Henry Oldenburg wrote Letter L-053 to Leeuwenhoek requesting that he examine muscle fibers and brains

Oldenburg wrote this letter, now lost, on February 22 O.S. in London when it was March 4 in Delft. It is known only from Leeuwenhoek's references to it in two subsequent letters. See Letter L-052 of 22 February 1677 for the two source letters.

Following up on requests by members of the Royal Society, Oldenburg asked Leeuwenhoek to investigate muscle fibers and the cortical and medullar parts of the brain.

In the two letters that he dated 12 and 22 February 1677 O.S. (L-052 of 22 February 1677 and L-053 of 4 March 1677 N.S.), Henry Oldenburg writes to Leeuwenhoek that his observations of water (Letter L-040 of 9 October 1676) were well received by the members of the Royal Society, although they find it hard to conceive of the quantity of little animals that L. claimed to have seen. They also ask L. to further study muscles and brains. Oldenburg also passes along the greetings of Robert Boyle and Nehemiah Grew.

This letter is calendared as Letter 3068 in Hall and Hall, The Correspondence of Henry Oldenburg, vol. XIII, July 1676 – July 1681, p. 218.

In Letter 31 [19] L-054 of 23 March 1677, Collected Letters, vol. 2, L. explains his method for calculating the number of little animals. In Letter 32 [20] L-056 of 14 May 1677, ibidem, L. further examines muscles and brains, as the members of the Royal Society had requested.