THE MECHANISMS l }"»7 



scrii, many such waves may arrive al it without tl 



evidently in order thai the intestine may not Buddenl 



whelmed with large masses of food thai the pylo ally 



opens, it mighl be thoughl thai its opening dep< 



tion of the upper pari of the intestine. It is true tl 



tion of the upper pari of the intestine does liol.l the pyloric sphinc 



closed, lmt this can not be the physiological stimulus, I 



quantities of chyme are never found here. 



The first clue to the real nature of the mechanism i by 



observing the behavior of the sphincter when solutions are intn 

 into the duodenum through a fistula. Acid solutio 

 cause a e plete inhibition of gastric evacuation, wh< alkaline solu- 



tions ha<l no effect. This difference indie :ids in cl with 



the duodenal mucous membrane reflexly excite contraction of the Bphi 

 ter, and thai it relaxes only after the acid has b 

 by mixing with the pancreatic juice and bile. 



On account of the greal importance of the pyloric mechanism in insur- 

 ing thai the chyme shall enter the intestine only in such quantities thai 

 it can be properly acted upon by the intestinal digesting juic< will 



be of interest to consider briefly some of the experimental observati 

 by which this mechanism has been studied. W< ma the 



evidence thai acid on tht stomach sid( of thi pylorus causes a 

 of tin sphincter: 1 When carbohydrate food is fed, it ordinarily 

 the stomach fairly rapidly, bul it' its acid-absorbing po 

 l>y mixing it with sodium bicarbonate, exit from the stomach atly 



delayed. 2 Proteins ordinarily leave the stomach m< than 



carbohydrates, bu1 it' acid proteins are fed, their • - much m 



rapid. (3 If a fistula is made into the pyloric vestibule through wl 

 some of the tents can be removed, ii will be found that 



the opening of the pyloric sphincter, a distinctly acid r< 



in the f 1: and furthermore if acid solutio 



fistula, they cau^e the pyloric sphincter to open, - 



its opening. 1 A similar effect of acid in 0] 



be demonstrated bj applying it to the pyloric mucosa o 

 stomach kept alive in oxygenated R 



Tl vidence thai acid on 



sphincter is as follows: 1 When acid is placed in I 

 a fistula, the sphincter will not open ; 2 V 

 ducts are ligated, the stomach empties much m< 

 and !n' discharge of protein is considcrabl 



is sutured to the intestine belov the cl lenum. N 



tion it was obsen cd that i he protein 



