Letter, from Antoni van Leeuwenhoek to Robert Hooke, dated at Delft Signed autograph Observations of human blood; an account of Regnier de Graff's experiment of a blood transfusion from one dog to another and then injected milk into one of the dogs; observations of milk; observations of Leeuwenhoek's sputum; concerning the larvae of fleas and their development; observations of organisms in pepper-water Transcribed and translated in 'Alle de brieven van Antoni van Leeuwenhoek', edited, illustrated and annotated by Committee of Dutch Scientists, vol 2, p 303 14 January 1678