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▼ SCOPE | HISTORICAL FEATURE 48 | SEPTEMBER 2012 | SCOPE
But Gavarret had not ceased thinking. In 1849 we see the next example in which he demonstrated that he was following developments at the interface between physics and medicine, in this case electricity. Conventional wisdom in France still broadly held to Volta’s electrochemical model to explain all galvanic sources, rejecting Galvani’s view of animal electricity as an innate property of living tissues. Gavarret published a careful review based on the best evidence he could find, concluding that much criticism of Galvani had been inappropriate, and that there was much new evidence to suggest that electric phenomena were inherent to all living matter. HEAT AND ELECTRICITY Gavarret planned to write a book about animal electricity. He said so in the introduction to his next book, on animal heat. 10 This book was a thorough review of a topic for which considerable advances in measurement techniques (figure 4) and understanding had recently occurred. This was to be the first in his Medical Physics series, in which he intended to review carefully each aspect of physics in its relationship to medicine. (In fact, none of his later books bore this series title.) Animal electricity would have been Volume 2 in this series. But controversy still surrounded this subject: Du Bois Reymond’s visit to Paris in 1850 did little to clear the air. 9 So, instead, Gavarret’s next book was a thorough review on the current state of electricity as a whole, publishing his Traité d’Électricitié in two volumes in 1858 and 1859. However, he omitted biomedical electricity, which he says needed to mature further before a proper review could be written. This book established his reputation as an academic author who could explain difficult concepts in easily-understood prose, without compromising scientific accuracy. The book was also soon published in German. He was immediately invited to serve as a member of a commission of the Ministry of Finance to give advice on the electric telegraph. This was at the start of the nineteenth-century communications revolution, both in extent and speed, with an impact comparable with that which arose from the introduction of the World Wide Web. Up to 1844, when the first electric telegraph line was installed from Paris to Tours, there were only five semaphore lines in France, and a message took 20 minutes to reach Toulon. Within 7 years, London and Paris were in instantaneous communication by a telegraph cable under the English Channel, and by 1860 there were 22,000 km of lines criss-crossing the whole of France. In 1861 Gavarret published a detailed book on the telegraph (figure 5). 11 This book was again followed by a German translation. LIGHT AND SOUND Gavarret’s next books, on optics and acoustics, endorsed his reputation as an outstanding educational communicator. They also serve to emphasise his understanding of his unique role – to understand contemporary developments in physics in depth, and to interpret them for his colleagues in medicine. Much had already been written on the optics of the eye, and he saw it as unnecessary to go over this well-tilled soil. So, instead, he wrote an interpretation of Gauss’s 1840 Dioptrishe Untersuchungen. In his book, entitled Images par reflexion et par refraction (1866), he gave a clear exposition of Gauss’s paraxial approximation for focal systems, giving a tool using principal and nodal points that could be easily applied in physiological optics. The preface of the 1891 translated Russian edition of Gavarret’s book emphasises its considerable value in the teaching of optics. In his last book 12 he reviewed the mechanisms of speech and hearing, drawing on the work of Helmholtz and Fourier, including several appendices of a more mathematical nature. The text itself draws strongly on experimental physics, including many examples of physical measurements applied to physiological acoustics (figure 6). BIOLOGICAL PHYSICS Gavarret was always concerned to avoid a too narrow interpretation of the physics syllabus for first-year medical students. He knew that there was insufficient time during his three physics lectures per week to do justice to the broader applications of physics to medicine. In response to this conflict, around 1866 he started to offer an advanced course called Biological Physics, where he assumed his audience had some knowledge not only of physics, but also of FIGURE 2. [TOP LEFT] Gavarret’s apparatus for the measurement of expired CO2 . 10 ▼ FIGURE 3. [TOP RIGHT] Cagniard de Latour’s siren. ▼ FIGURE 4. [MIDDLE LEFT] Intra-muscular temperature using thermocouples by A.-C. Becquerel (1788–1878): 1835. 10 ▼ FIGURE 5. [BOTTOM RIGHT] Electrical telegraph transmitter c. 1850. 11 ▼ FIGURE 6. [BOTTOM LEFT] Voice analysis using the dancing flame. 12 ▼ HISTORICAL FEATURE | SCOPE physiology, pathology and anatomy. Such was the interest in these lectures that typically more than half his audience consisted of qualified doctors, anxious to update themselves on the possible impact on their medical practice of new developments in physics. In 1869, he published a book derived from this course, Phénomènes physique de la vie. Once more we see him applying modern physics concepts to medical problems, allowing him to peer into the future whilst remaining cautious about inappropriate extrapolation from present knowledge. In the introduction he applauds the value of physical measurement, using the example of Marey’s multichannel measurements on intra-cardiac pressure: he was Marey’s examiner for his thesis in 1859. Étienne-Jules Marey (1830–1904) later became famous for his use of photographic methods for analysis of animal locomotion. He even included the comment that, since the brain is doing work during thinking, comparing, wanting and so on, its energy use may be sufficient cause and not just a necessary condition for all mental activity, and by implication subject to the same energy considerations as any other organ. In this he draws on the new concepts in physics that clearly excited him most, the reciprocity of forces and the conservation of energy. Using the terminology of the time, he says that travaille is as universal as mass, and that its conservation is as fundamentally true in living as in inorganic materials. It is here, he says, that physiological phenomena, heat, bio-electricity, muscular power and nutrition, will find their true explanation. In comparison with his British contemporaries, he felt no need to mention any apparent conflict with religious thought, although he had to fight against a residual belief in a vital life force, still maintained by the dominant French physiologist Claude Bernard (1813–1878). It was left to his younger colleagues Desplats and Gariel to write the next full medical physics text 13 in 1870, to which Gavarret added an introduction. POLITICS Jules Gavarret lived through a highly turbulent time in French history. He was just 4 years old when Napoleon ▼ SCOPE | SEPTEMBER 2012 | 49
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