1. Duck erythrocytes have been injected intravenously into rabbits, mice, and guinea pigs and at intervals thereafter microscopic examination of certain organs has been made.
2. In the guinea pig spleen extrusion of the nuclei of the duck cells has been observed with great regularity.
3. Attempts to reproduce this phenomenon in vitro have failed.
4. It is suggested that nuclear extrusion of this kind is conditioned by (a) the species into which the cells are transfused and (b) an intact spleen.