Antoni van Leeuwenhoek is best remembered as the first person to study bacteria and "animalcules," or one-celled organisms now known as protozoa. Unlike his contemporaries Robert Hooke and Marcello Malpighi, Leeuwenhoek did not use the more advanced compound microscope; instead, he strove to manufacture magnifying lenses of unsurpassed power and clarity that would allow him to study the microcosm in far greater detail than any other scientist of his time.

Leeuwenhoek was born on October 24, 1632, in Delft, Holland. Although his family was relatively prosperous, he received little formal education. After completing grammar school in Delft, he moved to Amsterdam to work as a draper's apprentice. In 1654, he returned to Delft to establish his own shop, and he worked as a draper for the rest of his life. In addition to his business, Leeuwenhoek was appointed to several positions within the city government, which afforded him the financial security...