In fumigating a room with formaldehyde great care must be exercised that the individual does not remain in the room after the gas begins to be liberated. After the process of fumigation has been completed the windows and doors should all be opened that the gas may escape. It is always best to have the doors and windows open from the outside so that it will not be necessary for any one to go into the room until the gas has blown out. AGENTS OF DISINFECTION Physical Agents The physical agents of disinfection are sunlight, electricity, pressure, dry heat, burning, boiling, and steam. Chemical Agents Chemical agents of disinfection are divided into two divisions—gaseous and liquid disinfectants. The gaseous disinfectants are: formaldehyde gas, sulphur dioxide gas, hydrocyanic acid gas, chlorin, oxygen, and oxone. Some of the most important liquid disinfectants are metallic salts, bichloride of mercury, silver and zinc salts, coal-tar creosote, carbolic acid, phenol, lysol, creolin and formalin. MEANS OF DISINFECTION Natural Means Nature’s means of disinfecting are by dilution, sunlight, desiccation, time and antibiosis. The direct rays of the sun are Nature’s greatest germicide. Few of the microörganisms will live in the direct rays, but there are none that will withstand them for more than a few hours. Germs can not withstand the effect of dryness. Thus we see there is in Nature that which works as a most efficient germicide. The combination of sunlight and dryness forms a most desirable means of disinfection. When germs become attenuated through the effects of these natural processes they do little harm when introduced into the body. One of the most important adjuncts to the work of disinfection is personal cleanliness and sanitation of the environment. Other Agents =Fire= is not a practical disinfectant. It can be used only with those articles that are of little or no value since the article that is being disinfected is destroyed. The burning of all refuse and garbage is by all means the best method. Burning is the most satisfactory and cheapest method in disinfecting sputum and other excreta from the body, and in disposing of articles of little value saturated or contaminated with such. The =dry heat= method of disinfecting requires specially built apparatus such as dry air sterilizers. This form is not practicable for use in disinfecting fabrics and other materials that are destroyed or injured by extremely high temperature required to destroy the germ life. Metals are easily injured by this method as they are likely to be scorched. All forms of life are destroyed in an hour’s time when exposed to a temperature of 150° C. Such articles as glassware will withstand this heat or even higher and may be thoroughly sterilized in from one to two hours. This insures proper penetration and sufficient heat to completely destroy all life.