ANIMAL ORGANIZATION. 119 



From this account it will be seen that a hair is, 

 in its origin, tubular ; the inner part being occu- 

 pied by the pulp. But as the pulp extends only 

 to that portion of the hair which is in a state of 

 growth, it never rises above the surface of the 

 skin ; and the cavity in the axis of the hair is 

 either gradually obliterated, or is filled with a 

 dry pith, or light spongy substance, probably 

 containing air. After a certain period, the bulb 

 diminishes in size, from the collapse of the 

 vessels, whose powers of supplying, nutriment 

 become exhausted. The first deficiency in its 

 nourishment appears in the cessation of the 

 deposit of colouring matter, and the hair in con- 

 sequence becomes grey. After a time, the 

 vessels becoming quite impervious, the bulb 

 shrivels, the hair is detached, and the canal 

 which its root occupied in the skin becomes 

 .obliterated. 



The hair of different animals, and even of dif- 

 ferent parts of the same animal, is very various 

 in its shape, texture, and mechanical properties. 

 Sometimes, instead of being cylindrical, the fila- 

 ments are more or less flattened, striated, deeply 

 grooved, or even beaded. Instead of being 

 solid, they may even be tubular : and they ex- 

 hibit also the greatest diversity in their length, 

 fineness, tenacity, rigidity, and disposition to 

 curl. All these varieties may be traced to cor- 

 responding differences in the form, and the rela- 



