Before the circulatory system was fully understood, many medical experts believed that the heart didn’t pump blood around the body but rather burnt it to create energy. Luckily, William Harvey was able to detail the full working of the veins, arteries and heart in 1628.
Until very recently, members of the British royal family suffered from a very rare affliction known as hemophilia B. This effectively prevented their blood from clotting properly, meaning any would or injury could be fatal as the blood would not stop flowing. The condition has affected them since a random mutation occurred in Queen Victoria’s genes.