of
incubation had been maintained. The average of 82 samples, taken for the
period of one year, showed 325 bacteria per cc.

[Illustration: FIG. 26. Effect of pasteurizing on germ content of milk.
Black square represents bacteria of raw milk; small white square, those
remaining after pasteurization.]

~Bacterial efficiency of continuous-flow pasteurizers.~ A quantitative
determination of the bacteria found in milk and cream when treated in
machinery of this class almost always shows a degree of variation in
results that is not to be noted in the discontinuous apparatus.

[Illustration: FIG. 27. Reid's Continuous Pasteurizer.]

Harding and Rogers[146] have tested the efficiency of one of the Danish
type of continuous pasteurizers. These experiments were made at 158 deg.,
176 deg. and 185 deg. F. They found the efficiency of the machine not
wholly satisfactory at the lower temperatures. At 158 deg. F. the average
of fourteen tests gave 15,300 bacteria per cc., with a maximum to minimum
range from 62,790 to 120. Twenty-five examinations at 176 deg. F. showed
an average of only 117, with a range from 300 to 20. The results at 185
deg. F. showed practically the same results as noted at 176 deg. F.
Considerable trouble was experienced with the "scalding on" of the milk
to the walls of the machine when milk of high acidity was used.

Jensen[147] details the results of 139 tests in 1899, made by the
Copenhagen Health Commission. In 66 samples from one hundred thousand to
one million organisms per cc. were found, and in 22 cases from one to
five millions. Nineteen tests showed less than 10,000 per cc.

In a series of tests conducted by the writer[148] on a Miller
pasteurizer in commercial operation, an average of 21 tests showed
12,350 bacteria remaining in the milk when the milk was pasteurized from
156 deg.-164 deg. F. The raw milk in these tests ran from 115,000 to
about one million organisms per cc.

A recently devised machine of this type (Pasteur) has been tested by
Lehmann, who found that it was necessary to heat the milk as high as
176 deg. to 185 deg. F., in order to secure satisfactory results on the
bacterial content of the cream.

The writer tested Reid's pasteurizer at 155 deg. to 165 deg. F. with the
following results: in some cases as many as 40 per cent. of the bacteria
survived, which number in some cases exceeded 2,000,000 bacteria per
cc.

~Pasteurizing details.~ While the pasteurizing process is exc