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 combination the 

 powers of organization 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 to a great 

 extent 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.) 



