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light and consequently secerns oxygen I worked in the 
dark. Indeed, then was formed after some time a splendid 
»oxygen-line” by Chlamydomonas. Owing to my experien- 
ces with the indifferent conduct of the Alga with geotaxis 
with regard to boiled out water, ] was not quite con- 
vinced. [| have always doubted the fact that the ,,oxygen- 
line’”, which form Bacteria and Protozoa under a coverglass, 
should be caused by want of oxygen. When examining 
more closely the circumstances, under wich the line is 
formed, we must confess, that there is not only a diminishing 
of the oxygen but that continually other substances must 
change their concentration. 
Especially the carbonic acid might play a great part, 
as the disappearance of oxygen must coincide with the 
formation of carbonic acid. The same observation is made 
by Pringsheim (1912, page 275), I tried to prove that 
the carbonic acid played a great, if not the only part in 
the formation of oxygen-lines. To that purpose Ï made 
culturus of Spirillum species Ï took a drop of the culture- 
fluid, covered this with a cover-glas, that was on one 
side a little further away from the object-glass by a wire 
of platina and let this preparation stand for some time. 
After a clear line had been formed, composed of the 
greater part of the Bacteria, the object-glass with the 
preparation was turned upside down and used as a lid 
for a little glass room; with a couple of rubberrings and 
a little vaseline the lid was shut air-tight. Through the 
little room gas could be conducted. At my disposal I had 
carbonic acid, oxygen and nitrogen. The carbonic acid 
was prepared in an apparatus of Kipp out of marble 
and hydrochloric acid, the oxygen came from a bombe. 
The nitrogen was obtained from nitrite. As far as neces- 
sary the gasses were purified by washing with the required 
reagentia, Only with carbonic acid I found it possible to 
get motion in the line formed by the bacteria. 
