Nehemiah Grew
Grew was one of the few researchers in the 17th century using the microscope, mostly on the anatomy and physiology of plants. Also a member of the Royal Society and often published in Philosophical Transactions, he corresponded directly with Leeuwenhoek. They commented on each other's observations, which sometimes differed. He edited the final six numbers of volume 12 of Philosophical Transactions and published three of Leeuwenhoek's letters, Letter L-060 of November 1677 to William Brouncker and two letters to himself, Letter L-070 of 18 March 1678 and Letter L-073 of 31 May 1678.
Grew got his medical degree from the University of Leiden in 1671, the same year that Leeuwenhoek married Cornelia Swalmius. Whether he knew enough Dutch to correspond with Leeuwenhoek in that language, we do not know because none of his letters to Leeuwenhoek have survived.
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Letter L-066 of 11 January 1678 is the first known letter to Leeuwenhoek from Grew, dated the same day as the letter that he and Robert Hooke both signed. Grew’s next letter to Leeuwenhoek is Letter L-071 of 20 April 1678. He wrote a third and final letter, Letter L-075 of 13 October 1678.
In addition, Leeuwenhoek wrote four other letters to Grew. Letter L-074 of 27 September 1678, discusses sweat-pores, saliva, and blood as well as a parasitic growth on grass affecting meadows outside Delft. Letter L-078 of 21 February 1679, about blood, saliva, liver-flukes in sheep, and the sperm of cod, never reached the Royal Society. Letter L-080 of 25 April 1679 discusses sperm of fish and birds, the testicles and sperm of a hare and of a dog, and calculations for determining the number of sperms in the milt of a cod. Leeuwenhoek’s final letter, Letter L-087 of 13 June 1679, asks for acknowledgement of the letters of 21 February and 25 April 1679.