Aprnry—Dissolved Gases and Fermentative Changes. 271 
J 
and nitrogen-oxidation more accurately describe the two stages of change, on the 
grounds that the phenomena dealt with in these studies are really processes of 
decay or eremacausis, and that it is important that it should be clearly shown that 
no such change can take place in organic matters without heat evolution, whether 
brought about by the action of organisms, or by the action of fire; that is to say, 
actual combustion. 
The terms suggested by Professor Hartley have the great advantage of accuracy 
in their application, and, as a matter of fact, I occasionally used the terms carbon- 
fermentation and nitrogen-fermentation in a similar sense in my first Paper,* 
but hesitated to propose their general adoption, hoping that less cumbersome 
terms would suggest themselves after the publication of the Paper. In the 
absence, however, of such suggestion, I now propose to adopt the terms carbon- 
oxidation, and nitrogen-oxidation, or nitrification, to respectively denote the first 
and second stages of aérobic fermentative changes which form the subject of these 
studies. With the adoption of these terms, we may also adopt the classification 
of all fermentable bodies into (1) carbon-oxidizable bodies, or all fermentable 
organic substances which have not undergone carbon-oxidation ; and (2) nitrifiable 
bodies, or ammonium compounds, and organic bodies which have suffered carbon- 
oxidation. 
Opsuct oF EXPERIMENTS. 
Turning now to the consideration of the experiments which I have to describe 
and discuss in this Paper—they have been made with the view of supplementing 
the information which I have already published upon the fermentative, and certain 
other, properties of the nitrifiable organic substances to be met with in natural 
waters. 
These substances may be divided into three classes, according to their origin: 
viz. (1) the organic matters derived from the carbon-oxidation of fermentative 
organic substances in solution, eg. those present in most good river-waters ; 
(2) those derived from peat, e.g. those to be found in upland surface-waters ; and 
(3) those derived from the organic matters or humus in soil, ey. those found in 
spring and well waters. 
Classes 1 and 2 have been dealt with in Parts I. and II. of my first communi- 
cation. I have now to take up the consideration of class 3, and I may add that, 
fortunately for my purpose, I have been able to employ a specimen of humus, the 
formation of which I knew beyond doubt to have been due to a true carbon- 
oxidation of fresh animal and vegetable solid refuse matters kept in a moist 
condition. 
* Loc. cit., p. 610, 
PFS 2 
