THE SKIN AND THE SKIN GLANDS 



1215 



In order to keep the cuticle supple and preserve it from the drying 

 effects of the atmosphere, it is kept constantly impregnated with a fatty 

 material known as sebum. This material is formed by the sebaceous glands, 

 which are distributed all over the surface of the skin wherever hair follicles 

 are to be found, the mouths of the glands opening into the hair follicles. A 

 sebaceous gland is a pear-shaped body, consisting of a secreting part and a 

 short neck opening into the follicle. The gland proper is composed of a 

 solid mass of cells. The outermost cells are flattened and generally show 



M if 



Stratum 

 corneum 

 Stratum 

 lucidum 

 Stratum 

 "granulosum 



Bete 

 mucosum 



r Cutis vera 



Jv 



FIG. 555. Vertical section through the skin of the palmar side of the finger, showing 

 two papillae (one of which contains a tactile corpuscle) and the deeper layer of 

 the epidermis. Magnified about 200 diameters. (SCHAFER). 



signs of proliferation. The cells lying internal to these are much larger, 

 and their protoplasm is transformed into a network, in the meshes of which 

 are granules which may show the reaction of fat. Further inwards the 

 protoplasmic network diminishes in amount, while the fatty granules increase 

 in size, so that, in the lumen adjoining the duct, we find only a mass of cell 

 debris and masses of fatty material. It has often been thought that the 

 secretion of sebum depended simply on a fatty degeneration of the cells. 

 The granules however, when they first appear, stain with acid fuchsin 

 rather than osmic acid, and one must regard the formation of sebum as an 

 act of true secretion, in which the secretory granules are gradually trans- 

 formed into the special constituents of the sebum. For it must be noted 

 that the sebum is not a true fat, nor does it correspond in composition with 



