OF THE HAIRS. 181 



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

 the cuticle is less easily obtained in large lamellae, 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 of a line thick, which measure 0-024-0-028 of a 

 line in the transverse direction of the hair ; 0-016-0-02 in that of its 

 length ; and are hardly more than 0-0005 of a line in thickness. The 

 same structure exists also in the upper part of the root of th^ hair; 

 of its lower part, on the other hand, so far as the inner root-sheath ex- 

 tends, two layers of the epidermis constantly occur. The outer (Fig. 

 (68 d is rendered especially obvious by the action of soda or potassa, and 

 with 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 0-0020-004 of a line in the 

 direction of the length of the hair. The whole outer layer measures 

 0-0016-0-002 of a line, whilst the inner layer upon the root has a thick- 

 ness of 0-0025-0-0035 of a line. Upon the bulb of the hair, the 

 two layers of cuticular plates pass with ja, tolerably defined margin 

 into soft nucleated cells, which are broad in the transverse direction of 

 the bulb, very short longitudinally, and somewhat longer in their third 

 diameter, which stands perpendicularly or obliquely to the longitudinal 

 axis of the hair. They are readily attacked by alkalies, or even by 

 acetic acid, possess without exception transverse and longish nuclei, and 

 finally pass, on the bulb, into the already described, round cells of which 

 it is formed.* 



* [We cannot agree with Professor Kdlliker that the cuticle of the hair passes into the 

 outer cells of the bulb. It may be worth devoting a little space to this matter, as the whole 

 question of the homology of the hair essentially turns upon it. So far from being able to 

 trace the two layers of the cuticle into the round cells of the bulb, we find that they cease 

 somewhat suddenly when the shaft begins to expand, while its substance is fibrous-looking 

 and contains only much elongated nuclei. Below this point, as Henle has correctly, figured 

 in his " Allgemeine Anatomic," PI. I. Fig. 14, the transverse striations of the cuticle are 

 absent ; and if the cuticular layer be viewed in section, it will be seen to be composed of a 

 more transparent substance, which gradually becomes thinner until it is hardly distin- 

 guishable as a distinct layer, and at the same time loses the oblique lamination, which it 

 has above, where it is continuous with the two layers of the cuticle proper. The careful 

 addition of caustic ammonia is particularly fitted to demonstrate the structure of this part. 

 In the first place, it raises up the outer layer of the cuticle from the inner, and shows that 

 the former, at any rate, is not continuous with any cells; and secondly, it dissolves and 

 forces out the substance of the lower soft portion of the bulb, so that the lower part of the 

 cuticle may be obtained as a transparent, colorless, and independent sheath, even from 



