Volumes 18, 19, and 20 of Alle de Brieven / Collected Letters became available at the end of 2024, completing the series begun in 1939. Download for free.
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Master list (pdf) of all 602 L-numbers, their Leeuwenhoek number, and their Collected Letters number
Wrote Letter L-579 of 1722-07-07 to James Jurin, a cover letter to Letter L-578, that no little animals are to be found in smallpox pustules; again opposes a proponent of spontaneous generation