694, REPORT—1899. 
with abundance of dextrose and protected from the access of oxygen, to fix atmo- 
spheric nitrogen. In the cultures, and presumably in the soil, the Clostridium 
was found to work when protected by a mantle of aérobic bacteria. In fact, the 
nitrogen-fixing Clostridium was working in the meshes of the oxygen-consuming: 
species, and forming gelatinous flocks like the well-known grains of kephir, or of 
ginger-beer plant. 
Yet another striking instance of symbiotic association has recently been given 
by Omeliansky. In experiments on nitrification at Bonn, the assertion had been 
made that the nitrifying organisms, 7.e. the bacteria known to oxidise ammonia. 
to nitrous acid, and nitrous acid to nitric acid, could be grown and made to do 
their specific work in media containing proteids or other organic nitrogenous. 
bodies, Now this was directly contradictory of the experience of Warington, 
Winogradsky, and other workers, who had found that one great peculiarity of 
these nitrifying organisms is that they refuse to grow on such media; they are in- 
capable of using organic nitrogen. Several workers then showed that the Bonn 
observers had inadvertently employed mixtures of two or more species, and 
Omeliansky undertook a critical investigation of the whole subject, and has put 
forward the following explanation of the tangle. 
If Nitrosomonas—the bacterium which oxidises ammonia to nitrous acid—and 
Mitrobacter—the bacterium which further oxidises nitrous to nitric acid—be sown 
together or separately on a medium containing organic nitrogen, no growth or 
change occurs. 
But if a bacterium capable of decomposing the organic nitrogenous medium, 
e.g. Bacillus ramosus, is added to the above-mentioned Nitrosomonas and Mitro- 
bacter, the associated three organisms are able to carry out all the processes and 
complete the cycle of nitrification. That is to say, B. ramosus breaks down the 
gelatine and ammonia is formed, this is then oxidised to nitrous acid by Nitroso- 
monas, and the nitrous acid is further oxidised to nitric acid by the Nitrobacter. 
If B. ramosus and Nitrosomonas only are sown together, then only nitrous acid 
is formed, because the latter organism is only capable of carrying the oxidation 
the one stage. 
If B. ramosus and Mitrobacter only are used, then only ammonia is formed, 
because the latter organism cannot oxidise ammonia. 
If we try to imagine the working of this association of organisms in the soil, 
and bear in mind the frequent co-existence and action of the de-nitrifying bacteria 
which Gayon and Dupetit, Giltay and Aberson, Warington and others have 
familiarised us with, a glimpse is obtained of the very complex symbioses 
which may be concerned in the circulation of nitrogen in Nature. Moreover, 
some of these de-nitrifying bacilli appear to be anaérobic, and can only work in 
the surface soil if protected from the access of oxygen; say, by an associated 
aérobic bacterium. 
Another interesting case is the following. Perdix a few years ago isolated 
from water an anaérobic bacterium which converts starches into sugars, which 
with the aid of a yeast can be fermented, the whole process going on in association. 
Other cases of symbiotic associations of bacteria exist among the forms con- 
cerned in the reductions of sulphates and the oxidation of sulphuretted hydrogen, 
the iron bacteria, &c. ; but I propose to mention only one or two further examples, 
taken from the true fungi, 
Symbiotic associations of fungi are probably common, but only a few cases are 
as yet established, and these principally among the ferment-fungi. 
Van Laer has called attention to the symbiotic co-existence of two yeasts in 
many beers, explaining certain peculiar after-fermentations as due to the action of 
one yeast acting on the medium improved for it by the other. 
The Japanese have long been in the habit of brewing a peculiar fermented 
liquor known as rice-wine, or saké. Rice grains are steamed, and when cool are 
infected with a mould fungus now known as Aspergillus Oryze. When the rice 
is quite mouldy, at which time it emits a peculiar odour like that of pineapples, 
the starch is found to be rapidly turning to sugar, under the action of a diastatic 
enzyme secreted by the fungus. 
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