[Effect of cold acclimatization of grass frogs on the heat resistance of their somatic muscles in summer].

During cold acclimation (+5 degrees C) of the grass frog Rana temporaria L. changes in heat resistance were observed for six of seven skeletal muscles examined. Changes in the resistance of different muscles were directed differently. Low-resistant muscles demonstrated an increased resistance, wheras high-resistant muscles showed a decrease resistance. Within 24 hours of acclimation, all the muscles demonstrated totally decreased heat resistance. By the end of acclimation (30 days), the resistance of muscles increased to approach the initial level. On the background of those situation changes, seasonal changes in resistance of muscles proceeded.