Henry Oldenburg wrote to Leeuwenhoek requesting that he examine muscle fibers and brains

March 4, 1677

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.

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.