178 E. CAPANNAJOURNAL OF EXPERIMENTAL ZOOLOGY (MOL DEV EVOL) 285:178–196 (1999)

© 1999 WILEY-LISS, INC.

Lazzaro Spallanzani: At the Roots of Modern BiologyERNESTO CAPANNA*Dipartimento di Biologia Animale e dell’Uomo Universitá “La Sapienza”Roma 00161, Italy

ABSTRACT The scientific work of Lazzaro Spallanzani is outlined, with emphasis on the ele-ments of originality in his introduction of the experimental method in biology. Particular stress isplaced on Spallanzani’s contribution to solving the Theoria Generationis, from the problems con-nected with the spontaneous generation of living creatures to those of natural fertilization andartificial insemination and, finally, those of regeneration. J. Exp. Zool. (Mol. Dev. Evol.) 285:178–196, 1999. © 1999 Wiley-Liss, Inc.

Vous passez pour le meilleur observateur del’Europe. Toutes vos experiences ont été faitesavec la plus grande sagacité. Quand un hommetel que vous nous annonce qu’il a ressuscité desmorts, il faut l’en croire. […] J’en peu de joursá vivre, Monsieur, je les passerai á vous lire, ávous estimer, et á vous regarder comme le pre-mier Naturaliste de l’Europe. Continuez, je vousprie, Monsieur, d’honorer de vos bontés et devos instructions le vieux malade de Ferney.(Letter to Spallanzani from Voltaire, dated “áFerney 6 juin 1776”)

OLD AND NEW PARADIGMSAfter previous centuries, especially the seven-

teenth, broke down the paradigms of classical sci-ence, it fell to the eighteenth century, in thehistory of scientific and philosophic thought, tobe the cradle of modern science. Lazzaro Spal-lanzani (1729–1799) was one of the leading fig-ures in this scientific renaissance.

In the sixteenth century, the rigorous theoreticaland experimental foundation of the Copernican sys-tem put in crisis the Aristotelian-Ptolemaic conceptof the cosmos. In the seventeenth century the physi-ology of Galen, the other great scientific paradigmof the ancient world, also suffered a crisis followingthe dramatic crash between theoretical philosophicconstraints and the new experimental science, be-tween deep thinkers and meticulous naturalists,between imaginative metaphysicians and the firstmicroscopists.

Emblematic of this scientific revolution was thequestion of how blood circulated. In fact, the physi-ology revolution was enacted in the seventeenthand eighteenth centuries on the phenomena ofblood circulation. Seventeenth-century science,where medicine and anatomy are concerned, was

*Correspondence to: Ernesto Capanna, Dipartimento di BiologiaAnimale e dell’Uomo Universitá “La Sapienza,” Via Boreli 50, Roma00161, Italy. E-mail: capanna@axrma.uniroma1.it

based on the system formulated by Galen (131–210) that substantially was accepted even in thenew scientific climate that formed. The greatVesalius (André van Vesele, 1514–1564), reformerof the teaching of anatomy, essentially acceptedthe Galenic doctrine, although he admitted com-plete separation between the right and left sec-tions of the heart. Galen’s system, in reality, wasnot a true “circulation” of the blood, but a con-tinuous production of blood by the liver that wasrendered vital in the heart during the diastole bythe air breathed in through the lungs. During thesystolic phase, blood was impelled throughout thebody, thereby transferring the animal spirit it de-rived from being mixed with air from the lungs.The vital principles of the Aristotelian basis of sci-ence are evident in this formulation.

Servetus (Miguel Serveto, 1511–1553), MatteoRealdo Colombo (1520–1599), Caesalpinus (An-drea Cesalpino, 1519–1603), and Fabricius (Giro-lamo Fabrizio da Acquapendente, 1537–1619)knew the anatomy of the greater and lesser cir-culation, but failed to realise the physiological im-port of the discovery and the quality of realscientific revolution implied by the precise defini-tion of the circulation of the blood. However, thefull understanding of this revolution did not es-cape William Harvey (1578–1657). The original-ity of this Englishman’s work was in a newmethod of approaching the problem: experiment-ing by measuring the parameters of the phenom-enon of the circulation.

Harvey broke down the Galenic paradigms and

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laid the foundations of modern physiology in the72 pages of Exercitatio anatomica de motu cordiset sanguinis in animalibus (1628) (Fig. 1). He un-equivocally demonstrated through experiment andmathematics that blood cannot be produced by theliver and continuously transferred to peripheralparts of the body, but that it circulates constantlyin the vasal system. Based on the volume of theventricular cavity when the heart is dilated andcontracted, he calculated the quantity of bloodpassing through the heart at each beat, which heassessed at 2 ounces (about 50 g). Consideringthat the heart beats about 72 times per minute,he inferred that the quantity of blood passingthrough the heart in one hour would be 540pounds (more than 200 kg). Justly, Harvey asked

himself how the liver can produce a quantity ofblood equal to three times the weight of a man ofnormal build.

Only about a century later do we encounter thegenial measurement experiments of blood pres-sure, performed by the Reverend Stephen Hales(1677–1765), and described by Spallanzani (1768a)as an “acuto ed eccellente Osservatore.” Introduc-ing a slender cannula in the arteries and veins,Hales obtained surprisingly accurate measure-ments of arterial and venous pressure in differ-ent animals, both in the systolic and in thediastolic phase. He verified differences of pressurein relation to different physical and psychic statesand measured the speed of the circulatory flow.

This propensity to measure biological phenom-ena is typical of this eighteenth-century phase ofscience, aimed at the observance of Galileo’s pre-cept in the Dialogo sopra i massimi sistemi (1632):“…the book of Nature is written in the languageof mathematics, and the characters are triangles,circles and other geometrical figures. Withoutcomprehending these instruments it is not hu-manly possible to understand one word; withoutthese it is like going round in circles in an ob-scure labyrinth.”1 The measurement and math-ematical interpretation of biological processes wasindeed the aim of the iathrophysicists and iathro-chemists, who in the physical analysis of the pro-cesses in the nascent science of physiology werethe precursors of Hermann Boerhaave (1668–1738), whose famous Istitutiones Medicae (1708)remained the master treatise on physiology through-out the eighteenth century.

In this climate, as new paradigms were formedbased on experimentation and microscopy, LazzaroSpallanzani came to grips in some of his first stud-ies with a problem concerning the circulation ofthe blood (Fig. 2) (Spallanzani, 1768a; 1773). Thecirculation in the vasa in capillamenta resolutahad been clearly demonstrated by Marcello Mal-pighi (1628–1694) (Malpighi, 1661), in whose wakeSpallanzani proceeded. However, his analysis hada precise aim: to verify the action of the cardiacmuscle in the movement of blood in veins and ar-teries of different sizes, down to the detail of ob-serving the coronary vessels. But the acuity of themeticulous observer is shown by a discovery made

Fig. 1. Title page of the Rotterdam edition (1648) ofWilliam Harvey’s Exercitatio anatomica de motu cordis.Corsini library of the Accademia Nazionale dei Lincei.

1“…il libro della Natura è scritto in lingua matematica, e i caratterison triangoli cerchi e altre figure geometriche, senza i quali mezzi èimpossibile a intendere umanamente parola; senza questi è un aggirarsivanamente in oscuro labirinto.” (G. Galilei, Dialogo … sopra i duemassimi sistemi del mondo tolemaico e copernicano. Firenze 1632)

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by Spallanzani that remained almost unknown,buried under the ponderous mass of his writings.He was the first to describe blood leukocytes. Af-ter having described with great exactitude theform of salamander red blood cells, he encountereda nucleated element clearly different in shape andsize, thus his discovery of leukocytes. He precededEnglish microscopist William Hewson (1739–1774), whom treatises of haematology and gen-eral histology, indicate as the discoverer of thisfamily of blood cells. Spallanzani, on the contrary,was perfectly aware of his discovery and of its nov-elty. In fact, he wrote: “I have discovered a spe-cies of globules which are smaller and present infar smaller numbers than the first ones.” Thenhe proves his great stature as a scientist, as pru-dent in concluding as he is accurate in observing:

“Since I myself doubted of my discovery, I wantedto make sure of it. I feared that the observationmight derive from an optical effect, since the nor-mal globules could be seen from the pointed endand thus be judged smaller and of a different na-ture. But after repeated, diligent and minute ob-servations I could be certain that the two speciesof globule must absolutely be distinguished”2

(Spallanzani, 1768a).

THE THEORIA GENERATIONISCertainly the fame that Spallanzani enjoys is due

more to his observations on the theory of genera-tion than to his observations on blood circulation,or his genial writings on the digestion and a thou-sand other things. The name Theoria generationis,in classical physiology and still in the eighteenthcentury, included all the biological phenomenawhose intrinsic involvement in philosophy and the-ology attracted the general interest of cultured per-sons and the unlettered masses. It was, in fact, amatter of understanding of the fundamental phe-nomena of the reproduction of organisms, embry-onic development, and parts regeneration of parts,along with the problem of organic life emerging frominorganic molecules.

If on the scientific plane these problems have beensubstantially resolved, on the philosophical andabove all the ethical plane they still agitate the con-sciences both of the cultured and the uninformed.This symposium is a clear example of the perpetualtopicality of the Theoria generationis and of theproblems that it brings in its train.

The formulation of the problem of the genera-tion was proposed by Aristotle (384–322 B.C.) inhis De generatione Animalium. It bears markedtraces of the metaphysical framework of the Greekphilosopher: The embryo is the result of the life-giving action of the sperm infusing the incorpo-real soul in the menstrual blood of the female,which is essentially inert and devoted exclusivelyto nourishing the embryo. Galen, on the contrary,imagined that the two seeds, masculine and femi-nine, participated equally in the constitution ofthe embryo. These two hypotheses, handed down

Fig. 2. Title page of Spallanzani’s De’ Fenomeni dellaCircolazione &. Library of the Department of Animal andHuman Biology, Rome University “La Sapienza.”

2“... ve ne ho scoperta una specie di più piccoli, quantunque innumero senza paragone minori. […] Veramente pria di dare l’assensoa me stesso ho voluto dubitarne per qualche tempo: Io temeva ciònascesse per ventura da inganno dell’occhio, potendomisi i volgariglobetti presentare in punta alla vista, e quindi giudicarli più piccolie perciò diversi di specie. Ma l’induzione di replicate, diligenti, eminute osservazioni mi ha fatto vedere, che le due specie de’menzionati globetti si debbono assolutamente distinguere.” (L.Spallanzani “Dell’azione del cuore ne’ vasi sanguigni, Modena 1768)

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through disputes, contrapositions, and attemptsat syncretism until the seventeenth century, werefiltered through a fine mesh of philosophical reflec-tions containing prohibitions that were the realhobbles on the progress of scientific knowledge. Anew vision of the organisation of the natural world,which opens with the great philosopher-scientistsGalileo (1564–1642), Descartes (1596–1650), New-ton (1642–1727), and Leibniz (1646–1716), and inthis New Science context the dramatic microscopi-cal discoveries of Leeuwenhoeck (1632–1723) Mar-cello Malpighi, and then of Abraham Trembley(1710–1784), John Turberville Needham (1713–1781), and Spallanzani put an end definitively tothe old Aristotelian and Galenic paradigms.

This time too, the scientific revolution springsfrom the work of that same great anatomist whooverturned the Galenic model of the circulationof the blood: William Harvey. In 1651 he publishedhis Exercitationes de generatione animalium (Fig.3), which repeats in its title the work of Aristotle.In its construction, the work is Aristotelian, butit marks the origin of a new construction of scien-tific thought based on the analysis of concretefacts, not on their consistency with philosophicalsystems. Thus in the course of a few decades, thisparadigm of the ancient world arrived at its de-finitive downfall. Harvey placed the origin of thenew organism in the egg. The substantial corre-spondence between the courses of development ofoviparous and viviparous creatures, well demon-strated in the works of Volcher Coiter (1534–1576)(Adelmann, 1933) and Fabricius (1621), convincedHarvey of the essential uniformity of the processesin the two categories of living creatures. Harvey,however, maintained (in this agreeing withAristotle) that the sperm performed its fertiliz-ing action through an immaterial principle andthat the later development of the eggs, producedby the wall of the uterus, took place through sub-sequent additions, part by part, starting from theblood that supplies the uterine walls. In termi-nology formulated later, we could say that Harveywas “ovist” since he situated the material basisof the future organism in the egg, and “epi-genesist” since he considered the phenomena ofdevelopment extrinsic to the potentialities con-tained in the egg.

True ovism came later, thanks to the succes-sion of observations of the female genital appara-tus of viviparous animals conducted in Hollandby Johann van Horne (1621–1670) and by theDane, Niels Stensen (1638–1686), in Italy calledStenone, anatomist of the Grand Duke of Tuscany.

But the decisive contribution is due to Renier deGraaf (1641–1673) in his De mulierum organisgenerationis inservientibus (1672). The egg, how-ever, was still invisible and remained so until1827, when it was discovered by Karl Ernst vonBaer (1792–1876). But, as Antonio Vallisneri(1661–1730) affirmed, the egg of the mammalshad to exist and to be produced by the ovary (Fig.4) (Vallisneri, 1721).

Galen’s paradigm of double seeding fell defini-

Fig. 3. Title page of the Hague edition (1680) of WilliamHarvey’s Exercitationes de Generatione animalium. Jupiteris shown opening an egg from which spring out many animalspecies: a baby, a deer, a bird, etc. Corsini library of theAccademia Nazionale dei Lincei.

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tively. The egg, then, is the origin of the new or-ganism and, according to the canon of orthodoxovism, that new organism was perfectly pre-formed,an invisible miniature inside the egg. In the con-struction of the ovist system, the role of sperm re-mained to be clarified. Harvey had not seen spermin the uterus of deer dissected immediately aftercoitus. This observation, which passed undiscussed,excluded physical action by the sperm in fertiliza-tion and led the ovists to formulate the theory ofan aura spermatica, volatile and spiritual, very Ar-istotelian flavor, able to set in motion the manifes-tation of the miniaturized germ within the egg. Weshall see hereunder Spallanzani’s contribution tothe confutation by experiment of this hypothesis ofthe aura spermatica.

OVISTS AND “VERMICELLAI”But while the egg of the viviparous animals re-

mained invisible, the spermatozoon did not. Onlyfive years after the work of de Graaf, another

Dutchman, Anton van Leeuwenhoeck, discoveredin human sperm minuscule creatures, animalculi,endowed with active motion, not so different fromthe microscopical animals he had discovered inrainwater.

Thus animalculism was opposed to ovism. Let itnot be thought, however, that the animalculist hy-pothesis derived immediately from the discovery ofthe spermatozoon. That hypothesis required manyyears and, above all, the elaboration of a strongtheoretical framework so that it could sustain a dia-lectical confrontation with that of the ovists.

The intransigence of the discoverer of spermaticanimalcules led Leeuwenhoeck to deny the veryexistence of the invisible ova viviparorum and tosustain that the animalcules were implanted di-rectly in the uterine wall. Further, the metaphorof the spermatic “worm” transformed in the foe-tus in the same way as the tadpole is metamor-phosed into the frog seemed impossible to proposeeven in animalculist circles. So that metaphor rap-idly was replaced by another, no less improbable,of the pre-formation of a homunculus, a little manin miniature inside the animalcule, seen or imag-ined, and exactly drawn by imaginative microsco-pists such as the Frenchman Francois de laPlantade (1670–1741) (Fig. 5). This hypothesiswas, with great determination, upheld by physi-ologists of great prestige such as Jan Swam-

Fig. 4. Title-page of Vallisneri’s Istoria della generazione(Venice 1721). Library of the Department of Animal and Hu-man Biology, Rome University “La Sapienza.”

Fig. 5. Table from Vallisneri’s Istoria della generazionewhere different spermatozoa are represented. Notice figuresVIII and VIIII showing the “Homunculus” according toFrançois de la Plantade. Library of the Department of Ani-mal and Human Biology, Rome University “La Sapienza.”

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merdam (1637–1680), author of the renownedBijbel der Nature.

Such was the state of the art when Spallanzanistarted studying the problem of generation andtackled it experimentally. A convinced ovist, likemost physiologists in the eighteenth century, he re-ferred ironically to the animalculists as vermicellai,a name he derived from the vermicelli spermatici(little spermatic worms).

The theoretical position accepted by Spallanzaniwas that upheld by Charles Bonnet (1720–1793) towhom he was bound in deep friendship, and byBaron Albrecht von Haller (1707–1777). An ovist,preformist philosophical position also was accept-able theologically. A preformation of the germ en-visaged even the preformation of the germs ofsucceeding generations, Charles Bonnet maintainedin his Palingénésie (1770), so allowing the Creatorto create with Eve all subsequent humanity.

The preformist hypothesis encountered severecriticisms on the scientific plane. A young Berliner,Caspar Fridric Wolff (1733–1794), meticulouslycontradicted, with detailed observations on thedevelopment of chicks, the description given byvon Haller. Wolff (1759) succeeded in demolish-ing the preformist theory by demonstrating thatchick organs proceeded to form one after anotheraccording to a decidedly epigenetic scheme.

On the basis of his frog development observa-tions, Spallanzani thought he had corroboratedHallerian preformism. Studied at the microscope,frogspawn seemed identical before and after fer-tilization. Not only that, it was never possible tosee the “vermicello spermatico” inside the egg af-ter fertilization. Spallanzani (1768b) believed thathe had demonstrated that the spermatozoon madeno contribution to egg development, thus refut-ing the animalculist thesis. Having found no ap-parent transformation in the fertilized egg, hethought he also had contradicted the epigeneticthesis. On this occasion, our Spallanzani did notshow great sagacity. It was easy to object, as theAbbé Felice Fontana (1730–1805) did in a letterto Spallanzani (Fontana 1768), that he repeatedalmost entirely in his Lettera ad un amico soprail sistema degli sviluppi (Fontana 1792), that theabsence of organization before fertilization wasclear evidence of the absence of preformation and,therefore, demonstrated epigenesis.3 Penetrationof the egg by spermatozoon was demonstratedmuch later, in 1875, by Oscar Hertwig (1849–1922), in sea-urchin eggs (Hertwig, 1875), consid-erably more transparent than those of the frog.Hertwig used optical instruments certainly more

adequate than the “Macchinetta di Lyonnet” thesimple microscope used by Spallanzani (Fig. 6).

Preformism met other difficulties of a scientificnature. I shall mention only a few, those thatSpallanzani tackled by experiment, including theproblem of spontaneous generation of living crea-tures from inanimate material: irrefutable andevident proof of epigenetic development of livingforms from organic material.

Another problem was whether the spermatozoonparticipated materially in fertilization, or whetherthis process was due to an immaterial auraspermatica. This question had an interesting cor-ollary in the problem of hybrids: How to explainthe inheritance of paternal character if the em-bryo develops from the egg alone.

Last, but not least in terms of theoretical im-portance, the problem of regeneration: How to ex-plain the regeneration in single organisms suchas the polyps described by Trembley, and that ofcomplex organs in more highly evolved animalsin the échelle des etres vivants like the lobster-claws of René-Antoine de Réaumur (1683–1757),or our Spallanzani’s heads of snails. If the organ-ism is preformed in the embryo, a fortiori it isdefinitively preformed in the adult. How, then, isit possible to replace a piece taken away?

NIHIL DE NIHILOIn the ancient world, the possibility that living

creatures were generated from the inanimate wasan accepted fact that presented no problem. Aris-totle did not exclude the hypothesis of generationfrom mud and from the putrefying substance of ani-mals without red blood ( ’αναιµα), or even of littlefishes. Also Lucretius (95–55 B.C.), for all his Epi-curean materialism, writes in De Rerum Natura:“Nothing can be created from nothing,” but a fewverses further on in the same work admits “Alsomany animals are generated from the earth, fromthe rain and from the heat haze of the sun.”4

It was only in the climate of the Galilean Nuova

3“Due sole cose non sono ben chiare per me nel vostro Prodromo,l’una risguarda la circolazione, l’altra la preesistenza del feto nell’ovonon fecondato. […] La seconda non mi par dimostrata chiaramente,almeno io non ne sento tutta la forza, perché i vermicellai e gliepigenesisti vi diranno che non veder nulla nell’ovo infecondato mostraappunto che non v’è l’animale prima della fecondazione, e chel’osservazione oculare sta tutta per essi. Che poi non veggiate nullad’organico né ancor dopo la fecondazione seguìta da poco vuol direche l’animale entratovi collo sperma, o i piccoli organini che si vanformando successivamente, sono ancora impercettibili all’occhio anchearmato di microscopio.” (Letter by F. Fontana to L. Spallanzani datedFlorence April 15th 1768)

4“Quas ob res, ubi viderimus, nihil posse creare de nihilo” (T.Lucretius Caro. De Rerum Natura I, 153–154); Multaque nunc etiamexistunt animalia terris, imbribus et calido solis concreta vapore.”(ib. V, 747–748)

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scientia that the hypothesis was put to the ex-perimental test. Francesco Redi (1626–1698) (Fig.7) knew medicine and Greek literature well.Homer, in the canto of the Iliad in which Achillesbeweeps the lifeless body of his companion Patro-clus, writes “I fear that through the wounds in-flicted by the bronze the flies may enter the hero’sbody and there give birth to worms, so that, thelife spent, all the flesh will putrefy” (Iliad XIX,23–37). So Redi recalls that he too “had alwaysseen flies, of the same species as those that willbe born, alight on the flesh before it putrefies”(Redi, 1668).5 Hence derives the famous experi-ment, certainly known to all: In sealed vessels no

flies were born from putrescent flesh, but manywere born in those left open. No flies were borneven in vessels left open to the air but protectedfrom penetration by flies by a sottilissimo velo diNapoli (ultra-fine Neapolitan fabric). Today, wewould say covered with gauze.

Rather than on the experiment itself, already wellknown, I should like to comment briefly on the pro-cess that impelled Redi to experiment, the scien-tific method that would later be typical of theprocedure of Spallanzani, i.e., (1) bibliographicalknowledge (Homer in this case), (2) critical personalobservation, and (3) the bringing to perfection ofan adequate experimental apparatus. Redi’s experi-ments are authoritatively confirmed by Swam-merdam, Vallisneri and Réaumur.

So we come to the period of Lazzaro Spallanzani,

Fig. 6. The Macchinetta del Lyonnet, i.e., the simple micro-scope constructed by Lyonnet, used by Lazzaro Spallanzanifor his microscopical observation. Table from Pierre Lyonnet’sTraité Anatomique de la Chenille (The Hague, 1762), Libraryof the Department of Animal and Human Biology, Rome Uni-versity “La Sapienza.”

5“Di qui io cominciai a dubitare; se per fortuna tutti i bachi dellacarne dal seme delle sole mosche derivassero, e non dalle carni stesseimputridite: e tanto più mi confermava nel mio dubbio, quanto chein tutte le generazioni da me fatte nascere, sempre io avea vedutosulle carni, avanti che inverminassero, posarsi mosche della stessaspezie, di quelle che poscia ne nacquero.” (F. Redi Esperienze soprala generazione degli Insetti. Firenze 1668)

Fig. 7. Portrait of Francesco Redi, from the front page ofthe “Opere di Francesco Redi” (Venice, 1742). Library of theDepartment of Animal and Human Biology, Rome University“La Sapienza.”

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when the epigenesis hypothesis of spontaneousgeneration, although denied at levels of complexorganization, presented itself anew at the level ofthat minuscule world that the new science of mi-croscopy unveiled. This time, however, a well-con-structed theoretical framework gave valid enoughsupport to experiments apparently conducted well.

We can trace this new construction back to therationalism of Descartes. The French philosopherwas very interested in the problem of regenera-tion and expressed his thought about it in vari-ous writings. The corpus, however, of his ideas inthis sector can be found only in a late-publishedposthumous collection (Clerselier, 1701), PrimaeCogitationes circa Generatione Animalium. ForDescartes, the generation of the higher animalstakes place through an epigenesis process that fol-lows the mixing of the two seeds, masculine andfeminine. However, the origin of the lower ani-mal and vegetable forms, and life itself, are pro-voked by the action of heat on putrescent material.In the one case as in the other, the process ispurely epigenetic, exclusively physical, and articu-lated through the addition of organic parts with-out the intervention of vital spirits or souls. Onthis Cartesian basis, Pierre-Louis Moreau deMaupertuis (1698–1759) founded this new systemof generation, adding to the generative causes ofliving creatures in the Cartesian model, i.e., heat,motion and fermentation, the idea derived fromNewtonian physics of an attraction between simi-lar particles (Maupertuis, 1745). In his Systèmede la nature (1754) he introduces the concept ofpsychic attraction between organic particles basedon a memory belonging to the material itself andable to direct its development. The intelligencethat regulates life and its development for Mau-pertuis was immanent in the material and doesnot transcend it.

The hypothesis of generation of Needham, thefirst Roman Catholic clergyman to be a memberof the Royal Society of London, is developed onan epigenic basis. From infusions of the most di-verse nature and origins, from the very Englishmutton broth to the infusion of pepper or cloves,Needham obtained the spontaneous birth of thoseanimalcules that, because of their birth from in-fusions, the German microscopist Ledermuller(1719–1769) had called Infusoria. He attempted,however, a vitalistic vision of the phenomenon,somewhat similar to that in the tradition of theJesuit Athanasius Kircher (1601–1680). It is nota physical attraction between molecules that gen-erates life but the exhalation of a life force pos-

sessed by every slightest fragment of living mat-ter, even after death.

The model proposed by Count Buffon (George-Louis Leclerc, 1707–1788) is definitely mechanis-tic. Buffon’s system of generation is certainly thebest put together of all those advanced in thewhole of the eighteenth century, and the most Car-tesian, in the sense of being a purely rationalmodel aimed at unifying preformism and epigen-esis, along with ovism and animalculism. In fact,his intention was to demonstrate that preformismand epigenesis were not analogous concepts, butthat preformism could easily find a place withinan epigenetic thesis. The epigenetic aggregationof molecules is due not to psychic memories butto physical mechanisms such as internal moulds(moulages intérieures). The germ of the future or-ganism is produced by the mingling of moleculescoming from both progenitors. But during the life-times of the two parents the molecules haveformed in the parental internal moulds and, somodified, are subsequently conveyed into the par-ents’ genital organs. This theory explained per-fectly both the inheritance of characteristics fromboth parents and the regular epigenic develop-ment toward a very precise prospective form.Preformism, then, exists at the molecular level,and not at that of the Homunculus curled up inthe spermatic worm of the imaginative drawingsof François de la Plantade. Today, when we knowabout the DNA template that determines the pri-mary structure of the proteins, we might betempted to read Buffon’s hypothesis a modern in-terpretative key attributing to Buffon a biologicalprophetic spirit, which certainly is not the case.

While Buffon was an excellent theorist, he wasnot an equally good experimenter. Thus, when heknew of Needham’s experiments and several timesmet him in Paris, he adopted the Englishman’sexperimentation and Needham put his best mi-croscope at Buffon’s disposal. In the collaborationbetween the two scientists, Buffon assumed theleadership but Needham did not complain of hissupporting role. As an experimenter and observer,Buffon was rather a muddler; not so Needham,who was a more careful experimenter. To cut along story short, the fundamental texts of thisSystema generationis were published between1745 and 1750. Needham began, with his Newmicroscopical discoveries in 1745; then in 1749Buffon published the first volume of his Histoirenaturelle générale et particulière in which he ex-posed his general system of animal reproduction(chapter one) and the results of his experiments

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on spontaneous generation (chapter five). Thereimmediately followed a French translation ofNeedham’s experiments (1750).

THE CHALLENGE TO NEEDHAMAND BUFFON

In those years, Spallanzani was a law student atBologna University. But certainly there was muchdiscussion of Needham’s marvelous experimentsand of Buffon’s system of generation in the scien-tific salon of Spallanzani’s cousin Laura Bassi(1711–1778), mathematician and physicist of Bolo-gna University, which the young Lazzaro frequentedand where his conversion to the physical scienceswas decided. When Spallanzani published theSaggio di osservazioni microscopiche concernenti ilsistema della generazione de’ Signori di Needham eBuffon (1765) (Fig. 8), he was already more than30 years old and a Professor of Philosophy at theUniversity of Modena, but above all he had behindhim consolidated experience as a microscopist andexperimenter. The publication of that essay cameafter nearly three years of careful experiments, eachrepeated several times. He did not risk preconceived

judgements against Needham and Buffon as Fa-ther de Lignac did in a virulent little book (Lettre áun Américain, Joseph-Adrien Le Large de Lignac,1710–1761), but he repeats the experiments ofNeedham, with whom he enters into correspon-dence. Obviously the Saggio immediately had greatsuccess among the preformists. Baron von Hallerand, above all, Charles Bonnet were exultant. Thelatter, who did not know Italian, had the work trans-lated by Trembley, his cousin, Genevan like him.On the contrary, Needham was not at all happywith the deductions that Spallanzani drew withstringent logic from the rigorous experiments thatled him to conclude that it was certainly notl’universale semenza, i.e., the universal seed, presentin the air, that generated living creatures, but the“germs” deposited by the previous generation of In-fusoria. Flying in the air there were, if anything,volanti ovetti, i.e., little flying eggs, an ovist andpreformist conclusion that contradicted the epige-netic hypothesis. The relationship, however, be-tween the two Roman Catholic priests was friendly,and Needham himself attended to the French trans-lation of the Saggio printed in Paris and London,

Fig. 8. Table from Spallanzani’s Saggio di osservazionimicroscopiche concernenti il sistema della generazionede’Signori di Needham e Buffon (Modena 1765). Library of

the Department of Animal and Human Biology, Rome Uni-versity “La Sapienza.”

LAZZARO SPALLANZANI 187

to which he appended some notes in defence of hisown theories.

Spallanzani sent Charles Bonnet (Fig. 9) a copyof the Saggio, hot from the press, which initiatedan intense correspondence and a profound friend-ship that lasted throughout the lives of the twogreat scientists. The complete works of Spal-lanzani, recently published on the initiative ofModena University, devote to the correspondencebetween Spallanzani and Bonnet (Di Pietro, 1984–1990) an entire volume of more than 500 pages:193 letters, equally divided between the two. Inthe letters written between 1757 and 1765, wecan follow the development of the controversy, thecounter-deductions of Needham and the argu-ments of Spallanzani. Some letters from Spal-lanzani are so long and detailed in their contents,often illustrated with drawings in his own hand,

as to be considered real treatises. Bonnet in replyto one of those long letters writes: “I thank you,Sir, for the letter you sent me, I should say in-deed the book, which I shall keep as such in mylibrary.”

In 1769 Spallanzani moved to the University ofPavia, which was becoming one of the major Eu-ropean universities thanks to a wise plan of theEmperor Joseph II of Austria. It was obligatoryfor a professor called to a new university to de-liver a solemn inaugural lecture to the teachingbody and all the students. Spallanzani chose asthe subject of his inaugural lecture the genera-tion of the organisms in infusions. Also in thistext, written in faultless Latin, Spallanzani wasprodigal of praise for Buffon and Needham. Hewrote: “I have not discussed these things attempt-ing to diminish the fame of Buffon (who am I tocontradict such an authority?), nor in order thatyou, my dear young men, reading and meditatingon this, should abandon him” (Spallanzani, 1770).6

His precise duty, however, being responsible forthe scientific development of those adolescents,was to form a critical spirit able to withstand theauthority of the famous. In fact, his criticism issharp of the exhumation he defines as gatheredfrom the science of the ancients, immaterial shap-ing forces that the new post-Galilean science haddefinitively banished.

The enthusiasm of Bonnet for that lecture wasuncontainable. “Your inaugural lecture seemed tome well thought and well written. It is a pity thatthe great Francesco Redi was not present, hewould hence been enthusiastic. With what greatpleasure Malpighi and Vallisnieri would have lis-tened to you.”7

Spallanzani’s Opuscoli di Fisica Animale evegetabile appeared in 1776 (Figs. 10 and 11). Thefirst of them bears the subtitle Osservazioni edEsperienze intorno agni Animalucci delle infusioni,in occasione di un esame della nuova Opera delSig. di Needham. The English priest had pub-lished Nouvelles recherches sur les découvertesmicroscopiques et de la génération des corpsorganisés (Needham, 1769) in which he tried to

Fig. 9. Portrait of Charles Bonnet. From the EdizioneNazionale delle opere di Lazzaro Spallanzani. Carteggi, Vol.2. Mucchi, Modena, 1984–1990.

6“Neque vero haec a me ita disputantur, ut contendam vel Buffoniiauctoritate munuire (quis ego sum, qui cum tanto Homine congrediaudeam?) aut vos dilectissimi Adolescentes ab eo legendo, medita-toque amovere.” (Lazari Spallanzani in Regio Ticinensis Gymnasiopublici naturalis historiae professoris prolusio &. Modena 1770)

7“Votre Prolusion m’a paru assez bien pensée que bien écrite. Jevous fais le remerciements. Pourquoi le célèbre Redi n’etoit pas la? Ilne vous auroit pas résisté. Avec quel plaisir encore les Malpighi etles Vallisneri ne vous auroient-ils écouté!” (Letter of Bonnet toSpallanzani, dated “de ma Retraite, le 20 d’Avril 1771”)

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bring his system back into favor. Spallanzani’s pa-tience was by now at an end, and in his Opuscolohis tone became harsh. Spallanzani challengedBuffon and Needham not so much on preformismor epigenesis, as on experimental method and therigor of experimental protocols: “He who proposesto investigate Nature with his mind cluttered withsome preconceived idea does not perform an ex-periment,”8 and again “in physics, he errs who in-stead of questioning Nature tries to intuit her.”9

Spallanzani aims these lapidary phrases as thosewho “have not too good a mastery of the difficult

art of observing well,” that is to say, in his opin-ion, Needham and Buffon. We too, who have madebiological experiment our profession should alwaysfeel this epistemological concern so well expressedin Spallanzani’s text.

Voltaire (Francois-Marie Arouet, 1694–1778)also entered the dispute with all the irony of whichhe was capable. Having received from Spallanzania copy of the Opuscoli di Fisica Animale e Vegeta-bile, he wrote in a letter to the Marquis ofVillevieille, dated from Ferney, August 26, 1776,“Would you believe that an Irish Jesuit has fin-ished by putting weapons in the hands of atheis-tic philosophy, sustaining that animals formthemselves. In brief, it has been necessary forSpallanzani, the best observer in Europe, to dem-onstrate unequivocally the fallaciousness of theexperiments of that imbecile, Needham. Believeme, my dear Marquis, there is nothing good inatheism.” Voltaire was mistaken: Needham was

Fig. 10. Title page of Spallanzani’s Opuscoli di FisicaAnimale e Vegetabile (Modena, 1776). Library of the Depart-ment of Animal and Human Biology, Rome University “LaSapienza.”

8“Chi discende ad interrogar la natura col capo preoccupato perqualche preferita sua ipotesi non fa Esperimento.” (L. Spallanzani,Opuscoli di Fisica Animale e Vegetabile, Tomo I)

9“…nella cose Fisiche per lo più sgarra, quando in vece di interrogarla Natura presumiamo d’indovinarla.” (L. Spallanzani, Ibidem)

Fig. 11. Table from the first volume of the Opuscoli ofLazzaro Spallanzani. Library of the Department of Animaland Human Biology, Rome University “La Sapienza.”

LAZZARO SPALLANZANI 189

neither a Jesuit nor Irish and, above all, he wasnot an imbecile. Two things, however, in Voltaire’sjudgement are exact: Spallanzani was the keen-est observer in Europe, and there is nothing goodin atheism.

NATURAL FERTILIZATION ANDARTIFICIAL INSEMINATION

After studying the organisms in infusions for 14years, Spallanzani was convinced that he had ter-minated definitively the chapter on spontaneousgeneration. As early as 1771 Spallanzani had be-gun to interest himself in the phenomenon of fer-tilization. He had published some first observationsin the Prodromo di un’opera da imprimersi sulleriproduzioni animali (Spallanzani, 1768b), but hewent into the problem in some detail in the secondof his Opuscoli di Fisica Animale e Vegetabile(Spallanzani, 1776). As a good, convinced ovist heinterpreted the little spermatic worms as parasitesin the seed, perhaps transmitted from one genera-tion to the next, as Vallisnieri thought happenedwith intestinal worms. Spallanzani was sure thatthey played no part in fertilization, a function heattributed to the seminal fluid.

With these theoretical assumptions, but withoutpreconceptions, Spallanzani set to work experimen-tally. He had observed spermatic animalcules inmany animals: various mammals, including man,fish and amphibians. Thus equipped with direct per-sonal experience, not basing his words on descrip-tions by previous authors, he could write: “For manyyears I had no longer read their discoveries aboutspermatic worms, therefore, I had only general ideasabout them. I should have liked even to cancel thosegeneral ideas from my memory in order to approachthe research as a Tabula rasa, myself open only tothe sense of sight, without concerning myself aboutthe discoveries of others.”10 For his first experimenthe chose amphibians.

Réaumur (Fig. 12), or rather his collaboratorMademoiselle Moustiers, the fine draughtswomanwho executed the illustrations for his Mémoirespour servir á l’Histoire des insectes had observedthat during the act of mating there issued fromthe cloaca of the male frog a jet of liquid “like thepuff of smoke from a pipe.” In 1736 Réaumur,

together with the Abbé Jean-Antoine Nollet (1700–1770), put into effect an experimental stratagem(Torlais, ’39a,b). He tried to enclose the “posterior”of the male in drawers made of various materials,pig’s bladder, taffeta, etc. The two naturalists in-tended on the one hand to collect the sperm and onthe other to verify whether this strange garmentcould prevent the fertilization of the eggs. Unfortu-nately Réaumur met with no success because thefrogs did not tolerate the unaccustomed garb andfreed themselves of it. Spallanzani was more care-ful in experimenting, more patient in observing, orperhaps, only luckier. Repeating Réaumur’s experi-mental set-up he succeeded in collecting a few dropsof sperm inside the drawers with which he hadclothed some green toads. To verify the real natureof this liquid, in subsequent experiments he wettedwith it some virgin eggs and obtained their com-plete development. Spallanzani repeated this experi-ment several times using different amphibianspecies, taking the sperm directly from the testisor from the vas deferens. He always obtained com-plete development of the eggs.

It must, however, be recalled that in artificial in-semination Spallanzani was preceded, perhaps bya year, by the Baron Weltheim von Harbke, whopracticed it in trout and salmon. It was Bonnet whogave the news of this to his Italian friend.11

In the article “Fecondazione Artificiale” (Artifi-cial Fertilization) he wrote for the EnciclopediaItaliana, Spallanzani wondered whether the prac-tice could be applied to viviparous creatures. Itseems that in reality the Arabs already practicedartificial insemination in horses in the MiddleAges (about A.H. 700), but this was not known inSpallanzani’s day. Our biologist made the experi-ment on a little dog, to be precise a female poodle.More than the audacity of the experiment, espe-cially performed by a priest, is the scientific cor-rectness with which it was conducted. The bitchwas not primiparous, therefore, her fecundity wascertain. She was kept segregated in a place towhich only Spallanzani possessed the key andfrom behavioral signs well-known to breeders, thephase was awaited when the bitch would be onheat and seeking the male, the phase most propi-tious for insemination. The seed spontaneously

10“Era da molti anni ch’io non aveva rivedute le loro scoperte suivermicelli spermatici e conseguentemente non mi restavano deipensamenti di questi naturalisti che le nozioni più generiche, le qualiavrei anche voluto cancellare dalla memoria, e così trovarmi cometavola rasa in queste ricerche per essere più adattato nel ricever leimmagini che mi venivano dal senso dell’occhio, senza preoccupazionedelle altrui invenzioni.” (L. Spallanzani, Opuscoli di Fisica Animalee Vegetabile, Tomo II)

11“Je viens de lire dans la seconde partie du tome XXXV de laBibliothèque des Sciences un extrait du tome XX des Mémoires del’Academie de Prusse, où se trouve un fait que nous intéresse tousdeux. Le voici. ‘Exposition abrégée d’une fécondation artificielle destruites et de saumons, qui est appuyée sur des expériences certaines,faites par un habile Naturaliste’ par M.r. Gleditsch, traduit del’Alemand.” (C. Bonnet, letter to L. Spallanzanini, dated “de maRetraite le 13 Janvier 1781”)

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emitted was collected and conserved at 30° Réau-mur. After injection of the seed into the vagina,the poodle was again kept sequestered until thesigns of pregnancy became unmistakable. Sixty-two days after injection of the seed, the animallittered three pups; two males and one female.

I have some doubts about the spontaneity ofthe sperm emission affirmed by Spallanzani. Heis forgiven the fib because it would have been em-barrassing to admit that a priest had mastur-bated a dog! Our incomparable Abbé is at thezenith of felicity: “I have succeeded in fecundat-ing a quadruped. The happiness I have had fromthis is among the greatest of my life, since I dedi-cated myself to experiment.”12 Bonnet, promptlyinformed of the event, wrote to his friend: “Thisis one of the most interesting new novelties thathave ever been offered for the consideration ofnaturalists and philosophers since the Creation….There is nothing finer or more original than thisexperiment. You have in your hands a preciousthread that will lead you to the most important

and un-thought of discoveries. And it is not im-possible that one day your discovery will find ap-plications in the human species of which we darenot think, the consequences of which would cer-tainly not be slight. You understand me….” (Bon-net, 1781).13 What would Bonnet, the strict Calvinisttheologian, have thought about the present-daypractices of assisted fertilization in man?

Probably this prospect did not interest Spallan-zani. For him, artificial insemination was an ex-perimental tool for investigating the intimatenature of the problem of generation. What is thenature of the “fertilizing virtue” of the sperm?

EXPERIMENT ON FILTRATION OFSPERM: A MISSED OCCASION

In the second of his Opuscoli di Fisica Animalee Vegetabile (1776), Spallanzani reports some tens

Fig. 12. Portrait of René-Antoine de Réaumur and the titlepage of his Mémoires pour servir á l’Histoire des Insects

(Amsterdam, 1737). Library of the Department of Animal andHuman Biology, Rome University “La Sapienza.”

12“Così a me riuscì di fecondar questo Quadrupede, e la contentezzach’io n’ebbi posso dire con veritá che è stata una delle maggiori cheprovato abbia in mia vita, dopodiché mi esercito nella sperimentaleFilosofia.”

13“C’est lá une des plus grandes et des plus intéressantes nouve-autés qui se soient offrtes aux yeux des naturalistes et des philosophesdépuis la Création du monde. […] Vous tenéz un fil précieux qui vousconduira aux découvertes les plus importantes et les plus imprévues.Je ne sais même si ce que vous venez de découvrir n’aura pas quelquejour dans l’espèce humaine des applications auxquelles nous nesongeons et dont les suites ne seront pas légères. Vous pénétrez assezma pensée.” (Letter of C. Bonnet to L. Spallanzani dated “de ma Soli-tude, le 13 Janvier 1781”)

LAZZARO SPALLANZANI 191

a certain quantity of toad sperm on a watch glass.In the bottom of another glass that he turned up-side down to cover the first, he stuck a dozen eggsof the same species. The eggs, however, remaineda few millimeters apart from the sperm. After fivehours the eggs were covered “as if by a dew,” fromthe condensation of the evaporated seminal fluid,but the eggs did not develop. He repeated the ex-periment several times, reducing the distance be-tween the sperm and the eggs, joining the twoglasses together with putty, or allowing air to cir-culate freely inside the system. The result wasalways the same.

So, the spermatic aura did not exist. Fertiliza-tion took place by physical contact between theeggs and the sperm. It remained to be clarifiedwhich fraction of the sperm was the active partin fertilization. With this aim, from 1781 onwardsSpallanzani conducted a series of experiments inthe filtration of spermatized water, that is, spermmuch diluted with water. The fertilizing power ofthis water diminished progressively in proportionto the thickness and the number of the filtersused, finally disappearing altogether. The fractionactive in fertilization remained trapped in the fil-ters, and so was material. Spallanzani counter-checked: He washed the filters with water andthis water used for filter washing then acquiredthe fertilizing property. It would have been enoughto examine this water under the microscope. Hewould have seen in it the abhorred “little sper-matic worms,” and resolved an old dispute. Hedid not do it.

Nearly 40 years later, the sperm filtration ex-periment was repeated by two young French bi-ologists, Jean-Louis Prévost (1790–1850) andJean-Baptiste-André Dumas (1800–1884). They,however, studied at the microscope the water inwhich the filters had been washed and saw in itthe spermatozoa, which they observed also in thegelatinous coats of amphibian eggs (Dumas, 1825).

THE JUMARTS, OR THE PROBLEM OFHYBRIDIZATION

Maupertuis (1745) wrote: “If all the animals ofa single species were already formed and con-tained within one father or one mother, respec-tively in the form of worms or eggs, would thesesimilarities be observed with both parents? If thefoetus were the worm that swims in the seminalliquid of the father, why should it sometimes re-semble the mother? Would a foal already formedin the mare’s egg develop a donkey’s ears becausea donkey had set in motion the parts of the egg?”

Fig. 13. Front page of the Dissertazioni di Fisica Animalee Vegetabile by Lazzaro Spallanzani (Modena 1780). Libraryof the Department of Animal and Human Biology, Rome Uni-versity “La Sapienza.”

of experiments on amphibians regarding the fer-tilizing power of the sperm. He detected thesperm, cooled it, heated it, and tried even to mea-sure the unitary dimension to be attributed to thesperm for it to fertilize an egg. Through compli-cated calculations based on assumptions unrelatedto the reality we know today, he arrived at thedetermination that the dimensional ratio betweenthe “spermatic particle” and the egg had to beabout one to 1 billion. For the eggs and sperma-tozoa of amphibians this value is not so far frombeing correct.

The most important experiments, for their in-trinsic epistemological significance, were those onthe nature of the fertilizing power. The accepteddoctrine at that time was that of the aura semi-nalis or aura spermatica, a sort of vapor emanat-ing from the sperm. Spallanzani, therefore, placed

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The preformist physiologists’ answers to thisobjection were never convincing. It must be saidthat in the eighteenth century hybridization be-tween different species was an accepted possibil-ity; not only between horse and ass, but also inimagination between mare and bull and betweenstallion and cow. This hypothetical cross-breed-ing would have given birth to the Jumarts inwhose existence Spallanzani (1775) believed un-reservedly on the strength of the report by ClaudeBourgelat, Inspector General of the School of Vet-erinary Science of France, who affirmed that hehad produced them several times. Buffon showedhimself more cautious, and biologically less inex-pert. In Volume XIV of his Histoire naturelle,Buffon reports that he had had occasion to ob-serve and to dissect one of these Jumarts and tohave come to the conclusion that it was a com-mon hinny.

Spallanzani had long been interested in theproblem of hybridization. He began to concernhimself with it in a short bibliographical publica-tion (Spallanzani, 1768c), Memorie sopra i mulidi vari autori in which he set out the state of theart in the question. But when he obtained the ar-tificial insemination of the poodle, he thought thathe had the right instrument for proceeding to ex-perimentation. Bonnet, in the letter alreadyquoted (Bonnet, 1781) is prodigal of advice: “Nowyou possess a sure and easy mean of determinewhether this or that species and this or that othercan procreate together […] you could try, by in-troducing through your syringe the sperm of apoodle into the uterus of a cat or a rabbit, or byintroducing the sperm of a cat or a rabbit intothe uterus of your poodle.”14

Today it is difficult not to smile at these pro-jected experiments. It seems absurd to us to thinkthat biologists of the quality of Bonnet andSpallanzani could think of producing a hybrid be-tween dog and rabbit. But in that bizarre, con-tradictory eighteenth century, the possibility ofcrossing a mare with a bull was accepted withoutdiscussion. Some even considered it possible tocross a rabbit with a hen. The great Réaumur(1749) discussed this in all seriousness, report-

ing that the experiment had been attempted by acertain Abbé Fontenue.

In the wake of his success with dogs, Spallan-zani (1783) attempted to cross dog with cat, andobviously failed. He had a project of crossbreed-ing a she-ass with a bull, to obtain the mythicalJumart, but never carried it out. He was moreoccupied (Spallanzani, 1780) with his experimentson the amphibia, more easily handled and whichhe already had used in experiments in fertiliza-tion. He attempted hybridization between urode-les and anurans, and between anurans of differentfamilies, Hylidae, Ranidae, Bufonidae, and Peloba-tidae, without achieving any success. He concludedthat crossbreeding between “batrachians” of dif-ferent species was not possible. The error inSpallanzani’s experimental approach was to at-tempt crosses between species systematically re-mote from each other, as was pointed out byArthur de l’Isle (1873), who a century afterSpallanzani’s experimentation succeeded in cross-breeding various congeneric anuran species.Spallanzani worked with species whose gametesmatured in the same period of the year, and couldnot have done otherwise.

LES COLIMAÇONS DU RÉVÉRENDPÈRE L’ESCARBOTIER

We come now to the problem of the regenera-tion of parts of animals, which, as we said at thebeginning, is situated in the context betweenpreformism and epigenesis.

One may well say that the problem of regen-eration, or “animal reproduction” as it was calledthen, was among the first that Spallanzani inves-tigated experimentally, starting in 1765. He pub-lished his first results of these experiments in hisProdromo di un opera da imprimersi sopra leriproduzioni animali (Spallanzani, 1768b). Thistheme in experimental biology was opened in sci-entific terms by Réaumur (1712), who describedthe regeneration of claws, nippers, and antennain various crustacean species. But if the claws ofcrustaceans did not present excessive philosophi-cal problems, the regeneration of an entire hydrafrom a fragment of it, described by Trembley(1744) (Fig. 14), unleashed a succession of disputeson the naturalistic plane—for example, if the littlecreatures were animals or plants—and also on themetaphysical and theological plane. What happensto the soul of the polyp? In which of the two frag-ments does the soul remains? If it remains in oneto animate the process of regeneration, how doesthe other fragment, in which it must be lacking,

14“Vous possedez á present un moyen bien sûr et bien facile devous assurer si telle ou telle espèces peuvent procréer ensemble etles espériences que vous-vous proposés […] ne vaudront pas cellesque vous tenteriez entroduissant avec votre seringue le sperme de cebarbet dans la matrice d’une lapine ou d’une chatte, et introduissantle sperme du lapin ou du chat dans la matrice de la chienne. ” (Let-ter of C. Bonnet to L. Spallanzani dated “de ma Solitude, le 13 Janvier1781”)

LAZZARO SPALLANZANI 193

manage to regenerate? One must, then, admit thatthe soul is not indivisible, but that it may be di-vided in two to make the two fragments regener-ate. In this argument, which today seems ridiculous,intervened the most famous naturalists of the time:von Haller, Bonnet, Réaumur, and even, as was onlyto be expected, Voltaire. Voltaire upheld the veg-etable nature of the hydra and so resolved the prob-lem simplicistatically. Bonnet and Réaumur directedtheir studies to the regeneration of the heartworm,of which the animal nature could not be doubted,and of which the regenerative capacities were wellknown. Spallanzani too devoted himself to thisexperimental analysis, but according to very pre-cise experimental protocols he sectioned the bodyof the earthworm at different distances from the

head and succeeded in determining what today iscalled a gradient of regenerative capacity. He di-vided the animal into several parts and noted thatnot only the part with the head regenerates, butalso the caudal part and intermediate fragmentsbetween the two. He even described the regen-eration of regenerated parts. Where, then, is theseat of the earthworm’s soul? But as Bonnet wrotein his Palingénésie “In physics, souls are very con-venient things. They are always available for anyeventuality, since they are invisible, untouchableand unknowable, and we can attribute to themwhatever one wishes.”

Even before publishing his discoveries in theProdromo, Spallanzani communicated them by let-ter to Bonnet (Spallanzani, 1778). The naturalistof Geneva was enthusiastic. He compared his Ital-ian friend to Redi and Malpighi (Bonnet, 1776).15

In that same year that the Prodromo di un op-era da imprimersi sopra le riproduzioni animaliwas published, Spallanzani was elected a mem-ber of the Institut de France. Then this veritablebox of wonders, “une petite boite toute pleine deprodiges,” as Bonnet put it (1768) was openedamong the academicians of France, revealing itsportentous contents. One gem in this collectionwas the phenomenon of the regeneration of snails’heads. The discovery was communicated to theAcadémie des Sciences de Paris and propagatedimmediately to the general public by an article inthe newspaper Avant-Coureur of May 20. The sen-sation aroused by the news was due to the factthat it was not the leg of salamander or the clawsof crab that were regenerated, but the heads ofcomplex organisms. The time had not yet arrivedwhen in Paris crowned heads fell under the guil-lotine without any hope of regeneration, but tothink of heads that could be re-grown from theneck was certainly not bad! Opposing parties wereformed. On one side were aligned those who, hav-ing attempted it unsuccessfully, did not believe inregeneration, and on the other those who did.Among the latter was the great Lavoisier (1743–1794), who although destined to lose his own headunder the guillotine of the Revolution, managedto see a snail’s regenerated. Between 1768 and1770, a great number of snails lost their heads,

Fig. 14. Front page of the Mémoires pour servir à l’Histoiredu Polypes d’eau douce (Genéve, 1744), by Abraham Trembley.Library of the Department of Animal and Human Biology,Rome University “La Sapienza.”

15“Toutes vos observations, toutes vos expériences, toutes vosréfléxions prouvent également vôtre patience, vôtre sacacité et vôtresagesse, Continués comme vous avés commencé. Je puis facilementprédire que vôtre nom sera placé a côté de celui des Redi et desMalpighi, vos illustres compatriottes.” (Letter of C. Bonnet to L.Spallanzani dated Genève, le 9 Octobre [et 1 Novembre] 1766)

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and only a small percentage of them developed anew one.

Spallanzani’s experiment was correctly set upon the basis of an exact knowledge of the animal’sanatomy. He described precisely how to cut it,noted himself that whenever the cerebral gan-glion, which he called the brain, was compromisedthe regeneration did not occur, and so on. Thushe anticipated the criticisms of those who did notobtain regeneration. The cut Spallanzani madewas oblique, not vertical, and others objected thatoperating in this way he cut off the skullcaps, notthe heads. Today we know that the phenomenonis considerably more complex than Spallanzani orthe other naturalists of the eighteenth centurycould imagine. The process involves factors of in-duction and of territorial competence with regen-eration dependent on what species is chosen forthe experiment, since in some Helix, e.g., H.nemoralis, the regenerative capacity is good, whilein others, e.g., H. ericetorum, it is rather limited.

Voltaire, too, began to cut off snails’ heads toobtain, in some cases, regeneration and in othersthe animal’s death, when the cut removed the an-terior ganglion of the periosophageal cingulum.The fantasy and sagacity of the great French phi-losopher are fully shown in his publication on thissubject (Voltaire 1768). The title alone exempli-fies the irony of which he was capable: LesColimaçons du Révérend Père L’Escarbotier, parla grace de Dieu capucin indigne, Prédicateurordinaire et Cuisinier du gran Convent de la Villede Clermont en Auvergne. Au Révérend Père Elia,Carme Chaussé, Docteur en Théologie. The allusionto the Reverend Father Spallanzani is obvious.

Bonnet, who harbored some resentment againstVoltaire, who had reproved him for the mysticismwith which he filled his scientific analysis, alertedSpallanzani: “He is making fun of you!… The poetplays at being a Naturalist”16 (Bonnet, 1768). ButSpallanzani was not of this opinion. In fact,Voltaire did not deny the possibility demonstratedby Spallanzani of regeneration of the head of thosemolluscs: In a letter to Bonnet, Spallanzani(1768d) minimized the episode and concluded:“Voltaire’s book has made the same impressionon me as the greater part of his work: it hasamused me.”17

The question of regeneration of snails’ headsneeded revision and a final word because thesensation it created had been too great. Spallan-zani took the subject up again in two texts(Spallanzani 1782, 1784) that focused exclu-sively on this problem. In the first, he intendedto close the question with a phrase that ex-pressed well his scientific personality: proud,intolerant of criticism by others, and absolutelyconvinced of the merits of his ideas and of hisexperimental tests. “Lo sperimentare comunqueè mestiere di tutti, lo sperimentare a dovere èsempre stato, e sará sempre, di pochi,” i.e., “Toexperiment whatever is work for everybody, to ex-periment as one should is, and always will be,work for few.”

THE INHERITANCE OF SPALLANZANIThe inheritance that Spallanzani left us stands

written in the phrase: the experimental methodas the fundamental instrument for investigatingbiological processes. Certainly in this approach hefollowed the line traced by the physicists of theFlorentine Accademia del Cimento, Galilean in itsapproach, which stated as its motto “Provando eRiprovando”, i.e., try and try again. But Spallan-zani succeeded in making this method an abso-lute discipline. In a text written in his maturityand published posthumously (Spallanzani, 1803b),he wrote almost as a spiritual testament: “This ismy fundamental method, whatever I tackle, eventhe most disparate things, so long as they havematerial causes: to take no account of the opin-ions, however authoritative and respectable, ofthose who have defined them before, but to dedi-cate oneself to a practical examination of thefacts.”18

The need to restrict my contribution to the phe-nomena of reproduction and development hasobliged me to neglect other fundamental worksperformed by Spallanzani, from fundamental oneson digestion (Spallanzani, 1780), and respiration(Spallanzani, 1803), to those on the orientation ofbats (Spallanzani, 1794), on animal electricity, andon marine bioluminescence (Spallanzani, 1794).

16“Elle roule sur vos expériences; vous vous amuserés á voir lepoëte s’ériger en garçon naturaliste, et vous reconnoîtrés qu’il dissertemieux sur un point de litterature que sur un point d’histoirenaturelle.” (Letter of C. Bonnet to L. Spallanzani dated Genthod, Oc-tober 8th 1768)

17“La brochure de Voltaire a causé en moi cette impression quej’eprouve de la plus grande partie de ses ouvrages, c’est á dire ellem’a fait rire.” (Letter of L. Spallanzani to C. Bonnet dated á Modenece 15 Novembre 1768)

18“Tale appunto essendo l’inalterabile mio metodo nelle coseeziandio le più universalmente abbracciate, ma che dipendono daifatti, di prescindere dall’autoritá ancorché rispettabilissima di chi leha stabilite allorquando discendo a un pratico esame de’ medesimifatti.” (Memorie sulla Respirazione, opera postuma dell’Abate LazzaroSpallanzani, Memoria III, § XXXI)

LAZZARO SPALLANZANI 195

Thus the stature of this great scientist mayseem diminished in this text by comparison withthis real greatness. I, however, believe that as ascientist Spallanzani is of a stature equal to thatof William Harvey. In fact, when speaking of thecirculation of blood one cannot fail to mention thegreat English physiologist, in the same way thatwhen tackling a problem by experiment in workingon the biological processes of development, in anybiology laboratory whatsoever, one cannot fail to paytribute to the memory of Lazzaro Spallazani.

ACKNOWLEDGMENTSSpallanzani’s papers are quoted as they appear

in the critical editions recently published, namely:

Le Opere di Lazzaro Spallanzani Pubblicate sottogli auspici della Reale Accademia d’Italia, 5 vols.Milano: Ulrico Hoepli, 1932–1936.

Edizione Nazionale delle opere di LazzaroSpallanzani, 22 vols. edited to date. Modena:Mucchi, 1984–1997.

LITERATURE CITEDAbeloss M. 1942. Sur la régéneration de la tête des Mollus-

ques Gastéropodes. CR Acad Sci, Paris 214:883–884.Adelmann HB. 1933. The “De ovorum Gallinaceorum genera-

tionis primo exordio progressuque et pulli gallinaceicreationis ordine” of Volcher Coiter, translated and edited.Ann Med Hist. New York.

Bonnet C. 1766. Letter to L. Spallanzani dated Octobre 9,1766. In: Di Pietro P, editor. Edizione Nazionale delle operedi Lazzaro Spallanzani, Carteggi, 1984–90. Mucchi: Modena.2:43–51.

Bonnet C. 1768. Letter to L. Spallanzani dated May 25, 1768.In: Di Pietro P, editor. Edizione Nazionale delle opere diLazzaro Spallanzani, Carteggi, 1984–90. Mucchi: Modena.2:76–80.

Bonnet C. 1770. La Plaingénésie Philosophique, ou idées surl’état passé et sur l’état futur des êtres vivants. Genève.

Bonnet C. Letter to L. Spallanzani dated January 13, 1781.In: Di Pietro P, editor. Edizione Nazionale delle opere diLazzaro Spallanzani, Carteggi, 1984–90. Mucchi: Modena.p 2:381–91.

Buffon GL. 1749. Histoire naturelle générale et particulière.Imprimerie Royale, Paris 1749. In: Pivetau J., editor. C.L.Buffon Oeuvres Philosophioques, Vol. 1. Paris: Presseuniversitaires. p 1954.

Clerselier C. 1771. Primae cogitationes circa generationeanimalium. Paris.

De l’Isle A. 1873. Sur l’Hybridation chez les Amphibies. AnnSci Nat, Vol. XVII, fascicule 3.

Di Pietro P. 1984-90. Edizione Nazionale delle opere diLazzaro Spallanzani, Carteggi Vol 5. Mucchi: Modena.

Dumas J-BA. 1825. Génération. Dictionnaire Classiqued’Histoire Naturelle, Tome VII. Paris.

Fabricii ab Aquapendens H. De formatione ovi pennutorumet pulli Padova 1621. In: Opera omnia anatomica etPhisiologica, 1687. Lipsia.

Fontana F. 1768. Letter to L. Spallanzani dated Florence,April 15, 1768. In: Di Pietro P, editor. Edizione Nazionaledelle opere di Lazzaro Spallanzani, Carteggi, 1984–1990.Mucchi: Modena. 4:334–35.

Fontana F. 1792. Lettera ad un amico sopra il sistema deglisviluppi. Firenze.

Galilei G. 1632. Dialogo dove nei congressi di quattro giornatesi discorre sopra i due massimi sistemi nel mondo tolemaicoe copernicano, proponendo ideterminatamente le ragionifilosofiche e naturali tanto per l’una quanto per l’altra parte.Firenze.

Hertwig O. Beitrage zur Kenntniss der Bildung, Befruchtungund Teilung der thierischen Eies. Morph Jahrb 1:347–434.

Malpighi M. 1661. De pulmonibus. Bologna.Maupertius PL. 1745. Venus phisique. Paris.Needham JT. 1750. Nouvelles observations microscopiques,

avec des découvertes intéressantes sur la composition et ladecomposition des corps organisés. Paris.

Needham JT. 1769. Nouvelles recherches sur les découvertesmicroscopiques et de la génération des corps organisés.Paris.

Réaumur, R-AF de. 1712. Observations sur diverses reprpduc-tions qui se font dans les écrevisse, les homards, les crabes&. In: Histoire del’ Academie des Sciences.

Réaumur, R-AF de. 1749. Art de faire écloir et d’énlever entoute saison des oiseaux domestiques de toutes espèces.Imprimerie Royale. Paris.

Redi F. 1668. Esperienze sopra la generazione degli Insetti.Firenze.

Spallanzani L. 1765. Saggio di osservazioni microscopicheconcernenti il sistema della generazione de’ Signori diNeedham e Buffon Modena.

Spallanzani L. 1766. Lettre to C. Bonnet dated A’ Bomporto,près de Modene ce 21 Septembre 1766. In: Di Pietro P, edi-tor. Edizione Nazionale delle opere di Lazzaro Spallanzani,Carteggi, 1984–1990. Mucchi: Modena. 2:25–41.

Spallanzani L. 1768a. Dell’azione del cuore ne’ vasi sanguigni.Modena.

Spallanzani L. 1768b. Prodromo di un’opera da imprimersisopra le riproduzioni animali. Modena.

Spallanzani L. 1768c. Memorie sopra i muli di vari autori.Modena.

Spallanzani L. 1770. Fecondazione artificiale. In: Prodromodella nuova enciclopedia Italiana. Siena.

Spallanzani L. 1770. Lazari Spallanzani in Regio TicinensisGymnasio publici naturalis historiae professoris prolusio &.Modena.

Spallanzani L. 1773. De’ fenomeni della circolazione osservatanel giro universale de’ vasi, de’ fenomeni della circolazionelanguente, de’ fenomeni del sangue indipendenti dall’azionedel cuore e del pulsar dell’arterie dissertazioni quattro.Modena.

Spallanzani L. 1776. Opuscoli di Fisica Animale e vegetabile[…] aggiuntevi alcune lettere relative ad essi opuscoli dalcelebre Signor Bonnet di Ginevra e da altri scritte all’Autore.Modena.

Spallanzani L. 1780. Dissertazioni di Fisica animale evegetabile, Modena.

Spallanzani L. 1782. Risultati di esperienze sopra la ripro-duzione della testa nelle lumache terrestri. In: Memprie diMatematica e Fisica della Societá Italiana, Tomo I. Ramaz-zini: Verona. p 581–612.

Spallanzani L. 1783. Lettera dell’Abate Spallanzani al sig.marchese Lucchesini. In: Opuscoli scelti sulle scienze e sulle

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arti, tratti dagli Atti delle Accademie, Tomo VI, parte II.Marelli: Milano. p 73–104.

Spallanzani L. 1784. Memoria seconda ed ultima sopra lariproduzione della testa nelle lumache terrestri. In: Memoriedi Matematica e Fisica della Societá Italiana, Tomo II, parteII. Ramazzini: Verona. p 506–602.

Spallanzani L. 1784. Memoria sopra le meduse fosforiche. In:Memorie di Matematica e Fisica della Societá Italiana.Ramazzini: Verona. VII:506–602.

Spallanzani L. 1794. Lettere sul volo dei pipistrelli acciecati.In: Giornale de’ letterati. Mugnaini: Pisa. CXIII:120–186.

Spallanzani L. 1803a. Mémoires sur la respiration par LazareSpallanzani traduits en français, d’après son manuscritindit, par Jean Senebier. Paschoud, Genève.

Spallanzani L. 1803b. Memorie sulla Respirazione, operapostuma dell’Abate Lazzaro Spallanzani. A. Nobile: Milano.

Torlais J. 1939a. Réaumur, un esprit encyclopédique en de-hors de l’ Encyclopédie. Desclée de Brouwer: Paris.

Torlais J. 1939b. Réaumur, Morceaux choisis, présentés etannotés par J. Torlais. Gallimard: Paris.

Trembley A. 1744. Mémoires pour servir á l’Histoire du Polyped’eau douce. Genéve.

Vallisneri A. 1721. Istoria della generazione dell’Uomo edegli animali se sia da’ vermicelli spermatici o dalleuova. Venezia.

Voltaire F-MA. 1768. Les Colimaçons du Révérend PèreL’Escarbotier, par la grâce de Dieu capucin indigne,Prédicateur ordinaire et Cusinier du gran Convent de laVille de Clermont en Auvergne. Au Révérend Père Elia,Carme Chaussé. Docteur en Théologie. Paris.

Wolff CF. 1759. Theozia generationis Halae and Salam, pub-lished 1774.