264 



these are finer the lighter their shade. It is, likewise, observed^ that 

 men of a bilious constitution, with dark hair, and inhabiting warm cli- 

 mates, have more hair, in other parts of the body, and that it is coarser 

 and more greasy. 



In whatever part of the body hairs may grow, they are, every where, 

 of the same structure, they all arise from a vesicular bulb in the adipose 

 cellular tissue; from this bulb containing a gelatinous lymph, on which 

 the hair seems to be nourished, the latter, at first divided into two or 

 three filaments which constitute a kind of root, comes out in a single 

 trunk, passes through the skin and epidermis, receiving from the latter 

 a sheath that covers it to its extremity, which terminates in a point. 



A hair, may, therefore, be considered as an epidermoid tube filled with 

 a peculiar kind of marrow. This spongy stem, which forms the centre 

 of a hair, is a more essential part of it, than the sheaths supplied by the 

 epidermis. Along this spongy and cellular filament, the animal oil of 

 the hair and the juices on which it is repaired flow. Though we see, in 

 some animals, vascular branches and very small nervous filaments direct- 

 ed towards the root of certain kinds of hair, and lost in it, as is the case 

 with the long and stiff whiskers of some of the quadrupeds, it is impos- 

 sible to say, whether in man, the hair or its bulbs receives vessels and 

 nerves. Is the human hair nourished by the imbibtion of the gelatinous 

 fluid contained in its bulb, or is it nourished on the fat in which the lat- 

 ter is imbedded? Are vessels distributed along their axis, from the root 

 to the extremity ? In favour of this opinion, it was usual to mention the 

 bleeding from the hair when cut, in the disease called plica fiohnica. But 

 this disease, lately observed in Poland, by tlie French physicians, appear- 

 ed to them a mere entangling of hair, in consequence of the filth of the 

 Poles, and of their habit of keeping their head constantly covered with 

 a woollen cap. The hairy scalp remains perfectly sound beneath the en- 

 tangled hair, and the only way to cure the complaint is to cut of the hair. 

 Fourcroy* thinks that each hair has several short branches that stand off 

 from it, which, according to the explanation given by Monge, favour 

 the matting of the hairs that are to be converted into tissues, by the pro- 

 cess called felting. 



CXXXIV. Among the most remarkable qualities of the hair one may 

 take notice of the manner in which it is affected by damp air, which, by 

 relaxing its substance, increases its length. It is on that account, that 

 hairs are used for the construction of the best hygrometers. NOT must 

 we omit either the readiness with which they grow and are reproduced, 

 even after being plucked out by the roots, as I have often seen after the 

 cure of tinea by a painful method : nor their insulating property, with 

 respect to the electric fluid, of which they are vjery bad conductors , a 

 remarkable property, vie.wed with reference to the conjectured nature of 

 the nervous fluid. 



The hairs possess no power of spontaneous motion by which they can 

 rise on the head, when the soul shudders with horror or fear; but they 

 do bristle at those times, by the contraction of the occipito-frontales, 

 which, intimately adhering to the hairy scalp, carries it along in all its 

 motions. 



They appear totally without sensibility : nevertheless, the passions 



Systems des connoissance chimgues, tome IX. p. 263. 



