_Laboratory demonstrations._--Factors of the environment of
a living plant or animal in the vivarium.
_Home exercise._--The study of the factors making up my own
environment and how I can aid in their control.
Environment.--Each one of us, no matter where he lives, comes in contact
with certain surroundings. Air is everywhere around us; light is necessary
to us, so much so that we use artificial light at night. The city street,
with its dirty and hard paving stones, has come to take the place of the
soil of the village or farm. Water and food are a necessary part of our
surroundings. Our clothing, useful to maintain a certain temperature, must
also be included. All these things--air, light, heat, water, food--together
make up our _environment_.
[Illustration: An unfavorable city environment.]
All other animals, and all plants as well, are surrounded by and use
practically the same things from their environment as we do. The potted
plant in the window, the goldfish in the aquarium, your pet dog at home,
all use, as we will later prove, the factors of their environment in the
same manner. Air, water, light, a certain amount of heat, soil to live in
or on, and food form parts of the surroundings of _every_ living thing.
[Illustration: An experiment that shows the air contains about four fifths
nitrogen.]
[Illustration: Apparatus for separating water by means of an electric
current into the two elements, hydrogen and oxygen.]
The Same Elements found in Plants and Animals as in their Environment.--It
has been found by chemists that the plants and animals as well as their
environment may be reduced to about eighty very simple substances known as
_chemical elements_. For example, the air is made up largely of two
elements, _oxygen_ and _nitrogen_. Water, by means of an electric current,
may be broken up into two elements, _oxygen_ and _hydrogen_. The elements
in water are combined to make a _chemical compound_. The oxygen and
nitrogen of the air are not so united, but exist as separate gases. If we
were to study the chemistry of the bodies of plants and animals and of
their foods, we would find them to be made up of certain chemical elements
combined in various complex compounds. These elements are principally
_carbon_, _hydrogen_, _oxygen_, _nitrogen_, and perhaps a dozen others in
very minute proportions. But the same elements present in the living things
might also be found in the environment, for example, water, food, the air,
and the soil. It is logical to believe that living things use the chemical
elements in their surroundings and in some wonderful manner build up their
own bodies from the materials found in their environment. How this is done
we will learn in later chapters.
[Illustration: Chart to show the percentage of chemical elements in the
human body.]
What Plants and Animals take from their Environment. Air.--It is a
self-evident fact that animals need air. Even those living in the water use
the air dissolved in the water. A fish placed in an air-tight jar will soon
die. It will be proven later that plants also need air in order to live.
[Illustration: The effect of water upon the growth of trees. These trees
were all planted at the same time in soil that is sandy and uniform. They
are watered by a small stream which runs from left to right in the picture.
Most of the water soaks into the ground before reaching the last trees.]
Water.--We all know that water must form part of the environment of plants
and animals. It is a matter of common knowledge that pets need water to
drink; so do other animals. Every one knows we must water a potted plant if
we expect it to grow. Water is of so much importance to man that from the
time of the Caesars until now he has spent enormous sums of money to bring
pure water to his cities. The United States government is spending millions
of dollars at the present time to bring by irrigation the water needed to
support life in the western desert lands.
[Illustration: The effect of light upon a growing plant.]
Light as Condition of the Environment.--Light is another important factor
of the environment. A study of the leaves on any green plant growing near a
window will convince one that such plants grow toward the light. All green
plants are thus influenced by the sun. Other plants which are not green
seem either indifferent or are negatively influenced (move away from) the
source of light. Animals may or may not be attracted by light. A moth, for
example, will fly toward a flame, an earthworm will move away from light.
Some animals prefer a moderate or weak intensity of light and live in shady
forests or jungles, prowling about at night. Others seem to need much and
strong light. And man himself enjoys only moderate intensity of light and
heat. Look at the shady side of a city street on any hot day to prove this
statement.
Heat.--Animals and plants are both affected by heat or the absence of it.
In cold weather green plants either die or their life activities are
temporarily suspended,--the plant becomes _dormant_. Likewise small
animals, such as insects, may be killed by cold or they may _hibernate_
under stones or boards. Their life activities are stilled until the coming
of warm weather. Bears and other large animals go to sleep during the
winter and awake thin and active at the approach of warm weather. Animals
or plants used to certain temperatures are killed if removed from those
temperatures. Even man, the most adaptable of all animals, cannot stand
great changes without discomfort and sometimes death. He heats his houses
in winter and cools them in summer so as to have the amount of heat most
acceptable to him, _i.e._ about 70 deg. Fahrenheit.
[Illustration: Vegetation in Northern Russia. The trees in this picture are
nearly one hundred years old. They live under conditions of extreme cold
most of the year.]
The Environment determines the Kind of Animals and Plants within It.--In
our study of geography we learned that certain luxuriant growths of trees
and climbing plants were characteristic of the tropics with its moist, warm
climate. No one would expect to find living there the hardy stunted plants
of the arctic region. Nor would we expect to find the same kinds of animal
life in warm regions as in cold. The surroundings determine the kind of
living things there. Plants or animals _fitted to live_ in a given locality
will probably be found there if they have had an opportunity to reach that
locality. If, for example, temperate forms of life were introduced by man
into the tropics, they would either die or they would gradually change so
as to become fitted to live in their new environment. Sheep with long wool
fitted to live in England, when removed to Cuba, where conditions of
greater heat exist, soon died because they were not fitted or _adapted_ to
live in their changed environment.
[Illustration: Plant life in a moist tropical forest. Notice the air plants
to the left and the resurrection ferns on the tree trunk.]
Adaptations.--Plants and animals are not only fitted to live under certain
conditions, but each part of the body may be fitted to do certain work. I
notice that as I write these words the fingers of my right hand grasp the
pen firmly and the hand and arm execute some very complicated movements.
This they are able to do because of the free movement given through the
arrangement of the delicate bones of the wrist and fingers, their
attachment to the bones of the arm, a wonderful complex of muscles which
move the bones, and a directing nervous system which plans the work.
Because of the peculiar fitness in the structure of the hand for this work
we say it is adapted to its function of grasping objects. Each part of a
plant or animal is usually fitted for some particular work. The root of a
green plant, for example, is fitted to take in water by having tiny
absorbing organs growing from it, the stems have pipes or tubes to convey
liquids up and down and are strong enough to support the leafy part of the
plant. Each part of a plant does work, and is fitted, by means of certain
structures, to do that work. It is because of these adaptations that living
things are able to do their work within their particular environment.
Plants and Animals and their Natural Environment.--Those of us who have
tried to keep potted plants in the schoolroom know how difficult it is to
keep them healthy. Dust, foreign gases in the air, lack of moisture, and
other causes make the artificial environment in which they are placed
unsuitable for them.
A goldfish placed in a small glass jar with no food or no green water
plants soon seeks the surface of the water, and if the water is not changed
frequently so as to supply air the fish will die. Again the artificial
environment lacks something that the fish needs. Each plant and animal is
limited to a certain environment because of certain individual needs which
make the surroundings fit for it to live in.
[Illustration: A natural barrier on a stream. No trout would be found above
this fall. Why not?]
Changes in Environment.--Most plants and animals do not change their
environment. Trees, green plants of all kinds, and some animals remain
fixed in one spot practically all their lives. Certain tiny plants and most
animals move from place to place, either in air, water, on the earth or in
the earth, but they maintain relatively the same conditions in environment.
Birds are perhaps the most striking exception, for some may fly thousands
of miles from their summer homes to winter in the south. Other animals,
too, migrate from place to place, but not usually where there are great
changes in the surroundings. A high mountain chain with intense cold at the
upper altitudes would be a barrier over which, for example, a bear, a deer,
or a snail could not travel. Fish like trout will migrate up a stream until
they come to a fall too high for them to jump. There they must stop because
their environment limits them.
[Illustration: A new apartment house, with out-of-door sleeping porch.]
Man in his Environment.--Man, while he is like other animals in requiring
heat, light, water, and food, differs from them in that he has come to live
in a more or less artificial environment. Men who lived on the earth
thousands of year ago did not wear clothes or have elaborate homes of wood
or brick or stone. They did not use fire, nor did they eat cooked foods. In
short, by slow degrees, civilized man has come to live in a changed
environment from that of other animals. The living together of men in
communities has caused certain needs to develop. Many things can be
supplied in common, as water, milk, foods. Wastes of all kinds have to be
disposed of in a town or city. Houses have come to be placed close
together, or piled on top of each other, as in the modern apartment. Fields
and trees, all outdoor life, has practically disappeared. Man has come to
live in an artificial environment.
Care and Improvement of One's Environment.--Man can modify or change his
surroundings by making this artificial environment favorable to live in. He
may heat his dwellings in winter and cool them in summer so as to maintain
a moderate and nearly constant temperature. He may see that his dwellings
have windows so as to let light and air pass in and out. He may have light
at night and shade by day from intense light. He may have a system of pure
water supply and may see that drains or sewers carry away his wastes. He
may see to it that people ill with "catching" or _infectious_ diseases are
isolated or _quarantined_ from others. This care of the artificial
environment is known as _sanitation_, while the care of the _individual_
for himself within the environment is known as _hygiene_. It will be the
chief end of this book to show girls and boys how they may become good
citizens through the proper control of personal hygiene and sanitation.