measures
heretofore mentioned will greatly reduce the germ content of the
milk.

=Cooling of milk on farm.= Bacterial growth is directly related to
temperature conditions, and with summer temperatures, such
development goes on apace, unless it is checked by early cooling.
The larger portion of bacteria that find their way into milk,
especially those that are previously in contact with the air, are in
a dormant condition, and are therefore not stimulated into immediate
growth, unless reasonably high temperatures prevail. In milk, which
comes from the animal at blood heat, this growth is greatly
stimulated. To counteract this effect, milk should be chilled as
soon after milking as possible. If the temperature is immediately
lowered to 50 deg. F., or lower, actual cell development is greatly
retarded, and the rate of souring, and other fermentative changes
thereby diminished. In this country ice is liberally used in
accomplishing this result. In Europe, the use of ice is much less
common. The employment of such artificial means of refrigeration
makes possible the shipment of milk for long distances by rail. New
York city now receives milk that is produced in Canada and
northeastern Ohio.

[Illustration: Fig. 16.--Effect of Cooling Milk.]

=Aeration of milk=. The custom has been extensively recommended of
subjecting milk to the influence of air in the belief that such
exposure permits of the interchange of gases that would improve the
quality. In practice, this process, known as aeration, is carried on
in different ways. In some cases, air is forced into the milk; in
others, the milk is allowed to distribute itself in a thin sheet
over a broad surface, falling in drops or tiny streams through the
air. Whenever this process is carried on at a temperature lower
than that of the milk, it results in more or less rapid cooling.

In earlier times, aeration was generally recommended and practiced,
especially in connection with the cheese industry, but carefully
controlled experiments fail to show that the process exerts any
material influence on the rate of germ development. If it is carried
out in an atmosphere more or less charged with bacteria, as in the
barn or stable, it is more than likely to add to the bacterial
content of the milk. While to some extent odors may be eliminated by
the process, the custom is not followed so generally now as it used
to be some years ago.

=Absorption of taints.= A tainted condition in