( 154 ) 
development of gas, which proved never to be the case with denitri- 
fying bacteria. 
In order to obtain perfectly convincing results, to the said culture 
liquids 10°/, gelatin often was added and, when in the boiled solu- 
tion, at about 380° C., some of the culture had been suspended, it 
was poured into a test-tube and solidified. The developing gas then 
remains as bubbles, nearly at the place of its origin, in the gelatin. 
This method (#tube-culture”) produces a sharp reaction on denitri- 
fication, especially when controlled by a parallel experiment, using 
the same culture gelatin, without nitrate or nitrite. 
This principle may also be used for a rough computation of the 
number of denitrifying germs in any material. So it was proved 
that circa 2000 of these organisms occur in 1 gr. of garden soil, 
and circa 100 in 1 gr. of canal water. 
In these experiments the potassium-salts may be replaeed by natrium- 
or magnesium-salts; calcium-nitrate, on the other hand, prevents even 
in dilute solution the growth of many bacteria. 
Before passing to the deseription of the different accumulation 
experiments, I have to make a general remark about their arrangement. 
Which species finally becomes most common in the used culture 
liquid depends on many circumstances, difficult to control, in parti- 
cular on the mutual numerical proportion of the individuals and the 
nature of the different species in the material originally used for the 
infection, and likewise on the condition of the microbes themselves 
in consequence of previous circumstances. 
This explains why, when using different materials of infection for 
the accumulation of one and the same species, it is sometimes necessary 
to modify the cultural conditions in accordance with the nature of that 
material. 
I insist on this circumstance in particular to explain the different 
accumulation experiments deseribed under B. stutzert, on the one hand 
from water by using tartrate, on the other hand from soil by using 
malate. 
3. Accumulation of Bacterium stutzeri, LEHMANN and NEUMANN !). 
This interesting bacterium was isolated in 1895 from straw by 
Burri and Srvrzer (le), whilst in 1892 Breau’) had already shown 
the presence of denitrifying bacteria thereon. 
1) LEHMANN i. Neuman. Bakteriologie. München 1896, S. 237. 
*) De la présence dans la paille d'un ferment aérobie, réducteur des nitrates. 
C.R. 1892, T. 114, p. 681. 
