MODERN CHEMISTEY. 457 



elements of vegetable life, and of animal life as derived from 

 it ; the same three compounds are rendered back as the 

 ultimate products of fermentation and decay. Liebig and 

 Berzelius have deeply studied these processes; and the 

 theory of fermentation proposed by the former has found 

 general adoption. It is based on the curious fact, of which 

 Chemistry is prolific in examples, that a body in a state of 

 intestinal motion or change among its particles may, by 

 mere contact, produce in another body analogous changes, 

 decompositions, and new products and this, though the 

 exciting body be infinitely small in proportion, and yields 

 none of its own elements to the products evolved. The 

 importance of this doctrine of ferments will be readily un- 

 derstood. It bears upon various familiar phenomena every- 

 where around us, but still more strikingly on the whole 

 theory of matters which act as poisons on the living frame. 

 We have scarcely got beyond the threshold of this great 

 mystery. It is easy to quote the rapid growth of fungoid 

 life ; and not impossible in theory to conceive that a minute 

 particle of morbid matter received into the body may 

 gradually evolve the phenomena of small-pox or other 

 zymotic disease. But beyond this comes the stranger fact of 

 that permanent change induced on the body by certain 

 diseases ; a change which, while unseen in any other function 

 of life, is so wonderfully attested by immunity from future 

 action of the same morbid cause. No atomic or other theory 

 can reach this phenomenon, which still lies hidden among 

 the arcana of life itself. 



The same cursory view we must take of another signal at- 

 tainment of Organic Chemistry, viz. the formation artificially 

 of various organic bodies, both of animal and vegetable kind, 

 not merely analogous, but identical with those presented to us 

 in nature. The number of the several substances thus pro- 

 duced now exceeds twenty; but does not yet include any 



