A technique was devised for obtaining marrow-free trabecular bone so that the trabecular and cortical bone composition of dog, steer, monkey and man could be studied. Vertebral body was cut in the frontal plane into slices 2 m m thick with an electric band saw, The cortical bone encircling each slice was trimmed off with a cleaver, leaving intact a lacy slice of trabecular bone. The marrow substance was washed away by fine and powerful jets of tap water obtained from a n adjustable nozzle. Marrow washing was discontinued when no trace of red color was visible on holding the slice in front of a strong light source.The quantities of water, volatile inorganic, organic and ash fractions in cortical bone was alike for all species. Likewise, the trabecular bone fractions of each was quantitatively similar. In general, density and amount of ash in cortical bone was higher than that in trabecular bone. The water and ash:organic ratio were higher in trabecular than in cortical bones.Ratios of trabecular to cortical ash for the bones in an entire dog skeleton were also determined. Based on this, volume or mass of the various bone fraction may be estimated when the weight of the ash for any particular bone is known. Steer.1. Cortical bone.

Hematopoietic cells isolated from the endosteal bone surface, that is,the endosteal marrow cells, were found to consist mainly (60 to 80 percent) of lymphoid and late-stage normoblast-like cells. Unlike the cells they resemble, the endosteal marrow cells showed an affinity for Sudan black, demonstrable nucleoli (Feulgen reaction), and an absence of hemoglobin. Assays showed that over one-half of the endosteal marrow cell population may be the colony-forming units, the CFU-S of Till and McCulloch. Thus, high concentrations of stem cells could be obtained from the endosteal bone surface by means of the present isolation technique.

Densities of the various bone fractions i.e., water, organic, volatile inorganic and ash fractions, as well as fat in the various animals have been studied. However. values reported by various workers failed to show consistency and uniformity, especially with respect to the volatile inorganic (often called "CO, fraction") and the ash fractions. These densities are prerequisite to the study of the volumetric composition of bone and bone marrow.In our study, the fat and organic densities found were similar to those previously reported. The volatile and non-volatile inorganic (ash) fractions had density values of 1.684 and 3.180, respectively. The ash density was much higher than values previously reported but it verifies a theoretical value deduced by the authors from published work.Our higher ash density was due to a smaller measured volume of this fraction obtained by applying a negative pressure to remove the small entrapped air bubbles from the ash sample prior to the water displacement measurement. Because a smaller portion of the total inorganic volume was used for the ash calculation, giving it a higher density, a larger balance of the total inorganic volume was left for the volatile inorganic density calculation. This accounted for ash and volatile inorganic densities which were higher and lower, respectively, than such values previously reported.Prior to the determination of the density of the non-volatile inorganic fraction, the ashing time and temperature were studied. Curves plotted from the results of such studies were described and explained.