Anton van Leeuwenhoek

Library of Congress

[b. Delft, Holland, October 24, 1632, d. Delft, August 26, 1723]

Leeuwenhoek made single-lens microscopes with exquisite lenses; with them he became the first person to see ciliated protists, which he called "animalcules" and "wretched beasties." He also discovered Hydra, rotifers, bacteria, and the sperm of dogs and other animals.

Antoni van Leeuwenhoek (1632–1723) was born, and also died, in the city of Delft in the Netherlands. Although a linen draper by profession, Leeuwenhoek learned to make lenses and built over five hundred simple microscopes to conduct his numerous personal experiments. With these instruments, Leeuwenhoek investigated the natural world, including water, soil, and human excretions. Because he is considered the first person to have viewed and documented the existence of microscopic organisms, including bacteria, he has been called the first of the microbe hunters.

His lack of formal scientific training led Leeuwenhoek to concentrate on making observations rather than offering theories. Although he never published his work, Leeuwenhoek described his findings in a series of 165 letters to the Royal Society of London, beginning in 1673 and ending only with his death. His first letter, dated April 28, 1673, details his microscopic inspections of mold and bees.

His most famous letter is dated October 9, 1676. This letter communicates the results of a series of experiments on water infused with pepper. Leeuwenhoek began by examining some snow-water that he had kept sealed for three years. He noted no creatures. He then added some peppercorns to the solution, and, after three weeks, he discovered the sudden appearance of a tremendous number of "very little animals." Judging by his calculations of their number and size, historians have surmised that Leeuwenhoek had become the first person to see bacteria. Colleagues reproduced his experiments in the months that followed. Given contemporary medical theories, it did not occur to Leeuwenhoek that what he saw with his microscope was in any way connected to disease, but his observations laid a foundation on which further investigations were born.

Bibliography

Dobell, C. (1932). Anthony van Leeuwenhoek and His "Little Animals." Reprint. New York: Dover Publications, 1962.

Palm, L. C. (1982). Antoni van Leeuwenhoek, 1632–1723: Studies on the Life and Work of the Delft Scientist Commemorating the 350th Anniversary of His Birthday. Amsterdam: Rodopi B.V.

— JENNIFER KOSLOW

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The Dutch naturalist and microscopist Anton van Leeuwenhoek (1632-1723), using simple microscopes of his own making, discovered bacteria, protozoa, spermatozoa, rotifers, Hydra and Volvox, and also parthenogenesis in aphids.

Anton van Leeuwenhoek was born on Oct. 24, 1632, at Delft. His schooling was informal, probably including some mathematics and physical sciences but no languages. At the age of 16 he was sent to Amsterdam to become an apprentice at a linendraper's shop where he remained for about 6 years.

In 1654 Van Leeuwenhoek returned to Delft and married Barbara de Mey, who was to bear him five children. He bought a house and shop and set up in business as a draper. He remained there for the rest of his life. His wife died in 1666 and in 1671 he remarried; his second wife bore him one child.

In 1660 Van Leeuwenhoek was appointed chamberlain to the sheriffs of Delft, an office which he held for 39 years. Little is known of his activities for the next 13 years; however, in his spare time he must have begun to grind lenses to make simple microscopes. As early as 1668 he took one of his microscopes on a visit to England and used it to examine chalk from the cliffs in Kent.

In 1673 Regnier de Graaf, a brilliant young physician of Delft, wrote a letter about Van Leeuwenhoek's work to Henry Oldenburg, Secretary of the Royal Society in London. This letter was published in Philosophical Transactions, and Oldenburg wrote to the author requesting further communications. Thus began a correspondence with the Royal Society which was to continue until Van Leeuwenhoek's death. All his observations were described in letters (at least 200), either to the Royal Society or to his friends, that were written in his own language, Nether-Dutch. He never wrote a scientific paper or a book. His letters are full of random observations, with little coherence, and were written in a conversational style. Despite the casual way in which he described his observations, he never confused the facts with his speculations, and so it is possible to identify easily many of the organisms he studied from his detailed descriptions.

The Royal Society elected him a fellow in 1680, an honor which pleased him although he never found time to visit London to sign the register. His discoveries soon made him famous, and many came to visit him in Delft. His enthusiasm for the study of nature never waned even in old age, and despite his infirmities he still continued to make observations and send letters to the Royal Society. After his death on Aug. 26, 1723, his daughter Maria sent a cabinet to the Royal Society which her father had prepared 22 years previously, containing 26 of his microscopes made from silver.

Van Leeuwenhoek's Microscopes

Apart from those microscopes sent to the Royal Society, Van Leeuwenhoek left 247 completely finished microscopes, most of which had an object mounted in front of the lens, and also 172 lenses mounted between metal plates. Properly speaking, the instruments were not microscopes at all but simple magnifying glasses. Each consisted of a single biconvex lens of remarkable clarity which was mounted between two metal plates. The lens was fixed, and the object to be examined was raised or lowered and rotated upon its axis by a coarse-threaded-screw. The lenses were of exceptional optical quality and had magnifying powers ranging from 50 to 200. The short (about 1 millimeter) focal lengths of the lenses would have necessitated placing the eye almost in contact with the lens, and it is not clear how Van Leeuwenhoek obtained the necessary illumination to achieve his remarkable results. He was always very secretive about his methods. Clifford Dobell suggested that he might have discovered some simple method of dark-ground illumination, whereas Barnett Cohen pointed out that the optical properties of spherical drops of fluid containing the objects under observation may have been used by Van Leeuwenhoek.

Microscopical Observations

Van Leeuwenhoek's curiosity was insatiable, and he examined everything he could with his microscopes, ranging from samples of about 200 biological species to mineral objects; he even attempted to observe the explosion of gunpowder.

Van Leeuwenhoek gave clearer descriptions of red blood cells than either of his contemporaries Marcello Malpighi and Jan Swammerdam. He first described them in 1674 and estimated their size to be, in modern terminology, 8.5 microns in diameter (the correct value is 7.7 microns). In 1682 he clearly described the nucleus within the red blood cells of fish, and in 1683 he noticed the sedimentation of erythrocytes from a suspension and their lysis upon addition of water. His description of the blood capillaries in the intestine in 1683 was accompanied by comments on a different type of capillary which contained "a white fluid, like milk"; he had discovered the lymphatic capillaries.

In 1677 Van Leeuwenhoek examined fresh semen, in which he observed living spermatozoa. His unique observations on microorganisms probably began in 1674, when he examined water from a lake near Delft. He gave the first description of the common green alga Spirogyra but also observed smaller organisms, which were probably free-living protozoa. Dobell believed that Van Leeuwenhoek saw Vorticella, Monas, Bodo caudatus, and Colpidium.

Van Leeuwenhoek also discovered parasitic protozoa, describing the flagellate Giardia in a sample of his feces, which also contained bacteria which can be identified as Spirochaeta. In a letter written in 1683 he describes and illustrates five different kinds of bacteria present in his own mouth: these can readily be identified as a motile bacillus, Selenomonas sputigena, a micrococcus, Leptothrix buccalis, and a spirochete. He continued to make observations on microorganisms until 1716, and while studying free-living protozoa, he also discovered other organisms such as Volvox, Hydra, and rotifers.

Van Leeuwenhoek's discovery of microorganisms has tended to overshadow his other work, which has not received full recognition. He was one of the first comparative anatomists, since he often followed a structure in several different species. As a pioneer of microdissection, he succeeded in obtaining results which are remarkable even by modern standards. Between 1680 and 1701 he carried out a series of microdissections, mainly on insects, and one of his most original discoveries was parthenogenesis in aphids. The parent aphids did not contain eggs, but young aphids just like the parent.

An Assessment

Van Leeuwenhoek's insatiable curiosity, coupled with remarkable tenacity and skill, makes him one of the most outstanding scientists of all time. In his own modest way he realized how rare his gifts were and also that other people's motives were not always those of a true student of nature. In a 1715 letter he noted: "Some go to make money out of science, or to get a reputation in the learned world. But in lens-grinding and discovering things hidden from our sight, these count for nought. And I am satisfied too that not one man in a thousand is capable of such study, because it needs much time … and you must always keep thinking about these things if you are to get any results. And over and above all, most men are not curious to know: nay, some even make no bones about saying, What does it matter whether we know this or not?"

Further Reading

The Collected Letters of Antoni van Leeuwenhoek was edited by a committee of Dutch scientists (8 vols., 1939-1967). A work on Van Leeuwenhoek and His Clifford Dobell, Antony van Leeuwenhoek and His "Little Animals" (1932). See also Abraham Schierbeek, Measuring the Invisible World (1959).

For more information on Antonie van Leeuwenhoek, visit Britannica.com.

(än'tōnē vän lā'vənhūk') , 1632–1723, Dutch student of natural history and maker of microscopes, b. Delft. His use of lenses in examining cloth as a draper's apprentice probably led to his interest in lens making. He assembled over 247 microscopes, some of which magnified objects 270 times. In the course of his examination of innumerable microorganisms and tissue samples, he gave the first complete descriptions of the bacteria, the protozoans (which he called animalcules), spermatozoa, and striped muscle. He also observed the red blood cells in his detailed study of capillary circulation. He was elected to the Royal Society of England in recognition of his work.

Bibliography

See his collected letters (Vol. I–VI, 1939–61).

Leeuwenhoek, Antoni Van (1632–1723), Dutch microscopist. Born the son of a basket maker on 24 October 1632 in Delft, Leeuwenhoek had little formal education. He moved when he was sixteen to Amsterdam, where he was trained and employed by a draper. In 1654 he returned to Delft, married his first wife, Barbara, and established his own drapery business. One child from this first marriage survived, his daughter Maria, who became her father's lifelong companion.

Leeuwenhoek entered civic life in 1660, when he became chamberlain to the sheriffs of Delft. In 1669 he passed the exam to become a city surveyor, and in 1679 he became official wine gauger to the city of Delft. His first wife died in 1666; Leeuwenhoek married his second wife, Cornelia, in 1671, and she died in 1695.

Leeuwenhoek's career as a tradesman and civic figure took a sharp turn in 1673, when he was introduced to the Royal Society of London by a letter from Reinier de Graaf (1641–1673), a prominent anatomist of Delft. De Graaf said that Leeuwenhoek had devised microscopes that were far superior to any then known, and he included a paper by Leeuwenhoek that offered observations of bits of mold, the eye and sting of a bee, and a louse. The secretary of the Society, Henry Oldenburg, was interested and encouraged further correspondence. Over the next fifty years, Leeuwenhoek wrote more than three hundred letters to the Royal Society. He read and wrote only Dutch, so these letters had to be translated into Latin for publication. The extracts printed in the Society's Philosophical Transactions constitute the bulk of Leeuwenhoek's published scientific work.

We do not know how Leeuwenhoek became interested in either microscopy or lens making. It has been suggested that his use of the draper's glass to examine woven cloth might have been a stimulus, but probably his acquaintance with de Graaf and Cornelius's Gravesande, another Delft anatomist, was more important. Whatever the stimulus, by 1671 Leeuwenhoek was making his own microscopes, and they had a unique design. Whereas the microscopes made by Robert Hooke (1635–1703) and other contemporaries were compound instruments, with both an objective lens and an eyepiece, Leeuwenhoek built simple microscopes, with a single beadlike lens mounted between two small thin metal sheets, usually brass. The object to be viewed was mounted on a pin on one side of the lens, and the eye was placed, almost touching the lens, on the other. The microscopes were successful because the tiny spherical lenses were exquisitely ground, or, in a few cases, blown. The measure of their success is what Leeuwenhoek was able to see through them.

In 1674 Leeuwenhoek examined cloudy water from a nearby lake and discovered it was teeming with tiny "animalcules," which we recognize as protozoa. Two years later, while continuing to study his tiny animals, he discovered in an infusion of pepper water some creatures that were much smaller, so small that, in his words, a million would not occupy the space of a grain of sand. Leeuwenhoek had discovered bacteria (although he never recognized them as a radically different form of life from protozoa). The Royal Society was quite excited by Leeuwenhoek's discovery of microscopic life, which he announced in his famous letters of 7 September 1674 and 9 October 1676, and other microscopists scurried to see for themselves. This was not easy, as no one had microscopes with the resolution of Leeuwenhoek's, but eventually his claims were confirmed.

Leeuwenhoek's other most notable achievement was the discovery of spermatozoa, which he announced in a letter of November 1677. He observed these first in humans, then in dogs, and eventually in more than thirty different species. After persistent study, he came to argue that each sperm was the seed of an individual creature and would give rise to the next generation if properly nourished in the womb. Since most contemporaries argued that the female provided the seed and the male merely some sort of fertilizing power, this was a radically new theory of generation. Leeuwenhoek believed that every element of an adult form was contained in a single sperm. However, he did not, as is sometimes stated, ever claim to see the form of a human within a human sperm.

Leeuwenhoek made other notable discoveries and observations. He was one of the pioneers of plant anatomy, taking a special interest in wood structure. He made a series of detailed studies of blood, observing the red blood cells, and was actually able to see single cells circulating through the capillaries in the tail of an eel, which he announced in a letter of 7 September 1688.

Leeuwenhoek became quite a famous figure in Delft (which, except for two early excursions, he never left). He entertained visitors willingly, although this proved quite time consuming in later life. The future James II of England (ruled 1685–1688) and Tsar Peter I of Russia (ruled 1682–1725) were among those who journeyed to Delft to see Leeuwenhoek and his wonders. When Leeuwenhoek had mastered a particular specimen, he would set up a permanent stand in his house, with a microscope devoted to that specimen, so that a visitor could go from station to station and observe swamp water, blood, insect parts, and other exotica without wasting time. This required a great number of microscopes, and it is estimated that Leeuwenhoek built over five hundred in his lifetime. Twenty-six, made of silver, were presented to the Royal Society after his death, with specimens attached; sadly, these have disappeared. But nine of his microscopes have survived and are the treasures of museums in Utrecht, Leiden, Rotterdam, Antwerp, and Munich.

One rather odd feature of Leeuwenhoek's life is that he was executor, in 1676, for the estate of the artist Jan Vermeer (1632–1675). Although other interaction between the two figures cannot be documented, it has been suggested that Vermeer learned optics from Leeuwenhoek, or perhaps vice versa, and it has been further suggested that Leeuwenhoek was the sitting subject for two of Vermeer's famous paintings, The Astronomer (1668) and The Geographer (1668–1669).

Although the Philosophical Transactions of the Royal Society was the primary forum for Leeuwenhoek's discoveries throughout his life, he did supervise the separate publication of several collections of those letters, in both Dutch and Latin, beginning in 1684 and continuing to 1722. However, he never wrote any kind of a synthesis of his work. Leeuwenhoek died in his home, at the age of ninety, on 26 August 1723, shortly after dictating a last letter to the Royal Society.

Bibliography

Primary Source

Leeuwenhoek, Antoni van. Alle de brieven. 12 vols. Amsterdam, 1939–.

Secondary Sources

Dobell, Clifford. Antony van Leeuwenhoek and His "Little Animals": Being Some Account of the Father of Protozoology and Bacteriology and His Multifarious Discoveries in These Disciplines. New York, 1958.

Fournier, Marian. The Fabric of Life: Microscopy in the Seventeenth Century. Baltimore, Md., 1996.

Palm, Lodewijk C., and Harry A. M. Snelders, eds. Antoni van Leeuwenhoek, 1632–1723: Studies on the Life and Work of the Delft Scientist Commemorating the 350th Anniversary of His Birthday. Amsterdam, 1982.

Schierbeek, Abraham. Measuring the Invisible World: The Life and Works of Antoni van Leeuwenhoek. London, 1959.

—WILLIAM B. ASHWORTH, JR.