Prevention of Viral Lymphoid Leukemia of Mice by Thymectomy.

1. Ninety-nine Z mice were injected with Gross “Agent A” (Selas filtrates). Leukemia was induced in 1 of 49 animals thymectomized at 4–6 weeks of age, and in 25 of 50 alternate non-thymectomized mice. No leukemias occurred in 41 uninjected controls. The experiments were terminated when the animals were 7–9 months of age. 2. Incidence of leukemia induced by virus was greater and the latent period shorter in females than in males. 3. Spontaneous Ak leukemia, from which this agent is derived, behaves similarly to viral leukemia with respect to relaton of sex to incidence and latency period. However, spontaneous leukemia occurs at a later age than this viral leukemia. 4. The thymus is the fulcrum of both lymphoma induction by this virus and of its spontaneous development in Ak mice; its presence is essential for development of this type of leukemia.