Conclusion
It may be seen, then, that if one was prepared to accept the existence of insulating sheaths on the nerves, all the arguments raised against the proposed identification of the nervous and electrical fluids, except one, could be answered satisfactorily. The single exception involved the question of how an electrical disturbance in the brain could be confined to a single nerve, and, as was indicated earlier, it was scarcely fair to hold this sort of objection against the electrical theory alone. In that case, there remained no convincing argument to show why one should not accept the identification of the two fluids. On the other hand, of course, it remained an open question as to whether there was any convincing argument to show why one should accept the identification either. Galvani thought that his experiments provided just such an argument.
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References
I thus reject at the outset the critical attitude adopted by Philip C. Ritterbush in his Overtures to Biology: The Speculations of Eighteenth-Century Naturalists (New Haven: Yale University Press, 1964), toward those eighteenth-century physiologists who sought to identify the nervous fluid with the electrical one. In the context of the time, and given the prevailing theories of nervous action and electricity, I regard the possibility of such an identification as a perfectly proper subject of scientific inquiry; the two fluids had been ascribed properties which were almost identical, and experiment had shown unequivocally that they were at least related, for electricity had been found to be remarkably effective in stimulating muscular contractions.
Albrechtvon Haller, A Dissertation on the Sensible and Irritable Parts of Animals (Baltimore: Johns Hopkins Press, 1936; a reprint of the English edition of 1755), pp. 8–9. The term “irritability” had been introduced into physiology by Francis Glisson in his Tractatus de natura substantiae energetica of 1672, during a discussion of the means whereby bile is discharged into the intestines.
Haller, A Dissertation on the Sensible and Irritable Parts of Animals, (Baltimore: Johns Hopkins Press, 1936), p. 24.
Albrechtvon Haller, A Dissertation on the Sensible and Irritable Parts of Animals (Baltimore: Johns Hopkins Press, 1936), p. 40. Whytt had presented his arguments in his Essay on the Vital and Other Involuntary Motions of Animals (Edinburgh, 1751).
Haller, A Dissertation on the Sensible and Irritable Parts of Animals (Baltimore: Johns Hopkins Press, 1936), p. 42
Haller, First Lines of Physiology, 2 vols. in one (New York: Johnson Reprint Corp., 1966; a reprint of William Cullen's translation of the third Latin edition of 1767), I, 233. The concept of irritability did not appear in the editions of 1747 and 1751, and it was not until the third edition that Haller included a reasonable account of this aspect of his work (Lester S. King, Introduction to the 1966 reprint, p. xl).
Haller, First Lines of Physiology, 2 vols. in one (New York: Johnson Reprint Corp., 1966), I, 236.
T. Morgan, Mechanical Practice of Physick, (London, 1735), pp. 145 ff.
Isaac Newton, Opticks, or a Treatise of the Reflections, Refractions, Inflexions and Colours of Light, (New York: Dover, 1952; based on the 4th edition, London, 1730), Query 24, p. 353. Consistent with his well-known mid-career abandonment of ether hypotheses, Newton, in Query 12 in the first (1704) edition of the Opticks, spoke simply of vibrations “being propagated along the solid fibres” of the nerves, without mentioning the ether at all. The wording of this Query remained unaltered in subsequent editions, although of course an entirely new interpretation had to be put on it following the addition of what became Query 24 in 1717. It would be interesting to know what prompted Newton to extend his ether hypothesis to the action of the nerves in the way he did, but so far as I am aware this is a question which Newton scholars have not yet investigated.
David Hartley, for example, in his Observations on Man (London, 1749), combined the last two possibilities. Haller, in his Elementa physiologiae (IV, 358), listed a number of others besides Morgan, Newton, and Hartley who had denied the existence of a nervous fluid, but I have not checked his references to see which particular variant of the vibration theory each espoused.
Lausanne, 1762.
For convenience the quotations are taken from the First Lines of Physiology (I, 219–220). In vol. IV of the Elementa physiologiae, the same arguments, sometimes expanded a little, appear on pp. 361–365. It is worth noting as well that several of the arguments had been given earlier by Boerhaave in his renowned Institutiones medicae (see, for example, the English translation published by W. Innys [London, 1742–46] under the title Dr. Boerhaave's Academical Lectures on the Theory of Physic (II, 310–313)). They were repeated by many other authors throughout the rest of the century.
Elsewhere in the Elementa physiologiae (IV, 378–379), Haller did argue against the ether hypothesis on the grounds that the ether could not be confined within the nerves. He was there concerned to argue, however, that the nervous fluid, whose existence he was by then taking for granted, was not to be identified with the ether; his argument was not designed to rule out the possibility of ether vibrations being confined in the nerves, and it certainly did not do so.
First Lines of Physiology, I, 220.
Ibid., p. 221.
Ibid., p. 243.
Ibid., pp. 236–237.
Ibid., p. 240.
Ibid., p. 221.
Ibid., p. 222.
This dating of Haller's first researches on irritability is due to Lester S. King, “Introduction” to First Lines of Physiology.
In view of the persistence in the literature of statements to the contrary, it perhaps needs to be emphasized that Benjamin Franklin was not the first to introduce the notion of a subtle electrical fluid into electrical theory, for the earlier effluvialists such as Nollet and Watson had also invoked such a peculiar fluid in their attempt to account for the phenomena. Franklin's innovation was that he regarded an electrified body as one containing either more or less than its normal quota of fluid, whereas his predecessors had described the electrified state in terms of an excitation of the fluid already present.
Thus Motte, in his authorized translation of Newton's Principia (London, 1726; reprinted London, 1968, p. 393), had described as an “electric and elastic spirit” the ether which Newton had invoked to explain, amongst other things, how “all sensation is excited, and the members of animal bodies move at the command of the will.” A few years later, Hales (Haemastaticks [London, 1733; reprinted New York, 1964], p. 59), cited some of Stephen Gray's experiments in support of the electrical theory. Then in the very paper in which he announced Musschenbroek's famous discovery to the world (Hist. l'Acad. Roy. Sci., 1746, Mém. p. 16), the abbé Nollet remarked that he considered a person who drew a spark from an electrified body “comme remplie on pénétrée d'un fluide subtil, dont la répercussion se fait sentir plus ou moins fort, plus ou moins profondément, à proportion de la grandeur du choc qu'il a reçu ... Cette commotion n'est qu'un mouvement de pression imprimé à un fluide fort élastique.” Nollet's explanation of the appearance of sparks in electrical discharges was framed in the same terms; it involved a “répercussion” of two opposing streams of electrical fluid. Haller cited Hausen, Boissier, and Deshais as other early proponents of the theory (Elementa physiologiae, IV, 378); Rothschuh has given a more complete listing in his article “Von der Idee bis zum Nachweis der tierischen Elektrizität” (Sudhoffs Archiv, 44 [1960], 25–44).
William Watson, Phil. Trans. Roy. Soc., 45 (1748), 76–85.
First Lines ... I, 221.
Ibid.
Ibid., p. 237.
IV, 378–380.
Lausanne, 1760. Henceforth referred to as Mémoires.
Tommaso Laghi (1709–1764) was professor of medicine at Bologna at the time. I have not been able to consult any of his works, but since my concern is with the arguments against the electrical hypothesis rather than those for it, the omission should not be significant. From remarks made elsewhere by Caldani (Haller-Caldani Briefwechsel, ed. E. Hintzsche, [Bern, 1966], p. 16), it seems likely that Laghi's defense of the electrical hypothesis appeared in his Epistola responsoria ad Caesarium Pozzi (Bologna, 1756).
Mémoires, p. 461.
Ibid., p. 207.
Ibid., p. 463.
Franklin's theory was expounded in a series of letters he wrote to his friends in London between 1747 and 1755 (the first detailed exposition being given in 1749). The letters were published under the general title Experiments and Observations on Electricity, Made at Philadelphia in America, the first group appearing in print in 1751. A new edition was prepared by I. Bernard Cohen, Benjamin Franklin's Experiments (Cambridge, Mass.: Harvard University Press, 1941); this is the edition I have used.
Benjamin Franklin's Experiments, p. 302.
I am currently preparing a detailed study of these aspects of Franklin's work.
For example, Fontana (Mémoires p. 207) began his critique of Laghi as follows: “Si M. Laghi en admet l'identité, voici ce que j'aurois à lui objecter, d'après le P. Beccaria”. (my emphasis).
Giambatista Beccaria, Dell' elettricismo artificiale e naturale (Turin, 1753).
Ibid., p. 17 (my emphasis): “ogni segno elettrico avvenga pel vapore, che da un corpo, in cui è in quantità maggiore si espande nell' altro, in cui è in minore quantità”.
Beccaria was not simply reverting to the traditional effluvial theory, however: as he pointed out himself, the impact of an outward-flowing stream of matter hardly provided a straightforward mechanical explanation for the inward motion of the bodies in its path.
Mémoires, p. 207.
Ibid. (my emphasis).
Haller's statement cited above (p. 241) that the nervous fluid is “reparable from the aliments” suggests another important difference between it and the electrical fluid. Ordinary matter and the electrical fluid were held to be independent species of being; the total quantity of each
Aepinus, Mém. Acad. Berlin (1756), pp. 119–121. For Wilcke's part in the discovery, see C. W. Oseen, Johan Carl Wilcke, Experimental-Physiker (Uppsala, 1939), pp. 50–51.
Aepinus, Tentamen theoriae electricitatis et magnetismi (St. Petersburg, 1759).
A useful summary of the work which led to this conclusion has been given by W. Cameron Walker in his article, “Animal Electricity before Galvani”, Annals of Science, 2 (1937), 84–113.
It was in fact sufficiently strong to convert Fontana himself to the electrical theory.
Luigi Galvani, Commentary on the Effects of Electricity on Muscular Motion, trans. Margarget Glover Foley; notes and introd. by I. Bernard Cohen (Norwalk, Connecticut: Burndy Library, 1953), p. 76.
It should be remarked that Galvani's views on the function of the nerves were rather unorthodox in ways quite unrelated to those discussed in this paper. He did not adopt the traditional view of the nervous fluid as the medium responsible for the transmission of impulses from the brain to the muscles. Rather, he regarded it as something whose circulation from the inside of a muscle to the outside (or perhaps vice versa) via a nerve resulted in the muscle contracting (Commentary, p. 82). This peculiar feature of his theory does not affect the preceding argument, however, since for Galvani as for everybody else, muscular contractions were still supposed in the end to be due to the flow of a subtle fluid through the nerves, and it was this fluid which he held to be electrical in character.
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Home, R.W. Electricity and the nervous fluid. J Hist Biol 3, 235–251 (1970). https://doi.org/10.1007/BF00137353
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DOI: https://doi.org/10.1007/BF00137353