456 Mr. J. S. R. Russell. Circumstances under which [May 18 7 



abolish the lesion in the lower animals, but, on the contrary, causes 

 distinct increased activity of it, is a well-established fact, which did 

 not require the further support which the results of these experiments 

 give to it. The chief interest in the present experiments, however, is 

 centred in the varying effect obtained according to the depth of ether 

 narcosis ; and they demonstrate very clearly how greatly shock to the 

 spinal cord may be increased by the depth of narcosis. That is, a 

 lesion of such severity and in such a situation as to cause very little 

 or no shock to the lumbar cord under moderate ether narcosis may 

 be made to produce considerable shock if the depth of narcosis be 

 greater at the outset. 



The results of bisection of the spinal cord in the lumbo-sacral 

 region prove, in confirmation of Sherrington's observations, conclu- 

 sively that the centres on whose action the knee jerk depends are 

 distinct in the two lateral halves of the cord, and are not dependent 

 on each other, either for control or for reinforcement. 



The Effects of Removal of a Cerebral Hemisphere. — The increase of 

 the knee jerk on the opposite side, which followed the removal of the 

 cerebral hemisphere of one side, is a result in keeping with the best 

 established views of the relation of the lower spinal centres to the 

 higher cortical ones ; for by removing the hemisphere the control 

 which the cortical centres are regarded generally as exercising over 

 the spinal centres of the opposite side chiefly was removed. 



The Immediate and Late Effects of Extirpation of portions of the 

 Cerebellum. — As has been seen, the knee jerk on the same side became 

 exaggerated both when one lateral lobe of the cerebellum or when one 

 half of the posterior part of the vermis was removed, and that this 

 increase of the knee jerk persisted for weeks, i.e., after all phenomena 

 which could be ascribed to " irritation " had passed off. It seems 

 justifiable therefore to attribute this to a " paralytic " rather than an 

 " irritative " lesion. This being the case, two hypotheses are open to 

 us in explanation of the phenomenon : either we must suppose that 

 the one half of the cerebellum exercises an energising influence on 

 the opposite half of the cerebrum, in virtue of which it causes the 

 opposite cerebral centres to hold in greater check the spinal centres 

 of the side of the spinal cord corresponding to the side of the cere- 

 bellar lesion; or that the one half of the cerebellum exercises a con- 

 trolling influence on the spinal centres on the same side of the spinal 

 cord. If the first of these hypotheses is accepted, then the increase 

 of the knee jerk is due to the diminished power of control of the 

 cerebral centres on those in the spinal cord in consequence of the loss 

 of the energising influence of the cerebellum on the cerebrum. If, on 

 the other hand, the second of these hypotheses be accepted, the in- 

 crease of the knee jerk is due directly to the taking off of cerebellar 

 control from the spinal centres. That the first of these hypotheses 



