Electron Microscopic Study of the Mammary Tumor Agent In Plasma Cell Tumors 1

SUMMARY-In a previous electron microscopic study of a series of plasma cell tumors induced in BALB/c mice, no intracytoplasmic type-A partie/es were identified. However, when plasma cell tumors were induced in BALB/c mice which were foster-nursed on C3H mothers to introduce the mammary tumor agent, intracytoplasmic type-A partie/es were identified in the cells of 7 of the 17 plasma cell tumors induced. This is further evidence for a relationship between the mammary tumor agent and this type of A par-tie/e.-JNat Cancer Inst 40: 1375-1385,1968. SOME TIME ago we analyzed with the electron microscope a series of primary and transplanted plasma cell tumors of the mouse. In the report of this study (1) it was noted that two types of doughnut-shaped particles were present in the cells of some tumors and only one type in the cells of other tumors. On this basis two types o