70G The Nitrifying Ferments of the Soil. 
would serve, tlie best was known to be that already charged with 
nilrMe, sucli as cave eartli, manured garden soil, the earth in 
the neighbourhood of stables and refuse heaps, &c. The neces- 
sary potash of course came from the ashes, the oxygen from the 
atmosphere, and the nitrogen in Boussingault's time was known 
to be supplied by the urine and animal matter, and to be con- 
verted by the putrefaction of these into ammonia before under- 
going oxidation and combination with the potash to form 
nitrate. 
For the jDotash of the ashes substitute the lime of the soil, 
and for the nitrogen of the animal matter that of the decaying 
vegetable matter of the soil, which is slowly given off as ammo- 
nia during the decay, and it is seen that the formation of 
nitrate of lime in soil proceeds on the same lines as that of 
saltpetre in the nitre-heap. That the formation of nitrate is 
encouraged by warmth, by moisture, by porosity of the soil, by 
tillage and other operations favouring free admission of air, and 
by the presence of lime or potash, was as well known fifty yean 
ago as it is to-day. But the combination of the atmospheric 
oxygen with the nitrogen and hydrogen of the ammonia result- 
ing from decaying vegetation was then, and for very many years 
afterwards, supposed to be as purely chemical an action as the 
combination of nitric acid, once formed, with lime or potash to 
produce nitrate of lime or nitrate of potash. 
Not indeed until 1877, when the experiments of Schloesmg 
and Miintz threw an entirely new light upon the matter, 
was any other opinion generally entertained, although 
Pasteur himself had in 18G2 suggested as probable that 
the oxidation in this case, as in the familiar one of the 
conversion of wine or beer into vinegar, might be due to 
the action of a living ferment, and not to simple contact 
with the air. Fifteen years after this suggestion the first 
experiments confirming it Avere published, and not until the 
jDresent year, that is after the lapse of nearly fifteen years 
more, has the prediction been fully and completely verified by 
the isolation and separate examination of at any rate two of 
the species of organisms concerned in the process. So slow in 
certain cases is the onward progress achieved by what we are 
accustomed to regard nowadays as the rapidly advancing strides 
of science ! A short sketch of the hunt after these organisms 
which followed on the publication of Schloesing and Miintz' 
results will disclose some reasons for the slow progress in this 
case and will be instructive in other ways. !Much light has 
been thrown on the obscure process of nitrification, and the 
organisms at last identified as being the true agents are so sin- 
