Measurement of Electrical Conductivity. 235 
factor in obtaining correct results with this method. In the second 
place, in dealing with large resistances such as one meets with in 
living tissues, it is difficult to discern the minimum in the telephone. 
Thirdly, it takes some little time to make a measurement by 
Kohlrausch’s method, and so it is inconvenient when one wants to 
get a continuous record of a changing conductivity. 
TIME IN MINUTES 
Fig, 2. Diagram showing the decrease of resistance of a stem of 
Tradescantia when treated with chloroform ten minutes after the commence¬ 
ment of the experiment. 
A method which is less known is that first described by 
Fitzpatrick (14) and later elaborated by Whetham (40), and which 
has also been described by Mcllhiney (24). 
In this case a direct current is alternated by a Commutator 
before it passes through an electrolytic resistance. The current is 
then passed through a second commutator rotating synchronously 
with the other, so that it is made direct again before it is passed 
through a galvanometer. The sketch of the connections will make 
the arrangements clear (Fig. 3). 
