(c) Boiling: Boiling is a cheap and

(c) Chemical e.g. liquids, solids and gaseous.

(A) Natural Disinfectants:

Fresh air and sunlight act as natural disinfectants because air dries up the moisture present in bacteria which is lethal to bacteria. Air also takes away the infectious material which gets diluted in large volume of the air and becomes less harmful. Direct and continuous exposure to sunlight is very harmful to bacteria due to the presence of ultraviolet rays in sunlight. Beddings and furniture may be exposed to strong sunlight for several hours for terminal disinfection.

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(B) Physical Disinfectants

(i) Burning: Burning is a very good and cheap method of disinfection. Inexpensive materials like dressings, swabs and rags can be disposed of by burning. But burning of infectious materials should be done in a specially designed apparatus known as incinerator. If incinerator is not available then burning should be done in the open away from the habitation. For burning the wet dressings etc.

some saw dust and kerosene oil may be put on the materials and then burnt. (ii) Dry Heat: Dry heat has a very low penetrating power, so bacterial spores are not easily killed by this method. Therefore a high temperature has to be maintained for a long time. For this purpose hot air oven is used where a temperature of 160° to 180°C is maintained. Dry heat is not suitable for heavy articles like mattresses etc. moreover it destroys nearly all fabrics.

This method is used for disinfection of glassware, syringes, swabs, dressings and sharp instruments. (iii) Boiling: Boiling is a cheap and efficient method of disinfection. Boiling the material in water for 15-20 minutes kills all germs and boiling for 30 minutes may kill all spores. This method is quite suitable for linen, handkerchiefs, bed sheets, cooking utensils, syringes etc.

For disinfecting the syringes, the plunger and the body of the syringe should be separated, wraped in gauge and then boiled in water. Germicidal power of boiling water is increased if 1% soap and washing soda is added to boiling water specially it is useful for disinfecting the linen and bed sheets etc. The clothes stained with blood or faeces must be washed with cold water first and then boiled in water. Otherwise a permanent stain of blood or faeces will be produced. Boiling has disadvantages that: (a) It is a slow process. (b) It is unsuitable for thick linens. (c) It is not suitable for woolen and synthetic clothes as they shrink and get destroyed by boiling.

(d) It produces permanent stains of blood and faeces. (e) Sharp instruments get blunt by boiling. (iv) Steam Under Pressure: Steam under pressure (saturated steam) is the most effective method of disinfection in hospitals and laboratories. For this purpose an autoclave is used. Steam under pressure can penetrate better than ordinary steam thus sterilization is more effective. When steam under pressure comes in contact with materials to be sterilized it immediately gives away latent heat and sterilizes them. Steam under pressure is the most relable method of disinfection for linen, gloves, dressings, syringes, certain instruments, glass apparatus and culture media.

This method should not be used for sterilization of plastics and sharp instr­uments. The articles which have been sterilized by autoclaving should not be exposed to the environment before use as they may get conta­minated. (v) Ionising Radiations: Sterilization by ionising radiations is a newer technique and is being increasingly used for sterilization of bandages, dressings, surgical instruments and catgut. The agents used for this purpose include: (a) Infrared rays from electrically heated element. (b) Ultraviolet rays from sunlight or mercury vapour lamp. (c) Ionising by isotopes or X-rays. The materials to be sterilized are put in polythene bags which are then exposed to ionising radiations.

These radiations have strong penetrating power with little or no heating effect. The advantages of this method are that: (i) The materials remain sterile until the bags are opened. (ii) It is most effective method of sterilization. The disadvantage of this method is that it a very costly method.

(C) Chemical Disinfectants:

Articles which cannot be sterilized by heat (dry heat or moist heat) may be sterilized by chemical agents. The manner in which the chemical disinfectants act is not fully understood. They chiefly act by oxidising and coagulating the protoplasm of bacteria. They also act by ionic coagulation, dessication, emulsoid action, absorption etc. Various types of chemical disinfectants include: Liquids e.g. phenol, lysol, hexachlorophane, chlorhexidine (hibitane) chloroxylenol (dettol), cetrimide, savlon, iodine, chlorine, hydrogen peroxide, alcohol, methylated spirit, formalin, acetone, mercurochrome, gentian violet,’acriflavin etc. Solids e.

g. lime, bleaching powder, DDT, BHC, potassium permanganate, mercuric iodide etc. Gaseous e.g. chlorine, ethylene oxide, formalin, sulphur dioxide and hydrocyanic acid gas etc.

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