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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