BILANES, BILENES, AND RELATED SUBSTANCES 135 



urine and feces was only the chromogen, and that urobihn and sterco- 

 biUn arose from it by oxidation during the extraction. Heilmeyer, 

 however, has observed the urobihn absorption spectrum in quite 

 fresh urines not previously exposed to light (1225); it is therefore 

 probable that both the chromogen and the oxidized form of the 

 pigment are present. 



Jaffe had reduced bilirubin to a urobilin-like substance, which was 

 later studied by Maly (1855,1856) and called "hydrobilirubin." It 

 may be described today as impure mesobilene-(b). Many early 

 investigators studied urobilin from various sources (e.g., normal and 

 pathological urine), and endeavored to determine its relation to 

 "hydrobilirubin." Since, however, none of their preparations was 

 pure, and since complicating factors such as complex salt formation 

 were then still unsuspected, the results were contradictory and con- 

 fusing. From reading MacMunn's work (1839) on the differences 

 between "normal" and "febrile" urobilin, for instance, one gains 

 the impression that he was largely misled by impurities such as 

 porphyrins (this was pointed out by Hopkins, 983,1333), and by the 

 vagaries of unintentional complex salt formation, but that in a few 

 cases he did observe a true difference. Although a difference between 

 the nitrogen content of urobilin and "hydrobilirubin" claimed by 

 Garrod and Hopkins (983,1334^) was shown later by Fischer to be 

 due to impure urobilin, the earlier workers also described spectroscopic 

 differences and differences in oxidizability, which Fischer disregarded, 

 but which were later confirmed. 



The problem appeared to be solved after Fischer isolated meso- 

 bilirubinogen (mesobilane) from several pathological urines (778,853, 

 cf. also 2982) and showed it to be identical with mesobilane prepared 

 from bilirubin. Fischer claimed that urobilinogen was identical with 

 mesobilirubinogen, and that urobilin was a hopelessly complicated 

 mixture of oxidation products. This view received general accept- 

 ance, and even today, more than twelve years after it became clearly 

 recognized as less than half the truth, it is found in practically every 

 textbook of physiology and in most textbooks of biochemistry. 



In 1920, Eppinger (697) considered it unfortunate that Fischer did 

 not investigate the fecal stercobilinogen and stercobilin. The omission 

 was remedied in 1932, when Watson, working in Fischer's laboratory, 

 isolated pure stercobilin (cf. above). Lemberg's ferric chloride oxida- 

 tion test (in 1934) demonstrated a clear differentiation between 

 "stercobilinogen" and mesobilane, and showed that most urines con- 



