In the previous chapter, we saw one of Leibniz’s early “wish lists,” detailing a motley grouping of desiderata for the improvement of the institution of medicine. There is another such list from a few years later, in 1675, to which Leibniz gave the title, Une drôle de pensée (A Funny Thought). He had just been to a spectacle in Paris in which an automaton in the form of a man was made to run across the surface of the Seine. The experience filled him with excitement and with ideas of his own. He rushed away to jot them down, and the resulting sketch tells of “a new sort of representations,” which would involve “magic lanterns, kites, artificial meteors, all manner of optical marvels; a representation of the sky and the stars.” There would be “fireworks, jets of water, vessels of strange forms; mandragores and other rare plants, . . . [r]are and extraordinary animals,” as well as a “machine for races with artificial horses,” not to mention “speaking trumpets.” He imagines that “the representation could be combined with some sort of story or comedy,” and that this story might include “extraordinary tightrope dancers. Perilous jumps.” The public could see “a child who raises a great weight with a thread,”1 and there would be an “anatomical theatre,” as well as a “garden of medicinal plants.” There would be “little number machines and other [things]. . . . Instruments that play themselves.” Leibniz imagines that “all honest men would want to have seen these curiosities, so that they would be able to talk about them” afterward. “Even women of quality,” he adds, would wish to be taken there. At this wonderland of “new representations,” “one would always be encouraged to push things further,” though it would also be necessary that in this charmed place “no one ever swears, nor blasphemes God.”2
Leibniz is wishing for many disparate things here, and in this list we see the kernels of interests that would in time develop into his great contributions to the study of subjects as various as mechanics, computing, chemistry, and anatomy. The one preoccupation that seems to pervade the list, however, beyond his lifelong interest in cultivating an institutional context for the promotion of natural philosophy and the mechanical arts, is the investigation of the boundary between the natural and the artificial. This is a preoccupation that within a few more years of composing the Drôle de pensée would yield Leibniz’s first contributions to the science of animal economy. It is already clear from this early text that Leibniz is interested in investigating the boundary between the natural and the artificial not simply so as to bring the latter to bear metaphorically on our understanding of the former, as had been the case with Descartes, but rather in order to work out a comprehensive account of nature as a whole, one that would account for fountains and animals in a single, comprehensive model. In this connection, as Jon Elster has sharply noted: “For Descartes the fountains offer only an analogy of a certain metaphysics, whose genesis certainly owes them nothing; Leibniz in contrast is intensely and concretely interested in the fountains as such.”3 Leibniz is not looking for points of analogy between hydraulics and other areas of mechanical physics on the one hand and a given model of corporeal substances on the other. Rather, he intends to show, as we will see in this chapter, that these apparently different domains of the natural world require substantively the same sort of explanation. Leibniz’s “physiology” is a physiology of the entire world, including animate and inanimate beings as well as artifacts.
Unlike medicine, which is interested in the human body and its preservation—and only instrumentally in such things as animals, plants, and chemical compounds—anatomy, physiology, and related disciplines are concerned with human and animal bodies in the aim of determining the manner in which their interrelated parts together execute the functions proper to an animal life. These disciplines remain, however, subordinate to medicine. They also remain at a level of analysis of the animal body that does not take into account its “organic” structure, that is to say, in Leibniz’s technical sense of the term, its composition out of machines within machines to infinity. It is in terms of this infinite composition that Leibniz will ultimately dare to propose that he can account for the self-motion of animal bodies by appeal to their “vegetative structure” alone (as he puts it in the controversy with G. E. Stahl), which is to say to the “material plastic nature” of organic bodies (as he puts it to Ralph Cud-worth). This will be what enables Leibniz to remain, by his own lights, a mechanist, and to reject vitalist theories of animal growth, development, and motion such as those of Cudworth and Stahl, while at the same time radically modifying earlier notions of what could qualify as “mechanism.” But first things first. In this chapter let us remain focused on Leibniz’s contribution to “animal economy,” an area of inquiry that is both temporally prior to, and more grounded in empirical investigation than, Leibniz’s theory of organic body, which will in turn be the focus of the following chapter.
In the introduction, we considered not just the scientific treatment of some of the phenomena of life by Leibniz’s predecessors, but also their understanding of the place of this sort of study within their respective philosophies. It was maintained that while for Aristotle the living world had been a domain of application par excellence of his most general philosophical principles, for Descartes the living world was perhaps equally important, but for an opposite reason: it was a domain to be explained away, rather than to be held up as paradigmatic of nature in general.
The question of the place of this domain in Leibniz’s philosophy as a whole is one that it will take us the rest of the book to flesh out. We will be considering Leibniz’s metaphysical analysis of the animal—which takes into consideration the union of, or harmony between, the animal soul and its corresponding organic body—in later chapters. In this chapter, we will consider Leibniz’s earliest efforts to model the animal body prior to the development of his theory of natural machines, as well as the continuing importance of these early efforts for Leibniz’s mature account of animals. The theory of natural machines or organic bodies that would emerge over the course of Leibniz’s middle-period philosophy would lead him to a natural philosophy akin to Aristotle’s in the sense that he would come to believe that the structure and motion of nature as a whole should be understood on the model of animal structure and motion. In his early animal-economical texts, in contrast, Leibniz would continue to seek, like Descartes, to understand the structure and motion of animals as just one, not atypical, case of the study of “merely” mechanical nature.
For Leibniz as for his contemporaries the study of any element or system of the natural world—including everything from forestry to hydrology to painting—is ultimately a part of “physics.” That particular subdomain of physics that deals with animal bodies and their motions, in turn, is animal economy. Leibniz may have adopted this term from Benjamin van Broekhuizen’s Oeconomia corporis animalis sive cogitationes succinctae, de mente, corpore, et utriusque conjunctione (The Economy of the Animal Body, or, Succinct Thoughts on the Mind, the Body and the Conjunction of Both) of 1672.4 Another important antecedent is Walter Charleton, who published his Oeconomia animalis novis in medicina hypothesibus superstructa et mechanice explicata (A New Animal Economy, Built upon Hypotheses in Medicine and Explained Mechanically) in 1659.5 There are other, still earlier occurrences of this term or some close cognate, such as Cornelis van Hogelande’s Cogitationes sive de Dei existentia item animae spiritualitas et possibilis cum corpore unio demonstrantur; nec non, brevis historia oeconomiae corporis animalis proponitur, atque mechanice explicatur (Thoughts, or, On the Existence of God, also Demonstrating the Spirituality of the Soul and Its Possible Union with the Body, Wherein Otherwise a Brief History of the Economy of the Animal Body Is Proposed, and Explained Mechanically).6 Usage of the term explodes in frequency in the second half of the seventeenth century, and Leibniz’s use of it seems to be but one instance of this explosion. It goes without saying that in the seventeenth century the social science of economics as we understand it did not exist, and so “animal economy” should not be understood as making reference to systems of exchange, markets, and such, nor as anticipating some future theory of “biopolitics.” That said, it is interesting nonetheless to reflect on the notion of animal economy in relation to the later science of economics. We might say that animal economy is a sort of limit case of micro-economics, looking into the internal economy of what in today’s economic science would be taken as the basic unit of analysis: the individual active body.
For Leibniz, “animal economy” denotes the study of the relation between organs and functions; thus it comprises anatomy and physiology, but particularly with an eye to the way the elements of these disciplines are coordinated in a living system. It is anatomy, physiology, and ethology at once. What it decidedly is not is “pneumatics,”7 as Leibniz strictly eschews any appeal to the inherence of a soul in the animal body within the context of animal-economical explanation. It is not that the animal does not have a soul (as will become clear in chapter 3, the animal body itself results from infinitely many souls or soul-like substances), but only that there is in his view a rigorous and autonomous scientific discipline that gains nothing from its mention. Of all his contributions to animal economy over a forty-year period, it is only in the polemic against Stahl, the final text we will be considering in this chapter, that Leibniz seeks to make explicit the boundary between animal economy and pneumatics, in the course of his argument against Stahl that the soul can play no theoretical role in the former discipline. In this chapter, we will be speaking of two distinct periods of Leibniz’s direct, active contribution to animal economy: first, the period extending from 1677 to roughly 1683,8 in which he wrote a series of very detailed studies of the nature of animal motion and “vegetation”; and the second, from 1709 to 1710, when he engages in debate with Stahl, returning to many of the ideas developed in the first period, while superimposing upon these the sophisticated metaphysics and the organic model of body that had been developed in the intervening years. In between these two periods, Leibniz develops his theory of organics, focusing upon the microstructure and infinitely complex organization of living bodies, with little evident interest in the core problems of animal economy as we have defined it above. To the best of our knowledge, between 1683 and 1709, Leibniz does not use the term “animal economy.”
To the extent that Leibniz is engaged in the study of animal economy, the animal is for him no less a machine than it had been for Descartes, but there are a number of differences between the two philosophers’ respective analyses of this machine. For one thing, Leibniz is willing to speak of animal machines in terms of their functional, as opposed to merely dispositional, unity. Machines of nature, for Leibniz, like the machines that we construct for our own reasons, have ends, and these ends may be understood in entirely mechanical terms, as rooted in the structure and motion of the mechanical body. Another difference lies in Leibniz’s ascription of species membership to animal machines, whereas, as we saw in the introduction, Descartes remains fairly silent as to how it is that a particular animal machine comes to be the kind of machine that it is. Yet another difference is the motivation each thinker has for studying animal economy: for Descartes, again, a complete account of the animal in mechanical terms was a necessary, if otiose, step in the comprehensive case he spent his life seeking to make for a mechanized natural philosophy. For Leibniz the initial interest in animal economy grows out of a prior interest not in mechanical natural philosophy but in the advancement of the institution of medicine. Finally, whereas for Descartes the analysis of the animal qua machine constitutes an exhaustive analysis of the animal, for Leibniz it is just the beginning. In the study of animal economy, Leibniz’s model of the animal is fairly independent of the one familiar to most students of Leibniz from his broader metaphysical concern with organic bodies and corporeal substances. As we will see in the following chapters, moreover, once Leibniz moves beyond animal economy and into metaphysics, the animal is a good deal more than a machine.
Leibniz offers his most comprehensive account of what is involved in animal economy in the De scribendis novis Medicinae elementis of 1682–83:
Analysis is the Method for as long as we are investigating the media or organs of any given function and the mode of their operating; and therefore we come to acquaintance with the body through its parts, by which when completed we will come to the Synthesis, and we will describe all of them coordinated into one, and the first Motor of motion and the liquid and solid instruments, and their connection, and altogether the entire economy of the animal, especially when by this very analysis we should discern by inquiring into the organs of a given function, that often the very same organ is devoted to several functions, just as in Machines the wisdom of their maker shines through especially, when many effects are brought about by few things.9
Animal economy, then, is ultimately a synthetic discipline, dedicated to apprehending the coordination of the organs of an animal body with one another. This coordination is, to speak anachronistically, literally “economical” in the sense that the designer of natural machines (which is to say, in the end, the chooser of this world of maximal variety and compossibility) may be seen to have brought about the maximum of effects with the minimum of organs, and with individual organs fulfilling multiple functions.
Medicine, as a practical endeavor, and indeed as a social institution in need of regulation and state support, is never far from Leibniz’s mind when writing on animal economy. As we saw in the previous chapter, Leibniz defines “medicine” as the prescription of a method to a mechanic, so that he will “be able to conserve the machine that has been entrusted to him, so that it will always operate correctly.” This definition clearly shows the intimate link between the disciplines of animal economy and medicine: because the human body is a machine consisting in organs with functions, study of the functioning of this sort of machine will yield tools for the diagnosis and treatment of malfunctioning machines by medical practitioners. Ultimately, for Leibniz, the study of animal economy is to be justified in terms of its usefulness to the practice of medicine. On his vision, animal economy, alongside chemistry, botany, and a handful of other fields, should contribute in its own way to the improvement of the diagnosis and treatment of illnesses.
In the study of animal economy, as we have seen, Leibniz believes no less strongly than Descartes that the animal is a machine. But what kind of machine is it? It is, to put it succinctly, a hydraulico-pneumatico-pyrotechnical machine of quasi-perpetual motion with a trademark activity specific to it. The principle aim of the present chapter is to make sense of this all-too-cryptic answer by providing a developmental summary of the early animal-economical texts, and also to consider in the light of these Leibniz’s late-period controversy with G. E. Stahl, in which the term “animal economy” makes one final appearance. This controversy will be of particular interest to us insofar as it constitutes Leibniz’s only comprehensive attempt to demarcate the study of animal economy from the study of the animal qua living thing, which is to say—as we will see by the end of this chapter, a perceiving and acting thing—and in so doing to mark out the boundary between animal economy as a domain of empirical science and the metaphysical reflection on animals that lies beyond its scope.
In saying that the animal body is both hydraulico-pneumatic as well as pyrotechnical, Leibniz is positioning himself in both the iatromechanical and the iatrochemical traditions. That is, he believes in a modified mechanical account of animal growth and motion, on which certain elements of these natural processes cannot be accounted for in terms of the motion of minute particles, but instead must be clarified by appeal to irreducibly qualitative, chemical processes.10 Recent scholars have argued that the line between iatromechanism and iatrochemistry is not nearly so clear as it was previously thought to be: virtually no one, in fact, defended an account of biological processes that did not grant a special explanatory role to chemistry.11 Leibniz’s hyphenated definition of the animal body, then, needs to be understood as a product of the widespread, and growing, perception in the late seventeenth century of the inadequacy of strict mechanism for explaining biological phenomena, as well as of the desire among many, including Leibniz, to retain the model of the machine in conceptualizing the animal.
In Leibniz’s view, Descartes had been correct to hold that the animal may be studied qua machine, but eventually the German philosopher would come to believe that this is not all an animal is, and in order to get the full account of it one must return to the Aristotelian view of the animal as a sensing and acting being. Leibniz’s contributions to the study of animals that are collected in the LH III manuscripts, currently being edited by the Berlin-Brandenburg Academy of Sciences for Publication in Series VIII of the Academy Edition of Leibniz’s writings, help us to gain a fairly clear picture of Leibniz’s development through these stages. It is first in the Machina animalis of 1677 that we see the doctrine of the animal machine defended as a distinctly natural-philosophical thesis, and over the course of the 1680s Leibniz continues to develop this doctrine by incorporating arguments not principally from Descartes and the Cartesians, defenders of the doctrine par excellence, but from Thomas Bartholin, Franciscus Sylvius, Thomas Willis, and other sources. Over the course of the late 1680s and into the 1690s, Leibniz grows increasingly dissatisfied with the “merely” mechanical model of the animal and struggles to develop a new model of it that can surpass the central ideas of the science of animal economy without, for that, rejecting them as simply false and lapsing into an untenable vitalism, according to which the soul is directly responsible for the motion of the body. The culmination of Leibniz’s long developing interest in animals both as machines and as something “more exquisite” or “more divine” than an artificial machine with respect to its structure, and, finally, as substances capable of perception and action, is undoubtedly to be found in the polemic against G. E. Stahl of 1709–10.
Let us turn now to a detailed analysis of the major treatises among the LH III manuscripts focusing on animal economy.
In this text of his early post-Paris period we find Leibniz’s first explicit reference to animal economy and also his first effort to contribute to this discipline as a domain of natural philosophy of intrinsic interest, even if ultimately subordinate in importance to medicine. In this short and, in parts, highly illegible manuscript, Leibniz seeks to explain how motion first arises in the animal body. As in the passage from the De scribendis novis Medicinae elementis cited above, here as well Leibniz describes the study of animal economy as ultimately a synthetic activity in which the interconnection of all the parts of the living system is considered, rather than the isolated functioning of any particular organ. Leibniz illustrates the synthetic character of this discipline by analogy to the proper understanding of a mill:
And this indeed in sum is seen to be the machine of the body, which sustains motion; other things should not be mixed into this description, as the description of motion in a mill-house is one thing, while another is the description of [its] various applications to squeezing out oil, to crushing grain, to splitting timber, which may be brought about by the work of this mill.13
Just as one would fail to grasp the principles of milling if she were to focus exclusively on any one subprocess involved in this industry, so too with the animal body. Leibniz continues:
[The] first motion is able to bring about the propulsion of the chyle from the stomach into the lacteous and subclavial veins, as well as the peristaltic motion of the intestines, and as well as the secretion of excrements by various ducts. All of which are to be separately explained by the intellectual reason of the first motion, or, which is the same, by that of Life. Whence it may be understood, to the extent that the Anatomists should retreat from the true method of describing a given machine, there is no more reason than that [they] are ignorant of the true economy of animal motion.14
It interesting to note in this connection that Leibniz will also draw on the example of a mill in one of his more famous arguments against a materialist theory of mind. Decades later, in the Monadology, he writes:
In imagining that there is a machine whose construction would enable it to think, to sense, and to have perception, one could conceive it enlarged while retaining the same proportions, so that one could enter into it, just like into a windmill. Supposing this, one should, when visiting within it, find only parts pushing one another, and never anything by which to explain perception.15
In both the Machina animalis and the Monadology, the body is no less mechanical than a windmill. Implicitly in the earlier text, and explicitly in the later, Leibniz believes that the capacity for perception can be understood neither by looking at some part of the mill nor at the totality of its structure. By the time of the Monadology, however, indeed by the time of the polemic against Stahl five years prior to it, Leibniz would come to see life as fundamentally wrapped up with perception, and thus as something alien to the study of animal economy. The details of the account Leibniz offers in the Machina animalis would change dramatically by the time of his most mature engagement with the problems of animal economy. In the 1677 text, Leibniz maintains that life itself may be understood as this first motion arising from the coction of nourishment. Later, in contrast, he will insist instead that there is a fundamental difference between force and the motion that arises from it; that the motion of animal bodies may be described by animal economy entirely without any consideration of the force that underlies it; that this force is ultimately to be accounted for in terms of the perceptions and appetites of immaterial subjects; and that life itself just is this perception and appetite. Here, in 1677, Leibniz is still a good distance away from such an understanding of animals and their place in his philosophy.
In the above passage from the Machina animalis we saw Leibniz expressing the common view to which he would remain committed throughout his work on animal economy, that the very first stage in the production of vital phenomena is the transformation of nutriment into chyle. His account of the early stages of this process is quite clear, from the intake of nutrition, which starts the process of vital motion, up through the circulation of the blood. We may divide this process into seven principal stages as follows:
As Enrico Pasini has noted, Descartes also begins L’homme with the transformation of aliment into chyle, the process of the production of blood, the movement of the heart, and the circulation of the blood. According to Pasini,
Leibniz, in his own version, departs in this connection from Descartes, preferring instead the formulation of Sylvius, whose description of the production of blood in the Praxeos medicae idea nova Leibniz follows in its essential points. Leibniz insists still more clearly on the rejection of final principles in the description of the animal machine, setting out from the conviction that it is one thing to describe the functioning of a machine in terms of the motion of its parts, while the ensemble of ends to which the machine can be determined is something else.17
Beyond the seventh stage in the outline above, it is not clear how Leibniz conceives the transition from circulation within the animal to locomotion by the animal. It is one thing to account for the inner motions of an animal body in entirely thermomechanical terms, quite another to explain how these motions might be translated into the goal-directed self-motion of the animal in its environment. This, however, as we will see, is a problem to which he would devote a great deal of thought within the next few years, particularly in the Corpus hominis of the early 1680s.
This text, which might also be given the longer title The Body of a Man, As of Any Animal, Is a Sort of Machine,18 reveals the great extent to which Leibniz sought to comprehend the problem of the body-machine in terms of sophisticated physiological science, independently of the metaphysical principles of perception and appetite that he would ultimately hold to be necessary in the most exhaustive account of the nature of animals. It also appears to be Leibniz’s first attempt to engage philosophically with the nature and ontology of biological species and with the very difficult problem of the transmission of kind-membership through sexual reproduction. We will investigate these aspects of the text at length in chapter 7.
Leibniz’s account in this text of the nature of the animal machine is remarkably similar to a passage in a work by Robert Boyle published only in 1686, thus most likely after the Corpus hominis. Boyle writes in the Free Inquiry into the Received Notion of Nature:
I look not on a human body, as on a watch or a hand-mill, i.e., as a machine made up only of solid, or at least consistent parts; but as an hydraulical, or rather hydraulico-pneumatical engine, that consists not only of solid and stable parts, but of fluids, and those in organical motion: and not only so, but I consider that these fluids, the liquors and spirits, are in a living man so constituted, that in certain circumstances the liquors are disposed to be put into a fermentation or commotion.19
Both Boyle and Leibniz want to say that fermentation or explosiveness needs to be added to fluidity, and that both of these need to be added to mechanicity in order to get at the true nature of the animal machine.20 Both Boyle and Leibniz are adding a further hyphenation to the already cumbersome “hydraulico-pneumatic machine” described in detail in Kaspar Schott’s Mechanica hydraulico-pneumatica of 1657. In this fascinating work, the German Jesuit scientist describes at length many of the same sort of machines that would so excite Leibniz’s imagination in the 1675 text with which we began this chapter. Schott explains that the term “hydraulico-pneumatic,” or the equivalent “aquatico-spiritual,” means simply “that which is driven by water and air,” and that by means of these two basic natural elements one can construct statues that are “hurled into the air by the violent force of the compressed air trapped inside, letting pipes and tubes swell up, imitating the motion and song of birds and other animals, and producing other such wonderful and exotic effects, that one can hardly understand how this could be done by the human spirit of invention.”21
Schott is a “mechanist” only to the extent that he is an enthusiast for machines, but is certainly no “mechanical natural philosopher” in the sense in which we understand this term, that is, someone committed to the view that all natural change can be explained in terms of the mass, figure, and motion of basic particles. Schott does not believe that exploration of the purported boundary between the natural and the mechanical must carry with it any presumption that the natural world consists only in such particles. In fact, for Schott mechanics is one of several branches of what he calls “magic,” alongside many others, including “magnetic, gnomonic, static, optic, dioptric, catoptric, hydraulic, pneumatic, pyrobolic, harmonic, phonocamptic, anacaptic, anaclastic, physiognomic . . . sympathetic, steganological, cryptographic, divinatory, kabbalistic, hieroglyphic,” and, finally “holy” magic.22 For the Jesuit author, the most basic kind of machine is the “tractoric” machine described in antiquity by Archimedes, Vitruvius, and others, which operates by means of gears and wheels. Schott’s own work takes its direct inspiration from Hero of Alexandria, the author of the first-century treatise Pneumatica and supposedly the inventor of the first steam engine.23
The Jesuit scientist’s work provides an example of early modern thinking about machines that goes well beyond the gear- and pulley-driven contraptions sometimes cited as a sort of caricature of the analogical imagination of seventeenth-century mechanist thinking and that also involves no presupposition of the absence of functional unity or teleology in machines. Although by the time Leibniz wrote the Corpus hominis in the 1680s he had considerably distanced himself from the somewhat backward and hermetic thinking with which Schott was surely associated (Schott’s greatest inspiration was the fellow Jesuit, Athanasius Kircher, who would in turn greatly influence the young Leibniz, and embarrass the somewhat older Leibniz), it is nonetheless clear that Leibniz’s conception of machines owes at least as much to the work of Schott, and perhaps others writing in a similar vein, as, for example, to the well-known animal-machine doctrine of Descartes. When Leibniz or Schott says that an animal body is a machine, this is not necessarily in order, as it were, to take the magic out of it. Leibniz is more cautious than Schott, and his vocabulary more in line with that of the novatores, but the lineage remains clear.
The Corpus hominis, along with the De scribendis novis Medicinae elementis of the same period (or perhaps somewhat earlier), is probably Leibniz’s most significant attempt at offering a systematic account of the hydraulico-pneumatico-pyrotechnical machine. He begins with the bold assertion that the human body, like the body of any animal, is a sort of machine, and that this machine is best understood in terms of its final causes. Unlike an earlier mechanist such as Descartes, however, who was only prepared to speak of the animal body in terms of its dispositional, rather than its functional, unity,24 Leibniz is fully ready to say that the body-machine is best understood in terms of its ends. “Any machine,” he writes,
is best defined in terms of its final cause, so that in the description of the parts it is therefore apparent in what way each of them is coordinated with the others for the intended use. Thus one who is to describe a given clock will say that it is a Machine made to display equal divisions of time, and therefore the function of a clock-hand lies in its uniform motion for some period of time.25
But if a clock is a time-telling machine, what sort of machine is an animal? It is, in the first place and most generally, a sort of perpetual-motion machine, superior to the artificial approximations of such machines in that it (i) is able to move itself so as to find and consume new fuel; and (ii) before it, as an individual machine, ceases to function, it can transmit its likeness to another, similar, machine through sexual reproduction. The animal is not only a perpetual-motion machine (of sorts) capable of nourishing and reproducing itself, it is also, depending on its kind membership, a machine that carries out an activity or cluster of activities peculiar to that kind. Leibniz makes both the general and the particular point in the Corpus hominis as follows:
The Bodies of Animals are Machines of perpetual motion, or, to put it more clearly, they are machines comparable to a certain fixed and singular species of perpetual organic motion that is always maintained in the world. Thus for as long as there are spiders there will be weaving machines, for as long as there are bees there will be honey-producing machines, and for as long as there are squirrels there will be dancing machines.26
In our treatment of the problem of species in chapter 7, we will return to some of the problems in this fascinating passage relating to the particular ends of particular kinds in greater detail. For now, it will be sufficient to briefly elaborate upon the two forms of perpetuity just noted. The first, again, is that of continuing to exist, either through the “refueling” that is nutrition or, since an individual animal machine cannot be sustained in this way forever, through transmission of the animal’s likeness, with the same functional ends, to other animal machines through sexual reproduction. Is this enough, though, to count as a perpetual-motion machine? It certainly would not have been for most of Leibniz’s predecessors who had dreamed of such things. Leibniz frequently criticizes his contemporaries for claiming to have designed perpetual-motion machines that nonetheless require an external energy source such as water.27 When Leibniz begins in the late 1670s to plan to develop wind-based energy sources for everything from the winding of clocks to the ventilation of mines, he nonetheless insists that “this invention will have the effect and the advantage of perpetual motion, even though there is none: for this perpetual motion, in the form in which it is sought, is impossible.”28
The idea of perpetual-motion machines and the history of the search for them in the seventeenth century is a very complicated one, as there were many different possible understandings of what might constitute such a machine. Many believed that if such a thing could be invented, it would function, like the perpetual motion of the tides, through the influence of a hidden spiritus mundi by which celestial motion is transmitted to an earthly contraption that bears some microcosmic affinity to the celestial bodies. Some, such as Cornelis Drebbel, claimed to have produced such contraptions. Leibniz, who mentions Drebbel on a number of occasions, and who may have had the Dutch alchemist in mind in rejecting the possibility of “pure” perpetual motion in the Corpus hominis, obviously must reject such a picture of perpetual motion for a number of reasons. For one, he firmly rejects any account of earthly motion as a consequence of a microcosm-macrocosm relationship between terrestrial beings and the planets. For him, a basic feature of mechanism, which he takes up from Descartes and Hobbes, is that motion everywhere obeys the same laws, and that what happens here on earth is in no way a “trickle-down” effect of some sort of more perfect motion elsewhere. When Leibniz clarifies in the Corpus hominis that animals are in fact machines of “quasi-perpetual motion,” then, he is using this term in a very attenuated sense, and also very consciously in a way that goes against accepted meanings.29 First, it seems odd to speak of a machine that has as its end simply being perpetual; there ought to be in addition some particular activity that it does perpetually. Second, some critics might argue, a perpetual-motion machine that needs perpetual refueling is not really perpetual at all. The dream of a perpetual-motion machine had always been that of a perpetual closed system.30
So an animal is a quasi-perpetual-motion machine with a species. It differs from the ideal perpetual-motion machine in that it requires constant refueling in order to exist. It differs from ordinary machines, or “organica artificialia,” in that it is both self-sustaining and self-reproducing.31 Leibniz berates other mechanists who dream in vain of a perpetual-motion machine in the stricter sense of a machine that requires no fuel at all:
In order that men should obtain this durability of action in their machines, they now add to them a quasi-perpetual machine that is made by nature, which is of course man himself, the pilot, who repairs what is weakened or broken down in time, who applies an external force, bringing agents together with patients . . . or in some other way conserves the power of the Machine.
In other words, artificial machines are only able to continue running because a certain kind of natural machine—a human being—tends to them by bringing them new fuel. But natural machines themselves require no such attendance: “Nature . . . brings it about that her Machine is able to do this very thing on its own, that is, that it be able now to be nourished, whereby worn-down parts and forces are renewed.”32
And even if the individual animal will eventually cease functioning, in death, it is still capable of a sort of perpetuity to the extent that it is capable of reproduction: “Machines of this sort are able to produce others similar to themselves [Machinae huiusmodi alias sibi similes producere possent].” Animals are perpetual-motion machines not just to the extent that they are self-nourishing machines but also, and more fully, to the extent that they are reproductive machines. Again, Leibniz believes that this is as close as nature ever comes to a perpetual-motion machine, and mechanists are deluding themselves if they hope for something both self-contained and perpetual. Eventually, the individual machine breaks down, but if all goes well it will not break down before transmitting its likeness to another machine; and even before it breaks down it requires constant sustenance from the outside. But it still qualifies as “a sort of” perpetual-motion machine to the extent that it moves itself so as to obtain its own sustenance and see to its own reproduction.
Self-nutrition requires self-motion, and as we saw in the Machina animalis, one of the great difficulties of the mechanical account of animal motion is the tremendous leap one has to make from the description of the internal motions of an animal body to the account of how these motions give rise to motion of the animal body as a whole. In the Corpus hominis, Leibniz attempts to explain this process as resulting from the swelling of bodily vessels:
As therefore the entire Machine must be moved with respect to place, it is necessary that the liquid be contained within the firm part or the vessel, and from there it is necessary that the liquor be able to move the vessel itself in which it is contained . . . The machines are able moreover to obtain something from the swelling; thus with one part inactive and restrained, another part will be moved forward, whence if done by alternations a progression arises . . . as comes to pass in leaping, swimming, and flying.33
This account is not much of an improvement over the Machina animalis, but at least Leibniz gives us some idea of how we might get locomotion out of internal thermomechanical processes. The basic insight is that a body is a vessel in which parts may differentially swell at different times, and that in swelling a part can bring about a resistance against the air, water, or earth supporting it. Through the alternating swelling of parts—limbs, fins, or wings, to be precise—an animal can move itself and thereby seek out its own fuel. Locomotion is thus conceived as nothing more than a facilitator of nutrition.
Nutrition is for Leibniz the process that underlies the machine’s pyrotechnical functioning, to the extent that the animal body is maintained by the conversion of fuel (that is, food), into a vital heat analogous to fire.34 Leibniz asserts in Section IV of the Corpus hominis that “the first mover in this machine is something analogous to a flame or to the Sun or a fixed star, from which there arises an ebullition which feeds itself.”35 The clearest antecedent for this view is Jean Fernel, who in his Physiologia of 1567 had argued that “all living things live by means of the heat enclosed within them,” and further that “if any basis is needed for advocating this, let it be the excellence of the Sun alone that is scrutinized: it acts as leader and ruler and regulator of the world, sheds its light over all living things, warms them equally by the temperament of its heat.”36
Leibniz, like Descartes before him, would hope to transpose Fernel’s theory into a distinctly mechanistic framework, arguing not that the animal body derives its vitality from a celestial source, but that it is literally a machine that harnesses the very same powers that make the celestial bodies hot and bright. For Leibniz, something similar to celestial burning happens when the excocted chyle mixes with the blood and produces fermentation:
Many think that it is the hot in the body that is fed by the humid; some appeal to the little flame in the heart, others to the fire without light,37 a certain I-know-not-what38 analogous to the elements of the stars . . . ; some say it is a certain fermentation, some that it is innumerable little explosions comparable to gunpowder: we think that in all of these a moderate and enduring boiling obtains, which is fed by a circulating matter that grows more and more rarefied and is also restored little by little. . . . We will thus rightly assert that an animal is not only a Hydraulico-Pneumatic machine, but also in a certain respect a Pyrotechnical one.39
In order to more adequately understand Leibniz’s account of the an- imal as a pyrotechnical machine that “burns” its food and gives off a waste analogous to smoke it will be useful to briefly summarize the scientific and natural-philosophical discussion of nutrition in Leibniz’s era, and to show also how exactly Leibniz positions himself within this discussion.
It might seem odd to think of nutrition as a metaphysical problem, yet within the framework of a corporeal-substance metaphysics, one cannot avoid the question as to precisely how what was previously external to and nonidentical with the corporeal substance becomes incorporated into it, and is thereby literally substantially transformed. Nutrition had been one of the basic processes of interest to the chemical tradition. For Paracelsus, digestion is an alchemical process par excellence, and the stomach is nature’s supreme alchemist to the extent that it skillfully separates the good from the bad (for Paracelsus alchemy is the “art of separation”) and incorporates the food into the body. It is the “archaeus” of the body for Paracelsus that is in charge of digestion and so of the preservation of life. According to one scholar, Paracelsus’s idea of archaeus (which, as we will see in the following chapter, is again picked up by Leibniz’s contemporary Henry More, and which serves as a fertile point of departure for Leibniz’s alternative theory of “material plastic natures”) is a later descendant of the “archonten” or “daimon of digestion” introduced by Proclus and Iamblichus.40 We do not have space to pursue this ancient pedigree here, but bring it up only to show how importantly linked, traditionally, were the problems of nutrition on the one hand and that of life on the other. For many premodern thinkers, to live is just to eat, or to endure in existence by substantially transforming the world into oneself. Indeed, as late as the polemic with Stahl of 1709–10, Leibniz has occasion to argue against the Helmontian theory of the “gastrianax,” according to which the stomach is ruled by a subordinate soul—ridiculed by Leibniz as a “little kinglet”41—that serves to carry out the process of nutrition and digestion. The various theories of immaterial principles in nature that would emerge in the late seventeenth century, such as Jean-Baptiste van Helmont’s gastrianax, More’s archaeus, Cudworth’s plastic natures, or Stahl’s body-preserving soul, emerge directly out of this long tradition of explaining the process of nutrition within the context of a corporeal-substance metaphysics.
In Leibnizian terms, an aggregate has whatever low degree of reality it has in virtue of the relative stability of the cohesion of its parts. A corporeal substance, in contrast, has no such cohesion; there is constant flux between it and its environment, and yet it is this capacity to endure throughout the flux that wins for it the status of true substance as opposed to mere aggregate. The corporeal substance is what is in constant communication with its environment, what has its being only through its environment, to the extent that it takes in material from its environment and transforms that material into itself. The soul or dominant monad has appetite, to be sure, but this is an appetite for ever more perceptions, not for food. Leibniz and many of his contemporaries are thus sharply opposed to many of the late Aristotelians, such as Agostino Nifo, for whom nutrition could not be reduced to the coction of chyle and its fermentation when mixed with blood, since on this account there is no fundamental change of the quality of the nutriment whereby it would become substantially part of the corporeal substance that has ingested it.42
In the debate with Stahl, as we shall shortly see, Leibniz repeatedly accounts for the cohesion of the organic body, and its simultaneous dependence on constant influx of material from the environment surrounding it, by comparison to the flame’s constant consumption of fuel. The image of a flame burning wood or oil is a common theme in early modern accounts of nutrition. For example, Pierre Gassendi believes that sensation arises when the soul is “kindled” in the body as fire is kindled in a log. “Food such as bread or herbs,” he writes,
is no more distant from living and sensing flesh than a log is form a light-giving and burning flame. . . . Just as . . . particles can be disentangled from a log, which particles will have a new power of lighting and heating once they move and arrange and dispose themselves in a new way, so spirituous particles can be obtained from dissociated food, which particles will possess an energeia of sensing once they are divided in a certain manner and disposed in a new way.43
Although Leibniz repeatedly denounces the “Epicureans” in his physiological writings, there is nonetheless considerable overlap in the problematics, and even in the terminology, of his work in the area of animal economy on the one hand and on the other that of Gassendi as well as his English disciple Walter Charleton.44 As already mentioned, Leibniz may, whether by a direct or indirect route, have appropriated the idea of a special science of “animal economy” from Charleton, who writes of the “Oeconomy of Nature in the body of Man; a System of innumerable smaller Machines or Engines, by infinite Wisdom fram’d and compacted into one most beautiful, greater Automaton: all whose parts are among themselves different in their sensible elements.”45 In the following chapter we will be discussing Leibniz’s belief, which he shares with Charleton, that the body-machine consists in “innumerable smaller machines”; here we are intent on understanding only the Leibnizian conception of animal economy, which does not include the machines-within-machines conception of the animal body that would emerge in Leibniz’s organic model some years later.
For Leibniz as for Charleton, animal economy is fundamentally rooted in the process of nutrition. Charleton sees the question of nutrition as the natural starting point of the science of animal economy,
not only because the Stomach, Gutts and other parts principally inservient thereto, being, by reason of impurities contain’d in them, more prone to putrefaction, ought therefore first to be taken out of the cavity of the Abdomen, to prevent noisomness; but because Nutrition seems to be, if not one and the same thing with, yet at least equal or contemporary to Generation it self.
He goes on to explicitly identify nutrition and generation as two aspects of one and the same process: “To nourish, what is it but to substitute such, and so much of matter, as is, by reason of exhaustion, wanting to the solid parts of the body, namely flesh, nerves, veins, arteries, &c.? . . . Nutrition is nothing else but Generation continued.”46 Both of these aspects are governed by what Charleton calls a “Plastic Spirit,” which works
within us through the whole course of our life, from our very first formation to our death; doth in the same manner perpetually regenerate us, out of a liquor analogous to the white of an Egg, by transmuting the same into the substance of the solid parts of our body. For, as I said before, Nutrition is necessary to all Animals, not only in respect of the Augmentation of their parts, while they are little Embryons; but also in respect of their Conservation after during life: because their bodies being in a natural consumption or exhaustion, would inevitably be soon resolv’d into their first elements, unless the providence of Nature had ordain’d a continual renovation or reparation of the parts, by substitution and assimilation of fresh matter, in the room of those particles dispers’d and consum’d. . . . The Depraedator . . . or Efficient cause of the perpetual consumtion of our bodies, seems to be, what all Philosophers unanimously hold it to be, the Vital Heat of the bloud, therein first kindled by the Plastic Spirit, continually renew’d by the Vital Spirit, and by the arteries diffus’d to all parts of the body, that they may thereby be warm’d, cherish’d, and enliven’d.
Thus, for Charleton as for Leibniz, what sets the animal body off from an aggregate such as a rock is precisely the lack of stability of its corporeal parts: it is constantly burning from within, and needs the burned or exhausted matter to be perpetually replaced. The fact that it is able to replace its “depredated” parts, and that fresh matter is able to come in and take on the form of the matter that has been burned up, already shows that the animal body is something of quite a different nature than an aggregate, and also shows that there can be no clear distinction between the initial generation of an animal and its subsequent manner of existence: for an animal to continue to live is for it to be continually regenerated.
Charleton suggests that “the Human Embryo perhaps is nourish’t before the Empsychosis.”47 Descartes, too, it is worth noting in passing, had seen the initial formation of the fetus as explicable in terms of nutrition. Stephen Gaukroger calls this account of fetal development “about as mechanist a route as is possible,”48 but whether this is what it is, or not, depends however on the metaphysics of nutrition of the author in question. For Agostino Nifo or, as we will see, for Stahl, nutrition is by no means a merely mechanical process: the preservation of the unitary body throughout the perpetual flow of the new material that it takes in is in fact the work of the soul, indeed it is the soul’s principal function. Charleton and Leibniz both align themselves with Descartes, as it happens: the fact that nutrition occurs before empsychosis means for them that nutrition cannot itself be a soul-driven process. As Leibniz repeatedly emphasizes, nutrition is a more basic process in the study of animal economy than is sense or voluntary motion, since sense requires the prior possession of organs of sense, which were in turn initially formed through nutrition. But for a Stahl or a Nifo there is nothing at all “mechanical” about the grounding of physiological processes, even fetal development, in nutrition.
Certainly the most common view of nutrition in the decades preceding Leibniz and Charleton’s interventions was that it involves the substantial transformation of food. To cite one useful reference work, Goclenius’s Lexicon Philosophicum of 1613 defines “nutrimentum” or “alimentum” in both the proper and metaphorical senses. The metaphorical sense includes odors and other signs of possible nutrition that do not themselves nutrify. In the proper, literal sense, nutrition may be either potential or actual, potential when the aliment is brought to the mouth and delected, and actual “when this aliment has been decocted and is incorporated into the substance of the living thing [ut in rei viventis substantiam concedat].” Goclenius cites Thomas Aquinas, for whom “to be nourished means, properly speaking, that in oneself something is received toward ones own bodily conservation.”49 Here the substantiality of the body is not explicitly mentioned, but in the context of Thomist metaphysics there is no reason why it should have to be.
Leibniz, as mentioned, agrees with Charleton that nutrition precedes—if not temporally in the development of the fetus, then at least in the order of explanation—the capacities for voluntary motion and sense. Indeed, as just mentioned, the study of nutrition is the foundation of the science of animal economy, as nutrition gives rise to those organs that are required for sensation. As Leibniz explains in the De scribendis:
In truth our medicine is better informed concerning nutrition than voluntary motion, and more concerning this Motion than the functions of sense, and it may be supposed that the machine is capable of nutrition, and sense free from animal motion; it is easier moreover to explain in what way we are nourished than in what way we perceive and act; indeed from aliments those parts are also generated which we require for the functions of the sensitive soul. It will be preferable to inquire into those parts first which are seen by a certain reason to be held in common with plants, than those that are characteristic of animals [alone].50
We have seen that for Leibniz, as for many of his contemporaries, nutrition is of fundamental importance in explaining the nature and motion of animal bodies, yet we have yet to determine what the precise mechanism of nutrition is. By what means is food transformed into bodily matter? We have also seen that Leibniz agrees with most other moderns in holding that nutrition is not a variety of corruption, and in holding that whatever it is, it must be entirely mechanical. In his view, nutrition is an instance of fermentation.
Ferments play a central explanatory role in the chemical tradition and are closely linked semantically to a number of notions, such as archaeus and seed, that would supposedly be anathema to the mechanical tradition. Yet fermentation is also, significantly, by far the most important process in early mechanist physiology.51 By appeal to fermentation, for example, Descartes believes himself able to account not just for the heat of the heart but also digestion and a number of other bodily processes. This is the same basic process, Descartes believes, that we witness in many seemingly distinct natural phenomena, including the production of heat in moist hay and the making of beer and wine. In all of its manifestations, fermentation may be defined as calorification from corruption, and Descartes holds it responsible for digestion, respiration, conception, and certain components of fetal development, among other phenomena.
Fermentation had been a central concept of chemical medicine since Paracelsus, and more noticeably with the transportation of Paracelsianism into the Anglo-Dutch sphere by Jean-Baptiste van Helmont and Franciscus Sylvius in the early seventeenth century.52 For these iatrochemical thinkers, fermentation occupies a central place in natural philosophy, as it makes possible an account of the origination of forms from—as in the case of van Helmont—the universal empty matter of water. As Betty Jo Dobbs explains, “the ferment originates [for van Helmont] in a divine idea and, as it operates upon the ‘empty’ matter, the ferment itself is internalized and becomes the archeus, the internal governing principle of the created being that insures the working out of God’s plan for its existence.”53
In Dobbs’s view, Descartes’ incorporation of the concept of fermentation into his physiology amounts to a prime example of the habit of early mechanists to restate common cultural assumptions “in terms of corpuscularian mechanisms that disguised but by no means eliminated their vitalistic components.”54 Yet this criticism may not be entirely fair. While there is no doubt some truth in the general point that the mechanists gain nothing in explanatory force by substituting “microstructure” for “form” or “virtue,” it is clear that Descartes conceives fermentation as a straightforwardly microstructural process, and that he conceives the changes it brings about not in terms of the emergence of new forms but in terms of the quantitative alteration of preexisting corpuscles. If he could not account for the details of these changes at the microlevel, this does not mean that in granting to fermentation a central place in physiological phenomena he does not have reason to hope that someday it might be explained in entirely mechanical terms. The same certainly holds true for Leibniz.
Another important figure in the background of Leibniz’s contribution to animal economy—including his eventual adherence to the view that the animal is a fermenting or pyrotechnical machine—is Thomas Willis, a physician and founding member of the Royal Society who published the treatise De anima brutorum in 1672. In many respects this treatise poses an important contrast to Charleton’s Gassendian physiology. Willis believes that fermentation is an inorganic process, defining it as the “inorganic motion of natural bodies.”55 He also believes that it can happen, however, in any number of kinds of body, including animate ones: “Bodies that are susceptible to fermenting are of diverse consistencies and conditions, as fine or course, liquid or solid, animate or inanimate, natural or artificial.”56 While he conceives fermentation as a strictly physical process, Willis nonetheless thinks that it can serve to propel a living body along the course of development proper to it: “Fermentation is the motion of internal particles, or of the principles of any given body, as the tendency towards perfection of the same body, and even by means of its transformation into another.”57 Willis sees fermentation spreading across the different natural kingdoms or “families,” and thus as a basic explanatory principle of geology, botany, and animal physiology.58 He believes that in the end fermentation is always the same across kingdoms: it is the motion of internal particles. But depending upon the sort of body in which it happens, it will contribute to transformation in a different way. For Leibniz as well, fermentation is a strictly chemical process, but each kingdom of nature has a chemistry specific to it:
There is so to speak a chemistry proper to animals, and the transformations that occur in the animal humors arise from chemistry no less than do vegetable liquors. Consequently, all bodies arise from chemistry, when we consider them not as structures but as masses, and when we apply to them physical operations consisting in an insensible process.59
This last point is key to understanding the role of fermentation in Leibniz’s conception of animal economy. For him, fermentation is a fundamental principle governing a number of processes in animal bodies, as it is also in plants and in minerals. However, it operates in the animal body not as an integrated structure of interconnected organs, but rather as a mass of fluids. Fermentation is at the root of the process that yields organs with functions out of a mass, and it is in this respect that for the study of animal economy fermentation is more basic or primitive than the study of voluntary motion or sense. It is also in this sense that an animal can be the object of study for chemistry and biology at once.
For Willis as for Descartes, fermentation is fundamentally a thermal process, responsible for the production of heat in the body. Thus Willis maintains that the souls of animals are at once “corporeal” and “igneous [igneam]”:
And even Brutes make use of a material and divisible soul inferior to that of man, [which is] coextensive with the whole body, as it is seen to be constituted from several [parts], . . . seeing therefore that between the soul and the body there is no intermediate, but rather the members and parts of the body are organs of the soul.60
While Willis presents much of his work in opposition to Charleton, this is not because he objects to the revival of Epicurean philosophy with which Charleton was associated, but because he believes that he is the superior interpreter of it. He calls upon Epicurus as an ancient authority for the view of the soul-body relationship he defends:
With this agrees the teaching of Epicurus passed on from antiquity, and revived again in our century, which introduces the clearly corporeal Soul, [and] which consists in the texture of subtle atoms, and asserts, . . . that from the mind of Gassendi there resounds this same, that the animal is a sort of loom, in which the body is the warp, while the soul is the woof.61
Leibniz takes up the view that with respect to animal economy the principle of life is “igneous,” but he denies strongly that this igneous principle is a soul. Instead, it is the body-machine itself that is igneous, and the full account of this igneous body-machine, at least from the Corpus hominis on, requires no mention of the soul. One may doubt that there is much difference between saying that there is an igneous and corporeal soul, on the one hand (Willis’s view), and on the other that the body is moved by a vital, igneous principle while the soul is something to be invoked only quite apart from any corporeal function (Leibniz’s view). But Leibniz’s insistence that the body-machine itself, and not the soul, is the igneous principle behind vital phenomena shows the extent to which he remains in his theory of animal economy true to the Cartesian view of the animal-machine, and to the Cartesian view—to which Willis assents, while nonetheless adopting the very un-Cartesian idea of a corporeal soul in animals—that there can be no subtle or rarefied substance that serves to mediate between the soul and the body.
This text overlaps significantly with the Corpus hominis of the same period, and even in its title reminds us of the great extent to which Leibniz conceives the study of animal economy as valuable principally in the service of the advancement of medicine.63 In this text, Leibniz calls the animal body a “Hydraulico-Pneumatico-Pyrobolic Machine.”64 More so than in the Corpus hominis, here Leibniz emphasizes the role of “spirit” in the body, which he conceives along with Descartes not as an intermediate principle between body and soul, but as the most rarefied part of the blood, separated out through excoction. This spirit, as already mentioned, has “the likeness of solar rays or of a flame or indeed of gunpowder . . . which we note in fermentations and reactions.”65 Leibniz calls this spirit the insensible “motor” in the body. Because he goes to such lengths to account for the production of this spirit directly through a mechanical process from the blood, Leibniz’s identification of it as the “motor” of bodily activity is a clear rejection of the alternative identification of the soul as the first mover in the body: “The motor in our body is insensible. Indeed, this is a certain continuous fluid diffused throughout the whole body, from which it can be understood that all things that are in contact with any given part of our body are easily sensed by us.”66
Ultimately, Leibniz traces the activity of spirit back to the process of nutrition, and he tellingly compares this relation to that between a flame and its oil. He asserts that “food is useful to spirit as oil is to the flame.” By the time of the polemic against Stahl, this comparison will come to play an argumentative role much more important than that of a mere analogy. Eventually, for Leibniz, the fact that vital motion in an animal may be traced back to aliment in the same way that the burning of a flame may be traced back to oil shows just what a superfluous measure it is to take recourse to the soul in accounting for vital phenomena: if you are going to insist that an animal moves only because it has a soul, then you may as well insist that candles are ensouled too. Leibniz will of course mean this point as a reductio ad absurdum, not as a defense of psychopyrism.67
In the De scribendis, as in the Machina animalis, Leibniz is interested in accounting for “life” (that is, perception and motion) in terms of the “economy” of the animal body. Later, in the polemic against Stahl, Leibniz decouples the faculty of perception—in view of which a substance may be said to be living—from the body and roots it in the simple immaterial substance. In the later writings, life is just perception, and perception is a nonbodily, spiritual faculty. What is most intriguing about the De scribendis is that it suggests that Leibniz’s mature metaphysical elaboration of just how perception, and the complementary notion of appetite, work in the nonbodily monad seems to have first been worked out in the course of explaining the perception and appetite of animal bodies in straightforwardly animal-economical terms. As Pasini notes, in this text the principal function of the human being is perception:
The individual substance, as we have seen, has an essentially perceptual nature, and accordingly is a machine oriented first of all towards perception. . . . There is a perfect correspondence, even if it is not made explicit, with Leibniz’s idea of appetition as the tendency of the substance towards perfection, manifested in the passage towards more distinct perceptions.68
Paragraphs 4–7 of the text (see Appendix 4) constitute its philosophical core. Here Leibniz says that perception is the primary function of the human body, and the procuring (procuratio) of perception is the secondary function. Here, in sharp contrast with the later writings, perception is dependent on the organs of sense; and the ordering of perceptions is dependent on the motion of the body. The greater facilitation of perceptions is the greatest end for an animal or human and is itself experienced as an agreeable perception. In this connection, the organs of generation are included among the organs of motion, as generation is the procurement of “a most agreeable perception through motion.”
The organs of nutrition, which humans and animals have in common with plants, must already be functioning in order for motion, and then sense, to arise. While Leibniz distinguishes these from the organs of motion, he also describes both the organs of motion and of nutrition as facilitating conditions for the procuring of perceptions (and thus as requisites for the achievement of the greatest human end), describing nutrition as the greatest facilitator of perceptions insofar as the particles of the body are continually in flux. Without nutrition neither the organs of motion nor of sense could continue to cohere for very long.
In this text, Leibniz continues to uphold the possibility of “perceiving machines,” and asserts that perception is a faculty of the organs of sense, which rely on the organs of motion for the procuring of more perceptions, which in turn rely on the organs of nutrition for their initial formation and for their enduring existence. In Leibniz’s most mature work on physiology, in contrast, as one would expect from the contemporaneous philosophical texts of the same period, the perception that is identified with life is no longer seen as a bodily process; and the body’s motion is something Leibniz now hopes to derive, as he writes to Stahl in 1709–10, from the body’s “vegetative structure alone.” Vegetation or nutrition, in turn, neither give rise to motion and perception, nor are they any longer something that need be explained in terms of the inherence of a soul-like substance, which is to say in terms of perception.
One of the great innovations to take shape by the time of the controversy with Stahl, an innovation that enables the mature theory of monads to take shape, is the separation of perception from the organs of sense, and the separation of appetite or procuratio from the organs of motion. The mature analysis of these faculties, though, seems unmistakably to be rooted in Leibniz’s early physiological interests, and only subsequently transferred out of the domain of physiology, all the while retaining its original structure. It could thus be argued that this is a case in which Leibniz works out a general account of what’s going on fairly early, but then eventually changes his idea as to what sort of entity this is to be an account of. Before looking at this important later development in detail, let us briefly consider some other developments in Leibniz’s animal-economical thought that occur between the period of the De scribendis novis and that of the encounter with Stahl.
In the previous chapter we saw Leibniz praising Johann Bernoulli as the ideal philosopher-physician in a letter to Bernoulli’s brother Jacques. Leibniz was evidently very impressed with Bernoulli’s two treatises from the 1690s, the one on effervescence and fermentation, the other on the motion of the muscles. What were the most important features of Bernoulli’s physiology for Leibniz? In the two treatises, the Swiss physician had sought to explain the contraction of muscle tissue (crispatio) in terms of a strictly mechanical effervescence. In his view, active tetrahedric corpuscles become lodged in the angles of star-shaped corpuscles, causing them to explode and setting free the bubbles of elastic air that they had contained, which in turn creates an effervescence visible to the observer.69
As Raphaële Andrault has argued,70 Leibniz’s earliest writings on medicine, including the project of animal economy that accompanies it, were marked first and foremost by the influence of Lorenzo Bellini and Nicolas Steno. At this early stage, as we have already seen, Leibniz is enthusiastic about the possibility of “mathematizing medicine”; as he writes in the Directiones studied in the previous chapter: “Bellini, if I am not mistaken, has begun to mathematize in medicine, and also Steno, as nearly everyone does.” By the dawn of the eighteenth century, Leibniz is much more skeptical about the possibility of such a mathematization, particularly in his encounter with the work of Johann Bernoulli.71 What seems to have changed, principally, is Leibniz’s understanding of the complexity of the animal body, and in particular of the infinite subdivisions in the body that bring it about that we cannot exhaustively know the ultimate processes of nature, even if we remain committed to the view, in principle, that what we can observe in the body needs to be tethered to mathematical concepts. As Leibniz writes to Michelotti in a letter on animal secretion of 1715: “There may be many mechanical causes that explain secretion. I suspect however that one should sooner explain the thing in terms of physical causes. Even if in the final analysis all physical causes lead back to mechanical causes, nonetheless I am in the habit of calling “physical” those causes of which the mechanism is hidden.”72 Here, then, “physical” contrasts with “mechanical” to the extent that the latter lends itself to immediate mathematization, given the state of our knowledge and our capacity for observation, whereas physical explanation remains avowedly hypothetical.
Earlier, it had been the work of Steno that served as a model for the possible mathematization of medicine and related fields of investigation. Steno had argued, most importantly in his Elementorum myologiae specimen seu Musculi descriptio geometrica (Specimen of the Elements of Myology, or a Geometrical Description of the Muscle) of 1667, that the nerves and muscles alike contract and expand without the influx or efflux of any new material: for the Danish physician, this argument was of particular importance for the broader argument against the animal spirits playing a role in animal motion. Steno is effectively attempting to demonstrate the mechanism of contraction more geometrico, namely, by showing how the shortening of the fibers that constitute the muscles is alone sufficient to account for muscular contraction.
Bernoulli’s invocation of effervescence was intended as in part a way of accounting for the swelling of the muscles through the “boiling of nerve juice with blood,” and thus through the motion of liquids, without for that having to reintroduce an account of muscular motion in terms of animal spirits.73 Leibniz expresses his full agreement with Bernoulli in this regard, as against Steno: “I shall easily concede to Steno that the nerves act by a certain shriveling [per crispationem], but this shriveling cannot be explained but by the influx of a fluid. Thus water makes cords contract, and so does heat in the case of the hair.”74
Ultimately, Leibniz believes that the sort of mechanical explanation that should be hypothesized in accounting for the motion of the muscles will be one that attributes an important role to elasticity, rather than to the action of fluids such as animal spirits. The elasticity of the inner parts is conceived as a sort of force (vis elastica) that keeps the body in motion through countless imperceptible vibrations in a manner analogous to the “vibrations” of perceptions that endure in the soul as memories. As Leibniz writes in a letter to Bernoulli of May 6, 1712:
In organic beings many things seem to consist in perpetual, imperceptible vibrations, which, when we perceive them to be at rest, are in fact being held back by contrary vibrations. Thus in truth we are led back to an elastic force. I suspect that memory itself consists in the endurance of vibrations. Thus there does not appear to be any use for a fluid that goes by the name of animal spirits, unless it is traced back to the reason itself of the elastic force.75
This strategy of explaining the dilation and contraction of the parts of the body in terms of an effervescence that brings about a sort of vibration far antedates Leibniz’s correspondence with Bernoulli and seems to be traceable most directly to the influence of Boyle’s New Experiments Physico-Mechanicall, Touching the Spring of the Air, and its Effects of 1660.76 Leibniz writes as early as the Corpus hominis of the mid-1680s:
While it is granted that the seat of effervescence is in the heart, it nonetheless is easily communicated to the whole body by the blood vessels, just as [when] we attempt to heat an enormous cask of wine with a small fire, if the fire be applied through a small copper utensil, connected with the vessel through a tube. Seeing moreover that in any ebullition there is an excessive dilatation, the vapor is nevertheless not expelled, but rather it is necessary that it in turn be pushed along, whence arises respiration, indeed in all exceedingly great efficient [causes] there is a certain reciprocation of restitutions such as we note in oscillating pendula, or in vibrating chords.77
What will be new by the time of the 1712 letter to Bernoulli is Leibniz’s interest in describing a mental process such as memory as parallel to the bodily vibration that is brought about by the elastic force and that keeps the body in perpetual motion. Bernoulli would hold that “in the whole machine of the human body, every smallest particle involved in a movement is moved either directly by an order of the soul or by muscles. All these muscles follow strictly and steadily the laws of mechanics.”78 We have already seen that Leibniz was very impressed with Bernoulli’s work, yet there is no way, given Leibniz’s conception of body and soul as parallel automata, that he could have agreed with his physician friend as to the dual sources of motion in the body. Leibniz would certainly agree that the muscles follow the laws of mechanics, and that the origin of motion in the muscles is a mechanically explicable pyrotechnical event, yet for him no “order of the soul” could make a difference in the succession of a corporeal substance’s states. The reason for this is spelled out at length in Leibniz’s arguments against Stahl’s account of how the soul moves the body.
As François Duchesneau has compellingly shown, around the same time as Bernoulli was accounting for the source of muscular motion in mechanical effervescence, Friedrich Hoffmann, Stahl’s mechanist colleague in Halle, was also introducing physiological agents of impetus in living bodies in order to account for vital phenomena.79 Hoffmann construed these agents as innate organic forces (vires insitae) that nonetheless could be accounted for in avowedly mechanical terms. Another important figure in the background to Leibniz’s own views is the Italian physician Giorgio Baglivi,80 who discerned irreducibly vital properties in nerve fibers.81 In the case of Hoffmann and Baglivi, what unites Leibniz with them is not support of or opposition to a vitalist account of animal motion: in the end, this is an anachronistic notion that could have meant nothing for Leibniz and his contemporaries. Rather, Leibniz, Hoffmann, and Baglivi are unified, against Stahl, in the view that the motion of an animal arises in the final analysis from a principle inherent in the nerves or muscles of the animal body rather than from the soul. Leibniz agrees that the body contains the principles of its own motion, and this will be the major point of contention around which his debate with Stahl circles. The debate, at least as both of its participants understood it, was not about vitalism, a notion that would not even come to be meaningful until well after the deaths of both Leibniz and his opponent. Yet if we must categorize Leibniz anachronistically in terms of this doctrine, we may say with firm conviction that he is an antivitalist: for him, the growth, motion, and preservation of a living body can be exhaustively accounted for without appeal to the soul. The soul is not responsible for life.
We have already seen that although chemistry and biology are distinct for Leibniz, he nonetheless recognizes that there is, as he repeats in the Animadversiones, a “chemistry specific to animals.”82 A clear example of this is his belief that volatile salts play a more important role in animal chemistry than in vegetable. Another example is the view that the specific trait of “animal glutinosity” lies in the fact that bodily fluids can harden when heated without diminishing in humidity, as he believes he has observed to happen in egg whites.83 Leibniz may not be able to contribute to medical research, but he can at least observe eggs frying and draw conclusions from what he sees. In the polemic with Stahl, Leibniz has developed a clear means of distinguishing the study of animal chemistry from that of animal economy. While it is true, he explains, that any given animal body arises from chemical processes, the chemical study of the animal body is the one that takes it as a mass, while the science of animal economy is interested in animal bodies not as masses but as structures. The fact that an animal is a structure rather than a mass may be discerned from its functioning as a whole, and this is precisely, as in the Corpus hominis of the early 1680s, its end-directedness, its only apparently oxymoronic “mechanical teleology.”
As in earlier texts, in his polemic against Stahl Leibniz explicitly distinguishes the natural machine from the “hydraulico-pneumatic machine” in that it is also a “pyriac [pyria]” machine. 84 Leibniz writes that “there are in animals eruptions and explosions similar to those of a cannon,”85 and again that “the animal body is a hydraulico-pneumatico-igneous machine; the force of impulsion [in animals] is born from explosions that arise in it like cannons.”86 Also as in the Corpus hominis, Leibniz compares the animal moved by the beating of the heart, or first motor, to the alchemical furnace whose heat is modulated by bellows and other implements: “We can easily conceive that the motive principle can augment or alter the energy in the body of an animal, in the same way that registers, bellows, or combustibles intensify or diminish the force of a stove.”87
As in the Corpus hominis, in the polemic against Stahl Leibniz discusses the status of species and their dependence upon sexual reproduction. In the later text, Leibniz understands the descent of animals through sexual reproduction to be a central part of this wisely chosen world, and just as the successive states of substances are always already contained in the present, preestablished harmony also brings it about that succeeding generations of a species are literally bound up with the prior generations, like so many links in a chain: “God created everything in his very great wisdom so that beings are born the one from the other like the links in a great golden chain.”88 As is the case with nutrition, mating and reproduction prove the divine coordination of things, in that an individual substance requires something outside itself, provided by divine wisdom, in order to fulfill its ends. For Leibniz, the natural machine differs from the aggregate precisely to the extent that the machine has its ends ordained by its structure, whereas if there are any ends to be had in aggregates, these will be ends that arise from the coming together of sundry machines.
We have recognized a great difference between machines and aggregates—or masses—, insofar as machines have their effects and their ends by virtue of their own structure, while the ends and the effects of aggregates are born of a series of struggles, thus of the meeting of diverse machines.
All the same, natural machines, too, have to “meet” other natural machines for the accomplishment of their ends:
The worm labors on its own in the sole aim of producing silk; however, in order for another silkworm to be born, there must also be the union of the male and the female, and thus the combination of a single animal with a foreign element; for this combination shows more clearly its coordination with divine wisdom.89
Ultimately, the end of every natural machine is reproduction, but there must also be a subordinate end in order for there to be a clear fact of the matter as to what is being reproduced. Thus silkworms give rise to silk-producing offspring, and, as Leibniz puts it in the Corpus hominis, “as long as there are squirrels there will be dancing machines.”
The point of contention around which the entire debate between Stahl and Leibniz rotates is the question whether or not the soul need be invoked in order to account for the structural unity of the animal body. Unlike in earlier texts, notably the Machina animalis, in which Leibniz maintains that the study of animal economy ultimately serves to unravel the nature of life, here Leibniz seeks to radically separate animal economy from inquiry into the nature of life, which he now sees as synonymous with perception. An animal is alive, but none of the phenomena treated by animal economy can reveal this. An animal is alive in virtue of its capacity to perceive, which is a soul-based and not a machine-based activity. The polemic against Stahl, then, is Leibniz’s first and only attempt to treat the subject of animal economy and at the same time to clearly demarcate it from the study of the soul, with which, he believes, Stahl himself has conflated it.
For the mature Leibniz, every living thing is ensouled, but it is not the soul’s function to hold the body together, as it is for Stahl. In Leibniz’s view, this function can be taken care of by the “vegetative force”90 alone. Leibniz mocks Stahl’s view of the soul as having a body-preserving function, borrowing a mocking comparison, originally made by the third-century Stoic philosopher Chrysippus,91 of the soul’s role in the body to that of salt in cured ham: “The very celebrated author identifies [the role of the soul] with the power of preserving the body from its own tending towards death, since otherwise the bodies of living things would decompose, so that future life would have the value of salt, as was said in jest of the soul of a pig.”92 In other words, if the body-preserving account of soul were correct, salt could just as easily be brought in to take over the porcine soul’s role once the pig has been slaughtered, since it would keep the flesh from rotting.
Leibniz is optimistic about the possibility of deducing the vegetative force, which preserves the body, “from the structure of the machine itself.”93 For him, life could not possibly consist in the preservation of the body, since the nutrition, metabolism, and excretion of wastes through which this preservation is effected is fundamentally little different from the manner in which a flame avoids extinction by burning up surrounding matter. And a flame, Leibniz insists, is patently not a living thing. In Leibniz’s view, again, this comparison shows that there is no sound reason for cordoning living beings off from mechanistic explanation on the grounds that their capacity for self-preservation cannot, as Stahl would have it, be explained without appeal to the inherence of a soul: “That life preserves itself in casting off alien substances and in conserving the substances that it appropriates to itself does not rule out mechanism any more than the fact that the flame attracts air and sends off smoke.”94 Leibniz cites experiments by Boyle to corroborate his view that an animal, like a flame, is in perpetual flux, and is nothing in itself without the constant appropriation of materials from the surrounding environment. The animal, in contrast with the flame, is constituted from fundamentally liquid parts, whose solidity arises only from the “cohesion that is produced by the conspiring movements of the fluid bodies.”95
In the end, Leibniz’s argument against the soul as body-preserver rests on the doctrine of preestablished harmony. For him, as we will discuss in detail in the following chapter, there can be no fundamental metaphysical distinction between what happens organically and what happens mechanically; the organic just is a “more exquisite [exquisitior]” and “more divine [divinior]” form of the mechanical. Indeed, such a distinction as Stahl would hope to make, in which organic phenomena happen through the action of the soul upon the body, would amount to a “violation of the mechanical laws of the body.”96 As Duchesneau explains, in the polemic against Stahl, “the concept of organism serves to establish the respective jurisdictions of the respective authorities of the corporeal and the psychic.”97 Leibniz denounces the soul-body relation imagined by Stahl as one of obedience through violence, whereas Leibniz envisions an “obedience through accord.”98 The soul cannot impose anything upon the bodily machine that the machine is not capable of producing spontaneously. The body is thus an automaton, as is the soul (by analogy to the body), in that both move from one state to the following state entirely in accordance with their own laws. The soul need not constantly “worry about the body”99 in order for the body to do what it has been made to do.
We see in this text Leibniz’s only comprehensive effort to explain the relation of animal economy to the study of the soul, or, to put this in a different way, the study of animal machines to the study of animal life. We see, for example, Leibniz’s mature expression of his view of the limitations of mechanistic explanation, that is, explanation in terms of sequences of proximate, efficient causes. The ultimate explanation lies in the metaphysics of divine creation, in God’s choice of the best of all possible worlds:
The full reason of things cannot be found in particular causes, but must be sought after in a general cause, from which immediately emanate the present state as well as the prior one. This general cause is the intelligent Author of the Universe, who chose this series among an infinity of others of which matter was capable.100
Although every body is ensouled for Leibniz, the soul nonetheless has no bodily function. The soul perceives, and this is a supercorporeal function. Any function of the soul within the body would be a violation of the doctrine of preestablished harmony, which by the time of this polemic has come to occupy a central—likely the central—explanatory position in Leibniz’s philosophy. In later chapters we will have occasion to discuss the full philosophical significance of the doctrine of preestablished harmony for Leibniz’s theory of the organic structure of bodies. Here, however, we will do well to succinctly lay out its uses in the polemic against Stahl.
In the polemic’s most thorough discussion of the doctrine of preestablished harmony, the twenty-first reply to Stahl’s “Observationes,” Leibniz makes oblique reference to his earlier publications on this revolutionary new doctrine and complains that the doctor from Halle has evidently not read these. Leibniz claims that the doctrine of preestablished harmony is justified by the fact that a soul is an unextended substance,101 insusceptible to natural creation or destruction. Since there is no “proportion [proportio]”102 between the monad and the bodily machine, Leibniz claims, there can therefore be no connection between the appetitions of the soul and the motion of matter. Thus, Leibniz thinks, one of the following two hypotheses must be true. Either, as the “Cartesians” hold—which is to say Malebranche and other occasionalists—God implicates himself in the affairs of the world in order to directly bring about the states of the body that are required by the appetites of the soul; or these two agree with one another by a preestablished harmony.
To hold that there can be some sort of proportion between soul and body, and thus causal influence from the one to the other, as does Stahl’s account of animal economy, is, Leibniz thinks, to do nothing more than to “substitute the soul for the animal spirits by a change of name,” a move Leibniz derides as “resting on I-don’t-know-what incoherent principles lacking in any value.”103 This is particularly interesting when we recall from the introduction Descartes’ vehement denunciation of the view that animal spirits are endowed with truly spiritual or soul-like properties. For both Descartes and Leibniz, a crucial component of the true mechanistic theory of bodies, including ensouled bodies, is that there can be no intermediate principle between the soul and the body that facilitates their cooperation. Leibniz believes that Stahl has unwittingly turned the soul itself into that intermediate principle between soul and body.
An important argument to which Leibniz returns frequently in this polemic is that if the soul could act upon the body, there would be no limit to its power, and thus no limit to what the body could do under its influence (potentia animae nullis limitibus coerceretur).104 Causes would have exceedingly great effects, whereas in fact Stahl, in Leibniz’s view, attributes too much cause to minimal effects. Leibniz notes in this connection that “inert” bodies also have impetus, which is in fact all that is required to explain motion in animals. Indeed, if one thinks something more is required, then one would be hard pressed to explain why, for example, an animal’s heart often continues beating long after it has been removed from the animal’s chest.
One theme of the late metaphysics of body, generally underemphasized in the secondary literature and very prominent in the polemic against Stahl, is the conceptual, if not actual, separability of the soul and the body. Thus Leibniz writes that “the soul, considered in itself, tends through final causes towards the goal that the corporeal machine, considered in itself, attains through efficient causes.”105 Leibniz believes that as with everything else in nature the states of a living body result directly from “internal movements and from the structure of the machine,” but that “since the internal parts are unknown to us, it may be easier to understand [the effects] from the final causes than from the efficient ones.”106 Everything in nature is governed by both final and efficient causes. For the science of animal economy, explanation in terms of efficient causes is more appropriate, yet because this science is at present underdeveloped, Leibniz thinks, physiologists must sometimes rest content with final causes. This view appears to contrast with Leibniz’s opening claim in the Corpus hominis that machines are always best understood through their final causes, though it is likely that the contrast is only apparent: throughout his physiological thought, Leibniz believes that both sorts of cause are of equal interest. Depending on the problem at hand, one may be of more interest than another. Where the most general description of an animal as a whole is what is at issue, final causes will tend to be of more interest; where the diagnosis of a particular, local illness is what is sought, correspondingly local, efficient causes will be more relevant.
In the encounter with Stahl, we see for the first time Leibniz’s explicit effort to distinguish between the animal-economical study of the body-machine on the one hand and the study of the organic body on the other. Yet we have not considered, except in passing, Leibniz’s theoretical understanding of the nature and structure of organic body. This will be the subject of the following chapter.
Let us first, however, seek to summarize the main points of both the method and content of Leibnizian animal economy. This discipline is, for Leibniz, the study of the animal qua machine. The animal is, in particular, a hydraulico-pneumatic machine, as earlier mechanists had recognized, as well as being a pyrotechnical machine, to the extent that its first motion is generated out of the production of heat in the excoction of chyle from the aliment it takes in. Because it is able to take in its own aliment, rather than being fueled by an external agent, it is also a sort of perpetual-motion machine. The fact that it can eventually pass on its likeness to another machine before ceasing to exist contributes to this perpetuity, even if Leibniz acknowledges that other theorists had understood the notion of perpetual-motion machine in a rather more narrow sense. Animal economy incorporates findings from a domain-specific science of animal chemistry—such as those concerning the excoction of chyle, or the fermentation that gives rise to vital heat—but it is distinct from chemistry to the extent that this discipline takes the animal as a mass, while animal economy is intent to understand it as a structure. Animal economy is, so to speak, doubly economical, both in that the designer of natural machines brings about the maximum of effects with the minimum of organs, and with individual organs fulfilling multiple functions, and in the sense that it eschews in principle any appeal to the inherence of a soul in the animal for the explanation of vital phenomena. The Leibnizian animal is, unlike that of Descartes, an ensouled entity, but the soul is responsible only for perception and appetition, functions that are beyond the scope of the study of animal economy.
We have begun to see why the artificial horses, speaking trumpets, and instruments that play themselves so fascinated Leibniz in the 1675 text with which we began this chapter. In blending the categories of the natural and the artificial, these creations would push the limits of our hard and fast distinction between these basic ontological categories. In important respects, Leibniz believed throughout his life that many elements of the traditional ontological distinction between these categories would need to be discarded: his animal economy, after all, amounts to a lifelong project of showing that the animal body is a special kind of machine. While we have traced Leibniz’s animal economy back to the 1670s, it is not until somewhat later that one of the most important special features of the machine of the animal body would take shape in Leibniz’s mature philosophy, namely, his notion of the organism of the body. This is a crucial theoretical development of Leibniz’s later philosophy, one that would only begin to be developed in the 1690s and that would only be explicitly described and given a name in the first decade of the eighteenth century. It is also a concept whose emergence in Leibniz’s thought marks the most significant moment in the general transition over the course of several decades, beginning already in the 1670s, from animal economy to subtle anatomy, or, to put it differently, from the macrostructure and overall functioning of hydraulico-pneumatico-pyrotechnical machines to the microstructure and organization of divine machines. It is to the notion of organism, and the related notion of organic body, that we will turn in the following two chapters.