The Origins of Medical Physics
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Invited paper
The origins of medical physics
Francis A. Duck
University of Bath, Bath, UK a r t i c l e i n f o a b s t r a c t
Article history:
The historical origins of medical physics are traced from the first use of weighing as a means of monitoring health by Sanctorius in the early seventeenth century to the emergence of radiology, phototherapy and electrotherapy at the end of the nineteenth century. The origins of biomechanics, due to Borelli, and of medical electricity following Musschenbroek’s report of the Leyden Jar, are included. Medical physics emerged as a separate academic discipline in France at the time of the Revolution, with Jean Hallé as its
first professor. Physiological physics flowered in Germany during the mid-nineteenth century, led by the work of Adolf Fick. The introduction of the term medical physics into English by Neil Arnott failed to accelerate its acceptance in Britain or the USA. Contributions from Newton, Euler, Bernoulli, Nollet,
Matteucci, Pelletan, Gavarret, d’Arsonval, Finsen, Röntgen and others are noted. There are many origins of medical physics, stemming from the many intersections between physics and medicine. Overall, the early nineteenth-century definition of medical physics still holds today: ‘Physics applied to the knowledge of the human body, to its preservation and to the cure of its illnesses’.
Received 12 February 2014
Received in revised form
13 March 2014
Accepted 14 March 2014
Available online 5 April 2014
Keywords:
History of medicine
Iatrophysics
History of physics
Medical electricity
Ó 2014 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
Introduction does not emit a beam as the Greek scholars had imagined. It would be another 600 years before Kepler added anything new to this
Historical origins are often difficult to determine. The discovery of X-rays by Wilhelm Conrad Röntgen in November 1895 offers an event, seductive in its clarity, for the origin of Medical Physics. But this marks only the start of ‘medical radiation physics’ [1]. This present short review gives in outline the key developments in medical physics up to the end of the 19th century. The later role of physics and physicists in the introduction of ionizing and nonionizing radiation into medicine is a subject for a separate historical review. understanding, by describing the creation of an inverted image on the retina by the crystalline lens.
My own geographical and temporal point zero for medical physics is much later, in the Italian Renaissance. Santorio Santorio
(1561e1636), also known as Sanctorius, was the first to take a measurement technique from physics and apply it successfully in medicine and physiology. The technique was weighing. He was appointed in 1611 as professor of theoretical medicine in Padua and soon published a slim volume, De statica medicina [3]. He had designed a whole-body scale, with which, for very many years, he had regularly weighed himself and everything that he ate, drank and excreted (Fig. 1). From this study he developed his theory of ‘insensible perspiration’ to account for the difference between material added and material excreted. Many later physiologists would learn the value of physiological measurement through similar weighing experiments [4,5]. His view of the body as a machine became a widely used metaphor in the succeeding decades.
The next important figure was the Italian physicist Giovanni
Borelli (1608e79), who was the first to make a serious attempt to place mechanistic ideas of the body on a firm mathematical footing.
The word that later became associated with these ideas is iatrophysics, ‘physics applied to medicine’, but only used in the narrow sense of a physiology that explained all the workings of the body in purely mechanistic terms.
Iatrophysics
Some links between physics and medicine may be found in the records from ancient civilizations [2]. A document from ancient
Egypt mentions the treatment of breast abscesses by cauterization, and Hippocrates described how skin temperature distributions could be mapped by using wet clay. Another Greek physician,
Herophilus, used a water clock to measure the pulse rate, applying the physics of time metrology to clinical assessment. The Arabic scholar Ibn al-Haytham (Alhazen) (965e1040), demonstrated by logic and experiment that the eye is simply a receiver of light, and E-mail address: f.duck@bath.ac.uk.
1120-1797/Ó 2014 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
F.A. Duck / Physica Medica 30 (2014) 397e402 observation and mathematical analysis. He set about applying the same principles to physiology. Borelli’s vocabulary describing the actions of living beings was exclusively mechanical: forces and moments, gravity and weight, contraction and expansion, volumes and velocities, swelling, binding and wrinkling, effervescence, mixing, and scraping. His analogies were mechanical too; pulleys and scales, goatskin bottles, sieves and balls of string. He gave an extensive analysis of the movements of muscles, and the forces they exert, when walking, lifting, flying and swimming. He included numerous detailed illustrations (Fig. 2). His was an entirely new quantitative approach to what later became known as biomechanics. Borelli also explored the causes of the internal motions of animals and correctly challenged several currently-held views. He described lung expiration as a passive process. He states that
‘respiration was not instituted to cool and ventilate the flame and heat of the heart’. He used the new alcohol thermometers of the Accademia del Cimento to show that the intra-cardiac temperature of a live stag was no different from the temperature within any other organ.
However, he struggled to describe how muscles actually work.
Borelli did his best with his mechanical models but, perhaps unsurprisingly, got it wrong. According to Borelli, muscle fibres swell and become harder and tighter, which causes a contraction between the ends of the muscle. This is caused by bubbles formed when nervous juice is shaken out into the muscle fibres. Later physicists also had views about this challenging problem. Isaac
Newton speculated that nervous action might be mediated by the aether. Bryan Robinson, a Dublin doctor and enthusiastic Newtonian, saw Newton’s aether acting in both nerves and muscles [4].
Figure 1. Sanctorius’ scale with which he measured his own weight, several times daily, for many years, demonstrating the existence of insensible perspiration. Frontispiece from John Quincy’s translation of Sanctorius’ Medicina Statica, first published in
1614 [3].
Borelli was born in Naples on 28 January 1608. He studied mathematics in Rome and spent time as professor of mathematics at the University of Messina. In 1656, Borelli was appointed as professor of mathematics at the University of Pisa. During his 12year stay there he made important contributions to mathematical astronomy, showing that the orbits of the moons of Jupiter were elliptical, and tracking the parabolic trajectory of a comet. Both
Newton and Huygens recognized the importance of Borelli’s anticipation of a gravitation force to explain these movements.
His reputation as an astronomer was established. Yet, at nearly
50 years old, he launched himself into a completely new area of study. He established his own anatomical laboratory, obtained human cadavers to dissect and brought in live animals and birds for vivisection. By the time Borelli left Pisa in 1668 he had accumulated all the experimental material that he required for his book on mathematics and physics as applied to physiology. His final years were spent in Rome where his De Motu Animalium [6] was published shortly after he died in 1679.
Figure 2. Mechanics of the spine. ‘If the spine of a stevedore is bent and supports a load of 120 pounds carried on the neck, the force exerted by Nature in the intervertebral disks and in the extensor muscles of the spine is equal to 25,585 pounds. The force exerted by the muscles alone is not less than 6404 pounds’. Borelli’s De Motu
Animalium Vol 1, 1680 [6]. Wellcome Library, London.
Borelli approached his subject as a mathematical physicist, not a physician. He knew that physics had converted star-gazing into astronomy, using a combination of improved experimental
399
Newton also proposed that sight resulted from vibrations in the aether in the optic nerve, caused when a stream of high velocity light particles strikes the retina. At a time before electricity was understood, this was the only means available to Newton by which he could express concepts of nervous activity.
The next major contributions came from two outstanding eighteenth century mathematicians, who were also close friends,
Daniel Bernoulli (1700e1782) and Leonhard Euler (1707e1783).
Bernoulli studied medicine and then, like his father, became an academic mathematician. In 1753 he made perhaps his most significant contribution to physiology, with his pupil Daniel Passavent, by estimating the work done by the heart, calculating that ‘the daily work done by the heart is equivalent to that required to raise a weight of 144,000 pounds to a height of one foot’ (about 24,000 m kg) [7]. Bernoulli thus anticipated by many decades the emergence of the concept of energy.
In 1775 Euler published an essay in which he set out the onedimensional equations for the conservation of mass and momentum in a distensible tube. Here we find the first serious application of differential calculus to a problem in physiology. In
Euler’s original formulation,
Figure 3. Pre- and post-Revolution headings from medical physics sections of L’Histoire de la société royale de médecine. Vol. 1, 1779 (top) and Vol.10 1798 (bottom) when the word ‘royale’ was omitted.
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Jallabert (1712e1768), professor of mathematics and of philosophy in Geneva, was among several who reported successful treatment of paralysis using electric shocks [12]. Many, however, including
Nollet, found the clinical response to be highly variable. By the time
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¼ 0 dz dz dt where s is the cross-sectional area, v the average velocity, p the pressure, g the reciprocal of the density of blood, t is the time and z the axial distance. This was a step-change in the application of mathematical physics to the inner workings of the body. Leibniz and Newton had provided new tools with which to study bodies in motion, and here we can see the first moves towards their use for physiology [8].
The origin of medical physics
The first use of the term Medical Physics (or to put it more accurately, Physique médicale) was in Paris in 1778. The term was introduced by the general secretary of the Société royale de médecine, Félix Vicq d’Azir (1748e1794) [9]. Physics was explicitly included in the work of this society alongside the other basic sciences such as botany, natural history and chemistry, and reinforced in the title of its journal, Les Mémoires de médecine de physique médicale. The contents were separated into sections, including
‘Observations of general physics applied to medicine’. Fig. 3 shows two decorative headings from the companion publication, L’Histoire de la société royale de médecine, demonstrating the complete change in political emphasis that was caused by the Revolution.
Amongst the papers we find Mauduyt de la Varenne (1732e
1792) making a critical study into the medical uses of electricity
[10]. The therapeutic use of electricity was then relatively recent, following the demonstration of charge storage in a Leyden Jar by
Peter Musschenbroek in 1746. Physicists had quickly started to explore its possible medical applications. In Paris, Abbé Jean-
Antoine Nollet (1700e1770) soon published his observations on the biological effects of electricity [11]. Echoing Sanctorius’ experiment, Nollet showed that cats and birds all lost weight after electrification (Fig. 4), ascribing this to increased ‘insensible perspiration’. He offered this possible therapeutic method to his medical colleagues, adding ‘If the doctor’s art does not reap the full benefit from what is apparently promised by a physicist, may I at least be forgiven for having believed in it, because it seemed to be true’. Jean
Figure 4. Abbé Nollet’s animal experiment, 1749 [11]. He measured the change in weight of cats and small birds after placing them either near to an electrified body or within an electrified cage. Electrified animals lost more weight than the controls. He also studied electrical effects on plants.
F.A. Duck / Physica Medica 30 (2014) 397e402 of Maudyut’s review, the Italian physicist Tiberius Cavallo (1759e
1809), working in London, was recommending the use of Lane’s
‘electrometer’, a calibrated spark-gap, to control the strength of the shock and so improve the consistency of therapeutic outcomes
[13,14]. physics was equally associated with the preservation and enhancement of a healthy life.
According to one biographer his lectures ‘concentrated principally on those phenomena of the animal body that can be reduced to the known laws of physical science’ [20]. This was demonstrated in the course syllabus [21]. There was a complete absence of Borelli’s micro-mechanical analogies to explain secretion, digestion and excretion. The failure of such models was now considered to be complete, and explanations were being sought in chemistry and vitalism. Instead, he concentrated on the strengths of physics: mechanics applied to musculo-skeletal movement, physics of the circulation, the eye and the ear. He added general sections on the principles of applying physics to medicine, and on the core skill of animal experimentation. A section on meteorology derived from the long-established view that illness is related to weather conditions. There were sections on the effects of heat, light, electricity and magnetism on the body. His interest in urban hygiene appears in a section on fireplace design.
The storming of the Bastille on 14 July 1789 was the trigger for events that saw France spiral into bankruptcy, chaos and terror, when everything and everyone associated with the old regime was swept away. A law passed on 7 August 1793 closed down all French academies and literary societies, including the Société royale de médecine. Lavoisier, in prison awaiting execution, wrote “(If) the physicist, . by the new avenues of possibility that his researches open up, does no more than extend human life by a few years, even a few days, he may aspire to the glorious title of benefactor of mankind” [15].
When Vicq d’Azir died shortly thereafter, he left a document that would, in due course, set Paris on the road to become the leading centre for medical training and research in Europe for the first half of the nineteenth century [16]. His plan recommended that basic sciences, including medical physics, should be an essential part of medical training. The plan was just a proposal, however, only a consultation document. As the Revolution in France developed, deeper political events caused the reorganisation of medical training to disappear from the agenda. Some scientists steered a careful course through the chaos. One such was the Comte de Fourcroy (1755e1809). In 1791 he launched a short-lived journal, La Médecine eclairée par les sciences physiques. In the introduction to the first issue he lays out his own vision: “The study of medicine always starts with the study of physics. It is not possible to be a doctor without being a physicist.”
Eventually a definition of medical physics emerged, in the 1814 revised edition of Nysten’s medical dictionary [22]. This definition is remarkable for its completeness, accuracy and conciseness:
Physics applied to the knowledge of the human body, to its preservation and to the cure of its illnesses. (Physique appliquée à la connaisance du corps humain, à son conservasion et à la guerison de ses maladie).
Absent are the conceptual restrictions associated with iatrophysics. The horizon is lifted high above the narrow constraints of physiological mechanics. Moreover, even with the passage of over two centuries since it was composed, this definition remains as general and as true today as it was then. Only the focus for emphasis has altered. Nineteenth century medical physics was dominated by physiological physics, ‘physics applied to the knowledge of the human body’. During the twentieth century the emphasis moved towards the use of physical techniques in the diagnosis and cure of illness. Modern trends in medicine are reemphasising the importance of a healthy life-style and environment. With an increasingly ageing population, it may be expected that the 21st century will see the full range of physical concepts and methods being applied more and more to the preservation of health, in addition to the present focus on cure of its ailments. This may range from a deeper involvement in non-ionizing radiation protection, providing biophysical judgements to interpret epidemiological ‘evidence’, through an increasing emphasis on rehabilitation engineering in all its facets, to the quantification of cellular scale forces on the cytoskeleton, with their bio-physical responses.
One small section in Hallé’s course concerned animal electricity, which was the latest hot topic in medical physics since Luigi Galvani (1737e1798) published his studies in 1791. Hallé led a study into Galvanism, one of the most comprehensive independent reviews at that time [23]. Then, shortly after Alessandro Volta (1745e
1827) had demonstrated his electric pile in 1800, Hallé built his own and compared electric treatment using it with that from an electric shock [24].
Jean-Noel Hallé (1754e1822) may reasonably be named as the founding father of medical physics [17,18] (Fig. 5). In December
1794 he was appointed as the professor of medical physics and hygiene at the new École de santé (School of Health) in Paris. Before the Revolution, Fourcroy had invited him to set out his suggestions for a course in hygiene [19]. His was a vision within which health was as much to do with the man-made physical environment as it was with diet and exercise. Medical physics has nowadays become associated with the diagnosis and treatment of disease. For Hallé,
By the time Hallé died in 1822, medical physics had a name, a formal definition, and a clear content. But new subjects can only be considered complete if they have a continuous longevity, independent of the lives and contributions of individual scientists. This was to became true for medical physics, first in Paris, and then elsewhere in France, in other European countries and finally across the Atlantic. Hallé’s successor, Pierre Pelletan, took the first full chair of medical physics, separating the subject from hygiene. Pelletan’s successor, Jules Gavarret (1809e1890), made many contributions during his extraordinary career as a medical physicist. For
Figure 5. Jean-Noel Hallé (1754e1822). Professor of medical physics and hygiene at the School of Health and then the Faculty of Medicine in Paris from 1795 to 1822.
Wellcome Library, London. F.A. Duck / Physica Medica 30 (2014) 397e402
401 example his first book, published in 1840, was the first to introduce the concept of inferential statistics for the analysis and comparison of medical therapies [25]. His influence facilitated the spread of medical physics to the other medical centres in France. physiological measurement, giving doctors the tools for measurement that would alter diagnostic medicine for ever. In 1868 Fick moved to Würzburg to become professor of physiology, staying there for the remainder of his eminent career. It was here, in 1870, that Fick proposed a technique that remains one of the standard methods by which cardiac output may be measured [33].
Text-books on medical physics
Medical physics failed to gain much purchase in Britain and the USA during this period. There may have been a language problem.
Before 1800, the word physics was scarcely used in English, largely restricted to translations from Latin, German or French texts. The English term was ‘natural philosophy’. It was much easier for continental scientists to find phrases such as physique médicale and medizinische physik than it was for British scientists and doctors to encapsulate the broad reach of links between the two disciplines under a single title. This semantic problem did not inhibit the scientific development of each separate intersection of physics with medicine, but it did serve to delay its coherence into a separate discipline in English-speaking countries. Neil Arnott was the first to use the term medical physics in English, in 1827. Through his international best-selling book on popular science [34] he created a public understanding of the intimate link between physics and medicine. But the claim that he was the first medical physicist [35] is not really supported by the evidence.
In 1855, the year before Fick’s Die medizinische Physik appeared in press, Gavarret published a book on animal heat under a general medical physics title [36]. It was an extensive revue of the deep physiological challenge; how do animals create and maintain their body temperature? It was a time when the general concept of energy and its conservation was being discussed by Europe’s most able scientists. In his seminal 1847 analysis, Über die Erhaltung der
Kraft, Hermann von Helmholtz (1821e1894) had already suggested that chemical force-equivalents, appropriate for investigating metabolic processes, could be identified, comparable with similar force-equivalents for thermal and electrical forms of energy [37]. By
1866, Gavarret was offering an advanced course to doctors in Paris, which he called Physique biologique, in which he further developed these ideas [38]. He declared work (travaille) to be as universal as mass, and its conservation to be as true for living as for inorganic bodies. Gavarret was marshalling his arguments for a final push against those physiologists who still retained a belief in ‘an independent directing force in the body’. He called it ‘a mere useless hypothesis . that the vitalist school invoke to explain the phenomena of nutrition and development’.