To follow the fate of hemoglobin within the body or to unravel the intricate skein of important functions carried on by the liver cell offers many difficult problems, but we are steadily progressing toward a better solution of them. Probably no substances have stimulated more interest and led to the production of more theories along these lines than urobilin and its mother substance urobilinogen. It now seems beyond reasonable question that these bodies are derived from hemoglobin, either with or without preliminary formation of bile pigments.
While there are several ingenious theories of their production, each one with its fatal defects, the most generally accepted is that of Friedrich von Müller, which is that urobilin comes only from bile pigments subjected to bacterial decomposition within the intestinal tract, and he points in corroboration to the supposed absence of urobilin from the excretions of patients with complete obstruction of the common
WILBUR RL, ADDIS T. UROBILIN: ITS CLINICAL SIGNIFICANCEPRELIMINARY REPORT. JAMA. 1912;LIX(12):929–933. doi:10.1001/jama.1912.04270090173005