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SummaryWhen germfree C3Hf/Pi mice are introduced into a conventional colony, there is a high death rate which is dependent on both age and sex. The death rate is higher in males than females, and higher in older animals than younger ones. The death rate remains high for approximately one month, following which it approaches that of conventional C3Hf/Pi mice.The authors gratefully acknowledge the technical assistance of Richard C. Parks and R. James Allred.

SummaryOf 67 germfree BALB/cPi mice autopsied at a median age of 21 months, 14/67 (21%) had lung tumors; 5/67 (8%), reticular neoplasms; and 4/67 (6%), angiomas. Mammary tumors, squamous cell carcinomas, adrenal cortical carcinomas, hepatomas, an ovary carcinoma, and a myoepithelioma were also observed. There was no discernible difference between the incidence of tumors observed in germfree BALB/cPi mice and that reported in the literature for conventional BALB/c mice.

SummaryA comparison of the total number of neutrophils and neutrophil precursors within the humerus of germfree and conventional mice revealed no statistically significant difference between the two groups. The distribution of marrow neutrophils with respect to morphologic type and the number of neutrophils in mitosis were similar in the two groups. There was, however, a slight, but significantly, lower concentration of blood neutrophils in germfree mice as compared to controls. Removal of mice from the germfree environment was associated with a rapid decrease in the number of mature and relatively mature neutrophils in the marrow and with a subsequent increase in potentially mitotic, immature neutrophils, following which the marrow returned to normal. Germfree mice responded to endotoxm administration with an increase in rate of release of neutrophils from the marrow, as do normal mice. It was concluded that in this model system the presence or absence of microorganisms in the environment could not be as...

SummaryThe effect on survival of mice innoculated with a splenotropic reticulum cell sarcoma was tested in splenectomized and mock-operated syngeneic mice. The splenectomized animals survived longer. Evidence was presented that this is probably due to rapid destruction of circulating cells, and that the tumor cells are protected by being sequestered in the spleen.