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evidence of the facts themselves that these could tell Harvey nothing
about the circulation； but we have his own distinct declaration as to
the considerations which led him to the true theory of the circulation
of the blood； and amongst these the valves of the veins are not
mentioned。
Fig。 4。The circulation of the blood as demonstrated by Harvey （A。D。
1628）。
Now then we may come to Harvey himself。 When you read Harvey's
treatise； which is one of the most remarkable scientific monographs
with which I am acquaintedit occupies between 50 and 60 pages of a
small quarto in Latin； and is as terse and concise as it possibly can
bewhen you come to look at Harvey's work； you will find that he had
long struggled with the difficulties of the accepted doctrine of the
circulation。 He had received from Fabricius； and from all the great
authorities of the day； the current view of the circulation of the
blood。 But he was a man with that rarest of all
qualitiesintellectual honesty； and by dint of cultivating that great
faculty； which is more moral than intellectual； it had become impossible
for him to say he believed anything which he did not clearly believe。
This is a most uncomfortable peculiarityfor it gets you into all
sorts of difficulties with all sorts of peoplebut； for scientific
purposes； it is absolutely invaluable。 Harvey possessed this
peculiarity in the highest degree； and so it was impossible for him to
accept what all the authorities told him； and he looked into the matter
for himself。 But he was not hasty。 He worked at his new views； and he
lectured about them at the College of Physicians for nine years； he did
not print them until he was a man of fifty years of age； and when he
did print them he accompanied them with a demonstration which has never
been shaken； and which will stand till the end of time。 What Harvey
proved； in short； was this （see Fig。 4）that everybody had made a
mistake； for want of sufficiently accurate experimentation as to the
actual existence of the fact which everybody assumed。 To anybody who
looks at the blood…vessels with an unprejudiced eye it seems so natural
that the blood should all come out of the liver； and be distributed by
the veins to the different parts of the body； that nothing can seem
simpler or more plain； and consequently no one could make up his mind
to dispute this apparently obvious assumption。 But Harvey did dispute
it； and when he came to investigate the matter he discovered that it was
a profound mistake； and that； all this time； the blood had been moving
in just the opposite direction； namely； from the small ramifications of
the veins towards the right side of the heart。 Harvey further found
that； in the arteries； the blood； as had previously been known； was
travelling from the greater trunks towards the ramifications。 Moreover；
referring to the ideas of Columbus and of Galen （for he was a great
student of literature； and did justice to all his predecessors）； Harvey
accepts and strengthens 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
thatin accordance with the views of Columbusthe 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 ventsthen from the roots of the veins it goes into the
trunk and veinsthen to the right side of the heartand 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 heartthat it is the propelling
apparatusand 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 out and collapse。 Harvey said it was
exactly the contrarythe 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 sayingI speak in the presence of
distinguished physiologists； but I am perfectly certain that they will
endorse what I saythat 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 knowI hope it is now a matter of popular knowledgeit is
the foundation of all rational speculation about morbid processes； it
is the on