14. VENTILATION.--The amount of fresh air required for ventilation has been hitherto very much underrated, because it has been assumed that the quantity of carbonic acid produced during respiration was the chief noxious gas to be carried off. The total amount of this gas produced by an adult in 24 hours is about 40,000 cubic inches, which in a Barrack room of 16 men would give 370 cubic feet per diem. Allowing 8 hours for the night occupation of such a room, when the doors and windows may be supposed to be shut, the product of carbonic acid would be 123 cubic feet, or about 15½ cubic feet per hour. This large quantity if not speedily carried away would undoubtedly be injurious to health; but there are other gaseous poisons produced with the carbonic acid which have still greater power to injure. Every adult exhales by the lungs and skin 48 ounces or 3 pints of water in 24 hours. Sixteen men in a Barrack-room would therefore exhale in 8 hours 16 pints of water and 15½ cubic feet of carbonic acid in the atmosphere of the room. With the watery vapour there is also exhaled a large quantity of organic matter ready to enter into the putrefactive condition. This is especially the case during the hours of sleep. And as it is a law that all excretions are injurious to health if reintroduced into the system it is easy to understand how the breathing of damp foul air of this kind, and the consequent reintroduction of excrementitious matter into the blood through the functions of respiration will tend to produce disease. This will be still more the case in sick wards overcrowded with sick, the exhalations from whom are always highly morbid and dangerous, as they are nature’s method of eliminating noxious matter from the body, in order that it may recover health. A much larger mass of air is required to dilute and carry away these emanations than is generally supposed. And the whole art of ventilation resolves itself into applying in any specific case the best method of renewing the air sufficiently, without producing draughts or occasioning great varieties in temperature.