Gaskell, Walter Holbrook
Gaskell, Walter Holbrook
(b. Naples, Italy. 1 November 1847; d. Great Shelford, near Cambridge, England, 7 September 1914)
Gaskell was descended from a prominent Unitarian family in the north of England. He was the third child and younger twin son of John Dakin Gaskell, barrister of the Middle Temple, who practiced his profession only briefly before retiring to private life. His mother, Anne Gaskell, was his father’s second cousin.
Gaskell attended the Highgate School, London, and in October 1865 matriculated at Trinity College, Cambridge, where he was elected to a scholarship in 1868. He graduated B.A. in 1869 as twenty-sixth wrangler in the Cambridge mathematical tripos. With the intention of making a career in medicine, he remained at Cambridge to study, science and quickly fell under the influence, of Michael Foster, who came to Cambridge in 1870 as Trinity College praelector in physiology. Although Gaskell completed clinical training at University College Hospital, London (1872–1874), and received an M.D. from Cambridge in 1878, he never practiced medicine. At Foster’s urging, he devoted himself instead to physiological research, beginning in 1874, when he went to Leipzig to work under Carl Ludwig in the famous physiological institute there.
Soon after returning to England in the summer of 1875, Gaskell married Catherine Sharpe Parker, daughter of R. A. Parker, a solicitor, and settled near Cambridge, where he continued his research. His income apparently came chiefly from private sources. From 1883 until his death he was university lecturer in physiology. In 1889 he was elected to fellowship of Trinity Hall, Cambridge, where he also served as praelector in natural science. The Royal Society named Gaskell as Croonian lecturer in 1881, a fellow in 1882, gold medalist in 1889, and Baly medalist in 1895. He received honorary doctorates from the universities of Edinburgh and McGill and served on the Royal Commission on Vivisection (1906–1912). He was survived by two of his four daughters and by his son, John Foster Gaskell.
Gaskell’s career in research can be conveniently divided into four periods, corresponding approximately into the following dates and dominant interests: (1) 1874–1879, vasomotor action; (2) 1879–1883, the problem of the heartbeat; (3) 1883–1887, the involuntary nervous system; and (4) 1888–1914, the origin of the vertebrates. Despite the apparent diversity of these interests, there is a remarkable internal unity to Gaskell’s work, one investigation leading logically into the next. Much of his work and approach demonstrate clearly the powerful influence exerted upon him by Michael Foster.
In 1874, at the suggestion and with the help of Carl Ludwig, Gaskell followed up work done earlier in the Leipzig laboratory on circulation in skeletal muscle. He focused on the quadriceps extensor muscles of the dog and recorded with a kymograph the effects of nerve action on the rate of blood flow from a severed vein. Upon returning to Cambridge in 1875, Gaskell continued to work on the same general problem but chose to work on the mylohyoid muscle of the frog. In the simpler tissues of the frog, where the arterial diameters could be measured directly with a micrometer eyepiece, Gaskell was able to clarify greatly a number of issues left doubtful in his work on the dog. His most striking result was that stimulation of the mylohyoid nerve in the frog invariably produced a steady dilatation of the arteries in the mylohyoid muscle. According to John Langley, “this was the most decisive instance known at the time of [vasodilator] action in a purely muscular structure.”1.
In 1878, after Rudolf Heidenhain had disputed several of his results and conclusions,2 Gaskell reinvestigated the effects of nerve action on circulation in the muscle arteries of the dog. He claimed, that his new work supported the results he had reached with the frog.” In the dog as in the frog,” he wrote, “the vasomotor system for the muscles consists essentially of vaso-dilator fibres. . . .”3.
By about 1880 Gaskell had turned from vasomotor action to the problem of the heartbeat. The shift was not abrupt, however, and emerged fully only after a transitional study on the tonicity of the heart and arteries. Gaskell found that acidic and alkaline solutions produced the same effects on cardiac muscle as on the smooth muscle of arterial walls. Both in the heart and in the arteries, acidic solutions induced muscular relaxation, while alkaline solutions induced muscular contraction. Gaskell used this result to propose a new mechanism for vasodilatation. He wished to replace the then standard View that dilatation depended on the action of ganglionic nerve centers. He suggested instead that the determining factor was the chemical condition, of the lymph fluid which surrounded the muscle walls of the arteries. When a muscle was inactive, this fluid was alkaline and would therefore contribute to vasoconstriction. But during muscular contraction, the surrounding lymph fluid became acidic, so that the muscle walls of the arteries would then relax and the end result would be vasodilatation. This hypothesis was supported by Gaskell’s observation that dilatation occurred in a muscle artery whenever that muscle contracted.
But Gaskell was already concerned with a problem of much wider scope than vasodilatation alone. He presented his work on tonicity as a contribution to the general problem of rhythmical motion, two important examples of which were vasomotor action and the heartbeat. He was obviously skeptical toward the prevailing idea that all forms of physiological rhythmicity depended on the action of nerve cells or ganglia. In this he followed the example of his mentor Foster, who was convinced that vasomotor action and the heartbeat were analogous and that both depended not on ganglia but on the inherent properties of relatively undifferentiated muscle tissue. It was directly to the problem of the heartbeat that Gaskell next turned, and it was Foster who most decisively influenced his approach.
In the Croonian lecture for 1881, dealing with the frog heart, Gaskell presented an important new method for studying heart action (later named the “suspension method”) and insisted that cardiac inhibition depended less on nerve or ganglionic mechanisms than on the inherent properties of the cardiac musculature. The role of the vagus nerve in inhibition was reduced to that of being the “trophic” (anabolic) nerve of the cardiac muscle. Yet in the same lecture Gaskell produced impressive evidence against Foster’s myogenic theory of rhythmicity and advocated instead the neurogenic view that discontinuous ganglionic discharges are responsible for the rhythmicity of the normal heartbeat. The background to this defection was exceedingly complex, but it derived from an initial assumption (which Foster himself accepted) that ganglionic impulses—whatever their role in rhythmicity—are somehow involved in coordinating the normal sequence of the vertebrate heartbeat.
Within three years Gaskell had resolved the problem of the heartbeat in favor of the myogenic theory far more persuasively than Foster had ever thought possible. Experiments on the tortoise heart were the source of Gaskell’s new conception of the heartbeat, presented at length in a classic monograph of 1883. He explained that he had turned from the frog heart to the tortoise out of conviction that “the study of the evolution of function.… is the true method by which the complex problems of the mammalian heart will receive their final solution.”4 What he had found was physiological and histologico-evolutionary evidence that both the rhythmicity and the sequential character of the heartbeat could be explained without reference to ganglionic action.
Gaskell insisted first that a small strip of muscle cut from the tortoise’s ventricle—and therefore clearly isolated from nerve structures—could nonetheless develop rhythmic pulsations at a rate equal to that of the normal heartbeat. Since, moreover, such a strip could continue to beat rhythmically for at least thirty hours after all stimulation had been discontinued, Gaskell argued that rhythmicity could arise automatically in cardiac muscle, that it was in fact “due to some quality inherent in the muscle itself.”5 This conclusion was in keeping with the somewhat similar and earlier work of Foster and Wilhelm Theodor Engelmann.
Far more novel and important was Gaskell’s evidence that the sequence, as well as the rhythm, of the heartbeat could be referred solely to the properties of cardiac muscle. As the heartbeat is followed in its course through all the cavities of the heart, distinct pauses are observed at the junctions between the separate cavities. And since it is precisely here, in these junction, that ganglia are most abundant, it had been assumed even by Foster that ganglia must play some important role in producing the pauses and thus in regulating the sequences. Gaskell was now able to offer an alternative explanation. That he was able to do so depended crucially on his decision to study the tortoise heart instead of the frog heart.
In the tortoise the cardiac nerves and their accompanying ganglia lie outside the heart itself and are relatively easy to remove. Gaskell found that their removal in no way affected the sequence of the heartbeat. He then focused on the cardiac tissue itself and sliced through the auricle until it consisted of two parts (As and Av) joined at an upper ligature by a narrow bridge of auricular tissue. When this bridge was made quite thin, Gaskell could See a wave of contraction pass up As and then, after a pause, down Av to the junction between auricle and ventricle, where another brief pause preceded ventricular contraction. Gaskell concluded that “the ventricle contracts in due sequence with the auricle because a wave of contraction passes along the auricular muscle and induces a ventricular contraction when it reaches the auriculo-ventricular groove.” 6 This conclusion was confirmed by continuing to narrow the tissue bridge until it seemed that another section would sever it completely. At that point, the waves of contraction passing up As were “blocked” at the bridge and were unable to pass down A,v. The sequence between auricular and ventricular beats was thereby destroyed.
Gaskell then showed that the three muscular cavities of the heart (sinus, auricle, and ventricle) were connected by two narrow rings of relatively undifferentiated muscle tissue through which the waves of contraction could be transmitted from one cavity to the next. To explain why there are normally pauses at the junctions between successive cavities, Gaskell began by positing an antagonism between the capacities for rhythmicity and for rapid conduction of contractile waves. He suggested that the capacity for rhythmicity was greatest in undeveloped muscle tissue, while the capacity for rapid conduction increased as muscle tissue underwent development and specialization. Since the least developed (least striated) muscle fibers are found in the sinus, it must possess the greatest capacity for rhythmicity, and so the heartbeat naturally begins there. The more highly developed auricular and ventricular fibers, on the other hand, are especially adapted to conduct the wave of contraction rapidly; but the muscle rings connecting the heart cavities consist of relatively embryonic tissue, and the contractile wave therefore passes more slowly through them. This, rather than ganglionic action, explained the pauses observed at the sinoauricular and auriculoventricular junctions.
Before the discovery of cardiac ganglia and vagus inhibition in the 1840’s, the heartbeat had generally been viewed as a simple peristaltic wave of contraction passing from one end of the heart to the other. In a distinctly evolutionary context, Gaskell now advocated a return to this view and repeatedly insisted that in every really important respect—in its rhythmicity and in its sequence—the vertebrate heartbeat depends in the first place not on nerve influences but on the properties of the cardiac musculature.
Gaskell’s work of 1883 did not immediately convince everyone, and the myogenic-neurogenic debate continued for some time, especially in Germany.7. The task of extending the myogenic theory to the mammalian heart proved more difficult than Gaskell had perhaps expected it to be, and he did not himself contribute to this extension. By about 1910 the extension had been accomplished—chiefly through the work of A. F. S. Kent and Wilhelm His, Jr., on the atrioventricular bundle in mammalian hearts, and through the work of Arthur Keith and Martin Flack on the mammalian cardiac pacemaker. With the possible exception of His, all of these workers depended fundamentally on Gaskell’s work. Before long, and especially through the British clinical cardiologists James Mackenzie, Thomas Lewis, and Arthur Cushny, Gaskell’s myogenic theory and his concept of heart block became incorporated into the pathology, pharmacology, and therapeutics of the heart. His conclusions have formed the basis of concepts of heart action ever since.
Although Gaskell’s interest in the heart did not end abruptly in 1883, it soon became bound up with and eventually submerged in a general study of the involuntary nervous system. The starting point for this work was Gaskell’s discovery that cold-blooded animals possess augmentor, as well as inhibitory, cardiac nerves. That mammals possess augmentor or accelerator cardiac nerves had been known for some time, and their existence in cold-blooded animals had been supposed by some. Particularly to explain the bewildering range and variety of the effects produced by vagus stimulation in the frog, the hypothesis had been advanced that the vertebrate vagus was not a simple nerve, composed solely of inhibitory fibers, but a compound nerve containing augmentor fibers as well. Decisive evidence for this hypothesis was lacking, however, and Gaskell himself specifically rejected it both in his Croonian lecture of 1881 on the frog heart and in his monograph of 1883 on the tortoise heart.
But after the summer of 1884, when Gaskell succeeded in distinguishing both inhibitory and augmentor cardiac fibers in the crocodile, he considered it probable that both sets of fibers were also present in other cold-blooded animals. In an elegant paper of 1884 he confirmed this view in the all-important case of the frog. Tracing the frog’s vagus from its origin in the medulla oblongata, he found it to consist of two branches which then joined in a large ganglion outside the cranial cavity to form a single nerve trunk which continued toward the heart. It was this trunk that was ordinarily used to examine the effects of vagus stimulation. Gaskell focused instead on the two preganglionic branches and found that stimulation of one branch resulted always in purely augmentor effects, while stimulation of the other resulted always in purely inhibitory effects. The so-called vagus, Gaskell concluded, was in fact the “vagosympathetic,” consisting of a mixture of purely inhibitory and purely augmentor fibers which could be clearly distinguished from one another prior to their merger in the large extracranial ganglion.
Gaskell seems to have been greatly impressed by this discovery. With the help of a Cambridge colleague, the morphologist Hans Gadow, he extended his investigation of the cardiac nerves to as many different species of cold-blooded animals as possible. They found that these nerves were distributed in basically similar ways in all the species they examined. In all cold-blooded vertebrates, as in mammals, there existed two sets of cardiac nerves performing separate, indeed opposing, functions. A flood of ideas now burst forth almost simultaneously from Gaskell, as functional and morphological considerations became intertwined and mutually reinforcing.
For one thing, Gaskell noticed while studying the cardiac nerves in a tortoise that the functional distinction between vagus and augmentor fibers was correlated with a striking morphological distinction: although both kinds of cardiac fibers originated from the spinal cord as medullated fibers, the accelerator fibers emerged from the sympathetic chain without medullas, while the vagus fibers retained their medullas throughout their course. By early 1885 Gaskell had confirmed this rule in a wide variety of vertebrate and mammalian species. Then, in 1886, he showed that vagus stimulation produced in the tortoise’s heart an electrical variation opposite in sign to that produced by stimulating the accelerator nerves. In thus providing demonstrable evidence that the two kinds of cardiac nerves did indeed perform opposing functions, Gaskell contributed to the rapidly developing field of cardiac electrophysiology, a field from which the electrocardiogram was soon to emerge.
Already, though, Gaskell was occupied with ideas of far broader significance. For him, as for Foster, the heart was just one example of an involuntary muscle; and he was confident that his results on cardiac innervation could be extended to the smooth muscles of the arterial, alimentary, and grandular system. Gaskell had long believed (again with Foster) that the inhibitory action of vagus fibers was a constructive, beneficial, or anabolic action. He therefore supposed that the action of the opposing augmentor fibers was destructive or catabolic, like that of a motor nerve, leading to exhaustion of muscle activity. When generalized to the involuntary system as a whole, this concept led to the notion that every involuntary muscle was innervated by two nerves of opposite action, one anabolic and the other catabolic. By further analogy with the cardiac nerves, Gaskell expected these anabolic and catabolic nerves to be histologically distinguishable from one another, particularly on the basis of their medullation after passing the sympathetic chain. It was under the inspiration of these leading themes that Gaskell undertook a full-scale, systematic investigation of the involuntary nervous system.
A classic paper of 1886 contains the major results of Gaskell’s work on the involuntary system. He found that the visceral or involuntary nerves arise from the central nervous system in three distinct groups. There is a cervicocranial outflow, a thoracic outflow, and a sacral outflow. In all three groups the visceral fibers leave the central nervous system as peculiarly fine, white, medullated fibers. But the fibers issuing from the thoracic region lose their medullas in the sympathetic ganglia and pass to the viscera as nonmedullated fibers. The fibers issuing from the cervicocranial and from the sacral regions retain their medullas as they pass to the periphery. In action the fibers issuing from the thoracic region appeared to be antagonistic to both the cervicocranial and the sacral outflows. In broad outline, this plan is still accepted, although significant modifications in detail and in terminology were soon made, especially through the work of another of Gaskell’s Cambridge colleagues, John Langley, and especially in light of the neuron theory.
From the point of view of basic physiological thought, perhaps the most important result of Gaskell’s work on the involuntary system was his discovery that the connection between the central nervous system and the chain of sympathetic ganglia is unidirectional, with the peculiarly small white fibers (the “white rami”) supplying the sole connection. Earlier in the century it had been thought that a system of gray rami returned from the sympathetic chain to the central nervous system, creating an interplay between two essentially independent nervous systems. Bichat had christened these two systems the “organic” (central) and the “vegetative” (sympathetic). Although this mode of thinking about the nervous system had since come under criticism, no broad generalization had taken its place until Gaskell clarified the relationship between the sympathetic chain and the central nervous system. He showed that the gray rami are in fact peripheral nerve fibers which supply the blood vessels of the spinal cord and its membranes and which issue not from the sympathetic chain but from the central nervous system, as do the white rami. There is, then, no real separation into “organic” and “vegetative” nervous systems,8 and, wrote Gaskell in 1908, “no give and take between two independent nervous systems . . . as had been taught formerly, but only one nervous system . . . as had been taught formely but only one nervous system, the cerebro-spinal,”9 So fundamentally did Gaskell alter the prevailing conceptions of the involuntary system that Walter Langdon-Brown could insist that “to read an account of this system before Gaskell is like reading an account of the circulation before Harvey.”10 After their elaboration and modification by Langley and others, Gaskell’s conclusions found clinical application, not only in the interpretation of referred pain by James Mackenzie and Henry Head but, more generally, in the work of Walter B. Cannon.
After 1888 Gaskell devoted all of his research to the problem of the origin of the vertebrates. This interest may at first seem remote from his earlier work, but it evolved logically out of his work on the involuntary nervous system. For what had especially struck Gaskell then was that the involuntary nerves arise not only from three distinct regions of the spinal cord but also from clearly defined segments within these regions. Deeply impressed by the similarity between this vertebrate arrangement and the central nervous system of the segmented invertbrates, he gradually elaborated the extraordinary theory that the vertebrates are descended from an extinct arthropod stock of which the king crab is the nearest living representative. He agreed that earlier attempts to trace the vertebrates to the segmented invertebrates had failed, but only because they all began with the assumption that the transition required a reversal of dorsal and ventral surfaces. This supposition was thought necessary in order to explain how it happens that in vertebrates the nervous system is dorsal to the alimentary canal, while in invertebrates the arrangement is reversed.
To explain this fact, Gaskell proposed the revolutionary hypothesis that the vertebrates arose by the enclosure of the ancestral arthropod gut by the growing central nervous system, and the formation of a new alimentary canal ventral to the nervous system. According to this conception, the vertebrate infundibulum Corresponds to the arthropod esophagus, the ventricles in the vertebrate brain to the arthropod Stomatch, and the vertebrate spinal canal to the arthropod alimentary canal. Perhaps the most controversial element in the theory was Gaskell’s notion that in the transition from invertebrate to vertebrate, a new alimentary canal was formed by epidermal invagination. This notion was in direct violation of two settled morphological tenets: (1) that the alimentary canal is the one system which endures throughout evolutionary change, and (2) that in all cases the alimentary canal arises from the hypoblastic germ layer, and never from the epiblastic layer, as Gaskell proposed. Against the first of these tenets Gaskell argued that it was folly to insist upon the importance and durability of the alimentary canal in evolution when the central nervous system, especially the brain, was so obviously the engine of upward progress. In making this point, he coined the aphorism “The race is not to the swift, nor to the strong, but to the wise.”11 Against the second tenet Gaskell argued that morphologists applied the germ-layer theory in a circular manner, deducing the layer from which a structure arose merely from its ultimate morphological destination.
Gaskell developed his remarkable theory in a series of papers from 1888 to 1906, and then—convinced that his ideas were not being seriously considered— gathered the evidence together in a full-length book, The Origin of Vertebrates (1908). Despite some minor support and a few pleas for open-mindedness, it too met a chilly reception from most morphologists, with one opponent accusing Gaskell of “diabolical ingenuity,”12 The direction of research since has gone against Gaskell’s brave attempt to trace the vertebrates to an arthropod ancestor. While they would probably acknowledge that Gaskell’s work contains interesting and suggestive material—on the endocrine System, for example—most morphologists today consider the vertebrates of common origin with the echinoderms.
A large, generous man of open and genial disposition, Gaskell was both criticized and admired for his inclination to bold generalization. His final years were clouded by his wife’s debilitating illness and by a feeling that his deeply loved theory of the origin of vertebrates was not receiving a fair hearing. Even at Cambridge, where Gaskell lectured on the topic until his death, his audience decreased over the years until, near the end, the poignant scene is drawn of Gaskell closing his course by shaking hands with a lone remaining auditor.13.
2. R. Heidenhain et al., “Beiträge zur Kenntnisse der Gefässinnervation, I, II. Uber did Innervation der Muskelgefässe,” in Pflügers Archiv für die gesammte Physiologie des Menschen und der Thiere, 16 (1878), 1”46.
3. “Further Researches on Vasomotor Nerves, “p. 281.
4. “On the Innervation of the Heart,” p.48.
6.Ibid., p. 64.
7. See, e.g., E. Cyon, “Myogen oder Neurogen?” in PflügersArchiv für gesammte Physiologie des Menschen und der Thiere, 88 (1902), 222–295.
8. See Donal Sheehan, “Discovery of the Autonomic Nervous System?,” in Archives of Neurology and Psychiatry, 35 (1936), 1081–1115.
9.Origin of Vetebrates, p.2.
10. Walter Langdon-Brown, “W. H. Gaskell and the Cambridge Medical School,” in Proceedings of the Royal Society of Medicine, 33 (1939), section of the history of medicine, 1–12, see 6.
11.Origin of Vertebrates, p. 19.
12. See the lively discussion following Gaskell’s paper, “Origin of Vertebrates,” in Proceedings of the Linnean Society of London, sess. 122 (1910), 9–15. The discussion (pp. 15–50) includes both supporters and opponents of Gaskell;’s approach and ideas. For an anonymous and largely unfavorable review of Gaskell’s book, see Nature, 80 (1909), 301–303. Gaskell’s response is ibid., pp. 428–429. Even more critical of Gaskell’s work was Bashford Dean, in Science, n.s 29 (1909), 816–818.
13. This paragraph is based in part upon a private communication from Lord Edgar Douglas Adrian, O.M., Nobel laureate in physiology or medicine, who was working at Cambridge during Gaskell’s final years.
I. Original Works. The Royal Society Catalogue of Scientific Papers, IX, 967; XII, 262; XV, 220–221, lists thirty-four papers by Gaskell up to 1900. The most important of these are “On the Innervation of the Heart, with Especial Reference to the Heart of the Tortoise,” of the Tortoise, “in Journal Of Physiology, 4 (1883), 43–127; and “On the Structure, Distribution and Function of the Nerves Which Innervate the Visceral and Vascular Systems,” ibid., 7 (1886), 1–80.
Other Papers discussed in the text are “On the Changes of the Blood-Stream in Muscles Through Stimulation of Their Nerves,” in Journal of Anatomy and Physiology, 11 (1877), 360–402; “On the Vasomotor Nerves of Striated Muscles,” ibid., 720–753; “Further Researches on the Vaso-Motor Nerves of Ordinary Muscles,” in Journal of Physiology, 1 (1878), 262–302; “On the Tonicity of the Heart and Arteries,” in Proceedings of the Royal Society, 30 (1880), 225–227, and in Journal of Physiology, 3 (1882), 48–75; “The Croonian Lecture: On the Rhythm of the Heart of the Frog, and on the Nature of the Action of the Vagus Nerve , “in Philosophical Transactions of the Royal Society, 173 (1882), 993–1033; “On the Action of the Sympathetic Nerves Upon the Heart of the Frog,” in Journal of Physiology, 5 (1884), xiii–xv; “On the Augmentor (Accelerator) Nerves of the Heart of Cold-Blooded Animals,” ibid., 46–48; “On the Anatomy of the Cardiac Nerves in Certain Cold-Blooded Invertebrates,” ibid., 362–372, written with Hans Gadow; “On the Relationship Between the Structure and Function of the Nerves Which Innervate the Visceral and Vascular Systems,” ibid., 6 (1885), iv–x; and “On the Action of Muscarin Upon the Heart, and on the Electrical Changes in the Non-Beating Cardiac Muscle Brought About by Stimulation of the Inhibitory and Augmentory Nerves, “ibid., 8 (1887), 404–415 See also “On the Relations Between the Function, Structure, Origin, and Distribution of the Nerve-Fibres Which Compose the Spinal and Cranial Nerves,” in Transactions of the Medico-Chirurgical Society, 71 (1888), 363–376.
Gaskell provides some historical background and an excellent account of his mature views on the heartbeat in “The Contraction of Cardiac Muscle,” in E. A. Schafer, ed., Textbook of Physiology, II (Edinburgh ), 169–227. Of uneven quality is his posthumous monograph, The Involuntary Nervous System, J. F. Gaskell, ed. (London, 1916).
The Origin of Vertebrates (London–New York, 1908), pp. 6–7, gives a complete bibliography of Gaskell’s papers on that topic up to 1906. The only other paper known to the author, cited in n. 12 above, provides a clear and succinct account of Gaskell’s theory.
There is apparently no central repository for Gaskell’s letters and MSS, and few seem to have survived. The library of the Cambridge Physiological Laboratory possesses Gaskell’s reprint collection, deposited in about 100 file boxes and fully indexed. A very few letters can be found in the sharpey-Schafer Papers at the Wellcome Institute of the History of Medicine, London.
II. Secondary Literature. This article is based chiefly on Gerald L. Geison, “Michael Foster and the Rise of the Cambridge School of Physiology, 1870–1900,” unpub. Ph.D. diss. (Yale, 1970), pp. 382–475, 493–513, passim For a clear analysis of Gaskell’s major work on the heart, see also Richard D. French, “Darwin and the Physiologists, or the Medusa and Modern Cardiology,” in Journal of the History of Biology, 3 (1970), 253–274, see 267–273.
Of the available accounts of Gaskell’s life and work, the most valuable is that by John Langley (see n. 1 above). Also useful are Walter Langdon-Brown (see n. 10 above) and Henry Head, in Dictionary of National Biography, 1912–1921, pp. 207–209. A critical reading should be given to F. H. Garrison and F. H. pike, in Science, n.s 40 (1914) 802–807.
Gerald L. Geison
"Gaskell, Walter Holbrook." Complete Dictionary of Scientific Biography. . Encyclopedia.com. (September 24, 2018). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/gaskell-walter-holbrook
"Gaskell, Walter Holbrook." Complete Dictionary of Scientific Biography. . Retrieved September 24, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/gaskell-walter-holbrook