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at all must be answered negatively, as is shown by the subsequent 
experiments. 
By starting every time from a single spore, cultures were obtained 
which remained identie to the material used for the sowing. If the 
mycelium, carefully separated from the spores was separately sown, 
no difference appeared between the product obtained from it and 
that from the spores. 
Possibly form II is the same as the brown form obtained some 
months ago by Fru. ScHIEMANN ') under the action of kaliumbichromate. 
In earlier experiments on the metabolism of Aspergillus niger 
irregularities had been found, which then could not be accounted 
for, but which can now be explained by the observed mutations. 
In the said experiments it was determined what percentage of the 
assimilated quantity of carbon was at a given moment bound in the 
body of the mould and what percentage was excreted as carbon: 
acid by respiration or otherwise. The first percentage may be called 
‘plastic aequivalent’ of the carbon, in accordance with the term 
used in researches on the luminous bacteria by Professor BeiErinck °) 
whereas the percentage of the carbon which at a given moment is 
respirated will be called “respiration aequivalent’. 
On a 0,3 °/, paraoxybenzoic acid solution (anorg. food : tapwater, 
WOI NEC Oo fH EO, 002°) Me SO: i == 9I= 330 
was found after 45 days a plastic aequivalent of the carbon of 34 °/,. 
In other cultures likewise on para-oxybenzoic acid and obtained 
by inoculation with the said culture, whose plastic aequivalent was 
84 °/, this number amounted after 27— 28 days respectively to 20 
and 16 °/,. 
As this lowering of the plastic aequivalent under the influence of 
the p-oxybenzoic acid might possibly be ascribed to the above mentioned 
mutation the question arose: Do forms I, IJ, and III quantitatively 
differ considerably in their metabolism ? 
The experiments resumed in Table II prove that this is really 
the case. 
The differences are, as we see, enormous and they sufficiently 
explain the described irregularities. 
By this method we are thus enabled to conclude to mutation even 
then when visible external differences between the cultures are 
wanting. 
Likewise as for the mutation of Penzeillium glaucum we see in 
1) Ber. d. Deutsch. Bot. Gesell. 1912 Heft 2, 28 Marz. 
2) Aliment photogène et plastique. Archives Neérlandaises, T. 24, p. 1 1891, 
