IXTERCOMMUXICABILITT OF TUBERCULOSIS. 
817 
generalised tuberculosis, or one in which there is tubercular affection 
of the udder ; and the necessity for total prohibition of the sale or 
use of such milk and the immediate slaughter of the animal is 
generally recognised. There is still a little uncertainty, however, as 
to whether the milk maybe infective in cases of localised tuberculosis, 
and in which the udder is apparently healthy. Still, in view of the 
many positive results obtained by the experimental feeding of animals 
with the milk of cows in which no udder lesion could be detected, it 
cannot be asserted that the milk is devoid of danger. Assuming that 
the active infective agent is never present in the milk except the 
tuberculosis has become general, the extreme difficulty of ascertaining 
clinically the exact time when a local affection becomes generalised, 
and the impossibility in some cases of detecting tubercular mammitis 
except on very careful post-mortem examination, warrants the adoption 
of measures in all cases equally stringent and as much calculated to 
conserve public health as in cases where no doubt exists of the disease 
being general. 
PREVALENCE OF THE DISEASE. 
If the evidence which I have presented to you, and such other 
evidence as we have at our command, is sufficient to be convincing of 
danger of infection of man by transmission from animals (as I think 
it is), the degree of danger will depend greatjy on the extent to which 
the disease exists in animals furnishing food materials for man, and it 
is necessary, therefore, to indicate, so far as is possible, the prevalence 
of the disease in these animals. In this paper, however, I shall 
confine myself to a consideration of the prevalence of the disease in 
cattle, as although it exists to a considerable extent in pigs and to a 
limited extent in sheep, the danger to be apprehended from these 
sources is infinitesimal compared with that from bovines. 
Unfortunately there is a dearth of reliable statistics having 
reference to the question of prevalence. Such as there are, however, 
prove it to be a very common disease in cattle in all countries of the 
world. It is only during the last few years that any systematic 
attempt has been made to ascertain the prevalence of the disease by 
rigid inspection of dairy stock and of slaughtered animals, and in those 
countries in which this is being done it will be a year or two before 
exact estimates can be formed. By that time, too, the aid f urnished 
by the results of the use of the tuberculin test will be available. In 
the meantime such estimates as can be got from reliable statistics at 
present at command will have to be depended oil. lor instance, in 
Great Britain, since t lie coming into force of the Pleuro-pneumonia 
Compulsory Slaughter Order, valuable data have been obtained. 
Under that Order all cattle affected with pleuro-pneumonia, all those 
that had been in contact with affected cattle, and all cattle on any 
farm on which the disease broke out were slaughtered, and tne 
veterinary inspectors were instructed to note to what extent tuber- 
culosis prevailed in the animals. I lie results in some counties as 
recorded in the 1892 report of the Veterinary Department of the 
Board of Agriculture— were startling. In London 25 per cent, of all 
the animals" slaughtered under the Order were tuberculous (in one 
herd fourteen out of twenty cows, and in several herds 30 and 40 per 
cent.), in Yorkshire 22*8 percent., in Midlothian 20 per cent., in 
