194 
$ 4 Here is discussed that the reaction to gravity 
takes no longer place after addition of small quantities of 
acid, base or salt to the water, in which the algae are. 
$ 5. Here is told, that the susceptibility of Chlamy- 
domonas to the light, just like that to gravity under the 
influence of added electrolytes is diminished. Besides a 
negative phototactical reaction a positive reaction can 
occur. The solutions in which the positive phototaxis acts, 
always contain so great an amount of an electrolyte, that 
a very slight increase of concentration causes insuscepti- 
bility to the light and to gravity. 
$ 6. The attaching of Chlamydomonas to the glass 
side (thigmotaxis) occurs, as the ends of the cilia stick to 
the glass. The thigmotactical phenomena only take place 
in solutions, which are not distinctly alkaline. In solutions 
which only contain acid, at any rate little salt, the phe- 
nomenon often occurs, when the amount of acid is nearly 
as large that the motility is very slight and also insus- 
ceptibility to light and to gravity acts. 
The individuals of Chlamydomonas can also mutually 
stick together with the cilia. This phenomenon can act 
so generally in a preparation, that it becomes also visible 
macroscopically. 
$ 7. Here are discussed the substances on which Chla- 
mydomonas reacts chemotactically. It is possibe to produce 
in the dark under cover-glass with Chlamydomonas an 
oxygen-line. This is not yet considered to be a proof, 
that Chlamydomonas really reacts to the oxygen of the air. 
Here is discussed how with the experiment under 
cover-glass also the carbonic acid concentration must 
change. By means of Spirillum species it could be shown, 
that under the influence of carbonic acid as a gas a 
removal of the oxygen-line, formed by Spirillum was 
caused; with nitrogen, oxygen and air, this was not possible. 
