446 GERMICIDES — DISINFECTANTS 



HEAT 



Heat is probably the most certain disinfectant, and may be em- 

 ployed either dry : flame, hot air ; or moist : steam, superheated steam 

 or as boiling water. Incineration is the best disinfectant for litter, 

 dressings and articles of little value. 



Steam. Steam may be used either at atmospheric pressure (Ar- 

 nold sterilizer) or under several pounds pressure, (autoclav). 

 There is nothing except the actual flame which is more destructive to 

 bacteria or more penetrating to fabrics than silperheated steam (under 

 5 — 15 pounds pressure), which gives a temperature of 220° — 230° 

 F. It has been demonstrated that moist heat at 230° F. will kill 

 the most resistant spores in 15 minutes. This is the favorite method 

 for disinfecting surgical dressings. Next in order for dressings 

 comes the Arnold sterilizer in which steam at 212° F. is used. For 

 the best results this should be employed for % hour or longer on 

 three successive days (fractional sterilization). 



Boiling water is mostly used for disinfecting instruments. If 

 sodium carbonate is added, it will prevent the corrosion of instru- 

 ments and at the same time raise the boiling point of the water. 

 Liquids which need sterilization (solutions of cocaine, etc.) may 

 be boiled if they are not destroyed by the heat. Dry heat is less 

 effective than moist and the temperature needs to be considerably 

 higher. 



Pasteurization is incomplete sterilization, in which most but not 

 all of the organisms are killed. It consists of exposing the liquid to 

 a temperature of about 160° F. for -J^ hoiir. It is employed on a 

 large scale to reduce the number of bacteria in milk. 



Cold acts as a preservative, but does not destroy bacteria. On 

 the contrary, it has been found in the case of ice cream that although 

 the number of bacteria will decrease for several days, after a time 

 they will show a marked increase, even when the temperature is 

 below freezing. 



METALS AND THEIR SALTS 



These combine with the albumen of the bacterial cells and form 

 metallic albuminates. Since they also form the same compounds 

 with the cells of the tissues, they form a hard scab or dense pre- 

 cipitate, do not penetrate deeply, and are soon destroyed by the 

 tissues. Most important are: 



Salts of Mercury — Bichloride, nitrate, oxide. 



Silver, Nitrate and the organic preparations. 

 Copper, Sulphate. 



Iron, Sulphate, subsulphate, chloride. 

 Zinc, Chloride, sulphate, acetate. 

 Bismuth, Subiodide, subnitrate. 



