le, sending blood into the ventricle; then
ventricular contraction, making the pulse, and sending the blood into
the arteries. He had thus demonstrated what had not been generally
accepted before, that the heart was an organ for the propulsion of
blood. To make such a statement to-day seems not unlike the sober
announcement that the earth is round or that the sun does not revolve
about it. Before Harvey's time, however, it was considered as an organ
that was "in some mysterious way the source of vitality and warmth, as
an animated crucible for the concoction of blood and the generation of
vital spirits."(3)

In watching the rapid and ceaseless contractions of the heart, Harvey
was impressed with the fact that, even if a very small amount of blood
was sent out at each pulsation, an enormous quantity must pass through
the organ in a day, or even in an hour. Estimating the size of the
cavities of the heart, and noting that at least a drachm must be sent
out with each pulsation, it was evident that the two thousand beats
given by a very slow human heart in an hour must send out some forty
pounds of blood--more than twice the amount in the entire body. The
question was, what became of it all? For it should be remembered that
the return of the blood by the veins was unknown, and nothing like a
"circulation" more than vaguely conceived even by Harvey himself. Once
it could be shown that the veins were constantly returning blood to the
heart, the discovery that the blood in some way passes from the arteries
to the veins was only a short step. Harvey, by resorting to vivisections
of lower animals and reptiles, soon demonstrated beyond question the
fact that the veins do carry the return blood. "But this, in particular,
can be shown clearer than daylight," says Harvey. "The vena cava enters
the heart at an inferior portion, while the artery passes out above. Now
if the vena cava be taken up with forceps or the thumb and finger, and
the course of the blood intercepted for some distance below the heart,
you will at once see it almost emptied between the fingers and the
heart, the blood being exhausted by the heart's pulsation, the heart
at the same time becoming much paler even in its dilatation, smaller
in size, owing to the deficiency of blood, and at length languid in
pulsation, as if about to die. On the other hand, when you release the
vein the heart immediately regains its color and dimensions. After that,
if you leave the ve