s widely in different
sections of the country, being greatest in the older dairy sections,
and in those supplying milk to the cities, on account of the
constant buying and selling of animals, thus giving more frequent
opportunity of introducing the disease into the herds. Throughout
the country at large, probably less than ten per cent of the cows
are tuberculous, and it is estimated that at least one per cent of
the diseased animals have tuberculous udders. It has been suggested
that the dilution of the milk of such animals with that of healthy
cows would remove a great part of the danger from milk. In the
case where the milk of a large number of herds is mixed, this may be
of some importance, but in no case is it safe to assume that
dilution of the milk of tuberculous cows is any guarantee of safety.

It has been shown that milk, perfectly normal in appearance, coming
from a tuberculous udder could be diluted a million times and still
produce the disease on inoculation into experimental animals. In the
case of swine, the susceptibility is so great that a single feeding
of infected milk, even in a very dilute condition, causes with
certainty the production of the disease.

Some observers maintain that the contamination of the milk with the
manure of tuberculous animals is of greater hygienic importance,
than that coming from diseased udders, since the number of animals
having tuberculosis of the lungs and intestines is far greater than
those with diseased udders.

=Economic aspects of bovine tuberculosis.= Not only is this disease
invested with much importance because of its inter-relation with the
human, but from an economic point of view alone, it is undoubtedly
the greatest scourge that affects the dairyman. Its insidiousness
makes it exceedingly difficult to recognize. The consequence is that
many fine herds become seriously involved before its presence is
recognized. In the main, the disease is introduced into a herd by
purchase, often by buying in pure-bred stock to improve the quality
of the herd. Where the disease has been established in a region for
some time, there is also danger that unheated factory by-products,
as skim milk and whey, may function in its spread. Where such
conditions prevail, the spread of the disease in the creamery
district is exceedingly rapid. When once introduced into a herd,
the disease sooner or later spreads from the originally affected
animal to others in the herd. Close contac