Memoir upon Hah. 355 



tuent principles of hair, M. Vauquelin thinks that the various 

 colours which distinguish this substance may be accounted 

 for. The black colour, according to him, is produced by a 

 black and bituminous-like oil, and perhaps also by the com- 

 bination of sulphur with iron. The red and flaxen colours 

 are owing to the presence of a red or yellow oil, the in- 

 tensity of which diminished by a small quantity of brown 

 oil makes the hair red. Lastly, the white is owing to the 

 absence of the black oil and sulphuretted iron. He thinks, 

 that in red and yellow hair, as well as in white, there is al- 

 wavs an excess of sulphur; since when the white metallic 

 oxides are applied to it, such as those of mercury, lead, bis- 

 muth, &c, they become black very speedily. The manner 

 in which this body acts upon metallic substances makes 

 him think that it is united to hydrogen. 



M. Vauquelin endeavours afterwards to explain the white- 

 ness which suddenly takes place in the hair of such persons 

 as are struck with profound grief, or surprised by great fear. 

 It must be supposed, he says, in order to explain this phseno- 

 menon, that at the moment when nature is in a state or re- 

 volution, and when consequently the natural functions are 

 suspended or changed in their nature, an agent is developed 

 in the animal ceconomy, which, passing into the hair, de- 

 composes the colouring matter of it. 



But what agent can produce this effect ? The acids ap- 

 pear to him to be alone capable of it : this at least is cer- 

 tain, that black hair plunged some time in these menstrua, 

 and particularly in the oxygenated muriatic acid, becomes 

 white very sensibly. 



The rapid production of an acid in the animal ceconomy 

 does not appear impossible to him, upon considering that a 

 movement of passion in men, as well as in animals, is suffi- 

 cient to change the nature of certain of their humours and 

 render them poisonous ; and seeing that the Galvanic fluid 

 often determines in animal and vegetable matters the forma- 

 tion of an acid or an alkali, according to circumstances. 

 As to the whiteness which hair gradually undergoes from 

 . he attributes it to the want of secretion of the colour- 

 ing matter. 



Independently of the animal matter which forms the 

 A a v basis, 



