Henry Baker drew this illustration of van Leeuwenhoek's microscopes in 1756.
1683: Anton van Leeuwenhoek writes a letter to Britain's Royal Society describing the "animalcules" he observed under the microscope. It's the first known description of bacteria.
Van Leeuwenhoek had a varied career in his hometown of Delft, Netherlands. He earned money with stints as fabric merchant, surveyor, wine assayer and minor city official. He also served as trustee of the estate of painter Jan Vermeer, who died bankrupt.
One thing he did not do was invent the microscope, regardless of his glorious association with that instrument. Nor did his well-known contemporary, the Englishman Robert Hooke. The compound microscope (using an ocular and an objective lens in series) was invented in the 1590s, some four decades before their birth.
Van Leeuwenhoek, in fact, didn't even use a compound microscope. Despite the eventual superiority of the concept, the compound designs of his time couldn't produce a clear image at much more than 20x or 30x magnification.
After seeing Hooke's illustrated and very popular book Micrographia, van Leeuwenhoek learned to grind lenses some time before 1668, and he began building simple microscopes. This jack-of-all-trades became a master of one.
His simple microscope design used a single lens mounted in a brass plate. A sharp point held the specimen for examination. One screw moved the specimen into position in front of the lens, and another screw moved it backward or forward into focus.
(Fewer than 10 of van Leeuwenhoek's original microscopes survive, but you can use these plans to build a replica if you're so inclined.)
Van Leeuwenhoek had to hold the 3- or 4-inch instrument close to his eye. Besides good lighting, it required sharp eyesight and a fair dose of patience. Van Leeuwenhoek had both. He built the best microscopes of his day, achieving magnifications above 200x.
Delft's deft optician also had a fair dose of curiosity. He started writing letters to England's Royal Society in 1673, with descriptions of what he saw. One letter in 1674 detailed his observations of lake water, in which he detected green spiral algae.
The Royal Society translated van Leeuwenhoek's letters from Dutch and published them in English and Latin. His missive of Sept. 17, 1683, detailed how he took plaque from between his teeth and from four other people, including two who had never cleaned their teeth. It was, he wrote, "a little white matter, which is as thick as if 'twere batter." Continuing:
I then most always saw, with great wonder, that in the said matter there were many very little living animalcules, very prettily a-moving. The biggest sort … had a very strong and swift motion, and shot through the water (or spittle) like a pike does through the water. The second sort … oft-times spun round like a top … and these were far more in number.
The "unbelievably great company of living animalcules … were in such enormous numbers," van Leeuwenhoek wrote, "that all the water … seemed to be alive." These are among the first recorded observations of living bacteria.
Van Leeuwenhoek was also the first to see foraminifera fossils in minerals. He discovered blood cells (confirming William Harvey's work on circulation a few decades earlier) animal sperm cells, nematodes and rotifers.
Van Leeuwenhoek sent more than just letters to London. He sent specimens, and some of his original samples were rediscovered in 1981 in the strong room of the Royal Society. Astonishingly, they were so well prepared that they could still be examined under modern microscopes.
So, van Leeuwenhoek's place in history is not as the inventor of anything, but as a scientist, the founder of experimental microbiology.
Source: University of California Museum of Paleontology
Christina Bonnington 17 Sep, 2012
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