208 PHYSIOLOGY AT THE FAKM. 



the stomach suspends the secretion of the gastric juice, and 

 thus arrests digestion. Yet, under favourable circumstances, 

 it is found that after such an operation the digestive action of 

 the stomach may be entirely recovered, so that chyme is per- 

 fectly formed, and the nutrition of the animal proceeds in a 

 manner little different from its effects in health. As to the 

 influence of the gastric nerves on the movements of the 

 stomach, it appears that irritation of these nerves during 

 digestion produces active movements of the muscular fibres 

 of the stomach, but that when the stomach is empty the 

 same kind of stimulus occasions no such effect. Correspon- 

 dent with this is the fact, that during digestion the pyloric 

 orifice is irritable so as to close against everything but chyme ; 

 but when digestion is completed, undigested food, and even non- 

 esculent substances, such as small metallic bodies, may pass 

 without opposition. 



Hunger and Thirst To the influence of the nerves of the 

 stomach, also, the sensations of hunger and thirst appear at first 

 sight exclusively to belong. The division, however, of the nerves 

 of the stomach does not allay the sensations of hunger, and the 

 repair of the blood through other channels than the stomach 

 allays hunger ; thus, while the nerves of the stomach are in 

 part concerned in hunger, it seems, nevertheless, to be mani- 

 fested in consequence of a deficiency of recruiting supplies in 

 the system at large. That the nerves of the stomach are in 

 part concerned appears from the fact, that the introduction of 

 non-alimentary substances appeases for a time the sensation. 

 In short, while the whole system suffers from an exhausted 

 state of the blood, the stomach is made to suffer more imme- 

 diately and largely from the prevailing deficiency. 



With respect to thirst, it depends not merely on the dryness 

 of the fauces, or throat, but on a deficiency of fluid in the 

 blood. It is relieved by an increase in the watery part of the 



