CHAPTEE X. 

 FOODS. 



Foods as Tissue Formers. In the last chapter we have 

 considered foods merely as sources of energy, but they are 

 also required to build up the substance of the body. From 

 birth to manhood we increase in bulk and weight, and 

 that not merely by accumulating water and such sub- 

 stances, but by forming more bone, more muscle, more 

 brain, and so on, from the things which we eat. Even 

 after full growth, when the body ceases to gain weight, 

 the same constructive processes go on; the living tissues 

 are steadily oxidized and broken down as they work, and as 

 constantly reconstructed. 



Foods are therefore needed, not only to supply the body 

 with work-power by their oxidation, but to supply material 

 from which new living tissue can be constructed. 



What Foods must Contain. Most foods serve for both 

 purposes, energy supply and tissue formation; they are 

 built up by the living cells into new tissue before they are 

 oxidized to set energy free. Our food must, therefore, 

 contain such substances as the body can utilize for tissue 

 formation.* The living tissues when analyzed are found 



What use have foods besides supplying energy to the body? 

 Illustrate from the growth of a child. Why are foods needed for 

 construction after growth has ceased? 



What purposes do most foods serve? Are they usually oxidized 

 before making tissue? What sort of substances must our food 

 contain? 



* Whether any food is ever oxidized in the body before being built up into 

 a tissue, as coal is burnt in an engine without ever forming part of the engine, 

 must still be regarded as an open question in physiology. The old doctrine that 

 some foods, as starch and sugar, were useful only to set free heat, and others, 

 as albumen and flesh, alone built tissue, must be given up. It seems certain 



[HO] 



