Is biology to be interpreted in the same physical and chemical terms as geology? Are biophysics and geophysics one and the same? One may freely admit that there cannot be two kinds of physics, nor two kinds of chemistry--not one kind for a rock, and another kind for a tree, or a man. There are not two species of oxygen, nor two of carbon, nor two of hydrogen and nitrogen--one for living and one for dead matter. The water in the human body is precisely the same as the water that flows by in the creek or that comes down when it rains; and the sulphur and the lime and the iron and the phosphorus and the magnesium are identical, so far as chemical analysis can reveal, in the organic and the inorganic worlds. But are we not compelled to think of a kind of difference between a living and a non-living body that we cannot fit into any of the mechanical or chemical concepts that we apply to the latter? Professor Loeb, with his "Mechanistic Conception of Life"; Professor Henderson, of Harvard, with his "Fitness of the Environment"; Professor Le Dantec, of the Sorbonne in Paris, with his volume on "The Nature and Origin of Life," published a few years since; Professor Schaefer, President of the British Association, Professor Verworn of Bonn, and many others find in the laws and properties of matter itself a sufficient explanation of all the phenomena of life. They look upon the living body as only the sum of its physical and chemical activities; they do not seem to feel the need of accounting for life itself--for that something which confers vitality upon the heretofore non-vital elements. That there is new behavior, that there are new chemical compounds called organic,--tens of thousands of them not found in inorganic nature,--that there are new processes set up in aggregates of matter,--growth, assimilation, metabolism, reproduction, thought, emotion, science, civilization,--no one denies. How are we going to get these things out of the old physics and chemistry without some new factor or agent or force? To help ourselves out here with a "vital principle," or with spirit, or a creative impulse, as Bergson does, seems to be the only course open to certain types of mind. Positive science cannot follow us in this step, because science is limited to the verifiable. The stream of forces with which it deals is continuous; it must find the physical equivalents of all the forces that go into the body in the output of the body, and it cannot admit of a life force which it cannot trace to the physical forces.