CHAPTER III 



FOODS 



19. Definition of Foods. We have learned that all 

 the cells of the body need food to keep them well and 

 to enable them to do their work properly. We have 

 learned that the blood and lymph are the great body 

 liquids from which each cell gets its food and to which 

 it gives off its wastes. How does the blood get its 

 food supply ? The supply in the blood would soon be 

 used up if it were not constantly renewed from the out- 

 side. We eat, drink, and breathe to furnish the blood 

 proper material to carry to the cells for their nourish- 

 ment and use. Not all substances taken into the 

 mouth can be used by the cells. Some are not only 

 useless but harmful and even poisonous. 



A food is any substance that enters the blood, and with- 

 out doing any Jiarm in the body helps to cause growth, to 

 repair the cells, or to give Jieat and mechanical energy. 



20. Kinds of Food. The body, like other machines, 

 wears out with use, but differs from them in that it is 

 self-increasing, self-repairing, and self-oiling. For this 

 pur-pose it needs tissue-building food stuffs known as 

 proteids. The locomotive consumes coal to produce 

 the heat which changes the water to steam, and the 



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