On the large scale the treatment of the milk would take place entirely in the jars in which it would be sent out, and the sterilisation and incubation would be conducted in different pieces of apparatus. The sterilisation would be effected either (1) by direct steaming, or (2) by hot water heated by steam. Fig. 55 shows the first type of sterilisation. The tank is of wrought iron or steel with strengthening pieces of angle iron. The door, with pulleys and counterweight for easy handling, is fastened steam-tight by hinged bolts. The apparatus is mounted on a stand at a convenient height for handling the bottles; and in front is another stand with channel iron rails to take the waggon in which the bottles or jars to be sterilised are packed. When the door is fast, steam is turned on, and regulated to produce the proper temperature by the thermometer fixed in the shell, in which a pressure gauge is also secured. After sterilising, the door is opened and the waggon drawn forward to the outside, allowed to cool, or removed elsewhere to cool, and allow space for a new charge. [Illustration: FIG. 55.—Sterilising Apparatus for sterilising milk on the large scale. The bottles of milk are sterilised, and the culture can then be added, and the incubation allowed to proceed in an insulated chamber.] The second method of sterilising is by hot water, as in Fig. 56. The bottles or jars are placed on a perforated false bottom in the rectangular tank, water run in up to the necks, and steam turned on; the lid is fastened with hinged and hooked bolts; a thermometer fastened in the lid, and with a long stem enclosed in metal, indicates the temperature. At the end of the sterilising process cold water is turned on, and at the same time the overflow water cock is opened; the cold water gradually reduces the temperature, and the incubating point is quickly reached. [Illustration: FIG. 56 Another Method of Sterilising (Dairy Supply Co., Ltd.).] Incubation in bottles or jars, sterilised in these ways, can best be conducted in an insulated room, with say, six inches of silicate cotton, granulated cork, or washed cow hair packed between two-inch by six-inch battens, covered with matching on either side, and lined with sheet zinc. It would be an advantage to have an air-lock or anteroom into which the waggons or trays of sterilised jars could be run, and the door of the anteroom closed before the door of the insulated room is opened. This would tend to prevent variations of temperature in the room, and also, by checking free communication with the outside air, decrease contamination. The waggons of jars would be run in, and culture added to each jar by a sterilised pipette. The atmosphere of the room would be kept pure by running in air frequently through a filter of moist cotton-wool by means of an electric fan, and at intervals the interior would be sterilised by the use of formalin vapour.