On the intravascular development of erythrocytes in the bone marrow of the adult rabbit

Abstract

Bone marrow has been one of the most difficult tissues to understand because it has proved so hard to reduce it to a sufficiently simple state for analysis. The older methods, consisting chiefly in classification of cell types, have led to the almost universal acceptance of the monophyletic theory, and in general to the conclusion that the developing red blood cells are formed in parenchymal spaces outside the vascular system, hence differing from the manner of development found in the embryo. Since it has been accepted that the red cells develop extravascularly, it has been obviously necessary to determine their mode of entry into the circulation. The two principal explanations offered have been: (1) That the endothelial lining of the vascular bed was incomplete, as in the spleen, and consequently the young cells could be forced through these openings; and (2) that the growing clumps of red cells cause erosion of the endothelial lining by pressure, and hence obtain entrance to the vascular bed. Drinker, Drinker and Lund were able to demonstrate that the endothelial lining in normal marrow is quite complete, but that in hyperplastic marrows this is probably not the case. They found that the injection mass was not so evenly outlined by the walls of the sinusoids in the hyperplastic as in the normal marrows. This difference they explained as due to young red cells which had eroded the endothelial wall by pressure, while, at the same time, these cells were so closely packed together that they prevented the injection mass from extravasating freely into the parenchyma. Our concept of the normal structure of the vertebrate bone marrow has'been considerably modified by the demonstration by one of us of a very elaborate capillary bed in the marrow of the adult pigeon.