Have you ever seen the word “pasteurized” on a carton of milk? You might think it means something about pastures – big grassy fields where animals graze. That’s usually how people pronounce it. But while it’s nice to think of the cows that gave us the milk sunning themselves in grassy pastures, the word actually refers to something that happens after the milk is out of the cow. Before milk goes into cartons and then on to the store, it undergoes pasteurization. The milk is heated to a specific temperature in order to kill any harmful microorganisms, or germs, that might make you sick. It has nothing to do with grassy fields! Instead, it’s named after the man who invented the process: Louis Pasteur.
Educational Background of Louis Pasteur
Louis Pasteur’s background gave no hint that he would become a great scientist later in life. Born in 1822 in Dole, France, he came from a long line of leather tanners. His family was poor, and Louis wasn’t even that interested in school as a child. He preferred fishing and drawing. He actually became very good at drawing portraits of his friends and family using pastels and pencil.
Things began to change when Louis went off to college. He began to study hard, but still struggled. His grades in chemistry – a subject he would later do important work in– were especially bad. He wanted to go to the prestigious Ecole Normale Superieure in Paris, but had to take the entrance exam twice! But even though he had setbacks, his hard work and dedication paid off.
While he was working to try to get into the Ecole Normale, Louis began attending lectures by a famous chemist, and decided that he wanted to be a chemist too. So, when he finally went to the Ecole Normale, that’s what he studied. After he got his doctoral degree, he got a job at the University of Strasbourg, teaching and doing research in the structure of chemical crystals.
He also met his wife, Marie, there. She was the daughter of the head of the university. At first, she wasn’t so sure about this serious, somewhat shy man. But after getting to know him better, she fell in love too, and they married. She would support him throughout their lives together, helping in the lab and with his papers.
Louis Pasteur’s Early Works
Even though Louis started out as a chemist, his most important work is in microbiology, or the study of organisms so small, you need a microscope to see them. This shift happened almost by accident, but as Louis himself reminded people, “In the fields of observation, chance favors the prepared mind.” In 1854, he got a new job at a university in northern France. While there, the owner of a factory came to him with a problem. His factory fermented sugar beets to make alcohol, but sometimes he ended up with a spoiled, sour elixir, instead of alcohol.
At this time, scientists didn’t know how fermentation worked. Some thought it was just chemicals rearranging themselves spontaneously under the right conditions. Most people just knew that when you left crushed grapes or soggy grain in a covered container for long enough, you got wine or beer. Louis wasn’t satisfied with those answers though, and set about trying to solve the mystery. He got samples of the good alcohol and the sour substance and put them under his microscope.
What do you think he saw?
He saw different kinds of microorganisms swimming around in them! The alcohol samples had yeast, which is a microscopic type of fungus. The sour stuff had bacteria, which is a completely different kind of microorganism! Both types float around in the air, but Louis was the first to realize that the yeast settled in containers of grapes or mashed grain and caused fermentation. Those tiny yeast ate up the sugars in the beets, used it to make energy, then got rid of the uhhh…waste that they didn’t need. That waste was the alcohol.
Studies in Microorganisms
Louis was hooked. He went on to study the microorganisms in wine and beer, finding new ways to make sure they weren’t contaminated by tiny critters that would spoil them. But he wasn’t just interested in making beverages safer, although this was very important for people’s health and the French economy. Louis wanted to know more about how these tiny microorganisms lived. If so many scientists were wrong about fermentation, what other discoveries were waiting to be made?
One idea that didn’t make much sense to Louis was “spontaneous generation.” Spontaneous generation was the idea that some living creatures just arose from nonliving things. Rotting meat made flies, some people thought, because they’d seen fly larvae on rotting meat. Louis thought that flies must be laying tiny eggs in the meat. He suspected that microorganisms, like the yeast in beer and wine, actually float around in the air, settling on things and, if the conditions are right, growing and multiplying.
Louis devised an ingenious way to demonstrate that living things didn’t just spring fully-formed from non-living things. He designed a bottle with a long, skinny neck that curved downward like the top of the letter S, opening toward the ground. He then boiled a broth, killing any microorganisms that were already in it. He poured some of the broth into the S-neck bottles, and some into bottles with necks that opened upwards, toward the sky.
Then he waited. After a few weeks, the bottles with the S-necks hadn’t really changed. But the ones with upward-facing necks had become cloudy. Looking at the liquid under a microscope confirmed that microorganisms had landed from the air and grown in it. But, microorganisms couldn’t land in the S-neck bottles, so that liquid stayed clear!
With all these accomplishments and discoveries to his name, you might be wondering, what else can one scientist do? A lot, it turns out! Louis wanted to study how microorganisms might be involved in causing diseases, and maybe even find ways to prevent or cure those diseases. Sadly, he was motivated by events in his own life: three of his daughters passed away from typhoid fever when they were young. He started studying two diseases caused by bacteria: chicken cholera and anthrax.
Chicken cholera is not a serious disease for humans, but is deadly to chickens, which you might have guessed from the name. Louis developed a vaccine for it almost by accident, but as with his study of microorganisms in alcohol, he was prepared to take advantage. Before going on vacation Louis gave an assistant specific instructions for how to infect some chickens with the bacteria they had been growing. But the assistant waited too long, and the cholera bacteria dried up. Lucky chickens!
But Louis didn’t think of himself as unlucky. Instead, he decided to give the chickens a dose of the dried-up, mostly-dead bacteria. These chickens got a little sick, but soon recovered. Later, Louis injected those same chickens with fresh, living cholera bacteria. Louis suspected that the first dose of mostly-dead cholera bacteria might actually protect the chickens from the living bacteria. He was right! The chickens didn’t get sick again!
Next, Louis heard about a vaccine for anthrax that a veterinarian named Jean Jaques Henri Toussaint had invented. Anthrax bacteria was deadly to both farm animals and people. He tested Toussaint’s vaccine, and it worked. In an unfair twist, Louis got credit for creating the vaccine, because his test was more widely covered in newspapers at the time. Sadly, Toussaint died only a few years later.
But Louis wasn’t done working on vaccines. The next disease he studied was truly terrifying: rabies. Rabies is a virus that causes animals, and unfortunate humans they might bite, to get a high fever, behave aggressively, fear water, and eventually die. There was no cure. Louis got to work, trying to develop a weaker version of the disease that could be used to make a vaccine. He tested it out on dogs. It seemed to work, but Louis wanted more time to experiment.
But the experiment was about to speed up. One summer day in 1885, a mother burst into the lab, gripping the hand of her nine year old son. Both were crying and distraught. The boy, Joseph Meister, had been bitten 14 times by a rabid dog. Louis was worried because he had never tried his vaccine on a human. But without help, Joseph would die. Louis had to try. Just as they had done with the dogs, Louis and his assistants injected Joseph with the vaccine several times over the course of weeks. Louis and the boy’s mother spent this time worrying and waiting. It can take weeks or months for a person to get sick with rabies after they’ve been bitten, so they wouldn’t know if the vaccine had worked for some time.
But time passed, and Joseph stayed healthy! He went back to school and playing outdoors, though I wouldn’t be surprised if he was afraid of dogs after that. People all over the world heard about the new rabies vaccine, and people came from miles away to receive it if they’d been bitten. Today, almost all pet dogs and cats get the rabies vaccine, though humans usually only get it if they’ve been bitten by a wild animal. Louis’s vaccine saved countless lives.
Louis Pasteur always wanted to use his work to serve others. Thanks to his work, we know a lot more about how microorganisms work, how they cause disease, and how to keep from getting sick from them. But Louis knew that wanting to do good wasn’t the same as actually doing it. He worked tirelessly, sometimes pacing the room late at night while he thought through a problem. He was careful and methodical in his work, trying to be sure he’d gotten it right, before he made any exciting announcements. But he also knew when to take advantage of an opportunity. If he didn’t, he never would have studied the yeast in fermented drinks, or how to make vaccines from weakened germs. He never would have saved Joseph Meister’s life with his rabies vaccine. Your milk wouldn’t be as safe to drink. So next time you notice something unexpected, or find something didn’t work the way you thought, think of Louis Pasteur, and keep examining it. Look at it carefully. You might discover something amazing!
Curtis, Robert H. (1993) Great Lives: Medicine. Macmillan, New York.
Dickman, Nancy (2016) Louis Pasteur: Germ Destroyer. Gareth Stevens Publishing, New York.