A Series of Cases giving a Positive Weil-Felix Reaction.

The Weil-Felix reaction has received general acceptance as an empiric laboratory test of considerable merit in establishing the diagnosis of typhus fever. The testimony of writers is uniform in affirming that the reaction is positive in over 90 per cent of cases of clinical typhus. It may appear as early as the fourth day of the disease, but usually does not develop until the second week and yields maximal titres about the time that the temperature returns to normal or shortly thereafter. Complete agglutination of the strain of B. proteus known as X19 in a dilution of the patient's serum greater than 1:50 is looked upon as of specific diagnostic significance. So far as can be determined the organism has no etiologic relationship to the disease and the mechanism of the reaction is not clearly understood. An excellent discussion of the immunological principles involved and the technique of the reaction has been published by Bengtson in the Public Health Reports, October 31, 1919.