Abstract
An acetone-soluble fraction has been extracted from loblolly pine pollen which appears to be as toxic for normal guinea pig leukocytes in vitro as a comparable fraction from virulent tubercle bacilli. Blood leukocytes from guinea pigs injected with heat-killed tubercle bacilli show a susceptibility to the acetone-soluble fraction of pine pollen which seems to correlate well with susceptibility to PPD but not with susceptibility to a polysaccharide I (glycoprotein) fraction isolated from unheated culture filtrates of virulent tubercle bacilli.