Permeability 243 
a logarithmic relation, appears to be completely unwarranted. The 
same result would be expected, if, after the first ten minutes, the 
intake of salt were a simple diffusion process governed by Fick’s law. 
Clearly no part of Trondle’s theory can be accepted. 
The Adhesion Theory 
J. Traube, in a long series of papers (1904 a, b, c, 1908, 1910 a, b, 
1911, 1913 a, b, c, 1919), has put forward a theory of permeability, 
the essential feature of which is that the capacity of a substance to 
diffuse into a cell depends on the extent to which it lowers the surface 
tension of water in contact with air. In the papers of Traube cited, 
the evidence for this will be found. The arguments against the 
adhesion theory are two, and they are fatal. In the first place the 
measurements of surface tension made by Traube are against air, 
whereas what is actually concerned is the surface tension of the 
solution (that in the cell wall in the case of plants) against protoplasm. 
There appears to be no direct relation between the surface tension 
of a liquid against air and its surface tension against another liquid, 
and there is no known way of calculating it. In the second place, as 
pointed out by Collander (1921), the measurements of Hober (1914, b) 
and, indeed, of Traube and Kohler (1915), show that whereas a great 
difference exists between acid and basic dyes in regard to their 
absorption by plant cells, there is no constant distinguishing difference 
between the two groups as regards the surface tension of solutions 
of them against air. Under these circumstances it does not appear 
worth while to discuss the theory in any detail. 
The extension of Traube’s theory in which the adhesion of the 
constituents of the protoplasm is also supposed to influence the per¬ 
meability, must, as pointed out by Collander, if it is to have a definite 
meaning, attribute permeability either to the solvent or adsorptive 
properties of the protoplasm. In the first case it becomes a solution 
theory, in the latter an adsorption theory as described below. 
Chemical Combination and Adsorption Theories 
A number of writers have held that some substances enter living 
cells by means of adsorption or chemical reactions. The substance 
combines chemically with, or is adsorbed by, a constituent of the 
protoplasm (or plasma-membrane). This disturbs the equilibrium 
between different cell constituents, with the result that the chemical 
or adsorption compound breaks down again and the substance is 
16—2 
