Adeney — Dissolved Gases and Fermentative Changes. 543 



action of the mixed organisms present would probably be shown most prominently 

 in the last-mentioned products, viz. the fermented organic matters. 



With these considerations in mind, I commenced a series of experiments as 

 long back as the autumn of 1891. The slowness, however, of some of the fermen- 

 tative processes under observation, combined with long-continued interruptions in 

 the course of the work by other duties, has hitherto prevented my being in a 

 position to publish any results. The scope of the investigation has also widened, 

 and very many points have arisen and demanded experimental study, which were 

 not anticipated at the commencement of the work. Even now, I cannot claim to 

 have finished the investigation of many of these points. 



My experiments, however, in so far as the original object of the investigation 

 is concerned, have now reached a sufficiently advanced stage, I think, to render 

 any further delay in publication undesirable. I therefore propose, in this com- 

 munication, to deal with such experiments as bear directly on the question 

 with which I started this investigation, viz. whether the amount of the dissolved 

 oxygen consumed during the complete fermentation of a polluted tvater might not he 

 regarded, for the purpose of water analysis, as a quantitative index to the amount 

 of fermentable substances originally present in it, provided that during the process 

 care is talcen to have the oxygen in excess in the water. And, further, whether 

 it might not be possible to separately estimate the volume of dissolved oxygen 

 consumed during each of the two distinct stages in which it is supposed the 

 nitrification of organic matter takes jjlace. I say supposed advisedly, because it 

 cannot be regarded as having been experimentally proved that the nitrification 

 of nitrogenous organic substances, or of non-nitrogenous organic substances mixed 

 with ammonium compounds, really takes place in two stages, except when the 

 fermentation is carried on under partially aerobic and partially anaerobic con- 

 ditions. There can be little doubt, for example, that in Munro's * experiment 

 on the nitrification of gelatin, in which, during the earlier stages of fermentation 

 he noticed putrefactive products and the formation of ammonia, free oxygen must 

 have been entirely absent from tlie lower layers of the solution he employed, 

 judging from its strength. 



It cannot be taken for granted, therefore, that the oxidation by fermentation 

 of gelatin, or other nitrogenous substance, in the continued presence of an excess 

 of free oxygen, would be "progressive," as above described, rather than "complete 

 from the commencement."t 



I may, however, anticipate in this particular, the experiments which I have to 

 describe, and state that they all go to show that the fermentation of such bodies 

 by the mixed organisms of soils and waters takes place in two perfectly distinct 



* Loc. cii., p. 641. 



■f See ScMtzenberger on "Fermentation," p. 244. International Scientific Series, 1891. 



