146 THE FEEDING OF ANIMALS 



208. Oxidases. The manner of this oxidation is one 

 of the difficult physiological problems. The present view, 

 and one based on very significant data, is that these 

 oxidations of the nutrients is the result of enzym action 

 and the oxidizing ferments are designated as oxidases. 

 The proteins, carbohydrates, and fats are first acted on 

 during digestion by the hydrolizing enzyms, and the 

 cleavage products are then further broken down, or 

 oxidized, by the oxidases. 



209. Proteins not wholly oxided. The proteins may 

 be partially burned to carbonic acid and water, but unless 

 used for tissue formation a portion of their substance 

 passes from the body principally in the form of urea and 

 uric acid, which are the prominent constituents of urine. 

 These compounds carry with them a certain proportion 

 of carbon and hydrogen which in ordinary fuel com- 

 bustion would more fully unite with oxygen. The heat 

 production from protein is therefore less in the animal 

 than in the furnace. 



210. Rate of oxidation of nutrients. This oxidation 

 in the animal is constant but not uniform. It varies with 

 the exercise the animal is taking and with the amount of 

 food that must be disposed of. The quantity of oxygen 

 needed is therefore variable, and when the demand for it 

 is largely increased the heart pumps faster, more blood 

 passes through the lungs, the breathing is more rapid and 

 the supply of oxygen is in this way augmented. 



ELIMINATION OF WASTES 



The various waste products from this combustion and 

 from the breaking up of the proteins within the animal 

 evidently must be disposed of in some manner. When 



