LECTURE XL 

 THE TUBERCULIN TEST FOR TUBERCULOSIS 



Tuberculin is usually seen in tablets or as a straw-colored 

 fluid, slightly more viscid than water. 



The active ingredients of tuberculin are chemical products of 

 the bacilli of tuberculosis. A certain broth is infected with the 

 virus of tuberculosis, which is allowed to multiply and grow 

 in this medium until it has become charged with the germ prod- 

 ucts. The whole fluid is then heated to kill the bacteria and 

 filtered through porcelain. Tuberculin should therefore be not 

 only germ-free, but heated to a high temperature, and cannot 

 be infectious. 



Effect on cattle. — Careful experiments have demonstrated 

 that tuberculin has no important effect, favorable or otherwise, 

 upon the health or milk flow of sound cattle ; and that the effect 

 on tuberculous cattle is not objectionable. An experiment was 

 conducted by the author at the Minnesota Experiment Station 

 some years ago, which included 23 sound and 5 tuberculous cows, 

 and compared the total milk flow and total butter fat of each 

 animal and of the herd for the week prior to test with the week 

 of test. In this experiment the cattle were given ordinary 

 handling, neither very rough nor unusually gentle. 



There was a moderate decrease in the milk flow during the 

 two days of test, not more than could be easily accounted for by 

 unusual handling of the cattle and the presence of strangers. 

 This decrease was almost made up during the succeeding five 

 days. There was a slight increase of butter fat during the 

 week of test. Both variations were easily within the limits of 

 normal variation. 



The experiment with the five tuberculous cows produced about 

 the same results, the difference being easily within the limits of 

 normal variations, as neither the total milk flow nor total butter 

 fat for the entire week was materially affected by the test. 

 Similar experiments have been made elsewhere, the results agree- 

 ing closely with this general statement. -It is undoubtedly pos- 



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