Adeney — Dissolved Gases and Fermentative Changes. 541 



quantities of fermentable matters, such as fresh sewage, when mixed with good river 

 water, soon indicated their presence by causing an absorption of dissolved oxygen, 

 and an evolution of carbon dioxide. 



These experiments satisfied me that the consumption of oxygen and the 

 formation of carbon dioxide, which must occur during the fermentation of small 

 quantities of organic matters in a water, when taken together, provided a most 

 delicate indication of the presence of such matters in a water. 



But little consideration, however, was necessary to lead one to anticipate that 

 a method of inquiry, based upon the determination of the changes in composition 

 of the dissolved gases, would lead to much more definite results, especially when 

 coupled with the determination of the inorganic nitrogenous products of the 

 fermentation — such fermentation to be conducted under suitable conditions. 



In explanation of my meaning, I would refer to the more recent researches on 

 nitrification. 



Dr. Munro,* Dr. P. F. Frankland,t and Mr. Warrington, :i: have all demon- 

 strated that the fermentation of ammonia to nitrous acid may occur in inorganic 

 solutions to which no organic matters have been added. M. Winogradsky§ has 

 extended these observations, and has not only shown that a nitrous fermentation 

 proceeds when organic matters are rigorously excluded from the cultivating 

 inorganic solutions, but he has also demonstrated that organic matters are formed 

 from inorganic materials at the same time, the first step in their formation, possibly 

 being, as suggested by him, tlie production of an amide from ammonium carbonate. 



We find, moreover, abundant evidence given in Munro's Paper, that unfer- 

 mented non-nitrogenous organic matter is positively prejudicial to nitrification, 

 and that, if present with anmionium salts in a water containing soil or water 

 organisms, they undergo fermentative changes before nitrification sets in. 



We have evidence also from the same author's Paper that the nitrification by 

 soil organisms of nitrogenous substances, with no added ammonium compounds, 

 follows a similar course. A putrid bacterial fermentation first takes place, during 

 which nearly the whole of the organic nitrogen is converted into ammonia, and this 

 ammonia apparently only begins to undergo nitrification after the first fermenta- 

 tion of the organic matter originally present has been completed. 



If, then, the nitrification, by the mixed organisms which ordinarily occur in 

 soils and natural waters, of organic substances containing nitrogen, or mixtures 

 of these containing no nitrogen with ammonium compounds, takes place in 

 two distinct stages as above indicated, it is probable that accurate determina- 

 tions of the more obvious products of each stage of fermentation, viz. carbonic 



*• Loc. cit., p. 653. t "I"!"!- Trans.," 181, p. 107. X " Chem. Soo. Journ.," 59, p. 484, 



§ " Annales de I'Institute Pasteur," vol. iv., pp. 213, 257, 760; vol. v., pp. 92, 577. 



4H2 



