THE POSITIVE RESPONSE 177 



stimulation I was often surprised to find the occurrence — 

 which appeared at first as an abnormal response — of gal- 

 vanometric positivity preceding the true excitatory reaction 

 of galvanometric negativity. Thus it appeared as if, in 

 consequence of stimulation, there originated two distinct 

 impulses, positive and negative, which travelled with different 

 velocities. The former travelled faster and, reaching the 

 responding point earlier, induced there the response of 

 galvanometric positivity. The negative wave with its 

 slower velocity of transmission reached the responding- 

 point later and induced the true excitatory effect of 

 galvanometric negativity. 



It was also found that the negative effect was much 

 the stronger of the two ; in consequence of this, if the two 

 impulses reached the responding-point about the same time, 

 the positive was completely masked by the predominant 

 negative. Hence in order to bring out the positive it was 

 necessary to apply the stimulus at a distance. The slow- 

 moving negative then lagged behind the positive to such an 

 extent as not to mask it. 



The following conditions are found to favour the exhi- 

 bition of the positive effect : — 



(i) The stimulus should be applied at a distance from 

 the responding point ; the response is then found to be 

 diphasic, positive followed by negative. A distance may 

 again be found where, owing to the enfeeblement of trans- 

 mitted excitatory effect, the negative impulse fails to reach 

 the responding-point ; in such a case there is an exhibition 

 of only the positive effect. Conversely, if the stimulus be 

 applied too near the responding-point, the negative effect 

 alone is exhibited, the positive being masked by the 

 predominant negative. 



(2) From what has been said it is easy to understand 

 that, with a very highly conducting tissue, the negative or 

 true excitatory effect will be transmitted with great rapidity ; 

 it will therefore mask the positive effect. Hence the 

 positive effect is more easily obtained with plants in 



