ich have found such great practical application in the
treatment of disease, in disinfection, and in the preservation of
various products, are almost entirely ignored in milking."

~Growth of bacteria in milk.~ Milk is so well suited as a medium for the
development of germ life that it might be expected that all
microorganisms would develop rapidly therein, and yet, as a matter of
fact, growth does not begin at once, even though the milk may be richly
seeded. At ordinary temperatures, such as 70 deg. F., no appreciable
increase is to be noted for a period of 6-9 hours; at lower temperatures
(54 deg. F.) this period is prolonged to 30-40 hours or even longer. After
this period has elapsed, active growth begins and continues more or less
rapidly until after curdling.

The cause of this suspended development is attributed to the germicidal
properties inherent to the milk.[40]

Milk is of course seeded with a considerable variety of organisms at
first. The liquefying and inert species are the most abundant, the
distinctively lactic acid class occurring sparsely, if at all. As milk
increases in age, germ growth begins to occur. More or less development
of all types go on, but soon the lactic species gain the ascendency,
owing to their being better suited to this environment; they soon
outstrip all other species, with the result that normal curdling
generally supervenes. The growth of this type is largely conditioned by
the presence of the milk sugar. If the sugar is removed from milk by
dialysis, the liquid undergoes putrefactive changes due to the fact that
the putrefactive bacteria are able to grow if no acid is produced.

~Relation of temperature to growth.~ When growth does once begin in milk,
the temperature at which it is stored exerts the most profound effect on
the rate of development. When milk is not artificially cooled, it
retains its heat for some hours, and consequently the conditions become
very favorable for the rapid multiplication of the contained organisms,
as is shown in following results obtained by Freudenreich[41]:

_No. of bacteria per cc. in milk kept at different temperatures._

77 deg. F. 95 deg. F.
5 hrs. after milking 10,000 30,000
8 " " " 25,000 12,000,000
12 " " " 46,000 35,280,000
26 " " " 5,700,000 50,000,000

[Illustration: FIG. 14. Effect of cooling