450 Mr. J. S. R. Russell. Circumstances under which [May 15, 



operation most of the animals showed a slight inequality of the knee 

 jerks, so that, although both were exaggerated, that on the side 

 corresponding to that from which the cerebellar lobe had been 

 removed was slightly the more so ; bat in some animals the inequality 

 was not evident. When half of the posterior part of the vermis was 

 removed, it was usually difficult next day to say which knee jerk was 

 the more active ; but, as in the case of the lateral lobe, after a few 

 weeks a difference on the two sides could be once more detected in 

 most of the animals. At this time the knee jerk on the opposite side 

 was usually as nearly as possible normal, while that on the same side 

 as the cerebellar lesion was more active than normal. In like manner 

 the increase of knee jerk produced by removal of the whole of the 

 posterior portion of the vermis persisted. 



If, after a one-sided lesion, either of the vermis or lateral lobes, 

 the animal was placed under the influence of ether, the inequality of 

 the knee jerks became more pronounced ; and if the anaesthetic was 

 pushed to the point at which abolition of the knee jerks results, that 

 on the opposite side usually disappeared sooner than did that on the 

 side corresponding. 



There seemed, therefore, little reason to doubt that the effects 

 obtained in connexion with the knee jerk when portions of the 

 cerebellum were removed were directly the result of the cerebellar 

 lesion. However, Professor Victor Horsley kindly drew my attention 

 to the fact that the proximity of the auditory nerve and labyrinth 

 made it necessary to institute control experiments, with a view to 

 excluding the possibility of the effects being wholly or partly due to 

 interference with one or other, or both, of these structures. He 

 suggested that the labyrinth should be extirpated on one side in 

 some animals, while in some others the 8th cranial nerve on one 

 side could be subjected to chemical excitation. I accordingly per- 

 formed the following control experiments. 



III. Extirpation of the Labyrinth on one side. {Control.) 



No inequality was produced in the knee jerks by this at the time 

 of the operation, nor was any alteration detected two weeks after the 

 operation, except in one instance, in which, two weeks after the 

 operation, the knee jerk on the same side as the ear lesion seemed 

 slightly more active than its fellow of the opposite side. As there 

 was suppuration in the deep wound in this case, it was thought that 

 the result probably depended on entrance of pus into the region of 

 the lateral lobe of the cerebellum on the same side, but no such con- 

 dition was macroscopically obvious at the autopsy, so that this case 

 is difficult of explanation. 



