HAIRS AND FEATHERS. 301 



will be raised in about twelve hours. After it is detached the 

 exposed surface appears covered with a dark coating. But if 

 the blister has been very active, another layer of a black colour 

 comes away with it. This is the rete mucosum, which gives to 

 the different races of men their various shades of colour. 



The nature of this substance has not yet been determined. 

 Neither nerves nor blood-vessels have been traced into it. It 

 has been considered as a semifluid deposit or secretion. Some 

 suppose it to contain a black matter in the negro, similar to the 

 pigmentum nigrum of the eye. But the only chemical fact 

 connected with it that we know is inconsistent with this supposi- 

 tion. Chlorine deprives it of its black colour, and renders it yel- 

 low. A negro by keeping his foot for some time in water im- 

 pregnated with chlorine gas, deprived it of its black colour and 

 rendered it nearly white ; but in a few days the colour returned 

 again with its former intensity.* This experiment was first 

 made by Dr Beddoes on the fingers of a negro.f 



CHAPTER XVI. 



OF HAIR AND FEATHERS. 



THESE substances cover different parts of animals, and are ob- 

 viously intended by Nature to protect them from the cold. For 

 this, their softness and pliability, and the slowness with which 

 they conduct heat, render them peculiarly proper. 



1. Hair is usually distinguished into various kinds, according 

 to its size and appearance* The strongest and stiffest of all is 

 called bristle ; of this kind is the hair on the backs of hogs. 

 When remarkably fine, soft, and pliable, it is called wool ; and 

 the finest of all is known by the name of down. But all these 

 varieties resemble one another very closely in their composition. 



Hair appears to be a kind of tube covered with a cuticle. Its 

 surface is not smooth, but either covered with scales or consist- 

 ing of imbricated cones. Hence the roughness of its feel, and 

 the disposition which it has to entangle itself, which has given 

 origin to the processes of felting and fulling. It is constantly in- 



* Fourcroy, ix. 259. f Beddoes on Factitious Airs, p. 45. 



