122 PROTOPLASMIC ACTION AND NERVOUS ACTION 



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barrier to the movement of ions is at the semi-permeable 

 plasma membrane. The increased conductivity observed 

 at death, or after cytolysis by saponin or other com- 

 pounds, favors this view, since semi-permeability is then 

 lost; i.e., there is a general parallelism between the ability 

 of salts, sugars, and other soluble compounds to pass 

 the plasma membranes and the electrical conductivity 



— a fact indicating that the 

 chief condition rendering 

 living cells such poor con- 

 ductors of electricity is 

 the impermeability of the 

 membranes to ions. From 

 these considerations we 

 should conclude that the 

 ions within the cell are free 

 to diffuse within the space 

 inclosed by the plasma 

 membrane. But the case 

 requires to be tested by 

 experiment, for it might 

 be held, in spite of the fore- 

 going considerations, that 

 the electrolytes are in some 

 manner chemically combined in living protoplasm and 

 are set free only at death. 



Hober has attempted to measure the conductivity of 

 the cell interior, using in part methods suggested to him 

 by Nernst. A device of the plan shown in Fig. i was first 

 employed.^ A rapidly alternating current is induced 

 in the circuit containing the two balanced condensers 

 ^ Hober, Arch. ges. Physiol., CXXXIII (1910), 237. 



Fig. I. — 7, inductorium; C, condenser; 

 G, spark -gap; S, coil (self-induction) of pri- 

 mary circuit; 53, coil of secondary circuit ; A, 

 adjustable condenser; B, condenser with 

 space between plates for insertion of vessel 

 (F) containing suspension of cells; D, detec- 

 tor in bridge^ Ri, Ri, resistances (from Hober, 

 loc. cit.). 



