6 CONDUCTIVITY AND PERMEABILITY 



in which T is the time of exposure, Kj^ and Km are constants, and 

 e is the basis of natural logarithms. We find by means of this 

 formula that in a solution^^ of NaCl 0.52 m (for which K^ = .018 

 and Km = -540) the net resistance after 10 minutes is 87.76 per cent 

 of the normal; after 30 minutes it is 64.26, and after 60 minutes it is 

 41.62, Knowing the net resistance we can calculate the protoplas- 

 mic resistance, as explained above. After 10 minutes the proto- 

 plasmic resistance is 117.12 per cent (corresponding to the net resist- 

 ance of 87.76 per cent). Since it is desirable to express all resistances 

 as per cent of the resistance in sea water we divide 117.12 by 140 

 (which is the protoplasmic resistance in sea water) and obtain 83.66 

 per cent. Proceeding in this way we find that after 30 minutes the 



TABLE I. 

 Velocity Constants at 15°C. 



protoplasmic resistance is 56.22 per cent and after 60 minutes 33.74 

 per cent. In order to fit the formula to these values we must change 

 the constants, putting K^p = 0.0234 (in place of K^ = 0.018) 

 and Kmp = 0.702 (in place of Km = 0.54). It is therefore evident 

 that in changing from net resistance to protoplasmic resistance we 

 merely shift the value of the constants. The question arises whether 

 this affects the general conclusions drawn from the study of net resist- 

 ance. In order to decide this question the constants for CaCl2 and 



*i See Osterhout, W. J. V., /. Biol. Chem., 1917, xxxi, 585. 



