In the schoolroom, each teacher and pupil should regard the ventilation of the room as the most important single factor in the success of their work.

The teacher has a sensitive thermometer and guide in, first, her own feelings and, second, the looks and attention of her pupils.

There should be vacant seats or chairs in every room so that those too near the window in winter can move out of the strong current of cold air.
[Illustration: A HEALTHFUL ARRANGEMENT OF WINDOWS AND SHADES The windows face in more than one direction.

The shades are hung in the middle, not only regulating the light in the room, but allowing free passage of air at the top.] Windows should reach well up toward the ceiling and be opened _at the top_, because the foul air given off from the lungs at the temperature of the body is warmer than the air of the room and consequently rises toward the ceiling.

It is just as important in ventilation to _let the foul air out_ as to let the fresh air in.