24 Relations between the Cerebellar and other Centres, (Re- 



present or not, and, further, a notable difference according to the 

 side of the cerebellum excited. 



The limits of the excitable region of the cerebellum will not now 

 be discussed, but we may here state that the most excitable area is 

 along the line of junction of the vermis superior with the lateral 

 lobe. (This, it will be noted, is that portion of the cortex of the 

 cerebellum which, in vertical position, is nearest the superior cere- 

 bellar peduncle.) 



For the purposes of the present communication excitation of the 

 cerebelium means excitation of this focal area. 



(a) Excitation of the Cerebellum ivhen " acerebral " Tonus is estab- 

 lished. — The effect of excitation of the cerebellum when ablation of 

 the cerebral hemispheres has produced general tonic contraction, in 

 extension of the trunk and limb muscles is a striking and constant 

 active relaxation so far as the triceps (of the side stimulated) is con- 

 cerned, and an active contraction of the biceps. 



In the absence of graphic record it is impossible to determine 

 precisely what is the nature of this effect on either the biceps or 

 triceps. 



We have, however, proved by the graphic method that — 



(1) The biceps contracts powerfully; 



(2) The triceps actively relaxes, i.e., it does not simply relax by 



ceasing to contract, but it relaxes so as to lose its normal 

 physiological tonus. 



The next step was of course the further investigation whether this 

 phenomenon is unilateral. We have found as the result of twenty- 

 nine experiments that the muscles of the right arm can be influenced 

 by excitation of both halves of the cerebellum, but that the effect is 

 very much greater from excitation of the right half, i.e., the same 

 side. In addition we have excited the two halves of the cerebellum 

 after median division of the organ, and then found that the effect was 

 practically limited to the same side. 



This is of course in harmony with the results of ablation of the 

 cerebellar hemispheres obtained by Luciani, Kisien Russell, and 

 Terrier and Turner. 



In five experiments it was interesting to find that excitation of the 

 left half of the cerebellum, i.e., that of the opposite side, evoked 

 relaxation of the biceps. This crossed effect we noticed early in the 

 investigation, and the similarity in the movements of the forelimb in 

 walking was very striking. 



The phenomenon of relaxation of the triceps and contraction of the 

 biceps can be obtained also by excitation of the sub-cortical white 

 substance of the cerebellum and of the peduncles in part. 



(b) Excitation of the Cerebellum when no " acerebral " Tonus is yet 



