Max Verworn has given us a very searching analysis of the molecular process in the catalytic aspect of metabolism in his _Biogen Hypothesis_ (1903), "a critical and experimental study of the processes in living matter." He simplifies the catalytic theory of the enzyma by tracing all the phenomena of life to the catalytic metabolism of one single chemical compound, the plasm, and regards its active molecules, the biogens, as the ultimate chemical factors of the vital process. While the enzyma hypothesis assumes that there are in each cell a great number of different enzyma which are all co-ordinated, and each of which only performs its little special work, the biogen hypothesis deduces all the vital phenomena from one compound, the biogenetic plasm; and thus the biogen molecules, which increase by division into parts, are the sole factors of biological catalysis. Verworn also points out the analogy between this enzymatic process of metabolism and the inorganic processes of catalysis--for instance, in the manufacture of English sulphuric acid. A small and constant quantity of nitromuriatic acid, with the aid of air and water, converts an unlimited mass of sulphuretted acid into sulphuric acid without being changed itself; the molecule of the nitromuriatic acid breaks up steadily by the giving-off of oxygen, and is then restored by the assumption of oxygen. The manifold and changeful phenomena of life and their sudden extinction at death seem to every thoughtful man to be something so wonderful and so different from all the changes in inorganic nature that from the very beginning of biological philosophy special forces were assumed to explain it. This was particularly due to the remarkable, orderly structure of the organism and the apparent purposiveness of the vital processes. Hence, in earlier days a special organic force (_archæus insitus_) was assumed, controlling the individual life and pressing the "raw forces" of inorganic matter into its service. In the same way a special formative impulse was supposed to preside over the wonderful processes of development. When physiology began to win its independence, about the middle of the eighteenth century, it explained the peculiar features of organic life by a specific vital force. The idea was generally received, and Louis Dumas endeavored thoroughly to establish it at the beginning of the nineteenth century (_cf._ chapter iii. of the _Riddle_).