Cannon, Walter B.
Cannon, Walter B.
Walter Bradford Cannon (1871−1945) was a most productive physiologist who exerted an important influence on the development of medical investigation in the United States. He was born in Prairie du Chien, Wisconsin, and was fond of tracing his own interest in scientific exploration to the fact that his forebears came from the French Canadian and Scotch–Irish pioneers who explored and settled this continent.
After graduating from the public schools of St. Paul, Minnesota, he put himself through Harvard College and Harvard Medical School, from which he graduated in 1900. The rest of his life was spent as a member of the faculty at Harvard, where he held the George Higginson professorship of physiology from 1906 until he became professor emeritus in 1942. During World War i, he did important work on surgical shock, first with Sir William Maddock Bayliss at University College, London, and later in the surgical research laboratory at Dijon. Briefer absences from Harvard enabled him to serve as visiting professor at the Sorbonne in 1929, in Peiping in 1935, and as visiting investigator at the Institute de Cardiologia in Mexico City in 1944.
Cannon’s investigations into the functioning of living organisms began while he was an undergraduate, rapidly rose to a level of international distinction during his first year in medical school, and continued virtually without interruption until his death. Although the total body of his contribution appears to range over a number of fields, it all grew by a series of closely connected steps from his studies as a medical student on the motions of the digestive tract. For these, he employed the newly discovered X rays to reveal the course of swallowed food rendered radiopaque by mixing with the salts of heavy metals. Unhappily, little was then known about the dangers of radiation, and later in life he suffered severely from a degeneration of the tissues of his hands and arms that required an almost endless series of plastic operations. It is not improbable that the early exposure to X rays also contributed to the malignant lymphoma that was originally diagnosed in 1929 and caused him uninterrupted discomfort until his death nearly two decades later.
The early work on gastrointestinal motility laid the practical and theoretical groundwork for modern understanding of the digestive process and for the use of the barium meal as a diagnostic tool. More importantly, perhaps, it gave to Cannon a lifelong interest in the way the autonomic nervous system helps to maintain the constancy of the internal environment.
Initially, during his work on digestion, he was sometimes frustrated by a sudden cessation of all gastrointestinal movement in the animal under observation. Soon, however, he noticed that these interruptions could be correlated with the onset of emotional tension. Even simple pain, as well as the more complex states of fear and anger, seemed to lead to a prompt cessation of the digestive process. By successive elimination of different parts of the autonomic nervous system, he was able to show quite clearly that the inhibition of digestive activity is carried largely by the splanchnic nerves, which constitute the sympathetic supply to a large portion of the abdominal organs including the adrenal glands. Conversely, the parasympathetic nerves, especially the vagus, were shown to bring about an increase in motility and, as Pavlov had demonstrated a little earlier, an increase in gastric secretion.
From here, Cannon went on to elaborate the hypothesis that the sympathetic nervous system and the adrenal glands together form a more or less unitary arrangement for adjusting the body to certain emergency situations. Conversely, the parasympathetic includes a number of more discrete elements, each of which is primarily concerned with one or another part of the body’s normal household economy—the digestion of food, the elimination of wastes, and even the protection of the eye against excessive light. His experiments and thoughts on these matters were brought together in the book Bodily Changes in Pain, Hunger, Fear and Rage (1915).
The idea that an endocrine gland, such as the adrenal, could be turned on and off according to circumstances encountered bitter opposition. In the course of an elaborate set of experiments designed to settle this controversy, which at times became unpleasantly warm both for participants and onlookers, Cannon devised the denervated heart as a sensitive indicator of adrenal secretion in the otherwise intact, unanesthetized animal. Three important lines of investigation grew out of this experimental preparation. First, Cannon used it to demonstrate that the sympathetic nerves produce their effects through the mediation of an adrenalin-like substance, which he called sympathin, that circulates in the blood after release. Second, he, and later his students, went on to show that many organs and even individual nerve cells become more susceptible to chemical influences after degeneration of their normal nerve supply. Finally, the same series of experiments led to the preparation of animals without any sympathetic nervous system at all. A large number of observations on such animals showed that they were entirely capable of leading satisfactory lives in the sheltered circumstances of the laboratory. What was lacking was the ability to adjust to abnormal or threatening circumstances. Extremes of temperature, vigorous exercise, hemorrhage, and a number of other stresses quickly resulted in serious dislocations of the general state of the animal and especially in the composition of its body fluids.
Building on these observations and on Claude Bernard’s famous dictum—La fixité du milieu intérieur est la condition de la vie libre—Cannon went on to make his most important theoretical contribution. Coining the term “homeostasis” to identify the tendency of all complex organisms to maintain a steady internal state, he detailed in a series of reviews and monographs the various mechanisms by which such constancy is achieved. His own experiments were, of course, primarily concerned with the role of the autonomic nervous system in determining the course of the assimilative, circulatory, respiratory, and excretory reactions involved. Certain subsidiary features of the theory, such as the previously mentioned distinction between the roles of parasympathetic and sympathetic divisions of the autonomic nervous system, have been considerably modified by further study; but Cannon’s over-all view has greatly influenced clinical practice as well as theory building in both physiology and psychology.
Cannon’s influence on the behavioral and social sciences may be clearly seen in current discussions of the nature of emotion and its physiological expression. Most important, perhaps, is the firm experimental foundation he provided for what is now referred to as “psychosomatic medicine.”
His early work on hunger called attention to the important role played by contractions of the stomach in the elaboration of the subjective sensation, a concept that was taken up and greatly elaborated by his contemporary, Anton J. Carlson (1916). Nevertheless, the bulk of his work, as he was at considerable pains to show, argued against the James–Lange conception that the subjective aspects of emotion result directly from sensations arising in organs and muscles involved in overt emotional responses. Later work has not yet completely clarified the nature of hunger, let alone that of more complex emotional awareness. However, it is certain that hunger involves factors other than mere awareness of gastric contraction, and theories of emotion cannot be categorized as either James–Lange or some obvious alternative. Nevertheless, Cannon’s work is still important for having shown us how to frame parts of these questions in clear experimental terms.
Cannon’s attempt to extend the theory of homeostasis into the social and economic sphere, undertaken most fully in the last few chapters of his book The Wisdom of the Body (1932), is not generally regarded as anything more than a stimulating but limited analogy.
Cannon’s influence on students and colleagues was very great. Fortunately, much of what he meant to them has been made readily available in his short but profound autobiography, The Way of an Investigator (1945), written a few years before his death. Here he put together with his usual economy a distillation of what he had found important, interesting, and diverting—both about his work as an investigator and about life in general. He was never particularly concerned with metaphysics; and his philosophy of science was primarily a matter of day-to-day common sense. Rather than defining knowledge, Cannon’s writings concentrate on its acquisition. His description of “serendipity” added a new word to the vocabulary of scientific discourse and has no doubt alerted the senses of innumerable investigators to the importance of the chance observation (Merton  1957, pp. 103–105).
Cannon’s outlook was basically that of the enlightened nineteenth-century liberal, and his attitude toward life as a whole was similar to his approach to laboratory investigation—simple, direct, devoted, and optimistic.
His liberalism was clearly evident in the interest he took in the Soviet Union during his visit there in connection with the International Physiological Congress of 1935. Although fully and painfully aware of the many restrictions on political liberty and basic human rights, he concerned himself mainly with the efforts being made to improve the health, education, and general welfare of the Soviet people. A little later, his personal friendship with a fellow physiologist, Juan Negrín, who was head of the Spanish government at the outbreak of the Falangist revolution, caused him to take an active interest in providing medical aid to the Loyalist armies and to the numerous refugees.
His laboratory attracted students and postdoctoral fellows from all over the world and thus contributed markedly to the increased international stature of American medical science during the 1920s and 1930s. For many years, Cannon helped guide the development of the American Physiological Society, serving on the council from 1905 to 1912 and as president from 1914 through 1916. As a charter member of the National Research Council’s Committee on Physiology, set up in 1916, he was an active participant in most of the council’s activities from then until his death and was one of the first Harvard scientists to help shape national scientific policy.
Although Cannon never sought the kind of intimacy with students and junior colleagues that became common in a later period, he was held in affectionate regard by all of them. He would go to great lengths to guide graduate students and fellows through the early difficulties of a research career, and all of them will recall the pains he took to teach them how to write succinct and informative scientific papers. Almost daily he presided over a kind of scientific salon at the departmental tea table. It was here that most of his associates learned to share not only his scientific experiences and outlook but also his warm and quietly humorous approach to life in general.
Robert S. Morison
(1915) 1953 Bodily Changes in Pain, Hunger, Fear and Rage: An Account of Recent Researches Into the Function of Emotional Excitement. 2d ed. Boston: Branford.
(1932) 1963 The Wisdom of the Body. Rev. & enl. ed. New York: Norton.
1945 The Way of an Investigator: A Scientist’s Experiences in Medical Research. New York: Norton.
Bernard, Claude (1878) 1930 Leçons sur les phénomènes de la vie communs aux animaux et aux végétaux. Pages 307−309 in John F. Fulton (editor), Selected Readings in the History of Physiology. Springfield, Ill.: Thomas.
Carlson, Anton J. 1916 The Control of Hunger in Health and Disease. Univ. of Chicago Press.
Lindsley, Donald B. 1951 Emotion. Pages 473−516 in S. S. Stevens (editor), Handbook of Experimental Psychology. New York: Wiley.
Merton, Robert K. (1949) 1957 Social Theory and Social Structure. Rev. & enl. ed. Glencoe, Ill.: Free Press.
Stellar, Eliot 1960 Drive and Motivation. Volume 3, pages 1501−1527 in American Physiological Society, Handbook of Physiology. Baltimore: Williams & Wilkins.
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