20 
Walter Stiles 
entrance of substance commences the instant the cells are placed in 
the solution but no doubt takes some time, and probably some very 
considerable time, before equilibrium is attained. The apparent iso¬ 
tonic coefficient will therefore vary with the time that has elapsed 
before the plasmolysed cells are observed. This was indeed recognised 
by Trondle, but he appears to regard the lowering of the apparent 
isotonic coefficient which must result with increase in the osmotic 
concentration of the cell as indicating an increase in permeability. 
If the opinions of Lepeschkin and Trondle have been interpreted 
aright, the so-called permeability factors or coefficients could only 
be used as quantitative measures of intake if the apparent isotonic 
coefficients were determined after a definite and constant time of 
immersion of the cells in the solution. Even then exosmosis is neg¬ 
lected, and it must be assumed that the substance does not react 
with a cell constituent. Defining the permeability of the cell to dis¬ 
solved substance as the quantity of the substance diffusing through 
unit area of the cell membranes in unit time when there is unit 
difference of concentration of the substance between the external 
solution and the cell sap, it is clear that the method of permeability 
coefficients could not be used without modification and elaboration 
to give measures of the permeability of cells to dissolved substances. 
Recovery from plasmolysis. If a cell is plasmolysed by a hyper¬ 
tonic solution of a penetrating substance, the entrance of the sub¬ 
stance into the cell, provided no complicating factors are present such 
as removal of the substance into an osmotically inactive state, or 
excessive exosmosis, will increase the osmotic concentration of the 
cell sap, and in consequence the cell will slowly recover from plasmo¬ 
lysis. Recovery from plasmolysis can thus be used as a test of per¬ 
meability, and has indeed been one of the favourite methods of in¬ 
vestigating permeability since it was first introduced. 
This method appears to have been first used by de Vries (1871 a) 
who showed the permeability of beet root cells to sodium chloride by 
its means. Later Klebs (1887, 1888) recorded the permeability of 
cells of Zygnema to glycerol on account of the recovery of cells of this 
alga from plasmolysis with a 10 to 20 per cent, solution of this sub¬ 
stance. Since then a number of attempts have been made to obtain 
quantitative data with regard to the entrance of salts and the per¬ 
meability of cells by means of plasmolytic data, and various methods 
have been devised which will now be described. 
Trondle s Method. Trondle (1920) has attempted to adapt this 
method to the measurement of the quantity of a substance absorbed 
