22 
Walter Stiles 
that is 
C 
[■- 
(V s - v 2 ) (V 3 + v 2 y 
8 V 2 V s 
In this way Lepeschkin found values for the rate of entrance into 
the cells varying between 67 x io -9 and 183 x io -9 gram-molecules 
of glycerol per sq. cm. per hour in the case of glycerol penetrating 
into Spirogyra. These numbers are taken as direct measures of the 
permeability. 
Values of the “permeability factor” were also obtained from 
calculations of the apparent isotonic coefficient of glycerol made at 
the same time on the same cells as those used for direct determinations 
of the “permeability.” 
This was done in the following way. It will be recalled that the 
cells were first plasmolysed in sucrose (of concentration C 0 ) and the 
volume of the cells measured after an hour. This volume is V 1 . The 
cells were then transferred to a solution of glycerol of concentration 
C and the volume measured again after the lapse of 0*5 hour and 
again after the lapse of a further two hours, the two volumes being 
respectively V 2 and V 3 . Since the cell is increasing in volume at 
the rate of y _ y 
2 
per hour, its volume immediately after addition of the glycerol should 
have been 
Hence the concentration of glycerol apparently isotonic with the 
sucrose used is 
Vo - 
v 3 -v 2 
c x - 
V 1 
and the apparent isotonic coefficient of glycerol is 
i-88 , 
t'X 
since i*88 is the isotonic coefficient of sucrose. 
Values of the “permeability factor” calculated in this way were 
found to be roughly proportional to the actual determinations of the 
permeability. Considering the very doubtful value of “permeability 
factors” it is surprising that the agreement should be as close as that 
actually found. 
Fitting’s Method. Fitting (1915) has devised a method for esti¬ 
mating the intake of salts by the rate of deplasmolysis, using cells of 
