182 SPECIAL HISTOLOGY. 



has a thickness of 0-0025 — 0-0035"'. Upon the bulb of the 

 hair, the two layers of cuticular plates pass with a tolerably 

 defined margin into soft nucleated cells, which are broad in 

 the transverse direction of the bulb, very short longi- 

 tudinally, and somewhat longer in their third diameter, 

 which stands perpendicularly or obliquely to the longi- 

 tudinal axis of the hair. They are readily attacked by 

 alkalies, or even by acetic acid, possess without excep- 

 tion transverse and longish nuclei, and finally pass, on the 

 bulb, into the already described, round cells of which it is 

 formed. 1 



i [We cannot agree with Prof. Kolliker that the cuticle of the hair passes into 

 the outer cells of the hulh. It may he 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 Anatomie,' PL 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 distinguishable 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 dis- 

 solves 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, colourless, and indepen- 

 dent sheath, even from the very darkest hairs; lastly, under favorable circumstances, 

 this reagent raises up a definite basement membrane from the outer surface of the 

 lowest part of the bulb, in immediate contact with the rounded "nuclei" of this part, 

 and this basement membrane may be traced upwards into direct continuity with the 

 homogeneous portion of the cuticle above-described. (In the ' Edinburgh Monthly 

 Journal of Medical Science,' for March, 1853, Mr. Dalzell states that the papilla of 

 the hair has a basement membrane. Is it this structure to which he refers?) In all 

 cases in which, in man or in animals, we have isolated the hair-bulb from its sac, it 

 seemed to have a definite limiting outer line down to the narrow neck by which it 

 passes into the hair-sac, though it was not often easy to obtain evidence that this 

 limiting line was the expression of a distinct basement membrane. However, the 

 same difficulty would occur with any dermic papilla; and it seems to us that there is 

 sufficient evidence to show that the cuticle of the hair is not the product of any 

 direct metamorphosis of cells, but represents a modified basement membrane 

 with a subjacent layer of peculiarly-altered blastema, corresponding precisely 

 with t lie " Nasmyth's membrane" and the enamel of the teeth. Vide infra, § on 

 Teeth.— Ens.] 



