ArRiL I, 1901.] 
THE TROPICAL AGEICULTURIST. 
663 
SOIL UACTERIA. 
(From Agricultural Gazette of New South Wales.) 
R. Helms. 
The discovery of the important part played by 
certain bacteria withiu the soil io converting nitro- 
genons substances into nitric acid, In which form 
plants assimilate one of their most important food- 
stuffs, has created a clearer conception of the pro- 
cesses by which such chemical changes are brought 
about. This, together with the discovery that 
certain plants by means of similar minute or- 
ganisms in their roots can utilise the nitrogen of 
the atmosphere, has opened out new vistas to 
scientific agriculture. 
Besides these oxidising organisms a number of 
others occur exteusively, which act in the reverse 
manner by reducing nitric acid to ammonia, or even 
to nitrogen, and thereby play, on the whole, an 
even more important part in the economy of nature, 
although in many instances their action is the 
reverse of benetioal to plant life. These are known as 
reduciug or deuitiifyiug organisms in contradistinc- 
tion to the first-mentioned, which have been 
named, nitrifying bacteria. 
Anything we can do to increase the development 
of the nitrifying bacteria, or to design methods for 
checking the too rapid multiplication of the reduc- 
ing organisms, will, at the same time, be the means 
of increasing the fertility of the soil, improving 
those soils that are poor, and maintaining the pro- 
ductiveness of more fertile ones, since, of all the 
faetors on which the fruitfulness of land depends, 
the power of nitrification is undoubtedlj' the most 
important. 
Investigations with this aim in view, carried on 
during late years in the greater number of coun- 
tries where agriculture is pursued according to ad- 
vanced principles and with modern appliances, 
have led to promising results, and these researches, 
together with the better understanding of the 
value of manures, are beginning to produce a re- 
volution in the theory and practice of agronomy. 
Since the 'functions of these organisms are con- 
siderably affected by their surroundings, and they 
behave d'.ilerently in diliferent soils and climates 
these diffeieoces may prove to be very pronounced 
in Australia where bith soil and climate are so 
extremely variable and peculiar. It is therefore 
not possible to accept as conclusive the results 
obtaiued by investigators in other countries, and it 
becomes necessary to study their behaviour under 
local conditions. 
Before farther discussing the different groups of 
soil bacteria and dwelling upon their characteris- 
tics, it is desirable to sketch the history of their 
discovery in an epitomised form, and to present 
the results hitherto obtaied by different investiga- 
tors. 
Historical. 
As far bick as 18(52, Pasteur surmised that nitri- 
fication in soil was due to micro-organisms. Up to 
his epoch-making iovestigations, fermentations were 
considered to be the result of purely chemical re- 
action, and it was but natural that, after pioving 
the importaut part played by the yeast organisms, 
he should go so far as to consider other pheno- 
mena involving complex chemical changes as beiug 
connected with similar microbes. 
Schloessing and Muntz proved in 1878 that the 
action of uiinute organisms caused nitrification, or 
the transformation of ammonium salts into nit- 
rates by oxidation. This fact was confirmed by 
Warrington in the same year, A definite know- 
ledge oi the specific organisms producidg the alter- 
ation of nitrous compounds were, however, not 
obtained. 
HersBus was the fir-it who, in 1886, applied the 
modern methods of bacteriological research to thia 
subject. He claims to have obtained positive results. 
H 
By means of elaborate investigations on a large 
number of bicteria obtained from soil, water, and 
air he managed to produce pure cultures. Among 
them he credited four distinct bacilli with nitrifying 
power. 
Frank soon after maae lengthy investig itions oa 
bacteria insolated from several kinds of soil, and 
obtained entirely negative results. In consequence 
he disputed the vital process in connection with 
nitrification. 
This conclusion was rebutted by Plath and Bau- 
mann in 1887. 
(Jelli and Marino Zucco in the meantime had 
experimented with five micrococci isolated from the 
highly nitrated water of Rome, but did not 
succeed in proving that any of these were the 
specially-qualified nitrifying organisms. 
Warrington examined, in 1888, a large number of 
bacteria obtained from soil for their nitrifying power 
without arriving at the desired result ; but when, 
instead of his pure cultures, he took ordinary soil 
for seeding his food media with, he always succeeded 
in inducing nitrification. These researches led hira 
to the conclusion that the specific organisms had 
yet to be found. 
Further, Percy Frankland and Grace Frankland 
have paid attention to this important question. 
Although they experimented with twelve different 
organisms isolated from soil, the result was in every 
case a negative one ; but, as with Warrington, 
when using a little of the soil from which the 
organisms had been obtained, nitrification was 
readily excited in the culture fluids. 
As these many experiments of such able bacterio- 
logists failed to prove a definite nitrifying organism 
the result of Schloessing and Mu:itz were attacked 
anew, and it was again doubted whether organisma 
played any part at pll in nitrification, 
At this stage the famous Winogradsky, of Zurich, 
took the question up, and by his masterly handling 
of the subject produced definite and important 
results, 
Prom the experience gained by experimenting 
with such a large number of different organisms 
during several years, and by the foremosi 
bacteriologists, it had become apparent that those 
capable of introducing nitrification could not be 
numerous, and that probably only one or two might 
exclusively possess this characteristic. It had, 
moreover, become plain to him that the organism 
in question did not thrive on the ordinary nutrient 
media composed of orgauic substances in general 
use for the official cultivation of pathogenic and 
other microbes. Winogradsky very ingeniously took 
advantage of this peculiarity. By showing ordinary 
gelatine plates with cultures derived from various- 
soil bacteria, he induced a vigorous growth of 
species that flourished in this medium, and then 
grafted in suitable fluids from the spots whioh 
showed no development, Thus he succeeded in 
separating the nitrifying organisms. Further dis- 
cussion of the methods, of manipulation is need- 
less, but he ultimately proved a somewhat oval- 
shaped organism to be possessed of the characteris- 
tic power to nitrify ammonium salts. 
The puzzle was solved at last, and led to more 
definite studies being continued by Winogradsky 
and others. The technique of bacteriology had 
meanvfhile been enriched by the clever invention 
of Kuhne, who provided a solid culture medium 
free from organic substances by galatioising silica. 
This allowed of reliable work beiug done in a more 
rapid manner. 
Several species, or may-ba varieties, of nitrate- 
producing organisms have been detected in soils 
from different parts of the globe, and it seemg 
fairly certain that nitrifying organisms are univer- 
sally distributed and found in most soils, but are 
present in greatest number in fertile areas, Less 
ia known of the nitrate-forming organisms, and 
