THE MOVEMENTS OF THE STOMACH 785 



must be ascribed to a nervous mechanism. Although the local 

 mechanism probably plays the greater part in this act of relaxation, 

 the normal emptying of the stomach is also largely dependent 

 on the integrity of the connection of this viscus with the central 

 nervous system. If both vagus nerves be divided in a dog below 

 the point at which they give oft* their branches to the lungs 

 and heart, a large amount of food may remain in the stomach in 

 an undigested condition. The secretion of gastric juice is deficient, 

 and the opening of the pylorus is not easily carried out. Such dogs 

 therefore tend to die of sapraernia, being poisoned by the absorption 

 of products of putrefaction from the gastric contents. Pawlow has 

 shown that animals can be kept alive for months after division of 

 both vagi if a gastric fistula be made, the animals be carefully fed, 

 and care be taken to wash out adherent non-digested portions of food 

 from the stomach. 



The opening of the pylorus depends not only on intragastric 

 events but also on the condition of the duodenum. It has been 

 shown by Serdjukow that the pylorus remains firmly closed so 

 long as the contents of the duodenum are acid. If alkaline fluid 

 be introduced into the stomach, this is rapidly passed into the duo- 

 denum. If, however, some acid be introduced at the same time into 

 the duodenum by means of a duodenal fistula, the pylorus remains 

 firmly closed, and no fluid passes into the duodenum until the acid 

 which was placed there has been neutralised by the secretion of 

 pancreatic juice and succus entericus. We have probably in the 

 walls of the alimentary canal a local nervous mechanism for the 

 movements of the pyloric sphincter. This may be played upon 

 by impulses starting either in the stomach or in the duodenum, 

 probably by the contact of acid with the mucous membrane. In- 

 creasing acidity on the side of the stomach causes relaxation of the 

 orifice, whereas acidity on the duodenal side causes contraction of 

 the pyloric sphincter. The exact parts, however, played in this 

 mechanism by the local system and by the central nervous system 

 respectively have not yet been thoroughly made out, though there 

 is no doubt that these movements may proceed independently of any 

 connection with the central nervous system. 



Stimulation of the peripheral end of the vagus nerves may exercise 

 varying effects on the stomach wall as well as on its sphincters. In 

 the normal animal stimulation of the peripheral end of the vagus as 

 a rule causes strong contractions of the oesophagus as well as of the 

 cardiac sphincter. After the administration of atropine, stimulation 

 of the same nerve will occasion dilatation of the cardiac sphincter. 

 On both cardiac and pyloric portions of the stomach the vagus 



exercises inhibitory as well as augmentor effects. So far as concerns 



50 



