Rabbit antibodies specific for the major tadpole and frog hemoglobin components of R. catesbeiana were used for the detection of the two hemoglobins inside single cells. The antisera, after fractionation by ammonium sulfate precipitation and diethylaminoethyl (DEAE)-cellulose chromatography, were conjugated with fluorescein isothiocyanate for the antifrog hemoglobin serum and tetramethylrhodamine isothiocyanate for the antitadpole hemoglobin serum. The conjugated fractions, refractionated by stepwise elution from a DEAE-cellulose column, were used for the fluorescent staining of blood smears, liver tissue imprints, and smears of liver cell suspensions. Both simultaneous and sequential staining with the two fluorescent preparations indicated that larval and adult hemoglobins were not present within the same erythrocyte during metamorphosis. In other experiments, erythroid cells from animals in metamorphosis were spread on agar containing specific antiserum. Precipitates were formed around the cells which contain the particular hemoglobin. The percentages of cells containing either tadpole or frog hemoglobin were estimated within the experimental error of the method. The data showed that the two hemoglobins are in different cells. It is concluded that the hemoglobin change observed during the metamorphosis of R. catesbeiana is due to the appearance of a new population of erythroid cells containing exclusively frog hemoglobin.

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