INTRODUCTION 



5 



cells. The amceba is a single cell, but our bodies con- 

 sist of millions upon millions of cells, each of which is 

 a living particle 

 like the amoeba. 

 Every cell in the 

 body takes in 

 foods and gives off 

 wastes ; it may be 

 said then that it 

 eats and breathes. 



l/acuole 

 Food 



The cells of the 



human body vary FIG. 2. Atypical cell. Modified from Wilson 

 7 , (Zinns). 



in size, shape, and 



consistency. Some are small, globular masses, some are 

 thin, flat, or scaly, and others are long, slender, and very 

 irregular. Some are very soft and like jelly, while 

 others are hard, firm, and like bone. Each cell has a 



special use, and 

 its size and shape 

 are such as to fit 

 it to best per- 

 form its func- 

 tion. Although 

 the cells differ 

 widely from one 

 1 * MUSCle cells another in ap- 

 pearance and 



FIG. 3. Various cells of the body (Zinns). \\$>Q theV are all 



composed chiefly of water (about three fourths), a sub- 

 stance quite like the white of an egg, called proteid, 



