Medical Officers of the Army of India.
metabiotic nature, i.e., carried out in definite sequence What we have practically
gained so far is the solution of a crude and complex mass, and we have reduced the
formidable molecule to a condition of instability whereby it is open to attack on all
sides by oxygen—for oxidation is in all processes of "purification" our final aim.
It is obvious that nothing further in this direction can be obtained under the con
-ditions prevalent so far, and we must now proceed to provide suitable conditions
for the play of other forces, viz., those that act only, or at their best, in the pres
-ence of free oxygen; and here too we have to distinguish stages. In the first
place with the partial access of oxygen, some of the intermediate products,
ammonia, amido-bodies, fatty acids and the dissolved residues of the first stage
must undergo a further resolution, by double decomposition into water
or hydroxy compounds, with the formation of nitrites. Here also we recognise the
rôle
of the free hydrogen; it breaks up the molecule of oxygen, seizing on on
o n e a t o m a n d s e t t i n g f r e e t h e o t h e r a t o m f o r t h e m o s t p o w e r f u l o x i d i s i n g e f f e c t s .
The nitrous compounds also act as carriers of oxygen from the air to the remain
-ing organic matter. But besides these purely chemical effects, we have those o
f aerobic fermentation in dealing with many of the intermediate products of the
first stage, and as a result we chiefly get nitrites, ammonia, carbonic acid and other
gases, into which the organic matter is finally transformed.
133
Partial oxidation.
Lastly, with the freer supply of oxygen we get the third and final stage of
complete oxidization of the nitrogenous and carbonaceous residues, with the
formation of nitrates, and thus both the carbon and nitrogen complete their cycles
and become available for plant food; in the plant they are again built up into
complex carbohydrate and proteid. Both these stages of oxidation are con--
nected with the life processes of different specific micro-organisms, in the former
the nitrosomonas , in the latter the ni t r obact erp l a y s i t s r e s p e c t i v e
r ô l e ;
t h e p r a c t i c a l
point to be noted is that the conditions favourable to the one are, when in excess,
less favourable to the other, and much of our success depends on our not confusing
these conditions, but in providing for each its proper stage in natural succession,
an essential rule, which, as we have seen, must be observed from first to last
if we are to obtain the best results from the specific action of each class of
organism. There is a well-defined course which the analysis follows, no stage of
which can be transposed, and we have to provide the optimal conditions for
each in succession, as in all technical processes which are the outcome of the
vital activity of living organisms. And furthermore, in doing this, we have but
to follow the order naturally provided; the original excrement contains in itself
the necessary organisms for its preliminary dissolution and we start with processes
already begun in the intestinal tract, and in each stage thenceforward we should
provide for the evolution and survival of the essential bacterial forms with the
Nitrification.
k k