562 THE SKIN. 



or less pigment-granules. In the Caucasian race these are best 

 observed in the region of the nipple of the breast, the external 

 female genitals, the scrotum, and the anus. In the colored races 

 (see Fig. 232) the columnar epithelia contain numerous blackish- 

 brown pigment-granules, always scattered around the central 

 nucleus, which itself remains uncolored. The pigment-granules, 

 by means of delicate filaments, are connected with the bioplasson 

 reticulum within the epithelia. Between the columnar, as well 

 as the neighboring cuboidal epithelia, the cement-substance is 

 invariably traversed by delicate transverse filaments, and con- 

 tains a varying number of homogeneous or granular bioplasson 

 bodies. These are growing epithelia, wedged between the older 

 formations, and interconnected with them by delicate offshoots. 

 Some authors have mistaken these lumps for connective tissue 

 or wandering cells. 



The epithelia of the rete mucosum are irregularly polyhedral, 

 also supplied with a diffuse coloring matter, and distinctly nucle- 

 ated. The cement- substance shows the connecting transverse 

 filaments, especially after treatment with chloride of gold. The 

 filaments (so-called thorns) are easily discernible in places which 

 were subject to a slight, continuous irritation (see page 323, Fig. 

 139). The cement-substance in this situation likewise holds 

 small, solid lumps of bioplasson, which are best marked and 

 most numerous in the localities exhibiting the thorns most 

 plainly. In the cement-substance of specimens successfully 

 stained with chloride of gold we find the beaded axis-fibrilla?. 

 Toward the periphery the cuboidal epithelia are slightly flat- 

 tened and finely granular, which indicates that the epithelia are 

 gradually dying, though the vitality is usually retained by the 

 nucleus. There may be layers above the rete mucosum, com- 

 posed of flat epithelia, either homogeneous or distinctly nucle- 

 ated, and readily stained by carmine, which shows that they 

 are endowed with a higher degree of vitality. 



The most external portion is composed of flat, imbricated 

 epithelia, which in the vertical section appear spindle-shaped. 

 Their horny nature is demonstrated by an irregular contour, by 

 the want of granulations, and by the absence of a nucleus. The 

 nucleus may be found, however, in the lowest portions of the 

 horny layer, though it is often only faintly indicated. The 

 properties of life in these epithelia are gradually lost, and are 

 entirely absent in the outermost, flattened epidermal scales. We 

 know that the epidermal scales desquamate during life, but the 



