STRUCTURE OF THE HAIR. 24-7 



into the focus are more superficially or more deeply situated. 

 We may easily satisfy ourselves, by means of transverse sections, 

 and with appropriate focussing, that the scales are in imme- 

 diate contact with one another by the borders of their plane 

 surfaces. 



In the lower parts of the hair follicle, the internal root- 

 sheath consists simply of a single row of the above-described 

 scales, that are easily to be distinguished from the cells of 

 Huxley's sheath, which are here still nucleated. At a higher 

 point the fc^-mer become more flattened, whilst the latter lose 

 their nuclei, so that the two sheaths can no longer be sharply 

 distinguished from each other. It nevertheless appears that 

 the scales of the internal root-sheath increase in number above. 

 Lastly, it may be observed that the scales of the internal root- 

 sheath swell up and then dissolve in solutions of potash and soda. 



HAIR. The hair itself is composed of a larger part that pro- 

 jects beyond the surface of the skin, the hair shaft, and of a 

 bulbous enlargement of the shaft, the hair root, from which a 

 proper sheath that surrounds the lowermost part of the hair, 

 and constitutes the so-called sheath of Huxley, together with 

 the cuticula of the root-sheath, are developed. 



If we examine a transverse section of a hair shaft to which 

 no reagents have been previously applied, it will be seen that the 

 margin is finely toothed, whilst the surface of the shaft is crossed 

 by fine lines, enclosing rhomboidal spaces, which correspond to 

 the apices of the teeth. The appearances presented remind 

 one involuntarily of the surface of the body of the scaly 

 Amphibia, and are the expression of thin scales investing the 

 hair, and representing the cuticula of the hair first described 

 by Hermann Meyer. 



The chief mass of the hair is formed by the hair substance 

 (fig. 201, Ji), i.e., a substance that in grey hairs is colourless, 

 lustrous as silver, and in which numerous fusiform longitudinal 

 dark-coloured granules occur. In coloured hairs, the hair sub- 

 stance, which is also called the cortical substance, includes a 

 variable quantity of differently coloured pigment granules. 



In the thick hairs of the beard, and also occasionally in the 

 hairs of the head, a central medulla occupies the interior of 



