find life
in milk congenial, whose effect upon the human system is not salutary,
and, if milk infected with those varieties is used for feeding infants,
the result is quite likely to be a disturbance of their digestive
system, producing diarrhea and cholera infantum and possibly death.

It was at one time common to add to milk certain antiseptics for the
purpose of preventing the growth of bacteria, and, except that the
preservatives acted quite as injuriously upon man as upon the bacteria,
the results, so far as merely keeping the milk went, were all that could
be desired. The chemicals added were borax, boracic acid, salicilic
acid, sodium carbonate, and other similar disinfectants. Gradually,
however, it has come to be known that, inasmuch as the milk when first
drawn from the cow's udder is sterile, that is, contains no bacteria,
and since it is quite possible to prevent the introduction of bacteria
into milk during the processes of milking, straining, and bottling,
there is no need of the addition of preservatives, provided particular
care is exercised in handling the milk.

_Effects of bacteria._

Since this care involves the expenditure of both additional time and
money, questions at once arise whether such expenditure is necessary,
whether the introduction of a few bacteria into the milk is
objectionable, and what the results are upon the persons drinking milk
containing bacteria. For our present purpose, the kinds of bacteria
which find their way into milk may be divided into two classes, namely,
those that are normally in milk and which tend to produce souring, and
those which accidentally enter and are able to produce disease in
persons drinking the milk. The first kind probably enter the milk from
the air or from the surface of the milk-pail, and in the milk increase
in numbers very rapidly and have the same effect in the milk and on
persons drinking the milk as any large amount of organic matter.

The second kind of bacteria are known as pathogenic; that is, are the
direct cause of disease when taken into the human system. Under ordinary
circumstances, this latter class will not be found in milk, since these
kinds of bacteria must come from some infected person, and if no such
person is in contact with the milk at any stage, then it is impossible
for the milk to become so polluted. However, those interested in
preventing the spread of disease through polluted milk argue that if the
conditions in a stabl