ecu 



THE SKIN. 



Fig. OVIII. 



improbable that this may serve to stimulate the subjacent true skin to a 

 more active formation of epidermis ; but the difference does not depend 

 solely on external causes, for it is well marked even in the foetus. 



Structure. The cuticle is made up of flattened cells agglutinated together 

 in many irregular layers. They at first contain nuclei with soft and moist 

 contents, and, by successive formations beneath them, are gradually pushed 

 to the free surface, become flattened in their progress into thin irregular scales, 

 for the most part lose their nuclei, and are at last thrown off by desquamation. 

 The deepest cells are elongated in figure, and placed perpendicularly on the 



surface of the corium (fig. cvm. 6), like 

 the particles of columnar epithelium ; 

 they are denticulate at their lower 

 ends, and fit into corresponding fine 

 dentictilations of the corium. These 

 perpendicular cells generally form one, 

 but in some places two or three strata; 

 above them are cells of a more rounded 

 shape, c. As the cells change their 

 form, they undergo chemical and 

 physical changes in the nature of their 

 contents ; for those in the deeper layers 

 contain a soft, opaque, granular matter, 

 soluble, as well as their envelope, in 

 acetic acid, whilst the superficial ones 

 are transparent, dry, and firm, and are 

 not affected by that acid. It would 

 seem as if their contents were converted 

 into a horny matter, and that a portion 

 of this substance is employed to cement 

 them together. 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 treat- 

 ment they are softened by the alkali 

 and distended by imbibition of water. 

 The more firm and transparent superficial part of the epidermis, d, may be 

 separated 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, and often give the mem- 

 brane 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 muco- 

 sum, and appears to fade as they approach the surface, but even the superfi- 

 cial part possesses a certain degree of colour. More special details respecting 

 the pigment have been already given (page Ixiii). 



The under or attached surface of the cuticle is moulded on the adjoining 

 surface of the corium, and, when separated by maceration or putrefaction, 

 presents impressions corresponding exactly with the papillary or other emi- 

 nences, and the furrows or depressions of the true skin ; the more pro- 

 minent inequalities of the latter are marked also on the outer surface of the 

 cuticle, but less accurately. Fine tubular prolongations of the cuticle sink 

 down into the ducts of the sweat-glands, and are often partially drawn out 



Fig. CVIII. SKIN OP THE NEGRO, IN 



A VERTICAL SECTION, MAGNIFIED 250 

 DIAMETERS. 



a, a, cutaneous papillae ; 5, under- 

 most and dark-coloured layer of oblong 

 vertical epidermis-cells ; c, raucous or 

 Malpighian layer ; d, horny layer. 



