Antonie van Leeuwenhoek is  universally acknowledged as the father of microbiology and the first  person to have observed bacteria.

While that might not sound like a shocker to you, depending on how you look at it,  it can seem… kind of impossible. Microscopes in the 17th century  were just getting started, and bacteria are really small.

So small that even with our modern microscopes, they can still be really hard to see. So without all of the fancy equipment, how did van Leeuwenhoek do  it hundreds of years ago? Funnily enough, to this day we don’t exactly know.

But he definitely did do it. So let’s try to understand how. [♪ INTRO] Before we can really dive into this mystery, let’s chat about microscope  science. Don’t worry, it won’t hurt.

So, the resolution of a microscope  refers to the smallest distance between two objects that you can make out. Not the smallest thing you can see, but how close two things can get to each other until they start looking like they’re touching. Only a few of van Leeuwenhoek’s  microscopes have survived to this day, but the ones we have been able to study have shown a resolution of as small as 1 micrometer.

That’s one millionth of a meter! Another microscope feature  to consider is magnification. This is how many times bigger than real  life the microscope makes the object look. van Leeuwenhoek’s microscopes have been found to have magnifications up to 266x.

While that’s certainly impressive,  that doesn’t quite solve the mystery, because modern microscopists generally say that you need at least 400x magnification  to see bacteria properly. For reference, most bacteria are  just a few micrometers long, tops. That’s bigger than van Leeuwenhoek’s resolution, but not by a whole lot, and  when you’re flirting with the lower limit of what you can  see, things get pretty fuzzy.

If it wasn’t hard enough that they’re  so small, bacteria also move around, and they’re usually transparent. When things are squiggling  around under a microscope, it’s hard to keep them in focus. But we know that van Leeuwenhoek  was able to observe live bacteria, as well as blood cells as they  moved through capillaries!

Not only that, but apparently his  setup was so user-friendly that he could have his own  interactive exhibit in his home, where visitors could look  through his microscope to see the blood circulating  in the tail of a live eel. He basically put the eel upside down in water, and then viewers would look  at the tail from the side. He also made a version where  he’d wrap the fish in wet fabric so it could lay flat under a microscope.

I guess eels just have…  conveniently transparent tails? In fact, he called these versions  of his microscopes “aalkijker,” which can be roughly translated to “eel watcher.” van Leeuwenhoek kept his  microscopy methods super secret. And to achieve these awesome feats of  science way back in the 17th century, many people think that he had to have been up to something that we just don’t know about.

Pinning down his methods has proven to be as slippery as the fish he was studying. In fact, both his contemporaries and  later scientists couldn’t pull it off, which honestly made his findings  take a bit of a credibility hit. Still, we know for sure that van  Leeuwenhoek did discover bacteria.

His publications include illustrations  where you can see the now-classic shapes of bacteria – rod, sphere, and spiral – and even their movement patterns and cilia. And similarly, his illustrations of blood cells reflect what we know them to look like now. He decided to call these  “animalcules,” or “little animals,” which is very cute, and he was really  dedicated to getting good samples. van Leeuwenhoek would collect samples  from his family and friends, himself – including his own poop – and even  from strangers on the street!

To add to his impressive  commitment, van Leeuwenhoek had no formal scientific training,  as getting a university education at the time was inaccessible to him. He was a textile merchant, and it wasn’t until he was 38 that he made his first microscope. Scientists come from all  backgrounds and walks of life.

Somehow, van Leeuwenhoek was  able to figure out a technique to build hundreds of microscopes, involving  highly technical glass-grinding skills, to get his little animalcule drawings. Though, that’s actually a pretty  small element of the mystery, because his birthplace of Delft in the Netherlands also happened to be a hub  for lens making and optics. We’re fairly sure that van  Leeuwenhoek was able to learn some glass grinding basics by simply  watching the local experts at work.

And he was in good company, too: Dutch glass artisans are also credited with having invented telescopes in the 1600s. They really knew what they were  doing with glass over there. But before we get into what van  Leeuwenhoek did specifically that was better than his contemporaries,  we need to go to a quick break.

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Generally, scientists have  uncovered three different lens-making techniques that  van Leeuwenhoek likely used. The first technique was  probably adapted from one of his microscopy contemporaries, Robert Hooke. Hooke’s method involved taking a thin glass rod, melting down the tip to make  a round bead at the end, and then snapping off the bead to use as a lens.

Hooke first published his technique in 1665, years before van Leeuwenhoek  first came onto the scene, so it’s not out of the question that  this is where Antonie got his inspo. Funnily enough, Hooke apparently  thirsted after van Leeuwenhoek’s elusive microscope-making techniques, since van Leeuwenhoek seemed to be able  to get much better images than him. But, a 2021 study shows that van Leeuwenhoek was probably using Hooke’s very own methods.

Oops. Still, Hooke notoriously  hated single-lens microscopes, such as the ones that van  Leeuwenhoek specialized in, so he may have bungled that one for himself. Either way, van Leeuwenhoek moved  on to other lens-making techniques, so we can’t accuse him of  only copying other people.

The second lens crafting method  he used was more well-known, taking a lens and grinding and polishing  it down to the right size and thickness. This resulted in a lens that was convex  on both sides, or “lentil-shaped.” The word “lens” comes from the Latin  word for “lentil” for this exact reason! The third technique was one van Leeuwenhoek  likely came up with all on his own.

According to a 2021 analysis of  some of his surviving microscopes, his highest-power lenses might have  been made through glass blowing. Instead of being perfectly  spherical, like Hooke’s lenses, or perfectly convex like the ground lenses, van Leeuwenhoek’s glass-blown lenses have various curve angles and  widths at different points. These lenses are also super smooth,  which probably helped van Leeuwenhoek get that extremely high magnification  and resolution that he needed.

But like all his other  methods, van Leeuwenhoek kept the details of his techniques close to the chest. That 2021 study had to infer  how his lenses were made by using a technique called neutron tomography, basically blasting a beam  of neutrons at the lenses to get super detailed images of their structure. In addition to the quality of his lenses, we need to talk about an important difference between Hooke and van Leeuwenhoek.

As we mentioned earlier, Hooke  hated single lens microscopes, so he mostly worked with compound  microscopes, which have multiple lenses. Van Leeuwenhoek, on the other  hand, almost exclusively used single lens microscopes, which are  scientifically called simple microscopes. While the vast majority of  modern microscopes are compound, both simple and compound microscopes  had their strengths and weaknesses, back in the 17th century when people had to make all their scientific instruments by hand.

Lenses are subject to something  called chromatic aberration if they aren’t aligned one  hundred percent perfectly. Lenses work by bending light, but each wavelength of light  bends slightly differently. That’s great when we get cool things  like rainbows through a prism, but not so great when you’re trying to focus all of your colors on a single  tiny point with your microscope.

And if you’re trying to concentrate  light through multiple lenses, your chance of getting chromatic  aberrations is even higher, which means your image doesn’t come out as clear. So this is where having a single-lensed  microscope may have come in handy. Even though compound microscopes  are generally stronger nowadays, van Leeuwenhoek’s simple  microscopes were able to get clearer images without all of those  aberrations at a higher magnification.

Hooke may have only had access  to about 50x magnification, whereas van Leeuwenhoek’s surviving  instruments go up to 266x. But remember that 266x magnification,  while impressive, is still not up to the 400x minimum that you need  to generally see bacteria clearly. Most likely, van Leeuwenhoek’s innovative  spirit didn’t stop at lens crafting.

He was also probably working with optical lighting techniques that he  didn’t tell people about. Most of the people around van Leeuwenhoek’s time, and even nowadays, were using a  lighting method called brightfield. This is when light is shone onto the sample  at an angle that bounces right back into the lens, and anything you see will show  up as dark objects on a light background.

On the other hand, darkfield illumination  directs the light source to bounce around the sample and reflect away from  the lens, so the only light that makes it back up through the  microscope lens for the viewer to see is anything that bounces  off of the sample itself. So instead of a dark sample  showing up on a light background, you see glowy shapes on a dark background. The glowing lines of darkfield  illumination give you much higher contrast than you typically get with brightfield, so you actually don’t need as strong of a  magnification to get a really clear image.

Based on how van Leeuwenhoek  described his microscopy results, we’re almost sure that he must have used darkfield illumination to get  his super clear view of bacteria. Though he might not have needed to  use darkfield to see blood cells, which only need about 40 to 100x magnification, his description of blood cells suggests  that he also looked at them with darkfield techniques, describing them as “sand grains… upon a piece of black taffety silk”. Still, all of this information  had to come about through some serious sleuthing by the scientists  that came after van Leeuwenhoek.

Aside from actively preventing  people from learning his techniques, van Leeuwenhoek wrote in a letter  once that he didn’t see much use in teaching posterity about his methods,  partly because not many students seemed interested in science beyond  getting a ton of money and fame. Y’all are getting money and  fame from doing research? So it seems that van Leeuwenhoek  was able to see bacteria, with just him and his single lens  microscope against the world, thanks to some pretty innovative  lens-making and lighting techniques.

At the end of the day, Antonie  van Leeuwenhoek was able to accomplish something really  groundbreaking that is still not easy to do with all of our  fancy, modern equipment today And even though hiding your  methodology is pretty uncool in the scientific community, there’s no doubt  that this guy really was the first person to see bacteria, with nothing but sheer dedication to the craft and a boatload of naysayers. Though he wouldn’t have had so many  naysayers if he just shared his methods! [♪ OUTRO]