The Use of Standard Slides in Semiquantitative Radioautography with Tritiated Compounds

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Abstract
Essentially identical smears can be prepared from a pooled suspension of Ehrlich ascites tumor cells labeled with tritiated thymidine. In these smears, the percentage of labeled cells and the mean grain count per labeled cell vary within narrow limits: in the same slide, within 2 to 5% of the mean of the slide. In smears processed together in the same manner, the percentage of labeled cells (calculated on 1,000 cells) varies within 2%, and the mean grain count per labeled cell (calculated on 50 cells) between 15 and 20% of the mean of all smears. Once the limits of variability are known, smears from the same cell population can be used to ensure the accuracy of procedures performed on separate batches of radio-autographs that have been processed separately but in a presumably identical manner. A comparison of the mean grain counts of standard smears from separate batches will indicate if variations, not otherwise detectable by the experimenter, have actually occurred during the radioautographic procedure.