248 HYDROBILIRUBIN. 



hydrobilirubin. It is purified by being redissolved in ammonia, re- 

 precipitated from this solution by the addition of acid and finally 

 washed with water. At first during the washing a considerable 

 amount of the substance passes into solution, but as the merely 

 adherent salts are washed away, it becomes less and less soluble in 

 water until at last it is almost insoluble. When dried it takes the 

 form of a dark reddish-brown amorphous powder, which is readily 

 soluble in alcohol and chloroform, and but sparingly soluble in pure 

 ether. It is also very soluble in alkaline solutions, to which it imparts 

 a yellow colour as of normal urine : when acidulated the solutions 

 turn red 1 . 



The acid solutions of hydrobilirubin show a marked absorption 

 band between b and F which becomes fainter if ammonia is added 

 until the reaction is alkaline. But on the subsequent addition of a 

 few drops of a solution of zinc chloride, the band reappears with 

 usually increased intensity, though shifted slightly towards the violet 

 end of the spectrum 2 . This alkaline solution to which the zinc salt 

 has been added also shows, in marked distinction to the acid solutions, 

 a brilliant fluorescence which is most characteristic of the substance, 

 being of a bright rosy-red colour by transmitted and bright green by 

 reflected light. 



Previously to the discovery of hydrobilirubin by Maly, a well- 

 characterised urinary pigment had been isolated and described by 

 Jaffe under the name of urobilin (see below), while about the same 

 time that Maly's work was carried on a pigment had been obtained 

 from faeces and described, under the name of stercobilin, as identical 

 with urobilin 3 . Careful comparison by Maly of his hydrobilirubin 

 with urobilin led him to assert the complete identity of the two 

 substances. This view has been most generally adopted and is 

 probably correct as a broad statement of facts. There are on the 

 other hand several observers who have expressed themselves against 

 the exact identity of these substances 4 . Their views are however 

 based on comparatively slight and inconclusive spectroscopic differences 

 between the natural and artificially prepared substances and on other 

 differences, such as of the intensity of their fluorescent activity, 



1 Maly, Centralb.f. d. med. Wiss. 1871, S. 849. Annal. d. Chem. Bd. 163 (1872), 

 S. 77. 



2 Vierordt, Zt.f. BioL Bd. ix. (1873), S. 160. See later ' Quantitative Spectral- 

 analyse,' 1876, S. 99. 



3 Vanlair u. Masius, Centralb.f. d, med. Wiss. 1871, S. 369. Of. Jaffe, Ibid. S. 

 465. 



4 See MacMunn, Clinical Chemistry of Urine, 1889, p. 105, or Jl. of Physiol. 

 Vol. x. (1889), p. 72. Contains all necessary references. But as against Bisque" 

 see also Maly, Pfliiger's Arch. Bd. xx. (1879), S. 331. 



