ABSTRACT
Antonie van Leeuwenhoek (1632-1723) was the first to describe numerous micro-
organisms from the gastrointestinal tract, which he described as “animalcules,” having
designed the first glass lenses for the microscope that were powerful enough to observe
bacteria. His curiosity brought him to investigate samples taken from his own mouth
and other people who never brushed their teeth, and he compared these findings with
people who brushed their teeth daily and used large amounts of alcohol. He even
investigated his own fecal samples in a period of diarrhea, compared these findings
with fecal samples of animals, and reported these observations to the Royal Society in
London (1).
