66 THE CARBON OF THE FOOD 



in venous blood ; the albumen in the blood does not 

 combine with oxygen. The oxygen may possibly 

 serve to convert into the gaseous state some unknown 

 constituent of the blood ; but those well-known 

 constituents, which are employed in reproduction, 

 cannot be destined to support the respiratory process ; 

 none of their properties can justify such an opinion. 



Without attempting in this place to exhaust the 

 whole question of the share taken by the bile in the 

 vital operations, it follows, as has been observed, 

 from the simple comparison of those parts of the 

 food of the carnivora which are capable of assimila- 

 tion, with the ultimate products into which it is con- 

 verted, that all the carbon of the food, except that 

 portion which is found in the urine, is given out as 

 carbonic acid. 



But this carbon was ultimately derived from the 

 substance of the metamorphosed tissues ; and this 

 being admitted, the question of the necessity of sub- 

 stances containing much carbon and no nitrogen in 

 the food of the young of the carnivora, and in that 

 of the graminivora, is resolved in a strikingly simple 

 manner. 



XII. It cannot be disputed, that in an adult carni- 

 vorous animal, which neither gains nor loses weight, 

 perceptibly, from day to day, its nourishment, the 

 waste of organised tissue, and its consumption of 

 oxygen, stand to each other in a well-defined and 

 fixed relation. 



