254 UEOBILIK 



(i) Normal urobilin. In acid alcoholic solution it shows one 

 absorption band, close to and enclosing F: this band disappears 

 when the solution is neutralised by alkalis. If treated with zinc 

 chloride in presence of ammonia this band is replaced by one 

 narrower and nearer the red end of the spectrum, while at the 

 same time a green fluorescence is observed, but much less marked 

 than in the case of febrile urobilin. (ii) Febrile urobilin. The 

 solubilities of this substance are the same as of the preceding 

 form. On the other hand the band at F is broader and darker 

 than is that of normal urobilin, and further in an ethereal acid 

 solution two other bands may be seen, one adjoining D towards 

 the red, the other mid-way between D and E. These last two 

 bands are invisible in urine. By prolonged .action of sodium 

 amalgam on an alcoholic solution of normal urobilin, fibrile urobi- 

 lin is obtained. The spectrum of normal urobilin is the same as 

 that of choletelin, but the substances differ with respect to the 

 greater ease with which choletelin may be reduced to febrile 

 urobilin. Normal urobilin is regarded as differing from hydro- 

 bilirubin, the evidence being deduced from spectroscopic obser- 

 vations. Febrile urobilin on the other hand is identical with 

 stercobilin and is apparently the pigment to which the absorption 

 spectra of the bile of some animals is due. 1 



In concluding this account of urobilin and allied substances it 

 may be well once more to draw attention to the fact that the 

 differences of opinion among the various observers is based almost 

 entirely on spectroscopic appearances. These are far from conclu- 

 sive for there is no guarantee that in any given case the solution 

 under examination contains only one pigment. It may contain at 

 most a preponderance of this one but frequently mixed with other 

 pigments which are derived either from the fluid originally oper- 

 ated upon, or are decomposition products resulting from the action 

 of the reagents employed. 2 The final solution of the questions 

 raised above will only be supplied by a purely chemical investiga- 

 tion of the several substances under discussion ; such an investi- 

 gation would however be one of extreme difficulty. 



Thudichum considered that normal urine contains only one pigment, 

 which he called urochrome. 8 Maly regarded this as the same as urobi- 

 lin. 4 More recently Thudichum has upheld his former views. 6 



1 Mac Munn, The Spectroscope in Med. 1880, p. 156. A tabular conspect of the 

 above statements is given by Halliburton, Chem. Physiol. and Pathol. 1891, p. 752. 



2 Thus Vierordt has shown that if the urinary pigments are precipitated by the 

 acetates of lead and extracted from this by absolute alcohol acidulated with oxalic 

 acid, the coloured solution thus obtained possesses optical properties quite different 

 from those of the original urine ; a result which indicates that the pigments have 

 been considerably changed during extraction. Die quantitat. Spectraianalijse, 1876, 

 S. 96. 



8 Brit. Med. Jl. No. 201, 1864, p. 509. 



4 Liebig's Ann. Bd. CLXIII. (1872), S. 90. 



6 Jl. Chem. Soc. Ser. 2, Vol. xm. (1875), pp. 397, 401. 



