1. Megakaryocytes were demonstrated in central venous blood of each of 23 patients who underwent cardiac catheterization. Cell counts ranged from 0.7 to 5.9 megakaryocytes per ml. of blood; the equivalent of one-third of these cells were considered to contain a full complement of cytoplasm. It has become evident that megakaryocytes are normal constituents of blood. 2. In an attempt to quantify megakaryocyte migration from the bone marrow it was calculated that from 20-50 per cent of the mature megakaryocyte population enters the blood and ultimately reaches the lungs. The possibility that all megakaryocytes migrate from the marrow is not precluded with certainty by these studies. 3. It was estimated that from 7-17 per cent of the body’s platelets are released in the pulmonary capillaries. If all megakaryocytes migrate from the bone marrow, then as much as 33 per cent of the platelet population is delivered to the blood in the lungs.

Infectious agents must acquire iron from their host to survive, and iron deficiency has been reported to protect against malaria in humans. We have tested the the susceptibility of Plasmodium falciparum to iron deprivation by studying the effect of desferrioxamine (DF), a specific iron chelating agent, on parasite growth in an in vitro culture system. We have found that DF inhibits the growth of P. falciparum at concentrations readily achievable in vivo, by a mechanism that may involve interference with the completion of schizogony.

Guinea pig reticulocytes were pulse-labelled with 59Fe bound to transferrin. Haemolysates prepared from these reticulocytes were subjected to rapid (NH1)2SO1 precipitation and then chromatography on an anion-exchange resin. ATP-bound 59Fe was the dominant species in the reticulocyte cytosol; 2,3-bisphosphoglycerate and GTP iron complexes were not detected despite the fact that these were stable with (NH1)2SO1 precipitation and readily detected with anion-exchange chromatography. AMP-bound Fe was a minor component of the cytosol following rapid (NH1)2SO4 precipitation, and the major component when iron was released from transferrin by haemolysates. We speculate that ATP-Fe may be degraded in the cell to permit utilization of its iron for haem synthesis.

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