

ii SENSIBILITY OF THE INTEKNAL OKGANS 123 



when it has been lost, the general muscular atony that accom- 

 panies vertigo ; it also explains the effects described by Goltz and 

 Flourens after lesions of the semicircular canals. 



It would, however, be a mistake to assume that labyrinthine 

 tone is an indispensable condition to the normal functions of the 

 muscles. For we have seen that in deaf-mutes, who exhibit no 

 rotatory or galvanic vertigo, the muscles function regularly in the 

 movements of the limbs, in standing, and in walking. On the 

 other hand, we have noted that the motor disorders produced by 

 destruction of the labyrinth or section of the eighth nerve in 

 animals disappear, or become perfectly compensated, in a com- 

 paratively short time. It is thus evident that the labyrinth does 

 not contain the only afferent nerve paths that reflexly keep up the 

 tone of the muscles. The far longer duration of the effects of 

 cerebellar as compared with those of labyrinthine deficiency shows 

 that cerebellar tone is maintained by other than the vestibular 

 paths ; many other afferent cerebellar paths ascend in the 

 cerebro-spinal axis, particularly those coming from the joints, the 

 tendons, and the muscles, which do not normally arouse any 

 conscious sensations through the cerebellum. 



In discussing the physiological theories of the cerebellum we 

 criticised that by which Ferrier maintains that it is the organ of 

 unconscious equilibration. A similar theory has been put forward 

 by other authors, on the strength of the experiments of Goltz, 

 Breuer, and Brown, on the functions of the vestibular organs. On 

 this theory the semicircular canals are the organ of the sense of 

 equilibrium, or static sense, as others more vaguely term it. Nagel 

 completely refuted this theory as follows : 



" It is certainly one of the functions of the labyrinth to main- 

 tain the equilibrium of the body in the different positions of rest 

 and in locomotion. Its activity is expressed in the subconscious 

 sensations of position and movement, and the reflexes necessary 

 to keep up equilibrium. But these reflexes are not in any way 

 specific to the labyrinth, since in this connection it always works 

 with the organs of the so-called muscle sense. Every disturbance 

 of the equilibrium of the body, when it leans to one side, involves 

 abnormal relations of tension in the muscles, tendons, fascia, joints 

 and skin, by which the afferent nerves of these tissues are excited, 

 and which, with the express aid of the labyrinth, reflexly produce 

 a movement in the opposite direction." 



This co-operation of the labyrinth in the normal maintenance 

 of equilibration as well as of orientation in respect of the vertical 

 is obviously expressed in the reflex regulation of muscular tone, 

 pointed out by Ewald. When the body leans to one side and is 

 likely to fall, the pasive movement excites the vestibular organs, 

 and thus reinforces the tone of the muscles which move the body 

 in the opposite direction. The movements of the eye which 



