Most of the old small tenements were built on this plan and are accountable for much of the lung disease in cities to-day.] If they could be combined with the natural, window system of ventilation, they would be less objectionable; but the first demand of nearly all of them is that the windows must be kept shut for fear of breaking the circuit of their circulation.

Any system of ventilation, or anything else, that insists on all windows being kept shut is radically wrong.

It is only fair to say, however, that most of these systems of ventilation attempt the impossible, as well as the undesirable thing of keeping people shut up too long.

No room can be, or ought to be, ventilated so that its occupants can stay in it all day long without discomfort.

In ventilating, we ought to _ventilate the people in the room_, as well as the room itself.