98 PHYSIOLOGICAL CHEMISTRY. 



2. Melanine. 



In all the dark -colored tissues of the body, in the choroid coat of 

 the eye, the rete Malpighi of the skin in the black and brown races, 

 and in individuals of dark complexion, in the hair, and in the substance 

 of melanotic tumors, there exists a coloring matter known as melanine. 

 When isolated or collected in compact masses, it is of a very dark 

 blackish-brown color ; but by its mixture, in different proportions, with 

 other colorless or ruddy semi-transparent ingredients of the tissues, it 

 may produce all the varying grades of hue, from light yellowish-brown 

 to nearly absolute black. It is deposited in the substance of cells in 

 the form of minute granules, and is usually more abundant in the 

 immediate neighborhood of the nucleus than near the edges of the cell. 

 A substance regarded as melanine has also been found by several 

 observers in certain morbid deposits under the crystalline form, espe- 

 cially as flat rhombic tablets with acute angles. 



The elementary analyses of melanine derived from different sources 

 do not exactly correspond with each other, although they approximate 

 within moderate limits. As the average result of analyses collected 

 by Hoppe-Seyler,* it contains, freed from ashes, the following pro- 

 portions, by weight, of carbon, hydrogen, nitrogen, and oxygen. 



COMPOSITION OF MELANINE. 



Carbon . 54.39 



Hydrogen 5.08 



Nitrogen 11.17 



Oxygen 29.36 



100.00 



Repeated observations show that it also contains iron, which has 

 been found by Lehmann in the proportion of 2.5 parts per thousand. 



Melanine is insoluble in water, alcohol, ether, and solutions of the 

 organic and mineral acids. Boiling solutions of potassium hydrate 

 dissolve it without change of color, but its color is destroyed by chlorine. 



Melanine is supposed to be produced by metamorphosis from the 

 hemoglobine of the blood. The fact that it contains iron gives a 

 certain probability to this view ; and it is a repeated observation that 

 black or blackish staining of the tissues sometimes appears in and 

 around old spots of congestion or ecchymosis. It also forms the prin- 

 cipal coloring matter of the hair, which probably contains most of the 

 iron derived from destructive assimilation of the blood-globules. 



3. Bilirubine, C 16 H 18 N 2 O 3 . 



The red or orange-red coloring matter of the bile. This substance 

 has been designated, by different writers, under the various names of 

 Biliphsein, Bilifulvine, Hematoidine, and Cholepyrrhine. It is formed 



* Handbuch der Physiologisch und Pathologisch-Chemischen Analyse. Berlin, 

 1870, p. 177. 



