The Nitrifying Ferments of the Soil. 
715 
vert it into a nitrite only and not into a nitrate ; and therefore, 
i as Warington remarks, they had " solved only half the problem 
of nitrification." The key to the remaining half was announced 
by Warington in June of this year, and by Winogradsky in 
July. Both have since published extended memoirs dealing 
with the subject. 
Although a particle of soil added to a suitable ammonia- 
cal solution will convert the ammonia first into nitrite and 
then into nitrate, and if sown in a suitable solution of 
nitrite will easily convert that into nitrate, yet the effect of 
successive cultures in these two different media is to bring 
about a decided difference in the power of the ferment. After 
a few cultivations in ammoniacal liquids the power of affecting 
nitrites is lost, as we have seen ; but it is equally true that after a 
very few cultivations in nitrite the power of affecting ammonia 
is lost. By proceeding in this way with one of his old liquids, 
using the method of successive cultivations in nitrite solutions 
combined with that of attenuation or dilution, Warington has 
produced a nearly pure cultivation of an organism, which as he 
asserts, and as I have verified at his request, has absolutely no 
power to oxidise ammonia, though easily converting nitrite into 
nitrate. Winogradsky, by cultivating particles of soil in nitrite 
until the power of attacking ammonia is lost, and then growing 
colonies on gelatinous silica, has obtained in a pure state an 
organism having the same properties, though not agreeing in 
form with that found by Warington. This, however, is less 
remarkable, since the nitrifying organisms separated by Wino- 
gradsky from soils of different origin are by no means identical 
in appearance, nor (and this is an important practical point) are 
they by any means possessed of the same energy. 
Amongst soils obtained from several parts of the world, 
Winogradsky finds that one from Quito contains a nitric ferment 
of quite exceptional energy. On the other hand, the European 
soils of Zurich and Gennevilliers contain a nitrous ferment of 
greater activity than those from exotic soils. The writer is 
examining in the same manner some varieties of English soil. 
According to Warington, pasture soil is much better supplied 
with the nitrous ferment, or worse supplied with the nitric 
ferment, than arable soil. Many points in the action of these 
ferments still require study, but we now know that the formation 
of nitrates in the soil is accomplished in two stages, by two 
distinct species of organism, the nitrons and the nitric ferments, 
neither of which can do the work of the other, but the latter 
waits to complete what the former began. 
Doubt on this point is removed by the result of inoculating 
