STIMULATIONTHE SENSES 



109 



in the physical sense, they are, compared with gases, only very 

 slightly compressible. The result is that the amplitude 'of the 

 sound vibrations in a liquid is excessively minute, but the force 

 involved is of correspondingly increased magnitude. We have 

 seen that the changes of pressure exercised by the chain of bones 



FIG. 4. Mechanism of the Organ of Corti. 

 Upper diagram at rest. Lower diagram when displaced by vibration. 



A, represents the basilar membrane. 



B, the arch of Corti. 



C, the reticular membrane. 



D, one of the hair cells. 



E, the tectorial membrane. 



F, a fibre of the auditory nerve. 



on the liquid in the cochlea correspond exactly with those in the 

 air, in contact with the drum, except that their amplitude is 

 decreased and their force increased. This would clearly be an 

 advantage in transmitting them to liquid. But, in other respects, 

 they must be precisely similar in the liquid to what would have been 

 the case if the sound waves had impinged directly on the liquid 

 itself. In this liquid we have, then, waves identical with those of 

 sound. 



