The author investigated the effect of radioactive hot spring bath on serum cholesterol levels. The chemical compositions of the spring waters used are described in Table I. As experimental subjects healthy men and healthy white rabbits were used. The following results were obtained. 1) Single bath. The total and ester cholesterol levels in the serum were measured by a modification of Bloor's method before and 1/2, 1, 2 and 3 hours after the radioactive thermal bath (41-43°C., for 5 minutes). The concentration of total and ester cholesterol had decreased following radioactive thermal baths (Hisui-no-Yu and Kenkyusho-Sen), and remained at a decreased level for l/2 to 2 hours, but tended to return to normalcy within three hours from the time of the bath. (Fig. 2, 3, 4, 5.) The plain-water bath and vapour bath used as a control (41-43°C., for 5 minutes and 44-47°C. for 10-20 minutes respectively), had no significant effect on the blood cholesterol levels (Fig. 7 and 8). 2) Series of baths. The author examined weekly for 4 weeks the changes in serum cholesterol in healthy subjects following "a series of baths" in radioactive hot springs. The total and ester cholesterol levels of the serum decreased during the first and second weeks and tended to return to the initial levels during the third and fourth weeks (Fig. 11). The total cholesterol levels of the serum in rabbits following "a series of baths" in KenkyushoSen (Rn-content; 10-40 Mache) increased during the second week, but the cholesterol levels of the serum, after bathing in Hisui-no-Yu (Rn-content: 300-400 Mache), tended to decrease during the first and second weeks (Fig. 9 and 10). From this experiment, it is concluded that the content of radon in hot spring water affects the concentrations of the serum cholesterol levels. 3) Following an intramuscular injection of A. C. T. H. or Cortisone, the concentrations of total cholesterol and ester cholesterol had decreased and remained at the low level for 4 hours (Fig. 12. 13, 14 and 15). 4) It is said that the reticulo-endotherial system plays an important part in cholesterol metabolism. The author injectt 5 ml. of 1% Indian ink into the aureal vein of the rabbits for the purpose of blocking the reticulo-endotherial system. These procedures were carried out once a day for 7 successive days. The total cholesterol levels of the serum in the bathed group (bathing in Kenkyusho-sen once a day for 4 weeks, 43°C., 5 minntes) were lower than those of the control (Fig. 16). From these findings, the author thinks that the fall in the serum cholesterol levels
following Misasa Hot spring bathing is due to the synthetic action of many factors such as the acceleration of oxydation in the living body, and the hyperfunction of liver cells, of hypophysealadrenocortical, of reticulo-endotherial systems and of various endocrine glands, caused by radioactive thermal bathing. Alternation of vegetative nervous system and various vitamine metabolism also take part in this phenomenon.