NERVOUS SYSTEM UPON SECRETION 179 



is capable of calling forth a secretion of pancreatic juice. It 

 is accordingly just as important, in experimenting upon the 

 effects of nerve stimulation upon secretion by the pancreas, to 

 make certain that no chyme passes from the stomach to the 

 duodenum, as it is in similar experiments upon gastric secretion 

 to make certain that no food or saliva passes from the mouth 

 to the stomach, upon the importance of which Pawlow himself 

 lays great stress and against which the oesophageal fistula was 

 intended to guard. 



The absence of such a precautionary measure seriously in- 

 validates the result of many of the earlier experiments of Pawlow 

 and his collaborators on the effects of vagal stimulation upon 

 pancreatic secretion. Thus, while Pawlow invariably obtained a 

 positive effect upon pancreatic secretion as a result of vagus stimu- 

 lation after certain preliminary procedures, which will presently 

 be described, had been carried out, Bayliss and Starling were quite 

 unable to find any result upon pancreatic secretion from stimula- 

 tion of the peripheral end of the vagus. It must hence be regarded 

 as a possibility that in Pawlow's experiments, as a result perhaps 

 of stimulation of movement of the stomach by the vagal excita- 

 tion, that acid which had escaped from the stomach set free 

 secretin from the duodenal mucous membrane, and this in turn 

 directly stimulated the pancreatic cells. Bayliss and Starling, 

 while not explicitly denying a control of secretion by the vagus, 

 state that they have not in several experiments been able experi- 

 mentally to demonstrate the fact, and certainly regard the chemical 

 stimulus as the adequate and efficient one. 



Hence judgment must be reserved regarding the control of 

 the pancreatic secretion upon the nervous side, and it must be 

 remembered that this serious defect exists in the experiments 

 hitherto made ; still the methods used may here be described 

 from their interest as leading up to the discovery of the 

 chemical control, and as the experimental basis of any future 

 attempts at a study of the influence of the gland nerves, when 

 the additional safeguard has been provided of a fistula between 

 pylorus and duodenum, or the separation of these by ligation. 



In preparing the permanent pancreatic fistula in the dogs 

 used for the experiments, Pawlow employed a slight modification 

 of the method used by Heidenhain. Heidenhain, in preparing his 

 fistulse, had completely resected the intestine in order to obtain 



