OF THE HAIRS. 195 



The falling out of the hairs certainly depends, in many cases, when, 

 for example, it takes place in the course of normal development, on 

 nothing else than a want of the necessary nutritive material, which in 

 the instance already explained, in speaking of the shedding of the hairs, 

 depends on the detachment of the hair from its matrix by the abundant 

 production of cells at the bottom of the hair-sac. In age, perhaps, it 

 arises simply from the obliteration of the vessels of the hair-sacs. 



The whitening of the hairs, which chiefly depends upon a decoloration 

 of the cortex, and less upon that of the almost colorless medulla, should 

 probably be here considered, for its normal occurrence in old age gives 

 it the significance of a retrogressive development. 



The frequent occurrence of cases, in which the hair grows gray first 

 at its point or in the middle, and the well-established instances of its 

 rapidly becoming white, are interesting, and strongly testify to the 

 vitality of the hair ; but it has not yet been shown, what peculiar -pro- 

 cesses in the elements of the hair produce the decoloration of its different 

 pigments. 



As in youth hairs which are shed are replaced by others, so at a later 

 age something similar appears to occur. It is quite certain that during 

 the period of full health and activity, a continual replacement of the 

 numerous hairs which fall out goes on ; furthermore that new hairs in 

 great numbers spring up at the time of puberty in certain localities, but 

 the manner in which this takes place is unknown. Inasmuch as even in 

 adults we find hair-sacs with little processes downwards, whose proper 

 hair has an abrupt clavate end, as in the child ; since further, in this 

 case it not unfrequently happens that two hairs come out of one aper- 

 ture, and even exist together in one sac ; and, finally, since in hairs 

 which have fallen out spontaneously, we invariably find roots like those* 

 which exist in the extruded hairs of the first shedding, it may be 

 assumed that an actual shedding of the hairs occurs, even at a later 

 period, in such a manner that the old hair-sacs produce new hairs while 

 they throw off the old ones. I do not, however, intend to affirm by 

 this, that an actual new formation of hairs does not occur after birth, 

 but only this much, that in adults they are certainly regenerated from 

 the already existing hair-sacs, especially if it be recollected that, accord- 



* [Henle (" Allg. Anat," p. 303) gives a very excellent description of this state of the 

 hair-bulb: " Instead of the soft cellular hair-bulb, we find an inconsiderable clavate enlarge- 

 ment, which is solid and fibrous, like the substance of the shaft, only more clear. From its 

 outer surface, short and irregular processes project downwards, which are probably the 

 notched lower edges of the outermost layers of the cortical substance ; they look like fibres 

 connecting the hair with the inner wall of the sac. This kind of root is found in hairs 

 which have fallen out spontaneously, and it is, therefore, probable that it belongs to a later 

 stage of development of the hair, or rather marks the conclusion of its development. When 

 the connection with the sac has ceased, which is the case in these clavate roots, the hair 

 grows no longer 5 probably it is no longer nourished, but falls out." 



