CH. XXXV.] MOVEMENTS OF THE STOMACH 529 



moved towards the pylorus, also ensures thorough admixture with 

 the gastric juice. The movements are observed to increase as the 

 process of chymification advances, and are continued until it is 

 completed. 



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 b^ilb 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. The object of this 

 movement appears to be, as just said, to carry the food towards the 

 pylorus as fast as it is formed into chyme, and to propel the chyme 

 into the duodenum ; the undigested portions of food are kept back 

 until they are also reduced into chyme, or until all that is digestible 

 has passed out. The action of these fibres is often seen in the con- 

 tracted state of the pyloric portion of the stomach after death, when 

 it alone is contracted and firm, while the cardiac portion forms a 

 dilated sac. Sometimes, 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. 



The subject has recently been taken up by Cannon. He gave 

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

 Bontgen rays shadow photographs of the stomach, because the bismuth 

 salt renders its contents opaque. His results mainly confirm those 

 of the earlier investigators ; the principal peristalsis occurs in the 

 pyloric portion of the stomach. The cardiac portion 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. 



Under ordinary circumstances, three or four hours may be taken 

 as the average time occupied by the digestion of a meal in the 

 stomach. But the digestibility and quantity of the meal, and the 

 state of body and mind of the individual, are important causes of 

 variation. The pylorus usually opens for the first time about twenty 

 minutes after digestion begins; it, however, quickly closes again. 

 The acid chyme provides a chemical stimulus for pancreatic secretion, 

 and the strongly alkaline pancreatic juice neutralises it ; as soon as 

 the intestinal contents are neutral, the pylorus again opens, more 

 acid chyme is thrust into the duodenum; more pancreatic juice 

 provided ; and so on until the stomach is finally emptied. 



Influence of the Nervous System. The normal movements of 

 the stomach during gastric digestion are in part controlled by the 



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