MULLER, JOHANNES PETER

born July 14, 1801, Koblenz, Fr. [of the Consulate] died April 28, 1858, Berlin German physiologist and comparative anatomist, one of the great natural philosophers of the 19th century. His major work was Handbuch der Physiologie des Menschen fr Vorlesungen, 2 vol. (183440; Elements of Physiology). Mller was the son of a shoemaker. In 1819 he entered the University of Bonn, where the faculty of medicine was permeated with a naturalistic romanticism, which the young Mller eagerly espoused. His thesis ber die Bewegungsgesetze der Tiere (1822; On the Laws of Movement of Animals) was written in the naturalistic manner. He continued his studies at the University of Berlin, where he came under the influence of the sober, precise anatomist Karl Rudolphi and thereby freed himself from naturalistic speculation. In 1824 he was granted a lectureship in physiology and comparative anatomy at the University of Bonn. In his inaugural lecture, Physiology, a science in need of a philosophical view of nature, he outlined his approach to science, maintaining that the physiologist must combine empirically established facts with philosophical thinking. Two years later he was appointed associate professor, and in 1830 he became a full professor. In the meantime, his voluminous Zur vergleichenden Physiologie des Gesichtssinnes . . . (1826; Comparative Physiology of the Visual Sense . . . ) brought Mller to the attention of scholars by its wealth of new material on human and animal vision; he included the results of analyses of human expressions and research on the compound eyes of insects and crustaceans. His most important achievement, however, was the discovery that each of the sense organs responds to different kinds of stimuli in its own particular way or, as Mller wrote, with its own specific energy. The phenomena of the external world are perceived, therefore, only by the changes they produce in sensory systems. His findings had an impact even on the theory of knowledge. Mller's monograph On Imaginary Apparitions was also published in 1826. According to this theory the eye as a sensory system not only reacts to external optical stimuli but can also be excited by internal stimuli generated by the imagination. Thus, persons who report seeing religious visions, ghosts, or phantoms may actually be experiencing optical sensations and believe them to be of external origin, even though they do not in fact have an adequate external stimulus. Because of his research Mller became the best known figure on the Bonn faculty of medicine. Maintaining an almost incredible level of output, he examined many problems in physiology, evolution, and comparative anatomy. He studied the passage of impulses from afferent nerves (going to the brain and spinal cord) to efferent nerves (going away from the same centres), further elucidating the concept of reflex action. By careful experiments on live frogs, he confirmed the law named after Charles Bell and Franois Magendie, according to which the anterior roots of the nerves originating from the spinal cord are motor and the posterior roots are sensory. He investigated the nervous system of lower animal species, the intricate structure of glands, and the process of secretion. When tracing the development of the genitalia, he discovered what is now known as the Mllerian duct, which forms the female internal sexual organs. He contributed to knowledge of the composition of the blood and lymph, the process of coagulation, the structure of lymph hearts of frogs, the formation of images on the retina of the eye, and the propagation of sound in the middle ear. In 1833 Mller was called to Berlin to succeed Rudolphi. In his new post he again carefully explored many problems concerning animal function and structure. His early years in Berlin were devoted mainly to physiology. His Handbuch der Physiologie des Menschen fr Vorlesungen was recognized throughout the world and established a beneficial interchange between physiology and hospital practice in Germany. It stimulated further basic research and became a starting point for the mechanistic concept of life processes, which was widely accepted in the second half of the 19th century. Inspired by the vast Berlin anatomical collection, Mller became interested again in pathology. After the demonstration by his assistant, Theodor Schwann, that the cell was the basic unit of structure in the animal body, he concentrated on the cellular structure of tumours with the aid of a microscope. In 1838 his work ber den feineren Bau und die Formen der krankhaften Geschwlste (On the Nature and Structural Characteristics of Cancer, and of Those Morbid Growths Which May Be Confounded with It) began to establish pathological histology as an independent branch of science. Mller also distinguished himself as a teacher. His students included the renowned physiologist and physicist Hermann Helmholtz and the cellular pathologist Rudolf Virchow. Beginning in 1840 Mller increasingly focused his research on comparative anatomy and zoology, in so doing becoming one of the most respected scholars in these subjects. He was a master at collecting and classifying specimens; he devised an improved classification of fish and, based on an ingenious analysis of vocal organs, did the same for singing birds. For several years he concentrated on the lowest forms of marine vertebrates, the Cyclostomata and Chondrichthyes. He painstakingly described the structures and complex development of members of various classes of the invertebrate phylum Echinodermata. His last research activities were concerned with the marine protozoans Radiolaria and Foraminifera. In 1827, 1840, and 1848, Mller suffered periods of depression that rendered him incapable of working for months on end. They may perhaps be attributedas his periods of explosive productivityto a manic-depressive disposition. It may also be regarded as the cause of his death in 1858. Some scholars have assumed that he died by his own hand. Johannes Steudel Additional reading Ulrich Ebecke, Johannes Mller, der grosse rheinische Physiologe (1951), includes a new edition of Mller's work ber die phantastischen Gesichtserscheinungen. See also Gottfried Koller, Das Leben des Biologen Johannes Mller 18011858 (1958), a biography that does justice to Mller's zoological achievements; Johannes Steudel, Le Physiologiste Johannes Mller (1963), a brief biography; and Walther Riese and George E. Arrington, Jr., The History of Johannes Mueller's Doctrine of the Specific Energies of the Senses: Original and Later Versions, Bull. Hist. Med., 37:179183 (1963).