80 BOVINE TUBERCULOSIS AND OTHER CATTLE DISEASES. 



to detect. Animals in the advanced stages sometimes fail to 

 react but the existence of tuberculosis in such cases should be 

 readily detected from the physical appearance of the animal. 

 There are at least two conditions under which an animal once 

 failing to react may at a later time react to the test. During 

 the incubation period of the disease, that is, when the tubercle 

 bacilli are within the body but before a lesion is developed, no 

 reaction will occur. L,ater, the animal will respond. Thor- 

 oughly encapsulated lesions will not permit response to tuber- 

 culin, but later may become active and cause reaction. These 

 facts are of great significance in pointing to the necessity of 

 frequent testing. 



Fraud. Dishonesty on the part of the attendants of the 

 cattle may be responsible for erroneous results of a test. It is 

 an important fact that a tubercular animal will not give two 

 reactions in succession. Thus a dairyman may inject his herd 

 a few days previous to an unwelcome expected test, and there- 

 by wholly mislead the man making the later test. Tuberculin 

 is readily purchased upon the market but its sale should be 

 subject to restrictions. Febrifuge drugs are said to be also 

 used to defeat the tuberculin test, by counteracting the febrile 

 conditions. Frauds may be extensively practiced, but unex- 

 pected tests will eventually expose the dishonest practice. 



Permanent identification ofani7nals. The thorough identifi- 

 cation of the animals is under most conditions a necessary 



matter. The liability of fraud 

 is very great when any com- 

 pulsion attends the application 

 of the test or the subsequent 

 disposition of the reacting ani- 

 mals. A useful means of iden- 

 tification is afforded by metal 

 ear-tags, numbered serially 

 and bearing a legend identify- 

 ing the official body respon- 

 sible for the test, as for in- 

 stance, a board of health or 

 a milk commission. Fig. 11 



Fig. U. 

 cattle. 



Ear-tag jor marking 



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