CHAPTER XXIX. The Contributions Made by Different Men During the Renaissance,

THE CONTRIBUTIONS MADE BY DIFFERENT MEN DURING THE RENAISSANCE, AND MORE PARTICULARLY BY WILLIAM HARVEY OF ENGLAND, TO OUR KNOWLEDGE OF THE CIRCULATION OF THE BLOOD, LYMPH AND CHYLE

Among the earliest known doctrines relating to the nature of the blood and its mode of distribution throughout the body are those attributed to Erasistratus and Galen; for the still more ancient ones, of which Diogenes of Apollonia, Aristotle and the Hippocratic writers are reputed to be the authors, are too incomplete to call for serious consideration in this place.

(a) The Doctrine Taught by Erasistratus.--Erasistratus, who was born at Julis in the Island of Ceos (Aegean Sea) during the third century before Christ, held the belief that the arteries contain only air, which is drawn into the lungs by way of the trachea and bronchi, whence it enters the pulmonary vein (called by him the “venous artery”). In its further course this air passes from the pulmonary vein into the left ventricle of the heart, and is then conveyed from that organ through the arteries to the different tissues of the body. Erasistratus further taught that the smallest subdivisions of both the arteries and the veins lie side by side in the tissues, and that, in certain abnormal bodily conditions, they communicate the one with the other through anastomoses; but that, in a normal condition of the body, no communication takes place between the two. In common with all other physicians of that time, he believed that only the veins carry blood. Here, then, we find the first glimmering of the truth with regard to the nature of the circulating medium and also with regard to the course which it pursues in one part of its circuit--that part, namely, where the two kinds of vessels become capillary in character. His substitution of air for blood in the arteries is plainly the principal error in his scheme.

(b) The Teaching of Galen and of Caesalpinus with Regard to the Nature of the Blood and Its Mode of Distribution.--Galen, in the second century of the present era, disputed the correctness of the doctrine taught by Erasistratus. His objections are thus stated: “Inasmuch as blood flows from an artery when it is wounded, one of two things must be the truth. Either blood was already contained in the vessel before it was wounded, or it must have found its way in from the outside. But, if the blood comes from the outside into a vessel which contains only air, then air must necessarily escape from that vessel (when wounded) before blood does--which is contrary to the fact, as blood alone flows out. Therefore arteries contain only blood.” As a further proof of the correctness of his statement Galen carried out the following experiment: In a living animal he placed two ligatures around an artery at points situated not far apart, and then made an opening in the vessel between the two ligatures. The intervening section of the artery, it was thus found, contained only blood. This experiment, it might reasonably be supposed, would have definitely settled the question; but such was not the case. The followers of Erasistratus immediately raised this objection: If the arteries contain blood, how may the air which is drawn into the lungs find its way to all parts of the body? Galen replied that the inhaled air does not pass through the lungs, but is rejected by them after it has cooled the blood. This refrigerating process, he claimed, constitutes the sole purpose of the respiratory act.

Although Galen’s idea regarding the true function of respiration is not in harmony with the doctrine taught by modern physiologists, it nevertheless represents a marked advance over the belief previously maintained. Even as recently as in the time of Albert von Haller (approximately 1760–1780) physicians still continued to believe that it was the function of respiration to cool the blood; and indeed it was scarcely possible before 1800 to offer a more correct physiology of the act of breathing, for it was not until after the lapse of many centuries that the advance in our knowledge of chemistry reached a point at which it became possible to find a satisfactory solution of so complicated a problem.

As to the nature of the blood itself Galen believed, as I have already stated more fully in Part I. (“Ancient Medicine”), that there are two kinds--spirituous blood (or spirit) and venous blood. He gave the name of spirituous blood to that which is found circulating in the arteries, and which is appreciably brighter in color than that which fills the veins. According to Flourens, the distinguished French physiologist of the nineteenth century, Galen was the first among the ancient anatomists to make this distinction of two different kinds of blood. To the spirituous variety Galen ascribed the function of nourishing the more delicately constructed organs like the lungs, while he claimed that the venous blood is suited to nourish only the coarser ones, like the liver, spleen, etc.

In his further development of a physiology of the circulation of the blood Galen, who as a rule expresses his ideas with great clearness, makes statements which I find it extremely difficult to comprehend. I am therefore tempted to assume that the copyists, to whom we are indebted for handing down his actual words from age to age, are the persons upon whom should be cast the blame for the obscurity of which I complain. However this may be, it is an unquestionable fact that the ablest physiologists, were they to be confronted to-day with the duty of solving this problem of the circulation under the conditions of knowledge which existed during the third century of our era, would surely not be able to provide a more correct solution than that which is credited to Galen. The problem was attacked repeatedly by some of the brightest and best-equipped minds of the Renaissance period, but not one of these exceptionally clever men was able to offer an entirely acceptable solution. Harvey alone, as will appear farther on in this account, solved the riddle once and for all.

The “spirit”--the purest part of the blood--is lodged, according to Galen, in the left ventricle; and, inasmuch as even the venous blood, if it is to fulfil in some degree the function of a nourishing fluid, must possess a certain proportion of “spirit,” it is clear that the two ventricles should communicate the one with the other; for how otherwise--thought Galen--is it possible for a certain amount of “spirit” to commingle with the venous blood? The locality at which this communication was assumed to exist was the interventricular septum; and, as nobody was able to find anything like a foramen in this membrane, it was asserted that the communication is effected through an infinite number of pores. For over one thousand years physicians accepted this porous character of the interventricular septum as an established fact. In his commentaries on Mondino’s “Anatomy” (1521), Berengarius of Carpi timidly ventured the statement that the openings of communication are not distinctly visible, and this apparently was the first feeble expression of doubt concerning the correctness of the prevailing doctrine. Vesalius, on the other hand, boldly denied their existence altogether.

According to Galen’s teaching the liver is the source of origin of all the veins, just as the heart is the starting-point of all the arteries. It is quite remarkable, says Flourens, that physicians who performed almost daily the operation of venesection should, during a long series of years, have failed to observe that this doctrine of blood flowing through the veins from the liver to the different parts of the body, could not possibly be true, inasmuch as at each such operation the vein always became distended with blood below (i.e., on the distal side of) the ligature which they applied to the part (arm, for example) before opening the vessel. This phenomenon, of course, indicated clearly that the blood in the veins flowed toward the heart, and not from any centrally located spot or organ toward the extremities. And yet--he adds--even so bright and thoughtful a man as Vesalius does not appear to have noticed this fact. Andreas Caesalpinus (1519–1603), on the other hand, did observe and correctly interpret the phenomenon; and he made the further observation that physicians were habitually applying the ligature above the spot which they expected to bleed, regardless of the fact that in so doing they were not acting in harmony with their belief concerning the circulation of blood in the veins. Caesalpinus also states, in one part of his writings, that “the blood, carried to the heart by the veins, receives in that organ its last transformation toward perfection, and is then--in this perfected state--transported by the arteries to the remotest parts of the body.” So far as it relates to the general movement of the blood this statement is correct, but it errs, as will be shown presently, in mentioning the heart as the locality where the perfecting process takes place. In his final remarks regarding the anatomical relations which exist in the two chambers of the heart Caesalpinus makes the following statement:--

Each ventricle possesses two vessels--one through which the blood reaches that chamber, and a second one which serves to carry it out of the ventricle. The vessel through which the blood enters the right ventricle is called the vena cava, and that by which it leaves this same chamber is called the pulmonary artery. The vessel through which the blood arrives in the left ventricle is called the pulmonary vein, and that through which it leaves this left chamber of the heart is known as the aorta.

The Circulation of the Blood as Elucidated by Michael Servetus.--Michael Servetus, a native of Villanueva, Spain, who in 1553 was burned alive at the stake near the city of Geneva, Switzerland, because of his heretical teachings, is not infrequently mentioned as the individual to whom credit is due for having furnished the first description of the lesser or pulmonary circulation. There is no question whatever regarding the justice of according to him at least a part of this honor, but one should be careful to specify that Servetus is entitled only to the credit of having been the first to teach that the blood, in its journey from the right to the left side of the heart, must pass entirely through the lungs. So far, his doctrine is correct; but he also taught at the same time that the fluid which enters the aorta from the left ventricle is not blood but perfected “vital spirit” (Galen), and that it becomes genuine blood only after it has tarried for a few brief instants in the ventricular chamber and has there been subjected to some unknown influence exerted by the heart itself. This second erroneous part of Servetus’ description seems to me to diminish very materially the credit to which he is otherwise entitled; and I cannot help feeling that Dezeimeris is right when he claims that Realdus Columbus, whose more perfect account of the lesser circulation was written only a little later than that of Servetus, is perhaps better entitled to the honor in question.

It is an interesting fact that Servetus introduces his disquisition on the circulation of the blood in the very midst of a treatise which bears the title “Restitution of Christianity,”--in other words, in a treatise which would never, under ordinary circumstances, be consulted by physicians in their search for information regarding an important problem in physiology like that of the circulation of the blood. In this physiologico-theological treatise Servetus, who--as I omitted to state--was a theologian as well as a physiologist, used the following expressions:--

The soul, says Holy Writ, is in the blood; as a matter of fact, the soul is the blood. And since the soul is in the blood, one should--if one wishes to learn how the soul is formed--endeavor to learn how the blood is formed; and, in order to learn how the blood is formed, it is necessary to ascertain how it moves. (Flourens.)

I am unable to state whether it was this particular chapter, or the work taken as a whole, which appeared to the ecclesiastical authorities--first those of France and afterward those of Geneva--to warrant the author’s condemnation as a heretic. And, when we are disposed to blame severely those bigots who, in the fifteenth and sixteenth centuries, manifested such a keen desire to destroy “heretics,” let us remember, with a proper sense of shame, that we still have in our midst, in this twentieth century and in this “land of freedom,” men of high social standing who are as virulent heresy-hunters as ever were the enemies of Servetus.

Experiments of Realdus Columbus.--Matthaeus Realdus Columbus, who was born at Cremona, Northern Italy, in the early part of the sixteenth century, acted for some time as Vesalius’ prosector, and must therefore have had ample opportunities for acquiring a thorough knowledge of the experimental method of studying questions in physiology. He wrote a description of the pulmonary circulation which was more lucid and nearer to the truth than any which his predecessors had furnished. This description, which will be found in his treatise on anatomy (Venice, 1559), was based largely upon experiments that he carried out upon living dogs. As rendered into English from the French version supplied by Dezeimeris, it reads as follows:--

When the heart dilates the blood passes from the vena cava into the right ventricle; from the latter chamber it is pushed into the arterial vein (the pulmonary artery), along which channel it is carried to the lung, there to be properly thinned and mixed with air. Ultimately the blood passes on into the venous artery (= the pulmonary vein), the function of which vessel is to carry this fluid, now charged with air through the action of the lung, into the left ventricle of the heart. Then follows the contraction (systole) of this organ, as a result of which action the tricuspid valves rise up into position and form a dam that prevents the return of the blood into the vena cava and the pulmonary veins. Simultaneously with this action the valves placed at the opening which represents the commencement of the aorta (left ventricle), and those placed at the opening which corresponds to the beginning of the pulmonary artery (right ventricle), yield and thus open the way for the distribution of the blood throughout the rest of the body.

The reader will, I believe, admit that this description, while perhaps not faultless, is distinctly superior to that given by Servetus.

Columbus’ experimental studies threw considerable light upon other matters relating to the physiology of the heart. He demonstrated, for example, that the fluid which enters the left ventricle from the lungs is genuine blood, and he also learned by the same method of investigation the true nature of the systole and diastole of the heart and the relations of these acts to the pulse and to the changes in the position of the heart. The discovery of all these facts constituted a material advance in our knowledge of the physiology of that organ; but, from this time onward, for a period of nearly three-quarters of a century, no further advance was made until William Harvey of England appeared on the scene. The explanation of the failure of such able investigators as Realdus Columbus, Vesalius, Servetus and others to push their researches still further is to be found largely in the fact that they were all still in bondage to the doctrines taught by Galen centuries earlier, and probably more particularly to that dogma which maintains that blood--if it is to be accepted as genuine or fully formed blood--must first have been elaborated in the depths of the liver. The impossibility of harmonizing such a dogma with the facts which by that time were well established, is too plainly evident to warrant further discussion in these pages.

Discovery of Valves in the Larger Veins by Fabricius ab Acquapendente.--The discovery of the presence of valves in the interior of the larger veins is credited by some to Cannani (1546) and by others to Fabricius ab Acquapendente (1574), but the best authorities appear to favor the claim of Fabricius to this honor. There are also a few authorities who maintain that Fra Sarpi, the celebrated monk and scientist of Venice, is entitled to be considered the discoverer of the valves in veins, but Tiraboschi, the historian of Italian literature, makes it clear that this claim is unfounded.

Although it was known to Fabricius that these valves are inclined toward the heart, he does not appear to have appreciated the fact that this arrangement is entirely incompatible with Galen’s doctrine that the flow of venous blood is from the liver toward the extremities; nor did any other anatomist, so far as I am able to learn, discover this incompatibility before it was pointed out by Harvey nearly fifty years later.

William Harvey, Who is Universally Acknowledged to be the Real Discoverer of the Circulation of the Blood.--William Harvey was born at Folkstone, England, in 1578, received his academic education at Caius College, Cambridge, and became a doctor of medicine in 1602, at the age of twenty-four. Four or five years before this event he went to Padua, Italy, to study medicine under Fabricius ab Acquapendente, who was considered at that period to be the ablest and most inspiring teacher of anatomy and physiology in Europe. It was from him, it may safely be assumed, that Harvey learned the importance of studying Nature herself, rather than books, when one is desirous of learning her secrets. Equipped with a thorough knowledge of the methods that may best be employed in making studies of this character, Harvey returned to England at the end of his long stay at Padua. He was soon afterward made a member of the College of Physicians of London, and in 1615 was elected to the Chair of Anatomy and Surgery in that institution. Later still, he was appointed one of the physicians of St. Bartholomew’s Hospital. He also held for several years the position of Court Physician, first to James the First and then to Charles the First. It was during this period of his professional career that he began working in earnest upon the problem of the circulation of the blood, and he kept steadily at this work throughout a period of several years. Among the manuscripts preserved in the British Museum there is one bearing the date of 1616 which shows that Harvey had already at this time reached conclusions which, in all essential respects, agree with those which appear in his final treatise published in 1628. The title of the latter work is, “Exercitatio anatomica de motu cordis et sanguinis in animalibus” (Frankfort, 1628).

Although, as I have shown above, several of the links in the chain of proofs bearing upon this question of the circulation had already been discovered before Harvey began his researches, he was not willing to accept them as proven facts until he had himself tested them thoroughly by the experimental method. Furthermore, they were often disconnected, and this lack of continuity obliged him to supply missing links at several points; in other words, nobody had as yet demonstrated the important fact that the blood travels regularly in an unbroken circuit, and it was to this great task that Harvey devoted himself at the period which we are now considering. He carried out all these investigations with the most painstaking care and made public announcement of his discoveries only after the lapse of an extraordinary length of time; his chief object being that ample opportunity might thereby be afforded for complete verification. The following are among the more important questions which he investigated and to which he furnished satisfactory solutions. He learned, for example, that the auricle and ventricle of each side of the heart do not contract simultaneously but in succession. When the right auricle contracts the blood which it then contains passes into the right ventricle; and when the right ventricle contracts the blood is driven into the pulmonary artery. From this vessel it passes ultimately into the pulmonary vein, and from the latter into the left auricle, which then contracts and drives the blood into the left ventricle. The latter chamber next contracts and forces the blood into the aorta, whence it is carried into all the arteries of the body. From these, in turn, it passes into the veins and thence back to the right auricle of the heart--the point from which it started. He corroborated the finding--by other anatomists who had preceded him--of membranous valves at the spots where the blood passes from one chamber to the other; and he compared these valves to little doors which open to permit the passage of the blood in one direction, but which close when there is any tendency for it to pass in the opposite direction. The valves of the right auricle, for example, allow the blood to pass into the right ventricle, but prevent it from returning into the auricle. Then, further, the valves of the right ventricle permit the blood to pass into the pulmonary artery, but prevent it from returning into the ventricle. The valves of the left auricle permit the blood to pass into the left ventricle, but do not permit it to return into the left auricle. Finally, the valves of the left ventricle allow the blood to pass into the aorta, but prevent it from regurgitating into the same ventricle. The valves with which the veins are equipped permit the blood to travel onward toward the heart, but do not permit it to back up into the arteries.

(After the portrait by Cornelius Jonson.)]

Galen taught that the arteries pulsated by reason of a “pulsific power” which they derive in direct continuity from the tunics of the heart. He tried to prove the correctness of his doctrine by experimental methods, but in this he failed. Harvey was convinced that the arteries do not pulsate by reason of their own inherent power, but by a force of impulsion communicated to the blood at the heart. He refers to this question in the following terms: “When an artery is opened the blood escapes in jets of unequal force; the alternate jets being stronger than the intermediate, and the stronger jets corresponding in time of occurrence, not with the systoles but with the diastoles of the artery. The artery, therefore, must be distended by impulsion, by the shock of the blood. If the artery dilates by reason of its own inherent power, the blood would not be expelled with the maximum force at the very moment when this dilatation occurs.” As evidence of the non-existence of Galen’s assumed “pulsific power,” Harvey mentions the fact that, in the case of a patch-shaped calcification of the crural artery which came under his observation, the pulsation took place as usual, but at a point below (distal to) the edge of the patch. The intervening patch of rigid calcareous matter was not able to prevent the traveling onward of the propelling power.

Harvey next takes up the consideration of the veins, and, after showing that they permit a flow of the contained blood in only one direction,--viz., that from the extremities toward the heart,--he calls attention to certain experiences which he has had: (1) When a cord is tied lightly around a limb the flow of blood is arrested only in the veins, because these vessels are located near the surface of the skin; but, if the cord is tied more tightly, the flow of blood is also arrested in the arteries, which lie at a relatively great depth. (2) When a vein is tied the resulting distension manifests itself only below (i.e., on the distal side of) the ligature; whereas, when an artery is similarly tied, the distension takes place above (i.e., on the proximal side of) the ligature. It is therefore plain that in the veins the blood flows from the individual parts toward the heart, but that in the arteries the flow is in the reverse direction--i.e., from the heart toward the individual parts. “If one reflects upon the nature of the movement of the blood,” says Flourens, “one will promptly realize how speedy it is. Scarcely has the blood entered the heart before it is hurried into the arteries; and then from these vessels it passes in an instant into the veins, from which, with almost equal speed, it finally travels back to the heart again. It is this never-ending movement from one channel into another, and then eventually back to the starting-point, which constitutes the circulation of the blood.... Modern physiology dates from the discovery of the circulation of the blood. Up to the time of this discovery physiologists followed the ancients; they did not dare to walk alone. Harvey had discovered the most beautiful phenomenon in the animal economy.... From this time forward, instead of swearing by Galen and by Aristotle, one had to swear by Harvey!”

Despite the great care which Harvey took to back up his scheme of the circulation of the blood with unimpeachable proofs of its correctness, he was obliged to pass through the same sort of experience as that to which Vesalius and scores of other pioneers in the field of scientific inquiry had been subjected. Two hostile forces stood constantly ready, during that fruitful period of the Renaissance, to attack with merciless bitterness all those who ventured to add new facts to our stock of knowledge in the domain of medicine. On the one side were the many men of small calibre, men filled with jealousy over the successes gained by co-workers in the same field; and on the other was marshaled the host of those who honestly believed that all medical wisdom ended with Galen. Before his death, however (hardly thirty years later), Harvey had the satisfaction of witnessing the almost unanimous acceptance of his dogma concerning the circulation of the blood. Louis the Fourteenth, King of France at this period, was so appreciative of the importance of Harvey’s discoveries that he appointed Dionis, the distinguished French anatomist, to demonstrate to the students of the Medical School of the Jardin des Plantes at Paris the circulation of the blood and other recent discoveries. Descartes (1596–1650), the celebrated French philosopher, paid an even greater compliment to the high character of the work accomplished by Harvey. His words, as quoted by Flourens, are as follows:--

If I am asked why the supply of venous blood does not become exhausted in flowing thus unceasingly into the heart, and why the arteries--since all the blood that passes through the heart must travel along these vessels--do not become filled to overflowing, I can see no good reason why I should not give to this question the very same answer that William Harvey, an English physician, to whom praise is due for having taught ..., has already given. [Then follows the text of Harvey’s reply.]

Our readers have doubtless noted the fact that, while Harvey, as I have endeavored to show in the preceding account, has clearly established his right to be considered the discoverer of the circulation of the blood in all its most essential features, his scheme fails to furnish any information concerning the composition of the blood and the manner in which it is built up into a life-giving fluid. In the minds of some this may seem to be an omission. A moment’s reflection, however, will satisfy any reasonable person that questions of this nature do not form a legitimate part of the problem which Harvey was engaged in solving, and that they therefore should receive separate consideration. Thus, for example, Harvey’s scheme fails to furnish satisfactory information concerning those portions of the circuit where the blood is obliged to travel through a system of communicating capillary channels, as happens in the lungs and in the tissues generally throughout the body. But Harvey had no means at his command for investigating a question of this nature. Capillary blood-vessels are invisible to the naked eye, and may be studied only with the aid of a microscope; but this instrument was not available until long after the time (1605–1616) when Harvey was engaged in carrying out his investigations into the circulation of the blood.

Other Discoveries Relating to the Vascular System.--To Vesalius is due the credit of having discovered the fact that anastomoses exist between the carotids and the vertebral arteries, thus explaining how a man may continue to live even after both carotids have been severed or ligated. His great rival, Fallopius, described these anastomoses in the most detailed manner, and he noted the further fact that an anastomosis with the basilar artery exists.

By the end of the sixteenth century a certain amount of progress had been made toward a correct knowledge of the lymphatics. Bartholomaeus Eustachius, for example, discovered the existence (in horses) of the thoracic duct, but he supposed it to be a vein. His description of this vessel reads as follows:--

In these animals there is a large vessel which extends downward from the inner aspect of the clavicular vein (= left subclavian vein). At the point where it joins the vein it is closed by means of a semicircular valve. This vessel is of a whitish color and it contains a scanty watery fluid. Not far from its starting-point it divides into two branches which very soon, however, join together again, and then, as a single trunk from which no further branches are given off, it passes down along the left side of the spinal column, penetrates the diaphragm, spreads itself out over the aorta, and ends in a manner unknown to me.

About one hundred years later (1647), Jean Pecquet of Dieppe, France, professor in the Medical School of Montpellier, rediscovered (in a dog) this same duct, with its tributary chyle ducts and also its point of entrance into the left subclavian vein; and, as he had rightly interpreted its nature, anatomists by common agreement accorded him the rights of discoverer.

At a still earlier date (1622) Caspar Aselli of Cremona, Northern Italy, professor in the Medical School of Pavia, discovered the chyle ducts. This discovery was made under the following circumstances, which reveal the fact that good luck sometimes plays an important part in the work of the searcher after truth in the departments of anatomy and physiology:--

Aselli was studying the distribution of the recurrent nerves and the movements of the diaphragm in a well-nourished living dog, when his attention was drawn to the presence of a large number of delicate white threads coursing as it were over the surface of the mesentery. Following the accidental injuring of one of these threads there escaped from the wounded structure quite a large quantity of chyle. Aselli, who instantly appreciated the full significance of what had happened, exclaimed, in the presence of the bystanders, “Eureka!” At the time he supposed that these chyle vessels terminated in the liver and contributed in some manner to the elaboration of the blood (in harmony with Galen’s universally accepted theory of sanguification); but later, after he had carried out a carefully conducted series of experiments, he was able to rectify this erroneous belief. (Haeser.)

Galen’s theory of sanguification may be stated as follows: The chyle is received into the veins of the intestinal wall and carried thence to the liver, in which organ they are all gathered together into a single venous trunk which has received the name of “vena portae”--the vein of the gateway. Everything that is destined to enter the liver passes through this portal vein. In the organ itself the chyle undergoes certain modifications, the result of which is, first, to deprive it of its impurities and then, in addition, to effect other changes that convert it into blood. Aselli’s glory, then, consists in his having shown that chyle is taken up from the intestinal mucous membrane by a set of its own vessels, and not by the veins, as taught by Galen.

In 1651 Olaus Rudbeck of Arosen, Sweden, discovered the lymphatics of the intestinal canal and followed their distribution into the lymph nodes; he also established their relations with the thoracic duct and with the venous system.

Thus, thanks to the series of brilliant discoveries made by William Harvey, Realdus Columbus, Fabricius ab Acquapendente, Pecquet, Aselli and a few others, the doctrine of the circulation of the blood and of the part played by the accessory chyle and lymphatic vascular systems, became firmly established before the end of the seventeenth century.