Although many workers have discussed the development of humoral antibodies in patients with meningococcic infections, the results of their observations have been irregular and at times conflicting. It has recently been concluded (1) that, of all the methods available at present, the agglutination test is the most reliable. These workers were unable to achieve high agglutinin titers by the use of the usual method of incubation for 2 hours at 37.50 C., followed by 18 hours in the refrigerator, but with the use of the "thread test" they obtained consistent titers ranging up to 1: 128 in patients with meningococcic meningitis and as high as 1: 64 in contacts. We have likewise not observed sufficiently high titers with the orthodox method of incubation followed by refrigeration, and since the "thread test" is difficult to perform, except by persons highly trained in its use, we looked for another method which would be both reliable and practicable for routine use. In the course of our search, we found that the use of centrifugation, in place of heating and refrigeration, gave consistently high titers on the sera of most patients during the course of meningococcic meningitis. The test is easy to perform and the results are highly specific. Sera obtained from patients with a variety of other diseases, including pneumococcic pneumonia and meningitis, gonococcic cervicitis, arthritis and meningitis and streptococcus viridans endo-

Summary and Conclusions A method for the determination of agglutinins against N. intracellularis by the use of the centrifuge is described and the theoretical reasons for its superiority are given. Four hundred and four specimens of serum from 121 subjects with and without meningococcal infections were examined by this method. The maximum agglutinin titer in the majority of the patients with meningococcic infections, or receiving antimeningococcic serum, was 1:16 or more, and titers ran up as high as 1:1024. Among the 35 control patients the maximum titer was above 1:8 in only two instances. It is concluded that the centrifuge-agglutination test is simple to perform and achieves a high degree of specificity combined with sufficient sensitivity for all practical uses.