200 STOMACH DIGESTION. 



various jellies and in soups. When acted upon by hydrochloric 

 acid and pepsin it becomes converted into gelatoses. In the stom- 

 ach these undergo no further change, but in the intestine gelatoses 

 become gelatin peptones under the influence of the trypsin of the 

 pancreatic juice. 



Movements of the Stomach. These were observed very 

 carefully by Dr. Beaumont in the case of St. Martin (p. 194), and 

 in order that we may the better refer to the results of recent 

 investigations we .will here quote his description. He says : 

 " The bolus, as it enters the cardia, turns to the left, passes the 

 aperture, descends into the splenic extremity, and follows the 

 great curvature toward the pyloric end. It then returns in the 

 course of the small curvature, makes its appearance again at the 

 aperture, in its descent into the great curvature, to perform similar 

 revolutions." This occupied in St. Martin's case from one to 

 three minutes. 



Before describing the results of Cannon's experiments as 

 recorded in the American Journal of Physiology, and which were 

 performed upon cats, we will first describe the movements of the 

 human stomach, as they are usually described. 



Before food enters the stomach, this organ being empty, its 

 walls are in apposition and its mucous membrane arranged in ruga?. 

 The first portions of food that enter separate the walls, but in all 

 portions except where the food is they are still in contact. The 

 presence of food stimulates the muscular coat, and as a result the 

 circular fibers begin to contract feebly and on the side of the great 

 curvature, setting up a wave of peristalsis which travels on toward 

 the pylorus, becoming stronger as it progresses. Just before it 

 reaches the antrum it appears to be stopped by the " pre-antral " 

 constriction, which is the name given by Hofmeister and Schiitz, 

 to whom we owe these observations, to a constriction of circular 

 fibers which surrounds the whole stomach in this region. This has 

 the effect of pushing some of the stomach-contents into the 

 antrum ; the sphincter antri pylorici now contracts, and the 

 antrum is practically shut off from the fundus. The muscular 

 coat of the antrum then contracts, and its contents are forced 

 against the pylorus. The pyloric muscle relaxes to permit liquid 

 material to pass through into the duodenum ; if, however, solid 

 particles come against it, the relaxation does not occur, but an 

 antiperistaltic wave is set up in the musculature of the antrum 

 which carries the materials back into the fundus, the separation 

 of the latter from the antrum having ceased owing to the relaxa- 

 tion of the sphincter antri pylorici. The contents are thus re- 

 tained in the stomach to be further acted upon by the gastric 

 juice until they are rendered sufficiently liquid to pass the pylorus. 

 During these muscular movements the food is not only carried 



