DISEASES COMMUNICABLE IN MILK 51 



as yet these efforts have not developed beyond the stage where they are 

 of more than scientific interest. 



Control by Tuberculin Testing. The plan that is probably most 

 familiar to Americans is that of testing animals with tuberculin and 

 destroying the reactors. If retests are made, there is little doubt that 

 herds would be enventually cleaned up but the system is too expensive 

 to be generally adopted. To apply it to a whole State would require an 

 army of testers and the value of property destroyed would be so great as 

 to be prohibitive. Moreover, a severe shortage of milk would very likely 

 result so that this method can be applied only in a limited way. Had it 

 been adopted before tuberculosis had obtained a firm hold of American 

 stock, it no doubt would have achieved success, but now it is too harsh. 



The Manchester Method of Control. In England, the Manchester 

 system is in use; it is based on the unsound hypothesis that tubercle 

 bacteria get into milk only through udder lesions or at least principally 

 that way. The law on which the system is based authorizes the proper 

 officials to collect milk samples and to visit dairies both within and with- 

 out the city proper. The milk of all dealers is submitted at regular in- 

 tervals to microscopical examination and is also tested by injection into 

 guinea-pigs. In case the mixed milk proves to be infected with tuber- 

 culosis germs the herds are visited and the animals examined physically by 

 a veterinarian. Animals with tuberculosis of the udder are removed from 

 the herd but the law does not provide for their destruction. Milk from 

 the animals removed must not be sold for human consumption nor can 

 the cow be kept with other cows in milk. There is nothing to prevent 

 their being kept with dry stock nor with calves and disinfection after 

 removal of the diseased animals is not required. It is easy to see that the 

 law is a compromise and was enacted in the belief that it would reduce the 

 amount of tuberculous milk on sale. It has been held, that by removing 

 the cows with udder lesions, the law would lessen the amount of open 

 tuberculosis in the herds and gradually effect their betterment. The 

 actual result has been that in the first few years after enactment bad 

 conditions were improved but so far as the milk is concerned it has been 

 found that after 10 years in Manchester the tuberculous samples dropped 

 down to 6 per cent, and in Sheffield to 9 per cent, and stayed there. 

 Statistics show that in neither city during the same period had there been 

 any percentage reduction of udder tuberculosis. 



The Ostertag Method of Control. The Ostertag method is based 

 on the theory that it is the open cases of tuberculosis that spread the 

 disease and that all but a few of these are detectable by frequent and 

 thorough physical examinations of the herds. As tuberculin does not 

 distinguish open from closed cases it is not used. The herd is examined 

 by a veterinary inspector after which there is a bacteriological examina- 

 tion of the milk. If tuberculosis is found in the milk or if animals whose 



