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 blood; and thirdly, he
was the first person who took a just view of the nature of the pulse.
These are the three great contributions which he made to the science of
physiology; and I shall not err in saying--I speak in the presence of
distinguished physiologists, but I am perfectly certain that they will
endorse what I say--that upon that foundation the whole of our knowledge
of the human body, with the exception of the motor apparatus and the
sense organs, has been gradually built up, and that upon that foundation
the whole rests. And not only does scientific physiology rest upon
it, but everything like scientific medicine also rests upon it. As
you know--I hope it is now a matter of popular knowledge--it is the
foundation of all rational speculation about morbid processes; it is
the only key to the rational interpretation of that commonest of
all indications of disease, the state of the pulse; so that, both
theoretically and practically, this discovery, this demonstration of
Harvey's, has had an effect which is absolutely incalculable, and the
consequences of which will accumulate from age to age until they result
in a complete body of physiological science.

Fig.5.--The junction of the arteries and veins by capillary tubes,
discovered by Malpighi (A.D. 1664).

I regret that I am unable to pursue this subject much further; but there
is one point I should mention. In Harvey's time, the microscope was
hardly invented. It is quite true that in some of his embryological
researches he speaks of having made use of a hand glass; but t