THE DIGESTIVE SECRETIONS 941 



Fresh human bile, as well as that of the carnivora, is golden red in color, but 

 changes into dark green on exposure. Evidently, it must contain a number of 

 pigments which are rather unstable and are altered by oxidation. The bile of the 

 herbivora is greenish in color. When fresh, it is very bitter, and has a slimy con- 

 sistency, due to its content in mucin. The latter pecuHarity, however, is imparted 

 to it not by the hepatic cells but during its passage into the gall-bladder. This 

 fact, that bile withdrawn from the hepatic duct and its tributaries is normally 

 clear, is of some functional importance, because if it were not, its flow might be 

 greatly retarded. Thus, we find that in extreme cases of biliary catarrh the 

 larger bile ducts are frequently blocked by mucous plugs, this stagnation of the 

 bile giving rise to an absorption of its pigments and the complex of symptoms con- 

 stituting jaundice or icterus. The viscosity of bile is 1.8 times as great as that of 

 distilled water at 37° C i It is usually neutral or faintly alkaline to litmus. Per- 

 fectly clear bile possesses a specific gravity of 1.008 to 1.010, while that collected 

 directly from the gall-bladder may present a value of 1.030 and over. 



The bile of all animals contains pigments, salts and cholesterol. In accord- 

 ance with Hammarsten,2 human bile obtained from a fistula of the hepatic duct 

 possesses the following composition: 



Water 97. 48 



Solids 2.52 



Bile salts '. . 93 



Taurocholate . 30 



Glycocholate . 63 



Fatty acids 0. 12 



Mucin and pigments . 53 



Cholesterol 0.06 



Lecithin and fat . 02 



Soluble salts. 0.81 



Insoluble salts 0.02 



The bile collected directly from the gall-bladder is more concentrated than 

 that withdrawn from the hepatic duct. This difference is usually said to be due to 

 an absorption of its water, but is caused in reality by an ingo of material from the 

 cells lining the outer biliary passage. In this way mucin, phosphoprotein and some 

 cholesterol are added to the hepatic bile. It has been shown, however, that the 

 mucin of the bile of the ox, dog and sheep is not a true mucin, because it does not 

 yield a carbohydrate group on being boiled with dilute acid, and is rather rich in 

 phosphorus. It is in reality a representative of the phosphoproteins and seems 

 to have no other function than that of anointing the surfaces of the biliary chan- 

 nels and intestines. The mucinoid material in human bile is true mucin. 



The amount of bile secreted in a day is estimated at 525 c.c, but since this value 

 has been obtained from cases of biliary fistula, it cannot serve as anything more 

 than a general guide. ^ Bile is secreted continuously, but not at a perfectly uniform 

 rate, because it is produced in smaller amounts during the early morning hours 

 and in greatest quantity after the noon-day meal. 



The Storage of Bile. — In the majority of animals the bile is col- 

 lected by the hepatic duct which is then united with the cystic duct to 

 form the common duct, or ductus choledochus. In man, the latter 

 opens into the duodenum about 10 to 12 cm. below the pylorus, where 

 it meets the pancreatic duct or duct of Wirsung to form a papillary 

 prominence. Obviously, this arrangement allows of a thorough mix- 



1 Burton-Opitz, Bioch. Bull., iii, 1914, 35. 



2 Ergebn. der Physiol., iv, 1905. 



3 pfaff and Balch, Jour, of Exp. Med., ii, 1897, 49. 



