SECT. 63.] HAIRS. I 13 



the latter, also, the outermost cells are perpendicularly placed. 

 These last-mentioned cells are, in the negro, brown throughout, 

 and in the white races, at least in the hairs of the labia majora, are 

 brown in the upper part. At the bottom of the hair-follicle the 

 external sheath, while its cells become gradually round, passes 

 continuously, and without any boundary line, into the round cells 

 of the hair-bulb which cover the papilla. The external root-sheath 

 is generally about 3 to 5 times as thick as the internal ; but not 

 unfrequcntly it becomes somewhat attenuated superiorly, and 

 below is invariably prolonged into a very thin lamella. In coarse 

 hairs, it measures in the middle of the root 00 18'" to crc^'", and 

 possesses 5 to 1 2 layers of cells. 



The internal root-sheath is a transparent membrane, which ex- 

 tends almost from the bottom of the hair-follicle over nearly two- 

 thirds of it, and then ends abruptly. It is connected externally 

 with the outer sheath, internally with the cuticle of the hair, so 

 that, in the normal condition, no space is found between it and the 

 hair. It is especially characterised by its great firmness and elas- 

 ticity, and consists, except in its lowest part, of two layers, the 

 proper internal sheath and the cuticle, which, in order to distinguish 

 it from that of the hair, must be designated the cuticle of the 

 internal root-sheath. 



The proper internal sheath presents two, or even three layers of 

 polygonal, elongated, transparent and somewhat yellowish cells, all 

 of which lie with their longitudinal axes parallel to that of the 

 hair. The most external layer (fig. 50, A.), is formed of elongated, 

 non-nucleated cells, o - oi6'" to o - 02'" in length, and - 004"' to 

 o - oo6'" in breadth, which are intimately united in the longitudinal 

 direction; and in the usual method of examination, after the 

 addition of acetic acid, soda, or potass, which make the hair swell 

 up, or after it has been teased out, exhibit elongated narrower and 

 wider fissures, thus presenting the appearance of a fenestrated 

 membrane. In perfectly fresh hairs, however, if all re-agents and 

 mechanical violence be avoided, for the most part not a trace of 

 openings is seen in the upper half of the layer in question ; and in 

 the lower (from the finely fibrous part of the cortex downwards), 

 at the most only indications of them, in the form of bright or 

 dark streaks (according to the focus), similar to those of the fibrous 

 substance of the shaft. We are forced, therefore, to regard these 

 openings as they are commonly seen (o - oo5'" to croo8"' in length, 

 and cool'" to 0'003'" in breadth), as produced artificially by the 

 tearing of thj membrane. Secondly, cells also occur in the root- 



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