144 SPECIAL HISTOLOGY. 



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 individuals 

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

 fair, a lighter or more deeply colored, frequently very dark pigment is 

 deposited in various other localities in the stratum Malpighii; in preg- 

 nant women in the linea alba, and in the face (rhubarb-colored 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 

 forearm ; 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 coloring matter or actual pigment granules are 

 deposited. When the skin is only slightly colored, it is mostly only the 

 neighborhood of the nuclei and in fact only of the lowermost layers of 

 cells which is implicated, so that in perpendicular sections the papillae 

 are seen to be surrounded by a yellowish fringe; darker shades are pro- 

 duced by the extension of the color to two, three, four, and more layers 

 of cells, and over the whole cell contents ; sometimes by a darker 

 coloration of the deepest layer of cells ; the two conditions commonly 

 coexisting. The horny layer also of the colored places of the skin, 

 has according to Krause, its cell walls slightly tinged; this appears, 

 however, only upon comparing them with those of uncolored parts of the 

 skin, and only in the more deeply-tinged parts. In the negro, and the 

 other colored human races, it is also only the epidermis which is colored, 

 whilst the corium completely resembles that of Europeans. The pig- 

 ment, however, is far darker and more abundant. In the Negro (Fig. 

 55), in whom, as regards the arrangement and size of the cells, the epi- 

 dermis is precisely like that of the European, it is the perpendicular 

 cells of the deepest part of the mucous layer which are darkest (dark 

 brown or blackish-brown), and they form a sharply marked fringe con- 

 trasted against the clear corium. To these succeed clearer but still 

 brown cells, which are accumulated particularly in the depressions be- 

 tween the papillae, but are also found on their points and lateral por- 

 tions in many layers ; finally at the boundary close to the horny layer 

 there follow brownish-yellow or yellow, often rather pale, more trans- 

 parent layers. All these cells are colored throughout, with the excep- 

 tion of their membranes, and especially the parts round the nuclei, 

 which, in the internal layers, are by far the darkest portions of the 

 cells.* The horny layer of the negro also inclines to yellow or brownish. 



* [The pigment in these cells seems of two kinds: a less intense yellowish pigment, and 

 a dark granular pigment. The latter is irregularly dispersed throughout the contents of the 

 cell, and in some parts it is conglomerated into small masses. It is generally especially 



