170 



LIFE PROCESSES OF MAN 



proteins are necessary for the growth and the repair of the 

 bodv, and that the carbohydrates and fats furnish heat to 

 keep the body warm, and energy for muscular work. The 

 unused fat is stored up as fatty tissue. All classes of 

 food are found in the various foods obtained from plants. 

 Some, like honey, are nearly pure carbohydrate, while the 

 English walnut contains, in addition to fat, a large quantity 



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Figure 188. — Microphotograph of Stomach. 



The stomach is an organ composed of several tissues arranged in 

 layers. The gastric glands are in the innermost ragged layer and 

 look like rows of black dots. 



of plant protein. Animal foods can furnish us with only 

 proteins and fats. In primitive times man used a re- 

 stricted diet and led an active out-of-door life. To-day 

 man is living on a mixed and varied diet. This is to be 

 regarded as an acquired habit and one that is questionable 

 when carried to an extreme. The question of how much 

 to eat is a modern problem, and on its solution depend our 

 health, length of life, and energy for work. 



