APPENDAGES OF THE SKIN. 81 



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 cold, retains 

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

 lungs, nose, ears, etc. The color is due to the pigment matter, which, in 

 old age, becomes more or less whitened. 



The Sebaceous Glands, imbedded in the true skin, are simple and 

 compound racemose glands, opening, by a common excretory duct, upon 

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

 all portions 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 lubricated and the hairs softened ; it is quite abundant in the region 

 of the nose and forehead, which often present a greasy, glistening appear- 

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



The Vernix caseosa which frequently covers the surface of the foetus at 

 birth consists of the residue of the sebaceous matters, 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 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 subcutane- 

 ous tissue; average the -^ 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 1.003 or J-OO4- 



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. 



The elimination of the sweat is not intermittent, but continuous ; but it 



