duced, and I do not believe there can be
produced, a tittle of evidence to show that, before his time, any one
had the slightest suspicion that a single drop of blood, starting in the
left ventricle of the heart, passes through the whole arterial system,
comes back through the venous system, goes through the lungs, and comes
back to the place whence it started. But that is the circulation of
the blood, and it was exactly this which Harvey was the first man to
suspect, to discover, and to demonstrate.

But this was by no means the only thing Harvey did. He was the first
who discovered and who demonstrated the true mechanism of the heart's
action. No one, before his time, conceived that the movement of the
blood was entirely due to the mechanical action of the heart as a pump.
There were all sorts of speculations about the matter, but nobody had
formed this conception, and nobody understood that the so-called
systole of the heart is a state of active contraction, and the so-called
diastole is a mere passive dilatation. Even within our own age that
matter had been discussed. Harvey is as clear as possible about it. He
says the movement of the blood is entirely due to the contractions of
the walls of the heart--that it is the propelling apparatus--and all
recent investigation tends to show that he was perfectly right. And from
this followed the true theory of the pulse. 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 bl