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Go to   to start streaming thousands of  documentaries and nonfiction shows. In the year 1675, I discovered very  small living creatures in rain water,   which had stood but few days in a  new earthen pot glazed blue within.  Those are the famous words that  Antony Van Leeuwenhoek used   to describe microbes.

Though he didn’t use the  word “microbe”--he called them animalcules--and   the letter itself is not exactly the one he  wrote. Leeuwenhoek’s version was written,   of course, in Dutch and then sent off to  Henry Oldenburg, the secretary of the Royal   Society in London who founded the publication  Philosophical Transactions. Oldenberg translated   Leeuwenhoek’s work into English and published it  in 1677.

The rest, as they say, is microbiology.  In 1932, the scientist Clifford Dobell  published a biography of Leeuwenhoek   called “Antony van Leeuwenhoek and his  “Little animals,”. Dobell introduces his   subject with some self-consciousness for  taking on the story of someone who--if   you’ve been interested in microscopy--you  have almost certainly heard of. And he wrote:  Dear reader: I know full well that you  and everyone else must have met Mr van   Leeuwenhoek many a time before; but please  let me reintroduce him to you, for he is a man   worth knowing more intimately.

Though he was born  exactly 300 years ago he is still very much alive,   and would be glad to make your better  acquaintance—provided only that you are   a “true lover of learning” (as of course you are). The fascination with Leeunwenhoek’s   work for Dobell and so many of us lies  in the scope of Leeuwenhoek’s curiosity,   and in the writing that documented his  many journeys into the microcosmos.  Born in the Netherlands in 1632, Leeuwenhoek was  a draper by trade, meaning that he sold cloth. He   took up microscopy as a hobby, learning to grind  lenses and turn them into a tool to see into   tiny worlds.

The simple microscopes he built were  better than many of those of his contemporaries,   producing images that were both more magnified and  more clear. Those of course compared to what the   average high school biology class has today,  they were very bad at both of those things.  The creatures Leeuwenhoek described  in his 1677 publication were not his   first description of tiny animals in water  though. In 1674, he wrote of “green streaks,   spirally wound,” a description that  later observers have taken to refer to   the filamentous green algae spirogyra.

He also  wrote of little creatures he’d found that were,   as he described them, “a thousand times smaller  than the smallest ones I have ever yet seen   upon the rind of cheese.” Those little cheese rind  creatures he was describing were likely mites.  Reading Leeuwenhoek’s work is kind of like  following an old treasure map. His words   lay out pathways and clues that help us navigate  through a drop of 17th century water. And if you   follow that map, at the end you find a wealth of  information, the knowledge of microbes and their   identities that was still unknown in his time, but  that in the centuries since has been accumulated.  For Dobell, Leeuwenhoek’s 20th century scientist  biographer, this treasure hunt was a long one,   borne out of his own enchantment with  these original discoveries and a desire   to better understand them.

He learned Dutch,  only to find that the 17th century Dutch of   Leeuwenhoek’s letters was impenetrable to  him And with World War I raging around him,   he had to set aside his attempts to  translate Leeuwenhoek’s work for some time.  But eventually, through what seems to be largely a  lot of determination, Dobell was able to work his   way through Leeuwenhoek’s letters. And that labor  of love led, naturally, to translating things like   Leeuwenhoek’s descriptions of his own poop. Per Dobell, Leeuwenhoek wrote the following:  I have usually of a morning a well-formed stool;   but hitherto I have had sometimes a looseness  of the bowels. […] My excrement being so thin,   I was at divers times constrained to examine it.

But Leeuwenhoek wasn’t documenting his stool just   for the sake of it. In that sample, he saw  an opportunity to observe the animals within.  I have at times seen very prettily moving  animalcules […] Their bodies were somewhat   longer than broad, and their belly, which was  flattened, provided with several feet, with   which they made such a movement through the clear  medium and the globules that we might fancy we saw   a pissabed running up against a wall. That description sounds promising,   but Dobell had a problem.

Leeuwenhoek had compared  his microbes to a “pissabed,” and like us,   Dobell had no idea what a “pissabed” is.  Even the original English translation he’d   read shrugged it off as a Dutch term with  no obvious English equivalent. Dobell had   to find a 17th century Dutch-English dictionary  to figure out that a “pissabed” is a woodlouse.  With that reference point, Dobell had enough  to diagnose Leeuwenhoek—very belatedly,   of course—with Giardia, the product of a  flagellate known as Giardia intestinalis.  At the time that Leeuwenhoek was identifying  the microbial residents of his stool,   he almost certainly didn’t know their role in  his poor digestion. Nor did he of course have   any name for them, or any of the other microbes  that we now know he saw.

And yet we can identify   rotifers from his characterization of  their wheeled heads, and vorticella   from his description of their belled bodies. The irony of our centuries-later fascination   with reconstructing and replicating Leeuwenhoek’s  work is that his contemporaries had a much harder   time of it. Leeuwenhoek didn’t help his  cause much, refusing to provide extensive   details of his methods and even keeping his  microscope-building techniques to himself.   He did, however, provide eight signed testimonies  from various men, including a minister,   to verify that he had made these observations.

Of course, signed testimony is one thing.   Reproducibility is another. Several of  Leeuwenhoek’s contemporaries tried and failed   to replicate his observations until finally  Robert Hooke—the famed microscopist and   writer-slash-illustrator of Micrographia—was able  to see the tiny animalcules Leeuwenhoek had seen.  Hooke however was willing to outline his specific  methods and demonstrate them, validating the   observations Leeuwenhoek had made and providing  others with the means to make their own microbial   ventures. And like Dobell centuries later,  Hooke was reportedly so taken with Leeuwenhoek’s   work that he learned Dutch to read his letters.

The legacy of Leeuwenhoek is in the microbes he   uncovered, but of course it was more than that.  It was also the curiosity that he passed on,   and the acts of interpretation that they  inspired—both literally with all of these   scientists taking up Dutch to just learn from his  letters, and then scientifically as we decipher   what microbes he must have seen. And so it seems fitting to close   with how Leeuwenhoek viewed his  own little animalcules. He said,   “Among all the marvels that I have discovered  in nature, these are the most marvelous of all.”  Thank you for coming on this journey with us as  we explore the unseen world that surrounds us.  This episode was brought to you by  CuriosityStream, a subscription streaming   service that offers thousands of documentaries and  non­fiction TV shows from some of the world's best   filmmakers, including award winning exclusives &  originals.

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