THE SKIN 21 



A rough prominence formed by several papillae 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 occu- 

 pied 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 swell- 

 ings 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 per- 

 spiration. 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 exer- 

 cise 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 flow- 

 ing in the skin loses some of its heat to the cool air in con- 

 tact with the skin. 



Effects of Alcohol upon the Skin. — The more blood 

 goes to the skin, the more blood is cooled. The body 



