CHAPTER XVI 

 PATHOLOGICAL PIGMENTATION 



MELANIN 1 



Melanin occurs normally as the coloring-matter of hair, of 

 the choroid of the eye, of the skin, in the pigment matter of 

 many lower animals, and most strikingly as a defensive sub- 

 stance in the " ink " ejected by squids to render themselves 

 invisible in the water. Pathologically melanin occurs chiefly 

 as the result of an excessive production of this pigment by cells 

 normally forming it, as in freckles, melanotic tumors, and 

 Addison's disease (probably). Cells that do not normally form 

 melanin probably do not acquire this power in pathological 

 conditions. Pathological failure to form melanin is also 

 observed, as in skin formed in the healing of wounds and after 

 syphilitic lesions ; or in albinism, in which the failure to form 

 melanin may often be attributed to hereditary influences. 



Melanin seems always to be produced through metabolic 

 activity of specialized cells. The idea, which was formerly 

 advanced, that it is derived from hemoglobin as a product of 

 disintegration, seems to have failed entirely of substantiation. 

 In malaria we frequently find a diffuse pigmentation of the skin 

 of such a nature as to suggest strongly a melanin formation, and 

 this has been cited as an example of the production of melanin 

 from hemoglobin. Carbone has proved, however, that this 

 malarial pigment is derived from hematin. The amount of 

 iron contained in melanin has been much investigated, 

 as bearing upon the question as to whether the melanin is 

 derived from hemoglobin or not, and the results obtained by 

 the best methods indicate that the amount of iron present is 

 usually extremely small, and often it is entirely absent ; further- 

 more, the presence of iron is no proof that the pigment is 

 derived from hemoglobin, since many other proteids contain iron. 



Composition of Melanin. The elementary composition 

 of different specimens of melanin examined by various observers 

 has been found to vary greatly. This probably depends on 



1 Literature and re'sume' given by v. Fiirth, Cent. f. Pathol., 1904 (15), 617, 

 hence only special references will be cited in the following discussion. 



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