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76
used for food. This part of the question will be
best summarised by quoting the recapitulations at
the close of the Report of the Royal Commission.
"We have obtained ample evidence that food derived from tuberculous
animals can produce tuberculosis in healthy animals. The
proportion of animals contracting tuberculosis after experimental use
of such food is different in one and another class of animals; both
carnivora and herbivora are susceptible, and the proportion is high in
pigs. In the absence of direct experiments on human subjects, we
infer that men also can acquire tuberculosis by feeding upon materials
derived from tuberculous food-animals.
The actual amount of tuberculous disease among certain classes
of food-animals is so large as to afford to man frequent occasions
for contracting tuberculous disease through his food. As to the
proportion of tuberculosis acquired by man through his food or
through other means, we can form no definite opinion, but we think
it probable that an appreciable part of the tuberculosis that affects
man is obtained through his food.
The circumstances and conditions with regard to the tuberculosis
in food-animals which lead to the production of tuberculosis in man
are, ultimately, the presence of active tuberculous matter in the food
taken from the animal and consumed by the man in a raw or insufficiently
cooked state.
Tuberculous disease is observed most frequently in cattle and
in swine. It is found far more frequently in cattle (full grown) than
in calves, and with much greater frequency in cows kept in town
cow-houses than in cattle bred for the express purpose of slaughter.
Tuberculous matter is but seldom found in the meat substance
of the carcase; it is principally found in the organs, membranes, and
glands. There is reason to believe that tuberculous matter, when
present in meat sold to the public, is more commonly due to the
contamination of the surface of the meat with material derived from
other diseased parts than to disease of the meat itself. The same
matter is found in the milk of cows when the udder has become
invaded by tuberculous disease, and seldom or never when the udder
is not diseased. Tuberculous matter in milk is exceptionally active in
the operation upon the animals fed either with the milk or with dairy
produce derived from it. No doubt the largest part of the tuberculosis
which man obtains through his food is by means of milk
containing tuberculous matter.
The recognition of tuberculous disease during the life of an animal