The Iron Reserve of a Normal Man.

No one seems to have attempted to measure the reserve of iron available for haemoglobin synthesis in man. Hahn (1937) estimated that 57 per cent of the total iron in a dog was contained in the blood haemoglobin, 20 per cent was stored in a form potentially available for haemoglobin syn'thesis, and 23 per cent was bound in myohaemoglobin, cell enzymes, etc., and was not available for haemoglobin formation. The available iron reserve of the dog was thus sufficient to replace about onethird of its circulating haemoglobin, and clinical experience of unassisted recovery from acute haemorrhage suggests a similar figure in man. The rate of haemoglobin regeneration after haemorrhage depends upon the stimulus to and response of the marrow as long as iron is freely available. A normal man can draw upon his iron reserve as well as upon dietary iron for blood regeneration after acute haemor'rhage, but if his iron reserve is depleted by repeated haemorrhage the rate of haemoglobin regeneration is limited by the dietary iron available. Thus if a man is kept anaemic by repeated bleeding, his rate of haemoglobin regeneration will fall progressively until, when his iron reserve is exhausted, a constant level is attained. This principle has been used in this experiment to calculate the size of the'available iron reserve of a normal man.