(b. Aberdeen [?], Scotland, 1673; d. London [?], England, September 1742), physiology.
Stuart, in 1738 the first Croonian lecturer on muscle physiology at the Royal Society, was a Scotsman of obscure origin and uncertain early history. After receiving his M.A. from Marischal College, Aberdeen, in 1691, he enrolled as a medical student at Leiden, on 14 December 1709, at the age of thirty-six, and graduated M.D. two years later. Appointed physician to Westminster Hospital, London, upon its creation in 1719, he was admitted licentiate of the College of Physicians in June 1720. In 1728 he was designated physician to the queen, admitted to the M.D. at Cambridge (Comitiis Regiis), and elevated to a fellowship in the College of Physicians. Stuart achieved some prominence in the College, serving as censor in 1732 and again in 1741. He was also elected fellow of the Royal Society in 1714, was a recipient of its Copley Medal many years later for his work on muscles, and achieved membership in the Académie Royale des Sciences.
Prior to the publication of his Croonian lectures as a special supplement to the Philosophical Transactions of the Royal Society in 1739, Stuart had contributed three well-received papers to the same journal. Two of these papers considered the role of bile as a stimulus to the peristaltic motion of the intestines and raised general questions regarding the “animal oeconomy,” and the third reported experiments attempting to demonstrate the existence of a fluid in the nerves. Stuart also published in 1738 a substantial essay on the structure and function of muscles: Dissertatio de structura et motu musculari. This essay was an expanded version of his inaugural dissertation for the M.D. at Leiden, presented in 1711.
Stuart’s principal concern both in his Dissertatio, and in the Croonian lectures based closely on it, was to demonstrate that a strict hydraulic iatromechanism was the best theory by which to account for muscular motion. Unlike contemporary British writers who in the 1730’s advanced theories of muscular action based on the wavelike movement of animal spirits and the jiggling of elastic nerve fibers, Stuart insisted that the mechanics of sanguinary and nervous fluids, and of their vessels, alone governs the action of the muscles. The forceful flow of blood in the arteries and veins and the trickle of liquid juice through the nerves suffice to cause and control muscular motion.
Stuart saw the muscles as an elaborate network of vessels and open spaces, in basic design not unlike the lungs. The proximate cause of systole is the elastic restitution of the walls of the muscular blood vessels, which had been expanded in a preceding diastole1. Alternate systole and diastole accelerates and retards blood flow through the capillary vessels. This effect in turn allows small quantities of nervous juice to exercise a large control over blood flow and, hence, over systole and diastole. Nervous control is concentrated in the neural fiber, which Stuart thought of as “a chain of distensile vesicles whose sides are covered with a net-work of elastic longitudinal and transverse blood-vessels.”2 Since blood flow is particularly difficult when the capillary vessels have been longitudinally stretched and their transverse diameters shortened, the dripping of nerve juice into the vesicles (around which the capillaries are woven) can quickly reverse the hydraulic circumstances. The dimensions of the neural vesicles will subtly alter with the addition of nerve juice, and this modification will cause capillary diameters to alter too. This later alteration can quickly intensify because the pressure of inflowing blood will multiply the initial effect. Dramatic alternations of blood flow within the muscles can throw them from systole to diastole, or vice versa. Antagonist muscles can thus be seen as if poised in a fine static balance, with the blood mass shared between them via commonly connected vessels ready to switch from one “balance pan” to another nearly instantaneously.3 The trickle of nerve juice, initiated by the immaterial spirit or mind, can therefore cause the elevation or depression of the muscle balance pans, that is, the systole and diastole of muscle pairs.
Stuart quite possibly derived his theory from analogous ideas on heartbeat and its nervous control introduced by Boerhaave in his Institutiones medicinae4. Stuart also resorted to several kinds of direct empirical evidence. He explored muscular anatomy through the microscope and with the hello of excarnation and injection techniques5 He tried to prove the elasticity of the blood vessels by tying arteries, veins, and nerves next to one another onto a wooden board and watching the blood vessels but not the nerves contract6. He dissected out a demonstration muscle pair and attendant vessels; common blood vessels and individual nerve supplies were clearly indicated in the special preparation7. Finally, Stuart tried to demonstrate his basic theory of muscle action by suspending a decapitated frog by its forelegs in a frame and then pushing down on the exposed spinal cord with a blunt probe. The hind legs of the frog twitched, and Stuart explained this by claiming that the probe forced a small quantity of nerve juice from the spinal cord into the appropriate muscles, the small increment of nervous liquid being sufficient mechanically to trip muscle contraction8.
It was for the decapitated “spinal frog” experiment that Stuart was most widely known by his eighteenth-century successors. It did not, however, originate with him. Decapitated spinal frog experiments can easily be traced into the seventeenth century and, in one form, perhaps even as far back as Leonardo da Vinci9. Robert Whytt credited the experiment to Stephen Hales, a contemporary of Stuart and a correspondent of Whytt10. But it was Stuart, because of the presumptive importance of the experiment to his iatromechanical theory, who gave it greatly enhanced attention and by doing so fixed the decapitated frog in the imagination of later eighteenth-century physiologists. Albrecht von Haller, at any rate, referred to Stuart’s “very useful facts,” 11 and Robert Whytt often mentioned Stuart’s work. 12 Both Whytt and Haller focused on the phenomena and largely ignored Stuart’s hypotheses. The experiment was borrowed, repeated, and made increasingly more sophisticated. The and made increasingly more sophisticated. The clarifying articulation of reflex theory in the latter half of the eighteenth century thus owes an unintended but consideable debt to Stuart, for as J. F. Fulton suggested, the decapitated frog became in that period “. . . one of the first martyrs of science.”13
1. Alexander Stuart, Dissertatio de structura et motu musculari (London, 1738), p. 120.
2. Alexander Stuart, Three Lectures on Muscular Motion, … (London, 1739). p. xiii.
3.Ibid., p. vii.
4.Dr. Boerhaave’s Academical Lectures on the Theory of Physic, II (London, 1743), pp. 75, sect. 190.
5. See, for example, Dissertatio,pp. 36, and 47.
6.Three Lectures, p. iii
7.Ibid., p. vi.
8.Ibid., pp. xxxvii-xxxix.
9. See, for example, Georges Canguilhem. La formation du concept de réflexe (Paris. 1955), p. 91.
10. See R. K. French, Robert Whytt, the Soul, and Medicine (London, 1969), p. 86.
12. French, op. cit., passim.
13. Quoted in Canguilhem, op. cit., p. 89.
I. Original Works. Stuart’s two principal extant works are Dissertatio de structura et motu musculari (London, 1738); and Three Lectures on Muscular Motion, Read Before the Royal Society in the Year 1738 (London, 1739). The British Museum Catalogue also lists Dissertatio medica inaugualis de structura et motu musculari, etc. (Leiden, 1711), and New Discoveries and Improvements in Anatomy and Surgery … With Cases and Cures (London, 1738).
Three of Stuart’s major papers are “An Essay Upon the Use of the Bile in the Animal Oeconomy, Founded on an Observation of a Wound in the Gallbladder,” in Philosphical Transactions of the Royal Society, 36 (1729–1730), 341–363; “Experiments to Prove the Existence of a Fluid in the Nerves,” ibid., 37 (1731–1732). 327–331; and “Explanation of an Essay on the Use of the Bile in the Animal Oeconomy,” ibid., 38 (1733–1734), 5–25.
II. Secondary Literature. Stuart has rarely been studied, although in recent years he has been receiving increasing notice. Biographical essentials can be found in Robert W. Innes-Smith, English-Speaking Students of Medicine at the University of Leyden (Edinburgh, 1932), 226; and more extensively in William Munk, The Role of the Royal College of Physicians of London, II (London, 1878), 109. More than passing mention of Stuart’s work is made in R. K. French, Robert, Whytt, the Soul, and Medicine (London, 1969), 90, 150–151; Karl E. Rothschuh, History of Physiology Guenter B. Risse, trans. (Huntington, N.Y., 1973), 138, 183; and Robert Schofield, Mechanism and Materialism: British Natural Philosophy in an Age of Reason (Princeton, 1970), 192–193. Also of considerable utility in setting the eighteenth-century context for Stuart’s work are E. Bastholm, The History of Muscle Physiology (Copenhagen, 1950): and Georges Canguilhem. La formation du concept de réflexe (Paris, 1955).
Theodore M. Brown