PROTOPLASMIC STRUCTURE 125 



known conductivity, Hober found that the suspension 

 gave the same effect as a NaCl solution of a concentra- 

 tion similar to that of blood plasma (i.e., between o.i 

 and 0.4 per cent). Further accuracy is not possible. 



Hober also used the method of measuring the con- 

 ductivity of cells by means of rapidly oscillating cur- 

 rents.^ According to theory, we should expect that the 

 higher the oscillatory frequency the less difference would 

 the presence of the membrane make. Under the condi- 

 tions, frog's muscle, which had been washed thoroughly 

 in sugar solution, behaved as if it had a conductivity 

 between o.i and 0.2 NaCl; the greater the frequency 

 of alternation the greater the conductivity. This is 

 . readily understood if we reflect that when the carriers 

 of the current (ions) have to pass through only very 

 short distances, they are not impeded in their movements 

 by the membrane. 



From the results of the experiments above Hober 

 reaches the following conclusion:^ ''It can be regarded 

 as certain that the blood corpuscles possess a very con- 

 siderable internal conductivity, even when the external 

 conductivity is minimal; i.e., that free ions are present 

 in their interiors, and that these are prevented from reach- 

 ing the outside only by the presence of a barrier to 

 diffusion"; i.e., the plasma membrane. 



The observations cited by Kite^ and others, as indi- 

 cating the impermeability of the internal protoplasm 

 to diffusing substances, are probably to be explained as 

 indicating the rapidity with which a semi-permeable 



^ Hober, Arch. ges. Physiol., CL (1913), 15. 



2 Hober, Physikalische Chemie der Zelle und der Gewebe (i9i4),p. 385. 



3 Kite, Biological Bulletin, XXV (1913), i. 



