CHEMICAL BASIS til' TIIK ANIMAL UuDV. 



THE PICMKNTS 01 1 KINK 1 



When fresh normal urines are examined Bpectrophotometrically 

 it is found that the extinction c..ettiei.-nt> (ao 

 given portion of the spectrum of the several thuds d.. n..t 1 

 constant ratio each to the other. If the urines contained duly 

 one colouriiig-suKstance, then no matter how much -lute 



value of the extinction coefficients varied for diilm-m regions of 

 tin- spectrum, their ratios would be constant for any given region. 

 From this it appears probable at the outset that even n. 

 urine is coloured by at least two if not more pigment-.- < MM 

 knowledge of these pigments is at present impeiteet and n! 

 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 laments of the body 

 fr<>m 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. /.y- 

 mogens) rather than by the fully formed pigment. In the n.-\t 

 place, since the colouring-matters are normally present in but 

 very small amount, and since they are not known to In- eiy-t.il- 

 lisahle or to form definite compounds with well-known precipi- 

 tant s. they have not as yet, with the exception perhai 

 uroliilin, been obtained either with any guarantee of their purity 

 or in quantities sufficient to admit of ultimate analy-i II 

 our knowledge of them is chiefly based upon their spectrosej 'it- 

 properties. They are further most probably far from stable sub- 

 stances, so that they may undergo some considerable < 1 

 either by mere exposure to the air (oxygen) or as the result of 

 the various and often different methods of extraction and pi. 

 tinn employed by various authors. This, together with the fact 

 that the position of the absorption band ..mewhat 



with the reaction of the solution and the nature of the solvent, 

 counts with but little doubt not only for th- extremely nu- 

 merous and insufficiently characterised pigments which h.- 

 one tini" or another been obtained from urine, but also for much 

 of the rontliet and confusion of opinion which exists as to t; 

 ture and relationships of those pigments of which we 

 with most confidence. 



1. Urobilin. C M H 40 N 4 7 . (?) 



This, the best known and most definitely characterised ot 

 urinary pigments, was first described by Jaffa* who regarded it as 



r rffi-ronc-os to tlm |.rinci|i.il earlier works on urinary pigment* we TMn< 

 ,7/vM"/. C/i'm. H.I. xi. (I**7).S. 537, and for all detail* ..>nitlt N,-n> 



\nt1 i \ l90. 

 ii-rordt, Die i/unntit. $irtmlanalytc, 1876, 8. 78. 



