CHEMICAL BASIS OF THE ANIMAL l,I)i 



may be partially precipitated from the urine by baryta water ;uul 

 completely by normal lead acetate. When tin- latter pre< ipitate 

 j. ended in water and decomposed by sulphuretted hydrogen, 

 Ids a colourless solution \vhii-h when evaporated to di\ 

 9 a dark amorphous residue insoluble in water, ether, cold 

 alcohol. acetic acid, and dilute mineral acids. The fully formed 

 pigment may, like its chromogenic forerunner, be partially pre- 

 cipitated by baryta water, the remainder being pivcipitable by tin* 

 subsequent addition of normal lead acetate. The baryta precipi- 

 tate contains the larger amount of the pigment, and bom it the 

 colouring-matter may be more easily obtained than from the 

 precipitate with the lead salt, since the latter carries down other 

 urinary pigments at the same time. The isolation of the urinary 

 melanin in a pure form from the baryta compound admits nf no 

 suitably concise description ; it must suffice here to state that an 

 impure product is obtained by decomposing the compound with 

 sodium carbonate assisted by gentle warmth and precipitating the 

 pigment from the resulting solution by a slight excess of sul- 

 phuric acid. The product when purified is partly insoluble, 

 partly soluble in acetic acid of 50 75 p. c. Of these portions 

 the former when dried is a brownish-black amorphous powder, 

 insoluble in either water, alcohol, ether, chloroform, or dilute 

 (mineral) acids, but readily soluble in alkalis. The lattei 

 obtained in too small amounts to admit of complete investigation. 

 (in analyst the pigment was found to contain iron (*2 p. <.) 

 and a considerable amount of sulphur (9 p. c.) and not to 

 show any absorption bands when its solutions were examined 

 spectroscopically. 



Tliis pigment appears to be identical with one previously il.-rribed 



under tin- name of phymatorhusin as obtained from nu-laiiotic tum-.ui>, 

 and el.'>ely allied to hyppoiuelauin obtained from similar tumours of 

 tin- horse'. 1 



When melanotic urines are treated with solutions of ferric 

 chloride, they yield, according to the concentration of t! 

 agent, 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 tli 

 (pientlx show a pink or red colouration which turns blue on tin- 

 addition of acids, owing to the formation of Prussian him-. The 

 latter reaction is not due to the melanotic pigment but to some 

 other substance simultaneously excreted.* 



1 IS.-r.l.-/. n. NVn.-ki. Arch. f. cr f >. I'.ith.J. u. rharmaicol. B.I. xx. (l*6), S. 346. 

 \MI< -ki u. si, ! r . II,!,!. H.I. xxiv. (1888), 8. 17. See alao Minra, Virchow'i Arck. 



H.I. < vii (\^i\. s. -.'50. 



- v. Jaks. h, /A. f. i>h v siol. Chem. Bd. xm. (1889), S. 385. 



17 



