CUTICLE, NAILS, HAIJl AND FEATHERS. 285 



constitution of their parietes, both with respect to 

 hygrometric properties, and to the degree and kind 

 of their assimilating power. In short, we are war- 

 ranted to conceive a nutrition to go on in this man- 

 ner with as exquisite niceness and as rich variety, as 

 by means of circulating liquids. Here, however, 

 we must stop. The particular laws by which the 

 ultimate minutiae of the process are accomplish- 

 ed, elude our inquiry. But they are not more mys- 

 terious in the epidermis, in nails, in hair, and in 

 feathers, on the doctrine which I have ventured to 

 advance, than in the organs in which the circulating 

 apparatus is traced in the most satisfactory man- 

 ner. 



This doctrine, it is obvious, may be also called in 

 to the aid of the physiology of insects and of that 

 of plants. To many of the latter, it will be found in- 

 dispensably requisite ; as, for example, those of the 

 class Cryptogamia, and more especially the tribe of 

 lichens. 



If it should occur to any person as an objection, 

 that we know the process of nutrition to be conduct- 

 ed in substances, which show that they possess no 

 hygrometric power, since they rapidly dry, as soon as 

 a communication with the animal body or the vege- 

 table root is cut off; I have only to observe, that 

 this hygrometric power is to be considered as regu- 

 lated by the living activity, and for the most part de- 

 pending entirely upon it. This supposition is equal- 



