Bovine Tuberculosis. 157 



Tuberculin cannot possibly produce tuberculosis, because it does 

 not contain any tubercle bacteria. It does not excite a latent tuber- 

 cle into activity. It is used the world over, and as yet no authentic 

 report of injury caused by its use has been recorded. All those who 

 have worked with tuberculin are agreed that it is one of the safest 

 and surest tests in detecting the presence of tuberculosis that is 

 known to the medical world. All are agreed, however, that it must be 

 properly used, and that all those physical conditions that would tend 

 to interfere with it must be avoided. If in its use these precautions 

 are taken, tuberculin is as sure as any chemical reaction. 



If the animal is sound when tuberculin is injected no reaction is 

 observed. If, however, the animal contains an active tubercle there 

 is a reaction which shows itself in a rise of the temperature beginning 

 from 8 to 16 hours after the injection and continuing for from 

 6 to 10 hours and possibly longer. Fig. 30 shows the curve of the 

 temperature reaction after injecting the tuberculin in a tuberculous 

 animal. 



It is stated, however, on good authority, that animals in advanced 

 pregnancy, give a rise of temperature when they are not tuberculous. 

 Cows in this condition should not be tested. They can be isolated 

 until a few weeks after delivery, when the test may be applied. It is 

 likewise asserted that occasionally animals in a very advanced stage 

 of the disease will not react. The animal in this case, however, is 

 easily recognized to be in a very bad condition. These and other 

 conditions that might modify the reaction must be imderstood by one 

 who is using the tuberculin. It often happens that other causes 

 give rise to a temporary elevation of temperature during the testing 

 period. These are readily differentiated from the tuberculin reaction 

 by the character of the temperatm-e curve. 



It must be remembered that tuberculosis when naturally contracted 

 may have a long and variable period of incubation. The tuberculin 

 does not give a reaction during this period. It is possible, therefore, 

 that an animal that has been associated with and infected by tuber- 

 culous cattle will not react, but will do so in from three to six months 

 thereafter, or as soon as the diseased process has actually begun. 

 While tuberculin is a most reliable diagnostic agent when properly 

 used, it may lead to erroneous conclusions when improperly appUed. 



6. How TO Eliminate Tuberculosis From a Herd. 



A few years ago this could not be accomplished without sacrificing 

 all the animals. With tuberculin, however, it is not difficult to detect 

 all diseased individuals. 



