1. Studies with the use of cell-free filtrates of brain in the acceleration of leukemia in the AKR mouse are presented.

  2. Cell-free filtrates of the brain of AKR leukemic mice were inoculated either intraperitoneally or intracerebrally into young adult AKR mice. The development of leukemia was accelerated in 53 per cent of the former and 47 per cent of the latter.

  3. Control experiments gave uniformly negative results, except when leukemic human brain was used as the source of the inoculum.

  4. The experiments indicate that the cell-free factor present in the brain of leukemic animals is capable of accelerating the development of leukemia in a leukemic strain of mice.

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Aided by grants from the Olivia Sue Dvore, Edward Friedman, Benjamin Fishbain, American Blood Research, and Damon Runyon Foundations, and the Illinois Division of the American Cancer Society.

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