matter; they feed, as the animals do, upon elements that have gone through the cycle of vegetable life.  The secret of vegetable life, then, is in the green substance of the leaf where science is powerless to unlock it.  Conjure with the elements as it may, it cannot produce the least speck of living matter.  It can by synthesis produce many of the organic compounds, but only from matter that has already been through the organic cycle.  It has lately produced rubber, but from other products of vegetable life.

As soon as the four principal elements, carbon, oxygen, hydrogen, and nitrogen, that make up the living body, have entered the world of living matter, their activities and possible combinations enormously increase; they enter into new relations with one another and form compounds of great variety and complexity, characterized by the instability which life requires.  The organic compounds are vastly more sensitive to light and heat and air than are the same elements in the inorganic world.  What has happened to them?  Chemistry cannot tell us.  Oxidation, which is only slow combustion, is the main source of energy in the body, as it is in the steam-engine.  The storing of the solar energy, which occurs only in the vegetable, is by a process of reduction, that is, the separation of the carbon and oxygen in carbonic acid and water.  The chemical reactions which liberate energy in the body are slow; in dead matter they are rapid and violent, or explosive and destructive.  It is the chemistry in the leaf of the plant that diverts or draws the solar energy into the stream of life, and how it does it is a mystery.

The scientific explanations of life phenomena are all after the fact; they do not account for the fact; they start with the ready-made organism and then reduce its activities and processes to their physical equivalents.  Vitality is given, and then the vital processes are fitted into mechanical and chemical concepts, or into moulds derived from inert matter—­not a difficult thing to do, but no more an explanation of the mystery of vitality than a painting or a marble bust of Tyndall would be an explanation of that great scientist.

All Professor Loeb’s experiments and criticisms throw light upon the life processes, or upon the factors that take part in them, but not upon the secret of the genesis of the processes themselves.  Amid all the activities of his mechanical and chemical factors, there is ever present a factor which he ignores, which his analytical method cannot seize; namely, what Verworn calls “the specific energy of living substance.”  Without this, chemism and mechanism would work together to quite other ends.  The water in the wave, and the laws that govern it, do not differ at all from the water and its laws that surround it; but unless one takes into account the force that makes the wave, an analysis of the phenomena will leave one where he began.