Electrocardiography in Practice, 3rd Edition, 1954, ed. Ashton Graybiel, Paul D. White, Louise Wheeler, and Conger Williams. W.B. Saunders Co., Philadelphia and London.

Fig. 1. A, Curve of action current (QRS and T waves) recorded from a frog's heart, with electrodes on apex and base (capillary electrometer). Stimulus applied to atrium is shown by interruption in black line.

B, Curve recorded from frog's heart with electrodes in the same position. The curve shows one large upward deflection—the injury effect—corresponding to what is now called S-T segment shift.