Clinical studies on the production of hemoglobin following the oral administration of iron indicate the physiologic activity of this substance in hypochromic anemia. Heath and his co-workers1 have shown that in such patients the intramuscular injection of ferric ammonium citrate is followed by a rise in hemoglobin representing approximately a quantitative reappearance of the injected iron as hemoglobin. Their observations suggest that the action of iron on the production of hemoglobin is not vaguely "catalytic" but bears a quantitative relationship to the formation of hemoglobin. The interest of investigators is, therefore, logically directed to the question of absorption of iron, since the degree of absorption of a given iron compound obviously controls the amount of iron available for the regeneration of hemoglobin.
Unless complete experiments on iron balance are performed, studies of absorption based on the elimination of iron in the feces are profitless. This is due to the