Along with tufts of green algae, he saw thousands of tiny creatures he dubbed “animalcules.” Centuries later, we now know that Leeuwenhoek’s animalcules inhabit every surface, nook and cranny of the ...

The microscopic world became visible with Antonie van Leeuwenhoek's improved lenses; he revealed a new world filled with 'animalcules', single-celled organisms that swim and tumble in water.