SKIN, that membrane of variable thickness which covers the whole body externally and extends inward into all the natural openings, where it changes its properties, becoming soft and moist, and hence known as mucous membrane. The skin is generally described as composed of three layers: the cuticle, the rete mu cosum, and the cutis vera, the last being the most internal. The cutis (dermis), or true skin, consists of two layers, of which the deeper is called the corium, and the more superficial, the papillary layer. The corium is composed of numerous fibers closely interlaced, and forming a smooth surface for the support of the papillary layer. It varies in thickness, being, as a general rule, thick on the ex posed parts and thin on the protected. The papillary layer is soft, and formed by numerous papillaa which cover its whole surface. It contains the expansions of the sensitive nerves. The rete muco sum (mucous network) lies immediately over the cutis, and in some measure di minishes the inequalities of its surface, being thicker between the papillie and thinner on their summit. It is composed of minute, nucleated cells, and is almost pulpy in consistence. It is very slightly developed in the white races, but is very distinct and thick in those that are dark er, the cells, which are filled with a pig ment, being that which gives the dark color to their skin. The cuticle, scarfskin, or epidermis is a disorganized scaly sub stance, serving to protect from injury the more delicate cutis. It is thickest on the most exposed parts; and on the palms of the hands and soles of the feet it consists of several layers. The skin performs various important functions. It is the
seat of common sensation, and is fur nished with numerous pores or openings which give passage to the sweat and other exhalations. It is in this way the great regulator of the heat of the body.
The different diseases of the skin may be classified into eight orders, distin guished from each other solely by the ap pearances on the skin, as follows: (1) Papulx, or pimples, little elevations of the cuticle of a red color, and not containing any fluid, as in the earliest stage of smallpox. (2) Sguamm, or scales, small, hard, thickened, opaque, whitish patches of unhealthy cuticle, as in leprosy. (3) Exanthemata, or rashes, superficial red patches varying in figure and size, and irregularly diffused over the surface, as in measles, scarlet fever, etc. (4) Maim, blebs or miniature blisters, as sometimes occur in erysipelas. (5) Postulx, or pus tules, circumscribed elevations of the cuticle containing pus, and having red in flamed bases, as in the eruption of small pox when at its height and maturity. (6) Vesiculx, or vesicles, small elevations of the cuticle, covering a fluid usually at first clear and colorless, but becoming afterward opaque and whitish, or pearly, as in cowpox and chickenpox. (7) Tuber cula, tubercles, small, hard, superficial tumors, circumscribed and permanent, or, if they separate at all, it is only par tially. (8) Namlx, spots or patches, aris ing from excess or deficiency of the color ing matter of the skin, and frequently occurring congenitally, or connected with some slight disorder of the digestive or gans or of the general health.