TISSUES OF THE BODY. 



147 



Fig. 140. Skin from a negro's leg. At a, 

 the papillae of the cutis, upon which the 

 cells of the epidermal layers may be 

 observed ; ef, older, and b and c younger, 

 strata. 



their diameter is greater, and may rise to 0-0114 mm. The outlines of 

 these cells are very delicate and difficult to distinguish ; they contain a 

 more or less granular, and frequently 

 yellow nucleus, 0-0045-0-0075 mm. in 

 diameter, whose shape is either roundish 

 or oval. Then there follow a consider- 

 able number of strata of cells lying one 

 over the other, in which, however, the 

 latter become gradually larger, ranging 

 from 0-0181 to 0'0280 mm. A poly- 

 hedral flattening is apparent at the same 

 time, and the cells seem to increase in 

 superficial extent, their nuclei becoming 

 paler and assuming more of a lenticular 

 form. All these layers of the rete Mal- 

 pighiicontainthe same spinous and ridged 

 cells already described as occurring in 

 strongly laminated mucous epithelium 

 (fig. 141 a). But besides these younger 

 epithelial elements, lymphoid cells which 

 have wandered out of the blood-vessels 

 are encountered in varying frequency ( 

 81). They may be distinguished by their 

 brilliant border, irregular outlines, and 

 very small size. Finally, we come to the smooth-edged cells of the horny 

 or outermost layers, or epidermis in the more restricted meaning of the 

 word, whose diameter is 0-0285-0 -0450 mm. From below upwards they 

 become more and more like flattened scales, formed of a transparent and 

 solid substance, without any immediately recognisable membrane (fig. 142). 

 Though in this respect they resemble the most superficial cells of lami- 

 nated mucous epithelia, they still differ from these in possessing no nuclei. 



This absence of a nucleus is, however, immaterial, for in young embryos 

 all, even the most superficial scales, are nucleated, 

 as also those on the adult body, at spots where the 

 skin is of a soft texture, and naturally moist. 



Now, as the layers of the epidermis lying one over 

 the other present a dull white or brownish appear- 

 ance, they must, more or less, damp the deep red 

 colour, due to its great vascularity, of the cutis lying 

 underneath, and, moreover, in a degree proportionate 

 to their thickness. 



We are taught this also by experience. In 

 those localities, namely, where the tint of the skin 

 is reddest, the epidermis is very thin, as on the lips 

 and cheeks. It attains, on the contrary, in the 

 sole of the foot and, with many individuals, in the 

 palm of the hand, a great thickness, combined with 

 a progressive decrease in the red flesh colour, until 

 at last at those points where the cuticle is thickest 

 nothing but the tinge of the epidermal layers is 

 apparent. This is also seen in weals. 



It is well known that the skin of Europeans presents at certain points 

 a brownish tint, lighter in blonde individuals than in brunettes. Among 



Fig. 141. So-called spinous 

 or ridged cells, a, from 

 the deeper layers of hu- 

 man epidermis; b, cells 

 from a papillary tnmoui 

 of the human tuiiguu. 



