OF THE UAIHS. 



175 



manner the cortical substance, which constitutes the principal bulk of 

 the hair, is produced. 



The dark spots, dots, and streaks of the cortex, are very various in 

 their nature, and are principally : 1, (jranular jiigment ; 2, cavities 

 filled -with air or Jhiid; and 3, nuclei. The action of caustic potass and 

 soda, which soften and swell up the cortical substance without attack- 

 ing the spots (Fig. 67), shows that they are in great measure nothing 

 but aggregations of pigment 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 tvith air. They are best studied in white hairs, where they 

 cannot possibly be confounded with pigment. Here we see dispersed 

 through the whole cortical substance round dots of 0-0004-'0008 of a 

 line, or longish streaks of 0'004 of a line in length, 0'0004-0'0008 of a 

 line 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 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 stria? 



or lines, which in dark hairs are jj , ' Ml' Us3 1''' ilMil liii *^jI 

 commonly connected with the pig- 

 ment-spots in such a manner that |i 

 the striiB 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 various numbers and degrees of 

 distinctness. I hold these streaks, 

 wliich are commonly most distinct in 

 pale or bright-brown hairs without 

 any medulla, to be sometimes the ex- 

 pression of the composition of the hairs by the above described fibre- 



FlO. 65. — J, a piece of a white hair after treatment with caustic soda; magnified 350 

 diameters: a, nucleated cells of the medulla without air; 6, cortical substance with a fine 

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

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



Pi- 

 a" 



65. 



