Abstract
The observations of Maximow 1 and Danchakoff 2 in fixed tissue, and of Sabin 3 in the living blastoderm, have demonstrated that the red blood cells differentiate intravascularly in the embryo. Maximow and others have contended that the adult bone marrow differs from the embryological vascular areas in the method of producing red cells. They believe that, in adult marrow, the erythrocytes develops in extravascular clumps, the mature cells later making their way into the bloodstream. This has been so generally accepted that most recent workers have concentrated on attempting to determine the mechanism whereby the adult erythrocytes obtain entrance to the circulation.
In studies on the vascular pattern of the pigeon's marrow with an hypolasia induced experimentally by starvation, an extensive system of intersinusoidal, collapsed capillaries lined by an embryological type of endothelium was observed for the first time. 4 These capillaries, evidently, are not normally patent to the circulating blood as are the transition capillaries which connect arterioles and venous sinuses. The cellular elements in the hypoplastic marrow are reduced to three types: fat cells, reticular cells, and endothelial cells; and the depleted cellular structure of the marrow is replaced by an increase of fat deposit.
The hypoplastic marrow of the starved animal recovers rapidly upon the resumption of an ordinary diet thus providing a simple physiological method of experimental control without the introduction of any complicating factors. When feeding is resumed and observations are made at varying intervals thereafter, it is possible to secure a series of marrows of various degrees of complexity, as normal cellularity is approached. An analysis of each stage, from the simple depleted to the normally cellular state, enables a clarity of interpretation and understanding of the normal process of blood-cell formation and development hitherto unknown.
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