MECHANICS OF THE INNER EAR 1 7 



which are the extreme peripheral parts of the sensory 

 organs. This membrane, however, is firmly attached to the 

 left side of the partition only. Its right end is free or seems 

 to be almost free. The kind of action exerted by this mem- 

 brane upon the hair tufts can only be guessed. The real con- 

 nections between, and the physical properties of, these tissues 

 are not well enough known. We may perhaps make this 

 action a little clearer by assuming that the upper membrane, 

 when the partition bulges upwards, pulls the hairs slight- 

 ly, and that a bulging of the partition downwards means 

 merely a relief from this pull. It is hardly worth while, how- 

 ever, to enter into details of a function which cannot be more 

 than hypothetical since there are no data upon which to 

 base any more definite theory. But there is little doubt, that 

 the points between the tufts of hairs and the membrane in 

 question are to be regarded as in the strictest sense the per- 

 iphery of the sensory apparatus of hearing. And we shall 

 scarcely make a grave mistake in assuming that a double 

 bulging, back and forth in the vertical direction, of the 

 partition causes a single shock in all those nerve fibres whose 

 termini are located in this part of the partition, and that 

 somewhere in the neurons a new process, perhaps a kind of 

 chemical process, is set up if more than one of such shocks 

 are received in quick succession, that the special character 

 of this new process is dependent on the frequency with which 

 these shocks follow each other, and that thus we perceive a 

 definite tone, occupying — according to the frequency of shocks 

 received — a definite point in the total series of sensations of 

 hearing. 



