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nature, it will be necessary for me first to call your attention 

 to a class of chemical phenomena which appears to me nearly 

 related to those changes which are produced by malaria. 



It is well known that the elements which enter into the 

 composition of many mineral substances are held together 

 by so feeble an affinity, that the slightest disturbing cause is 

 capable of producing their separation. The force which 

 binds together the elements of the fulminates of silver and 

 mercury, of the iodides and chlorides of nitrogen, and the 

 peroxide of hydrogen, is so feeble, that the slightest friction, 

 in some instances even a draft of air, is capable of tearing 

 them asunder. Organic compounds, and particularly those 

 formed under the immediate direction of vitality, such as the 

 constituents of the blood and secretions, being of a much 

 more complex nature than any mineral compound, yield to 

 influences even more slight than those just named, and give 

 rise to new and simpler productions. The ordinary process 

 of decay, in which the elements of all organized substances 

 begin to form simpler compounds by uniting with the oxygen 

 of the air when their vitality ceases, or of putrefaction, in 

 which they form such compounds from a new arrangement 

 amongst themselves, is a proof of the facility with which 

 chemical changes are accomplished. No leaf or stem can 

 lose its vitality without at the next moment producing new 

 compounds by decay ; nor can any animal substance, without 

 previous chemical preparation, be prevented from undergoing 

 the process of putrefaction. The compounds produced by the 

 ordinary process of decay, namely, carbonic acid, water, am- 

 monia, and nitric acid, are generally so simple in their nature 

 and harmless in their properties, as scarcely to be considered 

 injurious to animal life. The carbonic acid produced from 

 the fallen leaves of a woodland district would so soon and 

 so perfectly mix with the atmosphere, as not to render its 

 presence in excess at all appreciable. Even in summer, that 



