9 o 4 THE CEREBELLUM. 



muscles, their flaccid feel, the semiflexed droop of the limbs, which, as 

 the animal stands, sometimes appear to give way under it, especially if 

 the animal's attention be suddenly diverted. An illustration of the 

 paratonia is afforded by the slow slipping over of the eyeballs to the 

 crossed side, after the return jerk of nystagmus has replaced them in 

 the normal " forward " pose. The tonus of the lateral muscles pulling 

 toward the lesion seems insufficient to balance the tonus in the muscles 

 which swing the eyeballs in the opposite direction. 



The astasia of muscles, a tremor heightened or only appearing when 

 the musculature is set into action, Luciani attributes to imperfect fusion 

 of the simple contractions, which on the " tetanus " theory compose 

 willed contractions. It affects especially the muscles fixing the head, 

 and occurs in monkeys more markedly than in dogs. This is his 

 explanation of the " intention tremor." Some features of the peculiarity 

 of movement in both the early and later periods are no doubt due to 

 actions intended to correct the defects and disabilities. The animal 

 more or less rapidly learns by the experience of many failures, e.g. falls, 

 deviations in a particular direction, etc., to correct its mistakes as they 

 arise. Among such compensatory acts may be probably the spreading of 

 the limbs to right and left to give to the body a wider basis of support ; 

 also, perhaps, the incurvation of the trunk toward the side which is the 

 weaker. The dog that as a result of removal of the right cerebellar 

 hemisphere forges to the left in swimming, learns to swim straight by 

 keeping the lumbo-sacral part of the vertebral column curved appro- 

 priately to the right. By such compensatory innervation as this the 

 ataxia is gradually more or less successfully hidden. Luciani found that 

 ablation of the Eolandic area of the cortex of the cerebral hemisphere 

 largely hinders the development of this compensation for cerebellar 

 defect. He urges on various grounds that the cerebellum has an 

 important influence upon the activity of the Eolandic region of the 

 cerebral cortex, the left half of the cerebellum acting on and with the 

 right hemisphere of the cerebrum. The influence he describes to be of 

 a tonic and trophic nature, modifying the excitability of the Eolandic 

 cortex in a way comparable with that in which the afferent spinal root 

 modifies the excitability of the motor nerve cell. Bianchi, as a test of 

 the excitability, is reported to have faradised the sensori-motor cortex 

 some days after ablation of the crossed half of the cerebellum, without 

 obtaining results which to his mind establish clearly a departure from 

 the normal excitability of the cortex. Similar experiments have been 

 made by E. Eussell and Luciani, the former concluding that the excita- 

 bility may be raised, the latter concluding that the excitability is in 

 some points of the Eolandic area exalted, and in others depressed. 

 Luciani finds his " cerebellar influence on the cortex," trophic as it is 

 and thereby affecting excitability, chiefly effective on the Eolandic 

 region. 



Eegarding the field of distribution of the motor effects, both of 

 spastic and of asthenic type, it is clear that each lateral half of the 

 cerebellum mainly affects its own homonymous half of the body ; it is in 

 the eyeballs and hind-limbs that the more marked instances of any 

 bilaterality of its action are seen. It may be, however, that almost the 

 whole musculature is represented in each half of the cerebellum, and 

 Luciani points out that after total ablation of the cerebellum the defect 

 is everywhere greater than after lateral ablation. 



