There could be no vegetable or animal life without the sunbeam, yet when we have explained or accounted for the growth of a tree in terms of the chemistry and physics of the sunbeam, do we not have to figure to ourselves something in the tree that avails itself of this chemistry, that uses it and profits by it?  After this mysterious something has ceased to operate, or play its part, the chemistry of the sunbeam is no longer effective, and the tree is dead.

Without the vibrations that we call light, there would have been no eye.  But, as Bergson happily says, it is not light passively received that makes the eye; it is light meeting an indwelling need in the organism, which amounts to an active creative principle, that begets the eye.  With fish in underground waters this need does not arise; hence they have no sight.  Fins and wings and legs are developed to meet some end of the organism, but if the organism were not charged with an expansive or developing force or impulse, would those needs arise?

Why should the vertebrate series have risen through the fish, the reptile, the mammal, to man, unless the manward impulse was inherent in the first vertebrate; something that struggled, that pushed on and up from the more simple to the more complex forms?  Why did not unicellular life always remain unicellular?  Could not the environment have acted upon it endlessly without causing it to change toward higher and more complex forms, had there not been some indwelling aboriginal tendency toward these forms?  How could natural selection, or any other process of selection, work upon species to modify them, if there were not something in species pushing out and on, seeking new ways, new forms, in fact some active principle that is modifiable?

Life has risen by stepping-stones of its dead self to higher things.  Why has it risen?  Why did it not keep on the same level, and go through the cycle of change, as the inorganic does, without attaining to higher forms?  Because, it may be replied, it was life, and not mere matter and motion—­something that lifts matter and motion to a new plane.

Under the influence of the life impulse, the old routine of matter—­from compound to compound, from solid to fluid, from fluid to gaseous, from rock to soil, the cycle always ending where it began—­is broken into, and cycles of a new order are instituted.  From the stable equilibrium which dead matter is always seeking, the same matter in the vital circuit is always seeking the state of unstable equilibrium, or rather is forever passing between the two, and evolving the myriad forms of life in the passage.  It is hard to think of the process as the work of the physical and chemical forces of inorganic nature, without supplementing them with a new and different force.

The forces of life are constructive forces, and they are operative in a world of destructive or disintegrating forces which oppose them and which they overcome.  The physical and chemical forces of dead matter are at war with the forces of life, till life overcomes and uses them.