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Chemical temperature regulation in new-born mice. Immediately aider birth, mice are poikilotherm. Changes in environmental temperature cause characteristic variations in metabolic rate. If plotted as a function of rectum temperature, metabolic rate shows the same pattern under conditions of cooling or warming. Below normal rectum temperature, e. g. between around 360 and 320 C, O2~consumption increases with decreasing rectum temperature, but decreases with increasing rectum temperature. Basically the same relationship between rectum temperature and O~-consumption is found under conditions of constant (for several hours) environmental temperatures. The maximum average O2-consumption is obtained at a constant environmental temperature of 32 ° C. Overheating (1 hour at 400 C) destroys the relationship described and resuks in a simple reduction of O~-consumption with decreasing rectum temperature under conditions of low environmental temperatures. The increasing constancy of body temperature in the second week aiter birth is caused by the development of the fur on the skin (reduction of heat loss), rather than by that of feed back mechanisms. EINLEITUNG

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