The rete mucosum is thicker in the Negro than in the white man, and contributes somewhat to the softness of his skin. It contains also the colouring matter in the form of minute black particles diffused among its cells (fig. [72]). These particles disappear, more or less, as the cells become changed into scales; hence the outer part of the cuticle of the Negro is not so dark as the rete mucosum, but, as it is transparent, or nearly so, it allows the dark colour of the rete to show through it.
Persons commonly speak of the cuticle as if it were the whole thickness of the skin. Thus, when a blister has drawn, they say the skin is raised; whereas it is only the cuticle. This is forced off from the skin by the fluid effused into its softer layer—i. e. into the rete—in consequence of the irritating influence of the blister.
The cuticle has no nerves, and, therefore, no feeling. It may be cut or torn without pain. The snipping of a blister with the scissors is not felt, because the cuticle only is touched. It forms a covering to the whole surface of the body, and is invaluable as a means of preventing too great evaporation. Without it we should be dried up, almost mummified, by the end of a summer’s day. It also protects the delicate sensitive skin underneath. How sore is the knuckle when the cuticle has been rubbed off! The cuticle has, moreover, the accommodating property of becoming thickest where it is most wanted, as on the sole of the foot, and on the palms of the hands of blacksmiths, and artizans, and persons who handle the oar. And if any other part of the body be subjected to much friction, for instance, the knees of housemaids, or the shoulders of men who carry packs, the cuticle soon becomes thickened there.
Beneath the cuticle lies the “Cutis” or “True Skin” (c, fig. [70], and c and d, fig. [71]). It is a tough structure consisting of interlacing fibrous and fine muscular tissue, and contains the blood-vessels and nerves. The cuticle may be pared off without any bleeding; but directly the skin is wounded the blood flows. The cutis does not present an even surface next the cuticle, but shoots out into a number of little finger-like processes, called “Papillæ,” which project into the contiguous soft stratum of the cuticle, and are embedded in it. Thus the superficies of the skin is increased; and as the blood-vessels and nerves of the cutis are continued into the papillæ, they contribute very greatly to the sensitiveness of the skin. They are most numerous in parts where the sensitiveness of the skin is greatest; for instance, they are more numerous on the palmar, than on the dorsal, surface of the hand. Near the ends of the fingers and thumb they are arranged in a linear manner, forming the delicate ridges that encircle the cones of the pulps. Sections of these ridges are represented in fig. [70].
Fig. [72].
Fig. [71]. Skin.
The superficial or papillary part of the cutis is of finer and more delicate structure than the deeper or fibrous layer, and is, therefore, sometimes described as a separate layer. It is so represented in the accompanying figure (71, c).
As we are upon the subject of the cuticle and the papillæ, I will take the opportunity to say a word respecting two diseases of these structures, in which most of you, probably, have a personal interest. I mean “Warts” and “Corns.”