DISEASES OF THK SKIN. 459 



STRUCTIKE or THE SKIN. 



The skin consists prinmriiy ot" two parts: (^1) The siiperlieiul non- 

 vascular (without bh)od vessels) layer, tiie cuticle, or epidermis; and 

 (•J) the deep vasc-ular (with hhxxl vessels) layer, the coriuin, dernns, 

 or true skin. (See PI. XXXVIII, % 1.) 



The cuticle is maile up of cells placed side by side and more or less 

 modihed in shai)e by their mutual compression and by surface evapo- 

 ration and drvin<^. The superficial stratum consists of the cells diied 

 in the form of scales, which fall off continually and form dandruff. 

 The ileep stratum (the mucous layer) is formed of somewhat rounded 

 cells with large central nuclei, and in colored skin containinpj numer- 

 ous pigment granules. These cells have prolongations, or branches, 

 by which they communicate with one another and with the superficial 

 hiyer of cells in the true skin l>eneath. Through these prolongations 

 they receive nutrient licjuids for their growth and increase, and pass 

 on li(iui<ls absorbed by the skin into the vessels of the true skin 

 beneath. The living matter in the cells exercises an equally selective 

 power on what they shall take up for their own nourishment and on 

 what they shall admit into the circulation from without. Thus, cer- 

 tain agents, like iodin and belladonna, are readily admitted, whereas 

 others, like arsenic, are excluded by the sound, unbroken epidermis, 

 lietween the deep and superficial layers of the epidermis there is a 

 thin, translucent layer (septum lucidum) consisting of a double 

 stratum of cells, and forming a medium of transition from the deep 

 spheroidal to the superficial scaly cuticle. 



The true skin, or dermis, has a framework of interlacing i)undles 

 of white and yellow fibers, large and coarse in the deeper layers, and 

 tine in the superficial, where they approach the cuticle. Between the 

 fibrous bundles are left interspaces which, like the bundles, become 

 liner as they approach the surface, and inclose cells, vessels, nerves, 

 glands, gland ducts, hairs, and in the deeper layers fat. 



The .superficial layer of the dermis is foruied into a .series of 

 minute, conical elevations, or papilhe, projecting into the deep por- 

 tion of the cuticle, from which they are separated by a very fine 

 tiansparent membrane. This papillary layer is very richly supplied 

 with capillary bhvxl vessels and nerves, and is at once the seat of 

 acute sensation and the point fn»m which the nutrient li(|uid is 

 supplietl to the cells of the cuticle al)Ovtn It is also at this ])oint that 

 the active changes of inllammation are especially concentrated; it is 

 the immediately superposed cell layers (mucous) that become mor- 

 bitlly increased in the earlier stages of inHammati<m: it is on the 

 .surface of the papillary layer that the liquid is thrown out which 

 raises the cuticle in the form of a bli.ster, and it is at this point 

 mainly that pus forms in the ordinary pu.stule. 



