Studies on frogs, turtles, rabbits, cats, dogs, and man over more than 20 years and participated in by numerous associates, including Doctors Kruse, Waddel, Koenig, Criep, Hover, McLain, and Lauler have led to numerous conclusions:I. Contraction normally begins in the superior vena cava and spreads to auricles and ventricles. The evidence and proof include: a. Direct observation. b. Simultaneous recording of contraction of veins, auricles, and ventricles alone and combined with galvanometric recording of electrical variation. (Fig. 1.) c. Sequence of recovery from vagus inhibition. (Fig. 2.) d. Transmission of premature venous contractions to auricles and ventricles. (Fig. 2.) e. Photographic (cinema) recording.In man, the evidence is mainly derived from polygraphic and gal-vanometric records, the hitherto occasionally observed, but unexplained U-wave corresponding to the venous electrical variation observed in lower animals. It may be observed in most subjects by increasing galvanometer sensitivity as by...