The diagram (after Conn) shows the rapidity with which bacteria multiply in milk not properly cooled. A single bacterium (a) in 24 hours multiplied to 5 (b) in milk kept at 50° F.; (c) represents the number that develop from a single bacterium in milk kept 24 hours at 70° F. ] =Disinfectants.=—Antiseptics, such as benzoate of soda, formalin, boracic acid, etc., are not permissible _in_ milk, but _disinfectants_ such as soda, lime, washing powders, etc., should be freely used in cleaning utensils, bottles, floors and walls where milk is handled, so as to prevent as far as possible any infection. PASTEURIZATION [Illustration: Louis Pasteur, French scientist and originator of the process of pasteurization. ] Pasteurization depends upon the fact that almost all bacteria, and especially the disease-producing species, are checked in their growth and made harmless, if not totally destroyed, by instantaneous exposure to a temperature of 175° F., or a more or less prolonged exposure to lower temperature, for instance for 20 minutes to 157° or 30 minutes to 145°. These lower temperatures are recommended in the case of new milk to be consumed as such, in order not to change its digestibility. Pasteurizers with “holding devices” are therefore largely taking the place of the “continuous” sterilizing machines, which allow only momentary exposure to the highest temperature. Whatever method is used it is essential that after the heating is finished the milk should be cooled as quickly as possible to a temperature sufficiently low to prevent development of the germs that have not been entirely destroyed by the heat and which, if the milk is left for any length of time at a temperature favorable for bacterial life—anywhere between 65° and 110°,—will begin to grow again. Cool the milk to below 60° and if possible to 50° or 40°. Sometimes a second pasteurization is practiced, the milk being purposely allowed to stand at 70° to 80° for 12 to 24 hours after the first pasteurization for the germs which escaped destruction to develop into full-grown bacteria. They are then killed by the second heating before the milk is finally chilled to stop any further growth. Pasteurization can be done by placing the milk in any tin or enamelled or glass vessel, set in another vessel containing water (a double boiler). Heat until the milk has reached the desired temperature, hold it at that temperature the necessary time, and then place the vessel in cold running water or in ice water until the milk is thoroughly chilled. It is not advisable to place the hot milk in the ice box as cooling in air is too slow. Not until it is thoroughly cooled in water is it safe to put it in the ice box to _keep_ it cool. [Illustration: N. J. Fjord, Danish investigator ]