322 MECHANISMS OF THE DIGESTIVE TRACT. 



duce a movement of the gastric contents, from the cardia along the 

 greater curvature to the pylorus, and then back again along the lesser 

 curvature. These movements, together with subsidiary currents which 

 are set up, effect a thorough mixing of food and gastric juice. After a 

 time, which depends on the nature of the food taken, the stomach 

 movements acquire more of the characters of a peristaltic contraction. 

 We may observe a deep groove, produced by the contraction of the 

 circular muscles of the stomach, midway between pylorus and cardia 

 (the " transverse band "). This groove or constriction travels down 

 towards the pylorus, so tending to heap up the food, and to press it 

 against the pyloric opening. Finally, on the arrival of one of these 

 waves at the pylorus, a partial relaxation of this opening is brought 

 about, partly by inhibition of the circular sphincter pylori, partly by 

 contraction of the longitudinal muscular fibres. In consequence, the 

 fluid portion of the food in contact with the opening is pressed through 

 this opening into the duodenum. At the beginning of digestion only 

 fluids can pass from stomach into duodenum. As digestion advances, 

 the propulsive contractions of the stomach, especially at its pyloric end, 

 become more and more marked, and the relaxation of the pyloric sphincter 

 more complete, so that, towards the end of digestion, undigested pieces of 

 food can be forced through, and the stomach may empty itself entirely. 



The description of the stomach movements given by Hofmeister and 

 Schiitz, is very similar to that of Beaumont. These observers studied the 

 movements of the excised stomach, placed in a warm moist chamber. They 

 describe a typical movement as consisting of two phases. At first a con- 

 striction of the circular fibres starts near the cardia and passes towards 

 the pylorus, gradually increasing in strength until it reaches the region in 

 front of the antrum ("preantral constriction"). The transverse band now 

 contracts highly, while the preantral constriction is relaxing, shutting off the 

 antrum from the rest of the stomach, and this is followed by a general con- 

 traction of the muscles of the antrum. 



Cannon, 1 who has investigated the movements by observing the stomach 

 after administration of bismuth, by means of the Rontgen rays, has shown 

 that the movements observed by Beaumont and the two last-mentioned 

 physiologists were hardly physiological, and were produced by the abnormal 

 character of the irritant (thermometer tube in Beaumont's case), or other 

 abnormal conditions of the stomach. 



According to Cannon (whose results confirm those of Rossbach, 2 obtained 

 by direct observation of the exposed viscus in dogs), movements of the 

 stomach commence a few minutes after taking food, and consist of slight con- 

 strictions, which appear near the middle of the stomach, and course slowly 

 towards the pyloric end. As digestion goes on, the antrum elongates, and the 

 contractions grow stronger, but do not entirely divide the cavity until the 

 stomach is nearly empty. A wave takes about 30 seconds (in the cat) to 

 move from the middle of the stomach to the pylorus. The waves recur 

 regularly at intervals of 10 seconds, so that when one wave is beginning 

 several others are running in order before it, causing the stomach to be bulged 

 out between rings of constriction. The fundus during this time acts 

 as a reservoir for the food, and merely squeezes its contents gradually 

 into the pyloric part. Since no churning movements take place in the 

 fundus, salivary digestion can go on in this region for a considerable time, 

 before it is stopped by the acid gastric juice. 



1 Am. Journ. Physiol., Boston, 1898, vol. i. p. 359. 



2 Deutsches Arch. f. kiln. Med., Leipzig, 1890, Bd. xlvi. S. 296. 



