(b. Brunswick, Germany, 2 September 1873; d. Pontresina, Switzerland, 25 July 1927)
Magnus was raised in a rich intellectual environment that embraced medicine, the law, and the humanities. His father practiced law in Brunswick, one grandfather was director of the Hamburg library, and the other was a physician. Magnus’ initial career interests lay in literature and philosophy. Partly through the advice of a family friend, the chemist Richard Meyer, however, he decided to study medicine at Heidelberg. There his career was molded by such influential figures as Willy Kühne, the noted physiologist, and the chemist David Meyer; and he began lasting friendships with certain scientific figures, notably Jakob von Uexküll and Otto Cohnheim. In 1895, while still a medical student, Magnus showed his aptitude for original research in a paper presented at the Third International Congress of Physiology at Bern, dealing with a method for measuring blood pressure in an exposed artery. The further development and application of this technique was the subject of his doctoral thesis in 1898.
Magnus began his career in pharmacology, working first at Heidelberg as an assistant in 1898 and as a Privatdozent in 1900. At Heidelberg he continued investigations that he had begun as an undergraduate on the cardiovascular, renal, and intestinal systems, earning rapid and wide recognition for studies on the action of arsenic and of various pharmacologic agents in the gut, and on water balance in tissues.
In 1904 Magnus devised a now-standard technique in pharmacology for studying the responses of isolated muscle, suspending a loop of small intestine in warmed, oxygenated Locke-Ringer solution. Using the method to make a series of important observations on responses to alkaloid agents, on local reflexes, and on automatic rhythmicity, he discovered that the degree of stretching of the intestinal muscle determines the direction of stimulus conduction.
During his years at Heidelberg, Magnus made a series of visits to British research laboratories, beginning with a trip to work with E. A. Sharpey-Schafer at Edinburgh in 1900. Together they discovered the diuretic action of pituitary gland extracts. In 1905 Magnus went Cambridge to learn surgical techniques for studying the autonomic nervous system from J. N. Langley, in order to continue his analysis of the relations between drug effects and nerve supply on the motility of intestinal muscle. The critical event that shaped the direction of his future neurophysiological investigations was his 1908 visit to Charles Sherrington at Liverpool.
Magnus accepted the professorship of pharmacology at the University of Utrecht in 1908, since there was then no vacant chair of pharmacology in Germany. During the next two decades his Utrecht group issued over 300 papers. The major corpus of Magnus’ work, and that for which he is best known, deals with the reflex control of posture. He also continued an active program of teaching and research in pure pharmacology.
Magnus was noted as a teacher and speaker as well as a gifted investigator. The lectures he delivered in his pharmacology courses, published as Pharmakologisches Praktikum, reported on the latest research projects of his institute, particularly the pharmacology of the pulmonary circulation, and the isolation and identification of choline as the hormonal regulatory agent for intestinal muscle. The wide range of his interests, embracing history, philosophy, and botany, was demonstrated by a lecture series on Goethe as a natural scientist (1906).
Although present concepts of the body’ equilibratory system are principally an outgrowth of Magnus’ work, data on the role of the cerebellum in maintaining body attitudes had been accumulating slowly since experiments by François Magendie in the 1820’s. Toward the end of the nineteenth century, David Ferrier’s experiments on various animals led him to the idea of a cerebellovestibular connection, a germinal idea that helped launch the modern period of study of equilibratory functions.
The postural reflex studies by Magnus and his colleagues, particularly A. de Kleijn, were a model of the integrative neurophysiology being pioneered by Sherrington at Liverpool and Oxford. While Magnus was working with him in 1908, one of Sherrington’ research interests was muscle tonus in mammals. Analyzing the reflex pathways involved in the production and maintenance of tonus, Sherrington concluded that tone in mammals is due to postural reflexes, as P. Q. Brondgeest in 1860 had shown it to be for frogs and rabbits. In 1910, drawing in part upon his observations of the “reflex figures” assumed by decerebrate animals, Sherrington published a detailed analysis of the reflex control of stepping and standing.
Under Sherrington’s guidance, Magnus in 1908 had begun experiments on mammalian muscle tonus, drawing in part upon Uexküll’s work on the changing responses of the muscle bands in a marine worm to varying tensions. Encouraged by Sherrington to continue the investigation of equilibratory phenomena, Magnus and Kleijn published the first of their classic papers on the influence of head position on the tonus of extremities in 1912. The depth of Magnus’ subsequent studies is suggested by the fact that one observation he and Sherrington had made independently—that rotation of the head in the decerebrate animal changes the muscle tonus of the limbs—generated a series of eighty-two publications by the Utrecht group.
The investigations of Magnus and his colleagues showed the many automatic reflex actions through which an animal assumes and maintains body postures, by sequences of coordinated reflexes and by the types of static “figures” demonstrated so clearly in the decerebrate preparation. Their fundamental analysis of equilibratory functions involved, first, a detailed study of tonic neck muscle and labyrinth reflexes and of labyrinth righting reflexes, by which body postures change in response to various stimuli as an animal constantly adjusts to its needs and environment. They then restudied the various reflexes they had cataloged after ablating the cerebellum, cerebrum, brain stem, or cervical spinal cord, in order to localize the brain and spinal cord areas controlling posture.
Their study of the labyrinth organs, which was inspired in part by the work of J. R. Ewald, led Magnus and Kleijn to a fundamental analysis of the responses of the ear’s vestibular organs to natural stimuli. In one classic experiment they differentiated between the functions of the otolith organs and the semicircular canals by centrifuging anesthetized guinea pigs at high speed. The otolith membranes were detached by the procedure; but the canals, ampullae, and cristae remained intact. Magnus and Kleijn then found that reflexes resulting from static posture were abolished in the absence of the otolith mechanism but that the animals retained all the labyrinth reactions produced by rectilinear acceleration.
Through such studies Magnus’ research group founded our knowledge of the complex integrative reflex system by which the brain stem and cervical spinal cord control musculature. Step by step they documented the functions of the vestibular apparatus, tonic neck and labyrinth reflexes, and other postural and righting reflexes and their neural pathways and control mechanisms. Magnus summarized the work of his Utrecht laboratory, and surveyed the work of others in his field, in Die Körperstellung (1924), a monograph justly cited as a classic work in reflex physiology. At the time of his sudden death in 1927, at age fifty-three, he and Kleijn were under consideration for the Nobel Prize in physiology or medicine for their fundamental contributions to neurophysiology.
I. Original Works. Magnus’ writings include Goethe als Naturforscher (Leipzig, 1906); “Welche Teile des Zentralnervensystems müssen fü das Zustandekommen der tonischen Hals-und Labyrinthereflexe auf die Körpermuskulatur vorhanden sein,” in Plflügers Archiv für die gesamte Physiologie des Menschen und der Tiere, 159 (1914), 224–249; Körperstellung experimentell-physiologische Untersuchungen über die einzelnen beider Körperstellung in Tätigkeit tretenden Reflexe,über ihr Zusammenwirken und ihre Störungen (Berlin, 1924); and “Animal Posture,” in Proceedings of the Royal Society, 98B (1925), 339–353, the Croonian lecture.
II. Secondary Literature. See H. H. Dale, “In Memoriam Rudolf Magnus (1873–1927),” in Stanford University Publications, Medical Sciences, 2 (1930), 241–247; J. F. Fulton, “Rudolf Magnus 1873–1927,” in Boston Medical and Surgical Journal, 197 (1927–1928), 323–324; and I. N. W. Olninck, “Rudolf Magnus,” in E. W. Haymaker, ed., The Founders of Neurology (Springfield, Ill., 1953), pp. 149–152.
Judith P. Swazey