ELECTROLYTES IN LIVING MATTER ioi 



of concentration occur whose sense changes with the direction of the 

 current. When their average reaches a definite value, the physiological 

 effect becomes noticeable and the threshold is reached. 



" It is possible to calculate the average changes of concentration 

 without making excessively specific assumptions. We know that in 

 tissues the composition of the watery solution which acts as the elec- 

 trolytic conductor is not everywhere the same, and especially that it 

 is different inside and outside the cells. Semipermeable membranes 

 prevent the equalization by diffusion and only at such membranes can 

 changes in the concentration be produced by the current. In the in- 

 terior of a homogenous solution, the current cannot produce such an 

 effect, as in each instance just as many ions migrate into such an ele- 

 ment of volume as leave it. At the semipermeable walls, changes of 

 concentration must occur, inasmuch as the current carries salts to such 

 a membrane which blocks their further motion. Such salts as are 

 able to pass through the membrane undertake the conduction of the 

 current through the membrane. The seat of the electrical stimulation 

 must therefore be at the latter. 



" If a current of the density i carries the quantity v of salt to the 

 membrane, a migration of the salt away from the membrane must occur 

 through diffusion. The average change of concentration at the mem- 

 brane depends therefore upon the antagonistic effects of the current 

 and diffusion."* Nernst developed the equations for this process (ac- 

 cording to a method by Warburg), which show that the intensity of an 

 alternating current, which is just sufficient to produce a stimulating 

 effect, must increase in proportion to the square root of the number 

 of alternations in the second. Nernst tested this theory experimen- 

 tally in cooperation with Von Zeynek and Barratt, and found it true 

 for alternations from 100 to 2000. This proves that the experimental 

 data agree with the assumption that the electrical stimulation is due 

 to a change in the concentration of ions in the living tissues. Such 

 changes occur wherever the progress of ions is blocked, and this may 

 be at the limit of each individual surface film of protoplasm. In some 

 cases it may be at the surface of the protoplasmic layer of a cell, in 

 other cases, such blocks may occur inside a single cell. 



Nernst's experiments were concerned only with the physiological 

 effects of alternating currents, and he does not discuss the effects of con- 

 stant currents. While a constant current is passing through a nerve 

 or muscle, the latter generally remains at rest. As long as the current 

 continues to pass through, new ions must be carried to the poles. It 

 is difficult to understand why this should not result in any motor effect ; 

 here is a gap which needs to be filled. 



* Nernst und Barratt, Zeitsch. fiir Electrockemie, Vol. 10, p. 664, 1904. 



