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 arrested in the arteries, which lie at a relatively great depth. (2) When a vein is tied the resulting distension manifests itself only below (i.e., on the distal side of) the ligature; whereas, when an artery is similarly tied, the distension takes place above (i.e., on the proximal side of) the ligature. It is therefore plain that in the veins the blood flows from the individual parts toward the heart, but that in the arteries the flow is in the reverse direction—i.e., from the heart toward the individual parts. "If one reflects upon the nature of the movement of the blood," says Flourens, "one will promptly realize how speedy it is. Scarcely has the blood entered the heart before it is hurried into the arteries; and then from these vessels it passes in an instant into the veins, from which, with almost equal speed, it finally travels back to the heart again. It is this never-ending movement from one channel into another, and then eventually back to the starting-point, which constitutes the circulation of the blood Modern physiology dates from the discovery of the circulation of the blood. Up to the time of this discovery physiologists followed the ancients; they did not dare to walk alone. Harvey had discovered the most beautiful phenomenon in the animal economy From this time forward, instead of swearing by Galen and by Aristotle, one had to swear by Harvey!"

Despite the great care which Harvey took to back up his scheme of the circulation of the blood with unimpeachable proofs of its correctness, he was obliged to pass through the same sort of experience as that to which Vesalius and scores of other pioneers in the field of scientific inquiry had been subjected. Two hostile forces stood constantly ready, during that fruitful period of the Renaissance, to attack with merciless bitterness all those who ventured to add new facts to our stock of knowledge in the domain of medicine. On the one side were the many men of small calibre, men filled with jealousy over the successes gained by co-workers in the same field; and on the other was marshaled the host of those who honestly believed that all medical wisdom ended with Galen. Before his death, however (hardly