Antony van Leeuwenhoek

Discoverer of bacteria and refuter of spontaneous generation


Published: 17 May 2018 (GMT+10)
Antony van Leeuwenhoek, as painted by Johannes Verkolje, c. 1686. On the table is the Royal Society Letter of Fellowship.

Antony van Leeuwenhoek1,2 (1632–1723), is famous as the discoverer of the single-celled microorganisms we now call protozoa and bacteria. He called them ‘animalcules’.3 He also was the first to accurately measure red and white blood cells, spermatozoa, nerve and muscle fibres, and much, much more. He believed that the perfection he observed in such tiny organisms was due to their being created by God.

Encyclopaedia Britannica acknowledges: “His researches on lower animals refuted the doctrine of spontaneous generation, and his observations helped lay the foundations for the sciences of bacteriology and protozoology.”4 He never attended a university, wrote a book, or gave a lecture, but described his discoveries in letters to the Royal Society of London, which published them in its journal, Philosophical Transactions of the Royal Society.

Early life

Antony was born in Delft, then the third-largest city in the Dutch Republic,5 and which is now in South Holland, the largest and most populated province of the Netherlands. His schooling did not involve any language other than the local Nether-Dutch, spoken in South Holland, so he did not learn Latin, the scientific language of that day. Everything that he wrote was in Dutch, which meant that recipients such as the Royal Society had to translate his letters into English (or occasionally into Latin) for publication, and someone translated their replies into Dutch for him.

Vermeer’s view of Delft, 1660, detail

In 1648, at the age of 16, he was sent to Amsterdam to learn the drapery trade. He worked there for Scottish textile merchant William Davidson, becoming his cashier and accountant. In 1654, he returned to Delft, where he set up a drapery and haberdashery business and married Barbara de Mey, the daughter of a local textile merchant. They produced five children, although sadly only their second daughter, Maria, survived early infancy.6

He then lived in Delft for almost 70 years and was appointed to several municipal positions. One of these was Trustee for the estate of fellow-Delft artist Johannes Vermeer, who was born in the same year as Leeuwenhoek, but died in 1675 leaving a widow, 11 children, huge debts, and some of the world’s best paintings.

Hooke’s microscopic depiction of silk, from his Micrographia.

Becoming a microscopist

In or about 1668, he holidayed in London.7 Here, he undoubtedly saw English scientist Robert Hooke’s newly published and ‘best-selling’ book, Micrographia,8 which documented Hooke’s microscopic observations of many familiar objects. These included some high magnifications of woven silk fabric, which would have intrigued draper Leeuwenhoek; it also contained “the first published illustration of a microfungus”.9

Hooke’s book may well have stimulated Leeuwenhoek’s interest in lenses into the consuming passion it became. This involved his making his own high-magnification lenses, mounting them to form simple microscopes (see box), and then examining and measuring10 a host of miniscule objects in response to his growing insatiable curiosity regarding things imperceptible to the naked eye.

Communication with the Royal Society

One of Leeuwenhoek’s friends in Delft was a physician, Dr Regnerus de Graaf. On April 28, 1673, de Graaf wrote to Henry Oldenburg, the first Secretary of the Royal Society in London and founding editor of its Philosophical Transactions: “I am writing to tell you that a certain most ingenious person resident here, named Leeuwenhoeck [sic], has devised microscopes which far surpass those we have hitherto seen. …”11 He enclosed a letter from Leeuwenhoek describing the latter’s observations on the structure and growth of mould; on the sting, limbs, and eye of a bee; and on the head, feelers, and legs of a louse, which Oldenburg published (“English’d”) in the Philosophical Transactions.12 Intrigued, readers wanted to see what was described, so on August 15, 1673, Leeuwenhoek sent the relevant illustrations,13 with a note to say that because he couldn’t draw well, he had employed a draughtsman who had observed each object through a different lens.

Leeuwenhoek’s illustrations of bee stings (bottom row) and their sheaths (top row), as published in Philosophical Transactions.

Thus began a correspondence of some 200 letters from Leeuwenhoek to the Royal Society that continued for fifty years “on matters zoological, botanical, chemical, physical, physiological, medical, and miscellaneous (unclassifiable) … all written by himself in his own old-fashioned Dutch, though they were often translated by others into other languages, published in many different ways, and collected in various volumes at divers dates by different editors.”14 Henry Oldenberg, in fact, learned Dutch in order to translate Leeuwenhoek’s letters for himself.

Leeuwenhoek was particularly interested in blood. To observe and measure blood cells (discovered by Italian scientist Marcello Malpighi in 1665), he pricked his thumb and smeared the blood on a small glass tube. In his letter of 1 June 1674, he wrote: “The red globules of the blood I reckon to be 25,000 times smaller than a fine grain of sand.”15 This equates to about 8.5 microns, which is close to the modern measurement of ~7–8 microns.

First sighting of protozoa

In 1674, Leeuwenhoek examined some water from a freshwater lake called Berkelse Mere near Delft. In this, he saw some organisms that were manifestly protozoans, as described by him briefly in his letter to Henry Oldenburg:

“And the motion of most of these animalcules in the water was so swift, and so various, upwards, downwards, and round about, that ’twas wonderful to see: and I judge that some of these little creatures were above a thousand times smaller than the smallest ones I have ever yet seen, upon the rind of cheese, in wheaten flour, mould, and the like.”16

The birthday of bacteriology

Colourized illustrations of some of the many animalcules Leeuwenhoek observed.

Then in 1676, Leeuwenhoek wrote the now-famous 17½-page letter in which he described sighting bacteria, part of which Oldenburg published in the Philosophical Transactions 12(133):821–831, 1677. In it, he related what he saw on 24 April 1676, in water in which he had soaked pepper for about three weeks and to which he had twice added snow-water (the purest water available) to replace that which had evaporated away. He described three types of what we now call protozoa and then wrote:

“The fourth sort of little animals, which drifted among the three sorts aforesaid, were incredibly small; nay, so small in my sight, that I judged that even if 100 of these wee animals lay stretched out one against another, they could not reach the length of a grain of coarse sand; and if this be true, then ten hundred thousand [i.e. 100 × 100 × 100 = 1 million] of these living creatures could scarce equal the bulk of a coarse sand-grain.”17

Biologist Prof. D. Bardell commented: “An organism that is incredibly small compared with a protozoan is the reason for belief that van Leeuwenhoek discovered bacteria on 24 April 1676.”18

And Dutch microbiologist Prof. Albert Kluyver said: “The measures given leave no doubt that he observed bacteria here; consequently this is the first unmistakable description of representatives of this group of organisms, and there is every reason to consider the 24th April, 1676, as the birthday of Bacteriology.”19

Leeuwenhoek’s illustrations of bacteria from his mouth. Dobell identified these as A, a motile Bacillus. B, Selenomona sputigena. C. … D, the path of its motion. E, Micrococci. F, Leptothrix buccalis. G, A spirochaete, probably Spitochaeta bucalis.

In a further experiment with pepper-water, Leeuwenhoek described seeing “some very long and very thin particles … [that] moved with bendings, as an eel swims in the water; only with this difference, that whereas an eel always swims with its head in front, and never tail first, yet these animalcules swam as well backwards as forwards, though their motion was very slow.”20 Protozoologist Clifford Dobell commented: “A remarkably shrewd observation, which proves conclusively that L. was here dealing with bacteria. The organisms were evidently the long flexible thread-bacteria (Pseudospira C.D.) so common in infusions.”21

Later, Leeuwenhoek was astonished to find in scrapings from his teeth, “many very little living animalcules, very prettily a-moving”. Thus he discovered that we too are carriers of animalcules, which he also noted died when he drank hot coffee.22 So he was the first to observe that microbes are killed by heat. Because he discovered bacteria in the mouths of healthy people, including himself, it is understandable that he did not associate bacteria with disease, as we often do today. But most bacteria are harmless, just as he thought, and many are even beneficial, e.g. probiotics, and thus protected by our appendix. It wasn’t until 1860–64 that Louis Pasteur proved the germ theory of disease, and then devised pasteurization to destroy harmful bacteria, and further developed vaccination to train our immune system to combat them.

Skepticism, verification, fame

The Fellows of the Royal Society were hugely skeptical, and understandably so, as Leeuwenhoek, a layman, was describing phenomena that not one of these scientific intelligentsia had ever seen, much less looked for, or even imagined existed. Challenged, Leeuwenhoek assembled eight Delft gentlemen of repute, including a Lutheran minister, a notary, and a barrister, who peered through his microscopes, saw the animalcules, and wrote affidavits, which he then sent to the Royal Society by letter dated 5 October 1677.

Meanwhile, the Fellows had asked Hooke, who was their Curator of Experiments, to verify the observations. For several months he tried unsuccessfully, until finally, in November 1677, he was able to demonstrate the animalcules, and wrote: “ … much to wonder I discovered vast multitudes of those exceeding small creatures, which Mr Leeuwenhoek had described … and some of these so exceeding small, that millions of millions might be contained in one drop of water”.23 Hooke wrote a courtesy letter to Leeuwenhoek, dated 1 December 1677, in which he said “all the members present were satisfied”, and he contrasted the size of the tiny protozoa with that of the much smaller bacteria as “gygantick monsters in comparison of a lesser sort”.24

Confirmation! And reward! In 1680, Leeuwenhoek won recognition as a true scientist by being elected a Fellow of the Royal Society. His membership certificate was worded for his benefit in Dutch instead of the usual Latin.25

Membership of the Royal Society and publication of his letters in the Philosophical Transactions made Leeuwenhoek and his work famous all over the world. Not only scientists, but crowned heads too came to Delft to see him and peer through his microscopes. These included Tsar Peter the Great of Russia, King Frederick I of Prussia, the future King James II of England, and his daughter, the future Queen Mary II of England, to whom he presented two of his silver microscopes.

Contra spontaneous generation

People of Leeuwenhoek’s day who disregarded Genesis believed in the Aristotelian theory of spontaneous generation,26 e.g. that decaying meat produced maggots, dust produced fleas, wheat kept in a dark corner turned into mice, etc. As a Bible-believing Christian, Leeuwenhoek rejected spontaneous generation and repeatedly stated that the perfections he saw in his tiny organisms were created by God and were not the product of corruption. Some examples:

“We cannot in any better manner, glorify the Lord and Creator of the Universe, than that, in all things, however small soever they appear to our naked eyes, but which yet have received the gift of life, and power of increase, we contemplate the display of his Omniscience and Perfections with the utmost admiration.”27

“… as it is impossible for an elephant to be brought forth from dust or dirt, it is equally impossible for a Mite to be bred out of meal or any corrupted substance, or in any other manner than the regular way of generation I have described.”28

“From all these observations, most plainly we discern the incomprehensible perfection, the exact order, and the inscrutable providential care with which the most wise Creator and Lord of the Universe has formed the bodies of these Animalcules, which are so minute as to escape our sight, to the end that the different species of them may be preserved in existence. And this … must surely convince all of the absurdity of those old opinions, that living creatures can be produced from corruption or putrefaction.”29

Also his observation of the life cycles of insects (from eggs to larvae, to pupae, to adults which then laid eggs or produced live young), showed that they came from parents like themselves,30 and not from manure. And he saw this as a “confirmation of the principle that all living creatures derive their origin from those which were formed at the Beginning.”31

Today, spontaneous generation (the belief that a living thing can arise from non-living matter) is euphemistically called chemical evolution or abiogenesis,32 and is once again the dominant belief system of atheistic scientists. It is a natural and crucial predecessor of Darwinism; if all life evolved ‘naturally’ from a single-celled common ancestor, they reason, that itself must have also arisen from dead matter unaided.33 Proponents search the earth, the solar system, and the universe relentlessly, striving to find evidence of it so as to deny the creation account in Genesis.

Posthumous recognition

Leuwenhoek enjoyed excellent health for most of his life. He died on 26 August 1723, aged 90. He had sent the Royal Society such a detailed, first-ever description of the medical condition that caused his death that it is now called van Leeuwenhoek’s Disease! This very rare condition involves episodes of rapid involuntary contractions of the diaphragm, or diaphragmatic flutter, causing shortness of breath, rapid breathing and abdominal pulsations, so it is also known as Belly Dancer Syndrome.34


Although only a layman, Leeuwenhoek was one of the most outstanding researchers of all time, with an insatiable curiosity to discover the hidden secrets of nature. A major scientific concern was to refute the theory of spontaneous generation. His self-confessed purpose: “… in order to draw the World away from its Old-Heathenish superstition, to go over to the Truth, and to cleave to it.”35

“In his faith Leeuwenhoek was solidly Dutch Reformed. He often referred with reverence to the wonders God designed in making creatures small and great. His virtues were perseverance, simplicity, and stubbornness. He loved truth above any theory, even his own. He asked of his challengers only that they prove their points as he proved his.”36

A Leeuwenhoek microscope. They were all small; the plates were all less than 50 mm in length.

Maker of microscopes

Leeuwenhoek’s microscopes consisted of single lenses, which he made himself—over 500 of them—quite possibly one for each specimen that he examined over 50 years.

Making and using them

He was very secretive about how he made them—whether by grinding and polishing a piece of glass with increasingly fine grit, or by blowing a tube of hot glass to form a blob, or by drawing out a hot glass thread in a flame until it broke and then heating the end of one thread till it melted and formed a tiny globule.37 Or he could have used a combination of these techniques, as “all his lenses were biconvex or planoconvex”.38 All were of remarkable clarity.

How Leeuwenhoek used his microscopes
Science History Images / Alamy Stock Photo

He mounted each lens in a tiny hole between two thin metal plates riveted together that he made out of brass, silver or very occasionally gold,39 with the specimen in front of the lens on a sharp point that could be focused by two screws.40 The largest surviving plate measures 28 × 47 mm. The smaller the lens, the greater the magnification, but also the smaller the field of view, so the reverse side needed to be held very close to one eye for viewing because of the very short focus, and this required great patience on the part of the user.


His light source was a candle or the daylight, but not the sun, as he explained to his Royal Society readers: “I contemplate in a clear day, and sometimes by Candlelight, and to have still more light, I use sometimes a metal Concave Looking glass, but above all things you must have a care, not to make your view in the Sunshine, for if you do so, the Circumference of each Animal, will have almost as many Colours, as we see in the Rainbow.”41

Encylopaedia Britannica adds: “In order to observe phenomena as small as bacteria, he must have employed some form of oblique illumination, or other technique, for enhancing the effectiveness of the lens, but this method he would not reveal.”42

Where are they now?

After his death, his daughter, Maria, sent to the Royal Society a small cabinet containing 26 silver microscopes, with specimens still attached, which Leeuwenhoek had prepared for this purpose. Magnifications of these varied from 50× to 200×.43 In 1747, after Maria’s death, 517 instruments were put up for public auction.44 Of all the above, only 12 are reckoned to still exist.45 In 2009, Christie’s in London auctioned one; it sold for £260,000. The best is in the Utrecht University Museum. Its plate measures 24 mm × 46 mm, and it has a linear magnifying power of 266× and a measured resolution of 1.35µ.46 However, from Leeuwenhoek’s recorded observations, it is generally reckoned that he must have made some lenses that magnified 500×, with a resolution of 1.0µ.

In 1981, researcher Brian Ford discovered in the Royal Society archives nine packets of original samples sent by Leeuwenhoek in 1674, 1686, and 1687. Unopened for 300 years, “they were as well prepared as many modern specimens.”47

References and notes

  1. According to protozoologist and Fellow of the Royal Society, Clifford Dobell, who wrote Antony van Leeuwenhoek and his ‘Little Animals’, 1932, republished by Dover Publications, New York, 1960, leeuw means ‘lion’, hoek means ‘corner’, poort means ‘gate’, and van means ‘of’. So it has been suggested that the family was probably known to their neighbours as the family from the corner house in Leeuwenpoort = Lion’s gate (p. 301). Return to text.
  2. He wrote his first name, Antonj, ending with a Dutch long i (not English j), which various biographers have transliterated as Antony, Antonie, Antoni, or nonchalantly disregarded as Anton. His surname has also suffered at the hand of translators; in the English versions of his letters, published in the Royal Society’s Philosophical Transitions, it “is spelled in no less than 19 different ways” (Dobell, ref. 1, p. 303). Return to text.
  3. From the post-classical Latin word animalculum: a minute or microscopic animal, nearly or quite invisible to the naked eye, Return to text.
  4. Antonie van Leeuwenhoek, Dutch scientist, Encyclopaedia Britannica Editors. Return to text.
  5. Famed as the seat of the royal House of Orange when William I Prince of Orange, also known as William the Silent or William the Taciturn, took up residence there in 1572, and where he was assassinated in 1584. (Dobell, ref. 1, pp. 25 & 26.) Return to text.
  6. Barbara died in 1666, and in 1671 he married Cornelia Swalmius, who was a distant relative of his first wife, and who died 23 years later. Thereafter he was cared for by his spinster daughter, Maria, until his own death in 1723. Return to text.
  7. England and Holland were then temporarily at peace. The second Anglo-Dutch War ended in July 1667; the third was declared in March 1672. Return to text.
  8. Full title: Micrographia or Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses with Observations and Inquiries thereupon. The first edition appeared in 1665, the second in 1667. This was the first illustrated book on microscopy. Hooke used a compound microscope with a small plano-convex object lens and a large plano-convex eyepiece lens. However, the first lens created a halo of many colours, called chromatic aberration, which the second lens magnified, thereby increasing the distortion. This aberration limited the usefulness of such early compound microscopes to magnifications of about 20–30×. Hooke is famous for coining the term ‘cell’ in his discussion of the structure of cork, in 1663. He is also renowned for deriving Hooke’s Law (of elasticity) in 1660. Return to text.
  9. “Schem. 12, Fig. 1”, in Micrographia (ref. 8). Today this is identified as “the microfungus Mucor”, (Gest H., The Discovery of Microorganisms by Robert Hooke and Antoni van Leeuwenhoek, Notes Rec. R. Soc. Lond. 58(2):187–201, 2004). Return to text.
  10. Leeuwenhoek needed to create his own microscopic standards to measure this formerly invisible new world. The principal ones he chose to use were: a coarse sand-grain (modern equivalent about 870 µ, i.e. microns, 1 µ = a one millionth of a metre); a fine sand-grain (about 260 µ); a hair from his head (about 60–80 µ); and the eye of a louse (about 50–85µ), as per Schierbeek, ref. 15, pp. 55–56. Return to text.
  11. Quoted from Dobell, ref. 1, pp. 40–41. Return to text.
  12. Philosophical Transactions, 8(94):6037–6038, 1673. Return to text.
  13. Published by Oldenburg in Philosophical Transactions, 8(97):6116–6119, 1673. Return to text.
  14. Dobell, ref. 1, p. 44–45. Dutch editions began to appear in 1684 and Latin in 1685. Return to text.
  15. Schierbeek, A., Measuring the Invisible World, Abelard-Schuman, New York, 1959, pp. 110–11. Return to text.
  16. Leeuwenhoek’s Letter No. 6 (by Dobell’s reckoning) to H. Oldenburg, dated 7 Sept. 1674; translated from the Dutch original by Dobell in ref. 1, pp. 109–11. Return to text.
  17. Leeuwenhoek’s Letter No. 18 (by Dobell’s reckoning) to H. Oldenburg, dated 9 Oct. 1676; translated from the Dutch original by Dobell in ref. 1, pp. 132–33. Return to text.
  18. Bardell, D., The Roles of the Sense of Taste and Clean Teeth in the Discovery of Bacteria by Antoni van Leeuwenhoek, Microbiology Reviews, 47(1):123, March 1982. Return to text.
  19. Quoted by Shierbeek, ref. 15, p. 65. Return to text.
  20. Dobell, ref. 1, pp. 140–141. Return to text.
  21. Dobell, ref. 1, p. 141, Footnote 1. Return to text.
  22. Dobell, ref. 1, p. 239 & 248. Return to text.
  23. Published in Hooke, R., Microscopium, 1678, p. 83. Return to text.
  24. Dobell, ref. 1, p. 182–183. Return to text.
  25. Dobell, ref. 1, p. 49. Return to text.
  26. A belief widely propagated by Aristotle, who compiled and expanded the similar teachings of earlier Greek natural philosophers. Note: he predeceased Darwin, who did not publish his Origin of Species until 1859. Return to text.
  27. The Select Works of Antony Leeuwenhoek, Translated by Samuel Hoole, London, 1816, Vol. 1, p. 314. Return to text.
  28. The Select Works of Antony Leeuwenhoek, Translated by Samuel Hoole, London, 1816, Vol. 2, p. 173. Return to text.
  29. Ref. 28, p. 214. Return to text.
  30. This included parthenogenesis in aphids; the aphids he dissected did not contain eggs, but embryonic aphids just like the parent, Schierbeek, ref. 15, p. 106. Return to text.
  31. Schierbeek, ref. 15, p. 137. Return to text.
  32. A pseudonym for ‘spontaneous generation’ coined by Thomas Huxley in 1870. Return to text.
  33. But the scientific problems for abiogenesis are almost incalculably huge, see Return to text.
  34. The American Journal of Respiratory and Critical Care Medicine, Vol. 183, No. 10, May 15, 2011 describes one case out of only about 50 ever diagnosed. Return to text.
  35. From Leeuwenhoek’s Letter No. 81 (by Dobell’s reckoning) to the Royal Society, 19 March 1694, quoted by Dobell in ref. 1, p. 74. Return to text.
  36. Graves D., Scientists of Faith: 48 Biographies of Historic Scientists and Their Christian Faith, Chapter 17 Antonie van Leeuwenhoek, p. 71, Kregel Publications, Grand Rapids, USA, 1996. Return to text.
  37. This latter was Hooke’s method of making single lenses, as described in the Preface of his book, Micrographia (ref. 8), which Leeuwenhoek’s friends in England would undoubtedly have translated for him during his visit there in 1668. Hooke found the use of such small single-lens instruments “troublesome to be us’d, because of their smallness, and the nearness of the Object”, and he preferred to use a compound microscope. Return to text.
  38. Ford, B., The Clarity of Images from Early Single-lens Microscopes Captured on Video, Microscopy and Analysis, p. 16, March 2011. Return to text.
  39. Possibly to enhance the reflexion of light onto opaque specimens. Return to text.
  40. This was unsuitable for large living specimens, so he modified it by adding a glass tube, which he called an aalkijker, or ‘eel-viewer’, also translated as ‘aquatic microscope’. See Eel-viewer: showcase for visitors. Return to text.
  41. Letter of 9 June 1699, published in Philosophical Transactions 21(255):308, 1699. He was describing the bad chromatic aberration in sunlight. Return to text.
  42. Antonie van Leeuwenhoek: Dutch Scientist, Encyclopedia Britannica Editors. Return to text.
  43. As measured by Henry Baker (Philosophical Transactions 41(458):506, 1740), recalibrated to an image distance of 250mm, Brian Ford, The Leeuwenhoek Legacy, Biopress, Bristol, 1991, p. 131. Return to text.
  44. Robertson, L., van Leeuwenhoek microscopes—where are they now?, which lists 322 microscopes, 23 aalkijkers (ref. 40), and 172 lenses in brass holders. Return to text.
  45. Nine claimed traditionally, plus three new candidates discovered, one in 1982 and two in 2014, not all of certain provenance. For data on all 12, see Ford, B., Surprise of the Century—Three more Leeuwenhoek Microscopes. For pictures of 11 of these, see Single lens microscopes: Lens on Leeuwenhoek. . Return to text.
  46. According to Ford, B., The Leeuwenhoek Legacy, Biopress, Bristol, 1991, pp. 148–49. Return to text.
  47. Ford, B., The Leeuwenhoek Specimens. Return to text.

Helpful Resources

Should Christians Embrace Evolution?
by Norman C Nevin (Editor)
US $15.00
Soft cover
Six-Day Creation
by Robert Gurney
US $8.00
Soft cover

Readers’ comments

William H.
Thanks for this article, Russell. Well written and very interesting!! I like the quote from Leeuwenhoek in which he honors our God and not an imagined spontaneous creation (or in these days—evolution):

We cannot in any better manner, glorify the Lord and Creator of the Universe, than that, in all things, however small soever they appear to our naked eyes, but which yet have received the gift of life, and power of increase, we contemplate the display of his Omniscience and Perfections with the utmost admiration.

Comments are automatically closed 14 days after publication.