74 PHYSIOLOGY. 



tions: the mixing, trituration, and expulsion of the food. The 

 stomach movements are inhibited when the cat shows anxiety, rage, 

 or distress. Cannon has observed in cats that carbohydrate food 

 appeared in the intestine in ten minutes, while proteid did not 

 leave for an hour. Proteids also remained in the stomach twice 

 as long as the fats. 



CLOSURE OF THE PYLORUS. 



Each time the acid chyme escapes, it sets up a reflex act which 

 temporarily occludes the pyloric orifice, and, at the same time, 

 inhibits the propulsive movements of the organ. The acid mass of 

 chyme escaping the pylorus, excites an increased secretion of pan- 

 creatic juice and the acid is gradually neutralized. When this is 

 accomplished the escape of further acid chyme is permitted. This 

 regulatory action prevents disorder in the progress of digestion and 

 at the same time insures regularity in the transition from the acid 

 gastric digestion to the alkaline intestinal one. The opening of the 

 pylorus is due to the presence of free acid at the pylorus. Both 

 the closure of the pylorus and the opening of the pylorus can ensue 

 without the intervention of the nerves going to the stomach. The 

 acidity of the contents of stomach keeps the cardia closed. 



THE NERVOUS CONTROL OF THE STOMACH. 



As known to-day, the nerve-supply to the stomach is from both 

 the cerebro-spinal system and the sympathetic; its connection with 

 the former is through the medium of the vagi, with the latter by 

 the splanchnics through the solar plexus. The fibers of both sys- 

 tems distributed to the gastric muscles are nonmedullated. The 

 functions of the vagi have been conclusively proved to be motor, 

 for when they are stimulated by chemical, thermal, or other irri- 

 tants, there results a peristalsis throughout the whole viscus. On 

 the contrary, the fibers from the sympathetic system are inhibitory; 

 when they are stimulated, peristalsis is stopped and there is dila- 

 tation of the sphincter pylori. The stomach also has movements of 

 its own independent of the central nervous system. 



THE GASTRIC JUICE. 



Gastric juice mixed with food and water can readily be obtained 

 by the gastric sound or stomach-pump. Pure gastric juice cannot be 

 procured thus, for when the stomach is empty the flow of gastric 

 juice ceases and any surplus remaining in the stomach seems to be 

 reabsorbed, Its flow is begun again only as the result of stimuli; 



