This experiment was aimed at finding out what time interval and dose of irradiation would the most useful inhibitory effects on experimental tumor. The tumor used was solid type Ehrlich carcinomas experimentally induced in mice, and the total dose of each irradiation was 5,000R. The effect of irradiation was determined by the survival time of the tumor bearing animals (Table 1). The interval of 72 hours which is thought to be most appropriate was taken as the standard of the interval. As a result it was found that the irradiation of 5,000R at the interval of 72 hours with additional 100R at every 24 hours lengthened the survival time of the tumorbearing animals to 4.0 days in average. The survival time of the controls given no irradiation was 20.4 days in average (Tables 2-4, Fig. 1). Further, in those groups given additional dose of 200R or 300R every 24 hours, the length of survival days was rather shortened.
Besides these, some investigations were carried out to see what therapeutic effect such additional irradiation would have on the regional tumor and what systemic side-effects. The effect on the regional tumor was determined by the activity of succinic dehydrogenase system in the tumor and systemic irradiation damages in the blood picture (Tables 5-13, Figs. 2-6). The results revealed that in comparison to the group simply irradiated with 5,000R at interval of 72 hours, the group given additional 100R showed the recovery of the succinic dehydrogenase activity to be inhibited but the blood picture did not exhibit any appreciable change. In the groups given additional dose of 200R or 300R the succinic dehydrogenase activity was diminished and also the damage to blood picture was in such a state that it could not be lightly taken of. These findings indicate that when the irradiation is done at the interval of 72 hours and additional dose is given at the intermission period, such additional irradiation is effective at a certain appropriate dose. In this instance, the additional dose should be such as to inhabit the growth of tumor but not to cause much side-effect. In other woras, divided doses of irradiation should be within the range which would serve the very purpose of irradiation best.