der hungrily, sword in hand, slaying
and being slain, the relief would be only temporary. Even if one race
alone should hew down the last survivor of all the other races, that one
race, drifting the world around, would saturate the planet with its own
life and again press against subsistence. And in that day, the death
rate and the birth rate will have to balance. Men will have to die, or
be prevented from being born. Undoubtedly a higher quality of life will
obtain, and also a slowly decreasing fecundity. But this decrease will
be so slow that the pressure against subsistence will remain. The
control of progeny will be one of the most important problems of man and
one of the most important functions of the state. Men will simply be not
permitted to be born.

Disease, from time to time, will ease the pressure. Diseases are
parasites, and it must not be forgotten that just as there are drifts in
the world of man, so are there drifts in the world of micro-organisms--
hunger-quests for food. Little is known of the micro-organic world,
but that little is appalling; and no census of it will ever be taken,
for there is the true, literal "abysmal fecundity." Multitudinous as
man is, all his totality of individuals is as nothing in comparison
with the inconceivable vastness of numbers of the micro-organisms. In
your body, or in mine, right now, are swarming more individual entities
than there are human beings in the world to-day. It is to us an
invisible world. We only guess its nearest confines. With our powerful
microscopes and ultramicroscopes, enlarging diameters twenty
thousand times, we catch but the slightest glimpses of that profundity of
infinitesimal life.

Little is known of that world, save in a general way. We know that out
of it arise diseases, new to us, that afflict and destroy man. We do not
know whether these diseases are merely the drifts, in a fresh direction,
of already-existing breeds of micro-organisms, or whether they are new,
absolutely new, breeds themselves just spontaneously generated. The
latter hypothesis is tenable, for we theorise that if spontaneous
generation still occurs on the earth, it is far more likely to occur in
the form of simple organisms than of complicated organisms.

Another thing we know, and that is that it is in crowded populations that
new diseases arise. They have done so in the past. They do so to-day.
And no matter how wise are our physicians and bacterio