~Chemical Reagents.~--_Disinfectants_ (for the disinfection of glass and metal apparatus and of morbid tissues). ~Physical Agents.~ HEAT.--(a) _Dry Heat:_ 1. Naked flame (for the sterilisation of platinum needles, etc.). 2. Muffle furnace (for the sterilisation of filter candles, and for the destruction of morbid tissues). 3. Hot air (for the sterilisation of all glassware and of metal apparatus). (b) _Moist Heat:_ 1. Water at 56° C. (for the sterilisation of certain albuminous fluids). 2. Water at 100° C. (for the sterilisation of surgical instruments, rubber tubing, and stoppers, etc.). 3. Streaming steam at 100° C. (for the sterilisation of media). 4. Superheated steam at 115° C. or 120° C. (for the disinfection of contaminated articles and the destruction of old cultivations of bacteria). FILTRATION.-- 1. Cotton-wool filters (for the sterilisation of air and gases). 2. Porcelain filters (for the sterilisation of various liquids). METHODS OF APPLICATION. ~Chemical Reagents~, such as belong to the class known as antiseptics (_i. e._, substances which inhibit the growth of, but do not destroy, bacterial life), are obviously useless. Disinfectants or germicides (_i. e._, substances which destroy bacterial life), on the other hand, are of value in the disinfection of morbid material, and also of various pieces of apparatus, such as pipettes, pending their cleansing and complete sterilisation by other processes. To this class (in order of general utility) belong: Lysol, 2 per cent. solution; Perchloride of mercury, 0.1 per cent. solution; Carbolic acid, 5 per cent. solution; Absolute alcohol; Ether; Chloroform; Camphor; Thymol; Toluol; Volatile oils, such as oil of mustard, oil of garlic. Formaldehyde is a powerful germicide, but its penetrating vapor restricts its use. These disinfectants are but little used in the final sterilisation of apparatus, chiefly on account of the difficulty of effecting their complete removal, for the presence of even traces of these chemicals is sufficient to so inhibit or alter the growth of bacteria as to vitiate subsequent experiments conducted by the aid of apparatus sterilised in this manner. NOTE.--Tubes, flasks, filter flasks, pipettes, glass tubing, etc., may be rapidly sterilised, in case of emergency, by washing, in turn, with distilled water, perchloride of mercury solution, alcohol, and ether, draining, and finally gently heating over a gas flame to completely drive off the ether vapor. Chloroform or other volatile disinfectants may be added to various fluids in order to effect the destruction of contained bacteria, and when this has been done, may be completely driven off from the fluid by the application of gentle heat.