EXPEEIMENTS WITH DIFFEKENT FOODS. 249 



genous diet, they may live long when fed exclusively with, 

 nitrogenous food. 



Man is supported as well by food constituted wholly of 

 animal substances, as by that which is formed entirely of 

 vegetable matters, on the condition, of course, that it 

 contain a mixture of the various nitrogenous and non 

 nitrogenous substances just shown to be essential for 

 healthy nutrition. In the case of carnivorous animals, the 

 food upon which they exist, consisting as it does of the 

 flesh and blood of other animals, not only contains all the 

 elements of which their own blood and tissues are com- 

 posed, but contains them combined, probably in the same 

 forms. Therefore little more may seem requisite, in the 

 preparation of this kind of food for the nutrition, of the 

 body, than that it should be dissolved and conveyed into 

 the blood in a condition capable of being re-organized. 

 But in the case of the herbivorous animals, which feed ex- 

 clusively upon vegetable substances, it might seem as if 

 there would be greater difficulty in procuring food capable 

 of assimilation into their blood and tissues. But the chief 

 ordinary articles of vegetable food contain substances 

 identical in composition, with the albumen, fibrin, and 

 casein, which constitute the principal nutritive materials in 

 animal food. Albumen is abundant in the juices and 

 seeds of nearly all vegetables; the gluten which exists, 

 especially in corn and other seeds of grasses as well as in 

 their juices, is identical in composition with fibrin, and is 

 often named vegetable fibrin ; and the substance named 

 legumen, which is obtained especially from peas, beans, 

 and other seeds of leguminous plants, and from the potato, 

 is identical with the casein of milk. All these vegetable 

 substances are, equally with the corresponding animal 

 principles, and in the same manner, capable of conversion 

 into blood and tissue ; and as the blood and tissues in both 

 classes of animals are alike, so also the nitrogenous food of 

 both may be regarded as, in essential respects, similar. 



