716 PHYSIOLOGY 



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 development 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 contamina- 

 tion 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 injection into the veins of 5 c.c. of a solution of secretin, pre- 

 pared 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 

 rate of secretion was therefore doubled. We may conclude that the mechan- 

 ism, by which the increased secretion of bile is produced at the time when 

 this fluid is required in the intestine, is identical with that for the secretion of 

 pancreatic juice, and that in each case one and the same substance secretin 

 is formed by the action of the acid on the cells of the mucous membrane, 

 and, on absorption into the blood stream excites both the liver and pancreas 

 to increased activity. 



THE DIGESTIVE FUNCTIONS OF THE BILE 



Bile contains a weak amylolytic ferment. Its uses in digestion are 

 dependent, however, not on the presence of this ferment, but on the peculiar 

 action of the bile salts on the fermentative powers of the pancreatic juice. 

 It was shown long ago by Williams and Martin that the amylolytic power 

 of pancreatic extracts is doubled by the addition of bile or of bile salts. 

 Pawlow has stated that the same holds good 01 the proteolytic power of this 

 juice. Most important, however, is the part played by the bile in the diges- 

 tion and absorption of fats. The fat-splitting action of pancreatic juice is 

 trebled by the addition of bile, whether boiled or unboiled. This quickening 

 action of the bile probably depends, like its function in the absorption of 

 fats, on the peculiar physical properties of the bile salts, with those of the 

 lecithin and cholesterin which they hold in solution. Not only does such 

 a solution diminish the surface tension between watery and oily fluids, so 



