A change in the type of lesion produced by the fibroma virus has been observed. At about its 18th serial transfer in domestic rabbits the virus lost its ability to induce fibromas when administered subcutaneously. Instead, lesions developing in either the subcutaneous tissue or in the testicle were predominantly inflammatory in character and partly composed of lymphocytes and large mononuclear cells in place of fibroblast-like cells. Andrewes, working with the same virus in England, has observed a somewhat similar change. Passage of my changed virus through cottontail rabbits results in a transient recovery of the capacity to produce fibromata, while similar passage of Andrewes' inflammatory virus is without effect.

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