Traditionally, it has been thought that Alexander Fleming discovered penicillin when he noticed a mold growing on his Petri dishes: wherever the mold grew, bacteria died.
In fact, the true story is much more complicated... and INTERESTING!
The mold actually grew on Fleming himself, initially covering his feet below the ankles with a thin blue fuzz, and ultimately extending all the way up to the middle of his abdomen. Fleming remained moldy for about 6 weeks; during that whole time he observed that he didn't get sick even one time.
Fleming realized that the mold that had been growing on him was Penicillium, or bread mold. He set about culturing more mold on any bread he could lay his hands on, including the sandwiches and hamburger buns that belonged to his lab staff.
By the middle of 1939, Fleming had enough bread mold to fill a telephone booth... but then WAR broke out.
Fleming's mold-filled telephone booth was transported to the front. It was struck by a shell, and the mold was destroyed.
America realized: something had to be done, SOON! Every day, hundreds of soldiers were contracting gonorrhea in the line of duty!
Fleming had an idea: he immediately deployed a crack team of scientists to riffle through the refrigerators of students across Britain. A search revealed huge quantities of moldy food, yielding a precious supply of "penicillin", as it is now called.
However, administering penicillin was difficult. Often, an infected wound would be rubbed directly with a piece of moldy bread, leading to friction burns. It was even more difficult to give the drug intravenously, as crumbs would clog the IV tubing.
Two brilliant scientists, Florey and Chain, developed the idea of scraping the mold off the bread with a specially designed fork. They shook the mold off the forks into the special glass vials and plastic IV bags that penicillin comes in today.
