DIGESTION 379 



opening of the pancreatic duct, closing the intestine by sutures, 

 and stitching the orifice of the duct into the abdominal wound. 

 On stimulation of the vagus the juice will begin in two to three 

 minutes to drop from a cannula in the duct, and will continue to 

 flow for several minutes after cessation of the stimulus. The 

 sympathetic also contains secretory fibres for the pancreas. 

 Efferent fibres which inhibit the secretion have also been dis- 

 covered in the vagus. Their presence may be most clearly demon- 

 strated when that nerve is stimulated during the flow of pan- 

 creatic juice excited by the introduction of dilute acid into the 

 duodenum. Stimulation of the central end of the vagus and of 

 the other nerves is capable of reflexly inhibiting the pancreatic 

 secretion. Painful impressions have a strong inhibitory influ- 

 ence. This is one of the reasons why many observers failed to 

 detect the secretory nerves. The inhibition caused by vomiting 

 is probably due to impulses ascending the vagus. It is possible 

 that through these nervous channels the pancreatic secretion is 

 affected by the psychical conditions connected with eating and 

 the desire for food, just as in the case of the gastric secretion ; 

 but our information on this subject is scantier and less precise. 

 A flow of juice may undoubtedly take place within three or four 

 minutes after food is taken, but it is not quite certain whether 

 this is no! determined by the passage of some of the acid gastric 

 contents into the duodenum. 



Secretin. We have already referred to the fact that pancrea tic 

 secretion is excited by the presence of acid in the duodenum. 

 The mechanism of this action is of great interest. Two or three 

 minutes after the introduction of 0-4 per cent, hydrochloric acid 

 into the duodenum pancreatic juice begins to flow. A similar 

 effect is seen when the acid is placed in the jejunum, but not when 

 it is injected into the lower part of the ileum. It is obtained as 

 strongly and as promptly from an isolated loop of intestine when 

 all the nerves passing to it have been cut, and the solar plexus 

 extirpated, and also after the administration of atropine, which 

 paralyzes the endings of secretory nerves elsew r here. The secre- 

 tion accordingly does not depend upon a local reflex mechanism 

 with its afferent endings in the intestinal mucous membrane, 

 but upon some substance which is carried to the pancreas by 

 the blood, and acts directly upon its cells. This substance is 

 not the acid, for the injection of 0*4 per cent, hydrochloric acid 

 into the blood produces no effect upon the pancreas. It has been 

 shown by Bayliss and Starling that the exciting substance is a 

 diffusible body of low molecular weight, probably of organic 

 nature, but not a protein, which they call secretin. It is soluble 

 in alcohol or alcohol and ether, and is not destroyed by boiling. 

 It is produced in the mucous membrane of the jejunum or duo- 



