Galen said, as I pointed out just now, that the arteries dilate as
bellows, which have an active power of dilatation and contraction, and
not as bags which are blown out and collapse. Harvey said it was
exactly the contrary--the arteries dilate as bags simply because the
stroke of the heart propels the blood into them; and, when they relax
again, they relax as bags which are no longer stretched, simply because
the force of the blow of the heart is spent. Harvey has been
demonstrated to be absolutely right in this statement of his; and yet,
so slow is the progress of truth, that, within my time, the question of
the active dilatation of the arteries has been discussed.
Thus Harvey's contributions to physiology may be summed up as follows:
In the first place, he was the first person who ever imagined, and
still more who demonstrated, the true course of the circulation of the
blood in the body; in the second place, he was the first person who
ever understood the mechanism of the heart, and comprehended that its
contraction was the cause of the motion of the blood; and thirdly, he
was the first person who took a just view of the nature of the pulse.
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