360 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



since it has been found that it is this locality of the stomach which 

 yields the milk-curdling ferment in largest amounts. 



As regards the action of the nervous system on the secretion of 

 gastric juice, very little is known. It seems clear that this secretion, 

 like that of the saliva and of other glands, is a reflex process; for when 

 the stomach is empty there is no secretion of gastric juice, which only 

 takes place when proper stimuli are applied to the mucous membrane of 

 the stomach. Such stimuli may be either mechanical or chemical, and 

 the immediate result of their contact is to cause an increase in the 

 activity of the circulation through the walls of the stomach, with a con- 

 sequent increase in temperature which ma}^ amount to as much as 

 1 C. The mechanism of secretion, therefore, is, in all probability, 

 identical with that of other glands. The nerves which influence the 

 secretion are almost totally unknown, since no nerve has been found 

 whose stimulation leads to the secretion of gastric juice in a manner at 

 all analogous to that which results from the stimulation of the chorda 

 tympani in producing the secretion of saliva. It seems probable that the 

 centres whose reflex stimulation leads to the flow of gastric juice are 

 located in the stomach, for both the pneumogastric and sympathetic 

 nerves may be divided, and local stimulation of the gastric mucous 

 membrane will still lead to a flow of gastric juice. The pneumogastrics, 

 nevertheless, besides being the sensory nerves of the stomach, seem to be 

 concerned in the production of the vascular dilatation, which is of such 

 importance in the production of the secretion ; for, if both pneumo- 

 gastrics are divided during digestion, the mucous membrane of the 

 stomach becomes pale. The secretion of gastric juice is also undoubt- 

 edly in some way connected with the central nervous system, for Richet 

 has noted the fact that in a case of complete cesophageal stricture, 

 observation of the stomach through a fistulous opening into this organ 

 proved that the secretion of gastric juice followed the introduction of 

 acids or sugar into the mouth. 



4. GASTRIC DIGESTION IN CARNIVORA The importance of the stom- 

 ach in the operation of digestion varies greatly in different animals. 

 In the carnivora the action of the stomach is less constant than in the 

 herbivora, but is of greater importance. While its action is intermittent, 

 the intervals between its periods of activity and the duration of its 

 activity are more prolonged. Carnivora swallow their food in large frag- 

 ments, torn only small enough to be swallowed, and in many cases 

 swallow their prey entire. Their mastication is of slight importance, for 

 they feed on substances readily soluble in gastric juice, the only function 

 of the saliva being to render the food easy of deglutition, it having 

 scarcely any digestive function to fulfill. In carnivora, as already stated, 

 the conformation of the mouth, pharynx, and gullet enables large masses 



