4 2 
G. a. tfister: 
Water. 
2N 7 0 (oxidation). 
In fact, in the first place one kind of bacteria, which 
Winogradsky called nitroso-bacteria, bring about the change 
of ammonia to nitrous acid forming nitrites. 
Ammonia. Oxygen. NitrousAc 
2 NH3 f 30a = 21NH0 
Then a totally different form of bacteria step in, the nitro- 
bacteria. In fact, these are incapable of utilizing caibonate 
of ammonia ; but after this has been changed into mtrites 
by the nitroso bacteria, they oxidise these 1 Elites still 
further. Nitrous acid becomes nitric acid and thus mtia.es 
are formed. 
HNO 2 + O = HNO 3 . 
I take the opportunity to mention a most extraordmaiy 
fact which Winogradsky discovered while experimenting 
with nitroso bacteria. He proved that these can change 
ammonium carbonate into nitrous acid, m the daik, m a 
solution to which only purely mineral salts (carbonates, 
sulphates and chlorides of ammonium, sodium and mag- 
nesium) had been added. In other words, these bacteua 
can build up organic matter from purely inorganic matter, 
by assimilating carbon from carbon dioxide and by obtaining 
their nitrogen from ammonia. 
We have a further important factor 111 the numerous 
and much-talked-about bacteria which we find in the 
well-known nodules on the roots of leguminous plants ! heir 
presence enables the leguminous plants to absorb the free 
nitrogen from the air, and experiments have shown that after 
culitvation with clovers, lupines, peas, vetches, etc th 
soil contains much more nitrogen than before. Allow me 
to describe a simple but convincing experiment which 1 have 
ma White sand was sterilized by heating it to 150 C. foi 
two hours. Three pots were filled with this soil and lupines 
were planted in each pot. After the seed had well ger 
minuted some soil from a market garden (loam from Can- 
nington) was shaken up in water and this was filtered 
through cotton-wool. Part of this water was at once 
added to one of the pots, No. 2 ; the rest of the water was 
boiled, cooled rapidly and then added to the third pot 
The lupines in the 1st and 3rd pot after forty gays showed 
no nodules and were very weak, stunted plants, while . the 
second pot showed beautifully strong plants on the loots 
of which we found splendid nodules containing thousands 
of millions of bacteria and bacteroids from which pure 
cultures were made. Clearly this was a case of infection 
from the Cannington soil, and chemical analysis showed that 
nitrogen had been fixed in the soil which could only have 
been assimilated from the air. 
