8. Do not refrigerate the starter when it has reached the proper stage of development, as this retards the bacterial growth in the same manner as cold weather checks the growth of grain. It is preferable to dilute the starter, if it cannot be used when ready, with sufficient freshly sterilized sweet milk to hold the acidity at the proper point and thus keep the bacteria in the starter in a condition which will favor vigorous growth. 9. The starter should be propagated from day to day by adding a small quantity to a new lot of freshly prepared milk. For this purpose two propagating cans should be provided so that one starter may be in use while the other is being prepared. ~How long should a starter be propagated?~ No hard-and-fast rule can be given for this, for it depends largely upon how carefully the starter is handled during its propagation. If the starter is grown in sterilized milk kept in steamed vessels and is handled with sterile dippers, it is possible to maintain it in a state of relative purity for a considerable period of time; if, however, no especial care is given, it will soon become infected by the air, and the retention of its purity will depend more upon the ability of the contained organism to choke out foreign growths than upon any other factor. Experience seems to indicate that pure-culture starters "run out" sooner than domestic starters. While it is possible, by bacteriological methods, to determine with accuracy the actual condition of a starter as to its germ content, still such methods are inapplicable in creamery practice. Here the maker must rely largely upon the general appearance of the starter as determined by taste and smell. The supply houses that deal in cultures of this class generally expect to supply a new culture at least every month. ~Bacteria in butter.~ As ripened cream is necessarily rich in bacteria, it follows that butter will also contain germ life in varying amounts, but as butter-fat is not well adapted for bacterial food, the number of germs in butter is usually less than in ripened cream. Sweet-cream butter is naturally poorer in germ life than that made from ripened cream. Grotenfelt reports in sweet-cream butter, the so-called "Paris butter," only a few bacteria while in acid cream butter the germ content runs from scores to hundreds of thousands.