Boyle, Malpighi, and the Problem of Plastic Powers

Abstract

In this paper, I examine Boyle’s views on generation and his appeal to plastic powers as an explanatory agent following a brief overview of the secondary literature. Further, I also look at the relationship between Boyle and the Italian anatomist Marcello Malpighi, who was one of the most prolific medical writers in the second half of the seventeenth century. This paper looks at their correspondence, which included not only ideas about experiments and the mechanical philosophy, but mineral samples as well. I argue that Malpighi appropriated Boyle’s notion of plastic powers in his own writings as part of a mechanical account of generation. Thus, Boyle’s description of a plastic power was perceived as being mechanical by one of his own contemporaries similarly committed to the mechanical philosophy. In both Boyle and Malpighi, moreover, we see a shared philosophy regarding mechanical explanation. For each of them, mechanical explanations involve physical agents acting on matter. Their shared view implies an important shift in which the power of an explanatory agent like a plastic power is in its mechanical mode of operation.

I would like to thank Domenico Bertoloni Meli, William Newman, the editors of this volume, and two anonymous reviewers for many helpful suggestions and constructive criticisms on earlier drafts of this paper. Parts of this paper were presented at both the Early Modern Medicine and Natural Philosophy workshop held at the University of Pittsburgh and the 2012 Workshop on the History of Biology in Honor of Fred Churchill held at Indiana University. I wish to thank the audience members at each for insightful questions.

1 Introduction

This paper begins with the famed English chymist¹ Robert Boyle and the attempts throughout his corpus to explain the process of generation . The problem of generation is, essentially, one of how things in nature come to be. Thus, it is a much broader concept than that of reproduction, as the latter is restricted to how animals replicate themselves. Generation, in contrast, is the process by which a thing is formed and thus is not restricted to animals, but includes also the originative processes of both plants and minerals. Moreover, any kind of formative process requires something to organize the matter whence it is made into that which it will become. The agent responsible for this organization of matter has been conceived throughout history in a vast number of ways, from the λόγοι σπερματικοὶ of Plotinus to the formative faculties of Aristotle and later of Galen.² Yet, the distinctive feature throughout the history of these concepts prior to Boyle was that the explanatory power of these organizing principles came from the soul or faculty with which each was associated. The dramatic shift for which Boyle is responsible is that plastic or seminal principles are causes in virtue of their effects upon matter.

Table 13.1 List of Boyle’s use of the term ‘plastic’

By the seventeenth century, ‘plastic power ’ or ‘plastic force’ had become blanket terms for the formative power of generation , and they were nearly interchangeable with ‘seminal principle’.³ Seminal principles and their related plastic powers are potentially at odds with the mechanical philosophy. The tension arises in there being particles of matter that have powers which are not reducible to either matter or motion. As one of the most influential scholars of his time, Boyle was largely responsible for popularizing the so-called Mechanical Philosophy . Consequently, his appeal to any formative powers warrants further discussion.

In this paper, I examine Boyle’s views on generation and his appeal to plastic power s as an explanatory agent following a brief overview of the secondary literature. I aim to show that despite whatever tensions seminal and plastic powers might hold within a reductionist ontology, Boyle’s account of plastic powers nonetheless constitutes a mechanical explanation . Moreover, I show how Malpighi appropriated this concept and was influenced specifically by Boyle’s treatises on minerals. In both Boyle and Malpighi, we see a shared philosophy regarding mechanical explanation. For each of them, mechanical explanations involve physical agents acting on matter and thus producing noticeable, qualitative changes. Their shared view implies a kind of methodological shift in which they emphasize the production of those effects as the source of explanatory power.

2 Historiography

Earlier works on Boyle’s mechanical philosophy, exemplified by Marie Boas Hall’s scholarship, depict him as the defender of a rational, mathematically-based mechanical science that would ultimately replace the unscientific beliefs of alchemists.⁴ It has since been shown, however, that Boyle’s chymistry and his more general philosophy is very much informed by his alchemical pursuits, and moreover that the distinction between chemistry and alchemy simply cannot be made within a seventeenth-century context.⁵ More recently, the secondary literature on Boyle’s mechanical philosophy can be characterized into two groups: those who argue that Boyle’s experimental chemistry is ultimately incompatible with and independent of his mechanical program, and those who argue that his experimental chymistry is central to and perfectly consistent with his mechanical philosophy. In this long-standing debate that spans more than twenty years, Alan Chalmers and Antonio Clericuzio belong to the former, whereas Andrew Pyle, William Newman, and (to a lesser extent) Peter Anstey belong to the latter.

A re-examination of Boyle’s mechanical approach is much indebted to Antonio Clericuzio’s groundbreaking 1990 paper, “A redefinition of Boyle’s chemistry and corpuscular philosophy”. ⁶ Within the paper, Clericuzio challenges the traditional picture that Boyle’s corpuscular theory was thoroughly mechanistic , looking both at Boyle’s chymical influences and his employment of non-mechanical explanation s such as alchemical spirits. Clericuzio very sharply distinguishes between theories of matter which are subtly, yet importantly, different. His work, in that regard, is important because the applications of ‘mechanical’ are often murky and in need of disentangling. Further, it’s especially significant in the attention that it brought to Boyle’s corpuscular theory of matter. Clericuzio argues that Boyle’s work could be described as corpuscular, but not mechanical. Clericuzio has since provided a more detailed analysis of Boyle’s corpuscular theory in his 2000 book, Elements, Principles and Corpuscles. Within it, he argues that several of Boyle’s agents—including seminal principles—are not in fact mechanical, despite Boyle’s repeatedly asserting them to be.

Following Clericuzio’s original paper, Alan Chalmers published in 1993 a rather controversial paper entitled, “The Lack of Excellency of Boyle’s Mechanical Philosophy .” In the paper, he argues that, “far from there being an intimate and productive link between Boyle’s mechanical philosophy and his science, his scientific successes were achieved in spite, rather than because, of his allegiance to that philosophy.”⁷ He goes to argue as well that, “the case that Boyle makes for the mechanical philosophy can be seen to be very weak indeed.”⁸ At the crux of Chalmers’ argument is Boyle’s reliance in his chemistry on properties of matter (like plastic power s) which are not reducible to shape, size, and motion. In response to “The Lack of Excellency of Boyle’s Mechanical Philosophy,” Andrew Pyle and Peter Anstey engaged Chalmers in a three-way discussion published in Studies for History of Philosophy in 2002.⁹ Andrew Pyle wrote “Boyle on science and the mechanical philosophy: a reply to Chalmers,” which makes two counter arguments. The first, to which I am sympathetic, is that Chalmers assumes on the part of Boyle a strictly Cartesian program.¹⁰ In the second half of his response, Pyle argues that even if we were to restrict Boyle to a strictly Cartesian view, this more reductive program does actually play a positive role in Boyle’s empirical research, namely by emphasizing, “the centrality of local motion in all physical explanation, and invit[ing] us to posit, as explanatory properties in our intermediate-level explanations, only properties that look mechanizable.”¹¹

Anstey’s response to Chalmers, “Robert Boyle and the heuristic value of mechanism ,” involves a somewhat weaker connection between Boyle’s experimental chemistry and his mechanical philosophy. He argues that the latter serves as, “a heuristic structure that motivates and drives Boyle’s experimental programme.”¹² Further, Anstey argues that Boyle’s most important discoveries were both informed and confirmed by his mechanical philosophy, in much the same way that theory informs and confirms experiment. The same year (2002a), Anstey provided the first comprehensive analysis of the treatment of seminal principles within Boyle’s corpus in “Boyle on Seminal Principles.” Anstey’s paper categorizes Boyle’s works on seminal principles by topic so that studying them in his corpus becomes feasible. The amount of Boyle’s work addressed by this piece and the manner in which it is organized are quite impressive. In the article, we are presented with a Boyle in tension who thus posits seminal principles only with reticence. In Boyle’s account, Anstey argues, appeals to a seminal or plastic power are made in order to explain those features of generation that are beyond the explanatory means of the corpuscular hypothesis. In short, Anstey presents Boyle as caught in a catch-22. On the one hand, if seeds operate mechanically, then Boyle has no reason to appeal to them as an explanatory agent in the first place. On the other, in admitting nescience, Boyle has to allow for the possibility of non-mechanical causes.¹³

Anstey maintained that same position shortly after in his subsequent debate with Jonathan Walmsley in, “Robert Boyle and Locke’s ‘Morbus’ Entry: A Reply to J.C. Walmsley.”¹⁴ Their dispute over Boyle was within the context of an entry entitled “Morbus”—composed in John Locke’s handwriting—which Walmsley understood to be “vociferous in criticism” of Boyle’s corpscularianism and accepting instead of a distinctly non-mechanical program.¹⁵ While Locke’s views on disease and possible authorship of the Morbus entry remain outside the scope of this paper, the episode is nonetheless significant because Walmsely’s “analysis and conclusions are predicated upon the view that Boyle adhered to a strictly mechanical explanation of the operation of seeds .”¹⁶ Anstey explicitly denies this claim, citing the same two-horned dilemma described above.¹⁷

Walmsley replied in the same volume of Early Science and Medicine with “‘Morbus,’ Locke and Boyle- A Response to Peter Anstey”.¹⁸ He responds to Anstey’s denial that Boyle has an explicitly mechanical account of seminal and plastic power s, stating that

But the cause [of generation ] itself need not act in an extra-mechanical way. I see no examples of Boyle “declaring his nescience,” nor do I believe that there was an “unresolved tension” in his thought on this point – whenever he addressed himself to the question to the action of seminal principles, Boyle was clear that they were complex mechanical entities acting in a mechanical way to produce complex mechanical effects. There is nothing in the remarks that Anstey makes that shows Boyle to have had anything less than full confidence in mechanical explanation s for the action of seminal principles.¹⁹

Walmsley goes on to suggest that the source of Anstey’s trouble lies in his affinity with Clericuzio, as the latter rejects that the plastic power of seeds are mechanical. The problem, however, is that Anstey does not claim—as Walmsley would have us believe—that “Boyle maintained a ‘nescience’ about the modus operandi of seminal principles.”²⁰ But, herein lays a key difference that I hope to elucidate. Anstey’s claim is that Boyle is committed to an ontological nescience about the nature of any seed ’s plastic power. At the heart of the matter is this: Must the plastic power (or any chymical power, for that matter) be necessarily reducible to the mechanical qualities of matter per se, or is it sufficient that its mode of operation is reducible to shape, size, and motion?

The controversy surrounding Boyle’s mechanical philosophy took on a new dimension with the publication of William Newman’s 2006 book, Atoms and Alchemy: Chymistry and the Experimental Origins of the Scientific Revolution. Part of Newman’s argument involves alchemy’s contribution to corpuscular theories of matter and the mechanization of nature, the latter of which is frequently considered to be an essential part of the so-called Scientific Revolution. The last third of the book focuses on Robert Boyle ’s theory of matter and influences, most especially the Aristotelian chymist Daniel Sennert. In dealing explicitly with Boyle’s mechanical philosophy, Newman criticizes previous authors such as Clericuzio and Chalmers for their “implicit reliance on Cartesianism in framing their definitions of the mechanical philosophy.”²¹ Newman goes on to argue that, “[t]he fact that Boyle does not attempt to reduce all phenomenal change to the level of the prima naturalia or initial particles does not mean that his chymical explanations are not mechanical, since the aggregate corpuscles are also endowed with mechanical affections having explanatory force.”²²

Malpighi’s discussion of plastic power s has not elicited quite the same response as has Boyle’s, but it is nonetheless not without some controversy. In the monumental work, Marcello Malpighi and the Evolution of Embryology, Howard Adelmann writes that the plastic virtue is essentially, “a combination of the formal and efficient causes of Aristotle and the plastic or formative faculty of Galen.”²³ This reading of Malpighi is problematic because Malpighi’s career is marked by his attempt to explain anatomy in terms of the parts of a machine and with explanations totally devoid of reliance on the soul . Adelman’s influence can be seen more recently in Catherine Wilson’s 1995 book, The Invisible World, where she criticizes Malpighi as “thoroughly opportunistic and philosophically inconsistent in his explanatory apparatus, employing now the terms of Cartesian mechanism , which would explain growth as the process of fluid and particle accretion, now the language of plastic powers and unfolding, as each seemed suitable.”²⁴ Domenico Bertoloni Meli has recently argued contra Wilson that Malpighi likely borrowed the expression “plastic virtue” from Boyle. He bases that argument on Malpighi’s claim that any agent – even something like a soul – must act physically upon matter as a machine, regardless of its nature. Here, Malpighi presents a virtually identical philosophical stance as taken by Boyle in the Origin of Forms and Qualities. ²⁵

I hope to expand up on this view by investigating more deeply the relationship between Boyle and Malpighi. The correspondence between Boyle and Malpighi shows that they were familiar with each other’s works and that each scholar was highly regarded by the other. This exchange included not just ideas about the new experimental or corpuscular philosophy, but material objects such as mineral samples. Their correspondence and mutual influence has not yet received much attention in the secondary literature. What is especially telling is that Malpighi makes no references to a plastic power until after Boyle published Origin and Virtues of Gems, despite the fact that Origin of Forms and Qualities was in print several years before Malpighi’s treatises on the chick. This fact, along with their dialogue on minerals, indicates that Boyle and Malpighi not only shared a similar philosophical treatment of plastic powers, but also had in mind the same specific, corpuscular processes when describing agents involved in generation . The take-away is that Malpighi’s appeal to plastic powers as an “explanatory apparatus” just is a means of describing generation as “the process of fluid and particle accretion.”

3 Boyle on Generation

In order to understand Boyle’s views on generation , one must first distinguish between what he calls a seminal principle, a petrifick sprit, and a plastic power . These agents lack sharp distinctions, and there is much overlap between them. Boyle tells us, for example, that the source of the petrifick spirit could be a seminal principle (though he ultimately will deny this). Seminal principles are most often associated with plastic powers for Boyle. Further still, Boyle claims that the petrifick spirit is almost like a plastic power. That said, Boyle clearly has different processes associated with the production of minerals and the generation of living organisms. Thus, it is only fitting that he would conceive of their respective agents differently.

A plastic power —which is the focus of this paper—just is a molding agent that is responsible for organizing matter in generation . When Boyle uses the term, he seems to have one of two ideas in mind.²⁶ The first is the more general notion of a formative power. The source of that power could come from a number of agents, including the Galenic formative faculty, the soul or even on occasion the Neo-platonic world soul. It becomes clear from Boyle’s writings, however, that the only agent which could have that kind of formative power for the purposes of generation within his own framework is a seed , or a seminal principle. Boyle more frequently uses the term in a restricted sense , which is the power of a seed to generate a body.²⁷

To take a closer look at Boyle’s treatment of seminal principles, his discussion in Origin of Forms and Qualities (1665) makes it clear that Boyle conceives of their operations in terms of homogeneity of matter and transmutation. The discussion of homogeneity of matter fits with the generation project of the Origin of Forms and Qualities, since Boyle is attempting to explain how qualitative changes can mechanically derive from some universal, catholic matter. In the second half of the essay, Boyle cites experiments involving substantial changes, which he attempts to describe in terms of corpuscular philosophy. The example involves the development of a chick from diaphanous fluid within the egg.

Boyle explains that the substance of the egg undergoes a great change because of incubation and then is turned into a chick. That change, however, had not “been taken notice of, for the same purpose” that Boyle had, which is to explain the changes of a substance.

He states that any part of the diaphanous white of the egg is like the other, emphasizing a “similarity of substance.” Appealing then to observations, he writes about the “Rudiments of the Chick, lodg’d in the Cicatricula.” Given his views on generation , those rudiments are likely seminal rudiments. The cicatricula, which he describes as a “white Speck up on the Coat of the Yolk,” is nourished by the white of the egg until it becomes a great chick. On this view, the cicatricula belongs neither to the white nor the yellow of the egg. Rather, its contents act upon the fluids of the egg, both of which later act as nutriment.²⁸ He emphasizes the many different qualities that come from the uniform, diaphanous substance of the white of the egg, such as the various colors of the bird’s parts, fluids and solid parts such as bones. The speck will become a chick with a head, beak and claws before turning to the yolk for digestion, which is “reserv’d as a more strong and solid Aliment”.²⁹ Boyle’s focus, however, is on the nutritive white of the egg, which he describes as being so soft

… that by a little Agitation it may be made Fluid, and is readily enough dissolvable in cold water, this very Substance, I say, being brooded on by the Hen, will within two or three weeks be transmutated into a chick furnished with Organical parts…³⁰ so that here we have out of the White of an Egg, which is a Substance Similar, Insipid, Soft, (not to call it Fluid), Diaphanous, Colourlesse, and readily dissoluble in cold water, out of this substance, I say, we have by the new and curious Contrivement of the small parts consisted of, an Animal…³¹

Hence, Boyle describes the change of a quality-less, homogeneous substance into the parts of the chick in terms of transmutation. He extends that reasoning to the buds of plants also, describing how the buds transmute the sap, a “flegmatick Liquor, that seems Homogeneous enough,” into the bodies of plants which are endowed with various colors, medical virtues, and diverse qualities.³²

A final example demonstrating the relationship between transmutation and seminal principles in the Origin of Forms and Qualities can be found much later in his section on experiments when he is addressing transmutation specifically.³³ Here, Boyle complains of learned individuals who accept that elements can be transmuted into one another, and that they may be, “artificially destroy’d, and (without the intervention of a Seminal and Plastick power) generated or produc’d…”³⁴ He then goes on to consider the transmutation of rain water into earth. Of this process, Boyle writes that it would be a “very great difficulty to conceive, how a perfectly and exquisitely Homogeneous Matter should, without any Addition, or any Seminal and Plastick. Principle, be brought to afford great store of a Matter of much more Specifick Gravity then it self…”³⁵ Worth noting is that the seminal principle differs from something like rennet in that it not only is the agent of active change, but it acts as an organizing principle upon that matter. That organizing, plastic principle is unique to seeds .

A petrifick spirit, contrarily, is the result of a mixture. As such, it acts less as an organizing principle and is instead responsible for petrification of minerals by causing coagulation and reorganization of ingredients.³⁶ In his later work, Boyle seems hesitant even to discuss the formation of minerals in terms of generation . Boyle’s first description of the coagulation of minerals occurs in History of Fluidity.³⁷ Within the History of Fluidity, Boyle discusses the coagulation of bodies, like the curdling of milk by saline liquors, and he combats the chymical theory that salts are the agents responsible for hardening and coagulation.³⁸ One such counter-example he provides involves ice, which becomes hard by the cold rather than by salt. Boyle also considers egg shells, which are soft immediately after being laid, but soon harden from their interaction with air. He then continues with what he takes to be the more convincing counter-example: the internal fluid of the egg. He writes that the white of the egg coagulates and grows to create the various parts of the chick, such as its beak and bones. All of that hardening from fluids occurs, argues Boyle, without salts.

Boyle first gives a detailed account of his petrifick spirit within the essay, “Thoughts and Observations about the Generation of Minerals,” which was originally intended to be an addendum to the History of Fluids. ³⁹ Throughout the work, Boyle defends the thesis that minerals develop from a liquid state. He comes to this conclusion after rejecting other possibilities, which include the creation of minerals simultaneously to that of the Earth, leaving their production per se unexamined; as well as the Epicurean thesis that minerals are formed by the “casuall Coalition of congruous particles.”⁴⁰ Though Boyle acknowledges that minerals may have been developed by seminal principles via an internal heat, he ultimately thinks that mineral formation occurs by coagulated fluids resulting from a “petrifick spirit,” which he describes as “an Almost plastick Agent.”⁴¹

He goes on to describe the petrifick spirit as either an almost plastic agent, a sensible ingredient, or something like a ferment. In truth, Boyle sees each of these as different ways of describing the same properties of his Petrifick Spirit. The agent is plastic in the sense that it is a formative force capable of producing and solidifying new bodies. That the spirit acts like a sensible ingredient is on account of its being distinctly physical. Finally, it works like a ferment in the sense that it acts upon and coagulates passive matter. Each of these analogies describes the process which Boyle has in mind, namely that of matter acting upon matter and their resulting interaction. Further inspection of how the Petrifick Spirit is said to work helps to clarify the sort of agent that Boyle had in mind. Though it results in coagulation, it does so “less like that of the Cicatricula of an Egg” and more like the coagulation of milk curds with rennet. Recall that in the case of the egg, the coagulation that takes place is from homogenous material. With milk and rennet, however, a mixture takes place. Though Boyle is hesitant to characterize the process, he goes on to write of it that,⁴²

… to say little rather than Nothing at All to this difficulty,⁴³ I must put you in Mind that when I lately ‹spoke of› the Action of this Petrifick Spirit. I ‹made› express mention of a duely dispos'd matter. For in these Coagulations I take the Effect to be a thing that results as well from the Disposition of the Patient, as the Efficacy of the Agent; as wee see that Rennet of which ‹very› little will coagulate ‹a› great quantity of Milk, has no such operation at all upon water or Wine ‹&c.› Nor have I know [sic] the vapour of Lead to coagulate any other Liquors then Quicksilver.⁴⁴

Thus, matter involved in creating minerals is “duely dispos’d” in the sense that it is both the active agent and the passive matter that is acted upon.

Boyle’s “duely dispos’d” matter is clarified in his Origin of Virtues of Gems, published in 1673, 12 years after he wrote the manuscript on the generation of minerals. Boyle continues to defend his thesis that minerals—and specifically gems—are formed originally by hardening a liquid. In arguing thus, he presents several arguments that demonstrate that the heterogeneity of matter was, for Boyle, a key factor in the way in which minerals are formed. These include gems with heterogeneous matter or gems with extraneous mineral bodies within them.⁴⁵ In such examples, Boyle argues that this mixture would have occurred whilst they were still in liquid form. He writes, for example, that

… some (at least) of the Real Virtues of divers Gems may be derived from this [Petrifick Spirit], That whilst they were in a fluid form, (or at least not yet Hard’ned,) the Petresecent substance was mingled with some mineral solution or tincture, or with some other impregnated liquor, and that these were afterwards Concoagulated, or united and hardened, into one Gem…⁴⁶

Boyle describes the petrifick spirit working upon the corpuscles of varying mineral solutions or liquors in a fluid form— both an agent and a patient—as a result of these fluids mixing, whereby the corpuscles of each are mechanically affected in such a way that they coagulate together and their texture hardens. As the physical result of mixture, the petrifick spirit does not present the same challenge for Boyle’s thesis as does his appeal to seminal or plastic power s, which are responsible for the organization of catholic matter. Consequently, I wish to make plastic powers—those powers in generation not reducible to matter or motion—the focus of this chapter.

4 Plastic Powers as Explanation

Are the formative powers of seminal principles—plastic power s—introduced in just those cases where Boyle lacked a mechanical explanation , or is Boyle providing a kind of mechanical explanation despite his appeal to agents that go against the sparse ontology of someone like Descartes ? Put another way, could Boyle’s account of seminal principles and their corresponding plastic powers be rightly called a mechanical explanation? Herein lays the heart of Anstey’s two-horned dilemma. Anstey is absolutely right to claim that Boyle’s seminal or plastic principles commit him to nescience about the nature of the agents responsible for generation . But, the question at hand is whether that nescience precludes Boyle from providing for them a distinctly mechanical explanation, nonetheless. I would argue that it does not, insofar as the explanatory power of those agents comes from the structural or textural changes which those agents cause upon passive matter. Seeds can operate mechanically—as Boyle understands the term—regardless of the nature of their plastic powers.

Boyle deals explicitly with what he takes to be a mechanical explanation in his 1674 treatise, On the Excellency and Ground of the Corpuscular or Mechanical Philosophy . Beginning with his mechanical philosophy, Boyle recognizes that there are different sects of Mechanical philosophers. Of other Mechanical philosophers, he complains, “that they think [the Mechanical Philosophy] pretends to have Principles so Universal and so Mathematical, that no other Physical Hypothesis can comport with [the Mechanical Philosophy], or be tolerated by it.”⁴⁷ That kind of presumption Boyle inevitably describes as a mistake because mechanical principles are universal. They should, consequently, be inclusive and applicable to many explanations, rather than be exclusive and rejecting of certain explanations.⁴⁸ This claim is not insignificant either because it entails that on Boyle’s view a mechanical explanation must be able to account for those things, like plastic power s, that would be otherwise incompatible with the ontological commitments of the mechanical philosophy.

Boyle elaborates upon his main complaint against those who would appeal to agents like a plastic power or Platonic world-soul , which is not their postulation of the existence on such powers. Rather, his criticism is that they fail to explain how these agents work. The main topic which naturalists should seek to explain, he argues, is not so much what the agent is. Rather, the naturalist should focus on what changes the agent makes, and “after what manner, those changes are effected.” These changes, according to Boyle, can inevitably be explained in terms of and are reducible to matter and motion:

So that the Mechanical Philosopher being satisfied, that one part of Matter can act upon another but by vertue of Local Motion, or the effects and consequences of Local Motion, he considers, that as, if the propos'd Agent be not Intelligible and Physical, it can never Physically explain the Phænomena; so, if it be Intelligible and Physical, 'twill be reducible to Matter, and some or other of those onely Catholick affections of Matter, already often mentioned.⁴⁹

Here, it might be helpful to distinguish between a mechanical explanation and mechanical ontology. Dennis Des Chene has recently provided an excellent discussion of this distinction, arguing that “One could, and many philosophers did adopt mechanism as a method of explanation without adopting a mechanist ontology.”⁵⁰ An organizing principle such as a plastic power undoubtedly causes rather obvious conflict with an ontology that only includes matter devoid of such powers. Yet, we ought not to assume that Boyle has such a strictly bare ontology. Indeed, as touched upon in the historiography section, Boyle is somewhat notorious for positing corpuscles with various chymical powers, and yet he was still largely viewed by contemporaries as one of the most influential proponents of the mechanical philosophy. Indeed, he is largely responsible for the term.⁵¹

Moreover, Boyle is especially keen to maintain a methodological agnosticism about those things in nature that he has no experimental means to observe. Given that methodological agnosticism, it’s not surprising that he would accept nescience about the nature of agents involved in generation so long as he can explain their effects as reducible to the mechanical affections of matter. This black-boxing of the agent and insistence on its working as a physical agent in accordance to the mechanical laws of nature became a common application of the mechanical philosophy. Thus, I wish to put aside questions of Boyle’s ontology and focus instead on his own understanding of mechanical explanation .

That Boyle’s own treatment of plastic power s follows that prescription of a mechanical explanation is especially evident from his retorts to possible objections. In his Origin of Forms and Qualities Boyle considers the possible objection that the chick is fashioned by the soul , “lodg’d chiefly in the Cicatricula, which by its Plastick power fashions the obsequious Matter…” Boyle very likely had William Harvey in mind when presenting that objection. First, the passage bears resemblance to Harvey ’s own view. Moreover, Boyle’s explicit reference to the cicatricula strongly suggests that he was thinking of William Harvey.⁵²

To this complaint, Boyle answers that this objection does not invalidate his claim that the chick is a mechanically contrived engine. For, as he writes,

let the Plastick Principle be what it will, yet still, being a Physical Agent, it must act after a Physical manner, and having no other matter to work upon but the White of the Egg, it can work up that Matter but as Physical Agents, and consequently can but divide the Matter into minute parts of several Sizes and shapes, and by Local Motion variously context them, according to the Exigency of the Animal produc’d, though from so many various Textures of the produc’d parts there must naturally emerge such differences of Colours, Tasts, and Consistencies, and other Qualities as we have been taking notice of. That which we are here to consider, is not what is the Agent or Efficient in these Productions, but what is done to the Matter to effect them.⁵³

Note how Boyle ends this discussion by emphasizing how the explanatory power of the plastic power comes from its physical effects upon matter. Boyle elaborates on that point, stating that,

And when Man himself, who is undoubtedly an Intelligent Agent, is to frame a Building or an Engine, he may indeed by the help of Reason and Art, contrive his Materials curiously and skillfully, but still all he can do, is but to move, divide, transpose and context the several parts, into which he is able to reduce the Matter assign’d him.⁵⁴

Boyle goes on to explain how the external heat of incubation puts the parts of the substance into motion so that, “the Formative Power (whatever that be) doth any more then guide these Motions, and thereby associate the fitted Particles of Matter after the manner requisite to constitute a Chick…”⁵⁵ Thus, throughout his response to what is most likely Harvey ’s view, Boyle places the explanatory focus upon the material effects and modes of operations.

Recall that in the Origin of Forms and Qualities, Boyle extended his reasoning of the chick’s formation to that of the plant. In the same vein, he considers a similar objection to his theory of the chick, namely that the diverse qualities of the resulting plant are, “the productions of the Plastick Power residing in prolific Buds…” To this objection, Boyle replies that he, “shall return the same Answer that I did to the like Objection, when 'twas propos'd in the First Observation.”⁵⁶ In other words, whatever formative agent that plastic power might be, it must act in a physical manner.

In the Origins and Virtues of Gems, Boyle also considers the objection to his thesis of minerals developing fluids that a seminal principle must be involved. He replies by stating that there is “no absurdity” in seminal or plastic power s being harbored in liquid principles, citing the parts of animals which are turned to bones and the juices in trees which become bark.⁵⁷ His main point is that regardless of the nature of the agent, it must act upon the matter in exactly the same fashion, in this case by altering the mixed liquids mechanically. Thus, it is enough for Boyle to admit the possibility of his opponent’s agents or principles so long as the process by which they work is the same.⁵⁸ In this manner, Boyle is able to provide an inclusive application of his mechanical philosophy as described earlier.

Avoidance of anachronism requires that we look at Boyle both as he understood his own work and as he was understood by his contemporaries. I hope to have demonstrated that Boyle took a mechanical account to be one in which the force of an explanation comes from the agent’s mode of operation upon matter, the effects of which are reducible to the more catholic affections of matter. Those agents, then, may very well include matter that is endowed with certain powers. Seminal or plastic power s rightly meet this specification because- regardless of their nature- they must and do act as physical agents on matter. For the latter purpose of understanding Boyle’s reception by his own contemporaries, Malpighi proves to be especially helpful.

5 Malpighi and Boyle

Malpighi appropriated Boyle’s notion of plastic power s in his own writings. This usage by Malpighi is part of a mechanical account of the generation of bodies from heterogeneous fluids. Moreover, and perhaps more importantly, it shows that Boyle’s description of a plastic power was perceived as being mechanical by one of his own contemporaries similarly committed to the Mechanical Philosophy . That appropriation, however, was based on the works of Boyle’s that Malpighi had available to him. In short, Malpighi understands a plastic power to work very much like and to be related to Boyle’s petrifick spirit. Given what resources Malpighi had available to him, that Boyle had such a concept for the generation of animals in mind was a reasonable assumption on the part of Malpighi.

The essay in which Boyle is most explicit in print about the petrifick spirit remains his Origin and Virtues of Gems. This treatise was especially influential upon Malpighi. In a letter from Henry Oldenburg, dated 1672, Oldenburg explains that he is sending to Malpighi, along with the copper engravings for the illustrations of his embryological treatises of the chick and their resulting figures, a Latin edition of Boyle’s Origin and Virtues of Gems prior to its being published in Latin.⁵⁹ Boyle’s essay later came out in 1673 as Exercitatio de origine et viribus de gemmarum, and that letter of Oldenburg’s was published with Malpighi’s first embryological treatise, Pulli in Ovo. That latter fact is of interest, too, because it means that any of Malpighi’s contemporaries reading his earlier works on the chick would have known of his receiving and likely reading Boyle’s work.

Pulli in Ovo was the first of two treatises on the development of the chick egg. Both of these were written by Malpighi the previous year, 1671. They were published by the Royal Society in 1673 and 1675, respectively. From his observations on the egg, Malpighi concludes in Pulli in Ovo that

it is consequently right and proper to surmise [what] we are considering the primeval and simultaneous genesis of the [parts] of animals. For we may surmise that the chick together with the bounding saccules of almost all its parts lies concealed in the egg, floating in the colliquament, and that the nature of the latter results from the integration of the mingled nutritive and fermentative juices, through the joint action of which, when aroused, the blood is produced in successive steps and the parts formerly outlined erupt and swell out.⁶⁰

Malpighi’s second treatise on the chick egg, De Ovo Incubato, supports his previous claims. He maintains the “conjecture” that the parts of the chick are pre-formed within the egg after the simultaneous genesis of parts. At various stages Malpighi provides a chymical analysis by heating the substance of the chorion and amniotic fluids of the egg to see if they coagulate, in an attempt to understand its means of production.⁶¹

Previous commentators have pointed out that the “simultaneous genesis of parts” within the saccules puts him in stark contrast with proponents of pre-existence like Malebranche or Swammerdam.⁶² The latter assume that the rudimentary parts from which the embryo developed existed before fertilization. Development of the embryo before fertilization entails that the generation of the embryo is subsumed under growth, bypassing the problem of generation all together. For Malpighi, however, the pre-formed embryo does not exist before fertilization. Rather, the development of animal-embryos begins at fertilization from heterogeneous male and female components, and this would entail that some kind of production occurs.⁶³ That production happens via the simultaneous genesis of parts.⁶⁴ But explaining just how those rudimentary parts are produced remains a difficult task. One could imagine, then, how a plastic and organizing force that could explain how the rudiments form from fluids mechanically mechanically would be an especially helpful explanatory apparatus. Such an apparatus Malpighi gets from Robert Boyle .

The peak of the exchanges between Boyle and Malpighi happened after the death of Oldenburg primarily through Carlo Ronchi, a resident in London from Italy. At the beginning of 1686, Malpighi wrote to Ronchi expressing his deep admiration of Boyle and posed questions for Boyle about the latter’s work on blood.⁶⁵ Moreover, accompanying this letter was a package of books and Porretta crystals.⁶⁶ Boyle responded through Ronchi shortly after expressing his gratitude for the crystals, his high regards for Malpighi, and cheers for Malpighi’s good health.⁶⁷

There was much interest in the rest of the community of Italian anatomists in Malpighi’s correspondence with Boyle, and they wrote frequently to him inquiring about it. Most note-worthy for our purposes was Malpighi’s correspondence with Lorenzo Bellini. A letter from Malpighi to Bellini, who was also interested in the generation of minerals, shows the relevance which the crystals sent to Boyle by Malpighi had to the theory of minerals. In the letter, Malpighi explains that one particular crystal confirms Boyle’s opinion that minerals originate from fluid material. The crystal had an air bubble that would move, as if the internal contents of the stone had not entirely solidified.⁶⁸

Incidentally, Malpighi also sent a second package to Boyle including more crystals later that year. It seems to have been lost, however.⁶⁹ Nonetheless, Malpighi’s correspondence is very telling about the relationship between him and Boyle. Given that fact, Boyle’s description of coagulation in those works published in Latin can help to contextualize Malpighi’s own references to plastic virtues or powers in his own writings.

6 Malpighi’s Plastic Power

Malpighi’s first and most noted reference to plastic power s is found in his epistle to the Lyon physician, Jacob Spon. Malpighi sent a copy of the letter, dated November 1681, to the Royal Society in August of 1683. It was subsequently published in 1684. In the epistle, Malpighi describes the fecundation of several animals such as butterflies and a cow, as well as the fecundation of plants. It is not unlikely that Malpighi had Boyle specifically in mind when writing to Spon, either. Accompanying the copy of the epistle that Malpighi sent to the Royal Society was a letter to Dr. Francis Aston.⁷⁰ In that letter, Malpighi explained that he had already sent a copy of the epistle to the “Illustrious Robert Boyle ”.⁷¹ In fact, a copy of the epistle to Spon is still present in the archive of Boyle’s manuscripts and papers.⁷²

In the epistle, Malpighi makes only three references to plastic power s, the first of which is in passing.⁷³ The latter two references are in a later passage. He begins by describing that in butterflies, a sticky ichor drips from a structure attached at the end ovary through the vagina. Malpighi writes (boldface mine),

By this ichor the semen of the male and also another humor emited by a lateral chamber are received and maintained, and by all three of them eggs passing through the vagina are moistened and fecundated; and thus that plastic power is preserved for many days and communicated to eggs emerging at subsequent times. This, we may infer, is also true of the hen, where the energy of the semen received in a single mating is preserved to no small degree, with the result that eggs are fecundated even for some time thereafter. And since in the hen’s egg Nature does not scatter and sprinkle the semen of the cock or another menstruum fecundated by the semen upon the cicatricula alone, in which the rudiments of the parts lie concealed, but also moistens with plastic force the entire egg (that is to say, the aliment in the form of albumen and yolk), so that the whole is fecundated, and residue, too, the uterus is analogous to the hen’s egg, because it is swollen with humor and surrounds the ovule, it is therefore probable that the uterus and the humors it contains are also fecundated.⁷⁴

Given Malpighi’s general mechanical program, that he had in mind a more traditional, Galenic notion of the term ‘plastic’ in the passage is unlikely. Moreover, such a reading would be an awkward one, too. This part of Malpighi’s discussion is immediately preceded by a description of fluid particles in motion in which he explains that the male semen is able to fecundate eggs by mixing with an ichor from the vagina. In other words, fecundation occurs as the result of mixing two fluids. Further, that process is explained entirely in terms of particles of matter and motion. From all of this, Malpighi concludes that the compendium, the outermost boundaries of the chick, lie concealed within the cicatricula before incubation. Those first rudiments become visible only through motion and are formed separately from fluid.

Malpighi’s Vita, from his Opera Posthuma, explains more explicitly just how those rudiments become visible through motion. He concludes from several observations on incubated eggs that the fecundated egg contains the rudimentary parts.⁷⁵ Those rudimentary parts, Malpighi explains, are nothing more than a collection of fluid confined by an embankment. After incubation, the fluid becomes thinner as the solid parts are dissolved into furrows so that the humors flow and are confined to the cicatricula. Within the cicatricula, in the same manner described in his embryological treatises, the parts swell and grow making the first filaments visible. That happens, he explains, when the outermost parts are constructed, giving rise to cavities which are then filled by fluid, causing the early formation of the spine to emerge.⁷⁶

In the context of this discussion, that is, the initial simultaneous development of the parts within the compendium, there is another reference to these plastic power s. Malpighi writes,

[Nature] begins to form the rudiments of the parts to be delineated… by means of whose pores, as by so many glandular sieves, she separates the infenced fluid from the fluid in which it is immersed; and the fluid thus confined is pervaded by the plastic spirit and organized, when unsuitable substances have been transpired and its parts have been properly adapted.⁷⁷

Here, too, Malpighi appeals to the example of butterflies, whose wings and antennae are first sketched out in their outer parts, and then filled with fluid. Recall how, in Pulli in Ovo Malpighi describes the saccule as floating in a liquor of colliquament. The fluid which fills out the cavities formed by the outer parts later solidifies, and the parts are drawn out from their saccules. The carina (rudimentary parts of the spine) is formed similarly. Boyle and Malpighi are strikingly similar in this regard: Whereas Malpighi describes the organization and hardening of the fluid from the saccules to create the rudimentary parts of the chick by the plastic power , so too does Boyle describes the production of complex crystal formations. Both scholars describe the formation of a new being from the organized, coagulation of fluids resulting from mixture.

Another passage from Malpighi’s posthumous work confirms that he wrote on plastic power s within the context of Boyle’s work on minerals. In this particular essay, Malpighi is describing how fecundation of fruit occurs, especially those cases in which multiples occur. To explain, Malpighi appeals to juices and the power of the colliquament. In the case of unfertilized eggs Malpighi explains that because “the plastic virtue misses by chance”, there is merely an accumulation of particles. Malpighi compares the fruit to flowers, stating that multiples arise from an abundance of mixed juices and of floating particles.

Malpighi continues by comparing this process to the formation of stones. “Similar phenomena,” he writes, “also occur not infrequently in the concretion of stones.” For an example, he looks at jet, which forms a kind of “egg” from fluid materials in which diverse tinctures and particles are present due to the different densities (gravitas) of the particles. That process causes a kind of resistance which creates layers, like those of onions. The onion described in this passage is reminiscent of the layering displayed in his sketches from the embryological treatises. Indeed, Malpighi goes on to compare the stones to his observations in the incubated egg. Here, the center circle is the cicatricula, which contains the chick’s rudiments (the carina). He explains that the concentric circles of the stone exhibit a similar appearance (species) to the incubated egg, in which the many circles form around the carina by means of fermentation and get larger.⁷⁸

As with previous works, Malpighi continues to analyze their continued development in terms of the concretion of juices and the movement of fluid particles. Later, he mentions Boyle by name, stating that stones and gems are thought to derive their origins from fluids by “the most learned Boyle and Steno” (boldface mine):

Succedunt autem in prima gagatis productione tot ova, non quia lapides ab ovo viventium more ortum necessariò trahant, sed materiæ necessitate. Constat namque ex his, quæ à Doctissimis D.D. Boyle, & Stenone, habentur lapides & gemmas suam originem à fluidis trahere. Et quoniam primum fluidum salibus, & particulis fossilium, & mineralium ad minima solutis impregnatum turget, ideo intestino suscitato motu exagitatur, & ambientis pondere premitur, unde à centro extrusæ graviores medio fluido aequali vi circulum efformant, cui aliæ succedentes consimili compressione extrusæ alium addunt, quod pariter repetitur secundum copiam primi fluidi, & ejusdem heterogeneitatem.⁷⁹

What is more striking than Malpighi’s explicit mention of Boyle is the extent to which Malpighi’s language is parallel to that of Boyle’s own in the passage of the Exercitatio De Origine Et Viribus Gemmarum (The Origin of Gems and Virtues), in which Boyle explains specifically how he thinks that the petrific spirit acts upon matter:

Atque ut hactenus dicta in rem meam vertam, existimem, quasdam (saltem) ex veris Gemmarum quarundam Viribus posse ex eo derivari, Quod dum fluidam illae formam obtinebant (vel saltem necdum durantae errant) substantia Petrifica Minerali cuidam Solutioni tincturaeve, vel alii cuidam liquori impraegntato, comixta, haeque postmodum substantiae coagulatae, vel unitae durataeve fuerint in unam Gemmam…⁸⁰

That Malpighi’s vocabulary mirrors Boyle’s is especially striking given that Malpighi references such phenomena as impregnated liquors and stones all within a discussion of the fecundation of fruit. Outside of the context of Boyle’s own works, such references seem out of place.

Moreover, there are references in the passage which link it to other parts of the Origin of Gems and Virtues. For example, that Malpighi mentions both Steno and fossils is not unrelated. Both the Latin and English editions of Boyle’s Origin and Virtues of Gems include a preface from the editor which quotes Steno’s summation of Boyle’s argument for the formation of gems from fluid via the petrifick spirit.⁸¹ This three-page long quotation comes from the former’s Prodromus, in which Steno describes the formation of fossils.⁸² Curiously, though he published before Boyle’s work on gems, Steno fairly accurately explains Boyle’s thoughts on the matter in the introduction Prodromus.⁸³ Steno’s dissertation was later translated into English by Oldenburg, and the two were published together in a rare 1673 edition of Boyle’s Essays of the Strange Subtilty, Great Efficacy, Determinate Nature of Effluviums.⁸⁴

Further still, Malpighi mentions in the passage coagulation and heterogeneity. As discussed previously in this paper, both coagulation and heterogeneous fluids are key themes for Boyle’s work on minerals. Near the end of this discussion, Malpighi states that the generation of eggs requires an abundance of heterogeneous fluid, explaining the effects of the heterogeneity of matter in terms of fluids, volatile particles and motion. Thus, Malpighi’s plastic power is part of a mechanical account of the generation and consistent with the observations made in his embryological treatises published several years earlier.

7 Malpighi, Sbaraglia, and Mechanical Explanation

The idea that fecundation occurs as the result of a mixture is by no means a new one. Indeed, even on the Galenic view the embryo is a result of a mixing of seminal fluids which produces a formative faculty, or plastic and molding power. That power organizes the matter’s constitution.⁸⁵ What distinguishes Malpighi’s plastic power s from those of his medical predecessors is the manner and process by which he conceives that formative agent to work. For Malpighi, as for Boyle, the plastic agent is a distinctively physical one. Like Boyle, moreover, Malpighi is interested in explaining the effects of a plastic power in terms of matter and motion (in this case, the particle accretion of fluids). In that sense , Malpighi’s plastic powers are antithetical to the Galenic formative faculty. In the case of Malpighi and predecessors, it is important to remember that however similar their theories may initially seem to the present-day reader, that radical difference would not have been lost on their own contemporaries.

In a Riposta to Giovanni Sbaraglia, an Italian physician and one of Malpighi’s more prolific adversaries, Malpighi maintains that the mode of operation of the soul is mechanical, arguing that, “the soul is forced to act in conformity with the machine on which it is acting; therefore, a clock or a mill could be moved by a pendulum, an animal, a man, or even an angel, but it will always be moved in the same way.”⁸⁶ Thus, like Boyle, Malpighi emphasizes the mode of operation for the agents responsible for acting on matter rather than the nature of those agents themselves. Similarly, that the agent acts “in conformity with the machine” and physically upon matter is sufficient for that account to be considered mechanical for both Boyle and for Malpighi.

Sbaraglia replied with a rather harsh criticism to Malpighi’s argument. His response is an important one for understanding the episode, too, because it offers the present-day reader a unique perspective from a contemporary of both Boyle and Malpighi who, in many ways, defends a distinctly Galenic conception of the body. His main complaint of Malpighi’s view is the “modus mechanicus”—or mechanical mode—of explanation that it provides. In other words, the operation of the soul is not bound by the faculties, but by local motion.⁸⁷ From this Galenic perspective, the kind of explanation posited by Boyle and by Malpighi— one of bracketing off the agent and describing its effects in terms of matter and motion—is considered to be a distinctly mechanical one. When a seventeenth-century Galenist vehemently opposed to the mechanical philosophy criticizes the mechanical mode of explanation posited by those who likewise consider their explanations to be mechanical, it would be anachronistic to dismiss the accounts of either Boyle or Malpighi as simply unsuccessful or misguided.

8 Conclusion

Reading both Boyle and Malpighi together brings three levels of insight to the modern reader. First, it helps to clarify the concepts that each had in mind when evoking agents such as a plastic power in their accounts of generation . Analyzing Boyle’s influence upon Malpighi’s thoughts about generation shows that Malpighi provided a thoroughly mechanical account of generation. This account is explained in terms of the particle accretion in heterogeneous fluids. In a similar vein, Malpighi’s work allows one to see Boyle’s writings through the lens of a distinguished and especially relevant contemporary. This lens clarifies just how Boyle redefined a term traditionally associated with Neo-Platonism, faculties, and the soul into the context of the mechanical philosophy.

Second, because of Boyle and Malpighi’s influence and collaboration with others, we are informed about several other members of the intellectual community. For example, Nathaniel Highmore experimented with Boyle on the chick and dedicated his own embryological treatise to Boyle.⁸⁸ Steno, mentioned earlier, not only wrote on the generation of minerals in a treatise published with Boyle’s, but also was so distinguished at anatomy that Henry Oldenburg describes him as, “a Dane living at Florence who is second to none as an anatomist…”⁸⁹ Bellini, the fellow to whom Malpighi described the crystals mailed to Boyle, expresses to Malpighi through letters a considerable amount of interest in both the generation of minerals and the works of Robert Boyle . Yet, Malpighi too, was a well-known physician in Italy who was especially dedicated to mechanical explanation s. These are only a few examples that require further investigation and research, but it is important to remember that none of the figures we study were writing in isolation, but in frequent communication in a network with each other.

Finally, and most importantly, reading Boyle and Malpighi in the context of each other points to a more complex and multi-faceted understanding of both generation and explanation than previously assumed. It brings into focus questions about the mechanical philosophy and mechanical explanation s as understood by their contemporaries. Like Boyle, Malpighi was also well known for his mitigated skepticism and emphasis on observation. Further, like Boyle, he was committed to mechanical explanations. In stipulating that the plastic power must act physically upon matter, Boyle allows for the possibility of a mechanical plastic power. Malpighi seized upon that possibility. Triangulating between Sbaraglia, Boyle, and Malpighi allows us to disentangle the complex notions of mechanical explanations regarding experimental investigations in the seventeenth century.