LECTURE VI. 287 



that they are all made of the same kind of 

 material, which is impenetrable to mois- 

 ture. Hairs, feathers, scales, and horny 

 cuticle, resemble each other in this particu- 

 lar, and also in their chemical analysis. 



Mr. Hunter has shown the analogy of 

 the formation of feathers and hairs. Each 

 is formed by a vascular substance, which 

 ascends to some distance up their shafts. 

 Hairs are bulbous rooted, and the stronger 

 ones are more deeply implanted in the skin. 

 The capsule of the bulb, which is tough and 

 shining, being opened, is found to contain a 

 very vasc«lar pulp which can be injected, 

 and ascends up the shaft of the hair so 

 as successively to form it at the bottom ; 

 and thus to increase its length. I cannot 

 suppose this circumstance was commonly 

 known at the time Mr. Hunter made these 

 preparations, for a knowledge of this fact 

 much diminishes our surprise at the ac- 

 counts we have received of the plica polo- 

 nica, in which disease the hairs are said to 

 be ill-formed, matted, and to bleed from 

 their roots. 



