174 



SPECIAL HISTOLOGY. 



granules, which are deposited in the plates of the hair, are 

 especially frequent in dark hairs, and vary very much in 

 respect to their size and form. Dark spots of a second kind 

 are very similar to the pigment deposits, but turn out on 

 examination to be little cavities filled with air. They are best 

 studied in white hairs, where they cannot possibly be con- 

 founded with pigment. Here we see dispersed through the 

 whole cortical substance round dots of 00004 — 0008"', or 

 longish streaks of 0-004'" in length, 0-0004— 00008'" in breadth, 

 which, sometimes more scattered, sometimes more numerous 

 and arranged in irregular lines, run parallel with the axis of the 

 hair. The dark contours and somewhat clear centre of these, 

 attract attention at once, and call to mind fat granules, which, 

 in fact, for a long time I held them to be ; but they are nothing 

 but excessively minute cavities filled with air, which occur very 

 frequently also in fair, bright-brown, and bright-red hairs, often 



in very great numbers, while 



Fig. 65. 



A 



a 





they are wanting in very 

 dark hairs, and in the lower 

 half of the root of all hairs. 

 Thirdly, there occur in the 

 cortex, other tolerably dark 

 striae or lines, which in dark 

 hairs are commonly con- 

 nected with the pigment- 

 spots, in such a manner 

 that the striae form the ends of 

 the spots, or pass through them 

 axially; in white and pale hairs 

 they appear not unfrequently as 

 prolongations of the air cavities, 

 but in both kinds of hairs they 

 often occur independently, in va- 

 rious numbers and degrees of dis- 

 I hold these streaks, which are commonly most 

 distinct in pale or bright-brown hairs without any medulla, 



Fig. 65. A, a piece of a white hair after treatment with caustic soda, x 350 : 

 «, nucleated cells of the medulla without air; b, cortical substance with a fine fibril- 

 lation and prominent linear nuclei ; c, epidermis with its plates projecting more than 

 usual ; B, three isolated linear nuclei from the cortex. 



tinctness. 



