THE HAIR. 79 



same shape in the epidermis, and which line the hair-follicle so 

 as to form a sheath or vagina pili to the hair-bulb. The cells 

 which advance from the thicker portion of the medulla, in 

 the hair-follicle, become dry and flattened so as to form the 

 hard, scaly, cortical portion of the hair; the margin of the 

 latter, when examined by a good microscope, is always found 

 to be imbricated, or, in other words, the cells are superim- 

 posed, but their edges are one beyond the other, as in the 

 arrangement of tiles or slates on the roof of a house. It is 

 by friction that, as the cells advance from the root, and 

 become dry and detached, the hair grows thinner and thinner 

 from the loss of cortical scales, and by this simple process 

 the hair tapers to a point. The imbrication of these cells 

 renders wool of great value for the manufacture of various 

 fabrics. It is to the projecting serrated margins of the cells 

 that fine waved transverse lines on the surface of the hair 

 are due, and which are seen by the microscope. 



The cells immediately beneath the imbricated scales are 

 fusiform and flattened, so as to give rise to the fibrous 

 appearance. 



The colour of hair is due to pigment granules diffused be- 

 tween the cells, and which are sometimes confounded with 

 little air- cavities, best seen in white hairs, and between the 

 longitudinal fibres of the cortical substance. 



It is a remarkable fact, that " notwithstanding the closest 

 search, Laer was unable to discover any special pigment in 

 the hair, although the microscopical examination of the cor- 

 tical substance of differently coloured hairs, that is to say, 

 the existence of certain coloured molecules, indicates the 

 presence of a definite pigment. It is, however, well known 

 that white hair is especially rich in air, and that to this cir- 

 cumstance it mainly owes its glistening colour. Laer has 

 further shown, by numerous experiments on differently 



