Antonie van Leeuwenhoek

Antonie van Leeuwenhoek, born in Delft in 1632, was a Dutch microbiologist and microscopist during the country’s Golden Age. Largely self-taught in science, he is often called the Father of Microbiology and was among the first to study microbes. He is most famous for his groundbreaking microscopy work and for helping establish microbiology as a scientific field.

Raised in Delft, he worked as a draper as a young man and opened his own shop in 1654. He later became active in local politics and grew interested in making lenses. By the 1670s, he was using his own single-lens microscopes to explore microbial life. He was the first to observe and experiment with microbes, which he called dierkens, diertgens, or diertjes, and he was also the first to roughly measure their size. Most of these “animalcules” are now known as unicellular organisms, though he also saw multicellular ones in pond water. He documented the first microscopic views of muscle fibers, bacteria, spermatozoa, red blood cells, and crystals in gouty tophi, and was among the first to see blood flow in capillaries. He never wrote books but described his findings in messy letters to the Royal Society, which published many in their Philosophical Transactions.

Van Leeuwenhoek was born on 24 October 1632 and baptized as Thonis on 4 November. His father, a basket maker, died when Antonie was five. His mother came from a wealthy brewer’s family and remarried a painter; the family moved to Warmond around 1640. He had four older sisters. After his stepfather died when he was about ten, he lived with an uncle in Benthuizen. At 16, he became a bookkeeper’s apprentice at a linen-draper’s shop in Amsterdam, leaving after six years. In July 1654, he married Barbara de Mey in Delft; they had one surviving daughter, Maria, and four other children who died young. He bought a house in 1655 and lived there for the rest of his life, running a draper’s shop selling linen, yarn, and ribbon. His status grew: in 1660 he became chamberlain for the sheriffs in city hall, a job he held for nearly 40 years, which involved maintaining the building, heating, cleaning, opening for meetings, and keeping discussions confidential. In 1669 he was made a land surveyor by the court of Holland, and he also served as the official wine-gauger of Delft, overseeing wine imports and taxes. His first wife died in 1666; he remarried in 1671 to Cornelia Swalmius, with whom he had no children.

He was a contemporary of the painter Johannes Vermeer, baptized just four days earlier. Some suggest he appears in Vermeer’s paintings *The Astronomer* and *The Geographer*, but others see little physical resemblance. Since both were important men in a city of about 24,000 and lived near the main market, they likely knew each other. Van Leeuwenhoek acted as executor of Vermeer’s will when the painter died in 1675. His religion was Dutch Reformed and Calvinist; like Jan Swammerdam, he often spoke reverently of God’s wonders in creating creatures great and small, seeing his discoveries as proof of creation’s marvels.

While running his draper shop, he wanted to see thread quality better than existing magnifying lenses allowed. He became interested in lensmaking, though few records survive of his early work. He made lenses by heating a small rod of soda lime glass in a flame, pulling it apart to create two glass whiskers, then reinserting the end of one whisker into the flame to form a tiny, high-quality lens. A 2021 neutron tomography study of one of his high-magnification microscopes confirmed this method by showing the short glass stem characteristic of the technique. For lower magnifications, he also ground lenses. To keep his methods secret, he apparently encouraged others to think grinding was his main technique.

After developing his powerful lenses, he introduced his work to the prominent Dutch physician Reinier de Graaf. When the Royal Society published groundbreaking work by an Italian lensmaker in its journal *Philosophical Transactions*, de Graaf wrote to the editor Henry Oldenburg, praising Van Leeuwenhoek’s microscopes as far surpassing any seen before. In 1673, the society published a letter from Van Leeuwenhoek describing his microscopic observations of mold, bees, and lice. In 1674, he continued his correspondence.