419 



CHAPTER XIV. 



THE SKIX AXD ITS SECBETION. 



To complete the consideration of the processes of organic 

 life, and especially of those which, by separating materials 

 from the blood, maintain it in the state necessary for the 

 nutrition of the body, the structure and functions of the 

 skin must be now considered: for besides the purposes 

 which it serves (i), as an external integument for the 

 protection of the deeper tissues, and (2), as a sensitive 

 organ in the exercise of touch, it is also (3), an important 

 excretory, and (4) an absorbing organ; while it plays a 

 most important part in ( 5 ) the regulation of the tempera- 

 ture of the body. 



Structure of the Skin. 



The skin consists, principally, of a layer of vascular 

 tissue, named the corium, derma, or cutis vera, and an 

 external covering of epithelium termed the cuticle or 

 epidermis. Within and beneath the corium are imbedded 

 several organs with special functions, namely sudoriparous 

 glands, sebaceous glands, and hair-follicles ; and on its sur- 

 face are sensitive papillce. The so-called appendages of 

 the skin the hair and nails are modifications of the 

 epidermis. 



Epidermis. The epidermis is composed of several layers 

 of epithelial cells of the squamous kind (p. 30), the deeper 

 cells, however, being rounded or elongated, and in the 

 latter instance having their long axis arranged vertically 

 as regards the general surface of the skin, while the more 



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