obbes of Malmesbury, his contemporary, said of him, "He
is the only man, perhaps, that ever lived to see his own doctrine
established in his lifetime."

In one important respect Harvey's account of the circulation was
incomplete. He knew nothing of the vessels which we now speak of as
capillaries. Writing to Paul Marquard Slegel, of Hamburg, in 1651, he
says, "When I perceived that the blood is transferred from the veins
into the arteries through the medium of the heart, by a grand mechanism
and exquisite apparatus of valves, I judged that in like manner,
wherever transudation does not take place through the pores of the
flesh, the blood is returned from the arteries to the veins, not
without some other admirable artifice" (_non sine artificio quodam
admirabili_). It was this _artificium admirabile_ of which Harvey was
unable to give a description. On account of the minuteness of their
structure, the capillaries were beyond his sight, aided as it was by a
magnifying glass merely. He indeed demonstrated physiologically the
existence of some such passages; but it remained for a later observer,
with improved appliances, to verify the fact. This was done by Malpighi
in 1661, who saw in the lung of a frog, which was so mounted in a frame
as to be viewed by transmitted light, the network of capillaries which
connect the last ramifications of the arteries with the radicles of the
veins.

Harvey rightly denied that the arteries possessed any pulsific power of
their own, and maintained that their pulse is owing solely to the sudden
distension of their walls by the blood thrown into them at each
contraction of the ventricles. But the remission which succeeds the
pulse was regarded by him as caused simply by collapse of the walls of
the arteries due to elastic reaction. Knowing nothing of the muscular
coat of the arteries, he was unaware of the fact that the elastic
reaction of the arteries, after their distension, is aided by the tonic
contractility of their walls; the two forces, physical and vital, acting
in concert with each other--the former converting the intermittent flow
from the heart into an even stream in the capillaries and veins; the
latter, through the vaso-motor system, regulating the flow of blood to
particular parts in order to meet changing requirements.

It is somewhat surprising to find that such an accurate observer as
Harvey should have failed to recognize the significance and importance
of the system of l