352 POISONS, CONTAGIONS, MIASMS. 



by our senses, only through the phenomena which 

 it produces. 



In order to explain the effects of contagious mat- 

 ters, a peculiar principle of life has been ascribed 

 to them a life similar to that possessed by the 

 germ of a seed, which enables it under favourable 

 conditions to develop and multiply itself. It would 

 be impossible to find a more correct figurative re- 

 presentation of these phenomena ; it is one which 

 is applicable to contagions, as well as to ferment? 

 to animal and vegetable substances in a state of 

 fermentation, putrefaction, or decay, and even to a 

 piece of decaying wood, which by mere contact 

 with fresh wood, causes the latter to undergo gra- 

 dually the same change and become decayed and 

 mouldered. 



If the property possessed by a body of producing 

 such a change in any other substance as causes the 

 reproduction of itself, with all its properties, be 

 regarded as life, then, indeed, all the above pheno- 

 mena may be ascribed to life. But in that case 

 they must not be considered as the only processes 

 due to vitality, for the above interpretation of the 

 expression embraces the majority of the pheno- 

 mena which occur in organic chemistry. Life would, 

 according to that view, be admitted to exist in every 

 body in which chemical forces act. 



If a body A, for example, oxamide (a substance 

 scarcely soluble in water, and without the slightest 

 taste), be brought into contact with another com- 



