how successfully they cope with these invaders, new invaders continue to
arise--new drifts of hungry life seeking to devour us. And so we are
justified in believing that in the saturated populations of the future,
when life is suffocating in the pressure against subsistence, that new,
and ever new, hosts of destroying micro-organisms will continue to arise
and fling themselves upon earth-crowded man to give him room. There may
even be plagues of unprecedented ferocity that will depopulate great
areas before the wit of man can overcome them. And this we know: that no
matter how often these invisible hosts may be overcome by man's becoming
immune to them through a cruel and terrible selection, new hosts will
ever arise of these micro-organisms that were in the world before he came
and that will be here after he is gone.

After he is gone? Will he then some day be gone, and this planet know
him no more? Is it thither that the human drift in all its totality is
trending? God Himself is silent on this point, though some of His
prophets have given us vivid representations of that last day when the
earth shall pass into nothingness. Nor does science, despite its radium
speculations and its attempted analyses of the ultimate nature of matter,
give us any other word than that man will pass. So far as man's
knowledge goes, law is universal. Elements react under certain
unchangeable conditions. One of these conditions is temperature. Whether
it be in the test tube of the laboratory or the workshop of nature, all
organic chemical reactions take place only within a restricted range of
heat. Man, the latest of the ephemera, is pitifully a creature of
temperature, strutting his brief day on the thermometer. Behind him is a
past wherein it was too warm for him to exist. Ahead of him is a future
wherein it will be too cold for him to exist. He cannot adjust himself
to that future, because he cannot alter universal law, because he cannot
alter his own construction nor the molecules that compose him.