On September 17, 1683 Antonie van Leeuwenhoek wrote a letter to the Royal Society in London describing animalcules—tiny one celled animals invisible to the naked eye now known as protozoa. In doing so he inadvertently founded a new branch of science—microbiology.
Leeuwenhoek was an unlikely scientist. At the time most scientific investigation was the sole providence of gentlemen who had the education, leisure time for investigation, and the fortune to support the cost of their work. He was neither a gentleman nor particularly well educated. He came from a family of tradesmen or what the English called skilled mechanics. His father was a basket maker and his mother’s family were brewers. They were from Delft, a reasonably prosperous small city in the Netherlands province of South Holland.
As a young man Leeuwenhoek became a draper. He also worked as a surveyor, wine assayer and as a municipal official. His occupations made him comfortable, if not wealthy, and he was a respected member of the community. He was friends with and almost the exact contemporary of Delft’s most famous resident the painter Johannes Vermeer and was an executor of his estate when the master died in poverty in 1675.
His commercial success allowed Leeuwenhoek the time to pursue his growing interest in science. An avid reader, he had read Robert Hooke’s illustrated book Micrographia. Hook was working with primitive compound microscopes using two lenses. But the technology of these devices was primitive and could only magnify objects 20 to 30 times. Around the mid-1660’s he began to grind lenses in an attempt to create more effective instruments.
My high school science text credited Leeuwenhoek as the inventor of the microscope. As you can see, he was not. Compound microscopes had been around for nearly 40 years. His devices had single lenses, but the quality of the lenses was so high that he was able to achieve documented magnification of over 200 times. And evidence from his detailed observations indicates that some of the devices that he constructed may have neared a power of 500.
Leeuwenhoek’s breakthrough—and a closely guarded secret in his lifetime—was not discovered until 1957 when scientists discovered that he used finely drawn thread of molten glass to create perfect small spheres which became his lenses. The small lens would be set in a brass or silver plate in front of which would be a pointed rod on an adjustable screw which would hold the object being studied. Leeuwenhoek, working in the brightest natural light, would hold the device close to his eye.
Leeuwenhoek constructed at least 500 different devices, only a handful of which still survive. He often crafted new microscopes specifically for the specimens he wished to examine.
He made careful, extraordinarily detailed written observations of what he saw. These observations are so clear modern scientists can often identify the exact species of microbe he was observing. Since his drawing skills were poor, he later also hired a professional illustrator to make drawings to be enclosed in his letters to the Royal Society and other scientists.
His correspondence with the Royal Society continued for more than 50 years through his final illnesses. The Society frequently published his findings translated from Dutch to English or Latin in the Philosophical Transactions of the Royal Society, the most important scientific journal in the world at the time.
Among his main discoveries were infusoria, the unicellular animals in pond water now mostly classified as protists; bacteria from the human mouth; vacuoles, important structures in the cells of plants, fungi, and some protia; spermatozoa; the banded structure of mussel fiber; and the blood flow in capillaries.
In his later years Leeuwenhoek was famous. He was visited by William of Orange and other notables who he let make their own observations with his equipment. He even presented a microscope to Peter the Great of Russia when he was invited to visit the Tsar’s ship.
Active to the end, he died in Delft in 1723 at the age of 90.
In 1981 Leeuwenhoek’s original specimens, sent to the Royal Society were discovered in a remarkable state of preservation along with many of his handwritten notes in Dutch.
His life and work are a testament to the talent and persistence of a common craftsman.
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