The incubation of endotoxin with Na2Cr51O4 yielded a product which was well labeled. That the label was fixed on the endotoxin itself was shown by autoradiography on specific lines of precipitation formed in agar. Ultracentrifugation at 40,000 RPM sedimented 80 per cent of the total weight of the starting Boivin preparation. Agar diffusion patterns with subsequent autoradiographs demonstrated that the chromium tag was associated only with the heavy fractions of the pellet. The supernatant contained precipitable, but unlabeled endotoxin. Toxicity measurements showed that more than 99 per cent of the total toxicity resided in the pellet fractions.
The chromate-tagged endotoxin was specifically identified in plasma samples taken up to 6 hours after intravenous administration of LD50 or sublethal doses. The endotoxin was not totally detoxified in vivo since plasma collected 6 hours after the injection of even the sublethal dose was toxic when assayed in adrenalectomized mice. The endotoxin was specifically identified in urine specimens but it was no longer toxic or radioactive. Agar diffusion experiments indicated that only degraded material was present.