The earliest microscopes were essentially high-powered magnifying glasses developed by eyeglass manufacturers around 1600 and consisting of a tiny bead of glass held in a tube or between two metal plates. While many scientists used these tools to get a closer look at the world around them, the work of one particular Dutch researcher contributed much to the field of microbiology.

A draper from the city of Delft, the Netherlands, Antoni van Leeuwenhoek (1632– 1723) initially made microscopes as a hobby. It is rumored that he was inspired by the English scientist Robert Hooke’s (1635–1703) book Micrographia, an illustrated description of fleas, flies, plant cells, and Hooke’s own microscopes. In 1674, Van Leeuwenhoek began to do investigations of his own. Peering through his homemade lenses at specimens magnified more than 200 times, he observed what he called “very little animalcules,” objects that would later be identified as bacteria and protozoa. The population density of these animalcules, he estimated, was more than 1 million in each drop of liquid.

Wood, plants, insects, and crustaceans all found their way under Van Leeuwenhoek’s microscopes over the next several decades. He studied the bones, hair, teeth, eyes, muscles, and blood vessels of different animals and was the first person to give an accurate description of red blood cells. He was also the first to observe spermatozoa in human semen, fueling debate about the origins of conception. Van Leeuwenhoek’s studies showed that insects, vermin, and shellfish did indeed hatch from tiny eggs, an observation that helped refute the widely held doctrine of spontaneous generation.

Most of Van Leeuwenhoek’s discoveries were made public in the Royal Society of London’s publication Philosophical Transactions—including one of his illustrations, the first recorded visual representation of bacteria. But he carefully guarded the secret designs of his microscopes themselves, which would not be rivaled in quality until the 1800s.

ADDITIONAL FACTS

  1. Grinding glass to produce microscopes was a dangerous occupation. Although Van Leeuwenhoek lived to age 90, the toxic dust produced by glass grinding may have contributed to the death of another well-known Dutch lens maker, the philosopher Baruch Spinoza (1632–1677).
  2. Simple, single-lens microscopes were preferred during Van Leeuwenhoek’s time because the compound microscope—made with two lenses—increased chromatic aberration, in which colored fringes appear around the edges of the image because different wavelengths of light bend at different angles.
  3. Robert Hooke coined the term cell after noticing similarities between the cells of dried cork under a microscope and monks’ living quarters, called cells, in monasteries.