viii THE HTND-BEAIN 483 



opposite, cerebral hemisphere, and it is only later, after some 

 months, that the exaggerated voluntary efforts, directed to the 

 mechanical compensation of the cerebellar deficiency, may or can 

 produce an increase in the excitability and functional efficiency 

 of the centres. 



We controlled Eussell's experiments in two monkeys some 

 months after the extirpation of the right half of the cerebellum, 

 and in a dog only seventeen days after the same operation. The 

 excitability of the left cerebral motor area was diminished only at 

 certain points, while at others it appears either unaltered or 

 increased, in comparison with the right motor area. Not being 

 able at the time to give an adequate interpretation of this equivocal 

 result, we confined ourselves to bringing it into relation with the 

 fact that the anatomical and functional relations between the 

 cerebellum and cerebrum are mainly but not exclusively crossed. 



Gilberto Eossi eventually cleared up the matter by publishing 

 two brief but important experimental observations in 1912, which 

 were obtained with all possible technical precautions. 



The immediate effect of hemi-extirpatioii of the dog's cerebellum 

 is a diminution of excitability in the motor cortical area on the 

 opposite side, as compared with that on the same side as the 

 extirpation. This diminution can be seen during the whole of 

 the period in which the phenomena of deficiency persist. The 

 establishment of compensatory phenomena is, on the contrary, 

 accompanied by a definite increase of excitability in the motor 

 area of the opposite side, as compared with the side of the 

 extirpation. 



These new experimental data are a direct proof of the re- 

 inforcing action, for the most part crossed, which the cerebellum 

 exercises upon the cerebrum, while they further show that voluntary 

 effort suffices to repair and to compensate the phenomena of 

 deficiency, by raising the excitability of the cerebral motor cortex. 



On investigating the effect of simultaneous stimulation of the 

 cerebral and cerebellar cortex, Eossi found that faradic stimuli 

 applied to the cortex of one lateral half of the cerebellum in 

 all the lobes explored crus primum, crus secundum, lobulus 

 paramedianus raised the excitability of the cerebral cortex on 

 the opposite side. That is, no motor reaction was induced, but 

 the threshold of excitation of the central motor area of the 

 opposite side was lowered, which, by facilitating the motor effects, 

 made previously inefficacious currents effective. On the other 

 hand, faradisation of the same parts of the cerebellum on one side 

 caused no appreciable modification in the excitability of the 

 cerebral cortex on the same side. Very weak faradic currents 

 produce these effects, during slight narcosis of the animal. In 

 profound narcosis the stimulation of the cerebellum is ineffective. 

 These new experimental observations published by Eossi 



2 I 1 



