The poison of the disinfectant or antiseptic, whether it be in liquid or in gas form, is the essence of the material, and since the value of disinfectants is based on the crude raw materials which any one can buy, it is clearly unnecessary to buy expensive patented solutions for disinfectants when ordinary lime or carbolic acid are equally as good and can be had at much lower prices. A disinfecting solution, to be successful in its action, must be reasonably proportioned in volume to the amount of material to be disinfected, whether this be a liquid or clothing or the air of a room. It is the height of absurdity, for instance, to pretend to disinfect the air of a large room by burning a tablespoonful of sulfur on a shovel in the center of a room without even taking the trouble to close the door. It is absurd to attempt to disinfect the bed linen in a single pailful of hot water, since even if the water was hot at the beginning, it would be so reduced in temperature by the first piece that went in that its efficacy would be lost for everything else. It is equally absurd that a liquid from a bottle, no matter how much advertised, can effectually disinfect a room, either by a gentle sprinkling of the liquid on the walls and floor or by a more thorough spraying of the air with an atomizer containing the liquid. _Disinfecting gases._ Two gases are available for use in disinfection, and these are valuable particularly in killing germs left in a room after a patient suffering from an infectious disease has been removed. The diseases referred to in the following chapters are all of this nature, and one of these two gases ought to be used in every case; otherwise the room may continue to harbor germs of the disease for months or years with the possibility of infecting a future tenant at a time when his vitality was such as to make him an easy prey. Nor must the contents of the room be overlooked. The writer was recently told of a large family where one child had scarlet fever, recovering in September. The sick room was thoroughly disinfected, but the careful housewife, fearing damage to her blankets, had taken them to the attic before disinfection began. In the cold weather of February these blankets were brought down, and in six days the two children sleeping under them had contracted the disease. _Sulfur as a disinfectant._ When sulfur is burned, a gas is formed known as sulfurous acid, and until the last few years, it was the most common of all disinfecting agencies. The writer well remembers that when about to visit a city in South America infested with yellow fever, he was seriously advised to fill the inside of his shoes with sulfur as a precaution against the disease. He might as well have worn a red ribbon on his hat so far as any protection went, but it illustrates the confidence formerly shown in sulfur as a disinfectant.