1,260,000 798,000 32,000 5,770 3,900
Series II. 750,000 665,000 262,400 201,000 950 700 705
Series III. 1,350,000 1,100,000 260,000 215,000 575 610 650
Series IV. 1,750,000 ---- 87,360 ---- 4,000 3,500 3,600

It appears from these results that the most marked decrease in
temperature occurs at 140 deg. F. (60 deg. C.). It should also be observed
that an increase in heat above this temperature did not materially
diminish the number of organisms present, indicating that those forms
remaining were in a spore or resistant condition. It was noted, however,
that the developing colonies grew more slowly in the plates made from the
highly heated milk, showing that their vitality was injured to a greater
extent even though not killed.

_2. Destruction of disease bacteria._ While milk should be pasteurized
so as to destroy all active, multiplying bacteria, it is particularly
important to destroy any organisms of a disease nature that might find
their way into the same. Fortunately most of the bacteria capable of
thriving in milk before or after it is drawn from the animal are not
able to form spores and hence succumb to proper pasteurization. Such is
the case with the diphtheria, cholera and typhoid organisms.

The organism that is invested with most interest in this connection is
the tubercle bacillus. On account of its more or less frequent
occurrence in milk and its reputed high powers of resistance, it may
well be taken as a standard in pasteurizing.

~Thermal death limits of tubercle bacillus.~ Concerning the exact
temperature at which this germ is destroyed there is considerable
difference of opinion. Part of this arises from the inherent difficulty
in determining exactly when the organism is killed (due to its failure
to grow readily on artificial media), and part from the lack of uniform
conditions of exposure. The standards that previously have been most
generally accepted are those of De Man,[137] who found that thirty
minutes exposure at 149 deg. F., fifteen minutes at 155 deg. F., or ten
minutes at 167 deg. F., sufficed to destroy this germ.

More recently it has been demonstrated,[138] and these results
confirmed,[139] that if tuberculous milk is heated in closed receptacles
where the surface pellicle does not form, the vitality of this disease
germ is destr