Anatomy, Round Two

Cutting down to the heart of it all

Walter Isaacson
Oct 30, 2017 · 8 min read
Photo: GraphicaArtis/Getty Images

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The Centenarian

Shortly before he left Florence in 1508, Leonardo was at the hospital of Santa Maria Nuova, where he struck up a conversation with a man who said he was more than a hundred years old and had never been ill. A few hours later, the old man quietly passed away “without any movement or sign of distress.” Leonardo proceeded to dissect his body, launching what would be, from 1508 to 1513, his second round of anatomical studies.

We should pause to imagine the dandy-dressing Leonardo, now in his mid-fifties and at the height of his fame as a painter, spending his night hours at an old hospital in his neighborhood talking to patients and dissecting bodies. It is another example of his relentless curiosity that would astonish us if we had not become so used to it.

Twenty years earlier, while living in Milan, he had filled notebooks with his first round of anatomy drawings, including beautiful renderings of the human skull. Now he picked up the work again, and on one of the pages, above a set of drawings of muscles and veins in a partially skinned cadaver, he drew a respectful little drawing of his centenarian’s peaceful face, eyes closed, moments after his death. Then, on thirty more pages, he proceeded to record his dissection.

Leonardo’s hand was deft with both pen and scalpel. His close observation plus the strength of his visual memory made his drawings strikingly better than those in any anatomy texts before him. Mustering all of his draftsman’s techniques, he made detailed underdrawings in black chalk, then finished them with different colors of ink and washes. With his left-handed curved hatching lines, he gave shape and volume to the form of bones and muscles and with light lines added the tendons and fibers. Each bone and muscle was shown from three or four angles, sometimes in layers or in an exploded view, as if it were a piece of machinery he was deconstructing and delineating. The results are triumphs of both science and art.

His rudimentary dissecting tools took him down layer by layer even as the body, untreated, decomposed. First he showed the surface muscles of the old man, then the inside muscles and veins as he pulled off the skin. He started with the right arm and neck, then the torso. He noted how the spine was curved, then he got to the abdominal wall, the intestines, the stomach, and the membranes connecting them all. Finally he exposed the liver, which he said “resembled frozen bran both in color and substance.” He never reached the legs, perhaps because by then the body had decomposed too badly to make it bearable to handle. But there would be other dissections, probably twenty more, and by the time he finished his anatomy studies he would have beautifully illustrated every body part and limb.

In his quest to figure out how the centenarian died, Leonardo made a significant scientific discovery: he documented the process that leads to arteriosclerosis, in which the walls of arteries are thickened and stiffened by the accumulation of plaque-like substances. “I made an autopsy in order to ascertain the cause of so peaceful a death, and found that it proceeded from weakness through the failure of blood and of the artery that feeds the heart and the other lower members, which I found to be very dry, shrunken and withered,” he wrote. Next to a drawing of the veins in the right arm, he compared the centenarian’s blood vessels to those of a two-year-old boy who also died at the hospital. He found those of the boy to be supple and unconstricted, “contrary to what I found in the old man.” Using his skill of thinking and describing through analogies, he concluded, “The network of vessels behaves in man as in oranges, in which the peel becomes tougher and the pulp diminishes the older they become.”

The constriction of blood flow had caused, among other things, the centenarian’s liver to become so dry that “when it is subjected to even the slightest friction its substance falls away in tiny flakes like sawdust and leaves behind the veins and arteries.” It also led to his flesh becoming “the color of wood or dried chestnut, because the skin is almost completely deprived of sustenance.” The noted medical historian and cardiologist Kenneth Keele called Leonardo’s analysis “the first description of arteriosclerosis as a function of time.”

The Heart

On one of Leonardo’s pages of drawings of the human heart, done in ink on blue paper, is a reminder of the humanity, and even humanness, that suffuse his anatomical studies. At the top is a drawing of the heart’s papillary muscle and a description of how it shortens and elongates when the heart beats. Then, as if he were being too clinical, he let his mind wander and pen begin to doodle. And there, in loving profile, is a drawing of Salai, his beautiful curls flowing down his long neck, his signature receding chin and fleshy throat softly modeled with Leonardo’s left-handed hatching. In his chest is a section of a heart, with its muscles sketched in. An analysis of the drawing shows that the heart was sketched first. It seems as if Leonardo drew it, then sketched Salai around it.

Leonardo’s studies of the human heart, conducted as part of his overall anatomical and dissection work, were the most sustained and successful of his scientific endeavors. Informed by his love of hydraulic engineering and his fascination with the flow of liquids, he made discoveries that were not fully appreciated for centuries.

In the early 1500s the European understanding of the heart was not all that different from that described in the second century AD by Galen, whose work was revived during the Renaissance. Galen believed that the heart was not merely a muscle but was made of a special substance that gave it a vital force. Blood was made in the liver, he taught, and distributed through the veins. Vital spirits were produced by the heart and distributed through arteries, which Galen and his successors considered a separate system. Neither the blood nor vital spirits circulated, he thought; instead, they pulsed back and forth in the veins and arteries.

Leonardo’s studies of the human heart, conducted as part of his overall anatomical and dissection work, were the most sustained and successful of his scientific endeavors. Informed by his love of hydraulic engineering and his fascination with the flow of liquids, he made discoveries that were not fully appreciated for centuries.

In the early 1500s the European understanding of the heart was not all that different from that described in the second century AD by Galen, whose work was revived during the Renaissance. Galen believed that the heart was not merely a muscle but was made of a special substance that gave it a vital force. Blood was made in the liver, he taught, and distributed through the veins. Vital spirits were produced by the heart and distributed through arteries, which Galen and his successors considered a separate system. Neither the blood nor vital spirits circulated, he thought; instead, they pulsed back and forth in the veins and arteries.

Leonardo was among the first to fully appreciate that the heart, not the liver, was the center of the blood system. “All the veins and arteries arise from the heart,” he wrote on the page that includes the drawings comparing the branches and roots of a seed with the veins and arteries emanating from the heart. He proved this by showing, in both words and a detailed drawing, “that the largest veins and arteries are found where they join with the heart, and the further they are removed from the heart, the finer they become, dividing into very small branches.” He became the first to analyze how the size of the branches diminish with each split, and he traced them down to tiny capillaries that were almost invisible. To those who would respond that the veins are rooted in the liver the way a plant is rooted in the soil, he pointed out that a plant’s roots and branches emanate from a central seed, which is analogous to the heart.

Leonardo was also able to show, contrary to Galen, that the heart is simply a muscle rather than some form of special vital tissue. Like all muscles, the heart has its own blood supply and nerves. “It is nourished by an artery and veins, as are other muscles,” he found.

He also corrected the Galenic belief that the heart has only two ventricles. His dissections showed that there are two upper and two lower ventricles. These must have distinct functions, he argued, because they were separated by valves and membranes. “If they were one and the same, there would be no need for the valves that separate them.” In order to figure out how the ventricles work, Leonardo opened up a pig whose heart was still beating. The upper and lower ventricles open at different times, he discovered. “The upper ventricles of the heart are different in their functions and nature from those below, and they are separated by gristle and various substances.”

Leonardo did accept Galen’s incorrect theory that blood is warm because it is heated by the heart, and he wrestled with many theories of how this happened. He finally settled on the supposition that the heat is generated by the friction of the moving heart and the blood rubbing against the heart walls. “The whirling round of the blood in different eddies, and the friction it makes with the walls, and the percussions in the recesses, are the cause of the heating of the blood,” he concluded. In order to test his theory by analogy, as he often did, he considered whether milk became heated when it was churned. “Observe whether the revolution of milk when butter is made heats it” he put on his to-do list.

Walter Isaacson

Written by

CEO of the Aspen Institute. Author of The Innovators & bios of Steve Jobs, Einstein, Ben Franklin, and Henry Kissinger. Former editor of Time, CEO of CNN

Leonardo da Vinci
Leonardo da Vinci
Leonardo da Vinci

About this BOOK EXCERPT

Leonardo da Vinci

Biographer and journalist Walter Isaacson looks deeply into Leonardo da Vinci’s exploration of the human body and, in turn, helps us understand one of the greatest and most creative minds to ever walk the earth. Leonardo’s deep fascination with the human body impacted most other aspects of his genius, from his art and architecture, to his invention and scientific breakthroughs.

Biographer and journalist Walter Isaacson looks deeply into Leonardo da Vinci’s exploration of the human body and, in turn, helps us understand one of the greatest and most creative minds to ever walk the earth. Leonardo’s deep fascination with the human body impacted most other aspects of his genius, from his art and architecture, to his invention and scientific breakthroughs.

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