Wrote Letter L-001 of 1673年04月28日 to Henry Oldenburg about mould and a bee's stinger and eye

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

The original manuscript is not preserved at the Royal Society.

An excerpt was published in Philosophical Transactions, vol. 8, no. 94, 97, dated 19 May 1673, and the figures were published in no. 97, dated 6 October 1673. See Publication history below.

Leeuwenhoek wrote his first letter to Henry Oldenburg, secretary of England's Royal Society and editor of its journal, Philosophical Transactions, sent under cover of de Graaf's introduction. In this letter, Leeuwenhoek replicated and extended several of Robert Hooke's observations in Micrographia: mould, the stinger of a bee, and an eye of a bee. Oldenburg encouraged Leeuwenhoek to do more.

Leeuwenhoek noted the transport of fluid in mold, a theme that would concern him throughout his career. He saw a "globous substance" rise through the mold's stalk. The observation of globules would also recur through his letters, especially the early ones.

He observed a bee's parts, especially its mouth, sting, and eyes, in which he saw the same hexagonal shape as he could see with his un-aided eye in the bee's honeycomb.

He observed a louse and its feelers, legs, and mouth. He made his first attempt to measure microscopic sizes. Its "sting ... was at least five and twenty times less than one single hair."

Oldenburg added a sentence after Leeuwenhoek's observations:

So far this Observer: who doubtless will proceed in making and imparting more Observations, the better to evince the goodness of these his Glasses.

Some of those "more Observations" accompanied the drawings in the first letter, but Oldenburg didn't publish the drawings (below) and detailed explanations until the fall of 1673. By then, he had already received Leeuwenhoek's second letter.