Vitalism is the now-discredited hypothesis that only living tissue, by virtue of possessing some "life-force," can produce organic compounds. Among its greatest advocates was Berzelius and, more recently, Bergson. Although Wöhler's synthesis of urea posed a serious empirical challenge to this point of view, it was only with the production of an organic substance, acetic acid, from its elements, by the German chemist Adolph Wilhelm Hermann Kolbe in 1845, that belief in vitalism was finally undermined.