Letter, from Antoni van Leeuwenhoek to the Royal Society, dated at Delft Signed autograph Transcribed correspondence between Leeuwenhoek and Heinsius concerning the discovery that cochineal was an insect and compares it to a leaf beetle; observations of and experiments with cinchona bark; anatomy of cinchona bark 5 figures now no longer exist; engraved figures for publication are attached English translation see EL/L2/18 Transcribed and translated in 'Alle de brieven van Antoni van Leeuwenhoek', edited, illustrated and annotated by Committee of Dutch Scientists, vol 7, p 135 28 November 1687