ELEMENTARY DEMONSTRATIONS 157 



with the intestinal wall changes a substance called prosecretin into 

 secretin. 



The secretin is absorbed into the circulation and passing to the 

 pancreas excites the pancreatic secretion. The effect of secretin can 

 be obtained equally well after enervation of the solar plexus or injec- 

 tion of atropine. Prosecretin is inactive. It can be obtained in O9 

 NaCl extract of jejunum, and can be changed into secretin by boiling. 

 No secretin can be obtained from the ileum. The pure pancreatic 

 juice which is obtained in the above manner, has practically no- 



Fia. 138. Pawlow's method of establishing a gastric fistula. A, B. Incision ; S, seg- 

 ment of stomach separated off ; A, abdominal wall ; e, mucous membrane ; P, pylorus ; 

 0, oesophagus ; Rv, right ; Lv, left vagus nerve. 



action on fibrin, but is active towards starch. The juice is rendered 

 active towards fibrin by the addition of succus entericus (Bayliss and 

 Starling). The substance in the succus entericus which activates the 

 trypsinogen has been called entero-kinase (Delezenne). Pawlow ex- 

 cited the flow of pancreatic juice by stimulating the vagus. It is 

 possible that the flow is indirectly excited, for stimulation of the 

 vagus causes the passage of the acid gastric juice into the duodenum. 



Pawlow makes a permanent pancreatic fistula in the following way. 

 A small piece, including the opening of the pancreatic duct, is cut out 

 of the duodenum. The duodenum is sewed up without appreciable 

 reduction of its lumen. The excised piece is sewed into the abdominal 

 wall with the mucous surface outwards. The animal cage is kept well 

 covered with sand, so that the juice is absorbed when the animal lies 

 down, and does not irritate the edges of the fistulous opening. 



Pawlow finds that the activity of the ferments in the pancreatic 

 varies with the diet. The juice is richer in trypsin on a milk diet, in 

 amylopsin on a bread diet. There is more steapsin on a milk than on 

 a bread diet. 



