milk on the growth of
bacteria.]

Conn[42] is inclined to regard temperature of more significance in
determining the keeping quality than the original infection of the milk
itself. Milk which curdled in 18 hours at 98 deg. F., did not curdle in 48
hours at 70 deg., and often did not change in two weeks, if the
temperature was kept at 50 deg. F.

Where kept for a considerable period at this low temperature, the milk
becomes filled with bacteria of the undesirable putrefactive type, the
lactic group being unable to form acid in any appreciable amounts.
Running well water can be used for cooling, if it is possible to secure
it at a temperature of 48 deg.-50 deg. F. The use of ice, of course, gives
better results, and in summer is greatly to be desired. The influence of
these lowered temperatures makes it possible to ship milk long
distances[43] by rail for city supplies, if the temperature is kept low
during transit.

~Mixing night and morning milk.~ Not infrequently it happens when old milk
is mixed with new, that the course of the fermentative changes is more
rapid than would have been the case if the two milks had been kept
apart. Thus, adding the cooled night milk to the warm morning milk
sometimes produces more rapid changes in both. The explanation for this
often imperfectly understood phenomenon is that germ growth may have
gone on in the cooled milk, and when this material is added to the
warmer, but bacteria-poor, fresh milk, the temperature of the whole mass
is raised to a point suitable for the more rapid growth of all bacteria
than would have occurred if the older milk had been kept chilled.

~Number of bacteria in milk.~ The number of organisms found in milk
depends upon (1) the original amount of contamination, (2) the age of
the milk, and (3) the temperature at which it has been held. These
factors all fluctuate greatly in different cases; consequently, the germ
life is subject to exceedingly wide variations. Here in America, milk
reaches the consumer with less bacteria than in Europe, although it may
often be older. This is due largely to the more wide-spread use of ice
for chilling the milk _en route_ to market. Examinations have been made
of various supplies with the following results: Sedgwick and Batchelder
found in 57 tests of Boston milk from 30,000-4,220,000 per cc. Jordan
and Heineman found 30% of samples of Chicago milk to range from 100,000
to 1,000,000 while nearly one half were from 1-20,000