ELECTRICAL CHANGES IN LIVING TISSn-> i: ; 



differences- of potential of a concentration cell up to and beyond tin* 

 extent which is observed in living tissues. Supposing we have (Fig. 

 two solutions, A and B, each containing an electrolyte, UV, in diffeivm 

 concentrations separated by a membrane m. If u represents the velocity of 

 transmission of U through m, and v the velocity of V, then the electromotive 

 force of the cell is given by the formula 



If v is taken as very small, the membrane maybe regarded as semipermeable 

 for the corresponding ion V. Supposing we take potassium chloride as the 

 solution, we should have to make the concentration in B eight times that in 

 A, in order to get a current of a strength equal to that obtained from the 

 olfactory nerve of the pike, for example. Macdonald has made such an 

 assumption in order to explain the normal nerve current. He suggests that 

 the axis cylinder contains an electrolyte which is equivalent to a 2-6 per 

 cent, solution of potassium chloride. It is unnecessary, however, to assume 

 such great differences of concentration if we regard the membrane as itself 

 a solution of electrolytes, as has been suggested by Cremer, or if we take 

 different substances on the two sides of the membrane. In the case of two 

 electrolytes, UjV-i, U 2 V 2 (U being the cation in each case), separated by a 

 membrane with varying permeability for the different ions, the electro- 

 motive force of the cell is given by the following formula : 



where u lt v 1} u 2 , v 2 , are the velocities of the corresponding ions. We assume 

 that the concentrations of the two solutions are identical. Now it is evident 



that by making u 2 and v very small, the expression log. 10 - - may be 



u 2 + v l 



made to attain any quantity, and in the same way by making u^ + V 2 

 infmitesimally small the electromotive force of the combination will also 

 become correspondingly small. The thickness of the membrane does not 

 come into the formula, so that membranes of microscopic or even ultra- 

 microscopic thickness, which we have seen reason to assume as present in 

 and around cells and their parts, could perform all the functions required 

 of the hypothetical membrane in the above example. This is also the case 

 when Y! is the same as V 2 that is to say, there is a common anion or a 

 common cation on the two sides of the membrane. 



It must be remembered that the passage of a current through a membr 

 impermeable to one or other ion in the surrounding fluid will cause an 

 mulation of the ion at the surface of the membrane, so that this will 

 polarised. Such an accumulation at any surface will naturally ata 

 properties of the surface, including its surface tension. The const 

 the capillary electrometer depends on this fact. When mercury IE 

 with dilute acid or mercuric sulphate solution it takes a positive charg 



