176 SPECIAL HISTOLOGY. 



of the raucous layer of the epidermis, sometimes contain only 

 Fi „ e;, colourless granules, sometimes are so full of dark 

 pigment-granules, that they become true pigment- 

 cells. It must be added, that the chemical rela- 

 tions of the cortex are altered in the lower half of 

 the root, its elements becoming more sensitive to 

 the action of acetic acid, which does not affect the 

 plates of the shaft at all ; they swell up and dissolve in alkalies 

 also, much more quickly than those of the shaft. 1 



The colour of the cortical substance arises partly from spots of 

 pigment, to some extent from air cavities, and "partly from a 

 colouring matter diffused through and combined with the sub- 

 stance of the cortical plates. The first or the granular pigment, 

 exhibits all shades from clear yellow, through red and brown, 

 to black ; the diffused pigment is quite absent in white hairs, 

 and is scanty in clear, fair hairs ; it is most abundant in the 

 more opaque fair hairs and in red as well as in dark hairs, in 

 which it may by itself give rise to an intense red or brown 

 colour. The colour of the cortex depends especially upon 

 that of these two pigments, but sometimes the one, sometimes 

 the other predominates, and it is only in the very light and 

 in the very dark hairs that they are developed in about equal 

 proportions. 



§ 57. 



The medullary substance is a streak or cord which extends 

 in the axis of the hair, from the neighbourhood of the bulb 

 nearly to the point (figs. 65, 68). It is generally absent in the 



Fig. 67. Cells from the deepest part of the bulb of the hair, x 350 s a, from a 

 coloured bulb, with pigment granules and somewhat hidden nucleus ; b, from a 

 white hair, with a distinct nucleus and but few granules. 



1 [Reichert (' Bericht' for 1850, Mull. ' Archiv,' 1851) asserts that the cortical 

 substance of the hair is composed of superimposed laminae, and recommends, in order 

 to demonstrate the fact, that a hair should be treated with a solution of caustic 

 potass of 10 per cent., and then submitted to pressure. Under these circumstances, 

 "beautiful lamellae appear. The separate layers exhibit no trace of being composed 

 of fusiform cells ; they appear finely striated, and in places, hyaline ; sometimes elon- 

 gated spots appear, of which it cannot be determined with certainty whether they are 

 nuclei or perforations in the membrane." In some, there was no trace of these to be 

 seen. Reichert considers the fibres of the cortex to be artificial products, and was 

 unable to convince himself of the existence of nuclei in this part of the hair. — Eds.] 



