72 



THE SKIN. 



glands, consisting in vesicular dilatations which communi- 

 cate with a general reservoir from which the secretion is 

 discharged into a hair-follicle, or occasionally on the surface 

 of the skin through a single aperture. These glands are 

 very fully developed in the dog, the sheep, and horse. 

 Ercolani has noticed the coalescence of two or more of these 

 saccular glands in the dog and sheep. 



Fig. 170. Fig. 171. 



Fig. 172. 



Fig. 170. (ERCOLANI. ) Simple oil-glands from near the foot of the sheep. 

 Fig. 171. Compound oil-gland from the skin of the mammae in the ewe,. 

 Fig. 172. o, Stem of hair; c, Hair bulb and follicle ; b, Sebaceous glands. 



So far, then, the skin is seen to consist in a vascular and 

 sentient membrane, provided with myriads of glands for the 

 purpose of secretion, containing fine networks of blood-ves- 

 sels and lymphatics for absorption, and, at the same time, 

 protected by layer over layer of horny scales, which especially 

 prevent the indiscriminate penetration of substances into the 

 body through its surface. 



The secretion by the skin is abundant from both kinds of 

 glands. The sweat-glands have been estimated in man as 

 not less than 2,300,000 in number, and the length of each 



