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 1 and Chiodera - have obtained, 
by the action of potassium permanganate upon solutions of urobilin, 
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 mild 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 1S68, Jaffc, 4 as an outcome of a spectroscopic 
study of the urine, discovered a pigment with v. ell-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 Jafte, and from the zinc precipitate he succeeded in extracting the pigment 
in a remarkably pure condition, but in small quantity, and by a someAvhat 
complicated procedure. 
Mehu 5 later showed that saturation of the urine with ammonium sulphate, 
after acidification with Aveak 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 1 landless chromogen is decomposed by the acid 
1 Qazz. mcd. di Torino, 1896, vol. xlvii. No. 12. 
2 Arch. ital. dt clin. mcd., Milan, 1896, vol. xxxv. p. 505. 
3 Joum. Physiol., Cambridge and London, 1897, vol. xxi. p. 190. 
4 Centralbl. f. d. tried. Wissciisch,, Berlin, 1868, Bd. vi. S. 243 ; Virchoir's Archir, 1869, 
Bd. xlvii. S. 405. 
5 Bull. Acad, de me'd., Paris, 1878, tome vii. p. 671. 
