Iatromechanism

Iatromechanism was the programme, dominant from roughly 1660 to 1740, that sought to explain the living body entirely through the principles of mechanics: mass, shape, and the motion of particles, calculated where possible by mathematics. Its practitioners treated the body as a system of levers, pulleys, pipes, and vessels whose fluids obeyed the laws of hydraulics. (Porter, 2000) The label itself was not contemporary with the movement. Historians such as Albrecht von Haller used the word “iatromechanicus” only retrospectively in bibliographic notes, and Kurt Sprengel formalized the category as a distinct school only in 1799. (King, 1978)

The Organism as Machine

The organism-machine analogy predates Descartes by two millennia. Aristotle compared animal limb-movements to the mechanisms of war machines such as catapults, and he described animal motion as the release of stored-up energy in automatic devices. (Canguilhem, Georges, 1952/2008) What Descartes contributed was not the analogy but its totalizing ambition: his Traite de l’homme proposed to explain the entire living body as a machine built by God. Coulter argued that Descartes founded the Rationalist counterattack on medical Empiricism by holding that sense-perception is unreliable and that medical practice must rest on a comprehensive theory of physical causes deduced through mathematical reasoning, using “experiment” not to test principles but to exemplify them. (Coulter, 1975) As Canguilhem showed, this theory depended on two postulates usually neglected: a builder God as efficient cause, and the living as given prior to the machine, so that the animal-machine was always a rational reconstruction that assumed what it claimed to explain. (Canguilhem, Georges, 1952/2008)

The mechanist explanation was historically conditioned by the existence of automatons, machines that transform stored energy without requiring human muscular effort at the moment of action. (Canguilhem, Georges, 1952/2008) Mechanism could not, however, eliminate finalism: the construction of a machine cannot be understood without purpose and without man, and so one form of anthropomorphism (technological) merely substituted for another (political). (Canguilhem, Georges, 1952/2008)

Borelli and the Blurred Boundary

The conventional division between iatrochemistry and iatromechanism was never doctrinally sharp. Giovanni Alfonso Borelli’s De Motu Animalium (1680), the work most often cited as the founding text of iatromechanism, accepted the concept of fermentation and used chemical analogies extensively while professing a mathematical-mechanical framework. (King, 1978) Borelli explained muscular contraction through a “fermentation and ebullition” arising from the mixture of nerve juice with blood, invoking what he called a modus mechanicus that incorporated chemical processes within an avowedly mechanical system. (King, 1978)

The concept of “intestine motion” (the internal motion of particles in the blood) was a crucial fault line between iatromechanists themselves. Thomas Willis endorsed it as fundamental, Archibald Pitcairn fanatically rejected it, and Friedrich Hoffmann adopted it. King argued that this single concept renders untenable any rigid separation of iatromechanists from iatrochemists. (King, 1978)

The Rise of Mechanism over Chemistry

The shift from iatrochemistry to iatromechanism was driven partly by a demand for quantitative precision. At the turn of the eighteenth century, chemistry lacked the tools to compete in precision with mechanicians, especially when applied to physiological processes. (King, 1978) Those physicians who sought after maximum generality found much more appeal in physics than in chemistry, which worked at what King called a more “proximal” level of explanation with more limited generality. (King, 1978) Franciscus Sylvius applied chemical concepts — fermentation, acid-alkali opposition, salts — to physiology and pathology as a practicing clinician, but without the broader metaphysical ambition of van Helmont, confining chemistry strictly to medical explanation. (King, 1978) Robert Boyle did more than anyone to resolve the friction between chemists and corpuscular philosophers: he showed that the experimental data of the chemists confirmed the corpuscular philosophy while the corpuscularian framework explained chemical data better than chemical theory itself. (King, 1978)

The socioeconomic dimensions of the competition between chemical and mechanical physicians were as significant as the theoretical. Chemical physicians had challenged the Galenist establishment on three fronts simultaneously: therapeutic practice, social recognition with its economic benefits, and scientific validity. (King, 1978) The mechanists inherited and reframed this challenge, substituting mathematical respectability for the chemical physician’s claim to superior remedies.

Key Figures and Positions

Archibald Pitcairn represented the extreme reductionist position within iatromechanism. He denied fermentation entirely from the living body, arguing that all bodily functions were mechanical and that a living body was composed of canals of various kinds (the containing parts) and different sorts of fluids (the contained parts) functioning by mechanical principles alone. (King, 1978) His 1692 inaugural address at Leiden advocated attending only to the observable properties (vires) of medications and disease rather than hunting for hidden physical causes, but he failed to follow his own methodological principles in practice. (King, 1978)

Friedrich Hoffmann’s Fundamenta Medicinae (1695) represented a more moderate position. He adopted Cartesian matter theory (three grades of matter including subtle matter) rather than Newtonian physics, and gave a moderate role to fermentation as the “internal motion of particles” while rejecting vinous fermentation in the blood. (King, 1978) Hoffmann preserved Galenic temperament doctrine by reinterpreting it in corpuscular-mechanical terms, writing, as Temkin noted, “the habits of the mind follow the temperament of the body” in a mechanical vocabulary that kept the classification of patients by temperament useful into the nineteenth century. (Temkin, 1973)

Herman Boerhaave synthesized anatomy, physiology, iatromechanics, and chemistry under one roof at Leiden, defining mechanists in his 1703 oration as those who explain bodily operations from mass, configuration, and velocity through mathematical calculation. (King, 1978) He attributed a major role to ferments as the primary source of the “internal agitation” that maintained vital fluid motion, while wisely declining to impose a rigid system. (Henry E. Sigerist, 1933) Boerhaave’s eclecticism made Leiden the medical capital of Europe, but it also revealed the difficulty of maintaining the mechanist programme in its pure form.

The Mechanization of Qualities

Sanctorius’s use of the thermometer to measure Galenic qualities of hot and cold inadvertently destroyed them by substituting quantitative degree for objective quality. Temkin described this as a case of what Hegel called “die List des Begriffes,” the cunning of the concept, whereby an apparently helpful device effected the downfall of the subject it was meant to assist. (Temkin, 1973) The conversion of Aristotelian primary qualities into secondary, subjective sensations was as destructive to Galenic science as the elimination of the four elements as chemical constituents. (Temkin, 1973)

Yet Galenic practice (bleeding, purging, dietetics, and the prescription of galenicals) outlasted the fall of Galenic science, because practitioners had no reason to abandon treatments that had apparently worked for centuries. (Temkin, 1973) Iatromechanism thus failed to replace galenic-medicine as a unified medical philosophy: seventeenth-century physics and chemistry were too crude to support clinical medicine, and the elimination of all teleology hindered rather than aided the physician’s understanding of the organism. (Temkin, 1973)

Organism and Machine

The deepest philosophical difficulty with the iatromechanist programme was identified by Canguilhem. Organisms display self-construction, self-conservation, self-regulation, and self-repair, properties that machines entirely lack, since machine construction, conservation, and repair all require external human intervention. (Canguilhem, Georges, 1952/2008) Organisms have more latent purpose (polyvalence of organs, vicariousness of functions) and fewer rigid purposes than machines, reversing the common assumption that organisms are more purposive. (Canguilhem, Georges, 1952/2008) This meant that iatromechanism, at its most ambitious, was not merely a useful simplification but a category error: it modeled the organism on a derivative of the organism (the machine) and then claimed the derivative was the reality.

Failure and Legacy

Ackerknecht’s judgment was blunt: both iatrophysics and iatrochemistry were “bound to be failures” as clinical programmes, but their history demonstrates the danger of premature application of basic scientific data to clinical medicine and makes clear the quantity of basic knowledge required before such application becomes fruitful. (Ackerknecht, 1955)

The seventeenth-century Rationalist physicians (Descartes, Sylvius, Willis, Cheyne, Hoffmann, Boerhaave) had refurbished discredited Galenic categories by filling them with knowledge from chemistry, mechanics, and mathematics, reversing the Empirical priority of practice over theory. (Coulter, 1975) Sydenham and Baglivi initiated the Empirical response to this programme by invoking Bacon’s critique of metaphysics and calling for a return to Hippocratic observation and experience at the bedside. (Coulter, 1975) Georg Ernst Stahl, the leading chemist of his generation, rejected the application of both chemistry and mechanics to therapeutics entirely, arguing that the extraordinary effects of emotions on the body proved the existence of a vital principle irreducible to material causes. (Coulter, 1975)

By the mid-eighteenth century, strict mechanism was judged inadequate for living phenomena. John Hunter’s vitalism argued that organized matter possesses an inherent vital force distinguishing it from the inorganic. (Porter, 2000) By 1870, Galenism as a living tradition was over and Galen was “handed over to classicists, Arabists, and historians,” but mechanism in its strict seventeenth-century form had died earlier still. (Temkin, 1973) What survived was the aspiration to explain living bodies in the language of physics, an aspiration that would return in different form with nineteenth-century experimental physiology and twentieth-century molecular biology.

Scholarly Assessment

King’s central thesis is that the dichotomy between iatrochemistry and iatromechanism was historically constructed and conceptually misleading. The fundamental opposition was not between chemists and mechanists but between the old Aristotelian-Galenic philosophy of forms and faculties and the new corpuscular-philosophy of particles in motion, which both chemists and mechanists shared. (King, 1978) Historians should think of the complex development of the corpuscular philosophy and its relation to preexisting doctrine, “and not be misled by the one-sidedness of Pitcairn’s teachings. Above all, we should avoid the tyranny of labels.” (King, 1978)

Canguilhem’s approach was different but complementary: rather than dissolving the chemical-mechanical distinction, he argued that both chemical and mechanical explanations of life were inadequate because both modeled the organism on something external to it (the chemical reaction, the machine) rather than grasping the organism on its own terms. The machine metaphor worked only because it already presupposed what it claimed to explain. (Canguilhem, Georges, 1952/2008)