W. J. V. OSTERHOUT 5 



character of the solution, provided the conductivity of the solution 

 remains the same. We may therefore take .002857 as the fixed 

 value of Cjy. 



Let us now consider what values Cp assumes as the resistance 

 changes. In sea water we have^ R = 100 and 



C = 4;- = .002857 + Cp 

 100 



whence C/. = .007143 and Rp = 1 -r-Cp = 140. In the same manner 

 we find that when R = 90, Rp = 121.15, and when R = 10, Rp = 

 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 con- 

 stant 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 investigate this, 

 experiments were made with solutions of NaCl and CaCl2 (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 the conductivity 

 of the expressed juice was compared with that of sea water. As 

 no significant diff'erence was found we may consider that the con- 

 ductivity of the cell sap does not change sufficiently in these solutions 

 to alter our calculations. 



Let us now consider the changes in protoplasmic resistance which 

 occur in toxic solutions. When tissue is placed in NaCl 0.52 m the 

 net resistance falls rapidly. The death curve may be obtained 

 by means of the formula^" 



Resistance = 2700 ( — ^^^^ ] ( e '^^^ - e~^^^\ + 90* ~^^^ + IQ 



\Km -Ka)\ 



' 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 conductivity of the protoplasm is 

 much less than that of the cell wall. 



*" For the explanation of this formula see Osterhout, W. J. V., Proc. Am. Phil. 

 Soc, 1916, Iv, 533; /. Gen. Physiol. 1920-21, iii, 145, 415, 611. 



