3 During rest ab out 0,02 cal per minute are released from 1 cm muscle matter, whilst with extreme work load this is elevated to 50 times the resting value, i. e. approximately 1 caljmin. Aretention of this heat would mean an increase of body temperature by 1 ° C per min. As the heat con duction in the body tissues is rather bad, the heat release is almost solely effected through the blood flow. The circulation is regulated through the 3 3 oxygen consumption. A blood circulation of ab out 1 cm per cm muscle and minute, which is the upper limit under practical conditions, suffices to release 1 caljmin, provided that there is a difference in temperature of 1 ° C between the blood entering the -muscle and the interior of the muscle itself. Due to the relatively high circulation necessary to cover the oxygen demand the muscle is not in danger of being overheated, even with extreme work loads. Even if this circulation is interrupted there is no such danger, since at the same time the oxygen supply and, consequently, the heat production are discontinued. It is far more difficult, however, to maintain the heat balance of the whole body. A work load of 10 kcaljmin, which a healthy man is able to maintain for two hours, means an increase of body temperature by 5°C within 30 minutes unless the heat is released from the body. This, however, means a dangerous overheating of the body.