REVERSED POLAR EFFECTS IN LIVING TISSUES 203 



certain point, indicating that both of them now excited in 

 about equal degrees. This would constitute the A stage. 

 Beyond this would be the B stage, where the anode alone 

 would excite. 



I now proceeded to subject these theoretical inferences to 

 the experimental test. The special difficulty of this investiga- 

 tion lies in the fact that it is necessary to discriminate the 

 direct from the transmitted effect at the two electrodes, with 

 absolute certainty. For if the two points be not at a sufficient 

 distance, and if the conductivity of the intervening tissue be 

 great, the true effect of one electrode may be rapidly trans- 

 mitted, and appear at the other. For these reasons, the 

 plant Biophytum is not in this case a very suitable subject for 

 experiment, its conductivity being great, and its opposite 

 leaves not at a sufficient distance from each other. Mimosa, 

 however, may be made to serve the purpose, for, though its 

 conductivity is great, it is possible to select two leaves on 

 different branches of the same plant which are very far 

 apart. The plant Averrhoa is also appropriate, its conduct- 

 ing power being relatively slight. Electrical connections 

 may, in this case, also be made with opposite leaves widely 

 apart. In the case of Mimosa the excitatory effect is made 

 visible by the fall of the leaf, in the case of Averrhoa by the 

 depression of the leaflets. It is thus possible to render the 

 effect of the two electrodes mutually distinct. It is also 

 possible to distinguish the transmitted excitation, if any, by the 

 serial depression of the intervening leaves or leaflets during 

 the passage of the wave of excitation. 



As these excitatory effects are dependent on the physio- 

 logical condition of the tissue, we should expect that the 

 E.M.F. which produces reversal would vary with different 

 plants and their physiological conditions. The highest constant 

 E.M.F. available for my own investigations was 220 volts, 

 that being the pressure in the street-mains. I therefore 

 hoped that I might be fortunate enough to find plants in a 

 state to exhibit the expected reversal within this value. I shall 

 now proceed to describe actual experiments with various 



