122 HAIRS. [SECT. 66. 



example, when it occurs in the course of normal development — 

 merely on the want of the necessary nutrient material, which, in 

 the natural moulting of the hairs, as already explained, is owing 

 to the separation of the hair from its nutrient matrix, caused by 

 the exuberant growth of cells at the bottom of the follicle ; but, 

 in old age, it may simply depend upon the obliteration of the 

 vessels of the hair-follicle. The whitening of the hair also, which 

 depends chiefly upon a decoloration of the fibrous substance, and 

 less upon that of the almost colourless pith, is, doubtless, partly to 

 be referred to the same cause, for its normal appearance, in 

 advanced age, shows it to be also of the nature of a retrogressive 

 change. The frequent cases in which the hair first becomes gray 

 at the point or at the middle, and the well- authenticated instances 

 of its rapidly becoming white are interesting, and speak strongly 

 for the vitality of the hair ; although it is not yet known what 

 peculiar processes in the elements of the hair occasion the decolor- 

 ation of its different pigments. 



As in the earliest periods of life the cast-off hairs are replaced 

 by new ones, so we find something similar occurring at a later 

 period. It is quite certain that during the vigorous period of life 

 there is a continual replacement of the numerous hairs which are 

 shed ; further, that at the time of puberty new hairs shoot forth 

 in great numbers in certain localities, but how is unknown. Since 

 in the adult there are hair-roots with small processes downwards, 

 whose proper hair has an abrupt knob-shaped end, as in the child ; 

 since further,, two hairs not unfrequently .come out at one opening, 

 and can even be demonstrated existing together in one follicle; 

 and, lastly, since the roots of hairs which have fallen out sponta- 

 neously, are exactly similar to those of the cast-off hairs of the 

 first casting, it may be assumed that a real shedding also occurs at 

 a later period, and in such a manner that the old follicles produce 

 new hairs, and cast off the old ones, as has, in fact, been proved by 

 hanger. By this, however, I do not mean to assert that a forma- 

 tion of hairs from new rudiments does not also occur after birth ; 

 only this much, that in the adult, as in earlier periods, they are 

 regenerated from the pre-existing hair-follicle. This will appear the 

 more probable when it is recollected that, according to the observa- 

 tions of Heusinger, the tactile hairs of dogs, when pulled out, are, 

 within a few days, reproduced in the same follicle ; and, also, that 

 in the shedding of the hair in adult animals, the young hairs are, 

 according to Kohlrausch, developed from the old follicles. Also, 

 when the hairs which have fallen out after a severe illness, are 



