157 
tration in which the reaction can yet clearly be observed 
and the concentration, in which there is no question of 
a distinct reaction. Between these two limiting concen- 
trations there is one, denoting the point, on which, 
theoretically the transition from one state of motility to the 
other must take place. We call this concentration the critical 
transition concentration or the critical concentration. It is 
calculated from the limiting concentrations. All concentrations, 
which are between the limiting concentrations we call transi- 
tion concentrations. Whether for the stating of the limiting 
concentrations we make use of the reaction to gravity, 
on the light or on chematactica does not matter practically. 
The reaction to gravity can easily be observed macros- 
copically. By a sufficient motility there is soon formed a 
distinct amassing of the Alga on the bottom of the vessel. 
As limiting concentrations we now adopted the concen- 
tration, with which again exactly a distinct amassing took 
place in the lower layers of the fluid, (See fig. 1 B and 
C, page 34). and the concentration, in which no amassing 
took place any longer. (See fig. 1 D, page 34). It was 
supposed that with the critical transition-concentration the 
state of motility was always the same. 
& 2. Precautions, in order that the differences observed 
can be exclusively attributed to the changed 
quantities of electrolytes. 
We must take care that the circumstances under which 
the experiment takes place are such, that the differences 
which are observed, can be ascribed exclusively to the 
different concentration of electrolytes We must pay 
attention to the temperature and strength of the light, 
