Bone Marrow as an Organ.

Abstract

Before the mechanism of bone marrow as an organ could be analyzed, certain factors had to be clarified, among which are the structure of its vascular system and the maturation of blood cells, Chart 1 shows maturation as a constantly changing process with more than one variable. There are two critical points, (1) where the specific granules begin, and (2) where the last division of the myelocyte has taken place, giving a reduction to a common size and state of maturity, the leucocyte. The myelocytes are classified according to the number of granules, type A, having the first small clump of granules; type B, showing increasing numbers, and type C, the cell with the maximum number.

Supravital differential counts of blood and bone marrow of 5 normal and 2 abnormal rabbits are given in Tables I-III. Each survey included the epiphysis and shaft of each of the long bones and one rib. Table I shows that the normal rabbit's marrow contains about 70% granulocytes to 25% nucleated red cells. In early embryonic stages, only red cells are formed; during fetal stages, white cells are minimal; in the new-born rabbit the erythroid-mye-loid ratio of the bone marrow is nearly the reverse of that of the adult.

The proportions of the stages of granulocytes are shown in Table II. The first 5 rabbits had normal blood and bone marrow, and in them the major supply of cells was of myelocytes C—(85%) with minimal numbers of types A and B and myeloblasts. The delivery of granulocytes from normal bone marrow is rhythmic, based on rhythmic and orderly division and maturation; the mechanism of delivery depends on a reciprocal relationship between myelocytes C and early leucocytes. The last 2 rabbits had a leucocytosis, pseudoeosinophiles 71% and 68%, with the normal at 44%.