A text-book of the diseases of the ear / by Josef Gruber.

  • Gruber, Josef, 1827-1900.
Date:
1890
Catalogue details

Licence: Public Domain Mark

Credit: A text-book of the diseases of the ear / by Josef Gruber. Source: Wellcome Collection.

    163/618 (page 129)
    to correspond to the tone of the tuning-fork, and fastened upon a board (B), so that the sharply cut-off opening is opposite the tranches of the tuning-fork. The other opening carries an indiarubber tube with its end, or nozzle, adapted to fit the ear. The metal rod which supports the resonator is provided with a hinge (C), by means of which the resonator may be turned away from the tuning-fork, and allow the latter to be used without it. The under surface of the board is covered with indiarubber to prevent the conveyance of vibrations. Both tuning-fork and resonator may be changed at will. The apparatus is very useful for physiological experiments and for demonstrations. König1 s1 so-called sounding-rods are but little used. They are steel cylinders 20 mm. in diameter, and of different lengths ; and when struck with a hammer, nodes are formed at one-fifth of the length from each end, the rods being suspended at these points. Ten rods are used, the lowest making 4096, and the highest 32,768 vibrations per minute. In investigating sound-conduction through the bones with the tuning-fork, it should be noted that the patient may fancy he hears the sound, when in reality he has only perceived the me- chanical concussion of the vibrations : it is there- fore always well to allow him to describe his sensations. If he has really heard the tone, this is correctly described ; perhaps even sung after- wards. He should also be asked to indicate the locality of his sensations ; and it should not be forgotten that this depends partly upon the pitch of the tuning-fork, as well as that a perfectly constant perception for the same tone does not invariably exist, even with quite healthy organs. The examination should therefore be repeated at different times, at different parts of the cranium, and with tuning-forks of different pitch.2 If a vibrating tuning-fork is held in such a way that an edge of one of its branches is just opposite the external auditory meatus, the sound becomes for the moment extinguished. If the tuning-fork is turned round on its longitudinal axis opposite the auditory canal, the same thing happens four times in succession ; 3 and Urbantschitsch4 found that it also occurred when it is brought opposite the meatus from before backwards, or from above downwards. These phenomena are due to interference of sound-waves. According to the 1 Midler-Pouillet's Lehrbuch der Physik, 1877, i- Bd., 2 Abth. S. 551. - Compare Urbantschitsch, Ueber die von der Höhe des Stimmgabeltones und von der Apphcationsstelle abhängige Schallleitung durch die Kopfknochen.' Archiv für Ohrenheil- kunde, xii. Bd., S. 207, u. ff. 3 Gebrüder Weber, Die Wellenlehre. Leipzig, 1825, S. 506. 4 Centraiblatt iür die medicinische Wissenschaft, 1872, Nr. 8. 9 Fig. 56. Fig. 56 represents a small tuning-fork used by the author for the production of feeble tones. It is particu- larly suitable for examina- tion of one ear alone, as it can be more easily put into vibration without the knowledge of the patient. The tone is brought out by drawing the ends of the branches suddenly together with the fingers.