46 TROPIJSMS 



which do not go through will increase in concentration 

 at the surface of the membrane. It is the latter which 

 cause the electrotonic effects; according to Loeb and 

 Budgett 304 by secondary chemical reactions at the boun- 

 dary. Nernst has pointed out that a stationary condition 

 must arise at the surface of the membrane due to the fact 

 that the increase in concentration of ions by the electric 

 current gives rise to a current of diffusion of salt in the 

 opposite direction away from the membrane. ' ' The aver- 

 age change of concentration at the membrane depends, 

 therefore, upon the antagonistic effects of the current 

 and of the diffusion." 324 This must be kept ki mind 

 since otherwise the effect of the constant current should 

 increase constantly with its duration, which is not the 

 case, on account of the establishment of a condition of 

 equilibrium between the increase of the concentration of 

 ions at the boundary with the duration of the current 

 and the diminution of this concentration by the diffusion 

 of the ions in the opposite direction due to osmotic 

 pressure. 



