The plate he left out
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The calendar keeps 28 September for Alexander Fleming and penicillin. It is a useful date and a slightly too-clean one. Fleming himself later supplied a dawn scene — waking on 28 September 1928 with no plan to change medicine, then doing exactly that. Historians treat the sentence as a recollection, not a lab notebook. What the notebooks and the standard accounts agree on is plainer. In the late summer of 1928 he was working with Staphylococcus aureus at St Mary's Hospital in London. He went away. Plates sat out. When he came back in September, one of them had a mold on it, and around the mold the bacteria were gone.
He had not designed the experiment. Contamination was a nuisance he already knew how to notice. The 1928 plate was that habit pointed at a fungus. The mold was a Penicillium. The clear zone meant something in the colony was stopping the staph, or killing it. He kept the culture instead of discarding the plate. In March 1929 he named the substance penicillin, mostly so he would not have to keep saying "mould broth filtrate."
That is the discovery, and it is smaller than the legend. Fleming showed that the filtrate could act on some bacteria and not others, and he said it might matter in medicine. He did not turn it into a drug you could inject. Penicillin was unstable. Growing enough of it was a manufacturing problem, not a paragraph in a paper. Through the 1930s the observation sat there: real, published, and not yet a treatment.
Howard Florey and Ernst Chain, at Oxford, picked it up at the end of that decade with a team that treated the mold as a supply chain. They purified enough to run the animal experiments, then the desperate early human cases, then the problem of making more than a few doses. The war did the rest of the scaling, much of it in the United States, in deep tanks rather than bottles on a bench. In 1945 the Nobel Prize in Physiology or Medicine went to Fleming, Florey, and Chain together, "for the discovery of penicillin and its curative effect in various infectious diseases." The split is the honest version of the story. One man saw the ring. The other two made it a medicine.
The plate still matters, because without the ring there is nothing to scale. Accidents in biology are common. Keeping the plate, repeating it, and naming the stuff are the parts that are not accidental.
None of this is a photograph you can put on a shirt without lying. His plate was glass, agar, staph, and a greenish mold with a bald patch of bacteria around it. The Lab Pick is a drawn dish: a teal rim, colonies in colors a Petri dish does not actually grow, on a charcoal tee. It is an illustration of the object, not a replica of 1928. That is the right amount of distance. The story is the clear ring. The shirt is the dish you picture when someone says the word.
If you want the longer argument, it is this. Antibiotics did not arrive as a eureka on a Monday morning. They arrived as a contaminated plate, a named filtrate, a decade of not-quite-yet, and then a group of people who decided the not-quite-yet was a supply problem. The anniversary is worth keeping. The dawn quote is optional.