254 SKIN, HAIR, AND NAILS, BY ALFRED BIESIADECKI. 



it is requisite, according to Molesehott,* to take into considera- 

 tion, not only their strength, but the temperature at which they 

 are applied, and the duration of their action. 



In concentrated sulphuric acid the cuticle of the hair swells 

 to an extraordinary degree, forming a sheath to the hair sub- 

 stance that may even exceed the thickness of the hair itself. 

 When warmed to 40 50 C. (104 122 Fahr.), the cuticle 

 breaks up in a few hours into separate scales. 



It disintegrates more slowly in solutions of potash containing 

 4' 6 per cent., or in those of soda containing 3 per cent. In the 

 course of forty hours the cortex of the hair appears spiny, 

 owing to the elevation of the cells forming the cuticle that are 

 still adherent by their lower borders. 



The cortical substance of the hair, which can be split longi- 

 tudinally by mechanical means, breaks up, under the action of 

 concentrated sulphuric acid, into separate scales or laminae 

 (fibre cells), having a length of 0'05 0'08 of a millimeter, and 

 a breadth of 0*004 O'Ol of a millimeter, and containing thread- 

 like nuclei with a length of 0*02 0'03 of a millimeter. 



The medullary cells can be rendered very distinct by ma- 

 cerating hairs for a few days in a two per cent, solution of 

 potash. If the solution be stronger, they dissolve, and on the 

 addition of an excess of acetic acid to the solution, white pre- 

 cipitates are thrown down, that give Millon's and Fourcroy's 

 reaction. 



Very strong solutions of potash dissolve and destroy the 

 hair; in solutions of potash containing 4' 6 per cent, the sheath 

 of Huxley breaks up into its constituent cells, without swelling 

 up like the hair cuticle. 



The hair follicles vary in their length with the length and 

 thickness of the hair. Those of the long hairs of the head, 

 and thick ones of the beard, extend into the subcutaneous con- 

 nective tissue ; those of the larger hairs on the surface of the 

 body, as far as the lower part of the corium ; whilst the papillae 

 of the finest hairs (lanugo) are situated in the upper part of 

 the corium. They do not, however, run vertically, but always 

 form an acute angle with the surface of the corium. 



* Untersuchungen zur Naturlehre, Band iv., Heft 12. 



