MECHANICS OF THE INNER EAR I33 



stead of on the outside, and that they must, on the whole, 

 be much weaker in the former case. 



There can be little doubt that the process just spoken 

 of actually occurs. Some have insisted also on the possibility 

 of hearing when the middle ear is destroyed and no movements 

 of the stirrup occur. There is no reason why we should a 

 priori deny the possibility of a shock being received by the 

 nerve ends whenever a rhythmical change of molecular den- 

 sity takes its path directly through them. Such a molecular 

 wave might originate from a vibrating solid body being pressed 

 against skull or teeth, or from sound waves in the air strik- 

 ing the head and passing through it. 



We must not overlook the fact, however, that even when 

 the tympanum is totally destroyed, if sounds are perceived, 

 the perception need not be the result of the sound waves 

 simply passing through the nerves. Even in such a case stirrup 

 movements are not excluded. If Ave blow over the mouth of 

 a bottle, we cause rhythmical changes of density within the 

 bottle, and, as a natural consequence, the air in the 

 neck of the bottle rushes back and forth. These move- 

 ments may often be observed with the naked eye when a fiber 

 adherent to the inside of the neck of a bottle is forced by friction 

 to follow the movements of the air. Now, when rhythmic 

 changes of density occur in a middle ear whose tympanum is 

 destroyed, there must naturally occur a back and forth move- 

 ment of the air in the air passage, just as in the neck of a 

 bottle. These back and forth movements of the air may 

 cause by friction corresponding movements of the hammer 

 and anvil and thus of the stirrup. No doubt, stirrup move- 

 ments which are caused in this way must be of small magni- 

 tude. But no one who knows the surprisingly small amount 

 of mechanical energy which is sufficient to call forth a response 

 of the auditory organ will deny that they might result in an 

 auditory sensation. 



