v THE SENSE OF HEARING 211 



this annoyance lead the patient almost instinctively to repeat 

 Valsalva's experiment, that is, to introduce air into the tympanic 

 cavity. This proves that although closure of the tube is very 

 useful in the function of the ear it must not be permanent, but 

 the tube must open now and then in swallowing the saliva that 

 continually accumulates in the mouth, so as to re-establish the 

 normal pressure in the tympanum. ' Owing to absorption of the 

 air this constantly tends to drop, and thus the vibratory capacity 

 of the tympanic apparatus is gradually lessened. 



As the tube is usually closed, the view put forward by many 

 authors that it is designed for the perception of one's own voice 

 is obviously erroneous. This is proved by the observation that 

 the tone of a tuning-fork vibrating inside the mouth is not heard 

 (Schellhammer, Joh. Miiller). In cases in which the tube is 

 permanently open, owing to abnormal conditions, or where it is 

 prevented from closing by a catheter (Poorten), autophony may 

 occur, i.e. the voice seems to originate and re-echo strongly in 

 the internal ear, instead of in the oral cavity ; this causes great 

 discomfort to the patient. 



Secchi (Bologna, 1902), in opposition to the generally accepted 

 theory of Helmholtz that sound-waves are conducted by the 

 tympanic apparatus, advocated the view that the fenestra rotunda 

 is the only path by which tones pass from the outer air to the 

 labyrinth. It would exceed our limits to discuss his arguments 

 in detail, but if the main points can be refuted his hypothesis 

 falls to the ground. 



He inserted into the tympanic cavity of a living dog a metal 

 cannula, with a two-way stop, connected with a U-shaped 

 manometer 2 mm. in diameter, filled with coloured alcohol. 

 After equalising the pressure of the air contained in the cavity 

 with that of the external air by a half -turn of the screw, he 

 found that at each movement of deglutition made by the animal 

 the fluid in the manometer oscillated slightly owing to the 

 opening of the tube, and the pressure rose suddenly 4 mm. as 

 soon as the act of swallowing was completed and the tube closed 

 again. This positive pressure of the air contained in the cavity 

 (on an average 4 mm. alcohol) is easily explained on the assumption 

 that at the end of the act of deglutition "there is first closure 

 of the orifice of the tube, next of that of the canal, so that the 

 air therein enclosed which cannot escape by the mouth must- 

 necessarily enter the cavity and cause a positive pressure." 

 Independently of the mechanism of opening and closing the tube, 

 it happens sometimes when the animal has not swallowed for a 

 long time that the intra- tympanic pressure becomes positive, 

 owing to the action of the internal muscles of the tympanum. 

 At any sudden sound, weak or loud, deep or high, the little 

 manometer then shows a rise of pressure of 4 to 6, 7, 8 mm., in 



