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ANTONY VAN LEEUWENHOEK'

ON THE THREE-HUNDREDTH ANNIVERSARY OF IlIS BIRTH

EDWIN BROUN FRED

University of Wisconsin, Madison

This year the scientific world everywhere is celebrating theanniversary of the birth of Antony van Leeuwenhoek. Justthree hundred years ago in the fair and prosperous city of Delft,Holland, Antony, son of Philips Antonysz van Leeuwenhoek, wasborn. Like many another celebrity, young Leeuwenhoek sprangfrom a sturdy and honorable family of simple tastes and limitedmeans. His plain way of living and love for nature may pos-sibly be attributed in a measure to his parentage, but his re-markable power of seeing the hitherto unseen in the world ofmicroscopic life cannot in any way be explained by his heredity.The Leeuwenhoek family has been traced back for a few genera-tions but no record of remarkable skill has been discovered.

It takes many generations to evaluate a great man, and ofteinhis followers receive the praise while the original genius is almostforgotten. In a way this is true of Leeuwenhoek. His brilliantfollowers, of almost two centuries later, Pasteur, Koch, Lister,and others are well known for their important discoveries in themicroscopic world first opened up by Leeuwenhoek.

Leeuwenhoek, the Polymath of Microbiology, exhibited mar-velous technique as well as keen power of observation in hisstudies of protozoa, bacteria and other forms of life. No one,either before or since Leeuwenhoek, working with such simplemicroscopes has so clearly and accurately described the formswhich we call the microorganisms. Leeuwenhoek saw so manyof these small forms and told so accurately of their mode of life

1 Presidential Address delivered before the Society of American Bacteriolo,istsat its Thirty-fourth Annual Meeting, Ann Arbor, Michigan, December 29, 1932.

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JOURNAL OF BACTERIOLOGY, VOL. XXV, NO. 1

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that we are amazed at his keen perception and almost unbelievablepower of unlocking the secrets of nature. One may well imaginehis excitement when he first beheld these microscopic forms. Itis true that he did not try to connect the relation of these animal-cules to the applied field; his rBle was that of "creator of tinythings;" and in this role he stands out today as the pioneer ofmicrobiology.The world owes much to Leeuwenhoek. Although many years

passed before anyone truly appreciated the importance of hisdiscoveries, it is clearly established that he laid the foundationfor the great subject of bacteriology. From the small beginningof 1676, when Leeuwenhoek first saw bacteria in rain water, anentirely new science has developed, a science of microbiology whichto-day is throwing out ramifications into numerous fields. Fatehas linked the thirty-fourth annual meeting of the Society ofAmerican Bacteriologists with the tercentenary of the birth ofthe Father of Bacteriology. Of these three centuries, a scantseventy years are all that have been devoted to the serious appli-cation of a scientific study of the bacteria.

In the preparation of this paper, the autlhor has drawn freelyfrom a remarkable book entitled, "Antony van Leeuwenhoek andHis 'Little Animals'," by Clifford Dobell. This English proto-zoologist possesses an unrivalled knowledge of the Leeuwenhoekmanuscripts and it is indeed fortunate that he has seen fit topublish the results of his exhaustive studies.

EARLY LIFE

Leeuwenhoek was born on October 24, 1632. His father aswell as his grandfather were craftsmen, simple basket-makers,and his mother the daughter of a Delft brewer. In his familythere were seven children, five girls and two boys. Only one ofthe girls, Catharina by name, is mentioned in connection with herbrother's scientific achievements. About the personal life ofyoung Leeuwenhoek we know but little; his father died when hewas only five years old, and his early years were spent at Warmond,a small town near Leyden. Later we find him at Benthuizen,living with his uncle. At the age of sixteen he entered the shop

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of a linen-draper in Amsterdam, whiere he no doubt becameacquainted with the crude magnifying lens used to examinethreads in cloth. Perhaps this simple microscope showed thebeautiful patterns of threads interlaced in the warp and woof ofthe cloth. This introduction to the microscopic world no doubtstimulated his imagination to go beyond the thread counter andto delve into mysteries as yet unheard of. At any rate, Leeuwen-hoek began to grind better lenses and by means of these lenses tosee more of the invisible world. Nothing is known of the nextfive or six years except that when he was about twenty-two,Leeuwenhoek returned to Delft and married Barbara de Mey.This was, so far as we know, a happy marriage, of which therewere five children, though only one, named Maria, survived him.About this time (1654), Leeuwenhoek bought a house and set upa clothing store in Delft. Six years later he received an appoint-ment as Chamberlain to the Sheriffs of Delft, a position which heheld for thirty-nine years and thereafter until his death receivedthe salary of this office. At first this position paid only 314florins each year, but later 400 florins. Fortunately, as was thecustom of that time the position was largely a sinecure and thusLeeuwenhoek was free to devote his life to the grinding of lensesand the focusing of his microscopes on almost every object whichcame witlhin his reach.That Leeuwenhoek was interested in mathematics and had

more than a speaking acquaintance with this subject is indicatedin his letters and is recorded in the Dutch Archives. In the year1669 Leeuwenhoek was examined by the mathematician, GenesiusBaen, and found competent to perform the duties of surveyor(Schierbeek, 1930). The fact that he was qualified as a surveyorno doubt explains the mathematical calculations found in certainof his letters. Just ten years later in 1679, Leeuwenhoek waselected wine-gauger for the city of Delft. These positions, sur-veyor and wine-gauger, required the attention of a well-trainedman and thus is seems hardly conceivable that he should beclassed as an ordinary beadle as he has been by some of hisbiographers. Leeuwenhoek was in a very real sense a man ofaffairs in his native city of Delft.

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HOLLAND IN THE SEVENTEENTH CENTURY

To gain some idea of our man and his work, we must read hisoriginal letters and those of his associates and consider, too,conditions in Holland during his life. The seventeenth centuryincluded the reign of FXrederick Henry (1625-1647), the GoldenAge of Holland. At this time, the affairs of Holland flourished,an eastern empire was acquired, and conquests were made inSouth America. It was a time when religion and politics werenot always uppermost in the mind of man, certainly not in Leeu-wenhoek's mind, a period when learning, literature, and paintingreached a dazzling brilliancy.The Seventeenth Century is well known as the period of illus-

trious scientists not only in Holland but also in other countries.The roster of scientists for this era carries the names of such menas Robert Boyle, Christopher AWren, Robert Hooke, NehemiahGrew, Gottfried Leibniz, Mviarcello MIalpighi, Francesco Redi,Jan Swammerdam, John Ray, William Harvey, ChristiaanHuygens, Isaac Newton, and others of lesser fame. Fromthis grand array of geniuses and super-geniuses, it seems thatLeeuwenhoek received but little, either by direct contact or byreading. He could not read Latin or any other language buthis mother tongue. He never attended a scientific meeting, andnever had any contact with a university. In a v-ery real senseof the word he was a lone worker, though in later life he met andexchanged papers with certain of his contemporaries. Some ideaof how he disliked advice from visitors is indicated in his letterto Oldenburg (1675).

Your Excellency recormmends ine to makie use of the services of otherpeople, who are in a position to form a proper judgment of such things.Sir, I must say that there be few persons in this Town from whom Ican get any help; and among those who can come to visit me fromabroad, I have just lately had one who was much rather inclined todeck himself out with my feathers, than to offer me a helping hand.

THE LEEUWENHOEK MICROSCOPES

The first magnifying glasses were produced by spectacle-makers.At first only a low magnification (about 10 fold) was employed.

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Although the compound microscope was described by ZachariasJanssen of Middelburg as early as 1590 to 1610, it was never usedby Leeuwenhoek. The simple, small, biconvex lens preparedfrom glass, or in a few cases from rock-crystal, mounted betweentwo plates usually of brass, silver, or in rare cases, of gold, andfastened by little rivets was the form of microscope commonlyemployed by Leeuwenhoek. From the various descriptions ofhis instruments it seems that he also made use of two or threelenses mounted in the same frame. It should be borne in mindthat Leeuwenhoek was a glass-blower of no mean ability. Coupledwith this skill in working glass he showed rare ingenuity and ex-pert craftsmanship in the grinding and mounting of his simplelenses, a skill which he zealously kept to himself; and in spite ofthe requests of his learned friends, he refused to disclose thesecret of his success. He was a self-taught man and naturallyjealous of his own inventions; hence it is understandable that hewould not give away the details of his method of making micro-scopes and of their use.To adjust the lens to the object was so long and tedious a task

that it is not surprising that Leeuwenhoek used an individuallens for each object and fixed this object in place by gluing it onthe point of a pin attached to the microscope. Leeuwenhoekmade many microscopes; the exact number is not known, althoughhe left 247 not only with lenses but usually with objects in place.He also left 172 plates with one lens in each, or a total of 419lenses.A brief description of the microscopes by Leeuwenhoek, him-

self, is found in the extract of his letter of the 2nd of August, 1701,published by Weld (1848).

Honble Gentlemen:My last to your honours was dated the 21st June, wherein I humbly

offer'd you my observations about spiders, since when I have receivedthe book which treats of fishes, and the whole set of Philosophical Transac-tions for the year 1700, for which noble presents I return you my mosthearty thanks.

I have a small black cabinet, lacker'd and gilded, which has five littledrawers in it, wherein are contained thirteen long and square tin boxes,

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covered with black leather. In each of these boxes are two ground micro-scopes, in all six and twenty; which I did grin(l my-self, and set in silver;and most of the silver was what I had extracted from minerals, andseparated from the gold that was mixed with it; and an account of eachglass goes along with themn.2

This cabinet, with the aforesaid microscopes (which I shall make useof as long as I live), I have directed my only daughter to send to yourhonors, as soon as I aimi dead, as a mark of my gratitude, and acknowledge-ment of the great honor which I have received fromn the Royal Society.This account in Lecuwenhoek's own words gives some idea of themethods used in making these early microscopes.A description and in some cases diagrams of Leeuwenhoek's

lenses will be found in the papers of Folkes (1724), Baker (1753),Harting (1859), D)isney (1928), and Dobell (1932). Accordingto these accounts, l1jeeuwenhoek's instruments are not true micro-scopes at all, ini the sense in which we think of inicroscopes, butrather simple magnifying glasses generally consisting of a smallsingle biconvex lens. The object, and not the lens, was movedinto focus by means of screws.The magnification varied and at best did not exceed 200 to 300

diameters. How it was possible to see such small objects asbacteria with suclh a low magnification, and without the use ofdyes remains a matter of speculation. Perhaps the solution isto be found in the fact that LeeuN-enhoek possessed rare abilityin the grinding of his lenses, as well as in the preparation andilmounting of hiis o)bjects. To remove any doubt of the possibilityof his having, seen suclh small forms with a lens of low power,Chapman (1931) has imitated the conditions of the Leeuwenhoekexperiment. He mounted the front lens of a 1/12-inch objec-tive in muchi the same way as Leeuwenhoek and thus obtained amagnification of 125 diameters. Aftei a little practice with thistype of lens Chapman found that he could see yeast cells veryclearly and also bacteria. Dobell (1932) has advanced a quite

2 These inicroscopes wN-ere exhibited to Peter the Great, wN-hen he visited Delftin 1698. The Czar requested Leeuwenhoek to pay him a visit on his canal yachtoutside the town of Delft, and to bring some of his admirable microscopes,adding, that he wN-ould have gone to visit hiin at his residence, had it not been forthe wish he had to escape the notice of the multitude.

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different explanation to account for the remarkable clarity ofLeeuwenhoek's observations. He suggests that Leeuwenhoekmade use of some form of dark-ground illumination, for in a letterof 1675 Leeuwenhoek drew an analogy to the appearance of sandgrains on "black taffety silk." Although we do not have anyrecord of how Leeuwenhoek carried out his microscopic observa-tions it seems probable that his remarkable discoveries representsimply the reward of a keen eye coupled with unparalleled indus-try, rather than any revolutionary change in technique. Accord-ing to Hooke, Leeuwenhoek used a capillary pipette in the exami-nation of liquids.The size of objects which Leeuwenhoek examined was deter-

mined by comparison. For this purpose he used at various timesa grain of sand, the seed of millet or mustard, the eye of a louse,a vinegar eel, and still later hair or blood corpuscles. In this wayhe secured fairly accurate measurements of a great variety ofobjects.During his lifetime Leeuwenhoek refused to sell any of his

microscopes and it was not until many years after his death thata collection of his instruments was put up for sale. Harting tellsof the auction sale of these microscopes and of the fact that thegold microscopes of Leeuwenhoek were sold according to weight.Perhaps no other microscopes were ever sold on such a basis.Unfortunately, at present there are only 8 authentic specimens ofLeeuwenhoek's microscopes in existence (Dobell, 1932).

LEEUWENHOEK S DISCOVERIES IN BACTERIOLOGY

It was not until he was 41 years old that Leeuwenhoek beganto impart to the world the various things which were within therange of vision of his simple microscope. Fortunately, therelived in Delft at that time (1673) the famous Dr. Reinier de Graaf,a young physician of rare ability best known for his descriptionof the "Graafian follicle," who recognized the value of Leeuwen-hoek's work and persuaded him to send his reports to the scien-tific group in London. Thus through the influence of de Graafwho was corresponding with Oldenburg, the Secretary of theRoyal Society, the early letters of Leeuwenhoek were sent to this

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scientific body. During the same year, Constantijn Huygeinsalso sent to the Royal Society a letter describing the qualificationsof Leeuwenhoek. The value of these letters was soon recognizedand in 1680, Leeuwenhoek was elected a Fellow of the RoyalSociety, an honor which he prized highly. Leeuwenhoek's fond-ness for the smallest forms of life, the "little animals," as hecalled them, is recorded in many of his letters. This love of thesmall unicellular forms of nature kept up throughout his longlife of ninety-one years. His observations were submitted inthe form of letters, usually to the Royal Society of London, orto some of his friends. On his very death bed we find him callingfor his friend, Jan Hoogvliet, to translate two letters to send tothe Royal Society. No attempt will be made here to deal fullywith the variety of things which Leeuwenhoek described, butsimply to give certain examples of his discoveries relating to thebacteria, yeasts and moulds.The followiing description of the mouldly growvth on the surface

of meat is taken from Leeuwenhoek's first letter to the RoyalSociety, London, April 28, 1673. Unfortunately this letter is nota fair example of ILeeuwenhoek's work. The description is rathercrude.

A specimen of some observations made by a inicroscope, contrivedby M. Leeuwenhoeck in Holland, lately communicated by Dr. Regnerusde Graaf, written from Delpht, April 28, 1673.The mould upon skin, flesh, or other things, hath been by some repre-

sented to be shott out in the forin of the stalks of vegetables, so as thatsome of those stalks appeared with round knobs at the end, some withblossom-like leaves. But I do observe such mould to shoot up firstwith a straight transparent stalk, in which stalk is driven up a globoussubstance, which for the most part places itself at the top of the stalk,and is follow'd by another globul, driving out the first either sideways,or at the top, and that is succeeded by a third and more such ulobuls;all which make up at last one great knob on the stalk, an hundred timesthicker than the stalk itself. And this knob indeed consists of nothingelse than of many small roundish knobs, which being multiplied, thebig knob begins to burst asunder, and then represents a kind of blos-soms with leaves.

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Leeuwenhoek discovered yeasts in fermenting beer and wineas recorded in his letter of June 14, 1680: ". . . these seemto be quite round; others were irregular and seemed to consist oftwo, three or four of the aforesaid particles joined together."The discovery of bacteria is given in Leeuwenhoek's celebrated

letter of October 9, 1676, to the Royal Society. In this communi-cation, he mentions that one year earlier he found living creaturesin rain water which had been stored for a few days in a new tub.At this time he described bacteria and various kinds of animal-cules of which the majority were undoubtedly protozoa. He said:

The 2nd observation. Rain-water (After Dobell)

The 26th of May, it rained very hard. The rain abating somewhat,I took a clean glass and got rain-water that came off a slate roof, fetchedme in it, after the glass had first been swilled out two or three times withrain-water. I then examined it, and therein discovered some few verylittle animals; . ...

In the same report he attempted an estimate of the size of theselittle creatures, saying they (perhaps as Dobell suggests Monasvulgaris) were to a cheese-mite in the same proportion as a honeyBee to a Horse.

Apart from protozoa, he found exceedingly small animalcules,cc . . . .they well-nigh escaped the sight" in stored rain water,well and sea water. To satisfy his curiosity about the burningeffect of pepper, he prepared a pepper infusion. This he allowedto stand, and after about three weeks he found in this infusionfive sorts of animalcules, of which the fourth and fifth sorts werebacteria, probably bacilli. This account as given by Dobellfollows:

The fourth sort of little animals, which drifted among the three sortsaforesaid, were incredibly small; nay so small, in my sight, that I judgedthat even if 100 of these very wee animals lay stretched out one againstanother, they could not reach to the length of a grain of coarse sand;and if this be true, then ten hundred thousand of these living creaturescould scarce equal the bulk of a coarse sand-grain.

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In a letter of March 23, 1677, he observed that water whichhad been boiled would, when kept for 24 hours, show the presenceof living creatures.

In his famous letter of September 17, 1683, concerning scrapingsfrom teeth and again in 1693, he gave a description of the differentforms of bacteria. His own account follows:

Tho my Teeth are kept usually very clean, nevertheless when I viewthem in a Magnifying Glass, I find growing between them a little whitematter as thick as wetted flower: in this substance tho I could not per-ceive any motion, I judged there might probably be living Creatures.

I therefore took some of this flower and mixt it either with pure rainwater wherein were no Animals; or else with some of my Spittle (havingno Air bubbles to cause a motion in it) and then to my great surprizeperceived that the aforesaid matter contained very many small livingAnimals, which moved themselves very extravagantly. The biggestsort had the shape of A. (reference to a figure) their motion was strongand nimble, and they darted themselves thro the water or spittle, as aJack or Pike does thro the water. These were generally not many innumber. The 2d. sort had the shape of B. these spun about like a top,and took a course sometimes on one side, as is shown at G. and D. theywere more in number than the first. In the 3d sort I could not welldistinguish the Figure, for sometimes it seem'd to be an Oval, and othertimes a Circle. These were so small they seem'd no bigger than E. andtherewithal so swift, that I can compare them to nothing better than aswarm of Flies or Gnats, flying and turning among one another in asmall space.

Later in this same report he says:

I took in my mouth some very strong wine-Vinegar, and closing myTeeth, I gargled and rinsed them very well with the Vinegar, afterwardsI washed them very well with fair water, but there were an innumerablequantity of Animals yet remaining in the scurf upon the Teeth, yetmost in that between the teeth, and very few Animals of the first sort A.

I took a very little wine-Vinegar and mixt it with the water in whichthe scurf was dissolved, whereupon the Animals dyed presently. Fromhence I conclude, that the Vinegar with which I washt my Teeth, kill'donly those Animals which were on the outside of the scurf, but did notpass thro the whole substance of it.

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Returning to his letter of June 14, 1680, we find not only adescription of the yeasts, but also of the anaerobic bacteria. Leeu-wenhoek had apparently heard it said that life could not existin a closed vessel and with this in mind he sealed a glass tube con-taining an infusion of pepper. Five days later, he broke thisseal and found the infusion contained various kinds of bacteria.Another example from a letter of M. Antony Leeuwenhoek,

dated from Delft, November 4, 1681, is given below:

Containing an account of several new Discoveries made by him this lastSummer.

I have also several times this Summer walked into our Meadows, inorder to observe the fresh Excrements of Cows, Horses, and other Ani-mals, but I could not yet discover any Animals in them: but I foundmultitudes of these small Globules swimming in a clear liquor, some ofwhich were not above one sixth part, others not above a thirty sixthpart of a blood Globule.

In urine of a mare he found,

a great variety of differing Globules, some as big as thoseof blood, and composed of six others: these first were like a veryclose bunch of Grapes, whence though they were not perfectly round,yet I call them Globules; amongst these I found some 1/6 of a BloodGlobule,

In his homely way, Leeuwenhoek says the "Animals in thescurf of a man's Teeth are so many that I believe they exceed thenumber of Men in a kingdom."

In addition to his study of the occurrence of these microor-ganisms it must be remembered that Leeuwenhoek also began thefirst work on the physiology of the bacteria. The effect of heat,hot coffee, of acid, of tobacco on the bacteria were included inhis experiments. Indeed, we might well say that Leeuwenhoeklaid the foundation for our well-known process of pasteurization.His early experiments in which he observed the harmful effect ofheat on bacteria support this conclusion. In addition Leeuwen-hoek also was the first to prepare a nutrient medium for bacteria,e.g., his infusions of pepper and other condiments. These and

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many other important facts relating to the physiology of the micro-organisms are to be found in the letters of this savant from Delft.

During his long and productive life, Leeuwenhoek sent no lessthan 200 letters to the Royal Society of London. Usually eaclletter tells of some new discovery, often in an entirely new field.As reported by Dobell the signatures of these letters are not uni-form: the first 39 were signed Antony Lecuwenhoeck and the laterreports after 1683 Antonj van Leeiuenhoek, the c from -hoeckdropped and the van added. All told, the various Englishversions of his letters published in the Philosophical Transactionsof the Royal Society show 19 different ways of spelling the surname.

His work, as it appears in the letters, stands out in the form ofisolated pieces of information rather than as organized knowledgeconcerning the nature of microscopic forms of life. The methodof publishing his letters in chronological order has accentuatedthis point. If these same letters are rearranged according tosubject matter, seemingly unrelated facts fall into a natural se-quence, and thus the underlying thought becomes apparent.

It is indeed fortunate that these original manuscripts in therecords of the Royal Society are well perserved. The ink hasfaded but little, the drawings are in certain cases excellent, thelhand writing is clear and fairly easy to read.

THE TWVENTY-SEVEN, LOST LETTERS

The Nederlandsch Tijdschrift vooIr Genieeskunde (Dutchi Joutrnalof Medicine) at Amsterdam (1931) has recently published the 14(not 27) letters of Leeuwenhoek which have not appeared beforein print. During the years that these 14 letters have remainedundiscovered in the archives of the Royal Society, there havegrown up many wild speculations. It now appears that there isnothing mysterious about these letters. The story as taken fromDobell is somewhat as follows: The Dutch and Latin editions ofLeeuwenhoek's works begin with the 28th letter. Of the 27 ithas been found that 13 have already been published in the wholeor in part and hence only 14 remain. These 14 letters are nowreproduced in their original language and are also translated intoEnglish. In the main these 14 letters do not add anything very

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startling. They represent the early work of Leeuwenhoekwhichwas revised and in the main presented again in his later reports.

SPONTANEOUS GENERATION

Leeuwenhoek was not content simply to note the presence ofthe "animalcules" but also tried to find out the source of theseforms of life. That they could not originate by spontaneousgeneration was clear in Leeuwenhoek's mind although such aconception was quite at variance with that of many of his con-temporaries, notably Jean van Helmont. Leeuwenhoek vigor-ously opposed the idea of spontaneous generation as noted inhis letters of October 9, 1676 and of May 13, 1680. To explainthe presence of the "animalcules" in pure rain water or in rainwater sealed in glass tubes he suggested that the seeds of theseminute organisms can exist in water which is drawn up into theclouds and later scattered in the form of rain. Unfortunately,he did not attempt to extend his observations of this very im-portant phenomenon, and thus almost 100 to 150 years elapsedbefore the idea of spontaneous generation was shown to be false.

NATURE OF LEEUWENHOEK'S WORK

The question we may well ask is how it was possible for one manto cover such a wide range of subjects. The answer is not easy.His ability to "estimate what was worth doing and what couldbe done" shows that Leeuwenhoek possessed a creative mind ofthe highest order. In the words of Chapman, 1931, Leeuwenhoekpossessed an "infinite capacity for taking pains which may bedefined as genius." He was fortunate in many ways: no time-consuming administrative work fell to his lot; no popular subjectof the day demanded his attention; he loved his microscopes, andthat love grew stronger as the years went by. Unmindful of theworld of big things, he was satisfied to keep ever prying intonature's secrets. He did not attempt to seek the universal elixiror to accomplish the transmutation of the metals, which werethe popular fads of his day.The homely and simple language used in his letters to the Royal

Society give us some idea of his unique power of observation. A

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paragraph from Hoole's, "The Select Works of Antonv vanLeeuwenhoek," 1816, will bring out these points.

I have often heard, that many persons dispute the truth of what Iadvance in my writings, saying that my narrations concerning animal-cules, or minute living creatures, are merely of my own inventioni.And, it seems, sonme persons in France have even ventured to assert,that those are not in truth living creatures, which I describe as discover-able to our sight, and alledge, that after water has been boiled, thoseparticles in it which I pronounce to be animalcules will be still observedlto move. The contrary of this, however, I have demonstrated to irianyeminent men, and I will be bold to say, that those gentlemen who holdthis language, have not attained to a degree of proficiency to observesuch objects truly. For my own part, I will not scruple to assert, thatI can clearly place before my eye the smallest species of those animal-cules concerning which I now write, and can as plainly see them enduedwith life, as with the naked eye we behold small flies, or gnats sportingin the open air, though these animalcules are more than a million ofdegrees less than a large grain of sand. For I not only behold their mo-tions in all directions, but I also see them turn about, remain still, andsometimes expire; and the larger kinds of them I as plainly perceiverunning along, as we do mice with the naked eye.

It has been said that scientific curiosity is "the divine instinct."If this be true, then surely Leeuwenhoek should receive the mantleof Elijah; for probably no one has ever had to a greater degreethat insatiable desire to inquire into the processes of the micro-scopic world.Leeuwenhoek was not without honor during his lifetime.

Scientists and nobility came to Delft to see this man of the micro-scopic world. Peter the Great of Russia, Queen MIary of Williamand Mary, Frederick I of Prussia, and others stopped in Delft tocall on Leeuwenhoek. Like the public of to-day, these rulers ofthe seventeenth century were impressed with the scientific de-velopments of their day. They too were curious to know whatlies in the world beyond the unaided eye of man.

MICROBIOLOGY BEFORE AND AFTER LEEUWENHOEK

The influence of Leeuwenhoek's findings upon the discoveriesof subsequent workers is not easy to estimate. All that is modern

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ANTONY VAN LEEUWENHOEK

in microbiology has been influenced either directly or indirectlyby his observations. During his long life time, he examined theminute animals, and the bacteria in water from rain, from meltingsnow, from wells, from canals and from rivers. Indeed, whereverplant or animal substances were decomposing, he found variouskinds of bacteria. The originality and amazing insight of theman is well exemplified by the breadth of his discoveries.Of the immense number of objects examined, we shall speak

only of his studies of the bacteria. Leeuwenhoek was not contentmerely to see the bacteria in water which had been kept for daysand also in scrapings from the teeth, but he also studied the formsin pepper infusion which was kept in a closed bottle. Here hefound anaerobic forms, probably the butyric acid bacteria. Theseresults naturally led him to examine the sap of plants, soil, urineand manure where he also found great numbers of microorgan-isms. He observed the chief morphological types, the cocci,bacilli and spirilla.From the life of this wonderful man of Holland there are many

lessons we all may learn. There are to-day, no doubt, manyworks of nature still waiting for the keen eye and patient mindof a second Leeuwenhoek. Unaided by association with the bestminds of his day he rose to stand in first place among the world'sgreat microbiologists. His observations are examples of a self-trained scientist. He was endowed with rare mechanical skill,with insatiable curiosity, unparalleled patience and exquisitepower of observation. With these qualifications, it seems certainthat if he had worked at a later date he would have been quickto recognize the difference in behavior of microorganisms, as wellas the important role they play in health and disease. As shownin a letter to Robert Boyle, 1677, he was a modest, unselfish man.The numerous honors conferred upon him, the visits of royaltyfrom various nations, did not influence his simple tastes. Howbeautifully his own words written towards the close of his careerexpress his feelings towards science and scientists (Dobell trans-lation).As I aim at nothing but Truth, and, so far as in me lieth, to point out

Mistakes that may have crept into certain Matters; I hope that in so

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doing those I chance to censure will not take it ill: and if they wouldexpose any Errors in my own Discoveries, I'd esteem it a Service; allthe more, because 'twould thereby give me encouragement towards theattaining of a nicer Accuracy.

There is another characteristic of Leeuwenhoek we must mention:he possessed the art of turning his observations into a tale freefrom the formal stilted language of the usual scientific memoir.The original letters must be read to appreciate his simple, sincerestyle and conversational way of expressing his discoveries. Hisbiographer, Dobell, has very aptly described this style of Leeuwen-hoeck as typified by his letters. "Generally they are long andrambling and his thoughts come tumbling out with disconcertinginconsequence." "He never confuses his facts with his specula-tions."

It seems appropriate in closing to give the inscription from thesilver medal presented to Leeuwenhoek by the University ofLouvain which so beautifully describes the work of the FirstMicrobiologist:

In tenui labor, at tenuis non gloria

His work was with small things but his glory is not small

REFERENCES(1) ALFONSuS, H.: Antoni van Leeuwenhoek (zu seinem 300. Geburtstag).

Osterr. Milchw. Ztg., 1932, 39, 218-219.(2) BAKER, H.: Employment for the Microscope. In Two Parts. London,

1753, 442 pp.(3) BECKING, L. B.: Antoni van Leeuwenhoek, Immortal Dilettant (1632-1723).

Sci. Mo., New York, 1924, 18, 547-554.(4) BEIJERINCK, M. W.: De infusies en de ontdekking der bacterien. Jaarb.

Koninkl. Akad. Wetensch., Amsterdam, 1913, pp. 1-28; also Verzamel.Geschriften, Delft, 1922, 5, 119-140.

(5) BULLOCH, W.: History of Bacteriology. A System of Bacteriology in Rela-tion to Medicine, London, 1930, 1, 17-22.

(6) CHAPMAN, A. CHASTON: The Yeast Cell: What did Leeuwenhoeck see?Jour. Inst. Brewing, 1931, 37, 433-436.

(7) COLE, F. J.: Early Theories of Sexual Generation. Oxford, 1930, 230 pp.(8) DISNEY, A. N., WITH HILL, C. F., AND WATSON BAKER, W. E.: Origin and

Development of The Microscope (etc.). Roy. Microscopical Soc.,London, 1928, 303 pp.

(9) DOBELL, C.: The discovery of the coccidia. Parasitology, 1922, 14, 342-348.

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(10) DOBELL, C.: Antony van Leeuwenhoek (1632-1723). Parasitology, 1923, 16,308-319.

(11) DOBELL, C.: Antony van Leeuwenhoek and his 1"Little Animals." Hlar-court, Brace and Company, New York City, or N. V. Swets & Zeit-linger, Amsterdam, 1932, 435 pp.

(12) FOLKES, M.: Some account of Mr. Leeuwenhoek's curious Microscopes,lately presented to the Royal Society. Roy. Soc. (London) Phil.Trans., 1724, 32, No. 380, 446-453.

(13) HAAXMAN, P. J.: Het leven van een groot natuuronderzoeker. Antony vanLeeuwenhoek. Nederland. Tijdschr. v. Geneesk. 1871, 7, 1-86.

(14) HARTING, P.: Das Mikroskop. Theorie, Gebrauch, Geschichte. FriedrichVieweg und Sohn, Braunschweig, 1859, 950 pp.

(15) VAN HEST, J. J.: Antoni van Leeuwenhoek (1632-1723). Wochenschriftfur Brauerei, 1905, 22, 45-48, 61-64, 77-79, 95-98, 111-112.

(16) HOOLE, SAMUEL: The Select Works of Antony van Leeuwenhoek, containinghis Microscopical Discoveries in many of the works of nature. Whit-tingham and Arliss, London, 1816, 1, 314 pp.; 2, 344 pp.

(17) LEEUWENHOEK, ANTONY VAN: A specimen of some Observations made by aMicroscope, contrived by M. Leeuwenhoeck in Holland, lately com-municated by Dr. Regnerus de Graaf. Roy. Soc. (London) Phil.Trans., 1673, 8, No. 94, 6037.

(18) LEEUWENHOEK, ANTONY VAN: Observations, communicated to the Publisherby Mr. Antony van Leewenhoeck, in a Dutch Letter of the 9th of Octob.1676, here English'd: Concerning little Animals by him observed inRain- Well- Sea- and Snow-water; as also in water wherein pepper hadlain infused. Roy. Soc. (London) Phil. Trans., 1677, 12, No. 133, 821-831.

(19) LEEUWENHOEK, ANTONY VAN: Monsieur Leeuwenhoecks Letter to the Pub-lisher, wherein some account is given of the manner of his observing sogreat a number of little Animals in divers sorts of water, as was deliver'din the next foregoing Tract: English'd out of Dutch. Roy. Soc. (Lon-don) Phil. Trans., 1677, 12, No. 134, 844-846.

(20) LEEUWENHOEK, ANTONY VAN: Some new discoveries made with and concern-ing Microscopes. A letter of the ingenious and inquisitive Mr. Leeuwen-hoeck of Delft, sent to the Secretary of the Royal Society, October 5,1677. Hooke's Phil. Collections, London, 1678, p. 81-83.

(21) LEEUWENHOEK, ANTONY VAN: A letter of M. Anthony Leuwenhook, datedfrom Delft, November 4th, 1681. Containing an account of severalnew Discoveries made by him this last Summer. Hooke's Phil. Col-lections, London, 1681, No. 4, p. 93-98.

(22) LEEUWENHOEK, ANTONY VAN: An abstract of a Letter from Mr. AnthonyLeevvenhoeck at Delft, dated September 17, 1683, containing someMicroscopical Observations, about Animals in the scurf of the Teeth,the substance call'd Worms in the Nose, the Cuticula consisting ofScales. Roy. Soc. (London) Phil. Trans., 1684, 14, No. 159, 568-574.

(23) LEEUWENHOEK, ANTONY VAN: IV. The abstract of two Letters sent sometime since by Mr. Anth. Van Leeuwenhoeek, to Dr. Gale and Dr.Hooke. Roy. Soc. (London) Phil. Trans., 1693, 17, No. 196, 593-594.

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(24) LEEUWENHOEK, ANTONY VAN: IV. An Extract of a Letter from Mr. Anth.Van Leuwenhoek, Concerning Animalcules found on the Teeth; of theScaleyness of the Skin, &c. Roy. Soc. (London) Phil. Trans., 1693,(1693-94), 17, No. 197, 646-649.

(25) LEEUWENHOEK, ANTONY VAN Arcana Naturae Detecta. Editio Novissima,Auctior et Correctior. Joh: Arnold: Langerak, Lugduni, 1722, 515 pp.Continuatio epistolarum. Johannem du Vivie, Theodorum Haak, etJoh: Arn. Langerack, Lugduni, 1715, 124 pp.

(26) MIIALL, L. C.: The Early Naturalists, Their Lives and Works (1530-1789).MacMillan and Co., London, 1912, 396 pp.

(27) NORDENSKI6LD, E.: The History of Biology. Alf. Knopf., New York, 1928,629 pp.

(28) NUTTALL, G. H. F.: Notes bearing on Leeuwenhoek, etc. Parasitology,1921, 13, 398-407.

(29) Opuscula Selecta Neerlandicorum de Arte Medica, IX. Fasciculus Nonusquem Curatores Miscellaneorum quae vocantur. Nederland. Tijdschr.Geneesk. Collegerunt et Ediderunt. Amsterlodami, Sumptibus Socie-tatis, 1930 (1931), 145 pp., 15 plates.

(30) PLIMMER, H. G.: The President's address: "Bedellus immortalis." Jour.Roy. Micros. Soc., 1913, 121-135.

(31) SCHIERBEEK, A.: Een paar nieuwe bijzonderheden over van Leeuwenhoek.Nederl. Tijdschr. v. Geneesk., Amsterdam, 1930, 74, 3891-3899.

(32) WELD, C. R.: A History of the Royal Society. John W. Parker (London),1848, 1, 244-245.

(33) WELLER, CARL V.: Antony van Leeuwenhoek, 1632-1723. Ann. Internal.Med., 1932, 6, 573-584. on M

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