108 HAIRS. [SECT. 59. 



in white and fair hairs, but they are absent in quite dark hairs, 

 and in the lower half of the roots of all hairs. 



Lastly, there occur in the fibrous substance other moderately 

 dark slender streaks, or lines, which are, 1. the boundary lines 

 of the fibre-cells, and 2. their nuclei. All the plates of the 

 fibrous substance in the shaft of the hair contain spindle-shaped 

 nuclei, of o-oi'" to o-i6'" long, and 0-0005'" to 000 12'" broad, 

 which can be isolated by crushing white hairs which have been 

 boiled in caustic soda. Moreover, fine streaks of another kind are 

 observed in the fibrous substance, and especially in a ivhitish part 

 immediately above the bulb, which are produced by inequalities on 

 the surface of the plates forming the tissue. 



The above description of the cortex, or fibrous substance, is 

 especially applicable to the shaft of the hair. In the root, also, 

 so far as it is hard and dry, essentially the same conditions are 

 found; in its loAver half, where it gradually becomes softer, 

 finely fibrous, and then granular, the structure, too, becomes gra- 

 dually altered. Here the above-described plates become softer, 

 and assume more and more distinctly the form of elongated cells, 

 of o - o2o'" to 0024'" long, and o^ooo/" to o-on'" broad, whose 

 cylindrical, straight, or serpentine nuclei, of 0008'" to coi"', 

 become very perceptible on the addition of acetic acid, and can be 

 easily isolated. While the fibrous character thus becomes more 

 and more indistinct, the soft and shortened plates pass into oblong 

 roundish cells, with short nuclei, which, finally, are continued 

 without interruption into the elements of' the lowermost thickest 

 part of the hair, the bulb. These are round cells,, of o - oo3'" to 

 o'oo6'"j which lie closely packed together, and, like the cells of the 

 mucous layer of the epidermis, sometimes contain only colourless 

 granules, sometimes are so filled with dark pigment-granules, that 

 they are changed into true pigment-cells. We have still to men- 

 tion, that the chemical properties of the elements of the fibrous 

 substance are altered at the lower half of the root, inasmuch as 

 they become more easily affected by acetic acid, which does not act 

 upon the plates of the shaft at all, and also swell up and dissolve 

 in alkalies much quicker than in the shaft. 



The colour of the fibrous or cortical substance depends, firstly, 

 upon spots of pigment; secondly, upon air-cavities; and thirdly, 

 upon a colouring matter combined with the substance of the 

 plates constituting the tissue. 



§ 59. The medullary substance, substantia medullaris, oy pith, is 



