Henry Oldenburg wrote to Christiaan Huygens about doubting Leeuwenhoek's globules
Oldenburg wrote this letter on 2 February 1675 O.S. in London.
Oeuvres complètes vol. VII, pp. 416-417; original in French; translation from Correspondence of Henry Oldenburg vol XI, p. 177
As for Mr. Leeuwenhoek's observations, most of our investigators are of your opinion, much doubting whether these are not deceptions in his seeing. But I have recently received a long letter from him, in which he tells me of a new way of observing which he says removes any such doubt, yet by means of which he still sees, from what he says, almost the same things which he formerly saw with respect to globules etc. We here will try with time to discover whether he is mistaken or not.