STRUCTURE OF THE HAIR. 253 



double or triple series of non-nucleated cells surround the shaft 

 of the hair. 



At the level of the neck of the hair follicle the hair shaft is 

 invested by four or five rows of epidermic cells. In the excre- 

 tory passage of the hair follicle, which may contain two hairs, 

 each hair is surrounded by multiple layers of epidermal cells 

 (modified sheath of Huxley, together with the internal root- 

 sheath of Henle), that are again included by epidermic layers 

 (constituting the horny layer of the excretory passage). 



Transverse and longitudinal sections show also (1) that the 

 horny substance of the hair is developed from the hair cells 

 that is to say, from the cells of the root surrounding the 

 papilla ; (2) that the cuticle of the hair is also formed from 

 the cells of the hair root ; (3) that the cuticle of the root- 

 sheaths and Huxley's sheath develop from the peripheric cells 

 of the hair root. And lastly, (i) that the internal root- 

 sheath of Henle corresponds to the horny layer of the external 

 root-sheath. 



The development of the constituents of the hair shows also 

 that the sheath of Huxley, in opposition to the views of Kolli- 

 ker, must grow like the hair itself; that the hair is not thrust 

 upwards within the cuticle of the root-sheath, but between 

 Huxley's sheath and the internal root-sheath of Henle; and 

 that the latter, corresponding to the constantly advancing 

 horny layer of the external root-sheath is likewise thrust 

 outwards through the neck of the hair follicle. 



The forces by which these movements are effected are 

 (1) The constant production of new cells on the papilla at the 

 root of the hair, and (2) the pressure that the internal sheath 

 of the follicle, tightly embracing the root-sheaths, exercises in 

 forcing the contents of the follicle through the excretory 

 passage. 



The cells forming the deeper parts of the hair root resemble 

 those of the rete mucosum in their chemical characters. Acetic 

 acid renders the protoplasm more transparent, and the nucleus 

 more distinct. Dilute solutions of potash and soda cause them 

 to swell up, and then quickly dissolve both the cell and the 

 nucleus. 



In the description of the influence of reagents upon the hair 



