i8o TEXT-BOOK OF PHYSIOLOGY 



quick succession, as in the swallowing of water, the inhibition and relaxa- 

 tion are increased, and endure until the last act of deglutition. (Meltzer.) 

 These effects also follow stimulation of the glossopharyngeal nerve. 

 Whether the sphincter inhibition is the result of an inhibition of the 

 center which maintains the tonus, or a stimulation of an inhibitor center, 

 is uncertain. 



Though the tonus of the sphincter cardia is capable of being both 

 inhibited and augmented by the central nerve system, the most frequent 

 cause under physiological conditions for an augmentation of the tonus, is 

 the presence of hydrochloric acid on the gastric side of the cardia. In the 

 early stages of digestion when the percentage of the acid is below the 

 normal, the orifice frequently opens and food is regurgitated for a short 

 distance into the esophagus. The ascent of the food far into the esophagus 

 is prevented by a contraction and peristalsis of its muscle walls, by which 

 the food is returned to the stomach. As the free acid accumulates the 

 sphincter tightly closes the orifice. As this takes place after division of 

 the nerves passing to this region of the esophagus the inference is that the 

 contraction of the sphincter is brought about throguh the intermediation 

 of a local reflex nerve mechanism in the walls of the esophagus. 



It has recently been reported by Cannon that a similar inhibition or 

 relaxation of the musculature of the cardiac portion of the stomach is oc- 

 casioned by each act of deglutition and that it continues and increases if 

 the acts follow each other in quick succession. As the bolus descends the 

 esophagus and before it reaches its termination there is relaxation of the 

 musculature of the cardiac end, a fall of intragastric pressure, an enlarge- 

 ment of the stomach capacity and hence a readier receptivity of the bolus. 

 That this inhibition is caused by impulses descending the vagus is shown 

 by the effects which follow a moderate stimulation of the vagus nerve and 

 by the fact that it does not take place if the vagus nerves are divided. To 

 this inhibition and enlargement of the cardiac end of the stomach the 

 term receptive relaxation has been given. 



The investigations of Cannon previously referred to, show that not only 

 the sphincter cardiae, but other portions of the stomach walls exhibit differ- 

 ent forms of activity which for convenience of description are separately 

 described by him as follows: 



i. The Movements of the Pyloric Portion. The movements of this region 

 of the stomach were first studied and sketched by means of the Rontgen 

 rays by Cannon. Some of the changes in shape due to these movements 

 are shown in Fig. 74. Within five minutes after a cat has finished a meal 

 of bread there is visible near the duodenal end of the antrum or vestibule 

 a slight annular contraction which moves peristaltically to the pyloric orifice; 

 this is followed by several waves recurring at regular intervals. Two or 

 three minutes after the first movement is seen, very slight constrictions ap- 

 pear near the middle of the stomach, and, pressing deeper into the greater 

 curvature, course slowly toward the pyloric end. As new regions enter into 

 constriction, the fibers just previously contracted become relaxed, so that 

 there is a true moving wave, with a trough between two crests. When a 

 wave swings round the bend in the pyloric part, the indentation made by it 

 deepens; and as digestion goes on the antrum or vestibule elongates and the 

 constrictions running over it grow stronger, but, until the stomach is nearly 



