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, im 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,—piscivorows 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. 
