154 THE SWEAT GLANDS. 



The dermis is richly supplied with blood capillaries and 

 with lymph capillaries, but the epidermis has neither. Each 

 papilla is abundantly supplied with blood, having its own net- 

 work of capillaries. 



Hairs and nails are outgrowths of the epidermis. Their 

 deeper parts are embedded in the dermis, through which, 

 from the blood, they derive their nourishment ; thus, like the 

 epidermis itself, they are dead in the outermost part, and 

 these parts are supplied by growth from beneath. 



The Sweat Glands. A model of a cross-section of the 

 skin, showing the glands, hairs, etc., is very helpful. 



The sweat glands are minute tubes whose inner ends are 

 closed, and whose outer ends open upon the surface of the 

 skin. Place a linen tester on the palm of the hand, and note 

 the openings of the ducts of the sweat glands, or sweat pores. 

 Count the pores within the square shown. Measure this 

 square, and then estimate the number of sweat glands to a 

 square inch of the palm. The tube going inward pursues a 

 corkscrew-like course through the epidermis, then becomes 

 straighter, and, having passed through the dermis, is coiled up 

 in a ball in the connective tissue lying just underneath the 

 inner skin. We can fairly well represent this gland as fol- 

 lows : Take a small rubber tube, say one foot long ; close one 

 end ; tie the half with the closed end into a globular knot ; 

 around and between the coils place a network of red cord to 

 represent -the blood capillaries, as there is a rich supply of 

 these blood tubes around the coil. The cells forming the 

 walls of the coiled part differ from those of the Duct, or 

 straighter part of the tube. As the blood flows around the 

 coil, it gives off lymph ; and from the lymph the cells of the 

 gland take certain waste matters, which are passed out to 

 the surface of the skin. There is also some muscular tissue 

 around the walls of the gland. 



