THE BILE 805 



to each factor, we must compare the results obtained on an animal 

 possessing a Pawlow fistula with those obtained on an animal pro- 

 vided with a fistulous opening into the gall-bladder, the common bile- 

 duct in the latter having been ligated to ensure that the total secre- 



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tion of bile passes out by the fistula. In such animals we find, as we 

 should expect, that the secretion of bile is a continuous process, but 

 that, synchronously with the great outpouring of bile into the intestine 

 during the third hour after a meal, there is an increased secretion of 

 this fluid. The passage therefore of the semi- digested food from 

 the stomach into the duodenum causes not only a slow contraction 

 and emptying of the gall-bladder but also an increased secretion of 

 bile by the liver. What is the mechanism involved in the production 

 of these two effects ? The muscular wall of the gall-bladder, as has 

 been shown by Dale, is under the control of nerves derived both 

 from the vagus and from the sympathetic, the former conveying 

 motor and the latter inhibitory impulses. It is usual to suppose 

 that the entry of acid chyme into the duodenum provokes reflexly 

 the contraction of the gall-bladder, but the exact paths and steps 

 in this reflex act have not yet been fully determined. The increased 

 secretion of bile, which is produced by the passage of the acid chyme 

 through the pylorus, can be also evoked by the introduction of acid, 

 such as 04 per cent. HC1, into the duodenum, and occurs even after 

 division of all connection between the liver and the central nervous 

 system. Since the presence of bile is necessary for the full develop- 

 ment of the activities of the pancreatic juice, and its secretion is 

 initiated by the same sort of stimulus, i.e. acid applied to the mucous 

 membrane of the gut, the question naturally arises whether the 

 mechanism for the secretion of bile may not be identical with 

 that for the secretion of pancreatic juice. In order to decide 

 this point we must make a temporary biliary fistula by inserting 

 a cannula into the hepatic duct. A solution of secretin is then 

 prepared from an animal's intestine. In making this solution we 

 must be careful to avoid any contamination by bile salts, which 

 may possibly be adherent to the mucous membrane of the gut and 

 would in themselves, on injection, evoke an increased secretion of 

 bile. It is therefore better to extract the pounded mucous membrane 

 with boiling absolute alcohol, until this fluid, evaporated into a 

 small bulk, shows no trace of bile salts. The dried and powdered 

 gut is then boiled with dilute acid. On injecting the solution of 

 secretin so obtained into the animal's veins, an increased flow of 

 bile is at once produced. In one experiment, for instance, the injec- 

 tion into the veins of 5 c.c. of a solution of secretin, prepared in this 

 way, increased the secretion of bile by the liver from twenty-seven 

 drops in fifteen minutes to fifty-four drops in fifteen minutes. The 



