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Müller, Johannes Peter

system animals sensory external

[mü ler] (1801–58) German physiologist: made wide-ranging discoveries, contributing also to anatomy, zoology and neurology.

The Müller family were Moselle wine-growers, but Johannes’s father was a prosperous shoemaker in Coblenz. The boy entered the newly founded university at Bonn in 1819, and his combination of talent and great ambition soon attracted attention. In 1826 he became a professor there. When a post became vacant in Berlin, he took the remarkable step of proposing himself for the job, and got it. He was a frequent victim of depression and his death was probably due to suicide, but this is uncertain because he had forbidden an autopsy.

When well, he was intensely productive as a physiologist. His first work covered problems of locomotion in animals. Then, in 1820, he attacked the Bonn prize question: does the fetus breathe in the womb? Experiments on a ewe showed that the blood-colour entering and leaving the fetus indicated that it did respire. (Afterwards Müller was antagonistic to vivisection on warm-blooded animals, although he was a great user of frogs.) His later work was wide-ranging; he studied electrophysiology, the sensory system of the eye, the glandular system, the human embryo and the nervous system. He showed the value of microscopy in pathology, developing procedures now used in daily clinical work, especially on tumours. He worked on classification in zoology, especially on marine animals. He proposed the law of specific nerve energies in 1840. This states that each sensory system will respond to a stimulus (whether this is mechanical, chemical, thermal, or electrical) in the same way, specific to itself. Thus the eye always responds with a sensation of light, however it is stimulated; the ear with a sensation of sound, and so on. Man does not perceive the external world directly, but only the effects on his sensory systems. ‘In intercourse with the external world we continually sense ourselves’ – an important statement for philosophy.

His many pupils include , J Henle (1809–85) . He is widely regarded as the greatest of all physiologists.

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