Letter, from Antoni van Leeuwenhoek to the Royal Society, dated at Delft Signed autograph Investigation of 'raijs calomba', a medicinal root, and an experiment with an extract of the root, and a distillation of the root, with Leeuwenhoek's blood; observations of bladderstones 21 original figures no longer exist; engraved figures for publication are attached Transcribed and translated in 'Alle de brieven van Antoni van Leeuwenhoek', edited, illustrated and annotated by Committee of Dutch Scientists, vol 7, p 175 25 May 1688