骨導延長の機構に関する研究

　緒言

　骨導による臨床的応用は既に1603年Cappivacciが発表し，鼓膜疾患と内耳疾患の鑑別に使つている。有名なWeberのTestは1834年に記載された。1885年Bezoldは骨導聴力の成立に関して，鼓室小骨の振子様運動が内淋巴液を動かして骨導を感ずる。即ちcranio-tympanicのみが骨導の原因であると述べた。又骨導の延長に就いては卵円窓が正常より固くなる為に頭蓋から鼓室小骨えの振動が増加し，骨導延長を起すと説明した。

　1923年にRunge^1）はossiclesのrelative movementのみが蝸牛を刺激し得ると強調した。

　Nakamura finds that the sound conducted through the middle ear ossicle to be the causative factor in the mechanism of prolonged bone-conduction.

　(1) No evidence is found in establishing a relation between bone conduction and the state in which the mastoid cells may be developed, either, in the normal ear or that diseased with chronic otitis media. Bone conduction is measured by units of dynes applied to the tip of mastoid process through bone-conduction reciever.

　(2) In cases of chronic otitis media, a loss of 10 decibels in hearing is noted after the removal of incus is effected. Under similar conditions no change is noted in a case of a patient affected with otosclerosis.

　(3) The increase in sound of bone conduction when assisted by that sound passing through the ossicles of the middle ear as an auxiliary means of conduction is no more than 5 db equally, in the normal ear, the diseased ear with chronic otitis media or that with prolonged bone-conduction. However, when the ear is first subjected to a condition that causes a prolongation of bone-conduction which might be brought about by filling the external canal with water, the difference, whether or not the sound to be conducted through the ossicles, amounted to 10 decibels.

　(4) Experimentally, using rabbits, graphic waves obtained by electrical response of the cochlea are irrgular in shape; by removal of middle ear ossicles in the same animals such waves are decreased in their amplitude of excursion but at the same time they become uniform in character. The graphic waves obtained by filling the external canal with water become decreased in their harmonics but their character is delivered with more uniformity.

　(5) The causative factor in the condition that provokes prolonged bone-conduction is found without instituting operative procedure on the sound-conduction system.