434 PHYSIOLOGY CHAP. 



(6) They predominate in the side exclusively or mainly 

 affected, and appear to be more pronounced and varied in pro- 

 portion as the lesion is deeper and extends farther towards the 

 cerebellar peduncles. 



(c) When the peduncles are partly degenerated, in consequence 

 of previous removal of the vermis, the later destruction of a 

 lateral lobe only produces slight and transient irritative 

 symptoms. 



Terrier, however, showed that when there is actual irritation 

 or inflammation in the cerebellum the dynamic phenomena are 

 very different from what we had described. He found that when 

 a lateral lobe of the cerebellum was partially cauterised so that 

 the adjacent parts were irritated, rotation took place in exactly 

 the opposite direction to that which we observed after removal of 

 one side of the cerebellum. 



We had never performed cauterisation experiments on the 

 cerebellum as they appeared unsuitable for eliciting clear and 

 unequivocal physiological facts, but on repeating Terrier's experi- 

 ment on a number of animals we convinced ourselves of the 

 accuracy of his observations. We found that more or less pro- 

 found cauterisation of the cortex of a cerebellar lobe on one side 

 gave rise to symptoms that were almost exactly the opposite of 

 those seen after its removal. The disquiet and cries of pain are 

 absent the animal rather appearing depressed and subdued; 

 the pleurothotonus to the injured side is replaced by slight 

 pleurothotonus to the normal side ; the tendency to rotate and 

 actual rotation round the long axis from the operated towards the 

 healthy side is replaced by a tendency to rotate in the opposite 

 direction, i.e. from the healthy towards the operated side. 



On what does this reversal of effects depend ? The question is 

 still undecided. In reply to Terrier we advanced the hypothesis 

 that the cauterisation of the cerebellum irritates the adjacent 

 parts as well, including the dura mater, which is a sensory 

 membrane capable of producing symptoms of reflex inhibition on 

 excitation. This, however, is not an adequate explanation. Are 

 the pleurothotonus and rotation in the opposite direction to be 

 referred to the preponderance of inhibitory effects on the operated 

 side or to exaggerated activity on the healthy side ? A recent 

 experiment on dogs indicates that it depends on both these factors. 

 We observed that if before cauterising the cerebellum on one side 

 the two halves of the cerebellum were divided by a median sagittal 

 section, the animal appeared subdued with pleurothotonus to the 

 cauterised side, and a slight tendency to rotate towards the 

 healthy side. Next day the animal was quiet ; it lay on the flank 

 of the cauterised side, and if forcibly placed on the opposite side 

 made a half-turn to recover this position, but showed no tendency 

 to rotate on its axis ; if held up there was pleurothotonus to the 



