368 VETERINARY PHYSIOLOGY 



produced, and this is used as a test for the presence of bile 

 pigments (Gmelin's test). (Chemical Physiology.} 



The pigments are closely allied to haetnatoporphyrin and 

 haematoidin (see p. 213), and they are derived from haemo- 

 globin. Their amount is greatly increased when haemoglobin 

 is set free or injected into the blood. That they are formed 

 in the liver is shown by the fact that, when the liver is 

 excluded from the circulation, the injection of haemoglobin 

 does not cause their formation. 



The liver has the property of excreting not only these 

 pigments formed by itself, but also other pigments. Thus 

 the liver of the dog can secrete the characteristic pigment of 

 sheep's bile when this is injected into its blood. 



Cholesterin is a monatomic alcohol C 27 H 45 OH which 

 occurs free in small amounts in the bile. It is very insoluble 

 and is kept in solution by the salts of the bile acids. It 

 readily crystallises in rhombic plates, generally with a notch 

 out of the corner. On account of its insolubility, when it is 

 in excess in the bile or when the bile salts are decreased, 

 it may form concretions or biliary calculi gall stones which 

 may accumulate in the gall bladder and may get caught in 

 the bile passages, obstructing the flow of bile and leading to 

 its absorption throughout the system. Jaundice is thus pro- 

 duced. When these stones are passed by the rectum, their 

 nature is readily demonstrated by breaking them up in a 

 mortar, dissolving in hot alcohol, and allowing the solution to 

 cool, when the characteristic crystals separate out. (Chemical 

 Physiology.) The source of the cholesterin of the bile is not 

 definitely known. It is not an excretion of cholesterin formed 

 elsewhere, because the injection of cholesterin does not lead to 

 an increase in the amount in the bile. According to Naunyn's 

 observations it is most abundant in cases of inflammation of 

 the bile passages, and he therefore thinks that it is formed by 

 the breaking down of the epithelium lining these ducts. 



Fats and Lecithin. The true fats and the phosphorus con- 

 taining lecithin are present in small amounts in the bile, and 

 apparently they are derived from the fats of the liver cells, 

 and they may be increased in amount by the administration 

 of fatty food. 



Nueleo-protein and Muein. The bile owes its viscosity to 



