120 PHYSIOLOGY CHAP. 



Another experiment performed by Breuer on pigeons deprived 

 of the labyrinth showed that in these animals there is no rotatory 

 vertigo when they are blindfold or blinded. This fact was at first 

 disputed by Cyon and Hermann, but was ultimately confirmed by 

 Ewald, and by Strehl, a pupil of Hermann. 



Purkinje's experiments on pure galvanic vertigo were repeated 

 and better elucidated by Hitzig. He showed that during the 

 passage of a constant current of a given intensity, applied over 

 the two mastoid regions, there is, when the eyes are closed, a 

 sensation of falling to the side of the kathode, while first the head 

 and afterwards the body are bent to the side of the anode, as if to 

 avert a fall. If the eyes are kept open during the passage of the 

 current the environment seems to turn towards the kathode, 

 owing to the involuntary nystagmus of the eyes which occurs if 

 the current is tolerably strong. 



Breuer observed approximately the same phenomena in normal 

 pigeons, and found they were no longer produced when the 

 labyrinth was destroyed ; this was confirmed by Ewald, but 

 disputed by others. The labyrinthine origin of galvanic vertigo 

 was confirmed by Pollak in deaf-mutes. He found that in deaf- 

 mutes, in whom rotatory vertigo was absent, galvanic vertigo was 

 also absent. 



Independently of the passive movements of the organism as a 

 whole, we are aware, even with our eyes shut, of the position of 

 our body in the environment, if not in relation to the four points 

 of the compass, at least to the vertical, that is, to the direction of 

 gravity. It seems clear that this perception of the vertical depends 

 on tactile sensibility. In fact, the surfaces of support on which 

 the body rests in the erect, seated, or recumbent posture are 

 subjected to pressure or deformation by the weight of the body, 

 and this gives rise to tactile perceptions on which the power of 

 orientating our body along the line of gravity depends. But that 

 other than tactile sensations are involved may be deduced from the 

 fact that when we are immersed under water, although we lose 

 these tactile sensations, we are still able to orientate ourselves 

 relative to the vertical. Accordingly we must conclude that we 

 possess a sense-organ which makes us aware of the direction of the 

 force of gravity, apart from sight and touch. Many facts lead to 

 the conclusion that the labyrinth is the sense-organ in question. 

 But we need only refer to the conclusions of James, who saw that 

 if deaf-mutes, who have no rotatory vertigo, close their eyes under 

 water, they are no longer aware of their position in relation to 

 the vertical, and are seized with vertigo. 



The ingenious hydro-mechanical theory propounded by Mach 

 and adopted as a whole by Crum Brown and Breuer may be set 

 out in a. few words. It purports to explain how passive and 

 active movements and static postures are capable of exciting the 



