Abstract
It has been shown that the standard method of estimating and establishing the unitage of antirachitic agents by means of biologic assays on rats, does not conform to clinical experience. 1 For example, 40 units of irradiated milk, in other words 650 cc. daily, suffice to protect an infant from rickets whereas approximately 600 units of irradiated ergosterol (viosterol) or 240 units of cod liver oil are required to accomplish a similar result.
In an investigation of this problem an attempt was made to ascertain the antirachitic potency of the blood and the feces of infants who had been given these and other specific antirachitics. It was found possible to carry out satisfactory titrations of the blood when as little as 0.1 cc. of titrated blood was fed daily, or 0.8 for the period of 8 days in the course of the regular 10-day test. Usually twice this amount was fed and in some instances a total of 3.2 cc. of blood. Even less may be used if serum or plasma is fed. In an extended series of assays conducted in this way it developed that the relatively high potency of, for example, irradiated milk as compared to viosterol, could not be accounted for by the relative amounts of antirachitic factor in the blood. When protective doses were given, notwithstanding the fact that the clinical effect was about the same, a definitely larger number of units were found in the blood of the infants which had received viosterol. Evidently antirachitic effect clinically does not parallel the antirachitic content of the blood, as tested on rats. Possibly the explanation of the difference in activity when, for example, irradiated milk or irradiated ergosterol are given, can be ascribed to the production of dissimilar forms of the vitamin.
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