436 PHYSIOLOGY CHAP. 



positions in general which follow immediately on the cerebellar 

 lesions (whether they are regarded as effects of irritation of the 

 fibres of the peduncles and of the extra-cerebellar cells with which 

 those are connected, or whether they are referred to the paralysis 

 or disturbance of cerebellar functions by the lesion) must not be 

 regarded either as the converse, or as an exaggeration, of the defect 

 phenomena that appear in the second post-operative period. 



That vertigo is the true cause of forced movements and, 

 generally speaking, of the dynamic phenomena of the first post- 

 operative period is directly confirmed by clinical cases of cerebellar 

 disease, in which vertigo is a very frequent symptom. But the 

 indirect evidence afforded by the behaviour of monkeys with 

 lesions of the cerebellum is also most striking ; they soon learn to 

 avoid rotation on their long axis by clutching the surrounding 

 objects with their hands. If set upon the bare ground they 

 support not only their trunk but also their head on it. Further, 

 the fore-limb of the operated side is abducted as far as possible, 

 and the animal remains indefinitely motionless in this position in 

 order to avoid vertigo. 



The disturbance, produced either by irritation of the peduncular 

 fibres or by the sudden disequilibration of the functional activities 

 of the two sides by the sudden paralysis of one, may produce 

 vertigo. On the other hand, we know that independent of any 

 cerebellar lesion similar rotatory vertigo with actual rotation on the 

 longitudinal axis may be produced in dogs, either by section of the 

 vestibular nerve (Bechterew) or by a unilateral lesion of the 

 inferior olive (Probst). As the relations of the vestibular nucleus 

 and the olive with the cerebellum are known, it might be assumed 

 that here also the disturbance of cerebellar influence comes into 

 play in producing the rotation phenomenon. But even when the 

 cerebellum has been totally removed it is still possible to produce 

 galvanic vertigo in dogs (Purkinje and Hitzig) which proves that 

 vertigo may arise without active participation of the cerebellum. 

 There is evidence which tends to show that the rotary phenomena 

 which accompany vertigo depend actually neither on the cere- 

 bellum nor on the brain-stem, but solely on the so-called motor 

 zone of the cerebrum. In this connection the symptoms described 

 by Pagano after injections of curare are of great interest. If the 

 motor zone (sigmoid gyrus) is excited on the side opposite the 

 cerebellar hemisphere into which curare is injected, no localised 

 movements of this side result, and the rotation of the body round 

 the .longitudinal axis occurs in the opposite direction. Complete 

 removal of the motor zone on both sides entirely suppresses both 

 the general convulsions and the partial tonic contractions ; only 

 an increase in muscular tone is perceptible, particularly in the 

 muscles of the injected side. 



This series of facts shows that the dynamic phenomena of the 



