Harvey Discovers The Circulation Of The Blood
Author: Huxley, Thomas H.
Harvey Discovers The Circulation Of The Blood
1616
Contemporary with Galileo, and ranking but little below him in influence
upon the modern world, was William Harvey. Harvey's discovery of the
circulation of the blood, combined with the truly scientific methods by which
he reached, and afterward proved, his great result, has placed his name high
on the roll of science. Not only does his work stand at the foundation of
modern anatomy and medicine, but it has given him place in the ranks of great
philosophers as well. Huxley, himself so long and justly renowned in modern
science, rises to enthusiasm in the following account of his mighty
predecessor.
Harvey was born at Folkestone, England, in 1578, and lived till 1657. He
was educated as a physician, studying at Padua in Italy, and was early
appointed a lecturer in the London College of Physicians. In his lectures,
somewhere about the year 1616 or a little later, he began to explain his new
doctrine to his students; but it was not until the publication of his book
Exercitatio Anatomica de Motu Cordis et Sanguinis, in 1628, that the theory
spread beyond his immediate circle.
Huxley's account will perhaps give a clearer idea of Harvey's relation to
his predecessors and contemporaries, and of the value of his services to
mankind, than would a far longer biography of the great physician,
physiologist, and anatomist.
Many opinions have been held respecting the exact nature and value of
Harvey's contributions to the elucidation of the fundamental problem of the
physiology of the higher animals; from those which deny him any merit at all -
indeed, roundly charge him with the demerit of plagiarism - to those which
enthrone him in a position of supreme honor among great discoverers in
science. Nor has there been less controversy as to the method by which Harvey
obtained the results which 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 hypothesis that this is their normal condition, and that during
life they are filled with air. And it will be observed that it is not
improbable that Erasistratus' discovery of the valves of the heart and of
their mechanical action strengthened him in this view. For, as the arteria
venosa branches out in the lungs, what more likely than that its ultimate
ramifications absorb the air which is inspired; and that this air, passing
into the left ventricle, is then pumped all over the body through the aorta,
in order to supply the vivifying principle which evidently resides in the air;
or, it may be, of cooling the too great heat of the blood? How easy to
explain the elastic bounding feel of a pulsating artery by the hypothesis that
it is full of air! Had Erasistratus only been acquainted with the structure
of insects, the analogy of their tracheal system would have been a tower of
strength to him. There was no prima-facie absurdity in his hypothesis - and
experiment was the sole means of demonstrating its truth or falsity.
More than four hundred years elapsed before the theory of the motion of
the blood returned once more to the strait road which leads truthward; and it
was brought back by the only possible method, that of experiment. A man of
extraordinary genius, Claudius Galenus, of Pergamus, was trained to anatomical
and physiological investigation in the great schools of Alexandria, and spent
a long life in incessant research, teaching, and medical practice. More than
one hundred fifty treatises from his pen, on philosophical, literary,
scientific, and practical topics, are extant; and there is reason to believe
that they constitute not more than a third of his works. No former anatomist
had reached his excellence, while he may be regarded as the founder of
experimental physiology. And it is precisely because he was a master of the
experimental method that he was able to learn more about the motions of the
heart and of the blood than any of his predecessors, and to leave to posterity
a legacy of knowledge which was not substantially increased for more than
thirteen hundred years.
The conceptions of the structures of the heart and vessels, of their
actions, and of the motions of the blood in them, which Galen entertained, are
not stated in a complete shape in any one of his numerous works. But a
careful collation of the various passages in which these conceptions are
expressed leaves no doubt upon my mind that Galen's views respecting the
structure of the organs concerned were, for the most part, as accurate as the
means of anatomical analysis at his command permitted; and that he had exact
and consistent, though by no means equally just, notions of the actions of
these organs and of the movements of the blood.
Starting from the fundamental facts established by Erasistratus
respecting the structure of the heart and the working of its valves, Galen's
great service was the proof, by the only evidence which could possess
demonstrative value; namely, by that derived from experiments upon living
animals, that the arteries are as much full of blood during life as the veins
are, and that the left cavity of the heart, like the right, is also filled
with blood.
Galen, moreover, correctly asserted - though the means of investigation
at his disposition did not allow him to prove the fact - that the
ramifications of the vena arteriosa in the substance of the lungs communicate
with those of the arteria venosa, by direct, though invisible, passages, which
he terms anastomoses; and that, by means of these communications, a certain
portion of the blood of the right ventricle of the heart passes through the
lungs into the left ventricle. In fact, Galen is quite clear as to the
existence of a current of blood through the lungs, though not of such a
current as we now know traverses them. For, while he believed that a part of
the blood of the right ventricle passes through the lungs, and even, as I
shall show, described at length the mechanical arrangements by which he
supposes this passage to be effected, he considered that the greater part of
the blood in the right ventricle passes directly, through certain pores in the
septum, into the left ventricle. And this was where Galen got upon his wrong
track, without which divergence a man of his scientific insight must
infallibly have discovered the true character of the pulmonary current, and
not improbably have been led to anticipate Harvey.
The best evidence of the state of knowledge respecting the motions of the
heart and blood in Harvey's time is afforded by those works of his
contemporaries which immediately preceded the publication of the Exercitatio
Anatomica, in 1628. And none can be more fitly cited for this purpose than
the de Humani Corporis Fabrica, Book X, of Adrian van den Spieghel, who, like
Harvey, was a pupil of Fabricius of Aquapendente, and was of such
distinguished ability and learning that he succeeded his master in the chair
of anatomy of Padua.
Van den Spieghel, or Spigelius, as he called himself in accordance with
the fashion of those days, died comparatively young, in 1625, and his work was
edited by his friend Daniel Bucretius, whose preface is dated 1627. The
accounts of the heart and vessels, and of the motion of the blood, which it
contains, are full and clear; but, beyond matters of detail, they go beyond
Galen in only two points; and with respect to one of these, Spigelius was in
error.
The first point is the "pulmonary circulation," which is taught as
Realdus Columbus taught it nearly eighty years before. The second point is,
so far as I know, peculiar to Spigelius himself. He thinks that the pulsation
of the arteries has an effect in promoting the motion of the blood contained
in the veins which accompany them. Of the true course of the blood as a
whole, Spigelius has no more suspicion than had any other physiologist of that
age, except William Harvey; no rumor of whole lectures at the College of
Physicians, commenced six years before Spieghel's death, was likely in those
days of slow communication and in the absence of periodical publications to
have reached Italy.
Now, let anyone familiar with the pages of Spigelius take up Harvey's
treatise and mark the contrast.
The main object of the Exercitatio is to put forth and demonstrate by
direct experimental and other accessory evidence a proposition which is far
from being hinted at either by Spigelius or by any of his contemporaries or
predecessors, and which is in diametrical contradiction to the views
respecting the course of the blood in the veins which are expounded in their
works.
From Galen to Spigelius, they one and all believed that the blood in the
vena cava and its branches flows from the main trunk toward the smaller
ramifications. There is a similar consensus in the doctrine that the greater
part, if not the whole, of the blood thus distributed by the veins is derived
from the liver; in which organ it is generated out of the materials brought
from the alimentary canal by means of the vena portae. And all Harvey's
predecessors further agree in the belief that only a small fraction of the
total mass of the venous blood is conveyed by the vena arteriosa to the lungs
and passes by the arteria venosa to the left ventricle, thence to be
distributed over the body by the arteries. Whether some portion of the
refined and "pneumatic" arterial blood traversed the anastomotic channels, the
existence of which was assumed, and so reached the systemic veins, or whether,
on the contrary, some portion of the venous blood made its entrance by the
same passages into the arteries, depended upon circumstances. Sometimes the
current might set one way, sometimes the other.
In direct opposition to these universally received views Harvey asserts
that the natural course of the blood in the veins is from the peripheral
ramifications toward the main trunk; that the mass of the blood to be found in
the veins at any moment was a short time before contained in the arteries, and
has simply flowed out of the latter into the veins; and, finally, that the
stream of blood which runs from the arteries into the veins is constant,
continuous, and rapid.
According to the view of Harvey's predecessors, the veins may be compared
to larger and smaller canals, fed by a spring which trickles into the chief
canals, whence the water flows to the rest. The heart and lungs represent an
engine set up in the principal canal to aerate some of the water and scatter
it all over the garden. Whether any of this identical water came back to the
engine or not would be a matter of chance, and it would certainly have no
sensible effect on the motion of the water in the canals. In Harvey's
conception of the matter, on the other hand, the garden is watered by channels
so arranged as to form a circle, two points of which are occupied by
propulsive engines. The water is kept moving in a continual round within its
channels, as much entering the engines on one side as leaves them on the
other; and the motion of the water is entirely due to the engines.
It is in conceiving the motion of the blood, as a whole, to be circular,
and in ascribing that circular motion simply and solely to the contractions of
the walls of the heart, that Harvey is so completely original. Before him, no
one, that I can discover, had ever so much as dreamed that a given portion of
blood, contained, for example, in the right ventricle of the heart, may, by
the mere mechanical operation of the working of that organ, be made to return
to the very place from which it started, after a long journey through the
lungs and through the body generally. And it should be remembered that it is
to this complete circuit of the blood alone that the term "circulation" can,
in strictness, be applied. It is of the essence of a circular motion that
that which moves returns to the place from whence it started. Hence the
discovery of the course of the blood from the right ventricle, through the
lungs, to the left ventricle was in no wise an anticipation of the discovery
of the circulation of the blood. For the blood which traverses this part of
its course no more describes a circle than the dweller in a street who goes
out of his own house and enters his next-door neighbor's does so. Although
there may be nothing but a party wall between him and the room he has just
left, it constitutes an efficient defense de circuler. Thus, whatever they
may have known of the so-called pulmonary circulation, to say that Servetus or
Columbus or Caesalpinus deserves any share of the credit which attaches to
Harvey appears to me to be to mistake the question at issue.
It must further be borne in mind that the determination of the true
course taken by the whole mass of the blood is only the most conspicuous of
the discoveries of Harvey; and that his analysis of the mechanism by which the
circulation is brought about is far in advance of anything which had
previously been published. For the first time it is shown that the walls of
the heart are active only during its systole or contraction, and that the
dilatation of the heart, in the diastole, is purely passive. Whence it
follows that the impulse by which the blood is propelled is a vis a lergo, and
that the blood is not drawn into the heart by any such inhalent or suctorial
action as not only the predecessors, but many of the successors, of Harvey
imagined it to possess.
Harvey is no less original in his view of the cause of the arterial
pulse. In contravention of Galen and of all other anatomists up to his own
time, he affirms that the stretching of the arteries which gives rise to the
pulse is not due to the active dilatation of their walls, but to their passive
distention by the blood which is forced into them at each beat of the heart;
reversing Galen's dictum, he says that they dilate as bags and not as bellows.
This point of fundamental, practical as well as theoretical, importance is
most admirably demonstrated, not only by experiment, but by pathological
illustrations.
One of the weightiest arguments in Harvey's demonstration of the
circulation is based upon the comparison of the quantity of blood driven out
of the heart, at each beat, with the total quantity of blood in the body.
This, so far as I know, is the first time that quantitative considerations are
taken into account in the discussion of a physiological problem. But one of
the most striking differences between ancient and modern physiological
science, and one of the chief reasons of the rapid progress of physiology in
the last half-century, lies in the introduction of exact quantitative
determinations into physiological experimentation and observation. The
moderns use means of accurate measurement which their forefathers neither
possessed nor could conceive, inasmuch as they are products of mechanical
skill of the last hundred years, and of the advance of branches of science
which hardly existed, even in germ, in the seventeenth century.
Having attained to a knowledge of the circulation of the blood, and of
the conditions on which its motion depends, Harvey had a ready deductive
solution for problems which had puzzled the older physiologists. Thus the
true significance of the valves in the veins became at once apparent. Of no
importance while the blood is flowing in its normal course toward the heart,
they at once oppose any accidental reveral of its current which may arise from
the pressure of adjacent muscles or the like. And in like manner the swelling
of the veins on the further side of the ligature, which so much troubled
Caesalpinus, became at once intelligible as the natural result of the damming
up of the returning current.
In addition to the great positive results which are contained in the
treatise which Harvey modestly calls an Exercise and which is, in truth, not
so long as many a pamphlet about some wholly insignificant affair, its pages
are characterized by such precision and simplicity of statement, such force of
reasoning, and such a clear comprehension of the methods of inquiry and of the
logic of physical science, that it holds a unique rank among physiological
monographs. Under this aspect, I think I may fairly say that it has rarely
been equalled and never surpassed.
Such being the state of knowledge among his contemporaries, and such the
immense progress effected by Harvey, it is not wonderful that the publication
of the Exercitatio produced a profound sensation. And the best indirect
evidence of the originality of its author, and of the revolutionary character
of his views, is to be found in the multiplicity and the virulence of the
attacks to which they were at once subjected.
Riolan, of Paris, had the greatest reputation of any anatomist of those
days, and he followed the course which is usually adopted by the men of
temporary notoriety toward those of enduring fame. According to Riolan,
Harvey's theory of the circulation was not true; and besides that, it was not
new; and, furthermore, he invented a mongrel doctrine of his own, composed of
the old views with as much of Harvey's as it was safe to borrow, and tried
therewith to fish credit for himself out of the business. In fact, in wading
through these forgotten controversies, I felt myself quite at home. Substitute
the name of Darwin for that of Harvey, and the truth that history repeats
itself will come home to the dullest apprehension. It was said of the
doctrine of the circulation of the blood that nobody over forty could be got
to adopt it; and I think I remember a passage in the Origin of Species to the
effect that its author expects to convert only young and flexible minds.
There is another curious point of resemblance in the fact that even those
who gave Harvey their general approbation and support sometimes failed to
apprehend the value of some of those parts of his doctrine which are, indeed,
merely auxiliary to the theory of the circulation, but are only a little less
important than it. Harvey's great friend and champion, Sir George Ent, is in
this case; and I am sorry to be obliged to admit that Descartes falls under
the same reprehension.
This great philosopher, mathematician, and physiologist, whose conception
of the phenomena of life as the results of mechanism is now playing as great a
part in physiological science as Harvey's own discovery, never fails to speak
with admiration, as Harvey gratefully acknowledges, of the new theory of the
circulation. And it is astonishing - I had almost said humiliating - to find
that even he is unable to grasp Harvey's profoundly true view of the nature of
the systole and the diastole, or to see the force of the quantitative
argument. He adduces experimental evidence against the former position, and
is even further from the truth than Galen was, in his ideas of the physical
cause of the circulation.
Yet one more parallel with Darwin. In spite of all opposition, the
doctrine of the circulation propounded by Harvey was, in its essential
features, universally adopted within thirty years of the time of its
publication. Harvey's friend, Thomas Hobbes, remarked that he was the only
man, in his experience, who had the good-fortune to live long enough to see a
new doctrine accepted by the world at large.
It is, I believe, a cherished belief of Englishmen that Francis Bacon,
Viscount St. Albans and sometime lord chancellor of England, invented that
"inductive philosophy" of which they speak with almost as much respect as they
do of church and state; and that, if it had not been for this "Baconian
induction," science would never have extricated itself from the miserable
condition in which it was left by a set of hair-splitting folk known as the
ancient Greek philosophers. To be accused of departing from the canons of the
Baconian philosophy is almost as bad as to be charged with forgetting your
aspirates; it is understood as a polite way of saying that you are an entirely
absurd speculator.
Now the Novum Organon was published in 1620, while Harvey began to teach
the doctrine of the circulation, in his public lectures, in 1619. Acquaintance
with the Baconian induction, therefore, could not have had much to do with
Harvey's investigations. The Exercitatio, however, was not published till
1628. Do we find in it any trace of the influence of the Novum Organon?
Absolutely none. So far from indulging in the short-sighted and profoundly
unscientific depreciation of the ancients in which Bacon indulges, Harvey
invariably speaks of them with that respect which the faithful and intelligent
study of the fragments of their labors that remain to us must inspire in
everyone who is practically acquainted with the difficulties with which they
had to contend, and which they so often mastered. And, as to method, Harvey's
method is the method of Galen, the method of Realdus Columbus, the method of
Galileo, the method of every genuine worker in science either in the past or
the present. On the other hand, judged strictly by the standard of his own
time, Bacon's ignorance of the progress which science had up to that time made
is only to be equalled by his insolence toward men in comparison with whom he
was the merest sciolist. Even when he had some hearsay knowledge of what has
been done, his want of acquaintance with the facts and his abnormal deficiency
in what I may call the scientific sense, prevent him from divining its
importance. Bacon could see nothing remarkable in the chief contributions to
science of Copernicus or of Kepler or of Galileo; Gilbert, his
fellow-countryman, is the subject of a sneer; while Galen is bespattered with
a shower of impertinences, which reach their climax in the epithets "puppy"
and "plague".
I venture to think that if Francis Bacon, instead of spending his time in
fabricating fine phrases about the advancement of learning, in order to play,
with due pomp, the part which he assigned to himself of "trumpeter" of
science, had put himself under Harvey's instructions, and had applied his
quick wit to discover and methodize the logical process which underlaid the
work of that consummate investigator, he would have employed his time to
better purpose, and, at any rate, would not have deserved the just but sharp
judgment which follows: "that his [Bacon's] method is impracticable cannot I
think be denied, if we reflect, not only that it has never produced any
result, but also that the process by which scientific truths have been
established cannot be so presented as even to appear to be in accordance with
it." I quote from one of Mr. Ellis' contributions to the great work of Bacon's
most learned, competent, and impartial biographer, Mr. Spedding.
Few of Harvey's saying are recorded, but Aubrey tells us that someone
having enlarged upon the merits of the Baconian philosophy in his presence,
"Yes," said Harvey, "he writes philosophy like a chancellor." On which pithy
reply diverse persons will put diverse interpretations. The illumination of
experience may possibly tempt a modern follower of Harvey to expound the dark
saying thus: "So this servile courtier, this intriguing politician, this
unscrupulous lawyer, this witty master of phrases proposes to teach me my
business in the intervals of his. I have borne with Riolan; let me also be
patient with him." At any rate, I have no better reading to offer.
In the latter half of the sixteenth and the beginning of the seventeenth
centuries the future of physical science was safe enough in the hands of
Gilbert, Galileo, Harvey, Descartes, and the noble army of investigators who
flocked to their standard and followed up the advance of their leaders. I do
not believe that their wonderfully rapid progress would have been one whit
retarded if the Novum Organon had never seen the light; while, if Harvey's
little Exercise had been lost, physiology would have stood still until another
Harvey was born into the world.
