Iatrophysics

Iatrophysics or iatromechanics (fr. Greek) is the medical application of physics. It provides an explanation for medical practices with mechanical principles. It was a school of medicine in the seventeenth century which attempted to explain physiological phenomena in mechanical terms. Believers of iatromechanics thought that physiological phenomena of the human body followed the laws of physics. It was related to iatrochemistry in studying the human body in a systematic manner based on observations from the natural world though it had more emphasis on mathematical models rather than chemical processes.

Background

The Age of Enlightenment was an era of radically changing ways of thought in Western politics, philosophy, and science. Major sociological changes occurred in the Enlightenment, as well as industrial and scientific. In medicine, the Enlightenment brought several discoveries and studies that were impacted by changing ways of thought. For example, capillaries were discovered by Marcello Malpighi. Jan Baptist van Helmont (1580–1644) was the first to consider digestion a fermentation process and identified hydrochloric acid in the stomach. Pathological anatomy and clinical observation were also being integrated into the medical curriculum. The Enlightenment also directly influenced the field of iatrophysics through the development of Antonie von Leeuwenhoek's microscope, the advancement of the field of ophthalmology through the use of physics by René Descartes, and Newton's law of universal gravitation, idea of gravitational force, and his treatise ''Opticks''.

Subfields

Iatrophysicists drew inspiration from various established physical phenomena in order to explain how certain biological processes took place and how this can be applied towards medicine.

Particles

A key component of iatrophysical anatomy was the study of particles. This was particularly influenced by 17th century developments in microbiology, the most prominent being the microscope. Antonie von Leeuwenhoeck was a Dutch scientist who is known for his use of the microscope for identifying single-celled organisms. He was also the first to observe muscle fibers, bacteria, spermatozoa and blood flow in capillaries. Another famous figure in microbiology at the time was Robert Hooke, an English scientist most famous for his use of the microscope for the discovery of cells. In his most famous work, ''Micrographia'' (1665)'','' he attributed “occult properties” as elementary “contrivances of nature”. Like Galileo Galilei, he shared an iatrophysical viewpoint and saw living organisms as groups of small machines. The development of the microscope was largely influential in this view.

Mechanics

Machines were used as models by Iatrophysicists to quantitatively describe linear and rotational motion of various biological systems such as human limbs and animals. Some models came into existence before Isaac Newton's formulation of his three laws in classical mechanics, drawing on basic principles of statics and dynamics to represent how a biological system behaved. Giovanni Borelli was prolific in applying mechanics to a wide variety of humans and animals in different degrees of activity, drawing upon an array of simple machines and models for translational and rotational motion and equilibrium.

Fluids

Iatrophysicists were also interested in studying how bodily liquids and gases were processed. They sought to understand how blood circulated throughout the body and what effects it made on the body. System consisted of arteries, veins, and vasculature verified through experiment and microscope by Marcello Malpighi's observations of capillaries in animal lung tissue. Albrecht von Haller, as did Borelli, postulated that friction from the blood on vessel walls lead to body heat and even fever. A hydraulic model for motion by René Descartes implied the body had a system that maintained flow between the brain and muscles in equilibrium state through nerves and blood vessels.

Iatrophysicists

Starting in the 17th century, quantitative fields such as physics and mathematics began gaining legitimacy as a means of studying the natural world with the advent of theory, practices, and instruments. Static principles and simple machines were already in use to create various objects and buildings and thus were established tools that could be used to inspire models of biological systems. The development of medical instruments and techniques, such as the microscope and detailed dissections, changed how natural philosophers thought about how to explain the human body's properties. By enabling more detailed study of aspects of biology, let alone the human body, instrumentation and methods to directly study organic tissue allowed more opportunities for natural philosophers, Iatrophysicists in this case, to postulate and verify their theories. With inspiration from established explanations of natural phenomena and new informative means to study the human body available, iatrophysicists aimed to describe the human body and assert their explanation of various systems of the human body.

One example is the muscle and contraction. Various explanations on a macroscopic and microscopic scale were made to explain how muscles contracted and thus performed movements together. On a macroscopic scale through observation and anatomy, some iatrophysicists such as Borelli focused on explaining how muscles worked in conjunction together to form movements with dynamics or physical models. On a microscopic scale via observation and dissection, the contractility of muscle was to be explained by pneumatic expansion, a popular explanation supported by Descartes and Borelli, or inherent shape deformation, postulated by Nicolas Steno to an extent, based upon principles of fluids and statics. Other aspects of the human body such as circulation and digestion saw a number of explanations, and thus conflicting views based on the methodology used to derive and obtain an explanation, arise in the 17th and 18th centuries.

Prominent Iatrophysicists

One prominent iatrophysicist was Giovanni Borelli, who modeled the human body, various animals, and their motions using mechanical principles. A colleague of Marcello Malphigi, Borelli was a mathematician who made connections between what he observed in living things and inanimate but relatively simple systems. He dissected animals and examined how muscles were to increase mechanical advantage, observed how a variety of living things performed different movements and activities such as running, carrying loads, swimming, and flying naturally rather than by his intervention, and devised simple methods to calculate a person's center of mass. He also devised relatively simple experiments and devices to make his observations such as a plank and rod for center of mass and a spirometer for volume of air. At the end of his life, his work culminated in ''De Motu Animalium'' (1679), a publication showcasing his investigations in similarities and differences in muscles across living things and his understanding of the underlying mechanism of muscle contraction, expansion via influx of fluids or gases released from nerves. He also attempted to describe more complicated processes such as nerve transmission and digestion.

Another notable iatrophysicist was the French philosopher and mathematician René Descartes, who, as a consequence of his philosophy asserting that the human body and soul are two dual entities, treated the human body as a machine that could be quantified, disassembled, and studied. He attempted to model various phenomena such as the brain, movement, sleep, circulation, and senses with analogies to inanimate objects such as reservoirs, pipes, lenses and steam engines that often sought to maintain an equilibrium for certain states. Some of his claims often were independent of physical observation of the organ or body in question and emphasized what he deemed as "simple" or "rational" rather than reality. For example, he asserts that blood circulates throughout the body by expanding as vapor by the heart's heat rather than from contraction.

William Harvey postulated blood flow as a closed, continuous loop that run throughout body that contained a certain quantity of blood. To test his claim, Harvey dissected human corpses and animals and, based on his anatomical findings, devised a simple demonstration of how arteries and veins continuously carried blood throughout the body. Taking advantage of the fact that arteries and veins were at different depths below the skin, he tied a person's arm and had them squeeze a bar to shunt blood from arteries to veins, indicating that blood somehow traveled along arteries and into veins. His claim was elucidated by Malphigi's discovery of capillaries and how they were interconnected with arteries and veins.

One of the most influential iatrophysicists was Hermann Boerhaave, a Dutch physician and chemist at the Leiden University. Like other iatrophysicists, he viewed physiology as a mechanism. While he disagreed with the idea that the body and the mind were connected, he attributed everything related to the body to extension, impenetrability, or motion.

Francis Glisson was known for his work on circulation of the blood, the mechanisms of the nervous system, and hereditary diseases. He was largely influenced by Harvey's work on the sentient nature of blood and his work demonstrates iatrophysical ideology particularly through his views of attraction and irritability, or the concept of how the body fibers react to irritation. In his work, ''Anatomia hepatis,'' he argues that branches cross, and carried blood is separated in the liver. This in turn is sucked up by biliary vessels through an attraction that Glisson attributes as similar, magnetic, or natural.

Albrecht von Haller was another prominent iatrophysicist, who like Glisson, focused on physiology as mechanisms of body fibers. He shared Glisson's views on irritability, but unlike Glisson, attributed the reaction to external stimuli solely to body fibers, and not in the inherent power of matter as Glisson had suggested. In his work ''Physiologiae Corporis Humani'' (1757–1766), he described organs and muscles of the body as interwoven fibers. His viewpoints on muscles were that they had a contractile tendency which he termed ''vis mortua,'' or dead power. He attributed this muscle contraction to irritability, which he described as being an inherent power. He particularly made the distinction between irritability and sensibility, irritability being the power of muscular contraction and sensibility being nerve impulse. Therefore, a part was irritable if it contracted upon contact, and sensible if the contact impacted the mind.

Other Iatrophysicists

Santorio Santorio was a Venetian doctor who, in attempt to quantify human digestion, carefully measured his food/water intake and excretion weight over many years. To establish a mathematical relationship between food/water intake and excretion, Santorius designed a special chair that had a balance that weighed a subject's meal and consequent excrement. Based on these measurements, he then calculated the net change in weight for each day. In addition to knowing what he took in, he also analyzed the contents of his excretions and secretions, categorizing it by type and origin. He also made other clinical instruments to measure other medical quantities such as temperature and pulse.

Nicolas Steno

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