Skin

in physiology, the outer covering of the body. The skin varies in thickness from an eighth of an inch in the palm of the hand and on the sole of the foot to possibly the one-hundredth part of an inch in other places. The skin of a fair-sized adult is about two yards in area. The mucous membrane, or lining of the interior passages, is a continuation of the skin.

The skin consists of two layers, an outer and an inner. The outer skin is known as the epidermis or cuticle. The outer cells of the cuticle are scaly. They are most numerous on the palm of the hand and the sole of the foot where protection is most needed. The inner part of the cuticle contains the pigment that gives color to the complexion and forms one of the distinguishing marks of races. The epidermis of the hand is raised in parallel ridges arranged in patterns. As these patterns remain the same for life they serve for the identification of criminals.

The inner layer of the skin is known as the dermis cutis, and true skin. It contains the nerves of touch, the sweat glands, the sebaceous glands from which hair grows, and a system of blood vessels. The office of the outer skin, like the outer bark of a tree, is chiefly protective, and, as in the case of bark, the outer scales-the older cells-are thrown off and are replaced by others. The inner skin or cutis is protective also, but it is the seat, as stated, of essential systems of organs. The prick of a pin is not felt till the dermis is reached. No blood flows from a cut in the epidermis only. A blister is an accumulation of water between the outer and the inner skin.

See Hair; Thorn; Perspiration; Albino; Leather.