Leonardo da Vinci - Kathleen Krull [18]
For eyeballs (notoriously squishy and hard to cut), he had the brainstorm of coating them with egg white first. Then he boiled them, to make them firmer, like hard-boiled eggs.
He didn’t discard the bones and, in fact, was the first person to describe the human skeleton correctly. To discover how the parts of the body worked together, he would take a skeleton, insert copper wires where the muscles would go, and study how the contraction or relaxation of the wires caused different movements.
He once befriended a one-hundred-year-old man in a hospital, chatting for hours about his unusual longevity. Then the man died, and Leonardo immediately dissected his body to find out the cause of death. In describing the shriveled “artery that feeds the heart,” he may have written the first description of arteriosclerosis (the hardening of the arteries) in history. A short time after dissecting the old man, he dissected the body of a two-year-old child. He noted all the differences between the healthy young organs and those he found in the body of the old man.
More than a century ahead of his time, Leonardo theorized that the heart was a thick muscle that pumped blood. The heart, according to Galen, was not even a muscle at all, but some unique tissue unlike anything else in the body. And in Leonardo’s day, medical schools were teaching that blood came from two places—the liver as well as the heart.
Scientists then, and for centuries before, believed the valve to the heart to be a passive one. To test this, Leonardo created a glass model of the human aortic valve, inserting it into a cow’s heart filled with water. He then poured water into the valve with bits of paper mixed in so that he could follow the movement of this new water. With this experiment, he demonstrated the correct motions of the valve opening and closing: he proved the valve was active.
Leonardo was the first person known to make a drawing of a baby inside a womb, although it wasn’t entirely accurate. (The sacklike placenta was the wrong shape; it looked more like a cow placenta.) He was also one of the first to state that the mother and father have equal influence on an embryo—the belief of the day was that all characteristics of a baby came from the father.
Leonardo distilled his anatomy research into some 1,500 three-dimensional, multilayered drawings—again, he not only wanted to see but to record what he saw. The results were the first attempts at accurate depiction of human organs, muscles, and bones in history. His drawings have influenced medical textbooks to this day. There are cutaways and cross sections to show layers of an organ from various angles, as well as see-through images and sketches that portray as much motion as possible. His goal was to show the parts of the body in three dimensions. Five hundred years later, the drawings appear perfectly at home on the Internet.
Anatomy led to studies about vision and eyes, and Leonardo tried to break new ground in optics, although his knowledge was often primitive. In his day, many accepted Plato’s belief that we see because our eyes project rays of light onto objects, then the rays are reflected back to the eye in an image. But Leonardo questioned Plato: how could this be true? If it were, wouldn’t we see objects closer to us before we see ones farther away? But we don’t. Our eyes take in a scene all at once.
Leonardo observed that when a knife stuck in a table was made to vibrate, it gave the illusion of two knives. For Leonardo, this was more evidence that the eye receives images. It also told him that the eye finds it hard to distinguish images in quick succession.
As another test, Leonardo put a glass of water on a windowsill so that sunlight struck it. He observed that sunlight penetrated the glass and separated into different colors. His conclusion: the colors—the changes in