The Mechanism of Anemia*
Anemia is a reduction below normal of the capacity of the blood to transport the oxygen necessary for all animal life. The body tissues must be supplied with many times as much oxygen as can be carried in physical solution in the plasma. The hemoglobin normally present (15 to 16 gm. per 100 c.c. of blood) increases one hundred times the power of the blood to transport oxygen by carrying it in chemical combination. This amount of hemoglobin in solution in the circulating blood would greatly increase the osmotic pressure of the plasma beyond that of the surrounding tissues and so dehydrate the tissues. Hemoglobin in a red cell is outside the plasma, does not affect the osmotic pressure, and yet functions efficiently as an oxygen carrier since absorption and release of oxygen is as efficient as if the hemoglobin were in solution in the plasma. The red cell is thus simply a container1 for the necessary hemoglobin and functions as a cup on an endless-chain conveyor. It is normally filled with hemoglobin and is constantly making round trips from the lungs to the tissues. This conception of the function of the red cell applied to the different laboratory types of anemia is illustrated in Fig. 1. In addition to thinking of the red cell as a cup on an endless-chain conveyor, we should also visualize the total mass of circulating red cells as a vessel containing hemoglobin. The size of this vessel varies enormously in blood dyscrasias affecting the. . .