476 PHYSIOLOGY CHAP. 



this stimulation he noted rhythmical movements of one fore-limb, 

 movements of mastication, arching of back, etc. But these effects 

 were not exactly localised, although Nothnagel affirmed a certain 

 relation between the points at which the needle was inserted and 

 the reaction. 



Pruss (1901) attributed much importance to the direction of 

 the currents (ascending, descending, transverse) in the results 

 obtained by electrical stimulation of the cerebellar cortex. The 

 conclusions he arrived at in regard to cerebellar localisation 

 would be highly important if they could be accepted. But he 

 himself states that the currents which he employed to provoke the 

 reactions described were excessive. 



Negro and Eosaenda (1907) repeated these experiments upon 

 the rabbit's cerebellum with moderate faradic currents. On 

 stimulating the area which corresponded approximately to the 

 crus p/'i in tun of Bolk, they obtained unilateral contractions of the 

 facial muscles and anterior limb, which were sometimes isolated, 

 sometimes associated. Only when the current was unduly strong 

 did the reactions extend to the muscles of the two sides. With 

 unipolar stimulation they obtained more accurate localisation ol 

 the facial and fore -limb muscles, and found that the facial 

 centre lies more forward than the centre for the fore -limb. 

 Both lie somewhat internally, but their exact position was not 

 determined. 



Horsley and Clarke (1908), in a series of researches carried 

 out with more accurate methods, were able to demonstrate 

 that the stimulation had to be of enormously greater strength to 

 obtain motor reactions in faradising the cerebellar cortex than 

 was required to excite the cerebral motor centres; and that 

 even strong currents are not effective when the method of 

 bipolar excitation is employed. They came to the conclusion that 

 the cerebellar cortex is practically inexcitable ; that when motor 

 reactions are obtained, these are due to spread of the stimulus 

 to the subjacent nuclei of grey matter (dentate nucleus, roof 

 nucleus, Belters' nucleus, etc.), and, finally, that the results 

 obtained by previous observers were attributable to some fallacy. 



Pagano (1904) investigated cerebellar localisation by means of 

 chemical stimuli, and employed minute interstitial injections of a 

 solution of curare, because as previously noted by Tillie this 

 poison has a decidedly exciting action upon the nerve-centres. 



He succeeded in mapping out four distinct motor centres in 

 the cerebellum f< >r the muscles of different regions : 



(a) A paired centre for the fore-limb, lying near the crus 

 primum of Bolk. 



(&) A paired ^centre for the hind-limb, near the crus secundum. 



(c) An unpaired centre for the muscles of the neck, lying in 

 the lobulus simplex. 



