SKIN. l6l 



The root of the hair is embedded in the hair-follicle, formed by a tubular 

 depression of the skin, extending nearly through to the subcutaneous tissue; 

 its walls are formed by the layers of the corium, covered by epidermic cells. 

 At the bottom of the follicle is a papillary projection of amorphous matter, 

 corresponding to a papilla of the true skin, containing blood-vessels and 

 nerves, upon which the hair-root rests. The investments of the hair-roots 

 are formed of epithelial cells, constituting the internal and external 

 root-sheaths. 



The hair protects the head from the heat of the sun and from the cold, 

 retains the heat of the body, prevents the entrance of foreign matter into 

 the lungs, nose, ears, etc. The color is due to pigment matter. In old age 

 the hair becomes more or less whitened. 



The sebaceous glands, embedded in the true skin, are simple and com- 

 pound racemose glands, opening, by a common excretory duct, upon the 

 surface of the epidermis or into the hair-follicle. They are found in all por- 

 tions of the body, most abundantly in the face, and are formed by a delicate, 

 structureless membrane, lined by flattened polyhedral cells. The sebaceous 

 glands secrete a peculiar oily matter (the sebum), by which the skin is lubri- 

 cated and the hairs are softened; it is quite abundant in the region of the nose 

 and forehead, which often presents a greasy, glistening appearance; it 

 consists of water, mineral salts, fatty globules, and epithelial cells. 



The vernix caseosa, which frequently covers the surface of the fetus at 

 birth, consists of the residue of the sebaceous matter, containing epithelial 

 cells and fatty matters; it seems to keep the skin soft and supple, and guards 

 it from the effects of the long-continued action of the amniotic water. 



The sudoriparous glands excrete the sweat. They consist of a mass 

 or coil of a tubular gland duct, situated in the derma and in the subcutaneous 

 tissue, average J~ of an inch in diameter, and are surrounded by a rich 

 plexus of capillary blood-vessels. From this coil the duct passes in a straight 

 direction up through the skin to the epidermis, where it makes a few spiral 

 turns and opens obliquely upon the surface. The sweat-glands consist of a 

 delicate homogeneous membrane lined by epithelial cells, whose function is to 

 extract from the blood the elements existing in the perspiration. 



The glands are very abundant all over the cutaneous surface as many 

 as 3528 to the square inch, according to Erasmus Wilson. 



The perspiration is an excrementitious fluid, clear, colorless, almost 

 odorless, slightly acid in reaction, with a specific gravity of 1003 to 1004. 



The total quantity of perspiration excreted daily has been estimated 

 at about two pounds, though the amount varies with the nature of the food 

 and drink, exercise, external temperature, season, etc. 

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