=Parts of the Skin.=--The skin is about as thick as the leather of your shoe. It is fastened to the muscles beneath with fine white threads like spider webs. This is called _connective tissue_ because it connects the skin to the lean meat. The skin is made of two layers (Fig. 45). The upper layer is formed of cells. This is named _epidermis_ or _scarfskin_. The deeper layer is made largely of fine threads woven together. It is the _true skin_ or _derma_. There is no blood in the scarfskin, but there is a network of blood tubes in the true skin. It is the crowding of these with blood that makes the skin look so red when we get hot or excited. =The Use of the Skin.=--The skin has three chief uses. It protects the softer parts of the body from being hurt by rough or hard things which might touch it. It contains the organs of feeling. It helps keep the right amount of heat in the body. [Illustration: FIG. 45.--A thin slice through the skin, showing sweat glands, a nerve, and blood-tubes. Much enlarged.] The top part of the skin is dry and dead. This gives better protection than if it were moist and tender. Particles of it are wearing out and dropping off while other bits are growing beneath to take the place of the worn-out parts. The more this top skin is pressed on and rubbed, the thicker it becomes. For this reason it is twice as thick in the palms of the hand and on the soles of the feet. Scattered through the true skin are millions of tiny organs fastened to the ends of the nerve threads leading to the spinal cord and brain. These organs tell us when the skin is touched or when it is hot or cold or is being hurt. =The Pores and the Sweat Glands.=--On a warm day the skin becomes wet with a salty fluid called _sweat_ or _perspiration_. This flows from the tiny holes or pores in the skin. A good magnifying glass will show these pores arranged in rows on the ridges in the palm of the hand. From each pore a tube leads down into the true skin to a coiled tube forming the _sweat gland_ (Fig. 45). Sweat glands are present by the thousands in the skin of all parts of the body. They give out from one pint to a gallon of sweat daily. The more we work and the warmer the weather, the more the sweat flows. There is a little waste matter carried out of the body by the sweat, but its chief use is to cool the body. It does this by passing off in the air and carrying the heat with it. In this way the body is kept from getting too hot in summer. =The Color of the Skin.=--In the African race the color of the skin is black, in the Chinese it is yellowish, while in our race it is nearly white. The different hues are due to a coloring matter called _pigment_. This lies in the deep part of the scarfskin. Going out in the wind and sun causes more pigment to collect, and we say we are tanned. If the pigment collects in spots, it makes freckles.