Increase of blood cells, decrease of serum iron quantity and a slight degree of over-function of reticuloendothelial system will be induced, by transplantating some suitable amount (Prokg. 0.5g) of bone marrow in a dog's subfascia of femur. This has been caused in urging to utilize the accumulated iron owing to promotion of hematopoetic fanction; if we investigate it about organic iron, when the blood showing an increase, ferritin in the spleen showed a tendency toward decrease, but the deposits of hemosiderin in tissue has proved little alteration from its normal state, Contrary to this, any decrease in serum iron observed under infected state, would rightly be ascribed to the retained stock of iron due to excessive function of reticuloendothelial system, due to protecting infection; esp., what comes from the absorption and deposits of hemosiderin produced along with excited breakage of hemoglobin, or resulted from imperfect utilization of iron, in hematopoetic organs; so that, there is seen certain essential differences between the excessive function of reticulo endothelial system when hematopoetic organs is stimulated, and decrease in serum iron; further, on occasion when hematopoetic function is urged according to the bone marrow transplantation, we could realize that a close connection exists between the iron metabolism and function of reticuloendothelial system: at the same time, could verify partly the mechanism in creating blood cells the occasion.