64 Stiles and J 0rgensen. — Studies in Permeability. IV. 
of about 0-4 m. would be obtained ; and if % hours were chosen it would 
be 0*5 m. 
But even if it were possible to find a critical value for the concentration 
in this way the values so obtained for different alcohols would not support 
Czapek’s surface-tension theory. Thus, if 0-3 m. is regarded as the critical 
concentration of isobutyl alcohol required to produce exosmosis of electro- 
lytes, we obtain by comparison with other curves the following values for the 
various alcohols employed. The values of the surface tension of these 
solutions are taken from Czapek’s paper. 
Alcohol. 
Concentration. 
Methyl 
2*5 m. 
Ethyl 
1.4 m. 
Normal propyl 
0*65 m. 
Isobutyl 
o*3 m. 
Isoamyl 
0*09 m. 
Secondary octyl 
0*003 m. 
Surface tension. 
0-79 
0.74 
o*66 
o*6o 
o*59 
no data 
Thus a greater lowering of the surface tension in the case of the higher 
alcohols as compared with the lower is required to produce the same effect 
on the permeability of the cell. 
II. Chloroform , Chloral Hydrate, Ether, Urethane. 
Czapek himself admits that chloroform and chloral hydrate do not 
follow his surface-tension rule, and he therefore attributes to them a specific 
Fig. 11. Exosmosis of electrolytes from potato in solutions of chloral hydrate of various 
concentrations. 
toxic action. Ether, on the other hand, is found to follow the rule. It 
is difficult to understand what is meant by a specific toxic action, and why, 
if chloroform and chloral hydrate have a specific toxic action, ether, or for 
that matter any other substance, should not also have a specific toxic action. 
