9 6 



PHYSIOLOGY OF STREAMING MOVEMENTS 



SECTION 43. Conductivity and Resistant Powers of the different 



parts of the Cell. 



Living protoplasm appears to offer a somewhat greater resistance to 

 the passage of an electric current than dead * protoplasm,' a conclusion 



arrived at by Kiihne (I.e.) from a priori 

 reasoning, without experimental proof. The 

 latter can be obtained by passing a weak 

 current of low voltage through a Wheatstone 

 bridge arrangement, one section of which 

 includes a filament of Char a or Nitella. On 

 killing the cells by touching them with a 

 hot wire or by applying powerful induction 

 shocks, the galvanometer after a temporary 

 disturbance remains permanently deflected in 

 such a manner as to show that an increased 

 current is passing through the filament, i. e. 

 that the resistance of the filament has de- 

 creased. The deflection attains a maximum 

 in from a few minutes to an hour after the cell 

 has been killed, then usually slowly diminish- 

 ing as the cell-sap exudes from the cell and 

 the protoplast retracts. The decreased resis- 

 tance is apparently correlated with the change 

 from the condition of a viscous liquid to that 



f * *^> * C ' with the Coagulation of the 



protoplasm 1 . The same effect is produced 

 when the heated wire is applied to the ends 



FlG. 12. To show change of resistance 

 on death. The resistance fs prevents the 

 passage of strong currents through the 

 filament during adjustment. The/Velec- 



trodes rest on white clay in contact with 

 the ends of the cells which are covered on 

 top by vaseline. 



of the cells lying beyond the electrodes, and 

 hence out of the path of the current, and the 



same is also the case when the cells are treated with dilute HC1 (3 per 

 cent.) for thirty seconds, and then rapidly washed with water. 



If a filament of three cells is stimulated, it will be found that to pro- 

 duce a shock-stoppage requires a stronger current when the two end cells 

 are living than when they have been killed. The two experiments must, 

 however, always occur in the order given, and hence it is possible that 

 a previously sub-minimal stimulus may become an operative one, not 

 because the resistance of the filament as a whole has decreased so that more 

 of the current flows through it, but because the excitability has been 

 increased by the previous stimulation. Both factors are probably opera- 



1 See Appendix (Influence of Coagulation on Conductivity). 



