The Nih'ifi/ing Ferments of the Soil. 
709 
All these facts, and many others which there is no space to 
Retail, were perfectly congruous with the theory of a living nitri- 
fying ferment or ferments, and, indeed, were not explicable on any 
jther theory. But they went no distance towards isolating this 
ferment from the many species of microbes which inhabit the 
soil, in order to study its form, mode of life and reproduction, and 
(its chemical activity in pure cultures like those of the yeast plant. 
[Though no success attended the earlier efforts, they rendered 
lit probable that the nitrifying power is not common to many 
microbes, but probably confined to one or two distinct species. 
(Experiments with some of the common moulds, with yeast, and 
■with the vinegar ferment were made by Schloesing and Miintz 
I with negative results. The same observers published in 1883 
a short account of what they took to be the real nitrifying 
: microbe (separated to some extent from its associates by suc- 
I cessive cultivations in suitable liquids), which tiiey describe as a 
small, nearly round micrococcus, but in the light of our present 
knowledge it is certain that although they doubtless saw one or 
more of the organisms producing nitrification, they could not 
have accomplished the isolation of these in a pure state. 
Two unexpected facts which had cropped up were destined 
to have an important influence in the solution of this problem, 
although their true bearing was not seen until much later. 
' Warington, and all after him who carried out nitrification in 
liquid media, found the phenomenon to differ greatly in one 
respect from what takes place in the soil and in natural waters. 
For whereas, in soils and waters, we can rarely trace any inter- 
mediate compound between the ammonia which is being nitrified 
and the nitrate which is formed, the contrary is the general rule 
with artificial solutions. In nearly all of these a nitrite (that is 
a salt of nitrous acid containing an equivalent less of oxygen 
than the corresponding nitrate) is at first formed ; often no 
nitrate is produced until the whole of the ammonia has passed 
into the form of nitrite ; and in some cases it was observed by 
Warington and by the writer, that the action went no farther 
than the production of nitrite, which remained permanent, 
though as a general rule the nitrite eventually, and sometimes 
with great suddenness, was entirely converted into nitrate. 
Now, nothing is easier than to produce nitrites /roire nitrates 
by abstraction of oxygen, and many different species of microbe 
have been found to possess the power of doing this in the 
presence of organic matter, which they can burn up by the 
consumption of this oxygen. It was natural therefore foi' 
Gayon and Dupetit to suggest that the nitrites formed in 
artificial pitrificatioji were really products of the rednctioii of 
