134 UNIVERSITY OF MISSOURI STUDIES 



If not only a part or the whole of the tympanum is de- 

 stroyed, but the chain of ossicles is also lost, the mechanical 

 processes in the inner ear could be brought about by pressure 

 differences on the two windows. An air wave, coming in 

 through the external passage and the open middle ear, would 

 at any given moment affect the two windows with a slightly 

 different phase, arriving at one window a little earlier than 

 at the other. This difference of phase means, of course, a 

 difference of air pressure on the windows, and a difference of 

 air pressure on the windows, according to the laws 

 of mechanics, results in a movement of the internal fluid 

 from the point of higher to that of lower pressure. It is plain, 

 however, that this difference of phase, owing to the small distance 

 between the two windows, must be very slight ; and hearing which 

 results in this way must be rather weak. But its possibility cannot 

 be doubted. 



Few cases, therefore, will be found where a sound is 

 heard and we have to have recourse to the rather improbable 

 assumption that the mere passing of molecular waves of 

 density changes through the head and, thus, through the audi- 

 tory nerve ends directly results in some weak response of the 

 nerves. Nevertheless at least we may admit this assumption 

 as possible. To admit it as possible would not cause any diffi- 

 culty in comprehending the ordinary phenomena of audition, 

 which might thus seem to become more complicated because 

 such density waves must, of course, pass through the head 

 whenever anybody hears anything. But such effects on the 

 nerve ends, granted that they always exist, must ordinarily 

 be overpowered by the incomparably stronger stimulations 

 simultaneously received by the nerve ends by way of the 

 stirrup movement. 



Having studied the function of the human ear, it is in- 



