the milk of tuberculous cows, which was virulent when injected by
itself into animals, was innocuous when diluted with 40 to 100 times its
volume of healthy milk. This fact is hardly to be relied upon in
practice, unless the proportion of reacting to healthy cows is
positively known.

It has also been claimed in the centrifugal separation of cream from
milk[96] that by far the larger number of tubercle bacilli were thrown
out with the separator slime. Moore[97] has shown that the tubercle
bacilli in an artificially infected milk might be reduced in this way,
so as to be no longer microscopically demonstrable, yet the purification
was not complete enough to prevent the infection of animals inoculated
with the milk.

Another way to exclude all possibility of tubercular infection in milk
supplies is to reject all milk from reacting animals. This method is
often followed where pasteurization or sterilization is not desired. In
dairies where the keeping quality is dependent upon the exclusion of
bacteria by stringent conditions as to milking and handling ("sanitary"
or "hygienic" milk), the tuberculin test is frequently used as a basis
to insure healthy milk.

~Foot and mouth disease.~ The wide-spread extension of this disease
throughout Europe in recent years has given abundant opportunity to show
that while it is distinctively an animal malady, it is also
transmissible to man, although the disease is rarely fatal. The causal
organism has not been determined with certainty, but it has been shown
that the milk of affected animals possesses infectious properties[98]
although appearing unchanged in earlier phases of the disease.

Hertwig showed the direct transmissibility of the disease to man by
experiments made on himself and others. By ingesting milk from an
affected animal, he was able to produce the symptoms of the disease, the
mucous membrane of the mouth being covered with the small vesicles that
characterize the malady. It has also been shown that the virus of the
disease may be conveyed in butter.[99] This disease is practically
unknown in this country, although widely spread in Europe.

There are a number of other bovine diseases such as anthrax,[100]
lockjaw,[101] and hydrophobia[102] in which it has been shown that the
virus of the disease is at times to be found in the milk supply, but
often the milk becomes visibly affected, so that the danger of using the
same is greatly minimized.

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