238 Walter Stiles and Ingvar Jbrgenseri. 
definitely what was happening as regards the conductivity, and one 
would also be able to follow any changes continuously. Moreover 
such a method would require a much less complicated arrangement 
of apparatus. It would also allow working with a frequency of 
alternation in which polarisation would be negligible, such as one 
cannot reach with the commutator method. During recent years 
development in instrument-making technique has resulted in the 
production of such simple and reliable instruments for measuring 
even small alternating currents, such as Duddell’s Thermo- 
Galvanometer made by the Cambridge Scientific Instrument 
Company. Along such a line as this probably more numerous and 
more reliable results may be expected than those obtained hitherto. 
On the Passage of Electric Current through Living Tissues. 
In the preceding part of this paper we have described the 
methods available for measuring the electrical conductivity of 
living plant tissues, and we have emphasised the advantage of using 
a method which will provide us with a continuous record of the 
conductivity. It is therefore necessary to consider the phenomena 
that accompany the passage of the current through part of a living 
plant. 
In the case of living tissues we are of course dealing with a 
very complicated state of affairs, far removed from the relatively 
simple conditions which exist in the passage of a current through a 
solution of a single electrolyte. We have a large number of living 
cells separated by cell walls of dead material, and we have first to 
consider the possibility of the currents passing through the walls 
alone and avoiding the cells altogether. 
However there seems to be no doubt that the living cells do 
actually act as conductors, as is indicated by the very voluminous 
literature dealing with the effects of electric current on cell 
contents. 1 Each cell is however a very complicated system. It 
contains the cell-sap, which may consist of a solution of a variety of 
electrolytes and non-electrolytes, as well as the actual protoplasm 
which is separated by its limiting membrane characterised by its 
well-known so-called semi-permeable properties. Thus a change in 
conductivity may be due to alteration in the concentration of 
electrolytes or non-electrolytes in the cell-sap, or possibly to 
changes in the protoplasm, or to changes in the permeability of the 
protoplasmic membrane. 
1 See, c.g., Klemra (19) and Ewart (13). 
