h have made
his name famous. I think it is desirable that no obscurity should hang
around these questions; and I add my mite to the store of disquisitions
on Harvey, in the hope that it may help to throw light upon several
points about which darkness has accumulated, partly by accident and
partly by design.

About the year B.C. 300 a great discovery, that of the valves of the
heart, was made by Erasistratus. This anatomist found, around the
opening by which the vena cava communicates with the right ventricle,
three triangular membranous folds, disposed in such a manner as to allow
any fluid contained in the vein to pass into the ventricle, but not back
again. The opening of the vena arteriosa into the right ventricle is
quite distinct from that of the vena cava; and Erasistratus observed
that it is provided with three pouch-like, half-moon-shaped valves; the
arrangement of which is such that a fluid can pass out of the ventricle
into the vena arteriosa, but not back again. Three similar valves were
found at the opening of the aorta into the left ventricle. The arteria
venosa had a distinct opening into the same ventricle, and this was
provided with triangular membranous valves, like those on the right
side, but only two in number. Thus the ventricles had four openings, two
for each; and there were altogether eleven valves, disposed in such a
manner as to permit fluids to enter the ventricles from the vena cava
and the arteria venosa respectively, and to pass out of the ventricles
by the vena arteriosa and the aorta respectively, but not to go the
other way.

It followed from this capital discovery that, if the contents of the
heart are fluid, and if they move at all, they can only move in one way;
namely, from the vena cava, through the ventricle, and toward the lungs,
by the vena arteriosa, on the right side; and, from the lungs, by way of
the arteria venosa, through the ventricle, and out by the aorta for
distribution in the body, on the left side.

Erasistratus thus, in a manner, laid the foundations of the theory of
the motion of the blood. But it was not given to him to get any further.
What the contents of the heart were, and whether they moved or not, was
a point which could be determined only by experiment. And, for want of
sufficiently careful experimentation, Erasistratus strayed into a
hopelessly misleading path. Observing that the arteries are usually
empty of blood after death, he adopted the unlucky hyp