Yet he always presents his results in a way which, despite the imperfections of his language and his lack of scientific education, is a model for all other workers. He never confuses his facts with his speculations. When recording facts he invariably says "I have observed ...", but when giving his interpretations he prefaces them with "but I imagine ..." or "I figure to myself ..." Few scientific workers — or so it seems to me — have had so clear a conception of the boundary between observation and theory, fact and fancy, the concrete and the abstract. - Clifford Dobell, 1922

His Life

Thonis Philipszoon of Delft, Holland, was born on October 24, 1632, to Philips Thoniszoon, a basket maker, and Grietge Jacobs, a brewer’s daughter. As an adult, he preferred to sign himself “Antonj van Leeuwenhoek” (pronounced "AHN-toe-nee fahn LAY-oo-ven-hook"), that is, “Anthony from the Lion’s Corner”, after the location of his father's corner house near the Leeuwenpoort, the "Lion's Port" in Delft's East End. The use of 'van' was an affectation of social standing that he assumed for its cachet. Over the centuries, his first name has been variously rendered as Thonis, Theunis, Anton, Antoni, Antonij, Antonie, Anthon, Anthoni, Anthonie, Anthony, Antoine, or Antonio, etc., at the whims or native languages of the writers. Today, even the Dutch are inconsistent. A prominent journal of general and molecular microbiology printed by Springer Netherlands is named "Antonie van Leeuwenhoek", whereas the Netherlands Cancer Institute's hospital in Amsterdam is the "Antoni van Leeuwenhoek Ziekenhuis". Likewise, the unfamiliar spelling and pronunciation of 'Leeuwenhoek' invites numerous misspellings, such as Leewehoeck, Leuwenhook, Leuwenhoek, Leeuvenhoek, Leuvenhook and the like. Add to this mix the European penchant for Latinizing the names of prominent scientists, which supplies us with 'Antonius Leeuwenhoekius'.

Education and Career
Thonis’ only known formal education was at an undistinguished elementary school in the village of Warmond, followed by some time in the village of Benthuizen with an uncle, who apparently taught him some mathematics and physics. He never attended a university, however he did later (1669) obtain a certificate as a surveyor ("Landmeter") to qualify for a city planning assignment with the Delft government. From time to time throughout his career, he enjoyed an odd assortment of these lucrative political appointments, including 39 years as Chamberlain ("Camerbewaarder der Camer") and Alderman ("Generaal Wijkmeester") to the Lord Sheriffs ("Heeren Schepenen") of Delft. From 1679 until his death he was the official Wine and Liquor Assayer ("Wijnroeijer") of Delft. Although many of these municipal posts were probably sinecures that he discharged by proxy, he did in fact participate in the official survey of the city, including the accurate measurement of the height of the steeple of De Nieuwe Kerk. These positions apparently afforded him the leisure time and resources he would have needed to pursue his "amateur hobby" as one of the greatest discoverers of all time.

In 1648, at age 16, he began a five-year apprenticeship with a Scottish linen draper in Amsterdam to qualify for admission into the Cloth Worker’s Guild, returning to Delft in 1654 to open his own woolens shop. In addition to all his other occupations and accomplishments, he remained an active and prosperous fabric merchant ("Handelsman") for the rest of his long life.

In 1653, van Leeuwenhoek encountered his first simple microscope, a magnifying glass used by textile merchants to count threads and to check quality. Such lenses were capable of magnifying to a power of about three diameters. It is believed that about 1665 he also read Robert Hooke’s newly published Micrographia, which may have piqued his enduring interest in the world of the tiny. (Read Micrographia online at Project Gutenberg. Highly recommended! -ed.)

In 1654, when van Leeuwenhoek was 22, the city of Delft was devastated by an enormous explosion (the "Delft Thunderclap", Delftse Donderslag) of 30 tons of gunpowder being stored in a magazine in the Doelen Quarter. Curiously, he apparently never made any reference to that disaster.

His Work

Instruments
No two accounts of van Leeuwenhoek’s work agree on the number or quality of his little hand-held mikroskoops, or on the number of authentic instruments that have survived, if any. It is generally agreed that he constructed at least several hundred of them. He left about 250 finished instruments, most of which included a mounted specimen, and also about 200 mounted lenses. On his death, he bequeathed an ornately boxed set of 26 solid silver instruments with mounted specimens to London's Royal Society. All or most of his scopes have been lost, except perhaps a few questionably authentic pieces displayed in various European museums.

The devices were simple magnifying glasses consisting of a single spherical or biconvex lens mounted between two copper, brass or silver plates. The plates were about the size of a modern microscope slide, about 1 by 3 inches. The object to be examined was raised, lowered or rotated by threaded screws attached to the plate. His device thus also incorporated one of the first mechanical micromanipulation systems. (Hooke had already accomplished this in a different manner.) He must have found early on that the shallow depth of field of strong microscope lenses ruled out focusing on microorganisms by hand. His lenses were very small and, like modern objective lenses, had short focal lengths of 1-2 millimeters. They would have needed to be placed close to the eye and it would have required practice and good eyesight to use them. Many of the plates appear to have been shaped to be gripped between eyebrow and cheek in the manner of a jeweler's monocle loupe. The most likely technique would be to hold the plates in a horizontal position with the threaded stem used as a handle pointing away from the nose. (Most illustrations in textbooks and biographies show them being held in very improbable positions.)

Estimates of their magnifying power vary from about 200 to 500 diameters. (If the higher figure is true, he achieved about a third or a half of the highest magnification possible with visible light!) The known sizes of the objects he reported and the fine detail of his drawings do testify to their amazing optical perfection and to Thonis’ own skills as one of the very first microscopists in history.

Lenses
Contrary to the numerous references to van Leeuwenhoek as an inventor of microscopes to be found in many accounts of his work, he did not actually invent his single-lens microscope. The theoretical advantage of using as few lenses as possible was expounded in Hooke's "Micrographia". Hooke also described in detail the making of small round lenses by pulling and fusing fine glass whiskers into tiny spheres. Hooke's technique was moreover a mass-production process, as he fixed multiple spheres to a sheet of wax to simultaneously grind and polish away the attachment sites of the whiskers. His detailed descriptions of doing this suggest that he had practical experience actually making such lenses. He even described mounting a tiny single lens on a needle-hole pierced through a thin metal plate, i.e., a van Leeuwenhoek microscope. He thought these would be superior microscopes, but found them too difficult to use because of the need to hold them close to the eye. It was this disadvantage that induced him to add an eyepiece lens, creating his famous compound microscope. van Leeuwenhoek therefore appears to have picked up his design from Hooke and is therefore better viewed as a discover than as an inventor.

It will probably never be known whether van Leeuwenhoek really ground his lenses as he wanted all to believe. His constant dissembling that his construction method required prodigious time, skill and effort is consistent with his general reluctance to teach or encourage competitors. It has been conjectured (with no direct evidence) that he actually copied Hooke's recipe and made lenses by pulling and fusing spherical globules with smoother surfaces than he could ever have achieved by grinding. German traveling bloviator Zacharias Konrad Zetloch von Uffenbach, after a long visit during which van Leeuwenhoek courteously entertained him with a myriad of wonders, ungraciously wrote in his memoir:

When we further inquired of Herr Leeuwenhoek whether he ground all his lenses, and did not blow any? he denied this, but displayed great contempt for the blown glasses. He pointed out to us how thin his microscopia were, compared with others (This phrase seems to indicate that one man or the other had seen instruments of like construction that may have predated Antonj's own. - ed.), and how close together the laminae were between which the lens lay, so that no spherical glass could be thus mounted; all his lenses being ground, contrariwise, convex on both sides. As regards the blown glasses, Herr Leeuwenhoek assured us that he had succeeded, after ten years' speculation, in learning how to blow a serviceable kind of glasses which were not round. My brother was unwilling to believe this, but took it for a Dutch joke (a snide German euphemism for a lie - ed.); since it is impossible, by blowing, to form anything but a sphere, or rounded end. - von Uffenbach, 1710

Even so, it would seem an excessive investment of effort if each lens were laboriously ground rather than being made in a minute or two with a spirit lamp and a blowpipe. He often built a new microscope for each interesting specimen, unlike the modern method of using a single microscope and numerous mass-produced, disposable glass slides placed on a fixed or moveable stage. He treated the complete instruments as permanent settings for his choicest specimens, hence the hundreds he is believed to have constructed. Nobody ever recorded seeing him in the act of making a lens by any technique. In any case, single spherical or hand-ground biconvex lenses would have suffered from severe chromatic and spherical aberration.

Methods
It is widely assumed that his simple single-lens scopes were all that van Leeuwenhoek used to make observations. He was always very evasive and secretive about his techniques, both in the manufacture and in the use of his instruments, so there is room for speculation. He was aware of the use of multiple lenses to form compound microscopes as already introduced in 1590 by Zacharias Janszoon and employed by Robert Hooke. He may well have made a sort of two-piece compound microscope by using an additional loupe closer to the eye as an ocular lens (eyepiece) to augment the power of his instruments playing the role of the objective lens of a compound microscope. Hanging water droplets containing his organisms were themselves able to assist in increasing the apparent magnification, similar to the magnifying effect of spherical fish bowls. Judging from the position of the specimen mounting pin on the plate, he would have had to tilt his head to the side to view a hanging drop. Illustrations of his scopes do not show any other means of holding a liquid specimen, however in their testimony to the Royal Society, a delegation of clerics and scholars stated that he took up suspensions of pepper infusion in fine glass capillaries to view them. For viewing objects in bulk liquids, he fashioned a few test‑tube holders with attached lenses.

To investigate the circulation of blood in the fins of eels, he constructed a few special microscopes attached to a flat support with metal strips to immobilize the subject, what we might describe as a dissection microscope.

It is generally taught that it would be another 150 years before the staining of biological specimens would be introduced, but van Leeuwenhoek was the first to use histological staining, using the spice saffron to stain muscle tissue, thereby bringing out otherwise invisible detail. He also would have naturally hit upon obvious methods to compensate for the transparency and low optical contrast of many of his subjects. Shining light on the specimen from the side while pointing the scope toward a dark background would create a “poor man’s” darkfield illumination effect, as would toying with holding his finger off-centerline between the light source and the scope. It is not known whether he ever considered the use of colored light or filters to create color contrasts. Other than sunlight and an occasional reference to candles, it is not known what lighting he used or whether he used any mirrors or dimming filters. To create incident or epi-illumination, he could have either polished the plate around the lens or placed a thin mirror or white paper in that area to direct light back onto his side of an opaque specimen.

In "Micrographia", Hooke had already (1864) described several means of enhancing the illumination of objects. He made up for the dimness of objects caused by the small aperture of the microscope's objective lens simply by using a burning glass to light them very brightly. He used oiled paper or frosted glass filters to diffuse and soften the light and to protect his eyes. To provide dependable light in any weather or time of day, he invented the first microscope lamp. That consisted of an oil lamp mounted on a small stand with a glass globe filled with filtered brine in line with a large plano-convex lens. Together, these concentrated light onto the object. van Leeuwenhoek may well have used these or similar methods, but did not divulge them.

Antonj made extensive use of Robert Hooke's technique that we now term microtomy. This method is famously represented by Hooke's drawing of a slice of cork showing compartments he named "cells" after their resemblance to monks' quarters. Using a razor, van Leeuwenhoek cut very thin slices of all manner of plants, bone, insects or other opaque specimens so that he could see through them.

Publications
He never wrote a proper scientific paper, but communicated his discoveries in often rambling and folksy letters in Low Dutch, sent to Europe’s principal scientific societies, especially to the Royal Society.

The Royal Society was in the first years of its existence, having been granted a royal charter by Charles II in 1662. The founding and early membership were also the designers of modern English Speculative Freemasonry, including such intellectual giants of the "invisible college" as William (Viscount Brouncker), Robert Moray, Robert Boyle, William Petty, John Wilkins, Christopher Wren, Robert Hooke, Elias Ashmole and Isaac Newton. Although there is no irrefutable direct evidence, the very fact that he was an early member of the Society, and many other accumulated clues, suggest that van Leeuwenhoek, too, may have been a Vrijmetselaar or at least inspired by Masonic attitudes. Being a Mason would have been entirely consistent with his approach to science as referred to in the Dobell quote at the top of this article.

Society members challenged the very idea that such tiny living organisms as his "animalcules" could exist. Criticisms were convincingly rebutted with detailed accounts of his method of estimating their sizes by comparing their diameters to those of objects of directly measurable dimensions. With well-argued calculations, often using the simplifying assumption that his subjects could be treated as spherical or cylindrical objects, he estimated their volumes from their visible diameters. He showed that literally millions of microbes could fit in the volume of a grain of sand. By progressively comparing objects of decreasing size with one another, he proved for example that protozoan cilia are thousands-fold smaller than a human hair. In 1673 the still-skeptical Society sent a delegation to Delft. Their rave report confirmed van Leeuwenhoek's claims. On news of this amazing corroboration, even the future Queen Anne of England and Tsar Pyotr I of Russia sought demonstrations of his marvels. His permanent place in the history of science was now assured, and he was elected to full membership in the Society in 1680. There is no record of his ever attending a meeting in person, nor did he ever sign the Society's membership register.

Antonj did not consider his own artistic skills up to the important task of illustrating his findings, so he almost always hired limners (from 'illuminators', i.e., artists and engravers that we might now call illustrators or commercial artists) to do that sort of work.

 His Discoveries

The number and variety of van Leeuwenhoek’s original scientific discoveries is breathtaking. These are only a few of his most notable “firsts”:

1674 - In a single vial of pond scum that he had taken from the Berkelse Mere, a small lake near Delft, he discovered and described the beautiful alga Spirogyra, and various ciliated and flagellated protozoa. Occasional prior observations by others notwithstanding, this singular event might justly be considered the simultaneous births of the fields of microbiology, protozoology (now called protistology) and phycology.

1674 - He found that yeast consists of individual plant-like organisms.

1675 - He discovered and accurately described and differentiated erythrocytes in humans, swine, fish and birds. We now know that the typical diameter of a human erythrocyte is 7.7 micrometers ("microns", µm). Using his sequential comparisons, van Leeuwenhoek calculated it to be "rather less than" 8.5 µm, a marvelously accurate result given his tools. He in fact expressed these dimensions in his usual manner by comparing sizes to sand grains. He observed that almost one hundred erythrocytes in a row would equal the diameter of a sand grain that he estimated to be the equivalent of 1/30 inch across. (The metric system was not to be introduced until 1791.) In 1683, he also described the sedimentation of red cells upon standing and their lysis on addition of fresh rain water, but not of sea water.

1677 - He was the first to observe spermatozoa in humans, dogs, swine, mollusks, amphibians, fish and birds. He often opined that this was his greatest find. At least at first, he thought that they were parasites in the male genitalia. The role of bulk semen in reproduction was already recognized. Sources conflict as to whether he ever guessed that fertilization occurs when one or more of these "animalcules" in semen enter the ovum. It might be noted that, other than his limner, his only known lab assistant was one Ludwig Hamm, who is cited as participating in this discovery. This mention may have been preserved so that posterity might not be forced to assume any unseemly behavior on Antonj's part.

1679 and 1684 - He described the needle-shaped microscopic crystals of sodium urate that form in the tissues of gout patients in stone-like deposits called "tophi". In 1684, he correctly guessed that much of the pain of gout is caused by these sharp crystals poking into adjacent tissues. More than a century would pass before any further advance in the understanding of gout.

1680 - He found and described foraminifera ("wee cockles") in the white cliffs of England's Gravesend and nematodes in pond water.

Between 1680 and 1701 he carried out many microdissections, mainly on insects, making an enormous number of discoveries:

He wrote extensive accounts of the mouthparts and stings of bees.

He was the first to realize that “fleas have fleas”.

His keen perception enabled him to correctly conclude that each of the hundreds of facets of a fly's compound eye is in fact a separate eye with its own lens. This outlandish (but true) idea was met with derision by visiting scholars.

He discovered parthenogenesis ("virgin birth") in aphids, seeing that some parent aphids did not contain eggs, but fully formed young aphids. This tied in nicely with his belief in a preformationist theory of the nature of organic reproduction. (Charles Bonnet, who later extensively studied and theorized about the implications of parthenogenesis, is often erroneously credited with its original discovery. He falsely claimed this honor to help his gaining admission as a corresponding member to the French Academy of Sciences in 1740. - ed.)

1683 - In his most celebrated attainment, he discovered the bacteria in dental tartar, including a motile bacillus, selenomonads and a micrococcus.

1683 - He observed bacteria in feces, including a motile spirochete.

1683 - He found parasitic protozoa in feces (Giardia sp. and Balantidium sp.).

1683 - He saw the lymphatic capillaries, containing "a white fluid, like milk".

1698 - He described the blood capillaries in several species.

1702 - He observed the sessile ciliate protozoa Vorticella and Stentor, and the colonial protozoon Volvox in pond water, in which he followed and recorded daughter colony formation.

1702 - He discovered the diatoms, the bacillariophyta, in fresh water. As a rough gauge of the resolving power of his instruments, he was easily able to view and describe entire diatoms that are typically about 20-120 µm in length, but never noticed the characteristic pores in their frustules, which are usually somewhat less than 1 µm in diameter.

1702 - He viewed free-swimming and sessile rotifers in pond water. Some of these being just large enough to see with the unaided eye, others may have already noticed them, but his is the first published description. He was the first to describe the phenomenon of anhydrobiosis (ability to survive desiccation) in a species of bdelloid ("leech-like", referring to their style of locomotion upon a surface) rotifer, Philodina roseola.

Philosopher and mathematician Gottfried Wilhelm Leibniz (1646-1716) wrote to van Leeuwenhoek in 1715 that "It would be well for young people to be introduced to microscopic observation, for which a school of microscopy should be founded." This wish went unfulfilled for a long time. The development of the microscope stagnated for almost a whole century. The introduction of the improved achromatic objective lenses of Georg Plössl in the early 19th Century and the application by Ernst Abbe and Carl Zeiss of the Abbe Sine Condition in about 1860 finally brought the needed breakthroughs in the development of light microscopes with reasonably flat fields of view and minimal chromatic and spherical aberration. This development continues today at the major microscope manufacturers.

Antonj van Leeuwenhoek enjoys a rare distinction among revolutionary discoverers, in that he was widely recognized and honored for his genius in his own time. In 1716, when he was in his 84th year, the University of Louvain officially honored him by striking a gold medal with his likeness on the obverse and a view of the city of Delft on the reverse, in recognition of his work. A distinguished delegation from the university ceremoniously presented this to him in a bag made of woven gold bullion, along with a diploma. This incident corresponds roughly with the modern conferring of an honorary degree.

He died on 30th August, 1723, aged almost 91. He was interred at De Oude Kerk in Delft. His honorable status in the city entitled him to eighteen pallbearers.

In 1877, the Royal Society established the Leeuwenhoek Medal, awarded once each decade to the person judged to have made the most significant contributions to the field of Microbiology. Recipients have included such luminaries as Louis Pasteur (1895), Martinus Beijerinck (1905) and Sergei Winogradsky (1935).

More about His Discoveries

Links and Bibliography

To see gorgeous photomicrographs of rotifers, visit Graham Matthews' website.

Websites that explore the possibility that van Leeuwenhoek was a Freemason may be found at Antoni van Leeuwenhoek Centraal and Masonic Regalia Lodge.

An extensive Dutch treatise dedicated to van Leeuwenhoek, and displaying an impressive collection of his illustrations, may be found at the Euronet website.

Leeuwenhoek, A. De natis è semine genitali animalculis. R Soc (Lond) Philos Trans. 1678; 12:1040 –1043.

Dobell, C. (ed.) 1922, 1960. Antony van Leeuwenhoek and His ‘Little Animals’. Dover Publications, New York.

Hoole, S. 1977. The select works of Antony van Leeuwenhoek: Containing his microscopical discoveries in many of the works of nature (History of ecology). Arno Press. 

Ford, B.J. 1991. The Leeuwenhoek Legacy. Biopress, Bristol, and Farrand Press, London.  (See also Mr. Ford's account of his studies at this Website.)

Hirsch, E.D. Jr. (Ed.) 2006. What Your 5th Grader Needs to Know. New York: Delta Trade Books. (Anton van Leeuwenhoek, pp. 384-5).

Huerta, R.D. 2003. Giants of Delft: Johannes Vermeer and the Natural Philosophers : The Parallel Search for Knowledge During the Age of Discovery. 

Meyer, K. 1998. Geheimnisse des Antoni van Leeuwenhoek. Lengerich

Gloede, W. 1986. Vom Lesestein zum Elektronenmikroskop. Berlin

van Leeuwenhoek, A. 1695. Arcana naturae detecta. Delphis Batavorum. Delft