326 MILK AND THE PUBLIC HEALTH CHAP. 



Two of these 1 7 herds withdrew during the year. Of the 1 5 

 herds left on the list at the end of 1910, 12 were free from 

 tuberculosis and 3 were in process of being freed. Of the 1 2 

 only 4 were tubercle-free when first tested. In one of the 3 

 herds not free the procedure had been in operation between 

 two and three years, the percentage of infected cows being 

 reduced from 57'7 to IV'S. In the other 2 herds the pro- 

 cedure had only been started during the year. During 1910 

 1111 cows were tested, and of these 219 (19' 7 per cent) 

 reacted positively to tuberculin. Dr. Eobertson remarks : 

 " There is therefore now in Birmingham a recognised supply 

 of tubercle-free milk, the product of tubercle-free cows ; and 

 the demand for such milk appears to be spreading, particularly 

 in the better-class districts." 



Ostertag's Method. This procedure, originated by Professor 

 Ostertag of Berlin, is based upon the elimination of all cases 

 of " open tuberculosis " from dairy herds. The cases of open 

 tuberculosis, i.e. those in which tubercle bacilli are eliminated 

 externally, are obviously the only ones which are infective, and 

 if these can be separated fresh cases cannot arise amongst the 

 other animals. Tuberculin is useless to differentiate " open " 

 from other tuberculous cases, and the diagnosis is made by con- 

 tinued veterinary inspection and bacteriological examination. 

 The herd is annually examined by a veterinary inspector 

 followed by bacteriological examination of the mixed milk. 

 If tubercle bacilli are found in the milk or suspicious animals 

 detected clinically, specific veterinary and bacteriological 

 examination is again made of these animals. It is an 

 optional system. The animals with open tuberculosis must be 

 at once isolated and slaughtered for sale, while the premises 

 are thoroughly disinfected. The Birmingham Committee also 

 investigated this method and remark : 



It is obvious that much real good can be effected on Ostertag's 

 lines. Its being a voluntary measure is no doubt against it, and 

 while it remains voluntary the extent of its adoption will probably 

 not be great. At the same time it is a distinct step forward, and 

 on the farms where it is in operation it may confidently be expected 

 to somewhat reduce the prevalence of the disease. It will also 

 probably help to educate public opinion up to the point at which a 

 compulsory measure will be possible. 



