OF THE HAT US. 



185 



of polygonal, elongated, transparent, and somewhat yellowish cells, all 

 of which have their longitudinal axes parallel to that of the hair (Fig. 68). 

 The outermost layer (Fig. 72, A\ which alone was formerly known, the 

 inner root-sheath of Henle is formed of elongated cells without nuclei, 

 0-016-0-02 of a line in length, and 0-004-0-006 of a line in breadth, 

 which are intimately connected, and in the ordinary mode of investiga- 

 tion, after the addition of acetic acid, caustic soda, or potassa, which 

 swell up the hair, or after the hair has been teased out, present elon- 

 gated fissures between them, whence they appear like a fenestrated mem- 

 brane. In quite recent hairs, however, if all reagents and mechanical 

 injury have been avoided, we see hardly any trace of apertures in the 

 upper half of the layer in question, and in the lowerh&lf (from the finely 

 fibrous part of the cortex upwards), at most mere indications of them, in 

 the form of striae, clear or dark, according as they are in or out of focus, 

 and similar to those of the cortex of the shaft. We can hardly avoid 

 supposing, therefore, that the openings as they are commonly seen 

 (0-005-0-008 of a line in length, and 0-001-0-03 of a line in breadth), 

 are produced artificially by the teasing out of the membrane. Secondly, 

 cells also occur in the root-sheath, between which gaps are never visible. 

 These (Fig. 72, B\ which form a simple or a double layer (Huxley's 



Fig. 72. 



layer), are constantly situated internal to the common, and as far as I 

 have seen, always single, fenestrated layer of cells ; they are shorter and 



FIG. 72. Elements of the inner root-sheath ; magnified 350 diameters. ^?, from the outer 

 layer, 1, its isolated plates; 2, the same in connection, from the 'uppermost parts of the layer 

 in question, after treatment with caustic soda: a, apertures between the cells, b; 7>, cells of 

 the inner not-perforated layer, with elongated and slightly notched nuclei; C, nucleated cells 

 of the lowest part (single layer) of the inner sheath. 



