A Handbook of Health | Page 4

little remnants
which are not quite so useful as they once were, and which sometimes
cause trouble. But for the most part, all we have to do is to look long
and carefully enough at any organ or part of our bodies, to be able to
puzzle out just what it is or was intended to do, and why it has the
shape and size it has.
Why the Study of Physiology is Easy. There is one thing that helps to
make the study of physiology quite easy. It is that you already know a
good deal about your body, because you have had to live with it for a
number of years past, and you can hardly have helped becoming
somewhat acquainted with it during this time.
You have, also, another advantage, which will help you in this study.
While your ideas of how to take care of your body are rather vague, and
some of them wrong, most of them are in the main right, or at least lead
you in the right direction. You all know enough to eat when you are
hungry and to drink when you are thirsty, even though you don't always
know when to stop, or just what to eat. You like sunny days better than
cloudy ones, and would much rather breathe fresh air than foul. You
like to go wading and swimming when you are hot and dusty, and you
don't need to be told to go to sleep when you are tired. You would
much rather have sugar than vinegar, sweet milk than sour milk; and
you dislike to eat or drink anything that looks dirty or foul, or smells
bad.
These inborn likes and dislikes--which we call instincts--are the forces

which have built up this wonderful body-machine of ours in the past
and, if properly understood and trained, can be largely trusted to run it
in the future. How to follow these instincts intelligently, where to check
them, where to encourage them, how to keep the proper balance
between them, how to live long and be useful and happy--this is what
the interesting study of physiology and hygiene will teach you.
CHAPTER II
WHY WE HAVE A STOMACH
WHAT KEEPS US ALIVE
The Energy in Food and Fuel. The first question that arises in our mind
on looking at an engine or machine of any sort is, What makes it go? If
we can succeed in getting an answer to the question, What makes the
human automobile go? we shall have the key to half its secrets at once.
It is fuel, of course; but what kind of fuel? How does the body take it in,
how does it burn it, and how does it use the energy or power stored up
in it to run the body-engine?
Man is a bread-and-butter-motor. The fuel of the automobile is gasoline,
and the fuel of the man-motor we call food. The two kinds of fuel do
not taste or smell much alike; but they are alike in that they both have
what we call energy, or power, stored up in them, and will, when set
fire to, burn, or explode, and give off this power in the shape of heat, or
explosions, which will do work.
Food and Fuel are the Result of Life. Fuels and foods are also alike in
another respect; and that is, that, no matter how much they may differ
in appearance and form, they are practically all the result of life. This is
clear enough as regards our foods, which are usually the seeds, fruits,
and leaves of plants, and the flesh of animals. It is also true of the
cord-wood and logs that we burn in our stoves and fireplaces. But what
of coal and gasoline? They are minerals, and they come, as we know,
out of the depths of the earth. Yet they too are the product of life; for
the layers of coal, which lie sixty, eighty, one hundred and fifty feet
below the surface of the earth, are the fossilized remains of great forests

and jungles, which were buried millions of years ago, and whose leaves
and branches and trunks have been pressed and baked into coal.
Gasoline comes from coal oil, or petroleum, and is simply the "juice"
which was squeezed out of these layers of trees and ferns while they
were being crushed and pressed into coal.
How the Sun is Turned into Energy by Plants and Animals. Where did
the flowers and fruits and leaves that we now see, and the trees and
ferns that grew millions of years ago, get this power, part of which
made them grow and part of which was stored away in their leaves and
branches and seeds? From the one place that is the source