. Tumours, innocent and malignant; their clinical characters and appropriate treatment. t with pink a condition is termed albinism, and colourless animals,or albinos, occur among all classes of animals, vertebrateand invertebrate. Excessive development of black pigmentin the skin is known as melanism; this is much rarer thanalbinism. Abnormal distribution of pigment is common; in man itgives rise to the condition termed leucoderma when it affectsthe skin, and unequal distribution of pigment in the retina is 110 MELANOSIS 111 known as retinitis pigmentosa. Irregular patches of blackin
. Tumours, innocent and malignant; their clinical characters and appropriate treatment. t with pink a condition is termed albinism, and colourless animals,or albinos, occur among all classes of animals, vertebrateand invertebrate. Excessive development of black pigmentin the skin is known as melanism; this is much rarer thanalbinism. Abnormal distribution of pigment is common; in man itgives rise to the condition termed leucoderma when it affectsthe skin, and unequal distribution of pigment in the retina is 110 MELANOSIS 111 known as retinitis pigmentosa. Irregular patches of blackin the skins of horses cause them to be described as piebald,and when disseminated in small dots and irregular tracts theyare said to be grey. In the white races of men the pigment granules arealmost entirely confined to the cells of the rete mucosum, butwhen the pigmentation is very marked it will be founddistributed in the other tissues of the skin. The pigment, ormelanin as it is called, lies within the cells in the form eitherof black or of brown granules, or they may be uniformly. Fig. 64.—Anterior portion of a dace; each black spot contains a centralwhite dot representing au encysted parasite. stained by it. It is stated that white skin transplanted on toa negro soon becomes pigmented, and that when the skin ofa negro is grafted on to a white man it undergoes depig-mentation. It has long been known that leucocytes carrypigment. In amphibians and fishes pigment occurs in the branch-ing cells (Deiters cells) situated beneath the cells are filled with black melanin granules, obscuringthe nucleus. On exposure to light these protoplasmicprocesses retract, and the pigment is concentrated in thecell body, but when kept in the dark the processes areprotruded and the pigment is diffused in the surroundingstructures. The most remarkable example of pigment-formation isfound in cuttle-fishes (octopus and sepia). These inverte- 112 G0NNEGTIVE-TI88UE TUMOURS brates poss
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectneoplasms, bookyear19
