114 MANUAL OF PHYSIOLOGY. 



ment. In the main, the motions of the stomach are peristaltic. 

 They become very active about fifteen minutes after the intro- 

 duction of food, and gradually become more and more energetic 

 until the end of stomach digestion, which lasts about five hours. 



The result of the peristaltic motion is to move the food, par- 

 ticularly the part next the gastric wall, along the great curvature 

 towards the pylorus. A back current towards the cardiac ex- 

 tremity has been noticed running along the lesser curvature, and 

 the median axis of the food mass. At the same time a peculiar 

 rotatory motion of the gastric wall takes place, similar to that of 

 rolling a ball between the palms of the hands, so that the food 

 is twisted in a given direction, and the deeper lying portion is 

 brought into contact with the mucous membrane. 



While the fundus keep up considerable pressure on the con- 

 tents of the stomach, the indistinct peristaltic action of the central 

 part is intensified on nearing the pylorus into a strong circular 

 contraction, which proceeds as a definite wave towards the pyloric 

 valve, through which it gradually forces the more or less digested 

 food. At first only the fluid parts are allowed to pass, but towards 

 the later stages of digestion the fatigued pyloric muscle admits 

 solid masses into the duodenum. 



Nerve Influence on Stomach Motions. The stomach 

 has nerve connections with the cerebro-spinal axis through the 

 vagi, and the splanchnic branches of the sympathetic, and in the 

 walls of the organ itself are numerous ganglion cells. The sym- 

 pathetic connections do not seem to have any influence on the 

 muscular coats, for neither their stimulation nor section has any 

 marked effect on their movements. If the vagi be severed, stom- 

 ach contractions still occur, but no form of local stimulation pro- 

 duces the normal gastric motions, even if the organ be quite full 

 of food, therefore it would appear that the local nerve centres 

 are not sufficient to excite the normal rhythmical muscular ac- 

 tion. Moreover, stimulation of the cut vagi leading to the stom- 

 ach causes active movements when the stomach is full. It is not 

 merely the presence of food that produces the movements, as is 

 shown by the fact that the motions increase as the contents of the 



