1880.] 



Colouring-matters of Human Urine. 



221 



that it is premature to assume that urobilin is formed from bilirubin 

 by reduction. It would further appear from this experiment, and 

 from a careful study of Gmelin's reaction, that febrile urobilin repre- 

 sents an intermediate stage of oxidation of bile pigment. 



Identity of Gholetelin and Normal Urobilin. — It will be seen on com- 

 paring choletelin with normal urobilin that they cannot be dis- 

 tinguished from each other, being similar in colour, solubility, in spec- 

 trum, and in the changes which their respective spectra undergo with 

 reagents. But while choletelin is easily reduced back to febrile 

 urobilin, normal urobilin is not easily reduced, because the chemical 

 stability of the latter pigment is greater than that of the former. 



On the presence of a body having similar spectroscopic characters to 

 those of Febrile Urobilin in Bile. — When human bile is treated with 

 absolute alcohol to precipitate the mucus, &c, and shaken with chloro- 

 form, the latter takes up a good deal of colouring matter, but as a 

 general rule, gives only general absorption of the spectrum. From 

 this fact I had come to the conclusion that the solution could not have 

 contained urobilin, forgetting that the band of that pigment may be 

 invisible when the pigment has been removed from a neutral or 

 slightly alkaline fluid. The following experiments conclusively prove 

 that a body is present in bile which gives the same spectroscopic 

 characters as the body produced by the action of sodium amalgam on 

 bilirubin ; and its presence can be proved, not only in the bile of man, 

 but in that of the pig, ox, sheep, and probably in that of all animals 

 possessing a gall-bladder. 



Urobilin in Human Bile. — Here I shall principally refer to urobilin, 

 leaving an account of the discovery of hsematin in bile, until after the 

 production of the urinary pigments from haematin has been dis- 

 cussed. I have repeated the following experiments several times, 

 but select one experiment as an illustration of the method adopted for 

 the demonstration of the presence of urobilin. The bile was pro- 

 cured from a case twelve hours after death ; the gall- ducts and liver 

 of the subject were free from disease. The bile was treated with 

 absolute alcohol, filtered and shaken with chloroform, the latter 

 separated off after having been allowed to stand some time, and 

 filtered. This solution was orange in colour and gave no band at F. 

 A feeble band could be seen in deep layers covering D, the violet end 

 of the spectrum being shaded by the general absorption characteristic 

 of bilirubin. The chloroform Avas distilled off over the water-bath, 

 leaving a gamboge-yellow residue, which was extracted with alcohol, 

 which was then filtered, leaving a green-yellow stain on the filtering- 

 paper. The residue left after the extraction by the alcohol was an 

 orange powder consisting of almost pure bilirubin. 



The alcoholic solution was dark red when examined by transmitted 

 gaslight, and a duller red with transmitted daylight, and with the 



VOL. XXXI. R 



