464 PHYSIOLOGY CHAP. 



equilibrium, and he considered the motor disturbances which 

 follow lesions of the semicircular canals to be the effect of defective 

 or fallacious sensations of the position of the head, due to sup- 

 pression or alteration of the normal displacements and oscillations 

 of the pressure of the endolymph in the semicircular canals, by 

 which the ainpullar nerve -endings are excited. It was, however, 

 demonstrated by Cyon (1897) and confirmed by Gaglio that under 

 certain experimental conditions the endolymph may be entirely 

 drained away without producing any disturbance of equilibrium. 



At the same time Cyon's hypothesis that the semicircular 

 canals are the peripheral organ of space-perception is unproved, 

 as will be shown in Chapter II. of the next volume. As Gaglio 

 aptly observes, " We explore space with all our senses, and it is 

 the sum of the impressions which they make on our nerve-centres 

 that arouses in us the consciousness of relation, of the position of 

 equilibrium, and of the movements of our body in respect to the 

 environment." 



The principal function of the labyrinth is in Ewald's ex- 

 pression, already used by Hogyes its tone, by which muscular 

 tone is reflexly controlled ; and no other hypothesis is needed to 

 explain the motor disorders consequent on section or destruction 

 of the semicircular canals. The disturbance of the muscular 

 functions is so prominent that Ewald and many others before and 

 after him have called attention to it, and, as Gaglio remarks, it 

 is this which has led the observer so far from the truth. 



If we examine the theories of the physiology of the cerebellum 

 we find the same fallacy. Abstract ideas of equilibration, orienta- 

 tion, co-ordination, for a long while prevented attention from 

 being directed to the essential phenomena. 



In 1886 Ferrier, starting from the fact that the activity of 

 the cerebellum persists intact after removal of the cerebral hemi- 

 spheres, declared that organ to be independent of consciousness 

 and will, although he held it to be normally associated with the 

 activity of the fore -brain, since disturbances of equilibrium in a 

 given direction will under normal conditions provoke conscious 

 or voluntary efforts of a compensatory character in the opposite 

 direction. The same adjustments effected by the cerebellum rnay 

 therefore be carried out by the fore -brain independently of it. 

 The effects of cerebellar lesions were designated by Terrier paralysis 

 of reflex adjustments, and are to be carefully distinguished from 

 paralysis of spinal and cerebral reflexes, which never results from 

 uncomplicated cerebellar lesions ; so that in 1886 Ferrier looked 

 on the cerebellum merely as a centre in which a very complex 

 mechanismfor unconscious equilibration was developed during phylo- 

 genetic evolution. But as the cerebrospinal axis already in itself 

 contains mechanisms which are capable of reacting to each displace- 

 ment of the equilibrium of the body by appropriate instinctive 



