620 THE CHEMISTRY OF THE URINE. 



solutions have a tint like that of urine itself, and, like normal urine, 

 show no absorption-bands. There can be no doubt, therefore, that it is 

 the essential cause of normal urinary coloration. 



Physiological relations, Until quite recently, we had no knowledge 

 of the chemical relationship, or of the metabolic precursors of this im- 

 portant physiological pigment. But Biva x and Chiodera 2 have obtained, 

 by the action of potassium permanganate upon solutions of urobiliii, 

 a substance which they believe to be identical with urochrome. A. E. 

 Garrod 3 has added still more conclusive evidence for the existence 

 of a simple relation between this pigment and urobilin, by observing 

 that alcoholic solutions of pure urochrome, when treated with aldehyde 

 (which we may believe acts as a milct reducing agent), yields a pigment 

 showing the spectrum and all the more characteristic properties of 

 urobilin. The establishment of this relation is most important in 

 bringing our knowledge of physiological pigments into line, since, as 

 will be shown immediately, the derivation of urobilin from blood and 

 bile pigments is clearly established. We can now ascribe a similar 

 origin to the fundamental colouring matter of urine. 



(b) Urobilin. In 1868, Jaffe, 4 as an outcome of a spectroscopic 

 study of the urine, discovered a pigment with well-characterised pro- 

 perties, to which he gave the name of urobilin. 



This pigment is perhaps scarcely entitled to be classified among 

 the preformed pigments of normal urine, for it is present as a rule in 

 minimal amount and almost always in the form of a chromogen. But on 

 rare occasions the free pigment is found in the fresh urine of normal 

 individuals, and, moreover, the importance of urobilin in other respects 

 makes it necessary to give it a prominent place in this section. It was 

 the first physiological urinary pigment of which we had accurate know- 

 ledge from the point of view of genesis and metabolic history. Its 

 increase in disease is a familiar phenomenon. These facts and its well- 

 marked spectroscopic characters have made it predominant in the 

 literature of urinary pigments. Even at the present time it is some- 

 times described as the essential colouring matter of urine, an error 

 which is at once demonstrated if the spectroscopic indications of normal 

 urine and of weak solutions of pure urobilin are compared. 



Separation. When zinc chloride and ammonia are added to urine in due 

 proportion, a precipitate is obtained (cf. " Separation of Creatinin," p. 599), which 

 contains much of the urobilin present. This method of precipitation was used 

 by Jaffe, and from the zinc precipitate lie succeeded in extracting the pigment 

 in a remarkably pure condition, but in small quantity, and by a somewhat 

 complicated procedure. 



Menu 5 later showed that saturation of the urine with ammonium sulphate, 

 after acidification with weak sulphuric acid, produced a complete precipitation 

 of this pigment. The precipitate thus produced, which mainly consists of 

 pigmented urates, will yield to acid alcohol a solution, in which the character- 

 istic absorption-band of acid urobilin, to be later described, is easily seen. 

 Even when normal urine has been employed, the spectrum may be observed 

 after this procedure, for the bandless chromogen is decomposed by the acid 



1 G-azz. med. di Torino, 1896, vol. xlvii. No. 12. 



2 Arch. ital. di din. med., Milan, 1896, vol. xxxv. p. 505. 

 s Journ. PhysioL, Cambridge and London, 1897, vol. xxi. p. 190. 



4 CentraM.f. d. med. Wissensch., Berlin, 1868, Bd. vi. S. 243 ; Virchow's Archiv, 1869, 

 Bd. xlvii. S. 405. 



5 Bull. Acad. de med., Paris, 1878, tome vii. p. 671. 



