CONGRESS ON TUBERCULOSIS. 
461 
lute 4 y convincing. Tuberculosis is a disease that develops 
slowly, and, assuming for the moment that tubercle bacilli do 
occur in milk, and are a cause of disease in persons consuming 
such milk, it is obvious that, as a rule, the very act by which 
the infection is brought about destroys the only direct evidence 
of cause and effect that exists. 
One could only expect to be able to trace the disease to the 
milk when, after the onset of symptoms pointing to infection 
by way of the mouth, the cow from which the milk had been 
obtained was still available for examination. In practice this is 
rarely the case, and it is therefore not surprising that medical 
literature contains very few specific instances of the infection of 
human beings with tuberculosis by means of milk. It is 
obvious, however, that the entire absence of evidence of this 
kind would in no way exonerate milk from the suspicion of being 
one of the causes of human tuberculosis. 
We have already seen that, at least in this country, in a con¬ 
siderable number of cases of tuberculosis occurring in early life, 
the first seeds of the disease appear to have entered the body by 
way of the mouth. What proportion of these cases ought to be 
ascribed to tubercle-infected milk ? It scarcely appears to be 
possible to give a very confident leply to this question, though 
some distinguished authorities have not hesitated to express the 
opinion that practically all the cases of primary intestinal tuber¬ 
culosis occurring in childhood mav be set down to this cause. 
The late Sir Richard Thorne Thorne, in the Harben Lectures 
on the administrative control of tuberculosis, which he delivered 
in 1898, expressed his conviction that tuberculous milk was the 
main cause of tabes mesenterica in children, and he character¬ 
ized the loss of child life from this cause as appalling. The 
evidence on which this formidable charge was laid against the 
milch cow was of the following nature. The Registrar-General’s 
returns show that during the last fifty years there has been a 
marked decline in the death-rate from human phthisis, which 
is the form that tuberculosis generally takes when the bacilli 
are inhaled. On the other hand, during the same period there 
has been only a slight decline in the death-rate at all ages from 
that form of tuberculosis which is ascribable to alimentary in¬ 
fection, and among children under one year of age there has 
been a notable increase in the mortality from that form of the 
disease. The decline in the death-rate from phthisis is ascribable 
to the great improvements which have been effected during the 
last fifty years in the hygiene of human habitations, such as im- 
