There is one-third more food value in clean milk than in dirty milk, because its casein and sugar have not been spoiled and eaten by swarms of bacteria.

How great a difference careful cleanliness of this sort can make in milk is shown by the difference in the number of bacteria that the two kinds of milk contain.

Ordinary milk bought from the wagons in the open street, or from the cans in the stores, will contain anywhere from _a million_ to a _million and a half_ bacteria to the cubic centimeter (about fifteen drops); and samples have actually been taken and counted, which showed _five_ and _six millions_.
[Illustration: MILKING BY VACUUM PROCESS This method is used in many large dairies to avoid handling the udders or the milk.

Its chief drawback is that the long tubes are very difficult to keep clean.] Such a splendid food for germs is milk, and so rapidly do they grow in it, that dirty milk will actually contain more of them to the cubic inch than sewage, as it flows in the sewers.

Now see what a difference a little cleanliness will make! Good, clean, carefully handled milk, instead of having a million, or a million and a half, bacteria, will have less than ten thousand; and very clean milk may contain as low as three or four hundred, and these of harmless sorts.