THE MECHANISMS OP DIGESTION 495 



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 

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

 ter and moving along the intestine, mav__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. Repeated 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 19 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 the intestine should be attached to the 

 stomach distal to the anastomosis. 



The consistency of the food appears to have little influence on its rate of 

 discharge from the stomach at least in the case of potatoes. Distinctly 

 hard particles in the food retard the stomach evacuation. 



There is usually a considerable amount of gas in the part of the stomach 

 above the entrance of the cardia, on account of which this part of the 

 stomach has sometimes been called the stomach bladder. In the upright 

 position this gas forms a bright area in the x-ray plate (Fig. 155), but 

 when the person reclines it spreads to a new location. Its presence may 



