An attempt has been made to determine the optimal method of managing the lungs during cardiopulmonary bypass. The chemical behavior (oxygen saturation, acid-base balance) of the pulmonary venous blood indicates (a) that static inflation of the lungs with either a gas mixture of high oxygen content or ambient air is sufficient to maintain a proper internal milieu for the pulmonary vasculature when the bronchial collateral flow is the sole pulmonary perfusate, and (b) that in adult human beings artificial respiration up to 2 L./min. is necessary when the pulmonary perfusate consists of the coronary venous blood in addition to the bronchial collateral flow. The effective application of the heart-lung bypass procedure in physiological investigation is depicted by the studies on metabolic rate of the lung tissues and the measurement of bronchial flow. It is estimated that the bronchial collateral flow amounts to 8.8 ml./ min. or 0.7 per cent of the total systemic flow, and that the oxygen consumption of the lungs averages 1.6 ml./min. or 1 to 2 per cent of the total metabolic rate in the open-chest dogs. The pulmonary compliance did not change following either passive deflation or static inflation, but is transiently reduced after artificial respiration.

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An operative approach to the ventricular aspect of the aortic valve has permitted combined prosthetic replacement of the aortic and mitral valves. In the first clinical trial of the method, the pa-

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