Formation of bone marrow in fibroblast-transformation ossicles

The genesis of hemopoietic bone marrow was studied in matrix-induced transformation plaques and ossicles in subcutaneous spaces of thorax and abdomen of rat. With the advent of blood vessels in the plaque on day 9, there began a rapid and radical conglomerate shift, cartilaginous to osseous, which was nearly total in 72 hr. Incorporation of 59-Fe into heme provided a sensitive quantitative assay for hemopoiesis. On day 12 the first colonies of hemopoietic cells were observed. These developed adjacent to cavernous sinuses which had formed to fill the void left by chondrolysis. Total occupation of the ossicle with hemopoietic marrow was found on days 23-28. The thoracic region was favorable for the formation of hemopoietic marrow, whereas lower abdominal sites were disadvantageous.