710 
The Nitrifying Ferments of the Soil. 
the nitx'ates at first formed by the action of these reducing 
microbes, many of which are present in the soil. The writer 
succeeded in" disproving this by showing that nitrates are not 
reduced by the microbes of soil in the absence of organic 
matter other than that in the soil, but that under the same 
circumstances both nitrites and nitrates are freely produced 
from ammonia. The production of nitrite therefore remained 
as a usual characteristic of artificial nitrification not traceable 
in the natural process.' By varying the conditions, either 
nitrite or nitrate could certainly be produced at will, even in 
liquid media ; a high temperature, a small dose of inoculating 
material (soil or solution), a strong ammoniacal liquor, and a 
deep layer of it, being favourable to nitrite production, whilst 
with much soil, a low temperature, dilute solutions, and shallow 
layers freely exposed to air, nitrates could be produced without 
any intervening nitrite. But having once produced nitrite, we 
could not at will determine its transformation into nitrate 
except by re-inoculation with soil. 
What was the meaning of this ? Were there two organisms 
or species, one stopping its work at the production of nitrite, and 
the other carrying on the process ? Or did the methods of cul- 
tivation modify the activity of the nitrate-producing ferment and 
render it unable to complete its natural work ? These questions 
could only be answered decisively by successful isolation of the 
nitrifying ferments, the very existence of which some chemists 
were disposed to doubt anew as time went by and no announce- 
ment of their isolation appeared. 
The other unexpected fact came out in 1886, when the writer 
published experiments showing that nitrification had taken place 
in solutions to which no organic matter had been added except 
that in the drop of inoculating material ; and this induced him 
to state the question, " Is organic carbon essential to nitrifica- 
tion ? " In many other of his experiments the presence of organic 
matter was seen to be distinctly antagonistic to any nitrificatior 
provoked by the necessarily impure inoculations witvh soil, ordin- 
ary waters, or nitrifying solutions, all of which contain abund- 
ance of miscellaneous microbes, some of which are sure to flourisl 
and take the fas of the nitrifying ferments in the organic mediuii 
provided. A little sugar, tartaric acid, or other carbonaceou 
compound had hitherto been included by all experimenters ii 
the cultivation media, for the purpose of supplying the nitrifyinj 
organisms with carbonaceous food, it being the universall; 
' The writer has, however, found considerable quantities of nitrite in tli 
effluent from the soil filtering-beds of sewage farms. 
