CUTICLE, NAILS, HAIR AND FEATHERS. 281 



derations, that we are not entitled to believe in the 

 necessity of a circulation of fluids, for the purposes 

 of nutrition. 



Before stating the hypothesis which I propose to 

 substitute on this subject, I shall briefly recall a 

 few prominent facts, relative to the growth of Hair, 

 Nails, and Feathers. 



It is well known that no vessels can be traced in 

 many of their parts. If there is something like 

 bloodvessels in the soft ends of feathers, near to the 

 body of the animal to which they belong, there are 

 certainly no traces of such an apparatus towards the 

 extremities. Many of the organs now mentioned 

 are too dry to allow us to believe in a circulation, 

 even while their growth is most vigorous. 



At the same time, it must be remarked, that 

 there are facts which forbid us to suppose, that 

 these organs are mere secretions formed at their 

 roots, or the parts by which they are attached to the 

 animal body. Mere secretion and successive propul- 

 sion, never could have been maintained to constitute 

 the growth of feathers; because it is well known 

 that a developement takes place over all the extent 

 of their expanded substance, each pinion and each 

 serrature receiving a proportional enlargement dur- 

 ing growth. But while physiologists confine their 

 attention to the hair and the nails, they are some- 

 times disposed to conclude that these organs are 

 mere secretions or depositions ; and that their 



