esearches we have obtained the following
information with regard to the nature of the organisms concerned in this
process, and the conditions most favourable for their development.

_Ferments effecting Nitrification._

The importance of isolating and studying them microscopically was
recognised at an early period in these researches. Messrs Schloesing and
Muentz were the first to attempt this. They reported that they had
successfully accomplished this, and described the organism as consisting
of very small, round, or slightly elongated corpuscles, occurring either
singly or two together. According, however, to the most recent
researches of Warington, Winogradsky, and P. F. Frankland, nitrification
is not effected by a _single_ micro-organism, but by _two_, both of
which have been successfully isolated and studied.[106] The first of
these to be discovered and isolated was the _nitrous_ organism, which
effects the conversion of ammonia into nitrous acid; the second, which
has only been lately isolated by Warington and Winogradsky, effects the
conversion of nitrous acid into nitric acid. Each of these ferments thus
has its distinctive function to perform in this most important process,
the nitric ferment being unable to act on ammonia, as the nitrous
ferment is unable to convert nitrites into nitrates. Both ferments occur
in enormous quantities in the soil, and seem to be influenced, so far as
is at present known, by the same conditions. Their action will thus
proceed together. Nearly all we know as yet on the subject of their
nature is with regard to the nitrous ferment.

_Appearance of Nitrous Organism._

Mr Warington[107] thus describes the appearance of the nitrous organism:
"As found in suspension in a freshly nitrified solution, it consists
largely of nearly spherical corpuscles, varying extremely in size. The
largest of these corpuscles barely reaches a diameter of 1/1000th of a
millimeter; and some are so minute as to be hardly discernible in
photographs, although shown there with a surface one million times
greater than their own. The larger ones are frequently not strictly
circular. These forms are universally present in nitrifying cultures.
The larger organisms are sometimes seen in the act of dividing."

_Nitric Organism._

So far as at present known, the nitric organism is very similar in
appearance to the nitrous organism, so much so that it is difficult to
distinguish the one from the other. As t