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Communications to the Editor Vol. 61 substituted naphthoquinones. A positive color reaction for 2-hydroxy-1,4-naphthoquinones [ibid., 58, 1174 (1936)] was obtained with highly purified concentrates of vitamin K from alfalfa. The positions of ultraviolet absorption maxima reported in vitamin K concentrates, especially at 328 and 248 µ [Helv. Chim. Acta, 22, 310 (1939)], are close to the 334 and 250 maxima of phthiocol [/. Biol. Chern., 115, 479 (1936)], and the general shapes of the absorption curves are similar.We have made quantitative assays by our improved method [Biochem. J., in press] of phthiocol and several related compounds. In addition to the substances listed in Table I,we have tested lapachol and lomatiol. Both of these proved inactive, first at a 20-mg. level and later at a 100-mg. level. A preliminary test of a preparation of phthiocol monoacetate indicated a greater degree of activity than that of phthiocol.An aqueous solution of phthiocol was made by dissolving 2 mg. in each cc. of a 0.05 molal phosphate buffer, pH 7.4. The pH of the final solution was 7.0. Sufficient of this solution was injected daily into the breast muscle of chicks to equal the amount consumed by chicks on the 20-mg. level. A control group received the same amount of solution orally. The average prothrombin time for 6 injected chicks was 31.9 seconds, while that for 6 orally fed chicks was 32.4 seconds. An 0.05 molal phosphate buffer, pH 7.8, dissolved 4 mg. of phthiocol per cc. to a final pH of 7.1. Chicks receiving no vitamin K in the diet were given intravenously 2 mg. each of phthiocol in aqueous solution. A comparable group of chicks was

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Communications to the Editor 1613 In our previous communication (¡oc. cit.) we gave an extinction coefficient of = 385 at 248 niju for vitamin Ki but since that time a value of 540 has been obtained. The analyses of both preparations indicated that each was analytically pure. Our first value was probably due to instability of the vitamin on storage and toward light. For this reason we are not at present certain that 540 is the maximum value attainable. In this same communication line 38 column 1 should read "all have a potency of about 1000 units per mg." instead of, "all have potency of about 100 units per mg."Biochemistry Department