MECHANICS OF THE INNER EAR 21 



tition can spontaneously return after having been displaced, 

 but with a velocity that is only very small compared with 

 the velocity of its displacement. Of the two alternatives 

 the latter seems to be the more probable. 



We saw on a previous page, in our second imaginary 



case of a partition, that the fluid moves along the unyielding 



partition, causing friction on the sur- 



, , faces of the partition. The same friction 

 Protection of the , _ , . . , , , 



surfaces of the must be suffered by any part of the real 

 partition from partition as soon as it has reached its 



the friction upper or lower limit and as long as the 



of the fluid stirrup continues to move in the same 



direction, pushing the fluid on over the 

 initial parts of the partition. If we had to design an ap- 

 paratus to function thus, would we not see that the sur- 

 faces of the partition were sufficiently protected so that the 

 rush of the fluid over them could not injure them? It is 

 interesting to raise this question of protection with respect 

 to the actual partition in the tube. If we look above at fig- 

 ure 7, representing a cross-section of the partition, we 

 notice that the lower surface of the partition is well 

 protected from injury by friction of the fluid by a part of its 

 own structure, the tough basilar membrane. The upper sur- 

 face, however, with its delicate sensory cells would be ex- 

 posed to injuries by friction were it not for the membrane of 

 Reissner which we see stretching across the upper division 

 of the tube. The space between this membrane and the 

 partition does not communicate with the rest of the upper 

 division or with the lower division. It would therefore be 

 really more nearly correct, in speaking of a partition divid- 

 ing the tube into two divisions which communicate through 

 an opening at the extreme end, to call the total body between 

 the membrane of Reissner and the basilar membrane the 

 partition. No movements perpendicular to the plane of the 



