PHYSIOLOGICAL CHEMISTRY 397 



the fat-splitting power of the extract. Pancreatic lipase is very readily 

 destroyed in acid reaction, thus making it necessary to employ an 

 absolutely fresh gland from which to prepare the extract. 



The liberated fatty acid is held in solution by the bile, and so is 

 absorbed into the epithelial cells of the villi, wherein it recombines 

 with glycerine to form neutral fat. 



CHAPTER XV. 

 THE BILE. BACTERIAL DIGESTION. 



THIS is perhaps the most puzzling secretion in the whole of the 

 physiological chemistry. Its digestive action is very slight, so that 

 it would almost appear, at first sight, to be an excretion of effete 

 products rather than a useful secretion. Against such an idea, however, 

 stands the fact that it is poured into the beginning of the intestinal 

 tract, and not into the end of it, as we should expect were it an excre- 

 tion. Further, some of its constituents are reabsorbed into the portal 

 blood and carried back to the liver, to be re-excreted in the bile. In 

 other words, there exists a circulation of certain biliary constituents, 

 from liver to intestine by the bile, and from intestine back to liver by 

 the portal blood. The absence of this reabsorption of bile constituents 

 into the blood when there is a biliary fistula (produced by attaching the 

 central end of the bile duct to a wound in the abdominal wall) accounts 

 for the bile in such cases containing less solids than the bile obtained 

 from the gall bladder after death. Another reason for this difference 

 in composition is that reabsorption of water occurs in the gall bladder, 

 and that mucin or nucleo-protein are secreted by its mucosa. In the 

 case of a fistula of the bile duct the bile does not collect in the gall 

 bladder. 



Composition of Human Bile. In I. the bile was obtained from the gall 

 bladder of persons who had been accidentally killed, while in good 

 health : in II. the bile was obtained from a fistula during life. 



i. ii. 



100 parts contain 



Water, 86 97 



Solids, 14 3 



Viz. organic salts, - 9 G'9-1'8 



Mucin and bile pigment, ... - 3 0'5 



Cholesterol, 0'2 0'06-0-16 



Lecithin and fat, O'5-l -0 0'02-0'09 



Inorganic salts, 0'8 07-0-8 



