276 



ELECTRO-PHYSIOLOGY 



CHAP. 



pointed out, the electrotonic alterations (unlike excitation) 

 diminish rapidly in intensity with increasing distance from the 

 polarised tract, and finally become imperceptible. So that, when 

 immediately after closure of the polarising current the electro- 

 tonus is still undeveloped, the region in which it can be 

 demonstrated is necessarily even smaller than that in which it 

 appears definitely. 



Tschirjew subsequently repeated his experiments with the same 

 results, using the capillary electrometer (which is peculiarly 

 sensitive to rapid oscillations of current), and Bernstein's rheotome, 



FIG. 210. 



which of course are open to the same objections. Bearing in 

 mind the theory of this last ingenious instrument, it is evident 

 that it affords an easy means of leading a polarising current at 

 any given moment into the nerve, and interrupting it again 

 directly, at the same time leading off the electrotonic currents from 

 a distant tract of the nerve at different intervals after closure. 

 Bernstein's own method of experiment (as referred to above) is 

 explained by the following schema (Fig. 210). During the 

 rotation of the rheotome the polarising current is periodically 

 closed whenever the contacts dip into the mercury pools (qq), 

 the galvanometer circuit as often as the contact (^j 1 ) dips into 

 (q l ). The period of closure of the polarising current varies 

 between - and sec. : the direction of the led-off current 



