16 MASS. KXPEHIMKNT STATION BULLETIN No. 2S4 



turl)i(l tost fluid; the scn-uiii and test fluid arc thoroughly mixed, tho mixture is 

 incuhatefl for 24 hours or longer at body temperature; and the results are recorded 

 at the end of the incubation period. A test is regarded as positive when a deposit 

 has formed in the bottom of the tube with the test fluid partially or completely 

 clear, and upon shaking of the tube the deposit breaks up into fine clumps. In a 

 negative test the turbidity of the mixture is not changed. All birds whose samples 

 react positively are reported as reactors or "carriers." These birds are removed 

 from the flock and slaughtered for meat. 



39. — What is the rapid serum agghitination test? This test is a modi- 

 fication of the tube agglutination tesj. A small aiiiount of serum taken from 

 the blood sample is placed on a glass plate. To this serum is added a small 

 amount of test fluid whose turbidity is far greater than that of the test fluid 

 used for the tube method. The serum and test fluid are mixed by stirring and 

 after a few minutes the result of the test is recorded. A test is positive when 

 definite white clumps form in the serujii-test fluid mixture. In a negative test 

 the serum-test fluid mixture remains uniformly turliid. 



40. — What is the whole blood agglutination test.' The whole blood 

 agglutination test consists of mixing whole fresh blood or whole dry blood with 

 a stained test fluid which is quite similar to that employed for the rapid serum 

 method. The results are recorded within a few minutes after the blood and test 

 fluid are mixed. A positive test is indicated by definite clumps floating in the 

 mixture. A negative test shows no clumping. This test is used on the premises, 

 usually in the poultry house, and tested birds are retained in trapnests or impro- 

 vised retention coops until the results of the test are recorded. This makes it 

 possible to remove positive birds from the flock immediately. 



41. — Have any of these tests been adopted as standard? At the present 

 time, the macroscopic tube agglutination test is regarded as the standard test 

 for detecting pullorum disease carriers. This standard test is subject to modi- 

 fication or change when a more effective, inexpensive and efficient method or 

 test is discovered for pullorum disease eradication. 



42. — Has a test been developed which has proved practical and re- 

 liable in the hands of poultrymen? At the present time, no test for pullorum 

 disease eradication is recognized as reliable and effective when placed in the 

 hands of poultrymen or persons not properly trained. The different tests are of 

 such a nature that they recjuire thorough knowledge in the fields of biological 

 sciences in order to obtain most expeditious and successful results in eradication 

 of the disease. The results of a test must be judged by the quality of the operator 

 and the methods employed. 



43. — What is a reactor? A reactor is a bird whose serum gives a doubtful 

 or positive reaction in the serum-test fluid dilution of 1-25 after 24 hours' incu- 

 bation at body temperature. If only doubtful birds are found, they are subjected 

 to further examination. Postmortem examinations are often helpful in making 

 a diagnosis. 



44. — Do infected birds always show a positive agglutination test? 



Occasionally infected birds arc discovered at necropsy that did not react posi- 

 tively to the agglutination test. The serum dilution (proportion of serum to 

 test fluid) is an important factor in detecting such birds. The lower the dilution 

 the more infected birds will react. Infrequently, some birds may react at one test 

 and not at the next. Due to this fluctuation in reactions they are called inter- 

 mittent reactors. 



