1. The frequencies of the beat of cilia and flagella from various organisms have been determined at temperatures in the range 5-35°C.
2. Values of the activation enthalpy (ΔH‡, kcal./mole) and activation entropy (ΔS‡, e.u.) derived from the thermal dependence of frequency show a linear correlation of the form, ΔS‡ = 3·25 ΔH‡-50·75.
3. The corresponding isokinetic activation free energy is 15·6 kcal./mole.
4. The results support a hypothesis that the breakdown of an ATP-ATPase complex could be the common rate-limiting reaction for flagellar activity.
5. Values of ΔH‡ and ΔS‡ for the decay of length or tension in striated muscles also fall on the same regression line but some smooth muscles show deviations.