THE TUBERCULIN TEST FOR TUBERCULOSIS 201 



temperatures are not unusually low. To an expert a rise of 1.5 

 or less may be a plain reaction in some cases and only suspicious 

 or doubtful symptoms in others, so that the animal should be 

 held for retest after 60 days. If the normal temperatures run 

 100° P. or less, we would not ordinarily condemn on a 2 degree 

 rise. Experience and judgment are essential in this work. 



A first plain reaction should never be set aside for a subse- 

 quent negative retest, as the first test is the best and each sub- 

 sequent retest in general decreases in reliability. Obvious re- 

 actors should not as a rule be retested. 



The reaction. — The most typical reaction is one wherein there 

 is gradual rise and gradual decline of temperature, but many 

 plain reactions are not thus typical. Very abrupt changes in 

 an animal's temperature should be verified with a different 

 thermometer. One high temperature during (B), with the 

 others normal or nearly so, may be only doubtful or suspicious, 

 often it indicates an error in the record. Animals that react 

 sometimes show diarrhea, local swelling at the site of injection, 

 or shivering. 



The intradermal test. — This form of tuberculin test is a deli- 

 cate operation requiring special skill and experience. It is 

 made by injecting into the skin, usually in one of the folds under 

 the root of the tail, a few drops of a special tuberculin with a 

 short and very fine needle. 



Tuberculous animals exhibit reaction in the form of a per- 

 sistent, local swelling at the site of injection. This should re- 

 main 72 hours or more after the injection has been made. 

 Healthy cattle may have a temporary swelling but are nearly 

 or quite negative as a rule. 



The intradermal test in skillful hands is probably as accurate 

 as the thermal test and it has the great advantage of greater 

 speed with regard to the number of cattle that can be tested by 

 an operator in a given time. It is therefore less expensive than 

 the thermal test. 



The ophthalmic test. — This test is simpler in operation and 

 interpretation than the thermal and intradermal tests; but it 

 is less reliable for general work. It is made by putting special 

 ophthalmic tuberculin in the eye. This ophthalmic tuberculin 

 may be in either tablet or liquid form. A double treatment, 

 sensitized ophthalmic test, gives most accurate results. By this 

 method, the same eye is treated twice, with an interval of 3 to 



