The history of the discovery of penicillin.

While examining colonies of staphylococcus, Dr. Fleming noted that a form called Penicillium notatum contaminated his petri dish. After carefully placing the dishes under a microscope, he was amazed to find that the mold prevented the normal growth of staphylococci.

Later, Fleming grew a fairly strong form and confirmed his conclusions: there was some factor in the Penicillium mold that not only inhibits the growth of bacteria, but which can be used to fight infectious diseases.