390 POISONS, CONTAGIONS, MIASMS. 



mine, aromatic substances, volatile oils, and partic- 

 ularly empyreumatic oils, smoke, and a decoction of 

 coffee, completely destroy their contagious properties, 

 in some cases combining with them or otherwise 

 effecting their decomposition. Now all these agents, 

 without exception, retard fermentation, putrefaction 

 and decay, and when present in sufficient quantity, 

 completely arrest these processes of decomposition. 



A peculiar matter to which the poisonous action 

 is due, cannot, we have seen, be extracted from 

 decayed sausages ; and it is equally impossible to 

 obtain such a principle from the virus of small-pox 

 or plague, and for this reason, that their peculiar 

 power is due to an active condition recognisable 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 favorable condi- 

 tions to develop and multiply itself. It would be 

 impossible to find a more correct figurative repre- 

 sentation 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 fer- 

 mentation, putrefaction or decay, and even to a piece 

 of decaying wood, which by mere contact with fresh 

 w^ood, causes the latter to undergo gradually 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, w^ith all its properties, be 

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

 ena 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 expres- 

 sion embraces the majority of the phenomena which 

 occur in organic chemistry. Life would, according 

 to that view, be admitted to exist in every body in 

 which chemical forces act. 



