The Black Death, also known as the Bubonic Plague, was a huge, widespread plague that spread across Asia and Europe. It reached Europe in the late 1340s and continued for centuries afterward. An estimated 25 million people died; one in five residents died. Many people were killed by the plague, even injured and barely surviving. The Black Death affected many people. The cause of the plague was thought to be the bacillus Yersinia Pestis, which was the deadliest disease of the Middle Ages. The process begins when the bacillus enters the bloodstream and eventually ends up in the lymph nodes. This causes the glands to become enlarged and inflamed, causing buboes to appear in the groin, armpits, or neck. The plague is transmitted by a rat flea that obtains its bacteria from a rat. Eventually, the flea transmits the disease to humans. The flea's stomach is completely filled with bacteria, which prevents it from digesting blood. The flea draws blood from the already full stomach, forcing it to bring the swallowed object back to the mouth, which spreads the bacteria....