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CHAPTER III. 



ANIMAL NUTRITION IN GENERAL. 



§1. Food of Animals. 



Nutrition constitutes no less important a part of the 

 animal, than of the vegetable economy. Endowed with 

 more energetic powers, and enjoying a wider range of ac- 

 tion, animals, compared with plants, require a considerably 

 larger supply of nutritive materials for their sustenance, and 

 for the exercise of their various and higher faculties. The 

 materials of animal nutrition must, in all cases, have previ- 

 ously been combined in a peculiar mode; which the powers 

 of organization alone can effect. In the conversion of vege- 

 table into animal matter, the principal changes in chemical 

 composition which the former undergoes, are, first, the ab- 

 straction of a certain proportion of carbon; and secondly, the 

 addition of nitrogen.* Other changes, however, less easily 

 appreciable, though perhaps as important as the former, 

 take place in greater quantity, with regard to the propor- 

 tions of saline earthy, and metallic ingredients; all of which, 

 and more especially iron, exist in greater quantity in ani- 

 mal than in vegetable bodies. The former also contain a 

 larger proportion of sulphur and phosphorus than the latter. 



* 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 ultimate analysis. They found, in particular, 

 the same proportion of nitrogen in the chyle, whatever kind of food the ani- 

 mal habitually 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. {Mcmoires dc la Socicle dc Physique d d'llistoire 

 Naturelle dc Geneve^ v. 389.) 



