Antonie van Leeuwenhoek
In his youth van Leeuwenhoek was apprenticed to a draper. Later, a civil service position allowed him to give time to his hobby: grinding lenses and using them to study tiny objects. His simple microscopes were skillfully ground, powerful single lenses capable of high image quality. He looked at protozoa in rainwater, pond water and well water. He also looked at bacteria in the human mouth and intestine. In 1677, he first described the spermatozoa of insects, dogs, and humans.