380 



MANUAL OF PHYSIOLOGY. 



SEBACEOUS GLANDS. 



These belong to the outer skin, and commonly open into the 

 follicles of the hairs, but also appear on the free surface of the 

 lips and prepuce, etc., where no hairs exist. 



The secretion cannot be collected in great quantity in a normal 

 condition, but, as far as can be made out, it is composed of neutral 

 fat, soap, and an albuminous body allied to casein, and organic 

 salts and water, about 60 per cent. 



The secretion seems to be made up of the remains of epithelial 



FIG. 166. 



Section of Skin showing the roots of three hairs and two large sebaceous glands (d). 



(Cadiat.) 



cells which are thrown off from the inner surface of the glands, 

 while they are undergoing a peculiar kind of fatty degeneration. 

 These cells gradually get quite broken down during their sojourn 

 in the gland alveoli, and the secretion is finally pressed out by 

 the smooth muscle band which commonly embraces the gland 

 and squeezes it against the hair follicle. 



This secretion, the use of which is to lubricate the surface with 

 a fatty material, is cast off with the desquamated epithelium and 

 the hairs. The Meibomian glands of the eyelids are analogous 



