View report page

121
HUMAN AND ANIMAL TUBERCULOSIS.
Extract from the Third Interim Report of the Royal Commission appointed
to inquire into the relation of HUMAN and ANIMAL TUBERCULOSIS.
In our Second Interim Report we expressed the opinion, as the result of our
investigations, that a very considerable amount of disease and loss of life,
especially among infants and children, must be attributed to the consumption
of cow's milk containing tubercle bacilli.
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.
In natural tuberculosis in the cow, cases which show such obvious symptoms
of the disease as emaciation and cough should be considered separately from
the cases in which there are no such signs and in which the disease is to be
recognised during life only by means of the injection of tuberculin.
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 tuberculosis lesions and tubercle bacilli. No tuberculosis was found except
in one case (Cow F), 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 the cows obviously suffering from tuberculosis
(see Appendix: Cows B, C, and F) 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was obtained in the ordinary way or was withdrawn from the teat by means of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 tuberculous 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 cow-shed is almost constantly present
in milk as it reaches the consumer. Cows suffering from extensive tuberculosis
of the lungs must discharge considerable numbers of a 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 (such as B, C, and F), in company with
healthy cows in the cow shed 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.