by Rob Dunn
Initially, Galen’s work seemed to have been lost to science altogether. In Western Europe, not a single copy of one of his scrolls seems to have survived. But in the eastern part of the Roman Empire, his writings had, it would turn out, continued to be copied and translated, from Latin to Arabic and then from one Arabic copy to the next. Muslim scientists prevented ancient knowledge from being lost in its entirety, not just that of Galen but also more generally. Not all of Galen’s millions of words were translated, and meaning and context could be lost in translation, but his flame was passed. When scholars in Western Europe, particularly in Italy, rediscovered these translations, they cherished them—too much. Galen’s words seemed so advanced, relative to the knowledge of the time in Europe, that they were treated as literal scripture, wisdom handed down from an ancient that was to be revealed, not built upon. The sciences of anatomy and human biology came to circle Galen, Galen the great, Galen the perfect, Galen the prince.
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When Art Reinvented Science
A good painter has two chief objects to paint: man and the intention of his soul. The former is easy, the latter hard.
—LEONARDO DA VINCI (CIRCA 1490)
Late one afternoon in 1508, Leonardo da Vinci (1452–1519) was at the Santa Maria Nuova Hospital in Florence, a Church hospital. He was not a doctor, but he already knew more about the human body than almost anyone else who had ever lived, more even than Galen. He was talking with a very old man, a centenarian. The man, who is known to history simply as il vecchio, the “old one,” was kind and garrulous. He had lived a grand life. Da Vinci had just returned from Milan, and he was dressed in fine clothes—maybe his purple cloak, maybe the pink cape; he was worldly and beautiful. Da Vinci bent over il vecchio, his fingers touching the old man’s onion-paper skin gently. Then, suddenly, the man died. He died as if struck down. Da Vinci held the man with great kindness before pulling out his knives and beginning to dissect his body. He pulled back il vecchio’s clothes and cut into the warm flesh. This was a true autopsy, a word that comes from the Greek for “to see for oneself,” which is precisely what da Vinci wanted to do.
Today, we seem set on extending life indefinitely. Death is what we push off at all costs, by whatever means. To da Vinci, the goal of medicine was not to prevent death but, after a good life of reasonable length, to make death, in his word, sweet. A sweet death after a good life was the best that one could hope for. Most ways of dying in da Vinci’s time were brutal. Smallpox. Infection. Rabies. Malaria’s shivering ache. Or worse. But il vecchio had died without pain. He had died of an inevitable and natural process of some sort. But what was it about age that could cause so sweet an end? This was a mystery in which every person alive and every person yet to live had a stake.
The artist began with cuts to the chest, but he moved slowly. The man’s body was smaller and more delicate than that of the horses and cows he more often handled.1 Da Vinci would need patience to see each piece well—each finger, toe, vein, bone, and nerve. No cuts would be spared, and after each cut, a drawing would be done, to understand but also, simultaneously, to improve in the skill of depiction of inner truths. Da Vinci did not know what he was looking for; he was exploring. So little was known about the body. There had been minimal progress since Galen. Anything seemed possible. Perhaps the liver exploded. Perhaps the brain turned yellow. A million, a trillion scenarios lurked in the skin and organs, none of them any more likely than any other. Da Vinci pondered what he saw.2
Da Vinci’s beginnings, like those of many artists of the early Renaissance, were humble. He was born to an unwed mother in a small town in Tuscany.3 From there, it appears he was sent to live with his father in the town of Vinci, which would many generations later become known for him, as though the town of Vinci were named for Leonardo and not the other way around. In Vinci, Leonardo would later write, he slept outside in a crib. His life was that of a rural boy. The dark sky rose above him at night. And during the day, he watched the birds wake around him in the trees. One day, a kite landed so near him it brushed its tail on his face.
The details of Leonardo’s life seem special now, as they would to him later in life, a foreshadowing of greatness, a series of minor omens. But not then. His childhood was marked mostly by its very ordinariness, until he began to share his art. When da Vinci was about fourteen, his father, a notary, was asked by a man of little means to commission the painting of a crest on his shield. Da Vinci’s father gave the shield to his son to paint. Leonardo proceeded to cover the shield with the insignia of a monster, an insignia so marvelous that his father, Ser Piero, promptly sold it for a handsome sum and then fatefully (at least in the context of this book) replaced the shield with another like it, bought from somewhere else, at a lesser cost, emblazoned with a simple heart.
Whether the story of the shield is true or not, at some point, da Vinci’s artistic abilities were recognized by his father, so much so that when da Vinci was fourteen or fifteen—and after some arm-twisting by Ser Piero—the Florence-based artist Andrea del Verrocchio (1435–1488) offered the boy an apprenticeship. The apprenticeship was an open door4 through which da Vinci ran.
The apprenticeship, like nearly everything else in Florence at the time, was a luxury afforded by the city’s great wealth. Da Vinci was born at the beginning of the Renaissance. Da Vinci’s birth marks the rise of this new age in which knowledge and beauty began, once more, to be cherished. This rebirth is thought of in terms of its art and, later, science, but it was as much a thing of money as of intellect. In Florence, businesspeople, the Medici family in particular, had accumulated enough wealth to allow extravagant expenditures, including the purchases and commissioning of new art. Through their purchases and gifts, the wealthy created a culture in which artists could afford to live by art alone, a culture in which it paid artists to revisit the ancient techniques and even invent new ones. When the ancients were reconsidered, their work seemed perfect, and so it was an obvious first step for the artists of the time to relearn their ways. Once relearned, those ancient ways were, haltingly, built upon; it was out of this building that the art of da Vinci, Michelangelo, Titian, and so many other greats emerged.
Da Vinci trained with his mentor Verrocchio in a workshop in Florence for nearly a decade before he began taking on his own private, signed commissions, work that would pay the bills and more for the rest of his life. The first piece signed by da Vinci comes from a time when he was just starting to work on his own; it is a sketch of the Arno River valley in which water moves through the muscular hills of the valley like, as da Vinci would later note, blood through the heart.
As he began to work on his own, da Vinci benefited from patrons who were both grand in their expectations and, all things considered, remarkably patient. From the beginning, da Vinci worked very slowly. In order to paint, he first had to invent just the right paint. He had to invent new approaches to perspective. And, more than anything, he had to—or at least, he felt compelled to—dissect. Most Renaissance artists viewed dissection as useful training in the details of the body. Da Vinci and others needed to know the body so they could “reveal more effectively its power, fragility and reality in artistic form.” Leon Battista Alberti (1404–1472) was expressing a widely held (and essentially Greek) sentiment when he suggested that there were three elements of the body that needed to be studied for painting: the arrangement of the bones, the distribution and arrangement of the muscles, and, finally, the skin and the fat on which it rested. This was also the approach of Verrocchio, Michelangelo (1475–1564), and others. Da Vinci was like other artists of the time in that he studied bones, muscles, and skin, but he was unusual in the extent to which he also examined the rest of the body. He looked into its interstices; each time he performed a dissection, he was, as he would say of himself, like a boy who enters a deep and unknown cave. However frightening exploration could be, he always went further, deeper into the darkness so that he might find his way closer and closer to the truth. He looked to
see what was there but also how and to what end it worked. Da Vinci’s dedication to understanding the body gave his art a kind of visceral realism others aspired to; it also allowed him to make novel, scientific discoveries.
As he explored, da Vinci made breakthroughs, real scientific breakthroughs, that are acknowledged as such, in a dozen subfields of anatomy—the biology of eyes, neurobiology, reproductive biology, and the study of the blood vessels and heart. Even the very earliest of his surviving studies of anatomy (from about 1485, fifteen years after the drawing of the Arno River valley), a rough sketch on which he would build his future discoveries, displays connections among blood vessels and aspects of organs that had never before been documented.5 In his studies, da Vinci, like any scientist, could not always be sure what was an advance and what was a rediscovery, but he recorded what he found all the same. Arguably, his greatest achievements were his notes on the heart and blood vessels.6 Da Vinci’s dissections of hearts and blood vessels started with animals: a horse and then cows and more cows. In these animals, the vessels looked to him like the rivers he had explored as a child and loved to sketch as an adult. They ran through the body carrying blood and a kind of as-yet-unnamed magic. Where did they go? How did they work? What moved the blood? Why? In his earliest dissections, da Vinci struggled. He was so influenced by Galen’s teachings—nothing better had been done in a thousand years—that he convinced himself he saw forms in the body that were not there, forms Galen had posited. But with time, da Vinci would get better at trusting his eyes, at seeing what was and, based on what he saw, figuring out for himself how things worked. He was never fully free of Galen’s tether, but eventually he (and he alone) began to see new truths rather than merely affirm old ones.7
As he considered the flesh of humans and other animals, da Vinci came to see the body as a kind of machine, “a vehicle in which to get around and survive,”8 a vehicle of pumps, levers, and gears whose functions could be understood. Never before had this modern sentiment been so clearly held.9 In studying this machine, da Vinci, bit by bit, began to pick at Galen’s ideas, refining them where they seemed in conflict with what he saw and sometimes simply overturning them wholesale. Galen imagined the blood flowed from the liver (where he believed it was made) to the heart and then on to the lungs, where it was used up, but da Vinci observed that blood flowed through all of the veins and arteries, not just those linking the liver, heart, and lungs. To him, this seemed obvious. It also became obvious to da Vinci that the heart, not the liver, was the center of the system of blood vessels. The heart beat in the embryo. It beat first, and it was primary, the very essence of being alive. The brain was the seat of the soul (today we might say the seat of consciousness), but the heart was its agent, its muscular vessel. Da Vinci was the first to draw the four chambers of the heart accurately and to observe that the atria and the ventricles must contract in concert. He also noted the unidirectionality of blood through the heart’s valves and, ultimately, arteries. Blood went through one way only, not back. These modest advances were the first real anatomical progress in more than a thousand years.
Among da Vinci’s scientific discoveries in the blood vessels and chambers of the heart, two stand out, the way the Mona Lisa and The Last Supper stand out among his paintings. One was based on what we would now call a physiological model. Da Vinci looked to rivers and streams to understand the dynamics of flow; flow preoccupied him for the better part of a decade, beginning in 1498. Da Vinci dropped weighted floats, leaves, corks, paper, seeds, and even ink in water-filled tubes in the Arno River in an attempt to grasp how and why water moved. He saw eddies, little circles of water, that often formed when water pushed against the edges of rivers (or, in his experiments, glass tubes). He then drew or painted how these objects moved in order to understand the underlying movement of water.
Da Vinci was intrigued by how blood moved through the heart’s valves, valves that, like rocks in a river, could allow or, depending on their position, stop flow. Beginning in 1513, da Vinci made detailed dissections of the heart’s valves and nearby vessels while working at a hospital within the Vatican’s walls (where he had a modest feud with Michelangelo, who was also dissecting there at the time). Da Vinci’s work in the Vatican hospital is what allowed him to see the heart’s valves so clearly and to draw them in such great detail. They would not be drawn in more detail until the late 1800s.
Once da Vinci had characterized the physical attributes of the heart’s valves, he sought to understand how they worked. He couldn’t see the valves functioning in living animals, so instead, he returned to a physical system, the river, to understand a biophysical system, that of vessels, blood, and valves, and to make predictions about its function. This approach of using one system to model another is among the most common modern practices in science, but that was not the case in the time of da Vinci. Based on his river studies, da Vinci predicted, correctly, that blood would move more rapidly through narrower blood vessels. On average, it does.10 He also predicted that when the big left ventricle in the heart contracted, it would be difficult to keep blood from flowing back through the aortic valve into that ventricle before the valve shut. This valve opens and shuts about once a second. As a consequence, it must seal both tightly and rapidly. Da Vinci thought the answer to how this occurred was in vortices, little eddies of blood that formed in part because of bulges in the aorta just above each valve (later to be called the sinus of Valsalva, for the Italian anatomist). Da Vinci tested his prediction by blowing a glass version of an artery in which he could watch the movement of grass seeds in liquid; it was, in essence, an artificial aorta. In watching the seeds, he saw his ideas confirmed, at least to his own satisfaction. He imagined that as blood flowed through the valve at the exit of the left ventricle, eddies of blood would form to help to close the valve. He was right, though no one would realize it until 1968, when two engineers, Brian and Francis Bellhouse, confirmed da Vinci’s prediction using a method essentially identical to the one he had used: they built an artificial aorta and watched the movement of artificial blood.11 When they published their article, the Bellhouses assumed they were the first to notice these vortices. It was only a year later that they discovered that da Vinci had beat them to the punch by four hundred years.12
At left, a simplified version of the vortices based on da Vinci’s depiction. (Courtesy of Jennifer Landin) At right, a computer model of the same, produced some four hundred years after da Vinci’s death. (Copyright © 2014. Courtesy of Tal Geva, MD)
Da Vinci’s big revelation, though, came from what he saw in il vecchio, among the best-documented dissections of an entire human since ancient Alexandria.13 Da Vinci spent so much time with il vecchio that the man’s body began to rot, stink, and fall to pieces. The work was tedious and unpleasant. As da Vinci wrote in his notebooks (in a bit of extended, if complex, self-praise),
And if you have love for such things [as dissection] you will perhaps be prevented by your stomach, and if this does not prevent you, you may perhaps be prevented by the fear of passing the night in company with bodies flayed and fearful to look upon. And if this does not prevent you, perhaps you will lack good draughtmanship that should belong to such drawing, and if you have the draughtmanship it may not be accompanied by perspective. And if it is so accompanied you may lack the principles of geometrical demonstration and the principles for the calculation of the forces and power of the muscles; or perhaps you may lack patience, so that you will not be diligent.
Da Vinci lacked none of these things, and so in the old man he made many discoveries—even the cause of his death, a cause he ascertained by, once again, availing himself of his river model. By this point, da Vinci had already observed that as rivers grew older, they became more tortuous. A young river traveled down the land in a straight line, but as a river aged, it twisted as it deposited sand along shores. The water did not compress, so where it went through a narrower constriction, it had to move faster, with more pressure. The river would turn and na
rrow enough that, given sufficient time, it would get longer and longer until the pressure to go straight through a narrow curve was too much and the river would break. In the old man’s tortuous arteries, which had turned, twisted, and narrowed with age, da Vinci saw sections of arteries, the body’s most important rivers, that were so narrow blood could barely flow through. The man’s arteries were more fragile, twisted, and narrowed than da Vinci had observed in the vessels of “birds of the air and the beasts of the field.” Those twisted narrowings prevented the nourishment of the blood from reaching the places in the body where it needed to go, and so the body starved. Da Vinci did not know that the blood carried oxygen from the lungs and sugar from the liver. He did not know that without both of these things, the brain would starve in three minutes and the body would die. But he understood the basic consequences of the hardening and thickening of the walls of the arteries. In age, da Vinci discovered, arteries harden and narrow and, as a result, eventually clog. Il vecchio’s sweet death was due to what we would now call atherosclerosis.
Da Vinci could have written all of this up—together with equally groundbreaking work on other organs, birth, the biology of the fetus, the articulation of bones, and more—as the most comprehensive book of anatomy since Galen. He discussed the possibility of writing a “treatise on anatomy.” In the winter of 1510, he worked with an anatomist, Marcantonio della Torre (1481–1512), perhaps with the goal of producing such a treatise. One may actually have been produced. In 1518, da Vinci showed a document to the cardinal of Aragon. Could it have been da Vinci’s great opus, an opus lost to history? Some suspect it was. The only description that remains of the document is what the cardinal’s secretary noted:
This gentleman has written of anatomy with such detail showing by illustrations the limbs, muscles, nerves, veins, ligaments, intestines, and whatever else there is to discuss in the bodies of men and women, in a way that has never yet been done by anyone else. All this we have seen with our own eyes. He has also written of other matters, which he has set down in an infinite number of volumes all in the vulgar tongue, which if they should be published will be profitable and very enjoyable.