Radzewicz replied: "When he saw the dead bacteria around the mold he had the presence of mind to check it out further rather than just clean the dish. He did a "double check", just to see what was really going on, and was pleasantly surprized to find that a mold which was non-toxic to humans was toxic to bacteria. The mold was a complete accident of chance, but he had the book knowledge and work experience to understand what he was looking at. And fortunately, he got there before the graduate assistant arrived to mindlessly wash the whole glomp away."

Kylee replied: "Trial and error, his discovery was entirely accidental. He devised no tests, and formulated no hypothesis. He just stumbled upon it. FROM WIKIPEDIA: Accidental discovery Miracle cure."When I woke up just after dawn on September 28, 1928, I certainly didn't plan to revolutionize all medicine by discovering the world's first antibiotic, or bacteria killer," Fleming would later say, "But I guess that was exactly what I did." [2]. By 1928, Fleming was investigating the properties of staphylococci. He was already well-known from his earlier work, and had developed a reputation as a brilliant researcher, but quite a careless lab technician; he often forgot cultures that he worked on, and his lab in general was usually in chaos. After returning from a long holiday, Fleming noticed that many of his culture dishes were contaminated with a fungus, and he threw the dishes in disinfectant. But subsequently, he had to show a visitor what he had been researching, and so he retrieved some of the submerged dishes that he would have otherwise discarded. He then noticed a zone around an invading fungus where the bacteria could not seem to grow. Fleming proceeded to isolate an extract from the mold, correctly identified it as being from the Penicillium genus, and therefore named the agent penicillin. He investigated its positive anti-bacterial effect on many organisms, and noticed that it affected bacteria such as staphylococci, and indeed all Gram-positive pathogens (scarlet fever, pneumonia, meningitis, diphtheria) but unfortunately not typhoid or paratyphoid, for which he was seeking a cure at the time. It also affected gonorrhea, although this condition is caused by a Gram-negative pathogen. Fleming published his discovery in 1929 in the British Journal of Experimental Pathology, but little attention was paid to his article. Fleming continued his investigations, but found that cultivating penicillium was quite difficult, and that after having grown the mould, it was even more difficult to isolate the antibiotic agent. Fleming's impression was that because of the problem of producing it in quantity, and because its action appeared to be rather slow, penicillin would not be important in treating infection. Fleming also became convinced that penicillin would not last long enough in the human body (in vivo) to kill bacteria effectively. Many clinical tests were inconclusive, probably because it had been used as a surface antiseptic. In the 1930s, Fleming’s trials occasionally showed more promise,[3] and he continued, until 1940, to try and interest a chemist skilled enough to further refine usable penicillin. Fleming soon abandoned penicillin, and not long after Florey and Chain took up researching and mass producing it with funds from the U.S and British governments. They started mass production after the bombing of Pearl Harbor. When D-day arrived they had made enough penicillin to treat all the wounded allied forces."