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XI. 
THE COURSE AND NATURE OF FERMENTATIVE CHANGES IN NATURAL 
AND POLLUTED WATERS, AND IN ARTIFICIAL SOLUTIONS, AS INDI- 
CATED BY THE COMPOSITION OF THE DISSOLVED GASES. (Parr IV.) 
Hummus; rrs Formation anp Inriurnce 1n Nirrirication. By W. BE. ADENEY, 
Assoc. R.C.Se.1., F.1.C., Curator in the Royal University, Dublin. 
[Read Apri 21, 1897. | 
INTRODUCTION. 
In this continuation of my studies of the changes in composition of dissolved 
gases which accompany bacterial fermentations in waters, I propose to detail and 
discuss some experiments with certain organic substances which belong to the 
class termed in my previous communication, difficultly fermentable substances, to 
distinguish them from the class of substances which readily undergo fermentation 
in the presence of the micro-organisms ordinarily present in air and water, to 
which class most of the remaining known organic substances, with the exception 
of antiseptics, probably belong.* 
The organic substances which may be included under the heading of “ diffi- 
cultly fermentable ” are those found in good natural waters, and also those to be 
found in sewage, or other polluted waters, that have been subjected to complete 
fermentation under aérobic conditions, such as obtain during slow filtration through 
sand and soil. 
I have already dealt with some of the latter forms of organic substances, and 
also with some forms to be met with in natural waters, viz. peaty colouring 
matters. 
The substances which have been employed for the experiments that I have presently to 
describe may be regarded as representative of the organic matters which occur in cultivated 
souls, and which find their way more particularly into well and spring waters. 
Before proceeding, however, to the consideration of fresh experiments, it is 
* Trans. Roy. Dub. Soc. N.S., Vol. v., Part xi., p. 540, 1895. 
t Loc. cit., Tables V., IX., X., ete. 
t Loe. cit., Tables XIV., XV., and XVI. 
TRANS. ROY. DUBL. SOC., N.S. VOL. VI., PART XI. 28 
