Fifteen hundred cubic inches, or twenty-two quarts, of carbonic acid are expired from the lungs every hour, and thrown off into the surrounding atmosphere. Besides this, Sequin found that 18 grains of organized matter were thrown off per minute from the body in the form of insensible perspiration,--7 grains by the lungs, and 11 grains by the skin. Hence we may form some idea of the rapid corruption of the air in this stockade, where 30,000 men were breathing at one time. The foul and heavy vapors could not rise above the palisades unless a strong breeze prevailed; and even then they became so offensive as almost to extinguish life, like the deadly air of the Grotta del Cane. The exhalations from putrescent animal surfaces are always specifically heavier than the upper warm strata in the confined spaces where men are crowded together, such as the wards of hospitals. We find, according to Professor Graham, the vitiated air to be composed somewhat as follows: Phosphoretted hydrogen, sulphuretted hydrogen, carbonic acid, carburetted hydrogen, cyanogen with its compounds. The first gas is always recognized where the diseases of the internal organs are present, especially affections of the liver, stomach, bowels, and in fever and dysentery; and we observe the blackening of the lead plaster, &c., when the second is present. Stupor, headache, and sleepiness betray the presence of the other three gases. The diffusion of each gas is always inversely as the square root of the density of such gases. The density is thus, air being regarded as 1000:-- Phosphuretted hydrogen, 1240 Sulphuretted " 1170 Carburetted " 559 Carbonic acid, 1524 Cyanogen, 1806 IX. The report of the British Parliament Commission gives the following data in this important question: "The amount of carbonic acid in the air is about 1/2000 or .0005; the amount expired is about 1/12, or .083. Respired air contains 1/10 or 1 of carbonic acid, and this must be diluted ten times to make the air safe. Thus, 1/10 ÷ 10/1 = 1/100, or .01; and this again divided by 10, or 1/100 ÷ 10/1 = 1/1000 or .001, gives the amount of ventilation needed to reduce the air to that state of purity that only 1/1000 more of carbonic acid should be added to the air, when it would be represented by .0015 instead of .0005."