HEALTH × TECHNOLOGY

Leeuwenhoek Sees Microbes

1676 CE

History · Early Modern · Holocene · Meghalayan

Antonie van Leeuwenhoek, a cloth merchant of Delft licensed as a surveyor, ground his own lenses and sent what they showed to the Royal Society. His eighteenth letter, dated October 1676, described living creatures too small to be seen without an instrument, swarming in rainwater that had stood a few days in an earthen pot and multiplying in infusions of crushed peppercorns; he judged them ten thousand times smaller than the water fleas already known. His instruments were not the compound microscopes of the day but a single lens set in a brass plate, magnifying between about 25 and 250 times. Having no unit for such sizes, he gave them by comparison, against grains of sand, millet seeds and hairs, and his estimates fall close to values measured since. Henry Oldenburg translated the letter and published extracts from it in 1677. Acceptance was slow, since only an equally good lens could check the claim, and Leeuwenhoek had to send in the written testimony of eight witnesses.

Why it matters

A whole order of living things entered the record, and then waited. More than a century and a half passed before microscopy became the ground on which microbes could be understood to cause infectious disease and to recycle the chemical elements of the biosphere; the letters of the 1670s describe organisms whose importance nobody was yet in a position to suspect. What Leeuwenhoek had seen was settled only in the twentieth century, when his descriptions were matched to bacterial cells at a resolution finer than a thousandth of a millimetre.

Dating & uncertainty

The year turns on which act is counted. The letter describing the little animals is dated October 1676; the Royal Society published a translated and shortened version in 1677; and the letter itself dates the first sighting, of creatures in standing rainwater, to 1675. Accounts that treat the finding of micro-organisms as work shared with Robert Hooke spread it over the years 1665 to 1683, from the Micrographia to the description of bacteria taken from Leeuwenhoek's own mouth. None of these dates is contested; what the choice changes is whether the discovery is an observation, a letter or a publication.

Sources

1. Lane (2015), Philosophical Transactions of the Royal Society B: Biological Sciences · The unseen world: reflections on Leeuwenhoek (1677) 'Concerning little animals'doi:10.1098/rstb.2014.0344
2. Gest (2004), Notes and Records of the Royal Society of London · The discovery of microorganisms by Robert Hooke and Antoni van Leeuwenhoek, Fellows of The Royal Societydoi:10.1098/rsnr.2004.0055
3. Cocquyt et al. (2021), Science Advances · Neutron tomography of Van Leeuwenhoek's microscopesdoi:10.1126/sciadv.abf2402
4. Davis (2022), FEMS Microbiology Letters · Antoni van Leeuwenhoek: defining proportion in the microscopic realm during the 17th centurydoi:10.1093/femsle/fnac025

Our species’ history as one day

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if the 315,000 years of Homo sapiens were compressed into a single day