Longitudinal study of visual acuity (VA) from 6 to 17 years old have been carried out using the medical examination records of the graduates of a high school in Akita City in 1978 and 1988. The study subjects were completed their elementary and junior high school in Akita City and their numbers were 114 out of 236 male graduates in 1978 (78M), 54 out of 79 females (78F), 150 out of 322 male graduates in 1988 (88M) and 67 out of 115 females (88F). VA of decimal notation have been changed to visus logarithmus and then the mean values were caliculated. The highest values of mean-VA of each group were 1.21 at 8 years old(y) of 78M, 1.18 at 9y of 78F, 1 .17 at 7y of 88M and 1.15 at 8y of 88F, and their mean-VAs were fallen to about 0.4 at their 17y and the speed of decline of mean-VAs of 88M and 88F were faster than those of 78M and 78F . The cases of the lower vision at 17y showed earlier decline of VA. Stability of VA which showed the same VA more than continuous 3 years were 1.5+ and it seems that the normal VA of Japanese is 1.5 or more. Lower facial mascular strength that comes from the softness of foodstaff s makes trouble to control the mascules participate to lens . It would be a major cause of decline of VA.
To investigate the occurrence of infrasound in life environment, sound presure levels were measured at various places. In addition to this, levels of inf arsound perceptible to humans were examined. This experiment was performed in such places as under a bridge, inside an automobile and beside a cooling tower, where a single frequency in infarsound was predominantly observed. The results were as follows: 1) Beside a refrigerator, in a computer room and beside a cooling tower, the sound pressure levels of inf rasound were considerably low. 2) Beside a washing machine, a level of 81 dB, the highest level, was recorded at dehydration process. 3) The sound pressure level in wooden houses was found to be higher than that in concrete buildings, and the highest level in a wooden house was over 100 dB. 4) Considerably high sound pressure levels, 100 dB at 20 m from a running railroad carriage and 83 dB at 20 m from a running motor truck, were recorded. 5) Inside an automobile, levels over 110 dB were recorded when the wind-up vibration was generated. 6) The response rate of the subjects rose with an increase in the sound pressure level under each frequency. 7) Concerning the relations between frequency, sound pressure level and response rate, the 50% response levels of total response were 102 dB at 6 Hz, 93 dB at 10 Hz, 92 dB at 13 Hz, 85 dB at 20 Hz and 82 dB at 22 Hz respectively. 8) The 50% response level of total response decreased at a rate of -10 dB/octave. 9) The 20% and 80% response levels were located at +6 dB relative to the 50% response level, respectively.