68 Stiles and J 0 rgensen. — Studies in Permeability. IV. 
from Echeveria leaves. After one day, however, this had not happened, 
so the experiment was left for three days, when it had. 
On the other hand, certain anthocyan-containing objects were not used 
because they produced exosmosis in less than twenty-four hours from 
diluter solutions than they should have done according to Czapek’s theory. 
The long time required to produce the desired result in the case of 
Echeveria leaves in tertiary butyl alcohol Czapek explains as due to the 
slow rate of diffusion of the alcohol ; the rapid exosmosis produced from 
various tissues containing anthocyan is attributed by Czapek to secondary 
injury. 
It is obvious that with such methods of inquiry any desired result can 
be obtained, and even for these reasons alone it seems to us that Czapek’s 
results are open to grave suspicion. 
2 . The results of our own experiments described in this paper indicate 
that there is no critical concentration below which no exosmosis of cell con- 
tents takes place. In our chief experiments we have measured the exosmosis 
of electrolytes, which can be done with much more accuracy than that 
of anthocyan or tannin. It is clear that after any time exosmosis above a 
certain value will have resulted in some solutions and not in others, and it 
might be supposed that a solution which just produced a certain quantity of 
exosmosis in a certain time had the critical concentration for exosmosis. 
This concentration would, however, vary with time chosen. 
It may be noted here that Koltzoff ( 6 ) has already criticized Czapek 
for neglecting the time of reaction in his experiments. To this Czapek has 
replied (4) that he deals only with equilibrium conditions and has therefore 
eliminated the factor. Our experiments show, however, that Czapek could 
only have had equilibrium conditions in those solutions in which exosmosis 
had occurred, and that exosmosis took place, if slowly, in those where 
it was not measurable by Czapek’s imperfect method. The time factor 
is there ; it cannot be eliminated merely by neglecting it. From these 
considerations we do not accept Czapek’s supposition that there is a definite 
critical concentration required to produce exosmosis. 
3 . Koltzoff ( 6 ) and Vernon (11) have already called attention to the fact 
that Czapek measures the surface tension of his solutions against air, 
whereas what he is really concerned with in his experiments is the surface 
tension between the solutions and the plasma. Czapek assumes that the 
lowering of the surface tension of a liquid in contact with air, due to 
dissolved substances, runs parallel to the lowering of the tension when 
in contact with another liquid. Vernon quotes Clerk Maxwell, who states 
that by no known means can the surface tension between two immiscible 
liquids be determined from their surface tensions in contact with air. Thus, 
the relation between Czapek’s surface-tension measurements and the surface 
tensions actually existing in his experiments is unknown, and hence it is 
