In the late 1600s, the Dutch tradesman Anthoni van Leeuwenhoek began investigating the world of the very small using the first microscope, discovering a riotous world of protists, bacteria, and other previously unseen organisms. Subsequent generations of scientists have developed ever-more-sophisticated means of probing the microscopic world, bringing many mysteries of the biological realm into stunning relief.
source https://phys.org/news/2021-10-microscopy-home-biology-elusive.html