756 FUNCTIONS OF THE CEREBELLUM [CH. LI. 



movements to which the animal is subject. It can neither stand, 

 nor lie still, nor fly, nor maintain any fixed attitude. It executes 

 violent somersaults, now forwards, now backwards, rolls round and 

 round, or springs in the air and falls back to recommence anew. It 

 is necessary to envelop the animals in some soft covering to prevent 

 them dashing themselves to pieces by the violence of their move- 

 ments, and even then not always with success. The extreme 

 agitation is manifest only during the first few days following the 

 operation, and the animal may then be set free without danger ; but 

 it is still unable to stand or walk, and tumultuous movements come 

 on from the slightest disturbance. But after the lapse of a fortnight 

 it is able to maintain its upright position. At this stage it resembles 

 an animal painfully learning to stand and walk. In this it relies 

 mainly on its vision, and it is only necessary to cover the eyes with 

 a hood to dispel all the fruits of this new education, and cause the 

 reappearance of all the motor disorders." (Ferrier.) 



It is these canals which enable all of us to know in which direc- 

 tion we are being moved, even though our eyes are bandaged, and 

 the feet are not allowed to touch the ground. On being whirled 

 round, such a person knows in which direction he is being moved, 

 and feels that he is moving so long as the rate of rotation varies, 

 but when the whirling stops he seems, especially if he opens his 

 eyes, to be whirling in the opposite direction, probably owing to the 

 rebound of the fluid in the canals. The forced movements just 

 described in animals are due both to the absence of the normal sensa- 

 tions from the canals and to delusive sensations arising from their 

 irritation, and the animal makes efforts to correct the movement 

 which it imagines it is being subjected to. 



Artificial stimulation of the canals produces movements of the head and orbits, 

 and giddiness. Similar movements occur during bodily rotation, and giddiness is 

 the result of a rivalry of sensations which afford conflicting ideas of the position of 

 the body relatively to external objects. A certain proportion of deaf mutes lose their 

 sense or direction under water, cannot maintain their equilibrium when their eyes are 

 shut, exhibit no orbital movements when rotated, and never suffer from sea-sickness 

 or giddiness. This proportion is approximately the frequency in which abnormal 

 conditions of the canals have been found post-mortem in deaf mutes. 



Section and stimulation of the inferior cerebellar peduncles (the path by which 

 the vestibular fibres reach the cerebellum, see p. 682) cause incoodination, chiefly 

 evidenced by rotatory and circus movements similar to those that occur when the 

 nerve-endings in the semicircular canals are destroyed or stimulated. Stimulation 

 of the cerebellum itself and this has been done through the skull in man causes 

 giddiness, and consequent muscular efforts to correct it. The results of stimulation, 

 indeed, are precisely analogous to those of extirpation, only in the reverse direction. 

 Loss of muscular tone which follows extirpation of the canals is probably the result 

 of secondary changes in the brain. 



