The study of the amoeba cannot fail to
raise a host of questions in the mind of any thoughtful man.
As we have here the animal reduced, so to speak, to lowest terms, it
may be well to examine a little more closely into its physiology and
compare it briefly with our own.
The amoeba eats food as we do, but the food is digested directly
in the internal protoplasm instead of in a stomach; and once
digested it diffuses to all parts of the cell; here it is built up
into compounds of a more complex structure, and forms an integral
part of the animal body. The dead food particle has been transformed
into living protoplasm, the continually repeated miracle of life.
But it does not remain long in this condition. In contact with the
oxygen from the air it is soon oxidized, burned up to furnish the
energy necessary for the motion and irritability of the body. We are
all of us low-temperature engines. The digestive function exists in
all animals merely to bring the food into a soluble, diffusible
form, so that it can pass to all parts of the body and be used for
fuel or growth. In our body a circulatory system is necessary to
carry food and oxygen to the cells and to remove their waste. For
most of our cells lie at a distance from the stomach, lungs, and
kidney. But in a small animal the circulatory system is often
unnecessary and fails.
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