196 
The product. of the number of H-ions and OHions is 
constant. By this it is possible to examine separately the 
influence of the H-ions and of the OH-ions. In conse- 
quence of this we can find in a series with constant salt 
concentration, but with regularly increasing H-ion con- 
centration, two critical concentrations, while in a series 
with a constant H-ion concentration one critical concen- 
tration is found. 
$ 5. The critical concentrations and the limiting con- 
centrations are denoted in a rectangular coôrdinate system; 
on the ordinate-axis is stated the acid or base concen- 
tration and on the abscissa-axis the salt concentration. 
$ 6. Salt solutions with regularly changing H-ion 
concentrations were obtained bij adding small quantities 
of acid or base. By this we must observe special measures 
of precaution. 
With the acetate solutions, the fluids were made acid 
with acetic acid. In this case we obtain ,,buffer solutions”, 
which .offers special advantages. 
Chapter IV. 
$ 1. Here is discussed, that the H-ions and the OH-ions 
have a great influence on the motility of Chlamydomonas. 
To show this, we used mixtures of sodium acetate with 
acetic acid and with potassium hydroxyd, in which the 
amount of acetate was constant, whilst the H-ion con- 
centration changed regularly. 
$ 2. The experiments under influence of acid and 
alkaline solutions of K,SO,. KCI and KNO, were done 
sixfold, bij which the results were much more reliable. It is 
denoted how the critical concentration is calculated. By the 
use of a new culture the immediately preceding experiments 
were repeated to see whether the organisms of the new cul- 
ture were as sensible to electrolytes as those of the old 
