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Was carbonic acid led through, then the line changed 
its place to the middle of the preparation, was soon after 
that air or another gas led through again (oxygen or 
nitrogen), then the line removed to the outside. In some 
cases Î succeeded three times at a stretch with the same 
preparation to remove the line to the inside and then 
again to the outside. This removing took place very 
quickly. 
These experiments were done with Spirillum species. 
With Bacillus butyricus it was impossible to effect a 
distinct removing of a once formed oxygen-line under the 
influence of carbonic acid. [| will not make use of the 
negative result of the experiments with Bacillus butyricus 
to ascribe to these organisms a different conduct towards 
carbonic acid from Spirillum. We should remember that 
the experiment in a little glass room was more intricate, 
than it looked perhaps. We have to do with the loss and 
the taking up of gases by the culture-fluid. These pro- 
cesses are rather complicated. The experiment with Bacillus 
butyricus is made more difficult by the fact that these 
latter bring butyric acid into the culture-fluid. It will be 
understood that the presence of this acid can have a 
great influence on the effect of the carbonic acid on the 
place of the bacteria-line. 
Meanwhile Ï am of opinion that the experiments with 
Spirillum prove, that for this organism at any rate, the 
existence of airotaxis is very improbable. 
By the data [ obtained about the geotaxis, the photo- 
taxis and the inclination to stick fast of Chlamydomonas, 
it is proved how much these phenomena are influenced 
in a corresponding way by the quantities of electrolytes 
resolved in the surrounding fluid. Especially the sticking 
on the glass side and the positive phototaxis, which both 
occur with high concentrations of electrolytes, though 
those concentrations are not so high to bring about 
