378 VOMITING. [BOOK n. 



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 circu- 

 lar 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 con- 

 tents; 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 

 a thick fluid condition somewhat resembling pea soup and often 

 called chyme, to strain off this more fluid part into the duodenum, 

 and to submit the remaining still solid pieces to the further action 

 of the gastric juice. 



As digestion proceeds, more and more material leaves the 

 stomach, which is thus gradually emptied, the last portions which 

 are carried through being those parts of the food which are least 

 digestible, and any wholly indigestible foreign bodies which happen 

 to have been swallowed ; the latter may perhaps never leave the 

 stomach at all. The presence of food leads to the development of 

 the movements; but evidently it is not the mere mechanical 

 repletion of the organ which is the cause of the movements, since 

 the stomach is fullest at the beginning when the movements are 

 slight, and becomes emptier as they grow more forcible. The 

 one thing which does increase pari passu with the movements 

 is the acidity, which is at a minimum when the (generally alka- 

 line) food has been swallowed, and increases steadily onwards. 

 It has not however been definitely shewn that the increasing 

 acidity is the efficient stimulus, giving rise to the movements. 



The movements of even a full stomach are said to cease during 

 sleep. The nervous mechanism of the gastric movements had 

 better be considered in connection with that of the intestinal 

 movements. 



222. Vomiting. In a conscious individual this act is preceded 

 by feelings of naugea, during which a copious flow of saliva into the 

 mouth takes place. This being swallowed carries down with it a 

 certain quantity of air, the presence of which in the stomach, 

 by assisting in the opening of the cardiac sphincter, subsequently 

 . facilitates the discharge of the gastric contents. The nausea is 



