Stiles and Jargensen. — Studies in Permeability. IV. 71 
himself admits, substances which could lower the surface tension more than 
this might be present in the plasma membrane in diluter solution. Thus, for 
example, he says : 4 Meine Beobachtungen widerstreiten nun nicht direkt der 
Annahme, dass verdiinnte Emulsionen von Lezithin und Cholesterin das 
eigentiimliche Verhalten der Plasmahaut bedingen, doch bringen sie auch 
keinen weiteren Grund dafiir bei, dass die Annahme Overtons die allein 
richtige sein konne.’ Similarly, this writer also admits that proteins may be 
present in the plasma membrane. 
From this review of the details of Czapek’s work on the plasma 
membrane, it is clear that neither the experimental evidence nor any part of 
the theory based upon it can be accepted. 
The Application of the Laws of Mass Action to the Question 
of Exosmosis from Plant Tissue in the Case of Irrever- 
sible Changes of Permeability. 
When plant tissue is immersed in a solution of a substance we may con- 
clude that after a certain time, owing to diffusion through the intercellular 
spaces of the tissue and through the cell-walls, a large part of the outer layer 
of the protoplasm of the cells will be in contact with the solution. If the 
solute acts either physically or chemically with one or more substances 
in the protoplasm, the rate at which it does this will depend upon the con- 
centration of the solute at the limiting surface, and also upon the concentra- 
tion at the limiting surface of the substance with which it reacts. Other 
factors, such as temperature for instance, may also influence the rate 
of reaction. The concentration of the reacting substances at the interface 
between the two phases will depend upon the extent to which the surface 
tension is lowered according to the principle of Willard Gibbs, but this is 
only one of a number of factors which may affect the concentration at the 
interface. Schryver (7) has pointed out that in an action resembling some- 
what the one under consideration, namely that of the disaggregating action 
of salt solutions on globulins, the rate of diffusion of the substances in 
solution must also influence the rate of reaction. For if diffusion is slow the 
accumulation of solute in the surface layer may fall below that given by the 
Willard Gibbs rule, owing to the removal of the substance in the action 
at the interface at a quicker rate than it can be replaced by diffusion 
of solute from other parts of the solution. As the rate of diffusion will de- 
pend on the viscosity, Schryver concludes that ‘ the disaggregating action of 
salt solutions on the globulins is a function of two physical constants of the 
solutions, viz. the viscosities and the surface tensions ’. But of course it is 
understood that the salt solution has an action on the globulin. The surface 
tensions and viscosities influence the rate of the reaction ; they do not 
decide whether an action takes place or not. Other factors may come into 
