THE FOOD AND DIGESTION 343 



The pigments are closely allied to hsematoporphyrin 

 and hsematoidin, and they are derived from haemoglobin. 

 Their amount is greatly increased when haemoglobin is 

 set free or injected into the blood. They are formed 

 in the liver, since, 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. 



Cholesterin is a monatomic alcohol C 26 H 43 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 produced. When these stones are forced along the 

 bile passages as a result of muscular contraction, intense 

 agony biliary colic may be produced. When they 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, p. 12.) 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 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. 



