=Boiling.=--Perhaps the best and most valuable disinfectant in existence is boiling, because it is always at command, is applicable to most materials and objects, is an absolutely safe sterilizer and disinfectant, and needs very little if any preparation and apparatus for its use. One half hour of boiling will destroy all life; and most bacteria can be killed at even a lower temperature. Subjection to a temperature of only 70 deg. C. for half an hour suffices to kill the germs of cholera, tuberculosis, diphtheria, plague, etc. Boiling is especially applicable to textile fabrics and small objects, and can readily be done in the house where the infection exists, thus obviating the necessity of conveying the infected objects elsewhere, and perhaps for some distance, to be disinfected. =Steam.=--Of all the physical disinfectants steam is the most valuable because it is very penetrating, reliable, and rapid; it kills all bacteria at once and all spores in a few minutes, and besides is applicable to a great number and many kinds of materials and objects. Steam is especially valuable for the disinfection of clothing, bedding, carpets, textile fabrics, mattresses, etc. Steam can be used in a small way, as well as in very large plants. The well-known Arnold sterilizers, used for the sterilization of milk, etc., afford an example of the use of steam in a small apparatus; while municipal authorities usually construct very large steam disinfecting plants. A steam disinfector is made of steel or of wrought iron, is usually cylindrical in shape, and is covered with felt, asbestos, etc. The disinfector has doors on one or both ends, and is fitted inside with rails upon which a specially constructed car can be slid in through one door and out through the other. The car is divided into several compartments, in which the infected articles are placed; when thus loaded it is run into the disinfector. The steam disinfectors may be fitted with thermometers, vacuum formers, steam jackets, etc. _Gaseous Chemical Disinfectants_ Physical disinfectants, however valuable and efficient, cannot be employed in many places and for many materials infected with disease germs, and therefore chemicals have been sought to be used wherever physical disinfectants could not for one or more reasons be employed. Chemicals are used as disinfectants either in gaseous form or in solutions; the gaseous kinds are of especial value on account of their penetrating qualities, and are employed for the disinfection of rooms, holds of ships, etc. There are practically but two chemicals which are used in gaseous disinfection, and these are sulphur dioxide and formaldehyde.