DIGESTION 305 



band is usually contracted so strongly and continuously that a 

 distinct groove is seen to separate the tubular antrum from the 

 bag-like cardiac end. The suggestion of a massive constricting 

 ring of muscle is belied by an examination of the dead viscus. 

 The transverse band is really little more than a physiological 

 sphincter. The empty stomach is contracted and at rest. A 

 few minutes after food is taken contractions begin in the antrum, 

 and run on in constricting undulations (in the cat at the rate of 

 six in the minute) towards the pyloric sphincter. Each wave 

 takes about twenty seconds (in the cat) to pass from the middle 

 of the stomach to the pylorus. Feeble at first, they become 

 stronger and stronger as digestion proceeds, and gradually come 

 to involve the portion of the fundus next the sphincter of the 

 antrum, but their direction is always towards the pylorus, 

 never, in normal digestion, away from it. The food is thus sub- 

 jected to energetic churning movements in the pyloric end of 

 the stomach, and worked up thoroughly with the gastric juice. 

 Kept in constant circulation, it gradually becomes reduced to 

 a semi-liquid mass, the chyme, which is at intervals driven 

 against the pylorus by strong and regular peristaltic contrac- 

 tions of the lower end of the stomach, the sphincter relaxing 

 from time to time by a reflex inhibition to admit the better- 

 digested portions into the duodenum, but tightening more 

 stubbornly at the impact of a hard and undigested morsel. The 

 nature, as well as the consistence of the food, influences the 

 length of its sojourn in the stomach. Carbo-hydrate food passes 

 more rapidly through the pylorus than fatty food, and fat more 

 rapidly than protein. The reason is that the acidity of the 

 gastric juice varies with the different kinds of food, hydrochloric 

 acid being secreted in abundance in the presence of proteins, and 

 to a much smaHer extent in the presence of fats and carbo- 

 hydrates. Now, dilute hydrochloric acid when introduced into 

 the stomach remains there for a much longer time than water. 

 This depends upon the fact that such portions of the acid as get 

 into the duodenum stimulate afferent fibres in its mucous 

 membrane, and so cause reflex spasm of the pyloric sphincter. 

 When the acid chyme becomes neutralized to a certain point by 

 the bile and pancreatic juice, inhibitory impulses pass up from 

 the duodenum and cause the sphincter to relax. The cardiac 

 division of the stomach, with the exception of the portion that 

 borders the transverse band, takes no share in the peristaltic 

 movements. And, indeed, it is far more difficult to cause such 

 contractions by artificial stimulation in the fundus than in the 

 pylorus. The two portions of the stomach are partially, or in 

 certain animals from time to time completely, cut off from each 

 other by the contraction of the sphincter of the antrum. The 



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