Observations on the serum phosphatase levels of cows before and after infection with Brucella abortus were made as part of an experiment which involved periodical testing of 23 blood-constituents of 49 animals. The age of the animals used ranged from 18 months to 13 years.

It was found that thirty-nine cows which showed agglutinative titers after infection with Brucella abortus had a significantly lowered average phosphatase level for approximately two months after infection, compared with “pre-exposure” levels and average levels of nine non-infected control animals.

One exceptional animal which failed to show agglutinins after infection exhibited a rapid rise of its phosphatase level for five months, up to 300 per cent above the level of all other animals. A second overwhelming infection of this animal with Br. abortus, again caused a rapid increase of its phosphatase level. Six weeks later, however, this animal suddenly showed a rapidly ascending agglutination titer and the phosphatase level decreased simultaneously with the appearance of the titer.

These results are discussed 1) on the basis of possible similarities between antibodies and phosphatase molecules, and 2) on the basis of Sevag's concept that antigens act as biocatalysts and that “specific antibodies formed as final reaction products in response to antigenic stimuli fulfill the function of specific inhibitors of enzymes.” It is shown that the results can be explained by assuming that a Br. abortus antibody globulin acts as a specific inhibitor of phosphatase (“anti-phosphatase”). In order to explain the great increase of the phosphatase level in one animal which failed to show agglutinins after infection, it is further suggested that, in the absence of agglutinins and “anti-phosphatase,” Brucella antigen adds to the normally present phosphatase activity. Available information on the chemical nature of the Brucella antigen is reviewed and its similarity to enzymes pointed out. The need for further work, including an evaluation of the possible role of phosphatase in immunization, is stressed.

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