234 DIGESTION. 



quired by those who do not naturally possess it, and by con- 

 tinual practice may become a habit. There are cases also of 

 rare occurrence in which persons habitually swallow their food 

 hastily, and nearly unmasticated, and then at their leisure re- 

 gurgitate it, piece by piece, into their mouth, remasticate, and 

 again swallow it, exactly as is done by the ruminant order of 

 Mammalia. 



Influence of the Nervous System on Gastric Digestion. 



This influence is manifold; and is evidenced, 1st, in the sen- 

 sations which induce to the taking of food ; 2d, in the secretion 

 of the gastric fluid; 3d, in the movements of the food in and 

 from the stomach. 



The sensation of hunger is manifested in consequence of de- 

 ficiency of food in the system. The mind refers the sensation 

 to the stomach ; yet since the sensation is relieved by the in- 

 troduction of food either into the stomach itself, or into the 

 blood through other channels than the stomach, it would ap- 

 pear not to depend on the state of the stomach alone. This 

 view is confirmed by the fact, that the division of both pneu- 

 mogastric nerves, which are the principal channels by which 

 the mind is cognizant of the condition of the stomach, does not 

 appear to allay the sensations of hunger. 



But that the stomach has some share in this sensation is 

 proved by the relief afforded, though only temporarily, by the 

 introduction of even non-alimentary substances into this organ. 

 It may, therefore, be said that the sensation of hunger is de- 

 rived from the system generally, but chiefly from the condition 

 of the stomach, the nerves of which, we may suppose, are more 

 affected by the state of the insufficiently replenished blood than 

 those of other organs are. 



The sensation of thirst, indicating the want of fluid, is re- 

 ferred to the fauces, although, as in hunger, this is merely the 

 local declaration of a general condition existing in the system. 

 For thirst is relieved for only a very short time by moistening 

 the dry fauces ; but may be relieved completely by the intro- 

 duction of liquids into the blood, either through the stomach, 

 or by injections into the bloodvessels, or by absorption from 

 the surface of the skin or the intestines. The sensation of 

 thirst is perceived most naturally whenever there is a dispro- 

 portionately small quantity of water in the blood; as well, 

 therefore, when water has been abstracted from the blood, as 

 when saline or any solid matters have been abundantly added 

 to it. We can express the fact (even if it be not an explana- 

 tion of it), by saying that the nerves of the mouth and i'auces, 



