196 QUARTERLY JOURNAL. 



ished like the carnivorous. The only difference is, that in the for- 

 mer a larger share of fat is stored up than in the latter. 



In vegetable food, besides the albuminous and oleaginous prin- 

 ciples, there is a third principle which is not found in animal food; 

 this is the saccharine principle, comprehending starch, gum, sugar, 

 and the whole of the non-nitrogenized neutral compounds of which 

 I spoke in the beginning of this paper. 



This principle, containing no nitrogen, cannot contribute to the 

 formation of the organized tissues. Its uses are analogous to those 

 of fat. Its carbon combines with the surplus oxygen, and is con- 

 verted into carbonic acid, thus generating animal heat. For this 

 reason the saccharine principle is, by Liebig, classed with fat, 

 among the supporters of respiration. 



The oleaginous and saccharine principles of the food are not, 

 however, in all cases at once consumed by oxygen, introduced by 

 respiration. When the animal takes but little exercise, and the 

 respiration is consequently inactive, these principles find no sur- 

 plus oxygen to combine with, and then the oleaginous principle is 

 stored up as in the cellular tissue as fat, and the saccharine prin- 

 ciple by a change in its elements, gives off a portion of its oxygen, 

 and is converted into fat, which, as will be remembered, is a com- 

 bination of the same elements in different proportions. This is the 

 only instance in which one proximate principle is converted into 

 another in the animal body. This conversion, first maintained by 

 Liebig, was denied by Dumas, who undertook to show that in the 

 food of herbivorous animals there was sufficient oil to account for 

 all the fat of the animals, but I believe the point has subsequently 

 been abandoned by Dumas himself. It seems indeed very impro- 

 bable, that the grass eaten by a milch cow contains as much oil as 

 is found in her milk. 



It follows from this that in proportion as an animal takes more 

 or less exercise, will the oleaginous and saccharine principles be 

 consumed in the body or stored up as fat for future use. 



Let us now turn to the difference between the food of carnivo- 

 rous and herbivorous animals. Both contain the albuminous and 

 oleaginous principles, and the latter contains, in addition to these, 

 the saccharine principle. The foodof carnivorous animals is made 

 up of a large proportion of the albuminous principle, united with 

 a small portion of fat ; that is, of a large portion of the supporter 



