764 
From these it follows that the nature of the metabolism of the 
carbon does not change by substituting rubidium to potassium. Tke 
rubidium mycelium only proves to contain more glycogen as is 
shown by the greater plastic aequivalent of the carbon. 
We likewise perceive that also without production of spores the 
digestion of the intermediary products is possible, for in spite of the 
fact that after 18 days at the rubidium experiment only few spores 
appear, the plastic aequivalent of the carbon is lowered from 41.5 to 29°/,, 
Summary. 
1. Addition of 2.35 cm? normal sulfuric acid per 100 cm? culture 
liquid and of 0.5°/, boric acid but feebly influences the plastic 
aequivalent of the carbon. In the case of the boric acid we must 
ascribe the observed changes to mutation. 
2. The action of the factors that govern the development of 
Aspergillus niger must not be partially judged; thus, a high weight 
of mycelium cannot always be called favourable. This is not sufti- 
ciently taken into consideration by Ono, RicuTer, Bertrand and 
JAvILLIER. So it was proved for the action of certain concentrations 
of coppersulfate, zincchloride and zinesulfate, that these salts considerably 
increase the plastic aequivalent of the carbon, whereas the increase 
of the weight of mould is proportional to the retarded spore production. 
ie 
100000000 1000000 
Very dilute zine solutions ( gr. mol .ZnSQ,. 
7 Aq p: L.) have no influence. Coppersalts counteract the spore form- 
ing in all concentrations. 
3. Presence of manganese in minimal quantities does not change 
the plastic aequivalent of the carbon; it only acts on the velocity 
of the metabolism. 
The quantities of dry substance found by Brrtranp should be 
considered as values indicating the velocity of the process. 
4. By replacing potassium by rubidium the spore formation is coun- 
teracted, the weight of mould is increased, and the metabolism of 
the carbon (i. e. the change of the plastic aequivalent and of the 
respiration aequivalent in connection with time) remains unchanged. 
Finally my hearty thanks to Professor Dr. M. W. Beiyertnck and 
Professor Dr. J. BörsEKEN for their assistance in this investigation. 
Laboratories for Organic Chemistry and 
Delft, October 1912. Microbiology of the Technical Unwersity. 
