260 DIGESTION. 



be greater difficulty in procuring food capable of assimila- 

 tion 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. 



It is in the relative quantities of the nitrogenous and 

 non-nitrogenous compounds in these different foods that 

 the difference lies, rather than in the presence of substances 

 in one of them which do not exist in the other. The 

 only non-nitrogenous compounds in ordinary animal food 

 are the fat, the saline matters, and water, and, in some 

 instances, the vegetable matters which may chance to be 

 in the digestive canals of such animals as are eaten whole. 

 The amount of these, however, is altogether much less 

 than that of the non-nitrogenous substances represented 

 by the starch, sugar, gum, oil, etc., in the vegetable food 

 of herbivorous animals. 



It has been just remarked that man can live upon 

 animal matters alone, or upon vegetables. The structure 

 of his teeth, however, as well as experience, seems 

 to declare that he is best fitted for a mixed diet ; and 

 the same inference may be readily gathered from other 



