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TUBERCULOSIS IN CATTLE. 3 
i, 
has been collected during the fifteen years’ study has con- 
stantly pointed toward the existence of such a danger. The 
reasons which have led to the universal belief that milk may 
be a source of danger are essentially as follows: In the first 
place, ‘as we have seen, it has been demonstrated clearly 
enough that under certain circumstances the tubercle bacilli 
are found in the milk of tuberculous animals. Exactly at 
what stage of the disease the milk may become contaminated 
with the bacilli has been not so easily settled. While a 
variety of opinions have been held in the past, the practically 
unanimous opinion at the present time is that the milk does not 
become contaminated with the bacilli unless either there is 
generalized tuberculosis, or the udder itself is the seat of the 
tuberculous infection. If there is a tubercle in the milk gland, 
then the milk becomes contaminated. Those who have be- 
lieved that the milk may become infected, even in animals not 
suffering from udder disease, have probably either been dealing 
with cases of generalized tuberculosis in its advanced stages, 
and here it is also recognized that the milk may become in- 
fected, or they have probably had a case of udder disease so 
slightly advanced as to be not visible externally nor even with 
the post mortem examination usually given. If now the milk 
of tuberculous animals may thus contain the tubercle bacilli 
there appears to be no reason for doubting that the consump- 
tion of such milk may produce the disease. To this conclusion 
innumerable experiments have attested. 
The experiments which have been devised for determining 
the infectiousness of milk have been quite varied. Most of 
them have consisted of inoculating the milk into the abdomen 
of susceptible animals, the guinea pig being the animal com- 
monly used, simply because the guinea pig has shown itself 
to be very susceptible to the disease. Inoculations have been 
‘made in other animals, however, as well, such as pigs, rabbits, 
calves, and others. In other cases, however, the experiments 
have been made by feeding the milk to the animals in question, 
instead of inoculating them, on the manifest ground that ab- 
dominal inoculation is entirely different from consuming milk 
as food. These experiments have all given the same result, 
namely, that both the abdominal inoculation and the feeding 
of such milk to experimental animals is very likely, though not 
sure, to produce cases of disease. Hundreds and hundreds of 
positive results have been obtained where! perfectly healthy 
animals, either being inoculated with or fed upon milk from 
