764 BILE PIGMENTS. [App. 



Taurocholic acid is a compound of taurin and cholalic acid; thus: 

 Cholalic acid. Taurin. Taurocholic acid. 



C 24 H 40 5 + C 2 H 7 N0 3 S - H 2 = C^NO.S. 



Preparation. From the bile of dogs by a process similar to that for 

 glycocholic acid. It is separated from traces of this latter and from 

 cholalic acid by precipitation with basic lead acetate and ammonia l . 



BILE PIGMENTS. 

 These have been very briefly described on p. 248. 



Bilirubin . C 16 H 18 N 2 3 . 



It is found chiefly in the fresh bile of man and carnivora, to which it 

 gives the characteristic dark golden-red colour. It frequently constitutes 

 a considerable part of some kinds of gall-stones, not however as free 

 bilirubin but as a compound with earthy matter, chiefly chalk : the gall- 

 stones of oxen and pigs often contain 40 p. c. of this compound 2 . These 

 are therefore the best material from which to prepare bilirubin. 



Preparation. The gall-stones are treated with strong acetic or 

 dilute hydrochloric acid to separate the earthy matter and the residue 

 is thoroughly washed with water and alcohol and dried. From this 

 residue the prolonged action of hot chloroform extracts the bilirubin, 

 which may either be obtained in the amorphous form by precipitation 

 with alcohol of its solution in chloroform, or as well-defined crystals by 

 the slow evaporation of the chloroform solution. 



The most usual form of the crystals is that of rhombic prisms ; they 

 are readily soluble in chloroform and alkaline solutions only. 



By treatment with oxidising agents such as nitrous acid bilirubin 

 takes up oxygen and becomes biliverdin, the colour at the same time 

 changing to green. The possible oxidation does not end here, and if 

 continued a series of products are obtained each with a characteristic 

 colour as in the well known Gmelin's test 3 . Of these only the final 

 product of the oxidation has been obtained in a state of sufficient purity 

 to enable any definite statements to be made of its characteristics 4 . 

 This is the body known as Choletelin (see below). 



Biliverdin. C 16 H 18 N 2 O 4 . 5 



This product of the oxidation of bilirubin gives the characteristic 

 colour to the bile of herbivora, and to biliary vomits. It occurs also 

 probably at times in the urine of jaundice and in the pigmentary matter 



1 Parke, Tubing. Med.-chem. Unters. Bd. i., S. 160. 



2 Maly, Sitzber. d. Wien Akad. LVII. 1868, ir. Abth. Febr. Hft. 



3 Tiedemann und Gmelin, Die Verdauung, 1826, S. 79. 



4 Heynsius und Campbell, Pfliiger's Arch. Bd. rv. (1871), S. 497. 

 Maly, Sitzb. d. Wisn. Akad. LXX. (1874), in. Abth. 



