~Mixing night and morning milk.~ Not infrequently it happens when old milk is mixed with new, that the course of the fermentative changes is more rapid than would have been the case if the two milks had been kept apart. Thus, adding the cooled night milk to the warm morning milk sometimes produces more rapid changes in both. The explanation for this often imperfectly understood phenomenon is that germ growth may have gone on in the cooled milk, and when this material is added to the warmer, but bacteria-poor, fresh milk, the temperature of the whole mass is raised to a point suitable for the more rapid growth of all bacteria than would have occurred if the older milk had been kept chilled. ~Number of bacteria in milk.~ The number of organisms found in milk depends upon (1) the original amount of contamination, (2) the age of the milk, and (3) the temperature at which it has been held. These factors all fluctuate greatly in different cases; consequently, the germ life is subject to exceedingly wide variations. Here in America, milk reaches the consumer with less bacteria than in Europe, although it may often be older. This is due largely to the more wide-spread use of ice for chilling the milk _en route_ to market. Examinations have been made of various supplies with the following results: Sedgwick and Batchelder found in 57 tests of Boston milk from 30,000-4,220,000 per cc. Jordan and Heineman found 30% of samples of Chicago milk to range from 100,000 to 1,000,000 while nearly one half were from 1-20,000,000 per cc. The germ content of city milks increase rapidly in the summer months. Park[44] found 250,000 organisms per cc. in winter, about 1,000,000 in cool weather and 5,000,000 per cc. in hot summer weather. Knox and Bassett in Baltimore report 1,500,000 in spring and nearly 4,500,000 in summer. Eckles[45] studied milk under factory conditions. He finds from 1,000,000 to 5,000,000 per cc. in winter, and in summer from 15-30 millions. ~Bacterial standards for city supplies.~ It would be very desirable to have a hygienic standard for city milk supplies, as there is a butter fat and milk-solid test, but the wide spread variation in germ content and the impracticability of utilizing ordinary bacterial determinations (on account of time required) makes the selection of such a standard difficult. Some hold, as Park, that such a standard is feasible. The New York City Milk commission has set a standard of 30,000 bacteria per cc. for their certified milk and 100,000 per cc. for inspected milk. Rochester, N. Y. has attempted the enforcement of such a standard (limit, 100,000 per cc.) with good results it is claimed while Boston has placed the legal limit at 500,000 per cc. Quantitative standards would seem more applicable to "certified" or sanitary supplies than to general city supplies, where the wide range in conditions lead to such enormous variations that the bacterial standard seems too refined a method for practical routine inspection.