DIGESTIVE SYSTEM. 315 



whether these effects indicate the local state of the 

 stomach as the cause of the sensation, or merely its connec- 

 tion with other circumstances, which give rise to the feeling, 

 can scarcely be determined. Indeed, it is not proved that 

 the sensation of hunger arises from the state of the stomach, 

 in preference to the condition of the duodenum, or the ori- 

 fices of the lacteals. 



Thirst is accompanied with a sensation of dryness in the 

 mouth. This dryness may be occasioned by excessive ex- 

 penditure of the fluids, in consequence of the dryness or 

 saltness of the food which has been swallowed ; or to their 

 deficiency, from the state of the organs. 



Both hunger and thirst, besides being greatly influenced 

 by habit, exhibit very remarkable peculiarities according 

 to the species and tribes of animals. In each, the wants of 

 the system are provided by instincts, which, in the attain- 

 ment of their object, exhibit movements the most compli- 

 cated, and employ means the most various. 



Animals are frequently characterised by the kind of food 

 on which they subsist. Those which live on the spoils of 

 the animal kingdom are said to be carnivorous, when they 

 feed on flesh, piscivorous when they subsist on fishes, 

 and insectivorous when they prey on insects. Again, those 

 animals which are phytivorous, or subsist on the products 

 of the vegetable kingdom, are either granivorous, and feed 

 on seeds, graminivorous, pasturing on grass, or her- 

 bivorous, browsing on twigs and shrubs. 



Besides those substances which animals make use of as 

 food, water is likewise employed as drink, and as the vehicle 

 of nutritious matter. Salt is necessarily mixed with the 

 drink of the inhabitants of the ocean, and is relished by 



those of colder districts are satisfied with a less stimulating diet. The vigour 

 of the digestive organs of the latter is fit for the accomplishment of its ob- 

 ject, but the languid condition of the former calls for assistance. 



