A pleomorphic, intermittently acid-fast organism has been isolated in this laboratory and elsewhere with great regularity from mammalian tumors and from blood of tumor-bearing hosts. In the present study involving 1500 randombred and inbred mice, the percentage of animals harboring the organisms has been found to parallel rather closely the tumor incidence. In some groups bleedings were repeated at intervals throughout the life span and compared with tumor production as demonstrated microscopically in the same individuals. For example, 56/100 ICR/albino female mice produced tumors and 49 of the 56 yielded the organism from blood prior to appearance of tumors; whereas in males, where only 19/100 became tumor-bearing, there was a corresponding drop in number of positive bloods to 16.

When the isolate from mouse Sarcoma 180 was injected intraperitoneally into newborn ICR/albino males, the tumor incidence was increased—up to 83% of individuals surviving beyond 18 months, as compared to 20% in controls.

The possible significance in the neoplastic process of filter-passing forms of these bacteria, and of phages which they have been shown to harbor, is under investigation.

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Supported in part by a grant from the Cancer Research Foundation of Pittsburgh and in part by a grant from the Manfred Wahl Research Fund.

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