58 THE VITAL FUNCTIONS. 



and for the exercise of their various and higher 

 faculties. The materials of animal nutrition 

 must, in all cases, have previously been combined 

 in a peculiar mode ; which the powers of organ- 

 ization alone can effect. In the conversion of 

 vegetable into animal matter, the principal 

 changes in chemical composition which the 

 former undergoes, are, first, the abstraction of a 

 certain proportion of carbon ; and secondly, the 

 addition of nitrogen.* Other changes, however, 

 less easily appreciable, though perhaps as im- 

 portant as the former, take place in greater 

 quantity, with regard to the proportions of saline 

 earthy, and metallic ingredients ; all of which, 

 and more especially iron, exist in greater quantity 

 in animal than in vegetable bodies. The former 

 also contain a larger proportion of sulphur and 

 phosphorus than the latter. 



The equitable mode in which nature dispenses 

 to her innumerable offspring the food she has 

 provided for their subsistence, apportioning to 



* The recent researches of Messrs. Macaire and Marcet tend 

 to establish the important fact that both the chyle and the blood 

 of herbivorous and of carnivorous quadrupeds are identical in their 

 chemical composition, in as far, at least, as concerns their ulti- 

 mate analysis. They found, in particular, the same proportion 

 of nitrogen in the chyle, whatever kind of food the animal habi- 

 tually consumed : and it was also the same in the blood, whether 

 of carnivorous or herbivorous animals ; although this last fluid 

 contains more nitrogen than the chyle. {Memoires de la Socicte 

 de Physique et d'Histoire Naturelle de Geneve, v. 389.) 



