ELECTROMOTIVE DETECTION OF EXCITATORY PULSE 26 1 



tissue in any direction, from the stimulated point, there must 

 ahvays be an electromotive wave as its strict concomitant. 

 The moment, therefore, when the excitation reaches a given 

 point may be determined by observing the arrival of this 

 excitatory electrical disturbance of galvanometric negativity, 

 and for the detection of such an excitatory wave the gal- 

 vanometer takes the place of the motile leaflet. 



In order to prove that the excitatory mechanical and 

 electrical effects are strictly concomitant, it is only necessary 



Fig. ioS. Experimental Arrangements for Simultaneous Recording of 

 Mechanical and Electrical Responses 



Stimulus applied by thermo-electric stimulator, s, at A. Excitation reach- 

 ing B causes mechanical response of leaflet, which is recorded by 

 optical lever on drum at M. Simultaneous galvanometric negativity 

 recorded at E. 



to perform an experiment on a plant, such as BiopJivtiiiii, 

 which is provided with motile leaflets. We attach one of the 

 indicating leaflets to the Optic Lever, and connect its base B 

 with one of the electrodes of the galvanometer, the second 

 electrode of which is connected with a distant point of the 

 leaf (fig. 108). The two spots of light, one from the Optic 

 Lever indicating mechanical, and the other from the gal- 

 vanometer indicating electrical, response are adjusted to lie 



