Many proprietary compounds for milk preservation have been placed on the market in the past, but the use of all of these is illegal in most states. The federal law also prohibits their use in all dairy products that pass into interstate commerce. Within recent years a method for the preservation of milk was introduced by a Danish engineer, Budde, which consists of adding to milk a very small amount of peroxid of hydrogen which is a very efficient antiseptic. The peroxid is decomposed by some substance in the milk; the products of decomposition being water and free oxygen. The peroxid together with the application of heat at a comparatively low temperature (122° F.) is sufficient to destroy the larger part of the bacteria in the milk. Practical difficulties are encountered in the commercial application, so that it is probable the process will never be a commercial success. For the preservation of composite samples of milk for analytical purposes, such as the Babcock test, strong disinfectants, as corrosive sublimate, are employed. This material is very poisonous, and leaves the milk unchanged in appearance. Some coloring matter is therefore usually mixed with the sublimate in making the preservative tablets, so as to render their use more conspicuous. Corrosive sublimate not only stops all bacterial growth, but quickly destroys the life of the cells. Bichromate of potash is generally employed in the preservation of composite samples for the Hart casein test. =Destruction of bacteria in milk.= Actual destruction of the life of bacterial cells by heat is one of the most important ways for preserving milk. Heat easily destroys the vegetating, growing bacteria, while the spores, of which there are always a number in milk, are very resistant. If, however, the growing organisms are destroyed, the milk will keep much longer than if it had not been so treated. The process of pasteurization was first used by the French bacteriologist, Pasteur, for the treatment of the wines of his native district which were likely to undergo undesirable types of fermentations due to bacteria. From the wine industry it was applied in the brewing industry, and was later found to be of the greatest service in the dairy industry. The process of pasteurization may be briefly defined, as the heating of milk to temperatures, varying from 140° F. and upward for a longer or shorter time, and subsequently cooling to a low temperature, so as to prevent the germination of the spores that are not destroyed by the heating. =Effect of heat on milk.= When milk is heated it undergoes more or less profound changes, depending on the temperature and time of heating. Some of these changes are of practical importance, since they are more or less evident, and objectionable to the consumer.