412 DISEASES OF CATTLE. 



teen revealed. The reaction is absolutely specific. In those cases where it is 

 observed with animals which show lesions of another disease (actinomycosis, 

 hydatid disease, verminous bronchitis, distomatosis) , it may be affirmed that 

 there exists, in addition to these conspicuous changes, a tuberculous center which 

 alone has provoked the reaction. 



The failure to react does not necessarily imply absence of tuberculosis. Such 

 failures of tuberculin are very exceptional. They are seen most frequently with 

 animals affected with tuberculosis in a very advanced stage and made evident by 

 plain external signs. Sometimes, also, there are found at the post-mortem exam- 

 ination of animals which have not reacted small fibrous or calcified lesions in 

 such a condition that one is tempted to believe them cured. Whether sterile or 

 not these lesions have no tendency to increase, and they are not very dangerous 

 from the point of view of contagion. 



These opinions of two eminent authorities, living in different coun- 

 tries, after long experience of their own and after studying the results 

 of the many tests made in different parts of the world, should have 

 great weight. They are essentially the same throughout. 



In 1897 Voges compiled statistics of tuberculin tests the accuracy of 

 which had been determined by post-mortem examination. Of 7,327 

 animals tested it appeared that errors had been made with 204, or 

 2.78 per cent. In the work of the Pennsylvania Live Stock Sanitary 

 Board post-mortem examinations were made on about 4,400 reacting 

 cattle and the disease was found in all but eight of those which had 

 given characteristic reactions. 



The results of a much larger number of tests might be compiled at 

 this time but they would not materially change the average of those 

 already mentioned. It is plain that tuberculin is a remarkably accu- 

 rate test of tuberculosis; that the animals which react may be safely 

 considered as tuberculous and that when a careful clinical examina- 

 tion is practiced in addition to the test there are few animals in a 

 dangerous condition which escape detection. 



The first questions asked by those who oppose the adoption of the 

 tuberculin tests are : Is this test infallible ? and, If it is not infallible, 

 why should it be forced upon the cattle owners of the country? 



In answer to these questions it may be said that tuberculin is not 

 absolutely infallible, and yet it is by far the best method of diag- 

 nosing tuberculosis that has been discovered. It is much better 

 than any test known for pleuro-pneumonia when that disease was 

 eradicated. 



Practically all the animals that react are affected with tuberculosis 

 and should be separated from the herd, not only in the interest of the 

 public but in the interest of the owner of the herd. The best authori- 

 ties admit, after studying many thousands of tests, that there are 

 few, if any, mistakes made in condemning cattle which show a typical 

 tuberculin reaction. The errors are principally in the other direc- 

 tion — that is, some tuberculous animals are not discovered by the 



