Hering, Karl Ewald Konstantin

(b. Alt-Gersdorf, Germany, 5 August 1834; d. Leipzig, Germany, 26 January 1918)

physiology, psychology.

Ewald Hering was a strong and important personality among the German physiologists of his time. In his first publications he mastered the difficult problem of visual space perception and was able to challenge the great master in that field, Hermann von Helmholtz, proposing alternative views that emphasized the physiological rather than the physical aspects of sensation. As the main representative of the phenomenological tradition, an acute observer, and a shrewd critic, Hering exerted a great influence on contemporary sense physiology and on the evolution of modern psychology. Gestalt psychology in particular owes much to him.

The son of a village parson, Hering studied medicine at Leipzig under E. H. Weber, G. T. Fechner, Otto Funke, and the zoologist J. V. Carus, with whom he went to Sicily in the winter of 1858–1859 to study the genital and excretory organs of Alciopida, a genus of ringed worms, which were the subject of his doctoral dissertation. From 1860 to 1865 he practiced medicine and worked as an assistant in the polyclinic directed by Ernst Wagner, and from 1862 he was also lecturer in physiology. In 1861–1864 he published a five-part study on visual space perception in which he favored the nativistic theory, arguing that each point of the retina is endowed with three local signs: one for height, one for breadth, and one for depth. Thus he found himself in opposition to Helmholtz and other empiricists, who believed that location and space forms are learned and arise with continued experience. In this treatise Hering was concerned mainly with binocular vision, the identical points of the two retinas, and the horopter.

In 1865 Hering was called to Vienna to succeed Carl Ludwig in the chair of physiology at the Military Medico-Surgical Academy, the Josephinum. There he continued his studies of binocular vision but turned also to other subjects. Most important was his discovery, with Josef Breuer, of reflex reactions originating in the lungs and mediated by the fibers of the vagus nerve: inflation of the lungs, eliciting expiration, and deflation, stimulating inspiration. These reflexes, especially the former, have an important role in the regulation of respiratory movements, which are greatly altered after the vagi are sectioned (1868). Hering and Breuer spoke of self-regulation of respiration, and the reflexes were one of the first feedback mechanisms discovered in the physiological regulations. At that time Hering also investigated the functional structure of the liver and the mechanism of the respiratory variations of blood pressure (Hering waves) due to variations of the tonus of medullary centers (1869).

In 1870 the Josephinum was abolished and Hering was appointed to succeed Jan Purkyně at the University of Prague, where he remained for twenty-five years. He devoted most of his energy to research in sensory physiology, mainly of vision, and to more general conceptions, reported in his addresses, “Über das Gedächtnis als eine allgemeine Funktion der organisierten Materie” (1870), “Über die speciuschen Energieen der Nervensystem” (1884), and most important, “Zur Theorie der Vorgänge in der lebendigen Substanz” (1888). For Hering the two basic processes of life, assimilation and dissimilation, played a general role; and their mutual relation was at the base of both color vision and the function of temperature-sensing organs, as well as of the electrical phenomena in nerve and muscle, which he studied in his laboratory. In his color-vision theory Hering put forward (against the Young-Helmholtz theory of three visual substances and three colors) a three-substance, six-color theory supposing a red-green substance, a yellow-blue one, and a white-black one, each of which could be excited to respond in either dissimilation (catabolism) or assimilation (anabolism), corresponding to the sensations of white, yellow, and red or black, blue, and green, respectively. Strikingly different from the trichromatic theory—besides these three opposing pairs—was the postulate of an independent mechanism for the sensing of white and black. Thus Hering’s theory avoided the criticism raised against the Young-Helmholtz theory for neglecting the uniqueness of the six principal colors (red, yellow, green, blue, white, and black) and accounted for such subjective visual phenomena as contrasts (simultaneous and successive) and mixing of colors. He drew attention to the physiological aspects of sensory functions, in contrast with physical processes, emphasizing the distinction between the stimulus (physical) and the response (physiological).

In 1895 Hering succeeded Carl Ludwig at Leipzig and remained there for the rest of his life, studying color phenomena and devising new experiments and instruments for their demonstration in support of his theory, which had been criticized for several apparent contradictions. He died before publication of the final part of his last work, begun in 1905.

Hering had the power to generalize and penetrate to basic problems, but his approach could not lead to a significant advance and his theory had little heuristic value. Moreover, many of the suppositions on which he based his theories were incorrect. The progress of knowledge required a new approach and new methods, both electrophysiological and biochemical. A new era of nerve and sensory physiology began in the early 1920’s, leading to great advances in knowledge of the elementary response of the nerve fiber and nerve cell, of the organization of the neural pathways, of synaptic transmission, and of the processing of the signals at different stages of their course. Hering’s idea of a double response of different receptors and, accordingly, of two kinds of signals conveyed by each nerve fiber, proved to be wrong. On the other hand, differential sensitivity of receptors and phenomena of summation and inhibition were brought to light. The three photosensitive substances postulated by the Young-Helmholtz theory were identified and their reversible photochemical reaction elucidated. Thus, at the level of peripheral receptors, the eye functions as Hering’s opponents had postulated, but some of the points Hering raised against the trichromatic theory (such as yellow as the fourth basic color) can be accounted for at higher levels of the extremely complicated afferent pathway. The existence of the “on” and “off” elements in the retina recalls the two opposite effects in Hering’s “substances.” Different mechanisms in the retina are assumed for the sensing of luminosity (dominators) and of color (modulators), as in Hering’s theory. Yet Ewald Hering, who was for almost fifty years one of the two leading men in the physiology of vision, is hardly mentioned in recent textbooks.

BIBLIOGRAPHY

I Original Works. A bibliography of Hering’s writings up to 1907 can he found in Charles Richet’s Dictionnairede physiologie, II (Paris, 1909), 554. Among his publications are Beiträge zur Physiologic. Zur Lehre vom Orisitnne der Netzhaut, 5 pts. (Leipzig, 1861–1864); Die Lehre vom binokularen Sehen (Leipzig, 1868); Zur Lehre vom Lichtsinn (Vienna, 1872); “Der Raumsinn und die Bewegung des Auges,” in L. Hermann, ed., Handbuch der Physiologie, III, pt. 1 (Leipzig, 1879), 343–601; Zur Theorie der Nerventätigkeit (Leipzig), 1899); and Grundzüge der Lehre vom Lichtsinn, 4 vols. (Berlin, 1905–1920), translated by Leo M. Hurwich and Dorothea Jameson as Outlines of a Theory of the Light Sense (Cambridge, Mass., 1964). Extracts from Beiträge... and Zur Lehre vom Lichtsinn in English translation have been published in R. J. Herrnstein and E. G. Boring, eds., A Source Book in the History of Psychology (Cambridge, Mass.. 1965). Hering’s addresses are in Fünf Reden von Ewald Hering, H. E. Hering, ed. (Leipzig. 1921).

II. Secondary Literature, Obituaries include S. Garten, “Ewald Hering zum Gedächtnis,” in Pflügers Archie für die gesamte Physiologie..., 170 (1918), 501–522; C. Hess, “Ewald Hering,” in Archiv für Augenheilkunde, 83 (1918), 89–97, and Naturwissenschaften. 6 (1918), 305–308; and F. B. Hofmann, “Ewald Hering,” in Münchener medizinische Wochenschrift, 65 , pt. 1 (1918), 539–542. See also A. von Tschermak, “Ewald Hering. Zum 100. Geburtstag” ibid., 81 (1934), 1230–1233. Hering’s works and views in relation to modern physiology are discussed in L. M. Hurwich, “Hering and the Scientific Establishment,” in American Psychologist, 24 (1969), 497–514. There are many references to Hering in E. G. Boring, A History of Experimental Psychology (New York, 1929; 2nd ed., 1950); and his Sensation and Perception in the History of Experimental Psychology (New York, 1942).