PREFACE. IN a recent work by an eminent man of science, Dr. J. Reinke, Professor of Botany at the University of Kiel, there occurs a passage which I cannot do better than place in the forefront of this book as an indication of its aim. Physiology, writes Professor Reinke, has become the study of the movements which, taken together, make up life. There is no manner of doubt that nourishment, metabolism, reproduction, development, and sensation rest on processes of movement which depend on material systems of peculiar molecular conformation. For the bodies of plants and of animals are material systems whose conformation is of a most intricate character. So far as physiology has at present advanced in the analysis of these phenomena of movement, their problems have fallen naturally into two groups. The first of these groups of phenomena is comparatively transparent, and stands in agreement with the general processes of the material world it can be investigated by observation and experiment. We may, therefore, hope to decipher it completely, and to reduce it, in the end, to chemico-physical processes. Of this kind are the phenomena of nutrition, taking that word in its widest sense. But behind these l Metabolism see p. 27. vi PREFACE processes there stand the facts of development and of reproduction, and here, in all investigations, and in spite of every attempt to demonstrate a basis of physical energy, research finds itself confronted by an X, a factor which mocks every effort to explain it by physics or chemistry. And this X which lurks in all the phenomena of development takes a part in the nutritive processes also so essential a factor does it appear in all the processes of life that chemical and physical forces alone would not suffice to keep alive even the most rudimentary of organisms, not to mention creating such an organism out of non-living chemical con tituents. If this X force exists and can be established, it will give us the clue, I believe, to much more than the operations of physical nature. The following pages are an attempt to establish it, to define its character, and to indicate the lines on which this unknown factor in evolution seems to bring into a rational unity the phenomena of the physical world and the moral and aesthetic faculties of man. The time appears to have come for such an attempt. The fermentation of mind produced by Darwins massive and victorious promulgation of the evolution theory is beginning to subside it is now possible in some measure to take stock of what has been destroyed, of what has been left intact, by the immense tidal wave J. Reinke. DIE WELT ALS TAT, p. 173. The term development Enlcoicklung includes both what we commonly understand by that term as, the-transformation of an embryo into a complete animal and also what we call Evolution, the development of one species into another. PREFACE vii of new thought which then swept over the world. Some conceptions which were thought to have been submerged for ever are reappearing in more or less altered shapes, and science is called on to reconstruct a universe less one-sided, less aridly simple, than that which Darwinism, as at first understood, appeared to have left us. The result, so far as it is successful, will be the establishment of a spiritual view of the universe on a natural basis...