stirred up, thus filling the air with all sorts of impurities, irritating and disease-bearing. The stuffy atmosphere one notices when entering certain assembly halls and churches is nearly always due to lack of energy or method in cleaning, quite often through inaccessibility in 'dirt corners' or other hygienic fault in the design of buildings.
The combustion of gas and kerosene in living rooms rapidly vitiates the air. Each burner will use up as much oxygen as several persons, besides generating heat, moisture and often sulphurous acid gas, specially injurious to nose and throat. Stoves or grates for heating or cooking by gas should invariably be connected to a-flue to carry off the products of combustion. Even if used for lighting only, the discharge from lamps becomes very objectionable without ample provision for its escape from the room.
Smoke and vapors are unavoidable wherever cooking is going on, but through immediate and effective removal at the starting point, their spread can be prevented. There is no excuse for any odors invading the living rooms; indeed, if the vapors are properly taken care of, the air in the kitchen itself can be kept reasonably wholesome and pure.
Dust, smoke, gases or hot air from industrial sources which are often allowed to contaminate the air in workshops and laboratories can be classed as avoidable factors, since it is nearly always possible to localize them. Grinding wheels, buffers or other machinery should be equipped for this purpose with devices for mechanical suction to pick up and remove the dust or fumes before they can spread and do harm. Poisonous gases in laboratories should also be removed as soon as generated. Waste heat which would otherwise become annoying should be neutralized by insulation. The design of such arrangements requires special training and experience, but the principles of it can easily be understood and insisted upon by laymen.
The Vitiation of the Air through Heating, Cooling and Ventilating Apparatus.—Every one is familiar with the discomforts of modern heating apparatus. The most frequent complaints are of dryness, disagreeable odors or stuffy atmosphere, sometimes combined with overheating. These conditions are so common that they have almost come to be regarded as unavoidable drawbacks, more or less peculiar to certain methods of heating.
Since the capacity of air to absorb moisture increases with its temperature, heating, by any method, will have a drying effect. In clear cold weather, when the atmosphere out of doors contains little moisture, the relative percentage indoors may drop below a point to which most persons are acclimated. Unless made up by internal sources, some artificial supply of moisture seems desirable in such cases. It is, however, not necessary and not desirable, as is often recommended, to go