What did Antonie van Leeuwenhoek observe in saliva and teeth scrapings?

Antonie van Leeuwenhoek, a pioneer in the field of microbiology, used his self-made, high-quality single-lens microscopes to observe and document microscopic life forms he referred to as "animalcules".12

In his examinations of the human mouth, Leeuwenhoek successfully identified and documented bacteria within teeth scrapings. These observations were significant, as they provided some of the earliest documentation of microorganisms existing within the human body. His research into these tiny organisms, which he also isolated from sources such as rainwater and the intestine, helped lay the foundational work for the sciences of bacteriology and protozoology.12