INFLUENCE OF DISEASE UPON MILK 93 
tion of this character has been in operation for several 
years the tuberculin test may be added with very little 
objection. Fewer reactions will then be obtained and 
the reacting animals can be more readily replaced with 
non-tuberculous animals. 
When milk is produced especially for children’s use, 
however, the greater susceptibility of children to tubercle 
bacilli of bovine origin must be taken into account, and 
the most thorough methods for protecting milk from con- 
tamination with tubercle bacilli should be applied. 
Children’s milk should therefore be obtained only from 
herds which are tuberculin-tested at least once a year and 
which are subjected to a physical examination at least 
once each month. 
The efficiency of the clinical examination of dairy 
cows in preventing the contamination of a milk supply 
with tubercle bacilli as compared with the bacteriological 
examination of the milk for the presence of the bacilli 
is fairly presented in the following statement from the 
report of the British Commission on tuberculosis: “ The 
presence of tubercle bacilli in cow’s milk can be dis- 
covered, though with some difficulty, if proper means be 
adopted,” but “it is much easier to demonstrate with 
certainty by clinical examination that a cow is affected 
with tuberculosis and will in consequence perhaps pro- 
duce tuberculous milk.” Furthermore, milk from a cow 
eliminating tubercle bacilli is not constantly infected. 
On certain days, the organisms may be absent entirely 
or present in only small numbers. A single examination 
may therefore give misleading results. 
The destruction of tubercle bacilli in milk by heat. 
is considered in the chapter on pasteurization (page 203). 
V 
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