1. The effects of repeated transfusions of blood on the blood-destroying and blood-forming apparatus of normal and splenectomized dogs and rabbits have been described. An anemia which developed despite continued blood transfusions in two dogs splenectomized during plethora has also been studied.
2. The decrease or absence of reticulocytes from the blood stream during plethora and their increase during "plethoric anemia" are evidently due to depression and activation of bone marrow activity. The response of the bone marrow is not immediate upon the onset of anemia, but is delayed for several days.
3. The blood volume studies have served to emphasize the constancy of plasma volume under extreme experimental conditions, and the adaptability of the circulatory system to large increases in total blood volume.
4. Blood destruction and elimination, as measured by urobilin excretion, are greatly increased during the stage of plethora, but still more so during "plethoric anemia."
5. Despite intravenous introductions of large quantities of nitrogen in the form of whole blood, the total nitrogen, urea, and ammonia in the urine and feces are not raised appreciably for some time after the onset of plethora. The normal organism is apparently able to store large quantities of blood or its decomposition products. Upon the onset of a "plethoric anemia," there is an increase in urinary total nitrogen and urea excretion, which was lowered during the course of the anemia. Albuminuria is also found at this time. Other nitrogenous constituents and phosphates show no striking changes.
6. Blood pigment, chiefly in the form of hemosiderin, is deposited in enormous quantities in the spleen, liver, lymph nodes, and bone marrow. It occurs chiefly in phagocytes, though in late stages large extracellular masses are found. Increased pigment deposition can still be found several months after transfusions have been stopped.
7. Phagocytes containing erythrocytes are found rarely, if at all, and only in the acute cases, but their occurrence may be greatly masked by the coexistent congestion.
8. In splenectomized dogs the tendency to "plethoric anemia" is much more apparent, although a direct connection between the two events is not established. In rabbits, whose spleens constitute only 0.05 per cent of body weight, "plethoric anemia" is more easily produced.
9. In splenectomized animals pigment-bearing phagocytes are especially prominent in the liver, although lymph nodes and bone marrow apparently share in the extra work caused by the absence of the spleen. Lymph nodes with some of the characteristics of hemolymph nodes were found in various localities in all animals that had been made plethoric.
10. In rabbits blood pigment is deposited in the hemopoietic organs in large amounts, but under the conditions of our experiments, the picture and the experiment have been constantly complicated by early fatal intravascular agglutination and thrombosis. In the rabbit, as in human hemochromatosis, the pigment is found in two forms: hemosiderin granules, and smaller, dark spicules that do not react to the usual iron stains (probably hernofuscin). The latter pigment is also found seeded through the cells of the liver parenchyma.