He Looked Before Throwing It Away

Your child listens; you read. This page is here so you can answer the questions that come after the story. The script itself is available from the script button while the audio plays.

What this episode covers

He came back from holiday to find mould growing in a culture dish. A ruined experiment. Normally you throw it out.

But he looked first — and saw a clear ring around the mould where no bacteria were growing. The episode starts there, explains why it took another ten years before antibiotics reached patients, and ends with the warning the discoverer himself gave when he accepted his prize.

It is an episode about what luck needs in order to become a discovery.

What actually happened

• Alexander Fleming (1881–1955), a bacteriologist at St Mary's Hospital in London.

• In the summer of 1928, sorting through culture plates after a holiday, he found a plate where staphylococci had failed to grow around a patch of Penicillium mould.

• He cultured the mould separately and studied the properties of its broth systematically, publishing in 1929. From the original paper:

  • antibacterial power peaks at about seven days at 20 °C, declines after ten days, and is nearly gone in four weeks
  • the active agent filters readily, and he gave the filtrate the name "penicillin"
  • a few minutes of boiling does not destroy it, but an hour of boiling in alkaline solution, or autoclaving at 115 °C for twenty minutes, effectively does
  • it dissolves in alcohol but not in ether or chloroform

• The obstacle was instability. He could not purify and preserve it, so it did not become a treatment.

• In the early 1940s, Howard Florey and Ernst Chain at Oxford returned to his paper and succeeded in purifying and mass-producing it. It saved enormous numbers of wounded during the Second World War.

• In 1945 the three shared the Nobel Prize in Physiology or Medicine.

• In his Nobel lecture, Fleming warned about resistance — that misuse would let bacteria survive the drug. That warning has come true.

• Where he came from. Professor of Bacteriology at St Mary's Hospital, London (1928), raised in rural Scotland, and formed by his experiences in the First World War (PMID 39176366).

• Someone saw it first. More than thirty years earlier, in Italy, Vincenzo Tiberio had already observed the antibacterial action of mould (PMID 41235048) — the same position as Peter Plett in the Jenner piece, which the story calls by name.

• He did not know its size himself. Publishing in the British Journal of Experimental Pathology in June 1929, he made only a passing reference to penicillin's therapeutic potential (PMID 41235048).

Questions your child may ask

"How does mould kill bacteria?" Mould and bacteria compete for food in a small space, so some moulds make substances that interfere with bacteria. Penicillin blocks bacteria from building their outer wall. Human cells have no such wall, which is why it is comparatively safe for us — and why antibiotics are possible at all.

"So if I eat mouldy bread, will I get better?" No, and this is worth stating plainly. The moulds on bread are different species, and some produce toxins. Penicillin is a specific substance extracted and purified from a specific mould. That extracting and purifying is exactly the part that took another ten years.

"Why did it take ten years?" Because a discovery is not a medicine. Fleming found the substance but did not know how to collect, concentrate and store it. That was a problem of chemistry and manufacturing, and another team spent years solving it. For a child: a discovery is a beginning, not an ending.

"Are there really bacteria that the medicine doesn't work on?" Yes, and there are more of them each year. Bacteria multiply extremely fast, and any that happen to survive the drug go on to spread. That is why antibiotics should be used only when needed, and finished completely. Stopping halfway kills the weak ones and leaves the survivors.

"Wasn't he just lucky?" Luck was part of it, and he said so himself. But the same thing could have happened in other laboratories — mould on a plate is common. The difference is that he looked before throwing it away, and then spent months studying it properly.

Ideas inside the story

• Antibiotics — a medicine that attacks bacteria specifically.
• Resistance — survivors spread, and the drug stops working.
• Prepared chance — an accident becomes a discovery only for someone ready to catch it (the same theme as the Röntgen episode).

What is evidence, and what is received story

In the original paper Peak potency at about seven days, the name "penicillin" given to the filtrate, survival of brief boiling but destruction by autoclaving, and solubility in alcohol but not ether or chloroform. These are the details behind the story's line about how carefully he wrote things down.

Well-established history The 1928 discovery, the 1929 publication, the decade-long gap, Florey and Chain's purification and wartime use, the shared prize in 1945, and the warning about resistance in the Nobel lecture.

Deliberately left out The often-quoted detail that spores "blew in through an open window" is treated only lightly — there are competing accounts of how the mould arrived, including that it drifted up from a laboratory below. No specific discovery date is asserted either.

Sources and what followed

Original paper — Alexander Fleming, "On the Antibacterial Action of Cultures of a Penicillium…" (1929). Listed in Paperis' Shoulders of Giants under medicine.

What this discovery led to

• The antibiotic era — deaths from infection fell sharply. Surgery, cancer treatment and transplantation became possible largely because infection could be controlled.
• An industry for making medicines — turning a discovery into mass production became a discipline of its own.
• Resistance, still unsolved — flagged by the discoverer from the very beginning, and now among the World Health Organization's top priorities. It is still an open problem.

Try this together

• Talk about why a course of antibiotics must be finished. Children experience this directly, so it lands quickly.
• Leave a piece of bread or a tangerine in a sealed jar for a few days and watch the mould (do not eat it; discard afterwards). It gives a real sense that mould is a living thing.
• Think of one thing today you wrote off as a mistake, and look at it once more before throwing it away. That is where the story ends.