MELANINE. URO3ACINE. 103 



of arteritis ; but is really a simple effect of post-mortem imbibition, 

 as above stated. 



12. MELANINE. This is the blackish-brown coloring matter 

 which is found in the choroid coat of the eye, the iris, the hair, and 

 more or less abundantly in the epidermis. So far as can be ascer- 

 tained, the coloring matter is the same in all these situations. It is 

 very abundant in the black and brown races, less so in the yellow 

 and white, but is present to a certain extent in all. Even where 

 the tinges produced are entirely different, as, for example, in brown 

 and blue eyes, the coloring matter appears to be the same in cha- 

 racter, and to vary only in its quantity and the mode of its arrange- 

 ment; for the tinge of an animal tissue does not depend on its 

 local pigment only, but also on the muscular fibres, fibres of areolar 

 tissue, capillary bloodvessels, &c. All these ingredients of the 

 tissue are partially transparent, and by their mutual interlacement 

 and superposition modify more or less the effect of the pigment 

 which is deposited below or among them. 



Melanine is insoluble in water and the dilute acids, but dissolves 

 slowly in caustic potassa. Its ultimate composition resembles that 

 of hasmatine, but the proportion of iron is smaller. 



13. BILIVERDIXE is the coloring matter of the bile. It is yellow 

 by transmitted light, greenish by reflected light. On exposure to 

 the air in its natural fluid condition, it absorbs oxygen and assumes 

 a bright grass-green color. The same effect is produced by treating 

 it with nitric acid or other oxidizing substances. It occurs in very 

 small quantity in the bile, from which it may be extracted by pre- 

 cipitating it with milk of lime (Robin), from which it is afterward 

 separated by dissolving out the lime with muriatic acid. Obtained 

 in this form, however, it is insoluble in water, having been coagu- 

 lated by contact with the calcareous matter ; and is not, therefore, 

 precisely in its original condition. 



14. UROSACIXE is the yellowish -red coloring matter of the urine. 

 It consists of the same ultimate elements as the other coloring mat- 

 ters, but occurs in the urine in such minute quantity, that the 

 relative proportion of its elements has never been determined. It 

 readily adheres to insoluble matters when they are precipitated from 

 the urine, and is consequently found almost always, to a greater or 

 less extent, as an ingredient in urinary calculi formed of the urates 



