In 1936 Szent-Gy枚rgyi and his associates1 isolated a crystalline substance from lemons which they called citrin. They1a found that this substance corrected the increased capillary fragility in guinea pigs on a scorbutogenic diet and in human beings with certain pathologic conditions. They called it vitamin P. Subsequently, studies both on animals and on human beings were carried out by numerous investigators. It was shown that citrin, a flavanone glucoside, is composed of two fractions, hesperidin glucoside2 (formula I shows the aglycone), which is insoluble in water and is stable, and eriodictyol glucoside (formula II shows the aglycone), which is water soluble and sensitive to oxidation. Eriodictyol is demethylated hesperidin and contains the unstable orthohydroquinone group. It has been reported1b that the relative amounts of these substances in citrin vary with the ripening of the fruit used in its preparation and with the method of isolation. However,