"Simplest Physiological Experiments"
William Harvey famously discovered the circulatory system – the flow of blood from heart to the various body parts, and back. A lot of discoveries in science needed the relevant equipment to be invented first (think of Galileo and the telescope), but not in Harvey’s case, writes Siddhartha Mukherjee in The Song of the Cell . “He used the simplest physiological experiments to understand the workings of the heart.” Let’s look at how Harvey went about it. He punctured the arteries of animals when the blood had drained from them, “the veins were also eventually emptied of blood”. From this, he concluded that arteries and veins must be connected in a circuit. When he pinched the aorta, the heart swelled up with blood. And when he pinched the main veins, the heart was drained of blood. This implied that arteries lead blood from the heart, and veins lead blood to the heart. When Harvey examined the wall between the left and right side of the heart, he f...