Fig. 1. Allometric relationship between body mass and Na⁺, K⁺-ATPase activity of brain homogenates in mammals and birds. Values are means ± S.E.M. of Na⁺, K⁺-ATPase measurements at 37°C in mammals and corrected to 37°C in birds (see Materials and methods). Data from Tables 1 and 2. The lines are the best power fits to the data as described by the inset equations. P_i, inorganic phosphate.