A fraction of tubercle bacilli possessing primary toxicity.

Tubercle bacilli separated from young cultures were thoroughly extracted with monochlorobenzene at temperatures never exceeding 50 degrees C. From the soluble material, a fraction corresponding to approximately 1 per cent of the total bacillary weight was separated by fractional precipitation with petrolic ether at temperatures of 0 degrees or 4 degrees C.-depending upon the strain of bacilli. The monochlorobenzene-soluble-ether-insoluble material (fraction 7) prepared from BCG-P was found to contain 0.14 per cent nitrogen and 0.4 per cent phosphorus. Some of its other chemical characteristics are described. Fraction 7 proved unable to elicit tuberculin allergy in guinea pigs, but injection of 5 microg. of it into the skin produced severe local reactions. In albino mice, a single intraperitoneal injection of 20 microg. caused loss of muscular tone and of weight followed by death within 9 days. The only tissue reaction observed was a slight degree of peritonitis. In mice of the C57 BL strain, a single injection of 40 microg. also caused death in the same time, but with pulmonary hemorrhages-usually massive. Material similar to fraction 7 was obtained from one virulent, two attenuated, and one avirulent strain of mammalian tubercle bacilli (bovine and human). The fractions obtained from the various strains differed somewhat in solubility and toxicity. The more virulent the culture, the more toxic was the fraction obtained from it; but it is possible that this relation was the result of differences in the effectiveness of the extraction procedures, rather than of characteristics inherent to the cultures. Evidence is presented that the toxicity of fraction 7 accounts for much of the primary toxicity of tubercle bacilli.