OF THE HAIRS. 181 



parent (fig. 70 B), which do not swell up into vesicles by the 

 action of any reagent, 



and disposed in an im- ,g ' 



bricated manner, form ' . 



a simple membrane £ I 



which completely sur- i ; I 



rounds the cortex of W 

 the hair, in such a [ 

 way, that the deeper or 

 lower cells cover the 

 upper ones. By sulphuric acid also, the structure of the epider- 

 mis is readily made out ; the hair is, as it were, bristled at the 

 edges with the erected plates and by scraping or rubbing, the 

 cuticle is less easily obtained in large larnellse, but is readily 

 enough reduced to its elementary parts. 



On the shaft of the hair the cuticle consists only of a single 

 layer of plates 0*002 — 0-003'" thick, which measure 0-024 — 

 0028"' in the transverse direction of the hair ; 0-016 — 0-02'" 

 in that of its length ; and are hardly more than 0-0005'" in 

 thickness. The same structure exists also in the upper part of 

 the root of the hair ; at its lower part, on the other hand, so 

 far as the inner root sheath extends, two layers of the epidermis 

 constantly occur. The outer (fig. 68 d) is rendered especially 

 obvious by the action of soda or potass, and Avith a little 

 pressure frequently comes away from the hair with the inner 

 root sheath, whilst the inner layer becoming undulated, remains 

 lying upon the cortical substance, and may be easily studied, 

 as well in the side view as upon its surface. In hairs that are 

 torn out, this layer is found only where they are covered by 

 the inner root sheath, otherwise it remains behind in the hair- 

 sac. Its elements also, are broad cells without nuclei, covering 

 one another like tiles, which do not swell up in alkalies, and 

 are soluble with great difficulty; they are thicker than those of 

 the other layer, and measure only 0-002 — 0-004'" in the 

 direction of the length of the hair. The whole outer laver 

 measures 00016 — 0-002"', whilst the inner layer upon the root 



Fig. 70. A, surface of the shaft of a white hair, x 160; the curved lines mark 

 the free edges of the epidermic plates : B, epidermic plates from the surface, isolated 

 by the action of caustic soda, x 350. One or both of their longer edges are bent 

 round, and so appear dark. 



