56 FOOD OF CARNIVORA 



nothing else than the incombustible, or imperfectly 

 burned, parts of the food. 



In the preceding pages it has been assumed that 

 the elements of the food are converted by the oxy- 

 gen absorbed in the lungs into oxidised products ; 

 the carbon into carbonic acid, the hydrogen into 

 water, and the nitrogen into a compound con- 

 taining the same elements as carbonate of am- 

 monia. 



This is only true in appearance ; the body, no 

 doubt, after a certain time, acquires its original 

 weight. The amount of carbon, and of the other 

 elements, is not found to be increased exactly as 

 much carbon, hydrogen, and nitrogen has been given 

 out as was supplied in the food ; but nothing is more 

 certain than that the carbon, hydrogen, and nitro- 

 gen given out, although equal in amount to what 

 is supplied in that form, do not directly proceed 

 from the food. 



It would be utterly irrational to suppose that the 

 necessity of taking food, or the satisfying the appe- 

 tite, had no other object than the production of 

 urea, uric acid, carbonic acid, and other excremen- 

 titious matters of substances which the system 

 expels, and consequently applies to no useful pur- 

 pose in the economy. 



In the adult animal, the food serves to restore 

 the waste of matter; certain parts of its organs 

 have lost the state of vitality, have been expelled 

 from the substance of the organs, and have been 



