PHYSICO-CHEMICAL BASIS OF TRANSMISSION 391 



would have a corresponding effect upon the speed of 

 protoplasmic transmission. A lowering of the conduc- 

 tivity of the local bioelectric circuit should involve a 

 corresponding decrease in this velocity, since the maximal 

 distance, s, at which the local current still has stimulating 

 intensity, would be proportionately decreased by any 

 increase of electrical resistance. This critical distance 

 should, other conditions being equal, be proportional 

 to the conductivity of the circuit. Mayor's experiments 

 on the rate of transmission in the nerve net of the 

 medusa Cassiopea in dilute sea water show in fact that 

 within a considerable range of dilutions (down to 50 

 volumes per cent sea water) a close proportionahty 

 exists between the salt-content of the medium and the 

 transmission rate.^ This result indicates a direct 

 correlation of this rate with the electrical conductivity 

 of the medium. The recent investigation of Pond'' on 

 the speed of the contraction-wave in various forms of 

 muscle (cardiac and voluntary of frog and heart of 

 Limulus), using mixtures of balanced salt solution and 

 isotonic sugar solution, has shown that in these tissues 

 also the speed of transmission runs closely parallel 

 with the electrical conductivity of the medium. The 

 transfer of a muscle from a medium of low to one of 

 high conductivity is followed by a corresponding increase 

 in the speed of the contraction-wave, and vice versa. 

 Mayor's and Pond's observations are difficult to explain 

 except on the assumption that electric currents traversing 

 the cell-media are a chief factor determining the rate at 



^ A. G. Mayor, American Journal of Physiology, XLII (191 7), 4^9, 

 and XLIV, 591. 



2 S. E. Pond, Jour. Gen. Physiol, III (1921) 807. 



