Anatomy and Physiology

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ANATOMY AND PHYSIOLOGY

ANATOMY AND PHYSIOLOGY. The spread of dissection at the end of the thirteenth century—in itself quite unusual and remarkable given religious and anthropological prohibitions—is closely linked to the growing demand for surgical intervention, the increase of postmortem inspections for legal purposes, the epistemological need to provide medical practice with a rational basis founded on ocular demonstrations, and the related use of public anatomies as a means of self-advertisement and of gaining institutional legitimacy against the claims of unlicensed practitioners. Mondino de' Liuzzi's Anatomy, written in 1316, indicates that anatomically based inquiries had become part of university medical education. By the fifteenth century, annual anatomies were established as a part of the academic curriculum in the more important universities of Europe. The fifteenth and sixteenth centuries witnessed a shift in the function of dissection from a predominantly educational device providing visual validation for textual knowledge to an independent method of investigation and a source of anatomical and physiological information. It should be noted that the practice of human dissection was more the business of the physician than of the surgeon. As a consequence of long-established institutional constraints, surgeons were not allowed to practice internal medicine (and therefore to anatomize the so-called three cavities: abdomen, thorax, and head) and their anatomical skill was largely confined to the limbs.

THE DECLINE OF GALENISM

In the Middle Ages, the diffusion of anatomical and physiological knowledge was initially conveyed by the interpretation of authoritative texts rather than by the practice of dissection. Such works as Avicenna's Canon, Rhazes's Almansor, and Averroes's Colliget contained introductory sections on systematic anatomical description. The revival of Galenic texts, first in Bologna, Montpellier, and Paris in the fourteenth century, and then in the rest of the major European universities, contributed to the renewed interest in human dissection. The development of medical humanism (that is, the recovery of the ancients' medical legacy through a critical and philological restoration of their literary achievements) was a key factor in reviving anatomical inquiry. As also in the case of law, greater care for and attention to the ancient legacy generated over time a more critical attitude toward it and so ironically the reconstruction of the Galenic corpus, by bringing to light a series of discrepancies between authoritative text and dissected body, precipitated the decline of Galenism.

It is important to remember that Galen's medical system maintained a certain vitality (and some explanatory flexibility) until the end of the seventeenth century. Eclecticism and syncretism were a more frequent response among early modern practitioners than one might expect, above all because the therapeutic side of medicine continued to be conducted along traditional lines. The decline of Galenic anatomo-physiology among medical humanists and by anatomical investigators such as Andreas Vesalius (1514–1564), Michael Servetus (1511–1553), Realdo Colombo (1516?–1559), and Girolamo Fabrizi d'Aquapendente (c. 1533–1619) was an incremental process and involved the interpretation of specific discoveries.

A crucial watershed in the development of the new anatomy and physiology was William Harvey's (1578–1657) discovery of the circulation of the blood. In most physiological accounts prior to Harvey's discovery, the functions of pulse, respiration, and nutrition were interwoven into a coherent and self-contained system in which the venous apparatus and the liver constituted a sanguineous and nutritive system and the arterial apparatus and the heart a pneumatic system with the main function of maintaining the body's innate heat and of distributing its effects throughout the body by means of respiration and ventilation. The redefinition of vital functions resulting from Harvey's theory of circulation severed the long-accepted links between the movement of the blood, the nutrition of the parts, and the production of the innate heat. Further anatomical discoveries, such as Gasparo Aselli's lacteals (1622), Jean Pecquet's thoracic duct (1651), and Thomas Bartholin's lymphatics (1653), complemented Harvey's work on the heart and the circulatory system by delineating a separate vascular system in which the chyle was delivered not to the liver but directly to the vena cava and then to the heart. This anatomical research dispossessed several organs (principally the liver and the lungs) of their traditional functions. The discovery of the circulation of the blood, therefore, was only the first of a series of discoveries of various, related "circulations" and their description: the circulation of the nutritive fluid, the circulation of the lymph, and the circulation of the "nervous juice."

With respect to the relationship between anatomy and surgical practice, the status of surgery underwent a dramatic change during the eighteenth century. Surgeons pioneered new techniques and rose in professional standing. In keeping with the Enlightenment emphasis on the benefits of practical knowledge, surgery became a separate science, with a particular emphasis on experimentation. The development of surgery, especially in France, consolidated the association between anatomo-pathology (the view that diseases are anatomically localized), bedside teaching, and the modern hospital. The reunification of surgery with medicine was also facilitated by the fact that during the eighteenth century, for a number of social and institutional reasons, anatomical studies could rely on a more abundant supply of corpses (bodies of criminals, lunatics, and paupers).

PHILOSOPHICAL ALTERNATIVES

With the collapse of Aristotelian natural philosophy within the domain of the physical sciences, the philosophical synthesis of Aristotelianism, Hippocratism, and Galenism, which had represented the theoretical framework of the medical sciences for centuries, also began to lose its hegemonic status and was confronted with an array of new philosophical perspectives. Various lines of anatomical and physiological inquiry spread throughout the seventeenth century, founded on different strands of mechanical philosophy, varieties of corpuscularianism, and forms of chemical naturalism. Systems of medical explanation arose with the ambition of accounting for every manifestation of life, from the absorption of food to the circulation of the blood, from the processes of secretion and excretion to muscular activity, and from respiration to sensation. The two prevailing approaches came to be known as iatrochemistry and iatrophysics (being the application, respectively, of chemistry and mechanics to the study of the body). Of course, iatrochemistry and iatrophysics were not entirely discrete systems and it would be difficult to find a purely iatrochemical or iatrophysical account of the body in the seventeenth and eighteenth centuries. Authors as different as Giovanni Alfonso Borelli (1608–1679), René Descartes (1596–1650), and Thomas Willis (1621–1675) made use of chemical explanations to account for the production of the vital energy underlying physiological processes. An example of theoretical versatility was Franciscus de la Boë (called Sylvus; 1614–1672), a determined supporter of Harvey's doctrine who emphasized the importance of the chemical processes of fermentation and effervescence and managed to graft a chemical and circulatory physiology onto an originally Galenic framework.

Respiration was another physiological domain in which the chemical approach proved to be particularly fruitful. The long series of experiments conducted by Robert Boyle (1627–1691), John Mayow (c. 1641–1679), Joseph Black (1728–1799), and Joseph Priestley (1733–1804) led eventually to the final identification of the "vital air" as oxygen by Antoine-Laurent Lavoisier (1743–1794), who also demonstrated that some of the vital air was taken into the blood and had a decisive role in combustion and the maintenance of animal life. Although Georg Ernst Stahl (1660–1734), professor of medicine at the University of Halle, was no anatomist and rejected the findings of microscopic anatomy, he was concerned with the chemical composition of the body, and his chemical views had a certain influence on contemporary physiologists, especially those teaching at Montepellier. He distinguished the immaterial principle of life (the soul) from the body. However, despite obvious similarities to Descartes's dualism, Stahl's identification of the soul with the purposeful activity of nature was characteristic of the medical tradition rather than the Cartesian idea of the mind as a principle of consciousness. Stahl maintained that an organism was a living unit fundamentally different from a mere mechanism and that its material components were instrumental parts controlled by the immaterial soul.

Inspired by the new philosophies of nature advocated by Descartes, Galileo Galilei (1564–1642), Boyle, and Pierre Gassendi (1592–1655), and in contrast with the iatrochemical emphasis on the vital nature of the inner workings of the body, iatrophysical physiologists held the view that medicine, both in theory and in practice, was based upon purely mechanical principles, namely, matter and motion, particles (whether indivisible atoms or indefinitely divisible corpuscles), action by contact, and movement through pores. The demise of the old belief that anatomical structures and physiological functions were regulated by purposeful tendencies caused a radical change in the explanatory framework of physiology: secretion and excretion were accounted for without resorting to attractive faculties; the function of the lungs became the mixing of the component parts of the blood; digestion was interpreted as a process of grinding and mincing food; and health and disease were considered to depend on the movement, obstruction, or stagnation of the various fluids running throughout the body. With Isaac Newton's (1642–1727) theory of gravitation and Boyle's experiments on air, attention shifted from gross to fine structures, from the paradigm of the clockwork mechanism formulated in rudimentary mechanical terms to a more sophisticated model of hydraulic and pneumatic engineering that came to be understood as an integrated network of vessels regulated by quantitative laws. In addition, with the publication of Newton's Opticks (1704), physiologists were encouraged to use the notions of ether and extremely subtle spirituous effluvia in their accounts of physiological operations.

Iatrophysical anatomy was greatly assisted by developments in microscopic observation. Robert Hooke (1635–1703), in his influential Micrographia (1665), argued that with the use of the microscope, many so-called "occult properties" might be interpreted as elementary contrivances of nature. Following Galileo's suggestion in Il saggiatore (1623; The assayer) that living beings could be seen as assemblages of small machines, Marcello Malpighi (1628–1694) applied the microscope in his anatomical investigations to observe the smallest sections of animal and plant organs. Antoni van Leeuwenhoeck's (1632–1723) expertise in the use of the microscope further confirmed the particulate structure of matter.

The most influential synthesis of iatrophysics was Hermann Boerhaave's (1668–1738) system of medicine. Teaching at the University of Leiden, he explained the physiological operations of the body in mechanical terms. He dismissed the question of the connection between the body and the mind as irrelevant from a physiological point of view. His characterization of the relationship between the body and the soul was reminiscent of Spinoza's philosophy, in which the substantial attributes—thought and matter—were conceived of as two parallel manifestations of one substance; consequently Boerhaave argued that everything that involves extension, impenetrability, or motion had to be referred to the body.

THE EMERGENCE OF MODERN PHYSIOLOGY

Pre-modern physiology was based on a set of fundamental concepts established during centuries of interpretations, translations, and appropriations of Aristotelian and Galenic notions, such as complexion (the specific balance of the primary qualities characterizing each individual), humors (the bodily fluids governing specific functions), faculties (the inherent powers of the different parts of the body), and spirits (the vehicles of natural, vital, and animal operations).

Whereas throughout the Middle Ages anatomy was subordinate to a form of highly theoretical physiology, in the early modern period the relationship was reversed: anatomy became the experimental and observational point of reference on which physiological theorizing was based. This resulted in a steadily growing interest in the investigation of the material basis of life, independently of whether this basis could be explained in mechanical or vital terms. The most remarkable difference from past approaches was that the distinction between living and non-living bodies was viewed less as a result of the activity of the soul than as a function of the internal organization of matter. The so-called vitalist reaction in the eighteenth century was not so much a return to the notion of the soul (although Stahlian "animism" had a certain influence on medical theories at the time) as an affirmation of the specific vital nature of matter. The mechanical approach to the investigation of vital phenomena in the seventeenth century, especially in its Cartesian version, had effaced the concept of life itself by claiming that the manifestations of life were merely the result of various dispositions of inert matter. Eighteenth-century vitalism, therefore, can be seen as the expression of a latent materialism rather than as a form of animism.

Eighteenth-century anatomical investigations into the finer structures of the body placed particular emphasis on study of the nervous system. This, in turn, brought a greater awareness of the interdependence of living organisms and their environment, highlighting the ability of living structures to respond purposefully to their external milieu. It is no accident, then, that the study of the various forms of irritability became a central topic in the eighteenth century. In the second half of the seventeenth century, drawing on Harvey's speculations about the living and sentient nature of the blood, Francis Glisson (1597–1677) elaborated a comprehensive theory of irritability based on the notion of matter as a living and sentient principle. By irritability, Glisson meant the specific properties of the bodily fibers in perceiving and reacting to irritation.

The Swiss physiologist Albrecht von Haller (1708–1777), who taught at the University of Göttingen, adopted Glisson's theory of irritability but attributed the ability to react to external stimuli only to the fibers of the body and not to an allegedly perceptive power inherent in matter. In Elementa Physiologiae Corporis Humani (1757–1766; Elements of the physiology of the human body), he characterized the organs of the body as interwoven fibers. Muscles, as any other fibrous part, were deemed to be endowed with a general contractile tendency that he called vis mortua (dead power). Active muscular contraction depended on an immanent power that he called irritability. In the famous essay "De Partibus Corporis Humani Sensibilibus et Irritabilibus" (1752), translated into English in 1755 as "On the sensible and irritable parts of animals," he distinguished between irritability (muscular contraction) and sensibility (nerve impulse). He called a part irritable when it contracted upon being touched, sensible when the contact produced an impression in the mind. A great number of physiologists and naturalists working on the irritable properties of living bodies were inspired by Haller's research. William Cullen (1710–1790), professor of medicine at Edinburgh University, defined life as a function of the nervous power and insisted on the importance of the tonic contraction of the muscles. John Brown (1735–1788) maintained, more speculatively, that life was not a spontaneous state but one maintained by continuous stimulation or "excitement"; health was supposed to consist in maintaining the right proportion between them. While never popular in England or France, Brown's system (Brunonianism) was enthusiastically taken up in Italy, Germany, and the United States, where Benjamin Rush (1745–1813) became one of the most vocal supporters of Brown's ideas. Working on gland secretions, Théophile de Bordeu (1722–1776), professor at Montpellier, argued that each organ was naturally endowed with an inherent capacity to respond to external stimuli. A whole series of experiments on generation and regeneration (that is, the capability manifested by plants and some lower animals to grow again after some parts had been severed) performed by René-Antoine Réaumur (1683–1757), Abraham Trembley (1710–1784), Charles Bonnet (1720–1793), and Lazzaro Spallanzani (1729–1799), among others, provided further evidence for the existence of active vital powers in matter.

At the end of the century, the dominant discourse in physiology was vitalistic. Johann Friedrich Blumenbach's (1752–1840) idea of a "life-force" driving toward regeneration, John Hunter's (1728–1793) belief in a "life-principle" distinguishing living organisms from inanimate matter, and Erasmus Darwin's (1731–1802) notion of an intrinsic motility embedded in the fibers of living beings are only some of the many eighteenth-century conceptions of an original power of life not reducible to the mechanical powers of matter.

See also Boerhaave, Herman ; Boyle, Robert ; Cullen, William ; Descartes, René ; Galileo Galilei ; Gassendi, Pierre ; Haller, Albrecht von ; Harvey, William ; Hooke, Robert ; Leeuwenhoek, Antoni van ; Malpighi, Marcello ; Matter, Theories of ; Medicine ; Priestley, Joseph ; Scientific Method ; Vesalius, Andreas.