10 
Walter Stiles 
3. Determination of Permeability by Analysis 
of the Expressed Sap of Cells and Tissues 
or of Cell or Tissue Extracts 
Investigations of cell permeability by analysing the expressed sap 
of the plant material used after immersion in the experimental liquid 
have been made by a number of authors. The method is generally not 
applicable to single cells as only rarely can enough liquid be obtained 
from a single cell for the purposes of analysis, and in the case of cells 
forming part of tissues the individual cells cannot, of course, be 
separated from one another. Nevertheless, in two cases at least the 
method has been applied to single cells. Wodehouse (1917) made 
determinations of the permeability of single cells of the marine alga 
Valonia by this method. The “cells 1 ” of this plant are so large that 
1 to 2 c.c. of sap can be pressed out from cells of normal size, and 
up to 5 c.c. from large cells. Qualitative examination showed that 
potassium was much more abundant in the vacuole than in the sur¬ 
rounding medium (sea water), sodium and calcium were both present, 
but not more than a trace of magnesium although this occurs in 
some quantity in sea water. Chloride was present in high concentra¬ 
tion in the cell sap, but sulphate was absent although it occurs in 
fairly high concentration in sea water. Conversely nitrate was found 
in the vacuole, whereas in sea water there was not enough to be 
detected by the qualitative tests employed 2 . The cell wall appears 
to play no part in the selective absorption thus demonstrated, for if 
living cells are killed and then replaced in sea water sulphates are 
soon present inside the cell. 
The same method has recently been advocated for testing the pene¬ 
tration of dyes into living cells of Nitella (Irwin, 1922 a , b). The cells 
are so large that sufficient sap can be pressed out from a single cell 
for a colorimetric determination of the concentration of the dye that 
has penetrated into the cell. In this way it is held that quantitative 
investigation on the permeability of these cells to dyes is possible. 
A method employed by Janse (1887 h) for testing the permeability 
of Spirogyra cells to potassium nitrate consists essentially in testing 
an extract of the cells with diphenylamine. Filaments of the alga, 
after immersion for various times in potassium nitrate solution, were 
made to burst in water containing diphenylamine. If the time of 
immersion of the Spirogyra in potassium nitrate solution had been 
1 Valonia is a ccenocyte and the compartments are not regarded as true cells. 
2 These results have recently been confirmed by quantitative analysis 
(Osterhout, 1922 a). 
