628 THE CHEMISTRY OF THE URINE. 
this case the ferric salt acts as a mild oxidising agent, sufficient to form 
but not to destroy the pigment. 
With care a certain amount of indigo-blue may be obtained from 
most normal mines ; and, apart from the increase in actual disease, 
indoxyl may be present in considerable amount, and the urine yield 
a well-marked indigo reaction, when nothing more than constipation 
exists. 1 
Indigo-red is more liable to be formed from the urinary indoxyl 
when Jaffe's test is applied with the aid of gentle heat. Higher 
temperatures favour the formation of the red isomer, lower tempera- 
tures the blue. 2 In Weber's test for indieanuria both pigments are 
formed. The urine is treated, as in other methods, with its own volume 
of hydrochloric acid ; one to three drops of dilute nitric acid are then 
added, and the mixture heated to boiling. After cooling it is shaken 
with ether, when the urine, if rich in indoxyl, is found to retain a blue 
colour, while the supernatant ether is red or violet. The formation of 
indigo-red has no significance beyond such as is attached to that of 
indigo-blue. It may sometimes arise from the urine on the addition of 
strong hydrochloric acid alone (infra). 
(b) Urorosein. — Quite distinct from indigo-red is the red pigment, 
named "urorosein" by Xcncki and Sieber, 3 and since carefully studied 
by H. Rosin. 4 It is produced from its chromogen by the action of 
mineral acids ; best with the aid of an oxidising reagent, but frequently 
appearing when the urine is treated with strong hydrochloric acid alone, 
especially after standing. It is freely taken up, after its formation, by 
amyl alcohol, but is not soluble in ether. Alkalies immediately destroy 
its colour. The chromogen of urorosein is precipitated by saturation 
with ammonium sulphate. 5 
(c) Skatoxyl-red, which is formed from skatoxyl on oxidation, is never 
obtained from urine under ordinary circumstances (Rosin), though it may be 
produced in the urine of animals when skatoxyl has been given by the mouth 
(Brieger). 
It may be stated generally that when a red colour is produced in 
urine by the addition of strong acids (with or without the assistance 
of oxidising reagents), it will in the great majority of cases be due to 
urorosein or to indigo-red. The two pigments may be easily distin- 
guished, in that urorosein, unlike the indigo pigment, is not taken up 
on shaking with ether or chloroform, and is easily decolorised by 
alkalies. 6 
The Pigmentation of Pathological Urines. 
All the pigments and chromogens that we have so far described may be 
excreted in increased amount in disease. There are other pigments which 
only appear in the urine pathologically. 
In the urine of fever a well-marked band of urobilin may generally be 
seen without preliminary treatment, and uroerythrin is often present in more 
1 Cf. v. Jaksch, " Klinisehe Diagnostik," 1896, Aufl. 4, S. 406. 
2 Rosin, Virchow's Archiv, 1891, Bd. cxxiii. S. 519. 
3 Journ. f. prakt. Chem., Leipzig 1882, Bd. xxvi. S. 333. 
4 Deutsche mcd. IFchnschr., Leipzig, 1893, S. 51. 
5 Garrod and Hopkins, Journ. Physiol., Cambridge and London, 1896, vol. xx. p. 134. 
6 Rosin, Virchow's Archiv, 1891, Bd. cxxiii. S. 519. 
