Abstract
Summary A number of commercial liver extracts have been assayed for L. lactis Dorner activity in terms of vitamin B12. A considerable variation from brand to brand has been found and also a serious variation between different batches of the same brand. Although steps have been taken to eliminate artefacts due to method and the presence of inhibitors, it is not possible at the present time to correlate exactly L. lactis Dorner activity with clinical efficacy. It is thus premature to advocate the establishment of a “Dorner” assay unitage applicable to all liver extracts, but it is not too much to expect that, in the future, branded preparations will maintain a reasonably constant “Dorner” activity. The presumptive vitamin B12 content of “high potency” liver extracts is of the order of 10 μg./ml. whether of British, American or Continental manufacture. It is a pleasure to acknowledge the technical assistance of Mr. G. B. D. Grafham.
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