Honestly, Alexander Fleming was kind of a slob. If he had been a neat freak, you might not be alive today. It’s a bold claim, but the history of medicine is littered with "what ifs" that usually boil down to a person being in the right place at the right time with the right amount of clutter on their desk.
When people ask alexander fleming discovered what, the answer is almost always "penicillin." But that’s only half the story. The man actually discovered two things that changed how we view the human body's defense systems, and the way he found them says a lot about why some of the best science happens when we aren't looking.
The Cold That Led to Lysozyme
Before the world-changing mold showed up, Fleming had already stumbled onto something pretty cool in 1921. He had a nasty cold. Most researchers would have stayed home or at least wiped their nose, but Fleming—ever the curious (and slightly gross) scientist—allowed a drop of his own nasal mucus to fall into a petri dish full of bacteria.
He didn't throw it away. He watched it.
A few weeks later, he noticed something weird. The bacteria in that dish had literally dissolved where the mucus touched them. He called this substance lysozyme. It’s an enzyme found in our tears, saliva, and, yes, snot. While lysozyme wasn't powerful enough to kill the really "bad" germs that cause major diseases, it was the first time anyone proved the human body has its own built-in chemical weapons.
Fleming actually thought lysozyme was his best work. He was wrong about that, of course, but it laid the groundwork for his next, much messier accident.
The September Miracle: What Alexander Fleming Discovered
Fast forward to September 1928. Fleming was a professor of bacteriology at St. Mary's Hospital in London. He’d been working on Staphylococcus aureus—those nasty little round bacteria that cause boils, sore throats, and abscesses.
He decided to go on vacation to Suffolk with his family. Instead of cleaning his lab benches and bleaching his equipment, he just... left. He piled up his petri dishes in a corner of his lab and walked out the door.
When he came back on September 3, 1928, he started sorting through the stacks of old cultures. Most were ruined by common molds from the air. But one dish caught his eye.
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A mold called Penicillium notatum (now known as Penicillium rubens) had grown in the dish. Around the mold was a clear ring where the staph bacteria had simply vanished. They hadn't just stopped growing; they were dead.
"That's funny," Fleming famously remarked.
He wasn't shouting "Eureka!" He was just confused. He realized the mold was secreting something—a "mold juice"—that was a stone-cold killer for bacteria but seemingly harmless to human cells.
Why the discovery almost failed
You’ve probably heard that once he saw the mold, the world was saved. Not even close.
Fleming was a brilliant observer but a mediocre chemist. He struggled to isolate the actual "juice" from the mold. It was unstable. It broke down quickly. He published his findings in 1929 in the British Journal of Experimental Pathology, but nobody really cared. He even used it as a lab tool to help grow certain bacteria by killing off others, but he eventually gave up on the idea of it being a miracle drug.
For nearly a decade, the most important medical discovery in history sat on a shelf gathering metaphorical dust while the actual mold was kept alive in a few labs.
The Oxford Team: Turning "Juice" into Medicine
If Fleming is the father of penicillin, Howard Florey and Ernst Chain are the ones who actually raised the kid. In 1938, at Oxford University, these two scientists stumbled across Fleming’s old paper.
They had something Fleming didn't: a massive team and better equipment. Chain, a Jewish chemist who fled Nazi Germany, figured out how to stabilize the substance. Florey, an Australian pharmacologist, figured out how to test it.
They did a famous experiment with eight mice. They gave them all lethal doses of streptococci. Four got penicillin; four didn't. By the next morning, the four untreated mice were dead. The four treated ones were fine.
The Case of the Rose Bush
The first human trial was heartbreaking. In 1941, a policeman named Albert Alexander scratched his face on a rose thorn. The infection was horrific—abscesses all over his head, lungs, and even his eye had to be removed.
The Oxford team gave him their tiny supply of penicillin. He improved almost instantly. But they ran out. They even tried to "recycle" the drug from his urine, but it wasn't enough. He died because they couldn't grow enough mold.
How Penicillin Changed the Map of the World
World War II was the real catalyst. The US government realized that more soldiers died from infected wounds than from actual bullets. They poured millions into "Project Penicillin."
They found a better strain of mold on a moldy cantaloupe in a market in Peoria, Illinois. They figured out how to grow it in giant 25,000-gallon vats using "corn steep liquor," a byproduct of corn milling. By D-Day in 1944, the Allies had enough penicillin to treat every single wounded soldier.
What Most People Get Wrong About Fleming
There are a few myths that just won't die.
- Myth 1: He saved Winston Churchill's life twice. (Once from drowning and once from pneumonia). This is totally fake. Churchill was treated for pneumonia in 1943 with a different drug called "M&B," a sulfa drug.
- Myth 2: He was a loner who did it all. Fleming shared the 1945 Nobel Prize with Florey and Chain because he knew his discovery was just the beginning.
- Myth 3: It was an open window. Scientists have tried to recreate the "open window" contamination for years and failed. It's more likely the mold spores drifted up from a lab downstairs where they were studying molds for asthma research.
The Dark Side: Resistance
Fleming was smart enough to see the end of his own era. In his 1945 Nobel speech, he warned that if people used penicillin too much or in doses that weren't high enough, the bacteria would learn how to fight back.
He was right. Today, we call this antibiotic resistance. Superbugs like MRSA are basically the descendants of the bacteria that survived Fleming's "mold juice" and evolved to become tougher.
Actionable Insights for the Modern World
You can’t find a new antibiotic in your sink (please don't try), but you can respect the legacy of what Alexander Fleming discovered by being smart about how you use medicine today:
- Finish your prescription: If a doctor gives you antibiotics, finish the whole bottle. Stopping early leaves the strongest bacteria alive to mutate.
- Don't demand antibiotics for a cold: Colds are viruses. Antibiotics only kill bacteria. Taking them for a virus does nothing but help create superbugs.
- Check your history: If you're ever in London, you can actually visit the Alexander Fleming Laboratory Museum at St. Mary's Hospital. It’s restored to look exactly like the messy room where it all happened in 1928.
- Support new research: We haven't discovered a truly new class of antibiotics in decades. The "Golden Age" Fleming started is at risk, and we need new "accidents" to happen in labs today.