Protist, Vol. 153, 177–190, June 2002 © Urban & Fischer Verlag http://www.urbanfischer.de/journals/protistPublished online 29 May 2002

During the third and last century of the Renaissance,that great revival of art, literature, and learning allacross Europe, the amateur scientist Antony vanLeeuwenhoek (Fig. 1) was unobtrusively born in Oc-tober 1632 in the quiet but thriving Dutch town ofDelft. Also born that same year were other men des-tined for eternal fame in quite different fields: for ex-ample, John Locke, Baruch de Spinoza, ChristopherWren, Nicolaes Maes, and – in the very same town –Jan Vermeer. That date, interestingly enough, markedthe middle of the drawn-out Thirty Years War, with allits religious and political machinations and implica-tions, an off-again-on-again conflict sometimes pit-ting England against Holland (The Netherlands). Re-call that the 17th century also witnessed the begin-ning of the Enlightenment Period of history.

Although the man who is the subject of this brieftribute died in 1723, two months shy of his 91st birth-day, he and his impressive scientific contributionswere very little known and seldom publicized and ap-preciated until their major revelation in the 20th cen-tury more than 200 years after his death. It is true that

A Salute to Antony van Leeuwenhoek of Delft,Most Versatile 17th Century Founding Father of Protistology

John O. Corliss1

P.O. Box 2729, Bala Cynwyd, OA 19004, USA

“I’m well aware that these my writings will not be accepted by some, as they judge it to be impossible tomake such discoveries…” [but] “I will say once more that ‘tis my habit to hold fast to my notions only until I’mbetter informed or till my observations make me go over to others…”

A. van Leeuwenhoek in letters to the Royal Society (excerpts taken from English translations given by Dobell 1932)

FROM THE ARCHIVES

1fax 1-610-664-4904e-mail jocchezmoi@aol.com

Protist

1434-4610/02/153/02-177 $ 15.00/0

Figure 1. Antony van Leeuwenhoek, in his mid-fifties.A photograph of a portion of Dutch painter JohannesVerkolje’s celebrated mezzotint engraving of 1686,taken in 1970 for the author’s private collection of pic-tures of great protistologists.

W. Saville Kent (1880) and Otto Bütschli (1887), andsucceeding protozoologists knowing of the tremen-dous monographs on protists of these two prolific19th century giants in the field (Bütschli 1880–1889,Kent 1880–1882), were and have been quite aware ofsome of the Leeuwenhoek protistological discover-ies, but not always accurately or in detail.

The most comprehensive treatments to emerge ofLeeuwenhoek’s life and letters, and of his numerouscontributions to the many fields dependent in largemeasure on precise microscopical observation,have been the following: Cole (1937), Dobell (1932),Ford (1985, 1991), Schierbeek (1959, 1963; and as amajor editor, 1939–?, of a long-continued series ofvolumes published in both Dutch and English), and anumber of papers (not cited here) by several 20th

century Dutch microscopists or microbiologistswritten in their own language only. Shorter biogra-phies, but of some comparative historical value andto be noted for their accuracy, include accounts inBeltrán (1974), Bulloch (1938), Cole (1926, 1938),Corliss (1975, 1978–1979, 1992), Dobell (1923),Lechevalier and Solotorovsky (1965), Locy (1935),Meyer (1937), Nordenskiöld (1928), Rooseboom(1956), Singer (1959), and Zuylen (1981).

Popular “Father of” Titles for the Man from Delft

Before examining the life and works of Leeuwen-hoek, the amateur biologist who, with his simple buthigh-powered single-lens microscope made suchearly astounding observations on the theretoforelargely unseen world of cells, protists, animal andplant tissues, I should mention briefly the “discov-erer” titles generously – and usually deservedly – be-stowed upon him during the past century. If we con-cede that “Father of” does not confer sole or abso-lutely very first discovery in a field, then the followingaccolades are quite accurate: Father of Protistology,Father of Protozoology, Father of Phycology (at themicroscopic level), Father of Microbiology, Father ofBacteriology, Father of Hematology or Serology (hesaw erythrocytes and extended Harvey’s landmarkobservations of 1618 to include capillary circulationin tissues), Father of Plant (Microscopic) Anatomy,and even Father of Microbial Ecology.

Additional titles that may be a little exaggeratedor a bit over-extravagant would include Father ofParasitology (but he was indeed the first to see, de-scribe, and determine the sizes of symbiotic bacte-ria and protozoa from the digestive tracts or feces ofseveral invertebrates and vertebrates, including hu-mans); Father of Crystallography (a superb glass-

blower, he ground his own lenses with unusual pre-cision, sometimes from grains of pure sand); Fatherof (simple) Stain and (razor-blade) Sectioning Tech-nologies; and Father of Pesticide Control (he experi-mentally demonstrated the effects of certain chemi-cals on microorganisms and small invertebrates) .

Further accolades can be found, ones occasion-ally still in usage although they are or may be techni-cally quite incorrect. An outstanding example is thepersistent but falsely bestowed Father of Mi-croscopy title. Large-bodied compound micro-scopes, with eyepiece, draw tube, multiple lenses, amirror, etc., were in existence and usage a full halfcentury before Leeuwenhoek’s work and haveserved as models for modern equipment (see Brad-bury 1967, Singer et al. 1957, Woodruff 1939, andnumerous other compendia on microscopy and itshistory). Other examples of mostly inaccurate labelsinclude Father of Cytology (although his compara-tive observations on spermatozoa, for example,stand as landmarks in the history of biology); Fatherof Histology (but both plant and animal tissues didcome under his early scrutiny); Father of Embryol-ogy (yet he did observe early cell division stages ineggs of some invertebrates and in spores of someplant species, not to mention reproduction in thealga Volvox, and an account of the reproductive or-gans of ants; and he described budding in thecnidarian Hydra some four to five decades beforethe classical, long-well-known papers by Trembley,Baker, and other zoologists); Father of (microscopic)Mycology (he did offer early descriptions of yeastand some mold cells/spores); and Father of (micro-scopic) Neurology (he described hand-sectionedbovine optic nerve material in 1674 and 1675). Heeven contributed substantially to the field of micro-crustacean anatomy, perhaps inspired by his longand close friendship with Jan Swammerdam (born1637, died 1680) whose celebrated work on Daph-nia (then known simply as a water-flea or water-louse) first appeared in 1669 (in Dutch).

We certainly may conclude that if there were asection in the Guinness Book of World Records enti-tled “Most ‘Fathers’ of Scientific Fields,” the versa-tile Mr. van Leeuwenhoek would definitely rate afirst-place position in it!

Brief Account of Major Periods in Leeuwenhoek’s Life

It may be helpful to arbitrarily divide Leeuwenhoek’slong life span into roughly three periods, each ofabout 30 years’ duration. This biographical andoverview section is followed by more detailed atten-

178 J. O. Corliss

tion to his beloved “magnifying glass” (as he himselfcalled it) and to his recorded descriptions, includingreproduction of some of his (or his draftsmen’s) suf-ficiently accurate drawings to allow taxonomic iden-tifications to be made with considerable certaintytoday.

His First 30 Years

Born into a large family (but the only son) in Delft,Holland, on 24 October, 1632, young Antony wassent away for schooling until about age 15 or 16. Hemay have learned some rudimentary mathematicsand physics but didn’t take Latin or foreign lan-guages or other subjects which we in America todaycall requisite parts of a classical or “college prepara-tory” curriculum. At the age of 16, he was sent toAmsterdam to master the linen-draper trade. Sixyears later, he returned to Delft where he set up hisown shop and remained for the rest of his life.

In 1654, Antony married his first wife (Barbara)and they had five children, only one of whom, Maria,survived beyond early years. In fact, she becameher father’s faithful “right-hand man” for manydecades, passing away in 1745 at the ripe old age of(nearly) 89, surviving her nonagenarian dad by some22 years. The year 1654 was historically a very im-portant one for Delft: a huge explosion at its arsenalcaused fires killing thousands of its residents anddestroying much of the town. As fate would have it,spared among others were two of its young (22-year-old) inhabitants of particular interest to us here,Leeuwenhoek and Vermeer.

Incidentally, in 1664, to look beyond the first thirdof Antony’s life for a moment, his mother passedaway; both his father and his stepfather had diedmuch earlier. In 1666, his wife Barbara died; he re-married (to Cornelia) three years later; childless, shepassed away in 1694, leaving Leeuwenhoek withonly his loving daughter Maria as close companionfor the rest of his life.

His Second 30 Years

The “middle third” of Leeuwenhoek’s full life is full ofsignificant happenings. On the local scene, he be-came a well recognized citizen of the town, wasmade a municipal surveyor, named the official wine-gauger (did assaying all wines and spirits enteringDelft contribute to his longevity!?), and given thepost of Chamberlain to the Sheriffs Office (not a jan-itor’s job, as is sometimes suggested, but really anhonorary sinecure with a salary to help support –along with his drapery business income – his variousliving expenses while he did what he wished as a

naturalist of the microbial world, the latter a hobbyof his that was increasingly becoming known to oth-ers by the 1670s). In 1676, he was appointed the ex-ecutor of the estate of his departed close friend JanVermeer, whose art and philosophical outlook on lifeso much appealed to him.

‘Twas his only trip to London, in 1668 (during a lullbetween new sets of Anglo-Dutch Wars and twoyears after the terrible London fire), that undoubtedlyheavily influenced how he was to spend the rest ofhis life. Although Dobell (1932) and Dutch historianshave uniformly insisted that Leeuwenhoek’s passionfor objects microscopical was entirely self-gener-ated, modern investigator and biographer Brian Ford(1991) has offered the surprising but convincing sup-position that Robert Hooke’s (1665, 1667) Micro-graphia was seen and read (with the help of Englishfriends as translators) by him – and excited himgreatly during and well after that fateful trip. Recallthat Hooke described the intimate structure of anumber of textiles in his highly popular monograph,using a single lens magnifying glass; he also figured“cells” (the spaces left by them) in razor-blade sec-tioned cork, the discovery of his that biologists areapt to remember best. And, among other observa-tions made, Hooke postulated what causes chalk toappear white. Now Leeuwenhoek himself, as a tex-tile merchant, was well acquainted with the weavingpatterns, etc. in different kinds of cloth. And on histrip across the English Channel he became curiousabout the nature of the white cliffs of Dover, indepen-dently wondering about their reflection of light, etc.The careful drawings by Hooke – whose second edi-tion of Micrographia had become available very likelyby the time of the Dutchman’s visit to London – couldcertainly have stimulated Antony to delve further intosuch matters (while Hooke himself mostly went offinto other fields of investigation).

It is known that the two men corresponded,though they never met, and Hooke (born 1635, died1703) retained a lifetime high admiration forLeeuwenhoek’s subsequent microscopical observa-tions. In fact, it was Hooke who was behind the lat-ter’s nomination to the Royal Society, an honor be-stowed in 1680. But it was a friend and fellow resi-dent of Delft, the eminent anatomist Reinier deGraaf, who first brought Henry Oldenburg’s (firstSecretary of the Society) attention to Leeuwenhoekby letter in 1673 (the very year of de Graaf’s untimelydeath at the age of 32); and later that same year adelegation from the Society visited Delft and re-turned with glowing reports of the simple but effec-tive “microscopes” they had seen and the multipleuses of them by their ingenious Dutch maker. Thisresulted in an arrangement whereby Leeuwenhoek

Antony van Leeuwenhoek 179

would write to Oldenburg of his discoveries over themany years following that important visit. He wasstill penning and posting epistles (totaling >200) tothe Royal Society, most always handwritten and inhis native language, during his last days on earth inthe month of August 1723, some 45 years after thedeath of editor Oldenburg and of several others suc-ceeding him as Secretary of the Society.

On nine occasions during the period 1674–1687,incidentally, the Delftman included with his letterspackets of samples of materials he had examined.These were discovered and their dried contentsmeticulously reexamined and described, for the firsttime, by Ford (1985, and earlier notices citedtherein). It might also be mentioned here thatLeeuwenhoek’s devoted daughter Maria, a fewweeks after his death and on his wishes, sent to thataugust Society in London more than two dozen ofhis best homemade microscopes. Alas, they (mis)-managed to lose every single one of those preciousinstruments over time.

In this paper, quite appropriately, I shall limit mostof our attention to the “Letters,” some quite lengthy,that are concerned mainly with protistological orbacteriological material, giving them the numbersfirst assigned by Dobell (1932). Leeuwenhoek’s prin-cipal communications wholly or in part on thesesubjects were given numbers 6–150+ and ran fromthe year 1674 to 1716. Recall that numerous noteswere posted to other people or other destinationsthan the Royal Society. Their writer, with very littleformal or classical “higher” education, nonethelesstruly became a “man of letters”!

Leeuwenhoek’s observations on free-living pro-tists and prokaryotes (bacteria) and on symbiotic orparasitic species of these two major assemblages ofmicroorganisms were considered separately by Do-bell (1932), but since information on both is inter-mixed in many letters I shall not make such a dis-tinction in the present paper. In the second 30-yearperiod of the Father of Protistology’s long life, Let-ters No. 6 through 71 were penned. During his last30 years (see below), numbers 75 through 150 (plustwo more, numbered by Dobell as VII and XXIX) ap-peared.

In 1686, this man of growing fame sat for an oilportrait by the distinguished painter JohannesVerkolje, who had taken up permanent residence inDelft a dozen years before then. A mezzotint engrav-ing, made later the same year by the same artist andintroducing several small changes plus reversal ofthe image in the print, is the colored picture mostoften reproduced in major biographies and text-books alike that have appeared during the past cen-tury (and see Fig. 1).

His Third 30 Years

In the last third of his life, Leeuwenhoek finally com-menced to slow down a wee bit, but he still madenumerous contributions to the literature (againmostly via publication of his Letters, in Englishtranslation, in the Philosophical Transactions of theRoyal Society). The bulk of the relatively few draw-ings he made were published during the first half ofthis period, with the remainder from the last third ofthe preceding one (see Fig. 4). As mentioned above,we are concerned here principally with the observa-tions on protists and bacteria. The reader is referredto Ford (1991) for discussion of his remarkable con-tributions to other fields similarly requiring micro-scopical techniques.

His last letter on protozoa (not illustrated) waspublished in 1716, when he was 84 years old. Butrecall that Leeuwenhoek was still sending scientificletters to London on other topics during the finalyear of his life, 1723!

By now, the Delft protistologist had achieved in-ternational (well, European) fame, and he not onlyreceived many letters from admirers in all stations oflife but also requests to call on him personally.Among the latter, ones most flattering to him per-sonally were visits from royalty. For example, he en-tertained Queen Mary II of England, an Emperor ofGermany, and Peter I, Czar of Russia, bestowing mi-croscopes upon all of them. To his joy, the learnedPeter the Great conversed fluently with him in theDutch language. Various distinguished scholars ofthe time numbered among other visitors, as well asseveral scoundrels who intended to copy his worksor steal his jealously guarded “magnifying glasses.”

Leeuwenhoek diagnosed his own terminal illnessmore accurately than his physician did, who couldsuggest only excessive palpitations of the heart. Thedying man himself concluded that he was sufferingfrom bronchopneumonia… and so indeed he was,passing quietly away in bed, with only daughterMaria as family survivor, on 26 August 1723.

Leeuwenhoek’s Refined Single-Lens Microscope

The simple, postage-stamp size instruments withwhich the Father of Protistology made his amazingobservations over a 60-year period in the 17th andearly 18th centuries were hardly complex ones (seeFigs. 2, 3), but they afforded a resolution and a clar-ity in magnification that clearly surpassed that of thebulkier multi-lens “compound” microscopes of thetimes (and for scores of subsequent years). But it is

180 J. O. Corliss

the latter kind of microscope that ultimately, withmany refinements, gave rise to our superior moderninstruments manufactured today by Zeiss, Leitz,Spencer (American Optical), Bausch & Lomb, Olym-pus, Leica, and other companies. Thus there is goodreason (as stressed on a preceding page) not tolabel Leeuwenhoek as the Father of Microscopy, de-spite his excellent results with his own special mag-nifying glass, so superior to other single-lens‘scopes of then or ever since (see “how/why”below).

Dobell (1932) and especially Ford (1985, 1991)have offered such thorough descriptions of theLeeuwenhoek ‘scope that there is little need for meto give many details (of its structure, etc.) here. Butreview of a few facts will perhaps help the reader ap-preciate its uniquenesses and explain why its earlycritics were completely in error to “judge it to be im-possible to make such discoveries” as the Delft am-ateur microscopist did with this “primitive tool” (asthey imagined it).

Numbers and Sizes of the Microscopes

It is not generally realized that a great number ofthese instruments were made by the Dutch draper

Antony van Leeuwenhoek 181

Figure 2. The “simple” Leeuwenhoek hand-lens microscope, shown natural size. a. The front face (notice thetiny aperture behind which is located the single lens). b. The back face, revealing the mechanics of the instru-ment. c. Side view, showing further aspects of its construction. See text for details. These pictures are copies oforiginal photographs taken of the author’s personal brass replica of a typical Leeuwenhoek microscope and keptin his collection of protistological memorabilia.

Figure 3. Drawing of the front face of the author’s au-thentic brass replica of a Leeuwenhoek microscope,natural size, held in the hand of artist Lois Reid. Noticeits postage-stamp size!

from Delft: “hundreds” is a safe estimate. Over theyears of his long life, dozens must have been givenaway, with 26 alone to the Royal Society. How manywere donated or bequeathed to museums and suchrepositories in The Netherlands, his own country,does not seem to be accurately known. Some 250completely finished forms were auctioned off toHollanders in 1747, almost 24 years after his death.How many might have been discarded or disposedof for various reasons, by their inventor or others, isunknown. “Simple” though they may have been,fashioning even one of them was not a short-timetask. Replicas (how many? hundreds?) have ap-peared over the years, some more faithful than oth-ers to original designs, and/but their whereaboutsare also not completely known or easily deter-minable. I am pleased to possess a fine example ofthe latter kind myself, a personal gift from Dr. A.Schierbeek when I was privileged to make his ac-quaintance briefly in 1951 in Amsterdam (see Fig.2).

Sizes and shapes were not identical throughoutall the instruments known or still surviving (as origi-nals or presumably faithful copies) – either on pur-pose or sometimes supposedly by chance – mostlybecause an exact configuration of the frame (thetwo body-plates, riveted together or held togetherby screws) is not really essential from the point ofview of obtaining the best images of objects understudy. For example, using the nine surviving ‘scopesseen and measured by Ford (1991), lengths of thealways oblong plates ran from 32 to 47 mm, withwidths varying from 16 to 28 mm. Sometimes cor-ners were squared, sometimes quite rounded; andbottom halves of plates might be tapered to agreater or lesser extent. My own facsimile has basi-cally square corners, and both plates are roughly thesame size, measuring 42 mm (= 1 5/8 in.) by 23 mm(= 7/8 in.), with no posteriad tapering (Figs. 2, 3).

It might be noted that one of last year’s U.S.A.rectangular commemorative postage stamps, athand as I write this paper, measures 37 X 24 mm.Except for the long coarse-threaded screw (for low-ering and raising the stage on which the specimen islocated, to bring the latter into position opposite thelens-hole), which extends a variable distance be-yond the lower ends of the plates, the Leeuwenhoekmagnifying glass is indeed postage-stamp size. Thisapt comparison, first suggested by Ford (1991), isan excellent one, especially since most writers (in-cluding Dobell, and even Ford himself) publish pho-tographs and drawings considerably and mislead-ingly larger than the actual instruments being por-trayed. I have attempted to avoid that here (see Figs.2, 3).

Major Parts and Functions of the Apparatus

Details are not needed here. Suffice it to say that theclever craftsman Leeuwenhoek equipped his “sim-ple” microscopes with simple parts that can never-theless be used to carry out the very same functionsexpensively taken care of today by accoutrementssupplied to our sophisticated compound ‘scopes:for examples, a mechanical stage and a manipula-tive object-carrier, focusing and positioning gearsand screws (for both fine and coarse adjustments),and a path to a source of light (sun- or daylight; andsee below). The material to be examined could beaffixed directly onto the apical end of the object-car-rier; or if living material required an aqueousmedium, a tiny handmade capillary glass tube couldbe mounted on or glued to the carrier. For viewing,the operator need only hold the tiny ‘scope in his/herhand and position an eye opposite the viewing aper-ture on the front face/side, working the positioningscrews as needed for sharpest focus. But noticethat the focal length, the working distance betweenthe eye and the object, has to be a very short one in-deed, a disadvantage which even Leeuwenhoekcomplained of as tiring to maintain properly over along period of time.

Left out above has been the single most impor-tant part of the entire instrument: the lens itself, ofcourse! For best results, it should be a tiny well-ground and skillfully polished biconvex lens with aresolving power approaching 1.0 µm and a magnify-ing power (without spherical or chromatic aberra-tion) of 200–300+ diameters. It is held in place in asocket between the appressed pair of body-platesat the level of the pre-prepared aperture. No mirror isnecessary. Focus, and make and record your obser-vations: c’est tout! The lens in my replica allows amagnification of only 30X, but that is sufficient toobserve and roughly identify quite a few species ofciliates.

The kind of metal utilized for the plates is not ofimportance. Leeuwenhoek employed all kinds avail-able. The more expensive instruments, including theones often offered to select people as gifts, weremade of gold or, more likely, silver: both very pretty!Copper was sometimes used, but probably mostcommonly the metal chosen by the frugal inventorhimself was brass. My own copy is of brass.

Kinds of Lighting Employed

While Leeuwenhoek always advised visitors to looktowards a natural source of light (best would be sim-ply daylight) or a lighted candle placed an appropri-ate distance away, it is now believed (see Dobell’s

182 J. O. Corliss

heralds the discovery of diverse protists, none everseen before, thus marking the birth of protistology it-self. We owe knowledge of the existence of the note,as well as its careful translation from the originalDutch language, to the persistent and arduous two-decades-long investigative labors of the EnglishmanClifford Dobell (see Dobell 1932).

No. 18: Famous “Letter on the Protozoa”

This very lengthy multi-section epistle of Leeuwen-hoek’s (1677, but written in the fall of 1676), lessthan half of which was published (in translation) byOldenburg, the editor, in the Philosophical Transac-tions, became the presumed “First Letter” on free-living protists by the perceptive Delft observer, per-haps primarily because of Kent’s (1880) attention toit as the first, in some five pages of his own highly in-fluential leading volume on the Infusoria. But Kentwas familiar only with the parts that had appeared inthe Transactions. Dobell (1932) has supplied us – fill-ing more than fifty-four(!) full pages of his book – withan English translation of and comments on all sec-tions of that early and indeed “famous” Letter on theProtozoa, although mostly restricting his coverageto paragraphs containing specific mention of proto-zoa, algae, and bacteria. Today we also have Schier-beek’s (1960) illustrated 31-page booklet devotedsolely to that “Letter 18,” but it is written in Dutch.

Published Illustrations

While in the above and many subsequent Letters,diverse species of protists and prokaryotes were de-scribed verbally with sufficient precision (includinghelpful measurements) to allow their probable iden-tification by Dobell or other protistological special-ists, published figures appeared rather rarely; thuswe are often not allowed to have additional clues asto the organisms’ structural composition. Unlike hiscontemporary Robert Hooke and his biographerClifford Dobell, Leeuwenhoek was no draftsman. Hehired local artists, surely several over the last 60years of his life, and/but they are never named in hisletters. He often had them look through his micro-scopes to confirm the images he himself was see-ing; he also drew crude sketches for them to embel-lish. A few of his own direct attempts at providingoriginal drawings with his notes to the RoyalAcademy may be seen occasionally along the mar-gins of his script-pages housed in the Academy’sfiles. A number of his illustrations (by draftsmen) arereproduced in my Figure 4; and individual genera arementioned by their modern taxonomic names in theimmediately following section.

1932 excellent reasoning and conclusions drawn onthe subject) that the Delft experimenter himself musthave discovered some simple means of realizingdarkfield illumination. Secretive man that he was, henever imparted such information to anyone, butsome of his observations (e.g., seeing flagella onbacteria) would seem to have required such a tech-nique. Once again, the “simple” man from Delft hadbrilliantly devised a way to enhance his critical view-ing of organisms comprising the unseen world of mi-crobiology.

Nature and Identification of Small Organisms Observed

From the many accounts contained in the marveloussets of Letters sent to the Royal Society (and some-times elsewhere), we can get a feel for the incrediblebreadth of materials, biological and otherwise, sopainstakingly studied and so accurately describedby our amazing pioneer in the use of microscopy. Inthe present paper, however (as stated elsewhere), Iam limiting mention primarily to microorganismstoday identifiable and classifiable as protists (mainlythe eukaryotic algae and protozoa) and bacteria(prokaryotes), with emphasis on the former assem-blage.

A strong note should be made of the fact thatLeeuwenhoek was by no means a nomenclaturist;that is to say, he assigned no scientific names to thewee organisms he described. This is not surprising,of course (although people forget it), because helived and worked many decades before the en-trance of the great Swedish botanist and nomencla-turist Carolus Linnaeus (also known as Carl vonLinné) upon the biological scene. The official datesfor the nomenclatural beginning of proper (Latin orlatinized) binomial descriptors for species of plantsand animals (together, at that time, embracing allprotists and prokaryotes as well as the higher eu-karyotes) ultimately became 1753 and 1758, re-spectively (see current Codes of Nomenclature).

Celebrated Letter No. 6

In one of his earliest communications (dated 7September 1674) to the Royal Society, our buddingprotistologist gave clear, if brief, descriptions of thephytoflagellate Euglena viridis (“green in the middleand before and behind white”: Leeuwenhoek 1674),the filamentous algal protist Spirogyra, and someunidentifiable ciliates and flagellates, along with ro-tifers and other micro-inhabitants of a small fresh-water lake not far outside Delft. This Letter No. 6

Antony van Leeuwenhoek 183

184 J. O. Corliss

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).

Identification and Taxonomy of Wee “Animalcules”

This is not the place to treat the probable classifica-tion of Leeuwenhoek’s protists and prokaryotes(free-living or symbiotic, generally living material) inany detail, but it might be interesting to note thebroad distribution of the forms that he described ad-equately enough for our later probable identification.The higher-level taxonomic scheme of classificationemployed below is based primarily on quite recentoverview papers of Cavalier-Smith (1993, 1998:bacterial phyla included in the second) and/or of thewriter (Corliss 1994, 1998, 2000), with only minormodifications; and for the ciliated protozoa, seeCorliss (1979) and Lynn and Small (1997, 2002).Generic (and higher-level) names are indicated inplace. In some cases, the Delftman’s precise de-scriptions have allowed us today to recognize thevery species he managed to see by means of his“simple” ‘scope; a few of these are included in thepresent paper. Phyletic names are purposely givenin boldface script in the following paragraphs.

Kingdom BACTERIA. The prokaryotes are per-haps better broken up into several kingdoms, butthis is not of relevance to us here. Organisms in Fig-ure B, a-e, are all from the human mouth. PhylumSpirochaeta: several genera, but today exactnames of those seen and figured (e.g., see Fig. 4 B,d) by our Delft microbiologist are difficult to assign;quite possibly Treponema or Leptospira specieswere involved. Additional motile spirochetes wereapparently noted in samples of polluted water; theyare similarly difficult for assignment of exact genericnames, although there is little doubt of their havingbeen sighted. Phylum Proteobacteria: members ofthe enteric genera Escherichia and Spirillum? Phy-lum Selenobacteria: Selenomonas (Fig. 4 B, b,showing path of movement through the medium).Phylum Endobacteria: species of various genera(including Bacillus and Streptococcus?) may havebeen seen, even figured, but difficult to recognizewith taxonomic precision today from the suppliedinformation (Fig. 4 B, a, c, e). The anaerobic formshe tantalizingly and inadvertently discovered insealed vials of “soil-water” and/but never studiedfurther (see below) may likely have includedClostridium. Cyanobacteria (= the blue-green algaein much of the literature, still today): some probablyseen, including Spirulina or the very common fila-mentous Oscillatoria. It should be noted – and ad-mitted! – that seldom do microbiological textbookscredit Leeuwenhoek with “discovering” any truebacteria, free-living or symbiotic forms, that are rec-ognizable nomenclaturally (at the generic or specific

level) today. Perhaps their caution is commendable.The home “laboratory” of the Father of Microbiologywas obviously not equipped to isolate and cultivatestrains under aseptic conditions or to carry out thesophisticated staining or physiological/biochemi-cal/molecular tests required nowadays to determineexact taxonomic or phylogenetic relationships ofany minute microorganisms under study.

Most of the organisms reported by the skilled sin-gle-lens microscopist from Delft are representativesof all five of the eukaryotic kingdoms recognized byCavalier-Smith and the writer (see citations givenabove). Many such species, even at the level of pro-tists (essentially the only organisms treated below),are at least one or two orders of magnitude larger orlengthier than most of the common species or cellsof the prokaryotic bacteria mentioned above.

1. Kingdom PROTOZOA. Phylum Euglenozoa:Euglena and the colorless kinetoplastid Bodo, bothfree-living forms; plus Crithidia or Leptomonas (ofthe trypanosomatids), parasitic in tabanid horsefliesexamined. Phylum Dinozoa: likely some speciesseen, but unnameable from information provided us.Phylum Sporozoa (syn. Apicomplexa): Eimeria, inthe oocyst stage, in rabbit feces. Phylum Rhizo-poda (exclusive of foraminiferans, next entry,below): None! This is surprising, because diversefreshwater and soil amoebae sometimes abound infield collections. Perhaps most amoebae (that mighthave been in Leeuwenhoek’s samples) did not movefast enough to attract his attention? Or were notfree-floating in the fluid in his tiny vials? Or were toofragile to withstand his treatment? Nor did he seemto note any free or encysted stages (too small?) ofsymbiotic amoebae in the many samples of fecalmaterials he examined at various times. PhylumForaminifera (if accepted as a separate phylum):Elphidium, empty tests (see Fig. 4 A, i), found in1700 in the stomach of a shrimp. Leeuwenhoekseemed to be unaware – or had forgotten – Hooke’s(1665) earlier account of a very small foram (but afossil form and of a different genus) found in sand.But Hooke, in turn, did not cite Gesner’s (1565) finedescription of a similar although much larger fossilform (described as a snail, a microcephalopod) a fullcentury earlier.

Phylum Ciliophora: Specimens were seen thattoday are assignable to perhaps a dozen differentclasses or subclasses of this phylum, the largest inthe kingdom Protozoa (if we exclude fossil protists).Class Heterotrichea: Nyctotheroides (called Nyc-totherus by Dobell and others: but split off from thatgenus well after Dobell’s lifetime), from frog large in-testine (see Fig. 4 A, c). Class Spirotrichea, subclassHypotrichia: Euplotes; subclass Stichotrichia: Oxy-

Antony van Leeuwenhoek 185

tricha, Stylonychia, and Kerona, the last a very com-mon ectocommensal found on the cnidarian Hydra;subclass Oligotrichia: perhaps Halteria, a smallfreshwater ciliate known for its rapid erratic, “jumpy”movements through its medium. Class Litostom-atea: Dileptus and Enchelys. Class Phyllopharyn-gea: Chilodonella. Class Colpodea: surely Colpoda,so common as a soil or “terrestrial” ciliate, was seen– yet was never recognizably described. Class Pros-tomatea: Coleps (see Fig. 4 A, c). Class Oligohy-menophorea, subclass Peniculia: Paramecium,which Leeuwenhoek noted in conjugation, correctlyinterpreted as a sexual “copulation” not longitudinalfission as later workers (except O.F. Müller 1786)kept insisting on for another 200 years; subclassScuticociliatia: Cyclidium; subclass Hymenostoma-tia: Colpidium and very likely the ubiquitous Tetrahy-mena; subclass Peritrichia: Carchesium, probably C.polypinum (see Fig. 4 A, h); Cothurnia (see Fig. 4 A,g) and Vaginicola, in their loricae; Trichodina, a mo-biline peritrich that is another ectocommensal ofHydra; and Vorticella (see three individuals in Fig. 4A, f), whose attachment stalks were considered“tails.” Regarding solitary vorticellids, our patientobserver first, in 1676, described them as “wretchedcreatures” struggling in vain to disengage their bod-ies from debris in which their “tails” had become en-tangled; later, in 1713, he appreciated better thelives of these attached protozoa, even ascertainingthe function of their peristomial ciliature (“wheel-work,” in his words) in feeding.

Members of phyla of zooflagellates, both free-liv-ing and symbiotic forms, were often noted by ourFather of Protistology and Parasitology, but exactidentifications, even at the generic level, are difficulttoday. Some were probably colorless “phytoflagel-lates” that belong to the following kingdom (seebelow). What the Delft microscopist saw in fecal ma-terial from frogs, rabbits, and chickens – and in hisown diarrheric stools as well – was of great interestto Dobell, a recognized authority in parasitologicalprotozoology born 254 years after Leeuwenhoekand also an avid and perceptive observer of “weeanimalcules.” Dobell (1932) insisted that his greatpredecessor had certainly seen such tiny flagellatesas at least Chilomastix, Giardia, Hexamita, Tri-chomastix, and Trichomonas (of phyla Metamon-ada and Parabasala).

2. Kingdom CHROMISTA. This is essentially the“Stramenopila” of some workers. Phylum Chryso-phyta: Anthophysa vegetans (see Fig. 4 A, a),Spumella (formerly Monas), and Cercomonas, allcolorless chrysomonad flagellates with the first acolonial species with its stalks typically encrustedwith brown particles of ferric hydroxide (Leeuwen-

hoek’s accurate depiction is even better than that ofthe great O.F. Müller 1786 – its first rediscoverer –some 80 years later: contrast Fig. 3 of Corliss 1986with Fig. 4 A, a of the present paper). Other verysmall colorless flagellates, unnameable, may alsobelong here. Phylum Diatomeae: unnameable di-atoms. Phylum Opalinata: Cepedea, from frog largeintestine (see Fig. 4 A, d).

3. Kingdom PLANTAE. Only its algal groups areconsidered here. Phylum Charophyta (class Conju-gatophyceae): Spirogyra. Phylum Chlorophyta:Volvox (see Fig. 4 A, b), Chlamydomonas, Haemato-coccus, and Polytoma.

4. Kingdom FUNGI. Members of protist groupsthat are placeable here, all parasitic/symbiotic forms(chytrids, Microspora), weren’t described byLeeuwenhoek. But he did observe minute fungalspores and some hyphal forms having unicellularstages in their life cycles; for example, Phylum As-comycota (class Saccharomycetes): Saccharo-myces, some species of which are the common“brewers’ yeast.”

5. Kingdom ANIMALIA. Members of protist groupsthat are placeable here, for example, the all-parasiticMyxozoa, were not seen by Leeuwenhoek. Manyvery small, sometimes microscopic, invertebrate an-imals, however, were observed, including Hydra,various rotifers, worms, insects (larvae and adults),etc., multicellular organisms of phyla well beyondcoverage in the present paper.

Misconceptions of Leeuwenhoek and his Works

Some of the misconceptions or misunderstandingsof our modest microbiologist from Delft have alreadybeen alluded to on various preceding pages. Duringhis own lifetime his observations were, perhaps un-derstandably, often met with skepticism. Being thefirst person to reveal the theretofore hidden world ofthe microcosm – and the unlikely discoverer noteven a learned man with advanced degrees and/or aprofessorship in a great university (tsk, tsk!) – wasnot a particularly enviable position in which to ex-pect to find oneself’s being taken seriously or credi-bly. Fortunately for posterity, Leeuwenhoek was indue time accepted, through backing by the emi-nence of the Royal Society of London and by suchcontemporary recognized scientists as RobertHooke and, much later, such distinguished and au-thoritative protozoologists as Bütschli and Kent. Butas the Delftman philosophically wrote in one of hisletters in the autumn of his life, “It doesn’t strike meas odd that I meet with contradictions.” This was in

186 J. O. Corliss

response to the comment by an elderly acquain-tance in his town who had sadly but kindly prophe-sied, “My friend, you’ve got the truth but it won’t bereceived in your lifetime” (from translations in Dobell1932).

Leeuwenhoek was definitely a man ahead of histime. Perhaps saddest have been the widespreadmisunderstandings still present some 200 yearsafter his death – and even occasionally still today,despite the interest rekindled in recent decades. Do-bell (1932) often rather scathingly brings up scoresof mistakes and inaccuracies, even ones quite minorin nature, and he lists >25 variants in spellings of theman’s names (for which “careless” Dutch, English,French, and German writers are blamed)!

One amusing example of a “postdobellian” slip-up can be found in the deservedly popular book (itstitle inspired by a well-known ditty of JonathanSwift’s, who, by the way, lived in the time ofLeeuwenhoek) by the distinguished American proto-zoologist-parasitologist Robert Hegner (1938), whodepicted our good Father of Protistology peering in-tently through an elaborate compound microscopeset-up used by Robert Hooke and seeing amoebae,parasitic trypanosomes, and other protists that werefavorites of Hegner’s. But actually neither these or-ganisms nor that particular compound ‘scope wereever seen by the man from Holland! Somewhat simi-larly – and Dobell would turn over in his grave if heknew of this one – the Dover unabridged paperbackedition of Dobell (1932) has superimposed on itscover-portrait of Leeuwenhoek a parade of amoe-bae pseudopoding their way across the page: butour hero never saw (or at least, never described)such wee animalcules.

Leeuwenhoek’s Legacy and His Honors

I have briefly reviewed the life, works, and letters ofthe Discoverer of Protists on preceding pages. Wehave yet to consider a bit further the qualities of hischaracter and the overall breadth of his scientific in-terests and personal goals. The appropriate words“Leeuwenhoek legacy,” used in the titles of the in-sightful book by the super-sleuth Brian Ford (1991)and of the recent article by the ecologically orientedteam of Finlay and Esteban (2001), pay deservedtribute to the “natural philosophy of the kindLeeuwenhoek practiced [which] was rooted in a de-sire to understand, to clarify, and to communicate”(Ford, 1991). No flowery language, no obscurantism,no exaggerated sense of scientific superiority, whichqualities, in Ford’s opinion, “underpin much [of]modern science.” [Ouch!]

Honest and unassuming himself, Leeuwenhoekabhorred deceit, and if he has been remembered as“a cranky old man” it was because he did not suffercontemporary fools or rogues gladly. He was not aperson intent on hypothesizing. Instead, he was –much like our diligent Philadelphian Joseph Leidy ofthe 19th century, in this as well as other respects(Corliss 2001) – content with finding facts and lettingothers make wild speculations or draw lofty conclu-sions.

The above point is well illustrated in the Delft-man’s long overlooked, even if minor, contribution tothe much later eventual overthrow of the abiogene-sis doctrine (= spontaneous generation), that lifecould arise from inanimate materials. Having heardof the treatise by Francesco Redi (published in Ital-ian in 1668), he decided, in 1680, to carry out sometrials himself. Working patiently, he discovered thatno (metazoan) life arose in periodically examinedtubes filled from various muddy or polluted aquaticsources. But if such tubes in which “seeds” werepresent were sealed, then the “seeds” themselvescould multiply into teeming populations of tiny or-ganisms. He thus, unwittingly, discovered anaerobicbacteria, but, alas, he never followed up on suchwork. The reader will recall that Spallanzani’s cele-brated experiments on spontaneous generation didnot take place until nearly a full century later, and itwas not until still another 100 years had passed be-fore Pasteur and Tyndall convincingly put the finalnails to the coffin of abiogenesis (although with thepassage of yet another 150 more years, we do findtoday a few uneducated folk clinging to the attrac-tive ancient myth of instant life spontaneously reoc-curring or arising or being generated from non-livingthings). In fairness to Leeuwenhoek’s enterprisingcontemporary Louis Joblot (born 1645, died 1723) inParis, I should mention that the Frenchman, workingindependently a bit on abiogenesis himself, was thefirst to boil some infusions and then keep them inclosed containers: neither microorganisms nor otherliving material were ever found on his later (re)exam-ination of those infusions. This little experiment (de-scribed in Joblot 1718), like the earlier one by ourDutchman, has been widely overlooked by histori-ans of science.

Remember that our first inquisitive microbiologistwas not in the business, as it were, of confirmingearlier observations of predecessors: in any case,almost always, there were no predecessors! To thecategory of originality, beyond his morphologicaldescriptions of protists, we must also assign hisworks on feeding by protozoa, the coiling and un-coiling of stalks of attached ciliates, conjugation inprotozoa as a sexual phenomenon, reproduction in

Antony van Leeuwenhoek 187

Volvox, asexual fission in a number of protistanforms, budding in Hydra, discovery of parthenogen-esis in aphids, avoidance reactions of unicellular or-ganisms confronted with certain chemicals, ecologi-cal preferences of microorganisms, capillary circula-tion of blood cells, comparative morphology of in-vertebrate spermatozoa, structural histology ofplant and animal tissues, etc.

In protistology he was interested in and con-tributed to knowledge of his organisms’ biodiversity,several full centuries before that term became afashionable “household buzz word,” following E.O.Wilson’s (1992, and see earlier papers cited therein)relatively recent introduction of it into our modernecological literature at all levels in plant/animal sys-tematics.

Another important way in which Leeuwenhoekmade original contributions to the world of the invis-ible: he was the first conscientious measurer or“metrologist” (Dobell’s word) of his observed verytiny objects. Perhaps he got into the spirit of such atask with microbes from his experiences as thetown surveyor (he accurately figured out the heightof a local church steeple) or even more so as adrapery merchant, which involved much carefulmeasuring of goods for customers. We have to re-member that meters (and thus micrometers) hadnot yet been invented; the lowest unit of measure-ment in those times was the inch (with his “inch”0.75 mm longer than ours of today, according toDobell’s careful calculations). The Delftman dividedhis homemade inches-ruler into tenths. The nextproblem was to select tiny measurable-by-the-naked-eye objects that had quite a uniform lengthor diameter: his most popular choices were sandgrains (fine and coarse), millet seeds, vinegar eels (anematode), and the eye of a louse (the one com-monly found, still today, on the human head).Armed with such measurements, expressed in pre-cise fractions of an inch, he was thus enabled tostate that a given protist or cell measured a stilltinier fraction of that fraction. One finds that suchfinal figures are often very close approximations totoday’s known average lengths or diameters (in mi-crometers) of the protists in question. Two exam-ples will suffice in illustration of this point. A com-mon species of the small colorless chrysophytegenus Spumella (called Monas by Dobell and oth-ers) comes out with a diameter of about 12–15 µm;and a stichotrichian spirotrich ciliate of the genusStylonychia, with a length of about 140 µm. Re-markably accurate measurements!

In preceding pages, I have mentioned many of thehonors mostly very belatedly bestowed on Antonyvan Leeuwenhoek – for example, his “Father of” ti-

tles. During his busy lifetime of so long ago, hisprime recognition as an early microscopist of trulyunbelievable ability came with his appointment, atthe age of 47 (in 1680), as a Fellow of the esteemedRoyal Society of London, for which he was alwaysgrateful. Reproductions of his “simple hand lens”from time to time have reminded us of the marvels ofhis inventiveness, and we need to thank Brian Ford(1985, 1991) for his brilliant detective work in gather-ing data on – and even demonstrating – its effective-ness in revealing the hidden world of invisible sights.

In his 84th year, 1716, the devoted amateur scien-tist received a silver medal from the University ofLouvain, now in Belgium, in recognition of “his neveryet properly appreciated and celebrated discoveriesin Natural Philosophy.” Quite emotionally, the agedbut still active recipient replied (in the introductorypart of a lengthy thank-you letter: see Dobell’s 1932translation), “When I think on the flatteries ex-pressed in your letter I don’t only blush, but my eyesfilled with tears too, especially because my workwas not pursued in order to gain the praise I nowenjoy, but chiefly from a craving after knowledge,which I notice resides in me more than in most men.And there-withal, whenever I found out anything re-markable, I have thought it my duty to put down mydiscovery on paper, so that all ingenious peoplemight be informed thereof.”

There are other continuing reminders of the Fa-ther of Microbiology sensu lato in addition to inclu-sion of his name and portrait in biological textbooksand histories of science. A microbiological journal,Antonie van Leeuwenhoek, has been regularly pub-lished in The Netherlands. And a coveted Leeuwen-hoek Medal has been awarded every decade or soduring the past 125 years by the Royal Academy ofSciences of Amsterdam to distinguished microbiol-ogists around the world. The list is too long to citehere in full. The first recipient was, fittingly, C. G.Ehrenberg (see Schlegel and Hausmann 1996); andabout 65 years ago – again highly appropriately –the awardee was C. Dobell, the man who sopoignantly brought Leeuwenhoek back to life for allprotistologists today.

Thus lived, died, and finally immortalized… that17th century indefatigable Dutchman, a gifted andmost versatile single-lens microscopist with suchtremendous patience and dexterity and such incred-ible eyesight. Above all, he was a person with an in-satiable curiosity about the natural wonders of thefascinating microcosm surrounding us. In conclu-sion of this brief tribute to Leeuwenhoek, allow me(inspired by a term used by Woodruff 1938) to pro-pose one more accolade for him, viz., First Philoso-pher in Little Things.

188 J. O. Corliss

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