1057 
2. The nitrogennumber, by which is meant the nitrogen per 100 
parts of weight of assimilated carbon lowers with time; for a 
mature mould it is ea. 2 (glucose or levulose as source of carbon). 
3. The metabolism of the nitrogen has much resemblance to that 
of the carbon. 
a. An aceumuiation of carbon is combined with a high nitrogen- 
number ; inversely the mature mould has a low nitrogennumber. 
b. The nature of the metabolism of the nitrogen does not change 
under the influenee of many factors; neither is this the case with 
the carbon. 
c. The velocity of the metabolism is subject to great changes. 
d. The same factors that aecelerate the metabolism of the carbon 
also further that of the nitrogen. 
e. Substitution of rubidium for potassium is of little influence on 
the metabolism of the nitrogen. 
4. The nature of the metabolism of the nitrogen is independent 
of the source of nitrogen. At first the nitrogennumber is high, 
then it decreases whilst the freed nitrogen returns into the nutrient 
solution as ammonia. This is proved for the cases when ammonium- 
nitrate, ammoniumchlorid, or potassiumnitrate is given as nitrogen- 
food. Aspergillus niger, thus, reduces nitrates to ammonia but not 
to free nitrogen. Only in the culture tubes with a deticieney of 
nitrogen as to the quantity of carbon, no ammonia can return into 
the solution as it is directly used for the production of new cells. 
6. In the cases of a deficiency of nitrogen no fixation of atmos- 
pherie nitrogen could be observed. 
Finally my hearty thanks to Professor Dr. J. BöpseKEN and 
Professor Dr. M. W. Brrerinck for their valuable help in this 
investigation. 
Technical University, Orgamical-chemical Laboratory. 
Delft, November 1912. 
