ON THE NUTRITION OF 



growth consists entirely in a successive propulsion 

 of the existing parts, hy the new parts succeeding 

 at the root or point of secretion. This idea re- 

 ceives some countenance from the circumstance, 

 that a scratch on the nail of one of the fingers, 

 gradually changes its situation, by proceeding in 

 a direction from the root to the extremity of that 

 substance. In the hair, however, no such ap- 

 pearances have been observed ; and there is this 

 fact adverse to such a supposition, that, when the 

 hair changes from dark to grey, we do not find the 

 change beginning at the root, and proceeding to- 

 ward the extremity of the hair, but taking place si- 

 multaneously over its whole length. 



Another fact is, that the hairs have a maximum 

 length at which the growth is arrested : and this 

 differs in different individuals, and still more in dif- 

 ferent parts of the same body. That of the head ap- 

 pears somewhat vague, because the tout ensemble 

 presents no marked outline, the whole falling down 

 in one flaccid congeries ; but that of the eye-brows, 

 and that of the eye-lids, have a determinate length, 

 which contributes at once to utility and to the high- 

 est elegance. When cut short, it quickly reaches 

 its full length, and there invariably stops. These 

 circumstances shew, that each hair has a particular 

 constitution, by which all its parts, from the root to 

 the extremity, exercise a regulated reciprocal influ- 

 ence. We cannot suppose that the case is different 



