The specificity of tuberculin preparations obtained by chemical fractionation of unheated culture filtrates.

Such tuberculin preparations as are currently used for skin testing in human beings are not specific for tuberculous infection. There is, in particular, reason to believe that the kind of low-grade tuberculin sensitivity that is highly prevalent in many tropical areas is "non-specific". A new kind of tuberculin, obtained as supernatant after acid precipitation followed by alcohol precipitation of the unheated concentrate from ultrafiltration of a culture of tubercle bacilli of human type, has been compared with ordinary tuberculin by skin tests in man in East Africa (Malawi) and South India. The results, reported in this paper, indicate that the new preparation gives rise to much smaller non-specific reactions than does the ordinary tuberculin.