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The most important factor to be determined before calculating the work done by the heart is the quantity of blood forced from the ventricles at each systole. Most of the efforts to determine this quantity have been based either upon faulty observations upon the dead heart, or upon the uncertain data obtained by estimating the mean velocity of the stream of blood in the aorta. Professor Martin accordingly suggested to us that we should attempt to measure it directly on the isolated Dog’s heart. The work thus undertaken was carried on during the greater part of the university session, 1881-82, and the results obtained are given in the following pages. The method of isolating the heart was essentially that described in Professor Martin’s paper (Phil. Trans., 1883, p. 663). In the course of this work many unexpected difficulties arose, necessitating changes in the apparatus and the method of operating, and preventing us for a long time from obtaining any successful results. In our experiments it was necessary not only that the heart should live and beat, but that it should be in the best possible physiological condition, and any marked pulmonary œdema made an experiment nearly valueless. This most frequent cause of failure was mainly owing to the fact that, on account of the large quantity of blood required for an experiment, we were obliged to use Calf’s blood obtained from the butcher; very often this blood, as Professor Martin states in his paper, will bring about œdema of the lungs in a short time; large quantities of exuded serum pour out of the tracheal cannula, the air-passages in the lungs become choked up with liquid, and the circulation from the right to the left side of the heart is greatly impeded. We have succeeded, however, in making a considerable number of experiments in which all the conditions were favourable, the œdema of the lungs not occurring to any marked extent until after many observations had been made.

philosophical transactions of the royal society of london

VI. Experiments upon the heart of the dog with reference to the maximum volume of blood sent out by the left ventricle in a single beat and the influence of variations in venous pressure, arterial pressure, and pulse-rate upon the work done by the heart