eet 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.

~Effect of bacteria in wash water.~ An important factor in contamination
may be the wash water that is used. Much carelessness often prevails
regarding the location and drainage of the creamery well, and if same
becomes polluted with organic matter, bacterial growth goes on apace.
Melick[170] has made some interesting studies on using pasteurized and
sterilized well waters for washing. He found a direct rela