You are sure you have no money to spare to buy valves, and zinc tubes and plates, or to pay to workmen for making holes in your walls, and in your doors and windows. I admit that properly these trifling things should be done at the expense of the landlord to whom the house belongs. It should be as much his duty to make a house fit to live in, so far as due ventilation is concerned, as it is to keep it dry by covering it with a roof of tiles or slate. As landlords, however, are commonly themselves ignorant about these matters, you must learn to look to the affair for yourself. You will be the sufferer if the right thing be not done, therefore it is alike your interest and your duty to see that it is done. Suppose then that you have a hard landlord who will do nothing for you, and that you are so poor you can not spare a shilling or two for the purchase of metal tubes or plates. Then I will tell you what I would do, if I were in your shoes. I would borrow a large gimlet of the carpenter, and I would bore a row of holes through the upper part of the window frame in my bedroom, just above the glass, sloping them downwards a little, so that the rain may not be able to run in; next I would never quite shut the door of the chamber, and I would bore other holes through the frames of the windows down stairs, to act as channels of inlet. A few rough pegs of wood would serve to close some of the holes, if at any time too much air entered the room in consequence of a strong wind blowing outside. This is what I would do, rather than I would submit to be poisoned at night because I was poor. A single round hole, a little more than half an inch across, would allow as much air to pass through it, as would be sufficient to supply the breathing of one person, provided the air were driven along by the movements of a fan, or by other mechanical contrivance, with the force of a very gentle breeze. Generally, however, it does not move so fast as this through rooms, when only caused to do so by the greater pressure of external colder air. It is, therefore, better that the ventilating openings, both for inlet and departure, should altogether make up much more than a hole half an inch across. It is not possible to have too much fresh air in a room, provided only an uncomfortable and chilling draught is not allowed to blow upon the body of the inhabitant. You may easily prevent any discomfort or mischief from draught, even where a great abundance of air is admitted, by hanging a curtain to catch it and turn it aside. You will find, however, that there is very little chance of any troublesome draught when no fire is burning in the room, to make the air rush in with increased power, for it is fires, as you will remember, which cause quick and strong currents.