| German physiologist and comparative anatomist,
one of the great natural philosophers of the 19th century.
His major work was Handbuch der Physiologie des Menschen für
Vorlesungen, 2 vol. (1834–40; Elements of Physiology).
Müller 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
Müller eagerly espoused. His thesis Über 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 Müller 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 Müller 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.
Müller'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 Müller 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 François 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 Müllerian 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 Müller 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 für 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, Müller
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 Über den feineren Bau und die Formen
der krankhaften Geschwülste (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. Müller
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 Müller 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, Müller suffered periods of
depression that rendered him incapable of working for months
on end. They may perhaps be attributed—as his periods
of explosive productivity—to 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.
Additional reading
Ulrich Ebecke, Johannes Müller, der grosse rheinische
Physiologe (1951), includes a new edition of Müller's
work Über die phantastischen Gesichtserscheinungen.
See also Gottfried Koller, Das Leben des Biologen Johannes
Müller 1801–1858 (1958), a biography that does
justice to Müller's zoological achievements; Johannes
Steudel, Le Physiologiste Johannes Müller (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., 37:179–183 (1963).
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