Walter Stiles 
158 
In a series of observations on the exosmosis of electrolytes from 
plant tissue, principally potato tuber, Stiles and Jorgensen (1917 a) 
have shown that it is impossible to find for any substance among a 
number examined, a critical concentration below which exosmosis 
will not take place. Exosmosis takes place in all concentrations 
examined, slowly at first, then more rapidly, and as equilibrium is 
approached, more slowly again. These stages are passed through 
more rapidly the more concentrated the solution of toxic substance.. 
Czapek simply selected an arbitrary time and decided that if exosmosis 
had not taken place in that time it was not going to, with the ex¬ 
ception that in some cases this time was arbitrarily extended; in 
other cases rapid exosmosis was attributed to secondary injury. Such 
methods of enquiry are not very convincing, and Koltzoff (1912) 
criticised Czapek for neglecting the time factor in his experiments. 
Czapek replied to this (1914) that he dealt only with equilibrium 
conditions and a time factor does not therefore enter into the question. 
But unless the progress of an action is followed with time, it is not 
always possible to decide whether equilibrium conditions have been 
reached. In those experiments of Czapek in which exosmosis had 
not occurred after the lapse of an arbitrary time, it is at least con¬ 
ceivable that prolongation of the time of action might have revealed 
exosmosis. 
An important difficulty in Czapek’s theory pointed out by 
Koltzoff and Vernon (1913) arises from the fact that the surface 
tensions of the solutions used in his experiments were measured 
against air, while in the experiments themselves it is the surface 
tension of the solution against the outer layer of protoplasm which 
is in question, while by no known means can the surface tension 
between two immiscible liquids be determined from their surface 
tensions against air. Hence it is not at all likely that even in Czapek’s 
experiments those concentrations of different substances just pro¬ 
ducing exosmosis had the same surface tensions under the experi¬ 
mental conditions in question. The experiments of Stiles and J 0 rgensen 
have further shown that solutions which produce equal exosmosis of 
electrolytes have not necessarily the same surface tension against air. 
Having regard to this fact and to the exceptions to the rule recorded 
by Czapek himself, it seems clear that the permeability changes in 
the cell produced by toxic substances cannot be referred to surface 
tension alone. 
Further arguments against the acceptance of Czapek’s conclusions 
are that there appears no reason why a solution the surface tension 
