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 tJiorouglily adjusted to Ids environment, be- 

 cause of his continual and rapid progress. Disease may 

 be defined as the process by which the 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. 



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 amceba, 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 



psd 



FIG. 5. AN AMEBA, highly magnified. 

 nu, nucleus; psd, false foot. 



