HAIR. 129 



foreign to nutrition, can change so rapidly. M. Lepelletier 1 ascribes 

 it to two very different causes. First, to defective secretion of the 

 colouring fluid, without any privation of nutrition. In this case, the 

 hairs may live and retain their hold, as we observe in young individuals : 

 and secondly, to the canals, which convey the fluid into the hair, 

 being obliterated, as in old age. The same cause, acting on the nutritious 

 vessels of the bulb, produces, successively, privation of colour, death, 

 and loss of those epidermoid productions. 



According to other physiologists, the seat of colour is in the horny 

 covering of the hair ; and, in the largest hairs or spines of the porcu- 

 pine, this seems to be the case, the pith being white, and the horny 

 covering coloured. There is often an intimate relationship observed 

 between the colour of the hair and that of the rete mucosum. A fair 

 complexion is accompanied with light hair ; a swarthy with dark ; 

 and we see the connexion still more signally displayed in those animals 

 that are spotted the colour of the hair being variegated like that of 

 the skin. 



Hairs differ materially according to the part of the body on which 

 they grow. In some parts they are short, as in the armpits ; whilst 

 on the head it is not easy to say what would be the precise limit to the 

 growth, were they left entirely to nature. In the Malay, it is by no 

 means uncommon to see them touch the ground. 



The hair has various names assigned to it, according to the part on 

 which it appears, beard, whiskers, mustachios, eyebrows, eyelashes, 

 &c. In many animals it is long and straight ; in others crisped, when 

 it is called wool. If stiff, it is termed a bristle; if inflexible, a spine. 

 It is entirely insensible, and, excepting in the bulbous portion, is not 

 liable to disease. Dr. Bostock affirms, that under certain circumstances 

 hairs are subject to a species of inflammation, when vessels may be 

 detected, at least in some of them, and they become acutely sensitive. 

 Their sensibility under any known circumstances may be doubted. 

 They appear to be anorganic, except at the root ; and, like the cuticle, 

 resist putrefaction for a length of time. The parts that do not receive 

 vessels are nourished by transudation from those that do. Bichat and 

 Gaultier were of the opinion of Dr. Bostock ; misled, apparently, by 

 erroneous reports concerning plica polonica; but Baron Larrey 2 has 

 satisfactorily shown that plica is confined to the bulbs : the hairs them- 

 selves continue devoid of sensibility. 



It is difficult to assign a plausible use for the hair. That of the head 

 has already engaged attention ; but the hair, which appears on certain 

 parts at the age of puberty and not till then, and that on the chin and 

 upper lip of the male sex only, set our ingenuity at defiance. In this 

 respect, the hair is not unique. Many physiologists regard certain 

 parts, which exist in one animal, apparently without function, but 

 which answer useful purposes in another, to be vestiges indicating the 

 harmony that reigns through nature's works. The generally useless 

 nipple and mamma of one sex might be looked upon in this light ; but 



1 Trait de Physiologie Medicale et Philosophique, torn. iii. p. 42, Paris, 1832. 

 a Memoires de Chirurgie Militaire, t. iii. 108, Paris, 1812. 

 VOL. I. 9 



