THE EPIDERMIS. 



247 



deficient in tenacity, and is dissolved (or at least reduced to an apparently struc- 

 tureless condition) when treated with either of these liquids. They are fur- 



Fig. 36. 



Fig. 37. 



t 



Vertical section of Epidermis, from palm 

 of the hand : a, outer portion, composed of 

 flattened scales ; b, inner portion, consisting 

 of nucleated cells ; c, tortuous perspiratory 

 tube, cut across hy the section higher up- 

 Magnified 155 diameters. 



Vertical section of the Skin of the Thumb, 

 showing the Epidermis and outer layer of the 

 Corium; treated with acetic acid: a, horny 

 layer of Epidermis ; b, mucous layer ; c, cutis 

 vera ; d, single papilla ; e, composite papilla ; /, 

 epithelium of the perspiratory duct,' continuous 

 with the mucous layer of the epidermis; g, 

 canal of the same through the cutis; h, its 

 passage through the horny portion ; i, perspi- 

 ratory pore. 



ther distinguished in the operation of vesicating 

 agents; for the fluid which they cause to be 

 effused from the vessels of the cutis, raises 

 little else than the outer horny layer of the 

 cuticle, as it passes readily through the softer 

 tissue beneath. The internal layer of the 

 cuticle (Fig. 37, 5) was formerly supposed to 

 be a distinct structure, and was termed the rete 

 mucosum or stratum Malpighii; it is now well 

 known, however, to be chiefly formed by the 

 younger portion of the epidermis, whose cells 

 are not yet consolidated by the formation of 

 horny matter in their interior. In immediate 

 contact with the basement membrane of the 

 cutaneous papillae, however, there is usually 

 found a layer of elongated cells, resembling 

 those of columnar epithelium, arranged perpen- 

 dicularly to the surface of the corium (Fig. 38, 

 5, &) ; sometimes two, or even three strata of 

 such cells present themselves. They are ob- 

 viously different in character from those of the 

 superjacent layers, for they resist the action of 

 a solution of potash that is strong enough to 



Fig. 38. 



Vertical section of the Slan of the Thigh 

 of a Negro, more highly magnified : a, a, a, 

 three papillae of the Cutis; b, b, deepest 

 layer of columnar cells, deeply colored ; c, 

 spheroidal colls filling up the spaces be- 

 tween the papilUe, still dark ; d, upper more 

 faintly-colored portion of the mucous layer 

 of the epidermis ; e. horny layer, with 

 scarcely any perceptible color. 



