REQUIRED BY HERBIVORA. 157 



condition of their existence, because it is only as the 

 result of the change of matter in the body, that those 

 substances can be formed, which are destined to enter 

 into combination with the oxygen of the air ; and in 

 this sense we may say, that the non-azotized constituents 

 of the food of the herbivora impede the change of mat- 

 ter, or retard it, and render unnecessary, at all events, 

 so rapid a process as occurs in the carnivora. 



67. The quantity of azotized matter, 'proportionally 

 so small, which the herbivora require to support their 

 vital functions, is closely connected with the power 

 possessed by the non-azotized parts of their food to act 

 as means of supporting the respiratory process ; and 

 this consideration seems to render it not improbable, 

 that the necessity for more complex organs of digestion 

 in the herbivora is rather owing to the difficulty of ren- 

 dering soluble and available for the vital processes cer- 

 tain non-azotized compounds (gum ? amylaceous fibre ?)' 

 than to any thing in the change or transformation of 

 vegetable fibrine, albumen, and caseine into blood ; 

 since, for this latter purpose, the less complex digestive 

 apparatus of the carnivora is amply sufficient. 



68. If, in man, when fed on a mixed diet, starch 

 perform a similar part to that which it plays in the body 

 of the herbivora ; if it be assumed, that the elements of 

 starch are equally necessary to the formation of the bile 

 in man as in these animals ; then it follows, that a part 

 of the azotized products of the transformation of the 

 tissues in the human body, before they are expelled 

 through the bladder, returns into the circulation from 



14 



