142 



ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 



principal part of the shaft of the hair ; whilst the centre is frequently more 

 distinctly cellular. The constituent fibres of the shaft are marked out by 

 delicate longitudinal stripe, which may be traced in vertical sections of the 

 hair (Fig. 37, B.) ; but they may be still more completely demonstrated by 

 crushing the hair, after it has been macerated for some time in dilute acid. 

 In dark hairs, pigmentary granules are frequently scattered between the fibres; 

 but they are usually found in greater abundance in the central cells. The 

 Hair of Man is commonly reputed to be tubular ; but this is seldom if ever 

 the case, as is shown by microscopical examination of thin transverse sec- 

 tions (Fig. 37, c). The mistake has arisen from a misinterpretation of the 

 appearance of a dark band in the interior of the hair, when viewed by trans- 

 mitted light ; which is really due, partly to the presence of pigmentary mat- 

 ter in the central portion of the shaft, and partly to the refraction of light by 

 the cylindrical surface. The chemical composition of Hair, as already stated, 



Eg , ji. 



Eft:." ;, ,:.. :tni i 



I ! 



' 



Structure of Human Hair; A, external surface of the shaft, showing- the transverse striae and jagged 

 boundary, caused by the imbrications of the scaly cortex ; B, longitudinal section of the shaft, showing' 

 the fibrous character of the medullary substance, and the arrangement of the pigmentary matter; c, 

 transverse sections, showing the distinction between the cortical and medullary substance, and the cen- 

 tral collection of pigmentary matter, sometimes found in the latter. Magnified 310 diameters. 



is precisely the same with that of the horny Epidermis ( 162). Its colour- 

 ing matter seems related to Haematine ; it is bleached by Chlorine ; and its 

 hue appears to be dependent in part upon the presence of iron, which is found 

 in larger proportion in dark than in light hair. 



168. The real nature of the different elements of the Hair is ascertained, 

 by examining them at its base, where they become continuous with those of 

 the bulb. It is then seen, that the fibres of the shaft are identical with the 

 cells of the bulb ; these undergoing elongation, as they are pushed upwards 

 towards the mouth of the follicle, by the development of additional cells be- 

 neath ; and being proportionally diminished in diameter. Hence the shaft of 

 the hair is considerably narrower than the bulb. The central part of the hair 

 which more distinctly exhibits the cellular character, is derived from the pulp 

 or internal portion of the bulb ; whose constituent cells undergo less change. 

 And the imbricated layer of cells, that forms its fibrous envelope, may be said 

 to be a prolongation of the ordinary Epidermis over the surface of the hair; 

 being developed from the external portion of the bulb, where it is continuous 

 with the epidermic lining of the follicle. Thus we see that the whole tissue 

 of the Hair is derived from Epidermic cells, developed in peculiar abundance 

 from the base of the follicle ; some of these cells, however, retaining their 

 original form ; whilst others are transformed into fibres, and others converted 

 (like those of ordinary Epidermis) into llattened cells. They all have the 

 power, however, of drawing horny matter into their cavities ; and resist the 



