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Galen & Circulation
by Matthew Megill, Dartmouth College


And it is worth emphasizing, that Galen was familiar with Erasistratus's description of a pumping heart (PHP, 397). Erasistratus accurately described the heart, right down to the minute yet critical function of the valves (Harris, 196). But that third century, B.C. Alexandrian failed to discover circulation, because he believed that the arteries were filled entirely with pneuma - air. Galen, on the other hand, decisively refuted that theory, showing in the process that he had a more than passing familiarity with Erasistratus's writings (Galen, On Blood in the arteries). Did Galen, then, consider the heart as a pump for blood? While there are a range of opinions, I find Harris's conclusion to be convincing: Galen not only was familiar with the accurate pump model, but embraced it himself (279).

If Galen did have this understanding, he was barely a heartbeat from Harvey's most convincing piece of evidence for circulation. Harvey tells us that he first considered the circulation of the blood, when noting how much blood is expelled by the heart with each contraction: over the course of a full day, the amount was more than the body's intake of food by weight (67). Doing rough calculations, Harvey easily proved that the point is beyond doubt, and that the blood must be re-used. From here, circulation is but a short leap. That Galen should have so confidently considered blood to be a combustible fuel for the body, without even thinking of this simple calculation, must strike those of us with 20/20 hindsight as remarkable.

Harvey's other major points further serve to incriminate Galen's bias. Harvey pushed a rod up a vein, but was unable to go down it because of the valves (83). He proved quite simply the blood's backward flow in veins on a human arm (84-6), and he demonstrated that pumping spits blood from a cut artery (27). Finally, he noted that while a cut artery quickly clears the whole arterial system, there is no such effect for a cut vein (64). All of these observations were readily available in the second century.

To suppose that Galen was incapable of realizing the potential significance of these observations is absurd. In other facets of anatomy, experimental evidence compelled Galen to think creatively. For example, he suggested that unseen nerve channels allowed the brain to send message pneuma to the muscles (PHP, 453). But in studying the heart, Galen ignored observations contrary to his theory, and we must wonder what it was about Galen's theory of the heart that was so indispensable to him.

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