Martinus Beijerinck

Today is the anniversary of the death of the botanist Martinus Beijerinck (pronounced “by-a-rink”).

Beijerinck searched for the reason tobacco plants were dying.
In his research, Beijerinck ground up some diseased tobacco leaves and then pressed the juices through a bacteria filter. He was utterly shocked when the filtered, bacteria-free liquid still spread the disease.
After reviewing his experiment, Beijerinck concluded that a "contagious living fluid" was the culprit. It was a disease-carrying micro-organism that was smaller than bacteria and he called it a virus, the Latin word for poison."
Today, two of the most common viruses are the flu and the common cold.