The author investigated the effect of a series of thermal baths of Misasa (at 37°C for ten minutes) during ten days on the survival rate and fat index of liver in X-irradiated mice. The radioactive thermal baths prior to or following a lethal dose of total body X-irradiation (800r) were not able to modify the survival or death rate in mice. The radioactive thermal baths prior to LD 50 dose of X-irradiation (450r) improved the survival rate and decreased the liver injury. But the thermal haths following the same dose of
X-irradiation showed no protective effect and seemed to increase the injury of X-irradiation rather. The combination of thermal baths for ten days and daily X-irradiation of 50r for the successive 25 days produced more unfavourable result than control without baths. On the contrary thermal baths prior to the daily X-irradiation of 50r showed a marked protection concerning the lethal effect and fat index of liver in mice. Three kinds of baths were used in this experiment, namely natural strongly radioactive thermal bath of Misasa (50-80m. m. curies Rn per liter). natural weakly radioactive thermal bath (5-10m. m. curie; Rn per liter) and plain water bath. But no significant difference
was proved between the effects of these three kinds of baths.