THE CAUSES OF THE FERTILITY, ETC. 41 
and contains no chlorophyll. They are also characterized 
by the absence of ordinary sequal reproduction. Now, 
baccillus or bacterium are unsatisfactory terms, as really 
they have narrow technical meanings. The proper name 
for this class of organisms is Schizomycetes, a term to which 
I shall keep in this lecture unless 1 speak of that particular 
kind of schizomycetes which are called bacteria. The size 
of these organisms is usually i M (.001 millimeter) in dia- 
meter, and 1 5 ft (.001 to .005 millimeter) in length. There 
fore it is not to be wondered at that up to 400 million have 
been found in one grain of cultivated soil. 
The important discoveries of Fischer, Koch, Pasteur, 
Winogradsky, Hilfner and Stormer, and many others, 
have shown that these schizomycetes play a great part in 
the fixation of nitrogen in soils, and their work is of special 
importance to us in Western Australia. 
We know now that in all cultivated soils there are 
forms of schizomycetes, mostly bacteria, which are capable 
of forcing the inert free nitrogen to combine with other 
elements into compounds assimilable by plants. Wino- 
gradsky showed that one of these, Clostridium Pasteurianum, 
is enveloped by aerobic bacteria or by fungi living in symbi- 
osis, which prevent the access of free oxygen; and if the 
conditions of growth are favorable, i.e., if carbohydrates, 
potassium hydrogen phosphate, magnesium sulphate, sodium 
chloride, ferrous sulphate and manganese sulphate are 
present, Clostridium will fix nitrogen in proportion to the 
amount of sugar consumed. 
As a typical example of the many cases of nitrification 
which go on in sods, the decomposition of Urea [C -0 (NH 2 ) ) 
will serve well. 
Urea at first becomes carbonate of ammonia (NH,) 2 
CO , by a simple hydrolysis brought about by bacteria. 
This process may be explained as follows : — 
NHj NH, NH, 
I I I 
CO + HOH = C q|{ = C^° H + NH 3 
I I I 
Nil 2 NII, 
[CO, (NHj) + NH 3 ] + H,0 = C0 3 (NH 4 ), 
The carbonate of ammonia in its turn undergoes nitri- 
fication in two stages owing to the activity of the so-called 
nitrifying bacteria. Let me say at once that the term 
nitrification is rather unfortunate, as nitrification is only 
a particular phase of a cycle of changes undergone by nitro- 
gen in the process with which we have to deal. 
