MICROBIOLOGICAL REVIEWS, Mar. 1982, p. 121-126 Vol. 47, No. 10146-0749/82/010121-06$02.000/Copyright 0 1983, American Society for Microbiology

The Roles of the Sense of Taste and Clean Teeth in theDiscovery of Bacteria by Antoni van Leeuwenhoek

D. BARDELLDepartment ofBiology, Kean College ofNew Jersey, Union, New Jersey 07083

INTRODUCTION.............................................................. 121INVESTIGATIONS ON THE SENSE OF TASTE AND THE DISCOVERY OF BACTERIA. 122vAN LEEUWENHOEK'S PRIDE IN HIS CLEAN TEETH AND THE DEFINITIVE

EVIDENCE FOR THE DISCOVERY OF BACTERA .................................... 124CONCLUSIONS.............................................................. 125LITERATURE CiTED ............... ............................................... 126

INTRODUCTION

The discovery of protozoa, unicellular algae,unicellular fungi, and bacteria by Antoni vanLeeuwenhoek is well recorded in standardbooks on the history of microbiology (1, 4), thehistory of biology (5, 6), and the history ofmedicine (3). The discovery of such a variety ofmicroorganisms is the reason for books devotedentirely to van Leeuwenhoek (2). Furthermore,many microbiology and biology books, for what-ever purpose they were written, introductorytextbooks or otherwise, give some attention tothe discoveries.

It was a remarkable achievement to discovereucaryotic unicellular organisms, but it required.even greater skill to discover bacteria. Of themany discoveries made with single-lens micro-scopes that he constructed himself, the discov-ery of bacteria by van Leeuwenhoek is generallyconsidered by microbiologists to be his greatestdiscovery.

Although, as indicated above, there are nu-merous writings on the subject, from cursorymention to in-depth studies, there has been noconsideration given to what led van Leeuwen-hoek to the discovery of bacteria. No matter atwhat level one reads, whether superficial ac-count or lengthy treatise, one receives the im-pression that van Leeuwenhoek applied the mi-croscope to virtually anything or everything hecould observe with the instrument, and in doingso he happened to observe bacteria and otherkinds of microorganisms. There would havebeen nothing wrong in that, since whateverapproach was used, the discovery of bacteriaranks high in the history of microbiology. How-ever, although the discovery was fortuitous, itdid not occur from random observations. It wasfortuitous in the sense that while deliberatelyinvestigating a certain subject with a designed

approach, van Leeuwenhoek observed bacteriain the course of the study.

It is true that van Leeuwenhoek's numerousmicroscopic observations covered a broad spec-trum of subjects, but they were not made with-out definite aim. If one reads the letters vanLeeuwenhoek sent to the Royal Society in Lon-don, and the extant letters the Royal Society andindividual persons sent to him, one can see thathe pursued investigations which he originatedbecause the subject interested him and also thatstudies were made in response to requests byothers to investigate a specified subject with theaid of a microscope. Furthermore, the publishedworks of contemporary scientific investigatorswere the stimulus for studies by van Leeuwen-hoek.An example of a subject which interested van

Leeuwenhoek for many years was the diseasecalled gout. He sent reports on the study of goutto the Royal Society, considered himself moreknowledgeable about the disease than physi-cians, disagreed with a report on gout publishedin the Journal des Scavans, and on one occasionasked the Royal Society to send him informationconcerning the treatment for gout in England(19).A request from the Royal Society to examine

hair with a microscope is an example of a studyin response to the ideas of others (17). At thattime it was not known whether hair grew inlength by addition to the tip, as is the case inplants, or whether it grew from the bottom andpushed previous growth upward.Robert Boyle (1627-1691) made major contri-

butions to the study of chemistry and physics,among which was Boyle's Law concerning prop-erties of gases. The publication of an investiga-tion by Boyle in Philosophical Transactions wasthe cause for microscopic studies by van Leeu-wenhoek on certain chemical crystals (15), an

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example of the published work of a contempo-rary being the stimulus to study a new subject.The studies of gout, hair, and chemical crys-

tals did not lead to the discovery of any microor-ganisms. However, van Leeuwenhoek was alsocurious about the sense of taste, and whilepursuing investigations to satisfy that curiosityhe discovered bacteria.

INVESTIGATIONS ON THE SENSE OFTASTE AND THE DISCOVERY OF

BACTERIAVan Leeuwenhoek's first letter to the Royal

Society was dated 28 April 1673 and dealt withmicroscopic observations on mold, parts of abee, and parts of a louse. The original letter islost, but its contents are known from the reportpublished in Philosophical Transactions (7). Hisfirst letter dealing with the sense of taste wasthat of 19 October 1674 addressed to the RoyalSociety (9). The report of the discovery ofbacteria was contained in a letter sent to theRoyal Society and dated at Delft on 9 October1676 (16).The impetus for van Leeuwenhoek's interest

in the sense of taste is revealed in his letter of 19October 1674. A diminished sense of taste dur-ing the course of a mild illness was a good reasonto study that particular sense (9): "Last winterwhile being sickly and nearly unable to taste, Iexamined the appearance of my tongue, whichwas very furred, in a mirror, and judged that myloss of taste was caused by the thick skin on thetongue." ("Voorleden Winter sieckelijck sijnde,ende als bij na gansch geen smaeck hebbende,besichtichde ick verscheijde malen mijn tonge,die seer beslagen was, in een spiegel, endeoordeelde alsdoen, dat mijn gansch weijnigesmaeck veroorsaeckt wiert, door de dicke huijt,die op de tonge lach.")When speaking of "thick skin" (dicke huijt),

van Leeuwenhoek was referring to the furrycoating of his tongue, which he concluded wasinterfering with what he called the "little pointson the tongue" (punctgens op de tonge) thathave a role in the sense of taste. The little pointswere the papillae of the tongue, and the tastebuds are located in the papillae.van Leeuwenhoek then examined the little

points of the tongue with a microscope, usingthe tongue of an ox for the investigation. Oxtongues would have been easy to obtain in vanLeeuwenhoek's time, since before the discoveryand widespread application of practical methodsof refrigeration, all reasonable size communitieshad a slaughterhouse for domestic animals,since the time between killing an animal andconsuming the meat before decomposition oc-curred was short. He may also have obtained thetongue from a butcher's shop, as the tongues of

domestic animals were then, and still are, eatenas meat.

Microscopic examination of the little pointson the surface of the intact tongue, and afterremoval of the upper layer of skin, showed thatthe little points had "very fine pointed projec-tions" (seer subtijle puntige uijsteeksels) thatwere composed of "very small globules"(cleijne clootgens).That van Leeuwenhoek observed very small

globules in the papillae of the tongue should notbe interpreted as meaning that the globules werecells and hence that he discovered the sensoryreceptor cells for taste. "Globules" ("cloot-gens" or "klootgens" or "globule" in the let-ters), is, if not the most frequently used word, atleast one of the most frequently used words invan Leeuwenhoek's letters. He saw globules innearly everything he looked at with a micro-scope. Unless he gave further information aboutthe globules, as he sometimes did, it is difficultto understand what he was seeing. When hespeaks of "the globules that make the bloodred" (de globule die het bloet root maken), he isspeaking of red blood cells (11). However, in thesame letter he confounds the reader by statingthat the clear fluid, separated from the redglobules after clotting of the blood, was com-posed of globules. He further confounds thereader by allowing the serum to evaporate andthen reports that the dry matter which remainedwas made up of globules. Needless to say,together with many other materials he looked at,particles of soil and chalk were reported to becomposed of globules; it was reported that theglobules of chalk were transparent, and it wasthe way the transparent globules were arrangedthat gave chalk its white color (8).van Leeuwenhoek was criticized by scientists

in France for reports of globules in the manydifferent materials he observed microscopically.He knew about the criticism (11), and althoughhe claimed he did not mind it, it may havedisturbed him, since he brought the subject up inat least two letters to the Royal Society.The surface of the tongue has a bacterial flora,

and the bacteria residing there are not sparse.However, van Leeuwenhoek did not report theobservation of any microorganisms when exam-ining the tongue with a microscope.

After the investigation of the papillae of thetongue, van Leeuwenhoek turned his attentionto the constituents offood involved in the senseof taste. As will be seen later, he appeared to besatisfied that he had discovered the essentialcomponent of the tongue with respect to taste,namely, the globules.

Herring is a very popular Dutch food and isfrequently eaten raw. In a letter of 11 February1675 are details of an inquiry into the taste of

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herring (10). van Leeuwenhoek had been study-ing the formation of crystals after placing com-mon salt in water and allowing the water toevaporate at either room temperature or afterthe application of heat to quicken the process.He noted that at room temperature "squarecrystals" (viercantige stukie) were formed, butat the higher temperature the crystals had theappearance of "thin sharp-pointed pipes"(dunne spitse pijpjens). He then applied thisinformation to the taste of herring. He conclud-ed that the reason people do not like the taste ofcooked salted herring is because the heat ofcooking causes the salt to form sharp-pointedcrystals which irritate the globules of the tongue,whereas the preference for raw salted herring isbecause the salt crystals are square and lessirritating to the globules.

Microorganisms were not discovered in theinvestigation on the taste of herring, but themove away from the study of the tongue to thestudy of the role offood in the sense of taste wasa move in the right direction for the eventualdiscovery of bacteria. Although the surface ofthe tongue has a resident bacterial flora, it isdoubtful that van Leeuwenhoek would havediscovered bacteria if he had done further micro-scopic studies on the surface of that organ. It iseasier to observe bacteria in saliva than bacteriaon the tongue. van Leeuwenhoek made severalinvestigations on saliva, but did not see microor-ganisms. Even after he had discovered eucaryot-ic unicellular organisms and bacteria, and as aresult of thse discoveries examined saliva fromseveral different people for the purpose of deter-mining whether or not microorganisms are pres-ent in saliva, he reported that microorganismsare absent from saliva (18).

After the study on salted herring, van Leeu-wenhoek sent several more reports on the senseof taste to the Royal Society before his discov-ery of bacteria. The subjects of those reportswere investigations into the reason for the differ-ence in taste between salt and sugar and on thetaste of arum, asparagus, and cinnamon (12-14).Generally, the conclusions were that microscop-ic crystals or particles offood affected the micro-scopic globules in the little points of the tongueand that dissimilarities in the shapes of thecrystals or particles of unlike foods were thereason for differences in taste of different foods.

Starting in September 1675 and continuinguntil August 1676, van Leeuwenhoek did a se-ries of microscopic observations on rain, canal,well, and seawater. The results were communi-cated to the Royal Society in his letter of 9October 1676 and reported observations of sev-eral different eucaryotic unicellular organisms,namely, protozoans (16). The letter also an-nounced the discovery of bacteria. They were

not observed in the various natural waters stud-ied, but rather in an unnatural water environ-ment, pepper water.Why was van Leeuwenhoek studying water in

which peppers were being soaked or steeped? Itis unusual to find a report of just one investiga-tion in any of the many letters van Leeuwenhoeksent to the Royal Society. Usually a letter gavereports on several investigations. In addition tostudies on water from natural sources, vanLeeuwenhoek was continuing his studies on thesense of taste and at that time was trying todiscovery why pepper had such a potent taste:"After several endeavors, now and then, todiscover if possible the cause of the power, orheat, of pepper on our tongue ... I put about 1/3of an ounce of whole pepper in water, andplaced it in my office, for no other purpose thanthat the pepper should become soft, so that Icould better observe it." ("Na dat verscheijdedevoiren soo nu en dan, heb aengewent, ommewaer het mogelijk, te ontdecken, de kragt, ofhitte, die de peper op onse tonge aenbrengt ...ik heb dan op nieu ontrent 1/3 once heele peperin water geleijt, en op mijn comptoir gestelt, uijtgeen ander insigte, dan om dat de Peper soudesagt worden, omme deselve des to beter toconnen observeren.").van Leeuwenhoek allowed the pepper to re-

main in the water for about 3 weeks. He did notdescribe the vessel in which the pepper wassteeped or give the quantity of water used. Itmust have been an open vessel, with probablyjust enough water to cover the pepper, since hereported that he twice added some water be-cause of evaporation. On 24 April 1676 he exam-ined his steeped-pepper preparation with a mi-croscope and with "great wonder" (grooteverwondering) observed several kinds of micro-organisms in the water, including what are nowcalled bacteria.

Conclusions that bacteria were observed forthe first time are based on expressions vanLeeuwenhoek used with respect to the sizes ofthe microorganisms observed.

In some of his previous studies van Leeuwen-hoek had discovered protozoa. His written de-scriptions of one of the organisms allows it to berecognized as a species of vorticella, bell-shapedaquatic protozoans with a stalk by which theyattach to objects. Protozoans were reported asbeing "little animals" (kleijne diertgens). Littleanimals were observed in the pepper water, butvan Leeuwenhoek also reported that he sawother organisms that were "incredibly small"(ongelooflijk kleijn). An organism that is incredi-bly small compared with a protozoan is thereason for the belief that van Leeuwenhoekdiscovered bacteria on 24 April 1676. He alsoreported that by his judgment 100 of them ar-

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ranged lengthwise would not equal the length ofa grain of coarse sand and estimated that 106 ofthem would not equal the dimensions of a grainof coarse sand.

Later in the letter van Leeuwenhoek gave hisreport on the original purpose of the study, thetaste of pepper. He explained that sharp-pointedmicroscopic particles in pepper greatly irritatedthe microscopic globules of the little points ofthe tongue and that was the reason for the hottaste of pepper.van Leeuwenhoek's interest in the sense of

taste did not wane after his discovery of incredi-bly small organisms. He continued his reasearchon that sense and transmitted his findings to theRoyal Society for many more years.

VAN LEEUWENHOEK'S PRIDE IN HIS CLEANTEETH AND THE DEFITIVE EVIDENCE FOR

THE DISCOVERY OF BACTERIAThe report of the discovery of bacteria con-

sists of 72 words in a very long letter, which ifprinted in Microbiological Reviews would be 20or more pages in length. Except for noting theobservation of incredibly small organisms andcomparing their size with a grain of coarse sand,no other information about them was given.Therefore, the shape of the first bacteria to beseen is unknown. However, when estimatingtheir size van Leeuwenhoek spoke of them asbeing arranged lengthwise; thus, they may havebeen rod shaped.There have been speculations that some of the

other microorganisms reported in van Leeuwen-hoek's letter of 9 October 1676 were bacteria,but there are no meaningful foundations for suchspeculations.

It is a pity that van Leeuwenhoek did notprovide illustrations of the microorganisms re-ported in the letter of 9 October 1676. Hecertainly knew the value of drawings in scientificreports. Although he could not read the text of abook written by Francesco Redi (1626-1679), hecould understand the illustrations of microscop-ic observations included in the book (10).The definitive evidence for the discovery of

bacteria was sent to the Royal Society in a letterdated 17 September 1683 (20).van Leeuwenhoek was proud of his clean

teeth and described his regimen for keepingthem in that condition in his letter of 17 Septem-ber 1683. Each morning he rubbed his teeth,using salt as an abrasive, and then rinsed hismouth with water. After eating he picked histeeth with a toothpick and then rubbed themwell with a piece of cloth. He was well satisfiedwith his regimen and commented that few peo-ple of his age had such clean and white teeth. Hewas then just 5 weeks short of his 51st birthday.Despite his thorough regimen, on examining his

teeth with a magnifying mirror he found thatthey were not as clean as he thought: "Yet bydoing so my teeth are not clean, for when I lookat them with a magnifying mirror there remainsor grows between some of the molars and teeth alittle white matter, about as thick as batter."("Soo en sign mijn tanden daar door soo suijverniet, of wanneer ik deselve met een vergroot-spiegel besag daar blijft ofte groeijt, tusscheneenige van de kiesen, en tanden, een weijnigwitte materie, die soo dik is, als of het beslagenmeel.")Although the consistency of the batter-like

matter prevented good microscopic observa-tions, van Leeuwenhoek's suspicion wasaroused as to the possibility that living organ-isms were present in the white matter. He thenmixed some white matter with clean rainwater,after determining that the water was free of littleanimals. He also mixed some white matter withsaliva from his own mouth, after eliminating airbubbles in the saliva so that they would notinterfere with microscopic observations on themixture. Again, this is a case of van Leeuwen-hoek's belief, based on microscopic observa-tions, that saliva is free of microorganisms.

Microscopic examination revealed that thepreparations contained "many very small livinganimals, which moved very prettily" ("veeleseer kleijne levende dierkens, dier haar seeraerdig beweegden.")On this occasion van Leeuwenhoek made

drawings of the organisms, which are now repro-duced in virtually all introductory microbiologybooks and also in many higher-level books.Rod-shaped bacteria of different sizes were

observed and appropriate drawings were made.However, to look at reproductions of van Leeu-wenhoek's drawings can be misleading withrespect to some bacteria he saw, since the textof his letter is not usually given with the repro-ductions, and what is said in the text and whatsome drawings show are quite different. Thedrawings of bacteria which are probably misin-terpreted are those shown in his illustration ashaving a spherical shape, and consequently it isconcluded that van Leeuwenhoek observed coc-cus-shaped bacteria. According to the letterthese little animals "moved quickly" (vaardigevoortgang). Therefore, there is a question ofwhat fast-moving cocci can be found in mattertaken from between the teeth? Furthermore,other information in the letter casts doubt re-garding the observation of cocci. The letterstates that the organisms appeared at one time tobe "long and round" (lang-ront) and at anothertime to be just "round" (ront). van Leeuwen-hoek clearly states that he could not determinethe shape of these fast-moving organisms, i.e.,whether they were elongated or round, but pre-

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sented them in his illustration only as theyappeared when they seemed to have a sphericalshape and without a drawing of how they ap-peared when they seemed to him to be rodshaped.

Dobell translated the description of thesemicroorganisms at one time as being "oblong"and at another time as being "round" (2). There-fore, he is incorrect in stating that the microor-ganisms were coccus shaped, and he is evenmore remiss when he concludes that the organ-isms were micrococci, since micrococci are non-motile bacteria. Dobeil appears to have been ledastray by giving more attention to the illustra-tions than to van Leeuwenhoek's written de-scriptions. Indeed, he more or less admits to thatby making the following statement about vanLeeuwenhoek's illustrations (2): "To anybodyfamiliar with these organisms his figures speakso clearly that his words are almost superflu-ous."van Leeuwenhoek immediately extended his

study to see if he could find little animals inwhite matter from between the teeth of otherpeople. He collected samples from people ofboth sexes, and of different age groups, and alsofrom people with and without clean teeth. Hetook saliva from each person and, after ascer-taining that it was free of little animals, mixedwhite matter from between their teeth with theirsaliva. He also made preparations of white mat-ter in water. The mixtures consisted of one partof white matter and nine parts of saliva or water.That he did not find little animals in any of the

saliva specimens and also the fact, as previouslyreported herein, that he had not observed themin other studies to determine whether or notlittle animals occur in saliva casts more doubt onthe observation of cocci in matter from betweenhis teeth. Saliva has a relatively high concentra-tion of bacteria, with cocci being by far thepredominant form. If he could not observe cocciin any of the many specimens of saliva heexamined, would he have seen cocci in hispreparations of matter from between the teeth?

Included in the extended study were twowomen. Since he knew they cleaned theirmouths each day, one of them was most likelyhis second wife and the other was probably hisdaughter from his first marriage. His first wifedied in 1666, and four of the five children of thatmarriage did not survive infancy. An eight-year-old child was included in the study. A man wholed a sober life and did not smoke tobacco was amember of the group. He also included an oldman who smoked and frequently drank alcoholicbeverages. van Leeuwenhoek was quite curiousas to whether or not little animals could live in amouth which was frequently used to take inalcoholic drinks. This old man had lost most of

his teeth, having only a few of his front onesremaining, and they were very dirty. van Leeu-wenhoek asked him if he ever cleaned hismouth. The old man replied in a manner indicat-ing that he never did so with water, but heflushed his mouth every day with wine.

In all of the specimens van Leeuwenhoekobserved rod-shaped little animals, some ofwhich were larger than others, but the old manwho was fond of alcohol did not have any of thelarger kind of rod-shaped organisms. The fast-moving little animals that van Leeuwenhoek sawin white matter from between his own teeth andwhich he could not determine to be elongated orspherical were seen in all specimens of theextended study. In the matter from the man wholived a sober life van Leeuwenhoek saw, inaddition to the other kinds of organisms, spiral-shaped little animals. His written description isnot very good, but he provided a drawing show-ing the spiral form of the organisms. Unfortu-nately the drawing was not reproduced well inPhilosphical Transactions, and the originaldrawing is now lost. However, a good illustra-tion of the spiral-shaped organisms observed onthis occasion was included in van Leeuwen-hoek's Ondervindingen en Beschouwingen pub-lished in Delft in 1694.The letter of 17 September 1683 to the Royal

Society provides good evidence that van Leeu-wenhoek saw motile rod- and spiral-shaped bac-teria, but it is doubtful from the written descrip-tions of microorganisms reported therein that heobserved spherical-shaped bacteria.

CONCLUSIONSThat van Leeuwenhoek discovered bacteria is

well established, but there has been no previousconsideration given to the activities van Leeu-wenhoek was engaged in that led to the discov-ery.

It has most frequently been the practice ofthose interested in the history of microbiology toconcentrate specifically on the relatively fewletters written by van Leeuwenhoek that reportobservations of microorganisms and to neglectthe numerous other letters: hence, the reason itis well known that van Leeuwenhoek was thefirst person to see bacteria and also why there isa dearth of information on the events antecedentto the discovery. By reading some of the otherletters, those from April 1673 to September1683, one can see that he was engaged in alogical sequence of investigations on the senseof taste; it was his interest in that particularsense that caused him to place peppers in water,and it was in that experimental setup that bacte-ria were observed for the first time. Proof be-yond doubt for the discovery of bacteria came 7years later when van Leeuwenhoek gave written

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descriptions and made illustrations of bacteriafound in matter from between his own teeth andthe teeth of others. The illustrations should not,as is usually the case, be interpreted without theinformation provided by the written descrip-tions.

ACKNOWLEDGMENS

I thank the Royal Society, London, for allowing me accessto the original letters Antoni van Leeuwenhoek sent to theSociety.

LITERATURE CITED

1. Bulloc, W. 1938. A history of bacteriology. OxfordUniversity Press, London.

2. Dobdl, C. 1932. Antony van Leeuwenhoek and his "littleanimals." Reprinted in 1960 by Dover Publications, Inc.,New York.

3. Garson, F. H. 1963. An introduction to the history ofmedicine, 4th ed. W. B. Saunders Co., Philadelphia.

4. L1 _evale, H. H., and M. SoeoroIy. 1965. Threecenturies of microbiology. McGraw-Hill Book Co., NewYork.

5. Nod d, E. 1929. The history of biology. Alffed A.Knopf, New York.

6. Singr, C. 1959. A history of biology. Abelard-Schuman,London.

7. van Leewebek, A. 1673. A specimen of some observa-tions made by a microscope, coutrived by Mr. Leewqn-hoeck in Holland, lately communicated by Dr. Regnerus

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de Graf. Philos. Tram. 86037-6038. (em igures ofsomeof Mr. Leewenhoeck's micrscopical observations, to-gether with their explication. Philos. Trans. 8:6116-6118,1673.)

8. va Lenwemboek, A. 1674. Letter of 7 September 1674 tothe Royal Society, London. Royal Society, MS. L 1.7.

9. vnn Lsouwmibo.k, A. 1674. Letter of 19 October 1674 tothe Royal Society, London. Royal Society, MS. L 1.8.

10. VaLesa , A. 1675. Letter of 11 Febrary 1675 tothe Royal Society, London. Royal Society, MS. L 1. 11.

11. vn I_=wemek, A. 1675. Letter of26 March 1675 to theRoyal Society, London. Royal Society, MS. L 1. 13.

12. van Leewqs*, A. 1675. Letter of14 August 1675 to theRoyal Society, London. Royal Society, MS. L 1. 15.

13. van Lanw mhsek, A. 1676. Letter of 21 April 1676 to theRoyal Society, London. Royal Society, MS. L 1. 18.

14. 1 _Lesweabek, A. 1676. Letter of 29 May 1676 to theRoyal Society, London. Royal Society, MS. L 1. 20.

15. vain Leswemboek, A. 1676. Letter of 28 July 1676 to theRoyal Society, London. Royal Society, Boyle Lett.3:125-128.

16. v _ , A. 1676. Letter of9 October 1676 to theRoyal Society, London. Royal Society, MS. L 1. 22.

17. vIo Leuweubek, A. 1678. Letter of 14 January 1678 toIthe Royal Society, London. Royal Society, MS. L 1. 33.

18. van Lemweuhoek, A. 1679. Letter of 21 Fcbruary 1679 tothe Royal Society, London. (This letter never reached theRoyal Society, was lost, but found earlier this century.See Beddals, P. 1933. Leeuwenhock-brief no. 27 enandere gegevens. Ned. r'dschr. Geneeskd. 77:525-527.)

19. v Loenweahoek, A. 1681. Letter of 4 November 1681 tothe Ioyal Society, London. Royal Society, MS L 1. 64.

20. v uLewenboek, A. 1683. Letter of 17 September 1683 tothe koyal Society, London. Royal Society, MS. L 1. 69.

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