1841
V O L U M E 2 4 , NO. 1 1 , N O V E M B E R 1 9 5 2 Under the conditions of the method described, this required that the cholesterol concentration of the final colored solution be in the range 0.08 to 0.25 microgram per microliter. A few experiments on a given tissue serve to determine the most convenient magnitudes for extraction and aliquot volumes which will enable one to attain final concentrations in the desired range. For the rabbit adrenal, the volumes given here were quite satisfactory. The adrenal work is being continued. The precision of the over-all method, checked by caloulation of the standard deviation in thirteen analyses of adrenal and brain homogenates, is 10.0036 microgram of chaleEtero1 per mjcroliter of final colored resction mixture. For the range 0.08 to 0.25 microgram per microliter, the corresponding range of error is 4.5
tc 1
Ern
LITERATURE CITED
(1) Beemy, O.,Lowry, 0. H., Brock, M. J., and Lopea, J. A., J . BW. C h m . . 166,177(1946). (2) Foldes, F. F..and Wilson, B. C., ANAL.CHEM.,22,1210 (1950). (3) ,Giiek,D., "Teohniquesof Risto-and Cytochemistry." New York, Interseienoe Publishers,Inc.. 1949. (4) K i w d e y , G. R., and Sohaffert. R. R., J . Bid. Chem., 180, 315 (1949).
( 5 ) Malrnstrom, B. G.. and Gliek,
D.,ANAL.CHEM.,23, 1699 (I!
RECEITBDfor review May 28, 1952. Accepted Auguat 11 , 1952. No. XXIV in the series, Studies in Histochemistry. Aided by I grant from Division of Research Grants and lWlowships, Nations1 Institul.ea of Hedth, U. S. Public Health Service, Bethesda, Md.
,
An Improvement in the Vitamin 0 line 1 GLEN M. SHUE, LEO FRIEDMAN, A N D CHESTER D Division of Nutrition, Food and Drug Administration, Federal Security A(
N THE absence of reliahle chemical or physical chemical Ivariety method for the estimation of vitamin D potency in a wide of products, reliance must be placed on the biological a
assay. The U. S. Pharmacopeia method i8 based upon the cure of exnerimentallv induced rickets in rats
