AprnrY—Dissolved Gases and Fermentative Changes. 273 
No trace of sulphuretted hydrogen, nor of other products of putrefactive 
fermentation, such as are met with when sewage solid matters alone are kept 
under similar conditions, were detected. An examination for nitrates was also 
attended with negative results. 
Freshly precipitated manganese peroxide is also rapidly reduced to manganous 
carbonate when it is kept immersed in comparatively large volumes of sewage 
water, in which bacterial fermentation is actively proceeding. 
REDUCTION OF HYDRATED MANGANESE PEROXIDE IN THE PRESENCE OF ORGANIC 
Marrer DuE To LivinG ORGANISMS. 
I pointed out, in the Paper above referred to, that, when we consider the 
chemical characters of the peroxide of manganese, it seems impossible to avoid 
the conclusion that it owed its reduction to manganous carbonate, to the influence 
of some, at least, of the organisms which were abundantly present in the liquid 
with which it was saturated or immersed, and that the decomposition was analogous 
in character to that which Gayar and Dupetit* have shown nitre undergoes when 
it is present m a nutrient medium in which certain organisms are grown; and I 
showed, by means of thermo-chemical equations, that if the decomposition of the 
peroxide of manganese be thus regarded as the result of a fermentation, consisting 
of the direct oxidation of organic carbon at the expense of its available oxygen, 
the changes would be attended with considerable heat evolution, and would there- 
fore constitute a considerable source of energy to the organisms. 
We may now, however, take it for granted that the reduction of the moist 
peroxide, in the presence of organic matters, is the work of living organisms ; for 
since the publication of my Paper referred to, my friend and colleague, Dr. E. J. 
MecWeeney, has made the question a subject of bacteriological examination, and he 
has informed me that, in his experiments, in which he kept freshly precipitated 
manganese peroxide in carefully sterilized nutrient liquid media, no reduction of 
the peroxide was noticed, but that, in those experiments in which the nutrient 
media were seeded, after sterilization, with particles of the same fermented sludge 
as that with which I had worked, a rapid and very abundant growth and develop- 
ment of living organisms took place in the media; and at the same time it was 
noticed that the brown colour of the peroxide immersed therein was gradually and 
completely changed into a yellowish white. I subsequently examined this white 
substance myself, and found it to consist of manganous carbonate. I should add 
that the nutrient medium employed by Dr. McWeeney was a mixture of asparagine 
***Ann. de la Science Agronomique,” 1885, 1., 226; also abstract “Chem. Soc. Journ.,” xix, 
p- 828. 
