PROPERTIES OF PROTOPLASMIC MEMBRANES 149 



however, become charged and exhibit anomalous osmosis 

 under the influence of trivalent ions.^ 



The transport of the ions of salts, and consequently 

 the permeability of a given membrane to a diffusing salt, 

 are similarly affected by the electrical state of the 

 partition, and this influence has recently been studied by 

 Girard, using bladder membranes. If the polarization 

 of the membrane (P.D. between its opposite faces) has 

 a certain orientation, the penetration of a salt like 

 MgCli or Na2S04 in the one direction is facilitated, in 

 the other direction hindered.^ 



The application of the principles above to the case 

 of the plasma membrane is somewhat uncertain, since 

 the structure of the latter is in many respects different 

 from that of fixed porous membranes of macroscopic 

 dimensions. Yet variations in the P.D . across the plasma 

 membrane must have a corresponding effect on the 

 permeabiHty; this effect, however, is probably accom- 

 panied in living protoplasm by other effects, such as 

 chemical effects depending on the electrode-Hke action 

 of the membrane, and effects on colloidal dispersion. 

 There is no doubt that the permeabihty of many plasma 

 membranes, especially of irritable cells, is very sensitive 

 to changes of electrical condition; thus the turgor 

 motors of plants {Mimosa, Dioncea.) depend for their 

 action upon variations of permeability, which are 

 readily induced by the electric current. The passage 

 of a current through a muscle or nerve, in such a way as 

 to decrease locally the resting polarization of the cell- 



^ Cf. J. Loeb, Jour. Gen. Physiol., IV (1922), 463, and earlier refer- 

 ences there given. 



^ Girard, Jour, de Physiol, et de Path, gen., loc. cit. 



