GASTRIC SECRETION AND DIGESTION 81 



doubtedly weakens, so that they multiply less rapidly 

 when the chyme passes on to the small intestine, where the 

 conditions for bacterial growth are more favorable. It 

 is not surprising to find that the species of organisms which 

 thrive most in the stomach are those which themselves 

 produce acid. The " sour stomach " commonly referred to 

 is a stomach in which the generation of lactic acid from 

 sugars is actively taking place. This is a process very like 

 the familiar souring of milk. Indeed, milk is one source of 

 such acid fermentation in the stomach. Excessive acidity, 

 whether due to the native juice or to the activity of bac- 

 teria, may be a cause of discomfort and a hindrance to 

 digestion. Cannon has lately shown that acidity above 

 a certain degree delays the departure of food from the 

 stomach, and this is easily comprehensible when it is re- 

 called that after each brief relaxation the pylorus remains 

 closed until the acid which has just passed has been 

 neutralized or dispersed. Acidity within limits is a neces- 

 sary condition of gastric digestion, and this will be dis- 

 cussed later. 



The Secretion of the Gastric Juice. The glands of the 

 empty stomach seem to be quite inactive. The natural 

 supposition that they begin to secrete when food comes in 

 contact with the mucous membrane is not borne out by the 

 results of experiments. It is most important to note that 

 the juice may start somewhat in advance of the arrival of 

 food. The stomach as well as the mouth may be said to 

 water at the contemplation of a meal. Abundant evi- 

 dence of this fact has been furnished by the extraordinary 

 experiments of the Russian physiologist Pawlow upon 

 dogs. When a permanent opening has been made to the 

 interior of a dog's stomach a little gastric juice may issue 

 when the dog is merely shown food which he likes. 



That it is unnecessary to have actual contact with the 

 stomach wall is still better shown in the case now to be 

 described. A dog having a gastric fistula is subjected to a 

 second operation, by which the esophagus is severed and 

 the portion connected with the pharynx made to open 

 6 



