A comprehensive study of German materialism in the second half of the nineteenth century is long overdue. Among contemporary historians the mere passing references to Karl Vogt, Jacob Moleschott, and Ludwig Buchner as materialists and popularizers of science are hardly sufficient, for few individuals influenced public opinion in nineteenth-century Germany more than these men. Buchner, for example, revealed his awareness of the historical significance of his Kraft und Stoff in comments made in 1872, just seventeen years after its original appearance. A philosophical book which has undergone twelve big German editions in the short span of seventeen years, which further has been issued in non-German countries and languages about fifteen to sixteen times in the same period, and whose appearance (although its author was entirely unknown up to then) has called forth an almost unprecedented storm in the press, . . . such a book can be nothing ordinary; the world-calling it enjoys at present must be justified through its wholly special characteristics or by the merits of its form and content. ' Vogt, Moleschott and Buchner explicitly held that their materialism was founded on natural science. But other materialists of the nineteenth century also laid claim to the scientific character of their own thought. It is likely that Marx and Engels would have permitted their brand of materialism to have been called scientific, provided, of course, that 'scientific' was understood in their dialectical meaning of the term. Socialism, Engels maintained, had become a science with Marx.