I50 PROTOPLASMIC ACTION AND NERVOUS ACTION 



surface (i.e., cause depolarization), causes stimulation, 

 which, as will be shown below, is attended with an 

 increase of permeability. We must conclude that 

 electrical factors are of great importance in determining 

 the properties of living plasma membranes; variations 

 in the external electrical conditions occasion correspond- 

 ing variations in the membrane, and with these are 

 connected various physiological effects. The polar 

 disintegration shown by various cells through which 

 currents are passed also indicates a direct action on the 

 membrane; the character of this action is determined by 

 the direction of the current. The law of polar stimulation 

 is the expression of similar conditions in irritable tissues.^ 

 The physiological effects of salts and electrolytes are 

 undoubtedly to be referred largely to changes in electrical 

 conditions, as shown by the numerous parallels between 

 the action of salts in purely physical phenomena like 

 electrical endosmose or change of colloidal aggregation, 

 and their action on vital activities of various kinds. 



^ Cf. chapter on stimulation. 



