v THE SENSE OF HEARING 259 



more clearly and acutely than those transmitted by bone-conduction. To 

 this experiment it may be objected that the note of the prongs and that 

 of the stem of a tuning-fork are not comparable, so that the tone of the stem 

 only should be used. 



Schwabach's experiment is based on the observation that when trans- 

 mission of the sound-waves hi the ordinary way is obstructed, the fork 

 applied to the bone is heard somewhat longer than normally only of course 



FIG. 105. To show the changes in the optical images of the vibrations of a tuning-fork with 

 gradual decrease in the amplitude of the vibrations. (Gradenigo.) 



when the organ of Corti functions properly ; if this be also diseased, the tone 

 transmitted by the bones is heard with difficulty or not at all. 



In Gelle"'s experiment air is blown artificially against the external 

 auditory passage after the meatus has been hermetically sealed, until bone- 

 conduction of the tones becomes weakened, owing probably to the pressure 

 exerted on the organ of Corti by the tension of the tympanic membrane and 

 the chain of ossicles. If the perception of sound thus conveyed through the 

 bones is not weakened, it may be concluded that the articulation of the chain 

 of ossicles (stapes) is anchylosed. 



