Structure of the Skin

The structure of the skin is far more complex than appears on first glance. Most aston­ishing, perhaps, is the fact that the outer skin, the visible surface of the body, is composed of dead rather than living tissue. This same fact is true of the fingernails and toenails and the hair. They grow, obviously from the inside out. The cells thus appearing on the outer surface of the body are no longer alive. They have turned into a highly insoluble form of protein, called keratin, which is also found in the horns and hooves of lower animals.

The outer layer of the skin, composed of dry, dead cells, which are more or less flat­tened out and overlap each other somewhat like shingles on a roof, is sometimes called its "horny layer." These cells are constantly being shed and replaced by new cells, which take their origin in the germinative layer of the skin. This growing layer is made up of what are called Malpighian cells, named after Malpighi, the Italian anatomist, who first identified them.

The pigments which largely, though not altogether, determine the color of the skin are found in the Malpighian layer of cells. The color differences among the races of man­kind,  and  many of the social implications which follow, are thus crucially determined by the amount of skin pigment in the Mal pighian cells.

The outer layers of the skin are called the epidermis. Beneath is the dermis or true skin, also called the corium. This is tough, fibrous living tissue with undulating surfaces that pentrate into the epidermis above and into the subcutaneous tissue below. These undu­lations form series of ridges which are evident on epidermis, especially on the hands and feet. They create the unique pattern of the individual's fingerprints.

The dermis is well supplied with blood ves­sels, small capillaries which can greatly ex­pand and contract under nerve impulses and thus help control body temperature. Blushing is the phenomenon that occurs when the blood vessels expand. In the true skin layer are also to be found lymph vessels, nerve endings, sweat glands, sebaceous glands, and hair follicles.

The sensory nerve endings in the skin are capable of reporting a variety of sensations to the brain as we have already pointed out.

The hair follicles are tiny tubes which harbor the hair roots, one hair to a follicle. As long as the follicle is not atrophied (worn out), injured, or diseased, the hair continues to grow.

The sebaceous glands usually lie close to the hair follicles. Their function is to secrete an oily substance, called sebum, which helps to keep the hair lustrous and the skin soft. An excessive secretion of sebum will produce such appearances as the shiny nose and may be responsible for acne. The glands of the outer ear canal, which secrete ear wax, are