~Other tests.~ Any test to be of much service must be capable of being quickly applied. The writer believes for city milk inspectors that the acid test would serve a very useful purpose. This test measures the acidity of the milk. There is, of course, no close and direct relationship between the development of acidity and the growth of bacteria, yet in a general way one follows the other at normal temperatures. Where the temperature is kept rather low, bacterial growth might go on without much acid development, but in the great majority of cases a high degree of acidity means either old milk, in which there has been a long period of incubation, or high temperature, where rapid bacterial growth has been possible. Either of these conditions encourages germ growth and thus impairs the quality of the milk. The rapid determination of acidity may be made in an approximate manner so as to serve as a test at the weigh-can or intake. The test is best made by the use of the well known alkaline 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.