Abstract
VARIOUS investigations have indicated the cyclic nature of thyroid gland activity, increased activity being associated with winter and decreased activity with summer. Levine and Remington (1933) have suggested that the variable nature of thyroid activity might be due to a change in one or more of three environmental factors, namely, iodine content of food, temperature and light. Kligler et al. (1945) after observing in rats that the effects of changes in relative humidity were similar to those following thyroid stimulation suggested that changes in the relative humidity may cause increased thyroid activity.Many observations have been made to the effect that temperature is an important factor in relation to thyroid activity. Direct evidence of this has recently been reported by Dempsey and Astwood (1943) who found that the thyroid glands of rats secreted 1-thyroxine at the rate of 9.5 micrograms per day when kept at a temperature of 1°C., but .
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