The surest disinfection of all for soiled dressings is burning. In the preparation of sterile dressings there is nothing more destructive to bacteria or more penetrant to fabrics than superheated steam - i. e., steam under 5 to 15 pounds pressure, which gives it a temperature of 220o to 230o F. Doty, at the New York Quarantine Laboratory, found that a moist heat of 230° F. killed all germs in fifteen minutes, even anthrax spores, and even when placed in the center of large and tightly rolled bundles. Next in value is boiling in water (212o F.), as of instruments. Liquids may themselves be boiled, unless some constituent of the liquid is destroyed or volatilized by heat. These methods are spoken of as methods of sterilization. Pasteurization is incomplete sterilization, the liquid being exposed to a temperature of about 160o F. for half an hour; this destroys 99 per cent. of the bacteria of milk. Dry heat is less effective than moist, and some of the bacteria which succumb quickly to boiling will resist for a time a dry heat of 3500 or 4000 F.

Cold is preservative, but not sterilizing, as in refrigerators and cold storage; but it is not very active in destroying bacteria, and more or less bacterial action can go on in spite of a temperature below that of freezing. In ice-cream, for example, kept at a temperature of - 5.8° F. ( - 21o C), the government experts found that in most cases the number of living bacteria diminished in the cold for several days, then showed a pronounced rise in numbers, as if the bacteria had become inured to the cold. As demonstrating the failure of cold to check microbic growth, one sample of ice-cream, when fresh, showed 811,000 bacteria per gram; after eighteen hours, 1,010,509; after forty-two hours, 3,349,733; and after sixty-six hours, 4,405,000. This was while it was kept packed in a freezing mixture of ice and salt. Mitchell found that the typhoid bacillus survived in ice-cream for from twelve to thirty-nine days.

Successful cold storage requires the greatest care in the regulation of both temperature and moisture; for example, fresh eggs will stand a temperature of 28° F., but when three months old will freeze at a temperature below 30° F.