EFFECTS OF TUBERCULIN ON TUBERCULOUS 



COWS. 



F. L. Russell. 



Since June 10, 1892, we have been testing cows with tubercu- 

 lin, and during nearly all this time have had some tuberculous 

 animals under observation. The tests, together with the autop- 

 sies held, have impressed upon us the fact that tuberculin is a 

 very delicate agent for determining the presence of tuberculosis. 

 It is very doubtful if cows ever react under a properly made 

 tuberculin test unless they have tuberculosis. On the other 

 hand, however, it is very evident that cows sometimes have 

 tuberculosis or at least tuberculous growths in their bodies, and 

 yet fail to react under the tuberculin test. 



Others have observed that animals in an advanced stage of the 

 disease sometimes fail to react, but we have had no experience 

 of this sort. Unfortunately or otherwise, according to the 

 standpoint from which we view the matter we have not treated 

 many animals that were in a really bad physical condition. But 

 during all our experience with tuberculin in testing cows we 

 have been struck with the frequency of the failure of tuberculin 

 to cause reaction in cows that were but slightly diseased. They 

 will react at one time and not at another so that it is impossible 

 to predict with any degree of certainty what the result of inject- 

 ing tuberculin into a slightly diseased cow will be. 



The results of the tests of animals with tuberculin extending 

 over considerable periods of time are summed up as concisely 

 as practicable, in a table at the end of this paper. A few of the 

 most interesting and striking cases are discussed in the text 

 immediately following. 



One cow, Agnes, injected in June, 1892, underwent a plain 

 reaction, and in the light of subsequent experience, we are bound 

 to believe she was diseased at that time. The next time she was 

 tested was a vear and two davs later when she failed to react. 



