CHAPTER IX 

 FOODS AND THE THEORY OF DIGESTION 



THE body is constantly in need of new material. Oxi- 

 dation, as shown in the preceding chapter, rapidly destroys 

 substances at the cells, and these have to be replaced. Upon 

 this renewal depends the supply of energy. Moreover, 

 there is found to be an actual breaking down of the living 

 material, or protoplasm, in the body. While this does not 

 destroy the cells, as is sometimes erroneously stated, it 

 reduces the quantity of the protoplasm and makes neces- 

 sary a process of repair, or rebuilding, of the tissues. This 

 also requires new material. Finally, substances, such as 

 water and common salt, are required for the aid which they 

 render in the general work of the body. Since these are 

 constantly being lost in one way or another, they also must 

 be replaced. These different needs of the body for new 

 materials are supplied through 



The Foods. Foods are substances that, on being taken 

 into the healthy body, are of assistance in carrying on its 

 work. This definition properly includes oxygen, but the 

 term is usually limited to substances introduced through 

 the digestive organs. As suggested above, foods serve 

 at least three purposes : 



1. They, with oxygen, supply the body with energy. 



2. They provide materials for rebuilding the tissues. 



3. They supply materials that aid directly or indirectly 

 in the general work of the body. 



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