turned loose in their premises to protect their
crops.
They catch their food with the tongue, like the frog, but have
no teeth. Their rough skin and dull color are protective in their
resemblance to the earth in which they live. They can change
color somewhat to match their surroundings and also will play
dead, to escape observation. They never drink water, but absorb
it through the skin and may store considerable for use during
winter when they burrow in the earth and hibernate. It is this
stored water that toads sometimes eject when handled.
They burrow rapidly backwards in a way hard to understand , but
very efficient and will bury themselves, in a few minutes, if the
ground be soft.
They breed in water as do the frogs, but spend the rest of their
time on land. They also differ in other ways. The eggs are laid
in long strands, not in masses; the tadpoles are small and nearly
black and develop into toads at much smaller size than do frogs.
They emerge from the ponds in thousands when about the size of the
tip of your finger and it is these swarms of tiny toads that give
rise to the idea that they have come down in the rain. During
the breeding season they develop vocal powers of no mean extent,
their song being a rather sweet and bird-like trill.
Their eyes are even more handsome than the frog's. Altogether,
270 BIOLOGY FOR BEGINNERS
the toad is a useful and interesting animal and should never be
regarded with repugnance, much less, with enmity.
Tree Toads. Another member of the amphibia is the tree-
toad or tree frog (Hyla) which, though common, is seldom seen,
because of its almost perfect protective coloration. Its song
however is familiar enough when the " peepers' " cheerful chorus
ushers in the early spring. They vie with the chameleon in ability
to change color to match their surroundings, green, gray, brown,
yellowish, and even purple being among their varied disguises.
It seems hardly possible that so loud a song can be sung by a
tiny frog, little more than an inch in length, but if we are patient
and successful enough to hunt one out with a lantern at night,
the reason is clearer. The little Hyla can expand its throat into
a vocal sac twice the size of its head, and with this enormous
drum can produce its very remarkable music.
They are true tree climbers and on each toe have sticky discs
by which they can climb safely on the bark of trees and even
cling to glass. Their color, stripes, and shape protect them
perfectly from observation.
The eggs are laid in April; and the tiny reddish tadpoles feed
on mosquitoes. The adults include also ants and gnats on their
menu, which ought to give them a place in our affection. A curious
fact about their tadpole stage is that they often leave the water
before the tail is nearly absorbed, being apparently able to breathe
air earlier in their metamorphosis than do most other frogs.
Salamanders and Newts. The tailed amphibians, including
salamanders, newts, and mud puppies, are less known than they
should be. We have over fifty species in the United States, that
being more than are found in any other country. A very common
mistake, is to call these animals " lizards." They can readily be
distinguished because a lizard is a reptile and has scales like a
snake whereas the salamander is an amphibian and has a smooth
skin like a frog.
One often finds, in moist woods, tiny brown or orange red
creatures about three inches long, beautifully spotted with scarlet
and black. These are newts and very curious and interesting little
THE AMPHIBIA, LIFE HISTORY AND HABITS 271
fellows indeed. They can only live in moisture, and so are found
after rains and in wet places, although in adult form they breathe
air. They have the regular amphibian metamorphosis, though
they never absorb their tails. The newt, however, adds a very
curious stage to its life history, for after about two years of land
life it returns to the water, even from great distances, changes
color to olive-green, develops its tail fin again and by some means
is enabled to breathe the dissolved air in the water. Here, after
all these strange vicissitudes, breeding takes place, eggs are laid,
and the life history starts again.
The true salamanders are larger, there being several common
FIG. 92. The western brown eft, or salamander, Diemyctylus torosus.
From Kellogg.
species. The spotted salamander, black, with yellow spots, is
about six and one-half inches long, and the black salamander,
blue black and a little smaller, are two of the kinds most often
found and mistaken for lizards. All are harmless to handle, useful
as insect eaters and so helpless and interesting that they ought
never to be destroyed.
COLLATERAL READING
Metamorphosis: The Frog Book, Dickerson, pp. 1-7; Study of Animal
Life, Thompson, p. 258; Elements of Zoology, Davenport, pp. 451-457;
Textbook of Zoology, Packard, p. 184; Introduction to Biology, Bigelow,
pp. 389-414; Lessons in Zoology, Needham, pp. 178-196; Elementary
Zoology, Kellogg, p. 299; Biology of the Frog, Holmes, pp. 81-119;
Animal Activities, French, p. 179; Zoology -Text, Packard, p. 874;
Winners in Life's Race, Buckley, pp. 70-77; Cornell Nature Leaflet,
Vol. 10, No. 1, pp. 88-97; Life in Ponds and Streams, Furneaux, pp.
360-399.
Relatives: American Natural History, Hornaday, pp. 359-374; Frog
272 BIOLOGY FOR BEGINNERS
Book, Dickerson, pp. 53-239; Elementary Zoology, Davenport, pp. 325-
348; Practical Zoology, Davison, pp. 199-211; Elementary Zoology, Gallo-
way, pp. 296-305; Pet Book, Comstock, pp. 246-259; Handbook of Nature
Study, Comstock, pp. 181-199; Nature Study Leaflets (bound), pp. 185-
206.
SUMMARY
Metamorphoses of Frog.
Meaning of term, other examples, tadpole is "frog larva."
Egg, laid in water, surer fertilization, in spring.
Gelatinous protection, parts show in 10 days.
Tadpole (attached stage). Discs, three external gills.
Lives on yolk. Two weeks.
Tadpole (free swimmer), mouth develops.
Long intestine because vegetable feeder (explain).
Lateral line, caudal fin, operculum with left opening.
Two-celled heart, fish-like. Two months.
Tadpole, frog.
Mouth widens, intestine shortens, teeth develop.
Heart three celled, arteries change from gill to lung.
Lungs develop, air used, skin breathing.
Tail absorbed, legs develop. One month.
Adult frog.
Total time about three months, depends on food, temperature, etc.
Representatives.
Frog.
Toad, false ideas, real value.
Adaptations for food-getting.
. Tongue as in frog, no teeth.
Color, skill.
Distinctions from frog.
Toad Frog
Eggs in strands Eggs in masses
Nocturnal feeding Daytime feeding
Tadpoles small, black Tadpoles larger, lighter
No teeth at all No teeth on lower jaw
Rough skin Smooth skin
Tree toad (Hyla).
Adaptations, color protection, color change.
Discs for climbing, vocal sacs.
Tadpoles reddish, early develop lungs, eat insects.
Salamanders.
Distinctions from lizards.
Salamander Lizard
Common Not common
Smooth skin like frog Scaled skin like snake
No claws on feet Claws on feet
Metamorphosis like frog No metamorphosis
Harmless, useful and interesting.
CHAPTER XXX
THE REPTILES
Vocabulary
Iridescence, changeable rainbow colors.
Reticulated, marked with a network pattern.
Retracted, drawn back.
Constrictors, snakes that crush their prey in their coils.
There is probably no group of animals less understood, and
concerning which there is more abundant misinformation than the
reptiles. It is principally to correct some of these false ideas that
they are discussed here.
The reptiles include snakes, turtles, lizards, and crocodiles and
FIG. 93. A fence lizard, Sceloporus occidentalis. From Kellogg
and Doane.
the points in which they differ from amphibians are as follows:
1 . They never breathe by gills at any stage.
2 They have no metamorphosis.
3. Eggs are internally fertilized and have a shell, or young may
be born alive.
4. The body is covered with scales.
5. Feet, if present, are provided with claws.
273
274 BIOLOGY FOR BEGINNERS
False Ideas about Snakes. Of all the reptiles, the snakes are
the objects of more ignorant superstition and foolish prejudice
than any other form. To begin with, snakes are not " slimy "
and " nasty." Their skin is as clean as yours and feels cold merely
because of their lower bodily temperature. Snakes as a class are
absolutely harmless and positively useful. Out of the numerous
species inhabiting the United States only the rattler, copperhead,
moccasin, harlequin, and coral snakes, are dangerous to handle.
Snakes cannot jump from the ground when they strike nor do
they spring from a perfect coil. A snake's tongue is not a weapon
nor harmful in any way. It is an organ of touch only and is
thrust out merely to feel its surroundings. The process of
death is slow in any animal with a low nervous organism, and
though reflex motions persist in a snake long after death, the
setting of the sun has absolutely nothing to do with its death.
Snakes do not swallow their young to protect them; " hoop
snakes " do not roll like hoops; horsehairs do not turn into
snakes; and rattlers do not add one rattle per year, but usually
two or three, though some may be broken off. Removal of
fangs from a poisonous snake does not render it harmless since
other teeth take their place almost at once. Many snakes hiss;
some as loudly as a cat. Most snakes can swallow prey larger
than themselves. All snakes are muscular, graceful, and usually
swift of motion, while many are very beautiful.
I " There is no living creature which displays such a beautiful
pattern of colors and rainbow iridescence, as the reticulated
Python of the East Indies," says Wm. T. Hornaday.
Children are not born with any natural fear of snakes and
adults should never be allowed to terrify their minds with silly
snake stories and untrue and ignorant statements.
Adaptations. Another matter which is little appreciated in
regard to snakes, is the fact that there is perhaps no other animal,
except the bird, with a more highly specialized structure.
The whole animal, but particularly the head, is adapted for its
peculiar habit of catching and swallowing prey actually larger in
diameter than its own body. For this purpose there are numerous
THE REPTILES 275
sharp, incurved teeth on three sets of jawbones, any of which
will grow again to replace those that may be broken or torn out.
The lower jaw is not fixed directly to the skull, but is attached
to a separate bone, the quadrate, which in turn is attached to the
skull, thus permitting the jaw to move forward and backward, as
well as up and down. This enables the snake to literally crawl
outside of its victim, the upper teeth holding firmly while the
lower jaw is advanced; then the upper jaw takes a new hold, and
so on. The process is slow, often occupying hours, but there is
no chance for escape of the prey. The snake's teeth cannot bite
the food in pieces, so all its victims must be swallowed whole.
To permit this, the various bones of the skull, so solid in other
animals, are loosely attached in the snake, allowing the head to
expand when swallowing is taking place. The two halves of the
lower jaw are attached together by an elastic ligament which
allows them to open sidewise, so that the lower jaw is capable of
three motions, up and down, back and forward, and (each half)
sidewise.
The process of swallowing is so long that special adaptations
are provided to permit breathing to go on. The trachea may be
extended along the floor of the mouth, almost to the teeth, so that
air may reach the lungs, and moreover there is a large air chamber
behind the lung to store air for this purpose.
The gullet and stomach are highly elastic and the digestive
fluids very active, to accommodate food in such large doses. The
flexible ribs and lack of breast bone or limb girdles allow for the
passage of these enormous mouthfuls.
The delicate and slender forked tongue is protected during
swallowing by being retracted into a sheath. Its function is for
touch, rather than taste, which sense would be of very little use
to an animal which eats its food whole and sometimes alive.
Snakes obtain their food in three general ways: they may catch
it with the teeth and swallow it at once as does the common garter
snake; they may crush the prey in their coils, before swallowing,
as do all constrictors ; or they may have poison apparatus developed,
which stupifies or kills their victim immediately.
276 BIOLOGY FOR BEGINNERS
Poisonous Snakes. While, fortunately, there are few poisonous
snakes in the United States, their adaptations are very interesting.
The long front teeth of the upper jaw are either grooved or hollow
fangs, moveable in some snakes and fixed in others. These fangs
are connected with salivary glands which, in this case, secrete the
poisonous venom, and are so arranged that the act of striking,
compresses the gland and forces the venom into the wound made
by the fangs.
In common with most ideas about snakes, a great deal of non-
sense is current regarding the frequency and deadliness of the bite
of a poisonous species. To begin with, in all the United States
the annual death rate from snake bite is about two. Second,
all snake bites are not necessarily fatal. Third, unlimited whiskey
is not an antidote.
The facts of the case are about as follows, summarized from two
eminent authorities, Doctor Stejneger and W. T. Hornaday.
Learn to recognize and avoid three snakes: rattlers, copper-
heads and water moccasins. In all the United States there are
but five poisonous types, and the three mentioned are rare except
in certain localities. The rattlesnake is a fair fighter, never seeks
trouble, strikes only in self-defense, and always warns before
attacking, so that, with any reasonable care, it may easily be
avoided.
The copperhead goes by other names, sometimes being called
the " pilot snake " or " deaf adder," and as it attacks without
warning, is actually more dangerous than the rattlers, though
slightly less poisonous. It is usually found in the woods, is
seldom over three feet long, and is beautifully colored with
broad bands of old copper on a background resembling new
copper. Any snake remotely resembling this description is to be
avoided.
Treatment of Snake Bites. Bites are, fortunately, generally
received on the arms or legs, and are not necessarily, nor usually
fatal if properly treated. Campers in snake-infested regions can
obtain for five dollars or less, an outfit consisting of a hypodermic
needle, chromic acid solution, permanganate of potash, and liquid
THE REPTILES
277
strychnine, which with the anti- venom serum, now easily obtained,
constitute almost sure protection.
POISON APPARATUS OP i/VAKE.
After Linville and Kelly, by permission ofGinn and Co.
FIG. 94. Poison Apparatus of Snake.
Fig. 1 shows the structure of the skull. Note the two hinges which permit
a forward and backward motion of the quadrate bone. This allows the lower
jaw to be extended and drawn back to aid in swallowing the prey.
The very loose attachment of all the skull bones permits great freedom of
motion, needed when swallowing a victim larger than itself.
The fangs are grooved or hollow, forming an outlet for the poisonous venom.
Fig. 2 shows part of the head dissected away to expose the poison gland and
the muscles that press upon it when the snake strikes. The act of striking
forces the venom out through the fangs, into the wound.
Fig. 3 is a diagram showing the poison gland, duct and fang removed. Also
the secondary fangs which develop to replace the large ones, if they are in-
jured or torn out in striking.
278 BIOLOGY FOR BEGINNERS
In case of accident, the treatment should he as follows:
1. Cut the wound to promote free bleeding.
2. Tie a ligature above the wound.
3. Use anti-venom serum if at hand.
4. Give alcoholic stimulants in frequent, small doses: an excess
may cause death.
5. If no serum is available, inject either the chromic acid or
permanganate.
6. Inject liquid strychnine (15-20 minims) every twenty minutes
until spasms begin.
7. Ligature must be loosened at times to allow the circulation
of enough blood to prevent mortification.
8. Summon a doctor if possible, but it is the treatment of the
first hour that counts.
When you realize that only about two in over 100,000,000
persons die of snake bite in the United States, that we have
few venomous kinds of snakes in this country, and finally, that
rational treatment is usually successful, you can see how foolish
is the fear and hatred so often shown toward these really useful
and handsome animals.
Solomon selects as one of the mysteries of nature, " the way of
the serpent upon the rock " and surely their adaptations for loco-
motion are peculiar enough to warrant this distinction. They
have no legs, yet they travel, climb, and swim with ease and
rapidity. They accomplish these feats by means of the broad plates
on their ventral surface. These plates have their free edge toward
the rear, so will catch against the slightest roughness. To each
plate is attached a pair of ribs which operate somewhat as legs,
with each plate as a foot. To allow free motion of the ribs, the
vertebrae have a very flexible ball-and-socket joint, and the whole
body is provided with exceedingly strong muscles, so that a snake
really travels on hundreds of muscular legs (ribs).
This is a good example of analogy, the ribs and plates perform-
ing the same function as legs, but being of entirely different origin
and structure.
THE REPTILES 279
COLLATERAL READINGS
Types of Animal Life, Mivart, pp. 121-148; Forms of Animal Life,
Rolleston, pp. 67-73; Winners in Life's Race, Buckley, pp. 89-122; Animal
Life, Thompson, pp. 259-264; Elementary Zoology, Kellogg, pp. 303-326;
Textbook of Zoology, Linville and Kelly, pp. 348-363; Textbook of Zoology
(elements), Davenport, pp. 349-369; Textbook of Zoology, Colton, pp.
196-207; Lessons in Zoology, Needham, pp. 198-211; Advanced Text in
Zoology, Shipley and McBride, pp. 457-494; Advanced Text in Zoology,
Parker and Haswell, pp. 291-305; Advanced Text in Zoology, Claus and
Sedgwick, pp. 208-209; Practical Zoology, Davison, pp. 211-226; Familiar
Life of Field and Forest, Mathews, pp. 57-80; Talks About Animals, pp.
155-159, 211-216; American Natural History, Hornaday, pp. 313-353;
Reptile Book, Ditmars, entire; Economic Zoology, Kellogg and Doane, pp.
260-272; Reptiles and Batrachians of New York, Bulletin, entire.
- SUMMARY
Representatives.
Snakes, turtles, lizards, crocodiles, and alligators.
Characteristics.
No metamorphosis nor gills.
Eggs internally fertilized.
Scales, claws, young may be born alive.
Erroneous Ideas.
Not dirty nor dangerous, clean and useful.
Reason for "cold " feeling. Rattles per year.
Tongue for feeling only. Fangs, hissing.
Reason for slow death, "hair snakes," " hoop snakes."
Adaptations.
Food-getting, methods.
Caught by teeth and swallowed (garter snake).
Crushed before swallowing (boa constrictors).
Venom to kill or stupefy (rattler, cobra).
Adaptations for food-getting.
In-curved teeth, jaw attachment.
Elastic skull and jaw.
Tongue sheath, protrusible trachea, air sac.
Elastic gullet, strong digestive fluids.
Adaptations for locomotion.
Rib attachment to ventral plates.
Ventral plates (scutes).
Flexible spinal column.
Analogy between legs and ribs.
Poisonous snakes.
Apparatus, fangs, hollow or grooved teeth.
Fangs movable or fixed.
Poison from modified salivary glands.
Muscles for ejection of venom.
280 BIOLOGY FOR BEGINNERS
Kinds.
Rattle snakes (several species) known by rattle.
Copperhead (pilot or deaf adder) known by color.
Water moccasin (found in southern swamps, large).
Treatment of snake bites.
Promote bleeding.
Ligature above wound if possible.
Use serum or permanganate of potash or chromic acid.
Stimulate with little alcohol or strychnine.
CHAPTER XXXI
BIRDS, THEIR STRUCTURE AND ADAPTATIONS
Vocabulary
Flexible, easily bent.
Impair, to interfere with.
Competent, able.
Concave, curved in.
Eliminate, to excrete or throw off, as waste.
Coordinate, to make to work together.
Acute, keen.
The group of birds is one of the most familiar, useful, and
interesting, of all the animal kingdom. Among the vertebrates
they are the most highly specialized in structure, every organ
being adapted for the one object, namely, flight.
Birds are sharply distinguished from all other animals by the
following points, among many others:
1. Their body is covered with feathers.
2. Their forelimbs (arms) are developed as wings, solely for
locomotion and never for prehension.
3. The mouth is provided with a horny, toothless beak.
4. The body is supported on two limbs only (like man).
Adaptations for Flight. The general smooth outline, due to the
thick covering of feathers, permits easy and swift passage through
the air with little resistance. The flexible neck and legs provide
for easy " fore and aft " balance, while the wings, being attached
high above the bulk of the body, prevent danger from tipping
over sidewise. Lightness is secured by very slender, hollow, air-
filled bones, with few heavy joints; by numerous air sacs scattered
through the body; by feathers for covering and locomotion; and
281
282
BIOLOGY FOR BEGINNERS
by having teeth replaced by the light but strong beak. The
chief flight adaptations, however, are the structure of the feathers
and the wing. These will be discussed somewhat in detail.
BIRDS, THEIR STRUCTURE AND ADAPTATIONS 283
Feathers. Feathers are modified forms of scales and develop
in the same way from the skin. Some unchanged scales are always
found on the feet and legs, which remind one of their relationship
to reptiles. They are not evenly distributed over the bird's body,
but are found in certain feather tracts, between which the skin is
nearly bare, though the over-
lapping feathers do not re-
veal it. There are three
kinds of feathers; the soft
down which retains bodily
heat, the ordinary body
feathers that give the smooth
and graceful outline to the
otherwise angular form, and
the large quill feathers of
the wing and tail.
These latter are the ones
concerned in flight and con-
sist of a broad vane spreading
from an axis (the rachis)
terminating in a hollow quill.
The vane is made up of in-
numerable rays called barbs,
each like a tiny feather,
having projections called
barbules (little barbs) which
in turn are held together by
interlocking hooks of micro-
scopic size. This compli-
cated arrangement provides a vane which is very strong, light,
and elastic, and furthermore, if the barbules become unhooked
as when a feather is " split " by accident, the bird merely shakes
them or draws them through its beak, and the feather is whole
again. This is a great advantage over a wing membrane such as
is possessed by the bats which, if once injured, cannot be repaired.
The rachis is grooved and the quill hollow, both being adapta-
FIG. 96. Structure of quill feather.
284 BIOLOGY FOR BEGINNERS
tions to secure greater strength and less weight. At the base is
an opening through which nourishment was supplied during its
growth. The vane of the wing feathers is wider on one side of the
rachis than the other. When the wing strikes against the air it
tends to turn up, but rests against its neighbor and is held flat,
while on the return stroke it is free to turn. The air passes through
the wing as each feather partly turns on its axis (" feathering ")
and the wing meets less air resistance.
Uses of Feathers. The feathers provide the means of flight,
and aid in easy locomotion, by giving the angular body a smooth
outline. Moreover feathers, being one of the best heat-retaining
substances, serve to keep the bird warm, even in the coldest
weather, no matter how high or swift its flight. Their great
activity necessitates their high body temperature and the feather
covering retains this heat and makes possible their life in the upper
air. The feathers of most birds are oiled by a secretion taken
from a gland near the tail and spread on them by the beak. This
makes them waterproof and is best shown in swimming and diving
birds, which can spend hours afloat and suffer no discomfort.
Feathers have a further use in providing a colored covering
which helps birds in escape from discovery by enemies because of
its resemblance to their surroundings. This coloring may also be
used to attract mates.
Moulting. Birds shed their feathers at least once a year, so that
new ones may replace any that are lost or damaged. This is
especially important in the case of wing feathers. Some species
moult twice annually and may have differently colored plumage
at different seasons. This change of color is sometimes used for
protection and sometimes to attract mates. Wing feathers are
shed in pairs and gradually, so as not to impair flight.
SUMMARY OF USES OF FEATHERS
1. Flight.
2. Giving regular body outline.
3. Protection from cold and water.
4. Protective coloration.
BIRDS, THEIR STRUCTURE AND ADAPTATIONS 285
The Wing. The wing is almost as wonderful an organ as the
human hand, but although a modified arm, it has lost all power of
grasping and is adapted entirely for flight. The shoulder is strongly
braced by three bones, instead of two as in man, to withstand the
tremendous pull of the powerful muscles. There is the shoulder
blade, the collar bone (" wish bone "), and the coracoid bone ex-
tending to the sternum (breast bone). All three are devoted to
supporting the wing, using a sort of tripod arrangement, which is
very strong. The upper
and lower arm bones are *. a/wii
long, strong, and slender.
The wrist is lengthened as
are also the fingers; only
three are present, however,
the other two being sacri-
ficed for lightness. Thus
we have a long, three-
jointed lever, firmly at-
tached to the shoulder with
its leverage greatly in-
creased by the feathers. The problem now consists of providing
the necessary muscle to swing such an arm.
Power Required. To illustrate the difficulty involved, we may
take as an example the pigeon. It weighs about a pound and has
a wing spread of about two feet. This would mean that a boy or
girl of ordinary weight would have to swing through the air a pair
of wings each from fifty to seventy-five feet long at the rate of
two hundred to five hundred strokes per minute. Try to swing
your own arm at this rate for a minute, and then imagine the power
needed for a wing as long as a building lot front. If we think of
keeping up this form of exercise for forty-eight hours without rest,
we will have some idea of the bird's problem, and the marvelous
way in which it has been solved.
Muscles, competent for this task, could not be located on the
wing itself, as that would too greatly increase its weight, so we
find the breast bone enormously enlarged and attached to it,
FIG. 97. Wing structure of bird.
286 BIOLOGY FOR BEGINNERS
muscle tissue equal in some cases to one-third the whole weight
of the bird. To connect these muscles with the wing bones, a
very remarkable set of tendons pass over the shoulder joints like
ropes over pulleys and transmit the motion to the wing, much as
our fingers are closed by muscles located in the forearm.
Shape of Wing. The attachment of the feathers to the wing is
no less perfectly adapted for its purpose. The longest feathers
(primaries) are attached to the fingers where their leverage will
be greatest. Back of them come the secondaries, which brace
them at the base and cover the spaces between their quills. These
in turn are further supported by other rows, both above and below.
The outline of the wing as a whole, with its concave under surface,
thick forward edge, and thin flexible rear edge and tip, has just
the form which man has recently discovered best for his aeroplane,
and is beginning feebly to imitate.
Flight. In ordinary flight the wing stroke resembles horizontal
figure eight down and back, up and forward. The soaring of
birds, like the hawk, where they seem to fly without any motion
at all, is not understood. It may be due to slight wing motion,
to balancing, or to utilization of wind currents, but so far, man
has not satisfactorily explained, much less imitated it.
When man flies in the aeroplane, of which we are so proud.
he flies not like the bird, with beating wings, but rather like the
locust or beetle with stiff planes and a propeller behind. Thus
far we have no engine powerful enough to swing a vibrating
wing machine, large enough to carry a man in flight like a
bird.
Muscles. The " white meat " of a chicken is the mass of breast
muscles used in flight and the large breast bone with its projecting
ridge is familiar to all of us. This ridge gives additional room to
attach the powerful muscles. The outer layer of the white meat
separates easily from an inside portion, this latter being very
tender. The explanation is that the outer, larger, and tougher
muscle was the one used in pulling the wing, down and backward
in the " stroke " of flying, while the inner and more tender muscle
acts by way of a tendon over the shoulder to raise the wing for
BIRDS, THEIR STRUCTURE AND ADAPTATIONS 287
the next stroke, a much easier task and one which does not
toughen it.
Adaptations for Active Life. The act of flight requires more
work than any other form of locomotion. This is shown by the
enormous breast muscles that operate the wings, and the general
activity of the bird's whole life. Great amounts of energy are
required which means large food-getting and digestive ability.
This, in turn, demands a remarkably complete respiratory system
to provide for rapid oxidation and release of energy.
Digestion. Birds are provided with a crop for storage, a gizzard
in which small stones take the place of teeth for chewing, and
very powerful digestive fluids, all of which work together to care
for the vast amount of fuel needed to run so powerful an engine.
A bird usually eats several times its own weight of food every day,
so the common expression to " have an appetite like a bird " is
hardly a suitable comparison for a light eater.
Respiration. The respiratory organs consist of very finely
cellular lungs; behind these are the air sacs which hold the reserve
air and permit all the lung tissue to be used in supplying oxygen
to the blood. These air sacs also aid in this process. The rate of
respiration is very high and the normal temperature is from 102
to no degrees, which would be fatal to man and to most other
animals. Rapid oxidation means rapid production of waste
matters and these are removed largely by the very highly developed
lungs, there being little liquid urine eliminated by the kidneys,
and no sweat glands. Crystals of urea are excreted by the
kidneys.
Not only do the lungs provide the blood with oxygen for oxida-
tion, and also remove waste, but in addition supply the air for
singing, of which many birds require a large amount. It might
be of interest to mention that the bird's song is not produced in
the throat, but at the base of the trachea where the tubes from each
lung join. Here is located the " song box," a very delicate and
highly adjustable structure.
Circulation. To transport this large burden of digested food,
oxygen, and the waste products of oxidation, there is required a
288 BIOLOGY FOR BEGINNERS
very large powerful heart and well-developed blood vessels. The
rate of the heart beat is also very rapid.
Other Adaptations. Since the bird has devoted its forelegs
(arms or wings) to flight, it must needs balance the body on the
other pair, a thing which is done by no other group of animals
except man. As an adaptation for this, the legs are attached high
on the hips, so the body hangs suspended between them like an
ice pitcher. This prevents any tendency to lose balance when
walking, and permits the bird to bend easily and to pick up food,
which has to be done with the beak since the fore limbs cannot
be used for prehension.
Man, although he can balance on two legs, falls easily and has
to learn to walk, but no one ever saw a bird fall down, or have
any difficulty in walking. The difference is due to the fact that
the bulk of man's body is above the point of support at the hips,
while that of the bird swings below.
Perching. The bird usually perches on a support when at rest
or asleep and for this purpose has a very curious arrangement.
The tendon that doses the claws passes over the leg joints, hence
the more the leg is bent, the tighter the claws close up. Thus
when the bird settles down on a branch to sleep, the more it relaxes
and the more its legs bend, the closer the claws grasp the perch.
This and the balancing adaptations enable them to cling to a
swinging twig when awake, or to a perch when asleep, with no
possibility of falling.
Neck. The very flexible neck is another adaptation, especially
for food-getting, since the wings cannot be used for that purpose.
Not only is the bird balanced so as to bend easily but the length
of the neck corresponds to that of the legs; because of this the
bird can always reach the ground to pick up food.
Feet. The feet of birds differ widely in structure, depending
on the particular purpose required, and are a splendid example of
adaptation in themselves.
The common perching birds have three toes in front and one
behind. Climbing birds, like the woodpecker and parrot, have
two on each side, while swimming birds may have each toe with a
BIRDS, THEIR STRUCTURE AND ADAPTATIONS 289
separtae web like the coot, or a web connecting all four, like the
pelican, or only the front three, like the ducks and geese.
The birds of prey (hawks, owls, and eagles) have the toes provided
with powerful claws and muscles which constitute their " talons"
for catching food. While at the other extreme are birds like the
swifts, hummers, and whip-poor-wills, which have very tiny and
weak feet, since they live on insects or nectar, and spend most of
their time in the air.
Birds which wade along the shores in search of food have long,
slender legs, like the heron, snipe, crane, and plover, while in diving
birds, such as the loon and duck, the legs are so short and so far
back as to make walking very awkward.
Beaks. Just as great a range of adaptation is shown by the
beak of the bird. In all cases it is light, strong, and horny, thus
avoiding weight. With each class of birds the beaks vary, depending
on the nature of their food and the manner of catching it.
The hook-shaped, strong beak of the hawk and owl is a familiar
adaptation for the birds of prey while the very sharp, chisel-shaped
beak of the woodpecker enables him to drill deep into the trees
for nest holes and for food. Birds like the swifts, nighthawks, and
whip-poor-wills, which catch insects on the wing, have weak but
enormously wide beaks, often surrounded by hairlike feathers,
making a regular trap to catch their food. The duck's wide beak
with toothed edges is provided for scooping food from the mud
and straining it out between the notches when the head is shaken,
while the slender and sensitive beak of the snipe is used to probe
in the mud for single pieces of food. Parrots use their short-hooked
beak for defense, food-getting, and for climbing. Sparrows and
finches have short straight beaks for crushing seeds. The crossbill
has developed a real pair of pliers for opening cones, which contain
the seeds he eats, while at the other extreme is the humming bird
with its delicate tubular beak, able only to suck the nectar of
flowers.
Nervous System and Sense Organs. To properly coordinate
and control so complicated and highly adapted an organism, a
well-developed brain is necessary. In birds, for the first time, the
290
BIOLOGY FOR BEGINNERS
brain completely fills the skull; the cerebrum is broad and the
cerebellum especially large, as is to be expected in so active an
animal.
PAMMOT
FIG. 98. Bird Beak Adaptations.
Hawk, powerful, sharp beak for catching prey.
Woodpecker, chisel edged, for chipping wood.
Whip-poor-will, weak beak but wide mouth, surrounded by stiff hairs, for
catching insects on the wing.
Duck, wide beak with toothed edges, to dig up mud etc. and by shaking the
head, 'sift out the waste.
Snipe, slender and sensitive, for probing after food in the mud along the
shore.
Parrot, hooked and strong for climbing, and defense.
Finch, short and strong, for cracking seeds.
Cross-bill, a special device for opening cones to get seeds.
Humming bird, slender to suck nectar from flowers.
(After Wright and Coues.)
The optic lobes are also well developed but the olfactory (smell)
lobes are usually small and the sense of taste is poor, since the food is
swallowed without remaining in the mouth to be chewed and tasted.
BIRDS, THEIR STRUCTURE AND ADAPTATIONS 291
The bird's eye is a very wonderful instrument, the sight being
keen both at a distance and for close vision, and the change of
focus is very quickly made. This is necessary in birds, because
they must see clearly to pick up food at their feet, or detect an
enemy at a distance, observe their prey far off, or weave a nest
close at hand, and their ability along this line is unequaled by any
other animal.
Their hearing is usually acute though there are no external ears,
the openings being protected by a ring of feathers. Keenness of
this sense is useful to escape danger and to recognize the songs
and calls of their mates.
COLLATERAL READING
General Structure: Textbook of Zoology, Parker and Haswell, pp. 357-
366; Textbook of Zoology, Shipley and McBride, pp. 495-506; Winners
in Life's Race, Buckley, pp. 123-130; Forms of Animal Life, Rolleston,
pp. 46-66; Textbook of Zoology, Claus and Sedgwick, pp. 232-238; First
Book of Zoology, Morse, pp. 174-180; General Zoology, Colton, pp. 208-221;
General Zoology, Linville and Kelley, pp. 364-373; Elementary Zoology,
Davenport, pp. 370-419; Elementary Zoology, Needham, pp. 211-237;
Practical Zoology, Davison, pp. 226-261; Elementary Zoology, Kellogg,
pp. 327-372; Biology Text, Peabody and Hunt, pp. 62-100.
Flight of Birds: Animal Mechanism, Pettigrew, pp. 209-278; Animal
Locomotion, Marey, pp. 103-206; Winners in Life's Race, Buckley, pp.
130-135; Animal Life, Thompson, pp. 123-124; Textbook, Shipley and
McBride, pp. 501-502; Introduction to Zoology, Davenport, pp. 310-311.
Classification and Types: Economic Zoology, Kellogg and Doane, pp.
273-294; Birds of Eastern North America, Chapman, entire; Bird Life,
Chapman, entire; Citizen Bird, Wright, entire; Textbook of Zoology,
Linville and Kelley, pp. 374-397; General Zoology, Colton, pp. 222-245;
Types of Animal Life, Mivart, pp. 66-95; Little Brothers of the Air, Miller,
entire; American Natural History, Hornaday, pp. 171-309; N. Y. State
Museum Memoir, Vols. I and II, entire; American Geographic Magazine,
bird numbers, entire; Bulletins of U. S. Department of Agriculture; Bulle-
tins of Audubon Society; Bird Guides (Land Birds, Water Birds), Reed,
entire.
SUMMARY
Characteristics.
Feathers, wings, beak, two feet, shelled egg.
1. Adaptations for flight.
Shape, feathers to smooth outline.
Balance, neck, legs, attachment of wings,
202 BIOLOGY FOR BEGINNERS
Lightness, hollow bones, air sacs, feathers, beak.
Feathers.
Origin, modified, scales (other epidermal structures).
Distribution, tracts.
Kinds, down for warmth.
Regular feathers for outline.
Quill feathers for locomotion.
Structure.
(1) Vane, barbs, barbules, hooks.
Advantages: lightness and case of repair.
(2) Rachis, grooved for strength.
(3) Quill, hollow for strength lightness.
Shape, one sided for " feathering."
Uses, flight, contour, warmth, color, to shed water.
Moulting, for repair replacement and color change.
Wing, homologous to hand, not analogous.
Bones, three shoulder bones in tripod form.
Shoulder blade, narrow.
Collar bone (wish bone) united.
Coracoid, to breast bone, special for flight.
Arm bones long and slender.
Hand reduced to three fingers (why?).
Muscle power.
Muscles not on wing (why ?), cf. human hand.
Breast muscles one-third weight.
Outer and inner layers (white meat).
Large ridge on breast bone.
Tendons and pulleys at shoulders.
Shape of wings.
Feather arrangement, why longest feathers at end?
Concave below, flexible rear edge and tip.
2. Adaptations for active life.
Much energy, oxidation, food, food-getting, digestion, respira-
tion, circulation, excretion.
Digestion.
Crop for storage, flockwise feeding.
Gizzard for grinding in place of teeth (why?).
Powerful digestive fluids.
Respiration.
Lungs finely cellular (why?).
Air sacs for reserve air, air in bones.
High rate of breathing and temperature.
Excretion via lungs.
Use of air in song, location of syrinx.
Circulation.
Heart large, four chambered, rapid beat.
Blood vessels, large, especially to breast.
BIRDS, THEIR STRUCTURE AND ADAPTATIONS 293
3. Other adaptations.
(1) Attachments of legs for balance (cf. man).
Ease of picking up food, since no hands present.
(2) Perching.
Tendon action.
(3) Neck, flexible and muscular (why?).
(4) Feet.
Structure of toes
Examples
Adapted for
3 front; 1 rear
Song birds
Perching
2 front; 2 rear
Woodpecker
Climbing
Parrot
All webbed, separate
Coot
Swimming
All webbed, united
Pelican
Swimming
Three webbed, united
Duck, goose
Swimming
3 front; 1 rear, heavy claws
Hawk, owl, eagle
Catching prey
Small, weak
Hummer, swift
Little used
Long legs
Crane, heron
Wading
Legs short, far back
Loon, duck
Diving
5. Beaks. (Why not teeth).
Kinds
Examples
Adapted for
Hooked
Hawk, owl
Catching prey
Chisel shaped
Woodpecker
Drilling in trees
Wide but weak
Night-hawk
Catching insects on wing
Swift
Broad and notched
Duck
Scooping and straining
Slender and sensitive
Snipe
Probing in mud
Notched and hooked
Parrot
Climbing
Short and thick
Sparrows
Seed-eating
Crossed mandibles
Crossbill
Opening cones
Slender tube
Hummer
Sucking nectar
Nervous system.
Highly developed (why?).
Brain fills skull.
Cerebrum, cerebellum, and optics large.
Taste and smell not acute (why?).
Sight keen, wide range of focus.
Hearing keen for escape and recognition (song).
CHAPTER XXXH
BIRD HABITS
Vocabulary
Unmitigated, having no redeeming feature.
Excavated, dug out.
Inaccessible, hard to get at.
Stringent, strict.
Feeding. As before mentioned, their intense activity requires
that birds obtain large amounts of food. Almost every thing that
can be eaten comes to the table of some kind of bird, certain ones
eating animal food exclusively, others are strict vegetarians, while
many use a mixed diet.
Among those using animal food are large birds of prey, such as
hawks and owls, which feed upon rats, rabbits, field mice, and
other small animals, also upon some other birds. Then there are
many whose diet is largely or entirely fish, which they catch by
diving, as do the loon, grebe, pelican, and kingfisher. Some,
like the vulture and buzzard, are scavengers and eat any dead
animal that they can find; such birds have sight very keenly
developed. Probably the largest number of birds which enjoy
an animal diet live chiefly on insects which they may catch on
the wing (swifts), by burrowing (woodpeckers), from the ground
(robins), or on trees (warblers).
Many birds live almost exclusively on seeds, doing much good
by the destruction of weed seeds while others, such as blackbirds
and bobolinks, do considerable damage by their preference for
grain, peas, and rice. Various kinds of both wild and cultivated
fruits, especially berries, are preferred by certain birds for all or
part of their bill of fare, though usually the fruit-eaters have to
change to an insect diet during seasons when fruit is scarce.
294
BIRD HABITS
295
It sometimes happens that birds enjoy the same seeds or fruits
that man raises, or they may at times rob his yard of a stray chicken,
but very careful study has proven that there are but three or four
birds which do more harm than good. The rest many times repay
for their fruit by destruction of insects and vermin. The birds
in whose favor little can be said are the Cooper's and sharp-shinned
FIG. 99. Oriole's nest with skeleton of bluejay suspended from it,
the blue-jay probably came to the nest to eat the eggs, became en-
tangled in the strings composing the nest and died by hanging.
Photograph by J. S. Hanter. (From Kellogg.)
hawks, great horned owl, and English sparrow. The verdict
against the first three is based upon their destruction of poultry
and useful birds, while the sparrow is driving away many of our
more valuable and attractive native birds.
The English sparrow and possibly the starling also are examples
of the unwisdom of tampering with the balance of nature. Both
are European birds, introduced into this country by man. Abroad
they are not over numerous, but here, removed from their natural
296
BIOLOGY FOR BllGlXXLRS
enemies, they multiply unchecked and are becoming an unmitigated
nuisance.
Nest Building. The fact that the bird's egg requires continuous
external heat for hatching is a point in which they differ from all
lower forms and necessitates the construction of some sort of nest
to protect the eggs and retain heat. Next to migration, the highest
development of bird instinct is shown in some of their nest con-
struction. We must remember
that they have no hands or fore-
limbs to help, but merely beak
and feet, and their materials are
only such as they can find. Y<i.
when the wonderful home of an
oriole or humming bird is studied,
we realize that even with hands,
and brain, and tools, we could not
imitate them. Nests differ widely
both as to materials and construc-
tion. Earth, clay, sticks, grass,
hair, feathers, moss, and even
strings are some of the substances
used, while the structure itself
may vary from a mere hole in the
sand (ostrich) to the dainty nest of
a vireo.
Excavated Nests. Water birds
often lay their eggs on rocks, with
only sticks enough to keep the
eggs from rolling; holes in the ground serve for kingfisher, and
bank swallows, while owls and woodpeckers excavate homes in
hollow trees.
Woven Nests. Very simple grass nests are made by ducks
and wading birds. Among the most remarkable woven nests are
the covered pendant homes of orioles and vireos, hanging from
slender limbs where no thieving cat or red squirrel can come.
Horsehair and plant fibers are used and always seem to be so well
FIG. 100. Nest of humming bird,
made of sycamore down. (One-half
natural size.) From Kellogg.
BIRD HABITS
297
c.S.S
& *
M
0) O O
a
^ ^ c/3
il
.
298 BIOLOGY FOR BEGINNERS
selected and woven that the nest often withstands the storms of
several seasons, and is repaired and used again, frequently by the
same pair that built it.
Built-up Nests. Robins make a clumsy nest of clay, lined with
grass and feathers, placed on the big branches where cats easily
reach them. Swallows are much better masons and build clay
nests on barns and cliffs, which are very strong and inaccessible.
They roll the clay into pellets with the beak and build the walls
a little at a time, leaving one layer to dry before adding more,
lest it all collapse. The chimney swift (which is not a " swallow "
at all) builds a nest of sticks held together by a sticky saliva which
hardens into a strong glue. It is used in China to make a sort of
edible gelatine; it is from this fact that come the stories of the
" edible birds' nests " of that far-off land. These are merely some
of the various types of nests. Each species of bird builds its <>\\ n
peculiar structure, always in the same way, of similar materials,
and in the same kind of location. Yet there seems to be no way
in which one generation is taught to build like its ancestors, and
when we say it is due to instinct, we have not explained how they
learn to construct such perfectly adapted homes.
Both the nest building and the incubation (sitting) are usually
done by the female, though in some species the male helps in both
processes. On the other hand the cuckoo avoids either task by
laying her eggs in other birds' nests, where the young cuckoos
sometimes crowd out their foster brothers.
Eggs. Reproduction in birds is by means of eggs as has been
the usual method in all animals previously studied, but the size,
structure, and care of birds' eggs place them on a higher plane of
development. The development of birds' eggs requires constant
warmth. This necessitates the building of a nest and the constant
care of the parent, neither of which is usually required in lower
animals.
Structure. The egg consists of the actual growing point or germ
spot at the upper side of the yolk, the yolk surrounded by the
" white," this by a double membrane, and this in turn by the shell.
The germ cell is fertilized and from it the chick develops, The
BIRD HABITS 299
yolk and white both furnish food for the developing embryo,
somewhat as does the endosperm of a seed, while the membranes
and shell are protective coverings, porous enough to admit air to
the chick, and to allow the discharge of carbon dioxide. Fertiliza-
tion takes place in the ducts leading from the ovaries. Cell division
goes on for about twenty-four hours and then ceases, only to
recommence in case the egg is warmed and kept at proper
temperature.
As the tiny egg germ passes along the oviduct, the yolk and white
are added, layer by layer; these layers sometimes separate in a
hard boiled egg. The yolk is the real egg, corresponding to that
of fish or frog, while the white and shell are added nourishment
and protection somewhat like the jelly that coats the frog and toad
eggs.
Decay of stored eggs is caused by bacteria that pass through the
pores of the shell. If eggs that have no bacteria in them (i.e.
" fresh ") are sealed air-tight by a solution of water glass, they
do not decay as no bacteria can get in. If eggs are kept in cold
storage, the bacteria, even though present, do not develop and
the egg " keeps " for months with but little change.
The shape of most eggs is oval, for two reasons: they pack
better together in the nest, and cannot easily be rolled out. Try
to roll a bird's egg and it will follow a circle and come back to
about where it started. Eggs of birds making deep, safe nests
are not so oval, partly because they are safe without this adaptation.
The number of eggs varies with the amount of care that the
parent birds can give the young. It is greatest in those kinds,
whose young receive the least attention and which try to shift for
themselves early in life. This increases their chances of destruc-
tion and makes necessary more eggs if any are to survive. In case
of birds that are helpless when hatched and are fed and protected
by parents, the number is lower. Common wood and field birds
average about five, while game and river birds have twelve or
more; on the other hand birds of prey produce but one or two.
The size of the egg is greater in those species which hatch well
developed, since more stored food is required to carry on the longer
300 BIOLOGY FOR BEGIXXERS
development. In all cases, however, they are large in comparison
with eggs of other animals.
The color varies greatly and is probably protective in some cases
where nests are open and exposed. On the other hand, eggs laid
in burrows and deep dark nests are usually very white, possibly
to make them more visible.
Use. Since the egg is practically a store of food for a young
animal, it provides an especially nourishing and concentrated
form of human food which has been used by man for ages. Eggs
require no cooking, are rich in proteid and fat and are practically
all digestible. The egg crop of the United States is worth over
$300,000,000 per year.
Incubation. The time of " sitting " or incubation is in propor-
tion to the size of the egg and varies from thirteen to fifteen days
for small eggs, to forty or forty-five days in the case of the swan.
The female usually sits, but the ostrich is an exception. Some
other male birds help in the incubation. The temperature required
is 105 degrees and must be kept almost constant. In birds which
are helpless and have parental care, the incubation begins as soon
as the first egg is laid, and the chicks hatch one after the other,
but in those birds like our hens, where the chicks hatch fully
feathered and able to feed themselves, all the eggs are laid before
sitting begins, so that they may all hatch at once.
Bird Migration. One of the most mysterious and wonderful
instincts hi the world is that which controls the migration of birds.
The causes, methods, and means are little understood. Many
birds never migrate, such as the ostrich, fish-eaters, and parrots.
Crows, owls, jays, woodpeckers, and many others are practically
permanent residents.
Migration may be caused by food supply, climatic changes, or
may be made for breeding purposes. It is not easily understood
why some species leave abundant food and warmth in the tropics
to breed in the cold and barren North. Insect eaters have to migrate
as whiter kills their prey; water birds must leave their ponds
before they freeze over; fruit eaters follow the season of their diet
to some extent, but after all, this does not account for the majority
of cases.
Breeding
Wintering
Principal migration routes
FIG. 101. Distribution and migration of the Eskimo curlew. (From Cooke;
Yearbook, U. S. Department of Agriculture, 1914, see Pearse.)
302 BIOLOGY FOR BEGINNERS
Ducks, hawks, swallows, and swifts migrate by night, while
warblers, thrushes, orioles, sparrows and shore birds travel by day,
thus gaining opportunity for day time feeding, and nights for rest
and protection. The distances covered are enormous and could
hardly be believed, were they not abundantly verified. Here are
some examples of the start and finish of their journeys:
The bobolink travels from New York to Brazil
* ' black poll warbler from Alaska to South America 5 ,000 mi .
" night hawk " Yukon to Argentina 7,000 "
" shore birds " Arctic regions to Patagonia 8,000 "
" arctic tern " Arctic to Antarctic circles 11,000 "
This last is the champion long-distance traveller. They make
the round trip in twenty weeks.
While many birds migrate slowly, feeding by the way, and
averaging only twenty to thirty miles per day, there are others
which are marvels of speed and endurance. Bear in mind that it
is considered a record performance to drive a car from San Francisco
to New York, 2500 miles, in a week and that the trains require
about four days. Then look at some of these records.
Gray-cheeked thrush travels from Louisiana to Alaska in thirty
days, a distance of 4000 miles.
Golden plover travel from Nova Scotia to South America in
forty-eight hours, a distance of 2400 miles. Over the open ocean
without chance for rest, this bird uses two ounces of its fat as fuel
for the whole 2400 miles. Compare this with the fuel used in the
best aeroplanes, which even then have seldom travelled half this
distance without stopping. The tiny humming bird has a record
of 500 miles per night, across the Gulf of Mexico, and then is not
tired enough to rest, but often flies on inland to make a good
trip of it.
Routes. Wonderful as are birds' speed and endurance, a real
mystery surrounds their knowledge of the times and routes for
migration. Similar species follow the same routes year after year,
some going direct over the ocean (like many water birds) some
follow the West Indies across to South America; many cross the
BIRD HABITS
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BIOLOGY FOR BEGINNERS
Gulf of Mexico directly over 500 to 700 miles of open water.
Others follow the coasts or river valleys and may even go by one
From American Museum of Natural History.
FIG. 102. The birds carry their plumes only during the nesting season;
killing the parents means the slow starvation of the young.
route and return by another. How do they know the way? Keen
sight may help, but not over water or through dark nights and fogs.
They do not seem to follow water ways or mountain ranges in
BIRD HABITS 305
many cases. The memory and leadership of old birds, though
often helpful, cannot account for migration of young by them-
selves to lands they have never seen. We have to assume an
instinct of migration and a " sense of direction " developed to a
degree that we can only imagine, and that is really no explanation
at all.
Economic Importance of Birds. There is no group of animals to
which man is more indebted than the birds. It is highly probable
that without their aid, agriculture would be impossible, because of the
vast quantity of insect pests and weed seeds which they destroy.
The accompanying table shows the nature of the food which they
eat, and it is well to remember that they eat early and often.
Their greatest service is in the destruction of harmful insects
both as egg, larva, and adult. In some states where general bird
killing was permitted the insect enemies of crops increased to such
an alarming extent that stringent laws were put in force.
An unwise bird law cost the state of Pennsylvania nearly four
million dollars in a year and a half through the destruction which
it permitted among useful birds. At the end of this period, the
damage was so apparent that they repealed the law and appointed
a state ornithologist to look after the birds. Actual experiments
have been worked out with protected and unprotected bird regions
so that the fact of their essential service can no longer be
questioned.
Next to their destruction of harmful insects comes their work
against the seeds of weeds which, as the table shows, constitute
a large part of their diet. Many of the larger birds, such as hawks,
owls, and jays, destroy mice, rats, and other harmful vermin.
Some, like the crow, vulture, and buzzard, act as scavengers.
Almost as important are the products which man obtains from
the birds. Our domestic fowls produce flesh and eggs to the amount
of over half a billion dollars annually. This does not include the
value of game or wild birds. Feathers for millinery and bedding
are another valuable bird product, and where the feathers are
those of food birds, it is a perfectly legitimate one. In some
Pacific islands, where millions of sea birds have roosted for centuries,
306 BIOLOGY FOR BEGINNERS
vast deposits of manure, called guano, have accumulated, which
are very valuable for fertilizer.
A curious and rather pitiful use for birds is to detect poisonous
gases in mines and in warfare. Their rapid respiration and delicate
nervous system make them more sensitive than man to the presence
of dangerous gases. They are taken in cages into the mines or
trenches where their symptoms of suffocation give warning in
tune for the men to take precautions.
Another very specialized use for birds, which the war has greatly
developed, is the carrying of messages by pigeons, carefully trained
to return to their homes, when carried to the front and liberated.
Often they have been able to bring back messages through shell
fire where no man could live.
Last, but by no means least, is the value of birds to man as
companions and pets. If the world were deprived of all bird song
and color, it would be a dreary place, and even those who now
overlook them, would miss their accustomed presence.
There is no large group of animals with so few harmful members.
The food table indicates a few which destroy fowls or useful birds
and a few others that eat grains and useful fruits. Another class
of damage is in cases like that of the English sparrow and starling
where a foreign bird is interfering with our native species. The
accompanying " Black List " includes all having even a suspicion
against them, and shows how few there are, which do any harm
at all.
Positively harmful Possibly harmful
Cooper's Hawk Blue Heron
Sharp Shinned Hawk King Fisher
Pigeon Hawk Crow
Great Horned Owl Blue Jay
Snowy Owl Grackle
English Sparrow Cow Bird
COLLATERAL READING
Migration: Birds of North America, Chapman, pp. 5-6, 13-20; Bird
Life, Chapman, pp. 48-61; Travels of Birds, Chapman, entire; Citizen Bird,
BIRD HABITS 307
Wright, pp. .63-72; News from the Birds, Keyser, pp. 139-149; Wake
Robin, Burroughs, pp. 1-35; Bird Migration, Cooke, U. S. Bulletin 185,
entire; see also magazine references; see also in Encyclopedia, under
"Migration," " Nidification," "Egg."
Economic Importance: Our Vanishing Wild Life, Hornaday, entire;
Useful Birds and their Protection, Forbush, entire; Our Native Birds,
Lange, pp. 64-98; Birds of Eastern North America, Chapman, pp. 6-9;
Textbook, Kellogg, pp. 370-372; Birds that Hunt and are Hunted, Intro-
duction; Birds of Field and Village, Merriam, introduction, Chap. XV,
XXIV; Textbook, Davenport, pp. 311-314; Common Birds in Relation to
Agriculture, U. S. Bulletin, entire; How the Birds Help the Farmer, U. S.
Bulletin, entire; Bulletins of U. S. Department of Agriculture; Pamphlets
of the Audubon Society, etc., etc.
Beaks and Feet: Citizen Bird, Wright, pp. 37-42; Birds of Eastern North
America, Chapman, pp. 41-55; Textbook of Zoology, Kellogg, pp. 362-364;
Bird Guide (Water Birds"), Reed, introduction.
Life History and Habits: Handbook of Nature Study, Comstock, pp.
25-147; Outdoor Studies, Needham, pp. 47-53; Winners in Life's Race,
Buckley, pp. 168-180; Ways of the Wood Folk, Long, pp. 27-120; Familiar
Life in Field and Forest, Mathews, pp. 81-111; Upon the Tree Tops,
Miller, entire; Birds in the Bush, Torrey, entire; In Nesting Time, Miller,
entire; Bird Ways, Miller, entire; Nature Study and Life, Hodge, pp.
305-364; The Pet Book, Comstock, pp. 137-223; Nature Study Leaflets
(bound volume), pp. 253-290.
Nesting and Eggs: Bird Homes, Dugmore, pp. 11-15; Our Native Birds,
Lange, pp. 33-41; Bird Life, Chapman, pp. 64-70; Citizen Bird, Wright,
pp. 73-86; News from the Birds, Keyser, pp. 37-49; Birds of Field and
'Village, Merriam, see index; Animal Life, Kellogg, pp. 264-268; Animal
Life, Thompson, pp. 114-115, 264-267.
SUMMARY
Foods used.
Animal.
Rats, mice, rabbits, etc. Hawks, owls, birds of prey.
Fish Loon, pelican, kingfisher.
Scavengers Vulture, buzzard.
Insects on the wing. Swifts, night-hawks.
Insects under bark Woodpecker.
Insects on the ground Robins.
Insects on plants Warblers, vireos.
Vegetable.
Weed seeds Sparrows, etc.
Grains (rice) Blackbirds, bobolink.
Fruits Wax wing, blackbird.
General value of birds.
Harmful exceptions.
Cooper's and sharp-shinned hawks, great horned owl, English sparrow,
and starling (why so numerous?).
308 BIOLOGY FOR BEGINNERS
Nest Building.
Necessity for nest, warmth for egg and protection of young.
Kinds.
Excavated in earth Kingfisher, bank swallow.
Excavated in trees Woodpecker, owl.
Woven cup shaped Warblers.
Woven hanging Orioles, vireos.
Built up of clay Robin, eave swallow.
Built up of sticks Chimney swift (not swallow).
Eggs (cf. other forms of eggs as to size, covering, fertilization).
Structure.
Germ spot develops embryo.
Yolk for nourishment.
White for nourishment.
Membranes Protection, admit air, exit CO 2 .
Limy shell Protection, admit air, exit CO 2 .
Causes of decay and means of prevention.
Shape, " oval " for better fitting, will not roll.
Number, fewer where more parental care and young helpless.
Larger where young are precocial, average five.
Size, larger where chick hatches well developed.
Color, protective, white in dark nests.
Use as food for man.
Concentrated, need no cooking, all digestible.
Incubation.
Small eggs less time (13-15 days), larger 40-50 days.
Female usually ''sits."
Chicks hatch in series in altricial birds.
Chicks hatch all at once in precocial birds (why?).
Migration.
Causes, food scarcity, climatic changes, breeding.
Methods, night fliers; ducks, hawks, swallows, etc.
Day fliers; shore birds, warblers, thrushes.
Distances, from five to eleven thousand miles.
Travel in flocks for protection and direction.
Routes, rather definite, along coasts, mountain ranges, etc.
Not known how they direct themselves.
Examples of above instances.
BIRD HABITS 309
Economic Importance.
1. Destroyers of harmful insects.
2. Destroyers of weed seeds.
3. Destroyers of harmful rodents and other vermin.
4. Scavengers.
5. Producers of food, flesh and eggs.
6. Producers of feathers, .bedding, and millinery.
7. Guano for fertilizer.
8. To detect poisonous gases.
9. To carry messages.
10. To furnish enjoyment by their beauty and songs.
11. A few destroy useful birds or other animals.
12. Some destroy fruit or grain.
13. Some interfere with nesting of other birds.
For harmful species, see "Black List of Birds."
CHAPTER XXXIII
MAMMALS
Vocabulary
Ruminant, animals adapted for re-chewing their food.
Vertical, straight up and down.
Quadrupeds, four-footed animals.
The mammals constitute the highest group of the animal kingdom
because in them the development of the brain, intelligence, and
reason have reached the highest degree of specialization.
The birds excelled in adaptations for flight and in marvelous
instincts for nest-building and migration. The communal insects
have carried division of labor to a remarkable perfection, but if
we compare the real intelligence of these forms with that displayed
by a dog, a beaver, or a horse, not to mention man, we can see
that there is no question as to the mammal's position at the top.
Mammals include man, the apes, quadrupeds, bats, seals, whales,
etc., and are a very diverse group as the tabulation shows. They
vary in size from the tiny harvest mouse that can climb a wheat
stem, to the enormous whale, a hundred feet in length. They are
found in all parts of the world except on a few small Pacific islands
and are the group of animals with which man (himself a mammal)
has had most to do.
The chief characteristics of this important class are as follows:
1. The young are born alive (no external eggs).
2. The young are nourished with milk.
3. The body is more or less covered with hair.
4. The cerebrum is highly developed.
5. A diaphragm (breathing muscle) is present.
6. They have two sets of teeth and fleshy lips.
7. High circulatory development, left aorta only.
310
MAMMALS 311
Various Adaptations. Mammals include about 2500 different
species, which, compared with insects is a small number, yet their
habitat and mode of life varies so widely that they are a splendid
illustration of the modification of homologous parts for different
functions.
Limbs. All mammals have two pairs of limbs, usually provided
with five toes; some are modified for flight (bats), some for
swimming (seals, whales), some for rapid land locomotion (horse,
deer), some for climbing (squirrel), or for burrowing (mole), for
attack and defense (cat, tiger), for jumping (kangaroo), for
prehension (apes, man).
Teeth. In the same way the teeth may vary in structure and
use, there being usually four kinds present, the incisors, canines,
premolars, and molars. In some animals they are adapted for
tearing prey (tiger, lion), some for gnawing (rat, beaver), some for
grinding vegetable foods (horse, cow). All are of similar origin
and are merely different forms of the same organs.
Body Covering. The body covering also varies greatly. The
hairs of the dog or horse, the wool of the sheep, the quills of the
porcupine and the scales of the armadillo, are all of similar origin.
Claws, hoofs and nails, horns, bristles, manes and tails are also
developed from epidermal structures.
Four Important Orders. The mammals of North America
represent eight orders out of eleven, the three remaining orders
being found in Australia or the tropics. From this number we
shall study only four, the rodents, ungulates, carnivora, and
primates.
The Rodents (gnawers) include many of our commonest animals,
the rabbits, porcupines, guinea-pigs, chipmunks, squirrels, beavers,
rats, mice, and woodchucks. All these forms have teeth especially
adapted for gnawing: the front teeth (incisors) are chisel shaped,
strong, and provided with a continuously growing root, so that
they replace themselves as fast as they wear off. Also the front
edge is harder than the rear edge, so that they are self sharpening
since the cutting edge is always worn thin. These tooth adapta-
tions together with strong jaws and powerful jaw muscles fit the
312 BIOLOGY FOR BEGINNERS
rodents for their well-known occupation of gnawing their way
through life.
The Ungulates (hoofed animals) include some of our commonest
domestic animals, such as the horse, pig, cow, sheep, and goat.
Among its familiar wild members are the deer, antelope, tapir,
rhinoceros, hippopotamus, giraffe, camel, zebra, etc. All of
these most of us have seen in circuses and zoological gardens.
These animals live on vegetable foods and have back teeth (molars)
fitted for grinding. Most of them have a side-wise jaw motion
which also aids in this process. Their feet are encased in hoofs,
and the limbs are never used for prehension, being adapted only
for swift locomotion. There are never more than four toes in use
and frequently fewer are developed.
The Ungulates are divided into two groups:
1. Odd toed in which the weight is borne on one toe though
others may be present. They include the horse, rhinoceros, and
tapir.
2. Even toed in which the third and fourth toes bear the weight,
though two others are usually present.
These even-toed ungulates are again divided into two groups
called
1. The non-ruminants (pig, hippopotamus).
2. The ruminants (cow, sheep, deer, etc.).
The ruminants are so called from their habit of chewing their
food as a " cud." A cow, for example, first compresses its food
into a ball, swallows it into the first of the divisions of its four-
chambered stomach where it is stored. Later it is forced back into
the mouth, chewed thoroughly and swallowed again, but into
another stomach chamber, where the final processes of digestion
are completed. The advantage of 'this peculiar arrangement is
that much food can be hastily eaten and stored, to be chewed later.
This, for an animal which feeds in flocks, on bulky vegetable food
is of great importance, since it can get its share in haste and chew
it at leisure. The ungulates include most of our domestic animals.
From them we obtain the bulk of our animal food and clothing,
leather, horn, and other products and among them we find nearly
MAMMALS
313
all our beasts of burden. It would be almost impossible for man
to exist without this important group of animals.
The Carnivora (flesh eaters) are very highly specialized in
structure for the pursuit of prey, and in fact,, live largely upon
the ungulates whose adaptations have been along the line of keen
senses and swiftness to escape this very danger. The carnivora
have large, interlocking canine teeth, shear cutting molars, a very
strong jaw hinge, and
enormous muscles attached to
ridges on the skull. Their
skeleton is light and slender,
the jaw short and strong, and
the feet usually provided with
claws. These claws, in the cat
family, can be withdrawn into
sheaths, which keeps them
sharp and also permits a noise-
less approach upon their prey.
On the other hand, the dog
family cannot withdraw the
claws, which are therefore blunt and not used for prehension, but
for swiftness of chase, which is characteristic of their manner of
hunting. Their keenness of sight and smell have been especially
adapted for their manner of life.
The carnivora include two divisions: (1) the aquatic forms (seal,
sea lion, walrus) in which the limbs are short and web-footed;
(2) the land forms with long limbs and separate toes. These
land forms are divided into three groups, according to the manner
of walking:
1. Those walking flat on the foot (bear, raccoon).
2. Those walking on the toes only (dog, wolf, fox, hyena, cat,
tiger, lion, leopard, etc.).
3. Those walking partly on the toes (martin, mink, weasel, otter,
sable, skunk, etc.).
It will be noticed that, except for the dog and cat, none of the
carnivora are domestic animals, and few of them are used as food,
FIG. 103. After Wiederscheim.
314 BIOLOGY FOR BEGINNERS
while, on the other hand, most of our valuable furs are produced
by them.
The Primates. This group includes the highest of the mammals,
and comprises the monkeys, gorilla, chimpanzee, orang-utan,
gibbon, marmoset, and lemur, as well as man himself.
Their structural adaptations do not compare with those found
in many other orders, but the greater brain development and
intelligence places the primates at the head of the classification.
This brings up again the fact that brain development is the only
way in which man may hope to excel. He belongs to what is called
a " generalized order " of animals; that is, he is not structurally
adapted for any particular thing, such as flight, speed, strength,
swimming, etc., his only claim to distinction being along the line
of intellectual development.
There is nothing that man can do, if unaided by his intelligence
which many other animals cannot do much better; but when this
intelligence is at hand to direct him, there is no other animal that
can compete with him.
Structurally, man resembles the higher apes very closely. Al-
most every detail of their anatomy is similar skeleton, muscles,
teeth, position of eyes, structure of the hand, and even motions
and facial expressions. There are, however, certain structural
differences such as the more erect position, shorter arms, larger
and better-balanced skull, higher forehead, smaller canine teeth,
and his inability to use the big toe like a thumb for grasping.
These differences are utterly unimportant when compared with
the one great feature, the human brain. The brain of all the
primates is large but man's is one-third larger than the chimpanzee's
which most nearly approaches it in size.
Man has learned the use of tools, devised a spoken and written
language, found a means of controlling fire, and developed mental
faculties and social habits that place him in a position far above
the highest apes.
It is curious to note how three factors have contributed to man's
development. The erect attitude left the fore limbs free from use
in locomotion and permitted their development into the most
MAMMALS 315
wonderful organ of prehension in the world, the hand, which is
man's one point of high structural adaptation.
It is difficult to say whether the brain taught the hand, or the
hand helped develop the brain, but it is certain that these three
factors, erect position, hand, and brain, have been the essential
ones in man's development.
There is more structural difference between the lowest primates
(lemur) and the chimpanzee or gorilla, than there is between these
higher apes and man. Also there is a greater difference between
the lowest type of savage man and the highest type of civilized
man, than there is between the savage and the ape.
Results of Erect Posture. As a consequence of his erect posture,
man's hands are left free for use in grasping things. However,
nature does not give something for nothing, and man has to pay
for his upright position by certain disadvantages. In the first
place, since only one pair of limbs are used in locomotion, he must
balance upon two feet instead of four, and has the center of weight
high above the point of support. This necessitates the long and
difficult process of " learning to walk " which other animals do
not experience.
Placing the weight vertically on the hips instead of at right angles
to them, renders man more liable to hip, spinal, and foot, diseases
and deformities. The internal organs rest one upon another in a
vertical pile instead of lying side by side, producing a tendency
to pressure or displacement. When sick or tired we instinctively
lie down to relieve this strain.
The arteries of the arm-pit, neck, and groin are now exposed
toward the front, whereas in quadrupeds they face downward
and are protected. In man, the trachea and appendix open up-
ward, instead of forward, giving opportunity for the entrance of
irritating substances.
All these difficulties, which are the price of our erect posture,
are more than repaid by the advantage of the human hand and
the mental and social development which it has made possible.
It rests with the intelligence of man to overcome the natural
difficulties of his structure by especial attention to correct posture,
316
BIOLOGY FOR BEGINNERS
position of spinal column, and support for the arches of the feet.
The strain on the internal organs can be met by training the ab-
dominal muscles to support their extra burden, and by proper
exercise and breathing. All this is but a small price to pay for the
human hand.
Relationship. Contrary to the ideas of some ill-informed people,
no scientist has ever claimed that man is " descended from " an
ape or any similar form, neither is there any " missing link " to be
discovered. On the other hand scientists do agree that both man
From American Museum of Natural History.
FIG. 104. Brain case and face in ape and man. In the ape (young gorilla,
at the left) the brain case is comparatively low, and the face is shallow; in
man (adult white man, at the right) the brain case and the face are both very
deep; the face has been retracted beneath the brain case. Figure after Ritge.
and the apes are descended from a common ancestor from which
both lines have developed. This accounts for the very great
similarity in structure. In the same way, we resemble our cousins
though we are not descended from them, but are related by way
of a common ancestor, or grandparent.
Aside from man, the primates include:
1. The gorilla, the largest of the apes, a native of Africa. It
is erect, does not climb trees, and resembles man closely in structure,
though much stronger.
2. The chimpanzee, also found in Africa. Though smaller than
MAMMALS
317
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318 BIOLOGY FOR BEGINNERS
man, it resembles him more closely than the gorilla, in brain, face,
hands and ears.
3. The orang-utan, found in the East Indies, which also re-
sembles man in brain structure and skeleton.
4. The Old World monkeys and baboons (Asia- Africa), which
have narrow noses and long prehensile tails.
5. The New World monkeys (South America), with wide flat
noses and prehensile tails.
6. Marmosets (Mexico, Brazil), lemurs, (Madagascar), small
forms, not at all like man in structure.
COLLATERAL READING
MAMMALS
General Zoology, Colton, pp. 246-285; Textbook, Linville and Kelly,
pp. 408-435; Elementary Zoology, Needham, pp. 237-265; Handbook of
Nature Study, Comstock, pp. 212-307; Practical Zoology, Davison, pp.
261-292; Elementary Zoology, Galloway, pp. 343-379; Economic Zoology,
Osborne, pp. 420-464; Applied Biology, Bigelow, pp. 436-453; Economic
Zoology, Kellogg and Doane, pp. 295-320; Elementary Zoology, Kellogg,
pp. 373-401.
CARNTVORA
Winners in Life's Race, Buckley, pp. 279-314; Familiar Life in Field
and Forest, Mathews, pp. 112-244; American Natural History, Hornaday,
Chap. Ill; Riverside Natural History, pp. 353-479; American Animals,
Stone and Cram, pp. 207-285; Life of Animals, Ingersoll, pp. 82-230;
Textbook of Zoology, Packard, pp. 614-617; Anatomy of Vertebrates,
Huxley, pp. 350-363; Textbook of Zoology, Claus and Sedgwick, pp. 324-
327.
RODENTS
Textbook of Zoology, Linville and Kelly, pp. 398-407; Winners in Life's
Race, Buckley, pp. 209-323; Familiar Life in Field and Forest, Mathews,
pp. 245-279; American Natural History, Hornaday, Chap. VII; Riverside
Natural History, pp. 68-81; American Animals, Stone and Cram, pp. 71-
179; Life of Animals, Ingersoll, pp. 404-468; Talks about Animals, pp.
170-182; Textbook of Zoology, Packard, p. 252; Anatomy of Vertebrates,
Huxley, pp. 269-271; Animal Life, Jordan, Kellogg and Heath, p. 71.
UNGULATES
Winners in Life's Race, Buckley, pp. 256-279; American Natural
History, Hornaday, Chap. VIII; Riverside Natural History, pp. 233-352;
American Animals, Stone and Cram, pp. 28-70; Life of American Animals,
Ingersoll, pp. 231-385.
MAMMALS 319
PRIMATES
The Life of Animals, Ingersoll, pp. 7-57; Riverside Natural History, pp.
480-500; American Natural History, Hornaday, Chap. II; Animal Life,
Thompson, pp. 340-350; Types of Animal Life, Mivart, pp. 1-35; Winners
in Life's Race, Buckley, pp. 240-255, 333-353.
SUMMARY
Mammals excel in intelligence.
Birds excel in instinct and flight adaptations.
Insects excel in "division of labor" in communal forms.
Mammals vary in size from mouse to whale.
Mammals vary in distribution, relatively few in number (2500).
Characteristics.
1. Living young, egg matures internally. 4. High cerebrum.
2. Young nourished with milk. 5. Diaphragm.
3. Hair. Fleshy lips. 6. Two sets teeth
7. High circulation, left aorta.
Modifications of limbs (two pairs, five toed).
Adapted for . Examples
Swimming Whale, seal
Flight Bats
Land locomotion Horse, deer
Climbing Squirrel
Burrowing Mole
Fighting Cat, tiger, etc.
Jumping, Kangaroo .
Prehension Man
Modification of teeth (incisors, canines, pre-molar, and molars) .
Catching prey Lion, tiger, cat
Gnawing Beaver, rat, mouse
Grinding Horse, cow
Tusks Elephant
Modifications of body covering.
Hair Dog, horse, man
Wool Sheep
Quills Hedgehog, porcupine
Scales Armadillo
Claws, hoofs, bristles, tails, manes, etc., are other forms.
Rodents.
Representatives.
Adaptations.
Teeth for gnawing (incisors).
1. Chisel shape, self -sharpening.
2. Strong, powerful jaws and muscles.
3. Continuous growth (why?).
4. No canines.
320 BIOLOGY FOR BEGINNERS
Ungulates.
Characteristics, hoofed, vegetable food, large size.
Limbs for locomotion only.
Not more than four toes.
Odd toed, horse, rhinoceros, tapir.
Even toed.
Non-ruminant, pig, hippopotamus.
Ruminant, cow, bison, sheep, goat (hollow permanent horns), deer,
elk, moose (solid, shed horns).
Characteristics of ruminant stomach.
Reason for ruminant habit.
Value to man.
Food, meat, and milk, with all related products.
Wool, leather, horn, etc.
Transportation, horse, ox, camel, mule, llama, etc.
Carnivora.
Specialized for pursuit (ungulates for escape).
Characteristics.
Small incisors, interlocking canines, shear molars.
Strong jaws, jaw muscles, and immovable hinge.
Light strong body, keen senses, claws.
Aquatic forms (short limbs, webbed toes), seal, walrus, etc.
Land forms (long limbs, separate toes).
Plantigrade, bear, raccoon.
Intermediate, mink, weasel, otter, skunk.
Digitigrade (claws not retractile), dog, wolf, fox.
Digitigrade (claws retractile), cat, lion, tiger, etc.
Value to man.
Few for food, many for furs, aid in chase, enemies.
Primates.
Representatives, gorilla, chimpanzee, orang-utan, monkeys, gibbons,
lemurs, man.
Characteristics.
Generalized structure (meaning). Higher brain.
Man resembles other primates in
Skeleton, muscles, teeth, eyes, hand, habits.
Man differs from other primates in
Erect position, shorter arms, balanced head, forehead.
Smaller canines, non-opposible toe.
Brain and intelligence which results in
Tool using, fire control, language.
Social and moral development, mind, reason.
Factors in nian's development.
Erect attitude, and its consequences.
Hand free for prehension.
Brain development resulting as above.
Relationship of man and other primates via a common ancestry, not by
"missing links."
(See Hornaday for pictures of all mammals, especially primates.)
CHAPTER XXXIV
THE DEVELOPMENT OF MAN
Vocabulary
Unwarranted, uncalled-for.
Rudimentary, undeveloped traces of organs.
Fossil, remains of former plants or animals, embedded in rocks.
Evolution, gradual development, from simple to complex.
With an egotism which is entirely unwarranted, we are ac-
customed to speak of " man and animals " whereas we ought to
say " man and other animals," for certainly man is an animal
just as truly as the beast of the field.
By referring to the characteristics given in preceding chapters,
man's place in the zoological scale will be seen to be as follows:
Kingdom: animal.
Branch: vertebrate.
Class: mammals.
Order: primates.
The Idea of Evolution. As soon as man became intelligent enough
to make comparisons between himself and other animals, the
resemblances became apparent and led to the idea that some
relationship must exist with lower forms. Two thousand years
ago the Greeks discussed this fact and advanced various theories
to account for it.
Very gradually, information accumulated, and the idea of re-
lationship developed into the theory that not only man but all
living things, both plant and animal, are not only related, but
actually descended from common ancestors. This is called the
theory of descent, or evolution.
Evidences of Evolution. 1. Rudimentary Organs. Not only do
all animals resemble each other in general ways, but many forms
321
322 BIOLOGY FOR BEGINNERS
possess organs which are of no use to them, but are developed in
other groups for important functions.
For example, in the foot of the horse there are unused bones
which in other animals support separate toes. The ostrich has
small wings like those of other birds, but it cannot use them for
flight. The boa constrictor has remnants of a hip girdle though
it has never developed legs to use it.
In man there are about seventy such structures, well developed
in other animals but reduced in size and function in his body,
like remains of the scaffolding of construction left in a completed
building and showing thereby the process of its development.
Among these may be mentioned the appendix which in the rodents
is the largest part of the intestine, while in man it is reduced to a
small and apparently useless rudiment. Similarly we have small
canine teeth, but do not develop them to tear food like the dog;
we have an inturned ear tip and muscles to move it, but we do not
" prick up our ears " like a horse.
The list might be greatly extended, but the point is this, if
animals and plants are not developed from common ancestors,
why then do they have these resemblances in structure.
2. Embryological Resemblances. In the study of the develop-
ment of the embryos of all animals, it is found that the higher
forms pass through stages resembling lower types, as they develop.
The first stage of all plants and animals is the single fertilized
egg cell. In all cases this develops by almost identical steps, into
(a) a solid mass of cells, (b) a hollow sphere of cells, (c) an infolded
tubular form, and then up through more and more specialized
structures to the adult, whatever it may be. The early forms of
all vertebrate embryos are so similar that dog, cat, rabbit, or man
cannot easily be distinguished until well started toward adult form.
By watching embryonic development of the vertebrates we can
observe modifications of various structures, such as the gill arches,
which are present in all the early stages. These gradually develop
true gills in the fish, but become modified and reduced in the
higher forms, their rudiments appearing in man as parts of the
inner ear, lower jaw, and throat cartilages. Certainly, if animals
THE DEVELOPMENT OF MAN 323
were not related, they would not repeat the structure of lower
types as they develop into their final form.
3. Homologous Organs. In both plants and animals we find
parts, evidently of similar origin and structure, developed for very
different purposes.
1. Leaves are modified into petals or thorns.
2. Roots act as organs for climbing or storage.
3. Hoofs, nails, and claws are all of similar origin.
4. Scales, feathers, and hair are all modified forms of the same
epidermal structures.
5. The various appendages of crayfish and its relatives are
evidently of similar structure, but modified to perform many
functions.
Surely this modification of similar parts for different uses would
not be found if there were no relationship between the different
forms.
4. Geological Evidence.. Although the fossil remains are neces-
sarily incomplete, still there have been found many series showing
gradual development from primitive to present forms. This is
notably true of the horse whose ancestors have been traced in
fossil skeletons back to a small five-toed form unlike any living
representatives. Also in the case of birds and reptiles, remains
have been discovered, showing plainly their descent from a common
ancestor.
5. Domesticated Animals and Plants. We are continually
witnessing the development of different forms of plants and animals
in our methods of breeding, in which there is no question of relation-
ship of the new form to the old.
Our many kinds of dog are descendants from the domesticated
wolf; the different breeds of hogs from the wild boar; fowls,
pigeons, sheep, and cattle, with their numerous breeds and
races, have been developed purposely by man, from very different
ancestors.
From masses of such evidence, laboriously collected, all scientists
are agreed that all living things are related, the closeness being
indicated by the degree of similarity. They also agree that descent
324
BIOLOGY FOR BEGINNERS
has not been in a continuous straight line, like the steps upward
in a ladder, but that relationship is through common ancestors.
We have certain " family resemblances " to our cousins but we
are not descended from them; rather, we resemble them because
EXISTING GIBBON.
APES AND Asia.
MAN.
MAN CHIMPANZEE. GORILLA. ORANG.
(Homo sapient). Africa. Africa. Asia.
Asia, Europe.
Cro-Magnon and
other races.
More primitive spe-
cies, human and
prehuman.
Neanderthal race.
Piltdown race.
Heidelberg race.
GLACIAL OB
PLEISTOCENE
AGE.
Primitive Gib-
PLIOCENE bon of Eu-
AGE. rope
(Pliohylobatea). Unknown Pliocene
ancestors of man.
MIOCENE
AGE. Earliest Gibbons
of Europe
(Pliopithenu) .
Ancestral anthro-
OLIGOCENE. poids of Egypt.
(Propliopiihecius).
Unknown ancestral stock
of the Old World pri-
mates including 1 man.
FIG. 105. Ancestral tree of the anthropoid apes and of man.
(From Osborn's Men of the Old Stone Age. By special permission
of the publishers, Charles Scribner's Sons.)
of our common ancestors (grandparents), who contributed to the
inherited characteristics both of ourselves and them.
Proof of the fact of descent and evolution is only half of the
battle; it remains to be shown how nature has brought about the
THE DEVELOPMENT OF MAN 325
great modifications which have resulted in producing the in-
numerable forms of living things which inhabit the globe*
COLLATERAL READING
Primer of Evolution, Clodd, Chap. IX-X; Origin of Species, Darwin,
Chap. 14-15; Descent of Man, Darwin, Chap. 1-7; The Whence and Whither
of Man, Tyler, pp. 1-112; Applied Biology, Bigelow, pp. 561-573; Ascent
of Man, Drummond, pp. 59-98; Animal Life, Thompson, pp. 273-281.
SUMMARY
1. Relation to other animals.
Classification, look up characteristics of each group.
2. The idea of evolution.
3. Evidences of evolution.
(1) Rudimentary organs.
Toe bones of horse.
Wing of ostrich.
Hip bones in boa.
Appendix, canines, etc., in man.
(2) Embryological resemblances.
Beginning with one-celled egg.
Similar early stages.
Modification of organs.
(3) Homologous organs.
(4) Fossil remains.
(5) Changes due to domestication and breeding.
CHAPTER XXXV
THE METHOD OF EVOLUTION
Vocabulary
Isolation, separation.
Contemporary, one who lives at the same time.
Divergence, separation of lines of descent.
Predecessor, one who comes before.
Proof of the fact of similarity between the various forms of living
things, and of their very evident relationship, still leaves a more
difficult question to be answered. How did this descent and
modification take place, by what means has nature developed one
form from another?
The idea of evolution of living forms from previous simpler
ones had been in existence for centuries, but the first serious
attempt to explain the means by which the new forms evolved,
was made by Lamarck in 1809. He advanced the view that new
species arose by inheriting the results of use or disuse of organs.
For example, the giraffe, by constantly reaching for the leaves of
trees, developed its neck, and the offspring increasingly inherited
the characteristic until a new species was formed.
The time was not ripe for acceptance of Lamarck's ideas;
moreover, his theory was not in accordance with facts and was
forgotten for fifty years.
Darwin's Theory of Natural Selection. The date, 1859, marks
an epoch in biological thought and should never be forgotten. In
that year Charles Darwin, an English scientist, published his
" Origin of Species by Natural Selection " and established the
theory of evolution on a firm basis.
This theory is the corner stone of all recent science and the
foundation of all modern thought. It is not confined to biology
326
THE METHOD OF EVOLUTION 327
alone, but has influenced almost every branch of science. In its
broader features it is accepted by every biologist, although there
are many details still to be worked out.
Following is an outline of the chief factors assigned by Darwin
to account for the development of new species from common
ancestry.
1. Over-production of individuals.
2. Struggle for existence.
3. Variation among individuals.
4. Survival of the fittest.
5. Inheritance of favorable characteristics.
6. New forms better adapted to survive are thus " naturally
selected " as new species.
Darwin spent over twenty years of strenuous toil and study,
accumulating facts upon which to base his theory. Many able
men have since devoted their lives to the same end, but we can
here only briefly review the argument, following the outline given
above.
Over Production. A fern plant may produce fifty million spores
per year. If all matured they would completely cover North
America the second year. A mustard plant produces 730,000
seeds annually, which if all matured, would occupy two thousand
times all the land surface of the earth, in two years. The common
dandelion would accomplish the same in about ten years.
The English sparrow lays six eggs at a time and breeds four
times a year; if all survived there would be no room for any other
birds in the course of a decade. The codfish produces over a
million eggs per year; if all survived this would fill the Atlantic
solidly with fish, in about five years.
Most amazing of all is the rapidity of reproduction in bacteria
and protozoa. One of the latter, if it reproduced unchecked,
would make a solid mass of these microscopic animals as large
as the sun, in thirty-eight days.
Struggle for Existence. We know there is no such actual in-
crease; in fact the number of various forms changes but little.
328 BIOLOGY FOR BEGINNERS
In other words only a very small minority of these countless hosts
reach maturity. All cannot obtain either space or food to live.
Thus it is evident that only those best fitted for their surroundings
will survive, and the less fit will perish in the struggle.
Variation. It is a well-known fact that no two individuals of
any plant or animal are exactly alike; slight variations in structure
occur in all. This furnishes the material for nature to use in her
selection, and those forms, whose variations tend to adapt them
best to their environment, will survive while others perish.
Survival of the Fittest. This expression was first used by another
noted English scientist, Herbert Spencer, and almost explains
itself. If among the thousands of dandelion seeds produced, some
have better dispersal devices, these will scatter to better soil,
be less crowded, and so will survive, while those having poorer
adaptations will perish by over crowding. In so severe a struggle
where only a few out of millions may hope to Jive, very slight
variations in speed, or sense, or protection may turn the scale in
favor of the better-fitted individual. Any unfavorable variations
would surely be wiped out.
Inheritance. It is common knowledge that in general, the off-
spring resemble the parents. If the parents have reached maturity
because of special fitness, those of their descendants which most
inherit the favorable variation, will in turn, be automatically
selected by nature to continue the race.
New and Better Adapted Species. A continuation of this process
of natural selection will in time produce such differences in structure
and habit that the resulting forms must be regarded as new species,
genera, and finally higher groups. This process is aided when the
developing species are separated by distance, mountain ranges,
bodies of water, or climatic differences, so that they do not lose
their favorable variations by inter-breeding. This is the theory of
geographic isolation which was developed by Alfred Russell
Wallace, another English contemporary of Mr. Darwin.
Conclusions from the Theory. 1. Cause of Adaptations. It will
be seen that natural selection is constantly tending to fit the
individual more closely to its environment and thus accounts for
THE METHOD OF EVOLUTION 329
the marvelous adaptations of structure which we always find in
all living things.
2. Relationship of all Forms. Carrying the theory to its logical
conclusion it follows that all the species now on earth, or which
have lived there in the past, are descended from a few primitive
original forms. The further back the variation began, the greater
will be the difference between the present forms, and the more
distant will be then* relationship. Those more closely allied have
separated from a common ancestor in more recent times.
3. " Tree " Lines of Descent. Evidently our idea of the lines
of relationship and descent must be expressed in the figure of a
tree, whose main branches separated from the parent trunk early
in development and whose topmost twigs represent the present
living forms. These will be similar or different, depending on how
far back the divergence began.
4. Classification. Evolution provides for a natural method of
classification, now universally used, in which relationship and
descent are shown by the groups in which individuals are placed.
Thus members of a species are more closely related than those
of a genus or order. A class includes forms which began to diverge
further back than the members of a family. When we speak of any
forms as " belonging to the same order " or genus, we are really
expressing not only their likeness in structure, but the reason for
it, namely blood relationship and descent from common ancestry.
5. The Key to other Biologic Puzzles. Evolution accounts for
many facts otherwise unexplained. It tells us why we find fossil !
remains of simpler animals in older rocks, and of more highly
specialized forms in later formations. It accounts for the facts
of embryology mentioned in the previous chapter, such as the
occurrence of primitive structures in the embryos of higher forms,
which disappear before maturity. It explains the peculiarities of
geographic distribution of animals and plants, in accordance with
what we know of past and present relations of land and sea areas.
Some Things that Evolution does Not Teach. 1. That living
or extinct forms can be arranged in a straight line of descent, each ;
descended from its predecessor.
330
BIOLOGY FOR BEGINNERS
Geological History
Period
Characteristic Animal*
First
Occurrence of
Mammoth.
horse,
Glyphodonts
P/iocene
Deer Sloths.
Ape . Man
Day , Sta
Came/.
Ape . Ma
Elephant.
Sabre-tooth
CaT, Bear.
M on Hey.
Cow , Deer.
Crefaccous
Mammals
Birds .
RcpTiles
Marsupials .
Salamanders
Jurrass/c
RepTiles
Bird.
Crocodile.
Froq.
Triable
Reptiles .
Amphibians,
Mam ma/s.
Turtles.
Dinosaurs.
Reptiles.
Amphibians.
Reptiles
Devonian
Fishes.
Ostracoderms
flyriapods
Jr/urian
Invertebrates
fishes.
Scorpions
Invertebrates
Bryozoans.
Echinolds.
Ophiurolds
Cambrian
Crustaceans.
Molluscs.
Worms .etc.
drachiopods.
Tnlobites .
rocks - no
FIG. 106. From Pearse.
THE METHOD OF EVOLUTION 331
2. That " man is descended from a monkey."
3. That God can be left out of the scheme of Creation. Much
opposition was made to Darwin's work on this score, by people
who purposely or through ignorance, misinterpreted his conclusions.
While we cannot go into the argument here, rest assured that in
the minds of the greatest scientists and philosophers there is no
conflict between the conclusions of Science and Religion.
To quote Davenport " The Creator is still at work, and not
only the forces of Nature, but man himself, works with God in
still further improving the earth and the living things which it
supports."
COLLATERAL READING
Origin of Species, Darwin; Descent of Man, Darwin; Primer of Evolu-
tion, Clodd, entire; Evolution, Thompson and Geddes, entire; Story of
Primitive Man, Clodd, entire; Evolution, Coulter, entire; Ascent of Man,
Drummond, pp. 1-98; Whence and Whither of Man, Tyler, pp. 1-112; Win-
ners in Life's Race, Buckley, pp. 333-353; General Biology, Needham,
Chap. Ill; Animal Life, Thompson, pp. 273-339; Applied Biology, Bige-
low, pp. 561-573; Elementary Zoology, Galloway, pp. 380-395; Practical
Zoology, Davison, pp. 342-354; Elementary Zoology, Kellogg, pp. 403-409;
Economic Zoology, Osborne, pp. 465-480; Economic Zoology, Kellogg and
Doane, pp. 335-347; Elementary Text, Linville and Kelly, pp. 101-115;
Animal Life, Jordan and Kellogg, pp. 114-148; Animal Studies, Jordan,
Kellogg and Heath, pp. 281-289; Elements of Zoology, Davenport, Chap. 21;
article on " Evolution" by Huxley in Encyclopedia Britannica.
SUMMARY
1. Evolution idea very old.
2. Lamarck's theory of the inheritance of acquired characteristics not
accepted; not now considered correct.
3. Charles Darwin, 1859, "Origin of Species by Natural Selection."
4. The theory of natural selection, to account for origin of species.
(1) Over production.
(2) Struggle for existence.
(3) Variation.
(3) Survival of the fittest.
(5) Inheritance.
(6) Origin of better adapted forms.
5. Some conclusions from the theory.
(1) Accounts for adaptations.
(2) Indicates relationship of all forms.
(3) The " tree " line of descent.
332 BIOLOGY FOR BEGINNERS
(4) Present system of classification.
(5) Accounts for fossil series.
Accounts for embryo repetition.
Accounts for geographic distribution.
6. Evolution does not teach
(1) The "ladder" line of descent.
(2) The man-monkey descent.
(3) That evolution leaves God out.
NOTE. Darwin did not originate the evolutionary idea, at all, as
many seem to think; that was a very old belief. What he did was to
prove that natural selection was the means by which evolution was brought
about. There are doubtless other forces assisting natural selection in
carrying on this development, some of which are fairly well understood.
CHAPTER XXXVI
THE DEVELOPMENT OF CIVILIZED MAN
Vocabulary
Anthropology, the study of the development of man.
Diffidence, hesitation.
Obviously, plainly.
Relatively, comparatively.
Acquisition, something just obtained.
Degenerate, less developed than formerly.
We have been studying the development of living things and
man's relation to them, which brings us to another even more
fascinating branch of biology, the development of man himself,
a science called Anthropology.
We naturally think of man's development in terms of recorded
history, but we must remember that writing is a very recent art
and man's actual written records go back relatively but a little into
the far past from which we are still emerging. Greek writings
take us back about one thousand years B.C., Chinese, Egyptian,
and Arab records may possibly date as early as 3000 B.C., but
civilization was far older, and man, as a more or less human ani-
mal, much older still. Monuments and inscriptions may push back
the boundary by vague information covering perhaps ten thousand
years, though there is much dispute, and the data are uncertain.
Still further back amid the mists of human history we draw
conclusions from bones and stone implements, showing that man
existed as early as the glacial period, and was contemporary with the
cave bear, mammoth, and aurochs, all now extinct. One ventures
with diffidence to set a time in years for the date of these remote
ancestors of ours, but apparently human animals, erect, large-
brained, using weapons and tools, possessing the power of speech,
333
334
BIOLOGY FOR BEGINNERS
and perhaps the use of fire, existed one hundred thousand years ago.
Primitive .man apparently had a much smaller brain capacity
than his modern de-
scendants, a lower
forehead, sloping
brow, heavy jaws, and
receding chin. Still
he was obviously
human and, even
then, intellectually far
superior to the other
Primates.
His earliest home
must have been in
relatively warm
climates where nature
provided food and
shelter for her chil-
dren too ignorant to obtain them for themselves. His food was
fruit and nuts and such animals as he could capture, unarmed,
FIG. 107. Vertebra of young reindeer with flint
arrowhead imbedded in the bone. From the Cave
of Perigord, France. After Lartel and Christy.
See Kellogg.
FIG. 108. Drawing of mammoth on piece of mammoth tusk.
From the Cave of the Madeleine in Southwest France. The
drawing was made by prehistoric man of the early Post-Glacial
times. One- third size of original. From Kellogg.
and eat uncooked. This restricted his flesh foods mainly to clams
and oysters, to which the enormous shell deposits still bear testi-
THE DEVELOPMENT OF CIVILIZED MAN 335
mony in many places in central Europe. Evidently man soon
devised weapons, clubs, and spears perhaps, and later bows and
arrows. Then he became a wandering hunter having no fixed
home and changing his abode whenever game became scarce in
any one locality.
With a widespread scarcity of game came the necessity of taming
and raising food animals. Thus we have the herdsman wandering
with his flocks from place to place, as pasturage and food were
exhausted. Domestication of animals probably began with taming
FIG. 109. Remains of the Neanderthal man, in the Provincial Museum
of Bonn. From Weltall u. Menschheit, see Kellogg.
the wolf to aid him in the hunt, but the real progress was made
when tame cattle, sheep, and goats, partly took the place of wilder
game.
A wonderful advance was made when man hit upon the idea of
cultivating food plants for his flocks and himself. This permitted
a fixed habitation and for the first time, a real " home life " had a
chance to develop, with all that it means in comfort and social
progress. Doubtless the house was but a cave or tree shelter, but
when man settled to remain in one place, to cultivate and gather
336 BIOLOGY FOR BEGINNERS
his simple crops, community life and society had their earliest
beginnings.
Man's development is usually classified by the implements he
had learned to use.
1. Primitive Man. Without weapons, tools, or fire.
2. Old Stone Age. Stone weapons and tools, probably used fire.
Contemporary with mammoth and cave
bear.
FIG. 110. Skull cap of Pithecanthropus erectus, the
fossil man-like ape of Java. Shown from above and
in profile; from Wei tall u. Menschheit, see Kellogg.
3. New Stone Age. Used polished stone implements.
Perhaps made crude pottery.
Erected stone monuments, buried the dead.
A period of many wars and migrations.
4. Age of Metals.
(a) Copper and .gold first used because found pure in nature;
could be shaped by hammering and did not have to be
melted.
(b) Bronze, an alloy of melted copper and tin which made ex-
cellent implements and did not require great heat to melt.
(c) Iron, required skillful smelting and tempering, needing much
higher temperature. Best metal for all uses. Brings
us down to modern times.
THE DEVELOPMENT OF CIVILIZED MAN
337
TABLE I.
^howing Conditions in Europe during the Development of Man
Adapted from Osborn's "Men of The Old Stone Age"
Time
Cl imafe
dnirnals
Implements
Human races
Postglacial
25.00O years
J
Deer, bison, horse,
chamois, ibex
Iron /OOO B.C
Bronze /OOO yrs.
Pottery
Polisheaf stone
5000 yrs.
Carving, painting
Clipped flints
25,000 yrs.
Homo sapiens
Brain capacity eoOOcai
Cro-magon ffaco
Brain capacity reaOccm
4. Glacial Period
25.000 years
\
Reindeer, arctic far,
muskox
3. Interglacial
Period
100. 000 years
}
Bison, horse,
hippopotamus,
elephant, lion,
rhinoceros,
sabre -tooth tiger.
Neanderthal Race
Brain capacity I600ax
j -
Rough flints
Z5.000 yrs.
Piltdown Race
Brain capacity I400ca
3 Glacial Period
25.000 years
<^
Reindeer,
wooly mammoth
\
Hippopotamus,
rhinoceros ,
2. Inferglacial
Period
elephant,
stag, bison,
'
Heidelberg Race
200,000 years
;
horse
2.G/ov/o/ Period
25, OOO years
Reindeer,
wooly mammoth.
( Interglaciat
Period
JS.OOOyears
)
Hippopotamus,
elephant,
rhinoceros.
(Eoliths?)
1. Glacial Period
Z5.00O years
Mush ox in
England.
(Trinil race lived in Jow t
Brain capacity 9OOcfn
FIG. 111. From Pearse.
The period of written history extends back at most, only into
the bronze age so we can see how comparatively recent has been
our modern development, and how slow was man's progress in his
earlier stages.
338 BIOLOGY FOR BEGINNERS
With our modern civilization has come a complete change in the
manner of life. While we would not relish going back to the life
of the cave dweller, still we pay a penalty for our safer and easier
methods of living. Primitive man, if he survived at all, was neces-
sarily a hardy, outdoor animal, eating hard foods, having a sturdy
and little protected body, and literally " earning his bread by the
sweat of his brow." Now we have so learned to control our en-
vironment that we live quiet, safe, indoor lives, protect our tender
bodies with houses and clothes, and provide ourselves with .soft
FIG. 112. At right, a carved flint from Denmark,
of the Old Stone Age; at left, a polished stone axe
head from Ireland, of the New Stone Age. From
Kellogg.
and delicate cooked foods. On the other hand we have developed
our brain and nervous system so that it has to take over the work
previously done by muscle and brawn. Hence we are overworking
our latest acquisition, our intelligence, at the expense of our
bodies.
Is it any wonder then that we now have fat and flabby muscles,
weak lungs, delicate skin, and degenerate teeth, combined with
overworked nerves? If we are to develop to its highest efficiency
the wonderful mind which the Creator has given us, we have to
THE DEVELOPMENT OF CIVILIZED MAN 339
make special effort to keep our bodies strong, even though physical
strength is no longer the one essential in the struggle for
existence.
,To this end modern civilization is attempting, by healthful
living conditions, by education in biology and hygiene, and by
systematic exercise, to maintain as healthy a body as that of our
ancestor with the stone hatchet, combined with all the marvelous
abilities and achievements of the civilized mind.
We do not have to depend wholly upon the evidence of human
remains to get an idea of how our ancient ancestors lived. Some
Australian and African races are still almost in the stage of primi-
tive man. Some central African tribes have no houses but sleep hi
what are practically nests; they hunt with stone clubs, do not know
the use of even the bow and arrow, cultivate no crops, and eat
human flesh. Certain natives of Patagonia are still living in the
Stone Age so far as their culture is concerned. New Caledonia fur-
nishes examples of man but little further advanced, and some tribes
of Ceylon and Australia are living in even more primitive stages of
development. Still, low as this culture may be, it is yet wholly
unapproached or resembled by the life of the lower animals.
Anthropologists classify the human species in different ways,
but are generally agreed upon four, or perhaps five races, distin-
guished about as in the following table:
340
BIOLOGY FOR BEGINNERS
Lowest
Langua
Rapidl
i
Is
O cj
G C
II
.?*
i.al <
ll| I
&<K o
-
I I
w
111
III
p^l
THE DEVELOPMENT OF CIVILIZED MAN 341
COLLATERAL READING
Primer of Evolution, Clodd, Chap. XI: Story of Primitive Man, Clodd,
entire; Story of Creation, Clodd, entire; Whence and Whither of Man,
Tyler, pp. 211-308; Winners in Life's Race, Buckley, pp. 333-353; Animal
Life, Thompson, pp. 320-350; Man Before Metals, Joly, entire; Anthro-
pology, Tyler, entire; The Next Generation, Jewett, pp. 153-161.
SUMMARY
1. Records of ancient man from
Written history.
Monuments and inscriptions.
Stone implements and remains.
Human bones.
2. Characteristics of primitive man.
Brain larger than other animals.
Bram smaller than present man.
Low forehead and sloping brow.
Heavy jaw and receding chin.
3. Stages of development in occupation.
Primitive man without weapons or fire.
Hunter, using spear, bow and arrow, able to control fire.
Herdsman, wandering for food supplies, domestication of animals.
Cultivator of the soil, permanent home, crops stored for future.
4. Stages of development in implements used.
Primitive man without implements.
Old Stone Age.
New Stone Age.
Age of Metals
Copper.
Bronze.
Iron.
5. Results of present higher mental development.
Body less strong and hardy.
Brain greatly developed and may be overworked.
6. Races of modern man.
(See tabulation in text.)
CHAPTER XXXVH
FOOD
Vocabulary
Assimilated, made like and built into tissut.
Calorie, the amount of heat used to raise a pound of water 4 deg. F.
Ratio, proportion.
Lipoid, a tissue building substance, somewhat like fats.
Vitamines, active substances in some foods, necessary to health.
All living things are alive because energy is liberated within
them. This energy depends upon oxidation and oxidation involves
the union of oxygen with the living tissue. This process destroys
the substances oxidized, leaving behind waste products, carbon
dioxide, water, and nitrogenous compounds, and necessitating
the replacement of the oxidized tissue. . Replacement of tissue
means the taking in of food, which is a vital necessity to all living
organisms.
If food is assimilated faster than it is used, growth, or storage
of excess, results. In plants little energy is liberated and growth
may be continuous; in animals a point is reached where oxidation
balances assimilation and growth practically ceases.
Definition. Food may be denned as any substance which, when
taken into a living organism, produces energy or builds tissue.
The energy is necessary for any life, the tissue building may be to
repair used organs or for increase in growth.
The chemical composition of all living things is much the same.
They are composed of a small number of elements and all depend
upon the vitality of protoplasm for their life. (See ch. 3, 4, 5.)
Naturally the foods that produce these living tissues are also
similar in composition, though numerous in kind. The general
classes of food stuffs (nutrients) have been discussed in Chapter 4,
342
FOOD 343
where their composition and properties are tabulated, and grouped
as inorganic and organic matter. Here we shall take up their
functions in relation to the life and growth of animals, especially
as food for man.
Functions of Inorganic Foods. Water constitutes about sixty
per cent of all animal tissue, usually more than that in plants. It
is a necessity to plants in starch making and in both plants and
animals as a transporter and solvent for other foods. Though not
oxidized in the body it is a very essential part of all foods.
Mineral salts compose about five per cent of all animal tissue.
They are essential in formation of bone, teeth, blood, digestive
fluids, and are used to supply nitrogen, sulphur, phosphorus,
and iron for making protoplasm. Table salt, sulphate and phos-
phate of lime, and various nitrates are important examples.
Functions of Organic Foods. Proteids are the only food stuffs
containing nitrogen, and are therefore absolutely essential in pro-
duction of living tissue. They include some of man's most valuable
foods, such as lean meat, white of eggs, cheese, gluten in wheat,
legumin in peas and beans, etc. Proteid matter constitutes about
eighteen per cent of the weight of man's body. The chief function
of proteid foods is to build tissue. They build anew and repair
muscle and tendon, bone, cartilage, and skin and also compose
the corpuscles of the blood. Proteids may also be oxidized directly
and thus may be used to furnish energy. While this actually
takes place to some extent, it would be an expensive source of fuel
and it would also put too great a strain upon the digestive and
excretory organs if all energy were sought from this class of foods.
The fats and carbohydrates are the chief energy producers. The
former occur in fat meats, butter, fish, and eggs among animal
foods, and in olive and cotton seed oils, nuts, corn, and cocoa from
the vegetable world. The amount of fat needed varies with age,
occupation, and other conditions but if more is taken than is re-
quired, it may be stored, almost unchanged, to be drawn upon if
the energy supply becomes short. About fifteen per cent of the
human body is fat tissue and much of our energy is derived from
other amounts that are oxidized directly.
344 BIOLOGY FOR BEGINNERS
Carbohydrates (starches, sugars, and cellulose) comprise the bulk
of man's nourishment. They are found in all vegetable foods,
grains, potatoes, fruits, and nuts. Milk furnishes an important
animal sugar. Though occupying so large a place in our menu,
carbohydrates compose hardly one per cent of the body's weight.
This is because they are easily oxidized, furnishing much heat and
energy and if any excess is taken, it is changed into fat and stored
as such.
Thus it is seen that while proteid, fat, or carbohydrates may
all supply energy, neither of the latter can perform the proteid's
function in growth and repair of tissues. However, the fats and
carbohydrates serve to protect the valuable proteids by being first
oxidized and saving the proteids for tissue building which they
alone can perform. (See " Summary of Nutrients " at end of
chapter.)
Measurement of Food Values. There is no way of measuring
the tissue-building value of foods. But, since all may produce heat
and energy, they may easily be measured and their value as food
computed in terms of heat produced. The unit of measurement is
the " calorie " which is the amount of heat required to raise the
temperature of one pound of water four (4) degrees Fahrenheit.
Very careful experiments have shown that a man in an average
day's work requires food enough to produce 2800 calories of energy.
The amount of energy (number of calories) required varies with
age and occupation as shown in this table.
TABLE I
DAILY CALORIE NEEDS (APPROXIMATELY)
1. For child under 2 years 900 calories
2. For child from 2-5 years 1200 calories
3. For child from 6-9 years 1500 calories
4. For child from 10-12 years 1800 calories
5. Fof child from 12-14 (woman, light work, also) 2100 calories
6. For boy (12-14), girl (15-16), man sedentary 2400 calories
7. For boy (15-16), (man light 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
FOOD 345
The energy required for various degrees of exercise are shown
below and one can compute the number of calories used per day
by multiplying the calories per hour by the hours of each kind of
exercise per day. Do this and see how near it comes to the esti-
mate for a person of your age in Table I.
TABLE II
AVERAGE NORMAL OUTPUT OF HEAT FROM THE BODY
Average
Conditions of Muscular Activity Calories
per Hour
Man at rest, sleeping 65 calories
Man at rest, awake, sitting up 100 calories
Man at light muscular exercise 170 calories
Man at moderately active muscular exercise 290 calories
Man at severe muscular exercise 450 calories
Man at very severe muscular exercise 600 calories
Food Proportions. In order that the body may have tissue
building foods and fuel foods in healthful proportions, we ought
to eat from two to three ounces of proteid per day, and enough
fats and carbohydrates to make up the number of calories which
we may require as indicated above.
Since the fuel value of carbohydrates is only | to J that of fats,
our diet should have two or three times as much carbohydrate,
especially in warm weather, when the concentrated fuel of the fats
is less needed. Still another way of reaching the same result is
to take sV ounce of proteid for each pound of our weight, and enough
of the fuel foods (fats and carbohydrates) to make up the re-
quired number of calories, for energy production. This makes a
diet rather low in proteid especially for growing children, but our
usual mistake is to use too much, rather than too little proteid,
and one good authority sets the amounts even lower.
A safe proportion for growing boys and girls would be about
2 or 2J ounces of proteid per day, and enough fuel foods to supply
the required energy, which will depend upon the age and activity
as already stated.
346 BIOLOGY FOR BEGINNERS
The carbohydrates ought always to be more abundant than
the fats, because of the much greater amount of energy produced
by the latter. This is especially true in warm weather, when the
proportion of four times as much carbohydrates will be about the
proper diet.
If the above proportions are followed for all three food stuffs,
the ratio for all will be about,
Proteid, one; fat, one; carbohydrate, four.
Need of Mixed Diet. We require proteids, fats, and carbohy-
drates in about the proportions 1:1:4 but there is no one food
that contains these nutrients in these proportions, so it is evident
that a mixed diet is necessary. When foods are properly selected,
so that the above proportion is obtained, we have what is known
as a " balanced ration " and this should be the aim, both of those
who prepare and those who eat foods.
If we use a diet largely of lean meat, we have too high a per cent
of proteid. This excess is thrown off by the kidneys and intestines
as waste. It overtaxes these organs seriously and is an expensive
and unnecessary form of diet. In the same way an excess of fat
much above the given proportion, such as would come from a diet
rich in fat meats and butter, merely wastes the extra energy or
stores it as unnecessary fat tissue in the body.
A strict vegetarian diet is almost sure to be too rich in carbo-
hydrates and has the same result as do fats, fuel is wasted, too
little tissue material is provided, and fat tissue may also accumulate
from the starches being transformed and stored in this form.
Remember that, in general, most of the energy should come from
carbohydrates and fats, and only enough proteid be taken, to pro-
vide for tissue building and repair. If our diet proves to be high
in proteid, we are burning tissue foods for fuel, as well as putting
extra strain on our system, to remove the nitrogenous waste left
by proteid oxidation.
In general, man has learned to combine foods, to correspond,
roughly, to these needs as will appear if we look up the composi-
tion of familiar combinations, like the following,
"Meat and, potatoes," " Bread and butter," " Bread and milk,"
FOOD 347
" Bread and cheese," " Pork and beans," " Potato and gravy,"
" Cereal and cream," " Ham sandwich."
A study of the following table will show the number of ounces
of proteid, and the fuel or energy values, of some of our common
foods. The amounts of each food stuff taken are about the usual
portion or "helping" which one would receive at table, so we can
calculate how much proteid and energy our present diet provides,
and see if it corresponds to the amounts mentioned as suitable for
our age and occupation.
From this table, also, it is possible to determine whether one's
diet has the proper proportion of fat and carbohydrate, in pro-
portion to the proteid, if one is using the 1:1:4 ratio as a basis.
These tables are used through the courtesy of Professor Frank H.
Rexford, from whose "One Portion Food Tables " they are taken.
They furnish the easiest means of estimating whether one's diet is
properly balanced.
Digestibility of Foods. Not only must the nutrients in our foods
be present in the proper proportions, but they must be in a digesti-
ble form, or else they are wasted. Careful study shows that vege-
table proteids and fats are not so easily digested as those from
animal foods, though they seem to be cheaper.
This means that we must either use considerable animal food, or
else increase the apparent amount of vegetable proteids and fats
beyond the proportion suggested in the tables, because the body
does not so readily digest them. This fact balances their cheaper
cost to a great extent, and is also evidence that man is intended for
a mixed diet, obtaining much fat and proteid from animal sources,
and his carbohydrate foods from the plants.
Cost of Foods. Not only must our diet be selected with reference
to proper amounts of the nutrients and ease of digestibility, but
also with regard to the cost in money. This is affected by three
things, the actual price of the food, the amount of water and waste,
and the expense of preparation. It is more and more important that
we shall be informed as to the composition and cost of foods, and for
this purpose the Government has published many bulletins, which
can be had free of cost, by application to the Department of
348
BIOLOGY FOR BEGINNERS
FOODS PRIMARILY OF PLANT ORIGIN
FOOD AS WE EAT IT
OF THIS THE BODY CAN
USE
This Portion can Yield
to the Body in Energy
and Heat Units
Muscle
Builder
For Heat and
Energy
Proteid
Fat
Carbo-
hydrates
(Starch
and
Sugar)
Beverages
Cocoa
Ounces
.11
.01
.19
.16
.18
.18
.19
.22
.11
.1
.06
.14
.13
.12
.12
.12
.09
.07
.13
.04
.11
.21
.02
.05
.01
.04
Ounces
.33
,17
.27
.09
.04
.03
.08
.48
.13
.09
.008
.2
.16
.37
.18
.22
.16
.003
.02
.001
.03
.02
.02
.37
.01
Ounces
.19
.27
1.05
.93
1.04
1.07
1.2
1.18
.69
.73
.3
1.6
1.32
.93
1.3
1.28
.9
.59
.49
.4
.96
1.56
.78
.77
.15
.58
Calories
123
53
216.3
150.6
151.3
153.1
182.08
275
125.3
120.3
44.4
256.8
209
218.8
211.9
220
168.3
77.6
76.5
50.9
124.72
212.5
98.5
100.8
116.3
75
Coffee (cream and sugar only)
Bread
Biscuit soda
Bread corn
" graham . .
" wheat
" plain rolls
" and butter .
Crackers saltines
" soda
Toast dry
Cake
Chocolate layer
Cookies molasses
Doughnuts .
Frosted
Fruit
Soonsro
Cereals
Corn flakes
Oatmeal ...
Puffed rice
Rice
Shredded wheat (2)
Fruit
Apple baked
Bananas
Olives green
Oranges
FOOD
349
FOODS PRIMARILY OF PLANT ORIGIN. Continued
FOOD AS WE EAT IT
OF THIS THE BODY CAN
USE
This Portion can Yield
to the Body in Energy
and Heat Units
Muscle
Builder
For Heat and
Energy
Proteid
Fat
Carbo-
hydrates
(Starch
and
Sugar)
Miscellaneous
Brown gravy
Ounces
.03
.26
.36
.05
.08
.13
.29
.14
.65
.15
.1
.16
.12
.11
.26
.04
.09
.06
.38
.11
.1
.09
.13
.13
Ounces
.26
.27
.02
.74
.14
.32
.19
.31
.4
.42
.15
.3
.16
.28
.1
.25
.02
.22
.16
.07
.34
.04
.12
Ounces
.07
.32
2.00
.02
.04
.08
.12
1.44
1.4
1.51
1.
.49
.35
.55
.92
.02
.52
.29
.15
1
.17
.02
.33
.33
.02
Calories
81.2
114.3
286.2
100.4
47.8
103.4
80.1
282.8
297.2
362
177
148.8
102.4
149.5
146.3
100.1
70.4
102.1
67.6
182.8
124.8
16
60
91.2
192.8
Hash beef
Macaroni . . .
Salad dressing (French)
Nuts
Almonds
English walnuts . . .
Peanuts
Pie
Apple
Lemon
Mince ....
Pumpkin ... ...
Pudding
Blanc mange (chocolate)
Custard
Rice
Tapioca . . .
Salad
Egg mayonnaise
Fruit
Potato
Tomato (with mayonnaise)
Soup
Bean
Cream of celery
Consomme
Clam chowder
Tomato
Vegetable (canned)
350
BIOLOGY FOR BEGINNERS
FOODS PRIMARILY OF PLANT ORIGIN Continued
f
FOOD AS WE EAT IT
OF THIS THE BODY CAN
USE
This Portion can Yield
to the Body in Energy
and Heat Units
Muscle
Builder
For Heat and
Energy
Proteid
Fat
Carbo-
hydrates
(Starch
and
Sugar)
Sugars
Candy chocolate .
Ounces
.01
.06
.31
.22
.69
.05
.03
.01
.08
.04
.01
.04
.09
.09
.09
.1
.11
.04
.08
Oun es
.01
.15
.18
.65
.61
.002
.09
.003
.03
.02
.15
.09
.06
.26
.01
.03
.04
Ounces
.73
.95
.89
.25
1.08
.6
.21
.15
.16
.04
.52
.35
.03
.15
.54
1.26
.68
.26
.56
.18
.08
Calories
90
160
103.9
27
182
97.5
48.72
26.1
35.2
5.5
74.25
49.2
7
65.7
66.6
173.4
100.4
98.1
78
26.8
16.4
Chocolate almonds
]Vaple syrup
Sugar (granulated or loaf)
Vegetables
Beans baked
" kidney
" strinsr
Beets
Cabbage boiled
Celery
Corn canned . .
Carrots
Lettuce
Onions creamed
Potatoes sweet
" white mashed
" " baked
Succotash
Tomatoes sliced
" stewed . .
Agriculture at Washington. Lists of all publications will be sent
on application.
While we cannot devote enough space to the topic to compare
the different kinds of food, their cost and composition, and methods
of preparation, even a slight study of your own diet, in the light of
this chapter, will show two facts: first, Americans eat more food
FOOD
FOODS PRIMARILY OF ANIMAL ORIGIN
351
FOOD AS WE EAT IT
OF THIS THE BODY CAN
USE
""C ^%
S
831
It!
!-o
H <u a
.2 "5 ^
2
Muscle
Builder
For Heat and
Energy
Proteid
Fat
Carbo-
hydrates
(Starch
and
Sugar)
Beef
Corned
Ounces
.21
.26
.43
.37
.05
.26
.05
.19
.49
.48
.24
.32
.56
.44
.62
.26
.43
.67
.62
Ounces
!52
.07
.29
.36
.43
.34
.1
.24
.4
.45
.88
.17
.02
.16
.24
.4
.26
.59
.44
.51
Ounces
.02
.91
.3
.03
.03
.08
Calories
174.2
49.4
125.2
137.1
112.5
122.4
134.7
123.6
110.2
179.1
296
78.5
101 6
105.9
114.1
187
104
210
194.3
108
Dried
Round
Sirloin
Dairy Products
Butter
Cheese full cream
Ice cream
Milk whole
Oleomargarine
Eggs
Boiled (2) : .
Omelet
Scrambled
Fish
Cod
Halibut steak
Salmon canned . .
Fowl
Chicken (fricasseed)
Turkey
Lamb
Chops (broiled) ....
Leg. .
Mutton
Leg.
352 BIOLOGY FOR BEGINNERS
FOODS PRIMARILY OP ANIMAL ORIGIN Continued
FOOD AS WE EAT IT
OF THIS THE BODY CAN
USE
This Portion can Yield
to the Body in Energy
and Heat Units
Muscle
Builder
For Heat and
Energy
Proteid
Fat
Carbo-
hydrates
(Starch
and
Sugar)
Pork
Bacon
Ounces
.1
.47
.49
.41
.4
.33
.56
.24
.32
.21
.7
.65
.56
Ounces
.66
.95
.55
.49
.37
.48
.8
.02
.04
.04
.26
.1
.17
Ounces
1.2
1.19
1.19
Calories
188.6
309
203.2
314.2
279.7
302.7
278.1
32.2
47.6
36.4
152
104
107.1
Chops
Ham lean
Sandwiches
Cheese
Eee
Ham .
Sausages
Country
Shellfish
Clams
Lobster
Oysters
Veal
Cutlets ...
Leg
Liver
than is required and second, they have an idea that the most
expensive foods are the most nutritious.
These are serious mistakes, overtaxing both the digestive system
and the pocket book, and no subject of our study is more important
than the one giving us a clear idea of food values and selection.
Right and Wrong Diets. We are all too apt to let our artificial
" tastes " and the demands of fashionable customs over-rule our
FOOD 353
natural instincts and better judgment in the selection of foods.
Costly, highly-seasoned, stimulating, and unnatural substances
are frequent invaders of our digestive apparatus, to the detriment
both of our bodies and our bank accounts. For the majority of
people in normal health, meats, fish, eggs, milk, butter, cheese,
sugar, flour, meal, potatoes, and other vegetables make a fitting
and sufficiently varied diet the main point being to use them in
proportions suited to the actual needs of the body and not according
to acquired whims of the " appetite."
Another fact that is often misunderstood, even after a study of
nutrients, is the very essential nature of mineral salts, especially
From the American Museum of Natural History.
FIG. 113. A U.S. soldier in the field is allowed a daily ration
supplying 4199 calories of energy. A typical daily field ration supply-
ing this amount of energy is shown above.
iron, calcium, and potash compounds, which we obtain from green
vegetables, otherwise not rich in food value. As shown by the
"Summary of Nutrients" on p. 357, these mineral* compounds are
a necessary, though small part of every properly balanced diet.
Furthermore, the fact that many foods, especially of vegetable
origin, contain considerable indigestible matter such as cellulose,
or connective tissue, is also of value as supplying a certain bulk of
matter required to keep the digestive apparatus properly filled and
active.
A diet could be divised made up of highly concentrated and pre-
digested foods, which, though giving all necessary nutrients, would
be very harmful, because of relieving the digestive organs of the
354 BIOLOGY FOR BEGINNERS
work for which they have become adapted, and without which they
will not remain in health.
Cooking. Man is the only animal which has learned to build a
fire, hence is the only animal to use cooked food. This is not an
unmixed blessing, for our digestive apparatus and especially our
teeth are inherited from our animal ancestors, and, when provided
with cooked food, are relieved of work for which they were adapted.
This leads to disuse and so to degeneration. One seldom hears of
the lower animals suffering from decayed teeth or indigestion,
both of which are almost universal in man, due partly to too abund-
ant, too delicately prepared, and unnatural foods.
Cooking of food performs three functions: First, it changes the
mechanical and chemical condition so as to make it more easily
digestible ; second, it makes food more appetizing in appearance or
flavor, which quickens the flow of digestive fluids and actually aids
digestion; third, the high temperature kills any dangerous bac-
teria, organisms, or parasites that the food may contain. This is
very important.
Cooking meat develops its pleasing taste and odor, softens con-
nective tissue, and makes it " tender," though too high temperature
may harden the proteids of the lean portions. Beef extracts and
thin soups are very agreeable to the taste, but contain very little
nourishment since the meat proteids and fats are not soluble in
water. These broths are useful as appetizers or mild stimulants
but are of slight value as food.
In cooking eggs, especially by frying, the proteid (albumen) is
hardened and made less digestible than in the raw state. Milk,
also, if heated to boiling, is made less valuable as food; though
when pasteurized the heat is regulated so as to kill most bacteria,
but not to reach a point high enough to impair its food value.
When the vegetable foods are cooked the changes are chiefly the
softening of the cellulose and the breaking of the insoluble walls
around the starch grains, thus exposing them to digestive fluids
and partly dissolving the starch in the hot water or steam.
In baking all flour foods, the aim is to make the material " light,"
and porous so as to be more easily broken up and digested in the
FOOD 355
alimentary canal. This lightness may be secured by the mere
expansion of steam in the dough, but it is usually caused by use of
yeast or baking powder, which produce carbon dioxide within the
batter. The gluten (proteid), always present in flour, is sticky
enough to retain the gas, which expands with the heat of cooking,
filling the loaf with countless bubbles and making it porous. Finally
the heat stiffens the gluten and starch and drives out much of the
enclosed gas and we have the " light," porous, and digestible bread
or pastry, instead .of an indigestible paste of uncooked flour and
water.
" Special Foods." There are no foods for special organs. Fish
is not a " brain food," nor celery a " nerve food," nor meat a
" muscle food." The savage eats the heart of his fallen foe to ab-
sorb his courage, but we ought to be beyond that stage. If we use
a properly balanced diet our cells will select what they need in
proportion as we use them. The only way to increase the brain
power is to use the brain, not by eating foods rich in phosphorus
because the brain tissue contains this element.
If eating strong muscle made us strong, we ought to have a diet
of the toughest meat possible. However the only way to persuade
nature to give us more strength, is by using what we have and
furnishing her a proper food supply to select from.
To be sure, if phosphorous compounds are lacking, the nerves
will suffer; if proteid be absent, our muscle tissue might feel the
lack, but in a balanced diet this is never the case. An excess of any
element, above what is normally used in the body, does not develop
any special part, but is merely wasted. Extra proteid is not needed
for extra work; it is the fuel food that supplies the energy, the
proteid requirement being almost constant for all grown persons
and only slightly varying for younger people.
Lipoid. A shortage of fat in the diet, not only reduces the energy
produced, but has long been associated with a lowering of nervous
activity. This is now explained by the discovery of a substance
called lipoid, in the cell walls of the body, especially in the outer
layer of the nerve fibers and brain cells.
Lipoid resembles fat in many ways, but contains nitrogen and
356 BIOLOGY FOR BEGINNERS
phosphorus which ordinary fats do not. It is affected by alochol,
anaesthetics, and poisons and thus may be the means by which
these act upon the system. At all events it seems to be derived
from fat foods and is very essential to the nervous system.
Vitamines. It has been found that a diet restricted to a few
foods, especially if they all be cooked, does not always result in
proper nourishment, even though the balance may seem to be cor-
rect. This has led to the belief that there are substances called
vitamines in certain foods, which are necessary to health and are
destroyed by cooking. In order to supply these, the diet should
include a moderate amount of uncooked foods, such as fruits, let-
tuce, celery, tomatoes, milk, and butter.
Fruits and vegetables are important for another reason. They
produce alkaline substances when digested and these neutralize
harmful acids formed by the digestion of proteids. They are also
our chief source of iron and some other necessary mineral salts,
and cannot be safely omitted from the dietary, even though their
calorie value is not always very high.
If energy alone was all that is required of food we could get our
2500 calories from about twenty ounces of sugar or white of egg,
or half that amount of clear butter. Both our instinct and ex-
perience teach us that this would not support a healthful
life.
Dietary Diseases. Certain natives of Japan and the Philippines
live largely on rice. This supplies plenty of energy but lacks other
essential nutrients and they suffer from a disease called beri-beri,
which is quickly cured by a change of diet. Pellagra is a sickness
which occurs in our southern states, and seems to be caused by a
diet poor in proteid. Scurvy is another dietary disease, caused by
lack of fresh fruits and vegetables. It used to be common among
sailors whose long voyages forced them to live on salt meats with-
out any fresh foods, and was promptly relieved by use of fruit and
fruit juices when they came ashore. Long ago the sailing vessels
used to carry casks of lime juice to prevent this, and now it has
become a custom to refer to any sailor on a slow sailing vessel as
a " lime juicer."
FOOD
357
Experience teaches that
1. Food must be sufficient in amount.
2. Diet must contain proper proportion of the nutrients.
3. Diet must contain vitamines.
4. Diet must include a considerable variety of foods.
SUMMARY OF NUTRIENTS
Nutrients
Composition
Function
Foods containing
Proteids
C,H,0, N,S,P,
Build tissue
Lean meats, eggs,
K, Ca, Cl, Fe
Protoplasm
beans, peas, milk
Some energy
Carbohydrates
(C, H 2 , 0)
Energy
Sugar, cereals,
Stored as fat
bread, corn meal
Some tissue
Fats and oils
(C, H) O
Energy
Butter, lard, milk,
Stored as fat
cheese, olive oil,
nuts
Water
H 2 O
60% tissue
Taken as water in
Blood, fluids
all vegetables
Transporter
fruits, all foods
Mineral Salts
Phosphates
H 3 P0 4
Bone
Grains (whole)
Protoplasm
meats, fish, milk
Aid digestion
Salt
NaCl
Essential in blood
Taken as salt in
Appetizer
almost all food
Iron compounds
FeCO 3
Haemoglobin
Spinach, lettuce,
Oxygen carrier
green foods,
prunes, meats
Potassium com-
K 2 S0 4
Essential in blood
Vegetables
pounds
Calcium and
Ca, Mg
Regulate nerve and
Grains (whole)
magnesium
heart action
Vegetables
compounds
NOTE. Look up tests for as many of the above as you can.
NOTE. There are many kinds of proteids as,
(1) Myosin in meats; (2) legumin in peas and beans; (3) casein in
358 BIOLOGY FOR BEGINNERS
milk and cheese; (4) gluten in grains; (5) albumin in eggs; but all con-
tain nitrogen.
There are many kinds of carbohydrates as,
(1) Several kinds of starches (corn, potato, sago, arrow root).
(2) Many kinds of sugars (cane, saccharose: grape, glucose: milk,
lactose: fruit, fructose).
(3) Cellulose.
(4) Gums and resins (some of them).
THE FUNDAMENTAL PRINCIPLES OF CORRECT EATING
The human body is very much like an engine. It needs fuel to
keep it running. As it has to be built so must it be repaired from
time to time, also it must be regulated, hence, we need A Fuel
food; B Building or repair food; C -^Regulating food.
Fuel Foods. As in the case of an engine, the main requirement
is for fuel. Unlike an engine, however, if the human body does not
secure sufficient fuel it will literally burn to death, the tissues being
drawn upon to supply the fuel. On the other hand, the human
engine may easily become overstoked by an excess of fuel. The
following list shows the main fuel foods, the great foundation foods
of the diet, that supply energy for muscular work. Mental work
requires so little extra fuel that it is not necessary to consider it
specially. There are three groups of fuel foods. Here they are in
the order of their cost per calorie, those giving most energy for
the money heading the list.
1. Starchy Foods
Cornmeal Rice Split peas, yellow
Hominy Macaroni Dried navy beans
Broken Rice Spaghetti Bread
Oatmeal Cornstarch Potatoes
Flour Dried lima beans Bananas
2. Sugars 3. Fats
Sugar Candy Drippings Peanut butter
Corn syrup Molasses Lard Milk
Dates Most Fruits Salt pork Bacon
Oleomargarine Butter
Nutmargarine Cream
FOOD 359
About 85 per cent of the fuel for the body should come from these
groups, using starchy foods in the largest amounts, fats next, and
sugar least.
Building and Repair Foods. These are divided into proteids and
mineral salts.
1. Proteid, or " Body Bricks." These food elements are found
in greatest abundance in lean meat of all sorts (including fish, shell
food, and fowl), milk, cheese, eggs, peas and beans, lentils, and
nuts. There is also a fair amount of proteid in cereals and bread
(about 10 per cent), which are both building and fuel foods. Most
foods contain some proteid. Those above-mentioned are richest
in proteid and hence are termed " Building " or " Repair Foods."
The following is a list of the building and repair foods in the order
of their cost, those giving most building and repair material for the
money heading the list.
Beans (dried white) Bread, whole wheat Macaroni Eggs (second
Dried peas Bread, graham Mutton, leg grade)
Oatmeal Salt cod Beef, lean rump Halibut
Cornmeal Milk, skimmed Milk Porterhouse steak
Beans, dried lima Cheese (American) Beef, lean round Eggs (first grade)
Bread Peanuts Lamb, leg Almonds, shelled
2. Mineral Salts. These are found in milk, green vegetables,
fruits, and cereals made from the whole grains, and egg yolks.
Regulating Foods. 1. Mineral Salts. These minerals which
have been mentioned as repair foods, are also regulating foods
and help to keep the machinery running properly.
2. Water. Water is an important regulating food. Many
people drink too little. Six glasses of water a day is the average
requirement one between meals and one at meals.
3. Ballast or Bulk. This is furnished by cereals and vegetable
fiber, which is found in whole wheat or Graham flour, in bran,
leaves and skins of plants, and skins and pulp of fruits. Examples
are: Vegetables Lettuce, Parsnips, Carrots, Turnips, Celery,
Oyster Plant, Cabbage, Brussels Sprouts, Tomatoes, Salsify,
Spanish Onions, Spinach. Fruit Apples (Baked or Raw),
360 BIOLOGY FOR BEGINNERS
Pears, Currants, Raspberries, Cranberries, Prunes, Dates, Figs,
Oranges.
4. Hard Foods. Vigorous use of teeth and jaws is insured by
hard foods, such as crusts, hard crackers, toast, Zwieback, fibrous
vegetables and fruits, celery and nuts, which are necessary to
keep teeth and gums in a healthy condition.
5. Accessories or Vitamines. These are minute substances
(vitamines and Jipoids) present in a very small quantity in a number
of foods and apparently necessary to keep the body in health. That
is, the absence of these elements seems to lead to poisoning of the
body, which results in such disturbances as scurvy, beri-beri, and
other so-called " deficiency " diseases. Milk, eggs, whole wheat,
corn, oatmeal, potatoes and oranges, skins or hulls of cereals, fresh
meat, fresh peas and beans are thought to contain them. It seems
necessary to include the leaves of plants (green vegetables) when
the seeds (cereals, grain, flour, etc.) are used as food if the diet is
to be complete and well balanced. Fruit and vegetable acids are
regulating. They keep the blood alkaline and prevent constipation.
COLLATERAL READINGS
Principles of Nutrition, At water, entire; Studies in Physiology, Peabody,
pp. 41-61; Elements of Cookery, Williams and Fisher, pp. 136-142, look
through; Chemistry of Common Things, Brownlee, pp 242-265; Food
Materials, Richards, pp. 1-19; Pure Foods, Oleson, pp. 1-32; Plants and
their Uses, Sargent, look through; Source, Chemistry and Use of Food,
Bailey, look through; World's Commercial Products, Freeman, see index;
Food and Dietetics, Hutchinson, see index; Practical Hygiene, Harrington
and Richardson, see i ex; Feeding the Family, Rose, entire; Human
Foods, Snyder, see index; Children's Diet in Home and School, Hogan, see
index; Food and Dietetics, Norton, see index; The Cost of Food, Richards
and Norton, entire; Foods and their Adulteration, Wiley, see index; Ele-
mentary Biology, Peabody and Hunt (Pt. II), pp. 44-63; Physiology,
Experimental and Descriptive, Colton, pp. 167-193; Textbook in General
Physiology and Anatomy, Eddy, pp. 51-89; Applied Physiology, Overton,
pp. 51-66; Human Mechanism, Hough and Sedgwick, pp. 95-97; The
Human Body and Health, Davidson, pp. 35-44; The Human Body,
Martin, pp. 88-105; General Science, Clark, pp. 60-69; Elementary Physi-
ology, Huxley, pp. 250-252, 291-303; High School Physiology, Hewes,
pp. 87-91; Essentials of Biology, Hunter, pp. 330-350; U. S. Department
of Agriculture, Farm Bulletins, 23, 34, 74, 85, 93, 128, 142, 182, 249, 256,
295, etc.; Periodical, "The Forecast," Philadelphia.
FOOD 361
SUMMARY
Necessity of food.
Living things use energy.
Energy is released from food by oxidation.
Oxidation destroys tissue.
This tissue has to be replaced by food.
Excess of food used for growth or storage. (Compare plant and animal.)
Definition of food.
Functions of food-stuffs.
Inorganic. Water (60%). Transportation, solvent (photosynthesis).
Mineral salts (5%).
Phosphates, chlorides, nitrates, carbonates.
(Compounds of N, S, P, iron, lime, etc.)
Used in bone, teeth, blood, fluids, digestion, etc.
Organic. Proteids (18%).
Composed of C, H, O, N, S, P, etc.
Essential to living tissue, protoplasm.
Found in lean meat, eggs, cheese, wheat, beans, peas.
Fats (15%).
Composed of C, H, O.
Easily oxidized, produce energy, excess stored.
Found in fat meat, butter, eggs, fish, lard, cotton and olive oil, corn,
cocoa, etc.
Carbohydrates (little in tissues).
Composed of C, H 2 , O.
Produce energy or stored as fat.
Found as sugar in cane, fruits, beets, milk.
Found as starch in vegetables, grains, nuts, etc.
Found as cellulose in most vegetable foods.
Measurement of food values.
Energy value measured in "calories."
About 2800 calories needed by average individual.
Needs vary with age and occupation.
Food proportions.
Proteids from 2 to 3 ounces per day.
Fuel foods to make up remaining number of calories,
, ,_ . , c ( fats, one part,
obtained from | carbohydrates? two to four parts .
Less fats in warm weather.
Ratio about, proteid : fat : carbohydrates
(1) :(1): (4)
Balanced Ration.
No one food has nutrients in correct ratio.
Hence a mixed diet is necessary.
Animal food would be too high in fat and proteid.
Vegetable food would be too high in carbohydrates.
Excess of proteid, a dangerous and expensive source of energy.
362 BIOLOGY FOR BEGINNERS
Digestibility of Foods.
Vegetable fats and proteids less digestible than animal.
Value of both vegetable and animal foods.
Cost of Food.
Depends on price, waste, cost of preparation
Expense due to poor selection.
bad preparation or waste.
demands of artificial appetite.
Proper Diet.
Value of simple, standard foods.
Objections to highly seasoned or " fancy " dishes.
Importance of green vegetables for mineral salts.
Concentrated foods not good, bulk needed.
Cooking.
Functions, makes food more easily digested.
makes food more appetizing.
sterilizes food.
Faulty cooking may make food less digestible
Boiling vs. pasteurizing milk.
Effect of cooking on teeth.
No Foods for Special Organs.
Lipoid.
Vitamin es.
Dietary Diseases.
CHAPTER XXXVIII
NUTRITION
Vocabulary
Nutrition, all processes concerned with building up tissue.
Alimentary, pertaining to food or nutrition.
Fallacy, a mistaken idea.
Distended, swelled up or expanded.
Lacteals, lymph capillaries of the intestine which absorb fat.
Someone has said, " We live, not on what we eat, but on what
we digest." Food, even after cooking, is not usually in condition
to be made into tissue or to furnish energy.
Digestion produces two important changes in foods. First, it
makes them soluble to allow transfer by osmosis; second, it changes
them chemically to permit them to be assimilated. These changes
are brought about in two ways, first, mechanically by the teeth,
the motion of the stomach, and intestinal walls, second, chemically
by active substances in the digestive fluids, called enzymes or
ferments. The latter are the more important means of digestion;
there are several kinds, each acting on a particular foodstuff and
each secreted by different glands in various parts of the digestive
tract. They will be referred to later when these different regions
are studied.
Digestive Organs. The digestive tract or alimentary canal is
practically a continuous tube with many glands opening into it to
furnish digestive fluids, also with a rich blood supply to provide
for its activities and to remove digested foods. This food tube
consists of three general regions whose structure and functions will
be studied in order,
1. The mouth
2. The gullet and stomach
3. The intestines.
363
364
BIOLOGY FOR BEGINNERS
In the simpler animals the digestive canal may be lacking
(protozoa), or almost straight and uniform in size (worms), but in
Salivary &onef
Vermiform typemfa.
FIG. 114. Diagram of the alimentary canal. Modified from
Landon's, see Kellogg.
the higher animals and man it is much coiled to provide greater
surface for secretion and absorption, and also varies much in
NUTRITION 365
diameter, to permit the carrying out of special functions in various
parts.
The Mouth. So far as digestion is concerned, the mouth per-
forms two functions: in it the food is crushed or cut into smaller
portions and at the same time it is mixed with saliva, one of the
digestive fluids, whose function will be dealt with later. The
mouth cavity is bounded above by the palate, below by the tongue,
and at front and sides by the teeth, lips, and cheeks. There are
six openings into this cavity, from within, namely
1. Two nasal openings, behind the palate and connecting with
the nostrils, above.
2. Two eustachian tubes, also far back, high up at the sides
and connecting with the ears.
3. The trachea and gullet below, the former in front and con-
necting with the lungs, and the latter behind it and com-
municating with the stomach.
Other organs are immediately connected with the mouth cavity,
most of which can be seen by studying your own mouth with a
mirror or by looking into a friend's mouth with a small electric
light. The " roof of the mouth " or hard palate can be easily
recognized. Back of it is a downward projecting sheet of muscle,
the soft palate; at either side rounded projections may be seen,
which are tonsils.
Behind the soft palate and near the opening into the nasal cavity
is the location of adenoid growths which may obstruct the breath-
ing and have to be removed if they reach abnormal size. The
tonsils also sometimes become enlarged and act as nests for bac-
terial growth, necessitating their removal. Their function is not
thoroughly understood, and when diseased their removal is bene-
ficial.
The openings of the eustachian tubes are protected by their
high location and by folds of membrane beside them. The trachea
is protected by the base of the tongue and the epiglottis, which is
a door-like organ that covers the trachea during swallowing.
The Tongue. The tongue is easily studied, but few of us really
know its shape, size or structure. The best way to find out is to
366
BIOLOGY FOR BEGINNERS
look at it. It is a large muscular organ, nearly filling the front
part of the mouth cavity when the jaws are closed. It has great
freedom of motion and performs the following functions:
FIG. 115. Mouth and Throat.
The object of this plate is to show the relative position of tue organs of the
nose and throat, and especially to indicate the course taken by food in swal-
lowing, and air in breathing.
Note that these routes cross each other, making necessary the adaptation
mentioned in the text, to prevent food from entering the trachea when being
swallowed.
Attention is called to the size and thickness of the tongue, which we usually
think of as long and thin. Its base pushes back and the epiglottis closes down
when the food is passing.
Note also the large size of the nasal cavity and the projecting lobes which
help warm and moisten the air, catch dust, and provide surface for the nerves
of smell.
1. It is the organ of taste a sense which aids in selecting
foods and in promoting their digestion.
2. It aids in chewing, by automatically keeping the food be-
tween the teeth.
3. It is concerned in the process of swallowing, since it rolls
NUTRITION
367
.P.M
the food into proper shape, pushes it back toward the gullet, and
partly closes the trachea.
4. It helps to keep clean the inner surface of the teeth.
5. In man it is one of the organs concerned in speech.
The Teeth Structure. The teeth
are even more familiar and im-
portant organs. Each consists of
three parts, (1) the crown or ex-
posed portion, (2) the neck, a slight
narrowing at the edge of the gum,
and (3) the root or roots which are
attached to the jaw,
A section cut lengthwise through
a tooth shows that the crown is
covered by a very hard substance
called enamel, which protects the
exposed parts. The bulk of the
tooth consists of dentine, a softer
and more porous substance, while
the center is occupied by the pulp
which contains the nerves and
blood vessels of the tooth. The
root is covered by a bone-like coat-
ing, the cement, and through the
very tip is 'the opening by which
the nerves and blood vessels find
entrance.
Number and Kinds of Teeth.
It is easily seen that there are four
kinds of teeth in the mouth even
though the full number may not be there till the 20th year.
In the full set there are thirty-two, sixteen on each jaw, arranged
as follows: In front are eight incisors with sharp edges, whose
function is to cut the food, next on each side is one canine, or four
in all, which are pointed and which the lower animals use for tear-
ing food. In man they assist the incisors. Behind these on each
FIG. 116. Vertical section of a
tooth in jaw. E, enamel ; D, dentine ;
P M , peridontal membrane; PC,
pulp cavity; C, cement; B, bone of
lower jaw; V, vein; A, artery; N,
(After Stirling.) From
368 BIOLOGY FOR BEGINNERS
side come two premolars and three molars, all with rough flat
crowns and used to crush the food. The first or " milk " teeth
lack the premolars and one set of molars hence number but twenty
in all. The reason for having two sets is to allow for the growth
of the jaw. Hence, if the first teeth are allowed to decay and are
pulled too soon, the jaw never gets its proper shape and the later
teeth are crowded and irregular. At the proper times the roots of
the first teeth are absorbed and they make way easily for the
permanent teeth and the jaw is developed into proper shape.
The numbers of teeth are often expressed in fractional form,
and are easily remembered in this way. Beginning at the front in
the middle of the jaw and putting the upper teeth above and the
lower teeth below, we have the " dental formula " for the adult
and first sets as follows-:
Incisors Canines Premolars Molars
First set (20) ' f } ' jj |
2123
Permanent set (32)
L \ L o
The last pair of molars may not appear till about the 20th year
and are therefore called the wisdom teeth, as one is supposed to
have acquired some wisdom by that time.
Among other animals the teeth vary a great deal in size and
number, but there is none that has a greater variety of kinds.
Horses and cattle have molars greatly developed, cats and dogs
have canines long and sharp, while rats and squirrels develop the
incisors excessively for gnawing. Vegetable foods require broad
grinding teeth, animal food needs sharp canines and shear-cutting
premolars, while man, being adapted for a mixed diet, has all forms
moderately developed. Chewing is one of the mechanical processes
which prepares the food for chemical action by the digestive
fluids.
Glands. Digestive fluids are secreted by organs called glands.
A gland consists of a group of cells adapted for producing a fluid
NUTRITION
369
secretion. These cells are developed on the inner walls of a cavity
which usually opens into some other organ by way of a tube called
a duct.
These cavities may be simple and very small, like the mucous
glands that moisten all the digestive tract, or they may be very
large and complex like the liver. In either case they must have a
rich blood supply and nerves to control it and the action of the
TEMPORARY SET. >
PERMANENT SET
CHART S H O W INfr ORDER
SUCCESSION AMD Tine OF rut
CE OF TEETH
2>.\ IL^A \pRE-\
Jfca
nOLM
-i \
MOLAR
MOLAR
OF THE
H E
MOLAR
FIG. 117.
gland, as well. A gland, then, consists of the secreting cells, the
gland cavity, the ducts, the blood and nerve supply.
Salivary Glands. The principal glands of the mouth are the
salivary glands of which there are three pairs. The largest pair is
located beneath the ear on each side of the head and the ducts open
opposite the second upper molar. Inflammation of the glands
causes the mumps. The sub-maxillary glands lie within the angles
of the lower jaw and the sub-lingual pair are below the tongue,
beneath the floor of the mouth; ducts from both pairs open under
the middle of the tongue.
370
BIOLOGY FOR BEGINNERS
* S TO M AC H *~
Saliva. Saliva is a thin, alkaline fluid containing the enzyme
ptyalin, which changes starch to soluble sugar, but this action is
slight, since the food remains so short a time in the mouth. How-
ever, the other functions of saliva make it important that it be
thoroughly mixed with the food, since its presence in the stomach
stimulates the gastric glands. It also permits foods to be tasted,
since, only in solution will the food affect the nerves of this sense.
Furthermore, saliva aids in chewing and is indispensable in swal-
lowing food, so that its digestive function is only one of several,
and the quantity secreted is much greater than one might suppose,
being about three pints per day.
The steps of the digestion process in the mouth, then, are
1. Food mechanically crushed.
2. Food moistened for taste and swallowing.
3. Some starch changed to sugar*.
4. Very slight absorption of sugar, water, salts.
The Stomach. Passing
from the mouth, the food
enters the gullet, which at
a distance of about nine
inches enlarges into the
stomach. This organ is
located just beneath the
diaphragm with the inlet
at the left and close to the
heart. Except when fully
distended it is not the
smooth, pear-shaped organ
usually pictured, but may be collapsed and empty, or almost any
irregular shape, depending on its contents, and muscular move-
ments.
Its function is very largely to store and finely divide the food.
We usually eat at one time enough food to last for several hours.
This food must be stored somewhere and the stomach provides
the place. Also, chewing has only partly divided the food, so a
second function of the stomach is to furnish the mechanical separa-
Courtesy of Ginn and Company.
FIG. 118. From Hough and Sedgwick.
NUTRITION
371
tion of the food particles by the churning motion of its muscular
walls. The walls are also provided with millions of simple glands
which secrete the gastric fluid at the rate of five to ten quarts per
day.
Gastric Fluid. This gastric fluid contains hydrochloric acid and
two ferments, rennin and pepsin. The rennin acts on the casein
(milk proteid) changing it to curd,
in which form it is more easily
digested by other ferments.
(Note: rennin is used to " start "
cheese and in " junket tablets," the
latter made from calves' stomachs.)
Pepsin, acting only in the presence
of an acid, changes some proteids to
soluble peptones and also dissolves
much connective tissue, thus ex-
posing a greatly increased food sur-
face for digestion in the intestine.
Do not get the idea, that all or even
a great deal of proteid food is com- glan ?, s ma H n soi ^ ac ; a '
mouth of gland leading into a long
pletely digested in the stomach; in w id e duct, ft, into which open the
fact, as fast as they are finely terminal divisions; c, connective
divided, many proteids are dis-
charged into the intestine where the
pancreatic fluid completes the major part of proteid digestion.
The stomach, then, performs four functions, namely:
1. It acts as a storage for food.
2. It mechanically divides and separates food particles.
3. Rennin curdles casein.
4. Pepsin acts on some proteid and connective tissue.
Thus it is apparent that " stomach trouble " and digestive
trouble may not mean the same thing, and despite the common
idea, the bulk of digestive processes do not take place in the
stomach but in the small intestine.
The food as it is discharged into the intestine is called chyme
and consists of
FIG. 119. Section of pyloric
After Piersoe.
tissue of mucosa.
See Kellogg.
372
BIOLOGY FOR BEGINNERS
1. The fats all unchanged.
2. Most of the carbohydrates.
3. A large portion of the proteids.
4. Some sugars, peptones and water, which were not absorbed
in the stomach.
It is evident that, so far, the food has been mainly prepared for
digestion rather than digested, a process that is chiefly accom-
plished in the small intestine.
The Intestine. The stomach connects with the small intestine
by way of a muscular valve (the pylorus) which prevents the food
from passing before it is
thoroughly broken up in the
stomach.
The intestine is the most im-
portant portion of the digestive
tract, and consists of a coiled
tube about twenty-five feet in
length. The part next the
stomach is about twenty feet
long, about one inch in diameter
and is called the small intestine,
while the remaining five feet are
over two inches in diameter and
are called the large intestine.
FIG. 120. Mucous membrane of
the small intestine of the dog. A,
artery; B, vein; C, capillaries; D,
lacteals; E, glands of Lieberkiihn;
Ep., epithelial tissue. After^Cadiat.
See Kellogg.
The small intestine joins the
large at the lower, right side of
the abdomen, and at this point
is the location of the appendix.
Inflammation of this organ is called appendicitis.
Adaptations for Increase of Surface. In order that both secre-
tion of fluids and absorption of food may go on, much surface (for
osmosis) is required.
For this increase of surface, the intestine is adapted in three
ways:
1. Its great length and coiled position in the body.
2. Its inner lining projects in creases and folds.
NUTRITION 373
3. The lining of the small intestine is thickly covered with
microscopic projections (villi).
The villi are so fine and so numerous, that, under a lens, the
intestinal lining looks like a piece of velvet. By these means the
absorbing surface is increased five times, so that the total area of
the intestine is not less than twenty-five square feet, or about twice
as great as that of the skin.
Muscular Action. The intestinal walls are provided with layers
of involuntary muscles which perform two functions by their con-
traction and expansion.
1. They mix and separate the food, thus constantly exposing it
to digestive action.
2. They keep the food moving slowly through the digestive
canal.
The efficiency of digestion and absorption depends as much
upon these muscular movements as upon the chemical action of
the digestive fluids, themselves. To provide the fluids for intestinal
digestion there are three kinds of glands, (1) the intestinal glands,
(2) the liver, (3) the pancreas.
Intestinal Glands. The intestinal glands are small, simple and
very numerous, being located in the lining among the villi. They
secrete a strongly alkaline fluid containing sodium carbonate and
also enzymes that act on starches and sugars. This sodium car-
bonate (and other alkalis from the pancreatic fluid) combine with
part of the fats, forming soaps, which are soluble and are thus
absorbed.
The Liver. The liver is the largest gland in the body. It is
located between the diaphragm and stomach, thus being the upper-
most of the abdominal organs. The secretion of the liver is called
bile and is a thick brown liquid, of which about one quart is
produced daily. Bile has several important functions, as
follows:
1. Bile is, itself, a waste substance, removed from the blood.
2. It aids in digestion and absorption of fats.
3. It stimulates the action of the intestine.
4. It tends to prevent decay of intestinal contents.
374
BIOLOGY FOR BEGINNERS
ABSORPTION
The chief digestive action of the bile is on the fats which it makes
into a milk-like emulsion to be absorbed by the lacteals. If it is
prevented from entering the intestine, over half of the fats eaten
are not absorbed.
Another important function of the liver is the storage of excess
carbohydrate food, in the form of glycogen or liver starch which
the body may draw upon as a source of energy in emergencies. The
liver, then, excretes waste, secretes a digestive fluid, and stores food.
Pancreas. Lying between the lower side of the stomach and
the first fold of the intestine is the pancreas, whose secretion is by
far the most important in pro-
ducing the chemical changes
of digestion. The pancreatic
fluid is strongly alkaline, and
contains three enzymes:
trypsin, amylopsin, and steap-
sin.
The trypsin resembles pep-
sin and completes the digestion
of the proteids, changing them
into soluble peptones. The
amylopsin (like the ptyalin of
saliva) changes starch to sugar,
while the steapsin changes fats
to fatty acids, soluble soaps,
and glycerin, all of which are
easily absorbed.
FIG. 121. Chart showing process The pancreatic fluid thus
of absorption. completes the digestion of food
after it has undergone the pre-
paratory steps of (1) cooking, (2) chewing, (3) salivary digestion,
(4) gastric separation, (5) gastric digestion.
Absorption and Assimilation. The general purpose of digestion
is to put the foods in a soluble form so that they may pass through
the body's membranes by osmosis.
Absorption is the name given to the passage of digested food
NUTRITION 375
materials from the digestive tract to the blood. However, absorp-
tion in a living animal is not merely a mechanical " soaking up "
of prepared foods, but other changes take place, as the products of
digestion enter the circulation.
Absorption may take place (1) directly into the blood capillaries
which richly supply the walls of the stomach and intestine or
(2) indirectly, by way of the lymph capillaries of the villi (lacteals)
which eventually empty into the blood circulation also.
The capillaries of the gastric vein in the stomach walls absorb
some water, a little digested proteid, and still less sugar, but the
principal region of absorption is in the villi of the small intestine.
Here the thin walls and enormous surface bring the digested foods
close to the blood and lymph capillaries. Peptones, sugars and
fatty acids, salts and water are passed into the blood stream, while
the fats that have been emulsified are taken up by the lymph capil-
laries (lacteals) and carried by the lymphatic circulation to the
thoracic duct and finally emptied into the general circulation,
near the left jugular vein.
Assimilation. All the steps of digestion and absorption lead to
the final process of assimilation, which either builds up the cells
or supplies them with energy. For this purpose the blood carries
the absorbed foods to the tissues. These foods pass as lymph
(by osmosis) from the capillaries to the lymph spaces which sur-
round every living cell, and there the assimilation occurs. Every
cell of the body is practically an island, bathed on every side by
lymph, which brings from the blood the digested food stuffs (and
oxygen as well) and removes to the blood stream the waste matters
produced by the cells' activities.
Nutrition. All these processes by which food is obtained, pre-
pared, and built into tissues, are grouped together as nutrition
and include:
1. Food-getting, selection, and preparation.
2. Digestion .which mainly goes on in mouth, stomach, and
intestines.
3. Absorption which occurs principally in the small intestine
and stomach, by means of the blood capillaries and lacteals.
376
BIOLOGY FOR BEGINNERS
J!
O
bo as i; ex
2 S 58
1
-
fe PH C/3 C/2 ^ fe
In 3
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M WPn
NUTRITION 377
4. Assimilation which takes place wherever there is a living
cell to be nourished.
Attention should be called to the important part played by
osmosis in all these processes. It is concerned in the secretion of
all digestive fluids; in the absorption of digested foods through
the walls of the capillaries and lacteals, and in the passage of these
same foods outward from the capillaries, as lymph, in assimilation.
COLLATERAL READING
The Body at Work, Gulick, pp. 149-172; Civic Biology Hunter, pp.
296-312; Human Mechanism, Hough and Sedgwick, pp. 89-131; Studies
in Physiology, Peabody, pp. 75-166; Elementary Physiology, Huxley,
pp. 249-303; Applied Physiology, Overton, pp. 51-73; Physiology for Be-
ginners, Foster and Shore, pp. 128-156; The Human Body, Martin, pp.
106-146; General Physiology, Eddy, pp. 90-158; Physiology Textbook,
Colton, pp. 194-231; Human Body and Health, Davidson, pp, 76-105;
High School Physiology, Hughes, pp. 87-142.
SUMMARY
Digestive Changes.
1. Making food soluble (for osmosis).
2. Changing food chemically (for assimilation).
3. Changes caused by
(a) Mechanical action of teeth and stomach.
(b) Chemical action of fluids, enzymes, ferments.
Digestive organs (cf. with other animals).
1. Mouth
2. Gullet and stomach.
3. Intestine.
Mouth.
Functions in digestion.
1. Mechanical (chewing).
2. Chemical (saliva).
Openings and organs.
1. Nasal openings (2), where, how protected, into what.
2. Eustachian tubes (2), where, how protected, into what.
3. Trachea (relation of epiglottis and tongue).
4. Gullet.
5. Hard and soft palate.
6. Tonsils, adenoids.
378
BIOLOGY FOR BEGINNERS
Tongue.
Structure, size, position in mouth.
Functions.
1. Taste (what use for taste, where located).
2. Aid in chewing. Aid in swallowing.
3. Cleaning teeth.
4. Speech.
Teeth.
; Parts. Crown, neck, root (make diagram).
Structure.
1. Enamel (structure and function).
2. Dentine (structure and function).
3. Pulp region, nerves, and blood supply (why each).
Kinds:
Number
Name
Structure
Function
1st
2nd
Incisors
8
8
Canines
4
4
Premolars
8
Molars
8
12
Why two sets of teeth?
How does the change take place?
Special tooth adaptations in other animals,
Glands in general.
Definition.
Parts, secreting cells and ducts, blood and nerve supply.
Various degrees of complexity.
Salivary glands.
1. Parotid (where located, duct opening), mumps.
2. Sub-maxillary.
3. Sub-lingual.
Saliva.
Composition, alkaline, watery, three pints daily, ptyalin.
Functions.
1. Aids in tasting food (solution).
2. Aids in swallowing.
3. Stimulates gastric glands (alkali vs. acid).
4. Ptyalin acts on starches slightly.
Digestive changes in the mouth.
1. Food mechanically crushed.
2. Moistened for taste and swallowing.
3. Some starch changed to sugar.
4. Slight absorption of water, sugar
NUTRITION 379
etc.
Stomach.
Location.
Shape and size.
Functions.
1. Storage (why, what homologous organs).
2. Further separation of food particles.
3. Digestion of proteids by means of pepsin.
4. Coagulation of milk casein.
Gastric fluid.
1. From gastric (simple) glands, acid glands.
2. Amount, secretion aided by saliva if well mixed.
3. Composition ' Function
Hydrochloric acid Neutralize saliva, aid pepsin.
Pepsin Proteid to peptone.
Dissolves connective tissue.
Exposes more surface for digestion.
Rennin Coagulates milk proteid (casein).
Composition of chyme.
1. All fats unchanged.
2. Most carbohydrates (what exception?).
3. Much unchanged proteid.
4. Un-absorbed peptones, sugars, water, etc.
Intestine.
Pylorus, location and function.
Parts, small, large, colon, rectum, etc. (need not learn).
Appendix (lower right side).
Adaptations for increase of surface' (for osmosis for absorption).
Length, 25 ft., much coiled.
Walls in-folded.
Villi (each with blood vessels and lacteals).
Surface increased five times, twice area of skin.
Muscular intestinal walls.
Muscles involuntary.
Keep food moving along.
Mix food with fluids and crush it.
Very important in digestion.
Glands.
Intestinal.
Small, simple, numerous, in the intestine wall lining.
Secretion, alkaline; soda carbonate; sugar ferment.
Function, saponify fats, act on sugar somewhat.
Liver.
Largest gland, uppermost in viscera, over stomach.
Bile, thick, brown, one quart daily.
380
BIOLOGY FOR BEGINNERS
Functions, waste.
Aids digestion and absorption of fats.
Stimulates intestinal action.
Antiseptic action.
General functions.
Excretion of waste.
Secretion of a digestive fluid.
Storage of sugar excess as glycogen (why?).
Pancreas, location.
Fluid, abundant, alkaline.
Composition.
Ferment changes [to]
Amylopsin starch
Trypsin proteid
Steapsin fats
soluble
sugar
peptone.
fat acids, soaps, glyc-
erin.
Preparatory steps in nutrition.
Food-getting, cooking, chewing.
Salivary digestion, gastric digestion (further breaking up).
Intestinal digestion (most important).
What processes are these steps a preparation for?
Absorption.
What is the general purpose of digestion?
What is the process on which absorption is based?
Absorption is the passage of food from digestive tract to blood.
May take place,
1. Directly into capillaries in stomach and intestine walls.
2. Via lymph capillaries (lacteals) in villi.
Absorbing organs
Where
What absorbed
Where emptied
Gastric capillaries
In stomach walls
Water
Peptones
Sugar
General circulation
via gastric vein
Intestinal capillaries
In villi
Peptones
Sugars
Fatty acids
Water, salts
General circulation
via mesenteric
vein
Lacteals or lymph
capillaries
In villi
Emulsified fats
Thoracic duct to
left jugular vein
Assimilation.
Meaning of word.
Definition.
NUTRITION 381
Course of digested food.
Digestive organs to
Blood stream (osmosis).
Through capillary walls.
Into lymph spaces (osmosis).
Built into cell substance.
Blood transports food, etc., to tissues via capillaries.
Lymph transports foods, etc., to cells after leaving the capillaries.
Nutritive processes Where performed.
1. Food-getting, preparation
2. Digestion. Mouth, stomach, intestine.
3. Absorption. Stomach, small intestine by capil-
laries and lacteals.
4. Assimilation. In all living cells.
CHAPTER XXXIX
RESPIRATION
Vocabulary
Lymph, the liquid part of the blood, in contact with cells.
Pleural membranes, a double membrane covering lungs.
Intermittent, not continuous.
Depression, lowering.
Haemoglobin, the red, oxygen-carrying part of the blood.
Respiration is the process by which each cell of the body takes
in oxygen and gives off carbon dioxide and water. It is tissue oxi-
dation. The breathing movements, which renew the air in the lungs,
and the circulation of blood, which is the means of transportation
between lungs and tissues, are merely helps in the real process of
respiration which goes on in every cell of the body.
Need of Circulation. These breathing and circulatory processes
are required because of the distance of the living cells from the
outer air and merely serve to keep the lymph supplied with oxygen
and freed from waste. It is between the lymph and each living cell,
that respiration actually goes on.
The organs generally associated with respiration, such as the
lungs, trachea, etc., are really concerned with supplying oxygen to
the blood and removing wastes. No more actual respiration (cell
oxidation) goes on in the lungs, than in any other active tissue,
but it is in the lungs that the haemoglobin of the blood receives its
load of oxygen and unloads its carbon dioxide and water.
Development of Respiration. Respiration in the protozoa took
place by direct contact of each cell with the air dissolved in the
water. In the worms the blood circulated in the skin and obtained
its oxygen direct from the air. In still higher forms, like crayfish
or fish, gills were developed with great extent of surface to absorb
382
RESPIRATION
383
the dissolved oxygen in the water. Insects took their air directly
into the tissues and blood by way of their numerous complicated
air tubes and so got along with a simple circulation. In the birds
and mammals this is reversed and the air comes to one place only
FIG. 122. Bronchi and lungs, posterior view, showing position of heart.
1, 1, summit of lungs; 2, 2, base of lungs; 3, trachea; 4, right bronchus; 5,
branch to upper lobe of lung; 6, branch to lower lobe; 7, left bronchus; 8,
branch to upper lobe; 9, branch to lower lobe; 10, left branch of pulmonary
artery; 11, right branch; 12, left auricle of heart; 13, left superior pulmonary
vein; 14, left inferior pulmonary vein; 15, right superior pulmonary vein;
16, right inferior pulmonary vein; 17, inferior vena cava; 18, left auricle of
heart; 19, right ventricle. (After Sappey.) From Kellogg.
(the lungs), while a complex circulation carries the oxygen to all
parts of the body.
Organs of Breathing. The organs concerned with breathing
motions can be placed in two groups, (1) those concerned with
holding and carrying the air, and (2) those which change the size
of the chest cavity, causing the air to circulate.
384 BIOLOGY FOR BEGINNERS
Nose. The air system begins with the nose, which is adapted as
an entrance for air,
(1) By the hairs and moist mucus to catch dust.
(2) By the sense of smell to guard against bad air.
(3) By its long moist passages which warm and moisten the air.
The mouth was not intended as a breathing organ except in
emergencies, and habitual mouth breathers lose all the advantages
mentioned above.
Trachea. Passing from the nasal cavity to the back of the mouth,
the air enters the trachea. This is a large tube which opens into
the mouth at the back of the tongue, so that the food passes over
it when we swallow. Its upper end is therefore protected by the"
base of the tongue and by a sort of self-acting lid (epiglottis)
which closes when food is passing on its way to the gullet, which is
further back in the mouth cavity. The enlarged upper end of the
trachea is the larynx in which are situated the vocal (speech) or-
gans, and which may be seen externally as the " Adam's apple."
The walls of the trachea are supported by rings of cartilage, which
hold it open for free passage of air.
With the hand on the larynx, swallow a mouthful of food and
notice two things, (1) how it rises and contracts inward to meet
the epiglottis, (2) how the very base of the tongue moves back and
down over the opening. Both these movements are to allow the
food to pass over the top of the trachea and into the gullet.
Bronchi and Air Cells. At its lower end the trachea divides into
two branches (bronchi) extending to each lung, where they sub-
divide into countless minute bronchial tubes which finally terminate
in very thin-walled, elastic air cells of which the lung tissue is
largely made. Thus there is provided in one organ (the lungs)
enough surface for air osmosis to supply (via blood) the needs of
the millions of body cells that have no direct access to air.
The Lungs. The lungs fill all the body cavity from the shoulders
to the diaphragm except the space occupied by the heart and blood
vessels. They are very spongy, consisting mainly of the air tubes
and cells and a very extensive network of blood vessels and capil-
laries, all held together by connective tissue and covered on the
RESPIRATION
385
outside by a double (pleura!) membrane. Their shape is the same
as the chest cavity, the upper part of which they completely fill.
Between them is the heart and below is the diaphragm which
is a muscular partition curving upward so that the lower lung
surface is sharply concave. The pleura] membrane that covers
the lungs and lines the chest cavity is constantly moist and per-
mits free motion of the lungs, within the chest, for breathing.
?ui.noMATiy A fir.
TUBE
T~o PULMOMAHY Vei
-BLOOD
Fid. 123. Exchanges between blood and air in lungs. After Colton.
Pleurisy is an inflamed condition of these membranes which makes
breathing very painful and difficult.
Blood Supply. The pulmonary artery brings the dark (de-oxy-
genated) blood to the lungs, where it divides into an extensive
network of capillaries, completely surrounding each air cell. The
thin walls of both cell and capillary make easy the osmotic ex-
change of oxygen from air to blood, and of carbon dioxide and
water from blood to air, so that the pulmonary vein returns its
blood to the heart, purified and laden with oxygen for the tissues.
386
BIOLOGY FOR BEGINNERS
Air Capacity. The total capacity of the lungs is about 350 cubic
inches of which our ordinary breathing utilizes but about 30. By
extra effort we can take in and force out an extra hundred or more,
while there is about another hundred cubic inches which we can-
not get out at any one breath. When we realize the great import-
ance of oxygen to the tissues these facts ought to be an argument
for fresh air, deep breathing, and loose clothing. We use little
RESP.RAT.OH CHART. enough of our lungs, at
best, so every effort ought
, to be made to increase
their activity. The one-
third of the air which can-
not be forced out of the
lungs provides for continu-
ous osmosis. Breathing is
an intermittent process but
the blood's supply of air
has to be continuous,
hence the need for some
air always in the lungs.
A reason for deep breath-
(30
FIG. 124. Compare capacity utilized by
ordinary breathing with that of deep
breathing.
ing is to mix as much
fresh air with this " resi-
dual air " as is possible
at each breath.
Breathing Movements; The process of getting air into and
out from the lungs is rather complicated and consists of two sets
of operations, inspiration (breathing in) and expiration (breath-
ing out) which we somewhat wrongly call the acts of respira-
tion.
Inspiration: The Diaphragm. The chief breathing organ is the
diaphragm, a muscle (not a mere partition) which extends across
the body, curving upward, as a floor to the lung cavity. When
its muscles contract it tends to pull down straighter across the body,
thus giving the lungs more room, but compressing the abdominal
organs beneath it at the same time.
RESPIRATION
387
Rib Muscles. Second in importance are muscles between the
ribs which lift them up and outward, thus enlarging the lung cavity,
but, which is more important, bending the elastic rib cartilages,
which tend to spring the ribs back in place.
Air Pressure. The third important factor in inspiration is the
pressure of the outside air
which rushes in to occupy
the extra space thus pro-
vided and by so doing,
expands the elastic tissue
of the lungs. Inspiration,
then, consists of (1) de-
pression of diaphragm and
compression of abdominal
organs, (2) raising the
ribs and bending the rib
cartilages, (3) air pressure,
expanding the lung tissue.
Expiration. Expiration
is merely the springing
back of the organs that
have been compressed by
the movements of inspira-
tion. It consists of the
following steps: (1) the
elastic reaction of the com-
pressed abdominal organs,
(2) the springing back of
the rib cartilages, (3) the
I
FIG. 125. Lower half of thorax with
dorsal and lumbar vertebrae. A, sixth
dorsal vertebra; Ao, aorta; D, (lower)
diaphragm; D, (upper) aorta passing
through diaphragm; /, intercostal muscles;
O, cesophagus; IV, opening in diaphragm
for vena cava ascending; T T, tendons of
right and left crura attaching diaphragm
to 3rd and 4th lumbar vertebrae. (After
Allen Thomson.) From Kellogg.
contraction of the elastic
lung tissue.
All of these tend to make the lung capacity less and force out
the air, against its own pressure. The change of position of the ribs,
diaphragm and abdominal organs can be felt in our own bodies.
Rate of Breathing. This double process takes place from 16 to
24 times per minute, depending upon activity, position, and age.
388
BIOLOGY FOR BEGINNERS
The more oxygen the tissues need, the more rapidly the lungs have
to operate to supply the blood with it, to be carried to the tissues.
Air Changes in Breathing. Air contains only about 20 per cent
of oxygen. Of this, only about a quarter is absorbed in the lungs
by the haemoglobin of the blood. In the circulation, the haemo-
globin can give out only about one-half the oxygen it contains, so,
FIG. 126. Diagram to show the changes in the sternum, diaphragm, and
abdominal wall in respiration. A, inspiration; B, expiration; Tr, trachea;
St, sternum; D, diaphragm; Ab, abdominal wall. The shaded part is to indi-
cate the stationary air. From Martin- Fitz.
unless we breath deeply and keep our breathing apparatus in
healthy working order, the tissues may receive too little oxygen.
Since oxidation (union of oxygen with tissue) is the only source
of life energy, this matter is of very great importance.
Expired air loses about one-fourth of its oxygen, but receives
100 times as much carbon dioxide as it had when taken in, also a
RESPIRATION 389
large amount of water vapor and heat, together with a very little
organic waste matter.
Ventilation. The fact that air in a " close " room becomes un-
fit to breathe, is due mainly to the excess moisture and heat, and
not to the carbon dioxide, or lack of oxygen, as was formerly sup-
posed.
The carbon dioxide in the expired air is produced by the oxygen
from the lymph uniting with the carbon of the tissues. The water
is produced by oxidation of their hydrogen, and the heat is the
result of both oxidation processes. We use annually about 10,000
pounds of air (28.7 pounds per day) from which we take about
650 pounds of oxygen and give off about 730 pounds of carbon
dioxide. We breathe out about 9 ounces of water every day, which
would make half a pint in liquid form. These figures, while not
worth remembering, will give some idea of the amount of work
done by the respiratory organs and their importance to our life.
Proper ventilation is concerned, not only with supplying " fresh "
air, but with the removal of water vapor, heat, and least of all,
carbon dioxide. Here circulation of air in a room will often relieve
breathing conditions, by lowering the body temperature and re-
moving excess water vapor from the vicinity of the body. We
usually have oxygen enough in any ordinary air supply, and seldom
does the carbon dioxide cause trouble, but very often the tem-
perature and amount of water vapor produce unpleasant and even
dangerous results.
COLLATERAL READING
Physiology Textbook, Colton, pp. 105-137; General Physiology, Eddy,
pp. 312-339; Applied Physiology, Overton, pp. 206-219; Human Mecha-
nism, Hough and Sedgwick, pp. 162-176; Human Body and Health, Davison,
pp. 132-162; Studies in Physiology, Peabody, pp. 209-231; Human Body,
Martin, pp. 193-214; Elementary Physiology, Huxley, pp. 148-191; High
School Physiology, Hughes, pp. 179-196;
390 BIOLOGY FOR BEGINNERS
SUMMARY
Definition, Respiration is oxidation in the tissues.
Aided by " breathing movements " (oxygen from air to blood).
Circulation (oxygen from blood, to lymph, to tissues).
Lungs supply osmotic surface for all cells in one place.
Circulation transports oxygen to interior tissues.
Development in lower animals.
Protozoa, each cell in contact with dissolved oxygen.
Worms,- blood in contact with air in skin.
Crayfish, blood in contact with dissolved air (gills).
Insect, air brought to blood and tissues in tubes (tracheae).
Fish, blood in contact with dissolved air (gills).
Other vertebrates, blood aerated in lungs.
Organs of breathing.
1. Nose, adaptations, hairs to collect dust.
Smell, to detect bad air.
Moistening mucous membranes.
2. Trachea.
Connects mouth and lungs.
Opens back of tongue.
Stiffened by cartilage, larynx with vocal organs.
Protected by
Epiglottis.
Movements of tongue in swallowing.
Movements of larynx in swallowing.
Mucous glands and cilia.
3. Bronchi.
Two branches of trachea to lungs.
Each with many small branches.
Air cells at end of branches, vastly numerous.
4. Lungs.
Location, shape, boundaries.
Structure.
Air tubes and cells . . . surface for osmosis.
Capillaries . . . blood for transfer
Pleural membranes . . . moist for easy motion.
Blood supply.
Pulmonary arteries . . . dark, deoxygenated blood.
Pulmonary veins . . . lighter, oxygenated blood.
Capacity.
350 cu. in. total.
250 cu. in. possibly used.
30 cu. in. usually used in ordinary breath.
100 cu. in. residual air. Reason for "residual air."
RESPIRATION 391
Breathing movements
Inspiration (increases chest cavity).
(1) Diaphragm contracts and lowers (vs. abdominal organs).
(2) Rib muscles raise ribs (vs. elastic cartilage).
(3) Air pressure expands cells (vs. elastic walls).
Expiration (decreases chest cavity).
(1) Abdominal organs push diaphragm upward.
(2) Rib cartilages spring back.
(3) Lung cells contract.
Rate, 16-24 per minute, depends on age, activity, etc.
Air changes in breathing.
Air contains
Before inspiration After inspiration
79 % Nitrogen 79 %
20.96% Oxygen 16.02%
.04 % Carbon dioxide 4.38 %
traces Water vapor .60 %
little Heat much more,
none Organic impurities considerable.
Blood changes in lungs.
Just the reverse of the above.
Blood gains 4 to 5 % oxygen.
Blood loses about same amount carbon dioxide.
Blood loses water vapor, heat, organic waste.
Ventilation.
Large amount of air used.
Importance of oxidation.
Need for ventilation to supply oxygen.
to remove heat, water vapor, carbon dioxide.
CHAPTER XL
CIRCULATION
Vocabulary
Transportation, carrying from place to place.
Plasma, liquid portion of blood tissue.
Auricles, upper, receiving chambers of the heart.
Ventricles, lower, sending chambers of the heart.
The function of any circulatory system is transportation; the
blood is the carrier, the blood vessels are the roads, and the heart
is the motive power. Digested food is carried from the digestive
organs to the tissues, oxygen from the lungs to the tissues, waste
matters from the tissues to the lungs, skin, and kidneys, and in-
ternal secretions from their glands to places where they are used.
Development of Circulation. A circulatory system is not found
in very simple animals like protozoa, sponges, and hydra, because
they have so few cells that each can obtain its own food and oxy-
gen and throw off its waste, without the need of a set of organs for
carrying them. We do not find a transportation system within
our own home, nor even in a small village, for each individual
does his own carrying. In larger cities street railways are neces-
sary, while to care for a whole state, numerous railroads and canals
are required.
It is the same in animal structure. The simple forms have no
circulatory transportation; in higher types there are simple cir-
culatory organs (earthworm) . In still more complicated organisms,
a heart and blood vessels are required (crayfish), while in the ver-
tebrates, especially birds and mammals with their very highly
specialized organs, there is needed a very complete and complex
transportation system, in order that each cell may be supplied.
Now we may carry our comparison between cell functions and
life on Crusoe's island a step further and find another result of
392
CIRCULATION
393
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394
BIOLOGY FOR BEGINNERS
OfAGRAW OF CIRCULATION IN
MAMMALS
VEINS
ARTERIES
fpulmone
specialization. We will recall the likeness between the one-celled
protozoan and Crusoe. He had to perform for himself all the
functions of life, such as preparing his food, making his clothes
and building his home. The higher forms of life are like small
communities where one
man may build the
houses or another specia-
lize in making clothes.
This would correspond
to the first steps- in
specialization, as shown
by sponges, hydra, etc.
As the communities
grow, many men work
together at one trade to
supply all, and this
would illustrate the
grouping of specialized
cells into tissues, each
performing its function
for the whole animal
(earth worm). Then in
larger communities the
wants are more num-
erous, more groups of
men specialize in dif-
fent tato and supp.y
others at a distance with
their products. This is the stage represented by the higher animals,
where a transportation (circulatory) system is required. In man
this is accomplished by the blood, which is kept in motion by the
heart, and flows through arteries, veins, and capillaries.
The Blood. The blood is a fluid tissue constituting about T ^ of
the weight of the body. It consists of a liquid portion, calle'd the
plasma and solid portions, called the corpuscles or blood cells.
The plasma constitutes f the bulk of the blood and consists of
FIG. 127. Diagram showing circulation in
CIRCULATION
395
a liquid (serum) which carries the food and waste products, and a
proteid substance (fibrinogen), which when exposed to air aids in
forming a clot to stop bleeding. The corpuscles are of two sorts,
red and white; the former much more numerous, thus giving
the red color to the blood.
The red corpuscles are minute, disc-shaped, blood cells, so small
that ten million can be spread on a square inch, yet so numerous
FIG. 128. Blood corpuscles. A , magnified about 400 diameters. The red
corpuscles have arranged themselves in rouleaux; a, a, colorless corpuscles;
B, red corpuscles more magnified and seen in focus; , a red corpuscle slightly
out of focus. Near the right hand top corner is a red corpuscle seen in three-
quarter face, and at C one seen edgewise. F, G, H, I, white corpuscles highly
magnified. From Martin-Fitz.
that there are enough in the average body to form a row four times
around the equator. Their red color is due to a complex iron com-
pound (haemoglobin) which carries oxygen from the lungs to the
tissues. When laden with oxygen it is a bright red, but becomes
darker when the oxygen is removed, causing the difference in color
of the blood on going to and coming from the tissues.
The white corpuscles are really almost colorless and can change
396
BIOLOGY FOR BEGINNERS
their shape much like the amoeba. There are probably several
kinds and their functions differ, but seem to be concerned in aiding
the absorption of fats and in destroying disease germs in the blood.
They are formed in the lymph glands. They have the power to
penetrate the capillary walls and wander through the lymph spaces;
they collect at wounds and points of infection and oppose the at-
tack of disease germs.
Healing a Wound. In the healing of a cut there are several proc-
esses set at work by the blood. First, as the blood oozes out,
fibrinogen is exposed to the air, hardens to fibrin, entangles the
corpuscles, and the clot or scab forms. Then the blood supply is
automatically increased to bring extra white corpuscles on guard
to oppose infection; this causes the redness (inflammation). As
the fibrin forms, it contracts, causing the puckering of a scar and
as fast as new tissue is built, the clot or scab is shed. A slight
scratch or blister often lets only the plasma through, while a
" black and blue " bruise is in part due to breakage of capillary
walls and consequent clotting of blood under the skin.
Changes in Composition of Blood. The composition of the blood
is constantly changing as it receives and distributes its various
burdens. This is shown in the following table.
CHANGES IN COMPOSITION OF BLOOD
Blood loses
Blood receives
In all active tissues
Materials for growth, repair
and energy
Wastes of oxidation
Carbon dioxide and
water
Nitrogenous wastes
In walls of digestive
organs
Materials for making digestive
fluids and for growth, ac-
tivity, and repair of the di-
gestive organs
Digested nutrients
In the lungs
Carbon dioxide and water
Oxygen
In the kidneys and
skin
Water and urea
Carbon dioxide, etc.
CIRCULATION 397
Probably the blood is actually purest when leaving the kidneys,
though it is still dark colored, due to lack of oxygen. It is not
correct to speak of " dark blood " as always being " impure blood."
The Heart. The heart is a hollow, cone-shaped muscle, located
behind the breast bone, between the lungs, nearly on the center
line of the body; the point is downward and lies between the fifth
and sixth ribs a little to the left. Since the " beat " is strongest
near the tip it has given the idea that the whole heart is on the left
side, which is not true. The heart consists of two entirely separate
halves, right and left, each of which consists of a thin- walled auricle
and a thick muscular ventricle. The auricles act as reservoirs for
the incoming blood and permit a steady flow and rapid filling of
the ventricles. The ventricles, by alternate expansion and con-
traction, force the blood into the arteries and so around the body.
Between each auricle and its ventricle are valves which allow blood
to enter the ventricle but prevent its exit, except by the arteries,
and at the base of each artery are valves preventing the blood from
flowing back into the ventricles.
Action of Heart. The right auricle receives de-oxygenated blood
from the veins through which it has been collected from the whole
body. This passes through the valve into the right ventricle, which,
when it contracts, forces it to the lungs, via the pulmonary arteries.
In the lungs, the blood receives a new load of oxygen, unloads some
carbon dioxide and water, and returns via the pulmonary veins to
the left auricle. From here it passes through the valves into the
left ventricle and is thence forced out through the aorta to all parts
of the body. The ventricles contract and expand together so
there are two waves of blood sent out at each beat, one to the lungs
and one to the general circulation. While the ventricles are con-
tracting and forcing out their blood, both auricles have been filling
so there is no stop in the flow.
Rate of Beat. The rate of heart beat is normally 72 times per
minute in man; 80, in women; much higher in young children
and in very old persons, reaching the average at about twenty
years of age. Naturally, the amount of blood needed is affected
by exercise, temperature, food, excitement, pain, etc., and so all
398 BIOLOGY FOR BEGINNERS
these automatically change the rate of heart beat. When we run
upstairs (a bad habit, by the way) we use more energy, hence oxi-
dize more tissue, hence need more oxygen to be brought by the
blood, and produce more waste, which must be carried off, and the
heart has to work harder to meet this demand.
Blood Vessels. Arteries. All the vessels that carry blood away
from the heart are arteries regardless of whether they carry red
(oxygenated) or dark (de-oxygenated) blood. Arteries have elastic
muscular walls, and very smooth linings. Their function is to assist
and to regulate blood flow. Since they are elastic they expand
when blood is forced into them, and as the valves prevent it from
returning to the heart, their elastic contraction forces it to flow
on through the arteries and exerts pressure clear to the capillaries.
If it were not for this elasticity, which is greatest in the large
arteries, the circulation would be slow and unsteady and the ar-
teries themselves in danger of bursting under the sudden strain,
when the ventricles contract. In " hardening of the arteries "
this elasticity is lost and produces serious and usually fatal
results.
In general the arteries are protected by location beneath thick
muscles, but at the wrist and neck some large ones come near the
surface and this elastic wave of expansion can be felt, and is known
as the pulse.
The muscles in the artery walls perform the very important
function of regulating the amount of blood that reaches a given
organ. By a very complicated system of nerve control, these
muscles expand when more blood is required and contract when the
supply is not needed.
Capillaries. As the arteries leave the heart they divide again
and again, becoming smaller and thinner walled till they develop
into microscopic tubes with a wall of only one layer of cells. These
tiny blood vessels are the capillaries (" hair like ") and are so
numerous that they reach every living tissue of the body. Their
large area and thin walls permit osmosis to go on readily and it is
by way of osmosis from the capillaries that food actually reaches
the body cells. Absorption of food in the digestive tract and ex-
CIRCULATION
399
cretion of waste from tissues in lungs, skin, and kidneys are also
by way of these very important blood vessels.
FIG. 129. The lymphatic vessels. The thoracic duct occupies the middle
of the figure. It lies upon the spinal column, at the sides of which are seen
portions of the ribs (1). a, the receptacle of the chyle; b, the trunk of the
thoracic duct, opening at c into the junction of the left jugular (/) and sub-
clavian (g) veins as they unite into the left innominate vein, which has been
cut across to show the thoracic duct running behind it; d, lymphatic glands
placed in the lumbar regions; h, the superior vena cava formed by the junc-
tion of the right and left innominate veins. From Martin-Fitz.
Veins. On leaving an organ the capillaries unite to form veins,
which grow larger as they approach the heart, and always carry
400 BIOLOGY FOR BEGINNERS
blood toward this organ. Their walls are thinner than the arteries,
having little elastic or muscular tissue, but many of the larger ones
are provided with cup-like valves to prevent backward flow of
blood. Veins are often just beneath the skin and can be easily
seen on the back of the hand where the dark color of their blood is
conspicuous; enlargements show the location of the valves. Veins
have no pulse wave and the blood pressure is lower than in the
arteries. Except for the pulmonary veins, their blood is dark (de-
oxygenated) as compared with the redder, arterial blood. However,
this is of little use in deciding whether a wound has cut a vein or
artery, as on exposure to ah*, blood absorbs oxygen and brightens
in color.
Bleeding from an artery, if large enough to be serious, is in
pulse-like spurts, while the flow from veins is steady. This and
the location of the wound are the best means of distinguishing
the source of blood flow.
Lymph Circulation. A part of the blood plasma that diffuses
through the capillary walls into the spaces between the cells does
not return to the capillaries directly but is collected into the lymph
capillaries.
These tiny tubes connect all the lymph spaces together and unite
to form the lymph veins which eventually join to empty into the
blood stream near the left jugular (neck) vein. Thus, a part of the
plasma, instead of following the usual route (artery capillary
vein) may return as follows, artery capillary lymph space
lymph capillary lymph vein true vein. It is in the form
of this lymph that the blood actually nourishes the tissues and the
lymphatic circulation is just as necessary as that of the blood
as a whole.
Each cell of the body is practically an island surrounded by
lymph. This lymph has passed, by osmosis, through the capillary
walls, bearing in solution the digested food-stuffs from the ali-
mentary tract, and oxygen from the lungs.
These the cell uses in its life activities and throws off carbon
dioxide, water, and other wastes into the lymph, and thence into
the blood of the vein capillaries.
CIRCULATION 401
White corpuscles may pass through the walls of the capillaries
and thus get into the lymph spaces, from whence they may pass
out with the returning lymph, by way of the lymph capillaries,
to rejoin the blood, through the lymph system.
The lymph thus stands between the blood stream in the capil-
laries, and the living cells of the body. The blood leaves the heart
O
C. CtRAOH DtOflDE
F. FOOT3 //V SOLUTION'
IV. WASTE MATTER
conPusei.es
FIG. 130. Diagram to show relation between blood, lymph, and cells.
by one route, the arteries, and returns part way by two, namely
the veins and the lymph system. These unite before reaching the
heart again.
COLLATERAL READING
Civic Biology, Hunter, pp. 313-328; Studies "in Physiology, Peabody,
pp. 117-158; Elementary Physiology, Huxley, pp. 119-147; Applied
Physiology, Overton, pp. 156-191; Physiology for Beginners, Foster and
Shore, pp. 78-107; General Physiology, Eddy, pp. [159-203; Physiology
Textbook, Colton, pp. 48-104; Human Body and Health, Davison, pp. 106-
130; High School Physiology, Hughes, pp. 154-178.
SUMMARY
Function of circulatory system.
Transportation of food from digestive organs to tissues.
Transportation of oxygen from lungs to tissues.
Transportation of waste from tissues to lungs and kidneys.
Reasons for varying degrees of development.
Blood.
Composition. Plasma: (two-thirds bulk).
Serum, carrier of food and waste.
Fibrinogen, aids in forming clot.
402 BIOLOGY FOR BEGINNERS
Corpuscles: (one-third bulk).
Red, disc-shaped cells, minute, and numerous, contain haemoglobin
(oxygen carrier).
White, amoeboid, can penetrate tissues, destroy germs, help absorb
fats.
Blood and the healing of wounds.
1. Fibrinogen exposed, fibrin forms clot.
2. White corpuscles brought by extra blood supply.
3. New tissue built and scar forms.
Changes in blood composition. (See tabulation in text.)
Heart.
Shape, hollow, cone-shaped muscle.
Location, between lungs, behind breast bone, point to left.
Structure.
Auricles, thin walled, act as reservoirs, cause steady flow.
Ventricles, thick-walled, muscular, propel the blood.
Valves, at base of arteries and between auricles and ventricles, prevent
back flow of blood.
Action.
De-oxygenated blood from body, via caval veins flows to right auricle,
right ventricle, pulmonary artery, lungs.
Oxygenated blood from lungs returns via pulmonary vein to left
auricle, left ventricle, aorta, general body circulation.
Rate.
72-80 beats per minute.
Dependent on age, activity, state of mind, etc.
Arteries.
Carry blood from the heart.
Structure, smooth lining to permit easy blood flow.
Elastic tissue to allow for pressure and propel blood.
Muscular tissue to regulate blood supply.
Deeply placed for protection. Thick walled.
Veins.
Carry blood toward the heart.
Structure, smooth lining, pocket valves to prevent back flow.
Thin walled, and little elastic or muscle tissue.
Placed nearer the surface, no pulse wave.
Capillaries.
Connect arteries and veins.
Very thin, small, and numerous.
Provide surface for osmosis in nutrition, respiration, and excretion.
Lymph circulation.
Function.
Route.
CHAPTER XLI
EXCRETION
Vocabulary
Urine, the liquid excreted by the kidneys.
Urea, a nitrogenous substance in the urine, waste.
Duct, tube which carries excreted or secreted matter.
Excretion, throwing off of waste.
Secretion, production of useful substance by glands.
All the activities of the body require energy, whether in the mus-
cles, nerves, or glands. Energy implies oxidation, and oxidation
produces waste products which must be removed. The main
wastes of the body are carbon dioxide and water and nitrogenous
compounds (mainly urea) together with some mineral salts, chiefly
sodium chloride (common salt).
Organs of Excretion. The most important organs of excretion
are the kidneys and lungs; then come the intestine, liver, and last,
the skin which has other more important functions.
Kidneys. The kidneys are bean-shaped glands located near the
spine at the " small of the back." They are about two by four
inches in size and are usually imbedded in fat. Their internal
structure is too complicated for description here, but is perfectly
fitted for removing from the blood, urea, uric acid, other nitrogen
compounds, mineral salts, and water. Their blood supply is very
large and under high pressure, which is important in removal of
these wastes. As it leaves the kidneys in the renal veins, the blood
is actually purer than anywhere else in the body though it may still
be dark in color, due to lack of oxygen.
The ducts from the kidneys lead to the bladder where the urine
(which is constantly being excreted) is stored. The amount of
urine is usually about three pounds per day and the nitrogenous
403
404 BIOLOGY FOR BEGINNERS
wastes which it contains are of such character that if incompletely
removed, very serious diseases are sure to result.
Exposure to cold, drinking large quantities of water, and excess
of proteid food all tend to increase the amount of urine. As some
of the waste matters are not very soluble, it is a good thing to
*
FIG. 131. Section perpendicularly through skin, a, epidermis; b, pigmentary
layer of epidermis; c, papillary layer of dermis; d, dermis or true skin; e, fatty
tissue; /, g, h, sweat glands and duct; i, k, hair with its follicle and papilla;
I, sebaceous gland. (After Brubaker.) From Kellogg.
drink plenty of water to keep the kidneys well washed out. As a
rule we drink too little rather than too much.
The Lungs. The lungs are used as organs of excretion as well
as for the supply of oxygen, their wastes being carbon dioxide
mainly, together with considerable water and very little nitrog-
enous compounds.
EXCRETION 405
The Liver and Intestines. The liver and intestines are both
concerned with the removal of bile, a part of which is waste matter,
and the intestines also remove the unused food refuse, which, how-
ever is not strictly excretion.
The Skin. The skin excretes considerable water and only 1 per
cent of solid matter, mainly salts, and a very little urea. The
chief function of perspiration is to regulate the temperature of the
body.
Structure. While not primarily an organ of excretion, the struc- .
ture and functions of the skin may be discussed at this point.
The human skin is a much thicker and more important organ than
we usually suppose. When tanned into leather it resembles the
pig-skin cover of a foot ball.
It consists of an outer portion (epidermis) composed of many
layers of cells, the outer-most, dead, horny scales, the inner ones,
more active and larger. Its function is mainly protective and the
outer scales are constantly being rubbed off and replaced by new
from beneath. Where subject to much friction or pressure the epi-
dermis may grow to over a hundred cell layers in thickness, pro-
ducing the familiar callouses of hands and feet.
Hair, nails, and color cells are developed from the epidermal
layer in man. Scales, feathers, and claws are modified forms found
in other animals.
Beneath the epidermis is a thicker layer (the dermis) consist-
ing of tough fibrous connective tissue, richly supplied with blood
and lymph vessels, nerves, sweat, and oil glands.
Functions of the Skin. These include:
1. Protection from germ attack and mechanical injury.
2. Protection of inner tissues from drying. The skin, aided by
the oil glands, is nearly water proof, neither absorbing nor letting
out moisture, except at the sweat pores.
3. It is the location of most of our nerves of touch.
4. Excretion of sweat as a waste matter.
5. Excretion of sweat to regulate the temperature of the body.
This last statement needs explanation. Birds and mammals
are the only animals whose temperature does not change with
406 BIOLOGY FOR BEGINNERS
that of their surroundings. The rate of oxidation and hence the
production of heat varies even more than the outside temperature
and this means that a heat-regulating device is required.
Heat is required to evaporate water; therefore if moisture is
excreted on the surface of the skin, the body's heat is taken up in
evaporating it and consequently the skin is cooled. The blood
supply to the skin is great, the surface exposed for evaporation is
also large, and so by the use of the body heat to vaporize (dry off)
the perspiration, the blood, and hence the whole body, is cooled.
The greater our activity or the warmer the surrounding air,
the larger is the amount of perspiration, and hence the greater
cooling effect.
A complex system of nerve control .governs the blood supply
and gland activity of the skin, so that, mainly by its means our
temperature is kept at 98.5 degrees. The importance of this func-
tion of the skin is seen when we realize that a temperature of 8 or
10 degrees either above or below the normal is usually fatal.
COLLATERAL READING
Physiology Textbook, Colton, p. 381; General Physiology, Eddy, pp.
352-373; Applied Physiology, Overtoil, pp. 248-255; Human Mechansim,
Hough and Sedgwick, pp. 177-186; Human Body and Health, Davison,
pp. 175-190; Studies in Physiology, Peabody, pp. 232-252; Human Body,
Martin, pp. 215-229; Elementary Physiology, Huxley, pp. 193-247; High
School Physiology, Hughes, pp. 197-213.
SUMMARY
Waste, source, oxidation in tissues.
Kind, carbon dioxide, water, nitrogenous compounds, salts.
Organs of excretion.
1. Kidneys, location, small of back, near spine.
Size, two by four inches, bean shaped.
Blood supply large, high pressure.
Ducts connecting with bladder.
Remove water, urea, salts, etc. (3 Ib. daily).
2. Lungs.
Remove carbon dioxide, water, little nitrogenous waste.
3. Liver and intestines.
Remove bile and unused food stuff.
EXCRETION 407
4. Skin.
Removes water, salts, etc. (Not primarily excretory.)
Structure.
Epidermis, scale-like cells, loose.
Protective, callouses.
Modified as hair, nails, claws, horns, etc.
Dermis, fibrous cells.
Many blood and lymph capillaries.
Nerves, sweat and oil glands.
Functions.
Protection from germs.
Protection from injury.
Protection from drying of tissues.
Protection from water.
Sensation.
Excretion.
Temperature regulation.
Sweat excreted.
Evaporated by body heat.
Body therefore cooled.
CHAPTER XLII
THE NERVOUS SYSTEM
Vocabulary
Convolutions, irregular grooves in the surface of the cerebrum.
Voluntary, under control of the will.
Harmonize, to coordinate, to make to work together.
The brain is the one organ which in man is capable of greater
development than any other animal. No amount of training will
enable us to compete with the fish, bird, dog, or snake in speed,
strength, locomotion, or keenness of sense. Practically every
animal excels man in some way and the one thing that makes
man their superior is his greater intelligence, which means greater
brain development.
Despite this, we often devote more attention to other lines, in
which we cannot hope for really useful success, and leave to very
indifferent care the training of our one source of superiority.
While we cannot deal with the structure of the brain in detail,
the need of some controlling organ to regulate the complicated
functions of any animal's body is very apparent and we must
needs take up its study, if only very briefly.
Structure. The brain consists of three general regions, the
cerebrum, the cerebellum, and the spinal bulb. Connected with it
are the spinal cord and nerves which together with the brain com-
pose the central nervous system.
Cerebrum. The cerebrum constitutes about nine-tenths of the
brain; it occupies the upper part of the skull and is divided into
two halves or hemispheres. Its surface is deeply folded in ir-
regular grooves (convolutions) and consists of gray nerve cells,
while internally the bulk of its tissue is made up of white nerve
fibers.
408
THE NERVOUS SYSTEM
409
The vastly complex structure by which each cell is cross con-
nected to thousands of others, the
tree-like branching of the nerves, the
grouping in larger fibers and passage
from one part to another of the brain
and spinal cord, all will have to be
omitted. We know that it is the
most complicated organ in the world
but we are far from a complete
understanding of its structure, much
less its' mode of operation.
Experiment and disease have
shown that the cerebrum is the
center of intelligence, thought,
memory, will, and the emotions.
It is the region of conscious sensa-
tion, by which we perceive all that
goes on about us, and in it arise
the impulses which produce all our
voluntary motions.
Cerebellum. The cerebellum is
situated behind and below the cere-
brum, is much smaller, is not divi-
ded, and has shallower and more
regular convolutions. Its function is
mainly to regulate and harmonize
(coordinate) muscular action. This
is very essential. When we run, or FIG. 132. Central organs of the
skate, or walk, or swim, or throw a nervous system. F, TO, frontal,
temporal and occipital lobes of the
ball, we use nearly all of the five cere brum; C, cerebellum; p.pons
hundred muscles of our body, varolii; mo, medulla oblongata;
Each muscle fiber is controlled by a n ^~ ms : upper and lower limits of
* the spinal cord; CVII, 8th cervical
nerve; each nerve impulse must nerve; DXII> 12th dorsal nerve.
reach its muscle at the proper in- (Quain after Bourgery.) From
stant. When we stop to analyze the Kell gg-
simplest act and think how many muscles are made to work to-
410 BIOLOGY FOR BEGINNERS
gether in perfect harmony, we realize how important is this co-
ordination of muscular action by the cerebellum. Without it,
though the cerebrum might originate the impulse to do a certain
act, no regulated useful motion could result.
Medulla. The spinal bulb (medulla) is really an enlargement of
the spinal cord but is within the skull and closely attached to the
cerebellum. It is about the size of a walnut and is located at the
extreme base of the brain.
The spinal bulb is the center of control of respiration, circula-
tion, secretion, movements of digestive organs and of swallowing,
as well as other similar automatic and unconscious activities.
Naturally, death follows injury to this vitally important part of
the brain, though severe damage to the other parts may not be
fatal.
Spinal Cord. The spinal cord extends from the medulla through
the protective bony arch of each vertebra, down almost the whole
length of the spine, and from it branch the nerves that supply all
parts of the body, except those which spring from the brain directly.
The spinal cord is not merely a large nerve trunk, however, but is
the center of many involuntary muscular actions (reflex actions)
of the body and limbs. If we touch a hot stove, we do not have to
think to remove our hands. If something comes near an eye, we
do not have to depend on the brain to close the eye. Voluntary
action would take too long and injury would result before the brain
could have time to act, so all such reflex actions are centered in the
spinal cord and operate automatically but not unconsciously as do
the motions of the internal organs controlled by the medulla.
The spinal cord, then, has two functions:
(1) A connecting trunk between brain and other nerves.
(2) The center of reflex action.
Sympathetic System. On each side of the spinal column but
inside the body cavity are two rows of nerve ganglia which are
connected with each other and with the brain and spinal
cord.
From this double nerve chain extend branches to most of the
internal organs and to other ganglia located in the chest and ab-
THE NERVOUS SYSTEM
411
domen. The largest of these sympathetic ganglia is the solar
plexus, located just below the diaphragm, another is near the heart,
and a third low down in the abdomen.
The operation of the sympathetic system is not well understood
but it certainly controls the secretion of glands, the regulation of
blood supply in arteries, heart action, and probably many other
internal activities of which we are not conscious, but without which
we could not live.
The " sympathetic system " has nothing to do with " sympathy "
BRAIN - (MID-SECTION)
FIG. 133. Diagram of mid-section of human brain showing position of
important parts.
in its usual sense, but is so named since it seems to keep the in-
voluntary internal organs working in harmony, much as the cerebel-
lum coordinates the action of the voluntary organs.
It appears that our nervous system is capable of controlling
several kinds of action, for example:
1. Voluntary actions, originating in the cerebrum and co-
ordinated by cerebellum.
412 BIOLOGY FOR BEGINNERS
2. Involuntary and unconscious action of internal organs con-
trolled by medulla and sympathetic system.
3. Involuntary but conscious reflex actions controlled by the
spinal cord.
4. Actions, at first voluntary, that have become reflex (auto-
matic) by habit, like learning to walk.
Habit Formation. To accomplish a given act or thought, the
nerve impulse has to connect up various parts of the brain. At
first this is done with difficulty and we say we are " learning to
read " or to ride a bicycle or play a piano. However, repeated
voluntary acts soon make their proper nerve connections easier,,
as if a path were being worn in the brain along which the impulses
travel with greater and greater ease.
If we continue doing a certain act or thinking a certain way often
enough, it becomes the easiest way to act or to think, and we say
we have " acquired the habit." If we look up the derivation of
that word, habit, we find that it comes from " habeo," meaning to
have or hold. So instead of our getting the habit, as we say, the
habit has " got "us.
It is a serious thing to think of, for our whole life is a complex
mass of habits, things which hold us, acts and thoughts that
do themselves, and which we " just can't help." How careful we
should be that those brain paths are the best arranged so that
habits of thought shall be prompt and accurate. How watchful
we should be that only good and helpful paths be followed, for,
whether we wish it or not, the habit will get and hold us. It is only
too true that " As a man thinketh . . . so is he."
" 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 realize 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-little scar. The drunken Rip Van Winkle,
in Jefferson's play, excuses himself for every fresh dereliction by
THE NERVOUS SYSTEM 413
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 literalness, 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 com-
petent ones of his generation, in whatever pursuit he may have
singled out." James, Psychology.
COLLATERAL READING
Physiology Textbook, Colton, pp. 254-298; General Physiology, Eddy,
pp. 382-428; Applied Physiology, Overton, pp. 266-275; Human Mecha-
nism, Hough and Sedgwick, pp. 266-288; Human Body and Health, Davi-
son, pp. 215-236; Studies in Physiology, Peabody, pp. 253-290; Human
Body, Martin, pp. 230-262; Elementary . Physiology, Huxley, pp. 475-
551; High School Physiology, Hughes, pp. 214-234.
SUMMARY
Reason for Special Training of the Brain.
General Function, Control.
Parts of Nervous System.
1. Brain.
Cerebrum, location, size, shape, surface, character of substance.
Functions, intelligence, will, thought, sensation, voluntary
motion.
Cerebellum, location, size, surface.
Function, muscular coordination, for voluntary acts.
Medulla (spinal bulb), location, size.
Function, control of respiration, circulation, etc.
2. Spinal cord, location (cf. spinal column).
Functions, nerve connection.
Reflex control.
414
BIOLOGY FOR BEGINNERS
3. Nerves, to receive sensation, and transmit motion impulses.
4. Sympathetic system, location.
Structure, plexuses (solar, cardiac, abdominal).
Function, coordinates involuntary actions.
Nervous system controls
by means of
examples
1. Voluntary actions
2. Involuntary actions (un-
conscious)
3. Involuntary reflex (con-
scious)
4. Automatic actions
Cerebrum
Cerebellum
Medulla
Sympathetic system
Spinal cord
Whole system
CHAPTER XLIII
THE SENSE ORGANS
Vocabulary
Irritability, response of simple organs to environment.
Papillae, minute projections supplied with nerve endings.
Pigment, color substance.
Concentrate, to bring to one point, to focus.
Competent, able.
The chief function of the nervous system mentioned in the pre-
vious chapter was that of control. It has another equally im-
portant use, namely to keep us in touch with our surroundings by
what we call sensation.
Irritability. All living things respond more or less to their en-
vironment. Plants react to light, moisture, contact, and gravita-
tion, and thus have a very simple sort of sensation, usually called
" irritability." These responses are sufficient for their needs, as
our experiments have shown, and enable plants to reach food and
water supplies, to turn leaves toward light, to climb by means of
tendrils and to perform certain movements concerned in pollena-
tion and seed dispersal.
Touch. Even the simplest animals are affected by actual con-
tact with surroundings. The amceba recoils from hard or hot
particles, absorbs food when in contact with it, and thus may be
said to exhibit a primitive sense of touch.
In higher forms, the whole body surface possesses this sense
more or less. It is often especially developed in tentacles, hairs,
or papillae in various animals. In man the sense of touch is com-
mon to all parts of the skin, especially the finger tips, forehead, and
tongue. The human skin also possesses special nerves that receive
temperature, pressure, and pain sensations. If we gently touch
415
416 BIOLOGY FOR BEGINNERS
different places on the back of the hand with a pencil point, some
spots will feel warm and others cold, due to the presence or absence
of these temperature nerves.
Taste. All animals seem to prefer some foods and reject others.
We have to assume a sort of taste sense to account for this. To be
tasted, a substance has to be in solution and in contact with certain
organs near the mouth. The mouth parts, palpi and tongue are
the usual taste organs, and in man the different parts of the tongue
are sensitive to different tastes. The back part responds only to
bitter, the tip to sweet, the sides to sour, and the whole surface to
salty flavors. Much that we attribute to taste is really due to the
sense of smell; if eyes and nose are closed one can hardly dis-
tinguish between an apple, onion, or raw potato. Taste enables
animals to judge of foods, stimulates the flow of digestive fluids,
and in aquatic forms may give information as to their location
in the water.
Smell. Both touch and taste require the substance to be in
actual contact if it is perceived. Smell reaches a little farther
away and enables animals to detect substances in the form of
vapor or dilute solution, even though at a distance.
The organs of smell are sometimes hairs, often antennae, while
vertebrates have some sort of a " nose." They are usually near
the food-getting organs, and in air breathers, are associated with
the inlet to the lungs. Primarily the sense of smell is used to judge
of food and air supply but in many cases it is also useful in finding
food, detecting enemies, and locating mates. It is little developed
in aquatic animals but very keen in insects, carnivora, and most
ungulates.
Hearing. In contrast to the three senses mentioned above,
hearing puts us in touch with our surroundings through the me-
dium of sound waves conveyed by air or water. This brings within
range of our consciousness things at a much greater distance and
is the chief avenue of communication among all higher animals,
most of which possess some form of sound-producing organs.
The simplest ears in worms, molluscs, and crustaceans consist
of mere sacs lined with nerve endings. In insects the sacs are
THE SENSE ORGANS
417
covered with a tympanum or drum membrane, and possibly the
antennae are sensitive to sound vibrations as well. Ear organs
may be located on legs, abdomen, antennae, and head in various
animals.
Structure of the Human Ear. The vertebrate ear is a wonder-
fully complicated organ, consisting of an external ear which opens
Auditory
nerve
FIG. 134.
Basilar membrane
Eustachian tube
Semi-diagrammatic section through the right ear.
(After Martin.) From Kellogg.
into an auditory canal embedded in the skull. This canal is closed
at its inner end by the tympanic membrane, which separates it
from the middle ear.
The middle ear connects with the throat by way of the eusta-
chian tube which serves to equalize the air pressure on both sides
of the drum and thus prevents breakage, while permitting free
vibration. Across the middle ear extends a chain of tiny bones
which connects the tympanic membrane with a somewhat similar
membrane in the wall of the inner ear.
The internal ear consists of two general parts. The cochlea is a
cavity in the skull shaped like a snail shell, filled with a liquid and
418 BIOLOGY FOR BEGINNERS
lined with a complicated set of nerve endings, which receive the
sound impressions. The semicircular canals, three in number, are
little loop-shaped tubes each at right angles to the other, and
have to do with maintaining the balance of the body.
How We Hear. When a person speaks to you, he starts certain
air waves which are gathered in by the external ear, and conveyed
to the tympanum, which is thus made to vibrate. By means of the
bones of the middle ear, this vibration is communicated to the
fluid in the inner ear, and this in turn acts upon the nerve endings
of the cochlea. This disturbance of the nerve endings is trans-
mitted to the brain by way of the auditory nerves and we hear the
sound of words.
The human ear can distinguish vibrations varying from sixteen
to forty thousand per second, but we have reason to believe that
insects can hear sounds of higher pitch.
Care of the Ears. Fortunately this delicate and important
organ is deeply imbedded in the skull where little harm can reach
it, but care must be observed not to injure the tympanum by
probing with hard implements, ear spoons, etc., when trying to
clean the ear. In this connection it has been said that one ought
never to explore their ears with anything sharper than their elbow.
Ear wax has a useful function in keeping out dirt and insects,
and excess can be properly removed by ordinary washing. Foreign
bodies should be washed out and never removed by " poking "
with hairpins and other implements. Water which .enters the
ears in diving does no harm, and can easily be shaken out.
Ear ache or a discharge from the ear may indicate a serious con-
dition and should have immediate attention from a physician.
The brain and ear cavities are very close together at one point,
so that inflammation of the ear may reach the brain with fatal
results.
. Temporary deafness may be caused by inflammation of the
eustachian tubes as a result of a cold. Permanent deafness may
be caused by a blow on the ear bursting the tympanum, or by
disease of the middle or inner ear. It is always a serious matter
and should never be treated by advertising quack doctors, whose
THE SENSE ORGANS 419
only skill consists in their ability to separate their victims from
their money.
Sight. Plants and the lower animals respond to light but can
hardly be said to " see." The sensation of sight reaches us by
way of waves in the ether, which are studied more fully in Physics.
These light waves reach us from vast distances and at enormous
speed and put us in touch with a wider extent of our surroundings
than all the other senses combined. This fact, and its relation to our
other activities, make sight the most valued of all our senses. Yet
there is hardly an organ that we abuse more than we do our eyes.
The simplest eyes were mere colored spots connected with special
nerves to absorb light and tell its direction. Now we have lenses
developed to concentrate light upon these sensitive pigment spots,
muscles to adjust both lens and eye and various devices to protect
the whole.
Structure of the Human Eye. The eye is almost spherical in
shape, flattened a little from front to rear. The wall of the eye-
ball consists of three layers. The outer one is tough and white,
called the sclerotic coat, and shows in front as the " white of the
eye." The anterior surface of the sclerotic bulges out a little, and
becomes transparent in the circular region called the cornea.
The second coat, called the choroid, is richly supplied with
blood vessels and pigment (color) cells which prevent reflection of
light inside the eye-ball. This coat shows in front as the iris or
" color " of the eye. The iris is provided with muscles which regu-
late the size of the center opening, the pupil, according to the
amount of light.
The inner layer is the most delicate and complicated part of the
eye and is called the retina. It is really the expanded end of the
optic nerve and connects directly with the brain. It also has a dark
pigment and though only V of an inch in thickness, it consists
of at least seven distinct layers of cells which help in receiving the
impression which we call sight.
The lens of the eye is located just behind the iris and is con-
nected to the choroid by delicate muscles which can change its
thickness, to adjust for near or distant vision.
420
BIOLOGY FOR BEGINNERS
PLATE
S H O r T E H
A wo rwe
FIG. 135.
The space in front between the lens and cornea is filled with
a watery fluid and the ball of the eye is occupied by a jelly-like,
transparent substance, which keeps the eye in shape.
How We See. Light waves from an object pass through the
cornea to the lens which concentrates (focuses) them upon the
THE SENSE ORGANS 421
retina as you would focus a picture on the film of your camera.
The iris controls the amount of light entering the eye and the lens
muscles change its shape so that the picture on the retina may be
sharp and clear. The retina is affected by the light that falls
upon it and the impression is carried to the brain by the optic
nerve, as sight.
Protection of the Eye. Obviously, the eye cannot be buried in
the skull for protection, like the ear, but it is well guarded none the
less. The bony socket, walled in by the forehead, nose and cheek
ward off any but direct blows. The pad of fat on which it rests
saves it from jar or pressure. The eyebrows keep out perspiration
and the lids and lashes protect from dust. Tear secretion con-
stantly washes the front surface and a complicated set of reflex
actions helps us to ward off most injuries to this important sense
organ.
The Living Camera. The eye is often compared to a camera
and there are so many resemblances, that it may be helpful to
study this table of comparisons.
Part of eye corresponding to Part of Camera
Ball Camera box
Lens Lens
Lids Shutter
Iris Stops or diaphragm
Pupil Lens opening
Lens muscles Focusing devices
Black pigment Black lining
Retina Plate or film
In making this comparison it must always be borne in mind that
there are also fundamental differences. The eye is alive, the camera
is not. The eye produces a sensation which reaches the brain, the
camera makes a picture. The eye focuses by changing the
shape of the lens, the camera, by changing its distance from the
film.
422
BIOLOGY FOR BEGINNERS
Defects of the Eye. The care of the eye is dealt with in the
chapter on hygiene, but it is well to remember that seldom are they
perfectly normal and frequent examination by a competent physi-
cian is the only sure way of preserving their health. Below are
tabulated some of the common conditions and their causes, but
only an expert can determine the exact kind of lens or method of
treatment which will remedy the defect.
Condition
Defect of eye
Remedy
Near sight
Far sight
Astigmatism
Old age
Eye ball too long
Eye ball too short
Irregularity in shape of lens,
or cornea
Loss of lens adjustment result-
ing in far sight
Concave lens glasses
Convex lens glasses
Special cylinder lens glasses
Convex lens glasses
COLLATERAL READING
Animal Studies, Jordan, Kellogg and Heath, pp. 371-386; Animal
Life, Jordan and Kellogg, pp. 224-239; Physiology Textbook, Colton, pp.
284-300; General Physiology, Eddy, pp. 436-485; Applied Physiology,
Overton, pp. 268-275; The Human Mechanism, Hough and Sedgwick, pp.
244-265; The Human Body and Health, Davison, pp. 237-258; Studies
in Physiology, Peabody, pp. 291-320; The Human Body, Martin, pp.
263-294; Elementary Physiology, Huxley,5 pp. 367-457; High School
Physiology, Hughes, pp. 239-260.
SUMMARY
Response to environment.
1. Irritability.
2. Touch.
3. Taste.
4. Smell.
5. Hearing
(a) Structure of ear.
Outer ear, auditory canal and lobe.
Middle ear, bones, eustachian tube.
Inner ear, cochlea and nerve endings, semicircular canals.
THE SENSE ORGANS
423
Exampl
a % Us ^
|g !H
.B
c
s a" a"
S
424 BIOLOGY FOR BEGINNERS
(>) How we hear,
(c) Care of ears.
6. Sight.
(a) Structure of eyes.
Coats,
Sclerotic, white, thick, protective, cornea in front.
Choroid, blood vessels and pigment, iris in front.
Retina, dark, complicated, receives impressions.
Lens, convex, adjustable by muscles.
(&) How we see.
(c) Protection of the eye.
(d) The living camera.
(e) Defects of the eye.
CHAPTER XLIV
BIOLOGY AND HEALTH
Vocabulary
Excessive, more than necessary.
Mastication, chewing.
Flexible, easily bent.
Vagaries, whims.
One of the chief reasons for the study of biology is to learn how
to properly care for our own body and to maintain both it and its
surroundings in healthful condition.
The science which deals with the care and health of the body is
called hygiene; that which deals with keeping its environment
healthful is called sanitation.
A great many foolish " rules of hygiene " have been devised but
if we will apply our general knowledge of biology, mixed with a
goodly amount of common sense (which is not common), we can
construct our own. We know the amount and kinds of foods re-
quired, and can judge the evils of improper or excessive eating.
We know the need and process of digestion and can reach our own
conclusion as to chewing food, care of teeth, removal of waste, etc.
We have learned the use of oxidation and can see the reason for
correct posture, clothing, and exercise, which affect breathing.
In this way a sensible human being ought to be able to apply bi-
ology to his own life and it is much better than trying to memorize
any set of rules, however wise they may be.
In the same way, sanitation means the knowledge of biology
as applied to food and water supply, infectious diseases, ventila-
tion, sewerage, clean streets, etc.
In our elementary work we have studied both these subjects to
some extent. This chapter will. merely attempt to summarize a
few of the principal facts.
425
426 BIOLOGY FOR BEGINNERS
Health is the natural condition of the body, and yet, how many
have never been sick, or are now in absolutely perfect health. We
must remember that any lack of health is due to some biologic
mistake. While we can probably never know enough to absolutely
avoid disease certainly our study of biology ought to help us to
escape those troubles whose causes we do know. If we lived as
well as we knew how, everybody would be much stronger, healthier,
and happier. It is to call attention to some of the simpler ap-
plications of biology to health, that this chapter is written.
Hygiene of the Muscles. A great deal is being done with re-
gard to proper muscular exercise and it is well to understand some
of the reasons for the importance of this matter. The least impor-
tant result is one most often mentioned, namely the fact that ex-
ercises strengthen the muscles used. This is true but the following
results are much more important to health.
1. Exercise increases oxidation, from three to ten times; this
means that greater bodily energy is liberated.
2. From this it follows that the heat-regulating and excretory
organs are trained to their work.
3. Exercise withdraws the blood from the internal organs, to the
muscles and so relieves the tendency to over-supply and conges-
tion; this is shown by the " healthy color " of the complexion due
to the blood supply in the outer muscles; a very pale skin usually
indicates poor health.
4. Only by proper exercise do the heart and arteries receive
necessary training in supplying the blood to the tissues.
5. In the same way, exercise aids in the use and health of the
lungs and breathing organs.
6. Motion of the muscles is one of the chief causes of lymph
flow and we know that upon the lymph circulation depends the
nutrition of the tissues.
No rules can be given as to special kinds of exercise, since dif-
ferent people need different forms, just as we need different amounts
of food, but in general it may be said that any exercise should
bring about the results mentioned above, and should not be such
as to endanger or overstrain any part of the body.
BIOLOGY AND HEALTH
427
Proper exercise should
1. Be vigorous, continuous, and reasonably prolonged. For
FIG. 136. Superficial muscles of trunk, shoulder and back viewed from
behind. A, external occipital protuberance; 1-1, trapezius muscles; l' oval
tendon between right and left trapezius; l' insertion of trapezius; B, summit
of shoulder (acronium); 2-2', lateral muscle and insertion; 3, sterno-mastoid;
4, deltoid; 5, infraspinatus; 6, teres minor; 7, teres major; 8, rhomboideus
major; 9, part of external oblique muscle of abdomen. (After Allen Thom-
son.) From Kellogg.
example a brisk walk is one of the best of exercises, while a short
stroll or saunter does little good, though often mistaken for " ex-
ercise."
428 BIOLOGY FOR BEGINNERS
2. Useful exercise should use the body muscles as well as arms and
legs: walking, swimming, and throwing are good examples.
3. Exercise should cause full, deep breathing and preferably
should be in the open air. Loose clothing and erect position neces-
sarily follow.
4. Exercise should be varied and should occupy the mind as
well as the body; any movements, however excellent, lose much
if they are not enjoyed while being performed. This is the objec-
tion to many really beneficial " systems of exercise " which become
very distasteful because of lack of interest.
Hygiene of Digestion. For the general study of foods refer to
Chapter 37. The following is a summary of facts explained there:
1. The amount and kind of food should be adjusted to the work
of the body.
2. The " balance " of the ration should be maintained.
3. The food should be clean and properly prepared.
4. Usually the heartiest meal should come after the day's work
and should be preceded by a brief rest. Only when the brain or
muscles are not working, can the digestive organs get proper supply
of blood.
5. Eating between meals is usually a bad practice, especially
in case of sweet foods, as it prevents proper desire for, and diges-
tion of, the solid food which the body requires.
6. Water in abundance should be used both between and at
meals, but not to " wash down " unchewed food. It does not
" dilute the gastric fluid" but passes quickly from the stomach
and digestion is aided rather than hindered.
7. It is unnecessary to dwell upon the importance of thorough
chewing. The smaller the food particles, the greater the surface
exposed for digestion and the less burden is put upon the stomach.
The starch digestion in the mouth may not be very extensive, but
thorough mastication prevents over-eating and too rapid eating,
both of which produce more indigestion than all other causes put
together. " Leave the table hungry " is a good rule. Americans
eat too much, particularly of proteid foods, a habit which is both
unhealthful and expensive.
BIOLOGY AND HEALTH 429
8. Proper care of the teeth is necessary if food is to be thoroughly
chewed. It is sufficient to remember that tooth decay is a bac-
terial process, that the warmth and moisture of the mouth make
ideal conditions for bacterial growth, and that perfect cleanliness is
our only means of protection. This suggests frequent careful
brushing, use of antiseptic tooth washes, and a visit to a dentist
at least twice a year " whether you need it or not."
9. Violent exercise, severe study, worry, or any mental or
physical activity, at or near meal-times interferes with proper
digestion.
10. Regular attention must be given to the removal of waste
from the intestine, as a long series of illnesses can be traced to
lack of care in this regard.
Hygiene of Respiration. We have learned the use which the body
makes of oxygen in releasing the energy in our foods and keeping
us alive and active. Naturally, proper breathing is required if this
process is to go on in a healthful way.
We need to train our breathing muscles, because few of us know
how to breathe, even though we use the expression " natural as
breathing."
Deep breathing means using more lung tissue, getting more
oxygen, and developing the diaphragm and rib muscles,
properly.
We cannot use all our lung capacity at once, but should use all
we can. We train the other muscles for less important uses; why
not train our breathing muscles for the race of life?
Erect position and comfortable clothing are necessary if we are
to breathe properly.
The nose was made for breathing, not the mouth (see Chap. 39)
and any disease or growth which interferes with nose breathing
should be removed.
Ventilation. Deep breathing will do little good if the air breathed
is bad: this means attention to ventilation. Proper ventilation
should secure
1. A sufficient amount of air in proportion to the number
concerned
430 BIOLOGY FOR BEGINNERS
2. A slight continuous movement of air through the whole
room, without perceptible draughts.
3. A sufficient degree of heat to keep the body in comfort, usu-
ally 68 to 70 degrees.
4. A moderate amount of moisture in the air so that it will
neither interfere with evaporation from the skin, nor yet tend to
dry it.
5. The removal of chemical impurities and odors; the amount
of CO 2 should not exceed .06 per cent.
6. The removal of excess moisture which is especially great in
crowded rooms.
" Fresh air " is not necessarily cold air as some people seem to
think, though for sleeping rooms, the temperature should be
lower than in living quarters. Extreme cold is not an advantage
even in sleeping rooms, except in cases of tuberculosis, and many
people subject themselves to dangerous exposure in this way.
Air should be pure, cool, and abundant, but there is no virtue in
extreme coldness.
Dust Removal. Dust carries bacteria, hence air should be as
free from it as possible. This means replacing the broom and
feather duster by the vacuum cleaner and oiled dust cloth. Rugs
and hard- wood floors should take the place of the permanent carpet.
Smooth walls, simple furniture, and few hangings offer less oppor-
tunity for the accumulation of dust. Sprinkling, oiling, and
flushing the streets attain the same result for out-door dust.
Hygiene of the Eyes. The human eye is such a delicate and
necessary structure that its care should be emphasized, but just
because it is so complicated, no rules can be made which will
properly safeguard this most valuable sense organ. The one safe
procedure is to have the eyes examined by a competent expert
from time to time, even if no defect appears to be developing.
Reading in poor light, or at evening when the light is gradually
failing, is a common error. Almost as bad is the use of too bright
light directly facing the eyes, or reflected from too shiny paper in
books. Long continued use of the eyes on very fine print or sew-
ing causes severe strain, just as in continued use of any other organ.
BIOLOGY AND HEALTH 431
Actual defects in structure or, more often, over use under poor
conditions, produce " eye strain " and from this result headache,
sleeplessness, and nervous troubles of serious nature, in addition
to the damage to the eye itself. Common sense in their use, im-
mediate rest when any feeling of fatigue is caused, and prompt
advice from an expert, are the only rules for the care of our
eyes.
Hygiene of Bathing. Washing is primarily to remove dirt. Dirt
is objectionable for two reasons: it is offensive to refined people
and it often carries disease germs.
Washing to " keep the pores open " is not a true reason, because
the skin excretes but little waste, and the pores open quickly, even
in the dirtiest skin, when perspiration is required for heat regula-
tion.
However, there is a stronger argument for a daily cold bath,
because it gives the skin practice in adjusting itself to sudden
changes of temperature similar to those it encounters in every day
exposure. The cold shower or sponge bath, if followed by brisk
rubbing, causes the skin arteries to contract, and then expand
again, as evidenced by the glow of the skin.
This is precisely what the body should do when exposed to sud-
den chill of any sort, and if trained by frequent cold bathing, the
arteries will be ready to regulate the blood supply and no cold
or congestion will result.
Neither cold bathing nor swimming should be done within at
least an hour after meals, as the blood is needed to absorb the
food, and should not be diverted to the skin. The bath should
not be so cold, nor the swim so long continued, as to cause a per-
manent chill or prevent the warm reaction when the body is rubbed
dry.
The cold bath is primarily a means of prevention of " colds "
and all that they lead to; it should be taken daily in the morning,
immediately upon rising. The warm bath is solely a means of
cleansing the skin, should not be taken every day and only just
before retiring, when precautions to prevent chill can be observed.
A very hot bath should be taken only by physician's orders.
432 BIOLOGY FOR BEGINNERS
Hygiene of the Teeth. The importance of dental hygiene has
been mentioned before but cannot be too much emphasized.
Conditions in the mouth are ideal for the growth of bacteria which
cause decay. Warmth and moisture are sure to be present, and
unless great care is observed, particles of food will remain for the
bacteria to feed upon.
It is not a pleasant experiment, but if the teeth be scraped with
the finger nail and the odor of the substance removed observed,
we will have no doubt that decay is going on. The total area of
possible tooth infection is equal to that of two standard petri
dishes (over twelve square inches).
The decay of food between the teeth destroys the protective
enamel and the dentine then goes rapidly. The immediate re-
sults are bad breath, pain, and loss of teeth. Fully as serious are
the secondary consequences of poor chewing: indigestion, pus
diseases from infected gums, rheumatism, and nervous disorders.
Tonsils, throat, ears, and even the lungs may be infected from the
teeth.
The first or " milk teeth " deserve as great care as the permanent
set. If they decay and are removed too soon the jaws and face
never attain their proper shape and proportion, and the later teeth
will not fit properly together.
Hygiene of the Feet. With the possible exception of the eye,
no human organ has been worse abused than the foot. We crowd
our feet into air-tight leather boxes, bend the toes together, lift the
heel high off the ground and then wonder why we suffer from
corns, bunions, and fallen arches. Proper shoes should have their
inner edges nearly straight, heel low and broad, toe with room
enough so that the toes can separate and " wiggle." The uppers
should be flexible, as porous as possible, and not too tightly laced.
The arch of a normal bare foot should not touch the floor on the
inner edge and the shoe should be so shaped as to support this up-
ward curve. The selection of shoes should be guided by the ex-
pert advice of a doctor or trained fitter and not be governed by the
vagaries of style or the demands of fashion. Feet were made to
walk on, not to look at. In walking the feet should be carried
BIOLOGY AND HEALTH 433
forward with the toes straight ahead, not turned out as is commonly
done. " Toeing out " is as abnormal as " toeing in " but is so
common that it is less noticed.
Posture. Standing. The human animal is not as yet completely
adapted to his erect position. This makes especial care necessary
to achieve a healthful posture both in walking and sitting.
The head should be held up in a natural position with chin drawn
back, not stiffly, but with the feeling that you are pushing your
hat up. The shoulders may be either sloping or square by nature,
but need never be rounded forward. If we still walked on all fours
they would be pushed back by our weight; now we reverse the
process and carry weight upon them. This makes it especially
needful that we hold our shoulders back and our chest up to give
proper play to the lungs.
The abdominal organs tend to press each other down and for-
ward. This has to be met, partly by raising the chest and partly
by strengthening the front body walls, to hold them in place.
Sitting. In our modern life we do so much work sitting down,
especially reading and writing, that particular care has to be ex-
ercised in regard to this. The shoulders are apt to be bent forward,
the spine twisted sidewise, and the weight brought too high up by
sliding down in the chair. All these habits cramp the breathing
and digestive organs and may produce permanent deformity or
bad health. The obvious remedy is to sit back in the chair, with
shoulders up, and lean forward only from the hips.
Hygiene of the Nerves. Man has reached the stage where mental
activity takes the place of physical exertion and there is consequent
danger of one-sided development.
Mental fatigue is just as real as muscular fatigue. The brain
should not be forced to work when it is already tired nor when the
energy of the body has been used in hard physical labor.
Mental hygiene is just as important as physical hygiene. A well-
trained brain, developed by proper exercise, is vastly more valuable
than powerful muscles and needs even greater care in its develop-
ment. True education means just this training and developing of
a skillful brain, rather than merely storing the mind with various
434 BIOLOGY FOR BEGINNERS
kinds of information. Accumulation of facts is a very important
function of the brain, it is true, but is not to be compared with de-
veloping it to observe, think, and really reason.
Sleep is the period of rest from nerve activity, relaxation of
muscles, repair of waste, and growth of new tissue. Because chil-
dren are growing as well as using tissue by their intense activity,
they need more sleep than the adult. While seven to nine hours
sleep will do for most grown-ups, children ought to have from ten
to twelve hours.
The following are rules of individual hygiene as summarized
from the Yale Lectures on Hygiene by Professor Irving Fisher.
Air. Keep outdoors 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.
(b) By having it continuously ventilated while occupied.
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 many 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 gymnastics. 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 rest-
ing 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 them-
selves are killed by cold.
BIOLOGY AND HEALTH 435
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 not only good 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 swallow-
ing. There should be no more effort to prevent than to force swal-
lowing. It will be found that if you attend only to the agreeable
task of extracting the flavors of your food, Nature will take care
of the swallowing, and this will become, like 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 abnormal
foods. Thorough mastication takes time, and therefore one must
not feel hurried at meals if the best results are to be secured.
Sip liquids, except water, and mix with saliva as though they
were solids.
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 well out
of the way, in 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 pal-
atability at the time eaten: fruits, nuts, grains (including bread),
butter, buttermilk, salt in small quantities, cream, milk, potatoes,
436 BIOLOGY FOR BEGINNERS
and other vegetables (if fiber is rejected), eggs, custards, digested
cheese (such as cottage cheese, cream cheeses, pineapple cheese,
Swiss cheese, Cheddar cheese, etc.), curds, whey, vegetables, if
fiber is swallowed, sugar, chocolate, and cocoa, putrefactive cheeses
(such as Limburger, 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 excluding 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 proteid required is much less than ordinarily
consumed. Through thorough mastication the amount of proteid
is automatically reduced to its proper level.
The sudden or artificial reduction in proteid to the ideal standard
is apt to produce temporarily a " sour stomach," unless fats be
used abundantly.
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 auto-
matically.
Exercise and Rest. The hygienic life should have a proper
balance between rest and exercise 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.
BIOLOGY AND HEALTH 437
The exercise of the abdominal muscles is the most important
in order to give tone to those muscles and thus aid the portal cir-
culation. For the same reason erect posture, not only in standing,
but in sitting, is important. Support the hollow of the back by a
cushion or otherwise.
Exercise should always be limited 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 further
off than otherwise.
One should learn to relax when not in activity. The habit pro-
duces rest, even between exertions very close together, and enables
one to continue 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 ab-
normal mental states. This is to be done not so much by repressing
these feelings as by dropping or ignoring them that is, by divert-
ing and controlling the attention. The secret of mental hygiene
lies 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 produce health,
but as an end in itself, for which, in fact, even health is properly
sought. In addition, the individual should, of course, avoid in-
fection, poisons, and other dangers.
Occasional physical examination by a competent medical ex-
aminer is advisable. In case of illness, competent medical treat-
ment 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
public hygiene in city, state, and nation. He has a selfish as well
as an altruistic motive to do this. His air, water, and food depend
on health legislation and administration.
COLLATERAL READING
School Hygiene, Shaw, entire; Outlines of Practical Sanitation, Bashore,
see index; The Health of the City, Godfrey, see index; Handbook of Health,
438 BIOLOGY FOR BEGINNERS
Hutchinson, entire; Preventable Diseases, Hutchinson, entire; Civics and
Health, Allen, see index; Primer of Sanitation, Ritchie, entire; Good
Health, Jewett, entire; Mind and Work, Gulick, entire; The Human Body
and Health, Davison, see index; The Human Mechanism, Hough and Sedg-
wick, pp. 289-540; General Hygiene, Overton, see index; Practical Biology,
Smallwood, pp. 233-258; Applied Biology, Bigelow, pp. 525-560.
SUMMARY
Hygiene, care and health of body (exercise, breathing, food, eyes, etc.)
Sanitation, providing healthful surroundings (water supply, drainage,
infection, ventilation).
1. Hygiene of muscles.
Exercise, increases oxidation.
Trains heat regulating and excretion.
Prevents internal congestion.
Trains heart and arteries.
Trains breathing organs.
Aids lymph circulation.
Exercise should be vigorous, use body muscles, cause deep
breathing, occupy mind.
2. Hygiene of digestion.
Food should be
(1) Adapted to body needs.
(2) Balanced ration.
(3) Clean and well prepared.
(4) Eaten when rested.
(5) Eaten at regular times.
(6) Accompanied by water.
(7) Thoroughly chewed. .
Errors affecting digestion.
(1) Rapid eating.
(2) Insufficient chewing.
(3) Washing down food.
(4) Eating too much.
(5) Not getting rid of waste.
Care of teeth.
(1) Frequent cleaning.
(2) Use of tooth wash or powder.
(3) Consult dentist often.
3. Respiration.
(1) Train your breathing muscles, ribs and diaphragm.
(2) Loose clothing for free action.
(3) Erect position to allow lung action.
(4) Pure air supply; not necessarily cold.
(5) Air free from dust.
BIOLOGY AND HEALTH 439
4. Ventilation.
Essentials for proper ventilation.
Dust removal.
5. Care of the eyes.
Have frequent examinations.
Provide proper light, not too bright.
Avoid shiny papers.
Avoid continued severe use, producing fatigue.
Avoid reading in failing evening light.
Serious troubles follow abuse of eyes.
6. Hygiene of bathing.
Hot baths for decency and cleanliness
not to ""open the pores "
not too frequently
best at bed time to avoid chilling
Cold baths to train body against chilling
should be followed by rubbing and "glow "
best taken in morning
not too cold nor too prolonged.
7. Care of the teeth.
Conditions in mouth favor bacterial growth.
Harm to teeth from bacteria, decay and loss.
Other damage to health and looks, due to poor teeth.
8. Hygiene of the feet.
Danger from improper shoes.
Shape and material of shoes.
Correct habits of walking.
Support of the arches of the feet.
9. Correct posture.
Standing position.
Sitting position.
10. Hygiene of the nervous system.
Great development of nervous system.
Possibility of over strain and neglect of rest of body.
Importance of well-trained brain.
Importance of sleep.
CHAPTER XLV
CIVIC BIOLOGY
Vocabulary
Pessimism, looking on the "dark side" of things.
Civic, pertaining to government.
Prolific, abundant.
Conservation, saving from waste or damage.
Addiction, the grip of habit.
The preceding chapter has dealt mainly with biology as related
to the individual, but more important is our duty to the health of
the community, state, and nation.
Out of two and one-half million babies born in the United States
every year, one half die before reaching the age of twenty- three
years, and 500,000 die before their first birthday. Of the adults,
40,000 will have been invalids, 5000 will be in various institutions
for mentally or physically unfit, and 100,000 will be inferior to the
extent of reducing their value as citizens.
School examinations in Brooklyn show that 72 per cent of the
pupils need some form of medical treatment. If this ratio holds
for the United States it would mean 14,000,000 children who are
in need of health improvement. These figures are not given to
cause any feeling of pessimism or discouragement, but rather to
show what great need there is for civic control in all matters per-
taining to health, and for the intelligent cooperation of every
citizen in these measures.
Already modern methods of hygiene and sanitation have added
fifteen years to the human life. In the Spanish war we lost four-
teen men by disease for every one that died of wounds. In the
Russo-Japanese war, with modern sanitary precautions in force,
the Japanese lost only one by disease for every four killed, a record
fifty-six times as good as ours.
440
CIVIC BIOLOGY 441
No complete figures are available for the World War, but it is
certain that never before have the modern principles of sanita-
tion, vaccination, serum treatment, surgery, and the relation of
insects to disease, been so thoroughly applied.
Vaccination against typhoid was compulsory, the anti-tetanus
serum was universally used, new methods of treatment for in-
fected wounds, devised by Dr. Carrell and others, were in constant
use. Every soldier was provided with iodine to sterilize a wound
and aseptic bandages to make a temporary dressing.
As a result of these various applications of biologic science to
army methods, the loss from infectious disease was very low. " If
the Civil War death rate had obtained in the recent war, we would
have lost 138,518 American soldiers from typhoid, dysentery,
malaria, and small-pox instead of 273, which was the actual num-
ber," says Dr. Henry Smith Williams in one report (Dec. 1919).
We are waging a winning fight against disease and this chapter
will touch briefly upon some of the methods by which it is being
carried on. We are all soldiers in the army of Public Health and
cannot be too well informed as to what must be done to gain com-
plete victory.
Food Control. Almost every town and city has regulations as
regards food inspection. The stores, bakeries, slaughter houses
and milk stations are under supervision of official inspectors.
Foods must be protected from flies, bread must be wrapped,
food animals examined as to their health, and fair weight and
measure must be given the purchaser.
Water supplies are provided at enormous expense, the water
shed is carefully guarded from pollution, the water itself is filtered
and chemically treated to remove bacteria. Chemists and
bacteriologists are constantly employed to attend to these
matters.
Milk has always been a prolific source of disease among young
children and every means is now taken to secure its purity and
freshness. The farmer must have healthy cows and healthy men
to care for them, he must have clean stables and sterilized cans
and utensils. The inspectors of state or city enforce a list of rules
442 BIOLOGY FOR BEGINNERS
covering in some cases over sixty items that tend toward supply-
ing clean milk to the dealer in the city.
The dealer is again subject to equally careful control. He must
not let the milk get warmer than fifty degrees, he must provide
clean cans and handling conditions, he must sell in sealed and
labeled bottles, and his milk must be subject to examination for
bacteria, at any time. If any of these conditions are found danger-
ous, the milk is destroyed.
Milk normally contains bacteria, mostly harmless and some
useful, but the total must not exceed 100,000 per cubic centimeter
which is not very numerous for bacteria, though well-handled
milk ought to be kept far below this limit. Milk must have at
least 3.25 per cent of butter fat and must not contain any pre-
servatives, such as borax, soda, or formaldehyde.
Sanitation. Regulations as to sewage and garbage disposal are
in force in most cities, and means are provided at public expense
for the sanitary disposal of all wastes. Stables and outhouses are
either forbidden or restricted. Factories are not permitted to
pollute the air or water with their waste products.
Streets are drained, sprinkled, oiled, paved, and flushed with
water to remove dirt and to prevent dust. Trees and parks are
provided to improve the air and give places for outdoor rest to the
population.
Disease Prevention. It is in this department that modern hy-
giene has made its greatest progress. We now provide free hos-
pitals, clinics, and dispensaries where the sick may receive treat-
ment. We have visiting nurses, city physicians, and school health
'examinations to make sure that all who need help, shall receive it.
Stringent laws regulate vaccination, quarantine, and disinfection
of infected premises. Coughing, sneezing, and spitting are for-
bidden where they endanger the public health, and the public
towel and drinking cup are, fortunately, things of the past.
Campaigns of education by printed matter, pictures, school in-
struction and lectures, have been undertaken by city, state, and
national governments, as well as by life insurance companies and
institutions like the Rockefeller Foundation.
CIVIC BIOLOGY 443
As a result, we are becoming a longer lived and healthier nation.
Dirt, vermin, and disease are recognized as alien enemies and are
being removed or controlled.
Factory and Housing Conditions. The strongest constitution
cannot endure dark, ill- ventilated or crowded homes and factories.
Laws, inspection, and information are being combined to bring
about better conditions.
In most states child labor is forbidden or restricted, housing
conditions are looked after to some extent and fire protection is
usually well provided.
To carry out these many lines of civic biology, cities and towns
usually have a Board of Health, inspectors, and the assistance of
the police. In large cities public laboratories are maintained where
examinations of food, milk, water, and disease cultures are made.
There may be one or more city physicians, city chemists, and visit-
ing nurses who help enforce and carry out the regulations.
The street cleaning and fire departments perform their obvious
part as well as the city engineers who look after the drains, sewers,
and parks.
The Federal government devotes much of the work of the De-
partment of Agriculture and the Department of Commerce and
Labor, to matters pertaining to national health and the conserva-
tion of natural resources. They distribute quantities of valuable
literature, and carry out investigations along varied lines of civic
biology.
The Federal " Pure Food and Drugs " law was enacted in 1906
and regulates
1. Inspection of all food animals.
2. Standards of purity for food products.
3. Freedom from adulteration.
4. Prevention of harmful preservatives.
5. Proper labeling of drugs and medicines.
6. Proper labeling of package goods.
Patent Medicines. The consumption of patent medicines costs
the people of the United States $200,000,000 per year. This would
444 BIOLOGY FOR BEGINNERS
be well enough if the people were benefited by their use, but this is
rarely the case. On the other hand, most of them are fakes, some
are positively dangerous, all are outrageously expensive, and in
many cases their use delays proper treatment, till too late.
The Food and Drugs law obliged them to make no claims to
" cure " unless they could prove their claims and this rule has
practically removed that word from their vocabulary of fiction.
No patent medicine ever cured consumption, nor " kidney
trouble," nor catarrh, and they now are more careful in the wording
of their advertisements, though they still try to convey the same
impression.
" Consumption cures " are mainly opiates which lull the suf-
ferer into false security until past all help. Tonics and sarsapa-
rillas depend wholly upon alcohol for their effect. " Soothing
Syrups " for helpless babies are opium and morphine mixtures
and frequently lay the foundation for drug habits in later life, if
indeed the baby is not " soothed " into the sleep that knows no
waking.
Headache remedies are all heart-depressing drugs which deaden
the pain but do not remove the cause, of which the pain was merely
a warning.
Catarrh cures are usually cocaine or opium mixtures and often
lead to drug addiction; under recent laws they are much restricted.
The Food and Drug Law does not forbid the sale of these medi-
cines but it does oblige the maker to do two things :
1. He must put on the label the amounts of alcohol, morphine,
cocaine, opium, or other harmful drug which his medicine contains.
2. He must not " make any false or misleading statement "
as to the virtues of his particular " remedy."
This is one of the chief values of the law and applies to food
stuffs as well as medicines, so the only way to obtain the protection
which the law affords, is by reading the labels before you buy.
One can often judge of the character of a newspaper or maga-
zine, from the number and kind of patent medicine advertisements
which it carries. A reputable periodical will not now open its
columns to the false and misleading claims which some medicine
CIVIC BIOLOGY 445
manufacturers offer. Look over the literature that comes to your
home and draw your own conclusions.
COLLATERAL READING
Principles of Health Control, Walters, pp. 373-396; Civics and Health,
Allen, entire; The Human Mechanism, Hough and Sedgwick, pp. 477-540;
A Handbook of Health, Hutchinson, entire; Community Hygiene, Hutchin-
son, entire; Civic Biology, Hunter, pp. 373-396; Town and City, Jewett,
entire; Sanitation Practically Applied, Wood, see index; Handbook of
Sanitation, Price, see index; Sanitation in Daily Life, Richards, look
through.
Bulletins of U. S. Department of Agriculture, State Departments of
Health, Rockefeller Foundation, City Health Departments.
SUMMARY
1. Our responsibility for welfare of others.
2. The needs, as shown by health conditions.
3. Results of modern methods of hygiene.
4. Food control.
Food. Water. Milk.
5. Sanitation.
Sewage and garbage disposal.
Building restrictions.
Care of streets, parks, and trees.
6. Disease prevention.
Free care for the sick.
School examinations and clinics.
Laws as to spitting, etc.
Education in hygiene and cleanliness.
National, state, and individual publications and help.
7. Factory and housing conditions.
Laws as to conditions and hours of work.
Laws as to child labor. Compulsory school attendance.
Various boards and inspectors to carry out work in Civic Biology.
8. The Pure Food and Drugs Law.
9. Patent medicines.
CHAPTER XLVI
THE ECONOMIC BIOLOGY OF PLANTS
Vocabulary
Economic, pertaining to man's use.
Solvent, a substance used to dissolve others.
Utilize, to use.
Economic biology deals with the relation of living things to man,
either for use or for harm. The " economic importance " of a plant
or animal does not mean merely its value to man, but also includes
any way in which it may damage him. Usually the uses out-
number the injuries, but do not forget that both are included.
General Uses of Plants.
1. To supply oxygen and remove carbon dioxide in photo-
synthesis.
2. To aid in returning nitrogen compounds to the soil.
3. To regulate drainage of water (forests).
4. To supply foods for man and animals.
5. To provide fabric fibers (cotton, linen, hemp).
6. To provide fuel (wood, peat, and coal).
7. To provide paper materials.
8. To provide timber, cork, rubber.
9. To provide tanning materials (hemlock, oak and other barks) .
10. To provide dye stuffs.
11. To provide drugs and medicine, alcohol.
12. To provide turpentine, wood alcohol, acetic acid.
To balance this long list of uses for plant products, there are
but few ways in which they ever harm mankind. Some of these
have been studied in Chapter 17.
Of course bacteria head the list of harmful plants, in that they
cause many diseases, but do not forget that most bacteria are
446
THE ECONOMIC BIOLOGY OF PLANTS 447
useful and that some disease germs are not bacteria at all, but are
protozoan animals. Other fungi also cause harm to man's crops
and foods; among these are the rusts, molds, smuts, and mildews,
which have also been studied before. Some plants are poisonous
and do a little harm in that way; among these may be mentioned
certain mushrooms, poison ivy, water hemlock, etc. In cultivated
land, many wild plants cause harm by interfering with crop growth.
We call these " weeds " and they demand much labor and expense
for their control.
We shall now take up some of the economic applications of plant
biology in detail. -
Oxygen Supply. The importance of plants as a source of oxygen
and in removal of carbon dioxide has been explained in Chapter 13
but cannot be over-emphasized. Without this action of plants, the
supply of oxygen would be exhausted and no animal life could exist.
Nitrogen Fixation. The return of nitrogen compounds to the
soil by the action of certain bacteria has also been mentioned
(Chapter 17) and is one of the ways in which its fertility is main-
tained, while the natural decay of the plant tissue also aids in this
same process.
Control of Drainage. The regulation of drainage is brought
about by the forests, which act like enormous sponges, soaking up
the rains and letting the water filter slowly through the soil, instead
of rushing off in floods, as it does when heavy rains fall on barren
regions.
Foods. Cereal Grains. Of all plant parts used for food by man,
seeds are the most important, and among them the cereal grains
easily take first place.
These cereals (whence the name?) are the fruits of various grasses
and include wheat, corn, rice, rye, barley, oats, etc. They con-
stitute the most important group of food stuffs used by man
or other animals. In their composition these grains contain but
little water, hence they keep well, and store considerable food in
a small bulk: they are all rich in starch. Wheat contains much
proteid (gluten)' and corn is well supplied with oil, of which the
other grains contain but little.
448
BIOLOGY FOR BEGINNERS
The proteid of wheat makes its flour produce a sticky batter
resulting in the spongy " light " loaf which, no other grain will
yield. Macaroni is another wheat product that depends on this
FIG. 137 Wheat, (Triticum sativum, Grass Family,
Graminea). A plant and flower-cluster of beardless or
"club" wheat, a piece of the zigzag rachis, a spikelet, a
flower, and a kernel. (Baillon.) From Sargent.
fact for its wide use. The lack of fat in most cereals is made up
for by using butter, milk, or cheese with them when possible.
All cereals, especially if the whole grain be used, supply phos-
THE ECONOMIC BIOLOGY OF PLANTS 449
phorus, sulphur, potassium, calcium, magnesium, and sodium
compounds which are so essential to proper rations. (See Chapter
37.) They are easily cultivated, ripen quickly, yield largely, and
so constitute one of the first and most important crops raised by
man. The history of the cereals is the history of the human race,
wheat being found imbedded in Egyptian brick five thousand years
old. Other grains are found among the relics of the Swiss Lake
dwellers, perhaps much older, while the Chinese have cultivated
rice for over four thousand years and corn was used in America
long before the dawn of history.
Kinds of Cereals. Wheat is the most important vegetable food
in Europe and America. The United States leads in its production
with Russia in second place. Not only does it provide the white
bread of the world, but macaroni, spaghetti, vermicelli, etc., are
also wheat products.
Rice feeds more people than any other grain, being the chief
cereal of China, India, and southern United States and it is esti-
mated that one-half the population of the world depends upon it.
Corn was one of the first cereals to be used by savage tribes be-
cause it is easily cultivated in almost any climate; United States
also leads in the production of this grain. Not only is it valuable
as food for men and animals, as meal, canned or fresh, but starch,
corn syrup, glucose, oil, and gluten foods are among its
products.
Oats will thrive in colder climates than any other grain. It is
the principal cereal of Scotland, Norway, Sweden, and Iceland,
and is used for food and fodder in other temperate regions.
Barley also endures cold but will thrive in warmer regions as
well; it was formerly a valuable food, but is now more used for
fodder and for malt to make beer.
Rye will grow in poorer and rougher soil than any other grain
and Russia leads the world in its production. It makes the com-
mon " black bread " of Austria, Germany, Russia, and Sweden.
Buckwheat, despite its name, is not a true grain and while
pleasant in flavor, its flour has little food value; it is a native of
northern Asia and will grow in poor soil in temperate climates.
450
BIOLOGY FOR BEGINNERS
FIG. 138. Rice (Oryza sativa, Grass Family,
Gramineaf). P, upper part of rice plant, one-quarter
natural size; S, a spikelet from the same; w, rain-guard
or ligule at base of leaf-blade, inner view; natural size.
(Martius.) From Sargent.
THE ECONOMIC BIOLOGY OF PLANTS
451
Legumes. Next in importance to the cereals among the
seeds used for food are the legumes (peas, beans, and lentils) all
FIG. 139. Peanut (Arachis hypoga, Pulse Family, Leguminosai).
A , lower part of a plant showing the leaves and flowers above ground, and
ripening nuts and roots below; the surface of the ground indicated at el. B,SL
flower cut vertically to show, at the base, the small ovary containing the ovules,
and the long style extending through a slender tube which is surmounted by
the calyx and cirolla and is continued by a tube formed of the united filaments.
>C, a ripe nut cut lengthwise to show the two seeds. (Tanbert.) The plant
is an annual, i.e., it completes its life from seed to seed in one year; stems and
leaves somewhat hairy; flowers orange-yellow, fruit pale. Soon after pollen
has come upon the stigma, the stamens and corolla are shed and the ovary is
carried out beyond the calyx by a stalk which becomes 5-8 cm. long, and,
bending downwards, soon buries the little ovary in the ground. Once buried
the ovary ripens into the familiar pod-like nut. If it fails to get buried the
ovary withers. From Sargent.
452
BIOLOGY FOR BEGINNERS
members of the pea family to which also belong the clover, lo-
cust, etc.
The legumes are very valuable foods, rich in proteid and starch,
have little water or oil and hence keep well, though their proteid
(legumin) is not so easily digested as animal forms.
Nuts. Nuts are larger
and richer in proteid and
oil than grains or legumes
but are less used for food,
because the crop takes too
long to mature and is too
bulky to store. Nuts also
contain so much oil that
they do not keep nor digest
well.
The chestnut has little
oil and more starch than
other varieties. It is used
for food in Europe as are
also walnuts and pecans, to
some extent, while the
people of the tropics use
coconuts, peanuts, and
Brazil-nuts because cereals
do not thrive in such
climates.
FIG. 140. Coconut Palm (Cocos r\*\* Q A T? A r f
nucifera, Palm Family, Palmacea}. Plants
in fruit showing general form. (Baillon.) fa is a very valuable seed
The columnar trunk rises to a height of food product. It IS the
bears bright green leaves seed Qf ft fleshy beny ^^
on a shrub about 15 feet
high. Coffee belongs to the same family as quinine and madder
(a dye plant) as well as our common bluets, partridge berry, and
bed straw, and grows only in tropical regions, mainly in Brazil,
Arabia, and the East Indies.
Cocoa is more valuable as a food than coffee, though less used.
THE ECONOMIC BIOLOGY OF PLANTS
453
It is the seed of a small tropical tree growing in South and Central
America, Africa, and Ceylon. From the " cocoa bean," as it is
called, are made cocoa, chocolate, and cocoa butter. It must be
a
FIG. 141. Coconut.
A , fruit, showing husk cut vertically through the center, revealing the hard
shell of the nut.
B, nut viewed from below, showing the lines (a, a, a) along which the three
pistils are united; and between them the three germ pores, from the lower one
of which, ordinarily, the single germ emerges in sprouting.
C, lengthwise section through the fruit sprouting; notice the thick husk,
into and through which the young roots grow, the hard shell of the nut (black)
within which is the layer of solid seed food (coarsely dotted), and the liquid
food or "milk" (white) into which the enlarging cotyledon or seed leaf (finely
dotted) pushes its way and acts as an organ of absorption. (Warming.) The
husk is smooth and grayish brown, and is largely composed of coarse, tough
fibers. From Sargent.
observed that cocoa has nothing whatever to do with the coco-
nut which is a palm fruit while still another plant (coca) furnishes
from its leaves the dangerous drug cocaine.
454 BIOLOGY FOR BEGINNERS
Notice the different spellings: COCOA, beverage, chocolate;
COCONUT, food product, palm; COCA, plant, cocaine.
Another valuable group of seed products includes many spices,
such as mustard, nutmeg, mace, anise, celery, and caraway, while
castor oil and strychnine are important medicines obtained from
seeds.
Many seeds produce useful oils among which should be mentioned
cotton-seed, peanut, and almond, which are used for food; cocoa
and corn oils for soap and linseed (flax) oil for paints.
In all these important foods that man obtains from seeds, he has
been using the store of nourishment intended for use by the em-
bryo plant. Most seeds " keep " well and have a very concen-
trated store of food, an adaptation for reproduction of the plant,
which man has utilized for his own benefit.
Root Food Materials. Roots furnish a large part of one of man's
most valuable foods, namely, sugar. Sugar beets now produce
over half the world's supply of " granulated " or " white " sugar;
the rest comes from the stem of the sugar cane. Other products
from the beet-sugar industry are potash for glass-making, fodder
for cattle, and waste for fertilizer.
Among our common garden vegetables we have the roots of beet,
turnip, carrot, radish, parsnip, and sweet potato (not the common
potato, which is an underground stem).
Ginger, licorice, rhubarb, marshmallow, tapioca, and aconite
are all root products, used for food or medicines.
Stem Food Materials. Stems provide many forms of food among
which the sugar cane takes the lead and the potato comes next in
order.
Potatoes are used directly as food, and also furnish starch and
dextrine, the latter being the gum used on stamps, labels, etc.,
and also for finishing many kinds of cloth.
The pith of a certain palm stem furnishes sago starch and pearl
tapioca while arrow-root starch is from the underground stem of
a West Indian plant and is the most easily digested of all starches.
Cinnamon bark, asparagus, camphor, and witch hazel are food and
drug products also derived from stems.
THE ECONOMIC BIOLOGY OF PLANTS 455
Leaf Food Products. We usually think of leaves as fodder for
animals (grass, hay, etc.), but notice the list of those that we
commonly use ourselves. We must include the garden vegetables,
cabbage, lettuce, celery, spinach, pie plant, parsley, onion, cress;
the flavors of. mint and wintergreen; tea and tobacco; and the
drugs, cocaine and belladonna. Although leaves have little real
nourishment in them because not intended as storage places for
food, yet they are necessary to man's diet, since they supply many
of the mineral salts, especially iron and potassium compounds,
which are essential .to health.
Flowers. Flowers we seldom eat, but cauliflower is one excep-
tion, and cloves and capers are both flower products.
Fruits. Fruits furnish an extended list of foods for man. We
classify them as follows: pomes, such as apples, pears, and quinces;
stone fruits, like the peach, plum, cherry, apricot, and prunes;
citrus fruits, orange, lemon, grape fruit; simple berries, currant,
grape (raisin), blueberry, tomato; compound berries, such as
raspberry, strawberry, and blackberry; gourd fruits, pumpkin,
squash, cucumber, melon, and citron; miscellaneous, banana, date,
olive, peppers, vanilla, allspice.
Hops and opium are also fruit products and, though not foods,
may be mentioned at this point. Like leaves, fruits are not often
very concentrated foods, but supply sugar, acids, and mineral
salts which are very necessary to a proper diet.
Foods from the Spore Plants. The spore plants furnish but little
toward man's food, mushrooms being the only ones commonly
eaten, and of these many are dangerous and the best only one-sixth
as rich in proteid as meat.
Iceland moss is a curious lichen sometimes used in jellies and
medicines. Though we do not eat them to any extent we must
not forget that we could not do without spore plants, such as yeast
and certain bacteria that help in preparing such important foods
as bread, butter, and cheese.
Fiber Plants. Cotton is the most valuable plant fiber; it is an out-
growth of the outer coat of the cotton-seed, intended to aid in its
dispersal, and consists of strong, twisted fibers very well adapted
456
BIOLOGY FOR BEGINNERS
FIG. 142. Sugar-cane (Saccharum officinarum, Grass Family, Gramineai).
Plant in flower. A, part of spike, showing long silky hairs. B, spikelet de-
tached. C, flower, showing stamens, pistil and lodicules at the base. (Bentley
and Trimen.) Perennial, attaining a height of 13 ft.; stem variously colored,
2-5 em. thick. From Sargent.
THE ECONOMIC BIOLOGY OF PLANTS 457
for spinning. Not only is cotton made into thread and cloth,
but into batting, surgical dressings, paper, celluloid, and gun
cotton.
Flax which is the bast fiber of the bark of the plant of that name,
ranks next to cotton in value. From it are made linen thread,
cloth, and lace; canvas, duck, carpet warp, oil cloth, fine paper,
FIG. 143. Iceland Moss (Cetraria islandica, Shield-lichen Family, Parmc-
liacece). Plant, natural size, growing nearly erect from dry earth. (Luerssen.)
Upper surface brownish or olive, pale below, often red-stained at the base;
"fruit" forming chestnut-colored patches on the uppermost lobes. Native
home, North America and Eurasia. From Sargent.
and parchment. It is harder to prepare than cotton and is grown
chiefly in North Europe.
Jute is the bast fiber of certain plants of India; it is not so fine
nor durable as linen but is made into burlap, sacking, webbing,
and cordage.
Hemp is the bast fiber of a member of the nettle family and is
cultivated largely in Europe for its fiber uses, while in Asia an
intoxicating drug is prepared from the same plant. Hemp is coarse,
but stronger than flax and is used for sail cloth, cordage, and oakum.
Manila fiber is obtained from the leaves (veins) of a banana-
458 BIOLOGY FOR BEGINNERS
like plant of the Philippines. From this are made the best ropes,
binder twine, bagging, and sail cloth.
Coconut fiber comes from the outer husk of the coconut and
is used for cordage and for the familiar brown door mats.
FIG. 144. Sea Island Cotton (Gossypium barbadense,
Mallow Family, Malvacece). Flowering top, j. (Schu-
mann.) Similar to upland cotton but with seed black.
Native home, West Indies. From Sargent.
Other uses for vegetable fibers are in the manufacture of cheap
brushes, brooms, matting, packing, and upholstery.
Fuels. The next topic in our list of plant uses is fuel. While
this is of enormous importance, it needs little explanation, as all
are familiar with coal and wood and must know that gas is made
from the former. Peat is an important fuel in some parts of Europe
THE ECONOMIC BIOLOGY OF PLANTS
459
and consists of the partly decomposed and compressed peat moss,
similar to that in which florists pack their plants. From coal are
FIG. 145. Flax (Linum usitaiissimum, Flax Family,
Linaceas). Plant in flower. Young flower-cluster.
Seed, entire and cut vertically. (Baillon. ) Annual,
about 60 cm. tall; leaves smooth; flowers light blue;
fruit dry. Native home, Southeastern Europe and
Asia Minor. From Sargent.
also obtained a vast number of dyes, medicines, explosives, and
other products which will be studied in chemistry.
Paper Materials. All forms of paper are made from plant mate-
rial, chiefly from wood fibers of spruce, poplar, and similar trees.
460
BIOLOGY FOR BEGINNERS
Cotton waste, linen, and jute are important paper materials while
in Japan the young stems of the paper mulberry are used.
Timber. The matter of timber structure and of forest products
in general will be taken up later. The uses of timber are so numer-
ous that only a few can be mentioned; among these are:
General building
Ships
Vehicles
Pavements
Railroad ties
Furniture
Boxes
Bridges
Poles
Mine timbers
FIG. 146. Harvesting cork. (Figuier.) From Sargent.
Willow, ash, and hickory are split for making baskets, chairs,
and hats; rattan and wicker work are from similar sources. Pine
and spruce furnish excelsior for packing. Cedar supplies our
pencils, and mahogany and other fine woods are cut into veneers.
Two other very valuable tree products, though not timbers,
are cork and rubber. Cork is obtained from the bark of the cork
oak which grows largely in Southern Europe and is used not only
for stoppers, but to make linoleum, life preservers, packing, arti-
ficial limbs, handles, etc.
THE ECONOMIC BIOLOGY OF PLANTS 461
Rubber is made from the milky juice of several tropical trees
of South America and Asia; its uses are many and varied and
familiar to most of us.
Tanning Materials. The principal tanning- materials are ob-
tained from the bark of the oak, hemlock, willow, birch (Russia
leather), chestnut, and the South American quebracho.
Dye stuffs. Vegetable dyes have become much less important
since the development of the coal tar or aniline colors, however
indigo, logwood, and gamboge may be mentioned. The indigo
plant grows in India and Java and furnishes the familiar blue
dye; logwood grows in Central and South America and fur-
nishes red and black dyes, while gamboge is a yellow dye grown
in Siam.
Drugs. Several drug products have been mentioned elsewhere
so that merely a brief list will be given here :
Gums: Camphor (China), Arabic (Africa), Tragacanth (Asia).
Witch hazel from leaves and stems of a native plant.
Opium from milk of Chinese and Indian poppy fruits.
Cocaine from coca leaves (Peru).
Quinine from chinchona bark (Peru).
Strychnine, atropine, and nicotine are important plant drugs.
Alcohol is one of the most important plant drug products; it
has a multitude of uses other than as a beverage. It is utilized in
all chemical industries, as a solvent, fuel, preservative, and in
many other useful ways.
Alcohol is made by the action of yeast ferments on several kinds
of sugars. Apples, rye, and corn furnish whiskey; barley malt
is used for beer; grapes provide the sugar solution for wines;
molasses ferments to make rum.
All of these and some waste sugar liquors are fermented and
distilled to make commercial alcohol.
Distillation Products. The last topic in our list of plant uses
includes several products from distillation of wood or pitch. Crude
turpentine is the pitch of certain kinds of pine found in our South-
ern States, France, and Russia. From it the common turpentine
is made by distillation and rosin is left as a residue. Turpentine
462
BIOLOGY FOR BEGINNERS
is used in paints, and rosin in all kinds of varnish, soaps, cements,
and soldering. Wood alcohol, acetic acid, and charcoal are all
FIG. 147. Dyer's Indigo Shrub (Indigofera tinctoria, Pulse Family, Legu-
minoscB). Flowering branch; a, flower, enlarged; b, standard (uppermost
petal), back view; c, wing (side petal), inner view; d, e, keel-petal, inner and
outer views; /, flower with corolla removed; g, pistil; h, fruit, natural size;
i, seed; k, same, cut vertically. (Berg and Schmidt.) Shrub growing 2 m.
tall; leaves downy beneath; flowers reddish yellow; fruit dry. Native home,
Southern Asia. From Sargent.
THE ECONOMIC BIOLOGY OF PLANTS 463
made by distilling any kind of wood in large closed vessels. It
is an important industry in many wooded regions.
COLLATERAL READING
Elementary Studies in Botany, Coulter, pp. 342-418; Botany for Schools,
Atkinson, pp. 392-420; The World's Commercial Products, Freeman and
Chandler, entire; Plants and their Uses, Sargent, entire; Elementary
Biology, Peabody and Hunt, pp. 126-153; Domesticated Plants and Ani-
mals, Davenport, entire.
SUMMARY
Economic biology, the relation of living things to man, whether for good
or harm.
General uses of plants.
1. Supply oxygen, remove CO2. 7. Paper materials.
2. Regulate drainage. 8. Timber, cork, rubber.
3. Return nitrogen to soil. 9. Tanning materials.
4. Foods for men and animals. 10. Fabric fibers.
5. Fuel. 11. Dyestuffs.
6. Drugs, medicines, alcohol. 12. Distillation products.
Harmful plant forms.
1. Some bacteria (disease).
2. Some fungi (destroy crops, timber, etc.).
3. Poisonous plants.
4. Weeds.
Plant uses in detail.
1. Oxygen supply (Chap. 13), photosynthesis.
2. Nitrogen fixation (Chap. 17), soil bacteria, decay.
3. Drainage control (Chap. 50), forests as reservoirs.
4. Food materials.
Seed products.
Plant Location Uses
1. Cereals.
Wheat U. S., Russia Bread, macaroni, etc.
Principal food of white races.
Rice China, India Feeds half the world.
Corn North America Food, fodder, starch, oil, alcohol.
Oats North Europe Food, fodder.
Barley Central Europe Fodder, beer, food.
Rye Europe Dark bread, whiskev.
464
BIOLOGY FOR BEGINNERS
2.
3.
4.
Legumes.
Beans
Generally
Peas
cultivated
Lentils.
Nuts.
Chestnut
South Europe
Coconut
Tropics
Peanuts
America
Various seeds.
Coffee
Cocoa
Mustard \ Various
Nutmeg, etc. J
Cotton-seed 1
Peanut
Almond' Carious
Flax, cocoa J
important as proteid foods.
Food, starch, little oil.
Food, fiber.
Food, oil, butter.
Asia, S. America Beverage.
S. and Cent. Am. Beverage, chocolate, butter.
Spices and flavors.
Oils for food, soap, paint.
Root products.
Plant
Sugar beet
"Vegetables"
Beet, carrot Various
turnip, parsnip
Location Uses
Europe, U. S. Sugar, potash, fertilizer.
Food, supplying starch and min-
erals
Sweet potato
Southern U. S.
Food.
Ginger
India
Spice.
Licorice
Mediterranean
Flavor, medicine.
countries
Rhubarb
Various
Medicine.
Aconite
Europe
Medicine.
Cassava
Africa
Food starch.
(tapioca)
Stem products.
Plant
Location
Uses
Sugar cane
U. S., India,
Food, sugar, molasses, alcohol.
West Indies
Potato
U. S., Europe
Food, starch, dextrine.
Sago palm
East Indies
Starch.
Arrow root
West Indies
Starch.
Asparagus
Various
Food.
Cinnamon
Ceylon
Spice from bark.
Camphor
China
Gum for medicine, celluloid, etc.
THE ECONOMIC BIOLOGY OF PLANTS
465
Leaf products.
Fruits.
Uses
Food (mineral salts).
Flavors.
Beverage.
Smoking and chewing.
Drug (cocaine).
Pomes, apple, pear Stone fruits, plum, cherry, peach.
Citrous fruits, orange, lemon Berries, grape, currant, tomato
Comp. berries, strawberry, etc. Gourd fruits, squash, pumpkin,
cucumber.
Various fruits, banana, date, olive, vanilla, hops, poppy (opium),
Plant
Onion, cab-
bage
Lettuce, rhu-
barb
Mint, winter-
green
Tea
Tobacco
Coca
Location
Various
Various
India, China
Various
S. America
Spore plant products.
Mushrooms
Iceland moss (jelly)
5. Fiber plants.
Plant
Cotton
Location
India, Egypt,
Yeast (in making bread).
Bacteria (in making butter,
cheeses).
Uses.
Cloth, paper, explosives, batting,
Flax
Jute
Hemp
United States dressings, thread.
North Europe Linen, canvas, paper, lace.
India
Europe
Manila fiber Philippines
Coconut fiber Africa
Burlap, sacking, cordage.
Cordage, sail cloth, oakum.
Rope, twine, sail cloth.
Mats, brushes, upholstery.
6. Fuels.
Wood, charcoal, peat, coal, gas (by-products).
7. Paper.
Spruce, poplar, etc., cotton and linen waste.
8. Timber.
Buildings, furniture, ties, poles, boxes, baskets, chairs, pencils,
excelsior, veneers.
Cork, bark of cork oak, Southern Europe.
Stoppers, life preservers, linoleum, etc.
Rubber, juice of trees, South America and Asia
Tires, stoppers, elastics, raincoats, etc.
9. Tanning materials.
Barks of oak, hemlock, willow, birch, chestnut, quebracho.
466 BIOLOGY FOR BEGINNERS
10. Dyestuffs.
Indigo, India, Java (blue).
Logwood, South and Central America (black or red).
Gamboge, Siam (yellow).
11. Drugs.
Gums, camphor, arabic, tragacanth.
Opium, China, India. Milk of poppy fruits.
Cocaine, Peru. Leaves of coca plant.
Quinine, Peru. Bark of chinchona plant.
Alcohol from apples, rye, corn whiskey.
Alcohol from barley malt beer.
Alcohol from grapes and fruits wines.
Alcohol from molasses rum.
12. Distillation products.
Charcoal, wood alcohol, acetic acid, turpentine, rosin, pitch, tar.
CHAPTER XL VII
THE ECONOMIC BIOLOGY OF INVERTEBRATES
Vocabulary
Polyp, the coral animal, which is not an "insect."
Succulent, juicy.
Bivalves, two-shelled animals, such as clams.
Venomous, poisonous.
We shall take up the economic relations of animals in the same
way as we have plants, giving the general uses and harm done
and then taking up each large animal group, somewhat in detail.
The subject is so broad that many books have been written on
the economic relations of insects, birds, or mammals alone, so
we will be required to consult reference books for fuller information.
Try especially to find as many examples of each case as possible,
particularly animals which are familiar.
General Uses of Animals.
1. To supply food (flesh, eggs, milk, etc.).
2. For transportation (horse, ox, camel, dog).
3. To provide fabric fibers (silk, wool).
4. To provide fur (seal, mink, otter).
5. To provide leather (cattle, sheep, horse, etc.).
6. To provide feathers.
7. To provide various products, such as ivory, horn, glue,
gelatine, hair, etc.
8. To aid in pollenation and seed dispersal.
9. To act as scavengers.
10. To aid in destroying harmful animals and plants.
Harmful Kinds of Animals. From this list it is evident that
man owes about as much to other animals as he does to plants.
There are, however, a few harmful exceptions.
467
468 BIOLOGY FOR BEGINNERS
Certain protozoa cause disease (see Chap. 18 and 25) and some
parasitic worms (Chap. 20) also do considerable harm. Many
insects live upon the plants that man also uses for food and in this
way cause serious destruction to crops, while others transmit
disease (Chap. 25). To a very small extent " wild animals " harm
man directly and also destroy some of his domestic animals, but
this is of comparatively little importance.
Economic Value of Animals. In dealing with the economic im-
FIG. 148. A common bath sponge. From Kellogg and Doane.
portance of animals we shall take them up by groups beginning
with the simplest first, namely the protozoa.
Protozoa. These minute one-celled forms are of vast importance
to man insomuch as they are the source of food for higher animals
and these in turn finally provide man with nourishment, by way
of such important sources of food as clams, oysters, crustaceans,
and fishes, many of which find, in protozoa, their chief food supply.
Certain protozoa develop minute shells and the deposits of these
THE ECONOMIC BIOLOGY OF INVERTEBRATES 469
tiny skeletons have produced great layers of chalk and other rock,
which form important land areas such as the Dover cliffs in southern
England. Some of the pyramids are made of stone formed from
protozoan deposits.
Many protozoa perform valuable service as scavengers, and,
since they are mostly aquatic, aid in keeping our water supply
free from filth. On the other hand, a great many diseases are caused
by protozoa, among which are malaria, smallpox, yellow fever,
dysentery, scarlet fever,
etc. (See Chap. 13.)
Sponges. From the next
higher group, the sponges,
man obtains the various
forms of the common
" sponge." The sponge is
really the horny skeleton
of the sponge animal,
from which the jelly-like
flesh has been removed by
rotting and washing.
Sponges grow attached to
the sea bottom in various
warm regions, such as the
Mediterranean and Red
Seas, and Florida and West
Indian waters. The best
come from the Mediter-
ranean. A live sponge is a roundish smooth mass, rather dark
brown in color, provided with many pores for passage of water,
and having about the consistency of a piece of beef liver.
They are collected by divers or by dragging hooks, piled on
shore till the flesh rots off, washed, dried, sorted, and sometimes
bleached. The world's annual sponge crop is worth about
$4,000,000.
Coelenterates. The coelenterates include many curious and
beautiful animals such as the hydras, hydroids, jelly-fish, corals,
FIG. 149. Branching coral Acropora
470
BIOLOGY FOR BEGINNERS
and sea-anemones, but the only forms directly of use to man are
the corals. Colonies of these tiny animals, called coral polyps,
secrete so much limestone in their body walls that they form the
coral reefs which make up large parts of several continents, notably
Australia and the Pacific islands. Other coral reefs of very ancient
times now form important beds of limestone like the " corniferous "
ledges that cross central New York. The red coral used for jewelry
is another product of this group, found principally in the Mediter-
ranean.
Echinoderms. The echinoderms include the starfish, sea-urchin,
and sea-cucumber. Starfish are an enemy of the oyster and a
special effort is made to keep them out of oyster beds. The Chinese
and West Pacific peoples also use the sea-cucumbers for food, as
soup, and consider them a great delicacy.
Worms. As already stated in our study of worms (Chapter 20),
we owe to the humble earthworm a heavy debt for his services in
keeping the soil in fertile
condition; and we must not
forget that without this work
we should probably have
much difficulty with our
agriculture. On the other
hand, the parasitic worms,
such as tape-worm, hook-
worm, trichina, and other
intestinal forms, cause serious disease or death in man. Similar
forms, the flukes, infect our domestic animals, especially sheep,
which they attack by way of the liver and cause the death of
hundreds of thousands every year.
Molluscs. Primitive man, before he knew the use of fire, de-
pended upon raw molluscs for much of his food, as the enormous
shell heaps remaining to this day testify. Even yet we look upon
oysters, clams, mussels, and scallops as useful foods or luxuries,
depending on how far we live from the seacoasts where they are
caught. In all, except the scallops, we eat the whole body, the
bulk of which consists of the liver and reproductive glands. What
FIG. 150. Liver-fluke (Fasciola hepatica).
(Nearly twice natural size.) From Kellogg
and Doane.
THE ECONOMIC BIOLOGY OF INVERTEBRATES 471
we hear called the " ears " are really the muscles that held the
shell together and it is this muscle only which we eat in the case
of the scallop.
Clams are found along our whole Atlantic coast; oysters are
abundant south of Cape Cod with Chesapeake Bay as the center
of the industry, having the largest production of any region in the
world. The Pacific coast and foreign shores also furnish these
succulent bivalves, but even so, Chesapeake oysters are in demand
in the best markets of Europe, and the oyster yields the most
valuable water crop in existence. It is the leading fishery product
in fifteen different states. Aside from their value as food, mol-
lusc shells furnish us with " mother-of-pearl " for buttons, handles,
and ornaments, with crushed shell for chicken feeding, and with
the precious pearl of the jewelry store.
These latter are found in " pearl oysters " (not the edible species)
and are caused by the entrance within the shell of a grain of sand or
the irritation of a parasitic worm, which makes the oyster secrete
layer after layer of shell substance, to cover the offending particle,
much as the hand protects itself from irritation by growing a
callous layer. The most valuable pearls are found in the Persian
Gulf and on the coasts of Ceylon. Fresh-water clams furnish the
irregular " baroque " pearls and are found largely in the Mis-
sissippi and its branches.
Shells have always been used for ornaments and formerly passed
for money as well, the " cowrie " of Africa and the " wampum "
of our Indians being two examples. Wampum consisted of beads
cut from the colored parts of clam shells.
Snails and slugs are another group of molluscs, which, especially
in France, are valued as food. They do considerable harm in
gardens where they eat young seedlings and leaves. The shiny
trails so often seen on sidewalks are left by the slugs in their travels.
A near relative is the abalone of the California coast, whose
beautiful rainbow colored shell is used for ornaments and for a
great deal of inlaying work.
The third group of molluscs is called the cephalopods and in-
cludes the squid, cuttle fish, and octopus. Man uses squid for
472
BIOLOGY FOR BEGINNERS
fish bait, and obtains from the cuttle fish the true " sepia," a brown
ink-like pigment which the animal squirts out to hide itself when
attacked. The " cuttle bone " familiar in the canary cage is the
internal shell of this same mollusc.
Crustacea. The larger crustaceans, lobsters, crabs, shrimps,
and prawns are valuable sources of food to man; the smaller
forms are equally valuable as food for fish, and all are useful
scavengers. Of all these the lobster is most valuable. From twenty
to thirty million are annually caught along the coasts of New
England and Canada and the business is carefully regulated by
FIG. 151. The giant squid, Ommatostrephes calif ornica. From specimen
with body, exclusive of tentacles, four feet long, thrown by waves on
the shore of the Bay of Monterey. From Kellogg.
law to prevent their destruction by over fishing. " Soft shell "
crabs are merely the ordinary blue crabs, taken just after moulting
and before their new shells have formed.
Barnacles are curious crustaceans which attach themselves to
rocks, piles and even to the bodies of whales and bottoms of ships.
In the latter place they interfere with easy sailing and have to be
removed.
Acerata. Spiders as a whole are distinctly beneficial because
of their destruction of flies and other insects; their bite is seldom
serious to man, though some large tropical kinds can kill small
birds. Scorpions are found in Southern United States and tropical
THE ECONOMIC BIOLOGY OF INVERTEBRATES 473
America and Africa; their abdomen ends in a venomous sting,
which, while painful, is seldom fatal to man.
" Daddy-long-legs," which belongs to this group, is a very use-
ful citizen because he feeds almost entirely on plant lice.
Mites and ticks are degenerate parasitic forms which live on
the blood of mammals such as the dog, cattle, and man. The
itch is a disease produced by a mite, but,
thanks to the popularity of soap, it causes
little trouble.
Insects. The economic relations of in-
sects are so important and complicated
that we can only summarize them here.
Refer to any of the books on " economic
zoology " to get a full idea of their im-
portance. Over half of all insects are
harmful, 250 species attack the apple,
grape, and orange, alone.
As to their harmful activities, they
1. Destroy grain, vegetables, and fruit
crops.
2. Convey many kinds of disease (flies
and mosquitoes).
3. Injure domestic animals (flies and
mosquitoes, etc.).
4. Destroy buildings, clothing, etc.
(white ants and " moths ").
5. Annoy and injure man by bites and stings.
Their total damage in United States is over $200,000,000 per
year.
On the other hand, we owe to the insects many useful processes
and products such as
1. Pollenation of flowers of valuable plants.
2. Acting as scavengers (maggots, beetles).
3. Killing injurious insects (lady bugs which eat scale insects
and ichneumon flies that destroy tree borers).
4. Furnish silk (silk moth cocoon).
FIG. 152. A scorpion,
Centrums sp., from Cali-
fornia. (Natural size.) From
Kellogg.
474 BIOLOGY FOR BEGINNERS
5. Furnish honey and wax (bees).
6. Furnish dye (cochineal red from a scale insect).
7. Furnish shellac (gum secreted by a scale insect).
8. Furnish ink material (gall insects).
The following are some of the common injurious insects, which
you should know by sight, so as to destroy them whenever possible.
FRUIT TREE PESTS
Tent Caterpillar. Makes web nests in apple and cherry trees.
Caterpillar dark, with white stripe; moths light brown with white
stripe on front wings; eggs in belts around small twigs. Treat-
ment: collect and burn egg masses; destroy nests; spray with
poison early in the spring.
Codlin Moth. The familiar " apple worm " is the larva.
Eggs laid in young apple just after petals form, the larva hatches
in a few days and feeds around the core, making the " wormy "
apple. Treatment: spray with poison just after petals have fallen
and before the larva can get inside the fruit or calyx. This in-
sect costs New York state $3,000,000 per year.
Scale Insects. Small circular or oval scales on bark; these are
the bodies of the females under which eggs are deposited. Each
scale insect sucks its nourishment from the juices of the plant and
by their large numbers do great damage. Treatment: spray with
crude petroleum emulsion before buds start in spring; spray with
kerosene or whale oil emulsion during summer.
SHADE TREE PESTS
Tussock Moth. Handsome caterpillars with three black tufts,
four white tufts, and red head. Eggs covered by frothy white
substance. Treatment: destroy egg masses and use poison sprays.
Cottony Maple Scale. Masses of cotton-like scales on twigs
and leaves suck nourishment from tree like all scale insects.
Treatment: spray with kerosene or whale oil soap emulsions.
Borers. Larvae of various beetles bore under the bark and into
wood, loosening the bark, and killing trees; the irregular grooves
THE ECONOMIC BIOLOGY OF INVERTEBRATES- 475
under old bark are caused by them. Treatment: destroy infested
trees or branches; dig out borers in fall; encourage the birds.
GARDEN PESTS
Potato " Bug." A beetle whose familiar red larva .does damage.
Treatment: spray with poison. Arsenate of lead is better than
the familiar Paris green.
Squash Bug. A true bug; bad odor; eggs under leaves; feeds
by sucking juices. Treatment: kill adult bugs early in season
to prevent egg laying; destroy eggs.
Cabbage Worm. Larva of white or yellow butterflies. Treat-
ment: spray young plants with poison or dust older plants with
lime; catch adults in nets.
HOUSEHOLD PESTS
Flies and Mosquitoes. (See Chapter 25.)
Buffalo Carpet Beetle. Adults one-eighth inch long; have white
and red markings, may be brought in on flowers; larva covered
with bristles; eat carpets, feathers, etc. Treatment: take up
carpets and spray with benzine (outdoors); fill floor cracks; use
rugs.
Cockroaches and Croton Bugs. True bugs; scavengers; very
prolific. Treatment: use poisons, traps, cleanliness.
Clothes' Moths. Larva of small gray moth; often in webbed
cases; attack fur, woolen, etc. Treatment: frequent brushing;
tight packing; use of camphor or naphthalene; cold storage.
It will be noticed that some insects suck their food by piercing
the bark, while others eat the foliage. The former have to be
treated with " contact poisons," like oil emulsions and whale oil
soap, which will kill if they touch the body. The latter are de-
stroyed by " digestive poisons," such as Paris green and Hellebore,
which the insects eat with their food.
Among the beneficial insects we should learn to recognize the
" lady bug " a red beetle whose larvae feed on plant lice, and the
lace wing fly whose larvae also favor the same diet and thus protect
our plants. Another useful insect is the long-tailed Thallessa
476 BIOLOGY FOR BEGINNERS
with ovipositors two to four inches in length. This insect is often
feared and destroyed when really it lives on wood borers and is
very useful.
HARMFUL LEPIDOPTERA
Moths.
Bee moth, eggs laid in hive at night.
Meal moth, webs in meal, flour, and cereals.
Leaf rollers.
Codlin moth, eggs in apple blossoms; larvae are " apple- worms."
Currant and cherry worms, leaf and web nests.
Leaf miners, minute larvae eat parenchyma of leaves.
Clothes' moths, case makers in woolens and furs.
Peach tree borers, attack base of trees, dangerous.
Canker worms, "measure worms."
Currant worm, "measure worms."
Army worm, attacks grains, dangerous.
Tussock moth, eats shade and fruit tree leaves, dangerous.
Gypsy moth, leaf eater, dangerous.
Tent caterpillar, maker of "worms' nests," dangerous.
Butterflies.
Larvae generally harmful in some degree as leaf eaters.
Cabbage "worm," common and very harmful.
BENEFICIAL BEETLES
Tiger beetles, predaceous, as adult and larva, on insects.
Ground beetles, predaceous, very numerous, eat caterpillars and potato
beetles.
Water beetles, eat other larvae, snails, small fish, and decaying vegetation.
Carrion beetles, eat dead animals, manure, etc. Bury food.
Rove beetles, eat decaying matter.
Lady bug beetles, eat insect eggs, adults, lice, cottony scale.
HARMFUL BEETLES
Dermestids, eat fur, wool, carpet, dried meats, museum specimens.
Click beetles, larvae, wire worms, feed on grain roots.
Wood borers, larvae in trees.
Stag beetles, live on wood and sap.
Scarabs, lamellicorn beetles, a large order,
Scavengers, dung beetles.
Leaf eaters, adult on leaves, larvae on roots.
Pollen eaters.
Buck beetles, wood borers.
Leaf beetles, potato "bug," asparagus and cucumber "bugs." Grape.
Weevils, live on grains, nuts, fruits, etc., very harmful; engraver beetles
under bark.
THE ECONOMIC BIOLOGY OF INVERTEBRATES 477
INSECTICIDES
Chewing insects. May be poisoned in food.
Larvae of lepidoptera and coleoptera.
Currant worm and apple worm.
Potato beetle and larvae.
All other "worms," beetles, and "grubs."
Sucking insects. Must be killed by contact poisons.
Plant lice, aphids.
Scale insects.
True bugs (heteroptera).
For chewing insects use digestive poisons, such as
Paris green.
Arsenats of lead.
Hellebore.
For sucking insects use contact poisons, such as
Whale oil soap \ forlice>
Kerosene emulsion ;
Lime-sulphur wash for scale insects.
For apples use,
2-3 Ib. arsenate of lead, 1 gal. lime-sulphur, 50 gallons water.
For peach, plum, cherry, etc., use,
2. Ib. arsenate of lead, \ gal. lime-sulphur, 50 gallons of water.
For winter spraying use one part lime-sulphur to eight water.
FUNGICIDES
Use for blight, mould, rust, rot, or scab the following:
Bordeaux mixture.
Dilute lime-sulphur wash, as follows:
For apples, pears, etc.,
\.\ lime sulphur to 50 gallons water.
For plum, cherry, peach,
\ gallon lime-sulphur to 50 gallons of water.
COLLATERAL READING
Economic Zoology, Osborne, pp. 1-300; Insects Injurious to Fruits,
Saunders, see index; Insect Pests of Farm, Garden and Orchard, Sanderson,
see index; Economic Entomology, Smith, see index; Shell Fish Industry,
Kellogg, see index; Essentials of Biology, Hunter, Coral, p. 210; Worms,
pp. 215-219; Insects, pp. 261-265; Lobster, 228; Molluscs, pp. 269-271;
Elementary Biology, Peabody and Hunt, Bees (A. B.), p. 42; Insects (A. B.),
pp. 13-22; Crustacea (A. B.), p. 162; Protozoa (A. B.), p. 173; Applied
Biology, Bigelow, Protozoa, po. 312-316; Worms, pp. 340-345, 350;
Crustacea, p. 372; Insects, pp. 390-398; Vegetable Mould and Earthworms t
Darwin, Chap. VII; New York State Museum Bulletin, No. 103 and other
N. Y. State Bulletins; Cornell University College of Agriculture, Bui-
478 BIOLOGY FOR BEGINNERS
letins Nos. 142, 234, 252, 283, 333 and others. Rural School Leaflets, list
on application.
U. S. Department of Agriculture Bulletins, Farmers' Bulletins Nos. 165
264, 275, 564, etc., Bulletin No. 492, etc., Circulars Nos. 36, 98, etc.
The above Government publications are merely a suggestion; lists can
be had for the asking, and hundreds of useful pamphlets can be obtained,
especially in regard to insects.
(See also Chapter 25 on "Insects and Disease.")
SUMMARY
General uses of animals.
1. Food. 6. Feathers.
2. Transportation. . 7. Ivory, horn, glue, hair, gelatine.
3. Fabric fibers. 8. Pollenation, seed dispersal.
4. Fur. 9. Scavengers.
5. Leather. 10. Destroying harmful forms.
Harmful kinds of animals.
1. Protozoa (diseases).
2. Insects (destroy crops). (Transmit disease.)
3. Wild animals (destroy man and domestic animals).
Economic value of animals.
Protozoa.
1. Food for higher animals, clams, Crustacea, fish, etc.
2. Deposit shell as chalk beds.
3. Act as scavengers in water.
Sponges.
1. Skeleton of horny forms used as "bath sponge."
2. Preparation: collected, rotted, washed, dried, bleached.
Coelenterates.
1. Corals, reef, and continent builders.
2. Coral deposits, now limestone beds.
3. Precious coral.
Echinoderms.
1. Starfish harmful to oysters.
2. Sea-cucumbers eaten by Chinese, etc.
Worms.
1. Earthworms necessary in cultivated soil.
2. Parasitic worms cause disease in man and animals.
Molluscs.
1. Raw food, also cooked, clams, oysters, etc.
2. Shells furnish mother-of-pearl, buttons, chicken feed.
3. Precious pearls (Persia and Ceylon).
4. Shells for money and ornament.
5. Squids for bait and cuttle bone, sepia.
THE ECONOMIC BIOLOGY OF INVERTEBRATES 479
Crustacea.
1. Lobster, crab, shrimp, etc., for food.
2. Small forms for fish food, barnacles harmful.
Acerata.
1. Spiders useful in killing flies, etc.
2. Scorpions dangerous, but not fatal.
3. Daddy-long-legs feeds on plant lice.
4. Mites and ticks, parasitic and harmful to man and animals.
Harmful activities.
Insects.
1. Destroy crops. 3. Injure domestic animals.
2. Transmit disease. 4. Destroy clothing, buildings.
5. Annoy and injure man.
Useful activities.
1. Pollenation. 5. Furnish honey and wax.
2. Scavengers. 6. Dyes.
3. Kill injurious insects. 7. Shellac.
4. Silk. 8. Ink material.
Common Injurious Insects.
Fruit tree pests.
Tent caterpillar.
Codlin moth.
Scale insects.
Shade tree pests.
Tussock moth.
Cottony maple scale.
Various "borers."
Garden pests.
Potato "bug."
Squash bug.
Cabbage "worm."
Household pests.
Flies and mosquitoes.
Buffalo carpet beetle.
Cockroaches, croton bugs.
Clothes' moths.
Treatment.
Sucking insects with contact poisons.
Eating insects with digestive poisons.
Useful forms.
Lady bug.
Thalessa (an ichneumon fly).
Carrion beetles.
CHAPTER XL VIII
THE ECONOMIC BIOLOGY OF VERTEBRATES
Vocabulary
Isinglass, a kind of gelatin, not the substance in coal stove windows,
which is mica.
Appropriate, to take away for use (used as a verb).
Appropriate, suitable (used as an adjective.)
Fishes. The chief value of fish is as food, both for other animals
and for man. Out of 12,000 known species, at least 5000 are valu-
able as human food.
The annual catch of salmon, cod, halibut, mackerel, and herring,
amounts to many millions of dollars, while the shad, smelt, perch,
and bass are almost as valuable. The Pacific salmon alone are
worth about $15,000,000 per year and the Atlantic cod returns
about $20,000,000. In fact it was the cod returns in fisheries that
induced the settlement of New England and pictures of this cele-
brated fish may yet be seen in the state-house of Massachusetts,
on the bank notes of Nova Scotia and the postage stamps of
Newfoundland. The fish crop of Alaska in 1915 amounted to
three times the purchase cost of the whole territory.
Fish are eaten fresh, smoked, salted, dried, pickled, and canned.
Despite these various ways of preparation we do not use them as
extensively as we should.
The Government maintains departments of fisheries in thirty-
two states which regulate the times and methods of catching,
provides hatcheries for artificial raising of valuable kinds and dis-
tributes young fish to stock ponds and rivers, so that the supply
may not become exhausted.
Another important use for fish is as fertilizer since they are
480
THE ECONOMIC BIOLOGY OF VERTEBRATES 481
rich in phosphorous compounds which most plants need. The
menhaden is much used for this purpose as well as for its oil. In
1913 over a billion of this species were taken, from which were made
6,500,000 gallons of oil and 90,000 tons of fertilizer. The total
weight of the year's catch of this one kind was more than the
weight of all the inhabitants of Greater New York.
Cod liver oil is the easiest oxidized fat food in the world and
is valuable as a medicine. Isinglass, a fine quality of gelatine is
obtained from the air bladders of certain fishes. Glue is another
important product made from waste parts and bones of all sorts
of fish.
Amphibia. The chief value of this group lies in its activities
in destroying harmful insects. Frogs, toads, and salamanders,
all unite in feeding upon them, the toad being especially useful
in this respect. To a very much less extent, frog legs are used
for food; frogs might much better be left to fight insects, rather
than be used for this purpose.
Reptiles. We usually consider this group as useless or even
harmful, but with the rare exceptions of the venomous snakes,
the Gila monster, and a few man-eating crocodiles, this is not
true. Most snakes destroy either insects or harmful rodents,
though a few eat frogs, birds, or eggs.
The turtle family not only destroys insects, but the tortoise
furnishes flesh and eggs as foods and tortoise shell for ornaments.
Alligators and crocodiles are not particularly valuable and oc-
casionally are dangerous. Their hides are sometimes made into
leather.
Birds. The economic value of birds has already been mentioned;
they are our chief ally in the fight against our insect enemies;
they provide flesh and eggs for food; they supply feathers for
bedding and ornament; while their bright colors and sweet songs
have always made them cheerful companions and pets for man.
In order to preserve these valuable members of society we can
1. Learn to observe the laws made for their protection.
2. Help restrain their enemies, the plume hunters, game hogs,
cats, red squirrels, black snakes, and certain birds such as Cooper's
482 BIOLOGY FOR BEGINNERS
hawk, sharp-shinned hawk, great horned owl, and English spar-
row.
3. Help preserve the forests and city trees for their nesting.
4. Provide winter food for city birds.
5. Provide nesting boxes for some city species.
6. Try to inform others along these lines.
Mammals. Food. This group includes the animals that we
usually think of as of the most importance to man. The ungu-
lates furnish his chief sources of animal food, since here belong
cattle, sheep, and pigs, and many others. Man uses as flesh food
practically all hoofed animals with four toes, and from cattle also
obtains, milk, butter, and cheese. Besides these, rabbits, squirrels,
bears, raccoons, opossums, seals, and even bats, monkeys, and
whales are important foods for man. In fact all mammals ex-
cept the cat and dog. families are used as food by some group of
people or other.
Clothing. Next to their value as food, the mammal's chief
products are their body coverings, which man appropriates.
Sheep, goats, camels, and llama all produce valuable wools.
The list of fur-bearing animals includes the otter, mink, ermine,
marten, and their relatives, together with foxes, wolves, bears,
tiger, leopard, and even the humble skunk, while the sea otter
and seal are much more valuable. The seal herd, belonging to
the United States is the most valuable Government possession in
the world. Leather is obtained from the hides of cattle, sheep,
horse, hog, goat, seal, walrus, buffalo, and many other mammals
and is absolutely indispensable because it has no satisfactory
artificial substitute.
Various Products. The whale, largest of mammals, provides
several curious products; oil and a fine wax (spermaceti) are ob-
tained from some kinds. The oil whale also produces " whale
bone " which is made from a fibrous strainer device developed
from the roof of the mouth. Ambergris is an abnormal secretion
of the liver of sperm whales which is of enormous value as a
perfume.
Horn and bone products of many mammals are used for making
THE ECONOMIC BIOLOGY OF VERTEBRATES 483
ornaments, buttons, handles, etc. Ivory comes from the tusks
(teeth) of the elephant and walrus.
Transportation. Of much greater importance than these last
items, is the use of many mammals as beasts of burden. The
horse is easily first, with oxen, camels, dogs, goats, llamas, rein-
deer, water buffaloes, and elephants used in different countries to
a greater or less extent.
Pets. Mammals have been used by many as companions and
pets; in this class the dog is first, the horse, cat, and occasionally
other forms being admitted to this select society.
Among the mammals, also, are most of the " domestic " ani-
mals which man has learned to tame and breed for many of the
uses just mentioned. Here again, the dog comes first, as it was
probably derived from a domesticated wolf which primitive man
tamed for his company, protection, and aid in the hunt. Prob-
ably cattle or sheep were next controlled by man, though the
horse may have preceded them in learning to carry his master
in battle or the chase. To this list man is still adding useful
species either by breeding from present forms, or by taming new
ones when their value is discovered.
The other side of the account is represented by a few harmful
mammals, dangerous either to man himself, to his domestic ani-
mals, or to his crops. Among these are the large carnivora, such
as the tiger, lion, wolf, etc., which attack man or his flocks. In
this country carnivora destroy about $15,000,000 worth of stock
per year. The rodents, especially rats, mice, and squirrels do
enormous harm by destroying grains and other food stuffs. In
the case of the rat alone, the wastage amounts to about
$200,000,000 annually. Furthermore, rats and some squirrels are
infested with fleas which transmit the plague to man, and thus
are even more seriously harmful. As a whole it will be seen that
the mammals are not only extremely useful, but absolutely essen-
tial to man; without them our present civilization and mode of
life would be impossible.
484 BIOLOGY FOR BEGINNERS
COLLATERAL READING
. The following books have many references in various places; see index.
Familiar Fish, McCarthy; American Food and Game Fishes, Jordan and
Everman; American Animals, Stone and Cram; American Natural
History, Hornaday; Our Vanishing Wild Life, Hornaday; N. Y. Forest,
Fish and Game Commission Reports; The Frog Book, Ditmars; The Reptile
Book, Ditmars; Economic Zoology, Osborn, from page 311 to end; Useful
Birds, Forbush; Economic Value of Birds to the State, Chapman, N. Y.,
F. F. and G. Com.; Birds of Eastern North America, Chapman, pp. 6-7;
Bird Life, Chapman, Chap. I, and note; Birds of Eastern North America,
Reed, pp. 12-14; National Geographic Magazine, November, 1916, and
May, 1918; Domesticated Plants and Animals, Davenport; Birds in their
Relation to Man, Weed and Dearborn.
SUMMARY
I. Fishes.
1. Food for man (5000 species).
2. Food for aquatic animals.
3. Fertilizer.
4. Oil.
5. Glue, isinglass.
n. Amphibia.
1. Destroyers of insects.
2. Food (frog legs).
III. Reptiles.
Harmful activities.
1. Venomous snakes (rattler and copperhead).
2. Venomous lizard (Gila monster).
3. Man-eating crocodiles.
4. Destroy birds' eggs and young (black snake).
5. Destroy frogs (black and garter snakes).
Useful activities.
1. Destroy insects.
2. Destroy harmful rodents.
3. Furnish food (turtle meat and eggs).
4. Furnish shell (tortoise) and leather (alligator),
IV. Birds.
1. Destroy insects.
2. Destroy weed seeds.
3. Food (flesh and eggs).
4. Feathers.
5. Companions.
THE ECONOMIC BIOLOGY OF VERTEBRATES 485
How protect birds?
1. Obey and enforce protective laws.
2. Restrain their enemies.
(a) Plume hunters and game hogs.
(6) Cats, red squirrels, snakes.
(c) Cooper's hawk, sharp-shinned hawk, horned owl, English
sparrow.
3. Preserve forests and trees.
4. Provide winter food and summer homes.
V. Mammals.
1. Food, meat and milk (ungulates)
meat (various forms except dog and cat groups).
2. Clothing, wool (sheep, goat, camel, llama).
fur (rodents and carnivora).
leather (ungulates, etc.).
3. Various products.
From whale: oil, wax, "whalebone," ambergris.
From elephant: ivory.
From various mammals: horn and bone.
4. Transportation.
Horses, oxen, camels, reindeer, dogs, goats, llamas, water buffalo.
5. Pets.
Dogs, horse, cat, etc.
"Domestic animals."
6. Harmful mammals.
(1) Large carnivora (lion, tiger, wolf).
(2) Rodents (rats, mice, squirrels).
waste foodstuffs,
transmit disease.
CHAPTER XLIX
BIOLOGY AND AGRICULTURE
Vocabulary
Pulverizing, making into powder.
Tillage, plowing, cultivating, harrowing, or hoeing the soil.
Retain, to hold.
Diminishing, making smaller.
Civilization rests upon the soil. In so far as our knowledge
enables us to use the soil to best advantage, only so far can we
advance in population, wealth, and national growth. At present
we are far from realizing our greatest agricultural efficiency, as
the following tabulations show.
China supports 3500 people per square mile.
Japan " 2000
Belgium " 300
United States " 30 "
As to crop yields we compare as follows,
Maximum yield per acre U. S. yield per acre
Potatoes 500 bushels 96 bushels
Wheat 50 " 14 "
Corn 100 " 28 "
Oats 100 " 32 "
Evidently there is much to be learned before we shall obtain
the best results from our national resources.
Soil Formation. Soil is formed from rock by the action of heat
and cold, water and ice, bacteria and protozoa, which are all
engaged in pulverizing its particles and adding to it organic matter
and nitrogen compounds. Proper tillage admits air for plant use
486
BIOLOGY AND AGRICULTURE 487
and carbon dioxide to act chemically on the soil; it loosens the
soil grains to permit easy root growth and exposes new stores of
plant food for them to absorb. Loosening the top layers by
frequent tillage also forms a protective layer which retains water.
Soil Composition. Plants can obtain oxygen, hydrogen, and
carbon from air and water, but must depend' on the soil for all
compounds of nitrogen, phosphorus, and potassium which are
just as essential in the making of protoplasm.
To be fertile, a soil must contain compounds of these elements
in soluble form, available for plant use. The average soil contains
a supply of potassium compounds sufficient for 2000 years, phos-
phorous compounds to last for 130 years, but nitrogen compounds
only sufficient for 70 years' use. Yet nitrogen compounds are
more essential and used in greater quantity than either of the
others.
Evidently the supply of nitrogen is the limiting factor in de-
termining how long a soil will remain productive; hence its return
to the soil is one of the greatest problems in agriculture.
Maintaining the Soil. Every crop removes these essential
elements from the soil and erosion may rob it of as much more,
so man has learned to replace the removed substances by, 1. fer-
tilizers, 2. nitrifying bacteria, 3. crop rotation.
1. Fertilizers obtain potash as potassium chloride and sul-
phate, largely from German deposits. Phosphorous compounds
are obtained from bone ash and the phosphate rock found in
California and Florida. Nitrogen is supplied to the soil by
(a) Natural manures.
(b) Nitrate of soda from Chile.
(c) Slaughter house wastes.
(d) Ammonia compounds from coal distillation.
(e) Action of nitrifying bacteria.
A complete fertilizer should supply all three elements, but as
the soil often has enough of one or two, this is sometimes un-
necessary and analysis of the soil is the only sure way of deter-
mining its needs.
2. Bacteria, found in nodules on the roots of clover, peas, al-
488 BIOLOGY FOR BEGINNERS
falfa, and lentils, have the power of converting the free nitrogen
of the air into nitrogen compounds, available for plant use, so
clover crops actually benefit the land so far as nitrogen is con-
cerned.
Other bacteria help in decay of organic matter and return it
to the soil in useful forms; all dead tissue and natural manures
are acted upon in this way.
3. Rotation of crops merely applies what has just been said.
The farmer cannot use the same field for the same crop, year after
year, without removing the special soil compounds which that
crop requires and thus diminishing his return. He therefore
varies his crop so that clover or peas shall have a chance to replace
nitrogen compounds which wheat or corn may have removed.
He also alternates between crops that require hoeing and those
that do not, so that the soil may benefit by the different methods
of cultivation. Often the clover crop is plowed under so that the
organic matter as well as the nitrogen is returned to the soil.
Plant Breeding. Not only does biology bear upon soil condi-
tions .but also upon all that relates to seed planting, germination,
and growth. Especially is this true in the matter of testing and
selection of seed and in crossing and breeding of new varieties.
A glance at any seed catalog will show the great advances that
are being made by applying biologic methods to bettering the
varieties of plants.
In this same connection, all other methods of plant propaga 1
tion are concerned. Cuttings and grafts, pollenation, trans-
planting, and pruning all involve the use of biological information.
In 1900 the British Millers Association decided that the wheat
that was then raised in England was so unsatisfactory that they
engaged Prof. R. H. Biffen of Cambridge University to try to
improve the quality.
Professor Biffen obtained seed of all the different wheats, which
had any one desirable characteristic, such as stout straw, full
heads, immunity to rust, or resistance to cold weather. These
he raised separately, and cross-pollenated by hand, combining
their desirable features, till after years of effort, selection, crossing,
BIOLOGY AND AGRICULTURE 489
and rejection of the unfit, he developed the present English wheat
which combines nearly all the characteristics which the millers
demanded.
In the United States, Mr. Burbank stands at the head of our
plant breeders. By cross-breeding and rigid selection he has
developed many valuable new species. His improved potato adds
$17,500,000 to the annual income of the farmers of the United
States. He has increased the yield of some kinds of corn twenty
fold. He has improved known fruits in their quality, hardiness,
or resistance to insects. He has developed several new fruits,
either from wild species or by crossing. Many large and beauti-
ful flowers have been produced, such as the mammoth poppy
with a diameter of ten inches, and the delicate shasta daisy. One
of his most notable successes has been the spineless cactus, which
is now available as cattle fodder in regions where it is difficult to
provide food for stock.
Burbank's work is merely a very noted example of the ap-
plication of biologic laws to plant improvement, such as is being
carried on by all seedsmen and all intelligent farmers and gar-
deners. When we save seed from our best or earliest plants, keep
them separate from less satisfactory kinds, and plant their seed
again, we are following in the footsteps of these great breeders,
and utilizing the same laws of inheritance.
By similar methods, practically every plant that man culti-
vates has been improved and developed into forms that better
serve his purposes.
Plant Protection. Biology comes to the aid of the farmer in
his struggle against plant disease. Moulds, rusts, blights, and
bacterial attacks all have to be met by proper treatment of seed
with formalin, or the plant itself with fungus-killing sprays like
Bordeaux mixture.
Insect enemies and the means of checking them open another
chapter of farm biology. Here also belongs the study of useful
birds and their enormous value as insect destroyers.
Animal Husbandry. Principles of biology are also applied to
animal raising, their care and feeding, selection and domestica-
FIG. 153. Various races of pigeons, all probably descended from the
European rock dove, Columba lima, shown in lower right hand corner.
(After Haeckel.) From Kellogg.
BIOLOGY AND AGRICULTURE
491
tion. Especially is this true in the case of animal breeding for
improved varieties. Here are involved selection, inheritance,
and cross-breeding.
By following well-known biologic methods man can select al-
most any group of desirable characteristics and produce a breed
possessing them. As evidence of this, note the numerous and
widely different types of horse, cow, or dog that man has thus
developed.
In early years England had three general types of sheep,
FIG. 154. Typical American Merino ewe, a highly specialized breed of
sheep, with fine, close-set wool. (After Shaw.) From Kellogg.
some hornless, some with fine wool, and some producing good
mutton. By long and careful breeding and by rejecting all un-
satisfactory animals for propagation, they now have several races
that combine in a large degree all these useful features.
In similar ways we have different breeds of cows for different
purposes, the Jersey producing as much butter fat as ten ordinary
cows, the Holstein for large milk production, and the Hereford
for beef.
FIG. 155. Heads of various British breeds of domestic cattle, showing varia-
tions in shape of head and condition of horns: 1, Highland Scot; 2, Irish Kerry;
3, Aberdeen Angus; 4, Hereford; 5, Jersey; 6, Long-horned Midland. (After
Romanes.) From Kellogg.
BIOLOGY AND AGRICULTURE 493
Horses for trotting, running, draught, or mere appearance, are
bred and selected and their pedigrees so carefully recorded that
many a trotter can trace his ancestry much farther back than
most human aristocrats. The advantage lies with the horse in
another way, since his ancestors were valued because they could
do something well, and not merely because of the accident of birth.
Bacteria on the Farm. Care of milk on the farm has been al-
ready mentioned, but in cream, butter, and cheese as well, the
farmer is using some bacteria and opposing others. The char-
acteristic flavors and odors of butter and cheese are due to use-
ful bacterial action, 'while the spoiling and decay of these products
is due to attack of others.
Bacteria are working also in the preparation of ensilage and
the " curing " of meats and tobacco. In fact if you will look back
over your work you may be surprised at the extensive role of
bacteria as farm laborers.
Here are some of their activities, good and bad:
They aid in decay of organic matter for fertilizers.
They cause decay of valuable foodstuffs.
They help return nitrogen to the soil.
They cause many plant and animal diseases.
They aid in all dairy processes.
They spread disease by way of milk and other foods.
They help in producing ensilage.
They aid in curing meats, flax, and tobacco.
There is no branch of industry so important, and none so closely
associated with biology as the industry of agriculture. Most of
the material found in the chapters on economic biology both of
plants and animals, together with much under forestry and gen-
eral conservation methods, bears directly on this fundamental
occupation.
COLLATERAL READING
Agriculture for Beginners, Burkett, Stevens and Hill; The Fertility of
the Land, Roberts; Soil Fertility and Permanent Agriculture, Hopkins;
Principles of Agriculture, Bailey; Farmers for Forty Centuries, King; Fer-
tilizers, Voorhees; Practical Agriculture, Wilkinson; First Book of Farm-
ing, Goodrich; Cyclopedia of American Agriculture, Yols. II and III;
494 BIOLOGY FOR BEGINNERS
Milk and Us Products, Wing; Types and Breeds of Farm Animals, Plumb;
Commerce and Industry, Smith, pp. 20-85; Principles of Breeding, Daven-
port; Domesticated Animals, Shaler; First Principles of Agriculture, GoS
and Mayne; Science of Plant Life, Transeau, pp. 217-232.
PLANT BREEDING
Elementary Studies in Botany, Coulter, pp. 326-339; New Creations in
Plant Life, Harwood, entire; Origin of Cultivated Plants, De Candolle,
entire; Experiments in Plants, Osterhout, pp. 409-453; Botany for Schools,
Atkinson, pp. 455-478; The Living Plant, Ganong, pp. 426-444; Species
and Varieties (Mutation), De Vries, entire; Domesticated Animals and
Plants, Davenport, entire; Elementary Biology, Peabody and Hunt,
pp. 105-125, 241-300.
DOMESTIC ANIMALS
Elementary Zoology, Davenport, pp. 420-450; Domesticated Animals
and Plants, Davenport, entire; Economic Zoology, Kellogg and Doane,
pp. 321-334; Pet Book, Comstock, entire; Farm Bulletins.
SUMMARY
1. Importance of agriculture.
2. Lack of efficient development.
3. Soil formation.
4. Soil composition:
Potassium compounds.
Phosphorous compounds.
Nitrogen compounds.
Organic matter or humus.
5. Soil maintenance.
By fertilizers.
By bacterial action.
By crop rotation and cultivation.
6. Plant breeding.
7. Plant protection.
From insect enemies.
From fungus attack.
8. Animal husbandry.
Care and feeding of stock.
Breeding new forms.
9. Bacteria on the farm.
CHAPTER L
THE ECONOMIC IMPORTANCE OF FORESTS
Vocabulary
Erosion, washing away of soil.
Retention, holding.
Girdling a tree, cutting off a ring of bark and cambium to kill it
while standing.
Re-forestation, scientific replacement of trees when cut.
The great importance of forests is little appreciated. When
we are told that they occupy 35 per cent of the area of the United
States and that lumbering is our second largest industry, still
their most important services are overlooked.
VALUE OF FORESTS
Control of Water Supply. The most important service rendered
by forests is in regulating water supply. The forest area acts like
an enormous sponge absorbing the heavy rainfall, in its layer of
humus. This secures the following important results.
1. Prevents floods and causes steady flow.
2. Prevents drouth by storing water in the wet season.
3. Prevents washing of soil into rivers.
4. Keeps rivers at uniform level for transport.
The effect of forests in this regard can only be appreciated when
compared with an area which has no forest protection and is sub-
ject to heavy rainfall, such as the Bad Lands of Dakota. Here
the water runs off at once in floods, while between rains, the land
is almost a desert, due to drouth, and the rivers are so filled with
mud and so changeable in levels as to be useless for commerce
or power.
495
496
BIOLOGY FOR BEGINNERS
THE ECONOMIC IMPORTANCE OF FORESTS
497
Benefit to Soil. The early settlers regarded the forests as the
enemy to agriculture and so they were, in so much as some clear-
ings had to be made to make room for the farms, but in a larger
sense, the forests are a distinct benefit to the soil. Erosion, the
washing away of soil by rain, is one of the worst enemies of ag-
riculture and this is prevented by the forest areas, whose roots
hold back the earth and whose leaves protect the surface. Fur-
FOREST PRODUCTS IN 1907.
CLASSES
FIREWOOD.
LUMBER AND SHINGLES
POLES, POSTS. AND RAILS.
HEWED CROSS-TIES
COOPERAGE STCT,K
PULP-WOOD.
ROUND MINE TIMBERS
DISTILLATION WOOD...
FOREST MATERIAL REQUIRED
BILLIONS Or CUBIC FEET
Fig. 157. Uses of Lumber. From Smith's Commerce and Industry.
thermore, the organic matter (humus) which collects on the forest
floor, supplies an essential element to all fertile soils.
In some areas, the forests perform another function in pre-
venting the spread of wind-blown sand over fertile areas which
are thus saved for use.
Effect of Forests on Climate. While this may not rank with
the two preceding in importance, yet it is certain, that by its
retention of moisture, forests do modify the climate over large
areas and apparently influence local rain-fall as well. To a less
498 BIOLOGY FOR BEGINNERS
extent, forests affect climate by their action as a protection from
wind or sun.
Forests as Home for Birds and Game. This is a matter often
overlooked, but when we recall the enormous economic value of
birds, and realize that they depend largely on the forests for their
home, the importance of this factor is apparent. As a home for
fur-bearing animals, game, and fish the forests also are important
to man in many relations little realized.
Forest Products. When the economic value of forests is men-
tioned one naturally thinks of the lumber and other direct prod-
ucts as the most important. While not equal to those already
mentioned, the variety and value of the manufactured forest
products is enormous.
Time will not permit discussing each in detail so, in the tabula-
tion which follows, some of the most important items are mentioned.
FOREST PRODUCTS
1. Timber products.
Lumber Laths
Shingles Veneers
Railroad ties Poles
Mine timbers Ship timbers
2. Paper (spruce, poplar, etc.).
3. Fuel (wood, charcoal, coal).
4. Naval stores (pitch, tar, turpentine, rosin).
5. Tanning material (hemlock and oak bark).
6. Maple sugar.
7. Spruce gum.
8. Distillation products Uses
charcoal fuel
lamp black ink
tar tar paper, wagon grease, and wood
preservation
oil varnish, soap, disinfectants, ink
oxalic acid dyeing, bleaching, making formic
acid
acetic acid white lead paint, dyes, and medi-
cines
wood alcohol varnish, solvent, dyes, denaturing
alcohol, fuel, making formalde-
hyde, and smokeless powder
acetone explosives, films, dyes, and solvent
THE ECONOMIC IMPORTANCE OF FORESTS 499
1. Timber products.
NOTES ON TABULATION
(a) U. S. produces 38,000,000 thousand feet of "soft wood" lumber
per year, and 8,000,000 thousand feet of hard wood lumber.
(b) The chief kinds are
yellow pine from Carolina, Georgia, etc. (40 %).
white pine from Michigan, Wisconsin, Minnesota,
spruce and redwood from the Pacific slope.
(c) The enormous number of trees cut may be judged when we realize
that 65 % is wasted in making lumber.
<
Yellow Finer
(Including the Short
) I
L- 2
Billions of
(
Board Feet
* 4
t S
6
Leaf and Loblolly
fines)
Oak
UaK
\Vh\ia "Pi -no
\V nite .tine
Hemlock
Western Pine
Spruce
Maple
Cypress
Tulip Poplar
Bed Gum
Ml
Redwood
mmm
Chestnut
mmmm
Beech
mam
Birch
mmm
Cedar
mm
Basswood
mm
Hickory
mm
Elm
mm
Larch
mm
Ash
mm
Cottonwood
White Fir
Tamarack
Sugar Pine
Tupelo
Balsam Fir
I
Sycamore
1
Walnut
1
Lodgepole Pine
I
All Other
FIG. 158. Lumber production by varieties, 1910. (U. S. Forest Service.)
500 BIOLOGY FOR BEGINNERS
(d) Railroads use 2500 ties per mile there are about 200,000
miles in U. S. and the ties have to be replaced every seven
years; this means the use of about 70,000,000 ties per year.
2. Paper. A single New York daily newspaper uses for paper the spruce
trees from 44 acres per day.
The greatest amount of paper is made in New York, Wisconsin, and
New England.
3. Fuel. Coal is indirectly a forest product as it is the carbon from trees
of ages ago, partly decomposed under the earth by heat and
pressure.
4. Naval stores. These are so called because tar and pitch are used in
connection with ship building and cordage. The crude pitch is
obtained by notching the southern pines and collecting the product -
which is distilled, making tar, turpentine, and rosin. U. S. ex-
ports seven times as much turpentine and ten times as much rosin
as any other country. The value reaches $36,000,000 per year.
5. Tanning materials. Quebracho and other tropical woods could be
included.
6. Maple sugar. U. S. produces 50,000,000 pounds and 4,000,000 gallons
of syrup per year, of which Vermont and New York supply over
three-quarters.
7. Spruce gum. This gum forms in masses on the bark of spruces and is
gathered and cleaned in the winter. Really fine gum is worth
several dollars a pound.
8. Distillation products. Various kinds of hard wood are heated in
closed iron cylinders, destructive distillation goes on, charcoal
remains in the cylinders and the other products go off as vapors and
arq condensed and separated. We will learn more about this in
chemistry. For the present notice how many products there are.
and for what various and important purposes they are used.
FOREST ENEMIES
Man. Valuable as they are, forests have many enemies, and
strange as it may seem, one of the worst of them is man. Of
course we destroy much standing timber for necessary use and
for clearing for agriculture, but much more is utterly wasted in
other ways. Annual growth in the United States is 7,000,000,000
feet but the annual consumption totals over 20,000,000,000 feet.
Careless lumbering, in which only a few trees are used and many
destroyed, or wasteful methods, by which only one-fourth of the
cut timber ever becomes lumber, are some of man's methods of
attack. Cutting hemlock and using only the tan bark, leaving
THE ECONOMIC IMPORTANCE OF FORESTS 501
the stripped timber a total loss and danger in case of fire, is an-
other barbarous waste for which man is responsible. .
Fire is one of the forests' worst foes and except for lightning,
man is the author of them all. Sparks from locomotives and camp
fires of careless hunters account for some which start accidentally,
while grazers and berry pickers start fires on purpose to help their
crops, and men, clearing land, often lose control of their fires and
cause great destruction. In 1915 there were 40,000 fires, covering
6,000,000 acres, or over 1 per cent of all forests in United States,
which caused a loss of $7,000,000 and many lives. During the
same year 2j million were spent for forest protection or only
one-third the year's loss.
Insect Enemies. In our study of insects, the damage which
they do to crops was mentioned, and the forest crops are no ex-
ception. The saw fly, bark beetles, gyspy moth, tent caterpillar,
and tussock moth are some of the most harmful, and, unlike the
orchard pests, the extent of the forests makes spraying impos-
sible. The birds are almost our sole protection against these
forest enemies, though toads, snakes, and ichneumon flies do
their share.
Fungus Enemies. Whenever we see a shelf fungus on a tree
we may be sure that tree is doomed unless help is provided. But
the most damage is done by less conspicuous forms, such as the
rusts and blights, of which the chestnut blight is a notable ex-
ample. (Not only are the trees destroyed but their lumber is
ruined by fungi, both in standing timber and often after it is cut
and piled.)
Weather Conditions. Despite their great strength, trees often
fall victims to wind and snow, and in many regions great, strips
are blown down by tornadoes making the almost impassable
" windfalls " which later, when dead and dry, furnish ideal fuel
for forest fires. Sleet storms destroy many buds and even large
branches, especially if followed by severe winds, and thus damage
or kill many valuable forest trees.
Grazing Animals and Others. Large herds of cattle or sheep
often damage forests by trampling on the young trees and by
502 BIOLOGY FOR BEGINNERS
feeding on the limbs and leaves. Mice, porcupines, and rabbits
often girdle the trees by eating their bark, and some little damage
is done by birds and squirrels which eat their seeds.
FOREST PROTECTION
The value of the forests of the United States is evidently very
great, but only recently have efficient means been taken to pro-
tect them.
Legal Protection. To begin with, one of the most important
means of protection lies in the hearty cooperation of every citizen
in observing and enforcing the present forest laws as to fire pre-
vention and proper lumbering.
Careful Lumbering. The average lumberman harvests his
crop, but does not plant another. Hence we face the ever rising
cost of lumber, whereas, if the timber annually cut is regulated
so as not to exceed the year's growth the forest will continue to
produce like any other crop.
Reforestation. Another means of protection consists in re-
planting, either by setting out small trees, or cutting only mature
ones and leaving young and seed-bearing trees so that nature
can attend to the replanting.
Forest Reserves. The Government has established large forest
reserves which are kept by the Nation to protect drainage for
irrigation, to supply grazing areas, and provide timber under
supervised cutting. (See p. 496.)
Forest Rangers. To protect these enormous tracts of Govern-
ment forest from fire or theft, there is provided a body of expert
Forest Rangers under Government control.
These men patrol the forests, report and prosecute theft, and
organize to fight forest fires before they may get out of control.
This work has saved millions of dollars and many lives in the line
of fire prevention alone.
Forestry Schools. Furthermore, there are established Forestry
Schools at Cornell, Michigan, Syracuse, Yale, and elsewhere, in
which the scientific methods of lumbering, planting, and pro-
THE ECONOMIC IMPORTANCE OF FORESTS 503
tection are taught. For those unable to attend these institutions,
many bulletins and other publications are available from state
and national governments, giving valuable information regard-
ing this important source of our natural wealth.
The farmer who would cut down his apple trees to gather the
fruit, or who harvested a crop without planting another, would
be considered insane, yet the treatment of our forest resources
amounts almost to this. The sooner we realize the fact that a
forest is a crop to be tended and gathered, planted, and protected
like any other, the sooner our lumber, paper, and other products
will cease to increase in cost.
TIMBER STRUCTURE
A great deal of the value of lumber depends on one of three
factors, its durability, strength, or appearance. These in turn
depend upon the minute structure of the tree stem and though
this was discussed in Chapter XI, it needs to be recalled in this
connection.
A woody stem is made up of wood fibers and ducts (tracheids
in the evergreens). These are arranged in annual rings caused
by larger ducts forming in the spring, and fewer and smaller ones
in autumn and winter.
" Grain." Evidently a board cut from such a stem will have
alternate layers of harder and softer tissue which cause the
" grain " seen in most woods. If the board is cut from near the
side of a log, few annual rings will show on the surface, their
sides will be exposed for wear and will give a grain figure like
(A). If the board be cut near the center of the log (B) all the
annual rings will show and their edges are exposed for wear which
makes the lumber more durable and less liable to sliver up. The
former (A) is known as " bastard sawed " and the latter (B) as
" rift sawed " lumber. As a log is cut up, the first boards will
be bastard grain, then as the center is approached, more and
more nearly rift grain, and finally bastard cut after the center is
passed. Obviously there are more bastard than rift boards and
hence the latter are more expensive, as well as more durable.
504
BIOLOGY FOR BEGINNERS
Quarter Grain. In all stems there are pith rays extending from
pith to bark, but only in oak, maple, sycamore, and a few others
are they large enough to affect the grain of the timber. Since
these pith rays run toward the bark, a board cut at (C) would
show only their cut ends which would be too small to notice,
whereas, if the board be cut at (D) the pith rays will be cut more
or less side wise and will show as the plates or flakes which are
characteristic of " quartered oak," giving it its beauty and value.
In order to get as many boards as possible showing this flake
. FIG. 159. Diagram showing cause of grain in timber and various
methods of sawing so as to take advantage of the grain.
grain (side of pith ray) the logs are sometimes cut in quarters and
then sawed from the center outwards so as to show the sides of
as many pith rays as possible hence the term " quarter sawed "
or " quartered oak." The bastard cut oak, which shows only
the annual ring grain (as in A) is sold as " plain " oak and while
almost as durable is not nearly as handsome.
Heart and Sap-wood. As a tree grows larger, only the outer
annual rings carry sap in their ducts, while the inner region be-
comes practically dead, its only function being support. This
THE ECONOMIC IMPORTANCE OF FORESTS 505
center part is called the " heart wood " and is often darker in
color and more durable than the outer, live region or " sap-wood."
The heart of a tree may totally decay and yet cause the tree no
harm other than weakening its strength, but the sap-wood is neces-
sary to the growth of the tree and may even keep it alive when the
bark has been girdled.
Shrinkage and Warping. Fresh-cut timber contains much water
and the process of drying, called " seasoning," has to be thoroughly
accomplished before it can be used. This is because lumber
shrinks as it dries and no amount of nailing will hold poorly sea-
soned boards together. As a board dries there is a tendency for
the side nearest the bark to shrink fastest causing the board
to curve away from the center, or " warp." Unless the lumber
be properly piled and dried it may be rendered unfit for use.
Hard and Soft Woods. Trees can be grouped in two classes,
those with broad leaves, which are shed annually (maple, oak)
and those with needle-shaped leaves, which are not all shed at
one time (pine, spruce). The former produce " hard wood"
lumber and the latter " soft wood," though some broad-leaved
trees have lumber that is very soft (basswood, willow) and some
pines produce " hard pine " lumber, which nevertheless, is classed
as a " soft wood."
" Knots " in lumber are places where a branch has been broken
off and the scar covered by additional annual rings. If the wound
healed at once and no rot commenced, the knot is tight and does
not harm the lumber so much, but if the healing was incomplete,
a loose knot results and a knot-hole in the board is the result.
A tree grows in height only at the tips of new branches; it grows
in thickness layer by layer, over all parts, hence a nail driven into
a tree will always remain at the same height from the ground, but
will be covered, in time, by the growth in thickness.
Street Trees. In proportion to their number, trees are more
valuable in the city than in the forest. Shade trees add to the
cash value of property in the same way as do wide streets, good
pavements, and favorable location. A city always is proud of
handsome trees and shady streets, but often there is little care
506 BIOLOGY FOR BEGINNERS
exercised in their planting or maintenance. If quick growth and
immediate results are wanted, soft maples or poplars are used, but
these are short lived and rather easily broken by storms. Elms
and hard maples, on the other hand, grow slowly, but are sturdy
and live to great age.
City trees require special protection as they are especially
valuable and are not living under natural conditions. Insect
attacks can be overcome by proper spraying; damage by horses
and traffic can be prevented by guards around the trunks; suit-
able laws can be enforced to protect from damage by careless
linemen who cut out the tops to pass their wires; sidewalks and
curbs can be kept from injuring the roots; and " surgical " treat-
ment should be used when rot or injury makes wounds in any part.
COLLATERAL READING
Elementary Studies in Botany, Coulter, pp. 419-431; A First Book of
Forestry, Roth, entire; Care of Trees, Fernow, entire; Handbook of Trees,
Hough, look through; Nature Study and Life, Hodge, pp. 365-391; Prac-
tical Biology, Smallwood, pp. 376-388; Principles of American Forestry,
Green, entire; Trees of Northern United States, Apgar, look through;
Commerce and Industry, Smith, pp. 182-208; Our Native Trees, Keeler,
look through; "American Forestry" a monthly periodical.
SUMMARY
Value of Forests.
1. Control of water supply.
2. Benefit to soil, humus.
3. Effect on climate, wind protection.
4. Home for birds and game.
5. Forest products (see tabulation).
Enemies of the Forests.
1. Man, through careless lumbering, fires, etc.
2. Insect enemies.
3. Fungus diseases.
4. Weather conditions, sleet, frost, snow.
5. Grazing and other animals. Rodents.
Protection of Forests.
1. Laws, enforced and supported by people.
2. Careful lumbering.
3. Reforestation, planting, etc.
THE ECONOMIC IMPORTANCE OF FORESTS 507
4. Forest reserves held by the Government.
5. Forest rangers to protect reserves.
6. Forestry schools, to instruct people.
Timber Structure.
1. Grain, due to annual rings, bastard and rift, due to pith rays,
quarter and plain.
2. Heart and sap wood.
3. Shrinkage and warping.
4. Hard and soft woods.
5. Knots.
Street Trees.
1. Value.
2. Most useful kinds.
3. Means of protection.
CHAPTER LI
TOBACCO AND TABLE BEVERAGES
Vocabulary
Nicotine, a harmful ingredient of tobacco, an alkaloid narcotic.
Acreolin, an irritating substance in tobacco smoke.
Caffein, an alkaloid found in tea, coffee, and cocoa.
Cocaine, an alkaloid from leaves of coca plant. No connection
with cocoa.
Morphine, an alkaloid from the opium poppy juice.
The damage done by alcohol and tobacco are often dealt with
in the same chapters and spoken of together, as if they had much
in common. This is unfortunate, for young people, seeing men
little harmed by use of tobacco, will assume that alcohol is no
worse, and come to very wrong conclusions.
Tobacco does harm enough, wastes resources enough, but we
ought not to let alcohol assume any comparison of their relative
danger. This is not to excuse the use of tobacco, but to prevent
young persons from concluding that one is no more harmful than
the other, merely because they are often spoken of together. A
comparison of this chapter with the one on alcohol will make the
matter sufficiently plain.
Tobacco. It is well known that protoplasm in a young plant
or animal is more easily injured than when it has attained full
growth. The seedling plant is more easily killed by frost or heat;
the chick is harmed by exposure that would not be felt by the hen ;
the human infant is injured by various things which would not
affect the adult at all. This is not alone because of the deference
in size of body, but the growing active protoplasm is much more
sensitive than when it reaches maturity, and therefore is much
more seriously affected by stimulants and narcotics.
508 '
TOBACCO AND TABLE BEVERAGES 509
Herein lies the chief biologic argument against the use of to-
bacco. Tobacco contains a harmful alkaloid, nicotine, and also
produces when burned, carbon monoxid, which is a poisonous gas.
In addition if the smoke is inhaled, a substance called acreolin,
together with the smoke particles, increases the irritating effect.
If used by boys who have not attained the full physical ma-
turity of twenty years or more, these substances produce numerous
and serious results which should at least postpone the use of to-
bacco till later life.
Tobacco is narcotic in effect; narcotics tend to decrease bodily
efficiency and hinder growth. The physical effects, while not to
be compared with the ravages of alcohol, are nevertheless im-
portant and should be noted.
Irritation to Mucous Membranes. Smoking certainly irritates
throat and lungs, especially if the user " inhales." This opens
the way for germ attack in addition to the harm done to the tis-
sues by smoke and acreolin. The eyes are also irritated especially
when one smokes and reads at the same time.
Effect on Endurance. Any narcotic interferes with nerve con-
trol, especially of heart and lungs. That this is the case with
tobacco, has been abundantly proven by experiment. For this
reason, no trainer permits smoking by members of his team,
knowing well that endurance and " wind " cannot be developed
when tobacco is used. The United States forbids its use at West
Point and Annapolis because of its harmful effects, both physical
and mental. Figures obtained from six leading colleges show that
of those who " made the team " just twice as many were non-
smokers.
Effect on Growth. In some cases the use of tobacco seriously
affects digestive processes and in its early use the stomach usu-
ally revolts at its presence. The effect of excessive smoking may
even extend to the vital activities of protoplasm and actually
" stunt the growth " of various organs. This is common where
it is used when very young.
Effect on Mental Development. Many investigations at dif-
ferent schools and colleges have thoroughly proven that the use
510 BIOLOGY FOR BEGINNERS
of tobacco affects the brain enough to impair scholarship.
Dr. Meylan, physical director at Columbia, reaches these con-
clusions:
1. Smokers averaged eight months behind non-smokers in their
advancement.
2. Scholarship standing of smokers was distinctly lower.
3. Use of tobacco by students is closely associated with lack
of ambition, application, and scholarship.
Another investigation shows that:
1. Smokers average lower in grades.
2. Smokers graduate older.
3. Smokers grow more slowly in height and weight.
4. 95 per cent of honor pupils are non-smokers.
Dr. Andrew D. White, who for twenty years was president of
Cornell University, says, " I never knew a student to smoke ciga-
rettes who did not disappoint expectations, or to use a common
expression ' kinder peter out.' I consider a college student who
smokes as actually handicapping himself for his whole future
career." Dr. White was not a fanatic and used tobacco him-
self after he reached middle life.
In spite of such evidence boys certainly will note many success-
ful men, perhaps their own fathers, who do not seem to be harmed
by smoking, and, forgetting the difference in age, will draw wrong
conclusions. Tobacco would do less harm if it were more harm-
ful, so that its effects could be .more easily traced.
For such prospective smokers there are other arguments.
1. Tobacco certainly becomes a " habit." Do you want to be
" held " by a useless and probably harmful drug?
2. Tobacco is offensive to many people. Are you so selfish as
to gratify your taste to the discomfort of others?
3. Tobacco decreases your personal attractiveness. The odor
of breath, hands, and perspiration, the stains on fingers and
teeth, do not add to your good looks.
4. Tobacco is expensive. A regular- smoker spends more than
he realizes, on his indulgence. Don't you think you could have
more fun for your money?
TOBACCO AND TABLE BEVERAGES 511
5. The growth and manufacture of tobacco wastes soil, labor,
and money, sorely needed in productive lines of industry.
6. Smokers cause about one-fourth of the fires, both in buildings
and forests. You can scarcely find a factory without its " No
Smoking " signs on this account.
To quote from another authority in conclusion:
" Whatever difference of opinion there may be regarding the
effect of tobacco on adults, there is complete agreement among
those best qualified to know, that the use of tobacco is in a high
degree harmful to children and youth."
Tea and Coffee. To a degree much less than tobacco, these
beverages contain an alkaloid called caffein. As with tobacco,
their use is certainly not wise for the young. With adults, mod-
erate indulgence may do no harm or may even be beneficial,
though this is a matter which every person must decide for
himself.
Neither has much food value, both are rather costly, and both
tend to become habits. On the other hand they sometimes seem
to soothe the nerves (which ought not to need soothing), or to
permit one to continue work when nearly tired out, which also is
a rather doubtful benefit.
Cocoa and Chocolate contain less caffein and a great deal of fat,
hence are real foods. More people should learn to properly pre-
pare them and then tea and coffee would be less used, with benefit
to all concerned.
It seems almost unnecessary to say that no medicine or beverage
containing alcohol, opium, morphine, chloral, cocaine, or any of
their derivatives should ever be used except by advice of a rep-
utable physician. The awful danger of forming a " drug habit "
in this way has led to stringent laws, which we should all help
enforce.
512 BIOLOGY FOR BEGINNERS
TABULATION OF SOME COMMON DRUGS
Stimulants
Narcotics
Alcohol, slight first effect
Caffein in tea, coffee, and cocoa
Strychnine
Nux vomica
Gentian
Quinine
Alcohol, general effect
Nicotine
Opium, morphine, etc.
Chloral
Cocaine, heroin, etc.
Codeine
COLLATERAL READING
A Handbook of Health, Hutchinson, pp. 89-93, 103-107; The Human
Mechanism, Hough and Sedgwick, pp. 357-362, 377-379; Applied Biology,
Bigelow, pp. 551-553; The Next Generation, Jewett, pp. 136-144; Ap-
plied Physiology, Over ton, see index; General Physiology, Eddy, see
index; Principles of Health Control, Walters, see index; Civics and Health,
Allen, pp. 363-368; Elementary Biology, Peabody and Hunt, Ft. II,
pp. 75-81.
SUMMARY
1. Comparison of alcohol and tobacco.
2. Tobacco. Physical objections to its use.
Sensitiveness of growing protoplasm.
Smoking exposes to nicotine, carbon monoxide, acreolin, etc.
General narcotic effect.
Irritation to mucous membranes.
Reduces endurance.
Interferes with growth and digestion.
Seriously impairs mental development and scholarship.
Social objections to its use.
It becomes a useless habit.
It is a selfish habit, because offensive to many.
Decreases personal attractiveness, odor, stains, etc.
Unnecessary expense.
Wastes soil, labor, and money in its production.
Danger in causing fires.
3. Tea and coffee.
Contain caffein.
Very slight food value.
May harm digestion or nerves.
Certainly not good for young people.
Unnecessary expense.
TOBACCO AND TABLE BEVERAGES 513
4. Cocoa and chocolate.
Contain little caffein and much fat.
Useful as foods.
5. Coco-cola and similar drinks.
May contain harmful alkaloids.
Seems to become habitual.
Expensive.
ALCOH01
CHAPTER LII
L IN RELATION TO BIOLOGY
Vocabulary
Magnitude, size or importance.
Detriment, harm.
Acceleration, speeding up action.
Excessive, too great.
Morbid, abnormal.
Pre-disposition, tendency toward.
Potent, powerful.
Therapeutics, curative medicine.
The chemist would say that " alcohol " is one of a number of
similar compounds, containing carbon, hydrogen, and oxygen in
the proportions C2H tt O and would insist that we call it " ethyl
alcohol " or " grain alcohol " to distinguish it from wood alcohol,
glycerine, and many other similar forms. The physiologist or
physician would tell us that it is a narcotic poison in its action on
the tissues, disturbing especially the nervous system.
The reason that this substance demands a chapter in a biology
text is that man, from the earliest times, has used this drug be-
cause of its intoxicant effects, until now its bearing upon the
development of the human race has become one of the greatest
biological problems.
Alcoholic beverages may be classed roughly in three groups:
1. Beer (2-5 per cent alcohol) made from fermented barley.
2. Wine (15-20 per cent alcohol) from fermented fruit juices.
3. Whiskey (30-50 per cent alcohol) from either source, but
distilled to increase its strength.
In ancient times before modern methods of malting and dis-
tilling were invented, wine was a rare and comparatively unim-
514
ALCOHOL IN RELATION TO BIOLOGY 515
portant drink, but now, both the amounts used and the alcohol
contained, have so increased that alcoholic liquors are a biologi-
cal question of the first magnitude. In the discussion that follows
it must not be forgotten that alcohol is an indispensable chemical
substance, used as a solvent, preservative, and raw material in
numerous industries. These are matters that concern the manu-
facturing chemist, while biology has to do only with its effect
when used as a beverage by man.
Physical Effects. In the first place alcohol, although oxidized
in the body, cannot.be classed as a food, yet is often so called by
people who should know better. A food is " a substance which
when assimilated in the animal body builds tissue or produces
energy without harming the organism." Alcohol harms the
organism in various ways as will be shown, hence cannot be classed
as a food.
Alcohol is chiefly oxidized in the liver and the heat is lost by
the rush of blood to the skin (Atwater). This oxidation produces
uric acid which overworks the liver and kidneys, to the detriment
of both (Beebe).
Dr. Irving Fischer of Yale says, " These heat values cannot
be expended without at the same time poisoning the system with
alcohol, so it is not even technically correct to count the heat
value of alcohol as such."
Dr. Von Bunge, chemist of University of Basel says, " Alcohol
produces energy (heat) but increases the loss of heat still more;
the net result being a lowering of temperature; the feeling of
warmth is an illusion due to narcotic action on the nerves."
The same authority also says, " Beer does contain small amounts
of dextrine and sugar but we already eat too much of these, and
supplied by beer, they are fabulously expensive ; beer does not
promote digestion."
Despite this claim that alcohol is a food, no one really thinks of
using it for nourishment, but rather because of its narcotic effects
on the nerves. Opium and phosphorus are also oxidized in the
body, but no one claims food value for these poisons, and alcohol
belongs in the same class.
516 BIOLOGY FOR BEGINNERS
Alcohol, then, is not a food, because
1. It produces a net loss of energy, though oxidized.
2. It does not build tissue, but poisons it.
3. It furnishes its small apparent energy at great expense.
Effect on Nutrition. Alcohol withdraws water from all food-
stuffs and acts chemically on proteid, exerting a hardening action
in both cases and hindering the work of the digestive fluids. In
the same way it hardens and irritates the tissues lining the ali-
mentary canal, especially the walls of the stomach, where it al-
ways interferes with normal action, and may cause serious disease.
Alcohol certainly increases the flow of digestive fluids and its
medicinal use was based largely on this effect until it was found
that the abnormal flow caused a lack of fluids later, and that
glands that had been " stimulated " by alcohol, refused to re-
spond to the presence of mere food.
" Acceleration of gastric action is counter-balanced by inhibi-
tory effect of alcohol on the chemical processes of digestion."
Chittenden.
The direct effect of alcohol is shown most plainly in its action
on the liver, where, as already mentioned, it overtaxes and irri-
tates that important organ. Over 60 per cent of deaths due to
cirrhosis of the liver are cases where the disease was caused by
alcoholic liquors.
Effect on Circulation. The chief effect of even small amounts
of alcohol is to paralyze the vaso-motor nerves which control the
blood flow and heart action.
Thus with relaxed artery walls and lessened heart regulation,
the pulse is quickened, the blood is driven to the skin and mucous,
membranes, and the familiar " stimulant " effects rare poduced.
Notice in the first place that this is due, not to any " stimulation "
at all, but to a deadening of the nerve controls, and second, that,
although the skin feels warm, due to the excess blood, it is actually
losing heat, because so much blood has been brought to the surface.
"The general temperature is always lowered." Macey.
Not only this, but with continuous use alcohol keeps the capil-
laries relaxed, causing reddening of the skin and inflammation of
ALCOHOL IN RELATION TO BIOLOGY 517
the mucous linings, both of which favor the attacks gf various
diseases.
Alcohol reduces the control centers and so the circulatory
organs "run away"; they are NOT stimulated. One might as
well talk about stimulating a steam engine by removing the gov-
ernor. Yet this is a very common error.
Alcohol is never a stimulant, but always a narcotic, producing
its results by its interference with nerve control in every case.
" No amount of alcohol, however given, can increase the amount
of work done." - Dr. Woodhead, Cambridge University.
Aside from its interference with the normal distribution of blood
and consequent pre-disposition to colds and inflammations, its ex-
cessive use may permanently harden the arteries (arteriosclerosis),
or affect the heart muscles (fatty degeneration), though these are
not so important from a biologic standpoint as the more general
effects which even occasional use produces.
Effect on Respiration. The interference with blood regulation
is particularly harmful in the lungs, causing inflammation and
diminishing resistance to pneumonia and congestive diseases. At
the same time connective tissue is increased and the actual lung
capacity is lessened. A curious chemical result also ensues;
alcohol is so easily oxidized, that it uses oxygen actually needed
to release the energy from real foods. This appears to be a " stimu-
lation " of the breathing process, when as a matter of fact, the
added air is not sufficient to oxidize the alcohol alone. The final
result is loss of energy from the unoxidized food in addition to the
heat wasted by way of the skin, as shown above.
Effect on Excretion. This improper oxidation, and interference
with blood flow and skin functions produce excess of uric acid and
other wastes for the kidneys to dispose of, resulting always in
impaired function and sometimes in serious disease. Rheumatism,
Bright's disease, and fatty degeneration of the kidneys may be
caused or encouraged by excessive use of alcohol.
Effect on Nervous System. As has been shown, alcohol's prin-
cipal line of attack is by way of the nervous system and it is here
that its effects are most notable and most serious. In the evolu-
518 BIOLOGY FOR BEGINNERS
tion of the nervous system the centers of control develop in this
order:
1. Heart and circulation control.
2. Respiration.
3. Walking and large muscles.
4. Speech and other senses.
5. Moral and intellectual control.
The peculiar harm of the narcotic action of alcohol is, that it
impairs these nerve centers in reverse order. The higher emo-
tions, moral sense, modesty, judgment, and self-control are first
attacked, and from this effect arises the awful record of alcohol
as a cause of immorality and crime. Leaving the body control
but little impaired and able to carry out the impulses of a dis-
ordered mind, a man will commit crimes or perform acts which he
never would have thought of doing if his self-control had not been
affected by this dangerous narcotic drug. Further effects of al-
cohol are shown when the speech and sight centers are attacked,
as the thick speech and double vision of the alcoholic victim are
all too familiar evidence. Next the walking and other large muscles
are affected and the staggering gait and uncertain movements are
observed. Finally, the breathing is interfered with, the heart
action partially or wholly paralyzed, and the condition of " dead
drunkenness " or even death ensues.
If the order of its effects were reversed, alcohol would not be
so dangerous, because the body would then be unable to carry
out the demands of the deranged brain. Unfortunately, this is
not the case, and herein lies one of alcohol's greatest biological
dangers. Furthermore, alcohol actually attacks the brain tissue,
causing irreparable harm and producing the morbid desire for more
liquor so characteristic of the victims of this awful habit. The
apparent " nerve stimulation," so frequently mentioned, is merely
the paralysis of sense and self-control, leaving the body to act, often
more violently, it is true, but never increasing its effective energy.
" Even the feeling of rest due to slight indulgence in alcohol is
caused by its anaesthetic effect upon the sense of fatigue, which
is the safety valve of the human machine." Von Bunge.
ALCOHOL IN RELATION TO BIOLOGY 519
The whole case is thus summarized by Dr. Brubacher of
Jefferson Medical College, Philadelphia, " Alcohol deranges the
activity of the digestive system, lowers the body temperature,
impairs muscular power, diminishes the capacity for mental
work, and leads to actual changes in the tissues of the brain
and other organs."
Alcohol and Disease. Not only does alcohol have the specific
effects already mentioned but injures the general health in two
ways:
1 . It is a direct cause of certain diseases.
2. It lowers bodily resistance to nearly all diseases.
Examples of the first case have been mentioned in connection
with the various organs, such as:
Heart diseases, enlargement or fatty degeneration.
Inflammation of the liver, " hobnailed liver."
Inflammation of the stomach, indigestion.
Insanity.
Far more important, however, is the effect of alcohol in lower-
ing the resistance of the body to external attack, and in creating
abnormal internal conditions, which make the course of many
diseases more serious, though they were not caused by the use of
liquor.
This predisposition to disease is brought about in two ways:
1. The white corpuscles, which defend us against bacterial at-
tack, are destroyed, and the ability of the blood to provide anti-
toxins is lessened.
2. By the various disarrangements of nerve control, blood and
food supply, alcohol overstrains certain organs, and interferes
with the action of others, so that diseased conditions are produced.
Statistics compiled by the Life Insurance Companies of the
United States covering a period of twenty-five years, show some
remarkable results, as follows: More than twice as many users of
liquor died of pneumonia as abstainers, the ratio being 18 to 39,
and Dr. Osier states that " Alcohol is perhaps the most potent of
all predisposing causes of pneumonia." The same is true of tuber-
culosis, the ratio here being 9.9 to 21.8: that is, for every 31.7
520 BIOLOGY FOR BEGINNERS
persons who died of the disease, 21.8 were drinkers, and only 9.9
were abstainers. Or to put it still another way, if you do not use
alcohol, your chance of recovery is twice as good as though you
drank.
Not only in special diseases but in general health, the insurance
figures show the harm of alcohol. The lives of " light drinkers "
are shortened an average of four years, and that of " regular
drinkers " six and a half years. In general, the death rate shows
a margin of 26 per cent in favor of the non-user of alcohol. Not
only is the life shortened, but the user of alcohol is ill 2.7 times
as often as the abstainer, and his illnesses last 2.5 times as long;
this causes not only discomfort but loss of work and money.
We have spent much time studying the prevention of typhoid
and smallpox and yet alcohol kills more people than typhoid and
fifteen times as many as smallpox, in this country every year.
Perhaps the most awful item in this catalog of the effects of al-
cohol on the human organism is the fact that, throughout the
United States, 26 per cent of the inmates of our insane hospitals
owe their condition to the use of alcohol, either by themselves or
their parents.
Mr. Arthur Hunter, the chief actuary of the New York Life
Insurance Company, and President of the Actuaries Society of
America, from whose reports many of these facts have been taken,
sums up the case as follows:
" In my judgment, it has been proven, beyond peradventure of
a doubt, that total abstinence is of value to humanity; it is certain
that abstainers live longer than persons who use alcoholic
beverages."
Alcohol is not a Medicine. In this connection it is well to re-
member that alcoholic beverages are no longer credited with any
medicinal value, as shown by the following resolution, adopted by
the American Medical Association, June, 1917.
" Whereas, we believe that the use of alcohol as a beverage is
detrimental to the human economy; and
" Whereas, its use in therapeutics, as a tonic, or a stimulant, or
a food, has no scientific basis; therefore be it
ALCOHOL IN RELATION TO BIOLOGY 521
" Resolved, that the American Medical Association opposes the
use of alcohol as a beverage; and be it further
" Resolved, that the use of alcohol as a therapeutic agent be
discouraged."
The United States Pharmacopoeia, the accepted guide book
of medical preparations, was revised in 1917, and " whiskey "
and " brandy " were struck out from its lists, which are supposed
to contain all the useful drugs; "port wine" and "sherry"
were left out several years ago. Dr. Harvey Wiley, perhaps the
most celebrated food and drug chemist in this country, was chair-
man of the committee which made these changes. The present
opinion of the best physicians is well voiced by Dr. J. N. Hurty,
Secretary of the Indiana State Board of Health. He says, " Al-
cohol is opposed to the public health, for it hurts any animal
organism into which it is taken. It is not a food; it does not aid
digestion; it does not further the good of the body; on the con-
trary, it hurts."
Alcohol and Efficiency. Apart from its disastrous effect of health,
the results of the use of liquor on actual ability to do work must be
considered. The loss of labor due to alcohol -caused disease equaled
the work of 150,000 men per year in the United States alone under
unrestricted traffic. Sobriety will increase our total efficiency as a
Nation, from ten to twenty per cent, adding to the country's
wealth over two billion dollars besides what would have been
spent for the liquor itself. To balance this enormous total, the
revenue from liquor comes to less than half a billion.
Waste of Resources. Furthermore there is great waste of food
stuffs in the manufacture of liquor. The enormous amounts of
corn, barley, rye, and fruits can ill be spared when the cost of
living is so high. Coal and transportation facilities are also used
by the liquor business to a very great extent. Every pint of
beer wastes a pound of coal to make it, and other beverages in
similar proportions, to say nothing of the rolling stock required to
transport the raw materials and finished product. The time and
skill of thousands of workmen are engaged in the manufacture
and sale of liquors, which in the present shortage of labor in es-
sential industries might be much better employed.
522 BIOLOGY FOR BEGINNERS
Since writing the foregoing chapter, the people of the United
States have added to our Constitution the 18th amendment,
prohibiting the manufacture and sale of alcoholic beverages. If
this is properly enforced, most of the awful results of the use of
alcohol will disappear. It is to be hoped that, in the future, a
textbook will not have to contain a chapter on the evils of al-
cohol, any more than they would now on the evils of negro slavery.
The final outlawing of the liquor traffic can be attributed mainly
to
The long campaign of education as to its harm.
The economic waste of materials and labor.
The reduction in business efficiency.
The physical and moral effects.
COLLATERAL READING
Alcohol and the Human Body, Horsely and Sturge, entire; A Handbook
of Health, Hutchinson, pp. 93-103; Physiologic Aspects of the Liquor
Problem, Billings; Elementary Biology, Peabody and Hunt, Pt. II, pp. 64-
75; The Human Mechanism, Hough and Sedgwick, pp. 366-376; The
Next Generation, Jewett, pp. 118-125, 145-152; Applied Physiology,
Overton, see index; General Physiology, Eddy, see index; Principles of
Health Control, Walters, pp. 130-153 and index; Civics and Health, Allen,
pp. 345-362; Bulletins of the Scientific Temperance Federation, Boston;
"Alcoholism" in Everybody's Magazine, 1909; The Great American Fraud,
American Medical Association, Chicago.
SUMMARY
Introduction.
Composition, C 2 H 6 O. "Ethyl" or "grain" alcohol.
Character, narcotic poison. (Chloroform, ether, opium.)
Reason for study here. Its effect as a beverage.
Kinds of alcoholic beverages.
Beer, 2-5 % alcohol, made from malted barley.
Wine, 15-20 % alcohol, made from fruit juices.
Whiskey, 30-50 % alcohol, made from grains or fruits (fermented and
distilled).
Proper uses of alcohol.
Physical Effects of Alcohol.
I. Alcohol not a food, because
1. Though oxidized, it produces a net loss of energy.
2. Does not build tissue, but harms it.
ALCOHOL IN RELATION TO BIOLOGY 523
II. Effect on nutrition.
1. Makes food less digestible by
(a) Withdrawing its water.
(&) Hardening its proteid.
2. Action on digestive organs.
(a) Irritates all membranes.
(6) Hardens tissue of the walls.
(c) Causes abnormal flow of fluids.
(d) Irritates and overworks the liver.
III. Effect on circulation.
(a) Interferes with nerve control of heart, etc.
(b) Relaxes arteries and capillaries, strains heart.
(c) Blood driven to skin, temperature lowered.
(d) Permanent inflammation of internal organs.
(e) Possible cause of disease.
IV. Effect on respiration.
(a) Causes inflammation of mucous linings.
(&) Diminishes resistance to congestive diseases.
(c) Increases connective tissue, lessening lung action.
(d) Robs digested food of oxygen.
V. Effect on excretions.
(a) Causes excess of uric acid.
(6) Overtaxes the kidneys.
(c) May cause disease, rheumatism, gout, Bright's
disease, etc.
VI. Effect on nervous system.
(a) Paralyzes higher centers first.
(6) Later loss of bodily control.
(c) Actual harm to nerve tissues.
(d) Habit formation. Insanity.
VII. Alcohol and disease.
0) Direct cause of heart disease, enlargement, etc.
Inflammation of liver and stomach.
Insanity. Arterio-sclerosis.
(&) Lowers resistance by
(1) Destruction of red corpuscles.
(2) Predisposition to pneumonia, tuberculosis, etc.
(3) Affects length of life, illness, etc.
(c) Alcohol is not a medicine.
VIII. Waste of resources.
Foodstuffs.
Coal.
Transportation facilities.
Labor.
CHAPTER LIII
SOME GENERAL BIOLOGIC PROCESSES
Liberate, to set free.
Accomplish, bring about.
Petrified, turned to stone.
Vocabulary
Osmosis and Life. The life of any organism depends, first
upon getting food into its tissues, and second upon releasing the
energy from the food after it has assimilated it. These food-
obtaining processes include photosynthesis, digestion, absorption,
and assimilation. All these depend upon osmosis for their accom-
plishment.
After the food is available in the body, its energy must be re-
leased. This requires oxidation and again necessitates osmosis
for the passage of oxygen through the tissues. Oxidation liberates
the energy in the food and at the same time produces waste which
must be excreted. Here again osmosis is the essential process.
The tables which follow attempt to show this relation of os-
mosis to the vital processes of all plants and animals.
ESSENTIALS FOR OSMOSIS
In plant
In apparatus
Membrane
Root hair
Epidermal cell, etc.
Diffusion shell
Dense liquid
Cell sap
Protoplasm
Sugar solution
Less dense liquid
Soil water
Clear water
524
SOME GENERAL BIOLOGIC PROCESSES
525
OSMOTIC PROCESSES IN PLANTS
Absorption
Soil water
Wnfrr
*->
.S
Cell sap
o
^3
ti
Photosynthesis
Air
-
Chlorophyll
cells
bearing
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Transpiration
Sap
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Transportation
Sap
s
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Sap
>t, etc.
mosis)
s
(successive os
Digestion
Food in seed or root
s
u
Embryo or
plant
growing
'II 2
OSMOTIC PROCESSES IN ANIMALS
Respiration
Air in lungs
Oxygen
Blood
Carbon dioxide
Water vapor
Nitrogenous waste
526
BIOLOGY FOR BEGINNERS
Digestion
Food in digestive tract made soluble by
ferments
l| '.
U ca v
Blood
lyj
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Assimilation
Blood and lymph
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Tissues
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rt
Excretion
Urine and perspiration
'a
11
Blood in kidneys and
skin
E
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u
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Oxidation and Life. In the process of photosynthesis, plants
accomplish the manufacture of organic food and tissue out of in-
organic materials, carbon dioxide, water, and mineral salts.
Plants are able to do this because, by means of their chlorophyll,
they can absorb energy from the sunlight sufficient to unite these
inorganic materials into complex organic substances.
Animals cannot thus manufacture their own food, as they
do not possess chlorophyll. It is evident that they must depend
upon plants for all their organic food substances. Of course there
are animals who eat no plant foods, but they depend upon ani-
mals which do, so that in the end plants are the only food pro-
ducers.
The chief function of food is to provide energy to support the
life of the consumer. This energy came from the sun, was locked
SOME GENERAL BIOLOGIC PROCESSES 527
up in the food substance by photosynthesis, and has to be released
or set free by oxidation. Except as it is oxidized, the energy in
foods or fuels cannot be released. Hence the importance of oxi-
dation as the key which unlocks the store houses of solar energy,
and makes it available to support life. We do not know how the
energy, thus released by oxidation, produces what we call " life,"
but we do know, that without it, no life exists and that, when
oxidation ceases, life ceases too.
Outside of living energy there are two other general sources which
man has learned to use, the power derived from fire and that ob-
tained from water. In the case of heat energy we burn (oxidize)
various fuels such as wood, coal, gas, or oil. All these fuels are
originally derived from plant life. The energy which we set free
from them, therefore, came originally from the sun. Someone has
called coal " petrified sunshine"; this is almost true. When we
warm our hands at the open grate, or heat our house with coal,
or cook with gas, or light our rooms with electricity, we are setting
free in various forms, the energy absorbed from the sun by plants.
But suppose the mill is run or the electricity used is generated
by water power. Here, again the sun is the final source because its
heat has evaporated the water, which has risen as clouds, fallen
on the hills as rain, and, flowing down again to the sea, turns the
water wheels. To be sure there is no oxidation involved in this
process, but it shows how the sun, either by its light or its heat,
is the source of all our energy, both living and mechanical.
Circles in Nature. It might seem, since food is oxidized or fuel
is burned to release its energy, that the supply would be exhausted
and all life come to an end. Nature, however, works in circles,
reclaims all waste, and aided by the sun, recombines them into
useful compounds again.
The Carbon Circle. Carbon is one of the most necessary ele-
ments for all living things. Animals obtain it from plants and
plants get it from the carbon dioxide of the air. Plants take this
carbon dioxide from the air, combine it with water from the soil,
and lock up within the starch which is formed the energy of the
sun which formed it.
528
BIOLOGY FOR BEGINNERS
However, the carbon is not lost. When either plant or animal,
fire or decay, oxidize these plant products, carbon dioxide is set
free again in the same amounts as before, mixes with the at-
mosphere, and is ready for plant use again. No atom of carbon has
ever been destroyed or produced by life processes; it is merely
used over and over again.
The Oxygen Circle. Oxygen is equally important, both as
5ALT5(Ca, ria, P, F t ,n^, 5,
NITRATES . NITRITES
NH CO NITRATES
' PHOSPHATES
OTHER SALTS
EARTH -"WATER
FIG. 160. Diagram illustrating the cycle of living matter and energy in
animals, plants, yeast and bacteria. From Calkins.
being a part of all living tissue, and as the liberator of vital energy.
It is taken from the air whenever plants or animals breathe, or
wherever fire burns or substances decay.
All these processes combine the oxygen into carbon dioxide,
water, or other oxides, and one might suppose that it was per-
manently removed from circulation, but this is not the case.
Plants take this carbon dioxide and water, unite them to form
SOME GENERAL BIOLOGIC PROCESSES
529
starch, set free in the air the oxygen again, and thus this circle is
completed. A study of the diagrams will help to fix this in your
mind.
Nitrogen Circle. Nitrogen, also, is absolutely essential to all
living tissue and protoplasm as well as all proteid food. Plants
obtain nitrogen compounds from the soil, mainly as soluble ni-
trates. They use them in making their living tissues, which in
turn furnish to animals their only source of nitrogenous food.
Here again one would be justified in supposing that the nitro-
gen was out of reach of future use. If this were so, life would long
since have ceased, as ordinary soil contains only enough nitrogen
CYCLE.
mr
ffforo s Y/VTME 3 is
FIG. 161. Chart showing interdependence of plants and animals for
oxygen and carbon dioxide.
compounds to last about thirty years, if none were replaced.
All waste excreted from animals contains nitrogen compounds,
and in the course of nature this should get back to the soil as
natural manures. Whenever a plant or animal dies, decay takes
place, and much of its nitrogen is thus returned by the action of
certain decay bacteria. However, neither manures nor decay
would give back enough, especially as man disposes of all his
sewage by washing it into rivers or ocean where it cannot get
back to the soil from which it came.
Furthermore, much nitrogen is set free into the air by decay
and oxidation in such a way that plants cannot use it, except
it be combined with other elements. So there would be a serious
530
BIOLOGY FOR BEGINNERS
shortage if it were not for other means of return. It remains for
certain bacteria, living in the nodules which they form on the
roots of clover, peas, beans, alfalfa, and all members of this large
family of plants, to aid in making good the loss.
These bacteria take the free nitrogen from the air, combine it
into soluble compounds, and thus replace in the soil most of this
essential element, which decay and oxidation had set free in the air.
CYCLE.
FIG. 162. Diagram showing how nitrogen compounds, after being used
by plants and animals, are either returned to the soil by decay, or reclaimed
from the air. This completes the "nitrogen cycle."
Although the atmosphere contains an enormous amount (80 per
cent) of nitrogen, it is not in the form of compounds, and these
plants of the pea family are the only ones that can use free nitrogen.
Another means by which free nitrogen of the air is combined
into useful compounds is by the action of lightning, which con-
verts some into oxides. These are washed back to the soil by rain
and help in completing the circle.
In addition to these natural steps in the nitrogen circle we must
SOME GENERAL BIOLOGIC PROCESSES 531
remember that man has learned to use the energy of nitrogen
compounds in all his explosives and many other chemicals. This
interferes seriously with nature's plan, for the firing of one twelve-
inch gun wastes nitrogen enough to raise one hundred bushels of
wheat. To repair this loss we are just learning to artificially
combine the nitrogen of the air into useful compounds, and replace
them in the soil as fertilizers. Unless this is done, the end of the
nitrogen supply is in sight, due, as usual, to man's interference in
nature's processes. He wastes nitrogen as sewage, chemicals,
and explosives, so must do his part in completing the circle or
suffer the consequences.
NITROGEN IN THE SOIL
Removed by Replaced by
Life processes Manures
Decay (some kinds) Decay
Oxidation of useful forms Bacteria
Waste of sewage Electrical action
Industrial uses Artificial processes
Explosives Fertilizers
Other Elements. The circles which are followed by the other
elements found in plant and animal tissue are not so complicated.
Hydrogen comes and goes as water, of which there is a limitless
supply in most regions. The sulphur, phosphorous, potassium,
and other mineral compounds are usually abundant to begin with,
and are not set free by decay, but come back to the soil in usable
form.
If a soil becomes deficient in any of these, they are obtained
elsewhere as natural mineral deposits and replaced as artificial
fertilizer. In a state of nature this would never be necessary, as
the plants would die and decay where they grew and so return their
mineral salts to the soil that produced them. It is only when man
removes his crops, and uses them elsewhere, that artificial re-
placement is necessary.
532
BIOLOGY FOR BEGINNERS
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534 BIOLOGY FOR BEGINNERS
Evolution of Life Functions. Biology teaches that all living
things are alike in their fundamental life processes, that all forms
are related by descent from common ancestors; that as develop-
ment proceeds, they become better fitted to perform their life
functions, or in other words, become more highly specialized.
The accompanying tables are intended to summarize this de-
velopment in life processes, as shown in the forms which we have
studied. It is necessarily much condensed, but careful study will
reveal many of the facts brought out during the course.
COLLATERAL READING
Osmosis: Fundamentals of Botany, Gager, pp. 54-60; The Living
Plant, Ganong, pp. 165-179; Principles of Botany, Bergen and Davis,
pp. 36-39; Introduction to Botany, Stevens, pp. 35-39; Plant Physiology,
Duggar, pp. 64-83; Textbook of Botany, Coulter, Vol. I, pp. 302-309;
Applied Biology, Bigelow, pp. 85-97; Elementary Biology, Peabody and
Hunt, pp. 32-38; The Science of Plant Life, Transeau, pp. 166-178; General
Physiology, Eddy, pp. 136-142; College Botany, Atkinson, pp. 13-21.
SUMMARY
1. Osmosis in life processes (tabulated in text).
2. Oxidation, the release of energy.
Plants the ultimate source of food.
The sun the ultimate source of energy.
3. Circles in nature.
(a) The carbon circle (see diagram).
(b) The oxygen circle (see diagrams).
(c) The nitrogen circle (see diagrams).
(d) Other elements.
4. Evolution of life functions (tabulated in text).
CHAPTER LIV
THE HISTORICAL DEVELOPMENT OF BIOLOGY
Vocabulary
Spontaneous, without cause.
Mortality, death rate.
Enumerate, to make a list of, to number.
Rabies or hydrophobia, the disease caused by mad dog bite.
Virulence, disease producing ability.
Like all other sciences, biology has developed from small be-
ginnings, by the labor, study, and sacrifice of many men over a
long period of years. Biology might be said to have started when
man first became intelligent enough to observe the plants and
animals with which he was surrounded, and utilize or avoid them
as he found best.
HARD WON KNOWLEDGE
Circulation. We gain our present knowledge so easily and
take it so much for granted that we can hardly realize the struggles
by which even our simplest facts were obtained.
Every child knows that the blood circulates in the arteries,
but the ancients believed that they were air tubes and it was
only in 1603, after much opposition, that Harvey was able to
fully prove this fact of circulation.
Spontaneous Generation. We assume, as a matter of course,
that any plant or animal springs from a parent like itself, but up
to 1668 it was believed that maggots came from decayed meat,
that frogs came from mud, and that living things were produced
from non-living matter. At that date Redi discovered flies' eggs
and larvae and proved that the maggots were produced by flies.
The presence of bacteria in decaying substances was not explained
until 1850-70.
535
536 BIOLOGY FOR BEGINNERS
At that time Pasteur and Tyndall showed that bacteria would
not develop except when the medium had been exposed, and so
proved, even for these minute plants, that bacteria were produced
by bacteria, and in no other way.
The idea that life could come from dead matter was called the
FIG. 163. William Harvey. 1578-1667. From Locy.
theory of " spontaneous generation," and died hard. This is now
replaced by the belief that " all life comes from life."
Oxidation. We talk freely of oxygen and oxidation, but oxygen
was not discovered until 1774 when Priestley obtained it and
THE HISTORICAL DEVELOPMENT OF BIOLOGY 537
demonstrated some of its properties. Even then scientists be-
lieved that when a substance burned it gave off something in-
stead of combining with something (oxygen) as we now know to
be the case.
Vaccination. All of us are vaccinated and think nothing of it,
but before 1796, smallpox raged unchecked and was so common
that about 95 per cent of all people had it. We little realize the
struggle of Dr. Edward Jenner, an English physician, who was
the first to suggest vaccination as its cure.
He observed that the dairy maids who had had cow pox (a
mild form of smallpox) did not fall prey to the latter disease.
Reasoning from this he proposed to inoculate people with cow-
pox as a protective measure, and suffered ridicule, opposition,
and persecution before he could convince the public. Even now
there are a few misguided individuals who oppose vaccination,
even though its practice has made smallpox one of the rarest of
diseases.
DEVELOPMENT OF BIOLOGY
It would be impossible to enumerate here all the famous names
in biology or to sketch their contributions to our knowledge.
Only a few can be mentioned, but there are books, like " Bi-
ology and its Makers " by Locy, which deal with the subject in
fascinating style and treat of all the important discoverers.
A few of these are listed in the tabulation at the end of this
chapter, and a glance at it will show two things, how old some
of our biologic ideas are, and how young is our definite knowledge
sufficient to apply them. The Greeks theorized vaguely about
evolution and development, but it was over two thousand years
before Darwin and others proved it. Galen was the foremost
physician of his time, but modern medicine scarcely had its be-
ginnings till fifteen hundred years later.
Cells and Protoplasm. Hooke saw cell walls in cork bark in
1671, but it was nearly two hundred years before the importance
of the cell as a unit of tissue structure was proven by Schleiden
and Schwann in 1838-39. Both Schleiden and Schwanri noticed
538 BIOLOGY FOR BEGINNERS
the jelly-like substance in the cells but it was not until 1846 that
von Mohl called it "protoplasm" and fifteen years later, 1861,
Schultze showed that it was the fundamental material of both
plants and animals.
Louis Pasteur. Probably no one has applied biology to benefit
mankind to a greater degree than Louis Pasteur, born in France
in 1822: died 1895, " the most perfect man in the realm of
science." In 1857 he showed the relation of bacteria to fermenta-
tion and greatly benefited the wine industry of France by his
FIG. 164. The earliest known picture of cells from
Hooke's Micrographia (1665). Edition of 1780.
From Locy.
investigations. In 1865-68 a disease attacked the silk worms of
France and Italy and threatened to wipe out the industry.
Pasteur traced this to bacterial attack, and was able to suggest
means by which the silk business was saved.
Later his attention was turned to chicken cholera and other
animal diseases and from his researches along these lines he de-
veloped the treatment by inoculation, and laid the foundation
for all modern serum and anti-toxin treatments.
His most famous work was done in the treatment of rabies,
THE HISTORICAL DEVELOPMENT OF BIOLOGY 539
which consists in injecting weak doses of the hydrophobia germs
into the blood of a person bitten by a mad dog. By gradually in-
creasing the virulence of the injections anti-toxins are built up
in the patient's body and resist the real attack of the disease.
By this treatment the mortality has been decreased from practically
certain death to less than one per cent.
The world owes to Pasteur the foundation of all our modern
methods in bacteriology, our serum and anti-toxin treatments,
and all the lives that have been saved thereby. Possibly more
people owe their lives to the results of his work than to that of
any other man who ever lived.
Other Victories over Disease. At the Pasteur Institute many
discoveries have been made in the line of inoculation against lock-
jaw (tetanus), bubonic plague and other germ diseases, but none
has saved more lives than the anti- toxin for diphtheria. This
was developed by Roux, a fellow worker with Pasteur and by
von Behring, a German bacteriologist in 1894. By this use a
disease which annually caused the death of thousands of children,
now has its rate reduced about 80 per cent and if treatment is
given early in the case, recovery is almost certain.
Among others who have labored in the work against germ
disease may be mentioned Robert Koch, who studied the relation
of bacteria to human disease, especially in the case of tuberculosis
and Asiatic cholera. He was the first to identify these bacteria
and though he devoted his life to the work, did not discover a
specific cure for tuberculosis. However, his work has enabled us
to take preventive measures which are greatly aiding in suppres-
sion of this worst of the " ills that flesh is heir to."
Antiseptic and Aseptic Surgery. Sir Joseph Lister, an English
surgeon, was the first to fight the germs of the operating room by
the use of antiseptics, such as carbolic acid. This one discovery
has done more to prevent death by infection after operations
than any other of recent times. Modern surgery aims to keep
its wounds aseptic, that is, free from all germs by careful methods
of sterilization, but still relies on anti-septics to kill any germs that
may have found entrance. Before Lister's time infection of op-
540 BIOLOGY FOR BEGINNERS
erative wounds was to be expected now it would be considered
evidence of gross carelessness and very rarely occurs.
Among other names to be associated with modern advance
against disease is that of Paul Ehrlich. He is famous for his study
of the blood as related to immunity to certain diseases, and es-
FIG. 165. Sir Joseph Lister. 1827-1912. From Locy.
pecially because of his successful method of treating syphilis,
which before had been incurable.
Another scientist who worked along similar lines was the Russian,
Metchnikoff, who was the first to discover the functions of the
white corpuscles in combating disease germs in the blood.
Carrell and Flexner are two American scientists who are work-
ing at the present time to carry the fight against disease to a more
THE HISTORICAL DEVELOPMENT OF BIOLOGY 541
successful conclusion. Among many other discoveries, Carrell
has developed a very successful method of treating infected wounds
which saved thousands of lives during the war. Flexner has been
investigating anti-toxin treatments for infantile paralysis and
similar diseases.
Charles Darwin. If applied biology owes its greatest debt to
Pasteur and his successors, certainly theoretical biology owes
FIG. 166. Thomas Henry Huxley.
From Locy.
1825-1895.
more to Charles Darwin and his co-workers than to any other
man. His work along the line of evolution and natural selection
revolutionized all modern thought and has been briefly described
in Chapters 34 and 35.
Associated with him was Alfred Russell Wallace who reached
the same conclusions as Darwin, though working from different
facts and entirely independent of his ideas.
542
BIOLOGY FOR BEGINNERS
Huxley, another English scientist, defended and explained Dar-
win's theories, and Herbert Spencer, also English, applied them
to all lines of scientific thought. Upon the foundation laid by these
men, all modern biology is based.
Mendel's Law of Inheritance. In 1860 an Austrian priest, by
FIG. 167. Gregor Mendel. 1822-1884. Permission of Professor Bateson.
From Locy.
the name of Gregor Mendel, began raising peas in his garden at
Brim. He was not so much interested in the flowers or the abun-
dance of the crop as in other apparently less important matters.
He noted the shape of seed, and their color, the shape and
color of the pods, the height of the plant and other similar
characteristics. He kept each kind separate and cross-pollenated
THE HISTORICAL DEVELOPMENT OF BIOLOGY 543
them himself, so knew exactly the ancestry of each new set of
descendants. After years of patient experiment and careful record
he reached some conclusions. He found that if he crossed tall
with short that the next generation were hybrids but tall in ap-
pearance, that is, tallness had overcome shortness as a char-
acteristic in that generation.
Many characteristics were found to be stronger at first and
were called " dominant " characteristics. Those which were
crowded out were called " recessive." However when these
O
P
FIG. 168. Diagram to show the segregation and re-combination of the
factors (black and white) in the gametes, and the presence of both in the hybrid
F'. (From Morgan, see Calkins.)
hybrids were bred together both the original characteristics re-
appeared in a constant proportion of tall, short, and tall hybrids.
The reason is that the two characteristics remained separate
in the hybrids and did not blend, hence when hybrid was bred with
hybrid the next generation would combine these characteristics
according to the mathematical law of probabilities or chance.
To illustrate, let x and y stand for any two non-blending char-
acteristics. The first crossing would produce hybrid offspring
having xy characteristics, but if x were dominant, y would not
appear.
544 BIOLOGY FOR BEGINNERS
However if these xy hybrids are crossed together, four possible
combinations may occur, thus:
Joining x with x producing xx offspring.
" x " y " xy
" y " x " yx "
" y " y " yy "
Of course the xy and yx individuals are of the same kind and
are also like their xy hybrid parents, but the xx and yy offspring
have those characteristics only and are pure bred: their off-
spring with either x or y respectively would produce pure x or
pure y characteristics, despite their mixed ancestry.
Of course breeding is not so simple as this, because it cannot be
limited to one characteristic at a time, and some characteristics
do blend or average in the hybrids, but the law of inheritance,
known as Mendel's Law, has been proven true and is of great
value in plant and animal breeding.
Though Mendel published his conclusions in 1865 and 1869
little notice was taken of them and he died in 1884 without recog-
nition. Later the same conclusions were independently reached
by three other scientists who would have been credited with an
important discovery, but in 1900 Mendel's papers were found and
his long delayed appreciation arrived, sixteen years after his
death.
Briefly stated, his law comprises three facts:
1. Pure bred mated with pure bred of same kind give offspring
pure bred.
2. Pure bred mated with pure bred of different kind, hybrid
offspring.
3. Hybrid mated with hybrid the offspring will be one-half
hybrid, one-quarter pure bred like grandfather, one -quarter pure
bred like grandmother.
Law I. Pure bred with pure bred of same kind, x plus x makes
xx.
Law II. Pure bred with pure bred of different kind, x plus y
makes xy.
THE HISTORICAL DEVELOPMENT OF BIOLOGY 545
Law III. Hybrid bred with hybrid, xy plus xy makes xx, -\-2xy,
+yy or stated differently.
xy . . xy x y hybrid
t\ >"'
i
*" y. hybrid
xx xy_ yx_ yy xx xy
2 xy yx yy
xx 2xy yy
Luther Burbank. No one has made such successful applica-
tion of these laws of inheritance as has Luther Burbank. For
years he has been performing what might be called biologic miracles,
on his farm in Southern California.
A complete list of the new or improved plants which he has de-
veloped, would occupy a whole chapter, but some of the most
famous are
1. The Burbank potato which has increased our crop by mil-
lions of dollars and is said to have prevented the potato famine
that formerly devastated Ireland.
2. The spineless cactus which provides abundant stock food
for regions where none was to be had.
3. The " Primus Berry," a valuable cross between the dew-
berry and raspberry. It differs from both its ancestors and is the
first absolutely new species ever produced by man.
4. A cross between the plum and apricot called the " Plumcot "
which has the good qualities of both ancestors and some of its own.
5. The pitless plum and thin-shelled walnut explain themselves.
6. Among flowers, the Shasta daisy six inches in diameter, and
the ten -inch poppy, are well known.
He works by cross-pollenation, grafting, and rigid selection.
Specimens are collected from all over the world, raised in his
gardens, and crossed to develop desirable characteristics. They
are then cultivated in enormous numbers, to take advantage of all
possible variations, and only the best are selected.
Thus, by combining a deep knowledge of biologic laws, with
546 BIOLOGY FOR BEGINNERS
marvelous skill in their use, Mr. Burbank has developed plant
breeding to a degree never approached before.
COLLATERAL READING
Encyclopedia references on all persons and topics mentioned. Biology
and its Makers, Locy, entire; Main Currents of Zoology, Locy, entire;
Elementary Biology, Peabody and Hunt (Malaria), pp. 47-56, Pt. I;
Life of Pasteur, Frankland; Children's Stories of Great Scientists, Wright;
General Zoology, Linville and Kelly, pp. 436-451; Zoology, Parker and
Haswell, pp. 628-649; General Principles of Zoology, Hertwig, pp. 7-67;
General Zoology, Pearse, pp. 6-12; Manual of Zoology, Hertwig-Kingsley,
pp. 7-56; Biology, Calkins, pp. 219-232 (Mendelism); Mechanism of
Mendelian Heredity, Morgan, etc., entire; The Next Generation, Jewett,
pp. 20-24 (Mendelism).
THE HISTORICAL DEVELOPMENT OF BIOLOGY 547
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INDEX
A
abalone, ornamental use of, 471.
abdomen, of crayfish, 179; of grass-
hopper, 197; of butterfly, 206; of
honey bee, 213.
absorption (root), 53, 58; selective,
61; in an animal, 375.
acerata, 173; use as insect destroyers,
472, 473; mites and ticks, 473.
acetic acid, 461.
Agramonte, Dr., see yellow fever.
agriculture, close association with
biology, 493.
air bladder, of fish, 245.
alcohol, plant product, 461; wood,
462; narcotic, beverages containing,
514; physical effects of use of, SIS-
SIS; not a food, 516; and disease,
519; not a medicine, 520; and
efficiency, 521.
alga?, 127.
alimentary canal, 363, 364.
amoeba, 146-148.
amphibia, characteristics of, 252; use-
ful as insect destroyers, 481.
amylopsin, 374.
animals, general uses of, 467; eco-
nomic value of, 468; husbandry of,
489.
antennae, of crayfish, 182; of grass-
hopper, 194.
anthers, 109, 113.
anthrax, 137.
anthropology, 333.
antiseptics, 140.
antitoxins, 138, 139.
appendix, 322.
apple, structure of, 120; seed dis-
persal of, 121.
arrowhead from the Cave of Perigord,
France, 334.
arteries, 398.
arthropods, 158; characteristics,
classes, 172; classification, 173-177,
235.
ash, 121.
assimilation, 5, 375, 377.
astigmatism, 422.
Atwater, quoted on alcohol, 515.
auditory canal, 417.
auricle, 397.
B
baboon, 318.
bacteria, 4; shapes, 133; types, 134;
methods of study of, 135, 136;
useful forms of, 136; harmful, 137;
defences against, 137-141; rapidity
of reproduction, 327; useful, 447;
nitrifying, 487; good and bad ac-
tivities on the farm, 493.
bacteriology, 134; development of,
141.
barley, 449.
barnacles, 472.
bass-wood, seed, 122.
bast, root, 51, 56; stem, 77; fibers,
78; tubes, 78; see cotton, flax,
jute and hemp.
bark, structure of, 76.
baths, 431.
beak, of bird, 289.
bean, structure of, 34, 120.
bee, agent in pollenation, 110; honey,
structure of , 2 1 1-2 13 ; queen, drone,
worker, 213.
beetles, beneficial and harmful, 476.
Beri-beri, 356.
549
INDEX
Biff en, Prof. R. H., his experiments
to improve wheat, 489.
"Big Trees" (Sequoia) of California,
81.
bile, functions of, 373.
biology, definition of, 1; familiar, 2;
value of study, 425; application to
plant improvement, 488; to plant
protection, 489; historical develop-
ment of, 535; noted names in,
547, 548.
birds, characteristics, 281; structure,
281-287; habits of, 294-306; eco-
nomic importance of, 305, 481.
bladder, 403.
bladder-nut, seed of, 122.
blood, 394; changes in composition
of, 396.
brain, 408.
branches, opposite and alternate, 69;
forked, 70.
bronchi, 384.
Brubacher, Dr., quoted on alcohol,
519.
bubonic plague, 151.
buckwheat, 449.
bud (stem), structure, 72.
Burbank, Luther, noted for valuable
services in plant improvement, 489;
examples of his work, 545.
butterfly, structure, 205, 206; meta-
morphosis, 208-210.
caffeine, 511.
calorie, 344.
calcium, 15, 17, 23.
calyx, 109.
cambium, root, 51, 56; stem, 78,
80.
capillaries, 398.
carapace, 173, 179.
carbohydrates, 20, 21, 23; bulk of
man's food, 344, 346.
carbon, 14, 17; circle, 527.
carbon dioxide, 13, 18, 23, 47; in
leaves, 91, 98, 382, 528.
carnivora (flesh eaters), 313.
Carrell, Dr., treatment for infected
wounds, 441, 541.
Carrol, Dr., see yellow fever,
"castings," of earthworm, 162, 165.
catalpa, 121.
cattle, different breeds of, 491, 492.
cells, 27, 30; palisade (leaf), 95;
animal (one-celled), 146-150, 158,
198; Hooke's discovery of, 537.
cephalothorax (head-thorax), 173,
179.
centipede, 173.
cephalopods, see squid, cuttlefish,
octopus.
cereal grains, 447-450.
Chittenden, quoted on alcohol, 516.
chocolate, food value of, 511.
cirrhosis of the liver, 60 per cent, of
deaths caused by alcohol, 516.
cerebellum, 409.
cerebrum, 408.
charcoal, 461.
chemistry, 9.
chimpanzee, 316.
chlorophyll, 90, 92-93; property of,
96, 129, 526.
cholera, 137.
choroid coat, 419.
chrysalis, 207.
chyme, 371, 372.
cilia, of paramoecium, 149.
circulation, of earthworm, 162; fish,
244; frog, 259; bird, 287; need
for, 382; development of, 392;
effect of alcohol on, 516.
civic biology, 440.
clams, 471.
clematis, seed dispersal of, 122, 124.
cochlea, 418.
cocoa, 452, 453; food value, 511.
cocoon, 207.
codfish, value of, 480.
crelenterates, 469.
coffee, plant, 452; effects of beverage,
511.
compounds, 9; inorganic, 18, 19, 23.
conjugation, of paramcecia, 150.
INDEX
cooking, functions of, 354.
coral polyp, 157; coral reefs, 470.
cork, harvesting, 460.
corn, structure of, 36, 449.
cornea, 421.
corolla, 109, 110.
corpuscles, white, 138, 395; red, 395.
cortex, root cells, 51, 56; stem, 78.
cotton, 455; Sea Island, 458.
cotyledons, 32, 44.
crabs, "soft shell," 188; use as food,
472.
crayfish, structure of, 179-185.
crop rotation, 487, 488.
Crustacea, 172, 179; as food, 472.
culture medium, 133, 135.
cuttlefish, produces sepia, 472.
D
dandelion, 70, 121, 122.
Darwin, Charles, his "Origin of
Species by Natural Selection,"
326; chief factors to account for
development of new species from
common ancestry, 327; revolution-
ized modern thought, 541.
Davenport, 331.
deliquescent, 69
diaphragm, 385, 387.
dicotyledonous (having two coty-
ledons), 33, 79, 81.
diet, need of mixed, 346.
digestive system, of earthworm. 161;
of fish, 243; of frog, 258; of bird,
287; of man, 363-375.
diptera (two- winged), 220.
diphtheria, 137, 140.
diseases, eye, 137; transmission of
by insects, 232.
"disease germs," 150; prevention of,
442. i
disinfectants, 140.
distillation products, from plants
(wood), 461.
dogfish, 247.
drainage, regulated by forests, 447.
drone, 213, 215.
ducts, root, 51, 56; stem, 78.
dyes, vegetable, 461.
drugs, from plants, 461; danger of
drug habit, 511.
dysentery, 151; caused by protozoa,
469.
ear, various locations of, 416;
structure of human, 417; wax,
418; ache, 418; infection of, 432.
earthworm, 157; structure, 161, 162;
locomotion, 162; food, value of,
165, 470.
echinoderms, 470.
Ehrlich, Paul, famous for method of
treating syphilis, 540.
elements of matter, 9.
elm, 121.
embryo, plant, 31, 32, 43, 114; de-
velopment of fish, 246; study of
development of all animals, 322
embryological resemblances, 322.
endosperm, 31, 33, 113.
energy, 342; source of, 526, 527.
environment, 415.
enzymes (or ferments), 363, 374.
epidermis, root, 50, 56; stem, 78;
leaf, 90.
erosion, 497.
erysipelas, 137.
eustachian tubes, 365, 417.
evolution, idea and evidences of, 321,
322; method of, 326; of life
functions of plants, 532; of life
functions of animals, 533.
excretion, 6; system of in earth-
worm, 162; in insecta, 198; of frog,
261; organs of, 403; effect of
alcohol on, 517.
excurrent, 69.
exercise, importance of, 426-428;
beneficial, 436.
exo-skeleton, of crayfish, 180; of
grasshopper, 193.
expiration (breathing out), 386, 387.
eye, structure of human, 419, 420;
compared to camera, 421.
552
INDEX
factory and housing conditions, 443.
fats, 20, 22, 23; energy producer,
343, 346.
feathers, 283.
ferns, 127.
fertilization, plant, 108, 113, 114;
of fish eggs, 247; of the soil, 487.
fever, typhoid, 137, 142; yellow,
scarlet, 151, 469; cattle 90.
fiber plants, cotton, 455; flax, hemp,
jute, manila, 457; coconut, 458.
fibrinogen, 395.
filament, 113.
Fischer, Professor Irving, quoted,
434, 515.
fishes, structure, 239-246; nest, 247;
value as food, 480; as fertilizer,
481.
fission, 148.
flax, 457, 459.
Flexner, Dr., American scientist, 541.
flint, carved, of Old Stone Age, 338.
flower, function and structure of, 108.
fly, house (typhoid), 220; danger
from, 222, 223; rate of repro-
duction, 224.
food, definition, 342; functions of
organic and inorganic, 343; pro-
portions, 345; fuel, starchy, sugars,
fats, 358; building and repair
(protein), mineral salts, water,
ballast or bulk, 359; hard, vita-
mines, 360; public control of, 441.
forests, value of, for control of water
supply, 495 ; distribution of national
forests, 496; benefit to soil, 497;
effect on climate, 497; as home for
birds and game, 498; products of,
498; enemies of, 500, 501; fires in,
501; protection of, 502; reserves,
rangers, forestry schools, replanting,
502.
frog, development of, 253; structure,
254-261.
fruit, types of, 118, 119; functions
of, 119; structure, 120; economic
importance of, 124-125; use as
food, 455.
fruit tree pests, 474.
fuels, use of plants for, 458.
fungi (parasite), 127, 129; examples,
mushroom, 129; rust, smut, mil-
dew, mould, 130.
G
ganglia, 410.
garden pests, potato "bug," etc., 475.
gastric fluid, 371.
"General Sherman" tree (Sequoia),
81.
geotropism, the response of plant
parts to gravitation, 58; positive,
60, 62.
germ, diseases, 4; sterilization of, 141.
germicides, 140.
germination (plant), 41.
gills, 173; of arthropods, 182; fish,
241.
glands, 368; salivary, 369; pyorlic,
371; intestinal, liver, 373; pancreas,
374; kidneys, 403.
glycogen (liver starch), 374.
gorilla, 316.
Gorgas, Col. W. C., 229.
grafting, 79.
grasshopper, 193; structure, 193-198.
Grassi and Bignami, 231.
grippe and colds, 137.
ground-pines, 127.
guano, 305.
gullet, of man, 363, 370.
H
Harvey, William, circulation of the
blood, proved by, 535; portrait,
536.
habit formation, 412, 413.
haemoglobin, 388, 395.
hawk-moth posed before a jimson-
weed, 110.
hearing, sense of, 416.
heart, action of, 397.
INDEX
553
heat, 11; energy, 46.
heliotropism, the response of plant
parts to light, 88.
hilum (scar), 31, 34.
homology, 184.
hookworm, 166, 167.
Hooke, discovered cell walls, 537,
538.
horses, breeding and selecting for
trotting, running, draught, etc.,
493.
horse-tails, 127.
Hornaday, Wm. T., 274, -276.
household pests, 475.
Hunter, Arthur, actuary, N. Y. Life
Ins. Co., quoted on alcohol, 520.
Hurty, Dr. J. N., quoted on alcohol,
521.
Huxley, Thomas Henry, English
scientist, 211, 542.
hydra, 157, 234.
hydrogen, 12, 17, 19; supply of, 531.
hydrotropism, the response of plant
parts to water, 58, 61, 63.
hygiene, 2, 4; of eye, 422, 425, 430;
of muscles, 426; of digestion, 428;
of respiration, 429; of bathing,
431; of teeth, 432; of feet, 432;
of nerves, 433 ; public, 437; mental,
437.
hymenoptera (membrane winged),
211.
hypocotyl, primitive stem, 33; ap-
pears first, 42, 43.
Iceland moss, 457.
immunity, acquired, 139.
indigo shrub, 462.
incubation, 300.
influenza, 142.
inorganic matter, 1; examples of, 7,
15, 19.
inheritance, 328.
insecta, 173; classification, 193.
insects, agents in pollenation, 110,
113; and disease, 220-232; harm-
ful and useful activities, 473, 474.
inspiration (breathing in), 386, 387.
intestines, of man, 363, 372, 373, 405.
iron, 14, 17, 23.
iron oxide (rust), 14.
isinglass, fish product, 481.
James, William, quoted, 413.
jellyfish, 157.
Jenner, Dr. Edward, first to suggest
vaccination for smallpox, 537.
jute, 457; see bast.
kernel (seed), 31.
kidneys, 403.
King, A. F. A., 231.
Koch, Robert, identified bacteria of
tuberculosis and Asiatic cholera,
539.
leaves, functions of, 86; general
structure, 87; forms, 87; arrange-
ment, 88; . heliotropism, 88; modi-
fications of, 88; fall of, 88; other
functions, 99; use for food, 455.
labium, 194, 212.
labrum, 194, 212.
Lamarck, 326.
larva, of butterfly, 207; forms of,
217.
Lazear, Dr., see yellow fever.
legumes, 119; importance as food,
451, 452.
lemurs, 318.
lens, of eye, of camera, 420.
lenticels, 75.
lepidoptera (scale winged), 205; harm-
ful moths, 476.
leprosy, 137.
lichens, 127; rock, 128; Iceland moss,
455.
lipoid, 355.
554
INDEX
Lister, Sir Joseph, developed anti-
septic surgery, 539.
liver, 373, 405; cirrhosis of, 516.
lobster, 185; food value, 472.
lockjaw (tetanus), 137, 140, 142.
locomotion, of amceba 148; of
worm, 162; of crayfish, 186.
locust, 193.
Locy, "Biology and its Makers," 537.
lumber, production, 499; careless
lumbering, 500.
lungs, 382-386, 404; infection of, 432.
lymph, 382; circulation of, 400.
M
malaria, 151, 229; see protozoa.
mammals, characteristics of, 310;
valuable for food and clothing
products, 482; for transportation
and as pets, 483; a few harmful,
483.
mammoth, drawing of, from Cave of
the Madeleine, France, 334.
man, 314; development of, 321-325;
primitive, 334; Neanderthal, 335;
implements of different ages, 336;
races of, 340.
mandibles, of crayfish, 182; of grass-
hopper, 194; of honey bee, 212.
Manson and Ross, 231.
mantis, 201.
maple, 121; "key," 122.
"Mark Twain" tree (Sequoia), 83.
marmosets, 318.
mastication, 435.
maxillae, of grasshopper, 194; of
honey bee, 212.
maxillipeds (jaw feet), 182.
medulla, spinal bulb, 410.
membrane, mucous, of small intestine
of dog, 372; tympanic, of man. 417.
Mendel, Gregor, his "Law of In-
heritance," 542-545.
mental hygiene, 433, 437.
metamorphosis, of butterfly, 201, 208;
of amphibia, 252, 267.
metazoans, 154; forms of, 157.
Metchnikoff, Russian scientist, his
discovery of functions of white
corpuscles, 540.
microbes, 150.
micropyle (opening), 31, 35, 42, 113.
migration, of birds, 300; and distri-
bution of Eskimo curlew, 301.
milk, supervision to insure pure, 441,
442.
milkweed, 121, 122, 123.
mineral compounds, 19.
mineral salts, necessity for, 353, 356,
359.
molluscs, 157, 234; food of primitive
man, 470.
monkeys, 318.
mosquito 224; transmits yellow
fever, 225, 226; eggs of, 226;
control of, 227, 229; transmits
malaria, 231.
mouth, 365.
mussels, 471.
monarch butterfly, metamorphosis of,
209, 210.
monocotyledonous (having one coty-
ledon), 33, 79-81.
mosses, 127.
moth, compared with butterfly, 210;
harmful, codlin, tussock, 474.
moulting, of crayfish, 187; of birds,
284.
mushrooms, 129, 455.
myriopods, 173.
N
nasal openings, 365.
nectar glands, 110.
nervous system, of earthworm, 162;
of arthropods, 172, 198, 199; of
fish, 244; of frog, 261; of bird,
289; of man, 408; effect of alcohol
on, 517.
nests, of orioles, 295; of humming
bird, 296; excavated, woven, 296;
built-up, 298.
newt, 270.
nitrogen, 12, 17; fixation, 447;
INDEX
555
supplied to the soil, 487; circle,
529; waste of, 531.
nodes, 68.
nose, adaptation for breathing, 384.
nucleus (amoeba), 147.
nutrition, 5; digestive organs, 363;
absorption, 375.
nuts, 452.
O
oats, 449.
octopus, 471.
opsonins, 138.
orang-utan, 318.
organic things, 1; likeness of, 6.
organs, 27, 30; "essential," 112;
specialized, 157; homologous, 184,
323; rudimentary, 321; digestive,
363.
oriole's nest, 295.
orthoptera (straight winged), 193.
Osier, Dr., quoted on alcohol, 519.
osmosis, definition, 58; dependence
of root absorption on, 59; suc-
cessive, 61, 64, 65, 363; absorption
of food by, 374, 377; and life, 524-
526.
ovary, 109, 113; in frog, 263.
oviduct, in frog, 263.
ovules, 109, 113; structure, 114.
oxidation, 10; of tissue, 382; and
life, 526-531.
oxygen, 10, 11, 17, 18, 19, 91, 98,
103; soluble in water, 186; lymph
supplied with, 382; plant supply,
447; circle, 528; properties demon--
strated by Priestley, 1774, 537.
oysters, 470; "pearl," 471.
palate, of man, 365.
pancreatic fluid, 374.
paper materials, from plants, 459.
papillae, 415.
paramoecium, 148; structure, 149;
reproduction, 150; parasitic, 150.
parasites, plant, 127, 129; worms,
164-167, 468.
Pasteur, Louis, 137, 141; wonderful
services in applied biology, 538,
539.
pasteurization, of milk, 141.
patent medicines, 444.
pea, 35; seed dispersal of, 123.
peat, 459.
pellagra, 356.
penetration (soil), 42.
pith, stem, 79, 80.
pepsin, 371.
phosphates, 14.
phosphorus, 14, 15, 17, 531.
photosynthesis, process of starch-
making in leaves, 96-98; compared
with respiration, 101, 103.
physiology, 1.
pigeons, carrier, 306; various races of,
490.
pine, seed, 121, 122.
pistil, 109.
pitch, 461.
plants, general uses of, 446, 463;
breeding of, 488, 489.
plasma, 394.
pleurisy, 385.
plumule, 32, 33.
pollen, 109; protection of, 111, 113;
structure, 114.
pollenation, 108, 109; cross, 109,113;
biology applied to methods of, 488.
polycotyledonous (having three or
more cotyledons), 33; stems, 81.
pome, 119.
poppy, seed of, 122.
posture, 433.
potassium, 15, 17, 23, 531.
pneumonia, 137, 142; effect on
alcohol users, 519.
ptomaine (poisoning), 137.
prawns, as food, 472.
Priestley, properties of oxygen first
demonstrated by, 537.
primates, 314.
propolis, 216.
proteids, 20, 21, 23; function of in
man's food, 343, 344, 436.
556
INDEX
protoplasm, 25, 27, 30, 41, 147;
named by von Mohl, 1841, 537;
fundamental material of plants
and animals shown by Schultze,
538.
protozoa, 146; parasitic, 150, 152,
234, 327, 468; as scavengers, 469;
diseases caused by, 469.
pupa, of butterfly, 207.
pure food and drugs law, 443, 444.
pylorus, 372.
rabies, treatment for, 538, 539; see
Pasteur.
Redi, discoveries of, 535.
Reed, Dr., see yellow fever.
reforestation, 502.
rennin, 371.
reproduction, 6; function of the
flower, 108; by spores, 127; of
bacteria, 134; of amoeba, 148;
in paramoecium, 150; of crayfish,
187; of grasshopper, 200; of
honeybees, 214; of frog, 261, 267;
of birds, 298.
reptiles, 273-278; value as insect
destroyers, 681.
respiration, 5; plant, 86, 93; com-
pared with photosynthesis, 101;
of insects, 198; of frog, 260; of
bird, 287; development of, 382;
hygiene, 429; effect of alcohol on,
517.
retina, 419.
Rexford, Frank H., 347.
rheumatism, 432.
rice, 449.
rings, annual, see wood fibers.
Rockefeller Foundation, 442.
rodents (gnawers), 311; destroy
grain, 483.
roots, characteristics of, 49; structure
of, 50; function of, 51; normal,
fibrous, tap, fleshy, 53, 54; aerial,
aquatic, 54; adventitious: brace,
for propagation, 54; climbing,
parasitic, 55; hairs, 60; pressure,
61; as food, 454.
rosin, 461.
Roux, bacteriologist, 142; assisted
in developing diphtheria anti-toxin,
539.
rubber, 461.
ruminants, non-ruminants, 312.
rye, 449.
salamander, 271.
salmon, life history of, 248; value as
food, 480.
saliva, 370.
salvia-flower, 111.
sanitation, 4, 425.
scales, fish, 239.
scallops, 470.
scars, leaf, flower-bud, fruit, 75;
bud-scale, 76.
Schleiden and Schwann, proved im-
portance of cell, 537.
Schultze, see protoplasm.
sclerotic coat, 419.
scorpion, poisonous, 473.
scurvy, 356.
sea anemone, 157.
seed, structure of, 31; growth of, 34;
function of, 41; development of,
113; dispersal of, 119, 122; by
wind, water, animal, 122-124.
segments, of earthworm, 162; of
crayfish.
semicircular canals (ear), 418.
sensation, 6; in amoeba, 148; organs
of, in skin, 405; "irritability" of
plants, 415.
sepals, 109.
serum (blood), 395.
sewage, regulations regarding, 442.
shade tree pests, 474.
sheep, applied biologic methods of
breeding, 491.
shrimps, as food, 472.
sight, sense of, 419; near, far, 422.
skin, structure and functions, 404,
405.
INDEX
557
skull cap of fossil man-like ape of
Java, 336.
sleep, 434.
sleeping sickness, 151.
slugs, as food, 471.
smallpox, 139, 151; see protozoa,
469.
smell, sense of, 416.
snails, as food, 471.
snakes, false ideas about, 274; few
dangerous, 274, 276; poisonous,
276; treatment for bites, 276; use-
ful as insect destroyers, 481.
sodium, 15, 17, 23.
soil, formation of, 486; composition,
487; maintaining the, 487.
solar plexus, 411.
Spencer, Herbert, quoted, 328; ap-
plied Darwin's theories, 542.
spermaries, in frog, 263.
sperm nucleus, 113.
sphinx moth, 207.
spices, 454.
spinal bulb (medulla), 410.
spinal cord, 410.
spore-bearing plants, 127; classifi-
cation of, 127; as food, 455.
sponge, 155, 157, 234; value of, 468,
469.
squid, use as fish bait, 471.
stamens, 109, 113.
starch-making, in leaves, 91; see
photosynthesis.
steapsin, 374.
stems, function of, 68; kinds of:
shortened, 70; creeping, climbing,
71; fleshy, 72; use as food, 454.
Stejneger, Dr., 276.
stickleback, 247.
stigma, 109.
stomach, of man, 363, 370.
stomates, function of, 91.
stone axe head, New Stone Age,
338.
style, 109, 113.
sugar-cane, 456.
sulphur, 13, 15, 17, 531.
swimmerets, 182.
sympathetic system of nerve ganglia
411.
syphilis, 137; see Ehrlich.
tadpole, 267.
tanning materials, from plants, 461.
tapeworm, 164-166.
tar, 461.
taste, sense of, 416.
tea, effects of, 511.
teeth, decay, 137; structure, number
and kinds of, 367, 368; vertical
section of tooth, 367; care of, 429;
hygiene, 432.
tegumen (inner seed coat), 31, 38.
test, for oxygen, 10, 18; for proteids,
20; for starch, 22; for grape sugar,
22; for fats, 24.
testa, seed coat, 31, 44.
thistle, 121.
thorax, of grasshopper, 196.
timber, uses of, 460; products, 498;
structure, 503; quarter grain, 504.
tissue, 27, 30.
toad, habits of, 269.
tobacco, harmful effects of, 509-511.
tongue, of man, functions, 365-367.
tonsils, 365; infection of, 432.
touch, sense of, 415.
tracheae, 173; see arthropods, 193;
in man, 365, 382, 384.
trichina, 167.
trachoma, 151.
tree toad (hyla), 270.
tuberculosis, 137; effect of on alcohol
users, 519.
turgescence, the expansion of plant
cells by water, 58, 59.
turpentine, from pine pitch, 461.
typhoid, fever, 137, 142; vaccination
against, 441.
trypsin, 374.
U
ungulates (hoofed), 312.
urine, 403.
558
INDEX
vaccination, 139; 537.
vacuole, 147.
variation, 328.
vascular bundles, 80.
veins, 399, 400.
ventilation, 389, 429, 430.
ventricle, 397.
vertebrates, 158; development of,
235; classes and characteristics,
236.
Von Behring, a German bacteriologist,
142; helped develop anti-toxin for
diphtheria, 539.
Von Bunge, Dr., quoted on alcohol
515, 518.
villi, 373.
vitamines, 356.
W
Wallace, Alfred Russell, English
scientist, 328, 541.
water, 19, 23; necessity of, for plants,
58; vapor, 91; supervision of
supply, 441.
wax, 215.
wheat, 448, 449; improved, 489.
White, Dr. Andrew D., quoted, 510.
whooping cough, 137.
Wiley, Dr. Harvey, 521.
Williams, Dr. H. W., quoted, on
death rate in World War, 441.
wind, agent in pollenation, 111, 113.
wood (root), 51, 56; stern, 76; fiber,
78; hard and soft, 505.
Woodhead, Dr., quoted on alcohol,
517.
workers (honey bees), 213, 215.
World War, low loss from infectious
diseases, 441.
worms, parasitic: tape, hook, trichina,
164-169, 234, 470; see earthworm.
yellow fever, 151; conquest of by
Drs. Reed, Carrol, Lazear and
Agramonte, 229; see protozoa, 469.
yeast plants (fungi), 130.
zoology, 2.
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