762 PHYSIOLOGY 



provokes reflexly the concentration 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 0-4 per 

 cent. HC1, into the duodenum, and occurs even after division of all con- 

 nection 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 mate 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 con- 

 tamination 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 solu- 

 tion 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 rate of secretion was therefore doubled. We may 

 conclude that the mechanism, 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 the 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 of 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 

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



