144 COMPARATIVE ELECTRO-PHYSIOLOGY 



1 down ' curve was given by the individual excitation of the 

 left, and the ' up ' by the right. On the simultaneous excita- 

 tion of the two points, the resultant response was zero (). 

 But if the excitation of one say, the right be increased by 

 increasing the angle of vibration, the resultant differential 

 response is found to be * up.' It is obvious that a similar 

 effect would have been observed had the stimulation of the 

 right been kept the same, while its excitability was increased 

 by any external agent. In these cases we have two opposed 

 excitatory waves of similar phase, and of the same or unequal 

 intensities, interfering with each other. 



FIG. 100. (a) Isolated response of left side (down) and right side (up) ; 

 (b] null-effect when excitations are simultaneous ; (c), (d), (e) di-phasic 

 responses obtained with increasing difference of phase. 



We shall next take some simple instances in which, while 

 the stimulation is maintained constant, there is an increasing 

 difference of phase. If the right-hand striking-rod R, instead 

 of being set at zero, be set to the right, or at a plus angle, 

 the rotation of the handle will cause a slightly earlier excita- 

 tion of the right than of the left. If, on the other hand, the 

 rod be set at a minus angle, the excitation of the right will 

 be later than that of the left. Under these circumstances, 

 instead of the null-effect due to continuous balance, we shall 

 have a di-phasic response. It is also clear that as the phase 

 difference is increased, the neutralisation of effects will 

 become, less and less perfect, the separate constituent respon- 

 ses being thus rendered increasingly apparent. In fig. 100, c, 



