THE SEMICIRCULAR CANALS. 1199 



occiput downwards, the bird showed irregularity of movement and a 

 loss of equilibrium, as if one of its canals had been divided. If the 

 apparent position of surrounding objects is determined by the position 

 of the head, any sudden change in position might cause for a moment 

 disturbance of motion, and the same result might be expected to follow 

 a strabismus, at all events for the first few minutes. Cyon adjusted 

 glass prisms before the eyes of birds, so as to cause a squint, and the 

 result was loss, for a short time, of co-ordinating power. He also found 

 that after the disturbance of motion following section of the horizontal 

 canal on one side, consisting of oscillations in a horizontal plane and 

 round the vertical axis of the head, and of loss of equilibrium, support- 

 ing the head, by placing the finger below the beak, at once caused the 

 movements to disappear, and the bird became calm. Flight after such 

 an injury was almost impossible. At the end of eight or ten days, 

 all the symptoms described disappeared, except that there was still some 

 awkwardness in flying, but eventually this also disappeared, and the 

 movements of the bird were normal. The phenomena following section 

 of the vertical canals were of the same nature, the only difference being 

 as regards direction of movements. The movements of the head were 

 now from below upwards or from above downwards in a vertical plane 

 and around a horizontal axis, and the movements of the body, instead 

 of being mouvements de manage, or round a vertical axis, as after 

 division of a horizontal canal, were now backwards and forwards, as if 

 around a horizontal axis passing through the body. As Cyon held that 

 the perception of the position of bodies in space depends on the 

 position of the head, his general conclusions rest largely on this view. 

 Thus (1) to maintain equilibrium, we must have an accurate notion of 

 the position of the head in space ; (2) the function of the semicircular 

 canals is to communicate impressions that give an accurate representa- 

 tion of this position each canal having a relation to one of the dimen- 

 sions of space; (3) disturbance of equilibrium follows section; (4) 

 involuntary movements following section are due to abnormal excita- 

 tions ; (5) abnormal movements occurring a few days after the operation, 

 are caused by irritation of the cerebellum. 



It might be argued, as indeed was done by Bottcher, 1 that the 

 phenomena of Flourens were secondary, and that they were caused by 

 irritation of neighbouring parts of the brain, more especially of the 

 cerebellum. This view, however, is disproved by the fact that the 

 phenomena of Flourens appear immediately after section, whereas 

 similar phenomena, caused by irritation of the cerebellum, do not appear 

 until several days after the irritation. It is contradicted also by the 

 observation that if we divide, not two symmetrical canals, but on the 

 one side a horizontal and on the other a vertical canal, or if we cut two 

 canals on the same side, the phenomena of Flourens do not appear. It 

 is clear, therefore, that secondary lesions of the brain have nothing to 

 do with the phenomena. 



Hitherto we have considered the results obtained by experimental 

 physiologists. The functions of the canals have, however, been investi- 

 gated in another way, by physical experiment and by the application of 

 purely theoretical considerations. This has been done more especially 



1 Arch. f. Ohrenh., Bd. ix. ; see also Baginsky, Biol. Cenfralbl., Bd. i. S. 438; 

 Jacobson, Arch. f. Ohrenh., 1881-2, Bd. i.; 1894, Bd. xxii.; Hogyes, Arch. /. d. ges. 

 Physiol., Bonn, 1881, Bd. xxvi. S. 558. 



