The effect of various oxygen tensions on explanted bone marrow fragments was studied. It was found that gas mixtures containing 1, 3, 5, 10 and 12 per cent oxygen have an injurious effect on hemic cells. Bone marrow maintained in these gas mixtures showed various degrees of degeneration, which was the more pronounced the lower the oxygen tension. Mitotic activity was also found to be reduced under the influence of low oxygen tension.
Bone marrow cultures maintained in a gas mixture containing 15 per cent oxygen did not show appreciable changes and were similar to the controls.
Increased rate of maturation and multiplication occurred in bone marrow cultures maintained in an excess of oxygen, i.e. 50 per cent.
The significance of these findings in the light of observations on the effect of anoxia in vivo has been discussed, and reported findings on the effect of low oxygen tensions on other tissues in vitro have been briefly reviewed.