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From the collection of the 

z n 
z m 

o Prelinger 

v Jjibrary 


San Francisco, California 










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 

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. 




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 

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. 


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. 





Definition of Biology. Reasons for study. Organic things. In- 
organic things. Familiar biology. 


Processes common to organic things. 

Oxygen and oxidation. Occurrence, properties and uses of other 

common elements. 


Water; Carbon dioxide; Proteids; Fats; Carbohydrates; 
Method of testing. 


Protoplasm, its composition and properties. Cell, Tissues, Organs, 
System. Adaptation. 


Parts of typical seed. Bean and Corn seeds as examples. 


Conditions necessary. Stages hi germination. Corn and Bean. 


Characteristics. Structure. Functions. Adaptations. 


Use of water to plants. Turgescence. Osmosis, definition and 
essentials for. Root hairs. Geotropism. Hydrotropism. 


Characteristics. Functions. Kinds of branching. Forms of stems. 


External structure. Grafting. Internal structure, dicot. and monocot. 


Functions. General structure. Minute structure. Adaptation. 
Modified forms. Fall of leaves. 





Photosynthesis. Digestion. Assimilation. Respiration. Transpi- 


Structure and function of flower parts. Adaptations for pollenation 
by wind and insects. Pollen; Ovule; Fertilization stages. 


Definition; Types of fruits; Functions. Dispersal. Economic 


Classes of plants. Representatives. Fungi as type of spore plants. 


Kinds. Method of study. Useful and harmful forms. Natural and 
artificial protection. Antiseptics. Disinfectants. History. 


Relation to higher animals. Amoeba and Paramoecium as types. 
Life functions compared. 


Development. Specialization. Classification. 

Representatives. Structure. Adaptations. Economic importance. 

Parasitism. Earthworm. Trichina. Hookworm. Tapeworm. 


Characteristics. Classification. Scientific classification explained. 


Characteristics. Crayfish as type. Structure and adaptations of 
crayfish. Homology. Life history. 


Characteristics. Grasshopper as type. Structure of grasshopper. 
Adaptations. Life History. Economic importance. 


Structure and adaptations of each. Communal life and specialization 
of bee. Economic importance. 


Structure and Life History of Fly and Mosquito. Relation to dis- 
ease; how proven. Means of prevention and control. 


Classification of animals. Development. Classification and types 
of vertebrates. 




Structure, external and internal. Life History. Adaptations. 

Economic value. 

Characteristics of the amphibia. Structure of frog. Adaptations. 

Metamorphosis of frog. Toad, Salamander and Frog compared. 

Economic importance. 

Representatives. Characteristics. Adaptations. False ideas. 

Poisonous snakes. Treatment. 

Characteristics. Adaptations for flight. Adaptations for active 

life. Adaptations of beaks and feet. 

Food. Nesting. Eggs. Migration. Economic importance. 

Characteristics. Adaptations of limbs, teeth, and body coverings. 

Special adaptations of rodents, ungulates, carnivora and primates. 

Man's place in the group. 

Relation to other animals. Idea of evolution. Evidences of evo- 

Antiquity of the idea. Lamarck's theory. Darwin and Natural 

Selection. Summary of the theory; its conclusions. 


Ancient records. Primitive man. Stages in development. Imple- 
ments used. Results of higher mentality. Present races. 


Necessity. Definition. Functions of various food stuffs. Measure- 
ment of values. Proportions. Balanced ration. Digestibility. 
Cost. Cooking. Lipoid. Vitamines. 


Digestive changes. Digestive organs. Mouth. Teeth. Stomach. 
Intestine. Glands. Absorption. Assimilation. 


Development of organs, in lower forms. Structure and adaptation 
of nose, trachea, lungs, diaphragm. Changes in air and blood. Venti- 


Function. Blood, its composition and use. Heart. Arteries, Veins, 
Capillaries. Lymph circulation. 




Source of waste. Organs of excretion. Kidneys, Lungs, Skin. Heat 


Location and functions of cerebrum, cerebellum, medulla, . spinal 
cord, sympathetic system. Regions of control for various activities. 


Irritability. Touch. Taste. Smell. Hearing, structure of ear, 
care of ears. Sight, structure of eye, care of eyes. 


Hygiene of Muscles, of Digestion, Breathing. Bathing. Care of 
eyes, teeth, feet. Posture. Sleep. 


Food control. Sanitation. Disease prevention. Housing conditions. 
Food laws. Medicines. 


General uses. Harmful forms. Plant uses in detail. 


General uses of animals. Harmful forms. Importance of each 
group in detail. Harmful insects and their treatment. 


Fish. Amphibia. Reptiles. Birds. Mammals. 

Soil formation. Plant breeding and protection. Animal husbandry. 

Bacteria on the farm. 

Value of forests. Enemies of forests. Protection. Timber structure. 

Street trees. 

Tobacco, physical and social objections to its use. Tea, Coffee, 

Cocoa, and Chocolate. 

Composition and kinds of alcoholic liquors. Physical effects. Not 

a food. Alcohol and disease. Waste of resources. 

Osmosis in life processes. Oxidation. Circles in Nature. Evolution 

of life functions. 

Biologic development. The work of Pasteur, Roux, von Behring, 

Lister, Carrell, Flexner. Darwin, Huxley, Mendel, Burbank. 

INDEX.. 549 




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- 


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 



"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. 


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 


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. 


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. 


Biology, a study of living things. 

1. Derivation: Bios, Logos. 

2. Definition. 

3. Classes of things. 

Inorganic (meaning and examples). 
Organic (meaning and examples). 



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. 






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. 



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. 


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. 

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. 




In plants is per- 
formed by 

In animals is per- 
formed by 


Roots, leaves 

Teeth, claws, etc. 


Ferments in the tissues 

Stomach, intestines, 

glands, etc. 


All live tissues 

Intestine, stomach, etc. 



All live tissues 

Respiration (oxidation) 

Air spaces and tissues 

Lungs, gills, etc., all 




Kidneys, skin, etc. 


Flowers, leaves, ten- 

Legs, wings, fins, etc. 

drils, etc. 


Leaves, tendrils 

Nerves, sense organs 


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? 


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. 



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 



they are found, (3) enough of their characteristics or properties 
so that we can recognize them, and (4) their use to living things. 


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 

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. 



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. 


A living organism 

A steam engine 




To unite with 



By means of 



To produce 

Heat and energy 

Heat and energy 

Leaving waste 

Unused food 


Carbon dioxide (in 

Carbon dioxide (in chim- 


ney gas) 


A living organism . 

A steam engine 

Is alive 
Grows in size 
Repairs wear 

Is not alive 
Does not grow 
Wears out 
Cannot reproduce 

Similarities based on oxidation, differences based on functions of the 

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 


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. 


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 

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. 


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. 


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 (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 (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 


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 (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 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. 



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. 



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 



a Iron .01 
D Magnesium .11 
D Sodium .16 
D Potassium .18 
D Fluorine .22 
Chlorine .25 



FIG. 2. Elements composing a human body weighing 154 pounds. (Figures 
express pounds.) 


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. 




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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. 


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. 



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 

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- 

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 


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. 


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 


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) 


Complicated forms found in wood, paper, cotton, linen. 


(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 

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 

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. 










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2 3 gf 



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G< *- 


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. 


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. 



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 

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. 



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. 


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. 


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. 


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- 


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 

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. 


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- 


ology, Duggar, pp. 15-32; College Botany, Atkinson, pp. 1-12; Biology, 
Calkins, pp. 6-25; Encyclopedia Britannica, articles on "Physiology," 
"Protoplasm," "Protozoa." 


Protoplasm is the primary, essential living substance of all plants and 

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. 


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. 


Essential parts Function 

Protoplasm. Any of above properties. 

Cell wall. Gives form to cell. 

Nucleus. Controls growth and reproduction. 


3. Tissue. 


4. Organ. 


5. System. 


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, 



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 

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 






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. 


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 


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 


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. 



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. 


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 




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 

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 food soluble, just as truly as does an animal's stomach or 

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. 


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, 


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 


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 


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. 

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 


Micropyle (opening). Entrance of pollen, exit of hypocotyl. 
Tegumen (inner coat). 


2. Kernel. 

Embryo (miniature plant, always present). 

(1) Cotyledons (seed leaves) 

(a) Leaf-like (squash). 

(b) Store food, but come up (bean). 

(c) Store food below ground (pea). 

(d) Digest and absorb from endosperm (corn). 

(a) Monocotyledonous (one cotyledon) (corn). 

(b) Dicotyledonous (two cotyledons) (bean). 

(c) Polycotyledonous (several) (pine). 

(2) Plumule (undeveloped shoot). 

(a) Small if much stored food. 

(b) Large if little stored food. 

(3) Hypocotyl (part below cotyledons). 

(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. 


Bean (Dicot., no endosperm). The pod is the fruit. 
External structure. 
Shape, colof, etc. 

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. 

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. 


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. 

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. 




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 



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. 



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. 

& L CrRouNp LINE 


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 


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 

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. 


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 


by setting up experiments in which several seeds are given 
similar treatment, except that one of these factors is changed in 

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 

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. 


which is often as necessary as proving that it will occur with certain 

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. 


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 


Stages in germination: 

1. Emergence from seed coats. 

Adaptations, Micropyle, Cap on hypocotyl. 

2. Penetration of soil. 


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). 


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. 




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 

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, 



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 


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 



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. 


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. 


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 


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 

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. 


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. 


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. 


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. 







1. Epidermis 

Thin, brick shape 


Root hairs 

Thin, tubular, sensi- 



2. Cortex 

Loose, thin, round 



3. Central cylinder 


Thick, fibrous 



Thick, tubular 



Thin, tubular 



Delicate, active 


4. Root cap 

Loose, thin cells 


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 


General surroundings. 



Normal forms 


Adapted for 

1. Soil Roots 
(a) Fibrous 
(6) Tap-root 
(c) Fleshy 
2. Aerial 
3. Aquatic 


Wide surface 
Deep water supply 
Absorption from air 
Absorption from water 


1. Brace-roots 
2. Propagation 
3. Climbing roots 
4. Parasitic 


Support, climbing 
Stealing nourishment 

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. 




Gravitation, the attraction of the earth which draws everything 


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 



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. 


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. 


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 



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. 


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 



(pQS -) 



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 









FIG. 11. Note different direction taken 
roots, when attracted by moisture. 


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 

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 



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. 


teas DCft 








SOt L. 


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. 


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. 



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. 


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, 



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. 


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. 

(See references at end of Chapter LIII.) 

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. 

1. Definition. 

2. Processes dependent upon osmosis: 






Essentials for osmosis 

In plant 

In experiment 

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. 


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.) 
An adaptation for 
Penetration of soil. 
Obtaining water in soil. 
Obtaining nourishment. 
Positive in roots. 
Negative in stems. 

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. 




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 


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. 




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 


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. 


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 : 


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. 


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 

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 


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. 

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. 

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. 

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. 


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. 

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. 





Gum or hairs. 

Woolly packing. 

Leaf arrangement. 

Manner of growth. 
Bud scale scars. 


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. 




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.) 


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 




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. 


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. 



" 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 

From Sargent. 



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 

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 

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. 


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 



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- 



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 



FIG. 19. Sequoia Washingtoniana (Bureau Forestry, U. S. Dept. Agr.) 
From Atkinson. 



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 




External Features 






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 


Thin if young, corky in 

Protect from insects, 

older stems 

fungi and weather 

Retain water 


Thin walled, soft cells 

Food making and di- 


Bast fibers 

Thick and tough 


Bast tubes 

Long, tubular cells 

Downward transfer 

2. Cambium 

Very active, proto- 



3. Wood region 

Wood fibers 

Thick walled, stiff 



Thick walled, tubular 

Upward transfer 

4. Pith 

Thin walled, weak 


Pith rays 

Cross transfer 

Comparison of Dicot and Monocot Stems 

Features of each 



Outer layer 

Bark of several tissues 

Rind of one tissue 

Vascular bundles 

In regular rings 


Bulk of stem 



Supported by 

Wood region 




Not permanent 


Continuous in height 

In height only 

and thickness 


For lumber, fuel, etc. 

For food stored 

Usual shape 


Tall, slender 


Broad-leaved trees and 

Grasses, lilies, palms, 

common plants 

sugar-cane, etc. 


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 


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. 




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 


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. 





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. 


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. 



light and air, on both of which all the activities of the leaf 

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 

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 

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. 



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. 


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 


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 


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 



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 


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 


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. 

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). 

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). 


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. 


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 

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. 


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, 



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. 


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. 


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. 


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. 





Epidermis (upper 

One layer; irregular cells 

Prevents loss of water 

and lower) 


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 



Green, living grains in the 

Make starch 


Spongy cells 

Irregular, loose 

All leaf functions 

Have chlorophyll grains 

Air spaces 

Large and irregular 


Connect with stomates 



Duct bundles extending from 


the stem 





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- 




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, 


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. 



8t Proci. 
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 

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. 


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 

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 



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 

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. 


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. 


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 


To show that Leaves (and Stems) turn toward Light. Two 
thrifty plants are provided, one is placed in a light-tight box, 



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- 


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 

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. 



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 



to the upper and lower surfaces of a leaf, and will show the same 

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. 


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. 











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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 

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 



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 




FIG. 32. The flower is provided with 
means for seed production. 


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 


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 


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. 


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. 


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 


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. 



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, 



Botany for Schools, Atkinson, pp. 182-186; Elementary Biology, Peabody 
and Hunt, pp. 74-88. 


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. 


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. 

Anther Production of pollen. 

Filament Support of anther for pollenation. 


Stigma To catch pollen: sticky, sometimes 

Style To support stigma so as to catch 

Ovary Contains ovules, forms fruit. 


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. 


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? 


Definition: union of sperm nucleus of pollen with egg nucleus of the ovule. 


1. Produced by stamen (anther). 

2. Structure: one-cell stage. 
Three cell stage. 

Pollen tube (use ?). 
Sperm cells (use ?). 

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. 


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. 



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- 



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 

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 

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 



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. 


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 

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. 



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 


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 


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, 



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 


that they are the most important part of the plant for his 

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- 


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. 


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. 



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. 




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. 




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 


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 

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 



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 


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. 


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. 

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 


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 


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: 

food, sugars 

products, alcohol and carbon dioxide 
uses, bread and beer 



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 






FIG. 43. Some forms of useful and of harmful bacteria. (Greatly 


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 

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. 


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 


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 

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. 


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 


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- 


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." 


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 


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 


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 



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. 


Anti-toxin treatment 


Mild or dead germs intro- 

Serum of blood from im- 

duced into body 

mune animal introduced 

into body 


Body reacts and forms its 

Anti-toxins directly sup- 

own anti-toxins 



Immunity develops slow- 

Immunity provided at 

ly but persists longer 

once but for only the 

one case 

Diseases treated 



Typhoid fever 








212 deg. 

140-150 deg. (30 min.) 

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 

Less palatable 
Much reduced 

Unchanged, except 

Less digestible 





Point of Attack 

Disease caused 

Means of control 

via digestive 


Cook foods, destroy flies 
Secure pure water supplies 
Pasteurize milk, keep food cold 
and clean 


via lungs 

Measles, mumps 

Whooping cough 

Avoid dust, check "colds" 
Anti-spitting laws 
Quarantine laws, avoid contact 
with sick 
Good food, sleep, general 

via wounds 

Blood poisoning 
Tetanus, syphilis 

Pus infections 

Use of antiseptics and disin- 
Protect from further bacterial 

Foods or skin 
via insect trans- 

Yellow fever 

Destroy breeding places 
Cleanliness, screens, etc. 
See Chapter 25 on " Insects and 


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, 


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 


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. 



Rate of reproduction (why limited). 

Favorable conditions: food, moisture, warmth. 


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). 


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 


Hindered by dry conditions 


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 and potassium permanganate 

Burning sulphur (danger of bleaching) 

Development of Bacteriology. 

Pasteur, 1860-1880 

Von Behring, 1894, diphtheria 

Roux, 1894, diphtheria 




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 




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- 



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 

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. 





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 




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 


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). 


malaria sleeping sickness cattle fever 

smallpox dysentery trachoma 

yellow fever scarlet fever bubonic plague 


Amoeba Paramoecium 




Cell wall 




Flowing lobes 






Absorbed at any point 

Definite region of absorption 
Conjugation and fission 


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- 

See also references on "Insects and Diseases." 
1 Look through, note pictures especially. 


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. 





KOT i 

FIG. 47. Various types of protozoa, rotifers, and other organisms often 
found in aquarium cultures. (Greatly enlarged.) 



2. Economic importance, 

Food, scavengers, soil and rock formation. 
Producing certain diseases. 
Amoeba (a very simple protozoan). 

Where found. Appearance. 


Protoplasm, nucleus, lobes, vacuoles, food grains. 
Paramcecium. (A more specialized protozoan.) 

Where found. Appearance. How distributed. 


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. 


Life Functions 

in Amoeba 

and Paramoecium 

Digestion and assimi- 

By flowing lobes 
By contact anywhere 

By cilia 
In definite regions 


Contact with dissolved air 



Vacuole, variable 
Lobes, variable 
Responds to heat, light, 

Two vacuoles, definite 
Cilia, definite 


contact, moisture, etc. 

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. 




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. 



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 

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. 


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 

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 


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 




called called 


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 


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. 


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. 


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. 






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 

Many celled 

Specialized tissues and organs 

Digestive, respiratory and nervous sys- 

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 

Degree of Specialization 


1. Sponges 

Cells adapted for food getting, di- 
gestion and reproduction 

Bath sponge 

2. Coelenterates 

Tissues for the above processes and 
for locomotion 

Jelly fish 

3. Worms 

Organs well developed, nerves, blood 
vessels, muscles 


4. Molluscs 

Sense organs, gills, heart, etc. more 


5. Arthropods 

Great specialization, skeleton, all 
senses, very active, nervous sys- 
tem and instinct 


6. Vertebrates 

Great internal specialization, high 
special senses, brain, instinct, and 
reason, varied locomotion, skeleton 



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- 


3. Both of which mean success in the struggle for existence. 




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. 


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 



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- 

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 



retractor and protractor 
muscles of the pharynx,.. 

cesophageal pouches- 
seminal receptacles' 

cerebral ganglion 


FIG. 49. Dissection of the earthworm, Lumbricus sp. From Kellogg. 



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?) 




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, 



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 


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. 




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. 



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 











=3J 3 













10 ( 

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. 


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. 



Earthworm, tapeworm, hairworm, vinegar eel, leech, etc. (not cater- 

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. 


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. 


Adaptations for, 

1. Body muscles, two layers, different motions. 

2. Setae with their own muscles. 

3. Habit of flattening the " tail " region in burrow. 


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: 

Examples: setae, cilia, pseudopodia, all for locomotion, 
similar examples from fish, bird, man, etc. 



Harm or death to host. 


Loss of organs. . 

Absolute dependence. 
Need for vast reproduction. 

to parasite. 

WORMS 171 


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. 


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. 


" Horse hair snakes." 

Vinegar " eels." 
" Raining down " of earthworms. 




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 

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 ' 


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, 

Class, insecta 
Order, orthoptera 
Family, acrididae 
Genus, melanoplus 
Species, femur-rubrum. 




.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- 


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 

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 


of each successive group are known, a complete description is 

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. 



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 


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. 


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. 


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. 

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. 







Head-thorax united 



Carapace, gills 
Five pair legs 
No carapace, no gills 
Four pair legs 
Air sacs or tracheae 

Crab, shrimp 


Head and thorax separate 
Three pair legs; wings 
Breathe by tracheae 



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. 




Carapace, the external protective covering of the thorax in 


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. 


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 




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, 




opening of green (/land 



genital aperture 




FIG. 58. Ventral aspect of crayfish (Cambarus sp.) with the appendages of 
one side disarticulated. From Kellogg. 


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 



FIG. 59. The appendages from the entire right side of the body of a lobster, 
arranged serially to illustrate serial homology. From Calkins. 


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 


FIG. 60. Longitudinal section of the lobster showing the arrangement of the 
internal organs. From Calkins. 


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 

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. 


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. 


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. 

(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- 



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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. 


Contrast, worms, having only simpler tissues and organs, no skeleton, 


Crustacea, with high specialization, skeleton, active, aquatic. 

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.) 


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 


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. 

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? 




Trachea, a breathing tube, admitting air to the tissues. Plural: 

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 

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. 



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. 



/' \ 


grasshopper cricket locust 

true bugs lice scale insects 
flies mosquitoes fleas, gnats 

moths butterflies 
bees ants wasps 

auditory organ 
ocellus : 

' head compound eye I 



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 



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 


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 

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. 




L. 1-AB.Run. 

MX M AX I Ll_ AE . 


Lab. LABlUfl. 


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 


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 

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. 


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 


by many veins and, when not in use, are folded lengthwise, like a 
fan, beneath the narrower anterior wings. 


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." 


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- 


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 

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 



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 


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 

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. 


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, 


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. 

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). 

Antennae, one pair, functions, cf. crayfish. 
Eyes, simple, three, location, 
compound, structure, why not on stalks? 


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). 


Anterior thorax, Prothorax, Movable; legs attached. 

Middle thorax, Mesothorax, Strong; wings and legs. 

Posterior thorax, Metathorax, United to mesothorax wings and 

jumping legs. 

Functions: walking, clinging, leaping. 



Strength of muscles. 
Length of leverage. 
Free backward movement. 
Spines, pads, etc. 
Point of attachment. 


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. 


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. 




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. 


The butterflies and moths belong to the order lepidoptera (scale 
winged) and furnish a familiar type of quite a different group of 

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 



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- 

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 



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 

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. 



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 

lepidoptera. The bees, beetles, 
and flies all pass through 
similar series of changes 
which can be tabulated as 

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 





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. 



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 : 

Day flier 

Chrysalis for pupa 
Wings vertical when at rest 
Antennae knobbed 
Abdomen slender 


Night flier 
Cocoon for pupa 
Wings held horizontal 
Antennae feathery 
Abdomen stout 



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 


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 

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 


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 

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. 



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. 



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 


in passing back the pollen from the other legs and depositing it in the pollen 

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 


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 



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 



bee ' 




is called a 


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. 


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. 


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. 


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. 

Legs small and weak. 

Wings large, few veins, scaled, slow motion. 

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. 


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. 




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. 




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- 


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 



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 


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, 

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 



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 

Nasal discharges 
Open sores 



Privies 1 

infantile paralysis 








Open jore 




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 



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 

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 



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: 


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. 


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 


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 

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. 


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. 




Transmitted by 

Means of prevention 



Drainage and oiling of swamps 

Screening and isolation of patients 

Yellow fever 


As above 

Typhoid fever 


Destroy breeding places 

Kill breeding females in spring 

Screen food and waste 



As above 



Spotted fever 


Destruction of insect pest 

Cattle fever 



Relapsing fevers 


Cleanliness, destruction of pests 


Sleeping sickness 

Tsetse fly 

Protection against fly attack 

The "Plague" 

Fleas on rats and 

Destruction of rodent hosts 



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, 



Etc., etc. 

Typhoid fever 
Yellow fever 
Bubonic plague 



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). 

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 " 


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. 

Culex, common northern mosquito, body horizontal. 

Anopheles, malaria, body almost vertical. 

Stegomyia, yellow fever, tropical. 




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 

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, 




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, 


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. 


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 

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 



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 


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. 



Development of the branches of the Animal Kingdom. 

Branch. Examples (in notes) 






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- 

Jointed exo-skeleton, active. 

High developed senses and in- 

Size and brain development lim- 

Internal skeleton. 

No limit to size of brain. 

Less protected but more intelli- 

Classes of vertebrates 





Characteristics of vertebrates 

Spinal column 

Internal skeleton 

Dorsal nervous system. 

Two body cavities 

Two pairs of limbs or fewer. 



Frogs, toads, salamanders. 

Snakes, turtles, lizards. 


Rat, cow, cat, man. 

Sense organs on head. 
Jaws not developed from limbs. 
Eyelids, separate teeth. 
Ventral heart, red blood. 




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. 



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- 



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 


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 

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. 


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. 


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 

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, 



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 

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. 


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. 



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. 



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. 


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 

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. 


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. 


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. 


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 


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. 


Characteristics: bony skeleton, gills, scales, fins. 
External Structure. 

Shape, spindle outline for easy swimming. 

Scales, for protection and ease of motion (cf. crayfish). 


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. 

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. 

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. 


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. 

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. 

See summary in text. 




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. 





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 


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 

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 



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 


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 

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 


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 

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 


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. 



Front leg and arm 



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 
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 

Medium length, not so 
muscular in propor- 
Medium length, bones 
Five short toes, not 

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 

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. 


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 

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 


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 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 


FIG. 9 1 a. 

replaces it with fresh air, which is then swallowed and the process 

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 



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 


By Means of 

For the purpose of 

External features 


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- 

Three chambered heart 


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- 

Vision when partly sub- 

Landing after leaping 
Increasing leverage for 


Leaping and swimming 
Digesting proteids 
Digesting and absorbing all 

food stuffs 

Forcing blood through body 
Bringing blood to heart 
Carrying blood from heart 
Distributing blood to the 

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 


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 


3. Circulatory system 

Heart, auricles, and ventricle 
Arteries, aorta, etc. 
Capillaries, and veins 
Lymph vessels, and spleen 


4. Excretory system 

Kidneys, and their ducts (ureters), bladder 
Lungs, and skin 

5. Nervous system 

Brain: consisting of 

Olfactory lobes 


Optic lobes 



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 


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. ' 

Amphibia (two lives). 

Characteristics: metamorphosis direct fertilization 

no scales larva vegetarian 

three-celled heart adult carnivorous 

fairly developed brain 


Representatives: Frogs, tree-frogs, salamanders, toads, newts. 

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. 


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. 

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. 

'( 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 


Essentials for digestive system. 

Tubular canal. 

Glands for secretion. 

Devices to increase surface, for osmosis absorption. 
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. 

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. 



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 



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. 


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 

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 

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, 


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 


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. 


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. 

Relatives: American Natural History, Hornaday, pp. 359-374; Frog 


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- 

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. 

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. 

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. 




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. 



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 


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) 

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. 


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 

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 

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 



strychnine, which with the anti- venom serum, now easily obtained, 
constitute almost sure protection. 


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. 


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 

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. 



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. 



Snakes, turtles, lizards, crocodiles, and alligators. 

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." 

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. 



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. 



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 




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. 


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. 


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. 


1. Flight. 

2. Giving regular body outline. 

3. Protection from cold and water. 

4. Protective coloration. 


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. 


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 

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 


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 

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 


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 


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 

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 



brain completely fills the skull; the cerebrum is broad and the 
cerebellum especially large, as is to be expected in so active an 


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 

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. 


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. 


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, 


Feathers, wings, beak, two feet, shelled egg. 
1. Adaptations for flight. 

Shape, feathers to smooth outline. 
Balance, neck, legs, attachment of wings, 


Lightness, hollow bones, air sacs, feathers, beak. 

Origin, modified, scales (other epidermal structures). 
Distribution, tracts. 
Kinds, down for warmth. 
Regular feathers for outline. 
Quill feathers for locomotion. 

(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. 

Crop for storage, flockwise feeding. 
Gizzard for grinding in place of teeth (why?). 
Powerful digestive fluids. 

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. 

Heart large, four chambered, rapid beat. 
Blood vessels, large, especially to breast. 


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 


Adapted for 

3 front; 1 rear 

Song birds 


2 front; 2 rear 




All webbed, separate 



All webbed, united 



Three webbed, united 

Duck, goose 


3 front; 1 rear, heavy claws 

Hawk, owl, eagle 

Catching prey 

Small, weak 

Hummer, swift 

Little used 

Long legs 

Crane, heron 


Legs short, far back 

Loon, duck 


5. Beaks. (Why not teeth). 



Adapted for 


Hawk, owl 

Catching prey 

Chisel shaped 


Drilling in trees 

Wide but weak 


Catching insects on wing 


Broad and notched 


Scooping and straining 

Slender and sensitive 


Probing in mud 

Notched and hooked 



Short and thick 



Crossed mandibles 


Opening cones 

Slender tube 


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). 




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. 




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 



enemies, they multiply unchecked and are becoming an unmitigated 

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. 




& * 


0) O O 


^ ^ c/3 




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 

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 


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 

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 

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 


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. 

Principal migration routes 

FIG. 101. Distribution and migration of the Eskimo curlew. (From Cooke; 
Yearbook, U. S. Department of Agriculture, 1914, see Pearse.) 


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 



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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 


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 

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, 


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 


Migration: Birds of North America, Chapman, pp. 5-6, 13-20; Bird 
Life, Chapman, pp. 48-61; Travels of Birds, Chapman, entire; Citizen Bird, 


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. 

Foods used. 


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. 


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?). 


Nest Building. 

Necessity for nest, warmth for egg and protection of young. 

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). 


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. 

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?). 


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. 


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." 



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. 



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 

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 

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 


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 

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 

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 



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. 


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 


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, 



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 








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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. 


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. 


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- 


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. 


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. 



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. 


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). 

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. 


Teeth for gnawing (incisors). 

1. Chisel shape, self -sharpening. 

2. Strong, powerful jaws and muscles. 

3. Continuous growth (why?). 

4. No canines. 



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. 

Specialized for pursuit (ungulates for escape). 

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. 

Representatives, gorilla, chimpanzee, orang-utan, monkeys, gibbons, 

lemurs, man. 

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.) 



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 



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 


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 

Surely this modification of similar parts for different uses would 
not be found if there were no relationship between the different 

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 

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 

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 



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 



(Homo sapient). Africa. Africa. Asia. 

Asia, Europe. 

Cro-Magnon and 
other races. 

More primitive spe- 
cies, human and 

Neanderthal race. 

Piltdown race. 
Heidelberg race. 


Primitive Gib- 
PLIOCENE bon of Eu- 
AGE. rope 

(Pliohylobatea). Unknown Pliocene 
ancestors of man. 

AGE. Earliest Gibbons 
of Europe 

(Pliopithenu) . 

Ancestral anthro- 
OLIGOCENE. poids of Egypt. 


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 


great modifications which have resulted in producing the in- 
numerable forms of living things which inhabit the globe* 


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. 


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. 


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 



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 

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 

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. 


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 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. 



Geological History 


Characteristic Animal* 


Occurrence of 




Deer Sloths. 
Ape . Man 

Day , Sta 


Ape . Ma 


CaT, Bear. 

M on Hey. 

Cow , Deer. 



Birds . 

Marsupials . 





Reptiles . 

Mam ma/s. 












Worms .etc. 

Tnlobites . 

rocks - no 

FIG. 106. From Pearse. 


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 


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. 


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. 


(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. 




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, 




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 

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- 


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 

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 


his simple crops, community life and society had their earliest 

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 

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 

(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. 




^howing Conditions in Europe during the Development of Man 
Adapted from Osborn's "Men of The Old Stone Age" 


Cl imafe 



Human races 

25.00O years 


Deer, bison, horse, 
chamois, ibex 

Iron /OOO B.C 
Bronze /OOO yrs. 
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, 

3. Interglacial 

100. 000 years 


Bison, horse, 
elephant, lion, 
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 


wooly mammoth 



rhinoceros , 

2. Inferglacial 

stag, bison, 


Heidelberg Race 

200,000 years 



2.G/ov/o/ Period 
25, OOO years 

wooly mammoth. 

( Interglaciat 




1. Glacial Period 
Z5.00O years 

Mush ox in 

(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. 


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 

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 

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 


make special effort to keep our bodies strong, even though physical 
strength is no longer the one essential in the struggle for 

,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: 






O cj 

G C 


.?* < 

ll| I 

&<K o 


I I 






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. 


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 




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.) 



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 

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, 


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. 


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 

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. 


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. 


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. 


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 






This Portion can Yield 
to the Body in Energy 
and Heat Units 


For Heat and 




























Coffee (cream and sugar only) 

Biscuit soda 

Bread corn 

" graham . . 

" wheat 

" plain rolls 

" and butter . 

Crackers saltines 

" soda 

Toast dry 

Chocolate layer 

Cookies molasses 

Doughnuts . 




Corn flakes 

Oatmeal ... 

Puffed rice 


Shredded wheat (2) 

Apple baked 


Olives green 








This Portion can Yield 
to the Body in Energy 
and Heat Units 


For Heat and 




Brown gravy 



























Hash beef 

Macaroni . . . 

Salad dressing (French) 


English walnuts . . . 



Mince .... 

Pumpkin ... ... 

Blanc mange (chocolate) 



Tapioca . . . 

Egg mayonnaise 


Tomato (with mayonnaise) 


Cream of celery 

Clam chowder 
Vegetable (canned) 







This Portion can Yield 
to the Body in Energy 
and Heat Units 


For Heat and 




Candy chocolate . 



Oun es 









Chocolate almonds 

]Vaple syrup 

Sugar (granulated or loaf) 
Beans baked 

" kidney 

" strinsr 


Cabbage boiled 


Corn canned . . 



Onions creamed 

Potatoes sweet 

" white mashed 

" " baked 


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 







""C ^% 





H <u a 
.2 "5 ^ 



For Heat and 
































101 6 







Dairy Products 
Cheese full cream 

Ice cream 

Milk whole 


Boiled (2) : . 




Halibut steak 

Salmon canned . . 

Chicken (fricasseed) 


Chops (broiled) .... 

Leg. . 






This Portion can Yield 
to the Body in Energy 
and Heat Units 


For Heat and 


























Ham lean 



Ham . 





Cutlets ... 



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 

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 


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 

" 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 


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 

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." 



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. 





Foods containing 


C,H,0, N,S,P, 

Build tissue 

Lean meats, eggs, 

K, Ca, Cl, Fe 


beans, peas, milk 

Some energy 


(C, H 2 , 0) 


Sugar, cereals, 

Stored as fat 

bread, corn meal 

Some tissue 

Fats and oils 

(C, H) O 


Butter, lard, milk, 

Stored as fat 

cheese, olive oil, 



H 2 O 

60% tissue 

Taken as water in 

Blood, fluids 

all vegetables 


fruits, all foods 

Mineral Salts 


H 3 P0 4 


Grains (whole) 


meats, fish, milk 

Aid digestion 



Essential in blood 

Taken as salt in 


almost all food 

Iron compounds 

FeCO 3 


Spinach, lettuce, 

Oxygen carrier 

green foods, 

prunes, meats 

Potassium com- 

K 2 S0 4 

Essential in blood 



Calcium and 

Ca, Mg 

Regulate nerve and 

Grains (whole) 


heart action 



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 


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 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), 


Pears, Currants, Raspberries, Cranberries, Prunes, Dates, Figs, 

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. 


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 

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. 


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. 


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. 
Vitamin es. 
Dietary Diseases. 



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. 




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 


diameter, to permit the carrying out of special functions in various 

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- 

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 



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 

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 




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 

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 


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 | 

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 

Glands. Digestive fluids are secreted by organs called glands. 
A gland consists of a group of cells adapted for producing a fluid 



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 





2>.\ IL^A \pRE-\ 



-i \ 




H E 


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. 



* 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- 

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. 



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 

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. 



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 

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 

1. Its great length and coiled position in the body. 

2. Its inner lining projects in creases and folds. 


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 

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 

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 

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. 




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- 

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 


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 

3. Absorption which occurs principally in the small intestine 
and stomach, by means of the blood capillaries and lacteals. 





bo as i; ex 

2 S 58 



fe PH C/3 C/2 ^ fe 

In 3 



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M WPn 


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. 


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. 

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. 


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. 




Structure, size, position in mouth. 

1. Taste (what use for taste, where located). 

2. Aid in chewing. Aid in swallowing. 

3. Cleaning teeth. 

4. Speech. 

; Parts. Crown, neck, root (make diagram). 

1. Enamel (structure and function). 

2. Dentine (structure and function). 

3. Pulp region, nerves, and blood supply (why each). 


















Why two sets of teeth? 

How does the change take place? 

Special tooth adaptations in other animals, 
Glands in general. 


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. 

Composition, alkaline, watery, three pints daily, ptyalin. 

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 




Shape and size. 

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. 


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. 

Small, simple, numerous, in the intestine wall lining. 
Secretion, alkaline; soda carbonate; sugar ferment. 
Function, saponify fats, act on sugar somewhat. 

Largest gland, uppermost in viscera, over stomach. 
Bile, thick, brown, one quart daily. 



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. 

Ferment changes [to] 

Amylopsin starch 

Trypsin proteid 

Steapsin fats 


fat acids, soaps, glyc- 

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? 

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 


What absorbed 

Where emptied 

Gastric capillaries 

In stomach walls 


General circulation 
via gastric vein 

Intestinal capillaries 

In villi 


Fatty acids 
Water, salts 

General circulation 
via mesenteric 

Lacteals or lymph 

In villi 

Emulsified fats 

Thoracic duct to 
left jugular vein 


Meaning of word. 


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. 




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 




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. 


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 



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. 




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. 



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- 


FIG. 124. Compare capacity utilized by 
ordinary breathing with that of deep 

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- 

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. 



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 


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. 



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 


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- 

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. 


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; 



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 

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. 

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. 

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." 


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. 

Large amount of air used. 

Importance of oxidation. 

Need for ventilation to supply oxygen. 

to remove heat, water vapor, carbon dioxide. 



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 









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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 



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 



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. 


Blood loses 

Blood receives 

In all active tissues 

Materials for growth, repair 
and energy 

Wastes of oxidation 
Carbon dioxide and 
Nitrogenous wastes 

In walls of digestive 

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 


In the kidneys and 

Water and urea 

Carbon dioxide, etc. 


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 


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 

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- 



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 


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 

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. 


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 





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. 


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. 

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. 

Composition. Plasma: (two-thirds bulk). 
Serum, carrier of food and waste. 
Fibrinogen, aids in forming clot. 


Corpuscles: (one-third bulk). 
Red, disc-shaped cells, minute, and numerous, contain haemoglobin 

(oxygen carrier). 
White, amoeboid, can penetrate tissues, destroy germs, help absorb 

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.) 


Shape, hollow, cone-shaped muscle. 

Location, between lungs, behind breast bone, point to left. 


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. 

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. 

72-80 beats per minute. 

Dependent on age, activity, state of mind, etc. 


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. 


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. 


Connect arteries and veins. 

Very thin, small, and numerous. 

Provide surface for osmosis in nutrition, respiration, and excretion. 
Lymph circulation. 





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 



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. 


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 

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 


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. 


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. 


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. 


4. Skin. 

Removes water, salts, etc. (Not primarily excretory.) 

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. 

Protection from germs. 

Protection from injury. 

Protection from drying of tissues. 

Protection from water. 



Temperature regulation. 

Sweat excreted. 

Evaporated by body heat. 

Body therefore cooled. 



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 




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- 


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 

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 

From this double nerve chain extend branches to most of the 
internal organs and to other ganglia located in the chest and ab- 



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 " 


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. 


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 


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. 


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. 


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 

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. 



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 


1. Voluntary actions 

2. Involuntary actions (un- 
3. Involuntary reflex (con- 
4. Automatic actions 

Sympathetic system 
Spinal cord 

Whole system 




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 



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 

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 



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 

Structure of the Human Ear. The vertebrate ear is a wonder- 
fully complicated organ, consisting of an external ear which opens 


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 


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 

. 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 


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. 




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 


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 

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 



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. 


Defect of eye 


Near sight 
Far sight 

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 


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. 


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. 




a % Us ^ 

|g !H 



s a" a" 



(>) How we hear, 
(c) Care of ears. 

6. Sight. 

(a) Structure of eyes. 

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. 



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. 



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. 



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- 


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. 


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 

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 

Deep breathing means using more lung tissue, getting more 
oxygen, and developing the diaphragm and rib muscles, 

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 


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. 


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 

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- 

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 

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. 


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 

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 


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 


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. 


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, 


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- 

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 

Muscular exercise should hold the attention, and call into play 
will power. Exercise should be enjoyed as play, not endured as 

The most beneficial exercises are those which stimulate the 
action of the heart and lungs, such as rapid walking, running, hill 
climbing, and swimming. 


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. 


School Hygiene, Shaw, entire; Outlines of Practical Sanitation, Bashore, 
see index; The Health of the City, Godfrey, see index; Handbook of Health, 


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. 


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. 


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. 



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. 



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 

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 


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 

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. 


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 

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 


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 

" 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 

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 


manufacturers offer. Look over the literature that comes to your 
home and draw your own conclusions. 


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 

Bulletins of U. S. Department of Agriculture, State Departments of 
Health, Rockefeller Foundation, City Health Departments. 


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. 



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- 

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 



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 

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. 



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- 


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 

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. 



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. 



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. 



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 

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 


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. 



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 


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. 


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 

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 

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. 


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 



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. 


for spinning. Not only is cotton made into thread and cloth, 
but into batting, surgical dressings, paper, celluloid, and gun 

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- 


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 



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. 



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 
Railroad ties 





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. 


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 



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. 


made by distilling any kind of wood in large closed vessels. It 
is an important industry in many wooded regions. 


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. 


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. 














South Europe 





Various seeds. 

Mustard \ Various 
Nutmeg, etc. J 
Cotton-seed 1 

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. 


Sugar beet 
Beet, carrot Various 
turnip, parsnip 

Location Uses 

Europe, U. S. Sugar, potash, fertilizer. 

Food, supplying starch and min- 

Sweet potato 

Southern U. S. 







Flavor, medicine. 










Food starch. 


Stem products. 




Sugar cane 

U. S., India, 

Food, sugar, molasses, alcohol. 

West Indies 


U. S., Europe 

Food, starch, dextrine. 

Sago palm 

East Indies 


Arrow root 

West Indies 







Spice from bark. 



Gum for medicine, celluloid, etc. 



Leaf products. 


Food (mineral salts). 



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, 

Various fruits, banana, date, olive, vanilla, hops, poppy (opium), 


Onion, cab- 
Lettuce, rhu- 
Mint, winter- 


India, China 
S. America 

Spore plant products. 

Iceland moss (jelly) 

5. Fiber plants. 


India, Egypt, 

Yeast (in making bread). 
Bacteria (in making butter, 

Cloth, paper, explosives, batting, 


United States dressings, thread. 
North Europe Linen, canvas, paper, lace. 


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. 


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. 




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. 



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 


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 

Coelenterates. The coelenterates include many curious and 
beautiful animals such as the hydras, hydroids, jelly-fish, corals, 

FIG. 149. Branching coral Acropora 



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- 

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. 


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 



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 

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 


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 

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 

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 


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. 


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. 


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 


under old bark are caused by them. Treatment: destroy infested 
trees or branches; dig out borers in fall; encourage the birds. 


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. 


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 

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 


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. 


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. 


Larvae generally harmful in some degree as leaf eaters. 
Cabbage "worm," common and very harmful. 


Tiger beetles, predaceous, as adult and larva, on insects. 

Ground beetles, predaceous, very numerous, eat caterpillars and potato 


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. 


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. 



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. 

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. 


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. 


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- 


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.") 

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. 

1. Food for higher animals, clams, Crustacea, fish, etc. 

2. Deposit shell as chalk beds. 

3. Act as scavengers in water. 

1. Skeleton of horny forms used as "bath sponge." 

2. Preparation: collected, rotted, washed, dried, bleached. 

1. Corals, reef, and continent builders. 

2. Coral deposits, now limestone beds. 

3. Precious coral. 

1. Starfish harmful to oysters. 

2. Sea-cucumbers eaten by Chinese, etc. 

1. Earthworms necessary in cultivated soil. 

2. Parasitic worms cause disease in man and animals. 

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. 



1. Lobster, crab, shrimp, etc., for food. 

2. Small forms for fish food, barnacles harmful. 


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. 

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. 

Sucking insects with contact poisons. 

Eating insects with digestive poisons. 
Useful forms. 

Lady bug. 

Thalessa (an ichneumon fly). 

Carrion beetles. 



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 



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 

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 


hawk, sharp-shinned hawk, great horned owl, and English spar- 

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 

Horn and bone products of many mammals are used for making 


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. 



. 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. 

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. 


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 

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. 



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 



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 

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- 


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- 

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, 


and rejection of the unfit, he developed the present English wheat 
which combines nearly all the characteristics which the millers 

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. 



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 

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. 


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 


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; 


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. 


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. 


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. 


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. 



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. 


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. 






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- 












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 


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. 


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 


oil varnish, soap, disinfectants, ink 

oxalic acid dyeing, bleaching, making formic 


acetic acid white lead paint, dyes, and medi- 


wood alcohol varnish, solvent, dyes, denaturing 

alcohol, fuel, making formalde- 
hyde, and smokeless powder 

acetone explosives, films, dyes, and solvent 


1. Timber products. 


(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 


Leaf and Loblolly 


\Vh\ia "Pi -no 

\V nite .tine 

Western Pine 




Tulip Poplar 

Bed Gum 























White Fir 


Sugar Pine 


Balsam Fir 






Lodgepole Pine 


All Other 

FIG. 158. Lumber production by varieties, 1910. (U. S. Forest Service.) 


(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 

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 


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 

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. 


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 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 


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. 


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- 


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. 


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 

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. 



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 


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 


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. 


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. 

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. 


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. 



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 ' 


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- 

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 


of tobacco affects the brain enough to impair scholarship. 
Dr. Meylan, physical director at Columbia, reaches these con- 

1. Smokers averaged eight months behind non-smokers in their 

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? 


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 

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 





Alcohol, slight first effect 

Caffein in tea, coffee, and cocoa 


Nux vomica 



Alcohol, general effect 


Opium, morphine, etc. 


Cocaine, heroin, etc. 



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. 


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. 


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. 




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- 



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, 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. 


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." 

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 


the mucous linings, both of which favor the attacks gf various 

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- 


tion of the nervous system the centers of control develop in this 

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. 


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 

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. 


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 
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 


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 

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 

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 


" 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 

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. 


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 

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. 


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. 


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 

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. 


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. 

Transportation facilities. 



Liberate, to set free. 
Accomplish, bring about. 
Petrified, turned to stone. 


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- 

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. 


In plant 

In apparatus 


Root hair 
Epidermal cell, etc. 

Diffusion shell 

Dense liquid 

Cell sap 

Sugar solution 

Less dense liquid 

Soil water 

Clear water 





Soil water 




Cell sap 























Air spaces 







>t, etc. 


(successive os 


Food in seed or root 



Embryo or 


'II 2 


Air in lungs 


Carbon dioxide 
Water vapor 
Nitrogenous waste 




Food in digestive tract made soluble by 

l| '. 

U ca v 



^ S)^ 

"o o o > 


Blood and lymph 




for release of 



> (Used 



Urine and perspiration 



Blood in kidneys and 


s * 



^ 'i 

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- 

The chief function of food is to provide energy to support the 
life of the consumer. This energy came from the sun, was locked 


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. 



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, 





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 



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 

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 



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 



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. 


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 


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. 


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 

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. 




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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. 


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. 


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). 




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. 


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. 



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 


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 


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 


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, 


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- 


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 


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. 


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. 



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 


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 



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 


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 

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 

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 

Law II. Pure bred with pure bred of different kind, x plus y 
makes xy. 


Law III. Hybrid bred with hybrid, xy plus xy makes xx, -\-2xy, 
+yy or stated differently. 

xy . . xy x y hybrid 

t\ >"' 


*" 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 


marvelous skill in their use, Mr. Burbank has developed plant 
breeding to a degree never approached before. 


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). 











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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, 

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, 


ash, 121. 

assimilation, 5, 375, 377. 
astigmatism, 422. 
Atwater, quoted on alcohol, 515. 
auditory canal, 417. 
auricle, 397. 


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, 

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. 



Biff en, Prof. R. H., his experiments 
to improve wheat, 489. 

"Big Trees" (Sequoia) of California, 

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, 

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, 


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, 


centipede, 173. 
cephalopods, see squid, cuttlefish, 


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, 


compounds, 9; inorganic, 18, 19, 23. 
conjugation, of paramcecia, 150. 


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, 


crayfish, structure of, 179-185. 
crop rotation, 487, 488. 
Crustacea, 172, 179; as food, 472. 
culture medium, 133, 135. 
cuttlefish, produces sepia, 472. 


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, 


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. 



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, 

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, 

frog, development of, 253; structure, 

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. 


ganglia, 410. 

garden pests, potato "bug," etc., 475. 

gastric fluid, 371. 

"General Sherman" tree (Sequoia), 

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, 

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. 


Harvey, William, circulation of the 
blood, proved by, 535; portrait, 

habit formation, 412, 413. 

haemoglobin, 388, 395. 

hawk-moth posed before a jimson- 
weed, 110. 

hearing, sense of, 416. 

heart, action of, 397. 



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, 

horses, breeding and selecting for 

trotting, running, draught, etc., 


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, 

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, 

hymenoptera (membrane winged), 


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, 


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, 

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, 

lipoid, 355. 



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. 


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, 

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, 

milkweed, 121, 122, 123. 

mineral compounds, 19. 

mineral salts, necessity for, 353, 356, 

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, 

mushrooms, 129, 455. 

myriopods, 173. 


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; 



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. 


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, 

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- 

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, 


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, 


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. 



protoplasm, 25, 27, 30, 41, 147; 

named by von Mohl, 1841, 537; 

fundamental material of plants 

and animals shown by Schultze, 

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 

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, 

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, 


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 

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, 



skull cap of fossil man-like ape of 
Java, 336. 

sleep, 434. 

sleeping sickness, 151. 

slugs, as food, 471. 

smallpox, 139, 151; see protozoa, 

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, 

squid, use as fish bait, 471. 

stamens, 109, 113. 

starch-making, in leaves, 91; see 

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, 

style, 109, 113. 

sugar-cane, 456. 

sulphur, 13, 15, 17, 531. 

swimmerets, 182. 

sympathetic system of nerve ganglia 

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. 


ungulates (hoofed), 312. 
urine, 403. 



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, 

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. 


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, 


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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3605 f