72 Stiles and j0rgensen. — Studies in Permeability . IV. 
play also ; thus the effect of electric charges at the surface in influencing 
the concentration there of the reacting substances cannot be neglected. 
While we may conclude that the rate of the action increasing the 
permeability of the cell is dependent on the concentration of the active sub- 
stance at the surface of the cell protoplasm, we cannot say what function of 
the concentration the rate of reaction is. If the action were a purely 
chemical one we could say from the law of mass action that the rate 
of reaction is directly proportional to the active mass of the substance in the 
limiting layer. But besides chemical actions others are possible which 
might alter the state of aggregation of substances in the protoplasm — by 
solution, for instance, or by precipitation of a substance from a colloidal 
solution. In such cases the disaggregation effect is not simply proportional 
to the concentration of the solution. A reference to the solution or 
precipitation of certain proteins such as gliadin by alcohol is sufficient to 
show this, and we may mention Schryver’s work (9) on the cholate gel in 
the same connexion, in which he shows a most curious relation existing 
between concentration of solutions and their rate of disaggregation of 
the gel. 
Moreover, as far as we know, any substances present in the protoplasm 
are also present in the limiting layer, and it is quite possible that different 
substances in the plasma may be affected in different ways by the same 
solute. 
As it is doubtful what relation the concentration of the solute bears to 
its concentration at the interface, and as it seems likely that this latter 
quantity will vary at different parts of the tissue owing to variation in rates 
of diffusion connected with differences in position of cells in different parts 
of the tissue, it is difficult to draw conclusions as to what function of 
the concentration of the solution is the change of permeability produced 
by it. 
If, however, we consider a case in which the concentration is so high 
that the quantity of solute used up is negligible, and if we make the assump- 
tion that the concentration at the surface of the plasma membrane remains 
constant throughout the reaction time, we can from the ordinary laws 
of mass action obtain an equation connecting the exosmosis with time, and 
the curve representing this equation is of the same form as those obtained 
in the experiments described in this paper. 
For we may suppose that the increase in permeability of the cell is due 
to a change in a substance present in the outer layer of the protoplast, whose 
active mass before the experiment is M. Let us suppose that at any time 
t of the total amount M, a part m has been destroyed. 
The rate at which further destruction of the substances takes place will 
depend on the quantity left, M — m, and on the concentration of the external 
solution. 
