their view of the course
of the blood through the lungs, and he shows how it fitted into his
general scheme. If you will follow the course of the arrows in Fig. 4
you will see at once that--in accordance with the views of Columbus--the
blood passes from the right side of the heart, through the lungs, to the
left side. Then, adds Harvey, with abundant proof, it passes through the
arteries to all parts of the body; and then, at the extremities of their
branches in the different parts of the body, it passes (in what way he
could not tell, for his means of investigation did not allow him to say)
into the roots of the vents--then from the roots of the veins it goes
into the trunk and veins--then to the right side of the heart--and then
to the lungs, and so on.

That, you will observe, makes a complete circuit; and it was precisely
here that the originality of Harvey lay. There never yet has been
produced, 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