" 394 THE EXCRETIONS OF THE BODY 



SECOND SECTION 



EXCRETION THROUGH THE SKIN 



Various substances are eliminated by the skin through the sebaceous and 

 sweat glands, as well as through the so-called insensible perspiration. And 

 yet secretion through the skin has an essentially different purpose from the 

 excretion of urine and faeces, for its object is partly to protect the skin from 

 various sorts of injuries, partly to play a leading part in the regulation of 

 the body temperature. 



1. THE SEBACEOUS GLANDS 



With the exception of the palm of the hand and the sole of the foot, the 

 skin everywhere contains sebaceous glands, which secrete the so-called sebum. 

 Freshly secreted, this is an oily, semifluid mass, which hardens into a shining 



FIG. 146. Portion of the preputial gland of the mouse, after treatment with osmic acid, after 



Altmann. 



greasy coat on the surface of the skin, and consists of proteid substances, fat 

 and cholesterin. By means of this secretion the skin is oiled and is thereby 

 rendered soft, pliant and almost impervious to water. Even after a warm 

 bath, only those parts of the skin which contain no sebaceous glands exhibit 

 distinct traces of the effect of water. The skin in a bath at 32.5 C. takes 

 up about 0.0006 g. of water per square centimeter of surface, and in a bath at 

 39.5 C., 0.0048 g. For the entire skin (2 sq. m.) this would amount to 12 

 and 96 g. respectively (Spitta). The hair also owes its pliancy to the sebum. 



Fig. 146, which represents a portion of the preputial gland of a mouse, will 

 give some idea of the formation of the sebum. The vesicular end of the fundus 

 is filled with spherical granules, the periphery of which is formed by a fatty 

 membrane of greater or less thickness. Nuclei and cell boundaries are not visible, 

 being obscured by the granular structures. In the middle portion of the fundus 

 we see the ring-shaped granules more and more fused together, until in the 

 mouth a compact black mass is formed. We find the same black-colored secre- 

 tion throughout the ducts of the gland (Altmann). 



Certain experimental facts appear to indicate that the secretion of sebum 

 is under the influence of the sympathetic nerves (Arloing). 



