20 PHYSIOLOGY OF ALIMENTATION. 



has been removed and noting the rate at which this food is 

 discharged from the stomach. When acidulated protein is 

 fed, the hydrochloric acid of the gastric juice is allowed to 

 accumulate from the beginning. As is indicated in curve 

 B' in Fig. 3, corresponding to this fact, we find that acidu- 

 lated protein leaves the stomach as rapidly as pure carbo- 

 hydrate, in fact, the two curves almost coincide. 



It might be thought at first that the addition of an acid 

 to a pure carbohydrate meal would hasten its discharge 

 from the stomach. Experiment shows that this is not the 

 case, for a curve showing the velocity with which a meal of 

 crackers mixed with 0.4 percent hydrochloric acid leaves 

 the stomach practically coincides with that furnished 

 by an equally large meal consisting of crackers and water 

 only. How is this fact to be explained? We find an answer 

 in the observations of HIRSCH and SERDJUKOW quoted above, 

 who found that the presence of an acid in the duodenum 

 causes the discharge of food from the stomach to be delayed. 

 Whether this was due to a contraction of the pyloric sphincter 

 or to a cessation of the movements of the stomach could, 

 however, not be determined in their experiments. We 

 know now from CANNON'S researches that the peristaltic 

 movements of the stomach are continuous, so that HIRSCH'S 

 and SERDJUKOW'S findings must be explained through a 

 contraction of the pyloric sphincter. 



We see therefore that two factors are concerned in the 

 opening and closing of the"pylorus. The pylorus, opens when- 

 ever free hydrochloric acid of sufficient concentration is 

 present in the stomach. The opening of the pylorus allows 

 the escape of a part of the acid stomach contents into the 

 duodenum. As soon as the acid comes in contact with this 

 portion of the intestinal tract, however, the pylorus is made 

 to close and remains closed until the acid in the duodenum 

 is neutralized through the flow of the pancreatic juice and bile 

 into this portion of the gut. As will be shown later, the pres- 

 ence of acid in the duodenum is a determining condition 



