But all these strange and beautiful phenomena springing up in a world of inert matter are but faint symbols of the mystery and the miracle of the change of matter from the non-living to the living, from the elements in the clod to the same elements in the brain and heart of man. IV THE BAFFLING PROBLEM I Still the problem of living things haunts my mind and, let me warn my reader, will continue to haunt it throughout the greater part of this volume. The final truth about it refuses to be spoken. Every effort to do so but gives one new evidence of how insoluble the problem is. In this world of change is there any other change to be compared with that in matter, from the dead to the living?--a change so great that most minds feel compelled to go outside of matter and invoke some super-material force or agent to account for it. The least of living things is so wonderful, the phenomena it exhibits are so fundamentally unlike those of inert matter, that we invent a word for it, _vitality_; and having got the word, we conceive of a vital force or principle to explain vital phenomena. Hence vitalism--a philosophy of living things, more or less current in the world from Aristotle's time down to our own. It conceives of something in nature super-mechanical and super-chemical, though inseparably bound up with these things. There is no life without material and chemical forces, but material and chemical forces do not hold the secret of life. This is vitalism as opposed to mechanism, or scientific materialism, which is the doctrine of the all-sufficiency of the physical forces operating in the inorganic world to give rise to all the phenomena of the organic world--a doctrine coming more and more in vogue with the progress of physical science. Without holding to any belief in the supernatural or the teleological, and while adhering to the idea that there has been, and can be, no break in the causal sequence in this world, may one still hold to some form of vitalism, and see in life something more than applied physics and chemistry?