PHYSICO-CHEMICAL BASIS OF TRANSMISSION 397 



approaching each other from opposite directions undergo 

 mutual extinction where they meet. It is clear that 

 the processes determining transmission are in some 

 manner compensated or nullified where the waves meet; 

 and since each wave is associated with a bioelectric 

 circuit, and the two circuits, being equal and oppositely 

 oriented, must physically compensate each other when 

 superimposed, it is to be expected that any transmission 

 of electric influence and hence of stimulating effect 

 beyond their intersection will be impossible. The block- 

 ing of excitation-waves at regions of injury is probably 

 to be explained in a similar manner, as due to compensa- 

 tion of the action current by the injury current.^ 



The question of the part which interferences of this 

 kind play in the intact living organism (e.g., in the 

 central nervous system) is an open one. Recently 

 there have been attempts to explain physiological 

 interferences such as those of reciprocal inhibition, the 

 Wedensky phenomenon, vagus inhibition, etc., on the 

 basis of a lack of correspondence between the normal 

 rhythm of response and recovery in the receiving irritable 

 system and the rhythm of the series of nervous impulses 

 entering it from without.^ The Wedensky effect is an 

 example of such a phenomenon, the failure of the muscle 

 to respond after the initial contraction depending on 

 the coincidence of periods of increased decrement in 

 the motor end-plate with the periods at which the 



^ Mayor refers the mutual extinction of intersecting waves to the 

 refractor}^ phase of the tissue; "tissue which has been in contraction 

 cannot again contract until after an appreciable interval of rest." Elec- 

 trical compensation must, however, also be present, as in the analogous 

 cases of anelectrotonus and blocking at a region of injury. 



2 Keith Lucas, Conduction of the Nervous Impulse, chaps, xii, xiii. 



