A NEW THEORY OF HEARING. 339 



The points B (fig. 1) are now passing each other at the 

 level XY. The two membranes at this level have just 

 come to rest by virtue of their own elasticity, and the 

 fluid will now immediately commence to flow in both 

 directions (forwards and backwards) into the region of XY. 



We must now consider how these changes will affect 

 the organ of Corti. 



Let fig. 6, represent a transverse section across the 

 middle canal of the cochlea in the plane of the line XY of 

 figures 3, 4 and 5, and let us consider the changes just 

 described from a new point of view. 



The condition represented in fig. 3, was brought about 

 by inrush of fluid into the region of XY in both directions 

 simultaneously.- From this stage onwards the elasticity 

 of the membranes now stretched to their maximum 

 presses on the fluid between them, forcing it out in both 

 directions (forwards and backwards) with increasing 

 velocity till the stage represented in fig. 4 is reached, when 

 the membranes are at their normal position of rest but 

 are now advancing towards each other with maximum 

 velocity. During this first half of phase N (fig. 2) the 

 basilar membrane has been pressing upwards upon the 

 fluid which was simultaneously forced down upon it by 

 the Reissnerian membrane, with the result that not only 

 the fluid above the tectorial membrane but the whole of 

 the fluids between the basilar and the Reissnerian will 

 have been set in movement backwards and forwards away 

 from this region. The whole phase only lasts a moment, 

 but during that moment the fluid between the tectorial 

 membrane (T in fig. 6) and the organ of Corti (C in 

 fig. 6) will have been to some extent forced out, and by 

 way of the spiral sulcus to adjoining regions of the cochlea. 

 In other words the tectoria will have been suddenly banged 

 down upon the hairs which extend vertically between it 



