economy of Nature within us; so wonderful, indeed, that few can
believe the fact of living to be consistent with the real existence of
such a deadly environment as science pretends to reveal. It is a
common impression, therefore, that actual results fail to justify the
alarm sounded by sanitarians. Hence the necessity for calling
attention at the outset to an ample and manifest equivalent for the
deadly dose of confined exhalations taken daily by all civilized men.
We perceive that that dose is not lost, like the Humboldt River, in a
"sink," but reappears, like the wide-sown grass, in a perennial and
universal crop of diseases, almost numberless and ever increasing in
number, peculiar to house-dwellers. The trail of these plagues stops
nowhere else; it leads straight to the imprisoned atmosphere in our
artificial inclosures, and there it ends. That marvelous protective
economy of Nature within us, to which we have referred, is no
perpetual guaranty against the consequences of our negligence; it is
only a limited reprieve, to afford space for repentance; and unless we
hasten to improve the day of grace, the suspended sentence comes down,
upon us at last with force the more accumulated by delay.

Now, therefore, the grand problem of sanitary science (almost
untouched, almost unrecognized) proves to be no other and no less than
this:

What can be done to remedy the obstructive nature of an inclosure, so
that its gaseous contents shall _move off_, and be replaced by pure
air, as freely, as rapidly, and as incessantly, as in the open
atmosphere?

It happens to be the most necessary preliminary in approaching this
problem, to show how _not_ to do it, for that, respectfully be it