232 Walter Stiles and Ingvar Jorgensen. 
In a further series of experiments in which the same method 
was used, Osterhout (33) lias shown that electrolytes may produce 
a reversible change in permeability of the cell. 
A third series of experiments (34) was made by the same writer 
with a view to determining the effect of anaesthetics upon 
permeability. It was found that below a certain concentration of 
the anaesthetic a decrease in permeability is produced which is 
reversible; above a certain concentration of anaesthetic the decrease 
in permeability gives place rapidly to an increase in permeability 
which is due simply to toxic action and is not reversible: with 
further increase in concentration of the anaesthetic the preliminary 
period in which there is a decrease in permeability becomes so 
momentary as to be undetectable. Thus with anaesthetic action is 
associated a decrease in permeability of the protoplasm, the later 
increase in permeability which is observed with higher concentra¬ 
tions of the anaesthetic is common to the action of all toxic 
substances. 
Review of the Methods applicable for Conductivity 
Measurements in Living Tissues. 
t,. cr * , : .. . i.s:.: l\: 
In the preceding sections of this paper we have given a review 
of the work that has been already done in the direction of making 
use of electrical conductivity measurements in questions of plant 
physiology. This review is probably not complete ; in any case 
however it enables us to form an idea of the work that has been 
done, and gives us a basis for reviewing the methods which are 
available for further work based on the same underlying principles 
of method. 
In regard to measurements outside the plant, we have little to 
say here. Such measurements can be little different from those of 
ordinary electrolytes and present little difficulty compared with the 
measurement of conductivity in living tissues, which would seem a 
much more important thing to do satisfactorily. It is then more 
especially with the methods applicable to such measurements that 
we propose to deal in this section of our paper. 
The difficulties of using direct currents for such measurements 
are well known. Polarisation effects are produced at the electrodes, 
and these effects are more marked the smaller the surface of the 
electrodes. Now in such experiments as are involved in the subject 
we are considering it would seem generally necessary to use small 
electrodes of thin platinum wire which can be immersed in the 
