Hektoen International

A Journal of Medical Humanities

Van Leeuwenhoek’s discovery of “animalcules”

George Dunea
Chicago Illinois, United States


“I then most always saw, with great wonder, that in the said matter there were many very little living animalcules, very prettily a-moving. The biggest sort. . . had a very strong and swift motion, and shot through the water (or spittle) like a pike does through the water. The second sort. . . oft-times spun round like a top. . . and these were far more in number.” 1


Antonie Philips van Leeuwenhoek 1632 – 1723, commonly known as the “Father of Microscopy,” was the first to construct a microscope that would allow people to see living microscopic organisms, bacteria, and protozoa. He was born into a family of tradesmen living in Delft in the Dutch Republic. His father was a basket-maker and his mother’s family were brewers. He received no higher education and only spoke Dutch. At age sixteen he worked as a bookkeeper at a linen-draper’s shop in Amsterdam. Returning to Delft in 1654, he married a draper’s daughter. Helped by his business experience in Amsterdam, he opened his own textile and haberdasher shop, selling cloth but also such items as buttons and ribbons. In 1660 he was appointed to manage the operations of the Delft’s council meeting hall. He served as a minor city official and also worked as a wine inspector and surveyor for a small amount of work and a generous salary.

While working in his shop van Leeuwenhoek developed an interest in making lenses to see the details of the cloth he was selling. Such small lenses had been widely used by textile merchants, and he acquired his own magnifying glass. In time he became skilled in glass processing and lens grinding.

In 1668 he visited London and probably saw Robert Hooke’s 1665 copy of Micrographia with microscopic pictures of textiles. By 1671 he was himself making small, spherical lenses, some just one millimeter across. With these he built a single-lens hand-held microscope about 5cm long and capable of magnifying objects up to 300 fold (while Hooke’s compound microscope magnified only about 40 – 50 fold).

He was now able to study many objects. In 1673 he made detailed drawings of bee stings, a fungus, and a human louse. He discovered single-celled plants and animals (1674), red blood cells (1674), spermatozoa (1677 – later concluding that eggs were fertilized when entered by sperm), the pattern of muscular fibers (1682), the lymphatic capillaries (which contained a white milky fluid -1683), and the interior of the coffee bean (1687). He studied many minerals, even the products of a gunpowder explosion. All told he examined some 200 biological species.

In 1674 he looked at the water from a lake near Delft and was surprised to see tiny microscopic unicellular pond-water organisms which he called animalcules (1676). He was able to isolate such “very little animalcules” from different sources, such as rainwater, pond and well water, and also from the human mouth and intestine – probably free-living protozoa, motile bacilli, micrococci, and spirochetes. He saw parasitic protozoa, the flagellate Giardia in a sample of his own feces, five different kinds of bacteria present in his own mouth. He studied green algae. He observed the life-cycles of maggots and fleas, showing they went through a process of reproduction from eggs to maggots to pupae to adults. He studied the crystals in gouty tophy and noticed the blood flow in capillaries. He investigated aspects of reproduction, and by dissecting aphids discovered parthenogenesis.

At first his letters announcing these discoveries were met with skepticism and caused widespread doubt at the Royal Society. Could he really see all these things? It took until 1677 before his findings were fully accepted, after they were confirmed by Robert Hooke and he was visited by a delegation of churchmen and scientists. In 1680 he was elected to the Society (but never attended one of their meetings) and continued his association for the rest of his life by correspondence. He went on with his studies and made many more observations. He became famous and was visited by members of the royal families of Europe, William and Mary of England, Peter the Great, and philosophers such as Leibnitz.

Van Leeuwenhoek never published formal scientific articles in the then accepted language of science, Latin. Instead he made his discoveries known through a series of letters in colloquial Dutch, which had to be translated and of which he wrote some 560. During his life he made more than 500 lenses and some twenty-five different microscopes. He was a loner and worked without assistants. He was secretive, always keeping a monopoly for his business, not revealing all the details of his trade in order to avoid competition. He never told anyone how he made his lenses, and the secret of his particular technique went with him to the grave.


  1. Antonie Philips van Leeuwenhoek’s letters to the Royal Society, September 17, 1683





GEORGE DUNEA, MD, Editor-in-Chief


Fall 2018    |  Sections  |  Science

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