The studies were carried out by the Warburg technique and the obtained results corrected after establishing by the method of C a s c ar a n o et al. what part of the incubated slices participates in the respiration. Most of the studied tissues from small animals showed higher metabolic rate than the homologous tissues derived from large animals, but the difference was less pronounced than that between basal metabolic rates. The estimated sum of tissue metabolism in young rats approached 100% of their basal metabolic rate, but in the case of adult rats this figure amounted only to 70%>. These results indicate that the metabolism of tissues in vitro is markedly different from their metabolism in vivo. In the author's opinion the main reason for this discrepancy lies in the fast disappearance of the effect of central regulating systems (nervous and humoral) on the metabolic processes occurring in cells of the isolated tissues.

In adult (300-400 g) male Wistar rats, acclimated for 3 weeks either to moderate (13 ± 1°C) or acute (5 ± 1°C) cold the changes of the metabolic rate in intact animals, respiration of muscle and liver slices in vitro, urinary catecholamine excretion and total serum thyroxine concentration have been measured. After 21 days of acclimation to both temperatures the basal metabolic rate (BMR) was elevated. Acclimation to 5°C accelerated also the metabolic rate in vitro of both tissue tested, whereas acclimation to 13°C produced a slight e!evation of the metabolism of muscle slices and a decrease of that of liver slices. Urinary adrenaline excretion during exposure of rats to 5°C was 5 to 13 times higher than prior to exposure, whereas the rise in noradrenaline excretion was much less pronounced. In rats acclimated to 13°C after a rise of urinary excretion of both amines taking place during first few days, a drop to approximately initial level occurred. Practically no changes in total serum thyroxine concentration took p'ace at exposure to both temperatures. The authors conclude that observed rise in adrenergic system activity may fully explain acceleration of the metabolism of isolated tissues as well as BMR.