(1) Kawai and Tokia have devised four methods by which the dynamical measurements of Young's modulus and the internal friction of fibers and films are possible over a wide range of frequencies. Using one of these methods, that is with audio-frequency, we measured the Young's modulus of a rectangular strip (10mmx1. 5mm; 0. 075mm thick) taken from the fresh tympanic membrane of Japanese male cadaver, and obtained the value: 4. 0x10^8 dyne/cm^2. After Bekesy, the value obtained by the statical method, was 2. 0x10^8 dyne/cm^2. (2) The Young's modulus of the tympanic membrane is nearly equal to that of the rubber, and is not variable by stress. So the tympanic membrane seems to have a rubberlike elasticity.
For the purpose of studying the sectional curve of the tympanic membrane cut by a perpendicular to its basic plane (Fig. 2), authors made moulds of the figures of tympanic membranes (Fig. 1 B), by pouring paraffin into the eternal auditory meatus and taking photographs of side-figures of them, using fresh temporal bones of the Japanese cadavers for materials. After measuring the figures of the paraffin moulds and photographs, we determined the sectional curve of the membrane; it was similar to a witch of Agnesi. Stiffness of the middle point and the periphery of the tympanic membrane were deduced to be greater then that of the intermediate part.
In order to get the real ear response reflecting the actual characteristic of a receiver, the relationship among the sound pressures in the free field, at the entrance of a ear canal, ant at the ear drum was found by using the probe tube microphone, with the subject seated facing the sound source in the free field. From the results that the relation between the sound pressure at the entrance of the ear canal ant that at the ear drum was constant in case of both open ear and ear closed by a receiver, the real ear response of a receiver was found to be measured easily. After this experiment, the real ear response of two kinds of receivers were measured. As s results, the conversion coefficient from the conventional coupler response to the real ear response was shown concerning each receiver. By using this conversion coefficient, so far as we use the same kinds of receivers, it is possible to convert directly the real ear response from the coupler response which is easily and accurately obtainable without repeating the complicated measurement of the real ear response.
Sound-level meter was applied for the first time in measuring quantitatively the vocal activities of the communities of frogs and cicadas incorporated with the conventional hearing method which had been used in ecological investigations. By the above new method, the diurnal periodicities of these activities and their relations to environments were studied. Surrounding factors such as air temperature, relative humidity, water temperature, intensity of illumination and heat radiation were measured. To obtain the vocal activity quantitatively, sound level was measured as follows: microphone was usually placed at a distance from the community and songs picked up exceptionally near the microphone were eliminated from the data; measuring time was taken long enough to cover the trends ups and downs of activity of the community; it was ascertained that the distance between the microphone and the community did not vary widely; and the microphone was held in constant orientation with the community in consideration of the directivity characteristics. By using the sound-level meter it was found as follows: (1) In Terpnosia vacua diurnal vocal activity (average sound level) corresponded to illumination; (2) In summer cicadas (Platypleura Kaempferi, Cryptotympana japonensis and Graptopsaltria nigrofuscata) the average level of each species was maintained nearly constant in the daytime and their vocal activities appeared to be in saturation; (3) In Hyla arborea japonica the increase of activity at dusk corresponded to the decrease of illumination; (4) With these frogs seasonal ups and downs of activity was observed but there was no apparent relation with the age of the moon; (5) With same frog taken into consideration the type of variation of activity throughout a night was not apparently affected by the moon-light; (6) This frog sang throughout the night, while Rana rugosa sang in the former half of the night and Rana limnocharis in the latter half. So they manifested respectively their specific activities, and the types of time variation of average level in their activities were also characteristic. Relative activities of the three species of frogs were varied by their habitats and season and as the result of their sum-mation there appeared various type of nocturnal vocalization. It was assumed that the vocal activities of these animals were chiefly affected by the intensity of illumination.