1. The Arrhenius equation giving the relationship between the velocity of chemical reaction and temperature, was found suitable for the special case of the contraction rate of embryonic heart muscle fragments. 2. There was no constancy in the values of µ for the rate of contraction in culture, nor was the scattering evenly distributed around certain (more than one) points. 3. There seemed to be no correlation between µ and other functions such as the contraction rate, the site from which the piece was removed, the age of the embryo, etc.