The author investigated the changes of serum cholesterol levels and the histological findings of aorta of the cholesterol-fed rabbits, and the changes of serum cholesterol levels of the patients with hypertension following the radioactive hot spring bathing. The following results were obtained: 1) When 0.2 g. of cholesterol per Kg. of bodyweight was given to rabbits one time, the rise of the concentrations of serum cholesterol in the bathing group was lower and the recovery to the initial levels in the same group was faster than in the case of control (Table 1, Fig. 1.). 2) The author gave the rabbits 0.15 g. of cholesteterol per Kg. of bodyweight daily for 4 weeks. In this experiment, these rabbits were divided into 4 groups at follows. Group 1 Rabbits of this group were not bathed (as control). Group 2 Rabbits of this group were bathed in plain water (43°±1°C. 10 minutes) daily for 4 weeks. Group 3 Rabbits of this group were bathed in the radioactive Kenkyu-sho-sen (Rn-content: 10-40 Mache) in the same way as group 2. Group 4 Rabbits of this group were bathed in the radioactive Hisui-no-Yu (Rncontent:
300-400 Mache) in the same way as group 2. The concentrations of the serum cholesterol of the groups of radioactive thermal bathing remained lower than the control group. The concentrations of the serum cholesterol of group 4 were the lowest of all (Table 2 and Fig. 2). 3) In radioactive bathing groups, the atherosclerotic changes of aorta of the cholesterol-fed rabbits were slighter than the control (Table 3 and Fig, 3). 4) Following a series of radioactive hot spring baths, the total and ester cholesterol
levels in serum of the patients with hypertension decreased during the first and the second weeks and tended to return to the initial levels during the third and the fourth weeks (Table 4 and Fig. 4). 5) The author gave the rabbits 0.4 g, of cholesterol per Kg. of bodyweight and, 2 hours after this procedure, injected 5 mI. of 1% Indian ink into the aureal vein of the rabbit for the purpose of blocking the reticulo-endothelial system. These procedures were carried out once a day for 3 successive days. The serum total and ester cholesterol levels in the bathed group (bathing in Hisui-no-Yu once a day for 15 days, 42±1°C, 5 minutes) were lower those of the control and returned to initial levels more rapidly than the control (Table 5 and Fig. 5).