Benzene intoxication was induced in a number of rabbits in order to study the factors which regulate production of leukocytes. One or more of the marrows of long bones was completely extirpated. After varying intervals, the animals were killed. The regenerated marrow was studied. Comparisons were made with regeneration in normal animals and with the intact marrow of animals treated with benzene. The appearance of regenerated and intact marrow was correlated with the degree of benzene intoxication.
In normal animals, regeneration of extirpated marrow proceeded in a more or less sequential order. At first there was formation of sheets of primitive reticular cells and bone trabeculae, followed by fat cells and then by myeloid tissue. In severe benzene intoxication, the extirpated marrow regenerated only to the point of formation of primitive reticular cells. Further regeneration was halted at the point of formation of fat cells. Myeloid activity appeared to be predicated upon the presence of fat cells. At least, one part of the mechanism by which benzene induces aplasia of bone marrow is probably the inhibition of cell division and maturation past the level of the primitive reticular cell.