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) . 



