Jan Swammerdam's frogs

Abstract

Having discussed insect metamorphosis at length, Jan Swammerdam's Bybel der Natuure (1679/1737) reached its climax with a substantial description of the generation and muscular activity of frogs. This paper explores the rhetorical role of frogs in Swammerdam's ‘great work’, showing how they were the Archimedean point from which he aimed to reorder all of creation—from insects to humans—within one glorious, God-ordained natural history and philosophy. Swammerdam linked insects to frogs through a demonstration that all underwent epigenesis; and frogs were then linked to humans through a demonstration of their identical muscular activity. The success of Swammerdam's strategy required a theological reconstruction of the frog, traditionally an ungodly creature, such that trustworthy knowledge could be obtained from its body. Perhaps surprisingly, this act of theological cleansing is shown to be somewhat prefigured in the distinctly non-experimental natural history of Edward Topsell (1608). The paper also examines Swammerdam's interactions with the mystic Antoinette Bourignon, and his challenges in reconciling a spirituality of meletetics with a material epistemology in natural philosophy. Differences are revealed between the natural analogies given by Swammerdam in his published and unpublished writings, undermining to a certain extent the triumphal insect–frog–human rhetorical structure of the Bybel.

Introduction

Popular histories of neurophysiology frequently discuss how its pioneers, notably Galvani, developed the science through their experiments on frogs. Although true on a literal level, such accounts have the unfortunate effect of implying that the discovery of organic electricity was the aim, or even the foreseen outcome, of the earliest experiments. What I want to do in this paper is to begin by travelling in imagination to that moment when the frog first lay on the philosopher's table, without any preconceptions about historical outcome.

Once we begin, as these philosophers did, with the frog, a different set of questions begins to suggest itself. What would a natural philosopher be doing with a frog on his bench, or under the microscope, in the first place? Where might he have got it from? Was it difficult to obtain, to keep? What thoughts would naturally occur to him as he looked at the frog, and how might these affect what he did with it, or how he wrote about it? The physical demands of finding, keeping and experimenting with frogs, and their theology and folklore, all inflected the science produced from them.¹

This observation—that the frog, not the science, comes first—suggests a re-examination of the frogs of Jan Swammerdam (1637–80), the Dutch naturalist, anatomist, microscopist, naturalist and philosopher. With the possible exception of Marcello Malpighi, who investigated the lungs of frogs anatomically during the 1660s, Swammerdam was the first person to make extensive experimental use of frogs. As a student in Leiden (1662–63), Swammerdam had—like Malpighi—used frogs in respiratory experiments.² However, his major work on the creatures occurred in the late 1670s, the final years of his life, and thanks to these latter experiments he has been identified as the person who put the study of nerves and muscles on a rational, materialist basis.³ This paper analyses the rhetorical use of frogs within Swammerdam's final work, the Bybel der Natuure [Bible of Nature], arguing that they were not primarily intended to advance a rational, materialist account of muscles, but rather formed a ‘missing link’ in his theology of nature. Frogs were the Archimedean point that enabled Swammerdam to subsume both the lowest animals and man himself within one glorious, God-ordained natural history and philosophy.⁴ Along the way this entailed a dismissal of generation by putrefaction, the major theological way of thinking about frogs and certain other animals low down in the scala naturae. It also entailed an engagement with Cartesian debates about physiology and the philosophy of mind, and threw up challenges concerning the precise human analogues that frogs might suggest.

The production and context of the Bybel der Natuure

Swammerdam's frogs feature principally in his Bybel der Natuure, published in Leiden in 1737.⁵ The Bybel was compiled posthumously from Swammerdam's collected manuscripts by Herman Boerhaave, who chose the title in sympathetic reference to a phrase used by Swammerdam in a letter to his supporter Melchisédech Thévenot.⁶ Boerhaave's sources for the Bybel were fourfold. There were annotated versions of two previously published books, the Historia Insectorum Generalis (1669) and Ephemeri Vita (1675); and there were two unpublished manuscripts, one on bees and one on frogs. The work on frogs was done in the very last years of Swammerdam's life and set the capstone on what he himself called ‘een groot werk’ [a magnum opus].⁷

Unpublished archival work conducted by Matthew Cobb at the University of Leiden indicates that Boerhaave followed Swammerdam's intentions extremely closely in the structure of the book, and that the version we have is pretty much as it would have been had Swammerdam lived to see it published. One piece of evidence for the book's being as Swammerdam intended it is that at the end of several of the manuscript sections of the book, the title of the subsequent section is written in Swammerdam's hand.⁸ These correspond with the order of the sections in the published book. Another piece of evidence is that the manuscript figures and plates are also numbered in Swammerdam's hand. Because these are referred to in the correct order throughout the published book, they represent a clear ordering of the entire content, planned by Swammerdam and adhered to by Boerhaave. Some sections of the book also have a plan or order of contents written out in Swammerdam's hand.

What we have in the Bybel, then, is a carefully structured argument that follows the four types of insect metamorphosis laid out in the Historia Insectorum Generalis, but containing new research and climaxing, crucially, with new material on frogs.⁹ These comparisons were summarized in a table comparing the development of the frog with the four types of insect and—of which more later—a carnation (figure 1). The English translation of the comparative table rather lessens the force of the original Dutch. In the English version, the fifth stage of development is referred to as a ‘nymph’ in every case except for that of the frog, where it is referred to as a tadpole. In the original Dutch the worm of the frog develops into a ‘Vorsch-popken’ or ‘little frog-nymph’, popken (nymph/chrysalis/pupa) being used for every one of the six types, including the flower. The table had been printed in the Historia but here in the Bybel, for the first time, was detailed evidence on frogs to warrant their comparison with the other creatures. It was to be the great work's grand finale.¹⁰

Figure 1.

Swammerdam's table of comparison from The Book of Nature, part II, pp. 137–138. (Copyright © British Library Board (459.e.4); reproduced with permission.)

In terms of context, there were major personal and national upheavals that are candidates to help explain the development of Swammerdam's science between the publication of the Historia Insectorum Generalis in 1669 and his death in 1680. Nationally, 1672 was het Rampjaar, the year of disaster at the onset of the Franco-Dutch War (1672–78). Further from Swammerdam's door, the Third Anglo-Dutch War (1672–74) also rumbled on during this period. However, one struggles to find evidence for all this impinging upon Swammerdam's science. What seems to have been of much greater significance was the beginning of his relationship, in 1673, with the self-dubbed prophetess Antoinette Bourignon (1616–80). Bourignon is routinely described as a mystic, and indeed dramatic visions marked the beginning of her vocation. However, by the time that Swammerdam came across her she was best known for her biblical exegesis, produced in a network of private correspondence and put into printed circulation by her followers.¹¹ Bourignon preached the arrival of end times and a consequent need for extreme piety, maintaining a clever balance between stating that illumination was open to all while simultaneously satisfying her followers' psychological need to be led by one of superior insight. She had a small community of disciples living with her, but her main public platform was her writing.¹² After beginning a correspondence with Bourignon in 1673, Swammerdam went to join her Schleswig community in September 1675. Six months into his stay, he and another disciple were sent on a mission to Copenhagen to try and obtain the Danish King's protection for Bourignon's group. Swammerdam was unhappy living in Bourignon's company and returned to live with family members in June 1676.

Historians have struggled to reconcile the ‘religious’ and ‘scientific’ aspects of Swammerdam's life. His apparent credulousness regarding Bourignon sits uneasily for them with his supposed role as the harbinger of neurophysiology. Swammerdam's most dedicated scholar, G. A. Lindeboom, seemed to believe that his science was a doomed enterprise once he had encountered Bourignon, consoling himself merely that it had ‘failed to perish [completely] under the conflict between faith and science’. Lindeboom went on, disappointed: ‘[Swammerdam] … learned to give up his ambition, but he considered it now as his life-task to show the greatness of God in the works of the infinitely small living beings.’¹³

Swammerdam's relationship with Bourignon was longer and more complex than previous historians of science have implied.¹⁴ For one thing, as Mirjam de Baar has discovered, his correspondence with Bourignon went on longer than commonly supposed, continuing for at least a year after his return to Amsterdam. It is certainly true to say that Swammerdam had been distracted from what he stated, at the end of the Historia Insectorum Generalis, was to be his next project: namely further developmental experiments on the wings and coloration of butterflies.¹⁵ And it seems correct that he burned his writing on the silkworm at Bourignon's instruction (although not the plates, which had already been sent on). But even so, neither of Lindeboom's claims is quite true. Swammerdam's desire to demonstrate God's greatness in the world of tiny animals was an old ambition, predating his contact with Bourignon;¹⁶ and even after meeting her he maintained his characteristically early-modern, pugnacious attitude in relation to his discoveries.

Moreover, Swammerdam by no means capitulated easily to Bourignon's leadership, especially after he had met her in person. Many aspects of her community were a disappointment to him. He disliked her patronizing attitude, her slovenly housekeeping (dirty linen and greasy plates were a particular concern), and her unreasonable insistence on her knowing the will of God in the most trivial of matters (such as which kind of candles to purchase).¹⁷ Swammerdam could only keep the faith by reading and re-reading her writing. ‘If I did not have recourse to your writings, I should most certainly conclude that you are in a state of spiritual arrogance, with a serious case of pride that causes you to pass off your human actions as acts of divine wisdom.’¹⁸ Such a reliance on the written word did not sit easily with Swammerdam, who in Historia Insectorum Generalis had written a substantial defence of the experimental method as a means of knowing—in explicit opposition to the practice of citing the written word of that ‘infinity of philosophers’ who ‘neglect experiment and follow blind reason and the idle fancies of their minds’.¹⁹

Swammerdam had sympathy, perhaps, with Bourignon's scrutiny of the book, sharing a similar attitude in his reading of the book of nature.²⁰ Like Bourignon he rejected the idea that the ancients or even more recent authorities had the best perspective on truth; it could be improved by anyone through a process of humble scrutiny. In particular Swammerdam has been identified as a follower of Boyle, whose works were widely translated into Dutch.²¹ Boyle's ‘meletetics’, his reading of the book of nature, was notably similar to Swammerdam's.²² Essentially meletetics involved a meditative ‘reading’ of natural and made entities for their lessons in piety—generally through analogy rather than natural theology.

Bourignon, too, seemed to engage in a process of accommodation with Swammerdam. She apparently came to value his science somewhat, at least for the advantages it might bring her. One of Swammerdam's books was sent on as a gift to one potential ally, and on two occasions Bourignon urged Swammerdam to perform an anatomization to gain admittance to the King of Denmark's court and win his favour.²³ Elsewhere she conceded that Swammerdam's verse (presumably in Ephemeri Vita) was good, at least for those who had already received the light that would enable them to understand it truly.²⁴ In this same letter she rejoiced that ‘in these last days [the Holy Spirit] will teach all truths to men of goodwill, as much regarding nature as regarding grace’.

It was against all this background that, in the spring of 1678, Swammerdam harvested frogs' eggs and began the investigations that would take a key place in his self-proclaimed great work.

From insects to frogs via epigenesis

When a biblically aware early modern such as Swammerdam saw a frog, he saw something that was theologically problematic. Frogs featured just twice in the [original] Bible, both times in a bad light. They were one of the 10 Mosaic plagues, and reappeared in the book of Revelation as unclean spirits appearing from the mouth of the dragon, the beast and the false prophet.²⁵ In folklore, frogs were both the familiars of witches and ingredients in their spells. In 1645, for example, a witch found to have had an imp in the form of a frog was hanged in Cambridge.²⁶

Frogs carried their negative theological connotations into natural philosophy via theories about their generation. They were included with flies and other lowly creatures as animals whose creation could occur spontaneously through putrefaction, and therefore could be counterfeited by witches. Aristotle noted that some animals generated spontaneously, especially from putrefaction. Generally it was insects that were thus produced, as, for example, from a corpse. When these creatures then reproduced normally—that is, sexually—they produced imperfect forms, meaning that they had to metamorphose to reach their final, adult form. Thomas Aquinas gave the question of corruption and putrefaction a theological spin: the body's tendency to undergo this process was in contrast to the incorruptibility of the soul. This Thomist theology of the corruptible body was encapsulated in Ecclesiasticus 10:11: ‘For when a man is dead, he shall inherit creeping things, beasts and worms.’ It was given physical instantiation by the late medieval fashion for decorating tombs with images of bodies corrupted by worms, snakes and frogs.²⁷

In his History of Serpents (1608) Edward Topsell observed in a similar vein that frogs' organs were ‘corrupted’ and gave an account of how some of them are engendered ‘by carnal copulation’ (the godly method) and others ‘of the slime and rottennesse of the earth’ (the demonic).²⁸ Topsell's book has been dismissed as a mere plagiarism of Conrad Gesner's sixteenth-century Historiae Animalium.²⁹ Although it freely reuses Gesner's source material, the History of Serpents does, however, do some important original work in analysing it. Topsell was most concerned in his account of frogs to distinguish between what he considered their ‘natural’ and their ‘magical’ properties. The latter had no place in true learning; he dismissed one magical anecdote with the robust judgement that ‘this is as true as [that] a shoulder of Mutton worn in one's Hat healeth the tooth-ach’.³⁰ Another early-modern frog-factoid asserted that a water-frog's tongue, when laid upon a sleeping person, would cause him to blab his secrets while he slept. Topsell had no truck with this either: ‘Now if this magical foolery were true, we had greater need of frogs than of Justices of the Peace or Magistrates.’³¹

Yet this was no proto-scientific conclusion; to the modern reader, Topsell's examples of the natural properties of frogs are scarcely distinguishable from their magical ones. In one particularly splendid recipe (recycled from Albertus Magnus), Topsell explains how one should burn young frogs, put the resulting powder inside a cat, remove the cat's bowels, roast the cat, anoint it with honey and lay it beside the woods. Thus, he assures his reader, all the wolves and foxes will be lured out for killing.³² Physicians, who might be expected to operate in the realms of the material, will find that their healing frog-broths work best if their ingredients are withheld from the patient.³³ To modern ears, this method sounds more magical than that used by Topsell's witches, who did not make spells with frogs but simply used their venom to poison their husbands.³⁴

One quickly comes to realize that hidden powers and sympathies were very much a part of Topsell's world.³⁵ His distinction between natural and magical phenomena was not ontological but rather theological. Natural things are in harmony with God's order, whereas magical things go against it and are to be rejected. Hence, the witches make magical use of frogs for the purposes of murder, even if the process—poisoning—seems relatively ordinary. Doctors, in seeking to heal, do God's work, even through obscurantist means.

Women giving birth to frogs, however, presented a particular problem for Topsell.³⁶ This was because it was an instance of nature—supposedly under divine control—spontaneously behaving in magical fashion. The women had not sought out their misfortune. Or had they? Topsell noted that Roman Catholics were particularly subject to this problem, hinting that there might be some connection with the unclean spirits of Revelation and worship of the whore of Babylon. His other resolution to this difficult theological problem was to observe that the women concerned generally made a swift and full recovery, restoring things to their natural order.

Swammerdam's desire to disprove spontaneous generation in the Bybel was also theological in nature. Swammerdam wanted above all to demonstrate the unity of God's creation; to show that all was made with equal care and worked in the same, divine-natural way. ‘All God's works are governed by the same rules’, he asserted.³⁷ Swammerdam found something both theologically and aesthetically displeasing in the notion that God might create some creatures according to one law, and others to another. He offered multiple arguments to make his case, including the fact that even the largest animal is, at its first formation, no bigger than an ant. Indeed, the ant, Swammerdam pointed out in oblique reference to the proverbs of Solomon, is venerated for its diligence, and thus it chides those who would place man and the higher animals in a superior category. It was almost a kind of theological Occam's razor for Swammerdam to presume that all must be created by like means.

Swammerdam was dismayed at the recently published generational science of William Harvey, which claimed that there were two types of animal development: metamorphic and epigenetic.³⁸ The former were animals that appeared from the beginning of their development in their final form, whereas the latter developed their different parts gradually and separately. Harvey put insects in his category of lower animals, and ‘the more perfect animals with red blood’ (such as the noble lion and cock) were examples of animals produced by epigenesis. According to Swammerdam's gloss on Harvey, metamorphosis was dangerously close to the doctrine of generation by putrefaction, and thence to atheism:

we may easily see how rash and precipitate their opinion is, who esteem the larger creatures only as perfect, and the less as scarce worthy to be classed with animals; but, as they say, produced by chance, or generated from putrefaction; rendering, by such reasoning, the constant order of nature subject to chance.³⁹

Swammerdam would use the frog to blur the distinction between Harvey's ignoble and noble animals, and thus to reassert the dominion of divine law over all creation.

Before we turn to this part of Swammerdam's argument, however, the reader may well wonder whether Swammerdam was genuinely concerned that some people might believe in the atheistic doctrine of generation by putrefaction, or whether the charge of atheism merely provided a convenient rhetorical basis for attack on Harvey. It seems that generation by putrefaction was still a plausible phenomenon even around the time when Boerhaave was preparing Swammerdam's Bybel for publication. This may be seen in Jean Rousset de Missy's contemporary account of the sea-worms infesting Dutch ships.⁴⁰ Such ‘swarming vermin’ were likely candidates for generation through putrefaction, due both to their destructive and to their horribly prolific nature. The mystery of the worms' reproduction becomes the main object of the pamphlet's inquiry, and although Rousset has by its end made a ‘conjecture’ about their copulation, it remains far from certain. Swammerdam's English editor John Hill seemed to take generation by putrefaction for granted as late as 1758. His footnote on the parasitic worms in frog intestines affirmed that they could only have arisen there spontaneously, in direct contradiction to the arguments of Swammerdam's entire text.⁴¹ The more general connections of frogs and the demonic certainly pressed upon Swammerdam. He was probably aware that Bourignon had been accused of witchcraft, and in turn herself accused others of the practice; the world of supposed frog familiars was not so far from his own circle.⁴² Moreover, the apocalyptic frogs emanating from the mouth of the false prophet were an image that dogged anyone in Bourignon's position; their specifically Catholic connotation also came to bear on Swammerdam, who near the very end acknowledged that, if anything, his confessional position approached more nearly to Catholicism than to anything else.⁴³ Even when John Ray used frogs (citing Swammerdam) as a centrepiece of his own argument against spontaneous generation in the second edition of The Wisdom of God, his arguments were not quite so ontologically based as one might have expected. Ray's first argument, and the one to which he continually returns, is that if frogs are spontaneously generated then it must be God's doing; the phenomenon should simply be re-categorized as creation.⁴⁴ Although he adduces further evidence-based arguments, Ray does not definitively scotch the possibility that frogs (or other insects) can simply appear—instead, he defuses the theological problem that this phenomenon would present.

Whatever Swammerdam's reason for attacking Harvey, the Englishman's choice of adjective for the lower animals—‘creeping’—suggested a rhetorical response for Swammerdam to offer, for frogs had long been considered with the creeping (herpetic) lizards and serpents. In the Bybel he used his frogs as an in-between animal, standing midway between insects and the ‘larger, or sanguiferous’ animals. Frogs were already treated as less ‘blooded’ than higher animals; they were the food of the poor and also designated as acceptable to eat during Lent, not only because they came from the water, like fish, but also because they had little blood, and much phlegm, and were unlikely to arouse the passions.⁴⁵

In Historia Insectorum Generalis Swammerdam had already argued that there was but one kind of insect development, and that this was not a complete transformation (in today's sense) but rather a ‘gradual and natural growth’ and development of the insect's parts, all of which were present from the earliest stages.⁴⁶ The Bybel maintained the four-class categorization of insect changes developed in the Historia and added to it research on the development of the frog.

Thanks to his extraordinarily patient dissections of frogspawn and tadpoles, Swammerdam was now able to show in detail that the development of frogs was, like that of all insects, epigenetic.⁴⁷ ‘In the same manner [as the insects] the Tad-pole is not changed into a Frog, but becomes a Frog, by an unfolding and increasing of some of its parts’ (figure 2).⁴⁸ ‘It is evident … that [the frog] may and ought to be considered, in its original, as a real insect.’⁴⁹

Figure 2.

Epigenetic generation of the frog, from The Book of Nature, part II, tab. xlviii. (Copyright © British Library Board (459.e.4); reproduced with permission.)

Even when Swammerdam described the development of frogs, the traditional question of their ultimate origin was always in the background: at his rhetorical insistence, they were created, not putrefied by chance. In one apparently casual description of feeding, Swammerdam took care to bracket frogs together with those insects commonly associated with putrefaction (the ‘insects which are found in cheese, putrified flesh, and many fruits’).⁵⁰ What was proved of the frog should hold true for these insects also. Swammerdam's oft-quoted claim to have seen the ‘omnipotent finger of God’ upon the human louse was in fact another oblique reference to the frog, this time in its biblical context. Pharaoh's magicians managed to replicate the frogs by magic but failed to do so with the subsequent plagues of insects, causing Pharaoh to concede that he had seen ‘the finger of God’ in action and accusation. ‘Though the Ægyptian Magi could imitate other miracles which God performed by Moses, they were not able to produce these animalcules by their magic.’⁵¹ Swammerdam's rhetoric therefore emphasized that what was true of the insect—its intractability to magic; its generation not through putrefaction; its perfection; its epigenetic development—was also true of the frog. Thus my argument tends to disagree with the thesis that the emblematic and quotidian qualities of animals were completely separated by the early-modern period. Swammerdam had to work actively to make the frog a trustworthy embodiment of natural knowledge.⁵²

Swammerdam had successfully shown that the frog worked in the same way as insects, but making the bridge to higher animals and humans was fraught with difficulty, both theological and philosophical.

From frogs to humans via muscular physiology

In some ways Swammerdam had not yet achieved anything significant through his rhetoric, because frogs were already bracketed with insects through the theological smear of putrefaction. Indeed, a French dictionary of 1694 defined the frog as ‘an insect that commonly lives in marshes’. This low status caused frogs to be drawn into arguments about whether useful knowledge about humans could be gathered from animals at all; frogs and their congeners were frequently used as an ad absurdum rhetorical device to show how ridiculous this philosophical ambition was. In England, for example, William Perkins argued that the human body was made in God's image, but that if one followed through with the arguments of humanism one would be forced to concede that it was no different from a toad's.⁵³ In 1653, another Englishman sneered that there were those who so confused animals and humans that they must surely expect to dwell in heaven with ‘all the Toads and Frogs and poysonous Serpents’.⁵⁴

In defending his use of animal anatomy, William Harvey, too, was forced to confront the specifically shameful example of the frog, once again sticky with its demonic connections:

There are some, too, who say that I have shown a vainglorious love of vivisections, and who scoff and deride the introduction of frogs and serpents, flies, and other of the lower animals upon the scene, as a piece of puerile levity, not even refraining from opprobrious epithets.⁵⁵

Harvey—and Swammerdam—faced a double challenge: that animal anatomy was not applicable to humans, and that there was something innately undignified or improper about studying animals at all—especially the lower kinds.⁵⁶ Having, he hoped, dealt with and disproved the ungodly generation of insects by putrefaction, and the associated ungodly treatment of some animals as ‘imperfect’, Swammerdam was ready to treat frogs as noble and dignified comparators for the higher animals and humans. His method of doing this was by subjecting them to the type of muscular experiment that was usually reserved for the higher animals: cats, dogs and poultry (figure 3). Typically, their nerves were exposed and stimulated with all manner of things: pins, scalpels, heat, and caustic or ‘acrid liquors’. At least some of these were old experiments—one had been demonstrated to the Duke of Tuscany in 1668—but they now took their place in Swammerdam's rhetoric. Swammerdam's account of frog-nymph development and adult sexual anatomy moved upwards into an account of frogs as a model for understanding muscular activity in the higher animals.

Figure 3.

Swammerdam's frog muscle experiments and tadpole dissection, from The Book of Nature, part II, tab. xlix. (Copyright © British Library Board (459.e.4); reproduced with permission.)

Swammerdam noted some practical advantages of the frog: its muscles would continue to work long after they were dissected out of the body; its nerves were also particularly easy to lay bare.⁵⁷ However, these benefits were secondary to the place of the frog in Swammerdam's rhetoric. His theological desire to direct his gaze towards the frog was inseparable from the practical benefits that it happened to offer. (It had, for example, one major disadvantage: it was not readily available for experiment apart from one rather short season in the year.)

On dissecting out the spinal marrow, Swammerdam described finding a sort of beauty in the frog's body, a passage perhaps intended to enhance the animal's status. After a brief foray into iatrochemical speculation regarding the spinal cords and brains of various aquatic creatures, he proceeded to describe his experiments. Swammerdam found that his nerve–muscle preparation strongly contracted its muscular element when touched with scissors or other instruments.

Matthew Cobb has elucidated how in the subsequent series of experiments Swammerdam disproved the idea of a measurable ‘spiritous matter’ being transmitted from the nerve to the muscle when the latter contracted, or emanating from the mind.⁵⁸ What concerns us here, however, is the nature of the link meant by Swammerdam when he averred that ‘experiments on the particular motion of the muscles in the Frog … may be also, in general, applied to all the motions of the muscles in Men and Brutes.’⁵⁹

Two main points emerge from Swammerdam's account. First, he pointed out that muscles without antagonists are not under voluntary control, and that even those that do have antagonists often act in an involuntary fashion. For example, humans and animals react alike to being tickled, and even an action such as saluting another person can be provoked involuntarily ‘because another in our company takes off his hat’. A dream,⁶⁰ or a casual thought, noted Swammerdam, can have the same effect on our muscles as an apparently deliberate act of will; he was inclined to sweep up all muscular actions together as ‘always moved in a natural manner’. Second, Swammerdam deduced that the default status of muscles was one of contraction, and supposed acts of will (in practice mostly natural reactions) merely served to contract their antagonists. Our motions, he concluded, are ‘but seldom determined by us’.⁶¹

Swammerdam's mechanistic—even involuntary—account of muscle movement was of course very Cartesian in character.⁶² Insects seemed like a pretty safe and uncontroversial confirmation of Cartesian automatism of beasts. The English translator of Ephemeri Vita read the behaviour of insects in a distinctly mechanistic manner: ‘if we would understand how ’tis that Nature gives Life and Motion to these Automata, we must unloose the Case and take asunder the several Wheels and Springs'.⁶³ Such a reading, however, would look radical if the border between humans and animals were at all leaky, as Swammerdam claimed. At the time when Swammerdam was writing the Bybel, the still more radical materialism of Spinoza and others was just about to cause a serious backlash of scholarly conservatism.⁶⁴ Giving a mechanistic description of insects was one thing, but extending it to humans might be another.

However, in Swammerdam's mind at least, the unilateral discussion of animals and humans in terms of muscular action and will was far from impious. He shied away from discussing ultimate causes:

It is most evident that all God's works are governed by the same rules; and as the true and primitive origins of them are infinitely beyond the reach of our comprehension, so … all the knowledge and wisdom of philosophers, consists merely in an accurate perception of these elegant appearances or effects.⁶⁵

His desire was rather that his readers should see the ‘finger of God’ upon all creation, and humbly set aside their pride in themselves. All that insects showed was ‘proofs of [God's] infinite wisdom and power’.⁶⁶

The lessons from frogs for humans were in line with Boyle's meletetics: a male, clasping a female in the act of coition, resembled a peasant's hands clasped in prayer; and the tadpole's lengthy encumbrance by its tail reflected the difficulties that humans sought to shake off in their lifelong spiritual journeys.

The infant-man, who lived before in the water of the amnion, now breathes the vital air, which rushes into his lungs, and dilates and extends them. … On the other hand, his appendage of misfortunes and trouble, like the tail of the frog, yet adheres for a long time to him, for he is full of misery, and is born in tears; and it is very long before he comes to maturity of understanding, and full growth of body.'⁶⁷

Just as Topsell's text refuses anatomization along contemporary lines of nature and magic, so Swammerdam's nerves resist incorporation into a Whiggish narrative about the disproof of animal spirits. Having demonstrated that the muscle did not receive any physical substance upon contraction, Swammerdam then went on to speculate that what it did receive was an imponderable substance:

Therefore the spirit, as it is called, or that subtile matter, which flies in an instant through the nerves into the muscles, may with the greatest propriety be compared to that most swift motion, which, when one extremity of a long beam or board is struck with the finger, runs with such velocity along the wood, that it is perceived almost at the same instant at the other end.⁶⁸

It would be tempting to attribute Swammerdam's action-at-a-distance theory to a mystical theology acquired from Bourignon, but this is not plausible. Bourignon's ‘mysticism’ was actually of a fairly text-centred variety, albeit mediated by a spirit-to-spirit hermeneut in which God spoke directly to her. Her concern was to interpret the bible for the eschaton and thereby to promote true piety, not to see miraculous acts of God in the world. In fact Bourignon directly contradicted one correspondent who saw a friend's recovery from illness as miraculous. Similarly, Swammerdam had nothing but scorn for those persons who from ‘these natural and intelligible changes in bodies, have endeavoured to explain the resurrection of the dead’.⁶⁹ Swammerdam's analogical hermeneutic for reading the book of nature was, I would argue, extremely close to Bourignon's reading of the Bible, with a message of piety that did not probe or ontologically connect with the ultimate causes of wonders discovered therein. Moreover, I would be inclined to say that this similarity was what drew Swammerdam to Bourignon, rather than something that she produced in him.

Swammerdam's preferred way of thinking about animal muscles—as his reference to wood suggests—was not so much to consider the nature of the ‘subtile matter’ as to consider the analogy of muscular phenomena to those found in plants. In a letter to Thévenot late in November 1678 he wrote:

I am engaged in a treatise about [the muscle fibres of the frog]. But I lack the time to examine the muscular fibres. I always compare the muscular fibre with the herb fibres in the pod of the herba impatiens Dodonaei, that are extended contra naturam and contract at the least touch.⁷⁰

The etymology of impatiens, or noli-me-tangere (touch-me-not) was explained in relation to this behaviour in a pharmacological treatise of 1698. The herb, wrote the author, is so called ‘because when one touches the pod [fruit] of this plant it impetuously ejects its seeds, which tangle themselves around one's fingers and dirty one's hands.’⁷¹ The word chosen for seeds, ‘semence’, also meant semen, and in conjunction with the word ‘dirty’ the hint at human ejaculation seems unavoidable. And indeed, Swammerdam's decision to treat impatiens as his muscular model came between two letters describing the penises of cheese mites (whose vulva inserts into the penis) and of sea snails (which have muscles that respectively extend and contract the penis). The plant, as signifier for the muscle, was in turn signified by the penis.⁷²

Impatiens was, in Swammerdam's phrase, ‘extended contra naturam’, and in context his use of these words shades between Aristotle's description of mechanical motion and Aquinas's altogether darker use of the expression.⁷³ This is a significant slippage, because it was a vital part of Swammerdam's theology that everything in nature is natural; that is, aligned with God's governance. Thus to find the muscle, qua penis, counter to nature was a dangerous jag in an otherwise unifying world view. This was the point at which Swammerdam's carefully separated materialist philosophy (bodies wholesome for the making of metaphysical knowledge) and meletetic spirituality (the physical world as source of spiritual reflection) could all come apart. If the knower is at the mercy of bodily urges that run counter to God's laws, then how can knowledge that is produced by the body become trustworthy?

Fascinating though this may be, it takes us into imponderable realms of Swammerdam's sexual psychology. What is certain is that there were two potential human analogues for Swammerdam's epigenetic frogs, one negative (which he avoided) and the other elevated.

The negative version of frog-as-human was all around Swammerdam. During the Franco-Dutch War, the Dutch were widely caricatured as frogs by their enemies and by the English (figure 4).⁷⁴ Like frogs, they inhabited low-lying, swampy areas; Dutch peasants in particular were pictured in batrachian form, as fat, lazy and cunning. Needless to say, this was not an interpretation of the frog–human continuum that Swammerdam wished to stress.

Figure 4.

Anonymous, The Dutch Boare Dissected, or a Description of Hogg-Land (London, 1665). The poem concludes: ‘Frogs in great Number/Their Land doth Cumber,/And such-like Croaking People’. (Copyright © Trustees of the British Museum; reproduced with permission.)

Swammerdam's choice of plant comparator for the published version of his researches (as opposed to the unpublished noli-me-tangere) was of altogether higher status. The carnation (angelier) contained in his table, and in the plate illustrating frog epigenesis (figure 5), was a traditional symbol for the incarnation or passion of Christ.⁷⁵ The bloedeloose (bloodless) insects proceeded up to the half-blooded frog, and so on up to the fully bloody Christ-flower. One painting from the period, by Jan Davidszoon de Heem, combined two of these images in one: ‘the latent possibility of revival is attached to [a chrysalis amidst the corn]; and the carnation, placed near the paper inscribed Memento mori, means Resurrection through Christ’.⁷⁶

Figure 5.

Frogspawn, tadpole, frog and carnation, from The Book of Nature, part II, tab. xlvi. (Copyright © British Library Board (459.e.4); reproduced with permission.)

Swammerdam's choice of the diminutive popken (which shares its roots with the word for ‘doll’) to anchor all of his descriptions of metamorphosis develops our understanding of his Christic anchor-point for the metamorphic series:

the worms [of insects], after the manner of the brides in Holland, shut themselves up for a time, as it were to prepare, and render themselves more amiable, when they are to meet the other sex in the field of Hymen. Since the word Nymph [popken] expresses the nature of the thing better than any other … we shall adopt it … .⁷⁷

In Swammerdam's table and descriptions, the popken is the stage immediately preceding that in which the animal is in a condition to generate its species. This is Swammerdam's definition of perfection. It is not something that an organism either possesses or does not, as in Harvey's philosophy, but a state that all creatures will eventually attain—even, perhaps, the human ‘bride, the Lamb's wife’ (Revelation 21:9).⁷⁸

Conclusion

Swammerdam's frogs therefore had a vital theological role in his philosophy. From the insect to the frog via epigenesis, and from the frog to the human via muscular action, the whole of God's creation was now joined in one seamless, law-like continuity. In using them for this purpose Swammerdam lent a necessary kind of wholesomeness to the frog's body. His insistence that the frog's body was natural in the theological sense—aligned with God's will—is, as we have seen, strikingly similar to Topsell's aim in The History of Serpents written some 50 years previously. Although Topsell did not pursue any kind of experimental knowledge, he was nevertheless—like Swammerdam—part of a theological process that eventually made possible the making of knowledge from animal bodies. Wrestling with the evidence of the world and of texts, Swammerdam reached a (sometimes uneasy) resolution whereby he could gain metaphysical and spiritual knowledge from the natural world—thanks to his shriving of the frog. Frogs also provided Swammerdam with the specific means to engage in particular philosophy of his day, to intervene in debates about generation and to create his hopeful proof that ‘all God's works are governed by the same rules’.