APPLICATION OF THE TUBERCULIN TEST. 79 



Injection with tuberculin . The tuberculin is injected during 

 the evening at a time to allow an interval of ten hours before 

 the cows are milked the next morning. The insertion of the 

 hypodermic needle is accomplished with greatest facility and 

 least danger to the operator by leaning on the withers of the 

 cow and injecting upon the side opposite to the operator. 

 Asepsis is practically accomplished by dipping the needle in 

 concentrated carbolic acid each time before use. 



Temperatures after injection. Temperatures are taken every 

 two hours from the 10th to the 16th hours, and later in the 

 case of those animals showing an elevation to 103.5° at the 

 16th hour. It is frequently recommended that the tempera- 

 tures be taken from the 8th to the 20th hour. Such require- 

 ments impose serious hardship on the dairyman by the loss of 

 milk, due to the annoyance of the cows. For all practical 

 purposes the shorter period of taking temperatures is sufficient 

 to reveal a reaction. The animals should be under as quiet 

 and natural conditions as possible during the test. It is usually 

 desirable to allow them liberty, with access to drinking water, 

 between the 12th and 14th hours. 



Interpretation of temperatures . A rise of 1.5°F. above the 

 normal, if gradual and distributed over a period of several 

 hours, followed by a gradual decrease, constitutes a reaction. 

 Fig. 10 shows two typical tuberculin reactions. A brief 

 upward fluctuation of the temperature is not regarded as sig- 

 nificant. In the case of the ordinary well marked reactions, 

 it is not considered necessary to continue taking temperatures 

 after the fastigiuni has been passed. Animals exhibiting ques- 

 tionable reactions should be retested one month later, injected 

 with three times the usual dose of tuberculin. 



It is the rule not to condemn animals showing a rise of tem- 

 perature when in oestrum or when within six weeks of par- 

 turition. It is well to inject all such animals in a herd and to 

 retest later those exhibiting a fever. 



Limitations of tuberculin test. The tuberculin test does not 

 reveal facts concerning the extent of disease. Hence in a small 

 percentage of reacting cases no lesions can be found in post- 

 mortem, probably due to the fact that the lesion is too small 



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