CHAPTER XXXVII 



RESPONSE BY VARIATION OF ELECTRICAL RESISTIVITY 



Variation of resistance in Dtonaa, by ' modification ' Excitatory change, its 

 various independent expressions Characteristic difficulties of investigation 

 Morographic record by variation of resistivity Inversion of curves at death- 

 point Similarities between mechanical, electro-motive and resistivity curves 

 of death The true excitatory effect attended by diminution of resistance 

 Response of plant nerve by resistivity variation Independence of resistivity 

 and mechanical variations Responsive resistivity variation in frog's nerve, 

 and its modification under anaesthetics. 



IT was noticed by Burdon Sanderson that leaves of Dioncea 

 after ' modification ' exhibited a diminished electrical resist- 

 ance ; and this ' modification ' he found to be most easily 

 induced after the passage of an electrical current through 

 the tissue. Subsequent observers have also noticed a diminu- 

 tion of resistance in many cases when a tissue has been 

 subjected to electric shocks. These diminutions of resistance 

 are observed as more or less permanent after-effects. The 

 experiments in these cases depend on obtaining the galvano- 

 meter deflections caused by a small E.M.F., before and after 

 the modification. The larger deflection due to the same 

 E.M.F. after modification shows that the resistance of the 

 tissue has undergone a diminution. 



This method, however, is open to several objections. 

 The passage of constant or induction currents through the 

 tissue would not only give rise to polarisation effects, but 

 would also induce an unknown electromotive variation at 

 the two contacts on the surfaces of the tissue, to an extent 

 depending on their differential excitability. The observed 

 deflection by a small testing E.M.F. is thus affected, not 



