TISSUES OF THE BODY. 



391 



. 391. Cells of the root-sheaths. In- 

 ternal root-sheath, with Henk"s layer, 

 a; and Huxley's, b; c, cells from the 

 external sheath. 



outer by its lighter and more transparent appearance : it is, "besides, 

 thicker (fig. 389, d; 390, c, d). Two strata of large cells may be 

 remarked in it. The external (fig. 390, d; 391, a) (the root-sheath of 

 Herile) consists of transparent ovoid cells without nuclei, between 0*0377 

 and 0'0451 mm. in diameter. Between 

 these may be observed small narrow clefts, 

 which can be rapidly increased in size 

 by pressure, &c., owing to the brittle 

 nature of the whole mass. Within this, 

 again, there appears either a single or 

 double layer of cells first seen by Huxley 

 (fig. 390, c; and 391, b). These elements 

 are likewise transparent and polyhedral, 

 owing to pressure one against another. 

 Their axis parallel to that of the hair 

 is short, while their radial diameter 

 exceeds that of the elements compos- 

 ing Hentts layer (fig. 390, c, d). The 

 most important point of distinction be- 

 tween them, however, js that the cells of 

 Huxley's layer possess small narrow nuclei, 

 bringing to our recollection the appear- 

 ance of nail-cells seen from the side (p. 

 162, fig. 156). 



Below, towards the fundus of the hair follicle, the internal sheath con- 

 sists of only one layer of nucleated cells, which may be continuous with 

 the peripheral elements of the hair-bulb. Above, towards the outlet of 

 the follicle in the neighbourhood of the sebaceous glands, it ends, how- 

 ever, with a sharp, jagged border. 



214. 



We come now to the proper hair, into the bulb of which, as it rests on 

 and overlays the papillae, the cellular strata of the external and internal 

 root-sheaths are continued. 



In the hair-bulb (fig. 392, h), throughout its whole substance, with 

 the exception of a thin coating, the same small, round, and densely- 

 crowded cells are to be seen as those which form the external root-sheath 

 (fig. 393, a). Their contents are either colourless molecules, or there 

 appear in them (at one time in small quantity, at another in larger propor- 

 tion) granules of pigment varying in tint with the colour of the hair. 



Above, however, the nature of these cells is changed, and in many 

 hairs a contrast is distinctly seen, owing to the metamorphosis, between 

 the axial and peripheral portion ; we then speak of the medullary mass 

 (fig. 392, k) and cortical substance (I). 



In the ;first place, the cells of the latter become ovoid, while the 

 nucleus still preserves its original spherical form. Higher up we find 

 these cells transformed, through flattening, into a plate of 0'0451 mm. 

 and upwards in length, whose nucleus has become likewise long, narrow, 

 and rod-like (fig. 393, b). Higher still, where the stem has attained the 

 hard horny consistence of the shaft, the cells acquire the nature of thin 

 and flat oval plates, with irregular outline (c, d), with an increase in 

 length to about 0'0751 mm., the transverse diameter sometimes falling to 

 0'0045 mm. Their nuclei are either changed into very thin filiform 

 26 



