We know all about it; what we forget, perhaps, is, that even oxygen has its limitation: nothing can act but where it is, and, waste attends work, hold true for this vital gas as for other matters. Fire and lamp and breathing beings are all consumers of the oxygen which sustains them. What follows? Why, that this element, which is present in the ratio of twenty-three parts to the hundred in pure air, is subject to an enormous drain within the four walls of a house, where the air is more or less stationary. I am not speaking just now of the vitiation of the air – only of the drain upon its life-sustaining element. Think, again, of the heavy drain upon the oxygen which must support the multitudinous fires and many breathing beings congregated in a large town! ‘What follows?’ is a strictly vital question. Man can enjoy the full measure of vigorous joyous existence possible to him only when his blood is fully aërated; and this takes place when the air he inhales contains its full complement of oxygen. Is it too much to say that vitality is reduced, other things being equal, in proportion as persons are house-dwellers rather than open-air dwellers? The impoverished air sustains life at a low and feeble level; wherefore, in the great towns, stature dwindles, the chest contracts, men hardly live to see their children’s children. True, we must needs have houses for shelter from the weather by day and for rest at night; but in proportion as we cease to make our houses ‘comfortable,’ as we regard them merely as necessary shelters when we cannot be out of doors, shall we enjoy to the full the vigorous vitality possible to us.