In the later or creative stages we enter the domain of chemistry, for it is the chemist alone who possesses the power of reducing a substance to its constituent atoms and from them producing substances entirely new. But the chemist has been slow to realize his unique power and the world has been still slower to utilize his invaluable services. Until recently indeed the leaders of chemical science expressly disclaimed what should have been their proudest boast. The French chemist Lavoisier in 1793 defined chemistry as "the science of analysis." The German chemist Gerhardt in 1844 said: "I have demonstrated that the chemist works in opposition to living nature, that he burns, destroys, analyzes, that the vital force alone operates by synthesis, that it reconstructs the edifice torn down by the chemical forces." It is quite true that chemists up to the middle of the last century were so absorbed in the destructive side of their science that they were blind to the constructive side of it. In this respect they were less prescient than their contemned predecessors, the alchemists, who, foolish and pretentious as they were, aspired at least to the formation of something new. It was, I think, the French chemist Berthelot who first clearly perceived the double aspect of chemistry, for he defined it as "the science of analysis _and synthesis_," of taking apart and of putting together. The motto of chemistry, as of all the empirical sciences, is _savoir c'est pouvoir_, to know in order to do. This is the pragmatic test of all useful knowledge. Berthelot goes on to say: Chemistry creates its object. This creative faculty, comparable to that of art itself, distinguishes it essentially from the natural and historical sciences.... These sciences do not control their object. Thus they are too often condemned to an eternal impotence in the search for truth of which they must content themselves with possessing some few and often uncertain fragments. On the contrary, the experimental sciences have the power to realize their conjectures.... What they dream of that they can manifest in actuality.... Chemistry possesses this creative faculty to a more eminent degree than the other sciences because it penetrates more profoundly and attains even to the natural elements of existences. Since Berthelot's time, that is, within the last fifty years, chemistry has won its chief triumphs in the field of synthesis. Organic chemistry, that is, the chemistry of the carbon compounds, so called because it was formerly assumed, as Gerhardt says, that they could only be formed by "vital force" of organized plants and animals, has taken a development far overshadowing inorganic chemistry, or the chemistry of mineral substances. Chemists have prepared or know how to prepare hundreds of thousands of such "organic compounds," few of which occur in the natural world.