HAIR. 



[ 307 ] 



HAIR. 



Fig. 301. 



// ^ / 



Magnified 250 diameters. 



Portion of the root of a dark hair, slightly acted upon by soda : 

 a, medulla, the cells still containing air ; h, cortex with pigment ; 

 c, inner cuticular layer ; d, outer cuticular layer ; e, inner layer 

 of the inner root-sheath ; /, outer perforated layer of the same. 



consisting of flat, imbricated, epi- 

 thelial scales. In the natural state 

 of the hair, the existence of these 

 scales is only indicated by the 



Fig. 303. 



wmmmm\ 



Magnified l60 diams. 

 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. 



displaced by the liquid; moreover, on drying 

 Fig. 302. 



Magnified 360 diameters. 



Medullary cells with pale nuclei and fatty granules, 

 from a hair treated with soda. 



the hair, the air and black appearance return. 

 PI. 22. fig. 1 represents a white hau% in 

 which the medullary cells of the lower part 

 are filled with Canada balsam, whilst those 

 of the upper portion still contain air. Again, 

 examination by reflected light is equally con- 

 clusive, for under it the black medullary por- 

 tions become white, which would not be the 

 case did the blackness arise from pigment. 

 PI. 22. fig. 9 illustrates this in the hair of 

 the Lion; where a represents the hair as 

 seen by transmitted, and h, 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. 



presence of irregularly transverse and ana- 

 stomosing lines seen upon the surface, or 

 shght dentation of the margin (fig. 70 A). 

 But when the hair has been treated with an 

 acid or an alkali, the scales become sepa- 

 rated. Their free margins are directed to- 

 wards the unattached end of the hair. The 

 scales are much more distinct without treat- 

 ment in the hair of the newly-born infant 

 (PI. 22. fig. 3). They are very transparent, 

 somewhat quadrangular, flattened or curved 

 cells (fig. 303 B), not containing a nucleus ; 

 their margins or edges are often black, and 

 as the other parts are transparent, they are 

 apt to be overlooked. 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 cuticular 

 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 out- 

 wards. These layers are best seen in a hair 

 treated with an alkali, especially with the aid 



x2 



