172 SPECIAL HISTOLOGY. 



duced. Chlorine bleaches them. The ash amounts to about 

 1 — 2 per cent., and contains oxide of iron (more in dark hair) ; 

 oxide of manganese ; silica (traces) ; phosphate of magnesia and 

 sulphate of alumina were found by Jahn in white hairs ; and 

 according to Laugin, copper occurs in the greenish hairs of 

 those who work in copper and brass. 



§ 56. 



With regard to their more intimate structure, two substances 

 may be distinguished in all hairs without exception, and in 

 many there are three : 1, the cortical substance, or better, 

 fibrous substance, which constitutes by far the most considerable 

 portion of the hair and determines its form ; 2, the cuticle, a 

 delicate external investment of the fibrous substance ; 3, lastly, 

 the central medullary substance, which is often absent. 



The cortical or fibrous substance is longitudinally striated, 

 very often presents dark dots, is streaked or spotted and except 

 in white hairs, in which it is transparent, is more or less deeply 

 coloured ; the colour is sometimes distributed through the 

 whole substance with tolerable regularity, sometimes more con- 

 centrated in certain elongated, granular spots. The more in- 

 timate structure of the cortex of the hair, and the signification of 

 its spots and stria?, cannot be properly understood without the 

 use of acids and alkalies (which afford important aid in the 

 investigation of the hairs in general) and other manipulations. 

 If a hair be treated with concentrated sulphuric acid at a warm 

 temperature, its fibrous substance is much more readily broken 

 up than before, into flat elongated fibres of various breadths 

 (commonly 0002 — , 005"'), which are characterised particularly 

 by their rigidity and brittleness, and by their irregular, even 

 notched, margins and ends : in pale hairs they are clear, and 

 in dark ones have a dark tinge. These so-called hair-fibres are 

 not, however, the ultimate elements of the fibrous substance; 

 each of them, in fact, consisting of an aggregation of flat, mode- 

 rately-long fibre-cells or plates, which may be found isolated 

 among the fibres after the thorough action of sulphuric acid. 

 These (fig. 64), which may best be named the plates of the 

 fibrous substance, or the fibre cells of the cortex, are flat and 

 generally fusiform, 0-024—0-033'" long, 0-002— 0004'", or even 

 0005" broad, 00012— 00016" thick, with uneven surfaces and 



