14 



Thus the mere sight of food or the taking of pleasant food into the 

 mouth excites reflexly through the vagi a reflex secretion of gastric juice, 

 and this secretion can be also evoked by artificial stimulation of the 

 peripheral end of a cut vagus. The passage of acid chyme, of water, or 

 oil, from the stomach into the duodenum excites the flow of pancreatic 

 juice, the efferent channels, according to Pawlow, for the reflex being both 

 the vagi and the splanchnic nerves, since secretion of pancreatic juice 

 can be evoked by stimulation of either of these nerves. The secretion 

 of succus entericus is less distinctly due to the intervention of a dis- 

 tant nervous system, since it occurs under two conditions namely, (i) 

 mechanical distension of the gut ; and (2) introduction of inert pancreatic 

 juice. 



Previously to the publication of Pawlow's results, no physiologist had 

 succeeded in obtaining an invariable secretion of either gastric or pan- 

 creatic juice as the result of stimulation of any nerves. A few years after 

 the description by Pawlow of the production of pancreatic secretion by 

 stimulation at some point in the long reflex path, viz., from intestinal 

 mucous membrane, through medulla and vagus or splanchnics to pancreas 

 it was shown by Wertheimer in France and by Popielski in Russia that 

 the introduction of acid into the duodenum evoked a reflex flow of pan- 

 creatic juice, even after division of the vagi and splanchnics or complete 

 destruction of the spinal cord. These observers, therefore, regarded the 

 reaction as belonging to the type of peripheral reflexes, and located the 

 centre for the reflex in the ganglion cells, somewhere in the wall of the intes- 

 tine or in the pancreas itself. Previous observations by Bayliss and myself 

 had shown that the normal peristaltic movement of the intestine was a 

 peripheral reflex, the paths of which lay wholly within the walls of the 

 alimentary canal ; and we were therefore interested to determine the 

 conditions of the similar supposed reflex affecting the glandular activity 

 of the pancreatic outgrowth of the canal. A few experiments sufficed to 

 show that the so-called peripheral reflex secretion of pancreatic juice, 

 evoked by the introduction of acid into the duodenum or upper part of 

 the small intestine, occurred absolutely independently of any nervous 

 channels whatsoever, and that it was possible to isolate the pancreas from 

 the duodenum, to divide all the nerves going to a loop of the small 

 intestine, and then by injection of acid into this loop to evoke secretion of 

 pancreatic juice. Further observations showed us that the reaction, 

 instead of being nervous, was in reality a chemical one. The entry of 

 acid into the duodenum or upper part of the small intestine causes the 

 production in the mucous membrane of a chemical substance which we 

 call secretin. Since, as I shall show later, there are other secretins, we 

 may speak of this as the pancreatic secretin. This pancreatic secretin is 

 rapidly absorbed into the blood and travels with the blood to the gland, 

 the cells of which it excites to secrete. 



In order to obtain secretin, the method we have always adopted has 

 been to scrape off the mucous membrane of the duodenum and upper two 

 feet of the small intestine, to pound this up in a mortar with sand with 



