716 
The Nitrifying Ferments of the Soil. 
soil sterilised by heat with pure cultures of the nitrous and the 
nitric ferment. A little ammonia added to the soil inoculated with 
nitrons ferment is speedily oxidised to nitrite, which persists, 
whilst ammonia added to the soil inoculated with nitric ferment 
is not altered. On adding ammonia to soil inoculated with both 
ferments it is oxidised to nitrate with scarcely a passing trace of 
nitrite, just as we find happen in natural un sterilised soil. 
Things happen differently in liquid cultures because of the re- 
stricted supply of air. The nitrous ferment, which is larger, 
much more conspicuous in development, and much more, 
active in causing oxidation than the nitric ferment, hinders the 
development and activity of the latter so long as there is any 
ammonia present to attack. The nitric ferment, like the nitrous, 
refuses to grow on gelatine, and thrives in liquids absolutely 
free from organic matter. In all probability, though this has 
not yet been directly established, it obtains its supply of carbon 
from mineral carbonates in the same way as does the nitrous 
ferment. When grown in quantity in a transparent liquid, it 
coats the bottom of the vessel with an excessively thin, adherent 
film of a bluish grey colour. This gelatinous layer is seen under 
the microscope to be made up of masses of a very minute bac- 
terium, whose length is greater than its width, but does not 
exceed ^-oijoir of an inch (Winogradsky). 
The slow action of both ferments in comparison with better- 
known ones is well worthy of remark. In pure cultivations 
under favourable conditions an inoculation of the nitrous fer- 
ment only developes in sixteen days sufficiently to oxidise 3- of a 
grain of ammoniacal nitrogen per day. The nitrous ferment is 
still slower — after an intensive culture of six weeks it was nitrat- 
ing only ^ to I- grain of nitrous nitrogen per day. We have 
only space to add that from some experiments of Muntz on the 
nitrification of nitrogenous matter in presence of sea salt, it 
would seem almost certain that the Peruvian deposits of 
crude nitrate of soda are the results of a gigantic nitrification 
which formerly went on in the drying up residues of salt lakes. 
The same observer has found in the earth of the nitrifying cave- 
deposits of Venezuela a nitrifying organism which he describes 
as three or four times the size of that found in French soil. 
The practical point should not be lost sight of that nitrates 
are destroyed much more easily and much faster than they can 
be formed. A free supply of air above all things favours their 
preservation, whilst the presence of organic matter in the absence 
of air is certain, under natural conditions, to result in their 
destruction. This work, too, is brought about by microbes, and 
is a property common to a great number of different species. 
