The curative method of vitamin A assay

Abstract

Discrepancies in results of vit. A assay by the curative method are due to differing pathologic conditions of the animals at the end of the "depletion" period. These conditions occur much earlier than generally supposed and may be far advanced before any indication is seen in the wt. curve. Variations in response to vit. A dosage are thus inevitable. Pathologic conditions induced by avitaminosis A may also persist after wks. of dosing with large amt. of vit. A, or after several mos. on normal diet. The diversity of these conditions and their frequent lack of amenability to treatment constitute sources of error in the curative method which it seems impossible to eliminate. The theory of the "reserve stores" of vit. A and the practice of breeding so as to "reduce these reserves" in the experimental animals seem to require further examination. The effect of restricting the mother''s intake of vit. A appears to be not merely a lowering of these stores in the young animal but a diminution in its health and vitality. Apparently any satisfactory biologic assay of vit. A must be of the prophylactic type, aiming to detn., not the amt. of vit. A which will produce fairly satisfactory wt. curves in animals of inferior type, but the amt. which will keep first-class animals in first-class condition, as evidenced not only by wt. curves, but by post mortem examination of the tissues.