TUBERCULIN TKST 



223 



Tuberculin does not give a reaction during the period of 

 incubation. It does not cause a reaction in many, if not all, 

 cases of temporary arrest or healing of the lesions. This ren- 

 ders it difficult to intcBpret the negative results especially in 

 herds where there are many positive reactions. In such cases 

 there should be subsequent tests later. For this reason cattle 

 bought on the tuberculin test can not be considered uninfected 



Fig. 54. Irregular temperatures following tuberculin that are not caused 

 by tuberculosis {Curtice). 



as the result of the first test if they came from herds contain- 

 ing reacting animals. 



The practical value of tuberculin lies in its efficiency in 

 the arts of comparative and sanitary medicine. It is in the 

 practical application that difficulties are encountered. The 

 many details and precautions enumerated as absolutely essen- 

 tial to the best results are often considered too tedious and 

 time consuming, and consequently the practice has come too 

 generally into vogue of neglecting or ignoring many of the 

 precautions. In order that the test may be practicable, some 

 practitioners resort to a shorter method of procedure even at 

 the risk of an occasional error. 



§ 156. Prevention. Tuberculosis, like other infectious 

 diseases, can be very largely prevented. To accomplish this 



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