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penetrated by these vapours. Between the actually mechanical 

 method of taking solid matter into the air, such as when 

 waves are agitated by the wind, and the purely chemical 

 method, such as when a liquid is transformed into a vapour 

 by heat, there must be many intermediate stages. These 

 stages are required, apparently, as we can scarcely imagine 

 pure gases undergoing transformation similar to bodies in a 

 putrefactive state ; and we are not prepared with a theory by 

 which diseases will be communicated without the agency of 

 bodies in such a state of change — one of the oldest of theories 

 and one promising to live long. Besides, the fact of a 

 substance being found capable of being absorbed by metallic 

 salts, and containing carbon with nitrogen in such a large 

 amount, leads us to believe that bodies not very far removed 

 from the substances decomposed are found in the vapours, 

 and, if not far removed, capable of undergoing transformations 

 so as to become farther removed, and by such transformations 

 exercising their special influence. 



