CONDUCTIVITY AND PERMEABILITY 225 



the investigations of Brooks cited above. It would seem 

 that it is well founded, since if the cell were impermeable, 

 it could not obtain the salts necessary for its existence. 31 * 

 It is, of course, true that the electrical resistance of the 

 cell is much higher when alive than when dead, as is shown 

 by the work of Roth (1897), Bugarsky and Tangl (1897), 

 Stewart (1897), and Woelfel (1908), on blood corpuscles, 

 that of McClendon (1910), and Gray (1913, 1916) on sea 

 urchin eggs, that of Shearer (1919) on bacteria, as well as 

 the results of the writer. 



The seat of this higher resistance might be sought in 

 the interior of the cell, or at the surface. Plant cells offer 

 especially good material for this sort of investigation, 

 since in most cases the protoplasm forms a thin layer 

 surrounding a large central vacuole filled with cell sap. It 

 has been shown above, (pp. 198 and 199) that, in the cases 

 investigated, the sap has a conductivity which does not 

 differ greatly from that of the external solution. It 

 would therefore seem that the cause of the high resistance 

 is to be sought in or near the surface. Hober (1914, pp. 383, 

 442) has reached this conclusion as the result of experi- 

 ments on red blood corpuscles and muscles. He employed 

 two methods for measuring the conductivity of the 

 interio.r of the cell. The first depends on the fact 

 that a conducting body increases the capacity of a 

 condenser when inserted between the plates. The 

 second is based upon the fact that a conductor placed 

 in the centre of a coil of wire diminishes the strength of 

 an alternating current in the coil. Using these methods, 

 Hober finds that the conductivity is higher than when it 

 is measured in the usual way (in which the current passes 

 through the cell ) . He therefore concludes that the surface 



89 Cf. Osterhout (1916, E). 

 15 



