In order to make clear the high tone loss after the tympanoplastic operation, the central perforation or the perforation around the manibrium mallei was made on the cats' ear drum, and then the losses of the cochlear microphonics through the perforation were measured, and compared each other.
About 10dB more losses at the high frequency tones (4000-8000cps.) was recognized in the cases of the perforation around the manibrium mallei than in the cases of the central perforation.
From our past studies on the mechanism of the sound conduction of the middle ear, this was concluded as follows:
The drum membrane is stretched tightly between the short process and the umbo of the manibrium mallei and kept cornally by manibrium. The lack of this part makes decrease the stiffness of the drum membrane and the total sound conducting mechanism, and it diminishes the activity of the hightone conduction mechanism of the drum membrane.

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In order to make clear the mechanism of sound couduction of the ossicular system, the author investigated the alteration of the cochlear potentials after the partial adhesion at different points of the ossicular chain of many cats by the use of tissue adhesives (α-cyano-acrylate-monomer=Aron Alpha).
The following results were obtained:
(1) After adhesion of the manubrium of the malleus to the eardrum, there appeared the reduction in C. M. response even to 15-20dB in the range from 0.2 to 2kcps.
(2) Stiffness of incudo-malleolar joint resulted in no reduction in C. M. response. But adhesion of the incudo-malleolar joint to the epitympanum led to a loss of 10-20dB in the range from 0.2 to 1kcps.
(3) Adhesion of the incudo-stapedial joint improved the C. M. response up to 5dB in the range from 0.2 to 1kcps while there was no reduction in the higher frequency range.
(4) After stapedial fixation, a loss in the low to middle frequency range, was larger than high frequency range and the notchs were observed in 0.2 and 1kcps. It is persumed that the notch of 0.2kcps is largely due to the inner impedance while that of 1kcps indicates the resonant point of the stapes.
(5) Stiffness of the all ossicular chain by the partial adhesion at several different points showed that the resonant point of the all ossicular system is centered around 1kcps, and the loss of C. M. response is about 40dB in the low range, about 50dB in the middle range, and about 20dB in the higher frequency range.

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Various methods for binaural stimulation of animals (cats) were reviewed and discussed. A detailed description of our apparatus for binaural stimulation and of the method of calibration was given. The apparatus is a pair of earphone systems consisting of the metal earpiece, the portex tube and the dynamic earphone (Toshiba, TR-33). The output of the earphone was indicated by the sound pressure level of free field stimulation which produced an equal amplitude of the cochlear microphonics as that produced by earphone stimulation. This method is based on the assumption that an equal amplitude of the cochlear microphonics means an equal stimulus effect. Furthermore, by observing the cochlear microphonics, it was ascertained that the cross hearing was negligible by using this method.

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