I NFL UENCE OF NER VO US S YSTEM ON DIGEST I VE GLA NDS 407 



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 been also discovered in the vagus. 

 Their presence may be most clearly demonstrated when that nerve 

 is stimulated during the flow of pancreatic juice excited by the 

 introduction of dilute acid into the duodenum. Stimulation of the 

 central end of the vagus and oi the other nerves is capable of 

 reflexly inhibiting 

 the pancreatic secre- 

 tion. Painful im- 

 pressions have a 

 strong inhibitory in- 

 fluence. 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 pos- 

 sible that through 

 these nervous chan- 

 nels the pancreatic 

 secretion is affected 

 by the psychical con- 

 ditions 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 un- 

 doubtedly take place within three or four minutes after food is taken, 

 but it is not quite certain whether this is not determined by the 

 passage of some of the acid gastric contents into the duodenum. 



Secretin. We have already referred to the fact that pancreatic 

 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 



Fig. 165. Secretion of Pepsin. C shows the quantity 

 of pepsin(ogen) in the mucous membrane of the 

 cardiac end of the stomach at different times during 

 digestion; P, the quantity of pepsin(ogen) in the 

 mucous membrane of the pyloric end ; S, the quantity 

 of pepsin in the secretion of the cardiac glands. The 

 numbers marked along the horizontal axis are hours 

 since the last meal. About five hours after the 

 meal, S reaches its maximum. From the very be- 

 ginning of the meal C falls steadily down to the 

 tenth hour, and then begins to rise i.e., the gland- 

 cells of the cardiac end of the stomach become 

 poorer in pepsin(ogen) as secretion proceeds. 



