The difficulty in the isolated wards was, that it required a separate fire in each shaft in the summer. Where it is possible to get it near the kitchen or bake-oven fire, that answers a splendid purpose; but in the single wards it is not necessary to keep up a constant fire; a few sticks of wood every morning answer the purpose of keeping the air in the shaft warmer than the surrounding atmosphere, which, of course, creates the proper draught. These shafts were made very large--never less than thirty inches square and sometimes three feet by six feet. The popular plan of opening the water-closet windows and allowing much of the fresh air to enter the building that way was strenuously avoided; the windows in the closet were fastened shut, and then the air to supply this large exhaust shaft was drawn from the adjoining ward or room, which ventilated that ward and prevented any unpleasant odor from the closets returning into the ward. Wherever it was possible, a sheet iron or cast iron pipe was carried up into the centre of this shaft from the kitchen, laundry, bakery or any other constant fire, and where no heat from a permanent fire or from a steam coil could be obtained, a small stove for the purpose was provided. LEWIS W. LEEDS, _Germantown, Pa._ 7th mo. 26th, 1867. _The subjoined are a few of the Letters received from prominent Sanitarians and others._ Office of the Superintendent of Health, Providence, August 5, 1867. Friend Leeds. Your Lectures on Ventilation have been received. I am much interested in them, and think the views given are correct. I hope they will be widely circulated. Too much cannot be said to the people upon the subject. Ventilation is all-important. Indeed, I think that if the air could be constantly kept in motion, the worst sources of impure air in our cities would be rendered almost free from danger. In seasons of epidemic cholera, the most oppressive feature of danger is the stagnation which exists in the atmosphere. There was good sense and true philosophy in the old custom of burning bonfires to keep off disease. I must close, wishing you much success in your efforts to awaken the people to the importance of this subject. Truly yours, EDWIN M. SNOW, M. D., Superintendent of Health. * * * * * Bangor, Maine, August 23, 1867. My Dear Leeds. Your pamphlet was duly received. I have read it with much interest, and believe it to be worthy of extended circulation. It is the clearest paper on the subject I have yet read.