Johannes Peter Müller - continued...

It has been claimed that Müller’s depressive episodes in 1827, 1840, 1848, 1852, and 1855 were the results of an inherited manic-depressive condition (Steudel 1963, p. 26). In every case, however, his depression had a clear external cause. In 1827 Müller was exhausted from a full teaching load, extensive research, and the publication of two major books. The doctor who assessed his health for the Prussian government, his teacher Phillipp von Walther, found that he was suffering from “hypochondria”, a term then commonly used for depression (Haberling 1924, p. 79). Within a year, Müller was able to resume his research, but he subsequently avoided self-experimentation.

Between 1828 and 1830, Müller conducted extensive comparative studies of the endocrine and reproductive systems, publishing De glandularum secernetium and Bildungsgeschichte der Genitalien in 1830. He demonstrated that glands, not blood vessels, secrete substances that control bodily functions, and he identified the blood vessels responsible for male erections. He then made one of his greatest contributions to physiology, the experimental demonstration of British physician Charles Bell’s (1774-1842) and French physiologist François Magendie’s (1783-1855) hypothesis that the dorsal roots of spinal nerves (those initially heading upward along the back) carry mainly sensory fibers, whereas the ventral ones (those initially heading downward toward the belly) carry mainly motor fibers. Bell had proposed the idea in 1811 but had provided no experimental evidence; Magendie had conducted experiments in 1822, but his live dogs were in such distress that his results were questionable. In 1831 Müller thought of repeating Magendie’s experiments in frogs, hardier animals in which the spinal cord could be more readily exposed (Steudel 1963, p. 570). He not only confirmed Magendie’s findings; he encouraged aspiring physiologists to repeat his experiments, publicizing a new system in which young experimenters could study the functions of muscles and nerves.