THE ROLE which the vagus nerve plays in the production of reflex pulmonary vasoconstriction associated with pulmonary embolization has been studied by numerous investigators. De Takats and his colleagues1 found that atropine relieved the dyspnea produced by precapillary emboli in rabbits. They also lowered the fatality rate from massive pulmonary emboli in dogs by vagectomy and atropine. However, inferences drawn from mortality rates or symptom relief may be misleading. Studies on the hemodynamics of pulmonary embolism have demonstrated no marked changes with vagectomy.* These studies have all been undertaken with anesthetized animals or heartlung preparations. Since it is well known that anesthesia affects the pulmonary circulation,6 it was felt that the problem should be approached on intact animals without anesthesia.
In a previous study, graphite particles were injected into rabbits and their distribution studied in lung sections in order to determine the effect of anesthesia on vasoconstriction. It