THE HAIR AND NAILS 389 



epidermis becomes thick, forming a callus. A corn is a 

 thick layer of epidermis cells formed at one spot. It 

 hurts because it is pressed, by the shoe, into the true skin 

 beneath. 



The dermis, or true skin, is much thicker than the 

 epidermis. It is made up of tough fibers of connective 

 tissue, and has blood vessels and nerves. The surface of the 

 dermis has little elevations called papillae, some of which 

 contain the bodies that bring about the senses of touch 

 and of temperature (cf. 410). On the inner side of the 

 hands and fingers the papillae are arranged in rows . A layer 

 of fat is generally found under the dermis (cf. 369). 



The color of the skin is due to coloring matter in the 

 lower layers of epidermis cells. When the skin is tanned 

 by wind and sun, the coloring matter is increased. 

 Freckles are spots of coloring matter in the epidermis. 



393. The Perspiration. The perspiration is the liquid 

 poured out upon the skin by the sweat glands (Fig. 291). 

 These glands are tubes coiled at their lower ends, and set 

 into the lower part of the dermis. Their purpose is to 

 cool the body (cf. 74) . It is only when we are very hot 

 that the sweat collects on the skin in drops (sensible 

 perspiration). Ordinarily the perspiration is not noticed 

 (insensible perspiration). The sweat glands are under 

 the control of the nervous system; much or little perspira- 

 tion is given off, according as the body needs to give off 

 heat, or to retain it. 



394. The Hair and Nails. The hair and nails (Fig. 292) 

 are made of cells of the epidermis, but they have taken 



