MELANISM (from Gk. 11.0.ac, mclas, black), and ALBINISM ( from Lat. anots, white). Mel anism is a phenomenon due to excess of pigment, while albinism is due to its absence. Albinism is a pathological condition, while melanism is usually normal. Melanism occurs in insects, fishes, rep tiles. birds. and mammals, and is noticeable in man. While in animals and man albinism is the result of disease, it may occur in nature as a sport; thus we have albino varieties. The ab sence of pigment is normal in such Arctic animals as the polar bear. the northern or white owl, etc.; others turn white in winter, as the Arctic fox, the American varying hare. the ptarmigan, etc. The change of color in such eases is apparently due to cold, and is associated with the develop ment of numerous air-bubbles in the hair; in some eases there is no loss of pigment, which is merely concealed by the air-bubbles (Newbiginl.
In man the dark races owe the color of their skin to a black pigment deposited in the deeper layers of the this pigment in the blonde or white race being but slightly developed. As the darkest negroes inhabit the low torrid coast of West Africa, the pigmentation seems due to light, heat, and moisture combined. On the other hand, the cool damp climate of elevated or mountain regions and of the polar lands causes melanism. It is well known that the insects, more especially moths and butterflies, inhabiting Alpine slopes or mountain regions are darker than individuals of the same species, or of allied species, living on the drier and wanner lowlands. Packard has called attention to the melanotie mothslon the summits of the White Mountains of New Hampshire and along the coast of Labrador. Leydig was the first, perhaps. to point out that
variation toward greater darkness of coloring is connected with the action of moisture. The temperature experiments of Weisman, W. H. Edwards, and Merrifield have proved that be sides moisture and elevation cold is an im portant agent in excessive pigmentation, at least. of Lepidoptera and beetles, lint melanism is not entirely confined to northern animals. The blade leopard of Southern Asia is a melanotie variety or spurt. of the V0111111011 leopard. The varying hare is infrequently melanistie, It has been noticed that the butterflies on islands. which are always damper than the mainland, are in clined to be darker, whether in the East Indies or in Newfoundland.
The prevailing coloring matters in the pigments of mammals are the dull-colored melanins. The origin of these melanins is wrapped in doubt. The dark coloring matter of silkworm moths and other insects is probably due to the waste products of the blood. It has been thought that in mammals the pigment is directly derived from the haanoglohin of the blood. Floyd. however, has shown that the skin of the negro contains about twice as much iron as the white skin, ap parently due to the protcid present in the pigment granules. Another physiologist (D060110 thinks that the melanin is elaborated out of the plasma of the blood, and is not a derivative of the !emoglobin. but that the latter may itself be manufactured from some antecedent variety de rivative of melanin (Newhigin).
linmioultA PIM Newbigin, Color in Nature ( London. IS9S) ; Deli:Tine, "Origin of Melanin," in Journal of Physiology. vol. xi. (1890).