…at 3:16 AM.  Büchner was something like the Richard Dawkins of his day, a proseltyzer, not for Darwin, but for physiology and materialism.  His Kraft und Stoff was the best-selling book in Europe in the second half of the 19th-century after the Bible.  A young Einstein reportedly read it and was inspired by it.  Büchner is also the "old doctor" Nietzsche derides in Beyond Good and Evil, although as usual with Nietzsche it was a matter of the narcissism of small differences:   Nietzsche was deeply influenced by the German materialists, but rejected wholly their eliminativism about psychological phenomena.