554 THE MECHANICAL PROCESSES OF DIGESTION [CH. XXXV1L 



portions are gradually moved towards the pylorus, also ensures 

 thorough admixture with the gastric juice. 



The contraction of the fibres situated towards the pyloric end of 

 the stomach is more energetic and more decidedly peristaltic 

 than those of the cardiac portion. Thus, it was found in the case of 

 St Martin, that when the bulb of a thermometer was placed about 

 three inches from the pylorus, through the gastric fistula, it was 

 tightly embraced from time to time, and drawn towards the pyloric 

 orifice for a distance of three or four inches. In certain patho- 

 logical conditions, by a predominant action of strong circular 

 fibres placed between the cardia and pylorus, the two portions, or 

 ends, as they are called, of the stomach, are partially separated from 

 each other by a kind of hour-glass contraction. 



A few years ago the subject was taken up by Cannon. He gave 

 an animal food mixed with bismuth subnitrate, and obtained by the 

 Kontgen rays shadow photographs of the stomach, because the 

 bismuth salt renders its contents opaque. His results confirm those 

 of the earlier investigators; the principal peristalsis occurs in the 

 pyloric portion of the stomach. The cardiac portion (including the 

 fundus) presses steadily on its contents, and as they become chymified, 

 urges them onwards towards the pyloric portion ; the latter empties 

 itself gradually through the pylorus into the duodenum, and in the 

 later stages of digestion the cardiac part also is constricted into a tube. 



After an ordinary mixed meal it is usually stated that the 

 pylorus usually opens for the first time about half an hour after 

 digestion begins, and some of the acid chyme passes into the 

 duodenum. This, however, is incorrect, as food can be seen by the 

 X-ray method in the duodenum within a few minutes after a meal. 

 The action of this muscular ring is intermittent, and the explanation 

 of its alternate openings and closings may be briefly summed up in 

 the phrase used by Cannon : " the acid control of the pylorus." It is 

 necessary that the food should be retained in the stomach until it is 

 acid ; otherwise it would not, on reaching the duodenum, give rise 

 to the formation of secretin, the chemical stimulus for the flow of 

 pancreatic juice, and bile. He has found that acid on the gastric side 

 of the pyloric sphincter opens it, and acid in the duodenum closes it. 

 As soon therefore as the chyme is neutralised by the alkaline juices 

 of the duodenum, there is no longer any hindrance to the action of 

 the acid chyme in the pyloric end of the stomach in opening the 

 door which was temporarily closed by acid on its duodenal side. 

 This action does not occur if a ring is cut through the muscular 

 coat immediately beyond the pylorus, and so the effect from the 

 duodenum is a local reflex action mediated like the movements of 

 the small intestine by the plexus of Auerbach. 



The time taken for the complete emptying of the stomach is 



