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What Keeps Us Alive

Sources: A Handbook Of Health

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

ored 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


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 of all the force and energy

and power in this world, the sun.

That is why plants will, as you know, flourish and grow strong and green

only in the sunlight, and why they wilt and turn pale in the dark. When

the plant grows, it is simply sucking up through the green stuff

(chlorophyll) in its leaves the heat and light of the sun and turning

it to its own uses. Then this sunlight, which has been absorbed by

plants and built up into their leaves, branches, and fruits, and stored

away in them as energy or power, is eaten by animals; and they in turn

use it to grow and move about with.

Plants can use this sun-power only to grow with and to carry out a few

very limited movements, such as turning to face the sun, reaching over

toward the light, and so on. But animals, taking this power at

second-hand from plants by eating their leaves or fruits, can use it not

merely to grow with, but also to run, to fight, to climb, to cry out,

and to carry out all those movements and processes which we call life.

Plants, on the other hand, are quite independent of animals; for they

can take up, or drink, this sun-power directly, with the addition of

water from the soil sucked up through their roots, and certain salts[1]

melted in it. Plants can live, as we say, upon non-living foods. But

animals must take their supply of sun-power at second-hand by eating the

leaves and the fruits and the seeds of plants; or at third-hand by

eating other animals.

All living things, including ourselves, are simply bundles of sunlight,

done up in the form of cabbages, cows, and kings; and so it is quite

right to say that a healthy, happy child has a sunny disposition.

Plants and Animals Differ in their Way of Taking Food. As plants take

in their sun-food and their air directly through their leaves, and their

drink of salty water through their roots, they need no special opening

for the purpose of eating and drinking, like a mouth; or place for

storing food, like a stomach. They have mouths and stomachs all over

them, in the form of tiny pores on their leaves, and hair-like tubes

sticking out from their roots. They can eat with every inch of their

growing surface.

But animals, that have to take their sun-food or nourishment at

second-hand, in the form of solid pieces of seeds, fruits, or leaves of

plants, and must take their drink in gulps, instead of soaking it up all

over their surface, must have some sort of intake opening, or mouth,

somewhere on the surface; and some sort of pouch, or stomach, inside the

body, in which their food can be stored and digested, or melted down. By

this means they also get rid of the necessity of staying rooted in one

place, to suck up moisture and food from the soil. One of the chief and

most striking differences between plants and animals is that animals

have mouths and stomachs, while plants have not.