[Illustration: Fig. 3]

When the milk has been cooled by some rapid method, keep it cool until
it is used. This precaution is necessary because of the nature of
pasteurized milk. The temperature at which milk is pasteurized is
sufficient to kill all fully developed bacteria, but those which exist
in an undeveloped state, or in the form of spores, develop very rapidly
after pasteurization unless the milk is kept cold and clean. If these
bacteria were allowed to develop, the purpose of pasteurization would be
lost, and the milk would become as dangerous as it was originally. The
advantage of cooling milk rapidly will be fully appreciated upon
referring to Fig. 4, which illustrates the development of a single germ
in milk that is cooled rapidly and in milk that is cooled slowly.

[Illustration: Fig. 4]

39. STERILIZED MILK.--By sterilized milk is meant milk in which all
germs are destroyed by sterilization. Such milk is not sold by dealers,
but the process of sterilization is resorted to in the home when
pasteurization is not sufficient to render milk safe. This process,
which is the only positive means of destroying all germs, consists in
bringing the milk to the boiling point, or 212 degrees Fahrenheit,
allowing it to boil for three quarters of an hour, and then cooling it
rapidly. One who undertakes to treat milk in this way should remember
that it is difficult to boil milk, because the solids in the milk adhere
to the bottom and sides of the vessel and soon burn. However, this
difficulty can be overcome by sterilizing the milk in the bottles in
which it is bought.