A rough prominence formed by several papillæ growing through the epidermis at a weak spot and enlarging is called a . Small patches of pigment developing on the hands and face from much exposure to the sun are called . The growth of exposed dermis sprouting through an opening in the epidermis due to accident is called . (This should be scraped off and cauterized to aid the epidermis to grow over it again.) Sometimes a cut heals in such a way that no epidermis and therefore no pigment cells cover the place of injury, which is occupied only by white fibrous tissue (cicatricial tissue) of the true skin. In this case the mark left is called a cicatrice or . If pores or the openings of oil glands become clogged, but not enlarged, little swellings called may result. An enlarged pore filled with oil and dirt is called a . A spot present since birth, dark with pigment, and often containing hairs and blood vessels, is called a .
Regulation of Temperature.—As is well known, rapid
running or violent exercise of any kind causes profuse perspiration.
The sweat glands are connected with the brain
by means of nerves, and when the body has too much heat,
a nerve impulse from the lowest part of the brain causes the sweat glands to form sweat more rapidly. Heat and exercise
may cause the activity of the sweat glands to increase
to forty times the usual rate. The evaporation of the sweat
cools the body, for a large amount of heat is required to
evaporate a small amount of water (Exp. 4 and 5). This
is shown by the cooling effect of sprinkling water on the
floor on a warm day. By fanning we hasten the cooling
of the body (Exp. 4).
Exercise tends to heat the body, but it also causes us to breathe faster and causes much blood to flow through the skin. Both of these effects aid in cooling the body, for the cool air is drawn into the lungs, becomes warm, and takes away heat when it leaves; and the warm blood flowing in the skin loses some of its heat to the cool air in contact with the skin.
Effects of Alcohol upon the Skin.—The more blood goes to the skin, the more blood is cooled. The body
