CHEMICAL BASIS OF THE ANIMAL BODY. 259 



to contain iron ('2 p. c.) and a considerable amount of sulphur (9 p. c.) 

 and not to show any absorption bands when its solutions were ex- 

 amined spectroscopically. 



This pigment appears to be identical with one previously described under 

 the name of phymatorhusin as obtained from melanotic tumours, and closely 

 allied to hippomelanin obtained from similar tumours of the horse 1 . 



When melanotic urines are treated with solutions of ferric chloride, 

 they yield, according to the concentration of the reagent, either a dark 

 brown cloudiness or else a black precipitate soluble in excess of the 

 precipitant : this test is both delicate and characteristic. Further 

 when to these urines a dilute solution of sodium nitroprusside and 

 some caustic potash is added they frequently show a pink or red 

 colouration which turns blue on the addition of acids, owing to the 

 formation of Prussian blue. The latter reaction is not due to the 

 melanotic pigment but to some other substance simultaneously ex- 

 creted 2 . 



6. Indoxyl-pigments. 



Of the total indol formed in the alimentary canal, a por- 

 tion is excreted with the fseces, while the remainder is absorbed 

 and reappears in the urine united with potassium as ethereal 

 compounds of indoxyl with either glycuronic acid (p. 107) or 

 sulphuric acid (p. 200), the latter being known as urinary indican. 

 When warmed with hydrochloric acid these compounds are decomposed, 

 yielding indoxyl and the potassium salt of the corresponding acid. If 

 the decomposition is effected in the absence of oxygen, the indoxyl may 

 be in part gradually changed into an amorphous reddish substance, 

 indigo-red, which is insoluble in water, but yields a red solution 

 when dissolved in alcohol, ether or chloroform 3 . These solutions 

 show no certainly characteristic absorption bands. In presence of 

 oxygen and with most certainty by the action of an oxidising agent, 

 the indoxyl is readily converted into indigo-blue, whose properties and 

 solubilities have been already sufficiently described. Dilute solutions 

 of indigo-blue exhibit in thin layers one absorption band in the red 

 lying between a and B 25 (7; if the thickness of the solution be 

 increased this band widens out towards D and at the same time a 

 second faint band makes its appearance in the green lying between 

 D 50 E and D 77 E* 



1 Berdez u. Nencki, Arch. f. exp. Pathol. u. Pharmakol Bd. xx. (1886), S. 346. 

 Nencki u. Sieber, Ibid. Bd. xxiv. (1888), S. 17. See also Miura, Virchow's Arch. 

 Bd. cvn. (1887), S. 250. 



2 v. Jaksch, Zt. /. physiol. Chem. Bd. xm. (1889), S. 385. 



3 Cf. Nencki, Ber. d. d. chem. Gesell. Bd. ix. (1876), S. 299, and see Mac Munn, 

 Proc. Roy. Soc. Vol. xxxv. (1883), p. 370. 



4 Vierordt, Zt. f. Biol. Bde. x. (1874), S. 27, xi. (1875), S. 192. 



r 2 



