Extrinsic Factor in Pernicious Anemia: Ineffectiveness of Purified Casein and of Identified Components of the Vitamin B Complex

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Abstract
Careful purification by repeated precipitation or by extraction with dilute acid or alcohol required to render crude casein "vit.-free" was also essential to eliminate the extrinsic factor. A combination of casein so extracted with all the known members of the vit. B complex and other accessory nutritional factors, tested additively on 10 patients with Addisonian pernicious anemia, did not show the extrinsic factor activity of the pure casein. The extrinsic factor is regarded as a thermostable component of the vit. B complex as yet unidentified.