FOOD MATERIALS 1025 



divers ways to form the various types of compounds which make up the dif- 

 ferent parts of the bod}', e. g., the bones, teeth, muscles, vital organs, fat, etc. 



Body Oxidation Products, or Final Metabolic Products. — All of the 

 body compounds seem to be in a state of more or less constant chemical 

 change, i. e., new combinations of the elements are being produced. So 

 long as life lasts the body is constantly breathing in air and, in a sense, is 

 constantly burning itself up — oxidizing itself. The mere act of living 

 involves constant chemical changes in the body. Chemical changes keep 

 the body warm. Each motion of the body involves chemical change; 

 the more strenuous the motions, the more rapid the chemical changes. 



In the process of these changes, some of the body compounds are 

 constantly uniting with the oxygen of the air and are producing so-called 

 highly oxidized waste products, or final metabolic products, which the 

 body must finally rid itself of. Thus, the body finally burns its carbon 

 mainly to carbon dioxide, a colorless gas which it excretes by way of the 

 lungs; its hydrogen mainly to water; its nitrogen mainly to urea, a white 

 crystalline solid, which is held in solution and excreted in the urine and 

 perspiration; its sulphur and phosphorus to sulphates and phosphates of 

 calcium, sodium, potassium, magnesium, which also are white solids 

 excreted in the same manner as urea. Some other solid metabolic products 

 are similarly excreted. 



All these waste products the body proceeds to get rid of as rapidly as 

 possible, so all such products are ultimately returned to the air or to the 

 soil. Other things being equal, the quantity of these products which the 

 body excretes per 24 hours is in proportion to the amount of its physical 

 exertion per 24 hours. 



It should be mentioned that small amounts of certain metabolic 

 products are excreted in the feces, but in the main, the feces consist of any 

 indigestible materials taken in with the food, the remains of the food 

 that has escaped digestion, residues of digestive juices and bodies of 

 bacteria. 



Need of Food. — Because of these constant oxidizing processes which 

 are going on in the body, and because of the quantity of metabolic products 

 thus produced and excreted, the body soon wastes away if food be not 

 supplied. Hence, we eat to make up for the constant oxidation which the 

 body compounds are undergoing. More explicitly, the adult eats to 

 repair the body tissues constantly being torn down through the life pro- 

 cesses, and also to supply energy for physical motions; the child eats not 

 only to repair its body tissues and to supply energy for its intense activities, 

 but also for growth. This last fact must not be forgotten in feeding 

 the child. 



Elements Needed in Food. — Obviously, the food furnished must 

 contain the same elements as those which constitute the body. In the 

 case of the healthy adult, the amount of these elements furnished daily 

 should correspond to the daily losses of these elements; e. g., if the body 



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