A SMALL drop of citrated human blood is placed on a slide next to a somewhat larger drop of Ponceau 2R and the two drops are mixed, covered with a cover glass and examined both with ordinary and polarized light. Under the double action of the dye and the hypotonicity, all the red cells become perfectly spherical with a diameter ranging from 5.0 to 5.6µ and stain weakly orange-red. No birefringence is observed.