274 TUBERCULOSIS. 
responded, she is for some time protected from a second test. A 
dishonest dealer, therefore, may inoculate his cows privately and 
then put upon the market all those that respond to the test, knowing 
that for some time they will not again respond. One thing is 
certain. No farmer can be confident of keeping his herd free from 
this disease unless he can be assured by the tuberculin test that he is 
purchasing animals freed from every suspicion of the disease. 
Second: He must prevent his cattle from associating with 
strange cattle. If put out to pasture they must be kept by 
themselves and guarded against chance contact with strangers. 
Common watering troughs, in which miscellaneous cattle are 
watered, must be shunned. 
Third: He must not feed his calves upon milk from other 
herds. The way in which this is most commonly done is by the use 
of skim milk returned from a creamery or a separating station. 
From such a creamery the farmer does not get back his own milk, 
but always milk from another source, and, if there be a few cases 
of bovine tuberculosis of the udder in the neighborhood, the bacilli 
from these animals will soon be distributed through the separating 
station over the entire region contributing to the station. This is 
not mere theory, but positively ascertained fact. To such milk is to 
be attributed the large amount of tuberculosis among swine in 
recent years. The only safe procedure is for the farmer either to 
bring up his calves on the milk from his own healthy herd or to 
insist that all milk fed to them shall first be subjected to the process 
of pasteurizing or boiling. So convinced are the agriculturists in 
Denmark that this mixed milk is the cause of much of the bovine 
tuberculosis, that a law has been passed forcing the pasteurization 
of all milk which is thus brought to creameries for separation of the 
cream. The farmer is thus protected from the tuberculosis of his 
neighbors' herds. 
Treatment of a Tuberculous Herd. There appear to be four 
general methods of treating a herd after this disease breaks out in it: 
i. All advanced cases which are recognized as dangerous to 
the public, including all cases of udder tuberculosis, may be removed 
and the animals destroyed, the others being left undisturbed. 
