252 PIGMENTS OF URINE. 



As already stated herbivorous bile, as of ox and sheep, frequently shows 

 absorption bands even when fresh. These are regarded by MacMunn as due to a 

 substance to which he has given the name cholo-haematin since it occurs in bile 

 and, as the action of sodium-amalgam shows, is related to haematin. The bands 

 more usually seen are three, two near D and one near E, 1 



THE PIGMENTS OF URINE. 2 



When fresh normal urines are examined spectrophotometrically it 

 is found that the extinction coefficients (see p. 226) for any given 

 portion of the spectrum of the several fluids do not bear a constant 

 ratio each to the other. If the urines contained only one colouring- 

 substance, then no matter how much the absolute value of the 

 extinction coefficients varied for different regions of the spectrum, 

 their ratios would be constant for any given region. From this it 

 appears probable at the outset that even normal urine is coloured by 

 at least two if not more pigments 3 . Our knowledge of these pigments 

 is at present imperfect and almost limited to that of one substance, 

 namely urobilin, and even with respect to this one, considerable 

 difference of opinion exists as to its nature and relationships to the 

 other pigments of the body from which it is supposed to be ultimately 

 derived. The reasons for this are simple. It is extremely probable 

 that normal urine is often coloured by some chromogenic mother- 

 substance (cf. zymogens) rather than by the fully-formed pigment. 

 In the next place, since the colouring-matters are normally present 

 in but very small amount, and since they are not known to be 

 crystallisable or to form definite compounds with well-known pre- 

 cipitants, they have not as yet, with the exception perhaps of urobilin, 

 been obtained either with any guarantee of their purity or in quantities 

 sufficient to admit of ultimate analysis. Hence our knowledge of 

 them is chiefly based upon their spectroscopic properties. They are 

 further most probably far from stable substances, so that they may 

 undergo some considerable change either by mere exposure to the air 

 (oxygen) or as the result of the various and often different methods 

 of extraction and preparation employed by various authors. This, 

 together with the fact that the position of the absorption bands may 

 vary somewhat with the reaction of the solution and the nature of the 



1 JL ofPhysiol. Vol. vi. (1884), p. 24. 



2 For references to the principal earlier works on urinary pigments see Udranszky, 

 Zt. f.physiol. Chem. Bd. xi. (1887), S. 537, and for all details consult Neubauer u. 

 Vogel, Analyse des Harns, Aufl. ix. 1890. 



3 Vierordt, Die quantit. Spectralanalyse, 1876, S. 78. 



