Abstract
Sodium and potassium concentrations in different parts of the frog heart (sinus venosus, atrium and ventricle) were investigated at various seasons of the year. The sodium concentration showed a marked periodicity in all three parts of the heart: minimum in winter, maximum in summer. Potassium concentration showed no seasonal variations, except for reduction in potassium concentration of the ventricle in the second half of the year. The experimental results for sodium can be fitted by a sine curve, the differences between minimum (in winter) and maximum (in summer) representing 46.4% (for sinus venosus), 30.4% (atrium) and 34.0% (ventricle) of the spring-autumn values. Variation in the electrolyte concentration could be explained by changes in salt. and water metabolism induced by fluctuations in the temperature on one hand, and by the removal of the animals from their natural environment on the other.
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