CUTANEOUS GLANDS. 



On the head they are set in groups, on the rest of the skin for the most part singly. 

 Except those of the eyelashes, which are implanted perpendicularly to the surface, 

 they have usually a slanting direction, which is wonderfully constant in the same 

 parts. 



Chemical nature. The chemical composition of hair has been investigated princi- 

 pally by Vauquelin, Scherer, and Van Laer. When treated with boiling alcohol, and 

 with ether, it yields a certain amount of oily fat, consisting of margarin, margaric 

 acid, and olein, which is red or dark coloured, according to the tint of the hair. The 

 animal matter of the hair thus freed from fat, is supposed to consist of a substance 

 yielding gelatine, and a protein compound containing a large proportion of sulphur. 

 It is insoluble in water, .unless by long boiling under pressure, by which it is reduced 

 into a viscid mass. It readily and completely dissolves in caustic alkalies. By calci- 

 nation, hair yields from 1 to 1^ per cent, of ashes, which consist of the following ingre- 

 dients viz., peroxide of iron, and according to Vauquelin, traces of manganese, silica, 

 chlorides of sodium and potassium, sulphates of lime and magnesia, and phosphate of 

 lime. With the exception of the bones and teeth, no tissue of the body withstands 

 decay after death so long as the hair, and hence it is often found preserved in 

 sepulchres, when nothing else remains but the skeleton. 



Glands of the skin. These are of two kiiids, the sweat-glands, and the 

 sebaceous, which yield a fatty secretion. 



Fig. CXXIII. 



Fig. CXXIV. 



,-cf 



Fig. CXXIII. VERTICAL SECTION OP THE SKIN AND SUBCUTANEOUS TISSUE, FROM END 

 OP THE THUMB, ACROSS THE RIDGES AND FURROWS, MAGNIFIED 20 DIAMETERS (from 

 Kolliker). 



a, horny, and 6, mucous layer of the epidermis ; c, corium ; d, panniculus adiposus ; 

 c, papillae on the ridges ; /, fat-clusters ; </, sweat-glands ; 7t, sweat-ducts ; i, their 

 openings on the surface. 



Fig. CXXIV. MAGNIFIED VIEW OP A SWEAT-GLAND, WITH ITS DUCT (after Wagner). 



a, the gland surrounded by vesicles of adipose tissue ; 6, the duct passing through the 

 corium ; c, its continuation through the lower, and d } through the upper part of the 

 epidermis. 



p 2 



