DISEASES COMMUNICABLE IN MILK 41 



animals from infected herds. The value of tuberculin as a guide in pur- 

 chasing is very great but experience has shown that when 50 per cent, or 

 more of the cows react, a considerable number of the animals that do not 

 have arrested tuberculosis; consequently purchasers of non-reactors 

 must retest at frequent intervals. Failure to understand this has led 

 to costly experiences on the part of purchasers and to unjust charges of 

 dishonesty against the testers. 



A shortcoming of the tuberculin test is that it gives no idea of the 

 severity of the case. So, when animals are opened up, often only an 

 inconsequential lesion is found. In other words the test is regarded as 

 being too delicate by those who would exclude only open cases from their 

 herds. That the testing is a searching one is probably most fortunate 

 and it is likely that in the end less loss results from the removal of animals 

 to which a period of usefulness still remains than would occur if the test 

 was of such a character as to grade the cases. 



Of the animals which give good reactions about 98 per cent, show 

 lesions on slaughter and it is probable thorough examination of inaccessible 

 parts would increase this percentage but when the animals that for rea- 

 sons which have been given do not react are considered too, the percent- 

 age of accuracy of the test is only about 85 per cent., so that the building 

 up of a tuberculosis-free herd is a matter not of a year or two but of 4 to 

 8 years. 



Tuberculin Test as a Criterion for Excluding Milk from the Market 

 All of these imperfections have their bearing on the value of the tubercu- 

 lin test as a measure to secure the public health by shutting tuberculous 

 milk out of the market. The Supreme Court of the United States, the 

 Supreme Court of New Jersey and the courts of other States have de- 

 clared that the proper authorities may require the tuberculin test to be 

 applied to herds supplying milk to the communities within their jurisdic- 

 tion. Ordinances making the test compulsory are in force; they usually 

 make it optional whether the dealer shall test his herds or pasteurize 

 the milk. The question arises whether such ordinances are wise. In the 

 first place it should be recognized that the enactment of such an ordinance 

 has a very great educational effect. Producers and consumers alike are 

 made alive to the problem of tuberculosis as a whole and in particular as 

 to the relationship of dairying thereto. The question is thoroughly dis- 

 cussed and usually all concerned are gainers from the agitation. The en- 

 forcement of an ordinance helps the community to which it applies by re- 

 ducing the number of tuberculous cattle but in this respect the amount of 

 good accomplished depends in no small measure on the spirit in which the 

 farmer meets the ordinance. His knowledge of the herd and a belief on 

 his part that the removal of reactors is for his ultimate benefit are all but 

 essential to a thorough weeding out of diseased animals. But because 

 of faults inherent in the test itself, it is highly improbable that even a 



