Recent physiologic studies have tended to emphasize the relationship between the pressure of the blood returning to the heart through the veins and cardiac activity. Physiologists may be divided into two schools in this respect at present, one of which, under the influence of certain English workers, especially Starling, believes that it is venous pressure which determines cardiac output at each beat, by influencing the initial length or initial tension of the auricular and ventricular muscle. The "law of the heart," as developed by Starling, establishes a relationship between initial load and energy of contraction in the cardiac muscle as has been shown to exist in skeletal muscle. The other school, led by Yandell Henderson, while recognizing the influence of venous pressure up to a certain point, believes that above this there holds "uniformity of cardiac behavior" in which cardiac output does not necessarily vary with venous pressure but depends