Criteria of Response in the Bio-Assay of Vitamin E

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Abstract
Attempts to evaluate recognized gradations in negative and positive responses to vitamin E administration, based upon the number of live fetuses and the weight of the uterine contents at the sixteenth day of pregnancy in 600 rats used in assay tests, gave results not much superior to those obtained by treating responses as an “all or none” type, except for the recognition of a sub-minimal type of response otherwise classed as negative. On the other hand, the presence of two or more viable fetuses in utero at the sixteenth day of pregnancy was found to afford a criterion of positive response essentially equivalent to, and in certain instances more equitable than, that based upon delivery of progeny at term. In addition to advantages arising from the shortening of the test period for bio-assay, with the resultant economy of diet and animal care, examination of the uterus at the sixteenth day gives information especially pertinent to critical levels of response and prevents misinterpretation of certain atypical uterine states as negative responses to dose.