In splenectomized dogs the following observations on the erythroid elements were made:

1. There was no unusual postoperative depression of erythrocyte, hemoglobin or hematocrit values, and regeneration occurred at the same rate as in the control dogs.

2. A significant increase in the number of circulating reticulocytes was noted, which persisted for a longer duration than the associated thrombocytosis. There is a suggestion that the reticulocytes circulating during regeneration were more immature than those of the control animals.

3. Varying numbers of target cells accompanied by increased osmotic resistance were present in all the splenectomized dogs. Most also developed normoblastemia, particularly during active regeneration, which persisted thereafter in some of the animals. Howell-Jolly bodies were rare.

4. No significant bone marrow changes were noted.

It is suggested that:

1. In nonsplenectomized animals, most erythrocytes released from the bone marrow in response to blood loss are mature red cells rather than reticulocytes.

2. Postsplenectomy reticulocytosis is not dependent on a fall in hematocrit and is not a reflection of hemolysis or even of increased erythropoiesis, except, perhaps, in part during regeneration from the blood loss incurred at surgery.

3. Postsplenectomy reticulocytosis and normoblastemia are unaccompanied by alterations in the myeloid-erythroid ratio of the bone marrow and are probably largely due to a diminution of the normal inhibition of erythroid release from the marrow, permitting their earlier entry into the circulation.

4. The aforementioned changes are due specifically to the removal of the spleen itself, rather than merely to the removal of splenic blood from the portal circulation.

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