n6o THE EAR. 



pressure diminishing, while a diminution of pressure increased the 

 amplitude. It is more than probable that in all of these experiments 

 the amplitude has been over-estimated, as the restraining influence of 

 the tensor tympani and stapedius does not come into play after death. 

 Very feeble sounds no doubt cause a movement of the stapes so small 

 as to be invisible to the microscopic powers that can be employed in 

 such observations. The greatest movements occur with tones of medium 

 pitch. 



An interesting experiment may also be performed, in which the cat's 

 tympanum is used as a manometric capsule, after the well-known 

 method of Konig. Two small glass tubes are fixed with sealing-wax 

 into holes trephined in the tympanic bulla, and a tube carrying a 

 conical mouthpiece is also inserted into the external meatus. Gas is led 

 into the cavity by one of the small tubes, and it issues from the cavity 

 by the other tube to a small gas jet. When sound-waves, such as those 

 of organ-pipes, tuning-forks, or of the human voice, are conveyed by the 

 mouthpiece to the membrana tympani, flame pictures, similar to the 

 well-known flame pictures of Konig, may be seen on rotating a rect- 

 angular mirror in front of the flame. 1 



Transmission of sound to the labyrinth otherwise than by the 

 ossicles. The earlier physiologists, and in particular Scarpa, were of 

 opinion that sound passed from the tympanic membrane into the air in 

 the tympanum, and was transmitted to the labyrinth by the fenestra 

 rotunda, which was termed a secondary tympanum. Experiments made 

 by Weber-Liel, 2 by a method very similar to that of Burnett, already 

 described, supported this view, but on the whole it was not accepted by 

 the majority of physiologists. In 1894, Secchi 3 advocated the same 

 view, on the ground that, as the tympanum is a closed cavity, changes 

 in the position of the membrana tympani must be accompanied by 

 changes in the pressure of the air within the cavity. These variations 

 of pressure in the cavity are distributed over its walls, and as these are 

 rigid everywhere except at the fenestra rotunda, the variations of 

 pressure could be transmitted to the fluid in the labyrinth by the 

 fenestra rotunda. It must be remembered, however, that, from the 

 mechanical arrangements already described, almost all the energy of the 

 membrana tympani is conveyed to the fenestra ovalis by the chain of 

 bones. And if we suppose that pressures are communicated simultan- 

 eously to the fenestra ovalis and to the fenestra rotunda, to the first by 

 a chain of bones, and to the second by the air in the tympanum, any 

 inward pressure on the fenestra rotunda will be more than annulled by 

 the inward pressure on the fenestra ovalis, and that therefore there 

 must be an outward movement at the fenestra rotunda, when there 

 is an inward movement at the fenestra ovalis, a result which is 

 confirmed by experimental observation (M'Kendrick). Finally, inter- 

 ference with the movements of the chain of bones has a marked effect 

 upon the perception of sound, which could not be the case if they did 

 not play the more important part in the conduction of sound. At the 

 same time, it may be admitted that in exceptional cases, in which the 

 chain may be absent, hearing may still exist, in consequence of aerial 

 pressures being communicated to the membrane covering the fenestra 

 rotunda. 



1 M'Keudrick, "Text-Book of Physiology, " vol. ii. p. 687. 



- Centralbl.f. d. med. Wissensch., Berlin, 1876, Bd. xiv. S. 17. 3 Loc. tit. 



