Abstract
Filtrates from microbial heterotrophic activity assay experiments in which tritiated glucose was used as a radioactively labeled substrate were collected, and their radioactivities were determined. These filtrates were subsequently evaporated to dryness to remove tritiated water generated by metabolism of the labeled glucose; the residue was suspended to original volume with distilled water, and the tritium levels were again assayed. In the water samples assayed, the amount of tritium label retained by the microorganism was about 75% of that respired.