bacillus.
So far as statistics can be given on this subject, it seems probable
that not more than ten per cent of the cows reacting under the
tuberculin test would show tubercular bacilli in the milk, or would
develop tubercular reactions if the milk were used in inoculations. The
reason for this is probably that the tubercular growth in the cow does
not naturally attack the milk glands until the disease is well advanced,
and when the general appearance of the cow indicates severe illness, so
that any careful milkman would not use the particular milk, even if the
milk flow did not cease. It is not reasonable to assume that all milk
from tubercular cows is itself infected, nor yet that all children
drinking milk so infected will contract the disease. But the mere
possibility of demonstrating that a small percentage of tubercular cows
will cause human tuberculosis is sufficient to justify all possible
precautions against tubercular animals and against the distribution of
tubercular milk. In this connection it is worth while noting that the
cows most affected by tuberculosis are those confined in small crowded
stables, with no fresh air, with no exercise, and with insufficient or
improper food. Unfortunately it is not possible to trace the connection
between the particular animal responsible for the disease in a human
being, since the period required for the development of the disease is
so great that the possible time of onset is forgotten and the cause of
the disease entirely out of mind.

It can only be said, therefore, that laboratory experiments have
demonstrated the presence of the tuberculosis bacillus in milk from
tubercular cows, and that this bacillus is known to produce tubercular
lesions in man. It is wise, therefore, to eliminate the milk of
tubercular cows if healthy milk is to be provided.

_Methods of obtaining clean milk._

Aside from the infection of milk by specific disease-producing bacteria,
the milkman of to-day must be very careful to avoid a milk which shall
contain large numbers of bacteria of any type which, while not producing
any specific disease, nevertheless causes changes in the chemical
composition of the milk, which make it at the same time unfit as an
article of food for individuals and shows the possibility of other kinds
of infection.

There are two axioms to be followed if good clean milk is to be
produced, and those are that the milking and straining shall be done in
clean stable