Johan Ham

"best capable" scientific colleague
~ 1651
after 1723

Ham, from Arnhem, was a medical student in Leiden after 1671. He studied with Prof. Theodore Craanen, who had visited Leeuwenhoek. In 1677, Ham brought ejaculate from a gonorrhoea sufferer to examine under Leeuwenhoek's lens. In it, they found sperm, which Leeuwenhoek reported to the Royal Society in a letter to William Brouckner dated November 1677.

After completing his studies, Ham returned to Arnhem, where he practiced medicine and served as mayor.

Twenty years later, Nicholas Hartsoeker wrote a book taking credit for discovering sperm. Leeuwenhoek defended his own priority in a letter to Harman van Zoelen that mentions Ham.

Now the fact is that I attribute the first discovery of the Animalcules in the Male sperm not to Mr. Hartsoeker, but to Mr. Ham, whom because of his modesty, good judgment, and diligence I held in great esteem and whom among many People I deemed the one best capable of investigating the secrets of Nature.

This Mr. Ham, who was studying Medicine, as Professor Craanen wrote to me in the Year 1677, visited me in August 1677, and thereupon in November of the same Year, I wrote the Following discoveries to the Royal Society in London ...