single cow, as the mixing of the milk of a number of cows insures a
better average composition.

23. ADULTERATION OF MILK.--The composition of milk, and hence its
quality, is seriously affected by its adulteration. By this is meant the
extraction of any of the food substances from whole milk; the addition
of anything that tends to weaken or lower its quality or strength; the
use of coloring matter to make it appear of greater value than it
actually is; or the use of preservatives to prevent it from souring as
soon as it ordinarily would. It is, of course, illegal to adulterate
milk, yet it is sometimes done. The most convenient and possibly the
most common materials used to adulterate milk are water and skim milk.
The addition of water to milk decreases the quantity of all its food
substances, but the addition of skim milk reduces the quantity of fat
only. The color of the milk is often affected by the use of these
adulterants, but when this happens, yellow coloring is usually added to
restore the original appearance.

Sometimes the milk that a dairyman markets contains more fat than the
law requires; but even such milk cannot legally be skimmed nor diluted
with skim milk. The only thing that may be done to it is to mix it with
milk that is low in butter fat and thus obtain a milk that will average
the legal percentage. For instance, if milk from a dairy averages 5 per
cent, of butter fat, it may be diluted with milk that contains only 3
per cent, of butter fat, because the result of such mixing, which will
be milk averaging 4 per cent, of this food substance, will be the
legal standard.

24. To prevent milk from souring, dishonest milk dealers often put into
it such preservatives as soda, borax, and formaldehyde. There is no