Discovery Of The Blood's Circulation

William Harvey Lays the Basis of Modern Medicine

Galen

Blood, said the Greek physician Galen in the second century A.D., is manufactured in the liver from the food we eat, and is of two quite different and separate kinds. The two kinds are sucked up from the liver to the heart and sent out to the limbs and organs of the body from the heart’s two sides: the bright red blood through the arteries, far beneath the skin, and the other, darker variety through the veins which lie nearer the surface. The two varieties provide different elements for the nourishment of limbs and organs, and both pass through the lungs on their way, being cooled in the process. Hot blood, straight from the liver, is too fiery, must first be cooled by the air we breathe.
Much illness is caused by this blood being insufficiently cooled, and in cases of this sort the only treat­ment is to drain a little off with leeches, or by actually opening a vein and letting the fiery fluid run away. The blood when it reaches the limbs and organs of the body is used up entirely, and a new supply must constantly be produced in the liver from the food eaten.

William Harvey

This theory, incorrect, and verifiably so, in almost every detail, was subscribed to by the medical profession for fourteen hundred years. It remained for William Harvey, with his essay printed in 1628 under the imposing Latin title Exercitatio Anatomica de Motu Cordis et Sanguinis, to prove otherwise. His discovery, that the blood does not merely travel centrifugally to the extremities, get used up and disappear, but circulates continuously through heart, lungs, arteries and veins, an utterly novel, startling idea, is the basis of modern physiology, modern medicine. With its publication, medicine leapt from the ancient world to the modern, skipping a millennium and a half in the time it took to read the words, if a physician could read them calmly enough, in the seventeenth century, to get to the end: ”What is now to be said on the quantity and source of the blood is so novel and unheard of that I tremble lest I have mankind at large for my opponents. So much doth want and custom become a second nature…”
Harvey, after years of study in Padua, the anatomical workshop, men said, of the world, had estimated the quantity of blood sent out by the heart in each one of its pulses. He had been studying hearts of animals, birds, reptiles and men, noting their four chambers, measuring their dimensions, and he estimated that the amount of blood pumped by that organ was, in the case of an adult man, two fluid ounces with each beat. On average the human heart beat seventy-two times a minute, a fact with which even Galen would not have quarrelled. At that rate, a quantity of 72 x 60 x 2, or 8,640 ounces of blood, would be pumped out by it, in the course of every hour. This, Harvey saw, was three times the weight of the adult body. If all this vast quantity of blood were dissipated, as Galen had stated, if it had to be replaced by food, a man would be eating three times his own weight in every hour of the twenty-four.
This was obviously nonsense; and so it was, in Harvey’s mind, a logical step to a theory in which blood circulated from the heart to the extremities and hack again, before being re-used. The construction of the organ, with its four little chambers, two on each side of a central wall, and its valves which now, to Harvey’s eye, showed the direction in which the blood must flow, made his theory not only tenable but irrefutable. He went on, by a simple class-room experiment, to show that there were valves not only in the heart but in the veins. They were valves which allowed the blood to flow away from the extremities, toward the heart, and only in that direction, so that Galen’s theory of blood travelling outwards in the veins was doubly shattered.

Petit tourniquet engraving from 1798

Harvey’s experiment was to tie a bandage very tightly round the arm, midway between elbow and armpit, and twist the bandage with a small stick (a “tourniquet”) so that all flow of blood stopped. After two minutes the hand became blue and cold. Now if he released his bandage by a turn on the stick, leaving only a “medium tightness”, the hand would become engorged with blood and start to swell, at the same time displaying the valves in its surface veins as hard knots. Harvey’s explanation was: “The tight bandage not only obstructs the veins, but the arteries; whereby it comes to pass that the blood neither comes nor goes to the members. The medium bandage again obstructs the veins, while the arteries, lying deeper, being firmer in their coats and forcibly injected by the heart, are not obstructed but continue conveying blood to the limb. Wherefore follows the unusual fullness of the veins and the necessary inference that the blood flows incessantly outwards from the heart by the arteries, and ceaselessly returns to it by the veins. . . .”
(For any reader who cares to try Harvey’s experiment, it is worth noting that both “tight” and “medium” bandages on a limb are dangerous if kept on for more than a few minutes.)
Another experiment was to grasp a staff tightly, so that the veins in the forearm were displayed. Then, by pressing a finger-tip on them at various points, it was possible, observing closely, to see which way the blood flowed. There was no question about it: blood in the veins flowed to the heart, never away from it.
The circulation of the blood had been discovered, proved. From the left side of the heart, the lower of the two chambers on that side, or “left ventricle”, the blood was pumped out through the arteries to every part of the body. Then, through some “leakage” which Harvey failed to understand and at which he wisely made no effort to guess, it found its way into the veins and returned, this time to the right side of the heart, its upper chamber or “right auricle”. From here it passed through a one-way valve to the lower chamber on that side, the “right ventricle”, and was pumped out again, to the lungs, returning from them to the left side of the heart, an upper chamber or “left auricle”. A descent through the one-way valve on that side to “left ventricle”, and it set off again, through the arteries, to each part of the body.

Image of veins from Harvey's Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus

So much could be proved and Harvey was content to leave it at that. In one way, this was a measure of his greatness. He had made a discovery which could be proved, and by several different observations. He was satisfied; he would not try to extrapolate a complete physiology of circulation and respiration, because he had no means of proving it. That could wait. Others had been eager to manufacture nonsensical and involved theories from a few shreds of misinterpreted evidence, and the medical profession, which was then (and still, some say, remains) a religion, like English Law, unquestioned, unquestionable, sacrosanct, were anxious to go on believing them. One can only conjecture how history might be rewritten if the rulers, tyrants, statesmen and scientists who died as a result of “blood-letting” and other treatments, based on a misunderstanding of the function of the blood, had lived.
Harvey’s “wicked and heretical” theory was gradually accepted, simply because it was impossible to refute. His successors were able to establish, with microscopes that Harvey did not possess, that the arterial blood crossed to the veins at the end of its outward journey, through tiny, hair-fine pipes or “capillaries” (from the Latin word for “hair”) just under the skin. At this point it did its “work”, returning through the veins to be pumped to the lungs, where it underwent a chemical change, releasing the carbon-dioxide which it had brought back from the extremities, a waste-product of its work, and replacing it with oxygen.
All arteries, then, carry blood away from the heart and all, with the exception of one, carry bright red, oxygenated blood. All veins carry blood back to the heart and all, with the exception of one, carry dull red blood, full of carbon-dioxide, on its way to the lungs. The two exceptions are the pulmonary artery, which carries “used” blood from heart to lungs, and the pulmonary vein which brings oxygenated blood back from lungs to heart.
William Harvey was the man who made of “anatomy” a new science of the living, moving body, the science of physiology. For generations men had been content to deal with matters of quality, of “humours” and vital forces in the body, a “spiritus” which was somehow injected into the blood by the brain, and so forth. No one had ever used a yardstick, a scale, a unit of measurement; but Harvey, watching the exposed, beating heart of an animal, watching the organ draw itself together, contract into a small hard ball, push blood into the aorta, was the first man to ask, “how much?” “how often?” “which way?” and “where?”; to treat the body as a machine, find out what made it work. The consequences of his discovery were immense, the most important step that had ever been taken in medicine: one which has probably only been approached in magnitude by the twentieth-century discovery of antibiotics.
William Harvey was born, on 1 April, 1578, in Folkestone. His father was a well-to-do merchant and was able to send the boy to Kings School, Canterbury, and to Cambridge University. As soon as he had taken his B.A. degree he travelled to Padua, which was felt, in the seventeenth century, to be the finest medical school in the world, particularly for anatomical studies. Here he studied for several years under the great anatomist Fabricius, becoming a Doctor of Medicine in 1602, when he was twenty-four.
He returned to England, obsessed by what he had learnt, and although he was appointed physician at St Bartholomew’s Hospital in 1609, although he had plenty of patients and much to do, he remained principally concerned with anatomical problems. Unlike the doctors of the sixteenth century, who had been delighted by the beautiful proportions, the harmony, of the human body, Harvey was concerned with its movement, the only attribute, he pointed out, which made it different from a marble statue. And the two movements which were ceaseless from birth to death, the pulse and breathing, these were what Harvey was most interested in.
But his practice was growing, his professional reputation, despite this private obsession, was increasing with each month, and he had the greatest difficulty finding time for research. In 1616, after he had been appointed professor at the College of Physicians in London, he gave his first lecture, and from the manuscript notes that survive we can see that he had solved, in his own mind, the problem of the circulation of the blood. How his audience reacted we do not know, but Harvey knew enough of his colleagues in the medical profession to realize that they would be not only sceptical but outraged, even abusive, unless he made his theory fool-proof-physician proof. He went on with his experiments, dissecting men, animals, birds, snakes, anything, and measuring what he found.
Two years after this lecture he was appointed Physician-in-Ordinary to King James I and when that monarch died he went on to serve Charles I in the same capacity. Still he checked, double-checked, his theory, expanding it slowly and carefully, only as far as his observations justified.
It was not until he had been in royal service for ten years that, as we have seen, he published his famous monograph in 1628. Immediately there was a storm of anger. What right had this “heretic”, this “devil”, to toss aside the teachings of a thousand years? There were angry meetings of medical men, demonstrations in the street. To the general public he became a “crackbrain”.

Charles I holding a council of war at Edgecote on the day before the Battle

The Civil War added to Harvey’s problems. He had little interest in politics, but he was the king’s physician and as such he was present at the Battle of Edgehill, where his task was to take care of the young Prince of Wales and even younger Duke of York. While he was away his house was ransacked and many of his papers stolen or destroyed. History relates that he brought his young charges to a quiet hedgerow and had begun to read to them when a cannon-ball landed a few yards off. The king’s physician and the king’s two sons were then seen tearing across the field in search of shelter. Fortunately for history and mankind, they found it, and Harvey was allowed to go on for another decade working on embryology, the origin of human beings, their development in the maternal womb, a study to which he contributed greatly, but which is outside the scope of this article.
When the king moved his court to Oxford, Harvey was delighted ; he was able to continue his studies there. He was received with civility at first, then warmth, as his theory became gradually accepted, and at last he was made Warden of Merton College. He retired into private life in 1646, “much troubled with gout”.
During the eleven years of life that remained, his theory became accepted all over the world. In 1654 the College of Physicians wanted to confer upon him the highest possible honour, that of President, but Harvey declined, saying he was too old. He returned the compliment by erecting a new building for the college and equipping it with a library and a museum. He died, on 3 June, 1657, a widower and childless, bequeathing his estate at Burwash in Kent to the College of Physicians, and with it a fund for an annual lecture. The Harvey Oration is still given, each year.