The neuroscience of Helmholtz and the theories of Johannes Müller. Part 1: Nerve cell structure, vitalism, and the nerve impulse.

Hermann Helmholtz made monumental contributions to the neural sciences in the second half of the nineteenth century. Among his earliest achievements were experiments that challenged vitalism, microscopic studies on the structure of the nerve cell and its processes, and the first reasonable estimates of the speed of nerve transmission based on physiological experiments. In this, the first of a two-part article, we review Helmholtz's early contributions in biographical context and with reference to Johannes Müller's own thoughts. We reveal how Johannes Müller, considered by many to be the greatest physiologist of the first half of the nineteenth century, helped to launch and shape Helmholtz's career. We also show that Helmholtz was only willing to accept some of his mentor's theories, even though he had great admiration for Müller. The point will be made that Helmholtz owed a great debt to Müller, but even from his student days in Berlin he was an independent thinker with his own agenda, and never his strict disciple.