The discovery of the antirachitic potency of viosterol (irradiated ergosterol) created the hope that the strength of each of the many specifics for the treatment of rickets could be simply expressed in terms of a pure chemical substance. As is well known, the question of the proper dosage of viosterol led to the present knowledge of the exceedingly small amounts effective in the prevention or cure of rickets, and the hypercalcemia, pathologic calcification of the blood vessels and soft tissues, and other symptoms constituting the picture of hypervitaminosis due to enormous overdosage of this substance.1 But the variations in potency of different preparations, coupled with the previous lack of information regarding the chemical structure of vitamin D, led in this country and elsewhere to the abandonment of gravimetric units and the substitution of direct biologic assay in which the strength of each preparation is expressed in terms of rat
THE RELATIVE EFFICIENCY OF VITAMIN D PREPARATIONS IN DIFFERENT SPECIES. JAMA. 1932;99(7):565–566. doi:10.1001/jama.1932.02740590045015
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