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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 especially characterize life; but although 

 this power is exercised both by vegetable and by animal or- 

 ganizations, 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 combina- 

 tions of elementary bodies, which are elaborated in celhi- 

 lar or vascular textures, and converted into various pro- 

 ducts. The oak, for example, forms, by the powers of ve- 

 getation, 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 com- 

 bination, 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 the bland farina of the potato, 

 will produce in another the poisonous extract of the night- 

 shade. Yet all these, and thousands of other vegetable pro- 

 ducts, differing widely in their sensible qualities, agree very 

 nearly in their ultimate chemical analysis, and owe their pe- 

 culiar properties chiefly to the order in which their elements 

 are arranged; an order dependent on the processes to which 

 they have been subjected in the system of each particular 

 vegetable. 



