UNDOUBTEDLY for Marx the most important application of his theory was in the analysis of the character of economic crises. At the time serious study of this phenomenon was still in its infancy. There had been a few fertile but unsystematized observations by Sismondi as to the disrupting effects of competition and of production for a wide market; there had been the classic discussion between Malthus and Ricardo as to whether gluts and depression could be due to deficiency of consumption ; in Germany Rodbertus had developed his under-consumption theory of crises.