On that day, Delft Town Hall gatekeeper Antonie van Leeuwenhoek looked at water through a microscope. This wasn’t an improvised experiment – the former dealer in cloth enjoyed looking through polished glass at sheepskin or the wings of a fly... What happened later is well described by the verses of Nikolay Kolotsky:

Through Leeuwenhoek's magic instrument,

Our science has discovered

The traces of an amazing life

In a drop of water.

The discovery was confirmed by the Royal Society in London, and curious people were drawn in Delft. Among others, the amateur natural scientist introduced the world of microbes to Russian tsar Peter the Great. The latter became so disgusted by “little animals” that he ordered every soldier of the Russian army to kill them by the thousand. One should definitely take personal hygiene seriously as confirmed later by Korney Chukovsky. Jokes aside, Leeuwenhoek had discovered more than 200 microbes and built over three hundred microscopes over a span of fifty years.