Chapter 1 -- Introduction -- Until well into the first quarter of the nineteenth century all chemical substances were classified under two grand divisions, inorganic and organic. The inorganic or mineral compounds, whose chemistry was fairly well understood at the time, were obtained from lifeless materials under definite conditions which could be controlled in the laboratory. On the other hand, organic compounds were the products of living organisms, plant or animal. They were believed to be elaborated under the influence of the "vital force," i.e., the same force which was responsible for the growth of plant or animal. Hence one could no more hope to understand how such compounds were made than he could expect to know the meaning of life itself.