100 THE VITAL FUNCTIONS. 



tained in these fragments, affords them a supply of 

 nutriment adequate to their wants. It is evident, 

 that when, as in the preceding instances, large 

 quantities of indigestible materials are taken in 

 along with such as are nutritious, the stomach and 

 other digestive cavities must be rendered more than 

 usually capacious. It is obvious also that the struc- 

 ture of the digestive organs must bear a relation 

 to the mechanical texture, as well as the chemical 

 qualities of the food ; and this we tind to be the 

 case in a variety of instances, which will hereafter 

 be specified. 



The activity of the digestive functions, as well 

 as the structure of the organs, will also be regu- 

 lated by a great variety of other circumstances in 

 the condition of the animal, independent of the 

 mechanical or chemical nature of the food. The 

 greater the energy with which the more peculiarly 

 animal functions of sensation and muscular action 

 are exercised, the greater must be the demand for 

 nourishment, in order to supply the expenditure of 

 vital force created by these exertions. Compared 

 with the torpid and sluggish reptile, the active and 

 vivacious bird or quadruped requires and consumes 

 a much larger quantity of nutriment. The tortoise, 

 the turtle, the toad, the frog, and the chameleon, 

 will, indeed, live for months without taking any 

 food. Fishes, which, like reptiles, are cold-blooded 

 animals, although at all times exceedingly voracious 

 when supplied with food, can yet endure long fasts 

 with impunity. 



The rapidity of developement has also great 

 influence on the quantity of food which an animal 

 requires. Thus the caterpillar, which grows very 



