(b. Milton, Massachusetts, 14 May 1882; d. Milton, 27 March 1965)
Alexander Forbes was the youngest of seven children of a well-educated, well-to-do Unitarian Boston family. His father was William Hathaway Forbes, and his mother was Edith Emerson, the daughter of Ralph Waldo Emerson. Forbes graduated from Milton Academy in 1899 and then attended Harvard (B.A., 1904; M.A., 1905; M.D., 1910). He studied with Charles S. Sherrington at Liverpool (1911-1912) and with Keith Lucas at Cambridge (briefly in 1912). He returned to Harvard Medical School, where he remained until 1948. After 1948 he was professor emeritus and continued his research in the Harvard biological laboratories.
In 1910 Forbes married Charlotte Irving Grinell of New York. The couple had four children. Forbes lived his entire life in Milton, with summers at the Forbes family estate on Naushon Island (Massachusetts) or cruising the North Atlantic. His health was superb and he excelled at yachting, fancy skating, skiing, rock climbing, and canoeing; and for many years he piloted his private airplane. His only physical affliction was a moderate hearing loss, dating from about 1908.
Forbes’s primary scientific interest was neurophysiology, but equally strong was his love of the outdoors, the woods, rivers, and hills of New England, particularly the coast of New England and Labrador. He made contributions to navigation and, at the suggestion of Sir Wilfred Grenfell, he mapped the coast of Labrador by aerial photography, using the technique of oblique photogrammetry. For this he was awarded (1938) the Charles P. Daly Gold Medal of the American Geographic Society. He served with the U.S. Navy in both World Wars; in the first he installed radio compasses, and in the second he mapped an aerial route across northern Greenland.
Forbes was a scientific amateur in the best sense of the word. As a man of independent means, he engaged in his laboratory experiments, outdoor sports, yachting, and explorations because he loved them. He did little formal teaching. Not only did he defray much of the expense of his own activities, but for many years he anonymously supported others in the department of physiology.
Forbes’s greatest contributions to neurophysiology came early in his career. He was a technical innovator. About 1912 he installed what was probably the first string galvanometer in the New England area for the accurate measurement of the time relations of spinalcord reflexes. Later, using his experience with radio compasses, he developed a capacity-coupled electronic amplifier for greater sensitivity, and in 1920 he became the first to report the use of electronic amplification in a physiological experiment.
The paper by Forbes (with Alan Gregg, 1915) on the flexion reflex of the decerebrate cat, timed by means of the string galvanometer, was a landmark in neurophysiology. His most influential paper was a review entitled “The Interpretation of Spinal Reflexes in Terms of Present Knowledge of Nerve Conduction” (1922). The properties of the spinal reflexes were chiefly those described by Sherrington and his pupils (including Forbes himself). The knowledge of nerve conduction was developed chiefly by Lucas and E. D. Adrian. Forbes visited Adrian in 1921.
Forbes’s great contribution was to unite these two schools of thought and experimentation and thereby establish the form and direction of a major segment of American neurophysiology. In his paper he provided a coherent, consistent interpretation of the major features of reflex activity. Actually, many of the interpretations were erroneous, as Forbes readily admitted, but his ingenious suggestions inspired experiments and theorizing for at least twenty years. Through his influence on Norbert Wiener, Arturo Rosenblueth, and others, he contributed significantly to the development of the science of cybernetics.
Forbes himself considered his single most important scientific contribution to be the final establishment of the all-or-none law of nerve conduction. The experiments, planned by Forbes and carried out by his collaborators, showed that the strength of a nerve impulse is not diminished after it has passed through a local region of partial narcosis where the impulse was weakened but not extinguished. The impulse is a chain reaction, with local contribution of energy in amounts depending on the local condition of the nerve fiber, not on the previous history of the impulse elsewhere. The idea had been formulated previously by Adrian, but with inadequate experimental support. Forbes’s experiment was performed independently and simultaneously, with the same result, by Genichi Kato and his associates in Japan.
Forbes’s laboratory became a center for the training of both American and European neurophysiologists. Forbes participated in the early use of microelectrodes (large ones by modern standards) and fostered studies of the auditory system and the early development of electroencephalography in the United States. His studies of electrical responses of the brain under Nembutal narcosis paved the way for far-reaching later developments.
Among the most important of Forbes’s writings are the following: “Electrical Studies in Mammalian Reflexes. I. The Flexion Reflex,” in American Journal of Physiology, 37 (1915), 118-176, written with A. Gregg; “Amplification of Action Currents With the Electron Tube in Recording With the String Galvanometer,” ibid., 52 (1920), 409-471, written with C. Thacher; “The All-or-Nothing Response of Sensory Nerve Fibres,” in Journal of Physiology, 56 (1922), 301-330, written with E. D. Adrian; “The Interpretation of Spinal Reflexes in Terms of Present Knowledge of Nerve Conduction,” in Physiological Reviews, 2 (1922), 361-414; “The Nature of the Delay in the Response to the Second of Two Stimuli in Nerve and in the Nerve-Muscle Preparation,” in American Journal of Physiology, 66 (1923), 553-617, written with L. H. Ray and F. R. Griffith, Jr.; “Studies of the Nerve Impulse. II. The Question of Decrement,” ibid., 76 (1926), 448-471, written with H. Davis, D. Brunswick, and A. McH. Hopkins; “Tonus in Skeletal Muscle in Relation to Sympathetic Innervation,” in Archives of Neurology and Psychiatry, 22 (1929), 247-264; “The Mechanism of Reaction,” in C. Murchison, ed., The Foundations of Experimental Psychology (Worcester, Mass., 1929), pp. 128-168; “The Conflict Between Excitatory and Inhibitory Effects in a Spinal Center,” in American Journal of Physiology, 95 (1930), 142-173, written with H. Davis and E. Lambert; “Chronaxie,” in Physiological Reviews, 16 (1936), 407-441, written with H. Davis; “The Effects of Anesthetics on Action Potentials in the Cerebral Cortex of the Cat,” in American Journal of Physiology, 116 (1936), 577-596, written with A. J. Derbyshire, B. Rempel, and E. F. Lambert; “Activity of Isocortex and Hippocampus: Electrical Studies With Micro-electrodes,” in Journal of Neurophysiology, 3 (1940), 74-105, written with B. Renshaw and B. R. Morison; and “Electroretinogram of Fresh-water Turtle: Quantitative Responses to Color Shift,” ibid., 21 (1958), 247-262, written with H. W. Deane, M. Neyland, and M. S. Congaware.