Permeability 249 
The behaviour of a secondary octyl alcohol was similar, and the 
curves given by Thoday for chloroform and mercuric cyanide leave 
little doubt that these substances behave on the whole similarly to 
the alcohols examined. 
These results are simply explained. It is clear that these sub¬ 
stances bring about an increase in the permeability of the cell to 
substances dissolved in the cell sap (Czapek, 1910 a ; Stiles and 
Jprgensen, 1917 a), while at the same time it is to be supposed that 
the solute in the external liquid is itself capable of entering the cell. 
Fig. 11. Curves illustrating the influence of ethyl alcohol in concentrations 
10 M to 0-5 M on the absorption of water by potato tissue. (After Stiles 
and Jorgensen.) 
In the first stage of the experiment there will thus occur a rise in the 
osmotic pressure of the cell-sap on account of the addition to it of 
alcohol or other substance. If the permeability of the cell membranes 
remained unaltered we may suppose that the swelling in the most 
concentrated of the alcoholic solutions would be the same as that 
in distilled water at equilibrium, but the rendering permeable of the 
cell to the solutes in the cell sap brings about a diminution of osmotic 
pressure within the cell which accordingly loses water on account 
of this. Thus to the first stage of excessive swelling there follows a 
Phyt. XXI. V. 
17 
