(b. Greenwich, England, 8 March 1879; d. over Salisbury Plain, near Aldershot, England, 5 October 1916)
Lucas was the second son of Francis Robert Lucas, an inventor and engineer who supervised the laying of the early intercontinental submarine telegraph cables and who ultimately became managing director of the Telegraph Construction and Maintenance Company. Under his father’s influence, Lucas early displayed great mechanical ingenuity, remarkable manual dexterity, and a deep interest in science and engineering. His mother was the former Katherine Mary Riddle, granddaughter of Edward Riddle and daughter of John Riddle, successive directors of a school for sons of naval officers in Greenwich and both renowned as teachers of navigation and nautical astronomy.
From the Reverend T, Oldham’s preparatory school at Blackheath, Lucas went to Rugby School on a classical scholarship in 1893 and then on a minor classical scholarship to Trinity College, Cambridge, where he matriculated in 1898. Lucas had already decided to study science; and he began at once to read for the natural sciences tripos, in part I of which he took a first class in 1901. In keeping with his interests, and despite two full years of support on a classical scholarship, Lucas had as his director of studies at Trinity the noted physiologist Walter Morley Fletcher. In 1901, under the strain of his studies and the death of an old school friend in the Boer War, Lucas suffered a breakdown in his health and left Cambridge for two years. Part of this period he spent in New Zealand, where he carried out a bathymetric survey of a number of lakes.
By the time he returned to Cambridge in the autumn of 1903, Lucas had decided to devote himself to a career in physiological research. He had in fact already devised, at home and on his own, an impressive photographic recording method for tracing the events of muscle contraction. So clearly had he formulated his research interests that he was allowed to forgo the usual routine of organized course work and examinations for part II of the natural sciences tripos and was immediately given a place in the crowded physiological laboratory at Cambridge, initially in a sort of anteroom passageway and later in a small cellar.
In 1904 Lucas won the Gedge Prize and the Walsingham Medal and was elected fellow of Trinity College. He was appointed additional university demonstrator in physiology in 1907 and lecturer in natural science at Trinity College in 1908. In addition to the B.A. degree in 1901, Lucas received the M.A. from Cambridge in 1905 and the D.Sc. in 1911. He was elected fellow of the Royal Society in 1913, having been Croonian lecturer the year before. From 1906 to 1914 Lucas was a director of the Cambridge Scientific Instrument Company. A member of the Trinity College Council, he also helped to plan the new physiological laboratory built at Cambridge in 1914.
Upon the outbreak of World War I, Lucas enlisted and in September 1914 was assigned to the experimental research department of the Royal Aircraft Factory at Farnborough. There he applied his graphical recording methods to an analysis of roll, pitch, and yaw in airplanes. He also helped to design an accurate bombsight and a new magnetic compass which greatly improved aerial navigation and which was granted a War Office secret patent in July 1915. His contributions in this area were recognized in the published report of the Advisory Committee for Aeronautics. In September 1916, after repeated requests, he was allowed to attend the Central Flying School, where he quickly qualified as a pilot. He was killed, while flying solo, in a midair collision. He was survived by three sons and his wife, the former Alys Hubbard, eldest daughter of the Reverend C. E. Hubbard, whom he had married in 1909. After his death, his wife and sons changed their names by deed poll to “Keith–Lucas.”
Lucas’ career in physiological research was devoted wholly to investigating the properties of nerve and muscle, especially the characteristics in each of waves of excitation (what Lucas called “propagated distur-bances“). The dominant and most valuable features of his work in general were clarity, precision, and enormous methodological originality. To the design of physiological instruments he brought the same basic principle that he had already applied at Rugby to the design of a bicycle and an especially admirable microscope:1 the design itself should ensure the accurate operation of the device even in the face of shoddy worksmanship and wear and tear. On this basis he designed an instrument for the analysis of photographic curves from the capillary electrometer, a method of drawing fine glass tubes of uniform dimensions for the capillary electrometer, and a photographic time marker along the lines of Eint-hoven’s string galvanometer. To reduce the distortion produced by the inertia of recording levers, he used light levers or photographic methods where feasible. So integral to Lucas’ achievements were these and other instruments of his own design that he has been described as “essentially an engineer.”2
In addition to these important methodological contributions, Lucas produced a series of valuable experimental results and established at least one fundamental principle: the “all or none” law for ordinary skeletal muscle. Since the work of Henry P. Bowditch in 1871, it had been known that cardiac muscle follows an “all or none” rule: a given stimulus either evokes the maximum possible contraction, or it evokes no contraction at all; if a cardiac contraction does occur, its strength is independent of the exciting stimulus. Some indirect evidence existed that this principle applied as well to skeletal muscle, as Francis Gotch had explicitly suggested in 1902; but direct support for the suggestion was lacking. This support was provided by Lucas in two papers published in 1905 and 1909.
In the first paper, Lucas showed that when the frog’s cutaneus dorsi muscle is stimulated directly by electrical currents, the resulting contraction increases in discrete, discontinuous steps as the stimulus is increased. Whether the preparation is the cutaneus dorsi muscle as a whole (consisting of 150 to 200 individual muscle fibers) or only a small section of the muscle, these discrete steps are always fewer than the number of individual muscle fibers in the preparation. This result suggested that the individual muscle fibers fall into distinct groups according to their excitability and that each discrete step of increased contraction marks the excitation of an additional fiber or small group of fibers of similar excitability.
In the paper of 1909, Lucas confirmed these earlier results under more normal conditions, for he now evoked contraction not by direct stimulation of the cutaneus dorsi muscle but through stimulation of its motor nerve fibers. Persuasive evidence was thus produced that for each skeletal muscle fiber, as for cardiac muscle, contraction (if evoked at all) is maximal regardless of the strength of the exciting stimulus. A stronger stimulus increases contraction in an ordinary many-fibered muscle only because it activates a larger number of the individual constituent fibers; and the “submaximal” contraction of such a muscle is merely the maximal contraction of less than all of its fibers. The absence of submaximal contractions in the heart is not to be ascribed to any fundamental differences in the functional capacities of skeletal and cardiac muscle cells but, rather, to the fact that cardiac muscle is functionally continuous, its fibers being in connection with one another, while skeletal muscle fibers are separated by their sarcolem-ma. By 1914 the “all or none” law had been extended to motor nerve fibers by Lucas’ most celebrated student, Edgar Douglas Adrian, later a Nobel laureate in physiology or medicine.
In extending to another tissue a property previously established only for cardiac muscle, Lucas followed a course which is at least implicit in most of his work. Upon determining the temperature coefficient for nerve conduction, for example, Lucas pointed out that his mean value of 1. 79 for the ten degrees between 8°: and 18° C. was similar to values already obtained for muscle conduction, suggesting to him that the conduction process is fundamentally the same in nerve and muscle. In both kinds of tissue, he believed, conduction takes place in two stages; a preliminary local excitatory process at the seat of stimulation, and the subsequent production of a partially independent “propagated disturbance.” His attempt to show that the propagated disturbance in muscle is an electric and not a contractile disturbance3 probably reflects his search for underlying similarities among all excitable tissues.
Similarly motivated was Lucas’ comparison of conduction across the myoneural junction, across the A.V. bundle in the heart, and across the synapse in the central nervous system—in all these cases, he argued, impulses pass through a region of diminished conductivity, a “region of decrement.”4 In general, Lucas considered it folly to ascribe special properties to certain kinds of tissue unless and until every attempt had been made to explain the phenomena in terms of known properties common to all excitable tissues. This attitude is evident in his posthumous monograph, The Conduction of the Nervous Impulse (1917), in which the phenomena of the peripheral nerves are offered as a guide to processes in the central nervous system.
With respect to the refractory period, inhibition, and the summation of stimuli, Lucas conceived of them in similar terms and attributed them to similar causes, whether they took place in muscle tissue, peripheral nerves, or the central nervous system. In all excitable tissues, he believed, inhibition results when successive stimuli arrive too frequently for the tissue to recover from the impaired conductivity of the refractory period; summation, on the other hand, results when successive stimuli are so timed as to coincide with a temporary postrecovery phase of supernormal excitability and conductivity. This theory of summation, developed by Lucas in association with Adrian, differed essentially from the prevailing theory of Max Verworn and F. W. Fröhlich.
In addition to the “all or none” law and the Lucas-Adrian theory of summation, Lucas contributed to the physicochemical theory of excitation, although his role in this area was more that of an effective and suggestive critic than of a creative pioneer. His departure point here was Walther Hermann Nernst’s influential theory of the local excitatory process, according to which the threshold of excitation is reached when a certain difference of ionic concentration is produced at a semipermeable membrane contained in the excitable tissue. Drawing in part on the work of A. V. Hill, another young Cambridge physiologist and future Nobel laureate, Lucas argued that Nernst’s theory, properly conceived and appropriately modified, could account for virtually all the phenomena of local excitation. In his Croonian lecture of 1912, Lucas emphasized in typical fashion that what difficulties the theory did present “seem to dovetail into one another, being probably expressions of a common property of the tissues.”5
Lucas’ last research, published posthumously, dealt with the neuromuscular physiology of the crayfish. Besides discovering that the crayfish claw is innervated by two sets of nerve fibers—one responsible for the slow, prolonged contraction of the claw and the other for a brief twitch—Lucas also found that the phase of supernormal excitability is much more pronounced in the crayfish than in the frog, a circumstance that enabled him to produce further support for the Lucas-Adrian theory of summation.6 But, as Adrian has suggested,7 the choice of the crayfish as an experimental animal may reflect a shift of emphasis in Lucas’ thought far more significant than any of these immediate results. It may be that Lucas had decided to move explicitly and actively in the direction of comparative and evolutionary physiology, a deep and long-standing interest occasionally evident even during his earlier concentration on the frog’s neuromuscular tissue.
Almost from the beginning of his career Lucas had noticed that different excitable tissues do possess a few fundamentally different properties despite all attempts to emphasize their similarities. In particular, he found that the value of optimal exciting stimuli varies for different tissues in the same animal and for the same excitable tissues in different animals. So persistent, distinct, and quantifiable are these differences that Lucas was led to postulate the existence of three distinct “excitable substances.” Each of these substances was associated with a particular kind of tissue—one with muscle, one with nerve, and one with a hypothetical myoneural “junctional tissue”—and each responded differently to the same exciting currents, especially those of short duration. Moreover, for any one of these excitable substances, the optimal stimulus differed in different animals. In attaching the term “substances” to these characteristic differences in the excitability of different tissues, Lucas was probably influenced by the theory of “receptive substances” then being developed by John Langley, professor of physiology at Cambridge, Certainly Langley had helped to convince Lucas that the region between nerve and muscle contains something whose physiological properties differ markedly from those of ordinary nerve and muscle.8 That Lucas supposed this something to be a special kind of tissue, rather than a chemical substance, reminds us forcefully that his work preceded the general adoption of the hunoral (or chemical) theory of nervous transmission.
In any case, the concept of “excitable substances” was for Lucas only one of the implications to be drawn from the existence of fundamental differences in the excitability of different tissues. From another point of view, even these very basic differences could be referred to a common principle, for they represented “a point of obvious interest in the evolutionary history of the excitable tissues.”9 According to Adrian, Lucas developed his interest in the evolution of function while studying zoology at Cambridge and, under the impulse of this interest, “gave a course of lectures in the Zoology department on the comparative physiology of muscle.”10 An even more direct expression of this interest is provided in a two-part paper of 1909 on the evolution of function. In this paper Lucas both deplores and seeks to explain the lack of interaction between evolutionary concepts and physiological research. His explanation is historical, tracing the separation between function and evolution to the famous debate in the 1820’s between Georges Cuvier and Geoffroy Saint-Hilaire. Under Geoffroy’s influence, Lucas argues, physiology was excluded from the problem of animal classification and thereby lost the impetus to become a properly comparative and evolutionary science. In advocating a reunion of physiology and evolutionary concepts, Lucas emphasized that “the primary problem of comparative physiology— a problem whose investigation is wholly necessary for the understanding of the evolutionary process... [is] the question to what extent and along what lines the functional capabilities of animal cells have been changed in the course of evolution.”11 Lucas’ premature death prevents us from knowing to what extent, and with what success, he might have pursued this line of work. As it is, his work stands as a monument of clarity and precision in that era of neurophysiology which preceded the adoption of the chemical theory of nervous transmission and the development of important new methods of amplifying bioelectrical activity. 12
1. About 1925, Lucas’ microscope, an unorthodox arrangement with differential screws, was placed among the exhibits of the South Kensington Science Museum. See Col. F. C. Temple, “At Rugby”, in Keith Lucas, p. 48, n. 1.
2. See H. H. Turner, “Ancestry,” ibid., p. 12.
3. “On the Relation Between the Electric Disturbance in Muscle and the Propagation of the Excited State,” in Journal of Physiology, 39 (1909), 207-227, esp. 208-210.
4.The Conduction of the Nerrous Impulse, pp. 68-73.
5. “Croonian Lecture,” p. 516.
6. “On Summation of Propagated Disturbances in the Claw of Astacus, and on the Double Neuro-Muscular System of the Adductor,” in Journal of Physiology, 51 (1917), 1-35.
7. See E. D. Adrian, “Cambridge 1904-1914,” in Keith Lucas, pp. 105-106.
8.The Conduction of the Nervous Impulse, pp. 67-68.
9. “Croonian Lecture,” p. 517.
10. Adrian, Keith Lucas, p. 105.
11. “The Evolution of Animal Function,” pt. II, p. 325.
12. On the importance of the new amplifying methods, see J[oseph] B[arcroft], “Keith Lucas,” in Nature, 134 (1934), 475.
I. Original Works. A complete bibliography of Lucas’ publications is given in Keith Lucas (see below), pp. 129-131. His posthumous monograph, The Conduction of the Ncrrous Impulse (London, 1917), was based on the Page May memorial lectures, delivered by Lucas at University College, London, in 1914. Revised for publication by E. D. Adrian, the monograph emphasizes the work of Lucas and his students, especially Adrian. In addition to this monograph, Lucas published 32 papers, nearly all of them in Journal of Physiology. For insight into his general approach and guiding principles, the most valuable are “The Evolution of Animal Function,” in Science Progress, pt. 1, no. 1 1 (1909), 472–483; pt. 11, no. 14 (1909), 321–331; and “Croonian Lecture: The Process of Excitation in Nerve and Muscle,” in Proceedings of the Royal Society,85B (1912), 495–524.
Lucas established the “all or none” law for skeletal muscle in “On the Gradation of Activity in a Skeletal Muscle Fibre,” in Journal of Physiology,33 (1905), 125–137; and “The ’All–or–None’ Contraction of the Amphibian Skeletal Muscle Fibre,” ibid., 38 (1909), 113–133. Other important papers by Lucas include those cited in notes 3 and 6; “The Excitable Substances of Amphibian Muscle,” in Journal of Physiology,36 (1907), 113–135; “The Temperature Coefficient of the Rate of Conduction in Nerve,” ibid., 37 (1908), 112–121; “On the Transference of the Propagated Disturbance From Nerve to Muscle With Special Reference to the Apparent Inhibition Described by Wedensky”, ibid., 43 (1911), 46-90 ; and “On the Summation of Propagated Disturbances in Nerve and Muscle,” ibid., 44 (1912), 68-124, written with E. D. Adrian.
II. Secondary Literature. The basic source for Lucas’ life is Keith Lucas (Cambridge, 1934), a series of sketches by men who knew Lucas well at various stages of his life. Written in 1916, when Walter Fletcher planned to write a memoir of Lucas, these sketches were finally published in their original form after Fletcher’s death. The sketches, and their authors, are as follows : H. H. Turner, “Ancestry” and “Earliest Years” ; Col. F. C. Temple, “At Rugby” Sir Walter Fletcher, “Undergraduate Days” and “Return to Cambridge” G. L. Hodgkin, “New Zealand” ; E. D. Adrian, “Cambridge 1904-1914” and Col. Mervyn O’Gorman, Bertram Hopkinson, and Maj. R. H. Mayo, “Wartime.” For an evaluation of Lucas as scientist, the chapters by Fletcher and Adrian are the most valuable.
For other sketches of Lucas’ life and work, see Horace Darwin and W. M. Bayliss, “Keith Lucas,” in Proceedings of the Royal Society, 90B (1917-1919), xxxi-xlii ; C[harles] S. S[herrington], “Keith Lucas,” in Dictionary of National Biography, supp. 1912-1921, p. 347 ; and John Langley, “Keith Lucas,” in Nature, 98 (1916), 109. For a very brief attempt to place Lucas’ work in historical perspective, with excerpts from his writings, see Edwin Clarke and C. D. O’Malley, The Hurman Brain and Spinal Cord: A Historical Study Illustrated by Writings From Antiquity to the Twentieth Century (Berkeley, 1968), pp. 218-221.
Gerald L. Geison