CONDUCTIVITY AND PERMEABILITY 219 



solutions (having the same conductivity as sea water) 

 the resistance may rise to 300 or more ; and in this case 

 C would equal 1 -~ 300 = = .0033 (or less), and since some 

 of it must flow in the protoplasm the amount which trav- 

 erses the cell wall must be less than this. We are there- 

 fore safe in putting it as low as 1 -f- 350 = .002857. 



All the experiments hitherto made indicate that the 

 conductivity of the cell wall remains unaltered in spite 

 of changes in the chemical character of the solution, pro- 

 vided the conductivity of the solution remains the same. 

 We may therefore take .002857 as the fixed value of Cw. 



Let us now consider what values Cp assumes as the 



resistance changes. In sea water we have 32 R = 100 and 







C = v^ = . 002857 +Cp 



whence C P = .007143 and E P =1 ~- C P = 140. In the same 

 manner we find that when R = 90, Rp= 121.15, and when 

 R P =10.29. 



The changes in resistance thus far discussed have 

 been treated as though they occurred in sea water; in this 

 case the experiments indicate that the conductivity of the 

 cell sap remains practically constant and hence need not 

 be taken into account in our calculations. We may now 

 ask whether this is also the case when the changes in 

 resistance occur in other solutions. In order to investi- 

 gate this, experiments were made with solutions of NaCl 

 and CaCl 2 (of the same conductivity as sea water). The 

 tissue was placed in these solutions and removed after 

 various intervals of exposure. It was cut into small bits 

 and ground (so as to open the cells) and in some cases 



32 The total conductance of the protoplasm is greater than that of 

 the cell walls, but the protoplasm occupies a much greater fraction of the 

 conducting cross-section than the cell walls, so that the actual conduc- 

 tivity of the protoplasm is much less than that of the cell wall. 



