The air will then reach the breathing-zone,
instead of flowing on to the floor and chilling the feet, which is the
usual consequence of opening a window in winter. It seems tragic to
think that for lack of some such simple device, which anyone can make or
buy, there is now an almost complete absence of winter ventilation in
most houses.

[Sidenote: Air-fans]

Air should never be allowed to become stagnant. When there is no natural
movement in the air, it should be put in motion by artificial means.
This important method of practising air-hygiene is becoming quite
generally available through the introduction of electric currents into
dwellings and other buildings and the use of electric fans. Even a hand
fan is of distinct hygienic value.

[Sidenote: Heating Systems]

A wood or grate fire is an excellent ventilator. A heating-system which
introduces warmed new air is better than one acting by direct radiation,
provided the furnace is well constructed and gas-proof.

[Sidenote: Cool Air]

The importance of coolness is almost as little appreciated as the
importance of motion. Most people enervate themselves by heat,
especially in winter. The temperature of living-rooms and work-rooms
should not be above 70 degrees, and, for people who have not already
lost largely in vigor, a temperature of 5 to 10 degrees lower is
preferable. Heat is depressing. It lessens both mental and muscular
efficiency. Among the employes of a large commercial organization in New
York who were examined by the Life Extension Institute, some of the men
in one particular room were suffering from an increase of body
temperature and a skin rash. On investigation it was found that the room
in which they worked was overheated. There was no special provision for
ventilation. A window-board was installed, with the result that the men
recovered and no other cases of skin rash occurred in that room.

[Sidenote: Dry air]

As to dryness of air, there is little which the individual can do except
to choose a dry climate in which to live or spend his vacations.
Unfortunately, there is not as yet any simple and cheap way of drying
house air which is too moist, as is often the case in warm weather.

[Sidenote: Humidity]

In the cold season, indoor air is often too dry and may be moistened
with advantage. This may be done, to some extent, by heating water in
large pans or open vessels. But for efficient moistening of the air,
either a very large evaporati