Deficiency radiological rickets

Biological methods of assay for vitamin D were developed mostly during the period 1930-1945. Details of these basic techniques are well-documented in excellent reviews (Rosenberg, 1945 Bliss and Gyorgy, 1951). These assays are based upon measiu-ement of responses in D-deficient rats or chicks parameters such as prevention or cure of rickets are determined radiologically or by bone ash content. A salient feature about animal assays is the apparent species specificity exhibited by ergocalciferol and cholecalciferol. While the rat responds equally well to both vitamins, on the chick ergocalciferol is only about 3% as effective as cholecalciferol. 

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