Harvey Discovers the Circulation of the Blood
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Author: Huxley, Thomas.
المُؤلف: توماس هوكسلي.
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 ofGalileo, 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 madeis 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 hasbeen 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 mybusiness 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. Back to Main menu A project by History World International World History Center
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