Leeuwenhoek, Antoni van

(b. Delft, Netherlands, 24 October 1632;b. Delft, 26 August 1723),

natural sciences, microscopy.

Leeuwenhoek was the son of Philips Thoniszoon, a basket-maker, and Margriet Jacobsdochter van den Berch. He took his surname ( “Lion’s Corner” ) from the corner house near the Leeuwenpoort ( “Lion’s Gate” ) at Delft, which was owned by his father. The family belonged to the prosperous middle class of artisans, brewers, and lesser public officials, which was typical of the Golden Age of the Dutch Republic.

His father died at an early age, in 1638, and Leeuwenhoek was sent to the grammar school of Warmond, a village near Leiden. For some time afterwards he lived with a relative in Benthuizen, then, in 1648, moved to Amsterdam, where he was apprenticed to a cloth merchant. Returning to Delft, Leeuwenhoek began a career as a shopkeeper. On 29 July 1654, he married Barbara de Mey, daughter of Elias de Mey, a serge merchant from Norwich, England. They had five children, of whom only one, their daughter Maria, survived her father.

In 1660 Leeuwenhoek took up a new career as a civil servant with an appointment as usher to the aldermen of the municipality of Delft. In 1666 his wife died, and two years later Leeuwenhoek made one of the only two foreign trips that he took in his lifetime, visiting the chalk hills of Gravesend and Rochester in Kent, England. (His other occasion for travel abroad was a journey that he made to Antwerp in 1698 to see the Jesuit scholar Daniel Papenbroek.) Upon his return to Delft in 1669 he was appointed surveyor to the court of Holland.

Leeuwenhoek remarried on 25 January 1671. His second wife was Cornelia Swalmius, the daughter of Johannes Swalmius, a Calvinist minister at Valkenburg, near Leiden. She died in 1694; the one child of this marriage did not survive infancy. In the meantime Leeuwenhoek continued to advance in the service of the city of Delft, being made chief warden of the city in 1677 and, because of his mathematical skills, wine-gauger (or inspector of weights and measures) in 1679. The income and emoluments from these offices made him financially secure, especially in his old age, when the municipality, in gratitude for his scientific achievements, granted him a pension.

Leeuwenhoek’s scientific life may be said to have begun in about 1671, when he was thirty-nine years old. At that time, developing the idea of the glasses used by drapers to inspect the quality of cloth, he constructed his first simple microscopes of magnifying glasses, consisting of a minute lens, ground by hand from a globule of glass, clamped between two small perforated metal plates. To this apparatus he fixed a specimen holder that revolved in three planes. From these beginnings Leeuwenhoek went on to grind about 550 lenses in his lifetime. Although always secretive about his technique, he achieved lenses of increasing quality, of which the best that survives, in the University Museum of Utrecht, has a linear magnifying power of 270 and a resolving power of 1.4 μ (From his recorded observations it may be surmised that he must have actually made lenses of 500 power, with a resolution of 1.0µ.) Whatever his methods, Leeuwenhoek’s instruments were not surpassed until the nineteenth century.

To his work in lens-grinding Leeuwenhoek brought a good pair of eyes, mathematical exactitude, great patience, and even greater manual dexterity. These same qualities, together with a keen, practical intellect, served him in the exploration of the whole field of natural science that occupied him in fifty years of continuous work. Strictly speaking, his scientific training was incomplete—he never attended a university—and he was limited by his lack of skill in classical and foreign languages. He was, however, able to rely upon such friends as de Graaf and Constantijn Huygens (as well as upon professional translators) to aid him. He derived much of his scientific knowledge from Dutch authors—for example, Cornelis Bontekoe on medicine and Swammerdam on insects—and from Dutch translations of books that the was not otherwise able to read (Hooke on microscopy, Grew on plant anatomy, and Redi on insects). He gained new information, too, from correspondence with the Royal Society (which had to be translated) and from conversations with visiting scholars.

Still, Leeuwenhoek remained in relative scientific isolation. One consequence of this was that he was not always fully acquainted with the researches and theories of his fellow scientists, and so could not incorporate their sometimes valuable suggestions into his own work. But he was thus able to work with full independence and to make a sharp distinction between the empiricism and speculation that marked the sometimes chaotic world of seventeenth-century science. Leeuwenhoek apparently regarded speculation as an academic occupation and therefore out of his domain, and this attitude permitted him a certain degree of detachment. He usually set out his observetions fully, as facts, and only then, in a separate section, allowed himself to wonder what these facts might mean. (This caution is perhaps the reason that he did not publish a definitive work on microscopy.)

Leeuwenhoek’s chief area of endeavor was the microscopical investigation of organic and inorganic structures. His most important contributions were made in the field of general biology; his studies in other branches of science were largely excursions in the interest of solving fundamental biological problems. Leeuwenhoek’s method was based upon two presuppositions: that inorganic and organic nature are generally similar, and that all living creatures are similar in form and function. To demonstrate these similarities he attempted to study as many types as possible of any given group of organisms and then to generalize from this data; by drawing analogies between animals and plants, he sometimes succeeded in overcoming highly difficult problems in the interpretation of microscopic structures. Leeuwenhoek followed the Cartesian method in trying to apply his somewhat primitive knowledge of the laws of physics to living nature (and thereby exhibited some bias against chemical explanations).

Leeuwenhoek made his most important discovery early in his scientific career, in 1674, when he recognized the true nature of microorganisms. Starting from the assumption that life and motility are identical, he concluded that the moving objects that he saw through his microscope were little animals. He recorded these observations in his diary, and two years later, in a letter of 9 October 1676, communicated them to the Royal Society, where they caused a sensation. (Indeed, such was the disbelief of some of the fellows of that body that Leeuwenhoek felt obliged to procure written attestations to the reliability of his observations from ministers, jurists, and medical men.) Leeuwenhoek subsequently described, in about thirty letters to the Royal Society, many specific forms of microorganisms, including bacteria, protozoa, and rotifers, as his incidental discovery of ciliate reproduction. It was necessary to devise a scale by which to measure this formerly invisible new world, and Leeuwenhoek therefore developed a practical system of micrometry, utilizing as standards a grain of coarse sand (870 μ), a hair from his beard (100 μ), a human erythrocyte (7.2 μ), and bacteria in pepper-water (2—3 μ).

Microscopy, however, was only a tool that Leeuwenhoek put at the service of his two lifelong scientific concerns: his study of sexual reproduction, which was designed to refute the theory of spontaneous generation, and his study of the transport system of nutrients in plants and animals. He was drawn to the investigation of animal reproduction when, in 1677, a medical student, Johan Ham, of Arnhem, told him that he had seen animalcules in human seminal fluid. Ham presumed that these little animals had been generated by putrefaction; Leeuwenhoek, however, supposed them to be a normal component of semen throughout the animal kingdom. In the course of forty years, he described the spermatozoa of arthropods, mollusks, fishes, amphibians, birds, and mammals.

Such a persuasion led Leeuwenhoek to a new definition of the fertilization process. Having observed the spermatozoa, he was able to proceed beyond the prevalent notion that fertilization occurred from vapors arising out of the seminal fluid and to postulate that the spermatozoa actually penetrated the egg (although he was not able to observe this process). Assuming that the fast-moving spermatozoa were the was nourished by the egg and the uterus. He thus denied any generative role to the motionless (and therefore lifeless) egg, and placed himself in direct opposition to those who, like Harvey in the De generatione of 1651, held the egg to be the source of all new life. Leeuwenhoek thus arrived at an animalculist theory of reproduction. A critical case in point was that of reproduction in mammals. The ovists thought that the follicle (discovered by de Graaf and named after him) was, in fact, the egg, while Leeuwenhoek pointed out that it was impossible for the entire follicle to pass through the narrow fallopian tube to the uterus. (It is interesting to note that the actual mammalian egg was not found until 1826, when K. E. von Baer discovered it, and that the ovist–animalculist controversy persisted until 1875, when Hertwig demonstrated that fertilization represents the fusion of the nuclei of the spermatozoon and the egg.)

A corollary of Leeuwenhoek’s theory of reproduction was his denial, following in the footsteps of Swammerdam and Redi, of the Aristotelian theory of generation, whereby some animals were thought to originate from the putrefaction of organic matter. In particular the Aristotelians held that certain tiny animals—such as insects and intestinal worms—were very primitive in structure and were generated in this way. In a series of investigations Leeuwenhoek demonstrated the complex structure of mites, lice, and fleas, and described their copulation and life cycles. His studies took him as far as the problem of reproduction in the eel and in intestinal parasites.

Since he believed all living forms to be functionally similar to one another, Leeuwenhoek also made extensive investigations of reproduction in plants. In a letter of 12 October 1685 he drew upon his studies of the seeds of angiosperms to explain his theory of plant reproduction: since motionless plants could not copulate, each individual had to provide for its own propagation. the embryonic plant was therefore the source of new life; the endosperm was the primary nutritive uterus and the earth the secondary nutritive uterus for the seed of the plant. Since he considered the flower to be the beautiful but functionless ornament of the plant, Leeuwenhoek did not investigate the anthers and ovaries.

Leeuwenhoek endeavored to draw an analogy between the animal system and the plant system when he took up his second important area of investigation, the system of nutrient transport. He minutely analyzed the transport canals, particularly their walls, the transport media (as, for example, blood), and the nutritive matter to be moved. Having no concept of the cell, he imagined the system to be composed of pipes or vessels.

In his studies of animals, Leeuwenhoek distinguished among what he called air vessels, intestinal tubes, chyle vessels, blood vessels, and nerve tubes. He was however, not always able to interpret their functions, and he was not always successful in drawing analogies within the animal systems. For example, although he was aware of the morphological similarity of the cartilaginous rings in the bronchia of mammals and the chitinous spiral in the trachea of insects, he chose to consider the trachea a blood vessel surrounding the intestinal tube.

Leeuwenhoek was particularly attentive to the blood vessels and the blood. Harvey had described the circulation of the blood in 1628, while Malpighi discovered the capillaries in 1661 and, in 1665, observed the corpuscles for the first time (although he wrongly identified them as fat globules). Leeuwenhoek, unaware of Malphighi’s work, effectively rediscovered the blood corpuscles, in 1674, and the blood capillaries (in 1683). He went on to describe and measure the erythrocytes and their nuclei in fishes, amphibians, and mammals, and further investigated the walls of the blood vessels. (In the course of these studies Leeuwenhoek devised an ingenious apparatus—his famous “eel-spy”—to demonstrate the corpuscles and blood circulation in the tail of a live eel.) Nevertheless, Leeuwenhoek did not fully understand the function of the blood. Although he recognized it as the means whereby food particles were moved from the intestinal tube to the tissues, he rejected, on the basis of air-pump experiments, the notion that it might also serve to transport air.

Leeuwenhoek’s work coincided again with that of Malpighi (as well as that of Grew) in the area of plant anatomy. Indeed, the three must be considered the founders of that study. Leeuwenhoek brought remarkable insight to the three-dimensional structure of the root, stem, and leaf, and illustrated his findings with radial, tangential, and cross sections of those organs. He considered plant tissue to be composed of a complex of tubes surrounded by other tissues made up of globules (cells), but his terminology is often unclear because he only rarely understood the function of the structures that he identified.

For example, in a long letter to the Royal Society of 12 January 1680, Leeuwanhoek described the elements that make up several kinds of wood. It is clear that he here considered all vertical and horizontal woody tracts to be sap-transporting vessels, in opposition to Grew, who distinguished between air vessels and sap vessels. Leeuwenhoek had observed the cross–walls of the rays and sieve tubes in plants on many occasions, and had drawn elaborate diagrams of them. He now interpreted them as being valves, analogous to those in animal veins, and was thus led to formulate a theory whereby the sap was moved from valve to valve by purely mechanical means. Twelve years later, however, in a letter of 12 August 1692, he changed his mind and, in a lengthy comparison of microscopic structures in plants and animals, arrived at something very close to Grew’s theory. He now assumed the horizontal and vertical tracts in plants to be air tubes, and the secondary thickenings of these elements and the intercellular spaces between them to be sap vessels.

It was through letters—more than 300 of them, written to private scientists and amateurs in both Holland and other countries—that Leeuwenhoek made his work known. He wrote exclusively in Dutch, but had a few of his letters translated for the benefit of his correspondents. Primarily, though, he was indebted to the Royal Society of London for the publication of his views, and 190 of his letters are addressed to that body.

Leeuwenhoek’s correspondence with the Royal Society began, through the intermediacy of de Graaf, one of the Society Dutch correspondents, with his letter of 28 April 1673. This initial communication convinced the fellows of the great significance of his microscopic findings, and the Society prepared English translations or summaries of his letters for their philosophical Transactions (1673—17240). it is apparent from the few letters to Leeuwenhoek that survive that he must have exchanged letters with the Royal Society on a regular basis, and that his London correspondents encouraged him to investigate new fields. Leeuwenhoek, in return, transmitted in each letter an exact account of the state of these studies. (It is sometimes perplexing to the modern reader, who may be unaware of the interaction of Leeuwenhoek and the Royal Society, to try to surmount the seeming lack of order in the sequence of subjects treated in the letters.)

Beginning in 1679, the French journal Recueil d’expériences et observation sur le combat qui procéde du mége des corps published Leeuwenhoek’s letters, translating them from the Philosophical Transactions, and French summaries of them, drawn from the same source, appeared in the Journal des sÇavans, Latin extracts were made and published in the Acta eruditorum,beginning in 1682.

Leeuwenhoek himself did not publish his work until 1684, when he brought out some of his letters in Dutch; from 1684 onward he also published Latin translations. He initially edited, reprinted, and reissued some of his letters separately or in groups of two or three, a practice that has resulted in some bibliographical confusion. From 1687 he adopted a more systematic course of publication, however, and in 1718 he brought out a collected edition of his letters in Dutch, followed in 1722 by a Latin edition. (In 1932, in commemoration of the tercentenary of Leeuwenhoek’s birth, the Royal Academy of Sciences of Amsterdam and the Nederlands Tijdschrift voor Geneeskunde undertook a complete critical edition of all of his letters.)

Leeuwenhoek’s scientific achievements were recognized during his lifetime by both his colleagues and the public. In 1680 he was elected a fellow of the Royal Society of London; in 1699 he was Sciences; a correspondent of the Paris Académie des Sciences and in 1716 the Louvain College of Professors awarded him a silver medal. In addition to the pension that it gave him, the municipality of Delft made him special awards upon the publication of several of his books. The increasing number of eventually caused Leeuwenhoek to demand introductory letters; his guests included kings and princes, among them Peter the Great, James II, Frederick the Great, Elector August II of Saxony, and the Grand Duke Cosimo III of Tuscany. In his old age, Leeuwenhoek became a legend; to his displeasure, his fellow townsmen reverently referred to him as a magician.

Four pictures of Leeuwenhoek made during his lifetime remain. He is a figure in Cornelis de Man’s Anatomy Lesson of Dr.Cornelis’s Gravesande,, painted in 1681 and now in the old and New Hospital, Delft. in 1686 Johannes Verkolje made two portraits of him; one is a painting (now in the National Museum of the History of Science, Leiden), showing Leeuwenhoek holdings his diploma of fellowship in the Royal Society, while the other is a mezzotint engraving in which the subject is seen handling one of his small microscopes. Another engraving was made by Jan Goeree in about 1707, and shows Leeuwenhoek in his old age.

BIBLIOGRAPHY

I. Original Works. A complete list of the many editions of Leeuwenhoek’s works appears as an appendix to A. Schierbeek’s biography, cited below.

His own collected Dutch edition, the Brieven or Werken, consists of four (sometimes five) volumes: I.Brieven Geschreven aan de Wyt–vermaarde Koninglijke Wetenschapzoekende Societeit, tot London on Engeland, 10 pts. (LeidenDe;ft, 1684-1694), with a Register (Leiden, 1695)—the title page of each part gives a more substantial idea of its contents; II.Vervolg der Brieven in Londen aan de Wytvermaarde Koninglijke Societeit in Londen (Leiden, 1688), Tweede Vervolg Der Brieven(Delft,1688), Derde Vervolg Der Brieven (Delft, 1693), and Vierde Vervolg Der Brieven (Dutch, 1696),III. Vijfde Vervolg Der Brieven, Geschreven aanveerscheide Hoga Standspersonen En Geleerde Luijden (Delft, 1696), Sesde Vervolg Der Brieven (Delft, 1697),and Sevende vervolg Der Brieven (Delft, 1702); IV. Send-Briven (Delft, 1718).

His Latin edition also consists of four volumes; I. Arcana Natura Detecta (Leiden, 1722), Continuatio Epistolarum (Leiden, 1715), and Continuation Arcanorum NaturaeDetectorum (Leiden, 1722); II. Opera Omnia, Seu Arcana Naturae (Leiden, 1722)’ III. Epistolae ad Societatem Regiam Anglicam (Leiden, 1719); IV. Epistolae Physiological Super compluribus Naturae Arcanis (Delft, 1719).

The only comprehensive English translation of the letters is Samuel Hoole, The Select Works of Antony van Leeuwenhoek,2 vols. (London, 1798-1807), which, however, omits all references to animal reproduction.

The Collected Letters of Antone vau Leeuwenhoek, edited by the Leeuwenhoek Commision of the Royal Academy of Sciences of Amsterdam, presently comprises eight volumes (Amsterdam, 1939-1967) of 118 letters written between 1673 and 1692.

II. Secondary Literature. The most important recent works on Leeuwenhoek are C. Dobell, Antony van Leeuwenhoek and His “Little Animals” )London-Amsterdam, 1932; 2nd de., New York, 1958); and A. Schierbeek, Antoni van Leeuwenhode. Zijn Leven en Zijn Werken, 2 vol. (Lochem, 1950-1951), of which a concise English versionis Measuring the Invisible World. The Life and Works of Antoni van Leeuwenhoek FRS (London-New York, 1959).

Johannes Heniger

LEEUWENHOEK, ANTONI VAN (1632–1723)

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.

See also Academies, Learned ; Hooke, Robert ; Optics ; Scientific Instruments ; Scientific Revolution ; Technology .

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.

Anton van Leeuwenhoek

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). □

Leeuwenhoek, Antoni van (1632-1723)

Dutch microscopist

Antoni van Leeuwenhoek is best remembered as the first person to study bacteria and "animalcules," or one-celled organisms now known as protozoa. Unlike his contemporaries Robert Hooke and Marcello Malpighi, Leeuwenhoek did not use the more advanced compound microscope ; instead, he strove to manufacture magnifying lenses of unsurpassed power and clarity that would allow him to study the microcosm in far greater detail than any other scientist of his time.

Leeuwenhoek was born on October 24, 1632, in Delft, Holland. Although his family was relatively prosperous, he received little formal education. After completing grammar school in Delft, he moved to Amsterdam to work as a draper's apprentice. In 1654, he returned to Delft to establish his own shop, and he worked as a draper for the rest of his life. In addition to his business, Leeuwenhoek was appointed to several positions within the city government, which afforded him the financial security to spend a great deal of time and money in pursuit of his hobby, lens grinding. Lenses were important tools in Leeuwenhoek's profession, as cloth merchants often used small lenses to inspect their products. His hobby soon turned to obsession, however, as he searched for more and more powerful lenses.

In 1671, Leeuwenhoek constructed his first simple microscope. It consisted of a tiny lens that he had ground by hand from a globule of glass and placed within a brass holder. To this, he had attached a series of pins designed to hold the specimen. It was the first of nearly six hundred lenses ranging from 50 to 500 times magnifications that he would grind during his lifetime. Through his microscope, Leeuwenhoek examined such substances as skin, hair, and his own blood. He studied the structure of ivory as well as the physical composition of the flea, discovering that fleas, too, harbored parasites .

Leeuwenhoek began writing to the British Royal Society in 1673. At first, the Society gave his letters little notice, thinking that such magnification from a single lens microscope could only be a hoax. However, in 1676, when he sent the Society the news that he had discovered tiny onecelled animals in rainwater, the interest of member scientists was piqued. Following Leeuwenhoek's specifications, they built microscopes of comparable magnitude and confirmed his findings. In 1680, the Society unanimously elected Leeuwenhoek as a member.

Until this time, Leeuwenhoek had been operating in an informational vacuum; he read only Dutch and, consequently, was unable to learn from the published works of Hooke and Malpighi (though he often gleaned what he could from the illustrations within their texts). As a member of the Society, he was finally able to interact with other scientists. In fact, the news of his discoveries spread worldwide, and he was often visited by royalty from England, Prussia, and Russia. The traffic through his laboratory was so persistent that he eventually allowed visitors by appointment only. Near the end of his life, Leeuwenhoek had reached near-legendary status and was often referred to by the local towns-folk as a magician.

Amid the attention, Leeuwenhoek remained focused upon his scientific research. Specifically, he was interested in disproving the common belief in spontaneous generation, a theory proposing that certain inanimate objects could generate life. For example, it was assumed that mold and maggots were created spontaneously from decaying food. Leeuwenhoek succeeded in disproving spontaneous generation in 1683, when he discovered bacteria cells. These tiny organisms were nearly beyond the resolving power of even Leeuwenhoek's remarkable equipment and would not be seen again for more than a century.

Leeuwenhoek created and improved upon new lenses for most of his long life. For the forty-three years that he was a member of the Royal Society, he wrote nearly 200 letters that described his progress. However, he never divulged the method by which he illuminated his specimens for viewing, and the nature of that illumination is still somewhat of a mystery. Upon his death on August 30, 1723, Leeuwenhoek willed twenty-six of his microscopes, a few of which survive in museums, to the British Royal Society.

See also Bacterial growth and division; Bacterial kingdoms; Bacterial membranes and cell wall; Bacterial movement; History of microbiology; Microscope and microscopy

Leeuwenhoek, Antoni van

Antoni van Leeuwenhoek (1632-1723) is best remembered as the first person to study bacteria and one-celled animals now known as protozoa. Unlike his contemporaries, Leeuwenhoek did not use the more advanced compound microscope. Instead, he tried to manufacture magnifying lenses of great power and clarity that would allow him to study micro-coorganisms in far greater detail than any other scientist of his time.

Early Career

Although Leeuwenhoek's family was fairly well off, he received little formal education. After completing grammar school in Delft, Netherlands, he moved to Amsterdam to work as a draper's apprentice (a draper was a person who made and sold clothing). In 1654 he returned to Delft to establish his own shop and worked as a draper for the rest of his life. His medical achievements in lens grinding were actually a hobby rather than his main work. Lenses were an important tool in Leeuwenhoek's profession, since cloth merchants often used small lenses to inspect their products. His hobby soon turned to obsession, however, as he searched for more and more powerful lenses.

In 1671 Leeuwenhoek made his first simple microscope. It had a tiny lens that he had ground by hand from a globule (small ball) of glass and had placed in a brass holder. To this he had attached a series of pins designed to hold the specimen. It was the first of nearly six hundred lenses ranging from 50 to 500 times magnifications that he would grind during his lifetime.

Through his microscope Leeuwenhoek examined such substances as skin, hair, and his own blood. He studied the structure of ivory as well as the physical composition of the flea, discovering that fleas, too, had even smaller parasites on them.

Leeuwenhoek began writing to the British Royal Society in 1673 about his discoveries. At first, the Society gave his letters little notice, thinking that such magnification from a single lens microscope could only be a hoax (fake). The best microscopes had more than one lens to provide better clarity. In 1676, when he sent the Society the news that he had discovered tiny one-celled animals in rainwater, scientists became interested in his work. Following Leeuwenhoek's instructions, they built microscopes of comparable magnitude and confirmed his findings. In 1680 the Society unanimously elected Leeuwenhoek as a member.

Further Research

Until this time, Leeuwenhoek had been operating without any information on what other microscope developers were doing. He read only in Dutch and was unable to learn from the published works of Hooke and Malpighi, the other great microscopists of the time. As a member of the Royal Society, however, he was finally able to correspond with other scientists. In fact, the news of his discoveries spread worldwide, and he was often visited by royalty from England, Prussia, and Russia. The traffic through his laboratory was so persistent that he eventually allowed visitors by appointment only. Near the end of his life he had reached legendary status, and was often referred to by the local townsfolk as a magician.

Amid all the attention, Leeuwenhoek remained focused upon his scientific research. Specifically, he was interested in disproving the common belief in spontaneous generation, a theory proposing that certain inanimate (non-living) objects could generate life. For example, it was believed that mold and maggots were created spontaneously from decaying food. He succeeded in disproving spontaneous generation in 1683 when he discovered bacteria cells. These tiny organisms were nearly beyond the resolving power of even Leeuwenhoek's remarkable equipment and would not be seen again for more than a century.

Leeuwenhoek created and improved upon new lenses for most of his long life. For the forty-three years that he was a member of the Royal Society, he wrote nearly 200 letters that described his progress. However, he never wrote about the method he used to light up his specimens for viewing, and the nature of that lighting technique is still a mystery. Upon his death, Leeuwenhoek willed twenty-six of his microscopes—a few of which survive in museums—to the British Royal Society.

[See also Microscope, compound ]