Strip the earth of its thin pellicle of soil, thinner with reference to the mass than is the peel to the apple, and you have stripped it of its life.  Or, rob it of its watery vapor and the carbon dioxide in the air, both stages in its evolution, and you have a dead world.  The huge globe swings through space only as a mass of insensate rock.  So limited and evanescent is the world of living matter, so vast and enduring is the world of the non-living.  Looked at in this way, in the light of physical science, life, I repeat, seems like a mere passing phase of the cosmic evolution, a flitting and temporary stage of matter which it passes through in the procession of changes on the surface of a cooling planet.  Between the fiery mist of the nebula, and the frigid and consolidated globe, there is a brief span, ranging over about one hundred and twenty degrees of temperature, where life appears and organic evolution takes place.  Compared with the whole scale of temperature, from absolute zero to the white heat of the hottest stars, it is about a hand’s-breadth compared to a mile.

Life processes cease, but chemical and mechanical processes go on forever.  Life is as fugitive and uncertain as the bow in the clouds, and, like the bow in the clouds, is confined to a limited range of conditions.  Like the bow, also, it is a perpetual creation, a constant becoming, and its source is not in the matter through which it is manifested, though inseparable from it.  The material substance of life, like the rain-drops, is in perpetual flux and change; it hangs always on the verge of dissolution and vanishes when the material conditions fail, to be renewed again when they return.  We know, do we not? that life is as literally dependent upon the sun as is the rainbow, and equally dependent upon the material elements; but whether the physical conditions sum up the whole truth about it, as they do with the bow, is the insoluble question.  Science says “Yes,” but our philosophy and our religion say “No.”  The poets and the prophets say “No,” and our hopes and aspirations say “No.”

II

Where, then, shall we look for the key to this mysterious thing we call life?  Modern biochemistry will not listen to the old notion of a vital force—­that is only a metaphysical will-o’-the-wisp that leaves us floundering in the quagmire.  If I question the forces about me, what answer do I get?  Molecular attraction and repulsion seem to say, “It is not in us; we are as active in the clod as in the flower.”  The four principal elements—­oxygen, nitrogen, hydrogen, and carbon—­say, “It is not in us, because we are from all eternity, and life is not; we form only its physical basis.”  Warmth and moisture say, “It is not in us; we are only its faithful nurses and handmaidens.”  The sun says:  “It is not in me; I shine on dead worlds as well.  I but quicken life after it is planted.”  The stars say, “It is not in us; we have seen life come and go among myriads of worlds for untold ages.”  No questioning of the heavens above nor of the earth below can reveal to us the secret we are in quest of.