civ Journal of Comparative Neurology. 



was the most excitable after unilateral ablation of the cerebellum, 

 which difference in the excitability persisted, and was still present 

 even three months after the half of the cerebellum had been removed. 

 The results obtained when absinthe was administered to animals which 

 had been deprived of half the cerebellum also yielded highly interesting 

 and instructive results. The increased excitability of the opposite hemi- 

 sphere was evidenced by the exaggeration of the convulsions on the side 

 of the cerebellar lesion ; and it became also evident that the convul- 

 sions on the opposite side were diminished. Further, the curves ob- 

 tained from the extensor muscles of the anterior extremity on the side 

 of the cerebellar lesion showed that there was a marked alteration in 

 the second stage of the convulsive seizure, for the tonus characteristic 

 of this stage of similar convulsions evoked in dogs whose central 

 nervous system was intact was either replaced by clonic spasms, or a 

 large element of clonus was superimposed on the tonus. The curves 

 from the muscles of both anterior extremities showed this alteration 

 in the second stage of the convulsions when the whole instead of the 

 half of the cerebellum had been previously removed. 



The chief conclusions which appear to be warranted are that the 

 one half of the cerebellum does not, in any great measure, depend on 

 the cooperation of the other half for the proper performance of its 

 functions. The bulk of the impulses pass from one half of the organ 

 to the cerebrum, or spinal cord, without passing to the other half. 

 Three factors are responsible for the defective movements which re- 

 sult on ablation of different parts of the organ — incoordination, rigid- 

 ity, and motor paresis. The last of these is probably directly due to 

 the withdrawal of the cerebellar influence from the muscles, while 

 the exalted excitability of the opposite cortex cerebri, which results 

 after unilateral ablation of the cerebellum, is probably a provision for 

 compensation in this and and other connections. The one half of the 

 cerebellum controls the cells of the cortex of the opposite cerebral 

 hemisphere, and those of the anterior horns of the spinal cord on the 

 same side chiefly, and on the opposite side to a slight extent. It is 

 further suggested that either the cerebral hemisphere whose excitabili- 

 ty is increased inhibits the opposite hemisphere, or that, under normal 

 conditions, one half of the cerebellum inhibits the other half, which 

 inhibition being no longer operative, owing to ablation of half of the 

 organ, allows the remaining half to exert an increased control on the 

 opposite cortex cerebri, or on the spinal centres of the same side, or 

 possibly in both directions; but which is the most probable explana- 

 tion of the phenomena observed is at present left an open question. 



