STUDIES ON THE HETEROLOGOUS IMMUNOGENICITY OF A MENTHANOL-INSOLUBLE FRACTION OF ATTENUATED TUBERCLE BACILLI (BCG). I. ANTIMICROBIAL PROTECTION.

Small quantities of the non-toxic residue of phenol-killed, acetone-washed, and methanol-extracted tubercle bacilli of the BCG strain conferred a high degree of resistance on mice against otherwise lethal experimental infection with Klebsiella pneumoniae and with a number of other pathogenic bacteria. The heightened resistance reached a peak within 24 hours after administration of the fraction, but was already discernible immediately thereafter. A period of reduced resistance was not observed. The state of heightened resistance was invariably manifested for at least 10 days, and could frequently still be demonstrated after several weeks or months. The methanol-insoluble fraction was immunogenically active even in experimental circumstances under which living BCG exerted no effect. Its protective effect was more marked in females than in males. The optimum dosage must be determined empirically vis-á-vis the strain of infecting organisms and the experimental parameters of administration and testing. Administration of the fraction to breeding females reduced the incidence of a naturally occurring endemic pneumonitis among their young, and increased considerably the breeding productivity of the mothers. These effects were manifested as late as 11 months after treatment.