240 
Walter Stiles 
brought into harmony, for if the protoplasmic layer determining 
permeability is a viscous sol or gel, the rate of penetration of a sub¬ 
stance through the gel will, according to the formula of Einstein, 
Sutherland and von Smolukowski, depend on the size of the molecules 
as well as on the viscosity, and it is reasonable to suppose that 
molecular aggregates above a certain size may not be able to diffuse 
through the spaces between the particles of the disperse phase of the 
gel. Such considerations lead on to the whole question of the nature 
of solution into which we cannot enter here. 
A number of objections to Spaeth’s theory have been raised by 
Osterhout (1916 a), chiefly based on the fact that changes in viscosity 
of Laminaria thallus produced by placing this tissue in mixtures of 
sodium and calcium chlorides do not run parallel with changes in 
electrical resistance. What appears to the writer to be a very strong 
argument against the viscosity theory is that the changes in viscosity 
of a gel are scarcely great enough to account for any great differences 
in permeability (cf. Stiles and Adair, 1921). 
The theory of antagonism advanced by Osterhout (1916 b) 
assumes, as we have seen, that the permeability is inversely pro¬ 
portional to the electrical resistance of a cell, and that the resistance 
is proportional to the quantity and the thickness of a particular 
substance in the protoplasm. While this theory would not be incom¬ 
patible with a viscosity theory, inasmuch as the resistant substance 
might be a viscous one through which substances entering the cell 
had to diffuse, there are other possibilities. Thus, the substance to 
which the cell owed its resistance might be impermeable to entering 
substances, so that with increase in the relative amount of the im¬ 
permeable substance the proportion of the protoplasm (or plasma- 
membrane) through which material could enter would be smaller, and 
hence permeability would be reduced. In such a case the question 
of the correctness of a sieve or solution theory is left untouched. 
The Phase Inversion Hypothesis 
To account for the supposed action of various electrolytes on cell 
permeability, Clowes (1916 a, b, c; 1917 a, b, c) also makes use of the 
colloidal character of protoplasm. As protoplasm can be regarded 
as an emulsoid colloidal system, there will be a continuous phase of 
one composition (dispersion medium) through which is dispersed at 
least one other phase, the particles of which are not continuous. 
Clowes supposes changes in permeability are brought about by the 
continuous and discontinuous phases changing places, as is supposed 
