354 EXCRETION 



parts of the body, being thickest at points where there is 



greatest friction, as on the sole of the foot and the palm 



of the hand. 

 The inner layer, or dermis, contains the blood vessels, 



nerves, and various kinds of glands, and is easily recognised 



by its pink color. 

 Epidermis. — Examination with a microscope shows this 



layer to be composed of many cells held together by a 

 sort of cement. The lowest layer is 

 made up of a single row of active, 

 columnar, epithehal cells. These 

 cells absorb nourishment from the 



^ ,«n T. t- * *v, blood and lymph of the dermis. 



Fig. 162 — Portion of the epi- J L ' 



dermis, showing the transi- g^j^^J j^y oroMiih, produCC Other Cells 

 tlon from the loAver living i . o ; i 



cells to the upper horny wliich are gradually pushed up- 

 °°*^^^' ward. In this upward movement 



they gradually lose their columnar shape, and become 

 flattened, so that the upper layers of the epidermis consist 

 mainly of flattened cells. Gradually, too, the protoplasm 

 of these cells dries up and they are transformed into flat, 

 horny scales which make up the uppermost layer of the 

 epidermis. These outer horny scales are being constantly 

 worn away and renewed from below, and the epidermis, 

 as a whole, shows transition stages of cells from the active 

 cokunnar layers near the dermis, to the dead horny outer 

 layer above. Scattered among these cells may be found 

 occasional cells which contain pigment or coloring matter. 

 These are called pigment cells, and in the negro race they 

 are very abundant and give the black color to the skin. 

 The distinction between a blonde and a brunette is merely 

 a difference in the number of these pigment spots or cells. 

 Freckles are due to the collecting of these cells in spots. 



