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87
"Tuberculosis involving the udder is comparatively common
in cows, and in such cases their milk always contains tubercle
bacilli, and is therefore dangerous for human beings consuming it.
It was, however, undecided what is the danger, if any, attaching to
the milk of tuberculous cows in which the udder presents no
evidence of disease. We therefore took the opportunity of making
a number of observations and experiments bearing on this point.
The experiments were made with the milk of cows which had
contracted the disease in the natural way. None of the
cows investigated showed any sign of disease of the udder during
life, and in all, after slaughtering, the udder was carefully examined
for tuberculous lesions and tubercle bacilli. No tuberculosis was
found except in one case, in which one quarter of the udder showed
four small nodules. These could not possibly have been detected
during life.
We found that the milk of cows obviously suffering from
tuberculosis contained tubercle bacilli whether the milk was
obtained in the ordinary way or was withdrawn from the teat by
means of a sterilised catheter. The presence of tubercle bacilli in
the milk of cows clinically recognisable as tuberculosis, confirms
the opinion we expressed in our Second Interim Report that the
milk of such cows must be considered dangerous for human beings.
The experiments which we have carried out with regard to the
infectivity of the faeces of tuberculous cows were dictated by
knowledge of the fact that dirt of various kinds from cows and the
cowshed is almost constantly present in milk as it reaches the
consumer. Cows suffering from extensive tuberculosis of the lungs
must discharge considerable numbers of bacilli from the air
passages in the act of coughing, and some of the bacilli thus
expelled may find their way into the milk. But our experiments
indicate that the excrement of cows obviously suffering from
tuberculosis of the lungs or alimentary canal must be regarded as
much more dangerous than the matter discharged from the mouth
or nostrils. We have found that even in the case of cows with
slight tuberculous lesions tubercle bacilli in small numbers are
discharged in the faeces, while as regards cows clinically tuberculous
our experiments show that the faeces contain large numbers of
living and virulent tubercle bacilli.
The presence of tuberculous cows in company with
healthy cows in the cowshed is therefore distinctly dangerous, as
some of the tubercle bacilli which escape from their bodies in the
excrement are almost certain to find their way into the milk."