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truly to give the euique suum in this part of science, one often must 
retrograde half a century.” 
Not before 1856 the problem was again taken into research. In 
that year Reiser’) pointed out, that at the putrefaction of dung and 
flesh free nitrogen is produced. Later investigators have not been able 
to observe free nitrogen under these circumstances, in asmuch as 
no nitrate or nitrite are present, but the putrefaction of albuminous 
matter as such has still remained an open question from this point 
of view. 
It was Prrouzr ®), who in 1857, for the first time, with certainty 
stated the disappearance of nitrate during the putrefaction of animal 
matter. 
BoussinGAuLtT *) observed in 1858 the disappearance of salt-peter in 
the soil. He aseribed it “a une cause purement accidentelle, a une 
action réductrice, exercée par de la matiere végétale morte”. 
From the year 1873 date very interesting observations of SCHLOESING *) 
on nitrification. By studying the influence of oxygen on this process, 
he was led to the examination of denitrification. He found that nitri- 
fication in the soil was still very active, when it was held in a current 
of gas, which contained but 1,5 °/, oxygen. If he worked in a current 
of pure nitrogen, there not only occurred no nitrification, but even 
the nitrate, originally in the soil, disappeared entirely. He furthermore 
proved that at this decomposition nitrogen is formed. 
Experiments of Pasrrur and the well known investigation of 
SCHLOESING and Münz on nitrification, induced Gayon and Durerir *) 
to ascribe denitrification to the action of micro-organisms. In 1882 they 
communicated their first results and these put the bacterial nature of 
the process out of all doubt. Their elaborate and excellent researches 
on this subject were published in 1886 °). 
Our compatriots Girtay and ABERSON ‘) isolated, for the first time, in 
1892 a denitrifying ferment, and the prescription given by them for the 
artificial culture liquid has been followed by various later investigators. 
The attention of bacteriologists was again fixed on these ferments 
1) Expériences sur la putréfaction et sur la formation des fumiers. G. R. 1856, 
T. 42, p. 53, 
2) Remarques de M. Perovze. G. R. 1857, T. 44, p. 119. 
3) Nouvelles observations sur le développement des helianthiws soumis iV action 
du salpètre donné comme engrais C.R. 1858, T. 47, p. 807. 
4) Etude sur la nitrification dans les sols, C.R. 1873, T. 77, p. 203. 
5) Sur la fermentation des nitrates, G.R. 1882, T. 95, p. 644. 
6) Recherches sur la réduction des nitrates par les infiniments petits. Naney. 1886. 
7) Recherches sur un mode de dénitrification et sur le schizomyeéte qui la 
produit. Arch. Neerl. T. 25, 1892, p. 341, 
