THE EAE. 

 By JOHN GRAY M'KENDRICK and ALBERT A. GRAY. 



CONTENTS : The EXTERNAL EAR, p. 1149 The Auricle, p. 1149 The External Audi- 

 tory Meatus, p. 1150 Movements of the Auricle, p. 1152 The MIDDLE EAR, p. 

 1152 The Tension of the Meinbrana Tympani, and its Regulation, p. 1152 

 Movements of the Membrana Tympani in response to Sound Pressures, p. 1153 

 The Movements of the Malleus, p. 1155 The Movements of the Incus, p. 1155 

 The Movements of the Stapes, p. 1156 The Tensor Tympani, p. 1156 The 

 Stapedius, p. 1 157 The Movements of the Ossicles as a whole under the Influence 

 of Sound-waves, p. 1158 The Magnitude of the Movements of the Ossicles, p. 

 1159 Transmission of Sound to the Labyrinth otherwise than by the Ossicles, 

 p. 1160 Regulation of Atmospheric Pressure in the Tympanum, p. 1161 

 Auditory Reflexes, p. 1162 Binaural Audition, p. 1163 The INTERNAL EAR, p. 

 1164 General Mechanism of Internal Ear, p. 1164 The Utricle and Saccule, p. 

 1166 The Cochlea, p. 1168 Pitch, p. 1169 Beats, p. 1169 Beat Tones, p. 1170 

 Audibility as affected by Intensity, p. 1171 The Analytic Properties of the 

 Ear, p. 1171 Resonance, p. 1177 Probable Action of the Cochlea, p. 1179 

 Upper Partial Tones and the Theory of Dissonance, p. 1186 Combination Tones, 

 p. 1188 Objections to the Theory of Helmholtz, p. 1190 Other Theories, p. 

 1190 The Semicircular Canals, p. 1194. 



THE EXTERNAL EAR. 



The auricle. The most natural supposition is that the auricle reflects 

 sound-waves into the external ineatus. But cases of absence of the 

 auricle have been recorded without any appreciable diminution in the 

 power of hearing, 1 and persons from whom the external ear has been 

 removed have been found to possess normal hearing power. Experi- 

 ments upon the auricle, in which the depressions on its surface were 

 filled up, have given contradictory results. 2 M'Kendrick 3 found that 

 covering the external ear with plaster of Paris, leaving the entrance to 

 the canal free, weakened the intensity, and altered the quality of tones. 

 It must be observed that in such experiments the mass of the auricle 

 itself would not be able to vibrate to the same extent as in the normal 

 condition, and hence an apparent diminution of hearing may have been 

 due to a loss of vibrations conducted by the solid structures, and not to 

 the loss of the reflecting action of the auricle. 



Long ago, Boerhaave attempted to show mathematically that the concha 

 acts as a parabolic reflector, collecting and throwing vibrations into the 

 meatus. Savart, 4 however, demonstrated experimentally that this is not the 

 case. Still there is evidence that the concha does in a slight degree affect 

 acuteness of hearing by reflection. Thus 5 if a small tube, curved like a 



1 Allen Thomson, London and Edinburgh Month. Journ. Med. Sc., April 1847 ; Toynbee, 

 "Diseases of the Ear," London, 1868, p. 14. 



2 Schneider, " Inaug. Diss.," Marburg, 1855; Harless, Wagner's ' ' Handworterbuch d. 

 Physiol.," 1853, Bd. iv. S. 422. 



3 "Text-Book of Physiology, " vol. ii. p. 672. 



4 Journ. dephysiol. expdr., Paris, 1824, tome iv. p. 183. 



5 Politzer, "Diseases of the Ear," 1894, p. 710. 



