UNIVERSITY OF MISSOURI STUDIES 



erage is easily understood. To cause a fluid to move along 

 a narrow tube requires a considerable force because of the 

 friction resulting from the narrowness of the passage. 

 The ■ extent of movement, on the other hand, maj^ be 

 of any minuteness, the nerve ends certainly being sensitive 

 to the very slightest curving of their tufts of hairs of which 

 we shall have to speak again. It is of advantage, therefore, to 

 gain force at the expense of magnitude of displacement. 



Someone might here raise the question : Why are there 

 two windows when only one of them has a solid connection 

 with the tympanum? The answer to this 

 Why would not question is very simple. If there were 

 one window not a second window, the stirrup could 



be sufficient? not move at all. Imagine a bottle filled 



with water up to the stopper and the 

 stopper fitting the neck most accurately. Would it be possi- 

 ble to drive the stopper farther in? The water being incom- 

 pressible, it would not be possible for a moderate force 

 to drive a perfectly fitting stopper in any more than to pull it 

 out. The second window, closed by a flexible membrane, 

 is therefore necessary if the movements of the stirrup and 

 of the fluid in the tube are to take place. If it were not for 

 movements of the fluid, the round window would be super- 

 fluous. It is, however, not an essential condition that the sec- 

 ond window should open on the middle ear and not perhaps 

 directly on the external air space; for instance, on the exter- 

 nal auditory passage, or anywhere on the skull. But it is 

 an essential condition that the one window containing 

 the stirrup plate open on a drum and that the plate be 

 rigidly connected with the external membrane of this 

 drum. Thus every condensation or rarefaction of the 

 air outside the drum must result through movements of the 

 tympanum in like condensations or rarefactions inside the 

 drum ; the movements of the tympanum must result in move- 



