Leeuwenkoek's observation of bacteria.
A form of dark-field illumination was produced that allows bacteria in aqueous suspension to be observed with both a Leeuwenhoek microsocope and a compound microscope without a condenser. Possibly, this illumination was Leeuwenhoek's "particular method of observing" bacteria.
D001419:Bacteria / Q000166:cytology; D005197:Famous Persons; D006666:History of Medicine; D008029:Lighting; D008853:Microscopy / Q000266:history*