1893.] the Normal State of the Knee Jerk is altered. 457 



does not wholly meet the case is, I think, clear on two grounds. 

 The increase of the opposite knee jerk which is consequent on the 

 removal of the cerebral hemisphere of one side is not nearly so great 

 as that brought about by the removal of the lateral lobe of the cere- 

 bellum of the same side. When one cerebral hemisphere has been 

 first removed, and the opposite lateral lobe of the cerebellum is re- 

 moved, the knee jerk on the opposite side from the cerebral and on 

 the same side as the cerebellar lesion is further increased after the 

 second operation. It thus seems clear that the cerebellum exercises 

 an independent action on the spinal centres from that exercised by 

 the cerebrum, and that this action is of the nature of a control over the 

 spinal centres chiefly of the same side. That this is the chief expla- 

 nation of the phenomenon there appears little doubt ; but it does not 

 entirely negative the possibility of the first hypothesis being wholly or 

 in part true. 



The fact that the diminution of the knee jerk, on the side opposite 

 to that on which the lateral lobe of the cerebellum was removed, 

 was always of such short duration, points to that phenomenon as 

 being an " irritative " one, possibly one of inhibition. 



The curious ether "effect which was observed in this connexion is 

 easy of explanation as far as the knee jerk of the opposite side is 

 concerned, when it is considered alone ; for, if it be admitted that the 

 inhibitory influence of the cerebellar lesion is sufficient explanation for 

 the occurrence of diminution of the knee jerk, it is easy to understand 

 how the first effect of the ether would be to remove this inhibitory 

 influence, and by its direct action on the spinal centres to cause 

 exaggeration of the knee jerk. The effect of the ether on the knee jerk 

 of the same side as the cerebellar lesion is also easy of explanation, 

 when considered by itself, for the direct effect of the ether on the 

 spinal centres, when present in sufficient quantity, would be to cause 

 diminution, and finally abolition, of the knee jerk. When both 

 phenomena, i.e., those of the opposite sides, are considered together, 

 the explanation becomes more difficult ; for, in order that the explana- 

 tions suggested when the phenomena were separately considered 

 should hold good now that they are considered in conjunction, one of 

 two things must be admitted : either some influence on the spinal 

 centres of the side corresponding to that of the cerebellar lesion has 

 rendered them less capable of resisting the direct action of the ether ; 

 or some influence acting on the spinal centres of the opposite side has 

 rendered them more resistant to the action of that drug. 



These questions must for the present remain unanswered. 



That interference with the 8th nerve or labyrinth plays no part 

 in the phenomena which follow extirpation of parts of the cerebellum 

 is abundantly proved by the control experiments which were per- 

 formed in order to decide this question. 



VOL. Lin. 2 K 



