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 urines ; 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 indicanuria both pigments are 

 formed. The urine is treated, as in ojher 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 Nencki 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 tirobilin may generally be 

 seen without preliminary treatment, and uroerythrin is often present in more 



1 Cf. v. Jaksch, " Klinische Diagnostik," 1896, Aufl. 4, S. 406. 



2 Rosin, Firchow's Archiv, 1891, Bd. cxxiii. S. 519. 



3 Journ. f. prakt. Chem., Leipzig 1882, Bd. xxvi. S. 333. 



4 Deutsche mcd. Wchnsclir., 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. 



