An examination of sera from some 100 cases of active, pulmonary tuberculosis by routine quantitative methods of complement-fixation has shown no consistent correlation between the clinical history and the antibody titre of the serum.

It has been noted, however, that all tuberculous sera do not react equally well with carefully tested antigens prepared from S and R cultures of human tubercle bacilli. These two antigens are about equally efficient in detecting the complement-fixing anti-bodies in sera from cases of the chronic type, but the S antigen fixes specifically, in the presence of serum from the majority of acute cases, twice as much or more complement than is fixed by the R antigen. Serum from cases of the intermediate type usually fall between these extremes.

From the small number of cases studied, it would appear that the relative reactivity of sera with S and R antigens is more closely correlated with the activity of the tuberculous processes than is the actual concentration of complement fixing substances. Whether the S to R antibody index will prove to be valuable in prognosis as is suggested by these results, cannot however be determined without periodic determinations and correlation with a study of clinical progress. A study of this sort is now well advanced.

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