The Circulation of the Blood
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Thomas H. Huxley >> The Circulation of the Blood
If anybody wants to understand what Harvey's great desert really was, I
would suggest to him that he devote himself to a course of reading,
which I cannot promise shall be very entertaining, but which, in this
respect at any rate, will be highly instructive--namely, the works of
the anatomists of the latter part of the 16th century and the beginning
of the 17th century. If anybody will take the trouble to do that which
I have thought it my business to do, he will find that the doctrines
respecting the action of the heart and the motion of the blood which
were taught in every university in Europe, whether in Padua or in Paris,
were essentially those put forward by Galen, 'plus' the discovery of
the pulmonary course of the blood which had been made by Realdus
Columbus. In every chair of anatomy and physiology (which studies were
not then separated) in Europe, it was taught that the blood brought to
the liver by the portal vein, and carried out of the liver to the 'vena
cava' by the hepatic vein, is distributed from the right side of the
heart, through the other veins, to all parts of the body; that the
blood of the arteries takes a like course from the heart towards the
periphery; and that it is there, by means of the 'anastomoses', more or
less mixed up with the venous blood. It so happens, by a curious
chance, that up to the year 1625 there was at Padua, which was Harvey's
own university, a very distinguished professor, Spigelius, whose work
is extant, and who teaches exactly what I am now telling you. It is
perfectly true that, some time before, Harvey's master, Fabricius, had
not only re-discovered, but had drawn much attention to certain
pouch-like structures, which are called the valves of the veins, found
in the muscular parts of the body, all of which are directed towards
the heart, and consequently impede the flow of the blood in the
opposite direction. And you will find it stated by people who have not
thought much about the matter, that it was this discovery of the valves
of the veins which led Harvey to imagine the course of the circulation
of the blood. Now it did not lead Harvey to imagine anything of the
kind. He had heard all about it from his master, Fabricius, who made a
great point of these valves in the veins, and he had heard the theories
which Fabricius entertained upon the subject, whose impression as to
the use of the valves was simply this--that they tended to take off any
excess of pressure of the blood in passing from the heart to the
extremities; for Fabricius believed, with the rest of the world, that
the blood in the veins flowed from the heart towards the extremities.
This, under the circumstances, was as good a theory as any other,
because the action of the valves depends altogether upon the form and
nature of the walls of the structures in which they are attached; and
without accurate experiment, it was impossible to say whether the
theory of Fabricius was right or wrong. But we not only have the
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 acquainted--it occupies between 50 and 60 pages of a
small quarto in Latin, and is as terse and concise as it possibly can
be--when 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
qualities--intellectual 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 peculiarity--for it gets you into all
sorts of difficulties with all sorts of people--but, 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
that--in accordance with the views of Columbus--the 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 vents--then from the roots of the veins it goes into the
trunk and veins--then to the right side of the heart--and 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 heart--that it is the propelling
apparatus--and 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 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 that was
the most that he seems to have known anything about, or that was
accessible to him at that day. And so it came about, that, although he
examined the course of the blood in many of the lower animals--watched
the pulsation of the heart in shrimps, and animals of that kind--he
never could put the final coping-stone on his edifice. He did not know
to the day of his death, although quite clear about the fact that the
arteries and the veins do communicate, how it is that they
communicate--how it was that the blood of the arteries passed into the
veins. One is grieved to think that the grand old man should have gone
down to his tomb without the vast satisfaction it would have given to
him to see what the Italian naturalist Malpighi showed only seven years
later, in 1664, when he demonstrated, in a living frog, the actual
passage of the blood from the ultimate ramifications of the arteries
into the veins. But that absolute ocular demonstration of the truth of
the views he had maintained throughout his life it was not granted to
Harvey to see. What he did experience was this: that on the
publication of his doctrines, they were met with the greatest possible
opposition; and I have no doubt savage things were uttered in those old
controversies, and that a great many people said that these new-fangled
doctrines, reducing living processes to mere mechanism, would sap the
foundations of religion and morality. I do not know for certain that
they did, but they said things very like it. The first point was to
show that Harvey's views were absolutely untrue; and not being able to
succeed in that, opponents said they were not new; and not being able
to succeed in that, that they didn't matter. That is the usual course
with all new discoveries. But Harvey troubled himself very little
about these things. He remained perfectly quiet; for although reputed
a hot-tempered man, he never would have anything to do with controversy
if he could help it; and he only replied to one of his antagonists
after twenty years' interval, and then in the most charming spirit of
candour and moderation. But he had the great satisfaction of living to
see his doctrine accepted upon all sides. At the time of his death,
there was not an anatomical school in Europe in which the doctrine of
the circulation of the blood was not taught in the way in which Harvey
had laid it down. In that respect he had a happiness which is granted
to very few men.
I have said that the other great investigation of Harvey is not one
which can be dealt with to a general audience. It is very complex, and
therefore I must ask you to take my word for it that, although not so
fortunate an investigation, not so entirely accordant with later results
as the doctrine of the circulation; yet that still, this little
treatise of Harvey's has in many directions exerted an influence hardly
less remarkable than that exerted by the Essay upon the Circulation of
the Blood.
And now let me ask your attention to two or three closing remarks.
If you look back upon that period of about 100 years which commences
with Harvey's birth--I mean from the year 1578 to 1680 or
thereabouts--I think you will agree with me, that it constitutes one of
the most remarkable epochs in the whole of that thousand years which we
may roughly reckon as constituting the history of Britain. In the
commencement of that period, we may see, if not the setting, at any
rate the declension of that system of personal rule which had existed
under previous sovereigns, and which, after a brief and spasmodic
revival in the time of George the Third, has now sunk, let us hope,
into the limbo of forgotten things. The latter part of that 100 years
saw the dawn of that system of free government which has grown and
flourished, and which, if the men of the present day be the worthy
descendants of Eliott and Pym, and Hampden and Milton, will go on
growing as long as this realm lasts. Within that time, one of the
strangest phenomena which I think I may say any nation has ever
manifested arose to its height and fell--I mean that strange and
altogether marvellous phenomenon, English Puritanism. Within that
time, England had to show statesmen like Burleigh, Strafford, and
Cromwell--I mean men who were real statesmen, and not intriguers,
seeking to make a reputation at the expense of the nation. In the
course of that time, the nation had begun to throw off those swarms of
hardy colonists which, to the benefit of the world--and as I fancy, in
the long run, to the benefit of England herself--have now become the
United States of America; and, during the same epoch, the first
foundations were laid of that Indian Empire which, it may be, future
generations will not look upon as so happy a product of English
enterprise and ingenuity. In that time we had poets such as Spenser,
Shakespere, and Milton; we had a great philosopher, in Hobbes; and we
had a clever talker about philosophy, in Bacon. In the beginning of
the period, Harvey revolutionized the biological sciences, and at the
end of it, Newton was preparing the revolution of the physical sciences.
I know not any period of our history--I doubt if there be any period of
the history of any nation--which has precisely such a record as this to
show for a hundred years. But I do not recall these facts to your
recollection for a mere vainglorious purpose. I myself am of opinion
that the memory of the great men of a nation is one of its most precious
possessions--not because we have any right to plume ourselves upon
their having existed as a matter of national vanity, but because we
have a just and rational ground of expectation that the race which has
brought forth such products as these may, in good time and under
fortunate circumstances, produce the like again. I am one of those
people who do not believe in the natural decay of nations. I believe,
to speak frankly, though perhaps not quite so politely as I could
wish--but I am getting near the end of my lecture--that the whole
theory is a speculation invented by cowards to excuse knaves. My
belief is, that so far as this old English stock is concerned it has in
it as much sap and vitality and power as it had two centuries ago; and
that, with due pruning of rotten branches, and due hoeing up of weeds,
which will grow about the roots, the like products will be yielded
again. The "weeds" to which I refer are mainly three: the first of
them is dishonesty, the second is sentimentality, and the third is
luxury. If William Harvey had been a dishonest man--I mean in the high
sense of the word--a man who failed in the ideal of honesty--he would
have believed what it was easiest to believe--that which he received on
the authority of his predecessors. He would not have felt that his
highest duty was to know of his own knowledge that that which he said
he believed was true, and we should never have had those
investigations, pursued through good report and evil report, which ended
in discoveries so fraught with magnificent results for science and for
man. If Harvey had been a sentimentalist--by which I mean a person of
false pity, a person who has not imagination enough to see that great,
distant evils may be much worse than those which we can picture to
ourselves, because they happen to be immediate and near (for that, I
take it, is the essence of sentimentalism)--if Harvey had been a person
of that kind, he, being one of the kindest men living, would never have
pursued those researches which, as he tells us over and over again, he
was obliged to pursue in order to the ascertainment of those facts which
have turned out to be of such inestimable value to the human race; and
I say, if on such grounds he had failed to do so, he would have failed
in his duty to the human race. The third point is that Harvey was
devoid of care either for wealth, or for riches, or for ambition. The
man found a higher ideal than any of these things in the pursuit of
truth and the benefit of his fellow-men. If we all go and do likewise,
I think there is no fear for the decadence of England. I think that our
children and our successors will find themselves in a commonwealth,
different it may be from that for which Eliott, and Pym, and Hampden
struggled, but one which will be identical in the substance of its
aims--great, worthy, and well to live in.