W. R. Nichols, of Boston, found in passenger-cars 23.2 parts of carbonic acid to 10,000 parts of air, and in the Berkeley Street sewer 10.4 parts per 10,000. Wilson found in Portsmouth Prison, in cells containing six hundred and fourteen cubic feet of air, always occupied, 7.20 parts per 10,000, and in cells containing two hundred and ten cubic feet, occupied only at night, 10.44 per 10,000. Besides the carbonic acid, there is exhaled from the lungs a small amount of organic matter, of unknown composition. It forms a glutinous coating on the furniture, walls, and windows of closed rooms, decomposes rapidly, imparts a peculiarly offensive odor to the air of a badly-ventilated room, and poisons those who inhale it. Its quantity is so small that it has so far defied analysis. In a room contaminated by respiration alone, the odor of this substance begins to be perceived when the carbonic acid has increased to about 7 parts in 10,000, and 10 parts in 10,000 may be considered the maximum amount of carbonic acid allowable in dwellings. The following table shows how much carbonic acid artificial lights produce per hour: Petroleum, slit-burner, 10 candle-light, 1.98 cubic feet, Petroleum, round-burner, 7.6 ” 2.15 ” Oil-lamp, 4 ” 1.09 ” Candle, 1 ” .39 ” Coal-gas, slit-burner, 7.8 ” 3.25 ” Coal-gas, flat-burner, 10 ” 3 ” A five-foot gas-burner produces as much carbonic acid per hour as five men. As the most poisonous element of the breath can not readily be detected by analysis, the amount of carbonic acid is taken as a measure of the impurity of air contaminated by respiration. =Test for carbonic acid in air= (Pettenkofer’s method):