Letter, from Antoni van Leeuwenhoek to the Royal Society, dated at Delft Signed autograph Observations of a spleen of a sheep; observations of the sting of a flea Read to the Royal Society on 20 November 1706 4 figures in red chalk are attached English translation is EL/L4/6 Transcribed and translated in 'Alle de brieven van Antoni van Leeuwenhoek', edited, illustrated and annotated by Committee of Dutch Scientists, vol 15, p 315 English translation printed in 'Philosophical Transactions', vol 25, no 307, p 2305 1 June 1706