190 



THE INTELLIGENCE SERVICE 



also sets up currents in the electrolytic fluid (Fig. 39) from a to b, 

 b to c, etc. These currents are indicated by the galvanometers. 



FIG. 39. Diagram'to'show polarisation currents in a medullated nerve or in a 

 polarisation model. 



Emphasis must be placed on the fact that these electrotonic 

 currents are absolutely distinct from the nerve impulse as well 

 as from the wave of negativity or current of action and the 

 current of injury, (a) The former have a much greater velocity 

 than the nerve impulse, as indicated by the wave of negativity 



G' G2 



FIG. 40. Diagram showing electrotonic currents. P, polarising circuit ; G', G 2 , 

 galvanometers. 



(see 11 above), (ft] Their E.M.F. may attain a value twenty-five 

 times that of the current of injury. (7) The direction in which 

 electrotonic currents flow depends entirely on the direction in 

 which the primary current is flowing, reversion of the latter 

 leading to reversion of the former. Action and injury currents 

 always maintain a flow in the nerve from a stimulated or injured 

 part to a resting or uninjured portion of the nerve. 



