DIGESTION 315- 



below the origin of the cardiac nerves so that the heart cannot 

 be inhibited, stimulation of the lower end of nerve, with a 

 slowlv interrupted induced current, causes a flow of gastric 

 juice after a long latent period of a minute or two. 



This action of the vagus may be called into play, either 

 by the contact of suitable food with the mouth or by the- 

 sio-ht of food. This he demonstrated by making an 

 oeso})hageal fistula in a dog with a gastric pouch, so tliat 

 food put in the mouth escaped from the gullet and did not 

 pass into the stomach (fig. 151). Mere mechanical or 

 chemical stimulation of the mouth produces no effect, but 

 the administration of meat produces it. In a fasting dog 

 the sight of food produces, after a latent period of five 

 minutes, a copious flow of gastric juice. Pavlov calls this- 

 " psychic " stimulation. It is an example of how the 

 "distance receptor" in the eye reflexly brings about an 

 appropriate reaction — just as the "non-distance receptor" in 

 the wall of the stomach, under other stimuli, brings about 

 an appropriate reaction. 



(8) Chemical Stimulation. — There is some evidence that 

 the formation of gastric juice is also influenced by the action 

 of a chemical substance produced in the mucous membrane 

 of the pyloric end of the stomach. It has been found that 

 the iDJection into the blorxl-stream of an extract of this 

 membrane, made by boiling with acid or peptone, causes a 

 production of gastric juice. In all probability the initial 

 secretion of gastric juice is dependent on the nervous 

 mechanism, and the secondary secretion, when food is in the 

 stomach, on the action of this substance. The secretion is- 

 also increased by the presence in the stomach of meat 

 extracts and of weak solutions of alcohol. 



3. Movements of the Stomach. — These have been studied 

 by feeding an animal or a man with food containing bismuth, 

 and then applying X-rays, which are intercepted by the 

 coating of bismuth, so that a shadow picture of the shape of 

 the stomach is given (fig. 152). 



1. Character. — It is found that soon after food is taken, 

 a constriction forms about the angtdar incisure at the 



