Hendrik van Bleyswijk wrote to Gottfried Leibniz about encouraging Leeuwenhoek to take on students
On the topic of encouraging Leeuwenhoek to share his methods with students, Gottfried Leibniz had an exchange of letters in French with Hendrik van Bleyswijk in 1697 and 1698.
Leibniz replied to this letter on 24 December 1697, to which Bleyswijk responded on 17 February 1698.
Allgemeiner Politischer und Historischer Briefwechsel (General political and historical correspondence), vol. 14, May-December 1697
I am of your feeling, that we must give our Mr. Leeuwenhouck, with whom I shared your letter, some young students, not only to help him in these observations, but also to be able to continue after his death, but he is somewhat restrained to show others the method he uses in these observations, but I will not allow him to do so.