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Michael: Have you ever saved someone’s life? Maybe you’ve pulled a kid out of the street just in time, or fished a friend out of the river, or did the Heimlich maneuver on the guy sitting next to you at the deli. There’s a small group of people in history -- let’s just call them what they were... nerds... whose scientific contributions have saved -- not that it’s a contest -- like, hundreds of millions, if not billions, of people over time. Including you, probably.

Now, this isn’t a comprehensive list or anything. Frankly, history is full of life-saving, world-changing scientists. We just picked three of them. And it’s important to remember that science is both collaborative and cumulative -- researchers work with a whole team of people, and build on the work of those who came before them. No scientist is an island. But these are people who spearheaded both simple and revolutionary discoveries, from proving that germs exist, to convincing doctors to start washing their hands, to creating vaccines to stop common diseases.

First up, the guy whose name you’ll find on nearly every gallon of milk at the grocery store: Louis Pasteur, the founder of germ theory and the father of microbiology. Born in rural France in 1822, as a kid Pasteur was more interested in art than science, earning a Bachelor of Arts before turning his focus to chemistry and physics. He liked the idea of putting science to practical use in industry, and some of his early work focused on figuring out how to better manufacture wine. Hey, it was France.

Of course, people had been making alcoholic beverages since practically forever, but it was Pasteur who gave us our modern understanding of the fermentation process -- he showed that it’s the action of living, multiplying microorganisms, specifically yeast, that turns sugar into booze. That might be common knowledge today, but back then, people didn’t know much -- if anything -- about microbes. There had been some speculation about what we now call germ theory -- the idea that microorganisms might cause some diseases and make food spoil. But the prevailing scientific theory of the time was something called spontaneous generation, the notion that some organisms just sort of appeared out of thin air, or came to life from decaying organic matter. I’m not kidding, for a long time people thought baby mice came out of decaying hay, and maggots were born from rotting meat. Even after those specific things were disproven, people still believed that spontaneous generation was a thing under certain circumstances.

But not Louis. Building on the work of an 18th-century Italian physiologist named Lazzaro Spallanzani and others, Pasteur conducted what ended up being one of the most important experiments of all time. He boiled some broth in swan-necked flask, effectively sterilizing it -- so there were definitely no breeding bacteria or anything. The container allowed filtered air to enter the flask, but would catch any microbes in the bend of the neck. Then he waited, and nothing happened -- the broth never spoiled, meaning microbes weren’t just appearing out of thin air. But, if he tipped the glass so that the broth touched that filtering point in the neck that was catching all the microbes from the incoming air, the broth quickly began to go bad.

That one simple experiment showed that life didn’t just spontaneously appear out of nothing, but there were microbes in the air all around us. Basically: he proved that germ theory was real. With his new-found understanding of microbes in hand, Pasteur hit the bottles again, experimenting with techniques to keep wine and milk from spoiling. Then, in 1862, he found that heating up wine without actually boiling it would still kill bacteria and keep it from spoiling. That’s the process we now call pasteurization, and it’s still used today to protect and preserve a number of foods, like milk and other dairy products.

By this point, Pasteur was in his mid-forties, and he wasn’t doing too well, health-wise. He had a stroke and ended up partially paralyzed. Even so, he continued his experiments, and went on to invent the first laboratory-developed vaccine, for chicken cholera. He then went on to create vaccines for more diseases, like anthrax and rabies. The doctor Edward Jenner, who died about a month after Pasteur was born, had already discovered the smallpox vaccine in the late 1790s. But it wasn’t until Pasteur proved germ theory that people really began to understand how viruses and bacteria worked -- and with it, the real science behind vaccination.

You really can’t oversell the importance of getting the world on board with the idea that microbes can spread, causing infection and disease, so the next time you crack open a nice bottle of wine, don’t forget to raise a glass to Pasteur. In fact, Pasteur greatly influenced our next legendary lifesaver, the British surgeon who completely transformed surgical practices -- or, as I like to think of him, the guy who finally got doctors to wash their hands.

Joseph Lister started life in Essex, England in 1827. He was born into a wealthy Quaker family, and his father was an amateur scientist who helped design microscope lenses in his spare time. Lister was interested in science from a young age, and by college knew he wanted to both work as a surgeon, and do research to help improve medical knowledge in general. Which, as it turns out, was desperately needed at the time.

Let me paint a little picture for you: You’re living in Europe in the mid 1800s. You fall off a ladder and break your leg. Your friends throw you on a cart and wheel you to the hospital. The doctor says they have to operate, and you don’t get any anesthesia because it’s not really a thing yet. The surgeon walks in with dirty hands, unsterilized equipment, and an apron he likes to keep stained and bloodied for the street cred. You pass out from the pain, and when you wake up, your chances of surviving the coming infection are less than 50-50 on a good day, in a decent hospital.

That is the world Lister walked into after finishing his doctorate in the early 1850s. But don’t be too hard on the surgeons -- this was before Pasteur proved germ theory, and the common belief was that there wasn’t much they could do, since some wounds just spontaneously generated infections. But Lister wondered if there actually was a way to prevent those infections. He started noticing that patients with simple fractures -- where a broken bone didn’t pierce the skin -- were far more likely to recover than those with an open wound exposed to the air. This suggested that rather than springing from the wound itself, infection must somehow get in from the outside, and he started washing his hands and clothes before operating.

Around that time, he became a professor of surgery in Glasgow and read about Pasteur’s groundbreaking work on germ theory. It made a lot of sense to Lister. He figured that if outside germs were infecting wounds, then killing those germs should -- in theory -- prevent infection. Now, Pasteur stopped wine and milk from spoiling by heating them up, but it’s a lot harder to do that to human flesh. So Lister knew he needed to find the right chemical disinfectant. He chose carbolic acid, otherwise known as phenol, which is a kind of acid that’s extracted from coal tar. At the time, it was being used to disinfect sewers. And in 1865, Lister began experimenting with a diluted form of phenol, using it to sterilize his hands, instruments, wounds, and bandages. He even sprayed it into the surrounding air.

After collecting more than year’s worth of data, he published a paper explaining his new antiseptic technique -- one that had led to a dramatic drop in post-operative patient deaths. But, like so many discoveries, his new protocol was slow to gain traction -- some doctors thought it was too slow and expensive, or tried it but didn’t clean properly, so it didn’t work as well. Others still just didn’t believe in germs. But by 1880, after more than ten years of incredible results, his antiseptic principle was nearly universally accepted. Lister continued to improve surgical practices throughout his career -- for example, he introduced stitches made from sterilized catgut, which would dissolve instead of having to be pulled out. He went on to become Queen Victoria’s personal surgeon, and won a bushel of prestigious honors, including a lordship, for his many contributions. And maybe most prestigious of all...Listerine Mouthwash? That was named after him.

That Pasteur-Lister one-two punch has probably saved billions of lives over the last 150 years. Which brings us to our next science hero, who took preventative life-saving to a whole new level with an arsenal of modern vaccines, starting with the shots you probably got as a baby. Maurice Hilleman was born the youngest of eight children on a Montana farm in 1919. His life got off to a rough start when his mother and twin sister died during his birth, and he was raised on his uncle’s farm, tending chickens and reading Charles Darwin. Then he went on to do some scientific research of his own.

By his mid-twenties, Hilleman had already helped develop his first human vaccine, one designed to help protect overseas soldiers from encephalitis. We’ve talked about how vaccines work before -- but in a nutshell, they trigger your immune system to make antibodies against a particular disease, without actively making you ill with that disease. This creates a kind of memory for your immune system, so if you run into that disease in the airport or lunchroom or whatever, your immune system will be like, "hey, I know you," and start cranking out antibodies to fight it.

Generally, to make a vaccine, you first have to mass produce the virus or bacteria, by infecting cells grown in cultures, or sometimes chicken eggs. Then, once you’ve got a good working supply, you can work on weakening that pathogen to turn it into a vaccine. Basically you want to administer just enough virus or bacteria to get the antibodies flowing, without getting anyone too sick. Hilleman was like, the Superman of this process. Through his research on the influenza virus, he found that people did often develop an acquired immunity the the virus’s small -- but constantly evolving -- mutations. They did that on their own, without a vaccine. But every now and again, the virus made a major genetic leap -- one big enough to leave people with no resistance, and putting the population at risk for a wide-scale pandemic.

For example, in 1957, Hilleman heard about a really bad influenza outbreak in Hong Kong, and suspected a new strain was spreading. Once he and his colleagues got their hands on a sample of the virus, they found that most people did, in fact, lack the necessary antibodies to protect themselves from it. So, fearing the worst, Hilleman got a bunch of manufacturers to immediately start cranking out a vaccine. Over the next two years, about two million people died worldwide from that Asian flu. But the total would have been far higher without Hilleman’s foresight and emergency vaccine.

Around that time, Hilleman joined the Merck pharmaceutical company and started developing new vaccines against common childhood diseases. For example, an American virologist named John Enders had come up with a measles vaccine, but it proved too toxic to use. Hilleman developed an improved version by growing a weaker strain in chicken embryos -- and that vaccination alone is estimated to save over a million lives every year. Then, Hilleman developed a mumps vaccination by isolating the virus from a swab from his own daughter’s throat, and following the same protocol he’d used on measles. Later he combined the two with a third one for German measles, or rubella, creating the still popular MMR vaccine you probably, hopefully got as a toddler.

His team went on to develop many more vaccines, including those for Hepatitis A and B, chickenpox, meningitis, pneumonia, and others. They also contributed to a bunch of other major scientific breakthroughs, including isolating a new family of viruses -- the adenovirus, a common cause of upper respiratory infections in children and adults. And, like the work of Lister and Pasteur, his research has since influenced generations of researchers, paving the way for more medical breakthroughs and saving more lives.

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