CHAPTER XVI 

 PATHOLOGICAL PIGMENTATION ' 



MELANIN - 



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 substance in the "ink'' 

 ejected by squids to render themselves invisible in the water. Path- 

 ologically melanin occurs chiefly as the result of an excessive pro- 

 duction 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 me- 

 lanin may be attributed to hereditary influences.^ The function of 

 melanin is evidently that of protection from light rays, and Young ^'' 

 has found that isolated melanin from human skin absorbs violet and 

 ultra-violet rays. Probably this protection is responsible, at least in 

 part, for the relative infrequency of skin cancers in the colored 

 races.^'' 



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 



1 Literature bv Oberndorfer, Ergebnisse Pathol., 1908 (12), 460, and Hueck, 

 Zieofler's Beitr., 1012 (54), (58. 



2 Literature and resume given by v. Fiirth. Cent. f. Pathol., 1004 (15), 617; 

 Handb. d. Biochem.. 1, 742. 



2a The pigment of the so-called "melanosis" of the large intestine is neither 

 true melanin nor ordinary "waste" pigment (Henschen and Bergstrand, Ziegler's 

 Beitr., 1013 (56), 10.3). 



3 Gortner holds that dominant whites are due to the presence of antioxidase. 

 while regressive whites have neither the power to form pigments nor to inhibit 

 their formation (Amer. Naturalist, 1010 (44), 497). 



3a Biochem. Jour., 1014 (8), 460. 



3b However. Hanawa found white areas in sl;in less aflfocted by cliemical irri- 

 tants and infections than dark areas. (Dermatol. Zeit., 1013 (20), 761.) 



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