Final answer:
Leeuwenhoek called the bacteria he saw 'animalcules' and made significant contributions to the field of microbiology.
Step-by-step explanation:
Antoni van Leeuwenhoek, a Dutch scientist, called the bacteria he saw 'animalcules', which means little animals in Latin. He observed these microorganisms using a microscope that he designed himself. Leeuwenhoek was the first to discover and study bacteria, making significant contributions to the field of microbiology.
Learn more about Leeuwenhoek's discovery of bacteria