ne tablet which is composed of a
solid alkali, and the indicator, phenolphthalein. The tablets are
dissolved in water, one to each ounce used. A number of white cups are
filled with the proper quantity of the solution necessary to neutralize
say, 0.2 per cent. lactic acid. Then, as the milk is delivered, the
proper quantity is taken from each can to which is added the tablet
solution. A retention of the pink color shows that there is not
sufficient acid in the milk to neutralize the alkali used; a
disappearance of color indicates an excess of acid. The standard
selected is of course arbitrarily chosen. In our experience, 0.2 per
cent. acidity (figured as lactic), has proven a satisfactory point. With
carefully handled milk the acidity ought to be reduced to about 0.15 per
cent. The acidity of the milk may be abnormally reduced if milk is kept
in rusty cans, owing to action of acid on the metal.

[Illustration: FIG. 15. Apparatus used in making rapid acid test. A
definite quantity of the alkali solution and indicator is placed in the
white tea cup. To this is added the quantity of milk by means of the
cartridge measure which would just be neutralized if the acidity was 0.2
per cent. A retention of the pink color shows a low acid milk; its
disappearance, a high acid milk.]

~Kinds of bacteria in milk.~ The number of bacteria in milk is not of so
much consequence as the kinds present. With reference to the number of
different species, the more dirt and foreign matter the milk contains,
the larger the number of varieties found in the same. While milk may
contain forms that are injurious to man, still the great majority of
them have no apparent effect on human health. In their effect on milk,
the case is much different. Depending upon their action in milk, they
may be grouped into three classes:

1. Inert group, those producing no visible change in the milk.

2. Sour milk forms, those breaking up the milk sugar with or without the
formation of gas.

3. Digesting or peptonizing group, those capable of rendering the casein
of milk soluble and more or less completely digested.

A surprisingly large number of bacteria that are found in milk belong to
the first class. Undoubtedly they affect the chemical characteristics of
the milk somewhat, but not to the extent that it becomes physically
perceptible. Eckles[46] reports in a creamery supply from 20 to 55 per
cent. of entire flora as included in this class.

By far the mo