CHAP, i.] TISSUES AND MECHANISMS OF DIGESTION. 485 



may call the "churning" and the "propulsive" movements of the 

 stomach. 



When the stomach is empty all the muscular fibres as we have 

 said, longitudinal, circular and oblique, fall into a condition which 

 we may perhaps speak of as an obscure tonic contraction. /The 

 whole stomach is small and contracted, its cavity is nearly obli- 

 terated, and the mucous membrane, owing to the predominance 

 of the circular coat, is like the lining membrane of an empty artery, 

 thrown into longitudinal folds. As more and more food enters 

 the stomach all the coats become relaxed, with the exception of 

 the pyloric sphincter, which remains at first permanently closed, 

 and the less marked cardiac sphincter, which merely relaxes from 

 time to time at each act of swallowing. No sooner however do 

 the coats thus become relaxed than they set up obscure rhythmical 

 peristaltic contractions, giving rise to the "churning" movements. 

 These movements have been described as of such a kind that 

 the contents flow in a main current from the cardia along the 

 greater curvature to the pylorus, and back to the cardia along 

 the lesser curvature, subsidiary currents mixing the peripheral 

 portions of the contents with the more central ; it may be doubted 

 however whether any such regularity of flow is marked or constant, 

 and it is not easy to see by what combination and sequence of 

 contractions in the three coats, longitudinal, circular and oblique, 

 such a regular flow can be produced. But in any case, by such 

 rhythmical contractions the food and gastric juice are rolled about 

 and mixed together. These churning movements are feeble at 

 first, even though the stomach be filled and distended by a large 

 meal rapidly eaten; they become more and more pronounced as 

 digestion proceeds. 



Before digestion has proceeded very far the ' propulsive ' 

 movements begin. These occur at intervals, and are repeated at 

 first slowly but afterwards more rapidly. Each movement consists 

 in a contraction of the circular muscular fibres more powerful than 

 any taking part in the churning movements, and leading to a circular 

 constriction which, beginning apparently at about the obscurely 

 defined groove which marks the beginning of the antrum pylori, 

 travels down towards the pylorus, propelling the food onward. 

 This movement is accompanied or rather preceded by a relaxation 

 of, that is to say in all probability an inhibition of the permanent 

 contraction of, the sphincter pylori itself, in order that the gastric 

 contents may pass into the duodenum. But the occurrence of this 

 relaxation is determined by the nature of the gastric contents ; for if 

 the propulsive movement drives large undigested pieces towards 

 the pylorus, the sphincter is apt to close again, the result of which 

 is that the undigested morsels are carried back into the main 

 body of the stomach. 



The combined effect then of the churning and of the propulsive 

 movements is, after a certain part of the meal has been reduced to 



