CHEMICAL BASIS OF THE ANIMAL BODY. 255 



The methods given above for the preparation of urobilin, indicate 

 sufficiently the procedure requisite for its detection in solutions. As 

 already stated (p. 247) the position of the absorption band of urobilin is 

 very similarly situated to that of choletelin under certain conditions. 

 The conflict of opinion as to the identity of the two substances has been 

 dealt with above. 



It now remains to give a short account of the more recent views on 

 urobilin and its relationship to other pigmentary substances to which 

 reference has already been made '. 



Mac Munn distinguishes between two forms of urobilin, viz. normal 

 and febrile or pathological. They are both obtained from urine by the 

 same method (see above) and differ as follows, (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 eiliereal 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 urobilin 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 hydrobilirubin, the evidence being deduced 

 from spectroscopic observations. Febrile urobilin on the other hand 

 is identical with stereobilin and is apparently the pigment to which 

 the absorption spectra of the bile of some animals is due 2 . 



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 conclusive 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 



1 Mac Munn, Clinical Chem. of Urine, 1889, p. 104. Gives all necessary references. 

 For spectra see Jl. of Physiol. Vol. x. (1889), p. 116. 



2 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. 



