pplicable on a commercial scale must rest
largely upon the destruction of bacteria that are present in the milk.

The two possible methods by which bacteria can be destroyed after they
have once gained access is (1) by the use of chemical preservatives; (2)
by the aid of physical methods.

~Chemical preservatives.~ Numerous attempts have been made to find some
chemical substance that could be added to milk which would preserve it
without interfering with its nutritive properties, but as a general rule
a substance that is toxic enough to destroy or inhibit the growth of
bacterial life exerts a prejudicial effect on the tissues of the body.
The use of chemicals, such as carbolic acid, mercury salts and mineral
acids, that are able to entirely destroy all life, is of course
excluded, except when milk is preserved for analytical purposes; but a
number of milder substances are more or less extensively employed,
although the statutes of practically all states forbid their use.

The substances so used may be grouped in two classes:

1. Those that unite chemically with certain by-products of bacterial
growth to form inert substances. Thus bicarbonate of soda neutralizes
the acid in souring milk, although it does not destroy the lactic acid
bacteria.

2. Those that act directly upon the bacteria in milk, restraining or
inhibiting their development. The substances most frequently utilized
are salicylic acid, formaldehyde and boracic acid. These are nearly
always sold to the milk handler, under some proprietary name, at prices
greatly in excess of what the crude chemicals could be bought for in the
open market. Formaldehyde has been widely advertised of late, but its
use is fraught with the greatest danger, for it practically renders
insoluble all albuminous matter and its toxic effect is greatly
increased in larger doses.

These substances are generally used by milk handlers who know nothing of
their poisonous action, and although it may be possible for adults to
withstand their use in dilute form, without serious results, yet their
addition to general milk supplies that may be used by children is
little short of criminal. The sale of these preparations for use in milk
finds its only outlet with those dairymen who are anxious to escape the
exactions that must be met by all who attempt to handle milk in the best
possible manner. Farrington has suggested a simple means for the
detection of preservalin (boracic acid).[128] Whe