1912.] Instability of Cortical Points. 273 



is a tendency for whichever of the two is applied subsequently to break 

 through the effect of its opponent. 



Fig. 20. 



Experiment 15, Callothrix, 5.3.12. — Here the E point (E — F) on stimulation gives 

 flexor relaxation, and concurrent stimulation of the F point (C — D) reverses this to flexor 

 contraction, but at the same time there is an extensor contraction, so that both the 

 antagonists are in contraction at one and the same time. The cessation of the E stimulus 

 is followed by an epileptiform discharge in both the antagonists. An examination of the 

 ordinates numbered 1 — 7 on the two muscle tracings shows that the beats in these are 

 reciprocal. Thus ordinate 5 on the extensor tracing cuts the lowest point in a beat, 

 while the corresponding ordinate 5 in the flexor tracing cuts the top of a beat. Thus near 

 this point relaxation during a beat in one muscle was accompanied by contraction during 

 a beat in the other. 



VII. Post-central Convolution. 



We have on a number of occasions found stimulation of points in the post- 

 central convolution near the lower end of the intra-parietal sulcus modify the 

 epileptoid after-discharge following stimulations of points in the arm-area of 

 the pre-central convolution. Points in the post-central convolution when 

 stimulated immediately after cessation of a stimulation of a pre-central gyrus 

 are frequently able to evolve some return of the movement just previously 



