The exposure of human beings to ionizing radiation from natural sources is a continuing and inescapable feature of life on earth. This exposure exceeds that from all man-made sources combined for most individuals. In particular, radon (^<222>Rn, ^<220>Rn) and its progeny are the most important contributors to human exposure from natural sources. The present paper reviews the biological effects due to ionizing radiation and its protection, focusing on those due to natural radiation such as radon and its progeny. Although it is well known that inhalation of radon progeny at home may cause lung cancer in residents, the effect due to low dose radiation (quantitative relationship between radiation dose and health risk) remains unclear. Further studies are required for a right understanding for the radiation effect.

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The third report published by IPCC in 2001 said that the health effects of global warming have appeared in all of the world, and estimated that the average temperature in 2100 will increase 1.4 to 5.8 degrees centigrade compared with that in 1990. They also described both the direct and indirect effects including ecological, social and economic ones. The occurrence of heat stroke increases when daily maximum temperature is higher than 30℃ in Tokyo, and senior citizen older than 65 years are defined as a high risk group for heat stroke. It is observed that there is a "V"-shaped relationship between daily maximum temperature and daily mortality rates, characterized by mortality rates that are higher when the temperature is extremely low or higher than when the temperature is moderate. Besides, the V-shape moves horizontally according to the climate in Japan. Response to the heat stress of the young people in Thailand may be best among Japanese and Thailand people judging from the LF/HF and HF values. But it is suggested that young people working in air conditioned offices in the daytime have weak response to heat stress.

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This study was conducted to investigate the physiological and psychological responses after entering a room after outdoor-walking. In the experiments, the authors asked the subjects to take a walk outdoors, and then to stay in the chamber under two different conditions. The air temperature in the chamber was set at 26.0℃ or 26.3℃ with a relative humidity of 50% and 40%, respectively. These settings had the same SET*. The authors studied the relationship between physiological and psychological responses outdoors and within the chamber. Further more, it was examined whether the Two-Dimensional model by Kuno et al. was applicable for these responses. The results are as follows: 1) Heart rate, outdoor temperature and solar radiation were not related to each other. 2) Heart rate dropped immediately after entering the chamber. 3) Three skin temperature patterns were observed: (1) constant higher temperatures of 35.0-35.5℃ continued after entering the chamber; (2) temperatures fell to about 32.0℃ once, and immediately rose to about 34.0℃ and remained constant; (3) the temperature of one subject dropped excessively due to much sweating; 4) Thermal sensation changes could be classified into three patterns related to the patterns of skin temperature variation. 5) Differences in the physiological and psychological responses between the two settings could not be determined: and 6) in this experiment, the results for one subject did not conform to the Two-Dimensional model due to the skin temperature drop caused by the sweat-drenched clothing.

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We clarified the effects of water level and temperature on physiological and psychological responses during bathing in winter season. Eight healthy male volunteers served as subjects. They were requested to stand quietly for one minute in the bathroom, and to bathe for twenty minutes inside the bathtub filled up to the epigastrium or up to the sternoclavicular joint with the 39℃ and 42℃ water. Physiological parameters were systolic blood pressure at the upper arm, heart rate, tympanic temperature as the core temperature, skin blood flow at the forearm and sweat rate at the back of the hand continuously, and total sweating. At the same time, we measured thermal sensation and comfort votes as the psychological responses before and several times during bathing. As a result, the effect of water temperature contributed to raise the core temperature more than water level during bathing. Since present individual habit of bathing affects thermal comfort during bathing, two-step improvement, first lowering the bath water temperature, and next lowering the water level from the steroclavicular to epigastrium gradually, would be a good strategy for physiologically safe and psychologically thermal comfortable bathing.

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