“Enlightenment doctors,” writes G. S. Rousseau in a survey of seventeenth- and eighteenth-century medical discourse, “reduced human behavior to spirits, fibers, and nerves in their writings, creating a lush jungle of metaphor, which when brought under the lens of linguistic analysis proves to be a value-laden, subjective, and passionate labyrinth.”1 Although he did not seed this jungle—for millennia physicians had used metaphor and other figures to describe the motions and motivations of the invisible fluids ostensibly coursing through the nervous system—the seventeenth-century neurophysiologist Thomas Willis did more than most to cultivate this figurative foliage and to make it thrive. In Willis’s writing, the mechanisms of the nerves and brain flourish with a particularly profligate figurative energy. Because it stands as perhaps the most thoroughgoing attempt to reduce mind to brain at the time, and because it also ornaments an account of cerebral mechanism with a series of markedly baroque metaphors, Willis’s work serves as an ideal specimen for anyone interested in examining the grafting together of empirical neuroscience and figurative fictions of mind during this period.2 The prominence of both physiology and figuration in Willis’s texts demonstrates that both discourses must be taken into account if we are to understand early work in neurology.
More specifically, in describing the actions of body and mind, Willis frequently turns to his favorite trope—personification or prosopopoeia—in order to enliven a bit of neuroanatomy that proved uniquely important for his physiological system: the animal spirits. As in Descartes’s work, Willis’s neurophysiological system casts the animal spirits as emissaries of the incorporeal mind or, more properly, as particulate bits of matter coursing through the body’s (presumably) porous nerve fibers.3 The animal spirits actuate the volitional commands of the soul or psyche, just as they deliver sensory information to this sovereign mind, which remains ensconced in a theater or control room at the center of the brain.4 The animal spirits undergird the image of the mind as a sovereign ruling over a polity of subservient body parts.5 But Willis goes beyond Descartes in attributing more fully mindful activities to the spirits. In comparison to Descartes’s relatively restrained vision of these entities, Willis’s spirits are responsible for far more mental activities and for far more complex ones at that. In Willis’s work, the animal spirits make it possible for the body not simply to sense and to respond to its immediate environment but also to engage in “higher” forms of thought, such as reason and judgment. And, following this shift, Willis describes the spirits with a figurative abandon wholly absent from Descartes’s more stringently literal writings on them. In Willis’s work, the animal spirits behave like citizens and soldiers living, working, and dying in a metaphorical body politic, lorded over by the aforementioned incorporeal soul. They possess desires, thoughts, and emotions. They fall in love, go mad, suffer from disease, enjoy drugs, even dance. In short, thanks to the resources of personification, Willis’s spirits behave almost exactly like the human persons they inhabit and in a certain sense create. Willis’s personifying of the brain was so prominent in fact that in a survey of physicians who had advanced the cause of the animal spirits in the preceding century, George Cheyne singled out Willis for his figurative descriptions of neuroanatomy. As Cheyne notes, while some physicians used the animal spirits “to explain muscular Motion” or even applied “Geometry and Calculation” to their movements, it was “Willis [who] gave [the animal spirits] all the Advantages of Eloquence and Metaphor.”6
There is an irony in Cheyne’s praise since Willis himself, along with many of his scientific colleagues, imagined that his greatest achievement was the creation of painstakingly literal descriptions of the nervous system—descriptions that would serve, in turn, as the basis for a scientifically grounded and empirically accurate account of the mind.7 For instance, Willis explains that when he first began to lecture on the mechanisms of mind to students at Oxford (an institution where he held a professorship in natural philosophy), he frequently found himself indulging in free-floating fantasies before he undertook his dissections:
For the Province, which I hold in this Academy, requiring that I should Comment on the Offices of the Senses . . . and of the Faculties and Affections of the Soul, as also of the Organs and various provisions of all these; I had thought of some rational Arguments for the purpose, and from the appearances raised some not unlikely Hypotheses. . . . But when at last the force of Invention being spent, I had handled each again, and brought them to a severer test, I seemed to myself, like a Painter, that had delineated the Head of a Man, not after the form of a Master, but at the will of a bold Fancy and Pencil. . . . Thinking on these things seriously with my self, I awaked at length sad, as one out of a pleasant dream; to wit, I was ashamed that I had been so easie hitherto, and that I had drawn out for my self and Auditors a certain Poetical Philosophy and Physick, neatly wrong with Novelty and Conjectures.8
According to Willis, the only way to rid himself of the “Poetical Philosophy and Physick” that had obscured his first lectures was to focus instead on careful observation and committed empiricism. He would no longer “pin [his] faith on the received Opinions of others nor on the suspicions and guesses of [his] own mind.”9 Instead, he would “believe Nature and ocular demonstrations.”10 Indeed, in order to understand the “Faculties and Affections of the Soul,” he would observe the psyche’s underlying organs directly, which meant dissecting the brain: “Therefore thenceforward I betook my self wholly to the study of Anatomy: and as I did chiefly inquire into the offices and uses of the Brain and its nervous appendix, I addicted myself to the opening of Heads . . . [so that] some truth might at length be drawn forth concerning the exercises, defects, and irregularities of the Animal Government; and so a firm and stable Basis might be laid, on which . . . a more certain Physiologie of the Brain and nervous stock, might be built.”11 In this light, Willis’s careful observations of the brain can be seen as a way of casting into obscurity all those failed, figurative, and “poetical” attempts to capture the mind. Reading these passages, we might be tempted to believe that after millennia of describing the mind as a wax tablet or a fire or a storeroom or a cage filled with birds, Willis had finally given us something solidly literal with his dissections—a belief soon belied by his extravagant figuring of the nervous system.
Given Willis’s stated embrace of plain observation, and his corresponding antipathy toward accounts of the psyche produced by “a bold Fancy,” the prominence of figurative language in his writings should give us pause. Why would Willis—who steered away from “Poetical Philosophy and Physick”—use metaphor in his account of the brain? Stranger still, why does he personify pieces of the living person when dealing with the animal spirits? It might be tempting to read these “nervous figures” as attempts to ornament otherwise plainly scientific discourse or even as natural philosophical tools in their own right. Important scholarship on early science has taught us to appreciate how figurative language and other literary techniques could make vivid or even uncover truths about the natural world.12 Following these readings, we might imagine that Willis’s personifications enliven a dry and abstract anatomical treatise for a more general readership, or that they serve as linguistic instruments capable of opening up new ways of thinking about mind, matter, and their interaction.13 But if Willis’s figures are simply rhetorical ornaments, then it ought to be possible to strip them away without damaging his underlying message: that certain aspects of the mind can be reduced to the brain. In fact, such figures are not so easily extracted. As we will see, to deny these metaphors is also to deny Willis’s claim that one can arrive at a “firm and stable Basis” for studying the psyche by uncovering the foundations of “the Brain and nervous stock.” More specifically, I will show that metaphorical descriptions of the animal spirits make Willis’s project of understanding mind by means of matter appear plausible in the first place.
Likewise, even if we grant the stronger claim that these personifications are heuristic devices—that these figures not only illustrate a ready-made scientific truth but also orient a natural philosophical research project—then we must face the fact that their use deviates from the stated goal of Willis’s science. Willis contends that a plain accounting of the brain and nerves will provide an adequate picture of the mind. However, in practice much of his writing finds him narrating the dramas and dispositions of cerebral agents he could neither observe directly nor confirm through more oblique means. In this respect, Willis’s penchant for personification embroils him in the problems dissected by Wittgenstein, Ryle, and their followers. Following their analysis, we can see that Willis’s writing succumbs to the “homunculus fallacy”—though it posits a committee of thinking agents (the animal spirits) in addition to the customary sovereign soul. To understand the thinking person, Willis maintains that we must gain access to an occluded, interior physical space where, it turns out, the mind’s thoughts and actions are matched by tiny, internal reflections of the whole self. In doing so, Willis offers fiction in place of explanation. To this end, Willis’s neurophysiology rests not on a fully scientific understanding of mind-matter interaction but on a metaphorical fiction, one that gives the impression that the nerves, fibers, and spirits that populate the brain already behave as completely thinking minds.
Willis’s explicit account of his neuroscientific project, then, is contradicted by its rhetorical form. Willis would have his readers believe that in place of “poetical” descriptions of the psyche—in place, that is, of the slippery metaphors of mind that had proliferated for millennia—he instead offers the first scientifically grounded, because neuroscientifically adequate, account of the mind. He imagines that he can explain certain aspects of the mind by tracing its workings to otherwise “mindless” structures: cerebral organs or the elusive fluids traveling through the nerves. And in this respect, he maintains that, by carefully observing the brain, he can avoid the “clash” between manifest and scientific views of the psyche that have troubled so many other thinkers. But more careful attention to the formal features of his writing on the brain—to its unremarked-upon use of tropes like personification—complicates such claims. In order to understand the brain as an organ that produces the mind (as opposed to treating the brain as a mindless body part like the heart or spleen), he must first figure brain matter as inherently thoughtful or else face an explanatory gap.
None of this is to deny more generally the heuristic role figurative language can play in writing on the brain and mind; nor is it to claim that all figurative language necessarily distorts natural philosophy. I will consider some more productive nervous figures and fictions in the following chapters. In fact, it’s worth noting that even Willis himself sometimes employs metaphors that helpfully illuminate his scientific research—although, significantly, these other sorts of figures are not personifications. Nevertheless, we can only understand how figurative language and other literary devices work in natural philosophy if we understand in turn how and why they can go astray. And Willis’s writings demonstrate plainly how a certain kind of neuroscience—call it “reductive,” since it seeks to reduce aspects of the mind to mindless subpersonal mechanisms—necessitates the need not just for metaphor but for a specific kind of metaphor: personification. Hence, rather than replacing ill-fitting metaphors of mind with the solidity of nerves, arteries, and fibers, the matter that natural philosophers like Willis exposed in their dissections became the basis for new and even more elaborate figures. In this respect, we can discern in their work a surprising fact: that the line between flesh and figure was hazier than we might imagine during this period. Throughout the seventeenth and eighteenth centuries, the brain—understood as a bodily organ that somehow houses the mind—is itself a metaphor.
One way to appreciate the intermeshing of flesh and figure in Enlightenment neuroscience, and in Willis’s system more particularly, is to consider the depiction of the aforementioned animal spirits. Although they are the crucial component in almost any “modern,” or mechanistically minded, account of the brain and psyche in the seventeenth and eighteenth centuries, the spirits remain controversial subjects throughout the period. From Descartes and Willis’s time until the mid-eighteenth century, we witness a furious debate concerning the nature, provenance, and even existence of the animal spirits. For some, the animal spirits were authentic objects fit for sound scientific research; for others, they were entirely fanciful creatures baked up by the heated fancies of overweening virtuosi.14 Willis himself, at least in his explicit pronouncements on the subject, sides firmly with the former group. Speculations into the animal spirits’ activities appear on nearly every page of his detailed books on the brain. And although he could not witness the animal spirits directly, Willis remains convinced that their tracks and traces are present everywhere in the nervous system—if one knows how to look. In fact, one purpose of his much-vaunted dissections was to expose the fleeting evidence of the spirits. For Willis, the animal spirits were the key to the cryptic code uncovered in the coiled nerves beneath his scalpel. By tracking the movement of the animal spirits through the nervous system, and by analyzing the chemical composition of this spiritous nervous fluid, Willis would be able to make sense of the matter that makes the mind.
Why were the animal spirits so important for Willis? To answer this question a few words about his more general conception of mind and body are in order. In one respect, Willis’s vision of the brain and nervous system isn’t wildly different from that of René Descartes (one of his most important predecessors in these matters). Like Descartes, Willis is a dualist. He maintains that human beings possess a “Rational Soul” that is “Immaterial and Immortal.”15 Thanks to this rational soul, humans can engage in highly abstract forms of reasoning and freely will their actions.16 Also like Descartes, Willis installs this incorporeal soul at the center of the brain—though he places its seat in the corpus callosum (“the Middle or Marrowie part of the Brain”) rather than the pineal gland.17 Seated within Willis’s own version of the “Cartesian theater,” the rational soul “beholds the Images and Impressions” from the external world “as in a looking Glass,” and “according to the Conceptions and notions drawn from thence, exercise[s] the Acts of Reason, Judgment, and Will.”18 Importantly, the rational soul can accomplish such acts thanks to the hard work of the animal spirits, which carry sensory information to its cerebral “looking Glass” even as they carry out its commands.19 So far, so familiar. But Willis complicates this standard picture of the nervous system by positing the existence of a second “soul”: a corporeal or material counterpart that operates alongside, and sometimes even in conflict with, the aforementioned rational or incorporeal soul. Although it cannot scale the ideational heights of its purely immaterial companion, the corporeal soul, Willis contends, is responsible for a great deal of our mental life.20 Sensation, memory, imagination, emotion, certain forms of reasoning, and even mental disorders all result from the corporeal soul.21 For Willis, the corporeal soul is identical with the nervous system. It is his name, in part, for “the Animal Liquor or Nervous Juyce, flowing gently within the Brain and its Appendixes”—or, in other words, the animal spirits.22 In sum, Willis argues that human bodies contain two centers of intelligence, forged from entirely different substances: “Man is made, as it were an Amphibious Animal, or of a middle Nature and Order, between Angels and Brutes, and doth Communicate with both, with these by the Corporeal Soul, from the Vital Blood, and heap of Animal Spirits, and with those by an intelligent, immaterial, and immortal Soul.”23
With the sweep of Willis’s system in view, we can get a clearer picture of the aims and methods of his neuroscientific project. With two souls to consider, Willis’s neuroscience takes on two different tasks. It can examine the cerebral mechanisms that make possible the interactions of the “intelligent, immaterial, and immortal Soul” with the physical world, and it can study how these same mechanisms, “the Vital Blood, and heap of Animal Spirits,” produce thought and intelligence all on their own. As we will see, for Willis, both tasks mean paying careful attention to the work of the animal spirits in the nervous system—to their chemical composition but also to their winding journeys through the nervous labyrinth. Since it concerns an immaterial entity, the first task, from the perspective of the naturalist expert in physical matters, must be necessarily limited, tentative, and fraught with tricky theological and metaphysical questions (e.g., Is the rational soul born with the body? How does the ghost move the machine?). It should be no surprise, then, that Willis spends only a few pages of his voluminous writing wondering about the workings of the rational, incorporeal soul.
The second task—determining how the corporeal soul relates to various mental faculties and psychic events—captures most of Willis’s attention, since its singular focus on the matter of the nervous system promises more expansive, certain, and concrete knowledge as a result. Because certain mental functions simply are the movements of animal spirits navigating the nervous system, it follows that understanding the mental means observing and analyzing the body’s organs. If the natural philosopher can see the nerves and analyze the fluids flowing through them, then he or she can witness the corporeal soul, and hence parts of the mind, in action. This strategy fundamentally reorients how one might investigate the psyche. Rather than exploring the mind through introspection or through an analysis of the words and concepts we use to describe the mental, Willis wagers that we can know the mind by studying its physical substrate. We can map out mental interiority by looking at a different sort of “inwardness”: namely, the physical interiority of the brain and nervous system. In the language of modern philosophy, Willis believes that the scientific image (which, for him, would concern the fluids and mechanisms of the brain and nerves) can cast light on the manifest image (the late seventeenth-century psyche conceived as a congeries of imagination, passion, will, etc.). The subpersonal realm of the brain and its mechanisms can explain qualities of thought belonging to the whole person.
Willis’s vision of the two-souled body, and the different neuroscientific strategies that result from it, also influence his (strictly disavowed) poetic depictions of the dynamics and dramas unfolding within the nervous system. In one of the best accounts of the internal politics of early neurophysiology, Allison Muri points to a tension between two sometimes conflicting political allegories in Willis’s writing: what we might call an “absolutist” model, evident when Willis stresses the immaterial soul, and a more “democratic” model, which is manifest when the corporeal soul takes charge.24 As we might expect from a committed Royalist writer, Willis often represents the rational, immaterial soul as a king or emperor ruling over the body politic; from its place at the center of the brain, the “Intellect or Humane Mind, presiding in this Imperial seat, easily performs the Government of the whole Man.”25 In this image, the rational soul cogitates and commands, while the animal spirits serve as its unthinking thralls.26 However, when Willis analyzes the corporeal soul, his representations of the animal spirits shift accordingly. In this corresponding model, the spirits are transformed into thoughtful and autonomous citizens, perfectly capable of carrying out complex tasks within the body.27 For example, thanks to the complicated cerebral structures that hem them in—the “uncertain Meanders and crankling turnings and windings about” in the brain—the spirits “may flow out orderly of their own accord one series after another without any driver, which may govern or moderate their motions.”28 Willis even worries frequently that the “lower,” corporeal soul, comprising teams of fully self-sufficient animal spirits, will rebel against its “higher,” rational counterpart, producing civil war and strife in the body politic.29 His name for this event is madness.30
An evident ambiguity in Willis’s representation of the animal spirits results from these differing visions of the brain and how we might study it. When dealing mainly with the rational soul, he represents the spirits as passive and insentient matter, while at other moments, especially when he considers the corporeal soul, he casts the spirits as lively and aware creatures every bit as thoughtful as the persons containing them. The first strategy is on firmer scientific ground, since the spirits work just like any other fluid and so can be understood and analyzed accordingly. But it also significantly curtails the power of neuroscientific explanation, as it leaves most thought to the rational soul (a mysterious entity in the eyes of natural philosophy). The second strategy grants neuroscience greater explanatory power, since aspects of the psyche can be explained by studying nervous anatomy. But this means transforming the animal spirits into something that behaves differently from most kinds of matter. Before turning to a more general account of Willis’s conflicted descriptions of the animal spirits—and the cause of that conflict—let me focus on their portrayal in a single work, Willis’s Essay of the Pathology of the Brain, a text that manages to crystallize in just a few pages the aforementioned ambiguity. In these pages, the animal spirits serve as an explanatory principle in Willis’s system, even as they become personified as a result.
Before launching into an account of ostensibly nervous maladies like hysteria and epileptic fits, the Pathology begins by explaining how animal spirits make “normal” volitional acts possible. When we resolve on a certain action—to move an arm or speak a word, for example—a number of animal spirits, impelled by the force of one’s will, rush into a corresponding appendage in order to actuate our intention. As Willis explains, in their capacity as an “instrument of regular motion,” the animal spirits move a muscle by “being more thickly heaped up together, in the motive part [i.e., the muscle], and there spreading themselves in a more large space, they blow it up. . . . Spirits there more thickly gather together, and spreading themselves forth, they first intumifie this part, then going forward another, and so farther, . . . and by this means transfer an intumification, and therefore a motion, from one place to another.”31 Put more simply: the animal spirits are pushed through the nerves and then into a muscle, where they collect together until enough pressure builds up to actuate a connected and corresponding muscle. One can imagine a segmented hollow tube filling with water, section by section. The entire process is stringently mechanical—one of pressure building up and then releasing, with discrete particles knocking into one another—so much so that Willis, in a knowing metaphor, likens the dynamic energy created by the spirits’ movements to “the force of a pully or windlace” or to the “manner of gunpowder,” wherein the spirits are “as it were fired [and then] exploded or thrown out.”32
Just a few pages later in the same work, however, when Willis comes to explain more complex bodily dispositions, such as the fits and convulsions suffered by those with various nervous maladies, he suddenly grants the spirits more than mechanical agency. For instance, in the case of those prone to hysteria, the animal spirits themselves seem to suffer from a corresponding malady: “It is to be observed, that the animal spirits are in some more tender, and easily dissipable from their very birth; so that indeed they are not able to suffer any thing very strong or vehement to be brought to the sense or imagination, but straight they fly into confusions.”33 The sentence is tellingly ambiguous: the first clause speaks of a person’s animal spirits, but the second clause could refer either to the whole person (in which case the whole organism cannot “suffer any thing very strong or vehement”) or, once again, to the person’s animal spirits (and in this sense the animal spirits, understood as agents of sense and imagination, suffer). In a certain sense, the distinction is meaningless in Willis’s system, since, as we will soon see, the actions and reactions of a person and his or her spirits exactly reflect one another. In fact, in these pages Willis soon makes it clear that the seemingly mindless animal spirits that, just a few pages before could endure the violence of being fired from the brain into a muscle, like an artillery shell exiting a canon, can also be traumatized by overwhelming emotions and imaginative excesses: “Further, sometimes a violent Passion impresses on the spirits, though moderately firm, this kind of dissipation and inordination [i.e., a tendency for nervous hysteria], so that afterwards they are able to suffer nothing strongly, or to resist any injury.”34 As the Pathology marches along, the spirits take on a series of increasingly complex traits and capabilities. In the case of epileptics, sometimes the spirits are rebellious and intractable, and so to abate the fits these nervous particles might cause it is important to expose them to an astringent aroma, one that can “repress [these spirits] being too apt to grow fierce and to leap forth, . . . and compel them into order.”35 Similarly, when Willis wonders why “the use of opiats, brought a pleasing sleep” to a patient, he insists that “the reason was, because the animal spirits, as unquiet and furious as they were, yet by the Intanglement of the Narcotick Particles, they were bound as it were in Chains, that afterwards, without any resistance they were overcome by sleep.”36 One cure for spirits made furious by the venom of a spider bite is to delight them with music: “Musick with its flattering sweetness, doth congregate together, and mutually associate with ease the spirits so dissipated. . . . The same spirits, by reason of the Infection sticking to them, are apt to involuntary and Convulsive motions, [but] the melody disposes them, delighted together . . . until at length the particles of the venom, being quite evaporated, . . . they wholly shake off that madness.”37
I will have more to say about the formal and (more specifically) figurative qualities at play in passages like this later. For now, though, I want to draw attention to the paradox that cuts through Willis’s description of the animal spirits. When Willis details the activity of the animal spirits in the first passages quoted here—the ones dealing with volition, the twitch of a muscle, the lifting of a finger—he describes them as utterly thoughtless entities. Since the spirits actuate muscles through the buildup of pressure, they don’t need to possess intellect or instinct of their own. These spirits are simply unknowing particles impelled through the nervous system by the real intelligence at work here: the will, a faculty that Willis elsewhere identifies with the rational soul. However, having established the animal spirits as entirely unthinking things, Willis—in the proceeding pages dealing with various convulsions and epileptic fits rather than steady volitional acts—begins to invest them with mental properties. In this instance, the spirits are no longer thoughtless particles pushed about by sheer physical force but creatures capable of minimally mindful activities. They evince character traits every bit as complex as those of the whole person of which they are a part. Not only are they prone to “hysteria”; they can also be frightened by strong emotions and unpleasant imaginings. Not only are they capable of insubordination; they must be cajoled or restrained in different ways—through the use of drugs or music, for example. Strangest of all, the spirits don’t simply tumble blindly and impassively through the body, pushed along by exterior forces; they also dance. In a few brief pages of Willis’s writing, then, we find the animal spirits figured both as merely material particles no different in nature from stones or pinballs and as protoconscious entities capable of executing independent movements.
It’s precisely because Willis wavers in his description of the spirits, because he transforms mindless nervous fluid into thinking things, that his work often reads like poetry rather than pure science. Given the animal spirits’ prominence in Willis’s writing, it should be no surprise that his name became associated with them. What is surprising, though, is how often Willis’s readers saw in his description of the animal spirits the mark of the very “poetic” thinking he claims to have banished from scientific work on the brain. For example, Nicholas Robinson complains of “the Absurdness of all those fine Things talk’d of by Willis and others, concerning the Mechanism and monstrous Explosions of the Spirits”; these spirits, he goes on to say, are “mere Whimsies, and the speculative Fancies of a warm Brain, without any just Reasons, from the Operations of the Animal Oeconomy to support them.”38 Indeed, more than once Willis, thanks to his extravagant personifying of the animal spirits, was portrayed as a lunatic general marshaling an army of invisible animal spirits: “[Willis] was a man of uncommon penetration, and saw further into the heads of mankind than any of his contemporary brethren; and wrote many ingenious romances in a pleasing and nervous style. He was well known to have dealt much with familiar spirits, called animal. Having a great command over them, he could, for the entertainment of his acquaintance, make a million of them dance a jigg on the pineal gland of a fine lady, or on the point of a needle. He would send them on errands God knows where, and remand them back as quick as thought.”39 Writing more seriously, the physician Thomas Morgan shared the sense that Willis was writing “ingenious romances in a pleasing and nervous style.” Surveying the baroque technical discourse of Willis’s philosophy—“the Explosions and Suffocations of the animal Spirits . . . the chymical Effects, Changes, and Transmutations produced in the animal Body, by the various Mixtures, and mutual Actions and Reactions of Salts and Sulphurs in the Blood”—Morgan recommended nothing less than censorship:
This enthusiastick Cant Philosophy has furnish’d abundance of Gentlemen in the Profession of Physick, with Matter enough for Ostentation, and an inexhaustible fund of Absurdity and Nonsense, which is much admired by those who cannot judge of it. But, perhaps, it might be very well if the Parliament would take this Matter into Consideration, so far as to oblige all Physicians to talk English to their Patients, and not to amuse them with technical Words and Terms of Art, out of the Greek and Latin Languages, which they cannot understand, and which perhaps are seldom understood by those that use them.40
Morgan explains that Willis’s terms of art—namely, his descriptions of the animal spirits and their various chemical transformations—are literally just that: technical jargon meant to artfully “amuse” listeners with “ostentation,” “absurdity,” and “nonsense.” Willis’s language, in other words, was purely aesthetic in nature: it was to be “admired” but not “understood.” But this complaint suggests a second. If Willis’s words were semantically empty—a burnished surface concealing only hollowness—then terms like “animal spirit” denominated nothing real within the body. For Morgan, the animal spirits were merely linguistic entities, creatures that would be eradicated not by the cessation of life or the dampening of chemical reactions but by an act of Parliament banning hard words from the English language.
Although they were sometimes petty, frequently unfair, and often vicious, Willis’s critics were nevertheless among his most perceptive readers. These critics portrayed Willis not as he wanted—that is, as a careful observer battling against the illusions of fancy and the dead weight of tradition—but as he feared: a natural philosopher more interested in speculation and hypothesis than pure empiricism, a scientist who followed the dictates of his imagination rather than the order of nature, a writer who produced a “poetical philosophy and physick” instead of the “certain Physiologie” of the brain and its faculties. In this respect, these critics exposed the literary qualities of Willis’s writing—his use of metaphor and personification, his imaginative descriptions of the animal spirits’ journeys through the body and brain—that have been neglected in the celebratory, triumphalist accounts of his contemporaries, and even in the more balanced assessments of modern commentators.
How did the animal spirits manage to elude uncomplicated linguistic capture in Willis’s writing? Why do these entities continually introduce strange inconsistencies and fissures into the texts in which they appear? One answer to these questions can be found in the history of the spirits themselves. Although animal spirits had appeared in medical texts for millennia—they are engendered in Galen’s physiological writings and eventually worm their way into a host of early modern works—these entities undergo a subtle transformation during the late seventeenth century that differentiates their representation during that period from earlier manifestations.41 Speaking generally: whereas ancient and early modern writings on the animal spirits emphasize the ontologically ambiguous nature of these entities—the animal spirits, to play on their name, were seen as poised between the corporeal (or animal) and incorporeal (or spiritual) realms—Enlightenment thinkers frequently portray these entities as definitively material in nature.42 That is, the animal spirits in most Enlightenment texts are no different in substance from other material elements journeying through the body, such as blood, bile, urine, etc.43
This was certainly the case for Willis. Inspired by a lifelong interest in chemistry, Willis attributed the animal spirits to a biochemical process happening within the veins, arteries, heart, nerves, and brain.44 Specifically, Willis believed that blood, warmed and pressurized by the beating of the heart and by internal chemical reactions, would make its way to the brain, an organ that further refined and volatized the fluid flowing into it.45 From all this internal bodily ferment—from the buildup of pressure and heat, from the pumping of the heart and the sifting of the brain, from the sparks and smoke of chemical combustion—the animal spirits are born. Importantly, Willis insists that the resulting spirits must not be imagined as inert, stolid, heavy bits of matter. Willis’s animal spirits are necessarily energetic and light, since the process that creates them filters out heavier and more sluggish material. In fact, thanks to their highly agile and chemically charged nature, animal spirits evince a degree of self-motion and agency.46 Accordingly, a team of these spirits, powering through the windings of the nervous system, create a great deal of our mental life. For Willis, they are at the basis of sensations, memories, and even mental health.
It is tempting to imagine that the animal spirits, given their energetic and almost ethereal nature, possess abilities that are wholly unlike those of normal matter—that they attain some connection to a transcendent realm or that they retain an irreducible and inexplicable spark of vital force. Willis resists such theories. He insists, throughout his work, that there is nothing mysterious or otherworldly about the animal spirits or about the biochemical process producing and empowering them. The spirits’ ability to impel themselves through the nervous system can be explained fully by the interaction of more basic and utterly common chemical compounds.47 Fundamentally, the animal spirits result from the same chemical reactions that “supply the Springs of Hot Fountains for Bathes,” that make plants “to Bud forth, Grow, Flower, bear Fruit, Ripen,” and that produce the stomach acid that digests food.48 In all these cases, Willis argues, fermentation is at work, and “fermentation is an action or motion meerly Natural.”49 To be sure, for Willis, the biochemical process that creates certain thoughts in the brain must be more complex than the chemical reactions that create hot springs, fruition, or digestion—since a more complex entity, the nervous system, is involved—but it is not qualitatively different. That is, in all these processes, we witness a difference of degree but not of kind. If one can rationally reconstruct the physical properties that heat water, then in principle one can explicate how the brain and its animal spirits make thought, since fermentation fuels both activities.
To stress this point Willis, in a knowing and controlled metaphor, likens the brain to an alembic, a devise used to distill heated liquids (like wine):
It seems to me that the Brain with Scull over it, and the appending Nerves, represent the little Head or Glasie Alembic, with a Spunge laid upon it, as we use to do for the highly rectifying of the Spirit of Wine: for truly the Blood when Rarified by Heat, is carried from the Chimny of the Heart, to the Head, even as the Spirit of Wine boyling in the Cucurbit, and being resolved into Vapour, is elevated into the Alembick; where the Spunge covering all the opening of the Hole, only transmits or suffers to pass through the more penetrating and very subtil Spirits, and carries them to the snout of the Alembick: in the mean time, the more thick Particles, are stayed, and hindred from passing. Not unlike this manner, the blood being delated into the Head, its spiritous, volatil, and subtil Particles, being restrained within by the Skull, and its menynges, as by an Alembick, are drunk up by the spungy substance of the Brain, and there being made more noble or excellent, are derived into the Nerves.50
Willis’s image of the brain as an alembic is perfectly calibrated to extract the explanatory core of his neuroscientific project. Note that the figure transforms the nervous system, that most mysterious of organs, into a laboratory mechanism that must be readily intelligible to its operator. Indeed, it is precisely because the natural philosopher understands how the alembic works that it can serve as a reliable instrument for discovering otherwise unknown facts about the nature of matter. Thanks to Willis’s metaphor, that quality of inherent intelligibility is transferred to the brain and nerves. The figure also transmutes the substance of thought into something plainer: the vapor and subtle particles that emanate from heated wine. In doing so, it suggests that we can reconstruct the process whereby new and more complex qualities emerge from known, simpler ones. Both the vapor arising from distilled wine and the “volatile” particles released from the blood can be reduced to more basic elements. In both cases, a chemical reaction makes matter move, and this movement creates new qualities in turn.
I want to suggest that the ontological taming of the animal spirits in the late seventeenth century—their fixing as purely physical things rather than as a special category of hybrid spirit-matter—became both a major strength and weakness for Enlightenment neurophysiology like Willis’s. More specifically, such taming generates in turn the paradoxical representations we discover in his writing. On the one hand, treating the animal spirits as energetic but ultimately insentient material particles means that their movements could be tracked and quantified, their chemical fundamentals analyzed. In this respect, various mental qualities can be reduced to physical processes—processes that can then be studied like any other natural phenomena. On the other hand, this ontological taming also gives rise to the aforementioned “clash” between the scientific and manifest images of the mind, since now neurophysiologists must somehow explain how mere matter in motion, the stuff of the scientific image, becomes (or creates or actuates) more robust mental states—the concern of the manifest image. And it is precisely this clash between matter and mind that will force Willis to waver in his descriptions of the spirits: sometimes following scientific consensus and portraying them as chemically charged but unthinking particles, sometimes granting them thoughtful qualities when matter must become mental. Hence, throughout Willis’s writing—though especially in his accounts of the animal spirits—we witness a nervous fiction at play, with the manifest and scientific images projected or superimposed into the same space, in a manner that does not resolve or alleviate their tension.
To appreciate the bind Willis finds himself in, consider, first, just how powerfully explanatory the purely scientific conception of the animal spirits, and so of the brain and mind more generally, could be—at least in principle. Here, for example, is how Willis, writing in a strictly literal mode, accounts for mental faculties like imagination and memory: “For it seems, that the Imagination is a certain undulation or wavering of the animal Spirits, begun more inwardly in the middle of the Brain, and expanded or stretched out from thence on every side towards its circumference: on the contrary, that act of the Memory consists in the regurgitation or flowing back of the Spirits from the exterior compass of the Brain towards its middle.”51 In other words, as the animal spirits move outward from the center of the brain, we imagine things; as they move inward, we remember them. Although a single animal spirit, isolated from its compatriots and stilled in its impetuous movements through the nerves, is no more sentient than a spark of static electricity, a number of spirits, charged by chemical reactions within the body, produce much of our internal mental world. With this in mind, we can appreciate the explanatory strength of this ontologically stabilized version of animal-spirit physiology. By correlating the motions of animal spirits to various mental processes, Willis’s biochemical theory of cognition reduces most thought to the movements of strictly thoughtless things. In the course of doing so, it is able to speak about the mind as if it were a physical system like any other: a pulley or windlass, a cannon, or, if those examples are too inertly mechanistic, an alembic. For natural philosophers like Willis, knowing how the mind works means simply calculating the relations of force and motion that traverse the brain. Rather than examining imagination or memory on the level of the manifest image and the person—rather than resorting, that is, to introspection (What is my mind doing when I imagine things?) or conceptual analysis (What does it mean to remember past events?)—Willis’s science, fueled by the animal spirits, can reach a deeper explanatory level. It can scrutinize, within the body’s interior, the subpersonal physical processes happening “behind” or “beneath” the person’s imaginations and remembrances. By taking on the perspective of a third-person observer, it can attain a (presumably) clearer and more certain understanding of the mind and its mechanisms.
At the same time, though, this ostensibly complete and clear account of the psyche generates a weakness, since it seems to leave out a crucial element in any research on the mind: the mental. Understood in an entirely physical sense, acts of imagination and memory may be nothing but the pulsing of motion in the brain. Nevertheless, these faculties are marked by their experiential content—that is, they are mental processes actuated by thinking beings. When we speak of faculties like imagination or memory, we almost necessarily lapse into a description of trains of imagery and representations that can be manipulated or recalled in mental space. But this concern with the mental is entirely absent from Willis’s writing at its most literal. Although Willis is describing mental faculties in this passage, he explicates them using fully mechanical (and hence “mindless”) terminology: imagination is simply an “undulation or wavering of the animal Spirits, begun more inwardly in the middle of the Brain, and expanded or stretched out,” while memory “consists in the regurgitation or flowing back of the Spirits from the exterior compass of the Brain.”52 In other words, the connection between certain sparse, rigid movements (a flow inward, a flow outward) does not line up with more robust and abstract mental activities (“the sessions of sweet silent thought”) in any self-evident way.
The absence of anything properly mental in this passage becomes particularly acute if we compare Willis’s account of the animal spirits flowing back and forth to his accounts of the “tender,” “fierce,” rebellious, and frightened animal spirits inhabiting the minds of those suffering from various nervous pathologies. While both passages essentially describe the animal spirits moving through the brain, in the aforementioned moments from the Essay of the Pathology of the Brain, Willis attributes mental characteristics to the spirits—namely, desires, frustrations, uncertainties, but also dancing and delight—which his more austere renderings entirely avoid. In a move that I will discuss more fully later in this chapter, Willis links matter and mind in the passages from the Pathology by making it seem as if the animal spirits undergo small dramas and traumas within the brain—and that these events are reflected precisely in the conscious mind. But in place of inherently thoughtful matter laboring passionately within the nervous system, Willis in this explanation of imagination and memory offers only an account of particles moving blindly through the brain. In other words, in place of the mental (understood broadly as the relationship to psychic images, powers, and affections), Willis’s literal writings on the mind present only the material (understood as the flux of matter and motion within the body).
These disconnects were clearly on the mind of many readers of early neuroscience. For these readers, animal-spirits physiology seemed to raise as many problems as it solved, as they were often perplexed by the perceived division between the cerebral structures exposed in such writing and the mental faculties this brain matter somehow created. For them, the animal spirits—understood strictly as the chemically charged fluid that fueled the machine of the nervous system—fell into an epistemological gap. For example, in his bluntly titled Matter and Motion Cannot Think, Richard Bentley attempts to disprove “the Opinion of every Atheist and counterfeit Deist [who] believes there is no Substance but Matter” by pointing to the gap separating neurophysiological knowledge and mental life.53 For Bentley, this means demonstrating “that no Determinate Motion, as of the Animal Spirit[s] through Muscles and Nerves, can beget Sense and Perception.”54 To do so, Bentley stresses the evident difference between motion and sensation: “Why one motion of the Body begets an Idea of Pleasure in the Mind, and another of Pain, and others of the other Senses . . . this Knowledge exceeds our narrow Faculties, and is out of the reach of our discovery.”55 Similarly, Matthew Hole, writing even more bluntly, notes that “a Smith’s Anvil may lay as fair a claim to Sense and Understanding, as the purest and most minute Parts of the Animal Spirits of the Brain.”56 Even if one grants that the animal spirits are not entirely inert or passive bits of matter but rather particles capable of expatiating with impressive speed throughout the body, we still encounter the same disconnect between mind and matter since—even when they interact—particles in motion simply produce more motion, not some entirely new quality like thought. As John Broughton points out:
To talk of a determinate Course, a peculiarly modified Chanel, Action or Reaction, Percussion or Repercussion of Animal Spirits, being able to do the Feat [i.e., that a body should think, by virtue of being in one place and not in another], is equal Nonesence as to imagin a Stone tumbling down an Hill, and a Wave Rolling on the Sea, the one in terrible, the other in tumultuous Thoughts; for what really happens to the former, which is change of Place, happens to the latter, and no more . . . and therefore Motion alone is not, really, capable of producing Thought in a Body moving.57
Each of these accounts points to a gap in our knowledge of how matter relates to mind. After all, what we can glimpse of brain matter, or what we can theorize about the fluids and forces running through it, bears no resemblance to what we normally take to be mental qualities. While the rush of animal spirits through a specific set of cerebral folds in the brain might produce, say, the memory of seeing a blue bird, it is unclear how or why this happens, since there is nothing blue or birdlike in the character of the animal spirits, their movement, or even the nervous labyrinth they navigate. We can see, then, that what later philosophers would characterize as a clash between two entirely divergent perspectives on mind and matter—although it was never explicitly acknowledged as such—is evident in numerous seventeenth- and eighteenth-century accounts of the brain. More specifically, we can recognize that Willis’s work particularly, and animal-spirits physiology more generally, often serves as a locus for thinking about this problem.58
Given Willis’s claim to have reduced the mind to the brain, the focus on his work makes sense. Stranger still, though, is that Willis himself appears uninterested in exploring the questions and problems raised by his account of brain and mind. It is only when we turn to the formal qualities of his text, to his use of metaphor and figurative language, that we can discern his own response to the aforementioned explanatory gap. In the following section, I will argue that Willis uses figurative language to obviate the epistemological blind spot that mars most efforts to reduce mind to brain. Rather than face this explanatory gap head on, Willis, like other Enlightenment neurologists, opts for a different approach: the creation of a natural philosophical fiction that unfolds in parallel to—and in tension with—his strict scientific claims. The creation of this fiction does not answer the aforementioned questions, of course. What it does do, however, is give the impression that otherwise unthinking animal spirits could produce the lively effects of the conscious, reasoning mind.
Seen in the harsh light of the anatomy theater, the brains that Willis and his colleagues extracted from the body appeared as opaque organs. To the naked eye of the natural philosopher, the gap between the matter directly witnessed in such dissections and the mental world that this same matter somehow created would seem insurmountable. But seen through figurative optics, the otherwise senseless matter of the brain suddenly flourished with an illusory figurative life. In an unacknowledged act of poetic daring, Willis portrayed the animal spirits as persons (complete with their own thoughts, emotions, and desires) rather than thoughtless particles (which, as seventeenth- and eighteenth-century science would readily grant, they literally were). Thanks to these figures, the difficulty of explaining mind by means of matter seems to disappear in Enlightenment neurology.
That Willis used figure to this end becomes evident if we consider The Anatomy of the Brain, his first major work on the nervous system. That text turns to metaphor only when it shifts from a description of the brain and nerves to an account of how those organs work. Like so many early scientific texts, The Anatomy of the Brain employs a number of rhetorical devices to stage a scene of “virtual witnessing” for its readers.59 For example, its first ten chapters proceed as if the reader were gazing over the anatomist’s shoulder as he dissects the brain. Upon opening the cranium, Willis tells us, one can see a membrane that is “knit to the Skull in divers places”; beneath that covering is the brain itself, which “shews somewhat globous or spherical”; below the central mass of the brain is the cerebellum, which is “marked with certain turnings and windings about.”60 And so on. The language here is dry, descriptive, dull, and wholly bereft of metaphor. And while it is empirically accurate, such descriptions must make us wonder how all this matter manages to produce mental qualities. That is, no matter how deep Willis dives into the nervous system, we cannot see past a wall of flesh into real mental “interiority.” But beginning with chapter 12, Willis, having depicted “the Phaenomena or Appearances which the whole frame of the Brain and its Appendix is wont to exhibit in Anatomical Inspection,” next “inquire[s] into the actions and use” of the structures he has uncovered.61 There is a subtle but significant shift at this point in the text. We are no longer witness to a brain dissection but to a scene that is strictly impossible to see in reality: a tour through the nervous microcosm as it produces thought. Moreover, at this moment in the text, the literal descriptions of the brain suddenly take on figurative vitality. We discover that the “medullary” parts of the brain—previously described simply as “marrowy” and “white”—also serve as a “Mart or Exchange” for the animal spirits, a place where they can engage in “their commerce to the necessaries of life.”62 Likewise, the “cortical” part of the brain—the “outmost and Ash-colored” section—becomes the animal spirits’ “principal Shop or Workhouse,” a site where they are kept “as it were in distinct Cloisters or Cells to be drawn forth for the manifold Exercises of the animal Function.”63 As these passages demonstrate, the brain only begins to think in Willis’s writing once it has been figured. If, upon anatomical inspection, brain matter did not evince cognitive capabilities—if it appeared no more thoughtful than Henry More’s “Bowl of Curds”—then those capabilities could be grafted directly onto the tissues of the brain through figurative operations.
With this issue in mind perhaps, Willis more frequently compares the animal spirits to the persons they create. His favorite figure, to this end, is the soldier. For instance, he explains that, just after they are formed in the body, “the Spirits are disposed [as if they] were an Army spread abroad.”64 Soon these creatures “obtain Orders and Offices” and are thereby sent to far-flung regions of the “Animal Government.”65 But no matter how far removed, the spirits “whether they be set in Battel Array, or on the Watch, . . . perform the Commands carried outward from the Brain, . . . and effect Motion, and deliver presently to the Brain the news or any sensible thing impressed, whereby Sensation is made.”66 In certain respects, soldiers serve as ideal metaphorical counterparts for the animal spirits. Just as the spirits waver between true mindfulness and insensible materiality, soldiers similarly are tasked with an existence that is at once freely human as well as rotely mechanical. Although soldiers possess all the agency and volition of a normal human being, they curb and restrain these qualities in order to blindly execute the commands of their superiors. Hence, the soldier-spirits that man the watchtowers and battlements of the body in the above quotations are just intelligent enough to report messages to their superior officer (the brain itself in this case) but not so alive as to perform such actions without being “ordained” in the first place. These figurative soldiers, then, split the difference between the deterministic and mechanical world of matter and the mental world of real intelligence and emotion.
But throughout Willis’s work, dissension lurks in the ranks. Particular faces appear beneath uniform helmets, and human characteristics soon overwhelm martial order, as even the modicum of figurative energy that the soldiering metaphor grants the spirits soon grows too restrained for the needs of Willis’s system. After all, Willis seeks to explain not only how the body processes sensory information (a task easily accounted for by the movements of figurative soldiers running up and down the nerves); he also wants to understand how matter could create more robust mental states (a problem requiring more mindful metaphors in turn). Consider, for example, a moment where Willis notes that the nerves, which ostensibly carry the animal spirits, were smaller than the veins, which carry blood. This is the case, Willis reasons, because the spirits would become unwieldy in more spacious areas:
Therefore the Vessels carrying [the animal spirits], viz. the Nerves, in respect of the Fibres receiving them [the blood vessels], are made much lesser in proportion; lest perhaps by too great a supplement of the animal Spirits, and the too thick gathering of the fresh ones still into the nervous parts, the Army of the Veterans, before instructed, should be confounded, and so the orders of all being disturbed. . . . For indeed when at any time the Spirits are made too sharp, so that being therefore struck as it were with madness, they rush upon the nervous System with tumult and impetuosity; from thence a great unquietness and continual throwing about of the Members are wont to be excited, to which sometimes madness and fury succeed.67
Here we discover that animal spirits are not only like soldiers—they are also like different kinds of soldiers. Some are veterans; others are novices. When the two types mix, bodily processes are thrown into disarray. By granting age and experience to the spirits, then, Willis implies that these entities not only receive and execute commands but that they also retain memories and, by drawing upon these past experiences, improve their skills. In this case, Willis’s metaphors subtly push the spirits from the realm of pure matter and motion to that of the mental, a fact confirmed by his odd assertion in the above passage that, when young and old spirits mix, they suffer from madness and fury—mental states usually reserved for whole minds rather than the pieces that compose them.
What is only hinted at in the previous quotation—that the figured animal spirits behave more like fully fleshed-out human beings than dumbly mechanical matter with just a hint of intelligence—becomes more prominent elsewhere in Willis’s work. We discover that the spirits are not only young and old but also lazy and dissolute: “When the Animal Spirits, desire too much a sensible Delight . . . there is need of Reason to come between [them], whereby they being changed into Sacred and Moral Meditations, [the spirits] may be called away from their Carnal Genius; which Avocation[,] however, they obey not but difficultly and unwillingly.”68 We find out that when the spirits have been “distracted” or separated from one another, they seek out their partners again in the hopes of a “mutual embrace” and “folding of hands.”69 We learn that a “Melody introduced to the Ears” can “inchant with a gentle breath the Spirits there inhabiting.”70 Likewise, we are told that, “in the mid’st of Fear,” the spirits sometimes become “dejected” and therefore must be injected with a spark of hope by the attentive rational soul.71
As we have seen, some of Willis’s earliest readers faulted the physiologist for such descriptions. But we can better appreciate the problem with his personifications if we take a step back to consider the use and abuse of figurative language in early natural philosophy more generally. Because Willis’s personifications distort his literal account of the brain, one might maintain, along with Thomas Sprat or some inhabitant of Laputa, that metaphors add nothing but distracting illusions to otherwise self-subsistent scientific discourse. This is certainly not the case. Far from striving for plain literality in their writing and thinking—as if only a language comprising concrete nouns could adequately convey the stark discoveries of an austere empiricism—early natural philosophers purposefully turn to tropes in their work. As Courtney Weiss Smith in particular has pointed out, figurative language like analogy could enliven or ornament otherwise recondite material, but it could also perform real scientific work and be “productive of new discoveries” by guiding empirical research or linking dispersed research realms.72 For example, Robert Boyle argues that “proper Comparisons do the Imagination almost as much Service, as Microscopes do the Eye; for, as this Instrument gives us a distinct view of divers minute Things, which our naked Eyes cannot well discern . . . so a skillfully chosen, and well-applied, Comparison much helps the Imagination, by illustrating Things scarce discernible.”73 However, early natural philosophers also frequently worry that figures could lead them astray. Significantly, Boyle recommends only “comparisons” that are “proper,” “skillfully chosen,” and “well-applied.” Implicitly, other sorts of analogy—call them “improper,” “badly chosen,” or “misapplied”—might occlude the imagination with fantasies rather than presenting it with a “distinct view” of natural things.
Arguably, both sorts of figurative language—the “proper” and the “improper”—appear in Willis’s writing. We witness “proper comparisons” at work when Willis likens the brain and its elements to a physical structure, machine, or (especially) a chemical apparatus. As Alexander Wragge-Morley notes, Willis, well within the mainstream natural philosophy of his time, consistently compares the brain to “medium sized” objects like storehouses, beehives, or alembics, to make evident its nature.74 In fact, as we have seen, the alembic is an ideal analogy for Willis, since the comparison manifests the nervous system’s fundamental nature (i.e., it operates like a chemically charged furnace) for readers who cannot cut into craniums or experiment with nervous fluids. For example, should we want to understand how the animal spirits become chemically charged and activated within the body—thereby causing muscles to move and brains to think—Willis, in a related analogy, tells us that we ought to observe the interaction of “Nitre and Sulphur,” which “being only thoroughly heated, are exploded with a vehement Crash.”75 According to Willis, what occurs visibly in the explosion of niter and sulfur happens invisibly (though on a lesser scale and in a more controlled setting) within the muscles and nerves. In this instance, we can better understand the invisible process happening within the body by analogizing it with a more readily visible event. As Willis himself puts it: “It will be easie to shew the effect of this kind of notion [i.e., that the animal spirits explode within the body] . . . from Analogie.”76
Yet when reading Willis’s “proper” figures we also can understand why he shied away from these tamer mechanical or natural comparisons: they cast the animal spirits as dumb, determined, and docile—or, in other words, as mere thoughtless chemicals coursing through the nerves. Such comparisons aggravate rather than alleviate the central mystery of Willis’s system: How, exactly, do the chemical reactions impelling fluid through the nerves and brain lead to imagination, memory, sensation, even madness? After all, it is one thing to imagine that brain matter has some special quality that can generate thought; it is quite another to think the same thing of sulfur. To obviate such questions, Willis employs personifications: arguably “improper” figures that nevertheless prop up his system. Why are such personifications “improper”? By likening the animal spirits to human beings, Willis strains the sense of his similitude. Minds are made of matter, but minds are not exactly like matter insofar as they evince qualities that are distinct from purely material ones—a disturbing dynamic that Willis’s entire figurative system attempts to circumvent. In one respect, these figures work against Willis’s literal claims about how the brain works. As we have seen, Willis argues that the interaction of unthinking particles creates certain modes of thought—an argument that leaves us with the mystery of how we get something (the mental) from nothing (the thoughtless spirits). But what Willis loses in scientific rigor when using these metaphors he gains in explanatory power (though this power is ultimately spurious since it is grounded upon a figurative fiction). For to personify the animal spirits is to close, if only metaphorically, the aforementioned gap between matter and mind—and thereby safely reduce the former to the latter. Willis’s personifying of the animal spirits works against this gap, then, by grafting the mental upon the material. Suddenly mental events do not arise from otherwise mindless things; instead, the mental journeys all the way down—we find it imbricated and expressed in the very matter of the body.
To be sure, one might still make the case that Willis’s personifications serve as more effective cognitive tools than I have made them out to be. For example, Kathryn Tabb, in an important essay analyzing Willis’s views of madness, argues that such personifications allow the natural philosopher to avoid both mindless physiology and mysterious psychology. In Tabb’s estimation, by representing the animal spirits as inherently thinking things, Willis can treat madness as a phenomenon belonging to both body and mind. That is, Willis can attribute madness to physical mechanisms (e.g., the animal spirits, made chemically unbalanced, cause madness) without abandoning subjective mental states (e.g., these same spirits are themselves mentally unbalanced).77 While this view is appealing, it nevertheless turns on a more fundamental mystery. Because Willis never explicitly explains how the animal spirits can think—to do so would find him hunting for the animal spirits within the animal spirits, as it were—he tends simply to treat them, in practice, as inherently thinking things. But this sends his argument in circles. According to Willis, we know that madness results from mad animal spirits, but we only know that the animal spirits are mad because those entities cause madness. When Willis considers why the mad are often “audacious and very confident, so that they shun almost no dangers, and attempt all the most difficult things that are,” he argues that this is because their animal spirits are likewise “very fierce and provoked.”78 Melancholy, a disease marked by “fear and sadness,” results when the spirits—usually “transparent, subtle, and lucid”—become “obscure, thick, and dark, so that they represent the Images of things, as it were in a shadow, or covered with darkness.”79 It is hard to know where material causes conclude and mental effects commence in such cases—which is the point. In each passage, a torsion in figurative logic allows Willis to link brain and mind. Willis grants matter the characteristics of human beings and their minds in order to account for the way in which matter makes those minds. As a result, in his writing, the animal spirits reflect—and thereby also give rise to—more general mental characteristics. In this work, we come face to face not with melancholy and hysteric persons but rather with brains that happen to house melancholy and hysteric spirits. Hence, while Willis seeks to understand the qualities of matter that create mind, he can achieve this end only by writing a kind of neurophysiological fiction, one wherein his figurative language subtly pushes the animal spirits from the realm of pure matter to that of the mental, and one wherein every particle in the nervous system behaves as if it were a fully thinking mind as a result.
In this respect, we can see that Willis’s figurative spirits serve not only as personifications but as synecdoches. It is the alliance of these two figures that really “solves” the clash between manifest and scientific images for Willis. If Willis could not determine how a mass of insensible matter might add up to a living, thinking being—if ultimately he did not understand what force made the discrete pieces of the body coalesce into the unity of the mind—then one solution to this dilemma is to grant the characteristics of the whole (the brain) to the parts (the animal spirits). According to this oddly recursive logic, the animal spirits can constitute a thinking thing because they already act as thinking things—a point that perhaps recalls the frontispiece of Hobbes’s Leviathan, an image that depicts numerous tiny heads composing a larger being (and an icon I will return to). Consider an extraordinary passage where Willis explains what happens within the brain when someone falls in love. The sort of love that interests Willis here is “Love excited through Opinion,” that is, the kind of love that occurs when we desire someone or something without having witnessed the beloved firsthand.80 In this sort of love,
the Species of the Object being represented by the Imagination, is erected as an Idol in the Brain; about this many Spirits being employed, at first they weigh the noted Beauty, and its various Ornaments, when they worship it; for whatsoever we love, we imagine it fair, profitable, pleasant, and far above what in truth it is; then by reason of these kind of feigned Attributes, we more earnestly fall in love with the thing beloved; Further, the Spirits inhabiting the Brain, invite all the rest, flowing in the whole Nervous stock, to the worship of the Idol erected by themselves: wherefore the Inhabitants of every Sensory, watching the works of the Senses, look hither.81
Once again, we can see how Willis’s figures allow him to mirror mind and body. In this instance, the experience of the whole mind is reflected in the activity of its parts. The animal spirits—smitten by an imagined object—behave exactly as their properly human counterpart. That is, just as we might fall in love with an image or idea, our animal spirits—toiling away within the brain—can be similarly infatuated by a mental representation. Thanks to Willis’s relentless personifying, these spirits enjoy activities that their merely material state would normally preclude: they can “weigh the noted Beauty,” “worship it,” and “invite” their compatriots to observe the beloved idol.
The purpose of all this personifying should be evident: it allows Willis to stitch together the otherwise disparate realms of matter and mind. The semicolons in the above passage link more than independent clauses; they also link what normally would be entirely divergent views of the psyche. For example, Willis’s writing here shifts without warning between first-person, subjective accounts of a mind in love and third-person, objective descriptions of brain anatomy becoming enamored. The first clause in this passage describes events in the brain, while the second and third turn to a consideration of the conscious mind itself, as talk of “spirits” gives way to talk of a different agent—a “we” meant to stand in for subjective experience (“we love,” “we imagine,” “we more earnestly fall in love”). But Willis’s clauses can alternate easily between these viewpoints only because his metaphors have made mind and matter substantively indistinct. Had Willis strictly followed his scientific statements and described the animal spirits as they literally were, then his portrayal of a brain in love would have read more like a journey into Leibniz’s thinking machine: instead of amorous cerebral anatomy, he would have discovered only cold and unfeeling mechanisms. More specifically, had Willis avoided figurative language in this instance, he would have been forced to recognize two things: first, that love happens only to a thinking subject and, second, that although the material bodies that constitute this subject might create the experience of love, they cannot—by the standard of his own chemical theory of cognition—partake in it.
I have argued that Willis’s neuroscience generates, through its very insistence on replacing “poetic” accounts of the mind with a plain explication of the fluids and forces traversing the brain and nerves, a necessary figurative supplement. By attempting to explain aspects of the mind with more fundamental neural mechanisms, Willis effectively exposes a gap or clash between two discordant ways of studying the psyche. In the rare moments when his writing is literal in its description of the brain and its animal spirits, we can witness this clash in full effect, since in these cases it remains unclear how, for example, a rush of animal spirits from the center to the periphery of the brain produces acts of imagination. More commonly, though, Willis covers over this gap with figurative language and, in effect, writes nervous fictions. In these instances, the animal spirits are not depicted as heated chemicals moving through the nerves but instead as tiny persons in their own right. Through the power of personification, mental qualities like will, emotion, and cognition are projected directly onto the mechanisms of the nervous system.
The dynamic I have explored in Willis’s work—the dynamic whereby figurative language supplements an otherwise incomplete neurophysiology—is evident throughout seventeenth- and eighteenth-century writing. Indeed, Willis sets the course for the remainder of this period and its neuroscience. That is to say, he not only gave the period a scientific project—anatomizing the brain so as to determine the workings of the mind—he also bestowed upon his followers a complex figurative language to describe the psyche and, with it, a series of questions about the epistemological status of such figures and their relation to mind and matter. Descriptions of the animal spirits and their imagined movements and struggles within the nervous microcosm are evident in a host of eighteenth-century writing, not all of it explicitly scientific in substance or intent.
For example, Eliza Haywood’s novels—particularly those written in the first half of the eighteenth century—frequently depict the internal dramas unfolding both within a character’s psyche and upon the brain’s cerebral folds. In this respect, Haywood’s novels provide a clear example of the prevalence of animal-spirits physiology in the eighteenth century, as well as the various uses—all anticipated in Willis’s work—the figured spirits were put to during the period.82 Consider, for instance, Haywood’s description of a character recovering from mental shock in The Injured Husband: “he continued, for some Moments . . . fix’d in the same stupid Posture he had been in ever since he came into the Room; till, at last, the hurried Spirits beginning by little and little to resume their proper Stations, he fetch’d a deep Sigh, and . . . walk’d hastily to and fro, by that Action only discovering the inward Disorders that oppres’d him.”83 Here the spirits, in a conventional bit of imagery, are likened to little soldiers manning the battlements (or “stations”) of the body. Although they can be affected by a mental event (in this case, they are ruffled or “hurried”) they don’t seem to be particularly mindful things themselves, and once they “resume their stations,” the real human intelligence depicted here can reassert control, gather his thoughts, and engage in an introspective act. In still other passages, though, Haywood treats the animal spirits as inherently thinking things, as tiny homunculi, that reflect and perhaps explain the greater person’s mind. In the British Recluse, we find a character attributing the ability to resist present hardships and sad events to the parts and pieces of the nervous system: specifically, to melancholic, and hence mindful, animal spirits who have been worn down by still heavier experiences in the past: “but I had now been a good while accustom’d to receive Wounds of that nature, and my Spirits were too much depress’d with a continual Weight of Sorrow, to be able to exert themselves to resent almost any Usage.”84 In still another moment, this one from Lasselia, Haywood’s animal spirits have become so intelligent that they threaten to conflict with the desires of the whole mind. Here is a character confessing that her rapturous fantasies of love serve only to please her animal spirits, which, in this instance, behave like quarrelsome entities that must be fed with fantasies and cheered with ecstasies lest they plunge one into hopelessness: “Wrap’d in the extatick Contemplation, [she] went so far sometimes (as she afterwards confess’d) as to kiss, embrace, and possess, in Idea, a thousand nameless Joys, which Love too soon inspires a Notion of: but these Excesses we’ll suppose she permitted only, when she found there was a Necessity by chearing her languid Spirits with an imaginary Bliss, to preserve her from falling into a real Despair.”85
Haywood’s novels condense, into the confines of a single writer’s career, a mode of describing mind and brain prevalent throughout the seventeenth and eighteenth centuries but arguably first perfected in Willis’s neuroscience. Like Willis, Haywood figures the spirits as tiny persons so as to link the otherwise unlike substances of mind and matter. And as in Willis, the result is an oddly recursive natural philosophical fiction wherein mental qualities are projected upon the strictly mindless matter of the brain so that same matter can serve, in turn, as the cause of those mental qualities. In Haywood’s novels, a character is often sad or happy because his or her animal spirits are sad or happy—a state of affairs that necessitates a curious split in the novel’s perspective. Either the novel must narrate the same scene twice—once from the side of the mental, then once from the material—or it can begin by depicting the thoughts passing through a character’s psyche, only then to cut, without warning, to a view of the nervous flesh, made meaningful by metaphor, that serves as the ultimate cause and explanation of the character’s consciousness.
And, again, what holds true of Haywood holds for other writers of the period as well. For instance, as in Willis’s work, describing the animal spirits as tiny soldiers or servants, in thrall to the overarching mind or soul, remained a popular way of accounting for a host of mental activities like volition and sensation during the period. So we find Henry Brooke in his poem Universal Beauty comparing the animal spirits to “attendants” and “sprightly envoys”—subordinates who serve their superior dutifully by navigating the “winding paths” of the nervous system.86 But also as in Willis’s work, the spirits-as-soldier metaphor often persists alongside a more extravagant figuration: a figuration that casts these particles not as barely sentient matter with just a hint of intelligence but as something more like miniature reflections of the entire human being. Hence, Thomas Curteis became so concerned with the mental well-being of the animal spirits that he recommended a regimen of periodic rest and relaxation for the creatures: “The Animal Spirits, being tir’d out with the Toil, Motion or Thoughtfulness of the Day, require . . . an orderly Retreat from the exterior Organs, as also in a great measure from the Exercise of the interior Senses, for their own necessary Refreshment, instauration, [and] future Serviceableness.”87 But if the spirits can be tired out, they also can become overly anxious and aggressive as a result. Isaac Watts’s poem “The Hurry of Spirits” warns of “little restless atoms [that] rise and reign / Tyrants in sov’reign uproar”; these rebellious spirits, dangerous doubles of their normally obedient counterparts, can “impose / Ideas on the mind; confus’d ideas / Of non-existents and impossibles.”88 More nuanced feelings can inflict the spirits, as well. They seem particularly prone to “Melancholy, or the like Diseases,” as William Coward puts it.89 For example, John Beaumont, playing off the image of the animal spirits as soldiers, explains that these creatures can be “rendred fixt and melancholick” when they receive conflicting orders from mind and body.90 In this case, “being commanded here and there contrary ways, and almost distracted, [they] fall somewhat at length from their Vigour, and Natural Disposition.”91
Despite the many complaints and queries that always beset Willis’s work, the highly figurative animal-spirits physiology at the core of his system prospered long after his death. This is not to suggest, however, that the period witnessed no major pushback against such systems. In fact, the various critiques of early neuroscience like Willis’s—critiques that often focused on its literary or figurative qualities—will be a continual concern of this book’s remaining chapters. If anything, one of the central mysteries of eighteenth-century neuroscience is precisely why animal-spirits physiology seemed to survive, if not thrive, amid so much doubt and dissension. That particular question is the subject for another chapter.92 By way of concluding this one, though, I want to consider one more attack on Willis’s system, one that manages to expose incisively not only the epistemological gap at its center but also the figures and fictions that, as we have seen, work to cover over that gap. I’m thinking in particular of the work of Jonathan Swift.
There is some mystery about how much early neuroscience Swift read.93 There is no evidence, for instance, that he encountered Willis’s writings directly. Nevertheless, Swift would have learned about Willis’s scientific discoveries and about the animal-spirits physiology undergirding contemporaneous accounts of the nervous system from a text he certainly knew intimately: William Wotton’s Reflections upon Ancient and Modern Learning, a work mocked mercilessly in A Tale of a Tub and its appended satires. In this respect, much of Swift’s early satires can read like a parody of the animal-spirits physiology I’ve detailed above. For instance, these works are filled with moments where various aspects of the mind are reduced to the workings of heated and pressurized fluids traveling throughout the nervous system. Consider the Hack’s notorious vapor theory of madness in section 9 of the Tale (wherein “vapor” and “spirit” serve as synonyms). Although this chapter mocks numerous physiological and philosophical works, the animal spirits come in for special ridicule. For example, just as Willis insists that the difference between acts of imagination and moments of memory can be correlated to changes in the animal spirits’ movements, the Hack similarly will claim a king’s decision to conquer a neighbor or leave others in peace is due to the directions his spirits travel: the “Vapour or Spirit, which animated the Hero’s Brain, being in perpetual Circulation, seized upon that Region of the Human Body, so renown’d for furnishing the Zibeta Occidentalis [i.e., human shit] . . . left the rest of the World for that Time in Peace.”94 The recurrent joke of “The Mechanical Operation of the Spirit” works similarly. One way to undergo transcendent, enthusiastic, religious experiences, it turns out, is simply to work one’s bodily mechanism into the proper froth of heat and pressure (usually by shutting up one’s sense organs, rocking back and forth, drinking wine, etc.): “I am apt to imagine, that the Seed or Principle, which has ever put Men upon Visions in Things Invisible, is of a Corporeal Nature: For the profounder Chymists inform us, that the Strongest Spirits may be extracted from Human Flesh.”95
At least at first glance, the satire in such passages appears squarely aimed at early neuroscience’s tendency to reduce the mind to mindless brain matter (or, more properly, its insistence that various aspects of mind can be explained by mindless brain matter). In the hands of Swift’s virtuosi, “spirit”—which we might understand as the incorporeal soul or even a term for more general qualities of value or transcendence—becomes “animal spirit,” the senseless liquid flowing through our nerves. In the modern virtuoso’s estimation, the reduction of an ambiguous or mysterious entity like “spirit” to a mere chemical formula would give rise to a more certain and intelligible view of the psyche: one would be able to understand the basis of our thoughts and passions, and having observed them, even control them. Instead, Swift demonstrates that it leads to absurdity or mystery. In neuroscience, the stuff of spirit is explained away altogether, thereby reducing the person to a mindless machine or, if one wanted to be slightly kinder, treating spirit as a physical thing results in a further mystery, since it remains unclear how the directional movements of animal spirits cause different mental qualities.
Swift’s satire goes still farther by demonstrating that animal-spirits physiology is not grounded in empirical discoveries concerning the brain and its fluids, or even in a more conceptual argument concerning the nature and abilities of matter in general. Importantly, this reduction of the spiritual to the animal spirits is the result of a linguistic ambiguity. As materialists like Hobbes (clearly under attack throughout much of the Tale) were happy to note: trace the word “spirit” back to its Latin roots, and you’ll find that it refers not to ghostly incorporeal things but to “Wind, or Breath, . . . as when they call that aeriall substance, which in the body of any living creature, gives it life and motion, Vitall and Animall spirits.”96 Swift’s narrators in these satires clearly follow Hobbes on this point, noting that “whether you please to call the Forma informans of Man [the Aristotelian soul], by the Name of Spiritus, Animus, Afflatus, or Anima; What are all these but several Appelations for Wind?”97 The materialist reading of “spirit,” then, returns a term that is more abstract or ambiguous—that we might even say is being used as a metaphor of sorts for “higher,” nonmaterial things or truths—to its proper and physical basis in the body’s breath. Hence, for the Hack neuroscientist, when people speak of their mind (a spiritual substance) or their values (spiritual beliefs), they are in fact speaking of literal bits of wind and chemical elements navigating the nervous system, all of which can be grasped and quantified like any other spatiotemporal thing. And while it is certainly not the case that early neuroscientists like Willis or Descartes were materialists in the mold of Hobbes, we still can find a reflection of their actual methods in the Hack’s insistence on ontologically taming spirit.
But this only captures part of Swift’s satire on animal-spirits physiology. After all, as we have seen, actual early neuroscience, unlike the parodic version captured here, rarely reduces the mind to chemical fluids and leaves it at that. If it did, then it would present an intractable mystery rather than something that at least looked like scientific explanation, and the systems of Swift’s virtuosi would read more like careful reproduction than cutting parody. As I’ve shown, more commonly someone like Willis will draw on nervous figures and fictions to make his neuroscience work. Swift appears to have been aware of this strategy, since he seeks to expose it in his satires. He does so in a typically complicated way: he literalizes the neuroscientist’s metaphors. If natural philosophers personified the animal spirits in order to make brain matter seem like persons, then Swift strips away the personifications in order to show how much work such personifications accomplish in neuroscientific writing. Swift shows us what plain or unadorned neuroscience would look like in a passage from his “Mechanical Operation of the Spirit”:98
For, it is the Opinion of Choice Virtuosi, that the Brain is only a Crowd of little Animals, but with Teeth and Claws extremely sharp, and therefore, cling together in the Contextures we behold, like the Picture of Hobbes’s Leviathan, or like Bees in perpendicular swarm upon a Tree, or like a Carrion corrupted into Vermin, still preserving the Shape and Figure of the Mother Animal. That all Invention is formed by the Morsure of two or more of these Animals, upon certain capillary Nerves, which proceed from thence, whereof three Branches spread into the Tongue, and two into the right Hand. . . . That if the Morsure be Hexagonal, it produces Poetry; the Circular gives Eloquence; If the Bite hath been Conical, the Person, whose Nerve is so affected, shall be disposed to write upon the Politicks; and so of the rest.99
Although Swift knew Enlightenment neurology only indirectly, he imitates the style of the period’s physiological texts with surprising accuracy. Like Willis’s writings, Swift’s passage alternates between dry, medical details on the one hand (those capillary nerves that spread into the tongue) and wild, metaphorical speculation on the other (the brain is like a swarm of bees or like the picture of Hobbes’s leviathan or even like a mass of maggots).
But what is worth paying attention to in this passage—as is so often the case with Swift’s parodies—are the slight departures from the source material. For example, we can see that, in rewriting the work of thinkers like Willis, Swift literalizes the physician’s metaphors. To be sure, by literalizing the animal spirits Swift does not return them to their proper referent: chemically charged matter within the brain. Nevertheless, Swift makes these spirits as dumbly mechanical as their literally material nature suggests. Swift’s spirits do not think, feel, or love—they only bite. If for Willis the animal spirits are a mobile army of metaphors, metonyms, and anthropomorphisms, then for Swift they are only animals. More importantly, in literalizing the animal spirits Swift once again stresses the disconnect between the world of brain matter and the mental qualities the brain creates. Had Willis written this passage, he would have bridged this gap by discoursing on the inventive spirits that create poetry or the silver-tongued spirits that generate eloquence. Swift makes the gap only wider by forcing his readers to countenance the fact that somehow differently shaped bites can produce different mental qualities. In other words, if we laugh at this passage then we are laughing at the same disconnect that Leibniz points to when he discusses the differences between experiencing minds and observing brains. We are laughing, in short, at the explanatory gap, or the clash between the scientific and manifest images, made satirically manifest.
Behind Swift’s parody, then, is a serious point: without metaphor, natural philosophers like Willis have no way of knowing how the particles of matter within the brain add up to create a mind. This point becomes clearer still if we consider Swift’s odd invocation of Hobbes in this passage. In one respect, the reference to Hobbes is unsurprising. As I have noted, although Willis remained a devoutly religious dualist who certainly believed in a God-given incorporeal soul, his suggestion that matter alone could think (i.e., that it could think independently of the immaterial soul) pointed to more stringently materialist possibilities. Indeed, it’s no accident that the irreligious La Mettrie praised Willis’s work in his Man a Machine.100 In another respect, however, Swift’s allusion to Hobbes signals another telling departure from his source material. Swift’s claim that the virtuosi’s image of the brain appears “like the Picture of Hobbes’s Leviathan” neglects a key component of that picture. The frontispiece of Leviathan certainly does depict a crowd of tiny heads that—seen through the right figurative optics—might appear as a swarm of bees. But above that crowd—crowning it, as it were—is the head of the sovereign: an image of unity and coherence that this representation of the brain lacks. In other words, in Swift’s literalizing of Willis’s brain—a literalizing that stresses the merely material and thoughtless nature of the animal spirits—the crowd within the brain cannot create a head.