Wrote Letter 21 of 1677-10-05 (AB 33) to Henry Oldenburg

Text of the letter in the original Dutch and in English translation from Alle de Brieven. The Collected Letters at the DBNL - De Digitale Bibliotheek voor de Nederlandse Letteren

Leeuwenhoek wrote this letter, sent with a Latin translation, to Henry Oldenburg (who had died a month earlier in September) in reply to Oldenburg's letter of July 28/August 7. Leeuwenhoek wrote about skin, eels, fleas, and measuring and counting microorganisms.

Hooke published the second half of letter in Microscopium in early 1678, followed by a short discussion of Hooke's own efforts at lensmaking.

Leeuwenhoek enclosed five letters with the testimony of eight credible eye-witnesses to microorganisms in infusions.

J. Boogert, lawyer and notary in Delft
W. van der Burch
Hendrik Cordes, Lutheran minister in Den Haag
Robbert Gordon, medical student in Leiden
Benedictus Haan, Lutheran minister in Delft
Aldert Hodenpijl, manager of the Comanscolff, the St. Nicolaas guildhouse (of which Leeuwenhoek was a member) on the Oude Langendijk in Delft
Alexander Petrie, minister of the Scottish church in Rotterdam
Robert Poitevin, doctor of medicine

Volume 2 of Alle de Brieven / Collected Letters (p 449), probably following Dobell (p. 176), misidentifies the Leiden medical student as English baronet Sir Robert Gordon (1647-1704).

In 1694, Beneditcus Haan, by then living in Amsterdam, wrote another letter in support of Leeuwenhoek's observations.