14 THE VITAL FUNCTIONS. 



vehicle. But these, after having been converted 

 by the powers of vegetable assimilation, into the 

 substance of the plant, acquire the charac- 

 teristic properties of organized products, though 

 they are still the simplest of that class. In this 

 state, and when the fabric they had composed is 

 destroyed, and they are scattered over the soil, 

 they are fitted to become more highly nutritive 

 to other plants, which absorb them, and with 

 more facility adapt them to the purposes of their 

 own systems. Here they receive a still higher 

 degree of elaboration ; and thus the same mate- 

 rials may pass through several successive series 

 of modifications, till they become the food of ani- 

 mals, and are then made to undergo still further 

 changes. New elements, and in particular 

 nitrogen, is added to the oxygen, hydrogen and 

 carbon, which are the chief constituents of 

 vegetable substances : * and new properties are 

 acquired, from the varied combinations into 

 which their elements are made to enter by the 

 more energetic powers of assimilation apper- 

 taining to the animal system. The products 

 which result are still more removed from their 

 original state of inorganic matter: and in this 

 condition they serve as the appropriate food of 



* Nitrogen, however, frequently enters into the composition 

 of vegetables : though in general, in a much smaller proportion 

 than into the substance of animals, of which last it always ap- 

 pears to be an essential constituent. 



