HAIR. 



[ 305 ] 



HAIR. 



the bulb but contained within the folUcle, is 

 Fig. 296. 



-^i 





Blagnlfied 50 diameters. 



A hair of moderate size, contained in its follicle, a, 

 shaft ; b, root ; c, bulb or knob ; d, cuticle of the hair ; e, 

 inner sheath of the root ; /, outer sheath of the root ; g, 

 structureless membrane of the hair-follicle ; h, transverse 

 and longitudinal fibrous layer of the same ; i, papilla ; k, 

 excretory ducts of the sebaceous glands or follicles, with 

 their epithelial and fibrous layer ; I, cutis of the orifice of 

 the hair-follicle ; m, rete mucosum ; n, cutaneous epi- 

 dermis ; 0, termination of the inner sheath of the root. 



the root ih). The bulb encloses or surrounds 

 a conical or rounded body (i), the papilla or 

 pulp. 



Three varieties of hair are met with upon 

 different parts of the body : 1, consisting of 

 long, soft hairs, from 1 to 3" and more in 

 length, as the hair of the head ; 2, short, 

 rigid and thicker hairs, from 1-4 to 1-2" in 

 length, as in the eye-lashes; and 3, short, 

 very slender hairs, from 1-12 to 1-6" in 

 length, as in the down or woolly hairs of the 

 face, the back and extremities. 



When the shaft of a hair is examined 



under the microscope by transmitted light, 

 two structiu-es are mostly distinguishable, a 

 median, more or less black, somewhat irre- 

 gularly granular and linear portion — the 

 medulla or pith; and an outer, fibrous- 

 looking portion, mostly more or less coloured, 

 according to the colour of the hair, the cortex, 

 cortical or fibrous portion. 



The cortical portion is that upon which 

 the firmness, elasticity, and colour of the 

 hair depends, and constitutes the greater 

 portion of its bulk. It exhibits numerous 

 longitudinal striae, or interrupted dark lines 

 and dots. When acted upon by strong sul- 



Fig. 



297. 



Magnified 350 diameters. 



Plates and cells of the cortical substance of a hair, after 

 treatment with acetic acid. A, separated cells: 1, front 

 view (three of them isolated, two united) ; 2, side view. 

 B, a layer, composed of several cells. 



