( 516 ) 
Which ureum-splitting species will appear depends upon the com- 
position of the souree of carbon added and the degree of alkalinity 
of the culfure-medium. 
In $ 2 and $ 3 we shall revert to this more in detail. 
Ureum as a source of energy. 
Ureum gives to the ureum-splitters exclusively energy; in no 
circumstances whatever it is fit to serve at the same time as a source 
of carbon. 
Different experiments which I have made about this, corroborate 
the truth of former investigations; neither can ureum serve as oxidizable 
material in the sulphate-reduction; denitrification with ureum is also 
impossible. 
The part that ureum plays in the growth of microbes, is therefore 
sharply determined. Always the presence of some suitable source of 
carbon is necessary ; this carbon-compound is partly oxidated and there- 
fore also this part serves for energy, partly it is assimilated. 
For the above-mentioned oxidation of the source of carbon atmos- 
pheric oxygen is used; the quantity necessary is very small, which 
can be proved by cultivation in bottles with a stopper, which are 
entirely filled with the culture-liquid. 
Only the oxygen dissolved in the culture-liquid is then available 
tor the microbes and nevertheless ‘the ureum-splitting then takes 
place just as well as when the supply of oxygen is abundant. 
If, however, the culture-liquid has previously been made free 
from oxygen by boiling, after infection no ureum-splitting takes place 
in a bottle completely filled. 
From these experiments follows that a good ureum-splitting is 
possible, while only very little organic matter is oxidated. 
Now it is a fact that on the whole strong splitting ferments 
show in the cultures a very slight growth and from this it follows 
that also the quantity of carbon, necessary for the structure of bacterial 
bodies is very small. 
These facts prove that a small quantity of a suitable organic 
compound, in the presence of ureum, must be sufficient for a complete 
development of the organisms and a normal ureum-decomposition. 
Now, in order to ascertain what part of the sum of energy 
developed in the culture, is developed in the splitting up of the ureum 
the minimum quantity of carbon-compound, sufficient for a normal 
ureum-decomposition and growth, was determined. For this purpose 
experiments have been made with the afterwards described Bacillus 
