nigh gave up in despair. Yet it has recently been shown that if the sufferer returns only in a measure to the open-air habits of his remote ancestors, tuberculosis is one of the most curable of diseases. The biological guide to health is surer and simpler than tinkering with drugs, fussing with dietetics, and avoiding exposure. Man is of all animals least thoroughly adjusted to his environment, because of his continual and rapid progress. Disease may be defined as the process by which the body adapts, or attempts to adapt, itself to so sudden a change of environment that some organ has failed to work in harmony with the others. By disease the body comes into adjustment with the new condition, or attempts to do so.
Protoplasm.—The life and growth of man's body, as the life and growth of all animals and plants, depend upon the activity of the living substance called protoplasm, as manifested in minute bodies called cells. In fact, protoplasm cannot exist outside of cells. The cells of the human body and their relation to the body as a whole will next be considered.
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Fig. 5.—An Ameba, highly magnified. nu, nucleus; psd, false foot.
The Ameba.—Of all the
animal kingdom, the minute creatures that can be seen only with a microscope are most different from
man. One of the most interesting of these is the a-me'ba (Fig. 5;
spelled also amœba, see Animal Biology, Chap. II). A thousand of them placed in a row would hardly reach an inch. Some may doubt
whether the ameba is a complete animal. Study the figures of it, and
no head, or arms, or legs, or mouth can be found. It appears, when
still, to be merely a lump of jelly. But the ameba can push out any part of its body as a foot, and move slowly by rolling its body into the
