126 



COMPARATIVE ELECTRO-PHYSIOLOGY 



then, in this particular case, appears as a positive variation of 

 the resting-current. 



And, finally, we may imagine the pulvinus to have been 

 strongly excited, so as to be in the condition D or E. The 

 resting-current will in this case be upwards t. But the ex- 

 citability of the lower half, owing to fatigue, has now become 

 depressed, a condition which, as we have seen, tends to give 

 rise to the abnormal positive response, the responsive current 

 being thus downwards I. As the modified current of rest 

 is upwards, this abnormal current of response will appear as 

 a negative variation of it. 



All these cases are conveniently tabulated as follows : 



TABULAR STATEMENT OF THE RELATIVE DIRECTIONS OF THE CURRENT 

 OF REST AND THE RESPONSIVE CURRENT UNDER VARIOUS CONDITIONS. 



The various conditions mentioned may be induced 

 accidentally in the responding organ, or may be brought 

 about by the excitatory effect of experimental prepara- 

 tion. I give here the records of certain experiments 

 performed on Mimosa, in which some of these changes were 

 seen to occur as the result of stimulation (fig. 88). The 

 normal natural current is seen to be from above to below, as 

 represented by the dotted arrow. The first strong stimulus, 

 applied at the moment represented by the thick dot, gives 

 rise to a responsive current whose direction is from below to 

 above, Owing to the strong intensity of the stimulation, 

 there is here a slight indication of multiple response. As an 

 after-effect of stimulus, we observe that the normal resting- 

 current has undergone a reversal, the lower surface, which 

 was formerly positive, having now become relatively 

 negative, A second stimulus now gave rise to a response 



