BILE. 153 



Bilirubin, which is perhaps the most important of the bile pig- 

 ments, is apparently derived from the blood pigment, the iron 

 freed in the process being held in the liver. Bilirubin has the same 

 percentage composition as hsematoporphyrin, which may be pro- 

 duced from hsematin. It is a specific product of the liver cells 

 but may also be formed in other parts of the body. The pig- 

 ment may be isolated in the form of a reddish-yellow powder or 

 may be obtained in part, in the form of reddish-yellow rhombic 

 plates (Fig. 41, below) upon the spontaneous evaporation of its 



FIG. 41. 



BILIRUBIN (H^MATOIDIN). (Ogden.) 



chloroform solution. The crystalline form of bilirubin is prac- 

 tically the same as that of hxmatoidin. It is easily soluble in 

 chloroform, somewhat less soluble in alcohol and only slightly 

 soluble in ether and benzene. Bilirubin has the power of combin- 

 ing with certain metals, particularly calcium, to form combinations 

 which are no longer soluble in the solvents of the unaltered pig- 

 ment. Upon long standing in contact with the air, the reddish- 

 yellow bilirubin is oxidized with the formation of the green bili- 

 verdin. Bilirubin occurs in animal fluids as soluble bilirubin-alkali. 

 Solutions of bilirubin exhibit no absorption-bands. If an am- 

 loniacal solution of bilirubin-alkali in water is treated with a 

 )lution of zinc chloride, however, it shows bands similar to those 

 of bilicyanin (Absorption Spectra, Plate II), the two bands be- 

 tween C and D being rather well defined. 



Biliverdin is particularly abundant in the bile of herbivora. It 

 is soluble in alcohol and glacial acetic acid and insoluble in water, 

 iloroform and ether. Biliverdin is formed from bilirubin upon 

 >xidation. It is an amorphous substance, and in this differs from 

 )ilirubin which may be at least partly crystallized under proper 



