The total number of nucleated cells in the long bone of a mouse can be determined with some accuracy. Thus, in this species, values for marrow cells can be expressed as a total cell count per bone, a more meaningful number than values expressed as concentration as is done in most studies of other species. If the percent of total marrow in the skeleton that is contained in that bone is known, values can be expressed as "per mouse" (total marrow mass)--a still more meaningful value than values per bone. The total marrow mass of mice has been calculated previously on the basis of nucleated cells per humerus or per femur and the percent of the total marrow contained in that bone. However, that percent was based on rather tedious dissection of the entire skeleton and determining the amount of 59Fe that had been taken up by each bone. In the present study, mice were injected with 59Fe, skinned, and eviscerated. The carcass was then either cooked and all bones dissected out or simply cut into pieces containing various bones or bone groups. The percent of 59Fe taken up by various bones or bone groups as measured by the two techniques was virtually identical. The percent distribution between various bones was found to be fairly constant between 4 and 18 h after 59Fe injection and the same in mice aged 3 or 12 months. This simplified technique makes the measurement of total marrow mass a practical addition in studies of murine hematopoiesis.

Abstract. Neutrophil kinetics of acute experimental infection were studied with diisopropylfluorophosphate-32P labeling in 31 dogs inoculated intrabronchially with pneumococci. In vitro neutrophil labeling indicated a rapid transit time through the blood in early infections, with an elevated marginal granulocyte pool sometimes preceding an elevation of the circulating granulocyte pool. 13 hr after infection, the circulating and total blood granulocyte pools were increased but the rate of neutrophil transit through the blood was normal. During the recovery from infection there was a marked prolongation of neutrophil blood transit time, suggesting virtually complete cessation of bone marrow release of neutrophils into the blood. Labeling of neutrophils in vivo indicated an increased rate of emptying of the bone marrow storage pool proportional to the severity of infection as measured by the fever index. The change in the blood ratio of nonsegmented to segmented neutrophils was a much more accurate index of the severity of infection than the blood granulocyte concentration, correlating significantly with the fever index.

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The concentration of neutrophils and megakaryocytes was determined in the marrow of anemic mice of genotype W/Wu and their normal (+/+) litter mates. In all groups studied, the humerus of W/Ww mice contained significantly less neutrophils and megakaryocytes than did normal animals. Blood neutrophil concentration was less in all groups of W/Wv mice but in only one group which was the youngest group studied, did this value differ significantly from normal. The blood and marrow neutrophil response to endotoxin was similar in W/Wa and "+/+" animals. This suggests that the neutrophilic system of W/Wv mice responds to this stimulus in a relatively normal manner, much as their erythroid system responds to hypoxia, and androgens.