270 ApvrenEY—Dissolved Gases and Fermentative Changes. 
desirable to decide upon the use of two new terms to indicate the two stages by 
which organic substances successively suffer aérobic fermentative change in 
waters, as described in my previous communications. During the first, an organic 
substance in solution is completely broken up ; much the greater part of its carbon— 
about 90 per cent. in some cases*—is converted into carbon dioxide, and almost all 
its nitrogen into ammonia (with the one exception of pure urea, the nitrogen of 
which is partly changed into ammonia and partly into nitrous acidt). A small 
quantity only of organic matter remains after the completion of this stage, and 
that in a very much altered form. 
The characteristic feature of the second stage of change is the oxidation of the 
ammonia, which may have been formed during the first stage, or which may have 
been originally present in the form of an ammonium compound, to nitrous and 
nitric acids. 
The organic matters resulting from the first stage of change also suffer a more 
or less complete oxidation in company with the ammonia during this second stage, 
and appear to play the important part of determining the final oxidation of the 
ammonia to nitric acid,t since when they are entirely absent—a fact now well 
known—the product of oxidation is nitrous acid only.§ 
These organic matters also undergo a second stage of change i the absence of 
ammonium compounds; under these conditions, however, the change takes place 
extremely slowly; the products of the change are carbon dioxide and nitric 
acid. || 
It is important to note, in reference to these organic products of a first stage 
fermentative change, or, as we may call them, fermented organic matters, that, 
whatever changes they undergo, they never give rise to the formation of ammonia. 
It has been suggested to me to employ the terms bacteriolysis or aérobiolysis 
for the first stage, and to restrict the use of the term nitrification to the second 
stage, of change. The restriction of the term nitrification to the use in this sense 
is, I think, most advisable, and I propose to employ it only in this sense in this 
and in future Papers. 
It would also be convenient to adopt a simple word, such as bacteriolysis or 
aérobiolysis for the first stage of change; but, as my friend Professor W. N. 
Hartley, F.r.s., has pointed out to me, neither of these terms can be regarded as 
indicating with sufficient accuracy the true nature of the chemical changes which 
take place during its course. He has suggested that the terms carbon-oxidation 
* Loc. cit., Tables VII., VIII., XI., and XII. 
{ Loe. cit., Table XVII. 
{ Loe. cit., Tables III., V., VII., VIII., X., XIII., XV., and pages 587, 588. 
§ Loc. cit., Table XVI. 
|| Loc. cit., Table XIV, 
