1. The 100% fatal dosis for male pure strain DD mouse weighing 18.0-23.0 g was 600-700 r.
2. In the experimental X-ray injuries aiming at the fatality of mouse, the seasonal influence of summer shortened toe survival of mouse after irradiation.
3. In the case of total exposure to 700 r, a specific mortality curve with 2 large peaks at 4 th and 8 th day after irradiation and 1 excavation without death at 6 th day was obtained.
4. In the case of total exposure to 700 r, the survival period of the group without measuring the body weight after irradiation was found longer than that of the group with daily measuring of the body weight. Consequently, the authors cosidered that, in addition to the shere manual handling, the mental influence such as fear or suprise is a fairly large factor to the survival period.
5. The body weight after the irradiation had no relation to the survival period, but that at the time of the irradiation was presumed to be somewhat related to the survivah period or to the life span of the mouse.
