y for
addition to the cream. The propagation of the starter must be done
with especial reference to keeping it in good condition and in as
high a state of purity as possible.

In the past the starter was propagated, by adding the contents of
the bottle purchased to a small amount of milk that had been heated
and cooled; this, if kept in a warm place, would be curdled in
twenty-four hours, and could be used for the inoculation of a large
mass of milk, that had been treated in a like manner, and which,
when curdled, was added to the cream; a small amount was saved for
the purpose of again inoculating a mass of milk that had been heated
and cooled. Following this method it was very difficult to keep the
culture from becoming contaminated with other forms of bacteria.
More recently the most successful butter makers have propagated the
so-called "mother starters" in small vessels, and have used the
larger mass of starter for the inoculation of the cream alone.

Glass vessels are preferable for the propagation of the mother
starters since they are impervious and through the transparent wall
the condition of the ripened starter can be more easily determined
than in a metal or earthenware vessel. An ordinary milk bottle with
an inverted tumbler for a cover, to protect the starter from
contamination from the air, is a most convenient vessel.

The starters may be propagated either in whole or skim milk; the
former is preferable since, in most creameries, it can be more
easily selected. The quality of the milk used has much to do with
the quality of the starter; it should be as fresh and clean as it
is possible to obtain. The clean bottle should be filled half to
two-thirds full, covered and heated in some manner so that the milk
shall be at a temperature close to the boiling point for fifteen to
twenty minutes. The heating may be done by placing the bottles in
water, which is heated on a stove or by steam, or the bottles may be
subjected to streaming steam. The milk is cooled quickly and the
contents of the package purchased added and well mixed with the
milk. In the case of the dry starters, the mixing should be done
with especial care. The bottle is kept in a warm place and in
twenty-four to thirty-six hours, the milk should be curdled. A
second bottle must be treated as before and inoculated from the
first, and the process repeated daily since the bacteria must have
fresh food, if they are to be maintained in good conditio