THE HAIRS. 347 



to ten filaments, parallel with one another, and forming a tube 

 in the centre of the fasciculus. The tube, as well as the inter- 

 stices between the filaments, is filled with a fluid called the 

 marrow of the hair. This substance corresponds with one of 

 the layers of the rete mucosum of the skin, and contains the co- 

 louring matter. The probability is, that the whole hair is a 

 continuation of the rete mucosum, to which is joined the enve- 

 lope of the epidermis. The canal in the centre of the hair is 

 said to be unusually distinct in the hog's bristle ; it is also well 

 seen in the supercilia : the follicle and bulb are best studied in 

 the mustachios of the larger animals. According to Mr. Heu- 

 singer,* the substance of the hair, when examined with a mi- 

 croscope of strong power, exhibits an areolar appearance. 



Though the stalk of the hair is destitute of blood vessels and 

 of nerves, yet it is probable, from the sudden changes of colour 

 that sometimes occur in it from black to white, owing to terror 

 and grief, that there is a species of interstitial circulation going 

 on. The emaciated and peculiar appearance which sickness 

 gives to it, would also tend to support this opinion. Strictly- 

 speaking, the hairs are devoid of sensibility, yet, as the bulb is 

 planted over a sensitive papilla, they communicate certain sen- 

 sations by being removed or touched. Animals apply their 

 mustachios particularly to this use in groping through dark 

 places, or when they are deprived of sight. The hairs are emi- 

 nently hygroscopic, moisture lengthens, and dryness shortens 

 them ; this property has caused them to be applied to the con- 

 struction of hygrometers. 



In certain animals the hairs are erected by the contraction 

 of the subcutaneous muscle; the movement in the human sub- 

 ject corresponding with that, is the effect of great fright, and is 

 produced by the contraction of the occipito fronta-lis muscle. 



In the development of hair, the part which first forms is the 

 follicle, the young hair then pierces it at its summit, in the same 

 way that the tooth pierces its capsule. The death of the cap- 

 sule, or the drying up of its fluids, occasions the fall of the hair 

 and prevents its regeneration. In old men who are bald there 

 is no appearance of capsules; while in persons from whom the 

 hair has fallen, owing to sickness, as the capsules still remain, 



* J. Cloquet, loc. cit. 



