occupants are breathing an atmosphere that is not only poor in oxygen
but saturated with carbonic acid gas and other impurities conveyed by
the breath. Foul air such as this causes headache, dizziness,
faintness, nausea, and occasionally even more serious disturbances.
Those who live in "close" rooms day after day grow pale and languid;
their appetite fails and some of their natural power of resistance
against illness is lost. Many people are unhealthy simply because
they neglect to supply their living quarters with a steady stream of
air from the outside.

While it is impossible to keep the air in any room as pure as the
outside atmosphere, perfectly satisfactory ventilation can be easily
arranged. Some of the impure air in a house is always escaping of its
own accord and its place is taken by air from the outside. Thus, the
cracks around the windows and doors let bad air out and good air in;
and, besides, most building materials are porous. These natural
paths, however, must be supplemented. The simplest device for
ventilation, which is also the best, consists in opening a window at
the top and bottom. The width of the opening may be regulated so as
to permit the air in the room to change without occasioning
disagreeable drafts; if necessary the current may be broken by a
screen of some pervious material placed in the opening.

The bed-room should always be supplied with plenty, of fresh air,
which "quiets the nerves" and helps one to sleep soundly.
Furthermore, the temperature of the bed-room should be lower than the
temperature of rooms occupied during the day. Both these requisites
will be properly met by leaving a window open at night, which may be
done throughout the year in most climates, if one puts on enough
covering. There is no danger of catching cold from sleeping with the