the attack of infectious
diseases, which we call "survival of the fittest." The third, that
great, sustaining, conservative power of nature--heredity. More cheering
yet, these forces came, not merely fully armed, but bearing new weapons
fitted for our hands. The vigor and unconquerable toughness of the human
animal presented us with three glittering weapons, sunshine, food, and
fresh air.

"If the deadly bacillus breaks through the lines, put me in the gap!
With these weapons, with this triad, I will engage to hurl him back,
shattered and broken." "Equip your vanguard with them, and the enemy
will never break the line."

The survival of the fittest held out to us two weapons of strange and
curious make, one of them labeled "immunity," the other "quarantine."
"Give me a little time," she said, "and with the first of these I will
make seven-tenths of the soldiers in your army proof against the spears
of the enemy, as Achilles was when dipped in the Styx. With the other,
surround and isolate every roving band of the enemy that you can find;
drive him out of the holes and caves in which he lives, into the
sunlight. Hold him in the open for forty-eight hours, and he will die of
light-stroke and starvation. Divide and conquer!"

These reinforcements of ours have proved no mere figure of speech. They
have won many a battle for us already upon the tented field. They have
not merely made good their promises, but gone beyond them, and we are
only just beginning to appreciate their true worth, and how absolutely
we can rely upon them.

The first outpost of the enemy was captured with the sunshine-food-air
weapons, and a glorious victory it was,--great in itself, and even more
important for its moral effect and its encouragement for the future. To
pronounce an illness "consumption" had been from time immemorial
equivalent to signing a death-warrant. Even the doctors could hardly
believe it, when the first open-air enthusiasts began to claim that they
had actually cured cases of genuine consumption. For long there was a
tendency to mutter in the beard, "Well, it wasn't _genuine_ consumption,
or it wouldn't have got better."

But after a period of incredulity this gave way to delighted confidence.
The open-air method would cure, and _did_ cure, and the patients
remained cured for years afterward. Our first claims were barely for
twenty-five or thirty per cent of the threatened victims. Then we were
able to increase it to fifty