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Chapter XII. 



SECRETION. 



The capability of effecting certain chemical 

 changes in the crude materials introduced into 

 the body, is one of the powers which more espe- 

 cially characterize life ; but although this power 

 is exercised both by vegetable and by animal 

 organizations, we perceive a marked difference 

 in the results of its operation in these two orders 

 of beings. The food of plants consists, for the 

 most part, of the simpler combinations of ele- 

 mentary bodies, which are elaborated in cellular 

 or vascular textures, and converted into various 

 products. The oak, for example, forms, by the 

 powers of vegetation, out of these elements, not 

 only the green pulpy matter of its leaves, and 

 the light tissue of its pith, but also the densest of 

 its woody fibres. It is from similar materials, 

 again, that the olive prepares its oil, and the 

 cocoa-nut its milk ; and the very same elements, 

 in different states of combination, compose, in 

 other instances^ at one time the luscious sugar 

 of the cane, at another the narcotic juice of the 

 poppy, or the acrid principle of the euphorbium ; 

 and the same plant which furnishes in one part 



