165 
to denote by the H-ion concentration, also the reaction 
of an alkaline fluid. When we say that for a series with 
a constant salt concentration we find two critical con- 
centrations as regards the H-ions, this does not mean, 
that it is the H-ions in both cases, which cause the 
phenomenon studied by us. 
$ 5. How the results are represented graphically. 
The results of the experiments obtained with the series, 
can easily be represented graphically in a flat level 
(see 2 page 51; 4 page 56: 5 page 57). On the abscissa- 
axis of a rectangular bi-axial coôrdinate-system we plot 
the concentration of the salt. On the ordinate-axis is 
denoted the H-ion concentration or the acidity and the 
alcalinity of the solutions. The points, representing the 
critical concentrations, are connected one with the other; 
the curve obtained contains all the combinations of salt 
and H-ions and OH-ions, with which Chlamydomonas 
variabilis has a certain motility. The curves which are 
obtained by connecting the low limiting concentrations 
or the high limiting concentrations, denote each separately 
a certain state of motility. At the origin we put onthe 
abscissa-axis the figure zero; the points on the ordinate- 
axis denote the solutions, which contain no salt. From 
the origin is denoted on the ordinate-axis upwards the 
concentration of the added acid and downwards the con- 
centration of the added base. Only in the figure for 
sodium acetale-acetic acid-mixtures (see fig. 3 page 52) is 
denoted on the ordinate-axis the acidity by the hydrion 
concentration. Àt the origin we place there 107, that 
means the hydrion concentration of very pure water. 
When the concentrations are denoted in this way, the 
three curves, which we get by connecting the low limiting 
