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STUDIES IN PHYSIOLOGY 



If one examines the surface of the skin with a good hand 

 lens, one can detect the openings of the sweat tubes dotting 

 the tops of the ridges, and on a warm day the tiny drops of 

 perspiration can be seen oozing from these pores (Fig. 108). 



Structure of the Epidermis. In a section through the skin 

 one can easily distinguish the dermis from the epidermis. 

 The latter is composed of many layers of cells piled on each 



Horny layer. 



Epidermis. 



Columnar cells. 



Papillae of dermis 



containing blood 



vessels. 



Dermis. 



Nervous papilla 

 of dermis. 



FIG. 109. Vertical Section of Skin, highly magnified. 



other. On the outside surface, however, it is impossible 

 to make out the separate cells, for this horny portion of the 

 skin (Fig. 109) is composed of thin scales united by a cement 

 substance. We shall soon see that these dead scales, which 

 are easily rubbed from the surface, were once living cells. 



In the deepest part of the epidermis is a single layer of 

 columnar cells standing on end (Fig. 109). These are the 

 most active cells of the epidermis. They absorb nourishment 

 from the lymph that oozes from the blood vessels running 

 through the dermis, they grow, produce new cells by division, 



