EXCRETION. 



133 



Hairs and Nails. 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. Like the epidermis, they are dead in the 

 outermost part, and are supplied by growth from beneath. 



Examination of the Skin with a Lens. Place a linen tester, or 

 good pocket lens, 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. 



Epithelium or Epidermis 



Compound Glands 

 Fig. 51. Evolution of Glands. (After Landois and Stirling.) 



The Sweat Glands. The sweat glands are minute 

 tubes whose inner ends are closed, and whose outer ends 

 open upon the surface of the skin. The tube going 

 inward pursues a corkscrew-like course through the epi- 

 dermis, then becomes straighter, and, having passed 



