1893.] the Normal State of the Knee Jerk is altered. 449 



When after extirpation of one lateral lobe of the cerebellum the 

 opposite one was also removed, the knee jerk on the side correspond- 

 ing to that on which the lobe was more recently removed became 

 increased, while there was some diminution of the knee jerk on the 

 side on which the lobe was first removed, the two knee jerks being as 

 nearly as possible equal, and, while both knee jerks were exaggerated, 

 they were not as much so as was the one when only one cerebellar 

 lobe was removed. 



The depression of the knee jerk on the opposite side under these 

 circumstances was a phenomenon less marked than was the exaltation 

 of that on the same side as that from which the cerebellar lobe had 

 been removed. In order to test this point further, one cerebral hemi- 

 sphere was first removed, with the result that the knee jerk on the 

 opposite side became more active than it was before. 



A curious and interesting ether effect was observed in connexion 

 with this difference of the knee jerks on the two sides when one 

 lateral lobe of the cerebellum was removed. While the above results 

 obtained during ordinary moderate ether narcosis, the result was 

 exactly the reverse when anaesthesia was very profound, for then the 

 knee jerk which was formerly exalted became depressed, even 

 abolished, while that which was formerly lessened became markedly 

 exaggerated. 



The lateral lobe of the cerebellum on the same side as that on 

 which the cerebral hemisphere was removed was next extirpated, 

 when the active knee jerk on the opposite side became less so. 



On account of the risk of complication by injury of other parts, 

 no attempt was made to do more than remove the whole of the 

 posterior part of the vermis of one lateral half of this posterior por- 

 tion. When only the half of this posterior portion was removed, 

 there was slight increase of the knee jerk on the same side, but 

 this increase was in no way comparable to the great exaggeration 

 which followed removal of one lateral lobe. As far as could be 

 determined, the knee jerk on the opposite side was in no way altered 

 by this lesion. When the whole of the posterior portion of the vermis 

 was removed both knee jerks became slightly increased. 



2. The Late Effects of Extirpation of Portions of the Cerebellum. — 

 On the day after the operation of removal of one lateral lobe of the 

 cerebellum the knee jerk on the same side was still exaggerated, 

 though less so ; but although the knee jerks on the two sides were 

 still unequal, that on the opposite side was no longer feeble, but was 

 slightly exaggerated. In the course of the second and third days it 

 became difficult to be certain that any inequality existed on the two 

 sides, both knee jerks being very much exaggerated, though neither 

 of them as much so as was the one on the side of the lesion im- 

 mediately after the operation. A month or six weeks after the 



