120 ANIMAL FUNCTIONS. 



properties there is an essential difference in the articles 

 usually employed in diet. Some substances which con- 

 tain the elements of chyle in abundance, afford little 

 nutriment, because they do not readily go through the 

 digestive process ; while others which contain compara- 

 tively but a small quantity of these elements, afford 

 more nourishment, because they are more completely 

 dissolved by the gastric juice. Animals in the natural 

 state, adhere, with remarkable uniformity, to the same 

 kinds of food. There are many carnivorous animals 

 which feed only on a certain kind of flesh ; some upon 

 the flesh of quadrupeds ; others upon that of birds ; and 

 others again upon that of insects. Among herbivorous 

 animals, some subsist only on certain kinds of plants ; 

 others on certain parts of particular plants, as the seed, 

 the fruit, the leaves, and so on, while entire tribes of 

 insects appear to be exclusively attached to some one 

 species of vegetable matter. 



355. We have seen that there is a manifest connexion 

 between the substances on which animals feed, and the 

 structure of their masticating organs, indicating that the 

 selection is not the effect of accident, but depends on the 

 original conformation of the parts. Thus, as we have 

 already shown, the teeth of some are constructed for 

 seizing and tearing ; others for gnawing, and others only 

 for cropping the delicate parts of plants. The beaks and 

 claws of carnivorous birds, are most formidable weapons ; 

 while those of the goose and duck are formed only for 

 scooping and swimming. All these diversities of struc- 

 ture are obviously adapted to receive as great a variety 

 of food. We have seen, also, that the stomachs of ani- 

 mals are of different forms and capacities, and that there 

 is an intimate relation between their masticating organs, 

 and the powers of digestion. 



356. Man requires a Variety of Food. The structure 

 of our own species, as already shown, places man between 

 the carnivorous and herbivorous animals with respect 



Why do not substances containing equal portions of the elements of 

 chyle afford equal nourishment? What is said of the adherence of ani- 

 mals to the same kind of food? Where is man placed in the scale of 

 creation with respect to his food ? 



