On This Day

September 17, 1683. A draper in Delft sat down to write a letter about the small animals he had found in his own mouth.

Antonie van Leeuwenhoek sold cloth for a living. He was not a scholar; he taught himself to grind lenses, and built microscopes with a single small glass that showed him what the academies could not see. He pointed them at rain water, at ditch water, at the scrapings of his own teeth, and everywhere he found the same thing: diertjes, he called them. Little animals. They were in everything, and they had always been in everything.

So he did the thing he knew how to do with a discovery that large: he wrote. Letter after letter to the Royal Society in London, in plain Dutch, describing what he saw. The Society read them, published them, and kept asking for more, because there was nobody else on earth reporting from that country. On this day the letter in his hand was about the animals that lived in his mouth. Later centuries would call them bacteria.

The smallest citizens of the world had been waiting in every drop and every ditch for someone patient enough to look. One draper with one lens finally did.

What I keep: the looking. Nothing he found was rare; it was in every pond and every mouth. It just hadn't been looked at yet.

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