HAIR. 



[ 373 



the lower part are filled with Canada bal- 

 sam, whilst those of the upper portion still 

 contain air. Ap;ain, examination by reflected 

 light is equally conclusive ; for under it the 

 black medullary portions become white, 

 which would not be the case did the black- 

 ness arise from pigment. PI. 29. fig. 9 illus- 

 trates this in the hair of the Lion ; where 

 a represents the hair as seen by transmitted, 

 and b by reflected light. 



Cuticular coat. The shaft and root of 

 the hair, above the termination of the inner 

 root-sheath, are coated externally by a 

 firmly adherent, thin, simple, membranous 

 layer, consisting of flat, imbricated, epithe- 

 lial scales. In the natural state of the hair, 

 the existence of these scales is only indi- 

 cated by the presence of irregularly trans- 

 verse and anastomosing lines seen upon the 

 surface, or slight dentition of the margin 

 (fig. 298-4). But when the hair has been 



Fig. 298. 



HAIR. 



Fig. 299. 



Magnified 160 diameters. 



A, surface of the shaft of a white hair, the curved 

 lines indicating the free margins of the epidermic scales. 

 .B, scales isolated by the action of soda. 



treated with an acid or an alkali, the scales 

 become separated. Their free margins are 

 directed towards the unattached end of the 

 hair. The scales are much more distinct 

 without treatment, in the hair of the newly- 

 born infant (PI. 29. fig. 3). They are very 

 transparent, somewhat quadrangular, flat- 

 tened or curved cells (fig. 298 2?), not 

 containing a nucleus ; their margins or edges 



f / 



Magnified 250 diameters. 



Portion of the root of a dark hair, slightly acted upon 

 by soda : a, medulla, the cells still containing air ; 6, 

 cortex with pigment; c, inner cuticular layer; d, outer 

 cuticular layer; e, inner layer of the inner root-sheath; 

 /, outer perforated layer ol the same. 



are often black, and, as the other parts 

 are transparent, they are apt to be over- 

 looked. They are about 1-700 to 1-500" in 

 length, and one half or one third of this in 

 diameter. 



In the lower part of the root, below the 

 termination of the root-sheath, the cuticu- 

 lar coat is double, or consists of two layers. 

 The above-mentioned cuticle of the shaft 

 and upper part of the root forms the con- 

 tinuation of the innermost of these, which 

 possesses nearly the same structure, except 

 that the scales of which it consists are some- 

 what longer, and directed more obliquely 

 outwards. These layers are best seen in a 

 hair treated with an alkali, especially with 

 the aid of pressure ; they then become se- 

 parated (fig. 299), the inner, with the roo 

 of the hair, assuming an undulating form, 

 and remaining firmly adherent (c), whilst 

 the outer (d) remains attached to the inner 

 root-sheath, its cells also being broad and 

 without nuclei. At the bulb, both these 

 layers become transformed into soft cells 

 broader than long, with transverse nuclei, 

 finally becoming fused with the round cells 

 of the bulb. 



