v THE SENSE OF HEARING L>07 



of man and other annuals on pulling the tendon of the tensor by 

 a thread (Politzer, Lucae). 



The contraction of the tensor muscle usually takes place 

 reflexly. The sensory paths of the reflex are provided by the 

 acoustic nerve (Hammerschlag) : the stimulus is the increase 

 of intra-labyrmthine pressure (Politzer). 



The protective function of the tensor muscle has been oppo,M-i| 

 by the fact that it is not thrown reHexly into tetanic contraction 

 during the whole time that the vibrations of the tympanic 

 apparatus have to be moderated. Hensen and Strieker showed 

 that during audition tetanic contractions of the tensor tympani 

 do not occur, but only simple twitches (as seen on pushing in a 

 fine needle to make a lever arm); these seem to promote the 

 perception of tones, because the tympanic membrane thrown into 

 movement by the muscle vibrates more easily for high tones than 

 the membrane at rest. They further saw in dogs and cats, when 

 the tympanic cavity was opened, that the contraction of the 

 tensor occurs only at the commencement of a tone, and 

 subsequently diminishes and ceases though the tone persists. 

 Bockendahl (1880), a pupil of Hensen, sometimes obtained tetanic 

 contractions, which persisted for the duration of the tone. With- 

 out denying the possibility of this fact, Hensen believes that it 

 depends on imperfect fixing of the needle. In fact Pollack 

 (1886) confirmed Hensen's results in a new series of experiments 

 on the functions of the tensor tympani, and invariably obtained 

 only a simple momentary contraction at the commencement of 

 the sound. He further saw that the reflex contractions of the 

 tensor are feebler to low notes, and increase with increasing 

 pitch. When the labyrinth is destroyed the contractions of the 

 muscle become less, but do not cease entirely. After destruction 

 of both cochleae all contractions of the muscle and all movements 

 of the needle stuck into it cease. 



Ostmann (1898), by the otoscope, observed in patients with 

 ear-disease the reflex traction of the tympanum which is produced 

 by high notes and loud, unpleasant sounds, owing to the 

 contraction of the tensor. He further observed that in man it is 

 mainly or exclusively high tones that reflexly excite the tensor. 



These facts taken collectively make the protective function of 

 the tensor tympani very doubtful. 



As early as 1863, Mach, from theoretical considerations, 

 maintained that the tensor tympani produced an accotmnoi/"- 

 tion of the tympanum, which he based on the supposed power of 

 this muscle to alter the tension of the tympanic membrane so as 

 to adapt its vibrations to different tones. On this theory there 

 must for each tone of given pitch be a corresponding degree of 

 contraction of the tensor. But we have seen that, independ- 

 ently of any active intervention of the tensor muscle, the 



