136 SPECIAL HISTOLOGY. 



§ 43. 



As regards the colour of the epidermis, in the white races, 

 as has been said, the horny layer is colourless and transparent, 

 or slightly yellowish, the mucous layer yellowish white, or 

 brownish. The colour is deepest in the areola and in the nipple, 

 passing even into blackish-brown, especially in women during 

 pregnancy and after they have borne children: it is less intense 

 in the labia majora, the scrotum, and the penis, where for the 

 rest it varies greatly, being sometimes almost entirely absent, 

 sometimes very distinct, and is least considerable in the axilla 

 and round the anus. Besides these situations, which in most in- 

 dividuals are more or less tinged, in the dark-complexioned more 

 than in the fair, a lighter or more deeply coloured, frequently 

 very dark pigment is deposited in various other localities in 

 the stratum Malpighii ; in pregnant women in the linea alba, 

 and in the face (rhubarb-coloured spots) ; in persons who are 

 exposed to the sun, in the face, especially the brow, chin, and 

 cheeks; in the neck, the thorax, the back of the hands, the fore- 

 arm ; and in dark persons over almost the whole body. These 

 tints are not produced by special pigment-cells, but are seated 

 in the common cells of the mucous layer, round whose nuclei a 

 finely granular or more homogeneous colouring matter or actual 

 pigment granules are deposited. When the skin is only slightly 

 coloured, it is mostly only the neighbourhood of the nuclei and 

 in fact, only of the lowermost layers of cells which is impli- 

 cated, so that in perpendicular sections the papillae are seen 

 to be surrounded by a yellowish fringe ; darker shades are 

 produced by the extension of the colour to two, three, four, and 

 more layers of cells, and over the whole cell contents ; some- 

 times by a darker coloration of the deepest layer of cells ; the 

 two conditions commonly coexisting. The horny layer also of 

 the coloured places of the skin, has according to Krause, its cell- 

 walls slightly tinged ; this appears, however, only upon com- 

 paring them with those of uncoloured parts of the skin, and only 

 in the more deeply-tinged parts. In the Negro, and the other 

 coloured human races, it is also only the epidermis which is 

 coloured, whilst the corium completely resembles that of 

 Europeans. The pigment, however, is far darker and more 

 abundant. In the Negro (fig. 55), in whom, as regards the 



