CHAPTER XXIII 

 FOODS AND NUTRITION 



Need of Food. One of the most elementary sensa- 

 tions of the human body is that of hunger. It is simply 

 a provision of nature to tell us that the body needs food. 

 As we grow older we learn that the food must be chosen 

 with some care to enable the body to grow and maintain 

 itself in a state of health. All living matter requires 

 food, and food may be defined as anything which a plant 

 or animal takes into its body as nourishment. Anything 

 that we eat or drink which nourishes our bodies is food 

 for us. 



Bodily Energy. We have learned that a machine 

 which does work or produces energy must have energy 

 expended upon it. Our civilization at all times demands 

 supplies of food energy and supplies of mechanical energy. 

 Energy of one kind may be changed into energy of another 

 kind, but it is never created or destroyed. This is known 

 as the Law of the Conservation of Energy. The body is 

 often compared to a steam engine. When fuel is oxidized 

 (burned) in the fire box of a steam engine, the stored 

 energy in the fuel is released as heat energy. This heat 

 acts upon the water in the boiler and changes it to steam, 

 which has the power of expansion. This power may 

 then be used in doing mechanical work or in producing 

 heat again. The potential energy of the coal is changed 

 to kinetic energy. 



As in the steam engine, the source of energy in our 



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