An iron‐dextran complex* from which most of the uncomplexed dextran present had been removed by ultracentrifugation has been examined by electron microscopy and by gel chromatography. In the first technique, freeze‐drying to prevent aggregation and distortion followed by shadow‐casting with platinum‐iridium gave a clear impression of the particulate nature of the complex. The chromatographic experiments on Sephadex G200 confirmed the particle size and showed that the particle size distribution was not wide. The iron‐dextran component is thus seen as a small particle of approximately 3 nm diameter when examined only as the FeOOH ‘core’ and of approximately 13 nm diameter when the attached dextran is also observed. A structural model of the particle is presented with the dextran attached by the terminal metasaccharinic acid units to the FeOOH component.

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