PHYSIOLOGY OF THE DIGESTIVE GLANDS 477 



with fistulas of the abdominal walls. It appears here again that both a 

 nervous and a hormone mechanism exist. Mechanical stimulation of the 

 intestinal mucous membrane causes an immediate outfloAV of intestinal 

 juice, the purpose of which under normal conditions is evidently to assist 

 in moving forward the bowel contents. This mechanically excited juice 

 does not contain any enterokinase and only small amounts of the other 

 enzymes. Further evidence for nervous control of the secretion of intes- 

 tinal juice has been obtained by isolating three pouches of intestine be- 

 tween ligatures, and then denervating the central pouch by carefully 

 cutting all the nerves without wounding the blood vessels. On returning 

 the pouches to the abdomen and leaving them several hours, it has been 



Fig. 152. Loop of intestine after tying off the portions, cutting the nerves running to the middle 

 portion, and returning the loop to the abdomen for some time. (From Jackson.) 



found that the middle pouch becomes distended with secretion, whereas 

 the two end pouches remain empty (Fig. 152). If the pouches are left for 

 several days in the abdomen, however, the secretion from the denervated 

 portion disappears again. The explanation of the result is possibly that 

 the nerves under ordinary conditions convey impulses to the intestinal 

 glands, which tonically inhibit their activity. 



The existence of hormone control is evidenced by the fact that no 

 enterokinase is present in the intestinal juice unless pancreatic juice is 

 placed in contact with the mucous membrane. Injection of pancreatic 

 juice into the blood, however, does not cause any secretion of intestinal 

 juice ; whereas the injection of secretin has such an effect. 



