HAIR, 273 



is doubtless regenerated, and after its regeneration is usually- 

 stronger than it was previously. (See Plate XXIX.) 



It has not yet been ascertained by positive experiment 

 whether the hair is capable of reformation in those instances 

 in which both bulb and sheath have been removed : it is 

 most probable, however, that where they have been entirely 

 abstracted, no renewal of the hair could ensue. 



It is possible that in some cases the apparent regeneration 

 of the hair arises, not from the development of new hairs 

 in the primitive sheaths and upon the old germs, but from 

 the formation of new hair follicles and germs : of this, how- 

 ever, no proof has as yet been given. 



That a regeneration of new shafts of hair is continually in 

 progress, whether from new germs or the older ones is not 

 known, is proved by the detection of small and pointed hairs 

 just emerging from the skin in the scalp of even old persons. 



NUTRITION OF HAIR. 



Hairs are nourished in the same way as the epidermis 

 itself; that is, they do not receive into their own structure 

 either blood vessels or nerves, but derive their nutriment 

 from vessels which are so distributed as to come into close 

 contact with the tissues to be nourished. 



This indirect reception of the nutrient plasma explains the 

 very great susceptibility of the epidermis and its several 

 modifications to be influenced by causes affecting the general 

 health, and in consequence the circulation and the qualities of 

 the circulating fluid. 



The epidermic tissues being placed in situations the most 

 remote from the centre of the circulation, are endowed with 

 but a feeble degree of vitality, and which is readily de- 

 stroyed by causes affecting the amount and nature of the 

 circulating fluid received by them. 



The nutrient vessels and sentient nerves of each hair are 

 distributed around and outside the sheath, and not in a raised 

 papilla as generally described, although this may really be the 



