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The Plate Fleming Almost Threw Away

A cluttered London lab, a summer holiday, and a mould that drifted onto the wrong dish. The man who noticed couldn't make the medicine - so who did, and why did it take a world war?

7 chapters · 12 sourcesBy HistoraiPublished September 15, 2026

Questions about this story

How did Alexander Fleming discover penicillin in September 1928?

Alexander Fleming discovered penicillin after returning from a summer holiday to his untidy London laboratory at Saint Mary's Hospital. He noticed a stray mould on an abandoned culture plate that had dissolved the surrounding staphylococcus bacteria colonies. Fleming identified the mould as Penicillium notatum and named the active antibacterial substance penicillin in 1929.

Why was penicillin not used as a medicine immediately after its discovery?

Alexander Fleming could not turn penicillin into a practical drug because it was chemically unstable and produced only in tiny amounts. Lacking the advanced chemistry skills to purify and concentrate it, Fleming viewed penicillin mainly as a useful laboratory tool for isolating bacteria. By the early 1930s, he had largely moved on from researching it.

Who developed penicillin into a usable medical drug?

Pathologist Howard Florey and biochemist Ernst Chain rediscovered Fleming's research at Oxford in 1938 and successfully turned penicillin into medicine. Alongside biochemist Norman Heatley, who developed critical extraction methods using makeshift containers like hospital bedpans, they proved penicillin's effectiveness in mice and human patients before establishing industrial mass production in the United States.

What role did a cantaloupe melon play in the history of penicillin?

A mouldy cantaloupe melon found at a market in Peoria, Illinois, provided a superior strain of mould that yielded vastly more penicillin than earlier samples. American scientists paired this strain with deep-tank fermentation, allowing industrial-scale production that supplied enough penicillin to treat thousands of wounded Allied soldiers by D-Day in June 1944.

Read the full transcript

Period: 1928 - 1944 · 10 minutes · English · two hosts

c. 1928 CE

Fleming's Laboratory

Alexander Fleming, Scottish bacteriologist at St Mary's, Paddington
Famously brilliant and untidy - cluttered bench, stacked cultures
Interwar era: infections routinely fatal, no antibiotics yet

Ada: It's a summer's day in London, nineteen twenty-eight, on an upper floor of Saint Mary's Hospital in Paddington. There's a small laboratory here, and it is, frankly, a mess. Glass dishes stacked in leaning towers, cultures growing on the benches, a window open to the grimy air.

Theo: And this is a serious scientist's lab? It sounds like my kitchen.

Ada: It's the lab of Alexander Fleming, a Scottish bacteriologist, farm-born in Ayrshire, and by every account brilliant and gloriously untidy. Where colleagues scrubbed everything down, Fleming let old plates pile up for weeks before clearing them.

Theo: I'm Theo, by the way, and this is Historai, where we chase down how the world actually got the way it is. Ada, who's with me - set the stakes. Why does one messy man's bench matter?

Ada: I'm Ada. And it matters because in nineteen twenty-eight, if you got a bad infection, you often simply died. Pneumonia, blood poisoning, childbed fever after giving birth - routinely fatal, no reliable cure.

Theo: So there's genuinely nothing? A scratch could kill you.

Ada: A scratch could kill you. Fleming had seen it firsthand as an army surgeon in the First World War, watching wound infections take soldiers faster than any bullet. He came out of that distrusting the harsh antiseptics everyone swore by.

August 1928

Holiday in Suffolk

Fleming left staph plates stacked, un-incubated, on the bench
Departed August 1928 for The Dhoon, Barton Mills, Suffolk
Lysozyme (1922) had trained him to notice bacteria being killed

Ada: Now, that war experience matters, because Fleming had a habit of watching for things that killed bacteria without killing us. Years earlier, in nineteen twenty-two, he'd found a mild antibacterial substance in tears and mucus - he called it lysozyme.

Theo: So his eye was already trained to spot something dissolving the germs.

Ada: Exactly. Keep that in your pocket - it's why he noticed what a tidier man might have washed away. But first, it's late summer, and Fleming wants a holiday.

Theo: Please tell me he cleaned up before he left.

Ada: He did not. He was studying staphylococcus - a common, nasty bacterium - and he left a stack of culture plates sitting out on the bench, not tucked into the warm incubator where they belonged.

Theo: Just left them there, uncovered to whatever's floating around?

Ada: Just left them. Then he locked up and headed off with his family to his country house, The Dhoon, at Barton Mills in Suffolk, for the rest of August.

Theo: And London's weather does its thing while he's gone.

Ada: It does. A cool spell, then warmth - and that quiet, empty lab is about to do something no experiment had planned.

September 1928

The Clear Halo

Fleming rescued a discarded plate from the Lysol tray
Mould blob surrounded by a bacteria-free zone of dissolved colonies
'That's funny' - anecdotal; exact date (Sept 15?) uncertain

Ada: Fleming came back around the third of September. He starts going through the abandoned plates, dropping them into a tray of Lysol disinfectant to be cleaned. A former colleague, Merlin Pryce, drops by to chat.

Theo: So these dishes are basically already in the bin.

Ada: Practically. But Fleming picks one back up out of the tray, looks at it, and reportedly says, 'That's funny.'

Theo: What did he actually see?

Ada: A fluffy blob of mould had landed on the plate. And in a ring all around that mould, the staphylococcus colonies had simply dissolved - gone clear. The germs were dying right where the mould touched.

Theo: And I have to ask - is 'That's funny' really what he said, or is that too perfect?

Ada: Good instinct. It's the famous line, but it's anecdotal - nobody documented it in the moment, and honestly the exact date gets shaky too. You'll hear September fifteenth quoted, but Fleming himself was vague about it.

Theo: So the tidy version of the story is a little too tidy.

Ada: It usually is. What's not in doubt is the clear halo - and Fleming, primed by lysozyme, knew he was looking at something worth chasing.

1929 CE

'Penicillin', 1929

Spore likely from La Touche's mould lab below - a reconstruction
'Mould juice' killed staph, strep, meningococcus, diphtheria
Named penicillin 1929; published June 1929 - largely ignored

Ada: So where did this mould even come from? The leading theory is that a spore drifted up from the lab one floor below, where a mycologist named Charles La Touche was studying moulds linked to asthma.

Theo: Drifted up a stairwell and onto exactly the right dish. That's a lot of luck.

Ada: It is, and I'd flag it's a reconstruction, not proven. There's also Ronald Hare's later idea that the cool-then-warm weather let the mould grow first and the bacteria second - creating that inhibition zone. Also plausible, also a reconstruction.

Theo: Okay, so Fleming has this mystery mould. What does he do with it?

Ada: He grows more of it in broth, filters off the liquid - he actually calls it 'mould juice' - and tests it. It kills staph, streptococcus, meningococcus, diphtheria. And crucially, it doesn't harm white blood cells.

Theo: So it kills the invaders but not you. That's the whole dream.

Ada: The whole dream. The mould was Penicillium notatum, and in nineteen twenty-nine he named the active substance penicillin. He wrote it up in the British Journal of Experimental Pathology that June.

Theo: And the medical world goes wild, presumably.

Ada: The medical world shrugs. The paper is published - and almost nobody notices.

The 1930s

A Drug Nobody Could Make

Penicillin unstable, tiny yields - Fleming was no chemist
Couldn't purify or concentrate it into a usable medicine
Fleming used it as a lab tool, moved on by early 1930s

Theo: I don't get it. He's found something that dissolves killer bacteria and doesn't hurt human cells. How is that not front-page news?

Ada: Because Fleming couldn't turn it into a medicine. Penicillin was maddeningly unstable, the yields were tiny, and to concentrate and purify it you needed real chemistry - which wasn't Fleming's strength.

Theo: So he had the miracle in a flask but couldn't get it out of the flask.

Ada: Precisely. He could make a little 'mould juice' that faded fast. Try to inject that into a sick person at the doses you'd need, and you simply couldn't produce enough.

Theo: Did he even think of it as a drug?

Ada: Mostly not. He came to see it as a handy lab tool - you could use it to wipe out certain bacteria on a plate and isolate the ones you wanted to study. By the early nineteen thirties he'd largely moved on.

Theo: That's almost tragic. It's just sitting in the literature, waiting.

Ada: It is. Fleming himself later put it beautifully: 'One sometimes finds what one is not looking for.' But finding it and using it are two different things - and the using would take other people, and a war.

1938–1941

The Oxford Team

Florey, Chain and Heatley rediscovered Fleming's paper, 1938–40
Grown in bedpans by the 'penicillin girls'; mice test May 1940
Albert Alexander improved then died as supply ran out, 1941

Ada: Jump to Oxford, nineteen thirty-eight. A pathologist named Howard Florey and a German-Jewish refugee biochemist, Ernst Chain, are hunting through old papers for antibacterial substances - and they rediscover Fleming's forgotten article.

Theo: So the paper that got ignored finally lands in the right hands.

Ada: The right hands, and the right skills. A biochemist named Norman Heatley figured out how to extract and grow the stuff at scale - culturing the mould in whatever they could scrounge, including ceramic vessels and actual hospital bedpans.

Theo: Bedpans. The dawn of modern medicine, brewed in bedpans.

Ada: With a team of women called the 'penicillin girls' tending them. Then, May nineteen forty, the test that mattered: eight mice injected with deadly streptococcus. Four got penicillin, four didn't.

Theo: And?

Ada: The four untreated mice died. The four treated ones lived. Florey said, 'It looks like a miracle.'

Theo: What about a person, though? Mice aren't people.

Ada: February nineteen forty-one, an Oxford policeman, Albert Alexander, desperately ill with a raging infection - the romantic story says a rose-thorn scratch, though that's disputed. They give him penicillin, and within days he's astonishingly better.

Theo: So it works. That's the ending, right?

Ada: They ran out. They were so short they filtered the drug back out of his urine to reuse it - and still it wasn't enough. He relapsed and died in March. But the proof was undeniable, and now a world war needed it.

1941–1945

Mass Production and Nobel

Peoria, Illinois: mouldy cantaloupe strain + deep-tank fermentation
Enough penicillin by D-Day, June 1944 - thousands saved
1945 Nobel shared: Fleming, Florey, Chain; Fleming warned of resistance

Ada: Britain in nineteen forty-one is bombed, broke and stretched thin - no capacity to mass-produce a drug. So Florey and Heatley carry the work across the Atlantic, to a United States government lab in Peoria, Illinois.

Theo: And this is where cantaloupe comes in? I've been waiting.

Ada: It is. They needed a more productive mould strain, and they found a champion on a mouldy cantaloupe melon in a Peoria market. Pair that with deep-tank fermentation, and suddenly you can brew penicillin by the vat.

Theo: From a leaking plate in Paddington to industrial vats from a supermarket melon.

Ada: By D-Day, June nineteen forty-four, there was enough to treat Allied wounded on the beaches - thousands who'd otherwise have died of sepsis, saved. Fleming was knighted that year; in nineteen forty-five the Nobel Prize went jointly to Fleming, Florey and Chain.

Theo: Good that the team got recognized, not just the famous name.

Ada: And Fleming used his Nobel moment to warn us: misuse penicillin, and you'll breed bacteria that resist it. He called antibiotic resistance decades before it became the crisis it is.

Theo: So the man who found it also foresaw its limit. What a note to end on.

Ada: So think about the chain of it: an untidy bench, a spore on the wrong dish, a paper the world ignored for a decade, then a refugee, a pathologist, a melon and a war.

Theo: And the lesson isn't really 'lucky accident,' is it? It's that a discovery is nothing until someone builds the thing around it.

Ada: That's exactly it. Fleming noticed; Florey, Chain, Heatley and a whole factory of people made it real. Genius spots the clue - but it takes a crowd to save a life.

Theo: And if any of that made you want to pull a thread, you can interrupt us any time and just ask.

Ada: There's a whole further story in that Nobel warning - how penicillin's triumph seeded the age of drug-resistant bacteria we're wrestling with now. It's one tap away if you're curious.

Theo: This was Historai - where history answers back.

Research record