INTRODUCTION 



5 



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 preventable of diseases. The biological guide to 

 health is surer and simpler than tinkering with drugs, fuss- 

 ing with dietetics, and avoiding exposure. Man is of all 

 animals least thoroughly adjusted to his environment, be- 

 cause of his continual and rapid progress. Disease may 

 be defined as the process by ivJiicli tJie body adapts, or at- 

 tempts to adapt, itself to so sudden a change of environ- 

 ment 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 proto- 

 plasm, as manifested in 

 minute bodies called cells. 

 In fact, protoplasm can- 

 not exist outside of cells. 

 The cells of the human 

 body and their relation to 

 the body as a whole will 

 next be considered. 



FIG. 5. AN AMEBA, highly magnified. 

 , 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 amaba, 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 



