The Niirlfyinrj Fermentu of the (bi'ojY. 
of tlie air, which may carry in nitrifying germs, bnt does not 
always do so, be simply excluded by a plug of cotton-wool. 
Nay, the mere heating to 101° F. is fatal, and we infer that 
at this temperature the active organisms are killed. The 
temperature at which nitrification is most rapid is given by 
Schloesing and Miintz as 98°-99° F. Cold, of several degrees 
below freezing, as might be expected, is not fatal to the organ- 
isms, but it entirely suspends their activity, which, however, 
is manifested by a very slow nitrification at temperatures as low 
as 38° F. Baked soil has no power of starting nitrification. 
Traces of lead and mercury salts, salicylic acid, and most other 
antiseptics are fatal to the process ; and the absence of sufficient 
quantity of some base, such as lime, potash, soda, ammonia, or 
magnesia, will cause it to stop the moment the base is used up, 
although it may be re-started at any time by adding a little of 
any one of these bases in the form of carbonate. If added ia 
the pure or caustic state they may kill the ferment. 
As might be expected, not only ammonia salts but all nitro- 
genous substances capable of yielding ammonia by putrefaction 
or decay are eventually nitrified by the action of soil. Warington 
records many experiments of this sort with asparagine, milk, 
urine, rape-cake, &c., and the author has succeeded not only with 
urea and gelatine but with such simple nitrogen compounds as 
ethylamine and sulphocyanates. Should, however, the nitrogen 
compound be itself an antiseptic, it is not susceptible of nitrifi- 
cation ; thus thiocai-bamide, a compound containing precisely 
the same elements and in the same proportions as ammonium 
sulphocyanate, failed to nitrify. 
Many experiments were made by the method of inoculating 
suitable ammoniacal solutions, to ascertain the distribution of 
the nitrifying ferments in nature. Warington, summing up 
a number of trials, tells us that all samples of soil taken down 
to two feet in depth provoked nitrification, but that over this 
depth failures to nitrify increase in number, and at a depth of 
six feet and over the soil has lost this power. Froin this and 
other experiments it is certain that the first few inches of sur- 
face soil contain the ferments in vastly greater proportions than 
the subsoil. From the soil these ferments get into waters, and 
the power which rivers and wells possess of ultimately convert,- 
ing the ammonia of sewage into nitrate of lime depends on 
their presence. The writer, examining in 1886 various samples 
of river and well water, found that inoculation with one to five 
drops of any of them was sufficient to bring about nitrification 
in a suitable ammoniacal solution, bnt that rain water caught 
in a perfectly clean vessel is destitute of the power. 
