31-1 PHILOSOPHY OF ZOOLOGY. 



ing it for the particular parts, depositing it where want- 

 edj a nd removing those portions which have become su- 

 perfluous. 



CHAP. XII. 



DIGESTIVE SYSTEM. 



IN treating of the appetites, as occupying a conspicuous 

 place among the active powers, we had occasion to deline- 

 ate the characters of the instinct for food. In this place, 

 we have to investigate those organs over which this instinct 

 presides, and the important purposes which they serve in 

 the animal economy. 



Every one knows, that the sensation of hunger is felt 

 when the stomach is empty, but the nature of the connec- 

 tion between these circumstances has not been satisfactorily 

 explained. Some have ascribed the feeling to the fatigue 

 of the muscular fibre from the stomach being contracted, 

 and others to the friction of the rugae of its internal cover- 

 ing, while there have not been wanting many who refer it 

 to the stimulus of the accumulated gastric juice, or to the 

 acrimony of that fluid, arising from its unusual detention. 

 But the total absence of proof in support of any of these 

 opinions, renders it unnecessary to enter upon their ex- 

 amination. 



Many circumstances, however, are known, which promote 

 hunger, especially exercise, cold air applied to the skin, and 

 cold, acid, or astringent fluids introduced into the stomach. 

 Inactivity, warm covering, the attention diverted, and 

 warm fluids, have a tendency to allay the sensation *. But 



These facts serve to explain the circumstance of the inhabitants of 

 warm countries making use of food highly seasoned with hot spices, while 



