212 



THE SKIN. 



Fig. 140. — Skin of the Negro, vertical 



SECTION, MAGNIFIED 250 DiAMETERS 



(Kijlliker). 



outliues of tlie iudividual cells. Immediately above tliis, which may 

 1)6 looked iipou as the commenccmeut of the horny layer of the epi- 

 dermis (see below), is a stratum of 

 Fig. l-iO- considerable thickness in which the 



cells are much enlarged, and the 

 nuclei in many cases no longer 

 visible : towards the surface they 

 pass into the hard flattened scales 

 Avhich are to be thrown off by 

 desquamation. As the cells change 

 their form, they undergo chemical 

 and physical changes in the nature 

 of their contents ; for in the deeper 

 layers they consist of a, soft, granu- 

 lar, protoplasmic matter, soluble in 

 acetic acid, whilst the superficial 

 ones are transparent, dry, and firm, 

 and are not affected by that reagent. 

 It would seem as if their contents 

 were converted into horny matter, 

 and that a portion of this substance 

 is employed to cement them to- 

 gether. These dry hard scales may 

 be made to reassume their cellular 

 form, by exposure for a few minutes 

 to a solution of caustic potash or 

 soda, and then to water. Under 

 this treatment they are softened 

 by the alkali, and distended by 

 imbibition of water. 

 The more firm and transparent superficial part, or horny layer, of the 

 epidermis, d, may be separated after maceration from the deeper, softer, 

 more opaque, and recently formed part, which constitutes what is called 

 the Malpighian layer, or rete mucosum, c. 



Many of the cells of the cuticle contain pigment granules, and often 

 give the membrance more or less of a tawny colour, even in the white 

 races of mankind ; the blackness of the skin in the negro depends 

 entirely on the cuticle. The pigment is contained principally in the 

 cells of the deep layer or rete mucosum, and appears to fade as they 

 approach the surface, but even the superficial part possesses a certain 

 degree of colour. More special details respecting the pigment have 

 been already given (page 51). 



Between and amongst the cells of the Malpighian layer leucocytes 

 are occasionally observed. They have no doubt made their way here 

 from the corium. 



The under or attached surface of the cuticle is moulded on the adjoin- 

 ing surface of the corium, and, when separated by maceration or pu- 

 trefaction, presents impressions corresponding exactly with the papillary 

 •or other eminences, and the furrows or depressions of the true skin ; 

 the more prominent inequalities of the latter are marked also on the 

 ■outer surface of the cuticle, but less accurately. Fine tubular prolon- 

 gations of the cuticle sink down into the ducts of the sweat-glands, and 

 -are often partially drawn out from their recesses Avhcn the cuticle is 



a, a, cutaneous papilloe 

 most and dark-coloured laj 

 vertical epidermis-cells ; c, muc 

 Malpighian layer ; d, horny layer. 



h, under- 

 of oblong 



