forced into the rooms, and circulates before it finds its outlet at the floor level. The entire air of the room may be renewed from four to nine times per hour, according to the speed of the engine. This is done without the creation of draughts, a lighted taper held but a foot away from an exit or inlet hardly flickering. It will be understood that all the windows are closed, and that no air can enter the building except by the action of the fan. The currents caused by the opening of the swing doors is outward rather than inward, owing to the compressed state of the internal atmosphere.