212 PHYSIOLOGY CHAP. 



proportion to the intensity and pitch of the sound, and lasts 

 as long as the stimulus, at the close of which it drops back to 

 4 mm. This persistent reflex contraction of the endotympanic 

 muscles becomes weaker after administration of chloroform or 

 injection of chloral, and ceases almost entirely after complete 

 curarisation. 



The new experimental facts which the Bolognese otologist 

 cites in support of his view are therefore merely that the tympanic 

 membrane with the chain of auditory ossicles and its two muscles 

 represents an apparatus for reflex accommodation only; that the 

 transmission of tones to the labyrinth takes place exclusively 

 through the membrane of the fenestra rotunda, which, according 

 to Bezold, is capable of excursions five times as great as the 

 stapes ; that, finally, a certain amount of positive pressure in the 

 tympanum, produced by the periodic opening and closing of the 

 Eustachian tube, is indispensable to the normal functioning of 

 the middle ear. 



The weak positive pressure in the tympanic cavity of the 

 dog caused by the special manner in which the tube closes at the 

 end of deglutition (even assuming this to be universal in man 

 and all mammals, which is by no means proved) is a fact of little 

 importance. It may be regarded as a slight natural imperfection 

 in the mechanism of the tympanic ventilation, similar to those 

 demonstrated by Helmholtz in the dioptric apparatus of vision. 

 The above discussion on the function of the tensor tympani 

 shows that the most favourable condition for the conduction of 

 tones to the labyrinth is that the endotympanic pressure shall 

 be equal to that of the external air. That acoustic stimuli are 

 capable of evoking persistent (tetanic) reflex contractions of the 

 endotympanic muscles agrees with what Bockendahl assumed, 

 in contradiction to his master, Hensen. But in any case this 

 fact must be taken as the starting-point of new investigations of 

 the doctrine, still sub judice, of the inhibitory or protective 

 function of the tensor muscle, and not as evidence for the view 

 that the tympanic apparatus can really become accommodated to 

 different tones and noises. 



Lastly, the assertion that conduction of the air-waves to the 

 labyrinth takes place normally by the fenestra rotunda is a 

 flagrant contradiction of the whole of the facts above discussed, 

 and fully confirmed, in support of Helmholtz' theory of the 

 very delicate conducting functions of the tympanic apparatus. 

 It is true that the oscillations of the tympanic membrane 

 may not only be propagated by the chain of ossicles, but 

 may also produce waves of condensation and rarefaction in 

 the air enclosed in the tympanum, so as to impinge on the 

 membrane of the fenestra rotunda, which Bezold showed to be 

 capable of excursions four times as great as those produced in 



