CHAP, iv.] HEARING. 997 



rary deafness, especially to low notes, frequently ensues, in con- 

 sequence of the pressure within the tympanum not following 

 the changes of the pressure without. This however is soon 

 remedied by the act of swallowing, which opens the tube and 

 thus equalizes the pressure. 



An abnormal permanency in the closure of the tube is recog- 

 nized as a cause of deafness, and may be remedied by catheter- 

 ism of the tube, that is to say, opening up the tube by passing 

 an instrument into it from the pharynx. 



