THE MECHANISMS OF DIGESTION 461 



normal passage through the sphincter and, almost without exception, 

 none leaves by the fistula. When the pylorus is partly occluded, the 

 food sometimes passes in the usual way, and sometimes by the stomach. 

 The cause for this predilection for the pyloric pathway depends on the 

 pressure conditions in the gastric contents. Gastroenterostomy, there- 

 fore, is efficient only when gross mechanical obstruction exists at the 

 pylorus. The operation should never be performed in the absence of 

 demonstrable organic pyloric disease. 



Another objection to gastroenterostomy in the presence of a patulous i 

 pyloric sphincter rests on the fact that the food, after passing the sphinc- 

 ter and moving along the intestine, may again enter the stomach through 

 the fistula. This is most likely to occur when the stomach is full of 

 food, for under these conditions the stretching of its walls separates the 

 edges of the opening, the intestine being drawn taut between the edges, 

 so that the opening between the stomach and the intestine assumes the 

 form of two narrow slits, which act like valves permitting the food to 

 enter but preventing its escape from the stomach. Only seldom under 

 these circumstances can any food pass into the intestine beyond the 

 stomach opening. Kepeated vomiting after gastroenterostomy has been 

 observed in experimental animals only when obstructive kinks or other 

 demonstrable obstacles were present in the gut, the obstruction being lo- 

 cated in that part of the intestine beyond its attachment to the stomach. 



When the pyloric obstruction is complete, food must, of course, leave 

 by the fistula, digestion by the pancreatic juice and bile being still car- 

 ried on because of the fact that for a considerable distance down the 

 intestine, secretin, which we have seen is essential for the secretion 

 of these fluids, is still produced by the contact of the acid chyme with 

 the intestinal mucosa. Further provision for adequate digestion of 

 food in such cases is secured, as some of the food after leaving the 

 fistula passes back for a certain distance into the duodenum, where, however, 

 it soon excites peristaltic waves, which again carry it forward. This 

 insures thorough mixing with the digestive juices. From their experi- 

 mental experience Cannon and Blake 13 recommend that, when the 

 fistula has to be made, it should be as large as possible and near the 

 pylorus, and that the stomach afterwards should not be allowed to 

 become filled with food. To avoid kinking of the gut, they also recom- 

 mend that several centimeters of tlie intestine should be attached to the 

 stomach distal to the anastomosis. 



The effect of hyperacidity of the contents on the emptying of the 

 stomach has been studied by feeding animals with potatoes containing 

 varying percentages of hydrochloric acid. With an acidity of 0.25 per 



