Velthuysen was a supporter of Leeuwenhoek's work. They both were criticized negatively for their views. Velthuysen was a liberal member of the Utrecht city council who got into trouble with the Reformed church. In Leeuwenhoek's case, it was the local medical experts who criticized him.
As Leeuwenhoek explained:
My intention is not to stop my investigations in nature, but henceforward not to ask our physicians or surgeons for one thing or another. But on the other hand it is also true that I had previously resolved to stop my investigations, partly because some people have a low opinion of the labor they require, partly because those who, in my opinion, ought to be bent on drawing light and instruction from my discoveries have sent to dissuade me from these investigations.But when I am urged to continue my speculations by learned Gentlemen, among whom you are not the least, I take courage once more and say to myself, there is an excuse for these people.
This letter in June came early in a nine month period between Letter 28 of April 25, 1679, and Letter 29 of January 12, 1680. During that time, Leeuwenhoek wrote ten letters that have survived, none of which contained any scientific observations. Perhaps he felt neglected after his observations of microbes in Letter 18 of October 1676 had been verified the following year.
He did not know that he was soon to be voted in as a member of the Royal Society, which would urge him more than anything would to continue his work.
