ELECTRICAL CONDUCTIVITY, DISSOCIATION, IONIZATION 21 



during muscular, glandular, and nervous activity. The exact details of 

 the application are not as yet sufficiently understood to warrant our at- 

 tempting to do more than indicate the general lines along which the 

 problems are being investigated. To do so we must delve a little further 

 into physicochemical research, when we shall find that there are two further 

 facts concerning ionized molecules that must be of importance in connec- 

 tion with our problem. The first is that the contribution which each ion 

 makes to the equivalent (or molecular) conductivity of a solution is inde- 

 pendent of the other ion with which it is associated; and the second, that 

 ions differ considerably in their conducting power. Since the univalent 

 ions, K., Na., CL', N0 3 ', carry charges of equal magnitude,* and yet all do 

 not conduct to the same degree, they must move at different velocities 

 through the solution. We are driven, therefore, to the conclusion that, 

 exposed to the same electrical force, different ions have different mobili- 

 ties ; that is to say, when an electric current passes through a solution of 

 an electrolyte, the positively charged ions move towards the cathode at a 

 different rate from that at which the negatively charged ions move 

 towards the anode. Confirmation of this conclusion is obtained by exam- 

 ination of the concentration changes around the two electrodes of an 

 electrolytic cell. The actual velocity of each ion can be determined by 

 experimental means. The inequality in concentration of ions in different 

 regions of a tissue is no doubt the fundamental cause for the electrical 

 currents that are set up by injury and activity. 



*Thus Faraday showed that the amounts of the various ions liberated by electrolysis are in the 

 same ratio as their chemical equivalents. 



