152 SKIN AND ITS APPENDAGES. 



upon the shaft of the hair, it ceases abruptly at 

 the commencement of its root. Leydig has repre- 

 sented, as the epidermis of the root of the hair, a 

 layer of cylindrical cells, which are arranged perpen- 

 dicularly to its surface, but their existence is by no 

 means constant. 



?tence al sub " The cortical substance, the color of which varies 

 with the hair, is marked by longitudinal striae and 

 linear spots, which run in the same direction (PL 

 XXIV. fig. VII. 2). The elements of which it is 

 composed cohere very closely, but, by the aid of 

 caustic potassa, they can be readily separated and 

 recognised as long fusiform bodies, homogeneous in 

 their structure, without trace of nuclei, and contain- 

 ing, sometimes, pigmentary granules. The dark 

 linear spots seem to be simply cavities filled with air, 

 for they are found in white, as well as in colored 

 hairs (PI. XXV. fig. I). 



In the root of the hair the cortical substance pre- 

 sents again a different appearance ; in the bulb we 

 find regular polygonal cells with clearly defined 

 nuclei, and granular contents sometimes transparent 

 and at others charged with pigment (PL XXV. fig. 

 II. 6). A little higher up, these cells, and their 

 nuclei also, become elongated, and the outlines of the 

 cells gradually grow pale and disappear, whilst their 

 nuclei continue to elongate, and remain visible. They 

 finally, however, become pale and disappear also, or, 

 perhaps, they are converted into the fusiform bodies 

 of the cortical substance after their cell walls are 

 absorbed ? 

 sub- r me( j n n ar y cana i <j oeQ no t always exist, and, 



