In temperate climates the principal object of ventilation is the replacement of vitiated air with fresh. Artificial ventilation is produced either by inducing a movement of air by means of draught-chimneys, or by forcing in air through the agency of mechanical ventilators. A trial has been made at the Lariboisière Hospital of a system of ventilation in which the air is drawn from the roof and forced into flues that ramify into the several halls to be ventilated. At the moment of entering the halls the air is heated by being brought in contact with steam-pipes, so that a uniform temperature of 78° is maintained in the wards, with an atmosphere free from odor. Notwithstanding purity of air is secured, the mortality in this institution is not inferior to that in non-ventilated hospitals. This is attributed by M. Bouchardat to the mischievous influence of the high temperature which they endeavor to maintain. He favors heating and ventilation by open fire-places. This method is preferred in London, where fires are kept up in summer as well as in winter, at least in the principal office of the institution, and the windows are opened at all times when it is possible, while mechanical ventilating apparatus is used only exceptionally. The air, sucked in by the strong draught of the chimneys, enters by the joints of the doors and windows. The patients enjoy the sight of the fire and the pleasant feeling of direct radiation, while they collect around the hearths and breathe an air that has not been changed by contact with a heated surface. Possibly the English go too far in this direction. "The importance of pure air," says M. Proust, "has perhaps been exaggerated in some cases by the English physicians, whose example the Americans have followed. It is advisable, according to them, to leave the larger openings, no matter what the weather may be, the windows of dormitories and bedrooms, open during the night. These principles, almost universally observed in the countries of which we speak, entail, in our opinion, great inconveniences." There is really some danger in exposing one's self to cold during sleep.
The study of the questions of heating and ventilation has made considerable progress in France during the last fifteen or twenty years. The construction of numerous school-houses has especially been the occasion of many praiseworthy improvements, but much still remains to be done. Dr. Larget, in an interesting work on rural habitations, has pointed out an apparent relation between the number of openings indicated in the tax-list of doors and windows and the mortality. The general average, for France, of the number of openings per inhabitant, is one and a half. In one hundred departments, in which the number is less than the mean, fifty-five show a higher mortality, and forty-five a mortality equal to the average; while, in a hundred departments in which the number is greater than the mean, sixty show a lower rate of mortality than the average, and only twenty-five a higher rate.
Another point which is too easily forgotten is that, like the walls, floors are permeable to the air. The atmosphere is not bounded by