i8o PROTOPLASMIC ACTION AND NERVOUS ACTION 



oil from the continuous to the discontinuous phase 

 corresponding to an increase in conductivity and vice 

 versa. 



It will be remembered that water-insoluble colloidal 

 material (Cua FeCye) held in the interstices of a support- 

 ing structure forms the essential composition of the semi- 

 permeable membranes used in the osmotic pressure 

 determinations of Pfeffer and Morse; in such membranes, 

 also, permeability is changed by the action of salts. 

 The conditions in living membranes, while probably 

 similar, in the above broad sense, to those in such 

 structurally composite membranes, are vastly more 

 complex, chiefly on account of the constant presence of 

 the metabolic factor. Clowes propounds the general 

 hypothesis that ''variations in the permeability of the 

 protoplasmic membranes are attributable to the action 

 of electrolytes and metabolic products on delicately 

 balanced interfacial soap-films and emulsion systems, 

 and that proteins may play no part in the valve-Hke 

 mechanism controlling permeability other than to afford 

 a supporting filamentous or mesh-like structure."' 



Such an arrangement need not be taken too Hterally 

 as an exact model of the conditions in the protoplasmic 

 surface-films. It seems probable, however, that in the 

 plasma membrane there is a combination of a relatively 

 permanent supporting structure, presumably protein, 

 with a variable emulsion-like component whose water- 

 insoluble phase is normally so disposed as to block, 

 with a considerable degree of completeness, the interstitial 

 spaces or capillary channels of the membrane. Varia- 

 bility in this emulsion, under the influence of salt solu- 



' Clowes, op. cii.y p. no. 



