Man consumes one hundred gallons of air every hour, ordinarily with eighteen respirations per minute, and two hundred and six cubic feet of air is the minimum for the preservation of health. The minimum allowed to the English hospitals by artificial ventilation is twenty-two hundred cubic feet the hour. The patients of St. Guy's receive four thousand cubic feet of fresh air every hour. The quantity required by the sick is enormous, to compensate the products of respiration, and all the deleterious evaporations of the locality where they are placed, and all other effluvia of diverse natures. In the Hospital Lariboissaire, at Paris, where about fifteen hundred cubic feet of air are furnished by machinery every hour, a taint is perceptible in the atmosphere: and Morin, in his experiments at Hospital Beaujon, thought that two thousand cubic feet were hardly sufficient. Dr. Sutherland believes four thousand feet to be necessary. The quantity, however, is nothing compared to quality. The quality is of the highest importance. The air must contain the vivifying properties of its normal constitution, or it loses force, and death must ensue. The source of animal heat is in the mutual chemical action of the oxygen and the constituents of the blood conveyed by the circulation. When the atmosphere is impure the oxidating processes are much diminished. We receive into our lungs about one hundred gallons of air per hour, and from this we absorb about five gallons of oxygen, or about one twentieth of the volume of air inspired. "The essential and fundamental condition of all respiration is the reciprocal action of the nourishing fluid, and a medium containing oxygen." Dumas believes that oxygen is necessary to the conservation of the vitality and proper structure of the globules of the blood; also that the integrity of these organisms is one of the essential conditions to the arterialization of the nourishing stream. Milne Edwards, also, maintains that the great absorbing powers of the blood exist in the globules. The normal number of these globules is one hundred and twenty-seven out of the thousand component parts of the blood; but they vary according to the barometer of health; sometimes they are observed in disease to descend to sixty-five. Vierodt has shown how a certain limit in the number of blood globules in the mammalia cannot be passed in the descending scale without death taking place. Simon and others have also shown how a careful and nutritious regimen may increase these globules in the blood of the consumptive, bringing them up from sixty-four to even one hundred and forty-four. The blood of man is the richest of all the mammalia, and it contains, according to Berzelius, three times as many hydrochlorates as the blood of the ox. Its richness depends upon the species and individual, and also upon the degree of health, it varying according to the condition of the person.