354 Stiles and Jargensen.—Studies in Permeability. I. 
metal ions is due to the formation of substances in the plasma membrane 
which have much greater permeability than the original compounds they 
replace, with the result that a much greater rate of exosmosis of electro¬ 
lytes from the cell takes place. It has to be remembered that what we are 
measuring is the difference between absorption and excretion. It is not 
therefore altogether safe to take the increase in conductivity as a measure 
Time in hours 
Fig. I. Potato m j^~ 0 Solutions of various substances 
of diffusion out from the cell, or as a measure of the toxicity of the 
surrounding solution. 
Series 2. In this series the change in the conductivity of the external 
solutions was investigated for solutions of one substance in diffeient con¬ 
centrations. Copper sulphate, as in Series i, was used in the following 
N N N N N N 
concentrations: 
The accompanying 
135 5 250 5 500 ’ 1000 ’ 2000 5000 
curves show very clearly how the increase in conductivity, and consequently 
the increase in the number of ions present, is dependent on the strength of 
the solution. From to - there is a definite increase in exosmosis, 
5000 250 
N 
with increasing concentration of copper sulphate. —- gives actually 
N 
slightly less increase of conductivity than , although this difference may 
be within the limits of experimental error. 
