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Table IV. Showing Results of Agglutination and Fixation Tesis conducted at frequent
No. 236 was bred to bull which had record of transmitting infection. † Artificial infection with B. abortus. No. 240 vulyar infection. No. 135 vulvar. No. 138 intraurethral. No. 239 subcutaneous. No. 242 intraurethral. No. 19 subcutaneous. No. 137 vulvar. No. 18 intraurethra. No. 241 intraurethral. No. 437 subcutaneous. No. 136 intravulvar.
Cow No. 136 was negative over a period of about three months, then became positive, remained so for about six weeks, reverted to doubtful, then again to positive, and after this wavered in the fixation reaction until at the end she was practically negative.
No. 236 was bred to a bull having a record of transmitting infection, while negative to both tests. Six weeks later she was a complete reactor, and continued so. She aborted two months after the last test.
No. 437 changed over from negative to positive very soon after subcutaneous injection of abortus antigen, and continued positive by both methods to the end.
TABLE IV. Showing Results of Agglutination and Fixation Tests conducted at frequent
No. 18 changed from negative, after artificial infection, to positive, remained positive for a short time, and then reverted to negative (both tests). No. 19 became doubtful then positive, after artificial injection, remained positive a short time, and after prolonged wavering reverted to full negative.
No. 135 became a confirmed reactor after intravulvar infection, and remained so to the end, when she aborted. No. 138 changed to full positive after intraurethral injection,
very soon returned to negative by both methods. No. 239, after subcutaneous injection, became positive, and except for a temporary wavering, remained so to the end.
No. 249 slowly went over to doubtful, then reverted to full negative, and finally became full positive.
No. 242 wavered a long time after intraurethral injection, and at the end gave double negative reactions.
It will be seen in Table IV that all of the animals were clearly negative to both tests until after artificial infection, and that in several instances the negative tests extended over long periods of time, preliminary to infection.
BRIEF DISCUSSION AND SUMMARY.
By paying particular attention to the production of a potent bacterial antigen which is at best but slightly anti-complementary, and by following the rules governing both the agglutination and the complement fixation tests, these methods may be applied satisfactorily in the diagnosis of infectious abortion. Their constancy and reliability make them indispensable in the study and control of this disease.
We believe that the two methods are of equal importance, though of course the agglutination test is by far the simpler and more economic. However, for careful diagnosis the one serves as a check on the other, and it appears to us that the use of the one or the other alone would rob the serological diagnosis of much of its value, and leave the laboratory diagnostician very much in doubt as to the accuracy and value of his results.
The different tables show remarkable constancy of reactions, or where changes occur from negative to positive or from positive to negative, logical and steady transitions and consistency in the recorded data.
Occasional irregularities in the results of the tests must be conceded. Of particular concern to the operator are the negative reactions which are at times given by infected and even aborting cows at or near the time of calving. Various explanations have been offered for these results but only one appears to have received any serious consideration. According to this theory the infected animal is at this time so heavily charged with the Bang bacillus that when the blood is tested there is such an abundance of antigen in it as to neutralize its own agglutinin and anti-bodies in the presence of sufficient complement and therefore fail to react with the reagents of the test. This explanation has, however. not as yet been founded on sufficient evidence to be regarded as more than a theory.
The possibility of obtaining negative results by the two serological methods at or near the time of calving of infected animals should always be kept in mind, and further tests should be made on such animals after an appreciable interval following the calving. These apparent anomalies do not, however, seriously detract from the value of the tests.
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