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 ? (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 ?), a hair from his beard (100 ?), a human erythrocyte (7.2 ?), and bacteria in pepper-water (2—3 ?).

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