SENSE OF HEARING USES OF LABYRINTH. 789 



and the external air; and Dr. Jago holds that the normally closed condition 

 is a provision against the ingress of aerial undulations from the throat, 

 which, if admitted, would threaten the membrana tympaui with incessant 

 oscillations, and that as the moment seized for bringing the tympanum into 

 communication with the fauces must be one in which there can be no respi- 

 ratory current, the period selected is the instant of swallowing, at which 

 instant there is a compulsory suspension of respiration; so that neither shout- 

 ing, singing, whistling, nor coughing can be performed. 1 It also has the office 

 of conveying away mucus secreted in the cavity of the tympanum, by means 

 of the vibratile cilia which clothe its lining membrane; and the deafness 

 consequent on occlusion of this tube, is in part explicable by the accumula- 

 tion which then takes place in the cavity. From what has been stated, it is 

 evident that sonorous undulations in the air will be propagated to the fluid 

 contained in the labyrinth through the tympanum, the chain of bones,* 

 and the membrane of the fenestra ovalis to which the stapes is attached 

 without any loss, but rather an increase of intensity. It is of great impor- 

 tance, as Dr. Jago has shown, that the external surface of the membrani 

 tympani should be clean and free from moisture, since if it be rendered moist 

 the power of hearing is immediately lessened ; and since its inner surface is 

 continually moist, an additional argument is furnished for the view that 

 sonorous undulations are chiefly conveyed through the ossicula, and not 

 through the air contained in the tympanum. Why water should be chosen 

 as the medium through which the impression is to be made upon the nerve, 

 it is impossible for us to say with anything like certainty, in our present 

 state of ignorance, as to the physical character of that impression. But the 

 problem being to communicate to water the sonorous undulations of air, the 

 experimental results already detailed satisfactorily prove that whilst this 

 may be accomplished, in a degree sufficient for the wants of the inferior 

 animals, by the simple interposition of a membrane between the air and the 

 fluid the tympanic apparatus of the higher classes is most admirably 

 adapted for this purpose. The fenestra ovalis is not, however, the only 

 channel of communication between the tympanum and the labyrinth ; for 

 there is in most animals a second aperture, the fenestra rotunda, leading into 

 the cochlea, and simply covered with a membrane. It is generally supposed 

 that, the labyrinth being filled with a nearly incompressible fluid, this second 

 aperture is necessary to allow the free vibration of that fluid ; the membrane 



1 Lucse (Archiv f. Ohrenheilk., Bd. iii, p 186) maintains that exchange of air in 

 the tympanum iakes place during the ordinary acts of respiration, and that it is not 

 limited to the instant of swallowing. See Zuckerkandl, Zur Anat. u. Physiol. xler 

 Tuba Eustachiana, Monatssch. f Ohrenheilk., Dec. 1873, and Knapp's Archives of 

 Ophth. and Otol., 1874, vol. iv, No. 1, p. 126. 



2 For papers showing that sounds are chiefly conducted through the bones of the 

 tympanum, see J. Jago, in Proceedings of Royal Society, 1857-59, vol. ix, p. 134; 

 and J. Toynhee, in idem, 1859-60, vol. x, p. 32. See also on this point Dr. Gu-tav 

 Brunnen, on The Connection between the Ossicles of Hearing, in Knapp's Archives 

 of Ophthalmology and Otology, vol. iii, No. 2, p. 145, and Burnett, Monthly Journal 

 of Aural Surgery, July, 1871 ; 1'olitzer, Archiv f. Ohronheilk , Bd. iv, Heft 1. Buck, 

 however (Hinton's Report on Otology, Med.-Chir. Rev., April, 1873, p. 489), found, 

 on measuring with a micrometer the little lines into which starch-granules scattered 

 over the ossicula are thrown, that the vibrations of the malleus are twice as large as 

 those of the incus, and four times as larse as those of thp stapes, hence the intensity 

 of the sound-waves appears to undergo diminution on their passage from the mem- 

 brana tympani to the labyrinth. The views of Miiller, admitting waves of conden- 

 sation and rarefaction, are supported, in part at least, by Hensen and Schmidekara 

 (Untt-rsuch. d. Kinder. Instituts, 1869) and Henke (Zeits. f. rat. Med., Bd. xxxi), 

 who fastened glass threads to the ossicula, and observed great variation in the ampli- 

 tude of the vibrations, which were sometimes vertical and sometimes transverse 



